Continental-scale sediment mixing and dispersal across northern Gondwana: detrital zircon U-Pb-O-Hf isotopic evidence from the Cambro-Ordovician sandstones overlying the Arabian Shield

The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined <i>in-situ</i> U-Pb, δ¹⁸O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8–0.55 Ga and 1.1–0.9 Ga with subordinate peaks at ca. 2.2–1.7 Ga and 2.7–2.5 Ga. The δ¹⁸O secular variation mirrors global compilations with Archaean zircon defining a restricted δ¹⁸O range of ca. 4.0–8.0 ‰ and younger zircon showing wide variation in δ¹⁸O up to ca. 14 ‰. The ca. 0.8–0.55 Ga age peak has the largest variation in ε_Hf(t) with about half of all these Neoproterozoic zircon grains being juvenile (ε_Hf(t) &gt; 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved ε_Hf(t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1–0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1–0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ¹⁸O of post–Archaean zircon, together with the evolved ε_Hf(t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental–scale homogenization and dispersion process.