Zircon geochronology of the Oribi Gorge Suite, KwaZulu-Natal, South Africa: constraints on the timing of trans-current shearing in the Namaqua-Natal Belt

Abstract

The Oribi Gorge Suite is a voluminous suite of rapakivi granite-chamockite plutons which occur in the Mzumbe and Margate terranes of the eastern (Natal) sector of the Mesoproterozoic Namaqua-Natal Belt of Southern Africa. Previous geochronological studies have provided contradictory results for the age of emplacement of the suite. New single zircon evaporation dates and detailed SHRIMP zircon analyses for three of the plutons confirm the previously observed complexity with two episodes of intrusion at ∼1070 and 1030 Ma. Metamorphic growth of zircon at ∼1030 Ma is also recorded from the Oribi Gorge pluton. The two intrusive episodes are further apart timewise (∼45 Ma) than expected for plutons belonging to a single suite. The range of ages probably reflects long-lived, post-collisional trans-current shearing in the eastern (Natal) sector of the Namaqua-Natal Belt when conditions suitable for formation of similar, megacrystic, A-type granitoids were repeated. Similar granitoids from the western (Namaqua) sector of the Belt indicate that these tectonic conditions were regional in extent. Show more