Abstract

Ultramafic and mafic rocks of the Union complex, Maine, U.S.A. are interpreted as remnants of Iapetus oceanic crust based upon geological, geochemical, and structural considerations. These rocks were emplaced along a cryptic Acadian suture during North American–Avalonian collision. U–Pb analyses of zircons from the quartz diorite portion of the Middle Road unit yield a primary (crystallization) age of 410 ± 7 Ma marking a maximum age for collision and disappearance of Iapetus ocean floor. Other studies have shown a minimum time of peak Acadian deformation at 385–400 Ma, strongly suggesting that the Acadian event occurred in a period of less than 20 Ma in this portion of the northern Appalachians.

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