DETRITAL ZIRCON GEOCHRONOLOGY IN NORTHERN APPALACHIAN AVALONIAN TERRANES: INSIGHTS INTO BASIN DEVELOPMENT AND TERRANE JUXTAPOSITIONS
Four samples from the overlying Cambrian Sgadan Lake Formation in MacCodrum Brook contain sparser populations of zircon ages in the range 600 – 650 Ma, but their largest populations of zircons have ages of 540 – 550 Ma, with smaller younger populations around 530 Ma and older at 580 Ma. The youngest population ca. 520 Ma. These young populations are similar to those in samples from the Bengal Road Formation elsewhere in southeastern Cape Breton Island in which the youngest ages are between 520 Ma and 530 Ma. These results show that Cambrian units have similar source areas and cannot be readily distinguished from each other by detrital zircon data alone.
Comparisons with detrital zircon signatures in Cambrian sedimentary units from Avalonia in Newfoundland, the Antigonish Highlands, and southern New Brunswick show wide variation in signatures, both in the range of Ediacaran-Cambrian ages and in the abundance of Mesoproterozoic-Archean ages. This absence of systematic variation further demonstrates that presence of older grains should not be used to interpret the position of Avalonia during the Cambrian or the timing of its rifting from Gondwana. If Ganderia and Avalonia were temporarily juxtaposed by ca. 550 Ma as proposed in recent tectonic models, then zircon derived from Ganderia may have contributed to the prominent zircon age peaks at ca. 550 Ma.