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Margirier A.,CNRS Institute of Earth Sciences | Audin L.,CNRS Institute of Earth Sciences | Carcaillet J.,CNRS Institute of Earth Sciences | Schwartz S.,CNRS Institute of Earth Sciences | Benavente C.,Instituto Geologico Minero y Metalurgico
Earth Surface Dynamics | Year: 2015

The contribution of landslides to the Quaternary evolution of relief is poorly documented in arid contexts. In southern Peru and northern Chile, several massive landslides disrupt the arid western Andean front. The Chuquibamba landslide, located in southern Peru, belongs to this set of large landslides. In this area, the Incapuquio fault system captures the intermittent drainage network and localizes rotational landslides. Seismic activity is significant in this region with recurrent Mw9 subduction earthquakes; however, none of the latest seismic events have triggered a major landslide. New terrestrial cosmogenic dating of the Chuquibamba landslide provides evidence that the last major gravitational mobilization of these rotational landslide deposits occurred at ∼ 102 ka, during the Ouki wet climatic event identified on the Altiplano between 120 and 98 ka. Our results suggest that wet events in the arid and fractured context of the Andean forearc induced these giant debris flows. Finally, our study highlights the role of tectonics and climate on (i) the localization of large Andean landslides in the Western Cordillera and on (ii) the long-term mass transfer to the trench along the arid Andean front. © 2015 Author(s).

The upper reaches of the Río Santa (Huaraz, Perú) are highly affected by the mining activities of generally small and very small mining companies located in two specific areas, Cordillera Blanca, and Cordillera Negra, with the largest mining claims located in the districts of Recuay and Ticapampa. To assess the mobility and bioavailability of heavy metals in the abandoned tailings pond belonging to the Alianza mining company in the district of Ticapampa, and to identify the fractions to which they are associated we applied a sequential chemical extraction. The results were compared with studies into their mineralogical characterization, a quantitative chemical analysis and a determination of potential acidity and potential neutralization by the ABA (acid-base accounting) method applied to samples of tailings. The sequential extraction procedure confirmed the mode of general alteration observed in the area through mineralogical studies: a relatively easy mobility of Pb, and Cd, and considerable immobility with regard to Ag, Cr and Co, as well as an intermediate mobility of Cu, Zn, and As. Significant cadmium and lead contents found in the most mobile fractions of the tailings may represent an environmental threat, bea- ring in mind the toxic nature of these elements. Despite the low mobility of arsenic, the total quantities of this element are so high that the waters of the Río Santa are being affected.

Franco R.D.V.,RDVGeoconsulting | Thouret J.-C.,CNRS Magmas and Volcanoes Laboratory | Delaite G.,CNRS Magmas and Volcanoes Laboratory | Van Westen C.,International Institute for Geoinformation Science and Earth Observation | And 5 more authors.
Special Paper of the Geological Society of America | Year: 2010

Studies of the type, extent, and volume of Holocene pyroclastic and lahar deposits have concluded that future eruptions of El Misti volcano, even if moderate in magnitude, will pose a serious threat to the city of Arequipa, Peru. After describing the most probable volcanic scenarios at El Misti, this paper concentrates on lahar and flood risk assessment. Scenarios were derived with the help of the simulation codes LAHARZ and TITAN2D. The lahar risk assessment varies significantly depending on the method selected. LAHARZ simulations indicate that a considerable part of the urban areas and infrastructure could be severely affected. Losses due to impacts inflicted by lahars in three selected parts of the urban area are estimated to be in the order of 40-100 million U.S. dollars. In the case of TITAN2D, the resulting laharaffected area only includes infrastructure assets mainly located along the Río Chili. Results indicate that although simulation codes could be useful tools in the analysis of lahar hazard scenarios, it is still premature to regard them as accurate sources of information for actual decision making related to risk mitigation at the local level. More research is required to further adjust simulation codes and refine risk scenarios. The first priority for the mitigation of the volcanic hazard faced by the city of Arequipa should be improvement of the risk map (a hazard map has already been drawn and is under scrutiny) and the preparation of contingency plans. © 2010 The Geological Society of America. All rights reserved.

Willner A.P.,University of Stuttgart | Willner A.P.,Ruhr University Bochum | Tassinari C.C.G.,University of Sao Paulo | Rodrigues J.F.,University of Porto | And 3 more authors.
Journal of South American Earth Sciences | Year: 2014

High-pressure conditions of 11-13. kbar/500-540°C during maximum burial were derived for garnet amphibolite in the Tapo Ultramafic Massif in the Eastern Cordillera of Peru using a PT pseudosection approach. A Sm-Nd mineral-whole rock isochron at 465±24. Ma dates fluid influx at peak temperatures of ~600°C and the peak of high pressure metamorphism in a rodingite of this ultramafic complex. The Tapo Ultramafic Complex is interpreted as a relic of oceanic crust which was subducted and exhumed in a collision zone along a suture. It was buried under a metamorphic geotherm of 12-13°C/km during collision of the Paracas microcontinent with an Ordovician arc in the Peruvian Eastern Cordillera. The Ordovician arc is represented by the western Marañon Complex. Here, low PT conditions at 2.4-2.6kbar, 300-330°C were estimated for a phyllite-greenschist assemblage representing a contrasting metamorphic geotherm of 32-40°C/km characteristic for a magmatic arc environment. © 2014 Elsevier Ltd.

Tassinari C.C.G.,University of Sao Paulo | Castroviejo R.,Technical University of Madrid | Rodrigues J.F.,National Laboratory of Energy and Geology | Acosta J.,Instituto Geologico Minero y Metalurgico | Pereira E.,National Laboratory of Energy and Geology
Journal of South American Earth Sciences | Year: 2011

The ultramafic-mafic rocks of the Tapo Complex are exposed in the Eastern Cordillera of the Central Peruvian Andes. This complex is composed of serpentinised peridotites and metabasites with some podiform chromitite lenses and chromite disseminations and overlies the sandstones, conglomerates, and tuffs of the Carboniferous Ambo Group. The metagabbros and amphibolites show a tholeiitic affiliation and a flat REE spider diagram, with a slight LREE depletion and a positive Eu anomaly suggesting magmatic accumulation of plagioclase, in an ocean ridge or ocean island environment. Sm-Nd isotopic analyses were performed on chromite as well as on whole rock from the gabbro. All samples yielded an Sm-Nd isochrone age of 718 ± 47 Ma with an initial 143Nd/ 144Nd of 0.51213 ± 0.00005. The e{open} Nd (718 Ma) values calculated for both chromite and gabbro are in close agreement, around 8.0, implying that they were formed at the same time from the same mantelic magma source. Furthermore a K-Ar age on amphibole of 448 ± 26 Ma was obtained, interpreted as the cooling age of a younger orogenic event. These rocks represent slices of oceanic crust (from a dismembered ophiolitic complex), metamorphosed and later overthrust on upper Palaeozoic continental formations. © 2011 Elsevier Ltd.

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