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标题：Geochemistry of Palaeoproterozoic Rocks of Aravalli Supergroup: Implications for Weathering History and Depositional Sequence
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作者：Pavanesh K. Singh ; M. Shamim Khan
期刊名称：International Journal of Geosciences
印刷版ISSN：2156-8359
电子版ISSN：2156-8367
出版年度：2017
卷号：8
期号：10
页码：1278-1299
DOI：10.4236/ijg.2017.810074
语种：English
出版社：Scientific Research Pub
摘要：The Paleoproterozoic Aravalli Supregroup of rocks, hosted in Aravalli Craton of NW shield, is deposited in shallow and deep water conditions. The major lithologies are phyllites and quartzites with significant components of greywacks and dolomite. Geochemical indices in particular, CIA (Chemical Index of Alteration) values (avg. phyllites: 51.6 - 81.5, avg. quartzites: 57.4 - 95.5) calculated from the data of clastic rocks of ASG suggest minimum to highly intense weathering in the source region. Other indices including PIA, CIW and ICV along with plot patterns on the A-CN-K diagram also nearly endorse CIA based interpretation. These rocks possess relatively high Th/U ratios compared to that found in fresh igneous rocks or their high grade metamorphic equivalents. This high Th/U ratio is neither a source inheritance nor a result of oxidation state rather a manifestation of Th hosting mineral accumulation through sorting. Viewed in the context of present stratigraphic succession, the weathering history adduced from geochemistry does not seem compatible but matches well with earlier classification scheme wherein the evolution of Aravalli Supergroup was considered episodic.
关键词：Clastic GeochemistryAravalli SupergroupRajasthanPalaeoweatheringIndian Shield