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Testing final closure time of the Paleo-Asian Ocean along the Solonker suture by a transition of compressional and extensional setting

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Geoscience Frontiers 2020年第6期11卷 1935-1951页

作者： Haidong Zhang Jianchao Liu Jinkun Yang Jiakun Ge Jinya Wang Zhen Li The School of Earth Science and Resources Chang’an UniversityXi’an 710054China Department of Geology Northwest UniversityXi’an 710069China Laboratory of Mineralization and Dynamics Chang’an UniversityXi’an 710054China Anhui Branch of China National Geological Exploration Center of Building Material Industry Hefei 230022China

The giant Central Asian Orogenic Belt is an extensive accretionary orogen,of which the Solonker suture,as a major regional suture,coincides closely with an early Permian paleobiogeographical boundary.This suture is considered to mark the location of the final closure of the Paleo-Asian Ocean between the North China Craton and the Mongolian Terrane.Although the closure time of the Paleo-Asian Ocean along the Solonker suture has generally been regarded as Late Permian-Early Triassic,uncertainty remains because of a lack of typical collisionrelated features(e.g.,high-grade regional metamorphism and well-developed fold-thrust structures)and a scarcity of outcrops.The present study reports Early Permian foliated gabbros and dikes(288-275 Ma)and Middle-Late Permian undeformed layered gabbros,strongly peraluminous granites,and I-type granites(265-254 Ma)in the Xinhure area along the northern margin of the North China Craton.The Early Permian foliated intrusions have a subduction-related geochemical signature and were derived from partial melting of lithospheric mantle modified by subduction-related melts or fluids at the active margin of the North China Craton.In contrast,the Late Permian undeformed layered gabbros and strongly peraluminous granites were derived from partial melting of lithospheric mantle and middle-upper crust,respectively,triggered by asthenospheric upwelling.Therefore,a transition from an end-compressional to an extensional environment according to a transition from collision termination to postcollision of the North China Craton and Mongolian Terrane may have occurred between 275 Ma and 262 Ma.This time span can be considered as the final closure time of the Paleo-Asian Ocean along the Solonker suture.

关键词： Central Asian orogenic belt Solonker suture Layered gabbro strongly peraluminous granite Paleo-Asian ocean closure time

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Post-Orogenic granites in Pingwu Region, Northwest Sichuan: Evidence for North China Block and Yangtze Block Collision during Triassic

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Journal of China University of Geosciences 2009年第2期20卷 250-273页

作者：裴先治李佐臣丁仨平冯建赟李瑞保孙雨张亚峰刘战庆 State Key Laboratory of Continental Dynamics Northwest University Key Laboratory of Western China’s Mineral Resources and Geological Engineering of Ministry of Education Chang’an University Key Laboratory of Western China's Mineral Resources and Geological Engineering of the Ministry of Education College of Earth Science and Land ResourcesChang'an University Key Laboratory of Western China’s Mineral Resources and Geological Engineering of the Ministry of Education College of Earth Science and Land ResourcesChang’an University

The Nanyili （南一里）, Laohegou （老河沟）, and Shaiziyan （筛子岩） granitic intrusions are located in the southern margin of the Bikou （碧口） block in Pingwu （平武） area, Northwest Sichuan （四川）. The petrography and geochemical characteristics of the granitic intrusions as well as their source and tectonic settings are reported and discussed in this article. The Laohegou and Shaiziyan granites are with high SiO2 （69.89 wt.%-73.05 wt.%） and Al2O3 contents, and A/CNK=1.04-1.12. They are typical strongly peraluminous granites, with supersaturation in AI and Si. The abundance of ∑REE varies in the range of （33.13-89.12）×10^-6. The rocks show an LREE enrichment pattern and obvious Eu negative anomaly. The trace element geochemistry is characterized evidently by a negative anomaly of Ta, Nb, Ti, etc. and a positive anomaly of Rb, Ba, Sr, etc.. Zircons of the Nanyili granite have higher Th/U ratios, and their CL images have internal oscillatory zoning, suggesting that the zircons of the samples are igneous in origin. The LA ICP-MS zircon U-Pb isotopic concordia diagram yields an age of 223.1±2.6 Ma （MSWD=1.4）, which indicates that the granodiorite intrusions formed in the early Late Triassic. The Nanyili, Laohegou, and Shaiziyan granites have the characteristics of post-collisional granites and are regarded as post-orogenic granites. Thus, the granite intrusions are interpreted as syn-collisional granites that resulted from the crustal thickening caused by the collisions between the North China plate and the Yangtze plate during the Indosinian. The granitic intrusions formed in a transitional environment from syn- （compressional environment） to post-collision （extensional environment）.

关键词： strongly peraluminous granite LA ICP-MS dating geochemistry tectonic setting post-collision Bikou block.

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