Mantle wedge serpentinization and exhumation of eclogites: Insights from eastern Ladakh, northwest Himalaya

Abstract

In eastern Ladakh, northwest Himalaya, serpentinite layers occur in close association with eclogites. The occurrence of metamorphic olivine and talc in serpentinites suggests that the serpentinization and eclogitization took place under similar conditions (600 °C, 20 kbar). The serpentinites and eclogites show similar deformation, including the direction of normal shearing. The highly refractory nature of the serpentinite protolith, as shown by the composition of bulk rocks and chromite and the concentrations of Re and platinum group elements, indicates their derivation from mantle wedge. We propose that the serpentinites formed by hydration of the mantle wedge as a result of dewatering of the subducted slab. The serpentinites then facilitated exhumation of the subducted rocks by acting as a lubricant. At shallow depths, sediments are generally considered to be the lubricant for the exhumation, but serpentinites may commonly take over this role at greater depths. Under sediment-poor conditions, serpentinites may contribute to the exhumation even at shallower depths. This may explain the close spatial association of serpentinites and partially hydrated peridotites with many well-known high-pressure to ultrahigh-pressure metamorphic belts worldwide.