Magnetic and microstructural perspectives on faulting in carbonate rocks, northern Israel

Abstract

Shallow crustal faulting involves complex processes, including brittle and ductile deformation, frictional heating, and fluid interaction, which may all leave distinct geological signatures. However, deciphering these mechanisms is challenging. This study investigates the deformation near two faults in northern Israel: the active Nahef East fault and the Qiryat Shemona fault, a major strand of the Dead Sea Fault (DSF) system, both cutting through diamagnetic carbonate rocks. We employ a range of methods, including anisotropy of magnetic susceptibility (AMS), magnetic properties, electron backscatter diffraction (EBSD), and geochemical analyses to target specific faulting processes. Both faults exhibit magnetic fabrics with foliations formed by AMS maximum (K₁) and intermediate (K₂) axes which are scattered on a plane sub-parallel to fault surfaces, extending ∼0.5 m from these fault surfaces. In the Nahef East fault, slight changes in magnetic properties, overall mineralogy and microstructures such as lobate calcite grains, indicate moderate temperatures (<200-250 °C), and fluid interaction, which constrains grain reorientation and the development of crystallographic preferred orientation (CPO). Conversely, in the Qiryat Shemona fault, the small (∼5 μm) twinned calcite grains indicate moderate to high temperatures (>250–300 °C), high stress (≥100 MPa) and dry conditions, potentially reflecting the fault's maturity. Distinct deformation fabrics and microstructural features around these faults reveal localized plastic deformation. The results underscore a potential gap between the extent of deformation observed in natural faults and those replicated in laboratory experiments, likely due to limited sample size and timescale considerations in laboratory settings.