Intra-segment variations in subduction influence along the Eastern Lau Spreading Center and Valu Fa Ridge, Lau Backarc Basin, Southwest Pacific

Abstract

This manuscript presents results of geologic mapping along the Eastern Lau Spreading Center and Valu Fa Ridge, Lau backarc basin, southwest Pacific. The study documents geologic variations within six second-order spreading segments, expressed primarily in the morphology and depth of the spreading axis that depart from normal mid-ocean ridge (MOR) trends and are superimposed on the first order variations correlated with proximity to the arc volcanic front. These along-axis variations show a positive correlation with 206Pb/204Pb ratios from axial lavas, a commonly used indicator of relative subduction input. This suggests that local variations in subduction influence, mostly due to effects on magmatism, may be expressed as local variations in the geologic characteristics of the ridge. The nature and distribution of these variations, along with the observation of similar patterns in other backarc environments, suggests that the processes which control backarc spreading share a deep connection with arc processes.