Two pegmatites and mylonitic rocks from the Grampian Shear Zone yield U–Pb monazite ages of 806 ± 3 Ma, 808–9+11Ma, and 804–12+13, respectively. These confirm that shearing and pegmatite crystallization was essentially synchronous. Lower intercepts of c. 440 Ma indicate disturbance during Ordovician reworking. These new data question the concept of a single latest Proterozoic–early Palaeozoic orogeny in the Grampian terrane and the significance of the Great Glen Fault.

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