40 Ar- 39 Ar ages for dykes from the Falkland Islands with implications for the break-up of southern Gondwanaland

Abstract

40 Ar- 39 incremental-heating spectra analyses were made of five microgabbro dykes from the Falkland Islands, two of which yielded an acceptable plateau, and a third a close maximum estimate. All three indicate an age of dyke intrusion of about 190 Ma, supporting a single, published K-Ar date. This provides further support for the geological continuity of the Falkland Islands and the eastern Karoo Basin where dyke swarms of similar petrological affinities were intruded at about the same time. The age constrains the previously published palaeoreconstruction of the Falkland Islands, based on palaeomagnetic data, which places the Falklands immediately to the east of southern Africa, to be valid until at least the late Early Jurassic.