Late Cretaceous granitoids in Karakorum,northwest Tibet: petrogenesis and tectonic implications |
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Authors: | Lijie Liu Yue Chen Hongwei Tang Christopher Xiao |
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Institution: | 1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, China;2. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, China;3. School of Earth sciences, East China University of Technology, Nanchang, China;4. College of Earth Science, Chengdu University of Technology, Chengdu, China;5. Sichuan Bureau of Geology for Nuclear Industry, Deyang, China;6. Department of Earth and Atmospheric Sciences, College of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA |
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Abstract: | New zircon LA-ICP-MS U–Pb age, zircon Hf isotope, and whole-rock major and trace elemental data of the Late Cretaceous Ageledaban complex in the Karakorum Terrane (KKT), northwest Tibet, provide new constraints on the tectonic processes of the collision and thickening of the terrane between the Lhasa and Qiangtang terranes. The granitoids from the Ageledaban complex have a variable SiO2 content, from 62.83 to 73.35 wt.% and A/CNK<1.1 (except for YM61-2). They have rare earth element and trace element patterns that are enriched in light rare earth elements, Rb, Pb, Th, and U, and are depleted in Ba, P, Sr, Ti, and Nb, indicative of weakly peraluminous-metaluminous I-type affinity. Zircon U–Pb dating reveals that the Ageledaban complex was emplaced at ca. 80 Ma. Zircons from the monzogranite and monzonite samples with concordant 206Pb/238U ages about 80 Ma have a zircon εHf(t) of ?6.6 to ?1.1, corresponding to the Mesoproterozoic Hf crustal model ages (TDMC = 1.2–1.6 Ga); the remaining inherited zircons from the monzonite with concordant 206Pb/238U ages of about 108.1 Ma have εHf(t) values that range from ?8.3 to ?5.0, corresponding to the Mesoproterozoic Hf crustal model ages with an average of 1.6 Ga. These signatures indicate that the Ageledaban granitoids may have been derived from the partial melting of a mixed mantle-crust source. Together with the age and geochemical data in the literature, we propose that the collisional event in the KKT in northwestern Tibet would postdate the northern Lhasa–southern Qiangtang collision, which occurred first in the Amdo in the east and later in the Shiquanhe in central Tibet. Our results support the previous view that the collision of the Bangong–Nujiang suture zone (BNSZ) may be diachronous. |
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Keywords: | Late Cretaceous petrogenesis Karakorum Terrane Lhasa–Qiangtang collision zone Ageledaban complex Zircon U–Pb dating |
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