Microstructures and compositional variation in the intravolcanic bole clays from the eastern Deccan volcanic province: Palaeoenvironmental implications and duration of volcanism |
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Authors: | J. P. Shrivastava Mansoor Ahmad Surabhi Srivastava |
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Affiliation: | (1) Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2215, USA;(2) School of Earth Sciences, SRTM University, Nanded, 431606, Maharashtra, India;(3) Geochemistry Division, NGRI, Hyderabad, 500007, Andhra Pradesh, India;(4) Op. Andhra Pradesh, Geological Survey of India, Southern Region, Bandlaguda, Hyderabad, 500068, Andhra Pradesh, India |
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Abstract: | Clay minerals associated with intra-volcanic bole horizons of varied colours and thicknesses contain montmorillonite, halloysite and kaolinite, show distinct microstructures and microaggregates. In kaolinite, Fe3+ ions substitute for Al3+ at octahedral sites. Most of these clays are dioctahedral type, show balance between net layer and interlayer charges. The interstratified illite — smectite (I/S) mixed layers containing variable proportions of montmorillonite. Illite contains sheet-like, well oriented microaggregates. The parallel stacks of chlorite sheets show chlorite/smectite (C/S) mixed layers. Progressive enrichment of Fe and depletion of Al ions with the advancement of kaolinization process is observed. High order of structural and compositional maturity observed in these bole clays, indicate long hiatus between the two volcanic episodes. |
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