Petro-tectonic evolution of metamorphic sole of the Semail ophiolite, UAE

Abstract

The Semail ophiolite located in the eastern part of the Arabian platform preserves remnants of ocean plate stratigraphy and related metamorphic sole. To understand the petro-tectonic evolution of a metamorphic sole during subduction to obduction processes, here we investigate the garnet metagabbros from the metamorphic sole and the tonalites which intruded the mantle section of the Khor Fakkan Block. We present results from petrology, geochemistry, zircon U-Pb, Hf and O isotope analyses and phase equilibria modeling. The garnet metagabbro samples have E-MORB-type enriched-mantle compositions with zircon dates of ca. 89–96 Ma, and positive εHf(t) values ranging from 5.6 to 10.0. The tonalite is peraluminous with those range of ca. 87–92 Ma, and a range of positive εHf(t) values of 5.1–10.0. The similarity in εHf values from both the garnet metagabbro and tonalite samples suggests a strong relevance to their mantle source, indicating the role of subducted material during their formation. In contrast, the δ18O(zircon) values show distinctly different values of high δ18O(zircon) of ~13–16‰ for the tonalite and ~ 5–8‰ for the metagabbro samples, reflecting variations in the role of surface-derived source materials. The phase equilibria modeling of the garnet metagabbro shows high-pressure amphibolite facies metamorphism that preceded the peak granulite facies metamorphism, followed by lower pressure hydration and decompression. This clockwise P-T path might reflect partial melting and differentiation of mantle wedge section above subducted slab. Our results provide insights into the complex processes within a supra-subduction zone, implying differences in degree of partial melting of the ocean plate stratigraphic sequences including recycled oceanic slab and surface-derived marine sediments that were subsequently interacted with hydrothermally altered mantle at a mantle wedge during subduction to obduction processes that formed the Semail ophiolite during the Upper Cretaceous.