阿拉善地块北缘雅干花岗岩体地球化学、地质年代学及其对区域构造演化制约  

Geochronology and geochemistry of the Yagan granite in the northern margin of the Alxa block: Constraints on the tectonic evolution of the southern Altaids

作　　者：郑荣国[1] 吴泰然[1] 张文[1] 冯继承[1] 徐操[1] 孟庆鹏[1] 张昭昱[1] 

机构地区：[1]造山带和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

出　　处：《岩石学报》2013年第8期2665-2675,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41040017)资助

摘　　要：位于阿拉善北部中蒙边境地区的雅干花岗岩体以二长花岗岩为主,岩体的锆石离子探针U-Pb年龄为283.2±2.2Ma(n=14,MSWD=0.016)。该花岗岩体具有相对较低的SiO2含量(66.96%～70.71%),和较高的Al2O3(15.05%～16.05%)和(Na2O+K2O)含量(7.24%～9.19%),且岩体钠含量稍高(Na2O/K2O>1)。雅干花岗岩体总体上表现为高钾钙碱性及偏铝质-过铝质的特征。岩体稀土元素总含量为101.9×10-6～133.1×10-6,在稀土元素配分模式图中,岩体表现为轻-重稀土元素中等程度-强烈分异,同时具有明显的负Eu异常(δEu=0.59～0.77);在微量元素原始地幔标准化蛛网图中,岩体表现为亏损Nb、Ta、P、Ti,富集Ba、Rb、Cs、Th、K等大离子亲石元素;岩体同位素特征则表现为具有高的(87Sr/86Sr)i值(0.707654～0.710235)以及负εNd(t)值。根据雅干花岗岩体的形成时代、地球化学特征以及相关的沉积建造特征,可推断该岩体形成于后碰撞环境,表明古亚洲洋在阿拉善地块北缘北部地区的分支于早二叠世(283.2±2.2Ma)之前已经闭合。The Yagan granites,which are located in the northern margin of the Alxa block,mainly consist of mzonogranites. The zircon SIMS U-Pb age of the granites is 283. 2 ± 2. 2Ma （n = 14,MSWD = 0. 016）. The Yagan granites have relatively low SiO2 contents （66. 96% ～ 70. 71%） ,and high Al2O3 （15. 05% ～ 16. 05%） and Na2O ＋ K2O （7. 24% ～ 9. 19%） contents. They also exhibit high K calc-alkaine and metaluminous-peraluminous characteristics. Total rare earth element （REE） contents of the Yagan granites range from 101. 9 × 10-6 to 133. 1 × 10-6. They show enrichments of LREEs,and exhibit relatively moderate-strong negative Eu anomalies （δEu = 0. 59 ～ 0. 77） in the chondrite-normalized REE patterns. They display depletions of high field strength elemens （Nb,Ta,P,Ti） and enrichments of large ion lithophile elements （Ba,Rb,Cs,Th,K） in the primitive mantle-normalized trace element spiderdiagram. The granites also have high （87Sr/86Sr）i values（0. 707654 ～ 0. 710235） and negative εNd（t） values. Based on the geochemical characteristics and related sedimentary formations,it is concluded that the Yagan granites should be formed in the postcollisional setting. The age of the Yagan granites （283. 2 ± 2. 2Ma） implies that the branch of the Paleo-Asian Ocean in the northern Alxa region had been closed before the Early Permian.

关 键 词：阿拉善地块北缘 锆石SIMSU-Pb 后碰撞 

分 类 号：P618.51[天文地球—矿床学]