1.03.01. Andean Geology

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https://repositorio.sernageomin.cl/handle/0104/26202
Andean Geology es una revista revisada por pares que publica investigaciones y artículos de revisión de alta calidad sobre geología y ciencias relacionadas, con un enfoque en América del Sur, América Central, la Antártida y especialmente los Andes. La revista acepta contribuciones en español o inglés y está interesada en conjuntos temáticos de artículos. También publica trabajos de Paleontología sistemática, siempre que se enfoquen en la importancia cronoestratigráfica, paleoecológica o paleogeográfica de los taxones descritos.

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    Petrography and provenance of the Grupo Morro Solar sandstones (upper Berriasian-Valanginian) of Lima (77°01’ W, 12°10’ S) : Geodynamic and paleogeographic implications
    Autor(es):
    Alván, Aldo A.; Criales, Astrid H.; Bernuy, Augusto
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.280-305
    Número de Serie:
    2
    The sedimentary record of the continental margin of Lima, Peru (77°01’ W, 12°10’ S) plays a significant role in understanding the regional geology given its location along the westernmost part of a siliciclastic platform developed during the Early Cretaceous, prior to the Andean orogeny. In this contribution, the mineral composition of 20 samples of litho-quartzose sandstones and quartzose sandstones from the Salto del Fraile, La Herradura, and Marcavilca formations of the Morro Solar Group (Upper Berriasian-Valanginian) is examined by using the Gazzi-Dickinson method to shed light into sediment provenance. Results reveal that the sediments of the Morro Solar Group accumulated after the exhumation of a recycled orogen located in the Eastern Cordillera, which includes the Marañón Metamorphic Complex. This orogen is interpreted to be composed of sedimentary and volcanic rocks of Paleozoic and Triassic age. A minor provenance of metamorphic Precambrian rocks from the Amazon Craton is not totally discarded.
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    Curie isotherm in Central Chile : Gradient and geothermal flow analysis in the continental zone
    Autor(es):
    Cáceres A., David
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.268-279
    Número de Serie:
    2
    This study explores the relationship between magnetometry and thermodynamics in heat transfer within the Earth’s crust in central Chile. The radially averaged power spectrum analysis of magnetic data was used to determine the Courie point depth, from the city of La Serena (~30° S) to San Fernando (~34.5° S), and from the Andes Mountains (~70.5° W) to approximately 82° W. Offshore, the Curie isotherm shows an average depth of 22 km and is tentatively correlated with the Juan Fernández Ridge. Inland, significant differences are observed; on the one hand, the Curie isotherm reaches shallower depths, averaging 12 km from Ovalle to Illapel; on the other hand, a deeper zone, at approximately 39 km depth, is identified northeast of Valparaíso. An empirical equation is then employed to calculate the thermal conductivity of the rocks and determine the geothermal heat flow. The average geothermal gradient in the continental region of central Chile is 20 °C/km, with a maximum of 45 °C/km in the locality of Canela. In the Metropolitan Region of Santiago, the average heat flow is 50 mW/m², with a maximum of 57 mW/m² in the commune of Paine. The results obtained are consistent with a previous radiogenic study in the Santiago basin, suggesting that the method used in this research constitutes a novel technique that can be replicated to other regions of the country. The information provided in this contribution can be utilized for the design of geothermal energy systems and to improve the understanding of geological processes in the region.
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    Study of the Abitagua Batholith in the Sub-Andean Zone of Ecuador, using velocity models from seismic tomography
    Autor(es):
    Chalco, Dennys; Araujo, Sebastián; Balcázar Loaiza, Santiago; Ruiz, Mario
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.254-267
    Número de Serie:
    2
    The Abitagua Batholith is a Mid to Late Jurassic intrusive body in the Sub-Andean Zone of Ecuador. This batholith is theorized to be the source of alluvial gold in the Amazon rivers that drain from it, although due to its difficult access and location along protected areas it remains largely unexplored. This work aims to study the Abitagua Batholith using seismic velocity models that provide absolute and relative P-wave velocity and Vp/Vs ratios based on the inversion of the earthquake travel-time data recorded by the Ecuadorian survey networks RENSIG, RENAC, and ROVIG, and some stations of the Colombian Geological Service near the border with Ecuador. We use the absolute and relative P-wave velocity tomography models to describe the batholith’s vertical and horizontal components. The resolution in our velocity models displays values larger than 0.8 and cover all the crust and the upper mantle to depths of seventy kilometers. We identify two velocity anomalies, possibly associated with magmatic reservoirs under the batholith that, together with hypocenter data, suggest more recent magma intrusions. We conclude that these magmatic bodies relate to potential gold-bearing intrusions, which seem to concentrate near the transition zone between the negative and positive velocity anomalies, five kilometers north of the Jatunyaku River.
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    Assessing permafrost structures in headwater aquifers : An example from the Ojos del Salado massif, Andes mountains
    Autor(es):
    Ruiz-Pereira, Sebastián; Leray, Sarah; Marti, Etienne; Beriain, Eneko; Suárez, Francisco; Yánez, Gonzalo; Nagy, Balázs
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.239-253
    Número de Serie:
    2
    In arid regions, the hydrological evolution of high mountains is a matter of concern under current climate forcing and increasing freshwater demand. Mountain surface hydrology is key for water storage and release and determines the amount and quality of freshwater supply for downstream ecosystems, so predicting their evolution under climate change scenarios requires detailed spatial data on subsurface hydrodynamic properties.In the present contribution, a semi-direct characterization of periglacial areas and permafrost zonation was carried out along an altitudinal transect at the Ojos del Salado massif (27°06’ S; 68°32’ W) between 4,550 and 5,830 m a.s.l. by integrating geophysics (electrical resistivity tomography; ERT) and decade-long surface temperature datasets. ERT data evidence a permafrost altitudinal gradient from a negative control at 4,550 m a.s.l. up to consistent (>100 kΩm) permafrost-related resistivities above 5,260 m a.s.l. These resistivity structures are assumed to act as confining layers, accounting for thicknesses of 8 and 25 m at the Atacama (5,260 m a.s.l.) and Tejos (5,830 m a.s.l.) sites, respectively. The geophysically determined permafrost distribution is coherent with temperature-based Frost number estimates at all sites surveyed.The results presented here are required for aquifer parameterization under short- and mid-term hydrological connectivity changes, being therefore relevant for a better understanding of groundwater storage dynamics upon permafrost degradation in arid regions.
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    Microscopic analysis of garnet morphology in Santander Massif sillimanite-cordierite hornfels : Constraints on crystal nucleation and growth
    Autor(es):
    Chacón-Ávila, Carlos Alberto; Luna-Mendoza, Carolina; Ríos-Reyes, Carlos Alberto; Castellanos-Alarcón, Óscar Mauricio; Estupiñán-Durán, Hugo Armando; Zuluaga-Castrillón, Carlos Augusto; Jiménez-Triana, Carolina
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.221-238
    Número de Serie:
    2
    Understanding crystal growth in high-grade metamorphic rocks provides unique insights into metamorphic processes and geological evolution. This study investigates the petrographic characteristics, crystal growth mechanisms, and chemical composition of garnets from the Santander Massif of Colombia, a region known for its high-grade metamorphic rocks. Petrographic analysis reveals a discrepancy between anhedral to subhedral garnet forms on an outcrop scale and euhedral forms in hand samples, which may be due to limited or heterogeneous pressure and temperature conditions or spatial constraints at the outcrop scale, and more homogeneous conditions at the hand sample scale. Advanced techniques, including scanning electron microscopy (SEM) and atomic force microscopy (AFM), show that garnet crystals predominantly exhibit trapezohedral {211} and dodecahedral {110} faces, indicating different growth mechanisms. Electron probe microanalysis (EPMA) reveals a homogeneous chemical composition in the garnets, predominantly almandine with minor pyrope, grossular, and spessartine components. The application of cathodoluminescence (CL) and differential interference contrast (DIC) microscopy provides additional insights into mineral characteristics and growth features, contributing to a comprehensive understanding of garnet formation. These findings offer new valuable perspectives on the metamorphic conditions and processes of the rocks that form the Santander Massif.
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    Biostratigraphic implications of Kallidontus nodosus Pyle and Barnes in the Ordovician of the Eastern Cordillera, Argentina
    Autor(es):
    Voldman, Gustavo G.; Vaccari, N. Emilio
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.203-220
    Número de Serie:
    2
    A biostratigraphic reevaluation of the conodont faunas of the Acoite Formation at the La Ciénaga de Purmamarca, northwestern Argentina, is presented here to constrain its depositional age and improve its regional correlation. The new conodont assemblage, consisting of 636 elements, includes Balognathidae indet., Drepanodus arcuatus, Drepanoistodus pitjanti, D. cf. andinus, D. sp. A, Gothodus andinus, Kallidontus nodosus, Paroistodus sp., and Zentagnathus argentinensis. These species were obtained from the same beds sampled by previous authors, who attributed varying ages to the conodont assemblage. Of special importance is the record of K. nodosus, which allows for precise correlation of the lower levels of the Gothodus andinus Zone with the early Floian Prioniodus elegans Zone (Fl 1). This finding is consistent with the graptolite and trilobite data available at the La Ciénaga de Purmamarca, and it raises caution regarding the taxonomic determination of Baltoniodus triangularis, the index fossil for the Lower-Middle Ordovician Series boundary in other stratigraphic sections of the Acoite Formation along the Eastern Cordillera.
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    New environmental perspectives on the Jurassic Cuyo and Lotena groups, Neuquén Basin, Argentina, based on a multi-proxy approach
    Autor(es):
    Chalabe, Amira Celeste; Martínez, Marcelo Adrián; Olivera, Daniela Elizabeth; Zavala, Carlos; Lescano, Leticia
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.169-202
    Número de Serie:
    2
    With the main goal of reconstructing the environmental conditions of the Cuyo and Lotena groups during the Middle Jurassic period in the south of the Huincul Arch (central western Argentina), a multi-proxy approach, considering pollen, spores, algae, fungal remains, palynofacies, molluscs, ichnology, X-Ray diffraction, and petrographic and lithological analyses, was carried out. This work suggests a lacustrine environment for the Challacó Formation, shallow marine conditions influenced by strong fluvial discharges for the Lajas, Bosque Petrificado and Lotena formations, and an age no older than latest Early Bajocian for the uppermost part of the Lajas Formation.
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    Late Cretaceous mosasaurids of northeastern Brazil : A summary of their record and a paleobiogeographical survey
    Autor(es):
    Candeiro, Carlos Roberto A.; Foffa, Davide; Brusatte, Stephen L.; Fernandez, Marta; Diniz-Filho, José Alexandre; Vidal, Luciano S.; Dias, Tamires do Carmo; Lima, Isabela; Silva, Tatiane
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.150-161
    Número de Serie:
    1
    The coastal region of northeastern Brazil holds one of the most important records of mosasaurids from the Late Cretaceous of South America. Analysis of these discoveries allowed us to create a picture of the composition of the fauna, as well as the diversity and paleobiogeography of these clades. In the region, the mosasaurid fossils are contained in Cenomanian to Maastrichtian geological units of epicontinental marine origin, in the Cotinguiba (Sergipe-Alagoas Basin), Alcântara (São Luís Basin), Itamaracá (Paraíba Basin), Calumbi (Sergipe-Alagoas Basin), and Gramame (Paraíba Basin) formations. Paleogeographic data corroborate that these deposits represent low-latitude equatorial environments. The Brazilian fauna is represented by fourteen taxa from one family (Mosasauridae), two subfamilies (Mosasaurinae: Prognathodontini, Globidensini and Mosasaurini; Plioplatecarpinae: Plioplatecarpini), and some indeterminate mosasaurid specimens. Mosasaurids from the northeastern region of Brazil resemble Late Cretaceous marine reptiles from western Africa (Angola, Congo, and Morocco), suggesting faunal continuity in the seaway that bridged these areas. The study of this marine fauna is crucial to understanding the evolutionary and paleobiogeographic history of the group during the opening of the South Atlantic Ocean.
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    Thermal resetting of the Early Cretaceous volcanic rocks of Low Island, South Shetland Islands, Antarctica
    Autor(es):
    Bastías Silva, Joaquín; Silva, Paula; Inzulza, Sebastián
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.135-149
    Número de Serie:
    1
    The Albatross Hill Member is an Early Cretaceous volcanic and volcaniclastic succession, which overlays the sedimentary rocks of the Pencil Beach Member and together constrain the Cape Wallace Beds in Low Island, South Shetland Islands, Antarctica (63°15’ S, 62°12’ W). Along with other coeval volcanic units present in nearby Livingston Island, the Albatross Hill Member represents the first products of the magmatic arc after its resumption during the Cretaceous. The Albatross Hill Member is dominated by dacites with a widespread occurrence of secondary minerals, of which the latter occur partially replacing phenocrysts, filling veins and veinlets and, to a lesser degree, in the groundmass/matrix. 40Ar/39Ar analyses on plagioclase phenocrysts from two biotite dacites yield plateau ages between ~111 and 109 Ma, which are ~31 to 26 Myr younger than the 40Ar/39Ar groundmass plateau ages for the same samples. We suggest that this difference is associated with the presence of secondary minerals, which greatly affected the phenocrysts of the sequence and disturbed the 40Ar/39Ar analyses.
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    The Isomass Method : Verifying conserved elements in geochemically open geological processes
    Autor(es):
    Calderón Díaz, Sergio; Townley, Brian; Stanley, Cliford R.
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.117-134
    Número de Serie:
    1
    This contribution presents the Isomass method, aimed at verifying the conserved behaviour of elements in geochemically open systems even when the parent rock composition is lacking. The method estimates system size changes for a specific element that is assumed to be conserved by calculating the amount of material transfer for each of the other elements, thus verifying (or rejecting) the initial assumption. By analysing the calculated amount of material transfer (or daughter system size ratios), additional conserved elements (if any) can be identified. The Isomass method is used here to evaluate a set of numerically generated samples whose element concentrations derived after mass additions and losses are assigned to daughter rocks. In addition, it is also applied to three real datasets that examine soil formation, magmatic fractionation in a komatiitic lava, and hydrothermal metasomatism. The method is capable of: (1) determining which elements confirm their conserved behaviour for a variety of geological environments; (2) identifying which other elements are conserved, added or lost; (3) calculating the amount of material transfer; and (4) providing a measure of the extent of the conserved character of elements. The method illustrates that the whole-rock compositions of parent and daughter samples do not represent the actual material transfer that occurred during geochemically open geological processes, as conserved elements may appear enriched or depleted, and non-conserved elements may have concentrations that do not reflect the actual material transfers that took place. The Isomass method is therefore a proper and valuable tool for the verification of conserved elements and the investigation of material transfer in rocks.
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    Driving factors on wetland water area changes in the arid region of central-western Argentina (32° S) during the last two decades
    Autor(es):
    Rios, Leonardo D.; Moreiras, Stella M.; De Porras, M. Eugenia; Gomez, María L.; D´Ambrosio, D. Sabina
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.101-116
    Número de Serie:
    1
    The wetlands along the Leyes-Tulumaya stream in central-western Argentina (32° S) are part of an old, inactive paleo-stream bed of the Mendoza River. These wetlands have been drastically impacted during the last 20 years, reducing their water areas or even completely drying out. The causes and driving factors of this major environmental impact have yet to be explored. Understanding the interaction of the different natural and/or anthropic factors influencing these wetland area changes in the recent past is imperative to apply proper management and conservation plans. In this contribution, the water areas of three lakes along the Leyes-Tulumaya stream are mapped using a GIS environment from satellite imagery to track variations in the last two decades. Assuming that natural variables have been forcing these environmental changes, annual precipitation, soil moisture, evaporation indexes, and the stream flow of the Mendoza River, are analyzed. Changes in the lake water areas along the Leyes-Tulumaya stream are, however, hardly explained due to these natural variables, so anthropogenic factors might have been key and thus need to be further explored.
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    The orbicular granodiorite of Recoba Hill in the North Patagonian Batholith
    Autor(es):
    Soto, Aníbal; Hervé, Francisco; Calderón, Mauricio; Gregorina, Gianfranco
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.86-100
    Número de Serie:
    1
    A small body of orbicular granodiorite crops out on the Recoba Hill, immediately east of the town of Chaitén, in the mainland area called Chiloé continental, in southern Chile. The rock comprises cm-sized igneous cores with a single shell of fine-grained plagioclase-quartz-K-feldspar assemblages. It is hosted in a Miocene granodiorite, and it is crosscut by aplite and mafic dikes. No other mention of orbicular rocks has to date been reported for the >1,000 km long North Patagonian Batholith, suggesting that the conditions necessary for their formation were infrequent. Thermobarometric determinations indicate pressures lower than 2 kbar (less than 6 km depth) for its formation, a level much shallower than the estimated source depth of the older rocks of the batholith.
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    Phreatomagmatic mafic monogenetic volcanism related to salars : Two case studies from the Puna plateau, Argentina
    Autor(es):
    Orellana, Daiana; Grosse, Pablo; Guzmán, Silvina R.; Báez, Walter A.; Apaza, Facundo D.
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.63-85
    Número de Serie:
    1
    Mafic monogenetic volcanoes and salt pans or salars are ubiquitous in the Puna plateau of the Central Andes. In this contribution, we present the study of two Pleistocene mafic monogenetic centers, the Panqueque center emplaced on the western margin of the Salar de Arizaro and the Medialuna center emplaced within the same salar. Both centers had initial explosive phreatomagmatic activity that progressed to explosive magmatic (Strombolian) activity and ended with effusive activity. However, differences in magma flux, bedrock composition, and magma-water interaction resulted in deposits with different volumes and characteristics and, consequently, varied landforms. The magma batch that formed the Panqueque center (0.098 km3) passed through a heterogeneous bedrock marked by the transition between clastic and evaporitic deposits. Variable magma-water interaction generated two stages of phreatomagmatic activity, producing first a tuff ring or rings and then tuff cones, followed by Strombolian activity. Activity culminated with two phases of volumetrically dominant lava flows. In contrast, the much smaller Medialuna center (0.00016 km3) was formed by a magma batch that ascended through the mostly homogeneous halite-rich core of the salar. The magma interacted with water-saturated evaporitic sediments and fragmented close to the surface, generating a small asymmetric tuff ring. A minor final stage of magmatic activity consisted of ballistic fall activity and a lava cap at the conduit. The Panqueque center pyroclastic deposits do not show any specific feature that alludes to the salar environment, possibly because they formed at the salar margin where alluvial clastic sediments are abundant. Conversely, the Medialuna center deposits do have a few features, namely the lack of lithics, the possible total disintegration of the mechanically weak and friable evaporites into fine to very fine ash particles, and the presence of aggregates cemented by gypsum/salts that may be diagnostic of salar-related phreatomagmatic activity.
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    The brachiopod Kvania, a biostratigraphic marker across the Cambrian-Ordovician boundary in Andean Gondwana
    Autor(es):
    Benedetto, Juan L.
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.47-62
    Número de Serie:
    1
    The plectorthoid brachiopod Kvania is widely distributed in Upper Cambrian and Lower Ordovician rocks of the Central Andean basin of northwestern Argentina and southwestern Bolivia. In this contribution, Kvania lariensis Benedetto is reported for the first time in the Eastern Cordillera (Quebrada de Humahuaca area) of northwestern Argentina. Studied material comes from the Alfarcito Member of the Santa Rosita Formation (Santa Victoria Group) of well constrained earliest Tremadocian age (Tr1). The presence of Kvania lariensis in different localities of the Altiplano-Puna region and the Eastern Cordillera of Bolivia and Argentina allows proposing this species as a reliable biostratigraphic marker for the lowermost Ordovician of the region. On the basis of the phylogenetic hypothesis supporting the Protorthisina-Kvania-Gondwanorthis lineage, four phylozones are recognized across the Cambrian-Ordovician boundary. The basal member of the lineage is Kvania primigenia, which co-occurs with Parabolina (Neoparabolina) frequens argentina, is proposed here as a biostratigraphic marker for the upper Furongian (Stage 10). The base of the time slice Tr1 is indicated by the first appearance of Kvania lariensis, which is almost time-equivalent to the Jujuyaspis keideli trilobite biozone, whereas the descendent species Kvania azulpampensis is almost coeval with the Kainella andina trilobite biozone. Gondwanorthis calderensis calderensis, a more derived member of the lineage, indicates the upper part of the lower Tremadocian (Tr1), and is equivalent to the Kainella meridionalis trilobite biozone. The specimens of Kvania lariensis from the Alfarcito Member provide additional information about its phenotypic variablity, confirming the trend of increasing costellae number through ontogeny observed in the type material, and also corroborate that the lineage as a whole experienced a defined evolutionary trend to increasing both shell size and costellae number.
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    Lithofacies architecture within an intra-arc environment : A case study from the Permian-Triassic magmatic arc in the Chilean Frontal Cordillera (30-30.5° S)
    Autor(es):
    Castillo, Diego; Murillo, Ismael; Oliveros, Verónica
    Fecha de Publicación:
    2025
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.1-46
    Número de Serie:
    1
    In the Chilean Frontal Cordillera between 28.5 and 30.5° S, two volcano-sedimentary succesions of Late Guadalupian to Middle Triassic age croup out: the El Tapado (Late Guadalupian-Lopingian) and Guanaco Sonso (Late Lopingian-Middle Triassic) formations, representing the westernmost exposures of the Choiyoi Group and post-Choiyoi magmatism. Recently, these two units have been characterized in detail, shedding light into the tectonic and climatic context of the late stages of the Choiyoi magmatism, and, more generally, the geology of intra-arc successions in the southwestern Gondwana margin. In this work, we present a stratigraphy and lithofacies analysis of three stratigraphic sections studied in the La Laguna sector (30-30.5° S), comprising rocks of the El Tapado and Guanaco Sonso formations. The former is dominated by caldera-related rhyolitic to dacitic ignimbrites accumulated in depocenters associated with the extensional activity of major structures. Lacustrine and fluvial-alluvial deposits interbedded in this rock unit were mainly controlled by volcaniclastic input and subsidence dynamics, and record the transition from relatively humid conditions to semi-arid or even arid conditions during the Late Guadalupian-Lopingian, consistent with regional paleoclimatic observations. On the other hand, the Guanaco Sonso Formation presents mainly intermediate, proximal (near-vent) volcanic products that denote a varied volcanism in terms of composition and eruptive style, likely controlled by structures and tectonics. We conclude the southwestern Gondwana margin sustained high-explosivity, silicic volcanism (El Tapado) that transitioned into a more varied, mainly intermediate volcanism (Guanaco Sonso). This activity ultimately gave way to the basaltic-andesitic to bimodal products that characterized the final part of the pre-Andean stage during the Triassic in this region.
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    CARLOS PÉREZ DE ARCE RAVEAU (1947-2024) 45 años de dedicación a la Geocronología
    Autor(es):
    Puig G., Alvaro
    Fecha de Publicación:
    2024
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.562-563
    Número de Serie:
    3
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    The geology and geomorphology of Seymour (Marambio) Island, Antarctica
    Autor(es):
    Acosta Hospitaleche, Carolina; Gelfo, Javier N.
    Fecha de Publicación:
    2024
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.559-561
    Número de Serie:
    3
    Montes, M.; Nozal, F.; Olivero, E.; Gallastegui, G.; Santillana, S.; Maestro, A.; López-Martínez, J.; González, L. and Martín-Serrano, A. (2019). Geología y Geomorfología de isla Marambio (Seymour). (Montes, M.; Nozal F. y Santillana, S., Eds.). Serie Cartográfica Geocientífica Antártica; 1:20.000, 1ª edición. Acompañado de mapas. Madrid-Instituto Geológico y Minero de España; Buenos Aires-Instituto Antártico Argentino, 300 p. 236 ilustraciones, 6 tablas, 2 mapas. ISBN 978-84-9138-083-2. EUR 60,00
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    The subaqueous felsic volcanism from the Upper Member of the Cordón de Lila Complex, Antofagasta region, northern Chile
    Autor(es):
    Niemeyer, Hans
    Fecha de Publicación:
    2024
    Fuente o Serie:
    Andean Geology
    Páginas:
    pp.547-558
    Número de Serie:
    3
    This contribution presents the study of an Ordovician subaqueous felsic succession, formed by the ~400 m-thick Upper Member of the Cordón de Lila Complex (CISL), northern Chile. From bottom to top, the succession starts with two dacitic sills that intruded into the sediments of the lowermost part of the Upper Member. Then, it is followed by a thick sedimentary deposit, two rhyolitic lavas, a volcanoclastic felsic breccia with pyroclastic clasts, and ends with a red rhyolitic lava. The first rhyolitic lava shows centimetric to metric folds with a north-northwestern vergence, evidence of flow in that direction. In the volcanoclastic breccia, an abundant pumice-and-fiamme-rich green matrix wraps around lithic clasts, giving the rock an eutaxitic texture at the outcrop scale. This matrix and texture evidence is characteristic of hot pyroclastic flows deposited under subaqueous conditions. The described section of the breccia is formed by four coarsening-up sequences, reflecting respectively four pulses of building up energy. The lack of internal erosional features points to a single and continuous explosive eruption. An accidental granite clast in the upper part of the breccia suggests a connection with a granitic body, possibly the Pingo-Pingo monzogranite. The geochemical character of the felsic succession is calc-alkaline. The tectonic setting diagram shows a within-plate setting for the succession. This suggests a shift from the arc position inferred for the Lower Member of the CISL to a forearc continental setting for the Upper Member of the CISL.