The Gondwana connections of northern Patagonia

Abstract

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...

U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls

“…This approach differs from the method used by Lanci et al (2013), where interpreted ash ages were calculated from all zircons between 300 Ma and 250 Ma and included all ages within a dispersed range of up to 20 million years. Results from previous geochronology studies on tuffs within the Karoo Supergroup (Coney et al 2007;Fildani et al 2007, 2009; Lanci et al 2013;Rubidge et al 2013), tuffs within correlative basins (Rocha-Campos et al 2006Spalletti et al 2008;López-Gamundi et al 2013;Domeier et al 2011), and Permo-Triassic crustal plutonic rocks (Pankhurst et al 2014) in South America contained populations of inherited grains. Based on this known inheritance, indiscriminately including these older zircons in weighted age calculations is not a favourable approach to obtain reasonable maximum depositional ages for the Karoo tuffs.…”

Identifying Laurentian and SW Gondwana sources in the Neoproterozoic to Early Paleozoic metasedimentary rocks of the Sierras Pampeanas: Paleogeographic and tectonic implications

“…To the south (Fig. 2b), Cambrian granites (520-530 Ma) have been reported in the basements of the Sierra de la Ventana Tohver et al, 2012), the North Patagonian Massif (Rapalini et al, 2013;Pankhurst et al, 2014) and beneath the Magallanes basin of southernmost Patagonia (Sollner et al, 2000;Pankhurst et al, 2003;Hervé et al, 2010). U-Pb, Hf and O isotopic data of the Cambrian granites of the North Patagonian Massif testify to the presence of continuously recycled older crustal material in the source region of these granites, with largest inherited zircons peaks at 630, 1075 and 1850 Ma , similar to that of the "Puncoviscan Series" (Fig.…”

“…4 the flat slab segment (including some in Patagonia) and in the Paraguay belt in central Brazil are largely covered by younger sedimentary and igneous units (see Tohver et al 2006Tohver et al , 2012Pankhurst et al, 2014;McGee et al, 2014). Several contrasting geodynamic models have been proposed for the evolution of this large sector, but there is a general consensus that crustal accretion mainly took place during two Early Paleozoic orogenic events, the Pampean (Ediacaran-Early Cambrian) and Famatinian (Ordovician-Silurian) orogenies (e.g., Toselli, 1976, 1981;Aceñolaza and Miller, 1982;Rapela, 2000;Schwartz et al, 2008;Dahlquist et al, 2008;Mulcahy et al, 2011Mulcahy et al, , 2014Escayola et al, 2011).…”

The Gondwana Plate margin in the Weddell Sea sector: Zircon geochronology of Upper Paleozoic (mainly Permian) strata from the Ellsworth Mountains and eastern Ellsworth Land, Antarctica

“…The South African flank of this region must also have included rocks of the late Proterozoic Saldanian Orogen (Scheepers and Armstrong, 2002;Scheepers and Poujol, 2002), which extended south offshore (Tankard et al, 2009). Cambrian granitoids are also known from the North Patagonian Massif (Pankhurst et al, 2014) and Tierra del Fuego (Pankhurst et al, 2003), suggesting an extensive Cambrian magmatic province younger and outboard of the Saldanian Orogen. On break-up, the EWB migrated to its present position, relative to East Antarctica, and necessarily the FRB was translated to its present position after rotation and translation of the EWB (or accompanied translation of the latter).…”