Journal of Petrology | Volume 39 | Number 11-12 | Pages 1847-1864 | 1998
© Oxford University Press 1998
Geochemical and Nd, Pb, and Sr Isotope Data from Deccan Alkaline Complexes—Inferences for Mantle Sources and Plume–Lithosphere Interaction
1 Max-Planck-Institut Für Chemie, Abteilung Geochemie Postfach 3060, 55020 Mainz, Germany
2 Department of Earth and Planetary Sciences, McGill University 3450 University Street, Montréal, Québec, Canada, H3A 2A7
3 Department of Geology, St Xavier's College Bombay 400 001, India
Received October 1, 1997; Revised typescript accepted May 21, 1998
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Abstract |
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Previous chemical and isotopic studies based on alkaline rocks and carbonatites associated with large, continental flood basaltic provinces indicate their important role in monitoring plume–lithosphere interaction. We report new major and trace element data, and Nd, Pb, and Sr isotope ratios for various alkaline silica-undersaturated rocks and carbonatites from several Decca alkaline complexes in an attempt to evaluate the relative contributions of Réunion plume and Indian sub-continental mantles in their source regions. Major and trace element abundances for the most primitive silicate samples are consistent with an origin via small-degree partial melting of metasomatized mantle. Initial 87Sr/86Sr, 143Nd/144Nd and Pb isotope ratios for the most primitive alkaline silicate samples and associated carbonatites exhibit a large variation, and are attributed to mixing of three distinct mantle components—Réunion plume, continental lithosphere and asthenosphere (Indian MORB-like). For the silicate rocks, isotope ratios correlate with major and trace element composition and support derivation from distinct mantle sources. The data obtained here are consistent with previous models invoking Réunion plume–continental lithosphere interaction to explain the origin of Deccan alkaline complexes, which suggest a more prominent role of Réunion mantle during the early stages of Deccan volcanism involving small-degree melting of plume-modified lithosphere. With time, the isotope systematics of both alkaline and tholeiitic magmatism record a larger lithospheric imprint.
KEY WORDS: carbonatite; Deccan province; lithosphere; mantle plume; Réunion
* Corresponding author. Present address: Centre de recherche GEOTOP, Université du Québec à Montréal, succursale Centre-ville, CP 8888, Montréal, Québec, Canada, H3C 3P8. Telephone: (514) 987-3000, ext. 7019. Fax: (514) 987-3635. e-mail: c3204{at}er.uqam.ca
Present address: Lamont–Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA.
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