Contrasting isotopic mantle sources for Proterozoic lamproites and kimberlites from the Cuddapah basin and eastern Dharwar craton: implication for Proterozoic mantle heterogeneity beneath southern India

Rao, N. V. C. ; Gibson, S. A. ; Pyle, D. M. ; Dickin, A. P. (1998) Contrasting isotopic mantle sources for Proterozoic lamproites and kimberlites from the Cuddapah basin and eastern Dharwar craton: implication for Proterozoic mantle heterogeneity beneath southern India Journal of the Geological Society of India, 52 (6). pp. 683-694. ISSN 0016-7622

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Abstract

Kimberlites intruding the Precambrian basement towards the western margin of the Cuddapah basin near Anantapur (1090 Ma) and Mahbubnagar (1360 Ma) in Andhra Pradesh have initial Sr-87/Sr-86 between 0.70205 to 0.70734 and epsilon Nd between +0.5 to +4.68. Mesoproterozoic lamproites (1380 Ma) from the Cuddapah basin (Chelima and Zangamarajupalle) and its NE margin (Ramannapeta) have initial Sr-87/Sr-86 between 0.70520 and 0.7390 and epsilon Nd from -6.43 to -8.29. Combined Sr- and Nd-isotonic ratios suggest that lamproites were derived from "enriched" sources which have time-averaged higher Rb/Sr and lower Sm/Nd ratios than the Bulk Earth whereas kimberlites were derived from "depleted" source with lower Rb/Sr and higher Sm/Nd ratios. Calculated T-DM model ages suggest that the lamproite source enrichment (similar to 2 Ga) preceded that of kimberlites (similar to 1.37 Ga). Our work demonstrates the existence of isotopically contrasting upper mantle sources for Southern Indian kimberlites and lamproites and provides evidence for a lateral, isotopically heterogeneous mantle beneath the Cuddapah basin and eastern Dharwar craton. The significance of our results in the context of diamond exploration is also highlighted.

Item Type:Article
Source:Copyright of this article belongs to Geological Society of India.
Keywords:Petrology; Geochemistry; Kimberlite; Lamproite; Isotopes; Mantle; Andhra Pradesh
ID Code:97874
Deposited On:26 Dec 2017 11:11
Last Modified:26 Dec 2017 11:11

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