Geochemical Constraints on the Origin of the Ninetyeast Ridge, Indian Ocean
Abstract
The Ninetyeast Ridge (NER) is a south to north trending, 5000 km-long chain of submarine volcanoes extending from 31 degrees S to 10 degrees N where it disappears below the thick sediments of the Bengal Fan. The basaltic basement of the NER was sampled by DSDP and ODP drilling at 7 sites (basalt recoveries of 35 cm to 119 m). Drill core basalt has the geochemical characteristics (isotopic and incompatible element ratios) of ocean island tholeiitic basalt. With the objective of increasing sampling density and obtaining precise Ar-Ar constraints on eruption age, we dredged basalt (summer 2007) at 23 locations along the NER. Age and isotopic data are reported by Pringle et al. and Nobre-Silva et al., respectively, this session). Eruption ages, systematically increasing from south to north, are consistent with the NER forming as a hotspot track related to the Kerguelen hotspot. Based on whole-rock and glass compositions, we find that dredged basalt from the northern NER (1 to 3 degrees north) contain geochemically heterogeneous basalt (72 to 77 Ma) that reflects mixing of a Kerguelen-like component with an incompatible element depleted (e.g., Zr/Nb greater than 20) component that is geochemically distinct from SEIR MORB; however dredged basalt from the southern NER (19 to 26 degrees south) contain basalt (40 to 50 Ma) with the geochemical characteristics of Amsterdam or St. Paul or Kerguelen Island basalts. The geochemical differences between basalt from these three islands imply geochemically distinct sources; consequently, we conclude that the southern NER formed as an age progressive hotspot track that is related to both the Amsterdam/St. Paul and Kerguelen hotspots.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T54B..04F
- Keywords:
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- 8137 Hotspots;
- large igneous provinces;
- and flood basalt volcanism