Recon fieldwork in the "Middlest of Nowhere" in Saskatchewan, Canada
Summary by Alissa Kotowski: We went to Reindeer Lake in July 2026 to hunt for very old expressions of subduction plate boundaries in the Trans-Hudson Orogen, and it was an incredibly successful and exciting trip. Read the details below, written by Rosa de Boer, our team's paleomagnetic expert!
Written by Dr. Rosa de Boer
Reindeer Lake
Flying over the massive Reindeer Lake, we see a landscape of water, forest-covered islands, and exposed Precambrian rocks. Our float plane descends towards the quiet bay of a small, uninhabited island, where we will make camp. It is July 2026, and we have arrived in a remote corner of the Canadian Shield with a big question in mind: do these rocks preserve evidence of a nearly two-billion-year-old subduction zone? Alissa Kotowski, Richard Wessels, and I are here for a recon fieldwork, hoping to piece together the geological history of this spectacular area. For the next two weeks, this tiny island will be our home. Our camp consists of three small personal tents and a prospector tent that serves as our kitchen and headquarters. We are joined by our indispensable camp manager, Reid Allen, who takes care of most practicalities and keeps us alive while we focus on geology.
Sole Searching
In the early 2000’s, the Saskatchewan Geological Survey carried out a five-year field campaign to map the 1.9 Ga Precambrian rocks around Reindeer Lake. Although their work was aimed at mineral exploration, their lithological descriptions and maps form a valuable base for other research. Looking through their reports, Alissa recognized something intriguing: an ophiolite (a section of oceanic crust and upper mantle exposed at Earth’s surface) and possible metamorphic sole (a highly strained metamorphosed oceanic crust underneath an ophiolite) had been mapped by the survey team. Together, these features can contain evidence for subduction zone formation. This became the starting point for our expedition to study a very old geological record of this process. Through a combination of field observations, geochemistry, (micro-)structural analysis, thermobarometry and a bit of rock-magnetism we hope to reconstruct the pressure-temperature and deformation history of these rocks. Understanding subduction in Earth’s deep past is important for understanding the evolution of plate tectonics and how Earth’s geodynamic behavior has changed through time.
Embarking on an Adventure
A field expedition in ‘the middlest of nowhere’ requires some serious logistics. We make camp on our tiny island in the middle of the lake, which we deemed "the Ant Hill" to pay homage to the other inhabitants on the island. The island is the right place to camp because it gives us protection from bears and other large wildlife that prefer the mainland. To reach the outcrops on the mainland and surrounding islands, we have a daily commute using an inflatable Zodiac. We quickly learn that the most promising outcrops are on the lakeshore. Further inland, everything is heavily covered with trees, lichen, and millions of mosquitos. The effects of previous forest fires are still visible, with many trees partially burned and fallen, and large areas of the forest floor covered in charcoal and soot, making it almost impossible to traverse over land. With only 12 field days available to us and a lot of ground to cover, we focus on the most accessible outcrops and collect as many observations, measurements, and samples as we can. Two drones help us document the exposures and connect areas that are difficult to reach on foot. One afternoon, we noticed a rapid change in weather and headed back to camp. When we got back, a storm moved across the lake and over our island. While trees were falling down around us, lightning striking every few seconds and rain pouring down, we became worried that our camp and, more importantly, our latrine might flood. But by the next morning the weather is calm again and we are back to business. The rocks are still there, after all!
Geological Discoveries
At the end of Field Day 2, we found beautiful tectonized mantle peridotites that represent deep roots of ancient lithosphere, and the upper plate of an old subduction zone. We even found what we believe to be the contact between mantle rocks (on top) and crustal rocks (below)! Remarkable to see a 1.9-billion-year-old plate boundary! The focus of the rest of the fieldwork shifted to understanding what happened along this boundary. We studied the rock sequences on either side, representing the potential downgoing and overriding plates and examined the shear zone that marks their contact. We looked for different deformation phases and tried to untangle their signatures. Along the way, we collected targeted samples to reconstruct the thermal and deformational history of the rocks back in the laboratory. The rocks we studied form part of the Trans-Hudson orogeny, and record the assembly of the Hearne, Superior and Sask Cratons. Our observations suggest that this region preserves a previously unrecognized record of subduction initiation and infancy ~1.9 billion years ago.
Looking Forward
The recon fieldwork was a success, but now comes the next challenge, processing 144 kg of rock samples. These samples will help us piece together the geological story of Reindeer Lake and the questions that remain unanswered will help shape our next field adventure.
Thanks to all who made this possible!
This field expedition would not have been possible without the tremendous support of the people at the Saskatchewan Geological Survey, especially Tyrin Foley, Ralph Maxeiner, and Rachel Kepler. We are also very grateful for the generous funding provided by the Dr. Schürmannfonds for Precambrian Research. A special thanks goes to our lovely ‘neighbors’ on the lake for all their practical tips, local knowledge, and help along the way, as well as to all others that have contributed to the logistical efforts that made this expedition possible.
Slide through the pictures below for a sense of our life on Reindeer Lake!
Picture captions:
The Otter float plane that transported us to and from our remote island base camp
The Team: Richard Wessels, Reid Allen, Alissa Kotowski and Rosa de Boer
A close look at the first serpentinites.
Metapelite with gorgeous, big, pink garnet porphyroblasts.
Mantle tectonites of very old lithosphere!
A view inside our prospector tent, serving as both our field camp and geological headquarters.
Rosa in charge of our daily commute by Zodiac from one outcrop to the other.
Alissa collecting outcrop photos with the lovely Dronette (DJI Avata 360)
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