Large Igneous Province Record Through Time and Implications for Secular Environmental Changes and Geological Time-Scale Boundaries

Turmoil before the boring billion: Paleomagnetism of the 1880–1860 Ma Uatumã event in the Amazonian craton

Eleven new baddeleyite U–Pb crystallisation ages and associated whole-rock geochemistry on NE–NNE-trending tholeiitic dykes cutting across the north-eastern corner of the Archaean Kaapvaal Craton, the overlying Transvaal basin and the Bushveld and Phalaborwa igneous complexes collectively define a 1875–1835 Ma Black Hills Dyke Swarm (BHDS). Dyke ages do not discriminate between dyke trends or geographic location, but subdivide the BHDS into an older set of four more primitive dykes (MgO = 9.4–6.8 wt.%) and a younger set of seven dykes with more differentiated compositions (MgO = 5.6–4.2 wt.%). Despite being emplaced over a c. 40 Myr period, major element compositions are remarkably consistent with a single inversely modelled bulk fractionating assemblage of 57.5% plagioclase, 29.5% augite and 13.0% olivine. This fractionating assemblage requires an additional assimilation of bulk continental crust (at a low r-value of 0.2) for reversed modelling of parental rare earth elements. Even though this cr...

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Baddeleyite U–Pb ages and gechemistry of the 1875–1835 Ma Black Hills Dyke Swarm across north-eastern South Africa: part of a trans-Kalahari Craton back-arc setting?

On the south-easternmost Kaapvaal Craton, a NE-trending plagioclase-megacrystic dolerite dyke swarm, herein named the White Mfolozi Dyke Swarm (WMDS), has been identified. New U–Pb baddeleyite ages presented here indicate that the WMDS was emplaced within less than 10 million years, with our three most robust results yielding a weighted mean age of 2662 ± 2 Ma. The WMDS is coeval with the youngest dykes of a 2.70–2.66 Ga radiating dyke swarm already identified further north on the eastern side of the Kaapvaal Craton. This dyke swarm radiates out from the eastern lobe of the ca. 2.05 Ga Bushveld Complex. A clustering of ages from the WMDS and the 2.70–2.66 Ga radiating dyke swarm identify potential magmatic peaks at 2701–2692 Ma, 2686–2683 Ma and 2665–2659 Ma. Geochemical signatures of the dykes do not correlate with these age groups, but are rather unique to specific areas. The northern part of the eastern Kaapvaal Craton hosts relatively differentiated 2.70–2.66 Ga dolerite dykes that could have ...

U–Pb baddeleyite geochronology and geochemistry of the White Mfolozi Dyke Swarm: unravelling the complexities of 2.70–2.66 Ga dyke swarms across the eastern Kaapvaal Craton, South Africa

The age and country rock provenance of the Molopo Farms Complex: implications for Transvaal Supergroup correlation in southern Africa

The volcanic Hartley Formation (part of the Olifantshoek Supergroup, which is dominated by red bed successions) in South Africa recorded depositional and tectonic conditions along the western Kaapvaal Craton during the late Palaeoproterozoic. It formed in association with red bed deposition elsewhere in the cratonic hinterland and along the craton’s northern margin. However, the exact correlation of the Olifantshoek Supergroup with these other red-bed successions is hindered by poor geochronological constraints. Herein, we refine the age and palaeopole of the Hartley Formation, and provide geochronological constraints for large-scale 1.93–1.91 Ga bimodal magmatism on the Kaapvaal Craton (herein named the Hartley large igneous province). We present new age constraints for the mafic and felsic phases of this event at 1923 ± 6 Ma and 1920 ± 4 Ma, respectively, which includes the first reported age dating of the Tsineng Dyke Swarm that has been linked to Hartley volcanism. A mean 1.93–1.91 Ga palaeoma...

New U–Pb geochronologic and palaeomagnetic constraints on the late Palaeoproterozoic Hartley magmatic event: evidence for a potential large igneous province in the Kaapvaal Craton during Kalahari assembly, South Africa

Farnaz Alebouyeh Semami

Papers

New U–Pb geochronologic and palaeomagnetic constraints on the late Palaeoproterozoic Hartley magmatic event: evidence for a potential large igneous province in the Kaapvaal Craton during Kalahari assembly, South Africa