北秦岭松树沟榴辉岩的确定及其地质意义  

Identification and its geological significance of eclogite in Songshugou,the North Qinling

作　　者：陈丹玲[1] 任云飞[1] 宫相宽[1] 刘良[1] 高胜[1] 

机构地区：[1]西北大学大陆动力学国家重点实验室、西北大学地质学系,西安710069

出　　处：《岩石学报》2015年第7期1841-1854,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41090374;41472053;41430209);国家“973”计划项目(2015CB856103);长江学者和创新团队发展计划项目(IRT1281)联合资助

摘　　要：松树沟石榴石角闪岩(榴闪岩)呈透镜状产于松树沟超镁铁岩旁侧的斜长角闪岩中,一直以来被认为是形成于接触交代变质或麻粒岩相变质过程。详细岩相学及矿物元素分析,在榴闪岩的基质矿物、石榴石幔部及锆石包体中发现残留的绿辉石,而且石榴石也保存了明显的进变质主、微量元素成分环带,表明松树沟榴闪岩为榴辉岩退变质的产物,至少经历了从角闪岩相到榴辉岩相再到角闪岩相的三阶段顺时针PT演化过程。锆石定年结果得到榴辉岩的变质年龄为500±8Ma,原岩结晶时代为796±16Ma,与秦岭岩群北侧官坡超高压榴辉岩的变质年龄和原岩年龄完全一致,也与北秦岭区域高压-超高压变质时代和原岩的结晶时代一致。表明松树沟榴辉岩与北秦岭造山带已发现的高压-超高压变质岩石一起都应是古生代大陆深俯冲作用的结果,而松树沟超镁铁岩可能是俯冲的大陆板片在折返过程中携带的俯冲隧道中的交代地幔岩。The Songshugou garnet amphibolite occurs as lenses in amphibolite which is situated structurally next to the Songshugou ultramafic rock, and was considered to be formed by contact metamorphism or granulite-facies metamorphism so far. Detailed petrographic investigation and mineral elements analyses discovered relic omphaeites both in garnet and zircon and in the matrix, and garnets in this rock preserved prograde metamorphic zonation both in major and trace elements, indicating that the garnet amphibolite is a retrograde eclogite and experienced at least a three stages clockwise metamorphism evolution from amphibolite facies to eclogite facies and then back to amphibolite facies. Zircon U-Pb dating obtained metamorphic age of 500 ~ 8Ma and protolith age of 796 ~ 16Ma for the eclogite. These are consistent with the metamorphic and protolitb ages of Guanpo UHP eclogite which lies at the north margin of the Qinling Group as well as other HP-UHP rocks spread widely in the Qinling Group. It suggests that the Songshugou eclogite together with existing HP-UHP rocks in the Qinling Group all were formed by continental deep subduction in Early Paleozoie, and the Songshugou ultramafic rock may be the metasomatic mantle rock in the subduction channel and was carried to the shallow crust by the subducted continental slab during exhumation.

关 键 词：榴辉岩 变质作用 锆石U-PB年龄 松树沟 北秦岭 

分 类 号：P588.348[天文地球—岩石学] P597.3[天文地球—地质学]