Variable water input controls evolution of the Lesser Antilles volcanic arc

Abstract

Oceanic lithosphere carries volatiles, notably water, into the mantle via subduction at convergent plate boundaries. This subducted water exercises a key control on the production of magma, earthquakes, formation of continental crust and mineral resources. However, identifying different potential fluid sources (sediments, crust and mantle lithosphere) and tracing fluids from their release to observed surface expressions has proved challenging 1 . The two Atlantic subduction zones are valuable end members to study this deep water cycle because hydration in Atlantic lithosphere, produced by slow spreading, is expected to be highly non-uniform 2 . As part of an integrated, multi-disciplinary project in the Lesser Antilles 3 , we studied boron trace element and isotopic fingerprints of melt inclusions. These reveal that serpentine, i.e. hydrated mantle rather than crust or sediments, is a dominant supply of subducted water to the central arc. This serpentine is most likely to reside in a set of major fracture zones subducted beneath the central arc over the past ~10 Myr. Dehydration of these fracture zones is consistent with the locations of the highest rates of earthquakes and prominent low shear velocities, as well as time-integrated signals of higher volcanic productivity and thicker arc crust. These combined geochemical and geophysical data provide the clearest indication to date that the structure and hydration of the downgoing plate are directly connected to the evolution of the arc and its associated hazards.The 750 km-long Lesser Antilles volcanic arc (LAA), located along the eastern margin of the Caribbean Plate, is the result of slow (1-2 cm/year) westward subduction of Atlantic and proto-Caribbean oceanic lithosphere (Fig 1). Water hosted in hydrous phases within the subducting plate will be released as the slab sinks into the mantle and warms up. As the water migrates out of the slab the stress on faults is reduced, causing earthquakes. At the same time, the addition of water to the overlying mantle wedge reduces the solidus temperature which may enhance melting. LAA magma production rates lie at the lower end of the global range, probably due to the low convergence rates, and are very unevenly distributed, being greatest in the centre of the arc (Dominica and Guadeloupe) 4 . The LAA also displays notable along-arc variations in geochemistry, volcanic activity, crustal structure, and seismicity [5][6][7][8] . Subducting plate velocity and age are often held responsible for variations in convergent margin behaviour 9 but are unlikely to have first-order influence on lateral variations within the LAA as neither vary significantly along-strike. Instead, variations in LAA magmatism and seismicity have been proposed to reflect; (i) a combination of a strong north to south increase in sediment input 10 , (ii) subduction of bathymetric ridges below the central arc 11 , which may enhance plate stress and coupling, (iii) and/or subduction of strongly hydrated fracture zones 12 at several locations along arc (Fig. ...

Inferring Interseismic Coupling Along the Lesser Antilles Arc: A Bayesian Approach

“…In the Lesser Antilles, the subduction of fracture zones, or of oceanic ridges like the Barracuda Ridge and Tiburon Rise, have long been proposed to segment the seismogenic zone (McCann & Sykes, 1984). More recent studies found that larger b ‐values, indicative of stress release through a higher fraction of small earthquakes, and low shear‐wave velocities correlate with the location of incoming fracture zones on the American plates (Cooper et al., 2020; Schlaphorst et al., 2016). These authors relate this to excess dehydration due to fluids that are delivered into the subduction by the fracture zones.…”

Sr isotopes in arcs revisited: tracking slab dehydration using δ88/86Sr and 87Sr/86Sr systematics of arc lavas

“…It is increasingly recognised that the breakdown of serpentinite may be the main source of fluid delivered to the mantle wedge at sub-arc depths (e.g., Ringwood, 1974;John et al, 2004;Scambelluri et al, 2004;Spandler and Pirard, 2013;Cooper et al, 2020). The upper mantle section of the slab can be hydrated when the plate bends and faults near the trench (e.g., Ranero et al, 2003;Van Avendonk et al, 2011) and has been argued to form a major carrier of water into the mantle (Cai et al, 2018), although the effectiveness of serpentinization at the trench has been challenged by Korenaga (2017).…”

Halogen (F, Cl) Concentrations and Sr‐Nd‐Pb‐B Isotopes of the Basaltic Andesites From the Southern Okinawa Trough: Implications for the Recycling of Subducted Serpentinites

“… Plots of (a) Cl/K versus δ 11 B and (b) F/Nd versus δ 11 B for the lavas from southern Okinawa Trough lavas and 10 modern arcs (from GEOROC database: http://georoc.mpch-mainz.gwdg.de/georoc/ and Cooper et al., 2020; data with MgO > 4 wt.% were adopted). Each gray square represents the average values of each individual arc.…”