Image: The photo shows a fluid inclusion containing liquid water and a vapor bubble. The inclusion, contained in the mineral quartz, is about 25 micrometers in length.
Blacksburg, Va. — By summer 2005, researchers in the Fluids Research Laboratory at Virginia Tech will be able to look for evidence of water on Mars by examining submicroscopic bubbles in martian meteorites, determine whether fluids and silicate melts trapped in volcanic rock can help predict future eruptions, and locate buried mineral deposits using data from surface rocks. Robert Bodnar, University Distinguished Professor in the Department of Geosciences in the College of Science, has received equipment grants from the National Science Foundation (NSF) that will make the lab one of the best equipped for the study of fluid inclusions in the United States.
When minerals form on Mars or deep in a volcano on Earth, small droplets of fluid, vapor, or silicate may be trapped. These tiny, ancient samples contain the rock’s chemical history and represent time capsules from the moment they were sealed in a rocky envelope. Recovering that moment in time has been a long-term challenge for geoscientists.
“Scientists can learn a lot about the composition of such inclusions by observing their behavior during heating and cooling under the microscope,” said Bodnar, “but to really learn what is going on, you have to do quantitative chemical analysis.” Non-destructive techniques using lasers to approximate the compositions of inclusions have existed for many years. Now there is an instrument that goes a step further ñ actually digging or ablating into the inclusion and removing the fluid for direct chemical analysis.
Bodnar learned in late May that he has received a $400,000 Major Research Instrumentation grant from the NSF to purchase an “Excimer-laser Based Laser Ablation System coupled to an inductively coupled plasma mass spectrometer (LA-ICP-MS).” “It is the single most important analytical method for those studying the geochemistry of Earth fluids,” said Stephen E. Kesler, professor of geological sciences at the University of Michigan.
Last year, Bodnar had received $450,000from NSF and Virginia Tech to upgrade the lab with two Raman microprobes, one of them specifically designed for the analysis of petroleum inclusions. “It uses a UV laser and will help us understand whether a given basin or rock might host oil deposits based on analysis of fluid inclusions in surface rocks, which could save millions of dollars in fruitless drilling, or at least help identify the most promising sites,” said Bodnar.
The latest acquisition, which will be in place by next summer, will be a national resource. There are only three other LA-ICP-MS systems specifically designed for analysis of fluid inclusions in the world ñ at the Swiss federal technical university (ETH) in Zurich, where the system was developed, at the University of Leeds, and at Australian National University, Canberra. Bodnar’s newly equipped lab will become the National Laser Ablation ICP-MS Laboratory for Fluid Inclusion Analysis.
At a 2002 meeting in Denver, sponsored by the NSF and the Society of Economic Geologists, the establishment of an LA-ICP-MS laboratory in the United States was identified as a number one instrument priority, and it was suggested that it be located in Bodnar’s lab at Virginia Tech because of his long history of fluid inclusion research. Bodnar was invited to apply for an MRI and 37 leading scientists provided letters of support.
“There is no better location than Virginia Tech for such a laboratory in North America,” said Kesler. “Dr. Bodnar is a pioneer in work on both natural and experimental fluid inclusions and has a reputation for thoroughness that is important to the scientists that will use this facility.”
Bodnar’s interest in fluid inclusions began when he was a master’s student at the University of Arizona 25 years ago and continued through his PhD research at Penn State University to the present time. The Mars research is one of Bodnar’s recent interests, now shared by his students. Work to predict volcanic activity at the Vesuvius volcano that destroyed Pompeii in 79 AD is a joint project with researchers at the University of Naples. Bodnar’s early work on fluid inclusions involved studies of extinct volcanoes that host some of the world’s largest copper and gold deposits.
Bodnar is searching martian meteorites for samples of fluid inclusion, which are rare in these extraterrestrial samples. He and his graduate student, Megan Elwood Madden, a native of Jacksonville, Ill., are creating geochemical computer models to predict what fluids would have been on Mars at the time the rocks now comprising the meteorites were formed. “Our findings would help answer questions regarding the presence of water on Mars, which is crucial for the development and survival of life,” Bodnar said.
Madden, a Ph.D. student with funding from the NSF VTAdvance program, is examining fluid inclusions in other space material as well as in terrestrial meteorite impact sites, including Meteor Crater in Arizona. Previous studies of meteorites indicate that Earth is not so unique, as fluid inclusions indicate that water has been present on other bodies in the solar system at some time in their history (Zolensky, Bodnar, Gibson, Nyquist, Reese, Shih, Wiesmann, Science, Aug. 27, 1999).
Bodnar is looking at melt inclusions from the magma chambers associated with volcanoes. A melt inclusion is a droplet of silicate material, rather than a fluid, that was trapped in a mineral. “Our research collaboration with the University of Naples is looking at melt inclusions in the magma from Vesuvius,” Bodnar said.
Naples, with more than a million residents, sits on the flank of this active but sleeping volcano.
Luca Fedele a Ph.D. graduate of Virginia Tech who is a now faculty member at the University of Naples, and Claudia Cannetelli, a PhD student from Naples, have come to Blacksburg for the summer to conduct research on melt inclusions from the Vesuvius volcano. “The LA-ICP-MS system will enable us to analyze the composition of the melt inclusions to determine the composition of the Vesuvius magma at the time of eruption,” Bodnar said.
The researchers have determined that the composition of magma changes. “If the composition at a particular time can be related to when a volcano erupts, then knowing the composition might be an aid in predicting eruptions,” Bodnar said.
“Predicting volcano activity is an active area of research,” Bodnar said. Many researchers are studying Mount Rainier in Washington, another dormant volcano that is near 2.5 million people in the Seattle Tacoma metropolitan area.
Bodnar is also studying the role that volcanoes play in forming valuable mineral deposits. Volcanic magma can contain rich deposits of gold or copper ñ or not. Bodnar’s focus is porphyry copper deposits, which include the famous Bingham Canyon, Utah, and Butte, Mont., deposits, although he has studied gold deposits related to volcanoes as well (reported in The Economist Oct. 21, 1995). “One to two kilometers below the top of a volcano, as the magma chamber cools, minerals precipitate. Later, the volcano is eroded to reveal these deposits. When I study these deposits, I am studying the ‘fossil’ of a volcano,” Bodnar said.
“There are thousands of fossil (or extinct) volcanoes worldwide, but only a few have concentrations of metals that can be mined. Why? Fluid inclusions offer the key to answering this question,” Bodnar said.
As molten magma cools and crystallizes, water enters and is heated. What happens at this “magmatic hydrothermal, or hot-water, transition determines whether or not an ore deposit forms, he said. “We want to analyze melt inclusions and fluid inclusions that formed at the same time to try to understand what happens to the chemistry within the magma chamber as the system evolves from the magmatic stage to the hot-water stage.”
“The few LA-ICP-MS analyses of fluid inclusions that have been made provide information on the amount of metal that is dissolved in natural, ore-forming fluids, and analyses of melt and sulfide inclusions are providing important insights on the geochemistry of incompatible elements during magmatic crystallization,” said Kesler. “Preliminary data are challenging well established concepts and are likely to lead to completely new theories about the processes that form mineral deposits and other geochemical anomalies in the upper crust.”
Meanwhile, mining companies could save hundreds of millions of dollars in exploration costs if analysis of inclusions in surface rocks could indicate whether or not to drill.
Researchers from around the world will be able to use the new National Facility for Laser Ablation Analysis of Fluid Inclusions at Virginia Tech to explore rocks hundreds of millions of years old for knowledge ranging from how copper and gold deposits formed to the opportunities for life across the solar system.
Contact Dr. Bodnar at rjb@vt.edu or 540-231-7455
Contact Dr. Kesler at skesler@umich.edu or 734-763-5057 or 764-1435
