Petrography characteristics of the orbicular dioritic rocks in Luanping,Hebei province and the discussion of the genesis of orbicular structure

文章对滦平球状闪长岩作了详细的岩相学研究,并据此提出岩体中球状构造的形成机理.根据球核的不同,可将球分为三种类型,包括以同源岩浆组分为核的球、以异源捕虏体为核的球和没有明显壳层结构的球.球中壳层一方面表现为基本不含角闪石的浅色层和含有一定角闪石的暗色层交替发育的矿物组成韵律,另一方面表现为斑状半自形-它形斜长石梳状层与细粒半自形-自形斜长石层互层的矿物结构韵律.球中斑状斜长石显示清晰的格子双晶,而主岩和基质中的斜长石则为聚片双晶.研究表明,所描述的球状构造是通过岩浆同化捕虏体和岩浆结晶综合作用形成的.球壳的矿物组成韵律和矿物结构韵律受岩浆中水含量变化的控制.The Luanping dioritic pluton is special with an orbicular structure. According to the differences of the cores, the orbs in the pluton can be devided to three types: the orbs with comagmatic composition core, the orbs with enclaves core and the orbs without clear shells. On one side, the shells display mineral constitute rhythm which bleached layers almost without any hornblende and dark layers with some hornblende developed alternately. On the other side, the shells display mineral texture rhythm which porphyritic subhedral-anhedral plagioclase combing layers alternately developed with fine grained subhedral-eudral plagioclase layers. The porphyritic plagioclase in the orbs have clear grid twin, while the plagioclase in the host rocks and the matrix have multiple twin. The orbicular structure described in the article was formed by assimilation of enclaves and magma crystallization around the enclaves, the mineral constitute rhythm and the mineral texture rhythm of the shells probably controlled by the variation of water content in the magma.国家自然科学基金SCI(E)中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)061424-14322