Abstract
The Alumine Basin is a volcano-sedimentary depocentre located in the Andean retroarc at 39°S. It is the southern part of a major depositional system: the Bio Bio-Alumine Basin. Stratigraphical, geochronological, sedimentological and structural analysis allow us to conclude that the basin evolved through two stages: an Oligocene extensional stage filled with basalts and reworked volcaniclastic and pyroclastic deposits (Rancahue Formation) and a Miocene contractional stage, filled with alluvial and pyroclastic deposits covered by basaltic lavas (Chimehuin and Tipilihuque formations). The volcanic-rich (basaltic) infill of the extensional stage has a western provenance and was derived from widespread magmatic activity that took place during the Oligocene in the adjacent cordilleran axis. The contractional stage basin is an intramontane depocentre limited by uplifted blocks generated mainly by the inversion of Mesozoic extensional faults. It is strongly asymmetric and shows eastern provenance. Structural and geomorphological evidence indicate the existence of a non-depositional hiatus between the two stages.
Highlights
The Aluminé Basin is a volcano-sedimentary depocentre located in the Andean retroarc at 39°S. It is the southern part of a major depositional system: the Bío Bío-Aluminé Basin
Stratigraphical, geochronological, sedimentological and structural analysis allow us to conclude that the basin evolved through two stages: an Oligocene extensional stage filled with basalts and reworked volcaniclastic and pyroclastic deposits (Rancahue Formation) and a Miocene contractional stage, filled with alluvial and pyroclastic deposits covered by basaltic lavas (Chimehuín and Tipilihuque formations)
The contractional stage basin is an intramontane depocentre limited by uplifted blocks generated mainly by the inversion of Mesozoic extensional faults
Summary
La historia cenozoica del retroarco andino norpatagónico estuvo marcada por la alternancia de períodos tectónicos extensionales y compresivos ocurridos como producto de la dinámica variable del equilibrio de fuerzas que sustentaron la convergencia de las placas de Nazca y Sudamericana (Jordan et al, 2001; Folguera et al, 2003; Ramos y Folguera, 2009). La conformación geológica del área de estudio está caracterizada por la presencia de un basamento paleozoico cubierto de secuencias continentales y marinas mesozoicas que forman el borde occidental de la Cuenca Neuquina, sobre las cuales se disponen volcanitas, piroclastitas y sedimentitas paleógenas y neógenas, generadas durante el desarrollo del edificio orogénico andino (Fig. 2). Ambas fallas limitan la extensión de los afloramientos más importantes de la Formación Rancahue a la parte occidental del área de estudio, en donde la estructura mayor es un amplio e irregular antiforme NE-SW en el cerro Horqueta (Fig. 2), posiblemente relacionado con la existencia de una falla de la misma orientación en el basamento granítico. La Formación Rancahue se encuentra por debajo de la Formación Chimehuín e inclina al este entre 28° y 9°, acompañando la disposición del basamento que se levanta hacia la falla que se observa en el borde oeste (Fig. 2). No se ha encontrado la intercalación entre ambas unidades señaladas en los trabajos iniciales en el área (Turner, 1965)
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