Volcanic Rocks Came From Deep Inside Earth

If you’re on a volcanic island — such as one of the Hawaiian Islands — you may find a particular type of rock, known as an ocean island basalt, or OIB. These rocks actually originated deep within the Earth, but volcanic eruptions brought them to the surface.

Although the rocks may look the same — and all of them originated from the same layer in the planet’s interior — they’re not all the same chemically, with differences in trace elements and isotopic composition. How these dissimilar rocks could come from the same place has long been a puzzle to scientists.

Now, however, a group of present and former University of Arizona researchers have figured out why. They’ve created a model of dynamics in the Earth’s mantle — the hot, semi-molten layer below the crust. It indicates that plumes of hot rock originate in the lower mantle and then physically interact with chemically distinct piles of material above them before they reach the surface. That, in turn, produces the variability in the chemistry of rocks that’s seen in Hawaii.

Their findings are described in a recent article in the journal Nature Communications.

“This model provides a platform for understanding links between the physics and chemistry that formed our modern world as well as habitable planets elsewhere,” Curtis Williams, the study’s lead author, said in a release.

The differences in OIB samples provides scientists with new insights into the chemical structure and temporal evolution of Earth’s interior.

“In particular, it means that the Earth’s mantle — the hot rock below Earth’s crust but above the planet’s iron core — is compositionally heterogeneous,” said Williams, who now is doing post-doctoral work at the University of California, Davis. “Understanding when and where these heterogeneities are formed and how they are transported through the mantle directly relates to the initial composition of the Earth and how it has evolved to its current, habitable state.”

From Discovery News