Revista de la Asociación Geológica Argentina

Presente y futuro de las geociencias: una perspectiva moderna

2025-06-27T23:41:26+00:00

Upper Cretaceous-Cenozoic stratigraphy of the Austral-Malvinas basins in the Fuegian Andes: review and synthesis.

2024-12-12T12:41:26+00:00

Upper Cretaceous-Cenozoic stratigraphy of the Austral-Malvinas basins in the Fuegian Andes: review and synthesis. Based on new field data, biostratigraphy from nannoplankton, dinocysts, mollusks, and vertebrates, as well as zircon U-Pb geochronology,
this study presents a synthesis of the complex Upper Cretaceous–Cenozoic stratigraphy of the Austral and Malvinas foreland
basins in Tierra del Fuego. To simplify the analysis, thirty geological formations are grouped into four higher-rank stratigraphic units
that reflect the major tectonic, sedimentological, and architectural characteristics of the Fuegian Andes' depositional systems during
this time. The orogenic evolution of the Fuegian Andes was punctuated by multiple phases of contractional deformation, associated
with two primary tectonic events: an arc-continent collision and the development of a fold-and-thrust belt. These events generated
four major clastic wedges, bounded by key regional unconformities (u1, u3–u4, and u5), corresponding to the following stratigraphic
groups: i) San Diego Group (Upper Cretaceous–Danian), ii) Río Claro Group (Paleocene–early to middle Eocene), iii) La Despedida
Group (middle Eocene–Oligocene), and iv) Cabo Domingo Group (Oligocene–Miocene). The sedimentary deposits of these groups
are primarily turbiditic, comprising both axial (southeast- and east-directed, parallel to the foredeep) and transverse (northeast- and
north-directed, perpendicular to the foredeep) depositional systems.

Three-dimensional geological modeling of the central vein, Cerro Norte area, Casposo district, San Juan.

2024-10-07T21:47:32+00:00

The low-sulfidation deposit of the Cerro Norte system includes three main veins: Norte, Central, and Sur, composed of quartz-carbonate with replacement textures and breccias, containing gold, silver, and base metal sulfides. Mineralization occurs in fractures, forming subvertical veins that extend up to 950 meters in length. The Central Vein consists of two subparallel veins and a stockwork zone. A medium to high positive correlation was observed among the pairs Au-Ag, Au-Cu, Ag-Cu, Pb-Zn, Pb-Cu, As-Pb, As-Zn, Hg-Au, Mo-Zn, and Mo-As. The distribution of these metals was analyzed using a 3D geological model, in which lithologies and faults that segment
the vein were modeled. The highest concentrations of Au, Ag, base metals, and Mo in the eastern block of the central vein are predominantly located below the lithological contact between andesitic ignimbrites and a dacitic subvolcanic body. Elevated values above
this level are associated with faults and post-mineral dikes. In the western block, Au is concentrated in shallow zones, coinciding with the mentioned contact, whereas Ag, Pb, Cu, and Zn are also linked to faults in deeper zones. As and Hg are primarily found at depth, whereas Sb is more abundant in shallow zones. The metal distribution in Cerro Norte reflects the influence of rock permeability and geological structure on the transport and deposition of mineralizing fluids, with significant variations observed between the blocks of the central vein.

Dispersion and preservation of tephras in extra-Andean Patagonia associated with the H2 eruption of Hudson volcano during the late Holocene.

2024-12-16T12:48:41+00:00

In Patagonia, tephra deposits are associated with volcanoes from the Southern Volcanic Zone and the Austral Volcanic Zone of the Andean volcanic belt. Their spatial distribution is mainly influenced by the dominant westerly winds, dispersing and depositing the finest particles to the east of Andes, where arid climatic conditions prevailed during the Holocene. In this context, four sites located in southeastern Chubut were studied, where tephras preserved in deposits associated with ephemeral fluvial systems and dunes were identified and characterized, with evidence of local remobilization and primary deposition. The analyzed samples are mainly composed of a transparent vitroclasts population, accompanied by dark brown vitroclasts. Morphologies are typical of plinian phases, derived from bubble wall breaks in pumiceous fragments. Major-elements geochemistry of the volcanic glass indicated clustered compositions at the boundary of rhyolite-dacite-trachyte/trachydacite fields, consistent with the geochemistry recorded for the H2 eruption of Hudson volcano, whose dispersion was recorded to the E-SE. Also, radiocarbon dating of bones and charcoal associated with archaeological remains, recorded 40 cm below the layer, are consistent with H2 and give the tephra a maximum age between 3636 and 3882 cal. AP. In this way, H2 tephra can be considered a regional chronostratigraphic market of the Holocene in extra-andean Patagonia.

Characterization of the Cerrito Banco de Arizaro formation and its relationship with Cenozoic magmatism in the Southern Puna.

2024-10-15T11:45:55+00:00

The Cerrito Blanco de Arizaro Formation is part of the widespread Cenozoic volcanism in the Southern Puna region. It comprises three lava domes (Domes 1, 2, and 3) with subcircular to slightly elliptical shapes, emplaced on gentle slopes. Domes 1 and 2 lie east of the Aracar volcano, while Dome 3 is located east of the Vega de Arizaro. Dome 1 consists solely of coherent lava, whereas Domes 2 and 3 display both coherent lava and autobreccia facies. Petrographically, the rocks contain plagioclase, quartz, and biotite crystals within a glassy groundmass. All three domes exhibit flow foliation, marked by variations in vesicle abundance and distribution, indicating emplacement under laminar flow conditions. Geochemically, the domes are high-silica rhyolites with a calc-alkaline signature
and features suggesting intraplate magmatic affinity. Their silica-rich composition and low rare earth element (REE) enrichment imply advanced fractionation of phases such as hornblende, pyroxene, and accessory minerals. Compared to other rhyolitic bodies in the region, these domes are distinguished by a subtle negative Eu anomaly and moderate Sm/Yb ratios, consistent with crystallization at intermediate depths in the crust.

The basal friction in the modeling of the propagation of shallow landslides – debris flow using r.avaflow

2024-10-31T14:36:25+00:00

Landslides pose a significant natural hazard around the world and rainfall is the primary triggering factor in Colombia. Many investigations focus on the occurrence of landslides, and the areas affected by their propagation (runout) should also be considered. Landslide runout is influenced by different variables such as cohesion, variable density, erosion, and entrainment, where basal friction plays an important role. This investigation focuses on the influence of basal friction variation in modelling of shallow landslides using r.avaflow. The model is implemented in the Colombian southwestern (Mocoa). Where hours of rain triggered a clustered shallow landslides and chain processes, causing approximately 306 dead people. Some results from modeling shallow landslides under or overestimate the affected areas according to basal friction used. However, analysis indicates that basal friction equal to the internal friction of the material has better results. As well, they indicate that the minimum heights estimated ranging from 0.51 m to 0.61 m offer conservative results to perform hazard zoning of the possible affected areas.

Petrological and stratigraphic review of the Cerro del Corral area (San Ramón): new outcrops of pyroclastic rocks in El Diamante quarry and Sierra del Piojo (Carin IV quarry), Tandilia, Argentina.

2024-12-27T02:14:49+00:00

New studies conducted on previously recognized pyroclastic rocks, along with newly discovered outcrops in the sedimentary sequence of the Tandilia ranges, have enabled the establishment of correlations between areas with sparse and isolated exposures in the western, central, and southeastern sectors of Tandilia. In critical zones—due to poor outcrop quality and ambiguous stratigraphic positioning—several vertical profiles were analyzed on clay-rich levels and adjacent lithologies. Petrographic and X-ray diffraction analyses allowed for the identification of paragenetic clay associations, hydrothermal alteration zoning, and metasomatic replacement features. Geochemical analyses, including major oxides, trace elements, and rare earth elements, were performed on representative samples from the studied units. These data revealed a clear correlation between the basic pyroclastic rocks of the Sierra de los Barrientos (southeast) and those of the Sierra del Piojo (northwest). Additionally, equivalent levels of acid pyroclastic rocks were recognized in the Olavarría Formation, permitting stratigraphic correlation among quarry exposures in the Barker and Olavarría localities. We interpret the Las Águilas Formation as a basic pyroclastic event within the Cerro Largo Formation. Although both the Las Águilas and Olavarría Formations occur in the central Tandilia region (Barker area), they are not stratigraphically equivalent, being separated by the upper section of the Cerro Largo Formation. Consequently, we propose reclassifying the Las Águilas Formation as the Las Águilas Member within the Cerro Largo Formation.