Cycling of CO2 and H2O constrained by experimental investigation of a model ophicarbonate at deep subduction zone conditions

Eguchi, James; Dasgupta, Rajdeep

doi:10.1016/j.epsl.2022.117866

Cited by 7 publications

(20 citation statements)

References 67 publications

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“…Our experimental results revealed that H 2 O/aqueous fluids may depress the melting temperatures of carbonated basalts by hundreds of °C, resulting in the solidus of subducted oceanic crust intersecting with warm/cold slab geotherms, and enabling the extraction of slab‐trapped carbon to the convecting mantle by hydrous carbonatitic liquids at depths below ∼150 km. Combined with data from previous experiments, we suggest that hydrous carbonatitic liquids should provide a pervasive carbon recycling mechanism for most subducted carbon‐bearing rocks, that is, altered basalts, metagabbro (Poli, 2015), marls and limestones (Schettino & Poli, 2020), ophicarbonates (Eguchi & Dasgupta, 2022; Zhang et al., 2021), and carbonated pelites (Chen et al., 2023; Grassi & Schmidt, 2011; Thomsen & Schmidt, 2008). Water produced by dehydration reactions over the entire depth of a subducting slab is critical for removing carbon that has survived beyond subarc depths.…”

Section: Discussionsupporting

confidence: 69%

Carbon Dioxide Released From Subducted Oceanic Crust by Hydrous Carbonatitic Liquids

Zhang,

Wang,

et al. 2023

Geophysical Research Letters

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Aqueous fluids are essential to extract slab‐trapped carbon at forearc to subarc depths and interpret the decarbonation efficiency of global subduction zones. A large amount of carbon survives beyond subarc depths. The behavior of such carbon, however, remains unclear owing to a lack of experimental studies. Here, we investigate the decarbonation behavior of carbonated oceanic crust containing different amounts of H2O at pressures from subarc depths to the top of the mantle transition zone. We find that calcium‐rich carbonatitic liquids can form at temperatures of ∼950–1,150°C at depths below ∼150–300 km, corresponding to warm/cold thermal regimes in most subduction zones. Therefore, hydrous carbonatitic liquids should be pervasive in subduction zones, while extensive dehydration reactions and fluid activities are critical for creating carbonatitic liquids and preventing most of the surviving carbon from being subducted into the deep Earth.

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Section: Discussionsupporting

confidence: 69%

Carbon Dioxide Released From Subducted Oceanic Crust by Hydrous Carbonatitic Liquids

Zhang,

Wang,

et al. 2023

Geophysical Research Letters

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“…In previous H 2 O-bearing melting experiments of impure limestone rocks, the solidus has also shown a decrease from >950-1100 °C at pressures below 3 GPa 42,48 to between 850-900 °C over 4.2-6 GPa 19 . Most recently, such a melting curve has been observed for ophicarbonate 49 . The trend of decreasing solidus temperatures with increasing pressure is attributed to increasing H 2 O solubility in carbonatitic liquids with increasing pressure 49 .…”

Section: Resultsmentioning

confidence: 89%

“…Most recently, such a melting curve has been observed for ophicarbonate 49 . The trend of decreasing solidus temperatures with increasing pressure is attributed to increasing H 2 O solubility in carbonatitic liquids with increasing pressure 49 . However, the mechanism by which increasing H 2 O solubility in carbonatitic liquids relates to solidus depression is unclear.…”

Section: Resultsmentioning

confidence: 89%

Pervasive hydrous carbonatitic liquids mediate transfer of carbon from the slab to the subarc mantle

Chen

Zhang

Keshav

et al. 2023

Commun Earth Environ

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Carbonatitic liquids, as a medium for transferring carbon from the slab to the mantle at subarc depths, are thought to be restricted either to the hottest conditions or to be the hydrous melting of calcium-rich lithologies (i.e., carbonated gabbro and limestone rocks) in subduction zones. In this study, high-pressure experiments on carbonated hydrous pelites demonstrate that while silicate melts are produced at 2.5–4 GPa, hydrous carbonatitic liquids clearly dominate at 5–6 GPa. The stability of Ca-rich carbonate is strongly depressed by water at pressures exceeding ~4 GPa, promoting the formation of hydrous carbonatitic liquids at temperatures as low as ~850–900 °C; these temperatures correspond to intermediate thermal regimes at depths of 150–180 km. Hence, carbonatite production beneath arcs is more pervasive than previously thought, and the carbon cycle is most likely confined to depths of less than 200 km for many subduction zones.

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“…% K 2 O) compared to the starting materials used in Y. Zhang et al (2021) and Eguchi and Dasgupta. (2022), containing no alkali (Table 1).…”

Section: Comparison With Previous Experiments On the Apparent Solidus...mentioning

confidence: 99%

“…Hence melting behavior of ophicarbonate with a certain composition cannot represent the melting behavior of all subducted ophicarbonate. In addition, the temperature interval in the experiments of Eguchi and Dasgupta (2022) was set to be as large as 100°C, which resulted in a large uncertainty in the solidus temperature. Compared to extensive experimental studies on the phase relationships of oceanic basalt (e.g., Dasgupta et al, 2004;Elazar et al, 2019;Hammouda, 2003;Keshav et al, 2022;Kiseeva et al, 2012Kiseeva et al, , 2013Poli, 2015Poli, , 2016Thomson et al, 2016;Yaxley & Brey, 2004) and pelite (e.g., Brey et al, 2015;W.…”

mentioning

confidence: 99%

Coupled Cycling of Carbon and Water in the Form of Hydrous Carbonatitic Liquids in the Subarc Region

Chen,

Keshav,

Peng

et al. 2023

JGR Solid Earth

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The melting behavior of subducted ophicarbonate is experimentally investigated under conditions relevant for slabs at subarc depths (2.5–6 GPa and 650–1000°C). Hydrous carbonatitic liquids appear between 900 and 950°C at 2.5 GPa, between 800 and 850°C at 4–5 GPa, and at ∼800°C over 6 GPa. Water significantly depresses the thermal stability of carbonate, which drives the formation of hydrous carbonatitic liquid at low temperatures realistic for most subduction zones. Ophicarbonate fully dehydrates prior to wet melting. From an experimental point of view, the melting of ophicarbonate is essentially equal to the fluid–present melting of magnesite–bearing wehrlite lithology (i.e., meta–ophicarbonate). In the natural subduction process, the melting of meta–ophicarbonate occurs only when external water is available assuming dehydration fluid by ophicarbonate has been efficiently expelled at shallower depths. In the framework of the previously constructed dehydration history of subducting slab, the flux melting of meta–ophicarbonate at the slab–mantle interface is examined to be feasible under majority of geothermal conditions, even in cold subduction zones. Thus, hydrous carbonatitic liquid acts as a pervasive agent to transfer carbon from the slab surface to the mantle wedge at shallow depths beneath arcs. In contrast, ophicarbonate within the slab–serpentinized mantle just undergoes dehydration, and the vast majority of carbon retained in these lithologies is likely transported deeper into the mantle.

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Cycling of CO2 and H2O constrained by experimental investigation of a model ophicarbonate at deep subduction zone conditions

Cited by 7 publications

References 67 publications

Carbon Dioxide Released From Subducted Oceanic Crust by Hydrous Carbonatitic Liquids

Carbon Dioxide Released From Subducted Oceanic Crust by Hydrous Carbonatitic Liquids

Pervasive hydrous carbonatitic liquids mediate transfer of carbon from the slab to the subarc mantle

Coupled Cycling of Carbon and Water in the Form of Hydrous Carbonatitic Liquids in the Subarc Region

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