Análisis del estilo y cronología de la formación de la Cordillera de Vallenar (28°30-29°S): Influencias en la construcción del oroclino de Vallenar
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2018
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es
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Universidad Andrés Bello
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La latitud de Vallenar representa un cambio en una serie de rasgos geológicos regionales de primer orden, como son las rotaciones paleomagnéticas y la orientación de las estructuras principales, lo que ha sido definido como el Oroclino de Vallenar. Para develar posibles controles geológicos en su patrón de deformación, es necesario comprender el estilo estructural y cronología de la deformación de la Cordillera de la Costa oriental y Cordillera Frontal chilena a la latitud de Vallenar y compararlo con los descritos para el segmento norte del Oroclino.
Mediante compilación bibliográfica, y análisis estructural, se realizó un modelo estructural sintético entre los 28°30-29°S, el cual fue validado con modelamiento forward y comparado con el modelo estructural propuesto para la latitud de Copiapó.
Los resultados arrojaron un estilo estructural a la latitud de Vallenar, caracterizado por un sistema de fallas inversas de vergencia oeste sobreimpuestas a la deformación extensional Mesozoica en la Cordillera de la Costa, que involucra unidades estratigráficas del Triásico al Campaniano y en la Cordillera Frontal una tectónica compresiva bi-vergente (de vergencia este y oeste) que alza bloques de basamento Carbonífero Pérmico en el sector occidental y Triásico Inferior – Medio en el sector oriental.
La configuración estructural actual del orógeno Andino a esta latitud está controlada en gran parte por las fallas extensionales heredadas del Mesozoico y probablemente por suturas relictas del Paleozoico. Dentro de estas estructuras, la inversión de la Falla San Félix durante la Fase Incaica, juega un rol fundamental en la deformación de la Cordillera de la Costa y en su relación con la Cordillera Frontal, marcando el límite entre ambos dominios morfoestructurales.
A través de la comparación entre los limbos norte y sur del Oroclino de Vallenar, se identificaron variaciones latitudinales, principalmente en (1) la disminución de los espesores de las unidades Mesozoicas en el limbo sur, (2) cronología de la deformación diacrónica, con inicio de la actividad compresiva a los ~110 Ma en Vallenar y ~80 Ma en Copiapó, (3) mecanismo de inversión tectónica dominado por reactivación de fallas normales heredadas de las cuencas extensionales Mesozoicas en el segmento norte y por decapitación de estas estructuras en el segmento sur y (4) propagación de la deformación hacia el este desde el Cretácico Tardío hasta el presente en el limbo norte, mientras que en el limbo sur la deformación se propagó hacia el este entre el Albiano – Paleoceno y hacia el oeste en el Paleoceno – Mioceno.
Los factores que parecen tener mayor influencia en el oroclino son el mecanismo de inversión tectónica y la propagación de la deformación porque determinan la vergencia de las estructuras principales y el sentido del transporte tectónico.
The Vallenar latitude represent a change in a sequence of first order regional geological features, like paleomagnetic rotations and main structures orientation, that has been defined as Vallenar Orocline. To unveil possible geological controls is in the deformation pattern it is necessary understand the structural style and the deformation chronology of the western Coastal Range and eastern Frontal Range at Vallenar latitude and compare this with the features of northern Orocline segment. Through bibliographic compilation and structural analysis, a synthetic structural model was made between 28°30-29°S, then the model was validate with forward modeling and finally was compared with the structural model of Copiapó latitude. The results showed a structural style at Vallenar latitude characterized for a west-vergent thrust system superimposed at Mesozoic extensional deformation in the Coastal Range, that involving Triassic – Campanian stratigraphic united and a compressive tectonic bi-vergente (east and west) that uplift Carboniferous – Permic basement blocks in the western range and Triassic basement blocks in the eastern range. The actual Andean orogen structural setting at this latitude it is main controlled through Mesozoic inherited extensional faults and maybe of Paleozoic relic sutures. Between these structures, the San Félix fault inversion during the Incaic tectonic phase, it is a fundamental role in the Coastal Range and her relation with the Frontal Range, this mark the limit between both morph-structural domains. The latitudinal variations recognized, by the comparison between northern and southern limbs, was mainly (1) southward Mesozoic sequences thickness decrease, (2) diachronic deformation chronology, with start of compressive activity at 110Ma in Vallenar, and at 80Ma in Copiapó, (3) tectonic inversion mechanism dominated by reactivation of normal structures inherited of Mesozoic extensional basins in northern segment, and dominated by decapitation of these structures in southern segment, and (4) deformation propagation eastward since late Cretaceous until present in northern limb, , while in southern limb , the deformation was propagated eastward between Albian - Paleocene and westward since Paleocene to Miocene. The factors that possibly have greater influence in the Orocline, are the tectonic inversion mechanism and the deformation propagation, because determine the main structures vergence and the tectonics transport sense.
The Vallenar latitude represent a change in a sequence of first order regional geological features, like paleomagnetic rotations and main structures orientation, that has been defined as Vallenar Orocline. To unveil possible geological controls is in the deformation pattern it is necessary understand the structural style and the deformation chronology of the western Coastal Range and eastern Frontal Range at Vallenar latitude and compare this with the features of northern Orocline segment. Through bibliographic compilation and structural analysis, a synthetic structural model was made between 28°30-29°S, then the model was validate with forward modeling and finally was compared with the structural model of Copiapó latitude. The results showed a structural style at Vallenar latitude characterized for a west-vergent thrust system superimposed at Mesozoic extensional deformation in the Coastal Range, that involving Triassic – Campanian stratigraphic united and a compressive tectonic bi-vergente (east and west) that uplift Carboniferous – Permic basement blocks in the western range and Triassic basement blocks in the eastern range. The actual Andean orogen structural setting at this latitude it is main controlled through Mesozoic inherited extensional faults and maybe of Paleozoic relic sutures. Between these structures, the San Félix fault inversion during the Incaic tectonic phase, it is a fundamental role in the Coastal Range and her relation with the Frontal Range, this mark the limit between both morph-structural domains. The latitudinal variations recognized, by the comparison between northern and southern limbs, was mainly (1) southward Mesozoic sequences thickness decrease, (2) diachronic deformation chronology, with start of compressive activity at 110Ma in Vallenar, and at 80Ma in Copiapó, (3) tectonic inversion mechanism dominated by reactivation of normal structures inherited of Mesozoic extensional basins in northern segment, and dominated by decapitation of these structures in southern segment, and (4) deformation propagation eastward since late Cretaceous until present in northern limb, , while in southern limb , the deformation was propagated eastward between Albian - Paleocene and westward since Paleocene to Miocene. The factors that possibly have greater influence in the Orocline, are the tectonic inversion mechanism and the deformation propagation, because determine the main structures vergence and the tectonics transport sense.
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Tesis (Geólogo)
Palabras clave
Geología Estructural, Chile, Vallenar, Cordillera de Vallenar (Chile)