Second International Conference on the Geology of the Tethys, Cairo University, March 2007, P. 27-34 POST-EARLY EOCENE FOLDING AND FAULTING AT JABAL HAFIT, SOUTHEAST OF AL AIN, UNITED ARAB EMIRATES U. Zaineldeen*, and A. Fowler** * Department of Geology, Faculty of Science, Al Azhar University of Gaza, P.O. Box 1277, Gaza, Palestine ** Geology Department, Faculty of Science, United Arab Emirates University, P.O. Box 17551, Al-Ain, UAE ABSTRACT The present study presents the detailed structural study of Jabal Hafit, southeast Al Ain city, Abu Dhabi Emirate, United Arab Emirates. Combined structural mapping and field measurements, with analysis of aerial photographs were carried out at Jabal Hafit to understand and clarify the origin of Hafit structure. Although the major structure of Jabal Hafit is anticline fold, faults and joints are the main structural elements affected the Lower Eocene sediments in the study area. Four main directions of faults have been recognized. These directions include: NE-SW, E-W, NW-SE and N-S trends. Most of these faults were created during Late Cretaceous, and reactivated during Paleocene - Eocene and Miocene. E-W trending faults were created in Paleocene to Early Eocene. Surface faults show that faulting took place under shallow brittle deformation. Joints are the second major structural elements. The directions of these joints are from the oldest: NW-SE, N- S, E-W and NE-SW. Two generations of Tertiary folding affected the study area. The first generation includes Hafit anticline that plunges 02/343 to the north. The second generation is considered as a minor one and recorded in this study at Jabal Hafit. These minor folds are plunging 04/263 to the west and 02/082 to the east. INTRODUCTION Jabal Hafit forms conspicuous geological feature. It is one of the foothills of the Northern Oman Mountains (Fig. 1). It is located to the southeast of Al Ain city, United Arab Emirates. It is bounded to the north by Al Ain city, to the east by Al Jawa plain, to the southeast by Mazyad, to the south by Oman and to the west by Ain Al Faydah and Zakher. It is considered as one of the most prominent features of the city. The Hafit structure is one of several prominent Tertiary structures in the Northern Oman Mountains front which trends parallel to the mountain range. Its length is about 29km, the width is about 4-5km and it reaches an elevation of 1160m above see level. The Oman Mountains, southeastern part of the Arabian Plate, form an accurate belt parallel to the Gulf of Oman (Fig. 1). These mountains were formed in response to two main orogenic events in Late Cretaceous and mid-Tertiary. The first resulted from the Late Cretaceous (Coniacian- Maastrichtian) obduction of the Semail Ophiolite, and associated sedimentary and volcanic rocks (Sumeini, Hawasina and Haybi groups), onto the eastern margin of the Arabian platform (Glennie et al., 1973; Coleman, 1981; Searle et al., 1983; Lippard et al., 1986; Nolan et al., 1986; Boote et al., 1990; Roberston et al., 1990). The second compression occurred in Late Eocene-Miocene. This compression is marked by folding and reactivation of deep seated faults in the Upper Cretaceous – Tertiary sedimentary rocks in the foreland basin (Boote et al., 1990; Dunne et al., 1990; Searle et al., 1990). The second compression is related to the Zagros Orogeny in Iran (Ricateau and Riche, 1980; Searle et al., 1983; Searle et al., 1985; Searle et al., 1988; Searle et al., 1990). The study area is located at Jabal Hafit (Fig. 1) where Lower Eocene rocks covered the study area. The age dating of that horizon was documented by Anan et al. (1992) and Anan (1996). Combined structural mapping and field measurements, with analysis of ariel photographs and satellite imagery were carried out in order to understand and clarify the origin of Hafit structure. All investigated sets in the study area, were accessed by excellent road which winds its way right up to the summit, providing a panoramic view of the open countryside. Geology The study area is covered by Lower Eocene sediments. The sediments are well bedded massive limestone with some chert replacement bands and nodules (Plate 1). Field observations show that complex array of concentric cracks are filled with calcite. These cracks apparently form as a result of the contraction which accompanies the dewatering of fine- grained material that otherwise forms the concretion. Other concretions occur in limestone as geodes, which are seen in the form of cavities, surrounded by a layer of extremely well-developed crystals of calcite. The limestone has been locally dolomitized and rich in foraminiferal microfossils. These rocks are of Early Eocene age (Anan et al., 1992; Whittle and Alsharhan, 1994; Anan, 1996, 2004). The stratigraphy of Jabal Hafit was carried out by Hunting (1979), Cherif and El Deeb (1984), Warrak (1986), Anan et al. (1992) Hamdan and Bahr (1992), Whittle and Alsharhan (1994) and Boukhary et al. (2002). STRUCTURAL PATTERN OF JABAL HAFIT Jabal Hafit is a double-plunging anticline structure. It is plunging north in the United Arab Emirates and south in Oman. The Hafit structure consists mainly of two en-echelon anticlines (Noweir, 2000), the Hafit Anticline to the south and Al-Ain Anticline to the north. The limbs of the Hafit structures are dipping to the east and west. Warrak (1996) concluded that Jabal Hafit and other foreland folds in the Northern Oman Mountains formed prior to the main Zagros deformation which started in very Late Miocene and culminated in the Late Plio-Pleistocene (Stocklin, 1968; Murris, 1980). Hafit anticline was involved in Tertiary-age folding at western part of the Northern Oman Mountains where the Tertiary neoautochthonous sediments were involved. Although the major structure at Jabal Hafit is a major anticline fold, the field investigations show that the most dominant structural elements in the study area are faults and joints. Folds have been found in the study area but are considered as minor structural elements, beside the major anticline of Jabal Hafit. Seven investigated location sets have been established within the study area. All sets are located at the western limb of the major Hafit anticline near the core of the fold, where the beds are moderately dipping to the west (Fig. 2).