Deep Sourced Fluids for Peridotite Carbonation in the Shallow Mantle Wedge of a Fossil Subduction Zone: Sr and C Isotope Profiles of OmanDP Hole BT1B

Completely carbonated peridotites represent a window to study reactions of carbon-rich fluids with mantle rocks. Here, we present details on the carbonation history of listvenites close to the basal thrust in the Samail ophiolite. We use samples from Oman Drilling Project Hole BT1B, which provides a continuous record of lithologic transitions, as well as outcrop samples from listvenites, metasediments, and metamafics below the basal thrust of the ophiolite. Sr-87/Sr-86 of listvenites and serpentinites, ranging from 0.7090 to 0.7145, are significantly more radiogenic than mantle values, Cretaceous seawater, and other peridotite hosted carbonates in Oman. The Hawasina sediments that underlie the ophiolite, on the other hand, show higher Sr-87/Sr-86 values of up to 0.7241. delta C-13 values of total carbon in the listvenites and serpentinites range from -10.6 parts per thousand to 1.92 parts per thousand. We also identified a small organic carbon component with delta C-13 as low as -27 parts per thousand. Based on these results, we propose that during subduction at temperatures above >400 degrees C, carbon-rich fluids derived from decarbonation of the underlying sediments migrated updip and generated the radiogenic Sr-87/Sr-86 signature and the fractionated delta C-13 values of the serpentinites and listvenites in core BT1B.