The youngest volcanoes on the East Coast share an unusual geological link with islands on the opposite side of the Atlantic Ocean, a new study reports.
The new findings could explain the enigmatic origin of the 48-million-year-old volcanoes, which punched through Virginia's fractured crust long after other fiery eruptions ceased along the East Coast. The surprisingly young volcanoes also offer clues into the tectonic forces molding eastern North America's mountains and hidden underbelly. The results appeared online April 10 in the journal Geology.
"These young volcanoes are in an area where no one would expect to see volcanic activity," said lead study author Sarah Mazza, a geologist at Virginia Tech. "These rocks are our only physical window into processes that helped shape Virginia and even the whole southeastern Appalachia as well."
The time span between when the Virginia volcanoes and the last known volcanic activity on the East Coast is about 150 million years. The older eruptions were triggered by the breakup of Pangaea, the supercontinent that included North America, Africa and South America. The stretching of Earth's crust as the supercontinent split allowed huge volumes of magma to escape from the mantle. Now, however, the East Coast is a passive margin, meaning there are no rifting or colliding tectonic plates to birth volcanoes or big earthquakes, as occurs along the West Coast. (In Images: How North America Grew as a Continent)
This long break between tectonic activity and the emergence of Virginia volcanoes has baffled researchers. So instead, many geologists said a hotspot could explain the origin of the volcanoes. Hotspots are plumes of magma that rise upward from the mantle. These long-lived mantle plumes are thought to fuel the volcanic chains in Hawaii and Yellowstone National Park. A proposed hotspot trail runs from Missouri to Maine and could have cooked Virginia about 60 million years ago.
But the results of the new study tell a more complex story — one that doesn't match with a hotspot origin, Mazza said.