辽西医巫闾山地区晚侏罗世花岗岩脉中热液锆石的成因与定年  

Genesis and geochronology of hydrothermal zircons from Late Jurassic granitic dikes in Yiwulvshan area,western Liaoning

作　　者：张必龙[1] 朱光[1] 谢成龙[1] 陈印[1] 鞠林雪[1] 王浩乾[1] 

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《地质科学》2011年第2期483-509,共27页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目(编号:90714004);国家自然科学基金青年科学基金项目(编号:40902064)资助

摘　　要：辽西医巫闾山变质核杂岩经历过两阶段演化,晚侏罗世发育了围绕核部医巫闾山岩体周缘展布的长环形韧性剪切带(称为医巫闾山剪切带),早白垩世西侧叠加了北北东走向瓦子峪伸展韧性剪切带。在医巫闾山剪切带及其变形下盘中侵入了大量的晚侏罗世花岗岩脉,其所含的锆石包括古老继承锆石、新生岩浆锆石、热液锆石等多种类型。根据锆石阴极发光图像、稀土元素配分曲线以及U、Th、Pb含量等特征,判别出热液锆石存在3种成因类型,包括流体的溶解—再沉淀、富Zr热液的直接结晶及流体的交代改造。它们共同具有高U、P、Y、Nb、Hf、Ta含量与低Th/U比值特征,前两种热液锆石还强烈富集稀土元素,其球粒陨石标准化配分曲线平坦。而第3类热液锆石具有亏损LREE、强烈富集HREE的特征,其配分曲线高度倾斜,不但有别于岩浆锆石与前两类热液锆石,也与前人对此类锆石的认识不一致。分析结果显示,高普通铅含量的热液锆石无法获得合理年龄,而大多数极低普通铅含量热液锆石则给出147 Ma左右的可靠年龄,略晚于岩脉的侵位时间(155～147 Ma),有效地记录了区内晚侏罗世构造—岩浆事件的阶段。The Yiwulvshan metamorphic core complex in western Liaoning has experienced two stages of extensional evolution from late Jurassic an annular ductile shear zone （called Yiwulvshan shear zone） developed around the central Yiwulvshan pluton to early Cretaceous overprinted by thewell-known NNE-striking Waziyu ductile shear zone in the west. A large amount of late Jurassic granitic dikes, containing several types of zircons including old inherited zircons, new magmatic zircons and hydrothermal zircons, intruded in the Yiwulvshan shear zone and its deformed footwall. According to the characteristics of cathodoluminescence image, REE pattern and U,Th, Pb content, these hydrothermal zircons could be divided into three genetic types： dissolution-reprecipitation, direct crystallization by a zircon-saturated aqueous fluid and metasomatic alteration in hydrothermal fluid. They are all highly enriched in U, Pb, P, Y, Nb, Hf, Ta and other elements except for Th element, which leads to the Th/U ratios about 0.1. The former two types of hydrothermal zircons are also strongly rich in rare earth elements （REE） with flatchondrite-normalized REE pattens. But the third type has lower LREE and higher abundances of HREE with a steeper chondrite-normalized REE patten, significantly different from magmatic zircon and the former hydrothermal zircons, also disagreed with others＇ points. The analyses show that reasonable ages are unable to obtain from hydrothermal zircons with high common Pb content,but most of lower common Pb of hydrothermal zircons give a reliable age about 147 Ma, tightly following the emplacement of dikes （ 155 - 147 Ma） and effectively recording the late stage of late Jurassic tectonic-magmatic events.

关 键 词：热液锆石 阴极发光 稀土元素 晚侏罗世 医巫闾山地区 

分 类 号：P597[天文地球—地球化学] P588[天文地球—地质学]