Repositorio Digital Sernageomin
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Quaternary glaciolacustrine deposits around a Triple Junction site: Paleolakes at the foot of the Northern Patagonian Ice field (Argentina and Chile)
Get PDFThe area involved by the triple junction between the South American, Nazca and Antarctic plates activity was affected by Quaternary glaciations. Before 12,800 yrs BP an extended ice field occupied the top of the Patagonian Andes, irradiating glaciers towards the east and the west dominantly. Towards the east, the ice melted in piedmont lakes; towards the west, fjords melted into the Pacific Ocean. The Upper-Pleistocene climate amelioration caused the recession of those glaciers. Some piedmont lakes reversed their Atlantic outflow towards to the Pacific Ocean. The glaciers retreat caused the fluvial reactivations along crustal former faults that were located below the ice. The Patagonian ice field became therefore split into present Northern and Southern fields. At the second largest lake of South America, the Buenos Aires-General Carrera Lake, the water level dropped from about 500 m over present mean sea level to 230 m. Several glaciolacustrine deposits from this area are indicating significant variations caused by climatic changes, volcanism and tectonics, differing in spatial and temporal magnitudes. The triple junction activity involved subduction of the Chile Ridge below the continental South American plate, volcanic activity and faulting. During the glacier melting the Baker River captured three eastern-moving glacial systems towards the southwest, towards the Pacific Ocean. This rapid event is thought to occur 12,800 yrs BP. The lowering of these glaciolacustrine systems should be also interpreted in terms of the tectonic activity in the region and considering other processes operating in the lakes and within the watersheds.pp.94-10
Evaluación preliminar de peligro geológico en seis sitios de interés para la construcción de viviendas en la región de Los Ríos
Get PDFRevisor: Carlos Johnson N.15 p
Evaluación de peligro por remoción en masa en los sectores: Tres Espinos, Población Miramar y Agua de la Piedra, comuna de Valdivia, región de Los Ríos
No full textRevisor: Paola Ramírez ; Código de identificación interno: INF-LOS RIOS-07.202115 p
Minuta técnica : Tectónica y Zona de Falla Liquiñe-Ofqui en Los Andes Patagónicos
No full textMinuta técnica5 p
Campanian-Eocene dinoflagellate cyst biostratigraphy in the Southern Andean foreland basin: Implications for Drake Passage throughflow
No full textThe tectonic opening of the Tasmanian Gateway and Drake Passage represented crucial geographic requirements for the Cenozoic development of the Antarctic Circumpolar Current (ACC). Particularly the tectonic complexity of Drake Passage has hampered the exact dating of the opening and deepening phases, and the consequential onset of throughflow of the ACC. One of the obstacles is putting key regional tectonic events, recorded in southern Patagonian sediments, in absolute time. For that purpose, we have collected Campanian-Eocene sediment samples from the Chilean sector of Southern Patagonia. Using U-Pb radiometric dating on zircons and dinoflagellate cyst iostratigraphy, we updated age constraints for the sedimentary formations, and the hiatuses in between. Thick sedimentary packages of shallowmarine and continental sediments were deposited in the foreland basin during the early Campanian, mid-Paleocene, the Paleocene-Eocene boundary interval and the middle Eocene, which represent phases of increased foreland subsidence. We interpret regional sedimentary hiatuses spanning the late Campanian, early-to mid-Paleocene, mid-Eocene and latest Eocene-early Oligocene to indicate times of reduced foreland subsidence, relative to sediment supply. We relate these changes to varying subduction rates and Andean orogeny. Dinoflagellate cyst assemblages suggest that the region was under the influence of the Antarctic-derived waters through the western boundary current of the Subpolar Gyre, developed in the southwest Atlantic Ocean and thus argues for limited throughflow through the Drake Passage until at least the latest Eocene. However, the proliferation of dinoflagellate endemism we record in the southwest Atlantic is coeval with that in the southwest Pacific, and on a species level, dinoflagellate cyst assemblages are the same in these two regions. This suggests that both regions were oceanographically connected throughout the early Paleogene, likely through a shallow opening of a restricted Drake Passage. This implies a continuous surface-water connection between the south Pacific and the South Atlantic throughout the late Cretaceous-early Paleogene.pp.185-21
El Plutón sintectónico ordovícico El León, extremo suroccidental del Cordón de Lila, región de Antofagasta, Chile
Get PDFEl Plutón El León, ubicado en el Cordón de Lila, en la precordillera de la región de Antofagasta, Chile, es un cuerpo intrusivo que es parte del arco magmático famatiniano, en el borde suroccidental de Gondwana durante el Darriwiliano (Ordovícico medio). Presenta una marcada foliación magmática, se emplazó en la mesozona y se caracteriza por su composición granodiorítica, por tener grano grueso en su parte central y fino hacia los bordes y por alojar franjas concordantes métricas a decamétricas de rocas miloníticas. Adicionalmente, desarrolla una aureola metamórfica de contacto en su roca de caja. En este estudio se recolectaron cerca de 400 datos estructurales de la foliación magmática y milonítica en el plutón. La tendencia general de la foliación magmática es N77E junto con los indicadores cinemáticos S-C y con las micas con forma de pez de las milonitas indican que el movimiento de cizalle de estas fue de carácter normal-sinistral. Mediante el estudio de las microestructuras y evidencias petrográficas se identificó una continuidad de la deformación, desde el estado magmático, submagmático y de deformación en estado sólido de alta temperatura, hasta deformación sólida de baja temperatura. Durante su emplazamiento ocurrió un importante stoping magmático. Por otro lado, el desarrollo de milonitas al interior del plutón, con una deformación sólida de alta temperatura, sumado al carácter sinmagmático de la deformación y un componente vertical en el movimiento de cizalle son características que se ajustan a un modelo de emplazamiento del tipo pistón descendente para el Plutón El León. Su deformación marcaría la Fase tectónica compresiva Guandacol en el Cordón de Lila.pp.577-59
Reporte de visita técnica sector Villa Ignacio Carrera Pinto, Cañete-región del BioBío
Get PDFFecha de observaciones : 3 de junio de 20218 p
Peligro de remociones en masa en el sector sur de la región de Coquimbo
Get PDFInforme Registrado IR-21-88 ; Contiene Anexos: Anexo I.Resumen fotográfico del catastro de remociones en masa ; Anexo II.Resumen fotográfico del trabajo en terreno ; Anexo III.Campaña de terreno de verificacion de resultados ; Mapa de Peligros de Remociones en Masa en el sector sur de la región de Coquimbo, Escala 1: 250.000; Coordenadas: 70°19'O - 71°42'O / 30°43'S - 32°16'S107 p
Gold deposits in Chile
No full textUna revisión de yacimientos de oro y de metales básicos con oro, indican la existencia de por lo menos seis diferentes tipos de yacimientos, mayormente formados durante el Cenozoico con predominancia en el Mioceno. Los depósitos de edad mesozoica son de ocurrencia frecuente, pero menos relevantes en cuanto a tamaño y contenido de oro. Estos yacimientos hidrotermales están genéticamente vinculados con arcos magmáticos andinos, de orientación norte-sur, asociados a subducción. Debido a su relación con un magmatismo episódico migrante hacia el este, los yacimientos presentan una tendencia a distribuirse en diferentes franjas de orientación meridional, con una progresiva disminución de la edad de la mineralización hacia el este. Del análisis de un total de 82 yacimientos, la principal concentración de oro puede asignarse a depósitos tipo epitermal de alta sulfuración, pórfidos aurífero y pórfidos de cobre. Los yacimientos tipo epitermal de baja sulfuración, IOCG y mesotermal aparecen como menos importantes. Yacimientos cupríferos con mineralización aurífera subordinada constituyen una importante parte del total de la producción de oro en Chile. Los yacimientos tipo IOCG, y sobre todo los pórfidos cupríferos son y permanecerán como importantes recursos para contribuir a la futura producción de oro en el país. Los 82 depósitos con tonelaje y ley estudiados, representan un total de 11.662 t de oro contenido equivalente a 375 Millones de onzas excluyendo la producción pasada para los yacimientos que han sido explotados. Sin embargo, un número importante de yacimientos con gran tonelaje de metales básicos con oro subordinado (IOCG y pórfidos cupríferos) no publican su contenido de oro, por lo que las cifras acá entregadas podrían ser consideradas conservadoras. Estudios sistemáticos de geocronología, tipos de yacimientos y zonación, son necesarios para ampliar su entendimiento metalogénico, así como futuros resultados en exploración.pp.1-2
Mondaca Volcano lahar of December 3, 1762, Maule Region (35°28’S): one of the largest volcanic disasters in Chilean history
No full textThe Mondaca Volcano comprises a thick rhyolitic lava-field and a dome of similar composition, located near the Lontué River Valley headwaters in the northern part of the Southern Andes Volcanic Zone. It reaches a total volume of ~0.85 km3, and it is formed by 4 subunits, named Mondaca 1, 2, 3 and 4, which correspond to successive rhyolitic blocky lava flows, emitted from a rounded dome structure. They present well-preserved flow structures and, in the surroundings, restricted to the south and east of the dome, pyroclastic fall, as well as block and ash deposits are also exhibited. Downstream, along the Lontué River, a laharic deposit is recognized. The lahar was produced after the collapse of an ephemeral ~0.44 km3 lake generated after the river obstruction by viscous lavas, during the 1762 first eruptive phase. Proximal lahar facies are well exposed between 5 and 30 km from their source. The profuse agricultural activity has completely obliterated the lahar’s medium facies deposits along the Central Depression, but are well identified at the mouth of the Mataquito River, 180 km downstream, as a beige-coloured layer, interbedded within dark coastal beachsands. The identification of overflows and super-elevation deposits formed during the debris flow emplacement along the Lontué River valley, allows to determine a high flow mobility, with estimated velocities that locally reached up to 114 km/h. Petrographic characteristics in addition to chemical composition of lavas from the volcano, pyroclasts and juvenile blocks of the laharic deposit, indicate that all they correspond to high K calcoalkaline rhyolites with subalkaline affinity. These backgrounds, together with the geographical continuity between the lavas and debris deposits along the Lontué and Mataquito rivers, verify facies correlation and common origin as the result of the 1762 Mondaca Volcano eruption complex evolution. Although it was a mainly effusive eruption that could not be observed from Curicó, the collateral consequences would have been catastrophic over a vast area to the south of that city, and evidences one of the largest volcanic disasters in Chilean history. Probably because of the low density polulation at that time, the consequences could have been minor.pp.514-52