U-PB GEOCHRONOLOGY OF LATE PALEOZOIC PLUTONS, COBEQUID HIGHLANDS, NOVA-SCOTIA, CANADA - EVIDENCE FOR LATE DEVONIAN EMPLACEMENT ADJACENT TO THE MEGUMA-AVALON TERRANE BOUNDARY IN THE CANADIAN APPALACHIANS

Cobequid Highlands in the Canadian Appalachian orogen lie within Avalo nia adjacent to the Meguma Terrane. U-Pb (zircon) data show that the a ge range of voluminous bimodal plutonism in the highlands is from 358 to 363 Ma (late Devonian). This age range is much narrower than that p reviously suggested by Rb/Sr geochronology and confirms that the Cobeq uid Highlands preserve the youngest large-scale plutonic event in the Canadian Appalachians. Late Palaeozoic tectonic history of the Appalac hian orogen is profoundly influenced by predominantly dextral motion o n the Avalon-Meguma terrane boundary. This age of plutonism is coeval with previously published Ar-40/Ar-39 (muscovite) plateau ages derived from shear zones in the Meguma terrane adjacent to the terrane bounda ry, which is defined by the Minas fault zone. The NNE trending structu ral grain of the Appalachian orogen is disturbed in this area by the E -W Minas fault zone and pluton emplacement may have been associated wi th motion along this terrane boundary.