Geologists Explore Tasmania’s Hidden Gems
Through Mud and Mines, Students and Faculty Uncovered Garnets’ Rich Geological Stories
From left, geology Assistant Professor Megan Newcombe, master's student Kathryn Bickerstaff '23 and Ph.D. student Kathleen Stepien sort through rocks at Tasmania's Mornington Core Storage Facility.
Photos courtesy of Sarah Penniston-Dorland
The scent of eucalyptus and tea trees carried on a breeze, and the bizarre charm of long-snouted marsupials were a few of the natural wonders two faculty members and two graduate students from the University of Maryland’s Department of Geology experienced on a recent research trip to Tasmania. But their real focus was a different—and literal—kind of gem.
For a little over a week in January, the four scientists traipsed through mud to collect garnets from woods, mines and coastlines on the island south of the Australian mainland affectionately called “Tassie.” Garnets are a multicolored mineral widely used in jewelry and industry, but to geologists, they’re treasured time capsules containing secrets of Earth’s past.
“Rocks are in the Earth’s crust for a long time, and garnet grows over a long period,” said geology Professor Sarah Penniston-Dorland, one of the trip’s organizers. “It doesn’t just crystallize in a short time, so it’s a useful recorder of the history that rocks have experienced.”
As part of ongoing research funded by the National Science Foundation, Penniston-Dorland and co-organizer and geology Assistant Professor Megan Newcombe analyze the water content in garnets to explore a phenomenon called fluid flow during metamorphism, a process that occurs when rocks are transformed under heat and pressure.
By studying how water moved through rock during metamorphosis, geologists can better understand and predict natural disasters like earthquakes and volcanoes, as well as improve their ability to locate precious metals and other valuable substances underground.
The group headed to Tasmania after receiving an intriguing garnet sample.
“We read about this particular locality in Tasmania (that produced the sample),” Penniston-Dorland said, “and it looked like there was more complexity—and different generations—of garnets growing at different times and with different events of fluid flow.”
After landing in Tasmania’s capital city of Hobart, the group linked up with its host, geologist Ralph Bottrill of the Tasmanian State Geological Survey, and immediately got to work. On the first day, the group battled rain and big, biting flies in pursuit of garnet samples.
The UMD geologists hike through Cradle Mountain National Park in Tasmania.
“We were scrambling around in the mud and the woods, and I was thinking, ‘Is every day going to be like this?’” Penniston-Dorland said with a laugh. “The weather improved after that.”
At one point, geology master’s student Kathryn Bickerstaff ’23 donned a protective suit and respirator—a precaution against dust inhalation—and used a rock saw to extract samples.
Bickerstaff studies fluid-rock interaction in metamorphic rocks. She will now focus on samples collected from the Kara mine, adding that those garnets are “unique” because of their high water concentration and four distinct stages of mineralization.
Geology Ph.D. student Kathleen Stepien uses her mineral samples to study how the water in garnet can help trace fluid flow in metamorphism.
“The Kara garnet crystals have been special because they contain a relatively large amount of water—up to about 5,000 parts per million,” Stepien said. “Measuring the major and trace element compositions will provide clues to help us determine what the fluid history looked like at this locality.”
By the end of the trip, the group amassed enough rocks containing garnets to fill seven suitcases—including a spiky crocoite sample that triggered a security check that nearly caused them to miss their flight.
“I brought about 40 pounds of material back, mostly geologically unique rocks,” said Bickerstaff, who is also an avid rock collector. “Most notable minerals that I brought back are pieces of crocoite and atlantisite. These minerals are found in very few localities, and it is very hard to get your hands on some here in the states.”
Now back at UMD, the geologists look forward to digging into these samples to discover the secrets within.
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