Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Geological Magazine

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (19) Citing Articles via Google Scholar Google Scholar Articles by RAJESH, H. M. Search for Related Content GeoRef GeoRef Citation

Characterization and origin of a compositionally zoned aluminous A-type granite from South India

Department of Geosciences, Faculty of Science, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan

^* E-mail: rajesh{at}sci.osaka-cu.ac.jp

The Pan-African Ambalavayal granite intrudes the high-grade metamorphic terrain of northern Kerala, South India and is spatially associated with the Moyar and Calicut lineaments. The pluton was aligned nearly parallel to the northeast–southwest and east–west faults in the basement, consistent with magma ascent along pre-existing deep-crustal lineaments in an extensional tectonic regime. The pluton is characterized by the presence of iron-rich hydrous mafic minerals, primary magnetite, fO₂ above the Ni–NiO buffer and high initial emplacement temperatures near 1000 °C. Modal and textural analyses reveal two probable compositional zones within the pluton: outer and inner. Major element variations support this zoning and point to a peralkaline to metaluminous outer zone and a metaluminous to slightly peraluminous inner zone. Both zones exhibit major and trace element characteristics of the A-type granites with the outer zone belonging to the A₁ subtype and the inner zone to the A₂ subtype of Eby. The trace element trends observed from outer zone to the inner zone suggests that crystal fractionation may have been the dominant process in the generation of high levels of the incompatible elements in the case of inner zone samples. The high initial ⁸⁷Sr/⁸⁶Sr ratio (0.7135) and high Y/Nb ratios (Y/Nb > 1.2) are in the range expected for rocks derived from crustal protoliths. A petrogenetic model involving partial melting of a charnockitic, mafic to intermediate lower crust followed by limited fractional crystallization of the magma in a high-level magma chamber is proposed. The enrichment of HFSE and REE (except Eu) in the inner zone is considered the ultimate product of crystal–melt and volatile activity during the final stage of crystallization in a highly silicic (SiO₂ > 74 %) magma chamber.

This article has been cited by other articles:

				L. CHEN, C.-Q. MA, Z.-B. SHE, R. MASON, J.-Y. ZHANG, and C. ZHANG Petrogenesis and tectonic implications of A-type granites in the Dabie orogenic belt, China: geochronological and geochemical constraints Geological Magazine, September 1, 2009; 146(5): 638 - 651. [Abstract] [Full Text] [PDF]