Exhumed serpentinites and their tectonic significance in non-collisional orogens

We studied serpentinite samples from five river basins in a segment of the non-collisional Andean orogen in Ecuador (Cordillera Real). All samples are fully serpentinized with antigorite as the main polymorph, indicative of high-temperature serpentinization, while spinel is the only relic phase. Whole-rock rare earth element data suggest an abyssal setting for the protoliths. In-situ B isotope data on antigorite (delta 11B = -15.9‰ to +5.7‰) and chlorite (delta 11B = -6.3‰ to -3.6‰) favor serpentinization by crust-derived metamorphic fluids in a mantle wedge setting. Our data suggest four different mantle wedge-derived serpentinite slivers draining into the northern Cordillera Real stream network, likely associated with Triassic, Jurassic-Early Cretaceous, and potentially Late Cretaceous-Paleocene high-pressure low-temperature metamorphic sequences. We propose that serpentinites in non-collisional orogens are sourced from underplated slab slivers that undergo intense serpentinization by crust-derived metamorphic fluids in the mantle wedge prior to their exhumation during extensional phases.