南秦岭武当山十堰地区中生代镁铁质岩石成因与构造意义——岩石地球化学、锆石U-Pb年龄和Hf同位素制约  

Genesis and tectonic significance of Mesozoic mafic rocks in the Wudang Mountain—Shiyan Belt,South Qinling Orogen:Constraints from geochemistry and zircon U-Pb,Hf isotopes

作　　者：王嘉玮 王刚[2] 王宗起[2] 武昱东[2] 王东升[2] 王坤明[2] WANG Jiawei;WANG Gang;WANG Zongqi;WU Yudong;WANG Dongsheng;WANG Kunming(China University of Geosciences(Beijing),Beijing,100083;MLR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing,100037)

机构地区：[1]中国地质大学(北京),北京100083 [2]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037

出　　处：《地质论评》2021年第4期869-885,共17页Geological Review

基　　金：国家重点研发计划(编号:2016YFC0600202);中国地质科学院基本科研业务费项目(编号:YK1701)的成果。

摘　　要：南秦岭的北大巴山—武当山—十堰—随州一带发育大规模的镁铁质岩墙群,其岩石学成因为地质学家所广泛关注。本文对其中的武当山十堰地区黄龙—方滩一带发育的辉长岩体开展了全岩地球化学、SHRIMP锆石U-Pb年龄以及LA—MC—ICP—MS锆石Hf同位素组成研究。结果表明,辉长岩形成于晚三叠世(221.2±2.5 Ma);岩石地球化学组成显示辉长岩为亚碱性拉斑玄武岩系列,轻稀土富集重稀土亏损,其平滑右倾的稀土配分模式与E—MORB相似;中等Ti、Zr、Hf、Nb含量,亏损Rb、Sr等大离子亲石元素,以及结晶年龄锆石的ε_(Hf)(t)值在-13.5至6.18之间,表明岩石具有古老的两阶段Hf模式年龄(2103~1640 Ma)。综合分析表明:该套辉长岩岩浆为尖晶石二辉橄榄岩低压、中等程度部分熔融形成,并且其源区为亏损地幔与富集地幔组分混合成因;结合区域构造演化的相关资料,认为该套E—MORB性质辉长岩形成于类似汇聚边缘的构造环境,可能为受勉略洋壳俯冲影响,为俯冲—碰撞造山阶段产物。Large-scale mafic dikes are developed in Northern Daba Mountain—Wudang Mountain—Shiyan and Suizhou areas of the South Qinling Orogen.Their petrogenesis and tectonic evolution are widely of interst to geologists.In this paper,whole-rock geochemistry,SHRIMP zircon U-Pb age and the LA-MC-ICP-MS zircon Hf isotopic compositions are used to study the gabbro occurring in the Huanglong—Fangtan area of Wudang Mountain.The result indicates that these gabbros intruded during the Late Triassic(221.2±2.5 Ma);whole-rock geochemical data shows that the gabbros are sub-alkaline tholeiitic series with moderate concentrations of Ti,Zr,Hf and Nb,while exhibiting depletions of the large ion lithophile elements(LILE)such as Rb and Sr.The rare earth element(REE)distribution patterns display negative slopes with slight light rare earth element(LREE)enrichment and depletion of heavy rare earth elements(HREE),which are similar to that of enriched mid-ocean ridge basalt(E-MORB).Theε_(Hf)(t)value of magmatic zircons are between-13.5 and-6.18 with ancient twostage Hf model ages(2103~1640 Ma).In addition,the gabbros appear to have all originated from low-pressure and medium degree of partial melting of spinel lherzolite.The regional tectonic evolution combined with the new evidence for mantle enrichment,and the E-MORB affinities of the gabbros in this paper,suggests that these rocks formed in a convergent tectonic setting,affected by subduction of the Mianlue Ocean basin,and may thus be the product of the subduction—collisional stage.

关 键 词：岩石成因 中生代 辉长岩 武当山 南秦岭 

分 类 号：P597.3[天文地球—地球化学] P581[天文地球—地质学]