Repetitive orogeny in the northeastern Appalachians-new plate models based upon Newfoundland examples

Tectonophysics, 28 (1975) 39-87 0 Elsevier Scientific Publishing Company,

Amsterdam

- Printed

in The Netherlands

REPETITIVE OROGENY IN THE NORTHEASTERN APPALACHIANS NEW PLATE MODELS BASED UPON NEWFOUNDLAND EXAMPLES

-

M.J. KENNEDY Department of Geology, Memorial University of Newfoundland, Newfoundland (Canada) (Submitted

June

21, 1974; revised

version

accepted

St. John’s,

May 21, 1975)

ABSTRACT Kennedy, M.J., 1975. Repetitive orogeny in the northeastern Appalachians - New models based upon Newfoundland examples. Tectonophysics, 28: 39-87.

plate

Polydeformed recumbent fold complexes of upper greenschist to low amphibolite facies bound the central Ordovician ophiolite terrane of the northeastern Appalachians on both sides, separate it from the platforms on the northwest and southeast and impart a symmetry to the system which is particularly well displayed in northern Newfoundland. These metamorphic complexes or marginal crystalline belts contain metasedimentary and metavolcanic rocks whose deformation and metamorphism predate Ordovician ophiolitic rocks of the central part of the system and hence were not the product of Ordovician ocean-floor spreading. The metasediments of the marginal crystalline belts have characteristics similar to sediments of continental-rise prisms while the metavolcanic rocks are similar to island arc, or locally to ophiolitic sequences. Furthermore, the crystalline belts in Newfoundland contain linear mafic/ultramafic complexes within them of ophiolitic aspect and comparable age to the surrounding metamorphic rocks. In the northwestern marginal crystalline belt this mafic/ultramafic complex has not only controlled the late depositional development of the belt, but also apparently occupies the symmetry axis of the recumbent fold complex and is spatially related to deformation intensity. It is suggested that these maficlultramafic complexes represent remnants of small ocean basins that opened within the continental-rise prisms. Tectonism resulted from closure of these basins associated with some transform movement, bringing a continental fragment back into contact with the rest of the continental margin. Closure is dated as Late Cambrian in the northwest and Late Precambrian in the southeast. This new mechanism for deformation of the marginal crystalline belts explains many of the details of geologic development not accounted for by earlier models. The implications of these Late Precambrian-Early Paleozoic processes on both sides of the proto-Atlantic Ocean are investigated to elucidate later plate development in Newfoundland. It is suggested that the later Acadian (Middle Devonian) orogeny may have been the result of convergence of oceanic trenches, leading to formation of transform faults. If correct, continental collision took place locally but was not the fundamental cause of the orogeny. This accounts for facies distribution and the contrast in metamorphism, deformation intensity and structural style between the Acadian and the earlier erogenic episodes.

INTRODUCTION

The Appalachian Orogenic Belt can be followed from Newfoundland 3,200 km southwestward to Alabama in the United States. Despite impor-

40

tant differences that exist between different regions along strike within the belt, the northeastern Appalachians, particularly in Atlantic Canada and the northeastern United States, exhibit a general uniformity of geologic pattern which has led to the recognition of distinctive elongate belts or zones that extend for considerable distances (Poole, 1967; Zen et al., 1968; Rodgers, 1970; Williams et al., 1972 and 1974). The same is true of the southwestern part of the Appalachian System (King, 1959). In Newfoundland, the basic division is between platformal areas of the Western and Avalon Platforms (Kay, 1967; Kay and Colbert, 1965) on the northwest and southeast (Fig. 1) and the Central Paleozoic Mobile Belt of central Newfoundland (Williams, 1964a). These regions can be further subdivided on the basis of contrasting Ordovician and earlier depositional and structural development into tectonostratigraphic zones that can be followed, in a general way, throughout the Canadian Appalachians (Williams et al., 1972). The zones in Newfoundland have subsequently been given local names (Fig. 1) (Williams et al., 1974). These tectonostratigraphic zones reflect the symmetry of the system, first recognized by Williams (1964a) in which the Central Mobile Belt, consisting predominantly of Ordovician mafic volcanic and elastic sedimentary rocks in its axial region is flanked by Pre-Ordovician marginal crystalline belts (Fig. 1). These belts consist of metasedimentary and metavolcanic rocks

Fig. 1. Map of Newfoundland showing the major subdivisions of the Appalachian Belt and the allochthons of western Newfoundland. Zones are after Williams et al. (1974).

41

whose deformation and metamorphism predates the intervening Ordovician and whose facies and thickness contrast strongly with Ordovician and older rocks of the Western and Avalon Platforms. In the last decade, Newfoundland has been the site of extensive geologic investigations and the excellent coastal exposures have clarified the nature of different zones within the orogen and disclosed a more complete geologic history than is available from many other erogenic belts. A number of plate models have been proposed for the northeastern Appalachians. They rely heavily upon relationships in Newfoundland, where some of the best exposed ophiolites occur, either as transported remnants on the Western Platform (Lomond Zone) or as probable autochthonous sequences in the Central Mobile Belt (Notre Dame Zone). These models (Dewey, 1969; Bird and Dewey, 1970; Church and Stevens, 1971; Dewey and Bird, 1971; Church, 1972) all represent an important new approach to Appalachian development involving the interaction of continental and oceanic crust based upon the recognition of preserved oceanic crust within the orogen. They explain the distribution of lithology and the development of the belt in a far more satisfactory way than some older geosynclinical concepts. However, none of these models satisfactorily account for the deformation and metamorphic history of the belt. Long-lived processes such as the subduction of oceanic crust are invoked to account for the comparatively short-lived processes of deformation and metamorphism. Ocean-floor spreading and the formation of the Iapetus Ocean (Harland and Gayer, 1972) is generally considered to have begun in Late Precambrian to Cambrian time. In the northeastern Appalachians this post-dates the Grenville Orogeny. Within Canada the period from the end of the Grenville Orogeny to the base of the Cambrian has been named the Hadrynian Period (Stockwell, 1964). The models also suffer from the weakness of being primarily concerned with development of the northwestern parts of the orogen, mainly because this was the region that was best known at the time. Modifications of these models must account for all aspects of development and must relate these to each other in time to produce a developmental model not in conflict with the geologic evidence. The Appalachian System in the northeast was subjected to deformation and metamorphism at three different times; in Late Hadrynian time in the southeastern margin (Gander Zone), in Late Cambrian-Early Ordovician time in the northwestern margin (Fleur de Lys Zone), and in probable Middle Devonian (Acadian) time throughout the system. Recumbent isoclines formed in the two older phases contrast strongly with the later Acadian structures (tight upright folds). Emplacement of allochthonous ophiolites on the Western Platform is apparently not synchronous with extensive deformation of the adjacent crystalline belt, but is of early Middle Ordovician age. Even younger erogenic activity is evident in southern New Brunswick (Rast and Grant, 1973) and farther south involving Pennsylvanian rocks. All the models presently proposed for this region rely upon subduction/abduction

42

processes as the driving force for tectonism. Transform plate junctions are not considered, although large transcurrent faults sub-parallel to tectonic strike are widespread in the system. This communication not only modifies these earlier models, but also proposes a different mechanism for the development of the marginal crystalline belts. It is probably applicable to similar crystalline belts in other orogens. The mechanism involves the opening and subsequent closure of marginal ocean basins within continental margins on the northwest and southeast of the system, in association with the development of pre-Ordovician island arcs, which were subsequently deformed with the elastic rocks of the crystalline belts during closure of the marginal basins. This mechanism has been summarized for the northwestern marginal crystalline belt by Kennedy (1973). The subsequent development and extension of zones on to the Canadian mainland is also briefly discussed. Relevant geologic data are presented in the text but for more complete details of northeastern Appalachian geology the reader is referred to bibliographies contained in Neale and Williams (1967), Poole (1967), Zen et al. (1968), Kay (1969), Poole et al. (1970), Rodgers (1970) and Williams et al. (1972). THE WESTERN MARGINAL CRYSTALLINE THE BURLINGTONIAN OROGENY

BELT

(FLEUR

DE LYS ZONE)

AND

The western marginal crystalline belt of the Newfoundland Appalachian System separates the Ordovician and Silurian rocks of central Newfoundland from the Cambrian-Silurian dominantly sedimentary sequences of the Western Platform (Fig. 1). It has undergone erogenic deformation, metamorphism and plutonism before deposition of adjacent Ordovician rocks. This erogenic episode is here referred to as the Burlingtonian Orogeny. Extent in Newfoundland,

dating of its deformation

and metamorphism

Rocks of the western marginal crystalline belt of Newfoundland have been assigned to the Fleur de Lys Supergroup. They underlie most of the Burlington Peninsula in northwestern Newfoundland (Figs. 1 and 2) ,and consist of a thick sequence of semi-pelitic and psammitic schists with minor graphitic pelites, marbles, conglomerates and mafic volcanic rocks in the west and dominantly mafic and silicic volcanic rocks in the east (Fuller, 1941; Baird, 1951; Neale and Nash, 1963; Neale and Kennedy, 1967; Church, 1969; Kennedy et al., 1972). The Fleur de Lys of the Burlington Peninsula is bounded on the northwest by the Cabot Fault, a major sinistral transcurrent fault (Williams et al., 1970), and on the southeast another fault separating it from the Lower Ordovician Betts Cove Ophiolite Complex and the Snooks Arm Group (Upadhyay et al., 1971). This region of Fleur de Lys rocks can be extended northwards for a considerable distance, since exposures are provided by offshore islands 60 km to the northwest (Kennedy et al., 1973).

i

/

i

i

Snooks Arm Group@) Nipper’s tiarbour Group(N)

ORDOVICIAN(Arenig)

ci -

Lo

l..l..,

” _..._._I

Pacquet HaItuw

I.

rocks

Dwxtion

Direction

.j&j3CSIlurlanrocks

Facmg Facing

+ ++

assumed.

here

D = Dunamagon

mayoccur

of F2 Fofds (upwards)

of F2 Folds (sIdeways)

defined, Slide or Fault

------Tectonac

Reddatb Cove Gabbro Slide;

-!I

L.ORDOVICIAN &OLDER m m f$if#c BUltramaftc rocks Et. Betts Cove Ophiolite Comf CAMBRIAN-L.ORDOVIAN (Trematil Cape BrulC Porphyry

m

--*Tectonic

_. ..I

Group

Cape Saint John Group

ROCKS 8 OLDIE

Granitic

PLUTONIC

HADRYNIANL.ORDOVICIAN~T~~~~~CC)~~~,~~ FLEUR de LYS SUPERGROUP

LttitNLi

Fig. 2. Generalized geologic map of the Burlington Peninsula. P = Partridge Granite, B = Burlington Granodiorite, Granite, S = La Scie Granite. Sections A-B and C-D are shown on Fig. 4.

LOWER

SILURIAN-DEVONIAN

44

The region of Fleur de Lys rocks in the Burlington Peninsula is limited on the south by another major fault system. Fleur de Lys rocks also occur west of the Cabot Fault in the Hampden Zone (Fig. 1) near Deer Lake and at Grand Lake further to the southwest (Williams,‘1967a). Both occurrences have been considered to be allochthonous by Williams et al. (1972) but details of their exact situation are not known. Possible Fleur de Lys rocks also occur on the western side of White Bay (Lock, 1969,1972) in the Hampden Zone. Older rocks may be included with the Fleur de Lys in all three regions. Dating of the deformation and metamorphism of the Fleur de Lys relies heavily on indirect evidence, for although there are strong contrasts in structural style, complexity and metamorphic grade between Fleur de Lys and adjacent younger Ordovician and Silurian sequences, only one clearly unconformable relationship has been reported. Here, Siluro-Devonian sedimentary and volcanic rocks with Acadian structure nonconformably overlie the Burlington Granodiorite. It is intrusive into the Fleur de Lys and deformed with it (Neale and Kennedy, 1967). Hence, Fleur de Lys structure predates the Acadian. The easterly derived flysch at the top of the transported Humber Arm Supergroup contains microcline granite, granophyre and ophiolitic detritus (Stevens, 1970) presumably derived from rocks in an analogous position to the Burlington Peninsula and it is of Arenig or Llanvim age. Ophiolitic and silicic volcanic detritus presumably derived from the Fleur de Lys Supergroup of the eastern Burlington Peninsula occurs in the Arenig Snooks Arm Group and the Ordovician(?) Baie Verte Group (Church, 1969; Church and Stevens, 1971; W.S.F. Kidd, personal communication, 1974). Both these observations indicate that the Fleur de Lys was deformed and undergoing erosion by Early Ordovician time. No fossils have been found in the Fleur de Lys rocks, but carbonate breccias similar to those of the Middle Cambrian to Lower Ordovician Cow Head Breccia occur in the Fleur de Lys Supergroup on the western side of White Bay (Betz, 1948; Neale and Nash, 1963) and indicate that the Fleur de Lys probably contains rocks of Cambrian age. Most recently, the recognition of remnants of the deformed rocks like the eastern part of Fleur de Lys Supergroup within the Lower Ordovician ophiolite terrane of Central Newfoundland (Notre Dame Zone) on Long Island and Twillingate Island (Williams et al., 1972; Williams and Payne, 1975) provides further evidence that the Fleur de Lys rocks were probably deformed and metamorphosed in latest Cambrian or earliest Ordovician time. The term Burlingtonian Orogeny is here proposed for this widespread deformation and metamorphism. Stratigraphic development of the Fleur de Lys Super-group Peninsula and its relationship to the Western Platform

of the Burlington

The Fleur de Lys Supergroup of the Burlington Peninsula occurs in two areas separated from each other by a thin belt of less deformed mafic vol-

45

canic rocks and associated mafic and ultramafic rocks of the Ordovician(?) Baie Verte Group (Fig. 2). Determining the stratigraphic succession within such polydeformed metamorphic terranes as the Fleur de Lys is heavily dependent on understanding the structure and recognizing tectonic slides. Consequently, the stratigraphy of this supergroup is known in any detail only where structure has been studied in the northwest (Kennedy, 1971) and the northeast (Coates, 1970; Kennedy et al., 1972). The stratigraphic succession of the western outcrop is summarized in Table I. It largely depends on work at the northern end of this belt where three sequences of lithostratigraphic units (Kennedy, 1971) are separated from each other by structural discontinuities or tectonic slides (Fleuty, 1964a). The stratigraphic relations among these three sequences are unknown. Rocks like those of the White Bay sequence strike southwestward into the central part of this outcrop belt, where an older gneissic (Grenvillian?) basement is exposed (De Wit, 1974), and hence are considered to be the oldest. Marbles, marble breccias, quartz pebble greywackes and associated pelites occur within the Fleur de Lys on the eastern side of White Bay, where they are in tectonic slide contact with psammitic schists of the Fleur de Lys. These rocks have been tentatively interpreted as younger than the Eastern Sequence, since they are not represented in the north, where they could have been removed by tectonic sliding between the Eastern Sequence and the Advocate sequence. They also bear close lithologic resemblance to rocks of the upper (Early Paleozoic) part of the Dahadian Series of the British Isles (Downie et al., 1971; Harris and Pitcher, 1975), with which the Fleur de Lys is correlated (Church, 1969; Phillips et al., 1969; Kennedy et al., 1972; Kennedy, 1975). Furthermore, marble breccias associated with the greywackes strongly suggest correlation with the Middle Cambrian-Lower Ordovician Cow Head Breccia of western Newfoundland. Since the western Fleur de Lys contains a sequence of the order of 7 km of dominantly metasedimentary rocks of Hadrynian-Early Paleozoic age, it is reasonable to suggest that the lithologies most closely resembling adjacent Early Paleozoic lithologies are among the younger rocks preserved. The age of the Advocate sequence (Table I) presents further problems. This sequence consists of black pelite and pillow lava, gabbro and ultramafic rock (J.T. Bursnall, personal communication, 1971) in slide contact with the Eastern Sequence. In the eastern outcrop of the Fleur de Lys Supergroup, both the Birchy Schist and the Mings Bight Group occur at the base of the stratigraphic sequence on the east side of Mings Bight (Fig. 2). Above the Mings Bight Group the succession is totally different (Table I) since thick accumulations of mafic and silicic volcanic rocks are unknown from any other Fleur de Lys outcrop. Contacts exposed in the north indicate that the succession from Birchy Schist to Cape St. John Group is truly stratigraphic so that this contrast in later depositional development is real. Although the Nipper’s Harbour Group (Baird, 1951) has been interpreted as part of the Fleur de Lys by some workers, probably most of it is an extension of the Betts Cove Ophio-

w”

bi %

2 : z m E

South Cove Schist 350 m Slaughter House schist 300 m

Calc-silicate schists (contact not seen) Graphitic pelites calcareous pelites and semi-pelites (Slide)

Mafic tuffs and fine agglomerates with interbedded graphitic pelites and psammites

Pebbly muscovite psammites with semi-pelites. Impure marble near base.

Mings Bight Group (Flat point Fm.) 950 m

Birchy Schist 300 m

Graphitic pelites, pillow lavas, gabbros, ultramafic rocks

Birchy Schist 100 + m

Mings Bight Group 1000 f m

Pacquet Harbour Group 1500 + m

Cape St. John Group 1500 + m

Quartz pebble greywackes with rutiliferous quartz, marbles, marble breccias pelites

Greywacke/marble sequence of S.E. White Bay

Advocate sequence

Group/Formation Approx. thickness

Lithology

-

Base not seen

Dominantly silicic volcanic rocks, rhyolites, porphyritic rhyolites, ignimbites with minor pillow lavas, other mafic rocks, sandstones and caleareous pelites Dominantly mafic agglomerates, tuffs and pillow lavas minor silicic agglomerates and tuffs, rare semi-pelites and greywackes Pebbly muscovite psammites with semi-pelites, locally calcareous. Impure marble near base Mafic tuffs and agglomerates. minor metasedimentary rocks

Lithology

Eastern Fleur de Lys Supergroup

Sequence Group/ Formation Approx. thickness

Western Fleur de Lys Super-group

Stratigraphy and age of the Fleur de Lys Supergroup

TABLE I

Base not seen

Maiden Point Formation Lower Part of Curling Group

Lighthouse Cove Formation/Cloud Mountain Formation Bateau Formamation Early CambrianLate Hadrynian

Late Hadrynian

Cow Head Group (Upper) Forteau Formation Bradore Formation

Correlation with Western Platform (Lomond Zone)

~__._____

MiddleLate Cambrian?

_______

___-

Biotite gneisses, gneissic granitic rocks

Grenvillian gneissic basement

White Bay Sequence 2200 + m

Fsammitic and semi-pelitic schists locally pebbly with graphitic pelites and minor marbles (Slide) Pebbly psammitic and semipelitic schists minor graphitic pehtes and marbles. Dominantly psammitic schists of central part of outcrop belt

Harbour sequence 2190 m

TABLE I (continued)

Pillow lavas locally included in Pacquet Harbour Group

Helikian

Mid Hadrynian

Volcanism related to initial rifting of continent. Dykes?

48

lite Complex and is thus younger (Schroeter, 1971). However, some mafic volcanic rocks within it may belong to the Fleur de Lys. Mafic and ultramafic xenoliths are common in the southern part of the Cape Brule Porphyry, indicating the presence of a mafic and ultramafic foundation. Pillow lavas between the Cape St. John Group and the ultramafic belt at Tilt Cove (Beaver Cove Group of Dewey and Bird, op. cit.) may represent part of this foundation, but are more likely to be a local pillow lava unit within the Cape St. John Group and are consequently not differentiated on Fig. 2. Probably rocks shown as Pacquet Harbour Group in the middle of the Burlington Peninsula are partly representative of this mafic and ultramafic foundation (Gale, 1972). Work by B.F. Kean and J.R. de Grace (personal communication, 1974) has indicated that volcanic rocks previously assigned to the Cape St. John Group unconformably overlie the Snooks Arm Group, 2 km northeast of Tilt Cove but both contain the Acadian foliation. The nature of the contact between these Silurian(?) rocks and that part of the Cape St. John that is part of the Fleur de Lys deformed terrane is presently unknown. Tentative ages for parts of the Fleur de Lys stratigraphic sequence are also shown in Table I. Correlation of the upper part with the Cow Head Group (Stevens, 1970) has already been discussed. At lower stratigraphic levels lithologic resemblances of the predominantly quartz wacke sequence of the Eocambrian Maiden Point Formation (Cooper, 1937), the Summerside Formation (Bruckner, 1966; Stevens, 1970) of the west Newfoundland allochthons and the Fleur de Lys suggest their correlation. More specifically, mafic volcanism on the Western Platform shown by the Cloud Mountain Formation (Betz, 1939) and the Lighthouse Cove Formation (Williams and Stevens, 1969) are correlated with the Pacquet Harbour Group and/or the Advocate sequence. Dykes that are interpreted as feeders to these mafic volcanic rocks have yielded an 4oAr/3gAr age of 605 + 10 m.y. (Stukas and Reynolds, 1974a). Although only a thin elastic sequence underlies the basal Cambrian lavas of the Western Platform, thick quartzo-feldspathic sequences are preserved in the overlying Hare Bay Allochthon (Maiden Point Formation), also of Eocambrian age. It is thus probable that the rapid easterly thickening of the basal Cambrian of Belle Isle (Williams and Stevens, 1969) also occurred with older elastic deposits that are now only preserved in the allochthons and in the Fleur de Lys itself. A protracted history of deposition before the Cambrian is required to accumulate the thickness of elastic sediments preserved as the Maiden Point Formation and the lower part of the Fleur de Lys Supergroup. No undisputed correlative of the Portaskaig tilloid has been found in the Fleur de Lys. Structural Peninsula

development

of the Fleur de Lys Supergroup

of the Burlington

Major, generally recumbent Fz isoclinal folds face (in the sense of Shackleton, 1958) in opposing directions in each outcrop belt. These folds fold the

49

Dr slides and the S1 schistosity. They are themselves approximately coaxially refolded by later structures. The sequence of deformation in each outcrop belt is shown in Table II and described below. The western Fleur de Lys belt contains a predominantly steep second schistosity of foliation, Ss, in its central parts, associated with numerous tight to isoclinal (Fleuty, 1964b), mesoscopic Fz folds. In the northwest (Kennedy, 1971), the steep SZ schistosity becomes gently inclined and the Fz folds are recumbent, facing between northwest and northeast. Large F2 folds with limbs longer than 5 km are present. Orientation of D2 boudinage axes indicates that these folds have been generated by a maximum extension strain sub-normal to the fold axes since boudinage axes are sub-parallel to fold axes. No direct estimates of h-value (Flinn, 1962) can be made, but the absence of double boudinage axes suggests a value of 1 or more. F1 folds can be identified as mesoscopic structures producing interference patterns when refolded by Fz folds, but the absence of reversals of Ds facing direction or repetition of formations, except by large-scale Fz folding, makes the presence of large-scale F1 folds unlikely. The S1 schistosity is preserved between the Ss schistosity planes and as inclusions in post-D1 pre-Dz porphyroblasts. The first deformation, however, did lead to the formation of major tectonic slides. One of these slides pre-dates the development of Si schistosity since xenoliths of mylonites formed on it are enclosed in intrusive amphibolites which have themselves developed the S1 fabric. The slides may have formed while sedimentation was in progress, if the amphibolites are the intrusive equivalents of mafic volcanic rocks higher in the Fleur de Lys sequence (Kennedy et al., 1972). Later structures include two strain-slip fabrics best developed in the eastern part of the western belt at Coachman’s Cove. They both dip steeply here, trend to the northeast and northwest of the main Sz schistosity and are associated with tight mesoscopic folds. These structures become less intense as they are followed northwestwards into the region of gently inclined Sz near Fleur de Lys. Again, both fabrics are associated with extension normal to fold axes. These structures and the overall geometry of the Fleur de Lys structure in this region are shown in Fig. 3. Examination of Fleur de Lys rocks in thin section confirms the sequence of deformation described above. However in addition, post-D1 pre-Ds garnet and albite porphyroblasts preserve a crenulated inclusion trail of S1 indicating that Si was crenulated locally before the second deformation began. Two further points of structural importance are recognizable in the westem Fleur de Lys outcrop belt. Firstly, not only Ds and D4 structures but also Dz structures increase in intensity towards the southeast where the Advocate Sequence is preserved. Secondly, the change in attitude of structures from northwest to northeast across the northern end of the western outcrop (Fig. 3) has been interpreted by Kennedy (1971) as the result of even later refolding. This is based upon the assumption that Sz, S, and S, had fairly constant orientations at the time of formation. However, this

_

Dl

_

Diabase dykes and sills Tectonic slides

S, schistosity or L-S fabric. Minor tight to isoclinal F1 folds. Tectonic slides?

Crenulation of S,

Sz schistosity or L-S fabric. Major Fz isoclines northeast to northwest facing. Minor tight to isoclinal F2 folds

P2

D3

D4

Structure -. S4 strain-slip fabric or crenulation. Minor tight to open F4 folds. (Acadian?) S3 strain-slip fabric. F3 tight to open minor folds overturned to north

Phase

-

to chlorite

--

D2

“3

D4

Phase

.-

_

Upper greenschist facies (garnet grade) locally amphibolite facies (staurolite grade) Greenschist facies (biotite D1 grade)

Greenschist facies (biotite grade) locally upper greenschist facies (garnet grade)

Greenschist facies (biotite grade) locally amphibolite facies (kyanite grade)

Greenschist facies (biotite grade)

Retrogression grade.

Metamorphism

-

S, schistosity or L-S fabric. Local major F1 folds. Minor tight to isoclinal F1 folds. Tectonic slides

S2 schistosity or L-S fabric, locally a crenulation. Major Fz isoclinal folds, southward facing. Minor isoclinal to close F2 folds

Retrogression to chlorite grade

S4 strain slip fabric or crenulation. Open minor F4 folds (Acadian?) S3 strain-slip fabric. F3 isoclinal to open major and minor folds, overturned to south

_

Upper greenschist facies (garnet grade), locally greenschist facies (biotite grade) Greenschist facies (biotite grade)

Greenschist facies (biotite grade) locally amphibolite facies (kyanite grade) Greenschist facies (biotite grade, locally garnet grade)

Greenschist facies (biotite grade)

Metamorphism

Structure

histories of the Fleur de Lys Supergroup - Eastern Fleur de Lys Supergroup Western Fleur de Lys Supergroup

Structural and metamorphic

TABLE II

Fig. 3. Three-dimensional diagram of the structure of the Fleur de Lys Supergroup at the northern end of the western Fleur de Lys outcrop belt. Modified from Kennedy (1971 f. 0 = bedding, 2 = S2, 3 = Sa, 8, = S*, L = Late crenulation.

change in attitude may equally well reflect an original feature of Fleur de Lys defo~ation and late refolding may not have occurred, Depending upon which interpretation is correct, the tightness af the Fleur de Lys folds and hence, in general, the intensity of the deformations either increases upwards or laterally towards the Advocate sequence. In the eastern Fleur de Lys outcrop belt the st~ctur~ sequence is similar to that already described, although major D1 tectonic slides have not been recognized except possibly on the margins of ultramafic bodies in the eastern side of Mings Bight (Fig. 2). Less important, local D1 slides are present. The Sz schistosity in this belt is generally gently inclined, except where it is folded by later st~ctu~s. It shows a general east-west trend. The second schistosity, Sz, or an L-S fabric (Flinn, 1965) is usually the dominant fabric in rocks of the western part of this belt, but in the east and southeast Sz is only truly penetrative in the cores of tight recumbent synclines and S1 is generalIy well preserved away from these. Deformed vesicles and the mineral lineation of I)1 L-S fabrics indicate that the D1 stretching direction was inclined at a high angle to F1 fold axes, and the &value of the D1 deformation ellipsoid is

52

Burlingtonian

Orogen

FLEUR

DE LYS ZONE

; NOTRE

DAME

ZONE

pacquet

B

I I

I

-

Facing z.S2

Direction Schistoslty

Ganderian

of Ft Folds

H

I

Facmg Direction rS2Sch1stoslty

ZONE

of F2 Folds

I

10 Km

t Fill,,+

BOTWOOD

-

6 InI les

b

Orogen

D

C

GANDER

’

Facmg D!rectlon

ZONE

I ,

; AVALON I I

2

1

16miles 20Km

4 1

of F2 Folds

s.SS Sch#stoslty

f

ZONE

Fault

3 SS Schlstosity

Fig. 4. Cross-sections of the Burlingtonian Orogen in the eastern Burlington Peninsula and the Ganderian Orogen near Gander. Lines of section shown on Figs. 2 and 9, respectively. Lithologic legends as on Figs. 2 and 9, respectively.

approximately 1. Because of consistent D2 facing directions, large-scale F1 folds are considered to be absent, except between Mings Bight and Pacquet Harbour where a major downward-facing F1 anticline and syncline are present (Fig. 4). Mesoscopic F2 folds are generally tight to isoclinal structures where S2 is truly penetrative, but in the east where Ss is represented by a crenulation in many places, the F2 folds are close structures. Major, recumbent Fs fold cores are present between Mings Bight and Pacquet Harbour, west of Pacquet Harbour and in Confusion Bay (Figs. 2 and 4). They are isoclinal with limb lengths of approximately 6 km, and face between southeast and southwest. Ds boudinage axes are sub-parallel to Fs fold axes and thus the D2 maximum extension strain was oriented sub-normal to Fs fold axes. Fz folds have been locally refolded by co-axial Fs folds in Pacquet Harbour and further south in the central part of the peninsula, where this refolding results in the Da structures becoming locally downward facing. Fs folds are tight to isoclinal structures, with boudinage axes subparallel to fold axes in the north but farther south the F3 folds are more open. The major Fs folds are overturned to the south. Steep D4 crenulations and kink bands may be of Acadian age. The tightness of the Ds and Ds structures in this eastern outcrop of the Fleur de Lys apparently decreases southwards or southeastwards away from the ultramafic rocks of Mings Bight. This is reflected in the intensity of development of Ss and Ss and the tightness of Fs and Fa folds. Since these

structures have little or no plunge, this change does seem to reflect a lateral variation in intensity of successive deformations rather than a change of intensity with depth. However, the data are at present difficult to assess since some variation of Dz intensity is related to position with respect to major F2 folds. Major F2 folds are absent in the Pacquet Harbour Group 8 km or more south of Mings Bight (J. Tuach, personal communication, 1974), supporting the suggestion that Fs structures die out in this direction. The facing directions of Fz folds, the sense of overturning of Fs folds and the intensity of Ds and Da deformations exhibit a symmetry about the region where the Advocate sequence and the Baie Verte Group are preserved. Whether each individual deformation is the result of a rotational or irrotational strain is difficult to assess, but where strain variation does occur controlled by lithology, refraction of the Sz schistosity could be interpreted to indicate that the Dz deformation had some component of rotational or of simple-shear strain. h-values of approximately 1 support this tentative interpretation. Metamorphic and intrusive histories of the Flew- de Lys Super-group of the Burlington Peninsula Metamorphism of the Fleur de Lys is within the intermediate pressure and temperature facies series (Barrovian type). The highest grades occur within each outcrop belt rather than on the margins, metamorphic intensity thus shows a different distribution from deformation, although most Fleur de Lys rocks suffered extensive metamorphic recrystallization. Most rocks show textures that were produced after the first deformation and before the second, and most porphyroblasts (garnet and albite or oligoclase) grew at this time. However, albite shows a locally extended growth history that extends even later than the third deformation. Recrystallization is far less intense east of Confusion Bay. Kyanite and staurolite are restricted to small areas near Fleur de Lys and Pacquet Harbour where they have grown after the second deformation and before the third (Table II), and are associated with intense annealing and destruction of the Sz schistosity, particularly near Pacquet Harbour. Ds and D4 deformations are associated with local retrogression to biotite and chlorite grades. A wide variety of intrusive rocks occur within the Fleur de Lys Supergroup and can generally be recognized as having been emplaced prior to or early in the deformation history. In the western outcrop, hornblende amphibolites as dykes and sills are extensive in the central part of the belt and have been affected by both Sr and Sz. Small ultramafic intrusions with xenoliths of country rock, generally associated with amphibolites, also predate the S1 schistosity in this region. The Partridge Granite, a post-tectonic garnetiferous muscovite granite, occurs in the extreme north (Fig. 2). Other granitic rocks cut the western Fleur de Lys south of the region shown on Fig. 2, where synand post-tectonic examples are present (Bird et al., 1971). At the southern

54

end of White Bay extensive granitic rocks which intrude the Fleur de Lys probably post-date Sa, but earlier granites may be present. Deformed (preSs) mafic visions are also present here. In the eastern Fleur de Lys a variety of early silicic and mafic intrusive rocks are present. The Burlington Granodiorite predates the Sa schistosity. If granodiorite sheets involved in D1 slides on the eastern side of Mings Bight are related to it, it is reasonable to interpret it as a pre-D1 intrusion, possibly associated with volcanism of the Pacquet Harbour Group. The Cape BrulC Porphyry and associated quartz porphyry sheets that cut the Pacquet Harbour Group are demonstrably earlier than the S1 schistosity. The southeastem parts of this porphyry body may well be extrusive, but it is clearly intrusive in the north and probably related to Cape St. John volcanism. The Dunamagon Granite, a pink microcline granite, is also deformed in its margins by Ss and possibly S1, and the peralkaline La Scie Granite (Cockburn, 1971) also predates Fleur de Lys deformation. Pre-tectonic mafic intrusions are common as dykes in the Pacquet Harbour Group, but elsewhere they are rare. The pie-tectonic Reddits Cove Gabbro ~Cockbum, 1971) occurs in the extreme east of the peninsula. Intrusive rocks within the Fleur de Lys that have been deformed with it therefore apparently fit into two suites. A b~ic~ultrab~ic association related to mafic volcanism and a series of granitic and porphyry intrusions related to silicic volcanism. Ophiolites in the Flew de Lys Super-group of the Burlington Peninsula

Mafic and associated ultramafic plutonic rocks, other than the small intrusions that cut the Fleur de Lys and the xenoliths within the Cape Brule Porphyry, are extensive in the Advocate sequence and on the eastern side of Mings Bight. These rocks are deformed with the Fleur de Lys in their margins (Kennedy and Phillips, 1971) and are distinct from mafic and ultramafic rocks that occur as part of an ophiolite sequence at the base of the younger Baie Verte Group (J.F. Dewey and R.E. Norman, personal communications, 1972). This led Kennedy and Phillips (op. cit.) to conclude that these mafic/ ultramafic complexes deformed with the Fleur de Lys could not represent ophiolite, since they were of pre-Ordovician age. However, their association with black slates and pillow lavas of the Advocate sequence, which is in Di tectonic slide contact with the Fleur de Lys to the west, again raises the possibility that they represent the remnants of an ophiolite complex. Characteristic ophiolite stratigraphy has not been recognized within the Advocate sequence, but since it is internally disrupted by slides (J.T. Bursnall, personal communication, 1971), this is not surprising. The Advocate sequence occupies a unique position in the Fleur de Lys with respect to stratigraphy and structure, which is best explained by considering it as an ophiolitic remnant. The mafic and ultramafic complexes deformed with the Fleur de Lys on the eastern side of Mings Bight and probably slide bounded on their eastern

55

sides, are also interpreted as further representatives of this syn-Fleur de Lys ophiolite terrane. Ultramafic bodies of the Baie Verte Ultramafic Belt that extends southwestwards from Baie Verte to Flatwater Pond (Fig. 2) and beyond also show evidence of being deformed with the Fleur de Lys on their western margins (Kennedy and Phillips, 1971); they are separated from the Baie Verte Group by a later (Acadian?) tectonic slide (Bird et al., 1971), and are here interpreted as remnants of the same early ophiolite complex. This ophiolite interpretation is in general agreement with other workers, but is different with respect to their age. Previous workers have considered the ophiolites of the Burlington Peninsula to post-date Fleur de Lys deformation and to be of Early Ordovician age. Although this interpretation meets with no geologic objections with respect to those included in the Baie Verte Group on Fig. 2, the Advocate sequence is separated from the rest of the Fleur de Lys by a Di tectonic slide on the coast south of Coachman’s Cove. Interpretation of the Advocate sequence as part of the Fleur de Lys is also supported by development of composite mineral growth fabrics in the steatite margins of many of these bodies, of similar attitude to Ss of adjacent Fleur de Lys rocks. Pillow lavas in the central part of the Pacquet Harbour group outcrop of Fig. 2 are also very probably ophiolitic. This conclusion is supported by analytical results of Gale (1972). These ophiolitic rocks may form the base of the Fleur de Lys in this region. Recognition of the Advocate sequence as ophiolite has far-reaching implications for interpretation of the depositional and structural development of the Fleur de Lys Supergroup. DEVELOPMENTAL

MODEL

AND CAUSE

OF THE BURLINGTONIAN

OROGENY

The ophiolite of the Advocate sequence separates the Fleur de Lys Supergroup of the Burlington Peninsula into two stratigraphically and structurally distinct regions (Table III). Its existence indicates that the general principles of plate tectonics should be applicable to this region, and should provide evidence of plate movements in the northern Appalachians which predate Early Ordovician ocean-floor spreading. Previous models have not considered the causes of pre-Early Ordovician orogeny in this region apart from suggesting a general association with a consuming plate margin. However, the diastrophism caused by the Burlingtonian Orogeny is more likely to be the result of large-scale discrete changes in plate-tectonic regime. Volcanic and depositional

development

In the absence of petrochemical data, the recognition of volcanic sequences of ophiolitic or island-arc affinities must rely heavily upon field observations and petrographic identifications of the rocks themselves. Extensive metamorphism of the rocks makes exact petrographic identification of

Fleur de Lys Supergroup from base to top of Mings Bight Group as eontinentalrise prism of sediment Dyke swarm? on Western Platform (Lomond Zone)

Erosion of continent, formation of continentalrise prism of sediment

Rifting of Grenville continent followed by ocean-floor spreading

Greywackes, marbles. Greywackes possibly derived from local uplifts. Advocate sequence to southeast Dykes and sills

Ophiolite detritus, quartz and feldspar shed westwards to form upper part of Curling Group

Western Fleur de Lys _______~_.._ Deposits

Pillow lavas locally included in Pacquet Harbour Group

Outer edge of continentalrise prism of sediment to top of Mings Bight Group

Dykes?

Cape St. John and Pacquet Harbour Groups. Advocate sequence to northwest

processes -.___-.Eastern Fleur de Lys ..._ Deposits -.___ .Ophiotite detritus, quartz volcanic detritus shed southeastwards to form flysoh of Snooks Arm Group

Orogen in relation to plate-tectonic

Rifting of marginal basin, formation of island arc to southeast

-_ _..---.___-. Erosion and renewed oceanfloor spreading in Central Newfoundland (Notre Dame Zone) Closure of marginal basin

Process

Development of the Burlingtonian

TABLE III

Early Dr slide cut by dykes

Obduction of small oceanbasin ophiolite. D,---X)3 of Fleur de Lys (nappes facing away from closed marginal basin)

Tectonism

Earliest Cambrian Mid-Late Hadrynian

Cambrian

Latest CambrianEarliest Ordovician

Arenig

Age

57

the original igneous rocks impossible in many cases. However, lithologic associations with the Advocate sequence have already been used to argue that it is ophiolitic. Furthermore, the association of mafic and silicic volcanic rocks in the Pacquet Harbour and Cape St. John Groups east of the thick western Fleur de Lys elastic succession is suggestive of an island-arc environment. If these interpretations are correct (Fig. 5) the Advocate sequence must represent the remnants of a marginal ocean basin that formed inside an island arc presumably related to a northwesterly dipping subduction zone situated farther to the southeast. It can be dated lithostratigraphically with respect to Fleur de Lys deposition since it must post-date deposition of the quartz wacke sequence of the Mings Bight Group which occurs on each side of it. In post-Mings Bight time the depositional differentiation of the Fleur de Lys into western and eastern entities was established, since Cape St. John and Pacquet Harbour rocks are unknown in the western outcrop. The Birchy Schist may represent precocious volcanism associated with uplift that took place before the subsidence, rifting and ocean-floor spreading that formed the Advocate sequence. The extensive intrusive amphibolites of the western Fleur de Lys may be related to this rifting process. Comparison with the Lomond Zone of western Newfoundland, where extensive mafic volcanism occurred in latest Hadrynian-earliest Cambrian time provides a probable age (Stukas and Reynolds, 1974a) for initiation of the marginal basin. These lavas from western Newfoundland are petrochemically similar to those associated with known rifts (Strong and Williams, 1972; Strong, 1974b). The general geologic setting of the Fleur de Lys Supergroup with ophiolite of central Newfoundland to the east of it and the Grenvillian basement of western Newfoundland to the west, led Stevens (1970) to suggest that the Fleur de Lys represented a continental-rise prism of sediment. The case for a continental margin along the western side of the Appalachian System has been summarized and enlarged upon by Williams and Stevens (1974). Although the provenance of the western Fleur de Lys is unknown, partly because it is complexly deformed, this interpretation is supported by several independent lines of evidence. Indication that part of the Pacquet Harbour Group is ophiolitic (Gale, 1972), coupled with interpretation of the upper part of this group together with the Cape St. John Group as an island-arc complex, indicates the existence of oceanic crust in the region at this time. Recognition of the Gander Group of eastern Newfoundland as an analogous continental-rise prism on the other side of the Iapetus Ocean that has suffered Late Precambrian orogeny also points to the presence of an oceanic basin separating the two regions by Late Precambrian time (see below). Faunal provinciality was established for both sides of the Appalachians by Lower Cambrian (Palmer, 1971), again suggesting that an effective barrier (ocean?) was present prior to the Early Ordovician ocean-floor spreading that is assumed from preserved ophiolite complexes. Although there is some evidence of rifting leading to ocean formation at 820 m.y. (Rankin et al., 1969) in Virginia no direct evidence of activity this old is preserved in New-

~ADRYNIAN JW. Dyke Swarm

(650 m.y.1

SE. EMBRYONIC

;&:iian

T

> ‘<’ besement to Western Platform &w~tern . c - x \ - I , Crystailine

LATE

OCEAN

Belt

HADRYNIAN

OCEAN

, , MIDDLE , /

hbonate

/

CAMBRIAN

/

Bank

i

ISLAND

,I

/

ARC

/’

fl SUBDUCTION E. Burliwton CLOSING

LATE

CAMBRIAN-TREMADO~(Late OPtilOLlTE

leurde

NW.

Lys

DIVERGENT

BASIN

Phase)

COVER

PartlyTransform

MARGINAL

S ZONE Pvninsuia

OVER

CLOSED

MARGINAL

BASIN

June METAMORPHIC NAPPE ca 100 Km.

COMPLEX

SE.

Fig. 5. Deveiopmental diagram to illustrate the development of the Burlingtonian Orogen of the Newfoundland Appalachians from Earfy ~adryn~~ to Early Ordovician time.

59

a III

H

Fig. 6. Map of the Burlington and tectonic components.

Peninsula

to indicate

LEGEND EarlyOrdowcian Margmai Flaurde

Lys Island Arc

Fieurde

Lys(youn~er

Fleurde

Lys Continental

the distribution

Basin &Island AK

than MinqsBight

Grou

Rise

of major depositional

foundland. Events recognized on the eastern side of the system in Newfoundland may eventually provide further information on this point. Greywacke sedimentation of the youngest part of the western Fleur de Lys may be the result of derivation of sediment from uplifts associated with small ocean-basin formation within the continental margin itself. It is thus reasonable to interpret the Fleur de Lys Supergroup as a continental-rise prism that was split open at a late stage of its development by a marginal ocean basin forming behind and broadly contemporaneous with an island arc on its outer margin in probable earliest Cambrian time (Fig. 6). This marginal basin established depositional isolation for the eastern Fleur de Lys which continued to develop as an island-arc complex.

The deformation history of the Fleur de Lys can be interpreted as marking successive stages in the closure of the small ocean basin described above. However, the earliest D1 tectonic sliding which predates amphibolite emplacement may be the result of initial opening of the small ocean basin and mark a period of reverse faulting or normal faulting (Fig. 5). The polarity of the Burlingtonian structures on each side of the Advocate sequence with respect to facing, tectonic transport and intensity of deformation is most

60

significant in respect to closure of the marginal basin and is summarized in Fig. 7. It is assumed that the Dz facing direction reflects tectonic transport since the maximum axis 2 of the Dz formation ellipsoid is sub-normal to the F2 fold axes and large-scale F, folds are not present. The direction of tectonic transport for the Ds structures can also be inferred since 2 of the Ds deformation ellipsoid is sub-normal to the Fs fold axes, making the asymmetry of the folds reflect the overall sense of movement. The facing direction of the moderate-scale F1 folds in the eastern Fleur de Lys is also shown and interpreted to reflect tectonic transport. It will immediately be clear from Fig. 7 that the polarity of the F2 folds is reflected by the Fs folds and also possibly by F, folds. This coaxial refolding of earlier structures by renewed tectonic transport in the same direction results in older folds everywhere being downward facing in the hinges of younger ones. The tightness of the Fz and Fs folds is also shown in Fig. 7 and it will be noted that F, folds are tightest close to the ophiolite of the Advocate sequence and Fa folds also show similar development. Not only does the distribution of fold geometry and tightness further accentuate the unique role of the Advocate sequence,

Western

Fleur de Lys

-3

N.

* =I 2&

0

.. 2

OPHIOLITE

.

-. .-c

*.--* . _. . . ‘3

Facmg

w

Dtrectwn

Directon

.o.

of Ft Folds

of Overturning

of F3 Folds

&

-3,,

_

. . . :3

2

Eastern

OBDUCTION?

>-------)

., -

.

Fieurde

Fac,,,g 0: Beddmg

Lys

D,rect,onof 2:s2

F2 Folds 3-53

-

Fig. ‘7. Diagrammatic representation of the variation in structural style, facing and intensity with respect to geographic position within the Burlingtonian Orogen.

61

but also it suggests that this deformation history is the result of successive movements of an overlying sheet, thus providing a link between individual pulses of movement in small ocean-basin closure and deformation. Previously the structural development of the Fleur de Lys Super-group was interpreted to be the result of gravity tectonics off a rising gneiss dome (Kennedy et al., 1972) and although this type of tectonism may well have occurred within the continental-rise prism itself, the Burlington Peninsula marks the outer edge of the prism where small ocean-basin closure has occurred. If the structures were related to a mantled gneiss dome, their intensity would be expected to increase downwards, whereas in this region it increases laterally and/or upwards towards the Advocate sequence. A similar relationship between ophiolite displacement and deformation has been described by Williams and Smyth (1973) from the west Newfoundland allochthons; but here deformation is more localized, presumably since the ophiolite is far from its source, whereas the Advocate sequence is essentially autochthonous. The possibility that the transported west Newfoundland ophiolites were derived from the Burlingtonian suture is discounted since they lie to the east of slices containing older deformed mafic plutonic and volcanic rocks (Williams, 1973; Williams et al., 1973) probably derived from the eastern Fleur de Lys. The change from steep to flat structures within the western Fleur de Lys (Fig. 3) was originally interpreted to be the result of late refolding, but changes in lithospheric character required by recognition of the Advocate sequence as autochthonous ophiolite suggest that this particular structural feature may be original. D4 structures in the Fleur de Lys do not appear to be geometrically related to its internal suture and are here interpreted as later structures (Acadian?). The orientation of folds and fabrics in the Fleur de Lys suggests that the small ocean basin was closed by a general north---south movement (Figs. 2, 3, and 4). Aeromagnetic anomalies north of Pacquet Harbour suggest that the Advocate sequence extends eastwards in this direction, possibly suggesting that it may have originally been oriented east--west. However, the suture is oriented northeast-southwest, truncating the general strike of the eastern Fleur de Lys. It thus appears that the structure of the Fleur de Lys with a steep belt adjacent to the suture in the west can best be explained by closure of the small ocean basin and associated transform movement along its northwestern margin (Figs. 5 and 6). The presence of ophiolite detritus in Early Ordovician flysch to the west and east of the Burlingtonian orogen indicates that ophiolite was uplifted by Early Ordovician time. The role of metamorphism in these processes is not so clear. The highestgrade metamorphic rocks occur away from the suture on both sides and are restricted to small areas. In general, however, both the post-Dz, pre-Da local climax and the more widespread post-D1, pre-Da climax may be related to generation of heat within the sequence both by radioactive decay and from intrusive bodies. It is clear that the Advocate sequence was not the source of

62

I

%

300 Km

?

Basement inliefs(lnc.you~er granitic rocks) 8

Fig. 8. Extension of the Burlingtonian Appalachian region. M = Macquereau Schists, A = Arnold River Formation,

: Includes

Basement

and Ganderian orogens throughout the Canadian Group, S = Shickshock Group, SB = Sutton Bennet B = Basement rocks.

metamorphic heat, since the highest-grade rocks do not occur in contact with it. This provides another contrast with the west Newfoundland ophiolites, which were most probably hot at their time of displacement (Church and Stevens, 1971; Williams and Smith, 1973). In the Fleur de Lys, metamorphism of sufficient grade was probably produced by a general increase in heat flux supplied by intrusive bodies as opposed to deep burial by further supracrustal rocks now removed by erosion. The Advocate sequence appears to top the Burlingtonian erogenic complex. Possible extensions of the Burlingtonian complex in mainland Canada are shown on Fig. 8. The reader is referred to Willies et al. (1972) and Rast and Stringer (1974) for details of this discussion. THE EASTERN MARGINAL GANDERIAN OROGENY

CRYSTALLINE

BELT (GANDER

ZONE)

AND THE

The eastern marginal crystalline belt of the Newfoundl~d App~achian System separates Ordovician and Silurian sedimentary and volcanic rocks of east-central Newfoundland from the Hadrynian-Ordovician sedimentary and volcanic rocks of the Avalon Platform or Zone. The term Avalon Zone is preferred here since many of the rocks of this region are not platformal (Fig. 1). The crystalline belt underwent erogenic deformation, metamor-

63

phism and plutonism in pre-Middle Ordovician, probably late Hadrynian time. This erogenic episode is here referred to as the Ganderian Orogeny. Extent

in Newfoundland,

dating of its deformation

and metamorphism

The eastern marginal crystalline belt of the Newfoundland Appalachian System extends from the coast north of Gander in the northeast, 250 km southwestwards to Bay d’Espoir on the south coast of the island (Fig. 1). From here it continues westward around the large arcuate structure known as the Hermitage Flexure (Williams et al., 1970). This belt was first recognized as a significant component of Appalachian geology by Williams (1964a), but the age of its metasedimentary rocks and of emplacement of granitic rocks within it were generally considered to be Acadian in the absence of any clear evidence to the contrary (Williams, 1964b; Jenness, 1963). However, more recent work by Kennedy and McGonigal(l972) has indicated that rocks previously assigned to the Middle Ordovician Gander Lake Group comprise three separate tectonostratigraphic divisions (Fig. 9). The Mobile Bell t)

LEGEND(Central

/

DEVON IAN or OLDER &lGranibc

rocks

/

SILURIAN tj Botwood Group 633 MIDDLE ORDOVICIAN

q

Davidsvtlle

MIDDLE Mafx

Group

ORDOVICIAN

8 OLDER

8 Ultramafic

HADRYNIAN-CAMBRIAN? III

+g

Garnetlferous

granites

Musgravetown

Group

Love Cove Group

Fig. 9. Generalized geologic map of the Gander region modified from Kennedy and McGonigal (1972). Alterations in the Hare Bay region provided by R.F. Blackwood and on the coast north of Gander by A.B. Uzuakpunwa. Section E-F is shown on Fig. 4.

64

oldest consists of a series of ortho- and para-gneisses which are presently undated but are probably of Grenvillian age. This has been termed the Bonavista Bay Gneiss Complex (Blackwood and Kennedy, 1975). These basement gneisses are overlain by a thick sequence of dominantly metasedimentary rocks, with polyphase structure and upper greenschist to low amphibolite facies metamorphism, here termed the Gander Group (McGonigal, 1973) (Gander Lake Group of Kennedy and McGonigal). The Gander Group is overlain by Middle Ordovician black slates and greywackes of the Davidsville Group with much simpler structures. The relationships between these three divisions are interpreted to have been major angular unconformities of which only the youngest is preserved. The Gander Group and the Hare Bay Gneiss Complex both comprise the Gander Zone of Williams et al. (1974) and the eastern marginal crystalline belt of Fig. 1. Both components of this belt are recognizable in southern Newfoundland at Bay d’Espoir (Colman-Sadd, 1974) and similar lithologies and associated granitic intrusive rocks can be followed along the south coast of the island at least as far as Rose Blanche (P.A. Brown, personal communication, 1973) (Fig. 1). In south-central Newfoundland extensive regions of upper greenschist to low amphibolite facies metasedimentary rocks occur that have generally been considered to be the result of Acadian deformation and metamorphism of Paleozoic sequences. However, recognition of pre-Acadian tectonism in the Gander Group makes it likely that many of these rocks, which are locally continuous in outcrop with the Gander Group, represent further continuations of it. No clear evidence of gradational metamorphic contacts with known Paleozoic rocks in south-central Newfoundland is available. Extensive amphibolites do not occur in this metamorphic terrane, although mafic volcanic rocks are widespread in adjacent Ordovician sequences. These observations support the suggestion that metasedimentary rocks in south-central Newfoundland are largely the product of pre-Ordovician erogenic processes. Metamorphosed Lower Devonian sedimentary rocks north of La Poile in southwestern Newfoundland (Cooper, 1954) indicate local moderate-grade metamorphism of probable Middle Devonian age, but further study is required to indicate whether it is either related to adjacent granitic rocks or to Devonian regional metamorphism that may be more extensive than previously realized. The Gander Zone is separated from the Avalon Zone to the east by the Dover Fault (Blackwood and Kennedy, 1975) and from the northern part of the Botwood Zone to the west by an unconformity or a melange. Further south the contact is not exposed or has not been recognized. Deformation and metamorphism of the Gander Group is demonstrably earlier than Middle Ordovician (Caradoc) since the Davidsville Group unconformably overlies ultramafic rocks deformed with the Gander Group on the north shore of Gander Lake. The basal conglomerate and overlying coarse elastic sediments contain detrital biotite and garnet and pebbles of foliated ultramafic rock, granite and Gander Group lithologies. Farther north on the coast, the base of the Davidsville Group consists of a boulder-y mudstone or

65

melange containing fragments of the underlying metamorphic Gander Group rocks (Kennedy and McGonigal, 1972). Direct evidence of the age of the Gander Group sediments and the date of their subsequent deformation and metamorphism is lacking, since the Gander Group is not only unfossiliferous but also lithostratigraphic correlation between it and the Hadrynian-Cambrian rocks of the Avalon Platform is not possible. However, several lines of indirect evidence exist to suggest that the Gander Group was deformed in Hadrynian time. Firstly, a Rb/Sr whole-rock isochron from a granite pluton that cuts equivalents of the Gander Group and is deformed with them at Bay d’Espoir has yielded an age of 573 + 40 m.y. (R.F. Cormier, personal communication, 1973). Radiometric ages from granitic rocks that occur in a similar setting in northern Cape Breton Island have yielded an age of 562 f 80 m.y. (Cormier, 1972). Secondly, metamorphic detritus in late Hadrynian sandstones of the Avalon Platform (Jenness, 1963; Papezik, 1972; Poole, 1973) may ,well be derived from the Bonavista Bay Gneiss Complex, but may equally well be derived from the Gander Group. The abundance of cllstic mica at some horizons in the west makes the latter source more likely. It could be argued that these sandstones are a molasse-type facies that is at least in part derived from a rapidly eroding Ganderian Orogen and not solely derived from volcanic islands as envisaged by Hughes and Bruckner (1971). Thirdly, the Love Cove Group of volcanic and sedimentary rocks in the western Avalon Zone was deformed in Hadrynian time, since pebbles of deformed Love Cove rocks occur in adjacent late Hadrynian molasse (Jenness, 1963). Thus a major unconformity separates the molasse from the older deformed sequence. This unconformity is probably contemporaneous with deformation of the Gander Group. Radiometric studies of rocks deformed with the Gander Group and further study of geologic relationships between the Avalon and Gander Zones should provide further data to date the deformation with more precision, but evidence to date is consistent with a Hadrynian age for both the deposition and deformation of the Gander Group. The term Ganderian Orogeny is here proposed for the widespread post-Grenville erogenic activity that occurred within the eastern crystalline belt. Stratigraphic

development

of the Gander Group

The Gander Group in the Gander region consists of a thick monotonous sequence of semi-pelitic and psammitic schists which are locally pebbly. It can be subdivided into several formations. Marbles and calcareous horizons are extremely rare, but, locally, graphitic biotite schists and chlorite, muscovite schists are common. Because of its overall monotony, no detailed stratigraphic succession can be constructed. However, structural studies near Gander (McGonigal, 1973) and farther north on the coast indicate that the upper part of the succession contains graphitic schists and minor mafic metavolcanic rocks, which are underlain by the thick semi-pelites and psam-

66

mites so typical of the Gander Group as a whole. A similar succession is present in Bay d’Espoir, where silicic volcanic rocks are associated with mafic rocks high in the stratigraphic succession (Colman-Sadd, 1974). Thickness of the Gander Group is difficult to estimate on account of its intensely deformed condition, but the preserved succession must have been at least 8 km thick. Mafic tuffs and agglomerates that occur west of the main outcrop of the Gander Group on the coast (Fig. 9) probably correlate with the minor mafic volcanic rocks of the main outcrop. The stratigraphic position of the metasedimentary rocks of south-central Newfoundland included in the Gander Group is presently unknown. It would appear from the available data that the Gander Group represents a thick accumulation of elastic sedimentary rocks in which greywackes or quartz wackes predominate, overlain by more varied sediments intercalated with volcanic rocks. Structural

development

of the Gander Group

Although the deformation of the Gander group is polyphase, the major fold structures are Fz folds formed by the second deformation, Dz. The dominant schistosity is the second schistosity Sz which trends parallel to the margins of the eastern crystalline belt. It is gently inclined to flat in the central parts but dips moderately to steeply close to the contact with the Hare Bay Gneiss Complex in the east and the Davidsville Group in the west (Fig. 4). Minor tight to isoclinal Fz folds face upwards where Sz is steep and sideways between southeast and south where Sz is gently inclined. Boudinage axes are sub-parallel to fold axes indicating that 2 of the Dz deformation ellipsoid was sub-normal to Fz fold axes. No direct estimate of h-value has been made but it is probable that h = 1. Major south to southeastward-facing Fz folds have been identified in the Gander region (McGonigal, 1973) and farther south at Bay d’Espoir (Colman-Sadd, 1974). They are isoclinal largescale structures with limb lengths of approximately 20 km (Fig. 4). Minor F1 folds are rare but tight to isoclinal where seen, and the S1 schistosity is best’ preserved in Fz fold hinges or as inclusions within post-D,, pre-D2 porphyroblasts. Major D1 tectonic slides have not been identified within the Gander Group, but ultramafic rocks are in D1 tectonic slide contact with the Gander Group in the north. At Bay d’Espoir the contact between the equivalents of the Hare Bay Complex and the Gander Group is a D1 tectonic slide that has involved reconstitution of the adjacent gneisses. Consistency of Dz facing directions indicates that large-scale Fr folds are absent in the Gander Group. The third deformation, Ds, has formed minor tight Fs folds with an associated strain-slip fabric. These are overturned to the east in the region of recumbent Fz folds and steeply inclined with a similar sense of overturning where Sz is steep (Fig. 4). Again, Ds boudinage indicates that the Ds maxi-

61 TABLE Structural

IV and metamorphic

history

of the Gander

Group

Def. phase

Structure

Metamorphism

D4

Gently inclined strain-slip cleavage or crenulation Minor open F4 folds (Acadian?) S3 strain-slip fabric F3 minor folds overturned to south or southwest where S2 is flat

Retrogression to chlorite grade. (Local hornfels textures pre-date

D3

D2

DI

S2 schistosity or L-S fabric F2 minor tight to isoclinal folds Major F2 isoclines, south to southeast facing where recumbent

D, tectonic slides S, schistosity Minor F, tight to isoclinal folds.

Greenschist

facies (biotite

grade)

Greenschist facies (biotite Locally garnet grade Greenschist facies (biotite Locally garnet grade.

grade)

D4)

grade)

Upper greenschist facies (garnet grade) Locally amphibolite facies (staurolite and kyanite/sillimanite? grade) Greenschist facies (biotite grade)

mum extension strain was oriented sub-normal to F3 fold axes. Later strainslip cleavages or crenulations also affect the Gander Group and some may be of pre-Middle Ordovician age, but this is uncertain. Some crenulations that post-date hornfels textures which are developed in Gander and Davidsville Group rocks on the coast north of Gander are clearly of post-Ganderian, probable Acadian age (Table IV). The S2 schistosity of the Gander Group steepens westwards towards the Ordovician rocks. This is the result of Acadian folding since the unconformity with the Ordovician is now steep and cut by the Acadian cleavage. The S2 schistosity also steepens eastwards towards the basement rocks but this may be an original change in attitude rather than the product of later folding. Metamorphic

and intrusive histories of the Gander Group

Metamorphism of the Gander Group is generally in the intermediate pressure and temperature facies series (Barrovian type), but local late hightemperature low-pressure assemblages do occur. Grade is generally in the

68

upper greenschist facies but local amphibolite facies conditions are indicated by the occurrence of staurolite and possibly kyanite and/or sillimanite. Metamorphic grade is lowest close to the contact with the Davidsville Group. The metamorphic history is summarised in Table IV, where it will be noted that in general the highest metamorphic grade occurred after the first deformation and before the second, but local post-D2 pre-Ds garnet and staurolite grade metamorphism also took place. Post-D3 garnet, andalusite and cordierite occurs in places in the Gander Group, related to granitic intrusions that also cut Ordovician rocks and thus are clearly of post-Ganderian age. The Gander Group is cut by a variety of intrusive rocks. Mafic and ultramafic intrusive rocks occur as small deformed pods, dykes and sills within the Gander Group and have clearly been deformed with it as pre-D1 intrusions. Granitic intrusions are widespread. The most distinctive and numerous are garnetiferous muscovite granites which are locally biotite-bearing and generally associated with richly garnetiferous aplites and pegmatites. These granites generally occur as several distinct intrusive phases of pre-Dr, postD, pre-Dz and post-D, age. Sz schistosity is well developed in their margins and the main bodies were probably largely emplaced after the first deformation and before the second, but minor earlier and later intrusive phases do occur. These granites are peculiar in showing no clear metamorphic aureoles around them, although Barrovian metamorphic grade is generally higher in areas where they are numerous or extensive. They are clearly intrusive into the Gander Group. Other microcline granites cut the Gander Group in the Gander area and post-date the second deformation. They may be entirely post-Ganderian in age. Megacrystic K-feldspar, biotite granites that intrude the Hare Bay Gneiss Complex (Figs. 4 and 9) have not been seen cutting the Gander Group. They are earlier than the gametiferous granites which cut them and are probably older than the Gander Group, though post-tectonic with respect to the Hare Bay Gneiss Complex. Granodiorites which cut the garnetiferous granites and the Gander Group north of Gander are also intrusive into the Davidsville Group. Ophiolites

associated

with the Gander Group

Mafic and ultramafic rocks other than the small intrusions that occur within the Gander Group (Fig. 9) define a long discontinuous belt that bounds the Gander Group on the west in the Gander area, with the exception of one small inlier of Gander rocks that occurs west of it. Although it is not well exposed, the contact zone with the Gander Group can be seen in the north where this ultramafic belt is surrounded by the metamorphic rocks. Here, clinopyroxenites have been completely mylonitized on S1 or Sz to form actinolite schists with relict boudins of unmylonitized coarse pyroxenite locally within them. They are associated with steatite schists which contain S1 and/or Ss and later Fs folds. Clearly they have been subjected to all or most of the Ganderian deformation. Probably the ultramafic rocks

69

here are an infolded remnant of a once more extensive overlying ultramafic sheet thrust over the Gander Group. The tectonic contact between these ultramafic rocks and the Gander Group, their extent as a discontinuous belt towards the southeast, and the fact that structures in the Gander Group face away from them are here interpreted to indicate that they probably represent remnants of ophiolite. No ophiolite stratigraphy has been reported from them. Their western boundary is an unconformity on Gander Lake. Other ultramafic and mafic bodies occur within the Davidsville Group close to the Gander ultramafic belt. They may in part represent re-intrusions and/or faulted horsts of underlying mafic and ultramafic rocks (Jenness, 1958; McGonigal, 1973). DEVELOPMENTAL

MODEL

AND CAUSE

OF THE GANDERIAN

OROGENY

The following similarities with the Burlingtonian orogen suggest that the Ganderian orogen may have been formed by similar processes. (1) Both orogens occur between basement terranes (Long Range Complex and Bonavista Bay Gneiss Complex) and an ophiolite terrane (north-central Newfoundland). (2) Sediments of the Gander Group and the Fleur de Lys Supergroup show general similarity. Both contain great thicknesses of greywackes or quartz wackes. (3) Both show similar structural histories with major recumbent Fz isoclines of similar magnitude that face towards the forelands to the east and west. (4) Both show similar metamorphic histories with widespread porphyroblastic growth after the first deformation and before the second. (5) Both contain deformed mafic and ultramafic intrusive rocks within them. (6) Both contain linear mafic and ultramafic complexes of ophiolitic aspect which are deformed with the surrounding metasedimentary and metavolcanic rocks. (7) The Fs and Fs folds indicate repeated tectonic transport away from the ophiolitic belts. (8) Metamorphism and deformation are associated with emplacement of granitic bodies in both orogens. The following differences are also apparent between the two orogens. (1) Thick sequences of mafic and silicic volcanic rocks have not been recognized within the Gander Group. (2) Mafic and silicic volcanic rocks are widespread on the oceanic side of the Fleur de Lys Supergroup but those that do occur in the Ganderian orogen are found within the Gander Group, close to the foreland. Mafic volcanic rocks do occur west of the Gander ultramafic belt but the exposure is very limited. (3) Nothing is known about facing direction or tectonic transport in the

Gander Group west of the ophiolitic lineament and in this sense the ophiolitic lineament cannot be demonstrated to occupy the symmetry axis of a divergent metamorphic nappe complex. (4) Granitic bodies associated with orogeny are far more numerous in the Ganderian than in the Burlingtonian orogens. (5) The orogens underwent deformation and metamorphism at different times. Difference (5) above excludes the possibility that the Ganderian orogen represents a part of the Burlingtonian orogen rifted away by Early Ordovician ocean-floor spreading. This is also unlikely since the Gander Group and the eastern Fleur de Lys Supergroup are generally very different. However the older parts of the Fleur de Lys Supergroup and the Gander Group may have been deposited adjacent to each other at an early stage of opening of the Iapetus Ccean. The Cambrian part of the Fleur de Lys however must have been deposited after the Gander Group was deformed. Detailed information from the Ganderian orogen is still not sufficient to propose a plate mechanism for its development similar to that proposed for the Burlingtonian orogen. However there are sufficient resemblances to make it likely that a similar mechanism may have been operative. Perhaps the most obvious difference between the two belts is the absence of an exposed islandarc complex to the east of the ophiolitic belt at the northern end of the Ganderian Orogen. Mafic and silicic volcanic rocks which may be part of the Ganderian Orogen occur farther south, just east of the recognized Gander Group and also in south-central Newfoundland. The presence of mafic and silicic volcanic rocks in the Gander Group to the foreland (eastern) side of the ophiolitic lineament provides another contrast with the Burlingtonian Orogen. It is fairly clear that activity within a continental margin must have been responsible for the Ganderian erogenic episode rather than a major continental collision since the Ganderian erogenic episode is older than the Burlingtonian and hence the two crystalline belts would not have been formed by collision with each other. Consequently, a similar plate mechanism to that proposed for the Burlingtonian orogen, involving opening and subsequent closure of a marginal basin within the continental margin, is favoured here. Further interpretation is highly speculative. This basin may have been narrow enough to prevent clear stratigraphic differentiation in the later stages of depositional develcpment of the Gander Group. Furthermore, the spatial association between continental-rise prism sediments and probable island-arc volcanic rocks to the foreland side of the ophiolitic lineament also suggest that this region was close enough to the postulated subduction zone to receive material from partial melting of the descending oceanic lithosphere. Associated partial melting of the basement (Hare Bay Gneiss Complex) could be invoked to account for the widespread granitic rocks, particularly the garnetiferous granites, that are associated with the Ganderian orogeny but are rare in the Burlingtonian erogenic belt.

Correlatives of the Gander Group and its underlying basement are shown on Fig. 8. The reader is referreti to Williams et al. (1972) for details of this discussion. Basement rocks in these regions are rather different in many respects since they include sedimentary rocks of probable Helikian age as we8 as ortho- and para-gneisses. A small regiun of probable basement rocks occurs north of the Cobequid Fault in central Nova Scotia (Eisbacher, 1969) as well banded biotite gneisses. Recent work in New Brunswick has indicated that correlatives of the Gander Group with a probable older gneissic basement are preserved in the central part of the province (Rast and Stringer, 1974). Precambrian rocks possibly correlative with those of the Ganderian Urogen occur further south on the eastern side of the Appalachian System. Precambrian granites in eastern Massachusetts (Dedham and Hoppin Hill Granites} may represent remnants of a Ganderian erogenic complex. In Rhode Island, the Black&one Group shows close resemblance to the Gander Group and is generally considered to be of Precambrian age (Quinn, 197‘1). Other representatives may occur in the Piedmont farther south. LATER DEVELOPMENT OF THE NEWFOUNDLAND THE ACADIAN OROOENY

APPALACHIAN

SYSTEM AND

Following the Ganderian and B~rlingtonian orogenies? a long period of erosion of these complexes and sedimentation in intervening areas occurred, locally transgressing on to the old orogens. It was not punctuated by widespread deformation, metamorphism or plutonism until probable Middle Devonian time when the Acadian Orogeny took place. Ordovician rocks show marked contrasts in facies both within the Central Mob% Belt and between the Central Mobile Belt and the Western and Avalon Platforms. Silurian facies are more uniform. The allochthons of western Newfoundland were emplaced in early Middle Ordovician time with little or no extensive deformation, either in the source area or associated with their emplacement in the west, Apart from granodiorite or quota-dio~te plutons of early Ordovician age (probably related to mafic vol~~isrn~ no widespread Platonism took place and metamorphism of this age is also absent. Thus, although the emplacement of the allochthons would be considered to be Taconic (Rodgers, 1971) it is different from the Ganderian or Burlingtonian episodes which have extensive deformation, metamorphism and plutonism associated with them, Although the Burlingtonian Urogeny might be considered to be Taco&c in a general sense, it wiI1 be argued below that this orogenie episode and the transportation of the allochthons are separate events. Hence it is desirable to distinguish between them in terminology. The Acadian episode, on the other hand, is associated with widespread diastrophism. Acadian deformation extends from the eastern parts of the Western Platform (Lomond Zone) to the western parts of the Avalon Zone. Granitic intrusive rocks of probable Devonian age are also extensive in the Central Mobile Belt

72

and Acadian metamorphism grade. Ordovician

is also widely developed

to Lower Devonian

but generally

of low

deposition

The Ordovician and later depositional and structural development of the Newfoundland Appalachian System has been summarized by Williams et al. (1972 and 1974) and only the most significant aspects will be discussed below. In Ordovician times carbonate sedimentation in the Lomond Zone gave way in the Middle Ordovician to deposition of easterly derived flysch that is contemporaneous with emplacement of the allochthons into their present positions. In the Fleur de Lys zone ophiolite generation and the accumulation of an overlying pile of pillow lavas, agglomerates and volcanogenic sediments of the Baie Verte Group (Fig. 2) was of probable Ordovician age (Bird et al., 1971). This sequence has been considered as autochthonous by most workers and probably indicates a region of local ocean-floor spreading in Early Ordovician time. In the Notre Dame Zone, Early Ordovician ophiolites were overlain by thick Lower to Middle Ordovician island-arc sequences of volcanogenic flysch and pillow-lava units (Upadhyay et al., 1971; Strong, 1973; Strong and Payne, 1973; Stukas and Reynolds, 197413; Kean and Strong, 1975). In the Exploits Zone, pillow lavas which may form the top of an ophiolite complex are overlain by Middle Ordovician (Caradoc) black slates, cherts, argillites and greywackes which pass upwards into thick greywackes of Late Ordovician to Early Silurian age. In the Botwood Zone, the Ordovician is represented by black slates and greywackes with associated mafic and silicic volcanic rocks of the Middle Ordovician Davidsville Group. In the Avalon Zone shallow-water Ordovician shales and sandstones occur. Silurian sedimentation is more uniform across the system (Williams, 1967b). It consists of greywackes and sandstones, generally overlain by mafic and silicic volcanic rocks that pass upwards into red sandstones, shales and conglomerates and represent the steady filling of the basin formed by earlier ocean-floor spreading and associated island-arc volcanism. On the northwestern and southeastern flanks of the Central Mobile Belt, Silurian rocks rest unconformably on older sequences (Hampden, Fleur de Lys, Notre Dame and probably Botwood Zones) but in the Exploits Zone a generally conformable passage from Ordovician to Silurian greywackes occurs. Clearly, emergence of the flanks of the Central Mobile Belt was followed by later transgression northwestwards and southeastwards from the axial region. Silurian volcanic rocks are both mafic and silicic and again suggest affinities with island-arc terranes, but differ from the Ordovician island-arc rocks by being associated with shallow-water arenites and rudites. Lower Devonian rocks are severely restricted in Newfoundland. They generally consist of shallow-water marine to terrestrial sandstones and occur in small regions on the Western Platform (Rodgers, 1965), in the Central

13

Mobile Belt near La Poile (Cooper, 1954) and on the Avalon Platform (Williams, 1971a). The red sandstones at the top of Silurian sequences in the Central Mobile Belt may also be of Early Devonian age, but they are presently undated. Several major problems are presented by attempting to apply plate-tectonic interpretations to Ordovician and later stages of Appalachian development. (1) Ocean-floor spreading as shown by preserved ophiolite sequences ceased in Early Ordovician time. The nature and width of the ocean of that time is unknown, but faunal provinciality was established on both sides of the Appalachians in the Ordovician. (2) The allochthons of western Newfoundland were emplaced in Middle Ordovician time with little or no tectonism elsewhere in the System. (3) Extensive deformation did not occur again until Acadian (Middle Devonian) time when thick shallow-water to subaerial Silurian sequences had been deposited in many parts of the System. No clear suture related to this erogenic activity can be identified except possibly in southwest Newfoundland as the Cape Ray Fault (Brown, 1973), but the age of this suture is unknown. These problems are discussed below in relation to tentative plate models. The nature and extent

of Early Ordovician

ocean-floor

spreading

Although the Notre Dame Zone can be recognized from surface exposure and geophysical characteristics (Dainty et al., 1966; Weaver, 1967) as containing an ophiolitic basement, it exhibits a peculiarity that would not be expected if the crust had been generated by spreading from a single oceanic ridge similar to those which occur in most of the present major oceans. This ophiolite terrane, with its conformably overlying island-arc sequences, contains three regions in which older deformed plutonic and metavolcanic rocks occur. On Long Island, in the western part of the Notre Dame Zone, xenoliths of amphibolite occur in a granodiorite (D.A. Bradley, personal communication, 1970) as pre-intrusion tectonites, although the pluton and the surrounding island-arc volcanic rocks were deformed by the Acadian (Kean and Strong, 1975). Amphibolite fragments occur in an intrusive breccia that cuts the island-arc rocks and is deformed with them 7 km to the northwest of Long Island in the Notre Dame Zone (Bird and Dewey, 1970). An extensive deformed soda granite (Twillingate Granite) and associated deformed mafic and silicic volcanic rocks occur in the eastern part of the Notre Dame Zone in the Twillingate region whose deformation and metamorphism predates that of the surrounding ophiolite or island-arc volcanic rocks (Williams et al., 1972 and 1974). Further work (Williams and Payne, 1975) has demonstrated that the Twillingate granite has intruded both mafic and silicic volcanic rocks and that all these have undergone varying degrees of deformation before accumulation of the surrounding Ordovician volcanic rocks. Although

14

this conclusion has been contested by Strong and Payne (1973), it is clear that an older deformed block (remnant arc?) (Karig, 1972) exists in the ophiolite terrane here and that other blocks are probably present beneath Long Island and 7 km northwest of it. These blocks have presumably been isolated by diffuse Early Ordovician sea-floor spreading. Their composition would suggest that they are remnants of an older deformed island-arc terrane. They can be interpreted as possible parts of the eastern Fleur de Lys volcanic terrane which was separated from it by later diffuse spreading from several contemporaneous spreading centres or by migration of a single centre. The Baie Verte Group within the Fleur de Lys Zone may mark another attempt at spreading, localized along the older Burlingtonian suture. Orientation of sheeted dykes within the ophiolites of the Notre Dame Zone (Upadhyay et al., 1971; Strong, 1972) is northwest-southeast, approximately normal to orientation of the continental margins and to tectonic strike, indicating that the direction of spreading was oblique to the erogenic belt. These peculiarities suggest that the ophiolite terrane of the Notre Dame Zone was most probably formed in a marginal basin, behind a subduction zone. The spreading associated with this ophiolite generation may have been responsible for closing the marginal basin within the Fleur de Lys Zone. If this is so the age of this ophiolite should be broadly contemporaneous with the Burlingtonian Orogeny. Ophiolite basement to the Exploits and Botwood Zones cannot be directly observed. Pillow lavas at the base of the succession in the Exploits Zone, overlain by deep-water sediments (cherts and black shales) may well be the top of an ophiolite complex but in the Botwood Zone the Middle Ordovician flysch rests upon the Gander Group, at least in the east. Gravity observations for this region (Weaver, 1967) suggest that a mafic crust underlies most of these zones. Middle Ordovician black slates and cherts of the Exploits Zone are the only likely analogues of deep-ocean sediments preserved in the central part of the Newfoundland Appalachian System. They suggest geographic separation from sources of terrigenous elastic sediment until the Late Ordovician. These sediments must have been deposited either far from the island arcs and flysch terranes of adjacent zones or have been separated from them by oceanic trenches. Such conclusions suggest that the Early Ordovician Ocean was considerably more extensive than the combined width of the present Notre Dame, Exploits and Botwood Zones. Emplacement

of the west Newfoundland

allochthons

(Taconic

Orogeny)

The allochthons of western Newfoundland contain westerly transported sequences that must have originated in different parts of the erogenic belt, and were emplaced in Middle Ordovician time. The lower structural slices consist predominantly of sedimentary rocks (Bruckner, 1966) with westerly provenance (Stevens, 1970) and interpreted to represent parts of a continen-

75

tal-terrace wedge and continental-rise prism deposited east of their present position. The youngest formation of these slices consists of easterly derived flysch presumably shed from the rising Burlingtonian Orogen further to the east. Thus all these allochthonous sedimentary rocks were emplaced by probable gravity sliding westwards off the flanks of the rising Burlingtonian Orogen. The upper slices consist of a large ophiolite slice and smaller slices of deformed intrusive plutonic rocks, amphibolites, green schists and undeformed pillow lavas which occur to the west of the main ophiolite slices (Williams, 1973; Williams and Smyth, 1973). No source area for such an association of igneous rocks occurs in Newfoundland west of the Notre Dame Zone and it seems probable that the upper slices were derived from this zone. Such different source areas for separate parts of the west Newfoundland allochthons is supported to some extent by the relationships between each slice and the underlying rocks. All slices are separated from each other or the autochthon by melange, but the ophiolite slice has a locally preserved contact near its base with underlying mafic metavolcanic and minor metasedimentary rocks within the same slice. This contact has been interpreted by Williams and Smyth (1973) to be a thrust formed by displacement of the ophiolite from an ocean basin, that predates emplacement of all the slices of the allochthons into their present positions. The metamorphism and deformation of the metavolcanic and metasedimentary rocks at the base of the ophiolite slice has been interpreted as an aureole, attributed to overthrusting of hot ophiolite. The melanges, on the other hand, are probably in part depositional and in part tectonic (Bruckner, 1966; Stevens, 1970; Williams, 1971b) and are interpreted to be the product of assembly and emplacement of the individual slices of the allochthons into their present positions. Deformed gabbros, soda granites and polydeformed metavolcanic rocks are cut by undeformed mafic dykes and associated with undeformed pillow lavas in the small slices that occur to the west of the ophiolites. In the Humber Arm Allochthon this complex is known as the Little Port Slice Assemblage (Williams, 1973). A more westerly alkaline volcanic assemblage (Skinner Cove Formation) in another small slice contains Early Ordovician brachiopods in sedimentary rocks associated with pillow lavas (Strong, 1974a). In the Hare Bay Allochthon undeformed pillow lavas, in another small slice contain Tremadocian graptolites (Williams, 1971b; Williams et al., 1973) in interbedded shales. This association between deformed plutonic and metavolcanic rocks and undeformed volcanic rocks closely resembles that of the Notre Dame Zone and hence it has been suggested that these small slices and the main ophiolite slices which occur east of them were derived from the Notre Dame Zone (Williams et al., 1974) (Fig. 10). According to this interpretation, the deformed metamorphic rocks of the Little Port Slice Assemblage would be remnants of the Burlingtonian island-arc and the deformed rocks beneath the ophiolites would either be post-Burlingtonian sediments or the outer edge of Burlingtonian island arc scraped up and deformed by later overriding of the ophiolites. Although it is unusual for

76

LATE

CAMBRIAN-TREMADOC

ARENIG-LLANVIRN

SUSDUCTION

ZONE

LLANVIRN-CAAADOC SE. TWILLINGATE

BLOCK

GANDERIAN

CARADOC-ASHGILL

OROGEN

NW.

SE SLIDE BRECCIA

A&&MATE

OF FU%E

MAJOR FAULTS s SILURIAN WESTERN

ROCKS PLATFORM

CABOT FAULT

DOVER FA”!_T SE I , AVALON

Fig. 10. Diagrammatic section across northern Newfoundland to illustrate the proposed development of the Acadian orogen from Late Cambrian to Middle Devonian time. Zones in the lowest section are shown on Fig. 1. Flysch is shown by stipple, island arc volcanic rocks by uninverted “v”s for the Burlington orogen and inverted “~3 for later Ordovician island arcs. Early Ordovician ophiolite is solid black, older ophiolite striped.

ophiolite to be abducted across an island arc as depicted in Fig. 10, Papua does provide a clearcut example of this situation (Davis and Smith, 1971). Evidence that this occurred in Newfoundland is provided by small slices interpreted to be part of this arc preserved in front of the ophiolite slices. Recent radiometric age determinations on zircon have yielded an age of 508 I+5 m.y. for soda granite in the Little Port Slice Assemblage (Mattinson, 1975), approximately 40 m.y. older than the displacement of the ophiolite behind, dated by Dallmeyer and Williams (1975) as 460 k 5 m.y. by *‘AI-/~ ‘Ar release spectra of hornblende from within the aureole. The west Newfoundland allochthons therefore have a bimodal origin. An

77

early post-Burlingtonian and Post-Tremadoc phase involved abduction or displacement of ophiolite with associated fragments of Burlingtonian island arc westwards or northwestwards from the Notre Dame Zone, and a later Early Middle Ordovician phase of gravity sliding emplaced these sheets together with the less deformed sedimentary rocks of the underlying sheets further westwards or northwestwards into their present positions. The absence of widespread penetrative deformation associated with ophiolite obduction at this time signifies the absence of complete suturing as Early Ordovician ophiolite is still preserved in the Notre Dame Zone. Why obduction should have occurred at all is not known but again comparisons with New Guinea may be productive. Karig (1972) has suggested that abducted ophiolite is most likely to be small ocean-basin material produced by interarc spreading and abducted by reversal of polarity. This reversal of polarity led to postulated arc-arc collision in New Guinea and consequent abduction since the earlier island arc had been split into two by interarc spreading. Thus may well be the situation in Newfoundland since fragments of probable Burlingtonian island arc occur in the Notre Dame Zone and interarc spreading has lead to fragmentation of an older Burlingtonian island arc. Thus the ophiolite preserved in the Notre Dame Zone and abducted on to the Western Platform is considered marginal basin material. The probability of it being hot when displaced further supports an inter-arc origin. Milson (1973) from studies in Papua has suggested that marginal-basin oceanic crust may split as it approaches a subduction zone, providing further indications of the parallels between the Papuan and Newfoundland situations. Acadian structures

and metamorphism

The style of structures produced by the Acadian orogeny in northern Newfoundland contrasts strongly with that formed by the Ganderian or Burlingtonian orogenies. Acadian structures include tight upright folds associated with a penetrative foliation or slaty cleavage which is subsequently crenulated or folded by later open structures; recumbent isoclines and tight refolding of earlier structures are apparently absent. Metamorphism also presents strong contrasts, since Acadian metamorphism is generally of lower greenschist facies and locally sub-greenschist, whereas earlier metamorphism has reached amphibolite facies in many places. Southwestern Newfoundland is different in this respect since not only is all of north-central Newfoundland geology missing across the Cape Ray Fault (Brown, 1973, 1975) but higher-grade Acadian metamorphism and intense deformation may also be present. Although this could be the result of complete Acadian suturing as suggested by Dewey and Kidd (1974) the age of intense deformation and higher-grade metamorphism other than that present in the basement complexes is not established and metamorphic grade along the suture (Cape Ray Fault) is undoubtedly low. Higher-grade metamorphism and intense deformation superimposed upon the basement to the east may well be Gan-

derian rather than Acadian. It is unlikely that upright Acadian structures represent a higher structural level than that exposed in the Ganderian and Burlingtonian orogens, since either oceanic crust, pre-Ordovician deformed terranes or continental basement occur beneath Acadian deformed sequences with upright folds. Acadian structures are however more extensive than Ganderian or Burlingtonian structures, although they are less intense. Penetrative Burlingtonian structures have not been identified in the Lomond Zone, although some folds in the Maiden Point Formation of the Hare Bay Allochthon may be Burlingtonian (Smyth, 1971). Penetrative Ganderian structures are not present in the Avalon Zone, except possibly in the extreme west (Love Cove Group) and locally farther east. Acadian penetrative deformation has affected rocks from the eastern part of the Lomond Zone across the central part of the system to include the western part and possibly most of the Avalon Zone. The main penetrative Acadian fabric generally trends parallel to the dominant older fabrics of the Ganderian and Burlingtonian orogens. It follows the large arcuate trend of the Hermitage Flexure and also trends approximately east-west in the central parts of the Notre Dame Zone. Although the intensity of Acadian deformation shows considerable variation from place to place, it is possible to recognize a similar sequence of strain regimes in different parts of the belt. The first deformation produced a steep slaty cleavage or foliation associated with upright major folds in response to a vertical extension to uniaxial flattening strain. Major folds of this age generally plunge gently to moderately. This deformation was locally succeeded by refolding and development of a second steep strain-slip fabric, but generally the next event was a vertical shortening strain producing flat crenulations and no major folds. Subsequent northeast--southwest shortening formed a conjugate set of kink bands and local large-scale open folds. Major faults that form the boundaries between many of the tectonostratigraphic zones of Newfoundland were also active in the Acadian, but may have been initiated considerably earlier. The Dover Fault (Fig. 10) was probably active during the Ganderian (Blackwood and Kennedy, 1975). Most of these faults have an important component of transcurrent movement since not only do they have straight traces and separate zones of different stratigraphy over considerable’ distances, but also they bound regions of slightly different tectonic strike. The Luke Arm Fault which forms the boundary between the Notre Dame and Exploits Zones is peculiar in this respect, since its trace is not rectilinear. The age of these faults with respect to the later Acadian strain regimes is not known, but they deformed the main Acadian foliation. DEVELOPMENTAL

MODEL

AND CAUSE

OF THE ACADIAN

OROGENY

The early Acadian strain represents considerable crustal shortening across the erogenic belt, which was followed by vertical shortening, possibly in response to vertical thickening produced by the early strain, yet identifica-

79

tion of the plate process responsible for it is far from easy. Furthermore, the later Acadian strains involving strike-slip faulting and folding are the result of extension and shortening respectively along the length of the belt, and indicate an entirely different orientation of vectors. These could be related to transform plate movements. Indirect indications of subduction are provided by extensive island-arc volcanism in Ordovician (Strong, 1972 and 1973; Kean and Strong, 1975; Strong and Payne, 1973) and probably also in Silurian time. The distribution of these volcanic rocks does not clearly indicate where the subduction zone was situated, since they are extensive in the Notre Dame, Exploits and Botwood Zones, nor does it give any indication of the orientation of the descending plate. It has been suggested that the Dunnage Formation, a spectacular melange in the Exploits Zone (Horne, 1969) marks an oceanic trench and subduction zone (Bird and Dewey, 1970) and this remains the only indication of the possible position of a consuming plate margin. Although Ordovician and Silurian rocks close to the Dunnage are no more heavily deformed than elsewhere in the Newfoundland Appalachian System, these rocks are overturned in the Exploits Zone north of the Dunnage Formation (Williams, 196413) indicating a different tectonic regime than is usual for Acadian deformed rocks. Evidence of local, older, probably tectonic disturbance in this region is provided by Ordovician rocks locally unconformably overlain by Silurian rocks in the eastern part of the Exploits Zone (M. Kay, personal communication, 1972). Here, the Ordovician was inverted before the Silurian was deposited. Thus evidence for local folding of Ordovician rocks before deposition of the Silurian could be interpreted to mark the proximity of a zone of tectonic instability, possibly a subduction zone, on the southeastern side of the Exploits Zone, where the Dunnage Formation is preserved. A tentative generalized plate model for the Acadian Orogeny is illustrated in Fig. 10. Two subduction zones dipping away from each other in central Newfoundland are invoked to explain the occurrence of island-arc volcanic sequences right across the axial region of the belt. Geochemical reasoning for an east-dipping subduction zone in eastern Newfoundland has been provided by Strong et al. (1974). However, these data are difficult to evaluate with respect to post-Ganderian subduction, since the age of the individually analyzed granitic rocks is not indicated and several Ganderian granitic plutons have been included in this treatment. Whether subduction was taking place on two zones simultaneously is not known. Since the Acadian Orogeny did not form major overthrusts or nappes and high-grade metamorphism, any plate mechanism proposed as its cause should differ from that proposed for the Ganderian and Burlingtonian Orogenies. It should also differ from that responsible for major continental-collision orogenies such as that which formed the Himalayas. The Acadian Orogeny has resulted in preservation of autochthonous oceanic crust in central Newfoundland. The strain regime has evolved from shortening across the erogenic belt to elongation and shortening along its length. Complete suturing did not occur in the north but proba-

80

bly did farther to the southwest. Evolution of strain from crustal shortening across the belt to transcurrent movement along it could be the product of two different postulated situations. Either an unstable plate situation evolved from a consuming plate margin to a transform one, or irregularity of closing continental margins led to local preservation of oceanic crust and the development of late transcurrent faults by what has been termed transpression by Harland (1971). The first type of evolution occurs at triple junctions of the RTF of TTF type. Since no ophiolite younger than Early Ordovician is known, although orogeny did not occur until much later, this postulated triple junction was unlikely to involve an actively spreading ridge (RTF junction) and hence was more likely to be a TTF junction, where two subduction zones meet to form a transform fault. Although the orientation and magnitude of the subduction vectors are unknown, it is likely that such a triple junction would be unstable (McKenzie and Morgan, 1969) and would result in growth of a transform fault. According to this model, the crustalshortening strain of the earlier part of the Acadian would be the product of collision of trenches and the later transcurrent movements would be related to movement on the resulting transform fault. Transform movements would continue as long as the TTF junction continued to be active. Such a model would suggest that the age of the Acadian erogenic episode should change along the erogenic belt. Difficulties in dating the Acadian deformation due to the scarcity of fossiliferous Upper Silurian-Devonian sequences make this suggestion difficult to substantiate within the northeastern Appalachians. However, earlier Upper Silurian paratectonic orogeny in the Caledonian Belt of the British Isles (Cymrian episode of Rast and Crimes, 1969) may reflect such a change in age along strike. This mechanism of convergence of oceanic trenches was proposed by Dewey (1969) to account for Upper Silurian deformation in the Caledonian Orogenic Belt. Earlier transform movements on some of the major faults in central Newfoundland may be related to orientation of Early Ordovician ocean-floor spreading, since sheeted dykes, both in autochthonous ophiolites (Upadhyay et al., 1971; Strong, 1972) of the Notre Dame Zone and in allochthonous ophiolites of the Lomond Zone (Williams and Malpas, 1972), which originated in the Notre Dame Zone, trend northwest-southeast normal to the orientations of the continental margins and tectonic strike. Changes in age of Late Silurian to Middle Devonian orogeny would also be explained by transpression but more local variations could be expected. Whatever process caused the deformation and metamorphism of the Acadian, it must have been different from that which caused the Ganderian, Burlingtonian and Taconic orogenies since the products themselves are different. CONCLUSIONS

AND APPLICABILITY

TO OTHER OROGENIC

The Appalachian System in Newfoundland episodes: a Ganderian episode that terminated

BELTS

is the product of four erogenic with deformation and meta-

81

morphism in the Hadrynian, a Burlingtonian episode that terminated in deformation and metamorphism in the Upper Cambrian, a Taconic episode which emplaced alloehthons on to the Western Platform, and an Acadian episode that terminated in the Middle Devonian. Plate me~h~isms to account for the differences in timing and nature of the Ganderian and Burlingtonian episodes as opposed to the Acadian episode have been proposed based upon the concept that orogeny is the product of changes in plate-tectonic regime and that the type of orogeny reflects the type of change that took place. The mechanism responsible for the Burlingtonian and possibly the Ganderian episodes has not been proposed for any other erogenic belt to the author’s knowledge and has the advantage of explaining many aspects of development not explained by earlier proposals. All these erogenic complexes can be followed in a general way into the Appalachians of the Canadian mainland and beyond. The concept that erogenic belts are not the product of a single erogenic cycle involving deposition followed by subsequent plutonism, deformation and metamorphism is not new. Orogenic belts in many parts of the world have been known to record histories of repeated erogenic activity, but in many cases the implications of this in terms of cycles of plate movements has yet to be fully explained. Comparison of the northeastern Appalachians with the Caledonian erogenic belt of the British Isles is particularly important in this respect, since both formed a continuous belt at the time of their formation. In the Caledonian belt four erogenic episodes, identified as Cadomian, Crampian, Lakelandian and Cymrian (Rast and Crimes, 1969) are of comparable age and distribution to those of the northeastern Appalachians. It is interesting to note that there is some evidence that the Grampian episode term~ated later (Early to Middle Ordovician) than the Burlingtonian episode, whereas the Cymrian episode (Late Silurian) is older than the Acadian. The Lakelandian episode of Rast and Crimes is broadly comparable with what has generally been referred to as Taconic (Rodgers, 1971) in the Appalachian System. Closer comparison between individual regions in each of these belts provides further insights into erogenic processes. Comparison between the Burlingtonian and Grampian orogenies is particularly rewarding in this respect. Structural style and metamorphism in the Dalradian and Moinian rocks south of the Great Glen Fault is closely comparable to that of the Fleur de Lys Supergroup, although a high-temperature low-pressure facies series is locally developed in the Dalradian. However, no extensive island-am volcanic rocks or an internal ophiolitic suture is recognizable in the Dalradian. It is probable that this, if present, is presumably overlain by younger rocks of the Midland Valley and Southern Uplands of Scotland and their extensions into Ireland. In western Ireland the Moinian and Dalradian rocks are disposed as gravitational nappes off a central gneiss dome (Sutton and Max, 1969; Kennedy et al., 1972). The Burlin~oni~-Gr~pi~ complex was probably originally much broader than presently preserved in either

82

region. The marginal island-arc and ophiolitic suture are preserved in Newfoundland, whereas the gneiss domes that were probably situated to the northwest of the suture are preserved in the British Isles. The postulated island-arc complex to the southeast of the Dalradian may be locally preserved as the Tyrone Volcanic Series (Hartley, 1933; W.E.A. Phillips, personal communication, 1973). Detailed comparisons with other erogenic belts are beyond the scope of this paper, but crystalline belts of Ganderian or Burlingtonian type are common close to platformal regions or further into the centres of many orogens. Whether they have formed by processes similar to those proposed above is presently unknown, but the application of similar techniques and arguments to them may prove worthwhile. More data of all types are needed to accurately identify the processes responsible for orogeny. Only from this base can present models and proposals be tested and refined. ACKNOWLEDGEMENTS

This paper is based upon work supported by grants from the Geological Survey of Canada and the National Research Council of Canada, which are gratefully acknowledged. Gratitude is expressed to faculty and graduate students of the Department of Geology, Memorial University of Newfoundland for constant discussion and argument over the past several years. I am particularly indebted to my own graduate students, who have worked on structural aspects of Newfoundland geology and to my colleagues H. Williams, E.R.W. Neale and D.F. Strong of Memorial University and N. Rast of the University of New Brunswick. H. Williams, E.R.W. Neale and A.G. Smith are thanked for reading and making many helpful suggestions upon an early draft of the manuscript. Finally, gratitude is expressed to Professor H.B. Whittington for the provision of facilities in the Geology Department, Sedgwick Musuem, Cambridge, while I was on sabbatical leave.

REFERENCES Baird, D.M., 1951. The Geology of the Burlington Peninsula, Newfoundland. Geol. Surv. Can., Pap., 51-21. Betz, F.Jr., 1939. Geology and mineral deposits of the Canada Bay area, northern Newfoundland. Newfoundland Geol. Surv. Bull., 16. Betz, F.Jr., 1948. Geology and mineral deposits of southern White Bay. Newfoundland Geol. Surv. Bull., 24. Bird, J.M. and Dewey, J.F., 1970. Lithosphere plate-continental margin tectonics and the evolution of the Appalachian orogen. Geol. Sot. Am. Bull., 81: 1031--1060. Bird, J.M., Dewey, J.F. and Kidd, W.S.F., 1971. Occurrence of ophiolites representing Lower Paleozoic oceanic crust and mantle. Nature, Phys. Sci., 230: 28-31. Blackwood, R.F. and Kennedy, M.J., 1975. The Dover Fault: western boundary of the Avalon Platform in northern Newfoundland. Can. J. Earth Sci., 12: 320-325.

83 Brown, P.A., 1973. Possible Cryptic Suture in South-west Newfoundland. Nature, Phys. Sci., 246: 9-10. Brown, P.A., 1975. Basement-Cover Relationships in Southwest Newfoundland. Unpubl. thesis, Memorial University of Newfoundland. Briickner, W.D., 1966. Stratigraphy and structure of west central Newfoundland. In: W.H. Poole (Editor), Guidebook, Geology of Parts of the Atlantic Provinces. Ann. Meet., Geol. Assoc. Can., Min. Assoc. Can., pp. 137-151. Church, W.R., 1969. Metamorphic rocks of the Burlington Peninsula and adjoining areas of Newfoundland, and their bearing on continental drift in the North Atlantic. In: M. Kay (Editor), North Atlantic - Geology and Continental Drift. Am. Assoc. Pet. Geol., Mem., 12: 212-233. Church, W.R., 1972. Ophiolite: its deformation, origin as oceanic crust, and the mode of emplacement in erogenic belts, with special reference to the Appalachians. Publ. Earth Phys. Branch, Dep. Energy, Mines Resour., Ottawa, 42 (3): 71-85. Church, W.R. and Stevens, R.K., 1971. Early Paleozoic ophiolite complexes of the Newfoundland Appalachians as mantle-oceanic crust sequences. J, Geophys. Res., 76: 1460-1466. Coates, H.J., 1970. The Structural and Metamorphic History of the Pacquet HarbourGrand Cove Area of the Burlington Peninsula, Newfoundland. Unpubl. thesis, Memorial University of Newfoundland. Cockburn, G.H., 1971. Peralkaline granite and the associated plutonic rocks of the eastern division of the Fleur de Lys metamorphic complex of Newfoundland. Abstr. Proc. Geol. Assoc. Am. Annual Meet., Northeastern Section, Hartford, pp. 22-23. Colman-Sadd, S.P., 1974. The Geologic Development of the Bay d’Espoir Area, Southeastern Newfoundland. Unpubl. thesis, Memorial University of Newfoundland. Cooper, J.R., 1937. Geology and mineral deposits of the Hare Bay area. Newfoundland Dep. Natl. Res. Geol. Sect. Bull. No. 9. Cooper, J.R., 1954. La Poile-Cinq Cerf map-area, Newfoundland. Geol. Surv. Can., Mem., 276, 62 pp. Cormier, R.F., 1972. Radiometric ages of granitic rocks, Cape Breton Island, Nova Scotia. Can. J. Earth Sci., 9: 1036-1074. Dainty, A.M., Keen, C.E., Keen, M.J. and Blanchard, J.E., 1966. Review of geophysical evidence on crust and upper-mantle structure on the eastern Seabord of Canada. Am. Geophys. Union, Monogr., 10: 349-369. release spectra of hornblende from Dallmeyer, R.D. and Williams, H., 1975. 4oAr/3gAr the Bay of Islands metamorphic aureole, western Newfoundland: their bearing on the timing of ophiolite abduction at the Ordovician continental margin. Can. J. Earth. Sci., 12, in press. Davis, H.L. and Smith, I.E., 1971. Geology of Eastern Papua. Geol. Sot. Am. Bull., 82: 3299-3312. Dewey, J.F., 1969. Evolution of the Appalachian/Caledonian orogen. Nature, 22: 124129. Dewey, J.F. and Bird, J.M., 1971. Origin and emplacement of the ophiollte suite: Appalachian ophiolites of Newfoundland. J. Geophys. Res., 76: 3170-3206. Dewey, J.F. and Kidd, W.S.F., 1974. Continental collisions in the Appalachian-Caledonian erogenic belt: Variations related to complete and incomplete suturing. Geology, 2: 543-546. De Wit, M.J., 1974. On the origin and deformation of the Fleur de Lys metaconglomerate, Appalachian fold belt, Northwest Newfoundland. Can. J. Earth Sci., 11: 11681180. Downie, C., Lister, T.R., Harris, A.L. and Fettes, D.J., 1971. A palynological investigation of the Dalradian rocks of Scotland. Inst. Geol. Sci. London, Rep. 71/9, 30 pp. Eisbacher, G.H., 1969. Displacement and stress field along part of the Cobequid Fault, Nova Scotia. Can. J. Earth Sci., 6: 1095-1104.

84 Fleuty, M.J., 1964a. Tectonic slides. Geol. Mag., 100: 452-456. Fleuty, M.J., 196413. The description of folds. Proc. Geol. Assoc. Can., 75: 461-492. Flinn, D., 1962. On folding during three-dimensional progressive deformation. Q.J. Geol. Sot. London., 118: 385-433. Flinn, D., 1965. On the symmetry principle and the deformation ellipsoid. Geol. Mag., 102: 36-45. Fuller, J.O., 1941. Geology and mineral deposits of the Fleur de Lys area. Newfoundland Geol. Surv. Bull., 15. Gale, G.H., 1972. Paleozoic komatiite and ocean floor-type basalts from northeastern Newfoundland. Earth Plant. Sci. Lett., 18: 22-28. Harland, W.B. 1971. Tectonic transpression in Caledonian Spitzbergen. Geol. Mag., 108a: 27-42. Harland, W.B. and Gayer, R.A., 1972. The Arctic Caledonides and earlier oceans. Geol. Mag., 109: 289-314. Harris, A.L. and Pitcher, W.S., 1975. The Dalradian Supergroup. In: C. Dowrie et al. (Editors), A Correlation of the Precambrian rocks of British Isles. Geol. Sot. London, Spec. Rep., 6: in press. Hartley, J.J., 1933. The geology of northeastern Tyrone. Proc. R. Ir. Acad., Sect. B, 41: 184-285. Horne, G.S., 1969. Early Ordovician chaotic deposits in the central volcanic belt of northeast Newfoundland. Geol. Sot. Am. Bull., 80: 2051-2064. Hughes, C.J. and Briickner, W.D., 1971. Late Precambrian rocks of eastern Avalon Peninsula, Newfoundland - a volcanic island complex. Can J. Earth Sci., 8: 899-915. Jenness, S.E., 1958. Geology of the Lower Gander River ultramafic belt. Newfoundland Geol. Surv., Rep., 11. Jenness, S.E., 1963. Terra Nova and Bonavista map-areas, Newfoundland. Geol. Surv. Can., Mem., 327, 184 pp. Karig, D.E., 1972. Remnant Arcs, Geol. Sot. Am. Bull., 83: 1057-1068. Kay, M., 1967. Stratigraphy and structure of northeastern Newfoundland bearing on drift in North Atlantic. Bull. Am. Assoc. Pet. Geol., 51: 579-600. Kay, M. (Editor), 1969. North Atlantic - Geology and Continental Drift. Am. Assoc. Pet. Geol., Mem., 12, 1082 pp. Kay, M. and Colbert, E.H., 1965. Stratigraphy and Life History. Wiley, New York, 786 PP. Kean, B.F. and Strong, D.F., 1975. Geochemical evolution of an Ordovician island arc of the Central Newfoundland Appalachians. Am. J. Sci., 275: 97-118. Kennedy, M.J., 1971. Structure and the stratigraphy of the Fleur de Lys Supergroup in the Fleur de Lys area, Burlington Peninsula, Newfoundland. Proc. Geol. Assoc. Can., 24 (1): 59-71. Kennedy, M.J., 1973. Pre-Ordovician polyphase structure in the Burlington Peninsula of the Newfoundland Appalachians. Nature, Phys. Sci., 241: 114-116. Kennedy, M.J., 1975. The Fleur de Lys Supergroup: Stratigraphic comparison of Moine and Dalradian equivalents in Newfoundland with the British Caledonides. J. Geol. Sot. Lond., 131: 305-310. Kennedy, M.J. and McGonigal, M.H., 1972. The Gander Lake and Davidsville groups of northeastern Newfoundland: new data and geotectonic implications. Can. J. Earth Sci., 9: 452-459. Kennedy, M.J. and Phillips, W.E.A., 1971. Ultramafic rocks of the Burlington Peninsula, Newfoundland. Proc. Geol. Assoc. Can. 24 (1): 35-46. Kennedy, M.J., Neale, E.R.W. and Phillips, W.E.A., 1972. Similarities in the Early Structural Development of the Northwestern Margin of the Newfoundland Appalachians and the Irish Caledonides. Rep. 24th Int. Geol. Congr., Montreal, Sect. 3, pp. 516531.

85 Kennedy, M.J., Williams, H. and Smyth, W.R., 1973. Geology of the Grey Island, Newfoundland - northernmost extension of the Fleur de Lys Supergroup. Proc. Geol. Assoc. Can., 25: 79-90. King, P.B., 1959. The Evolution of North America. Princeton University Press, Princeton, N.J. 189 pp. Lock, B.E., 1969. Silurian rocks of west White Bay, Newfoundland. In: M. Kay (Editor), North Atlantic - Geology and Continental .Drift. Am. Assoc. Pet. Geol., Mem., 12: 433-442. Lock, B.E., 1972. Lower Paleozoic History of a Critical Area; Eastern Margin of the St. Lawrence Platform in White Bay, Newfoundland, Canada. Rep. 24th Int. Geol. Congr., Montreal, Sect. 6, pp. 310-324. Mattinson, J. W., 197 5. Early Paleozoic ophiolite complexes of Newfoundland: Isotopic ages of zircons. Geology, 3: 181-183. McGonigal, M.H., 1973. The Gander and Davidsville Groups: Major Tectonostratigraphic Units in the Gander Lake Area, Newfoundland. Unpubl, thesis, Memorial University of Newfoundland. McKenzie, D.M. and Morgan, W.G., 1969. Evolution of triple junctions. Nature, 224: 125-133. Milson, J., 1973. Papuan ultramafic belt. Gravity anomalies and the emplacement of ophiolites. Geol. Sot. Am. Bull., 84: 2243-2258. Neale, E.R.W. and Kennedy, M.J., 1967. Relationship of the Fleur de Lys group to younger rocks of the Burlington Peninsula, Ne~oundland. In: E.R.W. Neale and H. Williams (Editors), Geology of the Atlantic Region - the Lilly Memorial Volume. Geol. Assoc. Can., Spec. Pap., 4: 139-170. Neale, E.R.W. and Nash, W.A., 1963. Sandy Lake (east half) Newfoundland. Geol. Surv. Can., Pap., 62-28. Neale, E.R.W. and Williams, H. (Editors), 1967. Geology of the Atlantic Region - the Lilly Memorial Volume. Geol. Assoc. Can., Spec. Pap., 4, 292 pp. Palmer, A.R., 1971. The Cambrian of the Appalachian and eastern New England regions, eastern United States. In: C.H. Holland (Editor), Cambrian of the New World. WileyInterscience, New York, p. 169-217. Papezik, V.S., 1972. Detrital garnet and muscovite in Late Precambrian Sandstone near St. John’s, Newfoundland, and their significance. Can. J. Earth Sci., 10: 1697-1698. Phillips, W.E.A., Kennedy, M.J. and Dunlop, G.A., 1969. A geologic comparison of western Ireland and northeastern Newfoundland. In: M. Kay (Editor), North Atlantic Geology and Continental Drift. Am. Assoc. Pet. Geol., Mem., 12: 194-211. Poole, W.H., 1967. Tectonic evolution of the Appalachian region of Canada. In: E.R.W. Neale and H. Williams (Editors), Geology of the Atlantic Region - the Lilly Memorial Volume. Geol. Assoc. Can., Spec. Pap., 4: 9-51. Poole, W.H., 1973. Detrital garnet and muscovite in Late Precambrian Sandstone near St. John’s, Newfoundland, and their significance. Discussion. Can. J. Earth Sci., 10: 1697-1698. Poole, W.H., Sanford, B.V., Williams, H. and Kelley, D.G., 1970. Geology of Southeastern Canada. In: R.J.W. Douglas (Editor), Geology and Economic Minerals of Canada. Geol. Surv. Can., Econ. Geol. Rep., 1: 227-304. Quinn, A.W., 1971. Bedrock geology of Rhode Island. U.S. Geol. Surv. Bull., 1295. Rankin, D.W., Stern, T.W., Reid, J.C. and Newell, M.F., 1969. Zircon ages of felsic volcanic rocks in the upper Precambrian of the Blue Ridge, Appalachian Mountains. Science, 166: 741-744. Rast, N. and Crimes, T.P., 1969. Caledonian erogenic episodes in the British isles and northwestern France and their tectonic and chronological interpretation. Tectonophysics, 7: 277-307. Rast, N. and Grant, R.H., 1973. Transatlantic correlation of the Varisian-Appalachian orogeny. Am. J. Sci., 273: 572-579.

86 Rast, N. and Stringer, P., 1974. Recent advances and the interpretation of geological structure in New Brunswick. Geosci. Can., la: 15-25. Rodgers, J., 1965. Long Poing and Clam Bank Formations, western Newfoundland. Proc. Geol Assoc. Can., 16: 83-94. Rodgers, J., 1970. The Tectonics of the Appalachians. Interscience, New York, 271 pp. Rodgers, J., 1971. The Taconic orogeny. Geol. Sot. Am. Bull., 82: 1141-1177. Schroeter, T.M., 1971. Geology of the Nippers Harbour Area, Newfoundland. Unpubl. thesis, University of Western Ontario. Shackleton, R.M., 1958. Downward facing structures of the Highland Border. Q. J. Geol. Sot. Lond., 113 (for 1957): 361-392. Smyth, W.R., 1971. Stratigraphy and structure of part of the Hare Bay Allochthon, Newfoundland. Proc. Geol. Assoc. Can., 24 (1): 47-57. Stevens, R.K., 1970. Cambro-Ordovician flysch sedimentation and tectonics in west Newfoundland and their possible bearing on a Proto-Atlantic Ocean. In: J. Lajoie (Editor), Flysch Sedimentology in North America. Geol. Assoc. Can., Spec. Pap., 7: 165-177. Stockwell, C.H., 1964. Fourth report on structural provinces and time-classification of rocks of the Canadian Precambrian shield. Geol. Surv. Can., Pap., 64-17 (2): l-21. Strong, D.F., 1972. Sheeted diabases of Central Newfoundland: New evidence for Ordovician sea-floor spreading. Nature, 23 5 : 102-l 04. Strong, D.F., 1973. Lush’s Bight and Roberts Arm groups of Central Newfoundland: Possible juxtaposed oceanic and island-arc volcanic suites. Geol. Sot. Am. Bull., 84: 3917-3928. Strong, D.F., 1974a. An “off-axis” alkali volcanic suite associated with the Bay of Islands Ophiolites, Newfoundland. Earth Planet. Sci. Lett., 21: 301-309. Strong, D.F., 1974b. Plateau lavas and diabase dykes of northwestern Newfoundland. Geol. Mag., 111: 501-514. Strong, D.F. and Payne, J.R., 1973. Early Paleozoic volcanism and metamorphism of the Moreton’s Harbour-Twillingate area, Newfoundland. Can. J. Earth Sci., 10: 13631379. Strong, D.F. and Williams, H., 1972. Early Paleozoic flood basalts of northwest Newfoundland: their petrology and tectonic significance. Proc. Geol. Assoc. Can., 24 (2): 43-54. Strong, D.F., Dickson, W.L., O’Driscoll, C.F., Kean, B.F. and Stevens, R.K., 1974. Geochemical evidence for an east dipping Appalachian subduction zone in Newfoundland. Nature, 248: 37-39. dating of the Long Range Dikes, Stukas, V. and Reynolds, P.H., 1974a. 40Ar/3gAr Newfoundland. Earth Planet. Sci. Lett., 22: 256-266. Stukas, V. and Reynolds, P.H., 1974b. 40Ar/3gAr dating of the Brighton Gabbro Complex, Lush’s Bight Terrane, Newfoundland. Can. J. Earth Sci., 11: 1485-1488. Sutton, J.S. and Max, M.D., 1969. Gneisses of the northwestern part of County Mayo, Ireland. Geol. Mag., 106: 284-290. Upadhyay, H.D., Dewey, J.F. and Neale, E.R.W., 1971. The Betts Cove Ophiolite Complex, Newfoundland: Appalachian oceanic crust and mantle. Proc. Geol. Assoc. Can., 24 (1): 27-34. Weaver, D.F., 1967. A geological interpretation of the Bouguer anomaly field of Newfoundland. Dom. Obs. Can. Publ., 35, (5). Williams, H., 1964a. The Appalachians in northeastern Newfoundland: A two-sided symmetrical system. Am. J. Sci., 262: 1137-1158. Williams, H., 196413. Botvrood, Newfoundland. Geol. Surv. Can. Map 60-1963. Williams, H., 1967a. The Island of Newfoundland. Geol. Surv. Can. Map 1231A. Williams, H., 1967b. Silurian rocks of Newfoundland. In: E.R.W. Neale and H. Williams (Editors), Geology of the Atlantic Region - the Lilly Memorial Volume. Geol. Assoc. Can., Spec. Pap., 4: 93-137.

87

Williams, H., 1971a. Belleoram map-area, Newfoundland. Geol. Surv. Can. Pap., 70-65, 39 PP. Williams, H., 1971b. Mafic-ultramafic complexes of western Newfoundland and the evidence for their transportation. Proc. Geol. Assoc. Can., 24 (1): 9-25. Williams, H., 1973. Bay of Islands map-area, Newfoundland. Geol. Surv. Can., Pap,, 72-34, 7 pp. Williams, H. and Malpas, J.G., 1972. Sheeted dykes and brecciated dyke rocks within the transported igneous complexes, Bay of Islands, Newfoundland. Can. J. Earth Sci., 9: 1216-1229. Williams, H. and Payne, J.R., 1975. The Twillingate Granite and relationships among nearby volcanic groups in Notre Dame Bay - a possible remnant arc in the oceanic domain of northeast Newfoundland. Can. J. Earth Sci., 12: in press. Williams, H. and Smyth, W.R. 1973. Metamorphic aureoles beneath ophiolite suites and Alpine peridotites: Tectonic implications with west Newfoundland examples. Am. J. Sci., 273: 594-621. Williams, H. and Stevens, R.K., 1969. Geology of Belle Isle - Northern extremity of the deformed Appalachian miogeosynclinal belt. Can. J. Earth Sci., 6: 1145-1157. Williams, H. and Stevens, R.K., 1974. The ancient continental margin of eastern North America. In: C.A. Burk and C.L. Drake (Editors), The Geology of Continental Margins. Springer, New York, pp. 781-796. Williams, H., Kennedy, M.J. and Neale, E.R.W., 1970. The Hermitage Flexure, the Cabot Fault, and the disappearance of the Newfoundland Central Mobile Belt. Geol. Sot. Am. Bull., 81: 1563-1568. Williams, H., Kennedy, M.J. and Neale, E.R.W., 1972. The Appalachian Structural Province. In: R.A. Price and R. J. W. Douglas (Editors), Variations in Tectonic Styles in Canada. Geol. Assoc. Can., Spec. Pap., 11: 181--261. Williams, H., Smyth, W.R. and Stevens, R.K., 1973. Hare Bay Allochthon, northern Newfoundland. Geol. Surv. Can., Pap., 73-l (A): 8-14. Williams, H., Kennedy, M.J. and Neale, E.R.W., 1974. The northeastward termination of the Appalachian orogen. In: A.E.M. Nairn and F.G. Stehli (Editors), The Ocean Basins and Margins, 2. Plenum Press, New York, p. 79-123. Zen, E-an, White, W.S., Hadley, J.B. and Thompson, J.B. (Editors), 1968. Studies in Appalachian Geology: Northern and Maritime. Wiley-Interscience, New York.