麻粒岩相条件下熔融反应与矿物相转变机制的实验研究  

EXPERIMENTAL STUDY OF MELTING REACTION AND GENETIC MECHANISM OF MINERAL PHASE TRANS- FORMATION IN GRANULITE FACIES METAMORPHISM

作　　者：刘福来[1] 沈其韩[1] 耿元生[1] 徐学纯[2] 马瑞[2] 

机构地区：[1]中国地质科学院地质研究所 [2]长春地质学院开放实验室

出　　处：《地质学报》1997年第3期254-265,T001,共13页Acta Geologica Sinica

基　　金：地质矿产部青年地质学家基金(编号9603);博士后科学基金

摘　　要：麻粒岩相条件下石榴黑云斜长片麻岩实验结果表明,含水矿物黑云母(Bi)脱水熔融、长英质矿物部分熔融的性质主要受控于温度条件;而矿物相转变不仅受控于温压条件,而且与脱水熔融、部分熔融存在密切成因联系。依据Bi脱水熔融性质和石榴石(Gi)转变反应特征,可划分以下三个阶段:(1)当温度在700℃时,Bi转变为钛铁矿(Ilm)+磁铁矿(Mt)+H_2O,Gt转变为Mt,(2)当温度在730—760℃,Bi脱水熔融为富K_2O熔体(Melt)+Ilm+Mt,Gt转变为紫苏辉石(Hy)+堇青石(Crd);(3)当温度大于790℃时,Bi脱水熔融为Melt+Hy+Ilm+Mt+H_2O,Gt则转变为Hy+尖晶石(Sp)+Crd组合。熔体比例和熔体演化特征除受温压条件控制外,与长英质矿物部分熔融程度和脱水熔融性质关系密切。实验结果显示,在麻粒岩相变质作用以及与其相伴随的重熔作用(或区域性混合岩化作用)过程中,不仅存在传统的固相+固相(或流体相)的反应和脱水熔融反应,而且存在熔体参与的变质反应(即:未熔矿物与熔体之间的反应)。该项实验对深入探讨麻粒岩相矿物演化的成因机制及其动力学意义提供可靠的实验依据。High-temperature and pressure experiment on natural block rock indicates that dehydration-melting of hydrous biotite (Bi) and partial melting of felsic mineral in garnet- biotite- plagioclase gneiss are mainly controlled by temperature, while mineral phase transformation is not only controlled by temperature - pressure conditions, but also genetically associated with hydrous mineral dehydration-melting and felsic mineral partial melting. According to the characteristics of biotite dehydration-melting and garnet transforming reation three stages may be distinguished: (1) when the experimental temperature is 700 ℃, biotite transforms to ilmenite (Ilm) + magnetite (Mt) + H2O and garnet to magnetite (Mt); (2) when the temperature is 730-760℃, biotite is dehydrated and melted and transforms to K2O-rich melt + Ilm + Mt and garnet to hypersthene (Hy) + cordierite (Crd); (3) when the temperature is up to or higher than 790 ℃ , biotite is dehydrated and melted and transforms to melt + Hy +Ilm + Mt and garnet to the hypersthene (Hy) + spinel (Sp) + cordierite (Crd) assemblage. The melt proporation and its evolutional characteristics are mainly controlled by dehydration-melting of hydrous minerals and partial melting of felsic minerals besides P-T conditions. After all, in addition to the traditional solid+solid (or fluid) reaction and dehydration-melting reaction, the metamorphic reaction involving melt (reaction between unmelted minerals and melt) is one of the most important reactions in granulite facies metamorphism and its attendant remelting (migmatization). This experiment may provide dependable experimental data for an in-depth study of the genetic mechanism of mineral assemblage evolution and its geological dynamic signifance in granulite facies metamorphism of the studied region.

关 键 词：麻粒岩 岩相 熔融反应 矿物相 转变机制 

分 类 号：P588.346[天文地球—岩石学]