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La Zone des Andes Volcaniques Centrales (ZAVC) est la province magmatique la plus active système des Andes qui produit une grande variété de magmas, dont la composition s’étale des basaltes aux magmas calco-alcalins et aux shoshonites, et de structures volcaniques. Un des problèmes importants dans l’étude des systèmes volcaniques est la compréhension des processus qui contrôlent l’origine, la nature, et l’évolution des volatils au cours de l’ascension du magma. Les études menées sur les volcans de la ZAVC ont porté essentiellement sur la caractérisation des sources primaires et la contamination des magmas lors de leur ascension vers la surface. Peu d’études ont porté sur le problème du dégazage comme outil pour caractériser les processus magmatiques et la composition des gaz présents dans les systèmes volcaniques. L’objectif de cette étude et de déterminer les conditions magmatiques des systèmes actifs des volcans Irruputuncu et Lastarria par l’analyse des inclusions vitreuses dans les minéraux (plagioclases et pyroxènes). Les résultats montrent que les inclusions pour ces deux volcans ont une composition plus différenciée que la roche totale, ce qui suggère que la composition du verre représente un liquide résiduel transitoire, produit au cours d’une cristallisation fractionnée, lors de l’évolution du liquide et/ou du mélange avec un autre magma. Ce processus s’est produit à faible profondeur lors des dernières phases magmatiques. Il faut noter que toutes les inclusions vitreuses des produits des Andes centrales et du sud et de quelques arcs volcaniques ont des compositions plus évoluées que la roche totale et qu’il existe un enrichissement d’éléments comme Si, Na et K. L’interaction entre les minéraux et la riche totale indique la présence d’une zone de mush sous le système volcanique, mis en évidence par les minéraux en déséquilibre avec le liquide. Ainsi, lorsque le magma migre vers le haut (stocké dans des sills) il interagit avec la zone de mush et la résorption des minéraux permet d’incorporer des cristaux exotiques. En contrepartie, le magma en déséquilibre conduit à des cristaux de même origine. Les conditions pré-éruptives de pression, de température et de fugacité d’oxygène déterminées à partir des inclusions des produits d’Irruputuncu et de Lastarria sont de1.9-11.7 kbar, 810-970 °C et NNO+3, et sont semblables à celles observées pour d’autres volcans dans les Andes centrales au Nord du Chili. Les teneurs en volatils sont de 0-1500 ppm pour le Fluor, 10-3300 ppm pour Cl, 10-1600 ppm pour S, et 0-5 poids% pour H2O. Ces grandes gammes de pression, température et teneurs en volatil reflètent la variabilité des conditions de stockage des magmas et de capture des inclusions vitreuses dans les minéraux hôtes. Ceci a pu se produire à différentes profondeurs (6.3 à 15.2 km à Irruputuncu et 9.5 à 18 km au Lastarria) et dans des zones à différents degrés de refroidissement. De plus, la teneur en Soufre décroît inversement avec la pression et la température, et est lié directement à la fugacité d’oxygène. La teneur en volatile est semblable à celle d’autres systèmes volcaniques, ce qui suggère que la faible teneur en Soufre dans les inclusions témoigne de la séparation de cette phase en conséquence du refroidissement et de la cristallisation fractionnée d’un magma andésitique avant le mélange. Ces résultats montrent que les conditions magmatiques des volcans du nord du Chili et de la Bolivie sont similaires, probablement à cause du contexte tectonique et des processus magmatiques (mélanges et cristallisation fractionnée), des zones de stockage et des interactions entre magmas et fluides hydrothermaux identiques. Cependant, les volcans basaltiques présentent d’autres caractéristiques, ce qui indique que chaque système volcanique répond à des conditions dynamiques et tectoniques spécifiques. / The Central Volcanic Andes Zone (CVAZ) is the most active magmatic province in the Andean system, resulting in a wide variety of magmas, ranging from basalts to calc-alkaline and shoshonites dacites, and a variety of volcanic structures. One of the important problems in the study of volcanic manifestations is the understanding of the processes controlling the origin, nature and evolution of volatiles during ascent of magma. Studies conducted in the volcanoes of the ZVAC have focused primarily on the characterization of the primary source and contamination of magma as this rise to the surface. Few studies have addressed the problem of outgassing as a source of characterization of magmatic processes and the current composition of magma degassing which is present in the active volcanic systems. The objective of this research is to determine the magmatic conditions of Irruputuncu and Lastarria active volcanic systems, through the analysis of melt inclusions in minerals (plagioclases and pyroxenes). The results indicate that melt inclusions-hosted plagioclase and pyroxene both volcanoes have a more acid composition than whole rock, we suggest that glass compositions represent residual transitory melt that is found in the magma, like product of a fractional crystallization, to the evolution of the melt and/or mixing of magma. This process ocurr to shallow depth, which represents the lasts phases magmatic. It should be noted that in all the vitreous inclusions of the Central Andes, South and some island arcs, it is observed that the composition of the inclusions tends to be relatively more evolved than whole rock; it is suggest that slight enrichement of elements such as Si, Na and K occur at the between melt and minerals. Meanwhile, the interaction between minerals and whole rock indicate the presence of zone mush under each volcanic system, this is evidenced in large part by crystals in disequilibrium with the melt. Therefore, when that magma ascends (stored sills structure) interacts with the mush zone, reabsorption the minerals incorporating exotic crystals. On the other hand, when the magma is in equilibrium generate cognate crystals. The conditions of pressure, temperature and oxygen fugacity determined from the melt inclusions for pre-eruptive magmatic conditions in Irruputuncu and Lastarria systems vary between 1.9 to 11.7 kbar, 810-970 °C and NNO+3, similar to those observed in other volcanoes in the Central Andes of northern Chile. Otherwise, range of volatiles content varies in 0-1500 ppm F, 10-3300 ppm Cl, 10-1600 ppm S, 0-5 %wt H2O; this wide range of variation in the values of pressure, temperature and concentration of volatile, reflecting the variability of magma storage conditions during entrapping vitreous inclusions in the host crystal. This could at different depths (6.3 to 15.2 km Irruputuncu volcano and 9.5 to 18 km Lastarria volcano) and in areas with different degrees of cooling structures represented by sills. Moreover, the S content decrease with increase pressure and temperature, and is related directly with the fugacity of oxygen. The volatile content is similar in various volcanic systems, this suggest that the low S content in melt inclusions represent the separation of this phase as a results of cooling and fraccionate crystallization of a andesitic magma before of mixing. It appears that the magmatic conditions in the volcanoes of northern Chile and Bolivia have similar characteristic, due to the geotectonic context of this zone, resulting varied magmatic process, such as magma mixing, evolved fraccionate crystallization (rhyolitic magma), accumulation of magma in shallow areas, interaction between magmatic and hydrothermal fluids. However, basaltic volcanoes present differents characterics, which indicate that each volcanis system respond to a dynamic of geotectonic conditions and interaction with the environment. / La Zona Volcánica de los Andes Centrales (ZVAC) es la provincia magmática más activa en el sistema Andino, originando una gran diversidad de magmas, cuya composición varía de basaltos a dacitas con tendencia calcoalcalina a shoshonitica, y una gran variedad de estructuras volcánicas. Uno de los problemas importantes en el estudio de las manifestaciones volcánicas es la comprensión de los procesos que controlan el origen, naturaleza y evolución de los volátiles durante el ascenso del magma. Los estudios que se han realizado en los volcanes de la ZVAC se han concentrado fundamentalmente en la caracterización de la fuente primaria y la contaminación del magma a medida que estos ascienden a la superficie. Pocos estudios han abordado el problema de la desgasificación como fuente de caracterización de los procesos magmáticos y de la composición actual del magma en desgasificación que está presente en los sistemas volcánicos activos. El objetivo de esta investigación es determinar las condiciones magmáticas de los sistemas volcánicos activos Irruputuncu y Lastarria, a través del análisis de inclusiones vítreas en minerales (plagioclasas y piroxenos). Los resultados geoquímicos indican que las inclusiones hospedadas en los cristales de plagioclasa y piroxeno de los volcanes Irruputuncu y Lastarria tienen una composición química más ácida que la roca total, por lo que sugiere que la composición química del vidrio atrapado en los fenocristales representa el líquido residual transitorio que se alberga en el magma, producto de un ciclo de cristalización fraccionada, a la evolución del fundido y/o mezcla de magma. Este proceso ocurre a profundidades relativamente someras, donde se albergan las últimas fases del magma. Cabe destacar que en todas las inclusiones vítreas de los volcanes de los Andes Centrales, Sur y en algunos de arcos de islas, se observa que la composición de las inclusiones tiende a ser relativamente más evolucionada que la roca total; se sugiere que en el borde o límite donde interactúan el fundido y el cristal ocurre un leve enriquecimiento de elementos como el Si, Na y K. Por su parte, los estudios realizados entre MI-mineral y minerales-roca total indican la presencia de una zona mush bajo cada sistema volcánico, esto se evidencia en gran parte por cristales que no están en equilibrio con el fundido. Por lo tanto, cuando el magma asciende (almacenado en estructuras de sills) interactúa con la zona mush, que reabsorbe los minerales e incorporándolos como cristales. Por otra parte, cuando los magmas se equilibran forman cristales cognatos. Las condiciones de presión, temperatura y fugacidad de oxígeno determinadas a partir de las inclusiones vítreas, para las condiciones magmáticas en los sistemas Irruputuncu y Lastarria, varían entre los 1,9 a 11,7 kbar, 810 a 970°C y NNO+3, rangos similares a los observados en otros volcanes de los Andes Centrales del Norte de Chile. Por otra parte, el rango del contenido de volátiles varía entre 0-1500 ppm F, 10-3300 ppm Cl, 10-1600 ppm S, 0-6 %wt H2O; este amplio rango de variación en los valores de presión, temperatura y concentración de volátiles, reflejan la variabilidad de las condiciones de almacenamiento del magma durante el atrapamiento de las inclusiones vítreas en el cristal huésped. Esto ocurriría a diferentes profundidades (6,3 a 15,2 km para el volcán Irruputuncu y 9,5 a 18 km para el volcán Lastarria) y en zonas con distinto grados de enfriamiento, representados por estructuras de sills. Cabe destacar que el contenido de S disminuye con el aumento de la presión y temperatura, y se relaciona directamente a la fugacidad del oxígeno. (...)

The interaction of magma with continental crust at convergent margins is fundamental to understanding if and how continents grow. Isotopic and elemental data constrain the progressive stages of development of the magmatic underpinnings of the long-lived Aucanquilcha Volcanic Cluster (AVC), situated atop the thick continental crust of the central Andes in northern Chile. Whole rock data are used in conjunction with mineral compositions to infer processes that gave rise to eleven million years of intermediate, dominantly dacite, arc volcanism. A pulse of volcanic activity at the AVC between ~5 and 2 Ma is bracketed by more sluggish rates. We document chemical changes in the lavas that accompany this eruptive evolution. Trace element data suggest that crystal fractionation and magma mixing were the dominant mechanisms generating the diversity observed in the AVC whole rock data. Fractionation was dominant during early and waning stages of magmatism, and magma mixing was an important process during the high flux period. Peak thermal maturity of the AVC underpinnings coincided with the high magma flux and likely promoted open system processes during this time. Mineral compositions from zircon, amphibole, pyroxene, and Fe-Ti oxides confirm the importance of material recycling in the production of evolved AVC rocks. Various geothermometers were employed to calculate the pre-eruptive conditions of AVC magma using mineral compositions. Pressure estimates from amphibole and two-pyroxene barometry indicate crystallization depths of 1 ��� 5 kb and 4 ��� 6 kb, respectively. Temperature estimates from zircon, Fe-Ti oxides, amphiboles, and pyroxenes indicate temperatures ranging from ~700��C to 1100��C. Zircon temperatures are always the lowest (700��C - 950��C), and pyroxene temperatures are always the highest (1000��C - 1100��C), with Fe-Ti oxide and amphiboles temperatures falling in between. U-Pb ages from zircons and thermometry from individual samples evidence the thermal maturation and consolidation of the underpinnings below the AVC, presumably culminating in a large, crystal-rich mush zone where magmas were trapped and processed. It is in these middle to upper crustal zones where magmatic diversity is attenuated and giant, relatively homogeneous batholiths are formed. Isotopes of AVC lavas are similar to values observed from other central Andes volcanic centers. Lead isotopes are consistent with the AVC's location within a Pb isotope transition zone between the Antofalla and Arequipa basement terranes. Oxygen and Sr isotopic ratios are high and Nd isotopic ratios low with respect to a depleted mantle. Through time, ������Sr/������Sr values of AVC lavas progressively increase from lows of ~0.70507 to ~0.70579 (upper values of 0.70526 to 0.70680), and ��Nd values decrease from highs of -1.0 to -4.6 (lows of -1.6 to -7.3). Similarly, O isotopes (�������O) show a slight increase in base level through time from lows of 6.5��� to 7.0��� (highs of 6.75��� ��� 7.5���). Dy/Yb and Sm/Yb ratios also increased systematically from highs of 2.11 to 3.45, and 2.76 to 6.67, respectively. Despite the temporal isotopic variation, there is little isotopic variation with indices of fractionation, suggesting this signal is the consequence of deep magmatic processing, here attributed to an expanding zone of melting, assimilation, storage, and homogenization (MASH) of mantle-derived magma in the deep crust. Upward expansion brought the MASH zone into contact with rocks that were increasingly evolved with respect to Sr and Nd isotopes, explaining the isotopic shifts. Downward expansion of the MASH zone enhanced garnet stability during basalt fractionation, explaining the increased Dy/Yb and Sm/Yb ratios. Mass balance calculations involving Sr, Nd, and O isotope modeling are consistent with a crustal component making up 10 - 30% of AVC lavas, implying that although the history of central Andean magmatism is replete with large scale crustal recycling, the current phase is largely a crust formation event. / Graduation date: 2012

Debate persists on the timing, magnitude and style of crustal shortening, uplift and basin evolution in the Andes. Many studies suggest that the central Andes, including the Altiplano plateau, were gradually uplifted as a result of protracted Cenozoic retroarc shortening. However, recent isotopic studies conclude that the Andes instead rose in pulses, with the most significant event occurring at 10-6 Ma. Many researchers attribute these rapid pulses of uplift to lower lithosphere delamination events. A better understanding of the history of Cenozoic crustal shortening is essential for determination of the mechanism(s) of Andean uplift. The well-exposed Cenozoic San Jerónimo Group was studied in the Ayaviri basin of the northern Altiplano in southern Peru. The 3-5 km-thick succession is situated at 3900-4800 m elevation, between the Western Cordillera magmatic arc and the Eastern Cordillera fold-thrust-belt. New detrital zircon U-Pb geochronological results from four sandstones and one reworked tuff in the San Jerónimo succession show large age populations indicative of syndepositional volcanism between approximately 38 and 27 Ma. A 1600-m-thick magnetostratigraphic section further constrains the depositional timing and accumulation rate of the upper portion of the succession. Sedimentological observations show a rapid transition from cross-stratified braided-fluvial sandstones to proximal channel-fill and alluvial-fan conglomerates at ~30 Ma. Paleocurrent measurements show important temporal and spatial variations in sediment dispersal patterns while conglomerate clast counts show an upsection transition from almost exclusively volcanic input to increasing contributions of clastic, quartzite, and limestone detritus. The corresponding shifts in depositional environment and sediment provenance are attributed to the activation of new thrust structures in close proximity to the basin, namely the Pucapuca-Sorapata fault system, indicating the presence of an eastward advancing fold-thrust belt dating to at least 38 Ma and reaching the Ayaviri basin within the northern Altiplano plateau at ~30 Ma. / text

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Prehispanic Camelid Utilization PatternsIn the present study evidence concerning both the origin of camelid domestication and the subsequent development of herding economies is evaluated through the analysis of camelid survivorship/mortality curves. Because the bone fusion age stages proposed by Elizabeth Wing in 1972 have been used by archaeozoologists working in the Andes, it is possible to compare data from several sites. None the less, in the present study we have corrected errors in Wing's age attribution for the fusion of certain bones and recalculated the survivorship curves published for the sites of Tulan 52, Puripica 1, Telarmachay, Kotosh, Galindo, Huacaloma and Layzón. The resultant curves reveal clear differences between hunting and herding economies, as well as distinct levels of herding efficiency or strategies, which support previous hypotheses concerning the origins of domestication. / En el presente trabajo, se evalúa la evidencia relacionada con el origen de la domesticación de los camélidos sudamericanos y el subsecuente desarrollo de las economías de pastoreo a través del análisis de los perfiles de sobrevivencia/mortalidad de estos animales. Debido a que la tabla de grupos etarios en los camélidos sudamericanos (basados en el estado de fusión de ciertos huesos) utilizada por Elizabeth Wing en su estudio de la fauna de Kotosh (1972) ha sido utilizada por arqueozoólogos que trabajan en los Andes, es posible hacer una comparacion entre los datos provenientes de varios sitios. En el presente trabajo, sin embargo, se han corregido algunos errores en la atribución de edad propuesta por Wing para la fusión de ciertos huesos y recalculado los perfiles de sobrevivencia/mortalidad publicadas para los sitios de Tulan 52, Puripica 1, Telarmachay, Kotosh, Galindo, Huacaloma y Layzón. Los perfiles resultantes revelan claramente diferencias entre las economías de caza y pastoreo, así como distintos niveles de eficiencia o estrategias de pastoreo, que sustentan hipótesis previas concernientes a los orígenes de la domesticación.

Fishtail Points at Quebrada Santa María and the Antiquity of the Man in South AmericaIn light of new discoveries and theoretical proposals, the discovery of the first sites containing evidence of fish tail points at Quebrada Santa María, Chicama valley, northern Perú, contributes with new information that answers more than one of the questions concerning the first inhabitants of South America. / El descubrimiento de los primeros sitios con evidencias de la tradición de puntas de proyectil en cola de pescado en Quebrada Santa María, valle de Chicama, norte del Perú, por las caracteristicas de hallazgos, y a la luz de los nuevos descubrimientos y propuestas teóricas, plantea la posibilidad de contribuir con nuevos datos para dar respuesta a más de una de las interrogantes que tenemos sobre los primeros habitantes en Sudamérica.

Chronology and Connections: Preceramic Evidences at Asana SiteWith its long and continuous history of occupation, the site of Asana has a unique body of information to offer for the study of the Archaic Period in the south-central Andes. In this paper, I explore two important themes: the chronological sequence of occupation at the site with specific regard to the ways in which phases are defined, and the evidence from the site that describes the connections Asana had throughout its occupation with other regions of the Andean world. In the latter I examine in detail projectile point style and the sources of obsidian and other lithic materials found at the site. There is strong evidence for connections to the central Andes, the Colca valley, and the northern Chilean valleys. / Con su larga y continua historia de ocupación, el sitio de Asana tiene un único conjunto de información que ofrecer para el estudio del Periodo Arcaico en los Andes surcentrales. En este artículo, exploraremos dos temas importantes: la secuencia cronológica de la ocupación en el sitio con énfasis en los modos en que se definen las fases y la evidencia que describe las conexiones que Asana tuvo a través de sus ocupaciones con otras regiones del mundo andino. Por último se examinan en detalle los estilos de puntas de proyectil y las fuentes de obsidiana, así como otros materiales líticos encontrados en el sitio. Hay una fuerte evidencia para conexiones con los Andes Centrales, el valle del Colca y los valles del norte chileno.