Abstract

Metaturbidites of the Eastern Andes Metamorphic Complex, which crop out east of the Mesozoic-Cenozoic Patagonian Batholith, show significant differences in modal and chemical composition with those of the Duque de York Complex which crop out west of the batholith. The modal quartz content of the sandstones of the former is larger and does not spread out of the Transitional Continental field in QFL diagrams as does that of the latter. In the geochemical discrimination diagrams, sandstones from both units plot in distinct fields with little or no overlap. These features strongly suggest different provenance areas and depositional settings. The Eastern Andes Metamorphic Complex was deposited in a basin located on a passive continental margin, and the source area for the clastic rocks had cratonic affinities. By contrast, the rocks of the Duque de York Complex indicate deposition in an active continental margin, which included sedimentary, plutonic, and volcanic rocks, associated with a subduction zone and/or a strike-slip setting. These results suggest that the two units are not coeval, and that they represent deposition before and after the establishment of the active continental margin at the Pacific rim of Gondwanaland during the late Paleozoic or early Mesozoic.