Search Results (172)

During Precambrian subduction, banded iron formations (BIFs) may have represented an early significant input of carbonates and atmospheric sulfur into the lithospheric mantle, initiated the formation of carbonatite melts and probably triggered mantle metasomatic processes. Experimental modeling of the interaction of BIF-related metasomatic agents with upper mantle rocks, under Archean subduction geotherm, was performed in the simplified olivine–siderite–sulfur system. Experiments were carried out at 6.3 GPa, temperature range of 1150–1450 °C and durations of 20–60 h, using a multi-anvil high-pressure apparatus of a “split-sphere” type. Interaction of Fe,Ni–olivine and siderite with sulfur melt leads to the formation of pyrrhotite + orthopyroxene + ferromagnesite ± magnetite assemblage (1150–1250 °C, 40–60 h), as well as generation of sulfide (1350–1450 °C) and carbonate–silicate melts (1450 °C, 20 h); in all experiments, dissolution of diamond seed crystals is observed. Redox conditions are estimated to approximately correspond to ƒO₂ ~ CCO + 0.5 log. units. We demonstrated that during experiments, sulfidation of Fe,Ni–olivine and siderite and redox dissociation of siderite took place. It was shown that indicators of these processes are (1) polycrystalline orthopyroxene + pyrrhotite and pyrrhotite + ferromagnesite aggregates, inheriting shape of olivine and siderite crystals, respectively; (2) orthopyroxene zoned crystals with pyrrhotite inclusions; (3) pyrrhotite with ferromagnesite inclusions and ferromagnesite with magnetite + pyrrhotite inclusions. The obtained results with certain limitations can be used to constrain processes of metasomatic alteration of upper mantle rocks by agents enriched in iron, sulfur, and carbon under relatively oxidizing conditions (ƒO₂ ~ CCO + 0.5 log. units). Full article

The mantle of bivalves plays a fundamental role in shell formation and maintenance through biomineralization. Experiments performed on mantle–shell preparations using different experimental techniques revealed the presence of phosphorus (P)-containing compounds in the shell as the first mineral phase formed at the growing edge of the periostracum in the freshwater bivalve Limnoperna fortunei. The low P concentration in the shells suggests that phosphate is restricted to the growth regions and occurs at concentrations too low to be detected by techniques such as X-ray diffraction (XRD). Nevertheless, a crystal morphology closely resembling that of hydroxyapatite (HAp) was identified at the shell growth front, and a Ca/P ratio of 1.67, consistent with HAp, was determined in two of these regions. Fourier transform infrared (FTIR) spectroscopy also revealed the principal and most intense absorption band of the phosphate group (PO₄³⁻) at 1024 cm⁻¹. Enzymes such as carbonic anhydrase (CA), or proteins with equivalent functions, are likely involved in phosphate dissolution and the subsequent precipitation of calcium carbonate. In addition, the occurrence of calcium phosphate was confirmed in the shells of the marine bivalve Perna perna. Phosphate dissolution and carbonate precipitation during biomineralization suggest two important evolutionary advantages: first, the release and availability of phosphate, an essential nutrient for energy production and other metabolic functions; and second, the formation of a calcium carbonate shell, a structure indispensable for the protection, mechanical support, and survival of mollusks. Full article

Understanding the processes behind Earth’s CO₂ degassing is crucial for clarifying how carbon is cycled by geologic processes on our planet. Earth’s carbon degassing results from magmatic and metamorphic processes controlled by large-scale plate tectonics. However, the nature and amount of diffuse CO₂ fluxes from faults in continental rifts remain largely unconstrained. Recent research reports important CO₂ fluxes from deep faults over 17 × 10⁴ km² in the East African Rift System (EARS), highlighting the need for a more detailed inventory of diffuse soil emissions. Across such extensive regions, only satellite observations can provide the broad measurement range needed to meet the observational requirements for long-term, large-scale overlay datasets. While space-based data provide extended coverage for large-scale identification of CO₂ emission sources, to date, only the column-averaged total CO₂ atmospheric content has been measured from space. Range-resolved measurements of CO₂ concentration with the vertical accuracy needed to detect diffuse soil emissions are not available from space, preventing direct quantification of Earth degassing over large regions. In this paper, we focus on a new approach to measuring soil CO₂ fluxes by a statistical deconvolution of column measurements of global atmospheric CO₂ content. Anthropogenic increase, seasonal climatology at a small regional scale, and soil fluxes are measured without the use of ancillary measurements or model simulations. We combine petrology of fluid and melt phases in mantle rocks with a new satellite data analysis to reveal, for the first time, large CO₂ fluxes from the lithospheric mantle to the atmosphere in a much wider region than previously considered (22.4 × 10⁵ km²), including the Ethiopian and East African domes, where magmatism is no longer active or absent. We infer that diffuse soil emissions are measurable from space, and that Earth’s tectonic carbon fluxes are considerably more relevant than currently considered, with a crucial impact on the balance of the global carbon cycle. Full article

Anthropogenic CO₂ emissions have perturbed the global carbon cycle and increased atmospheric carbon concentrations to critical levels, making carbon capture and storage (CCS) a key strategy for mitigating climate warming. Natural carbon sequestration has operated continuously in marine environments throughout Earth history. Here, we investigate the growth mechanisms and carbon-sink significance of calcite concretions in the Mesoproterozoic Xiamaling Formation from the Zhaojiashan section and the Zhenzhuquan section in the North China Craton, using petrographic, elemental geochemical and C-O-Re-Os isotopic evidence. The presence of erosional surfaces and local truncation of host-rock laminae suggests that these concretions formed synsedimentarily or during early diagenesis near the sediment-water interface. The δ¹³C values (−5.05‰ to 1.54‰) of samples, together with δ¹⁸O-δ¹³C relationships, indicate a marine carbonate affinity and suggest that dissolved inorganic carbon was the dominant carbon source. In addition, the concretions display initial ¹⁸⁷Os/¹⁸⁸Os ratios as low as 0.136, close to the mantle Os end-member, implying a contribution from mantle-derived material during concretion formation. The middle rare earth element and yttrium (MREYs)-enriched patterns and slight positive Ce anomalies further indicate that concretion growth occurred mainly within the Mn- and Fe-reduction zones. We estimate that the calcite-concretion-bearing interval of the Xiamaling Formation sequestered 70.24 Gt C, equivalent to 257.56 Gt CO₂, serving as an archive of marine carbon burial in the Mesoproterozoic ocean. Microbially mediated carbonate precipitation may represent an effective carbon immobilization mechanism in marine sediments and has potential implications for the development of subseafloor carbon storage strategies, especially where biocatalysts and/or brine could accelerate seawater CO₂ mineral trapping to industrially relevant rates. Full article

The South Atlantic is a classic region of hotspot volcanism, with numerous intraplate magmatic structures, such as the Walvis Ridge, Rio Grande Rise, Fernando de Noronha Ridge, and Victoria-Trinda Ridge. These structures record mantle plume activity and plate tectonics since the breakup of the South America–Africa continent, but the spatiotemporal correlations of mantle end-members among different hotspot systems remain unclear. This paper uses the Unified Manifold Approximation and Projection Algorithm (UMAP) and Hierarchical Agglomeration Clustering Algorithm (HAC) to perform dimensionality reduction and cluster analysis on 288 basalt Sr-Nd-Pb isotope data from 12 major hotspot-derived seamount chains/rises in the South Atlantic, identifying three types of mantle end-members: EM-type, HIMU-type, and PREMA/FOZO-type. The results show that HIMU-type end-members are mainly distributed in St. Helena Island and its associated Guinea seamount chain; EMI-type end-members dominate the Walvis Ridge basement, Rio Grande Rise, and discovered seamount chain; and PREMA/FOZO-type end-members are mainly distributed in the Brazilian continental margin seamount chain. In terms of time series, EM-type magmatic activity began in the Early Cretaceous (~132 Ma), while HIMU-type hotspot activity appeared later (~82 Ma), and both were vertically superimposed on the Walvis Ridge basement. Based on the spatiotemporal distribution characteristics of mantle end-members in hotspots in the South Atlantic and Indian Oceans, this paper proposes a two-stage magmatism model for hotspots at the African margin: in the early stage, EM-type material, associated with continental delamination and ancient lithosphere recycling, preferentially melted, forming large-scale submarine plateaus or seamount chains; in the later stage, HIMU-type material, associated with the reactivation of subducted oceanic crust or Archean carbonated subcontinental lithospheric mantle (SCLM), melted and rose in weak areas of mature oceanic crust, forming smaller seamounts. This study provides a new perspective on the unified genetic mechanism of multiple hotspots in the South Atlantic and offers a reference for understanding the generation, evolution, and magmatic activity of hotspots during the breakup of Gondwana. Full article

The Changbai Mountain area, the largest Cenozoic intraplate volcanic field in eastern China, features abundant high-temperature hot springs and high geothermal potential. However, the genesis and aggregation patterns of its geothermal systems remain poorly understood. This study recalculates crustal and residual deep/mantle heat- flow components along a representative profile and synthesizes published geological, geophysical, geochemical, and geothermal evidence to characterize the main geothermal system elements, including caprock, reservoirs, water source, and migration pathways. Controlling factors are examined from three dimensions: deep dynamics, magmatic heat source, and fault characteristics. Results reveal a “Cold crust–Hot mantle” thermal structure. The heat-flow calculation indicates that crustal radiogenic heat contributes approximately 40% of the surface heat flow, implying a dominant deep heat contribution. The available evidence suggests the presence of potential hydrothermal reservoirs in carbonate and clastic rocks, possible HDR targets in deeper metamorphic rocks, and locally effective basaltic sealing units. Fault systems and meteoric recharge likely control fluid circulation. Geothermal systems are controlled by mantle upwelling and lithospheric thinning due to western Pacific Plate subduction, multi-source heat coupling, effective caprock sealing, and fault-controlled water–heat conduction. These results provide a conceptual framework for future geothermal exploration and testing. This study elucidates the aggregation patterns and genetic mechanisms, providing a theoretical basis for exploration and development. Full article

The Nam Xan gold deposit is located in the central Truong Son Fold Belt of Laos. It is a newly identified distal intrusion-related gold system (IRGS) in a continental arc setting. This study uses whole-rock geochemistry, Pb and S isotope systematics, and mineral-scale analyses to trace magmatic evolution and ore-forming processes. Whole-rock data indicate that the associated intrusive suite is a calc-alkaline volcanic-arc granite (VAG) series, derived from a subduction-modified mantle source with notable crustal contributions. Pb isotopes reveal mixing arrays rather than true isochrons. Monte Carlo modeling shows binary mantle–crust mixing for igneous rocks and ternary mixing with an additional radiogenic component in ore samples, indicating enhanced fluid–rock interaction during mineralization. Sulfur isotope data show a shift from magmatic sulfur (δ³⁴S ≈ −5‰) in early skarn-stage pyrite to heavier values (δ³⁴S ≈ +6‰) in gold-bearing stages, reflecting fluid evolution driven by cooling and redox changes. Mineral chemistry data demonstrate that gold is present both as invisible gold within arsenian pyrite and as free gold in late-stage fractures. Strong correlations between Au and As, along with elevated Co/Ni ratios and enrichments in Bi, W, and F, collectively support a magmatic-hydrothermal origin. These findings define a three-stage mineralization process: an initial phase involving high-temperature magmatic fluids, a main stage characterized by sulfidation and gold deposition, and a final stage marked by polymetallic overprinting. The Nam Xan deposit is therefore interpreted as the distal manifestation of a Permian arc-related magmatic system in which magmatic fluids migrated along structural conduits and precipitated gold through interaction with carbonate host rocks. The identification of these intrusions in the distal IRGS at Nam Xan informs regional exploration models in the Truong Son Fold Belt, demonstrating the potential of carbonate platforms near Permian intrusions for future mineral exploration. Full article

Subduction zones are crucial for regulating volatile exchange between the Earth’s surface and interior. Specifically, volatile migration in the mantle wedge controls arc magma genesis and outfluxes. However, the poorly constrained capacity of the forearc mantle wedge to retain volatiles limits our ability to quantify global volatile cycling. This study focuses on serpentinites from the Heimulin area and investigates volatile behavior during shallow forearc serpentinization and subsequent recrystallization within the forearc mantle wedge. This is achieved through analyses of carbon and sulfur contents and isotopic compositions, combined with thermodynamic modeling. The carbon content and isotopic composition of the two sample types, which represent different degrees of serpentinization, show no significant difference. However, carbon enrichment and magnesite formation were observed in serpentinites containing ribbon-textured lizardite. Sulfur systematics suggest that slab-derived dehydrating fluids can introduce sulfur into the mantle wedge, where it can be effectively retained in serpentinite systems as pyrite under low water–rock ratios. These findings imply that forearc serpentinites may play a role in volatile transport and serve as reservoirs for carbon and sulfur, which may have implications for understanding volatile cycling in subduction zones. Full article

Located in the north of Yunnan Province, China, the Wuding geothermal area is a typical medium- and low-temperature geothermal system with strong hydrothermal activity and development potential as a clean and renewable energy resource. This study systematically investigates the main controlling factors of the Wuding geothermal field through field investigation, hydrochemical analysis, and stable isotope analysis, and puts forward a genetic model of the geothermal field. The results show that the Wuding geothermal field is a medium- to low-temperature, conduction-dominated geothermal system, and its geothermal water is predominantly of the Ca–HCO₃ (calcium bicarbonate) type. The recharge area lies at an altitude above 2250 m, which is speculated to be within the mountainous area in the southwest of the study area. The underground hot water in the area is immature water. The source water circulates to the deep heat storage zone along faults, rises to the surface through heat convection, and is exposed as hot springs. Upon discharge, the geothermal water mixes with shallow cold water, with cold-water dilution accounting for up to 85% of the total volume. Using the silica thermometer, cation thermometer, and silicon enthalpy model, the maximum temperature of heat storage is estimated to be 91 °C, with the depth of geothermal water circulation reaching 2200 m. The thermal reservoir is composed of dolomites of the Upper Cambrian Erdaoshui Formation (∈3e) and Sinian Dengying Formation (Zbd). Its heat source is heat flow from the upper mantle and the decay of radioactive elements. Continuous heat flow to the thermal reservoir is maintained through the fold fracture zone and faults in the core of the Hongshanwan anticline. The proposed genetic model of the Wuding geothermal field provides a scientific basis for the sustainable redevelopment and utilization of this geothermal resource and is of significance for regional low-carbon energy use and socio-economic sustainable development. Full article

The northern Vietnam shelf, particularly the area adjacent to the Red River Fault Zone, is characterized by complex geology and active neotectonics. However, the patterns of degassing and the origins of hydrocarbon gases in this region remain poorly understood. In particular, the potential links between deep-seated fluid migration, fault systems, and gas anomalies in island groundwater systems have not been systematically investigated. This study presents preliminary results of dissolved methane, its homologues (C₂–C₅), helium, hydrogen, and carbon dioxide measurements in groundwater from Co To Island (Northern Vietnam), with the aim of identifying gas origins and assessing structural controls on fluid migration. A significant methane anomaly was discovered, with concentrations reaching up to 10% by volume in the northwestern part of the island. The hydrocarbon homologous series is traced up to pentane (C₅), and CO₂ content is also elevated, with a maximum of 5.4%. The average He concentration of 10.8 ppm significantly exceeds atmospheric equilibrium values, with maximum recorded concentrations of 18 ppm for He and 34.5 ppm for H₂. Stable carbon isotope analysis of methane (δ¹³C-CH₄ values ranging from −50.2‰ to −49.7‰ VPDB), combined with the presence of a complete C₁–C₅ hydrocarbon series and elevated mantle/crustal tracers (He, H₂), indicates a predominantly thermogenic/metamorphogenic origin for the gases, ruling out a purely biogenic source. The spatial distribution of anomalies is structurally controlled, closely associated with the NE-SW trending Co To Fault system and its intersections with subsidiary faults, as corroborated by recent electrical resistivity tomography data. These findings indicate intensive, focused gas leakage from a deep-seated source, likely related to thermogenic/metamorphic processes and active fault-mediated degassing. The results highlight the significant hydrocarbon potential of the region and underscore the critical role of neotectonic activity in controlling fluid migration pathways in island aquifer systems. Full article

Geothermal field characteristics fundamentally control hydrocarbon generation, phase evolution, and preservation, and are particularly critical in deep to ultra-deep hydrocarbon exploration. The Tazhong Uplift is a key area for deep to ultra-deep hydrocarbon exploration in the Tarim Basin; however, its deep thermal regime and controlling factors remain inadequately characterized. This study aims to accurately characterize the geothermal field and crustal thermal structure of the Tazhong Uplift to provide thermal constraints for ultra-deep exploration. We systematically compiled system steady-state temperature data from 24 wells, bottom-hole temperature (BHT) data from 51 wells, and rock thermal property measurements. Using the one-dimensional steady-state heat conduction equation, present-day geothermal gradients at 0–5000 m depths and terrestrial heat flow were calculated, and formation temperatures were predicted at deep horizons (6000–10,000 m). Results show geothermal gradients at 0–5000 m of 18.5–26.7 °C/km (average 23.06 °C/km) and heat flow of 39.3–59.8 mW/m² (average 48.1 mW/m²), both significantly higher than basin averages. The distribution of the geothermal field is jointly controlled by basement structure and rock thermophysical properties. Basement highs typically exhibit elevated geothermal gradients and high heat flow. The dual-layer structure of “upper clastic rocks (low thermal conductivity, high heat production) + lower carbonate rocks (high thermal conductivity, low heat production)” results in a vertical differentiation characterized by a “high-upper, low-lower” geothermal gradient. Notably, the thick Upper Ordovician mudstone acts as a regional “thermal blanket”, significantly reducing geothermal parameters in the northern slope area. Crustal thermal structure analysis indicates a “cold mantle” signature of cratonic basins, with a thermal lithosphere thickness of ~134–145 km and a Moho temperature of ~581 °C. These findings reveal that despite the ultra-deep burial (>8000 m), the “cold” thermal background and the thermal regulation of the overlying diverse lithologies maintain formation temperatures within a range favorable for liquid hydrocarbon preservation, significantly expanding the depth limit for oil exploration in the Tarim Basin. Full article

This study investigates the genesis of gold mineralization at the Rodruin prospect in the central Eastern Desert (CED) of Egypt, with the aim of constraining the relative contributions of metamorphic and magmatic fluids to ore formation. Gold mineralization at Rodruin is hosted by quartz–carbonate veins emplaced within a shear zone that transects low-grade metasedimentary sequences intruded by Ediacaran post-tectonic granitoids. It exhibits characteristics transitional between orogenic turbidite-hosted and polymetallic vein-type mineralization. Although metamorphic devolatilization is interpreted to have generated the dominant ore-forming fluids, adjacent granitoid intrusions acted primarily as a thermal engine, with only a limited direct input of magmatic-hydrothermal fluids. This interpretation is supported by the occurrence of magmatic-affiliated mineral inclusions (monazite, cassiterite, and zircon) coupled with generally low concentrations of trace elements typically enriched in granitic magmatic-hydrothermal fluids (Sb, Bi, Mo, W, Sn, Nb, and Ta), collectively indicating a subordinate magmatic contribution. Rare earth element (REE) patterns of the ore samples closely resemble those of the nearby granitoids, displaying LREE enrichment; however, a distinct positive Eu anomaly is restricted to the ore assemblages and is attributed to hydrothermal feldspar alteration supporting magmatic involvement in ore formation. Carbon and oxygen isotope compositions (δ¹³C = −6.6 to −2.36‰; δ¹⁸O = +15.7 to +19.7‰), together with REE signatures comparable to primitive mantle values and textural evidence for synchronous sulfide–carbonate precipitation, manifested by rhythmic banding of carbonates and sulfides unequivocally indicate a hydrothermal–metasomatic origin. Collectively, these lines of evidence support a hybrid metamorphic–magmatic model in which gold and associated base metals were predominantly transported by metamorphic fluids, whose mobilization and focusing were enhanced by the thermal influence of Younger granitic intrusions, whereas magmatic-hydrothermal fluids contributed only a minor proportion to the overall metal budget. Full article

Microbe–mineral interactions in lacustrine environments play a critical role in controlling carbonate diagenesis and preserving organic matter, particularly under the influence of hydrothermal processes. To improve the understanding of such processes, this study focuses on the diagenesis of different types of carbonates from the upper section of the Bayingebi Formation in the Yin’e Basin, revealing the association between lacustrine sedimentation and hydrothermal activity. According to mineralogical and geochemical evidence, the carbonates in the studied interval can be broadly classified into hydrothermal, hydrothermal-biogenic, and sedimentary types on the basis of their dominant genetic signatures. Hydrothermal carbonates are dominated by crystalline dolomite, with associated hydrothermal minerals rich in Fe, Ba, and Mg, while 87Sr/86Sr values are close to mantle source values, indicating substantial mantle hydrothermal fluid contributions. Hydrothermal-biogenic carbonates are dominated by mud-crystalline and spherical dolomite enriched in Mg, Na, and P. The ⁸⁷Sr/⁸⁶Sr values fall between the typical mantle-derived and paleolake water ranges, indicating a mixed hydrothermal signal, with possible microbial involvement indicated by mineralogical and textural features. Sedimentary carbonates are predominantly crystalline calcite, with ⁸⁷Sr/⁸⁶Sr values close to crustal source values, indicating the influence of terrestrial inputs. Moreover, there are significant relationships between different types of diagenetic carbonates and organic matter. Intense hydrothermal activity is associated with low TOC values and relatively unfavorable conditions for organic matter preservation. In contrast, sections with mild hydrothermal activity have higher TOC contents, and the nutrient contents and water temperatures are more conducive to enrichment with organic matter. Although based on a single fully cored borehole from the upper section of the Bayingebi Formation, this study provides a framework for understanding the coupling between carbonate diagenesis and organic matter enrichment in hydrothermally influenced lacustrine systems, with implications for future studies involving multi-core investigations across the basin. Full article

This study presents a new 1:10,000 geological map of the Monte Bove area (northern Apennines), produced through an original field survey, which allows a detailed reconstruction of Jurassic tectono-sedimentary evolution. The area is characterized by three wedge-shaped structural highs that emerged from the basin floor due to extensional tectonics, following the demise of the Early Jurassic carbonate platform. Stratigraphic and geometric relationships indicate that these highs were already established by the earliest Pliensbachian, bounded by steep fault escarpments and locally mantled by condensed pelagic deposits. Through the Jurassic, the fault-bounded blocks were progressively buried by predominantly micritic pelagic sediments, with evidence of onlap, unconformities, and reworking. The new geological map allows precise delineation of fault geometries and depositional contacts, highlighting the importance of synsedimentary tectonics in shaping basin architecture and documenting a consistent structural trend. Full article

The Hadamengou gold deposit, hosted in the Precambrian metamorphic basement, is a super-large gold deposit occurring along the northern margin of the North China Craton. Despite extensive investigation, the genesis of the gold mineralization is poorly understood and remains highly debated. This study integrates a comprehensive dataset, including fluid inclusion microthermometry and C-H-O-S-Pb isotopes, to better constrain the genesis and ore-forming mechanism of the deposit. Hydrothermal mineralization can be divided into pyrite–potassium feldspar–quartz (Stage I), quartz–gold–pyrite–molybdenite (Stage II), quartz–gold–polymetallic sulfide (Stage III), and quartz–carbonate stages (Stage IV). Four types of primary fluid inclusions are identified, including pure CO₂-type, composite CO₂-H₂O-type, aqueous-type, and solid-daughter mineral-bearing-type inclusions. Microthermometric and compositional data reveal that the fluids were mesothermal to hypothermal, H₂O-dominated, and CO₂-rich fluids containing significant N₂ and low-to-moderate salinity, indicative of a magmatic–hydrothermal origin. Fluid inclusion assemblages further imply that the ore-forming fluids underwent fluid immiscibility, causing CO₂ effusion and significant changes in physicochemical conditions that destabilized gold bisulfide complexes. The hydrogen–oxygen isotopic compositions, moreover, support a dominant magmatic water source, with increasing meteoric water input during later stages. The carbon–oxygen isotopes are also consistent with a magmatic carbon source. Sulfur and lead isotopes collectively imply that ore-forming materials were derived from a hybrid crust–mantle magmatic reservoir, with minor contribution from the country rocks. By synthesizing temporal–spatial relationships between magmatic activity and ore formation, and the regional tectonic evolution, we suggest that the Hadamengou is an intrusion-related magmatic–hydrothermal lode gold deposit. It is genetically associated with multi-stage magmatism induced by crust–mantle interaction, which developed within the extensional tectonic regimes. Full article