Abstract
Serpentinites are important reservoirs of fluid-mobile elements in subduction zones, contributing to volatiles in arc magmas and their transport into the Earth’s mantle. This paper reports halogen (F, Cl, Br, I) and B abundances of serpentinites from the Dominican Republic, including obducted and subducted abyssal serpentinites and forearc mantle serpentinites. Abyssal serpentinite compositions indicate the incorporation of these elements from seawater and sediments during serpentinization on the seafloor and at slab bending. During their subduction and subsequent lizardite-antigorite transition, F and B are retained in serpentinites, whilst Cl, Br and I are expelled. Forearc mantle serpentinite compositions suggest their hydration by fluids released from subducting altered oceanic crust and abyssal serpentinites, with only minor sediment contribution. This finding is consistent with the minimal subduction of sediments in the Dominican Republic. Forearc mantle serpentinites have F/Cl and B/Cl ratios similar to arc magmas, suggesting the importance of serpentinite dehydration in the generation of arc magmatism in the mantle wedge.
Highlights
Subduction of hydrated lithologies provides a mechanism for recycling fluid-mobile elements (FME) from surface reservoirs, such as the hydrosphere, atmosphere and sediments, into the Earth’s mantle
The halogen ratios of forearc mantle serpentinites may provide insight into the make-up of the slab in a given subduction complex, and help elucidate the extent to which abyssal serpentinites, altered oceanic crust, and sediments contribute to slab-derived fluids
Our paper expands on this work by presenting the halogen and B contents of Dominican Republic (DR) serpentinites, including those of abyssal origin and of the forearc mantle, with the purpose of evaluating the behaviour and fractionation of these elements in subduction zones
Summary
Subduction of hydrated lithologies provides a mechanism for recycling fluid-mobile elements (FME) from surface reservoirs, such as the hydrosphere, atmosphere and sediments, into the Earth’s mantle. This complex was formed by the subduction of the Proto-Caribbean oceanic lithosphere beneath the NE-migrating Caribbean plate. Samples representing obducted abyssal serpentinites were collected from the PPC and the northern RSJC (RD31, RD4, RD6a, RD8b) They are comprised of lizardite (low temperature serpentine phase) pseudomorphically replacing olivine and orthopyroxene. Samples representing subducted abyssal serpentinites were collected from the mélanges of Arroyo Sabana (RD87, RD89) and Jagua Clara (RD21a, RD91, RD94, RD650c, RD6-52a, RD6-54a) of the RSJC They are composed of antigorite (high temperature phase), with minor chlorite, talc and tremolite, except for RD94 that is predominantly lizardite with minor antigorite blades. A lack of metamorphic olivine in these samples further constrains their depth to
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