Hydrous Minerals Research Articles

High Resolution X-ray Diffraction Studies of the Natural Minerals of Gas Hydrates and Occurrence of Mixed Phases

The types and concentrations of gas hydrates collected from four different geological sites were analyzed using high-resolution angular dispersive X-ray powder diffraction, with synchrotron radiation as the source. Measurements were taken across a temperature range of 80 to 300 K and a pressure range of 0.1 to 80 MPa. All four gas hydrate samples showed the presence of three mixed crystal structures: structures I, II, and H. Additionally, the ice Ih structure was inherently present in all the natural gas hydrate minerals. The variation in the types and concentrations of gas hydrates can be attributed to the diversity of natural gases at different geographic locations.

Processes controlling magma fertility at buenavista del cobre porphyry copper deposit (cananea, méxico): A new petrogenetic model based on zircon u-pb dating and apatite geochemistry

The Buenavista del Cobre is a world-class porphyry Cu-Mo deposit located in the Cananea Mining District, northern Sonora, México. Using zircon U-Pb dating, we show that the Proterozoic Cananea Granite, unconformably overlain regionally by Paleozoic limestones hosting skarn deposits underlies the present-day pit. We also present new crystallization ages for host rocks of copper mineralization in the District, dating for the first time a volcanic rock of the Henrietta Formation at 186.8 ± 1.1/3.0 Ma and the El Torre Syenite at 176.3 ± 1.1/2.9 Ma. Zircon U-Pb dating of the different porphyritic bodies reveals that the magmatic activity at Buenavista del Cobre lasted at least 4 Myr, from 59.7 ± 0.5/1.1 Ma to 56.1 ± 0.2/0.9 Ma. The deposit is composed by several porphyry intrusions referred to as “ore-rich” and “ore-poor” based on their individual metal contributions, which provides the opportunity to study the origin and processes enhancing magma fertility in an individual deposit. Combining our new geochronological dataset with geochemistry of apatite from the different porphyries allows us to propose a new petrogenetic model for the Buenavista del Cobre deposit. As the apatite Eu and Ce anomalies overlap with no clear difference between the ore-rich and ore-poor intrusions, we propose that the magmatic oxidation states of the magmas were similar. However, differences in apatite REE signatures, as well as variations in apatite Sr compositions between the two groups suggest that fractional crystallization processes in the parental magma influence the fertility of the porphyries. Additionally, apatite Cl contents of ore-rich porphyry intrusions are higher (>0.4 wt%) than the ore-poor intrusions (<0.2 wt%), suggesting an important role of the initial Cl content of the magmas in the mineralization process. These observations give new insights on the petrogenetic processes at origin of porphyry magma fertility. We propose that the evolution of the parental melt by fractional crystallization of hydrous minerals (hornblende) at upper crustal levels induced low H2O content of the residual magma, resulting in the formation of ore-poor porphyries. In contrast, we suggest that fractionation of anhydrous minerals (plagioclase) increased the H2O content in the residual melt, leading to the formation of ore-rich porphyries. Our new data allow us to propose an original genetic model for the Buenavista del Cobre deposit, which involves two cycles of supply, cooling and partial crystallization. This contribution shows that petrogenetic processes controlling porphyry copper magmas fertility are recorded in the composition of apatite at the deposit scale and highlights the importance of considering apatite geochemistry as an exploration tool.

Discovery of calcium sulfate at different hydration states on Mars - based on perseverance SHERLOC analysis

Organic matter on planets is often co-deposited with evaporites, and evaporation of lakes in the Jezero region of Mars may have led to the deposition of abundant organic matter and minerals such as sulfates, making sulfates important minerals for preserving the remains of potential life on Mars, especially in different hydration states, will help to invert the variability of the Martian environment and provide guidance for the exploration of life on Mars. Raman spectroscopy can detect the molecular composition of organic matter and acid anion information of the target of interest, thus enabling in situ analysis of life information and its living environment. In order to realize the detection of life remains on Mars, The Perseverance rover is equipped with SHERLOC in situ material detection payload, which adopts a 248.6 nm deep ultraviolet (DUV) laser to simultaneously excite Raman and fluorescence signals of the target. In this paper, five scans in three modes (survey scan, HDR scan and detail scan) from two sites on Mars (Quartier and Bellegarde) were selected for preliminary analysis, and the presence of sulfate minerals at these two sites was confirmed. The detail scans at Quartier were analyzed in depth, and the presence of four calcium sulfate minerals, gypsum (CaSO4∙2 H2O), bassanite (CaSO4∙0.5 H2O), anhydrite (β-CaSO4) and gamma-calcium sulfate (γ-CaSO4)was inferred from the states of ν1 (SO4), ν3 (SO4) and hydrated peaks. The differences in the degree of hydration of calcium sulfate minerals suggest that there may have been active water activity on Mars. By comparing data collected by SHERLOC with spectra from spectral libraries, the composition of small-scale structures on Mars may be assessable. However, due to the complexity of the Martian geology, more accurate water activity will need to be combined with more detailed ions, temperatures, humidity, and other conditions for a more precise analysis.

Comprehensive Analysis of a Chloride‐Rich Topographic Depression in Terra Sirenum, Mars: A Possible Lost Basin With Astrobiological Significance

AbstractThe hygroscopic nature of chlorides gives them the potential to provide a harbor for microbes to adapt and survive in extreme conditions, which is pertinent to Mars, given its evolution of climatic conditions. Moreover, observations of secondary hydrous minerals in chloride‐rich regions have opened the case for a diverse geological environment on the Martian surface. Therefore, through comprehensive analysis, we aim to reconstruct the geological evolution of a chloride‐rich basin within Terra Sirenum. We conducted morphological, morphometric, and mineralogical analyses of the basin and its surrounding area to determine its geological evolution, longevity, and environmental condi5tions during its activity. Subsequently, we carried out a discharge analysis of the surrounding valley networks and determined the water activity using ionic forms of the associated mineralogy. We observed bright‐toned polygonal cracks within the basin as well as its surrounding terrain, suggesting that the basin extended beyond its present boundary. Mineralogical diversity and age dating of the basin and the surrounding area indicated different geochemical environments and cycles of wetting and drying until the late Hesperian. Whereas, sediment transport modeling suggests that the basin was hydrologically active for more than ten thousand years. Our results show a tell‐tale signature of a large sedimentary basin and a large‐scale geological process within the Terra Sirenum. The water activity modeling show that the geochemical composition of the basin was favorable to support the origin of life forms and/or sustain them and suggest promising aspects of the basin for future landing missions.

Geochemical constraints on reaction temperature and pressure and heat- and mass-transfer efficiency at Rainbow Hydrothermal Field

Seafloor vent fluids hosted by oceanic core complexes (OCCs) are thought to represent circulation of seawater-derived hydrothermal fluid along deeply penetrating, low-angle detachment faults. However, estimation of the source temperatures and pressures of such fluids has been limited because geochemical methods typically require vent fluid silica concentrations to be buffered by quartz, a condition not often met at oceanic core complexes. Here, we extend the calculation of the Si-Cl geothermobarometer to enable predictions of fluid Si concentrations in equilibrium with any Si-buffering mineral assemblage, rather than being restricted to quartz. We apply this method to Rainbow Hydrothermal Field vent fluid compositions and find that they are consistent with buffering by a plagioclase+talc+chlorite+tremolite mineral assemblage at conditions ranging from (430 °C, 359 bar) to (470 °C, 468 bar), which correspond to depths of 1.3–2.4 km below the seafloor. These estimates agree well with the locations of seismically imaged magma chambers within the Rainbow Massif. Additionally, calculations of fluxibility and Fe solubility support this relatively shallow origin for Rainbow vent fluids and imply relatively efficient heat and Fe extraction from the seafloor. We estimate that only 24–30 % of the heat content and almost no Fe is lost during upflow of Rainbow vent fluids.Compared to other OCC-hosted seafloor vents, the source region of Rainbow vent fluids is anomalously shallow, an observation consistent with geological interpretations of the Rainbow Massif. Vent fluids at Rainbow Hydrothermal Field have exhibited apparently stable and greater-than-seawater salinity for over two decades. We interpret these vent fluids as vapors derived from a higher-salinity source fluid that developed over multiple cycles of magma injection and phase-separation inherent to the formation of oceanic crust along slow-spreading, non-volcanic segments of oceanic spreading centers. Alternatively, higher-salinity source fluids could be derived from mineral hydration reactions associated with serpentinization of ultramafic rocks. The occurrence of greater-than-seawater salinity vent fluids is thus predicted to be a common feature of OCC-hosted vent fields, as indicated by several known examples, including the TAG, Kairei, and Edmond vent fields.

[formula omitted] Affects the crystalline calcium silicate hydrate minerals synthesized by fly ash-based silicon extraction solution and lime milk

When extracting amorphous silicon from fly ash using a strong alkaline solution, other elements such as Al also enter the silicon extraction solution in the form of AlOH4−. To systematically investigate the impact of AlOH4− on the synthesis of typical calcium silicate hydrate crystals in a silicon extraction solution, a specific amount of AlOH4− was added to the silicon extraction solution, and calcium silicate was hydrothermally synthesized at 90℃ and 230℃. Scanning electron microscopy (SEM) and Brunner−Emmet−Teller (BET) analysis revealed that with the increasing in AlOH4− content, microporous calcium silicate gradually loses its microporous morphology. While the specific surface area shows no significant change, the median pore diameter first increases from 1.47 nm to 1.58 nm and then decreases to 1.55 nm. The xonotlite fibers underwent a gradual refinement, diminishing from 0.28 to 0.15 µm. Simultaneously, the specific surface area increases from 28.87 to 56.8 m2/g. At an AlOH4− concentration of 3 mol/L, the microscopic morphology transforms into a sheet-like structure. X-ray diffraction (XRD) analysis reveals that AlOH4− promotes the formation of tobermorite while inhibiting the further development of calcium silicate. Additionally, Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance indicate that Al can replace Si in the calcium silicate hydrate system, primarily substituting positions the Q2 and Q3 sites. Qualitatively, it is suggested that with the increasing incorporation of Al, the polymerization degree of the silicon-oxygen tetrahedra decreases. According to experimental results, the concentration of AlOH4− should be below 0.05 mol/L when synthesizing microporous calcium silicate hydrate and less than 0.2 mol/L when synthesizing fibrous xonotlite-type calcium silicate hydrate.

Light δD apatites reveal deep origin water in North China Craton intracontinental granites and basalts

Water is essential to the formation of intracontinental granites, but its origin remains elusive. Here we address this scientific problem by analyzing D/H isotopes of apatites, hydrous minerals in Jurassic and Early Cretaceous granites and basalts from eastern North China Craton, where water was previously interpreted as derived from subducting slab. Results reveal extremely low δD values in pristine Early Cretaceous granitic (−203‰ to −127‰) and basaltic (−197‰ to −107‰) apatites, contrasting with relatively high δD values (−137‰ to −47‰) in Jurassic granites. Given the depth-dependent D/H isotopic fractionation during slab dehydration and high-water contents in coeval primitive mafic magmas, the Early Cretaceous magma water is attributed to the stagnant slab within the mantle transition zone. Secular change in the depth of water aligns with steepening of subducting Paleo-Pacific plate from Jurassic to Early Cretaceous, demonstrating the potential of apatite H isotopes in tracing water origin in granites and basalts.

Influence of mixing protocols on flow retention of one-part alkali activated slag systems

Poor workability and rapid flowability loss are among several challenges hindering the wider acceptance of alkali-activated slag (AAS) (i.e. shrinkage, efflorescence). Several attempts were made to solve this issue, focusing more on selected ingredients, proportions, type and dosage of admixtures, and addition sequence. This study shifted the focus to mixing protocol, highlighting its potential and effects on AAS flow retention considering mixing duration, sequence, and relaxation time. Various one-part AAS mixtures activated by 6 %, 8 %, and 10 % sodium metasilicate were tested. Mixing protocols were applied for 10–90 min, mixing with and without relaxation time. Mini-slump, flowability-loss rate, setting time, the heat of hydration, rheological properties, and compressive strength were evaluated. Changes in hydration products were also examined by XRD, FTIR and TGA. Pearson correlation coefficient and ANOVA were applied to identify the dominant factors. Results reveal the dependency of the optimum mixing protocol on the used activator dosage. A long mixing period with r intervals was more effective for high activator dosages due to the continuous breakdown of formed hydration products' links. Modifying the mixing protocol did not alter the amount of formed hydration products, regardless of the activator dosage. These findings pave the way to understanding the role played by the mixing protocol in mineral hydration for wider in-situ implementation of AAS and the flourishing potential of the ready-mix AAS market.

Simultaneous inversion of four physical parameters of hydrate reservoir for high accuracy porosity estimation

AbstractEstimation of the porosity of a hydrate reservoir is essential for its exploration and development. However, the estimation accuracy was usually less certain in most previous studies that simply assumed that there is a linear relationship between the porosity and single‐elastic wave velocities or other rock physical parameters, thus affecting the evaluation of the reserves. In the three‐phase Biot‐type equations that are fundamental to model a hydrate‐bearing reservoir, porosity, alongside hydrate saturation, mineral constituent proportions and hydrate–grain contact factor, is non‐linearly responded by density, compressional and shear wave velocities. To improve porosity estimation, we propose to invert simultaneously four‐parameter (porosity, hydrate saturation, mineral constituent proportions and hydrate–grain contact factor) using an iteratively nonlinear interior‐point optimization algorithm to solve a nonlinear objective function that is a summation of the squared misfits between the well log and three‐phase Biot‐type equation–modelled density, compressional and shear wave velocities. A test in Mount Elbert gas hydrate research well was conducted for the case of a gas hydrate stratigraphic test well where elastic wave velocities, density, porosity and mineral composition analysis data are available. The four‐parameter inversion yielded a lower root mean square error for porosity (0.0245) across the entire well‐logging section compared to previous estimations from the linear relationship, post‐stacked and pre‐stacked seismic traces as well as the pore‐filling effective medium theory model applied to other well cases. Additionally, the other three parameters demonstrated good agreement with well logs. Inversion tests conducted at three additional hydrate sites also produced accurate results. Consequently, the new method surpasses previous approaches in porosity estimation accuracy.

Low Thermal Conductivity of Epidote and Its Cooling Effect on the Oceanic Crust

AbstractEpidote is a potential water carrier in subducting oceanic crust, and it is involved in temperature records from blueschist and eclogite exhumed from subduction zones. Thermal conductivity (κ) and thermal diffusivity (D) of epidote were measured at 303–1,473 K and 0.5–3.0 GPa using the transient plane‐source method. κ and D values decreased with temperature before dehydration, but increase anomalously with temperature after dehydration, and finally decreased with crystallization of the decomposition products. Thermal conductivity and thermal diffusivity of epidote exhibited a positive pressure dependence. The obtained κ and D values of epidote were significantly smaller than those of nominally anhydrous minerals and other hydrous minerals. X‐ray computed tomography analysis revealed that the pores inside the recovered samples were partially connected. κ and D values were dominated by conductive heat transport before dehydration, while the anomalous increase in the thermal parameters after dehydration may have been caused by the fluid inside the connected pores. Using variable thermal conductivity obtained in this study, the thermal structures of warm subducting slabs associated with epidote‐blueschist and epidote‐eclogite facies were modeled. Our estimations revealed that the temperatures of warm slabs below the forearc with the epidote‐blueschist and epidote‐eclogite facies may be lower 7–10 and ∼40–50 K compared to those determined using a constant thermal conductivity value. This implies that the presence of epidote‐blueschist and epidote‐eclogite could reduce the temperature of the slab, which may alter the dehydration depth of the slab.

Mineral effects on methane hydrate formation and distribution in sand sediments

Methane hydrate is a promising energy resource widely occurring in the world, but the formation and distribution of methane hydrate in marine sediments with complex minerals remains unclear. Due to the small pore space and fine-grained size of clay minerals, the contact relationship between methane hydrate and clay mineral surface under excess water has not been characterized fully, which is required to investigate the mineral effect on methane hydrate formation. In this study, cryo-SEM was applied to observe the distribution of methane hydrate synthesized in pure quartz sands and the quartz sands mixed with montmorillonite or illite separately. According to the results of the research, methane hydrate dispersedly forms in the pore space away from and on the surface of quartz under a local excess water condition. In addition, methane hydrate occurs away from montmorillonite in pores with excess water and contacts the edge of montmorillonite under a local excess-gas condition. Moreover, methane hydrate was only observed to form away from illite aggregates in the pore with residual water. Montmorillonite and illite influence the preferable distribution of methane hydrate to occur away from mineral surface in excess water condition. In the sediments composed of different minerals, methane hydrate forms stochastically in the pore space and grows up individually. As a result, the findings of this study significantly expand the understanding of the formation and distribution of methane hydrate in marine sediments and the prediction of physical properties of hydrate-bearing sediments, and provide insights into natural gas hydrate exploration and production.

Heterogeneous water distribution in between peridotite xenoliths from Kaapvaal Craton kimberlites: Constraints on diamond barren nature of kimberlites

Nominally anhydrous mantle minerals (olivine, pyroxenes, garnets, etc.) in 11 peridotite xenoliths from four different uneconomic and economic Kaapvaal Craton kimberlite pipes (Matsoku, Thaba Putsoa, Pipe 200 and Bultfontein) have been investigated using Fourier transform infrared spectroscopy (FTIR). All xenoliths contain accessories of garnet, diopside, chromite, and phlogopite. High orthopyroxene content (>30 mol vol.%) in most xenoliths from all kimberlites and its interconnected channel-like nature hint towards hydrous siliceous fluid metasomatism. Peridotite xenoliths from uneconomic kimberlites show development of phlogopite and clinopyroxene (± chromite) forming veins and in garnet rims suggesting metasomatism by alkaline silico-carbonatite (possibly kimberlite-related) melt. The xenoliths contain significant H2O in olivine (17–62 ppm), orthopyroxene (21–230 ppm), and clinopyroxene (87–833 ppm), whereas garnets are dry and only show IR absorbance bands at > 3,670 cm−1 for contamination of hydrous minerals. Compared to the economic kimberlites in the Kaapvaal Craton, the uneconomic kimberlite xenoliths from this study have lower orthopyroxene and olivine H2O content. In the xenoliths affected by garnet breakdown metasomatism, the H2O content of orthopyroxene and olivine is higher and lower, respectively. The structural hydroxyl distribution profile across olivine and higher inter-mineral water partition coefficient, suggest diffusion of hydrogen and possible re-equilibration. Statistical analysis of the olivine spectra suggests that hydrogen bands at 3540, 3624, 3638, and 3672 cm−1 are a good discriminant of economic and uneconomic kimberlites and in literature, they are associated with metasomatism, weathering-associated processes, high water activity, and oxygen fugacity. The lower water concentration in xenoliths from uneconomic kimberlite from the margin of the craton than the economic kimberlites from the interior of the Kaapvaal Craton and identified metasomatism hints towards dehydration of xenoliths by water-poor and CO2-rich melts in tectonized cross-lithospheric zones causing diamond resorption and may be responsible for the diamond-poor nature of uneconomic kimberlites in northern Lesotho.

Stability and physical properties of brucite at high pressures and temperatures: Implication for Earth’s deep water cycle

Brucite is a common hydrous mineral on Earth and may contribute to the deep water cycle of the Earth, but its stability and structure under mantle conditions remain uncertain. In this study, we investigated the stability of brucite up to 60 GPa at 800 K and 45 GPa at 1850 K. Within the experiment P-T conditions, no theoretically predicted new phase was observed, and brucite remained in the P3¯m1 structure. With the determined thermal EoS of brucite and the elastic parameters of mantle minerals, we modeled the velocity and density profile of subducted hydrous harzburgite in the top lower mantle, assuming that the water was stored in brucite and phase D. Based on the modelling, 1 wt% water will reduce the velocity and density of harzburgite by ∼ 5 % and ∼ 2 %, respectively, yet whether the water is stored in brucite or phase D has weak influence on both density and velocity. With a water content up to 2.4 wt%, the density of hydrous harzburgite could be reduced to 2.2(2)%–2.8(2)% lower than the surrounding mantle, while the VP and VS of hydrous harzburgite are still 0.3(1)%–0.7(1)% and 0.7(2)%–1.8(2)% higher than that of the normal mantle. Thus, the low-density hydrous harzburgite may slow down the subducting of slab, despite being a high-velocity body in seismic observations.

Aluminum and Iron Effects on the Electrical Conductivity of the Dense Hydrous Magnesium Silicate Phase E

AbstractThe electrical conductivity of pure and Al/Fe‐bearing phase E was measured up to 950 K at 15 GPa using a complex impedance spectroscopy. Pure phase E shows comparable conductivity to that of phase D, and a few orders of magnitude higher than that of phase A and super‐hydrous phase B. Al‐bearing phase E does not exhibit a conductivity difference, while a certain amount of incorporated Fe prominently increases its electrical conductivity by a factor of 4. Unlike the sole substitution 2Al3+→Mg2++Si4+ in phase D and H, H+ is likely involved in the substitution. Proton conduction is the dominant conduction mechanism, while small polaron conduction becomes dominant with increasing Fe content. Phase E in subducted slabs at depth of the upper transition zone cannot explain the high electrical conductivity anomalies beneath the Philippine Sea or Northeast China. Other mechanisms such as dehydration of hydrous minerals is needed to account for them.

Binding properties of synthesized CS glasses activated by alkaline components

The paper presents the synthesis and evaluation of hydration and binding properties of individual minerals with glass-like structures in silicate systems, most often found in technogenic materials based on phosphorus and blast furnace slags. This work aims to determine the optimum composition of CS glasses to obtain binders with given properties, the hydration of glasses of different silicate and aluminosilicate compositions in the presence of solutions of soda, sodium hydroxide, and sodium metasilicate was investigated. The results of X-ray phase and differential-thermal analysis, and infrared spectrum are given, and the hydration structure of the calcium oxide-silicon oxide-alkali component system has been studied. The analysis of hydrate neoplasms of the studied binding systems shows that the most optimal conditions for the synthesis of stone strength with stable physical and mechanical properties are created in the presence of gel-like phase reinforced by hydrosilicates and hydroaluminosilicates of alkaline and alkaline-alkaline-earth composition, characterized by fiber-like structure and possessing the ability to epitaxial fusion with each other, as well as gel-like phase, which they reinforce.

The presences of water in the generation of calc-alkaline I-type granitic magmas at continental arc: Insight from Neoproterozoic Ailaoshan magmatism at the southwestern margin of the Yangtze Block, South China

Water is crucial in generating granitic systems; however, its role (i.e., dehydration, low to high water-fluxed melting) in granitic magmatism in continental arcs remains unsettled and poorly understood. Neoproterozoic arc-related igneous rocks are uncovered along the western margin of the Yangtze Block, presenting a complex compositional array ideal for deciphering the influence of water content within the continental arc and its geodynamic significance. The Jinping granites, in the Ailaoshan zone, are emplaced at 750 ± 4 Ma, as determined by zircon U-Pb dating. These medium to coarse-grained granites consist predominantly of plagioclase, quartz, K-feldspar, muscovite, and biotite. Characterized by high SiO2 (71.2–73.5 wt%), alkalis (K2O+Na2O=7.54–9.56 wt%) and low Fe2O3T (1.01–1.66 wt%), MgO (0.53–0.85 wt%), and CaO (0.15–0.93 wt%) concentrations, they exhibit high-K calc-alkaline signatures. The negative correlation between P2O5 and SiO2, alongside the positive correlation between Rb and Y, typifies the Jinping granites as I-type granites. Low La/Nb (1.96–3.43) and Nb/Ta (8.57–11.3) ratios, but high Th/La (0.28–0.46) and Zr/Sm (30.5–47.7) ratios, as well as whole rock εNd(t) (−0.4 to +1.3) and zircon εHf(t) values (+5.25 to +8.53) of the studied granites are similar to synchronous mafic rocks at the western margin of the Yangtze Block. These features suggest partial melting origin from the mafic lower crust. Thermodynamic modeling posits that the Neoproterozoic Ailaoshan I-type granitic rocks may have formed through water-fluxed melting (2.0–3.5 wt% H2O) under medium pressure conditions (9 kbar). It is postulated that slab rollback could have prompted water (as hydrous melt or fluids) release from hydrous minerals in the underlying cumulate mafic rocks, subsequently triggering water-fluxed melting in the lower crust. In contrast, high water-fluxed melting-generated adakitic granites with low K2O/Na2O ratios (<0.8) in the region, spatially and temporally associated with the Jinping granites, reflect higher water content in the deeper crust. This supports the notion that water was conveyed from depths to surface, facilitating the conversion of adakitic rocks into I-type granites as water content diminished. Thus, water content within the lower crust plays a pivotal role in the genesis of granitic rocks with varied compositions in a continental arc setting.

Volatile Elements Characterized by MarSCoDe in Materials at Zhurong Landing Site

The study of volatile elements on the Martian surface is a critical way to explore the geological evolution history of Mars. Volatile elements such as hydrogen (H), sulfur (S), and chlorine (Cl) on the Martian surface act as proxies for the potential aqueous or atmospheric environments that formed their corresponding phases. In this work, data collected from the Laser Induced Breakdown Spectroscopy and the Short Wave Infrared Spectroscopy of the Mars Surface Composition Detection onboard the Zhurong rover are employed to analyze the volatile elements (H, S, Cl) and their carriers in materials throughout the landing site. We found that S primarily concentrates in gypsum and other sulfates, and the carriers of H include hydrous mineral combinations such as gypsum, hydrated silica, and ferrihydrite. These altered minerals are probably the products of acid weathering processes, which may have occurred mostly during the relatively humid period of the Zhurong landing site since Amazonian.

Rate-and-state friction of epidote gouge under hydrothermal conditions and implications for the stability of subducting faults under greenschist metamorphic conditions

Epidote is a common hydrous mineral present in subduction zones subject to greenschist metamorphic conditions – and potentially an important control on the fault stability-instability transition observed under greenschist facies. We explore controls on this transition through shear experiments on simulated epidote gouge at temperatures of 100–500 °C, effective normal stresses of 100–300 MPa and pore fluid pressures of 30–75 MPa. We use rate-and-state friction to define these controls of temperature, effective stress and pore fluid pressure on gouge stability. Experimental results indicate that the epidote gouge is frictionally strong (μ ∼ 0.73) and the frictional strength is insensitive to variations in temperature or pressure. With increasing temperature, the epidote gouge exhibits a first transition from velocity-strengthening to velocity-weakening at sub-greenschist conditions (T < 100 °C) before transitioning to velocity-strengthening under greenschist metamorphic conditions (T > 300 °C). Elevating the pore fluid pressure or decreasing the effective stress promotes unstable sliding. The transition in gouge rheology at varied temperatures and pressures is explained by the competition between granular flow-induced gouge dilation and pressure solution-induced gouge compaction. Our results demonstrate that the rate-and-state frictional stability of epidote gouges support the potential for a fault stability-instability-stability transition for subduction under greenschist metamorphic conditions.

The effect of antigorite dehydration on velocity structure and water migration in subduction zones

The water migration in subduction zones, primarily driven by the phase transition in hydrous minerals, can give rise to hydrated regions with reduced velocity. A fundamental element in comprehending and deciphering these low-velocity zones revolves around acquiring insights into the stability and elasticity of relevant hydrous minerals. As one of the main water carriers in shallow areas, antigorite can dehydrate to form talc, forsterite, and fluid (talc–bearing peridotites) in deep areas of subduction zones, and then the talc thus serves as one of the minerals that can bring water to the deep Earth. Here, the elasticity of talc up to 24 GPa and forsterite up to 12 GPa are calculated by using the first principles method. The result supposes that the talc structure transforming from talc I to talc II is at a pressure between 6 GPa and 8 GPa, impacting the trend of elastic wave velocity in response to pressure. Furthermore, the elastic wave velocity of forsterite can be significantly affected by iron concentration. Meanwhile, a variation velocity model with antigorite consumption and talc content is set up for talc-bearing serpentinized peridotite based on the elastic properties of talc and forsterite in this study, and antigorite in Wang et al. (2022). The results of our model demonstrate a decrease in the low-velocity anomaly in subduction zones, particularly in deep regions or areas with higher initial serpentinization degrees. The results also suggest that the mode of antigorite dehydration can diminish the estimation of water content transported to depths of subduction zones, such as the Mariana Trench and Northern Japan subduction zones. The mode of antigorite dehydration thus provides a useful tool for constraining the composition, seismic velocity structure, and water migration in subduction zones.

Elasticity of epidote at high pressure and its implications for the velocity anomaly in subduction zone

Hydrous minerals play a critical role in modifying the physical and chemical properties of the Earth’s interior. Among those, epidote is an important hydrous mineral in greenschist and blueschist phases of the metamorphosed subducting crust at shallow depth (30-60 km). Here, we measured the compressional (P) and shear (S) wave velocities of a polycrystalline epidote sample at pressures up to 7 GPa and room temperature by means of ultrasonic interferometry. The obtained sound velocities and elastic moduli of epidote increase monotonically with pressure. Finite strain analysis on those data set yielded the elastic moduli and their pressure derivatives of epidote at ambient condition as follows: KS0=115.2GPa, G0=66.7GPa, Ks′=4.6, G′=1.1. Using the elastic properties of epidote, we set up a model to better understand the velocity jumps in the subducted oceanic crusts concerning the blueschist-eclogite transition at 60-90 km depths. Our results indicate that the calculated P and S wave velocity jumps are in good agreement with those seismic observations in the typical subduction zones such as northeastern Japan and southwestern Japan. The eclogitization from epidote bearing blueschist may provide an explanation for the wave velocity anomalies occurred in those regions.