c.2.02 Ga Ar40–Ar39 muscovite age from the Gulushabe fold structure, Motloutse Complex, near SW margin of Zimbabwe Craton: Imprint of Limpopo Complex or Magondi Belt tectonics?

Abstract

Meta-supracrustal rocks in medium-to high-grade terranes along Archean craton margins are, in the common case, more deformed than similar rocks within the craton. Multiple deformation episodes are possible and could be related to different stages of a single tectonic event or disparate ones. Geochronologic characterization of fabric forming minerals helps to place an individual deformational episode with respect to spatially associated tectonic events along the craton margin. This study focuses on the Shashe Group of metasedimentary rocks that define the large-scale Gulushabe fold structure in northeastern Motloutse Complex, Botswana, near its contact with the southwestern margin of the Zimbabwe Craton. Available detrital zircon geochronologic data indicate a depositional age of c.2.66–2.51 Ga for the protolith of these continental margin-type metasedimentary rocks. The upright NNE-trending Gulushabe fold structure is at variance with the regional northeasterly vergent folds from the northern–central Motloutse Complex and related to the Neoarchean (<2.65 Ga) NE-directed thrusting of the medium-grade terrane over the craton margin. ⁴⁰Ar/³⁹Ar geochronology of muscovite in quartz mica schist from the NNE-trending refolded northwestern minor fold closure of the Gulushabe fold structure yielded a plateau (96% of ³⁹Ar) age of 2018 ± 11 Ma. The significance of the age is addressed in terms of Paleoproterozoic tectonics in the bounding terranes: Limpopo Complex to the south and Magondi Belt to the north. In the process, the Archean antiquity and extent of the Motloutse Complex, and the provenance of Shashe Group rocks are clarified. The results highlight the importance of delineating overprint events to better understand the tectonics along the contact of Archean craton and medium-to high-grade terranes.