40AR/39AR MINERAL AGES FROM THE SOUTHERN CAPE-BRETON HIGHLANDS AND CREIGNISH HILLS, CAPE-BRETON ISLAND, CANADA - EVIDENCE FOR A POLYPHASE TECTONOTHERMAL EVOLUTION

40Ar/39Ar ages for hornblende and muscovite from plutons and metamorphic country rocks in the southern Cape Breton Highlands and Creignish Hills, together with previously published U-Pb, Rb-Sr and 40Ar/39Ar ages, document a complex tectonothermal history that included (1) episodes of plutonic activity at ca. 600, 565-560, 555, 500-490-(?470), and 410-395 Ma (all of which cooled through 500-400-degrees-C within ca. 20 m.y.); and (2) deformation in the late Precambrian (> 550 Ma) and the Late Silurian-Middle Devonian (415-380 Ma). The latter was associated with development of a positive flower-like structure during maintenance of medium-pressure, greenschist-amphibolite facies, regional metamorphic conditions that may be traced northward along the length of the Cape Breton Highlands. it may be correlated with the Kingston Complex and associated mylonite zone exposed in the Avalon Composite Terrane of southern New Brunswick. Northward it merges with a major high-grade, polydeformed belt within the Gander Zone of Newfoundland. This regionally significant tectonothermal event probably developed as a result of accretion of the Avalon Composite Terrane to Laurentia and is inferred to have occurred synchronously with collision of eastern North America and Gondwana (South America).