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Se llevaron a cabo una serie de modelos análogos en los que se combinaron diferentes sistemas de debilidades estructurales preexistentes a fin de entender su evolución vinculada a acortamiento regional en dirección ~ENE. El análisis de la deformación de las simulaciones fue realizado a través del software GEODEF 1.1, una herramienta que permite la cuantificación de la deformación en planta sobre la base de campos de desplazamiento. Los resultados obtenidos muestran que las heterogeneidades regionales de rumbo NNE se reactivan como estructuras dextrales inversas, si bien también se generan corrimientos neoformados de igual orientación. Asimismo, se obtuvieron desplazamientos de rumbo sinistral dominante para estructuras reactivadas de segundo orden de rumbo WNW, mientras que desplazamientos sinistrales inversos se registraron en aquellas de rumbo NW. La comparación de estos resultados con datos estructurales, cinemáticos y paleomagnéticos señala la existencia de transpresión dextral particionada para el precordillera norte desde el Mioceno. A su vez, los modelos no solo confirman los desplazamientos de rumbo sinistral para las estructuras WNW de la precordillera, sino que también sugieren que estas constituirían fábricas corticales preexistentes que fueron reactivadas durante la orogenia andina. Estas estructuras oblicuas han tenido un rol significativo en la construcción y evolución de la faja plegada y corrida, ya que segmentan la actividad de las estructuras paralelas al orógeno. Analogue models combining different sets of preexisting structural weaknesses were developed to understand their evolution during regional ~ENE shortening. Strain analysis of simulations was performed with the GEODEF 1.1 software, a tool that allows to quantify deformation in plan view on the basis of displacement fields. Results showed up that regional NNE heterogeneities are reactivated as dextral reverse-slip structures, though NNE neoformed thrusts are also present. Likewise, dominant sinistral strike-slip motions have been obtained for reactivated second-order WNW structures whereas sinistral reverse-slip has been recorded for NW ones. Comparison of these results with structural, kinematic and paleomagnetic data supports partitioned dextral transpression for the northern Andean Precordillera since the Miocene. Moreover, models not only confirm sinistral strike-slip motions for WNW structures of the Precordillera but also suggest that they would represent preexisting crustal fabrics that were reactivated during the Andean orogeny. These cross-strike structures have played a significant role in the construction and evolution of the fold and thrust belt as they segmentate the activity of orogen-parallel structures. Fil: Oriolo, Sebastián. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Cristallini, Ernesto Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina Fil: Japas, Maria Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Basicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Yagupsky, Daniel Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina

Analogue models combining different sets of preexisting structural weaknesses were developed to understand their evolution during regional ~ENE shortening. Strain analysis of simulations was performed with the GEODEF 1.1 software, a tool that allows to quantify deformation in plan view on the basis of displacement fields. Results showed up that regional NNE heterogeneities are reactivated as dextral reverse-slip structures, though NNE neoformed thrusts are also present. Likewise, dominant sinistral strike-slip motions have been obtained for reactivated second-order WNW structures whereas sinistral reverse-slip has been recorded for NW ones. Comparison of these results with structural, kinematic and paleomagnetic data supports partitioned dextral transpression for the northern Andean Precordillera since the Miocene. Moreover, models not only confirm sinistral strike-slip motions for WNW structures of the Precordillera but also suggest that they would represent preexisting crustal fabrics that were reactivated during the Andean orogeny. These cross-strike structures have played a significant role in the construction and evolution of the fold and thrust belt as they segmentate the activity of orogen-parallel structures.

Se llevó a cabo un estudio preliminar de fábrica magnética y petrofábrica en areniscas de la Formación Cuculí (Mioceno) en dos localidades de la Precordillera de San Juan y sus resultados fueron comparados con datos obtenidos a partir de estudios cinemáticos de otros autores en el mismo sector. El estudio de la anisotropía de susceptibilidad magnética (ASM) revela elipsoides triaxiales con grados muy bajos de anisotropía. Dado que las rocas analizadas no presentan evidencias macro– o microscópicas de deformación interna, se interpreta que los elipsoides de ASM representan fábricas mágneticas compuestas incipientes, donde la fábrica sedimentaria es un importante factor de control en su desarrollo., A preliminary study of magnetic fabric and petrofabric in sandstones from the Cuculí Formation (Miocene) was carried out in two localities from the Precordillera of San Juan and the results were compared with studies based on kinematic data obtained by other authors in the same localities. The study of the anisotropy of magnetic susceptibility (AMS) shows triaxial ellipsoids with very low degrees of anisotropy. Due to the lack of macro– or microscopic evidences of strain, it is interpreted that the AMS ellipsoids represent incipient composite magnetic fabrics, whose development is significantly influenced by the sedimentary fabric., Asociación Argentina de Geofísicos y Geodestas

This paper presents low-temperature thermochronological data and K‑Ar fault gouge ages from the Sierra de San Luis in the Eastern Sierras Pampeanas in order to constrain its low-temperature thermal evolution and exhumation history. Thermal modelling based on (U-Th)/He dating of apatite and zircon and apatite fission track dating point to the Middle Permian and the Triassic/Early Jurassic as main cooling/exhumation phases, equivalent to ca. 40-50% of the total exhumation recorded by the applied methods. Cooling rates are generally low to moderate, varying between 2-10 °C/Ma during the Permian and Triassic periods and 0.5-1.5 °C/Ma in post-Triassic times. Slow cooling and, thus, persistent residence of samples in partial retention/partial annealing temperature conditions strongly influenced obtained ages. Thermochronological data indicate no significant exhumation after Cretaceous times, suggesting that sampled rocks were already at or near surface by the Cretaceous or even before. As consequence, Cenozoic cooling rates are low, generally between 0.2-0.5 °C/Ma which is, depending on geothermal gradient used for calculation, equivalent to a total Cenozoic exhumation of 0.6-1.8 km. K-Ar fault gouge data reveal long-term brittle fault activity. Fault gouge ages constrain the end of ductile and onset of brittle deformation in the Sierra de San Luis to the Late Carboniferous/Early Permian. Youngest K-Ar illite ages of 222-172 Ma are interpreted to represent the last illite formation event, although fault activity is recorded up to the Holocene.

Geological, geochronological and isotopic data are integrated in order to present a revised model for the Neoproterozoic evolution of Western Gondwana. Although the classical geodynamic scenario assumed for the period 800e700 Ma is related to Rodinia break-up and the consequent opening of major oceanic basins, a significantly different tectonic evolution can be inferred for most Western Gondwana cratons. These cratons occupied a marginal position in the southern hemisphere with respect to Rodinia and recorded subduction with back-arc extension, island arc development and limited formation of oceanic crust in internal oceans. This period was thus characterized by increased crustal growth in Western Gondwana, resulting from addition of juvenile continental crust along convergent margins. In contrast, crustal reworking and metacratonization were dominant during the subsequent assembly of Gondwana. The Río de la Plata, Congo-São Francisco, West African and Amazonian cratons collided at ca. 630 e600 Ma along the West Gondwana Orogen. These events overlap in time with the onset of the opening of the Iapetus Ocean at ca. 610e600 Ma, which gave rise to the separation of Baltica, Laurentia and Amazonia and resulted from the final Rodinia break-up. The East African/Antarctic Orogen recorded the subsequent amalgamation of Western and Eastern Gondwana after ca. 580 Ma, contemporaneously with the beginning of subduction in the Terra Australis Orogen along the southern Gondwana margin. However, the Kalahari Craton was lately incorporated during the Late EdiacaraneEarly Cambrian. The proposed Gondwana evolution rules out the existence of Pannotia, as the final Gondwana amalgamation postdates latest connections between Laurentia and Amazonia. Additionally, a combination of introversion and extroversion is proposed for the assembly of Gondwana. The contemporaneous record of final Rodinia break-up and Gondwana assembly has major implications for the supercontinent cycle, as supercontinent amalgamation and break-up do not necessarily represent alternating episodic processes but overlap in time.

Neoproterozoic successions in South America are recordedin many areas of Brazil, Paraguay, Bolivia, Uruguay andArgentina. Some of these units show glaciogenic forma-tions like those represented in the Puga and Serra Azulformations in the Northern Paraguay Belt (Brazil) inagreement with their accumulation in a Snowball Earthcontext. However, in other cases, tillites or other glacio-marine deposits are absent, which may indicate a distantposition (tropical) regarding the ice cap, as occurs in theTandilia System (Argentina) related to a“Phantom glacial”context. In this contribution we show the comparisonbetween direct and indirect evidence of glaciations in theNeoproterozoic successions of South America. The Pugaand Serra Azul formations in the Paraguay Belt and SierrasBayas Group in the Río de la Plata Craton have beenchosen to describe the“Snowball Earth”and“Phantomglacial”models, respectively. By means of multiproxyanalysis it is also possible to indicate changes in paleocli-mate conditions in both cases. The presence of tillites isconsidered to be direct evidence of the extreme climaticconditions during deposition during a glaciation. Mean-while, more subtle evidence such as regional unconformi-ties related to drastic sea level changes, trends ind13C,events of phosphogenesis, constitute, among others, thetools to indicate the influence of Neoproterozoic globalglaciations during the deposition of the sedimentary units. Fil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Gómez Peral, Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Arrouy, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina

Neoproterozoic successions in South America are recorded in many areas of Brazil, Paraguay, Bolivia, Uruguay and Argentina. Some of these units show glaciogenic formations like those represented in the Puga and Serra Azul formations in the Northern Paraguay Belt (Brazil) in agreement with their accumulation in a Snowball Earth context. However, in other cases, tillites or other glaciomarine deposits are absent, which may indicate a distant position (tropical) regarding the ice cap, as occurs in the Tandilia System (Argentina) related to a ?Phantom glacial? context. In this contribution we show the comparison between direct and indirect evidence of glaciations in the Neoproterozoic successions of South America. The Puga and Serra Azul formations in the Paraguay Belt and Sierras Bayas Group in the Río de la Plata Craton have been chosen to describe the ?Snowball Earth? and ?Phantom glacial? models, respectively. By means of multiproxy analysis it is also possible to indicate changes in paleoclimate conditions in both cases. The presence of tillites is considered to be direct evidence of the extreme climatic conditions during deposition during a glaciation. Meanwhile, more subtle evidence such as regional unconformities related to drastic sea level changes, trends in δ13C, events of phosphogenesis, constitute, among others, the tools to indicate the influence of Neoproterozoic global glaciations during the deposition of the sedimentary units. Fil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Gómez Peral, Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Arrouy, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina

The geology and the tectonic evolution of the Río de laPlata Craton is reviewed, taking into account geochronological,isotopic and geophysical data. The craton consistsof voluminous granite-gneissic terrains (2.2?2.1 Ga) thatrepresent magmatism during the accretional stage of theorogeny. Coeval volcano-sedimentary basins are preservedas relics of supracrustal rocks, deformed andmetamorphosed during a collisional event that occurred atca. 2.1 Ga. Sm?Nd and Hf model ages between 2.7 and2.2 Ga, and positive to slightly negative eNd(t) valuesindicate a Neoarchean to Paleoproterozoic juvenile crustwhich underwent a short period of crustal recycling.Undeformed granitoids, gabbros and dolerite swarms withcalc-alkaline signature intruded at ca. 2.07 Ga correspondto the late- to post-tectonic stages of the orogeny.Exhumation, cooling and cratonization occurred duringthe Orosirian (2050?1800 Ma) and later anorogenicextension is recorded in tholeiitic dyke swarms intrudedat ca. 1.8 Ga in Uruguay and at ca. 1.6 Ga in the BuenosAires province of Argentina. There is no evidence ofMeso- or Neoproterozoic orogenic reworking and onlyone shallow granite intrusion in Uruguay andlow-temperature hydrothermal alteration in theNeoproterozoic cover of the Tandilia System can beascribed to far-field effects of the Brasiliano orogeny. Fil: Oyhantçaba, Pedro. Universidad de la República; Uruguay Fil: Cingolani, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Wemmer, Klaus. Georg-August-Universität Göttingen; Alemania Fil: Siegesmund, Siegfried. Georg-August-Universität Göttingen; Alemania