Petrology and age of the A-type Mulock granite batholith, northern Grenville Province, Ontario

Precambrian Research, 53 ( 1991 ) 199-231 Elsevier Science Publishers B.V., A m s t e r d a m

199

Petrology and age of the A-type Mulock granite batholith, northern Grenville Province, Ontario S.B. Lumbers a, Tsai-Way Wu b, L.M. Heaman a, V.M. Vertolli a and N.D. MacRae b a Department of Geology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ont. M5S 2C6, Canada b Department of Geology, University of Western Ontario, London, Ont. N6A 5B7, Canada ( Received May 22, 1990; revised and accepted May 24, 1991 )

ABSTRACT Lumbers, S.B., Wu, T.-W., Heaman, L.M., Vertolli, V.M. and MacRae, N.D., 1991. Petrology and age of the A-type Mulock granite batholith, northern Grenville Province, Ontario. Precambrian Res., 53: 199-231. The Mulock granite batholith is exposed over 530 km 2 in the northern part of the Grenville Province, 25 km north of North Bay, Ontario. The batholith has a U - P b zircon emplacement age of 1244 + 4 / - 3 Ma. Two regional tectonic events affected the batholith: ( 1 ) moderate-grade regional metamorphism; and (2) shearing and mylonitization related to the Grenville Front Tectonic Zone which slices across the northern third of the batholith. A suite of fine-to coarse-grained, pink, gneissic granites containing accessory fluorite and with colour indices between 1 and 27, dominate the batholith and are cut by abundant aplite dikes. Anorthosile dikes cut the granites and aplite in the central part of the batholith. The granites were originally alkali feldspar granite and syenogranite, and the coarser-grained varieties were originally hypersolvus. The suite is mainly metaluminous to marginally peraluminous; peralkaline varieties are rare. Most of the suite is subalkalic, but subordinate alkalic granites enriched in biotite and ferrohastingsite are early phases. The suite shows all the major and trace element compositions and elemental ratios diagnostic of A-type granite suites. Metamorphism altered the primary distribution of some of the trace elements, particulary Rb and F. The granites crystallized under relatively low pressures ( < 2 kb) from a high temperature, fluorine-enriched magma. Alkali feldspar fractionation accompanied by minor amphibole fractionation can account for chemical variations observed within the suite; the aplite dikes are products of residual magma. Magma generation occurred at lower crustal levels, probably by high-temperature, anhydrous partial melting of tonalitic to granodioritic, or felsic granulite source rocks, which had not previously undergone melt depletion. Mixed source rocks may have been involved, and the anorthosite dikes may be an expression of mantle-derived mafic magmatism that caused widespread crustal underplating and partial melting of the source rocks. The batholith appears to be part of an extensive magmatic episode in the northeastern North American craton, during which A-type granites and anorthosite were emplaced between 1.25 and 1.24 Ga.

Introduction A-type granites, characterized by high SiO2, N a 2 0 + K 2 0 , Fe/Mg, Ga/A1, large, highly charged cations such as Nb, Y, and the REE (except Eu), and by low CaO and MgO, occur world-wide throughout geological time (Collins et al., 1982; Anderson, 1983; Whelan et al., 1987 ). They show evidence of emplacement at high crustal levels, and associated rhyolitic volcanism is common. They are called anorogenic or A-type granites because many appear

to be related to updoming and rifting of continental crust under anorogenic conditions (Anderson, 1983). This designation has recently proved to be somewhat misleading, because several examples of A-type granites in orogenic and other tectonic settings have been documented (Whalen et al., 1987; Lumbers et al., 1991 ). Proterozoic A-type granites, ranging in age from 1760 to 1030 Ma, are particularly abundant across the North American craton in a zone up to 1000 km wide, extending northeast-

0 3 0 1 - 9 2 6 8 / 9 1 / $ 0 3 . 5 0 © 1991 Elsevier Science Publishers B.V. All rights reserved.

200

S.B. L U M B E R S ET AL.

ward from California to Labrador (Silver et al., 1973; Emslie, 1978; Anderson et al., 1980; Collerson, 1982; Anderson, 1983; Whelan et al., 1987 ). The Grenville Province constitutes much of the northeastern part of this zone, and several A-type granite plutons have been de-

scribed from the Quebec and Labrador segments of the Province, and to the north, in the Nain and Churchill Provinces (e.g. Emslie, 1978; Collerson, 1982; Miller, 1986, 1989; Whelan et al., 1987). In the Ontario segment of the Grenville Province, north of the Central

Pre-Batholith M e t a s e d i m e n t s [-~lPost-Batholith Anorthosite Di ~ ' ~ Soulhern Limit, G r e n v i l l e Front Tectonic

Zone

I ~ ] Age-Dating Sample, K-123 I - ~ Location of Chemically Analyzed Specimens + C o n t a c t of Batholith "~iii

O I

5 10 I I Kilometres

15 I

:!i'

t?

:

i A ' l : : :~i:i;'i

I) ~"':i:~?;ii!;il;,\ ps-2° ~Y:~~<2 "

'

::C~:(:,::)>x+,,,-2~

~:. +:'+: i. "..;.::

PA 3 " o M A ' 4 " ;

,.~~.. pA-2,.,,.s=9~

<';?~i.?; /+ .I+I ' :+i:

~;/- ~' ~

Z./.;

Fig. 1. Generalized geological map of the Mulock batholith and locations of chemically analysed specimens. Specimen codes correspond to those in Table A1 and indicate the type of granite analysed as follows: MA = metaluminous alkalic: Ml=metaluminous intermediate; MS=metaluminous subalkalic; PA =peraluminous alkalic; Pl=peraluminous intermediate; PS=peraluminous subalkalic; PaA=peralkaline alkalic; PaS=peralkaline subalkalic, A=aplite dike: ('=contaminated metaluminous subalkalic granite. Location of the batholith relative to major subdivisions of the Grenville Province is shown in the inset map.

PETROLOGY AND AGE OF THE A-TYPE MULOCK GRANITE BATHOLITH

Metasedimentary Belt (Fig. 1 ), A-type granites are poorly documented. Van Breemen and Davidson (1988) described possible A-type granites, ranging in age from 1742 to 1471 Ma, adjacent to the Grenville Province between Killarney and Sudbury. They indicated that similar granites may form a significant proportion of the metaplutonic rocks to the east in the Central Gneiss Belt (Fig. 1 ) of the Grenville Province, because the few felsic metaplutonic rocks in this region that have been dated, have ages between 1700 and 1400 Ma (see also Emslie, 1978). Geological reconnaissance mapping of part of this region by Lumbers ( 1971 a, b, c, 1973, 1975) showed that several granitic plutons are indeed candidates for A-type granite magmatism. Ongoing re-evaluation of specimens and data collected during this work has disclosed an exemplary intrusion, the Mulock batholith, which has now received sufficient study to show conclusively that it was the product of A-type granite magmatism. The batholith was emplaced prior to the last regional metamorphism in the Grenville Province, and data presented below show that it is similar geochemically to both Proterozoic and Phanerozoic A-type granites, particularly those described by Anderson ( 1983 ) from the midcontinent region, by Wu et al. (1989) and Lumbers et al. ( 1991 ) from the Central Metasedimentary Belt (CMB) in the southwestern part of the Grenville Province, by Collerson (1982) from Labrador, and by Whalen et al. ( 1987 ) from the Appalachian Orogen in Newfoundland. Its 1244 Ma emplacement age (see below) shows that the batholith is younger than the majority of A-type granites of the Mid-continent region and those adjacent to the Grenville Province, but is identical in age to the voluminous A-type granites in the CMB (Lumbers et al., 1991 ) and the Strange Lake pluton in Labrador (L.M. Heaman and R.R. Miller, unpublished data; Miller, 1986).

201

Previous work and field relationships The Mulock batholith was first mapped by Lumbers ( 1971a, b, c) during regional geological mapping in the North Bay and Tomiko areas. The geological setting of the batholith is shown on the Sudbury-Cobalt geological compilation sheet (Card and Lumbers, 1977). Wu (1984) collected additional specimens for detailed geochemical studies (Wu and MacRae, 1984) and Lumbers and Vertolli carried out additional mapping and detailed petrographic analyses to complete the present study. The locality of the specimen, K123, used to obtain the radiometric age of the batholith is shown in Fig. 1. The specimen was originally collected by Lumbers and Krogh for Rb-Sr wholerock age dating (Krogh and Davis, 1969a; locality No. 8). Zircon separates were obtained by Krogh from this specimen, which were subsequently analysed by Heaman. The batholith is an elongate intrusion exposed over 530 km 2 northeast of Lake Nipissing (Fig. 1 ). It extends northwestward for 53 km from Widdifield Township into the Grenville Front Tectonic Zone (GFTZ) (Lumbers, 1978) as far as Wickstead Lake (Fig. 1 ). Both the batholith and its enclosing rocks were recrystallized and deformed by moderate-grade regional metamorphism, so that the batholith rocks are now gneissic; primary igneous textures and mineralogy are either poorly preserved, or absent. From Widdifield Township to the GFTZ, gneissic foliation in both the enclosing rocks and the batholith strikes northwestward and dips vertically to 50 ° northeast (Lumbers, 1971a, b, c). Gneissic foliation trends in the northern third of the batholith, all within the GFTZ, show complicated patterns (Lumbers, 197 lb ), with mylonitic zones superimposed upon the gneissic foliation. Thus, emplacement of the batholith predates not only the regional metamorphism, but also the last major deformation along the GFTZ. Host rocks to the batholith are mainly metagreywacke, but near Wickstead Lake, the

202

batholith cuts metasediments of the Red Cedar Lake formation (Lumbers, 1978 ). Near the southern end of the batholith, the host rocks include a possible post-metagreywacke metasedimentary sequence derived from orthoquartzite, subarkose, potassic feldspar-rich impure sandstone and aluminous clay-rich sediments (Lumbers, 1978, 1982). Dikes and sills of the batholith rocks are locally abundant in metasediments up to 1 km from the northern, western and eastern contacts of the batholith and up to 5 km southwest from the southern contact where elongate satellitic intrusions up to 10 km long are also present (Fig. 1 ). Finegrained quartzo-feldspathic gneisses are found locally in the vicinity of these intrusions. The gneisses are chemically similar to granite phases of the batholith, and zircon obtained from one of the gneisses gave a U - P b age similar to the emplacement age of the batholith (T. Krogh, pers. commun., 1989). The gneisses could be derived either from volcanic rocks, or sills related to the batholith. Sparse xenoliths of metasediments occur in the batholith near all contacts with the host rocks. The xenoliths show various stages of digestion by the batholith rocks, and xenolithic phases of the bath-

S.B. LUMBERS ET AL.

olith are commonly enriched in biotite and amphibole, which suggests local contamination of the magma by the metasedimentary enclaves. Dikes of recrystallized and gneissic anorthosite cut rocks of the batholith between Poplar and Rock Island Lakes (Fig. 1 ), and small plutons of gneissic to massive troctolitic anorthosite lie just to the north of the batholith in Flett Township (Lumbers, 1971 b). Recrystallized and gneissic aplite dikes (Fig. 2), locally containing xenoliths of the coarser-grained granite of the batholith, are found in places throughout the batholith. Dikes and pods of granite pegmatite are present in highly deformed parts of the batholith, but their massive structure and the fact that some cut across gneissic foliation in the host granite suggest that they formed during a late stage of the superimposed regional metamorphism, rather than during batholith emplacement. However, host metasediments near the batholith contain deformed granite pegmatite dikes and pods which could be related to the batholith. Zircon from one such dike gave a U - P b zircon age similar to the emplacement age of the batholith (T. Krogh, pers. commun., 1990).

Fig. 2. Aplite dikes in gneissic augen granite with a zone of equigranular, fine-grained granite containing a few feldspar augen (near bottom-centre of the figure). Outcrop near the central part of the batholith in Merrick Township.

203

PETROLOGY AND AGE OF THE A-TYPE MULOCK GRANITE BATHOLITH

Fig. 3. Typical gneissic, augen granite. Some augen contain clear cores of primary mesoperthite. Outcrop near age-dating locality (sample K-123, Fig. 1 ), Merrick Township.

The typical granite of the batholith is a pink augen gneiss (Fig. 3) with coarse-grained, granular, recrystallized alkali feldspar augen surrounded by a finer grained groundmass of quartz, feldspar and mafic minerals. Most augen are elongate due to tectonic stretching, and this imparts a prominent gneissic foliation and lineation to the rock. Locally, the augen show extreme stretching where they coalesce to form discontinuous, parallel layers of alkali feldspar and quartz. Where least deformed, some augen cores contain clear, unrecrystallized, primary mesoperthite, which suggests that the augen represent primary mesoperthite phenocrysts in an originally coarsely porphyritic, hypersolvus granite. Equigranular granite, containing only a few or no alkali feldspar augen and similar in appearance to the aplite, is present throughout the batholith (see Fig. 2, near the bottom-centre, for a typical example ). This granite shows conflicting cutting relationships with the aplite, as shown in Fig. 2. Its boundaries with the host augen granite are commonly less sharply defined than those of the aplite dikes even though it contains xenoliths ofaugen granite. Both the augen granite xenoliths and the host equigran-

ular granite show the same degree of strain, so that the prominent augen structure of the xenoliths does not imply a deformation event preceding intrusion of the equigranular granite. Distinct variations in mafic mineral content developed in irregularly shaped zones unrelated to metamorphic layering are also evident in the augen granite throughout the batholith. The superimposed deformation severely restricts interpretation of these megascopic features of the pre-aplite granites, but one possibility is that the granites were emplaced by rapid injection of magma from a differentiating chamber with each injection differing slightly in composition and intruded before the preceding injection could completely crystallize. Petrographic and geochemical study of these various kinds of granite, summarized below, reinforces this possibility.

Petrographyand mineralogy Seventy-five thin sections of representative granite and aplite specimens were examined, and 69 of these were subjected to modal analyses in order to select specimens for chemical analysis, and to study textural and modal min-

204

SB. LUMBERS ET AL.

eral variations. The colour index of the granites ( 100 vol% feldspar and quartz) ranges between 1 and 27 and averages about 11. Mafic minerals consist of biotite, ferrohastingsite, titanite, magnetite containing exsolved hematite and ilmenite, apatite, allanite, and zircon. Magnetite locally forms oval to equant grains up to 4 mm across. Many of the granites and aplites contain up to 0.6% fluorite and a few contain sparse monazite. Muscovite, epidote and calcite are late alteration products, either intergrown with, or replacing, other minerals, or in microfractures. Feldspars consist of microcline showing grid twinning (AnoAb3.5Or96.5 to AnoAbT.iOr92.9), albite (Ano to Ans) and plagioclase (An6 to An27). Albite and plagioclase show only albite and pericline twinning, and where albite forms separate grains, it is unaltered. Where plagioclase is in contact with microcline, the two feldspars are separated by a narrow zone of albite which gradually becomes more calcic and grades into the plagioclase. Clear patches visible in the cores of some alkali feldspar augen are mesoperthite; the surrounding parts of the augen consist of equigranular to elongate aggregates of albite, microcline and quartz. The granitic rocks can be subdivided into

four petrographic groups based upon their texture, ferromagnesian mineral contents and colour index as shown in Table 1; note that the two leucocratic groups contain less calcic plagioclase than the other two groups. Modal quartz, alkali feldspar and plagioclase data given in Fig. 4a for 42 granites and two aplites also analysed chemically, show that nearly half of the specimens plot in the alkali feldspar granite field of Streckeisen ( 1976 ) and are free of plagioclase. The remainder plot mostly in the monzogranite field, but a few are in the granodiorite and alkali feldspar quartz syenite fields. This peculiar scattered distribution of the modal data is due to unmixing of primary igneous perthite (see Fig. 4b) and is discussed below in the geochemistry section. Dikes, sills and satellitic intrusions of the batholith in the host metasediments are mainly equigranular ferrohastingsite-biotite granite, modally similar to ferrohastingsite-biotite granite of the batholith. Some of the larger satellitic intrusions contain augen granite phases, and some dikes are leucocratic; aplite dikes are rare. Even though the Mulock granites are recrystallized, they retain vestiges of many of the petrographic and mineralogical traits of Pro-

TABLE 1 Grouping of Mulock granite according to textural and modal features Group

No. Texture specimens

Ferromagnesium minerals

Colour index

Plagiocl. comp. ( % A n )

average range

average range

Chemical equivalent

Ferrohastingsite- 29 biotite

augen

Ferrohastingsite biotite

14.4

9-27

8

0-23

Subalkalic and alkalic metaluminous; Alkalic peralkaline

Biotite

12

augen

Biotite

14.7

10-21

II

2-20

Subalkalic metaluminous Alkalic peraluminous

Leucocratic

19

augen equigranular

Biotite

5.7

1-9

7

0-12

Subalkalic metaluminous, peraluminous, peralkaline

4

fine-grained

Biotite

3.0

1- 5

7

0-12

Subalkalic peraluminous and peralkaline

Aplite

205

P E T R O L O G Y A N D AGE O F T H E A-TYPE M U L O C K G R A N I T E B A T H O L I T H

• Metaluminous, subalkalic Metaluminous, intermediate 0 Metaluminous, alkalic ,k Peraluminous,subalkalic [3 Peraluminous, intermediate /x Peraluminous,alkalic • Peralkaline, subalkalic 0 Peralkaline, alkalic / ~PPeraluminous,aplite d i k e / -I-Peralkaline, aplite d i k e /

Q

Q

/ ~ Modal

/ ~ Normative

a

L

\

/

b

+

//

/

A P Fig. 4. Comparison between modal (a) and CIPW normative (b) quartz, alkali feldspar and plagioclasedata for chemically analysed rocks of the batholith. The dashed line in (b) separates alkalic granites from intermediate and subalkalic granites. Areas defined by solid lines in (a) and (b) correspond to Streckeisen's (1976) subdivision of plutonic rocks accordingto modal Q-A-P data. terozoic A-type granites as described by Anderson (1983), among others. However, unlike many A-type granites, the Mulock granites contain magnetite, rather than ilmenite. F e / F e + Mg ratios in biotites range between 0.74 and 0.82 and are slightly less enriched in iron than biotite in most A-type granites. These differences are perhaps due to the superimposed metamorphism, because whole-rock F e O / FeO + MgO ratios of the granites are similar to those of typical A-type granites (see Fig. 8 ).

Geochemistry Analytical methods Nine major element oxides were determined by the heavy absorber fusion technique of Norrish and Hutton (1969). Na20, Nb, Zr, Y, Sr, Rb, Ba, Ga, Pb, Zn, Cu, Ni, Cr, and V were

analysed on pressed powder pellets, calibrated against international standards, by X-ray fluorescence spectrometry. Ferrous iron concentrations were determined by metavanadate titration (Wilson, 1955). Rare-earth elements, Ta, Hf, Cs and Sc were analysed by instrumental neutron activation (tNAA) methods as described by Gordon et al. (1968) and Gibson and Jagam (1980). Joint analyses of fluorine and chlorine were made using a single sample fusion and ion-selective electrode technique devised by Haynes ( 1978 ). The precision and accuracy of the major and trace element data can be evaluated from the replicate analyses of U.S.G.S. standard rock G-2 and internal standard UWO- 1 (see Tables 3 and 4). Zircons from a typical metaluminous subalkalic augen granite (specimen No. K123, ROM petrology collection) were used to obtain the radiometric age of batholith emplacement. Dissolution of the zircons and extraction of U

206

S.B. LUMBERS ET AL

I

I

I

I

I

I

I

1.4

1.2

Peraluminous

~

MULOCKBI~

/

."

~ ->
v Z

/

v " 1.o u

'.

~

----~wo.

0.8

))

713 ".'----~" ',

~J-

/

~ 01

•

•

A'i ~,a~..,.." 6.-

',o~. 9 e. • - / - • "'A- - _ _ ~ ¢ ~ 2 ' . . . . . . . . . . .

\

~,V~R

M e t a l u m i n o u s & Peralkaline

•

/

•', / .

,\

,/

~,' /

j

/

'\/~¢MB--~,~ A-TYPE GRANITES

0.6 I

I

I

50

55

60

I

I

65 70 SiO 2 (wt. 7oo)

I

I

75

80

Fig. 5. Molecularratio A 1 2 0 3 / ( C a O + Na20 + K 2 0 ), or A/CNK, and SiO2 (weightpercent) data for the Mulockgranites and aplites. A/CNK ratios correctedfor CaO in apatite. Referencefieldsfor the WolfRiver (Andersonand Cullers, 1978) and CMB (Wu et al., 1989) A-typegranites are shownfor comparison.Symbolsare the sameas in Fig. 4. and Pb from them closely followed the procedure of Krogh ( 1973 ). U and Pb isotopic compositions were determined according to the procedure described by Heaman et al. ( 1986 ), with the exception that both elements were loaded together on single, outgassed rhenium filaments using a silica gel technique. The total procedural blanks for U and Pb for this study were estimated to be 2a and 10 picograms, respectively. The errors in the P b / U and 2°7pb/ 2°6pb ratios are estimated to be 0.25% and 0.05%, respectively at the 2a level. Error estimation for the U - P b age is similar to the approach discussed by Davis (1982) and is also quoted at the 2 level. The age was calculated using the decay constants for 238U (1.55125X10 -1° a-l) and 235U (9.8485X10 -l° a -1 recommended by the Subcommission for Geochronology and Cosmochronology (Steiger and Jager, 1977 ). Thin sections and hand specimens of the analysed rocks are catalogued in the petrology collection of the Department of Geology, Royal Ontario Museum. Summaries of the major and trace element data are given in Figs. 5 to 15 and Tables 3 and 4. A table showing the major

and trace element data in detail is given in the appendix (Table AI ).

Major element chemistry The peculiar scattered distribution of the modal data for the granites in Fig. 4a, with no granites in the syenogranite field, is most likely due to unmixing of primary igneous perthite, relics of which are preserved in the augen granites. Thus, in order to properly characterize the granites, recourse to chemical data is necessary. Normative quartz, alkali feldspar and plagioclase data for the same specimens shown in Fig. 4a are given in Fig. 4b. This plot shows that all the granites and aplites lie either within, or close to, the alkali feldspar granite and syenogranite fields. The alumina-saturation (Shand, 1927) of the Mulock granites, measured by the molecular ratio A1203/ ( C a O + N a 2 0 + K 2 0 ) , or A/CNK, is shown as a function of SiO2 in Fig. 5. Many of the granites have A / C N K ratios less than 1.0 and are metaluminous to peralkaline, but some have ratios between 1.0 and 1.1 and are marginally peraluminous. The aplite dikes are either mar-

PETROLOGY AND AGE OF THE A-TYPE MULOCK GRANITE BATHOLITH

207

TABLE 2 A v e r a g e m o d e l a n a l y s e s o f m e t a l u m i n o u s , p e r a l u m i n o u s a n d p e r a l k a l i n e g r a n i t e s o f the M u l o c k B a t h o l i t h Rcf. ": n b:

Quartz Plagioclase Albite K-feldspar Muscovite Biotite Ferrohastingsite Opague minerals Titanite Apatite Zircon Allanite Epidote Calcite Fluorite Total Color index % An, p l a g i o c l a s e

1 7 mean

s.d. c

21.3 37.5 27.3 0.1 8.3 2.6 0.5 1.1 0.6 0.2 0.4 0.1 trace 100.0

2.5 6.0 5.1 3.7 2.9 0.6 0.7 0.3 0.1 0.3 -

14.2

2 2

3 12

mean

mean

21.6

23.9 34.4 27.1 0.2 8.6 2.2 0.6 1.6 0.5 0.2 0.3 0.4 trace trace 100.0

37.6 31.7 4.7 1.6 0.7 1.3 0.2 0.2 0.3 0.1 trace 100.0 9.1

14.6 10

4 3

5 3

6 10

s.d.

mean

mean

mean

2.5 2.7

19.1 40.1 24.1 0.5 11.8 0.1 1.2 1.0 0.4 0.4 0.4 0.6 0.3 100.0

21.4 34.5 32.7 0.4 7.9 0.9 0.8 0.3 0.4 0.4 0.2 0.1 100.0

29.1 33.1 30.8 0.6 4.3 0.2 0.5 0.7 0.2 0.2 0.2 0.1 trace trace 100.0

16.7

11.4

7,0 8

3.7 0.3 2.9 2.6 0.6 0.7 0.2 0.5 0.2 0.4 -

3

7 2

8 3

s.d.

mean

mean

4.7 6.6 4.9 0.6 2.5 0.4 0.4 0.5 0.1 0.1 0.1 -

16.8 38.7 34.6 0.2 5.9 1.7 1.6 0.1 0.2 0.2 trace 100.0

33.6 28.7 32.4 0.3 2.7 0.9 0.6 0.1 0.3 0.2 0.2 trace 100.0

9.9

5.4

2

9 1

10 1

34.3 35.4 27.0 1.5 0.5 0.7 0.1 0.2 0.1 0.1 0.1 100.0 3.3 12

34.3 40.0 25.2 0.2 trace trace 0.1 0.1 0.1 100.0 0.5

a 1 = M e t a l u m i n o u s a l k a l i c g r a n i t e ; 2 = m e t a l u m i n o u s i n t e r m e d i a t e g r a n i t e ; 3 = m e t a l u m i n o u s s u b a l k a l i c granite; 4 = p e r a l u m i n o u s alkalic granite; 5=peraluminous intermediate granite; 6=peraluminous subalkalic granite; 7=peralkaline alkalic granite; 8 = p e r a l k a l i n e s u b a l k a l i c g r a n i t e ; 9 = p e r a l u m i n o u s s u b a l k a l i c a p l i t e d i k e ; 10 = p e r a l k a l i n e s u b a l k a l i e a p l i t e d i k e . b N u m b e r o f m o d e s a v e r a g e d ; m i n e r a l s in vol.%. c Standard deviation (let).

ginally peraluminous, o r peralkaline. Moreover, subalkalic, intermediate and alkalic varieties also exist (see Fig. 6) and are clearly separated in Fig. 4b but not in Fig. 4a. Average modes for the various chemically defined granites given in Table 2 show that each type has a distinctive modal composition, although the subalkalic and alkalic metaluminous granites differ only slightly. Correlation of the chemically defined granites with the four groups of granites defined using only modal and textural data is given in the last column of Table 1. The alkalic varieties contain the most ferromagnesian minerals, and feldspars are mainly microcline and albite. Leucocratic subalkalic varieties are also rich in microcline and albite, and where plagioclase is present, it is less calcic than in the more mafic granites. Figure 1, which gives the distribution of the

various types of granite analysed, shows that subalkalic metaluminous and marginally peraluminous granites are distributed throughout the batholith. Peralkaline and alkalic granites are most abundant in the southern half, but because many of the granites cannot be reliably distinguished in the field, the distribution pattern may be an artifact of the sampling. Two or three samples of augen granites chosen for their variations in mafic mineral content were collected from single large, well exposed outcrops at a few localities. Analytical results of these samples show that the following types of augen granite are associated in individual outcrops: (1) alkalic peraluminous and alkalic metaluminous granites; (2) subalkalic metaluminous and subalkalic peralkaline granites; and (3) subalkalic peraluminous, alkalic peraluminous, and subalkalic peralkaline gran-

Nb Zr Y Sr Rb Ba Ga

FeO n F CI n

Fe203

Fe203 d MnO MgO CaO Na20 K20 P205 LOI Total

A1203

SiO2 TiO2

n b:

Ref. a:

0.75 0.11 0.50 1.23 0.01 0.19 0.39 0.43 0.92 0.04 0.09

20 380 25 236 90 1552 23

11 65 8 61 18 320 3

1.18 0.31 2.22 0.58 5 964 281 396 210 3

68.30 0.55 14.82 3.44 0.06 0.55 1.17 4.75 5.13 0.10 0.44 99.31

16 423 25 220 95 1360 27

-

-

69.84 0.61 14.05 4.22 0.07 0.42 1.19 4.44 4.91 0.09 0.28 100.12

mean

mean

s.d. c

2 2

1 7

1.41 0.16 0.40 0.87 0.02 0.23 0.41 0.47 0.34 0.07 0.07

s.d.

25 332 26 236 127 1194 24

6 39 4 53 21 212 3

1.61 0.34 2.26 0.90 8 1171 247 122 76 5

69.78 0.65 13.72 4.04 0.07 0.63 1.45 4.20 4.64 0.14 0.40 99.72

mean

3 12

29 457 30 249 109 1506 27

2.07 2.22 3 1016 270 1

67.45 0.64 14.77 4.54 0.06 0.65 0.74 4.44 5.15 0.13 0.71 99.28

mean

4 3

73.56 0.31 13.28 2.51 0.03 0.26 0.61 4.05 5.06 0.08 0.34 100.09

mean 2.07 0.17 0.75 0.88 0.02 0.20 0.42 0.31 0.41 0.04 0.16

s.d.

20 367 26 152 82 1304 24

17 240 17 147 136 709 22

9 28 6 63 43 350 3

1.23 1.07 0.35 1.67 1.44 0.67 l 7 590 410 400 97 3

69.72 0.43 14.33 3.45 0.04 0.65 0.95 4.08 5.30 0.08 0.53 99.56

mean

5 3

Average m ~ o r a n d t r a c e e l e m e n t c h e m i s t ~ o f t h e M u l o c k g r a n i t e s a n d a p l i t e s

TABLE3

38 540 33 133 108 866 29

2.31 1.81 1

69.15 0.50 13.66 4.60 0.08 0.27 0.89 5.09 5.17 0.03 0.36 99.80

mean

7 2

mean

10 1

75.40 76.41 0.06 0.01 12.84 12.99 0.86 0.14 0.01 0.00 0.00 0.00 0.33 0.03 4.06 5.76 5.32 4.50 0.09 0.09 0.17 0.17 99.14 100.10

mean

9 1

25 270 28 68 120 279 24

39 170 24 91 143 75 23

5 52 16 40 104 89 23

0.69 0.62 0.01 0.96 0.22 0.11 1 1 1 1368 234 488 28 212 172 1 1 1

74.51 0.19 12.41 2.28 0.02 0.11 0.26 4.59 4.76 0.05 0.40 99.58

mean

8 3

13 299 11 479 171 1884 23

69.50 0.49 15.44 2.68 0.03 0.75 1.84 4.10 4.50 0.12

mean

11

1 2 0.2 1 2 30 2

0.25 0.01 0.11 0.03 0.005 0.08 0.07 0.38 0.07 0.025

s.d.

O O~

0.90 9.36 0.97 440 0.43 14.41 6.20 3.63

0.83

9.90 0.96 489 0.41 17.81 6.90 3.02

8.85 0.96 311 0.51 9.82 5.14 3.28

0.86 9.59 1.07 406 0.49 14.72 6.26 3.46

0.86

0.90

9.59 9.11 1.02 1.02 526 338 0.66 1.07 12.84 5.85 7.51 4.72 3.41 3.27

0.88 10.26 0.91 400 0.91 7.82 6.37 3.96

0.94 9.35 0.95 361 2.10 2.95 3.81 3.71

0.97

1.00

9.38 10.26 1.03 0.90 309 359 1.57 2.60 0.52 0.86 0.82 2.22 3.39 3.35

1.00

1 =Metaluminous alkalic granite; 2 = metaluminous intermediate granite; 3 = metaluminous subalkalic granite; 4 = peraluminous alkalic granite; 5=peraluminous intermediate granite; 6=peraluminous subalkalic granite; 7=peralkaline alkalic granite; 8=peralkaline subalkalic granite; 9 = peraluminous subalkalic aplite dike; 10 = peralkaline subaluminous aplite dike; 11 = U.S.G.S. standard rock G-2, mean of 15 determinations. b Number of analyses averaged; oxides in wt.%, trace elements in ppm. c Standard deviation (10). a Total iron as Fe203. c A / C N K = m o l e c u l a r ratio A 1 2 0 3 / ( C a O + N a 2 0 + K 2 0 ) ; peraluminous > 1, metaluminous < 1, peralkaline < 1 with N + K > A. Corrected for CaO in apatite. LOI = Loss on ignition.

FeO/ FeO + MgO N a 2 0 + K20 A/CNK e K/Rb Rb/Sr Ba/Rb Ba/Sr Ga/AI

0

Z

c)

,<

,.q '-r'

0

rtl

>

© tO 0 ,.< > Z

210

S.B. LUMBERSET AL. 100

I

I

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I

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12,0 /'

"~,

_PIKES PEAK

/ ; 50

11,0

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o +

O

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Alkalic

9.0

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8.o

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ZX

10

• Subalkalic

7.0

Z

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A-TYPE ~' GRANITES

CMB

6.0

$.0 + 4.o

55

I

60

I

I

65 SiO 2 (Wt.

70 %)

75

80

Fig. 6. Na20 + K20 and SiO2 data for the Mulock granites and aplites. All data are in weight percent. Alkalic/subalkalic boundary from Irvine and Baragar (1971). Reference fields for the Pikes Peak (Barker et al., 1975), Wolf River (Anderson and Cullers, 1978) and CMB (Wu et al., 1989) A-type granites are shown for comparison. Symbols: • = metaluminous granites; A = peraluminous granites; @ = peralkaline granites; • with cross = peraluminous aplite; + = peralkaline aplite.

ites. Most of the equigranular granites sampied, all of which appear to be younger than the augen granites, and most of the aplite dikes are subalkalic peraluminous, but a few are subalkalic peralkaline. These relationships show that the alkalic granites and the most mafic subalkalic granites crystallized early and that late phases were entirely subalkalic and either peraluminous, or peralkaline. Anderson (1983) indicated that Proterozoic A-type metaluminous and peraluminous granites show a positive correlation of A / C N K with SiO2, such as shown by the reference field for the Wolf River batholith in Fig. 5. The Mulock granites and A-type granite intrusions from the CMB containing metaluminous, peraluminous and peralkaline phases show no such correlation (Fig. 5 ). Instead, A / C N K ratios of most of the Mulock granites show a narrow range throughout the entire range of SiO2 compositions. The alkalinity of the Mulock granites is shown by the N a 2 0 + K 2 0 , ( N a 2 0 + K 2 0 ) /

O 21.o 0,5

O.l

45

5'0

5'5

gO

65 SiO 2 (wt. ~)

I 70

i 75

80

Fig. 7. N a 2 0 + K 2 0 / C a O and SiO2 data for the Mulock granites and aplites. All data are in weight percent. The dashed line separates alkalic granites from intermediate and subalkalic granites and aplite. Symbols as in Fig. 4.

CaO and SiO2 data in Figs. 6 and 7. Figure 6 shows that several ferrohastingsite-bearing metaluminous, peraluminous and peralkaline granites, fall within the alkalic field of Irvine and Baragar ( 1971 ), and that five granites plot either on, or immediately below the alkalicsubalkalic boundary; these five granites are designated as intermediate in Table 3 and in Figs. 4a and 4b. Reference fields for the Wolf River and Pikes Peak A-type plutons and selected CMB A-type granites given in Fig. 6 overlap with that of the Mulock granites between 65 and 76% SiO2, The Mulock granites do not have the range in silica for precise determination of their alkali-lime index (Peacock, 1931 ), but Fig. 7 shows that the alkalic and subalkalic granites defined in Fig. 6, are clearly separated, with the alkalic granites

PETROLOGYAND AGE OF THE A-TYPEMULOCKGRANITEBATHOLITH

80

I

21 l

I

75

70

/

65

o 60

S

55

u

50

45

0.0

I 0.1

I 0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

FeO/FeO+MgO ( w t . ~ ) Fig. 8. F e O / F e O + MgO and SiO2 data for the Mulock granites and aplite. All data are in weight percent. Reference field for the Wolf River granites is from Anderson ( 1983 ). Symbols as in Fig. 4.

projecting to an index of less than 52 (alkalic) and the subalkalic granites projecting to an index of less than 56 (alkali-lime). Most of the A-type granites described in the literature (e.g. Anderson, 1983) also show projected alkalic and alkali-lime indices. Strong iron enrichment of the Mulock granites is depicted in Fig. 8. The degree of enrichment is similar to that reported by Anderson (1983) for Proterozoic A-type granites. (For comparison, the reference field for the Wolf River A-type granites is shown in Fig. 8.) Nearly all the granites plot within the tholeiitic field, and both the alkalic and subalkalic granites, which show only minor overlap, are enriched in iron relative to magnesium as silica increases. The relative iron enrichment is most marked in the aplite dikes and leucocratic, finegrained peraluminous and peralkaline late phases of the batholith and is accompanied by a decrease in TiO2 and CaO contents. K20/MgO and SiO2 data plotted in Fig. 9 also show the A-type nature of the Mulock granites. Most of the analyses fall in the reference field for A-type granites of Rogers and

Greenberg ( 1981 ), and again, the alkalic and subalkalic granites show no overlap. Granites of both groups show a depletion of MgO relative to K20 as SiO2 increases. The aplites and some late, leucocratic, fine-grained peraluminous and peralkaline granites contain no detectable magnesium and plot far to the left of the main field. These rocks were probably produced from residual melts.

Trace element chem&try The Mulock granites, whether they be peralkaline, metaluminous, or peraluminous, show all the characteristic trace element abundances and elemental ratios reported in the literature for A-type granites. Non-peralkaline Atype granites and highly differentiated granites derived from I-and S-type felsic granite magmas can overlap in their chemistry, but unlike the A-type granites, the highly differentiated granites show collinear relationships between increasing Rb, Rb/Sr, Rb/Ba, Ga/AI and Nb, and decreasing Ba, Sr, Zr, Y and Ce (Whalen et al., 1987). No such collinear relationships

S.B. LUMBERSET AL.

212 8o

I

I

I

'

~

I

!'''I

I

i

'

|

i ! e

I

,,,I

+

2.0 + 1.0

0.5 •

UBALKALIC

"-"

/.

/o

/

-

0.1

/

/

/

0.05

© 0

/ /

/

0.02

I

~

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-1

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0

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el•

•

$~z i

70

•

/

I

+1

+2

,

I

I

,,,,I

i

,

500

50 100 200 Y + Z r (ppm)

900

Fig. 10. R b / B a and Y + Z r data for the Mulock granites and aplites. Symbols as in Fig. 4.

Ioglo ( K 2 0 / M g O )

Fig. 9. K 2 0 / M g O and SiO 2 data for the Mulock granites and aplites. All data are in weight percent. Reference field shown for A-type granites is after Rogers and Greenberg ( 1981 ). The dashed line separates alkalic granites from intermediate and subalkalic granites and aplites. Symbols as in Fig. 4.

exist in the trace element data for the Mulock granites as is evident in the Rb/Ba, Ga/A1, Y and Zr data plotted in Figs. 10 and 11. In Fig. 10, only the aplite dikes and some of the late, peralkaline and peraluminous, highly siliceous granites show Rb/Ba and Y and Zr values that differ appreciably from all the rest. Moreover, highly differentiated granites have much higher Rb and much lower Sr contents than those reported in Table 3 for the Mulock granites. The high Ba content of the granites (Table 3) is within the 600 to 1600 ppm range reported by Anderson ( 1983 ) for A-type granites containing between 68 and 74% SiO2. K / R b ratios range between 207 and 671 and are also well within the range reported for A-type granites by Anderson ( 1983 ) and several other authors. Rb-Ba and Rb-Sr data for the Mulock gran-

5

I

'

I

~ I

I

'

I

'

I

i

I

0 4

•

~e e oyO~ 41'-"" ~ A

+ rx 3

• •

o

A

•

A

0

0

@

0 2

-

I

60

i

i

il

80 I00

I

200 Y + Z r (ppm)

I

I

400

j

I

600

,

i

800

Fig. 11. Ga/AI and Y + Z r data for the Mulock granites and aplites. Symbols as in Fig. 4.

ites show no clear trends for all the data, which suggests that the primary distribution of Rb was disturbed by alteration processes during cooling and later regional metamorphism of the granites. However, Rb-Ba data for the alkalic

P E T R O L O G Y A N [ ) AGE O F T H E A-TYPE M U L O C K G R A N I T E B A T H O L I T H

3000

'

I

J '

''I

'

'

'

©

1000

50¢

E n o.

en

100

4-

40

I 30

÷ [ 50

I

I

Ill

I 100

I

I 500

Sr p p m

Fig. 12. Trace element variations between Sr and Ba for the Mulock granites and aplites. Symbols as in Fig. 4.

granites, subalkalic metaluminous granites and some of the leucocratic, siliceous peraluminous granites define a poor negative correlation which could result from alkali feldspar fractionation. In marked contrast, Ba and Sr data provide more convincing evidence for alkalic feldspar fractionation. Ba/Sr ratios of the granites summarized in Table 3 show an overall decrease with increasing SiO2, and Ba and Sr data in Fig. 12 show a strong, positive correlation within both the alkalic and subalkalic granite suites. The Mulock granites have high Ga/A1 ratios (Table 3), which is diagnostic of A-type granites (Collins et al., 1982; Whalen et al., 1987). In Fig. 13, Ga/A1 ratios for the Mulock granites are plotted against various trace element abundances and major element ratios and compared to reference fields for the Topsails and CMB A-type granites. The data show that the Mulock granites are remarkably similar to the Silurian A-type granites of the Topsails igneous terrane in Newfoundland (Whalen et al.,

21 3

1987) and that they also overlap with A-type granites of similar age in the CMB. Pb and the transition metals, V, Cr, Ni, Ca and Zn, are present in trace amounts in the granites, but only Zn and Pb occur in amounts exceeding 20 ppm (see Table A 1 ). Cr (4-11 ppm) and V ( 1-20 ppm ) are highest in the alkalic granites and generally decrease as SiO2 increases. Cu (3-11 ppm ), Ni ( 1-8 ppm ) and Pb (5-54 ppm) show no obvious variation with SiO2. The high Zn content (23-202 ppm) for the granites, is typical of the levels found in A-type granites. Such high contents are promoted by excess alkalis in A-type granite melts and by complexing with F, which is characteristically high in A-type granites in general (Collins et al., 1982; Whalen et al., 1987) and in the Mulock granite (Table 3 ). REE data for representative samples of the various Mulock granite phases are given in Table 4, together with Ta, Hf, Sc, and Cs contents. The REE data were normalized to chondrites using the values reported by Evensen et al. (1978) and are shown graphically in Fig. 14 . The granites are enriched in REE with abundances ranging between 415 to 180 times chondrites for La and 32 to 5 times chondrite for Lu (Fig. 14). Such light REE enrichment patterns ( ( C e / Y b ) n = 3 0 . 8 to 6.5 are typical of A-type granites reported in the literature (e.g. Collins et al., 1982; Anderson, 1983). The alkalic granites (Nos. 1 to 3, Table 4, Fig. 14), which have the lowest SiO2 contents, show modest, negative Eu anomalies (Eu/Eu* = 0.80 to 0.63). Eu anomalies become much more pronounced in the subalkalic granites (Eu/ Eu*=0.66 to 0.11; Nos. 4 to 9, Table 4, Fig. 14) as SiO2 increases. The aplite dike (No. 10, Table 3, Fig. 14) has the lowest REE abundances of all the rocks analysed. Modal data in Table 2 show that allanite, zircon, titanite and apatite, the main REE-bearing minerals in the batholith, are least abundant in the aplites. This suggests that fractionation of these minerals in the pre-aplite granite magmas impoverished the aplite residual magma in REE. Such deple-

214

S.B. LUMBERS ET AL.

1000

I

I

I

I

I

1000

I

500

b I

I

I

~,,~\

I

i

500

PeraJ~kaJineCMB ~,4J'~;-~----~/ ,L~

-

100

W;

10(

0

0

0 u

50

.~

Topsails S u i t e . ~ / ~ / A

~ \

5(

]

g

z

go

10

Metalumi . . . . Granites

1

0

i

CMB i ~ /

.!

10

TopsaiiSuite~~min

(

(

ous CMR

Gra niles

)

t

I

t

"t ~

I

t

1

2

3

4

5

6

1

7

I

1.4

I 1

0

Ga/AI xl04

I

I

C

/-4

I 2

I

I I 3 4 Ga/AI x 10 4

I 5

I 6

I

Peralkaline CMB " ~ Granites

1,2 ///+/

~

f"

/~Topsails

7d~ ~ . i

, . : ~ , /&+, . . . . /r o yl £ ~ o~ / ~. l_J~_~~~

4Z 0.8

_

t . ~ _ - - - ~ - ~ - ~ A

~

^

I

Suite

/

.// / . ~

/

./

"

/

./

-

-~

-~

-~

I 3

I 4 Ga/AI x l 0 4

w

- - ' ~ M e t a l u m i n o u s CMB Granites

0.6

I 2

I 5

I 6

7

Fig. 13. Variation diagrams showing ( a ) KzO/MgO; ( b ) Na20/K20/CaO; (c) molecular ratio (Na20 + K20 )/AIzO3 (NK/ A); and (d, overleaf) Zr against Ga/A1. Reference fields for the Topsails A-type granites (Whalen et al., 1987 ) and CMB peralkaline and metaluminous A-type granites (Wu et al., 1989) shown in each diagram overlap with the Mulock data. Symbols as in Fig. 4.

PETROLOGY AND AGE OF THE A-TYPE MULOCK GRANITE BATHOLITH

2000

I

I

I

21 5

I

I

I

cl Topsails Suite ~ / / ; 1000

A : . o) ? - -

500

//

c.

[

, #

100

\~

/

=

Peralkaline CMB Granites

-F

50

I

I

1

2

I

i

I

I

3 4 Ga/AI xlO 4

5

6

Fig. ld. continued.

tion in REE during fractionation has also been observed in other A-type granite plutons (Anderson, 1983 ). Figure 14 shows that within analytical uncertainty the light REE patterns for the granites are broadly similar, but the heavy REE patterns show some divergence. The differences in the heavy REE patterns could be due to several processes, such as contamination of the granites by the host metasediments, selective mobility of heavy REE during metamorphism, removal of successive batches of magma from the source region and mixed source rocks. Available data negate detailed assessment of all the possibilities, but a few observations can be made. The effect of contamination by the host metasediments on the REE patterns was investigated by analysing two subalkalic metaluminous contaminated granites collected from outcrops containing numerous xenoliths of the host metagreywacke in various stages of digestion by the granites. Both the major and trace element chemistry of the contaminated granites (see Table A1 ) show minor to major de-

partures from that of their uncontaminated counterparts. Although the differences vary in magnitude, the contaminated granites are slightly enriched in Ba and enriched 5 to 6 times in St, and 4 to 6 times in Cr over their uncontaminated counterparts. Calcite-epidote veinlets are c o m m o n in the contaminated granites and probably account for the elevated Ba and Sr contents. The high Cr contents are derived from the host metasediments which contain up to 70 p p m Cr (Lumbers, unpublished data). REE analyses of one of the contaminated granites (No. 11, Table 4, Fig. 14) show that host-rock contamination can have profound effects on both the light and heavy REE abundances and patterns. Nevertheless, only the heavy REE of the uncontaminated granites are disturbed, which suggest that if wall rock contamination was a factor, then it was selective. Fluorite is known to concentrate heavy REE relative to light REE under certain conditions of metamorphism and pegmatite genesis (Clark, 1984). Moreover, fluorine is able to leach REE from minerals by fluorine-complex-

216

s.B. LUMBERS ET AL.

TABLE 4 Rare earth elements, Ta, HI', Sc, a n d Cs analyses o f the Mulock granites a n d aplites ~ Location b Sample c

MA-6 1

PA-2 2

PaA-2 3

Ms-7 4

Ms-2 5

Ms-18 6

Ms-14 7

Ps-9 8

PaS-3 9

A-I 10

C-2 11

12 mean

S.D. '~

La Ce Nd Sm Eu Gd Tb Yb Lu

75.7 157.4 72.6 11.7 2.55 8.35 1.18 3.05 0.51

92.0 194.0 87.0 15.2 2.84 11.2 1.66 5.09 0.84

66.2 142.7 63.8 11.3 2.06 8.99 1.33 4.17 0.73

93.1 179.6 62.8 9.40 1.47 6.96 .86 2.64 0.35

85.0 165.0 70.9 11.9 2.42 9.93 1.17 3.86 0.54

152.2 306.5 127.1 24.7 1.08 2.33 6.85 1.20

82.7 168.3 63.1 9.75 0.67 8.65 1.04 2.77 0.38

104.8 203.5 69.6 8.98 0.75 7.00 0.68 1.72 0.20

68.6 134.8 60.3 10.5 0.33 9.19 1.40 5.37 0.89

13.9 33.4 16.8 3.76 0.29 0.36 1.59 0.31

47.4 98.9 44.2 9.55 2.01 0.89 0.92 0.17

44.6 93.21 41.73 8.30 1.15 8.75 1.13 3.72 0.56

0.58 2.09 1.10 0.28 0.02 0.40 0.01 0.06 0.02

Ta Hf Sc Cs

1.83 12.4 9.50 0.93

2.19 13,0 12,0 0,83

2.02 14.0 6.96 0.62

3.34 10.2 5.50 0.47

1.80 5.7 9.20 1.86

2.84 14.0 1.26 0.86

1.90 11.7 1.21 0.30

2.63 3.9 2.01 0.31

2.89 13.1 0.81 0.19

2.66 1.4 0.19 0.13

0.54 23.42 4.74 1.10

3.95 8.62 7.95 7.86

0.08 0.07 0.07 0.19

409.8 301.3 . . . 0,68 0.63 9.9 8.9

338.0 . 0.53 17.7

639.4 17.4 0.35 11.6

366.7 0.22 15.7

387.2 0.28 30.8

291.4 0.11 6.5

73.0 2.61 0.29 5.5

210.8 6.72 0.79 27.9

REE G& Eu/Eu* (Ce/Yb)n

333.0 0.80 13.4

430.6 0.66 11.1

'~ All data reported as p p m except E u / E u * a n d ( C e / Y b ) n which are reported as relative to chondrite. b Sample n u m b e r used for location in Fig. 1. c I = m e t a l u m i n o u s alkalic granite; 2 = p e r a l u m i n o u s alkalic granite; 3 = peralkaline alkalic granite; 4 to 7 = m e t a l u m i n o u s subalkalic granites: 8 = p e r a l u m i n o u s subalkalic granite; 9 = peralkaline subalkalic granite; 10 = aplite dike; 11 = m e t a l u m i n o u s subalkalic granite c o n t a m i n a t e d by host rock m e t a s e d i m e n t s ; 1 2 = U n i v e r s i t y o f Western O n t a r i o s t a n d a r d U W O - I , m e a n o f 5 determinations. d S t a n d a r d deviation (1o). ~"Calculated G d is derived by linear extrapolation between Sm a n d Tb.

ing (Muecke and Clarke, 1981 ). If fluorine can be shown to be a mobile constituent during m e t a m o r p h i s m of the granites, then its presence as a REE complexing agent in the metamorphic fluids may have contributed to disturbance of the heavy REE patterns. In most A-type granites, primary fluorite is commonly intergrown with early marie minerals; however, some F can be incorporated into amphibole and biotite (Collins et al., 1982; Anderson, 1983). All of the primary marie minerals in the Mulock granites were completely recrystallized during regional metamorphism and they now lack intergrown fluorite. Most of the fluorite is interstitial to recrystallized quartz and feldspar grains elongated parallel to the metamorphic layering.

Some fluorite occurs as inclusions in recrystallized quartz and some forms microscopic lenses that cut across recrystallized quartz and feldspar at a high angle to the metamorphic layering. These textural relationships suggest that the fluorite is a metamorphic mineral. Assuming that fluorite was originally intergrown with primary mafic minerals, the fact that all the fluorite is now a metamorphic mineral associated exclusively with recrystallized quartz and feldspar, suggests that primary fluorite broke down into ionic species, and F became mobile as a component of the metamorphic fluids. Fluorine shows a poor correlation with (Ce/ S m ) n ratios and a good correlation with (Tb/ Y b ) n ratios (Figs. 15a and 15b) for all the

217

P E T R O L O G Y A N D AGE O F T H E A - T Y P E M U L O C K G R A N I T E B A T H O L I T H

5001 I

I

I

I

I

I

I

I

I

• M E T A L U M I N O U S GRANITE o PERALUMINOUS G R A N I T E [] PERALKALINE GRANITE • APLITE DIKE -t-CONTAMINATED METALUMINOUS GRANITE

200

100

O

.'- 5 0 t0

u. C 0

"~- 20

E

to J

10

111 ta

I

I

I

Ce

Nd

Sm

I

I

I

I

Eu Gd

I

Tb

Yb

tu

Fig. 14. Chondrite-normalized rare earth element patterns of Mulock granites and aplites. The numerical designations refer to the sample numbers in Table 4.

Mulock granites analysed for both REE and F (Nos. 2, 4, 5, 7, 8 and 9, Table 4). Yttrium, which is commonly concentrated in fluorite (Collins et al., 1982) also shows the same correlations (Figs. 15c and 15d) with the exception of sample No.6. This sample contains the highest amount of fluorite and the highest total REE content of all the granites analysed, and its elevated Y content is consistent with concentration of Y in fluorite. The mobility of fluorine in the granites during metamorphism, coupled with the apparent correlations between F and the heavy REE, are consistent with fluorine-complexing of heavy REE in metamorphic fluids to cause disturbance of the heavy REE patterns. Such a process implies

that the heavy REE are preferentially concentrated in fluorite to levels exceeding about 100 times chondrite. REE analyses of the fluorite is therefore required before the viability of this process can be assessed. Geochronology

Zircon grains in sample K123 were isolated using standard heavy liquid and magnetic separation techniques. The grains characteristically contain abundant fluid and crystalline inclusions, but care was taken to carefully select grains for analysis that were euhedral, colourless, transparent prisms which contained little or no visible cracks and inclusions. The U - P b

2 18

S.B. L U M B E R S E T AL.

2000

I

I

I

I

2000

I

I

o5 o9 e2

1000

I

O5

b

09 II 2 e4

1000 04

"Q.E5 0 0

'E5oo D.

e10

Q.

Q10

07

u,,

07

O8

o8

100 1.0

I

I

I

I

I

2.0

3,0

4.0

5,0

6.0

100 0.0

I 1.0

I

J 1.4

I 1.2

80

I

I

/ 6

i 1.6

I

100

I

80

C

I 1.8

2.0

I

I

I

I

I

061

d

60

60 A

~: 40 a. o..

O9 211 0 5 3e eI

40

09

a. Q.

05

07

02 e3

>e4

o1

e4 20

20

elO

O10 o8

lO 1.0

I

(Tb/Yb)N

(Ce/Sm)N 100

i

I 2.0

I 3.0

I 4.0 (Ce/Sm)N

I 5.0

e8

I 6,0

10 0.0

1 1.o

I

I !.2

I

I I 1.4 (Tb/Yb)N

I 1.6

1

I 1.8

2.0

Fig. 15. Trace element variations between ( a ) F a n d ( C e / S m ) n , ( b ) F and ( T b / Y b ) n , (c) Y and ( C e / S m ) n , and ( d ) Y and ( T b / Y b ) n . N u m b e r e d points refer to the sample n u m b e r s in Table 4 and REE patterns in Fig. 14.

TABLE 5 U-Pb zircon results for the Mulock batholith (sample K 123 ) Description

1 +100, OM, Abr 2 +100. OM, Abr, inclusions 3 - 3 2 5 , OM, Abr

Concentration

Atomic ratios

Apparent ages (Ma)

weight U (mg) (ppm)

Pb (ppm)

common Pb 2°6pb/ (pg) z°4Pb

2°8pb/ 2°6pb

2°6Pb/ 23su

0.107 0.408

83 59

20 16

11 473

10,122 660

0.2493 0.2640

0.173

79

18

18

9,214

0.2276

2°Tpb/ 235U

2°Tpb/ 2O6pb

2O6pb/ 2O7pb/ 238U 235U

2OTpb/ 2O6pb

0.21168 2.3895 0.21023 2.3680

0.08187 0.08169

1238 1230

1240 1233

1242 1238

0.20160 2.2524

0.08103

1184

1198

1222

Sample description: grain size ( + 1 0 0 = > 100 mesh), magnetic susceptibility (OM = magnetic at 0 degrees side tilt), Abr=abrasion treatment (Krogh, 1982 ). Atomic ratios corrected for blank and common Pb.

data for the three zircon fractions from sample K123 are shown in Table 5 and Fig. 16. The high total common Pb and the low 2°6pb/2°4pb ratio for zircon fraction 2 in Table 5 reflects the presence of some inclusions in this fraction.

The three zircon analyses are 0.9%, 2.0% and 8.9% discordant, and a discordia line that passes through these three fractions defines an upper intercept age of 1244_+4 Ma (44% probability of fit ) with a lower intercept age of 533

219

PETROLOGY AN[) AGE OF THE A-TYPE MULOCK GRANITE BATHOLITH

.23

MUL OCH m

BA THOL I TH

\

1250

0_

.2] 1200

1150

.19

1244

+4/-3

Mo

1100

235

207

Pb/ .17

1.7

1

!.9

~

I

2.I

,

U

I

2.3

2.5

Fig. 16. U - P b concordia diagram for zircon fractions from sample K 123.

Ma. The physical features of the three zircons indicate that they are magmatic in origin and the 1244 Ma age is interpreted as the time of emplacement of the batholith.

Petrogenesis Metamorphism, which caused almost complete recrystallization of primary igneous minerals in the Mulock granites, hinders inferences concerning the intensive parameters, T, f H 2 0 and fO2, during crystallization of the batholith, and the nature of the source rocks. However, the low CaO and Mgo contents of the Mulock granites render them particularly suitable for comparisons with experimental work in the Q z - O r - A b - A n - H 2 0 system. In Fig. 17a, normative Qz-Ab-Or compositions of the granites and aplites form an array of points that parallels the trend of the plagioclase-alkali feldspar cotectic in the system {Ab-Or-Q}97 An3 at 1 kb of James and Hamilton ( 1969 ). This distribution suggests that all

the points are related by fractional crystallization. The alkalic granites and subalkalic metaluminous granites are the earliest and least evolved, and the aplites are the latest and most evolved, and probably formed by the crystallization of a residual magma. This sequence is also supported by the inferred field relationships described above. Other geochemical data cited above also suggest that the compositional variations observed within the batholith are due to fractional crystallization. Impoverishment of REE in the aplites can be explained by fractionation of allanite, zircon, titanite and apatite in the pre-aplite granite magmas. Alkali feldspar fractionation is suggested by the strong correlation of Ba and Sr data in Fig. 12, by an overall decrease in Ba/Sr ratios with increasing SiO2 (Table 3), and by the marked negative Eu anomalies shown by the more siliceous granites in Fig. 14. Additionally, a plot of Y/ Nb and Ba/La data for granites analysed for all of these elements (Tables 4 and A I ) trends

220

S.B. LUMBERS ET AL.

Qz

Qz

~bl/~

2 9 1.8

metoluminous

granites,

An s

9

• e

Ab

V

V

V

V

Or

Fig. 17. Normative (CIPW) quartz, albite and orthoclase data for Mulock granites and aplites in comparison to experimental work in the granite system. Solid curved lines in (a) represent the quartz-feldspar and orthoclase-plagioclase cotectics for [ A b - O r - Q z ] 97 An3 at 1 Kbar (James and Hamilton, 1969). The grids of minimum melting points over a range of pressures and Ab/An ratios in (a) and (b) are after Anderson and Cullers ( 1978 ). The field of highly differentiated leucogranites and aplites in (a) may provide a total pressure estimate representing crystallization conditions for the batholith. The field of poorly differentiated, subalkalic metaluminous granites in (b) may approximate the composition of an initial parent melt driven from crustal fusion and, hence, a total pressure estimate for the fusion.

parallel to the alkali feldspar fractionation trend of Eby (1990). Thus, alkali feldspar fractionation was apparently a major factor in bringing about the chemical variations observed within the batholith. Such fractionation is also consistent with the hypersolvus character of the original granites, as deduced from textural evidence (see p.000). The granites are enriched in fluorine (Table 3). In fluorine-rich A-type granite magmas, Ca-amphiboles are early crystalline phases, resulting in the magma becoming enriched in the alkali feldspar component, and, ultimately, peraluminous with progressive crystallization (Collins et al., 1982). Among the Mulock granites interpreted from field relations to be the oldest phases are ferrohastingsite-enriched, alkalic, metaluminous and peralkaline granites. Fer-

rohastingsite is either absent, or scarce, in all the other phases (i.e. see Table 2), which suggests that early fractionation of the ferrohastingsite (or some other primary Ca-amphibole precursor in the unmetamorphosed granites) played a role in fractionation of the magma into metaluminous, peraluminous and peralkaline granites. Alkali feldspar and amphibole fractionation is consistent with the narrow range of A / C N K and SiO2 data in Fig. 5. Only minor changes in such fractionation trends could shift the magma from metaluminous or peralkaline to marginally peraluminous. However, other chemical data vary considerably, particularly for the early alkalic granites (see Fig. 13 ). This suggests that processes other than fractional crystallization cannot be rejected for these

PETROLOGY AND AGE OF THE A-TYPE MULOCK GRANITE BATHOLITH

granites. Processes such as partial melting of a mixed source region (e.g. Whalen et al., 1987), different degrees of partial melting, or nonequilibrium melting and removal of successive batches of magma from a suitable source (e.g. Barker et al., 1975 ) could have contributed to the chemical variations observed in this alkalic part of the suite. The fact that the batholith was partly emplaced within the Grenville Front Tectonic Zone, where Archean and Proterozoic meta-igneous and metasedimentary rocks are juxtaposed, suggests that a mixed source region could have been involved in the genesis of the Mulock granites. Nevertheless, the evidence seems to point to alkali feldspar and amphibole fractionation as the dominant processes in bringing about the compositional variations observed within the batholith. The field of points in Fig. 17a lies on the feldspathic side of the ternary minima for Ab/ An ratios greater than 7.8. This disposition of points relative to the various ternary minima is similar to several other A-type granites produced by H20- undersaturated melts (e.g. Barker et al., 1975; Anderson and Cullers, 1978; Collerson, 1982). A relatively dry magma is also indicated by the hypersolvus character of the original granites because hypersolvus granites characteristically crystallize at high temperatures from relatively dry magmas in nearsurface environments (Martin and Bonin, 1976). Anderson and Cullers (1978) showed that the normative Qz-Ab-Or composition of extremely differentiated granites relative to a grid of minimum melting points over a range of pressure and Ab/An ratios derived from experimental work on the Q z - A b - O r - A n - H 2 0 system can be used to estimate pressure (and depth ) at which A-type granite plutons crystallized. Moreover, the composition of undifferentiated portions of A-type granite plutons that have changed little since fusion, can be used to estimate depth of fusion. In Fig. 17a, the position of the highly differentiated Mulock leucogranite and aplite field relative to the grid of

221

Anderson and Cullers (1978) suggests that crystallization occurred at less than 2 kb ( < 7.6 km). This estimated pressure is consistent with the inferred hypersolvus nature of the original granites. The normative An content of this field averages 1.2. Subalkalic metaluminous biotite granites (Table 1, Fig. 17b) may be the most undifferentiated granites of the batholith because: ( 1 ) they are at least partly younger than the alkalic granites but older than the highly differentiated granites; (2) they show the highest average normative An content (5.9); (3) they contain the most calcic plagioclase; and (4) they are relatively low in SiO2 (Table 3 ). The compositional field of these granites in Fig. 17b is consistent with magma generation at pressures of 7 to 10 kb (27 to 36 km). These pressure estimates of crystallization and magma generation are similar to those given by Anderson (1983) for a variety of Proterozoic A-type granite plutons. If crystallization of the batholith occurred at less than 2 kb, then, conceivably, volcanism may have accompanied the plutonism. No unequivocal volcanic rocks related to the batholith are known, possibly because such rocks were removed by tectonic uplift and erosion. However, the fine-grained, quartzo-feldspathic gneisses present in the host rocks in the vicinity of the satellitic intrusions (see p.202) are possible candidates. Most studies of A-type granite petrogenesis (e.g. Barker et al., 1975; Collins et al., 1982; Anderson, 1983; Whalen et al., 1987; Creaser et al., 1991 ) favour melt production by high temperature ( > 9 0 0 ° C , Clemens et al., 1986; Creaser and White, 1991 ) partial melting of relatively anhydrous lower crustal source rocks. Geochemical properties of the Mulock granites also favour such a process over other mechanisms of granite magma production. Rb and Sr contents of the Mulock granites and trends shown by the trace element data (e.g. Figs. 10 and 11 ) are inconsistent with derivation of the granites by differentiation from Ior S-type granite melts. Moreover, low con-

222

tents of V, Cr and Ni (Table AI ) point to more felsic than mafic sources that produce M- and I-type granites. Differentiation processes related either to plutonic emplacement (e.g. Taylor et al., 1980; Martin and Bonin, 1976), or to external sources (e.g. Currie et al., 1988) and crust-mantle interactions (e.g. Bailey, 1978 ) fail to account for all the elemental ratios and systematic chemical variations common to both the Mulock granites and A-type granites in general (Collins et al., 1982; Anderson, 1983; Jackson et al., 1984; Whalen et al., 1987). That the Mulock granites were not derivatives of M-, I-, or S-type melts suggests that their major chemistry may reflect their source rock major chemistry. Except for the aplites and some highly differentiated leucogranites (Fig. 17a ), which probably formed by crystallization from a residual magma, all the granites share the following major chemical attributes: (1) high F e O / F e O + M g O and K 2 0 + N a , O / C a O ratios; (2) enrichment in highly charged cations, such as REE, Nb, Y and Zr; (3) enrichment in Ga and Zn; and (4) crystallization from relatively dry, high temperature, F-enriched magma. These attributes suggest that the source rocks were sufficiently geochemically evolved to produce a melt enriched in lithophile elements and not depleted in a granitic melt fraction. Highly aluminous source rocks, such as previously dehydrated shaley metasediments, which could melt to produce mainly peraluminous, two-mica Atype granites (e.g. Anderson and Thomas, 1985) are unlikely parents for the predominantly metaluminous Mulock granites. As discussed above, the mildly peraluminous granites present in the batholith can be explained by fractional crystallization. Anderson ( 1983 ) and Creaser et al. ( 1991 ) showed that vapourabsent, high-temperature partial melting of tonalitic to granodioritic igneous rocks not previously metamorphosed to the granulite facies could produce A-type granite with all the major geochemical attributes of the Mulock

S.B. LUMBERS ET AL.

granites. However, anhydrous felsic granulite and granulite facies rocks of tonalitic to granodioritic composition could also be suitable sources, providing they have not undergone melt depletion. Residual sources involving felsic granulite that had previously generated a granitic melt (e.g. Collins et al., 1982), fail to account for the high K 2 0 + N a 2 0 / C a O ratios of the Mulock granites and of A-type granites in general (Creaser et al., 1991 ). Superimposed regional metamorphism altered the primary distribution of some of the more mobile trace elements in the Mulock granites, particularly Rb and F. This trace element mobility reduces the likelihood that measurements of SrS6/Sr 87 initial ratios on whole-rocks would give meaningful constraints on the source rock isotopic composition. The only unequivocal, relic igneous minerals present in the granites, zircon and the clear mesoperthite cores present in augen of the coarser-grained granites, could potentially contain information on primary igneous isotopic ratios. Discussion

Major chemical attributes of the Mulock granites indicate that they crystallized from magma formed by high temperature, anhydrous partial melting of a lower crustal tonalitic to granodioritic source, or felsic granulite. A mixed source region is possible, but the source rocks did not undergo previous melt depletion. I-type granitic rocks of the Ingall Lake batholith (Lumbers, 1971b, c, 1978) form a major component of the Archean crust just north of the Mulock batholith in both the Superior and Grenville Provinces. The trondhjemite to monzogranite composition of the batholith makes it a possible source rock candidate for the Mulock magmatism, but its subsurface extent within the Grenville Province is unknown. Proterozoic anorthosite-mangerite-charnockite-granite (AMCG) suite rocks were emplaced in the same metasedimentary

PETROLOGY AND AGE OF THE A-TYPE MULOCK GRANITE BATHOLITH

accumulation that hosts the Mulock batholith. Felsic members of the AMCG suite could also be possible source rock candidates for the Mulock magmatism, but subsurface extents and emplacement ages of the suite are unknown. Anorthosite of the suite forms dikes in the Mulock batholith (Fig. 1 ), so at least some of the suite is younger than the batholith. The thickest and most extensive rock succession in the region is the metagreywacke accumulation that hosts the Mulock batholith. These metasediments were derived from the adjacent Archean terrain rich in I-type granitic plutonic rocks, mafic and felsic metavolcanics and subordinate volcaniclastic deposits (Lumbers, 1978). The chemical composition of the metagreywacke is grossly similar to tonalite and trondhjemite (Lumbers, unpublished data), but further geochemical data are required to assess these rocks as a possible source for the Mulock magmatism. A.P. Dicken (person. commun., 1990) obtained a preliminary S m - N d depleted mantle model age from one of the metaluminous subalkalic Mulock granites (MS-9, Table 1A). The TDM is 2360 Ma, with a ENd o f - 11.1. This age is markedly older than the 1244 Ma U - P b zircon emplacement age. Additional Sm and Nd isotopic analyses are required to assess the 2360 Ma result, but involvement of Archean a n d / o r Early Proterozoic rocks during one or more stages of the batholith's evolution seems indicated. Loosveld and Etheridge (1990) analysed several lower crustal melting models and concluded that a thermal anomaly of sufficient energy and duration is best produced by convective thinning of the mantle lithosphere during progressive, homogeneous crustal thickening. Lithospheric extension is accompanied by asthenospheric upwelling and results in a second order effect, mantle melting and the rise of mafic magma to underplate and intrude the crust. Anderson ( 1987 ) and Hoffman ( 1989 ) devised lower crustal melting models that involve large-scale convective mantle upwelling thousands of kilometres in diameter, caused by

223

the insulating effect of a stationary Proterozoic supercontinent. According to these models, invasion and ponding of mantle melts in the crust caused anhydrous partial melting of the lower crust. The models help to explain the spatial association of anorthositic rocks with several A-type granites. The chronology of plutonic, tectonic and metamorphic events in the region is insufficiently constrained to assess the suitability of these heat source models for generating the Mulock magma. However, the anorthositic dikes present in the batholith (Fig. 1 ) could conceivably be a product of a large pool of mafic magma that invaded and ponded in the lower crust (C.F. Anderson, 1987; Hoffman (1989). This magma could have heated the lower crust to generate the Mulock granites before differentiating anorthosite to be intruded into the granites. The dikes underwent the same metamorphic history as their enclosing granites and could therefore be only slightly younger. Moreover, small anorthosite stocks and several small bodies of ultramafic rock present in the metasedimentary host rocks to the north of the batholith (Lumbers, 197 lb, c) could also be products of this same mafic magmatism. Available gravity data (Gupta and Wadge, 1980) show that a mild positive gravity anomaly is centred over the anorthositic stocks and that a much larger, more intense, regional positive anomaly is centred about 60 km west of the batholith. This anomaly, which could be due to a large mass of mafic igneous rocks in the subsurface, has associated granite plutons of possible A-type affinity. Precise age dating of the anorthosite dikes and the other mafic intrusions would help in testing this hypothesis. Recently, a few precise U - P b ages have been reported from anorthosites that are part of large massifs in the Grenville Province of Quebec (Machado and Martignole, 1988; Higgins, 1989; Emslie and Hunt, 1990). These ages, combined with evidence of anorthosite emplacement between 1.29 and 1.25 Ga within the CMB (Lumbers et al.,

224

1991) suggest that anorthositic magmatism was indeed active in the Grenville Province over a time interval that includes the emplacement age of the Mulock batholith. Geochronological studies of A-type granites summarized by Anderson (1983), together with more recent age data indicate four major episodes of Proterozoic A-type granite magmatism within the North American craton; 1.6 to 1.8 Ga, 1.41 to 1.49 Ga, 1.34to 1.41 G a a n d 1.05 to 1.17 Ga. If Anderson (1987) and Hoffman ( 1989 ) are correct and large-scale mantle upwelling is the cause of these magmatic episodes, there may be a fifth episode. Indications of this episode are the widely separated 1.24 to 1.25 Ga Mulock, and CMB plutons in Ontario, the Strange Lake pluton in Labrador and the College Hill pluton in the Green Mountains of Vermont (Aleinikoff et al., 1990). Some isotopic evidence suggests that early deformation and metamorphism occurred along the Grenville Front Tectonic Zone (GFTZ), possibly as early as latest Archean or earliest Proterozoic time (Krogh and Davis, 1969b; Krogh, pers. commun., 1989 ). The facts that the batholith and its host rocks are deformed and recrystaUized by regional metamorphism and that the intensity of deformation shown by all of these rocks increases

S.B. LUMBERS ET AL.

toward and within the GFTZ, show conclusively that there was a late major deformation along the GFTZ after 1244 Ma. Green et al. (1988) also concluded that intense deformation occurred along the GFTZ in the Sudbury region after 1.24 Ga because diabase dikes of the 1.24 Ga Sudbury swarm were deformed.

Acknowledgements The geochemical portion of this study was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) operating grant (No. A5539) to NDM. Assistance in establishing a neutron activation analysis laboratory used in this study was provided by C. Pride and I.L. Gibson. Field assistance was provided to S.B. Lumbers by The Ontario Geological Survey. We thank D.W. Davis and J. Lawford Anderson for comments on early drafts of this paper and many helpful suggestions. We acknowledge two anonymous referees for critically reading the manuscript and suggesting several improvements in organization and presentation. We also acknowledge the assistance of M. Coutinho in preparing and typing the manuscript.

Nb Zr Y Sr Rb Ba Ga Pb Zn Cu Ni Cr V

FeO

Fe203

SiO2 TiO2 AI203 Fe203 c MnO MgO CaO Na20 K20 P205 LOI d Total

9 445 17 129 96 1261 19 5 36 7 1 9 7

67.98 0.51 15.24 0.96 0.04 0.78 0.66 4.71 6.06 0.05 0.55 97.54

I1 482 21 217 87 1536 22 25 58 11 8 9 4

69.03 0.51 15.16 3.60 0.06 0.33 1.30 4.67 5.06 0.06 0.39 100.17

13 315 16 234 62 2146 21 22 43 10 3 6 10

1.26 1.47

1.58 2.04 33 409 37 217 94 1165 25 25 69 10 5 8 6

68.66 0.45 15.48 2.98 0.04 0.44 0.80 5.57 5.01 0.11 0.36 99.90

MA-4

68.20 0.54 14.85 3.87 0.06 0.40 1.26 4.30 5.21 0.12 0.38 99.10

MA-3

MA-1

Sample b

MA-2

Metaluminous alkalic granite

Type:

36 327 33 270 113 1493 23 31 78 10 6 8 16

1.76 2.14

68.24 0.62 14.27 4.00 0.07 0.65 1.26 4.45 4.80 0.12 0.51 99.05

MA-5

21 352 23 328 106 1557 30 25 89 10 5 II 18

-

66.87 0.76 14.46 4.90 0.08 0.81 1.86 4.55 4.84 0.17 0.38 99.68

MA-6

19 330 24 256 74 1702 24 27 67 9 3 6 21

0.88 2.63

69.04 0.46 14.25 3.80 0.05 0.45 1.03 5.03 5.05 0.07 0.45 99.68

MA-7

5 500 20 192 83 1205 25 25 55 11 3 7 3

-

-

69.94 0.62 13.99 4.38 0.06 0.33 1.09 4.12 5.14 0.08 0.37 100.12

MI-I

Metaluminous Intermediate granite

27 346 29 248 106 1515 26 26 74 9 3 6 3

69.74 0.60 14.12 4.07 0.07 0.50 1.29 4.77 4.68 0.10 0.19 100.13

M1-2

35 392 36 253 149 1234 25 27 86 10 4 7 4

69.17 0.77 13.78 4.01 0.08 0.95 1.58 4.37 4.59 0.23 0.57 100.10

MS-1

32 355 30 258 157 1266 24 32 87 10 6 8 4

2.15 2.32

68.28 0.73 13.65 4.64 0.08 0.69 1.57 3.86 4.89 0.14 0.43 98.96

MS-2

28 336 28 253 139 1205 26 24 79 9 3 7 1

69.56 0.72 14.15 3.55 0.08 0.66 1.63 4.55 4.44 0.10 0.29 99.73

MS-3

Metaluminous subalkalic granite

t~ bO

ot"

> z

o

C

,-<

,>

0 .-q

c~

.7

TABLE A 1

Major and trace element data a

o c~ .<

Appendix

0

,.~

Nb Zr Y Sr Rb Ba Ga Pb Zn Cu Ni Cr V

Fe203 FeO

SiO2 TiO2 A1203 Fe203 c MnO MgO CaO Na20 K20 P205 LOI d Total

23 299 27 252 133 1330 24 27 86 10 4 9 19

1.37 3.48

68.69 0.82 13.23 5.28 0.08 0.85 1.75 3.93 4.47 0.19 0.20 99.49

20 271 24 261 129 1324 24 29 75 10 2 9 15

-

69.27 0.73 13.98 4.80 0.07 0.68 1.69 4.14 4.35 0.18 0.24 100.13

16 284 24 244 119 1226 26 24 81 10 3 11 17

1.34 3.17

68.56 0.86 13.44 5.25 0.08 0.81 1.90 4.03 4.32 0.22 0.65 100.12

MS-6

MS-4

Sample: b MS-5

Metaluminous subalkalic granite

Type:

TABLE A1 (continued)

29 349 22 231 186 151 24 26 59 10 5 8 5

1.68 0.92

71.54 0.41 13.99 2.70 0.05 0.27 0.90 4.41 5.05 0.03 0.55 99.90

MS-7

28 325 29 103 158 573 23 27 68 10 6 7 5

-

73.13 0.31 12.76 2.86 0.04 0.18 0.67 4.48 4.70 0.01" 0.19 99.33

MS-8

32 380 30 282 99 1383 25 31 86 11 8 10 15

1.76 2.14

68.63 0.67 13.98 4.14 0.08 0.80 1.68 4.00 4.59 0.15 0.19 98.91

MS-9

20 293 21 201 97 1099 24 23 61 9 3 7 n.d.

1.96 1.69

70.61 0.55 13.76 3.83 0.06 0.49 0.94 5.13 4.18 0.09 0.20 99.84

MS-10

18 366 20 188 110 1208 27 23 73 9 4 9 6

1.10 2.92

69.96 0.61 14.03 4.34 0.07 0.53 1.27 4.33 4.79 0.10 0.09 100.12

MS-11

24 339 33 309 129 1334 24 28 47 3 8 10 64

1.54 1.40

70.02 0.57 13.99 3.10 0.03 0.67 1.87 3.21 5.37 0.20 1.19 100.06

MS-12

27 580 27 163 132 1100 27 29 79 11 7 9 17

2.07 2.24

68.62 0.50 14.30 4.55 0.04 0.60 0.32 4.53 5.21 0.04 0.49 99.20

PA-1

36 466 38 333 104 1587 29 24 71 10 5 9 14

2.76 2.69

64.69 0.92 14.72 5.74 0.08 0.83 2.50 4.69 4.55 0.26 1.17 100.15

PA-2

24 325 26 252 90 1831 26 24 69 9 5 8 13

1.38 1.74

69.04 0.49 15.29 3.31 0.07 0.53 1.08 4.09 5.70 0.09 0.47 100.16

PA-3

Peraluminous alkalic granite

t'-.~ bJ

Nb Zr Y Sr Rb Ba Ga Pb Zn Cu Ni Cr V

FeO

Fe203

SiO2 TiO2 A1203 Fe203 c MnO MgO CaO Na20 K20 P205 LOI d Total

24 298 21 111 92 553 28 29 37 12 7 9 5

71.32 0.25 13.99 2.92 0.02 0.17 0.33 4.81 5.60 0.01 0.28 99.07

16 436 26 245 71 1358 26 27 76 10 4 10 18

67.96 0.57 14.40 4.33 0.07 0.95 1.27 4.07 5.03 0.13 0.70 99.48

21 318 20 174 149 1127 23 24 63 9 5 9 10

0.94 2.29

70.55 0.44 14.30 3.48 0.06 0.33 1.15 4.41 4.85 0.05 0.53 100.15

PI-3

PI-I

Sample: b PI-2

Peraluminous intermediate granite

Type:

TABLE AI (continued)

36 335 29 104 94 515 26 30 54 10 7 10 6

74.14 0.39 12.30 2.85 0.04 0.49 0.34 3.91 4.74 0.15 0.66 100.01

PS- 1

12 215 10 84 91 325 23 26 23 9 2 5 3

0.74 0.81

74.37 0.18 12.78 1.64 0.01 0.06 0.14 3.66 5.90 0.07 0.29 99.10

PS-2

22 222 22 133 122 680 22 24 52 9 4 6 6

0.93 0.95

75.04 0.23 12.94 1.99 0.03 0.18 0.42 4.32 4.66 0.09 0.29 100.19

PS-3

0.68 1.62

73.75 0.32 13.41 2.48 0.03 0.24 0.53 3.99 5.05 0.04 0.27 100.11

PS-4

11 234 17 151 94 776 20 54 202 9 3 5 7

Peraluminous subalkalic granite

6 132 8 157 209 569 19 22 24 9 4 6 8

-

73.87 0.21 13.53 1.35 0.02 0.17 0.43 4.44 5.22 0.05 0.37 99.66

PS-5

11 274 14 141 153 689 21 29 40 10 5 6 4

-

75.03 0.34 12.89 2.15 0.02 0.23 0.50 3.68 5.19 0.12 0.09 100.24

PS-6

19 151 14 70 192 286 27 35 37 n.d. 5 n.d. 5

0.53 0.77

75.34 0.16 13.02 1.39 0.01 0.11 0.65 3.68 5.47 0.02 0.30 100.06

PS-7

21 370 21 299 118 1443 24 26 58 10 4 8 21

1.57 2.30

69.07 0.70 14.77 4.13 0.06 0.69 1.55 4.21 4.54 0.11 0.29 100.12

PS-8

11 202 13 160 97 679 19 24 26 9 4 5 9

1.11 0.71

74.46 0.18 12.90 1.90 0.02 0.09 0.43 4.23 5.02 0.10 0.28 99.61

PS-9

,q

c) ©

z

tO c~

©

7~

23 472 28 184 117 1229 29 26 77 10 5 8 4

2.31 1.81

67.77 0.50 14.37 4.32 0.08 0.43 1.09 5.65 5.18 0.05 0.36 99.80

27 168 25 65 137 167 22 33 40 10 7 6 6

76.55 0.09 12.25 1.48 0.02 n.d. 0.28 4.71 4.30 0.03 0.48 100.19

a

Oxides in wt.%, trace elements in ppm. See Table 4 for REE data. b For location of samples see Fig. 1. Total iron expressed as Fe203. d Loss on ignition. e Not detected.

52 609 39 83 99 503 29 31 93 11 6 8 n.d.

-

Fe203 FeO

Nb Zr Y Sr Rb Ba Ga Pb Zn Cu Ni Cr V

70.53 0.49 12.94 4.88 0.08 0.11 0.69 4.53 5.16 0.01 0.35 99.77

SiO2 TiO2 A1203 Fe203 c MnO MgO CaO Na20 KzO P205 LOI d Total

27 377 24 96 79 523 25 19 33 9 2 6 3

72.00 0.36 12.44 3.61 0.03 0.32 0.36 4.19 5.22 0.03 0.47 99.03

PaS-2

5 52 16 40 104 89 23 31 15 8 4 5 3

0.01 0.11

0.69 0.96 21 266 35 43 145 146 26 25 48 8 5 6 7

76.41 0.01 12.99 0.14 n.d. n.d. 0.03 5.76 4.50 0.09 0.17 100.10

A-l

Aplite dikes

74.98 0.12 12.55 1.75 0.02 n.d 0.14 4.87 4.77 0.09 0.25 99.54

PaS-3

PaS-1

PaA-I

Sample: b

PaA-2

Peralkaline subalkalic granites

Peralkaline alkalic granites

Type:

TABLE AI (continued)

39 170 24 91 143 75 23 31 14 9 3 4 n.d.

0.62 0.22

75.40 0.06 12.84 0.86 0.01 n.d. 0.33 4.06 5.32 0.07 0.19 99.14

A-2

4 137 7 1451 65 2281 17 20 41 8 10 52 28

0.63 1.26

68.25 0.24 15.81 2.03 0.02 1.10 1.76 4.63 5.74 0.10 0.80 100.34

C-1

8 113 16 1529 56 1729 17 22 42 12 11 47 40

1.26 0.87

67.15 0.26 16.13 2.23 0.03 1.33 1.77 3.92 5.58 0.10 1.10 99.60

C-2

Contaminated granite

E'-

P~

~z

t,.,}

P E T R O L O G Y A N D AGE O F T H E A-TYPE M U L O C K G R A N I T E B A T H O L I T H

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231

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