Geochronology of the Lake Region of south-central Chile (39°-42°S): Preliminary results

Carboniferous, igneous, and metamorphic rocks, followed by Jurassic, Cretaceous, and particularly extensive Miocene granitoid plutons, crop out in the Andes of the Lake Region, as determined by new K-Ar and Rb-Sr whole-rock age determinations. Their spatial distribution appears to define the following: the westernmost and easternmost Paleozoic belts, an oblique belt of Jurassic age, a NNW belt of Cretaceous age developed mainly in Argentina but entering Chile at 39°30′S, and a N-S belt of Miocene batholiths and stocks. This distribution of plutons is unlike the west to east younging belts that have been described from the Andes between 28°S and 32°S. This difference could be related to the presence in the Lake Region of old lineaments oblique to the direction of the Andes and to the influence of the Liquiñe-Ofqui fault zone as a pathway for Miocene magmas. The narrowness of the zone of magmatism from late Paleozoic to Miocene times, compared to the wide outcrops of the Paleozoic accretionary wedge, could be explained by the lack of tectonic erosion during Mesozoic-Cenozoic subduction and the constant subduction geometry.