AR-40-AR-39 AGES FOR DYKES FROM THE FALKLAND ISLANDS WITH IMPLICATIONS FOR THE BREAK-UP OF SOUTHERN GONDWANALAND

Ar-40-Ar-39 incremental-heating spectra analyses were made of five mic rogabbro dykes from the Falkland Islands, two of which yielded an acce ptable plateau, and a third a close maximum estimate. All three indica te an age of dyke intrusion of about 190 Ma, supporting a single, publ ished K-Ar date. This provides further support for the geological cont inuity of the Falkland Islands and the eastern Karoo Basin where dyke swarms of similar petrological affinities were intruded at about the s ame time. The age constrains the previously published palaeoreconstruc tion of the Falkland Islands, based on palaeomagnetic data, which plac es the Falklands immediately to the east of southern Africa, to be val id until at least the late Early Jurassic.