钍石电子探针定年:记录小秦岭矿集区伟晶岩热液蚀变历史  

Thorite in pegmatite dated by electron microprobe reflecting hydrothermal alteration history in the Xiaoqinling gold district

作　　者：赵海香[1] 郑浩[1] Volker von SECKENDORFF ZHAO Haixiang;ZHENG Hao;Volker von SECKENDORFF(School of Earth Sciences and Engineering,Hohai University,Nanjing 21l100,China;Geod ynamics&Geomaterials Research Division,University of Wirzburg,Am Hubland,Wirzburg,D-97074,Germany)

机构地区：[1]河海大学地球科学与工程学院,江苏南京211100 [2]维尔茨堡大学地球动力学和地球物质研究中心,维尔茨堡,D一9704,德国

出　　处：《地质学报》2023年第8期2563-2574,共12页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41203011);中央高校业务费项目(编号2016B07814)联合资助的成果。

摘　　要：电子探针化学定年法(Chemical Th-U-total Pb Isochron Method,CHIME)以其原位、极高的空间分辨率、样品制备简单方便、不破坏样品、测试速度快、成本低等优点,被成功用于独居石、褐帘石、锆石、磷钇矿、晶质铀矿等副矿物定年,但应用于钍石定年仍不成熟。本文尝试利用电子探针对小秦岭矿集区元古宙伟晶岩脉中的钍石进行定年。显微镜下观察发现,热液钍石颗粒细小(<30μm),多与独居石共生,包裹在褐帘石中。我们对未发生蚀变或者蜕晶化的小颗粒钍石进行了电子探针Th-U-Pb化学法定年,得到的加权平均年龄为120.9±2.1 Ma(95%置信区间)。这一年龄与枪马金矿的矿化年龄一致,代表继该地区大规模花岗岩侵位活动之后,华北克拉通减薄过程中的又一次热液蚀变过程。Electron Microprobe Chemical dating(Chemical Th-U-total Pb Isochron Method,CHIME)has been successfully used on monazite,allanite,zircon,xenotime,uraninite and other accessory minerals.A rare study focused on thorite dating by Electron Microprobe.This paper attempts to use Electron Microprobe to date thorite in Proterozoic pegmatite dikes in the Xiaoqinling gold district,China.In this study we dated minute thorite grains(<30μm in size)by electron microprobe analysis.A geologically significant chemical Th-U-total Pb age mean value of 120.9±2.1 Ma(95%confidence interval)was determined.This age is in agreement with the mineralization age of the Qiangma gold deposit and reflects a hydrothermal overprint in the course of lithospheric thinning of the North China Craton,following widespread granite intrusion.

关 键 词：钍石定年 电子探针 小秦岭 华北克拉通 

分 类 号：P575.1[天文地球—矿物学] P597.3[天文地球—地质学]