Abstract

New U-Pb detrital zircon ages from seven samples from the Lower Cretaceous Katterfeld and Apeleg formations and Divisadero Group of Central Patagonia in the Aysen Region of Chile, establish the recognition of a Valanginian to earliest Aptian volcanic episode not identified in the rock record of the region, named herein as the Missing Volcanic Arc (MIVA). The available radiometric ages indicates that the inferred plutonic roots of this Missing Volcanic Arc are restricted to a segment 50-km wide and more that 200-km long exposed along the western side of the Patagonian Batholith, and more than 100 km to the west of the former arc of the previous Upper Jurassic to early Valanginian Ibanez Formation and related intra-arc basins, supporting a westward migration of the arc. This migration left a subsiding back-arc region where the former Ibanez Formation volcanic rocks were covered by the younger sediments of the Aysen Basin, a northern sub-basin of the Austral Basin. After approximately 10-11 Ma, during the early Aptian, the arc migrated eastwards, probably due to a shallowing slab, forming the Divisadero Formation and related plutons at approximately the same site of the former Ibanez arc. Our data also supports a 90 Myr continuous magmatism in western central Patagonian from the Late Jurassic to the Late Cretaceous.