Late Eocene Two-Pyroxene Trachydacites from the Southern Qiangtang Terrane, Central Tibetan Plateau: High-Temperature Melting of Overthickened and Dehydrated Lower Crust
| Autor: | Ji-Feng Xu, Feng Huang, Yun-Chuan Zeng, Bao-Di Wang, Shu-Hui Ren, Ming-Jian Li, Jian-Lin Chen |
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| Rok vydání: | 2021 |
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| Zdroj: | Journal of Petrology. 62 |
| ISSN: | 1460-2415 0022-3530 |
| Popis: | Orthopyroxene-bearing granitic rock (e.g. charnockite) is relatively rare but provides an excellent opportunity to probe the thermal and tectonic evolution of deep orogenic crust because of its distinct mineral assemblage. Here we present petrological, mineralogical, elemental, and Sr–Nd–Hf–O isotopic data for late Eocene (ca. 36 Ma; zircon U–Pb ages) volcanic rocks exposed in the Ejiu region in the southern Qiangtang Terrane to investigate how the central Tibetan crust evolved to its modern thickness and thermal state. The Ejiu volcanic rocks (EVRs) are trachydacites with anhydrous mineral assemblages (i.e. two pyroxenes, sanidine, plagioclase, and ilmenite, without amphibole and biotite) and geochemical characteristics (e.g. high P2O5 and TiO2) that resemble those of charnockite-type magmatic rocks. Mineral and whole-rock thermometry and hygrometry suggests that the parent magma crystallized under hot (~1000°C) and dry (H2O 1.5 GPa) and high temperature (>1000°C) generated the EVRs. Based on a synthesis of independent geological and geophysical data, we further suggest that the southern Qiangtang Terrane crust of the central Tibetan Plateau was thick, dry, and elevated during the Late Cretaceous to early Eocene time, and that it became abnormally hot owing to the ascending asthenosphere after lithospheric foundering during the middle Eocene. |
| Databáze: | OpenAIRE |
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