Duration of partial melting in the lower crust of the Limpopo collisional belt

Abstract

In convergent settings, the duration of partial melting in the lower continental crust dictates how lateral shortening is accommodated by the colliding plates. Here we use the example of the ca. 2700 Ma Southern Marginal Zone of the Limpopo Belt, South Africa, to accurately time the different steps of the granulite facies metamorphic event. We date garnet crystallisation in K‐poor leucosomes using Sm–Nd garnet isotopic data to have occurred at 2734 ± 9 Ma. Following deposition of the protolith and rapid burial, the crust remained molten for 17 ± 14 Ma. This estimate is within error similar to the 24 ± 12 Ma proposed for rocks that have evolved along a Barrovian P–T path. Our results suggest that the Southern Marginal Zone is the result of a collision between a large island arc or a continent with the Kaapvaal Craton, at a time global of geodynamic changes.