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

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 

机构地区：[1]State Key Laboratory of Continental Dynamics,Northwest University [2]Key Laboratory of Western China’s Mineral Resources and Geological Engineering of Ministry of Education,Chang’an University [3]Key Laboratory of Western China's Mineral Resources and Geological Engineering of the Ministry of Education,College of Earth Science and Land Resources,Chang'an University [4]Key Laboratory of Western China’s Mineral Resources and Geological Engineering of the Ministry of Education,College of Earth Science and Land Resources,Chang’an University

出　　处：《Journal of China University of Geosciences》2009年第2期250-273,共24页中国地质大学学报（英文版）

基　　金：supported by the National Natural Science Foundation of China (Nos. 40572121 and 40234041);MOST Special Fund from the State Key Laboratory of Continental Dynamics, Northwest University

摘　　要：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）.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. 

分 类 号：P541[天文地球—构造地质学]