The application of the sensitive high-resolution ion microprobe (SHRIMP) U/Pb dating technique to zircon and monazites of different rock types of the Sierra de San Luis provides an important insight into the provenance and timing of deposition of the sedimentary precursors as well as the metamorphic and igneous history of the various basement domains. Additional constraints on the Famatinian metamorphic episode are provided by Pb/Pb stepwise leaching experiments on one staurolite and two garnet separates. The results indicate that the sedimentary precursors of the Conlara Metamorphic Complex have a maximum age of c . 590 Ma, whereas the Pringles Metamorphic Complex metasediments appear to be sourced from the Pampean orogen in the Early Cambrian. Folded xenoliths within the c . 496 Ma El Peñón pluton suggest that the host Conlara Metamorphic Complex underwent a Pampean compression. From a 208 Pb/ 232 Th monazite age of 478 Ma for a migmatite from the Nogolí Metamorphic Complex, the structural evolution of this basement complex appears to be entirely post-Pampean. Onset of the Famatinian high-grade metamorphism, between c . 500 Ma and c . 450 Ma, follows a period of crustal extension on the western outboard of Gondwana and might not be related directly to a Mid-Ordovician accretion of the Cuyania Terrane.

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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...