April 16, 2013
Deformed Mantle Plume Caused Yellowstone Volcanism
April Flowers for redOrbit.com - Your Universe Online
The geologic formation of the supervolcano encompassing the Yellowstone National Park region has been the subject of much debate. A new study, led by the University of Rhode Island's Professor Christopher Kincaid, provides new evidence that may put an end to the debate by demonstrating both sides may be right.The international team of scientists used a state-of-the-art plate tectonic laboratory to show the volcanism in the Yellowstone region was caused by the defunct pieces of a former mantle plume that were severely deformed. Circulation currents, driven by the movement of tectonic plates at the Cascades subduction zone, also affected the plume.
Dense oceanic tectonic plates dive beneath buoyant continental plates in subduction zones. Mantle plumes are buoyant upwellings of hot magma beneath the Earth's surface. The debate over the origins of the Yellowstone caldera has centered on the role of the mantle plumes, with both sides arguing a different interpretation.
The simple view of mantle plumes, according to Kincaid, is they have a head and a tail. The head rises to the surface, producing huge magma structures. The tail interacts with the drifting surface plates, creating a chain of smaller volcanoes of progressively younger age. The Yellowstone formation, however, doesn't fit this mold. Yellowstone has an eastward trail of smaller volcanoes called the Snake River Plain. This plain has a mirror-image volcanic chain that extends to the west, the High Lava Plain. Detractors to the mantle plume theory say the two trails of volcanoes and the curious north-south offset prove the plume model simply cannot work for this region. Therefore, according to them, the plates-only model must be at work.
Kincaid's team, along with colleagues at the Australian National University, built a laboratory model of the Earth's interior to test these competing hypotheses. They used corn syrup to simulate the fluid-like motion of the mantle, as the syrup has properties that allow researchers to examine complex time changing, three-dimensional motions caused by the collisions of tectonic plates at subduction zones and their effect on unsuspecting buoyant plumes.
The researchers used the model to simulate a mantle plume in the Yellowstone region, finding that because of the subduction zone, it reproduced the characteristically odd patterns in volcanism that are recorded in the rocks of the Pacific Northwest.
"Our model shows that a simple view of mantle plumes is not appropriate when they rise near subduction zones, and that these features get ripped apart in a way that seems to match the patterns in magma output in the northwestern US over the past 20 million years," said Kincaid, a professor of geological oceanography at the URI Graduate School of Oceanography. "The sinking plate produces a flow field that dominates the interaction with the plume, making the plume passive in many ways and trapping much of the magma producing energy well below the surface. What you see at the surface doesn't look like what you'd expect from the simple models."
Kincaid intends to continue his research by conducting similar analyses of the geologic formations of the Tonga subduction zone and the Samoan Islands of the South Pacific. This is another area of debate over the role of mantle plumes.
"A goal of geological oceanography is to understand the relationship between Earth's convecting interior and our oceans over the entire spectrum of geologic time. This feeds directly into the very pressing need for understanding where Earth's ocean-climate system is headed, which clearly hinges on our understanding of how it has worked in past."
The findings of this study were published in a recent issue of Nature Geoscience.