浙江普陀花岗杂岩体中的石英闪长质包体:斜长石内部复杂环带研究与岩浆混合史记录

Complex zoning texture in plagioclases from the quartz diorite enclave in the Putuo granitic complex, Zhejiang province: record of magma mixing.

浙江普陀花岗杂岩体包含若干石英闪长质包体,该类包体中存在三种不同类型的斜长石:正常环带的斜长石、筛孔构造的斜长石和酸性斜长石为核的“反环带”斜长石。根据斜长石的环带构造特征和成分分析,认为本区的岩浆演化过程大致如下:下部基性岩浆注入到上覆酸性岩浆中并进行混合作用,酸性岩浆中已结晶的富钠质斜长石晶体进入偏基性的混合岩浆中,部分熔融形成筛孔构造;随着端员岩浆的进一步混合,富钠质斜长石晶体与中性混合熔体仅形成粗糙的边界,而保留原先构造特征;同时混合岩浆可以直接结晶出正常环带斜长石,呈单颗粒或以膜的形式包围其它环带构造的长石。本文还通过与平潭甬闪辉长岩杂岩体内筛孔斜长石的对比,认为斜长石的环带构造和成分可以反映岩浆源区特征和岩浆演化历史。

Three types of plagioclases with distinct zoning texture have been recognized from the recent investigation of the quartz-diorite enclave at Putuo, Zhejiang Province; normally zoned plagioclase, sieve-textured plagioclase and 'reverse-zoned' plagioclase. Based on the evidences from the components and textures of the plagioclase, the following scenario about the magma evolution is tentatively suggested. The initial basic magma in the deeper chamber injected into the host acid magma,in which the crystallization of oligoclase had already started. Then the sieve texture was formed after the plagioclases were incorporated into the mafic magma. In the later stage of the mixing process, the rough-interface was produced between acid plagioclase and melt. In addition, a normal zone was directly formed from the equilibrium mixing magma as a single crystal or the mantle. By comparing with the special sieved plagioclases in Pingtan complex, we suggest that the textures and chemical compositions of plagioclases record the features of magma sources and reflect the history of the magma evolution.