The Malta Horst is a NW-SE trending, 30 km-wide structural high situated on the southern Hyblean-Malta Plateau, which is an African continental indenter in collision with Eurasia. Sediments consist of a shallow marine carbonate platform succession (Mesozoic to Oligocene) capped by Miocene pelagic carbonates and marl. Utilizing seismic profiles, well data, and outcrop observations, this study provides the first description of kilometre-scale contractional structures within the horst and analyses the reactivation of normal faults by transcurrent movement under NW compression. The tectonic evolution of this foreland region is defined by five distinct phases (A through E), alternating between extension and compression. This cyclicity reflects the interplay between the migrating Calabrian Arc and the converging African craton. Initial NE-SW trending faults (Phases A and B) developed during the Late Oligocene to Early Miocene, coinciding with platform drowning. Following Tortonian uplift (Phase C), accelerated migration of the Calabrian Arc during Phase D triggered N-S extension, establishing the NW-SE and NE-SW normal faults that bound the Malta Horst. The neotectonic regime (Phase E) marks a return to dominance of the NW-directed compression by the African craton as the Calabrian Arc migration decelerated. This regional stress field has reactivated the NW-SE marginal normal faults through strike-slip motion. The combination of transcurrent drag and regional compression has inverted Phase A NE-SW normal faults into oblique reverse faults. These thrusts sole along a weak top Eocene evaporite décollement, producing a series of folds and inverted basins within 10 km of the horst's northeast margin. Onshore, these structures are manifest as en echelon, non-cylindrical, and doubly plunging folds that define the topography of Malta's northeast coast. These shear zone structures are thin-skinned deformations in Oligo-Miocene sediments controlled by thick-skinned, W-E transcurrent movement in the crust and Mesozoic sediments. Ongoing compression suggests an increase in seismic risk proximal to the Maltese Islands, with significant implications for local geohazard frequency and magnitude.
Peter Gatt (Thu,) studied this question.