Paleozoic terranes of the central Argentine‐Chilean Andes

Abstract

The recognition of accreted terranes and their importance in orogenesis has spurred the search for allochthonous fragments along the western and southern margins of South America. Here we present stratigraphic and petrologic data from Chile and Argentina between 29° and 33°S latitude that demonstrate the “suspect” nature of several major terranes, which we infer to have been accreted during the Paleozoic. Three lower‐middle Paleozoic terranes are described (from east to west): (1) the Pampeanas terrane, a Cambrian‐Devonian magmatic and metamorphic province built on late Precambrian basement at the margin of South America, (2) the Precordillera terrane, a Cambrian‐Devonian shelf‐slope‐oceanic basin assemblage bounded by mélanges on both sides and bearing many stratigraphic similarities to the lower‐middle Paleozoic of the Northern Appalachians, and (3) the “Chilenia” terrane, which has largely been obliterated by late Paleozoic magmatism and metamorphism. The distribution of Carboniferous continental, deltaic, and marine strata demonstrates that these three terranes were sutured together and part of South America by the end of the Devonian. Subsequent Permo‐Carboniferous plate interactions more closely resembled the modern Andean margin, with eastward subduction, accretionary prism formation, and minor terrane emplacement exposed along the present coast of Chile and eastward migrating arc magmatism from the present coast of Chile to western Argentina.

Metamorphic evolution of the Sierras de San Luis, Argentina: granulite facies metamorphism related to mafic intrusions

“…The present morphology and tectonic setting is very similar to that of the Rocky Mountain foreland province of the North American Cordillera (Jordan et al, 1983;Jordan and Allmendinger, 1986). Several workers have investigated the large Preandean crystalline blocks during the last 80 years (Gerth, 1913;Bonorino, 1961;Gordillo and Lencinas, 1979;Rapela and Shaw, 1979;Rapela et al, 1986Rapela et al, , 1998Ramos et al, 1986;dalla Salda, 1987;Jordan et al, 1983;Jordan and Allmendinger, 1986;Coira et al, 1982;Sims et al, 1998;Gervilla et al, 1997;von Gosen, 1998;Llambias et al, 1998;Grissam et al, 1998). Most attention was paid to the huge granitic batholites (Rapela et al, 1986(Rapela et al, , 1995(Rapela et al, , 1982 or the abundant ma®c-ultrama®c bodies (Bonorino, 1961;Sabalua, 1986;Malvicini and Brogioni, 1992;Mogessie et al, 1994Mogessie et al, , 1995Mogessie et al, , 1996Bjerg et al, 1997;Hauzenberger et al, 1996Hauzenberger et al, , 1997Gervilla et al, 1997).…”

Distribution, mineralogy, petrography, provenance and significance of Permian ash-carrying deposits in the Paraná Basin

“…Apropos it is worth specifying here that U-Pb radiometric dating on zircon from bentonite horizons of the Irati Subgroup gave 263 + Ma (Hachiro and Yamamoto, in preparation). Coutinho et al (1982) had previously directed attention to the occurrence of rhyolitic ash sources along the Argentinian Cordillera Frontal, Permian Choyioi Volcanics (Ramos et al, 1986), and "Formación Variscica de Choyioi" (Caminos et al, 1979). Farther southeast, another possible source is envisaged in the volcanic ignimbritic plateau of western La Pampa Province (Lambias and Leveratto, 1975).…”

Ordovician back arc foreland and Ocloyic thrust belt development on the western Gondwana margin as a response to Precordillera terrane accretion

“…[2] Interior mountain belts on the western margin of North and South America, to the east of the present tectonic trench, have been interpreted as a composite mosaic of microplates that collided or accreted to the continental lithosphere after traveling great distances [e.g., Coney et al, 1980;Ramos et al, 1986]. Intervening regions were defined as exotic terranes and are widely described as allochthonous lithosphere clasts [e.g., Howell, 1985].…”