New U‐Pb and 40Ar/39Ar age data from deformed and undeformed granitoids of the North Patagonian Massif establish the presence of Early Cambrian and widespread Ordovician magmatism in northern Patagonia. These data suggest that the Pampean (Cambrian) and Famatinian (Ordovician) magmatic belts of the Sierras Pampeanas are continuous into Patagonia. SHRIMP U‐Pb age spectra from detrital zircons of Cambro‐Ordovician metasedimentary rocks show patterns very similar to those from equivalent units of the Pampia block, over 500 km farther north. These results suggest that the North Patagonian Massif was likely part of the South American margin of Gondwana in the early Palaeozoic and strongly argue in favour of an authochtonous or para‐autochthonous origin for this block.

A multidisciplinary study (U-Pb SHRIMP geochronology, Hf and O isotopes in zircon, Sr and Nd isotopes in whole-rocks, as well as major and trace element geochemistry) has been carried out on granitoid samples from the area west of Valcheta, North Patagonian Massif, Argentina. These confirm the Cambrian age of the Tardugno Granodiorite (528 ± 4 Ma) and the Late Permian age of granites in the central part of the Yaminué complex (250 Ma). Together with petrological and structural information for the area, we consider a previously suggested idea that the Cambrian and Ordovician granites of northeastern Patagonia represent continuation of the Pampean and Famatinian orogenic belts of the Sierras Pampeanas, respectively. Our interpretation does not support the hypothesis that Patagonia was accreted in Late Palaeozoic times as a far-travelled terrane, originating in the Central Transantarctic Mountains, and the arguments for and against this idea are reviewed. A parautochthonous origin is preferred with no major ocean closure between the North Patagonian Massif and the Sierra de la Ventana fold belt.Supplementary material: [U-Pb SHRIMP Analytical Data, Geochemical Analyses and Sample GPS locations] is available at ww.geolsoc.org.uk/SUP00000 3 The hypothesis that Patagonia originated as a far-travelled terrane that became accreted to the rest of South America in Late Palaeozoic times (Ramos 1984) has proved remarkably resilient. It proposes collision of a Patagonian terrane with the rest of South America along a hypothetical suture now buried beneath the Río Colorado basin (Fig. 1), causing NEvergent deformation in the Palaeozoic sedimentary succession of the Sierra de la Ventana (Sierras Australes) and SW-vergent thrusting in northern Patagonia (von Gosen 2003 and references therein). Nevertheless, despite years of further investigation, relevant evidence is still scarce and sometimes inconclusive. Whereas some geophysical surveys have been claimed to show a major crustal discontinuity along the proposed suture zone (e.g., Chernicoff & Zappettini 2004), others have emphasized the complexity of the underlying block structure and the importance of east-west displacements, but do not indicate an overall difference in gravimetric signature across the boundary (Kostadinoff et al. 2005;Gregori et al. 2008). Palaeomagnetic data permit, but do not require, a small separation of the landmasses on either side in Devonian times (Rapalini 2005). Other authors have argued that Patagonia was an autochthonous part of South America (e.g., Varela et al. 1991; Dalla Salda et al. 1992). Rapela & Pankhurst (2002) and Pankhurst et al. (2003) supported the idea that the Early Palaeozoic Pampean and Famatinian magmatic belts of the Sierras Pampeanas might be traced continuously into the basement of the Sierra de la Ventana and northeastern Patagonia, respectively. Pankhurst et al. (2006) emphasized the idea that the North Patagonian Massif at least was an autochthonous part of South America, with a Carboniferous collision zone farth...