High-temperature Water Rock Interaction Research Articles

Formation of hydrothermal ferromanganese oxides from the Daigo-Kume Knoll in the middle Okinawa Trough, Japan

Many active hydrothermal sites resulting from active volcanism have been recognized in the Okinawa Trough, a nascent back-arc basin. Despite its importance for understanding whole hydrothermal circulation, low-temperature (LT) hydrothermal activity, which precipitates ferromanganese (Fe–Mn) oxides, has not been actively studied compared to high-temperature (HT) hydrothermal activity, which forms sulfide deposits. Therefore, in this study, we investigated the origin and formation of Fe–Mn oxides obtained from the outer rim of the Daigo-Kume Knoll caldera in the middle Okinawa Trough based on their chemical and mineral compositions. Composed of birnessite and todorokite, the Fe–Mn oxide samples contain low levels of trace elements, indicating their precipitation from LT hydrothermal fluids. This is the first report of hydrothermal activity at the Daigo-Kume Knoll. Based on an independent component analysis of elemental mapping data, it was determined that the hydrothermal activity consisted of two stages: a primary hotter LT hydrothermal fluid (roughly 30 °C–150 °C) that altered silicate debris and precipitated mainly Fe oxides, and a secondary colder LT hydrothermal fluid (roughly 30 °C) that precipitated mainly Mn oxides without alteration. The growth rate, estimated from the chemical composition, and the thickness of the Fe–Mn oxide samples indicated that the duration of the hydrothermal activity was about 17.7–29.5 kyr. In contrast to their LT hydrothermal origin, the high Mo/Mn ratio of the Fe–Mn oxide samples suggested that the LT hydrothermal fluids that precipitated the Fe–Mn oxide samples might be originally produced by HT water–rock interactions.

Elemental dissolution characteristics of granite and gabbro under high-temperature water-rock interactions

In the process of developing hot dry rock (HDR) through enhanced geothermal systems (EGS), it is necessary to inject circulating water to complete thermal energy extraction. However, the injected water will react with the high-temperature rock and produce mineral dissolution, which can destroy the artificial reservoir and affect the development of geothermal energy. To explore the influence of temperature on the solution composition and mineral dissolution after water-rock reaction, this study conducted water-rock interaction experiments on gabbro and granite at different heat treatment temperatures. Subsequently, the changes of solution composition and mineral dissolution with temperature after the reaction were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and XRD. The results demonstrated that Si, Na, Ca, K, Al, and Mg did not enter the aqueous solution at the same dissolution rate. Si was the primary solute in the solution, mainly resulting from the dissolution of quartz, and the dissolution rates of metallic elements were lower. In the granite-water interaction system, metallic elements such as Na, K, Ca, and Al showed a tendency to enter the solution at low temperatures, i.e., 150–180 °C, and the dissolution rate of Si reached its peak when the water was close to the supercritical state. With the increase in temperature, the dissolution rates of Si and metallic elements showed an initial increasing trend followed by a decrease. When water is in the subcritical to the supercritical state, abrupt fluctuations in the physical properties of water can strongly affect the dissolution of minerals or rocks. The results of this study provide insights into rock corrosion fatigue and mineral scaling in EGS water environment.

Reconstructing the evolution of an ancient continental arc: Implications from the temporally-spatially related shoshonitic to calc-alkaline intrusive magmatism in the North China Craton

Coeval shoshonitic and calc-alkaline to high-K calc-alkaline rock series were discovered in the eastern North China Craton (NCC). Here, we report zircon and titanite UPb dating, zircon oxygen isotopic, whole-rock major and trace element and SmNd isotopic data for these rocks. Zircon and titanite UPb geochronology suggests that the coeval shoshonitic to calc-alkaline mantle-derived magmas from the Jinan terrane were emplaced at ∼2.5 Ga and recorded multi-phases of metamorphic imprints. The shoshonitic series in Group I show higher K2O, but in contrast, the calc-alkaline to high-K calc-alkaline series (Group II) are characterized by higher Na2O. The two groups have enriched light rare earth elements (LREE) and depleted/nearly flat heavy rare earth elements (HREE). They also show negative anomalies in some HFSE and positive anomalies in LILE. Therefore, the geochemical data, SmNd and O isotopes included, show that the Jinan shoshonitic to calc-alkaline magmas were generated by melting of the metasomatized mantle at an ancient continental arc. Distinct geochemical features possibly suggest different mantle source features (metasomatic agents). The elevated zircon δ18O values imply that the weathering was significant during the end of Archean. In addition, the crustal reworking or intra-crustal recycling process played an important role in the continental crust evolution. The low-δ18O magmas documented here possibly indicate high-temperature water-rock interaction that occurs between continental crust and meteoric water. This study represents an example of co-existed shoshonitic and calc-alkaline mantle-derived magma derived from the melting of metasomatized mantle above an ancient subduction zone. Similar coeval associations of shoshonitic to calc-alkaline mantle-derived rocks, in combination with high-P granulites and crust-derived granites, may be used to constrain the ancient subduction-collisional belts.

Rare Time Series of Hydrothermal Fluids for a Submarine Volcano: 14 Years of Vent Fluid Compositions for Brothers Volcano, Kermadec Arc, New Zealand

AbstractHydrothermal vent fluids from Brothers submarine arc volcano were previously collected in 2004, 2005, and 2017. We present new data from 2018 along with a unique time series of a submarine volcano hosting two distinct types of hydrothermal venting to better understand subsurface processes and how they evolve over time. Samples were collected from known venting locations along the NW Caldera, the Upper and Lower Cone sites, and the newly sampled Upper Caldera site. The NW Caldera wall and Upper Caldera vent fluid compositions are controlled by high-temperature water-rock interactions and phase separation between 2004 and 2018. Fe/Mn molar values suggest that the magmatic impact on all fields has been increasing over time. The Upper Cone has varying influences, including short-term pulses of magmatic degassing, as revealed in K-Mg-SO4 ternary diagrams, Fe/Mn values, and δD and δ18O data. The Lower Cone is dominated by low temperatures and CO2 degassing and shows a pulse in magmatic influence in 2017, followed by a decrease toward earlier conditions in 2018. The 2017 pulse was accompanied by the increase of an enigmatic, soluble MgSO4 phase, potentially due to the “mining” of a magmatic brine sequestered inside the cone. Stable isotope data across the sites indicate pulses of magmatic waters in 2004 and 2017, immediately followed by episodes of more seawater-dominated fluids in 2005 and 2018. Magmatic degassing, phase separation, permeability, and mineral solubility all strongly influence changes in vent fluid composition. This study highlights the dynamic nature of the Brothers volcano hydrothermal system and the changes in fluid chemistry that may affect resultant mineralization.

Geochemical characterisation of the thermo-mineral waters of Greece.

Geothermal areas of Greece are located in regions affected by recent volcanism and in continental basins characterised by elevated heat flow. Many of them are found along the coast, and thus, water is often saline due to marine intrusion. In the current study, we present about 300 unpublished and literature data from thermal and cold mineral waters collected along Greece. Samples were analysed for major ions, Li, SiO2 and isotopes in water. Measured temperatures range from 6.5 to 98 °C, pH from 1.96 to 11.98, while Total Dissolved Solutes (TDS) from 0.22 to 51 g/L. Waters were subdivided into four main groups: (1) thermal; (2) cold; (3) acidic (pH < 5); and (4) hyperalkaline (pH > 11). On statistical basis, thermal waters were subdivided into subgroups according to both their temperature [warm (< 29 °C), hypothermal (29–48 °C), thermal (48–75 °C) and hyperthermal (> 75 °C)] and TDS [low salinity (< 4 g/L), brackish (4–30 g/L) and saline (> 30 g/L)]. Cold waters were subdivided based on their pCO2 [low (< 0.05 atm), medium (0.05–0.85 atm) and high (> 0.85 atm)]. δ18O–H2O ranges from − 12.7 to + 2.7‰ versus SMOW, while δ2H–H2O from − 91 to + 12‰ versus SMOW being generally comprised between the Global Meteoric Water Line and the East Mediterranean Meteoric Water Line. Positive δ18O shifts with respect to the former are mostly related to mixing with seawater, while only for a few samples these shifts point to high-temperature water–rock interaction processes. Only a few thermal waters gave reliable geothermometric estimates, suggesting reservoir temperatures between 80 and 260 °C.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10653-021-01001-1.

Hydrogeological research in the Tuyajto Lake at the Flamingo National Reserve (Atacama, Chile)

The Tuyajto Lake is a saline lake located in the Andean Altiplano of northern Chile, at the foot of the volcano of the same name. It is fed by springs located on its eastern and northern boundaries. These springs discharge groundwater from a volcanic aquifer. Arid conditions dominate in the area, with an average precipitation of less than 200 mm/year. The tritium content in some groundwater samples shows the contribution of modern recharge to the total groundwater flow. Recharge occurs by infiltration of snowmelt in the austral winter months and to a lesser extent by short but intense precipitation events during the summer. According to the vertical gradients of precipitation and its rainfall isotopic content (δ18O, δ2H), the recharge zone of the springs is located at the northern area of the lake, above 4,900 m a.s.l., along the slopes of the Tuyajto volcano, whereas the recharge to the springs discharging on the eastern area of the lake originates in the adjacent basins of Pampa Colorada and Pampa Las Tecas, at altitudes of between 4,400 and 4,700 m a.s.l. The water of these springs may contain measurable tritium. The chemical composition of groundwater is the result of meteoric water evaporation processes, high temperature water-rock interaction and the dissolution of buried old salt flat deposits. The groundwater flow is shallow, due to the presence of a regional low permeability ignimbrite formation, which precludes the formation of deep convective groundwater flow cells due to the high density. At the local scale, the Laguna Tuyajto behaves as a flow-through system compared to the regional groundwater flow. The persistence of the springs is essential for the existence of the brine sheet and maintaining the ecological conditions for the waterfowl.

Origin of geothermal waters from the Upper Cretaceous to Lower Eocene strata of the Jiangling Basin, South China: Constraints by multi-isotopic tracers and water-rock interactions

Fluids in geothermal reservoirs can be affected by the interaction with host rocks. To determine solute sources and water-rock interaction processes, this study collected water samples from the Upper Cretaceous to Lower Eocene strata of the Jiangling Basin, South China. Their chemical and isotopic (hydrogen, oxygen, strontium, boron) characteristics and the mineralogy of corresponding reservoir rocks were investigated. Five high-salinity water samples (343–359 g/L) were collected from deep boreholes tapping Paleocene to Eocene formations in the central basin. Seven water samples (four oilfield and three saline waters) were collected from boreholes tapping Upper Cretaceous formations in the northwestern part of the basin and had salinities of 23.1–81.4 g/L. These water samples showed depletion of Mg and SO4 and enrichment of K, Na, Ca and Cl, compared with the ion trajectories of evaporated seawater. The observed Cl/Br mass ratios (709–1390), Na/Cl molar ratios (0.79–1.01), Ca excess and Na deficit imply contributions of halite dissolution and multiple diagenetic processes of albitization, dolomitization, and calcite and anhydride cementation, which are consistent with the reservoir rock mineralogy. Chemical geothermometers of these geothermal fluids estimated temperatures of around 200 ± 20 °C and 125 ± 10 °C for hot brines and saline waters, respectively. Compared with the chemical compositions of Upper Cretaceous saline waters, the hot brines are enriched in K, Li, B, Sr, Rb, Cs, Br, Ba and transition metals such as Co, Ni, Cu, Zn, V, Ti and Mn. Correlations of δ18O–Li, δ18O–Rb, δ18O–Cs and δ18O–K values indicate that equilibrium with rocks caused enrichments in K, Li, Rb and Cs. Variations in 87Sr/86Sr ratios (0.706954–0.711249) and δ11B values (+8.7‰–+23.1‰) were used to find many discrepancies due to water-rock interactions involving basalt and clastic rocks. The integration of chemical and isotope data suggests that the geothermal waters in the Jianging Basin are derived from water-rock interactions and recharge of meteoric waters. In addition, the boron isotope data are consistent with traditional hydrogen, oxygen and strontium isotopes in terms of explaining water-rock interaction processes. Multi-isotopic characterization of Upper Cretaceous to Lower Eocene geothermal waters indicates that the isotopic compositions of water from the Jiangling Basin are consistent with a fluid signature of interactions involving basalt and clastic rocks with water derived from primary brine diluted by meteoric waters. The combined water chemistry and multi-isotope approach shows that high-temperature water-rock interaction is a major influence on the mineralization of hot brines in the Jiangling geothermal system.

Origin and evolution of the Neoproterozoic Dengganping Granitic Complex in the western margin of the Yangtze Block, SW China: Implications for breakup of Rodina Supercontinent

A better understanding of the origin and evolution of widespread Neoproterozoic granites along the western margin of the Yangtze Block is important in locating the position of South China within the Rodinia Supercontinent, and the mechanism by which the supercontinent was fragmented. Published and our new detailed geochronological and geochemical data from the Dengganping Complex show that it formed during an extended magmatic event during the Neoproterozoic. This was during the emplacement of a fractionated ca. 815 Ma syenogranite, which was followed by partial melting during ca. 740 Ma and the emplacement of a biotite monzogranite. The geochemistry of the syenogranite indicates it is: (1) a peraluminous high-K type of granite; (2) calc-alkaline; (3) fractionated; (4) enriched in Th, U, Zr, Hf and LREE (LREE/HREE values of 5.3–9); (5) depleted in Nb and Sr; (6) has a negative Eu anomaly (δEu = 0.3–0.5); (7) has whole rock εNd(t) value of −0.7 to +0.5; (8) has zircon εHf(t) value of −1.7 to +5.2; and (9) has zircon 18O values ranging from 5.13 to 7.38‰. These characteristics are indicative of a source derived from the partial melting of crustal material. The biotite monzogranite is: (i) peraluminous calc-alkaline to high-K calc-alkaline; (ii) enriched in LREE (LREE/HREE = 9.9–14.6), Rb, Ba, Th and U; (iii) depleted in Nb and Ta; (iv) has weak negative δEu and δCe anomalies; (v) has whole rock εNd(t) value of between −3.2 and −1.8; has relatively high positive zircon εHf(t) values of +4.1 to +13; and has zircon 18O values ranging from 3.44 to 6.75‰. These features are indicative of partial melting of a juvenile mafic crust that might have experienced a high-temperature water-rock interaction. By comparing the geochronology of Neoproterozoic magmatic rocks along the faulted western margin of the Yangtze Block, it is suggested that the region was part of the Rodinia Supercontinent when it started to breakup during widespread rifting between ca. 825 and 710 Ma. We believe the fault zone formed in response to an opening ocean was induced by the presence of a mantle plume during this period.

Hydrogeological research in the Tuyajto Lake at the Flamingo National Reserve (Atacama, Chile)

The Tuyajto Lake is a saline lake located in the Andean Altiplano of northern Chile, at the foot of the volcano of the same name. It is fed by springs located on its eastern and northern boundaries. These springs discharge groundwater from a volcanic aquifer. Arid conditions dominate in the area, with average precipitation less than 200 mm/year. The tritium content in some groundwater samples shows the contribution of modern recharge to the total groundwater flow. Recharge occurs by infiltration of snowmelt in the austral winter months and to a lesser extent by short but intense precipitation events during the summer. The vertical gradients of rainfall isotopic content (δ18O, δ2H) and precipitation points to the recharge zone of the springs being located at the northern area of the lake, above 4,900 m a.s.l. along the slopes of the Tuyajto volcano, whereas recharge to the springs discharging on the eastern area of the lake originates in the adjacent basins of Pampa Colorada and Pampa Las Tecas at altitudes between 4,400 and 4,700 m a.s.l. The water of these springs may contain measurable tritium. The chemical composition of groundwater is the result of meteoric water evaporation processes, high temperature water-rock interaction and dissolution of buried old salt flat deposits. The groundwater flow is shallow, due to the presence of a regional low permeability ignimbrite formation that precludes the formation of deep convective groundwater flow cells due to the high density of brines. At a local scale, the Tuyajto lake behaves as a flow-through system with respect to the regional groundwater flow. The persistence of the springs is essential for the existence of the brine sheet and maintaining the ecological conditions for the waterfowl.

Alkali‐halogen metasomatism of theCMcarbonaceous chondrites

AbstractMeteorite Hills (MET) 01075 is unique among theCMcarbonaceous chondrites in containing the feldspathoid mineral sodalite, and hence it may provide valuable evidence for a nebular or parent body process that has not been previously recorded by this meteorite group.MET01075 is composed of aqueously altered chondrules and calcium‐ and aluminum‐rich inclusions (CAIs) in a matrix that is predominantly made of serpentine‐ and tochilinite‐rich particles. The chondrules have been impact flattened and define a foliation petrofabric. Sodalite occurs in a 0.6 mm sizeCAIthat also contains spinel, perovskite, and diopside together with Fe‐rich phyllosilicate and calcite. By analogy with feldspathoid‐bearingCAIs in theCVandCOcarbonaceous chondrites, the sodalite is interpreted to have formed by replacement of melilite or anorthite during alkali‐halogen metasomatism in a parent body environment. While it is possible that theCAIwas metasomatized in a precursor parent body, then excavated and incorporated into theMET01075 parent body, in situ metasomatism is the favored model. The brief episode of relatively high temperature water–rock interaction was driven by radiogenic or impact heating, and most of the evidence for metasomatism was erased by subsequent lower temperature aqueous alteration.MET01075 is very unusual in sampling aCMparent body region that underwent early alkali‐halogen metasomatism and has retained one of its products.

Surface and Groundwater Hydrochemistry of the Menengai Caldera Geothermal Field and Surrounding Nakuru County, Kenya

In order to assess the sustainability and impact of production from geothermal reservoirs on hydrological systems, a thorough understanding of local and regional hydrogeological systematics is a prerequisite. The Menengai Caldera in the Kenya Great Rift Valley is one of the largest explored geothermal fields in the country. This paper presents a hydrochemical investigation of the Menengai Caldera geothermal field and the ground and surface waters of the surrounding Nakuru County. Our results demonstrated a similar, sodium-alkaline dominated, ionic composition across all water types. Geothermal wells return the highest cation/anion concentrations and largely demonstrate a meteoric source from their δ18O and δ2H signature. Wells MW-09 (central part of the caldera), MW-18 (eastern part) and MW-20 (central part) showed a more evaporitic signature, closely matching with our own calculated Lake Evaporation Line, suggesting an increased mixing influence of Lake Nakuru waters. MW-09 also showed evidence of high-temperature oxygen isotopic exchange and significant water-rock interaction. Lake samples largely demonstrated seasonal shifts in ionic and isotopic values. Lake Nakuru ionic composition and isotopic values increased throughout the 12-month wet–dry–wet season sampling period. This correlated with a decrease in area which suggests a lessening of water inflow and facilitates increased evaporation. Groundwaters demonstrated clear evidence of mixing between meteoric, irrigation and lake waters. These observations enhanced the understanding of the hydrological system surrounding the Menengai Caldera and, when combined with future studies, will provide a powerful tool to assess the sustainability and impact of soon-to-be completed geothermal power production operations.

Triple oxygen and hydrogen isotopic study of hydrothermally altered rocks from the 2.43–2.41 Ga Vetreny belt, Russia: An insight into the early Paleoproterozoic seawater

Abstract The early Paleoproterozoic represents a period of rapid changes in Earth systems that could have affected the stable isotopic composition of seawater. The well-preserved pillow structures, hyaloclastites and komatiitic basalts of the 2.43–2.41 Ga Vetreny belt, Baltic Shield provide a record of high-temperature water-rock interaction induced by contemporaneous seawater. Here we present results of mineralogical, fluid inclusion, hydrogen, and triple oxygen isotopic analysis of hydrothermal alteration products. Emphasis is given to vein-filling quartz and epidote as they likely formed at high water-rock ratios. Ten minerals pairs, quartz-epidote and quartz-calcite, returned temperatures of isotopic equilibrium between 286 and 387 °C, which compares well to the homogenization temperatures measured for saline fluid inclusions hosted in vein quartz. The computed δD and δ18O values of equilibrium fluids range between −31 and +12‰, and −1.36 and +3.20‰, respectively, which overlap with the isotopic composition of ice-free world seawater and fluids generated at submarine hydrothermal systems. This is the earliest piece of evidence suggesting that early Paleoproterozoic seawater had a δD value close to 0‰. We also present triple oxygen isotopic composition of quartz and epidote that formed in similar facies of hydrothermal alteration from the relatively young (6–7 Ma) oceanic crust as sampled by the ODP Hole 504B in the eastern Pacific Ocean. These data show similarity to the triple oxygen isotope analyses of the Vetreny belt rocks indicating that the 2.43–2.41 Ga seawater had the Δ17O value close to that of modern-day seawater. Due to small fractionation at 300–390 °C (αepidote-water ≈ 1), epidotes present a strong evidence that equilibrium fluids had Δ′17O values close to 0‰. Based on the previously published quartz-water calibration, the computed Δ17O values of equilibrium fluids range between −0.11 and −0.03‰, significantly lower than that of seawater or inferred seawater-derived fluids at low water-rock ratios. This can be explained by multiple factors including phase separation of fluids or/and presence of low-temperature quartz overgrowths. Both are reflected in the fluid inclusion data and in situ δ18O measurements by ion microprobe (SIMS) presented here. Overall, our study suggests that the δ18O, Δ17O and δD values of the 2.43–2.41 Ga seawater were −1.7 ± 1.1, −0.001 ± 0.011 and 0 ± 20‰ respectively, similar to the modern values, which reflects the dominant role of submarine hydrothermal alteration in the stable isotopic budget of seawater throughout Earth’s history.

Europium anomaly variation under low-temperature water-rock interaction: A new thermometer

The positive europium (Eu) anomaly, enrichment of Eu abundance relative to the neighboring elements, is often observed for water interacted with the rocks. Not only high temperature (~400°C) water-rock interaction such as seafloor hydrothermal fluids, but also relatively lower temperature interaction, less than 100°C, cause positive Eu anomaly. However, relationship between the degree of Eu anomaly and interaction temperature has not been investigated. Water-rock interaction experiments at three different reaction temperatures were performed in this study to reveal the cause of positive Eu anomaly. Comparison of the results under different solution chemistry and temperature conditions showed that the basalt containing plagioclase released larger abundances of REEs than the basaltic glass. The degree of Eu anomaly assessed by Eu/Eu* value was smaller when 0.7 M NaCl solution was used for liquid phase for both solid phases. On the other hand, the Eu/Eu* became larger with increasing reaction temperature for basalts interacted with ultra-pure water. Therefore, it is suggested that the Eu anomaly is potentially used as a fluid-rock interaction thermometer under low salinity condition.

Hydrothermal signature in the axial-sediments from the Carlsberg Ridge in the northwest Indian Ocean

Abstract 30 sediments grabbed from 24 sites between the equator and 10°N along the Carlsberg Ridge (CR) in the northwest Indian Ocean has been analyzed for bulk chemical compositions. Hydrothermal components in the sediments are identified and characterized. They mainly occur at 6.3°N as sulfide debris and at 3.6°N as both sulfide and high temperature water-rock interaction products. The enrichment of chalcophile elements such as Zn, Cu, Pb and the depletion of alkalis metals such as K and Rb are the typical features of hydrothermal components. High U/Fe, low (Nd/Yb)N and negative Ce anomaly infer the uptake of seawater in the hydrothermal deposits by oxidizing after deposition. However, the general enrichment of Mn in hydrothermal plumed-derived materials is not found in the sediments, which may indicate the limited diffusion of fluids or plumes, at least in the direction along the Carlsberg spreading center. The hydrothermal components show their similarity to the hydrothermal deposits from the Indian Ocean Ridge. At 3.6°N ultramafic rocks or gabbroic intrusions, may be involved in the hydrothermal system.

Major geochemical characteristics of geothermal brines from the Upper Rhine Graben granitic basement with constraints on temperature and circulation

This paper is the first to present the main geochemical characteristics of the native brines collected from all the geothermal wells penetrating the granite basement underlying the sedimentary cover, in the Upper Rhine Graben. These deep wells (from 2580 to 5000m) were only drilled in four geothermal sites (Soultz-sous-Forêts and Rittershoffen in France; Landau and Insheim in Germany). The Na–Cl geothermal brine samples collected from the granite returned TDS values ranging from 99 to 107g/l with pH values close to 5, along with Cl and Br concentrations and δD, δ18O and δ34S values that indicate a multiple origin with mixing between primary brine formed by advanced evaporation of seawater (probably until the stage of halite precipitation) and dilute meteoric water, plus contributions from halite dissolution following successive marine transgression-regression cycles from the Triassic to the Oligocene. Chemical, isotopic and gas geothermometers indicate concordant reservoir temperatures close to 225±25°C for all the fluids, even though the maximum temperature so far measured on site is 200°C. An exhaustive literature review has indicated that only the geothermal brine from the deep Cronenbourg well (2870m) ending in the Buntsandstein has similar chemical and isotopic compositions (apart from Br and Ca) to the fluids from the granite, with an identical estimation of reservoir temperature from geothermometry. Geothermal brine from the deep Bruchsal well (2540m), drilled down to the junction of the Buntsandstein and the Saxo-Thuringian formations, has a higher TDS value (120–125g/l) with its chemical and isotopic compositions giving a lower estimation of reservoir temperature (190±25°C). By contrast, geothermal brine from the Bühl well (2655m) ending in the Buntsandstein has an even higher TDS value of about 201g/l and a lower temperature-at-depth estimation of 110±25°C, close to the temperature measured on site (115°C). The above results indicate that the geothermal fluids collected from the granite probably originate from Triassic sedimentary formations located at great depth (≥4km) with temperatures close to 225±25°C in the centre of the Rhine Graben, but that their different TDS and Cl/Br values reflect the presence of several distinct geothermal reservoirs. Many discrepancies due to high-temperature water-rock interactions are revealed on comparing the chemical and isotopic compositions of the hot brines with those of cooler brines from Bühl and the Landau Eocene–Oligocene oilfield wells, among others. The hottest brines are much enriched in K, Ca, SiO2, Li, Rb, Cs, As, Sr, Ba, Mn, Nd, U and in metals such as Zn, Pb, Cu, Co, Cd, Sb, but are depleted mainly in Mg, SO4 and B and have much lower isotopic Li and B signatures. The He isotopic signatures of the gases associated with these fluids (R/Ratm. = 0.128 at Bruchsal and 0.252 at Insheim) confirm that the thermal anomalies are mainly crustal and not mantle-derived (1.46% and 2.88% of mantellic He, respectively, for the two sites). Thus it is concluded that the thermal anomalies are associated mainly with the convective circulation of hot fluids along probable NE–SW faults between the graben's deep sedimentary centre and the fractured granite basement at its edges. Moreover, the western part of the Upper Rhine Graben (the Landau, Insheim, Soultz, Rittershoffen and Cronenbourg sites) seems to be hotter than the eastern part (Bruchsal and Bühl). According to the U-Th isotope system, the minimum transit time of these deep geothermal brines would be about 1000years.

High-temperature water-rock interactions and hydrothermal environments in the chondrite-like core of Enceladus.

It has been suggested that Saturn's moon Enceladus possesses a subsurface ocean. The recent discovery of silica nanoparticles derived from Enceladus shows the presence of ongoing hydrothermal reactions in the interior. Here, we report results from detailed laboratory experiments to constrain the reaction conditions. To sustain the formation of silica nanoparticles, the composition of Enceladus' core needs to be similar to that of carbonaceous chondrites. We show that the presence of hydrothermal reactions would be consistent with NH3- and CO2-rich plume compositions. We suggest that high reaction temperatures (>50 °C) are required to form silica nanoparticles whether Enceladus' ocean is chemically open or closed to the icy crust. Such high temperatures imply either that Enceladus formed shortly after the formation of the solar system or that the current activity was triggered by a recent heating event. Under the required conditions, hydrogen production would proceed efficiently, which could provide chemical energy for chemoautotrophic life.

Deep water circulation at the northern Pyrenean thrust: Implication of high temperature water–rock interaction process on the mineralization of major spring water in an overthrust area

In an overthrust context of the northern Pyrenean area, groundwater is affected by high mineralization sources. A multi isotopic approach was used to track the origin of mineralization in a complex multilayer aquifer system.Through the study of a major regional spring, the Oeillal spring water (OSW) which shows a not yet investigated geochemical singularity, the aims of this study are to understand the hydrogeochemical evolution and the mineralization mechanisms of groundwater in a large scale aquifer extending over the northern Pyrenean overthrust (oriental Corbières).Based on an adequate set of geochemical and isotopic tracers including cosmogenic, stable and radiogenic isotopes, we have revealed complex hydrogeochemical processes that cannot be tracked with traditional hydrochemical and isotopic tracers. The high 87Sr/86Sr ratios of the OSW associated with relatively high concentrations in trace elements (Cs, Rb, Sr, B, Li) suggest the influence of brine from the Triassic deposits containing saliferous clay orsaline fluids from the fractured basement. The basement hypothesis may be considered regarding the hydro geochemical fingerprint of the Paleozoic basement, as demonstrated in previous study, and further data would be required to validate the contribution of basement fluids. Contrasting with marine primary brine and current seawater, the relatively high δ37Cl (0.22 and 0.39‰) of OSW attests the non-marine origin of the chloride ion. 36Cl/Cl shows that the OSW is issued from a mixing process between recently recharged water, lightly mineralized and significantly marked in 36Cl by the thermonuclear bomb pulse, and a saline deep end-member at secular equilibrium.This indicates that Cl− in these springs is primarily derived from subsurface, non-meteoric sources. The OSW's low Br/Cl molar ratio suggests the influence of simple dissolution of halite and/or the contribution of more complex secondary brine.The deep saline water may results from meteoric infiltration into the lower Jurassic aquifer in contact with Triassic deposits or deeper. High temperature promotes water–rock interaction enhancing leaching of Mg–K rich saliferous clay.This is supported by Environmental scanning Electron Microscopy (ESEM) analyses showing that (i) Cl is found in accessory minerals from the KCl–MgCl2–H2O system of the Triassic deposits, and (ii) Cs/Rb molar ratio is similar to that of OSW ranging between 0.13 and 0.7 and from 0.13 to 0.4 respectively.Laboratory experiments carried out on Triassic material show that high temperature water–rock interaction is suitable to explain the relatively high 87Sr/86Sr observed in groundwater. Such process can be investigated to confirm the deep origin of the OSW and to explain the signature of deep brines in contact with the Triassic deposits, under high temperature conditions.Basement fluid contribution may also be considered regarding the hydro-geochemical fingerprint of the Paleozoic basement, as shown in previous studies. Further data would be required to validate this hypothesis.

The triple oxygen isotope composition of the Earth mantle and understanding [formula omitted] variations in terrestrial rocks and minerals

It has been shown in numerous studies that terrestrial rocks and minerals fall on a line with slope ∼0.52 in a δO17 vs. δO18 diagram. In this study, we present new data on the triple isotope composition of the Earth mantle, crustal materials and low-T aqueous precipitates. Crustal materials show distinct variations in ΔO17 suggesting that the concept of a single terrestrial mass fractionation is invalid on small-scale. Observable variations in individual fractionation slopes θ are interpreted as temperature effects. We show that the Earth mantle is isotopically homogeneous and confirm the recent finding that the Earth mantle has a negative ΔO17. The difference in δO18 and ΔO17 between seawater and oceanic crust is discussed with respect to the effects of low- and high-temperature water–rock interaction.

The Influence of Hydrothermal Activity on the Li Isotopic Signature of Rivers Draining Volcanic Areas

We explore the geochemistry and the isotopic composition of lithium (δ7Li) of rivers draining volcanic islands (Guadeloupe, Iceland, Java, Martinique and Sao Miguel) with a specific focus on continental hydrothermal activity. Our preliminary results reveal a global-scale trend between δ7Li and the elemental ratio Li/Na in rivers draining volcanic islands. We suggest that this trend results from a mixture between waters with low δ7Li and high Li/Na, inherited from high-temperature water rock interactions, and waters with low Li/Na and high δ7Li, in which Li is controlled by the neoformation of clays during low-temperature chemical weathering in basaltic soils. This latter process can be described by a simple isotope fractionation model, consistent with reported values for isotopic fractionation factors between secondary weathering products and water.These data highlight the important potential role of continental high-temperature weathering processes on the oceanic budget of lithium.

Boron Behavior in the Rivers of Réunion Island, Inferred from Boron Isotope Ratios and Concentrations of Major and Trace Elements

A combined study of boron concentrations and isotopic ratios and of major and trace elements measured in Réunion waters, sampled up to four times between 1995 and 2012, illustrates boron behavior during water-rock interactions in tropical basaltic catchments. Boron isotope ratios measured in Réunion rivers and springs show a large range of variation between 1 and 48‰, that reflect mixed B sources and water-rock interaction processes: rain (δ11B≈40‰), hydrothermalism (δ11B≈0‰), low temperature basalt weathering in steep sided basins (δ11B≈30‰), and cycling within soil and vegetation (δ11B>40‰). Réunion rivers have schematically two types of δ11B signatures for low-temperature water-rock interactions: ≈30‰ for rivers with high weathering rates, and ≈45‰ for small forested catchments with relatively smoother slopes and lower weathering rates. High temperature water-rock interaction produces B enriched waters with a B isotopic signature close to that of the rocks. B behavior in the soil and vegetation cycle is more difficult to characterize but seems to result in soil solutions enriched in 11B, with δ11B≥45‰.