Collaborative Research: Origins of the Ontong Java Plateau, SW Pacific: A Stratigraphic and Geochemical Study of Exposed Plateau Basement in the Solomon Islands, Part 2

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9612112 Duncan This project is for a continuation of research into the origin and evolution of the world's largest oceanic plateau, the Ontong Java Plateau (OJP) in the SW Pacific. Previously funded study, complementing work on submarine OJP lavas drilled by the Ocean Drilling Program (ODP), focused on plateau basement sections on Santa Isabel and Malaita, Solomon Islands. This research involves the following tasks. FIELDWORK: Detailed, stratigraphically controlled sampling in south and southeastern Makira, in what is expected to be the deepest part of the Makiran section. 40Ar-39Ar DATING: Dating of samples from throughout the Makiran section is required to determine if 90 Ma and/or 122 Ma lavas are present, and to establish the significance and thickness of the 34 Ma and 64 Ma events. GEOCHEMISTRY AND PETROGRAPHY: Systematic major and trace element, and Nd-Pb-Sr isotopic analyses are required to define Makiran geochemical stratigraphy; in particular, the geochemical variation of OJP-type lavas with depth, the nature and stratigraphic extent of the broadly MORB-like basalts, and the nature and causes of intercalation of the two types. PLATINUM GROUP ELEMENTS (PGEs): Results from previous study show that lavas from Malaita and ODP drill sites are enriched in the siderophile elements W and Mo, and may indicate a core-mantle boundary origin for the OJP's mantle source. Further evaluation of this hypotheses requires determination of abundances of the ultra-siderophilic PGEs for a subset of OJP lavas.