Laser Ar-40/Ar-39 thermochronology of Archean rocks in Yellowknife Domain,southwestern Slave Province: insights into the cooling history of an Archean granite-greenstone terrane

Laser Ar-40/Ar-39 ages for hornblende, muscovite, and biotite from Archean plutonic rocks of Yellowknife Domain, southwestern Slave Province, compleme nt U-Pb ages from minerals with higher closure temperatures (zircon, monazi te, titanite). Together, the data indicate that the plutonic suites of diff erent ages (Defeat, Prosperous, Morose) coring three major thermal culminat ions in the domain have distinct Archean cooling histories until below appr oximately 250C (biotite closure). The cooling trajectories for successive s uites appear to document a decrease in cooling rate over the course of orog eny,possibly reflecting the build-up of heat within the orogen, coupled wit h a transition to lower rates of exhumation and (or) erosion. Greater struc tural relief over the Sleepy Dragon basement culmination may be responsible for slower cooling of the Morose Granite situated in its core. At or below the closure temperature of biotite the cooling curves converge with one an other, documenting a transition from "localized" to "regional" cooling. The fact that cooling waslocality specific until at least the biotite closure temperature suggests that, just as intrusion and related peak metamorphism were diachronous across the region, so was cooling to approximately 250C. U niform regional isotherms thus were not established until > 200 Ma after th e youngest Archean plutonism. The variable disturbance of biotite Ar spectr a, but generally not muscovite or hornblende, indicates that the Paleoprote rozoic thermal disturbance of Archean rocks in Yellowknife Domain did not e xceed 200-300C.