Jurassic Cretaceous Palaeogeographic Evolution of the Chilean Andes at 23°–24°S Latitude and 34°–35°S Latitude: A Comparative Analysis

Abstract

A comparative palaeogeographic analysis between the northern (23°-24°S) and central (34°-35°S) Chilean Andes during the Jurassic and the Cretaceous indicates that both regions had the following general palaeogeographic pattern: Successive volcanic arcs shifted to the east of the former arc, and backarc domains with a marine backarc basin in the latest Triassic to early Cretaceous, a continental backarc basin in the late Cretaceous, and a possible marine backarc basin, connected to marine forearc basins in the latest Cretaceous-earliest Tertiary. The particular evolution of these palaeogeographic domains shows some interesting differences. The evolution of the backarc basin in northern Chile corresponds to a single transgression-regression cycle, while the evolution of the backarc in central Chile corresponds to two such cycles. In the volcanic arc domain in central Chile an extensive intra-arc basin developed in the early Cretaceous. This basin was separated from the backarc basin by a volcanic ridge and extended from the Coastal Cordillera to the present international border, with a width of several tens of kilometres. The Neocomian marine sediments, present in the Coastal Cordillera at Antofagasta (EI Way Pm.) and Iquique (Blanco Pm.), correspond to forearc deposits related to the commencement of the early to late ("middle") Cretaceous Quebrada Mala volcanic arc. The similar palaeogeographic pattern which developed in both regions indicates an essentially similar tectonic regime along the continental margin during the late Triassic-Jurassic and Cretaceous. The differences detected in the evolution of some of the palaeogeographic domains were caused by local, though significant, variations in the dominant tectonic conditions and clearly demonstrate the existence of a palaeo segmentation of the mountain range at that time.