Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
Volume 125, Issue 6, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2019JB019060
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Funding
- International Continental Scientific Drilling Project (ICDP)
- Sloan Foundation-Deep Carbon Observatory [2014-3-01]
- National Science Foundation [NSF-EAR-1516300]
- NASA-Astrobiology Institute [NNA15BB02A]
- German Research Foundation [DFG: KO 1723/21-1]
- Japanese Society for the Promotion of Science (JSPS) [16H06347, KAKENHI 16H02742]
- European Research Council (ERC Adv) [669972]
- Swiss National Science Foundation [SNF:20FI21_163073]
- JAMSTEC
- TAMU-JR Science Operator
- Sultanate of Oman Ministry of Regional Municipalities and Water Resources
- Oman Public Authority of Mining
- Sultan Qaboos University
- CRNS-Univ. Montpellier II
- Columbia University of New York
- University of Southampton
- The Institute for Geoscience Research (TIGeR)
- NWO VIDI grant [WE.267002.1]
- ERC starting grant nanoEARTH [852069]
- European Research Council (ERC) [669972, 852069] Funding Source: European Research Council (ERC)
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The occurrence of the quartz-carbonate alteration assemblage (listvenite) in ophiolites indicates that ultramafic rock represents an effective sink for dissolved CO2. However, the majority of earlier studies of ultramafic rock carbonation had to rely on the surface exposure of reaction textures and field relationships. Here we present the first observations on ultramafic rock alteration obtained from the 300 m deep BT1B drill hole, ICDP Oman Drilling Project, allowing for a continuous and high-resolution investigation. Hole BT1B recovered continuous drill core intersecting surface alluvium, 200 m of altered ultramafic rock comprising mainly listvenite and minor serpentinite bands at 90 and 180 m depth, and 100 m of the underlying metamorphic sole. Textural evidence suggests that the carbonation of fully serpentinized harzburgite commenced by non-equilibrium growth of spheroidal carbonate characterized by sectorial zoning resulting from radially oriented low-angle boundaries. In the serpentinite, carbonate spheroids are composed of alternating magnesite cores and dolomite rims, whereas texturally similar carbonate in the listvenite is composed of Fe-rich magnesite cores and Ca-Fe-rich magnesite rims. The distinct compositions and mineral inclusions indicate that the carbonation extent was controlled by fluid accessibility resulting in the simultaneous formation of limited carbonate in the serpentinite bands and complete carbonation in the listvenite parts of BT1B. The presence of euhedral magnesite overgrowing spheroidal carbonate in the listvenite suggests near-equilibrium conditions during the final stage of carbonation. The carbonate clumped isotope thermometry constrains carbonate crystallization between 50 degrees C and 250 degrees C, implying repeated infiltration of reactive fluids during ophiolite uplift and cooling.
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