义敦岛弧措交玛岩体岩浆混合成因:镁铁质微粒包体的证据

发布时间：2019-04-30 17:16

【摘要】：义敦岛弧北部的措交玛岩基岩体主要由黑云母二长花岗岩和边部的花岗闪长岩组成。在黑云母二长花岗岩中存在有少量镁铁质微粒包体,其成分为闪长质,与寄主岩石接触关系从渐变到截然。在包体周围的寄主岩石中存在黑云母、角闪石自身的包含结构,角闪石包含黑云母,斜长石发育明显的溶蚀结构,核部斜长石被溶蚀成筛状,边部环带状斜长石溶蚀不明显,是基性岩浆注入到酸性岩浆中导致岩浆混合的结果。黑云母二长花岗岩具有更高的轻重稀土分异系数,闪长质包体轻重稀土分异系数较低,黑云母二长花岗岩和暗色闪长质微粒包体具有明显相似性的微量元素特征。寄主岩黑云母二长花岗岩锆石U-Pb年龄为236±1.9Ma,闪长质包体为235±3.9Ma,二者形成年代在误差范围内基本一致,可能为甘孜-理塘洋向西俯冲过程中,俯冲洋壳部分熔融形成的玄武质岩浆上涌底侵于壳-幔边界导致地壳的部分熔融形成酸性的黑云母二长花岗岩岩基。
[Abstract]:The Zaojiao mafic basement rock body in the northern part of Yiden island arc is mainly composed of biotite monzogranite and granodiorite on the edge. There are a few mafic microinclusions in biotite monzonitic granites, the composition of which is diorite, and the contact relationship with host rocks changes from gradual to complete. Biotite exists in host rocks around xenoliths, amphibole itself contains biotite, amphibole contains biotite, plagioclase develops obvious dissolution structure, core plagioclase is dissolved into sieve, and the edge ring-banded plagioclase is not obvious. It is the result of basic magma being injected into acid magma and resulting in magmatic mixing. Biotite monzonitic granites have higher LREE differentiation coefficient and lower LREE differentiation coefficient in diorite enclaves. Biotite monzonitic granite and dark diorite particulate xenoliths have obvious similarity of trace elements. The zircon U-Pb age of host biotite monzonitic granite is 2336 卤1.9 Ma, and the diorite inclusion is 235 卤3.9 Ma. The ages of their formation are basically the same within the error range, which may be during the westward subduction of the Ganzi-Litang Ocean. The upwelling of basaltic magma formed by partial melting of subducted oceanic crust invaded the crust-mantle boundary and resulted in the formation of acidic biotite monzonitic granite base during partial melting of the crust.
【作者单位】：中国地质大学地球科学与资源学院;中国地质调查局国土资源实物资料中心;云南省地质调查院;秦皇岛矿产水文工程地质大队;
【基金】：国家重点基础研究发展计划“973”项目(2015CB452604) 中国地质调查局研究项目(1212011220920)联合资助
【分类号】：P588.1

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