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The origin of the Chon Aike silicic large igneous province (SLIP) is a matter of intense debate, with contrasting hypotheses that range from intraplate settings linked to mantle plume impingement to subduction-related protracted arc magmatism in an active margin. In this study, we propose a new model for the origin of this SLIP based on a multidisciplinary dataset from Patagonia, a comprehensive literature review of southwestern Gondwana, and the results of 2-D thermochemical modeling. We demonstrate that the partial melting of subducted rocks during a massive slab break-off and the subsequent piecemeal sinking of a previously flattened oceanic lithosphere beneath southwestern Gondwana best reconciles most of the data from this magmatic province. Geophysical, geochronological, geochemical, and isotopic data from Chon Aike SLIP, combined with the understanding of the tectonic regime, ore deposits, Jurassic geological events in southwestern Gondwana and numerical modeling results, support an origin primarily linked to the partial melting of partially eclogitized metabasaltic and metasedimentary rocks, enhanced by a warm ambient mantle associated with supercontinent thermal insulation and the thermal effects of the Karoo mantle plume impingement. The demise of the flat slab through large-scale slab break-off would have led to the partial melting of a mixture largely composed of these extensively underplated components and mantle batches. These melts would have variably interacted with mantle and continental rocks and melts, resulting in the formation of most of the Chon Aike SLIP. The re-establishment of the magmatic arc after the initial stages of slab break-off seems to have only affected the northwestern part of this SLIP. [ABSTRACT FROM AUTHOR]

An outstanding question in the geological evolution of the Chilean Andes is the cause of the westward shift and relocation of magmatism from the High Andes (HA) to the Coastal Cordillera (CC) during the Late Triassic, Pre–Andean stage. The spatiotemporal distribution of Permian–Triassic–Jurassic igneous rocks in northern‐central Chile (20°S–32°S) reveals a significant westward magmatic shift of ∼120 km during the Norian time. Despite diverse proposed models, the precise geodynamic mechanism behind this shift remains unclear. To address this, we used 2D numerical modeling to investigate two contrasting scenarios: (a) subduction rollback and (b) subduction transference/jump and reinitiation by terrane accretion. Our modeling results strongly support Scenario B, where mantle density and the size of the oceanic plateau are crucial for triggering subduction jump and reinitiation. This model aligns with geological and geophysical evidence and offers new insights into unraveling the Pre– and Early–Andean evolution. Plain Language Summary: After decades of research, the geodynamic mechanism behind the Late Triassic westward relocation of magmatism from HA to CC in northern‐central Chile remains unresolved. This study employs 2D numerical experiments to investigate two competing scenarios: subduction rollback and subduction transference/jump and reinitiation by terrane accretion. Subduction models are tailored to the Andean margin, evaluating slab geometry and magmatic arc position to best fit geological observations. Key subduction parameters such as subducting plate velocity and slab age are constrained by paleoreconstructions for the study region and period. Factors like mantle density and the size of the oceanic plateau are critical triggers for subduction jump and reinitiation. Modeling results favor the terrane accretion scenario, revealing a ∼120 km westward magmatic shift for a 300 km‐wide oceanic plateau with a depleted mantle. This aligns with geological and geophysical observations, including Late Triassic subduction initiation with a new magmatic arc in CC and a lower mantle slab gap beneath the southwestern Pangea margin due to possibly catastrophic slab loss in the Middle–Late Permian. This study shed light on previously overlooked processes like oceanic plateau accretion/obstruction, slab detachment and eduction, and subduction jump and reinitiation, advancing our understanding of Triassic Pre–Andean evolution. Key Points: 2D numerical models investigate the evolution of the Pre− and Early−Andean margin through two contrasting geodynamic scenariosModeling supports subduction transference/jump and reinitiation over subduction rollback, unraveling the Pre– and Early–Andean evolutionTerrane accretion model supports a Late Triassic westward shift of the Andean magmatism, aligning with geological and geophysical evidence [ABSTRACT FROM AUTHOR]

The effect of mantle plumes is secondary to that of subducting slabs for modern plate tectonics when considering plate driving forces. However, the impact of plumes on tectonics and planetary surface evolution may nonetheless have been significant. We use numerical mantle convection models in a 3‐D spherical chunk geometry with damage rheology to study some of the dynamics of plume‐slab interactions. Substantiating our earlier 2‐D results, we observe a range of interaction scenarios, and that the plume‐driven subduction terminations we had identified earlier persist in more realistic convective flow. We analyze the dynamics of plume affected subduction, including in terms of their geometry, frequency, and the overall effect of plumes on surface dynamics as a function of the fraction of internal to bottom heating. Some versions of such plume‐slab interplay may be relevant for geologic events, for example, for the inferred ∼183 Ma Karoo large igneous province formation and associated slab disruption. More recent examples may include the impingement of the Afar plume underneath Africa leading to disruption of the Hellenic slab, and the current complex structure imaged for the subduction of the Nazca plate under South America. Our results imply that plumes may play a significant role not just in kick‐starting plate tectonics, but also in major modifications of slab‐driven plate motions, including for the present‐day mantle. Plain Language Summary: Subduction of cold, strong lithospheric slabs is the main plate driving force within mantle convection. However, hot upwellings, mantle plumes, may have a greater role in modulating plate motions and slab trajectories than previously thought. We use 3‐D numerical convection models that account for the weakening of rocks due to the accumulation of deformation to understand the effect that mantle plumes can have on subduction zones. We show that plumes can terminate subduction in a range of circumstances. We also test the effect of the amount of internal heating compared to heat from the core which is the major convective control on the importance of plumes. We discuss cases where these plume‐slab terminations may have occurred on Earth, in the geological past, and for the present day through plate reconstructions and consideration of seismic tomography. Key Points: Mantle plumes can terminate subduction in 3‐D, damage rheology convectionPlumes can modulate subducting slabs and plate tectonic regimesPlume‐slab interactions are plausible contributions to the Karoo‐Gondwana event [ABSTRACT FROM AUTHOR]

The Pampean flat slab in central Chile and Argentina is characterized by the inland migration and subsequent cessation of arc volcanism since the mid‐Miocene. Slab flattening also affects the distribution and number of intermediate‐depth earthquakes and the evolution of the overlying continental thermal structure. In this study, we combine thermal‐mechanical models with petrological models to examine temporal changes in pressure, temperature, and composition during flat‐slab subduction and estimate water carrying capacity, predicted melt distributions and predicted changes in melt composition. Model results indicate that the present‐day flattened Nazca plate carries water to ∼700 km inland from the trench and could cause flux melting if the material above the slab remains fertile. Observed slab seismicity matches areas where hydrated materials have ∼>3 wt% H2O in the oceanic crust and mantle lithosphere. Seismicity increases as slab water carrying capacity decreases (slab dehydration). As P‐T conditions and compositions of the rock trapped above the slab change during slab flattening, flux melting switches from a peridotite‐dominated early phase to a combined mid‐ocean ridge basalt/eclogite and peridotite melting at ∼8 Ma. The results provide broad consistency with known earthquake distributions, seismic velocities, and observed temporal and spatial changes in volcanic patterns above the Pampean flat slab and point toward the role of melt depletion in the decrease and ultimate cessation of arc volcanism in this region. Key Points: We estimate the water carrying capacities, melt distributions, and composition during the Pampean flat‐slab subductionThe predicted hydrated areas match the observed slab seismicity in the Pampean regionFlux melting above the flat slab is predicted to migrate inland, providing constraints on the causes of the spatiotemporal changes in magmatism [ABSTRACT FROM AUTHOR]

A detailed 3-D tomographic model of the whole mantle beneath the northern hemisphere (north of ~ 30°N latitude) is obtained by inverting a large amount of P-wave arrival time data (P, pP, and PP) to investigate transition of subducted slabs beneath Eurasia–Arctic–North America. We apply an updated global tomographic method that can investigate the whole mantle 3-D structure beneath a target area with high resolution comparable to that of regional tomography. The final tomographic model is obtained by performing independent calculations for 12 different target areas and stitching together the results. Our model clearly shows the subducted Izanagi and Farallon slabs penetrating into the lower mantle beneath Eurasia and North America, respectively. In the region from Canada to Greenland, a stagnant slab lying below the 660-km discontinuity is revealed. Because this slab has a texture that seems to be due to subducted oceanic ridges, the slab might be composed of the Farallon and Kula slabs that had subducted during ~60–50 Ma. During that period, a complex rift system represented by division between Canada and Greenland was developed. The oceanic ridge subduction and hot upwelling in the big mantle wedge above the stagnant slab caused a tensional stress field, which might have induced these complex tectonic events. [ABSTRACT FROM AUTHOR]

Serpentinization is among the most important, and ubiquitous, geological processes in crustal–upper mantle conditions (<6 GPa, <600°C), altering the rheology of rocks and producing H2 that can sustain life. While observations are available to quantify serpentinization in terrestrial and mid‐ocean ridge environments, measurements within subduction zone environments are far more sparse. To overcome this difficulty, we design a methodology to quantify and offer a first‐order estimate of the magnitude of "slab‐serpentinization" that has occurred over the last 5 Ma within the world's subduction zones by coupling four discrete tectonic and geophysical datasets—(a) raster grids of relic abyssal peridotite (peridotite exhumed from slow spreading mid‐ocean ridges but unaffected by pre‐subduction serpentinization) within ocean basins, (b) slab geometry, (c) thermal profiles and a (d) plate‐tectonic model. Averaged per year, our results suggest that 4.2–24 • 107 kg of H2 per annum could be generated from "slab‐serpentinization" within a subduction zone. Our estimate is 3–4 orders of magnitude lower than what is thought to be produced at mid‐ocean ridges, and 1–2 orders of magnitude lower than what could occur through serpentinization at trench flexure and when including possible mantle wedge serpentinization. Higher hydrogen production is correlated most strongly with the spreading history of ocean basins, underlaying the importance of the tectonic history of a slab prior to subduction. Plain Language Summary: The fate of most ocean crust formed at mid‐ocean ridges is to eventually subduct and be recycled into the mantle. Subduction zones therefore represent a key link between the rocks we see at the surface of the Earth, both in oceans and continents, and the underlaying mantle. However, subduction zones are impossible to observe directly and therefore difficult to fully understand the processes that shape them. Here, we designed a framework that coupled a series of discrete data sets to model how the composition of each subducting slab across the globe differs in order to provide an accurate estimate of "slab‐serpentinization." Serpentinization is the process that converts mantle rocks to serpentinite through exposure to water. A by‐product of this process is the formation of hydrogen gas. Using our framework, we estimated bulk fluxes of serpentinization in subducting slabs, and the corresponding flux of hydrogen. Key Points: First‐order estimate of the gross flux of "slab‐serpentinization" and the resulting (possible) hydrogen production (4.2–24 • 107 kg of H2 per annum)Seafloor spreading history and ocean basin evolution (prior to subduction) impart the strongest control on slab‐serpentinization possibility [ABSTRACT FROM AUTHOR]

The subduction of an active spreading center generates a clear signature in the temporal evolution of subduction zones. It disrupts the typical arc‐type magmatism and intraplate seismicity, enhances the emplacement of backarc plateau lava and profoundly change the tectonics and topographic relief. These distinct observations are commonly linked to a slab window opening and mantle upwelling. The Chile Triple Junction provides the ideal setup to study the mid‐ocean ridge subduction process where both sides of the spreading center continue to subduct. Here, we use 2‐D numerical petrological‐thermomechanical modeling to focus on transient geodynamic processes caused by mid‐ocean ridge subduction. Model results show slab separation along the ridge axis with the opening of a slab window. During the opening, partial melts from the spreading center migrate toward the subcontinental mantle and high temperatures in the forearc are predicted. The temporal evolution of the modeled temperature is consistent with observed heat flow data, and with magmatism and high‐temperature metamorphism recorded in Chilean forearc rocks. Such migrated partial melts might explain the low viscosity inferred and low seismic velocity anomalies imaged in the slab window beneath South America, and the common geochemical signature of the Chile Ridge, the Taitao Ophiolite and the backarc magmatism. Following slab separation, our models suggest forearc uplift and changes in the stress regime, processes which are consistent with deformation records. Summarizing, our model of the geodynamic evolution of the Chile Ridge subduction provides a consistent framework that explains diverse records of magmatism, metamorphism, deformation and mantle physical properties. Key Points: 2‐D models of mid‐ocean ridge subduction using petrological‐thermomechanical modelingSlab separation leads to the opening of a slab window and the migration of partial melts from the mid‐ocean ridge to the subcontinental mantleModels are consistent with geological, geophysical and geochemical observations in the Chile Triple Junction [ABSTRACT FROM AUTHOR]

Oceanic‐plates vertical tearing is seismically identified in the present‐day Earth. This type of plate tearing is frequently reported in horizontally‐oblique subduction zones where transform‐faulted oceanic plates are subducting (or subducted). However, the mechanisms behind vertical slab tearing are still poorly understood, thus we utilize 3D time‐dependent Stokes' flow thermo‐mechanical numerical models to further study this problem. We find that (a) the age offset of transform fault and (b) the horizontal obliqueness of subduction fundamentally control the tearing behavior of two generic, materially homogeneous oceanic slabs separated by a low‐viscosity zone. The two slabs sequentially bend, which combined with the age‐thickness difference between slabs, causes the differential sinking of them. Based on the modeling results, well‐developed slabs vertical tearing would happen when the oblique angle of subduction is ≥30° or the age ratio of the secondly bent to firstly bent slab being ∼<0.6. Quantifying the horizontal distance‐vector between sinking slabs, we find that subduction at medium‐low horizontal‐obliqueness angles (≤40°) of young lithosphere (slabs‐average ∼15 Myr) tends to produce fault‐perpendicular tearing. Contrastingly, old‐age slabs (average ≥ 30 Myr) with medium‐large obliqueness angles (∼>20°) tend to produce fault‐parallel tearing, related to differential slab‐hinge retreat or rollback. Correlations between slabs' (a) computed tearing horizontal‐width and (b) scaling‐theory forms of their subduction‐velocity differences, are reasonable (0.76–0.97). Our numerically predicted scenarios are reasonably consistent with plate‐tear imaging results from at least four natural subduction zones. Our modeling also suggests that continual along‐trench variation in subduction dip angle may be related to a special case of oblique subduction. Plain Language Summary: Oceanic tectonic plates can tear‐off through time as they plunge and sink into the Earth's mantle and are especially favored when plates have preexisting fault‐weak zones. Two primary conditions promote oceanic tectonic slabs' tearing: (a) Obliqueness of a plate's horizontal velocity with respect to the overriding‐plate coastline and trench, leading to the two slabs sequentially bending yet having differences in deformation; (b) Differences in slab‐age between two sides of a displaced fault‐zone that created an offset in plate age and thickness. To understand these processes, we present 3D numerical models that simulate tectonic evolution and deformations, and we compare model results with analytical studies as well as with natural observations from seismic imaging. Age differences across fault‐zones combined with subduction horizontal obliqueness control the generation and development of vertical tearing. Furthermore, two geometrical patterns of vertical tearing are largely consistent with observations. Our findings suggest that along‐trench changes in the steep angle between the slab and surface (dip angle) may be related to a special case of oblique subduction. Observing the age contrast across faults and the horizontal obliqueness of plates' motion allows predictions of the tearing pattern, evolution, and local mantle flow. Key Points: 3‐D numerical models are conducted to study the vertical tearing mechanism of the transform‐faulted oceanic slabs during oblique subductionThe horizontal obliqueness and slab transform age difference play dominant roles in determining the style of vertical slab tearingCorrelations between slabs' computed tearing width and scaling‐theory forms of subduction‐velocity difference, are useful and strong [ABSTRACT FROM AUTHOR]

The Middle Jurassic–Early Cretaceous evolution of the Neuquén Basin is traditionally attributed to a long phase of thermal subsidence. However, recent works have challenged this model. In view of this, we study the Late Jurassic Tordillo Formation, a non‐marine depositional unit that marks a shift to regional regression across the basin. Previous studies propose different causes for this regression, including the growth of the magmatic arc in the west, uplift in the south or extension in the north. We studied the Tordillo Formation in sections located at an intermediate position in the Neuquén Basin, in order to understand the tectonic processes active during sedimentation. We present evidence of normal faulting within the Tordillo Formation and the base of the overlying Vaca Muerta Formation. Some of these faults can be attributed as syndepositional. We characterize the Tordillo Formation as part of a distal fan‐playa lake depositional system with a contemporaneous western magmatic arc as the main source of sediment. When compared to the Late Triassic–Early Jurassic NE to NNE‐oriented rifting, which marks the opening of the Neuquén Basin, the Late Jurassic extension shows a switch in stress orientation; the latter is orthogonal to the north‐trending subduction zone. We interpret this change as a renewed phase of back‐arc extension induced by slab rollback along with minor distributed intraplate extension prior to opening of the South Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Subduction of bathymetric anomalies (e.g., an active ridge) can alter the morphology of subducted slabs and their coupling to surface processes. A natural laboratory to study these effects is the subduction of the Oceanic Chilean Ridge beneath the South American plate, which led to the formation of the Patagonian slab window. Its formation and subsequent northward migration contributed to the regression of Patagoniense sea and exhumation of marine strata to their present elevation. To date, there is no quantitative analysis of the effects on the sediment routing system of the slab window. We modeled the Neogene topographic change and foreland sedimentary evolution from the Andean Cordillera to Atlantic margin. Our results show that subcrustal‐driven subsidence correlated with accelerated subduction of the Nazca plate is required to explain the timing of the Patagonian transgression and thickness and spatial extent of marine beds during the incursion. In other words, traditional mechanisms, such as foreland flexure and global sea‐level rise, are insufficient. The subsequent regression and accumulation of mid‐Miocene alluvial‐fluvial deposits were associated with the growth of the Cordillera and a possible flattening of Nazca subduction in the middle Miocene. Isostatic uplift of ∼1 km due to lithospheric thinning during slab window formation can explain the foreland exhumation, sediment bypass, and increases in the offshore sedimentation rate. However, spatial‐temporal varying dynamic uplift is required to explain the along‐strike variations in foreland sedimentation. Our study provides new insights into the interplay between slab window formation, crustal deformation, and landscape evolution. Plain Language Summary: The geological evolution of southern Patagonia has been strongly affected by the subduction of Nazca Plate and the subsequent formation of Patagonian slab window. Different uplift and subsidence mechanisms have been proposed to explain its landscape and sedimentary history. However, it remains challenging to elucidate and quantify the impacts of contributing processes. This study focuses on modeling the surface evolution from the Andean Cordillera to the Atlantic margin over the entire Neogene. We propose that the landscape evolution of southern Patagonia involves three stages. Our results not only reveal the substantial contribution of Nazca Plate subduction to foreland sedimentation in early Miocene, but also a potential flattening of the subduction morphology in middle Miocene. Lastly, the isostatic uplift due to lithospheric thinning that accompanies Patagonian slab window formation could explain the foreland exhumation, sediment bypass, and increases in offshore sedimentation rate. Key Points: We modeled the landscape and sedimentary evolution across southern Patagonia and offshore basins since NeogeneThe Nazca plate subduction induced long‐wavelength foreland subsidence; it has likely flattened in mid‐Miocene, generating surface upliftThe Patagonian slab window affected the surface sediment routing system by generating isostatic/dynamic uplift since late Miocene [ABSTRACT FROM AUTHOR]

The process of slab tearing profoundly affects interchanges of material and energy between the lithosphere and asthenosphere and has been invoked as a trigger of magmatism in modern and ancient subduction‐collision systems. Horizontal slab tears may occur after continental collision and subsequent slab break‐off, whereas vertical slab tears may occur in response to along‐strike variations in rollback velocity, thereby ripping the subducting lithosphere. Previous studies have documented tearing of subducting slabs in modern convergent settings using geophysical methods, but in ancient collisional belts, where these methods cannot be applied, detection of slab tearing is more difficult, particularly if the oceanic plate was fully subducted and the geological evidence for subduction is limited. Here, we employ multiproxy element‐isotope imaging, as well as zircon petrochronology and whole‐rock geochemistry, to assess evidence of vertical tearing of the Mianlue slab in the Triassic Qinling Orogen in central China. Our results show evidence of anomalous, inferred tear‐related magmatism east of 107°E, at 225–210 Ma. Vertical tearing of the northward subducting Mianlue slab is recorded by geochemically anomalous igneous rocks, and the recognition of N–S to NE–SW trending boundaries defined by Sr‐Nd‐Hf isotopes, elemental ratios (Nb/Ta, and Ca/Al), Mg#, and reduced crustal thickness between 107° and 108°E. The inferred vertical tear may have been driven by slab rollback of the Mianlue slab at 225–210 Ma. The results show that multiproxy element‐isotope imaging (e.g., of εNd(t), εHf(t), (87Sr/86Sr)i, Nb/Ta, Mg#, and Ca/Al) can be used to reconstruct the evolution of fossil subduction systems. Plain Language Summary: Subduction zones are natural factories for the circulation of material in the Earth as they allow tectonic plates to descend into the mantle. Pieces of subducting plates, normally referred to as slabs, can be torn and segmented, but reconstructing the geometry of such tears in ancient convergent plate boundary settings is difficult. Based on the observation that slab tearing can trigger anomalous magmatism in convergent plate margins, we present a multiproxy geochemical and isotopic imaging method that enables us to understand the process of slab tearing in the Qinling Orogen (China) during the Triassic. We found that igneous rocks from the Qinling Orogen, east of 107°E, are geochemically anomalous (relative to typical arc rocks). These rocks are dated 225–210 Ma. By imaging various geochemical characteristics, our results demonstrate that the subducting Mianlue slab was likely torn at longitude 107°–108°E, thereby producing geochemically and isotopically anomalous mafic and felsic magmatism. Key Points: The geometry of slab tearing in an ancient orogen is constrained by a multiproxy geochemical approachAnomalous arc magmatism dated at 225–210 Ma is identified in the Qinling Orogen east of 107°EThe Mianlue slab underwent southward vertical slab tearing at 107°−108°E in the Late Triassic [ABSTRACT FROM AUTHOR]

Distinguishing the initiation of actual collision from flat‐slab subduction of oceanic buoyant highs along convergent margins is elusive because both can lead to inboard deformation and disrupt magmatic arcs. Volcanoes with nascent tear magmatic signatures provide a means to document both the occurrence and timing of actual oceanic buoyant high collision. There is a ~40‐year debate on when the true collision of the Yakutat plateau began in Alaska. Three newly identified ca. 1 Ma volcanoes with a north‐to‐south trench perpendicular orientation, nascent tear geochemical signatures, overlaying an imaged Yakutat slab tear, provide constraints on the timing of Yakutat collision and slab tearing. The ca. 1 Ma slab tear is coincident with Yakutat slab segmentation, northern continental Aleutian Arc rejuvenation, cessation of Wrangell Arc magmatism, increased collisional zone exhumation and eastern Yakutat trench abandonment. The documentation of nascent slab tear volcanoes may help resolve similar debates in other convergent margin settings. [ABSTRACT FROM AUTHOR]

Subduction of the Nazca plate results in the uneven distributions of earthquakes and arc volcanoes along the South America's western margin. Here, we construct a high‐resolution shear‐wave velocity model from immediately offshore to the backarc in South America, using advanced full‐wave ambient noise tomography. Our new model confirms and provides further constraints on three major features, including (a) extensive low‐velocity anomalies within the continental crust, (b) two high‐velocity flat slab segments located beneath southern Peru and central Chile, and (c) complex slab geometry at flat‐to‐normal transitional subduction. The flat slab segments roughly correlate with the volcanic gaps but not with the seismicity gaps. We suggest that variations of slab geometry along strike and down dip have significantly modified the flow patterns within the mantle wedge. Subduction of oceanic ridges has altered the slab dehydration processes, which can influence the distribution of arc volcanism and the occurrence of intermediate‐depth earthquakes. Plain Language Summary: The subduction of the oceanic Nazca plate beneath the South American continent results in abundant earthquakes and arc volcanoes, which are unevenly distributed along the margin. There is a lack of intermediate‐depth earthquakes and arc volcanoes beneath Peru and central Chile/Argentina. How the properties of the subducted slab influence the distribution patterns of earthquakes and arc volcanoes remains as a fundamental question to be answered. In this study, we use an advanced seismological imaging method to construct a high‐resolution seismic velocity model within the South American margin. Our new model reveals two flat subduction regions beneath southern Peru and central Chile, which roughly correlate with the observed gaps of arc volcanoes but not of the earthquakes. Our model suggests that the slab could be either torn or distorted when transiting from flat to normal subduction. We propose that the variations of slab geometry have significantly modified the mantle flow patterns within the mantle wedge, resulting in the uneven distributions of arc volcanoes. The subduction of the Nazca Ridge and the Juan Fernandez Ridge has played a critical role in controlling the occurrence of the intermediate‐depth earthquakes. Key Points: Strong low‐velocity anomalies distribute extensively within the continental crust along latitudes of 12°–28°S at 15–35 km depthsThe subducting slab is divided into four segments along the margin including two normal sections and two nearly flat sectionsThe two flat slab segments beneath southern Peru and central Chile correlate well with the volcanic gaps but not with the seismic gaps [ABSTRACT FROM AUTHOR]

A new seismic model for crust and upper mantle of the south Central Andes is derived from full waveform inversion, covering the Pampean flat subduction and adjacent Payenia steep subduction segments. Focused crustal low‐velocity anomalies indicate partial melts in the Payenia segment along the volcanic arc, whereas weaker low‐velocity anomalies covering a wide zone in the Pampean segment are interpreted as remnant partial melts. Thinning and tearing of the flat Nazca slab is inferred from gaps in the slab along the inland projection of the Juan Fernandez Ridge. A high‐velocity anomaly in the mantle below the flat slab is interpreted as relic Nazca slab segment, which indicates an earlier slab break‐off triggered by the buoyancy of the Juan Fernandez Ridge during the flattening process. In Payenia, large‐scale low‐velocity anomalies atop and below the re‐steepened Nazca slab are associated with the re‐opening of the mantle wedge and sub‐slab asthenospheric flow, respectively. Plain Language Summary: Taking advantage of the abundant information recorded in seismic waveforms, we imaged the seismic structure of the crust and upper mantle beneath central Chile and western Argentina, where the oceanic Nazca slab is subducting beneath the South American plate. The subducted Nazca slab is almost flat at a depth of 100–150 km in the north of the study area below the Pampean region, where the Juan Fernandez seamount ridge is subducting as part of the Nazca slab. The slab steepens again in the south in the Payenia region. Our model reveals pronounced low‐velocity anomalies within the Pampean flat slab along the inland projection of the Juan Fernandez Ridge, indicating that the Pampean flat slab is thinned or even torn apart. A high‐velocity anomaly is imaged beneath the flat slab, representing a former slab segment that was broken off during the slab flattening process and was overridden by the advancing young slab. Our model suggests a causal relationship between the oceanic ridge subduction and the flat slab formation. In the Payenia region, the slab re‐steepening resulted in the re‐establishment of the mantle wedge and induced hot mantle flow below the slab, which are characterized by low‐velocity anomalies in the model. Key Points: A new seismic model for the crust and upper mantle beneath central Chile and western Argentina is presentedThinning and tearing within the Pampean flat slab is detected along the inland projection of the Juan Fernandez RidgeA relic slab is imaged beneath the Pampean flat slab, reflecting slab break‐off during the flattening process [ABSTRACT FROM AUTHOR]

The South Chile ridge (SCR) intersects the Patagonian trench around 46°09′S, forming the triple junction among the Antarctic, Nazca, and South America plates. Subduction of the SCR since ~18 Ma produced the opening of a slab window beneath Patagonia and a noticeable magmatic gap in the cordillera, profuse volcanism and topographic uplift in the retroarc. To study seismicity distribution and present‐day stress resulting from this particular framework, we analyse databases of seismic events and earthquake focal mechanisms. Our study finds that clusters of intraplate crustal seismic events are disrupted by a ~450–470 km seismicity gap above the slab window. Calculated stress tensors depict a strike‐slip tectonic regime north of the triple junction, and ~W‐E compression to the south of the seismic gap. We propose that the seismotectonic behaviour of the upper plate is disturbed at the first order by the trench‐ridge intersection, leading to a heterogeneous stress field. [ABSTRACT FROM AUTHOR]

The Andean Subduction Zone is one of the longest continuous subduction zones on Earth. The relative simplicity of the two-plate system has makes it an ideal natural laboratory to study the dynamics in subduction zones. We measure teleseismic S and SKS traveltime residuals at >1000 seismic stations that have been deployed across South America over the last 30 yr to produce a finite-frequency teleseismic S -wave tomography model of the mantle beneath the Andean Subduction Zone related to the Nazca Plate, spanning from ∼5°N to 45°S and from depths of ∼130 to 1200 km. Within our model, the subducted Nazca slab is imaged as a fast velocity seismic anomaly. The geometry and amplitude of the Nazca slab anomaly varies along the margin while the slab anomaly continues into the lower mantle along the entirety of the subduction margin. Beneath northern Brazil, the Nazca slab appears to stagnate at ∼1000 km depth and extend eastward subhorizontally for >2000 km. South of 25°S the slab anomaly in the lower mantle extends offshore of eastern Argentina, hence we do not image if a similar stagnation occurs. We image several distinct features surrounding the slab including two vertically oriented slow seismic velocity anomalies: one beneath the Peruvian flat slab and the other beneath the Paraná Basin of Brazil. The presence of the latter anomaly directly adjacent to the stagnant Nazca slab suggests that the plume, known as the Paraná Plume, may be a focused upwelling formed in response to slab stagnation in the lower mantle. Additionally, we image a high amplitude fast seismic velocity anomaly beneath the Chile trench at the latitude of the Sierras Pampeanas which extends from ∼400 to ∼1000 km depth. This anomaly may be the remnants of an older, detached slab, however its relationship with the Nazca–South America subduction zone remains enigmatic. [ABSTRACT FROM AUTHOR]

The retroarc region of central Patagonia recorded three contractional stages (Late Triassic, Late Cretaceous, and Miocene) coincident with eastward broadening of arc magmatism. Inboard arc migration may be linked to shallowing of the subducted slab, subduction erosion of forearc regions, or a combination of both. Contractional episodes were followed by slab rollback, producing a series of extensional depocenters and magmatic belts across Patagonia at ~170-130 Ma, ~55-22 Ma and ~5 Ma. These rollback events weakened Patagonian crust through fracturing, mantle upwelling, and magmatic injection, favoring inception and propagation of subsequent contractional episodes. Phases of slab rollback and retroarc extension are reflected in εHf and εNd isotopic trends, with more juvenile trajectories corresponding to mantle upwelling into a broad asthenospheric wedge during slab retreat. Periods of crustal shortening are recorded by evolved εHf and εNd isotopic trajectories, demonstrating modified mantle sources. Mesozoic-Cenozoic extensional basins of Patagonia, such as the Chubut Basin, Cañadón Asfalto Basin, Río Mayo-Aysén Basin, Pilcaniyeu and Auca Pan-El Maitén magmatic belts/volcanogenic basins, and the Traiguén Basin were generated during episodes of slab rollback. In contrast, the extension-related San Jorge Gulf Basin constitutes an east-west-trending anomaly developed in an interval of the Cretaceous when the rest of western Patagonia experienced shortening. During this time, crustal evolution trends shifted from juvenile to more evolved and the arc expanded toward the continental interior most likely under a flat-slab regime. The San Jorge Gulf Basin is linked to Neocomian extensional structures in an intracratonic basin later influenced by compressional stresses linked to subduction zone in the west and incipient opening of the south Atlantic to east. • The evolution of the Northern Patagonian Andes comprises shallow slab subduction, slab-rollback and flare-up events. • Eastward arc broadening and flare-ups coincided with modification of the asthenospheric source during slab shallowing. • Westward arc retreat coincided with asthenospheric rejuvenation as indicated by more juvenile isotopic trajectories. • San Jorge Gulf Basin is an extensional basin in Patagonia that is not associated with extension during slab resteepening. [ABSTRACT FROM AUTHOR]