Precambrian evolution of the Avalon-terrane in the Northern Appalachians: a review ( USA).

Abstract

The Avalon terrane of the Northern Appalachians forms a distinctive tectonostratigraphic belt defined primarily by the presence of late Precambrian (circa 600 Ma) volcano-sedimentary and granitoid rocks overlain by Lower Paleozoic sequences containing Acado-Baltic fauna. Avalon terrane is exposed in eastern Newfoundland, Cape Breton Island and the northern Nova Scotian mainland, southern New Brunswick, coastal southeastern Maine, and southeastern New England. The Precambrian evolution of Avalon terrane includes two major tectonothermal events that involved both continental and oceanic basement. Onset of overlapping, Atlantic-realm platform conditions in the Cambro-Ordovician was accompanied by minor, within-plate rift volcanism and is in places succeeded by late Ordovician-early Devonian bimodal volcanic rocks, shallow marine sediments and rare peralkaline plutons. Deposition of widespread Devono-Carboniferous, molasse-like sequences associated with bimodal tholeiitic to alkaline volcanics form an overlap sequence with the remainder of the Appalachian orogen, although the present position of the Avalon terrance with respect to the orogen is locally controlled by major Alleghanian faulting. Undeformed Triassic redbeds and mafic volcanic rocks herald initial rifting of the present Atlantic Ocean.-from Author