“Much of central and eastern Duke Island is underlain by a large body of pyroxene gabbro that consists of varying proportions of olivine, hypersthene, augite, plagioclase, hornblende, and minor opaque minerals (Irvine, 1974). The gabbro intrudes deformed and metamorphosed Ordovician and Silurian sedimentary and igneous rocks [unit SOgi, here] and in turn is intruded by Cretaceous ultramafic rocks [unit Kum, here] * * *” (Berg and others, 1988). Gehrels and others (1987) report a U/Pb age of 226±3 Ma