冀西北后沟金矿田脆韧性剪切带年代学新证据:来自LA-ICP-MS锆石U-Pb年龄的发现  

LA-ICP-MS Zircon U-Pb Age of the Brittle-Ductile Shear Zones in Hougou Gold Orefield, Northwestern Hebei Province

作　　者：李长民[1,2] 李拓[3] 邓晋福[1] 苏尚国[1] 刘新秒[4] 

机构地区：[1]地质过程与矿产资源国家重点实验室,中国地质大学(北京)地球科学与资源学院,北京100083 [2]中国地质大学长城学院,河北保定071000 [3]天津大学化工学院,天津300072 [4]天津地质矿产研究所,天津300170

出　　处：《大地构造与成矿学》2012年第2期157-167,共11页Geotectonica et Metallogenia

基　　金：973项目(2006CB403508);国土资源部计划项目(1212010711814);国家自然科学基金重点项目(40234048)联合资助

摘　　要：通过系统的地质学研究,作者在后沟金矿田发现了近NE向的脆韧性剪切带,并对采自石垛口村北糜棱岩化石英正长岩样品中的锆石进行了成因矿物学研究,结果发现了两组锆石。一组为具有振荡环带的岩浆锆石,其LA-ICP-MS锆石U-Pb加权平均年龄为(383.4±2.8)Ma;另一组为在CL图像上无阴极发光充填在岩浆锆石边缘和粒间的不规则状的热液锆石,其LA-ICP-MS锆石U-Pb加权平均年龄为(154.4±1.3)Ma。通过对研究区具体情况的综合分析,作者认为前者代表水泉沟岩体东段的侵位年龄,后者代表区内脆韧性剪切带的形成年龄。考虑到东坪金矿田140Ma的成矿年龄与后沟金矿田154Ma的脆韧性剪切带的形成年龄相近,作者认为东坪和后沟金矿田可能存在多阶段构造-岩浆活动和热液流体成矿事件,但主要的成矿作用发生在燕山期,并且大多数金矿与燕山期的中酸性小岩体有关。Synthetic study shows that there are near NE brittle-ductile shear zones in the Hougou gold deposit. In order to study its forming age, the authors made a mineralogical and U-Pb geoehronologic study on the zircons from the mylonitized quartz syenite located to the north of the Shiduokou village in the shear zones. Two types of zircons, magmatic and hydrothermal origin are recognized. The magmatie zircons are characterized by euhedral-subhedral with clear magmatic oscillatory zones on cathodeluminescence （CL） images. Their U-Pb results gave a weighted mean ^206ph/^238U age of （383.4 ±2.8） Ma. The hydrothermal zircons are mainly irregular form and fill in the rim or interior of the magmatic zircons, dark-gray （non-luminescent） on the CL images. Their LA-ICP-MS zircon U-Pb age is （154.4±1.3） Ma, which indicates a Late Jurassic tectonic event. Combining with the geological facts, the authors suggest that the former age indicates intrusive time of the eastern part of the Shuiquangou alkaline complex, and the latter implies the age of the NE direction brittle-ductile shear zones. Considering the time gap of the ore forming age （ 140 Ma） of the Dongping gold deposit and the brittle-ductile shear zones age （ 154 Ma） , the authors propose that there are multistage structural-magmatic activities and hudrothermal ore-forming events in the Dongping and Hougou deposit fields, and the main mineralization stage of Au deposits is the Yanshanian peroid. Aand the gold deposits formation is mostly related to the magmatic activities of the intermediates acid small rock bodies in the Yanshanian period.

关 键 词：脆韧性剪切带 锆石U-PB定年 热液锆石 后沟金矿田 冀西北 

分 类 号：P597[天文地球—地球化学] P54[天文地球—地质学]