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Glacier retreat and the value of ecosystem services associated with water resources in the Paron basin-Huascaran National Park (Cordillera Blanca), 2009-2018

Los glaciares tropicales son indicadores sensibles del cambio climático. La pérdida del volumen de los glaciares tropicales en la cuenca Parón (Cordillera Blanca, Perú) es una muestra de esto a nivel global y se espera que tales cambios afecten a los servicios ecosistémicos que son únicos e insustituibles. Este estudio estimó el valor económico de los servicios ecosistémicos asociados con el recurso hídrico impactados por el retroceso glaciar en la cuenca de Parón-Parque Nacional Huascarán (Cordillera Blanca, Perú) entre los años 2009 y 2018. La metodología inició cartografiando los glaciares de 2009 a 2018 usando imágenes satelitales de alta resolución tomadas en temporada seca. Luego, se reconstruyeron las superficies 3D de los mismos usando la herramienta GLABTOP permitiendo calcular el volumen. Con los datos obtenidos se calculó el valor del servicio ecosistémico del turismo y recreación, y provisión de flujo hídrico. Los resultados indican que los glaciares de la cuenca Parón se han reducción de ~1.82% del área glaciar y en una tasa de deglaciación máxima de 0.08 (km2/año). Los resultados de la reconstrucción 3D muestran un 1.8% más de espesores entre los 40 y 60 m, con una pérdida de hielo de 1.02 km3, a una tasa máxima de 0.14 km3/año. Los valores monetarios presentes de los servicios de 2009 a 2018 se estimaron en $52 029.34 para el servicio de turismo y recreación y de $3 213 258.21 para el servicio de provisión de flujo hídricos, calculados a 8% de tasa de descuento. Por lo tanto, se recomienda que se debe incrementar la inversión en programas sobre la red hídrica de la cuenca de Parón, como mayores servicios, usos poblacionales o industriales.

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Petrological and geochemical constraints on the magmatic evolution at the Ampato-Sabancaya compound volcano (Peru)

In order to gain insights into continental arc magmatic processes, we have conducted a petrological and geochemical study of major and trace elements and Sr, Nd, and Pb isotopes of the Ampato-Sabancaya compound volcano, which belongs to the Andean Central Volcanic Zone (CVZ). Whole-rock compositions for Ampato and Sabancaya range from andesites to dacites (56.7–69.3 wt% SiO2) and both belong to a medium- to high-K calk-alkaline magmatic series. Ampato-Sabancaya samples are characterized by high contents of large-ion lithophile elements (LILE; e.g., K, Rb, Ba, Th), low concentrations of high field strength elements (HFSE; e.g., Nb, Zr) and heavy rare earth elements (HREE; e.g., Yb), with consequently high La/Yb and Sr/Y ratios. An increase in these ratios is usually interpreted as a result of magmatic differentiation in the presence of garnet in the deep crust. A detailed analysis reveals that the rocks of Ampato-Sabancaya display three different compositional groups. (1) The first, composed mainly of andesites (56.7–59.8 wt% SiO2), corresponds to lavas from the early stage of the Ampato Basal edifice, as well as pyroclastic deposits from the Ampato Upper edifice. (2) The second group corresponds to andesitic and dacitic compositions (60.0–67.3 wt% SiO2) from the Ampato Basal edifice (Moldepampa stage), the Ampato Upper edifice, and the Sabancaya edifice. (3) The third group corresponds to dacitic compositions (65.0–69.3 wt% SiO2) associated with the Corinta Plinian fallout and pyroclastic flow deposits from the Ampato Upper edifice. This last group of dacites, erupted during the Ampato Upper edifice stage, have drastically different compositions from the other groups with Sr/Y (<27) and Sm/Yb (<4.7) ratios lower than other lavas and lacking evidence of amphibole and/or garnet fractionation during their genesis. As a whole, Sr, Nd, Pd isotopic ratios suggest that mantle-derived magmas are significantly affected by assimilation processes during their evolution, due to the thick (65–70 km) continental crust beneath the CVZ in southern Peru. In summary, the magmatic evolution of group 1 and 2 can be explained by a two-step model in which primitive magmas evolved in the deep crust in the so-called melting-assimilation-storage-homogenization (MASH)-type reservoirs by assimilation-fractional crystallization (AFC) processes involving garnet and/or amphibole. Then, amphibole-dominated upper crustal AFC processes and magma mixing are responsible for the geochemical diversity of the main ASCV trend. In contrats, the group 3 dacites followed an upper crustal AFC process (without amphibole) from a different primitive magma, which did not suffer the high pressure, garnet-dominated AFC processes. This evolution highlights the complexities associated to magma genesis and differentiation at continental arcs contructed on a thick crust.

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The late Pleistocene Sacarosa tephra-fall deposit, Misti Volcano, Arequipa, Peru: its magma, eruption, and implications for past and future activity

Between 38.5 ka cal BP and 32.4 ka cal BP, a dacitic Volcanic Explosivity Index 5 eruption at Misti volcano emplaced the Sacarosa tephra-fall deposit. Its biotite phenocrysts, fine grain size, scarce lithics, and abundant loose crystals characterize the deposit at locations sampled. The eruption’s ~ 800 °C magma rose rapidly from ~ 10 km depth, culminating in a Plinian eruption which reached a mass eruption rate of 7.7 × 106–4.1 × 107 kg/s and emplaced about 3 km3 of tephra within tens of hours. The unit comprises two layers of subequal thickness separated by a diffuse contact with the upper distinguished by being slightly coarser and less well sorted than the lower. The deposit’s coarser upper layer indicates either climactic conditions or a lesser degree of fragmentation during the latter half of the eruption. Strong winds distributed the deposit southwest of Misti, where it crops out over at least 800 km2 and drapes the present site of Arequipa with up to 100 cm of tephra. The Sacarosa deposit is the first among the Cayma stage deposits, a distinctive group of felsic, biotite-bearing units, to be carefully described and its eruption characterized. Several Cayma stage deposits were emplaced by voluminous explosive eruptions similar to the Sacarosa eruption, representing a ~ 8.9–15.5 ky interval of powerful eruptions. Such an explosive eruption today would threaten Arequipa’s over 1,100,000 residents, many of whom live within the Sacarosa deposit’s distribution.

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Remote sensing data applied to the reconstruction of volcanic activity in the Valley of the Volcanoes, Central Volcanic Zone, Peru

The Valley of the Volcanoes is a representative area of the extension of the Quaternary Andahua Group with which it overlaps. Some of its eruption centres have renewed activity after more than 500 ka. Recreating the history of the Valley of the Volcanoes activity required satellite data and remote sensing-based methods for visualizing the terrain surface. We used SRTM 30 m DEM, channels 4, 3, 2; Landsat 7, 8 and ASTER images. We verified and refined the obtained data during field works using Structure-from-Motion (SfM) to create of 3D models of selected geoforms. Satellite data allowed us to create: Red Relief Image Map, Topographic Position Index and Normalised Difference Vegetation Index (NDVI) maps. In the Valley of the Volcanoes, we analysed 12 lava fields with a total area of 326.3 km2 and a volume of approx. 20 km3. We determined the number of eruption centres that yielded to 41 small lava domes and 23 scoria cones. This domes are classified as monogenetic volcanoes, however five of them can be considered polygenetic e.g. Puca Mauras. We used NDVI to develop chronology map of lavas. This allowed us to extract same-age eruption centres and associated volcanoes that represent the same eruptive time phase connected by fault lines: first generation (0.5–0.27 Ma) NW-SE and NE-SW, second (Pleistocene/Holocene) NNW-SSE and third (Holocene-Historical) again NW-SE and NE-SW. We carried out the reconstruction of the central part of the Valley of the Volcanoes because only there repeated phases of volcanic activity can be inferred with remote sensing and geological mapping. The results of this study led us to indicate that this area should be observed since it is very likely that future eruptions will occur.

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First archive of extensive N-fixation by volcanic lightning and implications for the prebiotic Earth

On Earth, most of the nitrogen (N) accessible for life is trapped in dinitrogen (N2), which is the most stable atmospheric molecule. In order to be metabolised by living organisms, N2 has to be converted into assimilable forms, also called fixed N. Nowadays, nearly all the N-fixation is achieved through biological and anthropogenic processes. However, in early environments of the Earth, before the emergence of life, N-fixation must have occurred via natural abiotic processes. Electrical discharges, including from thunderstorms and also lightning associated with volcanic eruptions is one of the most invoked processes. The occurence of volcanic lightning during explosive eruptions is frequent, and convincing laboratory experimentations support the role of this phenomenon, however no evidence of substantial N-fixation has been found in volcanic records. Here we report on the discovery of large amounts of nitrates in volcanic deposits from Neogene caldera-forming eruptions, which are well correlated with the concentrations of species directly emitted by volcanoes such as sulphur and chlorine. The multi-isotopic composition (&amp;#948;18O, &amp;#916;17O) of the nitrates reveals that they originate from the atmospheric oxidation of nitrogen oxides formed by volcanic lightning that occur during the eruption. According to these volcanic nitrate records, our first estimates suggest that about 60 Tg of N can be fixed during a large explosive event. Our findings hint at a unique role potentially played by subaerial explosive eruptions in supplying essential ingredients for the emergence of life on Earth.

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Characterization of the geothermal anomaly associated with the pre-andean reverse fault of Calientes, South of Peru: a multi-disciplinary approach.

In Peru, energy production is more than 75 % dominated by hydrocarbons (IEA, 2018) while at the same time, the Andes forearc is in a full demographic and economic development. However, the geothermal potential associated with reverse fault in the mountain range forearcs remains poorly studied compared to normal faults. &amp;#160;It is then essential to evaluate the geothermal potential associated with the Andes forearc thrust faults, in considering the environmental risks associated.The hydrothermal system associated with the Sama-Calientes fault, near the city of Tacna South of Peru (18&amp;#176;S) is a suitable field site to experiment how integrated studies could provide an exploration diagnostic. The Calientes hot springs (42-44&amp;#176;C) emerge on the Sama-Calientes fault, an active thrust which delimits the border between the Andes and the north extension of the Atacama Desert. With an integrated study of the hydrothermal fluids and gas geochemistry, XRD composition of the hydrothermal deposits and veins, structural geology, and 3D numerical modeling with COMSOL Multiphysics, we propose to characterize the thermal anomaly associated with the Calientes springs and faults, putting them in perspective with the other hydrothermal springs in the region. Preliminary results indicated that hydraulic breccia, veins, and concretions around the Calientes springs and faults are mainly composed of calcite, contrarily to the other hot springs sites inside the Andes (excepted the Ticaco hot springs). Free and dissolved gas of the springs associated with the high Andean volcanoes (Casiri, Yucamani, Tacora) are mainly composed of CO2 (90-100%), while those associated with the pre-andean faults (Sama-Calientes, Incapuquio) are mainly composed of N2 (60-100%). Volcanic-associated springs show high sulfate concentrations (48-54 mmol/L) compared to fault-associated springs (3-25 mmol/L).&amp;#160; A simple 3D numerical model with a surface DEM and a homogenous permeability indicates that the topography-driven flow lines contributing to the Calientes springs would come from the Tacora volcano, 40 km north-east of Calientes. More investigation will precise the organization of the hydrothermal cells and the associated thermal anomalies. This work will also contribute to understand the role of hydrothermal fluids in subduction zones and especially on seismogenic reverse fault dynamics.

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The temporal and spatial relationship between strike-slip and reverse faulting in subduction-related orogenic system: Insights from the Western slope of the Puna Plateau

The relationship between parallel and oblique to the orogen faults and the magmatic evolution is key to understanding the evolution of a hot orogen, such as the Central Andes. The Andean orogenesis along the southern Central Andes, during the Neogene is characterized by regional compression and magmatic processes associated with subduction. The outcome of this dynamic interaction between plate tectonics and magmatism has generated reverse, normal and strike-slip faults, both parallel and oblique to the trench. Despite the progress made on studying these fault systems, both their relationship with the stress field and their role in magma propagation into the shallow crust are still enigmatic. In this work, geomorphological observations are coupled with kinematic and dynamic analyses, as well as with kinematic forward modeling, to reconstruct the evolution of two main faults affecting the western slope of the Puna plateau, the Barrancas Blancas fault and the Tocomar fault, during the Neogene. The obtained data reveal that, between 17 and 10 Ma, the Barrancas Blancas fault had reverse activity, while the Tocomar fault had left-lateral strike-slip movement. At 10 Ma, the area was affected by the coeval reactivation of the Volcan de Punta Negra fault and the right-lateral activity of the Tocomar fault. During the last stage, strike-slip movement along the Tocomar fault favored the rise of magma, while the hydrothermal activity evolved along the Barrancas Blancas fault. The study results reveal that the oblique-to-the-orogen faults play a role in the segmentation of the reverse parallel-to-the-trench deformation and control the position of the volcanic centers, while the parallel-to-the-orogen faults control the relief development and the evolution of hydrothermal systems. The proposed model helps in understanding how magma rises to the surface associated with movement along reverse and strike-slip faults during the thickening of the crust.

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