Seismic structure and geologic history of the Dead Sea fault system in the Al-Ghab graben, northwest Syria

AL-IMAM, Anwar, ZAZA, Tarik, SAWAF, Tarif, AL-YOUSSEF, Wasif (Syrian Petroleum Company, Ministry of Petroleum and Mineral Resources, Damascus, Syrian Arab Republic)

BARAZANGI, Muawia, LITAK, Robert, SEBER, Dogan (Institute for the Study of the Continents, Cornell University, Ithaca, New York 14853, USA)


Abstract


About 250 km of new seismic reflection profiles are interpreted to obtain a new image of the tectonic architecture and geologic evolution of the Al-Ghab graben, a transtensional structure located along the Dead Sea “ leaky” transform fault system in northwestern Syria. In addition to the new seismic data, existing gravity, magnetic, and geologic data are combined with a digital elevation model and Thematic Mapper imagery in this study.

Seismic data indicate a dramatic difference between the northern and southern parts of the Al-Ghab basin. In the southern part, basin sediments thicken toward the south to over 6 km deep, with the depocenter trending NW. The depocenter has migrated several km north over time. The graben is bounded by two main N-striking faults, branches of the Dead Sea fault system. Several inferred strike-slip faults are also apparent on the seismic data east of the Al-Ghab graben. Farther north, a horst-like structure is noted in the central Al- Ghab depression. From this point north, the two main bounding faults appear to bifurcate into several smaller syndepositional faults bounding smaller basins. Seismic data clearly indicate that the maximum depth of the Precambrian basement within the Al-Ghab graben exceeds 10 km, more than twice as deep as previous estimates based on gravity data alone.

Outside the graben, seismic data can be tied to surface outcrops of Jurassic to Neogene ages, but only Quaternary sediments are exposed within the graben itself. With no well data currently available in the area, ages of the seismic reflectors thus cannot be unequivocally determined. However, preliminary interpretation of the seismic data is used as the basis for gravity modeling to attempt to constrain the timing of the initiation and main stage of subsidence in the basin. Results from a drilling program of two wells, currently underway, will be compared to the seismic and gravity interpretation to better determine the timing of sediment deposition in the Al-Ghab graben.


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