Petrogenesis of the Triassic andesites in the East Kunlun Orogen, East Tethys: implications for crustal maturation within an extensional setting

Author:

Zhao Xu12,Fu Lebing2ORCID,Santosh M.34,Wei Junhao2,Zhang Cheng5,Chen Jiajie6,Xu Chongwen2,Zhang Xinming2

Affiliation:

1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

2. School of Earth Resources, China University of Geosciences, Wuhan 430074, China

3. School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China

4. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia

5. Geological Survey Institute of Inner Mongolia Autonomous Region, Hohhot 010020, China

6. School of Earth Science, East China University of Technology, Nanchang 330013, China

Abstract

The tectonic and crustal evolution of the East Kunlun Orogen in the Triassic remains unclear. We investigated the Triassic andesites (235 and 216 Ma) to investigate these issues. The Mid- and Late Triassic andesites are calc-alkaline with enriched Sr–Nd isotopic compositions: ( 87 Sr/ 86 Sr) i  = 0.709210–0.709758 and ε Nd ( t ) = −8.0 to −6.9. The Mid-Triassic andesites have higher Mg, Cr and Ni contents and more depleted Hf isotopic compositions ( ε Hf ( t ) = −4.2 to 1.3) than the Late Triassic andesites ( ε Hf ( t ) = −7.4 to −5.8). These features are explained by the derivation of magma from partial melting of the mafic lower continental crust, although minor lithospheric mantle materials are also involved in the Mid-Triassic andesites. The andesites were generated in extensional settings related to slab break-off in the Mid-Triassic and lithospheric delamination in the Late Triassic, respectively. The Late Triassic magmatic suites are higher in K and represent a more mature continental crust, indicating that crustal reworking in extensional settings contributes to crustal maturation. In combination with the regional magmatic, structural and sedimentary records, we propose that the East Kunlun Orogen evolved from oceanic subduction in the Late Permian to Mid-Triassic through continental collision in the Mid-Triassic to post-collision in the Late Triassic.

Funder

Postdoctoral Research Foundation of China

National Natural Science Foundation of China

Fundamental Research Funds for the Central Universities

Publisher

Geological Society of London

Subject

Geology

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