秦岭造山带商南—西峡地区富水杂岩的变辉长岩中斜锆石与锆石U-Pb同位素年龄的差异  

Difference in U-Pb isotope ages between baddeleyite and zircon in metagabbro from the Fushui complex in the Shangnan-Xixia area,Qinling orogen

作　　者：李惠民[1] 陈志宏[1] 相振群[1] 李怀坤[1] 陆松年[1] 周红英[1] 宋彪[2] 

机构地区：[1]中国地质调查局天津地质矿产研究所,天津300170 [2]中国地质科学院地质研究所北京离子探针中心,北京100037

出　　处：《地质通报》2006年第6期653-659,共7页Geological Bulletin of China

基　　金：国家自然科学基金重点项目(编号:40032010-C);国家自然科学基金面上项目(批准号:40373032)资助。

摘　　要：秦岭造山带富水杂岩体的一些变辉长岩含有粒度较大且U、Pb含量较高的斜锆石和锆石,是U-Pb同位素测年的极好矿物。对该杂岩体的中粗粒角闪黑云辉长岩中的斜锆石和锆石分别进行了SHRIMP法和TIMS法U-Pb同位素年龄测定,获得斜锆石和锆石的U-Pb同位素年龄分别为501.4Ma±1.2Ma和480.0Ma±3.4Ma,两者相差约20Ma。对该岩石中部分斜锆石向锆石转化的现象及锆石的成因进行了初步研究,认为斜锆石的U-Pb同位素年龄应解释为秦岭富水杂岩中基性岩石的形成时代,而锆石的成因及其U-Pb同位素系统在变质作用过程中的变化比较复杂,对其U-Pb同位素年龄地质意义的合理解释需做进一步的研究。There are relatively coarse-grained baddeleyite and zircon with higher U and Pb contents in metagabbro from the Fushui complex in the Qinling orogen. They are very good minerals for U-Pb isotope dating. Baddeleyite and zircon from mediumand coarse-grained hornblende-biotite gabbro yielded SHRIMP and TIMS U-Pb ages of 501.4±1.2 Ma and 480.0±3.4 Ma respectively. The age difference between the two minerals is about 20 Ma. The transformation of some baddeleyite to zircon in the rock and zircon genesis were studied. The study shows that the baddeleyite age of 501.4±1.2 Ma should be interpreted as the formation age of intermediate-basic rocks in the Fushui complex of the Qinling orogen. However, the genesis of zircon and the change of its U-Pb isotope system is relatively complex in the process of metamorphism, so the rational interpretation of the geological implication of its age （480.0±3.4 Ma） needs more studies.

关 键 词：秦岭造山带 富水杂岩体 斜锆石与锆石 U-PB同位素年龄 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]