Magnetic fabrics of diamagnetic rocks and the strain field associated with the Dead Sea Fault, northern Israel

In order to exploit the potential of AMS axes (k₁, k₂, k₃) and magnitudes as a tool to estimate the strain field around major faults, the AMS of calcite-bearing diamagnetic rocks that crop out next to the Dead Sea Fault (transform) (DSF) were measured. The calcite-bearing Bar Kokhba limestone contains magnetic fabrics due mainly to the diamagnetic phase, as indicated by the low iron content (<130ppm), and strong negative susceptibilities of all the AMS principal axes. The magnetic fabrics are solely controlled by the alignment of c-axes of almost pure calcite crystals and help to assess the strain fields prevailing post-deposition and during the tectonic evolution of the DSF. Based on the AMS measurements of 146 diamagnetic samples as well as 65 paramagnetic samples, three groups of minimum k₃ AMS axes are defined: (1) ∼NNE-plunging axis; (2) ∼NW-SE axis; and (3) ∼E-W axis. The latter two groups of k₃ axes are aligned sub-parallel to Neogene to Pleistocene finite-strain axes inferred from meso-scale structures (i.e., folds, faults and veins) next to the DSF. This indicates that k₃ axes of diamagnetic rocks can be excellent proxies for strain field directions around major faults. Differences in the degree of anisotropy P′ (up to ∼2%) and in susceptibility difference Δk (up to ∼0.2) of the diamagnetic rocks are related to differences in strain magnitudes. Based on the proximity of the studied outcrops to the fault traces, the values of these variables reflect the stored inelastic strain within the calcite matrix due to repeated faulting activity.