藏北羌塘戈木错渐新世碱性钾质火山岩中绿核辉石的成因:岩浆补给—混合过程

Genesis of green-core clinopyroxenes in Gemucuo Oligocene alkaline potassic volcanic rocks from Qiangtang area,North Tibet:replenishing-mixing process of magma

藏北戈木错渐新世碱性钾质火山岩中单斜辉石斑晶普遍出现正环带、反环带和韵律环带结构,多具有"绿核辉石"的结构特征。通过矿物电子探针测得"绿核辉石"的核部有高Mg#和低Mg#两种不同成分,两者都不同程度发育有筛孔状熔蚀结构,环带结构主要发育在辉石的幔部到边部,与绿色核部存在明显的成分间断,幔部环带结构的成分变化范围相对较窄。"绿核辉石"的成分和结构特征反映了同源碱性钾质岩浆在壳内岩浆房中发生了岩浆补给-混合作用,复杂的环带结构记录了混合岩浆的结晶过程。

Normal, reverse and oscillatory zonings are commonly developed in clinopyroxene phenocrysts in Gemucuo Oligocene alkaline potassic volcanic rocks from Qiangtang area, North Tibet, and most of them have the characteristics of ＂green-core elinopyroxenes＂. The electron probe results show that the cores of ＂green-core eli- nopyroxenes＂ have high Mg# and low Mg# components, and both of which have sieve-like erosion structure. The zoning structure mainly developed on mantle and rim of pyroxene, which has a significant intermittent to the green core. The composition of mantle ranges relatively narrow. The composition and structural characteristics of these ＂green-core clinopyroxenes＂ reflect the homologous alkaline potassic magma experienced replenishing-mixing process in crustal magmatic chamber, and the complex zoning structure records the crystallization process of mixed magma.