Jurassic to miocene K-Ar dates from eastern central Patagonian Cordillera plutons, Chile (45 degrees-48 degrees S)

Thirty-nine K-Ar and one Ar-Ar radiometric dates from the eastern central M eso-Cenozoic Patagonian Batholith and eastern satellite plutons of the Ayse n Region, of southern Chile between latitudes 45 degrees and 48 degrees S, 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 Cretaceou s 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 intermitten t magmatism. Biotite K-Ar dates of c. 143-151 and 106-109 Ma, from cataclas tic granitoids, may be marking the time of deformation. A review of all rad iometric data on magmatic rocks from the region between 45 degrees and 48 d egrees 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.