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Sedimentary basins result from a complex interaction between mantle, crustal and surficial erosional-driven processes, which act at different time and spatial scales. While shortening and crustal loading drive flexural subsidence toward the foreland, stretching produces normal faulting and graben depocenters. In this contribution we analyze the Mesozoic-Cenozoic subsidence history of southern Patagonia, using backstripping from sixty eight oil well data and outcrops, distributed in the Santa Cruz and Chubut provinces, Argentina, in the Golfo San Jorge and Austral basins. These data are compared with three flexural analyses from six regional balanced cross sections along the southern Patagonian Cordillera, a stretching-thermal model (McKenzie) assuming lateral extension changes, five dynamic topography models localized in the core of the basins and a paleotopographic analysis derived from a paleolithospheric thickness approach (basalt geochemistry). The comparison between stratigraphic observations (backstripping in this case) and subsidence models provide us a residual subsidence value in southern Patagonia. These values are compared with dynamic topography and paleotopographic computations. No additional subcrustal forces are needed to explain the sedimentary accommodation during the Jurassic-early Cretaceous (extensional basin stage). However, from the late Cretaceous to the early Neogene, the foreland stages do require additional processes to account for the subsidence or uplift events. We reassert, like in our previous contributions, that subcrustal forces (lithospheric mantle thickness changes and asthenospheric flows) worked together with flexural accommodation to create a sedimentary basin, occasionally provoking drastic paleoenvironmental and landscape changes.

The geological record of the eastern Sierras Pampeanas province, in the modern Andean broken foreland of Argentina can be divided into four main events: (1) Proterozoic to early Paleozoic collisional tectonics, (2) middle-late Paleozoic anorogenic magmatism, relief generation and glacial paleovalley formation followed by (3) a classical foreland filling in the Permian and two proximal alluvial sedimentation associated with (3) Cretaceous rifting and (4) Neogene intermontane foreland accumulation. The region lacks Silurian, Triassic and Jurassic records, commonly associated with unknown deformation and/or no-sedimentation stages (bypass zone?). In this work, we analyzed the Mesozoic (Triassic-Jurassic) Pampean unconformity, using low- temperature thermochronological modelling. After a rapid Carboniferous cooling track, a Triassic reheating followed by a slow Jurassic to Cretaceous cooling. Considering that (1) no Triassic basins have been described to date in the eastern Sierras Pampeanas (i.e., reheating cannot be related to burial), (2) coeval surface heat flows are anomalously high in western Sierras Pampeanas, in the Ischigualasto basin, and (3) our petrogenetic modelling on Triassic basalts evidence mantle potential temperatures of ~1350-1400 °C (i.e., the heat source cannot be related with an anomalously high basal heat flows and/or mantle plumes); we interpreted the formation of the Mesozoic unconformity as a result of ridge collision and slab window formation, followed by slab rollback. Both processes might have affected not only the surface heat flow but also triggered a lithospheric thickness reduction, which drove isostatic rebound. In this context, the Jurassic history of the unconformity could be associated with cooling by erosion and exhumation until the Cretaceous, when the region was under extension. Our model agrees with other observations like the formation of back-arc hydrocarbon-productive Triassic-Jurassic depocenters to the west (Cuyo and Ischigualasto basins) and the magmatic evolution, from 28° to 34° SL, described along the Chilean margin. Fil: Martina, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Avila, Pilar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Davila, Federico Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Parra, Mauricio. Universidade de Sao Paulo; Brasil

In the Famatina range, Sierras Pampeanas of Argentina (SW Gondwana), subvertical calc-alkaline lamprophyric dike swarms crop out through >300 km. The dikes cut Ordovician units with a prominent NW-SE trending and are covered by continental sedimentary successions of Pennsylvanian to Permian age. The dikes show a strong structural control associated with Riedel fault systems. Detailed field analysis suggested a ∼N-S opening direction oblique to the attitude of dike walls and a left-lateral transtensional tectonics during the emplacement. 40Ar/39Ar geochronology of a lamprophyric sample defined a crystallization age (plateau; whole rock) of 357.1 ± 7.1 Ma (MSWD = 2.3). Coetaneous ductile zones with dominant strike-slip motion, documented along western Argentina for >600 km, suggest a regional event in SW Gondwana during the Mississippian. We propose that this deformation was the result of the counterclockwise fast rotation of Gondwana between 365 and 345 Ma, when the Famatina range and western Argentina occupied a sub-polar position. A transform margin along SW Gondwana better explains our (and others) data rather than a subduction margin. This scenario is also consistent with the occurrence of A-type granites and normal-fault basins within the foreland as well as bimodal volcanics. Fil: Martina, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Canelo, Horacio Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Davila, Federico Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: de Hollanda, María Helena M.. Universidade de Sao Paulo; Brasil Fil: Teixeira, Wilson. Universidade de Sao Paulo; Brasil

The understanding of modern topography, and basin and landscape evolution, requires clear comprehension of isostatic and dynamic forces (in addition to paleoclimate changes) over different temporal and spatial scales. Here we review different topographic features of South America using the residual topography concept at regional and local scales. Residual topography, the difference between modeled isostatic elevations and measured elevations, is considered the best measure of dynamic topography. We incorporate geological observations to test the dynamic topography for modern and ancient examples using local subsidence analyses, paleoelevation calculations from previous studies, and paleolithospheric thickness estimates based on geochemical studies of basalts. Three transects across the northern-central, southern-central, and southern Andes (Peruvian Andes-Solimoes-Amazonas, Precordillera-Pampas, and Patagonian areas, respectively) were inspected, particularly in areas affected by subduction of oceanic ridges, where subsidence and/or uplift may be influenced by dynamic forces. Our results show contradictory results among models and with respect to previous studies. The pericratonic and cratonic areas of Peru and Brazil, farther east from the leading edge of the Nazca ridge, show positive residual topographies (dynamic uplift) and local subsidence studies support residual subsidence driven by sublithospheric forces. The opposite occurs in Patagonia. Most geological interpretations and our subsidence models suggest the need for dynamic subsidence, which does not account for negative residual topography. In turn, estimates for the southern Central Andes show a relatively good match between subsidence models and residual topography in pericratonic areas (Pampas), which support dynamic subsidence and topography. But strong disagreements arise along the flat-slab segment, where dynamic uplift is expected from models of dynamic topography. We suggest that regional elevation is mainly ruled by lithospheric and crustal structure, along with bulk composition, as supported by dynamic forces that can change laterally and generate local morphological features such as isolated basins or promontories. Ongoing and future studies will help resolve these apparent contradictions.

Flat-slab segments are considered refrigerated areas given that the asthenospheric wedge is forced to shift hundreds of kilometres away from the trench, and the flat and coupled subducting plate acts as a thermal insulator. Although lithospheric-scale thermal analysis based on numerical modelling and geophysical observations abound, studies on the thermal history of sedimentary basins are scarce. In this contribution, we present a temperature data compilation from more than 60 oil wells within the Chilean-Pampean flat-slab segment and the transitional zones to normal subduction to the north and south in the south-central Andes. The geothermal gradient data are correlated with basin-basal heat flow estimated from 1D modelling, Curie point depths derived from aeromagnetic surveys, and previous crustal and lithospheric thicknesses estimations. Their distribution evidences a quite good consistency and correlation from region-to-region. Our modelling demonstrates that sedimentation changes are not sufficient to explain the variations illustrated in the geothermal gradient map, and that basal heat flux variations are required to reproduce the reported values. According to our results, the coldest basins develop over the flat slab or cratonward regions, whereas the highest temperatures on areas where the slab plunges. This suggests that the flat-slab geometry as well as the lithospheric structure affects the thermal state within the upper crust and particularly the sedimentary basins. Further studies will allow improving our database as well as the knowledge about the radiogenic contribution of the lithosphere and the asthenospheric heat input to the basins basal heat flow.

Mantle convection can drive long-wavelength and low-amplitude topography, which can occur synchronously and superimposed to tectonics. The discrimination between these two topographic components, however, is difficult to assert. This is because there are still several uncertainties and debates in the geodynamic community, for example, the scales and rates of dynamic topography. Geological, geomorphological, geophysical measurements, and/or landscape analyses might assist to validate models. In this contribution, we provide new geological evidences along the Central and Patagonian Andes, which demonstrate that dynamic topography has been an important component on the South American landscape formation as well as in the ancient western Gondwana. Our examples in the Argentine Pampas show that dynamic topography is required to explain not only the basin subsidence but also the whole observed topography. We also suggest that the dynamic components in this region are much lower than numerical models (average dynamic subsidence rates of ~0.04 mm/yr—this work— which contrast with the ~0.1 mm/yr estimated in the US). We also propose two strategies to analyze ancient cases. The first requires of comparing a total elevation proxy, like the equilibrium lines (or ELA) in glaciated areas, with model topography derived from geochemical studies of mantle rocks. A second strategy was the analysis of the Triassic rifting evolution of western Argentina (post-rift sag deposits). Sag deposit thicknesses exceed 2 km, which do not correlate with the 100 m thick thermal calculated by rift subsidence modeling.

The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of N-S reverse faults that disrupted a W-E Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ~9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ~477-470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the K-Ar dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<

The Precordillera terrane (Cuyania) in western Argentina is commonly accepted as an exotic fragmentderived from Laurentia in the Early Paleozoic. Evidence supporting such an interpretation is manly basedon similarities in the sedimentary cover successions and their paleontological content. Little is knownabout the basement of the Precordillera terrane. Its isotopic characterization is essential to betterconstrain the present areal distribution of the terrane and it may provide more insight into the pre-rifting evolution of the Precordillera terrane along the Iapetan margin of Laurentia. We present newSr and Nd isotope data of pre-Late Ordovician meta-igneous rocks from the Río Bonete region in NWArgentina, interpreted as the northernmost extent of the Precordillera. The Nd systematics of the RíoBonete basement rocks including greenschists and metagabbros (εNd(470)¼þ2.14e 0.19;TDM¼0.99e1.2 Ga), a garnet-amphibolite (εNd(470)¼ 0.53;TDM¼1.32 Ga) and a quartz-phyllite (εNd(470)¼ 3.83;TDM¼1.55 Ga), are similar to other pre-Ordovician meta-igneous rocks from Sierra de Umango, Pie dePalo and the Ullum xenoliths, usually interpreted as the basement of the Precordillera terrane. Nd modelages around 1.2 Ga are also typical from the Mesoproterozoic Grenvillian basement of southern NorthAmerica, currently exposed in the Llano region. In addition, the greenschists and metagabbros show arobust correlation with the Late Neoproterozoic Catoctin volcanics in the central Appalachians. The Srisotope data (when not disturbed) also supports this novel interpretation and suggests the presence ofthe Blue Ridge rifting event in Precordillera. According to our interpretation, some lithotypes includedwithin the basement complex of the Río Bonete area belonged to the basement of the Precordilleraterrane supporting previous correlation between both regions. Fil: Martina, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Astini, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Pimentel, Marcio. Universidade Do Brasilia. Instituto de Geociencias; Brasil

A well-constrained record of Miocene–Pliocene explosive volcanism is preserved within the broken foreland of Western Argentina along the Famatina Ranges. This paper focuses on the volcaniclastic record known as the Rio Blanco member of the El Durazno Formation. Three facies can be recognized in the study area: (1) massive tuffs; (2) volcaniclastic conglomerates and (3) pumiceous sandstones. These facies are interpreted as primary pyroclastic flow deposits (ignimbrites) and reworked volcanogenic deposits within interacting volcanic–fluvial depositional systems. Alternation between ignimbrites and volcanogenic sandstones and conglomerates suggest a recurrent pattern of sedimentation related to recurrent volcanic activity. Considering the facies mosaic and relative thicknesses of facies, short periods of syn-eruption sedimentation (volcaniclastic deposits) seem to have been separated by longer inter-eruption periods, where normal stream-flow processes were dominant. The volcaniclastic component decreases up-section, suggesting a gradual reduction in volcanic activity. The mean sedimentation rate of the Rio Blanco member is higher (0.44 mm/year) than those obtained for the underlying and overlying units. This increase cannot be fully explained by foreland basement deformation and tectonic loading. Hence, we propose subsidence associated with volcanic activity as the causal mechanism. Volcanism would have triggered additional accommodation space through coeval pyroclastic deposition, modification of the stream equilibrium profile, flexural loading of volcanoes, and thermal processes. These mechanisms may have favored the preservation of volcaniclastic beds in the high-gradient foreland system of Famatina during the Mio–Pliocene. Thus, the Rio Blanco member records the response of fluvial systems to large, volcanism-induced sediment loads.

In the northern extension of the Famatina and the southern Puna (NW Argentina) prominent rhyolitic volcanic rocks traditionally referred to as Ordovician are exposed, resting on metamorphic basement and covered by thick Late Paleozoic siliciclastic successions. We report new U-Pb SHRIMP ages from these rhyolites that show them to be of Mississippian (348-342Ma) age, thus identifying a previously unknown volcanic event in this portion of western Gondwana. Whole-rock geochemistry and Sr-Nd isotopic analyses suggest a crustal source for these rocks but with a juvenile input (εNd(t) between -2.91 and -0.3, and TDM values between 1.09 and 1.1Ga). This is different from the Early Paleozoic magmatism of western Argentina where crustal recycling took place without any involvement of mantle material. The Carboniferous magmatism is compatible with an extensional environment developed along the Terra Australis accretionary orogen as a result of tectonic switching processes. These rhyolites may be related to the coeval Mississippian A-type granites exposed to the east, in the Sierras Pampeanas, confirming the regional character of this magmatism. Fil: Martina, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Viramonte, Jose Maria. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto Geonorte; Argentina Fil: Astini, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Martins Pimentel, Márcio. Universidade do Brasília; Brasil Fil: Dantas, Elton Luiz. Universidade do Brasília; Brasil

En la región septentrional de la Precordillera, al NW de La Rioja, en el centro occidental de Argentina, afloran más de 4.000 m de rocas sedimentarias del Paleozoico superior entre las que se destaca una unidad basal psefítica, no descrita con anterioridad y cuyo análisis permite identificar un importante episodio de extensión cortical. El potente conglomerado (>1.000 m) de color morado, que proponemos denominar Formación Los Llantenes, se dispone en no concordancia sobre el basamento de la Precordillera Septentrional y por debajo del primer nivel con clara impronta glacigénica, asociado a la glaciación gondwánica. Mientras que su gran espesor y escasa distribución areal indican subsidencia localizada, la estratofábrica cruda, la mala selección granulométrica y la presencia de bloques superiores al metro indicarían que se trata de depósitos de abanicos aluviales de alto gradiente, dominados por flujos de gravedad. Su composición y granulometría gruesa revelan procedencia local, resaltos topográficos pronunciados y fuerte compartimen-tación paleogeográfica. Una compleja historia glacial sucede a la Formación Los Llantenes sobre la que se han labrado profundos paleovalles en forma de 'U' que alojan tilitas y diamictitas glacigénicas, pertenecientes a la Formación Cerro Tres Cóndores de edad viseana (Misisipiano Medio). La edad de los conglomerados de la Formación Los Llantenes, de naturaleza preglacial, quedaría acotada entre el sustrato del Devónico Medio, aflorante inmediatamente al sur de la región estudiada en sierra de Las Minitas, y el Misisipiano Medio (Formación Cerro Tres Cóndores), pudiendo parcialmente constituir un equivalente de la Formación Agua de Lucho (Tournaisiano-Viseano) que, en la región del Río del Peñón, también subyace a los niveles glacigénicos de la Formación Cerro Tres Cóndores. La expresión cartográfica con limitada extensión areal y el gran espesor que presentan las psefitas de la Formación Los Llantenes, sumado a la procedencia local, permiten interpretar el desarrollo de depocentros asociados con un marco tectónico extensional o transtensivo, conclusiones importantes para reconstruir la historia de la cuenca. In the northern part of the Argentine Precordillera, northwestern La Rioja, the Upper Paleozoic is over 4,000 m thick. Very coarse conglomerates from the basal section have not been described nor adequately interpreted. This work analyses this unit in the context of a stratigraphic revision of the upper Paleozoic of the region, and interprets the conglomerate as a rift deposit. The thick (>1,000 m) and coarse purple conglomeratic succession, herein named 'Los Llantenes Formation', non-conformably rests on the basement rocks of the region and underlies deposits of the first glacial record associated with the Gondwanan glaciation. While its great thickness and restricted areal extent indicate localized subsidence, the crude stratification, poor sorting and abundance of >1-m boulders indicate an origin related to high-gradient, low-efficiency alluvial fans. Their composition and coarse-grained size indicate local provenance, abrupt relief and incipiently developed drainage systems and a highly compartmentalized and abrupt paleogeography. A complex glacial history generated deep 'U'-shaped paleovalleys in the Los Llantenes Formation, developing paleovalleys that accommodated basal lodgment tills and glacial diamictites with sedimentologic features comparable to the Cerro Tres Cóndores Formation (Visean in age) exposed to the south. The age of the conglomerales of Los Llantenes Formation, clearly preglacial, can be stratigraphically bracketed between the Middle Devonian substrate cropping out to the south in the sierra de Las Minitas and the Middle Mississippian, age of the Cerro Tres Condores Formation. Consequently, Los Llantenes Formation may partly correlate with the Agua de Lucho Formation (Tournaisian-Vissean) that in the area of Río del Peñón, immediately to the south, underlies the glacigenic Cerro Tres Condores Formation. Mapping relationships with limited areal extent, together with the great thickness of Los Llantenes Formation and the local provenance, allow interpreting accommodation in extensional or pull-apart depocenters, conclusions that are relevant in order to reconstruct the history of the basin.