Paleomagnetism as a geochronological gauge for deformational events: Insights from the Najd-related Nugrus Shear Zone, Northern Nubian Shield

Abstract

Abstract The Nugrus Shear Zone (NSZ) of southern central Egypt is a major ductile shear structure with controversial origins. It lies east of the Hafafit Gneissic Complex (HGC) and separates the Central and South Eastern Desert terranes of Egypt. The NSZ has been correlated with the Najd Fault system in Saudi Arabia, and shares orientation and kinematic characteristics with the Najd fault. Previous microstructural studies of the NSZ and HGC have concluded a polydeformation history for the Nugrus area, involving early NW-ward thrusting, followed by NW-SE transcurrent shearing. This contribution reports a combined rock magnetic and palaeomagnetic study of the shear zone and wallrocks that gives a conclusive evidence for the previously mentioned tectonic scenario. Furthermore, the palaeopoles obtained correlate well with the available geochronologically dated poles from Northern Africa, leading to inferred ages for the deformation and thermal events of the area. These ages confirm the previous proposed tectonic models. Three components of Natural Remanant Magnetization (NRM) direction (CA, CB and CD) are identified. Component CA represents the Characteristic Remanent Magnetization (ChRM). Components CB and CD are considered to be secondary magnetization. CA is consistent with arc-related deformation and magmatism at ∼ 700–680 Ma. CB and CD represent the protracted Najd-related shear deformation and transpression at ∼ 650–550 Ma.