Thomas A. Chaimov

Mesozoic and Cenozoic deformation inferred from seismic stratigraphy in the southwestern intracontinental Palmyride fold-thrust belt, Syria

This paper was published in the Geological Society of America Bulletin. The Geological Society of America retains the copyright to this paper. Geological Society of America, P.O. Box 9140 , Boulder, CO 80301-9140 USA See also: http://www.geosociety.org/; http://atlas.geo.cornell.edu/syria/chaimov_gsa_bull_1992.html

Tectonic evolution of the Northern Arabian Plate in Western Syria

The primary geologic structures of the northern Arabian plate in western Syria include the intracontinental Palmyride mountain belt and the interplate boundary of the Dead Sea transform fault system. The Palmyride belt strikes NE and is sandwiched between two relatively stable crustal blocks of the Arabian platform: the Aleppo plateau in the north and the Rutbah uplift in the south. The Palmyrides were the site of an early Mesozoic aulacogen-type depression that was linked to the Levantine rifted continental margin in the eastern Mediterranean. The location of this postulated aulacogen may be genetically associated with a crustal zone of weakness, possibly a Proterozoic suture and/or shear zone, between the Aleppo and Rutbah crustal blocks. Uplift of the intraplate Palmyride depression initiated in the Late Cretaceous, penecontemporaneous with emplacement of ophiolites along the nearby Arabian plate boundaries in southern Turkey and western Iran. More intense episodes of shortening during the Cenozoic also appear to be temporally related to collision along nearby plate boundaries, implying that stresses have been transmitted hundreds of kilometers across the northern Arabian platform. The style and intensity of the inversion process vary considerably along the strike of the Palmyrides and involves both shortening by folding and reverse faulting as well as translation and rotation along numerous strike-slip faults. Such folds and faults clearly define at least three structurally distinct small crustal blocks within the Palmyrides. Shortening of about 20% in the southwest Palmyrides near Lebanon gradually dies out to the northeast near the intersection of the Palmyrides with the NW-trending Euphrates depression. Depth to metamorphic basement beneath the Palmyra mountain belt increases from 9 km in the northeast to 11 km in the southwest, compared with a basement depth of about 6–8 km in the adjacent Arabian platform, indicating that shortening along the Palmyrides has been insufficient to invert the previously extended basement morphology. Finally, slip measurements along the Dead Sea fault and estimates of crustal shortening in the Palmyride belt indicate that the northern segment of the seismogenic active Dead Sea fault in Lebanon and Syria is considerably younger (Pliocene) than the southern part (Miocene).

Crustal structure of central Syria: The intracontinental Palmyride Mountain belt

An edited version of this paper was published in Tectonophysics by Elsevier Science. Copyright 1992, Elsevier Science. See also: http://dx.doi.org/10.1016/0040-1951(92)90395-M; http://atlas.geo.cornell.edu/syria/Al-Saad-et-al_1992.html

Stratigraphy and structure of eastern Syria across the Euphrates depression

Abstract A N-S crustal-scale geotransect across the northern Arabian platform in eastern Syria reveals an alternating series of basement uplifts and basins separated by predominantly transpressional fault zones above an effectively uniform crust. Four major tectonic provinces are crossed along a 325 × 100 km corridor that extends from the Iraqi border in the south to the Turkish border in the north: the Rutbah uplift, the Euphrates depression, the Abd el Aziz structural zone, and the Qamichli uplift. These features are the manifestations of reactivated pre-Cenozoic structures that responded to forces acting along nearby Arabian plate boundaries, particularly Cenozoic convergence and collision along the margins of the northern Arabian platform i.e., the Bitlis suture and the East Anatolian fault in southern Turkey and the Zagros suture in Iran and Iraq. The database for this study consists of 3000 km of industry seismic reflection data, 28 exploratory wells, and geologic and Bouguer gravity maps. The deep crustal structure and, in part, the basement geometry along this transect are inferred from two-dimensional modeling of Bouguer gravity, whereas the shallow (about 8 km) structure is constrained primarily by well and seismic data. Features of the geotransect reveal: 1. (1) A relatively uniform crustal column approximately 37 km thick with only minor crustal thinning beneath the Euphrates. Crustal thinning may be slightly more pronounced beneath the Euphrates (about 35 km) to the southeast of the transect where the Bouguer gravity anomaly is slightly higher. 2. (2) Along the Euphrates depression, ongoing subsidence, which began during the Late Cretaceous, resulted in the deposition of at least 3 km of Late Cretaceous and Cenozoic rocks. The structural complexity of the Paleozoic and most of the Mesozoic sedimentary sections along the transect contrasts markedly with a relatively simple, flat-lying Cenozoic section along most of the transect. A notable exception is the Abd el Aziz uplift, where Cenozoic rocks are strongly deformed. 3. (3) While Euphrates subsidence continued throughout the Cenozoic, the inversion of the E-W-trending Abd el Aziz structure into a fault-bounded tilted block began in the Miocene, perhaps as a response to the last episode of intense Miocene collision along the nearby Bitlis and Zagros suture zones.

Bouguer gravity and crustal structure of the Dead Sea transform fault and adjacent mountain belts in Lebanon

This paper was published in Geology by the Geological Society of America (GSA), and GSA retains the copyright (1993). Geological Society of America, P.O. Box 9140, Boulder, CO 80301-9140 See also: http://www.geosociety.org; http://atlas.geo.cornell.edu/deadsea/publications/Khair1993_Geology.htm

COCORP profiles from the Montana plains: The Archean cratonic crust and a lower crustal anomaly beneath the Williston basin

New COCORP deep seismic reflection profiles from the Montana plains between the Rocky Mountains and the Williston basin image the crystalline continental basement of the Archean Wyoming cratonic province on a regional scale. The crust is, in general, reflective throughout its entire thickness. West of the Williston basin, the crust-mantle boundary is at the base of the reflective zone and is not marked by the presence of any distinctive reflections. The lowermost crust beneath the Williston basin is, in contrast, characterized by a prominent, laterally extensive zone of relatively high-amplitude reflections. If, as the spatial correlation suggest, the anomalously reflective lower crustal zone is causally related to the subsidence of the basin, then the data place constraints in addition to those of the sedimentary record on physical models for the evolution of the Williston basin.

Seismic Fabric and 3-D Structure of the Southwestern Intracontinental Palmyride Fold Belt, Syria

The Palmyride fold belt, a 400 × 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, northeast-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 the Neogene to Holocene. A new three-dimensional data cube, 60 × 70 × 10 km, generated on a Landmark Graphics workstation and based on approximately 700 km of two-dimensional sei mic 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 topographical and Bouguer gravity data 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, west-northwest-trending transcurrent (or transfer) faults link the short, en echelon northeast-trending thrust faults and blind thrusts of the Palmyrides. A pervasive regional decollment is not observed, even though Triassic vaporites host local detachments. There has been no wholesale transport of shallower strata on a regional decollment 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 (^sim50 km wavelength) and a small (^sim5-10 km wavelength) 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 indicate minor right-lateral shear coupled with compression in the Palmyrides.

Northern Arabian Platform Transect Across the Palmyride Mountain Belt: Syrian Arab Republic

An edited version of this paper was published by the Inter-Union Commission on the Lithosphere and the American Geophysical Union, and copyright is retained by these publishers. See also: http://atlas.geo.cornell.edu/syria/Al-Saad-et-al_1991.html