New host for carbon in the deep Earth

Boulard, E.; Gloter, Alexandre; Corgne, Alexandre; Antonangeli, Daniele; Auzende, Anne-Line; Perrillat, Jean-Philippe; Guyot, F.; Fiquet, G.

doi:10.1073/pnas.1016934108

Cited by 125 publications

(162 citation statements)

References 38 publications

(47 reference statements)

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“…4 that at 1,000 K, the minimum solubilities of carbonate minerals increase substantially with increasing pressure as e 0 increases. For example, when magnesite, expected to be an important carbonate mineral in the mantle stable up to 82 GPa (19), comes into contact with water, we predict that the aqueous fluid may contain at least millimolal levels of Mg 2+ and CO 2− 3 at ∼10 GPa and 1,000 K. As a result, magnesite is slightly soluble at the bottom of the upper mantle. Therefore, we predict that in the Earth's upper mantle aqueous fluids may be important hosts of oxidized carbon in addition to the solid phases and may transport a significant amount of dissolved carbon as carbonate ions.…”

Section: Equation Ofmentioning

confidence: 91%

“…We predict that MgCO 3 -an important mineral stable in the mantle up to 82 GPa (19) and insoluble in water at ambient conditions-becomes slightly soluble, at least millimolal levels at ∼10 GPa and 1,000 K. This result suggests that aqueous fluids may be carbon hosts and transport carbonate in the deep Earth, with important implications for the dynamics of the global carbon cycle (20,21). We validated our results at lower pressure, by comparing them with solubility data for calcite, finding good agreement with experiment.…”

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confidence: 91%

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Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Pan¹,

Spanu²,

Harrison

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

178

150

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Water is a major component of fluids in the Earth's mantle, where its properties are substantially different from those at ambient conditions. At the pressures and temperatures of the mantle, experiments on aqueous fluids are challenging, and several fundamental properties of water are poorly known; e.g., its dielectric constant has not been measured. This lack of knowledge of water dielectric properties greatly limits our ability to model water-rock interactions and, in general, our understanding of aqueous fluids below the Earth's crust. Using ab initio molecular dynamics, we computed the dielectric constant of water under the conditions of the Earth's upper mantle, and we predicted the solubility products of carbonate minerals. We found that MgCO 3 (magnesite)-insoluble in water under ambient conditions-becomes at least slightly soluble at the bottom of the upper mantle, suggesting that water may transport significant quantities of oxidized carbon. Our results suggest that aqueous carbonates could leave the subducting lithosphere during dehydration reactions and could be injected into the overlying lithosphere. The Earth's deep carbon could possibly be recycled through aqueous transport on a large scale through subduction zones.water solvation properties | carbon cycle | ab initio simulations | supercritical water W ater, a major component of fluids in the Earth's mantle (1, 2), is expected to play a substantial role in hydrothermal reactions occurring in the deep Earth at supercritical conditions (3, 4). Pressure (P) and temperature (T) increase with increasing depth (5) and at ∼400 km, where seismic discontinuities define the bottom boundary of the upper mantle, the pressure can reach ∼13 GPa and the temperature can be as high as 1,700 K (6-8). In this regime the properties of water and thus of aqueous fluids are remarkably different from those at ambient conditions. For example, water has an unusually large static dielectric constant e 0 ∼ 78 at ambient conditions; however, at the vapor-liquid critical point at 647 K, e 0 deceases to less than 10 (9), implying that ionwater interactions in solution are greatly modified. In turn these changes affect the solubility of minerals and hence chemical reactions occurring in aqueous solutions under pressure (10, 11).Measurements of the dielectric constant of water date back to the 1890s (12), but they are still limited to P < 0.5 GPa and T < 900 K, corresponding to crustal metamorphic conditions. Indeed, it is challenging to measure e 0 at high P and T because water becomes highly corrosive (11). Several models correlating experimental data suggested extrapolations of e 0 to ∼1 GPa and ∼1,300 K (e.g., refs. 13-15), which corresponds to only very shallow mantle conditions under the oceans; however, deeper mantle conditions relevant to plate tectonic processes could not be reached and different extrapolations showed poor agreement with each other (1). The current lack of knowledge of the dielectric constant of water under the P and T of the mantle hampers our ability...

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Section: Equation Ofmentioning

confidence: 91%

mentioning

confidence: 91%

Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Pan¹,

Spanu²,

Harrison

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

178

150

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“…Experimental studies and predictions by theoretical calculations suggest the formation of new carbonate structures (e.g., Isshiki et al 2004) at high pressure and temperature, some of them with carbon in tetrahedral coordination (Oganov et al 2008;Boulard et al 2011Boulard et al , 2015. In this study, we focus on the system CaCO 3 .…”

Section: Introductionmentioning

confidence: 99%

Phase transitions in the system CaCO3 at high P and T determined by in situ vibrational spectroscopy in diamond anvil cells and first-principles simulations

et al. 2016

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Schade, U. (2016): Phase transitions in the system CaCO3 at high P and T determined by in situ vibrational spectroscopy in diamond anvil cells and first-principles simulations. -Physics and Chemistry of Minerals, 43, 8, -43, 2015) and assigned to the phase transition of cc-IIIb to cc-III at 3.3 GPa. In addition, we observed a clear change between 5 and 6 GPa that is independent of the starting material and the pressure path and time path of the experiments. This apparent change in the spectral pattern is only visible in the low-frequency range of the Raman spectra-not in the infrared spectra. Complementary electronic structure calculations confirm the existence of three distinct stability regions of cc-III-type phases at pressures up to about 15 GPa. By combining experimental and simulation data, we interpret the transition at 5-6 GPa as a re-appearance of the cc-IIIb phase. In all types of experiments, we confirmed the transition from cc-IIIb to cc-VI at about 15 GPa at room temperature. We found that temperature stabilizes cc-VI to lower pressure. The reaction ccIIIb to cc-VI has a negative slope of -7.0 x 10 -3 GPa K -1 . Finally, we discuss the possibility of the dense cc-VI phase being more stable than aragonite at certain pressure and temperature conditions relevant to the Earth's mantle.3

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“…Depending on oxygen fugacity and pressure-temperature (P-T) conditions, carbon exists in the Earth's interior in the form of carbides, diamond, graphite, hydrocarbons, carbonates, and CO 2 (7)(8)(9)(10)(11). In the upper mantle, the oxygen fugacity (fO 2 ) varies from one to five log units below the fayalitemagnetite-quartz (FMQ) buffer, with a trend of a decrease with depth (6,(12)(13)(14)(15).…”

mentioning

confidence: 99%

“…The subduction of the oxidized crustal material occurs to depths greater than 600 km (4)(5)(6). The main carbon-bearing minerals of the subducted materials are carbonates, which are thermodynamically stable up to P-T conditions of the lower mantle (10,11,18). As evidenced by the compositions of inclusions in diamond, which vary from strongly reduced, e.g., metallic iron and carbides (19)(20)(21)(22)(23), to oxidized, e.g., carbonates and CO 2 (6,20,(24)(25)(26)(27)(28), carbonates may be involved in the reactions with reduced deep-seated rocks, including Fe 0 -bearing species (29)(30)(31).…”

mentioning

confidence: 99%

Mantle–slab interaction and redox mechanism of diamond formation

Palyanov

Bataleva

Sokol

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

175

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Subduction tectonics imposes an important role in the evolution of the interior of the Earth and its global carbon cycle; however, the mechanism of the mantle-slab interaction remains unclear. Here, we demonstrate the results of high-pressure redox-gradient experiments on the interactions between Mg-Ca-carbonate and metallic iron, modeling the processes at the mantle-slab boundary; thereby, we present mechanisms of diamond formation both ahead of and behind the redox front. It is determined that, at oxidized conditions, a low-temperature Ca-rich carbonate melt is generated. This melt acts as both the carbon source and crystallization medium for diamond, whereas at reduced conditions, diamond crystallizes only from the Fe-C melt. The redox mechanism revealed in this study is used to explain the contrasting heterogeneity of natural diamonds, as seen in the composition of inclusions, carbon isotopic composition, and nitrogen impurity content.carbonate-iron interaction | high-pressure experiment | mantle mineralogy | deep carbon cycle S ubduction of crustal material plays an important role in the global carbon cycle (1-6). Depending on oxygen fugacity and pressure-temperature (P-T) conditions, carbon exists in the Earth's interior in the form of carbides, diamond, graphite, hydrocarbons, carbonates, and CO 2 (7-11). In the upper mantle, the oxygen fugacity (fO 2 ) varies from one to five log units below the fayalitemagnetite-quartz (FMQ) buffer, with a trend of a decrease with depth (6,(12)(13)(14)(15). At a depth of ∼250 km, mantle is reported to become metal saturated (16, 17), which holds true for all mantle regions below, including the transition zone and lower mantle. The subduction of the oxidized crustal material occurs to depths greater than 600 km (4-6). The main carbon-bearing minerals of the subducted materials are carbonates, which are thermodynamically stable up to P-T conditions of the lower mantle (10,11,18). As evidenced by the compositions of inclusions in diamond, which vary from strongly reduced, e.g., metallic iron and carbides (19-23), to oxidized, e.g., carbonates and CO 2 (6,20,(24)(25)(26)(27)(28), carbonates may be involved in the reactions with reduced deep-seated rocks, including Fe 0 -bearing species (29-31). A scale of these reactions is determined mainly by the capacity of subducted carbonate-bearing domains. An important consequence of such an interaction is that it can produce diamond. However, studies on diamond synthesis via the reactions between oxidized and reduced phases are limited (32-35).To understand the mechanisms of the interaction of carbonbearing oxidized-and reduced-mineral assemblages, we performed high-pressure experiments with an iron-carbonate system; an approach was used that enabled the creation of an oxygen fugacity gradient in the capsules (Materials and Methods and SI Materials and Methods). Results and DiscussionThe experimental results and the phase compositions are given in Table 1 and Table S1, respectively. At temperatures of 1,000 and 1,100°C, the iron-car...

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New host for carbon in the deep Earth

Cited by 125 publications

References 38 publications

Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Dielectric properties of water under extreme conditions and transport of carbonates in the deep Earth

Phase transitions in the system CaCO3 at high P and T determined by in situ vibrational spectroscopy in diamond anvil cells and first-principles simulations

Mantle–slab interaction and redox mechanism of diamond formation

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