Graben Formation — the Maltese Islands — a Case History

Abstract

A B S T R A C T lilies, J.H., 1981. Graben formation -the Maltese Islands -a case history. In: J.H. Ulies (Editor), Mechanism of Graben Formation. Tectonophysics, 73:151-168.The structural setting of the Maltese Islands is governed by two rift systems of different ages and trends and the interference of both. Accompanying faults are exposed at many places along cliffs and belong to the most spectacular phenomena of rift faulting of the world.Malta is part of a wide shelf bridge that connects the Ragusa platform of southern Sicily and the Tripolitanian platform of northern Libya. The archipelago is underlain by a continental crust of African provenance. The older rift generation traversing the islands strikes about 50° to 70° to create a basin-and-range structure on western Malta, Comino and eastern Gozo. This micro-province is framed by two master faults at an average distance of 14 km. Crustal extension started during the Early Miocene, as observed by growth faulting and sedimentary dikes parallel to the future rift. A syndepositional uparching of about 200 m has preceded the physiographical rifting in post-Middle Miocene times. Discrete dip-slip faulting created an external wedge block, split by internal tilt blocks of antithetic character, both compensating an average 15% crustal spreading normal to the rift axis. Shoulder upwarping of approximately 120 m has evolved synchronously with the rifting.Structures of the first generation are crosscut by still active, second-generation rift faults, which on Malta strike about 120°, but on Gozo between 80° and 90°. These faults are associated with the Pantelleria rift, whose deep trough sets immediately south of the islands. Rifting was mainly originated during Late Miocene/Early Pliocene time to continue in parts up to the Present. A set of transform faults runs through the straits on both sides of Comino to form a complicated en echelon or Riedel shear structure on easternmost Gozo and westernmost Malta. Shoulder upwarping related to the Pantelleria rift has considerably tilted the block of Malta NNE-ward and caused the inundated river valleys of the natural harbour of Valletta.The superimposition of two rift structures of different trends has been caused principally by a rotation of the controlling stress regime about 10 m.y. ago. The active A f r o -Eurasian collision front is located about 200 km north and northwest of the islands. A contemporary change of plate tectonic stresses is discussed to explain the intraplate rift pattern on Malta as foreland-specific reactions to plate tectonic processes.

New insights into the genesis of the Miocene collapse structures of the island of Gozo (Malta, central Mediterranean Sea)

“…1b). From the geotectonic perspective, the archipelago is located in the northern African plate, and more specifically on the Pelagian Platform, a continental shelf between southern Sicily (Malta-Ragusa platform) and northern Libya (Tripolitanian platform) (Illies 1981 ; Fig. 1a).…”

“…1a). The general gentle NE dip of the Tertiary strata in the archipelago is attributed to upwarping and backtilting on the NE shoulder of the Pantelleria Rift (Illies 1980(Illies , 1981Grasso & Pedley 1985). An ENE-WSW-trending graben system around 15 km wide extends from southeastern Gozo to the central sector of Malta, including Comino and the straits between the three islands.…”

Landslide susceptibility modeling assisted by Persistent Scatterers Interferometry (PSI): an example from the northwestern coast of Malta

“…The study area comprises the NW coast of Malta and is limited northerly by Paradise Bay and southerly by an E-W-oriented tectonic discontinuity, named Great Fault, which crosses the island and structurally divides it into two sectors (Jongsma et al 1985;Dart et al 1993;Civile et al 2010). The study area is characterized by a horst and graben system that generates an alternation of lowlands and plateaus (Illies 1981): the graben corresponding to valleys and the horst to wide karst plateaus. The latter are made up of Upper Coralline Limestone Formation (Pedley and Clarke 2002) and limited by cliffs, which overlie Blue Clay gentle slopes (Alexander 1988;Devoto et al 2012).…”

Late Oligocene to Pliocene Extension in the Maltese Islands and Implications for Geodynamics of the Pantelleria Rift and Pelagian Platform

“…Within this geodynamic framework, different interpretations have been proposed for the tectonic evolution of the Maltese Islands that are characterized by Oligocene‐Miocene carbonates crosscut by two sets of ENE‐WSW and WNW‐ESE normal faults and by roughly N‐S Neptunian dykes confined in the lower units (Dart et al, ; Illies, ; Pedley et al, ; Reuther & Eisbacher, ). Neptunian dykes are particularly interesting for dating deformation, since they are bodies of younger sediments infilling fissures in rocks exposed on the sea floor (Bates & Jackson, ; Cozzi, ; Črne et al, ; Smart et al, ; Visser, ).…”

“…Reuther and Eisbacher () and Illies () divided the evolution of the graben system in three phases: (1) formation of the ENE‐WSW faults, (2) formation of the WNW‐ESE set, and (3) reactivation of the ENE‐WSW faults in dextral strike slip. Reuther and Eisbacher () did not consider the Neptunian dykes in their reconstruction, while Illies () associated them to an independent movement before rifting. On the other hand, Dart et al () suggested that both ENE‐WSW and WNW‐ESE fault sets are coeval and developed in response to N‐S extension during the Miocene and interpreted the Neptunian dykes as marking the onset of the extension.…”