East–West Cross–Section of the Precordillera: from San Juan City to Calingasta Valley Throught the San Juan River Valley
East–West cross–section of the Precordillera: from San Juan City to Calingasta Valley throught the San Juan River Valley Silvio H. Peralta1 1National University of San Juan, CONICET, Av. I. de la Roza and Calle Meglioli, 5400 Rivadavia, San Juan, Argentina. E–mail: speralta@unsj–cuim.edu Introduction The Precordillera Geological Province of the La Rioja, San Juan and Mendoza Provinces (Furque & Cuerda, 1979), stretches almost 400 km in length, and 110 km wide, at the Sierra de Villicum latitude. It is located in western Argentina, located between the Western Sierras Pampeanas to the east and Cordillera Frontal to the west, bounded by major tectonic features. From north to south the Precordillera extends from La Rioja Province, through the San Juan Province, ending on the southern margin of the Mendoza River. As a Geological Province, the Precordillera forms part of the composite Cuyania terrane (Ramos et al., 1984, 1986), which also includes the Sanrafelino–Pampeana Geological Province (San Rafael and Las Mahuidas Blocks) (Criado Roque & Ibáñez, 1979), and the Angaco Belt (Vujovich & Ramos, 1994) from the Western Sierras Pampeanas. The Precordillera represents a high–level fold–and–thrust belt, formed during the Andean (Miocene) orogenesis that produced crustal shortening which affecting the whole pile of Paleozoic, Mesozoic and Cenozoic rocks, with neotectonic features, which demonstrate that Andean deformation is still active. The structural style of the "thin skinned" thrust–and–fold belt of the Precordillera forms a N– S mountain chain, with a maximum elevation of 4340 m (Cerro Pircas) above sea level on the Sierra del Tontal. The Eastern Precordillera (Ortiz & Zambrano, 1981) is characterized by N–S striking imbricate faults with a westward vergence and thick skinned deformation in where, in general, limestone of the uppermost part of the San Juan Formation, form the base of the imbricates, resulting in a structural style similar to that of the Western Sierras Pampeanas.
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