浙江江山上墅组玄武粗安岩中单斜辉石环带特征及指示意义  

Characteristics and significance of the zoned clinopyroxene in basaltic trachyandesite from the Shangshu Formation,Jiangshan,Zhejiang Province

作　　者：刘清 郭国林[1] 张胜了 巫建华[1,2] 严兆彬[1,2] 陶继华[2] 王凯兴 Liu Qing;Guo Guolin;Zhang Shengliao;Wu Jianhua;Yan Zhaobin;Tao Jihua;Wang Kaixing(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang,Jiangxi 330013,China;School of Earth Sciences,East China University of Technology,Nanchang,Jiangxi 330013,China;Geological Environment Monitoring Institute of Jiangxi Geological Survey and Exploration Institute,Nanchang,Jiangxi 330006,China)

机构地区：[1]东华理工大学核资源与环境国家重点实验室,江西南昌330013 [2]东华理工大学地球科学学院,江西南昌330013 [3]江西省地质调查勘查院地质环境监测所,江西南昌330006

出　　处：《地质学报》2023年第5期1447-1462,共16页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42262009,41762005);核资源与环境国家重点实验室开放基金(编号2020Z04);研究生创新专项资金项目(编号DHYC-202216)联合资助的成果。

摘　　要：岩浆化学混合作用长期通过岩石地球化学进行识别,一直缺乏直接的矿物学证据。针对这一问题,我们对浙江江山碗瑶乡上墅组内薄层状玄武粗安岩夹层中的单斜辉石矿物环带开展了系统的矿物学研究工作,探讨其岩石成因、构造背景和岩浆动力学过程,为江山地区新元古代岩浆构造演化过程提供新的证据。研究表明,单斜辉石以斑晶和基质两种形式产出,斑晶发育核-幔-边结构,其中幔部和边部包含有较多的钛铁矿、单斜辉石和斜长石等矿物包裹体,表明经历了复杂的岩浆活动过程。电子探针分析表明,基质和斑晶辉石都属于普通辉石,斑晶辉石从核部、幔部到边部成分呈现规律性变化,CaO和MgO含量增加、Al_(2)O_(3)和Na_(2)O、K_(2)O含量逐渐降低,但是基质辉石具有相对较低的Ti、Al和Na含量,且与斑晶边缘成分类似。单斜辉石原位微量元素组成表明,斑晶单斜辉石从核部到边部具有相似的特征,呈现Th、La、Nd和Ta等元素相对富集,Nb、K、Ti和Pb等元素相对亏损的特点。温压计算结果显示斑晶和基质的形成温度较低(1040.3~1122.3℃),斑晶核部结晶深度较深(10~12 km),而富含矿物包体的幔部和边部结晶深度较浅(3~6 km),并且幔部具有最低的稀土总量(∑REE=44.33×10^(-6)~63.66×10^(-6))以及无明显Eu(Eu/Eu^(*)=0.98~1.12)负异常。上墅组玄武粗安岩中单斜辉石的成分特征和核-幔-边结构指示岩浆混合作用的存在,可能系由偏基性和偏酸性的岩浆在中—上地壳深度发生混合的结果,江山玄武粗安岩的形成可能与新元古代晚期华夏与扬子两大陆块碰撞拼贴完成后古岛弧内部的伸展有关。Magma mixing has been recognized by bulk geochemistry for a long time,but without direct mineralogical evidence presented.In this regard,we have carried out a systematic mineralogical study on the clinopyroxene(Cpx)both occur as phenocryst and matrix in the thin-bedded basaltic trachyandesite interlayers in the Shangshu Formation at Wanyao Township,Jiangshan city in Zhejiang Province,in order to reveal its petrogenesis,tectonic setting and magmatic dynamic processes,and provide new evidence for the evolution of Proterozoic magmatic structure in the Jiangshan area.The clinopyroxene phenocrysts develop a core-mantle-rim texture,and the mantle and rim contain many mineral inclusions such as ilmenite,clinopyroxene and plagioclase,indicating that it has experienced complex process of magmatic evolution.Both the phenocryst and matrix the clinopyroxene are augite,the composition of phenocryst,from core through mantle to rim,show regular changes,i.e.,the contents of CaO and MgO increased,and the contents of Al_(2)O_(3),Na_(2)O,and K_(2)O gradually decreased,but the matrix Cpx has lower Ti,Al and Na content and similar to the edge composition of the phenocryst.In-situtrace element composition of the zoned phenocrystal show similar characteristics from core through mantle to rim,showing the enrichment in Th,La,Nd and Ta and the depletion of Nb,K,Ti and Pb.Calculated temperature and pressure results show that the formation temperature of phenocrysts and matrix is relatively low(1040.3~1122.3℃),but the crystallization depth of phenocrysts is deep(10~12 km),while the crystallization depth of mantle and edge rich in mineral inclusions is shallow(3~6 km),and the mantle has the lowest∑REE contents(44.33×10^(-6)~63.66×10^(-6))and without a negative Eu anomaly(Eu/Eu^(*)=0.98~1.12).The composition and core-mantle-rim texture of clinopyroxene phenocrysts in the Shangshu Formation indicate the existence of magma mixing,which maybe the result of the mixing of basic and acidic magmas at the depth of middle-upper crust.The formati

关 键 词：单斜辉石 环带结构 构造意义 上墅组 江山 

分 类 号：P588.1[天文地球—岩石学] P57[天文地球—地质学]