Geochemistry and petrogenesis of mafic-ultramafic rocks from the Central Indian Ridge, latitude 8°S-17°S

Abstract:

This study investigates the formation of lower oceanic crust and geochemical variations of basalts along the Central Indian Ridge (CIR, lat. 7°45′S-17°10′S). Harzburgites, various gabbroic cumulates, medium to fine-grained oxide gabbros, diabases and pillow basalts are recovered from segment ends such as ridge-transform intersections (RTI), non-transform discontinuities (NTD) and transform offset areas by dredging. The occurrence of both harzburgites and gabbroic rocks with minor basalts at all segments ends, and leucogabbro intrusive into harzburgite at the 12°45’S NTD appear to indicate that oceanic crust at segment ends consist of mantle-derived harzburgites and gabbroic intrusions with a thin basaltic cover due to sparse magmatic activity. Basalts collected from the whole ridge area show wide compositional variations between N (normal)- and E (enriched)-MORB. T (transitional)-MORB with enriched affinities are more prominent than N-MORBs. There is no tendency of enrichment towards specific direction. (La/Sm)_N variations in MORB along the CIR (8°-21°S) fluctuates at a regional scale with local high positive anomalies which may reflect compositional heterogeneity of the sub-CIR mantle domain.