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The geothermal aquifer complex investigated in this study comprises a component of the eastern geothermal reservoir of Northern Algeria that is located close to the Algerian−Tunisian border. Seven thermal and two cold water springs were sampled in the framework of this study. The area hosts the region's second hottest spring discharging at a temperature of 67 °C. The thermal waters are carbogaseous type and are dominated by a Na−HCO 3 composition. Isotopic analyses of deuterium and oxygen-18 confirm their meteoric origin. Radiogenic strontium isotopes (87Sr/86Sr up to 0.710841) suggest interactions with a silicate basement, probably composed of granodiorites and micaschists. Interaction with the Triassic evaporites results in a total dissolved solids (TDS) concentration of up to 1773 mg L−1. The thermal waters emerging through the faults have a temperature ranging between 36 and 67 °C. These waters mix with cooler waters during their ascent. The use of various chemical geothermometers yielded a maximum reservoir temperature of 78–162 °C for the Bouhadjar region. Using the average regional geothermal gradient (43.5 °C·km−1) and the aforementioned temperature interval, an estimated depth range of 1793–3731 m was computed for the geothermal water reservoir. All the thermal waters are found oversaturated with respect to kaolinite and K−mica reflecting the dissolution of granodiorites and muscovite-rich micaschists. High P CO2 levels (0.07–1.07 atm) suggest the existence of a thermo-decarbonation reaction taking place in the tectonic collision zone. This highlights the important role played by major geological structures occurring in such a geothermal system. [Display omitted] • Existence of interactions between thermal waters and crystalline basement. • The reservoir's maximum temperature lies in the range: 78–162 °C. • Main reservoir occurs in the Cretaceous carbonates. • The region is tectonically active with high P CO2 reaching 1.07 atm. • Absence of mantle fluid upwelling. [ABSTRACT FROM AUTHOR]

Abstract Understanding the physical basics of tectonic events, related fluid flow and ore deposition represents one of the great challenges in modern geosciences. In this contribution, Sm-Nd ages of hydrothermal fluorites and U-Pb ages of carbonates and iron oxides from unconformity-related vein type deposits in the Schwarzwald next to the Upper Rhinegraben rift in SW Germany are used to distinguish different pulses of hydrothermal fluid activity and to understand their relation to large-scale tectonics and magmatism. While the fluorites are of Early Jurassic to Oligocene age, carbonate (calcite, dolomite, siderite) and hematite dated by U-Pb small-scale isochrons records formation from Permian to Quaternary with a clear culmination in the Neogene. These new age-data in combination with microthermometry data of primary fluid inclusions from growth zones in the fluorites and carbonates are used to constrain the timing of fluid signatures. This contribution shows that the ages are correlated with changes in fluid properties and/or tectonic events in the evolving continental crust. Comparison with published thermochronological data, apparent ages of URG-related volcanic rocks and the tectono-sedimentary evolution of the Upper Rhinegraben rift show clear correlations between the intensity of hydrothermal mineralization (and, hence, the intensity of fracture-bound fluid flow) with the U-Pb carbonate ages. This method accordingly provides an excellent tool to date rift-related processes like fluid flow, ore deposition and tectonic activation or reactivation of fractures. Fluid properties changed after the deposition of Middle Triassic Muschelkalk evaporites from low salinity, high temperature (1–6 wt.% NaCl eq , 200–270 °C, cooling late-metamorphic basement fluids) to high salinity, moderate temperature (20–26 wt.% (NaCl + CaCl 2), 50–170 °C, mixture of a modified bittern brine (“basement brine”) with halite dissolution brine). This change led to large scale ore deposition (fluorite-barite-quartz with Pb-Zn-Cu, Bi-Co-Ni-Ag-U, Fe-Mn ores). During the Paleogene and Neogene, previously separated aquifers from various sedimentary units were connected by juxtaposition of the fluid source rocks during Rhinegraben rifting, which resulted in variable salinity and temperature fluids (1–26 wt. % (NaCl + CaCl 2), 50–350 °C) by a multi-component fluid mixing process. Typical mineralization related to this shows barren or Pb-Zn-Cu veins with large amounts of barite. [ABSTRACT FROM AUTHOR]

Fluid mixing is an important process in the formation of many hydrothermal vein-type deposits. Here, we present evidence from hydrothermal fluorite-barite-quartz veins with Pb-Zn-Cu-(Ag)-sulfides and associated mineralization, indicating that mineral precipitation was initiated by mixing of fluids derived from multiple sources, including mixing between more than two end-member fluid compositions. Based on our observations, we relate the diversity of the hydrothermal veins of the Schwarzwald mining district in terms of mineral assemblage and fluid inclusion chemistry to the disturbed and transient geological environment during ongoing rifting. Literature data on the regional geology, current groundwater reservoirs, formation processes and hydraulic features are augmented by new fluid inclusion analyses from post-Cretaceous, hydrothermal vein minerals including microthermometry, crush leach, Microraman and LA-ICP-MS analyses of individual fluid inclusions. Petrography and microthermometry of fluid inclusions show complex sequences of alternating fluid signatures within different growth zones of one crystal. High (20–26 wt% NaCl + CaCl 2 ), moderate (5–20 wt% NaCl + CaCl 2 ) and low salinity (< 5 wt% NaCl + CaCl 2 ), sulfate- and/or CO 2 -bearing primary fluids were trapped during crystal growth. Such variations are commonly observed in minerals from different localities. Bulk crush leach analyses show significant variations in major element composition of the trapped fluids, within the overall Na-Ca-Cl-SO 4 -HCO 3 -system. These variations are caused by mixing of fluids from different aquifers and in various proportions. Ancient fluids show chemical similarities to modern groundwater aquifers that are available for direct sampling, such as granitic basement, Lower Triassic sandstones or Middle Triassic limestones and evaporites. Analyses of individual fluid inclusions by LA-ICP-MS support this interpretation and document the multi-component fluid mixing processes at individual localities recorded on the scale of single crystal growth zones. The latter data are used in a diffusion model to obtain the duration of mineral growth (before the fluid is homogenized), which implies very short-lived fluid events on the order of seconds to hours. By defining end member fluids and their proportions, we show that nearly all fluid mixtures are saturated with respect to barite. By contrast, fluorite-saturated fluids can only be modelled by mixing of a basement brine with fluids from Triassic sandstones. All fluid mixtures are strongly undersaturated with respect to galena, chalcopyrite and sphalerite, the most commonly observed ore minerals in the hydrothermal veins. As the calculated fluid mixtures are typically relatively oxidized and contain high sulfate/sulfide ratios, precipitation of sulfides was probably related to short-lived reduction events caused by an influx of hydrocarbons, by reactions with graphitic wall rocks in fractures by sulfidation related to fluid-rock reaction with the surrounding host rocks or an external influx of hydrocarbon-bearing fluids. The multi-aquifer fluid mixing processes involving aquifers of different chemical and physical constitution were triggered by brittle deformation related to rifting of the Rhine graben. This appears to be essential for the formation of a large number of mineralogically diverse hydrothermal ore deposits. [ABSTRACT FROM AUTHOR]

Ascertaining the enigmatic characteristics of the crystalline basement of the Qaidam basin, the deepest intracontinental basin yet located in the highest orogenic plateau with the thickest continental crust, has broad implications for the Cenozoic basin evolution, in particular, and intracontinental tectonics of Asia, in general. We carried out a comprehensive investigation on the ages and geochemical-isotopic characteristics of the Qaidam and Suganhu basement rocks obtained from drill-cores. Petrological observations and U-Pb zircon dating (LA-ICP-MS) of granitoid samples from drill cores indicate that Early Neoproterozoic, Early Paleozoic and Late Paleozoic-Mesozoic intrusions are largely represented, suggesting that the Qaidam and Suganhu blocks were involved into three tectono-magmatic episodes. Similar whole-rock geochemistry and Sr–Nd isotopic characteristics between the Early Neoproterozoic granitoids beneath the Qaidam basin and the contemporaneous basement rocks in the surrounding orogenic belts confirm the existence of pervasive Early Neoproterozoic metamorphism and magmatism along the present-day northern Tibetan Plateau. By comparing the trace and rare earth elements patterns as well as the Sr-Nd compositions of the Ordovician arc-related granitoids and Silurian-Devonian post-collisional granitoids beneath the Qaidam and Suganhu basins with the corresponding granitoids from the surrounding orogenic belts, we assert that the Proto-Tethys subduction events that were recorded within the Eastern Kunlun, Altyn Tagh and the Qilian Shan orogenic belts, were different. They generated distinctive subduction-related arc magmas, whereas the closure of the oceanic basins resulted in the amalgamation of the orogenic belts inducing subsequent extensive post-collisional magmatism within the Qaidam block. The widespread Permian and Triassic granitoids beneath the northwestern/northern Qaidam basin mainly involved a lower crust or a crust-mantle source including Mesoproterozoic crust. They demonstrate that the influence of the Paleo-Tethys evolution penetrated the Qaidam block northwards, reaching to the northern edges of the block. We conclude that the Qaidam block is not a craton as typical as the rigid Tarim block, but pertains to a tectono-magmatic rejuvenated craton, which is not mechanically-stronger than its surrounding regions. However, trapped between the lithospheric left lateral strike-slip Altyn Tagh fault system to the northwest and the Qilian Shan transpressional system to the northeast, the Qaidam block forms a relatively stable domain that escaped from significant Cenozoic deformation. [ABSTRACT FROM AUTHOR]

Though Yaoundé zone is characterized by abundant rains, access to safe drinking water becomes a difficult activity, because of climate change and pollution caused by human activities. Lineament zones on the earth’s surface are important elements in understanding the dynamics of the subsurface fluid flow. However, good exposures of these features are always lacking in some areas around Yaoundé, characterized by thick alteration. During field surveys these conditions, in many cases, hinder the proper characterization of such features. Therefore, an approach that identifies the regional lineaments on remote-sensing images (Landsat Thematic Mapper and shaded digital terrain models), with its large scale synoptic coverage, could be promising. This paper aims to the structural organization of lineament network in the crystalline basement of Yaoundé from remote sensing data and characterize them by statistical and geostatistical techniques. The results were validated on the basis of the geological maps, the hydrogeological maps and the outcrop data. Statistical analysis of the lineaments network shows a distribution along the N0–10, N20–30, N40–60 and N140–150. The correlation between the productivity of high yield wells and the closest lineament confirms that these lineaments are surface traces of regional discontinuities and act as main groundwater flow paths. [ABSTRACT FROM AUTHOR]

A structural model is developed for the south-central Taiwan fold-and-thrust belt that shows consistency across an array of data types and marks an important step forward in the consideration of geological hazards and risks. Although there is general agreement about the regional scale geology of Taiwan, there are considerable differences in the structural interpretations of its western fold-and-thrust belt. In this paper, we bring together results of our previous studies and add new data and data analyses to develop a consistent 3D structural model for the south-central Taiwan fold-and-thrust belt that can explain key aspects of the seismicity, GPS, and topography data. We interpret the fold-and-thrust belt to be a west-verging, imbricate thrust system developed above a single basal thrust that is breached by ENE-striking faults that are inherited from the continental margin. These breaching faults are associated with ENE-striking transverse zones in the fold-and-thrust belt that are marked by changes in stratigraphy, structural style, strike and dip of the basal thrust, and uplift of the stratigraphic contacts. Along the eastern flank of the fold-and-thrust belt, metamorphic basement rocks are involved in the thrusting. Shortening estimates range from 15 km to >25 km. Much of the seismicity is taking place beneath the basal thrust, in the basement, along the flanks of basement highs and lows where strike-slip and transpressive fault types are common. There are systematic changes in GPS displacement vectors and strain rates across the transverse zones. Topography is higher in areas where basement is involved in the thrusting. The proposed structural model has depth and along-strike consistency, and can explain aspects of the distribution of seismicity, faults types, GPS displacement vectors and strain rates, and topography of the study area, and can therefore be considered a viable model. [ABSTRACT FROM AUTHOR]

Abstract: The construction of the new 56km long Gotthard railway base tunnel in Switzerland opened a large number water conducting fractures and 122 water samples were collected along the Amsteg section of the tunnel and then chemically analyzed. The Amsteg section of the tunnel cuts across granites, gneisses and metarhyolites of the Alpine basement. The overburden of basement rocks above the tunnel axis is up to 2200m thick with rock temperature reaching 45°C. Sodium is the prime cation of most waters; calcium, potassium and magnesium are low to very low in concentration. The associated anions are carbonate/bicarbonate, sulfate and chloride in widely varying concentrations. High to ultra-high fluoride concentrations of up to 29mg/L F and high pH values of up to 10.4 are significant properties of the waters. Six chemical types of water can be distinguished reflecting the different types of fractured rock present in the section. Most of the waters can be viewed as ternary mixtures of dissolved natrite (Na2CO3), thenardite (Na2SO4) and halite (NaCl). The geological and hydrogeological context suggests a meteoric origin of the waters. The unique water compositions and characteristics result from interaction with continental basement rocks along the flow path. The assemblage of major minerals of the different rocks is generally very similar, but the rocks differ with respect to minor minerals and accessories. Derived rock data suggest that dissolution and precipitation of calcite and fluorite, albite dissolution, leaching of salty inclusions, sulfide oxidation by CO2, alteration of biotite to chlorite, precipitation of stilbite and hematite are the important processes that create the observed water compositions. Although fracture water acquires its composition exclusively by chemical interaction with crystalline basement rocks with very similar mineral assemblages, the resulting waters are of great chemical variability. [Copyright &y& Elsevier]

Abstract: Multi-scale mappings of fracture systems in the crystalline basement of Yemen are presented. Fracture datasets are described through statistical analyses of direction, length, spacing, density, and spatial distribution. Results are combined with field observations and can be directly used to model the geometry of the fracture networks in analog basement rocks, from multi-kilometric to decametric scales. The fractured reservoir analog is defined with a dual porosity model in which tectonic and joint systems correspond to the basement reservoir “backbone” and “matrix” respectively. These two end-members reveal contrasting geometrical, reservoir, and scaling properties. In tectonic systems, multi-scale geometries are “self-similar”, the fracture network shows fractal behavior (power-law length distribution and clustered spacing), and fault zones show hierarchical organization of geometrical parameters such as length, thickness, and spacing. In joint systems, the fracture network is scale dependent with exponential length distribution, and shows anti-clustered spacing. However, these two end-members have both well-connected properties, with fault zones acting as main drain and joint systems acting as the fluid supply. [Copyright &y& Elsevier]

Abstract: Aeromagnetic (AM) and Landsat Thematic Mapper (TM) data from the south-central Zimbabwe Craton have been processed for the purpose of regional structural mapping and thereby to develop strategic models for groundwater exploration in hard-rock areas. The lineament density is greater on TM than on AM images, partly due to the resolution of the different datasets, and also because not all TM lineaments have a magnetic signature. The derived maps reveal several previously undetected lineaments corresponding to dykes, faults, shear zones and/or tectonically-related joints, striking predominantly NNE, NNW and WNW. We suggest the possible hydrogeological significance of some of these patterns as follows: the aeromagnetic data can be used to map faults and fractures of considerable depth which are likely to be open groundwater conduits at depth (typically under tension), while TM lineaments, although not necessarily open (mostly under compression), represent recharge areas. The interpreted persistent lineation and well developed fracture patterns are correlated with existing boreholes and indicate a spatial relationship between regional structures and high borehole yields (>3 m3/h). This relationship is combined with other lithological and hydrogeological information to identify potential regional groundwater sites for detailed ground investigations. These are defined as dyke margins, faults, fractures/joints or intersections of any combination of these structures. Priority should be given to coincident AM/TM lineaments (e.g., NNW and NNE fractures) and continuous structures with large catchment areas (e.g., NNE and WNW faults). The late Archaean (2.6 Ga) granites are considered the most favourable unit because of their associated long and deep brittle fractures between numerous bornhardts (inselbergs) and kopjes. Several small-scale TM lineaments also form important local sources of groundwater for hand-dug wells. Based on measured rock susceptibilities from the area, we present a model of the typical magnetic responses from the possible groundwater exploration targets. The developed magnetic model could be applicable to similar terrains in other Archaean Cratons. [Copyright &y& Elsevier]

Abstract: Analysis of the distribution of oil pools in sedimentary cover has shown that known platform hydrocarbon fields are closely associated with faults in the crystalline basement and the sedimentary cover itself. Oil pools in the lower productive beds of the sedimentary cover are linked to faulted zones in the crystalline basement. A genetic relationship between oil fields and tectonic dislocations indicates a dominant role for vertical migration in the accumulation of commercial hydrocarbons in the Paleozoic. The conducted geochemical, palynological, geophysical and geological studies have shown that oil and gas pools in the upper sedimentary cover have been formed due to the vertical migration of hydrocarbons, which is also confirmed by the vertical alignment of the oil pools. [Copyright &y& Elsevier]

Abstract: High-precision temperature logging in deep and superdeep wells has permitted the study of the thermal regime in the granite–gneiss layer of the Earth''s crust. The long-term logging works have allowed the classification of temperature anomalies recorded in the crystalline basement. Most anomalies have been supposed to be caused by loosely aggregated, permeable zones. The classification reflects main types of processes at a great depth — such as injection, inflow and upward migration of gas-cut fluid. The results of great practical importance are obtained using our classification: some intervals — where temperature anomalies interpreted as inflow reservoirs were revealed — have produced fluid, and others interpreted as injection reservoirs absorbed borehole fluid during tests. [Copyright &y& Elsevier]

Abstract: The crystalline basement of the Salalah area (Dhofar, Sultanate of Oman) is the largest portion of Proterozoic basement of the Arabian-Nubian Shield outcropping in Oman. This paper presents new geochronological data and proposes a new lithostratigraphical subdivision of this basement. Four major units have been defined: I. The Juffa Group consisting of metasedimentary mica-gneisses, amphibolites and few meta-ultramafic lenses. II. The Sadh Group with two sub-units, the highly deformed and metamorphosed Banded Gneiss Complex intruded by the slightly deformed diorite and tonalite of the Mahall Complex. III. The Tonalite Group including three large calc-alkaline plutons, the gabbroic Hasik Complex, the dioritic-tonalitic Fusht Complex and the tonalitic Hadbin Complex. IV. The Granite Group comprising different type of dykes and small bodies, i.e. the Pegmatite Complex, the Marbat Granodiorite, the Leger Granite and the basaltic to rhyolitic Shaat Dyke Swarm. The source rocks of the clastic sedimentary protolith of the Juffa Group gneisses represent the oldest stage (>1300Ma) recorded in the geological evolution of the Salalah basement. Crustal accretion processes culminate around 800Ma. Extensive cyclic calc-alkaline magmatism during ca. 50Ma (830–780Ma), intercalated by intense deformation and recrystallisation at amphibolite facies (>815–790Ma), built up the major lithostratigraphical units (Juffa-, Sadh-and Main Intrusive Group). The intrusion of a large amount of aplites and pegmatites forming the Pegmatite Complex took place between 770 and 750Ma. The younger (750–700Ma?) emplacement of the Marbat Granodiorite, Shaat Dyke Swarm and Leger Granite mark the end of the magmatic and metamorphic activity in this area. Subsequently these units were exhumed to the surface and overlain by clastic sediments of the Marbat Formation of probable Ediacaran age (630–542Ma) and by the Phanerozoic sedimentary sequences. [Copyright &y& Elsevier]

Significant fracture and porosity sealing characterizes the sedimentary cover-basement interface in the northwestern margin of the Aquitaine Basin (France). Dolomite and calcite (and sometimes fluorite, barite and quartz) constitute most of the fracture fillings. They contain primary inclusions of brines having chlorinities in the range of 3.3 to 5.5 mol Cl/kg solution, with total homogenization temperatures in between 65 and 130 °C for quartz and slightly lower for dolomite, barite, fluorite and calcite. Crush-leach analyses indicate that brines are characterized by Na/K ratios of 5 to 40, Na/Li ratios of 20 to 530, and Cl/Br ratios of 200 to 1000, which are rather typical of deep basinal brines. The fluid δ18O signature is estimated to be &ap;6.6±1.8‰ SMOW for a crystallization temperature of 100±20 °C between 80 and 120 °C and the δD value is −30±10‰ SMOW.The fluid source for the fracture filling mineral is interpreted as a deep sedimentary brine expelled during a period of maximum subsidence in the Aquitaine Basin, which migrated along the sediment cover/basement interface which is characterized by high permeabilities below the Toarcian shales. The sealing is likely to be linked to the mixing of the brines with dilute ascending, hot waters. These dilute waters infiltrated from emerged zones, convected and heated at depth, reaching temperatures of 100 °C (up to 150 °C on the basis of cation geothermometry).Extensional activity, of probable Cretaceous age, related to the Gascogne Gulf rifting could be considered as the most likely cause of a significant fluid migration event at the basement/cover interface all along the margins of the French Massif Central. These processes are large scale as shown by the similarities of mineral sequences, fluid types and general features of most of the F–Ba–Pb–Zn deposits located at the basement–sedimentary cover interface.The mass transfer of Cl linked to this stage is significant and accounts for the early introduction of large amounts of chlorine in the granitoid microporosity. This probably explains the significant chlorine concentrations of the present-day fluids recovered in the granitoid aquifer. [Copyright &y& Elsevier]

Groundwater exploration in crystalline basement aquifers such as the Houtriver gneiss formation in the Limpopo province of South Africa is often described as complex. This is because groundwater availability in such aquifers is largely a consequence of the interaction of several processes related to recharge, underlying geological features and fracture connectivity of the aquifer rock matrix. In this study, an integration of geophysical and geological investigations is applied in inferring potential drill targets within the Houtriver gneiss crystalline basement aquifer system. Results from the magnetic and frequency domain electromagnetic surveys were combined with geological investigations to identify sites where vertical electrical resistivity sounding was applied to infer the thickness and layering of weathered and fractured zones, as well as to identify potential targets where test boreholes were drilled. Constructed geo-resistivity pseudo-sections suggested that groundwater occurrence within this formation is described by a heterogeneous multiple-layered and fractured aquifer system with the main groundwater bearing zones ranging from a depth of 30–72m in most cases. Ten potential drill sites were identified from which three test boreholes were drilled and used to validate the results through a lithostratigraphic conceptual model developed from the correlation of the geophysical results with drill logs. The integration of hydro-geophysical and geological methods thus provided a comprehensive approach for resource assessment in the Houtriver gneiss formation. • Multiple-method approach to groundwater exploration. • Houtriver gneiss crystalline aquifer studied. • Hydrogeophysical and geological tools used. • Multiple fractured zone from 30m to 72 m. • Test boreholes drilled to validate results and success. [ABSTRACT FROM AUTHOR]

From 2009 to 2016, a drastic increase in seismic activity occurred in the Central and Eastern US (CEUS), particularly in the Oklahoma-Kansas region. The majority of hypocenters were focused in the crystalline basement rock. Information regarding the physical properties (elastic wave velocity, peak strength, etc.) of rocks in the CEUS basement to date is sparse. Forecasting future seismic hazard and predicting the in situ response of the crystalline basement requires their geomechanical parameters be adequately constrained. This work assesses the mechanical and petrophysical properties of several sets of basement rocks from Oklahoma to provide a better framework for understanding intraplate seismicity and overall basement deformation in the continental United States. Laboratory experiments were conducted with granite, rhyolite and diabase basement rock samples collected from southern Oklahoma. Evolution of compressional and shear wave velocity with increasing confinement was measured through a series of ultrasonic velocity tests. A suite of uniaxial and triaxial tests were conducted to measure the elastic and inelastic deformation behavior of the basement rocks. Deformation data was evaluated using the Mohr-Coulomb criterion and compared with additional preexisting deformation data of igneous basement rocks. Dynamic and static elastic properties compare favorably with available field measurements and demonstrate the role physical properties can play in varying mechanical behavior. Granitic samples demonstrate moderate variation of intrinsic physical properties can alter elastic properties and failure behavior significantly. Water-weakening in the basement rocks may indicate fluid-assisted processes such as stress corrosion cracking enhance deformation in the crystalline basement. • We report the physical properties of crystalline basement rocks in Oklahoma. • Strength and petrophysical properties are quantified through laboratory tests. • Minute lithologic variations can greatly affect basement mechanical behavior. • Water-weakening may reduce basement rock strength without pore pressure changes. [ABSTRACT FROM AUTHOR]

Helium isotopes are useful for tracing terrestrial water movement and calculating residence times, which have important implications for radioactive waste disposal and carbon capture and storage projects. Helium concentrations are generally measured directly in water samples; however, this is not always possible. In this scenario, the He concentration equilibrium between pore waters and He accessible volumes (e.g., fluid inclusions, hereafter HAV) in minerals (e.g., quartz) can be utilized to determine He concentrations. In this study, the He partial pressure was measured in HAVs of quartz grains collected from cores of the Kola Super Deep Borehole (KSDB) using isothermal He extraction/saturation experiments. A large fraction of He was released from these samples during the first interval of isothermal heating, indicating a destruction of the unstable HAVs, likely due to decrepitation of fluid inclusions. We present a new approach to calculate He partial pressures using only the He fraction released from the stable HAVs. This approach gives a He partial pressure p He of ≅ 1.5 atm at depths of ~ 10 km. When combined with solubility data, this value suggests a high He concentration in the deep pore waters nearby the KSDB, ≅ 1.3 × 10−6 mol (cc H 2 O)−1, indicating a long residence time of He atoms in a deep water – mineral system, close to the age of the regional metamorphism (≅1700 Ma). The 3He/4He in the deep KSDB quartz samples (and the pore waters) are ~ 3 × 10−8, typical of radiogenic He generated in 10 km deep Archean rocks of the KSDB. Importantly, external fluxes are not needed to explain He isotope abundances in rocks, minerals and pore waters at these depths. [ABSTRACT FROM AUTHOR]