Abstract

Thirty-nine K-Ar and one Ar-Ar radiometric dates from the eastern central Meso-Cenozoic Patagonian Batholith and eastern satellite plutons of the Aysén Region, of southern Chile between latitudes 45° and 48°, combined with previous dating of seven plutons, have yielded six age groups: (1) Middle to Late Jurassic, (2) Early Cretaceous, (3) mid-Cretaceous, (4) Late Cretaceous, (5) Oligocene and (6) Miocene. In general, the Cretaceous and younger ages correspond to previous reported ages for other parts of the main batholith, but for the satellite plutons to the east show a wider age spectrum than the previously accepted Late Miocene dates. These results indicate a relatively continuous Late Jurassic to mid-Cretaceous plutonism, known to have been coeval with volcanic activity, followed by intermittent magmatism. Biotite K-Ar dates of c. 143-151 and 106-109 Ma, from cataclastic granitoids, may be marking the time of deformation. A review of all radiometric data on magmatic rocks from the region between 45° and 48°S in Chile shows a gap in Palaeocene ages that may correlate with a period of low-angle (flat slab) subduction between 65-50 Ma.