FSU Geologist's Discovery Published in 'Nature'

A Florida State University geologist is part of a team that found that not one, but two types of rocks are involved in the production of sea floor basalt, a volcanic rock, during the process of sea floor spreading.

The finding by FSU geologist Vincent J.M. Salters, who is a scholar/scientist at the National High Magnetic Field Laboratory at FSU and a member of the university's geological sciences department, and Henry J.B. Dick of the Woods Hole Oceanographic Institution has been published in the July 4 issue of the prestigious science journal Nature.

The discovery has large consequences for scientists' estimates of how much rock material melts, the temperature structure of the Earth's mantle - or the interior of the Earth - and how the volcanic activity is generated in the first place. Such considerations vary depending on the geography of the location in question.

In their paper "Mineralogy of the Mid-Ocean-Ridge Basalt Source from Neodymium Isotopic Composition of Abyssal Peridotites," Salters and Dick explain that they made the find while studying abyssal peridotites, which are the residues of melting during sea floor spreading. Sea floor spreading is the term used to describe the process of how new crust is created.

"It was previously assumed that only one type of rock melts to produce mid-ocean ridge basalt," Salters said.

The researchers' study led them to the conclusion that a second type of rock called pyroxenite, which is rarely seen at mid-ocean ridges, melts first in the process because it has a lower melting temperature than peridotite.

"The reason it has taken so long to discover the pyroxenite is because it melts away earlier, leaving the more common peridotite, which melts at a higher temperature," Salters said. "What we thought was a homogeneous source of basalt really isn't."

As sea floor spreading occurs, tectonic plates are pulled apart by material that disappears back into the mantle. New material is then thrust upwards to replace it. As the new material rises, its heat causes pyroxenite, then peridotite, to melt and thus create the ocean floor. This process is responsible for 80 percent of the volcanic activity on the planet.

Salters has studied mid-ocean ridge processes his entire career.

The three-year, National Science Foundation research project had Salters and Dick analyzing samples of rock taken from the floor of the Indian Ocean.