The Triassic Pichidangui Formation in central Chile (31°55′ to 32°20′) is a bimodal volcanic sequence composed of rhyolites, ignimbrites, basalts and basaltic andesites, and turbiditic sedimentary rocks. The basic lavas are completely different from the Mesozoic calc-alkaline “Andean” Jurassic and Lower Cretaceous rocks. They show primitive chemical characteristics such as a convex-up rare-earth element pattern similar to the ocean-plate basalts from the Nazca Plate but their Sm/Lu ratios reflect a more advanced degree of differentiation, similar to the Southern Volcanic Zone of the Andes. The chemical signature of the Pichidangui volcanic rocks is consistent with volcanism in a volcanic arc floored by a quasi-oceanic crust, either formed at the rim of Gondwanaland before its dismembering, or belonging to an allochthonous terrane.