Geology, petrochemistry, and genesis of the bimodal lavas of Osham. Hill, Saurashtra, northwestern Deccan Traps
DSpace at IIT Bombay
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Title |
Geology, petrochemistry, and genesis of the bimodal lavas of Osham. Hill, Saurashtra, northwestern Deccan Traps
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Creator |
SHETH, HC
CHOUDHARY, AK CUCCINIELLO, C BHATTACHARYYA, S LAISHRAM, R GURAV, T |
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Subject |
Deccan Traps
Saurashtra Osham Hill Rhyolaite Pitchstone Petrogenesis VOLCANIC-ROCKS CHEMICAL CLASSIFICATION SILICIC MAGMAS MANTLE SOURCES TRACE-ELEMENT PB ISOTOPE INDIA GEOCHEMISTRY ORIGIN SR |
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Description |
The Saurashtra region in the northwestern Deccan continental flood basalt province (India) is notable for compositionally diverse volcano-plutonic complexes and abundant rhyolites and granophyres. A lava flow sequence of rhyolite-pitchstone-basaltic andesite is exposed in Osham Hill in western Saurashtra. The Osham silicic lavas are Ba-poor and with intermediate Zr contents compared to other Deccan rhyolites. The Osham silicic lavas are enriched in the light rare earth elements, and have epsilon(Nd) (t = 65 Ma) values between -3.1 and -6.5 and initial (87)Sr/(86)Sr ratios of 0.70709-0.70927. The Osham basaltic andesites have initial epsilon(Nd) values between +2.2 and -1.3, and initial (87)Sr/(86)Sr ratios of 0.70729-0.70887. Large-ion-lithophile element concentrations and Sr isotopic ratios may have been affected somewhat by weathering; notably, the Sr isotopic ratios of the silicic and mafic rocks overlap. However, the Nd isotopic data indicate that the silicic lavas are significantly more contaminated by continental lithosphere than the mafic lavas. We suggest that the Osham basaltic andesites were derived by olivine gabbro fractionation from low-Ti picritic rocks of the type found throughout Saurashtra. The isotopic compositions, and the similar Al(2)O(3) contents of the Osham silicic and mafic lavas, rule out an origin of the silicic lavas by fractional crystallization of mafic liquids, with or without crustal assimilation. As previously proposed for some Icelandic rhyolites, and supported here by MELTS modelling, the Osham silicic lavas may have been derived by partial melting of hot mafic intrusions emplaced at various crustal depths, due to heating by repetitively injected basalts. The absence of mixing or mingling between the rhyolitic and basaltic andesite lavas of Osham Hill suggests that they reached the surface via separate pathways. (C) 2011 Elsevier Ltd. All rights reserved.
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Publisher |
PERGAMON-ELSEVIER SCIENCE LTD
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Date |
2014-10-15T08:25:11Z
2014-10-15T08:25:11Z 2012 |
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Type |
Article
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Identifier |
JOURNAL OF ASIAN EARTH SCIENCES, 43(1)176-192
http://dx.doi.org/10.1016/j.jseaes.2011.09.008 http://dspace.library.iitb.ac.in/jspui/handle/100/14677 |
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Language |
en
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