A large variation in elevation and gravity anomaly
prevails from the Red Sea coast to the interior of the Arabian Shield (AS)
across the Asir Igneous Province (AIP); The Asir Mountain
(AM) is developed on AIP. Here the elevation varies from 45-2700 m,
corresponding changes in F.A. are from –30 to +220 mgal and B.A.
from +22 to –175 mgal. Regression relationships between
elevation and gravity anomalies demonstrate significant changes in trend at
about 400 m threshold of elevation across the pediment west of AM, at about 45
km inland of the shoreline, flanking the Hizaz-Asir Escarpment (HAE). Gravity
anomaly variation along a traverse taken across HAE and AIP is interpreted here
in terms of anomalous masses in crust as well as due to deeper crustal
configuration. 2D gravity interpretation is, in part, constrained by surface
geology, available geologic cross-sections for crust, interpretations from the
IRIS Deep-Seismic Refraction Line, and to a lesser extent by the available
gross results from shear-wave splitting and receiver function analysis. The
gravity model provides probable solutions for the first time on geometric
configuration and geophysical identification: a) for the seaward margin of the
mid-Tertiary Mafic Crust (TMC) below sediment cover of the Asir pediment that
coincides with the 400 m threshold elevation. This signifies an anomalous
uplift at the rifting phase. Moho below TMC extends from 10-22 km
depth across HAE and west margin of AIP, b). Thinned continental
crust below the Asir margin whose upper layer coincides with a seismic
reflector is at about 22 km depth, c). Rift-margin characteristic detachment
fault associated with basaltic flows on top surface of TMC at its inner margin,
d). Two geologically mapped low-angle normal faults dipping to the east
developed between the basic rocks intruding the AIP and e). felsic pluton
farther east within AS. Large scale igneous activity followed by intense
deformation affecting AIP clearly owes their origin to the rifting architecture
of the AS at the Red Sea extensional margin.
V. E. Camp, “Island Arcs and Their Role in the Evolution of the Western Arabian Shield,” The Geological Society of Amrica, Bull, Vol. 95, 1984, pp. 913-921.
V. E. Camp and M. J. Roobol, “Upwelling Asthenosphere Beneath Western Arabia and Its Regional Implications,” Journal of Geophysical Research, Vol. 97, No. B11, 1992, pp. 15255-15271. doi:10.1029/92JB00943
J. Kemp, C. Pellaton and J. Y. Calvez, “Cycles in the Chelogenic Evolution of the Precambrian Shield in Part of Northwestern Saudi Arabia,” Dir. General Mineral Resour. Prof. Paper PP-I, 1982, pp. 27-41. Saudi Arabia Deputy Minist. Miner. Resour., Jiddah.
D. B. Stoeser and V. E. Camp, “Pan-African Microplate Accretion of the Arabian Shield,” The Geological Society of America, Vol. 96, No. 7, 1985, pp. 817-826.
R. J. Stern and P. Johnson, “Continental Lithosphere of the Arabian Plate: A Geologic, Petrologic and Geophysical Synthesis,” Earth-Science Review, Vol. 101, No. 1-2, 2010, pp. 29-67. doi:10.1016/j.earscirev.2010.01.002
M. E. Gettings, “Delineation of the Continental Margin in the Southern Red Sea Region from New Gravity Evidence,” In: Red Sea Research 1970-1975, Bull. No. 22, Ministry Pet. Mineral Resource, DGMR-Jiddah, Saudi Arabia, pp. K1-K11.
M. Kono, “Gravity Anomalies in East Nepal and Their Implications to the Crustal Structure of the Himalaya,” Geophysical Journal International, Vol. 39, No. 2, 1974, pp. 283-299. doi:10.1111/j.1365-246X.1974.tb05455.x
J. H. Healy, W. D. Mooney, H. R. Blank, M. E. Gettings, W. M. Kohler, R. J. Lamson and L. E. Leone, “Saudi Arabian Seismic Deep-Refraction Profile: Final Project Report,” Open-File Report USGS-OF-02-37, 1982, p. 429. including appendices, Saudi Arabia Deputy Minist. Miner. Resour, Jiddah.
W. D. Mooney, M. E. Gettings, H. R. Blank and J. H. Healy, “Saudi Arabian Seismic Deep-Refraction Profile: A Traveltime Interpretation of Crustal and Upper Mantle Structure,” Tectonophys, Vol. 111, 1985, pp. 173-246. doi:10.1016/0040-1951(85)90287-2
M. E. Gettings, H. R. Jr. Blank, W. D. Mooney and J. H. Healey, “Crustal Structure of Southwestern Saudi Arabia,” Journal of Geophysical Research Solid Earth, Vol. 91, No. B6, 1986, pp. 6491-6512.
C. J. Wolfe, F. Vernon and A. AlAmri, “Shear-Wave Splitting Across Western Saudi Arabia: The Pattern of Upper Mantle Anisotropy at a Proterozoic Shield,” Geophysical Research Letters, Vol. 26, No. 6, 1999, pp. 779-782. doi:10.1029/1999GL900056
M. R. Kumar, D. S. Ramesh, J. Saul, D. Sarkar and R. Kind, “Crustal Structure and Upper Mantle Stratigraphy of the Arabian Shield,” Geophysical Research Letters, Vol. 29, No. 8, 2002, pp. 831-834.
A. R. A. Aitken, P. G. Betts, R. F. Weinberg and D. Gray, “Constrained Potential Field Modeling of the Crustal Architecture of the Musgrave Province in Central Australia: Evidence for Lithospheric Strengthening Due to Crust-Mantle Boundary Uplift,” Journal of Geophysical Research, Vol. 114, No. B12, 2009.
M. Talwani, J. L. Worzel and M. Landisman,” Rapid Gravity Computations for Two-Dimensional Bodies with Application to Mendocino Submarine Fracture Zone,” Journal of Geophysical Research, Vol. 64, No. 1, 1959, pp. 49-59. doi:10.1029/JZ064i001p00049
C. Subrahmanyam and R. K. Verma, “Densities and Magnetic Susceptibilities of Precambrian Rocks of Different Metamorphic Grade (southern Indian shield),” Journal of Geophysical Research, Vol. 49, 1981, pp.101-107.
S. Dupre’, S. Cloetingh and G. Bertotti, “Structure of the Gabon Margin from Integrated Seismic Reflection and Gravity Data,” Tectonophys, Vol. 506, No. 1- 4, 2011, pp. 31-45. doi:10.1016/j.tecto.2011.04.009
G. S. Lister, M. A. Etheridge and P. A. Symonds, “Detachment Faulting and the Evolution of Passive Continental Margins,” Geology, Vol. 14, 1986, pp. 246-250. doi:10.1130/0091-7613(1986)14<246:DFATEO>2.0.CO;2