Newly identified segments of the Pacific¯Australia plate boundary along the North Fiji transform zone

The duration of activity that produced the Isle of Mull Tertiary igneous centre has been constrained to 2.52±0.36 million years (1sigma) using new high-resolution 40Ar/39Ar radiometric dating techniques. These new 40Ar/39Ar ages for Mull and also one from Skye, presented here, confine the duration of igneous activity to within one magnetic chron (3 million years within Chron C26r). However, the Mull and Skye Tertiary centres record a sequence of reversed and normal polarity intervals. Recalibration of tie points used to determine the magnetic polarity time scale cannot account for all of the observed changes in polarity from Mull and Skye. We propose that the new ages for the Mull and Skye centres indicate that these parts of the British Tertiary volcanic province developed fast enough to record shortperiod polarity intervals, which correspond to tiny wiggles in the marine magnetic anomaly record.