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A review of the formation of tectonic veins and their microstructures
Abstract and Figures
Veins are common features in rocks and extremely useful structures to determine stress, strain, pressure, temperature, fluid composition and fluid origin during their formation. Here we provide an overview of the origin and terminology of veins. Contrary to the classical tripartite division of veins into syntaxial (inward growth), antitaxial (outward growth) and stretching veins (no consistent growth direction), we emphasise a continuum between syntaxial and stretching veins that form from the crack-seal process, as opposed to antitaxial veins that grow without the presence of an open fracture during growth. Through an overview of geochemical methods that can be applied to veins we also address the potential, but so far little-investigated link between microstructure and geochemistry. There are basically four mechanisms with increasing transport rates and concomitant decreasing fluid–rock interaction: (1) diffusion of dissolved matter through stagnant pore fluid; (2) flow of fluid with dissolved matter through pores; (3) flow of fluid with dissolved matter through fractures and (4) movement of fractures together with the contained fluid and dissolved matter (mobile hydrofractures). A vein system is rarely the product of a single transport and mineral precipitation mechanism, as these vary strongly both in space and time within a single system.
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... Hydrothermal/metamorphic veins reflecting crystal growth in cracks are almost ubiquitous in rocks and are considered as the best record of fluid circulation and fluid-rock interaction at depth (e.g., Fisher et al., 1995;Verlaguet et al., 2011;Widmer & Thompson, 2001). Most of these cracks are interpreted to form by tensile or shear brittle failure of the rocks under high fluid pressures and/or changes in the magnitude or orientation of stresses (Bons et al., 2012;Oliver & Bons, 2001). ...
... Geochemical tracers, as fluid inclusions, trace elements and isotopes are generally used to provide clues on fluid compositions and sources (Roedder, 1984;Spandler & Pirard, 2013;Valley, 1986). Vein mineralization and microtextures inform about mineral precipitation and fluid supply mechanisms in veins, either by dominant local diffusive transport or larger scale advective transport (Bons et al., 2012;Oliver & Bons, 2001). Fluid flow patterns and distances over which fluids migrate are largely controlled by the material viscosity and the porosity-dependent dynamic permeability (Yarushina & Podladchikov, 2015). ...
... While the exact chronological relationships might be obscured by later deformation, the presence of high-pressure minerals allows setting back veins within the D1/D2 deformation stages and in a simplified evolutionary sketch presented in Figure 5. Indeed, a significant proportion of the quartz veins measured in the field also contain minerals diagnostic of high-pressure conditions (i.e., lawsonite or Fe-Mg carpholite; of Lefeuvre et al. (2020) is used in the following. In contrast to the dark, organic matter-rich crystals of lawsonite in the schist (LwsA), two types of creamy-colored lawsonite-bearing quartz veins are observed: (a) pluri-cm-to m-long veins containing stretched crystals (in the sense of Bons et al. (2012)) of lawsonite oriented parallel to the vein walls (LwsB) and to quartz crystals (±minor ankerite; Figures 6a-6d); (b) mm-to cm-large tensional cracks containing lawsonite crystals, in textural equilibrium with ankerite and quartz, oriented perpendicular to the vein walls (LwsC; Figures 6a and 6c). LwsB veins outline D1 folds in places, advocating for early formation during prograde-to peak burial (Figures 3c-3e, 5, and 6a-6c), whereas LwsC cracks form during D1 and/or D2 (Figures 5, 6a, and 6c). ...
In the Western Alps, oceanic lithosphere fragments recovered from subduction are exposed continuously across the Liguro‐Piemont domain. In this nappe‐stack, the Schistes Lustrés metasediments are volumetrically dominant and contain large amounts of high‐pressure lawsonite‐ and Fe‐Mg carpholite‐bearing veins. These veins formed close to peak burial conditions at 30–60 km depth where deep slow slips and tremors occur. In the 12 studied outcrops, vein thickness distribution fit power laws while vein spacings and clustering show significant deviations from power laws, interpreted as the result of truncation artifacts and, possibly, at least in part, of later ductile deformation. Vein distribution at the outcrop scale suggests that fluids mostly circulated pervasively through the rock rather than along major localized conduits, in agreement with geochemical studies. Through the study of vein textures at macroscopic and microscopic scales, we showed that these high‐pressure veins formed by an incremental crack‐seal mechanism under tensile and shear failure and possibly between extremely weak planes. The spacings between crack‐seal inclusion trails and bands, which is in the same order as slip increments for low frequency‐earthquakes, fit a power law for a small fractal range with a fractal exponent similar to those estimated for slow slip events and ordinary earthquakes. In addition, the shear stress drop estimated for these veins is consistent with those inferred for slow slips and tremors. Data suggest that these veins, formed at the downdip end of the seismogenic zone, may correspond to the record of successive low‐frequency earthquakes during subduction of the Liguro‐Piemont ocean.
... One classical and rigorous way of representing yield (for example, Bons et al., 2012) is shown in Figure 1a in Mohrspace (shear stress vs normal stress). A variety of different vein structures can form in this way (Bons et al., 2012) including crack-seal structures in particular (Sp€ ath et al., 2022). ...
... One classical and rigorous way of representing yield (for example, Bons et al., 2012) is shown in Figure 1a in Mohrspace (shear stress vs normal stress). A variety of different vein structures can form in this way (Bons et al., 2012) including crack-seal structures in particular (Sp€ ath et al., 2022). Failure occurs when the Mohr circle for stress touches the failure envelope. ...
... A cap model for yield is particularly important in discussing various types of failure discontinuities. Failure at the tensile end of the failure envelope is well discussed by Bons et al. (2012). Failure modes at the cap end are commonly considered as compaction bands (Elphick et al., 2021;Fossen et al., 2007;Holcomb et al., 2007;Issen & Rudnicki, 2000;Olsson, 1999). ...
... 맥 또는 세맥(vein)은 단열을 따라 흐르는 유체로부터 침전된 광물 집합체로, 유체와 그에 포함된 물질의 이동 에 대한 단서를 제공한다 (Oliver and Bons, 2001;Bons et al., 2012). 맥을 형성하는 유체의 이동 기작으로 확산, '단열을 따라 흐름(fluid flow through fractures)', 그리고 '단열의 형성과 함께 흐름(fluid flow with fractures)'이 제 안된 바 있다 (Bons, 2000;Bons et al., 2012). ...
... 맥 또는 세맥(vein)은 단열을 따라 흐르는 유체로부터 침전된 광물 집합체로, 유체와 그에 포함된 물질의 이동 에 대한 단서를 제공한다 (Oliver and Bons, 2001;Bons et al., 2012). 맥을 형성하는 유체의 이동 기작으로 확산, '단열을 따라 흐름(fluid flow through fractures)', 그리고 '단열의 형성과 함께 흐름(fluid flow with fractures)'이 제 안된 바 있다 (Bons, 2000;Bons et al., 2012). 이러한 유 체이동 기작과, 그에 따른 광물의 침전과정을 반영하는 맥의 미세조직은 괴상조직, 신장형 괴상조직 등으로 구 분된다 (Bons, 2000, Bons et al., 2012. ...
... 맥을 형성하는 유체의 이동 기작으로 확산, '단열을 따라 흐름(fluid flow through fractures)', 그리고 '단열의 형성과 함께 흐름(fluid flow with fractures)'이 제 안된 바 있다 (Bons, 2000;Bons et al., 2012). 이러한 유 체이동 기작과, 그에 따른 광물의 침전과정을 반영하는 맥의 미세조직은 괴상조직, 신장형 괴상조직 등으로 구 분된다 (Bons, 2000, Bons et al., 2012. 괴상조직은 수압 파쇄작용에 의해 단열이 형성됨과 동시에 유체가 이동하 는 경우 발달하는 조직으로, 급격한 유체압 감소로 인해 과포화(supersaturation)의 정도가 매우 높아지므로, 맥 내 에서 광물이 성장할 때 핵형성(nucleation)이 지속적으로 발생한다 (Bons, 2000;Oliver and Bons, 2001). ...
... BPV have been widely interpreted as the result of horizontal shortening caused by regional compression of sedimentary sequences (Cosgrove, 1993;Kenis et al., 2000;Bons et al., 2012;Rybak-Ostrowska et al., 2014;Ukar et al., 2017;Konon et al., 2021). Some authors indicated that BPV formed during folding with a significant contribution of flexural slip (Tanner, 1989;Smith et al., 2013). ...
... It is an explicit observation that the BPV propagated along preferred directions such as organic-rich laminae and the faces of lithological contrasts (Figs. 9, 10 and 13). Such failure is expected when the fluid pressure is high, and/or bedding contacts have low cohesion during layer-parallel compression (Bons et al., 2012). In this case, OM accumulation and clay minerals concentration usually lowers friction and cohesion along the bedding (c.f. ...
... Consequently, the mode I BPV within the Caledonian Foredeep Basin can be interpreted as the result of bed-parallel shortening related to the initial stage of folding (cf. Cosgrove, 1993;Kenis et al., 2000;Bons et al., 2012;Rybak-Ostrowska et al., 2014;Ukar et al., 2017;Konon et al., 2021). In addition, the lenticular mode I BPV in an en échelon arrangement with the internal structure showing host rock inclusions rotated along small-scale thrusts and bridges suggests bed-parallel contraction during the vein growth ( Fig. 12A-E). ...
... Open fractures are crucial fluid pathways for petroleum migration and mineral deposition in ultra-deep (≥6 km) reservoirs (Solano et al., 2011;Kang et al., 2013;Fall et al., 2015;Lyu et al., 2017;Li et al., 2019;Liu et al., 2021), and oversaturated pore fluids can enter tectonically induced fractures and precipitate mineral veins. As a result, the microstructures and fine-scale geochemical features of these mineral veins can record fluid events (Barker et al., 2006(Barker et al., , 2009Bons et al., 2012;Maskenskaya et al., 2014;Laubach et al., 2019). Delineation of deep-seated fluids is essential for understanding the evolution of ultra-deep reservoirs. ...
... Such deposits may record sequential changes of fluid temperatures, compositions, origins and horizon pressures during rock deformation (Becker et al., 2010;Fall et al., 2015;Laubach et al., 2019). In fractures, mineral veins can show various internal microstructures with different crystal shapes (blocky, fibrous, stretched etc.) and growth directions (e.g., either from the wall rock into the vein or in the opposite direction) (Ramsay, 1983;Passchier, 1996;Bons et al., 2012;Ukar and Laubach, 2016) (Fig. 1). ...
... In order to obtain in situ analysis of elemental concentrations in various parts of carbonate cement, total of 50 points of the same thin sections from two calcite veins were used to conduct optical cathodoluminescence (CL), Electron Microprobe Micro-Analysis (EMPA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Powdered calcite samples from 13 calcite veins and 20 wall rocks (Bons et al., 2012). (b) Basic scheme depicting growth of syn-and post-kinematic crystals during fracture opening (after Ukar and Laubach, 2016). ...
... The elongate blocky crystal texture of the comb ankerite-(albite) is characteristic of syntaxial veins (Figs. 4a-b, 10a-b;Bons et al., 2012). Quartz veins present recrystallization textures, with distinctive interpenetrated grain boundaries, attesting of bulging and subgrain rotation dynamic recrystallization (BLG and SGR, respectively; Fig. 10c; Stipp et al., 2002;Passchier and Trouw, 2005). ...
... All visible gold grains observed are enclosed within such quartz infilling at the Central Zone deposit (Fig. 10c). The presence of highly altered metagranitoid fragments within the veins suggests the existence of at least two vein opening-infilling events along the same structure ( Fig. 10b; Passchier and Trouw, 2005;Bons et al., 2012). The host rocks demonstrate strong alteration at the immediate selvages of the gold-bearing veins, the main alteration pattern consisting of strong albitization, sericitization, and pyritization (Fig. 10d). ...
... Furthermore, the geometries of D1b-related shear bands crosscutting the S1a penetrative cleavage and pyrite mantled σ-type porphyroclasts in the oriented sample record the regional N-NW-striking, left-lateral, strike-slip shearing during D1b deformation stage (Figs. 5, 6c, 16a2, b2;Gaboury et al., 2020;Perret et al., 2021a). On nonoriented samples, the geometry and texture of strain fringes around Py1a grains indicate antitaxial, nondeforming, face-controlled growth of the quartz-(sericite) assemblage as outlined in Figure 7c (Urai et al., 1991;Koehn et al., 2003;Passchier and Trouw, 2005;Bons et al., 2012). Strain fringes grew independently of the relative motion of both the fringe and object due to the C1b simple shearing. ...
Gold deposition in structurally controlled deposits is triggered by changes in the mineralizing fluid conditions. Recent research has demonstrated that in deposits with a well-established paragenesis, the processes that control the ore-forming fluid conditions, and thus the gold timing and deposition, can be inferred from the study of both textural and chemical characteristics of ore-bearing minerals such as sulfides, which are ubiquitous in almost every gold deposit type. In this contribution, we carried out a coupled investigation of (1) microscopic-scale expression of regional deformation, (2) textures of mineralized veins and pyrite generations, and (3) laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace element concentrations in pyrite from the Neoproterozoic Central Zone gold deposit, located in the poorly studied Gabgaba gold district, central Keraf suture, Sudanese Nubian shield.
The Central Zone gold mineralization is associated with late-collisional Keraf strike-slip shearing. It is expressed by visible gold-bearing quartz-ankerite-(albite) conjugate veins hosted by metagranitoids surrounded by metasediments. Some structurally lattice-bound gold occurs in proximal As-Au-Ni–enriched pyrite associated with sericite-albite-ankerite alteration. Vein textures and proximal pyrite oscillatory zoning and geochemical signatures indicate that vein infilling occurred as a response to sudden pressure drops and boiling of the mineralizing fluid. We therefore interpret the Central Zone deposit as a typical orogenic gold deposit, with microtextural evidence and geochemical data supporting the existence of earthquake-induced fault-valve processes.
... 60 Many gold-quartz vein arrays represent the uplifted roots of mineralizing systems 75 from the mesothermal regime (∼300-400°C) at around ∼10-15 km, which can be explained by the phenomenological fault-valve mechanism (Sibson et al., 1988). The faultvalve mechanism appeals to the conditions of the brittle-ductile transition where fluids released from metamorphic breakdown reaction from below the roots of the brittle fault system are pumped, under fluid pressures above the lithostatic, episodically into dilat- The mineral precipitates subsequently seal fractures (Ramsay, 1980;Bons et al., 2012); this study, high temperature (> 300°C) ductile equivalent of the fault-valve mechanism with nucleation of dilatant bands formed by cnoidal waves. The cnoidal wave mechanism provides a steady source of fluids on long geological time scales, allowing progressive chemical precipitation and syntaxial crystal growth from both sides of the fracture channel during a ductile process of continued compaction. ...
... Synchronously, the surrounding pore fluid in the matrix tends to infiltrate into the newly generated channels, which forms the fluid 245 paths for mineral transport as depicted by Figure 1(d). Consequently, the dissolved silica is transported by fluid flow and may precipitate along the interface across the matrix and the formed channels (fracture walls), forming the quartz veins with quartz crystals growing in the direction of vein opening (syntaxial growth) (Bons et al., 2012) as sketched in Figure 1(e). Since the instability presented is a steady-state solution, the cnoidal 250 wave instabilities provide both the sudden initial vein opening mechanism at the critical λ and the steady supply of new quartz-saturated fluids during the crystallization of the elongate, blocky to needle-like quartz crystals. ...
The formation of mineral deposits in mesothermal quartz veins is a complex process that has been the subject of much research. The classical fault-valve hypothesis suggests that mineralization occurs when metamorphic fluids are injected during a brittle event and then locked in to mineralize, but this hypothesis does not fully explain the regular spacing of repeated mineralized patterns that are often observed. This paper proposes a new mechanism for mineralizing systems based on the theory of cnoidal waves in solids. Cnoidal waves are standing waves that can persist for long times in materials under compressive and extensional regimes. We investigate mineral deposits by analytical and numerical methods and show that the cnoidal wave instability theory provides a plausible alternative mechanism for mineralizing systems. This study opens a new avenue for field studies to demonstrate that the mechanism-based cnoidal waves play an essential role in the formation of mineral deposits.
... To reconstruct fluid circulation in crustal rocks, numerous studies use trace element, isotope and geochronological data of hydrothermal structures such as veins or hydrothermally deformed rocks (e.g., Dempster, 1986;Dusséaux et al., 2022;Grambling et al., 2022;Hofmann et al., 2004;Incerpi et al., 2017Incerpi et al., , 2018Incerpi et al., , 2020Kralik et al., 1992;Manatschal et al., 2000;Marquer and Burkhard, 1992;Marquer and Peucat, 1994;Mulch et al., 2006;Peverelli et al., 2022aPeverelli et al., , 2022bPinto et al., 2015;Ricchi et al., 2019aRicchi et al., , 2019b. One advantage of targeting veinfilling minerals for this purpose is that they precipitate directly from the mineralizing fluid, whose geochemical and isotopic characteristics are recorded and can be used to investigate fluid pathways (e.g., Bons et al., 2012;Elburg et al., 2002;Pettke et al., 2000). In the Alps, one common vein-filling mineral that is stable throughout the metamorphic evolution of the orogen at greenschist-facies conditions is epidote [i.e., Ca 2 Al 2 (Al,Fe 3+ )Si 3 O 12 (OH)]. ...
... Vein growth microstructures from blocky to elongate are preserved ( Fig. 5; nomenclature after Bons et al., 2012). Epidote is euhedral to subhedral, and measures between a few and ca. ...
crust in orogens from rifting to tectonic inversion. Since granitic rocks have low primary water contents and dominate the continental crust, their hydration exerts important control on metamorphism and deformation of the continental crust during orogeny. It is therefore of great interest to determine whether the granitic continental crust is hydrated during rifting phases or after tectonic inversion. Because fluid circulation may occur at both stages, a comprehensive picture of hydration of the continental crust in inverted passive continental
margins can be obtained by the combination of different geochronometers and geochemical methods.
In this study, we combine U–Pb geochronology and Pb–Sr–O–H isotope geochemistry of epidote in hydrothermal veins in the Albula Pass area (eastern Swiss Alps) as powerful tools to trace hydration events in the continental crust in orogens. The Albula Pass area is part of the inverted Adriatic passive continental margin,
which was extensively affected by seawater infiltration during continental rifting in Jurassic times. Epidote geochronology elucidates the fluid circulation history in this rifted crustal section by revealing two hydration events that are not recorded by other datable minerals: (1) 85.2 ± 9.7 Ma and (2) 59.9 ± 2.7 Ma, showing that fluid circulation in the Adriatic passive continental margin continued after Late Cretaceous tectonic inversion. Epidote Pb–Sr–O–H isotope geochemistry characterizes pathways and fluid sources of the epidote forming fluids, which differ between the Late Cretaceous and the Paleocene fluid circulation events. The Late Cretaceous epidote-forming fluids were produced by compaction of sedimentary units beneath the Err nappe and release of modified seawater (i.e., formation/connate water) from marine sediments, while Paleocene veining was mainly mediated by syn-kinematically infiltrated meteoric water. The present geochronological and isotope data argue for multi-stage hydration of the continental crust in the inverted Adriatic passive continental margin. This work promotes the importance of the interplay of newly introduced and recycled fluid components in the hydrothermal alteration of the continental crust, and it highlights epidote as a powerful hygrochronometer and isotope tracer.
... 60 Many gold-quartz vein arrays represent the uplifted roots of mineralizing systems 75 from the mesothermal regime (∼300-400°C) at around ∼10-15 km, which can be explained by the phenomenological fault-valve mechanism (Sibson et al., 1988). The faultvalve mechanism appeals to the conditions of the brittle-ductile transition where fluids released from metamorphic breakdown reaction from below the roots of the brittle fault system are pumped, under fluid pressures above the lithostatic, episodically into dilat- The mineral precipitates subsequently seal fractures (Ramsay, 1980;Bons et al., 2012); this study, high temperature (> 300°C) ductile equivalent of the fault-valve mechanism with nucleation of dilatant bands formed by cnoidal waves. The cnoidal wave mechanism provides a steady source of fluids on long geological time scales, allowing progressive chemical precipitation and syntaxial crystal growth from both sides of the fracture channel during a ductile process of continued compaction. ...
... Synchronously, the surrounding pore fluid in the matrix tends to infiltrate into the newly generated channels, which forms the fluid 245 paths for mineral transport as depicted by Figure 1(d). Consequently, the dissolved silica is transported by fluid flow and may precipitate along the interface across the matrix and the formed channels (fracture walls), forming the quartz veins with quartz crystals growing in the direction of vein opening (syntaxial growth) (Bons et al., 2012) as sketched in Figure 1(e). Since the instability presented is a steady-state solution, the cnoidal 250 wave instabilities provide both the sudden initial vein opening mechanism at the critical λ and the steady supply of new quartz-saturated fluids during the crystallization of the elongate, blocky to needle-like quartz crystals. ...
The formation of mineral deposits in mesothermal quartz veins is a complex process that has been the subject of much research. The classical fault-valve hypothesis suggests that mineralization occurs when metamorphic fluids are injected during a brittle event and then locked in to mineralize, but this hypothesis does not fully explain the regular spacing of repeated mineralized patterns that are often observed. This paper proposes a new mechanism for mineralizing systems based on the theory of cnoidal waves in solids. Cnoidal waves are standing waves that can persist for long times in materials under compressive and extensional regimes. We investigate mineral deposits by analytical and numerical methods and show that the cnoidal wave instability theory provides a plausible alternative mechanism for mineralizing systems. This study opens a new avenue for field studies to demonstrate that the mechanism-based cnoidal waves play an essential role in the formation of mineral deposits.
... crystal growth into an oversaturated fluid (e.g. Bons et al. 2012). The grain size coarsening we observe towards the outer edge of the test wall (Figs 4c, 5d) is also indicative of extensive "recrystallization" (Pabich, Vollmen and Gussone, 2020) or, more precisely, post-depositional modification by overgrowth. ...
... This type of growth is referred to in the crystallographic literature of vein growth (i.e. crystal growth into free space in fluid filled rock cracks) as syntaxial growth (Bons, Elburg and Gomez-Rivas, 2012). ...
Electron backscatter diffraction (EBSD) analysis enables a unique perspective of the internal microstructure of foraminiferal calcite. Specifically, EBSD provides crystallographic data from within the test, highlighting the highly organised “mesocrystal” structure of crystallographically aligned domains throughout the test, formed by sequential deposits of microgranular calcite. We compared EBSD maps across the test walls of both poorly- and well-preserved specimens of the planktonic foraminifera species Globigerinoides ruber and Morozovella crater. The EBSD maps, paired with information about intra-test distributions of Mg/Ca ratios, allowed us to examine the effects of different diagenetic processes on the foraminifera test. In poorly-preserved specimens EBSD data shows extensive reorganisation of the biogenic crystal microstructure, indicating differing phases of dissolution, re-precipitation and overgrowth. The specimens with the greatest degree of microstructural reorganisation also show an absence of higher concentration magnesium bands, which are typical features of well-preserved specimens. These findings provide important insights into the extent of post-depositional changes both in microstructure and geochemical signals that must be considered when utilising foraminifera to generate proxy archive data.
... The folded sequence within the Bóixols-Sant Corneli anticline is affected by several fracture sets that include the main reverse, strike slip and normal faults affecting the anticline (the Bóixols thrust, the Montagut fault system and the Sant Joan fault system) and the background deformation (centimetric to metric fractures). We use the term "fracture" or "joint" to include fractures that show no evidence of shear, and we use the term "fault" to exclusively include shear fractures (Bons et al., 2012). The main fracture and fault characteristics (type, orientation, kinematics, and crosscutting relationships) and their distribution within the anticline are described below. ...
... Calcite cements precipitated in centimetric to metric non shear fractures are mainly characterized by blocky to elongated blocky crystals ranging in size from 0.2 to 5 mm and locally displaying mechanical twining ( Fig. 6e-f). Elongated blocky calcites have been observed in different veins exhibiting elongation direction perpendicular to fracture walls and indicating the mode I opening of the vein (Bons et al., 2012) (Fig. 6f). Under CL, cements within non-shear fractures display three kind of luminescence colors: (i) dark brown to non-luminescence; (ii) orange to bright yellow; and (iii) a non-luminescent to bright yellow concentric zonation (Fig. 6g-h). ...
Dating fold-related structures is critical to understand the timing, duration, and rate of fold growth as well as the sequential evolution of fold-and-thrust belts. In this contribution, we combine structural analysis of fractures with U-Pb dating of calcite veins related to the evolution of the Bóixols-Sant Corneli anticline (Southern Pyrenees) aiming to constrain the age and evolution of deformation and the duration of folding. Twenty-three U-Pb ages were obtained in the different sets of fracture-filling calcite veins, which span from Late Cretaceous to late Miocene (79.8 ± 1.2 Ma to 9 ± 4.6 Ma). These ages have been attributed to growth (71.2 to 56.9 Ma), fold tightening (55.5 to 27.4 Ma) and collapse (20.8 to 9.0 Ma) of the Bóixols-Sant Corneli anticline. This reveals a duration of 14 Myr for the folding stage and 28 Myr for the fold tightening, which translates in 42 Myr of the entire folding process and thus encompassing most of the Pyrenean compression.
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https://www.researchgate.net/publication/361272185_Spatio-temporal_variation_of_fluid_flow_behavior_along_a_fold_The_Boixols-Sant_Corneli_anticline_Southern_Pyrenees_from_U-Pb_dating_and_structural_petrographic_and_geochemical_constraints
... Advances in microstructural imaging of cemented and partially cemented opening-mode fractures containing characteristic crack-seal cement textures (Ramsay, 1980;Bons et al., 2012) indicate that fracture growth and porosity partitioning are controlled in part by synkinematic (during-opening) fracture cementation (e.g., Laubach et al., 2004a). Based on size-dependent porosity preservation, whereby sparse, large, partially open fractures are present amid abundant, fully cemented microfractures, Hooker et al. (2012) suggested that the primary mechanical effect of cement on fracture pattern evolution is to restore adhesion across fractures. ...
... This behavior mimics the development of myriad very closely spaced, sealed fractures, which have been noted in sandstones (Laubach, 1989;Onasch, 1990;Hooker et al., 2014;their Fig. 11b) and limestones (Davis, 2014;Hoyt and Hooker, 2021; their Figure 16). The texture sometimes forms at the slow-opening tips of tectonic "stretching veins" (Bons et al., 2012;their Figure 17b). The rock deformation and evolving stress distribution in such cases is akin to that which develops in compressive environments as a disjunctive cleavage (Engelder, 1979). ...
... Opalinus Clay with pore fluid pressures being close to lithostatic loading conditions could have favoured bedding (sub)parallel initial fracturing and subsequent tension gash opening (e.g., Sibson, 1981). The crack-seal texture of the subhorizontal tension gashes indicates a repeated and cyclic fracturing and healing by precipitation of fibrous calcite (e.g., Bons et al., 2012;Ramsay, 1980). In general, aperture opening during individual fracturing events are small, followed by precipitation of calcite. ...
... At the current stage, however, we do not have enough data to promote or exclude one of the two scenarios and this will be discussed in detail elsewhere. While fibrous veins document small incremental openings (Bons et al., 2012;Ramsay, 1980), slickenfibres might relate to stages of instantaneous slip with associated fast drops in pore fluid pressures, potentially yielding in enhanced incorporation of Fe, Mg, and Sr. Independently of which of the two scenarios holds, the fact that these elemental differences are consistent over all three sitings would either indicate a regional behavior in the case of (1) or a consistent phenomenological precipitation behavior in the case of (2). ...
The Middle-Jurassic Opalinus Clay is the foreseen host rock for radioactive waste disposal in central northern Switzerland. An extensive drilling campaign aiming to characterize the argillaceous formation resulted in a comprehensive drill core data set. The rheologically weak Opalinus Clay is only mildly deformed compared to the over- and underlying rock units but shows a variety of natural fractures. While these structures are hydraulically indistinguishable from macroscopically non-deformed Opalinus Clay today, their analysis allows for a better understanding of the deformation behaviour in the geological past. Here, we present an overview of the different fracture and fault types recorded in the Opalinus Clay and a detailed microstructural characterization of veins—natural dilational fractures healed by secondary calcite and celestite mineralizations. Macroscopic drill core analysis revealed five different natural fracture types that encompass tension gashes of various orientations with respect to bedding and small-scale faults with displacements typically not exceeding the drill core diameter. The occurrence of different fault types generally fits well with the local tectonic setting of the different drilling sites and with respect to the neighbouring regional fault zones. The microstructural investigations of the various vein types revealed their often polyphase character. Fibrous bedding-parallel veins of presumable early age were found to be overprinted by secondary slickenfibres. The polyphase nature of fibrous bedding parallel veins and slickenfibres is supported by differing elemental compositions, pointing towards repeated fracturing and mineralization events. Direct dating of vein calcites with U–Pb was unsuccessful. Nevertheless, age constraints can be inferred from structural orientations and fault slip kinematics. Accordingly, some of the veins already formed during sediment compaction in Mesozoic times, others possibly relate to Early Cenozoic foreland uplift. The youngest veins are most likely related to Late Cenozoic regional tectonic events, such as the Jura fold-and-thrust belt to the south and the Hegau-Lake Constance Graben to the northeast of the study area. During these latest tectonic events, previously formed veins acted as rheologically stiff discontinuities in the otherwise comparably weak Opalinus Clay along which deformation of the rock formation was re-localized.
... Calcite veins hosted in fractures not only record the source and physicochemical conditions of paleo-fluids (e.g., Boles et al., 2004;Bons et al., 2012;Holdsworth et al., 2019;Beaudoin et al., 2022) but also provide snapshots of local or even far-field expressions during deformation (e.g., Lacombe et al., 2021;Craddock et al., 2022). Recent progress in carbonate U-Pb geochronology opens new avenues for determining the timing of fluid circulation, hydrocarbon accumulation and fault activity (e.g., Roberts and Walker, 2016;Nuriel et al., 2017Nuriel et al., , 2019Hoareau et al., 2021;Lan et al., 2022). ...
... The sudden pressure drops accompanying extensional fracturing and dilatancy promoted fluid flow into the open fracture and simultaneously precipitated calcite along the fracture walls (Bons et al., 2012;Fig. 11). ...
... From a tectonic and metallogenic perspective, numerous studies have demonstrated that opening faults generally act as conduits for fluid flow and the emplacement of economically important ore bodies (Beach, 1975;Faulkner et al., 2010;Bons et al., 2012;Faulkner and Armitage, 2013;Funedda et al., 2018;Chauvet, 2019aChauvet, , 2019b. Mineralization in faults is often displayed as a veins array generally formed, in a brittle-ductile context, by the process of dilation. ...
... According to Bons et al. (2012), conjugate fracture sets, with or without infilling, provide information on the overall stress field direction (Fig. 9E). In our case the geometry of the veins in these corridors is poorly preserved which is presumably due to both stress retention during the gradual build-up of the system, or to post-mineralization deformation. ...
Tectonic and micro-tectonic studies at different scales are of primary importance in a modern metallogenic investigation. In the Ougnat massif of the eastern Anti-Atlas belt (Morocco), the barite ore deposit is hosted within mafic to felsic rocks of the Ediacaran Saghro and Ouarzazate groups together with their folded Paleozoic cover. Here, we provide for the first time new field-based data on the tectonic control of barite mineralization, and their relation with regional tectonic events. The mineralization occurs in brittle-ductile structures as a vein-type system, mainly hosted within NE-SW to E-W and NW-SE strike-slip-normal faults. Economic orebodies spread frequently along the Precambrian-Cambrian contact zone thus acting as open conduits for mineralized fluid flow. The geometry of hosted barite sigmoidal lenses corresponds to “pull-apart” or “tension gashes” openings, commonly arranged en echelon arrays along the bearing transcrustal faults. The occurrence of predominant massive and breccia internal texture implies a tectonic-mineralizing collapse process in an extensional tectonic context. Kinematic pattern, directional distribution and host-rock age relationship point to a syntectonic barite control probably occurred during the NW-SE Atlantic rifting, as already attributed to similar deposits in the neighboring Ougarta and Atlas-Meseta domains.
The barite ore is quantitatively and qualitatively more preserved in competent host rocks than those with ductile behavior, thus offering a useful hint for further barite exploration in this part of the Anti-Atlas fold and thrust belt.
... Stable isotopic data measured by SIMS within internal structure of the studied veins did not provide conclusive evidence of significant isotope variation across multiple crystal growth phases (Fig. 3A). This observation points toward a constant temperature regime and similar isotopic properties of the formation water during vein mineralization, implying that veins initiation and growth was a relatively brief temporal event that does not span a large range of time/temperature conditions in the basin evolution in agreement with what was previously proposed (Bons et al., 2012;Urai et al., 1991;Hilgers and Urai, 2005). According to our indirect estimate of mineralization age (i.e., based on fluid inclusion temperatures and model basin thermal history), the studied veins formed at different temperatures within each well, but within a narrow time interval of 70-90 Ma (Upper Cretaceous-Turonian/Campanian - Fig. 6A) across the basin. ...
... These observations are in favor for a formation under non-coaxial conditions. Therefore, at least some layer-parallel veins represent shear veins with an opening component (i.e., extension plus shear, see vein sketches in Figure 10a; Bons et al., 2012), which could have formed under a maximum principal stress at high angles to foliation (Fagereng et al., 2010) in the thrusting regime. Figure 12. ...
The exhumed Infrahelvetic Flysch Units in the eastern central Alps in Switzerland are a field analog to modern accretionary wedges at active plate boundaries. In these seismically active convergent settings, water‐saturated sediments undergo consolidation, and diagenetic to low‐grade metamorphic processes cause complex fluid‐rock interactions. To contribute to the understanding of structural and fluid processes and their interaction with seismic activity, we present quantitative information on the geometrical and spatial distribution of slate‐hosted calcite veins from the Infrahelvetic Flysch Units that show mutual overprinting relationships with the ductile phyllosilicate‐rich matrix. Two vein systems that form in the deeper part of the inner wedge are characterized: (a) layer‐parallel veins (meter‐scale) forming spatially repetitive vein‐arrays and (b) pervasively distributed, steep micron‐veinlets, that cross‐cut the thicker layer‐parallel veins and the ductile matrix. Synchrotron X‐ray Fluorescence Microscopy (XFM) is instrumental in detecting previously unseen densely spaced micron‐veinlets. The spatial distribution of micron‐veinlets indicates pervasive layer‐perpendicular fluid transport in response to dissolution‐precipitation creep through the wedge. Layer‐parallel veins form vein‐arrays with thicknesses on the meter‐scale suggesting that fluids are progressively localized in channels up‐scale. Both vein sets form in an alternating fashion with two different enhanced flux directions, which could be indicative for a critically stressed wedge with near‐lithostatic fluid pressures. The layer‐parallel veins and vein‐arrays could represent seismic events with low magnitude earthquakes (Mw up to 4.0) or slow‐slip events currently found at active plate boundaries, while micron‐veinlets and dissolution‐precipitation processes accommodate slow interseismic deformation.
... These are characterized by the widespread presence of calcite veins, that developed parallel to the bedding or on low-angles N-dipping planes, which often show successive folding and thrusting. The microstructural analysis of 8 sampled veins allowed their classification as antitaxial calcite veins, as described by Bons et al. (2012), and revealed the presence of three antitaxial growth stages in most of the samples, confirmed by the cathodoluminescence analysis. ...
... Reedmergnerite and quartz fillings exhibit finer grain sizes at their edges and coarser grain sizes in the central portions, implying that they are postkinematic cement (e.g., Gale et al., 2022), with kinematic apertures exceeding 500 μm. However, the presence of a median line in calcite fillings reflect they are synkinematic cements (e. g., Bons et al., 2012;Gale et al., 2022), which have kinematic apertures of more than 750 μm (Fig. 5c, d). Therefore, calcite U-Pb dating can accurately reveal the timing of fracture formation. ...
... Five polished thin sections (25 μm in thickness) and five doubly polished thicker sections (150 μm) were prepared and studied with an Olympus BX51 optical microscope and a Keyence VHX -1000 digital optical microscope at the GeoRessources laboratory (Nancy, France) (Fig. 2). Petrographic analysis of the veins was carried out on thin sections according to Bons et al. (2012) and Passchier and Trouw (2005). Petrographic analysis of fluid inclusions was carried out at room temperature on thick sections according to Van den Kerkhof and Hein (2001) and Wilkinson (2001). ...
... Syn-to late-tectonic veins are widespread in deformed rocks that have undergone various degrees of metamorphism during orogenic events. Their occurrence is indicative of fluid flow coupled with local remobilization and/or external supply of different elements into the suitable dilation sites (e.g., Bons et al., 2012). ...
... Then, several studies of ore deposits worldwide, such as porphyry ore deposits, volcanic massive sulfide (VMS) deposits, IOCG deposits, skarn deposits, and epithermal deposits, have revealed that they are controlled by specific structural/lithological settings (Bark and Weihed, 2012;Joly et al., 2010;Zoheir and Emam, 2012;Hor, 1998;Dalstra, 2014;Peng et al., 2019;Zhou et al., 2021;Santosh and Groves, 2022;Kwak et al., 2022). Among the different types of structural controls on mineralization, the most common are (1) expansion and contraction along faults/shear zones (Micklethwaite et al., 2015;Kwak et al., 2022); (2) intersection of two synmineralization structures (Robert et al., 1995;Robert and Kelly, 1987;Robert and Poulsen, 2001;Bark and Weihed, 2012;Kwak et al., 2022); (3) intersection of faults/shear zones with highly competent and/or chemically reactive rocks (Robert and Poulsen, 2001); (4) faults/shear zones along lithological contacts between competent and less competent rocks (Bierlein et al., 2006;Micklethwaite et al., 2015;Zoheir et al., 2019a,b,c); (5) areas dipping parallel to a stretch lineation and ( Alsop and Holdsworth, 2004;Alsop and Holdsworth, 2012;Alsop et al., 2021;Bons et al., 2012;Groves and Santosh, 2021); and (6) fold limbs and hinge zones (Robert and Poulsen, 2001). Therefore exploration and development of rock-hosted ore deposits at the regional, district, and orebody scales depend heavily on structural geology. ...
Geospatial Analysis Applied to Mineral Exploration: Remote Sensing, GIS, Geochemical, and Geophysical Applications to Mineral Resources presents state-of-the-art approaches on recent remote sensing and GIS-based mineral prospectivity modeling for Earth scientists, researchers, mineral exploration communities and mining companies. This book will help readers solve high complexity issues in remote sensing data processing, geochemical data analysis, geophysical data analysis, and appropriate applications of GIS techniques for data fusion designed for mineral exploration purposes. It contains updated knowledge of remote sensing imagery, geochemistry, geophysics and geospatial techniques that can assist in delineating the signatures and patterns linked to deep-seated, covered, blind or buried mineral deposits.
... Then, several studies of ore deposits worldwide, such as porphyry ore deposits, volcanic massive sulfide (VMS) deposits, IOCG deposits, skarn deposits, and epithermal deposits, have revealed that they are controlled by specific structural/lithological settings (Bark and Weihed, 2012;Joly et al., 2010;Zoheir and Emam, 2012;Hor, 1998;Blenkinsop and Doyle, 2014;Dalstra, 2014;Peng et al., 2019;Zhou et al., 2021;Santosh and Groves, 2022;Kwak et al., 2022). Among the different types of structural controls on mineralization, the most common are (1) expansion and contraction along faults/shear zones (Micklethwaite et al., 2015;Kwak et al., 2022); (2) intersection of two synmineralization structures (Robert et al., 1995;Robert and Kelly, 1987;Robert and Poulsen, 2001;Bark and Weihed, 2012;Kwak et al., 2022); (3) intersection of faults/shear zones with highly competent and/or chemically reactive rocks (Robert and Poulsen, 2001); (4) faults/shear zones along lithological contacts between competent and less competent rocks (Bierlein et al., 2006;Micklethwaite et al., 2015;Zoheir et al., 2019a,b,c); (5) areas dipping parallel to a stretch lineation and (Alsop and Holdsworth, 2004;Alsop and Holdsworth, 2012;Alsop et al., 2021;Bons et al., 2012;Groves and Santosh, 2021); and (6) fold limbs and hinge zones (Robert and Poulsen, 2001). Therefore exploration and development of rock-hosted ore deposits at the regional, district, and orebody scales depend heavily on structural geology. ...
This chapter focuses on spectral features of hydrothermal alteration minerals and lithologies in the visible and near-infrared, shortwave infrared, and thermal infrared wavelength regions. The technical characteristics of multispectral and hyperspectral sensors, synthetic aperture radar, and unmanned aerial vehicles will be deciphered for detecting the alteration minerals and zones, lithological units, and structural features associated with ore mineralizations. Explanations about data acquisition for the remote sensing data, preprocessing techniques, image-processing algorithms, accuracy assessment techniques, interpretation of remote sensing data for alteration mineral detection, lithological mapping, structural analysis, and case studies will be discussed in this chapter.
... Then, several studies of ore deposits worldwide, such as porphyry ore deposits, volcanic massive sulfide (VMS) deposits, IOCG deposits, skarn deposits, and epithermal deposits, have revealed that they are controlled by specific structural/lithological settings (Bark and Weihed, 2012;Joly et al., 2010;Zoheir and Emam, 2012;Hor, 1998;Dalstra, 2014;Peng et al., 2019;Zhou et al., 2021;Santosh and Groves, 2022;Kwak et al., 2022). Among the different types of structural controls on mineralization, the most common are (1) expansion and contraction along faults/shear zones (Micklethwaite et al., 2015;Kwak et al., 2022); (2) intersection of two synmineralization structures (Robert et al., 1995;Robert and Kelly, 1987;Robert and Poulsen, 2001;Bark and Weihed, 2012;Kwak et al., 2022); (3) intersection of faults/shear zones with highly competent and/or chemically reactive rocks (Robert and Poulsen, 2001); (4) faults/shear zones along lithological contacts between competent and less competent rocks (Bierlein et al., 2006;Micklethwaite et al., 2015;Zoheir et al., 2019a,b,c); (5) areas dipping parallel to a stretch lineation and ( Alsop and Holdsworth, 2004;Alsop and Holdsworth, 2012;Alsop et al., 2021;Bons et al., 2012;Groves and Santosh, 2021); and (6) fold limbs and hinge zones (Robert and Poulsen, 2001). Therefore exploration and development of rock-hosted ore deposits at the regional, district, and orebody scales depend heavily on structural geology. ...
Geological data provide information necessary for discovering mineral resources. Geological mapping is deemed a prerequisite for most exploratory surveys and constitutes many stages, including observing lithological and structural features in the field and recording these features on a map. The information collected in the field must be factual and thorough, gathered by many methods in traversing. In addition, since a preliminary knowledge of structural mapping, petrography, mineralogy, and stratigraphy is an asset for geological mapping, these issues will be thoroughly covered in this chapter.
... NGBCs may also affect the mechanical strength of fully cemented natural fractures accounting for the reactivation of cemented fractures in rock mechanics tests (Lee et al., 2015) and under natural conditions resulting in crack-seal cement textures (Bons et al., 2012;Ramsay, 1980). Although partially healed, open NGBCs may thus enhance the ability for natural, cemented fractures to be reactivated during the hydraulic stimulation of oil and gas and enhanced geothermal wells (Dahi Taleghani & Olson, 2014). ...
Natural fractures in shale and sandstone that formed under diagenetic and metamorphic conditions are frequently filled with mineral cement that lack residual fracture porosity visible under the petrographic microscope and that are generally interpreted to be impermeable. Scanning electron microscopy of calcite, dolomite, quartz, and barite fracture cement from low‐permeability, diagenetically altered shale and sandstone formations provides evidence of open and variably connected elongate pores or gaps with apertures of 10–600 nm, referred to as nanoscale grain boundary channels (NGBC). Electron backscatter diffraction of samples prepared using broad ion‐beam milling shows that NGBCs occur along grain boundaries of blocky or columnar fracture cement. Grain boundaries are either faceted or display undulation at the nanometer scale. NGBCs tend to increase in aperture with increasing maximum formation burial temperature, indicating dissolution‐precipitation kinetics influences grain boundary structure. Transmission electron microscopy reveals heterogeneous crystallographic domains with possible amorphous regions bridging across grain boundary channels. We propose a model of dynamic concurrent dissolution‐precipitation along grain boundaries that preserves NGBCs in carbonate and quartz fracture cements that have experienced diagenetic to low‐grade metamorphic conditions. While partially healed, NGBCs may be sufficiently connected to increase permeability of low‐permeability formations containing cemented fractures.
... perpendicular to the vein-host boundary. The vein morphology of domain (b) cannot be referred 280 to any classical microstructures (Fig. 7g; seeBons et al., 2012). Epidote in domain (b) is euhedral with lengths between ca. ...
... For example, reactions with the dissolved constituents from the rock (essentially a chemical soup) are likely to occur over numerous supersaturation thresholds instead of the single supersaturation as that applied in our experiments. However, despite the complexities of water-gas-rock interaction in a basin or tectonically active area, it is important to note that observed associated vein mineralogy is far less complicated -i.e., typically dominated by either carbonate or quartz (e.g., [25][26][27]. For example, veins in mudrock observed in some parts of the Wolfcamp Formation consist of early dolomite followed by calcite and finally very minor quartz 28 . ...
Many challenges related to carbon-dioxide ([Formula: see text]) sequestration in subsurface rock are linked to the injection of fluids through induced or existing fracture networks and how these fluids are altered through geochemical interactions. Here, we demonstrate that fluid mixing and carbonate mineral distributions in fractures are controlled by gravity-driven chemical dynamics. Using optical imaging and numerical simulations, we show that a density contrast between two miscible fluids causes the formation of a low-density fluid runlet that increases in areal extent as the fracture inclination decreases from 90[Formula: see text] (vertical fracture plane) to 30[Formula: see text]. The runlet is sustained over time and the stability of the runlet is controlled by the gravity-driven formation of 3D vortices that arise in a laminar flow regime. When homogeneous precipitation was induced, calcium carbonate covered the entire surface for horizontal fractures (0[Formula: see text]). However, for fracture inclinations greater than 10[Formula: see text], the runlet formation limited the areal extent of the precipitation to less than 15% of the fracture surface. These insights suggest that the ability to sequester [Formula: see text] through mineralization along fractures will depend on the fracture orientation relative to gravity, with horizontal fractures more likely to seal uniformly.
... The petrological outline of veins can help constrain the relative timing of opening and precipitation. For antitaxial veins, the precipitation rate equals or exceeds the opening rate, reflecting undoubtedly precipitation coeval with opening [Bons et al., 2012]. In contrast, blocky calcite indicates free precipitation of fluids in a void, due either to a fluid precipitating after joint development or to a fluid precipitating at slower rate than the rate of opening. ...
... Even veins of hydrothermal origin may be filled with fine and/or coarse-grained quartz crystals that exhibit a banded or layered structure (e.g., Fig. 1 in Fonseca et al. 2015) parallel to the host rock walls. These well-known arrangements, usually observed in large veins that can be traced for some meters at most, are related to progressive vein infilling processes by repeated crack-seal mechanisms (Bons et al. 2012;Ramsay 1980) and to mineralizing fluid diversion into shorter and wider cavities upon hydrofracture arrest (Bons 2001). The layering described, which can even be strengthened in metamorphic scenarios where the veins become overprinted by solid-state plastic deformation, can also be misinterpreted as sedimentary lamination/bedding. ...
The major raw material documented in the archeological sites of Olduvai Gorge (Tanzania) is a geological material with crystalline appearance, white or colorless, foliated or seemingly massive only at the outcrop scale, with a very high quartz-rich composition, and apparently of metamorphic origin, named by us in this paper: Crystalline Quartz-rich Raw Material (CQRM). Since the early days of research in Olduvai Gorge, a long-lasting terminological imprecision has allowed defining this material in a confused way as quartz or quartzite. Stubbornness in terminological imprecision reflects the complexity and specificity of CQRM related to a protracted and complex geological history composed by quartz-bearing metamorphic rocks of varied types and origins from recycling and/or tectonic reworking of much older Precambrian orogens and cratons. Currently the term quartzite is preferred by most researchers, despite being materials that have an appearance macro- and microscopic similar to quartz and show a response to fracture mechanics, and cutting-edge functional response is closer to quartz. In our view, it is crucial to undertake a comprehensive analysis of the CQRM from the structural, metamorphic, and petrological perspectives. Bearing this in mind, the main objective of the present study is to build a robust and conclusive petrological background that will enable an accurate identification and classification of this quartz-rich mineral resource. This geological material should be identified as “quartz.” The most diagnostic features supporting this interpretation can be summarized as some of the microstructural relics identified concur undoubtedly with a hydrothermal origin of the quartz and the recognition of special deformational structures at macro and micro scale point to tectono-metamorphic overprint of the hydrothermal quartz under granulite-facies conditions during the Panafrican orogenesis about 640 Ma ago.
... Quartz and feldspar have been deformed generally by cataclastic deformation in ESZ. The differential stresses resulted from the syntaxial quartz veins (Bons et al. 2012), observed in outcrop with strong growth competition of elongated quartz grain from the wall inwards (Fig. 10f) and is relatively low (Eteridge 1983). The low confining pressure also plays a role within this zone by creating tension gashes (Suh and Dada 1997) and dilatant microfractures, in which circulated fluids saturated in silica. ...
The Etam Shear Zone is a N to NNE trending strike-slip zone, and it displays a sinistral shearing mylonitic (ductile) zone and a brittle zone. Field observations and microstructural studies reveal that the ductile zone experienced strain partition. Primary minerals (quartz, K-feldspar, Plagioclase, and biotite) in wall rock (granodiorite) are gradually reduced towards the intensively deformed shear zone center. Quartz recrystallization also increases in the same direction. The structural evolution reveals the following: (1) a first phase of deformation D 1 underlined by S 1 foliation and mylonitic schistosity (Sm). This phase is oriented N10°E to N22°E and is associated with L 1 lineation (NNE-SSW, average plunge of 10° NE), F 1 fold (fold axis~ S60E), and asymmetric β 1 boudins of domino's type; (2) a second phase D 2 that develop F 2 folding, C 2 shearing planes (N60E to N75E and dipping strongly W to NW), and a late D 2 brittle event. Microstructures such as recrystallization, sub-grain boundary, myrmekites, and undulose extinction characterize the sub magmatic and post magmatic deformation. Kinematic markers (rotated mineral, shearing planes, and fold vergence) reveal an earlier dextral shearing movement in biotite gneiss followed by sinistral shear sense recorded in mylonites. The mica-chlorite-epidote assemblage defines a greenschist facies in the Etam Shear Zone. Metasomatic reactions (Plagioclase + K-feldspar + water = Quartz + Albite + Epidote + Chlorite) during pervasive alteration of some minerals have probably released silica during deformation that was carried by hydrothermal fluids and precipitated in pull-apart fracture to form hydrothermal syn-kinematic quartz veins.
... Detailed petrographic analysis was done to distinguish different types of veins (syntaxial, antitaxial, stretched) and their fabrics (e.g., fibrous, stretched, blocky, elongated, and blocky-elongate) according to Bons et al. (2012). Moreover, cross-cutting relationships between the veins were analyzed, allowing a better understanding of their kinematics, multiple reactivations, and deformation conditions. ...
U–Pb calcite dating is a powerful tool for the analysis of geological processes as calcite cements are ubiquitous and sensitive markers of diagenesis, fluid-rock interaction, fluid-flow, and fracturing. This technique provides the possibility of constraining the timing and history of deformation in diverse tectonic scenarios. We analyze calcite cement from fossil-shells, rock-matrix, and tectonic veins emplaced in shortened Permian limestone layers of the Chicomuselo fold-thrust belt (CFTB) in southeastern Mexico. We report 99 in situ U–Pb calcite ages with high temporal and structural resolution from fold/fault-related veins and from complexly fractured rocks. Samples selected with structural criteria provide better constraints on specific deformational events, while complexly veined zones provide an inventory of accumulated deformation within small rock volumes. Calcite cement ages cluster in 6 intervals: 290-260 Ma, 255-225 Ma, 210-180 Ma, 170-120 Ma, 60-40 Ma, and 20-5 Ma, associated with (i) Permian carbonate deposition and diagenesis, (ii) CFTB shortening, (iii) Faulting related to the early breakup of Pangea, (iv) Gulf of Mexico rifting, drifting and the Pacific tectonic influence, (v) Paleogene Mexican orogeny, and (vi) Chiapanecan orogeny and Polochic Fault System activity, respectively. All of these are important events in the evolution of the southern margin of the North American plate. This study demonstrates that calcite is resilient and reliable for preserving the history of diverse brittle deformational events imprinted in limestone.
... The Kodiak Landward Belt (KLB) in Uyak Bay consists of intercalated sandstone/siltstone and mudstone beds (Fig. 2a), with occasionally disrupted strata closer to its northern boundary marked by the Uganik Thrust Rowe et al., 2009). The veins from Landward Belt are Mode 1 (Mode 1 veins refer to mineralized fractures characterized by the opening direction perpendicular to the fracture plane; Bons et al., 2012) quartz-calcite veins oriented almost perpendicular to the bedding stratification ( Fig. 2a) and are interpreted as forming in the sediments during underthrusting, where the maximum compressive stress (σ 1 ) is in sub-vertical position Fisher and Byrne, 1990). The temperatures derived from fluid inclusions in Mode 1 quartz veins are in the range of 215-255 • C for the Landward Belt at Raspberry and Afognak islands (Vrolijk et al., 1988). ...
... During their formation, veins provide information on tension, strain, pressure, temperature, fluid origin, and fluid composition. Gold lodes and skarn mineralisation are two common instances [2]. Because there is plenty of fluid flow and open area for ore minerals to deposit, hydrofracture breccias are classic candidates for ore exploration. ...
The quartz veins in the Imonga region are confined to the primary ENE-WSW trend, which is quite consistent with the Kibara metasediments. The objective of this work was to study the topographic, structural and geochemical features of the mineralized quartz veins in the Imonga area. Field investigations have shown that the area is composed of seristoschists and quartzites, with seristoschists more abundant than quartzite. Mineralized quartz veins found with sericite schist have different compositions between quartz, iron oxide ± sericite and mafic minerals. Mineralized quartz veins contain 0.50 to 3.44 ppm Au, while quartz veins that are considered sterile contain less than 0.50 ppm Au. Since the concentration correlates with Au in samples with moderate Au content, Au exhibits a positive correlation with only Mo while it is negatively correlated with other metals such as Cu, Pb, Zn and Co. The studied ridges show signs of multiphase strain and it is associated with D2 strain in the region. The presence of quartz veins in the shear zone suggests that the site of gold mineralization is epigenetic. The main type of weathering includes sericitization. The general directional trend of Imonga quartz veins can be exploited for future geological exploration.
... Within the tectonic, hydraulic and dissolution breccia, other specific processes also played a role such as the mixing between saline metal-bearing fluids and a low saline (meteoric) fluid, inducing a sudden decrease in temperature and pressure (Haest et al., 2007;El Desouky et al., 2008a;Haest and Muchez, 2011). The importance of this mixing has been recognized at other similar evaporate-rich settings and tectonic environments (Bons et al., 2012;Cathelineau et al., 2021). The decrease in temperature was related to the upward migration of the mineralizing fluids from depth to the subsurface and by the mixing with meteoric water. ...
The Katanga Supergroup, host of several world class Neoproterozoic sediment-hosted stratiform copper and cobalt deposits, is part of the Central Africa Copperbelt (CACB). The origin and classification of the breccia, which is one of the most characteristic features of the Katanga Supergroup, has been a matter of discussion since the 19th century. Different nomenclatures and various classifications have been used in the mining operations across the CACB. The difficulty to identify genetically related types of breccia creates some problems in regional correlations and comparisons. In addition, their origin is most relevant for the metallogenesis of the world-class copper and cobalt sediment-hosted deposits. This paper classifies the breccia according to their characteristics, reviews the mechanisms of brecciation, and thus addresses their origin, and highlights their potential in metal resources. The different types of breccias found in CACB include sedimentary breccia (gravity flow, sedimentary breccia stricto sensu), dissolution and collapse breccia, hyaloclastite breccia, hydraulic breccia and tectonic breccia (thrust-breccia and fault breccia). The spatial and chronological distribution of these breccias in the CACB follows the geodynamic history of the area starting from early Neoproterozoic rifting up to the Lufilian orogeny and post-Lufilian tectonism.
During the Mesozoic and the Cenozoic periods, Europe recorded several tectonic events that have been interpreted as far-field tectonics. This may be diffuse tectonics that occur at the onset of a major tectonic event or propagation of the deformation away from orogenic fronts. In Western Europe, the deformations related to the opening of the Bay of Biscay and the formation of the Pyrenean belt are well described in the southern part of the Aquitaine basin, but little is known about the “Northern Aquitaine Platform”. We combine field observation with Unmanned Aerial Vehicle (UAV) imagery and U-Pb laser dating on calcite to determine the tectonic evolution in the Vendée Coastal domain. Our results highlight the occurrence of two main tectonic events since the early Jurassic: (1) At the transition from the Late Jurassic to Early Cretaceous, WNW-ESE striking normal faults exhibit a horst and graben pattern that emplaced at the onset of the opening of the Bay of Biscay. Their association with reactivated Variscan strike-slip faults is consistent with oblique extension processes. Such a tectonic event was accompanied by fluid flow coming from depth. (2) During the Late Cretaceous, fractures, wide-open folds, veins, and joints are consistent with the N-S shortening direction that occurs during the earliest stages of the N-S Pyrenenan compression. In both cases, the early stages of the main regional deformation stages are recorded in the “Northern Aquitaine Platform” in a far-field position and before the focus of strain in rifts or orogenic belts. In the Aquitaine basin as in many other places in Europe, the tectonic study of sedimentary platforms located far from the main plate-scale deformation zone provides new constraints on the early diffuse deformation process that predate the main tectonic phases.
This study shows a workflow to improve the visualization of fault-related heterogeneities from seismic data using a combination of color-processing (eXchromaSG Petrel plug-in) and ant-tracking leading to higher vertical resolution than wavelet-based methods. The reason is that only seismic amplitude differences between adjacent time slices matter, rather than trace similarity, and thus leans on the concept of seismic detectability rather than resolution (1/16th of the dominant wavelength vs. 1/4th). The workflow is applied to a producing hydrocarbon field in the Chalk Group on the Kraka salt dome in the Danish Central Graben. The results show structural lineations in 2D sections, having typical lengths of 200–1000 m, are generally inclined at quite shallow dips to bedding (typically 10°–45°), and terminate often at specific stratigraphic horizons. They form diffuse zones surrounding low-throw faults seen from seismic amplitude sections. In plan view on stratigraphic horizons, sets of parallel or near-parallel lineations can be seen, with individual segments often linked together to form 200–1000 m long segments. At connecting junctions, the eXchromaSG ant-tracked data shows highest values. Three orientations are observed: (1) NE–SW; (2) NW–SE; (3) concentric. Comparison to borehole image logs shows no clear relationship to the attribute in terms of fracture intensity, however, the orientations of both open and cemented fractures are strikingly similar. Given that amplitude changes within the chalk are mainly the result of porosity changes, it is proposed that the structural lineaments from this attribute reflect diffuse zones of lower or higher acoustic impedance surrounding faults, e.g. fault damage zones. We propose three processes for creating fault-related changes in acoustic impedance in chalks: (1) fault damage zones with open fractures having lower acoustic impedance; (2) fault damage zones with cemented fractures having higher acoustic impedance; (3) fault damage zones that have led to improved drainage of burial fluids, causing enhanced compaction and high acoustic impedance. They therefore are diagenetic zones surrounding faults and are as such related to areas of faulting. The three observed orientations are likely reflecting reactivation of structural weaknesses related to Permo—Triassic rifting (NE–SW) and Late Jurassic rifting (NW–SE), and concentric to salt doming. Importantly, these data provide high-resolution information on how faults interact at junctions, which provides valuable insights for modelling discrete fracture networks and reservoir compartmentalization. The results can thus be used as input for refining static and dynamic models of the main reservoirs but also for seals, within the context of Carbon Capture Storage, geothermal and hydrocarbon production.KeywordsStructural attributesChalkFaultsFractures
Fluid flow in fracture porosity in the Earth's crust is in general accompanied by crystallization or dissolution depending on the state of saturation. The evolution of the microstructure in turn affects the transport and mechanical properties of the rock, but the understanding of this coupled system is incomplete. Here, we aim to simulate spatio‐temporal observations of laboratory experiments at the grain scale (using potash alumn), where crystals grow in a fracture during reactive flow, and show a varying growth rate along the fracture due to saturation differences. We use a multiphase‐field modeling approach, where reactive fluid flow and crystal growth is computed and couple the chemical driving force for grain growth to the local saturation state of the fluid. The supersaturation of the fluid is characterized by a concentration field which is advected by fluid flow and in turn affects the crystal growth with anisotropic growth kinetics. The simulations exhibit good agreement with the experimental results, providing the basis for upscaling our results to larger scale computations of combined multi‐physical processes in fractured porous media for applications as groundwater protection, geothermal, and hydrocarbon reservoir prediction, water recovery, or storing H2 or CO2 in the subsurface.
To explore the genesis of the laminated calcite veins developed in the black shale of Chang 7 3 submember of the Ordos Basin, the petrology, microstructure and geochemistry of calcite veins are studied using thin sections, fluid inclusions, trace elements and isotopic geochemistry. The source, the time of formation, the mechanism of formation, and the dynamic background of the veins are discussed. The veins are mostly made up of calcite, mixed with lenticular or spindle‐shape solid wall rock inclusions. Three structures are identified in the calcite minerals: fibrous, rhombic cleavage, and wedge‐like structure. Trace elements and isotopes of carbon and oxygen confirm that the calcite veins were formed from a high density hydrothermal fluid. It is assumed that calcite veins formed prior to wall rock consolidation during the formation of the Qinling Orogenic Belt in the Middle and Late Triassic. The results show that the sedimentary sources of Chang 7 3 submember were influenced by hydrothermal materials besides terrigenous detritus. The fibrous calcite is different from the fibrous calcite reported in the morphology and mechanism of formation. In this way, the research complements and improves the morphology and the mechanism of formation of fibrous calcite.
The Salinarröt is the lowermost part of the Upper Buntsandstein/Middle Triassic and crops out in various places east of Jena. It is an evaporitic unit that represents the leached and altered product of a primary stratigraphic succession consisting of rock salt and anhydrite. It is made up by gypsum layers, which are interbedded with clays and marlstones, and it is intensely folded in many places. The cause for this folding is debated. Similarly, the formation of the fibrous gypsum (satin spar) varieties found within the Salinarröt is not entirely understood. Here we present new field observations that allow us to shed light on the formation of both the folds and the fibrous gypsum. We documented and analyzed gypsum structures, especially the fibrous gypsum, and different types of folding present in outcrops in the vicinity of Jena. The analysis of the orientation and the shape of the folds shows that their formation can be attributed to swelling and crystallization processes in the rock. The increase in volume during the transformation of anhydrite to gypsum and the crystallization of gypsum from aqueous solutions are the processes driving the formation of folds. The swelling and flaking of clayey layers allows for the penetration of fluids and therefore assists fold formation. Fibrous gypsum occurs mostly bedding-parallel and consists of vertically oriented fibers. It formed in bedding-parallel veins that opened vertically during subsidence caused by leaching of the rock salt below. Growth of the fibrous gypsum mainly took place after fold formation, and therefore did not contribute to it. Special types of fibrous gypsum consisting of fibers that are bent or that deviate from the vertical can be explained by shearing and other movements in the rock.
The analysis in this chapter attempts to quantify the coupling between pore space deformation and pore pressure in the earth's crust. Clearly, the state of free water deep in the crust is inseparable from the state of porosity, permeability, and pore pressure. If porosity and permeability are time-invariant, crusta) pore pressure at depth must be close to hydrostatic. This is in conflict with evidence for ubiquitous high pore pressure at depth. Consequently crusta) porosity, permeability, and water content must decrease with time, as pores close inelastically in the crust. When crusta) permeability is low, and its rate of decrease with porosity is large, pore pressure PP of trapped fluids must rise with time until spontaneous hydrofracturing, pulsed release of water, and the loss of some porosity occurs, followed by a drop in pore pressure and sealing of the system. After a PP buildup period, another hydrofracturing episode occurs. Because inelastic pore deformation is enhanced by shear stress, this episodic process is most probable in tectonically active areas. Dimensional analysis shows that tens to hundreds of PP episodes or 'burps,' each lasting 10 3-10 5 years, can occur before the crust dewaters in 10 6-10 7 years. Oceanic crust subduction may prolong this process to 10 8 years or more. High pore pressure can explain deep crusta) seismic reflectors and detachments, and large-scale horizontal fluid migration in the crust. Episodic pore pressure buildup and release in the crust can explain the formation of hydrothermal ore deposits and mineralized veins, and possibly some aspects of the mechanics of very large earthquakes.
Multi-element crust-leach analysis of H2O-CO2 inclusion fluids from a suite of six vein samples from gold-quartz veins in the Brusson district demonstrates that their solute chemistry (c. 5 wt.% NaCl equiv.) is dominated by sodium chloride with lesser amounts of calcium bicarbonate, potassium chloride and sodium bicarbonate. The gold-quartz veins formed as H2O-CO2 fluids of modest salinity and very uniform composition ascended from depth. Halogen ratios of the fluids are consistent with an ultimate origin for these fluids from deep-penetrating surface or connate waters although such a model requires extremely low fluid:rock ratios, to account for the hydrogen isotope composition of many similar deposits. -from Authors
Geochemical fronts for Sr isotopes have been identified within carbonate mylonites along the Gavarnie Thrust in the central Pyrenees. Over 200 samples have been analyzed for 87Sr/86Sr, including samples from seven measured sections through the thrust zone. A geochemical profile has been drawn through the maximum 87Sr/86Sr values at each sample site, and two separate geochemical fronts identified. The data show that Sr was transported southward along a 2m thick mylonite zone for at least 1.5 km. Fluid inclusion crush-leach analyses show that a Sr-rich hypersaline brine with a high 87Sr/86Sr ratio was trapped within Triassic redbeds beneath the Thrust; this is a likely candidate for the fluid that passed through the mylonites, increasing their 87Sr/86Sr ratios from depositional values close to that of Cretaceous seawater. Overall, fluid flow can be explained by a fault-valve model, with slow pervasive flow through the mylonite during plastic deformation punctuated by rapid flow into veins during seismic events. -from Authors
A total of 2128 calcitic and phosphatic shells, mainly brachiopods with some conodonts and belemnites, were measured for their , and values. The dataset covers the Cambrian to Cretaceous time interval. Where possible, these samples were collected at high temporal resolution, up to 0.7 Ma (one biozone), from the stratotype sections of all continents but Antarctica and from many sedimentary basins. Paleogeographically, the samples are mostly from paleotropical domains. The scanning electron microscopy (SEM), petrography, cathodoluminescence and trace element results of the studied calcitic shells and the conodont alteration index (CAI) data of the phosphatic shells are consistent with an excellent preservation of the ultrastructure of the analyzed material. These datasets are complemented by extensive literature compilations of Phanerozoic low-Mg calcitic, aragonitic and phosphatic isotope data for analogous skeletons. The oxygen isotope signal exhibits a long-term increase of from a mean value of about −8‰ (PDB) in the Cambrian to a present mean value of about 0‰ (PDB). Superimposed on the general trend are shorter-term oscillations with their apexes coincident with cold episodes and glaciations. The carbon isotope signal shows a similar climb during the Paleozoic, an inflexion in the Permian, followed by an abrupt drop and subsequent fluctuations around the modern value. The ratios differ from the earlier published curves in their greater detail and in less dispersion of the data. The means of the observed isotope signals for , , and the less complete (sulfate) are strongly interrelated at any geologically reasonable (1 to 40 Ma) time resolution. All correlations are valid at the 95% level of confidence, with the most valid at the 99% level. Factor analysis indicates that the , , and isotope systems are driven by three factors. The first factor links oxygen and strontium isotopic evolution, the second and , and the third one the and . These three factors explain up to 79% of the total variance. We tentatively identify the first two factors as tectonic, and the third one as a (biologically mediated) redox linkage of the sulfur and carbon cycles. On geological timescales (≥1 Ma), we are therefore dealing with a unified exogenic (litho-, hydro-, atmo-, biosphere) system driven by tectonics via its control of (bio)geochemical cycles.
We present petrologic and oxygen isotopic evidence for the interaction of deep crustal fluids with kyanite zone pelitic schist during amphibolite facies metamorphism of the Wepawaug Schist, south-central Connecticut. We focus on a sample of schist (sample MBW-1) cut by a 2–6 cm wide quartz vein. The vein is surrounded by zones of wallrock alteration (selvages) that are rich in micas relative to quartz and feldspar, have low , contain staurolite and kyanite, and vary in thickness from about 1–5 cm. Staurolite and kyanite are rare or absent beyond the selvage margins. We have measured the δ18O of quartz, plagioclase, muscovite, garnet, kyanite, staurolite, garnet, and biotite along several mm-scale resolution traverses across the quartz vein and the adjacent schist. Garnets in the selvages record core-to-rim increases in δ18O of nearly 2%. Modeling of prograde reaction histories indicates that this zonation requires the infiltration of external fluids. Beyond the selvage margins, isotopic zonation in garnet is about 0.8% from core-to-rim and is consistent with prograde reaction with little or no infiltration. We suggest, therefore, that the selvages were zones of significant fluid infiltration and that the region now occupied by the quartz vein was the major fluid conduit. Earlier petrologic studies (Ague, 1994b) indicated that quartz veins and adjacent selvages were conduits for major down-temperature flow of H2O-rich fluids with time-integrated fluid fluxes of ∼3 × 105 m3 m−2. Isotopic modeling of advective flow suggests that down-temperature fluxes of this magnitude would have increased bulk δ18O by ∼1‰, consistent with the isotopic record preserved by zoned selvage garnets. Quartz in veins surrounded by selvages from five other localities throughout the amphibolite facies have δ18O that is statistically indistinguishable from that of the bulk of the quartz in MBW-1. Thus, we conclude that the amphibolite facies portion of the Wepawaug Schist was a zone of major, channelized outflow of metamorphic fluids down the regional temperature gradient.During the latter stages of amphibolite facies metamorphism subsequent to the bulk of vein and selvage formation, MBW-1 was infiltrated by isotopically light fluids that were probably derived from synmetamorphic igneous intrusions. This infiltration modified the isotopic composition of plagioclase throughout the rock and, therefore, we suggest that the infiltration was pervasive. Muscovite retains its pre-infiltration isotopic composition, however, which suggests short timescales of fluid-rock interaction on the order of 103–104 years. The total duration of flow may have been longer than this because our calculations do not take episodic flow into account.Modeling of possible isotopic shifts resulting from diffusion of oxygen isotopes between matrix phases during slow cooling indicates that MBW-1 must have been dry for most of its retrograde cooling history.
We have investigated fluid-rock interaction processes during formation of metamorphic quartz veins that are abundant in the fold-and-thrust belt of the Rhenish Massif, southwest Germany. These veins record two successive assemblages that were formed in a different fluid-rock environment, which are (1) massive vein filling (elongate-blocky quartz, chlorite, apatite, albite) and (2) open space filling (euhedral quartz crystals, ankerite/dolomite, calcite, sulfides). Building on previous work that studied the field relationships, mineralogy, vein textures, fluid inclusion and wall rock alteration features, we have performed a detailed REE and stable isotope investigation of vein minerals, altered wall rocks (selvages) and least altered host rock metapelites. The REE and oxygen isotope data of vein quartz and altered wall rocks, in conjunction with mass balance analysis, support the conclusion that local mobilization of material was dominant during formation of the early massive vein filling assemblage, but that contributions from advecting fluids were also important. The pronounced shift in K/Na ratios in altered wall rocks and model fluid temperatures that are substantially higher (350-400 °C) than estimates for the surrounding host rocks clearly point to substantial fluid advection. Formation of the veins can be essentially explained by a crack-flow-seal model, which involves multiple repetition of vein opening, fluid advection and vein sealing events (consistent with the elongate-blocky textures of massive vein quartz). Each cycle was initiated with vein opening, resulting in enhanced permeability and considerable fluid advection leading to hydrothermal alteration of wall rocks. Conditions during each cycle then evolved towards a decrease in fluid advection, coupled with substantial diffusional leaching of silica from the wall rocks and precipitation in the veins. The formation of the later open space filling assemblage records a transition from an overall advection- to a diffusion-dominated regime. This is supported by vein mineral and fluid inclusion textures recording conditions of slow and undisturbed mineral growth, fluid inclusion data that point to a thermally equilibrated state (150-200 °C), and stable isotope data that demonstrate a local source for the vein minerals.
Fluid flow is an integral part of hydrothermal mineralization, and its analysis and characterization constitute an important part of a mineralization model. The hydrodynamic study of mineralization deals with analyzing the driving forces, fluid pressure regimes, fluid flow rate and direction, and their relationships with localization of mineralization. This paper reviews the principles and methods of hydrodynamic studies of mineralization, and discusses their significance and limitations for ore deposit studies and mineral exploration. The driving forces of fluid flow may be related to fluid overpressure, topographic relief, tectonic deformation, and fluid density change due to heating or salinity variation, depending on specific geologic environments and mineralization processes. The study methods may be classified into three types, megascopic (field) observations, microscopic analyses, and numerical modeling. Megascopic features indicative of significantly overpressured (especially lithostatic or supralithostatic) fluid systems include horizontal veins, sand injection dikes, and hydraulic breccias. Microscopic studies, especially microthermometry of fluid inclusions and combined stress analysis and microthermometry of fluid inclusion planes (FIPs) can provide important information about fluid temperature, pressure, and fluid-structural relationships, thus constraining fluid flow models. Numerical modeling can be carried out to solve partial differential equations governing fluid flow, heat transfer, rock deformation and chemical reactions, in order to simulate the distribution of fluid pressure, temperature, fluid flow rate and direction, and mineral precipitation or dissolution in 2D or 3D space and through time. The results of hydrodynamic studies of mineralization can enhance our understanding of the formation processes of hydrothermal deposits, and can be used directly or indirectly in mineral exploration.
Cambridge Core - Structural Geology, Tectonics and Geodynamics - The Mechanics of Earthquakes and Faulting - by Christopher H. Scholz
Fibrous veins are generally interpreted in terms of the crack-seal mechanism. Several aspects of fibrous veins (fibrous structure, curved fibres, symmetry of antitaxial veins) are however better explained by vein formation without fracturing. Mass transfer to such veins would be by diffusional transport rather than by fluid flow through the veins. Deformation by dissolution-precipitation creep can provide the driving force for the necessary mass transfer. Veins form when mass transfer is heterogeneous and precipitation is localised. Experiments were performed which enforced a chemical potential gradient, acting as the driving force for diffusional mass transfer. These experiments resulted in fibrous growths in aggregates of soluble salts (NaCl and KCl) saturated with brine. The experimental results support the theory that fibrous veins may form without fracturing and that rather than providing evidence for major fluid pathways, fibrous veins may instead represent localised precipitation during diffusional material transfer.
En-echelon calcite filled vein arrays and accompanying stylolites are developed in the carbonate unts of a ramp section in the upper plate of the Pineta Thrust Complex in the Cinca Valley of the Spanish Pyrenees. Non-fibrous euhedral calcite infillings often crosscut the pre-existing fiber patterns in discrete zones of late dilation. Carbon and oxygen isotope data were obtained from chronologically placed micro-samples of calcite both from rock matrix and sigmoidal veins. We interpret these data to indicate that the matrix calcite was massively exchanged with an externally derived fluid during an early porous flow regime prior to the development of the vein-stylolite system. -from Authors
Antitaxially grown fibrous pressure shadows are common on spherical pyrite framboids in Martinsburg slate near the Delaware Water Gap, N.J.; they provide precise estimates of strain and important insight into the kinematics of folding. Bridge-shaped curves and a general clockwise reorientation on both fold limbs accord well with folding by a rolling hinge mechanism, with fold couples nucleating and the short limbs then growing by layering rolling through hinges from upright to overturned limbs. Such a mechanism, long assumed but not previously documented, may explain the presence of extensive overturned limbs in overturned to recumbent folds (fold nappes) of orogenic belts.-from Authors
Geologic evidence suggests that some joints are tension fractures developed perpendicular to the least principal stress direction in rock. In this study the mechanics of natural tension fracturing is examined in light of the fluid pressure theory developed by Hubbert and Rubey (1959). The Griffith theory of failure, expressed in terms of effective stresses, is taken as the failure criterion for rocks. In addition one of the total principal stress directions is assumed to be vertical and equal to the bulk weight of the overburden to the depth considered. Calculations based on these assumptions indicate that tension fractures can develop at increasingly greater depth in the Earth as the ratio of fluid pressure to overburden weight approaches one. . . . Previously formed fractures can be opened up by fluid pressure at great depth in the Earth's crust. Such open fractures probably are important in the migration of ground water, hydrocarbons, and ore fluids.
Epigenetic Zn-Pb deposits in the Maestrat basin (eastern Spain) are hosted by dolostones that replace Aptian limestones. The deposits have morphologies ranging from mineralized breccias to stratiform, massive replacements. Sphalerite and galena cementing breccias precipitated as well-formed crystals; whereas, the stratiform replacements are characterized by textures such as colloform and skeletal or dendritic growths. Two mineralized areas are found: Valdelinares and Mas de la Mina-Cedraman. The highest ore grades (up to 11% Zn) and largest deposits (ca. 30,000 t of sulfides) occur as stratiform deposits in the Valdelinares area (Resurreccion and Restauracion mines). In the Valdelinares area, microthermometry of fluid inclusions reveals that ore-stage minerals precipitated by the mixing of two distinct fluids: fluid A, a high salinity brine, with salinity greater than 26 wt percent NaCl equiv and temperatures above 120degreesC, and fluid B, a low salinity fluid, with less than 15 wt% NaCl equiv and temperatures around 40degreesC. Fluid A-dominated brines are found in mineralized breccias located in the vicinity of major fracture zones; whereas, more dilute fluids are typical of massive ores. In the Mas de la Mina area, the presence of two fluids is less evident, although the ranges in both temperature and salinity also point to mixing. Na-K-Li-Cl-Br systematics of the inclusion fluids indicates that fluids A and B were evaporated seawater that did not significantly interact with K- and Li-rich sediments. The most diluted mixtures (fluid B) are characterized by relatively heavy Cl (delta(37)Cl = 1.11 and 1.19parts per thousand) compared to fluid-A dominated brines, which have delta(37)Cl values close to seawater (0parts per thousand). The sulfur isotope compositions range from -10.5 to 13.4 per mil for sulfides and between 16 and 17.8 per mil for barite. Such values are consistent with mixing of a metal-rich brine with small amounts of S-32-enriched sulfur and a sulfur-rich fluid with a delta(14)S close to the marine sulfate of Late Cretaceous to earl Paleocene age. The C and 0 isotope compositions of ore-stage calcite (delta(13)C from 0.6 to -7.8parts per thousand; delta(18)O from 17.2 to 20.9parts per thousand) are also explained by the precipitation from different mixtures of fluids A and B. From the geochemical data, it is inferred that fluid mixing played a key role in the formation of the Zn-Pb deposits in the Maestrat basin. Ore precipitation occurred in places where brines ascending through faults interacted with a dilute, sulfur-rich fluid. Deposits with the highest ore grade and size are related to areas where the most extensive mixing occurred.
Fluid inclusion data (microthermometry and Na-K-Li-Cl-Br chemistry) from Mississippi Valley-type Zn-Pb deposits in the Basque-Cantabrian basin, north Iberian Peninsula, indicate that fluid mixing occurred during mineralization. Cl/Br ratios of the ore-forming brines suggest that the high salinity was primarily acquired by evaporation of seawater. Only in deposits near salt domes (Orduna and Murgia diapirs) do the ore-forming brines have halogen signatures indicative of halite dissolution. Mixing of fluids frequently cannot be detected using only microthermometry or halogen data, although microthermometric data can indicate mixing where one of the end members is fresh water or a highly diluted fluid. Combining the two allows both the recognition of mixing and an estimation of the relative proportion of the different fluids involved. The effects of mixing on the salinity and halogen ratios of the resulting mixture have been calculated using four types of fluids: (1) seawater, (2) evaporated seawater before the onset of halite precipitation, (3) seawater evaporated past the point of halite precipitation, and (4) a halite-saturated brine at 25degreesC derived from halite dissolution. The calculated Cl/Br-Na/Br mixing curves have been compared to data from the Zn-Pb deposits of the Basque-Cantabrian basin and show that mixing between a residual brine and a balite-dissolution brine can account for the deposits in the Western Biscay district (Txomin, Matienzo, Barambio). Most of the ore-forming brines from the studied deposits around the Orduna and Murgia salt domes (Altube, Monteleon, Jugo) originated by halite dissolution, although there is also significant contribution (20-50 wt %) from a highly evaporated brine.
The compressive strength as a function of confining pressure and sample orientation was determined for three anisotropic sedimentary rocks (slate and two types of shales). The samples were tested over a confining pressure range of 0 to 40,000 psi, with pore pressure held constant at atmospheric pressure. The orientation of the plane of anisotropy (bedding or cleavage plane) was varied between 0 and 90 deg relative to the axial load. The test results indicate that anisotropic sedimentary materials fail or deform by shear along the bedding plane, shear across the bedding plane, plastic flow along the bedding plane, or internal buckling depending upon the orientation and/or the initial stress state. The strength data gathered were compared to three basic failure theories for anisotropic materials: (a) Walsh-Brace modification of Griffith’s theory; (b) single plane of weakness theory; (c) variable coefficient of friction and cohesive strength theory. It was found that over certain pressure ranges and orientations all three theories fit the experimental data. On the basis of experimental data an empirical relationship was proposed to be used in conjunction with the variable coefficient of friction and cohesive strength theory. This modified theory produced a good fit of the experimental data over all orientations.
As demonstrated by the chapters in this short course, stable isotope techniques are an important tool in almost every branch of the earth sciences. Central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances. Indeed, it was Harold Urey’s (1947) thermodynamically based estimate of the temperature-dependence of 18O/16O fractionation between calcium carbonate and water, and a recognition of how this information might be used to determine the temperatures of ancient oceans, that launched the science of stable isotope geochemistry. The approach pioneered by Urey has since been used to estimate temperatures for a wide range of geological processes (e.g. Emiliani 1955; Anderson et al. 1971; Clayton 1986; Valley, this volume). In addition to their geothermometric applications, equilibrium fractionation data are also important in the study of fluid-rock interactions, including those associated with diagenetic, hydrothermal, and metamorphic processes (Baumgartner and Valley, this volume; Shanks, this volume). Finally, a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium, a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems (Cole and Chakraborty, this volume).
In the fifty-four years since the publication of Urey’s paper, equilibrium fractionation data have been reported for many minerals and fluids of geological interest. These data were derived from: (1) theoretical calculations following the methods developed by Urey (1947) and Bigeleisen and Mayer (1947); (2) direct laboratory experiments; (3) semi-empirical bond-strength models; and (4) measurement of fractionations in natural samples. Each of these methods has its advantages and disadvantages. However, the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations, not all of which are in agreement. In this chapter, we evaluate the major methods for determining fractionation factors. …
Hydraulic fracturing, induced by thermal expansion of water, is invoked as a common phenomenon by which metamorphic fluid is progressively lost from a sediment pile undergoing metamorphism and subsequent orogeny. On linear thermal gradients, water loss may occur by this mechanism for all gradients greater than 12°C/km at depths greater than 5 to 10 km. During burial on lower gradients, water is retained in the pile and may cause widespread metasomatism.
Abstract Oscillatory zoning and fine-scale variations in trace element chemistry are commonly observed in hydrothermal minerals. It has been suggested that fine-scale chemical variations are caused by extrinsic changes in the parent hydrothermal system, such as varying fluid composition, pressure or temperature, as well as changes in mineral growth rate. In this study, LA–ICP–MS (laser ablation, inductively coupled plasma mass spectrometer) analyses were carried out on calcite crystals grown in Ca–NH3–Cl solutions doped with rare earth elements (REE). The variety of crystal morphologies observed (euhedral to acicular), likely relate to variations in trace element abundance and calcite supersaturation state. Crystals display oscillatory and sector zoning, with significant variations in REE concentrations among zones. Cyclic variations in REE concentrations (exceeding 10-fold) occur over distances of Keywords: calcite; experiment; hydrothermal; oscillatory; zoning Document Type: Research Article DOI: http://dx.doi.org/10.1111/j.1468-8123.2010.00305.x Publication date: February 1, 2011 $(document).ready(function() { var shortdescription = $(".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } $(".descriptionitem").prepend(shortdescription); $(".shortdescription a").click(function() { $(".shortdescription").hide(); $(".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher In this Subject: Geology By this author: BARKER, SHAUN L.L. ; COX, STEPHEN F. GA_googleFillSlot("Horizontal_banner_bottom");
Thermal water samples and related young and fossil mineralization from a geothermal system at the northern margin of the Upper Rhine Graben have been investigated by combining hydrochemistry with stable and Sr isotope geochemistry. Actively discharging thermal springs and mineralization are present in a structural zone that extends over at least 60 km along strike, with two of the main centers of hydrothermal activity being Wiesbaden and Bad Nauheim. This setting provides the rare opportunity to link the chemistry and isotopic signatures of modern thermal waters directly with fossil mineralization dating back to at least 500–800 ka. The fossil thermal spring mineralization can be classified into two major types: barite-(pyrite) fracture filling associated with laterally-extensive silicification; and barite, goethite and silica impregnation mineralization in Tertiary sediments. Additionally, carbonatic sinters occur around active springs. Strontium isotope and trace element data suggest that mixing of a hot (>100 °C), deep-sourced thermal water with cooler groundwater from shallow aquifers is responsible for present-day thermal spring discharge and fossil mineralization. The correlation between both Sr and S isotope ratios and the elevation of the barite mineralization relative to the present-day water table in Wiesbaden is explained by mixing of deep-sourced thermal water having high 87Sr/86Sr and low δ34S with shallow groundwater of lower 87Sr/86Sr and higher δ34S. The Sr isotope data demonstrate that the hot thermal waters originate from an aquifer in the Variscan crystalline basement at depths of 3–5 km. The S isotope data show that impregnation-type mineralization is strongly influenced by mixing with SO4 that has high δ34S values. The fracture style mineralization formed by cooling of the thermal waters, whereas impregnation-type mineralization precipitated by mixing with SO4-rich groundwater percolating through the sediments.
In the present work, we have analysed the experimental data presented in literature to characterize dispersion in porous media, at different dispersion regimes. The vast amount of data obtained by our group, together with the extensive data available from other sources, mostly for air and water at room temperature, provide a very detailed representation of the functions PeT = f1 (Pem, Sc) and PeL = f2 (Pem, Sc). Empirical correlations are presented for the prediction of the dispersion coefficients (DT and DL) over the entire range of practical values of Schmidt number and Peclet number. The simple mathematical expressions represent the data available, in literature, with good accuracy and they are shown to be a significant improvement over previous correlations.
