Continental transform–rift interaction adjacent to a continental margin: The Levant case study

Abstract

The propagation and geometry of plate-bounding faults such as the Dead Sea Transform (DST) are strongly related to interactions between major pre-existing fault systems and adjacent continental margins. We review, compile and evaluate the geological and geophysical data from major fault systems in the Levant, including the Carmel–Fari'a fault system (northern Israel), the Azraq–Sirhan Graben (ASG) and Irbid rift zone (northwest Jordan) and the DST, in the aim of better understanding their structure, evolution and mutual relations next to the Levant continental margin. We demonstrate that the continuous Late Cretaceous Carmel–Fari'a–ASG fault system serves as a good marker for reconstructing the Cenozoic sinistral motion of ~90–100km along the DST. Two deep basins (>2000m) on either side of the DST, Beteha (northeast Sea of Galilee) on the east and Bet She'an on the west, are filled by twice as much Neogene sediments as that in the surrounding regions. These basins were probably interrelated and formed coevally when the Irbid rift (northwestern Jordan and southern Golan Heights) and the DST fault systems interacted during the Middle Miocene. At that stage, the Arabian plate completed a relative ~35km northward movement and the initiation of volcanic activity defines a Miocene age (~16Ma). This evidence indicates an average, age-dependent, motion rate of ~8.5mm/year along the DST in the Early–Middle Miocene. After interaction with the DST, the active NW-striking Irbid rift opened the Lower Galilee valleys (Harod and Yisre'el) by the Carmel–Gilboa fault zone. This active rifting succeeded in cutting across the Levant continental margin. The DST segments north of the Dead Sea basin form a right-stepping pattern and the complex structure of the DST–Irbid rift interaction resulted in a ~5km deep basin extending from the Bet She'an region to the northern Sea of Galilee. The extensive NW-striking faults within the Galilee and NE-striking faults within the Golan Heights are also the result of the transform–rift interaction adjacent to the continental margin, rather than from transform motion alone. Results of 3-D lithosphere-scale numerical simulations of the faulting process associated with the northward propagating DST distinguish the role of different factors affecting the transform geometry. An oblique northwestward zone consisting of left-stepping segments is anticipated to be in a lithosphere with a flat regular structure lacking any pre-existing fault or rift zones. A number of extensional structures, east–west normal faults and local pull-apart basins are associated with the propagating transform. However, strike-slip motion across a realistic northeastward-trending continental margin slightly changes the direction of the propagating zone toward a N–S direction, eliminating most of the extensional structures. This study demonstrates how the trace and geometry of the DST is associated with the slope of the continental margin and pre-existing major fault system. The present observational-modeling approach might be useful to other plate-bounding faults and sheds light on features of large strike-slip fault systems.