Granitoids of the Coast Range of central Chile: Geochronology and geologic setting

The Southern Coastal Batholith of central Chile is mainly composed of calc-alkaline granitoids of Late Carboniferous to Permian age. There is no clear evidence of the existence of older plutonic rocks in the batholith. The granitoids are intruded into an accretionary prism which underwent contemporaneous metamorphism. Triassic high-level plutons of limited areal extent occur as post-tectonic bodies in the high P/T metamorphic belt of the subduction complex. Jurassic plutons, which increase in volume toward the northern limit of the area and beyond, are associated with a tectonomagmatic event which, in certain localities, remobilized and re-set the ages of the Paleozoic granitoids. Cretaceous plutons occur to the east of the Southern Coastal Batholith. Initial ⁸⁷Sr/⁸⁶Sr ratios of the Paleozoic granitoids (0.706 to 0.707) are higher than those of the Mesozoic plutons (∼0.704) which were derived from a source similar to that of the present-day volcanic rocks of this segment of the Andes. The northern limit of the Paleozoic rocks is presumed to be an east-west fault zone, apparently inactive since Jurassic times. The continuity of the Mesozoic granitoids is not affected by this boundary.