Gravity constraints on the structure of the northern margin of Tunisia: implications on the nature of the northern African Plate boundary

Summary Bouguer gravity data were analysed to determine the general crustal and upper‐mantle structure in northern Tunisia. Residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments. Residual gravity anomalies contain short‐wavelength anomalies superimposed on a long‐wavelength component that decreases in amplitude northward towards the Tunisian coastline. An edge‐enhancement analysis (e.g. enhanced analytic signals) of the short‐wavelength anomalies suggests a previously unknown east–west‐trending gravity anomaly south of 37°N with source depths of between 3 and 7 km. Modelling of residual and Bouguer gravity anomalies indicate that there are two possible solutions for the residual gravity decrease in northern Tunisia: (1) thickening of Cenozoic and Mesozoic sediments north of a strike‐slip fault or (2) a crustal and upper‐mantle low‐density zone interpreted as being crustal material of the remnant subducted African Plate. The latter result is favoured based on seismic tomographic images of the Mediterranean region, which implies that subducting material exists under the African coast, geological interpretations suggesting that the Tell Atlas may be a thrust wedge accreted by underplating of the African continental crust and seismic refraction models, indicating a thinning of sediments in northern Tunisia. The east–west‐trending gravity anomalies south of 37°N correspond to an important structural feature that may be related to either a structural boundary (e.g. a transform fault) or subduction beneath the African Plate.