Tectono‐Stratigraphic Insights on the Dynamics of a Complex Subduction Zone, Northern Peruvian Forearc

Two main types of subduction are recognized around the world: accretionary and erosive. The northern Peruvian margin is a well‐known example of a margin subjected to subduction erosion, but to date the along‐margin variability and temporal changes in subduction process and forearc basin evolution have not been characterized in detail. Interpretation of regional seismic lines and integration of oil‐industry wells and seafloor data captures the erosive nature of subduction underneath the forearc with only a minor accretionary component to the north. Episodes of uplift driven by plate coupling were followed by normal faulting/extensional collapse due to plate decoupling. This mechanism explains the dominance of normal faulting across the forearc until the Oligocene with a slight reactivation within the Miocene. The subduction history is complex and includes a reduction in plate convergence rate related to forearc crustal shortening, represented by large‐scale structures including the Peru fault (reactivated) and the Illescas fault‐propagation anticlines of the Northwest Peru transpressional system. This crustal deformation started in the Miocene. Integration with magnetic anomaly data indicates that activity of the present‐day transpressional system driven by tectonic escape of the Nazca Sliver toward the northeast, may explain the seismicity gap in southern Ecuador and northern Peru. An evolutionary model of the northern Peruvian margin shows how subduction zone geodynamics left its erosive fingerprint in the forearc basin configuration.

elements such as relative sea level, origin of accommodation for the thick basin fill, sedimentary environments and tectonic history have remained unresolved.
In this work we present a multi-scale analysis, addressing aspects of plate tectonics and basin structure and mega-sequences, based on the integration of oil industry and academic data sets of the northern Peruvian forearc which allows us to re-evaluate the models of subduction.The study area comprises a region from 1°S to 9°S in northwestern Peru, between the Peru Trench off Chimbote city to the south, and southwestern Ecuador to the north (Figure 1).This includes the forearc region of the Talara Basin.
The aim of this study is to analyze the basin and subduction zone elements in order to critically test the application of the subduction erosion model to the northern Peruvian forearc, especially to the Talara Basin.The results, defining the specific type of subduction mechanism in the area and its development through geological time, help us identify possible relationships between the subduction history and Talara Basin evolution.

Nazca Plate
The geodynamic conditions between the Nazca and South American Plates have varied over time.Pardo-Casas and Molnar (1987) determined the Farallon/Nazca Plate convergence rate and drift direction relative to the South American Plate.Convergence was slow from the end of the Cretaceous until the beginning of the Early Eocene with a drift direction generally to the north, which then changed to the northeast, accompanied by high convergence rate until an abrupt decrease during the Oligocene.At end-Oligocene, the convergence rate increased again, when the Farallon Plate split into the Nazca and Cocos Plates (Lonsdale, 2005).Today, the Nazca Plate is converging with the northwestern Peruvian margin in an east-northeast direction at rates of 5.97, 6.20, and 6.27 cm year −1 in the north, center and south, respectively (Kendrick et al., 2003cited in Villegas-Lanza et al., 2016a), and the age of the portion of plate in front of the Peru Trench ranges from 40 to 30 Ma, from north to south, based on the sea-floor age map from Müller et al. (2008;Figure 1a).Based on earthquake distribution and magnitude, volcanic activity and outcrop data, the present-day northern and central Peruvian margins overlie a segment of oceanic crust known as the Peruvian Flat Slab, which has a low-angle subduction plane beneath the South American Plate (Barazangi & Isacks, 1976, 1979;Ramos & Folguera, 2009).
The structural configuration in the northern region of the Nazca Plate is represented by the Grijalva (1-2 km-high scarp, 10-20 km wide and 680 km long), Alvarado and Sarmiento (1-2 km high, 10-20 km wide and 400 km long) Ridges.These features have southwest-northeast orientations and lie in front of the northern Peruvian forearc.They have been interpreted as ancient transform faults within the Farallon Plate by Mammerickx et al. (1975), and volcanic ridges by Lonsdale (2005).Some hundreds of kilometers to the south, Huchon and Bourgois (1990) identified a large northeast-orientated fracture zone called Virú (Figure 1b), which deviates to the north-northeast close to the Peru Trench, toward the Illescas hills, where it begins to show thrust-faulted structures around the Trujillo trough.These positive structural elements were interpreted as due to oceanic plate fragmentation induced by subduction, and linked to the south to the opening of the Mendaña Fracture Zone perpendicular to its trend, where new oceanic crust has been created since 3.5 Ma.Prince et al. (1974), Kulm et al. (1982), and Prince and Kulm (1975) considered the ridges to the west of the Peru Trench off Chimbote city to be the result of imbricate thrusting due to oceanic crust rupture.
Erosive margins are the result of subduction erosion and represent more than half of the present-day subduction margins around the world (Clift & Vannucchi, 2004;von Huene et al., 2004;von Huene & Scholl, 1991).However, subduction erosion is also present, to a lesser or greater degree, even in accretionary margins (Stern, 2011;von Huene & Lallemand, 1990), with small frontal prisms (von Huene & Scholl, 1991).In the process of subduction erosion, missing crustal material derived from the overriding plate is assimilated in the subduction channel, through shear with the subducting plate (Scholl & von Huene, 2007).This type of subduction implies tectonic erosion that can be frontal, over the lower slope of the forearc, and basal, at the base of the upper plate (Stern, 2011;von Huene & Lallemand, 1990;von Huene & Scholl, 1991).As a consequence, tectonic erosion causes thinning and loss of continental plate margin material by oceanic crust abrasion (Langseth et al., 1981;S. Murauchi & Ludwig, 1980) and a simultaneous landward retreat of the trench (Scholl et al., 1980;Scholl & von Huene, 2007, 2010).
Erosive margin models have been built across upper plate-trench-subducting plate profiles from Central America to central Chile, and western Pacific oceanic-continental plate boundaries (Clift & Vannucchi, 2004;Noda & Miyakawa, 2017;Scholl & von Huene, 2007).An important characteristic of erosive margins along this sector is the trench fill thickness, which is <1 km, except for Colombia and northern Ecuador (Scholl et al., 2015).The entire Peru Trench fill thickness is <1 km, which is consistent with an arid coast with low sediment supply, and is an indicator of the erosive nature of the Peruvian margin.In the south of the study area, at the latitudes of Bayóvar bay and Trujillo city, the subduction style was originally interpreted as an accretionary complex of more than 15 km length (Bourgois et al., 1988;von Huene et al., 1989;von Huene & Miller, 1988).However, toward the north, in the Gulf of Guayaquil, in southwestern Ecuador, the margin shows development of an incipient  (Müller et al., 2008) showing the location of the study area within the context of the oceanic Nazca Plate subducting beneath the continental South American Plate.(b) Bathymetry and topography from Global Multi-Resolution Topography (GMRT) synthesis showing the distribution of Ribiana-Petroperú 2D seismic surveys and well data over the Talara forearc basin.Current plate-convergence rate in cm year −1 (yellow arrows) by Kendrick et al. (2003, cited in Villegas-Lanza et al., 2016a).R, ridge; FZ, fracture zone.Coastal Range outcrops: (1) Lobos de Afuera island, (2) Lobos de Tierra island, (3) Illescas hills, (4) Paita hills, (5) La Brea hills, (6) Amotape-Tahuín hills.
accretionary prism (Collot et al., 2011).The central and southern Peruvian margins are being affected by the Nazca Ridge, an important bathymetric high in the oceanic crust that has migrated southwards along the margin, where the subducting portion has reconfigured the subduction zone and the tectonic evolution of the forearc through time (Contreras-Reyes et al., 2019;Hampel, 2002;von Huene & Lallemand, 1990).

Northern Peruvian Forearc and the Talara Basin
The northern Peruvian forearc is located on the Pacific convergent margin (Moberly et al., 1982).To the east, the area is bounded by Paleozoic low-grade metamorphic basement of the Coastal Range, intruded by granitic rocks of the Triassic magmatic arc (Bellido et al., 2009;Sánchez et al., 2006) (Figure 1b).
The Late Cretaceous to Late Eocene Talara Basin lies in the forearc along with the Oligocene-Miocene Tumbes basin and younger units.The Talara Basin-fill comprises an 8-km thick succession of mainly siliciclastic sediments (Travis et al., 1976) and is separated by angular unconformities from the Early Cretaceous and Paleozoic metasedimentary basement (Higley, 2004).The boundaries of the Talara Basin are poorly defined (Fildani et al., 2008), except for the eastern limit with the Coastal Range.Toward the north, Upper Cretaceous and Eocene units are found in southwestern Ecuador, to the south of the Chongón-Colonche mountains, with a good biostratigraphic correlation (Coxall, 2000;Frizzell, 1945;Galloway & Morrey, 1929;Hofker, 1956;Stainforth, 1948;Thalmann, 1946;Vaughan, 1937); therefore, there is a possibility that those units make up the northern boundary of the basin, passing through the Gulf of Guayaquil.In the same way, the southern sedimentary limit has been defined to the south of the Illescas hills as part of the Paleozoic mountains (Higley, 2004), although the Early Cenozoic portion of the Talara Basin may be correlated to the Trujillo Basin farther south (Thornburg & Kulm, 1981).

Data Sets and Methods
The main database for this study is seven regional seismic reflection lines that cover the subduction zone between the Nazca and South American Plates.These lines were acquired in 1993 by Ribiana Inc. in agreement with the state-owned company Petroperú S.A.This work uses the latest reprocessing performed by Spectrum (now TGS) in 2014, based on post-stack time migration and converted to depth domain using the processing velocity.The reason for displaying the seismic lines in depth is to avoid the effect of deep-water bathymetry in time domain that could mislead the seismic interpretation due to visual distortion of the subduction zone geometry.Oil-industry well data, intersecting the western end of seismic lines, were important as a control on mapping the boundaries of different forearc basin sequences.These subsurface data sets, including local seismic surveys, were provided by the Peruvian government institution Perupetro S.A.The onshore outcropping lithologies were covered by surface geological maps at a scale of 1:100,000 from the Geological, Mining and Metallurgical Institute of Peru (INGEMMET), and Lajo-Yáñez et al. (2022).In addition, bathymetry and topography data were obtained from Global Multi-Resolution Topography synthesis and Geersen (2019).Bathymetric surveys incorporate seafloor geological mapping, sampling and seismic surveys from research vessels in previous campaigns around the Peru Trench: Nazca Project in 1972 (Kulm et al., 1982;Prince et al., 1974;Prince & Kulm, 1975), SEAPERC in 1986 (Bourgois et al., 1988;Huchon & Bourgois, 1990), NAUTIPERC in 1991 (Bourgois et al., 1993;Sosson et al., 1994) and GEOPECO in 2000 (Krabbenhöft et al., 2004).Other data used are the seafloor magnetic anomalies map from the National Oceanic and Atmospheric Administration (Maus et al., 2009).Additional seismological and GPS velocity field data along the continental margin of Peru (Villegas-Lanza et al., 2016a) and Ecuador (Nocquet et al., 2014) were integrated.
This study started with bathymetry interpretation carried out to analyze the surficial structural features on the seafloor around the Peru Trench, integrated with geological mapping from vessels.Structural and stratigraphic interpretation of west-east seismic lines 93-01, 93-10, 93-16, 93-19, 93-23 and 93-25 characterized the northern Peruvian forearc basins at different latitudes and these lines were intersected by a south-north margin-parallel seismic line 93-20.Interpretation of faults and other structural elements through geological time enabled the structural restoration to inform the stratigraphic analysis.Integration with the seafloor study allowed calibration of shallow seismic stratigraphic and structural interpretations.Tectonic analysis of the plate boundary consisted of identifying and characterizing each element of the subduction system to determine the mechanism specific to the study area.An important point in this analysis was the timing of any changes in subduction process recorded by forearc basin evolution.Finally, an interpretation of the seafloor magnetic anomalies in front of the Peruvian and Ecuadorian margins of the South American Plate, delineated the geometry and structural configuration of the northernmost segment of the Nazca Plate.

Seafloor Structural Configuration Around the Northern Peru Trench
High-resolution bathymetry mapping by ship-based multibeam acoustic data (Figures 2a and 2b) was linked directly or indirectly to subsurface structural elements imaged in seismic lines.This information complemented the subsurface interpreted geology and vice versa, especially around the northern Peru Trench where it provided map views of the surface boundary of the South American Plate.

Oceanic Plate Bend Faulting
Slope shading of bathymetry (Figure 2b) highlights normal faults which can be easily seen on the present-day seafloor, identified as bend faults (Geersen et al., 2022;Kita & Ferrand, 2018;Ranero et al., 2005).A key observation of bend faults is their distribution within the Nazca Plate and relationship with adjacent structures.These faults surround the western margin of the trench, facing the Gulf of Guayaquil, Talara and Trujillo sector of the forearc (blue thin lines in Figure 2c).Bend faulting in the southern sector preserves a general north-northwest alignment, parallel to the seafloor magnetic anomalies map used in this work (Maus et al., 2009).This alignment suggests a spreading fabric source for the faults that then are reactivated as they approach the plate bending sector.From the area between lines 93-16 and 93-10 to the north, the trench axis direction changes northwards and bend faulting re-aligns with the new trench axis direction, suggesting the formation of new bend faults beside the reactivated ones.Mammerickx et al. (1975) identified parallel ridges on the seafloor, aligned to the northeast, in front of the northern Peruvian forearc and Gulf of Guayaquil, known as the Sarmiento, Alvarado, and Grijalva Ridges (Figure 2c), and classified them as fracture zones related to transform faults of the Farallon Plate.A fourth one identified in this work is named the Yáñez Ridge.However, Lonsdale (2005) argued that they do not cross the oceanic crust magnetic anomalies orthogonally, as in the case of the Mendaña fracture zone, and proposed an origin as volcanic ridges built over eruptive fractures not related to transform faults.

Thrust-and Strike-Slip Structures
To the south (∼8°S), around the Trujillo trough, a zone of seafloor structures related to thrust faults was documented by Huchon and Bourgois (1990) and Prince and Kulm (1975), herein named the Trujillo Ridges, which are connected to the Virú Fracture Zone.While the thrusts mostly strike northwards and dip eastwards, toward the Peru Trench (light-orange polygons with red jagged lines in Figure 2c), the Virú Fracture Zone has a northeast trajectory (dark-orange polygons in Figure 2c).In a wrench fault kinematic context, these two structural features could mark possible intraplate dextral transpressional deformation of the Nazca Plate.To the southeast of the Trujillo Ridges (∼9°S), another area of ridges off Chimbote city aligned to the trench western margin was identified by Bourgois et al. (1988), Kulm et al. (1982), and Prince and Kulm (1975).These positive geomorphological structures are herein termed the Chimbote Ridges (southeasternmost orange polygons with red jagged lines in Figure 2c).Based on interpretation of single-and multi-channel seismic, previous authors interpreted the structures as westward-directed imbricate thrusts related to oceanic crust rupture.The ridges can be imaged in detail through ship-based bathymetry data compiled in Figure 2a.The eastern flank of these ridges is flat and dips steeply toward the trench, while the western side shows a fault-like scarp.Thus, the Chimbote Ridges could also belong to the transpressional system.

Northern Peru Trench
Bathymetry augmented by HSV (Hue, Saturation, Value) color model (Figure 2a) shows the Peru Trench as a deep and elongated flat surface bounded by the South American Plate margin and the outcropping oceanic crust, which define the inner and outer trench walls, respectively.The trench bathymetry represents the youngest undeformed sedimentary layer of the trench fill at depth ranges between 6 and 4.5 km below sea level (kmbsl), in front of the northern Peruvian margin.It gets narrower and shallower to the north, being less than 4 kmbsl, as it is affected by the Carnegie Ridge (Michaud et al., 2009).The eastern margins of the Alvarado and Yáñez Ridges cross and deform the trench, and from that point to the north the trench top becomes shallower.Seismic data shows a trench fill with an average thickness of 0.5 km.

Northern Peru and Southern Ecuador Slope and Shelf
In order to determine the slope along the Ecuadorian-Peruvian forearc, the 200-m sub-sea contour was extracted from the bathymetric map since it approximates the shelf edge (light-gray polygon in Figure 2c).Thus, in map view, the slope widens to the north in the Gulf of Guayaquil and to the south of the Illescas hills.The Peru Bank, identified in the northern sector, is raised as an important elongated morpho-structural element that has a southwest-northeast axis direction and a similar flat shallow water relief as the shelf.

Geological Configuration of the Northern Peruvian Forearc and the Talara Basin
West-east and south-north geological transects were built based on the longest and most representative seismic lines across the northern Peruvian forearc at different latitudes, integrated with well data, research vessel surveys and outcrop mapping.Predominant structural styles are described in conjunction with the main sedimentary mega-sequences.

Northern Zone (3°S-4°S)
The seismic line 93-01 (Figure 3a) shows a transverse section of the forearc northern region.Upper Cretaceous-Paleocene formations are absent in this sector in contrast to biostratigraphically-constrained Late Cretaceous deposits in southwestern Ecuador (Coxall, 2000;Frizzell, 1945;Galloway & Morrey, 1929;Hofker, 1956;Stainforth, 1948;Thalmann, 1946;Vaughan, 1937).This suggests no sedimentary continuation or later erosion between Peruvian and Ecuadorian forearc basins at that time.In the north, the stratigraphy comprises Eocene strata of the Talara Basin, overlain by Oligocene, Miocene and Pliocene strata of the Tumbes Basin, which is calibrated by well Corvina-40-X-1 to the east (Figure 3a).The Eocene mega-sequence does not reach the trench inner wall, likely due to non-deposition, possibly augmented by erosion, suggesting an uplifted area during that period, which is overlain by Miocene-Pliocene strata.The Coastal Range is not imaged by this seismic line since it is located further to the east.
The structural features seen at this latitude are predominantly normal faults, mostly concentrated in the slope, accompanied by folding and few associated short-displacement reverse faults.Integration with geological surface maps and oil-industry seismic and well data shows a southwest-northeast trend of the normal faults around the shelf.It also captures a northwest-directed tilting and thickening of the Early Eocene mega-sequence, suggesting accommodation was higher in the northwest of the Talara Basin at this time.
Oligocene sedimentation filled the northwestern depression.However, local variability is related to growth fault activity on a structure named here as the Peru fault (cyan thick line in Figure 3).Miocene sequences exhibit divergent seismic facies toward the fault, confirming syn-sedimentary behavior at that time (seismic reflectors between green dashed lines in Figure 3), until they onlap the footwall block.To the west of the half-graben, Eocene and Miocene mega-sequences are conformable, which means that this sector was stable and without accommodation during the half-graben formation.With a listric geometry, the Peru fault is interpreted as a critical deep structural element deforming the continental crust.
The upper 3 km of the Peru fault plane slightly overturns eastwards, and bounds a deformed footwall anticline.Reflectors onlap this area (green dashed line in Figure 3b) and are truncated by a conspicuous unconformity (red dashed line in Figure 3b).Short-displacement inversion of the half-graben was identified in the uppermost 1.5 km of the fault (cyan dashed line in Figure 3b), forming a subtle harpoon structure.In this section, spectral decomposition performed by Borda and Bianchi (2020) on a seismic cube, 4 km to the south of line 93-01, through Miocene sequences, indicates later strike-slip behavior of the Peru fault.This seismic attribute shows a stratigraphic feature, possibly related to a fan with a sedimentation direction to the SE, whose frequency anomalies show a dextral displacement (Figure 3c).These observations suggest that compressional stress extended across the west of the Peru fault and reactivated it with dextral strike-slip kinematics producing an oblique inversion, still in the Miocene.Folding and uplift of the entire sedimentary fill identified below the Peru Bank (submarine plateau at the center of Figure 3), including the underlying Paleozoic basement, is consistent with subsequent compressional stress until the Pliocene.
Finally, another group of large listric faults defines a horst close to the continental margin edge (left-hand side of Figure 3a).Pliocene strata, onlapping the erosive top of the Miocene mega-sequence on the horst, suggest an Early Pliocene age of formation, likely related to a period of subsidence.Several normal faults affect mostly the Oligocene and younger strata along the slope.The normal fault density in the forearc is higher from the west of the Peru fault until the trench, and may represent one of the last deformation phases in the area as a stress release period following the compression.

Central Zone (4°S-5.4°S)
Interpretation of line 93-10 (Figure 4) demonstrates a near-constant thickness of stratified units within the Upper Cretaceous-Paleocene and Eocene mega-sequences overlying the Paleozoic basement.These units extend from the Coastal Range westward to the trench inner wall.The Eocene mega-sequence overlies nearly parallel Upper Cretaceous-Paleocene strata, generally with a subtle unconformity, which indicates no abrupt tectonic deformation during sedimentation through this period.Eocene strata extend across all of the forearc, which suggests a major area of accommodation during this period, as seen in the northern zone.The Oligocene mega-sequence is almost completely restricted to the deepest half of the margin slope, and overlies Eocene strata with a sub-parallel contact.The Miocene mega-sequence overlies the Eocene and Oligocene units with an angular unconformity, denoting a Pre-Miocene structural rearrangement.Pliocene strata also have discordant contact with older units.
The only structural style characterizing this central zone is normal faults, which formed across the forearc, most of them dipping to the west.Most of these faults record extensional strain from the Eocene, with some reactivation before the Pliocene.As a result of this crustal deformation, major subsidence was produced by deeper normal faulting that terminates close to the subduction zone, resulting in a hanging-wall syncline.Resultant accommodation was filled by Oligocene, Miocene and Pliocene mega-sequences.The central zone is the best example of slope collapse in the study area.
Local seismic surveys, well logs and outcrops in the Negritos oilfield (right-hand side of Figure 4a) allow integration of data from line 93-10 to the La Brea hills (local sector of Coastal Range, including the Triassic magmatic arc).The structural and stratigraphic configuration is of rotated blocks, bounded by listric normal faults, and comprising the Eocene and Upper Cretaceous-Paleocene mega-sequences overlying the Paleozoic meta-sedimentary basement.Some faults are syn-sedimentary and were activated in the Early-Middle Eocene, controlling the deposition of fluvio-deltaic systems (Lajo-Yáñez et al., 2022), which are overlain by Upper Eocene deep-water deposits.Biostratigraphic and core data from deep wells indicate Upper Cretaceous systems developed in environments ranging from transgressive shelf to deep-water.

Southern Zone (5.4°S-7°S)
Similar to the central zone, lines 93-16 and 93-19 (Figures 5 and 6) show the western boundary of Upper Cretaceous-Paleocene sediments at the trench inner wall.The Eocene mega-sequence shows a dramatic thickness decrease seaward and is overlain by Miocene, Pliocene, and Pleistocene deposits, separated by unconformities.As in the central zone, Upper Cretaceous-Paleocene and Eocene mega-sequences are sub-parallel, confirming no major tectonic deformation between them.Both mega-sequences onlap the western flank of the subcropping Coastal Range; however, calibration with nearby wells SP1-1X and SP2-1X-ST indicates that only the Eocene along with Oligocene and Miocene mega-sequences continue further eastward, covering the large structure.
The structural style is partly extensional, represented by a high density of mostly-westward dipping normal faults concentrated in the slope and at the plate edge.Antithetic normal faults appear in the southernmost lines.The other structural component is compressional, marked by a kilometer-scale group of large fault-propagation anticlines, herein named Illescas since they formed in front of the Illescas Paleozoic high, resulting in shortening of the continental crust.These structures are documented in lines  and show apparent west-dipping reverse faults, suggesting a general eastward direction of the compression, concordant with the Nazca Plate drift direction.The folding appears to affect not only the continental crust, but the oceanic crust.The angular unconformity of the Miocene over the folded older sequences at the top of the anticline zone suggests that the structural deformation took place shortly before, or at the beginning of the Miocene.Seafloor dives NP26 and NP34 performed by the Nautile submersible (Sosson et al., 1994)   records a large-scale uplifted Paleozoic structure, ∼12 km from dive NP34, that appears to be part of the Illescas fault-propagation anticlines.Some of the normal faults cut the Illescas fault-propagation anticlines, and the overlying unconformable Miocene strata, which shows them to have been the last to form.
Twenty five northward seafloor dives from this submersible in front of the Bayóvar bay (Figure 5a), and in combination with a hydrosweep survey from the research vessel Sonne, identified Pleistocene debris-avalanche deposits on the slope (Bourgois et al., 1993).The distribution of these deposits was controlled by a group of three main curved collapse scarps that were mapped with bathymetry collected by the Jean Charcot cruise (Bourgois et al., 1988;von Huene et al., 1989).Integration with seismic lines 93-16 and 93-19 (Figures 5 and 6, respectively), crossing the mapped area, shows discontinuous seismic reflections with internal low amplitudes bounded by an erosional base located in the lower slope.These deposits are distributed seaward, adjacent to the middle slope, which is delimited by the upper and middle scarps related to normal faulting.The location of this slope segment just above the Illescas fault-propagation anticlines is consistent with an unstable slope formed by uplift.The lowermost scarp, originally interpreted to be related to the subduction zone, is well displayed in line 93-16 as a listric fault cutting the plate wedge tip and ending up as thrusts in the oceanic deposits that overlie the oceanic crust basement, producing a gravity-driven slide.This third scarp is at ∼5 km up dip from the identified subduction entry in this study.The interpretation associates these structures to an unstable submarine slope conducive to development of mass-transport deposits (MTDs) that flowed into the trench.

Lateral Variability in the Forearc
The south-north line 93-20 (Figure 9) provides the critical seismic-stratigraphic tie between the main west-east geological transects, and gives spatial context to the stratigraphic and structural features, recording the variable distribution of the mega-sequences along the northern Peruvian forearc.As the basal mega-sequence of the Talara Basin, the Upper Cretaceous-Paleocene strata have a near constant and considerable thickness of about 2.5 km from the south to the central zone and then thin toward the north, pinching out before the intersection with line 93-01.Characteristic benthic foraminifera from oil-industry well data suggest initial outer-shelf deposition (100-200 m) in the Late Cretaceous that changed to bathyal-to-abyssal (200->2,000 m), and ended in shelf-to-marginal-marine (200-10 m) in the Paleocene.In an opposite sense, the Eocene mega-sequence appears thicker in the northern half of the forearc; however, west-east lines support the evidence for an angular unconformity below the Miocene and younger mega-sequences, which means that Eocene strata could have originally been more regional.Within this mega-sequence, local seismic surveys record a thicker Lower Eocene sequence to the north, whose benthic foraminifera indicate deposition in a bathyal-to-middle-shelf environment (2,000-100 m), which is absent in the southern area.Middle and particularly Upper Eocene deposits covered the whole basin, characterized by shelf-to-marginal-marine (200-10 m) and bathyal-to-abyssal (200->2,000 m) environments, respectively.The Oligocene mega-sequence, deposited in a middle-shelf-to-marginal-marine environment (100-10 m), presents along-margin discontinuity, which suggests part truncation by the unconformity and is onlapped by Miocene and Pliocene strata, representative of outer-shelf environment (200-100 m).Accommodation history in the northern Peruvian forearc can therefore be summarized as follows: (a) high sea level in Late Cretaceous, probably coinciding with global highstand (Haq, 2014;Kominz et al., 2008;K. G. Miller et al., 2005;Simmons et al., 2020)  High-density normal faulting has resulted in a collapse configuration to the forearc, mostly in the center and south, which was the main mechanism for producing forearc accommodation for the Talara and younger basins since the Eocene.In addition, the two largest forearc-scale structural features associated with crustal shortening, are identified north and south of line 93-20.They are the Peru growth fault (thick cyan lines in Figure 10) and the Illescas fault-propagation anticlines (thick light-green lines in Figure 10), respectively.The compressional and transpressional (reactivation) deformation related to these large structures suggests a Pre-or Early-Miocene initiation.The relationship between those fault groups is interpreted as sequential stresses; reverse faults responded to compressional stress due to the acceleration in Nazca Plate drift and once the stress started to diminish, the margin of the South American Plate experienced subsequent extensional collapse in the Oligocene.These events are thought to have continued until the Quaternary and be associated with the stress build-up and release intervals due to plate coupling and decoupling, respectively, identified by Bourgois et al. (2007), DeVries (1988), and Pedoja et al. (2006).

Trench Fill
Zoomed-in views of the trench from seismic lines respectively), show that the sedimentary fill thickness is ∼0.6 km in the northern and central zones, and ∼0.4 km in the southern zone.The trench fill also extends landward beyond the trench, underneath the continental margin.Contorted reflectors suggest that part of the sediments that entered the subduction zone were deformed by friction at the base of the South American Plate.In addition, seismic data also indicate the shallower bathymetry of the trench in the northern zone, ∼4.7 km deep, compared with the central and southern zones, ∼5.2 km deep.The segment of seismic line SIS-72 was taken from Collot et al. ( 2011) and re-interpreted in this study.Lines SIS-72 and 93-10, in the northern and central zones, respectively (Figures 11a and 11b), image the trench fill with moderate-amplitude, subparallel and continuous seismic reflections.South of the seismic surveys, turbidite successions were cored in local basins around the Trujillo Ridges, during the Nazca Project campaign (Prince et al., 1974), where a pilot core of ∼5 m length and shorter piston cores recovered an intercalation of clay and turbidites of Pleistocene-Holocene age.The silty base is composed of quartz, feldspars, rock fragments, and organic matter, which indicates a continental source.Seismic data from this area and around the Mendaña fracture zone acquired also in the SEAPERC campaign (Huchon & Bourgois, 1990), show similar seismic facies to those found in lines SIS-72 and 93-10, which suggests the occurrence of turbidite deposits in the northern and central zones of the northern Peru Trench.By contrast, in the south, seismic facies of the trench fill in line 93-16 (Figure 11c), are discontinuous with low-to-moderate amplitudes in a chaotic pattern, which suggests the development of MTDs, characteristic of an unstable submarine slope (Posamentier & Martinsen, 2011), as seen in Ecuador to the north, off the study area (Ratzov et al., 2010).These trench deposits are in front of the MTDs identified in the middle and lower slopes at the same latitude (Bourgois et al., 1993), and complete the longitudinal section of the MTD complex through line 93-16.
In central (line 93-10) and southern (line 93-16) zones, a subgroup of normal faults (white lines in Figure 11) cut the oceanic crust to the base of the trench fill, and do not rupture the seafloor, either because they do not have a displacement great enough or they have been buried by younger oceanic strata.In addition, thicker oceanic deposits are preserved in some grabens indicating syn-sedimentary fault movement and in other cases with upward continuation of the fault with shorter displacement, suggesting reactivation periods.These features demonstrate that the fault density is much more than what is captured by bathymetry data alone.

Continental Margin Wedge
The degree of margin accretion has been represented in conceptual models (Clift & Vannucchi, 2004;Cloos & Shreve, 1988;Noda, 2016;von Huene et al., 2004;von Huene & Scholl, 1991).In the north, near the Peru-Ecuador border, part of line SIS-72, shows a poorly-developed accretionary prism with a duplex structure within the Paleozoic basement (yellow lines in Figure 11a).In the central zone, based on line 93-10, a small accretionary prism is identified with two duplex structures in the margin wedge (yellow lines in Figure 11b), involving the Paleozoic basement and the Upper Cretaceous-Paleocene mega-sequence.This is the sector that shows the highest degree of accretion although it is still incipient.The southern zone, represented by line 93-16, is where no accretion has been produced, so that the South American Plate edge abuts the trench with no frontal thrust (Figure 11c).These characteristics at the three different latitudes show a spatial variability of the margin wedge accretion along the northern Peruvian margin.
There is a proportional relationship between the thickness of trench sediments (≥1 km) entering the subduction zone and the amount of accretion (Clift & Vannucchi, 2004;Scholl et al., 2015;Scholl & von Huene, 2007;von Huene & Scholl, 1991).However, the study area shows that not only the subducting trench fill is involved in accretion, but also oceanic crust deposits (blue and cyan transparent layers in Figure 11).Thus, in the northern zone, the very small accretionary prism, 5 km wide, is consistent with the thickness of subducting oceanic crust deposits plus trench sediments less than 1 km thick.In the central zone, incipient accretion is greater than in the north, and correlates with the thickest oceanic crust deposits along with the trench fill.This material reaches a thickness of 2.2 km at the plate boundary and shows a wrinkled appearance, likely related to friction with the overriding plate during subduction.In the southern zone, where there is no accretion, oceanic deposits plus trench fill are thinner, averaging ∼0.7 km.This relationship seen in the three zones depicts the importance of sediment subduction in the subduction process.

Subduction Channel
The subduction channel is a layer of viscous material sandwiched between the base of the overriding plate and the downgoing slab and acts as a lubricant in the subduction process (Cloos & Shreve, 1988).When oceanic plate deposits, trench fill, and lower slope sediments enter the subduction zone in a subduction erosion environment,   they become part of the subduction channel (Scholl & von Huene, 2010) as viscous material with high pore fluid pressure along the subduction zone (Shreve & Cloos, 1986;Vannucchi et al., 2012) that hydrofractures the overriding plate, dislodging and dragging fragments due to active interface mega-thrusting (Kukowski & Oncken, 2006;von Huene et al., 2004).
In the study area, seismic data allow tentative interpretation over the first ∼20 km of the subduction interface from the trench, and suggest that the subduction channel underlies the mega-thrust plane with variable thickness and extent.It was possible to delineate the subduction channel as a single and undifferentiated layer beneath the South American Plate margin (pale yellow layer in all the seismic lines).The comparative analysis in Figure 10 involves the variation in thickness of the subduction channel.Northern and central areas show the thickest section with ∼1 and ∼1.3 km, respectively; while it is much thinner in the south, reaching ∼0.3 km, which is consistent with the total thickness of subducting oceanic crust deposits and trench sediments.This relationship also reflects how important is the process of sediment subduction in subduction erosion.

Deformation at Subduction Entry
A set of high-angle reverse faults with short displacement (red lines in Figure 11) is affecting the South American Plate margin wedge, the trench fill, and the oceanic crust deposits at the subduction entry; mostly in the northern and central zones.These faults are continuous across the subduction plane and are consistent with a later tectonic event, unrelated to offscraping.Compressional stress is interpreted to have produced this brittle deformation in response to the difficulty in the advance of the Nazca Plate at subduction entry.Only a few of these reverse faults are developed a little further landward from the subduction entry.In the south, a conspicuous listric normal fault (black curved lines in the center of Figure 11c), described in previous sections, affects the subduction entry, cutting the continental margin wedge and dipping into the oceanic crust deposits as a result of a gravity-driven slide, which is consistent with extensional stress and more efficient subduction erosion.

The Nazca Sliver Escape
The seafloor magnetic anomaly map from Maus et al. (2009) shows structural deformation in the northern part of the Nazca Plate (Figure 12a), herein named the Talara Segment.In the south of this segment, a right-lateral shift of the magnetic anomalies, aligned to the Mendaña fracture zone, clearly delineates a dextral displacement of the Virú fracture zone (red bold line in Figure 12b).Therefore, this large structure has been interpreted as a shear zone that appears to be linked to the reverse-fault structures of the Trujillo Ridges that fit with a change in trajectory of the strike-slip kinematics to the north-northeast (orange jagged lines in Figure 12b), confirming the observations of Lonsdale (2005).The similarity of alignment and geometry between the Trujillo and Chimbote Ridges further south suggests the same causative strain, therefore, we assign these ridges to the same system.In the north, the Grijalva Ridge, interpreted as a shear zone, is overprinted by a left-lateral displacement of magnetic anomalies.This structure bounds the oceanic crust portion to the north, delimited also by the southern shear deformation, which led to the interpretation of the Nazca Sliver (center of Figures 12b and 12c).
The seafloor magnetic anomalies map also shows two areas with different anomaly alignments to the north and west of the Nazca Plate (Figure 12a).Based on integration with the seafloor ages from Müller et al. (2008) and Farallon/Nazca Plate-drift reconstruction from Pardo-Casas and Molnar (1987), it is interpreted that in the Oligocene (∼26 Ma), when the Farallon Plate split into the Nazca and Cocos Plates, creation of a microplate was initiated and, at the same time, a second microplate formed from the East Pacific Rise (mid-ocean ridge).These two new sections of oceanic crust expanded and pushed the Talara Segment of the Nazca Plate, one to the south and the other to the east.We interpret that the resultant stress expelled the Nazca Sliver in a northeast direction.

The Northwest Peruvian Transpressional System
The geometry and kinematics of the Nazca Sliver correlate with the major structures of the northern Peruvian margin in a transpressional model.In the south, the northeast projection of the Virú-Trujillo dextral-shear structure follows the Illescas fault-propagation anticlines (orange and light-green jagged lines in Figure 12c, respectively), deviating the structural alignment to the north-northwest.Continuing to the north, the other element interpreted as part of the transpressional system is the Peru growth fault (cyan line in Figure 12c), which was incorporated into the system when it underwent dextral strike-slip reactivation.Based on the angular unconformity of the Miocene strata over the deformed Cretaceous, Eocene and Oligocene mega-sequences, the main compressional strain of the sliver was produced probably in the Middle Miocene, as a result of an increase in plate-convergence rate and a change in movement direction of the Nazca Plate.
To the northwest of the Peru fault, continental crust is folded and thickened, uplifting the area that was partially eroded, and giving rise to the shallow-marine plateau of the Peru Bank.This crustal shortening is seen until the Pliocene mega-sequence, which indicates that the last major compression by the Nazca Sliver occurred in the Peru fault footwall during the Pliocene-Pleistocene transition.The Yáñez, Alvarado, and Sarmiento Ridges are located within the Nazca Sliver, where the intersection of the first two with the localized deviations identified in the bend-faulting alignment around the uplifted area of the trench (between latitudes of seismic lines 93-01 and 93-10) would indicate a dextral strike-slip kinematic behavior.Therefore, we interpret the ridges as minor shear zones.Further northeast, projection of the Northwest Peruvian transpressional system coincides with the deep and active Puná-Pallatanga fault analyzed by Tamay et al. (2021) (upper right side of Figure 12c).Earthquake focal mechanisms determined its dextral strike-slip behavior from the Gulf of Guayaquil to the southern (c) Interpreted present-day configuration of oceanic microplates, formed since Farallon Plate split, which pushed the Talara Segment of the Nazca Plate, producing the Nazca Sliver.The two main structures that deformed the continental crust are the Peru fault (cyan line) to the north, and the Virú-Illescas transpressional system (red, orange-and light-green-jagged lines) to the south.Seafloor ages adapted from Müller et al. (2008).FZ, fracture zone; NAS, North Andean Sliver; SZ, shear zone.

Ki-v
Western Cordillera (Ecuadorian Northern Andes).The shared trajectory and kinematics with the Peru fault suggest a transference of deformation from the Nazca Sliver to the North Andean Sliver (NAS), in northwestern Ecuador.Some small normal, reverse, and even reactivated faulting identified in the youngest strata suggest a compressional-extensional strain related to the Nazca Sliver to date.
Using the GPS velocity field map by Nocquet et al. (2014), shown as orange and red arrows in Figure 12c, three seismological sectors are differentiated.The NAS has a clear motion toward the east of 15 mm year −1 .However, the middle sector, involving southern Ecuador and northern Peru, has a minor motion to the southeast of about 5 mm year −1 , coinciding with the seismicity gap in the study area and the position in front of the Nazca Sliver and the transpressional system.To the south, plate motion resembles that of the NAS; therefore, variable along-margin locking is interpreted as related to the stress deviation of the Nazca Sliver to the northeast.

Seismological Expressions of the Transpressional System Activity
Along convergent margins, earthquakes occur as ruptures that propagate along the mega-thrust in a subduction complex (McCann et al., 1979).The Andean plate margin has experienced many earthquakes during historical times but there are some segments referred to as seismicity gaps.This is the case in northern Peru and southern Ecuador, where no M w > 8 subduction-related earthquake is known to have occurred (Nocquet et al., 2014;Villegas-Lanza et al., 2016a).The major seismological activity on the northern Peruvian margin is represented by two mega-thrust earthquakes recorded in 1953 (Espinoza, 1992) and 1959 (Ioualalen et al., 2014), with M w 7.3 and M w 7.5, and at focal depths of 33 km and >20 km, respectively (rupture areas represented by red ellipses in Figure 13a).The two epicenters are aligned to the Peru fault azimuth.Other two significant mega-thrust events are the tsunami earthquakes that occurred in the south of the study area (Nocquet et al., 2014;Villegas-Lanza et al., 2016a; rupture areas represented by blue ellipses in Figure 13a); one in 1960 with M w 7.6 and at a focal depth between 5 and 25 km (Pelayo & Wiens, 1990), located within the area of the Illescas fault-propagation anticlines, and the other in 1996 with M w 7.5 and around 7-10 km deep (Ihmlé et al., 1998), in front of the Chimbote Ridges, close to the trench.The focal mechanism suggests a low-angle thrusting for the two tsunami earthquakes.Duperret et al. (1995) defined the two major areas of earthquakes at a depth greater than 6 km recorded by the world seismic network, from 1981 to 1992 on the northern Peruvian margin (Figure 13b), which coincided with the area of the Peru fault and the Illescas fault-propagation anticlines.The focal mechanism method determined reverse and strike-slip fault kinematics in the north, and reverse in the south.These data confirm the relationship between two main areas of earthquakes in the study area and the transpressional system of the northern Peruvian forearc.Daudt et al. (2009) reported an earthquake of M w 4.7 on 22 April 2007 (Figure 13c), with an epicenter located in the Peru fault area, altering oil seepages in the Talara region, and increasing temporarily oil production from its oilfields.From February to September 2009, four periods of earthquakes were recorded to the west of the Illescas hills by the National Seismic Network of Peru (Figure 13c).Villegas-Lanza et al. (2016b) identified a reverse kinematic stress followed by a 5-month period of relative quiescence, and then a final event with normal-kinematic stress.This seismically active area is located exactly over the Illescas fault-propagation anticlines interpreted in this work, thus, the first and the third seismic events, which occurred at 8-12 km depth, confirm the existence and activity of these large structures.

Tectonic Configuration of the Talara Basin
A chronostratigraphic chart, shown in Figure 14, was constructed to analyze the tectonic factors involved in the evolution of the Talara Basin within the geodynamics of the northern Peruvian forearc.The chronostratigraphic logs of the Talara Basin built from northern, central, and southern seismic interpretations, and calibrated with well data, are integrated with the oxygen-isotope-derived eustatic sea-level history in the Pacific region (Kominz et al., 2008;K. G. Miller et al., 2020) and the plate-convergence rate of the eastern Pacific margin through the Mesozoic and Cenozoic (Larson & Pitman, 1972;Pardo-Casas & Molnar, 1987).
Throughout the Ypresian, Oligocene and Miocene, the long-term eustatic sea-level curve is in phase with plate convergence rate.Periods of concomitant sea-level rise and increase in plate convergence rate may have been amplified by an increase in mid-ocean ridge spreading (Flemming & Roberts, 1973;Mörner, 1980;Vail et al., 1984).In the same way, the greatest sea-level fall periods match with plate convergence rate decrease.This close correlation between both curves is consistent with a tectonic component to relative sea level behavior from the Eocene onwards.Data integration allowed the construction of a subduction-erosion rate curve throughout the Talara and younger basins since the plate-convergence rate specifically represents the Farallon/Nazca Plate motion.Based on regional stratigraphic studies (Euribe, 1976;Gonzales, 1976) and benthic foraminifera documentation (Cushman & Stone, 1949;Frizzell, 1943;Stainforth, 1954;Vegas, 1970;Weiss, 1955), the Talara Basin can be subdivided in a lower succession, deposited from the Campanian to the Danian, of marine shelf deposits overlain by deep-water sediments, passing upwards into marginal marine facies.The upper basin fill, of Ypresian to Priabonian deposits, shows an alternation of shallow-and deep-water sequences.The transition between these two sections coincides with the increase in plate-convergence rate in the Ypresian.The lower stratigraphy is consistent with a gradually subsiding forearc with a long-term eustatic sea-level fall and no evidence of specific tectonic activity.Seismic interpretation shows that the upper section is characterized by fault-controlled sedimentation, where uplift-collapse events took place, resulting in subsidence acceleration mostly in the central and northern areas.Variability in geological settings throughout this period reflects the high degree of tectonism, which is related to the abrupt increase in plate convergence rate from 5 to 15 cm year −1 , with a rate of 12 cm year −1 through part of the Middle Eocene to the end of the Late Eocene.This high rate through almost all the Eocene represents the Farallon Plate drift acceleration, interpreted as the period with the maximum subduction erosion rate.Therefore, the geodynamic transition in the Eocene marks an important geological change in the Talara Basin stratigraphy.

3-D Tectono-Stratigraphic Evolution of the Northern Peruvian Forearc
Forearc, subduction entry and seafloor characterization, and plate-tectonic data have been integrated to propose a six-stage 3-D evolutionary model for the northern Peru forearc (Figure 15): 1.Initial Triassic magmatic arc development with minor forearc subsidence, which did not allow any basin development.2. Development of the marginal-rift Lancones-Alamor Basin related to subduction due to slab roll-back (Winter et al., 2010) in the inner forearc from Early Cretaceous magmatic arc emplacement until the Late Cretaceous. 3. Late Cretaceous Redondo Formation extended from the Lancones Basin to the outer forearc due to subsidence triggered by initiation of subduction erosion.A significant increase in subsidence rate in the Early Eocene, with subsequent erosion resulting in the Peru Bank as a current offshore geomorphological element.Since then, an alternation of compressional stress and extensional release periods led to episodes of forearc uplift and subsidence, respectively.

Evidence for Long-Term Subduction Erosion
Critical indicators of long-term subduction erosion at the northern Peruvian margin since the Early Eocene include forearc subsidence along with gravitational normal faulting, due to thinning of the overriding plate edge by basal tectonic erosion, and minor or no accretionary prism development.These characteristics are well represented in the main subduction-erosion models (Clift & Vannucchi, 2004;Cloos & Shreve, 1988;Noda, 2016;Scholl et al., 1980;von Huene et al., 2004), which are important in understanding the spatial and temporal distribution of accommodation in forearc basins and fault activation through uplift-collapse events.
Additional evidence for long-term subduction erosion is the magmatic arc retreat (Kukowski & Oncken, 2006), in the context of a non-variable dip angle for the subducted slab.The model addresses the distance between a trench and an abandoned magmatic arc as related to continental margin truncation (Scholl & von Huene, 2010).This setting can play an important role in the configuration over time of the forearc basin, showing how the frontal and basal erosion of the continental margin leads to cannibalization of parts of the forearc basin and basement, with area reduction through geological time (Moore, 2001), producing landward trench migration.As the margin front is consumed, the active arc retreats leaving older emplaced intrusive massifs closer to the trench.In the northern Peruvian forearc, the shortest distance between the outcropping Triassic magmatic arc (Coastal Range) and the current trench is ∼85 km.In the subsurface, this distance is much shorter at ∼35 km from the front of the Triassic intrusive body to the subduction zone, which highlights the intense subduction-erosion activity.

Conclusions
The northern Peruvian forearc represents a continental margin configured by subduction erosion with marked along-margin variability.In the south, there is no accretion, while the central and northern areas exhibit a poorly-developed accretionary prism.The margin is characterized by clear truncation (margin consumption) and subsidence by basal material loss, considered the main mechanism of forearc basin accommodation.
Second-order discontinuities identified along the forearc include a nonconformity separating the Paleozoic metasedimentary basement from overlying sedimentary sequences and an angular unconformity between the Talara and younger basins.The Cretaceous-Paleocene section of the Talara Basin was controlled by glacio-eustasy, while in the Eocene, sedimentation was strongly influenced by episodes of uplift followed by extensional collapse, moderated by tectono-eustatic sea-level changes.Absence of a basin-scale unconformity between these mega-sequences suggests a continuous long-term subduction-erosion process overprinted by gravity-driven normal faulting.Uplift episodes are related to short periods of Nazca Plate advance during the Oligocene and Miocene.
The Nazca Sliver is a portion of oceanic crust identified to the north of the Nazca Plate (Talara Segment).It is interpreted to have formed and escaped by pushing of microplates of the East Pacific Rise development from the Oligocene (∼26 Ma, when the Farallon Plate split into the Nazca and Cocos Plates) and an acceleration in mid-ocean ridge spreading rate in the Early Miocene (∼20 Ma).During this period, crustal shortening across the forearc took place, producing the northwest Peruvian transpressional system, represented by the configuration of the strike-slip-reactivated Peru fault and Illescas fault-propagation anticlines.Decrease in the rate of plate convergence since the Late Miocene (∼12 Ma) implies that the rate of north-eastward escape of the Nazca Sliver has also been reduced in northern Peru since then.
The northern Peruvian margin provides a model for understanding spatial and temporal variability in structural development and forearc basin responses to subduction zone processes over ∼80 My.The Peruvian model may have application in better understanding of forearc tectono-stratigraphic relationships in more ancient convergent margin complexes.

Figure 2 .
Figure 2. High-resolution integrated bathymetric and topographic maps showing the main surficial structural features in the oceanic crust, the Peru Trench, and the South American Plate margin (source: Global Multi-Resolution Topography [GMRT] synthesis and Geersen (2019)).(a) HSV (Hue, Saturation, Value) color model, (b) Slope shading and (c) Interpretation maps of the different morpho-structural elements potentially involved in the northern Peruvian and southern Ecuadorian forearc configuration.Seismic lines (red) and well data (yellow circles) used for subsurface interpretation, where the Illescas faulted-anticlines (light-green dashed lines) and Peru fault (cyan dashed lines) are the proposed structures in this work.R, ridge; FZ, fracture zone; MTDs, massive transport deposits.

Figure 3 .
Figure 3. (a) Uninterpreted and interpreted west-east seismic line 93-01, crossing the northern part of the northern Peruvian forearc, and also the Peru Bank.As this line does not cover the trench, the western section of line SIS-72 was projected onto this line due to their proximity (∼21 km).Seismic profile only was taken from Collot et al. (2011) and interpreted in this work.(b) Zoomed-in view of the upper section of the Peru fault showing the syn-sedimentary activity during the Miocene.(c) Spectral decomposition on a 3D survey by Borda and Bianchi (2020), approximately located by the blue dashed circle in basemap, ∼4 km to the south of line 93-01, the displacement of frequency anomalies indicates a possible strike-slip reactivation of the Peru growth fault during the Miocene, that formed a half-graben in the Oligocene.Wireline logs used are gamma ray (green), spontaneous potential (red), and deep resistivity (black); values increase to the right.OCB, Oceanic crust basement; SC, Subduction channel; Pz+, Paleozoic basement and older units; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene.
in the Chiclayo canyon, sampled Paleozoic black schists and quartzites, which correlate with the basement drilled by deep wells in the oilfields and outcrops in the Coastal Range.Seismic line 93-25 (Figure 8) crosses the Chiclayo canyon and

Figure 4 .
Figure 4. (a) Uninterpreted and interpreted west-east seismic line 93-10, located in the central part of the northern Peruvian forearc from the Peru Trench to the Coastal Range.This is a section with extensive well control for interpretation (Negritos oilfield), which shows a larger development of the Talara Basin Cretaceous to Eocene mega-sequences than to the north and south.The main structural characteristic is the high density of normal faulting verging to the west, giving a configuration of a collapsed forearc.(b) Zoomed-in view of the main unconformities between Eocene, Oligocene, Miocene and Pliocene mega-sequences.Wireline logs used are gamma ray (green), spontaneous potential (red), and deep resistivity (black); values increase to the right.OCB, Oceanic crust basement; SC, Subduction channel; Pz+, Paleozoic basement and older units; K-P, Upper Cretaceous and Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene.

Figure 5 .
Figure 5. (a) Uninterpreted and interpreted west-east seismic line 93-16, representing the south of the northern Peruvian forearc, passing through the Nazca Plate and the Peru Trench to the Bayóvar bay.An incipient Illescas fault-propagation anticline is forming (light-green line) and deforming the continental crust.Nautile submersible survey helped interpretation of the shallow stratigraphy on the slope.The Cretaceous of the Talara Basin is restricted to the center and west.(b) Zoomed-in view of the mass-transport deposits (MTDs) on the lower slope.OCB, Oceanic crust basement; SC, Subduction channel; Pz+, Paleozoic basement and older units; K-P, Upper Cretaceous and Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene.
, (b) northern subsidence in Early Eocene, (c) relative sea-level rise in Middle and Late Eocene due to continental margin subsidence produced by local normal faulting within the basin, and (d) subsequent normal faulting from the Oligocene.

Figure 6 .
Figure 6.(a) Uninterpreted and interpreted west-east seismic line 93-19, further south in the northern Peruvian forearc, covering the section between the Peru Trench and the Paleozoic Coastal Range represented by the Illescas hills, where the Triassic magmatic arc is currently outcropping.(b) Zoomed-in view of the mass-transport deposits (MTDs) on the lower slope.Wireline logs used are gamma ray (green) and deep resistivity (black); values increase to the right.OCB, Oceanic crust basement; SC, Subduction channel; Pz+, Paleozoic basement and older units; K-P, Upper Cretaceous and Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene; BSR, Bottom-simulating reflector.

Figure 7 .
Figure 7. (a) Uninterpreted and interpreted southwest-northeast seismic line 93-23, to the southwest of the Illescas hills, in the northern Peruvian forearc.The Illescas fault-propagation anticlines pushed the continental crust against the Triassic intrusive massif, which prevented passage of the subduction channel underneath.(b) Zoomed-in view of the anticline related to the continental crust shortening.OCB, Oceanic crust basement; Pz+, Paleozoic basement and older units; K-P, Upper Cretaceous and Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene; BSR, Bottom-simulating reflector.

Figure 8 .
Figure 8.(a) Uninterpreted and interpreted southwest-northeast seismic line 93-25, to the southwest of the Lobos de Tierra island, in the northern Peruvian forearc, crossing the Chiclayo canyon (left-hand side), where the Nautile submersible (Sosson et al., 1994) sampled part of the seafloor made up of Paleozoic black schists and quartzites lithologically similar to the basement drilled in the Talara oilfields and outcropping in the Coastal Range.The sub-sea outcrop implies a large-scale uplifted structure and supports the fault-propagation anticlines from seismic interpretation.(b) Zoomed-in view of an Illescas fault-propagation anticline.OCB, Oceanic crust basement; Pz+, Paleozoic basement and older units; K-P, Upper Cretaceous and Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene; BSR, Bottom-simulating reflector.

Figure 9 .
Figure 9. (a) Uninterpreted and interpreted south-north seismic line 93-20, along the northern Peruvian forearc, showing the Peru growth fault, to the north, and the Illescas fault-propagation anticline, to the south.(b) Zoomed-in view of the Illescas fault-propagation anticlines affecting the continental crust and Paleozoic basement.(c) Zoomed-in view of the Peru growth fault and the anticlines developed in the footwall as a result of its strike-slip reactivation.For location of the line see Figure 2. Pz+, Paleozoic basement and older units; K-P, Upper Cretaceous and Paleocene; E, Eocene; O, Oligocene; M, Miocene; P, Pliocene; BSR, Bottom-simulating reflector.

Figure 10 .
Figure 10.West-east geological profiles from seismic lines along the northern Peruvian forearc.Most of the lines intersect with south-north line 93-20 (red dashed line).The Talara Basin extends from the Coastal Range westward to the Peru Trench.High-density normal faulting has resulted in a forearc collapse configuration.The two main structural elements identified in the forearc are the Peru growth fault (thick dark line) to the north and the Illescas fault-propagation anticlines (thick light-green line) to the south, which are part of the crustal shortening that locally uplifted the forearc.

Figure 11 .
Figure 11.Trench zoomed-in views of seismic lines (a) SIS-72 in the north, (b) 93-10 in the center and (c) 93-16 in the south.The close-ups in lines SIS-72 and 93-10 show the only minor development of the accretionary prism, with less than 10 km of duplex formation starting from the trench.The surrounding low degree of deformation is marked by short-displacement reverse faults (red lines).Line 93-16 shows no accretion to the south, and mass-transport deposits are identified in the slope and trench fill, represented by chaotic seismic facies.

Figure 12 .
Figure 12.(a) 2-arc-minute resolution magnetic anomaly grid (Maus et al., 2009) of oceanic crust off Peru and Ecuador continental margins, and (b) zoomed-in view.(c)Interpreted present-day configuration of oceanic microplates, formed since Farallon Plate split, which pushed the Talara Segment of the Nazca Plate, producing the Nazca Sliver.The two main structures that deformed the continental crust are the Peru fault (cyan line) to the north, and the Virú-Illescas transpressional system (red, orange-and light-green-jagged lines) to the south.Seafloor ages adapted fromMüller et al. (2008).FZ, fracture zone; NAS, North Andean Sliver; SZ, shear zone.

Figure 13 .
Figure 13.The transpressional system interpreted in the northern Peruvian forearc includes the Peru fault to the north (thick cyan line) and the Illescas fault-propagation anticline (thick green jagged lines).(a) Rupture areas of all the largest earthquakes (>7.3 M w ) registered in the forearc; two occurred in the north in 1953 and 1959 (red ellipses), and two tsunami earthquakes in the south in 1960 and 1996 (light blue ellipses).(b) Focal mechanisms from earthquakes recorded between 1981 and 1992, showing reverse and strike-slip kinematics to the north, and reverse to the south.(c) Earthquake registered in 2007 to the north, and earthquake monitoring through 2009 with focal mechanism of the four largest to the south.Note that all the seismological expressions compiled in all the different periods are concentrated in two main areas coinciding with the Peru fault to the north and the Illescas fault-propagation anticline to the south.Geological features are described in Figure 2c.FZ, fracture zone; SZ, shear zone.

Figure 14 .
Figure 14.Chrono-tectonostratigraphic chart of the northern Peruvian forearc showing the relationship of Talara Basin development with the plate convergence rateand eustatic sea-level curves.The basin was formed during a period of subduction erosion coincident with an abrupt increase in the convergence rate of the Nazca and South American Plates.During this period, instability in the forearc also increased due to a high incidence of uplift-collapse events preserved in the stratigraphic record as episodes of extensional fault-controlled sedimentation.Eustatic sea level started to track convergence rate, possibly due to an increase of mid-ocean ridge spreading.

Figure 15 .
Figure 15.3-D geodynamic evolution of the northern Peruvian forearc, in a scenario of a trench and abandoned magmatic arc interaction.(a) No forearc accommodation during the Triassic magmatic arc formation.(b) Volcano-sedimentary Lancones-Alamor Basin in the inner forearc during Albian aulacogen.(c) Eocene outer forearc collapse due to major margin consumption, during major subduction-erosion regime.(d) Outer forearc crustal shortening (transpressional system: PF, Peru fault; IA, Illescas anticlines) produced by the Nazca Sliver northeastward escape.(e) Miocene sedimentation over the deformed forearc through an angular unconformity after a period of crustal shortening.(f) Intermittent transpressive system activity at the end of the Pliocene, folding the Peru fault footwall.