Oppositely dipping thrusts and transpressional imbricate zone in the Central Eastern Desert of Egypt

摘要

This paper documents the 40-60 km wide ENE-WSW trending Mubarak-Barramiya shear belt (MBSB) in the Central Eastern Desert of Egypt by examining its structural styles, kinematics and geometry. Our study revealed the existence of prevalent dextral and minor sinistral conjugate shear zones. The MBSB is metamorphic belt (greenschist-amphibolite) characterized by at least three post-collisional (740-540 Ma) ductile Neoproterozoic deformation events (D_1, D_2 and D_3) followed by a brittle neotectonic deformation (D_4). D_1 event produced early top-to-the-northwest thrust displacements due to NW-SE shortening. D_2 produced discrete zones of NNW-trending upright folds and culminated in initiation of major NW-trending sinistral shear zones of the Najd Fault System (NFS, at c. 640-540 Ma ago) as well as steeply dipping S_2 foliation, and shallowly plunging L_2 lineation. NW-to NNW-trending F_2 folds are open to steep and vary in plunge from horizontal to vertical. D_2 deformational fabrics are strongly overprinted by D_3 penetrative structures. D_3 is characterized by a penetrative S_3 foliation, steeply SE- to NW-plunging and shallowly NE-plunging stretching lineations (L_3), asymmetric and sheath folds (F_3) consistent with dextral sense of movement exhibited by delta- and sigma-type porphyroclast systems and asymmetric boudinage fabrics. D_2-D_3 represent a non-coaxial progressive event formed in a dextral NE- over NW-sinistral shear zone during a partitioned transpression in response to E-W-directed compression during oblique convergence between East and West Gondwana developed due to closure of the Mozambique Ocean and amalgamation of the Arabian-Nubian Shield in Cryogenian-early Ediacaran time.