Postdoc Spotlight: Geochemist Marion Garçon

Marion Garcon
Friday, September 04, 2015 

Growing up surrounded by the French Alps seems like the perfect backdrop to develop a fascination with Earth’s reliefs that have been forming long before human life existed. Marion Garçon, a DTM Postdoctoral Fellow, was lucky enough to do just that. 

While sitting in a high school Earth sciences class about plate tectonics, Garçon says she discovered that her home in the Alps, where she spent her summers hiking up those mountains and her winters snowboarding down them, was once covered by several thousand meters of water a few hundred million years ago. Upon realizing people were actually studying rocks to understand how those mountains, and others like them, were formed, she was hooked.

At college, however, her path became less clear.

During her first year at the University of Grenoble in France, Garçon chose to get a science degree, majoring in physics, chemistry, and Earth sciences. She loved math, and did not want to give up her physics classes, so she decided to pursue an undergraduate degree in physics and chemistry.

Garçon’s goal at the time was to earn a master’s degree in glaciology and geophysics, so having an undergraduate degree in physics and chemistry seemed beneficial for future projects. However, after enduring two summer internships in glaciology and geophysics in front of a computer screen trying to resolve equations in fluid mechanics to model glacier fluctuations and Earth’s geodynamics, Garçon had had enough. 

“I figured I did not want to spend my whole life doing models on a computer and I started having doubts about pursuing a career in Earth sciences,” says Garçon looking back on her career. Then, “Catherine Chauvel, my Ph.D. advisor, offered me an internship in geochemistry during the first year of my master’s...and I loved it.”

DTM Postdoctoral Fellow Marion Garçon in the field in Canada. Here she is sampling old sedimentary rocks in the Superior Province with DTM Staff Scientist Steven Shirey in June 2014. (Photo courtesy of Marion Garçon)

From that point on, Garçon could be found collecting sediment samples in the field, crushing rocks into fine powder, or developing new analytical procedures and techniques in a lab to get better results for her own research. Her favorite part of her work now, she says, is discovering the chemistry of the rocks that she collects. After they are crushed, she studies them to determine the petrography and geochemistry of each sample.

“What is really exciting about the whole process is that when you analyze new samples, you don’t really know what the results will be until you actually get the numbers out of the instruments. Sometimes, you’re lucky and get a very exciting number; sometimes the compositions are just normal, or worse, the opposite of what you thought. Then, you have to understand why, and make new measurements, calculations, and models. I think this is what I really like about my work, having challenges and finding a way to resolve them,” says Garçon.  

At DTM, Garçon’s work aims to understand the formation, evolution, and composition of the continental crust at the beginning of Earth’s history about 3 billion years ago. She analyzes chemical and isotopic compositions (Nd, Hf, and Pb isotopes) of old sedimentary rocks drilled from the Barberton Greenstone belt in South Africa. These detrital rocks consist of a mixture of minerals and rock fragments that have been eroded from Earth’s very first continents, and are one of the only surviving witnesses of what happened at the beginning of Earth’s history.

Most of Earth’s first continents have disappeared; so Garçon says one way to study them is to look at what is left in the sedimentary record today. By studying these records, she says she can determine the average composition of the first continents and trace the history of the early Earth’s crust. 

“The first half of Earth’s history is a key period for so many things that we still do not really understand: the apparition of life, the apparition of water, the emergence of continents, etc.,” says Garçon. “Studying these rocks is very exciting, it’s a unique opportunity to unravel the processes that ultimately led to the formation of the Earth that we know today.”  

This is a piece of sedimnetary rock formed 3.25 billion years ago in South Africa. You can see rock fragments in it. Those have been eroded from continents that were at the surface of the Earth 3.25 billion years ago! (Image courtesy of Marion Garçon)

As her fellowship comes to an end at DTM, Garçon will be embarking on two new exciting adventures. 

The first will be a yearlong fellowship with former DTM Postdoc Maud Boyet at the Laboratoire Magmas et Volcans in Clermont-Ferrand, France. While there, Garçon will measure 142Nd isotopes on sedimentary rocks that she and DTM Staff Scientist Steven Shirey collected in the Superior Province of Canada in June 2014. She hopes to see whether some very old crust, i.e., crust that formed in the first 500 million years of Earth’s history, was involved in the formation of the Superior Province, the largest known mass of continent formed during the Archean period of Earth’s history.

The second will be a larger, three-year project at ETH Zurich, where the Swiss National Science Foundation awarded Garçon the Ambizione Fellowship. This fellowship will start in September 2016, and will support her Nd-Hf-Sr-Pb isotopic analyses, field trips to Canada to collect more sedimentary rocks with Shirey, and the development of new analytical techniques. Garçon will also be working with rocks collected last summer by former DTM Postdoctoral Fellows Jonathan O’Neil and Hanika Rizo from the Saglek-Hebron area of Canada.

Within the next ten years, Garçon says she would like to have a professor position, but she would also like to lead her own lab so she can develop cutting-edge analytic techniques and innovative science projects that will lead to exciting discoveries.

“I think that analytical progress in developing new methods is a powerful way for science to advance and for new ideas and concepts to emerge, so I really want to be part of that.” 

Written by Robin Dienel, 4 September 2015