Late Quaternary hydrothermal sedimentation adjacent to the Central Lau Spreading Center

The partition geochemistry of 10 sediment cores collected adjacent to the southward-propagating Central Lau Spreading Center (CLSC) has been studied. The hydrothermal oxide component in these sediments is mainly formed of Mn oxides containing other hydrothermally associated elements (e.g., Fe, Zn, Cu, Mo and Pb). The Mn oxides represent distal plume fall-out derived from hydrothermal vents. Hydrothermal Mn accumulation rates are between 2.6 and 74.4 mg cm−2 ka−1 during the 0–30-ka period and between 2.1 and 12.8 mg cm−2 ka−1 during the 30–120-ka period. Recent (<30 ka) hydrothermal input to the sediments adjacent to the CLSC has been more variable than in the older sediments from the area. This may be attributed to localised hydrothermal activity occurring behind the propagator, and possibly to magma chamber development. Periods of enhanced hydrothermal input from the CLSC at ca. 30 ka and 175 ka appear to be contemporaneous along the CLSC; however, an enrichment in Mn at ca. 112 ka probably represents distal hydrothermal plume fall-out from increased activity on the Valu Fa Ridge in the southern Lau Basin. Hydrothermal Mn input derived from the CLSC is below that from the VFR.