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The results obtained in this work evince that the metallic mineral deposits located in the northern region of the Chilean-Pampean flat slab (in northern Chile and north-western Argentina), at approximately 27° 30′S, would be related to the subduction of the Copiapó aseismic ridge. The analysis of the gravity anomalies and vertical gravity gradient allows inferring a deflection and truncation of the main trend of the Andean structures at the extrapolated zone of the Copiapó ridge beneath South America. Thus, the general NNE-trend of the Andean structures are rotated locally to an ENE-strike within the area of the Ojos del Salado – San Buena Ventura lineament. We explain that this anomalous behavior of the gravity derived anomalies is related to the deformational effects imprinted by the ridge subduction. Regions with a low subduction angle (

Gravimetry is a routine part of the geophysicists toolset, historically used in geophysics following the geodetic definitions of gravity anomalies and their related “reductions”. Several authors have shown that the geodetic concept of a gravity anomaly does not align with goals of gravimetry in geophysics (the investigation of anomalous density distributions). Much of this confusion likely stems from the lack of widely available tools for performing the corrections needed to arrive at a geophysically meaningful gravity disturbance. For example, free-air corrections are completely unnecessary since analytical expressions for theoretical gravity at any point have existed for over a decade. Since this is not easily done in a spreadsheet or short script, modern tools for processing and modelling gravity data for geophysics are needed. These tools must be trustworthy (i.e., extensively tested) and designed with software development and geophysical best practices in mind.We present the Python libraries Harmonica and Boule, which are part of the Fatiando a Terra project (https://www.fatiando.org). Both tools are open-source under the permissive BSD license and are developed in the open by a community of geoscientists and programmers.Harmonica provides tools for processing, forward modelling, and inversion of gravity and magnetic data. The first release of Harmonica was focused on implementing methods for processing and interpolation with the equivalent source technique, as well as forward modelling with right-rectangular prisms, point sources, and tesseroids. Current work is directed towards implementing a processing pipeline for gravity data, including topographic corrections in Cartesian and spherical coordinates, atmospheric corrections, and more. The software is still in early stages of development and design and would benefit greatly from community involvement and feedback.Boule implements reference ellipsoids (including oblate ellipsoids, spheres, and soon triaxial ellipsoids), conversions between ellipsoidal and geocentric spherical coordinates, and normal gravity calculations using analytical solutions for gravity fields at any point outside of the ellipsoid. It includes ellipsoids for the Earth as well as other planetary bodies in the solar system, like Mars, the Moon, Venus, and Mercury. This enables the calculation of gravity disturbances for Earth and planetary data without the need for free-air corrections. Boule was created out of the shared needs of Harmonica, SHTools (https://github.com/SHTOOLS), and pygeoid (https://github.com/ioshchepkov/pygeoid) and is developed with input from developers of these projects.We welcome participation from the wider geophysical community, irrespective of programming skill level and experience, and are actively searching for interested developers and users to get involved in shaping the future of these projects.

One challenge to numerically simulate the subduction of cold oceanic lithosphere under continental lithosphere is the preservation of the decoupling between the subducting and upper plates for tens of millions of years. One strategy to simulate the persistence of the decoupling is the continuous entrainment of a weak layer (i.e. with low effective viscosity) at the top of the oceanic plate, representing a lubrication between both plates. However, variations on the thickness and rheological structure of this weak layer affect the geodynamic evolution of the subducting plate, modifying the geometry and degree of interactions between the lithospheric plates. In the present work we evaluated how the variation of the geometry, viscosity and density of the weak layer, relative to the surrounding lithosphere, can affect the lubrication between the two lithospheric plates. We performed a series of 2D numerical simulations using a finite element code for thermochemical convection. The code solves the Stokes flow for a fluid using the Boussinesq approximation in a Cartesian coordinate system, considering that the viscosity varies exponentially as a function of the temperature. In the present visco-plastic approach, the effective viscosity is determined by the combined effect of a viscous component, assuming the Frank-Kamenetskii rheology, and plastic deformation, following the Byerlee's friction law. In our numerical scenarios, the subduction is produced by the negative buoyancy of the cold oceanic lithosphere, without the imposition of an external velocity as boundary conditions. The time range of the simulation is of the order of 50 million years. In the initial simulation, a weak zone is imposed in the region between the two plates. This zone presents low viscosity and density relative to the surrounding lithosphere. As the oceanic slab is subducted, the weak zone is deformed and dragged. This removes the lubrication until utterly coupling the lithospheric plates, generating the thickening of the continental lithosphere below the trench region. To preserve the decoupling along all the simulation time, an extra continuous weak layer on top of the oceanic plate is added with low density and viscosity. In this scenario, the first weak zone is still dragged by the subducting plate, but the additional weak layer keeps a lubrication zone between the plates, preventing the coupling of the two lithospheric plates. Therefore, adding a continuous weak layer on top of the oceanic crust together with a weak zone prevents the coupling of the subducting and overriding plates when the effective viscosity of the weak layer is smaller than ~1019 Pa s. These numerical scenarios are used to analyse the subduction pattern of the Nazca plate observed in the southeastern portion of South America, using as constraints the slab geometry of the subducting oceanic plate derived from the Slab2 model.

The occurrence of a Neogene shallow subduction stage, as well as, a Pliocene slab-tearing, and steepening of the Nazca plate in the southern Central Andes are well established. However, a satisfactory explanation for the origin and connection between these complex processes is still elusive. In this contribution, we revise the late Cenozoic tectonic and magmatic evolution of the southern Central Andes between 35° and 38° S and discuss different proposals for the Miocene slab shallowing and its Pliocene destabilization. Recent plate kinematic reconstructions show that Neogene arc-front expansion linked to slab shallowing, fold belt reactivation in the main cordillera and intraplate contraction in the San Rafael Block correlates with the subduction of the ancient Payenia plume, a deep mantle anomaly potentially rooted in the lower mantle. Also, the Nazca slab tear determined from tomographic analyses and subsequent slab steepening may also be a direct consequence of this plume subduction process. Considering the westward drift of South America and the presence of several neighbor hotspots over the Nazca plate, the Payenia plume overriding could be the first of future episodes of plume–trench interaction in the Andes.

Combined models from satellite gravity measurements and terrestrial observations provide a model of Earth’s gravity field with high spatial resolution and accuracy. In this work, we used the combined EIGEN-6C4 model and satellite-only GOCE data, both corrected for topography, to study the crustal structure of the transition zone between the Southern Central Andes and Patagonian Andes, adjacent foreland zone and Atlantic passive margin. We calculated gravity anomalies and vertical gravity gradients for mapping crustal density heterogeneities with the aim of validating and discussing previously proposed crustal models. This work provides additional geophysical constraints for several crustal structures that were discussed and proposed on the basis of geological evidence, such as the Pampean-Pan-African boundary that borders the western edge of the Rio de la Plata craton or the Famatinian paleogeographic boundary that juxtaposes the Laurentia-derived Cuyania and Pampean basement blocks. However, other gravimetric contrasts need to be further evaluated in relation to their tectonic significance, including the Malvinas Fault Zone through the Atlantic passive margin and the internal structure of the North Patagonian Massif. In this work, we highlight that new gravity field models are useful for identifying and mapping with high-precision crustal-order features, providing an innovative tool in geophysical exploration and development of tectonic and paleogeographic models.

The kinematics of the Farallon-Phoenix-South America triple junction during the Cretaceous and Paleogene periods remain incompletely resolved. Geological studies have interpreted Paleocene-Eocene ridge subduction beneath Patagonia based on the documentation of slab window magmatism and shut-off of the Andean arc. Nevertheless, a new regional synthesis of studies assessing the Paleogene tectonic evolution of Patagonia, focused on a key Andean segment between 45°S and 46°30′S, shows inconsistencies in this interpretation. In particular, the presence of two separate areas with simultaneous slab window-related magmatism and an intervening sector that registered plate-wide contraction, along with a spatiotemporal mismatch between magmatism location and ridge kinematics, preclude a single ridge-trench interaction. As reviewed here, it is likely that the oblique collision of a segmented ridge accounts for the latitudinally variable tectonomagmatic evolution in Paleogene times. Finally, this study highlights the potential of the geological record for decoding the complex configurations of midoceanic ridges during subduction.

The southern Puna plateau is a conspicuous example of a high-elevation orogenic plateau in a non-collisional setting. This orogenic sector is currently located above an anomalously shallow subduction segment, in which timing and relation to upper-plate tectonics have been widely overlooked. This subduction segment, here referred to as the southern Puna shallow subduction (SPSS), is characterized by a ~200 km wide shallow area located at ~300 km from the trench at a depth of ~100–120 km and dipping 10–12° to the east. To determine the onset of the SPSS and its link to the tectonic and magmatic activity in this region, we analyzed the tectonomagmatic record of the southern Puna plateau from preexisting datasets. Also, we present a new approach based on global subduction data that provides a straightforward methodology to extract potential paleo-slab angles from the bedrock arc record. This analysis reveals that a pronounced eastward arc-front migration and magmatic broadening took place at ~26 Ma and was preceded by ~4 Ma of reduced magmatic activity, which we link to the inception of the SPSS. As expected in shallow subduction settings, a change to basement-cored distributed deformation south of 25°S in the southern Puna plateau coincides with the beginning of shallow subduction. Also, the SPSS is coincident with the enigmatic post-Eocene intraplate deformation of the Otumpa Hills located at ~950 km from the trench. We suggest that this succession of events is not fortuitous and that the development of the SPSS impacted directly the overriding plate since the Oligocene contributing to the building of one of the largest topographies (>3 km) and thickest orogenic crusts (~70–60 km) on Earth. The shallow subduction would have acted jointly with Cenozoic changes in plate kinematics and climate enhancing Andean orogenesis at studied latitudes.

Plate kinematic reconstructions show that the Farallon-Phoenix (Aluk) spreading center subducted under South America sometime between the Late Cretaceous and the Paleogene periods. Geological studies have supported a ridge-trench interaction in Patagonia during Paleocene to Eocene times mostly based on the documentation of slab window magmatism and Andean arc-quiescence. However, a revision of most recent works dealing with the Paleogene tectonic evolution of Central Patagonia between 39 °S to 50 °S highlights inconsistencies in this model. Particularly, the existence of two discrete areas with simultaneous slab window-related magmatism separated by a sector with plate-wide contraction, along with a spatio-temporal mismatch between magmatism location and ridge kinematics, preclude a single ridge-trench interaction. With the purpose to better understand this complex tectonic setting, we integrated this updated geological evolution into a plate kinematic model. We propose that the oblique collision of a segmented Farallon-Phoenix/Aluk mid-ocean ridge would explain the latitudinally variable tectonomagmatic evolution of Patagonia during early Paleogene times. Finally, this work adds resolution to geodynamic processes in active margins where complex midocean ridge-trench interactions take place. Fil: Gianni, Guido Martin. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina Fil: Pesce, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina Fil: Soler, Santiago Rubén. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina

Intraplate seismicity in the Southern Central Andes has been mostly documented to the north of 35°S, while similar phenomenon south of these latitudes is not known so far. In order to contribute to this issue, we analysed seismicity in the Andean back-arc region between 38°S and 39°S through a seismological experiment using a local broadband seismic network in the Neuquén Basin. In this study, we aim to determine the background (base) seismicity of the region, and integrate the results with gravimetric data and previous geological knowledge to identify potential sources of the seismic activity. In addition to low-grade seismicity we recorded a Ml = 3.78 strike-slip earthquake ∼ 100 km west of Neuquén city on November 19, 2015. Seismicity location could be controlled by thermo-mechanical properties of the lithosphere linked to the previous tectonic evolution. On the other hand, the triggering factor could be related to E-W Andean stress-field or to human-induced activity. Fil: Correa Otto, Sebastian Ariel. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Nacif Suvire, Silvina Valeria. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Pesce, Agustina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Nacif, Andres Antonio. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina Fil: Gianni, Guido Martin. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Furlani, Renzo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Gimenez, Mario Ernesto. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ruiz, Juan Francisco. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina

Plate tectonic theory implies that mantle plumes may be eventually overridden by lithosphere during continental drift. These events have particular tectonomagmatic consequences for active margins and hence related orogenic processes. Since the first documentation of plume overriding and the definition of the plume-modified orogeny concept, only few examples have been recognized in the geologic record. In this study, we analyze the Neogene tectonic evolution of the Southern Central Andes between 35° and 38°S and its potential relation to the subduction of the Payenia plume as a recent analogue of this process. Through a series of tectonic reconstructions we show that progressive Payenia plume overriding correlates with Neogene arc-front migrations linked to slab shallowing, fold belt reactivation in the Main Cordillera and intraplate contraction in the San Rafael block. Additionally, Nazca slab tear determined from tomographic analyses and subsequent diachronous steepening of the subducted plate may also be an aftermath of plume subduction as often described in the final stages of plume-modified orogeny. Finally, we propose a modern analogue for processes previously described, dating back to the Mesoproterozoic, which provides further insights into these complex settings. Fil: Gianni, Guido Martin. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Garcia, Hector Pedro Antonio. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Lupari, Marianela Nadia. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Pesce, Agustina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina