Potassium-Argon mineral dates on intrusive rocks from the Foveaux Strait area

Abstract

Potassium-argon dates on biotite and hornblende separated from six intrusive rocks from the north shore of Foveaux Strait (between Pahia Peninsula and Bluff) and Ruapuke Island range from 253 m.y, (late Permian) to 133 m.y, (early Cretaceous). The younger dates, however, are discarded because of wide discordance between the biotite and hornblende determinations, and petrographic evidence of alteration. The accepted range of ages is from 250 m.y. to 217 m.y., although the younger of these, corresponding to about middle Triassic, are regarded with caution because of minor discordance between the biotite and hornblende dates in the two rocks concerned. Nevertheless, the possibility that intrusion of some of the rocks extended into the Triassic is recorded and briefly discussed.