The closure of the Rocas Verdes Basin and early tectono-metamorphic evolution of the Magallanes Fold-and-Thrust Belt, southern Patagonian Andes (52–54°S)

The hinterland Western Domain of the Magallanes Fold-and-Thrust Belt (MFTB) between 52°-54°S is part of a poorly studied region of the southernmost Andean Cordillera. This domain consists of NNW-SSE trending tectonic slices of pre-Jurassic basement units and Late Jurassic-Early Cretaceous ophiolitic complexes and volcano-sedimentary successions of the Rocas Verdes Basin (RVB). New detrital zircon UPb ages of metatuffs and metapsammopelites constrain episodes of Late Jurassic rift-related volcanism (ca. 160 Ma) followed by Early Cretaceous sedimentation (ca. 125 Ma) during the opening of the RVB. Shear bands developed in the RVB units further record the initial phases of the Andean Orogeny. The 30-km wide thrust stack located on top of the Eastern Tobífera Thrust consists of mylonitic metatuffs, metapelites and metabasalts with a NE-verging brittle-ductile S1* foliation. Phengite-bearing metatuffs commonly record pressure-temperature (P-T) conditions between ~3–6 kbar and ~ 210–460 °C, consistent with underthrusting of the RVB beneath the parautochthonous magmatic arc in the west. Peak metamorphic conditions of ~6 kbar and 460 °C are derived from a metapsammopelitic schist with textures of contact metamorphism overprinting early mylonitic structures (at least S1*). A back-arc quartz-diorite, intruded at ca. 83 Na, is in contact with the metapsammopelites and constrain the minimum age of deformation at deep crustal depths. Campanian-Maastrichtian (ca. 70–73 Ma) 40Ar/39Ar phengite dates from a mylonitic metapelite indicate the timing of thrusting and backthrusting during the initial uplift of the underthrusted crustal stack. These findings reveal a ~ 400 km along-strike connection of mylonite belts in a continent-verging thrust structure that became active at the onset of the Andean orogeny during the closure of the Rocas Verdes back-arc marginal basin

Structural, tectonic and glaciological controls on the evolution of fjord landscapes

The fjord landscape of South America, stretching ~ 1500 km between Golfo Corcovado (~ 43°S) and Tierra del Fuego (~ 56°S), is the largest continuous fjord landscape on Earth. This paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models. First-order geological structures are represented by strike-slip faults forming lineaments up to hundreds of kilometres long. The strike-slip faulting has been active since Late Cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to ~ 10 km long. A detailed analysis of these second-order lineaments from digital image data was carried out in three sectors. In Sector 1, located northwest of the North Patagonian Icefield, there are three distinct mean orientations, characterized by a main nearly orogen-parallel orientation (az. ~ 145°) and two orogen-oblique secondary orientations (az. ~ 20° and az. ~ 65°). In Sector 2, located west of the South Patagonian Icefield, there are also three separate mean orientations, with most of the lineaments concentrated between azimuths 0° and 80° (mean at ~ 36°); and two other orogen-oblique means at azimuth ~ 122° and ~ 163°. In Sector 3, around the Cordillera Darwin, there is a single main orogen-parallel mean at ~ 100-115°. In all three sectors, mapped fjord orientations bear a striking similarity to the structural data, with fjords orientated preferentially in the same direction as structural lineaments. We infer that successive glaciations followed the same ice-discharge routes, widening and deepening pre-existing geological structures at the expense of the surrounding terrain to create the fjord landscape. This study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological.Fil: Glasser, Neil F.. Aberystwyth University; Reino UnidoFil: Ghiglione, Matias. 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"; Argentin

Estructuras y entrampamientos plio-pleistocenos (tardíos) en la plataforma deformada mendocina, lindero de piedra, Cuenca Neuquina

Lindero de Piedra oil block,from northeastern Neuquén basin, is located 15 km NE of Malargüe cityin Mendoza Province. In this sector of theMendoza platform, very young mineralized anticlineswerestudied through interpretation of 3D seismic data (2017), and an analysis of their kinematic evolutionwas performed. Within the study region, three stages of folds generation are observed, each onepresenting a north-south orientation, and an in-sequence evolution towards the east. The foldgeneration is interpreted to be a consequence of inversionof normal faults during Plio-Pleistocene(Holocene?)compressional phases. We discard the influence of dikes intrusion in Mio-Pliocenetimes as deformational drivers, since seismic data show that those igneous bodies are deformedby inversion tectonics.These Pliocene-Pleistocenetraps can be considered the youngest formed inthe basin. The late formation of these structures can be linked to a late advance of the Andeanorogenic front, thatwas propitious for hydrocarbons entrapment due to coeval maturation and lateexpulsion of hydrocarbons in southern Mendoza. Likewise, rupture of Pliocene structures during thePleistocene-Holocene and the incipient traps generation at more eastward positions are observed.Accordingly, we propose the existence of an Andeancompressional phase, younger than previouslyconsidered,that could have lasted up to Holocene times.Fil: Stein, Julián E.. No especifíca;Fil: Ghiglione, Matias. 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"; ArgentinaFil: Hlebszevitsch, Julio C.. No especifíca;10º Congreso de Exploración y Desarrollo de Hidrocarburos y Simposio de Recursos No ConvencionalesArgentinaInstituto Argentino del Petróleo y el Ga

Post-glacial deformation of the eastern Magallanes-Fagnano transform fault system, Tierra Del Fuego, Argentina

Tierra del Fuego is crosscut by a major transform fault, the Magallanes-Fagnano Fault that accommodates sinistral strike-slip motion between Scotia and South America plates. The present-day relative velocity between these plates estimated using GPS measurements is 5.9 ± 0.2 mm.yr-1. Major events occurred along this fault in 1879 and 1949. The 1949 magnitude was Mw ~ 7.5-7.8 with several aftershocks of similar magnitude, but the precise localization of corresponding rupture zones is not possible using seismological data. Since the onset of strike-slip, suggested at the Late-Miocene, glacial advances have rejuvenated most of the rupture markers. Until now, the Quaternary slip rate remained unknown and investigations regarding the last 1949 ruptures were scarce. In this work, we focus on the fault behavior associated with the post-glacial stress regime over its 80-km inland eastern section, using beryllium cosmogenic-nuclide dating, combined with high-resolution Pleiades imagery and fieldwork analyses of geomorphological markers. We identified a dead valley in which the drainage network has been abandoned following the retreat of a Wurmian glacier. We dated the abandoned drainage within the valley at < 18 ± 2 ky, which fixes the beginning of the tectonic deformation record. We quantified the sinistral offset accommodated by the fault across this valley of 115 ± 5 m. These results yield a minimum 6.4 ± 0.9 mm.yr-1 slip-rate since 18 ky. Our study shows that in this context geomorphic and instantaneous fault slip rates are mostly the same, suggesting a stable fault behavior since glaciers retreat. On the other hand, we mapped the superficial ruptures that resulted from the 1949 earthquake and its aftershocks. We measured several man-made features left-laterally shifted. Two fences are crosscut with horizontal displacements of respectively 4 m ± 0.2 m and 6.5 m ± 0.5 m. A third sinistral offset of 6.2 ± 1 m has been measured in the foundation of an abandoned broken bridge that spanned over the fault line. Therefore, we suggest that surface-ruptures length associated with the 1949 earthquake are greater than previously estimated. If these offsets are characteristic for main earthquakes along Magallanes-Fagnano Fault, their recurrence period should be in the order of one thousand years.Fil: Roya, Sandrine. Universite Grenoble Alpes; FranciaFil: Vassallo, Ricardo. Universite Grenoble Alpes; FranciaFil: Martinod, J.. Universite Grenoble Alpes; FranciaFil: Ghiglione, Matias. 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"; ArgentinaFil: Sue, C.. Universite de Bourgogne; FranciaFil: Allemand, Pascal. Universite Claude Bernard Lyon 1; Francia8th International Symposium on Andean GeodynamicsEcuadorEscuela Politécnica NacionalFrench Institut de Recherche pour le Développemen

Detrital isotopic record of a retreating accretionary orogen: An example from the Patagonian Andes

U-Pb zircon geochronology and isotopic records have played an influential role in our understanding of convergent margin dynamics. Orogenic cyclicity models link tectonic regimes with magmatic isotopic signatures in advancing orogens, relating compressional regimes with evolved signatures and extension with juvenile signatures; however, such frameworks may not apply for retreating orogens, which commonly produce substantial crustal heterogeneities during backarc rifting and ocean spreading. We explore the Mesozoic to Cenozoic Patagonian Andes tectonic evolution, combining U-Pb zircon ages, bulk rock εNd, and new detrital zircon εHf from the retroarc basin to understand the associated magmatic arc evolution during retreat and advance of the margin. Our results reveal a protracted phase of isotopically juvenile magmatism between 150 and 80 Ma, which began during backarc extension and persisted long after the margin switched to a contractional regime. We propose that the prolonged juvenile isotopic trend started mainly due to trenchward migration of the arc during backarc extension (150–120 Ma) and persisted due to partial melting of underthrusted juvenile attenuated and oceanic crust during backarc basin closure (120–80 Ma). This interpretation implies that tectonic stress alone does not predict isotopic trends, and factors like assimilation or the composition of underthrusted crust are important controls on magmatic isotopic composition, especially in retreating and transitional orogens.Fil: Rey, F. M.. University of Texas at Austin; Estados UnidosFil: Malkowski, M. A.. University of Texas at Austin; Estados UnidosFil: Fosdick, J. C.. University of Connecticut; Estados UnidosFil: Dobbs, S. C.. University of Stanford; Estados UnidosFil: Calderón, M.. Universidad Andrés Bello; ChileFil: Ghiglione, Matias. 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"; ArgentinaFil: Graham, S. A.. University of Stanford; Estados Unido

Tectonic Subsidence Modeling of Diachronous Transition From Backarc to Retroarc Basin Development and Uplift During Cordilleran Orogenesis, Patagonian-Fuegian Andes

Backstripped tectonic basin subsidence histories are critical for interpreting phases of lithospheric deformation and paleoenvironmental change from the stratigraphic record. This study presents new subsidence modeling of the Rocas Verdes Backarc Basin (RVB) and Magallanes-Austral retroarc foreland basin (MAB) of southernmost South America to evaluate along-strike changes in tectonic subsidence related to the Late Jurassic through Miocene history of the Southern Andes. We compiled composite stratigraphic sections for seven basin localities that span 47°–54°S from published sedimentological records of paleoenvironment, paleobathymetry, and geochronology. Modeling results resolve regional trends in basin tectonic subsidence, uplift, and sedimentation rate that influenced the depositional environment during five broad phases of RVB-MAB development: (a) Late Jurassic tectonic subsidence and basin deepening associated with rift-related backarc extension that postdated regional diachronous rift-related magmatism. (b) Southward younging of Early to Late Cretaceous pronounced acceleration in tectonic subsidence interpreted as the initiation of flexural loading and development of the MAB foreland basin system. (c) Late Cretaceous (ca. 85–70 Ma) tectonic uplift within the central foredeep ∼49° to 52°S, coeval with a shift from slope to shelf deposition at these latitudes. (d) A protracted period of low-magnitude basin uplift and relative tectonic quiescence during the Paleogene, with the exception of southernmost localities; and (e) Synchronous latest Oligocene-early Miocene tectonic subsidence linked to basin deepening and transgression across the northern and central basin sectors. Backstripped tectonic subsidence analysis corroborates existing interpretations for orogenic development in the RVB-MAB and sheds new light on complex polyphase basin histories where extension precedes convergence.Fil: VanderLeest, Rebecca A.. University of Connecticut; Estados UnidosFil: Fosdick, Julie C.. University of Connecticut; Estados UnidosFil: Malkowski, Matthew A.. University of Texas at Austin; Estados UnidosFil: Romans, Brian W.. Virginia Tech University; Estados UnidosFil: Ghiglione, Matias. 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"; ArgentinaFil: Schwartz, Theresa M.. United States Geological Survey; Estados UnidosFil: Sickmann, Zachary T.. University of Texas; Estados Unido

Tectonic evolution of the eastern margin of the southern patagonian andes fold-thrust belt, from foredeep depocenter to uplift stages: u-pb detrital zircon geochronology and kinematic-structural modeling

The beginning of the Austral-Magallanes foreland basin is recognized by the appearance of Punta Barrosa Formation sandy turbidites above Zapata Formation fine-grain deposits, this event marks the on-set of the compressional phase and hinterland uplift of the Southern Patagonian fold-thrust belt (Fig. 1). During foredeep deposition, the study region receives ~5000 m of marine sedimentation. Using detrital zircon U-Pb geochronology in ten sandstone samples, we calculate maximum depositional ages (MDA) of the units belonging to that stratigraphic sequence which began at 96.0 ± 1.5 Ma (first sandstones beds of Punta Barrosa Formation).Fil: Albano, Juan F.. 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"; ArgentinaFil: Lombardi, Laura. 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"; ArgentinaFil: Tobal, Jonathan Elías. 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"; ArgentinaFil: Rocha, Emilio. Puspetrol S.A.; ArgentinaFil: Raggio, Fernanda. YPF - Tecnología; ArgentinaFil: Vander Leest, Rebecca A.. University of Connecticut; Estados UnidosFil: Fosdick, Julie C.. University of Connecticut; Estados UnidosFil: Quesada, Paulo. Universidad de Aysen;Fil: Calderón, Mauricio. Universidad Andrés Bello; ChileFil: Ghiglione, Matias. 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"; ArgentinaXXI Congreso Geológico ArgentinoPuerto MadrynArgentinaAsociación Geológica Argentin

Constraints on deformation of the Southern Andes since the Cretaceous from anisotropy of magnetic susceptibility

The southernmost segment of the Andean Cordillera underwent a complex deformation history characterized by alternation of contractional, extensional, and strike-slip tectonics. Key elements of southern Andean deformation that remain poorly constrained, include the origin of the orogenic bend known as the Patagonian Orocline (here renamed as Patagonian Arc), and the exhumation mechanism of an upper amphibolite facies metamorphic complex currently exposed in Cordillera Darwin. Here, we present results of anisotropy of magnetic susceptibility (AMS) from 22 sites in Upper Cretaceous to upper Eocene sedimentary rocks within the internal structural domain of the Magallanes fold-and-thrust belt in Tierra del Fuego (Argentina). AMS parameters from most sites reveal a weak tectonic overprint of the original magnetic fabric, which was likely acquired upon layer-parallel shortening soon after sedimentation. Magnetic lineation from 17 sites is interpreted to have formed during compressive tectonic phases associated to a continuous ~ N-S contraction. Our data, combined with the existing AMS database from adjacent areas, show that the Early Cretaceous-late Oligocene tectonic phases in the Southern Andes yielded continuous contraction, variable from ~ E-W in the Patagonian Andes to ~ N-S in the Fuegian Andes, which defined a radial strain field. A direct implication is that the exhumation of the Cordillera Darwin metamorphic complex occurred under compressive, rather than extensional or strike-slip tectonics, as alternatively proposed. If we agree with recent works considering the curved Magallanes fold-and-thrust belt as a primary arc (i.e., no relative vertical-axis rotation of the limbs occurs during its formation), then other mechanisms different from oroclinal bending should be invoked to explain the documented radial strain field. We tentatively propose a kinematic model in which reactivation of variably oriented Jurassic faults at the South American continental margin controlled the Late Cretaceous to Cenozoic evolution of the Magallanes fold-and-thrust belt, yielding the observed deformation pattern

Tectonic evolution of the eastern margin of the Southern Patagonian Andes fold-thrust belt: U-Pb detrital zircon geochronology and kinematic-structural modelling

We present a multidisciplinary study in the Austral-Magallanes basin combining U-Pb geochronology and provenance analysis with structural modelling to unravel the evolution of the fold-thrust belt and related foreland basin sedimentation. Our approach is innovative for the studied area, where the foreland stratigraphic record comprises a stack of marine deposits exceeding 5000 m in thickness. Using zircon U-Pb geochronology from 13 samples distributed through the foreland deposits in the Southern Patagonian Andes at 51°20′S latitude, we calculated maximum depositional ages and analyzed regional variations in provenance. The older sample, with an age of 96.0 ± 1.5 Ma, corresponds to the first sandstone beds of the Punta Barrosa Formation, whereas the uppermost sample, with an age of 17.9 ± 0.4 Ma stems from the Santa Cruz Formation. Furthermore, the presented data help to complete the geochronological information existing for the South Patagonian Andes, by informing the regional geodynamic framework and timing variations. Linking new and previously published data regarding detrital zircon provenance, maximum depositional ages analysis, thermochronology and stratigraphic data with a balanced structural cross section, we propose a step-by-step model combining the kinematic evolution of the fold-thrust belt orogenic front with the basin history. A wedge-top setting for the Late Cretaceous is recognized, as well as two minor uplift events by Eocene time, followed by a major Miocene tectonic exhumation event.Fil: Albano Garcia, Juan Francisco. 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"; ArgentinaFil: Lombardi, Laura. Universidad de Buenos Aires; ArgentinaFil: Rocha, Emilio. Pluspetrol S.a.; Argentina. YPF - Tecnología; ArgentinaFil: Tobal, Jonathan Elías. 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"; ArgentinaFil: Aramendía, Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; ArgentinaFil: Fosdick, Julie C.. University of Connecticut; Estados UnidosFil: Stevens Goddard, Andrea L.. Indiana University. Departament Of Geological Sciences; Estados UnidosFil: VanderLeest, Rebecca A.. Texas A&M University; Estados UnidosFil: Ramos, Miguel Esteban. 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"; ArgentinaFil: Giampaoli, Pablo. Gerencia de Geociencias y Reservorios ; Ypf Sociedad Anonima;Fil: Kress, Pedro. Yacimiento Petroliferos Fiscal S.a.; ArgentinaFil: Raggio, Fernanda. Gerencia de Geociencias y Reservorios ; Ypf Sociedad Anonima;Fil: Ghiglione, Matias. 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"; Argentin