Repositorio Digital Sernageomin
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Phreatomagmatic mafic monogenetic volcanism related to salars : Two case studies from the Puna plateau, Argentina
No full textMafic 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.pp.63-8
Thermal resetting of the Early Cretaceous volcanic rocks of Low Island, South Shetland Islands, Antarctica
No full textThe 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.pp.135-14
Reporte y caracterización de remociones en masa en Isla Lemuy, comuna de Puqueldón, región de Los Lagos
No full textInforme Técnico -- Unidad Ejecutora: Dirección Regional Los Lagos, Puerto Varas21 p
The Isomass Method : Verifying conserved elements in geochemically open geological processes
Full text linkThis 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.pp.117-13
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)
Full text linkIn 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.pp.1-4
Áreas expuestas ante la amenaza de flujos e inundaciones, sector Cruz de Caña, comuna de Coquimbo, Región de Coquimbo
No full textInforme Técnico -- Unidad Ejecutora: Unidad de Asistencias Técnicas y Emergencias Geológicas y Unidad Peligros Geológicos y Ordenamiento Territorial61 p
Avances en la geología de la parte occidental de la isla Navarino (55° S), región de Magallanes y de la Antártica Chilena
Full text linkInforme Registrado IR-24-11359 p
CARLOS PÉREZ DE ARCE RAVEAU (1947-2024) 45 años de dedicación a la Geocronología
Full text linkpp.562-56
Evaluación de remociones en masa sector predio Casa Piedra, comuna de El Carmen, región del Ñuble
Full text linkInforme Técnico -- Unidad Ejecutora: Unidad de Asistencias Técnicas y Emergencias Geológicas, Concepción7 p
Opinión técnica de peligro geológico en predio Estero Las Leñas, comuna de Valdivia, Región de Los Ríos
No full textInforme Técnico -- Unidad Ejecutora: Unidad de Geología Aplicada, Dirección Regional de Los Ríos, Valdivia14 p