New insights on structures and active faults in northeastern Tunisia (Utica-Mateur region) from a gravity analysis: Geodynamic implications

Gravity data were analyzed in conjunction with earthquake, seismic reflection, and geological data to investigate the upper crustal structure of the Utica-Mateur region of northeastern Tunisia and relate this structure to the current tectonic environment of northern Tunisia. To accomplish this goal, gravity anomaly maps were constructed using isostatic gravity residual methods, match-filtering to create residual anomalies, and horizontal gravity gradients. Additionally, the depths to the major density contrasts were determined using a 2D power spectrum analysis and Euler deconvolution and 2D forward modeling. The residual gravity anomalies interpreted in conjunction with gradient determined lineaments indicate that there are several gravity maxima related to uplifted regions bounded by lineaments that trend mainly to northeast- and northwest. Based on the Euler deconvolution analysis, the majority of these lineaments are located at shallow depths (<6 km) and can be related to the seismic activity of the region. Correlating these newly imaged lineaments, uplifts and subsiding areas with seismicity and focal mechanism studies, a new structural map is proposed for the Utica-Mateur region. The majority of the region can be interpreted by uplifts and subsiding (pull apart basins) areas bounded by strike-slip faults that contain compressional and extensional stress components. This stress regime is thought to be caused by the reactivation of older structures by the current compressional stress regime due to the convergent of Africa and Eurasia and active rifting of the Sicily basin. However, the proposed recent segmentation of a northeast-retreating subducting slab under Africa that caused a major lithospheric discontinuity to the south of the Utica-Mateur region added second and third order tectonic variations. These variations modified the stress regime which caused the formation of strike-slip faults and the gravity analysis indicates that the entire Utica-Mateur region is still affected by this stress field change.