U-Pb Age Constraints on the Stratigraphy and Tectonic History of the Avalon Terrane, New Brunswick, Canada

Abstract

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 in 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; it correlates with most volcanism and plutonism in the type Avalon Terrane of Newfoundland. The ca. 550 Ma activity formed bimodal volcanic rocks and high-level plutons, probably in an extensional setting, U-Pb ages of xenocrystic zircons from Avalonian igneous rocks indicate both Archean and Proterozoic components at depth in Avalonian basement, an observation consistent with Pb isotopic signatures which suggest an old, radiogenic crustal source (the African craton?) for the magmatic products.