Recent University of Delaware graduate Sierra Patterson’s interest in rocks began when she was a child and her great uncle would mail Patterson’s grandmother letters from his home in Arizona. With those letters, he would also send a rock. Her grandmother would read Patterson the letters, show her the rocks and, eventually, started giving her the rocks to keep.

This set off a life of rock collecting. Patterson began traveling to rock and gem shows with her dad and estimates that she has about 300 pounds of rocks in her bedroom at home. When she arrived at UD for a visit as a high school student, she realized that she could study rocks and have a potential career in the field.

“I didn’t realize it was a career until I visited UD,” said Patterson. “I saw they had a really awesome mineralogical museum and we walked in and I talked to someone there. My high school didn’t offer any sort of earth science courses. I started looking into it more and I applied for geological sciences at UD.”

While an undergraduate at UD, Patterson worked on a research project with Jessica Warren, associate professor in the Department of Earth Sciences. They looked at the alteration of mineral assemblages in abyssal peridotites — the main rock type in the Earth’s upper mantle, the layer below the crust—from Gakkel Ridge, a tectonic plate boundary located in the Arctic Ocean.

The work began in 2017 with two other members of Warren’s lab group, Kendra Lynn and Cécile Prigent, both post-doctoral researchers at the time, helping Patterson with her first research project.

That research was recently published in the Lithos scientific journal with Patterson serving as the lead author on the paper.

Patterson recently graduated with a master of science degree in geological sciences at the University of South Carolina. She said that it was incredible to get that research experience as an undergraduate at UD and credits Warren, Lynn and Prigent for all their help and guidance.

“I definitely wouldn’t be where I am today without everything Jessica has done for me,” said Patterson. “Also, the two co-authors, Kendra and Cécile, have been wonderful to work with on this project, it really has been a joint effort.”

Warren said that Patterson set a high bar in terms of undergraduate research.

“Sierra stuck with this research when she was here and even when she was working on a master’s degree, she was going back and forth with us on drafts so that was a huge commitment,” said Warren. “The other two co-authors on the paper were both post-docs in my group and spent a lot of time with Sierra as well, teaching her things and looking at samples with her. So it was nice to have such a collaborative effort.” 

Gakkel Ridge research

To conduct the study, the research team looked at 40 Gakkel peridotites from 19 dredges spanning roughly 600 kilometers of the ridge.

The samples were gathered from a research cruise in 2001 from a German and United States expedition up to the Arctic Circle that collected rock samples from the seafloor by dredging, basically dragging a metal basket on the seafloor.

“Whenever they do that, they put higher up on the dredging wire a detector that measures for temperature anomalies and particulate anomalies,” said Warren. “From that, they would see anomalies that indicate the possibility of a hydrothermal plume.”

Warren said that people get excited about hydrothermal plumes — spots on the ocean floor where hot fluids shoot out  — because they support unique ecosystems and communities of organisms in the deep ocean. But finding them is like finding a needle in a haystack.

Because the Gakkel Ridge has plates that are taking a long time to move apart, it is generally cool, which is not necessarily an environment where scientists would expect to find a lot of hydrothermal vents.

However, results from this study show minerals from hydrothermal alteration suggesting probable relation to vent field sites.

“We had spent a lot of time looking at the Gakkel samples and talking about how we could understand the hydrothermal processes from the rock perspective,” said Warren. “There was data from the ocean water showing hydrothermal plume activity, but nobody had gone to the rocks and asked, ‘Does that confirm it and can it tell us anything more about what happened?’ ”

To analyze the samples, they used a scanning electron microscope at UD’s W. M. Keck Center for Advanced Microscopy and Microanalysis (Keck CAMM), looking at the petrography, or description and classification, of the rock’s minerals.

They rated these rock samples on a scale of 1 to 5, with 1 indicating unaltered minerals and 5 indicating fully altered, finding most of them to be around a 3.5 — moderately to highly altered.

Patterson said that by looking at the alteration of the mineral assemblages, they were able to learn about temperature and pressure conditions from the fluid circulation in the oceanic lithosphere, the solid and rigid outer layer of the planet associated with the oceanic crust.

“One of the biggest and exciting conclusions of this paper and project is that our models, which are then supported by petrographic observations, suggest that the formation of minerals, particularly tremolite and talc, require temperatures greater than 500 degrees Celsius,” said Patterson. “That implies that hydrothermal fluid circulation can be at depths greater than 20 kilometers in the Gakkel lithosphere.”

American Geophysical Union Conference

In addition to having this paper published recently, another beneficial aspect of Patterson’s research was that she had the opportunity to travel in 2018 to the American Geophysical Union Conference in Washington D.C., where she did a poster presentation on the research.

“It was wonderful because not only did I get to talk about the research, which was great practice and the people gave great feedback, but one of the people that we talked to ended up being a reviewer on the paper,” said Patterson.

She added that it was a great experience to be in a major city for almost a week, to learn about new instruments in the field, and that she was able to network and meet a lot of scientists, which was especially beneficial as she was about to apply to graduate schools.

“With grad school right around the corner and grad school applications, I got to meet my at-the-time future master’s adviser, Michael Bizimis, at the conference which was really nice because that helped to put a face to a name,” said Patterson. “I also joined the Mineralogical Society of America, the Geological Society of America and a women’s geology organization. It was so much fun and an all-around awesome experience.”