U-series isotope data on Lau Basin glasses: The role of subduction-related fluids during melt generation in back-arc basins

Abstract

New thermal ionization mass spectrometry U-series disequilibrium data are presented for 24 basaltic to dacitic glasses from active spreading centres in the back-arc Lau Basin (SW Pacific), together with additional inductively coupled plasma mass spectrometry trace element analyses and Sr-Nd-Pb isotope data. Valu Fa Ridge samples, adjacent to the arc front, have high U/Th and (230Th/238U) <1, implying a recent (≪350 ka) addition of a U-rich slab-derived fluid. The Valu Fa data can be combined with existing 230Th-238U data for the Central Tonga arc to infer a fluid addition event at ∼ 50 ka. The similar sources and time scales for fluid transfer beneath the Valu Fa Ridge and beneath the arc it..