SUPERVOLCANOES OF COASTAL MAINE

The Coastal Maine volcanic field is a well-preserved Silurian volcanic field that hosts generally undeformed volcanic rocks with spectacular volcanic textures. The Coastal Maine volcanic field consists of at least four volcanic complexes spanning approximately 160 km of the Maine coastline. Each complex hosts a volcanic sequence 1-4 km thick, including thick ash flow tuffs, consistent with the >1000 km³ eruptive volumes of supervolcanoes. The bimodal plutonic/volcanic centers of coastal Maine make up a province comparable in both lifespan and size of individual eruptive centers to the Altiplano Puna complex (deSilva et al., 2008), the Southern Rocky Mountain volcanic field (Lipman, 2007), and the Mogollon-Datil volcanic province (Elston, 1984). They represent pulsed eruptions of silicic melt derived largely by crustal anatexis. The coastal Maine volcanic complexes are in contact with their parent plutons, leaving little doubt about their genetic relationships. Rocks from each complex have been dated from 419 to 424 +/- 2 Ma. The age of the complexes and the uplift and erosional history of the coast of Maine have provided a rare situation in which entire cross-sections of the volcanic-plutonic complex, from ash flow tuffs to the bottom of magma chambers, are visible, providing excellent sites to study the volcano/pluton interface. Each supervolcano succession is rooted in a mafic and silicic layered pluton, supporting models of initiation of eruptions by influx of mafic magma into the parent chamber. Ignimbrite flare-ups and the generation of volcanic fields hosting rhyolitic supereruptions are commonly associated with thick silicic crust and/or high mantle heat flux, consistent with genesis in a setting of continental crustal extension. The coastal Maine volcanic complexes are likely to have erupted under these conditions, in a back-arc setting on the Gander terrane, prior to its docking with North America. The coastal Maine volcanic events are roughly correlative with the ~420 Ma Lau mass extinction, raising the possibility that volcanic aerosols associated with these eruptions may have contributed to the extinction event.