Tectonosedimentary evolution of the Coastal Cordillera and Central Depression of south-Central Chile (36°30′-42°S)

ENCINAS, A.; SAGRIPANTI, L.; RODRÍGUEZ, M.P.; ORTS, D.; ANAVALÓN, A.; GIROUX, P.; OTERO, J.; ECHAURREN, A.; ZAMBRANO, P.; VALENCIA, V.

EARTH-SCIENCE REVIEWS

ELSEVIER SCIENCE BV

Año: 2021 vol. 213

0012-8252

The forearc of south-central Chile (36◦30′ -42◦S) is characterized by the presence of a Coastal Cordillera and a lowlying area known as the Central Depression. The origin of these morphostructural units has been largely debated.They have been ascribed to different ages between the Cretaceous and the Pliocene, and tectonic causes thatinvolve extensional or contractional deformation and have been related to Andean evolution or accretionaryprocesses in the forearc. To investigate the geologic evolution of the Coastal Cordillera and Central Depression inthe cited area, we based on stratigraphy, sedimentology, geochronology (U?Pb, LA-ICP-MS), structural geology,and geomorphology. Our studies, which are based on our own data and a thorough bibliographic review, indicatethe following sequence of events in the tectono-sedimentary evolution of the forearc of south-central Chile duringthe late Cenozoic. The area was subjected to extensional tectonics caused by slab rollback during the OligoceneearlyMiocene, resulting in the genesis of a series of basins filled with volcanic, continental, and marine depositsthat extended from the present Chilean coast to the retroac. The extensional basins were tectonically invertedduring the late Early-Late Miocene, and most of the forearc became a positive relief that was subjected to fluvialerosion. The West Andean Thrust, a major reverse west verging fault in the limit between the Central Depressionand the Andean Cordillera, caused significant uplift of the western flank of the Andes. This triggered flexuralsubsidence and the accumulation of coarse-grained deposits in the forearc during the Pliocene-Pleistocene. Thesudden increase of sediment flux to the trench during this period caused a change from non-accretion or subductionerosion to accretion in the margin of south-central Chile. Progressive growth of the accretionary wedgegave birth to a forearc high, the Coastal Cordillera, which was uplifted in the last 2 Ma. Some forearc areas placedabove subducted oceanic fracture zones did not experience uplift during this period due to the significanttransport of fluid that inhibited the deformation of the accretionary wedge. Our studies show that the lateCenozoic tectono-sedimentary evolution of the forearc in the study area is complex and involves different processesrelated to Andean evolution in the first stage and accretionary processes acting exclusively in the forearc ina second stage. The Coastal Cordillera and the Central Depression of south-central Chile were developed in thelast 2 Ma and are much younger than classically considered.