The present study reviews the main geological features, with emphasis on structural controls, affecting the geoeconomic potential of the green schist-hosted talc deposits of the western sector of the San José Belt (Colonia Department, Uruguay) located in the Narancio, Dante Ramos and Zafiro Sector mines. The analysis of the regional geology allows us to define two complementary genetic models for the talc deposits: i) hydrothermal alteration of basic volcanic rocks rich in magnesium, and ii) metasomatic processes in the contact between dolomites and acidic intrusive rocks. Finally, the productive history of the Narancio Mine is synthesized and the geometry, the volume of the lenticular bodies and the quality of the talc deposits of the Zafiro Sector are discussed with the purpose of allowing a better evaluation of its economic potential.

The very thick (up to 6000 m thick) Miocene Vinchina Formation was deposited between 16 and 8 Ma ago and later covered by more than 2500 m of Pliocene-Pleistocene sediments in a broken foreland basin. The very thick sedimentary pile accumulated in a medium to low-gradient basin must have suffered intense mechanical compaction during burial.

Seventy thin sections of unaltered sandstones collected in three sections along the depositional strike of the Vinchina Formation at the Sierra de Los Colorados, La Rioja Province, northwestern Argentina, were analyzed under the microscope for determining compactional paths and controls.

The role of compaction in sandstone diagenesis was firstly assessed using the change in intergranular volume (IGV), which is the sum of all cement and remaining primary porosity. It is clear from the IGV analysis that most of the studied sandstones lose more porosity by compaction (COPL) than by cementation (CEPL). In general compaction increased from the upper to the lower member of the Vinchina Formation (i.e with depth) and there is a clear trend of the compaction index ICOMPACT increase from the northern, shorter Los Pozuelos to the central, thicker La Troya sections. Surprisingly, the thickest southern El Yeso section shows anomalous results possibly due to the extensive development of cements as indicated by the highest CEPL values. Cements are related to the depositional environment (gypsum, calcite) and clast composition (zeolites). Early cements may have prevented further compaction while late cements may have produced open fabrics by dissolution of matrix and framework clasts. Both cases show that diagenetic processes are not homogeneous basin-wide and that the diagenetic pathways are not only controlled by the increase in burial depth but also by characteristics associated with depositional environments and framework clast composition.

We also attempted to relate compaction to burial depth based on the nature (point, long, concave-convex and sutured contacts) and the number (contact and packing indexes) of grain-to-grain contacts in the studied sandstones. The sandstones present predominance of concave-convex grain-to-grain contacts and IC indexes mostly between 3 and 4. Sutured contacts are uncommon, and stylolites were not observed at all. Persistence of open fabrics, floating textures and point grain-to-grain contacts at different depths are the result of dissolution-cementation processes. A clear trend of increasing mechanical compaction with depth is only seen along the northern coarser-grained but thinner Los Pozuelos section. Although compaction seems to have increased with depth and also from north to south, the thickest but overall finer-grained El Yeso (southern) section do not show a clear pattern of change with depth. This behavior seems to be the result of at least four main factors: 1) mean sandstone grain-size, 2) thickness of muddy intervals, 3) development of early diagenetic cements, and 4) depth of burial.

Comparison with comparable examples suggests that similar compactional characteristics are achieved between 3.5 and 6 km of maximum burial depths. However, cumulative thickness of the Vinchina basin-fill indicate that the base of the Vinchina Formation may have been buried at 8.5 km deep but preliminary backstripping models suggest that by 5 Ma this surface may have reached up to 10 km depth. Alternatively, recorded repetitive episodes of deformation, uplift, and erosion (progressive unconformities) in the Vinchina basin may have prevented the sedimentary pile to be deeply buried and therefore allow to reconcile the observed compactional textures with depth of burial.

The results obtained in this work show that the analysis of mechanical compaction in sandstones constitutes a complex task and in occasions there is not a linear relationship between the contact indexes and depth of burial. Sandstone compaction is controlled not only by the depth of burial but also by other factors such as, time, geothermal flow, matrix content, the development of early cements, the ratio between ductile and rigid lithic fragments and, in tectonically active basins the development of progressive unconformities. Therefore, in most cases, it is very speculative to extend diagenetic conditions to basin-wide scales. In particular, the porosity-depth relationship must be based on primary porosity only.

During the Late Cretaceous Andean orogeny, the compressive deformation associated with the shallowing of the subducting slab caused the development of the arc-related igneous rocks known as the Naunauco Belt. This study presents petrographic, mineralogical and anisotropy of magnetic susceptibility data for the Varvarco Intrusives (the Varvarco Tonalite, Butalón Tonalite and Radales Aplite), which crop out in the Cordillera del Viento, Neuquén Province, Argentina. The assembly of plutons was formed by mafic magma episodic injection. Amphibole and biotite compositions suggest that the Varvarco Tonalite is related to calc-alkaline, I-type magmas, typical of subduction environments. Different geothermobarometers based on amphibole and plagioclase compositions for the Varvarco Tonalite suggest shallow emplacement conditions (∼2–3 kbar, equivalent to ∼12 km depth). Apatite fission-track analyses give exhumation ages of 67.5 ± 8 Ma for the Varvarco Tonalite and 50.3 ± 5.9 Ma for the Butalón Tonalite. A calculated continuous fast exhumation rate of at least 330 °C Ma−1 is consistent with the shallow emplacement conditions, textural data and geobarometric estimations. In agreement with the thermal profile, the magmatic system was exhumed by ∼12 km within c. 2.1 Ma implying a geothermal gradient of ∼62.5 °C km−1. The last step of exhumation occurred between ∼65.3 and 56.9 Ma. The magmatic fabrics observed in the studied plutons reflect mostly magma chamber processes. The Varvarco Intrusives represent satellite calc-alkaline plutons of the North Patagonian Batholith which were emplaced syn- to post-tectonically with respect to a major deformation stage of the Southern Central Andes.

This work presents new biostratigraphic data based on calpionellids and calcareous dinoflagellate cysts for the Tithonian in Central Chile. This stratigraphic interval is mostly represented by a thick marine succession of limestone and sandstone known as Baños del Flaco Formation. This formation originated in the shallow-water setting of a carbonate ramp and correlates with other well-studied units in the Neuquén basin of Argentina. Calpionellids and calcareous dinogflagellate cysts are studied on the Chilean side of the Andes for the first time. The recognition of several calpionellids and calcareous dinogflagellate cyst species within the lower Baños del Flaco Formation allowed the identification of a preliminary microbiostratigraphic zonation. Calcareous dinoflagellate cysts include eleven species that defines the Colomisphaera tenuis, and Colomisphaera fortis zones, whereas six chitinoidellid species allowed the identification of the Chitinoidella and Crassicollaria zones, with the Slovenica, Boneti and Remanei subzones. These new microbiostratigraphic data suggest a latest early to earliest late Tithonian age for the studied interval.

Some recent models challenge the position and extension of the assumed oceanic basins formed through the break-up of Rodinia, and the tectonic processes involved in the Gondwana assembly, making the investigation of the Early Neoproterozoic record of great relevance. Within the South-American Atlantic margin, the Punta del Este Terrane (PET) of the Dom Feliciano Belt (DFB) comprises a unique Tonian to Ediacaran record, and has a strategic position to reconstruct spatio-temporal relationships with the southern African orogenic belts. Novel zircon U–Pb and Lu–Hf data from the PET basement orthogneisses display Tonian magmatic ages (805–760 Ma) and Hf isotopic signatures indicative of mainly crustal/metasedimentary sources, (Nd TDM ages: 2.2–1.9 Ga, and εHf(t): − 12 to − 4). The basement paragneisses yielded late Paleoproterozoic to Neoproterozoic U–Pb ages, but dominantly positive εHf(t) values. The presented results confirm the correlation of the PET with the Coastal Terrane of the Kaoko Belt, and discard the idea of the Nico Pérez Terrane as a source. Detrital zircon U–Pb and Lu–Hf data from the Rocha Formation yielded a main peak at ca. 660 Ma, with the Neoproterozoic grains showing a εHf(t) between + 1 and + 14. The deposition age of the Rocha Formation is constrained by the youngest detrital zircon age peak (660 Ma), and the beginning of the deposition of the Sierra de Aguirre Formation (580 Ma). The data indicate common sources with the Marmora Terrane, and it is thus proposed that the Rocha Formation belongs to the Gariep Belt, and it was juxtaposed during the Ediacaran to the DFB.

Potential field filters are widely used in exploration and interpretation of geologic structures,
archaeological sites, hazards assessment, and in engineering and environmental studies. There are countless filters and attributes and their number keeps growing: directional, horizontal and vertical derivatives; analytic, monogenic and direct analytic signals; modules; local phase; tilt angle; azimuth; local (horizontal, vertical and total) wavenumbers; theta function; high order derivatives; enhancements; normalizations. Furthermore, almost all of these filters can be applied to other filters—often named with overwhelming acronym combinations making it almost impossible to keep up with the particular and general development of this field. In this work, we present a review of more than 200 publications
and compile more than 50 proposed methods in a unified mathematical framework, and an easy-to-follow notation. We asses all the methods, their definitions, connections, variations, redundancies and limitations, including a vast list of references and some historical notes. We improve and amend some points—regarding not only its mathematical applications but also the attributions that correspond to each method. We also establish connections with other fields of research—seismics, mathematics, image analysis—in which the same or similar techniques are used, but have remained isolated and unknown to each other.

In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essential to determine the controls of the deformation within the upper plate and the dip angle of the subducting lithosphere. In this study, we evaluate the degree of influence of both the configuration of the upper plate (i.e., thickness and composition of the rock units) and variations of the subduction angle on the lithospheric thermal field of the southern Central Andes (29°–39°S). Here, the subduction angle increases from subhorizontal (5°) north of 33°S to steep (~30°) in the south. We derived the 3D temperature and heat flow distribution of the lithosphere in the southern Central Andes considering conversion of S wave tomography to temperatures together with steady-state conductive thermal modeling. We found that the orogen is overall warmer than the forearc and the foreland and that the lithosphere of the northern part of the foreland appears colder than its southern counterpart. Sedimentary blanketing and the thickness of the radiogenic crust exert the main control on the shallow thermal field (<50 km depth). Specific conditions are present where the oceanic slab is relatively shallow (<85 km depth) and the radiogenic crust is thin. This configuration results in relatively colder temperatures compared to regions where the radiogenic crust is thick and the slab is steep. At depths >50 km, the temperatures of the overriding plate are mainly controlled by the mantle heat input and the subduction angle. The thermal field of the upper plate likely preserves the flat subduction angle and influences the spatial distribution of shortening.

Mineral chemistry of the magmatic biotites from the syn-mineral dacitic porphyry of Morro del Cobre.
Mineral chemistry of the magmatic biotites from the dacitic porphyry of Morro del Cobre (Frontal Cordillera of San Juan province) reveals that they are Mg-biotites, typical of precursor porphyry Cu intrusives. Biotite geothermobarometry confirms the hydrous and oxidant character of the magma which evolved to shallower chambers

Clay mineral characterization is a valuable tool for unraveling the evolution of continental sedimentary basins. The Fiambala ´ basin is a foreland Andean basin located in the Southwest of the province of Catamarca (Argentina), on the flat subduction segment. In order to characterize its paleoenvironment and post-depositional evolution, petrographic, X-ray diffraction (XRD), and scanning microscopy (SEM-EDS) studies were carried out in detrital and volcaniclastic samples from the Tambería, Guanchín, and Rodados de la Puna Fms. Petrographic and XRD analyses show a predominance of phyllosilicates, quartz, plagioclase, and low proportions of feldspar and anhydrite, sporadic calcite, analcime, heulandite, and hematite. In the XRD fraction <2 μm, minerals from the smectite and illite groups dominate, with lower proportions of chlorite and kaolinite. An analyzed tuff level presents smectite solely in this fraction. The textural-compositional analyses of SEM-EDS show that illite and chlorite have a detrital origin. Their preservation would be consistent with the dominance of an arid climate in the region during the erosion and deposition of material from the source areas. The smectites are of the magnesium-rich beidellite-montmorillonite type and, together with the zeolites would be authigenic as a product of the alteration of both the volcanic material and magnesian detrital phases (chlorite and biotite), possibly under the influence of an alkaline environment related to the arid climate. From a thermal point of view, the presence of smectite throughout all stratigraphic succession allows interpreting maximum temperatures that, even in the deepest levels of the basin, inhibit the development of prograde phases (such as smectite/illite and smectite/chlorite mixed-layered) and allow the preservation of smectite. Based on the authigenic clays present in the basin, paleogeothermal gradients of between 13 and 18 ◦C/km (considered a fill of 4000 m thick) and between 8 and 11 ◦C/km (considered a fill of 6000 m thick) could be estimated.

New X-ray diffraction (XRD) data, scanning electron microscopy (SEM) analysis, and X-ray energy dispersive spectrometry (EDX) microanalysis on clay minerals are presented for Cretaceous-Cenozoic sedimentary sections studied in the La Flecha and La Troya Sur creeks, located in the Argentine Precordillera. The characterization of clay mineral assemblages, including the discrimination of detrital and authigenic phases, allows inferences to be made about paleoclimatic and paleoenvironmental conditions as well as the postsedimentary history of these foreland clastic sedimentary depocenters. Mineralogical analyses carried out in the Cretaceous Ciénaga del Río Huaco Fm. and the Cenozoic Puesto La Flecha, Vallecito, Vinchina, and Zapallar Fms. show the presence of illites, smectites, illite/smectite mixed-layer clays (I/S, with R0 and R1 ordering types), sporadic corrensite, and subordinate amounts of chlorite and kaolinite, among other non-clay phases, such as analcime and heulandite. Illite and chlorite are interpreted as detrital phases, reflecting the composition of the source area, and smectite, I/S R0 and R1, and corrensite are interpreted as authigenic phases developed in the matrix or as massive pore filling within the clastic levels. Compositional analyses allow for smectites to be characterized as di- and trioctahedral Mgrich, and are interpreted as a product of the combination of two main controls: (1) that from the parent material (volcaniclastic material and magnesian silicates) and (2) that of the primary composition of pore fluids associated with alkaline lake systems. These smectites are precursors of prograde diagenetic phases developed under a low thermal regime (< 120 °C). R0 and R1 I/S formed from Mg-dioctahedral smectites mainly within the matrix, with an increase of illite % in R0 and R1 with depth, and corrensite formed from trioctahedral Mgsmectites mainly as massive pore fillings. Finally, the conclusions obtained from these new data reinforce that, in some cases, authigenic phases associated with mesogenesis (e.g., corrensite) would allow us to make inferences about the precursor authigenic material and
therefore about some paleoenvironmental conditions. This, in turn, underlies the importance of making detailed analyses of clay mineral assemblages in reconstructions of the sedimentary and post-sedimentary history of basins close to areas with active tectonism, such as foreland basins.