河南省西峡县桑坪红柱石巨晶的显微结构特征及成因探讨

MICROSTRUCTURE AND GENESIS OF ANDALUSITE MEGA-CRYSTALS FROM SANGPING TOWN, XIXIA COUNTY, HENAN PROVINCE

采用电子背散射衍射(EBSD)、扫描电镜—能谱、电子探针和显微激光拉曼光谱等手段,对河南西峡桑坪矿床的红柱石巨晶的显微结构、成分及包裹体特征进行了分析,探讨了红柱石巨晶和黑十字包裹体的变质温度、物质来源和成因。红柱石巨晶有两个世代:第一世代位于巨晶的核部,粒度细小且较纯净;第二世代位于巨晶边部,粒度较大。第二世代红柱石内部发育沿[100]_(And)和[010]_(And)方向延伸的黑色十字状包裹体,形态同时还受到红柱石晶体对称性的控制。其平均矿物组成为:石英(71.5%),黑云母(21.4%),碱性长石(3.1%),钛铁矿(1.2%),石墨(0.8%),石榴子石(2.1%),是红柱石快速生长过程中从围岩捕获的组分结晶形成。桑坪红柱石属角闪岩相区域变质和后期普通角闪石角岩相热接触变质作用叠加的产物,其热接触变质的热峰期变质温度为575~646℃,对应的压力上限为255~204 MPa。

By means of electron backscattering diffraction(EBSD), SEM, EPMA and laser micro-raman spectroscopy, the microstructures, compositions and inclusions of andalusite mega-crystals from the Sangping deposit in Xixia County, Henan Province are analyzed and the metamorphic temperatures, material sources and genesis of andalusite mega-crystals and black cross inclusions are discussed. The results show that the andalusite mega-crystal has two generations: the first generation is in the core of the mega-crystal, and the particle size is small and pure;The second generation is located at the edge of the mega-crystal with a larger grain size. In the second generation andalusite, black cross-shaped inclusions extending along the directions of [100]_(And)& [010]_(And) are also controlled by the symmetry of andalusite crystals. Its average mineral composition is: quartz(71.5%), biotite(21.4%), potassium feldspar(3.1%), ilmenite(1.2%), graphite(0.8%), and garnet(2.1%), which are the crystallization of the components captured from the surrounding rock during the rapid growth of andalusite. Sangping andalusite is the superposition product of regional amphibolite facies metamorphism and later thermal contact metamorphism of hornblende hornfels facies. The thermal peak of thermal contact metamorphism is 575-646 ℃, and the corresponding upper limit of pressure is 255-204 MPa.