Structural architecture and tectonic evolution of the Yelleg inverted half graben, northern Sinai, Egypt Adel R. Moustafa * , Hussein G.A. Fouda 1 Department of Geology, Faculty of Science, Ain Shams University, Cairo 11566, Egypt article info Article history: Received 14 October 2013 Received in revised form 27 December 2013 Accepted 3 January 2014 Available online 11 January 2014 Keywords: Gebel Yelleg Gebel Falig Syrian Arc folds Inverted half graben Transpression abstract The Gebel Yelleg area includes a number of folds belonging to the northern Sinai Syrian Arc structures. Detailed surface structural mapping and subsurface (seismic and borehole) data show that the Gebel Yelleg structures are related to Late Cretaceous-Early Tertiary inversion of a Jurassic asymmetric (or half) graben formed during the opening of Neotethys. The inversion structures include a large (45-km long) asymmetric fold (Yelleg Anticline) with a steep flank overlying the southeastern (main) bounding fault of the inverted half graben as well as some right-stepped en echelon folds overlying the northwestern bounding fault of the half graben. The large inversion anticline is dissected by a large number of long, nearly orthogonal normal faults whereas the en echelon folds are dissected by transverse normal faults and two sets of oblique-slip faults. Inversion of the northern Sinai extensional basins is related to Africa- Eurasia convergence and was probably transpressional with a small component of dextral slip. This study shows that the magnitude of inversion in the northern Sinai fold belt decreases toward the southern boundary of the Jurassic extensional province. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Gebel Yelleg (G. Yelleg) is one of three major NEeSW oriented asymmetric anticlines in northern Sinai (Egypt) that belong to the northern Sinai fold belt (Moon and Sadek,1921; Sadek, 1928; Shata, 1959). This fold belt is part of the Syrian Arc system of Krenkel (1925) which is an S-shaped belt of NEeSW oriented anticlines extending from Palmyra in NE Syria to the central Western Desert of Egypt passing through northern Sinai. The three major asym- metric anticlines of northern Sinai (Maghara, Yelleg, and Halal) have SE vergence and are several tens of kilometers long (Fig. 1). The forelimbs of these anticlines are very steeply dipping, vertical, or overturned in places and are bounded by reverse faults (e.g. the Maghara Fold; Al-Far, 1966). Besides these three major anticlines that form the topographic highs of northern Sinai, several smaller folds (up to 10 km long) are also present. The G. Yelleg large asymmetric anticline is bordered on the north by a number of smaller NEeSW oriented folds (Falig, Meneidret Abu Quroun, and Meneidret El Etheili Folds) and on the south by the ENE-WSW oriented faults of the Sinai Hinge Belt of Shata (1959), Figure 2. Two different stress regimes were proposed in the past for the development of the northern Sinai folds. These are: 1) tangential NWeSE oriented compressive stress (Moon and Sadek, 1921; Shukri, 1954; Said, 1962; Youssef, 1968; Abdel Aal et al., 1992) or 2) shear couple (Moustafa and Khalil, 1989, 1995). Shata (1959) proposed a vertical stress model of basement uplift. Moustafa (2010) proposed that the northern Sinai folds were formed by positive structural inversion of Early Mesozoic extensional sub- basins based on surface geological mapping aided by some sub- surface data. Ayyad and Darwish (1996) and Yousef et al. (2010) also proposed basin inversion for similar structures in offshore northern Sinai. The southern edge of the Syrian Arc province in northern Sinai is defined by ENEeWSW oriented faults of the Sinai Hinge Belt (Fig. 1). The latter represents the southern rift boundary of the Neotethys extensional province and separates this province from a platformal area to the south (Moustafa et al., 2014). The acute angle between the steep forelimb of the G. Yelleg Fold (and its underlying inverted fault) and the Sinai Hinge Belt (Fig. 1) perhaps indicates that the Early Mesozoic rifting in northern Sinai was oblique. The main objectives of this paper are to study the geometrical characteristics of the Yelleg inversion anticline (Fig. 2) and to throw light on the structural architecture and tectonic evolution of this portion of the northern Sinai fold belt. This study is based on detailed surface geological mapping of 1100 km 2 area at a scale of * Corresponding author. Tel.: þ20 10 0359 1177. E-mail addresses: armoustafa@sci.asu.edu.eg, armoustafa@hotmail.com (A. R. Moustafa). 1 Present address: Saudi Aramco, Dharan, Saudi Arabia. Contents lists available at ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo 0264-8172/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpetgeo.2014.01.001 Marine and Petroleum Geology 51 (2014) 286e297