The Miocene Torres del Paine Intrusive Complex

The Miocene Torres del Paine Intrusive Complex (12.5 Ma; Michel et al., 2008) is formed by a subhorizontal granitic laccolithic that intruded on top of a mafic body. It extends for more than 12 km with a maximum thickness of 2.5 km. The laccolith is emplaced along a shallow to subhorizontal thrust fault, which is associated with internal folding and faulting developed during an early, pre-intrusion, thin-skinned tectonic phase that deformed the Cretaceous country rock (Halpern, 1973; Michael, 1991). Where the intrusion is thickest, it connects downwards with a subvertical feeder dyke emplaced along an old high-angle reverse fault, thought to be related with a period of thick-skinned tectonic shortening that caused a several kilometer uplift to the western block and consequent erosion of the stratigraphic cover (Skarmeta and Castelli, 1997). The granite intruded as a series of three sheets, each one underplating the previous sheet along the top of the basal Paine Mafic Complex. High-precision U-Pb geochronology in single zircon defines a time frame of 90 ± 30 k.y. for the emplacement of the >2000-m-thick granite laccolith (12.593±0.009 Ma to12.431±0.006 Ma respectively, for the first and last sheet of the laccolith; average growth rate: 0.0005 km3 y, total volume: ~88 km3; Leuthold et al., 2012). These results permit identification of the pulses in a 20 k.y. range, which is markedly lower and much more precise than previous data for crustal magma chambers infill.