Post-orogenic magmatism from within the Al Mukalla terrane, Yemen: a record of Cambrian extension within a Neoproterozoic arc terrane

Late tectonic granitoids that cut a deformed sequence of volcanic and sedimentary rocks (Tha’lab Group) comprising the Al Mukalla terrane have been investigated by whole rock major and trace element geochemistry, Sm-Nd and feldspar Pb isotope compositions, and U-Pb zircon geochronology. The 696 ± 12 Ma age determined for one such intrusion, the Mukalla granite, demonstrates that the Mukalla arc had formed and been juxtaposed with Azania and the Al Mahfid terrane before ca. 700 Ma. Its eNdt value of -0.2 and elevated feldspar Pb isotope values collectively indicate the involvement of some ancient continental material during its petrogenesis. Two other bodies were intruded ca. 550 Ma, and another, the Burum granite ca. 520 Ma. These 550-520 Ma bodies are calc-alkalic or alkaline and share a similarly slightly evolved isotopic signature to the Mukalla granite. The isotopic signature obtained for the Mukalla granite is consistent with development of an intra-oceanic Mukalla arc, which was influenced by sediment derived from Azania, rather than an Andean-style arc that developed on it. The final closure of the Mozambique Ocean is located farther east. Intrusion of the younger granitoids was likely facilitated by transcurrent faulting, akin to the Najd fault system of Saudi Arabia.