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Shrimp zircon ages and petrology of lower crustal granulite xenoliths from the letseng-la-terae kimberlite, lesotho: Further evidence for a namaqua-natal connection

Abstract:

Recrystallized zircons extracted from intermediate granulites of the Letseng-la-Terae Diamond Mine in northeastern Lesotho provide evidence that the Tugela Terrane of the Mesoproterozoic high-grade Namaqua-Natal mobile belt may extend -200 km farther west than previously thought. The rock-forming minerals in the investigated lower crustal granulites contain garnet, clinopyroxene, plagioclase and quartz or garnet, wollastonite, plagioclase and quartz. Calculated values for peak granulite-facies metamorphism are ∼13 kbar and ∼850°C. Thermal overprint and therein granulite-facies metamorphism occurred during the late Mesoproterozoic and is documented by SHRIMP metamorphic zircon ages of 1018 ± 18, 1126 ± 10 and 1127 ± 6 Ma. These ages are in good agreement with the timing of other events in the Namaqua-Natal belt. High-grade metamorphism was probably caused by crustal thickening resulting from continent-arc collision, followed by underplating of hot mantle melts. © 2013 December Geological Society of South Africa.