A crustal model based mainly on gravity data in the area between the Bermejo Basin and the Sierras de Valle Fértil, Argentina

The Sierras Pampeanas ranges of central-western Argentina (26°00′S to 33°15′S, 63°30′W to 68°30′W; an area about 450 km wide and 800 km long) consists of a series of uplifted basement blocks bounded by deep sedimentary basins of relatively low relief and covered by modern sediments. The basement blocks of the Sierras Pampeanas are bounded by longitudinal faults that originated during or were reactivated by the Andean Orogeny, then uplifted by reverse faults during the late Tertiary and the Quaternary. Utilizing primarily gravity data, interpreted with the aid of geological information and seismological and seismic data, we developed models consistent with: (1) seismic data on the Moho, and (2) a significant regional gradient of “g” from west to east. In order to be consistent with (1), we took into account the gravimetric effects of the subhorizontal Nazca plate, whereas to be consistent with (2), it was necessary to wedge the Bermejo Basin sediments under very dense positive masses within the upper crust underlying the Sierra de Valle Fértil. Two crustal models were developed by inversion of the Bouguer anomaly. These fully fit the Bouguer anomaly and the geological data and reveal two zones of high density that are interpreted as paleosutures.