Geometric changes of plate boundaries along part of the northern Dead Sea Transform: Geochronologic and paleomagnetic evidence

Abstract

The Korazim block, an elevated pressure‐ridge, along with the faults bounding the Sea of Galilee and Hula pull‐apart basins are internal structures of the Dead Sea Transform plate boundary. K‐Ar dates and paleomagnetic data from basalt flows and sedimentary strata are utilized to determine the stratigraphy and the deformation of the region. The integration of the two methods, together with structural data, yield high‐resolution age determination of the stratigraphic sequence and provides insight into the timing and style of deformation. The Korazim block is covered in its southern and central areas by Pliocene basalt flows (the Cover Basalt, 5.1–3.6 Ma, and Ruman Basalt, 2.9–2.2 Ma, formations) and in its northern area by basalts (Yarda Basalt, 0.9–0.8 Ma) and sediments (3.0–2.3 and 1.6–0.9 Ma) of Plio‐Pleistocene age. The magnetic polarity of a total of 29 lava flows and intercalated sedimentary strata is mixed; the mean magnetic declination of the 29 sites shows an anomalous direction which yields 11.4° ± 4.0° counterclockwise rotation with respect to the expected field. The mean inclination of 46.0° ± 4.1° does not significantly deviate from the expected field. The anomalous declination is interpreted as the consequence of faulting and block rotation accommodating internal deformation. This deformation did not begin before late Pliocene to early Pleistocene, probably not before 0.9 Ma, and may still be active. Simultaneous right‐lateral slip (of 50–175 m) with a small reverse component (of 30–90 m) along NW trending faults and 11° counterclockwise rotation created internal deformation of the Korazim pressure ridge. This deformation is the consequence of left‐lateral slip along the Almagor strand of the Dead Sea transform, subparallel to the plate slip vector. Thus a compression component was formed which presumably led to the internal deformation of the Korazim block. The recent deformation of the Korazim block in relation to the age of adjacent structures and to the age of the Dead Sea Transform permits temporal resolution of geometric changes which must typify transform boundaries such as the Dead Sea Transform. Internal structures within transforms may change, along with the transform internal geometry, and become inactive, while new structural features may develop.