长英质片麻岩中堇青石的一种可能的形成机制——以南极拉斯曼丘陵高级区为例  

A Possible Mechanism of Cordierite Formation in the Quartzofeldspathic Gneisses: A Case Study on the High_grade Region of the Larsemann Hills, East Antarctica

作　　者：任留东[1] 王彦斌[1] 陈廷愚[1] 赵越[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《岩石矿物学杂志》2001年第1期29-35,41,共8页Acta Petrologica et Mineralogica

基　　金：原地质矿产部青年地质学家基金;南极办和国家自然科学基金! ( 4970 2 0 33和 49772 15 4)项目资助

摘　　要：本文通过对南极拉斯曼丘陵长英质片麻岩变质过程中堇青石与其它矿物之间结构关系的研究 ,识别出明显不同的两种组合Pl+Kfs+Qtz(Grt)和Crd +Opq +Spl±Qtz,认为区内高级变质作用向深熔作用转化过程中发生了长英质组分和镁铁质组分的分凝。分凝出的长英质熔体与堇青石的形成没有直接关系 ;镁铁质组分较富Mg、Fe ,贫Si、Ca ,当镁铁质组分达到一定的富集程度时即形成堇青石。时间上 。Based on an investigation of the texture relationships between cordierite and other minerals of the Quartzofeldspathic gneisses in the Larsemann Hills, East Antarctica, especially the corrosion and crosscutting relationships between cordierite and other minerals, the authors discerned two distinct assemblages, viz., the felsic assemblage Pl+Kfs+Qtz(Grt) and the mafic assemblage Crd+Opq+Spl±Qtz. Texture and composition analysis suggests that cordierite might have been derived from the media quite likely in the melt state. That is, during the transformation from high_grade metamorphism to anatexis of the high grade rocks in the study area, the melt appeared first: Bt+Sil+Qtz→Grt+Melt, followed by the segregation of felsic and mafic components. The two components in the melt were immiscible and differentiated into two parts, Melt 1 and Melt 2, which crystallized separately and formed the felsic and mafic mineral assemblages, respectively. Cordierite was not formed as a cotectic magmatic phase relatively late in peraluminous melts and the presence of the mineral had no direct relation with the felsic melt. The mafic components rich in Mg and Fe but poor in Si and Ca may have been concentrated to form cordierite. Although the mafic component was substantially derived from biotite, the contact of biotite and cordierite can rarely be found due to the face that there existed a time gap between biotite decomposition and the final crystallization of cordierite. Temporally the cordierite crystallized at the late stage of anatexis essentially brought about in the decompression process.

关 键 词：长英质片麻岩 深熔作用 堇青石 形成机制 变质作用 

分 类 号：P588.345[天文地球—岩石学]