5 páginas.

Trabajo presentado en el 8th International Symposium on Andean Geodynamics (ISAG), realizado en Quito-Ecuador, del 24-26 setiembre, 2019. Evento organizado por el Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN) del Ecuador, y el French Institut de Recherche pour le Développement (IRD).

Active transpressive deformation has been occurring along the Andean hyperarid forearc for the last 3 Myrs but many of these faults are still not described even if able to produce large damaging earthquakes. Active faulting along the northern part of the Arica Bend can be recognized due to the presence of well-preserved and sharp fault scarps indicating recent surface slip. During the Mio-Pliocene, deposition within the forearc continental basins resulted in the formation of vast fan deposits and conglomerates of the Moquegua Formation, which can be considered as bedrock in this exposure study (~45-4 Ma; Tosdal et al., 1984; Sebrier et al., 1988a; Roperch et al., 2006). The typical vertical Purgatorio fault scarps offset both the Moquegua bedrock and several younger geomorphic features associated with <300kyrs climatic and 400 years old volcanic extreme events. This study focus on quanti...

Existe un debate actual sobre el principal factor que controla los procesos de erosión en los Andes occidentales: McPhillips et al., 2014 proponen que la erosión depende fuertemente de la ocurrencia de terremotos mientras que otros estudios, reportan correlaciones positivas entre las variaciones climáticas y la erosión de la cuenca (Carretier et al., 2014; Reber et al., 2017) basadas en dataciones con nucleídos cosmogénicos (10Be). En el sector de Curibaya el deslizamiento Aricota, rellenó el valle y formó un gran dique que dio origen a la laguna Aricota, utilizando nucleídos cosmogénicos (10Be), Delgado et al., (2016) fecharon el deslizamiento (dique) en ~17 ka. Nosotros en este estudio tenemos la oportunidad de comparar (1) la tasa de erosión a partir del volumen de sedimentos acumulados en la laguna desde su formación, y (2) la tasa de denudación a partir de la concentrac...

The central part of the Western Andes holds an exceptional concentration of giant paleolandslides involving very large volumes of rock material (v > km3). While those gravitational slope failures are interpreted consensually as an erosional response to the geodynamic activity of the Andes (relief formation and tectonic activity), the question of their triggering mechanisms remains enigmatic. To clarify the respectiveroles of climatic versus seismic forcing on the Andean landslides, new temporal constraints on paleomovements are essential. Here, we focus on one of those giant slope failures, the Aricota giant rockslide that damned the Locumba valley in southern Peru. We conducted fieldwork, high-resolution DEM analysis and cosmogenic nuclide dating to decipher its development history and failure mechanisms. Our results point to the occurrence of two successive events. A giant failure mobi...

Our understanding of the style and rate of Quaternary tectonic deformation in the forearc of the Central Andes is hampered by a lack of field observations and constraints on neotectonic structures. Here we present a detailed analysis of the Purgatorio fault, a recently recognized active fault located in the forearc of southern Peru. Based on field and remote sensing analysis (Pléiades DEM), we define the Purgatorio fault as a subvertical structure trending NW-SE to W-E along its 60 km length, connecting, on its eastern end, to the crustal Incapuquio Fault System. The Purgatorio fault accommodates right-lateral transpressional deformation, as shown by the numerous lateral and vertical plurimetric offsets recorded along strike. In particular, scarp with a 5 m cumulative throw is preserved and displays cobbles that are cut and covered by slickensides. Cosmogenic radionuclide exposure datin...

In situ-produced 10Be is one of the most commonly used TCN in quantitative geomorphology due to the fact that its production rate is relatively well constrained in the ubiquitous quartz mineral whose integrity minimizes the possibility of contamination by meteoric 10Be. Easily decontaminated from meteoric 10Be, it is in addition reliably measured using the Accelerator Mass Spectrometry technique for which its detection limit is lower than 104 at.g-1. However, volcanic or mafic areas are generally quartz free, which hamper the routine use of 10Be. In the case of a quartz poor lithology, an alternative possibility is to rely on 10Be - feldspars. Two preliminary studies (Kober et al., 2005 and Blard et al., 2013a) already provided promising results, demonstrating that (1) the decontamination protocol classically applied to quartz (Brown et al., 1991) efficiently removes all the meteoric 10B...

Este trabajo presenta 71 edades de exposición a la radiación cósmica (berilio-10) de fases de avance y retroceso de glaciares andinos. Proporcionan cronologías glaciares para 3 áreas de estudió alineadas en un transecto norte-sur de la cordillera occidental de los Andes Centrales: al suroeste de los nevados Hualcán (Cordillera Blanca; 6122 m; 9ºS; región Ancash) y Pariacaca (5758 m; 12ºS; región Lima) y al sur del Cerro Ticllo Ticllo (5400 m; región Arequipa). Las cronologías fueron obtenidas por investigadores del proyecto FONDECYT 144-2015. En dichas áreas de estudio se recogieron muestras de 1-2 kg de roca, en superficies de bloques morrénicos (datan avances glaciares) y lechos rocosos con pulimento glaciar (datan fases de deglaciación).

30 samples have been collected for the cosmogenic dating of expanding and shrinking glacial phases southwesternward of Nevado Hualcán (9º, 12'S; 77º, 31'W, 6122 m), in the Cordillera Blanca (Peru).The set includes 28 moraine boulder surface samples and 2 polished bedrock surface samples. The resistivity of 3 samples of moraine boulder surfaces, measured in the AMS facility ASTER, did not allow us to estimate the accumulation of 10Be. Therefore, it was not possible to estimate the exposure age of these samples. However, it was possible to obtain 27 10Be glacial ages: 25 boulder ages from 5 moraine sets (M5-M1) and 2 polished bedrock ages (between M2-M1). 5 boulder ages seem too high, probably because of cosmogenic inheritance. Nevertheless, despite the uncertainties, the remaining 22 ages seem consistent with their geomorphological context. Nowadays, the oldest moraines (M5) are higher...