Crustal structure beneath the Tell and Atlas Mountains (Algeria and Tunisia) through the analysis of gravity data

Abstract

Bouguer and isostatic residual gravity anomaly maps were analyzed for the general crustal structure under the Tell and Atlas Mountains of Algeria and Tunisia. Two-dimensional gravity models and profiles of topography, free-air and Bouguer gravity anomalies were constructed to provide estimates of the crustal thickness and the degree of isostatic compensation. The thickest crust (38–40 km) was found beneath the Saharian Atlas in northern Algeria, whereas under the Tunisian Atlas it is approximately 34–36 km. There is little evidence of crustal thickening due to the formation of the Tell Mountains. Large amplitude negative Bouguer, small amplitude, positive free-air gravity and small amplitude, positive isostatic residual gravity anomalies suggest that Saharian and Tunisian Atlas are partially isostatically compensated with regions of possible overcompensation in Algeria. The boundary between the Saharian and Tunisian Atlas is characterized by negative isostatic residual anomalies, suggesting overcompensation and a thick crustal root; however, the cause may be low density material in the upper crust. The amplitude and width of Bouguer gravity anomalies, and two-dimensional gravity models across the Saharian and Tunisian Atlas indicate that there was a greater amount of crustal shortening in Algeria than in Tunisia.