Abstract

Detailed 40Ar/39Ar laser step-heating analyses of mineral separates from five volcanic units in Namibia and Angola and five intrusions in Namibia yield important geochronological data for the Etendeka igneous province. Ten plateau dates on plagioclase, hornblende, and biotite between 131.7 ± 0.7 and 132.3 ± 0.7 Ma were obtained, and a late syenite from the Messum intrusive complex yielded a slightly younger hornblende plateau date of 129.3 ± 0.7 Ma. Magnetostratigraphy of the volcanic rocks in three sections up to 700 m thick, laterally spanning more than 100 km, suggests that the flows record only two geomagnetic polarity reversals. Precise temporal coincidence with the Paraná flood volcanic province in South America indicates that Etendeka volcanism does not represent a significantly younger phase of magmatism that migrated from northwest to southeast over 10 m.y., as has recently been proposed. The duration of intrusive activity was at least 2–3 m.y. longer than recorded by volcanism, and its total duration awaits further constraints.

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