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A pesar del creciente número de estudios sobre el efecto del cambio climático en los glaciares peruanos y su impacto en la seguridad hídrica, existe una brecha de conocimiento sobre cómo la minería afecta a los glaciares. Esta problemática adquiere mayor relevancia considerando que el Perú es un país minero, donde los principales proyectos actuales y numerosas concesiones se ubican en la zona altoandina. Con esta tesis se presenta una aproximación a los impactos de la minería en los glaciares Rinconada y Ananea, cercanos al centro poblado La Rinconada en la Cordillera Apolobamba, Puno. Se realizó un análisis anual de cobertura glaciar de 1985 a 2022 mediante el Índice Normalizado de Diferencia de Nieve. Para el mismo periodo, se aplicó un análisis multitemporal cada 5 años de la cobertura no-natural usando el algoritmo de aprendizaje automático Random Forest. Ambos análisis fueron computados en la plataforma Google Earth Engine con imágenes satelitales de mediana resolución espacial (Landsat 5 y 8, Sentinel 2) con corrección atmosférica. Los resultados indican que la cobertura glaciar de la Cordillera Apolobamba se redujo alrededor del 43 % entre 1985 (161.4 km²) y 2022 (92.1 km²). Asimismo, el área urbana aumentó en un 1 176 % entre 1990 (17 ha) y 2022 (200 ha), mientras que el área degradada incrementó en un 289 % entre 2010 (1 774 ha) y 2022 (3 389 ha). Los cambios de la cobertura glaciar y no-glaciar fueron analizados mediante el coeficiente de correlación de Pearson con tres indicadores socioeconómicos claves ligados a la actividad minera incluyendo datos de población, producción y precio del oro en la región. Este análisis permitió establecer un alto grado de asociación positiva entre el crecimiento de la actividad minera y la reducción de la cobertura glaciar. Este caso y el potencial de impactos mineros en la evolución glaciar actual y futura resaltan la urgencia de desarrollar y fortalecer una agenda ambiental para la protección de glaciares y cabeceras de cuenca en el Perú considerando lecciones aprendidas en la región, en particular en Argentina. / Despite an increasing number of studies on the effect of climate change on Peruvian glaciers and its impact on water security, there is a knowledge gap on how mining affects these glaciers. This issue becomes even more relevant considering that Peru is a mining country, where the main current projects and numerous concessions are located in the high-Andean region. This thesis presents an approach to the impacts of mining on the Rinconada and Ananea glaciers, close to the town of La Rinconada in the Apolobamba mountain range, Puno. An annual analysis of glacier coverage from 1985 to 2022 was conducted using the Normalized Difference Snow Index. For the same period, a 5-year multitemporal analysis of non-natural coverage was applied using the Random Forest machine learning algorithm. Both analyses were computed in the Google Earth Engine platform with medium spatial resolution satellite images (Landsat 5 and 8, Sentinel 2) with atmospheric correction. The results indicate that the glacier coverage of the Apolobamba mountain range decreased by about 43 % between 1985 (161.4 km²) and 2022 (92.1 km²). Likewise, the urban area increased by 1 176 % between 1990 (17 ha) and 2022 (200 ha), while the degraded area increased by 289 % between 2010 (1 774 ha) and 2022 (3 389 ha). Changes in glacier and non-glacier coverage were analyzed using the Pearson correlation coefficient with three key socioeconomic indicators linked to mining activity, including population, production, and gold price data in the region. This analysis established a high degree of positive association between the growth of mining activity and the reduction of glacier coverage. This case and the potential impacts of mining on current and future glacier evolution highlight the urgency of developing and strengthening an environmental agenda for the protection of glaciers and headwaters in Peru considering lessons learned in the region, particularly in Argentina.

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The goal of this study is to determine the source of gold and the role played by organic carbon and arsenic in the formation of sediment-hosted gold deposits. The effect of and link between these two ubiquitous ingredients yet remains unresolved, even though most mineable gold in the Earth’s crust is hosted by this type of deposits. In this work, we tackled these fundamental questions in a case study of the Shahuindo and Algamarca deposits in the Marañon Fold and Thrust Belt of the Peruvian Andes. These deposits are representative of sediment-hosted deposits in which gold mineralization is closely associated with both carbonaceous material and arsenian pyrite. We combined a range of complementary approaches including regional-scale basin analysis, mineralogical, geochemical, and fluid-inclusion studies, coupled with modeling of fluidrock interactions. Our results show that both Shahuindo and Algamarca deposits are located in an imbricated system of four thrust-related anticlines. The mineralization, which is predominantly present in the form of invisible gold in arsenian pyrite, is hosted by sandstone reservoirs of the Cretaceous Chimú, Carhuaz and Farrat formations of an overmature petroleum system. The intersection of thrust structures with transverse strike-slip faults controlled the location of the gold mineralization. Analyses of quartzhosted fluid inclusions for homogenization temperature, salinity and element concentration patterns collectively point to a magmatic origin of the mineralizing fluid(s). In addition, our fluid-inclusion data reveal intensive interactions between the fluid and organic carbon within the sedimentary basin, leading to large concentrations of CO2 CH4 and H2S in the fluid. These reactions result in an enhancement of Au solubility in the form of AuI hydrosulfide complexes, due to the increase in H2S and pH in the fluid. These key chemical changes in the fluid upon its reaction with organic matter promoted the transport of gold through the fold and thrust belt, followed by the gold-bearing fluid accumulation in structural traps such as anticlines, and subsequent gold intake by arsenian pyrite. The ensemble of the results obtained in this work allowed us to propose a novel genetic model of formation for Shahuindo and Algamarca deposits. The model integrates the positive combined effect role of organic carbon and arsenic in the transport and concentration of gold, coupled with a favorable structural architecture of the fold and thrust belt. Furthermore, our data point to a concealed porphyry-style mineralization that may be present beneath the basin hosting the Shahuindo and Algamarca epithermal deposits. The results of this work contribute to the improvement of exploration strategies for sediment-hosted gold deposits in Northern Peru and worldwide. / L'objectif de cette étude est de déterminer la source de l'or, le rôle du carbone organique et de l'arsenic dans la formation des gisements d'or hébergés dans des sédiments. L'effet et le lien entre ces deux ingrédients omniprésents dans de tels systèmes n'ont pas encore été élucidés, même si la majeure partie de l'or exploitable dans la croûte terrestre se trouve dans ce type de gisements. Dans ce travail, nous avons abordé ces questions fondamentales par une étude de cas en choisissant les gisements de Shahuindo et d'Algamarca situés dans la ceinture de plis et chevauchements du Marañon dans les Andes péruviennes. Algamarca et Shahuindo sont représentatifs des gisements hébergés dans des sédiments dans lesquels la minéralisation aurifère est étroitement associée à la fois au carbone organique et à la pyrite arséniée. Dans cette étude, nous avons combiné une série d'approches complémentaires, comme l'analyse structurale et de bassin à l'échelle régionale, des études minéralogiques, géochimiques et d'inclusions fluides, associées à la modélisation thermodynamique des interactions fluides-roches. Nos résultats montrent que les gisements de Shahuindo et d'Algamarca sont situés dans un système imbriqué de quatre chevauchements et anticlinaux associés. La minéralisation, sous forme d’or « invisible » dans la pyrite arséniée, se trouve dans les réservoirs grèseux des formations crétacées Chimú, Carhuaz et Farrat appartenant à un système pétrolier surmature. Les intersections d’anticlinaux ou de failles de chevauchement avec des failles transverses de décrochement ont contrôlé l'emplacement de la minéralisation aurifère. Nos analyses des inclusions fluides piégées dans le quartz démontrent, par leurs températures d’homogénéisation, salinités et signatures d’éléments trace, une origine magmatique des fluides minéralisateurs. En outre, elles révèlent des interactions intenses entre le fluide et le carbone organique au sein du bassin sédimentaire, conduisant à de fortes teneurs en CO2, CH4 et H2S dans le fluide. Ces réactions ont entraîné une augmentation de la solubilité de l'or sous forme de complexes hydrosulfurés, en raison de l'augmentation du pH et de la concentration en H2S dans le fluide. Ces changements de composition du fluide ont favorisé le transport de l’or à travers le bassin sédimentaire plissé et faillé. Puis les fluides aurifères se sont accumulés dans des pièges structuraux comme les anticlinaux, et l’or a été finalement incorporé dans la pyrite arséniée. L'ensemble des résultats obtenus dans ce travail nous permettent de proposer un nouveau modèle génétique de formation pour les gisements de Shahuindo et d'Algamarca. Ce modèle intègre l'effet combiné du carbone organique et de l'arsenic dans le transport et la concentration de l'or, couplé à un environnement structural très favorable, dans un bassin sédimentaire plissé et faillé. En outre, nos données indiquent qu'une minéralisation cachée de type porphyrique pourrait exister en profondeur, sous les sédiments encaissants les gisements épithermaux de Shahuindo et d'Algamarca. Les résultats de ce travail contribueront à l'amélioration des stratégies d'exploration des gisements d'or dans les sédiments du nord du Pérou et dans le reste du monde. / El objetivo de este trabajo es determinar el origen de los fluidos mineralizantes y el rol del carbón orgánico y el arsénico en la génesis de los depósitos de oro hospedados en sedimentos. El rol y el vínculo entre estos dos ingredientes omnipresentes aún sigue sin resolverse a pesar de que la mayor parte del oro explotable en la corteza terrestre se concentra en este tipo de depósitos. En el presente trabajo vamos a abordar estas dos interrogantes primordiales mediante el caso de estudio de los depósitos de Shahuindo y Algamarca en la faja corrida y plegada del Marañon de los Andes peruanos. Depósitos representativos de depósitos de oro hospedados en sedimentos, en los cuales la mineralización de oro se encuentra estrechamente asociada con la materia orgánica y la pirita arsenical. En este trabajo combinamos una serie de metodologias complementarias que incluyen el análisis estructural y de cuenca a escala regional, estudios mineralógicos, geoquímicos y de inclusiones fluidas, combinado con modelamiento termodinámico de las interacciones fluido-roca. Los resultados muestran que los depósitos de Shahuindo y Algamarca se encuentran localizados en un sistema imbricado de cuatro sobreescurrimientos y anticlinales asociados. La mineralización, la cual se encuentra predominantemente en forma de oro invisible en pirita arsenical, esta hospedada en reservorios de areniscas cretácicas de las formaciones Chimú, Carhuaz y Farrat de un sistema petrolero sobremadurado. La intersección entre los anticlinales o fallas de sobreescurrimiento con las fallas de rumbo transversales controlaron la localización de la mineralización de oro. Los datos obtenidos de las inclusiones fluidas en cuarzo (temperatura de homogenización, salinidad y patrones de concentración de elementos) indican un origen magmático. Adicionalmente los datos de inclusiones fluidas revelan intensas interacciones entre el fluido y el carbón orgánico presente en la cuenca sedimentaria, produciendo altas concentraciones de CO2 CH4 y H2S en el fluido. Estas reacciones resultan en un incremento en la solubilidad del oro en forma de complejos de hidrosulfuro, debido al incremento del H2S y el pH en el fluido. Esto promueve el transporte del oro atreves de la cuenca sedimentaria plegada y fallada, posteriormente los fluidos auríferos son acumulados en trampas estructurales tales como anticlinales, y por último el oro es extraido del fluido por la pirita arsenical. El conjunto de datos obtenidos en este trabajo permite proponer un novedoso modelo genético de formación para los depósitos de Shahuindo y Algamarca. Este modelo integra el efecto positivo combinado del carbón orgánico y el arsénico en el transporte y concentración del oro, junto a un ambiente estructural favorable, en la faja corrida y plegada. Además, nuestros datos indican la posible presencia de una mineralización oculta del tipo pórfido por debajo de los sedimentos que albergan a los depósitos epitermales de Shahuindo y Algamarca. Estos resultados contribuyen a mejorar las estrategias de exploración para depósitos de oro hospedados en sedimentos en la faja corrida y plegada del Marañon y en otros contextos similares alrededor del mundo.

An increase in population in rural agricultural communities and higher demand for food throughout Bolivia create the need for increased agricultural production. The objective of this study was to assess the suitability of the GLEAMS model as a tool for evaluating fertilization and cropping system practices for potatoes in the Andes of central Bolivia, and make recommendations for the continued development of the model as an analysis tool to improve sustainable crop production. Model suitability was evaluated through assessment of model representation of observed potato farms and behavior of simulated soil nitrogen (N) and N transformation trends; validation with field data taken from six agricultural sites in central Bolivia for runoff volume, soil total Kjeldahl N concentration, crop production, and crop N uptake; and sensitivity analysis. Validation of model output with observed values was completed both graphically and by determining the root mean square error standard deviation ratio (RSR) and the percent bias (PBIAS). RSR and PBIAS values for runoff volume were 4.0 and 65%, 4.5 and 4%, and 2.7 and 55% for three respective experimental plot repetitions using a calibrated SCS curve number of 90. The RSR and PBIAS, respectively, for soil total Kjeldahl N concentration were 3.0 and -2.2%. The RSR and PBIAS, respectively, for crop dry matter production were 7 and 21%. The RSR and PBIAS, respectively, for crop N uptake were 10 and 21%. The mineralization processes in GLEAMS must be improved before model application to central Bolivia, where agricultural production is highly dependent on mineralization of organic N from soil and applied animal manure. Recommendations for model improvement and development include modification to the process that determines mineralization from the soil potentially mineralizable N pool; validation of the percolation volume and nitrate leaching losses; and improved model representation of banded manure application. / Master of Science / CCRA-2 (Watershed Modeling)

Doctor en Ciencias, Mención Geología / The Sierra Baguales Mountain Range (SBMR) forms the eastern foothills of the Patagonian Andes located between 50º and 51º S, topographically isolated from the Southern Patagonian Icefield (SPIF) and under the influence of the Westerly Winds. Its landscape shows glacial deposits and morphologies, potentially useful for the reconstruction of the Pleistocene Holocene glaciations, which occurred in the vicinity of the Patagonian Ice Cap, and possibly showed individual responses to environmental change after the Last Glacial Maximum (LGM). Using simple and multivariate statistical methods, the morphometry of 143 glacial cirques, distributed between the current eastern limit of the SPIF and the easternmost SBMR, approximately 200 km from the Pacific coast, was analyzed. For the latter sector, using photo-interpretation, Geographic Information Systems (GIS) and field work, the first glacial and periglacial geomorphological map of the area was constructed. The relationship between the Geological Strength Index (GSI), rainfall gradient, and cirque areas, which were occupied and eroded by former alpine glaciers, was also established. To this end, theoretical profiles of the ice topography, based on a perfect plasticity model, were developed. Ages of local environmental changes were estimated using 14C dating. Equilibrium Line Altitude (ELA) variations were interpreted based on geomorphological evidence and the accumulation area ratio (AAR).The lowering of the ELA was converted to the change in temperature by multiplying it with an average atmospheric lapse rate. For the SBMR, it is possible to recognize two glaciation levels which rise towards the interior of continent. Their spatial distribution and elevation were controlled by tectonic factors (Andean uplift), the rainfall gradient and the climate contrast from east (temperate maritime) to west (dry cold), present in southern Patagonia since the LGM. The lower group of glacial cirques is distributed in the lower areas of the main valleys. These have no current evidence of snow or glacial processes and have been subject to fluvial erosion and gravitational processes. These cirques can be associated with outlet glacier advance of the Patagonian Ice Cap during the Holocene, and were probably partially or completely covered with ice during the LGM or prior glaciations. On the other hand, the upper group of glacial cirques is located east of the SPIF and mainly in the eastern section of the SBMR. Their size is reduced progressively to the east due to the increased resistance of the rocks on which they developed and the regional rainfall gradient. These cirques show evidence of lateral and frontal moraines of alpine glaciers, some of which are currently active. This cirque group corresponds to those glaciers that remained after the middle Holocene, favored by a gentle slope and aspect, in addition to low temperatures prevailing in the highest marginal sections of the SPIF and particularly the SBMR. Radiocarbon ages can be considered as evidence of environmental change linked to the temperature decrease and rainfall increment resulting from the latitudinal shift and the increase in strength of the Westerly Winds during the middle Holocene. For the SBMR, where the local atmospheric temperature from the Tardiglacial was approximately 3.8±0.8°C colder than today, temperatures possibly remained lower in relation to the regional context, mainly due to the cold and dry climate prevailing towards the interior of the continent, and the elevation of the basins where the former alpine glaciers were located, which eventually advanced and coalesced to form a small Icefield. Such advances could be related to variations in the Frias Lobe, at the same latitude of the SBMR but closer to the SPIF eastern margin.

Esse trabalho propôs a realização de um estudo das características morfológicas e iconográficas das coleções de cerâmicas arqueológicas do acervo do Museo Hermógenes Mejía Solf, localizado em Jaén, na Alta Amazônia peruana. O objetivo central da pesquisa foi entender padrões e variações de estilos visualmente observeis a partir da identificação de conjuntos de artefatos cerâmicos que conformam o acervo do referido museu, bem como a comparação dos mesmos com estilos arqueológicos tradicionalmente conhecidos como característicos de regiões adjacentes à área de pesquisa, a saber: da Costa Norte lambayecana, da Serra de Cajamarca (e das Terras Baixas amazônicas. O trabalho justifica-se, entre outros aspectos, pela exiguidade de pesquisas arqueológicas dedicadas à Alta Amazônia peruana, bem como pela riqueza do patrimônio arqueológico salvaguardado pelo museu. Os dados levantados e resultados das análises apontam para a identificação de um palimpsesto de formas e estilos, reforçando a hipótese de um intenso contato entre povos andinos e amazônicos no chamado Período Tardio da cronologia relativa usualmente adotada na arqueologia andina. / This work proposed the study of the morphological and iconographic characteristics of the archaeological ceramic collections of the Hermógenes Mejía Solf Museum, located in Jaén, in the Upper Peruvian Amazon. The main objective of the research was to understand patterns and variations of styles visually observable from the identification of artifactual sets that conform the museum ceramic collection, as well as the comparison of them with archeological styles traditionally known as characteristic of adjacent regions to the research area, namely the northern coast of Lambayeque, the Sierra de Cajamarca (and the Amazonian Lowlands). The work is justified, among other things, by the lack of archaeological research dedicated to the Peruvian Upper Amazonia, as well as the richness of the archaeological heritage preserved by the museum. The data collected and results of the analyzes point to the identification of a palimpsest of forms and styles, reinforcing the hypothesis of an intense contact between Andean and Amazonian peoples in the so - called Late Period of relative chronology usually adopted in Andean archeology.

Apesar da existência de vários estudos geológicos detalhados no segmento norte do Andes, muitos aspectos estão ainda por serem resolvidos, principalmente aqueles concernentes ao tipo, grau e evolução metamórfica, ambiente tectônico de formação e correlação com margem paleozóica do continente Gondwana e com os terrenos mesozóicos oceânicos. A Cordilheira Central dos Andes Colombianos, é representada por um complexo polimetamórfico com magmatismo associado e uma fina pilha de sedimentos suprajacente em algumas partes da cordilheira. O embasamento desta cordilheira é principalmente composto por rochas metamórficas e por isto a sua compreensão deve ser feita a partir do entendimento dos processos de metamorfismo que afetaram a área. Na Cordilheira Central, a caracterização dos distintos processos geológicos, tem sido interpretada em termos de eventos orogênicos em escala regional, pelo que muitas incongruências são percebidas na aplicação dos diferentes modelos e o análise detalhado da evolução metamórfica permitiria separar os diferentes eventos e a possibilidade de reconstruir as condições de pressão e temperatura (P-T) da crosta, podendo definir a natureza do ambiente tectônico assim como a relação entre as unidades. Nos arredores da cidade de Medellín (municípios de Caldas e El Retiro) afloram rochas metamórficas com protólitos básicos e pelíticos (Anfibólio Xistos de Caldas e Xistos de Ancón), com alguns aportes de material granítico, às vezes metamorfisado (Gnaisse de La Miel). Outro conjunto de rochas metabásicas e metapelíticas associadas apresenta-se ao oriente destas unidades. Este conjunto de rochas é nomeado Anfibolitos, Migmatitos e Granulitos de El Retiro. A termobarometria nos Anfibólio Xistos de Caldas indicam condições de pressão e temperatura próprias da facies anfibolito e descrevem uma trajetória em sentido antihorário sem ficar claro o caminho de regresso das condições de retrometamorfismo. As pressões nestas rochas variam entre ~6.3 e 13.5 Kb com variações relativamente estreitas da temperatura, com valores que estão entre ~550 e 630ºC. No caso dos Xistos de Ancón, a trajetória resultante é em sentido anti-horário e reflete aumentos de temperatura evidenciados na petrografia pela presença de sillimanita e o regresso da trajetória é pela zona da cianita. As temperaturas neste conjunto variam entre ~400 e 555ºC para pressões constantes de 5 e 6Kb en condições de metamorfismo progressivo. O retrometamorfismo apresenta pressões entre ~7.6 e 7.2Kb com temperaturas ~645 e 635ºC, além de temperaturas entre ~500 e 600ºC com pressão constante de 6Kb. No conjunto de rochas de El Retiro, apresenta-se uma forte descompressão com variações estreitas no campo da temperatura, apresentando valores de pressão entre ~8.7 e 2.7Kb com variação na temperatura de ~740 e 633ºC. As unidades conhecidas como Anfibólio Xistos de Caldas, Xistos de Ancón e Gnaisse de La Miel, evidenciam uma historia metamórfica comum de processos de tipo colisional. Os Anfibólio Xistos de Caldas e os Xistos de Ancón poderiam representam fragmentos de crosta oceânica com sedimentos pelíticos intercalados, a qual foi exumada, além de ter um corpo metagranítico relacionado (Gnaisse de La Miel) cuja geoquímica evidencia seu caráter colisional. Este corpo granítico pode ser o resultado do metamorfismo ou do processo de exumação que afetou a região e gerou o pacote de xistos ou pelo menos começou fazer parte da história geológica da área logo depois da formação dos xistos. As rochas de El Retiro (Anfibolitos, Migmatitos e Granulitos de El Retiro) sugerem que seja um bloco que colidiu com as de Caldas (Anfibólio Xistos de Caldas, Xistos de Ancón e Gnaisse de La Miel) e a partir de então têm uma história conjunta, no mínimo, a partir do Triássico, como é indicado pela geocronologia e pela ausência de estruturas regionais entre estas unidades. Finalmente um possível processo de rifteamento que da origem a pontos restritos de calor e que geram as rochas em facies granulito, assim como estruturas de cisalhamento mais marcadas em alguns litotipos. / In spite of the existence of several detailed geological studies in the northern segment of the Andes Cordillera, many aspects are still to be resolved, mainly those concerning the type, grade and metamorphic evolution, tectonic setting formation and correlation with the Palaeozoic margin of Gondwana and with Mesozoic oceanic terranes. The Central Cordillera is represented by a polimetamorphic complex with associated magmatism, and a thin pile of cover sediments in some parts of the mountain range. The basement of the Central Cordillera is mainly constituted by metamorphic rocks and for that its comprehension should be done from the understanding of the metamorphism that affected the area. In the Central Cordillera, the characterization of the different geological processes has been interpreted in terms of orogenic events in regional scale, however, a lot of incongruities are perceived in the application of the different models, and the detailed analysis from the metamorphic evolution would permit the separation distinct events and the reconstruction possibility of the crusts pressure and temperature (P-T) conditions, being able to define the nature of the tectonic setting, as well as the relation among the units. In the surroundings of the city of Medellín (Caldas and El Retiro cities) occur metamorphic rocks with basic and pelitic protolites (Amphibole Schist of Caldas and Schists of Ancón), with some contributions of granitic material, sometimes affected by metamorphic processes (Gneiss of La Miel). Another group of metabasic and metapelitic rocks associated is observed to the east of these units. This group is named Amphibolites, Migmatites and Granulites of El Retiro. The group Amphibole Schist of Caldas and Schists of Ancón could be formed in an distal environment and under reduct conditions and later inserted to the continent by a possible subduction zone. El Retiro rocks could be correspond to the continental basement of the area and it leaves of them it can correspond to impure sediments, of continental margin, formed under high grade metamorphic conditions. The metamorphism in these last rocks was more intense, originating the rocks in the granulite facies in portions of the crust in which the partial pressure of H2O was relatively lowers, as well as of migmatites, result of the anatexis of quartz-feldspatic composition rocks, in places which the partial pressure of H2O was higher. This metamorphism was accompanied of intense deformation, which to have juxtaposed both migmatites and granulites blocks. Therefore later there was intense interaction fluid-rock, as well as restricted points of heat caused by igneous intrusions and that are responsible for the variations in the size of grain of the minerals and especially by the fortress retrometamorphic reequilibrium and by the fluids transport. Thermobarometric data in Amphibole Schist of Caldas indicate pressure and temperature conditions of the amphibolite facies and they describe a counterclockwise path, with no precise retrometamorphic P-T-t trajectory. The pressures in these rocks vary between 6.3 and 13.5Kb with narrow variations of the temperature, with values between ~550 and 630ºC. In the case of the Schists of Ancón, the result is a counterclockwise path and it reflects increases of temperature evidenced by the occurence of sillimanite and the return of the path to the kyanite zone (amphibolite facies). The temperatures in this group vary between ~400 and 555ºC for constant pressures of 5 and 6Kb in prograde metamorphic conditions. The retrometamorphism presents pressures between ~7.6 and 7.2Kb with temperatures aproximately between ~645 and 635ºC, besides temperatures between ~500 and 600ºC with constant pressure of 6Kb. The El Retiro set presents a strong decompression with narrow variations in the temperature field, showing pressure values between ~8.7 and 2.7Kb with temperatures of ~740 and 633ºC.