New preliminary magnetostratigraphy study of the Karoo Large Igneous Province (LIP) Stormberg lavas, SaniPass section, Kwazulu Natal Province (SA) -Lesotho border.

Abstract:

The Karoo Large Igneous Province (LIP), which is exposed in parts of South Africa, Antarctica and Australia, was emplaced as a complex of mafic intrusions and lava flows preceding the breakup of these continents and the opening of the Indian Ocean. This province is considered to have formed in the Early Jurassic with peak magmatic activity centred between 184 and 183 Ma. The details of the timing of emplacement of the Karoo LIP are still disputed, with discussion ranging from a brief emplacement interval (Moulin et al. 2012) to a more prolonged duration of emplacement up to 12 million years (Jourdan et al. 2005; 2008). Disagreements in part have resulted from inconsistent geochronologic age determinations and the need for further paleomagnetic data for these rocks. To better understand the duration and timing of Karoo volcanism, we resampled (2018 and 2019) in complete detail the classic Sani Pass section, the Drakensburg escarpment, at the South Africa – Lesotho border. A total of 663 core samples were collected from a sequence of 54 sites, in what we interpret to be independent cooling units from the basal contact between Elliott Group strata and the lowermost basalt at 2093 m to the top of the section at 2856 m. Our sampling collection, intended to provide quality estimates of the ChRM of each volcanic unit sampled, clearly includes volcanic units that were not previously sampled in this section. Preliminary results show a normal to reverse polarity transition that is consistent with the early work of Van Zijl (1962a,b), but far more detailed in terms of interpreted transitional directions in comparison to results by Rehacek (1995) and Kosterov et al. (1997). Susceptibility vs. T experiments for material from each site show that the ChRMs are carried by Ti-poor titanomagnetite, consistent with petrographic and geochemical data.