新疆西准噶尔夏尔莆岩体岩浆混合的岩相学证据

夏尔莆岩体由寄主岩石、微粒镁铁质包体和中基性岩墙群组成,具丰富、典型的岩浆混合岩相学特征.野外露头,寄主岩石中暗色矿物分布不均并发育暗色矿物集合体、微小的镁铁质包体和不均匀混合条带;包体具有明显的塑性变形,与寄主岩石或界线截然或渐变过渡,常发育反向脉和寄主岩石中的长石巨晶(捕虏晶);中基性岩墙群与微粒镁铁质包体紧密共生并延伸方向基本一致,发育寄主岩石中的长石捕虏晶,被寄主岩的反向脉横切.在镜下,包体与寄主岩混合带中均发育斜长石异常环带和多种不平衡矿物共生现象,包体中发育针状磷灰石.这些特征表明镁铁质包体和中基性岩墙群来源于与寄主岩石同一岩浆事件的基性岩浆,并与其发生了强烈的岩浆混合作用.岩相学特征为夏尔莆岩体岩浆混合成因提供了重要佐证.

Petrographic evidence for magma mixing of Xiaerpu granite in West Junggar, Xin jiang

Xiaerpu granite is composed of host rock, mafic microgranular enclaves and intermediate-basic dyke swarms, with the development of abundant and typical petrographical evidence of magma mixing. In field outcrops, dark minerals are distributed asymmetrically, and dark mineral aggregates, mafic microgranular enclaves, bands of nonuniform mixing are well developed. Mafic microgranular enclaves show characteristics of strong plastic distortion and clear boundary or transitional relationships with host rocks, with well developed reversed veins and captured feldspar phenocrysts (captured crystals). Basic dyke swarms and mafic microgranular enclaves occur closely and are distributed in the same direction, and basic dyke swarms contain the captured feldspar phenocrysts of the host rock, also traversed by the reversed veins of the host rock. Under the microscope, abnormal zoning of plagioclase and many types of disequilibrium mineral associations are developed in enclaves and bands of nonuniform mixing, with the acicular apatite developed in enclaves. These phenomena suggest that mafic microgranular enclaves and basic dyke swarms might have originated from basic magma formed at the same time as the host rock, and they probably experienced strong magma mixing. Petrographic features pro-vide important evidence for magma mixing of Xiaerpu granite.