An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt: Naude's Nek section (South Africa)

Moulin, Maud; Fluteau, Frédéric; Courtillot, Vincent; Marsh, Julian; Delpech, Guillaume; Quidelleur, Xavier; Gérard, Martine and Jay, Anne E. (2011). An attempt to constrain the age, duration, and eruptive history of the Karoo flood basalt: Naude's Nek section (South Africa). Journal of Geophysical Research: Planets, 116(B7), article no. B07403.

DOI: https://doi.org/10.1029/2011JB008210

Abstract

We have carried out paleomagnetic sampling of a ∼750 m sequence of the Karoo large igneous province (Naude's Nek Pass, South Africa). K-Ar dating (Cassignol-Gillot) has been performed on four samples from the 650 m upper unit (mean age 179.2 ± 1.8 Ma) and a sample from the lower unit (184.8 ± 2.6 Ma). A succession of two phases of volcanism is suggested. The lower 25 flows (115 m thick) have recorded a reversed polarity; the next 23 flows (135 m thick) are transitional and contribute a detailed record of the “Van Zijl” (1962) Jurassic reversal. The upper 38 flows (500 m thick) have normal polarity. Directional groups (DGs) of lava flows with quasi-identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events. Altogether, 19 DGs and 10 sheet lobes yield a sequence of 29 distinct directions. This could correspond to a total eruptive activity shorter than 3000 years, less than one per mil of the total duration over which the section was emplaced. We obtain a new paleomagnetic pole for South Africa at ∼180 Ma (λ = 75.2°N, ϕ = 276.4°E, A₉₅ = 5.8°, N = 19), which is consistent with earlier reports.

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