I reproduce here “in extenso” a wonderful article from Claude Granpey published on its website: http://claudegrandpeyvolcansetglaciers.com
Up to now, the common theory about the origins of Yellowstone was that the so-called supervolcano was born from a hotspot, in other words a mantle plume emerging from our planet’s core. But a new simulation shows that the conventional hypothesis was wrong. The plume could not have reached the surface because it was blocked by a slab from an ancient tectonic plate.
The simulation results of the model, which is the first to replicate the complex interaction between a mantle plume and a sinking slab, were detailed last month in Geophysical Research Letters.
Geologists at the University of Illinois built the model to replicate both the plate tectonic history of the surface and the geophysical image of Earth’s interior. Not only did the researchers create a three-dimensional view of Yellowstone’s interior, they did so over the past 40 million years in an attempt to re-create the eruptions that have dotted the U.S. from Oregon to Wyoming. However, they found it impossible to re-create most of the recent eruptions because of the presence of a slab which was driven deep into Earth’s mantle about 100 million years ago when the Pacific and North American plates began converging.
According to the scientists, the mantle flowed around the sinking slab causing pressure to build toward the front. Their model shows that 15 million years ago the pressure difference became too much to bear and the slab began to tear. The plume below pulsed through the slab, leading to massive outpourings of magma which appear consistent with the Steens–Columbia River flood basalts.
Despite the gaping hole in the center of the sunken slab, the plume did not continue to rise through it because the mantle is highly viscous. So as the slab continued to sink, it pulled the surrounding mantle down with it, ultimately sealing the hole and blocking the plume from reaching the surface for the next 15 million years.
The favoured hypothesis cannot explain the string of volcanic eruptions since those first flood basalts, including the formation of Yellowstone’s caldera, which happened only 2.1 million years ago. As a consequence, a new explanation for Yellowstone’s formation needs to be found, as well as an additional heat source for Yellowstone! One researcher thinks this could come from the Juan de Fuca Ridge in the Pacific Ocean. Although that’s almost 1,600 kilometers away from Yellowstone’s hotspot today, the ridge can easily affect the middle of the North American Plate. Because it lies just slightly west of the Cascadia subduction zone, the young seafloor is easily shoveled east beneath the North American Plate. So it is likely that some event, millions of years ago, spurred a lot of heat within the Juan de Fuca Plate, which was then shoveled underneath the North American Plate and swept along with that string of volcanic eruptions until it eventually helped form Yellowstone’s gaping caldera in the Rocky Mountains.
Whatever the origin of Yellowstone’s volcanism, the model makes it clear that slabs are much more important than previously thought.
March 26, 2016. Yellowstone , United- States :
Sources: C Granpey , Scientific American: http://www.scientificamerican.com/
Photos : Geo , maxisciences.com .