Paleogeographic, magmatic and paleoenviromental scenarios at 30°SL during the Andean Orogeny: Cross sections form the volcanic-arc to the orogenic front (San Juan province, Argentina)

ALONSO, SUSANA; LIMARINO, CARLOS O.; LITVAK, VANESA D.; POMA, STELLA; SURIANO, JULIERA; REMESAL, MARCELA

Cenozoic Geology of Central Andes of Argentina

Instituto del Cenozoico, Universidad de Salta

Lugar: Salta; Año: 2010;

In order to summarize the Eocene-Pliocene evolution of the Andean region at 30ºS latitude, seven paleogeographic stages are defined. Paleogeographic Stage I (Middle Eocene-Early Oligocene) comprises volcanic activity along the Andes (Valle del Cura Formation) and fluviolacustrine sedimentation in retroarc positions (Puesto La Flecha Formation). During the Late Oligocene-Earliest Miocene (Paleogeographic Stage II) mesosilicic lava flows were erupted in the Andes (Tillito Formation) and minor volcanic activity was also registered in the Rodeo-Iglesia Basin (Las Trancas Formation). The paleogeography of the region underwent dramatic changes during the Early Miocene (Paleogeographic Stage III) when the Andean compression formed the La Tranca thrust. At this time, basandesitic volcanism prevailed in the Andes (Escabroso Formation), piedmont breccias along the orogenic front and eolian deposits (Vallecito Formation) in distal areas.  Paleogeographic Stage IV (Early-Middle Miocene) is represented by andesites and basandesites (lower Cerro de Las Tórtolas Formation) and retroarc conglomerates (La Ollita Formation). Volcanism extended to the east within the foreland area (Cerro Morado Formation) temporarily separating the Bermejo Basin into two sub-basins. Dacitic volcanism (upper Cerro de Las Tórtolas Formation) and intramontane retroarc sedimentation (Los Bañitos Formation) characterized Paleogeographic Stage V (Middle-Late Miocene). In Precordillera, the continuous eastward migration of the orogenic front relocated the foreland basin in the Jachal valley. During Paleogeographic Stage VI (latest Miocene) the Cordillera de  Colangüil was completely uplifted, thus separating the Rodeo and Valle del Cura Basins. Andean volcanism almost entirely ceased as from the Pliocene (Paleogeographic Stage VII) and thick sequences of playa lake sediments were deposited in the Rodeo-Iglesia Basin. The orogenic front was ultimately transported to the east until it reached its present day position.