Exhumation of Limpopo Central Zone granulites and dextral continent-scale transcurrent movement at 2.0 Ga along the Palala Shear Zone, Northern Province, South Africa

Abstract

The Palala Shear Zone is part of a major tectonic lineament in southern Africa, which extends over 1000 km from central Botswana to the Soutpansberg in South Africa. The lineament is situated between the Central Zone of the Limpopo Belt and the Kaapvaal Craton. At its main exposure, in the Koedoesrand Window 50 km E of Ellisras, Northern Province, the Palala Shear Zone comprises a c. 15 km wide mylonite zone which can be subdivided into a Northern, Central and Southern Domain. This study addresses the tectono-metamorphic history of the Palala Shear Zone in the Koedoesrand Window and its role in the tectonics of the Limpopo Belt. In order to do this, structural and petrographical work was combined with geochronology. Age data from relic mineral parageneses show that metapelites from the Central Domain underwent granulite facies metamorphism around 2.6 Ga. However, because of an intense Proterozoic overprint, field relationships of the Archean event are largely disrupted. During a second high-grade event at c. 2.0 Ga, granulite facies metamorphism was reached in the Northern Domain and the adjacent Limpopo Central Zone. Charnockites were emplaced in the Northern Domain after 2.1 Ga and were affected by retrograde amphibolite and greenschist facies metamorphism around 1.97 Ga. Post-orogenic transcurrent faulting under (sub)greenschist facies conditions characterizes the Central and Southern Domains. Field observations and microstructural investigations indicate a dextral shear sense for the retrograde mylonitisation. These findings document that the Palala Shear Zone played an important role during the exhumation of the Proterozoic granulites in the Limpopo Central Zone, associated with a transpressive orogeny between 2.05 and 1.95 Ga. Low-grade post-orogenic transcurrent faulting in the Palala Shear Zone at c. 1.9 Ga may be associated with the transtensional opening of the Soutpansberg and Palapye grabens. On the basis of the tectono-metamorphic history in the Koedoesrand Window and regional geophysical, geochemical and sequence-stratigraphic data, the Palala Shear Zone is interpreted as a Proterozoic suture zone, along which the Archean Kaapvaal and Zimbabwe Provinces were juxtaposed.