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Keywords = carbonate mantle melts

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26 pages, 3270 KiB  
Review
Carbon Isotopes in Magmatic Systems: Measurements, Interpretations, and the Carbon Isotopic Signature of the Earth’s Mantle
by Yves Moussallam
Geosciences 2025, 15(7), 266; https://doi.org/10.3390/geosciences15070266 - 9 Jul 2025
Viewed by 443
Abstract
Carbon isotopes in magmatic systems serve as powerful tracers for understanding magma evolution, mantle processes, the deep carbon cycle, and the origin of Earth’s carbon. This review provides a comprehensive overview of carbon isotope measurements and behavior in magmatic systems, highlighting recent technological [...] Read more.
Carbon isotopes in magmatic systems serve as powerful tracers for understanding magma evolution, mantle processes, the deep carbon cycle, and the origin of Earth’s carbon. This review provides a comprehensive overview of carbon isotope measurements and behavior in magmatic systems, highlighting recent technological advancements and scientific insights. We begin by examining methods for measuring δ13C in volcanic gases, vesicles, glasses, melt, and fluid inclusions. We then explore the behavior of carbon isotopes in magmatic systems, especially during magmatic degassing. Finally, we evaluate what recent advances mean for our understanding of the carbon isotope signature of the Earth’s upper mantle. Full article
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21 pages, 6935 KiB  
Article
Internal Structure and Inclusions: Constraints on the Origin of the Tancheng Alluvial Diamonds from the North China Craton
by Qing Lv, Fei Liu, Yue-Jin Ge, Zhao-Ying Li, Xiao Liu, Yong-Lin Yao, Yu-Feng Wang, Hai-Qin Wang, Sheng-Hu Li, Xiao-Dong Ma, Yong Zhang, Jia-Hong Xu and Ahmed E. Masoud
Minerals 2025, 15(6), 588; https://doi.org/10.3390/min15060588 - 30 May 2025
Viewed by 453
Abstract
The internal growth patterns and surface micromorphology of diamonds provide a record of their multi-stage evolution, from initial formation within the mantle to their eventual ascent to the Earth’s surface via deeply derived kimberlite magmas. In this study, gemological microscopic examination, Diamond View [...] Read more.
The internal growth patterns and surface micromorphology of diamonds provide a record of their multi-stage evolution, from initial formation within the mantle to their eventual ascent to the Earth’s surface via deeply derived kimberlite magmas. In this study, gemological microscopic examination, Diamond ViewTM, Raman spectroscopy, and electron probe analysis were employed to analyze the surface features, internal patterns, and inclusions of the Tancheng alluvial diamonds in Shandong Province, China. The results show that surface features of octahedra with triangular and sharp edges, thick steps with irregular contours or rounded edges, and thin triangular or serrated layers are developed on diamonds during deep-mantle storage, as well as during the growth process of diamonds, when they are not subjected to intense dissolution. The rounding of octahedral and cubic diamond edges and their transformation into tetrahedral (THH) shapes are attributed to resorption in kimberlitic magma. These characteristics indicate that the Tancheng diamonds were commonly resorbed by carbonate–silicate melts during mantle storage. Abnormal birefringence phenomena, including irregular extinction patterns, petaloid and radial extinction patterns, and banded birefringence, were formed during the diamond growth stage. In contrast, fine grid extinction patterns and composite superimposed extinction patterns are related to later plastic deformation. The studied diamonds mainly contain P-type inclusions of olivine and graphite, with a minority of E-type inclusions, including coesite and omphacite. The pressure of entrapment of olivine inclusions within the Tancheng diamonds ranges from 4.3 to 5.9 GPa, which is consistent with that of coesite inclusions, which yield pressure ranging from 5.2 to 5.5 GPa, and a temperature range of 1083–1264 °C. Overall, the evidence suggests that Tancheng diamonds probably originated from hybrid mantle sources metasomatized by the subduction of ancient oceanic lithosphere. Full article
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18 pages, 9668 KiB  
Article
Superdeep Diamond Genesis Through Fe-Mediated Carbonate Reduction
by Jing Gao, Bin Chen, Xiang Wu, Xiaojing Lai, Changzeng Fan, Yun Liu and Junfeng Zhang
Geosciences 2025, 15(5), 163; https://doi.org/10.3390/geosciences15050163 - 1 May 2025
Viewed by 672
Abstract
Superdeep diamonds and their syngenetic inclusions are crucial for understanding Earth’s deep carbon cycle and slab–mantle redox dynamics. The origins of these diamonds, especially their links to iron (Fe) carbides and ferropericlase with varying Mg# [=Mg/(Mg+Fe)at], however, remain elusive. In this [...] Read more.
Superdeep diamonds and their syngenetic inclusions are crucial for understanding Earth’s deep carbon cycle and slab–mantle redox dynamics. The origins of these diamonds, especially their links to iron (Fe) carbides and ferropericlase with varying Mg# [=Mg/(Mg+Fe)at], however, remain elusive. In this study, we performed high pressure–temperature (P-T) experiments (10–16 GPa and 1200–1700 K) across cold-to-warm subduction zones using a multi-anvil press. The results reveal a stepwise Fe-mediated carbonate reduction process for the formation of superdeep diamonds: MgCO3 → Fe-carbides (Fe3C/Fe7C3) → graphite/diamond. This mechanism explains two phenomena regarding superdeep diamonds: (1) anomalous 13C depletion results from kinetic isotope fractionation during 12C enrichment into the intermediate Fe-carbides; (2) nitrogen scarcity is due to Fe-carbides acting as nitrogen sinks. Ferropericlase [(Mg,Fe)O] formed during the reactions in our experiments shows Mg# variations (0.2–0.9), similar to those found in natural samples. High Mg# (>0.7) variants from lower temperature experiments indicate diamond crystallization from carbonatitic melts in the shallow lower mantle, while the broad Mg# range (0.2–0.9) from experiments at higher temperatures suggests multi-depth formation processes as found in Brazilian diamonds. These findings suggest that slab–mantle interactions produce superdeep diamonds with distinctive Fe-carbides and ferropericlase assemblages as inclusions, coupled with their 13C- and nitrogen-depleted signatures, which underscore thermochemical carbon cycling as a key factor in deep carbon storage and mantle mineralogy. Full article
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18 pages, 5021 KiB  
Article
Influences of Alkali-Carbonate Melt on the Electrical Conductivity of Dunite—Origin of the High Conductivity Anomaly Within the Tanzanian Cratonic Mantle
by Xiaoge Huang and Weiqi Dai
Minerals 2025, 15(5), 466; https://doi.org/10.3390/min15050466 - 30 Apr 2025
Viewed by 510
Abstract
Archean craton comprises ancient and stable continental lithosphere, lacking significant seismic activity, magmatic activity, and tectonic deformation. Typically, its lithospheric mantle exhibits high electrical resistivity. However, within the Archean Tanzanian cratonic mantle, a high conductivity layer has been discovered, with an electrical conductivity [...] Read more.
Archean craton comprises ancient and stable continental lithosphere, lacking significant seismic activity, magmatic activity, and tectonic deformation. Typically, its lithospheric mantle exhibits high electrical resistivity. However, within the Archean Tanzanian cratonic mantle, a high conductivity layer has been discovered, with an electrical conductivity of approximately 0.1 S/m. We conducted the electrical conductivity experiments on olivine aggregates containing sodium carbonate at the pressure of 3 GPa and the temperature ranging from 600 to 1200 °C. It was found that a very small amount of alkali-carbonate melt can significantly increase the electrical conductivity of dunite. The mass fraction of alkali-carbonate melt is less than 2.0 wt% in the highly conductive layer of the Tanzanian cratonic mantle. The permeability barriers made the melts preserve within the depth range of 80 to 120 km. Therefore, the presence of alkali-rich carbonate melts may be the best mechanism to explain the high conductivity anomaly in the lithospheric mantle of the Tanzanian craton. In contrast, the carbonate melts with high mobility migrated directly to shallow depths along fractures in the mobile belt/rift zone, leaving a dry and resistive residual mantle. Full article
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17 pages, 2921 KiB  
Article
Melting Curve of Potassium Carbonate K2CO3 at High Pressures
by Jiaqi Lu, Siyuan He, Rebecca Lange and Jie Li
Minerals 2025, 15(3), 217; https://doi.org/10.3390/min15030217 - 24 Feb 2025
Viewed by 1062
Abstract
Melting of carbonated rocks in the mantle influences the Earth’s deep carbon cycle and the long-term evolution of the atmosphere. Previous studies of the high-pressure melting curve of K2CO3 have yielded inconsistent results, with discrepancies of nearly 200 °C at [...] Read more.
Melting of carbonated rocks in the mantle influences the Earth’s deep carbon cycle and the long-term evolution of the atmosphere. Previous studies of the high-pressure melting curve of K2CO3 have yielded inconsistent results, with discrepancies of nearly 200 °C at 3 GPa and more than 400 °C at 12 GPa. Here, we report constraints on the melting curve of K2CO3 at pressures up to 20 GPa from in situ ionic conduction experiments and Pt sphere experiments. To help resolve the large discrepancies, we tested the ionic conduction method against the well-established differential thermal analysis (DTA) method and conventional Pt sphere method at the ambient pressure of 1 bar. Furthermore, ionic conduction experiments were conducted on sodium chloride (NaCl) to reduce uncertainties in pressure calibration of the multi-anvil press. We also modified the configuration of the in situ ionic conduction experiments to minimize the influence of thermal gradient on melting point determination. Finally, we inspected the effect of water by varying the initial sample state and container wall thickness in the Pt sphere experiments and applied X-ray radiography as a reliable and efficient method to examine the products. Compared with the results from the ionic conduction experiments, the melting point of K2CO3 from the Pt sphere experiments was found to be 200~400 °C lower, likely due to a small amount of water trapped by hygroscopic K2CO3 in closed platinum (Pt) capsules. We find that anhydrous K2CO3 remains more refractory than Na2CO3 at elevated pressures. Full article
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23 pages, 103115 KiB  
Article
Miocene Petit-Spot Basanitic Volcanoes on Cretaceous Alba Guyot (Magellan Seamount Trail, Pacific Ocean)
by Igor S. Peretyazhko, Elena A. Savina and Irina A. Pulyaeva
Geosciences 2024, 14(10), 252; https://doi.org/10.3390/geosciences14100252 - 25 Sep 2024
Cited by 1 | Viewed by 1323
Abstract
New data obtained from core samples of two boreholes and dredged samples from the Alba Guyot in the Magellan Seamount Trail (MST), Western Pacific, including the 40Ar/39Ar age determinations of basanite, and the mineralogy of basanite, tuff, tuffite, mantle-derived inclusions [...] Read more.
New data obtained from core samples of two boreholes and dredged samples from the Alba Guyot in the Magellan Seamount Trail (MST), Western Pacific, including the 40Ar/39Ar age determinations of basanite, and the mineralogy of basanite, tuff, tuffite, mantle-derived inclusions in basanite and tuff (lherzolite xenolith and Ol, Cpx, and Opx xenocrysts), and calcareous nannofossil biostratigraphy, have implications for the guyot′s development and history. Volcanic units in the upper part of the Alba Guyot main edifice and its Oma Vlinder satellite, at sea depths between 3600 and 2200 m, were deposited during the Cretaceous 112 to 86 Ma interval. In the following ~60 myr, the Alba Guyot became partly submerged and denuded with the formation of a flat summit platform while the respective fragment of the Pacific Plate was moving to the Northern Hemisphere. Volcanic activity in the northeastern part of the guyot summit platform was rejuvenated in the Miocene (24–15 Ma) and produced onshore basanitic volcanoes and layers of tuff in subaerial and tuffite in shallow-water near-shore conditions. In the Middle-Late Miocene (10–6 Ma), after the guyot had submerged, carbonates containing calcareous nannofossils were deposited on the porous surfaces of tuff and tuffite. Precipitation of the Fe-Mn crust (Unit III) recommenced during the Pliocene–Pleistocene (<1.8 Ma) when the guyot summit reached favorable sea depths. The location of the MST guyots in the northwestern segment of the Pacific Plate near the Mariana Trench, along with the Miocene age and alkali-basaltic signatures of basanite, provide first evidence for petit-spot volcanism on the Alba Guyot. This inference agrees with the geochemistry of Cenozoic petit-spot basaltic rocks from the Pacific and Miocene basanite on the Alba Guyot. Petit-spot volcanics presumably originated from alkali-basaltic melts produced by decompression partial melting of carbonatized peridotite in the metasomatized oceanic lithosphere at the Lithosphere–Asthenosphere Boundary level. The numerous volcanic cones with elevations of up to 750 m high and 5.1 km in basal diameter, discovered on the Alba summit platform, provide the first evidence of voluminous Miocene petit-spot basanitic volcanism upon the Cretaceous guyots and seamounts of the Pacific. Full article
(This article belongs to the Section Geochemistry)
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20 pages, 6773 KiB  
Article
A Geochemical and Isotopic Investigation of Carbonatites from Huangshuian, Central China: Implications for Petrogenesis and Mantle Sources
by Hao Zhao, Antonio Simonetti, Stefanie Simonetti, Xiaopeng Cao and Yushan Du
Minerals 2024, 14(9), 953; https://doi.org/10.3390/min14090953 - 21 Sep 2024
Cited by 1 | Viewed by 1699
Abstract
The exact geological processes involved in the formation of subduction zone-related carbonatites remain ambiguous, along with their implications for crustal/carbon recycling in carbonatite melt generation. This study provides new geochemical and stable (C, O) and radiogenic (Sr, Nd, Pb) isotope data for Huangshuian [...] Read more.
The exact geological processes involved in the formation of subduction zone-related carbonatites remain ambiguous, along with their implications for crustal/carbon recycling in carbonatite melt generation. This study provides new geochemical and stable (C, O) and radiogenic (Sr, Nd, Pb) isotope data for Huangshuian carbonatite, located within the Lesser Qinling Orogen, with the aim to decipher its complex petrogenetic history. The carbonatites display elevated CaO, low MgO and alkali contents, and significant enrichments of Pb, Mo, and HREEs compared to typical carbonatites. The δ13CPDB (−4.6 to −4.9‰) and δ18OSMOW (+6.6 to +7.8‰) values plot within the field of primary igneous carbonatites. The carbonatites are characterized by consistent radiogenic isotopic compositions [(87Sr/86Sr)i = 0.70599–0.70603; εNd = −10.4 to −12.8; 206Pb/204Pb =16.24–17.74]. These combined results suggest that the carbonatites represent late-stage differentiation products of a parental, mantle-derived carbonatite melt. Their corresponding Sr-Nd-Pb isotopic compositions support the hypothesis that the Lesser Qinling carbonatites originate from a heterogeneous upper mantle source involving an EMI-like mantle component coupled with minor assimilation of the basement rocks. The parental carbonatite melt was derived by the melting of carbonate-bearing subcontinental lithospheric mantle metasomatized as the result of Early Triassic subduction of the Mianlue Ocean. Full article
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25 pages, 10774 KiB  
Article
Recycling of Au during Serpentinization of Ultramafic Rocks: A Case Study from Neoproterozoic Forearc Ophiolites, Egypt
by Basem Zoheir, Astrid Holzheid, Aliaa Diab, Azza Ragab, Fatma Deshesh and Amr Abdelnasser
Minerals 2024, 14(9), 916; https://doi.org/10.3390/min14090916 - 6 Sep 2024
Viewed by 2060
Abstract
Gold, along with other highly siderophile elements, is hosted by Fe-Ni sulfide phases within peridotites and mantle melts. In this context, the lithospheric mantle emerges as a principal reservoir, providing materials crucial for the inception, augmentation, conveyance, and genesis of auriferous CO2 [...] Read more.
Gold, along with other highly siderophile elements, is hosted by Fe-Ni sulfide phases within peridotites and mantle melts. In this context, the lithospheric mantle emerges as a principal reservoir, providing materials crucial for the inception, augmentation, conveyance, and genesis of auriferous CO2-rich mantle fluids. EPMA and laser ablation ICP-MS data, integrated with petrographic and SEM studies, were used to assess the transfer of base and precious metals into the Earth’s crust, discerning between inputs from subduction-related processes and post-formation metasomatism. The study focuses on sulfide minerals in serpentinized peridotites of the Abu Dahr ophiolite in the Eastern Desert of Egypt. Originating in a supra-subduction setting during the Neoproterozoic era, the Abu Dahr peridotites underwent serpentinization and contain discrete sulfide minerals, including pentlandite, nickeloan pyrrhotite, millerite, chalcopyrite, and violarite. The uneven distribution of calcite ± magnesite ± serpentine veins throughout the host ophiolitic rocks reflects the intricate interplay of serpentinization and carbonation, as fO2 and fCO2 conditions fluctuated. Geochemical data of the host rocks reveal a progressive geochemical evolution marked by concurrent silicification and carbonate alteration, driven by the interaction of ultramafic rocks with hydrothermal fluids, ultimately leading to the extensive silicification and formation of birbirite. The ICP-MS data show that pentlandite contains up to 6.11 ppm of Au, pyrrhotite up to 0.41 ppm, millerite 0.34 ppm, and violarite 0.12 ppm. The gold concentration in pentlandite is significantly higher than in pyrrhotite, millerite, and violarite, which exhibit lower but detectable levels of Au. Desulfurization reactions of sulfide minerals during progressive serpentinization triggered the release and redistribution of Au as well as base metals and highly siderophile elements. Published thermodynamic modeling at temperatures below 300 °C and pressures of 50 MPa closely replicates the mineral assemblage observed in the Abu Dahr ophiolites, including sulfide assemblages and variations in major elements such as Mg and Fe. This suggests that the serpentinization process, along with associated hydrothermal fluids, played a crucial role in the mobilization and redistribution of gold, particularly affecting its incorporation into secondary sulfides. The mobilization of Au and other highly siderophile elements during serpentinization occurred in an environment marked by strong oxidation, as indicated by the presence of acicular antigorite, magnetite, millerite, and goethite intergrowths. Full article
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15 pages, 2088 KiB  
Article
Water Speciation and Storage Capacity of Olivine under the Reduced Fluid—Peridotite Interaction
by Igor N. Kupriyanov, Alexander G. Sokol and Alexey N. Kruk
Minerals 2024, 14(2), 119; https://doi.org/10.3390/min14020119 - 23 Jan 2024
Viewed by 1517
Abstract
The key features of the interaction between peridotites of the continental lithospheric mantle and reduced hydrocarbon-rich fluids have been studied in experiments conducted at 5.5 GPa and 1200 °C. Under this interaction, the original harzburgite undergoes recrystallization while the composition of the fluid [...] Read more.
The key features of the interaction between peridotites of the continental lithospheric mantle and reduced hydrocarbon-rich fluids have been studied in experiments conducted at 5.5 GPa and 1200 °C. Under this interaction, the original harzburgite undergoes recrystallization while the composition of the fluid changes from CH4-H2O to H2O-rich with a small amount of CO2. The oxygen fugacity in the experiments varied from the iron-wustite (IW) to enstatite-magnesite-olivine-graphite/diamond (EMOG) buffers. Olivines recrystallized in the interaction between harzburgite and a fluid generated by the decomposition of stearic acid contain inclusions composed of graphite and methane with traces of ethane and hydrogen. The water content of such olivines slightly exceeds that of the original harzburgite. Redox metasomatism, which involves the oxidation of hydrocarbons in the fluid by reaction with magnesite-bearing peridotite, leads to the appearance of additional OH absorption bands in the infrared spectra of olivines. The water content of olivine in this case increases by approximately two times, reaching 160–180 wt. ppm. When hydrocarbons are oxidized by interaction with hematite-bearing peridotite, olivine captures Ca-Mg-Fe carbonates, which are products of carbonate melt quenching. This oxidative metasomatism is characterized by the appearance of specific OH absorption bands and a significant increase in the total water content in olivine of up to 500–600 wt. ppm. These findings contribute to the development of criteria for reconstructing metasomatic transformations in mantle rocks based on the infrared spectra and water content of olivines. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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31 pages, 13388 KiB  
Article
Primary Composition of Kimberlite Melt
by Sergey Kostrovitsky, Anna Dymshits, Dmitry Yakovlev, Jing Sun, Tatiana Kalashnikova, Igor Ashchepkov and Olga Belozerova
Minerals 2023, 13(11), 1404; https://doi.org/10.3390/min13111404 - 1 Nov 2023
Cited by 4 | Viewed by 3178
Abstract
The compositions (mineralogy, major- and trace-element chemistry of rocks and minerals, and Sr-Nd-Hf isotope systematics) of two kimberlite bodies, the Obnazhennaya pipe and the Velikan dyke from the Kuoika field, Yakutian kimberlite province (YaKP), which are close to each other (1 km distance) [...] Read more.
The compositions (mineralogy, major- and trace-element chemistry of rocks and minerals, and Sr-Nd-Hf isotope systematics) of two kimberlite bodies, the Obnazhennaya pipe and the Velikan dyke from the Kuoika field, Yakutian kimberlite province (YaKP), which are close to each other (1 km distance) and of the same Upper Jurassic age, are presented. The kimberlites of the two bodies are contrastingly different in composition. The Obnazhennaya pipe is composed of pyroclastic kimberlite of high Mg and low Ti composition and is characterized by high saturation of clastic material of the lithospheric mantle (CMLM). The pyroclastic kimberlite contains rare inclusions of coherent kimberlite from previous intrusion phases. The Velikan dyke is represented by coherent kimberlite of relatively high Fe and high Ti composition, having neither mantle xenoliths nor olivine xenocrysts. The similarity of the isotopic geochemical characteristics for kimberlites from both bodies and their spatial and temporal proximity suggest that their formation is associated with the presence of a single primary magmatic source located in the asthenosphere. It is proposed that the asthenospheric melt differentiated into two parts: (1) a predominantly carbonate composition and (2) a carbonate–silicate composition, which, respectively, formed (a) low Fe and (b) Mg-Fe and high Fe-Ti petrochemical types of kimberlites. Both parts of the melt had different capabilities to capture the xenogenic material of the mantle rocks. The greater ability to destroy and, subsequently, capture CMLM belongs to the melt, which formed a high Mg type of kimberlite and which, according to the structural–textural classification, more often corresponds to the pyroclastic kimberlite. It is suggested that the primary kimberlite melt of asthenospheric origin is similar in composition to the high Fe, high Ti, coherent kimberlite from the Velikan dyke (in wt. %: SiO2–21.8, TiO2–3.5, Al2O3–4.0, FeO–10.6, MnO–0.19, MgO–21.0, CaO–17.2, Na2O–0.24, K2O–0.78, P2O5–0.99, CO2–12.6). It is concluded that the pyroclastic kimberlite contains only xenogenic Ol, whereas some of the Ol macrocrysts with high FeO content in the coherent kimberlite have crystallized from the melt. The similarity of Sr-Nd-Hf isotope systematics and trace element compositions for kimberlites of different ages (from Devonian to Upper Jurassic) in different parts of the YaKP (in the Kuoika, Daldyn and Mirny fields) indicates a single long-lived homogeneous magmatic asthenospheric source. Full article
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16 pages, 8316 KiB  
Article
The Peritectic Reaction of Olivine as the Mechanism of the Ultrabasic–Basic Evolution of the Diamond-Forming Silicate-Carbonate-(C-O-H) System: Experiments at 6.0 GPa
by Yuriy A. Litvin, Anastasiya V. Kuzyura and Anna V. Spivak
Minerals 2023, 13(8), 1040; https://doi.org/10.3390/min13081040 - 4 Aug 2023
Viewed by 1475
Abstract
Melting phase relations of the diamond-forming olivine (Ol)–jadeite (Jd)–diopside (Di)–(Mg, Fe, Ca, Na)-carbonates (Carb)–(C-O-H-fluid) system are studied in experiments at 6.0 GPa in the polythermal Ol74Carb18.5(C-O-H)7.5-Omp74Carb18.5(C-O-H)7.5 section, where Ol = Fo80 [...] Read more.
Melting phase relations of the diamond-forming olivine (Ol)–jadeite (Jd)–diopside (Di)–(Mg, Fe, Ca, Na)-carbonates (Carb)–(C-O-H-fluid) system are studied in experiments at 6.0 GPa in the polythermal Ol74Carb18.5(C-O-H)7.5-Omp74Carb18.5(C-O-H)7.5 section, where Ol = Fo80Fa20, Omp (omphacite) = Jd62Di38 and Carb = (MgCO3)25(FeCO3)25(CaCO3)25(Na2CO3)25. The peritectic reaction of olivine and jadeite-bearing melts with formation of garnet has been determined as a physico-chemical mechanism of the ultrabasic–basic evolution of the diamond-forming system. During the process, the CO2 component of the supercritical C-O-H-fluid can react with silicate components to form additional carbonates of Mg, Fe, Ca and Na. The solidus temperature of the diamond-forming system is lowered to 1000–1020 °C by the joint effect of the H2O fluid and its carbonate constituents. The experimentally recognized peritectic mechanism of the ultrabasic–basic evolution of the diamond-forming system explains the origin of associated paragenetic inclusions of peridotite and eclogite minerals in diamonds, as well as the xenoliths of diamond-bearing peridotites and eclogites of kimberlitic deposits of diamond. Diamond-forming systems have formed with the use of material from upper mantle native peridotite rocks. In this case, the capacity of the rocks to initiate the peritectic reaction of olivine was transmitted with silicate components to diamond-forming systems. Full article
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25 pages, 1106 KiB  
Review
Diamond Formation via Carbonate or CO2 Reduction under Pressures and Temperatures of the Lithospheric Mantle: Review of Experimental Data
by Yuliya V. Bataleva and Yuri N. Palyanov
Minerals 2023, 13(7), 940; https://doi.org/10.3390/min13070940 - 13 Jul 2023
Cited by 2 | Viewed by 3334
Abstract
Existing ideas about the polygenic origin of diamonds in nature involve various processes, mechanisms, and driving forces for diamond crystallization, including redox reactions, changes in P-T conditions, evolution of melt or fluid composition, and others. According to classical models, in the lithospheric mantle, [...] Read more.
Existing ideas about the polygenic origin of diamonds in nature involve various processes, mechanisms, and driving forces for diamond crystallization, including redox reactions, changes in P-T conditions, evolution of melt or fluid composition, and others. According to classical models, in the lithospheric mantle, diamond formation occurs at depths of 120–210 km and temperatures of 900–1500 °C as a result of metasomatic processes. The driving forces in these models are considered to be redox reactions leading to the reduction of carbonates, carbonate melts, or CO2 to elemental carbon. In this study, we provide a review and systematization, as well as experimental issues and possible future directions of experimental studies, on diamond crystallization from carbonate carbon through redox reactions at P,T (pressure, temperature) conditions relevant to the lithospheric mantle. These studies have demonstrated that silicon, metals (FeSi, Fe, Fe-Nialloys), carbides (SiC, Fe3C, Fe7C3), reduced components of C-O-H fluid, sulfides/sulfide melts, Fe-S-C melts, and the application of an electric field (potential difference) can act as reducing agents for carbonate/carbonate-bearing melts or CO2 fluid, leading to the formation of diamond and graphite. The experimental data reviewed in this paper not only indicate the fundamental possibility of diamond formation from carbonate carbon through the reduction of carbonate, carbonate-bearing phases, or CO2 in the mantle, but also reveal the characteristic features of the resulting diamonds. Furthermore, the significance of potential reducing agents (fluid, sulfide, silicon, metal, and carbide) in various geodynamic settings, including the lithospheric mantle at depths insufficient for stabilizing iron or carbides, has been identified. Full article
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32 pages, 14769 KiB  
Article
Mineral Assemblage of Olivine-Hosted Melt Inclusions in a Mantle Xenolith from the V. Grib Kimberlite Pipe: Direct Evidence for the Presence of an Alkali-Rich Carbonate Melt in the Mantle Beneath the Baltic Super-Craton
by Alexander V. Golovin, Alexey A. Tarasov and Elena V. Agasheva
Minerals 2023, 13(5), 645; https://doi.org/10.3390/min13050645 - 6 May 2023
Cited by 10 | Viewed by 2957
Abstract
This report deals with the first mineralogical examination of secondary crystallized melt inclusions (CMIs) in healed cracks within olivine in a mantle peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province). In contrast to micro/nano-inclusions in diamonds, the studied CMIs are [...] Read more.
This report deals with the first mineralogical examination of secondary crystallized melt inclusions (CMIs) in healed cracks within olivine in a mantle peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province). In contrast to micro/nano-inclusions in diamonds, the studied CMIs are quite large (up to 50 µm), so that the mineral composition of the CMIs can be determined via conventional analytical approaches, e.g., Raman spectroscopy and scanning electron microscopy. Garnet peridotite is a coarse-grained mantle rock that equilibrates at 3.3 GPa and 750 °C (corresponding to a depth of ~100 km). The CMIs are therefore tiny snapshots of melt that existed in the shallow lithospheric mantle and were entrapped in olivine. In total, nineteen mineral species were identified among the daughter magmatic minerals of the CMIs. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg-, Mg- and Ca-carbonates; Na-Mg-carbonates with the additional anions Cl, SO42− and PO43−; alkali sulfates; chlorides; phosphates; sulfides; oxides; and silicates were established. Within the mineral assemblage, carbonates were predominant, with their abundance being more than 62 vol.%. The CMIs contained twelve alkali-rich minerals; nine of them were Na-bearing and showed bulk molar (Na + K)/Ca ≥ 1. The CMIs’ parental melt was an alkali-rich carbonate liquid that contained low amounts of SiO2 (≤9.6 wt%) and H2O (≤2.6 wt%). According to our estimates, the time of complete equilibration between olivine within the healed cracks and host olivine in the mantle at the calculated P-T parameters for the studied xenolith should be no more than several years. Based on this geologically short time span, a genetic link between the studied CMIs and the magmatism that formed the V. Grib kimberlite pipe is suggested. Full article
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32 pages, 9894 KiB  
Article
Phonolite-Carbonatite Liquid Immiscibility at 3–6 GPa
by Anton V. Arefiev, Anton Shatskiy, Altyna Bekhtenova and Konstantin D. Litasov
Minerals 2023, 13(3), 443; https://doi.org/10.3390/min13030443 - 20 Mar 2023
Cited by 1 | Viewed by 2007
Abstract
Liquid immiscibility plays an important role in the formation of carbonatites and associated alkaline Si-undersaturated magmas. Experiments in the sodium carbonate-aluminosilicate systems suggest that the carbonate-silicate miscibility gap is limited by crustal and shallow mantle pressures (up to 2.5 GPa). Unlike in the [...] Read more.
Liquid immiscibility plays an important role in the formation of carbonatites and associated alkaline Si-undersaturated magmas. Experiments in the sodium carbonate-aluminosilicate systems suggest that the carbonate-silicate miscibility gap is limited by crustal and shallow mantle pressures (up to 2.5 GPa). Unlike in the potassium-rich carbonate-aluminosilicate systems, the carbonate-silicate miscibility gap was established at pressures of 3.5–6 GPa. It is therefore interesting to elucidate the immiscibility range under intermediate pressures, corresponding to 100–200 km depths. Here we conducted experiments over 3–6 GPa and 1050–1500 °C in the systems corresponding to immiscible melts obtained by partial melting of carbonated pelite (DG2) at 6 GPa and 1200 °C. We found that partial melting begins with the alkali-rich carbonatite melt, while immiscible phonolite melt appears over 1050–1200 °C at 3 GPa, 1200 °C at 4.5 GPa, and 1200–1500 °C at 6 GPa. As pressure decreases from 6 to 3 GPa, Na becomes less compatible, and the concentration of the jadeite component in clinopyroxene decreases by a factor of 1.5–6. As a result, the compositions of the immiscible phonolite and carbonatite melts evolve from ultrapotassic (K2O/Na2O weight ratio = 10–14) resembling silicic and carbonatitic micro-inclusions in diamonds from kimberlites and placers worldwide to moderately potassic (K2O/Na2O = 1–2), which may correspond to phonolitic and associated carbonatitic melts of the spinel facies of the shallow mantle. Full article
(This article belongs to the Special Issue Sulphate and Carbonate Minerals)
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32 pages, 12193 KiB  
Article
The Dynamics of Transformation of Lithospheric Mantle Rocks Beneath the Siberian Craton
by Yury Perepechko, Victor Sharapov, Anatoly Tomilenko, Konstantin Chudnenko, Konstantin Sorokin and Igor Ashchepkov
Minerals 2023, 13(3), 423; https://doi.org/10.3390/min13030423 - 16 Mar 2023
Viewed by 1976
Abstract
The problem of heat–mass transfer in the permeable areas above the asthenosphere zones was numerically studied based on an examination of the inclusion content in the minerals (olivine and clinopyroxenes) of igneous and metamorphic rocks of the lithospheric mantle and the Earth’s crust; [...] Read more.
The problem of heat–mass transfer in the permeable areas above the asthenosphere zones was numerically studied based on an examination of the inclusion content in the minerals (olivine and clinopyroxenes) of igneous and metamorphic rocks of the lithospheric mantle and the Earth’s crust; evaluations of thermodynamic conditions of the inclusion formation; and experimental modeling of the influence of hot reduced gases on rocks in the mantle beneath the Siberian craton. The flow of fluids of a certain composition from the upper-mantle magma chambers leads to the formation of zonal metasomatic columns in the ultrabasic mantle lithosphere in the permeable zones of deep faults (starting from the lithosphere base at 6–7 GPa). When petrogenic components enter from the magma pocket, depleted ultrabasic lithospheric mantle rocks change to substrates, which can be considered as the deep counterparts of crustal rodingites. Other fluid compositions result in strong calcination and pronounced salinization of the metasomatized substrates or an increase in the garnet content of the primary ultrabasic matrix. A region of alkaline rocks forms above these areas, which changes to pyroxenes, amphiboles, and biotites. The heat–mass transfer modeling for the two-velocity hydrodynamic model shows that gas–fluid and melt percolation lead to an increase in the thermal front velocity under convective heating and a pressure drop in flow. It is also shown that grospidites are considered to be eclogites, are found in the permeable zones of the lithospheric mantle columns serving as conduits for the melt/fluids and represent the products of the carbonated metasomatic columns. The carbonization caused by proto-kimberlite melts may essentially decrease the diamond grade of kimberlites due to carbon oxidation. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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