Recurring volcanism in New England focused by a region of thin lithosphere

The Appalachian Orogen experienced extensive volcanism through the early Paleozoic, as well as ∼200 Ma. Unlike most of the northern Appalachians, the New England region saw repeated episodes of volcanic activity between 293 and 120 Ma. An anomalous region in the upper mantle beneath New England underlies these distinct volcanic rocks. Low values and lack of anisotropy in seismic velocity imply elevated temperature and suggest sub-vertical flow in the upper mantle. Our new constraints on the depth to the lithosphere–asthenosphere boundary (LAB) show that thinned lithosphere underlies the region of localized repeated anorogenic volcanism in New England. The upper mantle directly beneath the shallow LAB is not unusually warm, while surrounding regions have significantly lower temperatures. Changes in the type of igneous rocks erupted between 150 and 120 Ma, from kimberlites in Ontario to felsic plutons in New England, correlate with variations in lithosphere thickness and imply that these variations existed by 125 Ma. It is also plausible that thin lithosphere is inherited from the time of Appalachian collisions at ∼450 Ma. Our overall conclusion is that the region of presently thin lithosphere beneath New England is unusual and has focused volcanic activity within it since ∼300 Ma.