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. Issue 1 (12th January 2022)

• Record Type: Journal Article
• Authors: de Obeso, Juan Carlos; Kelemen, Peter B.; Leong, James M.; Menzel, Manuel D.; Manning, Craig E.; Godard, Marguerite; Cai, Yue; Bolge, Louise
• Is Part Of: Journal of geophysical research. Volume 127:Issue 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-12
• Subjects: Oman -- ophiolite -- listvenite -- serpentinization -- peridotite -- Oman Drilling Project; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022704
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: 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. 87 Sr/ 86 Sr 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 87 Sr/ 86 Sr values of up to 0.7241. δ 13 C values of total carbon in the listvenites and serpentinites range from −10.6‰ to 1.92‰. We also identified a small organic carbon component with δ 13 C as low as −27‰. Based on these results, we propose that during subduction at temperatures above >400°C, carbon‐rich fluids derived from decarbonation of the underlying sediments migrated updip and generated the radiogenic 87 Sr/ 86 Sr signature and the fractionated δ 13 C values of the serpentinites and listvenites in core BT1B. Plain Language Summary: Samples from Oman Drilling Project Hole BT1B provide a record of interactions of fluids rich in carbon dioxide with mantle rocks. These interactions lead to the formation of listvenites, rocks composed mainly of magnesite and quartz. Here, we describe the formation of listvenites in the Oman ophiolite using Strontium and Carbon isotopes to characterize the source and nature of the fluid that pervasively transform the mantle rocks that now store vast amounts of carbon dioxide. Key Points: Strontium and Carbon were added to the peridotites during alteration Strontium isotopes point to Hawasina calcite‐bearing clastic sediments C as source of fluids Alteration fluids are derived from decarbonation reactions of subducted sediments