Fault Striae Analysis and Paleostress Reconstruction of the Northern Tectonic Province (Egyptian Nubian Shield): Insights into the Brittle Deformation History of the Northern East African Orogen

Abstract

Abstract The Egyptian Nubian Shield (ENS), the northwestern continuation of the East African Orogen (EAO), comprises a variety of three lithologically and structurally different tectonic provinces—southern compressional-, central transpressional/wrench-, and northern extensional- provinces. The extensional tectonic province (ETP) extends from Qena‒Safaga shear belt up to the northern tip of the ENS. Several lines of evidence indicate extensional regime in the ETP, such as mantle delamination-induced post-orogenic magmatism and bimodal Dokhan Volcanics, together with the pervasive E‒W dyke swarms and the E‒W (to ENE‒WSW) oriented extensional fractures. The present work is devoted to carry out the fault striae analysis and paleostress reconstruction of the northern tectonic province (ENS) in attempt to add more contribution to the brittle deformation history of the northern EAO. Field measurements collected from six areas (I‒VI) have been processed using Win-Tensor Software. Analysis of fault-slip data revealed four paleostress tensor stages (groups or regimes) that prevailed in the ENS. The stress states and related tectonic regimes are characterized by the stress regime index R' and the horizontal stress axes as follows: 1st stage: transpression (R' = 1.91), E‒W compression (SHmax = N090°‒270° E); 2nd stage: transtension (R' = 1.16), N‒S compression (SHmax = 174°‒354° E); 3rd stage: transpression (R' = 1.81), NE‒SW compression (SHmax = N053°‒233° E); 4th stage: extension (R' = 0.31), E‒W extension (Shmin = N074°‒254° E). The 1st stage can be related to the oblique convergence between E and W Gondwanalands. The 2nd stage was probably concurrent with the N- to NNW-ward migration of the Central Eastern Desert syn-collisional delamination (triggering orogen-parallel extensional collapse) to the North Eastern Desert post-collisional delamination. The 3rd stage was controlled by the generally N‒S shortening which affected the northern and central ENS, post-dating the formation of volcanosedimentary Hammamat Basins. The 4th stage is akin to retreat of the Cadomian arc and the Red Sea rifting.