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Geocronología U-Pb De Zircones Detríticos Del Grupo Yura En Tacna

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Geocronología U-Pb De Zircones Detríticos Del Grupo Yura En Tacna UNIVERSIDAD NACIONAL DANIEL ALCIDES CARRIÓN FACULTAD DE INGENIERÍA ESCUELA DE FORMACIÓN PROFESIONAL DE GEOLOGÍA TESIS: Geocronología U-Pb de Zircones Detríticos del Grupo Yura en Tacna Para optar el Título Profesional de: Ingeniero Geólogo Autor: Bach. Angel Carlos SALAS COLCA Asesor: Dr. Favio MENA OSORIO Cerro de Pasco, Perú – 2018 Esta tesis es dedicada a mis seres queridos que se encuentran lejos y en especial a mi madre y a mi hermana. “En la ciencia hemos de interesarnos por las cosas, no por las personas” Marie Curie ii RECONOCIMIENTOS La elaboración de esta tesis se realizó gracias al proyecto GR41A ―Registro de variaciones climáticas en los sedimentos durante el Mesozoico y Cenozoico del Sur de Perú‖ realizada en el Instituto Geológico Minero y Metalúrgico (INGEMMET) con el apoyo del FONDECYT, el cual tuvo como responsable al Dr. Aldo Alván, que es también el asesor del presente trabajo y Coordinador General del Convenio 216-2015 entre INGEMMET y FONDECYT (CIENCIACTIVA, Perú). También agradezco al Ing. Elvis Sánchez e Inés Trinidad por su apoyo, y a mis compañeros del proyecto: Edid Iquiapaza, Iván Becerra, Yacory Bustamante y Katerin Ramirez. Finalmente agradezco a todas aquellas personas, que de algún modo contribuyeron con el presente estudio. iii RESUMEN La presente tesis titulada: ―Geocronología U-Pb en zircones detríticos del Grupo Yura en Tacna‖ está enfocada en reconstruir el marco geodinámico de depositación de las areniscas del Grupo Yura en el departamento de Tacna, y en modo general de la cuenca Arequipa-Tarapacá, por tanto se elabora un modelo paleogeográfico del jurásico- cretácico inferior de la cuenca Arequipa, que abarco desde el sur peruano, norte de Chile y la parte noroccidental de Argentina. El método empleado es la geocronología U- Pb en los zircones detríticos (detrital zircón) del Grupo Yura, que tiene por finalidad descifrar la procedencia sedimentaria, relacionado a diversas fuentes generadoras de zircón (principalmente arcos magmáticos), adicionalmente se estudia: la morfología externa de los zircones, por medio de la observación petrográfica; y la estructura interna de los zircones [OZP], mediante imágenes de catodoluminiscencia. Se estudiaron un total de doce (12) muestras las cuales pasaron por un procedimiento que consiste en la separación granulométrica, gravimétrica, magnética y finalmente la selección a mano de zircones (entre 80 y 100 granos) con ayuda del microscopio estereoscópico. Tres (3) muestras fueron colectadas en los alrededores del cerro Challatita, ocho (8) en el cerro Chachacumane, y dos (2) en la quebrada Ataspaca. Los análisis U-Pb, la morfología y las estructuras internas de los zircones de la Formación Cachíos, Formación Labra y Formación Hualhuani, presentan muchas similitudes, por lo cual todos los resultados son interpretados del mismo modo. La principal forma que tienen los zircones es redondeada, esto indica una fuente de rocas metamórficas y/o rocas sedimentarias con alto grado de madurez, en menor cantidad se encuentran zircones con hábito prismático a piramidal; la estructura interna de estos cristales revela que la mayoría son redondeados y poseen los patrones de zoneamiento oscilatorio [OZP] propios de un crecimiento en un ambiente magmático, la otra parte de los zircones posee núcleos heredados o xenocrísticos y bordes fenocrísticos, los cuales representan crecimiento en el ambiente metamórfico. Los resultados de geocronología U-Pb presentan una moda (~80%) entre 500 a 700 Ma, la cual está relacionada a la orogenia Pampeana, el segundo mayor grupo de edades esta entre 900 y 1200 Ma, y las rocas parentales son el Macizo Arequipa y la faja orogénica Sunsas-Grenville, en cantidades menores se obtuvieron edades de 200 a 300 Ma (rift Mitu), proveniente de la Cordillera Oriental, y las edades >1200 Ma representan el reciclaje sedimentario del Cratón Amazónico y/o la edad del protolito del Macizo Arequipa (~1.9 Ga). El amplio espectro de edades entre 500 – 700 Ma del presente estudio y anteriores, solo puedo ser originado en un arco magmático, en este caso la Orogenia Pampeana, el cual represento el principal rasgo topográfico positivo, localizado en el margen oriental de la cuenca Arequipa, y la ausencia de edades andinas (< 200 Ma) señalan la ausencia del vulcanismo durante la depositación del Grupo Yura, es decir, el arco volcánico se encontraba inactivo, probablemente ocasionado por subducción ―flat-slab‖. Palabras clave: geocronología U-Pb, zircones detríticos, cuenca Arequipa, Grupo Yura, cuenca Mesozoica, procedencia sedimentaria, geología andina iv ABSTRACT The present study titled ―U-Pb Geochronology in Detrital Zircon of Yura Group at Tacna‖ is focused in building of the geodynamic setting of deposition of sandstones of Yura Group at Tacna, and a major scale of the Arequipa – Tarapacá Basin, therefore a palaeogragraphic model of Jurassic-lower cretaceous of Arequipa basin is elaborated, this one included southern Peru, northern Chile and possibly noreasthern Argentina. The methodology used is detrital zircon U-Pb geochronology, its purpose is unravel the sedimentary provenance related to several sources of zircon (mainly magmatic arcs), furthermore the outer morphology of zircons is studied by petrographic observation; and internal morphology of zircons [OZP] by cathodoluminiscence imaging. Twelve (12) samples were studied, they passed through granulometric, gravimetric, magnetic separation and hand picking (between 80 and 100 grains) with stereomicroscope. Three (3) samples were collected around cerro Challatita, eight (8) at cerro Chachacumane, and two (2) at quebrada Ataspaca. U-Pb analysis, morphology, and internal structures of zircón from Cachíos Formation, Labra Formation and Hualhuani Formation, all of them exhibit many similarities, so they were interpreted in the same way. The mostly morphology of zircon is rounded, it points a source from metamorphic rocks and/or highly mature sedimentary rocks, and the minority of them have prismatic and pyramidal habits, the internal structures of this crystals reveal that they are rounded and have zoning pattern oscillatory [OZP] belonging of a magmatic environment, the other part have an inherited or xenocristic core and a fenocristic rim, which represent a metamorphic environment. The results of U-Pb geochronology have a mode (~80%) between 500 to 700 Ma, this one is related to Pampean Orogeny, and the second group of ages are between 900 to 1200 Ma, and the parental rocks are the Arequipa Massif and Susnsas-Grenville belt, in smaller quantities there are ages between 200 to 300 Ma (Mitu rift) coming from Cordillera Oriental and the ages >1200 Ma represent sedimentary recycling of Amazonian Craton and/or Arequipa Massif’ protolith (~1.9 Ga). The broad spectrum of ages between 500 to 700 Ma in this study and others, it is only possible that they were derived from a fossil magmatic arc, in this case the Pampean Orogeny, which was the mainly positive feature in the landscape, located in the east, and the lack of andean ages (< 200 Ma) points out an absence volcanism during Jurassic and lower Cretaceous, so the volcanic arc was inactive during deposition of Yura Group, probably because of flat slab subduction. Key words: U-Pb geochronology, detrital zircón, Arequipa basin, Yura Group, Mesozoic basin, sedimentary provenance, Andean geology v RESUMO A presente tesis intitulada ―Geocronologia U-Pb em zircões detríticos do Grupo Yura em Tacna‖ esta focada em reconstruir o quadro geodinâmico de depositó dos arenitos do Grupo Yura em Tacna, e no modo geral da bacia Arequipa – Tarapacá, portanto é feito um modelo paleogeografico do juraássico e cretáceo inferior da bacia Arequipa, que cobria o sul do Peru, o norte do Chile e o nordeste da Argentina. O método usado é a Geocronologia U-Pb em zircões detríticos (detrital zircón) do Grupo Yura, que tem como objetivo decifrar a procedencia sedimentar, relacionado a diferentes fontes geradoras dos zircões (principalmente os arcos magmáticos), adicionalmente é estudado: a morfología externa dos zircões através da observação petrográfica; e a estrutura interna dos zircões por meio de imagens de catodoluminescência. Doze (12) amostras foram estudadas, elas passaram por um procedimento que consiste na separação granulométrica, gravimétrica, magnética e finalmente a seleção à mão dos zircões (entre 80 y 100 grãos) com ajuda do estereoscópio. Três (3) amostras foram coletadas nas proximidades do cerro Challatita, oito (8) no cerro Chachacumane e duas (2) amostras na quebrada Ataspaca. As análises U-Pb, a morfología e as estruturas internas dos zircões da Formación Cachíos, Formación Labra e Formación Hualhuani, apresentam muitas semelhanças, pelo qual os resultados são interpretados da mesma maneira. A principal forma que os zircões têm eles é arredondado, isso indica uma fonte da rochas metamórficas e/ou rochas sedimentares muito maduras, em menos quantidades se encontram zircões com hábito prismático e piramidal; a estrutura interna destes cristais revela que a maioria são arredondados e têm padrões de zoneamento oscilatório [OZP] pertencente a um ambiente magmático, a outra parte têm núcleos herdado o xenocristálicos e bordas fenocristálicos, os quais representam o crescimento em um ambiente metamórfico. Os resultados da geocronología U-Pb representam uma moda (~80%) entre 500 a 700 Ma, a qual está relacionada a Orogénese Pampeana, o segundo maior grupo de idades está entre 900 a 1200 Ma, e as rochas parentales são o Macizo Arequipa e a faixa orogênica Sunsas-Grenville,
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