Martian Bubbles as Time Capsules?
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 Robert Bodnar, University Distinguished Professor in the Department of Geosciences in the College of Science, Virginia Tech, "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 - 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.
Bodnar's lab already had 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 - 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.
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.
"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 - 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.
"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.