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

Maud Moulin (1) , Frédéric Fluteau (1) , Vincent Courtillot (1) , Julian Marsh (2) , Guillaume Delpech (3) , Xavier Quidelleur (3) , Martine Gérard (4) , Anne E. Jay (5)

1 IPGP - Institut de Physique du Globe de Paris
2 Department of Geology
3 GEOPS - Géosciences Paris Sud
4 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
5 Department of Earth Science and Technology [Imperial College London]

We have carried out paleomagnetic sampling of a similar to 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 similar to 180 Ma (lambda = 75.2 degrees N, phi = 276.4 degrees E, A(95) = 5.8 degrees, N = 19), which is consistent with earlier reports.

Domaines: Volcanologie

Maud Moulin, Frédéric Fluteau, Vincent Courtillot, Julian Marsh, Guillaume Delpech, et al.. 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 : Solid Earth, 2011, 116 (B7), pp.B07403. ⟨10.1029/2011JB008210⟩. ⟨hal-00585560⟩