K-Ar and Fission Track Mineral Age Determination of Igneous Rocks Related to Multiple Magmatic Arc Systems Along the 23°S Latitude of Chile and NW Argentina

Abstract

K-Ar and fission track mineral age determinations and fission track length measurements were performed on several plutons which together form a cross section along 23°S lat. running from the Coastal Cordillera of northern Chile to the Cordillera Oriental of northwestern Argentina. The spectrum of apparent mineral ages of the different plutons, ranging from about 530 to 30 Ma, support the present general ideas about the magmatic and tectonic evolution of this area. A strong relation is seen between the mineral ages and variations of the subduction regime. The plutons intruded at different depths; some of them belong to the Jurassic-early Cretaceous magmatic arc system 10 to 12 km deep, while others of the mid-Cretaceous magmatic arc system and especially those related to the late Cretaceous-Palaeogene magmatic arc systems were emplaced at shallow depths. These plutons were brought to the surface in the final emplacement of the arc systems by tectonic uplift. The mineral ages of Palaeozoic basement rocks, situated farther to the east, show a more complex history with fmal uplift during Eocene-Oligocene tectonism.