4D analogue modeling of transcurrent structures and interactions with thrust front: insights from SW Sicily and the Sicilian Channel

Analogue models were used to investigate the 4D evolution of a transcurrent structure and its interaction with a preexisting thrust front. An analysis of 7 models applying (i) pure strike-slip, (ii) transtension (10/20/30 degrees) and (iii) transpression (10/20/30 degrees) kinematics shows important structural variations in the area of transcurrent fault. Some models closely resemble the geometries of natural interaction observed between the transcurrent transfer zone of the Sicilian Channel (Italy) and the Maghrebian fold-and-thrust belt. The experimental apparatus consists of a box with three independent rigid base plates. These plates were covered by a 4-cm-thick layer of quartz sand. During the first phase of deformation the thrust front was created as the upper plate was sliding on the fixed plate. In the second phase the lower plate was sliding under the fixed plate. The shape of the fixed plate permitted to build a transcurrent fault and at the same time the thrust front was reactivated. The analogue models were analyzed by X-Ray Computer Tomography (XRCT).This technique allows visualization of the interior of a model during deformation without destroying it (4D analysis). In the area of SW Sicily and northern part of the Sicilian channel, two main structures, the Maghrebian fold-and-thrust belt and a transfer zone, interact. The most recent interaction was recorder during the Belice earthquake sequence in 1968 and the calculated focal mechanisms are compatible either with a pure E-W thrust plane or with a prevalently right-lateral movement on a NNW striking, WSW dipping plane. Analyses of multichannel seismic reflection profiles acquired in the northern part of the Sicilian Channel were used to analyze the Sciacca Fault which displays a positive flower structures. The outermost thrust sheet (bottom of Gela Nappe) is interpreted by many authors as a complex, imbricate wedge, involving the sequences of a foredeep basin. The Gela Nappe is well exposed along the southern coast of Sicily, where both Sciacca Fault and Gela Nappe can be observed. The observations suggest that the SW of Sicily and the northern part of the Sicilian Channel were shaped by the occurrence of two tectonic processes, the Maghrebian fold-and-thrust belt emplacement and transcurrent fault acting simultaneously and overlapping each other. The interpretation of seismic reflection profiles, merged into a 3-D model together with the bathymetry, and its comparison with analogue models demonstrated a fair match between the models and natural case. Main equivalences are (i) the presence of well-developed flower structures along the transcurrent structure, (even within a transtensional experiment), (ii) rotation of the thrust front during deformation and (iii) segmentation of transcurrent structure in the area of the thrust front. Additionally, the results of 4D analyses of analogue models give a new perspective of fault development under different transcurrent regimes.