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Brian J Fryer - One of the best experts on this subject based on the ideXlab platform.
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origin of archean tonalite trondhjemite granodiorite ttg suites and granites in the fiskenaesset region southern west greenland implications for continental growth
Gondwana Research, 2013Co-Authors: Hua Huang, Ali Polat, Brian J FryerAbstract:Abstract Mesoarchean to Neoarchean orthogneisses (2.95–2.79 Ga) in the Fiskenaesset region, southern West Greenland, are composed of an older suite of metamorphosed tonalites, trondhjemites, and granodiorites (TTGs), and a younger suite of high-K granites. The TTGs are characterized by high Al 2 O 3 (14.2–18.6 wt.%), Na 2 O (3.4–5.13 wt.%), and Sr (205–777 ppm), and low Y (0.7–17.4 ppm) contents. On chondrite- and N-MORB-normalized trace element diagrams, the TTGs have the following geochemical characteristics: (1) highly fractionated REE patterns (La/Yb cn = 14–664; La/Sm cn = 4.3–11.0; Gd/Yb cn = 1.5–19.7); (2) strong positive anomalies of Sr (Sr/Sr* = 1.0–15.9) and Pb (Pb/Pb* = 1.4–34.9); and (3) large negative anomalies of Nb (Nb/Nb* = 0.01–0.34) and Ti (Ti/Ti* = 0.1–0.6). The geochemical characteristics of the TTGs and trace element modeling suggest that they were generated by partial melting of hydrous basalts (amphibolites) at the base of a thickened magmatic arc, leaving a rutile-bearing eclogite residue. Field observations suggest that spatially and temporarily associated tholeiitic basalts (now amphibolites) in the Fiskenaesset region might have been the sources of TTG melts. The high-K granites have steep REE patterns (La/Yb cn = 3.8–506; La/Sm cn = 2.7–18.9; Gd/Yb cn = 0.92–12.1) and display variably negative Eu anomalies (Eu/Eu* = 0.37–0.96) and moderate Sr (84–539 ppm) contents. Four outlier granite samples have variably positive Eu (Eu/Eu* = 1.0–12) anomalies. Given that the granodiorites have higher K 2 O/Na 2 O than the tonalites and trondhjemites, it is suggested that the granites were derived from partial melting of the granodiorites. It is speculated that the dense eclogitic residues, left after TTG melt extraction, were foundered into the sub-arc mantle, leading to basaltic underplating beneath the lower rust. Melting of the granodiorites in response to the basaltic underplating resulted in the production of high-K granitic melts. Formation of the Fiskenaesset TTGs, the foundering of the eclogitic residues into the mantle, and the emplacement of the high-K granites led to the growth of Archean continental crust in the Fiskenaesset region.
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Origin of Archean tonalite–trondhjemite–granodiorite (TTG) suites and granites in the Fiskenæsset region, southern West Greenland: Implications for continental growth
Gondwana Research, 2013Co-Authors: Hua Huang, Ali Polat, Brian J FryerAbstract:Abstract Mesoarchean to Neoarchean orthogneisses (2.95–2.79 Ga) in the Fiskenaesset region, southern West Greenland, are composed of an older suite of metamorphosed tonalites, trondhjemites, and granodiorites (TTGs), and a younger suite of high-K granites. The TTGs are characterized by high Al 2 O 3 (14.2–18.6 wt.%), Na 2 O (3.4–5.13 wt.%), and Sr (205–777 ppm), and low Y (0.7–17.4 ppm) contents. On chondrite- and N-MORB-normalized trace element diagrams, the TTGs have the following geochemical characteristics: (1) highly fractionated REE patterns (La/Yb cn = 14–664; La/Sm cn = 4.3–11.0; Gd/Yb cn = 1.5–19.7); (2) strong positive anomalies of Sr (Sr/Sr* = 1.0–15.9) and Pb (Pb/Pb* = 1.4–34.9); and (3) large negative anomalies of Nb (Nb/Nb* = 0.01–0.34) and Ti (Ti/Ti* = 0.1–0.6). The geochemical characteristics of the TTGs and trace element modeling suggest that they were generated by partial melting of hydrous basalts (amphibolites) at the base of a thickened magmatic arc, leaving a rutile-bearing eclogite residue. Field observations suggest that spatially and temporarily associated tholeiitic basalts (now amphibolites) in the Fiskenaesset region might have been the sources of TTG melts. The high-K granites have steep REE patterns (La/Yb cn = 3.8–506; La/Sm cn = 2.7–18.9; Gd/Yb cn = 0.92–12.1) and display variably negative Eu anomalies (Eu/Eu* = 0.37–0.96) and moderate Sr (84–539 ppm) contents. Four outlier granite samples have variably positive Eu (Eu/Eu* = 1.0–12) anomalies. Given that the granodiorites have higher K 2 O/Na 2 O than the tonalites and trondhjemites, it is suggested that the granites were derived from partial melting of the granodiorites. It is speculated that the dense eclogitic residues, left after TTG melt extraction, were foundered into the sub-arc mantle, leading to basaltic underplating beneath the lower rust. Melting of the granodiorites in response to the basaltic underplating resulted in the production of high-K granitic melts. Formation of the Fiskenaesset TTGs, the foundering of the eclogitic residues into the mantle, and the emplacement of the high-K granites led to the growth of Archean continental crust in the Fiskenaesset region.
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Field and geochemical characteristics of Mesoarchean to Neoarchean volcanic rocks in the Storø greenstone belt, SW Greenland: Evidence for accretion of intra-oceanic volcanic arcs
Precambrian Research, 2010Co-Authors: J.c. Ordóñez-calderón, Ali Polat, Brian J Fryer, Joel E. GagnonAbstract:Abstract The Storo greenstone belt, southern West Greenland, consists of thrust-imbricated slices of Mesoarchean (>3060 Ma) and Neoarchean (ca. 2800 Ma) mafic to ultramafic volcanic rocks, volcaniclastic sediments, and gabbro–anorthosite associations. The belt underwent polyphase metamorphism at upper amphibolite facies conditions between 2650 and 2600 Ma. The contacts between the Mesoarchean and Neoarchean volcanic rocks, and surrounding Eoarchean to Neoarchean tonalite–trondhjemite–granodiorite (TTG) gneisses are tectonic and typically bounded by high-grade mylonites. Regardless of age, the volcanic rocks are dominated by mafic amphibolites with a tholeiitic basalt composition, near-flat to slightly enriched light rare earth element (LREE) patterns (La/Smcn = 0.91–1.48), relatively flat to slightly depleted heavy-REE (HREE) (Gd/Ybcn = 1.0–1.28), and pronounced negative Nb–Ta anomalies (Nb/Nb* = 0.34–0.73) on chondrite- and primitive mantle-normalized diagrams. These geochemical characteristics are consistent with subduction zone geochemical signatures and partial melting of a shallow (
Jasper Berndt - One of the best experts on this subject based on the ideXlab platform.
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magmatic and metamorphic history of paleoarchean tonalite trondhjemite granodiorite ttg suite from the singhbhum craton eastern india
Precambrian Research, 2014Co-Authors: Dewashish Upadhyay, Ellen Kooijman, Sabyasachi Chattopadhyay, Klaus Mezger, Jasper BerndtAbstract:Texturally controlled dating of zircon from Paleoarchean tonalite–trondhjemite–granodiorites of the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite batholith (Phases I, II, and III) from the Singhbhum craton in eastern India reveals a polycyclic evolution of the Archean crust. The granitoid suites were emplaced in two pulses at 3.45–3.44 Ga and 3.35–3.32 Ga. Tonalites and trondhjemites of the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.45–3.44 Ga together with Phase III of the Singhbhum Granite pluton while granites belonging to the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.35–3.32 together with Phase I and Phase II of the Singhbhum Granite pluton. Both crustal units underwent an early phase of relatively high-grade metamorphism at 3.30–3.28 Ga followed by extensive fluid-induced alteration during low-grade metamorphism at 3.19–3.12 Ga, and 3.02–2.96 Ga. The two units have also been marginally affected at ca. 2.52 Ga and 1.06 Ga by major metamorphic events in the North Singhbhum Mobile Belt and the Singhbhum shear zone at the northern margin of the craton. The zircon grains in granites have inherited cores with ages of ca. 3.61 Ga and 3.46–3.41 Ga and with well-developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source. The emplacement of the expansive granitoids belonging to the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite was synchronous with the amphibolite-facies metamorphism (ca. 3.32 Ga) of older meta-igneous and metasedimentary rocks belonging to the Older Metamorphic Group. Major felsic crust formation in the craton occurred in a narrow time interval between 3.46 and 3.32 Ma with minor contributions of material as old as 3.6 Ga. The complex polycyclic evolution of the Paleoarchean crust in the Singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism.
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Magmatic and metamorphic history of Paleoarchean tonalite–trondhjemite–granodiorite (TTG) suite from the Singhbhum craton, eastern India
Precambrian Research, 2014Co-Authors: Dewashish Upadhyay, Ellen Kooijman, Sabyasachi Chattopadhyay, Klaus Mezger, Jasper BerndtAbstract:Texturally controlled dating of zircon from Paleoarchean tonalite–trondhjemite–granodiorites of the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite batholith (Phases I, II, and III) from the Singhbhum craton in eastern India reveals a polycyclic evolution of the Archean crust. The granitoid suites were emplaced in two pulses at 3.45–3.44 Ga and 3.35–3.32 Ga. Tonalites and trondhjemites of the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.45–3.44 Ga together with Phase III of the Singhbhum Granite pluton while granites belonging to the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.35–3.32 together with Phase I and Phase II of the Singhbhum Granite pluton. Both crustal units underwent an early phase of relatively high-grade metamorphism at 3.30–3.28 Ga followed by extensive fluid-induced alteration during low-grade metamorphism at 3.19–3.12 Ga, and 3.02–2.96 Ga. The two units have also been marginally affected at ca. 2.52 Ga and 1.06 Ga by major metamorphic events in the North Singhbhum Mobile Belt and the Singhbhum shear zone at the northern margin of the craton. The zircon grains in granites have inherited cores with ages of ca. 3.61 Ga and 3.46–3.41 Ga and with well-developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source. The emplacement of the expansive granitoids belonging to the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite was synchronous with the amphibolite-facies metamorphism (ca. 3.32 Ga) of older meta-igneous and metasedimentary rocks belonging to the Older Metamorphic Group. Major felsic crust formation in the craton occurred in a narrow time interval between 3.46 and 3.32 Ma with minor contributions of material as old as 3.6 Ga. The complex polycyclic evolution of the Paleoarchean crust in the Singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism.
Klaus Mezger - One of the best experts on this subject based on the ideXlab platform.
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formation of archean continental crust constrained by boron isotopes
Geochemical Perspectives Letters, 2019Co-Authors: Matthijs A Smit, Klaus Mezger, Anders Schersten, Tomas Naeraa, Robert Emo, Erik E Scherer, Peter Sprung, Wouter Bleeker, Alessandro Maltese, Yue CaiAbstract:The continental crust grew and matured compositionally during the Palaeo- to Neoarchean through the addition of juvenile Tonalite-Trondhjemite-Granodiorite (TTG) crust. This change has been linked ...
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magmatic and metamorphic history of paleoarchean tonalite trondhjemite granodiorite ttg suite from the singhbhum craton eastern india
Precambrian Research, 2014Co-Authors: Dewashish Upadhyay, Ellen Kooijman, Sabyasachi Chattopadhyay, Klaus Mezger, Jasper BerndtAbstract:Texturally controlled dating of zircon from Paleoarchean tonalite–trondhjemite–granodiorites of the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite batholith (Phases I, II, and III) from the Singhbhum craton in eastern India reveals a polycyclic evolution of the Archean crust. The granitoid suites were emplaced in two pulses at 3.45–3.44 Ga and 3.35–3.32 Ga. Tonalites and trondhjemites of the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.45–3.44 Ga together with Phase III of the Singhbhum Granite pluton while granites belonging to the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.35–3.32 together with Phase I and Phase II of the Singhbhum Granite pluton. Both crustal units underwent an early phase of relatively high-grade metamorphism at 3.30–3.28 Ga followed by extensive fluid-induced alteration during low-grade metamorphism at 3.19–3.12 Ga, and 3.02–2.96 Ga. The two units have also been marginally affected at ca. 2.52 Ga and 1.06 Ga by major metamorphic events in the North Singhbhum Mobile Belt and the Singhbhum shear zone at the northern margin of the craton. The zircon grains in granites have inherited cores with ages of ca. 3.61 Ga and 3.46–3.41 Ga and with well-developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source. The emplacement of the expansive granitoids belonging to the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite was synchronous with the amphibolite-facies metamorphism (ca. 3.32 Ga) of older meta-igneous and metasedimentary rocks belonging to the Older Metamorphic Group. Major felsic crust formation in the craton occurred in a narrow time interval between 3.46 and 3.32 Ma with minor contributions of material as old as 3.6 Ga. The complex polycyclic evolution of the Paleoarchean crust in the Singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism.
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Magmatic and metamorphic history of Paleoarchean tonalite–trondhjemite–granodiorite (TTG) suite from the Singhbhum craton, eastern India
Precambrian Research, 2014Co-Authors: Dewashish Upadhyay, Ellen Kooijman, Sabyasachi Chattopadhyay, Klaus Mezger, Jasper BerndtAbstract:Texturally controlled dating of zircon from Paleoarchean tonalite–trondhjemite–granodiorites of the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite batholith (Phases I, II, and III) from the Singhbhum craton in eastern India reveals a polycyclic evolution of the Archean crust. The granitoid suites were emplaced in two pulses at 3.45–3.44 Ga and 3.35–3.32 Ga. Tonalites and trondhjemites of the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.45–3.44 Ga together with Phase III of the Singhbhum Granite pluton while granites belonging to the Older Metamorphic Tonalitic Gneisses were emplaced at ca. 3.35–3.32 together with Phase I and Phase II of the Singhbhum Granite pluton. Both crustal units underwent an early phase of relatively high-grade metamorphism at 3.30–3.28 Ga followed by extensive fluid-induced alteration during low-grade metamorphism at 3.19–3.12 Ga, and 3.02–2.96 Ga. The two units have also been marginally affected at ca. 2.52 Ga and 1.06 Ga by major metamorphic events in the North Singhbhum Mobile Belt and the Singhbhum shear zone at the northern margin of the craton. The zircon grains in granites have inherited cores with ages of ca. 3.61 Ga and 3.46–3.41 Ga and with well-developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source. The emplacement of the expansive granitoids belonging to the Older Metamorphic Tonalitic Gneisses and the Singhbhum Granite was synchronous with the amphibolite-facies metamorphism (ca. 3.32 Ga) of older meta-igneous and metasedimentary rocks belonging to the Older Metamorphic Group. Major felsic crust formation in the craton occurred in a narrow time interval between 3.46 and 3.32 Ma with minor contributions of material as old as 3.6 Ga. The complex polycyclic evolution of the Paleoarchean crust in the Singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism.
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Neoarchaean crustal evolution in the Congo Craton: evidence from K rich granitoids of the Ntem Complex, southern Cameroon
Journal of African Earth Sciences, 2000Co-Authors: R. Tchameni, Klaus Mezger, N. E. Nsifa, Andre PoucletAbstract:Abstract The Neoarchaean (2.6 Gal K rich granitoids of the Ebolowa area (Ntem Complex, Congo Craton) in southern Cameroon form small massifs trending north-northwest-south-southeast to north-south and contain xenoliths of the surrounding Tonalite-Trondhjemite-Granodiorite (TTG) series and of the greenstone belt country rocks. The granitoids range in modal composition from granodiorite to granite and leucogranite. The rocks display high SiO2 (69–76.5%), Na2O+K2O (5.5–9.1 %) and K 2 O Na 2 O (0.5–1.9). They are metaluminous to slightly peraluminous (0.9 The formation of these late granitoids in the Ebolowa area is attributed to a large-scale tectonothermal event around 2.6 Ga that led to the formation of similar granitoids throughout the extensive Ntem Complex. The intrusion of these granitoids is probably the terminal tectono thermal episode following the Archaean accretion and differentiation of the northwest Congo Craton.
Ali Polat - One of the best experts on this subject based on the ideXlab platform.
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Lithological, structural, and geochemical characteristics of the Mesoarchean Târtoq greenstone belt, southern West Greenland, and the Chugach – Prince William accretionary complex, southern Alaska: evidence for uniformitarian plate-tectonic processes
Canadian Journal of Earth Sciences, 2016Co-Authors: Ali Polat, Thomas F. Kokfelt, Kevin Burke, Timothy M. Kusky, Dwight C. Bradley, Annika Dziggel, Jochen KolbAbstract:The Mesoarchean Târtoq greenstone belt, southern West Greenland, consists of tectonically imbricated slices of metamorphosed basalt, gabbro, peridotite, and sedimentary rocks and is intruded by felsic rocks (now mylonites) with well-preserved duplex structures, representing a relict accretionary prism. The Târtoq greenstone belt is a remnant of a supra-subduction zone ophiolite that originated as back-arc basin oceanic crust. Following the initiation of intra-oceanic subduction, the back-arc oceanic crust accreted to the overriding plate, forming an accretionary prism. The felsic mylonites are compositionally akin to Archean tonalite–trondhjemite–granodiorite suites. Field observations, along with geochemical and zircon U–Pb age data, indicate that the protoliths of the felsic mylonites were derived from partial melting of back-arc basalts in the accretionary prism and emplaced along thrust faults between 3012 ± 4 and 2993 ± 6 Ma. It is proposed that the partial melting of the basalts likely occurred in response to ridge subduction. The Upper Cretaceous turbiditic greywackes of the Chugach – Prince William accretionary complex in southern Alaska are intruded by Paleogene felsic dykes. These felsic dykes appear to have been derived from partial melting of subducted and (or) accreted oceanic crust during slab window magmatism. Archean granitoid–greenstone terrains share many geological characteristics of Phanerozoic subduction–accretion complexes such as the Alaskan and Altaid subduction–accretion complexes, consistent with the operation of uniformitarian geological processes in the Archean. The Archean Earth might have been dominated by numerous smaller plates and greater ridge length than today that would have resulted in more frequent ridge-accretionary prism interactions and larger volumes of tonalite–trondhjemite–granodiorite generation in subduction–accretion complexes.
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origin of archean tonalite trondhjemite granodiorite ttg suites and granites in the fiskenaesset region southern west greenland implications for continental growth
Gondwana Research, 2013Co-Authors: Hua Huang, Ali Polat, Brian J FryerAbstract:Abstract Mesoarchean to Neoarchean orthogneisses (2.95–2.79 Ga) in the Fiskenaesset region, southern West Greenland, are composed of an older suite of metamorphosed tonalites, trondhjemites, and granodiorites (TTGs), and a younger suite of high-K granites. The TTGs are characterized by high Al 2 O 3 (14.2–18.6 wt.%), Na 2 O (3.4–5.13 wt.%), and Sr (205–777 ppm), and low Y (0.7–17.4 ppm) contents. On chondrite- and N-MORB-normalized trace element diagrams, the TTGs have the following geochemical characteristics: (1) highly fractionated REE patterns (La/Yb cn = 14–664; La/Sm cn = 4.3–11.0; Gd/Yb cn = 1.5–19.7); (2) strong positive anomalies of Sr (Sr/Sr* = 1.0–15.9) and Pb (Pb/Pb* = 1.4–34.9); and (3) large negative anomalies of Nb (Nb/Nb* = 0.01–0.34) and Ti (Ti/Ti* = 0.1–0.6). The geochemical characteristics of the TTGs and trace element modeling suggest that they were generated by partial melting of hydrous basalts (amphibolites) at the base of a thickened magmatic arc, leaving a rutile-bearing eclogite residue. Field observations suggest that spatially and temporarily associated tholeiitic basalts (now amphibolites) in the Fiskenaesset region might have been the sources of TTG melts. The high-K granites have steep REE patterns (La/Yb cn = 3.8–506; La/Sm cn = 2.7–18.9; Gd/Yb cn = 0.92–12.1) and display variably negative Eu anomalies (Eu/Eu* = 0.37–0.96) and moderate Sr (84–539 ppm) contents. Four outlier granite samples have variably positive Eu (Eu/Eu* = 1.0–12) anomalies. Given that the granodiorites have higher K 2 O/Na 2 O than the tonalites and trondhjemites, it is suggested that the granites were derived from partial melting of the granodiorites. It is speculated that the dense eclogitic residues, left after TTG melt extraction, were foundered into the sub-arc mantle, leading to basaltic underplating beneath the lower rust. Melting of the granodiorites in response to the basaltic underplating resulted in the production of high-K granitic melts. Formation of the Fiskenaesset TTGs, the foundering of the eclogitic residues into the mantle, and the emplacement of the high-K granites led to the growth of Archean continental crust in the Fiskenaesset region.
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Origin of Archean tonalite–trondhjemite–granodiorite (TTG) suites and granites in the Fiskenæsset region, southern West Greenland: Implications for continental growth
Gondwana Research, 2013Co-Authors: Hua Huang, Ali Polat, Brian J FryerAbstract:Abstract Mesoarchean to Neoarchean orthogneisses (2.95–2.79 Ga) in the Fiskenaesset region, southern West Greenland, are composed of an older suite of metamorphosed tonalites, trondhjemites, and granodiorites (TTGs), and a younger suite of high-K granites. The TTGs are characterized by high Al 2 O 3 (14.2–18.6 wt.%), Na 2 O (3.4–5.13 wt.%), and Sr (205–777 ppm), and low Y (0.7–17.4 ppm) contents. On chondrite- and N-MORB-normalized trace element diagrams, the TTGs have the following geochemical characteristics: (1) highly fractionated REE patterns (La/Yb cn = 14–664; La/Sm cn = 4.3–11.0; Gd/Yb cn = 1.5–19.7); (2) strong positive anomalies of Sr (Sr/Sr* = 1.0–15.9) and Pb (Pb/Pb* = 1.4–34.9); and (3) large negative anomalies of Nb (Nb/Nb* = 0.01–0.34) and Ti (Ti/Ti* = 0.1–0.6). The geochemical characteristics of the TTGs and trace element modeling suggest that they were generated by partial melting of hydrous basalts (amphibolites) at the base of a thickened magmatic arc, leaving a rutile-bearing eclogite residue. Field observations suggest that spatially and temporarily associated tholeiitic basalts (now amphibolites) in the Fiskenaesset region might have been the sources of TTG melts. The high-K granites have steep REE patterns (La/Yb cn = 3.8–506; La/Sm cn = 2.7–18.9; Gd/Yb cn = 0.92–12.1) and display variably negative Eu anomalies (Eu/Eu* = 0.37–0.96) and moderate Sr (84–539 ppm) contents. Four outlier granite samples have variably positive Eu (Eu/Eu* = 1.0–12) anomalies. Given that the granodiorites have higher K 2 O/Na 2 O than the tonalites and trondhjemites, it is suggested that the granites were derived from partial melting of the granodiorites. It is speculated that the dense eclogitic residues, left after TTG melt extraction, were foundered into the sub-arc mantle, leading to basaltic underplating beneath the lower rust. Melting of the granodiorites in response to the basaltic underplating resulted in the production of high-K granitic melts. Formation of the Fiskenaesset TTGs, the foundering of the eclogitic residues into the mantle, and the emplacement of the high-K granites led to the growth of Archean continental crust in the Fiskenaesset region.
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Field and geochemical characteristics of Mesoarchean to Neoarchean volcanic rocks in the Storø greenstone belt, SW Greenland: Evidence for accretion of intra-oceanic volcanic arcs
Precambrian Research, 2010Co-Authors: J.c. Ordóñez-calderón, Ali Polat, Brian J Fryer, Joel E. GagnonAbstract:Abstract The Storo greenstone belt, southern West Greenland, consists of thrust-imbricated slices of Mesoarchean (>3060 Ma) and Neoarchean (ca. 2800 Ma) mafic to ultramafic volcanic rocks, volcaniclastic sediments, and gabbro–anorthosite associations. The belt underwent polyphase metamorphism at upper amphibolite facies conditions between 2650 and 2600 Ma. The contacts between the Mesoarchean and Neoarchean volcanic rocks, and surrounding Eoarchean to Neoarchean tonalite–trondhjemite–granodiorite (TTG) gneisses are tectonic and typically bounded by high-grade mylonites. Regardless of age, the volcanic rocks are dominated by mafic amphibolites with a tholeiitic basalt composition, near-flat to slightly enriched light rare earth element (LREE) patterns (La/Smcn = 0.91–1.48), relatively flat to slightly depleted heavy-REE (HREE) (Gd/Ybcn = 1.0–1.28), and pronounced negative Nb–Ta anomalies (Nb/Nb* = 0.34–0.73) on chondrite- and primitive mantle-normalized diagrams. These geochemical characteristics are consistent with subduction zone geochemical signatures and partial melting of a shallow (
Andre Pouclet - One of the best experts on this subject based on the ideXlab platform.
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Palæo- and Neoproterozoic granitoids and rhyolites from the West Congolian Belt (Gabon, Congo, Cabinda, north Angola): chemical composition and geotectonic implications
Journal of African Earth Sciences, 2000Co-Authors: Jean-paul Vicat, Andre PoucletAbstract:Various Palaeo- and Neoproterozoic granitoid bodies and related rhyolites are located in the West Congolian Belt. The Palaeoproterozoic granitoids, dated around 2 Ga, exhibit an Archaean-type Tonalite-Trondhjemite-Granodiorite suite chemical signature and are related to the Eburnean tectnno-magmatic event. In contrast, Neoproterozoic granitoids and rhyolites, dated around 1 Ga, have chemical geotectonic signatures that range from orogenic to intraplate (Nb-negative anomaly, large ion lithophile element enrichment and high field strength element depletion). However, a late Kibaran orogenic event (1.35-1.00 Ga) is unknown in this area. The Neoproterozoic magmatism is interpreted as a consequence of the initiation of pre-Pan-African rifting, which implies the formation or the reactivation of major crustal strike-slip faults with asthenospheric upwelling and the generation of a thermal anomaly. This thermal anomaly could have been responsible for magmatic processes involving the lower crust, as encountered in post-orogenic environments.
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Palæo- and Neoproterozoic granitoids and rhyolites from the West Congolian Belt (Gabon, Congo, Cabinda, north Angola): chemical composition and geotectonic implications
Journal of African Earth Sciences, 2000Co-Authors: Jean-paul Vicat, Andre PoucletAbstract:Various Palæo- and Neoproterozoic granitoid bodies and related rhyolites are located in the West Congolian Belt. The Palæoproterozoic granitoids, dated around 2 Ga, exhibit an Archæan-type Tonalite-Trondhjemite-Granodiorite suite chemical signature and are related to the Eburnean tectnno-magmatic event. In contrast, Neoproterozoic granitoids and rhyolites, dated around 1 Ga, have chemical geotectonic signatures that range from orogenic to intraplate (Nb-negative anomaly, large ion lithophile element enrichment and high field strength element depletion). However, a late Kibaran orogenic event (1.35-1.00 Ga) is unknown in this area. The Neoproterozoic magmatism is interpreted as a consequence of the initiation of pre-Pan-African rifting, which implies the formation or the reactivation of major crustal strike-slip faults with asthenospheric upwelling and the generation of a thermal anomaly. This thermal anomaly could have been responsible for magmatic processes involving the lower crust, as encountered in post-orogenic environments.
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Neoarchæan crustal evolution in the Congo Craton: evidence from K rich granitoids of the Ntem Complex, southern Cameroon
Journal of African Earth Sciences, 2000Co-Authors: R. Tchameni, K. Mezger, N. E. Nsifa, Andre PoucletAbstract:The Neoarchæan (2.6 Gal K rich granitoids of the Ebolowa area (Ntem Complex, Congo Craton) in southern Cameroon form small massifs trending north-northwest-south-southeast to north-south and contain xenoliths of the surrounding Tonalite-Trondhjemite-Granodiorite (TTG) series and of the greenstone belt country rocks. The granitoids range in modal composition from granodiorite to granite and leucogranite. The rocks display high SiO2 (69–76.5%), Na2O+K2O (5.5–9.1 %) and K2O/Na2O (0.5–1.9). They are metaluminous to slightly peraluminous (0.9
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Neoarchaean crustal evolution in the Congo Craton: evidence from K rich granitoids of the Ntem Complex, southern Cameroon
Journal of African Earth Sciences, 2000Co-Authors: R. Tchameni, Klaus Mezger, N. E. Nsifa, Andre PoucletAbstract:Abstract The Neoarchaean (2.6 Gal K rich granitoids of the Ebolowa area (Ntem Complex, Congo Craton) in southern Cameroon form small massifs trending north-northwest-south-southeast to north-south and contain xenoliths of the surrounding Tonalite-Trondhjemite-Granodiorite (TTG) series and of the greenstone belt country rocks. The granitoids range in modal composition from granodiorite to granite and leucogranite. The rocks display high SiO2 (69–76.5%), Na2O+K2O (5.5–9.1 %) and K 2 O Na 2 O (0.5–1.9). They are metaluminous to slightly peraluminous (0.9 The formation of these late granitoids in the Ebolowa area is attributed to a large-scale tectonothermal event around 2.6 Ga that led to the formation of similar granitoids throughout the extensive Ntem Complex. The intrusion of these granitoids is probably the terminal tectono thermal episode following the Archaean accretion and differentiation of the northwest Congo Craton.