Chemical evolution, petrogenesis, and regional chemical correlations of the flood basalt sequence in the central Deccan Traps, India |
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Authors: | L Melluso M Barbieri L Beccaluva |
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Institution: | (1) Dipartimento di Scienze della Terra, Università di Napoli Federico II, via Mezzocannone 8, 80134 Napoli, Italy;(2) Dipartimento di Scienze della Terra, Università di Roma “La Sapienza”, Italy;(3) Dipartimento di Scienze Geologiche, Università di Ferrara, Italy |
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Abstract: | The lava sequence of the central-western Deccan Traps (from Jalgaon towards Mumbai) is formed by basalts and basaltic andesites
having a significant variation in TiO2 (from 1.2 to 3.3 wt%), Zr (from 84 to 253 ppm), Nb (from 5 to 16ppm) and Ba (from 63 to 407 ppm), at MgO ranging from 10
to 4.2 wt%. Most of these basalts follow a liquid line of descent dominated by low pressure fractionation of clinopyroxene,
plagioclase and olivine, starting from the most mafic compositions, in a temperature range from 1220° to 1125°C. These rocks
resemble those belonging to the lower-most formations of the Deccan Traps in the Western Ghats (Jawhar, Igatpuri and Thakurvadi)
as well as those of the Poladpur formation. Samples analyzed for87Sr/86Sr give a range of initial ratios from 0.70558 to 0.70621. A group of flows of the Dhule area has low TiO2 (1.2–1.5 wt%) and Zr (84–105 ppm) at moderate MgO (5.2–6.2 wt%), matching the composition of low-Ti basalts of Gujarat, low-Ti
dykes of the Tapti swarm and Toranmal basalts, just north of the study area. This allows chemical correlations between the
lavas of central Deccan, the Tapti dykes and the north-western outcrops. The mildly enriched high field strength element contents
of the samples with TiO2 > 1.5 wt% make them products of mantle sources broadly similar to those which generated the Ambenali basalts, but their high
La/Nb and Ba/Nb, negative Nb anomalies in the mantle normalized diagrams, and relatively high87Sr/86Sr, make evident a crustal input with crustally derived materials at less differentiated stages than those represented in
this sample set, or even within the sub-Indian lithospheric mantle. |
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Keywords: | Petrogenesis basalts basaltic andesites central Deccan Traps India |
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