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Search Results: 1 - 10 of 5972 matches for " Alfredo Lahsen "
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Ages and geochemistry of Mesozoic-Eocene back-arc volcanic rocks in the Aysén region of the Patagonian Andes, Chile
Parada,Miguel A.; Lahsen,Alfredo; Palacios,Carlos;
Revista geológica de Chile , 2001, DOI: 10.4067/S0716-02082001000100002
Abstract: eighteen new radiometric ages (fourteen 40ar-39ar, four k-ar), combined with previously published ages, confirm the existence of three main extensional back-arc volcanic events, previously defined by stratigraphic relationships, in chilean patagonia (aysén region). these three events developed during the middle jurassic -early cretaceous (160-130 ma). cretaceous (114-75 ma), and eocene (55-46 ma). based on distinct geochemical data and sr-nd isotopic characteristics of the back-arc volcanic rocks collected north and south of 46°30's, two mesozoic-eocene magmatic domains are recognized: northern magmatic domain (nmd) and southern magmatic domain (smd). most analyzed basalts and intermediate volcanic rocks of the nmd have alkaline affinities and depleted to slightly depleted sr-nd isotopic values similar to those derived from an asthenosphere-dominated source. the smd mafic volcanic rocks have a subalkaline character and more enriched sr-nd isotopic signatures, comparable to those derived from a lithospheric source. the felsic volcanic rocks of the smd have lower end values and slightly higher initial 87sr/86sr ratios than the nmd felsic rocks, suggesting a larger crustal contribution in the magma sources. the geochemical and isotopic distinction between nmd and smd felsic rocks could be influenced by the presence of paleozoic metamorphic rocks as basement of the volcanic rocks of the smd. moreover, the compositional distinction between basalts of both domains may correspond to differences in magnitude of extension, the nmd being the one where the extension would have been greater and, consequently, the lithosphere thinner
Ages and geochemistry of Mesozoic-Eocene back-arc volcanic rocks in the Aysén region of the Patagonian Andes, Chile
Miguel A. Parada,Alfredo Lahsen,Carlos Palacios
Revista geológica de Chile , 2001,
Abstract: Eighteen new radiometric ages (fourteen 40Ar-39Ar, four K-Ar), combined with previously published ages, confirm the existence of three main extensional back-arc volcanic events, previously defined by stratigraphic relationships, in Chilean Patagonia (Aysén region). These three events developed during the Middle Jurassic -Early Cretaceous (160-130 Ma). Cretaceous (114-75 Ma), and Eocene (55-46 Ma). Based on distinct geochemical data and Sr-Nd isotopic characteristics of the back-arc volcanic rocks collected north and south of 46°30'S, two Mesozoic-Eocene magmatic domains are recognized: Northern Magmatic Domain (NMD) and Southern Magmatic Domain (SMD). Most analyzed basalts and intermediate volcanic rocks of the NMD have alkaline affinities and depleted to slightly depleted Sr-Nd isotopic values similar to those derived from an asthenosphere-dominated source. The SMD mafic volcanic rocks have a subalkaline character and more enriched Sr-Nd isotopic signatures, comparable to those derived from a lithospheric source. The felsic volcanic rocks of the SMD have lower eNd values and slightly higher initial 87Sr/86Sr ratios than the NMD felsic rocks, suggesting a larger crustal contribution in the magma sources. The geochemical and isotopic distinction between NMD and SMD felsic rocks could be influenced by the presence of Paleozoic metamorphic rocks as basement of the volcanic rocks of the SMD. Moreover, the compositional distinction between basalts of both domains may correspond to differences in magnitude of extension, the NMD being the one where the extension would have been greater and, consequently, the lithosphere thinner Edades y geoquímica de las rocas volcánicas del trasarco del Mesozoico-Eoceno en la región de Aysén de los Andes patagónicos, Chile. Diez y ocho nuevas edades radiométricas (catorce 40Ar-39Ar, cuatro K-Ar) junto con las ya publicadas confirman la existencia de tres eventos volcánicos (previamente definidos por relaciones estratigráficas) en la Patagonia chilena (Región de Aysén) durante el intervalo Mesozoico-Eoceno: Jurásico Medio-Cretácico temprano (160-130 Ma), Cretácico (114-75 Ma) y Eoceno (55-46 Ma). Sobre la base de las características geoquímicas e isotópicas de Sr y Nd de las rocas volcánicas estudiadas, se pueden reconocer dos dominios magmáticos Mesozoico-Eoceno: Dominio Magmático Norte (DMN) y Dominio Magmático Sur (DMS). Los basaltos y rocas intermedias del DMN tienen afinidades alcalinas y valores isotópicos de Sr-Nd deprimidos a moderadamente deprimidos similares a aquellos derivados de una fuente dominada por material as
Evolución geológico-geomorfológica cuaternaria del tramo superior del valle del río Laja
Ricardo Thiele,Hugo Moreno,Sara Elgueta,Alfredo Lahsen
Revista geológica de Chile , 1998,
Abstract: La historia geológica del Cuaternario en el tramo superior del valle del río Laja corresponde a una compleja interrelación entre volcanismo, procesos de remoción en masa y sedimentarios aluvio-fluviales. El valle fue modelado inicialmente por la acción glaciaria del Pleistoceno inferior en rocas de las formaciones terciarias Cura-Mallín y Trapa-Trapa, además de rocas plutónicas, sobre las cuales se disponen en discordancia cuatro grandes unidades cuaternarias; el cono poligénico de Quilleco, una secuencia de rocas volcánicas pleistocenas, el volcán Antuco y el deposito de avalancha volcánica de Antuco. Los depósitos del cono poligénico de Quilleco representan a facies mixtas volcano-sedimentarias intermedias y distales de los estratovolcanes que originaron las secuencia de rocas volcánicas pleistocenas con las cuales engranan lateralmente. El volcán Antuco corresponde a un estratovolcán mixto y compuesto, de composición basáltica y andesítico-basáltica, cuya actividad se inició ca. 130.000 a A.P. La primera etapa de su desarrollo (Antuco 1) culminó 9.700± 600 a A.P. con el colapso gravitacional lateral del edificio, que originó la gran avalancha volcánica de Antuco, cuyos materiales represaron el desagüe natural del lago del Laja y de sus quebradas afluentes. El colapso gravitacional fue el resultado de una actividad eruptiva freatomagmática de tipo Bandai-San la que produjo, casi simultáneamente, flujos piroclásticos turbulentos, de tipo de oleadas de base húmeda, compuestos de cenizas basálticas negras cuyos depósitos primarios se han denominado Arenas Negras de Trupán-Laja. El volcán actual (Antuco 2) incluye un cono principal de lavas y escorias y la emisión de, al menos, tres flujos piroclásticos importantes de poco espesor, localmente separados por depósitos de corrientes de barro y coluvios. Posteriormente, debido a la ruptura del represamiento del lago del Laja, las cenizas negras fueron removidas hasta la Depresión Central, donde formaron un gran abanico aluvial de aproximadamente 50 x 60 km2. Quaternary geological-geomorphological evolution of the uppermost course of the Río Laja Valley. The Quaternary geological history of the uppermost the Río Laja valley shows a complex interrelation between volcanic, mass wasting, and alluvial and fluvial sedimentary processes. The valley was initialiy carved by Lower Pleistocene glacial action on a Tertiary basement (Cura-Mallín and Trapa-Trapa Formations, intrusives), over which four major Quaternary units were deposited unconformably: the polygenic Quilleco alluvial cone, a Pleistocene volcanic sequence,
Estimation of Default Probabilities: Application of the Discriminant Analysis and the Structural Approach for Companies Listed on the BVC  [PDF]
Lahsen Oubdi, Abdessamad Touimer
Journal of Financial Risk Management (JFRM) , 2017, DOI: 10.4236/jfrm.2017.63021
Abstract: This article aims to compare the calculated results of the structural approach (Internal Ratings-Based IRB) and the discriminant analysis (Z-score of Altman, 1968), based on data from companies listed on the BVC for the period from 02 January 2014 to December 31, 2014. The structural approach is directly linked to the economic reality of the company; the default takes place as soon as the market value of these assets falls below a certain threshold. The major constraint for this approach is the determination of the probabilities of default. This situation is overcome by using the Black & Scholes (1973) model, based on Monte Carlo simulations. While the Z-score method is a financial analysis technique of business failure predictions, which is based on financial and economic ratios.
Evolución geológico-geomorfológica cuaternaria del tramo superior del valle del río Laja
Thiele,Ricardo; Moreno,Hugo; Elgueta,Sara; Lahsen,Alfredo; Rebolledo,Sofia; Petit-Breuilh,M. Eugenia;
Revista geológica de Chile , 1998, DOI: 10.4067/S0716-02081998000200007
Abstract: quaternary geological-geomorphological evolution of the uppermost course of the río laja valley. the quaternary geological history of the uppermost the río laja valley shows a complex interrelation between volcanic, mass wasting, and alluvial and fluvial sedimentary processes. the valley was initialiy carved by lower pleistocene glacial action on a tertiary basement (cura-mallín and trapa-trapa formations, intrusives), over which four major quaternary units were deposited unconformably: the polygenic quilleco alluvial cone, a pleistocene volcanic sequence, and the products of the antuco volcano and the antuco volcanic avalancha. the quilleco polygenic cone includes mixed intermediate and distal volcano-sedimentary facies which interfinger with the pleistocene volcanic sequence derived from coeval stratovolcanos. the antuco volcano is a mixed and composite andesitic to basaltic andesitic stratovolcano of basalt, which commenced its activity ca. 130,000 yr b.p. its first constructive phase (antuco 1) culminated at 9,700± 600 yr b.p. with the lateral gravitational collapse of the edifice; this event produced the major antuco volcanic avalancha which dammed the natural outlet of lago del laja and its tributaries. the gravitational collapse was the final result of a bandai-san type phreatomagmatic eruptive event associated with almost simultaneous wet turbulent pyroclastic base surges made up of black basaltic ash (arenas negras de trupán-laja). the present antuco volcano (antuco 2) includes the eruptive event that built the main cone with lavas and scoria falls and the eruption of, at least, three pyroclastic flows, locally separated by mud-flow and colluvial deposits. later, due to the rupture of the lago del laja dam, the ash deposits were remobilized by debris flows which came down from the upper reaches of the river to the central depression where they formed a major alluvial fan of approximately 50 x 60 km2.
Submarine earthquake rupture, active faulting and volcanism along the major Liqui e-Ofqui Fault Zone and implications for seismic hazard assessment in the Patagonian Andes Ruptura sísmica submarina, tectónica y volcanismo activo a lo largo de la Falla Liqui e-Ofqui e implicancias para el peligro sísmico en los Andes patagónicos
Gabriel Vargas,Sofía Rebolledo,Sergio A Sepúlveda,Alfredo Lahsen
Andean Geology , 2013,
Abstract: The Liqui e-Ofqui fault zone (LOFZ) in the Patagonian Andes is an active major transpressional intra-arc fault system along which Quaternary faulting and volcanism develop. Subaerial and submarine geomorphologic and structural characterization of latest Pleistocene-Holocene faults and monogenetic volcanoes allows us to assess geological cartography of active faults and the kinematic model for recent tectonics during postglacial times, since 12,000 cal. years BP. This allows increasing the basic geological knowledge necessary for determining the seismic hazard associated with cortical structures in the Aysén region in southern Chile. Fault cartography and field observations suggest dominant dextral-reverse strike slip along north-south and locally NNW-striking faults, dextral-normal strike slip along NE to NNE- striking faults, and sinistral strike slip along east-west faults. This kinematics is consistent with regional SW-NE shortening in the context of a major transpressional fault zone. Holocene and even historic monogenetic and sub-aquatic volcanism occurred in this tectonic setting in a close spatial relationship and probably favored by the activity and local architecture of faults. Submarine fault scarps and deformed sediments observed at the bottom of the Aysén Fjord were associated with the destructive April 2007 Mw6.2 earthquake located along the LOFZ. Our observations show that this earthquake occurred along dextral 15-20 km long N-S structure named Punta Cola Fault (PCF). This fault system is located some kilometres to the east of the main N-S Río Cuervo Fault (RCF). Most of the epicentres of the seismic swarm during 2007 were located along or in between both structures. The study area is a transference zone between N-S regional branches of the LOFZ. The cartography of fault segments proposed here together with geophysical and geologic data suggest that large earthquakes Mw6.2-6.5 can be typically expected along most of the active faults. Besides, seismic hazard assessment should also consider the possibility of earthquake magnitude in the order of 7.1 along the main fault systems like the RCF. La Zona de Falla Liqui e-Ofqui es un sistema de intraarco activo y paralelo al contacto entre las placas tectónicas de Nazca y Sudamérica, a lo largo del cual el fallamiento y el volcanismo cuaternarios están estrechamente asociados. A partir de observaciones geomorfológicas y estructurales subaéreas, la prospección subacuática de fallas con evidencia de actividad pleistocena tardía-holocena y la caracterización de volcanes monogenéticos, se propone una
Dyslipidemia in internal medicine
Rodolfo Lahsen M.
Medwave , 2010,
Abstract:
Submarine earthquake rupture, active faulting and volcanism along the major Liqui?e-Ofqui Fault Zone and implications for seismic hazard assessment in the Patagonian Andes
Vargas,Gabriel; Rebolledo,Sofía; Sepúlveda,Sergio A; Lahsen,Alfredo; Thiele,Ricardo; Townley,Brian; Padilla,Cristóbal; Rauld,Rodrigo; Herrera,Maria José; Lara,Marisol;
Andean geology , 2013, DOI: 10.5027/andgeoV40n1-a07
Abstract: the liqui?e-ofqui fault zone (lofz) in the patagonian andes is an active major transpressional intra-arc fault system along which quaternary faulting and volcanism develop. subaerial and submarine geomorphologic and structural characterization of latest pleistocene-holocene faults and monogenetic volcanoes allows us to assess geological cartography of active faults and the kinematic model for recent tectonics during postglacial times, since 12,000 cal. years bp. this allows increasing the basic geological knowledge necessary for determining the seismic hazard associated with cortical structures in the aysén region in southern chile. fault cartography and field observations suggest dominant dextral-reverse strike slip along north-south and locally nnw-striking faults, dextral-normal strike slip along ne to nne- striking faults, and sinistral strike slip along east-west faults. this kinematics is consistent with regional sw-ne shortening in the context of a major transpressional fault zone. holocene and even historic monogenetic and sub-aquatic volcanism occurred in this tectonic setting in a close spatial relationship and probably favored by the activity and local architecture of faults. submarine fault scarps and deformed sediments observed at the bottom of the aysén fjord were associated with the destructive april 2007 mw6.2 earthquake located along the lofz. our observations show that this earthquake occurred along dextral 15-20 km long n-s structure named punta cola fault (pcf). this fault system is located some kilometres to the east of the main n-s río cuervo fault (rcf). most of the epicentres of the seismic swarm during 2007 were located along or in between both structures. the study area is a transference zone between n-s regional branches of the lofz. the cartography of fault segments proposed here together with geophysical and geologic data suggest that large earthquakes mw6.2-6.5 can be typically expected along most of the active faults. besides, seismic
PREVENCIóN DE DIABETES MELLITUS TIPO 2
Lahsen M,Rodolfo; Liberman G,Claudio;
Revista chilena de nutrición , 2003, DOI: 10.4067/S0717-75182003000200002
Abstract: type 2 diabetes mellitus is a significant cause of morbidity and mortality, with an increasing incidence associated with the observed increasing prevalence of obesity. various strategies have been tested to determine the feasibility to delay or prevent its onset. changes in lifestyle, insulin sensitizer drugs, and inhibitors of the absortion of carbohydrates and lipids are included, with encouraging results. at the present time, changes in lifestyle, understood in the context of a multidisciplinary support to the patient, constitute the intervention of greater impact. on the other hand, diverse drugs used in trials of prevention of cardiovascular events have demonstrated certain effect in delaying or preventing the appearance of type 2 diabetes mellitus, which opens a new scenario for studies that will be developed in the near future
PREVENCIóN DE DIABETES MELLITUS TIPO 2 PREVENTION OF TYPE 2 DIABETES MELLITUS
Rodolfo Lahsen M,Claudio Liberman G
Revista Chilena de Nutricíon , 2003,
Abstract: La Diabetes Mellitus tipo 2 presenta una importante morbilidad y mortalidad y una incidencia está en aumento, que se asocia al aumento observado en la prevalencia de la obesidad. Diversas medidas han sido evaluadas con el fin de retrasar o prevenir su aparición, entre las cuales se incluyen cambios en el estilo de vida, fármacos insulinosensibilizadores, e inhibidores de la absorción de carbohidratos y lípidos, con resultados esperanzadores. En la actualidad, los cambios en el estilo de vida, entendidos en el contexto de un apoyo multidisciplinario al paciente, constituyen la intervención de mayor impacto. Por otro lado, diversas clases de fármacos empleados en estudios de prevención de eventos cardiovasculares han demostrado cierto efecto en retrasar o prevenir la aparición de Diabetes Mellitus tipo 2, lo cual abre un nuevo escenario para los estudios que se desarrollarán en el mediano plazo Type 2 Diabetes Mellitus is a significant cause of morbidity and mortality, with an increasing incidence associated with the observed increasing prevalence of obesity. Various strategies have been tested to determine the feasibility to delay or prevent its onset. Changes in lifestyle, insulin sensitizer drugs, and inhibitors of the absortion of carbohydrates and lipids are included, with encouraging results. At the present time, changes in lifestyle, understood in the context of a multidisciplinary support to the patient, constitute the intervention of greater impact. On the other hand, diverse drugs used in trials of prevention of cardiovascular events have demonstrated certain effect in delaying or preventing the appearance of type 2 Diabetes Mellitus, which opens a new scenario for studies that will be developed in the near future
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