浙江雁荡山火山-侵入杂岩的岩浆混合作用——暗色包体中长石环带的证据  

Magma mixing in the Yandangshan volcanic-intrusive complex, Zhejiang Province: Evidence from feldspar zoning of the mafic microgranular enclave

作　　者：颜丽丽[1,2] 贺振宇[2] 刘磊[3] 赵志丹[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质科学院地质研究所/大陆构造与动力学国家重点实验室,北京100037 [3]南京大学地球科学与工程学院,江苏南京210023

出　　处：《地质通报》2015年第2期466-473,共8页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:41102028);中国地质科学院地质研究所基本科研业务费重点项目(编号:J1311)

摘　　要：浙江雁荡山是中国东南部燕山晚期巨型火山-侵入杂岩带的重要组成部分。对其中央侵入相石英正长斑岩的暗色微粒包体中的斑晶和基质斜长石进行了详细的内部结构和成分分析,揭示了斜长石复杂环带的成因和相关的岩浆作用过程。斑晶斜长石由熔蚀的核部和表面干净的幔部组成,边部包裹有钾长石膜。核部斜长石呈浑圆状或港湾状,内部发育筛状结构,An成分显著低于幔部斜长石,代表来自酸性岩浆房中早期结晶的斜长石捕掳晶。同时,幔部斜长石与自形、表面干净的基质斜长石具有类似的An含量,且两者均含有针状磷灰石的包裹体,应结晶自与暗色微粒包体相应的基性岩浆。长石的复杂结构记录了雁荡山火山-侵入杂岩形成过程中的岩浆混合作用和岩浆演化过程。岩浆混合之后的火山喷发活动,造成岩浆房的压力突然减小,温压条件达到钾长石结晶的区域,在石英正长斑岩的斑晶斜长石和暗色包体中的斑晶与基质斜长石外均形成钾长石膜,构成反环斑结构。The Yandangshan volcanic-intrusive complex in Zhejiang Province is an important component part of the immense Late Yanshanian volcanic-intrusive complex zone in southeastern China. In this study, the authors conducted a detailed investigation of the interior texture and complex zoning patterns of the phenocryst and groundmass plagioclase grains of the mafic microgranular en-clave in the central intrusive quartz porphyritic syenite, which is used to constrain the formation of the complexly zoned plagioclase and the corresponding magmatic processes. The plagioclase phenocryst consists of resorbed core, clear mantle and is rimed by K-feld-spar. The rounded or embayed core is characterized by sieve texture with An content generally lower than the content of the mantle, which represents plagioclase xenocrysts captured from the host felsic magma. The plagioclase mantle and plagioclase in the groundmass show similar An values and contain inclusions of acicular apatite, which should crystallize from the mafic magma related to the mafic microgranular enclave. The complex feldspar zoning recorded the magma mixing and evolution processes during the generation of the Yandangshan volcanic-intrusive complex. Subsequent to the magma mixing, the eruption induced abrupt decreasing of pressure of the magma chamber and, as a result, the crystallization path moved to the alkali feldspar＋liquid field. K-feldspar mantle formed along the phenocryst plagioclase of the quartz porphyritic syenite and the phenocryst and groundmass plagioclase of the mafic micro-granular enclave, yielding an anti-rapakivi texture.

关 键 词：雁荡山 火山-侵入杂岩 暗色微粒包体 斜长石环带 岩浆混合 

分 类 号：P588.14[天文地球—岩石学] P588.12[天文地球—地质学]