Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles

Abstract

Volatiles expelled from subducted plates melt the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonised lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Qκ-1/Qµ-1 > 0.6) and VP/VS (>1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids towards the back-arc. The strongest attenuation (1000/QS~20), characterising melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper plate properties, past tectonics, and resulting melt pathways, collectively condition volcanism.

Global Hydrogen Production During High‐Pressure Serpentinization of Subducting Slabs

“…Hick et al. (2022) came to a similar conclusion using seismic attenuation models, showing that the Lesser Antilles Island Arcs were likely formed through devolatilization of the subducting slab, with the pre‐subduction tectonic history of the ocean slab imparting a strong control on the evolution of the mantle wedge and arc. Above the forearc mantle, fluid inclusions from the volcanic arc of the Lesser Antilles preserve strongly positive δ 11 B signatures, interpreted to be derived from the serpentinization of the oceanic mantle (Cooper et al., 2020).…”

“…Recently, a number of studies have developed techniques to map features forward in time, from ocean basins onto subducted slabs (Harmon et al., 2019; Hicks et al., 2022; McGirr et al., 2021). Here we extend the approach of McGirr et al.…”