"BEFORE PANGEA" GEOHERITAGE CORRIDOR, QUEBEC CITY TO GULF OF MAINE

GSA formally recognizes the value of geoheritage sites to society. A potential geoheritage corridor between Quebec City and the coast of Maine roughly follows the route of Benedict Arnold's 1775 adventure to seize Canada. It parallels the trans-Newfoundland cross section that has strongly influenced Appalachian tectonic models, and coincides with Global Geoscience Transect 8 along which deformation is less severe than in southwestern New England. The corridor focuses on four regions (southern Quebec, Boundary Mountains, central Maine, and coastal Maine), each of which reveals clues to the Late Precambrian-Paleozoic opening of the Iapetus Ocean between Laurentia and Gondwana, and its closure on the Appalachian mega-suture that consolidated Pangea.

In Quebec, a clear record tells the story of continental rifting, development of a SE-facing continental margin, SE-dipping subduction terminated by collision with an arc, and subsequent reversal of subduction polarity. In Maine, the record is less clear, and significant questions pose both research opportunities and communication challenges. Paleozoic strata deposited peripheral to Gondwana became the locus of arc magmatism and upper plate extension, then later accreted to the Laurentian margin; thus, peri-Gondwanan terranes were transferred to Laurentia at the expense of Iapetus while younger back-arc basins and seafloor spread in their wake. Early arrivals were hit hard by late-arriving terranes with cooler, thicker lithosphere. In one model, strongly deformed rocks in northern Maine (Hurricane Mountain melange) delineate an intra-Iapetan arc-arc collision. The Central Maine Basin arguably lies between the two halves of an older arc (Ammonoosuc-Casco Bay). Perhaps most intriguing is the possibility, if subduction entered Iapetus from outside, that Cambrian volcanic rocks in Penobscot Bay formed along the same sinuous convergent plate boundary as the one responsible for Laurentia-arc collision in the Early Paleozoic. Finally, departure of terranes from Gondwana, supported by paleomagnetic but sparse geologic data, implies a Rheic Ocean outboard of Iapetus.

An in-progress field guide will attempt to strike a balance between what we know and don't, at a level both useful to researchers and appealing to the public.