Pulsed emplacement under the Uyaijah granite ring structure, eastern Saudi Arabia—results from 3D gravity-magnetic inversion

The Uyaijah ring structure (URS), situated within the Precambrian Kushaymiyah Igneous Complex (KIC) at the eastern edge of the Arabian Shield, consists of three large laccoliths: two granitic and one granodioritic, intruded by late mafic dikes. The transverse fault zone (TFZ), belonging to the Najd Fault System of Saudi Arabia, transects the URS along its major axis. The digital elevation map for the URS is first correlated with surface geology to clarify the effects of faulting on the elevation of the pluton. Next, the complete (terrain-corrected) Bouguer anomaly (CBA) map for the URS, based on 145 gravity stations, is examined to investigate the source of the URS through 3D-gravity inversion modeling. A pronounced CBA “low” (< 50 mgal amplitude) occupies the central part of the URS; this is interpreted as the lower density root of the pluton. Three-dimensional gravity inversion modeling traces the source magmatic body through sections at 2–10 km below sea level; this model is largely complemented by results from the 3D magnetic inversion of the RTP aeromagnetic anomalies. The gravity-magnetic inversion indicates that the pluton root zone lies below the SW of the URS at ~ 10-km depth; this value is significantly different from previous depth estimates of ~ 4.75 km. The root zone is noticeably offset by the TFZ. These results suggest a genetic relationship between pluton expansion and updoming, dyking, and faulting that probably reaches down to the base of the upper crust, involving pulsed emplacement.