Evidence of Water Found Deep in Earth’s Crust

KNOXVILLE — Research at the University of Tennessee calls into question geologists’ traditional understanding of how deeply surface water penetrates into the earth’s crust.

Dr. Claudia Mora, a UT geology professor, and Dr. Lee Riciputi, an Oak Ridge National Laboratory research scientist, used a special mass spectrometer to study stable isotopes of oxygen that record the penetration of water into rock that once was deep in the planet’s crust.

Mora said the findings raise new questions about the way surface water interacts with the top layer of the Earth.

“Surface water penetrated much deeper into the crust and into hotter rock than we’ve thought possible,” Mora said. “The water then left the rocks faster than is thought possible or the rocks cooled faster than is possible. Or both.”

The research is based on a study of the ratios of different oxygen isotopes found in rocks taken from northern Idaho. Mora said the rocks from deep in the crust were brought to the surface by the forces of plate tectonics. The stability of minerals in the rock indicates the depth at which the rocks formed.

“The ratios of isotopes is a chemical fingerprint of the origin of water that interacted with the rock,” Mora said.

The secondary-ionization mass spectrometer uses an ion beam to sputter the top surface of a mineral sample and analyzes the resulting ions.

Scientists then can examine samples on a sub-microscopic scale. The spectrometer at ORNL is one of the few in the world capable of work on such small samples, Mora said.

An article describing the research appeared in the December issue of Science magazine. Mora and Riciputi are married, and this is their first joint publication. An ORNL colleague, David R. Cole, was a co-author.