Geomorphological and geophysical features of the deep structure of southern Pie de Palo, Sierra Pampeanas

Abstract

The results of the present study show relationships between geomorphologic and geophysical evidences with a structure found in the upper crust south of the Pie de Palo range, that should be similar in size. For this purpose, a chart of Bouguer anomalies was calculated from gravity values for the Pie de Palo range and surrounding areas. Besides, the Euler deconvolution method was applied, with window widths from 20 to 25 km and structural indices of 0.5 and 1. The responses obtained with this method using both indices point to a concentration of solutions in correspondence with the following structural features found by geologic research: the Desaguadero-Bermejo megafault; the eastern boundary of the Precordillera; the El Molle megafracture. Moreover, the existence of an important accumulation of trapezoidal shaped solutions was determined south of the Pie de Palo range. Their sources respond to depths from 10 to 20 km. The geomorphologic evidences found in this region seem to corroborate the existence of the formerly mentioned rising structure in the surface, as suggested by the successive migrations of the course of the San Juan river to the north, and of the courses of the Mendoza and Tunuyán rivers to the south and west, which took place in prehistorical and historical times. This tectonic elevation can be compared to the one occurred during 1977's earthquake (Ms7.4) in the province of San Juan, during an important earthquake, when the Pie de Palo range rose 1.20 metres after the seismic event.