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- Title
Carbon Geochemistry of the Active Serpentinization Site at the Wadi Tayin Massif: Insights From the ICDP Oman Drilling Project: Phase II.
- Authors
Ternieten, Lotta; Früh‐Green, Gretchen L.; Bernasconi, Stefano M.
- Abstract
A large part of the hydrated oceanic lithosphere consists of serpentinites exposed in ophiolites. Serpentinites constitute reactive chemical and thermal systems and potentially represent an effective sink for CO2. Understanding carbonation mechanisms within ophiolites are almost exclusively based on studies of outcrops, which can limit the interpretation of fossil hydrothermal systems. We present stable and radiogenic carbon isotope data that provide insights into the isotopic trends and fluid evolution of peridotite carbonation in ICDP Oman Drilling Project drill holes BA1B (400‐m deep) and BA3A (300‐m deep). Geochemical investigations of the carbonates in serpentinites indicate formation in the last 50 kyr, implying a distinctly different phase of alteration than the initial oceanic hydration and serpentinization of the Samail Ophiolite. The oldest carbonates (∼31 to >50 kyr) are localized calcite, dolomite, and aragonite veins, formed between 26°C and 43°C and related to focused fluid flow. Subsequent pervasive small amounts of dispersed carbonate precipitated in the last 1,000 years. Macroscopic brecciation and veining of the peridotite indicate that carbonation is influenced by tectonic features allowing infiltration of fluids over extended periods and at different structural levels such as along fracture planes and micro‐fractures and grain boundaries, causing large‐scale hydration of the ophiolite. The formation of dispersed carbonate is related to percolating fluids with δ18O lower than modern ground and meteoric water. Our study shows that radiocarbon investigations are an essential tool to interpret the carbonation history and that stable oxygen and carbon isotopes alone can result in ambiguous interpretations. Plain Language Summary: Water‐rock interactions that have biological and economic importance have received increasing interest in recent years. Carbon species, stored in the atmosphere, biosphere, oceans, and lithosphere, are profoundly affected by biotically and abiotically controlled exchange reactions among these reservoirs. Carbon is an essential element for life and contributes to the greenhouse effect in the form of CO2 and CH4. Unraveling water‐rock reactions that transform atmospheric CO2 into thermodynamically stable carbonates helps to better understand long‐term carbon storage in the lithosphere and its long‐term influence on climate and to better evaluate the potential for life within the lithosphere. This study uses samples recovered by drilling mantle sequences of the Wadi Tayin Massif in Oman and presents chemical data to evaluate carbon sources, speciation, and transformations. The Wadi Tayin Massif is located in the Samail Ophiolite and comprises mantle rocks. Mantle rocks react in contact with water to form serpentine and create an environment that promotes the transformation of CO2 into carbonates. Our results demonstrate large‐scale carbonization of the massif and a dominance of dispersed carbonate formation below the surface. Our study provides insights into the carbon cycle and will help to evaluate the potential of mantle rocks to store carbon and sustain life. Key Points: Two carbonate occurrences are observed: localized dolomite, calcite, and aragonite veins and pervasive dispersed carbonatesCarbonate precipitation in the peridotite occurred in the last 50 kyr at moderate temperatures, post‐dating ocean‐floor serpentinizationThe oxygen isotope composition of dispersed carbonates indicates precipitation from highly 18O‐depleted fossil groundwater
- Subjects
SERPENTINITE; HYDROTHERMAL carbonization; GEOCHEMISTRY; LITHOSPHERE; PETROLOGY; HISTORICAL geology
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 12, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB022712