A new grand mean palaeomagnetic pole for the 1.11 Ga Umkondo large igneous province with implications for palaeogeography and the geomagnetic field

Abstract

corresponds with a normal or reversed geomagnetic field relative to other continents can constrain the relative orientations between cratons with time-equivalent data. This interpretation is particularly important in comparison to Laurentia as it bears on Kalahari's involvement and position in the supercontinent Rodinia. The dominance of south-directed declinations within the Umkondo Province was previously used to suggest that these directions are the same polarity as reversed directions from the early magmatic stage of the Keweenawan Midcontinent Rift of Laurentia. Two Umkondo sills with northerly declinations have U-Pb baddeleyite ages of ca. 1109Ma that are temporally close to dated Midcontinent rift units having reversed directions. Based on this comparison, and paleomagnetic data from younger units in the Kalahari Craton, we favor the option in which the sites with northerly declinations from the Umkondo Province correspond to the reversed polarity directions from the early magmatic stage in the Midcontinent Rift. This interpretation allows for the Namaqua-Natal metamorphic belt of Kalahari to be a conjugate to the Grenville margin of North America and for Kalahari to have become conjoined with Laurentia within the supercontinent Rodinia subsequent to Umkondo LIP magmatic activity. IntroductionPaired paleomagnetic and geochronologic data demonstrate that between ca. 1112 and 1108 Ma there was large-scale magmatism across the Kalahari Craton over an area of ∼2 x 10 6 km 2 ( Fig. 1; Hanson et al., 2004a). Extrusive components of this province are exposed as tholeiitic basalts that occur at the top of the Umkondo Group in Zimbabwe and Mozambique (Swift, 1962;McElhinny, 1966;Moabi et al., 2015) and as rhyolite lavas, pyroclastics and tholeiitic basalts within the Kgwebe Formation of northern Botswana (Modie, 1996;Hanson et al., 2006). However, the majority of exposed remnants of the Umkondo Large Igneous Province (LIP) are shallow-level mafic intrusions de Kock et al., 2014) which are interpreted as feeders to more extensive flood lavas that have largely eroded away (Hanson et al., 2004a).The widespread extent of these intrusions has led to the inference that the lavas covered nearly Swanson-Hysell et al. (2015) (2011) for sources for the geological data. The inset map shows the location of the main map and the broader geological context. The thick translucent gray line on the inset map indicates the interpreted shape of the Kalahari Craton on the interior of the late Mesoproterozoic orogenic belts that is used in the paleogeographic reconstructions (Fig. 4) (Hanson et al., 2004bSöderlund et al., 2010), post-1.83 Ga dolerite sills in the Soutpansberg Group (Brandl, 1981(Brandl, , 1985Geng et al., 2014), and the widespread 0. basement correspond to the Umkondo event is a reasonable one, it is largely untested since there are precise age constraints for only a small fraction of the total exposed intrusions. If high-quality paleomagnetic data can be generated from a given sill, the distinct paleomagnetic poles ...

PmagPy: Software package for paleomagnetic data analysis and a bridge to the Magnetics Information Consortium (MagIC) Database

“…All the code can be run to replicate the data analysis or to modify and/or extend it. An additional benefit of using notebooks is that they can easily be shared as static html files or exported as pdf files that can be included as the supporting information to submitted articles [e.g., Swanson‐Hysell et al ., ].…”

Direct Mesoproterozoic connection of the Congo and Kalahari cratons in proto-Africa: Strange attractors across supercontinental cycles

“…1.1 Ga Huila-Epembe (HE) dikes and related mafic rocks across the Congo craton in Angola and northernmost Namibia (Fig. 1), the results of which can be compared to the well-established paleomagnetic pole from the coeval Umkondo LIP from the Kalahari (Swanson-Hysell et al, 2015). Methods are fully described in the GSA Data Repository 1 .…”

“…1110 ± 3 Ma S1646 S1647 S1606 S1601 ca. 1104 Ma S1602 S1604 S1605 JS1507, JS1508 S1609 S1656 S1655 S1651 S1650 S1659 Lubango Rodinia (Swanson-Hysell et al, 2015;Kasbohm et al, 2016) and the derivation of Congo from the breakup of Nuna (Salminen et al, 2016). Based on the distribution of Umkondo igneous rocks in the Kalahari craton, including two wellconstrained dike swarms, de Kock et al 2014inferred the existence of a major magmatic center for the LIP near the northwest edge of the craton.…”

Evaluating the Relationship Between the Area and Latitude of Large Igneous Provinces and Earth's Long‐Term Climate State

“…1109 Ma Umkondo is another Precambrian LIP that is constrained to have erupted in the tropics, although it is not known to be associated with any glaciation (no glacial deposits are found within the contemporaneous Midcontinent Rift basin; Swanson-Hysell et al, 2019). We reconstruct the paleolatitude of the Umkondo LIP at the time of emplacement using the paleomagnetic pole of Swanson-Hysell et al (2015) and find that effectively all of the LIP (or ~2.0 Mm ) erupted within the tropics, an area that is slightly smaller than that estimated for the Franklin LIP (Fig. 7.4c).…”