Article ID Journal Published Year Pages File Type
5784761 Precambrian Research 2017 35 Pages PDF
Abstract
The newly described Sperrgebiet Domain is a part of the Palaeo- to Mesoproterozoic Namaqua-Natal Province that is exposed as a basement inlier within the Pan-African Gariep Belt in SW Namibia. Clastic metasediments of the c. 1700 Ma Aurus Schist of the Sperrgebiet Domain exhibit Pan-African fabrics and metamorphic mineral assemblages that are not present in the low-grade metamorphic Gariep Supergroup against which it is tectonically juxtaposed. Metapelitic and semi-pelitic schists consist of phengitic white mica, chlorite, minor garnet and quartz ± biotite, and contain pseudomorphs after a prismatic aluminous mineral, likely chloritoid or staurolite. Calculated pseudosections for four mica schist samples constrain P-T conditions of around 10 kbar and 500 °C, and the late paragenesis of garnet indicates that these conditions were attained along a prograde, clockwise trajectory. These conditions and the low apparent geotherm (∼14 °C.km−1) are typical of subduction zone metamorphism, and are similar to those documented for peri-contemporaneous accretionary metamorphism in the adjacent Damara Belt to the NE. A subduction origin has also been proposed for exotic 'blueschist' blocks within the Gariep Belt; however, the absence of an accretionary metamorphic imprint in the Gariep Supergroup indicates that the Sperrgebiet Domain was decoupled from these lithologies for much of the Pan-African Orogeny. Our results are the first indication that the continental margin of the western Kalahari Craton may have been subducted during the latter stages of Pan-African convergence and Gondwana assembly.
Related Topics
Physical Sciences and Engineering Earth and Planetary Sciences Geochemistry and Petrology
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