Growth of granite–greenstone terranes at convergent margins, and stabilization of Archean cratons

ELSEVIER

Tectonophysics 305 (1999) 43–73

Growth of granite–greenstone terranes at convergent margins, and stabilization of Archean cratons Timothy M. Kusky a,Ł , Ali Polat b b

a Boston University, Center for Remote Sensing, 725 Commonwealth Ave., Boston, MA 02215, USA Department of Geological Sciences, University of Saskatchewan, now at Max-Plank Institut fu¨r Chemie, Postfach 3060, 55020 Mainz, Germany

Received 3 April 1998; accepted 27 July 1998

Abstract Archean granite–greenstone terranes represent juvenile continental crust formed in a variety of plate tectonic settings and metamorphosed through a complex series of structural and magmatic events. Most Archean granite greenstone terranes appear to have acquired their first-order structural and metamorphic characteristics at convergent plate margins, where large accretionary wedges similar in aspect to the Chugach, Makran, and Altaids grew through offscraping and accretion of oceanic plateaux, oceanic crustal fragments, juvenile island arcs, rifted continental margins, and pelagic and terrigenous sediments. Buoyant slabs of parts of Archean oceanic lithosphere may have been underplated beneath these orogens, forming thick crustal roots characterized by interleaving between the depleted slabs and undepleted asthenosphere. Back-stepping of the subduction zones after accretion of plateaux and arcs caused the arcs magmatic fronts to migrate trenchward through the accretionary wedges. Dehydration of the subducting slabs hydrated the mantle wedges below the new arcs and generated magmas (sanukitoid suite) in the mantle wedge, whereas other magmas (tonalite, trondhjemite, granodiorite or TTG suite) appear to have been generated by melting of hot young subducted slabs. Eventual collision of these juvenile orogens with other continental blocks formed anatectic granites, then thickened the crust beyond its ability to support its own mass, which initiated gravitational collapse and decompressional release of syn- to late-tectonic granitoids from wedges of fertile mantle trapped between underplated oceanic lithospheric slabs, and aided in the cratonization of the granite–greenstone terranes. Deeply penetrating structural discontinuities such as shear zones and sutures provided pathways for fluids and granitoids to migrate into the mid- and upper-crust, forming ore deposits and plutons. Most preserved granite–greenstone terranes have been tectonically stable since the Archean, and form the cratonic interiors of many continents.  1999 Elsevier Science B.V. All rights reserved. Keywords: Archean; greenstone belt; granites; tectosphere; cratons; ophiolite

1. Introduction Understanding the origin of stable continental cratons hinges upon recognizing which processes Ł Tel.:

C1 617 353 4247; Fax: C1 617 353 3200; E-mail: [email protected]

change the volume and composition of continental crust with time, and how and when juvenile crust evolved into stable continental crust. The evidence from the preserved record suggests that the preserved continental landmass has been growing since the early Archean, although the relative rates and mechanisms of crustal recycling and crustal growth

0040-1951/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 1 9 5 1 ( 9 9 ) 0 0 0 1 4 - 1

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T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

are not well known, and have been the focus of considerable geological debate (e.g., Fyfe, 1978; Dewey and Windley, 1981; Armstrong, 1991; McCulloch and Bennett, 1994; Taylor and McLennan, 1995). The oldest rocks known on the planet are the circa 4.0-Ga Acasta gneisses (Bowring et al., 1989, 1990) from the Anton terrane of the Slave Province (Kusky, 1989). The Acasta gneisses are chemically evolved, and show trace and REE patterns similar to rocks formed in modern supra-subduction zone settings (Bowring et al., 1989, 1990). Maruyama et al. (1991) and Komiya et al. (1999) suggest that the oldest known sedimentary sequence (the circa 3.8-Ga Isua supracrustal assemblage) is an accretionary complex. A few circa 4.2-Ga zircon grains have been found

(e.g., Froude et al., 1983), but it is not clear if these were ever parts of large continental land masses. Rudnick (1995) estimates that approximately half of the present mass of continental crust was extracted from the mantle during the Archean. Exposed portions of the Archean lithosphere (Fig. 1) are broadly divisible into two main categories (e.g., Goodwin, 1996). The first are the ‘granite–greenstone’ terranes, containing variably deformed assemblages of mafic volcanic=plutonic rocks, metasedimentary sequences, remnants of older quartzo-feldspathic gneissic rocks, and abundant late granitoids. The second main class of preserved Archean lithosphere is found in the highgrade quartzo-feldspathic gneiss terranes. Relatively

Fig. 1. World map showing distribution of Archean cratons and areas underlain by Precambrian crust (compiled from: Unesco, 1976; Condie, 1981; Hoffman, 1989, 1997; Abbott and Mencke, 1990; Goodwin, 1991, 1996; de Wit and Ashwal, 1997). Cratons labelled as follows: 1 D Slave Province, 2 D Superior, 3 D Wyoming, 4 D Kaminak (Hearne), 5 D North Atlantic (Nain, Godthaab, Lewisian), 6 D Guiana, 7 D Central Brazil (Guapore), 8 D Atlantic (Sa˜o Francisco), 9 D Ukranian, 10 D Baltic (Kola), 11 D Aldan, 12 D Anabar, 13 D Sino–Korean, 14 D Tarim, 15 D Indian, 16 D Pilbara, 17 D Yilgarn, 18 D Gawler, 19 D Kaapvaal, 20 D Zimbabwe, 21 D Zambian, 22 D Angolan, 23 D Kasai, 24 D Gabon, 25 D Kibalian, 26 D Uweinat, 27 D Liberian, 28 D Maritanian, 29 D Ouzzalian, 30 D Napier Complex, 31 D Prince Charles Mountains, 32 D Vestfold Hills, 33 D Heimefront Ranges, 34 D deeply buried Archean rocks of the East European Shield, 35 D Tajmyr.

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

little deformed and metamorphosed cratonic cover sequences are found over and within both types of Archean terrain, but are especially abundant on southern Africa’s Kaapvaal craton (Fig. 1, Brandl and de Wit, 1997). Also included in this category are some thick and laterally extensive carbonate platforms similar in aspect to Phanerozoic carbonate platforms (e.g., Grotzinger, 1989; Danielson and Kaufman, 1996) indicating that parts of the Archean lithosphere were stable, thermally subsiding platforms (Kusky and Hudleston, in press). In this contribution we focus on describing the tectonic setting of juvenile Archean rocks from Archean granite–greenstone terranes to understand mechanisms of continental growth, and we look at processes that converted these juvenile terranes into mature continental crust. Insight into these processes will contribute to our understanding of why Archean granite–greenstone terranes form the stable cratonic cores of many continental interiors (Fig. 1). Although we recognize the importance of processes including impact melting in the earliest Archean, sub-continental plume and hot-spot related magmatism, these processes typically involve significant reworking of older crust with variable amounts of juvenile magmatic additions to the continental landmass, and they probably involve relatively little new addition of mass to the continents (but see McKenzie and Bickle, 1988 for an alternative view). The small size of Archean continents probably allowed most plumes to be diverted to their edges (e.g., Gurnis, 1988) where they would form oceanic plateaux that are preserved abundantly in the geological record. Here, we examine convergent margin processes from Archean granite–greenstone terranes, including accretion of juvenile island arcs, oceanic plateaux, collapsed back-arc basins, oceanic crust, and migration of arc=trench systems through accreted magmatic and sedimentary sequences. We approach this synthesis by emphasizing specific, well-documented examples of each type of process from different cratons, emphasizing the Superior, Slave, Yilgarn, and Zimbabwe cratons. We also compare these processes to those of Proterozoic and Phanerozoic orogens to arrive at a general synthesis of the processes that enable juvenile crust of granite–greenstone terranes to form the cratonic cores of so many continents.

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2. Mechanisms of growth of juvenile crust at convergent margins 2.1. Juvenile island arc accretion Many Archean granite–greenstone terranes are interpreted as juvenile island arc sequences that grew above subduction zones, and later amalgamated during collisional orogenesis to form new continental crust (Burke et al., 1976; de Wit and Ashwal, 1986, 1997; Park, 1991; Kiyokawa and Taira, 1995). The island arc model for the origin of the continental crust is supported by geochemical studies, which show that the crust has a bulk composition similar to arcs (e.g., Taylor and McLennan, 1995; Rudnick, 1995). As emphasized by Hamilton (1988, 1998), island arcs are extremely complex systems that may exhibit episodes of distinctly different tectonics, including accretion of ophiolite fragments, oceanic plateaux, intra-arc extension with formation and preservation of back-arc and intra-arc basins (e.g., Saleeby, 1992; Aitchison and Flood, 1994; Tardy et al., 1994; Stern et al., 1995a,b; Vergara et al., 1995; Xue et al., 1996; O’Brien et al., 1997). Many juvenile arcs evolve into mature island arcs in which the magmatic front has migrated through its own accretionary wedge, and many evolve into continental margin arcs after they collide with other crustal fragments or continental nuclei. The Schreiber–Hemlo greenstone belt is located in the northeastern section of the greenstone– granitoid Wawa subprovince of the Superior Province, which extends from the Vermilion district of Minnesota in the west to the Kapuskasing structural zone in the east (Fig. 2; Williams et al., 1991). The belt is composed of ca. 2750–2695 Ma mafic to felsic volcanic, 2720–2690 Ma mafic to felsic intrusive, and 2705–2697 Ma siliciclastic sedimentary (turbidite) rocks (Fig. 3; Table 1; Corfu and Muir, 1989a; Corfu, 1989b; Williams et al., 1991; Fralick, 1997). Field relations indicate that both turbidites and volcanic sequences are faultbounded (Polat et al., 1998). The Schreiber–Hemlo greenstone belt terrane is typical of many proposed Archean island arc terranes, and also shows evidence for accretion of oceanic fragments, and migration of the magmatic front through the subduction=accretion complex. These processes are discussed in detail

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T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

Fig. 2. (a) Subprovince map of the Superior Province (modified after Card, 1990). (b) Simplified geological map of the study area, showing the location of the Schreiber–Hemlo belt (modified after Williams et al., 1991). LSHFZ D Lake Superior–Hemlo fault zone. Open rectangle shows the location of Fig. 2. TTG D tonalite–trondhjemite–granodiorite.

here, as an example of the complexities of juvenile island arc accretion in the Archean, obscured by later significant geological events. Volcanic rocks consist mainly of tholeiitic pillow basalts, and 10-cm to 1.5-m-thick tholeiitic basalt

flows, komatiites and komatiitic basalts with well preserved spinifex texture, and tholeiitic and calcalkaline basalts to rhyolites. There are minor cherts, iron formations, and gabbros within these mafic– ultramafic volcanic sequences. Chert layers, banded

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73 47

Fig. 3. Geological map of the Santoy Lake–Middleton area of the Schreiber–Hemlo greenstone belt. The northern part of the map is modified from Walker (1967). HW17 D Highway 17; CPR D Canadian Pacific Railroad.

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Table 1 Summary of the lithological, geochronological, geodynamic, and structural characteristics of the Schreiber–Hemlo greenstone belt (from Polat et al., 1998) Lithological unit(s)

Age (Ma)

Interpreted geodynamic setting

Origin

Tectonostratigraphic nature

Deformation Block–matrix relations phase

Komatiites, Mgto Fe-tholeiites and tholeiitic gabbros

2750–2700

Oceanic plateau(s)

Mantle plumes

Allochthonous

D1 ,D2 ,D3

Siliciclastic turbidites

2705–2697

Convergent margin

Island arc trench

Allochthonous

D1 ,D2 ,D3

Tholeiitic to calc-alkaline basalts to rhyolites TTG plutons

2720–2695

Oceanic island arc

Slab to wedge melting

Autochthonous to allochthonous

D1 ,D2 ,D3

2720–2690

Magmatic arc

Slab melting

Autochthonous

D2 ,D3

Mafic to felsic sills and dykes

2690–2680

Magmatic arc

Slab to wedge melting

Autochthonous

D2 ,D3

Lamprophyres

2680–2674

Accretion-related extension

Lithospheric mantle

Authochthonous

D3 ,?

iron formations and pillar basalts suggest a marine origin for these volcanic sequences (see Isozaki et al., 1990; Thurston, 1990; Ohta et al., 1996). The geochemistry of tholeiitic basalts and associated komatiites suggests an intra-oceanic (oceanic plateau) geodynamic setting (Table 1; Polat et al., 1996a, 1998). Other units of tholeiitic and calc-alkaline basalts to rhyolites have geochemical characteristics of intra-oceanic arcs (Table 1; Polat et al., 1998). Plateau and arc basalts cannot be distinguished in the field. Both volcanic and sedimentary tectonic sequences are intruded by syn-kinematic, slabderived high-Al, high La=Ybn tonalite–trondhjemite–granodiorite (TTGs; see Martin, 1986; Drummond and Defant, 1990; Kerrich et al., 1996), and

Exotic blocks of ocean plateau basalts in matrix of sheared turbidites. Native blocks of gabbros in matrix of sheared basalts Exotic(?) or native blocks of ryolites in matrix of sheared turbidites Exotic blocks of ryolites in matrix of sheared ocean plateau basalts No block–matrix relations observed Native blocks of tonalites and gabbros in matrices of sheared turbidites and basalts No block–matrix relations observed

subduction-derived gabbroic sills and dikes. Collectively these lithological sequences are cut by late kinematic, ca. 2680–2674 Ma lamprophyre dikes (Fig. 4; Table 1). Sedimentary rocks consist of interbedded, distal turbiditic greywacke sandstones, siltstones, and shales, with minor black chert layers (Walker, 1967; Purdon, 1995; Polat et al., 1998). The thickness of turbidite beds ranges from a few centimeters to one meter. Sandstones tend to be more abundant and thicker than inter-bedded shales and siltstones. Conglomerates are minor, and occur primarily in turbidite channels. Primary sedimentary structures (e.g., parallel bedding, cross-bedding, grading) are intensely deformed throughout the belt (Figs. 3

Fig. 4. Interpreted geological cross-sections corresponding to field traverses from the Steel Lake (A–A0 ) and Ripple Lake (B–B0 ) areas. Inset diagrams are based on detailed field observations. For locations see Fig. 3. For purposes of illustration the sizes of transposed folds are exaggerated. Arc-derived distal turbidites and oceanic plateau fragments were tectonically juxtaposed and imbricated by D1 thrust faults. These thrust faults were overprinted by, and reactivated as, strike-slip faults during D2 . Both sedimentary and volcanic units underwent intense transposition, tectonic wedging, fragmentation, and mixing during D1 and D2 , forming broken formations and tectonic melanges.

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and 4; Kuhns et al., 1994; Polat et al., 1998). Petrographic observations and high-precision ICP–MS trace element data suggest a magmatic arc provenance for these trench turbidites (Table 1; Polat et al., 1998). At lower greenschist facies, the Schreiber section of the belt is less metamorphosed than the Hemlo area, for in the Hemlo area, amphibolite facies metamorphism is predominant. Primary igneous textures and pillow geometries of volcanic rocks are well preserved outside of major shear zones. Overprinting relationships between various types of structural fabrics (e.g., folds, shear zones, thrusts) suggest that the Schreiber–Hemlo greenstone belt underwent three phases of deformation. Polat (1998) and Polat et al. (1998) provide detailed description of these deformation phases. The earliest phase of deformation (D1 ) is defined by rotated thrust faults, SSE-verging, tight asymmetric folds, sheath folds, and steeply dipping foliation and associated mineral elongation lineations. D1 reflects tectonic imbrication of oceanic plateaus, island arcs, and arc-derived turbidites in a subduction–accretion complex. D2 is dominated by ENE-striking, right-lateral, orogenparallel strike-slip faults, and steeply dipping thrust shear zones: the presence of coeval strike-slip and compressional structures is consistent with a rightlateral transpressional deformation. Fragmentation of oceanic plateau, island arc, and trench turbidite deposits resulted in broken formations and a tectonic melange during D1 and D2 formation phases (Polat, 1998). Contacts between turbidite and volcanic belts are typically marked by several meter-thick D2 strike-slip fault zones. Along these strike-slip faults, D1 thrust fabrics such as S–C planar fabrics and asymmetric porphyroclasts are locally preserved, suggesting that the D1 thrust faults were overprinted by, and reactivated as, the D2 strike-slip faults (Figs. 3 and 4). The common orientation of S1 foliations and L1 lineations in the volcanic and sedimentary rocks, as well as the presence of the D1 thrust faults and tight to isoclinal folds in both volcanic and sedimentary sequences suggest that turbidites and mafic–ultramafic volcanic sequences were structurally juxtaposed and imbricated during D1 . The most pronounced D3 structure in the study area is the right-lateral Lake Superior–Hemlo fault zone (LSHFZ; Fig. 2; Hugon, 1984; Muir and El-

liott, 1987). D3 in the Schreiber–Hemlo region is attributed to subprovince accretion (Polat et al., 1998). In Phanerozoic orogenic belts, the occurrence of tectonically juxtaposed oceanic (e.g., mid-ocean ridge basalts, seamounts, oceanic plateaus) and arcderived trench turbidites is considered as evidence for ancient subduction zones (see Isozaki et al., 1990; Polat et al., 1996b; Kusky et al., 1997a). Oceanic basalts in Phanerozoic subduction–accretion complexes are often older than turbidites against which they are juxtaposed (Jones et al., 1993). Collectively, the occurrence of interleaved fragments of oceanic plateau and arc-derived turbidites in the late Archean Schreiber belt occurred by D1 convergent margin tectonics and are comparable to Phanerozoic subduction–accretion complexes of Japan (Isozaki et al., 1990; Jones et al., 1993; Kimura et al., 1994). Similarly, tectonically juxtaposed fragments of oceanic crust and arc-derived turbidites in various greenstone belts of the Superior Province have been interpreted as Archean subduction–accretion complexes (Hoffman, 1991; Kimura et al., 1993). The late stages of D1 and D2 were accompanied by the intrusion of syn-kinematic, mafic to felsic dikes and sills ranging from a few centimeters to several hundred meters in thickness, primarily along the D2 strike-slip faults and S1 planes. The absence of D1 fabrics in these dikes and sills suggest that their intrusion post-dates tectonic juxtaposition of trench turbidites with oceanic arc and plateau fragments. The geochemistry of the dikes and sills suggests oceanic slab-derived melts for felsic intrusions, and slab-dehydration, mantle wedge-derived melts for mafic and intermediate intrusions (Table 1; Kerrich et al., 1996; Polat et al., 1998). The intrusion of subduction-derived, syn-kinematic mafic to felsic igneous rocks into imbricated turbidite, arc, and oceanic plateau sequences suggests juxtaposition of these contrasting lithologies above an Archean subduction zone. The transition from D1 to D2 reflects the evolution from thrust tectonics above a subduction zone to right-lateral transpression. The intrusion of subduction-derived igneous rocks into subduction–accretion complexes is an important feature of Phanerozoic subduction–accretion complexes, such as the Chugach accretionary complex of Alaska (Page et al., 1986; Bradley et al., 1994; Kusky et al., 1997a,b), the Shimanto accre-

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tionary complex of Japan (Hasebe et al., 1993), the Altaid accretionary complexes of Central Asia (Sengo¨r and Natal’in, 1996), and the Cordilleran accretionary complexes of British Columbia (Hollister and Andronicos, 1997). The Schreiber–Hemlo greenstone belt evolved as a juvenile magmatic arc and forearc accretionary wedge above an Archean subduction zone. This arc saw episodes of accretion of normal ‘MORB-like’ oceanic crust, oceanic plateau basalt, trench turbidites, and was intruded by arc magmas when the magmatic front migrated through the forearc as a normal product of accretionary growth of the wedge. D1 -related thrusts and=or D2 strike-slip faults in the fore-arc region of the Schreiber–Hemlo magmatic arc may have provided conduits for the uprising slab and wedge melts (TTG and sanukitoids, respectively; Wyllie et al., 1997; Rapp, 1997), and induced decompressional partial melting in the sub-arc mantle wedge to produce the subarc mantle-derived gabbros (Figs. 5 and 6). A close relationship between orogen-parallel strike-slip faulting and magmatism has recently been recognized in several Phanerozoic transpressional orogenic belts, including the North American Cordillera (Tikoff and Saint Blanquat, 1997; Hollister and Andronicos, 1997; Kusky et al., 1997a), Japanese island arcs (Isozaki et al., 1990), and British Caledonides (Hutton and Reavy, 1992), suggesting that as in Phanerozoic counterparts, orogen-parallel strike-slip faulting in the Schreiber– Hemlo greenstone belt played an important role in lateral crustal accretion and magma emplacement. The structural and geochemical data obtained from the late Archean (2750–2667 Ma) Schreiber– Hemlo greenstone belt of the Superior Province, Canada, suggest that the subduction–accretion complex formed above a NNW-dipping subduction zone (Fig. 6). The formation of me´lange in this belt (Polat and Kerrich, in review) can be explained by arc (orogen)-parallel strike-slip faulting deforming the Archean accretionary wedge. The tectonic evolution of the Schreiber belt is comparable to Phanerozoic subduction–accretion complexes that evolved at oblique convergent plate boundaries (see McCaffrey, 1992; Hansen, 1992; Curtis, 1997; Fuh et al., 1997). The structural characteristics of the Schreiber– Hemlo greenstone belt are similar in many respects to those of the Vermilion district of the Wawa sub-

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province to the west, and in the Abitibi greenstone belt to the east, suggesting that oblique plate convergence was a continental-scale phenomenon during the growth of the southern Superior Province in the late Archean (see Hudleston et al., 1988; Bauer and Bidwell, 1992; Robin and Cruden, 1994; Mueller et al., 1996; Kusky and Hudleston, in press). Accretion of immature oceanic arcs appears to have been a major mechanism of crustal growth in Archean orogens. Reymer and Schubert (1986) and Stein and Goldstein (1996), however, argued that oceanic arc-accretion alone is insufficient to account for the rapid crustal growth in Precambrian shields. Furthermore, most oceanic arcs are characterized by mafic composition (Arculus, 1981; Anderson, 1982), whereas the continental crust is andesitic in composition (Taylor and McLennan, 1995). 2.2. Ophiolite accretion Ophiolites are a distinctive association of allochthonous rocks interpreted to form in a variety of plate tectonic settings, including oceanic spreading centers, back-arc basins, forearcs, arcs, and other extensional magmatic settings including those in association with plumes (e.g., Moores, 1982; Sylvester et al., 1997). A complete ophiolite grades downwards from pelagic sediments into a mafic volcanic complex that is generally made of mostly pillow basalts, underlain by a sheeted dike complex. These are underlain by gabbros exhibiting cumulus textures, then tectonized peridotite, resting above a thrust fault that marks the contact with underlying rock sequences. The term ‘ophiolite’ refers to this distinctive rock association, and should not be used in a purely genetic way (cf. Bickle et al., 1994) to refer to allochthonous oceanic lithosphere rocks formed at mid-ocean ridges. Very few complete Phanerozoic-like ophiolite sequences have been recognized in Archean greenstone belts, leading some workers to the conclusion that no Archean ophiolites or oceanic crustal fragments are preserved (e.g., Bickle et al., 1994). However, as emphasized by Sylvester et al. (1997), the original definition of ophiolites (Anonymous, 1972) includes ‘dismembered’, ‘partial’, and ‘metamorphosed’ varieties, and there is no justification for new arbitrary definitions that attempt to exclude portions of Archean

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T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

Fig. 5. (a, b) Transposed beds, folds, shear planes, and veins within turbidites. (c) A rhyolitic melange block within mylonitized volcanic matrix (Steel Lake area). (d) A gabbroic block in a sedimentary (pelitic) matrix (Ripple Lake area, view toward NNE). (e) An epidotized, silicified basaltic block within a sheared volcanic matrix (Middleton area, view toward SSW; top of photo to the right). (f) Sigmoidal quartz veins in volcanic rocks of the Middleton area, indicating right-lateral shearing during D2 (plan view).

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73 53

Fig. 6. Interpreted geodynamic evolution of the Schreiber–Hemlo greenstone belts, and the formation of me´lange. Primitive mantle-normalized trace element diagrams discriminating tectonically imbricated and fragmented ocean plateau tholeiites, tholeiitic to calc-alkaline arc volcanics, trench turbidites, and arc gabbros and TTG are from Polat et al. (1998).

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Fig. 7. Structural sequence columns through several Archean greenstone belt sections interpreted as ophiolites.

greenstone belts that contain two or more parts of the full ophiolite sequence, especially in structurally complex settings such as found in greenstone belts like the Schreiber–Hemlo belt (e.g., Harper, 1985; de Wit et al., 1987; Kusky, 1990, 1991). Similarly, many Proterozoic ophiolites are dismembered, or partial sequences (Kro¨ner, 1985; Berhe, 1990; Dann, 1991). Archean oceanic crust was possibly thicker than Proterozoic and Phanerozoic counterparts, resulting in accretion predominantly of the upper section (basaltic) of oceanic crust (Burke et al., 1976; Moores, 1986; Hoffman and Ranalli, 1988; Burke, 1995). The crustal thickness of Archean oceanic crust may in fact have resembled modern oceanic plateaux (e.g., Sleep and Windley, 1982). If this were the case, complete Phanerozoic-like MORBtype ophiolite sequences would have been very unlikely to be accreted or obducted during Archean orogenies. In contrast, only the upper, pillow lavadominated sections would likely be accreted. Portions of several Archean greenstone belts have been interpreted to contain dismembered or partial ophiolites, that are more complete than the basalt= chert slivers preserved in the Schreiber–Hemlo belt (Fig. 7). Accretion of MORB-type ophiolites has been proposed as a mechanism of continental growth in a number of Archean, Proterozoic, and Phanero-

zoic orogens (Table 2). It is worthwhile to investigate these claims to better understand the crustal structure and tectonic setting in which these Archean ophiolites formed. Several suspected Archean ophiolites have been particularly well-documented. One of the most disputed is the circa 3.5-Ga Jamestown ophiolite in the Barberton greenstone belt (Fig. 7) of the Kaapvaal craton (Fig. 1; Brandl and de Wit, 1997). de Wit et al. (1987) describe a 3-km-thick tectonomagmatic sequence including a basal peridotite tectonite unit with chemical and textural affinities to Alpine-type peridotites, overlain by an intrusive– extrusive igneous sequence, and capped by a chert– shale sequence. This partial ophiolite is pervasively hydrothermally altered and shows chemical evidence for interaction with sea water with high heat and fluid fluxes (de Wit et al., 1990). SiO2 and MgO metasomatism and black-smoker-like mineralization is common, with some hydrothermal vents traceable into banded iron formations, and subaerial mudpool structures. These features led de Wit et al. (1982, 1992) to suggest that this ophiolite formed in a shallow sea, and was locally subaerial, analogous to the plume-impinged Reykjanes ridge of Iceland. In this sense, Archean oceanic lithosphere may have looked very much like younger oceanic plateaux lithosphere.

North-American Cordillera (Ben-Avraham et al., 1981; Samson and Pachett, 1991; Richards et al., 1991; Condie, 1997a) Northern Andes and central America (Storey et al., 1991; Alvarado et al., 1997) Tarim basin (Sengo¨r et al., 1996)

Phanerozoic

Japan (Kimura et al., 1994)

Birimian Shield (Abouchami et al., 1990; Boher et al., 1992) Arabian–Nubian Shield (Kro¨ner, 1985; Stein and Goldstein, 1996) Trans-Hudson orogen (Stern et al., 1995a)

North-American Cordilleran ophiolites (Moores, 1982; Coney, 1989; Saleeby, 1992) Southeast Pacific and Australian ophiolites (Hamilton, 1988; Aitchison et al., 1994)

Qinling belt, China (Xue et al., 1996) Appalachians (Dennis and Wright, 1997; O’Brien et al., 1997)

Appalachians (van Staal and Colman-Sadd, 1997)

Galice basin, U.S. Cordillera (Burchfiel et al., 1992)

Appalachian ophiolites (Dewey and Bird, 1971; Melancon et al., 1997)

North-American Cordillera (Samson and Pachett, 1991; Saleeby, 1992; Miller et al., 1992) Andes and Central America (Tardy et al., 1994; Vergara et al., 1995) Gamilaroi terrane, Australia (Aitchison and Flood, 1994)

Rocas Verdes basin, Chile (Hanson and Wilson, 1991)

Tethyan ophiolites (Moores, 1982; Dewey, 1977; Sengo¨r, 1990; Polat et al., 1996a)

Trans-Hudson (St-Onge et al., 1989) Pan-African orogen (Bodinier et al., 1989) Karakaya basin, Turkey (Sengo¨r and Yilmaz, 1981)

Trans-Hudson orogen (Stern et al., 1995a,b) Arabian–Nubian Shield (Berhe, 1997)

Yavapai orogen (Dann, 1991) Grenville orogen (Garrison, 1981)

Yavapai–Mazatzal orogens (Condie, 1986) Baltic Shield (Park, 1991)?

Tarney et al. (1976)

Pilbara craton (Ohta et al., 1996) Arabian–Nubian Shield (Kro¨ner, 1985; Berhe, 1990) Baltic Shield (Park, 1991)

Southeast Pacific (Hamilton, 1988

Pan-African orogeny, central Brazil (Pimentel and Fuck, 1992) Birimiam terrane (Boher et al., 1992) Arabian–Nubian Shield (Windley et al., 1996)

Trans-Hudson orogen (Stern et al., 1995a) Yavapai-Mazatzal orogens (Condie, 1986) Baltic Shield (Park, 1991)

Aldan–Stanovik Shield (Dobretsov et al., 1997) Kaapvaal craton (Brandl and de Wit, 1997) Yilgarn craton (Myers and Swager, 1997) Pilbara craton (Barley, 1997)

Slave Province (Helmstaedt et al., 1986; Kusky, 1991) Superior Province (Kimura et al., 1993) Kaapvaal craton (de Wit et al., 1987; de Ronde and de Wit, 1994) Yilgarn craton (Fripp and Jones, 1997)

Altaids and Nippinoids (Sengo¨r and Natal’in, 1996)

Japan (Matsuda and Uyeda, 1971)

Uralides (Hamilton, 1970)

Arabian–Nubian Shield (Sengo¨r and Natal’in, 1996)

Yilgarn craton (Sengo¨r and Natal’in, 1996)

Arc-trench migration=Turkic-type orogeny accretion

Kaapvaal craton (de Ronde and de Wit, 1994; de Wit et al., 1992) Yilgarn craton (Myers, 1993)

Back-arc basin acrretion

Superior Province (Hoffman, 1991; Jackson and Cruden, 1995)

Norinal (MOR) ocean crust accretion or ophiolite obduction

Superior Province (Card, 1990; Isua greenstone belt (Maruyama et al., Sa˜o Francisco craton (Baars, 1997) Percival et al., 1994; Polat et al., 1998) 1991)

Oceanic island arc accretion

Kostomuksha greenstone belt (Puchtel Pilbara craton (Myers, 1993; et al., 1997a) Kiyokawa and Taira, 1995) (Abbott, 1996) Aldan–Stanovik Shield (Dobretsov et al., 1997) Burke et al. (1976)

Superior Province greenstone belts (Desrochers et al., 1993; Kimura et al., 1993; Xie et al., 1993; Polat et al., 1998) Belingwe greenstone belt (Kusky and Kidd, 1992) Yilgarn craton (Myers, 1993)?

Proterozoic

Archean

Oceanic plateau accretion

Table 2 Major accretionary processes that played an important role in the growth of the continental crust during the Archean, Proterozoic, and Phanerozoic orogenies

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Several partial or dismembered ophiolites have been described from the Slave Province (Figs. 1, 7 and 8), although these too have been disputed (e.g., King and Helmstaedt, 1997). From the Point Lake greenstone belt in the central Slave Province, Kusky (1991) described a fault-bounded sequence grading downwards from shales and chemical sediments (umbers) into several kilometers of pillow lavas intruded by dikes and sills, locally into multiple dike=sill complexes, then into isotropic and cumulate-textured layered gabbro (Fig. 9). The base of this partial Archean ophiolite sensu stricto is marked by a 1-km-thick shear zone composed predominantly of mafic and ultramafic mylonites, with less-deformed domains including dunite, websterite, wherlite, serpentinite, and anorthosite. By using down-plunge projections and section-balancing techniques, Kusky (1991) estimated that the shear zone at the base of this ophiolite accommodated a minimum of 69 km of slip. Although this still allows the ophiolite to have formed at or near extended older continental crust that forms the Anton terrane to the west (Kusky, 1989), the actual amount of transport was probably much greater. Syn-orogenic conglomerates and sandstones were deposited in several small foredeep basins, and are interbedded with mugearitic lavas (and associated dikes), all deposited=intruded in a foreland basin setting (Kusky, 1991). Kusky (1986, 1990) suggested that portions of the Cameron and Beaulieu River greenstone belts of the southern Slave Province contain ophiolitic components (Figs. 7, 8 and 10). The belts are cut by numerous layer-parallel shear zones, but some sections are composed mostly of tholeiitic pillow basalts, others contain approximately equal quantities of pillows and dikes, and a few sections consist of nearly 100% mafic dikes (Fig. 10). The bases of these greenstone belts are marked by shear zones up to 500 m thick (locally containing me´langes), with tectonic blocks of gabbro, mafic volcanics, peridotite, and slivers of the underlying quartzofeldspathic gneiss (with extensive mafic dike complexes, Fig. 11) and its autochthonous cover. Original relationships between dikes in the basement complex and dikes in the basal parts of the greenstone belts have not been established, but older-generation mafic dikes do not cut intervening sedimentary sequences, nor the shear zone that separates the greenstone belt from

the basement (Fig. 10). Helmstaedt et al. (1986) describe a pillow lava sequence that grades down into sheeted dikes and gabbro from the Yellowknife greenstone belt (Figs. 7 and 8), but interpreted the basal contact of the belt as an unconformity on a banded iron formation, an interpretation questioned by Kusky (1987). The dikes and pillow lavas are geochemically similar to MORB (MacLaughlin and Helmstaedt, 1995), although Isachsen et al. (1991), and Isachsen and Bowring (1997) have shown that the Yellowknife greenstone belt contains several different, and probably unrelated volcanic and sedimentary sequences, separated by as much as 50 Ma and spanning an age interval of 200 Ma. Harper (1985) and Wilks and Harper (1997) describe rocks of the South Pass area in the Wind River Range, Wyoming, as containing a dismembered metamorphosed Archean ophiolite. This ophiolite contains all of the units of a complete ophiolite except the basal peridotite tectonite, and contacts between all units are shear zones. Cumulate textures in ultramafic rocks and gabbros are present, as are small exposures of a sheeted dike complex. Pillow lavas are associated with metapelites and banded iron formation. It has been argued (Bickle et al., 1994) that the paucity of well-developed sheeted dike complexes known from Archean greenstone belts indicates that they are not ophiolites. But sheeted dikes are not well-preserved in many Phanerozoic ophiolites, especially when they are metamorphosed and deformed to the extent that most Archean greenstone belts are. Abbott (1996) argues that sheeted dikes are not necessarily formed in every ocean floor sequence. Despite this, sheeted dike complexes have been discovered in several of the ophiolitic greenstone belts described above. Well-developed sheeted dike complexes have also been mapped in several locations in the Kalgoorlie terrane of the Yilgarn craton (Fripp and Jones, 1997). Multiple cooling units of dolerite, high-Mg mafic rocks, and serpentinite are truncated at an angle between 35º and 80º by an unconformably overlying mafic volcanic breccia, pillow breccia, and lenses of pillow lava that strike parallel to bedding in overlying sedimentary rocks in the Kanowna Lake area. Fripp and Jones (1997) interpret this unit as a sheeted dike complex overlain by a volcanic carapace. At the Cowan Lake Six Islands locality (Fig. 12), Fripp and Jones (1997) describe

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Fig. 8. Tectonic map of the Slave Province showing locations of the Cameron River, Point Lake and Yellowknife greenstone belts. (modified after Kusky, 1989). The ‘Yellowknife Domain’ is the area between the Yellowknife and Cameron River greenstone belts. Cross-hachured areas contain circa 2.7–4.0-Ga gneissic rocks and remnants (typically as enclaves in circa 2.5-Ga granites) of the Anton terrane; unpatterned areas represent metasedimentary rocks (dominantly graywacke turbidite sequences), intruded by younger granitoids, and the checkered pattern represents circa 2.7–2.6-Ga magmatic rocks of the Hackett River arc.

58 T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

Fig. 9. Map of part of the Point Lake greenstone belt, showing ophiolitic stratigraphy (from Kusky, 1991). See Fig. 8 for location.

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Fig. 10. Map of part of the Cameron River greenstone belt, showing dike=sill complex (from Kusky, 1990). See Fig. 8 for location.

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60 T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73 Fig. 11. Map of dike complex in granitoid basement complex of the Cameron River greenstone belt in the Upper Ross Lake area (after Kusky, 1990). See Fig. 8 for location.

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Fig. 12. Map of cliff section of sheeted dike complex in the Lake Cowan section of the Kalgoorlie greenstone belt. Inset shows map of the Yilgarn craton, showing location of the Kalgoorlie greenstone terrane (modified after Fripp and Jones, 1997).

lherzolite and dunite that grade up into websterite and gabbro with pyroxenite layers. These rocks are overlain by high-Mg mafic and picritic basalts that occur in multiple tabular cooling units, interpreted as sheeted dikes, that exhibit both one-way and two-way chill margins. These are overlain by chert, silicified mudstone, shale and graywacke turbidites, which locally occur as partially assimilated xenoliths (containing zircons) within the intrusive rocks. Fripp and Jones (1997) interpret the Lake Cowan greenstone locality to include the peridotitic lower plutonic sequence that marks the transition zone between mantle and crust in ophiolite suites. This transition zone sequence is overlain by a sheeted dike complex, but the extrusive magmatic carapace is omitted by faulting at this locality. Fripp and Jones (1997) note the many similarities between the Kalgoorlie ophiolites and Phanerozoic ophiolites such as the Samail, Troodos, and Bay of Islands massifs.

Kimura et al. (1993) interpret parts of the Larder Lake and Beardmore–Geraldton greenstone belts in the Abitibi and Wabigoon subprovinces of the Superior Province to include ophiolitic fragments accreted in arc environments, in a manner analogous to the setting of the basalt=chert slivers of the Schreiber– Hemlo belt described above. The Larder Lake belt occurs in the southern part of the Abitibi greenstone belt, and consists of pillow basalts and banded iron formation (BIF) tectonically stacked with terrigenous turbidites. The pillow basalts and BIF are interpreted to be the upper part of an oceanic plate stratigraphy, offscraped and interdigitated with trench turbidites in an accretionary wedge setting similar to Alaska (Kusky et al., 1997a) or Japan (Isozaki et al., 1990). Williams et al. (1991) and Kimura et al. (1993) also suggest a similar exotic origin for basalts and iron formation tectonically interleaved with terrigenous turbidites in the Beardmore–Geraldton area in

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the southern part of the Wabigoon subprovince. In both of these examples, the accreted trench turbidites and ophiolitic slivers are intruded and overprinted by arc-related plutons and lavas, formed when the trench stepped back and intruded its own accretionary wedge. A similar accretionary wedge setting and oceanic crustal origin for slivers of basalt in greenstone belts of the Pilbara craton has been proposed by Isozaki et al. (1992). Evidence for the creation and obduction of oceanic crust in the Archean is not limited to field relationships as described above. Jacob et al. (1994) report that the geochemistry of diamondiferous eclogites from the Udachnaya Mine, Siberia (Puchtel et al., 1997b), are most consistent with derivation from subducted slabs of Archean oceanic crust that were extensively hydrothermally altered prior to subduction. Similarly, many eclogite samples from South African kimberlites are also interpreted as remnants of subducted Archean oceanic crust (e.g., Jagoutz et al., 1984; MacGregor and Manton, 1986). In summary, dismembered ophiolites are a widespread component of Archean greenstone belts, and many of these apparently formed as the upper parts of Archean oceanic crust. Most of these appear to have been accreted within forearc and intra-arc tectonic settings. The observation that Archean greenstone belts have such an abundance of accreted ophiolitic fragments compared to Phanerozoic orogens suggests that thick, relatively buoyant, young Archean oceanic lithosphere may have had a rheological structure favoring delamination of the uppermost parts during subduction and collisional events (Hoffman and Ranalli, 1988). 2.3. Oceanic plateau accretion Oceanic plateaux are thicker than normal oceanic crust formed at mid-ocean ridges: they are more buoyant and relatively unsubductable, forming potential sources of accreted oceanic material to the continental crust at convergent plate boundaries (Burke et al., 1978; Ben-Avraham et al., 1981; Richards et al., 1991; Burchfiel et al., 1992; Desrochers et al., 1993; Abbott, 1996; Abbott et al., 1997; Sengo¨r et al., 1996). Accretion of oceanic plateaux has been proposed as a mechanism of crustal growth in a number of orogenic belts, includ-

ing Archean, Proterozoic, and Phanerozoic examples (Table 2). Oceanic plateaux are interpreted to form from plumes or plume heads that come from the lower mantle (D00 ) or the 670 km discontinuity, and they may occur either within the interior of plates, or interact with the upper mantle convective=magmatic system and occur along mid-ocean ridges (e.g., Kincaid et al., 1996; review by Abbott and Mooney, 1995). Storey et al. (1991) suggest that oceanic plateaux may be sites of komatiite formation preserved in Phanerozoic through Archean mountain belts, based on their correlation of allochthonous komatiites and high-MgO lavas of Gorgona Island, Curac¸ao, and in the Romeral fault zone, with the Cretaceous Caribbean oceanic plateau. Portions of several komatiite-bearing Archean greenstone belts have been interpreted as pieces of dismembered Archean oceanic plateaux (Kusky and Kidd, 1992; Abbott and Mooney, 1995; Puchtel et al., 1997a). For instance, parts of several greenstone belts in the southern Zimbabwe craton (Blenkinsop et al., 1997; Fig. 13) are allochthonous (Kusky and Winsky, 1995) and show a similar magmatic sequence including a lower komatiitic unit overlain by several kilometers of tholeiitic pillow basalts. Kusky (1998) proposed that these represent a circa 2.7 Ga oceanic plateau dismembered during a collision between the passive margin sequence developed on the southern margin of the Zimbabwe craton and an exotic crustal fragment preserved south of the suture-like Umtali line (Fig. 13). The geochemistry of some of the basalts in the Schreiber–Hemlo belt suggests that they formed in an oceanic plateau setting that was later accreted to the forearc of a large juvenile arc system. This tectonic collage later collided with other crustal fragments to form the core of the North American craton. Kimura et al. (1993) interpret geologic relationships in the Malartic–Val d’Or area of the Abitibi subprovince of the Superior Province to contain an example of accreted oceanic plateau material. Komatiitic and tholeiitic magmatic suites are geochemically similar to oceanic plateau basalts from Gorgona (Kimura et al., 1993), and the tectonic slices in the greenstone belt that contain these rocks, preserve early tectonic fabrics interpreted to result from accretion of the oceanic plateau. These rocks are intruded by a suite of calc-alkaline magmas, which

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Fig. 13. Map of the Zimbabwe craton, showing distribution of oceanic plateau like greenstone belt fragments in black (modified after Kusky et al., 1997a).

Kimura et al. (1993) interpret as forming in late extensional basins. They suggest a general model in which oceanic plateaux and normal oceanic crust are

accreted in arc environments, which causes a backstepping of the subduction zone. As the accretionary complex grows it is overprinted by calc-alkaline

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magmatism as the arc migrates through the former subduction complex. Further magmatic and structural events can be caused by late ridge subduction and strike-slip segmentation of the arc. The geodynamic interpretation of Archean komatiites is however controversial; the eruption of komatiites are attributed to several other geodynamic settings including mid-ocean ridges (de Ronde and de Wit, 1994), intra-oceanic plume setting (Jochum et al., 1991; Xie et al., 1993; Arndt et al., 1997), subduction zones (Parman et al., 1997), and continental rifts (e.g., Nisbet et al., 1993a). Similarly, ocean floor tholeiites with flat REE patterns are interpreted either as remnants of Archean mid-ocean ridge basalt (AMORB; Ohta et al., 1996), or Archean oceanic plateaus (Kimura et al., 1993; Xie et al., 1993). The presence of more-abundant komatiites, high-Mg tholeiites, and slab-derived, high-La=Ybn , high-Al TTG’s suggests slightly higher average mantle temperatures in the Archean than the post-Archean, resulting in thicker Archean oceanic crust up to 25 km (Sleep and Windley, 1982; McKenzie and Bickle, 1988; Drummond and Defant, 1990; Langmuir et al., 1992; Martin, 1993; Grove et al., 1994; Condie, 1997b). In addition, slightly higher mantle temperatures in the Archean mantle may have produced large numbers of oceanic plateaus, up to 60–80 km thick, derived from mantle plumes (Storey et al., 1991; McDonough and Ireland, 1993; Nisbet et al., 1993b; Abbott, 1996; Arndt et al., 1997). Average geochemical compositions of the continental crust, however, are not consistent with ocean plateau accretion alone. For example, modern ocean plateaus such as Ontong Java, Kerguelen, and the Nauru basin have near flat REE patterns on chondrite-normalized diagrams (see Floyd, 1989; Salters et al., 1992; Mahoney et al., 1993), whereas the continental crust has LREE-enriched patterns. Similarly, areally extensive Mg- to Fe-tholeiite sequences of the Superior Province and the Arabian–Nubian Shield (Fig. 1, Berhe, 1997), which are interpreted as fragments of Archean and Proterozoic ocean plateaux, respectively, have nearly flat REE patterns (Kro¨ner, 1985; Xie et al., 1993; Desrochers et al., 1993; Polat et al., 1998). Parts of many Archean, Proterozoic and Phanerozoic greenstone belts interpreted as oceanic plateau fragments are overprinted by arc magmatism, sug-

gesting that they either formed the basement of intraoceanic island arcs, or they have been intruded by arc magmas following their accretion (Abouchami et al., 1990; Desrochers et al., 1993; Condie, 1997a). Condie (1997b) suggested that the upper and lower continental crusts have grown through the accretion of oceanic island arcs and ocean plateaus, respectively. In summary, accreted oceanic plateaux may form a significant component of the continental crust, although most are structurally disrupted and overprinted by arc magmatism. 2.4. Back-arc basin accretion The formation, closure, and preservation of back-arc basin sequences has proven to be a popular model for the evolution of some greenstone belts (Table 2; see also van Staal and ColmanSadd, 1997), especially since a direct comparison between the Mesozoic Rocas Verdes of Patagonia and Archean greenstone belts was made by Tarney et al. (1976). Despite the elegance of this model and its apparent applicability to numerous greenstone belts, Stern and de Wit (1997) caution that the analogy is only directly applicable to those greenstone belts with simple histories, emphasizing that the evolution of the Rocas Verdes spans only 50 Ma. Like some Archean greenstone belts, Mesozoic Rocas Verdes igneous rocks include mainly pillow basalts, dikes, sills, and gabbros, interpreted as partial ophiolite sequences formed along mid-ocean ridge type spreading centers (Dalziel et al., 1974; Stern and de Wit, 1997). Mafic dikes that are compositionally similar to those in the ophiolitic sequences cut older, dominantly tonalitic–trondhjemitic basement rocks. These formed when the arc sequence was rifted, forming a narrow basin with igneous sequences initially fed by dikes that intruded through the older basement. As spreading continued, a midocean ridge style spreading center developed, in which oceanic crust was generated. Platform and coarse-grained arc-derived sediments were deposited on the east and west sides of the basin, whereas chert and fine-grained turbidites overlie pillow lavas in the center of the basin (de Wit and Stern, 1981). Closure of the back-arc basin formed folds and cleavage in sedimentary rocks, and initiated major shear zones in the basement and ophiolitic rocks. Some por-

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tions of the ophiolitic sequence were thrust over a foreland basin sequence developed during basin closure, whereas other portions of the igneous sequence were shortened in situ and remain essentially autochthonous (de Wit and Ashwal, 1997). Paradoxically, the dominance of buoyant subduction styles in the Archean should have led to dominantly compressional arc systems, but many workers suggest back-arc basins (which form in extensional arcs) as a modern analog for Archean greenstone belts. Several workers have proposed that rocks of the ‘Yellowknife domain’ (Fig. 8) in the southern Slave Province may have been deposited in a back-arc basin (e.g., Kusky, 1986; MacLaughlin and Helmstaedt, 1995; Isachsen and Bowring, 1997). Data supporting this interpretation include the geochemical signature of metavolcanic and intrusive rocks that is consistent with intrusion through older continental crust (MacLaughlin and Helmstaedt, 1995), and zircons in felsic volcanic rocks with ages older than the main volcanic sequence, and approaching the age of the nearby gneissic rocks (Isachsen and Bowring, 1997). In a relationship reminiscent of the Mesozoic Rocas Verdes, the eastern margin of the proposed back-arc basin is marked by a tonalitic gneiss complex, cut by extensive mafic dikes that are compositionally similar to those of the adjacent greenstone (ophiolitic) belts (e.g., Fig. 9; Kusky, 1990). Other back-arc basin settings have been proposed for components of the Sa˜o Francisco (Baars, 1997), Aldan–Stanovik (Dobretsov et al., 1997), Kaapvaal (Brandl and de Wit, 1997), Yilgarn (Myers and Swager, 1997) and Pilbara (Tarney et al., 1976; Barley, 1997) cratons. Many assignments of back-arc basin geodynamic settings including that of the Yellowknife domain are based in part on the geochemical affinities of lavas in ‘tectonic discriminant analysis’. Particular emphasis has been placed on Nb–Ta–Th–La systematics. Recent studies have shown that the depletion of Nb and Ta with respect to Th and La is not unique to arc and back-arc lavas (Klein and Karsten, 1995; Karsten et al., 1996). Thus, the depletion of Nb and Ta in many Archean greenstone belts may not necessarily indicate arc or back-arc geodynamic settings. The diverse geochemical characteristics, particularly in Th–Nb–La systematics, of Archean intra-oceanic komatiites and Mg- to Fe-tholeiites may imply het-

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erogeneous mantle plumes (Polat et al., 1999), such as the Iceland Plume (Hemond et al., 1993; Furman et al., 1995; Hards et al., 1995), rather than a back-arc geodynamic setting.

3. Arc–trench migration and accretionary orogens; a paradigm for the Archean Sengo¨r and Natal’in (1996) discuss a special class of collisional mountain building that they term ‘Turkic-type orogeny’ (i.e., accretionary orogens), in which large, sub-continent-size accretionary complexes which magmatic arc axes have migrated through are built on one or two of the colliding continents before collision, and are later displaced by strike-slip faulting. These accretionary wedges are typically built of belts of flysch, disrupted flysch and me´lange, and accreted ophiolites, plateaux, and juvenile island arcs (e.g. Kusky et al., 1997b). Sengo¨r and Natal’in (1996) review the geology of several Phanerozoic and Precambrian orogens, and conclude that Turkic- or accretionary-type orogeny is one of the principal builders of continental crust with time (Table 2). Sengo¨r and Natal’in’s observations and model are particularly applicable to the record of Archean granite–greenstone terranes, which typically show important early accretionary phases followed by intrusion by arc magmatism (e.g., Jackson and Cruden, 1995; Kusky and Vearncombe, 1997), possibly related to the migration of magmatic fronts through large accretionary complexes. In examples like the Schreiber–Hemlo belt and other parts of the Superior Province, many sub-parallel belts of accreted material are located between continental fragments that are separated by many hundreds of kilometers, and thus may represent large accretionary complexes that formed prior to a ‘Turkic-type’ collision. Late stage strike-slip faulting is important in these Archean orogens, as in the Altaids and Nipponides, and may be partly responsible for the complexity and repetition of belts of similar character across these orogens. Turkic- or accretionary-type orogens may also experience late-stage extension associated with gravitational collapse of the orogen, especially in association with late collisional events that thicken the crust in the internal parts of the orogen. In the Archean,

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slightly higher mantle temperatures may have reduced the possible height that mountains would have reached before the strength of deep-seated rocks was exceeded, so that extensional collapse would have occurred at crustal thicknesses lower than those of the younger geological record (e.g., England and Bickle, 1984; Kusky, 1993). This idea is discussed further in the following section.

4. Late-stage granites and cratonization Granite–greenstone terranes are ubiquitously intruded by late- to post-kinematic granitoid plutons, which may play a role in or be the result of some process that has led to the stabilization or ‘cratonization’ of these terranes (e.g., Kusky, 1993, 1998; Abbott et al., 1997). Most granite–greenstone terranes also have a thick mantle root or tectosphere (Jordan, 1988; Abbott et al., 1997), characterized by a refractory composition (depleted in a basaltic component), relatively cold temperatures, high flexural rigidity, and high shear wave velocities (Ballard and Pollack, 1987; Grand, 1987, 1994; Bechtel et al., 1990). Outward growth and accretion in granite–greenstone terranes provides a framework for the successive underplating of the lower parts of depleted slabs of oceanic lithosphere (Helmstaedt and Doig, 1975; Helmstaedt and Shulze, 1989), particularly if some of the upper sections of oceanic crust are offscraped and accreted, to be preserved as greenstone belts, or eroded to form belts of graywacke turbidites. These underplated slabs of depleted oceanic lithosphere will be cold and compositionally buoyant compared to surrounding asthenosphere (providing that the basalt is offscraped and not subducted and converted to eclogite) and may contribute to the formation of cratonic roots (Abbott, 1991). One of the major differences between Archean and younger accretionary orogens is that Archean subducted slabs were dominantly buoyant, whereas younger slabs were not (e.g., Abbott, 1991). This may be a result of the changing igneous stratigraphy of oceanic lithosphere, resulting from a reduction in heat flow with time, perhaps explaining why Archean cratons have thick roots and are relatively undeformable compared to their younger counterparts. Geometric

aspects of underplating these slabs predict that they will trap supra-subduction mantle wedges of more fertile and hydrated mantle (Kusky, 1993, 1986), from which later generations of basalt can be generated. Many granites in Archean terranes appear to be associated with crustal thickening and anatexis during late stages of collision. However, some late-stage granitoids may be a direct result of decompressional melting associated with upper-crustal extensional collapse of Archean orogens thickened beyond their limit to support thick crustal sections, as determined by the strength of deep-seated rocks (e.g., Dewey, 1988). Decompressional melting generates basaltic melts from the trapped wedges of fertile mantle, which intrude and partially melt the lower crust. The melts assimilate lower crust, become more silicic in composition, and migrate upward to solidify in the mid to upper crust, as the late- to post-kinematic granitoid suite (e.g., Nelson, 1991; Kusky, 1993). In this model, the tectosphere (or mantle root) becomes less dense (compositionally buoyant) and colder than surrounding asthenosphere, making it a stable cratonic root that shields the crust from further deformation. Late-stage strike-slip faults that cut many Archean cratons may also play an important role in craton stabilization (e.g., Kusky, 1998). Specifically the steep shear zones may provide conduits for massive fluid remobilization and escape from the subcontinental lithospheric mantle, which would both stabilize the cratonic roots of the craton, and initiate large-scale granite emplacement into the mid and upper crust.

5. Conclusions: continental growth at accretionary convergent margins Although the rate of continental growth is a matter of geological debate (Fyfe, 1978; Dewey and Windley, 1981; Armstrong, 1991; McCulloch and Bennett, 1994; Taylor and McLennan, 1995), most geological data indicate that the continental crust has grown by accretionary and magmatic processes taking place at convergent plate boundaries since the early Archean (Burke et al., 1976; Sleep and Windley, 1982; Friend et al., 1988; Card, 1990; Condie, 1994, 1997a; Taylor and McLennan, 1995; Sengo¨r and Natal’in, 1996;

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Windley et al., 1996). Arc-like trace-element characteristics of continental crust suggest that subduction zone magmatism has played an important role in the generation of the continental crust (Hofmann, 1988; Tarney and Jones, 1994; Rudnick, 1995; Taylor and McLennan, 1995). Convergent margin accretionary processes that contribute to the growth of the continental crust can be divided into five major groups (Table 2): (1) oceanic plateau accretion; (2) oceanic island arc accretion; (3) normal ocean crust (mid-ocean ridge) accretion=ophiolite obduction; (4) back-arc basin accretion; and (5) arc–trench migration=Turkic-type orogeny accretion. We have illustrated these processes using specific well-studied examples of each, emphasizing the Schreiber–Hemlo area of the Superior Province because it shows features related to several of these process. These early accretionary processes are typically followed by intrusion of latestage anatectic granites, late gravitational collapse, and late strike-slip faulting. Together, these processes release volatiles from the lower crust and mantle and help to stabilize young accreted crust and form stable continents. Isotopic data from numerous Archean and postArchean orogenic belts are consistent with the accretion of juvenile material, rapid and episodic crustal growth (Reymer and Schubert, 1986; Samson and Pachett, 1991; Boher et al., 1992; Taylor and McLennan, 1995; Stein and Goldstein, 1996; and references therein). Stein and Hofmann (1994) proposed that episodic crustal growth and major orogenic events may have been associated with major plume activities throughout earth history. They defined this relationship as mantle overturn and major orogenies (MOMO). This model can explain global, episodic accretion of Archean komatiite–tholeiitic basalt sequences. However, the abundance of synto post-kinematic TTG in the Archean upper continental crust, rather than ultramafic–mafic volcanic sequences (Taylor and McLennan, 1995), requires the production of voluminous slab, mantle wedge, and lower crustal-derived calc-alkaline arc magmas as complementary to plateau accretion (Drummond and Defant, 1990; Feng and Kerrich, 1992; Martin, 1993). Sengo¨r et al. (1993) and Sengo¨r and Natal’in (1996) proposed a new type of orogeny, so-called

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‘Turkic or accretionary-type orogeny’, for continental growth. These orogenic belts possess very large sutures (up to several hundred km wide) characterized by subduction–accretion complexes and arcderived granitoid intrusions, similar to the CircumPacific accreted terranes (e.g., Alaska, Japan). These subduction–accretion complexes are composed of tectonically juxtaposed fragments of island arcs, back-arc basins, ocean islands=plateaux, trench turbidites, and micro-continents (Sengo¨r, 1993; Sengo¨r and Natal’in, 1996). Another important feature of these orogens is the common occurrence of orogen parallel strike-slip fault systems, resulting in lateral stacking and bifurcating lithological domains (Sengo¨r and Natal’in, 1996). In these respects, the accretionary-type orogeny may be considered as a unified accretionary model for the growth of the continental crust.

Acknowledgements We thank Steve Marshak, Peter Hudleston, John Percival, and Celail Sengo¨r for thoughtful reviews of the manuscript. Kusky acknowledges support by NSF grant 9706699, and Polat acknowledges support from an NSERC grant (part of NSERC-IOR to MITEC (CAMIRO) 93EOR) awarded to R. Kerrich.

References Abbott, D., 1991. The case for accretion of the tectosphere by buoyant subduction. Geophys. Res. Lett., April 1991, pp. 1–4. Abbott, D., 1996. Plumes and hotspots as sources of greenstone belts. Lithos 37, 113–127. Abbott, D.H., Mencke, W.H., 1990. The length of the global plate boundary at 2.4 Ga. Geology 18, 58–61. Abbott, D., Mooney, W., 1995. The structural and geochemical evolution of the continental crust: support for the oceanic plateau model of continental growth. Rev. Geophys. Suppl. Uni. Geod. Geophys. 1991–94, 231–242. Abbott, D.H., Drury, R., Mooney, W.D., 1997. Continents as lithological icebergs: the importance of buoyant lithospheric roots. Earth Planet. Sci. Lett. 149, 15–27. Abouchami, W., Boher, M., Michard, A., Albarede, F., 1990. A major 2.1 Ga event of mafic magmatism in west Africa: an early stage of crustal accretion. J. Geophys. Res. 95, 17605– 17629. Aitchison, J.C., Flood, P.G., 1994. Gamilaroi terrane, a Devonian rifted intra-oceanic island arc assemblage, NSW, Australia. In:

68

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

Smellie, J.L. (Ed.), Volcanism Associated with Extension at Convergent Plate Margins. Geol. Soc. London Spec. Publ. 81, 155–168. Aitchison, J.C., Blake, M.C., Flood, P.G., Jayko, A.S., 1994. Paleozoic ophiolitic assemblages within the southern New England orogen of eastern Australia: implications for growth of the Gondwanan margin. Tectonics 13, 1135–1149. Alvarado, G.E., Denyer, P., Sinton, C.W., 1997. The 89 Ma Tortugal komatiitic suite, Costa Rica: implications for a common geological origin of the Caribbean and eastern Pacific region from a mantle plume. Geology 25, 439–442. Anderson, A.T., 1982. Parental basalts in subduction zones, implications for continental evolution. J. Geophys. Res. 87, 7047–7060. Anonymous, 1972. Ophiolites. Geotimes 17: 24–25. Arculus, R.J., 1981. Island arc magmatism in relation to the evolution of the crust and mantle. Tectonophysics 75, 113– 133. Armstrong, R.L., 1991. The persistent myth of crustal growth. Aust. J. Earth. Sci. 38, 613–630. Arndt, N.T., Albarede, F., Nisbet, E.G., 1997. Mafic and ultramafic magmatism. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 233– 254. Baars, F.J., 1997. The Sa˜o Francisco Craton. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 529–557. Ballard, S., Pollack, H.N., 1987. Diversion of heat by Archean cratons: a model for southern Africa. Earth Planet. Sci. Lett. 85, 253–264. Barley, M.E., 1997. The Pilbara Craton. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 657–664. Bauer, R.L., Bidwell, M.E., 1992. Contrasts in the response to dextral transpression across the Quetico–Wawa subprovince boundary in Northeastern Minnesota. Can. J. Earth Sci. 27, 1521–1535. Bechtel, T.D., Forsyth, D.W., Sharpton, V.L., Grieve, R.A.F., 1990. Variations in effective elastic thickness of the North American lithosphere. Nature 343, 636–638. Ben-Avraham, Z., Nur, A., Jones, D., Cox, A., 1981. Continental accretion: from oceanic plateaus to allochthonous terranes. Science 213, 47–54. Berhe, S.M., 1990. Ophiolites in north and east Africa: implications for Proterozoic crustal growth. J. Geol. Soc. London 147, 41–57. Berhe, S.M., 1997. The Arabian–Nubian Shield. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 761–771. Bickle, M.J., Nisbet, E.G., Martin, A., 1994. Archean greenstone belts are not oceanic crust. J. Geol. 102, 121–138. Blenkinsop, T., Martin, A., Jelsma, H.A., 1997. The Zimbabwe Craton. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 761–771. Bodinier, J.L., Dupuy, C., Dostal, J., 1989. Geochemistry of Precambrian ophiolites from Bou Azzer, Morocco. Contrib. Mineral. Petrol. 87, 43–50.

Boher, M., Abouchami, W., Michard, A., Albarede, A., Arndt, N.T., 1992. Crustal growth in west Africa at 2.1 Ga. J. Geophys. Res. 97, 345–369. Bowring, S.A., Williams, I.S., Compston, W., 1989. 3.96 Ga gneisses from the Slave Province, Northwest Territories. Geology 17, 969–1064. Bowring, S.A., Housh, T.B., Isachsen, C.R., 1990. The Acasta gneisses: remnant of Earth’s earliest crust. In: Newsom, H., Jones, J. (Eds.), Origin of the Earth. Oxford University Press, Oxford, pp. 319–343. Bradley, D.C., Haeussler, P.J., Kusky, T.M., 1994. Timing of Early Tertiary ridge subduction in southern Alaska. In: Till, A. (Ed.), Geologic Studies in Alaska by the U.S. Geological Survey during 1992. U.S. Geol. Surv. Bull. 2068, 163–177. Brandl, G., de Wit, M.J., 1997. The Kaapvaal Craton. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 581–607. Burchfiel, B.C., Cowan, D.S., Davis, G.A., 1992. Tectonic overview of the Cordilleran orogen in the western United States. In: Burchfiel, C.B., Lipman, P.W., Zoback, M.I. (Eds.), The Geology of North America, The Cordilleran Orogen: Conterminous U.S. Geol. Soc. Am. C-3, pp. 407–478. Burke, K., 1995. Did plate tectonics operate in the Archean? Precambrian 95, Montreal, Prog. Abstr., p. 277, Burke, K., Dewey, J.F., Kidd, W.S.F., 1976. Dominance of horizontal movements, arc and microcontinental collisions during the later permobile regime. In: Windely, B.F. (Ed.), The Early History of the Earth. Wiley, New York, pp. 113–129. Burke, K., Fox, P.J., Sengo¨r, A.M.C., 1978. Buoyant ocean floor and evolution of the Caribbean. J. Geophys. Res. 83, 3949– 3954. Card, K.D., 1990. A review of the Superior Province of the Canadian Shield, a product of Archean accretion. Precambrian Res. 48, 99–156. Condie, K.C., 1981. Archean Greenstone Belts. Developments in Precambrian Geology 3, Elsevier, Amsterdam, 434 pp. Condie, K.C., 1986. Geochemistry and tectonic setting of early Proterozoic supracrustal rocks in the southwestern United States. J. Geol. 94, 845–864. Condie, K.C., 1994. Greenstones through time. In: Condie, K.C. (Ed.), Archean Crustal Evolution. Elsevier, Amsterdam, pp. 85–120. Condie, K.C., 1997a. Contrasting sources for upper and lower continental crust: the Greenstone Connection. J. Geol. 105, 729–736. Condie, K.C., 1997b. Plate Tectonics and Crustal Evolution. Butterworth-Heinemann, Bath, 492 pp. Coney, P.J., 1989. Structural aspects of suspect terrains and accretionary tectonics in western North America. J. Struct. Geol. 11, 107–125. Corfu, F., Muir, T.L., 1989a. The Hemlo–Heron Bay greenstone belt and Hemlo Au–Mo deposit, Superior Province, Ontario, Canada, 1. Sequence of igneous activity determined by zircon U–Pb geochronology. Chem. Geol. 79, 183–200. Corfu, F., Muir, T.L., 1989b. The Hemlo–Heron Bay greenstone belt and Hemlo Au–Mo deposit, Superior Province, Ontario, Canada, 2. Timing of metamorphism, alteration and

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73 Au mineralization from titanite, rutile, and monozite U–Pb geochronology. Chem. Geol. 79, 201–223. Curtis, M.L., 1997. Gondwanian age dextral transpression and spatial kinematic partitioning within the Heritage Range, Elleseworth Mountains, West Antarctica. Tectonics 16, 172–181. Dalziel, I.W.D., de Wit, M.J., Palmer, K.F., 1974. Fossil marginal basin in the southern Andes. Nature 250, 291–294. Danielson, A., Kaufman, A.J. (Eds.), 1996. Geology and Geochemistry of the Transvaal Supergroup, Southern Africa. Precambrian Res. 79, 200 pp. Dann, J.C., 1991. Early Proterozoic ophiolite, central Arizona. Geology 19, 590–593. Dennis, A.J., Wright, J.E., 1997. The Caroline terrane in northwestern South Caroline, U.S.A.: Late Precambrian–Cambrian deformation and metamorphism in a peri-Gondwanan ocean. Tectonics 16, 460–473. de Ronde, E.J., de Wit, M.J., 1994. Tectonic history of the Barberton greenstone belt, South Africa: 490 million years of Archean crustal evolution. Tectonics 13, 983–1005. Desrochers, J.-P., Hubert, C., Ludden, J.N., Pilote, P., 1993. Accretion of Archean plateau fragments in the Abitibi greenstone belt, Canada. Geology 21, 451–454. Dewey, J.F., 1988. Extensional collapse of orogens. Tectonics 7, 1123–1139. Dewey, J.F., Bird, J., 1971. Origin and emplacement of the ophiolite suite: Appalachian ophiolites in Newfoundland. In: Bird, J.M. (Ed.), Plate Tectonics. J. Geophys. Res. 76, 3179– 3206. Dewey, J.F., Windley, B.F., 1981. Growth and differentiation of the continental crust. Philos. Trans. R. Soc. London A 301, 189–206. Dewey, J.J., 1977. Suture zone complexities: a review. Tectonophysics 40, 53–67. de Wit, M.J., Ashwal, L.D., 1986. Workshop on the Tectonic Evolution of Greenstone Belts. NASA=Lunar and Planetary Institute Technical Report 86-10, 227 pp. de Wit, M.J., Ashwal, L.D. (Eds.), 1997. Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 809 pp. de Wit, M.J., Stern, C.R., 1981. Variations in the degree of crustal extension during the formation of a back-arc basin. Tectonophysics 72, 229–260. de Wit, M.J., Hart, R.A., Martin, A., Abbott, P., 1982. Archean abiogenic and probable biogenic structures associated with mineralized hydrothermal vent systems and regional metasomatism, with implications for greenstone belt studies. Econ. Geol. 77, 1783–1802. de Wit, M.J., Hart, R.A., Hart, R.J., 1987. The Jamestown ophiolite complex, Barberton mountain belt: a section through 3.5 Ga oceanic crust. J. Afr. Earth Sci. 6, 681–730. de Wit, M.J., Tredoux, M., Hart, R.A., Eos 71, 969–970. de Wit, M.J., Roering, C., Hart, R.J., Armstrong, R.A., de Ronde, C.E.J., Green, R.W.E., Tredoux, M., Peberdy, E., Hart, R.A., 1992. Formation of an Archean continent. Nature 357, 553– 562. Dobretsov, N.N., Popov, N.V., Smelov, A.P., Bogomolova, L.M., Moscovchenko, N.I., Barton, J.M., Jr., 1997. The Aldan–

69

Stanovic Shield. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 710–729. Drummond, M.S., Defant, M.J., 1990. A model for trondhjemite–tonalite–dacite genesis and crustal growth via slab melting: Archean to modern comparisons. J. Geophys. Res. 95, 21503–21521. England, P.C., Bickle, M.J., 1984. Continental thermal and tectonic regimes during the Archean. J. Geol. 92, 353–368. Feng, R., Kerrich, R., 1992. Geochemical evolution of granitoids from the Archean Abitibi Southern Volcanic Zone and the Pontiac subprovince, Superior Province, Canada: implications for tectonic history and source regions. Chem. Geol. 98, 23– 78. Floyd, P.A., 1989. Geochemical features of intra-plate oceanic plateau basalts. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins. Geol. Soc. London Spec. Publ. 42, 215–230. Fralick, P., 1997. Neoarchean Evolution of the Wabigoon Subprovince: Evidence from the Sedimentary Record. Western Superior Lithoprobe Transect, Third Workshop Report. Friend, C.R.L., Nutman, A.P., McGregor, V.R., 1988. Late Archean terrane accretion in the Godthab region, southern West Greenland. Nature 335, 535–538. Fripp, R.E.P., Jones, M.G., 1997. Sheeted intrusions and peridotite–gabbro assemblages in the Yilgarn Craton, western Australia: elements of Archean ophiolites. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 422–437. Froude, D.O., Ireland, T.R., Kinney, P.D., Williams, R.S., Compston, W., Williams J., A.R., Myers, J., 1983. Ion-microprobe identification of 4,100–4,200 Myr-old detrital zircons. Nature 304, 616–618. Fuh, S.C., Liu, C.S., Lundberg, N., Reed, D., 1997. Strike-slip faults offshore southern Taiwan: implications for the oblique arc–continent collision processes. Tectonophysics 274, 25–39. Furman, T., Frey, F., Park, K.H., 1995. The scale of source heterogeneity beneath the eastern neovolcanic zone, Iceland. J. Geol. Soc. London 152, 997–1002. Fyfe, W.S., 1978. Evolution of the Earth’s crust: modern plate tectonics to ancient hotspot tectonics. Chem. Geol. 23, 89– 114. Garrison Jr., J.R., 1981. Coal Creek serpentinite, Llano uplift Texas: a fragment of an incomplete Precambrian ophiolite. Geology 9, 225–230. Goodwin, A., 1991. Precambrian Geology. Academic Press, London, 666 pp. Goodwin, A., 1996. Principles of Precambrian Geology. Academic Press, London, 327 pp. Grand, S.P., 1987. Tomographic inversion for shear velocity beneath the North American plate. J. Geophys. Res. 92, 14065– 14090. Grand, S.P., 1994. Mantle shear structure beneath the Americas and surrounding oceans. J. Geophys. Res. 99, 11591–11621. Grotzinger, J.P., 1989. Facies and evolution of Precambrian carbonate depositional systems: emergence of the modern platform archetype. In: Controls on Carbonate Platform and Basin

70

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

Development. Soc. Econ. Paleontol. Mineral. Spec. Publ. 44, 79–106. Grove, T.L., Gaetani, G.J., de Wit, M.J., 1994. Spinifex textures in 3.49 Ga Barberton Mountain belt komatiites: evidence for crystallization of water-bearing, cool magmas in the Archean. Eos 75 (16), 354. Gurnis, M., 1988. Large scale mantle convection and the aggregation and dispersal of supercontinents. Nature 332, 695– 699. Hamilton, W.B., 1970. The Uralides and the motion of the Russian and Siberian platforms. Geol. Soc. Am. Bull. 81, 2553–2576. Hamilton, W.B., 1988. Plate tectonics and island arcs. Geol. Soc. Am. Bull. 100, 1503–1527. Hamilton, W.B., 1998. Archean tectonics and magmatism. Int. Geol. Rev. 40, 1–39. Hansen, V.L., 1992. Back flow and margin parallel shear within an ancient subduction accretion complex. Geology 20, 71–74. Hanson, R.E., Wilson, T.J., 1991. Submarine rhyolitic volcanism in a Jurassic protomarginal basin, southern Andes, Chile and Argentina. In: Harmon, R.S., Rapela, C.W. (Eds.), Andean Magmatism and its Tectonic Setting. Geol. Soc. Am. Spec. Pap. 265, 13–27. Hards, V.L., Kempton, P.D., Thompson, R.N., 1995. The heterogeneous Iceland plume: new insights from the alkaline basalts of the Snaefell volcanic centre. J. Geol. Soc. 150, 1003–1009. Harper, G.D., 1985. A dismembered Archean ophiolite, Wind River Mountains, Wyoming (USA). Ophioliti 10, 297–306. Hasebe, N., Tagami, T., Nishimura, S., 1993. Evolution of the Shimanto accretionary complex: a fission-track thermochronologic study. In: Underwood, M.B. (Ed.), Thermal Evolution of the Tertiary Shimanto Belt, Southwest Japan: An Example of Ridge–Trench Interaction. Geol. Soc. Am. Spec. Pap. 273, 121–136. Helmstaedt, H., Doig, R., 1975. Eclogite nodules from kimberlite pipes of the Colorado plateau— samples of subducted Franciscan-type oceanic lithosphere. Phys. Chem Earth 9, 95– 112. Helmstaedt, H., Shulze, D.J., 1989. Southern African kimberlites and their mantle sample: implications for Archean tectonics and lithosphere evolution. In: Kimberlites and Related Rocks. Blackwell, Carleton, pp. 358–368. Helmstaedt, H., Padgham, W.A., Brophy, J.A., 1986. Multiple dikes in the lower Kam Group, Yellowknife greenstone belt: evidence for sea floor spreading? Geology 14, 562–566. Hemond, C., Arndt, N., Liechtenstein, U., Hofmann, A.F., 1993. The heterogeneous Iceland Plume, Nd–Sr–O isotopes and trace element constraints. J. Geophys. Res. 98, 15833–15850. Hoffman, P.F., 1991. On accretion of granite–greenstone terranes. In: Robert, F., Sheahan, P.A., Green, S.B. (Eds.), Nuna Conference on Greenstone Gold and Crustal Evolution, Val d’Or. Geol. Assoc. Can., pp. 32–45. Hoffman, P.F., 1997. Tectonic genealogy of North America. In: van der Pluijm, B., Marshak, S. (Eds.), Earth Structure: An Introduction to Structural Geology and Tectonics. McGraw Hill, London, pp. 459–464. Hoffman, P.F., 1989. Precambrian geology and tectonic history

of North America. In: Bally, A.W., Palmer, A.R. (Eds.), The Geology of North America, Vol. A. An Overview. Geol. Soc. Am., pp. 447–512. Hoffman, P.F., Ranalli, G., 1988. Archean oceanic flake tectonics. Geophys. Res. Lett. 15, 1077–1080. Hofmann, A.W., 1988. Chemical differentiation of the Earth: the relationships between, mantle, continental crust, and oceanic crust. Earth Planet. Sci. Lett. 90, 297–314. Hollister, L.S., Andronicos, C.L., 1997. A candidate for the Baja British Columbia Fault system in the Coast Plutonic Complex. GSA Today 7, 1–7. Hudleston, P.J., Schultz-Ala, D., Southwick, D.L., 1988. Transpression in an Archean greenstone belt, northern Minnesota. Can. J. Earth Sci. 25, 1060–1068. Hugon, H., 1984. The Hemlo deposit: mineralization within a dextral shear zone. Ont. Geol. Surv. Misc. Pap. 119, 212–216. Hutton, D.H.W., Reavy, R.J., 1992. Strike-slip tectonics and granite petrogenesis. Tectonics 11, 960–967. Isachsen, C.I., Bowring, S.A., 1997. The Bell Lake Group and Anton Complex — a basement cover sequence beneath the Yellowknife greenstone belt revealed and implicated in greenstone belt formation. Can. J. Earth Sci. 34, 169–189. Isachsen, C.I., Bowring, S.A., Padgham, W.A., 1991. U–Pb zircon geochronology of the Yellowknife volcanic belt, N.W.T.: new constraints on the timing and duration of greenstone belt magmatism. J. Geol. 99, 55–67. Isozaki, Y., Maruyama, S., Furuoka, F., 1990. Accreted oceanic materials in Japan. Tectonophysics 181, 179–205. Isozaki, Y., Endo, H., Ohta, I., Suzuki, S., Maruyama, S., Kimura, G., 1992, Middle Archean (3.3 Ga) Cleaverville accretionary complex in northwestern Pilbara block, W. Australia. Symp. Evolving Earth, Okazaki, Abstr., pp. 128–131. Jackson, S.L., Cruden, R.A., 1995. Formation of the Abitibi greenstone belt by arc–trench migration. Geology 23, 471– 474. Jacob, D., Jagoutz, E., Lowry, D., Mattey, D., ad Kudrjavtseva, G., 1994. Diamoniferous eclogites from Siberia: remnants of Archean oceanic crust. Geochim. Cosmochim. Acta 58, 5191– 5207. Jagoutz, E., Dawson, J.B., Hoernes, S., Spettel, B., Wanke, H., 1984. Anorthositic oceanic crust in the Archean Earth. 15th Lunar Planet. Sci. Conf., pp. 395–396. Jochum, K.P., Arndt, N.T., Hofmann, A.W., 1991. Nb–Th–La in komatiites and basalts: constraints on komatiite petrogenesis and mantle evolution. Earth Planet. Sci. Lett. 107, 272–289. Jones, G., Sano, H., Valsami-Jones, E., 1993. Nature and tectonic setting of accreted basalts from the Mino terrane, central Japan. J. Geol. Soc. London 150, 1167–1181. Jordan, T.H., 1988. Structure and formation of the continental tectosphere. J. Petrol. Spec. Lithosphere Iss., pp. 11–37. Karsten, J.L., Klein, E.M., Sherman, S.B., 1996. Subduction zone geochemical characteristics in ocean ridge basalts from the southern Chile Ridge: implications for modern ridge subduction system for Archean. Lithos 37, 143–161. Kerrich, R., Polat, A., Wyman, D., Hollings, P., 1996. Trace element systematics of TTG plutons of the late Archean

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73 Schreiber–Hemlo greenstone belt, Canada: implications for petrogenesis. Eos 77, F849. Kimura, G., Ludden, J.N., Desrochers, J.P., Hori, R., 1993. A model of ocean crust accretion for the Superior province, Canada. Lithos 30, 337–355. Kimura, G., Sakakibara, M., Okamura, M., 1994. Plumes in central Panthalassa? Deductions from accreted oceanic fragments in Japan. Tectonics 13, 905–916. Kincaid, C., Schilling, J.G., Gable, C., 1996. The dynamics of off-axis plume-ridge interaction in the uppermost mantle. Earth Planet. Sci. Lett. 137, 4–29. King, J.E., Helmstaedt, H., 1997. The Slave Province, NorthWest Territories, Canada. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 459– 479. Kiyokawa, S., Taira, A., 1995. Obducted island arc origin for a middle Archean greenstone belt: west Pilbara coastal greenstone belt, western Australia. Precambrian 95, Montreal, Prog. Abstr., p. 75, Klein, E.M., Karsten, J.L., 1995. Ocean ridge basalt with convergent margin affinities from the Chile Ridge. Nature 374, 52–57. Komiya, T., Maruyama, S., Masuda, T., Appel, P., Nohda, S., 1999. 3.8–3.7 Ga plate tectonics on the Earth; field evidence from Isua accretionary complex, West Greenland. J. Geol. (in press). Kro¨ner, A., 1985. Ophiolites and the evolution of tectonic boundaries in the late Proterozoic Arabian–Nubian Shield of northeast Africa and Arabia. Precambrian Res. 27, 277–300. Kuhns, R.J., Sawkins, F.J., Ito, E., 1994. Magmatism, metamorphism, and deformation at Hemlo, Ontario, and the timing of Au–Mo mineralization in the golden giant mine. Econ. Geol. 89, 720–756. Kusky, T.M., 1986. Are greenstone belts in the Slave Province allochthonous? In: De Wit, M.J., Ashwal, L. (Eds.), Workshop on the Tectonic Evolution of Greenstone Belts. NASA=Lunar and Planetary Institute Technical Report 86-10, pp. 135–139. Kusky, T.M., 1987. Comment on ‘Multiple dikes in the lower Kam Group, Yellowknife Greenstone Belt: evidence for Archean sea-floor spreading?’ Geology 15, 280–282. Kusky, T.M., 1989. Accretion of the Archean Slave Province. Geology 17, 63–67. Kusky, T.M., 1990. Evidence for Archean ocean opening and closing in the southern Slave Province. Tectonics 9, 1533– 1563. Kusky, T.M., 1991. Structural development of an Archean orogen, western Point Lake, Northwest Territories. Tectonics 10, 820–841. Kusky, T.M., 1993. Collapse of Archean orogens and the generation of late- to post-kinematic granitoids. Geology 21, 925– 928. Kusky, T.M., 1998. Tectonic setting and terrane accretion of the Archean Zimbabwe craton. Geology 26, 163–166. Kusky, T.M., Hudleston, P.J., 1998. Growth and demise of an Archean carbonate platform, Steep Rock Lake, Ontario, Canada. Can. J. Earth Sci., in press. Kusky, T.M., Kidd, W.S.F., 1992. Remnants of an Archean

71

oceanic plateau, Belingwe greenstone belt, Zimbabwe. Geology 20, 43–46. Kusky, T.M., Vearncombe, J.R., 1997. Structural aspects. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 91–124. Kusky, T.M., Winsky, P.A., 1995. Structural relationships along a greenstone=shallow water shelf contact, Belingwe greenstone belt, Zimbabwe. Tectonics 14, 448–471. Kusky, T.M., Bradley, D.C., Haeussler, P., Karl, S., 1997a. Controls on accretion of flysch and me´lange belts at convergent margins: evidence from the Chugach Bay thrust and Iceworm me´lange, Chugach Terrane, Alaska. Tectonics 16, 855–878. Kusky, T.M., Bradley, D.C., Haeussler, P., 1997b. Progressive deformation of the Chugach accretionary complex, Alaska, during a Paleogene ridge–trench encounter. J. Struct. Geol. 19, 139–157. Langmuir, C.H., Klein, E.M., Planl, T., 1992. Petrological constraints of mid-ocean ridge basalts: constraints on melt generation beneath ocean ridge. In: J.P. Morgan, Blackman, D.K., Sinton, J.M. (Eds.), Mantle Flow and Melt Generation at MidOcean Ridges. Trans. Am. Geophys. Union 71, 183–280. MacGregor, I.D., Manton, W.I., 1986. Roberts Victor eclogites: ancient oceanic crust. J. Geophys.Res. 91, 14063–14079. MacLaughlin, K., Helmstaedt, H., 1995. Geology and geochemistry of an Archean mafic dike complex in the Chan Formation: basis of a revised plate tectonic model of the Yellowknife greenstone belt. Can. J. Earth Sci. 32, 614–630. Mahoney, J.J., Storey, M., Duncan, R.A., Spencer, K.J., Pringle, M., 1993. Geochemistry and geochronology of Leg 130 basement lavas: nature and origin of the Ontong-Java Plateau. Proc. ODP, Sci. Results 130, 3–22. Martin, H., 1986. Effect of steeper Archean geothermal gradient on geochemistry of subduction zone magmas. Geology 14, 753–756. Martin, H., 1993. The mechanisms of petrogenesis of the Archean continental crust — comparison with modern processes. Lithos 30, 373–388. Maruyama, S., Masuda, T., Appel, P., 1991. The oldest accretionary complex on the earth, Isua, Greenland. Geol. Soc. Am. Abstr. Prog. p. A429. Matsuda, T., Uyeda, S., 1971. On the Pacific type orogeny and its model: extension of the paired belts concept and possible origin of marginal seas. Tectonophysics 11, 223–236. McCaffrey, R., 1992. Oblique plate convergence, slip vectors, and forearc deformation. J. Geophys. Res. 97, 8905–8915. McCulloch, M.T., Bennett, V.C., 1994. Progressive growth of the Earth’s continental crust and depleted mantle: geochemical constraints. Geochim. Cosmochim. Acta 58, 4717–4738. McDonough, W.F., Ireland, T.R., 1993. Intraplate origin of komatiites inferred from trace elements in glass inclusions. Nature 365, 432–434. McKenzie, D., Bickle, M.J., 1988. The volume and composition of melts generated by extension of lithosphere. J. Petrol. 29, 624–679. Melancon, B., Hebert, R., Laurent, R., Dostal, J., 1997. Petrological and geochemical characteristics of the Bolton Quebec Appalachians. Am. J. Sci. 297, 527–549.

72

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73

Miller, E.L., Miller, M.M., Stevens, C.H., Wright, J.E., Madrid, R., 1992. Late Palaeozoic paleogeographic and tectonic evolution of the western U.S. Cordillera. In: Burchfiel, B.C., Lipman, P.W., Zoaback, M.I. (Eds.), The Cordilleran Orogen: Conterminous U.S. Geol. Soc. Am., G-3, pp. 57–106. Moores, E., 1986. The Proterozoic ophiolite problem, continental emergence, and the Venus connection. Science 234, 65–68. Moores, E.M., 1982. Origin and emplacement of ophiolites. Rev. Geophys. 20, 735–750. Mueller, W.U., Daigneault, R., Mortensen, J.K., Chowen, E.H., 1996. Archean terrane docking: upper crust collision tectonics, Abitibi greenstone belt, Quebec, Canada. In: Kusky, T., van der Pluijm, B., Coney, P., Condie, K. (Eds.), Tectonic Setting and Terrane Accretion in Precambrian Orogens. Tectonophysics 265, 127–150. Muir, T.L., Elliott, C.G., 1987. Hemlo tectono-stratigraphic study, district of Thunder Bay. Ont. Geol. Surv. Misc. Pap. 137, 117–129. Myers, J.S., 1993. Precambrian history of the west Australian craton and adjacent orogens. Annu. Rev. Earth. Planet. Sci. 21, 453–485. Myers, J.S., Swager, C., 1997. The Yilgarn Craton. In: de Wit, M., Ashwal, L.D. (Ed.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 640–656. Nelson, K.D., 1991. A unified view of craton evolution motivated by recent deep seismic reflection and refraction results. Geophys. J. Int. 105, 25–35. Nisbet, E.G., Cheadle, M.J., Arndt, N.T., Bickle, M.J., 1993a. Constraining the potential temperature of the Archean mantle: a review of the evidence from komatiites. Lithos 30, 291–307. Nisbet, E.G., Martin, A., Bickle, M.J., Orpen, J.L., 1993. The Ngezi Group komatiites, basalts, and stromatolites on continental crust. In: Bickle, M.J., Nisbet, E.G. (Eds.), The Geology of the Belingwe Greenstone Belt. Balkema, Rotterdam, pp. 121–166. O’Brien, B.H., Swinden, H.S., Dunning, G.R., Williams, S.H., O’Brien, F.H.C., 1997. A Peri-Gondwanan arc–back-arc complex in the Iapetus: early-mid Ordovician evolution of the Exploits Group, Newfoundland. Am. J. Earth Sci. 297, 220– 272. Ohta, H., Maruyama, S., Takahashi, E., Watanabe, Y., Kato, Y., 1996. Field occurrence, geochemistry and petrogenesis of the Archean mid-ocean ridge basalts (AMORB) of the Cleaverville area, Pilbara Craton, western Australia. Lithos 37, 199–221. Page, R.A., Plafker, G., Fuis, G.S., Nokleberg, W.J., Ambos, E.L., Mooney, W.D., Campbell, D.L., 1986. Accretion and subduction tectonics in the Chugach Mountains and Copper River Basin, Alaska: initial results of the Trans-Alaska Crustal Transect. Geology 14, 501–505. Park, A.F., 1991. Continental growth by accretion: A tectonostratigraphic terrane analysis of the evolution of the western and central Baltic Shield, 2.50 to 1.75 Ga. Geol. Soc. Am. Bull. 103, 522–537. Parman, S.W., Dann, J.C., Grove, T.L., de Wit, M.J., 1997. Emplacement conditions of komatiite magmas from the 3.49

Ga Komati formation, Barberton greenstone belt, south Africa. Earth Planet. Sci. Lett. 150, 303–323. Percival, J.A., Stern, R.A., Skulski, T., Card, K.D., Mortensen, J.K., Begin, N.J., 1994. Minto block, Superior province: Missing link in deciphering assembly of the craton at 2.7 Ga. Geology 22, 839–842. Pimentel, M.M., Fuck, R.A., 1992. Neoproterozoic crustal accretion in central Brazil. Geology 20, 375–379. Polat, A., 1998. Geodynamics of the Late Archean Wawa Subprovince Greenstone Belts, Superior Province, Canada. Ph.D. Dissertation, University of Saskatchewan, Sask., 217 pp. Polat, A., Kerrich, R., Wyman, D., Hollings, P., 1996a. Plume and magmatic arc accretion in the late Archean Schreiber– Hemlo greenstone belt: evidence from trace element systematics, Superior Province, Canada. Eos 77, F849. Polat, A., Casey, J.F., Kerrich, R., 1996b. Geochemical characteristics of accreted material beneath the Pozanti–Karsanti ophiolite, Turkey: intra-oceanic detachment, assembly and obduction. Tectonophysics 263, 249–276. Polat, A., Kerrich, R., Wyman, D.A., 1998. The late Archean Schreiber–Hemlo and White River–Dayohessarah greenstone belts, Superior Province: collages of oceanic plateaus, oceanic arcs, and subduction–accretion complexes. Tectonophysics 289, 295–326. Polat, A., Kerrich, R., Wyman, D.A., 1999. Geochemical diversity in oceanic komatiites and basalts from the Late Archean Wawa greenstone belt, Superior Province, Canada: trace element and Nd isotopic evidence for a heterogeneous mantle. Precambrian Res. 94, 139–173. Puchtel, I.S., Hofmann, A.W., Jochum, K.P., Mezger, K., Shchippansky, A.A., Samsanov, A.V., 1997a. The Kostomuksha greenstone belt, NW Baltic Shield: remnant of a late Archean oceanic plateau? Terra Nova 9, 87–90. Puchtel, I.S., Shchipansky, A.A., Samsonov, A.V., Zhuralev, D.Z., 1997b. The Karelian granite–greenstone in Russia. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 699–706. Purdon, R.H., 1995. Lithostratigraphy and provenance of the Neoarchean McKellar Harbour Sequence, Superior Province, Ontario, Canada. Unpubl. M.Sc. Thesis, Lakehead University, 103 pp. Rapp, R.P., 1997. Heterogeneous source regions for Archean granitoids: experimental and geochemical evidence. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 267–279. Reymer, A., Schubert, G., 1986. Rapid growth of some major segments of continental crust. Geology 14, 299–302. Richards, M.A., Jones, D.L., Duncan, R.A., DePaolo, D.J., 1991. A mantle plume initiation model for the Wrangellia flood basalts and other oceanic plateaus. Science 254, 263–267. Robin, P.Y.F., Cruden, A.R., 1994. Strain and vorticity in ideally ductile transpression zones. J. Struct. Geol. 16, 447–466. Rudnick, R.L., 1995. Making continental crust. Nature 378, 571– 578. Saleeby, J.B., 1992. Petrotectonic and paleogeographic settings of U.S. Cordilleran ophiolites. In: Burchfiel, B.C., Lipman,

T.M. Kusky, A. Polat / Tectonophysics 305 (1999) 43–73 P.W., Zoaback, M.I. (Eds.), The Cordilleran Orogen: Conterminous U.S. Geol. Soc. Am., G-3, pp. 653–683. Salters, V.J., Storey, M., Seving, J.H., Whitechurch, H., 1992. Trace element characteristics of Kerguelen-Head plateau basalts. Proc. ODP, Sci. Results 120, 55–62. Samson, S.D., Pachett, P.J., 1991. The Canadian Cordilleran as a modern analogue of Proterozoic crustal growth. Aust. J. Earth Sci. 38, 595–611. Sengo¨r, A.M.C., 1990. Plate tectonics and orogenic research after 25 years: a Tethyan perspective. Earth Sci. Rev. 27, 1–201. Sengo¨r, A.M.C., 1993. Turkic-type orogeny in the Altaids: implications for the evolution of continental crust and methodology of regional tectonics. Trans. Leicester Literary Philos. Soc. 87, 37–51. Sengo¨r, A.M.C., Natal’in, B.A., 1996. Turkic-type orogeny and its role in the making of the continental crust. Annu. Rev. Earth. Planet. Sci. 24, 263–337. Sengo¨r, A.M.C., Yilmaz, Y., 1981. Tethyan evolution of Turkey: a plate tectonic approach. Tectonophysics 75, 181–241. Sengo¨r, A.M.C., Natal’in, B.A., Burtman, V.S., 1993. Evolution of the tectonic collages and Palaeozoic crustal growth in Eurasia. Nature 364, 299, 307. Sengo¨r, A.M.C., Graham, S.A., Biddle, K.T., 1996. Is the Tarim basin underlain by a Neoproterozoic oceanic plateau? Geol. Soc. Am. Abstr. Prog. 28=7, A-67. Sleep, N., Windley, B.F., 1982. Archean tectonics: constraints and inferences. J. Geol. 90, 363–379. Stein, M., Goldstein, S.L., 1996. From plume head to continental lithosphere in the Arabian–Nubian Shield. Nature 382, 773– 778. Stein, M., Hofmann, A.W., 1994. Mantle plumes and episodic crustal growth. Nature 372, 63–68. Stern, C.R., de Wit, M.J., 1997. The Rocas Verdes ‘Greenstone Belt’, Southernmost South America. In: In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 791–801. Stern, R.A., Syme, E.C., Lucas, S.B., 1995a. Geochemistry of 1.9 Ga MORB- and OIB-like basalts from the Amisk collage, Flin Flon Belt, Canada, Evidence for an intra-oceanic origin. Geochim. Cosmochim. Acta 59, 3131–3154. Stern, R.A., Syme, E.C., Lucas, S.B., 1995b. Paleoproterozoic (1.90–1.86 Ga) arc volcanics in the Flin Flon Belt, TransHudson orogen, Canada. Contrib. Mineral. Petrol. 119, 117– 141. St-Onge, M.R., Lucas, S.B., Scott, D.J., Begin, N.J., 1989. Evidence for the development of oceanic crust and for continental rifting in tectonostratigraphy of the early Proterozoic Cape Smith belt. Geosci. Can. 16, 119–122. Storey, M., Mahoney, J.J., Kroenke, L.W., Saunders, A.D., 1991. Are oceanic plateaus sites of komatiite formation? Geology 19, 376–379. Sylvester, P.J., Harper, G.D., Byerly, G.R., Thurston, P.C., 1997. Volcanic aspects. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 55–90. Tardy, M., and 12 others, 1994. The Guerrero suspect Terrane

73

(western Mexico) and coeval arc terranes (the Greater Antilles and western Cordillera of Columbia) a late Mesozoic intra-oceanic arc accreted to America during the Cretaceous. Tectonophysics 230, 49–73. Tarney, J., Jones, C.E., 1994. Trace element geochemistry of orogenic igneous rocks and crustal growth models. J. Geol. Soc. London 151, 855–868. Tarney, J., Dalziel, I.W.D., De Wit, M.J., 1976. Marginal basin ‘Rocas Verdes’ complexes from S. Chile: A model for Archean greenstone belt formation. In: Windely, B.F. (Ed.), The Early History of the Earth. Wiley, New York, pp. 131– 146. Taylor, S.R., McLennan, S.M., 1995. The geochemical evolution of the continental crust. Rev. Geophys. 33, 241–265. Thurston, P.C., 1990. The Superior Province-emphasizing greenstone belts. In: Gold and Base-Metal Mineralization in the Abitibi Subprovince, Canada, with Emphasis on the Quebec Segment. Geol. Dept (Key Centre) and University Extension, University of Western Australia, Publ. 24, pp. 1–52. Tikoff, B., Saint Blanquat, M.S., 1997. Transpressional shearing and strike-slip partitioning in the late Cretaceous Sierra Nevada magmatic arc, California. Tectonics 16, 442–459. Unesco, 1976. Geological World Atlas, 1:10,000,000. Unesco and Commission for the Geological Map of the World, Paris. van Staal, C.R., S.P., Colman-Sadd, 1997. The Central mobile belts of the northern Appalachians. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 747–780. Vergara, M., Levi, B., Nystrom, J.O., Cancino, A., 1995. Jurassic and early Cretaceous island arc volcanism in the Coast range of Central Chile. Geol. Soc. Am. Bull. 107, 1427–1440. Walker, J.W.R., 1967. Geology of the Jackfish–Middleton area. Ontario Department of Mines, Geology Report 50, pp. 1–41. Wilks, M.E., Harper, G.D., 1997. Wind River Range, Wyoming Craton. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 508–516. Williams, H.R., Stott, G.M., Heather, K.B., Muir, T.L., Sage, R.P., 1991. Wawa Subprovince. In: Thurston, P.C., Williams, H.R., Sutclife, H.R., Stott, G.M. (Eds.), Geology of Ontario. Ont. Geol. Surv., Spec. Vol. 4, Part 1, pp. 485–539. Windley, B.F., Whitehouse, J., Ba-Bttat, M.A.O., 1996. Early Precambrian gneisses and Pan-African island arcs in Yemen: crustal accretion of eastern Arabian shield. Geology 24, 131– 134. Wyllie, P.J., Wolf, M.B., van der Laan, S.R., 1997. Conditions for formation of tonalites and trondhjemites: magmatic sources and products. In: de Wit, M., Ashwal, L.D. (Eds.), Greenstone Belts. Oxford Monogr. Geol. Geophys. 35, 256–266. Xie, Q., Kerrich, R., Fann, J., 1993. HFSE=REE fractionation recorded in three komatiite basalt sequence, Archean Abitibi greenstone belt: implications for multiple sources and depths. Geochim. Cosmochim. Acta. 57, 4111–4118. Xue, F., Lerch, M.F., Kro¨ner, A., Reischmann, T., 1996. Tectonic evolution of the east Qinling Mountains in the Palaeozoic: a review and new tectonic model. Tectonophysics 253, 271–284.