AR-40 AR-39 AMPHIBOLE AGES FROM THE KINGSTON COMPLEX, NEW-BRUNSWICK -EVIDENCE FOR SILURIAN-DEVONIAN TECTONOTHERMAL ACTIVITY AND IMPLICATIONS FOR THE ACCRETION OF THE AVALON COMPOSITE TERRANE/

The Kingston complex of southern New Brunswick, Canada, is a regional, NE-trending belt of mafic and felsic dikes bordered by dextral ductil e shear zones. The complex separates two contrasting late Precambrian- early Paleozoic tectonostratigraphic assemblages near the NW margin of the Avalon composite terrane. Rhyolitic dikes within the complex reco rd an early Silurian crystallization age. Dike orientations suggest th at emplacement of the complex accompanied sinistral movement interpret ed to reflect accretion of the Avalon composite terrane to cratonic No rth America. Mafic dikes within the complex display greenschist to epi dote-amphibolite facies metamorphic assemblages that developed during dextral transpression. Amphibole concentrates from seven metamorphosed mafic dikes record Late Silurian to Early Devonian (ca. 416-390 Ma) A r-36/Ar-40 vs. Ar-39/Ar-40 isotope correlation ages, interpreted to da te closely the dextral transpressive deformation. Together with other recent age data, the Ar-40/Ar-39 results suggest that regionally exten sive Silurian-Early Devonian tectonothermal events are recorded along the inboard margin of the Avalon composite terrane. The data also prov ide well-defined constraints for the transition from sinistral to dext ral movement recorded along many major northern Applachian faults. In Maritime Canada, this transition is likely to have been associated wit h a kinematic reversal that occurred between initial Silurian accretio n of the Avalon composite terrane and Silurian-Devonian docking of the outboard Meguma terrane.