Late Paleoproterozoic mafic magmatism and the Kalahari craton during Columbia assembly

Cedric Djeutchou,Camilo E Gaitán,Ashley P Gumsley,Hervé Wabo,Michiel O De Kock,Ulf Söderlund

doi:10.1130/g48811.1

Abstract

Abstract The 1.87–1.84 Ga Black Hills dike swarm of the Kalahari craton (South Africa) is coeval with several regional magmatic provinces used here to resolve the craton's position during Columbia assembly. We report a new 1850 ± 4 Ma (U-Pb isotope dilution–thermal ionization mass spectrometry [ID-TIMS] on baddeleyite) crystallization age for one dike and new paleomagnetic data for 34 dikes of which 8 have precise U-Pb ages. Results are constrained by positive baked-contact and reversal tests, which combined with existing data produce a 1.87–1.84 Ga mean pole from 63 individual dikes. By integrating paleomagnetic and geochronological data sets, we calculate poles for three magmatic episodes and produce a magnetostratigraphic record. At 1.88 Ga, the Kalahari craton is reconstructed next to the Superior craton so that their ca. 2.0 Ga poles align. As such, magmatism forms part of a radiating pattern with the coeval ca. 1.88 Ga Circum-Superior large igneous province.

Highlights

The Paleoproterozoic to Mesoproterozoic supercontinent formed by assembly of Archean cratons starting at 1.9 Ga and was fully amalgamated as late as 1.65–1.58 Ga (Meert, 2012; Pisarevsky et al, 2014; Pourteau et al, 2018)
We present new paleomagnetic data from 36 Black Hills dike swarm (BHDS) dikes together with existing data from the 1.89–1.87 Ga Mashonaland sill province (Söderlund et al, 2010; Hanson et al, 2011) and the 1.88– 1.87 Ga post-Waterberg sill province (Hanson et al, 2004)
Baddeleyite grains extracted from an 8–10-m-thick north-northeast–trending dike were divided into three fractions and dated by isotope dilution–thermal ionization mass spectrometry (ID-TIMS) at the Department of Geosciences, Swedish Museum of Natural History in Stockholm

Summary

Introduction

The Paleoproterozoic to Mesoproterozoic supercontinent (referred to as Nuna, Hudsonland, or Columbia) formed by assembly of Archean cratons starting at 1.9 Ga and was fully amalgamated as late as 1.65–1.58 Ga (Meert, 2012; Pisarevsky et al, 2014; Pourteau et al, 2018). The current 1.89–1.83 Ga paleomagnetic record of Kalahari can be enhanced by studying its magmatic provinces (Fig. 1). The combined BHDS, Mashonaland, and Post-Waterberg sill provinces, and Soutpansberg Basin magmatism (Klausen et al, 2010; Lubnina et al, 2010; Olsson et al, 2016) form an ∼50 m.y. record.

Results

Conclusion