The origin of the Coastal Volcanic Belt, easternmost Maine: A petrological and geochemical study

Volcanic rocks in the Machias-Eastport area represent the thickest and best dated Silurian-Early Devonian volcanic succession in the Coastal Volcanic Belt. These rocks belong to an important magmatic episode associated with the initiation of the Acadian Orogeny. Based on a trace element classification, Silurian rocks form a continuous subalkalic sequence between basalt and rhyolite. Eastport Fm. rocks have a more bimodal character. Silurian mafic rocks contrast in composition with respect to Devonian samples having, in general, higher incompatible element and LREE contents and lower Zr, Y, Eu, Ta and Nb contents.; Tectonic discrimination diagrams indicate a volcanic-arc tectonic setting for Silurian rocks, while the Eastport Fm. mafic samples have a transitional nature. Eastport Fm. rhyolitic samples and Late Devonian basalts indicate a clear within plate setting.