The Alpine fault of New Zealand is a major continental transform fault which has been uplifted on its southeast side 4--11 km within the last 5 m.y. This uplift has exposed the Alpine schists, which have been metamorphosed from the adjacent torlesse graywackes. The Alpine schists increase in metamorphic grade from prehnite-pumpellyite facies 9--12 km from the fault through the chlorite and biotite zones of the greenschist facies to the garnet-oligoclase zone of amphibolite facies within 4 km of the fault. These metamorphic zone boundaries are subparallel to the fault for 350 km along the strike. The K-Ar and Rb-Sr ages of the schists increase with distance from the fault: from 4 m.y. within 3 km of the fault to approximately 120 m.y. 20 km from the fault. Field relations show that the source of heat that produced the argon depletion aureole was the fault itself. Adopting a friction model for the fault and applying the known geological history of motion of the Alpine fault, we show that the metamorphism resulted from frictional heating during the 360-km right lateral slip on the Alpine fault during the Mesozoic (Rangitata) period of fault motion (140--80 m.y. ago). Fault motion began again in the Plio-Pleistocene Kaikoura orogeny, with 120 km of further right lateral slip and 4--11 km of uplift. Frictional heating during this episode produced the argon depletion. Quantative models for both the metamorphism and the argon depletion require that the frictional shear stress acting on the fault during both episodes of fault motion was at least 1--1.5 kbars. If, alternatively, it is assumed that all fault motion took place in the last 30 m.y., this does not change our conclusion with respect to the stress required for the argon depletion.