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Strike-slip fault-propagation cleavage in carbonate rocks: The Mattinata Fault Zone, Southern Apennines, Italy
Abstract
Disjunctive, spaced solution cleavage in carbonate rocks is genetically associated with the propagation of the left-lateral, strike-slip Mattinata Fault in the Gargano Promontory, Italy. Typical cleavage development is restricted within the 200–300-m wide fault zone, which is bounded by virtually unfractured wall rocks. The cleavage consists of sub-parallel solution surfaces, which are often reactivated as sheared solution planes. Geometrical and kinematic relationships exist between the fault and the associated cleavage planes, thus: (1) cleavage–fault intersection lines lie parallel to the fault and the sheared cleavage rotational axes and (2) the cleavage–fault angle is almost constantly equal to 40°. A model for the development of the Mattinata Fault is proposed in which the cleavage surfaces are interpreted as fault-propagation deformations. Cleavage nucleates as solution planes at the front of the advancing fault as the result of stress concentration in this region. Two distinct, time-sequential processes are shown to operate during the fault propagation: (1) typical millimetre- to centimetre-spaced solution surfaces form in the distal tip zone of the advancing fault plane; (2) as the tip advances, the fault plane breaks through the cleavage as minor shear displacements reactivate some of these nascent surfaces. These observations may prove useful in understanding mechanisms for fault-controlled enhanced/reduced permeability and fluid pathways.
... Geologic mapping Bedrock mapping was completed using traditional field techniques that included use of Brunton Compass, Global Positioning System (GPS) satellite receiver, topographic base map, rock hammer for sampling, hand lens for mineral identification, and field notebook for recording all data. Bedding, foliation, and fracture data were plotted on rose diagrams and equal area nets using Daisy software (Salvini et al., 1999). The field equipment for surficial mapping included a trenching shovel, hand auger, trowel, Munsell Color Chart, and topographic maps generated from LiDAR elevation data. ...
... The attitudes of planar structures intersecting the well were calculated from Acoustic Televiewer and caliper logs using WellCAD TM software. Structural data for the wells were plotted on rose diagrams and contoured equal area nets using Daisy Software (Salvini et al., 1999) and compared with structural data from bedrock geologic maps. ...
... Fractures (or joints) throughout the field area were measured (n = 3,251) and divided into 20 separate geographic domains (Kim, 2017b). Based on frequency azimuth rose diagrams and equal area nets plotted using Daisy software (Salvini et al., 1999), the statistically dominant steeply dipping (> 60 degrees) fracture sets were calculated for each of these geographic domains. Generally, the four dominant fracture sets strike: N-S, NNE-SSW, NW-SE, E-W, and NE-SW. ...
Between 2016 and 2019, the Vermont Department of Environmental Conservation discovered that groundwater from over 50% (355/628) of wells and springs in the Bennington area had perfluorooctanoic acid (PFOA) concentrations > 20 parts/trillion (ppt) (Vermont action level). The distribution of contaminated wells was complex, with very different PFOA concentrations in closely-spaced wells (<100 m apart). PFOA was introduced into the environment by a factory that produced Teflon™-coated fabrics from about 1978–2002. Manufacturing involved PFOA expulsion from smokestacks followed by atmospheric transport, deposition, and downward leaching to the aquifer system. The fractured rock aquifer was characterized through physical components (geologic mapping, spatial analysis of wells, and geophysical logging) to build a Three-dimensional conceptual model and then map the spatial distribution of chemical groundwater tracers (PFOA, major and trace elements, stable isotopes, and and recharge ages), adding a fourth temporal dimension. The field area consists of four imbricated metamorphic rock slices bounded by thrust faults. The dominant fracture sets that overprint these slices control the N-S and E-W topographic “grain.” Geophysical logging divided wells into those completed internal to or on the margins of thrust slices. Major and trace element analysis shows that groundwater can be spatially discriminated into carbonate (TDS, Ca, Mg, HCO 3 ), shaly (Sr, U, SO 4 ), and siliceous (K, Si) groups. Depleted H 2 O stable isotope signatures characterize the siliceous group. Recharge-ages determined from CFC11, 12, and 113 and tritium correlate with geochemical groups and were divided into “older” (~1953–73) and “younger” (1963–88), which predate and are synchronous with factory operation, respectively. Our conceptual model shows recharge from highlands to the west and east flowing toward the Bennington valley where it is locally tapped by wells along thrust faults or fracture zones. This water has older recharge ages and anomalously low PFOA concentrations (<6.7 ppt in 12 of 15 samples, mean = 7.9 ppt) compared to the majority of wells in this region, which are completed in the internal portions of thrust slices. These wells contain groundwater with younger recharge ages and high PFOA concentrations (mean = 290 ppt) and occurrence (>20 ppt in 28/36 samples), indicating mixing of younger and older waters.
... The polarization effect in the fault zone was interpreted by [17] in terms of fracture fields. The direction of the fracture cleavages expected for the HF was calculated using the package FRAP [59] (see the Appendix A in [17]). The model results suggested that for this fault kinematics, the predominant fracture cleavage is represented by synthetic cleavages (i.e., Riedel shear), that here develop with a mean azimuth of N4 • (the blue rose diagram in Figure 2D). ...
... A sketch representing the right-lateral fault movement in the N90° direction (black arrows), with the regional stress field (red arrows), and the kinematic components of the local stress field (K1 and K3). The expected fracture systems (cleavages and extensional fractures) calculated using the package FRAP [59] are illustrated as well. (D) The orientation of the expected predominant extensional fractures (blue rose diagram, mean azimuth of N139°), together with the combined results of ground motion polarization at stations ND6 and ND7 (red rose diagram). ...
... A sketch representing the right-lateral fault movement in the N90 • direction (black arrows), with the regional stress field (red arrows), and the kinematic components of the local stress field (K1 and K3). The expected fracture systems (cleavages and extensional fractures) calculated using the package FRAP [59] are illustrated as well. (D) The orientation of the expected predominant extensional fractures (blue rose diagram, mean azimuth of N139 • ), together with the combined results of ground motion polarization at stations ND6 and ND7 (red rose diagram). ...
Site effects refer to the modification of ground shaking caused by the local geological conditions that can result in the strong amplification of ground motion. The best-known cause for site effects is the presence of superficial soft soil deposits, which are considered in seismic design codes of many countries through the use of scaling factors. Rock sites are assumed to show no local site amplification. However, even at rock sites, seismic waves can be locally amplified at frequencies of engineering interest, with larger motion along one site-specific azimuth on the horizontal plane (the so called “directional site resonance or amplification”). These effects have been related to the presence of large-scale open cracks or microcracks in different geological environments (faults, landslides, volcanic areas) everywhere with a common signature: maximum amplification occurs transverse to the predominant fracture strike. In this paper, we summarize our main results obtained in the last decade with regard to several fault zones with different kinematics, where ground motion is polarized (and amplified) perpendicularly to the predominant fracture field as an effect of the stiffness anisotropy. In order to give a further constraint, we also show some cases where the directional amplification effects were compared with the S-wave splitting analysis method.
... La ricostruzione tettonica di un settore crostale prevede l'analisi di dati strutturali raccolti in terreno (faglie, fratture, foliazioni, etc.). Una delle attività svolte è stata proprio quella di utilizzare i dati di faglia per la determinazione, attraverso l'utilizzo del software Daisy3 (Salvini et al., 1999;Salvini, 2017), del paleo-campo/i di stress responsabili della deformazione osservata e della loro relazione con la cinematica delle due faglie. ...
... Angelier, 1979Angelier, , 1984 basate sull'equazione di Bott (1959) che calcola la direzione di scivolamento sul piano di faglia parallela allo sforzo tangenziale massimo sul piano: il tensore di stress risultante sarà quello per cui lo scarto tra il valore misurato e quello teorico dell'angolo di pitch sia minore per la totalità dei dati trattati, che appartengono alla stessa fase deformativa; o ancora con metodologia Montecarlo, che determina la condizioni di stress più favorevoli allo sviluppo della deformazione osservata attraverso il confronto con un grande numero di paleo-stress generati casualmente. In questo lavoro, per effettuare l'inversione delle faglie è stato utilizzato il software Daisy3 (Salvini et al. 1999;Salvini, 2017) analisi per ottenere il tensore/i di stress verosimilmente compatibile con la deformazione osservata. ...
... Per caratterizzare l'organizzazione spaziale del valore di H/S è stata analizzata la frequenza rispetto alla distanza dei valori di H/S attraverso l'utilizzo di transetti strutturali (Salvini et al. 1999), incluso come tool nel software Daisy3 fig. 18). ...
... The roof collapse of cavities commonly produces an inversely graded breccia with finer chaotic material at the base and coarser material towards the top (Loucks, 2001). Some LDBBs in the Gargano Promontory were previously described very briefly by Martinis and Pavan (1967), Salvini et al. (1999), Morsilli et al. (2004) and Jablonská et al. (2018). However, their spatial range, textural variation, and 3D geometry with respect to the regional structural setting have not yet been documented. ...
... The Gargano Promontory was affected by multiple phases of tectonic deformation (Salvini et al., 1999;Tondi et al., 2005). The Late Jurassic -Late Cretaceous is characterized by extensional tectonics (Graziano, 1999;Borgomano, 2000;Santantonio, 2012), whereas NE -SW -oriented horizontal compression was the most dominant in the Miocene -Pliocene (Bertotti et al., 1999). ...
... Fault-related breccias produced by abrasion and dilatation are well documented in large-scale fault zones (Walsh et al., 2008). In the Gargano Promontory, breccia of such a scale is related to the E-W oriented Mattinata Fault (Salvini et al., 1999), an important crustal fault that accumulated more than 2 km horizontal displacement (Tondi et al., 2005). (Fig. 14 C) The studied breccias also show convincing evidence of solution and collapse (Fig. 14 C). ...
Large discordant breccia bodies (LDBBs) are important record keepers of the tectonic and gravitational evolution in platform-to-basinal settings, and have important implications for fluid-flow migration and compartmentalization of tight carbonate reservoirs. In the Gargano Promontory of southern Italy, LDBBs occur within a Cretaceous slope and basinal carbonate succession. We use field mapping and Unmanned Aerial Vehicle (UAV) -based Structure from Motion (SfM) Photogrammetry to document otherwise inaccessible cliff-side exposures of seismic-to subseismic-scale vertical discordant breccias. LDBBs are up to 50 m in width, more than 80 m in height and display internal chaotic or aligned clast fabrics. The formation which generally contains the LDBBs is characterized by beds of cherty pelagic limestone intercalated with calcarenites, calciturbidites and horizons of mass transport deposits. The mass-transport deposits can be correlated across the chaotic breccia bodies, indicating only slight or no vertical displacement across the adjacent walls. The bases of the breccia bodies are always hidden below current sea level, while the rarely exposed tops are capped by bedded intervals of the host rock formation. Timing and origin of the studied breccias were determined using several lines of evidence, such as stratigraphic provenance of clasts in breccias, mutual relationships of structural and sedimentologic features, and previous studies which establish that the age of dolomitizing cements in the LDBBs formed at different times and by different processes (fault shearing and solution collapse). This work investigates the size, shape and geometry of these breccia bodies whilst also providing cm-scale detail of the textural features in otherwise inaccessible outcrops. We suggest that breccias formed as a result of solution exploiting a pre-existing fracture network characterized by large-scale vertical strike-slip or oblique-slip faults. Initial displacement along these faults created a wide fault damage zone, where fluid migration was later focused to create a zone highly susceptible to solution and subsequent periodic sidewall collapse.
... It is characterized by D 0 values < 1.6. Particle size analysis is therefore needed to better decipher and make inferences on the time-space evolution of micro-mechanisms responsible of the development of both crystalline and carbonate fault rocks (Sammis et al., 1987;Marone and Scholz, 1989;Blenkinsop, 1991;Salvini et al., 1999;Billi et al., 2003;Billi, 2007;Storti et al., 2007). Several cataclastic micro-mechanisms have been documented in carbonate rocks with low values of primary porosity (Billi et al., 2010, and references therein). ...
... Intragranular Extensional Fracturing (IEF), chipping, and shear fracturing have been addressed as the most common micro-mechanisms (Gallagher et al., 1974;Allegré et al., 1982;Hadizadeh and Rutter, 1982;Sammis et al., 1987;Biegel et al., 1989;Marone and Scholz, 1989;Blenkinsop, 1991;Sammis and King, 2007). Their localization within discrete fault rock volumes is interpreted as a major control of both size distributions and shapes of survivor grains (Blenkinsop, 1991;Salvini et al., 1999;Billi et al., 2003Billi et al., , 2003Billi et al., , 2005Billi et al., , 2007Storti et al., 2007) as well as the frictional properties of single fault zones (Han et al., 2010;Tisato et al., 2012;Di Toro et al., 2011;De Paola et al., 2011, 2015. IEF is common in the early evolutionary stages of cataclasis, developing grain-supported fault rocks with sub-angular, poorly sorted, survivor grains. ...
... Accordingly, the time-dependent evolution of cataclasis could be profoundly affected by the structural diagenesis of carbonate fault rocks (Laubach et al., , 2014. In fact, both chemical and physical compaction and cementation of fault rocks can modify the shape and size distribution of survivor grains (Rutter, 1983;Salvini et al., 1999;Gratier et al., 2003;Billi, 2010;. In this work, we integrate both microstructural investigation and statistical analysis to document the threshold values, distribution, and dimensional properties of inherited host rock fragments within natural carbonate fault rocks. ...
... A total of 28 faults were mapped and measured by use of the DEM filter ( Fig. 4b). Fault azimuths were then plotted as rose diagrams using the Daisy software (Salvini et al., 1999). Moment tensor data from three earthquakes cataloged as 071886A, 102684B, and 201704031740A in The Global Centroid-Moment-Tensor (CMT) catalog (Dziewonski et al., 1981;Ekström et al., 2012) were plotted into stereonets using the Daisy software (Salvini et al., 1999) and provided the relative movement of one group of NE-SW-striking faults and another group of NW-SE striking faults (Fig. 5). ...
... Fault azimuths were then plotted as rose diagrams using the Daisy software (Salvini et al., 1999). Moment tensor data from three earthquakes cataloged as 071886A, 102684B, and 201704031740A in The Global Centroid-Moment-Tensor (CMT) catalog (Dziewonski et al., 1981;Ekström et al., 2012) were plotted into stereonets using the Daisy software (Salvini et al., 1999) and provided the relative movement of one group of NE-SW-striking faults and another group of NW-SE striking faults (Fig. 5). ...
One of the three narrow rift belts that mark the southern end of the East African Rift System (EARS) intersects the Makgadikgadi Basin of northeastern Botswana. Although tectonic activity in the region is known to have influenced the evolution of these pans, the interrelationship between shoreline geometry, fault strikes, and the intersection of the underlying tectonic terranes has yet to be fully realized. We analyzed faults and subsurface structures in the region of the pans using a field investigation in combination with satellite imagery and geophysical data, to constrain the influence that the regional tectonic regime has had on the formation of the present-day pan geometry. We find that pan shorelines are controlled by the intersection of three preferred fault orientations which can be understood in the context of the “older” terranes they overlie, namely the Magondi Belt and the Limpopo Belt. We propose that the pronounced curvature of the southern Magondi Belt has influenced the eastward curvature of the rift-related faults and was likely produced by the impingement of the developing fold belt on the Zimbabwe Craton. Furthermore, limited focal mechanism solutions data from earthquakes north and south of the pans suggests a change in regional extension direction from NW-SE to NE-SW. Determining the relationship between these fault orientations and the underlying tectonic terrains is an important step in understanding the formation of the Makgadikgadi Basin, and more broadly the current tectonic regime of Botswana. The evidence of fault-controlled shorelines within an evaporitic environment may also have implications for regional groundwater activity.
... Although many authors agree that the MF (Figure 1B) is the main structure involved in the development of the GP sector, its kinematics is controversial. Many authors reported that MF had a left-lateral strike-slip kinematics (Funiciello et al., 1988;Salvini et al., 1999), but several researchers considered the hypothesis of a reactivation with right-lateral motion during the late Pliocene until today (Chilovi et al., 2000;Tondi et al., 2005). In contrast, many other authors have always considered this structure as a right-lateral strike-slip structure (Piccardi, 1998). ...
... It can be also observed, in the vertical cross-sections 3 and 4 (Figure 7), that in the NE of GP, seismicity is not present above 20 km and that earthquakes seem to concentrate around the area of the MF system, whose depth is estimated to range between 15 and 20 km (Piccardi, 1998;Valensise et al., 2004;DISS Working Group, 2018). For the MF shear zone, we assumed a depth of 20 km and a width of 4 km (Figure 7, green line and rectangle in vertical cross-sections) smaller than that assumed by Salvini et al. (1999) in order to reduce over-interpretation errors. ...
Historical seismic catalogs report that the Gargano Promontory (southern Italy) was affected in the past by earthquakes with medium to high estimated magnitude. From the instrumental seismicity, it can be identified that the most energetic Apulian sequence occurred in 1995 with a main shock of MW = 5.2 followed by about 200 aftershocks with a maximum magnitude of 3.7. The most energetic earthquakes of the past are attributed to right-lateral strike-slip faults, while there is evidence that the present-day seismicity occur on thrust or thrust-strike faults. In this article, we show a detailed study on focal mechanisms and stress field obtained by micro-seismicity recorded from April 2013 until the present time in the Gargano Promontory and surrounding regions. Seismic waveforms are collected from the OTRIONS Seismic Network (OSN), from the Italian National Seismic Network (RSN), and integrated with data from the Italian National Accelerometric Network (RAN) in order to provide a robust dataset of earthquake localizations and focal mechanisms. The effect of uncertainties of the velocity model on fault plane solutions (FPS) has been also evaluated indicating the robustness of the results. The computed stress field indicates a deep compressive faulting with maximum horizontal compressive stress, SHmax, trending NW-SE. The seismicity pattern analysis indicates that the whole crust is seismically involved up to a depth of 40 km and indicates the presence of a low-angle seismogenic surface trending SW-NE and dipping SE-NW, similar to the Gargano–Dubrovnik lineament. Shallower events, along the eastern sector of the Mattinata Fault (MF), are W-E dextral strike-slip fault. Therefore, we hypothesized that the seismicity is locally facilitated by preexisting multidirectional fractures, confirmed by the heterogeneity of focal mechanisms, and explained by the different reactivation processes in opposite directions over the time, involving the Mattinata shear zone.
... Within the fault core, the presence of tectonic stylolites and S-C structures evidences processes of pressure solution and/or frictional sliding [54,55]. Such processes are associated with contractional stress concentration and slip accommodation imposed by the advancing thrust [64,65]. By contrast, within the damage zone, the widespread presence of veins represents dilational sites where calcite precipitated [66,67]. ...
... The fluid-rock interaction is also recorded in the δ 18 O fluid obtained from clumped isotopes, yielding values between -1.8 and -0.1‰VSMOW. These values may result from interaction between meteoric waters, which have typically negative δ 18 O values, and marine carbonates, with δ 18 O values around 0‰PDB [64]. This fact is supported by the calculated Mg/Ca and Sr/Ca molar ratios, indicating the involvement of meteoric fluids, and the diluted elemental composition in Cc1 with respect to Cc0, showing lower REY concentration and lower Mg, Mn, and Sr contents (Figure 12(a)). ...
A well exposed thrust in the Southern Pyrenees was selected to characterize the transfer of fluids along and across a fault zone and to determine the thrust behavior as conduit or barrier to fluid migration. The studied thrust juxtaposes a Cenomanian-Turonian carbonate sequence in the hanging wall against a Coniacian carbonate succession in the footwall. Structural data, and petrological and geochemical analyses applied to calcite veins and host rocks, reveal different diagenetic histories between the footwall and the hanging wall. Such differences are interpreted to result from the low permeability of the foliated cataclasite. Within the footwall, three fracture sets (F1 to F3) and a chaotic breccia have been recognized. F1 to F3 fractures were cemented by three generations of calcite cement, Cc1 to Cc3, respectively, whereas the breccia was cemented by Cc1 and Cc2. Results suggest that during the development of fractures F1 to F3, the fluid regime changed from percolating meteoric waters, at temperatures around 50 ºC, to upward migrated formation fluids, at 110 ºC. Contrary to the footwall, the hanging wall was only affected by a crackle breccia cemented by calcite cement Cc4, which is the same cement recognized on the main thrust plane. Cc4 precipitated from formation waters migrating upward along the thrust plane, at 95 ºC. Therefore, during deformation, the studied thrust acted as a transversal seal and as a longitudinal path for fluids.
... Within the fault core, the presence of tectonic stylolites and S-C structures evidences processes of pressure solution and/or frictional sliding [54,55]. Such processes are associated with contractional stress concentration and slip accommodation imposed by the advancing thrust [64,65]. By contrast, within the damage zone, the widespread presence of veins represents dilational sites where calcite precipitated [66,67]. ...
... The fluid-rock interaction is also recorded in the δ 18 O fluid obtained from clumped isotopes, yielding values between -1.8 and -0.1‰VSMOW. These values may result from interaction between meteoric waters, which have typically negative δ 18 O values, and marine carbonates, with δ 18 O values around 0‰PDB [64]. This fact is supported by the calculated Mg/Ca and Sr/Ca molar ratios, indicating the involvement of meteoric fluids, and the diluted elemental composition in Cc1 with respect to Cc0, showing lower REY concentration and lower Mg, Mn, and Sr contents (Figure 12(a)). ...
Petrographic and geochemical analyses (δ¹⁸O, δ¹³C, ⁸⁷Sr/⁸⁶Sr, clumped isotopes, and elemental composition) coupled with field structural data of synkinematic calcite veins, fault rocks, and host rocks are used to reconstruct the episodic evolution of an outstanding exposed thrust zone in the Southern Pyrenees and to evaluate the fault behavior as a conduit or barrier to fluid migration. The selected thrust displaces the steeply dipping southern limb of the Sant Corneli-Bóixols anticline, juxtaposing a Cenomanian-Turonian carbonate unit against a Coniacian carbonate sequence. Successive deformation events are recorded by distinct fracture systems and related calcite veins, highlighting (i) an episodic evolution of the thrust zone, resulting from an upward migration of the fault tip (process zone development) before growth of the fault (thrust slip plane propagation), and (ii) compartmentalization of the thrust fault zone, leading to different structural and fluid flow histories in the footwall and hanging wall. Fractures within the footwall comprise three systematically oriented fracture sets (F1, F2, and F3), each sealed by a separate generation calcite cement, and a randomly oriented fracture system (mosaic to chaotic breccia), cemented by the same cements as fracture sets F1 and F2. The formation of fractures F1 and F2 and the mosaic to chaotic breccia is consistent with dilatant fracturing within the process zone (around the fault tip) during initial fault growth, whereas the formation of the latest fracture system points to hybrid shear-dilational failure during propagation of the fault. The continuous formation of different fracture systems and related calcite cementation phases evidences that the structural permeability in the footwall was transient and that the fluid pathways and regime evolved due to successive events of fracture opening and calcite cementation. Clumped isotopes evidence a progressive increase in precipitation temperatures from around 50°C to 117°C approximately, interpreted as burial increase linked to thrust sheet emplacement. During this period, the source of fluid changed from meteoric fluids to evolved meteoric fluids due to the water-rock interaction at increasing depths and temperatures. Contrary to the footwall, within the hanging wall, only randomly oriented fractures are recognized and the resulting crackle proto-breccia is sealed by a later and different calcite cement, which is also observed in the main fault plane and in the fault core. This cement precipitated from formation fluids, at around 95°C, that circulated along the fault core and in the hanging wall block, again supporting the interpretation of compartmentalization of the thrust structure. The integration of these data reveals that the studied thrust fault acted as a transverse barrier, dividing the thrust zone into two separate fluid compartments, and a longitudinal drain for migration of fluids. This study also highlights the similarity in deformation processes and mechanisms linked to the evolution of fault zones in compressional and extensional regimes involving carbonate rocks.
1. Introduction
The study of outcrop analogues in fractured carbonate reservoirs is important to better understand the characteristics and evolution of synkinematic fracture systems and their control on fluid migration during crustal deformation [1–4]. In areas undergoing compressional regimes, the largest fluid fluxes, mass transfer, and heat transport commonly occur along the main thrust faults and related fracture networks because of the loading induced by thrust sheet emplacement [5–7]. By contrast, fluid flow rates in adjacent rock-matrix and poorly connected synkinematic fractures are commonly very low and fluid composition are often rock-buffered [6, 8]. In some cases, the development of thrust systems may also inhibit vertical fluid transport inducing fluid overpressure [9–11] leading to hydraulic fracturing [12–14]. Whether a fault zone will constitute either a conduit or barrier to fluid migration depends, among other factors, on the architecture of the fault zone and the permeability associated with the developed structures [15, 16]. Since the fault zone consists of a fault core, which is usually formed of low-permeability fault rocks, and a damage zone, which mainly includes extensional fractures and faults, overall permeability of the fault is conditioned by the amount, the spatial distribution, and the internal composition of these two fault zone elements [15, 17]. Besides, such structural permeability is dynamic and may vary spatially and temporally across the fault zone due to successive episodes of fracture opening and cementation [18, 19].
Although numerous studies based primarily on structural and numerical data have provided conceptual and analytical models on the architecture, mechanical properties, and fluid flow along fault zones [7, 15, 20], there exist only a few studies coupling field data and geochemistry of synkinematic minerals filling fractures that characterize the fluid migration through a thrust zone [21–25] and its spatial behavior as a conduit or barrier system [26, 27]. An outstanding exposed thrust in the Southern Pyrenees was chosen as a case study to evaluate qualitatively the fault-related permeability and its control on the fluid flow within and around the fault zone. Here, we combine structural, petrological, and geochemical data of calcite veins and host rocks present in the studied thrust zone. Therefore, the main objectives of this paper are (i) to determine the origin, composition, and temperature of the vein-forming fluids and the timing of fluid migration in relation to the fracturing events and (ii) to discern the fluid pathways, the extent of fluid-rock interaction, and the transfer of fluids across a fault zone during thrusting. The field and lab results are then compared with other studies reporting fluid flow within fault zones in other geological settings to generalize our conclusions to fault zones in carbonate settings.
2. Geological Setting
The Pyrenees constitute an asymmetrical and doubly verging orogenic belt that resulted from the Alpine convergence between the Iberian and European plates from Late Cretaceous to Oligocene, causing the inversion of previous Mesozoic rift basins and their incorporation into the thrust system [28–32]. The Pyrenean structure consists of a central antiformal stack of basement-involved thrust sheets from the axial zone [30], flanked by two oppositely vergent fold-and-thrust belts and their related Cenozoic Aquitaine and Ebro foreland basins [30, 33] (Figure 1(a)).
(a)
... Left-lateral, strike-slip motion post-dating the early Cretaceous, as well as Pleistocene to present-day tectonic activity are well constrained along this strike-slip corridor (Argnani et al. 2009). A change from right-to left-lateral strike-slip motion has been proposed within this corridor based on local studies (Salvini et al. 1999;Tondi et al. 2005). Schettino and Turco (2011) used the Mattinata fault trend to accommodate Cretaceous motion in their reconstruction. ...
In plate kinematic reconstructions, the restoration of rifted margins and their fossil equivalents exposed in orogens remains challenging. Tight fit reconstructions rely on the mapping of margins rift domains, their restoration to their pre-rift crustal thickness, and the removal of the oceanic and exhumed mantle domains. At present-day margins, high-resolution wide-angle seismic imaging allows mapping and measurement of rift domains; however, restoring fossil margins is trickier because they are largely overprinted and partially lost during convergence. Here, we present a new kinematic model for the Mesozoic rifting along the Tethys–Atlantic junction, which relies on two assumptions: (1) the width of the fossil Alpine Tethys rift domains was comparable to that of their present-day analogs, and (2) the necking zones of the former tectonic plates can be mapped, dated and used as kinematic markers. This reproducible workflow allows us, for the first time, to restore the rifted margins of the Alpine Tethys. Our reconstruction shows: (1) a westward propagation of extension through the Ionian, Alpine Tethys and Pyrenean rift systems from the Triassic to the Cretaceous, (2) the segmentation of the Mesozoic Tethyan rifted margins by strike-slip corridors, (3) the opening of an oceanic gateway at 165 Ma as mantle was exhumed along the entire Alpine Tethys and (4) the subdivision of the Mesozoic oceanic domain into compartments that were later consumed during subduction. This new model is supported by published data from the Alps, the Ionian Sea, the Pyrenees and the southern North Atlantic.
Graphical abstract
... The extracted lineaments (mapped in Figure 2) were accumulated into a database and analyzed using the DAISY3.5.28 software [88] to identify the lineament domain through a polymodal Gaussian grid analysis according to methods presented in [5,84]. A significant number of lineaments cluster into domains: groups of lineaments with orientations about a given azimuth. ...
Regional-scale swarms of subparallel linear topographic features, known as lineament domains, are a common feature of planetary surfaces. Lineament domains are superficial manifestations of the crustal stress field trajectory. Notably, one of the effects of active tectonics is seismicity. Italy is one of the most seismically active regions in the Mediterranean, with many destructive earthquakes that have occurred in past centuries. Here, we assess the seismic meaning of the main lineament domain in the tectonically active region of Central Italy. We describe the use of an automated analysis of satellite imagery coupled with spatial grid analysis to identify three lineament domains of the Central Apennines. Spatial and azimuthal comparisons of the main lineament domain (i.e., the Apennine Domain), with the known locations of earthquakes (moment magnitude of Mw > 5.5) that occurred during the past century, revealed the most seismically active tectonic areas and their spatial distributions. Further, we present a conceptual seismo-geodynamic model for the Central Apennines, which is characterized by regional arching and explains the presence of an extensional tectonic regime in the upper crustal layer of the active Apennines fold-and-thrust belt.
... Geostatistical analysis of the mapped structures included azimuthal analyses of their orientation either by frequency (upper part of the rose diagrams in Fig. 7) or cumulative length (lower part of the rose diagrams in Fig. 7). This was performed using a polymodal procedure that included the best fit with a family of Gaussian curves that represented independent azimuthal groups within each system (Wise et al., 1985;Salvini et al., 1999;Cianfarra and Salvini, 2016b;Maggi et al., 2016). In this way, each Gaussian peak corresponds to a preferential orientation with its statistical parameters, namely, its modes, and the related mean azimuth and angular standard deviation (sd). ...
The Claritas Fossae (CF) is an elongated system of scarps and depressions >900 km long, representing the western boundary of the Thaumasia Region to the south of the Tharsis volcanic province. Although there is general agreement on the tectonic nature of such major physiographic feature, the processes that led to its formation are still debated. This study aims to better understand the tectonic evolution of the CF by combining two methodologies: kinematic numerical modelling and structural mapping. Through kinematic numerical modelling, we reproduce the present-day long-wavelength topography (hundreds of kilometres) at CF along four across-strike topographic profiles through the activity of a crustal listric normal fault. We observe that the modelled fault reaches the base of the crust, located at 80 km of depth, without changes in its listric geometry, suggesting a rather homogeneous thick crust. The accuracy of the results is based on the calculated mean misfit between the Martian and modelled topography. In two of the four profiles, the misfit is locally relatively higher, suggesting that the normal dip-slip component alone hardly explains the entire tectonic setting. Through structural mapping, we explore the depressions and scarps that feature the entire study area. We identify four sets
of lineaments with different kinematics. The angular and crosscutting relationships between the sets suggest a Riedel-type arrangement within a dextral strike-slip shear zone. Thus, we propose a tectonic evolutionary model of the CF that involves a polyphase evolution made up of a Noachian-Early Hesperian right-lateral strike-slip phase followed by a Late Hesperian-Early Amazonian transtensional reactivation characterised by a significant normal dip-slip component. Our results suggest that the tectonics on Mars were not exclusively single or longterm deformations and that multiple subsequent tectonic events may have contributed to the present-day setting.
... The later year is also known to have been affected by a severe drought in the investigated region (ARPAE, 2023). Salvini et al., 1999) reporting the strike values of faults mapped in the study area. The red field (named 1) represents the dominant trend, while the purple field (named 6) is the least representative. ...
Groundwater is a vital source of freshwater, serving ecological, environmental, and societal needs. In regions with springs as a predominant source, such as the Northern Apennines (Italy), resilience of these springs to climate-induced recharge changes is crucial for water supply and ecosystem preservation. In this study, Nadìa Spring in the Northern Apennines is examined through an unprecedented array of multidisciplinary analyses to understand its resilience and unique characteristics. The Nadìa Spring's exceptional response, characterized by a sustained base flow even in the face of drought, is attributed to a combination of factors including a substantial groundwater reservoir, a complex network of faults/fractures, slope instabilities, and karst dissolution. The investigation reveals a dual porosity system in the aquifer, consisting of fast-flow conduits and a diffuse fracture network. While fast-flow conduits contribute to rapid responses during high-flow conditions, the diffuse system becomes predominant during low-flow periods. This dual porosity structure helps the spring maintain a consistent base flow in the face of climate-induced recharge fluctuations. The study shows that Nadìa Spring exhibits remarkable resilience to year-to-year variations in recharge, as evidenced by stable minimum discharge values. While the spring has undergone a decline in discharge over the past century due to long-term climate change, it is becoming more resilient over interdecadal timescales due to transition to a diffuse drainage system that mitigates the impact of reduced recharge. The availability of a century-long spring discharge monitoring was a crucial piece of information for understanding the spring's discharge response and drawing conclusions about its long-term resilience to recharge fluctuations. Continuing long-term monitoring and research in the future will be essential to validate and expand upon these findings in the context of changing climatic conditions. This research serves as a model for assessing strategic groundwater discharge points in geological settings similar to the Northern Apennines.
... From oldest to youngest, the quartz veins are: 1) thin, subvertical, and curvilinear, 2) thin and foliation-parallel, and crosscut vein generation 1, and 3) thick and crosscut vein generations 1 and 2. The generation 1 and 2 veins could be related to thrust loading and subsequent shearing, respectively. Rose diagrams and contoured equal area nets (Salvini et al. (1999) for the dominant foliation (Sd) ("bedding") and fractures in the vicinity of the Franklin well. ...
... Although it is commonly considered a slight deformation structural domain with respect to the flanking ftb's, the structural setting of the Apulian Platform is rather complicated as it represents a zone of interaction between the neighboring opposite-verging chains. The kinematic models proposed for the whole central Mediterranean area consider the Apulian Platform as part of the Adria microplate [8][9][10], which was dissected since Late Cretaceous by a major, left-lateral tectonic lineament crosscutting the whole continental lithosphere [11][12][13]. Within the Apulian Platform, the presence of Upper Cretaceous-Eocene, NE-trending structural grabens [14] were interpreted by Vitale et al. [15] as due to an abortive rift system Cretaceous-Paleocene in age. More recently, following the work of Korneva et al. [16], Laurita et al. [17], and Panza et al. [18,19], Agosta et al. [20] documented the occurrence of Cretaceous transtensional tectonics by investigating the structural control exerted by high-angle faults bounding the bauxite deposits exposed in the Murge Plateau of southern Italy. ...
This work focuses on a ca. 55 km-long extensional fault zone buried underneath the fore-deep deposits of the southern Apennines, Italy, with the goal of deciphering the Cenozoic fault growth mechanisms in the Outer Apulian Platform. By considering public 2D seismic reflection profiles , well logs, and isochron maps data, the study normal fault zone is interpreted as made up of four individual fault segments crosscutting Top Cretaceous, Top Eocene, Top Miocene, and Top Pliocene chrono-stratigraphic surfaces. The computed cumulative throw profiles form either bell-shaped or flat-shaped geometries along portions of the single fault segments. The computed incre-mental throw profiles also show an initial fault segmentation not corresponding with the present-day structural configuration. Data are consistent with the initial, post-Cretaceous fault segments coalescing together during Miocene-Pliocene deformation and with fault linkage processes localizing at the stepover/relay zones. Pleistocene faulting determined the evolution of a coherent fault system. The computed n-values obtained for the single time intervals by considering the maximum fault throw-fault length relations indicate that the fault segments formed scale-dependent geome-tries. Variations of these computed values are interpreted as due to the higher degree of maturity reached by the entire fault system during Miocene to Pleistocene deformation.
... The strike, dip angle, and dip direction were acquired from FMI log. Then, they were plotted on the lower hemisphere of stereonet in the Daisy software (Salvini et al., 1999). As a result, contour diagrams of poles, rose diagrams of strikes and dip directions, and histograms of dip angles were obtained. ...
Planar structures including stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces, and fractures of carbonate Early Triassic Kangan Formation were evaluated in the central Persian Gulf. Core X-ray computed tomography (CT), Fullbore Formation Micro-Imager (FMI) log, and cores were used to detect the structures. Furthermore, conventional borehole logging data, routine core analysis, and petrographic thin sections were employed to assess the reservoir properties. Stereographic projections demonstrated that the reservoir has two sets of planar structures. The first group contains shallowly-dipping structures, consisting of stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces. These structures have been created by sedimentary and diagenetic processes. The other set includes deformation-related structures that are steeply-dipping and occurred scarcely, like fractures. Spearman correlation coefficients between the frequency of each planar structure and reservoir characteristics (porosity and permeability) were calculated to reveal the numerical relationship between the parameters. The significant correlation coefficients indicate that stylolites, solution seams, and filled tension gashes diminish reservoir quality while bedding and cross-bedding surfaces have enhanced reservoir characteristics. The strongest correlation was observed as a strong negative relationship between the frequency of stylolites and permeability in K2 reservoir unit. This study implies that sedimentary and diagenetic factors are more effective in controlling the reservoir quality than deformation factors in the studied formation. The present work also indicates that each used method has unique advantages and disadvantages. Therefore, simultaneous utilization of the methods to investigate planar structures would have the best efficiency.
... The major lineament patterns were also classified according to the dominant bending deformation (horizontal or vertical lineament). The lineament azimuths of the two data sets, the vertical and horizontal curvature, were statistically analyzed by polymodal Gaussian fitting (Salvini et al., 1999;Wise et al., 1985) to identify predominant domains. ...
The present paper investigates the oil migration and lineament distribution in fault zones within a sedimentary basin, showcasing the results from an integrated use of geochemical, and remote sensing data along the Fazenda Belém Fault Zone (FBFZ) in the Potiguar Basin, Brazilian Equatorial Margin. Lineaments were detected from a LiDAR digital elevation model data set using the quantitative method of morphology recognition based on horizontal and vertical curvature calculation and mapping. The polynomial regression-based spatial distribution of 20S/(20S + 20R) C29 steranes is successfully used in oils from offshore and onshore reservoirs of the Potiguar Basin, tracing field-scale oil migration direction. These multidisciplinary analyses revealed that the oil initially migrated from an offshore area along the NE-oriented fault zone, and then parts moved along the branches of this zone to finally reach the areas of the onshore reservoirs. In addition, NE-oriented lineaments enhanced the near-surface fluid circulation, while they commonly correspond to the topographic features and fault zones. Anisotropy tensors and slip- and dilation tendency calculated from the lineament map also indicate that the geometric complexity of the lineament pattern is influenced by present-day and partitioned stress fields in the Potiguar Basin. The integration of remote-sensing and geochemistry analyses at the FBFZ area proved to be effective in approaching the tectonic aspects of a fault zone in a petroleum basin, as well as in investigating the field-scale migration of oil along the fracture corridor in a fault zone.
... A total of 28 faults were mapped and measured by use of the DEM filter. Fault 114 azimuths were then plotted as rose diagrams using the Daisy software (Salvini et al., 1999). 115 Moment tensor data from two earthquakes cataloged as 071886A and 102684B in The Global ...
... We analyzed structural data from scanlines using a combination of cross-plots, stereonet projections, rose diagrams, and histograms . For analysis we used software including DAISY 4.96.5 (Structural Data Integrated System Analyser; Salvini et al., 1999), Python 3.0 Jupyter notebook scripts and MSOffice Excel 2012. ...
... Conversely, those characterized https://doi.org/10.1016/j.marpetgeo.2019.104045 Received 15 May 2019; Received in revised form 8 September 2019; Accepted 12 September 2019 by a low amount of primary porosity often deform by means of combined opening-mode and/or pressure solution-assisted deformation mechanisms (Rispoli, 1981;Peacock and Sanderson, 1995;Willemse et al., 1997;Salvini et al., 1999;Graham et al., 2003;Agosta and Aydin, 2006;Agosta et al., 2009Agosta et al., , 2012Antonellini et al., 2008;Aydin et al., 2010;Lamarche et al., 2012;Korneva et al., 2014;Wennberg et al., 2016;Parrino et al., 2019). In particular, platform carbonates form either massive or layered successions depending upon their original depositional environment and diagenetic evolution (Lavenu et al., 2014(Lavenu et al., , 2015Rustichelli et al., 2016;Tavani et al., 2016;Panza et al., 2019). ...
We construct an innovative static-dynamic integrated workflow capable of bridging the gap between input geological data, inherent to a lacustrine carbonate outcrop containing karst geobodies, and the description of the flow patterns and quantification of the multi-well productivity index (MWPI) for a particular well configuration in the outcrop. The workflow incorporates additional features stemming from the use of Machine Learning-based methods to mitigate lack of data in the locations away from the sections of input signals, along with the construction of new upscaling methods to assess the MWPI matrix. The ML-enhanced geostatic model hinges upon shallow surface geophysical data collected using Ground-Penetrating Radar (GPR) techniques. Furthermore, by discretizing the flow equations and adopting a flow-based upscaling method, we construct correlations between well flow rates and pressure drawdown in a typical five-spot well configuration. In this setting, we analyze the sensitivity of each well productivity with respect to heterogeneity distribution and correlations in the karst system within the outcrop. Computational simulations illustrate the ability of the integrated workflow proposed herein to improve prediction of hydraulic-connectivity between well pairs, which appear manifested in the entries of the MWPI matrix, whose magnitude aims at quantifying the effects of the karst geobodies upon geofluid production.
... According to the classic structural criterions like strike and dip of fault and bedding, pitch angle of slickenline and kinematic indicators on the polished fault surface (i.e Riedel shears and steps) (Petit, 1987;Doblas, 1998;Fossen, 2010), 145 brittle and ductile structures were measured (supplementary material 1) in 34 station across the study area (supplementary material 2). All structural measurements were analyzed by the Windows program DAISY V5.39 (Salvini et al., 1999;http://host. uniroma3.it/progetti/fralab/Downloads/Daisy_Program/) for projecting brittle and ductile structural data and obtaining the maximum compression orientation (stress inversion). ...
The Central Iranian Micro-plate (CIM) is a dismembered piece of northern Gondwana. The aim of this study is to reconstruct the post-Early Cretaceous structural evolution of the western edge of CIM in the light of the integration of regional to the micro-scale structural data with minor Anisotropy of Magnetic Susceptibility (AMS) analyses. Our original field measurements on the structural architecture of the study area show main NW-SE and E-W structural trends that are accompanied by structural evidence for superposition. However, paleostresses obtained from fault and fold analysis (stress inversion method on faults and statistically π‐plane and β‐axis solution on folds), statistical Fry center-to-center analysis on the oriented thin-sections integrated with AMS results suggest that the study area has experienced a NE-SW-directed compressional regime since Paleocene time followed by a post-Early Miocene, roughly N-S-directed, regional compressional regime. Furthermore, the results of this work confirm the consistency between regional-micro structural analysis and AMS analysis. The most of samples show composite (sedimentary + tectonic) magnetic fabric and intermediate arrangement in the orientation of the magnetic fabric. Reconciling our results with published structural and AMS data suggests the changes in the regional stress regime in the western CIM has been occurred in response to the long-term stress transition from the infant Late Cretaceous–Paleogene subduction of the Neo-Tethys Ocean to the mature Cenozoic stages of the Zagros collision and the consequent Neogene tectonic reorganization in the hinterland domains of the southern Eurasian plate
... Paleostresses orientations by fault and fracture inversions were performed to identify the regional deformation history. The statistical analyses and fault and fracture inversion have been performed using the Daisy3 freeware (v.522_e, Salvini et al. [94]; http://host.uniroma3.it/progetti/fralab/ accessed 29 November, 2021). ...
We present the effect of neotectonics in intracratonic settings as revealed by the surface, brittle deformation associated to a regionally-sized shear corridor, which affects Southeastern Bra-zil. The deformation zone is characterized by the presence of nearly orthogonal fracture sets, interpreted as systematic and non-systematic joints often cutting Quaternary deposits. An original methodology of fault and joint inversion by the Monte Carlo converging approach is used to infer multiple paleostress fields. The method provides the best orientation of the principal paleo-stresses responsible for the observed fracturing. At each step of the inversion process, structures are uniquely associated to the stress tensor that provides the lowest error. The results showed the poly-phased tectonic history of the shear corridor studied and paleostresses compatible with a regional strike-slip motion. Specifically, an E-W, left-lateral shear was followed by an E-W, right-lateral kinematics related to the post-Paleogene drifting of South American Plate and its clockwise rotation. The latter tectonic event is presently responsible for brittle deformation observed in Quaternary deposits. The proposed deformation corridor may represent the Cenozoic reactivation of an ancient weakness zone. We speculate that the described intraplate strike-slip deformation belt represents the continental prosecution of the Rio de Janeiro fracture zone.
... In the field, geometrical features, such as trace length and orientation, distribution, displacement, infill material, and also type and mode of deformation associated with fractures were analyzed. Structural data were statistically analyzed by Gaussian fitting automated techniques in order to detect different populations of fractures as well as the mean and standard deviation values (Salvini et al., 1999). ...
The Argentinean Andean region hosts a vast geothermal resource clustered by active magmatic and tectonic activity. One of the most studied geothermal areas is the Tuzgle-Tocomar geothermal system in Central Puna (NW Argentina). However, despite the existence of several studies since the 1970′s highlighting the geothermal potential of the area, only highly schematic and dissimilar conceptual models have been proposed for the Tocomar Geothermal System. This study presents new detailed geological-structural and hydrogeochemical data, together with in-situ permeability analysis of fault zones and Raman spectroscopic characterization of hydrothermal-alteration minerals. The electrical generating capacity has also been evaluated using the volumetric method and a stochastic approach. A new comprehensive conceptual model of the studied area was constructed highlighting the role of the Calama-Olacapato-El Toro (COT) fault-system in the circulation of hydrothermal fluids. The reservoir of the Tocomar geothermal system has a Na⁺-Clˉ(HCO3)ˉ composition and an estimated temperature of ∼235 °C. Such a reservoir is hosted in fractured Ordovician rocks and controlled by the COT-like Chorrillos transpressive fault at 1000–1500 m depth b.g.l. The water isotopic data and hydrological features indicate a regional recharge beyond the Tocomar sub-basin boundaries (>5000 m a.s.l.). Additionally, the main hydrothermal reservoir receives inputs of magmatic fluids from the degassing of the intra-crustal rhyolitic magma chamber of the Tocomar volcanic center. The Monte Carlo simulations suggest that the Tocomar geothermal system has a probable power production capacity above 1.23 MWe (P90), 6.18 MWe (P50) and 11.67 MWe (P10) at different confidence levels. All calculations were biased towards minimum values, thus a tighter definition of the resource size and fracture porosity would significantly impact on the predictions. Notwithstanding, the strategic position of the Tocomar geothermal field encourages move forward towards more in-depth exploration phases.
... The directional and length attributes of the identified lineaments were compiled into separate databases, and then analyzed by using the software Daisy 3 (http://host.uniroma3.it/progetti/fralab/; Salvini et al., 1999). A polymodal Gaussian fit was conducted to analyze the azimuthal frequency of our data and to identify the main trends or lineament domains as proposed by Wise et al. (1985). ...
The subsidence/uplift patterns of forearc basins are controlled by subduction dynamics and are strongly dependent on the nature of the margin (erosive vs. accretionary). Here, we explore the role that increased megathrust shear force plays in triggering and sustaining the short wavelength topography of coastal forearc regions at erosive margins, where subsidence is supposed to prevail. The northern Colombian coastal forearc contains a ~ 1000 m-high mountain range (Baudó Range) that abruptly stands-up for ~300 km along the northwestern Pacific margin of South America, where the buoyant Nazca plate is subducting at a shallow angle. Field observations and stratigraphic data of Cretaceous to late Neogene volcanic and sedimentary rocks, suggest that the Baudó Range has been uplifting since the middle-late Miocene. The uplift seems to continue nowadays as evidenced by the irregular cliffed and bluffed coastline, steep slopes and high topographic ruggedness in one of the wettest regions on Earth, where weathering and landscape smoothing is expected to be intense. Earthquake focal mechanisms, together with regional-scale N-S-trending sinistral reverse fault structures, west-verging folding, and NW- and NE-oriented topographic lineaments, seems to be related to a trench-perpendicular mostly compressional stress regime. The residual topography along the coastal range of the northern Colombian forearc indicates under-compensation, which may suggest that the relatively thin (~20 km-thick) crust cannot support isostatically the observed topography. We propose that increased shear force along a wide seismogenic zone linked to the shallow subduction of the Nazca plate and a poorly lubricated interface, due to limited sediment dispersal into the trench, drive the ongoing topographic uplift of the region. In contrast, the smoother relief and lower elevations in the southern Pacific coast of Colombia could be explained by a deficit of shear force available to support higher topography
... This domain corresponds to a structural high constituted of a thick succession of Mesozoic carbonates forming a gentle and asymmetric anticline dissected by an active and complex array and linkage of faults. In this tectonic context, "pull-apart basins" develop, linked to the strike-slip and extensional tectonics filled by late Pleistocene continental deposits shaped by processes of karstic origin [61][62][63][64]. This domain is morphologically characterized by a large central karst plateau with a succession of reliefs and depressions and karst landforms represented by dolines, structurally controlled poljes, and remnants of karst surfaces testify intense dissolution processes on the fracture network due to the intense tectonics. ...
A first-order seismic characterization of Northern Apulia (Southern Italy) has been provided by considering geological information and outcomes of a low-cost geophysical survey. In particular, 403 single-station ambient vibration measurements (HVSR techniques) distributed within the main settlements of the area have been considered to extract representative patterns deduced by Principal Component Analysis. The joint interpretation of these pieces of information allows the identification of three main domains (Gargano Promontory, Bradanic Through and Southern Apennines Fold and Thrust Belt), each characterized by specific seismic resonance phenomena. In particular, the Bradanic Through is homogeneously characterized by low frequency (<1 Hz) resonance effects associated with relatively deep (>100 m) seismic impedance, which is contrasting corresponding to the buried Apulian carbonate platform and/or sandy horizons located within the Plio-Pleistocene deposits. In the remaining ones, relatively high frequency (>1 Hz) resonance phenomena are ubiquitous due to the presence of shallower impedance contrasts (<100 m), which do not always correspond to the top of the geological bedrock. These general indications may be useful for a preliminary regional characterization of seismic response in the study area, which can be helpful for an effective planning of more detailed studies targeted to engineering purposes.
... These data were inverted to obtain the paleostress directions using the computer software Daisy v522e (http://host.uniroma3.it /progetti/fralab/; Salvini et al, 1999;Storti et al., 2005). Fault inversion was conducted after back tilting the bedding to a supposed depositional angle of 3 • toward the northern quadrants (e.g., Blair and McPherson, 1994) to reconstruct the orientation of the principal paleostress axes (σ1, σ2 and σ3) at the time of sedimentation. ...
Abstract
The upper plate of the Arabia-Eurasia collision zone experienced orogen-perpendicular to orogen-parallel extension from 25-22 to 10-9 Ma. Although such an extension occurred during widespread collisional deformation, it is not clear if it is a local feature or if represents a major phase of upper plate extension. In this study we combine anisotropy of magnetic susceptibility (AMS) with fault kinematic analysis and sedimentologic data from 16.2- to 7.6-My-old deposits of the Upper Red Formation of the intermontane Tarom Basin (NW Iran). These strata present syndepositional, normal faults and offer the possibility to gain new insights into the spatial extent of such a Miocene extension. AMS data from the central and northern sectors of the basin document a tectonic fabric with a magnetic lineation parallel to the strike of the orogen, suggesting a compressional tectonic overprint. Conversely, the southern margin of the basin presents a purely sedimentary magnetic fabric despite a ∼ NE–SW orogen-perpendicular extension. This suggests that basin formation was not driven by extensional tectonics. Rather, the normal faults are gravity instabilities induced as also documented by coeval landslide deposits. This allows concluding that the orogen-perpendicular extension observed in few sectors of the collision zone is not regionally pervasive and hence it is not controlled by large-scale processes. Combined, our results indicate that if orogen-parallel extension associated with tectonic denudation and metamorphic core complex development occurred in certain sectors of the collision zone (Takab complex), it must have ended before 19-16 Ma, when widespread upper plate contractional deformation started.
Keywords
orogen-perpendicular extension, orogen-parallel extension, Arabia-Eurasia collision zone, Anisotropy of Magnetic Susceptibility (AMS), synsedimentary normal faults, Tarom intermontane basin basin
... The kinematics of fault slip were mainly identified based on classical criteria on polished fault surfaces (e.g., Petit, 1987;Fossen, 2010). Structural analysis consisting of paleostress inversion and statistical analysis of the measured fault slip and bedding data, respectively, were performed with the Windows program DAISY v5.3 (Salvini et al., 1999) in order to obtain the paleostress directions of the region through time. Furthermore, a NE-SW-trending structural cross section, oblique to the general trend of the study area, has been drawn upon the measured structural data to illustrate the relation between ore body and structural architecture of the Komsheche mine. ...
The Triassic carbonate-hosted Komsheche deposit of Central Iran, in the central segment of the Alpine-Himalayan orogen, is an ideal test site for tectonic-controlled ore formation processes. The mineralization consists of barite, fluorite, minor galena, and subordinate pyrite and chalcopyrite, and gangue minerals of dolomite, quartz, siderite, organic material, and calcite. Radiogenic isotopes point to multiple sources. The Pb composition in galena indicates an origin of Pb from upper crustal material. Barite generations II and III have ⁸⁷Sr/⁸⁶Sr = 0.709147 to 0.709595, higher than those of the Triassic host rocks, but more similar to the composition of Paleozoic basement and Miocene seawater. The chondrite-normalized REE patterns of fluorite crystals are subhorizontal with slightly negative or no Eu anomalies and weak enrichment of the MREE. The composition of fluorite, combined with the Pb and Sr isotopic data, reflects a process of fluid-rock interaction for the mineralizing fluids along favorable lithological and structural sites. The anatomy of the Komsheche deposit is dominantly controlled by the fault architecture. The (U-Th)/He thermochronology of fluorite grains from Komsheche yields a range of ages from Early Cretaceous to Pliocene, in concordance with the multistage tectonic evolution of the Zagros orogen. Our proposed model is that the barite-fluorite deposits of Central Iran formed during alternating tectonic episodes, including Early Cretaceous extension, post-Cretaceous - Oligocene compression, Oligo-Miocene extension, and finally Miocene and younger compression. The spatial-temporal correlation of our results with those of other studies along the Alpine-Himalayan and Atlas Mountains domains reveal a tight coupling between tectonism and formation of sediment-hosted fluorine-bearing (±Ba, Pb±Zn) deposits throughout the Mesozoic and Cenozoic. Incipient deposits formed in the Mesozoic along extension-related basement faults and subsequent deposit generations formed during reactivation / inversion of pre-existing structures.
... The tectonic structures of Enceladus' SPT were mapped (Section 3.1) using a geographic information system geodatabase and were statistically analyzed by means of DAISY3 (Salvini et al., 1999) and SID software for automatic lineament identification . The data are available in Rossi (2020). ...
The South Polar Terrain (SPT) of Enceladus is a site with eruptions of gas and water ice particle plumes, which indicate internal geodynamic activity. These eruptions are located along a series of tectonic structures, that is, the Tiger Stripe Fractures (TSF), which are composed of regularly spaced, linear depressions. The SPT is surrounded by sinuous chains of ridges and troughs (the Marginal Zone). To unravel the tectonics that affect the region and its evolution, we performed specific structural mapping and quantitative analyses of brittle features from remotely sensed images. The results are consistent with a block rotation model, in which several tectonic regimes coexist. The TSF are left‐lateral strike‐slip faults that bound rigid elongated blocks. The blocks rotate clockwise and are enclosed in a regional scale right‐lateral kinematic framework expressed in the Marginal Zone. These two opposite and complementary kinematic regimes induce transtensional and transpressional regimes within the SPT. An evolutionary tectonic model is proposed for the past and future evolution of the SPT. This model confirms the role of tectonic‐related kinematics in icy satellites and contributes to preparations for future missions.
... The structural measurements on the post-Neogene faults in the study area reveal the WNW-ESE trend of the strike-slip faults with the shallow plunging of the slicken lines (Fig. 14). The post-Neogene paleostress analysis using the stress inversion method based on the rotax analysis (Wise and Vincent, 1965;Salvini and Vittori, 1982;Salvini et al., 1999;Storti et al., 2006;Tavani et al., 2011) option in the Daisy software (version: 5.38) on the post-Neogene faults indicated the WNW-ESE trend for maximum principal stress (σ1) with a subvertical σ2 axis (Fig. 14d). ...
In this study, the analytical hierarchy process (AHP) was used to enhance the accuracy of the results obtained from the geomorphic analysis of tectonic activity. For this purpose, the relative tectonic activity index was computed by applying different and specific weights to each index based on the general geological and structural conditions of the study area. The Kuh-e-Sarhangi Mountain with a NE-SW strike is located in the northern part of the Tabas Block in the Central Iran Plate. The Kuh-e-Sarhangi Fault is considered one of the major faults in Central Iran and shows evidence of Quaternary activity. In this study, in order to evaluate the activity of the faults, six morphotectonic indices were computed and the different conditions which influenced the morphometric factors were considered and analyzed. The relative tectonic activity of Kuh-e-Sarhangi was classified based on the analytical hierarchy process method. These results were confirmed by field studies. The results of this method fitted well with some independently detected Quaternary faults and other reactivated faults in the Kuh-e-Sarhangi Mountain. With a right-lateral movement, some of these faults have caused the displacement of rivers up to 900 meters. The dispersal of the high tectonic activity classes based on the AHP method conforms to the post-Neogene activity of the region. The distribution of the classes illustrates that morphotectonic anomalies correspond with the incised alluvial fans and terraces and the bisected and displaced rivers in the study area. Accordingly, the integration of the results of field investigations, satellite images, morphometry, and the AHP method shows a high accordance with the active structures and demonstrates that the study area is tectonically active. This analysis illustrates the recent movements of the Kuh-e-Sarhangi Fault and the activity of the Lut Block due to the convergent movement of the Arabian plate toward Eurasia.
... According to the Koehn et al. (2016) classification, the stylolites in our study area are wave-like type stylolites. Bed-perpendicular stylolites formed and were subsequently reactivated as shear-fractures (Petit and Mattauer, 1995;Salvini et al., 1999;Thomas et al., 2012;Watkinson and Geraghty Ward, 2006) in a mixed dip-slip/strike-slip regime (Rabelo et al., 2020) (e.g., Fig. 2B). In addition, two main sets of cross-orthogonal, bed-perpendicular fractures and veins strike ~ N-S and ENE-WSW to WNW-ESE, respectively (Figs. 6E and 9C, D). ...
Epigenetic karstic systems in carbonate rocks commonly result from progressive dissolution by acidic meteoric waters over thousands to millions of years. The generation of secondary porosity and permeability improvement due to dissolution in carbonate reservoirs of geofluids (e.g., groundwater, hydrocarbons, and CO2) can profoundly impact reservoir storage capacity and subsurface fluid flow. This study investigates the control of structural discontinuities such as stylolites, fractures, and primary sedimentary discontinuities on the generation of multiscale karst dissolution cavities by epigenetic fluid percolation in a Late Cretaceous carbonate sequence
(Jandaíra Formation) in the Potiguar Basin, Northeastern Brazil. The study relies on micro- and macroscale analyses such as stratigraphic logs, field structural investigations, rock strength data collected in the field (Schmidt hammer), microtomographic and drone images, thin section analyses, porosity and permeability laboratory measurements. The results show that bed-perpendicular stratabound and non-stratabound stylolites and fractures can be enlarged due to meteoric water percolation until they merge and form a single channel system
that crosscuts all sedimentary multilayers. Bed-parallel stylolites are ubiquitous in carbonate sequences overprinting bed interfaces and layers. Where not dissolved, bed-parallel stylolites have low porosity and permeability and thus can act as barriers to vertical fluid flow. Where dissolved, such stylolites can contribute to horizontal fluid flow and form channel porosity. The results of this study led to a formulation of a conceptual model of rock dissolution along structural and sedimentary discontinuities that affects carbonate rock successions in the subsurface.
... Quite controversial is the kinematics of this structure (see Argnani et al., 2009, for a review). It has been interpreted as right-lateral (Bosellini et al., 1993;De Dominicis and Mazzoldi, 1989;Doglioni et al., 1994;Finetti et al., 1989;Guerricchio, 1986), left-lateral (Billi et al., 2007;Favali et al., 1993;Funiciello et al., 1992;Salvini et al., 1999), right-to left-lateral inverted (de Alteriis, 1995;Gambini and Tozzi, 1996) or a reverse fault (Ortolani and Pagliuca, 1989). ...
Seventeen layers characterized by soft-sediment deformation structures (SSDS) were identified within the “calcari di Fiumicello”, an upper Messinian (Miocene) stratigraphic unit (30 m thick), cropping out in the northern sector of the Gargano Promontory (Apulia, southern Italy). Facies analysis was performed on the whole outcrop and detailed sedimentological investigations were carried out on the deformed beds, in order to interpret the deformation mechanism, the driving mechanism and the possible trigger agent. Deformed layers occur in some thin-bedded ooidal limestones, skeletal calcarenite, as well as in some pebble-size conglomerate, alternated with marls, deposited in a protected embayment or barrier-island-lagoon system, possibly characterized by high salinity, and tidal influx. SSDS can be classified as load- and slump/slide structures. The continuous exposures allow us to follow a single deformed layer along tens of meters, hence several types of lateral variations were observed that can be summarised as follows: (1) SSDS disappear within a few meters (with a decreasing pattern of their deformation or in an abrupt way); (2) deformed layers laterally change in thickness and morphology; and (3) a single deformed bed can laterally correspond to two deformed beds. Most of the soft sediment deformation features were identified as liquefaction and/or fluidization features related to seismic shocks (seismites). Seismites are often used as an indicator of seismic events, especially along small outcrops, trench excavation and core analysis. This study highlights the value of the sedimentological analysis for paleoseismic investigations, with the aim of improving criteria for identifying seismites in the sedimentary record, and their suitability as marker of seismic events.
... Abbreviations: Bt-biotite, Chl-chlorite, Cpx-clinopyroxene, Hbl-hornblende, Pl-plagioclase, Ser-sericite, and Qz-quartz. the fault population slip data was applied in order to obtain the regional paleostress direction using the computer program Daisy v526c (Salvini et al., 1999) (http://host.uniroma3.it/progetti/fralab/) shown in Fig. 3A and B. ...
... Classical structural analysis was performed in 34 sites distributed in several passages distributed through TBR and the most of the TBV (except its southwestern part) to reconstruct the structural evolution of the Salitre carbonates in the study area. Different deformation elements (i.e., joints, veins, tectonic stylolites, and fold limbs) were measured (n = 433 data) and statistically analysed using Daisy software (Salvini et al., 1999). Structural data were integrated with fracture attribute quantification (mostly spacing) in all the speleo-stratigraphic units ( Fig. 2B) identified by Klimchouk et al. (2016). ...
Fractured and karstified carbonates are often major aquifers and hydrocarbon reservoirs. The Toca da Boa Vista (TBV) and Toca da Barriguda (TBR) caves in NE Brazil, which form the longest cave system in South America, developed in a gently folded, layered and fractured Neoproterozoic carbonate sequence made of different lithological units (limestones versus siliciclastic rocks and marls) with variable bed properties (bed thickness, surface roughness of bed-to-bed interlayers) and fracture attributes (spacing, height). The functional organization of the hypogenic cave system has been recently revealed, with subdivision in three speleo-stratigraphic storeys which, from bottom to top, acted as recharge, lateral redistribution and outflow components of the rising fluid flow system, respectively. Structural analysis and new fracture data from TBV and TBR indicate that the stratigraphic setting controlled the fracture pattern development during two tectonic phases, which determined the fluid flow anisotropy during speleogenesis. We found that mechanical and fracture stratigraphy, in conjunction with bed thickness and bed-to-bed interlayer characteristics, controlled the spacing and height of fractures and, as a result, strongly influenced the fluid flow pattern and functional organization of the cave system. In particular, bed-normal rising fluids localized along m- to tens of m-spaced throughgoing fractures developed in the lower and upper storeys, whereas horizontal and bed-parallel fluid flow was focused in a package of thin carbonates, siliciclastics and marls with cm-spaced, strata-bound fractures. This fluid flow anisotropy is attained also due to the presence of rough-walled, bedding-parallel interlayers (i.e., burial stylolites) in the lower massive grainstone which hampered bed-parallel flow, and smooth, planar bedding-parallel interlayers which enhanced lateral fluid movements in the well-layered and fractured middle storey units. Therefore, we conclude that in heterolithic layered carbonate packages, the intricate hypogenic karst pattern is related to heterogeneous fluid flow behaviour associated with the structural complexity imparted by the mechanical versus fracture stratigraphy.
... Doblas 1998;Fossen 2016). Fault slip data were inverted through direct and Rotax (rotation axis) inversion methods using the software Daisy v526c (Salvini et al. 1999) (http://host.uni roma3.it/progetti/fralab/) to reconstruct the orientation of the regional palaeostress field (Figure 4(a)). ...
The Early Cretaceous was an important epoch in the evolution of the Earth system in which major tectonic episodes occurred, especially along the Alpine–Himalayan belt. The paucity of reliable palaeogeographic data from the central segment of this geological puzzle, however, hampers the reconstruction of a panoramic view of its Early Cretaceous palaeogeography and geodynamic setting. Here we present multidisciplinary provenance data from Lower Cretaceous strata of the overriding plate of the Neo-Tethyan subduction zone (the Sanandaj–Sirjan Zone; SSZ, of central Iran), including structural, basin-fill evolution, petrographic and geochemical analyses. Sandstone provenance analysis of Lower Cretaceous red beds suggests the occurrence of sub-mature litho-quartzose sandstones attributed to an active continental arc margin in convergent setting predominantly derived from plutonic, quartzose sedimentary and metamorphic rocks exposed in the central SSZ. Weathering indices indicate moderate chemical weathering in the source area which may be related to close source-to-sink relationships or arid climate. Our palaeogeographic reconstructions and original geological mapping indicate that the erosion of uplifted basement rocks exposed in horst blocks provided the sediment sources for the syn-extensional deposition of uppermost Jurassic–lowermost Cretaceous conglomerates and Lower Cretaceous siliciclastic red beds within a continental retro-arc basin during initiation of the ‘Neo-Tethys 2ʹ. The polyphase tectonic reactivation along the principal fault of the study area controlled the syn- and post-extensional tectonostratigraphic evolution that reflect the corresponding mechanical decoupling/coupling along the northern Neo-Tethyan plate margin.
... Conversely, those characterized https://doi.org/10.1016/j.marpetgeo.2019.104045 Received 15 May 2019; Received in revised form 8 September 2019; Accepted 12 September 2019 by a low amount of primary porosity often deform by means of combined opening-mode and/or pressure solution-assisted deformation mechanisms (Rispoli, 1981;Peacock and Sanderson, 1995;Willemse et al., 1997;Salvini et al., 1999;Graham et al., 2003;Agosta and Aydin, 2006;Agosta et al., 2009Agosta et al., , 2012Antonellini et al., 2008;Aydin et al., 2010;Lamarche et al., 2012;Korneva et al., 2014;Wennberg et al., 2016;Parrino et al., 2019). In particular, platform carbonates form either massive or layered successions depending upon their original depositional environment and diagenetic evolution (Lavenu et al., 2014(Lavenu et al., , 2015Rustichelli et al., 2016;Tavani et al., 2016;Panza et al., 2019). ...
... Fault zone architecture and permeability structure in carbonates The Caine et al. (1996) model described above, which predicts high along-fault permeabilities and low cross-fault permeabilities, has been confirmed and detailed by other outcrop and numerical studies conducted in carbonate rocks. For instance, Salvini et al. (1999) studying the left-lateral strike-slip Mattinata Fault, in the Gargano Promontory, Italy, focused on the mechanisms of cleavage development and reactivation along propagating fault zones and their implications for secondary permeability in hydrocarbon and other fluid reservoirs. They showed that, beyond the master slip surface and associated bands of cataclastic breccias in the core, as the fault propagates, a disjunctive, spaced solution cleavage within the damage zone is often reactivated as synthetic sheared planes. ...
To contribute to the understanding of the impacts of fault reactivation induced by reservoir exploitation, we describe the final series of laboratory experiments, numerical simulations and microstructural analysis conducted during the ‘Fault Reactivation in Carbonates’ research project. In the project, the structure and hydromechanical properties of carbonate-hosted fault zones were investigated. For the analyses here reported, faults were artificially generated by direct shearing composite blocks made of layers of reservoir analogue rocks (outcrop travertine or synthetic grainstone) intercalated with one layer of a sealing analogue rock (synthetic carbonate mudstone). Post-direct shearing, cylindrical plugs containing the fault zone and parts of intact rock were cored out from the blocks and tested in a triaxial test rig, simulating fault reactivation. Varied stress paths and pore-pressure conditions representative of fluid depletion and injection were considered. In parallel, two-dimensional mechanical models representative of the direct shear experiments were developed using smoothed particle hydrodynamics (SPH). We observed a continuous reduction in fault transmissibility during direct shearing, followed by a permeability reduction of 50–80% with increasing mean effective stress in the subsequent fault reactivation tests. Experimental fault zone geometries produced during direct shear were broadly reproduced by the two-dimensional modelling approach. We also detected that the inclusion of the carbonate mud sealing rock into the fault zone caused greater compaction of the fault materials when compared to experiments conducted without carbonate mud layers. We conclude that with fault displacement, increasing incorporation of carbonate mud sealing material into the fault zone and the concomitant development of gouge results in the continuous reduction of fault transmissibility/permeability. This occurs in the two very different limestone host-rock types and for all the stress configurations investigated. Discussions on these results and also on the outcomes of the research project as a whole are presented in the paper.
... Several major faults of diverse age and kinematics are evident in the region. Within this fault system, the Mattinata fault in the southern Gargano is the most profound fault (Ortolani and Pagliuca, 1987;Funiciello et al. 1988;Salvini et al. 1999;. It has been associated with many large earthquakes. ...
The important question of absolute dating of seismic phenomena has been the study of several researchers over the past few decades. The relevant research has concentrated on 'energy traps' of minerals, such as quartz or feldspar, which may accumulate chronological information associated with tectonic deformations. However, the produced knowledge so far, is not sufficient to allow the absolute dating of faults. Today, Luminescence and Electron Spin Resonance (ESR) dating methods could be seen as offering high potential for dating past seismic deformed features on timescales ranging from some years to even several million years. This preliminary study attempts to establish the potential of three different carbonate fault zones hosting fault mirror-like structures, to be used in luminescence and ESR dating, based on their microstructural, mineralogical and palaeo-maximum temperatures analysis. The results indicated that the collected samples can be considered datable fault-rock materials, since they contain suitable minerals (quartz) for luminescence and ESR dating, have experienced repeated cataclastic deformation and have been subject to various physical and chemical processes as well as pressure and temperature conditions.
The fracture-cave reservoirs controlled by strike-slip faults are the main targets for oil and gas exploration of ultra-deep carbonate in the Tarim Basin. It is of great significance to clarify the distribution rules of fractures related to strike-slip faults for guiding the exploration and development of ultra-deep oil and gas. In this study, six groups of strike-slip fault 3D models based on discrete element numerical simulation method have been created to investigate characteristics of fault-related fracture development and distribution law. In addition, we compared the modeling results to the measurement of fractures from the outcrop of a strike-slip fault in the Northern Tarim Basin to verify their validity. The results show that the stress environment is stable in the simple strike-slip section, and fractures intersecting with the strike-slip direction at a small angle are the principal fracture. In the releasing stepover and double-bend sections, the maximum principal stress changes from horizontal to vertical during the formation of pull-apart zones, where the principal fractures intersect the strike-slip direction at a large angle. The maximum principal stress in the restraining stepover and double-bend section remains horizontal, but their strikes change significantly with the increment of fault displacement. Thus, fractures intersecting the strike-slip direction at a small angle will become principal fractures early on, while those parallel to or anti-intersecting the strike-slip direction at a small angle will become principal fractures later. There are obvious differences in the development of fractures in different structural positions of strike-slip faults. Fractures are mainly concentrated in the fault tips, connections, and fault plane, and the magnitude of the fault damage zone is relatively larger in the first two. Compared with fault displacement, the principal damage zone (PDZ) shows stronger control on the distribution and development intensity of fractures. With the increment of fault displacement, the width of the fault damage zone and the fracture density first rapidly increases before the formation of PDZ and then slows down. Moreover, the formation time of PDZ in the restraining double-bend and stepover section is earlier than the simple strike-slip, releasing double-bend, and releasing stepover sections, and absorb more strain before the formation of the principal displacement zone. Thus, the restraining sections have the highest fracture intensity, followed by the pull-apart sections, then the simple strike-slip section. The results play an important role in understanding the development law of fractures related to strike-slip faults in different arrangements and move modes.
The vein-type Qole-Kaftaran Pb-Zn and Cu deposit with middle Eocene volcanic host rock, located at the easternmost edge of the Toroud-Chah Shirin metallogenic belt, is chosen to characterize its structural architecture and further investigate the linkage between structures and ore-mineralization. The Qole-Kaftaran deposit is also situated at 20 km north of the active basement Toroud fault zone. To this end, field base structural study is integrated with remote sensing and ICP-OES geochemical analysis is used. Variable strikes of faults and fractures are propagated in the study area while a NE-SW strike as the significant fault trend is identified in the frequency aspect. This kind of propagation of diverse fault strikes can be interpreted as relatively tectonic maturity in the study area. Brittle and ductile derived- Paleo-stress results suggest an old almost vertical maximum compression direction (with possible age of post-Eocene- Early Miocene) and a post-Early Miocene horizontal NW-SE- directed maximum compression direction. Our result also points to the direct controlling impact of brittle structures on the distribution of alteration and Pb-Zn and Cu mineralization. In which, alteration and vein-type Pb-Zn and Cu mineralization are arranged along and at the hanging wall of the NE-SW extensional faults and grabens.
Exposed in large, continuous outcrops in Provence, southern France, the Castellas fault formed as a normal fault in the Upper Cretaceous and was reactivated as a left-lateral fault in the Eocene. Structural, petrographical, isotopic, and geochronological analyses shed light on the sequence of deformational-diagenetic stages of the fault zone and help identify properties that controlled fluid-flow behavior through time. Abrupt contrasts in fracture abundance compared to the undeformed host rock define a damage zone containing fractures arranged in regularly spaced clusters. We identified eleven episodes of calcite cementation within opening-mode fractures and host rock primary pores. Cement fabrics, sediment fills, and geochemistry show evidence of shallow burial environments. U–Pb geochronology of calcite cements indicate two main deformational phases of the fault zone during the Albo-Cenomanian Durancian uplift and Eocene Pyrenean orogeny at ca. 90 Ma and 50-40 Ma, respectively. Deformation created poro-permeability, but cementation followed shortly after, pervasively occluding most of the fault zone porosity by the end of the Eocene.
Several giant oilfileds (∼700 million bbl of recoverable reserves) have been discovered during recent exploration in the Ordovician carbonates in zone between the Awati and Manjiaer depressions, Tarim Basin, China. These oilfields are deeply buried (>7000 m), and most productive wells are found adjacent to fault zones, suggesting faults may play a crucial role in reservoir development. Here, we use petrographic, microanalytical and geochemical techniques on different stages of void-filling calcite cements to decipher the tectonic-fluid evolution history. Vugs are generally occluded by V1 and V2 calcite cements, which precipitated from marine and burial diagenetic fluids. Two major episodes of fluid invasion are evident in each set of fractures from Middle Ordovician strike-slip faults (F1) to Late Devonian to the Permian strike-slip faults (F2). The sub-horizontal fracture-filling F1 calcite cements show the involvement of near-surface marine to marine-evolved brines, given that δ¹⁸Ocarb, restored δ¹⁸Ow values and rare earth element and yttrium (REY) profiles of F1-1 calcite cements are comparable to Ordovician seawater. The F1-2 calcite cements are characterized by negative δ¹⁸Ocarb, positive restored δ¹⁸Ow, and apparent Ce positive anomalies. The sub-vertical fracture-filling ferroan F2-1 calcite cements with fluorescence show the highest restored T(Δ47) (up to 125 °C), high restored δ¹⁸Ow values (up to +7.0‰ VSMOW), and an enrichment in MREE, which is consistent with an origin from hot hydrocarbon-bearing basinal brines. The subsequent F2-2 calcite cements may have precipitated during the Late Permian from mixing of basinal brines and deeply circulated meteoric water, as suggested by significantly negative δ¹⁸Ocarb values, cooler restored T(Δ47), negative restored δ¹⁸Ow values (down to −5.9‰ VSMOW), and flat REY patterns. The ⁸⁷Sr/⁸⁶Sr ratios of calcite cements are similar to coeval seawater. This study highlights the importance of fault-related fluid circulation in the development of a hydrocarbon reservoir, and may be applicable to other deep carbonate-hosted reservoirs.
The dense fault network that separates the tectonic units of northern Victoria Land to the E from the East Antarctic Craton to the W represents a regionally sized, NNW‐SSE trending deformation zone that is also known as the Rennick Graben Fault system (RGF). This long‐lived deformation zone is characterized by great structural complexity, with the superposition and polyphasic reactivation of regional faults; it is known to have been active since the Cambrian‐Ordovician, when it formed as a suture zone between different terranes, up to the recent. Its complete framework and geodynamic evolution are still debated and have only been partially investigated. In this research, we explore the Meso‐Cenozoic tectonic framework of the RGF by investigating the paleostress fields that characterized the last geodynamic events in the area and their associated brittle deformation. We analyzed faults and fractures data collected at 89 sites during several PNRA ItaliAntartide expeditions and combined fault‐slip data inversion with the azimuthal orientation of faults and the spatial distribution of fracture intensities across the RGF. The results from this multi methodological approach confirm the existence of two geotectonic provinces (Bowers Mountains province to the E and Usarp Mountains to the W) characterized by different spatial distributions of brittle deformation, which are significantly more intense in the Bower Mountains domain. Here, the repeated reactivation of the RGF led to the superposition of two recent (Meso‐Cenozoic) major tectonic events, with prevalent strike‐slip kinematics and characterized by fault reactivation with right‐lateral movement overprinting the previous left‐lateral event.
This report and spreadsheet calculator contain Microsoft Excel-based equations that are useful in structural geology to calculate plunge or apparent dip when measuring lineations on a plane. The spreadsheet allows users to measure the trend or the plunge of a lineation and calculate the corresponding unknown value of trend or plunge. The spreadsheet provides the user with two options:
Option 1: Calculates the plunge of a lineation from the measured strike and dip of a plane and the measured trend of a lineation.
Option 2: Calculates two potential trends of a lineation from the measured strike and dip of a plane and a measured plunge of a lineation. The user can decide which trend is appropriate for their data.
Qom region is one the significant area insight of geological features in Central Iran. Several researches have been studied about the Cenozoic strata in terms of sedimentology, Stratigraphy and paleontology but, few structural detail data are available from this area. The most important exposure of the rock unites at the west of the Qom city is related to the Eocene volcanics, Lower Red, Qom and Upper Red Formations. The major structures at this area is Kamar Kuh and Mil anticlines, Yazdan syncline, Dochah and Sefid kuh faults. Dochah Fault with E-W trending and ~70° dipping to the northward placed at the northwest termination of Qom-Zefreh Fault as a recent sinistral strike slip fault. This fault with ~15 km length separate Mil anticline from Yazdan syncline and eliminates the southern limb of Dochah overturned anticline. In this study, we focused on the Dochah Fault damaged zone in order to paleostress analysis using geometric and kinematic characteristics of fault slip data, which is achieved from the deformed Qom and Upper Red Formations. For this purpose, 100 fault slip data with precise and accurate geometric and kinematic characteristics have been measured in the field and analyzed with software Dasiy and Rotax methods. In order to determine the sense of shearing of the faults, the criteria of Petit (1987) and Doblas (1998) have been used. While the trend of the major structures is east-west but, most of slip data is related the transverse oblique slip faults, because the Dochah Fault passes through the soft materials of Lower Red Formation and consequently it is not possible or too hard to find the slicken line. Meanwhile, our results indicate the attitude of the axes of the maximum and minimum principal stress (σ1, σ3) as 030/05 and 285/05, Geometric and kinetic structural analysis related to the dochah fault and according to the spatial arrangement of the main stress axes indicate the readiness of the left-hand section on the right-hand section, especially in the western parts of the region (Caspian) attributed. oblate shape of field stress ellipsoid shape (R~0.7). Based on the field stress ellipsoid shape and the rotation of the fault data regarding the Anderson's theory for the compressive stress regime, the stress transition trajectory map has been prepared. The arrangement of maximum stress trajectories is consistent with the general stress regime in the Iranian crust and is consistent with the activity of the Dochah Fault. Different criteria have been proposed to evaluate the activity of a fault in terms of seismicity. In experimental studies, there are various estimates for selection for the part of the fault that the movement rediscovers for each tectonic seismic zone. Here, the possibility of moving Dochah Fault has been estimated by the method of Lee et al. (1997). In this method, the angular relationship between maximum principal stress axis (σ1) and the pole of the fault plane considered in order to evaluate the Fault Movement Potential (FMP) based on equation “FMP=f (G, σ)”. The angle between maximum principal stress axis (σ1) and the pole of Dochah Fault (θ) is equal to ~40° and so FMP=0.33 based on equation FMP= (θ-30°) ⁄ (30°) if θ∈[30°,60°]. This value of FMP indicates the low seismic potential of Dochah fault for movement and Creating earthquakes.
Dogan area with surficial Copper-oxide mineralization located at the northeast of Iran, where the northeastern edge of Toroud-Chah Shirin volcano-magmatic belt hosts the numerous Copper-oxide deposits. The Dogan area lies at 18 Km north of the ENE-WSW striking active left-lateral and basement Toroud fault zone in which dominantly deformed by brittle structures. The original field-based structural measurements in the study area that characterized structural anatomy of the Dogan which show the main faults have E-W, NW-SE and NE-SW orientation. We also identified right- lateral E-W striking south Dogan fault zone with longer than 15 km length and NE-SW striking north Dogan reverse fault. Paleostress inversion analysis has performed on all the measured faults that yield horizontal NW-SE directed maximum compression direction (sigma 1) for faulting in Dogan area. Furthermore, integration of fieldbased data and remotely sensed data reveled that Copper-oxide mineralization and associated alterations are tightly aligned along the E-W and rather the N-S to NW-SE fault zones. To identify the role of the faults in Copper-oxide mineralization at Dogan area, our results suggest that major deep faults, dense fracture zones, and fault intersection zones provide weak and low-pressure zones for concentrating the Cucontaining fluids that are high potential places for copper-oxide mineralization.
To fully characterise the behaviour of carbonate rocks in the subsurface it is important to understand their textural heterogeneity, and how their textures may be modified by faulting. A number of fault zones were investigated in detail, firstly analysing the microstructural, petrophysical as well as mechanical properties of the host rocks. Secondly, describing the fault zone architectures by mapping fault rock distributions and fracture patterns. Lastly, correlating the deformation mechanisms forming the faults to the initial rock properties and the stress conditions during faulting. Moreover, triaxial laboratory deformation was performed on a large number of host rock samples covering all carbonate rock types, as well as the whole range of porosities (<1-52%). Deformation mechanisms that resulted in sample’s failure were studied in order to compare them with the naturally-occurring deformation. Moreover, permeability changes were investigated induced both by natural faulting and laboratory deformation. The results proved to be comparable, and showed that simplified rules may be derived in terms of predicting hydraulic properties of deformed carbonates. For instance, permeability generally seems to decrease due to deformation for carbonates with porosity >10%, and may be either increased or decreased for lower porosity samples. Higher porosity (>10%) carbonates fail due to distributed or localized cataclastic flow or focused damage around the macropores, resulting in porosity reduction. Lower porosity (<10%) carbonates fail in a brittle manner due to brecciation and transitional- or brittle- shearing, leading to porosity increase. Significant reduction in permeability, however, may only be produced by diagenetic processes, such as recrystallization and cementation, or very high-strains, which are able to create fine-grained cataclasites. However, even though these fault rocks gain very low permeability, they become prone to brittle deformation. Therefore, these potentially sealing fault rocks may be cut by open fractures if were subjected to further faulting or uplift, and hence, while creating permeability anisotropy in the reservoir, they may not form good seals. Nevertheless, several fault examples in this study showed fracture blunting at the surface of the fault rocks suggesting that fault sealing is possible both in highly-porous and very tight carbonates.
Low-porosity carbonates in San Vito lo Capo underwent two episodes of faulting: extensional faulting in the late Miocene and strike-slip faulting in the Plio-Pleistocene. Limestones and dolostones reacted differently to these faulting events. The first extensional faulting event within the limestone formed localized faults with a single fault core surrounded by a damage zone. The fault rock was either dolomitized as deformation proceeded or resealed by calcite cement after brecciation. The dolomitized fault rocks were reactivated during the following strike-slip faulting, forming polyphase breccias. On the other hand, strain was distributed in dolostones throughout a wider area during the extensional faulting forming a pulverized fault zone. The pulverized rock experienced cataclastic deformation during the following strike-slip faulting forming anastomosing networks of cataclastic shear bands. Fault cores hosted in the limestone appear to have acted as flow conduits until they were cemented or hardened due to evolving cataclasis. The cataclastic shear bands in the dolostone are likely to form baffles to flow, at least on a local scale. The fracture spacing in the damage zone also varies significantly between the lithologies. In particular, damage zones in the limestone have a 5–10 cm fracture spacing whereas fracture spacing is 0.5–3 cm in the dolostone. It is likely that the differing mechanical and chemical properties of the dolostone and limestone were responsible for creating contrasting fault zone architectures.
Fault zone architecture and related permeability structures form primary controls on fluid flow in upper-crustal, brittle fault zones. Qualitative and quantitative schemes for evaluating fault-related permeability structures are developed by using results of field investigations, laboratory permeability measurements, and numerical models of flow within and near fault zones. The fault core and damage zone are distinct structural and hydrogeologic units that reflect the material properties and deformation conditions within a fault zone. Whether a fault zone will act as a conduit, barrier, or combined conduit-barrier system is controlled by the relative percentage of fault core and damage zone structures and the inherent variability in grain scale and fracture permeability.
Low-temperature deformation is characterized by heterogeneous strain in which the bulk of the material clearly retains its primary texture. Deformation is by grain-scale crystal plasticity, rotation, fracture, and pressure solution, and by transgranular mechanisms that crosscut numerous grains. The important low-temperature crystal-plastic features are twin lamellae, deformation bands, and undulatory extinction. Strain magnitudes and stress and strain tensor orientations can be determined with a variety of methods that are based on mechanical twins, platy grain orientation, grain center distribution, and fault geometry and slip directions. Different deformation mechanism associations, expressed by the partitioning of the total strain into different mechanisms, are related to the ductility and environment of deformation. Deformation fronts separating different mechanism associations are defined on the basis of changes in the crystal-plastic component of strain. -from Author
In heavily over-consolidated clays there is a marked peak in the
observed relation between shear stress and shear strain. As the strain
increases, the stress falls from a peak to a much smaller residual
stress. Slopes made from such a clay often fail progressively many years
after construction. Sliding occurs on a concentrated slip surface, and
it is found that the mean resolved shear stress on that surface is
markedly less than the peak shear strength. Concepts from fracture
mechanics, and in particular the J-integral, are used to derive
conditions for the propagation of a concentrated shear band of this
kind. The results indicate the presence of a strong size effect, which
has important implications for the use of models in soil mechanics. An
elastic analysis makes it possible to determine the size of the end zone
in which the shear stress on the shear band falls to its residual value.
An attempt is made to assess the possible sources of the time-dependence
governing propagation speed of the shear band. They include pore-water
diffusion to the dilating tip of the band (which governs the rate at
which local strength reductions can occur), viscoelastic deformation of
the clay (which allows a gradual build-up of strain concentration at the
tip of the band), and the weathering break-down of diagenetic bonds.
Conjugate strike-slip fault zones that cover metre-scale areas at Beadnell, Northumbria, and Kilve, Somerset, were initiated as conjugate vein arrays. Early conjugate faults are linked by the propagation of one fault that eventually by-passes the other fault. A model for the development of strike-slip faults is presented, using fault and vein geometries and the position of damage zones with respect to the master faults as an indication of the propagation direction. This model includes the evolution of networks from (1) the initial random development of vein arrays, to (2) the isolated development of several unconnected conjugate fault segments that pass into vein arrays, through (3) the intersection of a conjugate set of master faults and linkage with minor antithetic faults, and the formation of new vein arrays with extensional geometries after a linked network of faults is established, to (4) breaching of intersection points by dominant faults, and finally (5) the propagation towards oversteps that are breached to form a through-going fault. The geometry of the active structures simplifies with time, as strain is localised along the master fault, but the complexities are preserved in the fault walls.
Areas of reorientated bedding at contractional oversteps between strike-slip faults are here called strike-slip relay ramps. Metre-scale examples are described from the Jurassic sediments at East Quantoxhead, Somerset U.K. Larger strike-slip relay ramps occur in the Rio de Peixe Basin, NE Brazil, along the Newport-Inglewood Trend, California, and in the Bovey Basin, SW England. Although the geometry and development of strike-slip relay ramps are similar to those of relay ramps in normal fault systems, there are differences in the structures which accommodate the transfer of displacement between the overstepping faults. Whereas strike-slip relay ramps are typically transpressional, with pressure solution often occurring, relay ramps in normal fault systems are dominated by extension or transtension. Care needs to be taken when interpreting areas of reorientated bedding between overstepping faults, particularly when displacement directions are unknown, for example when using seismic data. This is because relay ramps can occur in both strike-slip and normal fault zones.
Volume changes of a granite, a marble, and an aplite were measured during deformation in triaxial compression at confining pressure of as much as 8 kb. Stress-volumetric strain behavior is qualitatively the same for these rocks and a wide variety of other rocks and concrete studied elsewhere. Volume changes are purely elastic at low stress. As the maximum stress becomes one-third to two-thirds the fracture stress at a given pressure, the rocks become dilatant; that is, volume increases relative to elastic changes. The magnitude of the dilatancy, with a few exceptions, ranges from 0.2 to 2.0 times the elastic volume changes that would have occurred were the rock simply elastic. The magnitude of the dilatancy is not markedly affected by pressure, for the range of conditions studied here. For granite, the stress at which dilatancy was first detected was strongly time dependent; the higher the loading rate the higher the stress. Dilatancy, which represents an increase in porosity, was traced in the granite to open cracks which form parallel with the direction of maximum compression.
This paper is included in the Special Publication entitled 'Faulting, fault sealing and fluid flow in hydrocarbon reservoirs', edited by G.Jones, Q.J. Fisher and R.J. Knipe. Pressure solution plays a major role in fault initiation and development in carbonate rocks. Strike-slip faults in the Triassic and Jurassic limestones of Somerset, UK, initiated as en echelon extension fractures, which became linked by pressure solution seams. Shear occurred along the pressure solution seams as the bridges between the veins rotated. The linked vein-pressure solution seam systems developed into pull- aparts and eventually into through-going faults. Normal fault planes in the Cretaceous Chalk at Flamborough Head, Yorkshire, UK, commonly have the pitted appearance of slickolites. Phyllosilicates are often concentrated along faults in Chalk, the thickness of the phyllosilicate gouge being proportional to fault displacement. The enrichment of phyllosilicates along the faults is due to pressure solution rather than simply to phyllosilicate smear. Pressure solution can be concentrated at the contractional quadrants of faults, particularly where there is a contractional overstep onto an adjacent fault. Metre-scale oversteps between strike-slip faults in Somerset often have pressure solution seams, while contractional oversteps and bends at Flamborough Head are accommodated by compaction of beds, with pressure solution apparently being important. The concentration of phyllosilicates by pressure solution can hinder fluid flow along and across faults in carbonate rocks. A high density of pressure solution seams between overstepping faults can effectively link these faults, increasing both the effective length of the barrier to fluid flow and the fault seal potential.
Here we call attention to a weakly developed pencil cleavage as an indicator of the pervasiveness of lateral shortening within the sedimentary sequence of the Appalachian Plateau. The pencil cleavage appears in Upper Devonian shales as a set of closely spaced vertical partings, and it gives the shale a crude lineation similar to the pencil structures in slate districts. The strike of the shale pencil structures parallels the strike of stylolitic solution cleavage in limestones and is normal to the direction of lateral shortening indicated by deformed fossils. These deformation markers generally conform with the variation in trend of the Appalachian Plateau folds. Where the strike of the pencil cleavage diverges from the fold axes, the relation between cleavage and folding suggests that the cleavage formed first.
Mesozoic pelagic limestones in Umbria (northern Italy) were deformed by Miocene-Pliocene flexural slip folding under 1 to 2 km of cover; there are no signs of metamorphism. Under these conditions the deformation was brittle, as indicated by extension veins and by foraminifera that show no measurable distortional strain. Nevertheless, the limestone is often tightly folded; the folding mechanism combined dissolution of limestone along stylolites subparallel to fold axes with deposition of sparry calcite in extension veins normal to the stylolites. Thus, at the scale of a hand specimen, deformation occurred through rigid-body displacements, but e-twinning in the vein calcite shows a minor component of distributed strain. Spaced cleavage on the limbs of major folds also formed by dissolution. This is shown by (1) the presence of insoluble residues on the cleavage surfaces, (2) imbrication of insoluble chert nodules that indicates tens of percent shortening parallel to bedding, (3) deflection of cleavage away from strain shadows protected by chert nodules and toward places where the nodules have been telescoped, and (4) offsets of bedding at bedding-cleavage intersection that resulted from removal of limestone by dissolution along the cleavage surfaces.
A hand-specimen-size buckle fold from a fault zone in the Appalachian Plateau of New York shows a fanning spaced cleavage attributed to pressure solution because of the truncation of fossils and the presence of residual material in the cleavage laminae. Apparent slip on the cleavage is interpreted to be the result of the removal of material along laminae oblique to bedding. The fold is cut along the cleavage and partially unfolded by rigid-body rotation of the segments, thereby eliminating the offsets of bedding without slip parallel to the cleavage. Field evidence suggests that the material removed from the cleavage laminae is present locally as cement.
We used a torsional geometry to grow shear ruptures in two fine-grained rock types. The sample has a slot that is loaded to produce a strong mode 3 shear stress concentration. The onset and growth of the damage zone is detected by monitoring the elastic stiffness of the samples. We find that the samples continue to harden after the onset of fracture. This is initially accompanied by oblique tensile cracks forming at the stress concentration. The peak in supported load apparently corresponds to the onset of strain localization, with the development of cross-cutting shear fractures. We attempted to estimate the partitioning of energy dissipation between elastic and frictional components with a fracture mechanics analysis. The elastic energy increases with normal stress, but scatter in the inelastic data does not allow identification of convincing trends. The sample is too small to develop a complete transition to a shear rupture. The geometry of the fractures is used to explain the energy relations as well as other experimental observations
Micromechanisms of rock failure (axial splitting and shear failure) are examined in light of simple mathematical models motivated by microscopic observations. The elasticity boundary value problem associated with cracks growing from the tips of a model flaw is solved. It is shown that under axial compression, tension cracks nucleate at the tips of the preexisting model flaw, grow with increasing compression, and become parallel to the direction of the maximum far-field compression. When a lateral compression also exists, the crack growth is stable and stops at some finite crack length. With a small lateral tension, on the other hand, the crack growth becomes unstable after a certain crack length is attained. This is considered to be the fundamental mechanism of axial splitting observed in uniaxially compressed rock specimens. To model the mechanism to shear failure, a row of suitably oriented model flaws is considered and the elasticity boundary value problem associated with the out-of-plane crack growth from the tips of the flaws is solved. It is shown that for a certain orientation of the flaws the growth of the out-of-plane cracks may become unstable, leading to possible macroscopic faulting. On the basis of this model the variations of the ``ultimate strength'' and the orientation of the overall fault plane with confining pressure are estimated, and the results are compared with published experimental data. In addition, the results of a set of model experiments on plates of Columbia resin CR39 containing preexisting flaws are reported. These experiments are specifically designed in order to show the effect of confining pressure on the crack growth regime. The experiments seem to support qualitatively the analytical results.
(Accepted for publication May 22, 1978)
ABSTRACT: Illies, J.H. and Greiner, G., 1979. Holocene movements and state of stress in the Rhinegraben rift system. In: C.A. Whitten, R. Green and B.K. Meade (Editors), Recent Crustal Movements, 1977. Tectonophysics, 52: 349-359.
A belt of seismotectonic activity and Holocene crustal deformations traverses Western Europe and forms a 800-km-long subplate boundary. The main segments are the Rhinegraben, the seismic zone straight through the Rhenish massif, the Lower Rhine embayment, and the Zuider Zee depression (The Netherlands). Seismicity and Holocene fault action of the Rhinegraben are controlled by a sinistral shear motion parallel to the graben axis. Accompanying this simple shear motion there are also extension shear, compression shear, and Riedel shear. Extensional tectonics characterize the faulting in the Rhenish massif and the rifting in the Lower Rhine embayment.
In-situ stress data, obtained by using the strain relief technique, confirm principal stress directions, approximately equal to those obtained by fault plane solutions of earthquakes. The calculation of excess stress revealed very high stresses in the Central Alps, whereas minimal to negative values were found in the Rhinegraben and other zones of seismic activity. Stress generation in the area of the Central Alps corresponds with strain release along the rift system which traverses the foreland.
The Upper Cretaceous to end-Miocene process of Alpine plate convergence and folding has been replaced since Pliocene times by epeirogenic uplift and consequent denudation of the mountain range. We assume that the observed state of stress is mainly caused by a sideways extension of the mountain body due to the effects of unloading and topography.
In the south-east border of French Central Massif, near Anduze, limestone series of Upper Jurassic age are affected by an association of deformations which occurred during a single tectonic phase. Thus chronologically appeared: 1. (1) Conjugated shear planes with vertical intersection (dextral and sinistral microdisplacement). 2. (2) Concentric folds with approximately east-west axis trend associated with stylolitic joints. 3. (3) Conjugated shear planes with horizontal intersections (microthrusts to north or south). The study of these different deformations gives way to the reconstitution of both successive states of stress during time and local variations in direction of the stress ellipsoid axis.
Thrust faults are typically discontinuous. Based on the relative positions of adjacent fault segments, the discontinuities along thrust faults can be classified into two major groups: along-strike and down-dip. Adjacent fault segments are linked by transfer structures such as secondary dip-slip faults, tear faults, folds, cleavages, and pull-apart openings. Duplex structures are compressional down-dip discontinuities associated with echelon thrust faults with relatively large overlaps. Duplex structures in general, and cleavage duplexes in particular, are analyzed by calculating stresses due to interacting echelon mode II cracks. The results indicate that there are significant increases in the maximum compressive stress, mean stress, and maximum shear stress at the stepover area. The orientations of the planes upon which the largest compressive stresses act in the model are approximately consistent with the orientations of the cleavage planes in a few duplexes described in the literature.
A simple model for rock deformation by pressure solution, assuming grain boundary
diffusive mass transfer to be deformation rate controlling, is presented. The model
leads to a constitutive flow law which is of the same form as that for Coble creep.
It is argued that the presence of a fluid film in stressed grain boundaries leads to
enhanced diffusivity of solute particles in the grain boundary. Some simple experiments
are described, which demonstrate rapid diffusion in solutions in pores, much
slower diffusion in stressed interfaces and deformation by pressure solution.
By using the theoretical model, and by assuming that the pressure of the interfacial
solution is equal to the applied normal stress, so that available experimental
data on the effect of pressure on mineral solubility could be used, rates of deformation
by pressure solution have been calculated. These are compared with rates of deformation
by crystal plastic and high temperature diffusive flow processes, by using
deformation mechanism maps. Predicted transition conditions between various
deformation mechanisms are found to be consistent with those inferred from the study
of textures of naturally deformed rocks.
Opening-mode splay fractures have been observed within clusters near fault tips. The spatial distribution of splay fractures along faults influences fluid flow and lends insight into the mechanical processes of faulting. Slip gradients along faults produce stress concentrations which promote the development of opening-mode splay fractures along faults. Since the slip distribution depends on the distribution of frictional strength along faults, spatial variations in the frictional properties may influence fracture localization. Variations in friction coefficient along faults can reduce the stress singularities at fault tips and promote the development of multiple fractures inwards from the fault tips. The conditions that promote splay crack localization are examined using analytical and numerical fault models. Single splay fractures develop at locations of abrupt friction coefficient change and/or at fault tips when the frictign coefficient near the tips is less than a critical value. Fault models with linearly increasing friction coefficient toward the fault tip promote the development of multiple splay fractures within broad zones near the tip.
Upper Eocene north-south compression, east-west traction, brittle structures, microfaults, France
Detailed mapping of the structures exposed in northeastern Tennessee reveals a complex deformation sequence consisting of the following stages: 1) early thrust faulting, 2) folding, 3) intermediate thrust faulting, 4) intermediate folding, 5) normal faulting, 6) strike-slip faulting, and 7) jointing. Each stage is composed of one or more structures. Once a structure formed, it may have remained active over several stages of deformation. Based on cross-cutting relationships among the structures and the transport directions determined from thrust faults, it appears that the deformation stages up to and including normal faulting (Stage 5) are consistent with a series of incremental deformation events driven by similar causative forces associated with the Alleghanian Orogeny. In particular, the results in this study reveal three nested fracture networks which were potential pathways for fluid migration during tectonic deformation and may still play a role in current fluid migration. -from Authors
Traces of many normal faults form an array of closely spaced
overstepping segments. In three dimensions, fault segments may either be
unconnected or link vertically or laterally into a single continuous
fault surface. The slip distribution along segmented faults is complex
and asymmetric, and the point of maximum slip generally is not located
at the center of a segment. In relay zones between segments, slip
gradients may be gentler or steeper, depending on the spatial fault
arrangement. Branch points are characterized by steep slip gradients.
One explanation for these observations is mechanical interaction between
neighboring faults which occurs through local perturbation of the stress
field. Three-dimensional (3-D) boundary element models show that the
degree of fault interaction and hence the degree of asymmetry in the
slip distribution increases with increasing fault overlap and downdip
fault height and with decreasing fault spacing and Poisson's ratio.
Interaction is strongest for faults with uniform shear strength and
decreases if there exists a zone of greater shear strength near the tip
line. This analysis provides a mechanical rationale for more frequent
occurrence of overlapping segments relative to underlapping segments and
for the limited range of the ratio between segment overlap and spacing
along natural faults. Echelon segment configurations promote
interaction, maximize the capacity to accommodate slip, and do not
necessarily require a strike-slip movement component. Model
idealizations of some outcropping fault arrays and of branching/merging
faults capture a wide variety of common field observations. Consistent,
mechanically based 3-D normal fault models can be obtained by combining
different types of field data such as fault slip-to-length ratios,
location of maximum slip, segment overlap-to-spacing ratios, and
footwall uplift/hanging wall subsidence. By capitalizing on these data
one can understand the mechanics of faulting, constrain the boundary
conditions that govern the formation and growth of faults, and provide a
rationale for interpreting normal faults in seismic surveys.
We consider and discuss the presence of discontinuities in the crust as a major source of stress perturbations. Based on 2-D distinct-element modelling, we reconstruct the local stress field around a vertical discontinuity in various geological contexts. The resulting stress distribution reveals that major directional stress changes occur near the tips of the discontinuity so that stress deviations can reach values as large as 50 °. We establish simple relationships controlling stress changes around a pre-existing fault zone as a function of (1) the remote differential stress magnitude, (σ1 − σ3), (2) the friction coefficient on the discontinuity, and (3) the strike of the discontinuity relative to the far-field stress.As a geological example, we present the Morez Fault Zone in the internal Jura. Paleostress reconstruction in forty-two sites indicates that the trends of the Mio-Pliocene compression are N110 ° on average near the fault, whereas they are N130 ° in the surrounding areas. A comparison between the results of the tectonic study and those of theoretical modelling suggests that the 20 ° counterclockwise deviation is directly related to the reactivation of this large weak zone. We thus evaluate the role of mechanical decoupling along pre-existing zones of weakness, especially with consideration to the accommodation of the Alpine deformation in the Jura belt.
Deformed belemnites are important strain markers because they allow calculation of actual length changes in deformed rocks. They have been studied in the deformed Lower Lias sequence of part of the French Alps by measuring the orientation of about 100 belemnites at each locality, recording the amount of extension of as many as possible, and locating the sector of arc on the bedding plane occupied by extended belemnites. For comparison, studies on a similar but undeformed Lower Lias sequence in southern England show that dispersed belemnites have no strong initial preferred orientation, and that a proportion of undeformed belemnites show cross-fractures that would allow extension of the rostra from the onset of deformation.Graphs of frequency vs orientation for belemnites at locations deformed by irrotational strain lead directly to an estimate of two-dimensional strain ratio and orientation. Non-random initial distributions and rotational strain produce more complex graphs, which are treated only qualitatively. Extension-orientation graphs show that many deformed belemnites lie within the sector of extension of the strain ellipse. These graphs provide estimates of 1 + e1 and 1 + e2, which can be cross-checked using the orientation of the lines of no finite longitudinal strain derived from measuring the maximum sector of arc occupied by extended belemnites.Examples from the French Alps show how the rotational and irrotational strain of initially random samples may be distinguished, and how the more complex case of deformation of non-random samples differs from these. The direction of rotation of the strain ellipse can be derived from the geometry of the graphs of frequency and elongation.
Fracture mechanics theory and field observations together indicate that the shear stress on many faults is non-uniform when they slip. If the shear stress were uniform, then: (a) a physically implausible singular stress concentration theoretically would develop at a fault end; and (b) a single curved ‘tail fracture’ should open up at the end of every fault trace, intersecting the fault at approximately 70 °. Tail fractures along many small faults instead range in number, commonly form behind fault trace ends, have nearly straight traces and intersect a fault at angles less than 50 °. A ‘cohesive zone’, in which the shear stress is elevated near the fault end, can eliminate the stress singularity and can account for the observed orientation, shape, and distribution of tail fractures. Cohesive zones also should cause a fault to bend. If the cohesive zone shear stress were uniform, then the distance from the fault end to the bend gives the cohesive zone length. The nearly straight traces of the tail fractures and the small bends observed near some fault ends implies that the faults slipped with low stress drops, less than 10% of the ambient fault-parallel shear stress.
The growth of cracks in photoelastic material and glass under compression is being studied as part of an investigation of brittle fracture of rock. In compression the most severely stressed crack is inclined at about 30° to the axis of compression. Such cracks, when either isolated or placed in an array, grow along a curved path which becomes parallel with the direction of compression. When this direction is attained, growth stops, unless applied compression is increased considerably. Cracks in certain en échelon arrays start to grow at much smaller applied stress than that required to enlarge an isolated crack.
Western Europe is traversed by the Rhinegraben rift system. The stages of graben formation evolved coincidentally with the culminations of compressional folding in the Alps. Rhinegraben rifting has been controlled by mantle diapirism, but the Alpine orogeny by subduction of lithosphere. Presumably, Alpine subduction forced compensating mantle uplift in the foreland.
The Middle Eocene to Oligocene crustal spreading of the Rhinegraben implies a state of stress with a maximum horizontal component parallel to the graben axis (about 20‡). In the same area, the Recent average direction of maximum compressive stress is of about 320‡ (NW), as calculated by in-situ stress measurements, fault-plane solutions of earthquakes and Recent crustal movements. The rotation of the stress components relative to the crust of stable Europe evolved subsequent to counterclockwise rotations of microplates in the Mediterranean. A model is proposed which ascribes these rotations to alterating shear motions of the Afro-Arabian macroplates relative to stable Europe exerting a ball-bearing effect to the intervenient microplates. The postulated motions are in accord with the patterns of inhomogeneous ocean floor spreading east and west of the African plate. The stages of Alpine plate collision had induced a significant readjustment of intraplate stress conditions, and deformation in the cratonic foreland of stable Europe.
Considered evidences show that stylolite formation succeeded rock induration in limestones of many ages from Middle East localities. Observations of B. M. Shaub, allegedly proving origin of some North American stylolites prior to consolidation, are examined and pronounced inconclusive as to relative times of stylolite formation and rock hardening. Existing stylolite seams may facilitate subsurface fluid movement, thus affecting oil migration, accumulation and production. Stylolite development in limestones, like compaction in shales, causes expression of part of the contained fluids: but such expression occurs late in rock-history, not predominantly at an early stage as in the case of normal compaction. Stylolite formation entails local supersaturation of the solvent water, and consequent local redeposition, thus reproducing in many limestones the same type of fluid expression as is occasioned in some sandstones by cementation related to grain interpenetration.
Extract
Before describing the theory I have propounded to account for what is called “slaty cleavage,” it will probably be the best for me to explain briefly the nature of this structure and of the problem to be solved. Most stratified rocks can be split with more or less facility in the plane of their bedding, but in certain districts, greatly disturbed by elevatory forces, besides this line of weakness, there occurs another, only remotely connected with the bedding, and often so much more decided, that they were at first confounded, and the stratification overlooked, until the true nature of cleavage was pointed out by Professor Sedgwick. In most districts possessing cleavage, the stratified beds are much contorted, and dip at all angles, whilst the cleavage passes through them with more or less regularity, in some cases quite independent of the bedding. I should occupy far too much time if I were to describe one-half of the facts connected with this very extensive subject, and shall therefore confine myself to hut few.
It is most important to bear in mind that cleavage is quite distinct from jointed structure. Joints are mere cracks and fractures, whereas cleavage is a structural weakness affecting the whole mass of rock. The question, therefore, is, how this structural weakness was developed? Mr. Fox, of Cornwall, found that a kind of laminated structure was produced by passing an electric current through clay, and Hunt has since repeated, confirmed, and extended his observations. I, however, think this electrical ...
Introduction.
During the last few years the subject of slaty cleavage has gradually attracted the attention of geologists, and much valuable information regarding it has been accumulated. Professor Sedgwick's clear description of the leading phænomena connected with cleavage*, leg geologists into the right path, and since the publication of his views in 1835 we rarely meet with those unintelligible descriptions, so common in the earlier writers, in which the cleavage and the stratification are confounded together in hopeless confusion. Subsequent observers have added materially to our knowledge, and various remarks illustrating the subject will be found scattered through the writings of Professor Sedgwick, Sir R. I. Murehison, Professor Phillips, Sir H. T. De la Beche and Mr. Austen, in addition to which Mr. Darwin has just given us a large collection of observations upon cleavage made in various parts of South America, with some important generalizations to which the extended field of his researches gives treat weight. The most valuable of his remarks appear to be those which connect together the cleavage of slates and the foliation of gneiss, mica slate,.&c.
Still we had no knowledge of the general laws which governed the formation of the cleavage and regulated its direction, and without previously discovering these it was idle to speculate upon the causes which had produced it. I have now endeavoured to supply part of this deficiency and to establish some general laws relating to the subject, which have been deduced from new observations and from combining insulatted facts
Temporal relationships between cleavage formation and folding in sedimentary rock sequences can vary from either phenomena preceding the other to both occurring simultaneously. Knowledge of this relationship, however, is required to understand fully the relationship of cleavage orientation to finite strain and the origin of cleavage refraction across competent-incompetent layers. Evidence from the Goldenville Formation provides an example of cleavage formed before folding by approximately 50% pressure-solution removal of material, resulting in cleavage planes normal to bedding during active folding. Because cleavage in the Goldenville Formation formed perpendicular to bedding before folding and was passively rotated and extended by bedding-parallel simple shear during fold amplification, the resulting cleavage planes cannot lie in the XY plane of the finite-strain ellipsoid. Differential shear between metagray-wacke and slate beds accounts for the observed cleavage refraction, and the bedding-cleavage angle provides a good estimate of the shearing across these beds during active folding. If cleavage can be shown to postdate folding in other examples, it is possible that cleavage planes will lie in the XY plane of the finite-strain ellipsoid.
Regional-scale, subparallel linear topographic features characterize almost all planetary surfaces. This experiment concerns their tectonic meaning by focusing on map limits or domains through which individual swarms of these linear features are developed. These domain limits are contrasted with map boundaries of better-known structural features in a tectonically active region (Italy) to seek clues to stress environments and times of origin of the lineaments. The study uses regional raised relief maps to filter the lineament data to a very simple subset: those strictly topographic features of a length and prominence capable of retaining detectability through generalizations required by relief-map production. A total of 5,372 lineaments were drawn using 4 differently lighted images of 1:1,000,000 scale relief maps of Italy. Seven different tests were used for reliability and reproducibility of the data. Rose diagrams were prepared for 86 subareas by computer fitting of gaussians to azimuth-frequency histograms. Individual azimuthal "petals" of these roses were then correlated to delimit the general area over which a given azimuthal swarm is developed. The precise swarm boundaries were then located by computer contouring the population density of lines of each swarm on the original data set. In this way, 48 local swarms were mapped. Boundaries of these swarms correlate poorly with traditional litho-tectonic provinces. Instead, they seem to be associated with basin axes, broad arches, coastal flexures, areas of normal fault swarms, and projections of structural grain from adjacent sea floors. The 48 domains may be grouped into 8 noncontiguous but azimuthally compatible super-swarms covering much of Italy. The most prominent of the super-swarms are greatly expanded versions of regional structural grains: trend of the Po Basin, axis of the upper Adriatic Basin, zone of south Alpine underthrusting, and landward extensions of structural grain of the Tyrrhenian Sea. From these relationships, a model for lineament-swarm origins is proposed, involving very minor regional stretching of the thin, brittle carapace of extremely large, sometimes subtle, structures deforming by ductile mechanisms at depth.
Traditional fracture analysis emphasizes the statistics of fracture orientations at individual stations. A new method, the azimuth versus traverse distance plot (AVTD), is proposed, whereby map patterns and fracture domain boundaries receive much greater emphasis. The method can be applied to any area where outcrop is nearly continuous and map data can be represented by strike alone. Ideal features for the method are nearly vertical joint sets which can be plotted on the proposed AVTD diagrams and contoured with concentration factor statistics somewhat analogous to those used for equal-area plots. Examples of AVTD plots are given for jointing in the S Beartooth Mountains, Wyoming, illustrating ways in which generally overlooked joint set patterns may be identified and ways in which joint domain boundaries may be integrated in geologic mapping using the plots. The examples show the utility of the method in assigning relative ages to fracture domains, in relating the domain distributions to other structures, and in testing for tectonic heredity of older fractures by upward propagation through an unconformity. -Authors
Micrites of the Jurassic Twin Creek Formation in the Idaho-Utah-Wyoming thrust belt show spaced cleavage developed during folding and thrusting. Cleavage in each thrust sheet forms mainly by pressure solution, aided by elevated temperatures and pressures caused by increased overburden as a result of emplacement of earlier overriding thrust sheets. Within each thrust sheet, cleavage develops early and is contemporaneous with microscopic to mesoscopic buckle folds and faults. Large-scale ramp folds, formed during major motion on the thrust, postdate the cleavage and passively rotate it into major fans.-Authors
Various brittle geological structures form from the tip of preexisting joints. Experiments have been carried out to investigate their mechanical origin and to find out whether a planar defect can propagate in its ownplane under mode II geometrical conditions and in particular, whether mode II can be an elementary fracture mechanism. A biaxial loading device (plane strain) allowed direct observation of fracture propagation from an angled slot in plates of Polymethylmethacrylate (PMMA, Altuglas) and sandstone (low and high porosity). These experiments suggest that mode II cannot exist as an elementary (primary) fracture mechanism but can only be a macroscopic fracture phenomenon which must necessarily involve tensile (mode I) microcrack formation. The latter is linked to stress concentrations in the prolongation of the existing joint. These ideas can be used to interpret some types of natural faults. -from Authors
Mixed mode I+III loading of a fracture front results in out-of-plane propagation into echelon stepping fractures. Because a planar fracture geometry is the exception rather than the rule, and because the introduction of even a minor component of mode II or III loading is known to promote out-of-plane propagation, an understanding of mixed mode fracture growth is imperative to analyze fracture behavior. We have loaded cracks in mixed mode I+III within polymethyl methacrylate (PMMA or Plexiglas) rectangular blocks resembling conceptual fracture mechanics models of mixed mode loading and have analyzed the resulting geometries. The observed angle of twist of echelon fractures from the parent crack plane increases with the ratio KIII/KI and falls below theoretical predictions. Fracture propagation paths depend not only on the load ratio applied but also on sample geometry, loading configuration, and interaction among growing fractures. Sample geometry and loading configuration are approximately accounted for using analytical determinations of the stress intensity factors. We propose that interaction among growing fractures may contribute to the discrepancy between theoretically predicted twist angles and those observed in these and other mixed mode I+III experiments. Analysis of these experimental results has motivated the design of a new sample and loading configuration to test the propagation paths of uniformly loaded mixed mode I+III fractures.
We present a model for the nucleation and growth of faults in intact
brittle rocks. The model is based on recent experiments that utilize
acoustic emission events to monitor faulting processes in Westerly
granite. In these experiments a fault initiated at one site without
significant preceding damage. The fault propagated in its own plane with
a leading zone of intense microcracking. We propose here that faults in
granites nucleate and propagate by the interaction of tensile
microcracks in the following style. During early loading, tensile
microcracking occurs randomly, with no significant crack interaction and
with no relation to the location or inclination of the future fault. As
the load reaches the ultimate strength, nucleation initiates when a few
tensile microcracks interact and enhance the dilation of one another.
They create a process zone that is a region with closely spaced
microcracks. In highly loaded rock, the stress field associated with
microcrack dilation forces crack interaction to spread in an unstable
manner and recursive geometry. Thus the process zone propagates unstably
into the intact rock. As the process zone lengthens, its central part
yields by shear and a fault nucleus forms. The fault nucleus grows in
the wake of the propagating process zone. The stress fields associated
with shear along the fault further enhance the microcrack dilation in
the process zone. The analysis shows that faults should propagate in
their own plane, making an angle of 20 deg-30 deg with the maximum
compression axis. This model provides a physical basis for 'internal
friction', the empirical parameter of the Coulomb criterion.
The cohesive force across the fault plane is considered in order to understand the physical mechanism of rupture at the tip of a longitudinal-shear crack. The elastic field around the tip of a crack and the condition of rupture growth are systematically derived from the assumption that the cohesive force is given as a function of the displacement discontinuity. This assumption is more physically meaningful than those originally used by G.I. Barenblatt in 1959 and 1962. The stress field around the tip is calculated for several models of cohesive force, and is shown to be nonsingular even at the tip. The condition of rupture growth that is used to determine the rupture velocity turns out to be equivalent to the Griffith criterion and the relation employed by B. V. Kostrov in 1966, but the specific surface energy is defined more clearly in this paper. The growth of a crack is an important problem, not only for the estimate of strength and other rheological properties of material, but also for the study of seismic sources. To describe the process of rupture as a spontaneous phenomenon, one has to specify the change in the dimension of a crack in addition to the boundary condition of the surface of the crack. This change in dimension can be discussed by considering the yielding mechanism at the tip. The elastic field of the medium containing a crack has a strong stress concentration near the tip of the crack, which possibly causes the fracture in this region and enforces the development of the crack. This idea is shown to be consistent with the criterion proposed by Griffith [1921], which is a 'nonlocal' theory, based on the energy balance of the whole material surrounding the crack. The former, which is concerned only with the 'local' state in the vicinity of the tip, is often more convenient than Griffith's criterion for application to practical problems as well as for the understanding of the physical mechanism of rupture growth. In this paper the case of a longitudinal-shear crack for which the mathematical representation has already been given [Ida and Aki, 1972] is discussed.