Denudation of mantle harzburgites and mantle heterogeneity observed in MORB from the Central Indian Ridge, latitude 8°-17° S

Abstract

This study investigates the formation of lower oceanic crust and geochemical variationsof basalts along the Central Indian Ridge (CIR, lat. 7°45′&#8211 17°10′ S). Harzburgites, variousgabbroic cumulates, medium- to fine-grained oxide gabbros, diabases, and pillow basaltswere recovered by dredging from segment ends such as ridge-transform intersections(RTIs), non-transform discontinuities (NTDs), and transform offset areas. The occurrenceof both harzburgites and gabbroic rocks with minor basalts at all segments ends, andleucogabbro intrusive into harzburgite at the 12°45′ S NTD indicates that oceanic crust atsegment ends exposes mantle-derived harzburgites and gabbroic intrusions with a thinbasaltic cover due to sparse magmatic activity. Basalts collected along the entire ridgeshow wide compositional variations between N (normal)- and E (enriched)-mid-oceanridge basalt (MORB). T (transitional)-MORBs with enriched affinities are more prominentthan N-MORBs. There is no tendency of enrichment towards specific directions.(La/Sm)N variations in MORB along the CIR (8°&#8211 21°S) fluctuates at a regional scale withlocal high positive anomalies reflecting compositional heterogeneity of the sub-CIRmantle domain.e gabbros, diabases, and pillow basaltswere recovered by dredging from segment ends such as ridge-transform intersections(RTIs), non-transform discontinuities (NTDs), and transform offset areas. The occurrenceof both harzburgites and gabbroic rocks with minor basalts at all segments ends, andleucogabbro intrusive into harzburgite at the 12°45′ S NTD indicates that oceanic crust atsegment ends exposes mantle-derived harzburgites and gabbroic intrusions with a thinbasaltic cover due to sparse magmatic activity. Basalts collected along the entire ridgeshow wide compositional variations between N (normal)- and E (enriched)-mid-oceanridge basalt (MORB). T (transitional)-MORBs with enriched affinities are more prominentthan N-MORBs. There is no tendency of enrichment towards specific directions.(La/Sm)N variations in MORB along the CIR (8°&#8211 21°S) fluctuates at a regional scale withlocal high positive anomalies reflecting compositional heterogeneity of the sub-CIRmantle domain.