Xenoliths in Proterozoic kimberlites from southern India: petrology and geophysical implications.

J. Ganguly, P. K. Bhattacharya

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Abstract

There are no published records of mantle xenoliths in basalts from India. A few relatively fresh ultrabasic and eclogite xenoliths have been recovered from the kimberlite pipes of the Wajrakarur-Lattavaram area of southern India. The mineralogy of the ultrabasic xenoliths is described; these include garnet harzburgites, lherzolites, wehrlites and olivine clinopyroxenites. Some of the garnet-bearing nodules have spinel, and most have phlogopite. The geotherms defined by the calculated P-T conditions of mineral equilibria in these ultrabasic xenoliths and in the Cretaceous xenoliths from N Lesotho, southern Africa, are very similar. This similarity implies nearly steady-state thermal conditions in the upper mantle beneath continental shield area over at least 1000 m.y. The inferred P-T regime of the Indian xenoliths also suggests that the lithosphere was = or >185 km thick during the mid-Proterozoic. The ultrabasic and eclogite xenoliths have been derived from depths of 100-180 km and 75-150 km, respectively. The chemical compositions of garnet, which include a low Ca variety, seem to suggest that the Proterozoic mantle beneath the Indian Shield was progressively more 'fertile' with increasing depth at the time of kimberlite eruption. -J.M.H.

Original languageEnglish (US)
Pages (from-to)249-265
Number of pages17
JournalUnknown Journal
StatePublished - Jan 1 1987

ASJC Scopus subject areas

  • Environmental Science(all)
  • Earth and Planetary Sciences(all)

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