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标题：Origin of trondhjemite and albitite at the expense of A-type granite, Aravalli orogen, India: Evidence from new metasomatic replacement fronts
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作者：Parampreet Kaur ; Naveen Chaudhri ; Nusrat Eliyas 等
期刊名称：Geoscience Frontiers
印刷版ISSN：1674-9871
出版年度：2019
卷号：10
期号：5
页码：1891-1913
DOI：10.1016/j.gsf.2018.09.019
语种：English
出版社：Elsevier
摘要：AbstractThe A-type Harsora-Dadikar granites in the Alwar complex of northern Aravalli orogen, NW India provide evidence for subsolidus-requilibration of feldspars. They record three new discrete stages of albitisation, producing trondhjemite and albitite sequentially at the expense of original granite. Stage-I metasomatism deanorthised the magmatic oligoclase and transformed the grey least-albitised granite to pinkish grey microcline-oligoclase granite. Stage-II converted the latter to trondhjemite by replacement of microcline to oligoclase. Stage-III metasomatism led to the formation of albitite/albite granite from trondhjemite, where the metasomatically formed oligoclase was replaced by albite. This stage of metasomatism resulted in nearly complete disappearance of amphibole and biotite, producing a monomineralic rock (albitite), which is consistent with Korzhinskii theory of infiltration metasomatism. The reaction fronts delineating the Stage-II and Stage-III are sharp and easily discernible by their prominent color differences in Harsora on the outcrop scale. Chemically, the mineral transformations during three stages are manifested by the differential gains/losses in Na, K, Ca, Rb, Ba, Sr, Fe and Mg. The formation of albite, Cl-rich marialitic scapolite and Cl-rich amphibole in the albitised granites are suggestive of Na- and Cl-brines as the metasomatising fluids. The fluid-rock interactions, which can significantly transform the pristine mineralogy of granitoids, should be carefully considered to avoid any misinterpretations about their petrological history.Graphical abstractDisplay OmittedHighlights•Three discrete stages of albitisation formed by Na- and Cl-rich fluid.•Transformation of original granite Stage-I moderately-albitised granite (Stage-I) trondhjemite (Stage-II) albitite (Stage-III).•Two sharp replacement fronts well displayed on the outcrop scale.•The fluid activity was quite extensive and widespread in the northern Aravalli orogen.
关键词：KeywordsenAlbitisationA-type graniteTrondhjemiteAlbititeAlwar complexNW India