Using Paleomagnetism to Determine Paleographic History and Tectonic Relations of the Sinclair Terrane, Namibia

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The Sinclair terrane, near the western margin of the Kalahari craton in southern Namibia, is home to low-grade metasedimentary and metavolcanic rocks of Mesoproterozoic age [Hoal, 1993, Precambr. Res. 63]. Its high level of exposure is anomalous relative to the highly metamorphosed Precambrian terranes of the Rehoboth inlier and the Namaqualand/Bushmanland metamorphic complex to the north and south, respectively [e.g. Becker et al., 2006, J. Afr. Earth Sci. 46]. This low-grade nature of the Sinclair terrane is suitable for paleomagnetic studies. Robust, well-dated paleomagnetic poles from Sinclair rocks should provide critical constraints on tectonic models for the Namaqua-Natal-Maud orogeny (NNMO), and may also prove useful in general models for Rodinia supercontinent assembly. Previous paleomagnetic studies were conducted using natural remnant magnetism (NRM) and alternating field (AF) demagnetization data without the use of field stability tests (conglomerate, fold, and baked-contact tests) to constrain the age of magnetization [Piper, 1975, Geophys. J. R. astr. Soc. 40]. This showed a need to resample the area with the necessary constraints and was done during the summer of 2011 and 2012.

Siliciclastic sediments and lava flows of the Guperas Formation, as well as a post-Guperas bimodal dyke suite, were sampled around the town of Helmeringhausen. The samples are being prepared and analyzed in the Yale University paleomagnetism laboratory using alternating-field and controlled-atmosphere thermal demagnetization techniques. Results are showing best results from the post-Guperas dykes, revealing a stable characteristic remanence directed shallowly to the north or south. Within the directly overlying Auborus Formation, clasts of volcanic rocks that are likely sourced from Guperas flows and post-Guperas dykes show highly dispersed remanence directions. This indicates a Proterozoic age of remanence. A positive baked-contact test on the dykes, intruding older volcanic rocks of the Barby Formation, has been performed and shows a transition from the post-Guperas dyke direction to an intermediately dipping direction to the south-southwest. Samples have also been collected for U-Pb geochronology, which will provide precise ages for the resulting paleomagnetic poles obtained in this study.

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Geological Society of America Abstracts with Programs, v. 45, issue 7, p. 113