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首页> 外文期刊>Journal of Asian earth sciences >Mafic and pelitic xenoliths in the Kinnaur Kailash Granite, Baspa river valley, NW Himalaya: Evidence of pre-Himalayan granulite metamorphism followed by cooling event
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Mafic and pelitic xenoliths in the Kinnaur Kailash Granite, Baspa river valley, NW Himalaya: Evidence of pre-Himalayan granulite metamorphism followed by cooling event

机译：喜马拉雅山西北部Kinaur Kailash花岗岩中的铁镁质和胶质岩生物岩：喜马拉雅前花岗石变质和冷却事件的证据

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摘要

Mafic and pelitic xenoliths occurring within the early Palaeozoic Kinnaur Kailash Granite (KKG) in the Baspa river valley, NW Himalaya record pre-Himalayan regional metamorphism at a range of pressure (P)-temperature (T) conditions that span amphibolite to granulite facies. The key evidence of granulite metamorphism is a xenolith of two-pyroxene mafic granulite in which orthopyroxene occurs as both discrete grains and microscopic needles exsolved parallel to prismatic cleavage of the clinopyroxene host. The rock records an average peak metamorphic temperature of 840℃. Garnetiferous mafic xenoliths display coronae of garnet around plagiodase and clinbpyroxene, and of sphene around ilmenite. These coro-nae were developed by near-isobaric cooling after peak metamorphism at 730℃ and 8 kbar. Pelitic xenoliths have the assemblage biotite-plagioclase-quartz ± garnet ± K-feldspar ± muscovite, and record P-T ranges of 7.0-9.0 kbar and 500-700 ℃ which indicate lower to middle amphibolite facies metamorphism of these rocks. Quartz, feldspar and mica in the pelitic xenoliths commonly show optical evidences of crystalloplastic deformation which indicate that the rocks were sheared before being engulfed as xenoliths in the KKG. The findings of this study imply that the present day metamorphic assemblages and shear fabrics in HHCS rocks need not be attributed solely to the Himalayan orogeny.
机译：喜马拉雅山西北部Baspa河谷的早古生代Kinnaur Kailash花岗岩（KKG）内发生的镁铁质和胶质岩质碎屑岩记录了喜马拉雅山前的区域变质，其变化范围涵盖了成闪石到花岗石相的一系列压力（P）-温度（T）条件。花岗石变质作用的关键证据是二py铁镁铁质花岗石的异岩体，其中邻位py烯以离散的晶粒和微观针状体平行于斜rox体的棱柱形劈裂而出现。岩石记录的平均峰值变质温度为840℃。石榴石质镁铁质异岩在斜纹酶和克林比罗烯周围显示出石榴石的冠冕，在钛铁矿周围显示出蝶形的冠冕。这些冠状病毒是在730℃和8 kbar的峰值变质后，通过近等压冷却而形成的。柱状异种石具有黑云母-斜长石-石英±石榴石±K长石±白云母的组合，记录的P-T范围为7.0-9.0 kbar和500-700℃，表明这些岩石的中低角闪岩相变质作用。胶体生质中的石英，长石和云母通常显示出结晶塑性变形的光学证据，这表明岩石在被包埋为KKG中的生质之前就被剪切了。这项研究的结果表明，HHCS岩石中当今的变质组合和剪切构造不必仅仅归因于喜马拉雅造山作用。

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