Chemical and isotopic constraints on the origin of basalts from Ninetyeast Ridge, Indian Ocean: results from DSDP Legs 22 and 26 and ODP Leg 121

Abstract

There are significant variations in isotope ratios and highly incompatible element ratios between sites, which suggest that the mantle source for the ridge basalts was compositionally variable. The authors agree with previous models that relate Ninetyeast Ridge to a mantle plume in the southern Indian Ocean. The tholeiitic, iron-enriched, and voluminous character of the ridge basalts is typical of oceanic islands associated with plumes on or near a mid-ocean ridge. The major element data, like the gravity data, strongly suggest that the ridge was erupted on or very close to an active spreading center. Isotopically, the most likely plume that created the excess magmatism on the Ridge is the Kerguelen-Heard plume system, but the Ninetyeast Ridge basalts do not represent a simple mixing of the Kerguelan plume and mid-ocean Ninetyeast Ridge basalt mantle. -from Authors