Characterisation of granites from the Midyan terrain, NW Saudi Arabia

Abstract

Five, Neoproterozoic, poorly studied felsic intrusives from NW Saudi Arabia have been subjected to a detailed geological, geochemical and mineralogical study to identify their characteristics and to understand their processes of formation. The results have indicated that the individual plutons in the region are each subtly different. This is mainly displayed by the existence of different types of granites, based on chemistry and petrography (peralkaline, alkaline and calc-alkaline) and mineralogy (particularly the presence of different types of amphibole, both sodic and calcic). The granites were most likely derived by low-pressure, partial melting of crustal rocks with possible crustal contamination, followed by fractional crystallization and later sub-solidus alteration by fluids. The geochemical differences between the granites could be related to their formation during different stages of the region’s evolution. The granites contain relatively high contents of rare earth elements and rare metals, mostly hosted by phosphates (monazite-Ce and xenotime), Nb oxide (fergusonite-Y) and possible rare earth carbonates (synchysite). Further detailed geochemical study would determine the economic significance of the studied granitoids and allow understanding how the plutons were fit into tectonic setting of the region.