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Investigation of hydromechanical behavior of fluid-saturated tight rock is motivated by the need to quantify the effect of changes of fluid pressure p and mean stress P on rock deformation, hydrothermal fluid, and mass transport. In particular, hydromechanical properties of low porosity crystalline rock are required for analysis of geological processes including areal hydration or dehydration, mineral weathering, and fault mechanics. In this study, poroelastic parameters – drained bulk modulus K, and Biot coefficient α – governing the volumetric response of Westerly blue granite, a typical crystalline rock of low porosity are measured. Three additional hydromechanical properties, unjacketed bulk modulus K s ′ , expansion modulus H, and permeability k, are also measured. For the Terzaghi effective mean stress of 1.0 < P′ = P - p < 25.0 MPa, the unjacketed bulk modulus K s ′ = 57.5 GPa is constant within the range of mean stresses investigated but other poroelastic coefficients exhibit effective mean stress dependency; the ranges are 13.2 < K < 32.3 GPa, 19.0 < H < 60.0 GPa, 0.83 > α > 0.38, and 20 > k > 5 nanodarcy. The agreement between poroelastic coefficients determined from various methods suggests that the underlying linear elastic assumption in Biot's theory of poroelasticity is applicable to Westerly blue granite over small increments of effective mean stress. Highlights: A procedure for saturation of tight, low-porosity rock is illustrated. Biot coefficient, unjacketed, expansion, and drained bulk moduli are measured and verified using different approaches. [ABSTRACT FROM AUTHOR]

ABSTRACT The anisotropy at the grain scale significantly impacts cracking behavior of crystalline rocks. However, the anisotropy of mineral structure, especially the grain shape and orientation has been inadequately addressed in studies on hydraulic fracturing. To bridge this gap, this paper introduces a coupled hydro‐grain‐texture model (HGTM) based on discrete element model (DEM) that investigates the influence of grain shape and orientation on fluid‐driven cracking processes in crystalline rock. The HGTM can consider the different mineral grain shapes and orientations by changing the aspect ratio and rotating coordinate axes. Our studies covered six distinct in‐situ stresses, three grain shapes, and five grain orientations. Initially, we present a comprehensive examination of the microcracking processes of hydraulic fracturing. Then the influences of in‐situ stress, grain shape, and grain orientation on cracking processes were studied. The results underscore that both mineral grain and in‐situ stress interplay to influence the hydraulic fracturing of the crystalline rocks. The proposed HGTM can well mimic the propagation process of hydraulic fracturing by comparing with the experimental results and the results reveal that hydraulic fracturing in crystalline rocks is a highly complex process. This research clarifies the complex interplay between grain texture and hydraulic fracturing, offering invaluable insights for optimizing stimulation practices. [ABSTRACT FROM AUTHOR]

The northern Andes of southern Colombia contain a rich geologic history recorded by Proterozoic to Cenozoic metamorphic, igneous, and sedimentary rocks. The region plays a pivotal role in understanding the evolution of topography in northwestern South America and the development of large river systems, such as the Amazon, Orinoco, and Magdalena rivers. However, understanding of the basement framework has been hindered by challenging access, security concerns, tropical climate, and outcrop scarcity. Further, an insufficient geochronologic characterization of Andean basement complicates provenance interpretations of adjacent basins and restricts understanding of the paleogeographic evolution of southern Colombia. To address these issues, this paper presents a zircon U-Pb geochronological dataset derived for 24 bedrock samples and 19 modern river samples. The zircon U-Pb results reveal that the Eastern Cordillera of southern Colombia is underlain by basement rocks that originated in various tectonic events since ca. 1.5 Ga, including the accretion of discrete terranes. The oldest rocks, found in the Garzon Massif, are high-grade metamorphic rocks with contrasting Proterozoic protolith crystallization ages. Whereas the SW part of the massif formed during the Putumayo Orogeny (ca. 1.2-0.9 Ga), we report orthogneisses for the NE segment with protoliths formed at ca. 1.5 Ga, representing the NW continuation of the Rio Negro Jurena province of the Amazonian Craton. In contrast, crystalline rocks of the Central Cordillera primarily consist of Permian-Triassic (ca. 270-250 Ma) and Jurassic-Cretaceous (ca. 180-130 Ma) igneous rocks formed in a magmatic arc. In southernmost Colombia, the Putumayo Mountains mainly consist of Jurassic-Cretaceous (180-130 Ma) plutonic and volcanic rocks. Furthermore, we analyzed the heavy mineral abundances in modern river sands in southern Colombia (spanning 1°N-5°N) and found that key minerals such as garnet and epidote can be utilized to trace highgrade metamorphic and igneous lithologies, respectively, in the river catchments. The differentiation of basement ages for separate tectonic provinces, combined with heavy mineral abundances in modern sands, can serve as unique fingerprints in provenance analyses to trace the topographic and exhumational evolution of different Andean regions through time. [ABSTRACT FROM AUTHOR]

Crystalline rocks in the subsurface are of interest for geothermal energy extraction, nuclear waste storage, and, when weathered or fractured, as aquifers. Compliant discontinuities such as microcracks, cracks and fractures may nucleate and propagate due to changes in pore pressure, stress and temperature. These discontinuities may provide flow pathways for fluids and, if fracturing extends to surrounding rocks, may allow escape of fluids to neighbouring formations. Monitoring such rocks using sonic logs, passive seismic, borehole seismic and surface seismic requires understanding of the propagation of elastic waves in the presence of such discontinuities. These may have an anisotropic orientation distribution as in situ stress may be anisotropic. As crystalline rock may display intrinsic anisotropy due to foliation and the preferential orientation of anisotropic minerals, quantification of the relative importance of intrinsic and microcrack‐induced anisotropy is important. This may be achieved based on the stress sensitivity of elastic wave velocities. A method that allows both the orientation distribution of microcracks and the stress dependence of their normal and shear compliance to be estimated independently of the elastic anisotropy of the background rock is presented. Results are given for anisotropic samples of gneiss from Bukov in the Czech Republic and granite from Grimsel in Switzerland based on the ultrasonic velocity measurements of Aminzadeh et al. The microcrack orientation distribution is approximately transversely isotropic for both samples with a preferred orientation of microcrack normals perpendicular to foliation. This preferred alignment is stronger in the sample of gneiss than in the granite sample, and the normal and shear compliance of the microcracks decreases with increasing compressive stress. This occurs because the contact between opposing faces of the discontinuities grows with increasing compressive stress, and this results in a decrease in elastic anisotropy with increasing compressive stress. At low stress, the ratio of microcrack normal compliance to shear compliance is approximately 0.25 for the granite sample and 0.7 for the sample of gneiss. The normal compliance ZN for both samples decreases faster with increasing compressive stress than the shear compliance ZT, resulting in a decrease in ZN/ZT with increasing compressive stress. [ABSTRACT FROM AUTHOR]

Rocks often have a rate effect on mechanical behaviors and exhibit a negative Poisson's ratio (NPR) effect after being thermally damaged. However, to date, their combined role in mechanical behaviors has not been clarified. This study micromechanically explores the rate and NPR effects on the compressive behaviors of thermal-damaged rocks using the compression-hardening grain-based model (CHGBM) implemented by the Universal Discrete Element Code (UDEC). The original, moderately, and highly thermal-damaged Suizhou granite samples were subjected to unconfined compression tests for calibrating UDEC-CHGBM. With developing thermal damage from the original state, the rock sample decreases in the peak stress and modulus, exhibiting a transition of pre-peak stress-stain relation from the approximately linear to nonlinear, and a transition of Poisson's ratio from the positive (lateral extension) to negative (lateral contraction). Our UDEC-CHGBM reproduced these experimental phenomena with reasonable accuracy. With increasing strain rates, the peak stress and modulus increase in a power law manner. The dynamic increase factors of the peak stress and modulus also increase with enhancing thermal-damaged degrees. Due to the thermal damage, the grain contact increased in the maximum allowable closure, thus enhancing compression-hardening capacity and nonlinear characteristics, resulting in a promotion of the rate effect. Lateral contraction deformation can reduce the proportion and magnitude of the tensile stress within the sample, and inhibit intergranular microcracking. The NPR effect depends on both the degree of thermal damage and strain rate. We shed light on the synergistic effects of the rate and NPR on macro- to micromechanical behaviors of thermal-damaged rocks. [ABSTRACT FROM AUTHOR]

This study analyzes the heavy metal pollution in cultivated soils developed from different parent materials in Yunnan Province and assesses their risk levels. The results show significant regional differences in soil heavy metal pollution, greatly influenced by the type of parent material. Cadmium (Cd) pollution is most severe in multiple parent material soil regions, particularly in areas with carbonate and purple rocks, exhibiting a high pollution risk. Other heavy metals such as zinc (Zn), copper (Cu), and lead (Pb) also show varying degrees of enrichment in different parent material zones, posing potential pollution risks. The soil pollution levels of heavy metals were classified using the geo-accumulation index method. It was found that soils developed from carbonate rocks and purple rocks have the most severe heavy metal pollution, while soils from quartzitic rocks, acidic crystalline rocks, and basalt exhibit relatively lower pollution levels. By analyzing the characteristics of heavy metal pollution in different parent materials, this study provides a scientific basis for regional soil pollution management and sustainable agricultural development. [ABSTRACT FROM AUTHOR]

Rock permeability, an important factor in subsurface fluid migration, can be influenced by microcracks and chemical weathering due to water–rock interactions. Understanding the relationship between permeability, chemical weathering, and microcracks is crucial for assessing fluid flow in rocks. This study focuses on the hydrogeological characteristics of granite and gneiss, potential host rocks for high-level radioactive waste disposal in South Korea. Samples were analyzed for permeability, porosity, P-wave velocity, and chemical weathering indices. Regression analysis revealed a weak correlation between permeability and both porosity and rock density, while an inverse correlation was observed between permeability and chemical weathering indices. Interestingly, some samples showed low permeability (10−21 to 10−22 m2) despite high weathering, while others showed high permeability (10−18 to 10−19 m2) despite low weathering. SEM-EDS analysis indicated the presence of microcracks within the rocks or the filling of these cracks with secondary minerals. The findings suggest that chemical weathering generally increases pore size and porosity, but actual permeability can vary depending on the presence and connectivity of microcracks and the extent to which they are filled with secondary minerals. Therefore, both chemical weathering and microcrack connectivity must be considered when evaluating the hydrogeological characteristics of crystalline rocks. [ABSTRACT FROM AUTHOR]

Maps of diluvial boundaries for the North American midcontinent are presented by state and by sedimentary basin. The upper diluvial boundary is the base of Ice Age sediments. For most of the study area, the basal diluvial boundary is the erosional unconformity between Precambrian crystalline rock and the Phanerozoic sedimentary record. The exceptions are Proterozoic to Cambrian rifts: the Midcontinent, East Continent, Fort Wayne, Reelfoot, Rough Creek Graben, and Rome Trough rifts. These are remnants of severe crustal disruption at the onset of the Flood, with varying ratios of volcanic and sedimentary fill. This paper focuses on the basal marine diluvial boundary and the upper diluvial boundary, excluding the rifts, showing the volume and distribution of sediments of the Ice Age. Deep Proterozoic rifts will be addressed in Part II. Detailed state maps of the basal diluvial boundary are shown in the appendix. Maps of the study area reveal cratonic basins of varying size, show a thickening of diluvial strata toward the south, and show the extent of Ice Age deposition. All these aid in understanding the work of the Flood in this region. [ABSTRACT FROM AUTHOR]

On the basis of data on the geochemical characteristics ((La/Yb)N, Eu/Eu*, and content of Th) of clay rocks of Podolian Transnistria, Southeastern Poland, Belarus and Volyn, Lithuania, the vicinity of St. Petersburg, Southeastern White Sea region, and Arctic Norway, categories of rivers that transported fine-grained aluminosilicate clastic material to sinks that existed during the Vendian and Early Cambrian were reconstructed in the west of the East European Platform. The distribution of data points of clay rocks of the Volhynian time on the (La/Yb)N–Eu/Eu* diagram with the fields of the composition of the pelitic fraction of bottom sediments in the mouth of modern rivers of various categories allows us to assume that, for Lithuania and Podolian Transnistria, the feeding provinces were, among other things, paleowatersheds composed of volcanic formations. For Eastern Belarus and the Southeastern White Sea region, the influence of erosion products supplied by rivers flowing through igneous/metamorphic terranes (crystalline basement) is noticeable. A significant part of the clastic material was carried by rivers that drained sedimentary formations, as well as large rivers, i.e., rivers whose length exceeded 1000 km and whose drainage area was more than 100 000 km2. The existence of the latter is confirmed by the presence of detrital zircon in the rocks of the Zhukov Formation of Southeastern Poland, borrowed possibly from the rocks of Fennoscandia. In the Redkinian time, along with large rivers (rivers of category 1) and rivers fed by the products of erosion of sedimentary formations (rivers of category 2), transport of fine-grained clastic rocks was also carried out by rivers that drained rocks of the crystalline basement (rivers of category 3; this is typical of Belarus and Volyn, the Southeastern White Sea, and Arctic Norway) and by rivers flowing through areas of distribution of volcanic associations (rivers of category 4). The distribution of data points of the clay rocks of the Kotlin stage on the (La/Yb)N–Eu/Eu* diagram suggests that the main agents of transport of fine-grained aluminosilicate clastic material to sinks at that time were large rivers and rivers fed by fine-grained particulate matter owing to the erosion of predominantly sedimentary rocks. The Early Cambrian paleowatersheds were apparently composed not only of crystalline rocks but also of sedimentary formations. All of the above is in fairly good agreement with the previously established fact of a gradual increase in the contribution of erosion products of sedimentary rocks to the formation of Vendian–Early Cambrian sedimentary sequences from Podolian Transnistria to Arctic Norway. [ABSTRACT FROM AUTHOR]

Determining the mechanisms by which the earliest continental crust was generated and reworked is important for constraining the evolution of Earth's geodynamic, surface, and atmospheric conditions. However, the details of early plate tectonic settings often remain obscured by the intervening ~4 Ga of crustal recycling. Covariations of U, Nb, Sc, and Yb in zircon have been shown to faithfully reflect Phanerozoic whole-rock-based plate-tectonic discriminators and are therefore useful in distinguishing zircons crystallized in ridge, plume, and arc-like environments, both in the present and in deep time. However, application of these proxies to deciphering tectonic settings on the early Earth has thus far been limited to select portions of the detrital zircon record. Here, we present in situ trace-element and oxygen isotope compositions for magmatic zircons from crystalline crustal rocks of the Acasta Gneiss Complex and the Saglek-Hebron Complex, Canada. Integrated with information from whole-rock geochemistry and zircon U-Pb, Hf, and O isotopes, our zircon U-Nb-Sc-Yb results reveal that melting of hydrated basalt was not restricted to a single tectonomagmatic process during the Archean but was operative during the reworking of Hadean protocrust and the generation of juvenile crust within two cratons, as early as 3.9 Ga. We observe zircon trace-element compositions indicative of hydrous melting in settings that otherwise host seemingly differing whole-rock geochemistry, zircon Hf, and zircon O isotopes, suggesting contemporaneous operation of stagnant-lid (oceanic plateau) and mobile-lid (arc-like) regimes in the early Archean. [ABSTRACT FROM AUTHOR]

The permeability evolution of fractures in geologic media plays a pivotal role in various geo-mechanical activities, ranging from energy resources recovery to the deep geologic disposal of hazardous materials. This paper presents both laboratory and computational investigations into the evolution of fracture permeability under the influence of varying confining stress levels in a crystalline granitic rock from the Canadian Shield. Steady state permeability experiments were conducted to assess variations in fracture permeability in areas where stress conditions may significantly change due to large-scale underground excavations. A high accuracy laser scanner was used to capture the geometric features of the fracture surface, enabling the numerical simulation analysis of stress-induced hydromechanical behavior. The fracture permeability evolution was systematically investigated under both isotropic stress and deviatoric stress conditions, including four loading–unloading sequences and a series of sequentially increased deviatoric stresses. Simulations of fracture closure under increasing confining pressure and corresponding fluid flow process were performed incorporating a model constructed from fracture elevation data obtained through scanning. The results demonstrate a reduction in permeability exceeding 50% as the triaxial confining stress increases from 5 to 40 MPa. Additionally, permeability hysteresis during stress relief was observed. These findings are relevant to deep geological construction activities where excavation leads to the development of an excavation damage zone and stress alterations, affecting overall fluid flow process. Highlights: The fracture permeability evolution in Lac du Bonnet granite under four loading–unloading sequences has been systematically investigated. Stress-induced fracture closure process and its corresponding fluid flow process were simulated based on a model constructed from fracture elevation data obtained through scanning techniques. Fracture permeability showed a clear dependence on stress level and permeability hysteresis was observed during the stress relief. [ABSTRACT FROM AUTHOR]

A rock can undergo hardening deformation during compression and have a memory of the hardening action, which can be displayed when unloaded. This compression-hardening memory effect (CHME) is related to the micromechanical response of the heterogeneous rock microstructure. However, to date, the related mechanism has not been fully characterized. Here, we proposed a grain-based model (GBM) implemented by the Universal Distinct Element Code (UDEC) (version 6.0) to reproduce the cyclic compression test of Jinchuan granite and then investigate the CHME mechanism and its influence on the loading/unloading response of the rock. The results showed that the UDEC-GBM by the compression-hardening memory model (CHMM) reproduces the experimental hysteresis and hardening stress‒strain response, while the traditional linear elastic model (LEM) does not. The grain contact causes nonlinear deformation during compression, enhancing its compressive stiffness. When unloaded, the pre-enhanced compressive stiffness can be remembered, leading to hysteresis and plastic deformation. As a result, the synthetic sample can reserve some of the strain energy and create tensile stress zones, inducing intergranular microcracks and intragranular failure zones. As the peak compressive stress applied in the predisturbed stage increases, the CHME strength increases, influencing the deformation and failure of the synthetic rock sample. Overall, the synthetic rock sample's peak compressive strength decreases as the peak compressive stress applied in the predisturbed stage increases. We shed light on the micromechanical mechanism of CHME, which results from the irreversible increase in the compressive stiffness of grain contacts during compression. Highlights: The rock microstructure exhibits the compression-hardening memory effect (CHME), which can be characterized by the grain-based model. CHME stems from the irreversible enhancement of grain contact stiffness under compression. CHME can lead to the concentration of local tensile stress and rock failure upon unloading, thereby influencing subsequent mechanical responses. [ABSTRACT FROM AUTHOR]

A large mantle helium anomaly and separate domains of high heat flow are the predominant manifestations of bimodal magmatic activity in the Milford valley. The mantle helium anomaly (1.9–2.6 R/Ra) covers 270 km2 and is subdivided into two separated domains: a cold shallow groundwater regime and high temperature hydrothermal activity. The zone of anomalous heat flow covers >100 km2 and is also subdivided into two adjacent domains, comprising hydrothermal activity at Roosevelt Hot Springs (RHS) (3–7 W/m2) and conductive heat flow (100–180 mW/m2). While the transfer of heat and mantle helium at RHS are coupled, heat and helium transfer are decoupled in the adjacent cold groundwater regime to the west. Both the mantle helium and geothermal anomalies are attributed to recent mafic‐felsic magmatic intrusions of >400 km3, however, the absence of volcanic eruptions <500,000 years indicates magmas stall before rising to shallow crustal level <10 km depth. Deep level magmatism produces a felsic composition melt, which is inferred to be responsible for the widespread and near uniform range of diluted mantle helium values. A thick and impermeable mass of crystalline granitic basement rock at the mid‐crustal level divides the ascent of mantle helium into separate flow paths. It may also impede the rise of buoyant magma trapping thermal energy that facilitates partial melting, slow cooling, and development of a thick thermal aureole. Partitioning of convective and conductive thermal regimes and independent flow paths supplying deeply derived helium characterize the development of a large long‐lived magma‐related geothermal system. Plain Language Summary: Productive high‐grade geothermal resources, a form of renewable energy, are associated with volcanic centers and zones of hydrothermal activity in regions undergoing crustal thinning. The Milford valley in southwest Utah is host to a long dormant volcanic center whose modern expression is mostly limited to hydrothermal activity at Roosevelt Hot Springs, which has produced energy since 1984. The US Department of Energy established the Utah FORGE enhanced geothermal systems (EGS) field laboratory in an adjacent zone of extensive hot dry crystalline rock to advance new methods of energy production. Newly discovered additional natural expression of the geothermal system occurs in the shallow cold groundwaters defined by infiltration of deep‐derived mantle helium. It is the primary indication of undiscovered zones of high heat flow and geothermal resources concealed beneath the surface. The isotopic composition of the helium, plus the high geothermal heat flow, suggest that helium is derived from a large body of magma (>400 km3) that is similar in composition to the volcanic deposits that erupted 500,000 to 800,000 years ago in the nearby Mineral Mountains. A thick mass of impermeable granitic rock forms a barrier to magma ascent, suppressing the recent volcanic activity, and producing geothermal resources instead. Key Points: A large groundwater mantle He anomaly and geothermal resources are shallow manifestations of mafic‐felsic magmatism in the lower crustTwo pathways transect the crust transferring mantle He with or without heat at Roosevelt Hot Springs and the adjacent cold groundwater regimeMid‐crustal granitic basement rock impedes the rise of buoyant magma trapping thermal energy that facilitates partial melting and slow cooling [ABSTRACT FROM AUTHOR]

Bedrock geology is crucial in structuring alpine plant communities. Old studies mainly focused on the compositional differences between alpine plant communities on carbonate rocks and crystalline rocks, i.e., calcareous vs. siliceous vegetation. Increasing attention is being paid to bedrock types other than calcareous or siliceous ones, viz. those which have intermediate geochemical characteristics between pure calcareous and pure siliceous ones. Among these types of 'intermediate' bedrocks, calc-schists and serpentines are generally characterized by vegetation comprised of a mixture of basiphilous and acidophilous species. We selected several sites in alpine grasslands in the Western Italian Alps, on calc-schist and serpentine bedrocks, located at 2500 ± 100 m above sea level. X-ray fluorescence quantification of major and trace elements, combined with stereomicroscopic examination of bedrock samples with a petrographic approach, revealed a much broader range of bedrock types than recognized by inspection of geological maps. The vegetation investigated in our study was mostly composed of a set of species found more or less frequently in alpine silicicolous or calcicolous plant communities of the Alps and other European mountains. The carbonate content in the bedrock was one of the main drivers of variation in grassland vegetation, not necessarily related to soil pH. There were no distinctive species uniquely characterizing grassland vegetation on serpentines or calc-schists. [ABSTRACT FROM AUTHOR]

U–Pb dating of zircon via laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) has become a primary method for determining the age of crystalline rocks and the provenance and maximum depositional age of (meta)sedimentary rocks. Although chemical abrasion has become a standard approach for mitigating Pb loss in zircon dated via high‐resolution thermal ionization mass spectrometry (CA‐TIMS), laser ablation dating is rarely accompanied by chemical abrasion. We evaluate the accuracy of U–Pb dates acquired via LA‐ICP‐MS relative to CA‐TIMS through analysis of a large database of paired analyses from the same zircon crystals. We show that laser ablation 206Pb/238U dates are systematically younger than their CA‐TIMS counterparts, with a greater shift in detrital zircon (−2.0%) versus igneous or metamorphic zircon (−0.9%). Although systematic biases related to “matrix effects” may be a contributing factor, our analysis suggests that unmitigated cryptic Pb loss is likely widespread in laser ablation U–Pb datasets. [ABSTRACT FROM AUTHOR]

We numerically solve the acoustic radiative transfer equation for seismic S‐waves via Monte Carlo simulation. By assuming a von Kármán‐type random medium with anisotropic scattering, we are able to simulate a realistic medium and determine its attenuation properties. In this study, we present an improved method, called QEST, to determine the frequency‐dependent intrinsic and scattering attenuation by nonlinear envelope inversion for a 1‐D multilayer model. Additionally, the spectral source energy of earthquakes and the energy site amplification of stations are determined. The code was applied to real data from the northern and southern Leipzig‐Regensburg fault zone (LRZ), Germany, as well as fluid‐induced earthquakes at the Insheim geothermal reservoir, Germany. The attenuation was analyzed in several frequency bands between 4.2 and 33.9 Hz and between 6.0 and 67.9 Hz, respectively. The inversion results reveal that the crystalline crustal subsurface along the LRZ shows little to no depth dependence, but there are differences in attenuation between the north and south. At Insheim, the near‐surface sedimentary basin exhibits significantly greater absorption and scattering than the crystalline basement. The inversion also shows that isotropic scattering can be an oversimplification and thus underestimate attenuation. Plain Language Summary: Seismic attenuation is an important property of the subsurface. It determines the amplitude decay of a seismic wave emitted by an earthquake with time and distance. Seismic attenuation can be divided into scattering and intrinsic attenuation. Scattering is caused by small‐scale heterogeneities in the earth, while intrinsic attenuation is caused by anelastic processes such as internal friction. Differentiating between scattering and intrinsic attenuation poses a challenge. In this study, we present an advancement for the determination of seismic attenuation that considers the heterogeneity of the Earth's crust. We apply this new method to three distinct regions to assess the depth‐dependent scattering and intrinsic attenuation. The findings reveal that pure crystalline rock exhibits little depth dependence, whereas the attenuation properties of a sedimentary basin differ significantly from those of the underlying crystalline rock. Overall, quantifying depth‐dependent seismic attenuation enhances our ability to accurately estimate seismic hazards. Key Points: We invert for frequency‐dependent intrinsic and scattering Q with anisotropic scattering using envelope fitting in a multilayer modelWe estimate seismic moments and corner frequencies for small earthquakes using a 1‐D attenuation modelWe observe a strong attenuation contrast between a sedimentary basin and the underlying crystalline basement [ABSTRACT FROM AUTHOR]

Mineralogical and geochemical studies have been undertaken on the Triassic to Lower Jurassic Adigrat Sandstone of the Blue Nile Basin of central Ethiopia to infer its source rock type, paleoweathering, and paleoclimatic history. The Adigrat Sandstone occurs at the basal section of the Mesozoic sedimentary formation and unconformably overlays the Neoproterozoic–Paleozoic crystalline rocks, or locally, the Karroo sediments in the northern Blue Nile Basin. A mineralogical study reveals that quartz (Q), feldspars (F), and lithic fragments (L) are the framework grains of the sandstone. On the QFL diagram, the plot of the modal composition of the sandstone mainly falls within the feldspathic arenite and quartzose arenite fields. The geochemical data of the lower section of the sandstone mainly falls within the arkose and subarkose fields, whereas the upper section data falls within the quartzose and sublithic arenite fields. Mineralogical and geochemical weathering indices indicate that the provenances of the Adigrat Sandstone were exposed to pronounced weathering intensity, where the lower part of the sandstone was controlled by arid to semi‐arid conditions, whereas the upper section was linked to humid to semi‐humid (tropical to subtropical) climatic conditions. Mineralogical and geochemical data also indicate that mafic to intermediate basement rocks were the primary source rocks of the sediment. Perhaps the sediment was assumed to have been reworked by multi‐cyclic sedimentary processes. The discriminant function diagram, the REE pattern, La/Th vs. La/Yb, and the Th–Hf–Co plot are consistent. A comparison of provenance studies for the Adigrat Sandstone in the Blue Nile Basin and the Mekele outlier of northern Ethiopia indicates that the sediment of the former is highly sorted, experienced higher weathering intensity, and compositionally derived from mafic to intermediate crystalline rocks. On the other hand, the sediment of the latter is essentially a weathering product of felsic rocks. [ABSTRACT FROM AUTHOR]

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We developed Vp, Vs, Vp/Vs ratio, and Poisson's ratio models of the uppermost crust (<4 km depth) from the eastern San Francisco (SF) Bay (California, USA) to near the Calaveras fault along a 15-km-long, linear profile. Upper crustal velocities are highly variable beneath, west, and well east of the Hayward fault. We observe eight notable features, from west to east: (1) Near San Francisco Bay, there is an J2-km-wide structure with high Vp/Vs ratios (up to 5) and Poisson's ratios (up to 0.48) extending from the surface to the base of our model, which we suggest the structure is a near-vertical fault that lies along a straight-line projection between the Silver Creek fault to the south and the Point Richmond fault to the north. The structure may be part of an j90-km-long fault along the eastern SF Bay. (2) The western East Bay Plain, the lower lying area between the bay and the hills, includes up to 800 m of low-velocity sediments (Vp j1600-3000 m/s, Vs j500 m/s to j1000 m/s), underlain by higher velocity basement rocks (Vp j3000-5800 m/s; Vs j1000-1500 m/s). (3) Between j1 km and 3 km east of the Bay shoreline, sediments thin in a series of steps (likely faults) toward the Hayward fault. (4) Between j3 km west and j1 km east of the Hayward fault (at the East Chabot fault) at depths greater than 1 km, basement Vp (up to 6000 m/s) and Vs (up to 2800 m/s) are high, and Vp/Vs ratios (<2) and Poisson's ratios (<0.3) are low, suggesting crystalline rocks. Furthermore, a near-vertical zone of low Vp/Vs ratios and Poisson's ratios is between near-surface traces of the Hayward and East Chabot faults, likely corresponding to the San Leandro Gabbro of Ponce et al. (2003). (5) Eastward of the East Chabot fault in the upper 1.5 km, basement Vp (j3000 m/s to j4200 m/s) and Vs (j1200-2000 m/s) are lower than those west of the fault. (6) In the eastern Hayward/Oakland Hills, there are zones of laterally varying, high- and low-velocity (Vp j2500-3000 m/s) Jurassic-Cretaceous and Tertiary sediments in the shallow subsurface that likely extend much deeper than imaged. (7) Seismic energy that propagates westward from sources east of the Hayward fault (HF) appear weaker than energy that propagates eastward from sources west of the HF, suggesting that the HF acts as a partial barrier to shallow seismic energy propagation into the more populated eastern SF Bay area. (8) Unlike many fault zones, it appears that the active trace of the Hayward fault (in our study area) is not cored by a prominent, low-velocity zone relative to rocks to the east and west of the active trace. However, the active trace does mark a prominent change from relatively higher velocities to the west and lower velocities to the east. [ABSTRACT FROM AUTHOR]

Varying external conditions in the metallogenetic process of crystalline rocks contribute to the complex mineral and textural characteristics, rendering the mechanical properties highly heterogeneous at the mineral scale. This research focused on the influences of minerals with relatively low strength and stiffness (soft minerals) in crystalline rocks on their cracking behavior. A particle‐based discrete element method (DEM) was first employed to establish random grain‐based models (GBM) of crystalline rocks containing soft minerals with different contents, strengths, and stiffnesses. On this basis, responses of the mechanical properties and crack propagation to these parameters were systematically investigated and an optimized micro‐parameter calibration method for real CT (computed‐tomography) ‐based GBM was then proposed considering the characteristics of soft minerals. The results demonstrate that with the decrease of the strength of soft mica, the intragranular cracks are prone to initiate and propagate inside the soft minerals and lead to the final crack coalescence. The decrease in the stiffness of soft minerals enhances their controlling effects on the cracking propagation. Based on the CT‐based granite model, it was found that a heterogeneous stress field is produced due to the spatial distribution of the soft (mica) and hard (quartz and feldspar) minerals, and the mica minerals tend to terminate cracks or force cracks to deflect or bypass individual grains during crack propagation. This study sheds light on the damage and failure processes of crystalline rocks with contrast mineral components. [ABSTRACT FROM AUTHOR]

The Elbistan (Chardak) earthquake with magnitude Mw = 7.5 or 7.6 happened in Eastern Anatolia on 06.02.2023 at 10:24 UTC, following the strongest in the region of East Anatolian (Pazarcık) earthquake with Mw = 7.8 which occurred on the same day at 1:17 UTC to the south of the region. The Elbistan earthquake activated adjacent segments of the Chardak and Uluova faults with left-lateral strike-slip displacements. The resulting seismic ruptures have a total length of 190 km, of which 148 km are represented by sinistral lateral slip. Their maximum amplitude of 7.84 m was recorded 8 km east of the epicenter. The strike-slip seismic ruptures of the Elbistan and East Anatolian earthquakes represent exposure of their focal zones on the land surface. Both earthquakes exceed average values of these parameters for continental earthquakes of strike-slip type in terms of focal zone sizes and amplitudes of seismic displacements. At the same time, both sources do not propagate deeper than the upper part of the crust (16–20 km). Ophiolite assemblages covering the same depths are widely spread in the area of focal zones of both earthquakes. Two maxima were found in the distribution of seismic strike-slip displacement along the epicentral zone of the Elbistan earthquake (i) amplitudes of 5.7–7.84 m in the Chardak fault zone and (ii) amplitudes of 3.5–5.1 m in the Uluova fault zone. Both maxima coincide with the areas of ophiolites or their contacts with basement rocks. In crystalline basement rocks, the sinistral strike-slip amplitudes are significantly reduced. We attribute the increased values of focal zone sizes and displacement amplitudes of both earthquakes to the rheological features of ophiolites, which increase a possibility rocks slipping during seismic movements. We explain the fact that the sources of both earthquakes cover only the upper part of the crust by the uplift of the top of rocks with reduced P-wave velocities, including the upper mantle and the lower part of the crust, and interpret them as heated rocks with reduced strength. [ABSTRACT FROM AUTHOR]

In the past fifteen years, the contamination of the Italian marine coastal environments by asbestos cement materials (ACMs) represents a known crux mostly reported or denounced by mass media and environmental associations. A recent research reporting compositional and textural data related to ACMs found in the beach deposits of a protected natural reserve (Cape Peloro, Messina, Italy) induced the author to perform new petrographic and textural analyses on the Cape Peloro beach sands, pebbles, cobbles (BSPC), and technofossils (bricks, tails, slab, concrete), associated with the previously studied ACMs, in order to compare the data with those of the ACMs previously reported in the literature. The petrographic investigations allowed the author to determine that beach sands and weakly gravelly sands were characterized by a quartzo–lithic signature, being mainly composed of metamorphic grains of quartz (50–60%) and metamorphic lithics (40–50%, mainly composed of polymineral quartz + microcline, quartz + plagioclase, quartz + biotite, quartz + muscovite grains, and monomineral opaque minerals, plagioclase, k-feldspar, and almandine garnet grains), whereas the pebbles and cobbles were made of acid intrusive (granitoids) and metamorphic rocks (gneiss, augen gneiss prevailing). Pebbles and cobbles made up of porphyroids could derive from the cannibalization of the underlying lower to middle Pleistocene siliciclastic deposits of the Messina Formation. Differently, the gneiss, augen gneiss, and granitoids forming the beach pebbles and cobbles, being present both in the crystalline rocks of the Aspromonte Unit and in the clasts of the SGMF, could originate from both of them. Textural investigations allowed the author to characterize grain size, shape parameters, and roundness in the beach deposits. These were mostly composed of sands and weakly gravelly sands with medium grains. Parameters, such as elongation and flatness, showed higher values in the BSPC than in the technofossils. The shapes of the BSPC were mostly from oblate to equant, whereas the shapes of the technofossils were mostly from bladed to oblate. The main differences depended on the original shape of the technofossils, being mostly platy, and their softer composition. The roundness was from angular to sub-rounded. In the Ionian coast of the Cape Peloro peninsula, the source areas for the well-rounded ACM found on the beach and in the beach deposits could have at least four different origins: (i) Possible landfills widespread since the 1970s in the intensively urbanized coastal areas. (ii) Direct abandonment in the coastal area. (iii) Direct abandonment in the streams. (iv) Activities to counteract the erosion/lack of sediment using non-conforming materials. Considering the diffused damage caused by the coastal erosion affecting most of the Italian coast and the obvious increasing dispersion of the asbestos fibers from the ACMs over time, effectual counter actions to prevent further contamination and guidelines for clean-up efforts are necessary. [ABSTRACT FROM AUTHOR]

Fluid flow through fractured media is typically governed by the distribution of fracture apertures, which are in turn governed by stress. Consequently, understanding subsurface stress is critical for understanding and predicting subsurface fluid flow. Although laboratory‐scale studies have established a sensitive relationship between effective stress and bulk electrical conductivity in crystalline rock, that relationship has not been extensively leveraged to monitor stress evolution at the field scale using electrical or electromagnetic geophysical monitoring approaches. In this paper we demonstrate the use time‐lapse 3‐dimensional (4D) electrical resistivity tomography to image perturbations in the stress field generated by pressurized borehole packers deployed during shear‐stimulation attempts in a 1.25 km deep metamorphic crystalline rock formation. Plain Language Summary: Time‐lapse electrical geophysical sensing is used to image 3D changes in rock stress generated by an isolated and pressurized interval of a borehole in a deep, dense, fractured rock formation. Key Points: Remotely monitoring stress is challenging but important for relating geomechanical behavior to flow pathways during energy productionBulk electrical conductivity is sensitive to stress in crystalline rockTime‐lapse electrical resistivity tomography can be used to remotely monitor 3D changes in effective stress [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) is an effective tool for revealing the rock failure mechanism. However, research has found that over 90 % of test tensile failure sources cannot be captured. Furthermore, previous studies on thermal damage and AE characteristics have neglected the influence of mineral and grain boundary strength. Given this, this study establishes a Grain-Based Model that can accurately reflect the irregular shape of minerals. The model also considers the influence of minerals and intergranular strength. Firstly, an analysis is conducted to investigate thermal crack generation rules. Secondly, the quantitative investigation of temperature and grain size on AE properties is examined through moment tensor inversion. Finally, a comparative analysis explores the disparities in thermal crack generation and AE characteristics between different modelling methods. The results indicate that the phase transition of quartz causes significant structural damage, resulting in a sharp increase in microcracks. Additionally, the number of thermally induced cracks decreases as grain size increases. AE magnitudes exhibit a normal distribution with AE frequency and follow a power-law distribution with the cumulative number of AE events. The maximum magnitude gradually decreases with increasing temperature, while magnitude shows no significant correlation with grain size. The frequency of large-magnitude events decreases with rising temperature but increases with grain size. The formation pattern of thermally induced cracks and the distribution of AE failure sources strongly correlate with mineral and intergranular strength. Therefore, to accurately depict failure mechanisms in crystalline rocks, the models should consider the influence of mineral and intergranular strength. Highlights: The Grain-Based Model was employed to investigate the influence of grain size and temperature on the mechanical properties and failure mechanism of crystalline rocks. The influence of grain size and temperature on the acoustic emission characteristics of crystalline rocks was quantitatively studied based on moment tensor inversion. The differences in the study of thermal damage and acoustic emission characteristics of crystalline rocks using different modeling methods were revealed, and the sources of the differences were analyzed. [ABSTRACT FROM AUTHOR]

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In the Central Eastern Alps, an increasing number of high-altitude streams display high concentrations of toxic solutes such as Al, F-, Mn, and Ni that may strongly exceed drinking water limits. Previous studies have shown that these elements are mobilized from rock glaciers occurring at the origin of the streams. This is caused by the weathering of pyrite producing sulfuric acid and therefore promoting the leaching of these elements from the crystalline host rocks. After mobilization, the elements are temporally stored and enriched in the rock glacier ice. Today, the climate-change-induced accelerated melting of rock glaciers thus leads to a quick and focused export in summer when ice melt export rates are high. The temporal storage of mobilized elements in the rock glacier ice opens up the opportunity to use the strong chemical signal in the streams to track rock glacier melt dynamics and to identify the governing processes controlling the export of ice melt. To test this and to assess the consequences of accelerated rock glacier melt on streamwater quality, here we present a two-year dataset (2021, 2022) of monitoring a high-alpine stream originating from an intact rock glacier located in Eastern Switzerland. The monitoring includes monthly sampling and discharge measurements at the rock glacier outlet, as well as continuous tracking of the geogenic fluxes of toxic solutes using a pressure and conductivity probe. Our monitoring revealed high annual fluxes with strong seasonal variation, whereby the fluxes were highest during the warm summer months. In 2021, the annual fluxes were up to several tons each, which is remarkable given that the area of the rock glacier covers only about 40'000 m2. Interestingly, in 2022 the fluxes were about 30 % lower despite the record-high summer temperatures. A similar difference was observed for the annual discharge recorded for the two years. This suggests that the export of both ice melt and toxic solutes are strongly controlled by the amount of water from snowmelt and precipitation infiltrating into the rock glacier system. The dry weather and low discharge rates in 2022 thus likely lead to lower export rates compared to 2021, when snow height and precipitation rates were above average. Nevertheless, in both monitoring years the degradation of the rock glacier significantly contributed to the discharge of the downhill stream. Based on these aspects, we present conceptual models for accumulation of toxic solutes in rock glacier ice well as for their water driven mobilization during accelerated rock glacier degradation. Finally, we argue that monitoring solute fluxes exported from rock glaciers is a promising future research direction for obtaining more reliable estimates of the amount of ice melt exported from rock glaciers. [ABSTRACT FROM AUTHOR]

A linear structure which is interpreted to be a fault was identified within the Precambrian basement complex rocks of the Ogbomoso Southwest Sheet 222 geological map, southwest Nigeria. The ground magnetic and electrical resistivity methods were used to investigate the structure and determine its physical characteristics. Five (5) traverses with lengths varying from 700–800 m and trending approximately NW–SE were established perpendicularly to the suspected fault. Total magnetic field data were acquired at 10 m interval, corrected for diurnal variation and inverted into 2D magnetic models using the Geosoft Oasis montaj software package. Dipole-Dipole resistivity data were acquired along the traverses using a dipole length of 20 m with expansion factor n varying from 1 to 5 and modelled to generate 2D resistivity structures with the DIPPROTM software package. Thirty-seven (37) depth sounding datasets were acquired, quantitatively interpreted and the results used to generate geoelectric sections across the suspected geologic feature. Three major magnetic dyke lineaments D1, D2 and D3 (60 – 164 m wide and 70 – ∞ depth extent) characterised by peak negative (−44 to −81 nT) magnetic anomalies and equivalent resistivity lineaments R1, R2 and R3 (50 – 140 m wide and 40 to >60 m depth extent) typified by low resistivity (10 – 750 Ωm) vertical discontinuities were delineated. The northern edges of lineaments D2 and R2 coincide significantly with the spatial location of the suspected fault F¹ – F¹ while D1 and R1 and D3 and R3 correlated and are newly identified parallel faults F² – F² and F³ – F³ to F¹ – F¹ and probably syngenetic with it. Geological observation of laterally displaced segments of porphyroclastic gneiss and absence of significant vertical displacement of the basement bedrock shoulders (from 2D magnetic and resistivity images and geoelectric sections) suggest that F¹ – F¹ is a strike slip fault. [ABSTRACT FROM AUTHOR]

This article presents the results of deep seismic studies over the Sikhote-Alin fragment of the 8-DV reference geophysical profile running across the large fold structures of the Pacific tectonic belt, that is, the Sikhote-Alin Orogenic Belt with the superimposed Middle Amur sedimentary basin and the East Sikhote-Alin volcanoplutonic belt. A deep seismic section of the Earth's crust and upper mantle with the distribution of longitudinal wave velocities is constructed. In the upper part of the section, P-wave velocities vary from 4.0–5.0 km/s within the Middle Amur sedimentary basin and the eastern part of the Eastern Sikhote-Alin volcanoplutonic belt to 5.5–5.6 km/s in the central part of the Sikhote-Alin Orogenic Belt. It was established that the thick Paleozoic sedimentary complex within the Middle Amur sedimentary basin is faulted and folded in a complex manner. Crystalline rocks with a compressional wave velocity of 6.0–6.2 km/s occur at depths from 8 to13 km in different parts of the Middle Amur sedimentary basin and at depths of 4–6 km within the Sikhote-Alin orogenic complex. Compressional wave velocities of the crust in the Sikhote-Alin fragment of the 8-DV profile are between 6.3 and 6.35 km/s. The crust varies in thickness from 32–34 km in the northern part of the fragment to 36–37 km in its central and eastern parts. Along the Moho, P-wave velocities are 8.1–8.3 km/s; a number of areas with reduced Vp of 7.8 to 8.0 km/s were identified in the junction zones of large crustal blocks. P-wave data were used to identify anomalies which were correlated with structural-tectonic zones, deep fault zones, and seismicity. The thick Middle Amur sedimentary basin was distinguished along the Central Sikhote-Alin deep fault. This basin is filled by Paleozoic low-velocity deposits and is displaced along the fault plane by 4–5 km at its junction with the Sikhote-Alin Orogenic Belt. Zones of increased heterogeneity in the upper crust projected onto the area within the contours of the Middle Amur sedimentary basin are characterized by increased seismicity. [ABSTRACT FROM AUTHOR]

To estimate catchment-scale hydrogeological parameters such as hydraulic conductivity (k) and specific yield (Sy), the streamflow recession analysis method proposed by Brutsaert and Nieber (1977) was used. The analysis employed the technique of fitting a theoretical recession curve to the observed data in which three points of transition between the short- and long-term flow regimes were determined. This method is a simple, fast, and cheap alternative to standard point-based hydrogeological methods using investigations carried out in hydrogeological boreholes. The study area covered the mountainous catchment of the Biała Lądecka River, located in south-western Poland and composed of metamorphic rocks. The hydrogeological environments drained by the Biała Lądecka are two zones, i.e. the zone of weathered covers and rock debris and the zone of fractured rock mass. The k values determined based on the recession analysis were in the boundary zone of the range from 10-4 to 10-5 m/s and they represented the upper range of the values reported in the literature (from 10-4 to 10-7 m/s). The Sy values at a level of 0.38-1.02%, in turn, entirely fitted the literature data. The results confirm the thesis that the recession method, despite certain limitations in terms of its applicability, can be well adapted to the conditions of a mountainous catchment composed of crystalline rocks where a cool temperate climate prevails. [ABSTRACT FROM AUTHOR]

In order to identify the sedimentary processes, depositional environment, and provenance, the study used sieving and SEM-EDS to analyze the particle size and quartz grain microtextures from sediments in the central part of the Gulf of Guinea. Samples were collected from three locations (Yoyo, Mbiako, Mouanko) for grain size analysis and particle size parameters such as mean, sorting, skewness, and kurtosis were determined. In general, the sediments are dominated by medium-grained sands (81.14%). The descriptive statistics and bivariate relationship plots of different particle size parameters show that the sediments are medium to fine, moderately well classified, fine-to-very fine skewed towards fine with platykurtic. Most of the sands come from a river-type environment, as well as beaches, and transported by saltation. The transport mode of the fine sands is dominated by suspension transport. Rolling is the dominant mode of transport for coarse sands. Twenty-five features were known and clustered according to their types of origin. Among them, eighteen features characterize the mechanical origin, four belong to the chemical origin, and three represents mechanical/chemical origin. Quartz microtextures show that the mechanical, mechanical/chemical, and chemical are mostly associated with fluvial, littoral, and aeolian processes. The quartz grains in the sediments from the central part of the Gulf of Guinea are resulting mostly from crystalline source rocks. Furthermore, shapes (angular, subangular, sub-rounded) indicate that these sediments were transported by a medium to high-energy environment, short transport or quick deposition. Moreover, occurrence of sub-rounded grains militated for far-source materials. [ABSTRACT FROM AUTHOR]

Earth's deep continental subsurface is a prime setting to study the limits of life's relationship with environmental conditions and habitability. In Precambrian crystalline rocks worldwide, deep ancient groundwaters in fracture networks are typically oligotrophic, highly saline, and locally inhabited by low‐biomass communities in which chemolithotrophic microorganisms may dominate. Periodic opening of new fractures can lead to penetration of surface water and/or migration of fracture fluids, both of which may trigger changes in subsurface microbial composition and activity. These hydrogeological processes and their impacts on subsurface communities may play a significant role in global cycles of key elements in the crust. However, to date, considerable uncertainty remains on how subsurface microbial communities may respond to these changes in hydrogeochemical conditions. To address this uncertainty, the biogeochemistry of Thompson mine (Manitoba, Canada) was investigated. Compositional and isotopic analyses of fracture waters collected here at ~1 km below land surface revealed different extents of mixing between subsurface brine and (paleo)meteoric waters. To investigate the effects this mixing may have had on microbial communities, the Most Probable Number technique was applied to test community response for a total of 13 different metabolisms. The results showed that all fracture waters were dominated by viable heterotrophic microorganisms which can utilize organic materials associated with aerobic/facultative anaerobic processes, sulfate reduction, or fermentation. Where mixing between subsurface brines and (paleo)meteoric waters occurs, the communities demonstrate higher cell densities and increased viable functional potentials, compared to the most saline sample. This study therefore highlights the connection between hydrogeologic heterogeneity and the heterogeneity of subsurface ecosystems in the crystalline rocks, and suggests that hydrogeology can have a considerable impact on the scope and scale of subsurface microbial communities on Earth and potentially beyond. [ABSTRACT FROM AUTHOR]

Whether from the near-surface or at great depths, geothermal energy aims to harness the heat of the Earth to produce energy. Herein, emphasis is put on geothermal reservoirs and their cap rock in crystalline rocks, in particular, the basements of sedimentary basins and volcanic islands in the context of subduction. This study is based on a case study of three examples from around the world. The aim of this paper is to show how the study of newly formed minerals can help the exploration of geothermal reservoirs. The key parameters to define are the temperature (maximum temperature reached formerly), fluid pathways, and the duration of geothermal events. To define these parameters, numerous methods are used, including optical and electronic microscopy, X-ray diffraction, microthermometry on fluid inclusions, chlorite geothermometry, and geochemistry analysis, including that of isotopes. The key minerals that are studied herein are phyllosilicates and, in particular, clay minerals, quartz, and carbonates. They are formed because of hydrothermal alterations in fracture networks. These minerals can have temperatures of up to 300 °C (and they can cool down to 50 °C), and sometimes, they allow for one to estimate the cooling rate (e.g., 150 °C/200 ka). The duration of a hydrothermal event (e.g., at least 63 Ma or 650 ka, depending on the site) can also be established based on phyllosilicates. [ABSTRACT FROM AUTHOR]

Activating closed natural fractures (NFs) in hot dry rock (HDR) reservoirs is a critical way to improve fluid conductivity and stimulate production. However, the current hydraulic fracturing simulation technology is limited in its ability to investigate the interaction mechanism between hydraulic fractures (HFs) and NFs under the interference of mineral heterogeneity in HDR. In this study, we combine a modified hydro-grain-based model (hydro-GBM) and the smooth joint model (SJM) to establish a discrete element model of granite with closed NFs, investigating the effects of in-situ stress, approach angle, and physico-mechanical properties of NFs on interaction modes. Our results show that mineral heterogeneity induces HFs on both sides of the borehole to propagate asymmetrically along low-strength minerals and mineral boundaries, enhancing the complexity of HFs. As the approach angle, NF interface friction coefficient, or NF bond strengths decrease and differential in-situ stress or NF permeability increases, the offset of HFs propagating along NFs increases, thus promoting the activation degree of NFs and resulting in a decline in the average activity level of acoustic emission (AE) events and the proportion of large events in NFs. Furthermore, numerical simulations reveal the evolution laws of fracturing results, such as breakdown pressure, fracture propagation pressure, spatial distribution of microcracks, fluid pressure field, and normal stresses on NFs, which provide valuable insights for constructing complex and efficient fracture networks in HDR reservoirs. Highlights: A smooth joint coupling hydro-grain-based model is proposed to describe the crystalline rock with closed natural fractures from the mineral grain scale. The model reproduces the interaction modes between hydraulic fractures and natural fractures similar to the experimental results. Effects of in-situ stress, approach angle, and physico-mechanical properties of natural fractures on interaction processes are deeply analyzed. Evolution laws of normal stresses and AE responses for natural fractures during interactions are revealed. [ABSTRACT FROM AUTHOR]

New U–Pb ages of detrital and igneous zircons of the Uppermost Unit of Crete shed light on its provenance and on Eohellenic to Eoalpine imprints in the eastern Mediterranean. The detrital zircons of all nappes show Variscan ages and are characterized by a Minoan-type age spectrum, which is typical for the NE margin of Gondwana. Parts of the metasedimentary rocks are unexpectedly young. Their detrital zircon ages continue via the Permian until the Late Triassic, Middle Jurassic and Early Cretaceous. The high-grade metamorphic rocks of the Asterousia crystalline complex are likely equivalents of the low-grade metamorphic trench and fore-arc deposits of the Vatos nappe pointing to Late Cretaceous slab roll back. The presence of both late Permian detrital zircons and Late Cretaceous arc-type granitoids suggest that the Uppermost Unit of Crete is derived from the late Permian/Late Cretaceous magmatic belt situated north of the Sava–Vardar–Izmir–Ankara Suture in the Strandja–Rhodope area. To achieve their recent position on Crete, the nappes had to travel more than 500 km. The traveling path is well tracked by rocks of the Upper Cycladic Unit, which are similar to those of the Uppermost Unit of Crete. The large displacement of the Cretan nappes was controlled not only by nappe transport, but probably also by dextral strike–slip along the North Anatolian Fault Zone and related counterclockwise rotation of the Anatolian block since the Eocene. [ABSTRACT FROM AUTHOR]

Based on lithogeochemical data related to the fine-grained clastic rocks of the Volyn, Valdai, and Baltic groups in the western part of the East European Platform (Belarus and Volyn, partly Lithuania), categories of rivers that transported the fine-grained aluminosiliciclastics to the sinks were reconstructed. It is concluded that the formation of Vendian and Lower Cambrian sedimentary sequences in this area was controlled mainly by river systems similar to modern large rivers (catchment area >100 000 km2) and rivers draining sedimentary rocks (catchment area <100 000 km2). The fine-grained aluminosiliciclastics transported by them was delivered mainly from areas composed of rocks of the platform crystalline basement and, in part, sedimentary rocks. The distribution of data points of Vendian–Lower Cambrian mudstones on the (La/Yb)N–Eu/Eu* and (La/Yb)N–Th diagrams with fields of the pelitic and silty–pelitic sediments at the mouths of modern different-category rivers shows that mafic rocks of the Volyn–Brest large igneous province, apparently, were not suppliers of the fine-grained aluminosiliciclastics in the indicated time intervals. [ABSTRACT FROM AUTHOR]

Poisson's ratio for earth materials is usually assumed to be positive (Vp/Vs > 1.4). However, this assumption may not be valid in the critical zone because near Earth's surface effective pressures are low (<1 MPa), porosity has a wide range (0%–60%), there are significant texture changes (e.g., unconsolidated vs. fractured media), and saturation ranges from 0% to 100%. We present P‐wave (Vp) and S‐wave (Vs) velocities from seismic refraction profiles collected in weathered crystalline environments in South Carolina and Wyoming. Our data show that ∼20% of the subsurface has negative Poisson's ratios (Vp/Vs values < 1.4), a conclusion supported by borehole sonic logs. The low Vp/Vs values are confined to the fractured bedrock and saprolite. Our data support the hypothesis that weathering‐generated microcracks can produce a negative Poisson's ratio and that Vp/Vs values can thus provide insight into important critical zone weathering processes. Plain Language Summary: When a material is squeezed, the ratio between the change in height and width is described by an elastic parameter called Poisson's ratio. Most earth materials have a positive Poisson ratio, meaning the material will expand when squeezed (e.g., Playdough or wet sand). Materials with a negative Poisson's ratio rarely occurs naturally and will shrink in all directions when squeezed. Cork is a common material with a Poisson's ratio of approximately zero. Cork is ideal for bottling wine because its width does not change when pushing it into the bottle's narrow neck. Here we use surface‐based measurements to quantify Poisson's ratio from P‐wave (Vp) and S‐wave (vs.) velocities in the top 50 m of Earth's surface. Our results show an unexpected result—material in the CZ has a negative Poisson's ratio. We believe this unexpected behavior is caused by the combination of low effective pressures and small and irregular cracks created during rocks' transformation into soil. The cracks have a greater impact on the material's ability to resist compression. At the same time, most of the rock is still coherent and thus only experiences a minimal loss of shear strength. Key Points: Vp/Vs values in the critical zone can be less than 1.4, suggesting a negative Poisson's ratioIn near‐surface environments, the assumption that materials have a positive Poisson ratio is not always justifiedLow Vp/Vs ratios may identify the onset of physical weathering in crystalline rock [ABSTRACT FROM AUTHOR]

In Ecuador and Colombia there is a belt of crystalline rocks of the Jurassic age, in which discoveries of copper porphyry-type mineral deposits have been made during the last decades. The reason for carrying out the present study is in the northern part of the Putumayo department, a prospective area for the discovery of porphyry-type mineral deposits of Cu-Mo, like Mocoa. For the identification of geochemical anomalies from the regional exploration stage, geostatistical modeling is used through the conditioned turning bands simulation tool, using data from 443 fine current active sediment samples, taken in basins within the study area draining mainly Jurassic age rocks. The automatic cartography of turning bands carried out for each of the elements under study identified four anomalies of regional importance, corresponding to geochemical signatures in the identification of copper porphyry systems on the surface. [ABSTRACT FROM AUTHOR]

In this article, a high-resolution acoustic emission sensor, accelerometer, and broadband seismometer array data set is made available and described in detail from in situ experiments performed at Äspö Hard Rock Laboratory in May and June 2015. The main goal of the hydraulic stimulation tests in a horizontal borehole at 410 m depth in naturally fractured granitic rock mass is to demonstrate the technical feasibility of generating multi-stage heat exchangers in a controlled way superiorly to former massive stimulations applied in enhanced geothermal projects. A set of six, sub-parallel hydraulic fractures is propagated from an injection borehole drilled parallel to minimum horizontal in situ stress and is monitored by an extensive complementary sensor array implemented in three inclined monitoring boreholes and the nearby tunnel system. Three different fluid injection protocols are tested: constant water injection, progressive cyclic injection, and cyclic injection with a hydraulic hammer operating at 5 Hz frequency to stimulate a crystalline rock volume of size 30 m × 30 m × 30 m at depth. We collected geological data from core and borehole logs, fracture inspection data from an impression packer, and acoustic emission hypocenter tracking and tilt data, as well as quantified the permeability enhancement process. The data and interpretation provided through this publication are important steps in both upscaling laboratory tests and downscaling field tests in granitic rock in the framework of enhanced geothermal system research. Data described in this paper can be accessed at GFZ Data Services under 10.5880/GFZ.2.6.2023.004. [ABSTRACT FROM AUTHOR]

Crystalline rocks, exposed in different parts of the world and over about one-third of India, have complex aquifer systems, which pose a challenge to mapping groundwater dynamics. Electrical resistivity tomography in quasi-3-D and electrical logging of some borewells carried out in an experimental 'hydrogeological park' in southern India, which has numerous boreholes and other geophysical information for validation, were unable to map the existence of deeper bedrock fractures and their connectivity. We have attempted electric-field vector resistivity imaging (EVRI), a new tool, to resolve the possible fracture-induced deep interconnectivity in a hard rock aquifer system. In the experiment, multiple two-orthonormal-channels independent receiver nodes for potential measurements are deployed and illuminated with several current injections between ∼ 0.9–3.7 A in full 3-D fashion, which allowed for improved mapping of resistivity variation than earlier approaches. The EVRI-derived full 3-D model shows the presence of fractures for depths between 20 and 70 m with substantial resistivity variations, supported by some borewells hydraulic investigations. It has also enhanced lateral resolution for depths > 30 m and almost doubled the depth of investigation than earlier electrical models. EVRI results revealed unweathered/unfractured granitic rock with no significant signature of fractures beyond 70 m depth that corroborates with existing borehole logs and hydrogeological conceptual model. Therefore, this study demonstrates the potential of EVRI for 3-D mapping of heterogeneous crystalline rocks, which would greatly help in groundwater management. [ABSTRACT FROM AUTHOR]

The lower age boundary of the Upper Precambrian basal sequences of the Polar Urals (Nyarovei Group) is determined on the basis of mass U–Pb (LA-ICP-MS) dating of detrital zircon. The upper boundary of the basal sequence is determined from U–Pb (LA-ICP-MS) dating of zircon from overlapping volcanic rocks of the Nemyurgan Formation. It is thus established that the Nyarovei Group formed during a narrow period in the end of the Late Riphean (~750–650 Ma). The recognition of the group as a Middle Riphean straton is erroneous. A dominant role in the formation of the Nyarovei Group was played by erosion products of adjacent blocks of crystalline rocks, the fragments of which probably include the polymetamorphic complexes in the Kharbei–Marunkeu Anticlinorium of the Polar Urals. [ABSTRACT FROM AUTHOR]

Most of the contaminant conceptual models in weathered crystalline bedrock aquifers in Brazil rely on data collected using conventional site investigation methods, at insufficient spatial resolution for associating contaminant distributions with observed heterogeneity. The DFN methodology was adapted for the characterization of a chlorinated solvent contaminated weathered crystalline bedrock aquifer, located in the region of the Jurubatuba district, Sao Paulo city, Brazil. The objective of this research is to establish a detailed 1-D conceptual model to show variable contaminant distribution within the bedrock matrix under different fracture and weathering conditions. The numerous depth-discrete rock sample analyses, assigned to specific geologic features, indicate the presence of PCE-Dense Non-Aqueous Phase Liquid (DNAPL) at discrete-depth intervals along the profile. These zones are mainly related to the lithological contacts and interfaces among the weathered bedrock. The soft and hard weathered-bedrock transition zone does not indicate a sharp decrease in the contaminant mass retention within the bedrock matrix for the studied area. This indicates that contaminant mass storage in the bedrock remains beyond this drilling method-defined interface, which can potentially sustain dissolved VOC concentrations over time and maintain the continuous vertical mass flux into deeper parts of the aquifer. There is a demonstrated need for an appropriate characterization methodology including high-resolution soil coring and sampling to delineate contaminant distribution over crystalline weathered bedrock aquifers. This is a key assumption for the definition of appropriate remedial and groundwater management strategies. [ABSTRACT FROM AUTHOR]

Scipione Breislak may be considered as one of the most renowned Italian 'Plutonists' at the end of the eighteenth and beginning of the nineteenth centuries. In the 1790s, he was a professor of Physics at the Military Academy of Nunziatella in Naples, where he also devoted himself to the study of Vesuvius and the Phlegraean Fields. Thus, he acquainted himself with volcanic phenomena. Breislak's works about the volcanic fields of Campania (Southern Italy) disclosed how Torbern Olof Bergman's theories and Antoine-Laurent de Lavoisier's chemistry had affected his belief in the idea that volcanic eruptions were triggered by ignition of petroleum deposits. After a voluntary exile in France, owing to the downfall of the Roman Republic, Breislak returned to Italy and settled in Milan, where he was appointed as an Inspector of Gunpowder in 1802. Due to his new administrative duties, he had the opportunity to continue studying mineralogy and geology, focusing primarily on the stratigraphy of Lombardy and of the Alps. During the 'Milanese period', he published the Introduzione alla geologia (Introduction to geology, 1811), which may be regarded as the first Italian handbook about the 'new' science of Geology. In the monograph, he also drew on Huttonian ideas in order to describe the lithostratigraphic features of crystalline rocks. Without neglecting Breislak's volcanological hypotheses, this paper aims to analyze the influence that nineteenth-century Plutonist (Huttonian) geological theories had on the Earth's history that he depicted in the Introduzione alla geologia. The influence of Plutonism—a term that Richard Kirwan introduced to define James Hutton's geological system—may also be recognized in Breislak's rejection of transition rocks. Indeed, according to him: "nature does not make passages or transitions, and each of its products has a specific and particular way to exist" (Breislak 1811, volume 1, pp. 308–309). [ABSTRACT FROM AUTHOR]

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This study focused on evaluating the efficiency and complementarity of image enhancement techniques for lithological discrimination and mapping in the upper parts of Benue Trough using Landsat 8 data. To achieve this, image enhancement techniques such optimum index factor, band ratio, principal component analysis, and minimum noise fraction were applied on Landsat 8 OLI data covering parts of the Upper Benue Trough. False colour composites (FCC) were created from three most informative derivatives of these image enhancements. The FCCs were compared in terms of their capability to differentiate different lithological units in the study area by comparing the FCCs with existing geological map. The results show that the FCC created from band ratios provided the highest amount of information, while those created based on optimum index factor provided the least amount of information with respect to lithological discrimination. Additionally, it was observed that the FCCs created from the derivatives of band ratio, principal component analysis and minimum noise fraction provide complementarity. Thus, the three FCCs from these three enhancement methods were fused into a single image, which further aided lithological discrimination. By combining the outputs from three image enhancement techniques, most of the sedimentary and crystalline rocks in the study area were successfully delineated. The method adopted in this study particularly the fusion of outputs from band ratio, principal component analysis and minimum noise fraction represents a novel approach that is suitable for lithological mapping in remote areas, particularly arid and semi-arid terrains with considerable rock exposure. [ABSTRACT FROM AUTHOR]

Understanding the residence time, flow velocities, and storage volumes in fractured rock aquifers is essential for assessing the sustainable use of groundwater in island aquifer systems. Environmental tracers such as tritium (3H) and sulfur hexafluoride (SF6) that enter the aquifer systems through natural hydrological processes are effectively used to quantify the "apparent age" of young groundwater (<60 years) to calculate these aquifer characteristics. The island of Tobago is predominantly a fractured rock aquifer system that contains groundwater sub-basins that produce 100–1000% more than their calculated recharge. In this study, we analyzed ten samples from groundwater wells throughout the island for environmental tracers to establish the "apparent age" of the groundwater. We then estimated the active flux and storage volume of the aquifer. The 3H results of ten wells throughout the island range between 0.02 and 0.60 TU. The groundwater samples to the south of the island possess more pre-modern groundwater ages (older ages) than samples in the north of the island. These tritium values reveal age ranges between 18 and 60–plus years. This finding suggests that fractures create flow paths oriented towards the southern parts of the basin that enable the transport of groundwater across significant topographic boundaries and watershed divides. Additionally, the data may support that southern wells are connected to isolated old sources of groundwater. SF6 values range between 0.91 and 7.97 (part per trillion volume) with an interpreted age range between 18 and 39 years. Both tracers support the original hypothesis that longer residence time waters are located south of the island except for three SF6 samples which are believed to be affected by "excess air". [ABSTRACT FROM AUTHOR]

During fluvial transport pebbles are subject not only to abrasion but also to breaking. Pebbles from the river Ammer (mostly carbonate rocks) show that breaking is a frequent and essential event. Due to frequent breaking, pebbles of carbonate rocks rarely attain a symmetrical final shape (spheroid). Crystalline rocks without schistosity break less frequently, hence spheroids are more frequent. [ABSTRACT FROM AUTHOR]

In impact crater lakes, the lacustrine sedimentary records may not solely reflect climatic changes but also potential erosional effects from lithologically distinct impactite formations. The hydrochemical and biogeochemical processes during the deposition of the Nördlinger Ries impact crater lake, which fall in the range of the mid-Miocene Climate Transition, were studied by analysing microcrystalline authigenic carbonates in a drill core succession, using stable oxygen and carbon isotopes in conjunction with biomarkers. These investigations revealed an early sulfidic interval characterized by thiophenes, iso- and anteiso-C 15:0 acids derived from sulfate reducing bacteria, and dolomites with low to intermediate δ13C carb values. The subsequent distinctive interval is characterized by extremely 13C-enriched dolomite (δ13C carb up to +20.93 ± 0.05‰ V-PDB), decline of iso- and anteiso-C 15:0 acids and is rich in an Archaea-derived archaeol that is 13C-enriched (−14.7‰), indicating extensive methanogenesis in sulfate-depleted lake porewater during early diagenesis. The sulfate decline results from successive sulfate reduction when replenishment by sulfate-bearing inflow water is limited. The carbonates exhibit enriched 18O due to pronounced evaporation in a long-resided water body and enriched 13C by methanogenesis. A change in provenance of water derived from the sulfur-rich suevite (impact melt-bearing breccia) and crystalline source rocks to the sulfur-poor Bunte Breccia (continuous ejecta blanket) is required. Intermittently high Si/Al and Zr/Al at the high δ13C interval suggests sporadic short-term runoff increase, leading to fluctuating physiochemical lake conditions. A subsequent decline in both δ13C carb and archaeol indicates a decreasing lake level with intermittent subaerial exposure events, supported by bioturbation and mud cracks. The concomitant lake oxygenation is well supported by increasing Pr/Ph ratios and lipids derived from aerobic methanotrophs (13C-depleted 3-methyl-hopanoids). In the youngest unit, allochthonous lignites and biomarkers from lacustrine/soil sources appear, high total sulphur contents and thiophenes recur, and stable C and O isotope values decrease again. These observations suggest another major provenance change of the inflowing solutes, with increasing influx from weathered pyrite-bearing Jurassic claystones. These findings demonstrate that the climatic record expected from the stable carbon and oxygen isotopes of the Ries carbonates is strongly overprinted by hydrochemical and biogeochemical processes due to changing ion influx from substrate rocks, along the course of the successive ejecta erosion and catchment changes. Such an intrinsic control of lacustrine biogeochemical processes is also expected for other hydrologically closed impact crater lake basins, where catchment rocks with distinctively different lithologies are present. [ABSTRACT FROM AUTHOR]

Rayleigh wave group velocity dispersion data of moderate magnitude (Mw 5.4) earthquake of Assam, North-East (NE) India, is used to retrieve regional shear wave crustal velocity models. The earthquake located within the northeast part of the Indian continent is well recorded by 10 broadband seismic stations situated on the Indian, Eurasian, and Burmese plates to generate excellent Rayleigh waveforms. Wave propagation paths transverse different geotectonic units in the collision zones of India–Eurasia and India–Burmese in and around NE India. We divide the data into outer and inner station groups depending on epicentre distance. Paths of the inner group mainly pass through the Indian plate, and the outer group crosses the inter-continent zones. The dispersion data and corresponding shear wave structure are not dependent on group division or epicentre distance, indicating diversity in the tectonic and geological setup. Paths crossing the Bengal basin (BB) with thick sediment layers have low velocities, and older crystalline rocks of the Shillong Plateau and Himalayan region have high velocities in the uppermost 10–15 km crust. A very high contrast of crustal velocity is noticed along the paths of Agartala (AGART) and Dhubri (DHUB) stations located at similar epicentre distances and an azimuthal difference of only 55°. Path to AGART along the BB has very low crustal velocities, while DHUB along the entire Shillong Plateau region has very high velocities. Four stations of the inner group within the Indian plate have a high difference in crustal velocities: low velocities within thick sediments of BB and high velocities in the older crystalline rocks of the Shillong plateau. In contrast, in the northern part of the Indo-Burma subduction zone, the subsurface structure shows repeated underthrusting of low-velocity material from the down-going plate and over-thrusting of high-velocity material from the overriding plate. [ABSTRACT FROM AUTHOR]

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