Journal Article

Differentiation Processes of Deccan Trap Basalts: Contribution from Geochemistry and Experimental Petrology

T. SANO, T. FUJII, S. S. DESHMUKH, T. FUKUOKA and S. ARAMAKI

in Journal of Petrology

Volume 42, issue 12, pages 2175-2195
Published in print December 2001 | ISSN: 0022-3530
Published online December 2001 | e-ISSN: 1460-2415 | DOI: http://dx.doi.org/10.1093/petrology/42.12.2175
Differentiation Processes of Deccan Trap Basalts: Contribution from Geochemistry and Experimental Petrology

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The Deccan Traps basalts can be divided into sub-groups based on the inferred type and/or amount of contamination. The elemental characteristics of Ba, Sr, TiO2 and Zr/Nb are used to classify the sub-groups; the least-contaminated group has Ba contents <100 ppm, Sr 190–240 ppm and TiO2 2·0–4·0 wt %, and the most-contaminated group has TiO2 contents <1·5 wt % and Zr/Nb ≥ 15. Analyses of 325 basalts, which were collected from 27 well-distributed sections through the Deccan Traps, demonstrate that the least- and most-contaminated groups are distributed widely. To understand the shallow-level fractionation of the Deccan Trap magmas, melting experiments were conducted at atmospheric pressure (100 kPa) at both fayalite–magnetite–quartz (FMQ ) and nickel–nickel oxide (NNO) oxygen fugacities for three Mg-rich basalts, one of which belongs to the least-contaminated group. The results indicate that the phenocryst assemblage and the chemical trend of the least-contaminated basalts can reasonably be explained by fractional crystallization in shallow chambers under FMQ-buffered conditions. The inferred fractional crystallization process also reproduces the chemical trend of the most-contaminated basalts, implying that crustal contamination was not accompanied by the shallow-level fractional crystallization.

Keywords: Deccan Traps; fractional crystallization; crustal contamination; melting experiment; tholeiitic magma

Journal Article.  8997 words.  Illustrated.

Subjects: Petrology

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