Shift from arc to within-plate magmatism at 635 Ma as recorded by Neoproterozoic dikes, southern Midyan terrane, NW Arabian Shield

Abstract

The tectonic evolution of the Arabian-Nubian Shield began with formation of intra-oceanic arcs followed by collisions between these in Tonian-Cryogenian time and culminated in Ediacaran continental collision to form Gondwana. We provide new insights into the middle stage of this tectonic evolution by focusing on two Neoproterozoic dike swarms of different age in northern Arabia. The 695–700 Ma Za’am dikes were emplaced about the time of collision between the Midyan and Hijaz terranes whereas the 635 Ma Bayda dikes were emplaced ∼ 60 million years after collision. These record a shift from relatively unfractionated 695 Ma arc-type magmas in the south to fractionated 635 Ma within-plate alkaline magmas in the north. Our results document mantle source and crustal evolution beneath the Midyan terrane during and after terrane accretion, revealing a tectono-magmatic transition from SSZ-type magmas accompanying arc collision to post-terrane accretion within-plate magmatism through Cryogenian time. In addition, our results confirm the potential of dike studies for reconstructing the tectono-magmatic-metallogenic evolution of orogens.