Caracterización y evolución geológica del complejo metamórfico andino oriental y la secuencia volcanosedimentaria Jurásica en la Península La Carmela (48,5°S), Región de Aysén del General Carlos Ibáñez del Campo
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2018
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es
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Universidad Andrés Bello
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La península La Carmela, ubicada a los 48,5° S, en la Región de Aysén del General Carlos Ibáñez del Campo, constituye un lugar de interés geológico poco estudiado, donde afloran rocas devónicas – carboníferas, pertenecientes al Complejo Metamórfico Andino Oriental (CMAO), a las cuales sobreyacen las formaciones Arroyo La Mina e Ibáñez (i.e. Complejo El Quemado), de edad jurásica, las cuales conforman una interrogante en el contexto de la evolución del margen occidental de Gondwana. En el presente trabajo se realiza una caracterización y análisis de evolución geológica, cuya metodología de trabajo se desarrolla a partir de observaciones recabadas en terreno, y a trabajos en gabinete, tales como un levantamiento geológico, descripción petrográfica de láminas delgadas, y un análisis de proveniencia sedimentaria por medio del software ImageJ.
El CMAO corresponde a un complejo de subducción compuesto por rocas de bajo a muy bajo grado metamórfico, mayormente pizarras, filitas y esquistos, además de metabasaltos que afloran en el sector Norte de la península. El protolito del CMAO está constituido por sucesiones turbidíticas marinas, que se habrían depositado en un ambiente de margen pasivo, cuyas fuentes sedimentarias serían fundamentalmente de bloques continentales, tanto cratónicas como mixtas, recibiendo aportes de basamento alzado. Contemporáneo a la depositación de sucesiones turbidíticas, tuvo lugar el emplazamiento de basaltos alcalinos de intraplaca (OIB), los que formaron el protolito de los metabasaltos del CMAO. Posteriormente, durante el Devónico – Carbonífero, el inicio de la subducción dio lugar a dicho complejo acrecionario, y con ello episodios de deformación compresiva, principalmente dúctil.
En la zona de estudio, la Formación Arroyo La Mina se compone por una sucesión de 50 m de brechas sedimentarias, que sobreyacen al CMAO mediante un contacto por falla, y a su vez es sobreyacida, de manera concordante, por la Formación Ibáñez, compuesta principalmente por tobas, mostrando un espesor de 90 m en la localidad de estudio. Esta secuencia volcanosedimentaria se habría originado durante un período tectónico extensional jurásico, y su depositación syn-rift estaría controlada por estructuras normales con actitud N-S y NE-SW. Subsecuentemente, a raíz de eventos tectónicos compresivos entre el Cretácico tardío – Mioceno medio, se habría dado la inversión tectónica positiva de dichas estructuras normales, generándose zonas de cabalgamiento del CMAO por sobre la secuencia volcanosedimentaria (i.e. deformación de piel gruesa), con actitud NE-SW y NWW-SEE, donde la última dirección sería atribuible a fallas conjugadas, formadas a partir de estructuras transcurrentes mayores, de tipo dextral.
La Carmela peninsula is located at 48,5° S, in the Región de Aysén del General Carlos Ibáñez del Campo, and it’s a place of geological interest, with limited information, where there are Devonian – Carboniferous rock outcrops that belong to Eastern Andean Metamorphic Complex (EAMC). These rocks are overlain by the Arroyo La Mina and Ibáñez (i.e. El Quemado Complex) formations and they have a Jurassic age, which constitute a question factor at the western gondwanian margin’s evolution. In this work, a characterization and a geological analysis are made, and the work methodology consists in fields observations and post-field works, such as a geological gathering, petrographic descriptions of thin sections, and a sedimentary provenance analysis by the ImageJ software. The EAMC is a subduction complex, which is composed of low – very low metamorphic grade, such as shales, phyllites and schists, in addition to metabasalts, which are outcropped at the North sector of the peninsula. The EAMC’s protolith corresponds to marine turbiditic successions, which would have been deposited at a passive margin setting, whose sedimentary sources would be, mainly, continental blocks, and they are both cratonic and mixed sourced, with inputs from uplifted basement. Contemporaneously with the deposition of turbiditic successions, there was an emplacement of alkaline intraplate basalts (OIB), which are the protolith of the EAMC’s metabasalts. Later, during the Devonian – Carboniferous ages, the onset of the subduction generated the accretionary complex (i.e. EAMC) and, therefore, compressional deformative episodes, mainly of ductile type. The Arroyo La Mina Formation is a 50 m thickness succession, which is composed by sedimentary breccias and they overlain to the EAMC by a fault contact. Also, this Formation is overlain by the Ibáñez Formation, which is composed by tuffs, mainly, and it has a 90 m thickness at the study zone. This volcanosedimentary secuence would have originated during a jurassic extensional tectonic period, whose syn-rift depositation would be controlled by normal structures, with N-S and NE-SW directions. Subsequently, due to compressional tectonic events that happened at the Late Cretaceous – Middle Miocene ages, it would have generated a positive tectonic inversion of the mentioned structures, therefore it would have occurred the thrust of the EAMC above the volcanosedimentary secuence (i.e. thick skinned deformation), with NE-SW and NWW-SEE orientations, where the last direction would be associated to conjugate faults, which formed from major dextral strike-slip structures.
La Carmela peninsula is located at 48,5° S, in the Región de Aysén del General Carlos Ibáñez del Campo, and it’s a place of geological interest, with limited information, where there are Devonian – Carboniferous rock outcrops that belong to Eastern Andean Metamorphic Complex (EAMC). These rocks are overlain by the Arroyo La Mina and Ibáñez (i.e. El Quemado Complex) formations and they have a Jurassic age, which constitute a question factor at the western gondwanian margin’s evolution. In this work, a characterization and a geological analysis are made, and the work methodology consists in fields observations and post-field works, such as a geological gathering, petrographic descriptions of thin sections, and a sedimentary provenance analysis by the ImageJ software. The EAMC is a subduction complex, which is composed of low – very low metamorphic grade, such as shales, phyllites and schists, in addition to metabasalts, which are outcropped at the North sector of the peninsula. The EAMC’s protolith corresponds to marine turbiditic successions, which would have been deposited at a passive margin setting, whose sedimentary sources would be, mainly, continental blocks, and they are both cratonic and mixed sourced, with inputs from uplifted basement. Contemporaneously with the deposition of turbiditic successions, there was an emplacement of alkaline intraplate basalts (OIB), which are the protolith of the EAMC’s metabasalts. Later, during the Devonian – Carboniferous ages, the onset of the subduction generated the accretionary complex (i.e. EAMC) and, therefore, compressional deformative episodes, mainly of ductile type. The Arroyo La Mina Formation is a 50 m thickness succession, which is composed by sedimentary breccias and they overlain to the EAMC by a fault contact. Also, this Formation is overlain by the Ibáñez Formation, which is composed by tuffs, mainly, and it has a 90 m thickness at the study zone. This volcanosedimentary secuence would have originated during a jurassic extensional tectonic period, whose syn-rift depositation would be controlled by normal structures, with N-S and NE-SW directions. Subsequently, due to compressional tectonic events that happened at the Late Cretaceous – Middle Miocene ages, it would have generated a positive tectonic inversion of the mentioned structures, therefore it would have occurred the thrust of the EAMC above the volcanosedimentary secuence (i.e. thick skinned deformation), with NE-SW and NWW-SEE orientations, where the last direction would be associated to conjugate faults, which formed from major dextral strike-slip structures.
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Tesis (Geólogo)
Palabras clave
Sedimentación, Geología, Chile, Región de Aysén del General Carlos Ibáñez del Campo, Jurássico