A Pan-African core complex in the Sinai, Egypt

B. Blasband; P. Brooijmans; P. Dirks; W. Visser; S. White

B. Blasband Department of Geology, Institute of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, the Netherlands
P. Brooijmans Department of Geology, Institute of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, the Netherlands
P. Dirks Department of Geology, Institute of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, the Netherlands; (*present address: University of Zimbabwe, Mt. Pleasant, Harare, Zimbabwe)
W. Visser Department of Geology, Institute of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, the Netherlands
S. White Department of Geology, Institute of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, the Netherlands

Keywords: extension, non-coaxial deformation, orogenic collapse, Precambrian

Abstract

In the late Precambrian history of the Wadi Kid area in the Sinai, Egypt, two deformation phases are clearly recognized. The first phase, D1 (pre-620 Ma), produced a steep regional foliation, axial planar to upright F1 folds, in rocks of a lower-greenschist grade. This compressional phase of deformation is interpreted in terms of subduction in an island-arc setting. The second phase, D2 (post-620 Ma), is mainly expressed by the widespread development of sub-horizontal mylonitic zones with a total thickness of 1.5 km. Shear sense indicators give a consistent regional transport direction to the northwest, with local indications of reversal to the southeast. This event is associated with regional LP/HT metamorphism, indicative of high thermal gradients. Because of the LP/HT metamorphism, the change in geochemical nature of the granitoids, and the orientation of the dykes, we interpret the mylonitic zones as low-angle normal shear zones related to core-complex development during an extensional event with the transport reversal being induced by doming. We postulate that orogenic collapse was responsible for the transition from the D1 compressional phase to the D2 extensional phase.