华北板块北缘古大洋闭合时间的限定--来自四子王旗西后壕子同碰撞花岗岩的证据  

Time constraints on the closure of the Paleo-Asian Ocean on the northern margin of North China Craton: Evidence from Xihouhaozisyn-collisional granites in Siziwang Qi area

作　　者：孟庆鹏[1] 贺元凯[1,2] 张文[1] 吴泰然[1] 郑荣国[1] 徐操[1] 张昭昱[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室/北京大学地球与空间科学学院,北京100871 [2]中国冶金地质总局矿产资源研究院.北京100025

出　　处：《地质通报》2013年第11期1749-1759,共11页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41040017)

摘　　要：位于华北板块北缘四子王旗北部的西后壕子花岗岩体的CamecaIMS-1280-SIMS锆石U—Pb年龄为266Ma±2Ma。该岩体主要由二长花岗岩组成，以出现大量颗粒较大的白云母为特征，具有较高的SiO2含量（75．21％-76．69％），A／CNK值多大于1．1，CIPW标准矿物中刚玉的含量也都高于1％。在球粒陨石标准化稀土元素配分图解上，Eu具有强烈的负异常（δEu=0．03～0．11），REE呈现出明显的M型四分组效应，部分微量元素也表现出non-CHARAC的性质。在原始地幔标准化微量元素配分图上，元素Ba、Nb、sr和Ti相对亏损，Cs、Rb、Th和Pb相对富集。在构造环境判别图解中，所有样品均落入同碰撞花岗岩区域。结合区域地质背景及以上特征，西后壕子岩体应为强过铝质的高分异S型花岗岩，形成于二叠纪晚期的陆一陆碰撞环境中。270-260Ma期间，四子王旗地区发育EW向的碰撞花岗岩带，限定华北板块与南蒙古微大陆沿索伦缝合带的闭合时间为二叠纪晚期。Xihouhaozi pluton is located in the north of Siziwang Qi area, northern North China Craton. Cameca IMS-1280- SIMS zircon U-Pb dating indicates that it was emplaced at 266Ma＋2Ma. Monzogranite, as the dominant composition, has abundant large-size muscovites. Geochemical analyses show that the pluton is characterized by high SiO2 （75.21%-76.69%）, A/CNK ratios （mostly〉l.1） and normative corundum abundances （mostly〉l%）. Furthermore, the Xihouhaozi granite displays strong negative Eu anomalies （~Eu=0.03-0.11）, striking Ba, Nb, Sr and Ti depletions, and slight Cs, Rb, Th and Pb enrichments. It presents a spec- tacular M-type tetrad effect in the P,.EE distribution patterns as well as non-CHAIkAC （charge-and-radius-controlled） trace element behavior. Tectonic discrimination diagram shows that the pluton might have been formed in a syn-collisional tectonic setting. In combination with regional geology, the authors hold that the Xihonhaozi granite belongs to highly fractionated peraluminous S-type granite and was generated during the continent-continent collision in the late Permian period. During 270-260Ma, a synconllisional granitic belt was formed in Siziwangqi area, which constrained the closure of the Solonker suture of the North China Craton with southern Mongolia in the late Pemaian period.

关 键 词：S型花岗岩 二叠纪晚期 碰撞花岗岩带 四子王旗 华北板块北缘 SIMS锆石U—Pb 

分 类 号：P541[天文地球—构造地质学] P597.3[天文地球—地质学]