Uplift in the broken Andean foreland of the Argentine Santa Bárbara System (SBS) is associated with the contractional reactivation of basement anisotropies, similar to those reported from the thick-skinned Cretaceous-Eocene Laramide province of North America. Fault scarps, deformed Quaternary deposits and landforms, disrupted drainage patterns, and medium-sized earthquakes within the SBS suggest that movement along these structures may be a recurring phenomenon, with yet to be defined repeat intervals and rupture lengths. In contrast to the Subandes thrust belt farther north, where eastward-migrating deformation has generated a well-defined thrust front, the SBS records spatiotemporally disparate deformation along structures that are only known to the first order. We present herein the results of geomorphic desktop analyses, structural field observations, and 2D electrical resistivity tomography and seismic-refraction tomography surveys and an interpretation of seismic reflection profiles across suspected fault scarps in the sedimentary basins adjacent to the Candelaria Range (CR) basement uplift, in the south-central part of the SBS. Our analysis in the CR piedmont areas reveals consistency between the results of near-surface electrical resistivity and seismic-refraction tomography surveys, the locations of prominent fault scarps, and structural geometries at greater depth imaged by seismic reflection data. We suggest that this deformation is driven by deep-seated blind thrusting beneath the CR and associated regional warping, while shortening involving Mesozoic and Cenozoic sedimentary strata in the adjacent basins was accommodated by layer-parallel folding and flexural-slip faults that cut through Quaternary landforms and deposits at the surface.Broken-foreland basins such as the foreland of the Cenozoic southern Central Andes evolve in areas where retroarc convergence is accommodated primarily along reactivated, high-angle structures (e.g., [1–3]). Rather than forming an extensive region of consistently sloping mean topography (e.g., [4]) and a well-defined deformation front (e.g., [5, 6]), as in orogenic wedges that host thin-skinned foreland fold-and-thrust belts, uplift along high-angle structures in thick-skinned broken forelands is generally diachronous and spatially disparate (e.g., [3, 7]). These morphotectonic end members of foreland deformational styles are well exemplified by the Subandean foreland fold-and-thrust belt of Bolivia and north-western Argentina, and the broken foreland of the north-western ArgentineanSanta Bárbara and Sierras Pampeanas uplifts (Figure 1). The Santa Bárbara morphotectonic province is a seismically active low-strain region [8], characterized by discrete ranges of limited strike length that occur far away from the principal topographic front of the Andean orogen [4, 9] and that constitute a contractionally reactivated Cretaceous extensional province (e.g., [10–12]).The recognition and definition of fault chronologies in low-strain broken forelands and within continental interiors located far from plate boundaries is an important and timely topic in tectonics [13, 14]. Such faults, often active over time scales of 103 to 104 years and with long recurrence intervals, present a major problem when seeking an overall understanding of the spatiotemporal characteristics of foreland deformation, as well as when evaluating seismic hazards [15–22]. Research topics that need to be investigated in order to better understand the ongoing tectonic and sedimentary processes that characterize such environments include the areal extent affected by tectonically active structures, the subsurface geometries of faults, and deformational styles, as well as the impact of faulting on the geomorphic evolution. Addressing some of these topics may ultimately help to better establish the spatiotemporal characteristics of deformation and unravel the degree of activity of deformational processes in broken-foreland areas. The first and most basic step in such an endeavor is to determine fault geometries, and to assess fault kinematics and their possible relationships with reactivated crustal anisotropies, prior to determining fault chronologies and deformation rates. We therefore chose such an approach in this study, focusing primarily on open questions relating to the seismotectonic character of the south-eastern sector of the broken foreland of the Santa Bárbara System. In addition, we reviewed the impact of Quaternary tectonism on the landscape in this morphotectonic province.We have examined suspected active faults in the piedmont zones of the Candelaria Range (CR), in the southern SBS at approximately 26°S (Figures 1 and 2), that may exist within the sedimentary cover rocks and whose activity may have been driven by blind thrusting in the basement rocks. Previous investigations have suggested that the main fault responsible for the uplift of the CR extends to the surface and that a fault in the western piedmont roots in the basement (e.g., [23–25]). However, these interpretations appear to be at odds with the structural relationships shown on the Geological Map of Salta [26]. This map indicates that the northern and southern terminations of the CR form an elongated basement uplift with doubly plunging drape folds, and it includes no indication of any major faults bounding the range. This suggests that the uplift of the CR could have been associated with motion along a blind thrust, while the adjacent piedmonts of the range may have been ruptured by structures possibly associated with flexural-slip folding in the sedimentary cover rocks and that resulted from ongoing shortening in the adjacent basement blocks.Barcelona et al. [24] carried out a remote sensing and geomorphic analysis of the large-scale morphostructural characteristics of the greater CR region; they proposed a multistage tectonic evolution involving spatially separated thick-skinned and thin-skinned deformation styles. These authors identified a major fault scarp in the western piedmont of the CR and inferred a principal range-bounding fault delimiting the eastern flank of the CR. They furthermore suggested that a low mountain-front sinuosity along the western flank of the range is evidence of strong tectonic activity along a range-bounding fault.For our research, we have built on these interesting results and carried out further investigations into the manifestations of Quaternary tectonic activity at three selected field sites. Valuable insights into the location and geometry of potentially active faults with poor morphologic expressions within humid regions can be achieved through a combination of geophysical and geomorphic analyses (e.g., [27–29]). In particular, the use of data combined from near-surface geophysical techniques, high-resolution digital elevation models (DEMs), and geomorphic field mapping has provided a robust methodology, which to reduce ambiguities in the deciphering of paleo-seismological features such as those suspected to exist within the SBS (op. cit.). We analyzed east- and west-dipping piedmont faults and tilted Quaternary alluvial-fan deposits on both flanks of the CR that are suggestive of Quaternary tectonic activity. Fault scarps up to 30 m high appear to be the most pronounced features of tectonic origin in the intermontane basins of the SBS province. These scarps lend themselves to detailed inspection because they have been cut by rivers and expose deformed Tertiary sedimentary strata in the inferred hanging walls. In order to further assess the piedmont zones of the CR and to locate additional, possibly active faults and infer their geometries, we first conducted a geomorphic mapping. As a second step, we then used near-surface geophysical techniques, including 2D electrical resistivity tomography (ERT) and seismic-refraction tomography (SRT), across these fault scarps in order to characterize the fault geometry at depth. In a third step, we interpreted two oil-industry seismic reflection lines to link the observed surface structures to deep-seated geometries.The seismically active foreland of the north-western Argentinean Andes between latitudes 23°S and 33°S is the type locality for broken forelands (Figure 1; [1, 30]); here, the accumulation of shortening during repeated earthquakes is suggested by variably deformed Quaternary deposits, tectonic landforms, and reverse-fault-bounded mountain ranges ([31][7, 24, 32–34]). In some cases, these mountain ranges are not bounded by faults with sufficient displacement to explain their relief, but they instead consist of extensive basement-cored antiforms associated with sedimentary drape folds, underlain by blind faults (e.g., [2, 7, 32, 34, 35]). Taken together, these different structural and tectono-geomorphic phenomena reflect the complex long-term effects of protracted Cenozoic shortening in the broken Andean foreland, superimposed on crustal heterogeneities. As such, the structural character of this region is akin to the Cretaceous-Eocene basement uplifts of the North American Laramide province (e.g., [1, 3, 36, 37]) and the seismically active Tian Shan of Central Asia [38, 39].The structures associated with the SBS record the inversion of the Cretaceous Salta Rift [10, 11, 23, 40]. At a latitude 23°S, this morphotectonic province transitions into the thin-skinned Subandes foreland fold-and-thrust belt (Figure 1). Ongoing spatially and temporally disparate tectonic activity within the SBS has created a topography with asymmetrically uplifted mountain ranges, intervening sedimentary basins, and tectonically forced drainage patterns and landforms with evidence of different stages of tectonic inversion [7, 24, 25, 32, 41–43].The CR of the SBS belongs to a series of spatially separated, reverse-fault-bounded or basement-cored ranges associated with concealed faults within the broken foreland of the Andes (Figures 1 and 2; [24, 33, 44]). The uplift history of the SBS ranges is directly related to the spatially and temporally disparate eastward migration of Andean deformation within this sector of the foreland [12, 45–48]. This is in stark contrast to the tectonically active deformation front of the Subandes fold-and-thrust belt to the north, where the style of deformation is related to regional décollements that dip gently toward the west [49–56] (Figure 1).The N-S trending basement-cored asymmetric antiform of the CR is located between latitudes 25.5° and 26.5°S, and between longitudes 65.5° and 64.5°W (Figure 1). The interior of the range exposes deformed Upper Precambrian to Lower Cambrian metasediments [57, 58], while folded sedimentary cover rocks are preserved around the flanks of the range and dip outwards [35, 59, 60]. These latter units comprise terrigenous and marine Cretaceous and Paleogene strata of the Salta Group, followed by continental clastic deposits of the Mio-Pliocene Orán Group [12] (Figure 3).The oldest units of the Salta Group consist of red conglomerates and sandstones of the Pirgua Subgroup [12, 61]. These syn-rift deposits are succeeded by post-rift sandstones and calcareous strata of the Balbuena Subgroup [62, 63], as well as lacustrine mudstones of the Santa Bárbara Subgroup [64]. These rift-related units are unconformably overlain by strata of the syn-orogenic Metán and Jujuy subgroups of the Orán Group. The majority of these strata are sandstones, conglomerates, and shaly deposits [26, 65].These units are in turn unconformably overlain by Plio(?)-Pleistocene alluvial-fan conglomerates [26]. All piedmont zones of the CR are covered by these coarse deposits, which form an integral part of multiple, gently inclined geomorphic surfaces that occur at successively lower elevations away from the CR. Except for the lowest, active, alluvial-fan surface, all of these surfaces are isolated remnants of formerly contiguous and coalesced alluvial fans that have been incised since they were abandoned as active depositional environments.It is important to note that, while inspection of surface faults is relatively straightforward in the generally arid Sierras Pampeanas broken-foreland province (between latitudes 27°S and 33°S), as is also the assessment of seismogenic structures, particularly in the western part of that morphotectonic province (e.g., [66]), such features are more difficult to discern in the humid SBS province. A dense vegetation cover and rapid climate-driven modification of tectonically controlled geomorphic features render a seismotectonic evaluation of this region far more challenging (e.g., [7, 67–69]). In this environment, rupture zones, faults, and fold scarps have often been erosionally modified or even obliterated. Where vestiges of these tectonic landforms have been preserved, they are often concealed by dense vegetation [70] or have been further modified by anthropogenic influences. This compromises the collection of unambiguous geological, geomorphic, kinematic, and geochronological data used to characterize the level of tectonic activity.Because of the dense vegetation cover within the CR piedmont zones that makes it difficult to detect fault scarps in the broken foreland, together with the highly dynamic surface-process regime that tends to rapidly modify seismogenic features in the landscape, we decided to use a combination of geological and geophysical methods to identify faults with possible Quaternary tectonic activity. Our field observations and a careful analysis of outcrops helped us develop and test a model of fault activity that could then be further evaluated using electrical resistivity images, seismic-refraction tomography, and seismic reflection profiles.Our study of the geomorphic features was based on inspection of high-resolution digital elevation models (DEMs) and satellite imagery, with subsequent field validation for each fan on both sides of the CR. This allowed us to identify anomalies in the fluvial network and to unambiguously record different alluvial-fan generations within the piedmont zones. In order to develop a detailed geological map with particular emphasis on the youngest deposits and landforms, and to assist in mapping the different generations of alluvial fans and terraces, we used true color images from Landsat 8 (bands 2, 3, and 4) together with Google Earth images (Figure 2). Additional maps that included parameters such as relief, slope, and drainage characteristics were generated from two DEMs with spatial resolutions of 12.5 m and 5 m. These DEMs were generated from ALOS PALSAR data that we obtained from the Alaska satellite facilities [71]. The 5 m resolution DEM was acquired from RESTEC, the Remote Sensing Technology Center of Japan. We also analyzed the local relief and drainage characteristics using the TopoToolbox program [72, 73]. Finally, we used the 5 m resolution DEM to generate six longitudinal river and surface profiles to assist with our mapping and with interpretation of the tectono-geomorphic evolution of the piedmonts. The resulting river-gradient maps, together with the derived drainage networks and river/surface longitudinal profiles, helped us to identify the presence of fault and fold scarps.A number of electrical resistivity tomographic (ERT) surveys were completed in the eastern and western CR piedmont areas to identify and characterize the geometry of fault zones at depth (Figure 4). The depth of penetration in such surveys usually depends on the electrode separation and the length of the profile; for example, for an electrode separation of 6 m, the maximum depth of penetration ranges between 50 and 60 m. Resistivity contrasts between areas in the subsurface with different properties (e.g., [74]) and lateral heterogeneities can reveal fault architecture and the associated kinematics and deformation patterns, at least to some extent (e.g., [28]). The ERT surveys were all conducted with identical dipole-dipole electrode configurations and recorded with 48 electrodes at 6 m spacings, to achieve 288-m-long profiles at each of the selected survey sites. The profiles were designed with orientations perpendicular to the scarps of the suspected faults, with each profile centered on the highest point of the scarp to ensure that any possible fault continuation on either side of the surface expression of the structure was also covered. We chose to conduct our surveys during the arid season, when the water table level typically drops to between 50 and 60 meters below the surface; this information was obtained from farmers whose water supplies depend on local wells, which are regularly monitored. In order to achieve greater penetration along the East Candelaria piedmont profile, we followed an ephemeral stream channel across the scarp of the inferred fault (Figures 4(b) and 5). We used an ARES georesistivity meter from GF Instruments Inc. (http://www.gfinstruments.cz) to obtain fully automated measurements.The apparent resistivity values were automatically inverted using RES2DINV software [74], which follows a 2D inversion method developed by Loke and Barker [75]. This routine is based on a smoothness-constrained least-squares inversion implemented using a quasi-Newton optimization technique [76].The optimization adjusts the 2D resistivity model by iteratively minimizing the residuals of the apparent resistivities. The root mean-square (RMS) error is then taken into account when evaluating the efficiency of the minimization process in the least-square approach, for all data sets and configurations. We considered an RMS error<10 good enough for the model to be accepted. For the two profiles on the western flank of the CR (Profiles E1a and E1b; Figures 2, 4(a), and 5), the inversion yielded good results after four iterations using the electrical data obtained for Profile E1a. The eastern Profile E2 (see location in Figures 2, 4(b), and 5) also yielded an acceptable inversion model after four iterations. Finally, for the easternmost profile (E3) on the eastern flank of the CR region (see location in Figures 4(c), and 5), we obtained a feasible model after just two iterations.Following our geomorphological and morphometric analyses and the ERT surveys, we carried out three seismic-refraction tomography surveys (S1, S2, and S3) at approximately the same locations as the ERT surveys (Figures 2, 4, and 5). We used a GEODE Exploration Seismograph connected to 24 vertical-component 4.5 Hz geophones spaced 10 m apart (Figure DR1). The seismic source consisted of an accelerated weight of 100 kg and a 2 m height-acceleration path; we used three impacts (or shots) per site on average, in order to be able to improve the signal-to-noise ratio by stacking the three sets of results for each shot point. On seismic line S1, we also used two additional shot points, at 30 m and 70 m offsets from the first geophone along the profile line. This configuration was repeated symmetrically for the last geophone in the seismic line, as shown in Figure DR1 in our data repository. Other additional shots were used at 125 m, 185 m, and 255 m from the first shot position (Figures 2–4 and DR1). For seismic line S2 (Figures 2 and 4 y DR1), we carried out shots at 5, 30, and 70 m offsets from the first geophone on the line, and at 5, 30, 70, and 110 m offsets from the last geophone. Three additional shots were also made at intermediate positions, at distances of 125, 185, and 255 m from the first shot. For seismic line S3 (Figures 2 and 4), we carried out seismic acquisitions using shots at 5 m and 35 m offsets from the first geophone and shots at 5 m and 35 m offsets from the last geophone. Four additional shots were also used at intermediate positions 90, 145, 170, and 210 m from the first geophone. The S1 seismic line was therefore the longest and the S3 seismic line the shortest in our study, due mainly to access limitations.We processed the seismic-refraction tomography data using SeisImager/2DTM software (available from http://www.geometrics.com), which follows a methodology proposed by Hayashi and Takahashi [77]. This method uses a direct modeling algorithm developed by Moser [78] and Hayashi and Takahashi [77], based on a technique sensitive to inhomogeneities in the subsurface represented by lateral changes in seismic wave velocities. We performed an inversion for hand-picked first P-wave arrivals. By comparing observed travel times with theoretical travel times from a preliminary layered model, we generated a final seismic velocity model following ten inversions for each seismic profile. Our results were consistent, with an RMS error of 3.2% for the western CR line (S1), an RMS error of 4.1% for seismic line S2, and an RMS error of 3.6% for seismic line S3. The residuals were determined quantitatively after each iteration and cross-checked qualitatively for the space distribution of modeled ray paths. Using different initial seismic velocity models and good ray-path coverage with the inversion of the 2D P-wave velocity refraction data, the results were shown to be consistent to a depth of about 80 or 90 m (e.g., [79]).We obtained well-log data from one petroleum exploratory well and six oil-industry seismic reflection profiles provided by Yacimientos Petrolíferos Fiscales (YPF) of Argentina. We used the eastern half of lines 45112 and 45113 (Figure 1), which were located in the northern part of the intermontane Choromoro basin on the western side of the CR. Both lines were approximately perpendicular to the CR main axis (Figure 1). The Rosario de la Frontera Norte x-1 well was located to the south of Rosario de la Frontera town, northwest of the CR (Figure 1). Importantly, the seismic lines cross the homocline that developed in the sedimentary cover units on the western flank of the CR as a result of uplift of the range. In this area, the partially eroded sedimentary cover forms a rather straight line of westward-sloping flatirons at the contact with the piedmont gravels. The approximately east-west oriented seismic reflection lines cover a length of about 25 km, with a separation of about 4 km.The SEGY seismic-line data were analyzed together with the well logs and combined with the surface geology to derive a subsurface geological model. We then compared this model with the shallow-penetration geophysical data that we had obtained. We first applied a frequency filter to remove residual noise and then performed a time-to-depth conversion using Move2D software (Petroleum Experts, Midland Valley Exploration Ltd.), making use of seismic velocities from the well data and the YPF seismic data. We next used the uppermost units of the sedimentary strata in the well log to tie stratal boundaries to the seismic stacks for the interpretation. The well depth was 3200 m, which means that it penetrated the stratigraphy (Figure 3) from the Quaternary (Piquete Formation) to the Tertiary, terminating in the Upper Cretaceous (Lecho Formation, Balbuena Subgroup). We also extrapolated imaged strata from surface outcrops on the western flank of the CR, where the underlying sedimentary strata (including Lower Cretaceous units) are exposed.These data were combined together and integrated into a structural model based on an earlier analogue model from Seggiaro et al. [80]. The cross-sections were forward-modelled using 2D area-balancing techniques, with the algorithms provided in the Move2D program, in order to obtain the best geometric match between the observed geological field conditions and the model. Trishear techniques (e.g., [81]) were used to derive the geometry of the basement fault responsible for the drape folding of the sedimentary cover rocks.The broken Andean foreland has been strongly influenced by tectonic processes that have impacted the Quaternary landscape evolution, to the present day. This influence is manifested by drainage reorganization (Figures 4(a)–4(c)), the tilting of the various alluvial-fan surfaces, and the presence of fault scarps. In this section, we first report on the results of our geological and geomorphic observations in the CR. We then characterize faults in the CR piedmonts using the results from ERT and SRT surveys. Finally, we use seismic reflection profiles to extend our near-surface interpretation of possible fault geometries down to greater depths. In this study, we have identified five fault scarps in the CR piedmonts through remote sensing, but due to limited accessibility we had to restrict our data collection in the field to three of these structures, which we named according to their locations: the West Candelaria fault in the western CR piedmont, and the East Candelaria and Copo Quile faults in the eastern CR piedmont (Figure 2). Over time, erosional modification has smoothed the profiles of these scarps to the extent that they may now appear at first sight to be fold scarps. However, the straightness of the scarps and the narrow widths of the features, together with the data from our geophysical analyses (see below), indicate that the fault tips must be within at most a few meters of the surface, but most likely they broke the surface.We were able to use the elevation of the fan surfaces in the CR piedmont, their lateral continuity and degree of dissection to separate them and associated fluvial terraces into five different geomorphic and stratigraphic units. These units record stages of fan formation, subsequen tincision, and renewed fan deposition at subsequently lower elevations within the piedmont. In the westernmost sector of our study area, there are dissected and deformed conglomerates (Figure 2) that probably have a similar alluvial-fan origin as closely spaced conglomeratic alluvial-fan remnants. Episodic incision has generated four stratigraphic units that correspond to different levels of alluvial fans and fluvial terraces (Q1-Q4) that define a staircase morphology. The youngest unit (Q5) is an undifferentiated conglomeratic Quaternary sediment fill in the present-day drainage channels (Figure 2). The first, and topographically highest fan surfaces and their deposits (Q1) are only found on the eastern side of the CR (Figure 6(a)-1); these are the fan surfaces closest to the range and they have been deeply incised, with locally high relief of approximately 50 m (Figures 6(b)-1 and 6(b)-2). They comprise boulder conglomerates and coarse, matrix-supported conglomerates, often intercalated with thin layers of sand and silty clay (Figures 6(b)-1 and 6(b)-2). These older fan surfaces appear to have been tilted by tectonic warping following their formation because their inclination is locally greater than 5° and, in some cases, up to 12°. If the gradients of the fan remnants are extrapolated back toward their source areas in the CR, the proximal fan surfaces would project to the highest levels of the mountain range and they would not reach the mountain fronts, where the streams would have originally deposited the conglomeratic fan gravels. This suggests that the incision of the oldest fan surfaces was closely linked to tectonism in the piedmont zones, which may also have been accompanied by a drop in base level. Such a tectonic interpretation is supported by the polymict composition of the fan gravels, which includes rock types that are exposed along the entire range and is not restricted to the basement rocks of the high range interior (Figure 6). A monomict, basement-dominated composition would be expected had the piedmont fans and terraces been originally associated with such a high source area.The second, less dissected group of fan deposits and corresponding surfaces (Q2) is found on both sides of the CR (Figure 6(a))-2). These fans occupy a lower part of the piedmont and are characterized by lower local relief. The exposed fan strata consist of coarse conglomerates with overlying layers of silt and interbedded gravels (Figures 6(b)-3 and 6(b)-4).The Q2 fan remnants of the west CR piedmont are characterized by well-lithified conglomerates that dip up to 9° toward the west (Figure 6(b)-5). These units directly overlie Cretaceous and Paleogene sandstones and siltstones that dip at between 25° and 30° toward the west.Fluvial terraces are sculpted into the older alluvial-fan deposits. The terrace (Q3) comprises coarse to very coarse basement gravels from the interior of the range, together with intercalated sandy to silty layers. The exposed cover gravels of the younger fluvial terrace (Q4) are matrix-supported and conglomeratic. The youngest unit (Q5) defines aggrading strata within the main piedmont drainages and their tributaries (Figure 2).The oldest eastern fans (Q1) have been offset by the East Candelaria fault (Figures 2, 5, and 6(a)-1, 6(b)-1, 6(b)-2) with an east-side-up displacement. These fans are the most eroded and are now only represented by scattered surface remnants along the length of the eastern piedmont of the CR. Activity along the East Candelaria fault interrupted the eastward-directed drainages from the CR and started the dissection of the fan surfaces; the younger Q2 alluvial-fan surface was then generated at a lower elevation (Figures 2 and 4). The East Candelaria fault is located 2 km to the east of the range (Figures 2, 5 (Profile 3), Figures 4(b) and 4(b′⁠)). It strikes approximately north-northwest, extends for about 20 km, and cuts through the geomorphic surfaces associated with both the Q1 and Q2 alluvial-fan deposits. The vertical offsets of the fan surfaces are about 20 m (Figure 5, Profile 3). In the south-eastern portion of the CR piedmont, the surface that corresponds to Q1 is displaced by 20 m relative to the elevation of the Q2 surface, while in the northern part of the fault the offset is at least 30 m (Figures 4(b) and 4(b′⁠)). The light blue color in Figure 4(b′⁠) that represents the smooth surface of Q2 (Figure 4(b)) also highlights the spatial arrangement of the drainage and the relationships between the abandoned Q1 fan surface and the younger Q2 fan surface. The older Q1 fan surface was probably incised and eroded after movement along the East Candelaria fault had uplifted the fan surface, forcing the drainage to flow northward.To the east of the East Candelaria fault is the Copo Quile fault scarp. This is the shortest of the faults in the eastern piedmont of the CR that appear to be associated with Quaternary activity, extending for about 8 km along a north-northwest strike direction (Figure 5, Profile 4). This fault cuts the Q2 alluvial-fan gravels and offsets them vertically by about 25 to 30 m (Figure 4(c)). From Figure 4(c′⁠), it can be seen that the slope of the fan surface offset by the fault is gently inclined toward the east. This setting clearly documents that the fluvial network in this area has been diverted by faulting. Some of the drainages were able to maintain their eastward flows while the Copo Quile fault was active, but others were forced to change their courses southward to avoid the growing topography associated with the active fault.In the western part of our study area, the conglomerates of the remnants of the oldest Plio-Pleistocene piedmont strata (Unit J) are incised by streams sourced in the CR (Figures 2 and 4). These gravels are in angular unconformable contact with the Plio-Pleistocene strata of the Jujuy Subgroup [7, 26]. The Q2 fans in the western piedmont were also affected by faulting. The West Candelaria fault, with its prominent, 17-km-long, uphill-facing scarp strikes parallel to the orientation of the CR (Figures 2 and 4). It is a layer-parallel structure between the Neogene strata of the Metán Subgroup that dips at 30° toward the west. The fault offsets the Q2 alluvial fan vertically by up to 20 m (Figure 5(a)). The fault trace is clearly visible as a straight line on satellite imagery, in the DEM, and in the field (Figure 4(a)), even though the scarp is rather gentle and has been erosionally modified. A second fault trace is evident to the west of the central part of the West Candelaria fault (Figures 5 and 6(b)-5 (Profiles 1 and 2)). Outcrops exposed in rivers cutting across these structures reveal an angular relationship between the tilted Quaternary conglomerates and the underlying deformed Tertiary strata (Figure 6(b)-4), confirming the sustained deformation in the piedmont. The smooth Q2 fan surface terminates abruptly against the straight fault-line, but the fan level continues across it in the form of a tilted, dissected fluvial terrace. These relationships are well expressed on our slope map of the western flank of the CR (Figure 4(a′⁠)), where the smooth Q2 surface (blue) abuts the flatiron landforms of the Mesozoic rocks (red and yellow-colored sectors) that cover the westernmost flanks of the CR. Beyond the fault scarp to the west, the slope remains gentle, but this area is incised by numerous ephemeral streams.As in the eastern piedmont, our field mapping and visual correlation in the field is based on the geological map of Metán [26], lateral pinch-outs and the chronology developed for the SBS basins by Hain et al. [7], and we conclude that all incised and erosionally modified surfaces in the western piedmont belong to the Q2 fan surface.To analyze the tectonic imprint on the landscape in greater detail, we generated six longitudinal river and geomorphic-surface profiles across the western and eastern slopes of the CR, using our 5 m resolution DEM data (Figure 7). The longitudinal profiles of the present-day river courses across the western flank of the CR do not show any knickpoints at the fault locations or within the basement areas. We therefore suggest that faulting in the piedmont zones along the West Candelaria fault was followed by protracted incision and the reestablishment of a concave longitudinal river profile. It is not known when the reestablishment of this equilibrium profile was completed, but the gentle gradient suggests that either the West Candelaria fault did not remain to be active for long, or the tectonic forcing was relatively weak compared to the erosional processes. Knickpoints do exist within the CR (Figure 7, Profile 5), but rather than indicating tectonic forcing they are interpreted to be related to outcrops of resistant Precambrian basement rocks.The topographic profiles across the inclined alluvial-fan surfaces clearly reveal the sites of faulting responsible for the two uphill-facing scarps of the West Candelaria fault and the less well-expressed fault to its west (Figures 2, 5 (Profiles 1 and 2), Figures 4(a) and 4(a′⁠)). In the longitudinal profile, the fan sectors to the west of these faults are more steeply inclined than would be expected for an equilibrated alluvial-fan profile.In light of the regional compressional tectonics affecting the Santa Bárbara System, these observations suggest that the greater inclination of the fans (between 5° and 12°) to the west of the West Candelaria fault reflect tilting in the hanging wall of possibly west-dipping, thrust faults that have generated east-facing scarps (see Sections 4.2, Section 4.3, and Section 4.4 describing the results of our geophysical surveys).Finally, our geomorphic analysis and the extensive field inspections of all major drainages that originate in the CR and cross the transition area between the range and the piedmont zones have revealed that a previously reported major range-bounding fault on the eastern side of the CR (i.e., [24, 35]) does not in fact exist. None of the alluvial-fan surfaces covering the transition area between the range and the piedmont are offset by faulting, nor do any of the river-cut exposures reveal any evidence of deformed or cataclasized rocks within a fault zone. Knickpoints do exist in the metamorphic basement rocks of the range interior and are most likely controlled by lithology or they reflect regressive knickpoints related to upstream-migrating incision processes related to regional-scale basement upwarping. Importantly, no knickpoints exist in the longitudinal profiles crossing the range front, however. Taken together, the east-west asymmetry of the range and its doubly plunging northern and southern terminations must therefore be the result of differential tilting, which we suggest is likely to have been related to blind faulting beneath the range. In contrast, the three main scarps in the piedmont zones associated with the West Candelaria, the East Candelaria, and the Copo Quile faults are interpreted as being of related to surface rupture (Figure 4). These inferred fault scarps are further analyzed below using our newly acquired geophysical data.The E1a and E1b ERT profiles across the western CR piedmont (Figures 2 and 4) were measured perpendicular to the fault scarp, as shown in the geological and slope maps (Figures 2 and 4(a)). From the limited amount of outcrop in the area that is accessible for direct inspection, together with the well-log information, we inferred that all sedimentary rocks in the immediate subsurface are of Cretaceous or Tertiary age, and that these are covered by Quaternary alluvial-fan gravels (Figure 6(b)-4). Our geological observations in the river exposures across the scarp indicated that faulting was layer-parallel and related to flexural slip; this faulting did not rupture the Metán Subgroup strata obliquely. In addition, we observed the alluvial-fan sediments in an angular unconformity with the Metán Subgroup strata and the associated alluvial-fan remnants are tilted westward. We carried out tomography surveys at two sites where the faulted nature of the scarp could be inferred from the vertical offsets (Profile E1a shows a 3 m offset; Profile E1b shows a 15 m offset). The resistivity values obtained ranged between 6 and 800 ohm∗m, with an RMS error of 5.1 after four iterations. The maximum penetration depth was about 65 m. A significant lateral variation in resistivity from west to east was found between -20 and 20 m of profile length, indicating an abrupt horizontal change from low to high-resistivity zones at elevations of between 1360 and 1350 m. In the eastern part of the same survey, at elevations of between 1370 and 1360 m, and between 0 and 100 m of profile length, we recorded a low-resistivity layer that thinned towards the east. Immediately below this low-resistivity layer, we imaged a highly resistive layer of approximately double the thickness of the layer above it. In the western part of the profile, we noted an upper high-resistivity layer about 5 to 10 m thick, overlying a low-resistivity layer.Approximately 1100 m further to the north, we measured electrical properties along Profile E1a using the same survey configuration (length: 288 m; number of electrodes: 48; electrode spacing: 6 m; quadripoles: 802; Figure 8). After four iterations, we obtained a reliable RMS error of 3.0%, with resistivity values varying between 7 and 1100 ohm∗m and a maximum penetration depth of 65 m. This profile showed high resistivities in the upper 25 m along its entire length, with maximum values of 909 ohm∗m. The section between -60 and 10 m of profile length (Figure 8) emerged as a conductive zone, where the resistivity values decreased to 7 ohm∗m at depths greater than 23 m. This is similar to observations along the southern profile (E1b), although in that case a topographic step exists at the surface and the amplitude of the resistivity anomaly is smaller. We observed on Profile E1b an abrupt vertical reduction in resistivity with increasing depth immediately above the conductive zone described above. Both profiles on the western flank of the CR showed a coherent subsurface resistivity structure.The S1 seismic tomography profile (Figure 8), which was recorded at the same location as the ERT Profile E1b (Figure 4), revealed a seismic velocity structure consistent with Vp values that increased with depth. We noted lateral variations in Vp close to the inferred fault, suggesting localized variations in thickness. The different velocity layers were continuous along the entire E-W profile. The layer characterized by a Vp of approximately 1270 m/s recorded an increased thickness in the central part of the profile; this is in good agreement with the topography of the ground surface above. Another anomaly in seismic velocities was found between about 1360 and 1340 m elevation and at a distance of between 20 and 70 m along the profile. An approximately 10-m-thick low-velocity layer was recorded at a shallow depth in the central part of the profile between -30 and 10 m of profile length.The E-W orientation of the E2 and S2 profiles is perpendicular to the inferred orientation of the East Candelaria fault at depth (Figures 2 and 4). This structure has a minimum topographic offset in excess of 22 m. We used a similar electrode configuration to that used for Profiles E1a and E1b on the west side of the CR. After four iterations, the inversion resulted in a reasonable RMS error of 4.2%. The resistivity model displayed an almost vertical major discontinuity close to the center of the profile, coinciding with the position of the north-northwest oriented morphological scarp. The western half of the profile is dominated by high-resistivity values, while lower values (between 1 and 10 ohm∗m) are characteristic of the area to the east of the scarp. The thin uppermost layer exhibits high resistivities across the entire E-W transect.Results from the S2 seismic profile were obtained from the same location as the E2 electric profile; this profile shares the same central reference point (Figure 9). The identified velocity layers are continuous from west to east. The shallower layers are parallel to the surface and therefore have a gentle eastward inclination. Between -20 m and 80 m horizontal distance along the profile, layers with high velocities get closer to the surface. These high-velocity layers define an area in the central part of the profile in which the thicknesses of the different layers decrease noticeably as they approach the surface; the sediment cover in this central part of the seismic line was negligible. We note that the vertical shift in velocities for layers in the eastern portion of the velocity model was consistent with the location of the resistivity discontinuity in the corresponding model.East of the East Candelaria fault and at a distance of approximately 10 km from the eastern flank of the CR, the E3 profile (obtained by merging three intersecting electrical profiles) crosses a wedge-like structure with a total length of 576 m (Figures 2 and 4); we used a total of 1869 quadripoles (Figure 4(c)) to measure this section.The resistivity results indicate a range between 0.5 and 250 ohm∗m. The final model of this profile was obtained after two iterations, with an RMS error of 7.3%. Along this profile, we identified a high-resistivity layer in the upper 15 m, with a gentle westward inclination; at a 480 m horizontal distance of profile length, the inclination of this layer changes to an easterly orientation.At 288 m of profile length (central part of the profile) in the shallow part of the profile, there is a westward-inclined layer (orange color) toward the 0 m mark of the profile; this layer becomes progressively deeper and more conductive. The layer also becomes thicker to the west and is covered by a thin layer with lower resistivities (1 to 17 ohm∗m). On the eastern shallow part of the traverse from 288 m of profile length until the eastern end of the profile, there is a high-resistivity layer with a thickness of approximately 5 m. Immediately below the high-resistivity surface layer (Figure 10; red color), there is a layer about 30 m thick (blue and green colors) of low resistivity that is inclined westward; this layer changes its inclination to an easterly inclination at about 480 m horizontal distance in the eastern (elevation of 690 m) sector of the profile. Between 384 and 480 m horizontal distance of profile length and at elevations between 660 and 650 m, there is a high-resistivity area in the east that is characterized by resistivities of about 40 ohm∗m (yellow area below the blue layer in Figure 10). This high-resistivity layer appears to have broken through the conductive layer above it (blue layer).Our results from the S3 seismic profile covered the easternmost 250 m of the E3 electrical profile (Figure 10). The modeled velocity profile indicates high velocities (>2500 m/s) close to the surface in the westernmost part of the profile, at an elevation of 672 m, with a strong vertical velocity gradient; the isovelocity layers were inclined at approximately 30° toward the east, before becoming subhorizontal in the eastern part of the profile, at an elevation of 652 m. The low-velocity layers became distinctly thinner towards the west, while layers with velocities between 1175 and 2000 m/s are thicker. Results from the eastern end of the profile thus indicate a horizontally layered seismic velocity structure. Layers with intermediate velocities reach the surface between 60 and 80 m horizontal distance along the profile indicating a lack of horizontal continuity in the seismic velocity layers.The two stacked seismic reflection profiles are located a few kilometers to the west of the West Candelaria fault. We also used well-log data from a petroleum-exploration borehole located near the town of Rosario de la Frontera (Figure 1) to tie the identified reflectors to geological units observed in the field. We were thus able to identify the entire stratigraphic column on the basis of vertical variations in acoustic impedance associated with the different layers. The low-intensity reflections with a chaotic signal and poor lateral continuity are likely due to the imaging of metamorphic basement rocks at a depth of 4100 m. An angular unconformity was imaged between basement rocks and the overlying syn-rift deposits of the Cretaceous Pirgua Subgroup, as expected from regional stratigraphic relationships. The Pirgua strata are in turn overlain by the post-rift sediments of the Balbuena and Santa Bárbara subgroups, which have a high signal amplitudes. By extrapolating the imaged units to the surface, they can be clearly seen to be the subsurface equivalents of the west-dipping sedimentary cover rocks of the CR (Figures 1 and 11).The combination of structural data collected in the field and the results of the analysis of the seismic reflection profiles enabled us to model the deformation of the sedimentary cover rocks of the CR using Move2D. First, we attempted to model the deformation in the context of a surface-breaking fault according to the model of Barcelona et al. [24]. In these model runs, the basement rocks exposed in the range interior would have had to be uplifted 2 km higher compared to their present-day position to generate the folded strata. As we were not able to generate the same flexure on the cover strata as observed in the seismic line with a reactivated fault cutting to the surface, we modeled the deformation features by introducing a blind fault under the CR, similar to other ranges in the broken foreland (e.g., [2, 34, 82]). Accordingly, by using the Trishear method (i.e., [81]) and by assuming a blind fault under the CR, we were able to generate an asymmetric fold in the sedimentary cover strata that mimics the field relationships and seismically imaged geometries much better. We therefore conclude that blind faulting underneath the CR is a viable mechanism to explain the deformation of the sedimentary cover rocks of the CR and the Quaternary faulting and warping of the alluvial-fan gravels in the piedmont. Based on the observed relationships, we present a model of the deformation features in Figure 12.In Section 5.1, Section 5.2, and Section 5.3, we discuss the characteristics of all three faults identified in the piedmonts of the CR (Figure 1).We review recent structural models in relation to our own field, geomorphic, and geophysical observations and present a simple model for the structural evolution of this foreland sector.Our tectono-geomorphic analysis of the three main faults in the piedmonts of the CR revealed that spatial variations in topographic gradients within the region are controlled by these three structures. In addition, movement along these faults on both sides of the CR has fundamentally influenced the piedmont fluvial networks, resulting in the development of a trellis drainage pattern. Local uplift along the piedmont faults caused streams to change their flow directions from range-perpendicular to either northward or southward, parallel to the fault scarps. In other cases, sustained incision was able to keep pace with uplift along the piedmont faults, leaving fluvial terraces behind and resulting in the subsequent formation of new alluvial-fan surfaces at successively lower elevations. The gradients of the alluvial-fan terraces are generally greater in the older fan surfaces, suggesting regional uplift and tilting during the growth of the CR. Locally, however, pronounced steps interrupt the longitudinal profiles of the older fan terraces, where we inferred the locations of the piedmont faults. Interestingly, our study did not reveal any evidence of Quaternary activity along a major emergent reverse fault on the eastern range front, nor did we find evidence of any such significant structure bounding the western side of the CR. The basinward dip directions of strata along the flanks of the range and the decreasing inclination of the exposed Cretaceous and Tertiary strata below the western piedmont support these observations (Figure 11). These general characteristics of the gently sloping surfaces only change in the vicinity of the piedmont faults. In light of the warped Cretaceous strata and their contact with unconsolidated Quaternary piedmont gravels along the western flank of the range, the low mountain-front sinuosity index obtained in a remote sensing study by Barcelona et al. [24] is not an indication of tectonic activity. The low sinuosity index may instead reflect the sharp contrast in erodibility between these different lithologies. This scenario is identical to that on the western flank of the Sierra de Quilmes basement uplift in the north-western Sierras Pampeanas (e.g., [82, 83]) and other, asymmetrically uplifted basement blocks in that morphotectonic province (e.g., [2]).In the western piedmont of the CR, we identified three major scarps (Figure 2), but due to limited accessibility, we focused only on the West Candelaria fault for the geophysical surveys. The models from the two electrical profiles (E1a and E1b; Figures 2, 4, and 8) show low apparent resistivity areas directly beneath the inferred fault scarps, which is consistent with the low resistivity of the shaly strata of the Metán Subgroup sedimentary units. In the northern profile (Profile E1a), the fault zone has high-resistivity areas that are about 30 m wide on either side (east and west); this is in good agreement with the expected properties (high resistivity) of the alluvial-fan gravels on the western flank of the CR. These gravels comprise metamorphic rocks from basement outcrops that are characterized by high resistivities. The same situation applies to the southern part of the CR along Profile E1b (Figure 8). Profile E1b (Figure 8) also reveals an abrupt horizontal change in resistivity values, which helps to unambiguously determine the location of the West Candelaria fault. Higher seismic velocities that may represent compacted sedimentary strata were vertically translated toward the land surface, which leads to the interpretation of a low-conductivity zone in the model along Profile E1b (Figure 8); in the western part of this profile, the progressive growth of isovelocity layers beneath the inferred fault scarp coincides with the low-resistivity area of the fault zone (Figure 8). The orientation of the fault plane (at -80 to -20 m horizontal distance along the profile) is consequently best explained as representing a west-dipping thrust fault. In the eastern portions of both profiles (E1a and E1b) (Figure 8), the high-velocity and low-resistivity characteristics may relate to shale-rich lithologies. A 25-m-thick layer with relatively high resistivity is interpreted as representing alluvial-fan deposits. At a horizontal distance of 20 m from the center of Profile S1 (Figure 8), the alluvial-fan deposits onlap the fault and form a zone of homogeneous seismic velocities with exceptionally high electrical resistivity. In our interpretation, gravels of metamorphic basement rocks, together with Cretaceous siltstones and sandstones, were deposited in former river channels along the length of the north-south striking West Candelaria fault and compacted during the Quaternary. The shallow low-resistivity layer on top of the alluvial-fan deposits in Profile E1b (0–50 m) may well be an artifact probably related to a manmade freshwater pond located about 30 m to the north of the profile. The seismic-refraction results for Profile S1 in this area provide more stable, less noisy images the data obtained from the electrical profiles.Our two seismic reflection lines from the western CR piedmont allow us to extrapolate the subsurface strata to 7 km depth; the seismic reflection lines also permit us to trace stratal boundaries to the piedmont faults and the tilted outcrops of the sedimentary units that are draped over the CR basement rocks. Importantly, the location of the West Candelaria fault coincides exactly with its up-dip projection from the seismic-reflection stack that corresponds to the sedimentary strata of the Metán Subgroup (Figure 11). No other cross-cutting or steeply dipping faults originating in the basement rocks below can be discerned in the seismic sections. We therefore interpret the West Candelaria fault to be a flexural-slip fault that developed during bed-parallel movement along weak beds within the Neogene sedimentary strata.On the eastern side of the CR, across the East Candelaria fault, the electrical profiles show high-resistivity values which we interpret as being due to the characteristics of the alluvial-fan deposits (i.e., the high resistivity of the basement-derived conglomerate). This contrasts with the very eastern part of the profile, which presents significantly lower resistivities, possibly reflecting more conductive material such as Tertiary shaly strata. These observations are consistent with the seismic tomography results, which reveal subhorizontal layers with sedimentary characteristics beneath the ground surface, in the upper 40 m of the profile. To the east of the electrical-tomography survey, a marked decrease in resistivity values indicates a change in rock type. This sharp transition in resistivities coincides with the suspected fault location, as well as with the displacement of layers with higher velocities towards the surface in the central part of the seismic tomography profiles (Figure 9). The existence of strata from the Santa Bárbara Subgroup exposed along strike beyond the mapped area to the south (red circle in Figure 1; see photo in Figure 6(b)-6), dipping at 80° toward the east, suggests the presence of a fault. The sharp transition in both resistivity and seismic velocity characteristics also suggests the existence of an east-dipping, high-angle fault, which would best explain this disruption of the alluvial-fan deposits.Our easternmost geophysical survey in the CR piedmont crosses the north-south striking wedge-like structure that we identified as the Copo Quile fault in the morphological analysis. The high-resistivity layer at the top of the electrical profile (Figure 10, E3), which thickens toward the west, corresponds to alluvial-fan deposits. These units consist of basement-derived conglomeratic gravels, which explains why this top layer is characterized by high resistivity. Below this level, there is a low-resistivity layer approximately 30 m thick, which we interpret as representing a shaly horizon. This layer has been broken up and uplifted as a result of thrust movements along the Copo Quile fault, cutting through the sedimentary layers at 400 m horizontal distance of profile length, and at elevations of 670 and 650 m (Figure 10, E3). Furthermore, the SRT image reveals a major topographic step, which is similar to the geometry inferred for the other faults (Figure 10, S3). In addition, we observe a vertical change in the velocity gradient and twisted isovelocity lines toward the Copo Quile fault zone. In the ERT profile, the fault zone is characterized by intermediate electrical resistivities values. The results of the ERT and SRT surveys point to the existence of a significant vertical offset in the subsurface layers, which may have forced the development of the wedge-like structure associated with the Copo Quile fault. Moreover, intermediate resistivity values in the westernmost, shallower part of the resistivity model (Figure 10, E3) suggest the existence of unconsolidated sandy or conglomeratic sediments to the west of the wedge-like structure, possibly associated with the youngest phase in the activity of the fault. Growth of this wedge-like structure must have prevented sediments from being transported farther east, resulting in their accumulation behind the wedge.Our structural assessment of the west-dipping West Candelaria fault, the east-dipping East Candelaria fault, and the west-dipping Copo Quile fault (Figure 2) has enabled us to document the Quaternary tectonic activity in the intermontane basins of the central Santa Bárbara morphotectonic province reflected in the deformation of sedimentary cover rocks in the vicinity of the CR. In view of the bed-parallel slip, this deformation must have been forced by deeper-seated processes in the basement rocks that promoted the shortening of the sedimentary strata of the adjacent basins. In contrast to structures in other parts of the Santa Bárbara System and the transition zone between it and the Eastern Cordillera (e.g., [7, 31, 33, 84]), there is no evidence that the West Candelaria fault is a steeply dipping structure which roots into a deep-seated, contractionally reactivated normal fault in the basement. Instead, our detailed field inspections and tectono-geomorphic analyses suggest that the West Candelaria fault is a shallow-rooted surface-breaking structure. In contrast to earlier studies in the western Candelaria piedmont (i.e., [35]), our investigations therefore do not support any model involving a bivergent, pop-up structure that originated in the basement.In this context, it is important to emphasize that, within the CR, no knickpoints were detected in the longitudinal river profiles that could be associated with the location of the investigated faults, nor were any cataclasized fault zones detected along the flanks of the range. Our knickpoint map (Figure DR2) clearly shows the absence of knickpoints in the transitions between the range and the piedmont areas, where faults had been inferred previously [24]. Furthermore, the Q1 alluvial-fan deposits onlap the basement rocks of the eastern CR without any interruptions. This setting is reminiscent of the Sierra de Quilmes basement uplift [82, 83] or the Pie de Palo range [34, 85] in the broken foreland of the Sierras Pampeanas farther south (~31°S). By analogy with this style of deformation and in view of the geomorphic and geological evidence presented herein, we suggest that the uplift of the CR was driven by a major west-dipping blind fault beneath the range, which also resulted in the drape folding of the sedimentary cover rocks. Our modeling of the observed deformational features suggests that blind thrusting under the CR and associated drape folding and warping of strata in the CR and its piedmonts is a realistic model to reconcile the different observations.In this context, deformation in the intermontane basins may therefore represent second-order, thin-skinned structures that formed during the course of basement-involved deformation and uplift. Accordingly, shortening in the mechanically weak strata of the multilayer Cretaceous rift-fill units and the Cenozoic strata of the intermontane basins on both sides of the CR consequently resulted in flexural-slip thrust faults that broke through to the surface. The cumulative effect of this process was to produce linear fault scarps that are responsible for the formation of the observed trellis drainage patterns and diversions of fluvial channels. This scenario is reminiscent of the evolution of Quaternary flexural-slip faults in areas of flexural-slip folding in the Pamir-western Kunlun and southern Tian Shan regions of Central Asia (e.g., [86, 87]).Taking into account the results of previous investigations into the Santa Bárbara System and our own new observations and results, we propose that the piedmonts of the broken foreland of the Santa Bárbara System’s range uplifts were shaped by a complex, multistage tectonic evolution. The first stage involved extensional processes during the Cretaceous generating normal faults of different scales that bounded a continental graben system [31, 46, 84, 88]. As with other former extensional provinces elsewhere in the Andean foreland (e.g., [89, 90]), these extensional faults were then contractionally inverted during Cenozoic Andean mountain building, resulting in a broken foreland with a spatially and temporally disparate evolution of mountain ranges and intervening basins [4, 7, 23–25, 35, 44]. Sustained shortening, however, also continued to affect the Mesozoic rift-related and Cenozoic syn-orogenic cover rocks in the intermontane basins between the uplifted ranges, resulting in additional basin compartmentalization and interruption of fluvial connectivity and sediment transport toward the undeformed foreland.In our analysis, we have combined the results of a desktop study with field-based geological and geomorphic observations and geophysical evidence across selected piedmont faults of the Candelaria Range, in the broken foreland of the Santa Bárbara System of north-western Argentina. We have been able to show that the intermontane basins of the broken foreland are tectonically active on Quaternary time scales, but we are currently unable to place more definitive bounds on the timing of this activity or to determine whether or not it is indeed associated with seismicity. Small to moderate earthquakes have been recorded within the SBS on decadal time scales by regional [91] and global [92] seismic networks. Damaging earthquakes have also occurred frequently in the past [93, 94].Macroseismic records from the vicinity of the CR extend back to 1692, when an earthquake with an epicenter to the north of the range and an estimated magnitude of M 7 devastated the settlement of El Esteco [93, 95–98]. Other historical earthquakes in the region occurred in 1826 (Trancas, M 6.5), 1927 (Rosario de la Frontera, M 6.1), and 1931 (El Naranjo, M 6.3) [93, 94, 99]. Damage also occurred in the immediate vicinity of the CR (to the north) during the 2015 Mw 5.8 El Galpón earthquake with a depth of 17 km (Figure 1) [95, 98].Bearing in mind the modern and historical seismicity in the region, the information on faulting collected during our investigations suggests that the Quaternary fault scarps are an integral part of sustained foreland deformation. However, this style of highly differentiated deformation and the lack of a clear deformation front combine to emphasize the difficulty in efficiently assessing the level of tectonic activity and spatiotemporal trends of potential seismogenic deformation within this morphotectonic province. In the CR piedmont areas, multiple reactivation of the same faults would have been required to generate the pronounced heights of the various scarps (West Candelaria fault: 15 m; East Candelaria fault: 30 m; and Copo Quile fault: 25 m). Alternatively, these scarps could have developed during episodes of aseismic creep, similar to a scenario inferred for active reverse faults in Central Asia (e.g., [100]). In either case, in light of the regional characteristics of seismicity (i.e., [93]), the CR piedmont faults do not appear to have been active very recently (i.e., the last tens to hundreds of years), despite their pronounced morphologic expression, nor has any significant (M >5) seismic activity been recorded recently. There has also been no earthquake damage to infrastructure during the last 150 years. For more advanced future assessment of potential seismogenic hazards associated with the identified faults in the CR piedmonts, it will be necessary to develop a reliable chronology of Quaternary faulting using cosmogenic nuclide dating or optically stimulated luminescence dating of the offset alluvial-fan surfaces, and to define individual surface-rupture events.Although only qualitative, our assessment of a rather low level of activity on the investigated CR piedmont faults is consistent with the long recurrence interval of strong earthquakes in this region and compatible with the low-strain rates that appear to characterize this sector of the Andean foreland (e.g., [8]). Additional strain-rate data with a higher spatial resolution, as well as additional information on rock types, structural geometries, and topography, will be required for further analysis of the relationships and mechanical coupling effects that could cause earthquake ruptures in this environment of differentially loaded, neighboring faults (e.g., [101, 102]).We used a combination of near-surface geophysical methods, tectono-geomorphic observations, structural field mapping, and morphometric analysis in the Santa Bárbara morphotectonic province of the broken Andean foreland, as a model methodology to derive a comprehensive characterization of fault-rupture zones in an area with recurrent M 7 earthquakes and strong erosional processes. By integrating geomorphic, geological, and geophysical methods, we have been able to document Quaternary deformation processes in the piedmonts of the Candelaria Range in the Santa Bárbara System that are an integral part of sustained Cenozoic foreland shortening in the north-western Argentinean foreland. Although the high rates of erosion and dense vegetation cover make it difficult to assess active tectonic structures in this environment, our approach has been able to corroborate the presence of prominent morphologic scarps within the alluvial-fan deposits of the Candelaria Range piedmonts that are associated with subsurface flexural-slip fault zones.On the western piedmont of the Candelaria Range, sharp transitions in electrical resistivity and seismic-refraction data across a 17 km long and 15 m high scarp that has offset and deformed Quaternary alluvial-fan gravels and caused a change in the drainage network, support the interpretation of a fault at depth. Seismic reflection data across this scarp suggest that the observed fault scarp is associated with bedding-plane slip within the Neogene Metán Subgroup strata. The deformation observed suggests that this fault is related to flexural-slip folding in units that have been subjected to protracted folding in a basin between adjacent uplifting and deforming basement ranges. On the basis of our geophysical data and field observations, we suggest a similar origin for the piedmont faults to the east of the Candelaria Range.The deep-seated processes shaping both piedmont regions are not known at the same level of detail. Nevertheless, the near-surface structure, the orientation, and the overall morphologic character of the identified fault scarps support a model of deformation that involves shortening and flexural-slip folding along rheologically suitable layers in the Mesozoic and Cenozoic sedimentary strata. The broken foreland of the north-western Argentinean Andes thus combines the effects of a thick-skinned deformation style with basement-cored uplifts and the formation of fault scarps related to folding and bed-parallel deformation processes in the intervening basins between these uplifted areas.In view of the neotectonic deformation style, the typical range of magnitudes for present-day seismicity, and the historical character of seismicity in the broken-foreland region, the heights and lengths of the Quaternary West Candelaria, East Candelaria, and Copo Quile scarps appear to be related to cumulative movement along faults. Repeated offsets during moderate-to-large earthquakes in the Quaternary are the most likely origin for these scarps, which suggests recurrent, spatially disparate seismogenic Quaternary deformation processes in the broken foreland.The authors declare that there is no conflict of interest regarding the publication of this article.A. Arnous was supported by a doctoral fellowship from CONICET, Argentina; the German-Argentinean University Network DAHZ/CUAA (Riesgos naturales grant to M. Strecker and A. Gutierrez); and the StRATEGy international training center at Potsdam University, funded by the Deutsche Forschungsgemeinschaft (DFG grant # STR 373/34-1 to M. Strecker). We thank the Secretaría de Minería of Salta Province for the seismic reflection data. We thank R. Alonso, R. Mon, F. Hongn, and G. Aranda for discussions and logistical help.Figure DR1: (A) equipment used in the seimic survay images of the used in the seismic survey; (B) survey design showing location of the source point and the receivers in the three seismic profiles.

中文翻译：

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阿根廷西北部安第斯山脉（26°S）低应变破碎前陆（SantaBárbara系统）的新构造活动

阿根廷圣巴巴拉系统（SBS）破碎的安第斯前陆的隆升与基底各向异性的收缩活化有关，类似于北美厚皮的白垩纪-始新世拉拉酰胺省的报道。SBS内的断层陡峭，第四纪沉积和地貌变形，排水模式中断以及中型地震表明，沿着这些结构的运动可能是一种反复出现的现象，但尚未确定重复间隔和破裂长度。与更北端的Subandes逆冲带相反，东移的变形产生了明确的逆冲锋面，SBS记录了沿一阶已知结构沿时空分布的形变。我们在此介绍地貌桌面分析的结果，SBS中南部坎德拉里亚山脉（CR）基底隆起附近沉积盆地中的构造野外观测，二维电阻层析成像和地震折射层析成像调查以及对可疑断层的地震反射剖面的解释。我们在CR山麓地区的分析表明，近地电阻率和地震折射层析成像调查结果，显着的断层弯折位置以及地震反射数据成像的更大深度的结构几何形状之间具有一致性。我们认为，这种变形是由CR下方的深层盲推和相关的区域翘曲驱动的，相邻盆地的中，新生代沉积地层缩短时，层状平行褶皱和弯曲滑移断层贯穿了第四纪地貌和沉积物，而破碎的陆相盆地如新生代中南部安德斯中部的前陆演化在弧后收敛主要沿着重新活化的高角度结构（例如[1-3]）进行的地区。而不是像地形楔块那样形成薄薄的前陆褶皱和冲断，形成一个均匀倾斜的平均地形（例如，[4]）和明确定义的变形锋（例如，[5，6]）的广阔区域地带，在厚皮的破碎前陆中沿高角度结构的隆起通常是历时性的，并且在空间上是不同的（例如，[3，7]）。这些前陆变形型的构造构造末端成员很好地体现了玻利维亚和西北阿根廷的亚次山地前陆褶皱冲断带，以及阿根廷西北部的圣巴巴拉（SantaBárbara）和塞拉拉斯潘帕尼亚斯隆起的破碎前陆（图1）。圣巴巴拉构造带省是地震活跃的低应变地区[8]，其特征是离散的有限走向长度范围，远离安第斯造山带的主要地形前缘[4，9]，构成了收缩活化的白垩纪重活化层。在低应变断裂的前陆和远离板块边界的大陆内部，断层年代的认识和定义是构造学中一个重要而及时的话题[13，14]。这样的缺点 通常在103到104年的时间范围内活跃，并且间隔很长，当寻求对前陆变形的时空特征的全面了解以及评估地震危害时，这是一个主要问题[15-22]。为了更好地了解表征此类环境的正在进行的构造和沉积过程，需要进行研究的主题包括受构造活动结构影响的区域范围，断层的地下几何形状，变形样式以及断层对构造的影响。地貌演化。解决其中一些问题可能最终有助于更好地确定变形的时空特征，并弄清断陆地区变形过程的活动程度。这项工作的第一步也是最基本的步骤，是确定断层的年代和变形率，然后确定断层的几何形状，并评估断层运动学及其与复活的地壳各向异性的可能关系。因此，我们在本研究中选择了这种方法，主要侧重于与圣巴巴拉系统破碎的前陆东南部的东南构造相关的开放性问题。此外，我们还回顾了第四纪构造对这个构造构造省的景观的影响。我们检查了南SBS约26°S的坎德拉里亚山脉（CR）的山前带中的可疑活动断层（图1和2） ），可能存在于沉积覆盖岩中，并且其活动可能是由在地下岩石中的盲目推力驱动的。先前的研究表明，导致CR隆升的主要断层延伸至地表，而西部山前根的断层则位于地下室（例如[23-25]）。但是，这些解释似乎与萨尔塔地质图上显示的结构关系不一致[26]。该图表明，CR的北部和南部终端形成了一个延长的基底隆升，褶皱褶皱倍增，并且没有迹象表明该范围有任何重大断层。这表明CR的抬升可能与沿盲冲的运动有关，而该范围的相邻山麓可能已被可能与沉积覆盖岩中的弯曲滑动折叠有关的结构破裂，而这种结构是由于相邻基底块不断缩短所致。[24]对较大CR区的大规模形态结构特征进行了遥感和地貌分析；他们提出了一种多阶段构造演化方法，涉及空间上分离的厚皮和薄皮变形形式。这些作者确定了CR西部山前的主要断层陡坡，并推断出界定CR东部侧翼的主要范围边界断层。他们还提出，在该山脉西侧的山前低弯度是沿山脉边界断层强烈构造活动的证据。对于我们的研究，我们以这些有趣的结果为基础，并进一步研究了三个选定现场的第四纪构造活动的表现形式。通过结合地球物理和地貌分析，可以获得对潮湿区域内形态表达较差的潜在活动断层的位置和几何形状的宝贵见解（例如[27-29]）。特别是，近地地球物理技术，高分辨率数字高程模型（DEM）和地貌场制图相结合的数据的使用提供了一种可靠的方法，可以减少诸如此类古国地震特征解密过程中的歧义。怀疑存在于SBS中（同上）。我们分析了南北两侧的东西向的山前断层和倾斜的第四纪冲积扇状沉积物，这暗示了第四纪构造活动。在SBS省的山间盆地中，高达30 m的断层陡坡似乎是构造起源的最明显特征。这些陡峭的岩壁很容易进行详细检查，因为它们被河流割断，并在推测的悬挂壁中暴露出变形的第三纪沉积地层。为了进一步评估CR的山前带并找到其他可能活动的断层并推断其几何形状，我们首先进行了地貌映射。第二步，我们使用了近地表地球物理技术，包括2D电阻层析成像（ERT）和地震折射层析成像（SRT），跨越这些断层陡峭区域，以表征深处的断层几何形状。第三步，我们解释了两条石油工业地震反射线，将观察到的表面结构与深层几何形状联系起来。阿根廷西南安第斯山脉西北部在23°S和33°S之间的地震活跃前陆是类型局部性用于破碎的前陆（图1； [1，30]）；在此，反复变形的第四纪沉积物，构造地貌和逆断层边界的山脉提示了缩短期的积累（[31] [7，24，32–34]）。在某些情况下，这些山脉不被断层所限制，断层没有足够的位移来解释它们的浮雕，而是由与沉积悬垂褶皱相关的广泛的以地下室为核心的反型组成，并由盲断断层所掩盖（例如[2，7，32， 34，35]）。综合起来，这些不同的结构和构造-地貌现象反映了破碎的安第斯前陆长期新生代缩短的复杂长期影响，叠加在地壳异质性上。因此，该区域的结构特征类似于北美拉拉米德省的白垩纪-始新世基底隆起（例如[1、3、36、37]）和中亚地震活跃的天山[38、39] ]。与SBS相关的结构记录了白垩纪萨尔塔裂谷的反转[10，11，23，40]。在南纬23°，这个构造构造省过渡到薄皮的Subandes前陆褶皱冲断带（图1）。SBS内部正在进行的时空上截然不同的构造活动已经形成了不对称抬升山脉的地形，SBS的CR属于一系列空间上分离的，逆断层-断层-断层-断层-断层-断层-断层-断层-断层-断层-断层-断层-与安第斯山脉破碎的前陆内的隐蔽断层有关的边界或地下室核心范围（图1和图2； [24、33、44]）。SBS范围的隆升历史与前陆该区域内安第斯变形的时空向东迁移直接相关[12，45-48]。这与北部的苏巴德斯褶皱冲断带的构造活动变形锋面形成鲜明对比，那里的变形风格与向西缓慢倾倒的区域纵断面有关[49-56]（图1）。CR的以NS趋势为基底的以芯为中心的不对称反型位于南纬25.5°和26.5°之间，以及经度65.5°和64.5°W之间（图1）。山脉内部使变形的上前寒武纪暴露于下寒武统变质沉积物[57，58]，而折叠的沉积覆盖岩保留在该山脉的两侧并向外倾斜[35，59，60]。后一个单元包括萨尔塔群的陆源和海洋白垩纪和古近系地层，其次是密奥—上新世奥兰群的陆相碎屑沉积物[12]（图3）。萨尔塔群的最古老的单元由红色砾岩和砂岩组成。皮尔瓜小组[12，61]。这些裂谷沉积物是由裂谷后的砂岩和巴尔布埃纳亚群的钙质地层所继承的[62，63]，以及圣巴巴拉子群的湖相泥岩[64]。这些与裂谷有关的单元被奥兰群的同造山Metán和Jujuy子群地层一致地覆盖。这些地层中的大部分是砂岩，砾岩和泥质沉积物[26、65]。这些单元反而被Plio（？）-更新世冲积扇状砾岩覆盖[26]。这些粗糙的沉积物覆盖了CR的所有前山地带，这些沉积物形成了多个平缓倾斜的地貌表面的组成部分，这些地貌表面出现在远离CR的较低高度处。除了最低的，活跃的冲积扇面以外，所有这些表面都是以前连续且聚结的冲积扇的遗留物，这些扇形积木自从被废弃为活跃的沉积环境以来就被切割掉了。重要的是，虽然在一般干旱的塞拉内斯·潘皮亚纳斯断陆省（在27°S和33°S之间的纬度）的地表断层检查相对简单，但震源构造的评估也很容易，尤其是在该构造构造省的西部（例如，[66]），在潮湿的SBS省更难辨别此类特征。茂密的植被覆盖和由气候驱动的构造控制地貌特征的快速修改使得该地区的地震构造评价更具挑战性（例如，[7，67-69]）。在这种环境下，断裂区，断层和褶皱经常被侵蚀或什至消失。在保留了这些构造地貌的痕迹的地方，它们常常被茂密的植被所掩盖[70]，或者由于人为的影响而被进一步修饰。这就破坏了用于表征构造活动水平的明确的地质，地貌，运动学和地质年代学数据的收集。由于CR山麓区域内的植被茂密，难以检测到破碎前陆的断层赤道，以及由于高度动态的地表过程往往会迅速改变景观中的地震成因，因此我们决定结合使用地质和地球物理方法来识别可能具有第四纪构造活动的断层。我们的现场观察和对露头的仔细分析帮助我们开发和测试了断层活动模型，然后可以使用电阻率图像，地震折射层析成像和地震反射剖面对其进行进一步评估。我们对地貌特征的研究基于对高分辨率数字高程模型（DEM）和卫星图像的检查，随后对CR两侧的每个风扇进行了现场验证。这使我们能够识别河流网络中的异常，并明确记录山前区内不同的冲积扇世代。为了绘制详细的地质图，尤其是最年轻的沉积物和地形，并协助绘制不同年代的冲积扇和阶地，我们将Landsat 8（波段2、3和4）的真实彩色图像一起使用Google Earth图片（图2）。从两个DEM分别生成了包括浮雕，坡度和排水特征等参数的其他地图，空间分辨率分别为12.5 m和5 m。这些DEM是根据我们从阿拉斯加卫星设施[71]获得的ALOS PALSAR数据生成的。从日本遥感技术中心RESTEC获得了5 m分辨率的DEM。我们还使用TopoToolbox程序[72，73]分析了当地的泄洪和排水特征。最后，我们使用分辨率为5 m的DEM生成了六个纵向河流和地表剖面，以帮助我们进行制图并解释山麓的构造-地貌演化。生成的河流坡度图，以及派生的排水网络和河流/地面纵向剖面，有助于我们识别断层和褶皱的存在。在东部和西部CR山前地区完成了许多电阻层析成像（ERT）调查，以识别和表征深层断层带的几何形状（图4）。在此类勘测中的穿透深度通常取决于电极间距和轮廓长度；例如，对于6 m的电极间距，最大穿透深度在50至60 m之间。具有不同特性（例如，[74]）的地下区域之间的电阻率差异和横向非均质性至少可以在一定程度上揭示断层构造以及相关的运动学和变形模式（例如，[28]）。所有ERT调查均使用相同的偶极-偶极电极配置进行，并以6 m的间距记录48个电极，在每个选定的调查地点获得288米长的剖面图。剖面的设计方向垂直于可疑断层的陡峭面，每个断面均以陡峭的最高点为中心，以确保也覆盖结构表面表达两侧的任何可能的断层延续。我们选择在干旱季节进行调查，那时地下水位通常会下降到地表以下50至60米之间。这些信息是从农民那里获得的，他们的供水依赖当地的水井，并定期进行监测。为了沿东坎德拉里亚山前山剖面获得更大的穿透力，我们沿着一条短暂的河道横穿推断断层的陡坡（图4（b）和5）。我们使用了GF Instruments Inc.（http://www.gfinstruments.cz）的ARES地电阻率仪进行全自动测量。使用RES2DINV软件[74]自动将视在电阻率值反转，该方法遵循由开发的2D反演方法洛克和巴克[75]。该程序基于使用准牛顿优化技术[76]实施的受平滑度约束的最小二乘反演。该优化通过迭代最小化视电阻率的残差来调整二维电阻率模型。然后，对于所有数据集和配置，在最小二乘法中评估最小化过程的效率时，都会考虑均方根（RMS）误差。我们认为RMS误差<10足以使模型被接受。对于CR西侧的两个剖面（剖面E1a和E1b；图2、4（a）和5），使用剖面E1a获得的电数据，经过四次迭代后，反演结果良好。东部剖面E2（参见图2、4（b）和5中的位置）在四次迭代后也产生了可接受的反演模型。最后，对于CR区域东侧的最东侧剖面（E3）（见图4（c）和5），我们仅经过两次迭代就获得了一个可行的模型，然后进行了地貌和形态计量学分析以及ERT调查中，我们在与ERT调查大致相同的位置（图2、4和5）进行了三个地震折射层析成像调查（S1，S2和S3）。我们使用了与24个垂直分量4相连的GEODE勘探地震仪。间隔10 m的5 Hz地震检波器（图DR1）。地震源由100 kg的加速重量和2 m的高度加速路径组成。我们平均每个站点使用了三种影响（或镜头），以便能够通过堆叠每个镜头的三组结果来提高信噪比。在地震线S1上，我们还使用了两个额外的发射点，分别沿着剖面线与第一个地震检波器相距30 m和70 m。对于地震线中的最后一个地震检波器，对称地重复此配置，如我们的数据存储库中的DR1所示。在距第一个射击位置125 m，185 m和255 m处使用了其他附加射击（图2-4和DR1）。对于地震S2线（图2和4 y DR1），我们在距地震线上第一个地震检波器5、30和70 m的位置，以及5、30、70，与最后一个地震检波器相距110 m。距中间位置125，185和255 m的中间位置还进行了另外三次射击。对于地震线S3（图2和图4），我们使用距第一个地震检波器偏移5 m和35 m的炮弹和距最后一个地震检波器偏移5 m和35 m的炮弹进行地震采集。在距第一地震检波器90、145、170和210 m的中间位置还使用了四次额外的射击。因此，在本研究中，S1地震线最长，S3地震线最短，这主要是由于访问限制。我们使用SeisImager / 2DTM软件（可从http://www.geometrics.com获得）处理地震折射层析成像数据。 ），该方法遵循Hayashi和Takahashi [77]提出的方法。该方法基于对地震波速度横向变化所代表的地下不均匀性敏感的技术，使用了Moser [78]和Hayashi和Takahashi [77]开发的直接建模算法。我们对手工挑选的第一个P波到达进行了反演。通过将观察到的传播时间与初步分层模型中的理论传播时间进行比较，我们针对每个地震剖面进行了十次反演后生成了最终的地震速度模型。我们的结果是一致的，西部CR线（S1）的RMS误差为3.2％，S2地震线的RMS误差为4.1％，S3地震线的RMS误差为3.6％。在每次迭代后定量确定残差，并定性地对模型射线路径的空间分布进行交叉检查。使用不同的初始地震速度模型和良好的射线路径覆盖以及二维P波速度折射数据的反演，结果显示与大约80或90 m的深度一致（例如[79]）。从阿根廷的YacimientosPetrolíferosFiscales（YPF）提供的一口石油勘探井和六处石油工业地震反射剖面中获得了测井数据。我们使用了45112和45113线（图1）的东半部分，它们位于CR西侧的山间Choromoro盆地的北部。两条线都大致垂直于CR主轴（图1）。Rosario de la Frontera Norte x-1井位于CR西北部的Rosario de la Frontera镇南部（图1）。重要的，由于该范围的抬升，地震线穿过了在CR西侧沉积盖层单元中形成的高线。在该区域，部分侵蚀的沉积层在与山前砾石接触时形成了一条相当向西倾斜的熨斗直线。大约东西方向的地震反射线全长约25 km，相距约4 km。将SEGY地震线数据与测井数据一起进行分析，并与地表地质相结合，以得出地下地质模型。然后，我们将此模型与我们获得的浅穿透地球物理数据进行了比较。我们首先应用了一个频率滤波器以去除残留的噪声，然后使用Move2D软件（Petroleum Experts，Midland Valley Exploration Ltd.）进行了时间到深度的转换，利用来自井数据和YPF地震数据的地震速度。接下来，我们使用测井仪中沉积层的最上层单元将地层边界与地震堆栈联系起来进行解释。井深为3200 m，这意味着它从第四纪（Piquete组）到第三纪贯穿了地层学（图3），终止于上白垩统（Lecho组，Balbuena子群）。我们还从CR西侧的表层露头成像的地层推断出来，那里暴露了潜在的沉积地层（包括下白垩统），这些数据被组合在一起并整合到基于Seggiaro等人早期模型的结构模型中等 [80]。使用2D区域平衡技术对横截面进行正向建模，使用Move2D程序中提供的算法，以便在观察到的地质场条件和模型之间获得最佳的几何匹配。三剪切技术（例如，[81]）用于推导导致沉积覆盖层垂褶折叠的基底断层的几何形状。破碎的安第斯前陆受到构造过程的强烈影响，该过程影响了第四纪景观演化，今天。这种影响通过排水重组（图4（a）–4（c）），各种冲积扇表面的倾斜以及断层陡坡的存在来体现。在本节中，我们首先报告CR中我们的地质和地貌观测结果。然后，我们使用ERT和SRT调查的结果来描述CR山麓中的断层。最后，我们使用地震反射剖面将可能的断层几何形状的近地表解释扩展到更大的深度。在这项研究中，我们通过遥感识别了CR山麓中的五个断层，但是由于可访问性有限，我们不得不将实地数据收集限制为以下三个结构，我们根据它们的位置命名：西坎德拉里亚西部CR山前的断层，东部CR山前的坎德拉里亚和Copo Quile断层（图2）。随着时间的流逝，侵蚀改性已使这些毛刺的轮廓平滑到一定程度，以至于乍一看它们似乎是折痕。但是，陡峭的直线度和狭窄的特征宽度以及我们的地球物理分析数据（请参见下文）表示断层尖端必须在距离地面最多几米的范围内，但很可能会破坏表面。我们能够使用CR山麓中的风扇表面高程，其横向连续性和解剖程度来分离它们和相关的河床阶地分为五个不同的地貌和地层单元。这些单位记录了扇形形成，次精密切割以及在山麓内随后较低高度上重新沉积的扇形沉积的阶段。在我们研究区域的最西端，有解剖和变形的砾岩（图2），其冲积扇起源可能与紧密分布的砾岩冲积扇残余物相似。间歇式切口已生成四个地层单元，分别对应于不同级别的冲积扇和河流阶地（Q1-Q4），这些阶梯层定义了楼梯形态。最年轻的单元（Q5）是当今排水通道中未分化的砾岩第四纪沉积物（图2）。仅在CR的东侧发现了第一个也是地形上最高的风扇表面及其沉积物（Q1）（图6（a）-1）；这些是最接近该范围的风扇表面，并且已被深切，具有大约50 m的局部高浮雕（图6（b）-1和6（b）-2）。它们包括巨石砾岩和粗糙的，由基质支撑的砾岩，通常夹有薄层的沙子和粉质粘土（图6（b）-1和6（b）-2）。这些较旧的风扇表面在形成后似乎已因构造翘曲而倾斜，因为它们的倾斜度局部大于5°，有时甚至高达12°。如果将扇形残余物的坡度推回CR的源区，则扇形近端的表面将突出到山脉的最高水平，并且它们将不会到达山前，在那儿溪流原本会沉积成团风扇碎石。这表明最老的扇形表面的切口与山前地区的构造运动密切相关，这也可能伴随着基准面的下降。扇形砾石的多微生物成分支持这种构造解释，其中包括沿整个范围暴露的岩石类型，并且不限于高范围内部的基底岩石（图6）。如果山前的扇形和阶地最初与如此高的源区相关联，则将有望成为一个由地下室主导的单一微生物组成。第二个较少解剖的扇形沉积物群和相应的表面（Q2）位于CR的两侧（图6（a））-2）。这些风扇位于山麓的下部，其特点是局部起伏较小。裸露的扇形地层由粗砾岩和上覆的粉砂层和夹杂的砾石组成（图6（b）-3和6（b）-4）。西CR山麓的Q2扇形残余物特征是岩性良好的砾岩。向西倾斜9°（图6（b）-5）。这些单元直接覆盖在向西倾斜25°至30°之间的白垩纪和古近纪砂岩和粉砂岩中。河床阶地雕刻在较老的冲积扇沉积物中。阶地（Q3）包括该范围内部的粗糙至非常粗糙的地下砾石，以及插层的砂土至粉质层。较年轻的河流阶地（Q4）的裸露覆盖砾石是基质支撑的砾岩。最年轻的单元（Q5）定义了主要的山前排水系统及其支流中的凝结地层（图2）。最老的东部扇（Q1）已被东坎德拉里亚（East Candelaria）断层所抵消（图2、5和6（a）-1） ，6（b）-1、6（b）-2），且位移朝东。这些风扇受侵蚀最严重，现在仅沿CR东部前山的长度散布着表面残留物。东坎德拉里亚断层的活动中断了CR向东的排水，并开始了扇形表面的解剖。然后在较低的高度上产生了较年轻的Q2冲积扇表面（图2和4）。东坎德拉里亚断层位于该范围以东2公里处（图2、5（剖面3），图4（b）和4（b′））。它撞击西北偏北，延伸约20公里，并切穿与Q1和Q2冲积扇沉积物相关的地貌表面。风扇表面的垂直偏移约为20 m（图5，轮廓3）。在CR山麓的东南部，对应于Q1的地表相对于Q2地表的高程偏移了20 m，而在断层的北部，偏移量至少为30 m（图4（ b）和4（b'⁠））。图4（b'）中的淡蓝色代表Q2的光滑表面（图4（b））也突出了排水的空间布置以及废弃的Q1风扇表面和较年轻的Q2风扇表面之间的关系。沿东坎德拉里亚断层运动抬升了风扇表面之后，较老的Q1风扇表面可能被切开并腐蚀了，迫使排水流向北流动。东坎德拉里亚断层以东是科普基尔断层陡坡。这是华北东部山前断层中最短的断层，似乎与第四纪活动有关，沿北-西北走向走向延伸了约8 km（图5，剖面4）。该断层切割了Q2冲积扇砾石，并使它们垂直偏移约25至30 m（图4（c））。从图4（c'⁠），可以看出，由断层错开的风扇表面的倾斜度向东逐渐倾斜。此设置清楚地证明该区域的河流网络已被故障转移。在Copo Quile断层活动期间，一些排水系统能够保持其向东流动，但另一些排水系统则被迫向南改变路线，以避免与活动断层相关的地形不断扩大。在我们研究区域的西部，这些砾岩最古老的上新世-前更新世山前地层（J单元）的残余物被CR中的水流切割（图2和4）。这些砾石与Jujuy子组的上新世-上新世地层有一定角度的不整合接触[7，26]。西山麓的Q2粉丝也受到断层的影响。西坎德拉里亚断裂带突出 与CR方向平行的17公里长的上坡陡峭走向（图2和4）。它是Metán子群的新近系地层之间的平行层结构，向西倾斜30°。断层使Q2冲积扇垂直偏移达20 m（图5（a））。在断层痕迹很平缓并且已经过侵蚀改造的情况下，在DEM和现场（图4（a））中，在卫星图像上，断层痕迹清晰可见为一条直线。在西坎德拉里亚断层中部以西有明显的第二条断层迹线（图5和6（b）-5（剖面1和2））。穿过这些结构的河流露出的露头揭示了倾斜的第四纪砾岩与下层变形的第三纪地层之间的角度关系（图6（b）-4），确认山麓的持续变形。光滑的Q2风扇表面突然终止于笔直的断层线，但风扇水平继续以倾斜的，切开的河流阶地的形式在其上继续延伸。这些关系在我们的CR西部侧面的坡度图上得到了很好的表达（图4（a'⁠）），其中光滑的Q2表面（蓝色）与中生代岩石（红色和黄色扇形）的熨斗地形相接。覆盖了CR最西端的侧面。除了断层陡坡以西，该斜坡仍然平缓，但该区域由众多短暂的河流切割而成。与东部的皮埃蒙特一样，我们的野外测绘和野外视觉关联均基于Metán的地质图[26]， Hain等人为SBS盆地开发了横向收缩和年代学。[7]，因此，我们得出结论，西部山前的所有经切割和侵蚀改造的表面均属于Q2扇形表面。为了更详细地分析景观上的构造印记，我们生成了六个纵向河流和地貌表面分布图，覆盖了西，东斜坡。 CR，使用我们5 m分辨率的DEM数据（图7）。如今，穿越CR西翼的河道的纵剖面在断层位置或地下室区域内均未显示任何拐点。因此，我们建议沿西坎德拉里亚断层的山前带断层，然后进行长时间的切割，并重建凹形的纵向河廓。还不知道何时完成此平衡曲线的重建，但是平缓的坡度表明，西坎德拉里亚断层没有长时间保持活跃，或者与侵蚀作用相比，构造作用相对较弱。弯角内确实存在拐点（图7，剖面5），但并没有表明构造强迫是将其解释为与抗寒前寒武纪基底岩的露头有关。倾斜冲积扇面的地形轮廓清楚地揭示了断层的位置造成了西坎德拉里亚断层的两条上坡陡坡以及其西部欠发达的断层（图2、5（剖面1和2），图4（a）和4（a′））。在纵向剖面上，这些断层以西的扇形扇面比平衡冲积扇形剖面所期望的扇形倾斜更陡。覆盖范围和山麓之间过渡区域的冲积扇表面都没有被断层所抵消，任何河流切割的暴露都没有揭示出断层带内有变形或分解的岩石的迹象。拐点确实存在于山脉内部的变质基底岩石中，最有可能受岩性控制，或者它们反映了与上游迁移切口过程有关的回归拐点，而上游切割过程与区域尺度基底翘曲有关。重要的是，但是，在与范围前沿相交的纵向轮廓中不存在拐点。两者合计，该范围的东西向不对称性及其北端和南端的双重下陷必定是倾斜差异的结果，我们认为这可能与该范围以下的盲断有关。相反，与西坎德拉里亚，东坎德拉里亚和科珀基尔断裂有关的山前带中的三个主要陡坡被解释为与地表破裂有关（图4）。下面使用我们新获得的地球物理数据进一步分析这些推断的断层陡坡。垂直于断层陡坡测量了整个CR CR山前的E1a和E1b ERT剖面（图2和图4），如地质图和坡度图所示（图2和4（a））。根据可直接检查的区域中露头数量有限以及测井信息，我们推断出近地下的所有沉积岩都是白垩纪或第三纪的，这些都被第四纪冲积层覆盖了。扇形砾石（图6（b）-4）。我们在陡坡上的河流暴露中进行的地质观察表明，断层是平行的且与挠曲滑移有关。该断层并未使Metán亚组地层倾斜。此外，我们观察到冲积扇沉积物与Metán亚组地层成一定角度不整合，并且相关的冲积扇残留物向西倾斜。我们在两个位置进行了层析成像调查，可以从垂直偏移推断出断层的缺陷性质（剖面E1a显示3m偏移；剖面E1b显示15m偏移）。所获得的电阻率值介于6到800 ohm * m之间，经过四次迭代后，RMS误差为5.1。最大穿透深度约为65 m。在剖面长度的-20至20 m之间发现了从西到东电阻率的显着横向变化，表示海拔在1360至1350 m之间从低电阻率区域向高电阻率区域突然变化。在同一调查的东部，在海拔1370至1360 m之间以及剖面长度在0至100 m之间的地方，我们记录了一个向东变薄的低电阻率层。在此低电阻率层的正下方，我们对高电阻层进行了成像，其厚度约为其上方层的两倍。在剖面的西部，我们注意到上层高电阻率层约5至10 m厚，覆盖了低电阻率层。在距北约1100 m处，我们使用相同的测量配置沿剖面E1a测量了电性能（长度：288 m；电极数量：48；电极间距：6 m；四极杆：802；图8）。经过四次迭代，我们获得了3.0％的可靠RMS误差，电阻率值在7到1100 ohm * m之间变化，最大穿透深度为65 m。该剖面图显示出沿其整个长度的上部25 m的高电阻率，最大值为909 ohm * m。轮廓长度在-60至10 m之间的部分（图8）出现为导电区，在深度大于23 m时电阻率值降至7 ohm·m。这与沿南部剖面（E1b）的观测相似，尽管在这种情况下，表面存在地形阶梯，并且电阻率异常的幅度较小。我们在轮廓E1b上观察到电阻率在垂直方向上突然下降，其深度正好在上述导电区域上方。CR西侧的两个剖面都显示出连贯的地下电阻率结构。S1地震层析成像剖面图（图8）记录在与ERT剖面E1b（图4）相同的位置，揭示了地震速度结构与随深度增加的Vp值一致。我们注意到接近推断断层的Vp横向变化，表明厚度局部变化。不同的速度层沿整个EW剖面是连续的。Vp约为1270 m / s的层在轮廓的中心部分记录了增加的厚度；这与上方地面的地形非常吻合。在海拔大约1360至1340 m之间以及沿剖面距离20至70 m之间发现了另一个地震速度异常。在轮廓长度的-30至10 m之间，在轮廓中心的浅层记录了大约10米厚的低速层.E2和S2轮廓的EW方向垂直于推定的方向东坎德拉里亚断层深处（图2和图4）。该结构的最小地形偏移量超过22 m。我们使用了与CR西侧轮廓E1a和E1b相似的电极配置。经过四次迭代，反演导致4.2％的合理RMS误差。电阻率模型显示出接近剖面中心的几乎垂直的主要不连续性，与北-西北方向的形态陡坡的位置相吻合。剖面的西半部以高电阻率值为主，较低的值（在1到10 ohm * m之间）是陡峭带以东区域的特征。最薄的最上层在整个EW断面上表现出高电阻率。S2地震剖面的结果是从与E2电剖面相同的位置获得的；该轮廓共享相同的中心参考点（图9）。识别出的速度层从西到东是连续的。较浅的层与表面平行，因此具有缓和的向东倾斜。沿轮廓线在-20 m至80 m的水平距离之间，高速层靠近表面。这些高速层在轮廓的中心部分定义了一个区域，随着层的接近，不同层的厚度会显着减小。地震线中心部分的沉积物覆盖微不足道。我们注意到，速度模型东部各层速度的垂直变化与相应模型中电阻率不连续的位置一致。东坎德拉里亚断层东部且距东侧约10 km CR的E3轮廓（通过合并三个相交的电气轮廓获得）穿过楔形结构，总长度为576 m（图2和4）；我们总共使用了1869个四极杆（图4（c））来测量这一部分，电阻率结果表明范围在0.5至250 ohm * m之间。经过两次迭代后获得了此配置文件的最终模型，RMS误差为7.3％。沿着这个剖面，我们在上部15 m处发现了一个高电阻率层，向西倾斜 在轮廓长度的水平距离480 m处，该层的倾斜度改变为向东方向。在轮廓长度的288 m（轮廓的中央部分）的浅层中，存在一个向西倾斜的层（朝向配置文件的0 m标记；该层变得越来越深，导电性越来越强。该层也向西变厚，并被具有较低电阻率（1至17 ohm * m）的薄层覆盖。在从剖面长度288 m到剖面的东端的导线的东部浅部，存在一个高电阻率层，其厚度约为5 m。在高电阻率表层正下方（图10；红色），向西倾斜约30 m厚的低电阻率层（蓝色和绿色）；该层在剖面的东部（海拔690 m）扇形中将其倾斜度更改为向东倾斜，水平距离约为480 m。在剖面长度水平距离384至480 m之间以及海拔660至650 m之间的高处，东部有一个高电阻率区域，其特征在于电阻率约为40 ohm * m（图10中蓝色层下方的黄色区域） ）。该高电阻率层似乎已突破其上方的导电层（蓝色层）。我们的S3地震剖面结果覆盖了E3电剖面的最东端250 m（图10）。建模的速度剖面表示在剖面最西端靠近地面的高速（> 2500 m / s），海拔672 m，垂直速度梯度较大；等速层向东倾斜约30°，然后在剖面的东部变为水平以下，高度为652 m。低速层向西明显变薄，而速度在1175至2000 m / s之间的层更厚。因此，剖面东端的结果表明是水平分层的地震速度结构。中等速度的层沿着剖面到达地表水平距离为60至80 m，表明地震速度层缺乏水平连续性。两个堆叠的地震反射剖面位于西坎德拉里亚断层以西数公里处。我们还使用了位于Rosario de la Frontera镇附近的石油勘探井眼的测井数据（图1），将确定的反射器与野外观察到的地质单元联系起来。因此，我们能够基于与不同层相关的声阻抗的垂直变化来识别整个地层柱。具有变质信号且横向连续性较差的低强度反射很可能是由于对4100 m深度的变质基底岩石进行了成像。正如区域地层关系所预期的那样，在基底岩石与白垩纪皮尔瓜亚群的上覆裂谷沉积之间成像了一个角度不整合面。反过来，Pirgua地层被Balbuena和SantaBárbara子群在裂谷后的沉积物覆盖，这些沉积物具有较高的信号幅度。通过将成像单元外推到地表，可以清楚地看到它们是CR西倾沉积沉积岩的地下等价物（图1和图11）。地震反射剖面的分析使我们能够使用Move2D对CR沉积盖层的变形进行建模。首先，我们尝试根据Barcelona等人的模型对表面破裂断层背景下的变形进行建模。[24]。在这些模型运行中，暴露于山脉内部的地下岩石必须比其当前位置高出2 km，才能产生折叠的地层。由于我们无法在覆盖层上产生与在地震线上观察到的相同的挠曲，而对地表重新激活了断层切割，因此我们通过在CR下引入盲断层来模拟变形特征，类似于断层中的其他范围前陆（例如[2，34，82]）。因此，通过使用Trishear方法（即[81]）并假设CR下有一个盲断层，我们能够在沉积盖层中产生不对称褶皱，从而更好地模拟了场关系和地震成像的几何形状。因此，我们得出的结论是，CR下的盲断层是解释CR沉积盖层的变形以及山前冲积扇砾石的第四纪断层和翘曲的可行机制。根据观察到的关系，我们在图12中给出了变形特征的模型。在5.1、5.2和5.3节中，我们讨论了在CR山麓中识别出的所有三个断层的特征（图1）。到我们自己的领域，地貌和地球物理观测，并为该前陆部门的结构演化提供了一个简单的模型。我们对南北前山的三个主要断层的构造-地貌分析表明，该区域内地形梯度的空间变化由这三个结构控制。另外，沿CR两侧这些断层的运动从根本上影响了山前河流网络，从而导致了格状排水模式的发展。沿山前断层的局部隆升使水流的流动方向从垂直于范围的方向改变为与断层陡坡平行的向北或向南的方向。在其他情况下，持续的切口能够跟着山前断层的隆起保持同步，从而留下河床阶地，并导致随后在较低的高度上形成新的冲积扇面。在较旧的风机表面，冲积扇阶地的梯度通常较大，这表明在CR的生长过程中区域性隆起和倾斜。但是，在局部，明显的台阶中断了较旧的扇形阶跃的纵向剖面，我们在此推断了山前断层的位置。有趣的是 我们的研究没有发现沿东部山脉前缘的一个重要的新兴逆断层的第四纪活动的证据，也没有发现任何这样的明显结构限制CR西部的证据。沿该山脉两侧的地层向底倾斜方向以及西部山前下方裸露的白垩纪和第三纪地层的倾斜度减小，都支持了这些观测结果（图11）。缓倾斜表面的这些一般特征仅在山前断层附近改变。考虑到弯曲的白垩纪地层及其与该山脉西侧未固结的第四纪山前砾石的接触，巴塞罗那等人在一项遥感研究中获得了较低的山前正弦指数。[24]不是构造活动的指示。低的波纹度指数反而可以反映出这些不同岩性之间的可蚀性的鲜明对比。这种情况与西北山脉Sierras Pampeanas的Sierra de Quilmes基底隆起的西部侧面（例如[82，83]）以及该构造构造省的其他非对称隆起的基底块（例如[2]）相同。 ）。在CR的西部山麓中，我们确定了三个主要陡坡（图2），但是由于可及性有限，我们仅将西坎德拉里亚断层集中在地球物理调查上。来自两个电气剖面（E1a和E1b；图2、4和8）的模型显示，在推断断层陡坡正下方的表观电阻率区域很低，这与Metán亚组沉积单元的泥质岩层的低电阻率相一致。在北部剖面（剖面E1a）中，断层带两侧（东，西）宽约30m的高阻区；这与CR西侧冲积扇砾石的预期特性（高电阻率）非常吻合。这些砾石由基底露头的变质岩组成，具有高电阻率的特征。同样的情况也适用于沿剖面E1b的CR南部（图8）。剖面E1b（图8）还揭示了电阻率值的突然水平变化，这有助于明确确定西坎德拉里亚断层的位置。代表压实沉积地层的较高地震速度被垂直地平移到陆地表面，这导致沿着剖面E1b解释了模型中的低电导率带（图8）。在该剖面的西部，推断断层陡坡下方等速层的逐渐增长与断层带的低电阻率区域相吻合（图8）。因此，最好将断层平面的方向（沿剖面的水平距离为-80至-20 m）解释为代表西倾冲断层。在两个剖面（E1a和E1b）的东部（图8），高速和低电阻率特征可能与富页岩岩性有关。具有相对较高电阻率的25米厚的层被解释为代表冲积扇沉积物。在距剖面S1中心20 m的水平距离处（图8），冲积扇沉积在断层之上，形成具有均一的地震速度带，具有极高的电阻率。在我们的解释中，变质基岩的砾石，以及白垩纪粉砂岩和砂岩，沿着南北走向西坎德拉里亚断裂的长度沉积在前河道中，并在第四纪压实。E1b剖面（0–50 m）中冲积扇沉积物顶部的浅层低电阻率层很可能是人工产物，可能与剖面北部约30 m的人造淡水池塘有关。该剖面S1的地震折射结果提供了从电剖面获得的数据更稳定，噪声更少的图像。我们来自西部CR山前的两条地震反射线使我们可以将地下地层外推至7 km深度；地震反射线也使我们能够追踪到山前断层和沉积单元的倾斜露头的地层边界，这些沉积单元覆盖在CR基底岩石之上。重要的是，西坎德拉里亚断层的位置与地震反射叠加层的上倾投影正好重合，该反射叠层对应于梅塔亚组的沉积地层（图11）。在地震剖面中，无法识别出源自地下基底岩石的其他横切或陡倾断层。因此，我们将西坎德拉里亚断层解释为弯曲滑动断层，它是在新近纪沉积地层内沿薄弱层的床层平行运动过程中形成的。在CR的东侧，横跨东坎德拉里亚断层，电学剖面显示出高电阻率值，我们将其解释为是由于冲积扇沉积物的特征（即基底衍生的砾岩的高电阻率）。这与剖面的最东部形成对比，该剖面的电阻率大大降低，可能反映出诸如第三纪泥质岩层之类的更多导电材料。这些观察结果与地震层析成像结果一致，后者显示了剖面上方40 m的地下地下具有沉积特征的沉积特征。在电断层扫描调查的东部，电阻率值显着下降表示岩石类型发生了变化。电阻率的这种急剧变化与怀疑的断层位置相吻合，以及地震层析成像剖面中心部分中具有较高速度的层向地面的位移（图9）。从圣巴巴拉地区亚组的地层存在，并沿着走向超出地图区域的走向暴露于南部（图1中的红色圆圈；见图6（b）-6中的照片），向东倾斜80°，表明存在一个错误。电阻率和地震速度特征的急剧转变也表明存在东倾的高角度断层，这可以最好地解释冲积扇沉积的这种破坏。在形态学分析中我们确定为科普基尔断裂的南向撞击楔形结构。电气轮廓顶部的高电阻层（图10，E3）向西变厚，对应于冲积扇沉积物。这些单元由源自地下的砾岩组成，这解释了为什么该顶层具有高电阻率的特征。在此水平以下，有一个约30 m厚的低电阻率层，我们将其解释为代表一个泥质层。由于沿科普基尔断裂的推力运动，该层被破坏和抬升，在剖面长度水平距离400 m处，海拔670和650 m处切穿沉积层（图10，E3）。此外，SRT图像显示出主要的地形步骤，这与为其他断层推断的几何形状相似（图10，S3）。此外，我们观察到了速度梯度的垂直变化和等速线向科波基尔断裂带的扭曲。在ERT剖面中，断层带的特征在于中间电阻率值。ERT和SRT调查的结果表明，地下层中存在明显的垂直偏移，这可能已迫使发展了与Copo Quile断层有关的楔状结构。此外，在电阻率模型的最西端，较浅的部分，中等电阻率值（图10，E3）表明，楔形结构以西存在未固结的砂质或砾岩沉积物，可能与活动最年轻的相有关。错误。这种楔形结构的生长必定阻止了沉积物向更远的东部输送，从而导致沉积物在楔形物后方堆积。我们对西倾西坎德拉里亚断层的结构评估，东倾的东坎德拉里亚断层和西倾的Copo Quile断层（图2）使我们能够记录下圣巴巴拉地区中部构造山区的第四纪构造活动，该活动反映了该地区沉积盖层的变形。 CR附近。鉴于床层平行滑动，这种变形一定是由基底岩石中更深层次的过程所强迫的，该过程促使相邻盆地的沉积层缩短。与圣巴巴拉系统其他部分以及它与东部山脉之间的过渡带的构造形成对比（例如[7，31，33，84]），没有证据表明西坎德拉里亚断层是陡倾构造根源是地下室中根深蒂固，收缩后重新激活的正常断层。代替，我们的详细现场检查和构造地貌分析表明，西坎德拉里亚断层是浅根断层结构。与西方坎德拉里亚山麓的早期研究（即[35]）相比，我们的研究因此不支持任何涉及地下室中出现的双重，弹出式结构的模型。在这种情况下，必须强调以下几点：在CR中，在纵向河流剖面中未检测到可能与所调查断层的位置相关的拐点，也未在该范围的两侧检测到任何催化裂化带。我们的弯折点图（图DR2）清楚地显示了山脉和山麓地区之间的过渡带中没有弯折点，之前已经推断出断层[24]。此外，Q1冲积扇沉积在东部CR的基底岩石上，没有任何中断。此设置让人联想到更南的塞拉内斯潘皮亚纳斯（Sierras Pampeanas）破碎的前陆（〜31°S）的塞拉利昂德奎尔姆斯地下室隆起[82，83]或派德帕洛山脉[34，85]。通过类比这种变形方式，并根据本文提供的地貌和地质证据，我们认为CR的隆升是由该范围以下的一个主要向西倾的盲断带驱动的，这也导致了该褶皱的悬垂褶皱。沉积覆盖岩。我们对观测到的变形特征的建模表明，CR下的盲冲和相关的CR及其山前地层的悬垂褶皱和翘曲是调和不同观测结果的现实模型。因此，山间盆地的形变可能代表了二阶薄皮结构，这些结构是在地下室引起的形变和隆升过程中形成的。因此，CR两侧多层白垩纪裂谷充填单元的机械弱地层缩短和山间盆地的新生代地层因此导致了弯曲滑动逆冲断层穿透到地表。该过程的累积作用是产生线性断层陡坡，导致观察到的网格排水模式的形成和河流通道的转移。这种情况使人想起了中亚的帕米尔-西部昆仑和天山南部地区的弯曲滑动褶皱地区第四纪弯曲滑动断层的演化（例如，[86，87]）。考虑到以前对圣巴巴拉系统的调查结果以及我们自己的新观测结果，我们建议圣巴巴拉系统隆升的前陆破碎山麓是由复杂的，多阶段的构造演化形成的。第一阶段涉及白垩纪的伸展过程，产生不同尺度的正断层，这些断层限制了大陆grab陷系统[31、46、84、88]。与安第斯前陆其他地区的其他前伸展省一样（例如，[89，90]），这些伸展断层在新生代安第斯山脉建造过程中被收缩倒转，形成了破碎的前陆，山脉在空间和时间上有不同的演变。中间盆地[4，7，23–25，35，44]。持续缩短，但是 此外，在隆起范围之间的山间盆地中，中生代裂谷相关的和新生代的同造山覆盖岩也继续受到影响，导致了盆地的进一步划分和河流连通性的中断以及沉积物向未变形前陆的输送。一项基于桌面的研究结果，该研究结果基于实地地质和地貌观测资料，并在阿根廷西北部SantaBárbara系统破碎的前陆坎德拉里亚山脉的选定山麓断层上提供了地球物理证据。我们已经证明了破碎前陆的山间盆地在第四纪时间尺度上是构造活动的，但是我们目前无法确定此活动的时间范围，也无法确定该活动是否确实与地震活动有关。在SBS内，通过地区[91]和全球[92]地震网络以年代际尺度记录了中小地震。过去也经常发生破坏性地震[93，94]。CR附近的大地震记录可以追溯到1692年，当时震中位于该范围以北，估计震级为M 7，破坏了定居点。 Esteco [93，95–98]。该地区的其他历史地震发生在1826年（特兰卡斯，M 6.5），1927年（Rosario de la Frontera，M 6.1）和1931年（El Naranjo，M 6.3）[93，94，99]。在2015 Mw 5期间，在CR的紧邻区域（北部）也发生了损坏。考虑到该地区的现代和历史地震活动，根据该地区的现代和历史地震活动，在我们调查期间收集到的有关断层的信息表明，第四纪断层陡峭是必不可少的部分持续的前陆变形。但是，这种类型的高分化形变和缺乏清晰的形变锋面相结合，凸显了难以有效评估该构造构造省内的构造活动水平和潜在成因形变的时空趋势。在CR山前地区，将需要对同一断层进行多次活化，以产生各种陡坡的明显高度（西坎德拉里亚断层：15 m；东坎德拉里亚断层：30 m；科普奎尔断层：25 m）。或者，这些陡峭现象可能是在抗震蠕变过程中形成的，类似于中亚活动性反向断裂所推断出的情况（例如[100]）。在这两种情况下，根据地震活动的区域特征（即[93]），CR山前断裂似乎都不是最近才活动的（即过去几十至几百年），尽管它们的形态表达很明显。 ，最近也没有记录到任何重大（M> 5）地震活动。在过去的150年中，基础设施也没有遭受地震破坏。为了将来更进一步评估与CR山麓中已确定的断层有关的潜在地震危险，有必要使用胶结冲积扇面的宇宙成因核素测年法或光激发发光测年法来开发可靠的第四纪断层年代学，并定义个别的表面破裂事件。尽管只是定性的，但我们对相当低水平的断层评估被调查的CR山麓断层的活动与该地区强地震的长复发间隔相一致，并且与显示安第斯前陆这一部分特征的低应变率相吻合（例如[8]）。附加应变率 我们对所研究的CR山前断层活动度较低的评估，与该地区强地震的复发间隔长，符合安第斯前陆这一带的低应变率相吻合（例如[ 8]）。附加应变率 我们对所研究的CR山前断层活动度较低的评估，与该地区强地震的复发间隔长，符合安第斯前陆这一带的低应变率相吻合（例如[ 8]）。附加应变率需要进一步的空间分辨率数据，以及有关岩石类型，结构几何形状和地形的其他信息，以进一步分析在差异加载的邻近断层环境中可能导致地震破裂的关系和机械耦合效应（例如[101，102]。我们结合使用了近地表地球物理方法，构造-地貌观测，结构场制图和安第斯前陆断裂的圣巴巴拉构造省的形态计量学分析，作为模型方法来推导对M 7地震反复发生和强侵蚀过程地区的断裂破裂带进行了全面表征。通过整合地貌，地质和地球物理方法，我们已经能够记录圣巴巴拉系统坎德拉里亚山脉山麓的第四纪变形过程，这是阿根廷西北前陆持续新生代前陆缩短的组成部分。尽管高侵蚀率和茂密的植被覆盖使得很难在这种环境下评估活跃的构造结构，但我们的方法已经能够证实坎德拉里亚山脉山麓冲积扇沉积物中存在明显的形态赤道。地下弯曲滑动断层带。在坎德拉里亚山脉的西部山前，一条长17 km，高15 m的陡坡上电阻率和地震折射数据的急剧转变，使第四纪冲积扇砾石发生偏移和变形，并引起了排水网络的变化，为深层断层的解释提供了支持。跨此陡峭带的地震反射数据表明，观测到的断层陡峭带与新近纪梅坦亚群地层内的层理面滑动有关。观察到的变形表明，该断层与单元的弯曲滑动折叠有关，这些单元在相邻的隆起和变形基底范围之间的盆地中经历了长时间的折叠。根据我们的地球物理数据和现场观察，我们建议坎德拉里亚山脉以东的山前断层的起因相似。在相同的详细程度上，尚不清楚塑造两个山麓区域的深层过程。然而，已识别断层陡峭带的近地表结构，方向和整体形态特征支持了一种变形模型，该变形模型涉及沿中生代和新生代沉积层中流变学上合适的层的缩短和挠曲滑动折叠。因此，阿根廷西北部安第斯山脉的破碎前陆将厚皮形变型的影响与基底带芯隆起相结合，并在这些隆起区之间的中间盆地中形成了与褶皱和床平行变形过程有关的断层陡坡。鉴于新构造变形的类型，当今地震活动的典型震级范围是 以及断陆地区地震活动的历史特征，西坎德拉里亚第四纪，东坎德拉里亚第四纪和科珀基尔陡峭带的高度和长度似乎与沿断层的累积运动有关。在第四纪中至大地震期间重复偏移是这些陡峭岩的最可能的起因，这表明在破碎的前陆中，反复发生，空间上相异的地震成因的第四纪形变过程。这篇文章 Arnous得到了来自阿根廷CONICET的博士奖学金的支持；德国-阿根廷大学网络DAHZ / CUAA（里斯高斯自然基金会授予M. Strecker和A. Gutierrez）；以及波茨坦大学的战略国际培训中心，由Deutsche Forschungsgemeinschaft（DFG授予STR 373 / 34-1，由M. Strecker资助）资助。我们感谢萨尔塔省的矿产局的地震反射数据。我们感谢R. Alonso，R。Mon，F。Hongn和G. Aranda的讨论和后勤帮助。图DR1：（A）用于地震勘测的地震记录图像的设备；（B）勘测设计，显示三个地震剖面中源点和接收器的位置。