Petrogenesis of basaltic lavas from the West Pacific Seamount Province: Geochemical and Sr‐Nd‐Pb‐Hf isotopic constraints

Abstract

In this study we report new major and trace element, Sr-Nd-Pb-Hf isotopic compositions and Ar-Ar ages for basaltic lavas from seven poorly studied seamounts/guyots in the Western Pacific Seamount Province (WPSP). A review of new and published Ar-Ar ages for seamounts/guyots confirm no linear age progression, as would be expected if these seamounts were produced by the Pacific Plate moving over a stationary mantle plume. These samples exhibit an alkalic character and can be produced by small-degree partial melting of garnet pyroxenite with CO₂. Their isotopic data identify four mantle end-members (DMM, EMI, EMII and HIMU) in the WPSP source region. These results confirm previous studies that invoke multiple contemporaneous plumelets in the region and a heterogeneous upper mantle reservoir which has been overprinted by multiple discrete hotspots, which create an anomalous and heterogeneous upper mantle because of mixing/overlapping EMI, EMII, and HIMU tracks, and age progressive volcanism is totally obscured. We propose a model where relict fragments of enriched mantle with distinct isotopic compositions residing in the upper mantle were a product of the formation of the adjacent large oceanic plateaus. These events introduce heterogeneity in the depleted mantle. The infiltration and metasomatism of these relict enriched components by carbonatitic fluids from the low velocity zone, create a source that then underwent small degrees of decompressional melting. The partial melts exploited pre-existing lithospheric faults as an upwelling conduit and the resultant seafloor lava flows have obscured evidence to those preexisting lithospheric faults.