Fault cores, formed through localized deformation within fault zones, preserve records of strain, temperature, and fluid interactions, reflecting both long-term aseismic fault activity and short-term seismic processes. Magnetic properties, highly sensitive to chemical and physical changes, provide a novel and underutilized tool for investigating faulting processes and fault core evolution. This study focuses on magnetic properties to reconstruct the deformation histories of fault cores along two major continental-scale fault systems, the Dead Sea Fault (DSF, Israel) and the Red River Fault (RRF, China). The shallower rocks exposed along the DSF, compared to the deeper rocks along the RRF, together with differences in their exhumation histories, provide an opportunity for a comparative analysis of fault core evolution.
Along the DSF in southern Israel (Elat), juxtaposed red gouge and green clay smear record markedly different deformation histories. The red gouge exhibits a progressive reduction in magnetic grain size, reflecting intense shearing, comminution, and thermal alteration, with isotopic data pointing to its derivation from Neoproterozoic crystalline basement rocks. Mineralogical analyses indicate authigenic illite-smectite formation at temperatures of 240–300 °C at inferred depths of 2-5 km. In contrast, the green clay, which retains sedimentary signatures of Turonian shales, was incorporated at shallower depths during Miocene faulting. These results document the evolution and maturation of DSF fault cores from deep, high-temperature gouge formation to shallow sedimentary smearing.
Along the RRF in Yunnan Province, integrated magnetic, mineralogical, and geochemical analyses provide clear evidence for pervasive fluid infiltration. Magnetic grain size and concentration decrease systematically from the host rocks to cataclasites and fault gouges, accompanied by enrichment in volatiles, rare earth elements, and calcite. These patterns indicate infiltration by hydrothermal fluids. Strong correlations between magnetic and geochemical parameters establish rock magnetic properties as sensitive indicators of fluid-rock interactions.