R. W. H. Butler

Transcurrent fault activity on the Dead Sea Transform in Lebanon and its implications for plate tectonics and seismic hazard

Fault activity within the Lebanese transpression zone, one of the classic examples of restraining bend development on a continental transform, is here investigated using dated geomorphological features. The northern part of the Yammouneh Fault, commonly considered to be the principal active strand on this part of the Dead Sea Transform, has been inactive for the past 5 Ma. Field observations show that basalts, dated as late Pliocene hi age, apparently offset by the Yammouneh fault, unconformably overlie it. The active transcurrent structure is principally, perhaps exclusively, the Roum Fault. The Lebanese transpressive zone has evolved through tune, with migration of fault activity. These results confirm the overlapping transform hypothesis for the Dead Sea system, require the active triple junction between the transform and the Tethyan collision belt to lie offshore SE Cyprus, and have profound implications for assessing seismic hazard hi the Levant.

Testing thrust tectonic models at mountain fronts : where has the displacement gone?

The alternative relationships that can exist between a mountain front and the adjacent foreland basin have been recognized for many years. However, seismic reflection data from such areas are commonly of poor quality and therefore structural models may contain large uncertainties. In view of scientific and commercial interest in mountain belts, we have reviewed the methods for discriminating between alternative interpretations using a case study from the Montagna dei Fiori in the central Apennines, Italy. In this area Mesozoic and Tertiary carbonate sediments are juxtaposed with a foredeep basin containing up to 7 km of Messinian and Plio-Pleistocene siliciclastic sediments. A new structural model for this area demonstrates how the structures in this area form a kinematically closed system in which displacement is transferred from the thrust belt to blind structures beneath the present-day foreland. Growth strata show that Pliocene shortening was initially rapid (15 mm a−1) followed by slower rates during the final stages of deformation. Variations in structural elevation indicate a component of basement involvement during thrusting, and this is further supported by magnetic modelling. The results illustrate the interaction of thin- and thick-skinned structures in the central Apennines, and the methods for discriminating between alternative structural models.

Thrusting and strike-slip tectonics in the Alto Molise region (Italy): implications for the Neogene-Quaternary evolution of the Central Apennine orogenic system

The Alto Molise area belongs to the Apennine orogenic belt, which has been developing since the Late Cretaceous as a result of the Europe–Africa collision. This area is characterized by the complex superposition of different palaeogeographic domains that developed during the Mesozoic along the passive southern margin of Tethys Ocean. These domains have been subdivided into four main structural units; from shallowest to deepest they are: the Sannio pelagic basin, the Latium-Abruzzi carbonate platform, the Molise pelagic basin and the Apulia carbonate platform Units. Until the present study, the tectonic relationship among these units was thought to have been mainly determined by Early Messinian to Late Pliocene thrusting. This paper reports the results of a new geometric and kinematic analysis of the Alto Molise area. This new interpretation of the Alto Molise structural style indicates that strike-slip tectonics played a primary role during post-Pliocene times, greatly modifying the previous Alto Molise thrust structures. Two main tectonic events are recorded, consisting of the Pliocene thrusting of the Molise domain onto the Apulia platform followed by the post-Pliocene disruption and rotation of the pre-existing compressional structures by N–S-oriented, high-angle, right-lateral strike-slip faults. These faults are manifest in the Apulia platform as narrow shear zones, but propagate towards the surface into wider belts of strike-slip and oblique-slip deformation. We have compared our results with published structural, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) data from the Central Apennines. This comparison suggests that the superposition of the younger strike-slip tectonic deformation on the older fold and thrust structures in the Alto Molise area is consistent with block-rotation of a segmented orogen, applied to the whole Apennine system.

Late Proterozoic rift faults and basement—cover relationships within the Ben More thrust sheet, NW Scotland

Recently proposed models for the tectonic evolution of Northern Scotland, involving lithospheric extension during the late Precambrian, are supported by new discoveries and interpretations of early normal faults within the Moine Thrust Belt. Such structures control the preservation of Torridonian sediments beneath the sub-Cambrian unconformity. The Ben More thrust ramp from basement into the Cambrian cover may have been controlled by the early faults. Major synclines within the Ben More thrust sheet appear as tightenedhalf-grabens and thus are composite structures. This may require a re-examination of the field relationships between these folds and the apparently syn-tectonic alkaline intrusions that have been used to date thrust activity. The Ben More thrust sheet of the Moine Thrust Belt contains the most easterly outcrops of Torridonian Supergroup (late Proterozoic) in Scotland (Fig. 1). These sediments and their Lewisian basement are unconformably overlain by the Cambrian quartzites of the Eriboll Sandstone Group. The stratigraphic relationships of these units, with the two unconformities (Cambrian on Torridonian, Torridonian on Lewisian) discordant so that the Cambrian sediments overstep from Toridonian onto Lewisian basement, have been known for over a century. However, the nature of the overstep and its implications for the Precambrian arrangement of Torridonian and Lewisian rocks, is less established. Soper & Barber (1979) inferred the presence of major upright folds with wavelength in excess of 30 km so that Torridonian sediments lie preserved in synclines while the crests of the anticlines are eroded beneath the sub-Cambrian unconformity. This model for Precambrian basement–cover relationships has