班公湖—怒江俯冲增生杂岩带东段晚古生代辉绿岩锆石U-Pb年龄、Hf同位素特征及其构造意义  

Late-Paleoanthics diabase from the eastern part of the Bangong Lake-Nujiang subduction belt:U-Pb geochronology,Hf isotopic composition and geological characteristics

作　　者：任飞[1] 尹福光[1] 彭智敏[1] 潘桂棠[1] 魏栋 REN Fei;YIN Fuguang;PENG Zhimin;PAN Guitang;WEI Dong(Chengdu Center,China Geological Survey,Chengdu 610081,China;Sichuan Institute of Geological Engineering Investigation Group Co.,Ltd,Chengdu 610072,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]四川省地质工程勘察院集团有限公司,四川成都610072

出　　处：《地学前缘》2022年第2期164-179,共16页Earth Science Frontiers

基　　金：国家自然科学基金项目(92055314);中国地质调查局地质调查项目(DD20190375,DD20190053)。

摘　　要：嘉玉桥—同卡混杂岩带位于班公湖—怒江俯冲增生杂岩带东段嘉玉桥至邦达地区,1∶250000区域地质调查将其主体厘定为晚古生代混杂岩,但缺乏准确的同位素年代学与地球化学约束。本文选择该带邦达岩组中的辉绿岩作为研究对象,开展详细的岩相学、地球化学及年代学工作,揭示班公湖—怒江俯冲增生杂岩带的形成时间及构造环境。结果表明,辉绿岩明显具有N-MORB型的地球化学性质,同时富集大离子亲石元素(Rb,Ba),亏损高场强元素(Nb,Zr),其岩浆源区为尖晶石二辉橄榄岩经过约30%的部分熔融,一致指示岩浆源区可能源于受俯冲流体交代影响的亏损地幔源区。辉绿岩的锆石LA-ICP-MS U-Pb年龄为(330.9±1.6)Ma,代表了辉绿岩的结晶年龄,指示邦达辉绿岩形成于早石炭世,进一步揭示班公湖—怒江俯冲增生杂岩带存在古特提斯洋演化残留地质信息。邦达早石炭世N-MORB型辉绿岩的厘定,为进一步认识班公湖—怒江俯冲增生杂岩带早石炭世的构造环境,探讨班公湖—怒江特提斯洋的时空演化提供了重要依据。The Jiayuqiao Tongka mélanges are located within the eastern part of the Bangong Lake Nujiang subduction-accretion complex belt from Jiayuqiao to Bangda area whose spatial distribution,material composition,tectonic setting and genesis have been discussed to some extent by previous researchers but have not been studied in detail.For example,the formation era of the subduction-accretion complex has been determined to be the Late Paleozoic by geological survey(1∶250000)but lacked precise geochronological and geochemical constraints.In this contribution,the diabase of the Bangda Formation is investigated through detailed petrographic,geochemical and chronologic analyses to shed light on the development time and tectonic setting of the Bangong Lake Nujiang structural zone.The diabase was found to be enriched in LILEs(Rb,Ba)and depleted in high HFSEs(Nb,Zr)and exhibited the geochemical characteristics of N-MORB.Its LREE pattern indicated a depleted N-MORB mantle source,while geochemical analysis further suggested the diabase is sourced from 30%partial melting of spinel lherzolite formed in a back-arc rift basin.The LA-ICP-MS U-Pb dating of zircon from the diabase yielded an average zircon age of(330.9±1.6)Ma,which represents the crystallization age of diabase,indicating the Bangda diabase is formed in the Early Carboniferous epoch,and supporting the notion that the Bangong Lake Nujiang structural zone retains geological information of the residual Paleo-Tethys.The results of this study on the Early Carboniferous N-MORB diabase provided an important reference for the reconstruction of the regional tectonic setting as well as for future studies on the spatio-temporal evolution of the Paleo-Tethys in the Bangong Lake Nujiang region.

关 键 词：班公湖—怒江俯冲增生杂岩带 嘉玉桥—同卡增生杂岩带 U-PB年龄 N-MORB 大地构造 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]