SEISMIC FABRIC AND 3-D STRUCTURE OF THE SOUTHWESTERN INTRACONTINENTALPALMYRIDE FOLD BELT, SYRIA

The Palmyride fold belt, a 400 x 100 km transpressive belt in central Syria that is the northeastern arm of the Syrian arc (which includes t he Negev fold belt in the Sinai), is the result of late Mesozoic and C enozoic inversion of a late Paleozoic and Mesozoic, northeast-trending , linear intracontinental basin located within the northern Arabian pl atform. The southwestern Palmyrides, near the Dead Sea transform fault system and the Anti-Lebanon mountains, are characterized by short wav elength (5-10 km) en echelon folds separated by small intermontane bas ins that developed mainly in the Neogene to Holocene. A new three-dime nsional data cube, 60 x 70 x 10 km, generated on a Landmark Graphics w orkstation and based on approximately 700 km of two-dimensional seismi c reflection profiles, elucidates the structure of the upper 10 km of the crust in the southwestern Palmyrides. Visualization of the subsurf ace structure, which is represented by a prominent Upper Cretaceous re flection surface in the data cube, is augmented by topographical and B ouguer gravity data of the same region. Preexisting discontinuities, p robable normal fault relicts of the Mesozoic Palmyride rift, likely co ntrolled the development of individual Neogene thrusts. The new subsur face image shows important structural features not identified in outcr op. Short, west-northwest-trending transcurrent (or transfer) faults l ink the short, en echelon northeast-trending thrust faults and blind t hrusts of the Palmyrides. A pervasive regional decollment is not obser ved, even though Triassic evaporites host local detachments. There has been no wholesale transport of shallower strata on a regional decollm ent that decouples Mesozoic and Cenozoic rocks from underlying Paleozo ic rocks. Unlike topographic relief, which only roughly resembles subs urface structures, the Bouguer gravity signature of the southwestern P almyrides closely mimics underlying shallow geologic structures both o n a large (approximately 50 km wavelength) and a small (approximately 5-10 km wavelength) scale. Relatively uncommon reflections from deform ed Paleozoic rocks and the excellent correlation between Bouguer gravi ty and shallow structures indicate a general concordance between shall ow Mesozoic and Cenozoic rocks and deeper Paleozoic rocks. Hence, Pale ozoic rocks either deformed together with shallower strata, or structu res within Paleozoic rocks controlled the development of shallower Neo gene and younger structures. Our structural analysis and many other re cent studies of the region indicate minor right-lateral shear coupled with compression in the Palmyrides.