ItemStrain partitioning of active transpression within the Lebanese restraining bend of the Dead Sea fault (Lebanon and SW Syria)Gomez, F.; Nemer, T.; Tabet, C.; Khawlie, M.; Meghraoui, M.; Barazangi, M. (Geological Society of London, 2007)Recent neotectonic, palaeoseismic, and GPS results along the central Dead Sea fault system elucidate the spatial distribution of crustal deformation within a large (~180 km long) restraining bend along this major continental transform. Within the "Lebanese" restraining bend, the Dead Sea fault system splays into several key branches, and we suggest herein that active deformation is partitioned between NNE-SSW strike-slip faults and WNW-ESE crustal shortening. When plate motion is decomposed into strike-slip parallel to the two prominent NNE-SSW strike-slip faults (the Yammouneh and Serghaya faults) and orthogonal motion, their slip rates are sufficient to account for all expected strike-slip motion. Shortening of the Mount Lebanon range is inferred from the geometry and kinematics of the Roum fault, as well as preliminary quantification of coastal uplift. The results do not account for all expected crustal shortening, suggesting that some contraction is likely accommodated in the Anti Lebanon range. It also seems unlikely that the present kinematic configuration characterizes the entire Cenozoic history of the restraining bend. Present-day strain partitioning contrasts with published observations on finite deformation in Lebanon demonstrating distributed shear and vertical-axis block rotations. Furthermore, the present-day proportions of strike-slip displacement and crustal shortening are inconsistent with the total strike-slip offset and the lack of a significantly thickened crust. This suggests that the present rate of crustal shortening has not persisted for the longer life of the transform. Hence, we suggest that the Lebanese restraining bend evolved in a polyphase manner: An earlier episode of wrench-faulting and block rotation, followed by the later period of strain partitioning. ItemGeologic and Strategic Comments on Oil Resources in the Arabian Gulf RegionBarazangi, Muawia (2007-04-06T17:31:33Z)Peak oil production in the Middle East's Arabian/Persian Gulf region and worldwide could be delayed if major multinational and national oil companies would invest more heavily in drilling and extraction technologies and push to explore new sites. Barazangi argued that the "exploration story" in the Middle East is not yet complete. Two-thirds of the world's proven recoverable oil reserves exist in the Arabian Gulf, and there are more oil fields to be discovered through offshore and deep-water drilling, as well as more oil to be extracted from existing fields. Barazangi stressed the fact that only seven countries worldwide (Saudi Arabia, Iran, Iraq, Kuwait, United Arab Emirates, Venezuela, and Russia) contain 80 percent of the world's proven recoverable oil reserves. Five of those are notably in the Arabian Gulf region and share Islamic cultures. He argued that in order to better understand oil issues in the Gulf, the world must understand the Arab and Persian people, and Islam's history and culture. ItemGlobal Positioning System measurements of strain accumulation and slip transfer through the restraining bend along the Dead Sea fault system in LebanonGomez, F.; Karam, G.; Khawlie, M.; McClusky, S.; Vernant, P.; Reilinger, R.; Jaafar, R.; Tabet, C.; Khair, K.; Barazangi, M. (Blackwell Publishing, 2007)Approximately 4 yr of campaign and continuous Global Positioning System (GPS) measurements across the Dead Sea fault system (DSFS) in Lebanon provide direct measurements of interseismic strain accumulation along a 200-km-long restraining bend in this continental transform fault. Late Cenozoic transpression within this restraining bend has maintained more than 3000 m of topography in the Mount Lebanon and Anti-Lebanon ranges. The GPS velocity field indicates 4-5 mm yr-1 of relative plate motion is transferred through the restraining bend to the northern continuation of the DSFS in northwestern Syria. Near-field GPS velocities are generally parallel to the major, left-lateral strike-slip faults, suggesting that much of the expected convergence across the restraining bend is likely accommodated by different structures beyond the aperture of the GPS network (e.g. offshore Lebanon and, possibly, the Palmyride fold belt in SW Syria). Hence, these geodetic results suggest a partitioning of crustal deformation involving strike-slip displacements in the interior of the restraining bend, and crustal shortening in the outer part of the restraining bend. Within the uncertainties, the GPS-based rates of fault slip compare well with Holocene-averaged estimates of slip along the two principal strike-slip faults: the Yammouneh and Serghaya faults. Of these two faults, more slip occurs on the Yammouneh fault, which constitutes the primary plate boundary structure between the Arabia and Sinai plates. Hence, the Yammouneh fault is the structural linkage that transfers slip to the northern part of the transform in northwestern Syria. From the perspective of the regional earthquake hazard, the Yammouneh fault is presently locked and accumulating interseismic strain. ItemUpper crustal velocity structure and basement morphology beneath the intracontinental Palmyride fold-thrust belt and north Arabian platform in SyriaSeber, D.; Barazangi, M.; Chaimov, T.; Al-Saad, D.; Sawaf, T.; Khaddour, M. (Blackwell Publishing on behalf of The Royal Astronomical Society and The Deutsche Geophysikalische Gesellschaft, 1993)The intracontinental Palmyride fold-thrust belt, which is the site of an inverted Mesozoic rift, is sandwiched between two crustal blocks, the Aleppo plateau in the north and the Rutbah uplift in the south. The 400 x 100 km belt merges with the Dead Sea fault system in the southwest and gradually ends near the Euphrates depression in the northeast. Very dense (i.e., 100 m geophone spacing), reversed and multifold seismic refraction profiling was carried out to map approximately the upper 15 km of the crust in the early 1970s. These refraction data are utilized to model sedimentary rock thickness, seismic velocity, and basement morphology. Extensive data coverage also enables identification of the major faults of the region. A 2-D ray tracing technique is used in the modeling. Interpretation of these data indicates that five distinct velocity layers characterize the upper crust of the northern Arabian platform in Syria. The P-wave velocities within these layers are (in km s-1): 2.0-2.8, 4.0-4.4, 5.2-5.3 , 5.5-5.7, corresponding to sedimentary rocks from Quaternary to late Precambrian in age, and 5.9-6.0, corresponding to metamorphic basement. A comparison of the velocity models with the available drill hole information and seismic reflection profiles shows strong velocity variations in a given geologic formation, depending on the depth and location of the formation. The depth to metamorphic basement beneath the Palmyride fold belt clearly shows a deep trough, filled with Phanerozoic sedimentary rocks. These rocks decrease in thickness from about 11 km in the southwest to about 9 km in the central segment of the belt. The basement depth is about 6 km in the Aleppo plateau and not less than 8 km in the Rutbah uplift. Deeper basement in the Rutbah uplift is probably the result of a Precambrian rifting episode, clearly identified to the south in Jordan and Saudi Arabia. Cenozoic crustal shortening of about 20-25% across the southwestern segment of the Palmyride belt has not been sufficient to substantially reduce the size of the basement trough beneath this mountain belt. Finally, northeast decreasing basement depth in the Palmyrides supports the idea that the Palmyride Mesozoic rifting was developed as an aulacogen of the rifted Levantine margin along the eastern Mediterranean. ItemStratigraphy and structure of eastern Syria across the Euphrates depressionSawaf, T.; Al-Saad, D.; Gebran, A.; Barazangi, M.; Best, J.; Chaimov, T. (Elsevier Science, 1993)Along a 450 km transect across central Syria seismic reflection data, borehole information, potential field data and surface geologic mapping have been combined to examine the crustal structure of the northern Arabian platform beneath Syria. The transect is surrounded by the major plate boundaries of the Middle East, including the Dead Sea transform fault system along the Levantine margin to the west, the Bitlis suture and East Anatolian fault to the north, and the Zagros collisional belt to the northeast and east. Three main tectonic provinces of the northern Arabian platform in Syria are crossed by this transect from south to north: the Rutbah uplift, the Palmyra fold-thrust belt, and the Aleppo plateau. The Rutbah uplift in southern Syria is a broad, domal basement-cored structure with a thick Phanerozoic (mostly Paleozoic) cover of 6-7 km. Isopachs based on well and seismic reflection data indicate that this region was an early Paleozoic depocenter. The Palmyra fold-thrust belt, the northeastern arm of the Syrian Arc, is a northeast- southwest trending intracontinental mountain belt that acts as a mobile tectonic zone between the relatively stable Rutbah uplift to the south and the less stable Aleppo plateau to the north. Short wavelength en echelon folds characterized by relatively steep, faulted southeast flanks dominate in the southwest, most strongly deformed segment of the belt, while a complex system of deeply rooted faults and broad folds characterize the northeast region, described in this study. The Aleppo plateau lies immediately north of the Palmyride belt, with a combined Paleozoic and Mesozoic sedimentary section that averages 4-5 km in thickness. Although this region appears relatively undeformed on seismic reflection data when compared to Palmyride deformation, a system of near vertical, probable strike-slip faults crosscut the region in a dominantly northeasterly direction. Gravity and magnetic modeling constrains the deep crustal structure along the transect. The crustal thickness is estimated to be approximately 38 km. Interpretation of the gravity data indicates two different crustal blocks beneath the Rutbah uplift and the Aleppo plateau, and the presence of a crustal-penetrating, high-density body beneath the northeast Palmyrides. The two distinct crustal blocks suggest that they were accreted possibly along a suture zone and/or a major strike-slip fault zone located approximately in the present-day position of the Palmyrides. The age of the accretion is estimated to be Proterozoic or early Cambrian, based on the observation of a pervasive reflection (interpreted as the Middle Cambrian Burj limestone) in the Rutbah uplift and in the Aleppo plateau and by analogy with the well-mapped Proterozoic sutures of the Arabian shield to the south. ItemGeologic evolution of the intraplate Palmyride basin and Euphrates fault system, SyriaSawaf, T.; Brew, G.; Litak, R.; Barazangi, M. (Museum Nationale D'Histoire Naturelle, France, 2001)The Palmyride Basin and the Euphrates fault system are two Late Paleozoic / Mesozoic rifts that formed on the southern margin of the NeoTethys Ocean. Data collected during hydrocarbon exploration are analyzed to determine the geologic history and regional tectonic implications of these structures. The Palmyride Basin formed during Late Paleozoic aulacogen-type rifting and subsequent Mesozoic thermal subsidence and fault reactivation. Basin inversion in the Cenozoic resulted in the formation of the Palmyride fold and thrust belt. In contrast, the Euphrates fault system is an aborted intracontinental rift, formed during the Late Cretaceous, that experienced minor transpression in the Cenozoic. Both these structures are hypothesized to have formed along zones of Proterozoic crustal weakness inherited from the accretion of the Arabian plate. Both regions also contain significant hydrocarbon reserves; predominantly gas in the Palmyride Basin and oil in the Euphrates fault system. The tectonic histories of these features are inseparably linked to the intraplate stresses generated in the northern Arabian plate by the polyphase opening and closing of the adjacent NeoTethys Ocean. ItemSeismic reflection structure of intracratonic Palmyride fold-thrust belt and surrounding Arabian platform, SyriaMcBride, J.; Barazangi, M.; Best, J.; Al-Saad, D.; Sawaf, T.; Al-Otri, M.; Gebran, A. (American Association of Petroleum Geologists (AAPG), 1990)Seismic reflection and drillhole data from central Syria provide a detailed view of the subsurface structure (10-15 km depth) of the relatively little studied intracratonic Palmyride fold and thrust belt. The data set, together with surface geologic mapping, constrain a structural/stratigraphic section spanning the northeast sector of the belt and the surrounding subprovinces of the Arabian platform. The seismic and drillhole data show Mesozoic stratigraphic sequences thickening rapidly into the Palmyrides from the adjacent, arched Paleozoic platforms. Neogene (Alpine) folding and thrusting of the Mesozoic basin, as documented on the seismic data, are sharply restricted to the narrow width of the belt (~100 km), which is in contrast to the relatively undeformed, Phanerozoic strata of the platforms to the north and south. The regional subsurface structure of the northeastern Palmyrides consists of a northeast-plunging anticlinorium whose outer flanks are marked by smaller superimposed asymmetric, anticlines associated with outward verging thrusts, giving this part of the belt a rough symmetry. The general structural style of folding is characterized by simple, relatively narrow anticlines and broad synclines that can be traced concordantly from the surface to at least 5 km depth on the seismic data--the level of any decollement appears to be below the imaged Mesozoic sequence. A fundamental feature of the surrounding Arabian platform subprovinces is a deep (~6-7 km, maximum) and pervasive bright reflection that forms the base of the reflective section of the platform but disappears abruptly beneath the Palmyrides. This basal reflector is important as a regional strain marker and may represent a Cambrian/Infracambrian carbonate-evaporite sequence or a remarkably uniform crystalline basement surface. The seismic and drillhole data support the hypothesis of the Palmyrides beginning as a Permian-Triassic failed rift, connected to the Levantine passive continental margin, that was inverted and complexly deformed by the interfering effects of Cenozoic movements along the Dead Sea (Levant) transform fault system and the Turkish Bitlis (Tauride) convergent zone. The seismic data provide a first-time view into the extent and depth of the early basin formation and subsequent compressional deformation, and as such provide a necessary basis for constraining reconstructions of northern Middle East plate motions. ItemMesozoic-Cenozoic evolution of the Intraplate Euphrates fault system, Syria: Implications for regional tectonicsLitak, R.; Barazangi, M.; Beauchamp, W.; Seber, D.; Brew, G.; Sawaf, T.; Al-Youssef, W. (The Geological Society of London, 1997)A lack of dramatic surface geologic structures along the Euphrates River in Syria belie a complex tectonic history revealed by newly-released seismic reflection and well data. We document the intraplate Euphrates fault system, characterize the variation in structural style along its 350 km length in Syria, and infer its Mesozoic-Cenozoic tectonic and deformational history. We then relate the deformation of the Euphrates system and other proximate intraplate structures to nearby Arabian plate boundary processes in order to develop a new model for the kinematic evolution of the northern Arabian plate. Throughout most of Mesozoic time, the Euphrates area experienced minor deposition compared to the Palmyride trough to its southwest, and the Sinjar trough to its northeast. During latest Cretaceous time, however, significant sinistral transtension occurred along the length of the Euphrates fault system in Syria, with graben formation especially noteworthy in southeastern Syria. This episode was probably related to events at nearby plate boundaries, and may have reactivated a zone of weakness formed during Pan-African accretion of the Arabian plate. A Paleogene sag basin formed over the graben system in southeastern Syria. Neogene continental collision along the northern and eastern Arabian plate boundaries precipitated minor reactivation of the Euphrates fault system in a dextral transpressional sense, in concert with significant inversion and the main phase of uplift of the nearby Palmyride and Sinjar mountains. ItemStructure and evolution of the petroliferous Euphrates graben system, southeast SyriaLitak, R.; Barazangi, M.; Brew, G.; Sawaf, T.; Al-Imam, A.; Al-Youssef, W. (American Association of Petroleum Geologists (AAPG), 1998)The northwest-trending Euphrates graben system is an aborted intracontinental rift of Late Cretaceous age that has subsequently been hidden by Cenozoic burial. Approximately 100 km wide, the system comprises an extensive network of grabens and half grabens extending some 160 km from the Anah Graben in western Iraq to the Palmyride fold belt in central Syria, where it becomes more subdued. The youngest prerift rocks are presently at a maximum depth of about 5 km. Based primarily on interpretation of 1500 km of seismic reflection profiles and data from 35 wells, we mapped a complex network of numerous branching normal and strike-slip faults, generally striking northwest and west-northwest. Both branched and single-strand linear normal faults of generally steep dip, as well as positive and negative flower structures, are manifest on seismic sections. No single rift-bounding fault is observed; instead, a major flexure coupled with minor normal faulting marks the southwestern edge of the basin, with considerable variation along strike. To the northeast, deformation diminishes on the Rawda high near the Iraqi border. The Euphrates graben system likely formed in a transtensional regime, with active rifting primarily restricted to the Senonian and with an estimated maximum extension of about 6 km. Minor Cenozoic inversion of some structures also is evident. Approximately 30 oil fields have been discovered in the Euphrates graben system since 1984. Recoverable reserves discovered to date reportedly exceed 1 billion barrels of oil and lesser amounts of gas. Light oil is primarily found in Lower Cretaceous sandstone reservoirs juxtaposed by normal faulting against Upper Cretaceous synrift sources and seals. ItemSeismic fabric and 3-D upper crustal structure of the southwestern intracontinental Palmyride fold belt, SyriaChaimov, T.; Barazangi, M.; Al-Saad, D.; Sawaf, T.; Khaddour, M. (American Association of Petroleum Geologists (AAPG), 1993)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 the Negev fold belt in the Sinai, is the result of Late Mesozoic and Cenozoic inversion of a Late Paleozoic and Mesozoic, NE-trending, linear intracontinental basin located within the northern Arabian platform. The southwestern Palmyrides, near the Dead Sea transform fault system and the Anti-Lebanon mountains, are characterized by short wavelength (5-10 km) en echelon folds separated by small intermontane basins that developed mainly in Neogene to Recent times. A new three-dimensional data cube, 60 X 70 km, generated on a Landmark Graphics (TM) workstation and based on approximately 700 km of two-dimensional seismic reflection profiles, elucidates the structure of the upper 10 km of the crust in the southwestern Palmyrides. Visualization of the subsurface structure, which is represented by a prominent Upper Cretaceous reflection surface in the data cube, is augmented by the topography and Bouguer gravity of the same region. Preexisting discontinuities, probable normal fault relicts of the Mesozoic Palmyride rift, likely controlled the development of individual Neogene thrusts. The new subsurface image shows important structural features not identified in outcrop. Short, WNW-trending transcurrent, or transfer, faults link the short, en echelon NE-trending thrust faults and blind thrusts of the Palmyrides. A pervasive regional decollement is not observed, even though Triassic evaporites host local detachments. There has been no wholesale transport of shallower strata on a regional decollement that decouples Mesozoic and Cenozoic rocks from underlying Paleozoic rocks. Unlike topographic relief, which only roughly resembles subsurface structures, the Bouguer gravity signature of the southwestern Palmyrides closely mimics underlying shallow geologic structures both on a large (~50 km wavelength) and a small (~5-10 km) scale. Relatively uncommon reflections from deformed Paleozoic rocks and the excellent correlation between Bouguer gravity and shallow structures indicate a general concordance between shallow Mesozoic and Cenozoic rocks and deeper Paleozoic rocks. Hence, Paleozoic rocks either deformed together with shallower strata, or structures within Paleozoic rocks controlled the development of shallower Neogene and younger structures. Our structural analysis and many other recent studies of the region are indicative of minor right-lateral shear coupled with compression in the Palmyrides.