This session aims to host contributions on innovative studies about fluid, melt and mineral inclusions and relationships with their host mineral phases from any field of Geosciences, spanning from magmatism, metamorphism and deep mantle dynamics to palaeoclimatology and sedimentary processes, oil & gas and ore deposits. We welcome contributions presenting innovative and advanced tools to investigate natural samples and experimental studies. Early career researchers are strongly encouraged to present their research work.
Orals: Wed, 6 May, 14:00–15:45 | Room 0.16
Diamonds provide unique snapshots of otherwise inaccessible regions of Earth’s mantle, preserving mineral, melt, and fluid inclusions that record pressure, temperature, and redox conditions at the time of entrapment. Redox conditions are a key control on mantle mineralogy, carbon speciation, and melt generation, yet natural constraints at depths greater than ~250 km remain scarce.
Here we report diamond-hosted inclusions that document an active redox-driven metasomatic process in the deep upper mantle. Two diamonds from the Voorspoed mine (Kaapvaal craton, South Africa) contain coexisting nickel-rich metallic and carbonate inclusions, accompanied by silicate and oxide phases. Integrated infrared and Raman spectroscopy, electron microprobe analysis, transmission electron microscopy, and synchrotron micro-diffraction reveal the presence of a metallic Ni–Fe alloy with Ni# = 100 × Ni/(Ni + Fe) ≈ 85 and a Ni-rich carbonate with Ni# ≈ 89 within the same growth zones of the host diamonds. The extreme Ni enrichment of both phases indicates a genetic link and disequilibrium conditions during diamond formation.
Pressure-sensitive Raman and infrared signatures of coesite, N2 and CO2, together with the presence of high-pressure silicates including a K-rich NAL phase and Na–Al–rich pyroxene, constrain diamond formation to depths of ~280–470 km. These depths overlap with conditions where subducted carbonated oceanic crust is expected to intersect its melting curve.
We interpret the inclusion assemblage as a direct record of interaction between an oxidized carbonatitic–silicic melt derived from subducted material and a reduced, metal-bearing peridotitic mantle. Infiltration of this melt into reduced mantle lithologies triggered oxidation reactions, the redistribution of Ni between the alloy, olivine, and carbonate, and the growth of diamonds. Rather than recording equilibrium conditions, the high Ni# values of the alloy and carbonate reflect transient chemical exchange during metasomatism.
These observations provide rare natural evidence for deep mantle redox reactions involving carbonatitic–silicic melts and demonstrate the power of diamond-hosted inclusions to capture dynamic mantle processes. Such metasomatism may represent an important mechanism for mantle oxidation and enrichment, with implications for the generation of enriched alkalic magmas, including kimberlites and some ocean island basalts.
How to cite: Weiss, Y., Kempe, Y., Remmenik, S., Tschauner, O., Navon, O., and Holland, T.: Nickel-rich metallic and carbonate inclusions in diamonds: snapshots of redox-driven metasomatism in the deep upper mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4096, https://doi.org/10.5194/egusphere-egu26-4096, 2026.
Diamond is an extraordinary material of the Earth’s deep interior, characterized by remarkable thermo-elastic properties and chemical stability. However, pure diamond itself does not provide definitive information about the pressure and temperature at which it forms but in principle, these conditions can be determined by measuring the stress state of minerals trapped as inclusions at the time of diamond growth (Angel et al. 2022). Indeed, inclusions and defects in diamond have the potential to provide fundamental constraints on the mechanisms of plate tectonics and carbon and volatile cycles in the Earth if the depth and temperature of diamond growth are known. Olivine is one of the most common mineral phases found within diamonds. However, most olivine inclusions entrapped in diamonds are surrounded by cracks, show evidence of fluid rims (Nimis et al. 2016) and the calculated residual pressures are so low that they indicate diamond growth and olivine entrapment outside the diamond stability field (Angel et al. 2022). This is clearly unrealistic and indicates the need to investigate the mechanisms responsible for the release of residual inclusion pressure, which are not accounted for by the simple elastic geobarometry model that has been successfully applied to inclusions in garnets from ultra-high-pressure metamorphic rocks (Murri et al. 2018, 2022).
In this work we will therefore (i) review what is currently known about the effects of cracking and plastic deformation in diamond, as well as other factors that may contribute to the reduction in inclusion pressures; and (ii) discuss possible approaches to identify and quantify the key mechanisms responsible for low inclusion pressures that will then allow the entrapment conditions of the majority of inclusions in diamond to be determined.
References:
Angel, R. J., Alvaro, M., & Nestola, F. (2022). Crystallographic methods for non-destructive characterization of mineral inclusions in diamonds. Reviews in Mineralogy and Geochemistry, 88(1), 257-305.
Murri, M., Mazzucchelli, M. L., Campomenosi, N., Korsakov, A. V., Prencipe, M., Mihailova, B. D., ... & Alvaro, M. (2018). Raman elastic geobarometry for anisotropic mineral inclusions. American Mineralogist, 103(11), 1869-1872.
Murri, M., Gonzalez, J. P., Mazzucchelli, M. L., Prencipe, M., Mihailova, B., Angel, R. J., & Alvaro, M. (2022). The role of symmetry-breaking strains on quartz inclusions in anisotropic hosts: Implications for Raman elastic geobarometry. Lithos, 422, 106716.
Nimis, P., Alvaro, M., Nestola, F., Angel, R. J., Marquardt, K., Rustioni, G., ... & Marone, F. (2016). First evidence of hydrous silicic fluid films around solid inclusions in gem-quality diamonds. Lithos, 260, 384-389.
Acknowledgments
This work has been supported by the InROAD+ 2025 - Fostering ERC talents @UNIPV assigned to M. Murri and by the Fondazione Cariplo grant agreement #2023-2431 assigned to M. Alvaro.
How to cite: Murri, M., Gilio, M., Nestola, F., and Duretz, T.: Olivine inclusions in diamond: towards real entrapment conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1628, https://doi.org/10.5194/egusphere-egu26-1628, 2026.
Over geological timescales, processes such as subduction and convection have generated and distributed geochemical heterogeneities in the Earth’s mantle. Basaltic eruptions at oceanic islands sample the mantle and preserve their diverse geochemical signatures in crystal-hosted melt inclusions (MIs), revealing significant heterogeneity on short lengthscales. While mantle heterogeneity is well documented spatially, its temporal expression during the course of a single eruption, and its influence on magma evolution and volatile budgets, remain poorly constrained.
The Canary Islands mantle is thought to comprise depleted and enriched lithologies overprinted by metasomatism involving carbonated and hydrous melts [1]. Here, we investigate how this heterogeneous mantle was sampled over the course of the 2021 Tajogaite eruption (La Palma), whose erupted products exhibited time-dependent geochemical variability [2]. We analysed olivine-hosted MIs using electron microprobe (major elements and S), ion microprobe (H₂O, CO₂, Cl, F), LA-ICP-MS (trace elements), and Raman spectroscopy (CO₂ density in bubbles). Since up to 85% of a MI’s volatile budget can be stored within its bubble [2,3], we also analysed experimentally homogenised MIs to reconstruct total volatile contents. We find temporal changes in MI compositions, including increasing MgO contents and decreasing Zr/Y ratios, consistent with progressive tapping of deeper and less fractionated magma batches during the eruption. Although H₂O contents decrease with time from 1.9 to 0.4 wt%, the highest CO₂ concentrations (up to 1.0 wt%) occur in homogenised MIs from Stage 2B of the eruption, suggesting enhanced contributions from CO₂-rich magmas.
We use time-resolved variations in REE ratios to trace changes in melting depth and the relative contributions of depleted and enriched melts; Rb–Ba–Nb–Ta systematics to constrain the role of minor hydrous phases; and Hf–Zr correlations to assess the imprint of carbonatitic metasomatism. By linking temporal variations in magma composition with in situ gas flux measurements and changes in eruptive style, we evaluate how the expression of mantle heterogeneity may have influenced gas emissions and eruption dynamics.
References:
[1] Gómez-Ulla et al. (2018) Chemical Geology 10.1016/j.chemgeo.2018.07.015
[2] Scarrow, J. H. et al. (2024) Volcanica 10.30909/vol.07.02.953980
[3] Schiavi, F. et al. (2020) Geochemical Perspectives Letters 10.7185/geochemlet.2038
[4] Buso, R. et al. (2025) Communications Earth & Environment 10.1038/s43247-025-02958-y
How to cite: Buso, R.: Melt inclusion constraints on the temporal evolution of magma and mantle during the 2021 Tajogaite eruption (La Palma) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19370, https://doi.org/10.5194/egusphere-egu26-19370, 2026.
For millennia humans have pondered the question "Are we alone in the universe?" In recent decades the search for evidence of life beyond earth has focused on the search for habits in which liquid water is now or has in the past been present, as well as the search for organic molecules in extraterrestrial (ET) samples. These efforts have, in turn, spurred significant technological advances to develop methods to analyze fluid inclusions (FI) in ET materials, including meteorites and more recently ET samples collected and returned to earth by various missions that have visited a variety of planetary bodies.
Some early reports of fluid inclusions in meteorites in the 1970s were later found to be artifacts introduced during sample preparation. As a result, the study of FI in extraterrestrial samples entered a dark period in which any reports of FI in meteorites were dismissed as likely representing fluids introduced after the samples reached earth. The study of FI in ET samples gained renewed interest following the discovery and documentation of aqueous FI in halite in the Monahans (1998) H5 chondrite. The halite and its contained FI were clearly present before the meteorite reached earth, and subsequent studies confirmed that the age of the halite and its contained FI was 4.7 ±0.2 Ga. This discovery spurred new interest to search for FI in meteorites, now using sample preparation methods that avoid introducing water or other fluids into the sample.
In the last two decades much progress has been made in identifying FI in meteorites and mission returned samples, and there are now dozens of well documented reports of FI in these samples. The rarity of FI in ET samples, combined with the generally small size of the FI (less than approximately 1-2 microns in many cases), has led to efforts to develop and improve analytical techniques to characterize the FI. To this end, our group has determined the bulk chemical and H & O stable isotopic composition of individual FI in Zag and Monahans (1998) halite and asteroid Ryugu pyrrhotites using cryo-Time of Flight Secondary Ion Mass Spectrometry (cryo-TOF-SIMS). In this presentation we will summarize some of these recent efforts involving careful and sophisticated sample preparation and analysis methods.
How to cite: Bodnar, R., Dolocan, A., Zolensky, M., Han, J., Hanna, R., Gerba, I., Chan, Q., Ireland, T., Le, L., Matsumoto, M., Tsuchiyama, A., Matsumoto, T., and Nakamura, T.: What have we learned about the distribution of water and organic molecules in the solar system from studies of fluid inclusions in meteorites and mission return samples?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14702, https://doi.org/10.5194/egusphere-egu26-14702, 2026.
Natural hydrogen is considered to be of utmost importance for the transition towards a low carbon energy system. As natural hydrogen systems can be hosted by a variety of geological settings, they are extremely versatile so that generation, migration, and accumulation processes are often insufficiently understood. This contribution presents the results of a case study that was carried out to determine the origin and evolution of CH4- and H2-rich fluids trapped in faulted, felsic granulite from the Bohemian Massif (Lower Austria). Samples were taken in an active quarry, where the granulite occurs spatially associated with tectonically incorporated, partly serpentinized, ultramafic lenses.
Fluid inclusions are found in quartz and garnet. While the inclusions in quartz are clearly of secondary origin, the ones in garnet are primary and therefore related to the high-grade granulite facies metamorphism. Raman spectroscopy measurements revealed a complex polyphase composition. The primary inclusions contain CH4 and H2 as well as several (hydrous) mineral phases. Three mineral parageneses can be distinguished: (i) granitic, (ii) Al-silicates, and (iii) hydrous Mg-silicates. The secondary inclusions generally contain no solid phases and mainly consist of CH4, H2, N2, and H2S (± H2O). Based on microthermometry measurements combined with thermodynamic calculations, the secondary inclusions in quartz can be attributed to fluid migration during the latest stage of exhumation at conditions of approximately 200 °C and 60 MPa corresponding to a depth of 2 to 2.5 km. Serpentinization at low temperature is further evidenced by lizardite being the predominant serpentine polymorph. Whereas H2, CH4, and H2S in secondary inclusions are related to low temperature serpentinization and accompanying carbon hydrogenation (Fischer-Tropsch type) reactions, the gas species in the primary inclusions are of deep-crustal or mantle origin. Observations during Raman spectroscopy measurements, however, may also indicate an impact of photocatalytic reactions triggered by the laser on fluid composition in the primary inclusions.
How to cite: Pengg, A., Bakker, R. J., and Misch, D.: Methane and hydrogen in fluid inclusions of metamorphic and hydrothermal origin: Implications for natural hydrogen system analysis and exploration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6278, https://doi.org/10.5194/egusphere-egu26-6278, 2026.
Atmospheric nitrogen (N2) is the dominant constituent of Earth’s atmosphere and exerts a first-order control on surface pressure, climate sensitivity(1), and long-term habitability(2). Despite its importance, quantitative constraints on past atmospheric nitrogen partial pressure (pN2) remain limited(3). Fluid inclusions in hydrothermal quartz record the composition of crustal fluids as well as the composition of Earth’s ancient atmosphere (4, 5), but reconstructing atmospheric pN2 from inclusions is complicated by radiogenic overprints and fluid evolution(6). We present a new method using N2-Ne-Ar elemental and isotopic systematics applied to fluid inclusions in ~20 Ma quartz veins from the Alps and Himalaya mountains ranges in order to evaluate the preservation of atmospheric nitrogen signals. Mixing relationships between N2/22Ne and 21Ne/22Ne are used to distinguish atmospheric components from crustal contributions, with nucleogenic 21Ne tracing crustal inputs. Linear trends allow extrapolation to air-saturated water endmembers and reconstruction of atmospheric pN2. Samples from low-grade geological contexts yield pN2 estimates consistent with the modern atmosphere, indicating closed-system behavior after entrapment. In contrast, samples influenced by syn-tectonic metamorphism show excesses in N2 (elevated apparent pN2), reflecting addition of crustal nitrogen. These results demonstrate the potential of combining fluid inclusions and noble gas geochemistry to link crustal fluid processes with atmospheric evolution.
1. R. Wordsworth, R. Pierrehumbert, Hydrogen-nitrogen greenhouse warming in Earth's early atmosphere. Science 339, 64-67 (2013).
2. E. E. Stüeken et al., Marine biogeochemical nitrogen cycling through Earth’s history. Nature Reviews Earth & Environment 5, 732-747 (2024).
3. D. C. Catling, K. J. Zahnle, The archean atmosphere. Sci Adv 6, eaax1420 (2020).
4. B. Marty, L. Zimmermann, M. Pujol, R. Burgess, P. Philippot, Nitrogen isotopic composition and density of the Archean atmosphere. Science 342, 101-104 (2013).
5. G. Avice et al., Evolution of atmospheric xenon and other noble gases inferred from Archean to Paleoproterozoic rocks. Geochim Cosmochim Ac 232, 82-100 (2018).
6. D. V. Bekaert, G. Avice, B. Marty, Fluid inclusions: tiny windows into global paleo-environments. Commun Earth Environ 6, 820 (2025).
This work received funding from the European Research Council (ERC) under the European Union's Horizon Europe Research and Innovation Program (Grant Agreement 101041122 to Guillaume Avice).
How to cite: Su, G., Avice, G., Vayrac, F., and Melis, R.: Reconstructing atmospheric nitrogen pressure from N2-Ne-Ar systematics in quartz-hosted fluid inclusions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5575, https://doi.org/10.5194/egusphere-egu26-5575, 2026.
Abstract: The Tahe Oilfield in the northern Tarim Basin contains one of China's largest Ordovician carbonate reservoirs. Influenced by multi-phase tectonic uplift and subsidence, significant differences exist in hydrocarbon accumulation between the Tahe area and its periphery. This study focuses on the Ordovician Yingshan (O₁₋₂y) and Yijianfang (O₂yj) formations in the Tahe and surrounding areas. Integrating systematic analysis of source rocks, structure, reservoirs and fluid inclusion, the diagenetic processes and evolutionary sequences of the target strata were clarified, the phases and timing of hydrocarbon charging were determined, and a hydrocarbon accumulation model was established to identify the controlling factors behind differential accumulation. The key findings are as follows:
(1) Hydrocarbon properties and reservoir types vary across the study area. Crude oil density increases—and oil becomes heavier—from south to north, whereas the dryness coefficient and maturity of natural gas gradually increase from northwest to southeast. Reservoir types transition concentrically from south to north in the following sequence: dry/wet gas reservoirs → condensate gas reservoirs → volatile oil reservoirs → light oil reservoirs → medium oil reservoirs → heavy oil reservoirs.
(2) Fluid inclusions exhibit distinct characteristics in different wells. In the Yingshan Formation, blue inclusions dominate in Well YQ8 (East Yuqi) and Well TS3 (Deep Tahe), indicating high-maturity hydrocarbons. Well YQX1 (West Yuqi) contains a mixture of blue, yellow, and orange inclusions, reflecting the coexistence of high- and low-maturity hydrocarbons. Well TP18 (Tuoputai) is dominated by yellow~green inclusions, corresponding to medium~low maturity hydrocarbons. In the Yijianfang Formation, Well YJ1X (Yuejin) contains both blue and yellow~green inclusions, representing high and medium~low maturity levels.
(3) Multiphase hydrocarbon accumulation is evident, with significant variation in charging timing among wells. In the Yingshan Formation, Well YQ8 experienced three accumulation phases: Middle Hercynian (338~305 Ma), Middle Yanshanian (130~111 Ma), and Late Himalayan (22~16 Ma). Well YQX1 underwent a single phase during the Middle~Late Himalayan (31~6 Ma). Well TS3 recorded three phases: Late Caledonian (458~454 Ma), Early Yanshanian (191~173 Ma), and Late Himalayan (22~18 Ma). In the Yijianfang Formation, Well TP18 had three accumulation phases: Indosinian (233~210 Ma), Middle Yanshanian (138~123 Ma), and Late Himalayan (21~13 Ma); Well YJ1X experienced two phases: Middle Yanshanian (134~117 Ma) and Late Himalayan (22~12 Ma).
(4) Differential hydrocarbon accumulation is jointly controlled by multiple factors. Variations in hydrocarbon generation and evolution of source rocks determine the fundamental reservoir types and fluid properties. Differences in tectonic evolution directly influence the phases and timing of hydrocarbon accumulation, with multiphase tectonic activity serving as the primary driver of the complex hydrocarbon distribution patterns observed in the study area.
These results provide a theoretical foundation and technical reference for further exploration of hydrocarbon accumulation in deep to ultra-deep strata.
Keywords: Fluid inclusions; Differential hydrocarbon accumulation; Ordovician; Tahe area; Tarim Basin
How to cite: Feng, T. and Chen, Z.: Hydrocarbon Accumulation Differences in the Deep Ordovician Reservoirs of the Tahe Oilfield and Its Peripheral Regions, Tarim Basin, Western China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6438, https://doi.org/10.5194/egusphere-egu26-6438, 2026.
Abstract: The Permian–Triassic in the Shawan Sag, Junggar Basin, serves as a key reserve replacement area of the basin; however, its hydrocarbon charging history is complex due to multi-source and multi-stage charging. This study integrates inclusion analysis (including petrographic analysis, fluorescence spectroscopy, microthermometry, and gas-liquid ratio measurements) with source rock thermal evolution to systematically reconstruct the hydrocarbon charging history of the Permian–Triassic reservoirs in the Shawan Sag. Results demonstrate that two stages of hydrocarbon inclusions were developed in quartz grains and calcite cements of the Triassic Karamay Formation, with the fluorescence spectral maximum-intensity wavelength (λmax) of 473.69–500.33 nm and 436.67–470.51 nm, respectively, and homogenization temperature (Th) peaks of the coexisting aqueous inclusions at 90–100 ℃ and 120–130 ℃. These correspond to hydrocarbon charging events in the Early–Middle Jurassic and Early–Late Cretaceous. The hydrocarbon inclusions formed during the Cretaceous charging have a gas-liquid ratio (Fv) of approximately 4.43%–6.67%, and the paleo-pressure coefficient during accumulation, which is calculated via inclusion paleo-pressure analysis is about 1.25–1.40, indicating an overpressured environment. Three stages of hydrocarbon inclusions were identified in quartz grains, siliceous cements, and calcite cements of the Permian Upper Wuerhe Formation, with λmax of 477.33–496.88 nm, 458.68–473.33 nm, and 436.67–455.38 nm, respectively. The Th peaks of the coexisting aqueous inclusions are respectively 80–90 ℃, 110–120 ℃, and 140–150 ℃, corresponding to Late Triassic–Early Jurassic, Early Cretaceous, and Paleocene–Eocenecharging events, respectively. The hydrocarbon inclusions formed during the Early Cretaceous charging have a Fv of 3.08%–4.45% and the calculated reservoir pressure coefficient is 1.35–1.60. Hydrocarbon inclusions formed since the Paleogene have a Fv of 6.32% and a reservoir pressure coefficient of 1.74, indicating a strongly overpressured environment. Integrated analysis reveals three phases of hydrocarbon charging in the study area: ① Late Triassic–Jurassic: The source rocks of the Lower Wuerhe Formation entered the hydrocarbon generation window. Early hydrocarbons migrated along active faults and were initially trapped, forming inclusions within quartz grains. ② Cretaceous–early Paleogene: Source rocks reached the oil generation peak, the formation overpressure reactivated faults, enabling large-scale hydrocarbon charging, with hydrocarbon inclusions mainly trapped within quartz and calcite cementation. ③ Paleogene–present: Source rocks have entered the high- to over-mature stage, intense overpressure reactivated the faults again, high mature oil and natural gas charged into the reservoirs, with hydrocarbon inclusions predominantly trapped in calcite cements.
Keywords: Junggar Basin; Shawan Sag; Permian–Triassic; fluid inclusions; paleo-pressure; hydrocarbon charging history
How to cite: Zhao, Z., Liu, H., and Cheng, B.: Characteristics of Fluid Inclusions and Analysis of Hydrocarbon Charging History in the Permian–Triassic Reservoir of the Shawan Sag, Junggar Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2440, https://doi.org/10.5194/egusphere-egu26-2440, 2026.
The Au-rich sulfide saturation during deep magmatic evolution of hydrothermal ore-forming systems has emerged as a frontier in recent research. However, the underlying formation mechanisms and their coupling with shallow mineralization remain controversial. The North China Craton (NCC), one of the most significant gold province globally, exhibits characteristics of short-term and explosive mineralization, providing an ideal natural laboratory to investigate gold enrichment processes. Here, we present an LA–ICP–MS study of sulfide inclusions (SIs) and CO2-bearing compound droplets from mantle xenoliths in Fangcheng basalts and intermediate-mafic dikes in Guocheng gold deposit.
We discovered SIs in both mantle xenoliths and dikes from different depths within the same magmatic system. The SIs in mantle xenoliths contain Au contents (0.01–0.98 ppm, mean 0.15 ppm, n=102) that are 2-5 orders of magnitude higher than whole-rock mantle peridotites from the eastern NCC, indicating significant Au pre-enrichment during the sulfide saturation stage. Furthermore, the prevalent occurrence of SIs in phenocrysts at the Mg-rich and Fe-rich zones of hornblende phenocrysts exhibit higher Au contents (0.03–1.90 ppm, mean 0.36 ppm, n=49), suggesting that multi-stage crust-mantle mixing triggered sulfide melting and further promoted gold enrichment. Element ratios of the SIs largely correspond to those of unaltered bulk ore, indicating that the dikes and ore share a common origin, with the magmatic sulfides having served as a key transport medium of Au and ore-forming elements. In addition, by simulating the diffusion of olivine to record the constraints on the rapid ascent of magma, we suggest that CO2-bearing compound droplets inhibited sulfide precipitation and redissolution, allowing Au-rich SIs to retain their metal enrichment during ascent.
We propose a continuous metal-enrichment model for deep magmatic systems, providing new insight into the efficient transfer of metals from the mantle and lower crust to shallow hydrothermal systems.
How to cite: Yan, Z. and Tan, J.: Sulfide inclusions reveal deep Au pre-enrichment and efficient metal transfer to hydrothermal systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2561, https://doi.org/10.5194/egusphere-egu26-2561, 2026.
The fluid diapir is formed through the upward intrusion of fluids along pre-existing fracture zones, with hydraulic fracturing and fluid charge occurring at the uplift point of the overpressure interface. The DF1-1 diapir is the most typical fluid diapir in the Yinggehai Basin, characterized by multi-layer gas accumulation. In this study, petrography observation, laser Raman spectroscopy analysis, micro-thermometry, approximate calculation of fluid inclusion capture pressure and natural gas characteristics have been integrated to delineate the natural gas dynamic accumulation process and summarize the accumulation model of DF1-1 diapir. Results suggest that four-episode natural gas with different composition have been documented in the DF1-1 diapir. The first and second episode of hydrocarbon gas-dominated charging occurred at 3.4-2.9Ma and 1.8-0.4Ma, respectively. The third and fourth episode were dry gas and inorganic CO2, which occurred at 0.4-0Ma. The paleo-pressure evolution of HL1 Formation was reconstructed following a model of “pressurization-release--pressurization”. And the coupling relationship between the Formation paleo-pressure evolution and the natural gas charge history was elucidated. Based on these analyses, this conformed to an overpressure-controlled episodic gas accumulation model, and the accumulation process of the DF1-1 diapir can be summarized as follows: initially, gas accumulated in deep reservoirs, with formation pressure increasing to fracture pressure, leading to diapir opening and subsequent gas loss or adjustment to shallower reservoirs along diapir faults for further accumulation. Simultaneously, gas filled the reservoirs and episodic diapir activity in the later stages resulted in rapid gas charging. This process is the primary factor contributing to the heterogeneity of gas distribution.
How to cite: He, Z.: Hydrocarbon Accumulation Processes and Model Controlled by Overpressure Evolution of the DF1-1 diapir in the Yinggehai Basin, South China Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3867, https://doi.org/10.5194/egusphere-egu26-3867, 2026.
The abnormally high pore pressure is developed in the Huangliu Formation reservoirs of the Ledong X structure on the slope of the Yinggehai Basin. The present maximum pressure coefficient reaches 2.3, indicating a strongly overpressured system. The development and evolution of reservoir overpressure are closely associated with multi-stage natural gas charging. Based on fluid inclusion petrography and laser Raman spectroscopic analysis of gas inclusions, the pressure evolution of the Huangliu Formation reservoirs was reconstructed.
The results show that three types of gas inclusions occur in the Ledong X area: N₂–CH₄, CH₄–CO₂, and CO₂ inclusions. Three episodes of fluid charging were identified. The first stage was dominated by hydrocarbon gas charging at approximately 2.3 Ma. The second and third stages involved mixed CO₂–CH₄ charging, initiating at ~1.8 Ma and ~0.5 Ma, respectively.
The pressure evolution of the Huangliu Formation reservoirs can be divided into two main stages: (1) an early pressure build-up stage and (2) a re-pressurization stage following formation fracturing and pressure release. During 2.3–0.8 Ma, combined hydrocarbon gas and CH₄–CO₂ charging caused a rapid increase in reservoir pressure, with pressure coefficients exceeding 2.3. Subsequent formation fracturing led to pressure dissipation and partial loss of early-charged gas. Since approximately 0.4 Ma, renewed large-scale natural gas charging during the third stage has caused reservoir pressure to rise again, ultimately reaching the present overpressured state.
These results demonstrate that gas charging plays a key role in overpressure development and pressure evolution in deep, overpressured gas reservoirs, providing new constraints on gas accumulation and preservation in the Yinggehai Basin.
Keywords：fluid inclusion，Raman spectrum、paleo-pressure restoration、natural gas charging history、Yinggehai Basin
How to cite: Yue, X.: Natural Gas Charging and Pressure Evolution in the Slope of the Yinggehai Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10469, https://doi.org/10.5194/egusphere-egu26-10469, 2026.
Fluid inclusions (FIs) represent an invaluable source of information for investigating hydrothermal systems, as they preserve composition, temperature and pressure of entrapment of the fluids circulating during mineral growth at depth.
In this study, rock cores of two deep wells (Mofete 3 and Mofete 5) from Mofete geothermal field (Campi Flegrei caldera) were selected to investigate the chemical-physical conditions occurring in the hydrothermal system through fluid inclusion study. Three types of fluid inclusions were identified: Type 1 two-phase liquid -rich fluid inclusions; Type 2 multi-phase liquid + vapor bubble + one or more daughter minerals; Type 3 monophase (vapor) fluid inclusion. Type 1 FIs occur in quartz and calcite at 1324m (Mofete 3) and 1750m (Mofete 5) of depth respectively and can be distinguished petrographically in primary and secondary (Type 1a and Type 1b). Type 2 FIs are hosted within quartz, scapolite and anhydrite of Mofete 5 well at 2492, 2607 and 2698 m of depth. They appear primary Type 3 FIs are prevalently secondary. They occur in Mofete 5 well at 2607 and 2698m of depth within quartz and scapolite
Microthermometric experiments were carried out on Type 1 and Type 2 FIs. At 1324m of depth, Type 1a FIs (Mofete 3) show temperature of homogenization (Th) between 178 °C and 291 °C with a mode around 215 °C, while Type 1b has Th between 195 °C and 257 °C with a modal value at 240 °C. Salinity of Type 1a FIs ranges between 2.7 and 5.1 wt.% NaClequiv. with a mode at 3.5 wt.% NaClequiv.. Type 1b FIs show salinity in the range 3.4-6.9 wt.% NaClequiv. with mode around 4.5 wt.% NaClequiv..
At 1750m of depth (Mofete 5) Th of Type 1a FIs are between 250 °C and 273 °C with a modal value at ~255 °C. Type 1b FIs have Th between 271 °C and 299 °C mode around 285 °C. Salinity of these inclusions has been determined in only 3 Type 1b FIs giving consistent results at 2.9 wt.% NaClequiv..
Type 2 FIs revealed Th in the range 317-453 °C with the mode ~380 °C (2698m of depth Mofete 5) and 331-434 °C mode at ~360 °C (2607m of depth Mofete 5). At 2492m of depth we obtained only 3 data, giving a range between 347 and 383 °C. Salinities determined in Type 2 FIs are: 38-58 wt.% NaClequiv. (2698m of depth Mofete 5), 40-65 wt.% NaClequiv. (2607m of depth Mofete 5). At 2492m of depth we determined only one salinity data which is 44 wt.% NaClequiv..
Our data highlights an increase in the temperature of homogenization from Type 1a to Type 1b FIs. We would also remark that although FIs show an increase of temperature in time, Type-2 FIs are hypersaline fluids (~50% NaCleq. Wt%) with Th comparable to present day measured deep well temperatures, and salinities similar to fluids circulating at these depths.
The increase in Th of FIs in the shallower hydrothermal system points toward an increase in the activity of the system.
How to cite: Masi, M., Marianelli, P., and Fulignati, P.: Fluid inclusion constraints on the Mofete geothermal system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11407, https://doi.org/10.5194/egusphere-egu26-11407, 2026.
Ultramafic bodies hosted within subducted continental crust can provide unique opportunities to investigate crust-mantle interaction. Crustal-derived melts and fluids can interact with the surrounding mantle and be trapped as primary inclusions in phases crystalized during the process. The study of these inclusions provides direct constraints on crust-mantle interaction during the subduction of the continental crust. In Svartberget (Western Gneiss Region, Norway), a garnet-peridotite body hosted by migmatitic gneiss exhibits a complex network of crosscutting veins with a composition ranging from olivine-garnet-websterite to phlogopite-garnet-websterite and garnetite. Previous studies ascribed the presence of all these different generations of veins to a metasomatic interaction between a crustal-derived fluid (from country rock) and the ultramafic body (Vrijmoed et al., 2013). In order to better investigate this process from the fluid perspective, we present a study of multiphase solid inclusions (MSI) trapped in garnets and clinopyroxenes of phlogopite-garnet-websterite and phlogopite-garnetite veins.
The phlogopite-garnet-websterite is coarse-grained and the major mineral phases are clinopyroxene, orthopyroxene, garnet, phlogopite and amphibole. Two types of MSI, ~ 30 µm in diameter, occur either isolated or in clusters in poikilitic clinopyroxene and skeletal garnet. They frequently exhibit negative crystal shape. These were investigated with micro-Raman spectroscopy to determine the main mineral assemblages. Type I inclusions contain quartz and feldspar polymorphs, i.e., kumdykolite and kochetavite. Type II consists of quartz, cristobalite, pyrophyllite, carbonates, corundum, and CO2.
Phlogopite-garnetites are dominated by poikilitic garnet and phlogopite with minor clinopyroxene and amphibole. Garnets host primary MSI (~ 30 µm) consisting of quartz, plagioclase, feldspar polymorphs (kumdykolite and bonaccorsite), biotite, muscovite, osumilite, and CO2 bubbles. Often in these inclusions, zircons occur as accidentally trapped phases.
Type I MSI in phlogopite-garnet-websterite and MSI in the garnetites have a mineral assemblage suggesting a granitoid composition, and thus they represent a trapped granitic melt potentially similar to the original melt that metasomatized the peridotite body. Type II inclusions in phlogopite-garnet-websterite might represent a COH fluid. Further analysis on the geochemistry of these inclusions will help to better constrain crust-mantle interaction, fluid evolution during metasomatism, and incompatible trace elements and volatiles mobility during crustal subduction.
Vrijmoed et al. (2013) Metasomatism in the Ultrahigh-pressure Svartberget Garnet-peridotite (Western Gneiss Region, Norway): Implications for the Transport of Crust-derived Fluids within the Mantle. J Petrol, 54(9), 1815-1848.
How to cite: Polyák, P. Á., Borghini, A., Cuthbert, S., Vrijmoed, J. C., and Majka, J.: Multiphase solid inclusions in Svartberget peridotite body, Western Gneiss Region (Norway): Implications for crust-mantle interaction and mantle metasomatism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13674, https://doi.org/10.5194/egusphere-egu26-13674, 2026.
