RAPID ERUPTION OF SKYE LAVAS INFERRED FROM PRECISE U-PB AND AR-AR DATING OF THE RUM AND CUILLIN PLUTONIC COMPLEXES

The interpretation of rocks of the British Tertiary Volcanic Province has played an important role in the historical development of many con cepts in igneous petrology. Exposures of lavas, sub-volcanic rocks and plutonic complexes have allowed a detailed understanding of the field relationships between such units in the context of flood-basalt magma tism(1-3). Nevertheless, age control has been a source of much controv ersy and a limiting factor in comparing these relationships to recent developments in the theoretical modelling of magmatism within continen ts(4). Here we report precise Pb-206/U-238 zircon ages of 60.53 +/- 0. 08 Myr (2 sigma) for the Rum basic/ultrabasic pluton and 58.91 +/- 0.0 7 Myr for the Cuillin gabbros, Skye, which tightly constrain eruption of the greater than 1.5-km-thick Skye lavas to a maximum duration of 1 .6 +/- 0.2 Myr. These dates yield magma production rates for the Skye lavas of about 2.2 x 10(-3) km(3) yr(-1) comparable with rates inferre d for individual magmatic centres produced by melting related to mantl e plumes below ocean basins. In addition, the approximately 30 km of l ithospheric thinning suggested by magma chemistry is required to have occurred in less than 2 Myr.