Shallow crustal stress and neotectonic framework of the Malta platform and the southeastern Pantelleria Rift (Central Mediterranean)

Abstract

Detailed field studies have been carried out in the Hyblean Plateau , Maltese and Pelagian Islands in order to verify the timing of onset and mechanisms of the major neotectonic structures exposed in these mainland zones of the Pelagian Block. On the island of Lampedusa, on the southern shoulder of the Linosa Graben, NNW-SSE trending faults reveal evidence of sinistral strike-slip displacements since latest Miocene and continuing into recent time. Associated NW-SE trending structures are characterized by normal faulting and E-W trending structures, displaying dextral movements, are less well developed and serve as conjugate shear planes to the NNW-SSE trending sinistral structures. On the volcanic island of Linosa NNW-SSE and NW-SE trending faults control the alignement of volcanic vents and displace Quaternary volcanics. The same tectonic pattern is observed on the Ionian side of the Hyblean Plateau, where Plio-Quaternary structures connected with the neotectonic evolution of the Malta Escarpment are mainly grabens controlled by NW-SE master faults. These grabens intersect coastal horsts elongated in a NNW-SSE direction and flanked by faults subparallel to the trend of the adjacent submerged scarp which defines the western margin of the Ionian basin. The Maltese Islands, lying on the northeastern shoulder of the Malta graben, are dominated by a NE-SW trending set of normal faults, the product of a Lower Miocene aborted stage of rifting . Evidence of the Miocene onset of rifting in southern Iblea is the growth of the Ispica Fault System which parallels in trend, time and evolution, the NE trending Victoria Lines System on Malta and Gozo. On the Maltese Islands, these older NE trending faults are cut by yo unger NW-SE trending normal faults. Dextral movements are recorded on E-W trending fault planes as well as on northeasterly trending older structures, partly reactivated during post-Messinian time. In the Pantelleria Rift , which includes the main submerged grabens of the Strait of Sicily, such as the Pantelleria, Malta and Linosa troughs, the principal faults trend N 80°-100°, N 120°-130° and 150°-160°. A NW oriented maximum horizontal principal stress SHmax active during neotectonic times on wide areas surrounding the Pelagian Block was confirmed by analysis of field structures and by in situ stress determinations carried out on Malta and on southern Iblea. The present day stress system causes a mainly pure shear deformation on the Pelagian Shelf. Conjugate E-W trending dextral and subordinate NNW-SSE trending sinistral strike-slip faults, lead to the development of feather and pull-apart grabens with an overall NE-SW oriented extension. The neotectonic structures on the western belt of the Hyblean Plateau are dominated by a dextral strike-slip zone , the Scicli Line. This line, together with a number of associated faults, transects from south to the north, the western margin of the Hyblean Foreland. In situ determined shallow crustal stresses and the analysis of the fault pattern lead to a model of the fault kinematics of the Pantelleria Rift system and its influence on the neotectonic processes on the Hyblean Foreland. In a regional context the Scicli Line and accompanying faults cutting the western margin of the Hyblean Plateau are seen as part of a complex transfer zone. This transfer zone or incipient transform connects the southeastern termination of the Pantelleria Rift with the "external " Plio-Pleistocene thrust sheets along the southern front of the Maghrebian Chain. According to this hypothesis, this 80 Km long (about 200 Km, including its offshore extension) tectonic line , plays the same role as better known transform structures connecting axial zones of intraplate spreading with zones of plate convergence.