Hydrothermal Interaction Research Articles

Late Ediacaran carbonate production and REE+Y signatures tracing redox conditions in a Cadomian retroarc basin, Central Iberian Zone, Spain

The late Ediacaran carbonate production recorded in a Cadomian retroarc basin from the Iberian Peninsula provides an excellent opportunity to evaluate the tectonic and redox factors that controlled the infill of the foredeep troughs, located between uplifted orogenic wedges and exposed forebulge transects. In the Central Iberian Zone of the Iberian massif, the carbonates of the Villarta Formation follow two geographic belts, which represent short-term mosaics of uplifted and tilted fault-bounded basement highs. These recorded the nucleation of fringing reefal (rich in Cloudina and Sinotubulites microfossils embedded in thromboid textures) and shoal and back-barrier complexes, which episodically fed slope-related megabreccia lobes and channels. REE+Y datasets from the impure carbonates reflect contamination by detrital material, hydrothermal interaction and variable redox conditions, ranging from oxic to dysoxic, the latter emphasized by the deposition of kerogenous black shales in distal parts of the foredeep trough.

Near-surface soil hydrothermal response feedbacks landslide activity and mechanism

Surface moisture has recently been reported to be used in regional-scale landslide early warning. Nevertheless, near-surface multi-depth hydrothermal measurements as a hillslope scale are often less concerned and rarely linked to landslide kinematics. In this paper, we selected two neighboring landslides with different deformation mechanisms as case studies. Using in-situ multi-source sensors, we monitored real-time soil temperature and moisture at specific depths within approximately 1.5 m. The measurements span two complete monsoon seasons, representing concurrent dry and wet hydrological extremes. Statistical Pearson correlation analysis was employed to quantify the relationships between landslide activity and environmental variables such as soil temperature and moisture content. The results indicate that the near-surface soil temperatures and moisture contents contribute to a better understanding of the factors controlling landslide activity, in which variations synergistically reflect hydrothermal interaction and potential deformation mechanisms. These soil temperatures and moisture contents at certain depths (specifically at 20, 50, and even 100 cm) show moderate to strong correlations (with Pearson correlation coefficient values ranging from 0.4 to 0.8) with landslide deformation. In cases where discrete daily rainfall data exhibited unsatisfactory correlations due to their data attributes, soil temperature and moisture effectively served as alternative indicators for rainfall inputs, aiding in the analysis. Overall, this work emphasizes the critical influence of soil moisture and temperature on landslide dynamics. This study also highlights the need for comprehensive monitoring and forecasting strategies that consider a wide range of environmental factors to mitigate landslide risks associated with climate change, particularly in the context of intensified extreme weather events.

Tracing the Fe-enriched quartz vein-type wolframite mineralization: Wolframite U-Pb dating and compositions of wolframite and scheelite from the Anglonggangri and Jiaoxi areas, Xizang, China

Critical factors controlling Fe-enriched wolframite formation in the quartz vein-type wolframite deposit are in controversy. The Jiaoxi and Anglonggangri are typical examples of quartz vein-type wolframite mineralization found in western Lhasa terrane. The Jiaoxi wolframite comprise dominantly early hübnerite with late ferberite, whereas, the Anglonggangri wolframite are mainly ferberite. Wolframite U-Pb dating yields direct timing of 11.0 ± 0.2 Ma and 9.7 ± 0.2 Ma for Jiaoxi and Anglonggangri tungsten mineralization, respectively. Ages together with enrichment of Nb, Ta, Ti, and Sc and depletion of Sr and most Eu anomaly within Anglonggangri wolframite confirm that metals and fluids were mainly derived from the ore-forming garnet-muscovite granite. Iron and Mn mapping of garnet in the garnet-muscovite granite suggests this granite has changed from the early Mn-enriched to late Fe-rich affinity. Therefore, initial ore-forming fluids exsolved from garnet-muscovite granite have Fe-rich composition, that was significantly modified during tungsten mineralization. Positive trend between Mg and Fe/(Fe + Mn) of wolframite indicates biotite breakdown from country rock of biotite-muscovite granite to add Fe and Mg into fluid during greisenization. Meanwhile, decomposition of plagioclase and K-feldspar provided Ca, Sr, and Eu to form late scheelite. Enrichment of Sr with positive Eu anomaly and decline of REE, Nb, and Ta are typical features of the highly evolved and modified fluid. Positive and negative Eu anomalies within the same wolframite grains reveal the oxidized character and fluctuating composition of fluid during wolframite precipitation. By contrast, negative Eu anomaly and low Mo abundance of scheelite indicate the reducing fluid during scheelite crystallization. Identification of metal and fluid sources for Anglonggangri ferberite highlights the evolved granites play more crucial roles on ferberite formation than early hübnerite crystallization and Fe addition from country rocks during hydrothermal interaction.

Hydrothermal Interaction Properties of Unsaturated Frozen Soil Studied Using a Modified Soil Freezing Characteristic Curve

Hydrothermal Interaction Properties of Unsaturated Frozen Soil Studied Using a Modified Soil Freezing Characteristic Curve

Subsurface anatomy of the Irazú–Turrialba volcanic complex, inferred from the integration of local and ambient seismic tomographic methods

SUMMARY Irazú and Turrialba are a twin volcanic complex that marks a distinct stop in volcanism along the Central America volcanic arc. We present a new traveltime velocity model of the crust beneath Irazú and Turrialba volcanoes, Costa Rica, and interpret it considering the results of previous ambient noise tomographic inversions. Data were acquired by a temporary seismic network during a period of low activity of the Irazú–Turrialba volcanic complex in 2018–2019. Beneath the Irazú volcano, we observe low P-wave velocities (VP = 5 km s−1) and low velocity ratios (VP/VS = 1.6). In contrast, below the Turrialba volcano, we observe low S-wave velocities (VS = 3 km s−1) and a high VP/VS (= 1.85) anomaly. We found that locations of low VP and VS anomalies (−15 %) correspond well with shear wave velocity anomalies retrieved from ambient noise tomography. At shallower depths, we observe high VP and VS anomalies (+15 %) located between the summits of the volcanoes. Subvertical velocity anomalies are also observed at greater depths, with high VP and VS anomalies appearing at the lower limits of our models. We propose a complex structure of an intermediate magmatic reservoir, presenting multiphase fluid states of a liquid-to-gas transition beneath Irazú and a juvenile store of magmatic fluid beneath Turrialba, while shallow fluid transport provides evidence of magmatic–hydrothermal interactions.

Tectonic-magmatic-hydrothermal interactions in a hot dry rock geothermal system: The role of the transfer and normal faults in the Acoculco caldera (Mexico)

In the Acoculco caldera (hot dry rock system) two geothermal boreholes were planned to intersect fracture systems in the carbonate basement. Even though the caldera is located in an area of active deformation with high rainfall, a scarce permeability was recognized. To shed light on this apparent mismatch, we investigate the area by integrating a structural and kinematic dataset on faults and fractures with the volcanological data. The results highlighted two main coeval fault systems, NW- and NE striking respectively, and two associated minor N-S and E-W striking sets, affecting the area of the Acoculco caldera and controlling its volcanic evolution. The kinematic analysis on fault-slip surfaces demonstrated that the NW-striking faults are characterized by two superposed movements: the first comprises right strike-slip to right lateral oblique-slip, while the second is dominantly normal. In contrast, the NE-striking structures display only dominantly normal movements. We explain the kinematic evolution by two recurring events, determined by the interplay between regional extension and uplift: when a crustal extension was dominant in the region (first kinematic event), the NW- and NE-trending structures played the role of transfer and normal faults, respectively; in contrast, when uplift predominated (second kinematic event) both the pre-existing NW- and NE-striking faults acted with normal movements. The location of eruptive centers is controlled by the permeability along the regional faults and their step-over zones. A closer analysis carried out in the surroundings of the geothermal boreholes suggests that deformation migrated northwards, and that fractures are sealed in this sector of Acoculco, thus strongly reducing permeability. In this view, the most promising areas for potential permeability at depth might occur northwards, beyond of the Acoculco caldera, and along the NW-trending structures. In conclusion, the fault kinematics is influenced by periods of increased partial melting of the lithosphere, the latter determining anomalous heat flux and uplift. This process interacts with the fluid pathways that are in turn controlled by the tectonic segmentation, and this is a new model to explain the tectonic-magmatic and hydrothermal interaction of this region.

Determination of the Effect of Zinc Acetate as a Doped Substance on the Properties of Cadmium Sulfide Nanomaterials by using a Hydrothermal Interaction Technique

In the current work, cadmium sulfide nanoparticles (CdS) NPs were synthesized via the hydrothermal interaction technique. Especially, the deviation in zinc Acetate Zn(CH3CO2)2 with 0.5% 1.5%, and 2.25% was examined for its part in nanoparticles size. The nanoparticle size seems to reduce from 149.7 nm to 116.3 nm by enhancing the zinc acetate Zn(CH3CO2)2. With increasing zinc acetate Zn(CH3CO2)2 in CdS (Cadmium Sulfide) small lattice phase changes appeared due to angle peaks of diffraction shifting toward higher angle. The standard crystallite size and lattice parameters were analyzed through X-ray diffraction (XRD) characterization. The average crystallite size and volume unit cell were found to increment with increasing Zinc acetate Zn(CH3CO2)2 concentrations. Absorption peaks in the UV visible spectra corresponding to zinc acetate Zn(CH3CO2)2 of CdS (Cadmium Sulfide) were analyzed at various wavelengths of 368 nm and 369 and 371nm. These findings show the tuning ability of structural, and optical characteristics of cadmium sulfide (CdS) NPs.

Strongly Peraluminous Highly Fractionated I-Type Granite from Bangong–Nujiang Metallogenic Belt, Tibet: Implications for Continental Evolution and Evaluation of Economic Potentiality

The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma’s evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits.

Mineralization process of the Mazhala Au–Sb deposit, South Tibet: Constraints from fluid inclusions, H-O-S isotopes, and trace elements

The Mazhala deposit is a typical Au-Sb deposit in the northern Himalayan orogenic belt that has increasingly attracted worldwide attentions. However, debates remain regarding the source of ore–forming fluid and its evolutionary process. Herein, we investigate the genetic and compositional evolutionary characteristics of different types of pyrite grains in order to better constrain the ore–forming fluid source and ore–forming processes by means of Using in-situ trace and sulfur isotope data of pyrite and inclusion temperature and H-O isotope data of quartz. Based on the occurrence and morphological features of pyrite, four types of pyrite (Py0, Py1, Py2, and Py3) have been identified. The framboids of pyrite Py0 have high contents of Au, Ag, Cu, Pb, and Sb, with Co/Ni < l, and their δ34S values range from −34.0‰ to −19.3‰, indicating a sedimentary-diagenetic origin. Py1 pyrite exhibits stark core-rim structure. The contents of Sn, Ti, Be and W in Py1c are higher, with Co/Ni > 1. The δ34S of Py1c ranges from 0.30 to 3.9‰ (mean = 1.7‰), indicating a magmatic hydrothermal transformation origin. Py1r, Py2, and Py3 differ greatly in pyrite morphology and trace element contents, with Co/Ni < 1, indicating as hydrothermal sedimentary transformation origin. The δ34S values of Py1r, Py2, and Py3 vary from 1.4 to 6.50‰, interpreted as the presence of metamorphic sulfur sources. The δ34S values of Py1-Py2-Py3 firstly increases and then decreases, indicatinga fluid mixing process. The Mazhala ore–forming fluid is typical of low temperature (270–291 °C), low salinity (1.1–5.0 wt%NaCl equiv) and CO2-enrichment, with H-O isotopic compositions of quartz resembling magmatic and/or metamorphic water, which makes us to infer a mixture of magmatic and/or metamorphic water source for the Mazhala ore-forming fluid. The early pyrite grains were dissolved and reprecipitated under the action of fluid. In the process of multistage hydrothermal interaction, Au and other trace elements were released from the primary pyrite lattice into the fluid, forming the gold–bearing ore–forming fluid. Separation of fluid phase coupled with significant change in the pH value of fluid prompted the co-precipitation of Au and Sb to form the Mazhala Au-Sb deposit.

Desert Abiotic Carbon Sequestration Weakening by Precipitation

Desert carbon sequestration plays an active role in promoting carbon neutralization. However, the current understanding of the effect of hydrothermal interactions and soil properties on desert carbon sequestration after precipitation remains unclear. Based on the experiment in the hinterland of the Taklimakan Desert, we found that the heavy precipitation will accelerate the weakening of abiotic carbon sequestration in deserts under the background of global warming and intensified water cycle. The high soil moisture can significantly stimulate sand to release CO2 at an incredible speed by rapidly increasing microbial activity and organic matter diffusion. At this time, the CO2 flux in the shifting sand was synergistically affected by soil temperature and soil moisture. As far as soil properties are concerned, with less organic carbon substrate and stronger soil alkalinity, the carbon sequestration of shifting sand is gradually highlighted and strengthened at low temperature. On the contrary, the carbon sequestration of shifting sand is gradually weakened. Our study provides a new way to assess the contribution of desert to the global carbon cycle and improve the accuracy and scope of application.

Oxygen and nitrogen-doped carbon particles derived from pyrolysis of Chlorella vulgaris and Spirulina platensis microalgae as an efficient electrode material for supercapacitor application

This study consists of the thermal activation of Chlorella vulgaris and Spirulina platensis microalgae with a potassium hydroxide (KOH) chemical agent in a carbon dioxide (CO2) atmosphere and the formation of nitrogen and oxygen-doped material from the hydrothermal interaction of the obtained activated carbons with nitric acid. The obtained nitrogen and oxygen-doped activated carbons were used in the production of electrochemical super capacitors. The morphological properties of the obtained pores were evaluated by transmission electron microscopy (TEM). Electrochemical properties were evaluated according to the cyclic voltammetry (CV) method in sulphuric acid (H2SO4), potassium chloride (KCl), and sodium hydroxide (NaOH) electrolytes with a scanning rate in the range of 2.5–50 mVs−1. Nitrogen and oxygen doped electrode electrochemical capacitor based on Spirulina platensis microalgae showed the highest specific capacitance of 99.53 Fg−1 at a scanning rate of 2.5 mV s−1 in 1 M H2SO4 electrolyte. In contrast, the supercapacitor based on an activated carbon electrode from Chlorella vulgaris microalgae showed the highest specific capacitance of 156.04 Fg−1 at a scan rate of 2.5 mV s−1 in 1 M KCl electrolyte.

Response of soil hydrothermal processes within the active layer to variable alpine vegetation conditions on the Qinghai‒Tibet Plateau

Alpine vegetation plays an important role in the thermal stability of the permafrost under a warming climate, as it affects ground hydrothermal dynamics. The response of soil hydrothermal dynamics in the active layer to permafrost degradation under different alpine grassland types is unclear on the Qinghai‒Tibet Plateau. In this study, long-term soil temperature and soil water content in the active layer were monitored in situ from October 2010 to December 2018 at five sites in the Kaixinling permafrost region on the interior Qinghai‒Tibet Plateau along the Qinghai–Tibet Railway. The sites included an alpine steppe (AS), three alpine meadows (AM) with different degrees of degraded vegetation, and an alpine swamp meadow (ASM). Based on field-monitored data, the variations in soil temperature, soil water content, and freeze–thaw processes were examined in the active layer. The response characteristics of the soil hydrothermal processes to climate change were analysed under the different alpine grasslands. The results showed that the duration of the thawing and freezing stages of the active layer of the AMs was shorter than that of the ASM and the AS. The average mean annual soil temperature (MAST) in the active layer of the AM ((−1.25 ± 0.50) °C) was lower than those in the AS ((−0.71 ± 0.39) °C) and ASM ((−0.45 ± 0.57) °C), while the AM had the highest rate of soil temperature increase ((0.2 ± 0.06) °C per year). The annual amplitude of ground temperature in the active layer increased with the transition direction of the alpine vegetation type from ASM to AM to AS. The small surface offset (SO) and thermal offset (TO) (absolute values) indicated that the ground thermal state of the AM was more unstable, as it was more sensitive to the increase in air temperature than the ASM or the AS. Soil properties controlled the distribution of soil water content within the active layer, but vegetation improved the shallow soil structure by producing more belowground phytomass, thus, enhancing soil water content in the 0–30 cm layer. The average soil water content at depths of 0–30 cm was directly proportional (p < 0.05) to the phytomass. Soil water contents at depths of 0–30 cm in the ASM ((37.7 ± 5.3)%) and the AM ((40.8 ± 5.9)%) were significantly higher than those in the AS ((22.7 ± 3.2)%). These results provide valuable insight into the hydrothermal interactions between the degradation of permafrost and alpine vegetation under a warming climate.

Mineralizations of Nb–Ta–Li and rare-earth elements in the Jiabusi rare-metal deposit, Inner Mongolia, China: Constraints from monazite, cassiterite, and bastnasite U–Pb geochronology and geochemistry

The Jiabusi Nb–Ta–Li deposit is a medium-sized rare-metal deposit discovered in central Inner Mongolia in recent years, and it is accompanied by Rb-Cs-REEs mineralization. Its magmatic and metallogenetic ages, magmatic source attributes, and mechanisms of magmatic evolution and related mineralization are not known. To identify these characteristics, with multi-stage granitic intrusions of the Jiabusi deposit as study objects, investigations relating to petrography, lithogeochemistry, monazite–cassiterite–hydrothermal bastnasite LA-ICP-MS U–Pb geochronology, and Nd isotopes were systematically conducted. The following results were obtained: The LA-ICP-MS monazite U–Pb ages of the metallogenetic Li-mica albite granite and granitic pegmatite are 148±7 and 141±2 Ma and 141±3, 137±2, 136±3, and 132±2 Ma, respectively; the cassiterite U–Pb ages of the Ta–Rb ore bodies are 148±2 and 146±1 Ma; and the bastnasite U–Pb age of the magmatic hydrothermal fluid is 116±1 Ma. These ages indicate that there were two episodes of granitic magmatism and related rare (rare-earth) metal mineralization in the Jiabusi area during the Yanshanian period (Jurassic–Cretaceous). Geochemical analysis results reveal that the barren biotite granite is characterized by high SiO2 (75.89 wt%) and high alkali (Na2O + K2O = 8.48 wt%) and a relatively high FeOT/(MgO + FeOT) value (0.92) and a relatively high Zr + Nb + Ce + Y content (393×10−6), whereas Al2O3 (12.35 wt%), CaO (0.51 wt%), and MgO (0.13 wt%) contents are all relatively low. These results indicate that the biotite granite is A-type granite, with characteristics similar to those of A1-type granite. The Li-mica albite granite is characterized by high F (0.95%-2.76%) and strongly peraluminous nature (A/CNK = 1.26–2.34). Meanwhile, it is strongly enriched in Cs, Li, Rb, Nb, and Ta but extremely depleted in Ba, Sr, P, Ti, Zr, and light REEs, with quite a strong negative Eu anomaly (δEu <0.01), an evident lanthanide tetrad effect (TE1,3 = 1.36–1.44), and Zr/Hf (3.0–4.0) and Nb/Ta (0.5–1.0) ratios deviating from those of a normal magmatic system. X-ray fluorescence and electron probe microanalysis surface scanning imaging analysis revealed the activity of F-REE-rich hydrothermal fluid and related REE mineralization in the uppermost part of altered granites. These features indicate that the metallogenetic ore bodies underwent higher degrees of magmatic fractionation and F-rich fluid–present melt–hydrothermal interaction. The Li-mica albite granite and multi-stage granitic pegmatite have consistent Nd isotope characteristics (εNd(t) = −3.4 to −3.9) and relatively concentrated two-stage model ages (TDM,2 = 1174–1247 Ma), suggesting that they are quite likely syngeneic multi-stage products with different degrees of fractional crystallization. Through comprehensive analysis of the results in this study and from previous research, the Yanshanian (Jurassic–Cretaceous) granite in the Jiabusi area is inferred to quite likely have originated from the partial melting of the ancient lower crust caused by lithospheric thinning and asthenospheric upwelling along the northern margin of the North China Craton, and it is revealed that a large amount of juvenile crustal materials had contributed to this process.

Deep sourced magma and ore-metal mobility in the D. João de Castro submarine volcano (Azores): a mineral chemistry and melt inclusion study

The D. João de Castro is a submarine volcano with known hydrothermal activity located in the Terceira ultra-slow spreading rift within the Azores triple junction (ATJ). Several well-known mafic and ultramafic rock-hosted seafloor hydrothermal systems lay along the Mid-Atlantic Ridge, to the north and to the south of the Azores platform, yet little is known about seafloor hydrothermal activity, ore-metal availability, and magmatic–hydrothermal interactions within the ATJ. Here, we investigate multi-phase melt inclusions hosted in early formed phenocrysts (olivine, clinopyroxene and plagioclase), and metallic precipitates found in groundmass vesicles. Combining detailed petrographic observations with geochemical data and thermobarometry calculations, we assess P–T conditions of early formed phenocrysts, melt pathways towards surface, timing of sulfide saturation and composition of immiscible sulfide melts. Results show that D. João de Castro is characterized by a multi-level magmatic system where primary melt segregated from the upper mantle and moved up through the oceanic crust with little residence time. Sulfide saturation with the formation of immiscible magmatic sulfide liquid (Fe–Ni–Cu) occurred early in primitive magmas with clinopyroxene and olivine crystallization and continued during plagioclase crystallization. At shallower levels, the magmatic degassing of volatiles carrying base metals (Cu–Zn–Pb–Co) and Ba have contributed to the element budget of the D. João de Castro hydrothermal system. The study of multi-phase melt inclusions and vesicles at D. João de Castro submarine volcano contributes to the understanding of source to surface magmatic processes at the Terceira Rift and underline the importance of magmatic degassing into seafloor hydrothermal systems.

Nitrogen, helium, and argon reveal the magmatic signature of fumarole gases and episodes of outgassing from upper-crustal magma reservoirs: The case of the Nisyros caldera (Aegean Arc, Greece)

The chemical composition of gases emitted by active volcanoes reflects both magma degassing and shallower processes, such as fluid-rock hydrothermal interaction and mixing with atmospheric-derived fluids. Untangling the magmatic fluid endmember within surface gas emission is therefore challenging, even with the use of well-known magma degassing tracers such as noble gases. Here, we investigate the deep magmatic fluid composition at the Nisyros caldera (Aegean Arc, Greece) by measuring nitrogen and noble gas abundances and isotopes in naturally degassing fumaroles. Gas samples were collected from 32 fumarolic vents at water-boiling temperature between 2018 and 2021. These fumaroles are admixtures of magmatic fluids typical of subduction zones, groundwater (or air saturated water, ASW), and air. The N2, He, and Ar composition of the magmatic endmember is calculated by reverse mixing modeling and shows N2/He = 31.8 ± 4.5, N2/Ar = 281.6, δ15N = +7 ± 3 ‰, 3He/4He = 6.2 Ra (where Ra is air 3He/4He), and 40Ar/36Ar = 551.6 ± 19.8. Although N2/He is significantly low with respect to typical values for arc volcanoes (1,000–10,000), the contribution of subducted sediments to the Aegean Arc magma generation is reflected by the positive δ15N values of Nisyros fumaroles. The low N2/He ratio indicates N2-depletion due to solubility-controlled differential degassing of an upper-crustal silicic (dacitic/rhyodacitic) melt in a high-crystallinity reservoir. We compare our 2018–2021 data with N2, He, and Ar values collected from the same fumaroles during a hydrothermal unrest following the seismic crisis in 1996–1997. Results show additions of both magmatic fluid and ASW during this unrest. In the same period, fumarolic vents display an increase in magmatic species relative to hydrothermal gas, such as CO2/CH4 and He/CH4 ratios, an increase of ∼50 °C in the equilibrium temperature of the hydrothermal system (up to 325 °C), and greater amounts of vapor separation. These variations reflect an episode of magmatic fluid expulsion during the seismic crisis. The excess of heat and mass supplied by the magmatic fluid injection is then dissipated through boiling of deeper and peripheral parts of the hydrothermal system. Reverse mixing modeling of fumarolic N2-He-Ar has therefore important ramifications not only to disentangle the magmatic signature from gases emitted during periods of dormancy, but also to trace episodes of magmatic outgassing and better understand the state of the upper crustal reservoir.

Wasteless Synthesis and Properties of Highly Dispersed MgAl2O4 Based on Product of Thermal Activation of Gibbsite

The study showed that the interaction of the product of centrifugal thermal activation of gibbsite with an aqueous solution of magnesium nitrate at a cationic ratio Mg:Al = 1:2 leads to the formation of mixed double hydroxides both under hydrothermal treatment at 150 °C and at room temperature. The subsequent thermal treatment at 550 °C of the product of mild interaction leads to ~90% alumina-magnesia spinel and ~10% MgO, while the treatment of the hydrothermal interaction product leads to ~100% spinel with the stoichiometric composition MgAl2O4. The obtained spinel samples possess a high specific surface area (above 100 m2/g) and a hierarchical pore structure formed by the micron-level particles of different sizes (1–2 and 10–20 μm) consisting of ~70 nm crystallites with ~3 nm pores; the samples differ mostly in the total volume and quantitative ratio of the pores. The samples have Lewis acid sites of moderate strength on the surface, the amount of which is much lower to how it is when compared with a sample prepared by precipitation in that they also differ by quantity from each other as well (503 μmol/g for stoichiometric spinel and 304 μmol/g for sample with admixture of MgO). As the calcination temperature is raised to 850 °C, the acidity decreases—only weak Lewis acid sites are observed, the amount of which is also higher for stoichiometric spinel (161 and 39 μmol/g, respectively). The method proposed for the synthesis of alumina-magnesia systems provides a high dispersion and a much lower surface acidity for the oxides; in addition, it minimizes or completely excludes wash water, in distinction to the precipitation method.

Groundwater Interacting at Depth With Hot Plastic Magma Triggers Phreatic Eruptions at Yugama Crater Lake of Kusatsu-Shirane Volcano (Japan)

Interpreting the triggering mechanisms for phreatic eruptions is a key to improving the hazard assessment of crater lakes. Yugama Crater Lake at Kusatsu-Shirane volcano, Japan, is the site of frequent phreatic eruptions with the recent eruptions in 1982–83, 1989, and 1996, as well as volcanic unrest, including earthquake swarms in 2014 and 2018. To understand the magma–hydrothermal interaction beneath Yugama Crater Lake, we analyzed lake waters from November 2005 to May 2021. From 2005 to 2012, Cl and SO4 concentrations decreased slowly, suggesting the development of a self-sealing zone surrounding the crystallizing magma. We focused on Ca, Al, and Si concentrations as representatives of the breach and dissolution of minerals comprising the self-sealing zone and the Mg/Cl ratio as an indicator for enhanced interaction between groundwater and hot plastic rock within the self-sealing zone. In 2006–2007, the Ca, Al, Si concentrations and the Mg/Cl ratio increased. No Cl and SO4 increase during this period suggests the self-sealing zone was leached by deep circulating groundwater rather than by magmatic fluids injection. After the 2014 earthquakes, Ca, Al, and Si increased again but were associated with a significant Cl increase and a pH decrease. We believe that the HCl-rich magmatic fluids breached the self-sealing zone, leading to fluids injection from the crystallizing magma to the Yugama crater. During this period, the Mg/Cl ratio did not increase, meaning that magmatic fluids ascending from the breached area of the self-sealing zone inhibited deep intrusion of groundwater into the hot plastic rock region. In 2018, magmatic fluids ascended through the self-sealing zone again with less intensity than in 2014. All eruptions since 1982 have been accompanied by a Mg/Cl ratio increase and a Cl decrease, whereas, when a significant HCl input occurs, as in 2014, no eruptions and no Mg/Cl ratio increase occurred. This demonstrates that the groundwater–hot plastic rock interaction, rather than the magmatic fluids input, played an essential role in triggering phreatic eruptions; i.e., phreatic eruptions can potentially occur without clear signs of fresh magma intrusions.

Mineralogical and geochemical study of serpentinized peridotites from the North-Western Pyrenees: New insights on serpentinization along magma-poor continental passive margins

The peridotite massifs from the North-Western Pyrenean belt are fragments of a short-lived mid-Cretaceous hyper-extended rift inverted by the Pyrenean orogeny. We studied the petrology, mineralogy and geochemistry of 32 hydrothermally altered peridotites from the Montaut, Turon and Urdach massifs. This study aims to bring new constraints on the nature of serpentinization processes from domains having experienced various degrees of crustal hyper-extension and mantle exhumation in a context analogous to non-volcanic ocean-continent transitions.The three massifs studied are mainly composed of spinel-lherzolites and sample the same sub-continental mantle lithosphere as Eastern Pyrenean refertilized-peridotite massifs. They display contrasted degrees of hydrothermal alteration and serpentinization during cooling (e.g., serpentine contents ranging from 1 to 100 wt%) as well as variable reaction paths. The Montaut massif, located below an extremely thinned Paleozoic upper crust, records cooling from high temperature hydrothermalism with incipient serpentinization affecting mostly pyroxenes (serpentine, tremolite, talc, clinochlore assemblage; ~350–450 °C) to the formation of lizardite-chrysotile and magnetite after olivine (~200 °C–350 °C). The Turon peridotites, which remained below the detached Mesozoic pre-rift cover after complete removal of the crust, are little serpentinized and have no magnetite, suggesting serpentinization during the latest stages of cooling (< 200 °C). The Urdach massif comprises magnetite-bearing ophicalcites as well as magnetite-poor serpentinites formed concurrently when mantle was exhumed to the sub-seafloor at the margin toe (down to ~200 °C). Each massif shows selective enrichments in fluid mobile elements, in particular, Cs, Sb and Li, indicative of hydrothermal interactions with fluids deriving from neighboring sediments and continental crust, likely mixed with seawater-derived fluids for the Urdach peridotites. Our results show that the formation of magnetite in the studied samples is not tied solely to temperature, and point to a role of fluid composition in the development of the different serpentinization pathways observed from one massif to the other, and within a same massif in the case of Urdach.The development of complex sequences of temperature-, and composition-controlled reaction paths distinguish serpentinization in the Western Pyrenees peridotites from that commonly observed in the oceanic sub-seafloor. It results in variable redistribution of iron between magnetite and serpentine minerals, with the predominance of Fe-rich lizardite in magnetite-poor serpentinized peridotites. It likely controls local redox conditions and H2 production; suggesting that the impacts of serpentinization on the production of dihydrogen will vary from passive margins to oceanic sub-seafloor.

Experimental analysis of a thermoactive underground railway station

Little is known about the real energy potential of thermoactive underground infrastructures, such as railway stations, that can act as a heating/cooling provider for the built environment. This study presents the results of thermomechanical full-scale in situ testing and numerical analysis of a thermoactive underground train station. The thermal performance and related geostructural impact of a portion of the new underground energy infrastructure (UEI) installed at the Lancy-Bachet train station in Geneva (Switzerland) are analyzed. Heating and cooling tests simulating real operative geothermal conditions are considered. Particular attention is given to (i) the monitored wall–tunnel hydrothermal interactions, (ii) the thermal response of the UEI to heating/cooling thermal inputs and (iii) the thermomechanical behavior of the energy geostructure. Among the main results of this study, it is shown how the hydrothermal tunnel behavior considerably varies on a seasonal basis, while the train circulation completely drives the airflow in the tunnel. The UEI shows a strong heat storage potential due to the main conductive heat transfers between the geostructure and soil, while lower heat fluxes are detected at the wall–tunnel interface. The extraction potential is of lower magnitude with respect to storage because of the limited range of operative fluid temperatures and of the concurrent action of temperature variations at the tunnel boundaries affecting the materials within the UEI. Preliminary guidelines for the thermal response test execution on underground thermoactive infrastructures are also reported. The monitored thermomechanical behavior suggests different wall behaviors in the vertical and longitudinal directions. Low-magnitude strains are recorded, while the mechanical capacity of the existing geostructure can satisfactorily sustain concurrent thermomechanical actions.

Well placement optimization for large-scale geothermal energy exploitation considering nature hydro-thermal processes in the Gonghe Basin, China

Doublet well system composed by extraction and injection wells is widely used for heat production from deep geothermal reservoirs. The large-scale implementation of doublet well systems lead to hydro-thermal interaction with the natural hydro-thermal flow system; this affects heat production efficiency and sustainable management of geothermal energy and groundwater resources. However, the interaction between artificial operations and nature hydro-thermal status was seldom considered in the well placement optimization. In this study, the natural status of hydro-thermal flow was determined by fitting numerical modeling output to the groundwater level and temperature observations, in a realistic site of the Gonghe Basin, China. The well separation and relative position were then optimized against background water flow direction. It was found that a well separation of 1200 m with the injection well located upstream (south) to the extraction well can maximize the volume of injected water entering extraction well, without influence on the outflow temperature. Based on this finding, we further compared the effects of “extensive well placement” where the wells were located sparsely in entire geothermal field, and “intensive well placement” where the wells were located centrally in a local region. The calculation showed that the performance of intensive well placement was superior to extensive well placement with higher outflow temperature and lower interruption in groundwater levels. Further optimization of intensive well placement resulted in the outflow temperature higher than 92 °C under the total outflow rate of 30,000 m3/d for 30 years, and the groundwater level changes can be controlled below 6.0 m. The multiple-step well placement optimization approach and novel intensive heat production mode regarding nature status of hydro-thermal flow in geothermal reservoirs, provides important reference to the other geothermal field for large-scale geothermal exploitation.