北秦岭武关地区丹凤群斜长角闪岩地球化学特征、锆石SHRIMP测年及其构造意义  

Geochemistry and SHRIMP Zircon U-Pb Dating of Amphibolites from the Danfeng Group in the Wuguan Area,North Qinling Terrane and their Tectonic Significance

作　　者：闫臻[1] 王宗起[2] 陈隽璐[3] 闫全人[1] 王涛[1] 张英利[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院矿产资源研究所,北京100037 [3]西安地质矿产研究所,西安710054

出　　处：《地质学报》2009年第11期1633-1646,共14页Acta Geologica Sinica

基　　金："十一五"国家科技支撑计划项目(编号2006BAB01A11);国家自然科学基金项目(编号40772137);中国地质调查局地质调查项目(编号1212010611807;1212010711816)资助的成果

摘　　要：本文运用岩石学、地球化学和同位素年代学对分布于丹凤县武关地区的丹凤群斜长角闪岩进行了相对系统研究,岩石学和地球化学特征表明该套岩石为岛弧钙碱性玄武岩,不具备蛇绿岩单元组成特性。锆石SHRIMP测年结果表明,该套岩石中包含有古元古代～晚泥盆世(2489～360Ma)多个时期的锆石;锆石CL图像以及锆石形状研究以及区域同位素年代学、古生物化石资料共同显示,丹凤群中可能包含有泥盆纪岩石组合。分析前人对丹凤群的区域研究资料,我们认为丹凤群并非一套具有单一地层时代以及相同构造环境的岩石地层单位,而是一套由不同时代不同构造环境的岩石组合构成的俯冲-增生杂岩。区域上,丹凤群与其南侧的武关岩群、罗汉寺岩群以及部分刘岭群共同构成华北板块南缘俯冲-增生体系,其中分布有大量与俯冲作用相关的泥盆纪钙碱性侵入体,这些事实进一步证明华北板块南缘洋盆消亡时间上限至少可以持续到晚泥盆世末期。The petrology, geochemistry and isotopic dating of amphibolites from the Danfeng Group in the Wuguan area, Danfeng County, are systemically studied in this paper. Petrology and geochemical analysis demonstrate that these amphibolites are characterized with island-arc calc-alkaline basalts and do not belong to ophiolite. Zircon SHRIMP dating suggests that the amphibolite sample contains Paleo- Proterozoic to Late Devonian （2489~360Ma） zircons. CL images and morphology of zircons, along with regional geochronology and fossils data together suggest that the Danfeng Group probably contains Devonian rock assemblage. Thus, we suggest that the Danfeng Group consists of different geochronology and tectonic environments of rock assemblages, showing characters of subduction-accretion complex. Regionally, Wuguan, Luohansi and some Liuling Groups are exposed in the south of the Danfeng Group, consisting of a subduction-accretion system in the southern margin of the North China plate; abundant Devonian subduetion-related calc-alkaline plutons crop out within this accretionary system. These facts suggest that the ended time of ocean basin along the southern margin of the North China plate should last to the late Devonian at least.

关 键 词：斜长角闪岩 岛弧 俯冲-增生杂岩 丹凤群 北秦岭 

分 类 号：P597.3[天文地球—地球化学] P588.125[天文地球—地质学]