AN OVERVIEW OF INTERPRETED NORTHWEST AFRICAN CRUSTAL FRAGMENTS IN THE NORTHERN APPALACHIAN OROGEN

Ganderia, Avalonia and Meguma are terrane assemblages that form the eastern part of the northern Appalachian orogen. They can be distinguished based on combinations of their cover sequences, pre-cover rock types, magmatic, metamorphic and deformational histories, geochemistry, and U-Pb detrital zircon data. Ganderia is generally interpreted as having Amazonian affinity, Avalonia as Amazonian and/or Baltican, and Meguma as NW African, with possible Amazonian influence. Older Proterozoic crustal fragments scattered among these terrane assemblages and in offshore areas have provenance inconsistent with other components of the terrane assemblages. Sedimentary rocks with detrital zircon signatures characteristic of the Paleoproterozoic Taghdout Group in the Anti-Atlas of Morocco have been discovered in (1) the COST No. G-1 well of the Georges Bank in offshore Massachusetts, (2) the Hutchins Island quartzite of the otherwise Ganderian Penobscot Bay inlier of coastal Maine, and (3) the Thoroughfare Formation associated with inferred Ganderian rocks of Grand Manan Island in southern New Brunswick. The oldest dated arc-related igneous rocks associated with Avalonia are ~800-730 Ma, in the Mount Ephraim block in the Cobequids Highlands of Nova Scotia. The fault-bounded Burin Group of eastern Newfoundland contains ~760 Ma mafic rocks associated with marble. Rocks interpreted as Avalonia in New Brunswick and Rhode Island include ~770-730 Ma detrital zircon. The ~770-730 Ma rocks and zircon ages may be related to the Pan-African I orogeny recorded in the Anti-Atlas region of Morocco. Other orogenies of that age are not known in West Africa, and arc-related igneous rocks of that age are rare in Baltica and Amazonia. If some of these rocks occur in both Ganderia and Avalonia, they may have mixed Amazonian, NW African and/or Baltican sources. Rocks of the COST No. G-1 well have been interpreted as a fragment that was transferred from NW Africa to North America during the formation and breakup of Pangea, but may alternatively be older components of the Meguma terrane. The distribution of these possible NW African crustal fragments in Ganderia, Avalonia and Meguma is enigmatic, and the timing and mechanisms of their emplacements remain a topic of investigation.