Abstract

The Coastal Batholith of south-central Chile between latitudes 33 degrees and 40 degrees S is composed of calc-alkaline granitoids emplaced in a relatively restricted time period. New SHRIMP U-Pb zircon ages on eight quartzdioritic to granitic rocks collected over a distance of 800 km yielded ages between 300 and 320 Ma, Pennsylvanian ( late Carboniferous). Lu-Hf isotopic analyses on the same zircon grains have initial epsilon Hf-(i) values from +1.67 to -5.64. The delta O-18 ratios for that grains range from 6.4 to 8.6 parts per thousand. These new isotopic data point to a relative homogeneous source with prominent components of the continental crust. The calculated Mesoproterozoic Depleted Mantel model ages, in addition to the short span of intrusive ages give insights to the position of the proto-Gondwana margin and the changing subduction mechanism at the end of late Paleozoic time.