How should terrane assemblages be defined in the northern Appalachian orogen?
Yvette D. Kuiper, Colorado School of Mines
Sandra M. Barr, Acadia University
Abstract
The Gondwana-derived terrane assemblages of Ganderia, Avalonia, and Meguma form the eastern part of the northern Appalachian orogen. They were defined as 'zones' in the 1970s based primarily on their cover sequences. Currently, distinguishing criteria include pre-cover rock types, magmatic, metamorphic and deformational histories, geochemistry, and U-Pb detrital zircon data. Ganderia is generally interpreted as having an Amazonian affinity, Avalonia as Amazonian and/or Baltican, and Meguma as NW African, with possible Amazonian influence. Proterozoic basement fragments, scattered throughout these terrane assemblages and in offshore areas, may have NW African affinity, and provenance inconsistent with other components of the terrane assemblages.
Sedimentary rocks with a detrital zircon signature characteristic for 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. 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 to have occurred in West Africa, and arc-related igneous rocks of that age are rare in Baltica and Amazonia. If some of the NW African rocks are interpreted as parts of both Ganderia and Avalonia, it implies that they somehow 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 could alternatively be interpreted as basement of Meguma.
The existence and unknown histories of these interpreted NW African basement fragments lead to the question of how Ganderia, Avalonia and Meguma should be (re-)defined. Do Ganderia and Avalonia include NW African basement and sources, or should the NW African fragments be considered separately? Does Meguma have NW African basement, and should it be included in its definition? How should these terrane assemblages be defined?
Session
Session 6: Advances in Geology, Geochronology, Geophysics