Geochemical Constraints on Spatial‐Temporal Distribution and Origin of Anomalous Mantle in the Western Pacific Basins

Abstract Seafloor basalt samples recovered from the Caroline Basin (CB), the Parece Vela Basin (PVB), and the Western Philippine Sea Plate (WPSP) are analyzed for whole‐rock major and trace elements (including H 2 O), Sr‐Nd‐Pb‐Hf isotopes and 40 Ar‐ 39 Ar age‐dating. Two geochemically distinct mantle domains (I and II) are identified for the first time in these marginal basins and their spatio‐temporal distribution and origin are discussed. The Mantle Domain I (PVB and Ayu Trough basalts) has normal mantle‐like H 2 O/Ce ratios and TiO 2 /V ratios, whereas the Mantle Domain II (WPSP and CB basalts, and Mariana fore‐arc basalts) has distinctly lower TiO 2 /V, distinctly more radiogenic Sr and Pb isotopes and higher H 2 O/Ce ratios. The normal mantle‐like H 2 O/Ce of Mantle Domain I indicates negligible influence from subducted components. We provide evidences that the Mantle Domain II extends to the Pacific large low shear velocity province (LLSVP) based plate tectonic reconstruction, and such an Indian‐type mantle ubiquitously exists beneath the Mesozoic Pacific Plate. Our geochemistry results indicate that the giant mantle plumes in LLSVP have played a key role in transporting lower mantle depleted and H 2 O‐rich components to the upper mantle.