We present 3D thermal and rheological models of a key intra-plate locality of South America: the southernmost limit of the Río de la Plata Craton area (which encompasses the Claromecó Basin, the Sierras Australes, and the Colorado Basin). Both models were calculated on the basis of a previously published 3D lithospheric scale density model, after the population of the different units with thermal and rheological properties. Firstly, the steady-state conductive thermal field was modelled using different thermal properties in accordance with the assumed lithological composition of the units. Moving forward, the strength distribution was calculated considering the resulting thermal field and published rheological properties for common rock types as input for the different layers that compose the 3D density configuration of the area. Our main results suggest that the thickness and composition of the crust exert a first-order control on the present-day thermal field of the area and, subsequently, on the lithospheric strength. Particularly, we identified a rheologically weak lithospheric zone that coincides with previously proposed inherited Paleozoic structures of Gondwana. This inherited lithospheric fabric could have controlled the opening of the Colorado Rift Basin during the early Late Jurassic. In that sense, the present day high strength of the Rio Negro and Colorado transfer zones associated with the mafic infill of Colorado rifting in the Mesozoic suggests that the weak zones should have necessarily been developed during (at least) Paleozoic to early Mesozoic times.
This supports the hypothesis that the reactivation and interaction of the latter with the Gondwanic weak lithospheric zone could have deformed and uplifted the Sierras Australes during the Gondwanides Orogeny.

We present new chronological data for the southernmost sector of the Eastern Sierras Pampeanas system of central Argentina. Recent excavations at the Cueva Los Bancos site in Sierra del Morro hill provided a date of ca. 9400 calendar years ago. This is the earliest absolute chronology of this sector, considered an ecotone between mountains and plains. Data provided will allow us to include this site in the discussion of the initial peopling of the region.

To understand the subsurface stratigraphy and structure of the Laguna Merín Basin (LMB), data from 42 magnetotelluric stations were interpreted by performing 1-D and 2-D inversions along three profiles perpendicular to the main basin borders. The Aiguá-India Muerta-Chuy Lineament (AICL) constitutes the southern boundary of the LMB and is characterised by a subvertical sinistral transtensional fault with a general orientation of N85°E. The basin's northern boundary, represented by the Cebollatí-Merín Lineament (CML), is characterised by a set of echelon dextral transpressional faults with a general orientation of N50°. Both faulting sets are associated with maximal horizontal stress oriented NE-SW. The infill of the LMB comprises thick Jurassic-Cretaceous igneous rocks (average of ~1500 m) overlying a crystalline Precambrian basement and overlain by ≤500 m-thick Cretaceous-Cenozoic sedimentary sequences. Likewise, a very deep (> 3500 m) conductive body was identified in the basement between the CML and AICL, coincident with the highest values of gravimetric Bouguer anomalies recorded in Uruguay. Shallow Cretaceous-Cenozoic sedimentary sequences show resistivities between 1 and 25 Ω.m, an average thickness of 250 m, and a maximum thickness of 500 m. The deeper Jurassic/Cretaceous igneous rocks show average resistivities between 40 and 252 Ω.m, and a maximum thickness of nearly 2000 m with intercalations of conductive layers (< 25 Ω.m) of unknown nature in the lower half of the basin infill. A tentative 3-D model is proposed to represent the early stage of magmatic emplacement during the opening of the South Atlantic Ocean.

The amalgamation of southwestern Gondwana during the late Neoproterozoic Brasiliano/Pan-African orogenic cycle involved the tectonic interaction of the Congo, Kalahari and Rio de la Plata cratons, together with numerous smaller basement fragments scattered throughout South America. A comprehensive review of U-Pb and Lu-Hf spot analyses in zircon provides new insights on the pre-Brasiliano crustal growth of the main tectonic domains of the southern South American Platform from the Archean to the early Neoproterozoic. The results highlight similarities between five basement fragments, from south to north: the Nico P´erez Terrane, Tijucas Terrane, Camboriú Complex, Luis Alves Terrane and Curitiba Terrane. Whereas these units have variable characteristics, especially concerning differing degrees of tectonic reworking in the late Neoproterozoic, they share similarities in their geological evolution. They were all originally accreted in the Archean, as evidenced by Hf TDM model ages and zircon inheritance, and later experienced intense orogenic reworking during the Rhyacian and Orosirian. The Paleoproterozoic record is diverse and indicates a complex episodic evolution instead of a single orogenic event. Conspicuous diachronic magmatic events took place locally in the Late Paleoproterozoic and Mesoproterozoic, interrupting an otherwise relatively stable tectonic setting until the Neoproterozoic. The Archean origin and strong crustal signatures of the main Paleoproterozoic units distinguish these terranes from the Rio de la Plata Craton, evidencing instead stronger affinities with African crustal blocks such as the Congo and Kalahari cratons. This relationship has implications for the geodynamic reconstruction of southwest Gondwana that extend into the early Neoproterozoic, as it contextualizes the genetic link between the main Tonian events in the region, namely the formation of the S˜ao Gabriel Terrane and the emplacement of the magmatic protoliths of the basement of the Punta del Este Terrane. They can be understood as marginal and within-plate manifestations of an accretionary orogen, respectively. The basement of the Punta del Este Terrane has signatures compatible with the recycling of ancient crust through the mixture of mantellic magmatic input with the partial melting

Coupled U–Pb and Lu–Hf LA-ICP-MS detrital and igneous zircon data were obtained from etasedimentary sequences (Kaserer Formation, Schmirntal Quartzite, Seidlwinkel Formation, Bündnerschiefer Basin, Riffler Basin) of the western Tauern Window (Eastern Alps). Results show maximum deposition ages between the Late Permian and the Triassic, indicating protracted sedimentation and magmatism between the Late Paleozoic and the Mesozoic. The Lu–Hf fingerprint shows a change from subchondritic to variable subchondritic to suprachondritic compositions at ca. 290 Ma, possibly documenting the transition from Late Paleozoic Variscan post-collisional processes to intracontinental extension. Lithospheric thinning and magmatic underplating may explain the observed Hf isotopic evolution as the result of mixing of crustal and mantellic sources. From a paleogeographical perspective, results confirm that the Tauern Window was situated between Alpine basement units (South Alpine, Austroalpine and External Massifs) and the Bohemian Massif during the Permian–Triassic.

We present the first palynological assemblages collected from the fine-grained variegated beds that overlie the De La Cuesta Formation at Puerta de Las Angosturas, Sierra de Narváez, Catamarca Province, Argentina. Five samples from two different stratigraphic levels provided spores, non-taeniate, taeniate, and sulcate pollen grains referred to the Lueckisporites/Weylandites (LW) Biozone. The palynofloras are equivalent to those previously reported for the Los Jumes area and, therefore, the variegated sequences that overlie the De La Cuesta Formation at both flanks of the Sierra de Narváez are entirely equivalent, not only lithologically but also in fossiliferous content and age. These assemblages are analogous to those isotopically dated at 278.84±0.22 Ma (Kungurian) in the Valle Hermoso area (La Rioja Province), which constitute a key stratigraphic horizon to link the initial phases of the Permian volcanic arc and the sedimentation in the retroarc basins. The recognition of diagnostic taxa of the LW Biozone confirms earlier correlations with the Striatites Biozone of the Chacoparaná Basin and the Lv Biozone from Brazil. The different ages recently reported for the succession analyzed here in Sierra de Narváez and La Veteada Formation, suggest that these units should not be correlated. Moreover, while the strata overlying the De La Cuesta Formation records the Permian post-orogenic sedimentation in the Paganzo Basin, the La Veteada Formation accounts for the transition to the rifting conditions that characterized the triassic basins of northwestern Argentina.

Palynology is one of the most useful tools for constructing biostratigraphic charts in the late Paleozoic basins of South America, but the lack of radiometric ages often makes it difficult to establish the precise age of the biozones. This paper focuses on two points: (i) the description of new Argentinian palynological assemblages referred to the Lueckisporites/Weylandites (LW) Biozone and (ii) the application of a new isotopic age that enables more confident large-scale correlations with the neighboring Paraná Basin of Brazil. The palynofloras were recovered from the upper part of the De La Cuesta Formation that crops out in the retroarc basin of the Paganzo Basin, more specifically obtained from mudstones intercalated with limestones, cherts, and tuffs interpreted as being deposited in a shallow water body. The assemblages are characterized by an abundance of bi-taeniate pollen grains of the Lueckisporites complex and multitaeniate pollen grains such as Lunatisporites, Protohaploxypinus, Striatopodocarpidites, Tornopollenites, and Vittatina. Colpate pollen grains are also represented by Marsupipollenites and Pakhapites. A U-Pb CA-ID-TIMS age of 278.84 ± 0.22 Ma, obtained from a tuff level interstratified with the fossiliferous strata, allows the age of the LW Biozone in the Paganzo Basin to be constrained for the first time and the adjustment of the record Lueckisporites virkkiae in Gondwana. Moreover, this date enables precise correlations with other basins, such as the San Rafael Basin (Yacimiento Los Reyunos Formation) in Argentina and the Brazilian Paraná Basin (Iratí Formation).

Lago Roca is a NE–SW elongated lacustrine body located to the south of Lago Argentino, the largest lake of the UNESCO ‘Los Glaciares’ National Park. An extensive high-resolution seismic survey carried out within the Lago Roca, integrated with geological information gathered in the area, have allowed to produce: (a) a complete bathymetric map of the lake; (b) a basement topography map and a structural map; and (c) an analysis of the geometry, distribution, and thickness of the sedimentary infill. Two sub-basins were recognized in Lago Roca, separated by a central basement high that shows a pop-up structure. The northern and southern margins of the lake basement are bounded by NE–SW trending strike-slip faults that constitute subsidiary faults strands of the regional structural lineament known as the ‘Lago Argentino transfer fault’. The shallow, low magnitude seismicity recorded in the area supports the interpretation that this fault segment is active at the present. The relative motion along the fault led to the deformation of the sedimentary infill of the lake, which was also affected by several subsidiary normal faults oriented parallel to the Lago Argentino transfer fault. Data show the peculiar asymmetry in the sedimentary filling of Lago Roca, typical of those of pull-apart basins generated along transform margins. A simplified model for the evolution of Lago Roca is also here proposed, based on the analysed data and the regional tectonic background.