Morphotectonic and Gravimetric Analysis of the La Burra Valley, Central Precordillera, San Juan, Argentina

PERUCCA, LAURA P.; VARGAS, HORACIO NICOLAS; BEZERRA, FRANCISCO HILARIO; ROTHIS, LUIS MARTÍN; LARA, GABRIELA; VASCONCELOS, DAVID; ALCACER, JUAN MANUEL; AUDEMARD, FRANCK

Advances in Geomorphology and Quaternary Studies in Argentina

Springer

Año: 2019; p. 92 - 113

This work describes new evidence of Quaternary tectonic activity inthe La Burra intermountain valley in the Central Precordillera, San Juan Province, Argentina. Quaternary structures are located in the eastern piedmont of the Sierra de la Crucecita, and western piedmont of the sierra de Talacasto (30º 54??31º S and 68º 47??68º 55? W), about 70 km northwest of the city of SanJuan. By means of morphotectonic analysis, the main deformation features havebeen identified and located in both piedmonts, named from north to south: LasCrucecitas and Vertientes faults (in the eastern piedmont of the Sierra de LaCrucecita) and the Western Talacasto fault system (in the western piedmont ofthe homonymous range). The faults affect alluvial deposits from Late Pleistoceneto Holocene ages. They are defined by a series of features, typical ofcompressive environments such as: slope scarps (eastern piedmont of the Sierrade La Crucecita) and counter-slope scarps (western piedmont of the Sierra deTalacasto), fluvial strath terraces restricted to the hanging block of faults, sagponds, aligned springs, diverted and obstructed drainage, deeply incised andsinuous streams in the hanging blocks, alluvial fans with anomalous slopes,among other features that evidence their Quaternary activity. Six Quaternaryalluvial levels were identified, from the most recent Q1 to the oldest Q6,according to their relative elevation, presence or absence of desert varnish andpavement and degree of incision. The faults affect Q6 to Q2 alluvial levels incoincidence with the east-verging thin-skinned structural style typical of theCentral Precordillera. This deformation is related to the regional tectonics that have been active in the Precordillera area. Besides, the main geological structures were identified by the analysis and interpretation of gravimetric anomalies, employing data obtained from WGM12 (World Gravity Map 2012), which includes earth and satellite gravity data derived from the EGM2008 model. The gravimetrical response of the crustal blocks that compose the area under study, shows a correlation with the most superficial crustal structure and could be associated to the different morphotectonic domains recognized in the region.