Timing of relay ramp growth and normal fault linkage, Upper Galilee, northern Israel

摘要

We investigate a kilometer-scale steep relay ramp structure in the Galilee, northern Israel. The data indicate an asymmetric fold above the buried tip of the southern boundary fault as well as at the lower part of the ramp. Structural analysis suggests that the buried tip of the bounding fault is only a few hundred meters below the surface. A sequence of colluvial wedges, exposed at the base of the southern flank of the relay ramp over the blind tip of the boundary fault, presents successively decreasing angles from 67° at the bottom to 30° at the top. The lower three wedges rest at angles greater than the angle of repose, suggesting tilting during and after deposition. We suggest that the increasing angle of the wedges is the result of the development of the monocline over the buried tip of the boundary fault, which in turn reflects the development of the entire relay ramp structure. Paleomagnetic measurements test this hypothesis. Samples from three of the four lower wedges and the carbonate fill in the fractured bedrock yield northerly declination and positive inclination. Inclination anomalies are 19.4° ± 3.3° and 11.3° ± 1.8° for the fractured bedrock and the wedges, respectively. These anomalies reflect part of the tilt. Paleomagnetic measurements and optically stimulated luminescence (OSL) constrain the time of initial deformation of the monocline above the southern boundary fault between 780 ka and 461 ± 75 ka (OSL age of wedge 1) and the termination of deformation to 176 ± 22 ka (OSL age of wedge 5). These bounding ages suggest tilting rates that range between 1°/16 kyr and 1°/8 kyr. Termination of tilting along the southern flank of the relay ramp and the fact that the tip of the buried normal fault is only a few hundreds of meters below the surface suggest that the relay ramp may be close to being breached by a connecting fault.