Petrology and geochemistry of the Mesoproterozoic Vattikod lamproites,Eastern Dharwar Craton,southern India: evidence for multiple enrichment of sub-continental lithospheric mantle and links with amalgamation and break-up of the Columbia supercontinent

Numerous lamproite dykes are hosted by the Eastern Dharwar Craton, southern India, particularly towards the northwestern margin of the Cuddapah Basin. We present here a comprehensive mineralogical and geochemical (including Sr and Nd isotopic) study on the lamproites from the Vattikod Field, exposed in the vicinity of the well-studied Ramadugu lamproite field. The Vattikod lamproites trend WNW–ESE to NW–SE and reveal effects of low-temperature post-magmatic alteration. The studied lamproites show porphyritic texture with carbonated and serpentinized olivine, diopside, fluorine-rich phlogopite, amphibole, apatite, chromite, allanite, and calcite. The trace-element geochemistry (elevated Sr and HFSE) reveals their mixed affinity to orogenic as well as anorogenic lamproites. Higher fluorine content of the hydrous phases coupled with higher whole-rock K₂O highlights the role of metasomatic phlogopite and apatite in the mantle source regions. Trace-element ratios such as Zr/Hf and Ti/Eu reveal carbonate metasomatism of mantle previously enriched by ancient subduction processes. The initial ⁸⁷Sr/⁸⁶Sr-isotopic ratios (calculated for an assumed emplacement age of 1350 Ma) vary from 0.7037 to 0.7087 and ?Nd range from ??10.6 to ??9.3, consistent with data on global lamproites and ultrapotassic rocks. We attribute the mixed orogenic–anorogenic character for the lamproites under study to multi-stage metasomatism. We relate the (1) earlier subduction-related enrichment to the Paleoproterozoic amalgamation of the Columbia supercontinent and the (2) second episode of carbonate metasomatism to the Mesoproterozoic rift-related asthenospheric upwelling associated with the Columbia breakup. This study highlights the association of lamproites with supercontinent amalgamation and fragmentation in the Earth history.