Geochemical signature variation of pre-, syn-, and post-shearing intrusives within the Najd Fault System of western Saudi Arabia

• Intrusive emplaced within, around the Najd Fault in the Arabian–Nubian Shield.
• Their geochemistry reflects change in tectonic regime.
• Change from compressional volcanic arc nature to extensional within plate.
• Pre-shearing rocks are tholeiitic and calc-alkaline in island or continental arc.
• Syn- and post-shearing rocks are peraluminous of post-orogenic uplift and collapse.

Late Precambrian intrusive rocks in the Arabian–Nubian Shield emplaced within and around the Najd Fault System of Saudi Arabia feature a great compositional diversity and a variety of degrees of deformation (i.e. pre-shearing deformed, sheared mylonitized, and post-shearing undeformed) that allows placing them into a relative time order. It is shown here that the degree of deformation is related to compositional variations where early, usually pre-shearing deformed rocks are of dioritic, tonalitic to granodioritic, and later, mainly post-shearing undeformed rocks are mostly of granitic composition. Correlation of the geochemical signature and time of emplacement is interpreted in terms of changes in the source region of the produced melts due to the change of the stress regime during the tectonic evolution of the Arabian–Nubian Shield. The magma of the pre-shearing rocks has tholeiitic and calc-alkaline affinity indicating island arc or continental arc affinity. In contrast, the syn- and post-shearing rocks are mainly potassium rich peraluminous granites which are typically associated with post-orogenic uplift and collapse. This variation in geochemical signature is interpreted to reflect the change of the tectonic regime from a compressional volcanic arc nature to extensional within-plate setting of the Arabian–Nubian Shield. Within the context of published geochronological data, this change is likely to have occurred around 605–580 Ma.