U-PB AGE CONSTRAINTS ON THE STRATIGRAPHY AND TECTONIC HISTORY OF THE AVALON TERRANE, NEW BRUNSWICK, CANADA

Six new U-Pb ages for Avalonian plutonic and volcanic rocks from the eastern Caledonia Highlands, southern New Brunswick, indicate that magmatic activity occurred between 625-600 Ma ago with another, probably separate, major episode at ca. 550 Ma. This gap is igneous activity is consistent with differences in the metamorphic and deformational character of rocks from the two episodes. The 625-600 Ma activity was calc-alkalic and probably occurred in an Andean-type magmatic arc. The ca. 550 Ma activity formed bimodal volcanic rocks and high-level plutons, probably in an extensional setting. -from Authors