Seismic velocities in outcropping units in the western flank of the la Invernada range, San Juan Precordillera

En este trabajo se muestran determinaciones de velocidades de ondas sísmicas P (Vp) en un sector (Reserva Don Carmelo) del flanco occidental de la sierra de la Invernada, Departamento Ullúm, Provincia de San Juan. Las velocidades obtenidas con el método de refracción sísmica indican valores de Vp de 550; 1.670 y 4.134 m/s y espesores de 1 m y 7 m aproximadamente, para un modelo de dos capas apoyadas sobre un substrato correspondiente a la mayor velocidad. Las unidades aflorantes reconocidas abarcan grauvacas y areniscas muy bien compactadas que se correlacionan con los valores más altos de Vp determinados en el experimento geofísico para los niveles interpretados a mayor profundidad. Asimismo los valores más bajos de Vp son consistentes con material de tipo aluvional situado en las capas sísmicas más superficiales (< 7m de profundidad). Otras unidades relevadas en el terreno indican afloramientos de diabasas y gabros, los cuales no han sido explorados geofísicamente. Sin embargo, a partir de la comparación de las litologías y velocidades sísmicas Vp observadas con bases de datos globales, es posible predecir la continuación en profundidad de las litologías máficas con velocidades sísmicas de Vp aún mayores que aquellas determinadas en superficie. Estos resultados son de interés debido a que ayudan a identificar una posible faja ofiolítica en Precordillera, en un sector donde el espesor cortical actual estimado en 64 km aproximadamente, estaría engrosado.P-wave seismic velocity (Vp) determinations are shown in this work for a region in the western flank (Don Carmelo nature reserve) of the la Invernada range in the Ullúm Department of the San Juan Province. The velocities obtained using the seismic refraction method indicate Vp values of 550; 1.670 and 4.134 m/s and thicknesses of 1 m and 7 m approximately, for a two-layer over a higher Vp half space model. The exposed units show greywacke and well compacted sandstones, which have a good correlation with the deepest and higher Vp values of the seismic model. Also the lowest Vp values are consistent with alluvial material located in the shallower seismic layers (< 7m depth). Other units observed on the surface exhibit outcrops of diabases and gabros, which were not geophysically explored. However, a comparison between the observed lithologies and Vp values with a global database predicts the continuation at depth of mafic rocks associated with even higher Vp values than those determined at the surface. These results are of interest because they help us to identify an ophiolite belt in the Precordillera, a region presently characterized by an overthickened crust of 64 km.Fil: Perez Lujan, Sofia Beatriz. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Alvarado, Patricia Monica. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Güel, Arturo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Saez, Mauro. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; ArgentinaFil: Vujovich, Graciela Irene. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Laboratorio de Tectónica Andina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentin

The Late Neoproterozoic-Early Paleozoic basin of the western Argentine Precordillera: Insights from zircon U-Pb geochronology

In central-western Argentina, a belt including marine metasedimentary rocks and mafic-ultramafic bodies occurs throughout the western margin of the Precordillera. The belt is considered as the suture zone between the poorly known Chilenia terrane and the Cuyania terrane, part of the composite West Gondwana margin. It is assigned to the Late Neoproterozoic-Early Devonian based on fossil fauna and radiometric ages. In the southern sector of this belt, in the Peñasco area, two units crop out. The Peñasco Formation comprises metasandstone and metapelite spatially associated with mafic metavolcanic and metahyaloclastic rocks. Metagabbro bodies intrude the succession. The Garganta del León Formation consists of metasandstone and scarce metapelite where tractive and deformational sedimentary structures are preserved. Both units are affected by low-grade metamorphism, but the main foliation S1 and crenulation cleavage S2 are better developed in the Peñasco Formation rocks. U-Pb data on detrital zircon of two metasandstone samples from these units show a dominant detrital input from sources with 1.0–1.3 and 0.65–0.53 Ga ages. Detritus may come from reworked sedimentary units or from igneous/metamorphic complexes from the Cuyania terrane basement that was possibly exhumed in the Ocloyic orogen. A Gondwanan provenance for the Late Neoproterozoic-Cambrian population would also be plausible. A ca. 460 Ma zircon population in the Garganta del León Formation is interpreted to be derived from the Famatinian Arc. This would imply that the deposition of the sediment occurred after the collision of the Cuyania terrane against West Gondwana, and that the Ocloyic orogen acted as a barrier for detritus from the Famatinian Arc and other rocks further east.Fil: Boedo, Florencia Lucila. 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: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: Vujovich, Graciela Irene. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentina. 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: Martins Pimentel, Márcio. Universidade do Brasília; BrasilFil: Ariza, Juan Pablo. 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; ArgentinaFil: Barredo, Silvia Patricia. Universidad de Buenos Aires. Facultad de Ingeniería; Argentin

Structural setting of the Chanic orogen (Upper Devonian) at central-western Argentina from remote sensing and aeromagnetic data. Implications in the evolution of the proto-Pacific margin of Gondwana

The basement of the Central Andes located in central-western Argentina (31º20′S - 69º22′W) is composed by the Cuyania and Chilenia terranes which were amalgamated to Gondwana in the Early-Mid Paleozoic. Between the Precordillera (Cuyania) and Frontal Cordillera (Chilenia) there are exposures of marine metasedimentary rocks associated with mafic rocks with an E-MORB chemical signature that represent the remnants of an extensional basin developed between both terranes. The stratigraphic features and the distribution of the Early-Mid Paleozoic units along the Western Precordillera were constrained by remote sensing techniques. This allowed us to identify two stages in the evolution of the sedimentary in-fill of the marine basin: an initial stage (Mid-Late Ordovician) marked by widespread extensional tectonics and a finning-upwards sequence interbedded with volcanic-plutonic mafic rocks; and a Late Ordovician?-Devonian where the sedimentation was characterized by the development of coarsening-upwards sequences with low participation of mafic rocks. Flattened parallel folds associated with pre-Andean thrusts have locally a top-to-the SW vergence. These pre-Andean (Late Devonian) structures are the relics of the Chanic orogen whose double vergence is the result of the control exerted by previous structures related to the ordovician rifting. This is constrained by the residual and regional magnetic anomalies which reflect an important correlation between deep and surface structures. We propose the inception of a subduction zone with an eastward polarity on the proto-Pacific margin of Gondwana as the responsible for the compressive geotectonic framework that led to the closure of the Western Precordillera basin during the Late Devonian and the development of the Chanic thick-skinned-dominated orogen.Fil: Ariza, Juan Pablo. 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; ArgentinaFil: Boedo, Florencia Lucila. 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: Sanchez, Marcos 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. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Christiansen, Rodolfo Omar. 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; ArgentinaFil: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Vujovich, Graciela Irene. 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: Martínez, Myriam Patricia. 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; Argentin

Caracterización petrológica y geoquímica de las rocas máficas y ultramáficas del norte del cerro valdivia, San Juan, Argentina

The Cerro Valdivia is one of the southest expressions of Sierras Pampeanas. On the north, different metamorfic rocks with mafic and ultramafic composition are related with Pie de Palo Complex (1018 My). In this study, metamorfic units with mafic and ultramafic protolites were identified. Talc schist, anfibolic schist and masive anfibolites rocks experimented low to medium grade of regional metamorfism according their mineral associations. Geochemical analysis confirms the igneous procedence with mafic and ultramafic composition, emplaced as cumulates in arc/back arc environment in mesoproterozoic times.Fil: Carbajal, Fabricio. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geología; ArgentinaFil: Sánchez, María Victoria. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Palacio Balderramo, Gladis Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Ariza, Juan Pablo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Mendoza, Nilda. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geología; ArgentinaXIII Congreso de Mineralogía, Petrología Ígnea y Metamórfica, y MetalogénesisCórdobaArgentinaAsociacion de Mineralogia y MetalogeniaComisión de PetrologíaAsociación Geología Argentin

Geodynamic controls on magmatic arc migration and quiescence

Reconfigurations of magmatic arcs through time have been recognized since pioneering works, describing inland and trenchward arc migrations or magmatic shut-off lasting for several millions of years. These modifications present variable magnitudes and rates of arc migration and magmatic broadening, and different arc quiescence time spans. The time-space behavior of magmatic arcs has been attributed to a diversity of geodynamic processes acting at convergent margins largely associated with modifications in the upper-plate or changes in plate kinematics. Identifying a geodynamic process responsible for a particular spatiotemporal arc history from the geological record is not straightforward. This task is further complicated where more than one process influencing arc position acted in concert. To assess these issues, it is essential to have a deep understanding of how each process influences the space-time arc behavior and modifies the geological context. To date, a joint comparison highlighting similarities and differences in how these phenomena impact arc dynamics and the associated geological framework is still missing from the literature. In this study, we provide a state-of-the-art synthesis of processes controlling arc migration and quiescence. Then, we extract diagnostic elements from the literature to build a synthetic table to aid in the task of discerning a dominant geodynamic process from the geological record. In this task, we considered the first-order characteristics of the space-time arc evolution and diagnostic features of the geological context associated with each geodynamic process. Finally, this synthesis stresses that the combination of both perspectives, understanding the space-time arc pattern and the associated geological framework, provides the best approach to unravel a dominant process controlling arc migration and shut-off.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; ArgentinaFil: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentin

The mafic-ultramafic belt of the Argentine Precordillera: A geological synthesis

In central-western Argentina, a mafic-ultramafic belt occurs throughout the western margin of the Precordillera. This belt is interpreted as the suture zone between the Cuyania terrane and the Chilenia terrane, both accreted onto the Gondwana margin during the Early Paleozoic. The belt comprises rocks from different setting and age and can be divided into a northern (28-32°S, present coordinates) and a southern sector (south of 32°S). The northern sector includes MORB (Mid-Ocean-Ridge Basalts)-like metabasalt, metagabbro and minor metadiorite and wehrlite associated to marine sequences. The southern sector comprises serpentinite, ultramafic cumulate, mafic granulite and gneiss not exposed in the north as well as metagabbro, metabasalt and minor metahyaloclastite spatially associated to marine successions. Due to their geological similarities, the southern sector can be correlated with the Argentine Frontal Cordillera mafic-ultramafic belt exposed southwestwards. In the southern sector, the evolution of the belt began during the Late Neoproterozoic, with the generation of continental margin sequences related to MORB magmatism. This extensional regime would be related to the rifting of a continental block, that includes the Cuyania and Chilenia terranes, from southern Laurentia. During the Middle Ordovician-Early Devonian, a second extensional regime occurred along the entire belt, where passive margin successions along with E-MORB magmatism developed on a thinned continental crust. A pre-Devonian deformation phase D1, possibly related to the Ocloyic orogeny, only affected the southern sector of the belt. Whereas a deformation phase D2 is registered throughout the belt and it is related to the collision of the Chilenia terrane against West Gondwana in the Middle-Late Devonian.Fil: Boedo, Florencia Lucila. 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: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Ariza, Juan Pablo. 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; ArgentinaFil: Vujovich, Graciela Irene. 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. Secretaria de Industria y Mineria. Servicio Geológico Minero Argentino. Instituto de Geología y Recursos Minerales; Argentin

Constraining a mafic thick crust model in the Andean Precordillera of the Pampean flat slab subduction region

Elastic properties in twelve representative rock samples from Central and Western Precordillera in the Andean backarc region of Argentina between 30 and 31S were estimated from detailed petrological analysis. Thus, P and S seismic-wave velocities (Vp, Vs) as well as Poisson´s ratio (s) among other parameterswere derived for gabbros, leuco-gabbros and wehrlites, in greenschist and amphibolite metamorphic conditions using a framework of a wide variety of empirical observations from active continental margins. In addition, Vs lithosphere models along two westeeast cross sections were obtainedusing a joint inversion of teleseismic Rayleigh waves and receiver functions. These models clearly delineate the upper-plate crustal structure and the flat-slab subduction of the Nazca plate at about 100 km depth in this region. The suggested seismic velocity structure shows a relatively low (<3.3 km/s) Vslayer located in the first 15e18 km depth, then an increase of it from 3.3 to 4 km/s between 20 and 55 km depth with a mayor change at 40 km depth beneath the Precordillera showing an increase in Vs from 3.3 to 3.8 km/s. The Moho discontinuity was identified at around 65 km depth beneath the Precordillera(Vs ¼ 4.3 km/s) and shows a low shear-wave velocity contrast in comparison with the upper continental mantle´s parameters. Using this seismological model, Vs estimations derived from the petrological analyses for the 12 collected samples can be projected at depths greater than 30 km. These geophysical andpetrological results agree with the hypothesis of a mafic thickened and partially eclogitized lower crust beneath the Precordillera, which has been predicted previously on a base of seismological studies only.Our petrological and seismological results collectively support a thick crustal model of a mafic eultramafic composition extending to middle-to-lower crustal levels beneath Central and Western Precordillera; this region correlates with a suture zone between the eastern Cuyania terrane and the western Chilenia terrane.Fil: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Ammirati, Jean Baptiste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; Argentina. Ministerio de Ciencia, Tecnologí­a e Innovación Productiva. Agencia Nacional de Promoción Cientí­fica y Tecnológica. Fondo para la Investigación Cientí­fica y Tecnológica; ArgentinaFil: Alvarado, Patricia Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Juan. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Vujovich, Graciela Irene. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geologicas. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

High resolution images above the Pampean flat slab of Argentina (31-32ºS) from local receiver functions: Implications on regional tectonics

In the flat slab region of the South Central Andes (∼31–32◦S), geological observations suggest that the regional crustal structure is inherited from the accretion of different terranes during the Ordovician. These structures were later reactivated, first in extension during the Triassic and later in compression during the Andean uplift since the Miocene. Seismological observations confirmed that those fault structures extend to depth with décollement levels that accommodate current crustal shortening in the region. In order to get better insight on the regional tectonics we computed higher frequency receiver functions (RF) from local slab seismicity of intermediate ∼100 km depth. Using a common conversion point (CCP) stacking method we obtained cross sections showing high vertical resolution crustal structure at the transition between the Precordillera and the Frontal Cordillera. In addition we performed a joint inversion of our high frequency RFs with surface wave data from ambient noise tomography allowing us to constrain absolute seismic wave velocities. Our higher resolution images reveal more structural details down to a depth of 80 km and laterally over the flat slab in good agreement with previous studies. Our results help to better identify very shallow discontinuities in seismic velocities. Recent petrological analyses combined with our high-resolution RF structure correlates with a crustal mafic composition and partial eclogitization in the lower crust. We observe a shift in the crustal structure between the Precordillera (east) and the Frontal Cordillera (west). Regional seismicity and previously determined focal mechanisms superimposed over our images indicate this shifting is a thrust structure extending down to a depth of 40 km. Our results suggest the presence of a master fault between the Cuyania (Western Precordillera) and Chilenia (Frontal Cordillera) terranes that probably accommodates the crustal deformation in the Pampean flat slab region since the Late Ordovician.Fil: Ammirati, Jean Baptiste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Perez Lujan, Sofia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; ArgentinaFil: Alvarado, Patricia Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Beck, Susan. University of Arizona; Estados UnidosFil: Rocher, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; ArgentinaFil: Zandt, George. University of Arizona; Estados Unido

The E-MORB like geochemical features of the Early Paleozoic mafic-ultramafic belt of the Cuyania terrane, western Argentina

The Argentine Precordillera is located in the central western region of Argentina, within the Central Andes. Throughout its westernmost sector, mafic and ultramafic bodies including serpentinites, mafic granulites, basaltic dikes/sills and pillow lavas are associated with metasedimentary rocks deposited in a deep marine and slope environment. These magmatic units, which are known as the Precordillera ultramafic-mafic belt, are considered to have a range of Early Paleozoic age based on published UePb zircon ages and fossil fauna. The entire sequence shows the effects of complex polyphase Paleozoic deformation and was subjected to a low grade metamorphism considered to be of middle-late Devonian age. The chemistry of the Peñasco and Cortaderas mafic dikes and sills in the southern part of this belt, which are largely plagioclase þ clinopyroxene-bearing tholeiitic basalts, is the focus of this study. These volcanic rocks all have E-MORB-like major and trace element and εNd (þ6.0 to þ9.3) signatures with similarities to those previously reported throughout the belt. The new descriptions and major and traceelement analyses presented here confirm the similarity of the E-MORB-like chemistry of the Early Paleozoic mafic rocks along the entire belt, which spans some 500 km in length. There is a general consensus that these units are exposed as a consequence of the collision of the Chilenia terrane against the Gondwana margin during the middle to late Devonian, but the details of timing, the origins of the continental blocks and the nature of the collision are still debated. The results presented support the western Precordillera basaltic dikes/sills as having formed in the early stages of oceanic rifting along the Gondwana (Precordillera) continental margin with their E-MORB-like character reflecting mixing of depleted and enriched mantle and continental lithospheric sources.Fil: Boedo, Florencia Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Vujovich, Graciela Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Kay, S. M.. Cornell University; Estados UnidosFil: Ariza, Juan Pablo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Fisicas y Naturales. Instituto Geofisico Sismologico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perez Lujan, Sofia Beatriz. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

The Cuyano proto-ocean between the Chilenia and Cuyania terranes: Rifting and plume interaction during the Neoproterozoic - Early Palaeozoic evolution of the SW Gondwana margin

The Precordillera mafic–ultramafic belt (PMUB), located in central-western Argentina, comprises mafic and ultramafic bodies interlayered and/or in tectonic contact with marine siliciclastic units. Whole-rock, mineral geochemistry and Nd–Sr isotope analyses performed in magmatic rocks suggest a relatively different spatial and temporal evolution along the belt. The southern PMUB (south of 32° S) evolved as an intra-continental rifted margin with an enriched mid-ocean-ridge basalt (E-MORB) tholeiitic to alkaline magmatism, to a proto-ocean basin (the Cuyano proto-ocean) with tholeiitic normal-MORB geochemical signature. Based on neodymium model ages (TDM), the magmatic activity started during the late Neoproterozoic Era and continued into the early Palaeozoic Era. Instead, the northern PMUB (28–32° S) evolved as an intra-continental rifted margin with dominant tholeiitic E-MORB to continental flood basalt (CFB) magmatism during the early Palaeozoic Era. ϵNd values (þ3.4 to þ8.4), rare earth element trends and high-field-strength element systematics, together with an estimated potential mantle temperature of c. 50–100°C above ambient mantle, suggest the PMUB magmatism derived from an enriched mantle source related to the effect of a rising plume linked to the Iapetus Ocean opening. In particular, TDM estimations of 600–550 Ma agree with reported magmatism in central to southern Appalachians. The magmatism in the PMUB, and those registered in the Neoproterozoic Catoctin Formation and in the Southern Oklahoma Aulacogen in the conjugated Laurentian margin, seem to be contemporaneous, sharing a similar plumeenriched mantle source. In this context, the E-MORB signature identified along the PMUB can be described as a plume-distal ridge tectonic setting over an extended margin.Fil: Perez Lujan, Sofia Beatriz. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Boedo, Florencia Lucila. 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: Ariza, Juan Pablo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geología; Argentina. 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; ArgentinaFil: Vujovich, Graciela Irene. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; Argentina. 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: Alvarado, Patricia Monica. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Kay, Suzanne M.. Cornell University; Estados Unido