Remnants of arc-related Mesoarchaean oceanic crust in the Tartoq Group of SW Greenland |
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| Authors: | Kristoffer Szilas Vincent J Van Hinsberg Alex FM Kisters J Elis Hoffmann Brian F Windley Thomas F Kokfelt Anders Scherstén Robert Frei Minik T Rosing Carsten Münker |
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| Institution: | 1. Geological Survey of Denmark and Greenland - GEUS, Øster Voldgade 10, 1350 Copenhagen K, Denmark;2. Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark;3. Natural History Museum of Denmark, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark;4. Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, United Kingdom;5. Department of Earth Sciences, Stellenbosch University, Matieland 7602, South Africa;6. Steinmann Institut für Geologie, Universität Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany;7. Geologisch-Mineralogisches Institut, Universität zu Köln, Zülpicher Str. 49b, 50674 Köln, Germany;8. Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom;9. Department of Earth and Ecosystem Sciences Division of Geology, Lund University, Sölvegatan 12, 223 62 Lund, Sweden;10. Nordic Center for Earth Evolution, NordCEE, Denmark |
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| Abstract: | The Tartoq Group, located in SW Greenland, consists of supracrustal rocks of mainly tholeiitic basaltic composition, including pillow lavas, sills/dykes and gabbros, as well as ultramafic rocks. Metamorphic grade ranges from greenschist facies to granulite facies. The Tartoq Group crops out as a series of blocks and slivers that are imbricated with originally intrusive Mesoarchaean TTG orthogneisses. The supracrustal rocks form part of a SE vergent fold and thrust belt consistent with the imbrication of TTG gneisses and supracrustal rocks along a convergent margin. LA-ICP-MS U–Pb zircon dating of an intrusive TTG sheet yields a minimum age of 2986 ± 4 Ma for the Tartoq Group. This age is consistent with MC-ICP-MS Lu–Hf and Sm–Nd isotopic whole-rock data for mafic samples from different blocks of the Tartoq Group, which yield errorchron ages of 3189 ± 65 Ma and 3068 ± 220 Ma, respectively. The mafic supracrustal rocks of the Tartoq Group have chondrite-normalized REE patterns with LaCN/SmCN of 0.67–1.96 and rather flat primitive mantle-normalized multi-element patterns, except for scattered LILE contents, and generally negative Nb-anomalies with Nb/Nb* of 0.26–1.31. Th/Yb varies between 0.06 and 0.47 and Nb/Yb between 0.45 and 4.4 indicative of an arc affinity when compared to rocks from modern settings. The similar geochemistry of the different lithological units, together with their coeval formation, as evident from trace element geochemical trends, supports a co-magmatic origin for the rock assemblage and their formation as imbricated relics of oceanic crust. Accordingly, we propose that the Tartoq Group represents remnants of Mesoarchaean oceanic crust, which formed in a suprasubduction zone geodynamic environment. |
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