STRUCTURE OF THE INTRAPLATE EASTERN PALMYRIDE FOLD BELT, SYRIA

The Palmyride Fold Belt is an aulacogen within the Arabian plate linke d to the Levantine continental margin, which contains > 10 km of Phane rozoic sediments. Inversion of this Mesozoic basin began during Late C retaceous time, although most deformation was clearly post-Oligocene. Recent field mapping shows that almost all the structures have resulte d from a phase of northwest-southeast compression followed by major de xtral transpression. Early northwest-southeast compression resulted in northeast-southwest-aligned fold axes in the central and southeast Pa lmyrides, many of which were subsequently rotated by progressive dextr al simple shear during Neogene to Recent time. The north-south-aligned sinistral Dead Sea fault is the major wrench fault aligned at 45-degr ees to the maximum compressive stress. The conjugate eastwest-striking dextral Jhar fault and the northwest-southeast-aligned Bishri fault h ave accommodated limited dextral shear and clockwise rotation of north east-southwest-aligned folds (Jebels Mrah, Ash Shaer). In the northern Palmyrides, dextral strike-slip faults aligned along Reidel fractures (R1) cut the flanks of earlier domal structures (Jebel Abu Rajmein). Subordinate antithetic R2 Reidel shears aligned north-northeast-south- southwest are transtensional sinistral strike-slip faults showing mino r extension that cut through the earlier domal structures (for example , Ras' al Hawa depression in Jebel Abu Rajmein). Northwest-southeast-a ligned faults (for example, Jebel Bilas cross-trend faults) show north east-southwest extension at right angles to the Palmyride shortening d irection. This extension parallels the major Euphrates graben trend in eastern Syria and northwestern Iraq and also parallels some aligned P liocene-Pleistocene volcanic rifts south of Damascus and in the Jebel Druze (Jebel Arab) region of southern Syria and northern Jordan. A reg ional Palmyride strain ellipse is presented to explain the geometry of all these structures. The Ad Daww depression is a northeast-southwest -aligned transpressional basin containing around 2 km thickness of Ter tiary sediments. The basin is bounded to the west by a sinistral shear couple along the Cherrife structural trend in the central Palmyrides, along the north by the dextral Jhar fault, and along the southeast by the compressional southeast Palmyrides. In the southeast Palmyrides, structural style is one of a series of northeast-southwest-aligned nar row anticlines in the Mesozoic platform sediments with upright to nort hwest-dipping, southeast-facing axial planes. Shortening amounts are v ery small in the eastern Palmyrides (approximately 1 km) and taken up almost entirely by folding, but these increase slightly toward the wes t to probably approximately 20 km in the Cherrife region. Tight box fo lds and slightly asymmetric folds in the southeast Palmyrides have a l ocalized basal detachment along the Triassic gypsum horizon, which in some examples flows into the fold core (Jebel Hayyan). There is no evi dence for a major basal detachment underlying the Palmyrides. All fold ing and faulting can be related to disharmonic folding of the Mesozoic sediments above a Triassic evaporite sequence and subsequent dextral transpression. The lack of overthrusting explains the absence of any f oreland basin caused by lithospheric flexuring on the Rutbah platform. The major Palmyride deformation in Miocene-Pliocene times was concomi tant with the opening of the Red Sea, with the closing of the Bitlis-Z agros suture zone in eastern Turkey and central Iran, and with the mai n sinistral strike-slip motion along the Dead Sea fault.