Epilogue: What if Anything Have We Learned About Precambrian Ophiolites and Early Earth Processes?

Precambrian Ophiolites and Related Rocks Edited by Timothy M. Kusky Developments in Precambrian Geology, Vol. 13 (K.C. Condie, Series Editor) © 2004 Elsevier B.V. All rights reserved.

727

Chapter 22

EPILOGUE: WHAT IF ANYTHING HAVE WE LEARNED ABOUT PRECAMBRIAN OPHIOLITES AND EARLY EARTH PROCESSES? TIMOTHY M. KUSKY Department of Earth and Atmospheric Sciences, St. Louis University, St. Louis, MO 63103, USA

The chapters in this book have presented clear, even unequivocal evidence that Precambrian ophiolites are preserved in many Precambrian terranes. Proterozoic examples are abundant, especially in the Arabian Nubian Shield, where ophiolites have been recognized for many years. Archean examples are more controversial but a number of excellent examples of whole, dismembered, and metamorphosed ophiolites are described in this volume. In this brief epilogue, we assess what, if anything, we have learned about the early Earth from the identification of specific sequences as ophiolitic. In addition, we present a new list of criteria to help discriminate between ophiolitic and other sequences. The recognition that many of the allochthonous mafic/ultramafic complexes in Archean and Proterozoic greenstone belts are ophiolites provides researchers with a much longer record of oceanic processes than the record from Phanerozoic ophiolites alone. From this record we are able to deduce that the classical Penrose model (Anonymous, 1972) for the structure of ophiolitic lithosphere is too simplistic to explain the great variations found in ophiolites over this greater sample of time. The Penrose model for ophiolite stratigraphy is too restrictive to explain even present day sea floor and Paleozoic ophiolites, which all show much greater diversity (related to spreading rate, temperature, magma supply, etc.). Since modern environments and young ophiolites rarely conform to this strict definition, it makes little sense for Precambrian ophiolites to be held to this standard for recognition. It is more sensible to allow the diversity of modern ophiolites to be a guide to recognizing older ophiolites and their tectonic settings, and then to try to determine, through comparison, if there are any significant secular changes in ophiolitic structure and stratigraphy with time. With this caveat in mind, the chapters in this book have identified dozens of Precambrian ophiolites that contain an ophiolitic igneous stratigraphy. This basic recognition opens the way for a myriad of other studies on the chemistry, structure, thickness, rheology, biology, and other aspects of ancient oceanic crust and lithosphere that are only beginning to be appreciated. Once this recognition becomes more widespread and accepted, even greater insight to processes on the early Earth will be obtained. DOI: 10.1016/S0166-2635(04)13022-3

728

Chapter 22: Epilogue

1. KOMATIITES, BONINITES, BIF’S, AND PODIFORM CHROMITES It has long been held that komatiites are abundant in Archean greenstone belts and that the Archean oceanic crust may have been dominantly komatiitic, reflecting early higher mantle temperatures. However, komatiites are much less common than many workers originally thought, and they do not necessarily mean much hotter mantle (see Parman and Grove, 2004). There has been a disproportionate number of studies of komatiites from Archean greenstone belts compared to other rock types, because petrologists have focused on the unusual aspects of these rocks, but they typically do not form more than a few percent of any greenstone terrain. However, they do appear to be more abundant in Archean terrains than younger ophiolites (e.g., Alvarado et al., 1997). Boninites are geochemically distinct mafic rocks that have been suggested to be absent from Archean terrains. As reported in several chapters in this volume (see Polat and Kerrich, 2004; Shchipansky et al., 2004; Stern et al., 2004), boninites have now been identified in several ophiolitic Proterozoic and Archean greenstone belts extending back in time to the 3.8 Ga Isua belt, suggesting that these ophiolites formed in environments similar to their modern counterparts. Boninites of Phanerozoic age occur in ophiolites or intraoceanic island arcs, such as the Izu-Bonin-Mariana arc system. These primary liquids are interpreted as second-stage high-temperature, low-pressure melting of a depleted refractory mantle wedge fertilized by fluids and/or melts, above a subduction zone. Precambrian boninitic lavas are likely products of the same conjunction of processes, suggesting that mantle melting processes above subducting slabs was broadly similar in the Archean to that of today. Podiform chromites form very distinctive deposits in many Phanerozoic ophiolites, and have been found in a few places on the modern sea-floor. Podiform chromites form small clusters of typically orbicular and nodular textured chromite in dunite pods, enclosed within mantle harzburgite tectonite. These chromite pods are distinctive, both physically and chemically, from layered chromite of layered ultramafic intrusive complex in continents (such as the Bushveld) and arcs (see Lago et al., 1982; Nicolas and Azri, 1991; Leblanc and Nicolas, 1992; Stowe, 1994; Butcher et al., 1999; Edwards et al., 2000). Until recently, podiform chromites were not known from any Archean greenstone belts, but their documentation in the Zunhua ophiolitic mélange and Dongwanzi ophiolite of North China (Kusky et al., 2004a; Huang et al., 2004) shows clearly not only that these rocks are ophiolitic, but that mantle melting processes in the Archean were similar to those of younger times. We suggest that since podiform chromites are only known from ophiolites, that they are as distinctive for recognizing a rock sequence as an ophiolite as the presence of the entire Penrose sequence. Banded Iron Formations (BIF’s) are a major component of many Archean greenstone terranes, and are described from several of the ophiolitic sequences in this volume. While the origin of BIF’s has been controversial, and there are several different origins (e.g., Fowler et al., 2002; Coward and Ries, 1995; Simonson, 1985), Hofmann and Kusky (2004) have shown how BIF’s in low-grade greenstone terranes may mark sites of regional structural detachment, with iron and sulfide mineralization focused along early shear zones.

2. Transitional Ophiolites

729

Workers in other greenstone terranes, particularly those that are more highly deformed and metamorphosed, should note the relationships at Belingwe, and re-assess whether or not BIF’s in other greenstones and Precambrian ophiolite terranes may mark the sites of major regional detachment and displacement. Several authors (e.g., Bickle et al., 1994; Hamilton, 2003) have noted that some Precambrian greenstone belts show evidence of contamination by continental type material, and have then suggested that this means that they cannot be fragments of oceanic crust and lithosphere. These authors have failed to note that many modern and Phanerozoic ophiolites also show such contamination (e.g., Moores, 2002), invalidating those arguments. Nonetheless, apparent contamination by continental crustal material presents interesting constraints on the origin of these ophiolites. For instance, apparent crustal contamination can mean lavas were derived from unusual mantle, such as an older forearc environment, where subduction-related processes may have depleted the mantle leading to unusual, apparently contaminated geochemical signatures (see Parman and Grove, 2004). Alternatively, some ophiolites may be truly contaminated, having formed near a stretched continental margin. Some ophiolites seem to preserve magmatism near these margins, and some even have subcontinental lithospheric mantle and/or crust preserved. We coin a new term for these ophiolites, and call them transitional ophiolites.

2. TRANSITIONAL OPHIOLITES Several of the ophiolites described in this volume appear to have formed within the transition from rifted continental margins to ocean spreading centers during early stages of ocean opening, then were structurally detached and/or deformed and incorporated into convergent margins during ocean closure. These ophiolites are distinctive from classical Penrose-style ophiolites and others formed in forearc and back arc environments. During early stages of ocean formation, continental crust and lherzolite of the subcontinental mantle is extended forming graben on the surface, and ductile mylonites at depth. Sedimentary basins may form in the graben, and as the extension continues magmatism sometimes affects the rifted margin, either forming volcanic rifted margins, or migrating to a spreading center forming a oceanic spreading center. New asthenospheric mantle upwells along the new ridge, and may intrude beneath the extended continental crust. In some cases, wedges of extended mid-to-lower continental crust overlying mylonitic lherzolitic subcontinental mantle become intruded by numerous dikes and magmas from this new asthenospheric mantle. In this case, magmas may pool both above and below the stretched continental crust, forming mafic/ultramafic cumulates in igneous contact with older continental crust (see Fig. 1 in the Introduction to this volume). Dikes from these magma chambers may then feed a crustal gabbroic magma chamber closer to the surface, which in turn may feed a dike complex and basaltic pillow/massive lava section. If preserved, this unusual sequence forms what we term a “transitional ophiolite”, grading down from subaquatic sediments, to pillow lavas, dikes, sheeted dikes, layered gabbro, dunite and pyroxenite cumulates, then remarkably into stretched, typically mylonitic granitic mylonites, underlain by lherzolite.

730

Chapter 22: Epilogue

The lherzolite tectonic may be underlain by harzburgite tectonite or harzburgite. Recognition of this relationship represents a major advance in understanding some of the ophiolitic complexes described in this volume, and elsewhere. Examples of this type of transitional ophiolite are found in the Proterozoic Jourma complex, and in some of the Slave Province ophiolites (see papers by Peltonen and Kontinen, 2004, and Corcoran et al., 2004). Modern analogs for such transitional ophiolites are found around the Red Sea, including at Tihama Asir, Saudi Arabia, where a 5–10 Ma old transitional ophiolite has a dike complex overlying layered gabbro, which in turn overlies continental crust. Also, on Egypt’s Zabargad Island, oceanic mantle is exposed, and it is likely that the crustal structure near this region preserves transitional ophiolites as well. The main lesson here is that ophiolites may form in many tectonic settings, from extended continental crust, to mid ocean ridges, to forearcs, arcs, back arcs, to triple junctions along convergent margins.

3. PROTEROZOIC OPHIOLITES The formation of the Gondwanan supercontinent at the end of the Precambrian and the dawn of the Phanerozoic represents one of the most fundamental problems being studied in Earth Sciences today. It links many different fields, and there are currently numerous and rapid changes in our understanding of events related to the assembly of Gondwana. One of the most fundamental and most poorly understood aspects of the formation of Gondwana is the timing and geometry of closure of the oceanic basins which separated the continental fragments that amassed to form the Late Proterozoic supercontinent. Final collision between East and West Gondwana most likely occurred during closure of the Mozambique Ocean, forming the East African Orogen including the Arabian-Nubian Shield. Neoproterozoic ophiolite fragments have been recognized as a component part of many nappe complexes associated with sutures in the Arabian-Nubian Shield. The recognition of these ophiolite-decorated sutures played a major role in understanding the formation of the Arabian-Nubian Shield as an amalgam of different arc and microcontinental terranes that collided during the closure of the Mozambique Ocean (Stern, 1994; Kusky et al., 2003), but also contributed to many scientists’ acceptance that plate tectonics extended back in time to 890 Ma, the age of the oldest Arabian ophiolite (see Stern et al., 2004; Johnson et al., 2004). The chemistry of the Arabian Shield ophiolites include both tholeiitic and calc-alkaline varieties, with minor boninites, suggesting that they largely formed in a forearc environment, with extensive partial melting of the mantle. Many of the ArabianNubian shield ophiolites formed over a critical interval of Earth history that saw many changes in the Earth’s biota and climate, yet very few studies have yet been aimed at the sedimentary sequences that overlie these ophiolites, potentially preserving a treasure drove of information about the Neoproterozoic Earth.

4. Archean Ophiolites

731

4. ARCHEAN OPHIOLITES Over the course of several decades, a number of possible partial and dismembered ophiolite sequences have been described from a number of Archean greenstone belts of different ages and locations (e.g., de Wit et al., 1987; de Wit and Ashwal, 1997; Fripp and Jones, 1997; Harper, 1985; Kusky, 1989, 1990, 1991). However, 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 (Bickle et al., 1994; Hamilton, 1998, 2003). These ideas were challenged by the recognition of a complete but partially dismembered Archean ophiolite sequence from the North China Craton (Kusky et al., 2004a), that was later found to be associated with mantle tectonites in mélange beneath the ophiolite (Li et al., 2002). This discovery has important implications for understanding other Archean greenstone belts, many of which contain only part of the typical ophiolite assemblage. With a complete assemblage present in at least one locality, it is more likely that the other reported partial sequences are truly parts of ophiolites, and not representative of some other tectonic setting that was unique in the Precambrian. Some workers have even suggested that the mechanisms of planetary heat loss changed so much with time so that what resembles an ophiolite from the Archean record is actually equivalent to a continental rift in the younger rock record. The Penrose definition of ophiolites (Anonymous, 1972; cf. Brongniart, 1813, 1821) includes “dismembered”, “partial”, and “metamorphosed” varieties, with rock types the same as those that typify Archean greenstone belts. Ophiolite-like relationships have been described for many years from Archean greenstone belts (Hess, 1955), yet many of the examples of partial ophiolites in Archean terrains were questioned, because no complete sequences were found anywhere. If such sequences were found in younger, Phanerozoic mountain belts, the ophiolitic origin for the rock sequence would not likely be questioned. In this book, many such ophiolitic sequences are described, and the authors take the approach of using the same criteria to identify ophiolites in very old rocks as they do in younger orogenic belts. The application of different paradigms to the Archean and Phanerozoic is no longer necessary, although detailed studies are beginning to reveal some differences in the style of older and younger sea floor spreading. Better quantification of these differences and similarities will help constrain geochemical, geodynamic, and thermal modeling of what effects the Archean mantle thermal and melting regime had on the structure of oceanic lithosphere produced in those times. Archean oceanic crust was possibly thicker than Proterozoic and Phanerozoic counterparts, resulting in accretion predominantly of the upper basaltic section of oceanic crust. However, structural repetition and complexities in greenstone belts makes it very difficult to assess original thicknesses, as shown by papers in this book, and in Kusky and Vearncombe (1997). The crustal thickness of Archean oceanic crust may have resembled modern oceanic plateaux (e.g., Kusky and Kidd, 1992; Kusky and Winsky, 1995; Kusky, 1998), but if average oceanic crust was this thick, then they would not be topographically high standing plateaus, and the term plateau would be meaningless. If this were the case, the rheological stratification of the oceanic lithosphere would have been different (Hoffman

732

Chapter 22: Epilogue

and Ranalli, 1988), and complete Phanerozoic-like MORB-type ophiolite sequences would have been very unlikely to be accreted or obducted during Archean orogenies. In contrast, only the upper, pillow lava-dominated sections would likely be accreted. Future research should be directed at considering what the consequences of changes in the style and/or composition of accreted oceanic material has on the structure and composition of the continental crust. For instance, the observation that Archean greenstone belts have 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 (see Hoffman and Ranalli, 1988; Kusky and Polat, 1999). Subcrustal oceanic lithosphere slabs may have been underplated beneath cratons, forming mantle roots (Kusky, 1993). Descriptions of the various Precambrian ophiolites in this volume has shown that many are contained within thrust complexes that include elements formed at different stages of ocean opening and closing, with a strong bias toward convergent margin environments such as suprasubduction zone or arc-related spreading centers, accretionary wedge material, triple-junction related magmas and arc magmas that have migrated through these orogenic collages. Many of these ophiolites are parts of orogenic complexes that have experienced complex tectonic histories, similar to those of material accreted to younger accretionary orogens (Kusky et al., 2004b; Sengör and Natal’in, 2004). As in younger ophiolites, at present we observe a huge variation in inferred crustal thickness of ophiolites, and in the units that are preserved. With present limited data, and the amount of structural complication, it is not yet possible to assess whether or not there has been a demonstrable secular change in the thickness of oceanic crust (e.g., Moores, 2002). However, obtaining better constraints on the thickness and petrological relationships in Precambrian ophiolites remains a high priority for the Earth Sciences, since these are sensitive indicators to the nature of how the Earth lost the extra heat produced during the Precambrian. Since the current range of known ophiolitic thicknesses and internal stratigraphic relationships from Precambrian ophiolites are within the range of those from the Phanerozoic to present regime, we favor the idea that Precambrian ophiolites were not drastically thicker than those of younger times, and that much of the heat from the Precambrian Earth was lost though a greater total ridge length, and faster spreading rates, rather than production of dramatically thicker melt columns. Such relationships would produce a Precambrian Earth dominated by smaller oceanic plates, more triple junction interactions, and a younger average age of subducting lithosphere. Thicker sedimentary piles of graywacke turbidities on subducting plates would lead to fewer mélanges being formed (see Kusky et al., 2004b), and to more low-angle subduction with many ridge subduction events and belts of near-trench magmas intruding the accretionary margins and ophiolites, forming the TTG suite. The smaller oceanic plate size does not necessarily mean that continents were also smaller. We know, for instance, that Precambrian quartzites such as the Mt. Narryer required long rivers on large continents to form the extensive mature sands, and that some Archean strike slip faults (Sleep, 1992; Kusky and Vearncombe, 1997) and Archean passive margin sequences (Kusky and Hudleston, 1999) both had lengths exceeding 1,000 km.

4. Archean Ophiolites

733

Table 1. Criteria for recognition of a rock sequence as an ophiolite Indicator

Importance

Full Penrose sequence diagnostic in order

Status Status in Phanerozoic in Dongwanzi Ophiolites rare, about 10% suggested, needs documentation and verification

Conclusion

not conclusive

Podiform chromites w/nodular textures

diagnostic

about 15%

present

diagnostic

Full sequence dismembered

convincing

about 30–50%

dismembered units present

convincing

3 or 4 of 7 main units present

typical for accepting Phan. Ophiolite

about 80%

6 of 7 units known; dikes still uncertain (age)

convincing

Sheeted dikes

distinctive, nearly diagnostic

about 20–30%

suggested, age needs verification

not conclusive

Mantle tectonites

distinctive

about 20–30%

present

distinctive

Cumulates

present, not distinctive

about 70%

present

supportive

Layered gabbro

typical

about 70%

present

supportive

Pillow lavas

typical, not distinctive

about 85%

present

supportive

Chert, deep water seds

typical

about 85%

present

supportive

Co-magmatic dikes and gabbro

necessary, rare to about 15% observe

present

distinctive

High-T silicate defm. rare, but as inclus. in melt pods distinctive

about 10%

present

distinctive

Basal thrust fault

necessary (except in rare cases), not diag.

about 60%

present

supportive

Dynamothermal aureole

distinctive, almost diagnostic

about 15%

not determined

inconclusive

Sea floor metamor

distinctive

all

present

supportive

Hydrothermal vents black smoker type

distinctive

rare

present

strongly supports (continued on next page)

734

Chapter 22: Epilogue

Table 1. (Continued) Indicator

Importance

Status Status Conclusion in Phanerozoic in Dongwanzi Ophiolites Ophiolites are defined on the basis of field relationships and the overall rock sequence. Many workers have added chemical criteria to the ways to recognize and distinguish between different types of ophiolites. Some of the more common traits are: MORB chem.

distinctive

about 65%

present

distinctive

CA chemistry

common

about 30%

present in some units

inconclusive

Flat REE

distinctive

about 65%

present

distinctive

Boninites

distinctive of SSZ

rare but increasingly recognized

not known

inconclusive

Terranes in which Precambrian ophiolites are found resemble younger accretionary orogens, such as Alaska, the Altaids, or the Philippines, where each of these has long history and many magmatic events (Kusky et al., 2004b; Sengör and Natal’in, 2004; Encarnacion, 2004). Comparative studies between accretionary orogens and Precambrian cratons, orogens, and ophiolites are likely to continue to yield useful insights about how the early Earth operated. 5. IS IT AN OPHIOLITE? Several authors have presented various schemes to purportedly discriminate between ophiolitic and other sequences (e.g., Pearce, 1987; Wood et al., 1979), although most of these are either arbitrary, or based on models of what the authors believe Precambrian ophiolites should have looked like (e.g., Bickle et al., 1994). Here, we present a shamelessly uniformitarian list of criteria that can be used to determine the likelihood of whether or not a partial, dismembered, or complete sequence is ophiolitic, though comparison with betterunderstood Phanerozoic sequences. For comparison, the Dongwanzi ophiolite is compared to Phanerozoic ophiolites, and it stands up well to such comparison, and would clearly be called an ophiolite if it were preserved in a Phanerozoic orogen. Table 1 can be used for other questionable sequences, by replacing the column for the Dongwanzi ophiolite with the sequence in question. REFERENCES 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.

References

735

Anonymous, 1972. Ophiolites. Geotimes 17, 24–25. Bickle, M.J., Nisbet, E.G., Martin, 1994. Archean greenstone belts are not oceanic crust. J. Geology 102, 121–138. Brongniart, A., 1813. Essai d’une classification minéralogique des roches mélangées. Journal of Mines 199, 1–48. Brongniart, A., 1821. Sur le gisement ou position relative des ophiolites, euphotides, jaspes, etc., dans quelques parties des Apennines. Ann. Mines Rec. Mém. Exploit Mines 6, 177–238. Butcher, A.R., Pirrie, D., Prichard, H.M., Fisher, P., 1999. Platinum-group mineralization in the Rum layered intrusion, Scottish Hebrides, UK. Journal of the Geological Society of London 156, 213– 216. Corcoran, P.L., Mueller, W.U., Kusky, T.M., 2004. Inferred ophiolites in the Archean Slave Craton. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 363–404. Coward, M.P., Ries, A.C., 1995. Early Precambrian Processes. Geological Society of London Special Publication 95, p. 295. de Wit, M.J., Ashwal, L.D. (Eds.), 1997. Greenstone Belts. In: Oxford Monographs on Geology and Geophysics, vol. 35, p. 809. 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. African Earth Sci. 6, 681–730. Edwards, S.J., Pearce, J.A., Freeman, J., 2000. New insights concerning the influence of water during the formation of podiform chromitite. In: Dilek, Y., Moores, E., Elthon, D., Nicolas, A. (Eds.), Ophiolites and Oceanic Crust. Geological Society of America Special Paper 349, 139–147. Encarnacion, J., 2004. Northern Philippine Ophiolites: Modern Analogues to Precambrian Ophiolites. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 615–626. Fowler, C.M.R., Ebinger, C.J., Hawkseworth, C.J., 2002. The Early Earth: Physical, Chemical and Biological Development. Geological Society of London Special Publication 199, p. 360. 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.J., Ashwal, L.D. (Eds.), Greenstone Belts. In: Oxford Monographs on Geology and Geophysics, vol. 35, pp. 422–437. Hamilton, W.B., 1998. Archean tectonics and magmatism. International Geology Reviews 40, 1–39. Hamilton, W.B., 2003. An alternative Earth. GSA Today 13, 4–13. Harper, G.D., 1985. A dismembered Archean ophiolite, Wind River Mountains, Wyoming (USA). Ophioliti 10, 297–306. Hess, H.H., 1955. Serpentinites, orogeny, and epeirogeny. In: Poldervart, A. (Ed.), Crust of the Earth (A Symposium). Geological Society of America Special Paper 62, 391–408. Hoffman, P.F., Ranalli, G., 1988. Oceanic flake tectonics. Geophysical Research Letters 15, 1077– 1080. Hofmann, A., Kusky, T.M., 2004. The Belingwe Greenstone Belt: Ensialic or Oceanic? In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 487–537. Huang, X.N., Li, J.H., Kusky, T.M., Chen, Z., 2004. Microstructures of the Zunhua 2.50 Ga Podiform chromite, North China Craton and implications for the deformation and rheology of the Archean oceanic lithosphere mantle. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 321–337.

736

Chapter 22: Epilogue

Johnson, P.R., Kattan, F.H., Al-Saleh, A.M., 2004. Neoproterozoic ophiolites in the Arabian Shield: Field relations and structure. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 129–162. 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., 1999. Growth and Demise of an Archean carbonate platform, Steep Rock Lake, Ontario, Canada. Canadian Journal of Earth Sciences 36, 1–20. Kusky, T.M., Kidd, W.S.F., 1992. Remnants of an Archean oceanic plateau, Belingwe greenstone belt, Zimbabwe. Geology 20, 43–46. Kusky, T.M., Polat, A., 1999. Growth of Granite-Greenstone Terranes at Convergent Margins and Stabilization of Archean Cratons. In: Marshak, S., van der Pluijm, B. (Eds.), Special Issue on Tectonics of Continental Interiors. Tectonophysics 305, 43–73. Kusky, T.M., Vearncombe, J., 1997. Structure of Archean Greenstone Belts. In: de Wit, M.J., Ashwal, L.D. (Eds.), Tectonic Evolution of Greenstone Belts, Oxford Monograph on Geology and Geophysics, pp. 95–128. 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., Abdelsalam, M., Tucker, R., Stern, R., 2003. Evolution of the East African and Related Orogens, and the Assembly of Gondwana. Special Issue of Precambrian Research 123, 81–344. Kusky, T.M., Li, J.H., Glass, A., Huang, X.N., 2004a. Origin and emplacement of Archean ophiolites of the Central Orogenic belt, North China craton. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 223–274. Kusky, T.M., Ganley, R., Lytwyn, J., Polat, A., 2004b. The Resurrection Peninsula ophiolite, mélange, and accreted flysch belts of southern Alaska as an analog for trench-forearc systems in Precambrian orogens. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 627–674. Lago, B.L, Rabinowicz, M., Nicolas, A., 1982. Podiform chromitite ore bodies: a genetic model. J. Petrol. 23, 103–125. Leblanc, M., Nicolas, A., 1992. Ophiolitic chromitites. International Geological Reviews 34, 653– 686. Li, J.H., Kusky, T.M., Huang, X., 2002. Neoarchean podiform chromitites and harzburgite tectonite in ophiolitic melange, North China Craton: Remnants of Archean oceanic mantle. GSA Today 12 (7), 4–11. Moores, E.M., 2002. Pre-1 Ga (Pre-Rodinian) ophiolites: Their tectonic and environmental implications. Geological Society of America Bulletin 114, 80–95. Nicolas, A., Azri, H.A., 1991. Chromite-rich and chromite-poor ophiolites: the Oman case. In: Peters, Tj., Nicolas, A., Coleman, R.G. (Eds.), Ophiolite Genesis and Evolution of the Oceanic Lithosphere. Kluwer Academic, Boston, pp. 261–274.

References

737

Parman, S.W., Grove, T.L., 2004. Petrology and geochemistry of Barberton komatiites and basaltic komatiites: evidence of Archean fore-arc magmatism. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 539–565. Pearce, J., 1987. An expert system for the tectonic characterization of ancient volcanic rocks. J. Volcanol. Geotherm. Res. 32, 51–65. Peltonen, P., Kontinen, A., 2004. The Jormua ophiolite: A mafic-ultramafic complex from an ancient ocean-continent transition zone. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 35–71. Polat, A., Kerrich, R., 2004. Precambrian arc associations: Boninites, adakites, magnesian andesites, and Nb-enriched basalts. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 567–597. Sengör, A.M.C., Natal’in, B.A., 2004. Phanerozoic analogues of Archean oceanic basement fragments: Altaid ophiolites and ophiorags. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 675– 726. Shchipansky, A.A., Samsonov, A.V., Bibikova, E.V., Babarina, I.I., Konilov, A.N., Krylov, K.A., Slabunov, A.I., Bogina, M.M., 2004. 2.8 Ga Boninite-hosting partial suprasubduction zone ophiolite sequences from the North Karelian greenstone belt, NE Baltic Shield, Russia. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 425–486. Simonson, B.M., 1985. Sedimentologic constraints on the origins of Precambrian iron-formations. Geological Society of America Bulletin 96, 244–252. Sleep, N.H., 1992. Archean plate tectonics: what can be learned from continental geology?. Canadian Journal of Earth Sciences 29, 2066–2071. Stern, R.J., 1994. Arc Assembly and continental collision in the Neoproterozoic East African Orogen: Implications for the assembly of Gondwanaland. Annual Reviews of Earth and Planetary Sciences 22, 319–351. Stern, R.J., Johnson, P.R., Kröner, A., Yibas, B., 2004. Neoproterozoic ophiolites of the ArabianNubian Shield. In: Kusky, T.M. (Ed.), Precambrian Ophiolites and Related Rocks. In: Developments in Precambrian Geology, vol. 13. Elsevier, Amsterdam, pp. 95–128. Stowe, C.W., 1994. Compositions and tectonic settings of chromite deposits through time. Economic Geology 89, 528–546. Wood, D.A., Joron, J.L., Treuil, M., 1979. A re-appraisal of the use of trace elements to classify between magma series erupted in different tectonic settings. Earth Planet. Sci. Lett. 45, 326–336.