Tectonic history of the northern Nabitah fault zone, Arabian Shield, Kingdom of Saudi Arabia

Abstract

Geologic mapping combined with structural, petrographic, and geochemical investigations were used to evaluate the motion and paleogeographic setting of the northern Nabitah fault zone. The orientation and asymmetry of small structures in three areas along the fault zone suggest that motion was primarily left-lateral strike slip. East of the fault zone, the Afif terrane is underlain by a north-trending granodioritic batholith that is interpreted to be the plutonic core of a volcanic arc (herein named the Nabitah arc) whose activity was coincident with Nabitah faulting. Available geochronologic data indicate that the Nabitah fault zone and arc were active at 710 Ma and that activity may have continued until about 670 Ma. Relicts of a prebatholithic island-arc ophiolite crop out as roof pendants and septa east of the fault zone. Analysis of petrologic, geochemical, and geochronologic data suggests that these rocks may have formed a terrane older than 800 Ma that was continuous from the Nabitah fault zone to the Nuqrah belt. These rocks may have been moved northward by Nabitah faulting from an original position opposite the Asir terrane. Scale-model comparisons with Recent and Phanerozoic volcanic arcs suggest that the Nabitah fault zone may have been a transform fault that developed as a result of sinistral oblique subduction east of the Al Amar fault. According to this model, the Abt schist would have formed in an accretionary prism and the Murdama group would have been deposited in a fore-arc basin. Analogs for thrust faults in the northern Arabian Shield are found in modern arcs developed behind oblique subduction zones. The orientations of the Najd faults may reflect initial formation as normal faults in the fore-arc region of such an arc system. Based on the presence of similar lithologies, similar structure, and analogous tectonic setting, the Mother Lode District in California is reviewed as a model for gold occurrences near the Nabitah fault zone in this report.