Pub Date : 2020-03-24DOI: 10.1002/9781119508229.ch26
V. Kutcherov, K. Ivanov, E. Mukhina, A. Serovaiskii
Research subject. Experimental modelling of the transformation of complex hydrocarbon systems under extreme thermobaric conditions was carried out. The results obtained were compared with geological observations in the Urals, Kamchatka and other regions.Material and methods. The materials for the research were a model hydrocarbon system similar in composition to natural gas condensate and a system consisting of a mixture of saturated hydrocarbons and various iron-containing minerals enriched in 57Fe. Two types of high-pressure equipment were used: a diamond anvils cell and a Toroid-type high-pressure chamber. The experiments were carried out at pressures up to 8.8 GPa in the temperature range 593–1600 K.Results. According to the obtained results, hydrocarbon systems submerged in a subduction slab can maintain their stability down to a depth of 50 km. Upon further immersion, during contact of the hydrocarbon fluid with the surrounding iron-bearing minerals, iron hydrides and carbides are formed. When iron carbides react with water under the thermobaric conditions of the asthenosphere, a water-hydrocarbon fluid is formed. Geological observations, such as methane finds in olivines from ultramafic rocks unaffected by serpentinization, the presence of polycyclic aromatic and heavy saturated hydrocarbons in ophiolite allochthons and ultramafic rocks squeezed out from the paleo-subduction zone of the Urals, are in good agreement with the experimental data.Conclusion. The obtained experimental results and presented geological observations made it possible to propose a concept of deep hydrocarbon cycle. Upon the contact of hydrocarbon systems immersed in a subduction slab with iron-bearing minerals, iron hydrides and carbides are formed. Iron carbides carried in the asthenosphere by convective flows can react with hydrogen contained in the hydroxyl group of some minerals or with water present in the asthenosphere and form a water-hydrocarbon fluid. The mantle fluid can migrate along deep faults into the Earth’s crust and form multilayer oil and gas deposits in rocks of any lithological composition, genesis and age. In addition to iron carbide coming from the subduction slab, the asthenosphere contains other carbon donors. These donors can serve as a source of deep hydrocarbons, also participating in the deep hydrocarbon cycle, being an additional recharge of the total upward flow of a water-hydrocarbon fluid. The described deep hydrocarbon cycle appears to be part of a more general deep carbon cycle.
{"title":"Deep Hydrocarbon Cycle","authors":"V. Kutcherov, K. Ivanov, E. Mukhina, A. Serovaiskii","doi":"10.1002/9781119508229.ch26","DOIUrl":"https://doi.org/10.1002/9781119508229.ch26","url":null,"abstract":"Research subject. Experimental modelling of the transformation of complex hydrocarbon systems under extreme thermobaric conditions was carried out. The results obtained were compared with geological observations in the Urals, Kamchatka and other regions.Material and methods. The materials for the research were a model hydrocarbon system similar in composition to natural gas condensate and a system consisting of a mixture of saturated hydrocarbons and various iron-containing minerals enriched in 57Fe. Two types of high-pressure equipment were used: a diamond anvils cell and a Toroid-type high-pressure chamber. The experiments were carried out at pressures up to 8.8 GPa in the temperature range 593–1600 K.Results. According to the obtained results, hydrocarbon systems submerged in a subduction slab can maintain their stability down to a depth of 50 km. Upon further immersion, during contact of the hydrocarbon fluid with the surrounding iron-bearing minerals, iron hydrides and carbides are formed. When iron carbides react with water under the thermobaric conditions of the asthenosphere, a water-hydrocarbon fluid is formed. Geological observations, such as methane finds in olivines from ultramafic rocks unaffected by serpentinization, the presence of polycyclic aromatic and heavy saturated hydrocarbons in ophiolite allochthons and ultramafic rocks squeezed out from the paleo-subduction zone of the Urals, are in good agreement with the experimental data.Conclusion. The obtained experimental results and presented geological observations made it possible to propose a concept of deep hydrocarbon cycle. Upon the contact of hydrocarbon systems immersed in a subduction slab with iron-bearing minerals, iron hydrides and carbides are formed. Iron carbides carried in the asthenosphere by convective flows can react with hydrogen contained in the hydroxyl group of some minerals or with water present in the asthenosphere and form a water-hydrocarbon fluid. The mantle fluid can migrate along deep faults into the Earth’s crust and form multilayer oil and gas deposits in rocks of any lithological composition, genesis and age. In addition to iron carbide coming from the subduction slab, the asthenosphere contains other carbon donors. These donors can serve as a source of deep hydrocarbons, also participating in the deep hydrocarbon cycle, being an additional recharge of the total upward flow of a water-hydrocarbon fluid. The described deep hydrocarbon cycle appears to be part of a more general deep carbon cycle.","PeriodicalId":12504,"journal":{"name":"Geophysical Monograph Series","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85488614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-24DOI: 10.1002/9781119508229.ch16
N. Solomatova, R. Caracas, R. Cohen
To improve our understanding of the Earth’s global carbon cycle, it is critical to characterize the distribution and storage mechanisms of carbon in silicate melts. Presently, the carbon budget of the deep Earth is not well constrained and is highly model‐dependent. In silicate melts of the uppermost mantle, carbon exists predomi nantly as molecular carbon dioxide and carbonate, whereas at greater depths, carbon forms complex polymer ized species. The concentration and speciation of carbon in silicate melts is intimately linked to the melt’s composition and affects its physical and dynamic properties. Here we review the results of experiments and calculations on the solubility and speciation of carbon in silicate melts as a function of pressure, temperature, composition, polymerization, water concentration, and oxygen fugacity.
{"title":"Carbon Speciation and Solubility in Silicate Melts","authors":"N. Solomatova, R. Caracas, R. Cohen","doi":"10.1002/9781119508229.ch16","DOIUrl":"https://doi.org/10.1002/9781119508229.ch16","url":null,"abstract":"To improve our understanding of the Earth’s global carbon cycle, it is critical to characterize the distribution and storage mechanisms of carbon in silicate melts. Presently, the carbon budget of the deep Earth is not well constrained and is highly model‐dependent. In silicate melts of the uppermost mantle, carbon exists predomi nantly as molecular carbon dioxide and carbonate, whereas at greater depths, carbon forms complex polymer ized species. The concentration and speciation of carbon in silicate melts is intimately linked to the melt’s composition and affects its physical and dynamic properties. Here we review the results of experiments and calculations on the solubility and speciation of carbon in silicate melts as a function of pressure, temperature, composition, polymerization, water concentration, and oxygen fugacity.","PeriodicalId":12504,"journal":{"name":"Geophysical Monograph Series","volume":"52 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85910713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-24DOI: 10.1002/9781119508229.ch4
Bin Chen, Jianwei Wang
It is believed that the core formation processes sequestered a large majority of Earth’s carbon into its metallic core. Incorporation of carbon to liquid iron may significantly influence its properties under physicochemical conditions pertinent to the deep magma ocean and thus the chemical evolution of terrestrial planets and moons. Compared to available experimental data on the physical properties of crystalline iron alloys under pressure, there is a remarkable lack of data on the properties of liquid iron‐rich alloys, due to experimental challenges. Here we review experimental and computational results on the structure and properties of iron or iron‐nickel liquids alloyed with carbon upon compression. These laboratory data provide an important foundation on which the interpretation of ultrahigh pressure laboratory data and the verification of theoretical data will have to be based. The low‐pressure data can be used to validate results from theoretical calculations at the same conditions, and high‐pressure calculations can be used to estimate and predict liquid properties under core conditions. Availability of the liquid properties of Fe‐C liquids will provide essential data for stringent tests of carbon‐rich core composition models for the outer core. 4
{"title":"Structure and Properties of Liquid Fe‐C Alloys at High Pressures by Experiments and First‐Principles Calculations","authors":"Bin Chen, Jianwei Wang","doi":"10.1002/9781119508229.ch4","DOIUrl":"https://doi.org/10.1002/9781119508229.ch4","url":null,"abstract":"It is believed that the core formation processes sequestered a large majority of Earth’s carbon into its metallic core. Incorporation of carbon to liquid iron may significantly influence its properties under physicochemical conditions pertinent to the deep magma ocean and thus the chemical evolution of terrestrial planets and moons. Compared to available experimental data on the physical properties of crystalline iron alloys under pressure, there is a remarkable lack of data on the properties of liquid iron‐rich alloys, due to experimental challenges. Here we review experimental and computational results on the structure and properties of iron or iron‐nickel liquids alloyed with carbon upon compression. These laboratory data provide an important foundation on which the interpretation of ultrahigh pressure laboratory data and the verification of theoretical data will have to be based. The low‐pressure data can be used to validate results from theoretical calculations at the same conditions, and high‐pressure calculations can be used to estimate and predict liquid properties under core conditions. Availability of the liquid properties of Fe‐C liquids will provide essential data for stringent tests of carbon‐rich core composition models for the outer core. 4","PeriodicalId":12504,"journal":{"name":"Geophysical Monograph Series","volume":"107 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78363319","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-24DOI: 10.1002/9781119508229.ch6
M. Santoro, F. Gorelli, K. Dziubek, D. Scelta, R. Bini
The structural and chemical changes to which carbon dioxide is subjected with increasing pressure and temperature are discussed here with the purpose of following the modifications of this important geochemical material on proceeding from the Earth’s surface down to the core‐mantle boundary. The relevance of metasta-bilities, and then of kinetic controlled transformations, is evidenced in the P‐T ranges characteristic of both molecular phases and extended covalently bonded structures. From a chemical point of view, this analysis high-lights how the characterization of the melting of the extended structures would represent an important step to understand the role of this compound in the chemistry of the Earth’s mantle.
{"title":"Structural and Chemical Modifications of Carbon Dioxide on Transport to the Deep Earth","authors":"M. Santoro, F. Gorelli, K. Dziubek, D. Scelta, R. Bini","doi":"10.1002/9781119508229.ch6","DOIUrl":"https://doi.org/10.1002/9781119508229.ch6","url":null,"abstract":"The structural and chemical changes to which carbon dioxide is subjected with increasing pressure and temperature are discussed here with the purpose of following the modifications of this important geochemical material on proceeding from the Earth’s surface down to the core‐mantle boundary. The relevance of metasta-bilities, and then of kinetic controlled transformations, is evidenced in the P‐T ranges characteristic of both molecular phases and extended covalently bonded structures. From a chemical point of view, this analysis high-lights how the characterization of the melting of the extended structures would represent an important step to understand the role of this compound in the chemistry of the Earth’s mantle.","PeriodicalId":12504,"journal":{"name":"Geophysical Monograph Series","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83219304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-24DOI: 10.1002/9781119508229.ch11
E. Boulard, F. Guyot, G. Fiquet
Ferromagnesite (Mg,Fe)CO3 plays a key role in the transport and storage of carbon in the deep Earth. Experimental and theoretical studies demonstrated its high stability at high pressure and temperature against melting or decomposition. Several pressure-induced transformations of ferromagnesite have been reported at conditions corresponding to depths greater than ~1100 km in the Earth’s lower mantle. Although there is still no consensus on their exact crystallographic structures, evidences are strong of a change in carbon environment from the low-pressure planar CO32ion into carbon atoms tetrahedrally coordinated by four oxygens. High-pressure iron-bearing phases concentrate a large amount of Fe3+ as a result of intracrystalline self-redox reactions. These crystallographic particularities may have significant implications on carbon reservoirs and fluxes in the deep Earth.
{"title":"High‐Pressure Transformations and Stability of Ferromagnesite in the Earth's Mantle","authors":"E. Boulard, F. Guyot, G. Fiquet","doi":"10.1002/9781119508229.ch11","DOIUrl":"https://doi.org/10.1002/9781119508229.ch11","url":null,"abstract":"Ferromagnesite (Mg,Fe)CO3 plays a key role in the transport and storage of carbon in the deep Earth. Experimental and theoretical studies demonstrated its high stability at high pressure and temperature against melting or decomposition. Several pressure-induced transformations of ferromagnesite have been reported at conditions corresponding to depths greater than ~1100 km in the Earth’s lower mantle. Although there is still no consensus on their exact crystallographic structures, evidences are strong of a change in carbon environment from the low-pressure planar CO32ion into carbon atoms tetrahedrally coordinated by four oxygens. High-pressure iron-bearing phases concentrate a large amount of Fe3+ as a result of intracrystalline self-redox reactions. These crystallographic particularities may have significant implications on carbon reservoirs and fluxes in the deep Earth.","PeriodicalId":12504,"journal":{"name":"Geophysical Monograph Series","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73748732","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-24DOI: 10.1002/9781119508229.ch19
V. Stagno, Y. Kono, V. Stopponi, M. Masotta, P. Scarlato, C. Manning
The circulation of carbon in Earth’s interior occurs through the formation, migration, and ascent of CO 2 ‐ bearing magmas throughout the convective mantle. Their chemical composition spans from carbonatitic to kimberlitic as a result of either temperature and pressure variations or local redox conditions at which partial melting of carbonated mantle mineral assemblages occurs. Previous experiments that focused on melting relations of synthetic CO 2 ‐bearing mantle assemblages revealed the stability of carbonate‐silicate melts, or transitional melts, that have been generally described to mark the chemical evolution from kimberlitic to carbonatitic melts at mantle conditions. The migration of these melts upward will depend on their rheology as a function of pressure and temperature. In this study, we determined the viscosity of carbonate‐silicate liquids (~18 wt% SiO 2 and 22.54 wt% CO 2 ) using the falling‐sphere technique combined with in situ synchrotron X‐ray radiography. We performed six successful experiments at pressures between 2.4 and 5.3 GPa and temperature between 1565 °C and 2155 °C. At these conditions, the viscosity of transitional melts is between 0.02 and 0.08 Pa˙s; that is, about one order of magnitude higher than what was determined for synthetic carbonatitic melts at similar P‐T conditions, likely due to the polymerizing effect of the SiO 2 component in the melt.
{"title":"The Viscosity of Carbonate‐Silicate Transitional Melts at Earth's Upper Mantle Pressures and Temperatures, Determined by the In Situ Falling‐Sphere Technique","authors":"V. Stagno, Y. Kono, V. Stopponi, M. Masotta, P. Scarlato, C. Manning","doi":"10.1002/9781119508229.ch19","DOIUrl":"https://doi.org/10.1002/9781119508229.ch19","url":null,"abstract":"The circulation of carbon in Earth’s interior occurs through the formation, migration, and ascent of CO 2 ‐ bearing magmas throughout the convective mantle. Their chemical composition spans from carbonatitic to kimberlitic as a result of either temperature and pressure variations or local redox conditions at which partial melting of carbonated mantle mineral assemblages occurs. Previous experiments that focused on melting relations of synthetic CO 2 ‐bearing mantle assemblages revealed the stability of carbonate‐silicate melts, or transitional melts, that have been generally described to mark the chemical evolution from kimberlitic to carbonatitic melts at mantle conditions. The migration of these melts upward will depend on their rheology as a function of pressure and temperature. In this study, we determined the viscosity of carbonate‐silicate liquids (~18 wt% SiO 2 and 22.54 wt% CO 2 ) using the falling‐sphere technique combined with in situ synchrotron X‐ray radiography. We performed six successful experiments at pressures between 2.4 and 5.3 GPa and temperature between 1565 °C and 2155 °C. At these conditions, the viscosity of transitional melts is between 0.02 and 0.08 Pa˙s; that is, about one order of magnitude higher than what was determined for synthetic carbonatitic melts at similar P‐T conditions, likely due to the polymerizing effect of the SiO 2 component in the melt.","PeriodicalId":12504,"journal":{"name":"Geophysical Monograph Series","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80286767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-24DOI: 10.1002/9781119508229.ch9
M. Merlini, S. Milani, J. Maurice
We report an overview of the crystal structures of carbonates determined ab‐initio with X‐ray single crystal diffraction techniques at mantle conditions. The determined crystal structures of high‐pressure polymorphs of CaCO 3 have revealed that structures denser than aragonite can exist at upper and lower mantle pressures. These results have stimulated the computational and experimental research of thermodynamically stable polymorphs. At lower mantle conditions, the carbonates transform into new structures featuring tetrahedrally coordinated carbon. The identification of a systematic class of carbonates, nesocarbonates, cyclocarbonates, and inocarbon-ates reveals a complex crystal chemistry, with analogies to silicates. They provide fundamental input for the understanding of deep carbonatite melt physical properties. The possible polymerization of carbonate units will affect viscosity, and the reduced polymerization in crystal structures as a function of oxidation state could suggest that also oxidation state may affect the mobility of deep carbonatitic magmas. Finally, we report two high‐pressure structures of mixed alkali carbonates, which reveal that these compounds may form wide solid solutions and incorporate a sensible amount of vacancies, which would allow incorporation of high‐strength elements and therefore play an important role for geochemical element partitioning in the mantle.
{"title":"Structures and Crystal Chemistry of Carbonate at Earth's Mantle Conditions","authors":"M. Merlini, S. Milani, J. Maurice","doi":"10.1002/9781119508229.ch9","DOIUrl":"https://doi.org/10.1002/9781119508229.ch9","url":null,"abstract":"We report an overview of the crystal structures of carbonates determined ab‐initio with X‐ray single crystal diffraction techniques at mantle conditions. The determined crystal structures of high‐pressure polymorphs of CaCO 3 have revealed that structures denser than aragonite can exist at upper and lower mantle pressures. These results have stimulated the computational and experimental research of thermodynamically stable polymorphs. At lower mantle conditions, the carbonates transform into new structures featuring tetrahedrally coordinated carbon. The identification of a systematic class of carbonates, nesocarbonates, cyclocarbonates, and inocarbon-ates reveals a complex crystal chemistry, with analogies to silicates. They provide fundamental input for the understanding of deep carbonatite melt physical properties. The possible polymerization of carbonate units will affect viscosity, and the reduced polymerization in crystal structures as a function of oxidation state could suggest that also oxidation state may affect the mobility of deep carbonatitic magmas. Finally, we report two high‐pressure structures of mixed alkali carbonates, which reveal that these compounds may form wide solid solutions and incorporate a sensible amount of vacancies, which would allow incorporation of high‐strength elements and therefore play an important role for geochemical element partitioning in the mantle.","PeriodicalId":12504,"journal":{"name":"Geophysical Monograph Series","volume":"73 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85989484","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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