Abstract

The Duque de York Complex constitutes a post-Early Permian to pre-Early Cretaceous metasedimentary succession that crops out at the Madre de Dios and Diego de Almagro archipelagos along the Chilean Patagonian Andes. The petrography and geochemistry of sandstones and mudstones of this complex have been analyzed to characterize its source and depositional tectonic regime. Sandstone modal compositions are dominated by feldspar and, in similar but smaller proportions, by quartz. The mineralogical composition of the sandstones and mudstones is compatible with a low-grade sub-greenschist facies metamorphism. This did not affect significantly the geochemical compositions of these rocks. Nevertheless, the geochemical analyses reveal variable K+ enrichment, especially in the mudstones. Chemical Index of Alteration values of the sandstones and mudstones range between 58 and 71, indicating that the sediment underwent moderate chemical alteration in the source area or during transportation. Sandstone modal compositions are consistent with erosion of the plutonic roots of a magmatic arc. Geochemical provenance indices suggest a relatively evolved source, close in composition to typical continental magmatic arc granodiorite. Deposition of the detritus is most likely to have occurred within an active continental margin. Geochronological, petrographic, and geochemical similarities between the metasediments of the Duke de York Complex, the LeMay Group (Western Antarctica) and the Permian-Late Triassic Rakaia terrane (New Zealand) suggest a common geodynamic set-up for these three successions. This likely constituted an extensive late Paleozoic-early Mesozoic active continental margin, possibly along the Antarctic sector of Gondwana