Jebel Tays ophiolitic thrust sheet, Saudi Arabia: tectonic setting, petrogenesis and geochronological framework

Abstract

The Arabian Nubian Shield (ANS) records multiple episodes of terrane amalgamation associated with the closure of the Mozambique Ocean and the amalgamation of Gondwana. Evidence for such amalgamation events are recorded by repeated ophiolite decorated sutures across the ANS. The Jebel Tays ophiolite is situated in the eastern portion of the ANS, within the Ad Dawadimi Basin and surrounded by the Abt Schist. This basin separates the Afif and Ar Rayn arc terranes and represents one of the last terrane amalgamation events affecting the exposed ANS. I identify mafic magmatism associated with Jebel Tays as a low titanium island arc tholeiite with forearc affinity (boninitic) in contrast to the island arc tholeiite magmatism of the nearby Halaban ophiolite. Furthermore, I place robust zircon ages on mafic magmatism of 678 ± 5.1 Ma for the gabbros of Jebel Tays and 674.4 ± 5.7 Ma for the Halaban ophiolite. Based on the stratigraphy and structure of Jebel Tays and the sub-greenschist nature of the thrust contacts I propose that Jebel Tays represents a forearc ophiolitic thrust sheet. Its obduction was associated with extensive serpentinite mud volcanism within a forearc environment associated with a west dipping subducting slab. From detrital zircons obtained from the Abt Formation I constrain deposition of the Ad Dawadimi basin sediments to ca 600 Ma, making them Ediacaran in age, a date that coincides with a new LA-ICP-MS monazite metamorphic age of 599.8 ± 5.8 Ma obtained from a trondhjemite that cross cuts the Jebel Tays body. This is in agreement with previously published 40Ar/39Ar ages which I interpret as metamorphism associated with final basin closure and the amalgamation of the Afif and Ar Rayn Terranes.