海底玄武岩中的中酸性玻璃质熔体研究及其意义

The intermediate and acidic glassy melts in the matrix of the sea-floor basalts were studied in this study. Our results indicate that the character of the chemical composition of the glassy melts is constrained precisely by the cooling rate of magma. The compositions of the glassy melts become increasingly acidic with decreasing cooling rate. The acidic glassy melts were derived from crystal fractionation of a basaltic parental magma in the matrix of the basalt. With increasing SiO2 in glassy melts, Al2O3 and Na2O rise at first, and then decrease, the turning point is in SiO2 62% (wt). This characteristic is determined by the mineral crystallization of the matrix magma. During the early-stage crystallization, augite fractionation played a dominant role, resulting in a rapid increase in SiO2, Al2O3 and Na2O, and abrupt decrease in FeO, MgO and CaO in the residual glassy melts. During subsequent stages of crystallization, plagioclase became a dominant fractionating phase, consuming most of Al2O3 and Na2O in the residual melts. This study is important for understanding the evolution of mantle-derived magmas and the petrogenesis of (ultrabasic) basic-acidic rocks associations in some important tectonic settings, and for diagnosing ancient ophiolite suites.

项目将对海底玄武岩中新发现的中酸性玻璃质熔体进行系统研究，结合对基质矿物的研究，探讨中酸性玻璃质熔体与基质岩浆结晶程度的关系及其与基质矿物间元素配分关系，进而研究中酸性玻璃质熔体的成因及海底玄武岩浆的演化过程。这将对了解一些重要构造位置基性-- 酸性岩石组合的成因、洋壳的形成模式、大洋板块及其周边岩浆活动过程具重要意义。