The paleomagnetic ambient temperature has been determined from samples at various distances from a Grenville diabase dike cutting late Proterozoic tonalitic gneiss near Mattawa in the Grenville Province, Canada. Using the 40Ar/39Ar technique, the intrusion age of the dike is estimated to be 570¿3 Ma from a 0.5-mm-diameter chilled margin chip. The paleo-ambient temperature of the country rock at the time of dike intrusion, 184¿¿40 ¿C, was calculated from Jaeger's <1964> one-dimensional heat conduction model. The burial depth of the presently exposed rocks is estimated to be 6.5¿1.7 km, assuming a surface temperature of 15 ¿C and a geothermal gradient of 26 ¿C/km. This depth at 570 Ma is discordant with the presence of Ordovician shallow-water (≤100 m) limestones about 200 km distant, suggesting that differential uplift may have occurred between the two areas. ¿ American Geophysical Union 1993