Age and geochemistry of volcanic clasts from DSDP Site 445, Daito Ridge and relationship to Minami-Daito Basin and early Izu-Bonin arc magmatism

• We report Ar–Ar ages of detrital minerals in cores from DSDP Site 445, Daito Ridge.
• We examine the geochemistry of volcanic clasts in sediments from DSDP Site 445.
• Clasts are subduction-related, and unlike OIB-like basalts from the Daito Basin.
• Clasts have Sr, Nd, Pb and Hf isotope ratios similar to the early Izu-Bonin arc.
• Geographic and tectonic relationships between differing magma sources are explored.

The age and character of volcanism on the Daito Ridge is important for understanding the tectonic evolution of the Philippine Sea plate and the initiation of subduction that formed the Izu-Bonin-Mariana Island arc at about 50 Ma. We report new major, trace element and Nd, Sr, Pb and Hf isotope data for basaltic clasts from volcaniclastic sediments drilled at DSDP Site 445 on the Daito Ridge, and new Ar–Ar ages for minerals from the same location. Ages indicate that volcanic material in the core is as young as 47–49 Ma, similar in age to OIB-like basaltic sills from the adjacent Minami-Daito Basin and similar in age to the earliest volcanic rocks from the Izu-Bonin-Mariana (IBM) Island arc. The basaltic clasts have the major and trace element character of subduction-related rocks from mature island arc settings, and are unlike boninites or other rocks formed in proposed arc initiation sequences. Isotopic compositions are consistent with melting of mantle wedge with an Indian Ocean signature (i.e., elevated 208Pb/204Pb relative to 206Pb/204Pb and 177Hf/176Hf relative to 143Nd/144Nd), containing subduction components derived from seawater altered Pacific Ocean MORB. Isotopic compositions overlap with those for boninites from the early northern IBM arc, suggesting that extraction of arc magma during Cretaceous–Eocene magmatism on the Daito Ridge and adjacent remnant arcs in the northern Philippine Sea, formed part of the depleted mantle wedge that was remelted during the initiation of IBM arc magmatism. Based on tectonic models, the Daito arc mantle wedge was probably isolated and cut-off from volatile replenishment by the initiation of subduction along the orthogonal trend of the proto-IBM arc. Collision of the Oki Daito Ridge may also have contributed to the waning of arc volcanism on the Daito Ridge and the contemporaneous eruption of OIB-like basalts in the Minami-Daito Basin.