Abstract Early Paleozoic rocks are widespread, superbly exposed, and reach several thousand metres thick in southern South America. A largely quadripartite geotectonic subdivision of this huge area encompasses: (1) intracratonic basins forming the sedimentary cover of the Amazonian craton (Brazilian collage); (2) a clastic platform surrounding the Amazonian craton and the Pampia Terrane (Sierras Subandinas and Cordillera Oriental); (3) subduction-related parautochthonous volcanic arcs and associated volcano-sedimentary basins (Puna–Famatina arc); and (4) crustal fragments accreted to the proto-Andean margin of Gondwana (e.g. Cuyania Terrane). In this context, disparity in the geodynamic histories, preserved record and geological knowledge are remarkable. Biostratigraphical frameworks allow the recognition of global chronostratigraphical Ordovician subdivisions with fairly good resolution in the Early and Middle Ordovician of the Precordillera and the Early Ordovician of the Cordillera Oriental of Argentina. In Sierras Subandinas and Cordillera Oriental of Bolivia the Ordovician statigraphy is almost complete, although these extensive regions are still poorly known. In addition, trilobite-rich assemblages from the Cordillera Oriental and brachiopod-rich ones from Precordillera and Famatina offer a remarkable template for dissecting regionally different scenarios underlying Ordovician diversifications. Overall, a more complete knowledge of this key area of Gondwana will certainly enhance our understanding of the global dynamics during the Ordovician.

Abstract The southern Patagonian Cordillera south of the present location of the Chile Triple Junction (46.5°S) preserves distinctive deformational and backarc magmatic features that are a consequence of a series of northward-propagating ridge collision events that started at ca. 14 Ma. An abrupt increase of ~2000 m of topographic elevation and the exhumation and uplift of mid-Miocene to Pliocene plutons within the cordillera south of the Chile Triple Junction is accomplished by horizontal compressive deformation (both thin- and thick-skinned) within the Patagonian fold-thrust belt. Ridge-trench collisions have formed asthenospheric slab windows beneath the southern Patagonian Cordillera. Backarc magmatism associated with slab window formation includes a distinctive suite of adakites and extensive outpourings of oceanic island basalt (OIB)-like plateau basalts. The adakites formed from the partial melting of the young, hot trailing edge of the Nazca plate that preceded slab window opening, whereas the OIB-like plateau basalts formed from dynamic asthenospheric flow as the slab windows opened up beneath the backarc.