High-mature to overmature source rocks constitute a critical material basis for deep oil and gas exploration in ancient petroliferous basins. However, intense thermal evolution induces extensive kerogen cracking and depletion of residual organic matter, resulting in the failure of conventional evaluation indicators and thereby severely limiting the accurate assessment of source rock effectiveness and resource potential.Taking the high-mature to overmature source rocks (with vitrinite reflectance Ro > 1.3%, locally reaching up to 3.0%) from the Fengcheng Formation and Lower Urho Formation of the Permian System in the Junggar Basin as the research objects, this study is grounded in geological constraints. Firstly, regional geological surveys, outcrop observations, and limited drilling core analyses were conducted to provide basic parameters for original organic carbon restoration. Meanwhile, preliminary method selection was performed by integrating the geological-geochemical differences among various formations and sags. On this premise, three methods—namely the degradation rate method, forward modeling method, and chemical kinetics method—were applied to restore the original organic carbon of the two sets of source rocks (Fengcheng Formation and Lower Urho Formation). The original organic matter types were inferred from the maceral characteristics of kerogen, which was employed to compare the adaptability and restoration accuracy of the three methods. Eventually, the original organic carbon restoration coefficients corresponding to each formation and sag were determined.Additionally, utilizing single-well logging data, a logging TOC (Total Organic Carbon) prediction model was established based on linear regression. Combined with the optimized restoration coefficients, the original organic matter abundance of single wells was calculated, realizing the accurate assessment of the original organic matter abundance of high-mature source rocks. The results indicate that after restoration, the TOC, hydrocarbon generation potential, and HI (Hydrogen Index) of the two sets of source rocks in the study area are significantly enhanced compared with those before restoration. Specifically, for the Lower Urho Formation in the Fukang Sag, the average post-restoration TOC is 1.73%, representing a 10% increase from the pre-restoration value; for the Fengcheng Formation in the Shawan Sag, the average post-restoration TOC is 0.99%, a 67% rise compared with the pre-restoration level. This evaluation method clarifies the original organic matter abundance and hydrocarbon generation potential of high-quality source rocks in sparsely explored sags, and effectively addresses the key challenges in the assessment of high-mature to overmature source rocks.

Keywords: High-mature to overmature source rocks; Organic carbon restoration; Logging prediction; Junggar Basin; Permian

How to cite: Liu, Y., Liu, H., and Cheng, B.: Restoration of Original Organic Carbon and Evaluation of Hydrocarbon Generation Potential for High-Mature to Overmature Source Rocks: A Case Study of the Permian Source Rocks in the Junggar Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3079, https://doi.org/10.5194/egusphere-egu26-3079, 2026.

Dense Hydrous Magnesium Silicates (DHMSs), as potential important water reservoirs in the Earth's interior, are critical for understanding the global water cycle, mantle composition and dynamic processes. Superhydrous phase B (shy-B), as a member of the DHMSs family, is considered an important hydrous phase in the mantle transition zone (MTZ) and even in the uppermost lower mantle (ULM) due to its high water content. Given the abundance of aluminum (Al) and iron (Fe) in the mantle, investigating their effects on the physical properties of shy-B better approximates realistic Earth's interior conditions. In this study, structural characterization and physical property analysis of synthesized Al-bearing shy-B, Fe-bearing shy-B and Fe-Al-bearing shy-B were performed under high pressure using a diamond anvil cell combined with synchrotron radiation single-crystal X-ray diffraction, infrared absorption spectroscopy and Raman scattering spectroscopy. Based on the Birch-Murnaghan (BM) equation of state fitting, the effects of different Al and Fe contents on the bulk modulus of shy-B were quantified, and the variations of density and bulk velocity with pressure were further derived, providing constraints for modeling the geodynamic processes of water subduction and transport.

How to cite: Chen, S., Li, X., and Li, F.: Equations of State of Superhydrous Phase B with Varying Mg, Al and Fe Contents: Implications for Water Transport in the Mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6068, https://doi.org/10.5194/egusphere-egu26-6068, 2026.

The deep carbon cycle is crucial for understanding Earth's global carbon budget and the exchange of volatiles between the surface and the interior. Carbonates are the primary carriers of carbon into the deep mantle via subducting oceanic lithosphere, yet their stability and distribution remain subject to significant uncertainty. While current understanding of carbonate stability and elasticity is largely based on end-member minerals, the effects of complex cation mixing, which is prevalent in natural systems, are poorly constrained. In this study, we synthesized a series of multi-cation carbonates with varying cation compositions (Ca, Mg, Fe) and investigated their crystal structures and elastic properties under in situ high-pressure and high-temperature conditions using synchrotron X-ray diffraction and Brillouin scattering. Our results demonstrate that the random substitution of cations significantly modulates the phase stability and sound velocities of these carbonates. Specifically, the combined effects of Mg and Fe substitution for Ca induce distinct elastic anomalies and anisotropy variations that deviate from the behavior of end-member phases. These findings provide critical constraints for interpreting seismic observations in subduction zones and the deep mantle. By clarifying the influence of cation chemistry on carbonate elasticity, this work enhances our ability to quantify deep carbon reservoirs and understand the dynamic processes governing the global carbon cycle.

How to cite: Zhang, J., Li, X., and Li, F.: High-Pressure Stability and Elasticity of Multi-Cation Carbonates: Implications for the Deep Carbon Cycle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8521, https://doi.org/10.5194/egusphere-egu26-8521, 2026.

Mantle-derived fluids are increasingly recognized as key contributors to hydrocarbon and natural hydrogen resources, yet their phase relations, compositions, and evolutionary pathways remain poorly constrained. Petrological observations and experiments suggest that deep hydrogen reacts with carbon-bearing materials to form hydrocarbons such as methane, resulting in the coexistence of H₂ and CH₄ in the upper mantle. In contrast, surface natural hydrogen accumulations commonly contain >90% H₂. This disparity points to significant fluid fractionation during ascent, potentially driven by phase separation. However, a lack of data at high pressure and temperature has prevented clear constraints on the phase behavior and thermodynamic properties of H₂-CH₄ systems under upper mantle conditions.

In this study, we investigate the structure and thermodynamic properties of the H₂–CH₄ system under upper mantle conditions using first-principles molecular dynamics simulations integrated with available experimental constraints. Simulations were performed for pure H₂, pure CH₄ and H₂–CH₄ mixtures over a wide range of compositions under upper mantle conditions. Long-range interactions were treated using the SCAN+rVV10 functional. The resulting simulation data were used to construct P–V–T equations of state and to develop a thermodynamic model for the H₂–CH₄ binary system. Our results show that at high hydrogen concentrations, H₂ and CH₄ exhibit fluid immiscibility, leading to the segregation of hydrogen-rich fluids. This immiscibility becomes more pronounced with decreasing pressure and temperature, consistent with conditions expected during fluid ascent. Radial distribution function analyses indicate that both components remain molecular, with no evidence for additional species formation under the investigated conditions. Large-scale simulations involving up to 1012 atoms reproduce the same immiscibility behavior, confirming the robustness of the results.

These findings place new constraints on the phase behavior of H₂–CH₄ fluids in the upper mantle and provide a plausible mechanism for the generation of hydrogen-rich fluids observed at Earth’s surface. The thermodynamic models developed here offer a quantitative framework for future studies of deep hydrogen cycling and mantle hydrocarbon systems.

How to cite: Gao, H., Li, Y., Zhang, Z., and Ni, H.: Phase Behavior and Immiscibility of H2–CH4 Fluids Under Upper Mantle Conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4772, https://doi.org/10.5194/egusphere-egu26-4772, 2026.

Fluorine (F) and water (H₂O) are critical volatiles in magmatic systems. They play a vital role in magmatism, hydrothermal metallogenesis and so on. Previous studies have studied the effects of F on melt viscosity and element diffusion. However, the impact of fluorine on electrical conductivity, and the coupled effect of F-H₂O, remain poorly constrained. We performed in-situ electrical conductivity measurements on metaluminous rhyolitic melts in a piston cylinder apparatus combined with a Solartron 1260 impedance analyzer. The experimental conditions spanned 0.5–1.0 GPa and 700–1200 °C with different contents of F and H₂O. The results show that H₂O can significantly enhance the electrical conductivity of metaluminous rhyolitic melt, with an increase of 0.5-1.0 log units by adding ~4 wt% H₂O. In contrast, adding ~4 wt% F can only increase the electrical conductivity by 0.2–0.3 log units. Moreover, the fluorine-water coupling effect is less than the sum of their independent contributions. This result indicates that the non-linear coupling mechanisms between the two volatiles must be considered when evaluating their speciation and transport behavior. Additionally, we found that the influence of F on the electrical conductivity of rhyolitic melts varies with the aluminum saturation index (ASI). The effect of fluorine becomes more pronounced with increasing ASI. Based on the measurement data, we established a general electrical conductivity model for F-H₂O-bearing metaluminous rhyolitic melts, which can be applied to constrain high-conductivity anomalies in the Earth's crust. For example, the high-conductivity anomaly beneath the Gangdese belt in southern Tibet can be explained by the existence of 8–22 vol% of melt with >6 wt% H₂O; and the conductivity anomaly in the upper crust of the Yellowstone volcano corresponds to 11–24 vol% of melt. This study highlights the characteristics of electrical conductivity for F-H₂O-bearing melts, providing key physical constraints for understanding volatile migration in magmatic-hydrothermal systems.

How to cite: Li, S. and Guo, X.: Electrical Conductivity of F-H2O-bearing Rhyolitic Melts: Implications for High-Conductivity Anomalies in the Crust, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8918, https://doi.org/10.5194/egusphere-egu26-8918, 2026.

The distribution of water in Earth’s deep interior critically influences planetary differentiation and long-term geodynamics. However, the water content of the lower mantle is poorly constrained, as its estimation depends on complex, redox-sensitive partitioning processes under extreme pressure–temperature conditions during magma ocean crystallization.

To address this, we perform large-scale simulations of magma ocean crystallization using a machine learning interatomic potential—trained on first-principles data and specifically optimized for bridgmanite and silicate melt. This approach enables efficient sampling of a vast parameter space, including pressures, temperatures, melt water contents, and oxygen fugacities relevant to the early lower mantle. We use these simulations to quantify the water partition coefficient between bridgmanite and melt and to assess redox controls on iron partitioning between the mantle and core.

Our results reveal that water is highly incompatible in bridgmanite, with its partitioning strongly modulated by redox state. Numerical models based on our partition data indicate that upon lower mantle crystallization, a substantial portion of Earth’s deep water was sequestered into a long-lived basal magma ocean, leaving the overlying solid mantle relatively dry. Furthermore, we find that oxygen fugacity profiles remained largely stable throughout this process. Our analysis suggests Earth’s water was predominantly accreted during its early formation stages, with only a limited addition post mantle differentiation—a budget that could be supplied by a small mass fraction of a late veneer with CI chondrite–like composition.

These findings provide novel quantitative constraints on deep-Earth water storage and redox evolution, offering pivotal insights into the coupled chemical and thermal history of the early Earth and the dynamics of magma ocean crystallization.

How to cite: Wan, L., Li, Y., and Ni, H.: Redox-State Dependent Water Partitioning and the Sequestration of Earth’s Deep Water in a Basal Magma Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5194, https://doi.org/10.5194/egusphere-egu26-5194, 2026.

The ability to reconstruct the thermal history of a basin is essential in modeling reservoir and source rock quality. In carbonate rocks, conventional thermal indicators could not be used, for apatites and vitrinite are hard to be found. The clumped isotope palaeothermometer and U-Pb dating are promising technique for constraining the thermal history of basins. In this study we test if carbonate clumped isotope thermometry could be used to explore the thermal histories.

This paper collects the drill cores of Cambrian and Ordovician carbonate rocks in Awati-Keping region, Tarim Basin, northwest China. The calcites and dolomites are relatively homogeneous. The Carbonate components of Ordovician strata yield statistically indistinguishable clumped isotope temperatures(TΔ₄₇), ranging from 108.4 to 189°C. The U-Pb ages are from 483 to 525Ma. The thermal evolution paths of the carbonate clumped isotope temperature (TΔ₄₇ ) in the Awati-Keping region are simulated using the first order rate approximation model.

From this study , it shows that the thermal history evolution of the Awati-Keping region can be divided into three stages: ① Slow heat flow decline stage: During the Cambrian-Ordovician periods, the heat flow values (45-55 mW/m²). As the Tarim Basin evolved into a craton, the terrestrial heat flow gradually decreased to 41-45 mW/m² by the Carboniferous. ② Rapid heat flow evolution stage: Influenced by Early Permian tectonic-thermal events, a transient peak heat flow (60-70 mW/m²) occurred in the Awati-Keping region. ③ Heat flow recession stage: During the Mesozoic-Cenozoic, heat flow values in the Awati-Keping region declined to 35-45 mW/m². The Early Permian high-temperature strata in the Awati-Keping region resulted from combined effects of burial depth and anomalous high heat flow events. Both magmatic eruptions and mantle plume upwelling contributed to the anomalous high heat flow event during the Early Permian.

The maturity evolution of the Yuertus Formation source rocks in the Awati-Keping region can be divided into three stages since deposition: gradual maturation during Cambrian-Early Carboniferous, rapid maturation acceleration during Late Carboniferous-Late Permian, and maturation stagnation from Triassic to present. The Shunbeixi area exhibits lower thermal evolution degree of source rocks, which is favorable for hydrocarbon accumulation.

How to cite: Xu, Q.: Reconstructing Thermal Histories in Carbonate Basins: A Clumped Isotope and U-Pb Dating Thermometry Approach from the Tarim Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4206, https://doi.org/10.5194/egusphere-egu26-4206, 2026.

Conventional models attribute anomalously high Poisson’s ratios in Earth’s interior to the presence of fluids or melts. Here, we propose a fundamentally different mechanism, which is rooted in the unique crystal chemistry of lawsonite (CaAl₂Si₂O₇(OH)₂·H₂O). Our high-pressure experiments reveal anomalous changes in the elastic tensor of lawsonite at ~4 GPa and ~9 GPa, which are linked to phase transitions involving hydrogen-bond reorganization. Compared to typical mantle minerals, lawsonite exhibits moderately low P-wave velocity (V_P) and very low S-wave velocity (V_S). More notably, it is characterized by exceptionally high isotropic aggregate Poisson’s ratio (0.32–0.38) and V_P/V_S ratio (1.92–2.27), which serve as diagnostic identifiers in the interpretation of seismic models. In hot subduction zones, such as Cascadia and Southwest Japan, lawsonite provides a key mineralogical mechanism for the high-Poisson’s-ratio anomalies observed at 20–50 km depth, presenting a viable explanation distinct from conventional models that invoke overpressured fluid-saturated oceanic crust. In colder subduction systems such as NE Japan, the presence of 20–40 vol.% lawsonite can account for the regional-scale seismic anomalies observed at 50–90 km depth. Furthermore, we find that the localized ultra-low shear-wave velocity zone at 50–60 km depth in oceanic crust is most likely caused by lawsonite enrichment. The seismologically unique signature of lawsonite and its compatibility with seismic models underscore how this mineral could have a critical role in facilitating water transport into the deep mantle.

How to cite: Li, X.: Single-crystal elasticity of lawsonite at high pressure: Implications for high Poisson's ratio and VP/VS zones in subduction zones, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10976, https://doi.org/10.5194/egusphere-egu26-10976, 2026.

Coal represents a crucial energy form within the carbon cycle of the Earth's lithosphere and serves as a significant reservoir for hydrocarbon energy sources, such as natural gas. As a plastic stratum, coal rock governs the formation of structural fractures under intense stress conditions in deep strata, thereby influencing the accumulation of oil and gas. In recent years, China National Petroleum Corporation (CNPC) has extended its coalbed methane exploration from depths shallower than 1,000 meters to those exceeding 2,000 meters, achieving large-scale production in the Junggar Basin and the Ordos Basin. This endeavor has become a pivotal business segment for the company in enhancing its reserves and production capacity.

The coal reservoirs in the Middle-Lower Jurassic of the Kuqa Depression in the Tarim Basin are buried at depths ranging from 0 to 8,000 meters. The cumulative thickness of coal seams is 40 to 260 meters, with a single layer thickness of 1 to 19.5 meters. The coal reservoirs buried at depths of 1,500 to 5,000 meters are relatively continuously distributed, covering an area of 5,730 km². Based on experimental analysis such as CT scanning, scanning electron microscopy, nuclear magnetic resonance, and nitrogen adsorption, outcrop and drilling samples have been conducted. It is reported that the coal reservoirs in this area have developed cleats, which are distributed in a linear and networked manner. There are 8 to 15 surface cleats per 10 cm and 13 to 24 end cleats per 10 cm. The reservoir spaces are connected, with microfractures being developed, indicating good reservoir conditions. The microfractures are mainly vertical and interlayer fractures, with good connectivity. The surface porosity ranges from 2.32% to 12.32%, and the connected porosity is 5.12%.Scanning electron microscopy reveals the development of cellular pores, primary pores, and hydrocarbon-generating pores. The matrix porosity is 10.4% to 15.5%, with the development of micro-pores (less than 10 nm) and mesopores (10 to 1,000 nm), which is conducive to the occurrence of adsorbed gas and free gas. Micropores (less than 2 nm) account for 63.4%, serving as the main adsorption space, while macropores with diameters ranging from 100 to 3,000 μm are the main occurrence space for free gas. Under the later strong thrust nappe action, the concentrated development area of coal is a regional differential structural deformation and strike-slip transformation zone, which controls the generation of fractures and the development intensity of structural fractures, and is a potential sweet-spot for reservoir development.

How to cite: Wang, J., Xu, X., and Zhang, H.: Characteristics of deep coal reservoirs and structural fractures controlling in Middle-Lower Jurassic of the Kuqa Depression in the Tarim Basin, China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16263, https://doi.org/10.5194/egusphere-egu26-16263, 2026.