Residue-Melt Relationships; Os isotopes from the Ontong Java Plateau
Abstract
The Os isotope composition of mantle-derived melts and their associated residues commonly do not overlap, even for simplest case of MORB and abyssal peridotites. This study utilises basalts drilled on ODP Leg 192 from the Earth's largest igneous province, the Ontong Java Plateau (OJP) and mantle peridotites from the island of Choiseul in the Solomon Islands, which are part of the arc-OJP collision zone. Trace element studies suggest that the peridotites are residues to the OJP. ODP Leg 192 basalts from across the plateau yield a Re-Os isochron age of 121.5±1.7 Ma and an initial 187Os/188Os ratio of 0.1295±0.0011. The initial Os isotope value from the isochron is within error of many of the Choiseul peridotites, although they extend to sub-chondritic values. High Re contents (>1000 ppt) in the basalts suggest that they are produced by melting beyond suphide-out in the mantle, corresponding to ∼30% partial melting. By contrast, the peridotites record ∼20% partial melting. However, their very low S contents (<25 ppm) indicate that although they have not reached sulphide-out they are residues to high-temperature melting beneath the OJP. The generation of such a high precision isochron using the Re-Os isotope system indicates the source of the OJP is remarkable homogenous at the scale of melting beneath the OJP, but that the Choiseul peridotites represent lower melting residues at the edges of the plume which produced the OJP.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....14351P