3.35 Ga komatiite volcanism in the western Dharwar craton, southern India: Constraints from Nd isotopes and whole-rock geochemistry

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Jayananda, M. and Kano, T. and Peucat, J.-J. and Channabasappa, S. (2008) 3.35 Ga komatiite volcanism in the western Dharwar craton, southern India: Constraints from Nd isotopes and whole-rock geochemistry. Precambrian Research, 162 (1-2). pp. 160-179. ISSN 03019268

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Official URL: https://doi.org/10.1016/j.precamres.2007.07.010

Abstract

We present field, petrographic, Sm-Nd whole-rock isochron and whole-rock geochemical data for komatiites from Sargur Group greenstone belts of the western Dharwar craton. Field evidence such as pillow structure indicates their eruption in a marine environment. Petrographic data reveal that the igneous mineralogy has been altered during post-magmatic hydrothermal alteration processes corresponding to greenschist- to lower amphibolite facies conditions with rarely preserved primary olivine and orthopyroxene. A 16-point Sm-Nd whole-rock isochron gives an age of 3352 ± 110 Ma for the timing of eruption of komatiite lavas. About 60 of the studied komatiite samples show Al-depletion whilst the remaining are Al-undepleted. The Al-depleted komatiites are characterised by high CaO/Al 2O 3 ratios (1.01-1.34) and low Al 2O 3/TiO 2 (5-16) whereas Al-undepleted komatiites show lower CaO/Al 2O 3 ratios (0.59-0.99) and higher Al 2O 3/TiO 2 (17-26). Trace element distribution patterns of komatiites suggest that most of the primary geochemical and Nd isotopic compositions are preserved with only minor influence of post-magmatic alteration processes and negligible crustal contamination. The chemical characteristics of Al-depleted komatiites, such as high (Gd/Yb) N together with lower HREE, Y, Zr and Hf, imply their derivation from deeper upper mantle with garnet (majorite?) involvement, whereas lower (Gd/Yb) N slightly higher HREE, Y, Zr and Hf suggest derivation from shallower upper mantle without garnet involvement. The observed chemical characteristics (CaO/Al 2O 3, Al 2O 3/TiO 2, MgO, Ni, Cr, Nb, Zr, Y, Hf, REE) indicate derivation of the komatiite magmas from different depths in a plume setting, whereas sub-contemporaneous felsic volcanism and TTG accretion can be attributed to an arc setting. In order to explain the spatial association of komatiite volcanism with contemporaneous mafic-felsic volcanism and TTG accretion we propose a combined plume-arc setting. Nd isotope data of the studied komatiites indicate depleted mantle reservoirs which may have evolved by early (>4.53 Ga) global differentiation of the silicate Earth as suggested by Boyet and Carlson Boyet, M., Carlson, R.W., 2005. 142Nd evidence for early (>4.53 Ga) global differentiation of silicate Earth. Science 309, 577-581 or extraction of continental crust during the early Archaean. © 2007 Elsevier B.V. All rights reserved.

Item Type: Article
Additional Information: cited By 78
Uncontrolled Keywords: geochemistry; greenstone belt; isotopic composition; komatiite; lava; mantle; marine environment; neodymium isotope; petrography; samarium; volcanism, Asia; Dharwar Craton; Eurasia; India; South Asia
Subjects: Faculty of Science > Earth Sciences > Geology
Divisions: Jnana Bharathi / Central College Campus > Department of Geology
Depositing User: Mr. Kirana Kumar D
Date Deposited: 05 Mar 2016 10:35
Last Modified: 05 Mar 2016 10:35
URI: http://eprints-bangaloreuniversity.in/id/eprint/1807

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