IMAGING THE ARABIAN SHIELD CRUST: AN APPLICATION OF POTENTIAL-FIELD DATA TO CRUSTAL STUDY OF NEOPROTEROZOIC BASEMENT

The largely Neoproterozoic Arabian Shield crops out in western Arabia and similar crust underlies Phanerozoic sediments in the Arabian Platform to the north and east. Reduced-to-the-pole (RTP), first vertical derivative, upward-continued, and other transformations of magnetic data that cover ~1,000,000 km² of the region and the Red Sea between 19° and 24° N provide detailed imaging of the crust. Limited gravity data cover the south. The shapes and intensities of RTP anomalies generally correlate well with known geology, and image contacts, faults, shear zones, intrusions, and contrasting regions of volcanic, sedimentary, and high-grade rocks in fine detail. But in the southeast and southwest discrepancies between the magnetic signature and known geology raise questions about existing geologic models and suggest the presence of large-scale concealed or hitherto unrecognized geologic structures. Upward continuation suggests such structures are present at depths of 5-10 km, raising the possibility of a regional crustal décollement separating upper from deeper crustal structures, compatible with the layered structure of the shield known from seismic-refraction data. Elsewhere, magnetic data image basement structures extending beneath Phanerozoic sediments as much as 200-350 km from the Shield margin. Most conspicuous among these structures are northward extensions of a sedimentary basin and a volcanic arc from the northeastern edge of the Shield – the Central Arabian Magnetic Anomaly – and extensions of major shears and suture zones. The magnetic fabric of the Shield is truncated at the shoreline, where it is replaced by a very different fabric related to the Red Sea basin; no evidence that continental crust extends beneath the basin is seen. Where available, gravity data provide additional insights into shield structure, locally revealing crustal features not apparent from the magnetic data. These include a major gravity low coincident with a granite batholith that magnetically has a “noisy” signature revealing little geologic information. Gravity identifies the regional extent of the batholith and indicates a spatial relationship between the batholith margin and gold mineralization. Gravity elsewhere evidences a close spatial relationship between gold deposits and a mafic crustal block.