Deep sourced fluids for peridotite carbonation in the shallow mantle
wedge of a fossil subduction zone: Sr and C isotope profiles of OmanDP
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.
87Sr/86Sr 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. δ13C in the listvenites and
serpentinites range from -10.6‰ to 1.92‰, including a small organic
carbon component with δ13C as low as -27‰ that
reaffirms the presence of carbonaceous material in Hole BT1B. The source
of the radiogenic Sr was probably similar to Hawasina metasediments that
underlie the ophiolite, with values up to 0.7241 in clastic lithologies.
These results indicate that decarbonation reactions in such clastic
sediments, during subduction at temperatures above 500°C, form carbon
rich fluids that could have migrated updip, supplying radiogenic
87Sr/86Sr and fractionated
δ13C to BT1B serpentinites and listvenites.