Provenance of late neoproterozoic and cambrian sediments in avalonia: Constraints from detrital zircon ages and Sm-Nd isotopic compositions in southern new brunswick, Canada

Neoproterozoic though Cambrian clastic sedimentary and/or metasedimentary rocks occur in the Hammondvale Metamorphic Suite (HMS; ca. 680-620 Ma) and the Broad River (ca. 620 Ma), Coldbrook (ca. 560-550 Ma), and Saint John (ca. 540-490 Ma) groups in the Avalonian Caledonia terrane of southern New Brunswick. Evolved Nd isotopic values show that the HMS and the metasedimentary rocks of the Broad River Group were in part derived from older cratonic material. The presence of Mesoproterozoic and the absence of Paleoproterozoic zircon in the HMS suggest that the source of this older cratonic material was the Amazonian craton. In contrast, sedimentary rocks of the Coldbrook Group show generally positive ε_Nd values and likely were derived from local Avalonian sources. More evolved isotopic signatures in the lower Saint John Group indicate a return to older cratonic source areas. Detrital zircon from the lowest part of the Saint John Group has Mesoproterozoic ages like those of the HMS but also has 2000- and 800-Ma ages. The Mesoproterozoic grains are likely from Amazonia, but the additional 2000-800-Ma grains suggest a new source area, likely the West African craton. The increasingly evolved Nd isotopic values, the absence of Mesoproterozoic zircon, and the addition of 2000- and 800-Ma zircon in Early Cambrian sediments suggest that by the Early Cambrian Avalonia was deriving detritus exclusively from the West African craton. This transition in provenance apparently started after transtensional rifting recorded by volcanic and sedimentary rocks in the Coldbrook Group and continued through the Cambrian as Avalonia moved along strike-slip faults from its location along the Amazonian margin closer to the West African margin before starting its journey to Laurentia.