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Chemical evolution, petrogenesis and regional chemical correlations of flood basalt sequence in the Central Dekkan Traps, India
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Petrogenesis of late Cenozoic mafic alkaline rocks of the Nosy Be archipelago (northern Madagascar): relationships with the Comorean magmatism.
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Magmatic activity northeast of Roccamonfina Volcano, Southern Italy: Petrology, geochemistry and relationships with Campanian volcanics.
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Mantle sources and crustal input as recorded in high-Mg Deccan Traps basalts of Gujarat (India)
No full textNear-primitive picritic basalts in the northwestern Deccan Traps have MgO > 10 wt.% and consist of two groups (low-Ti and high-Ti) with markedly different incompatible element and Nd-Sr-Pb isotope characteristics. Many elemental characteristics of the low-Ti picritic basalts are similar to those of transitional or normal ocean ridge basalts. However, values of ratios like Ba/Nb (13-30) and Ce/Pb (4-11), and isotopic ratios e.g., epsilon(Nd)(t) +0.3 to -6.3 (Pb-207/Pb-204), 15.63-15.75 at (Pb-206/Pb-204 18.19-18.84, delta O-18(olivine) as high as +6.2 parts per thousand) are far-removed from ocean-ridge-type values, indicating a significant contribution from continental crust. The crustal signature could represent crustal contamination of ascending magmas; alternatively, it could represent a minor component within the Indian lithospheric mantle of anciently subducted sedimentary material or fluids derived from subducted material. In contrast, the high-Ti picritic basalts are chemically and isotopically rather similar to recent shield lavas of the Reunion hotspot (e.g., epsilon(Nd)(t) +2 to +4) and to volcanic rocks along the postulated pre-Deccan track of this hotspot in Pakistan. Neither type of picritic basalt is parental to the voluminous flows comprising the bulk of the Deccan Traps. However, many of the Deccan primary magmas could have been derived from mixtures of a high-Ti-type, Reunion-like source component and a component more similar to, or even more incompatible-element-depleted than, average ocean-ridge mantle. (C) 2006 Elsevier B.V. All rights reserved
Chemical evolution, petrogenesis, and regional chemical correlations of the flood basalt sequence in the central Deccan Traps, India
No full textThe 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 16 ppm) 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 1220degrees to 1125degreesC. 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 for Sr-87/Sr-86 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 northwestern 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 high Sr-87/Sr-86, 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
The transition from alkaline to tholeiitic rocks and source enrichment processes for Orosei-Dorgali volcanic rocks (NE Sardinia, Italy).
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