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- Testing the application of the Trishear kinematic model for
fault-propagation folding: Results from 2D analogue model
Authors: Berenice Plotek
Abstract: Understanding the mechanics, geometry, and kinematics of fault-propagation folding has become a major research field. Laboratory experiments have provided useful insights because they allow observing in real-time the progressive development of folding. We perform 2D analogue modelling to study the velocity field during fault-propagation folding and compare it with those proposed by the Trishear kinematic model. In this regard, we employ the non-intrusive, particle image velocimetry (PIV) technique to obtain both fault-parallel and fault-perpendicular velocity profiles during different stages of experiment development. Hanging wall vectors reveal a gradual decrease in the parallel component of velocity towards the footwall, while the perpendicular component turns negative, fitting well with the Trishear kinematic model. In addition, we compare the observed fold shape to the fold shapes predicted by the Trishear model for various apical angles and prove that Backlimb Trishear provides a useful approximation of the velocity field of the experiment. Although some researchers have investigated the kinematic field of fault-propagation folds using numerical models, fewer studies have addressed this issue using physical models. The present research explores the application of the Trishear method to fault-propagation folds based on analogue simulations. Keywords. Kinematic Trishear Model; 2D analogue model; Particle image velocimetry; Fault-propagation folding; Backlimb Trishear.
PubDate: 2023-04-24
Issue No: Vol. 80, No. 1 (2023)
- The occurrence of graphite in Campo del Cielo as a clue to understanding
the formation scenario of non-magmatic iron meteorites
Authors: Laura Noel García, Marcela Saavedra, Pouyan Shen, María Eugenia Varela, Laura Baque
Abstract: The purpose of this research is to assess the carbon vapor deposition scenario as proposed in the literature for graphite formation in non-magmatic iron meteorites. For this aim, graphite occurrence in a sample of the Campo del Cielo Argentinean iron meteorite was explored through optical and electron microscopy, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry. From the results, an alternative setup shall be considered for graphite formation, which would provide evidence for understanding the formation of non-magmatic meteorites, still under discussion.
PubDate: 2023-04-20
Issue No: Vol. 80, No. 1 (2023)
- Thermotectonic influences of the La Escalerilla Granite on the structural
control of the tungsten veins of the San Román and La Puntana mines (La
Carolina, San Luis, Argentina)
Authors: Eduardo Rossello, Teresita Montenegro
Abstract: The tungsten-bearing veins of San Román and La Puntana mines constitute a series of quartz biextended bodies along about two km with potencies of the sub metric order that were exploited between the 40s and 70s through trenches and subsurface works. They are arranged in parallel on the contact of the metamorphic host of the San Luis Formation with the La Escalerilla Granite assigned to the lower Paleozoic, both units of the crystalline basement of the Sierra de San Luis. It is proposed that volumetric changes occurred during its late emplacement favored thermotectonic phenomena linked to the structural control of the mineralization by developing potential spaces subparallel to the vicinity of its controlled contact by the pre-existing planar anisotropies of its shale host rocks. In addition, the differential thermal contraction of the quartz during the passage from b to a, with respect to the other mineralogical constituents of the granite dome, produced during its cooling, a decrease in pressure with boiling of the pneumatolytic hydrothermal fluids enriched in immiscible elements. This mechanism generated in the domes of the La Escalerilla granite porosity and the concentration of fluids enriched in tungsten that migrated towards the overlying veins with a significant absence of greissinification and pegmatization. It is proposed that the power of the veins is related to the volumetric decrease of the intrusive throughout its contact and that they tend to thin out as they move away from the contact of the intrusive body.
PubDate: 2023-04-06
Issue No: Vol. 80, No. 1 (2023)
- A semi-quantitative risk assessment of debris flow in northernmost
Patagonia, Argentina
Authors: Damián Groch, Marisa Gloria Cogliati, Michel Jaboyedoff, Verónica Gil
Abstract: Debris flows cause human losses and material damages in many countries around the world. The associated risk often remains unknown because of uncertainties and the lack of data. This paper presents a semi-quantitative risk assessment of debris flow based on a Risk Matrix Approach to overcome that limitation. Three risk levels were defined through hazard and vulnerability analysis. Hazard scenarios were modeled in Flow path assessment of gravitational hazards at a regional scale (Flow-R). Vulnerability was analyzed and defined according to the physical characteristics of the elements-at-risk. Huaraco and Huinganco basins, in the north of Patagonia were selected for detailed analysis based on the frequency and consequences of the debris flows occurred from the 19th to the 21st centuries, which had recurrence intervals between 30 and 56 years. A detailed study of the 8 February 2013 episode revealed extremely high flow velocities and peak discharges that carried huge boulders and produced extensive damage. The risk assessment determined that under present conditions 38 people might be severely affected by landslides in the high magnitude scenario, with losses up to 5.2 million USD due to the destruction of roads, bridges, and buildings by debris.
PubDate: 2023-03-22
Issue No: Vol. 80, No. 1 (2023)
- Preliminary resource assessment of El Galpón area (Salta, Northwest
Argentina) from fluid geochemistry studies and the Volumetric Method
Authors: Agostina Chiodi, Florencia Luna, Valeria Simon, Walter Baez, Esteban Bertea
Abstract: Within a global warming scenario in searching the energy transition from fossil fuels to free-CO2 energy sources, as well as the improvement in energy efficiency and diversification, geothermal energy is positioned as a promising energy source. This paper presents new geochemical and isotopic data of the fluids related to the El Galpón geothermal system with the aim to: investigate the physicochemical conditions of the fluids within the geothermal reservoir, present a conceptual model of the geothermal system, and carry out an evaluation of the geothermal potential of the area. The geochemical characterization was carried out by direct sampling of water and subsequent analysis of its chemical and isotopic composition, while the 3D geological modeling was carried out by using the LeapfrogGeo software. The deep geothermal reservoir, hosted within with the Pirgua Subgroup, has sodium bicarbonate composition and temperatures of ~111 °C, while the deposits of the Balbuena Subgroup would constitute the seal of the system. Recharging meteoric water could reach depths of up to 6 km, acquiring the temperatures estimated by geothermometers in an area of normal geothermal gradient. During the ascent to the surface, favored by the structures, the geothermal water undergoes mixing processes with more superficial aquifers, sodium sulfate chloride in composition, hosted in the Orán Group. The geothermal potential of the modeled area, expressed as heat stored both in the rock and in the fluids, would be 4.33 * 1017 J.
PubDate: 2023-02-17
Issue No: Vol. 80, No. 1 (2023)
- High temporal and spatial resolution analysis by SfM-MVS of the
morphological changes of the coast in El Picaflor beach, Punta Indio,
Buenos Aires, Argentina
Authors: Francisco Aldo Cellone, Luciano López, Guido Bacino, Irene Brayer
Abstract: The coast of Punta Indio, in the middle estuary of the Río de la Plata, has been affected in recent decades by a strong erosional process. In particular, it has been detected that the erosive rates on the Picaflor beach are higher than those on the rest of the coast. For this reason, the coastal infrastructure, the natural environment, and the tourist activities are compromised. The aim of the work is to carry out an analysis of the coastal hydrodynamics and the evolution of the coastline with high temporal and spatial resolution. A study of coastal hydrodynamics and surveys using SfM-MVS photogrammetry were carried out. From the analysis of the 2D and 3D information, an average value of shoreline retreat of -0.71 m/a was obtained, and a predominance of erosion over accumulation was observed along the entire beach. The triggering factors of the erosive processes may be due to human alterations in the natural environment. Wave impact can have a significant contribution to erosion, directly proportional to the time of wave impact and would occur mainly under medium-intensity wave conditions. The heterogeneities recorded in the beach erosional rates may be due to variations in the general orientation of the coast as well as in the profile of the beach and to differences in land use.
PubDate: 2023-02-13
Issue No: Vol. 80, No. 1 (2023)
- Lithospheric structure in the Pampean flat-slab using inversion of
receptor functions and dispersion curves in la Sierra de San Luis
Authors: Marina Escobares, Silvana Liz Spagnotto, Augusto Francisco Morosini, Marcos Ariel Sánchez, Andrés Nacif
Abstract: At this work, we obtained Vs velocity models from the joint inversion of receptor functions (RF)
and dispersion curves. To obtain the RF, we started from earthquakes of magnitudes greater
than Mw 5.8 recorded by the UNSL broadband seismological station. We classified the
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receiver functions according to the azimuth of the earthquakes and separated them into two
sectors. The classification was as rays cross relatively different areas of the crust, lithospheric
and shallow sublithospheric structures. The main crustal and upper mantle discontinuities
below the station have a change in depth and velocity according to the azimuth of the ray. The
depth of the Mohorovicic discontinuity was the same on both sides (from 42 to 45 km), but not
a discontinuity 20 km deep, which is present on the east side and could be attributed to a
boundary between rheologically distinctive crusts and probably developed in different orogenic
cycles. This study makes it possible to detect an important rheological change (10 km deep),
which can be attributed to the detachment zone (decollement) related to the structuring of the
uplift front of la Sierra de San Luis. It is important to note the decrease in wave speed between
60 and 100 km depth. This area would be linked to the development of an anomaly in the
mantle that produced an arc volcanism associated with the flat subduction of the Nazca plate
in the Andean foreland.
PubDate: 2023-02-13
Issue No: Vol. 80, No. 1 (2023)
- Deformational structures of the northern portion of the footwall of the
Guacha Corral shear zone, Sierras de Córdoba
Authors: Stefania Radice, Fernando J. D´Eramo, Emiliano V. Marani, Lucio P. Pinotti, M. Natalia Maffini, M. Alejandra Boffadossi, M. Eugenia Muratori, Manuel Demartis, Jorge E. Coniglio
Abstract: The northern part of the footwall of the Guacha Corral shear zone in Sierra de Comechingones is dominated by a migmatic sequence classified as metasedimentary and mafic metatexites. The contacts between both lithologies are generally transitional and are characterized by different morphologies depending on the percent of melt. The results obtained from the structural analysis of migmatites allow us to determine a progressive succession of non-coaxial and compressive deformational events in the study area. The main deformational event would be linked to the occurrence of partial melting processes that generated migmatization in the footwall at conditions of 650-700 °C and 0.5 a 0.6 GPa. Anatexis would have occurred simultaneously with ductile mylonitization at amphibolite facies along the Guacha Corral shear zone in the hanging wall during the Famatinian Orogeny. In the footwall, this shear zone generated a textural and mineralogical reworking of the migmatic rocks, expressed as narrow shear belts with compressive and inverse kinematics. Dynamic metamorphism within this zone occurred under greenschist facies conditions (400-450 °C and 0.2-0.4 GPa). The progressive cooling of footwall rocks from ~700 °C at 475 Ma to ~500 °C at 400 Ma, integrated with petro-structural study allowed us to document a long history of deformation activity related to the Guacha Corral shear zone in this portion of Sierras Pampeanas.
PubDate: 2023-02-13
Issue No: Vol. 80, No. 1 (2023)
- Cerro Granito Granitoids: lithology, 40Ar/39Ar geochronology and regional
correlations
Authors: Monica Graciela Lopez de Luchi, Eduardo Rossello, Carmen I. Martínez Dopico, Gilles Ruffet
Abstract: Cerro Granito is an oval shaped hill, with a maximum height of 890 m above sea level, which outcrops in the middle of Jurassic layers as an anticlinorium, marking out the regional line of the Huincul Ridge that subdivides the Neuquén basin in two. The core of Cerro Granito is composed mainly of (1) biotitic-amphibolic gray granodiorites, (2) biotitic-epidotic light gray monzogranites, (3) biotitic porphyritic pinkish gray leucogranites (4) biotitic porphyritic gray tonalites and (5) decametric dikes of gray andesites, slightly green purple, with an approximate NW-SE strike. From the central sector and towards the NE, intense fracturing, and a predominance of aplopegmatitic dikes trending NNE are recognized. In the present work, new petrographic data of five magmatic facies are provided, two of which were radiometrically dated. The 40Ar/39Ar age older than 281 Ma for the amphibolic biotitic granodiorite, together with the existence of a porphyritic biotitic tonalite facies, reinforce the proposal of linking the plutonic units of Cerro Granito with the Chachil Plutonic Complex. This igneous event would be equivalent to the one exposed in the Chilean Coastal Batholith and pre-dates the climax of the Choiyoi event. After approximately 90 Ma, the next magmatic record corresponds to an andesitic dike, which confirms that the final exhumation of the granitoids was after 190 Ma (Sinemurian - Pliesbachian) and, from all points of view, prior to the deposition of the marine sequences of the Toarcian Lajas Formation.
PubDate: 2023-02-13
Issue No: Vol. 80, No. 1 (2023)
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