岩浆密度及其重要意义

Magma Density and its Significance

本文通过计算不同构造环境的原生玄武岩岩浆密度,首次提出了两种原生玄武岩浆密度类型:岛弧玄武岩浆(AB)密度类型(Ⅰ);WB+MORB岩浆密度类型(Ⅱ)。指出Ⅰ型岩浆密度受控于岩浆起源的fO2和fH2O条件;Ⅱ型岩浆密度则与岩浆起源压力有关。原生岩浆密度可作为判定岩浆产出的地球动力学背景的重要标志之一。考察岩浆密度与压力的关系,指出原生玄武岩浆密度在一定程度上控制了岩浆房的发育部位(深度),制约了岩浆结晶的温压条件,并对岩浆侵位与喷发产生重要影响。在岛弧地区,岩浆密度与地壳厚度变化严格地控制着岛弧岩石系列(Tb-CA-Sh)的时空演变,决定了岩浆的演化途径和结晶条件。利用岩浆密度资料,反演并建立了义敦岛弧区的地壳双层结构模式。

The paper has calculated magma density of basaltic rocks from various tectonic settings. It firstly suggested that two types of magma density: Ⅰ density type of primary basaltic magmas in Arc Regions; Ⅱ density type of primary basaltic magmas in Within Plate and Mid-Ocean-Ridge. The paper points out that Ⅱ magma type concern with the pressure and temperature conditions on which magmas formed, and Ⅰ magma density is controlled by fO_2 and fH_2O in source of basaltic magmas. So, the density of primary basaltic magmas is a important criteria to distinguish geodynamics settings in which magmas formed. Considing the relationship of density with pressure, the paper suggests that density of primary basaltic magmas controls on the depth of magma chamber and condition of temperaturepressure on which magma crystallized, on the some extent, and make effect on intrusion-eruption of magmas. In the regions of island-arc, magma density and the crust thickness control on time-space evolution of rock series(Th-CA-Sh) and decide the crystallization condition and evolution path of magmas. Using data about magma density, 'two-layer' model of crust structure in Yidun Island-Arc regions, westhern Sichuan Province, has been established.