Pleistocene Strain Partitioning During Transpression Along the Dead Sea Transform, Metulla Saddle, Northern Israel

Abstract

The geometry and kinematics of deformation in the Metulla Saddle, a ~4 km-wide and ~9 km-long highly deformed structure across the Dead Sea Transform (DST) between the Hula basin and the Lebanese restraining bend (LRB) is reviewed. The variety of structures exposed provides a unique opportunity to investigate the style and sequence of deformation associated with a transform plate boundary through geological mapping, meso-structural and anisotropy of magnetic susceptibility (AMS) analyses, interpretation of high resolution seismic reflection profiles, and radiometric dating. Cretaceous and Tertiary rocks within the Metulla Saddle are faulted and folded into broad anticlines and synclines, with more intense localized shortening manifested by tight folds and thrust duplexes. There are several structural features that attest to the dominance of a N-S component of shear imposed on the plate boundary zone, including nearly vertical fault planes, horizontal striae, alternating throw from one side of the fault to the other, and an assemblage of en-echelon folds and “positive flower structures”. Kinematic analysis of fault data and principal AMS axes reveals strain axes, which are compatible with simple shear deformation along ~ N-S striking left-lateral faults. Numerous structures revealing the transpressive nature of the Metulla Saddle, including N-S striking reverse faults, reactivated normal faults with reverse motion, and copious N-S trending folds of different scales. Kinematic analyses of these features as well as that of principal AMS axes support distributed E-W shortening within the deformed blocks. Numerous ~ E-W striking calcite-filled veins emplaced in the Metulla Saddle manifest a perpendicular N-S extension response. The U-Th radiometric ages of calcite precipitates obtained and K-Ar dating of folded basalts indicate that Pleistocene activity occurred interchangeably along N-S trending strike-slip faults, N-S trending contractional structures, and ~ E-W calcite-filled veins. The structural analysis provides evidence for the transition from an early (pre-Pleistocene) phase of pure (non-partitioned) strike-slip motion to a late (Pleistocene) phase of convergent strike slip. The latter phase is characterized by strain partitioning during transpression, which is demonstrated by discrete left-lateral strike-slip motion across weak N-S faults and the development of a (mini) fold-thrust belt in response to transform-normal shortening. The contractional structures that evolved in the Metulla Saddle are best interpreted as indicating increased convergence along the DST from the Hula basin northward during the Pleistocene. The increased convergence might be attributed to a more easterly position of the Pleistocene pole of rotation between the Arabian plate and the Sinai sub-plate relative to the pole position describing the total motion in the last 5 Ma.