Sr-Nd isotope geochemistry of the early Precambrian sub-alkaline mafic igneous rocks from the southern Bastar craton, Central India

Srivastava, R.K., Ellam, R.M. and Gautam, G.C. (2009) Sr-Nd isotope geochemistry of the early Precambrian sub-alkaline mafic igneous rocks from the southern Bastar craton, Central India. Mineralogy Petrology, 96(1-2), pp. 71-79. (doi: 10.1007/s00710-009-0049-2)

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Sr–Nd isotope data are reported for the early Precambrian sub-alkaline mafic igneous rocks of the southern Bastar craton, central India. These mafic rocks are mostly dykes but there are a few volcanic exposures. Field relationships together with the petrological and geochemical characteristics of these mafic dykes divide them into two groups; Meso-Neoarchaean sub-alkaline mafic dykes (BD1) and Paleoproterozoic (1.88 Ga) sub-alkaline mafic dykes (BD2). The mafic volcanics are Neoarchaean in age and have very close geochemical relationships with the BD1 type. The two groups have distinctly different concentrations of high-field strength (HFSE) and rare earth elements (REE). The BD2 dykes have higher concentrations of HFSE and REE than the BD1 dykes and associated volcanics and both groups have very distinctive petrogenetic histories. These rocks display a limited range of initial 143Nd/144Nd but a wide range of apparent initial 87Sr/86Sr. Initial 143Nd/144Nd values in the BD1 dykes and associated volcanics vary between 0.509149 and 0.509466 and in the BD2 dykes the variation is between 0.510303 and 0.510511. All samples have positive εNd values the BD1 dykes and associated volcanics have εNd values between +0.3 and +6.5 and the BD2 dykes between +1.9 to +6.0. Trace element and Nd isotope data do not suggest severe crustal contamination during the emplacement of the studied rocks. The positive εNd values suggest their derivation from a depleted mantle source. Overlapping positive εNd values suggest that a similar mantle source tapped by variable melt fractions at different times was responsible for the genesis of BD1 (and associated volcanics) and BD2 mafic dykes. The Rb–Sr system is susceptible to alteration and resetting during post-magmatic alteration and metamorphism. Many of the samples studied have anomalous apparent initial 87Sr/86Sr suggesting post-magmatic changes of the Rb–Sr system which severely restricts the use of Rb–Sr for petrogenetic interpretation.

Item Type:Articles
Additional Information:The original publication is available at
Glasgow Author(s) Enlighten ID:Ellam, Professor Rob
Authors: Srivastava, R.K., Ellam, R.M., and Gautam, G.C.
Subjects:Q Science > QE Geology
G Geography. Anthropology. Recreation > GE Environmental Sciences
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Mineralogy Petrology
Copyright Holders:Copyright © 2009 Springer-Verlag
First Published:First published in Mineralogy Petrology 96(1-2):71-79
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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