阿拉善地块北缘乌力吉岩体锆石U⁃Pb年代学、地球化学及其对区域构造演化的制约  

Zircon U⁃Pb Chronology and Geochemistry of the Wuliji Intrusions in the Northern Alxa Block:Constraints on the Tectonic Evolution of the Southern Altaids

作　　者：张善明[1,2] 贺中银 赵鹏彬 胡二红 王亚楠[4] 周彦波 Zhang Shanming;He Zhongyin;Zhao Pengbin;Hu Erhong;Wang Yanan;Zhou Yanbo(School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;Inner Mongolia Mining Development Co.,Ltd.,Huhhot 010011,China;Shanxi Mineral Resources and Geological Survey,Xi’an 710068,China;Faculty of Earth Resources,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]内蒙古矿业开发有限责任公司,内蒙古呼和浩特010011 [3]陕西省矿产地质调查中心,陕西西安710068 [4]中国地质大学资源学院,湖北武汉430074

出　　处：《地球科学》2021年第1期101-121,共21页Earth Science

基　　金：内蒙古自然资源厅矿产地质调查项目(Nos.NMKD2016-06,NMKD2014-10).

摘　　要：阿拉善地块北缘是研究古亚洲洋最终闭合过程的重要区域,该区大面积出露的石炭−二叠纪火成岩尚缺乏深入探讨,直接导致古亚洲洋最终闭合时间的认识无法统一,进而制约了中亚造山带南缘中部晚古生代构造演化问题的讨论.通过选取的乌力吉岩体位于恩格乌苏断裂带和巴丹吉林断裂带之间,处于沙拉扎山构造带内,对其开展了系统的岩相学、全岩地球化学及锆石U-Pb年代学研究.结果显示,岩体主要由花岗闪长岩和花岗岩组成,花岗闪长岩2件样品加权平均年龄分别为:266.00±1.00 Ma(MSWD=0.69)、267.76±0.97 Ma(MSWD=0.26).花岗岩3件样品加权平均年龄分别为:254.57±0.99 Ma(MSWD=0.79)、253.70±1.70 Ma(MSWD=2.50)、252.50±2.90 Ma(MSWD=4.70).SiO2含量:花岗闪长岩64.13%~67.17%,花岗岩68.08%~75.29%;Na2O+K2O含量:花岗闪长岩6.40%~7.00%,花岗岩7.09%~7.94%,均属中等分异的I型花岗岩.Nb、Ta、P、Ti明显亏损,K、Zr、Hf具明显正异常.轻稀土(LREE)富集,重稀土(HREE)亏损且分馏明显,LREE/HREE=6.49~17.45.(La/Yb)N值:花岗闪长岩6.21~8.80,花岗岩9.21~22.06.地球化学特征反映两期侵入体具壳幔混合特性,以壳源为主,表现分离结晶和晚期流体交代作用特征.综合沉积建造及岩石地球化学认为,古亚洲洋可能在二叠纪前已经闭合,阿拉善地区于二叠纪进入板内演化阶段,乌力吉一带处于区域性同造山挤压向造山后伸展折返或后碰撞伸展环境.The northern Alxa block is the key area for studying the closing of the Paleo-Asian Ocean,whereas the Permo-Carboniferous igneous in this area have been rarely investigated,leading to the time and way of the closing of the Paleo-Asian Ocean can not be unified directly,and more importantly,restricting a deeper insight into the tectonic evolution of the central southern Altaids in late Paleozoic.In this paper,we carried out a systematic study of the petrography,whole rock geochemistry,zircon U-Pb dating for the Wuliji intrusions,which are located in the Shalazhashan structural belt that spreading between the Engewusu fault belt and Badanjilin fault belt.Our results demonstrated that the Wuliji intrusions are mainly composed of granodiorite and granite,the weighted average ages of two samples from granodiorite are 266.00±1.00 Ma(MSWD=0.69)、267.76±0.97 Ma(MSWD=0.26),and the weighted average ages of three samples from granite are 254.57±0.99 Ma(MSWD=0.79)、253.70±1.70 Ma(MSWD=2.50)、252.50±2.90 Ma(MSWD=4.70).The SiO2 contents of the granodiorite are between 64.13%-67.17%,while the granite are between 68.08%-75.29%,the Na2O+K2O contents of the granodiorite are between 6.40%-7.00%,while the granite are between 7.09%-7.94%,both are I-type granites with medium degree of differentiation.They are depleted in Nb、Ta、P、Ti and HREEs,but relatively enriched in K、Zr、Hf and LREEs,the total content rations of LREE and HREE are between 6.49−17.45 and the fractionation of the HREEs is obvious.The(La/Yb)N values of granodiorite are between 6.21-8.80,while the granite are between 9.21-22.06.Geochemistry shows that the two stages intrusions were resulted from crust-mantle interaction with the crust as the major magmatic source and the separate crystallization,fluid metasomatism.The geological,elemental and isotopic evidences show that the Paleo-Asian Ocean maybe closed in Pre-Permian,and the Alxa was in-board evolution since Permian,the Wuliji area was under the transformation phase from regional syn-orogenic squeez

关 键 词：乌力吉岩体 石炭-二叠纪 壳幔混合 后碰撞 古亚洲洋 地球化学 

分 类 号：P597[天文地球—地球化学]