Tese de Doutorado IGc/USP iii AGRADECIMENTOS Este trabalho deve muito a algumas pessoas e instituições que, direta ou indiretamente, contribuíram para a realização desta Tese. A minha orientadora Prof. Dra. Maria Helena Bezerra Maia de Hollanda, por brindar-me a oportunidade de realizar estudos de pós-graduação, ouvir com interesse e ânimo todas as questões, dúvidas e problemas que surgiam durante o processo de reflexão. Ao SERNAGEOMIN (Oficina Técnica -Puerto Varas) e ao Dr. Jorge Muñoz Bravo

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... ela amizade e apoio nos trabalhos de campo e fornecimento dos dados Ar-Ar. Gostaria também de agradecer ao Dr. Paul Duhart e aos Srs. Eduardo Rogel, Ricardo Santibañez, Roberto Flores pela amizade, companhia, esforço e gratos momentos nos difíceis trabalhos de campo. Ao Sr. Eduardo Córdoba pelo fornecimento das bases topográficas. ; pelos dados, apoio e compreensão. À minha esposa, Maria Amália Mellado, por todo apoio, carinho e amor, e paciência. A FAPESP, que financiou durante 36 meses minha pesquisa com a bolsa de doutorado e reserva técnica. A todos agradeço, profundamente, e dedico o resultado do trabalho. Mauricio Alejandro Mella Barra -Tese de Doutorado IGc/USP iv "O copernicanismo e outros ingredientes essenciais da ciência moderna sobreviveram apenas porque, em seu passado, a razão foi freqüentemente posta de lado" Paul Feyerabend Mauricio Alejandro Mella Barra -Tese de Doutorado IGc/USP v RESUMO MELLA, M.A. Petrogêneses do Complexo Vulcânico Yate (42º30'S), Andes do Sul, Chile. 2008. 151f. Tese (Doutorado) -Instituto de Geociências, Universidade de São Paulo, São Paulo. ABSTRACT MELLA, M.A. Petrogêneses do Complexo Vulcânico Yate (42º30'S), Andes do Sul, Chile. 2008. 151f. Tese (Doutorado) -Instituto de Geociências, Universidade de São Paulo, São Paulo. The Yate Volcanic Complex (CVY) is located in the Southern Volcanic Zone of the Chilean Andes, at 42°30'S, comprising the Yate, Gualaihué and Hornopirén volcanoes. The Yate volcano is a major compound type in which effusive activity occurred since Upper Pleistocene (c. 122 ka) until Holocene. Hornopirén and Gualaihué are minor, and represent strombilian-and shield-type volcanoes, respectively. Effusive activity in Hornopirén extended since Lower to Middle Pleistocene (c. 1,4 Ma to 260 ka), and in Gualaihué was around Middle Pleistocene (c. 440 ka), with subordinate phreatomagmatic eruptions during Holocene. Four types of basalt and basalt andesite associations (BABs) were recognized in YVC: (i) a high-Al and low-Mg group (BAB-A), with olivine-clinopyroxene-plagioclase phenocrystal assembly; (ii) a high-Mg and low-Al group (BAB-AM), with olivine-plagioclase; (iii) a high-Mg group (BO), with olivine and, (iv) a K-rich group (BAB-K) including two incongruent mineral assemblies, olivineplagioclase and clinopyroxene-orthopyroxene. Sr (and Pb) isotopic ratios show different patterns for BABs. When compared together, BAB-A is the most radiogenic group, with 87 Sr/ 86 Sr ratios higher than 0.70440 showing no correlation with Rb/La ratios. This suggests that isotopic (and incompatible element) enrichment may not be exactly related to crustal contamination. Quantitative modeling points to partial melting, in c. 1% water (slab-derived fluids), of an enriched peridotite as a possible mechanism involved in the genesis of BAB-A magmas. Similar petrogenetic model is envisaged for BAB-AM and BO; however, minor water contents during melting should be required for. Striking features of mineral disequilibrium suggest each (K-rich) crust assimilation and magma mixing influenced compositional signature of the BAB-K magmas. Magma mixing and mingling seems to be also an important petrogenetic mechanism in genesis of the evolved magmas (silica-rich basalt andesites, andesites, dacites) from the YVC, as shown by petrographic (olivine-clinopyroxene [Mg# 0,8], coexisting with clinopyroxene-orthopyroxene [Mg# 0,76-0,63]) and geochemical features. Genesis of amph-riolites, however, can be explained to each partial melting of amphibolite crust or ~12 km-deep fractional crystallization from an andesitic magma. In summary, the magmatic evolution of YVC, from the Middle Pleistocene to Holocene, is dominated by geochemically distinct basic magmas emplaced along NS-and SW-trending structures. Chemical and mechanical interaction between these magmas occurred into the magma chamber, located at the junction of those structures. In addition, partial melting of the crust produced the most evolved magmas of the complex.