Alkali amphiboles from Late Archean gneiss of the Wuhe Group. Anhui, Central China——not an indication of high P/T metamorphism(英文)
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    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Al2O3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。

    Abstract:

    In some alkali gneisses of the late Archean,Wuhe Group in central Cliina, occurrenco of blue amphibole and jadeite has been reported and used as indicators for high P/T metamorphism concurrently with that of the Zhangbaling Group. Petrochomical studies indicate that foliated gneisses contain cliaractcristic amphibolite facies assemblage, alkali amphiboles+acmite+microcline+biotite +quartz士albite士hematite. Alkali amphiboles are zoned with cores of igneous Mg-Aifvedsonite and rims of amphibolite faccies magnesioriebeckcite; these alkali amphiboles contain extremely low Al2O3 and high in both Fe2* andFe3+and Fe3+;they are- distinctly different from crossitic amphiboles of the Zhangbaling Group. Sodic pyroxenes lack jadeitic component and have pure acmite composition. The observed mineral assemblage including abundant mmicrocline, the compositions of blue amphiboles, the low jadoite occurrence of analyzed acmitic pyroxenes, and P-T estimates all suggest that the the investigated gneisses of the Wuhe Group were products of the amphibolite facies but not high P/T blueschist facies metamorphism. Previous reports of the jadeite occcurrence in the Wuhe Group and in high P/T metamorphic rocks of central China were not supported by the published microprobe data, nor our petrological results.

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刘忠光,王小民,崔善奎,梁万通,荆延仁,潘国强,夏木林,1992,Alkali amphiboles from Late Archean gneiss of the Wuhe Group. Anhui, Central China——not an indication of high P/T metamorphism(英文)[J].岩石矿物学杂志,11(3):205~224.,1992,[J]. Acta Petrologica et Mineralogica,11(3):205~224.

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