Rock metals suggest
volcano’s source

---

Associated Press

Rare grains of metal taken from rocks found in Oregon and California suggest that volcanic hot spots which produced the Hawaiian Islands are fed from deep in the Earth's core rather than near the surface.

In a study published this month in the journal Science, researchers measured tiny grains of rock collected from slabs of ocean crust that have been pushed up in the Klamath Mountains of Northern California and southwestern Oregon.

The samples contain large amounts of osmium, which is rarely found on the surface but is believed to occur in relatively high concentrations in the Earth's core some 1,700 miles below the crust.

"These types of osmium grains are harder than the devil to find," said University of California-Santa Cruz geologist Quentin Williams. "I'm quite impressed that they found some."

Earlier studies of lava from volcanoes in Hawaii and Siberia revealed high concentrations of two very rare osmium isotopes -- or slightly different versions of the same atom.

Some researchers suspect that hot spots which feed magma to volcanoes originate just 60 miles below the crust, while others believe the source is much deeper, perhaps at the boundary between the outer mantle and the inner core of the planet.

Stanford researcher Anders Meibom and Robert Frei of the University of Copenhagen compared osmium isotope levels in the rock samples from California and Oregon with the lava samples from Hawaii and Siberia and found they were remarkably similar.

Their findings indicate the lava came from deep in the mantle but Meibom and Frei said reservoirs of osmium isotopes could exist higher in the mantle.

Williams, however, said it was strong evidence of a deep source of magma near the core.

"All of these sites from Hawaii in the middle of the Pacific to Asia to North America show grossly similar osmium isotope characteristics," Williams said.