The fate of carbonate in oceanic crust subducted into earth's lower mantle

Drewitt, James W. E.; Walter, Michael J.; Zhang, Hongluo; McMahon, S. C.; Edwards, David J.; Heinen, Benedict J.; Lord, O. T.; Anzellini, Simone; Kleppe, Annette K.

doi:10.1016/j.epsl.2019.01.041

Cited by 32 publications

(30 citation statements)

References 68 publications

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“…However, the Clapeyron slope of CaCO 3 + SiO 2 → CaSiO 3 + CO 2 is positive and takes place at pressure/temperature conditions warmer than the coolest slab geotherms 40 . Observations that MgCO 3 is less thermally stable than CaCO 3 support the survival of CaCO 3 rather than MgCO 3 along a cold subducted slab geotherm to the lowermost mantle 36 , 41 (Fig. 3 ).…”

Section: Discussionmentioning

confidence: 91%

“…Whether a crossover in the carbonate-silicate exchange reaction takes place in the deep Earth depends on whether carbonates are preserved in Earth's lower mantle to at least 1800-km depth. Previous studies have identified barriers to carbon subduction and stability in the lower mantle, particularly melting 15,39 and reduction [40][41][42] . If carried in cold subducting slabs, MgCO 3 and CaCO 3 may avoid melting as their melting temperatures 22 are higher than some predicted cold slab geotherms 36 .…”

Section: Discussionmentioning

confidence: 99%

“…Any solid carbonate in the mantle will be in contact and may equilibrate with silicates in all mantle environments and with free silica in basalt-rich compositions. MgCO 3 and CaCO 3 have been observed in experiments [40][41][42] to undergo decarbonation reactions with free silica over a pressure range of~40 to 60 GPa. However, the Clapeyron slope of CaCO 3 + SiO 2 → CaSiO 3 + CO 2 is positive and takes place at pressure/temperature conditions warmer than the coolest slab geotherms 40 .…”

Section: Discussionmentioning

confidence: 99%

“…The gray dotted line indicates the reversal boundary of the carbonate-silicate exchange reaction proposed by this study, whereas previous theoretical predictions are illustrated by yellow-shaded region [28][29][30] . The cyan and orange lines indicate the decarbonation reactions of CaCO 3 + SiO 2 40 and MgCO 3 + SiO 2 41 , respectively. The black dashed line shows the melting curve of MgCO 3 -CaCO 3 system constrained by Thomson et al 22 .…”

Section: Discussionmentioning

confidence: 99%

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Reversal of carbonate-silicate cation exchange in cold slabs in Earth’s lower mantle

Dorfman

Badro

et al. 2021

Nat Commun

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The stable forms of carbon in Earth’s deep interior control storage and fluxes of carbon through the planet over geologic time, impacting the surface climate as well as carrying records of geologic processes in the form of diamond inclusions. However, current estimates of the distribution of carbon in Earth’s mantle are uncertain, due in part to limited understanding of the fate of carbonates through subduction, the main mechanism that transports carbon from Earth’s surface to its interior. Oxidized carbon carried by subduction has been found to reside in MgCO3 throughout much of the mantle. Experiments in this study demonstrate that at deep mantle conditions MgCO3 reacts with silicates to form CaCO3. In combination with previous work indicating that CaCO3 is more stable than MgCO3 under reducing conditions of Earth’s lowermost mantle, these observations allow us to predict that the signature of surface carbon reaching Earth’s lowermost mantle may include CaCO3.

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Section: Discussionmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Reversal of carbonate-silicate cation exchange in cold slabs in Earth’s lower mantle

Dorfman

Badro

et al. 2021

Nat Commun

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“…MgCO 3 (magnesite) + SiO 2 (stishovite) = MgSiO 3 (silicate) + C (diamond) + O 2 (5) (Seto et al 2008;Maeda et al 2017), and magnesite, MgCO 3 , has been observed to react with metallic iron to produce reduced phases (Dorfman et al 2018). The reactivity of iron-bearing carbonates with silica is only just starting to be investigated, however (Drewitt et al 2019). Oxygen fugacity plays a major role in determining the stability of reactions involving iron, but control of redox conditions within the diamond-anvil cell is still in its infancy.…”

Section: What Reactions Occur Between Carbonates and Silicates?mentioning

confidence: 99%

Deep Earth carbon reactions through time and space

McCammon

Bureau

Cleaves

et al. 2020

American Mineralogist

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Reactions involving carbon in the deep Earth have limited manifestations on Earth's surface, yet they have played a critical role in the evolution of our planet. The metal-silicate partitioning reaction promoted carbon capture during Earth's accretion and may have sequestered substantial carbon in Earth's core. The freezing reaction involving iron-carbon liquid could have contributed to the growth of Earth's inner core and the geodynamo. The redox melting/freezing reaction largely controls the movement of carbon in the modern mantle, and reactions between carbonates and silicates in the deep mantle also promote carbon mobility. The 10-year activity of the Deep Carbon Observatory has made important contributions to our knowledge of how these reactions are involved in the cycling of carbon throughout our planet, both past and present, and has helped to identify gaps in our understanding that motivate and give direction to future studies.

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