Long-term (7 Ma) strain fluctuations within the Dead Sea transform system from high-resolution U-Pb dating of a calcite vein

Abstract

The onset of the Dead Sea transform has recently been reevaluated by U-Pb age-strain analyses of fault-related calcite taken from several fault strands along its main 500-km-long sector. The results suggest that the relative motion between Africa and Arabia north of the Red Sea was transferred northward to the Dead Sea transform as early as 20 Ma and along a ∼10-km-wide deformation zone that formed the central rift with contemporaneous bounding sinistral motion. The Gishron fault is the western bounding fault with normal and sinistral fault offsets that placed Proterozoic crystalline rocks and a cover of Cambrian sandstones in fault contact with Cretaceous-Eocene carbonates. Fault-related calcite veins are common in the Gishron fault zone, and we report the results of a detailed study of one sample with nine calcite fillings. Low fluid inclusion entrapment temperatures <50 °C, stable isotopes values of −3.3−0‰ (δ13C; PDB) and 15.3‰ to 17.6‰ (δ18O; SMOW), and low rare earth element (REE) concentrations within the nine calcite fault fillings indicate that a local, meteoric fluid fed the Gishron fault zone over ca. 7 Ma at depths of <2 km. Laser ablation U-Pb ages within the thin section range from 20.37 Ma to 12.89 Ma and allow a detailed fault-filling chronology with the oldest calcite filling in the middle, younging outward with shearing between the oldest eight zones, all of which are finally crosscut by a perpendicular (E-W) vein. All nine calcite fillings have unique mechanical twinning strain results (n = 303 grains). Shortening strain magnitudes (−0.28% to −2.8%) and differential stresses (−339 bars to −415 bars) vary across the sample, as do the orientations of the shortening (ε1) and extension (ε3) axes with no evidence of any twinning strain overprint (low negative expected values). Overall, the tectonic compression and shortening is sub-horizontal and sub-parallel to the Gishron fault (∼N-S) and Dead Sea transform plate boundary. Most strikingly, the 7 m.y. period of vein growth correlates exactly with the timing of fault activity as evident within the 10-km-wide deformation zone in this evolving plate boundary (between 20 Ma and 13 Ma).