摘要
冲绳海槽海底玄武岩中存在着三种不同世代的单斜辉石 ,即斑晶、微晶和基质辉石 ,它们的平均粒径分别约为 4 0 0 μm、30 μm和 5 μm。斑晶辉石在电子探针下可见到明显的核部与边部之分 ;微晶辉石无明显的环带构造 ;基质辉石粒径细小但数量较大。这三个世代的辉石在成分上差异较为明显 ,从斑晶辉石的核部→边部和微晶辉石→基质辉石 ,成分从富铁向富镁、钙方向演化 ,这与封闭体系的辉石成分演化趋势正好相反。辉石的形态和成分特征反映出该玄武岩浆存在岩浆混合的特征。它们也可反演该地幔岩浆的活动过程 :源自上地幔的拉斑玄武岩浆 ,在从源区向浅部岩浆房上升、运移过程中 ,受到携带相对富铁单斜辉石的较酸性岩浆的注入、混合 ;在浅部岩浆房中 ,混合岩浆结晶形成斑晶的边部和微晶辉石 ;基质辉石则是岩浆喷出洋底后淬冷结晶的结果。
Based on optical microscope and electron microprobe studies of clinopyroxenes in the basalt from Okinawa Through, we found three different generations of clinopyroxenes: phenocryst pyroxene, microphenocryst pyroxene and groundmass pyroxene, with average size of 400μm±, 30μm± and 5μm±, respectively. There are obvious compositional differences among these three different pyroxene generations. From the core of phenocryst pyroxene, through microphenocryst pyroxene and the rim of phenocryst pyroxene, to groundmass pyroxene, the chemical composition evolved from Fe rich to Mg and Ca rich, which is opposite to the compositional evolution trend of pyroxene crystallized in closed system. The morphologic and compositional features reflect the magma mixing beatures of the basalt magma, and demonstrate the dynamic process of this mantle magma: The tholeiitic magma from the upper mantle was mixed by the magma carrying the Fe rich pyroxene in the process moving up to the magma chamber; the mixed magma at magma chamber crystallized microlites and the rim of phenocryst; groundmass pyroxene was resulted from the quenching process of eruption. Consequently, clinopyroxenes in the Okinawa basalts keep well the records of the dynamic process of mantle magma.
出处
《高校地质学报》
CAS
CSCD
2002年第4期416-422,共7页
Geological Journal of China Universities
基金
国家自然科学基金资助项目 (4 9972 0 2 5 )
