Ultramafic xenoliths from Kutch, northwest India: Plume-related mantle samples?

The Deccan flood basalt province of west-central India has been linked to t he Reunion plume, and reconstructions suggest that the Kutch region was ove r the plume at the time of Deccan volcanism at 65-68 Ma. Field relations an d isotopic data indicate that the alkaline basalts of Kutch. which occur to the NNW of the main Deccan tholeiitic province, preceded the main flood-ba salt volcanism and ale related to the limited plume incubation period. Seve ral plugs of these alkali basalts contain small spinel peridotite xenoliths of mantle origin. The minerals of the spinel peridotites have been analyze d for their major, trace, and rare-earth element (REE) concentrations using election microprobe and LAM-ICPMS techniques. The modes and mineral chemis try, especially of the clinopyroxenes, indicate a fertile mantle; modeling of the clinopyroxene REE data is consistent with <5 to 15% of partial melti ng of a primitive mantle source material in the spinel peridotite field. Su bsequent cryptic metasomatism introduced LREE, U, Th, anti Zr. The xenolith s may represent: (1) young lithosphere generated during the lithospheric ex tension that preceded the main Deccan volcanism; or (2) material from the u ppermost parts of the rising plume, brought to the surface by the first sta ges of the volcanism. Their low equilibration temperatures (less than or eq ual to 900 degrees C) and their textural and chemical similarity to xenolit h suites from other Phanerozoic intraplate settings favor the first alterna tive. However the extensive cryptic metasomatism may reflect the influence of the rising Deccan plume.