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Allen P Nutman - One of the best experts on this subject based on the ideXlab platform.
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new 1 20 000 scale geological maps synthesis and history of investigation of the isua supracrustal belt and adjacent orthogneisses southern west greenland a glimpse of eoarchaean crust formation and orogeny
Precambrian Research, 2009Co-Authors: Allen P Nutman, Clark R L FriendAbstract:Abstract The Isua area in the Nuuk region, southern West Greenland contains the Eoarchaean Isua supracrustal belt (mostly amphibolites derived from basalts, with chemical sedimentary rocks, felsic rocks and ultramafic units) and orthogneisses with similar ages that flank it to the north and south. These rocks suffered polyphase metamorphism up to amphibolite facies conditions and strain is generally high, but nonetheless the Isua area has most of the world's occurrences of Eoarchaean rocks preserved in a low strain state. This means that structural, geochemical and isotopic studies of Isua area rocks can provide the least ambiguous data on the origin and tectonic evolution of Eoarchaean crust. New Isua colour digital geological maps at 1:20,000 scale (observed outcrop geology and interpretive solid geology) and a synthesis are presented here. These incorporate advances in structural observations, re-interpretations of the lithologies and the large amounts of zircon dating produced since publication in 1986 of the last geological map of the entire Isua area. Essential in the synthesis is that the Isua area contains a southern ca. 3800 Ma Terrane and a northern ca. 3700 Ma Terrane. Many of the rocks in the two Terranes of different age are broadly similar in appearance, but have been distinguished by U–Pb zircon dating. The boundary between the Terranes lies within the Isua supracrustal belt and is most likely at a highly tectonised unit of chert, BIF and carbonate rocks named the dividing sedimentary unit, that contains sparse 3940–3750 Ma detrital zircons. In the ca. 3700 Ma Terrane to the north, no >3750 Ma detrital zircons have been found. The Isua supracrustal belt part of the ca. 3700 Ma northern Terrane has three geochemically distinct sub-Terranes dominated respectively by ≥3715 Ma boninites, ≥3715 Ma island arc tholeiites plus picrites and 3710–3700 Ma andesitic–dacitic rocks or sediments derived from them. In the Eoarchaean, these different arc- and maybe fore-arc related rocks were imbricated and juxtaposed with the ca. 3800 Ma Terrane along the dividing sedimentary unit, which was the structural decollement. The ca. 3800 Ma Terrane is also interpreted as a complex arc assemblage, similar in origin to the 3700 Ma one, but containing small amounts of older ≥3850 Ma crust. The assembly of these different Terranes occurred between 3690 Ma (youngest rocks unique to the northern ca. 3700 Ma Terrane) and 3660 Ma (oldest distinctive intrusions common to both Terranes). Hence our synthesis shows that Isua crustal evolution was by several juvenile crust formation steps restricted to the 3800 or the 3700 Ma arc-related Terranes, followed by complex collisional processes with later tectonic partitioning. This resembles crustal evolution widely seen in other younger Archaean Terranes, and points to a continuity of crust formation along convergent plate boundaries back to at least 3800 Ma.
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new pieces to the archaean Terrane jigsaw puzzle in the nuuk region southern west greenland steps in transforming a simple insight into a complex regional tectonothermal model
Journal of the Geological Society, 2005Co-Authors: C R L Friend, Allen P NutmanAbstract:In the south of the Nuuk region of West Greenland our 1980s mapping recognized four Archaean gneiss Terranes (Fœringehavn, Tre Brodre, Tasiusarsuaq and Akia Terranes) with different protolith ages and separate early tectonothermal histories. Later in the Archaean these were juxtaposed and then experienced the same 2700–2500 Ma tectonothermal events. Here we abandon extrapolation of only these four Terranes across the whole region, and distinguish two new Terranes in the NE. The northernmost Isukasia Terrane (previously regarded as the northernmost exposure of the Fœringehavn Terrane) consists of Palaeoarchaean rocks (>3600 Ma) tectonically bounded on its south by the 3075–2960 Ma Kapisilik Terrane; these were juxtaposed and metamorphosed together by 2950 Ma. The previously recognized Fœringehavn Terrane to the SW is another, separate entity of Palaeoarchaean rocks that was juxtaposed with adjacent Terranes only after c . 2800 Ma. Hence in an increasingly complex regional model, there were several mid- to Neoarchaean Terrane assembly events, with superimposed ‘orogenies’ from c . 2950 Ma until after 2700 Ma. Although the Fœringehavn and Isukasia Terranes were incorporated into the later Archaean Terrane collage at different times, they might be fragments from a larger Palaeoarchaean complex rifted apart from c . 3500 Ma onwards.
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inventory and assessment of palaeoarchaean gneiss terrains and detrital zircons in southern west greenland
Precambrian Research, 2004Co-Authors: Allen P Nutman, Clark R L Friend, Shaun L L Barker, Vic R McgregorAbstract:Geochemical methods to advance knowledge on the early Earth require supplies of well-preserved >3600 Ma rocks and minerals (e.g. zircon). One of the most important resources for these are small domains within high metamorphic grade Palaeoarchaean gneisses in the Archaean Craton, southern West Greenland. In the Nuuk region these gneisses occur as two Terranes (totalling ∼3000 km2) with differences in their pre-3600 Ma histories, and they are tectonically separated from each other by younger rocks. In the north is the Isukasia Terrane (early metamorphic grade amphibolite facies). It is devoid of pre-3600 Ma in situ partial melt and contains locally well-preserved 3690 and 3810 Ma tonalites, ≥3810 Ma ultramafic rocks plus the tectonically composite Isua supracrustal belt with some locally well-preserved ∼3800 and 3710 Ma volcanic and sedimentary materials. To the south is the Faeringehavn Terrane (up to granulite facies in the Palaeoarchaean) that is dominated by 3850–3660 Ma migmatites containing variable amounts of in situ 3660–3600 Ma partial melt. Akilia island in this Terrane contains some ∼3850 Ma tonalites, mafic and sedimentary rocks – the world's oldest-known sediments. Domains of lower total strain and anatexis on some of other islands near Akilia has left small amounts of well-preserved 3850 Ma tonalite. There are two less known smaller bodies of Palaeoarchaean rocks north of the Nuuk region. The Qarliit Tasersuat assemblage consists of polyphase, migmatitic gneisses with lenses of mafic and siliceous rocks. Two SHRIMP zircon dates reveal 3600–3700 Ma rocks, strongly affected by ∼3600 and 2770 Ma metamorphisms. The Aasivik Terrane also consists of polyphase migmatitic gneisses, and previous SHRIMP U/Pb zircon reconnaissance dating of three samples found components up to ∼3600 Ma old with strong reworking in 2720–2550 Ma events. The West Greenland Archaean Craton is a collage of Palaeo- to Neoarchaean Terranes, assembled in several Archaean events. Metasediments within post-Palaeoarchaean Terranes are devoid of ≥3600 Ma detritus, but are dominated by zircons of the same age as major crust-forming TTG suites of their Terrane. Metasediments along Terrane boundaries, even those in contact with Palaeoarchaean Terranes, contain very few (<5%) ≥3600 Ma detrital zircons. Therefore, these sediments are not a significant resource for ancient zircons. The scarcity of ≥3600 Ma detritus within these sediments supports a model that the Palaeoarchaean bodies (Faeringehavn, Isukasia, Qarliit tasersuat and Aasivik) are allochthonous Terranes captured within an Archaean accretionary system and comprise a tectonic assembly of juvenile crustal blocks with different age. The metasediments in contact with the Isukasia Terrane are dominated by ∼3070 Ma detrital zircons and were first metamorphosed (along with the adjacent Isukasia Terrane) at ∼2960 Ma. On the other hand, metasediments in contact with the Faeringehavn Terrane are dominated by ∼2831 Ma detrital zircons, and thus were deposited after sediments in contact with the Isukasia Terrane had already been tectonically emplaced and metamorphosed. Although the Palaeoarchaean Terranes were incorporated into the Archaean Terrane collage at different times, they might have been spawned from a single larger body of ancient crust broken up from ∼3500 Ma onwards.
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timing of late archaean Terrane assembly crustal thickening and granite emplacement in the nuuk region southern west greenland
Earth and Planetary Science Letters, 1996Co-Authors: Clark R L Friend, Allen P Nutman, P D Kinny, H Baadsgaard, V R McgregorAbstract:A breakthrough in understanding the structural and metamorphic evolution of Archaean gneiss complexes occurred with the recognition that the Nuuk region of southern West Greenland comprised separate Terranes assembled in the late Archaean. From northwest to southeast these are: the Akia (3220-2970 Ma), Akulleq (3870-3600 and 2820 Ma) and Tasiusarsuaq (2920-2860 Ma) Terranes. The minimum time of assembly is recorded by the first event common to all component Terranes. Using SHRIMP UPb zircon geochronology the oldest events common to all Terranes (including emplacement of crustally derived granites, contemporaneous metamorphism and anatexis) have been dated at 2710–2725 Ma. In the Akulleq Terrane areas where in situ diatexite formed, abundant granitoid sheets were intruded and common growth of metamorphic zircon (mostly low ThU) in most lithologies occurred. In the Akia and Tasiusarsuaq Terranes there was only intrusion of a lesser number of ∼ 2720 Ma granitoid sheets, because metamorphic zircons of that age have not been found. The ∼ 2720 Ma event is interpreted as marking, or shortly following, Terrane assembly, when the diverse components of the Akulleq Terrane were tectonically juxtaposed with the other two. This new documentation of metamorphic and associated igneous events within an accreting cratonic region is an illustration that the stabilisation of extensive areas of Archaean gneisses can be due to accretionary tectonics long after the individual components were first formed.
Clark R L Friend - One of the best experts on this subject based on the ideXlab platform.
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new 1 20 000 scale geological maps synthesis and history of investigation of the isua supracrustal belt and adjacent orthogneisses southern west greenland a glimpse of eoarchaean crust formation and orogeny
Precambrian Research, 2009Co-Authors: Allen P Nutman, Clark R L FriendAbstract:Abstract The Isua area in the Nuuk region, southern West Greenland contains the Eoarchaean Isua supracrustal belt (mostly amphibolites derived from basalts, with chemical sedimentary rocks, felsic rocks and ultramafic units) and orthogneisses with similar ages that flank it to the north and south. These rocks suffered polyphase metamorphism up to amphibolite facies conditions and strain is generally high, but nonetheless the Isua area has most of the world's occurrences of Eoarchaean rocks preserved in a low strain state. This means that structural, geochemical and isotopic studies of Isua area rocks can provide the least ambiguous data on the origin and tectonic evolution of Eoarchaean crust. New Isua colour digital geological maps at 1:20,000 scale (observed outcrop geology and interpretive solid geology) and a synthesis are presented here. These incorporate advances in structural observations, re-interpretations of the lithologies and the large amounts of zircon dating produced since publication in 1986 of the last geological map of the entire Isua area. Essential in the synthesis is that the Isua area contains a southern ca. 3800 Ma Terrane and a northern ca. 3700 Ma Terrane. Many of the rocks in the two Terranes of different age are broadly similar in appearance, but have been distinguished by U–Pb zircon dating. The boundary between the Terranes lies within the Isua supracrustal belt and is most likely at a highly tectonised unit of chert, BIF and carbonate rocks named the dividing sedimentary unit, that contains sparse 3940–3750 Ma detrital zircons. In the ca. 3700 Ma Terrane to the north, no >3750 Ma detrital zircons have been found. The Isua supracrustal belt part of the ca. 3700 Ma northern Terrane has three geochemically distinct sub-Terranes dominated respectively by ≥3715 Ma boninites, ≥3715 Ma island arc tholeiites plus picrites and 3710–3700 Ma andesitic–dacitic rocks or sediments derived from them. In the Eoarchaean, these different arc- and maybe fore-arc related rocks were imbricated and juxtaposed with the ca. 3800 Ma Terrane along the dividing sedimentary unit, which was the structural decollement. The ca. 3800 Ma Terrane is also interpreted as a complex arc assemblage, similar in origin to the 3700 Ma one, but containing small amounts of older ≥3850 Ma crust. The assembly of these different Terranes occurred between 3690 Ma (youngest rocks unique to the northern ca. 3700 Ma Terrane) and 3660 Ma (oldest distinctive intrusions common to both Terranes). Hence our synthesis shows that Isua crustal evolution was by several juvenile crust formation steps restricted to the 3800 or the 3700 Ma arc-related Terranes, followed by complex collisional processes with later tectonic partitioning. This resembles crustal evolution widely seen in other younger Archaean Terranes, and points to a continuity of crust formation along convergent plate boundaries back to at least 3800 Ma.
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inventory and assessment of palaeoarchaean gneiss terrains and detrital zircons in southern west greenland
Precambrian Research, 2004Co-Authors: Allen P Nutman, Clark R L Friend, Shaun L L Barker, Vic R McgregorAbstract:Geochemical methods to advance knowledge on the early Earth require supplies of well-preserved >3600 Ma rocks and minerals (e.g. zircon). One of the most important resources for these are small domains within high metamorphic grade Palaeoarchaean gneisses in the Archaean Craton, southern West Greenland. In the Nuuk region these gneisses occur as two Terranes (totalling ∼3000 km2) with differences in their pre-3600 Ma histories, and they are tectonically separated from each other by younger rocks. In the north is the Isukasia Terrane (early metamorphic grade amphibolite facies). It is devoid of pre-3600 Ma in situ partial melt and contains locally well-preserved 3690 and 3810 Ma tonalites, ≥3810 Ma ultramafic rocks plus the tectonically composite Isua supracrustal belt with some locally well-preserved ∼3800 and 3710 Ma volcanic and sedimentary materials. To the south is the Faeringehavn Terrane (up to granulite facies in the Palaeoarchaean) that is dominated by 3850–3660 Ma migmatites containing variable amounts of in situ 3660–3600 Ma partial melt. Akilia island in this Terrane contains some ∼3850 Ma tonalites, mafic and sedimentary rocks – the world's oldest-known sediments. Domains of lower total strain and anatexis on some of other islands near Akilia has left small amounts of well-preserved 3850 Ma tonalite. There are two less known smaller bodies of Palaeoarchaean rocks north of the Nuuk region. The Qarliit Tasersuat assemblage consists of polyphase, migmatitic gneisses with lenses of mafic and siliceous rocks. Two SHRIMP zircon dates reveal 3600–3700 Ma rocks, strongly affected by ∼3600 and 2770 Ma metamorphisms. The Aasivik Terrane also consists of polyphase migmatitic gneisses, and previous SHRIMP U/Pb zircon reconnaissance dating of three samples found components up to ∼3600 Ma old with strong reworking in 2720–2550 Ma events. The West Greenland Archaean Craton is a collage of Palaeo- to Neoarchaean Terranes, assembled in several Archaean events. Metasediments within post-Palaeoarchaean Terranes are devoid of ≥3600 Ma detritus, but are dominated by zircons of the same age as major crust-forming TTG suites of their Terrane. Metasediments along Terrane boundaries, even those in contact with Palaeoarchaean Terranes, contain very few (<5%) ≥3600 Ma detrital zircons. Therefore, these sediments are not a significant resource for ancient zircons. The scarcity of ≥3600 Ma detritus within these sediments supports a model that the Palaeoarchaean bodies (Faeringehavn, Isukasia, Qarliit tasersuat and Aasivik) are allochthonous Terranes captured within an Archaean accretionary system and comprise a tectonic assembly of juvenile crustal blocks with different age. The metasediments in contact with the Isukasia Terrane are dominated by ∼3070 Ma detrital zircons and were first metamorphosed (along with the adjacent Isukasia Terrane) at ∼2960 Ma. On the other hand, metasediments in contact with the Faeringehavn Terrane are dominated by ∼2831 Ma detrital zircons, and thus were deposited after sediments in contact with the Isukasia Terrane had already been tectonically emplaced and metamorphosed. Although the Palaeoarchaean Terranes were incorporated into the Archaean Terrane collage at different times, they might have been spawned from a single larger body of ancient crust broken up from ∼3500 Ma onwards.
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timing of late archaean Terrane assembly crustal thickening and granite emplacement in the nuuk region southern west greenland
Earth and Planetary Science Letters, 1996Co-Authors: Clark R L Friend, Allen P Nutman, P D Kinny, H Baadsgaard, V R McgregorAbstract:A breakthrough in understanding the structural and metamorphic evolution of Archaean gneiss complexes occurred with the recognition that the Nuuk region of southern West Greenland comprised separate Terranes assembled in the late Archaean. From northwest to southeast these are: the Akia (3220-2970 Ma), Akulleq (3870-3600 and 2820 Ma) and Tasiusarsuaq (2920-2860 Ma) Terranes. The minimum time of assembly is recorded by the first event common to all component Terranes. Using SHRIMP UPb zircon geochronology the oldest events common to all Terranes (including emplacement of crustally derived granites, contemporaneous metamorphism and anatexis) have been dated at 2710–2725 Ma. In the Akulleq Terrane areas where in situ diatexite formed, abundant granitoid sheets were intruded and common growth of metamorphic zircon (mostly low ThU) in most lithologies occurred. In the Akia and Tasiusarsuaq Terranes there was only intrusion of a lesser number of ∼ 2720 Ma granitoid sheets, because metamorphic zircons of that age have not been found. The ∼ 2720 Ma event is interpreted as marking, or shortly following, Terrane assembly, when the diverse components of the Akulleq Terrane were tectonically juxtaposed with the other two. This new documentation of metamorphic and associated igneous events within an accreting cratonic region is an illustration that the stabilisation of extensive areas of Archaean gneisses can be due to accretionary tectonics long after the individual components were first formed.
John W F Waldron - One of the best experts on this subject based on the ideXlab platform.
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detrital zircon characterization of early cambrian sandstones from east avalonia and se ireland implications for Terrane affinities in the peri gondwanan caledonides
Geological Magazine, 2019Co-Authors: John W F Waldron, David I Schofield, Graham Pearson, Chiranjeeb Sarkar, Yan Luo, Robert J DokkenAbstract:The Caledonides of Britain and Ireland include Terranes attributed to both Laurentian and Gondwanan sources, separated along the Solway line. Gondwanan elements to the south have been variably assigned to the domains Ganderia and East Avalonia. The Midland Platform forms the core of East Avalonia but its provenance is poorly known. Laser ablation split-stream analysis yields information about detrital zircon provenance by providing simultaneous U–Pb and Lu–Hf data from the same ablated volume. A sample of Red Callavia Sandstone from uppermost Cambrian Stage 3 of the Midland Platform yields a U–Pb age spectrum dominated by Neoproterozoic and Palaeoproterozoic sources, resembling those in the Welsh Basin, the Meguma Terrane of Nova Scotia and NW Africa. Initial eHf values suggest that the Neoproterozoic zircon component was derived mainly from crustal sources < 2 Ga, and imply that the more evolved Palaeoproterozoic grains were transported into the basin from an older source Terrane, probably the Eburnean Orogen of West Africa. A sample from Cambrian Stage 4 in the Bray Group of the Leinster–Lakesman Terrane shows, in contrast, a distribution of both U–Pb ages and eHf values closely similar to those of the Gander Terrane in Newfoundland and other Terranes attributed to Ganderia, interpreted to be derived from the margin of Amazonia. East Avalonia is clearly distinct from Ganderia, but shows evidence for older crustal components not present in West Avalonia of Newfoundland. These three components of the Appalachian–Caledonide Orogen came from distinct sources on the margin of Cambrian Gondwana.
V R Mcgregor - One of the best experts on this subject based on the ideXlab platform.
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timing of late archaean Terrane assembly crustal thickening and granite emplacement in the nuuk region southern west greenland
Earth and Planetary Science Letters, 1996Co-Authors: Clark R L Friend, Allen P Nutman, P D Kinny, H Baadsgaard, V R McgregorAbstract:A breakthrough in understanding the structural and metamorphic evolution of Archaean gneiss complexes occurred with the recognition that the Nuuk region of southern West Greenland comprised separate Terranes assembled in the late Archaean. From northwest to southeast these are: the Akia (3220-2970 Ma), Akulleq (3870-3600 and 2820 Ma) and Tasiusarsuaq (2920-2860 Ma) Terranes. The minimum time of assembly is recorded by the first event common to all component Terranes. Using SHRIMP UPb zircon geochronology the oldest events common to all Terranes (including emplacement of crustally derived granites, contemporaneous metamorphism and anatexis) have been dated at 2710–2725 Ma. In the Akulleq Terrane areas where in situ diatexite formed, abundant granitoid sheets were intruded and common growth of metamorphic zircon (mostly low ThU) in most lithologies occurred. In the Akia and Tasiusarsuaq Terranes there was only intrusion of a lesser number of ∼ 2720 Ma granitoid sheets, because metamorphic zircons of that age have not been found. The ∼ 2720 Ma event is interpreted as marking, or shortly following, Terrane assembly, when the diverse components of the Akulleq Terrane were tectonically juxtaposed with the other two. This new documentation of metamorphic and associated igneous events within an accreting cratonic region is an illustration that the stabilisation of extensive areas of Archaean gneisses can be due to accretionary tectonics long after the individual components were first formed.
Brian F Windley - One of the best experts on this subject based on the ideXlab platform.
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a new Terrane subdivision for mongolia implications for the phanerozoic crustal growth of central asia
Journal of Asian Earth Sciences, 2002Co-Authors: Gombosuren Badarch, Dickson W Cunningham, Brian F WindleyAbstract:Abstract We present a new Terrane synthesis for Mongolia that incorporates geological, geochemical and geochronological data from more than 60 years of Mongolian, Russian and joint international studies. Forty-four Terranes are distinguished and classified into cratonal, metamorphic, passive margin, island arc, forearc/backarc, accretionary complex, or ophiolitic types. New detailed stratigraphic columns for all Terranes are presented which summarize the geological evolution of each Terrane. Our analysis reveals that small Precambrian cratonic blocks in the Hangay region acted as a central nucleus around which Paleozoic arcs, backarc/forearc basin assemblages, associated subduction complexes and continental slivers were accreted. The temporal and spatial order of accretion and amalgamation was complex and probably not simply from north to south with time. The timing of Terrane accretion is partly constrained by sedimentary overlap assemblages and post-amalgamation intrusive complexes. The main stages of amalgamation occurred during the Neoproterozoic, Cambrian–Ordovician, Devonian, Pennsylvanian–Permian and Triassic. The arcuate trends of Terranes around the central Hangay region provide the first-order structural grain for Mongolia. This crustal anisotropy has played a major role in controlling the geometry and kinematics of all subsequent Phanerozoic deformation and reactivation of structures in the region, including the Cenozoic development of the Altai and Gobi Altai. Our results provide the most detailed synthesis to date of the basement geology of Mongolia which should provide an important crustal framework for interpreting the Phanerozoic tectonic evolution of a large part of Central Asia. In addition, our synthesis allows the economic resources of Mongolia to be placed in a modern tectonic context.
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early precambrian gneiss Terranes and pan african island arcs in yemen crustal accretion of the eastern arabian shield
Geology, 1996Co-Authors: Brian F Windley, Martin J Whitehouse, Mahfood A O BabttatAbstract:Within the Precambrian of Yemen, we have identified four gneiss Terranes and two island-arc Terranes on the basis of existing literature, mapping, and our own field observations, together with new Sm-Nd isotopic data. The two western gneiss Terranes can be correlated with well-documented Terranes (Asir and Afif) in Saudi Arabia. To the east of these, the Abas and Al-Mahfid gneiss Terranes yield Sm-Nd model ages ( t DM ) of 1.7–2.3 Ga and 1.3–2.7 Ga, respectively, and cannot be correlated with any documented Terranes in Saudi Arabia. These two Terranes are separated by a Pan-African island-arc Terrane that has been obducted onto one or both of the gneiss Terranes, and a second arc bounds the Al-Mahfid gneiss Terrane to the east. Our discovery of extensive Proterozoic to late Archean gneisses in Yemen provides important constraints upon the much-discussed tectonic framework of northeast Gondwana and the rate of Pan-African crustal growth. The Terranes in Yemen may be correlated with comparable Terranes on the eastern margin of the Arabian Shield and in northern Somalia. Thus Yemen provides a link between the arc collage of the Arabian Shield and the gneissic Mozambique belt of East Africa.
