【摘要】 冲绳海槽海底玄武岩中存在着三种不同世代的斜长石 :斑晶、微晶和基质斜长石 ,它们的平均粒径分别为 10 0 μm±、13μm±和 2μm±。斑晶斜长石在结构上存在核部与边部之分 ,在成分上反映为 An值出现明显的两级“台阶”,即 An值在80～ 90间波动的核部“平台”和 An值在 60～ 70间波动的边部“平台”,边部“平台”的成分与微晶斜长石一致。斜长石的结晶温度显示 ,斑晶核部温度为 12 50℃± ,边部温度为 10 50℃± ,而基质斜长石的结晶温度在 950℃±。笔者认为斜长石的这些特征 ,基本反映了该玄武岩浆的活动过程 :斑晶斜长石的核部记录了源区特征 ,边部及微晶斜长石反映了岩浆房中活动的特征 ,基质斜长石则记录了岩浆喷出洋壳后的过程。更多还原

【Abstract】 There are three different generations of plagiclases in the basalt of Okinawa Tr ough: phenocryst, microphenocryst and groundmass plagioclase. The average size o f phenocryst is 100 μm ±, microphenocryst 13 μm± and with groundmass plagioc lase 2μm±. Electron microprobe analysis shows that there are distinctive compo sitional differences between core and edges of the phenocryst, that is, a higher platform in the core and a lower platform in the edges. The An values of the hi gher platform in cores vary from 80 to 90, and for the lower platform in edges t he An values are between 60 and 70, which well agree with the chemical compositi on of microphenocryst. Based on the plagioclase geothermometer, the temperatures of phenocryst core and edge were found to be about 1250℃ and 1050℃, respectiv ely. The temperature of groundmass plagioclase is just about 950℃. We thus cons ider that these characteristic features of plagioclases record the dynamic proce ss of the basaltic magma: the core of phenocryst reflecting the features of magm a source, while the edges of phenocryst and microphenocryst indicating the featu res of the magma chamber, and the groundmass plagioclase recording the eruption process.更多还原