Oligocene HP metamorphism and anatexis of the Higher Himalayan Crystalline Sequence in Yadong region,east-central Himalaya |
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| Institution: | 1. Institute for Earth and Environmental Sciences, University of Potsdam, Karl-Liebknecht Str. 24–25, 14476 Potsdam, Germany;2. German Research Centre for Geosciences (GFZ), Inorganic and Isotope Geochemistry, Telegrafenberg, 14473 Potsdam, Germany;1. Geowissenschaftliches Zentrum, Universität Göttingen, 37077 Göttingen, Germany;2. Department of Earth Sciences, Dalhousie University, Halifax, NS B3H 4R2, Canada;3. NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;4. Department of Geology, University of Leicester, LE1 7RH, UK;5. Department of Geological and Environmental Science, Stanford University, CA 94305, USA;6. University of Kashmir, Hazratbal, Srinagar, 190 006 Jammu and Kashmir, India;1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China;2. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100085, China;3. Zhejiang Institute of Geological Survey, Hangzhou 311203, China;4. School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, China;1. Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56126 Pisa, Italy;2. C.N.R., Istituto di Geoscienze e Georisorse, UOS Pisa, via Moruzzi 1, 56124 Pisa, Italy;3. Dipartimento di Scienze della Terra, Università di Torino, via Valperga Caluso 35, 10125 Torino, Italy;4. Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Azenbergstrasse 18, 70174 Stuttgart, Germany;5. C.N.R., Istituto di Geoscienze e Georisorse, UOS Pavia, via Ferrata 1, 27100 Pavia, Italy;6. Dipartimento di Geoscienze, Università di Padova, via Gradenigo 6, 35131 Padova, Italy |
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| Abstract: | The Higher Himalayan Crystalline Sequence (HHCS) provides an excellent natural laboratory to study continental subduction, crustal melting and tectonic evolution of orogenic belt generated through the collision of India with Eurasia. Our petrological study and phase equilibrium modeling reveal that the pelitic migmatites in the HHCS of Yadong region, east-central Himalaya, preserve an early mineral assemblage garnet, kyanite, biotite, quartz, plagioclase, K-feldspar, rutile and ilmenite, and a late sillimanite- and/or cordierite-bearing assemblage, and underwent the high pressure (HP) and high temperature (HT) granulite-facies metamorphism and associated partial melting under P–T conditions of ca. 12 kbar and 825–845 °C, followed by nearly isothermal decompression and isobaric cooling. The anatexis of the migmatites occurred dominantly through dehydration-melting of both muscovite and biotite during the prograde metamorphism. The melt produced in the peak metamorphic conditions is about 20 to 30 vol.% of the rocks, and a significant amount of melt has been extracted from the source leading to the formation of Himalayan leucogranites. The zircon U–Pb dating data shows that the migmatites probably witnessed a prolonged melting episode that began at ca. 30 Ma and lasted to ca. 20 Ma. These results show that the thickening lower crust of the Himalayan orogen experienced long-lived and continued HP and HT metamorphism and pervasive anatexis, supporting the models on channel flow. |
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