A Paleomagnetic Reanalysis of the Auborus Formation, Namibia

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Along the western margin of the Kalahari craton in southern Namibia, late Mesoproterozoic volcanic and sedimentary rocks of the Sinclair region are locally preserved at subgreenschist metamorphic grade [Hoal, 1993, Precambr. Res. 63, 143-162], thus amenable to paleomagnetic study. The youngest unit in the Sinclair succession is the Auborus Formation. comprising redbeds deposited after the cessation of Sinclair magmatism and during the waning stages of regional folding. A previous study of the Auborus Formation, utilizing data only from the natural remanent magnetization (NRM), found a well clustered, single-polarity direction differing from the present field at the sampling sites [Piper, 1975, Geophys. J. R. astr. Soc. 40, 313-344], suggesting that the Auborus Formation is likely to produce a high-quality paleomagnetic pole with proper demagnetization and field tests.

We collected oriented samples through most of the Auborus stratigraphy in 2011 and 2012. Preliminary results from detailed thermal demagnetization exhibit broad agreement with Piper’s [1975] NRM data, and show a two-polarity hematite-borne characteristic remanence directed shallowly N-S. Directions are better grouped after correction for tectonic tilt, indicating a Proterozoic age of remanence because the Ediacaran-Cambrian Nama Group is flat-lying throughout the region. Present results are limited to the lower part of the Auborus Formation, in which a single reversal of the magnetic field has been documented. Analysis of the upper part of the formation is in progress, but we have already added three quality criteria (vector analysis, positive fold test, and reversals) to the Auborus pole of Piper [1975]. Along with a companion study of older units in the Sinclair terrane [Panzik et al., this meeting], our results will provide important constraints on regional tectonics of the western Kalahari craton, its role in Rodinia reconstructions, and late Mesoproterozoic geomagnetic reversal frequency.

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Geological Society of America Abstracts with Programs, v. 44, issue 7, p. 598