中国中部安徽晚太古代五河群碱性角闪石——并非高压变质的指示矿物(英文)  

ALKALI AMPHIBOLES FROM LATE ARCHEAN GNEISS OF THE WUHE GROUP,ANHUI,CENTRAL CHINA——NOT AN INDICATION OF HIGH P/T METAMORPHISM

作　　者：刘忠光[1] 王小民[1] 崔善奎 梁万通[3] 荆延仁 潘国强 夏木林 

机构地区：[1]美国斯坦福大学地质学系,斯坦福94305 [2]南朝鲜国立教育大学地球科学系 [3]长春地质学院地质系 [4]安徽省区域地质大队

出　　处：《岩石矿物学杂志》1992年第3期205-224,共20页Acta Petrologica et Mineralogica

摘　　要：在中国中部晚太古代五河群的碱性片麻岩中,曾报导有蓝色角闪石和硬玉的存在,并且认为它们是与安徽张八岭群同期的高压变质矿物。本文作者经过对岩石和矿物成分的详细研究,证实五河群中的碱性角闪石+锥辉石+斜长石+黑云母+石英±钠长石±赤铁矿等矿物组合是典型的角闪岩相变质矿物组合,这些碱性角闪石的核部是岩浆岩成因的镁钠铁闪石,其边部是角闪岩相变质成因的镁钠闪石,这些碱性闪石的Al_2O_3含量特别低,而FeO和Fe_2O_3含量很高,它们与张八岭群的青铝闪石在化学成分上差别很大。五河群片麻岩中的钠质辉石是很纯的锥辉石而没有硬玉组分。从含大量微斜长石的矿物组合、蓝色角闪石的矿物成分、低硬玉质的钠辉石和估算的温度和压力条件来看,我们认为五河群的片麻岩并不是高压蓝闪片岩相的变质产物。此外,以前关于五河群和中国中部其他变质岩中(如张八岭群)有关硬玉的报导中所发表的电子探针和化学分析资料与辉石的化学分子式不符,我们的岩石学研究也没有证实硬玉的存在。In some alkali gneisses of the Late Archean Wuhe Grorp in central China occurre-nce of blue anphibole ant jadeite has been reported and used as indicators for highP/T metamorphism concurrentIy with that of the Zhangbaling Group. Petrochemicalstudies indicate that foliated gneisses contain characteristic amphibolite facies assem-blage, alkali amphiboles+acmite+microcline+biotite+quartz±albite± hematite. Alkaliamphiboles are zoned with cores of igneous Mg-Arfvedsonite and rims of amphibolitefacies magnesioriebeckite; these alkali amphiboles contain extremely low Al_2O_3 and highin both Fe^2+and Fe^3+; they are distinctly different from cxossitic amphiboles of theZhangbaling Group. Sodic pyroxenes lack jadeitic component and have pure acmite compo-sition. Tho chserved mineral assemblage including abundant microcline, the compositionsof blue amphiboles, the low jadeitic component of analyzed acmitic pyroxenes, and P-Testimates all suggest that the investigated gneisses of the Wuhe Group were products ofthe amphibolite facies but not high P/T blueschist facies metamorphism. Previous ro-ports of the jadeite occurrence in the Wuhe Group and in high P/T metamorphic rocksof contral China wete not supported by the published microprobe data, nor our potrolo-gical results.

关 键 词：角闪石 碱性 高压变质 矿物 

分 类 号：P578.955[天文地球—矿物学]