Source zone modelling for the Harrat Al-Birk, Red Sea coast: insight from crustal rheological parameters and gravity anomaly interpretation

The source model for evolution of the Harrat Al-Birk (HAB) is presented by constructing a 2D integrated crustal model using gravity anomalies and the rheological parameters computed from receiver function analysis (REF) results. The Bouguer anomalies are of average amplitude 20 mGal over the HAB which quickly change into an Axial Gravity Low (AGL) further inland on the Arabian Shield Crust (ASC) showing a consistent fall by ~ 110 mGal. Within this region, an anomalous gravity high, called the Jabal As-Swdah Gravity High (JSGH), of 60 mGal amplitude and 55 km wavelength, occupies the higher grounds where the peak elevation reaches 2,800 m. An analysis of the computed rheological parameters, namely, Vp, Vp/Vs ratio, density, Lame’s first and second constants, bulk modulus, Young’s modulus, Poisson’s ratio, and acoustic impedance, suggests that the lower crust is grossly uniform, whereas the upper crust is laterally heterogeneous. The integrated crustal model is inferred to be a mosaic of adjoining crustal blocks whose primary features are (i) a Moho up-warp by ~ 5 km over a distance of ~ 40 km beneath JSGH; (ii) a sharp bulge in Moho by 58% (42.5 to 17.5 km) coinciding with the Tertiary Gabbro Dyke Zone (TGDZ). The TGDZ appears to form a crust-pervasive vertical magma sheet of width 14–25 km; (iii) crustal thinning of 60% is attained at the rifted transitional crust below HAB; and (iv) the source zone for the HAB basalts is originated under the JSGH, for which the dykes and fault zones acted as conduits fringing the coast.