Fast tectonometamorphism and exhumation in the type area of the Barrovian and Buchan zones

The beginning of the Grampian episode of tectonometamorphism in Scotland is dated by collision and obduction of the Ballantrae Ophiolite Complex at 47 8 +/- 8 Ma. For the first time we have used zircon and garnet to radiometri cally date the peak of the Caledonian Buchan and Barrovian tectonometamorph ism in their type areas as contemporaneous at 467 +/- 2.5 Ma. Detrital garn et from the neighboring Southern Uplands flysch terrane has the same radiom etric age and occurs in 465 +/- 2.5 Ma molasse in the Midland Valley. We sh ow that the entire Grampian episode lasted 15 +/- 2.5 m.y. and that it took fewer than 7.6 m.y. to expose high-grade rocks following the peak of metam orphism. Those who study Precambrian orogeny should note the brevity of thi s Scottish tectonometamorphic episode and the speed of exhumation.