Late Holocene environmental and hydro-climatic variability inferred from a shallow lake record, blowout dunes, Argentinian western Pampas, South America

Isabel Vilanova, Alfonsina Tripaldi, Karsten Schittek, Leandro Rojo, Eduardo L. Piovano, Steven L. Forman, Esteban G. Jobbágy, Guillermo Heider, Jorge Chiesa
2 022
Journal of South American Earth Sciences Volume 116, June 2022
The Pampas plains of southern South America were predominantly dry, eolian-shaped landscapes, besides some interposed humid phases, during most of the late Pleistocene-Middle Holocene, evolving to humid-subhumid grasslands hosting an increasingly large number of shallow lakes in the late Holocene. These lakes proved to preserve in their sediments worthy evidence to interpret past environmental-ecological conditions, offering tools to analyze climatic variability and human impacts during the last millennia. This is the case of the shallow lake Primera Laguna, located in the western and driest edge of the Pampas. Here, we present a multiproxy study from this shallow lake with the aims of contributing to reconstruct its past stages, infer the climatic scenarios that drove its evolution, evaluate the potential anthropogenic role in these changes, and correlate/analyze this record with available data from other Pampean lakes. We analyzed a high-resolution palynological record, accompanied by macroscopic charcoal accumulation rates, C/N, C and N stable isotopes, magnetic susceptibility, and sediment geochemistry, of a 41-cm long sediment core, extracted from the deepest sector of the lake. An age-depth model based on AMS chronology indicates a preserved lake history for the past ∼1400 cal yr BP. Ecological and sedimentological interpretations allowed us to propose four main periods during this time lapse. For the first period (1375–1069 cal yr BP, 575–881 CE), the integrative interpretation indicates a very low shallow lake –mostly oligotrophic, alkaline, and clear water–, dominated by the accumulation of epiclastic silty fine sand from the surrounded eolian landscape and covered by xerophytic vegetation. In the second period, between 1069 and 738 cal yr BP (881–1212 CE), we inferred a trend to rising lake levels and mesotrophic conditions, and more pollen taxa than the previous period, and with lake margins dominated by cattails and sedges. The third period (738–193 cal yr BP, 1212–1757 CE) was characterized by more variable and lower lake levels compared to previous periods and more frequent desiccation processes at the lake margins. Then, during the fourth period (last 195 cal yr, 1757–2015 CE), there was a gradual transition towards a larger and more stable shallow lake with a deeper water column, and under a turbid state probably related to eutrophication. From the comparison between Primera Laguna record and the previously studied Nassau shallow lake, located in the same eolian landscape, we found a synchronic evolution, implying common drivers of change in terms of climatic variability and human impact. Correlation with shallow lakes from the more humid belt of the Pampas suggests widespread increases of water availability in the region since ∼1500 cal yr BP, variable/lower lake levels during ∼600–200 cal yr BP, and a shift to positive hydrological balances up to the present highstands.
Pub-Tripaldi-Late Holocene environmental and
https://www.sciencedirect.com/science/article/pii/S089598112200116X

On Pole Position: Causes of Dispersion of the Paleomagnetic Poles Behind Apparent Polar Wander Paths

Bram Vaes, Leandro C. Gallo, Douwe J. J. van Hinsbergen
2 022
JGR Solid Earth, Volume127, Issue4 April 2022
Paleomagnetic poles used to compute apparent polar wander paths (APWPs) are strongly dispersed, which was recently shown to cause a large fraction (>50%) of these poles to be statistically distinct from the APWP to which they contributed, suggesting that current statistical approaches overestimate paleomagnetic resolution. Here, we analyze why coeval paleopoles are so dispersed, using the paleopoles behind the most recent global APWP and a compilation of paleomagnetic data obtained from <10 Ma volcanic rocks (PSV10). We find that paleopoles derived from sedimentary rocks, or from data sets underrepresenting paleosecular variation (PSV), are more dispersed and more frequently displaced. We show that paleopoles based on a smaller number of paleomagnetic sites are more dispersed than poles based on larger data sets, revealing that the degree to which PSV is averaged is an important contributor to the pole dispersion. We identify as a fundamental problem, however, that the number of sites used to calculate a paleopole, and thus the dispersion of coeval paleopoles, is essentially arbitrary. We therefore explore a different approach in which reference poles of APWPs are calculated from site-level data instead of paleopoles, thereby assigning larger weight to larger data sets. We introduce a bootstrap-based method for comparing a collection of paleomagnetic data with a reference data set on the same hierarchical level, whereby the uncertainty is weighted against the number of paleomagnetic sites. Finally, our study highlights that demonstrating smaller tectonic displacements requires larger paleomagnetic data sets, and that such data sets can strongly improve future APWPs.
Pub-Gallo Leandro-On Pole Position-Causes
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022JB023953

Hallazgos paleoindios en el Rio Negro Medio: nuevos aportes de San Gregorio de Polanco, Uruguay

Hugo Gabriel Nami
2 022
Sociedades e Cultura Material, v. 35 n. 57 (2022)
La colonización y dispersión humana en ambos hemisferios del continente americano es uno de los temas antropológicos y arqueológicos más atractivos del proceso de poblamiento mundial. Estrictamente vinculado con esas investigaciones y la meta de aportar información adicional para ahondar en varios temas de tecno-morfología lítica Paleoindia, se dan a conocer un grupo de artefactos recientemente registrados en la zona de San Gregorio de Polanco, cuenca media del Río Negro, República Oriental del Uruguay. Los mismos posibilitan continuar ampliando la base de datos y profundizar en el conocimiento de diversos aspectos de la distribución de puntas Fell, litos discoidales y artefactos de filos retocados unifaciales correspondientes a los grupos tempranos regionales. Además, las observaciones presentadas permiten discutir las similitudes de esos vestigios con los encontrados en otros lugares de las Américas.
In the world colonization process, the peopling and human dispersion of the Americas is one of the most attractive anthropological and archaeological issues. Strictly linked to these investigations and the goal of providing additional information and delving into various themes of Paleoindian lithic techno-morphology, this paper reports a group of
artifacts recently recorded in the San Gregorio de Polanco area (middle Río Negro basin, Uruguay). They allow expanding the database and deepen our knowledge of various aspects of the distribution of Fell points, discoidal stones, and retouched unifacial edge artifacts corresponding to the early regional groups. In addition, the observations presented serve to discuss the similarities of these remains with those found in other places in the Americas.
Pub-Nami-Hallazgos paleoindios en el
https://bell.unochapeco.edu.br/revistas/index.php/rcc/article/view/7066

The birth of the Gondwanide arc: Insights into Carboniferous magmatism of the North Patagonian Andes (Argentina)

María Belén Yoya, Sebastián Oriolo, Pablo González, Florencia Restelli, Emiliano Renda, Florencia Bechis, Jerónimo Christie Newbery, Paulo Marcos, Ezequiel Olaizola
2 023
Journal of South American Earth Sciences Volume 123, March 2023
New geological, structural, and geochemical information was obtained for the late Paleozoic basement of the North Patagonian Andes. The studied rocks are mainly formed by foliated diorites and gabbro-diorites with a primitive continental arc signature, according to trace elements patterns. Similar petrological and structural characteristics, together with previously reported ages between ca. 330 and 323 Ma, permit the correlation of these rocks with plutonic bodies located in the North Patagonian Andes, North Patagonian Massif and Cordillera de la Costa of Chile, documenting the onset of Gondwanide subduction along the proto-Pacific margin of Gondwana between ca. 37 and 45°S. Geochemical and geochronological data, together with field evidence, suggest mafic magma replenishment during the construction of this large batholith. The presence of sheeted zones and magmatic fabrics allow to interpret pluton emplacement in a highly coupled system linked with a tectonically active setting, under pressure conditions of ca. 6 ± 1 Kbar.
Pub-Oriolo-The birth of the
https://www.sciencedirect.com/science/article/pii/S0895981123000366?ssrnid=4297…

The hydrocarbon potential of the offshore Talara Basin, Perú

Eduardo A. Rossello, Stephen P.J. Cossey, Guzmán Fernández
2 022
AndGeo vol.49 no.1 Santiago ene. 2022
La cuenca Talara costa afuera es la extensión occidental de su parte continental que contiene los campos petroleros productores de hidrocarburos desde mediados del siglo XIX en Perú. Esta se encuentra sobre la zona de subducción en el margen activo de los Andes, donde la placa oceánica de Nazca está subduciendo bajo la continental de América del Sur. La porción marina de la cuenca se evaluó utilizando un relevamiento sísmico 3D de alta calidad donde los horizontes de mapeo interpretados son discordancias dentro del Eoceno, así como del Paleoceno superior y el Cretácico Superior. Las posibles rocas generadoras son las lutitas marinas negras del Cretácico de la Formación Redondo (Campaniano), las calizas de la Formación Muerto (Albiano) y las lutitas marinas del Terciario temprano. Se propone que el objetivo principal de la exploración petrolera en alta mar sean las turbiditas de aguas profundas del Paleoceno/Eoceno originadas por aportes desde las tierras altas del noreste, creadas por la elevación compresiva de los Andes. Se considera que los principales sellos en el sector costa afuera sean lutitas de la Formación Lagunitos del Eoceno superior y las lutitas de la Formación Chacra, que también son sellos en el campo terrestre Litoral. El modelo de maduración térmica muestra que existen dos cocinas de hidrocarburos en la parte costa afuera de la cuenca, una en el norte y otra en el sur. La fuente probable del Cretácico alcanzó el inicio de la madurez (VR=0,63%) a una profundidad de 3.250 a 3.285 m (10.663-10.778 pies) entre 30 y 39 Ma (Eoceno tardío al Oligoceno). Es importante destacar que las rocas generadoras del Cretácico permanecen dentro de la ventana de petróleo al ingresar en el Eoceno tardío. Los estudios satelitales muestran una gran emanación actual de petróleo en alta mar, en la parte sur de la cuenca y la sísmica 3D presenta indicadores directos de hidrocarburos (DHI) en imágenes como puntos planos y reflectores de simulación de fondo (BSR). El modelado de cuencas sugiere que las vías de migración de los hidrocarburos habrían sido ascendentes hacia el este, en dirección a las trampas en tierra y, por lo tanto, habrían llenado primero las trampas en alta mar a lo largo de la vía de migración. Se concluye que la cuenca Talara costa afuera ofrece excelentes oportunidades de exploración en un área productiva probada donde se han identificado múltiples prospectos.
The offshore Talara Basin is the western extension of the hydrocarbon producing onshore fields since the mid-1800s area of Peru and is also located above the subduction zone of the active continental margin of South America. The offshore portion was evaluated using high quality 3D seismic where mapping horizons are all unconformities within the Eocene as well as the unconformities at the top Paleocene and top Cretaceous. Possible source rocks are the Cretaceous black marine shales of the Campanian Redondo Formation, the limestones of the Albian Muerto Formation, and the marine shales of the Paleogene. The primary target offshore is expected to be deep-water turbidites of Paleocene/Eocene age with a depositional source from the northeast from highlands created by the compressional uplift of the Andes. The main seals offshore are expected to be shales of the upper Eocene Lagunitos Formation and shales in the Chacra Formation, which are also seals in the onshore Litoral field. Thermal maturation modeling shows that two hydrocarbon kitchens exist in the offshore portion of the Talara basin, one in the north and another in the south. The probable Cretaceous source rocks reached the onset of maturity (VR=0.63%) at a depth of 3,250 to 3,285 m (10,663-10,778 ft) between 30 and 39 Ma (Late Eocene to Oligocene). Importantly, the Cretaceous source rocks stay within the oil window once they enter it in the late Eocene. Satellite studies show a large offshore present-day oil seep in the southern part of the basin and 3D seismic shows direct hydrocarbon indicators (DHIs) imaged as flat spots and bottom simulating reflectors (BSR). Basin modeling suggests hydrocarbon migration pathways would have been updip (to the east) into the onshore traps and would therefore have first filled the offshore traps along the migration pathway. We conclude that the Talara Basin offshore offers excellent exploration opportunities in a proven productive area where multiple prospects have been mapped.
Pub-Rossello-The hydrocarbon potential of
https://www.scielo.cl/scielo.php?pid=S0718-71062022000100001&script=sci_arttext…

Reconstructing paleoenvironmental and diagenetic dynamics from clay mineral assemblages in the Neogene Fiambalá Basin, NW Argentina

Virginia Valeria Reinoso Carbonell, Gilda Collo, Cecilia A. Wunderlin, Pablo H. Alasino, Patricia L. Ciccioli, Sebastian Rocher, Santiago Maza
2 022
Social Science Research Network, 06/2022, 24pp
Clay mineral characterization is a valuable tool for unraveling the evolution of continental sedimentary basins. The Fiambalá basin is a foreland basin located in the Southwest of the province of Catamarca (Argentina), on the flat subduction zone of the Nazca Plate below the South American. In order to characterize its paleoenvironment and post-depositional evolution, we carried out petrographic, X-ray diffraction (XRD) and scanning microscopy (SEM-EDS) studies in detrital and volcaniclastic samples from the Tambería, Guanchín and Rodados de la Puna Fms. Petrographic and XRD analyzes show a predominance of phyllosilicates, quartz, plagioclase, low proportions of feldspar and anhydrite, sporadic calcite, analcime, heulandite and hematite. In the fraction < 2 microns, minerals from the smectite and illite groups dominate, with lower proportions of chlorite and kaolinite. An analyzed tuff level only presents smectite in this fraction. The textural-compositional analyzes of SEM-EDS show that illite and chlorite have a detrital origin and 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 generated as a product of the alteration of 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. Paleogeothermal gradients of between 13 and 18 °C/km and between 8 and 11 °C/km, could be estimated considering thicknesses of ca. 4000 m and ca. 6400 m, respectively.
Pub-Ciccioli-Reconstructing paleoenvironmental and diagenetic
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4067330

¿Qué edad tiene el Núcleo Interno de la Tierra?

Augusto E. Rapalini
2 022
Temas De Biología Y Geología Del NOA, Vol. 12 Núm. 2 (2022)
La sismóloga danesa Inge Lehmann (Figura 1) descubrió en 1936 la existencia del Núcleo Interno (NI) de nuestro planeta (Lehmann, 1936). Tras casi 90 años de investigaciones, principalmente pero no únicamente, sismológicas, es mucho lo que se ha avanzado en el conocimiento del fragmento más recóndito del interior de la Tierra. A pesar de ello, lo que sabemos del NI es aún muy esquemático, preliminar y en muchos casos hipotético. Como sabemos desde la escuela primaria, el interior de la Tierra se divide, en base a su composición química, en Corteza (que puede ser continental u oceánica), Manto y Núcleo (Figura 2). Esta división fue descubierta por los pioneros de la Sismología a principios del siglo XX. Mientras que la Corteza tiene espesores que van desde cerca de los 70 km, en algunas grandes cadenas montañosas, hasta literalmente cero, en las cordilleras centro-oceánicas (o dorsales), el Manto se extiende hasta los 2900 km de profundidad…
Pub-Rapalini-Que edad tiene el
https://portalderevistas.unsa.edu.ar/index.php/ibigeo/article/view/3878/3767

Estructuración y evolución tectónica neoproterozoica-mesozoica del Uruguay mediante la aplicación de métodos geofísicos potenciales, con énfasis en la región central del Cinturón Dom Feliciano

Grado: Tesis Doctoral

Alumno: Pablo Andrés Nuñez Demarco  

Año: 2022

Directora: Dra. Claudia Beatriz Prezzi  

Codirectora: Dra. Leda Sánchez Bettucci

Consejera de Estudios: Dra. María Julia Orgeira

Resumen

El objetivo general de esta tesis es contribuir a la comprensión de la evolución tectónica proterozoica y mesozoica del Uruguay mediante el análisis integrado de relevamientos gravimétricos y magnetométricos terrestres, aéreos y satelitales y de datos geológicos y estructurales. En particular, se hace foco en el estudio de la evolución tectónica de la zona central del basamento cristalino del Uruguay, localizada en el departamento de Lavalleja (-33°40'34° S; -54°40'55°30' O).  Dicha zona, donde afloran la Formación Barriga Negra y los intrusivos graníticos de los complejos Polanco y Santa Lucía, comprende los sectores centrales de la cuenca aulacogénica mesozoica y del Cinturón Dom Feliciano y su límite con el Terreno Nico Pérez. En consecuencia, resulta clave para comprender la estructuración y evolución neoproterozoica y mesozoica del escudo uruguayo.  Para poder interpretar los datos magnetométricos y gravimétricos de manera rigurosa se llevaron a cabo revisiones detalladas de los diversos métodos y técnicas comúnmente aplicados al análisis de campos potenciales (análisis espectral, deconvolución de Euler, filtros). Estas revisiones llevaron a establecer correcciones e innovaciones metodológicas que permiten realizar simplificaciones en los procesos y obtener una mayor certidumbre en los resultados. En particular, con respecto al análisis espectral se definieron los límites de algunos de los parámetros requeridos para los cálculos de profundidad de fuentes magnéticas, estableciendo nuevos criterios y condiciones más rigurosas para su correcta aplicación. Asimismo, se desarrollaron diversos programas en Matlab y modelos para el testeo de los diversos métodos y técnicas y sus parámetros. A partir de los datos disponibles y de los relevados en el marco de esta tesis se trabajó en tres escalas diferentes. Se realizó una interpretación de gran escala de anomalías magnetométricas correspondientes a modelos globales. Se llevó adelante un estudio de escala regional, a partir de relevamientos aeromagnéticos y gravimétricos de la República Oriental del Uruguay. Finalmente, se trabajó a escala local con datos gravimétricos terrestres relevados en el departamento de Lavalleja, en combinación con nuevo mapeo geológico-estructural. El análisis de modelos globales permitió reevaluar las estructuras y límites del Cratón del Río de la Plata y cuencas suprayacentes. Las interpretaciones de escala regional y local posibilitaron establecer la estructuración paleoproterozoica, neoproterozoica y mesozoica del Uruguay. Se identificaron diversos enjambres de diques máficos paleoproterozoicos y mesozoicos y se determinó el rumbo e inclinación de algunas estructuras, así como su cronología. A partir de la integración de los resultados obtenidos se propone un nuevo modelo para la apertura del rift mesozoico, el cual involucra una zona de transferencia controlada por la reactivación de estructuras correspondientes al cinturón Dom Feliciano.

 

Abstract

Neoproterozoic-Mesozoic tectonic structuring and evolution of Uruguay through the application of potential geophysical methods, with emphasis on the Dom Feliciano Belt central region. The aim of this thesis is to contribute to the understanding of the Proterozoic and Mesozoic tectonic evolution of the Uruguayan shield through the integrated analysis of gravimetric and magnetometric, land, aerial and satellite surveys; and geological and structural data. In particular, it focuses on the study of the tectonic evolution of the central zone of the crystalline basement of Uruguay, located in the department of Lavalleja (-33°40'34°S; -54°40'55°30 'W). This area, where the Barriga Negra Formation and the granitic intrusions of the Polanco and Santa Lucía complexes crop out, comprises the central sectors of the Mesozoic aulacogenic basins, the Dom Feliciano Belt and its limit with the Nico Pérez Terrain. Consequently, it is key to understanding the Neoproterozoic and Mesozoic structure and evolution of the Uruguayan Shield. In order to interpret the magnetometric and gravimetric data in a rigorous way, detailed reviews of the various methods and techniques commonly applied to the analysis of potential fields (spectral analysis, Euler deconvolution, filters) were carried out. These reviews led to the establishment of corrections and methodological innovations that allowed simplifications in the processes and resulted in a greater certainty of the results. In particular, with regard to spectral analysis, the limits of some of the parameters required for the depth calculations of magnetic sources were defined, establishing new criteria and more rigorous conditions for their correct application. Likewise, various Matlab programs and models were developed for testing the various methods and techniques and their parameters. Based on the available data and those surveyed in the framework of this thesis, analysis and interpretations were carried out on three different scales. A large-scale interpretation of magnetometric anomalies corresponding to global models was performed. A regional scale study was carried out, based on aeromagnetic and gravimetric surveys of Uruguay. Finally, we worked on a local scale with land gravity data collected in the department of Lavalleja, in combination with new geological-structural mapping. The analysis of global models made it possible to re-evaluate the structures and limits of the Río de la Plata Craton and overlying basins. Interpretations on a regional and local scale made it possible to establish the Paleoproterozoic, Neoproterozoic and Mesozoic structure of Uruguay. Various swarms of Paleoproterozoic and Mesozoic mafic dikes were identified and the strike and dip of some structures, as well as their relative chronology, were determined. From the integration of the obtained results, a new model is proposed for the opening of the Mesozoic rift, which involves a transfer zone controlled by the reactivation of structures corresponding to the Neoproterozoic Dom Feliciano Belt.

 

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Caracterización de estructuras del manto superior en la región del extremo norte de la Península Antártica, mediante un análisis de las anomalías de velocidad sísmica

Zambrano, Oscar Marcos; Gulisano, Adriana Maria; Poma, Stella Maris; Ruocco, María Inés
2 022
Revista de la Asociación Geológica Argentina Volumen 79 (3) 03-2022
Se realizó una tomografía sísmica de inversión conjunta basada en los residuales de tiempo de viaje de las ondas P y S, con el objeto de estudiar la estructura sísmica del manto superior infrayacente a la dorsal Sur del Scotia y extremo norte de la Península Antártica. La misma se basó en registros sismográficos adquiridos en forma continua en estaciones sismológicas situadas en bases antárticas argentinas, procedentes del Proyecto Argentino Italiano para la gestión y mantenimiento de la red ASAIN: Antarctic Seismograph Argentinian ItalianNetwork. Las señales analizadas corresponden a eventos sismotectónicos locales de moderada a elevada mag-nitud ocurridos entre los años 2009 y 2019. Para la inversión discreta de los datos se implementó el método de regularización. Los resultados fueron evaluados mediante pruebas de resolución sintéticas. Se caracterizaron e interpretaron las estructuras sísmicas resueltas en las tomografías. El estudio se complementó mediante la estimación del módulo de Poisson y de la anomalía de velocidad acústica Vφ, lo cual permitió incorporar condiciones de restricción y por tanto de valoración a la interpretación de las tomografías. Se destaca la presencia de una anomalía negativa de velocidad de onda S en el sector de la cuenca Bransfield, en correspondencia con lo reportado por otros autores. Se interpreta como una región de la corteza y manto sometida a modificaciones del estado reológico (disminución de la rigidez, incremento de la incompresibilidad y aumento de la anelasticidad) causadas por un flujo térmico anómalo proveniente de una fuente localizada a mayor profundidad en el manto.
Characterization of upper mantle structures in the northern region of the Antarctic Peninsula, through an analysis of seismic velocity anomalies.
In order to study the seismic structure of the upper mantle underlying the South ridge of Scotia and the northern end of the Antarctic Peninsula, a joint inversion seismic tomography, based on the travel time residuals of the P and S waves, was carried out. It was based on seismographic records acquired continuously at seismological stations located in Argentine Antarctic bases, from the Argentine-Ita-lian Project for the management and maintenance of ASAIN: Antarctic Seismograph Argentinian Italian Network. The signals used correspond to local seismotectonic events of moderate to large magnitude that occurred between 2009 and 2019. The regularization method was implemented for the data discrete inversion. The results were evaluated by synthetic resolution tests. The seismic structures resolved with the tomographies were characterized and interpreted. The study was complemented by estimating the Poisson's modulus and the bulk sound velocity anomaly, which allowed the incorporation of restriction conditions and, therefore, assessment conditions in the interpretation of the tomographies. The presence of a negative S-wave velocity anomaly in the Bransfield basin sector is highlighted, in correspondence with that reported by other authors. It is interpreted as a region of the crust and mantle subjected to modifications of the rheological condition (decrease in rigidity, increase in incompressibility and increase in anelasticity) caused by an anomalous thermal flux from a source located deeper in the mantle.
Pub-Poma-Caracterización de estructuras del
https://revista.geologica.org.ar/raga/article/view/937/1612

Compositional, thermal, and tectonic contributions to the present-day elevation of the Central Andes and their forearc and foreland regions

Claudia Beatriz Prezzi, Federico Ibarra
2 022
Revista de la Asociación Geológica Argentina, Vol. 79 No. 1 (2022)
Los Andes Centrales están caracterizados por una serie de unidades morfoestructurales que presentan rasgos estratigráficos, es-tructurales y geomorfológicos distintivos. Destacan a simple vista las marcadas variaciones topográficas transversales al orógeno. Estudios teóricos sobre la elevación de los continentes han discretizado distintas componentes que contribuyen a la elevación obser-vada, prevaleciendo las contribuciones composicional y térmica. Investigaciones previas han demostrado que la región presenta una alta variabilidad en su composición cortical y estado termal. Estas variaciones podrían ejercer un control en la topografía regional, como ya ha sido señalado en un estudio previo del plateau Altiplano-Puna. En esta línea, este trabajo se propone investigar la re-lación entre la elevación actual de los Andes Centrales, su composición cortical y estado térmico. La contribución térmica esperada para cada unidad morfoestructural fue calculada en base al desarrollo de modelos térmicos 1D construidos utilizando datos de flujo térmico superficial. Con el objetivo de remover la contribución composicional de la corteza a la elevación observada, se calculó una elevación normalizada. Dicha elevación fue comparada con la contribución térmica estimada para evaluar su ajuste en cada unidad morfoestructural. El plateau Altiplano-Puna y la Cordillera Occidental muestran una buena correlación, sugiriendo que la composición y temperatura controlan su elevación actual. Por el contrario, en los otros sectores se observa un desajuste. El análisis detallado de cada unidad sugiere que los procesos tectónicos de subducción, las contribuciones del manto y los estados transitorios (i.e. no es-tacionarios, en desequilibrio) deben ser también considerados como contribuciones importantes al estado térmico y/o a la elevación actual.
The Central Andes of South America are characterized by different morphotectonic units that exhibit distinctive stratigraphic, structural, and geomorphic features. In particular, the topographic variations across the orogen are remarkably notorious. Theoretical studies on the elevation of continents have discretized distinct components that contribute to the observed elevation, among which the compositional and thermal contributions prevail. Previous investigations in the Central Andes have shown that the region presents a high variability in its crustal composition and thermal state. Such variations could exert a first-order control on the regional topography, as shown previously for the Altiplano-Puna plateau area. This study, therefore, sets out to investigate the relationship between the present-day elevation of the Central Andes, its crustal composition, and its thermal state. We first calculated the predicted thermal contribution for each morphotectonic unit based on 1D geotherms modeled on the basis of surface heat-flow data. In order to remove the compositional contribution of the crust, we then calculated a normalized elevation. This elevation was compared to the predicted thermal contribution to evaluate their fit in each morphotectonic unit. The Altiplano-Puna plateau and the Western Cordillera exhibit a good correlation, suggesting that composition and temperature control their present-day elevation. Conversely, the other areas show a significant misfit. The detailed analysis of the remaining morphotectonic units suggests that tectonic processes at the subduction zone, mantle contributions, and transient states need to be considered as important contributors to the present-day thermal state and/or elevation.
Pub-Prezzi-Compositional thermal and tectonic
https://revista.geologica.org.ar/raga/article/view/1527
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