Tectonic Escape (Indentation) in Central Saudi Arabia, Possibility and Exploration Potential

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractTectonic analysis indicates a high possibility of tectonic escape (P. others, 1982, Armijo, R and others, 1986) structures in central Saudi Arabia that could bear significant hydrocarbon exploration potential. This study aims to introduce a new tectonic model that explains several surface and subsurface newly mapped structures in central Saudi Arabia. Potential fields, seismic and surface geology data are integrated to accomplish this study.Basement terrane analysis of the Arabian shield and its eastern continuation beneath the sedimentary basin indicates the general north-south orientation with differences in width and composition. It shows that the maximum crust thickness is in the middle of the outcropping shield with a promontory extending 200 km toward east in subsurface (Central Arabian Arch) where Triassic (Khuff) marine carbonates overlay the basement directly. The crust shows gradual thinning eastward from this promontory till the offshore Arabian Gulf. Some terranes show wedging-out and others show narrowing against the eastern side of the basement outcrops. This pattern suggests the tectonic escape of the wedging out and narrowing terranes against the competent Afif terrane since the InfraCambrian accretion of Arabia. The terrane accretion occurred by westerly driven terranes collided against the thick promontory of the Afif terrane causing dispersion toward south and north through east-west accommodation zones. Long segments of unusual east-west surface structures (faults and strike of strata) over the boundaries of the subsurface basement promontory from north and south are thought to be a dragging of the dispersed terrane fragments at the promontory boundaries. West of these east-west zones, deformation is concentrated at the north-south terranes with curved hard link transfer zones. This InfraCambrian tectonic setting is believed to have been reactivated during Phanerozoic tectonic phases to express its escape tectonics pattern further-up till outcrops. Re-distribution of the Phanerozoic stresses at that inherited basement fabric controlled the geometry of the sub-basins and their filling during extension phases. It controlled also the preferable locations of structural positive inversion during compression phases to form the fault related fold traps. This approach explains the diversity of structural styles in the sedimentary cover (compression, transpression, and transtension) that formed simultaneously during the Late Cretaceous compression but with different directions.