Migmatite-granite relationships: origin of the Cooma Granodiorite magma, Lachlan Fold Belt, Australia

Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy Pub Date : 2001-04-01 DOI:10.1016/S1464-1895(01)00055-2

R.H. Vernon , S.W. Richards , W.J. Collins

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引用次数: 29

Abstract

Most published interpretations infer that the Cooma Granodiorite (southeastern Australia) was formed by more or less in situ melting of metasedimentary rocks of the Cooma Complex. Detailed work has shown that melting of metapelites, which occurred by biotite breakdown during D3 (after muscovite had disappeared), produced relatively immobile, plagioclase-poor or plagioclase-free leucosomes that are compositionally unsuitable as the source magma for the granodiorite. However, melting of feldspathic metapsammitic rocks, which occurred during D5, as P-T conditions followed an anticlockwise path, produced mobile, plagioclase-rich leucosomes that are more appropriate for the granodiorite source magma. Though gradations from metapsammite-derived migmatite to Cooma Granodiorite are present, accumulation of magma derived locally from metapsammite melting appears to be unable to account for all of the exposed body of Cooma Granodiorite, implying some ascent of similar magma from deeper levels of the source rocks.

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混合岩-花岗岩的关系：澳大利亚拉克兰褶皱带库马花岗闪长岩岩浆的起源

大多数已发表的解释推断，库马花岗闪长岩（澳大利亚东南部）或多或少是由库马杂岩的变质沉积岩原位熔融形成的。详细的工作表明，在D3期间（白云母消失后），由于黑云母分解而发生的变细岩熔融，产生了相对不动的、贫斜长石或无斜长石的隐色体，这些隐色体在成分上不适合作为花岗闪长岩的源岩浆。然而，在D5期间，由于P-T条件遵循逆时针路径，长石化闪长岩发生熔融，产生了更适合花岗闪长岩源岩浆的流动的富含斜长石的隐体。尽管存在从变质闪长岩衍生的混合岩到库马花岗闪长岩的渐变，但变质闪长石熔融产生的局部岩浆堆积似乎无法解释库马花岗矿的所有裸露体，这意味着类似岩浆从源岩的更深层次上升。

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Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy

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