Mantle derived xenoliths in India are known to occur in the Proterozoic ultrapotassic rocks like kimberlites from Dharwar and Bastar craton and Mesozoic alkali igneous rocks like lamrophyres, nephelinites and basanites. The xenoliths in kimberlites are represented by garnet harzburgites, lherzolites, wehrlite, olivine clinopyroxenites and kyaniteeclogite varieties. The PT conditions estimated for xenoliths from the Dharwar craton suggest that the lithosphere was at least 185 km thick during the Mid-Proterozoic period. The ultrabasic and eclogite xenoliths have been derived from depths of 100-180 km and 75-150 km respectively. The Kalyandurg and Brahmanpalle clusters have sampled the typical Archaean subcontinental lithospheric mantle (SCLM) with a low geotherm (35 mW/m 2 ) and harzburgitic to lherzolitic rocks with median X mg olivine > 0.93. The base of the depleted lithosphere at 185-195 km depth is marked by a 10-15 km layer of strongly metasomatised peridotites (X mg olivine > ~0.88). The Anampalle and Wajrakarur clusters 60 km to the NW show a distinctly different SCLM; it has a higher geotherm (37.5 to 40 mW/m 2 ) and contains few subcalcic harzburgites, and has a median X mg olivine = 0.925. In contrast, the kimberlites of the Uravakonda and WK-7 clusters sampled quite fertile (median X mg olivine ~0.915) SCLM with an elevated geotherm (> 40 mW/m 2 ). The lamrophyres, basanites and melanephelinites associated with the Deccan Volcanic Province entrain both ultramafic and mafic xenoliths. The ultramafic group is represented by (i) spinel lherzolites, harzburgites, and (ii) pyroxenites. Single pyroxene granulite and two pyroxene granulites constitutes the mafic group. Temperature estimates for the West Coast xenoliths indicate equilibration temperatures of 500-900 o C while the pressure estimates vary between 6-11 kbar corresponding to depths of 20-35 km. This elevated geotherm implies that the region is characterized by abnormally high heat flow, which is also supported by the presence of linear array of hot springs along the West Coast. Spinel peridotite xenoliths entrained in the basanites and melanephelinites from the Kutch show low equilibrium temperatures (884-972°C). The estimated pressures obtained on the basis of the absence of both plagioclase and garnet in the xenoliths and by referring the temperatures to the West Coast geotherm is ~ 15 kbar (40-45 km depth). The minimum heat flow of 60 to 70 mW/m 2 has been computed for the Kutch xenolith (Bhujia hill), which is closely comparable to the oceanic geotherm. Xenolith studies from the West Coast and Kutch indicate that the SCLM beneath is strongly metasomatised although the style of metasomatism is different from that below the Dharwar Craton.

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The Deccan flood basalt province of west-central India has been linked to the Reunion plume, and reconstructions suggest that the Kutch region was over the plume at the time of Deccan volcanism at 65-68 Ma. Field relations and isotopic data indicate that the alkaline basalts of Kutch, which occur to the NNW of the main Deccan tholeiitic province, preceded the main flood-basalt volcanism and are related to the limited plume incubation period. Several plugs of these alkali basalts contain small spinel peridotite xenoliths of mantle origin. The minerals of the spinel peridotites have been analyzed for their major, trace, and rare-earth element (REE) concentrations using electron microprobe and LAM-ICPMS techniques. The modes and mineral chemistry, especially of the clinopyroxenes, indicate a fertile mantle; modeling of the clinopyroxene REE data is consistent with <5 to 15% of partial melting of a primitive mantle source material in the spinel peridotite field. Subse quent cryptic metasomatism introduced LREE, U, Th, and Zr. The xenoliths may represent: (1) young lithosphere generated during the lithospheric extension that preceded the main Deccan vol canism; or (2) material from the uppermost parts of the rising plume, brought to the surface by the first stages of the volcanism. Their low equilibration temperatures (<900°C) and their textural and chemical similarity to xenolith suites from other Phanerozoic intraplate settings favor the first alter native. However, the extensive cryptic metasomatism may reflect the influence of the rising Deccan plume.

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