The study area is between Sierra de Aconquija in the east and Sierra de Fiambalá in the west (Figure 1 and Figure 2). To the north is the Hualfín-Las Cuevas ranges. It is bordered to the northeast by Campo del Arenal and to the south by the Belén, Andalgalá, and Pipanaco salt flats (Figure 2 and Figure 3). The Fiambalá, Hualfín - Las Cuevas range tilt northwestward due to reverse fault displacement along their eastern edges and are separate from the study area by the Hualfín Valley (Figure 3 and Figure 4). The Fiambalá range strikes the NNE and is separated from the Hualfín range by the Ampujaco dextral fault. The Hualfín and Las Cuevas range strike the NE; they are displaced by the Atajo dextral fault (Figure 3 and Figure 4). The Hualfín Valley extends southwards between the Fiambalá and Cerro Pampa and between the Belén range and Cerro Pampa (Figure 3 and Figure 4).

1) Ranges and hills: The Atajo fault is a regional structure that falls on morpho-structural units that suffered deformation during Andean tectonism. The ranges to the east of the Atajo fault form the southern foothills of the Sierra de Aconquija (Cerros Atajo and Huyaco and the Capillitas, Santa Barbara, Yacochuyo, and Amanao ranges) (Figure 4). The Cerro El Durazno is a remnant promontory of the Farallón Negro volcano’s cone, which was cut by the Atajo’s fault. Scars on the Cerro Atajo show the sliding and collapse of its SW flank, which accounts for at least 1/4 of its surface. Cerro Huayco has a triangular morphology, with the western side connecting to the eastern edge of the La Ovejería range (Figure 3 and Figure 4).

The Ovejería Block and the Farallón Negro Volcanic Complex are west of the

Atajo fault (Figure 3 and Figure 4). The Farallón Negro Volcanic Complex, located north of the La Ovejería range, was formed between 13 and 5 Ma because of the magmatic activity in the area. This volcano may have reached a height of 6000 m [54] and produced vein-like Au (Mn, Ag, As, Pb, Zn) and Cu-Au porphyry mineral deposits [52] . The volcano’s caldera is oval in morphology with an NW strike and covers about 166 km², but the volcanic deposits span a wider area (Figure 3).

The La Ovejería range is 24.5 km long, 7 km wide, and 3100 meters above sea level. It is made up primarily of metamorphic rocks. The Venado range is 45.4 km long, 23.6 km wide, and rises 2700 m a.s.l. It is almost entirely composed of granitic rocks. The Belén range-Cerro Pampa is 57.4 km long and 16.6 km wide, and its northern end reaches 3200 m a.s.l. (Figure 3). The Carrizal and Algarrobal ranges are separated by the Talayacu River south of the Venado range, which the La Agüita River separates. The Carrizal range is approximately 14 km long, and the Algarrobal range is about 22 km long. The Carrizal and Algarrobal ranges and Quemado Hill form a block of NE strike made of granitic rocks about 40.5 km long and 14 km wide (Figure 3).

2) Valleys and fields: The Ampujaco valley extends with an NNE strike between the Venado range to the east and the Cerro Pampa to the west; at its widest point, it reaches 8 km in length (Figure 5(a)). This valley connects to the narrower Suncho valley to the north, which strikes E-W and separates the Ovejería and Venado ranges, through which the Suncho River flows into the Ampujaco valley (Figure 3, Figure 4, and Figure 5(a)).

The Tampa-Tampa (to the north) and Vis-Vis (to the south) fields are located on the western edge of the Atajo fault and occupy areas of 8.6 km² and 6 km², respectively. These fields were identified as caldera structures associated with mineralized zones [52] [91] [92] (Figure 3 and Figure 4).

3) Alluvial fans of the Ampujaco Valley: On the eastern flank of Cerro Pampa, alluvial fans have distinct morphologic characteristics that distinguish them from others nearby. They were identified as the second level of the area (Figure 5(a)). Half-buried remains of alluvial fans, between 4 and 6 km long and up to 2 km wide, can be found to the south of the Ampujaco river valley, similar to those found on Cerro Pampa’s eastern flank (Figure 3 and Figure 5(a)). One of these piedmont deposits (Figure 5(a)) comprises sandstone from the base to the top, with intercalated lenticular conglomerates and matrix support. Passes into finely stratified conglomerates near the top, with a predominance of metamorphic, granitic, and volcanic clasts. The distal zone of the fan was eroded, leaving 5-meter-thick terraced levels.

This deposit is covered laterally by poorly sorted conglomerate facies, load-bearing clast with a fine matrix, and gravel-sized clasts of granitic, metamorphic, and scarcely volcanic composition; the blocks are more significant. Currently, the morpho-structural landscape of the Sierras Pampeanas is represented by mountain ranges and blocks, which are divided into smaller mountains with different orientations., sub-angular, approximately 50 cm in diameter, and predominantly granitic, compared to the underlying fan. The conglomerate disappears in the distal zone, to the north, beneath a stratified conglomerate at the base (35˚NW dip), in contact with the Paleogene sediments (very cohesive orange-brown sandstones with a 58˚W dip of the strata) (Figure 6(a)).

There is a sedimentary sequence about 11 meters thick, of stratified greenish-yellowish pellets (35˚NW dip), with concretions (Figure 6(b)), south of the outcrops in Figure 5(a), below the cenoglomeratic-conglomeratic sequence, which can be correlated with the San José Formation [100] of the Santa Maria Valley because of their lacustrine characteristics [60] .

We can interpret from the various dips of these sedimentary units that a blind reverse fault, which is verging to the east, produced the plunge to the west on the geomorphic surface of the terraced levels of the alluvial fans (Figure 6(c)).

4) Alluvial fans of the Algarrobal range: An alluvial fan with a surface area of

12,500 m² is represented by a geoform with an E-W strike at the southeast end of the Algarrobal range; the fan’s apex is at the height of approximately 1200 m a.s.l. and is partially impacted by the Chañaryaco reverse fault (Figure 3 and Figure 5(a)). The northern end of the deposit, which corresponds to Level 1 of the regional alluvial fans, is crossed by the Cuesta de Belén (PR46) (Figure 5(a)). The remains of alluvial fans like the one described and others that correspond to the second level can be seen to the north and along the same flank of the range (Figure 5(a)). The alluvial fan of the Cuesta de Belén has a typical morphology. It has a raised relief and a wavy geomorphologic surface dissected by the drainage network, indicating intense erosion. Faults divide the fans in the middle section to the north (Figure 5(a)). The fan mainly comprises conglomerate, generally well-selected and cohesive, load-bearing clasts, gravel-sized and isolated blocks up to 1.5 meters in diameter. The matrix is sparse near the foothills and more abundant in the distal and lateral facies; bedding is tabular parallel (DDD, 095˚/55˚), sloping towards the base and nearly horizontal towards the top (Figure 7(a)). The clasts are rounded to subrounded in shape, spherical, subprismatic, and discoidal in shape. They comprise lithic fragments of grey and pink granite, porous volcanic, and a few metamorphic clasts [60] .

Conglomerate deposits in some areas are on a granitic basement or in contact with undifferentiated Cenozoic rocks, such as brown, friable sandstones rich in gypsum (Figure 7(a)). A continuous level of fault breccia with a 118˚/55˚ orientation (DDD), about 50 cm thick, is observed in the contact between the latter (Figure 7(a)). Its surface geomorphology and conglomeratic composition differ significantly from the adjacent fans (Levels 3 and recent). Levels 3 and recent are modern alluvial deposits with a flat geomorphologic surface and rich sandy-silty supporting matrix (Herazo et al., 2017). An alluvial fan (Level 1) with smaller dimensions can be seen northeast of the Cuesta de Belén, but it is heavily consolidated on granite rock (Figure 5(a) and Figure 7(b)). This fan offsets the Chañaryaco reverse fault, which gives the conglomerate layers a solid tilt to the southeast (DDD, 133˚/48˚) and is far from the mountain front (Figure 5(a) and Figure 7(b)).

The alluvial fans at the SE end of the Algarrobal range and the southern end of the Ampujaco River, which correspond to levels 1 and 2 (Figure 5(a)), are geoforms unrelated to the elements that were necessary for their formation (such as the raised relief at its head, the source area of the materials, transport drainage, etc.), which managed to accumulate these volumes of rock that are currently strongly consolidated and in an advanced erosion stage. The alluvial fans described have a high relief, coarse granular composition, deep dissection from surface drainage, and are impacted by faulting. The younger alluvial fans (Level 3 and current level) (Figure 5(a)) have less dissected and fault-free reliefs, which starkly contrast with this. The age of the alluvial fans at Levels 1 and 2 is believed to be between the Pliocene and Pleistocene.

1) Atajo fault: The reverse vertical component of the Atajo fault, which has an NNW strike and measures about 69.5 km in length (Figure 3, Figure 4, and Figure 8(a)), dips 60˚ and 80˚ to the east. Granitic and mylonitic rocks are displaced over Cenozoic sedimentary rocks in the northwest region of Cerro Atajo and over volcanic rocks of the Farallón Negro Volcanic Complex (Figure 3 and Figure 9(a)). The displacements between the Hualfín - Las Cuevas and La Ovejería - Cerro Huayco ranges (Figure 3, Figure 4, and Figure 8(a)) demonstrate that it also has a component of dextral horizontal movement.

According to [52] and [91] [92] , the Tampa-Tampa and Vis-Vis basins are caldera structures with associated mineral deposits (Figure 3). We can interpret that displacement along the Atajo fault produced releasing and restraining bends by analyzing the geometry and morphology of the fault from satellite images, field data, and the morphologies of the Tampa-Tampa and Vis-Vis basins connected to mineralized zones (Figure 8(a)).

The Tampa-Tampa and Vis-Vis basins are linked to the releasing bend zones, while the western edge of Cerro Huayco is linked to the restraining bend zone (Figure 8(a)). Northwest of Cerro Atajo, on the northeast edge of the volcanic caldera, is where you will find the Tampa-Tampa field (Figure 8(a)). It is about 8.6 km² in size, and the faults overlap by about 4 km (Figure 8(a)). The Vis-Vis field, south of the La Ovejería range, is elongated, covers a surface area of 6 km², and has faults that overlap by about 4.5 km (Figure 8(a)). The Atajo fault created a 4.2 km long restraining stopover between the edges of the La Ovejería

range and Cerro Huayco (Figure 8(a)). The La Ovejería range included the Cerro Huayco. To make the dextral displacement of the Cerro Huayco, the Atajo fault split the northeastern end of the La Ovejería range, tilting the regional foliation in the metamorphic rocks that make them up towards the west, in the La Ovejería range, and to the east, in the Cerro Huayco (Figure 3 and Figure 8(a)).

The Farallón Negro Volcanic Complex’s eastern boundary is also divided by the Atajo fault, and the Cerro El Durazno is a volcanic cone remnant of the NE. The measured fault planes on the Atajo fault strikes to the NW and NNW, respectively, west of the Cerro Atajo and Cerro Huayco, indicating a close relationship with the main trace of the fault and its geometry (Figures 8(a)-(c)). The Atajo fault would have been vital in causing the volcanic caldera to collapse (Figure 8(a)).

2) Las Vizcachas fault: The Las Vizcachas fault measures roughly 15 km (Figure 8(a) and Figure 10(a)). The fault occupies the central zone approximately 3 km wide, where other structures have the same strike on its side (Figure 10(a)). The stereonet software represented 27 measurements of the fault zone in Schmidt’s net, lower hemisphere [95] [96] (Figure 10(b)).

Satellite images clearly show the curved nature of this fault, as well as its general NW strike and dextral horizontal displacement. It forms the boundary between Cerro Atajo and Cerro Huayco to the east (Figure 9(b)). It enters the Farallón

Negro volcano’s caldera to the northwest, offsetting and cutting the Atajo fault (Figure 8(a), Figure 9(c), and Figure 10(a)). The secondary conjugate structures accompanying it confirm de dextral horizontal displacement (Figure 9(c)).

There are zones of both transtension and transpression in the horizontal shear zones. “Palm tree structures” are typically compressional structures with convex geometry [101] . The fault also caused the NE end of the La Ovejería range to split apart, creating a narrow valley home to the Jejenes river and only 3 km long and 180 m wide (Figure 10(a)). The field’s most definitive evidence is the positive flower geometry produced in the metamorphic rocks (Figure 11).

3) Buenaventura fault: The Buenaventura fault, which has a normal displacement and dips 70˚ to the NNW [101] , limits the La Ovejería range to the north (Figure 4, Figure 8(a), and Figure 10(a)). Little evidence of displacement of the fault plane was found in the outcrops, but in the MW23 well located to the north of it, the basement was found in the subsoil at a depth of 128 m, indicating the dip and character of the surface of the fault [102] .

4) San Lucas fault: The San Lucas fault, which is 7 km long, strikes NW, exhibits sinistral displacement, and creates a small pull-apart basin that is 1.14 km² in size. The basin has an elliptical shape, a 1.7 km length, and a major axis that strikes NW (Figure 8(a)). This depression contains subvolcanic intrusives rocks from the Farallón Negro Volcanic Complex [52] , which broke through the igneous-metamorphic basement (Figure 3 and Figure 8(a)).

Metamorphic rocks on the western side of the San Lucas fault display a fault plane (DDD: 267˚/52˚) (Figure 12(a)) and striations (DDD: 198˚/05˚) (Figure 12(b)) that are composed of horizontal displacement. The measured fracture planes in the region preferentially strike in the direction of the San Lucas fault,

which is to the NW (Figure 8(a) and Figure 12(c)). Secondary conjugate fractures are also identified (Figure 12(b)), supporting the claim that the fault has been displaced sinistrally. Normal faults in this area cut quartz veins in the metamorphic basement (Figure 13).

5) Ampujaco fault: This fault represents a linear tectonic feature with an NW strike about 30 km long and can be seen in satellite images. It exhibits reverse vertical displacement components, an SW dip, and dextral horizontal displacement (Figure 3 and Figure 4). Granitic rocks from Cerro Pampa are brought into contact with rocks from the Farallón Negro Volcanic Complex and metamorphic rocks from the La Ovejería range by this fault (Figure 3). It delineates the boundary between the Fiambalá and Hualfin ranges, which were displaced by this fault (Figure 3 and Figure 4). At the northwest end of the La Ovejería range, the fault plane has an attitude of 240˚/80˚ (DDD) (Figure 3).

6) Belén fault: This NE strike fault is 50 km long (Figure 3 and Figure 4). The fault creates a small valley (8 km long) bordered to the west by the Belén range and to the east by the Cerro Pampa by dividing the southern sector of a mountainous block of granitic rocks (Figure 3 and Figure 4). The valley widens towards the Belén field, where the town of Belén is situated and reaches a width of 3.20 km; to the north, it connects with the Hualfin valley, where the fault does not outcrop (Figure 3 and Figure 4). This reverse fault dips to the west (DDD: 245˚/30˚); at its northern end, it places granitic rocks on top of Neogene sediments (Figure 14).

7) Pampa fault: The fault limits the Ampujaco Valley’s western boundary (Figure 3 and Figure 4). It is a broken, 29 km-long reverse fault that lifts and tilts the Cerro Pampa to the west (Figure 5(a)). As another reverse fault that

raises the stratification planes of Paleogene sedimentation that are orange-brown (DDD: 273˚/58˚) and the deposits of alluvial fans formed by highly consolidated conglomerates, possibly dating to the Early Pleistocene (DDD: 275˚/35˚), this fault’s quaternary reactivation is visible 2.4 km to the east of the main fault (Figure 5(a) and Figure 6). These tectonic morphologies were described by [103] as outer faults, a byproduct of fault migration, creating a piedmont promontory between the two faults in tectonically active regions (Figure 6(c)). Some fracture planes were measured on the western edge of the Ampujaco valley, indicating a preferential NNW strike (Figure 5(b)). Good examples of faults with various geometries created in the foothills because of the reactivation of earlier faults can be found in the Tafí valley [85] .

8) Chañaryaco fault: The 39 km long fault strikes in the NE (Figure 3 and Figure 4). Its morphotectonic expression is seen in the mountainous block of the Venado, Talayacu, Carrizal, and Algarrobal ranges, as well as Quemado hill, rising and tilting toward the west (Figure 4). Smaller structures limit the Talayacu, and Carrizal ranges on their eastern edge, tilting them to the west by verging to the east (Figure 3 and Figure 4). Highly consolidated alluvial fan deposits, which make up Level 1 of these deposits in the foothills of this mountain block, east of the Chañaryaco fault, are being affected by normal and reverse structures of recent tectonic. These deposits are thought to date back to the Pliocene-Pleistocene (Figure 7(a)).

The reactivation of the Chañaryaco fault created these structures. Some have oblique orientations concerning the Chañaryaco fault’s strike, with a generally NS strike and opposite dip directions (Figure 7(a)). The 1000-meter-long reverse fault La Cuesta (DDD: 118˚/55˚) tilted the alluvial fan, separating it from the Algarrobal range and disposing of conglomerate layers with a strong dip to the east (DDD: 095˚/55˚) and eroding it (Figure 5(a) and Figure 7(a)). The fault occurs where the brown sandstone meets the conglomerate deposits that make up the alluvial fan (Figure 7(b)).

The reactivation of the Chañaryaco fault also caused the tilting to the east and dismemberment of another alluvial fan (Level 1, Figure 5(a)) to the north, where the flank of the Algarrobal range forms a strongly curved inlet, concave to the east (Figure 5(a) and Figure 7(b)). The height of the counter slope of one of these residual deposits, which reaches approximately 90 m, can be seen in the satellite image. This is the product of the fault’s tilting, which resulted in the conglomerate strata having a strong SE dip (DDD: 133˚/48˚) (Figure 7(b)).

The magmatic activity allowed the Farallón Negro Volcanic Complex to form near the end of the Tertiary, resulting in porphyry copper and epithermal deposits (Figure 3). The dikes and subvolcanic intrusives were emplaced in the volcanic complex along a structural pattern that had a NE preferential trend at the start of the volcanic activity (CED: 8.10 - 8.50 Ma) but later changed to an NW strike (DAT: 7.39 Ma; DMM: 5.95 - 6.14 Ma and RL-VM) [29] (Figure 8(a)).

The volcanic complex’s internal fracturing also has a preferential NNW to NW trend (Figure 8(b), Figure 10(b)). The Farallón Negro Volcanic Complex’s tectonic-magmatic evolution was controlled by the counterclockwise rotation of the shortening axis [29] .