Diversity of Archean crust in the eastern Tula Mountains,Napier Complex,East Antarctica |
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| Institution: | 1. Institute of Geological Sciences, Polish Academy of Sciences, Warsaw, Poland;2. Faculty of Earth Sciences, University of Silesia in Katowice, Sosnowiec, Poland;3. School of Earth and Planetary Sciences, Curtin University, Perth, Australia;4. Korea Basic Science Institute (KBSI), Ochang Campus, Republic of Korea;1. Czech Geological Survey, 11821 Praha 1, Czech Republic;2. Université de Strasbourg, CNRS, Institut de Physique du Globe de Strasbourg, UMR 7516, 67084 Strasbourg, France;3. Institute of Geophysics ASCR, v.v.i., Boční II/1401, Prague 4 14131, Czech Republic;4. Department of Earth Science, University of California, Santa Barbara, CA 93106, USA;1. Korzhinskii Institute of Experimental Mineralogy, Russian Academy of Sciences, Academician Ossipyan str., 4, Chernogolovka, Moscow District, 142432, Russia;2. Department of Petrology, Moscow State University, Moscow, Russia;3. Department of Geology, University of Johannesburg, Johannesburg, South Africa;4. Department of Earth and Environmental Sciences, BIUST, Botswana |
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| Abstract: | The Napier Complex of Enderby and Kemp Lands forms the north-western part of the East Antarctic Shield and consists predominantly of gneisses and granulites metamorphosed during a ca. 2.8 Ga high-grade and a ca. 2.5 Ga ultra-high temperature event. The western segment of the Napier Complex includes coastal outcrops, islands and nunataks around Amundsen and Casey Bays, and the Tula Mountains. This region records some of the highest metamorphic temperatures measured on Earth, affecting a variety of gneisses as old as ca. 3.8 Ga. Five samples of orthogneiss from the less-studied eastern Tula Mountains, including three granitic, one trondhjemitic and one dioritic gneiss, were dated by zircon U-Pb Secondary Ion Mass Spectrometry (SIMS). The three orthogneisses yield protolith ages of 3750 ± 35 Ma (granitic), 3733 ± 21 (trondhjemitic) Ma and 3560 ± 42 Ma (dioritic), whereas the two other granitic orthogneisses record ages of 2903 ± 14 Ma and 2788 ± 24 Ma. Zircon growth during metamorphism occurred at 2826 ± 10 Ma, and also between 2530 Ma and 2480 Ma. Samples from the Tula Mountains can be geochemically subdivided into Y-HREE-Nb-Ta depleted and undepleted groups. Eoarchean granitoids are included in both geochemical groups, as are Meso- and Neoarchean granitoids. The Y-HREE-Nb-Ta depleted granitoids can be generated by medium- to high-pressure melting of mafic crust, whereas undepleted granitoids can be generated by low-pressure melting. However, relatively high potassium contents in most samples, and the presence of xenocrystic/inherited zircon in some, reflect the likely involvement of felsic crustal sources. This diversity in granitoid composition occurs across the Napier Complex. The lack of a simple correlation between protolith age and geochemical type is an indication that magmatism during the Eoarchean (and later) involved diverse sources and processes, including re-melting and recycling of various crustal components, rather than just the formation of juvenile crust. |
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