Re-Os and Lu-Hf isotope evidence for recycled materials in the source of the Ontong Java Plateau lavas
Abstract
Previous studies of Ontong Java Plateau (OJP) lavas reveal ocean-island-like Pb, Nd, and Sr isotopic signatures that fall within a limited range yet define two distinct isotopic types, the Singgalo and Kwaimbaita. Lavas of both groups are products of very large degrees of melting. It is not clear what the origin of the two groups is, although the Kwaimbaita signature has been suggested to represent the plateau's main mantle source, probably originating from the lower mantle. Our work on samples from the central part of the Solomon island of Malaita and Ocean Drilling Program (ODP) Sites 807, 1185, and 1187 shows that the two groups of OJP lavas also possess distinct age-corrected 187Os/188Os signatures, (0.117-0.170 for Kwaimbaita-type lavas and 0.279-0.421 for Singgalo-type lavas) and different from ocean-ridge basalt values (average 0.125). Hf isotope data for the same samples show a slight difference between Singgalo- and Kwaimbaita-type lavas in 176Hf/177Hf, consistent with previous results for ODP lavas. The Re-Os and Lu-Hf results (1) reinforce the interpretation that the Kwaimbaita magma type is derived from the principal OJP mantle source, inferred to be non-chondritic mantle similar to that involved in the source of several other flood basalt provinces; and (2) suggest the influence of old, lower continental crustal material or ancient pelagic sediments in the source of the Singgalo-type lavas. A lower crustal influence may be explained by incorporation of ancient, delaminated mafic continental crust into a thermochemical plume; such incorporation could provisionally involve dense ex-crustal material that had accumulated in the lower mantle or less dense material that had stagnated at mid-mantle depths.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T31B2595T
- Keywords:
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- 1040 GEOCHEMISTRY / Radiogenic isotope geochemistry;
- 8137 TECTONOPHYSICS / Hotspots;
- large igneous provinces;
- and flood basalt volcanism;
- 8415 VOLCANOLOGY / Intra-plate processes