For most travelers, Lofoten is a place known for its stunning fjords, mountains, endless hours of summer daylight, and delicious fish. For geologists, it is also a remarkably pristine window into Earth’s lower crust. Here we find 1.8 billion year old rocks with very little overprint, where original structures and mineral compositions from the time of their formation are well preserved. More simply, these incredibly old, dry rocks sat at about 45km depth before they were exhumed to Earth’s surface only a few hundred million years ago.
The focus of our expedition was geologic hydrogen, a key player in today’s renewable energy landscape–when used in fuel cells, energy is produced with only water as a byproduct. More broadly, our motivation is to understand deep fluid processes and the hydrogen-rock reactions that can occur throughout the crust and mantle. So why look for traces of fluids in such a dry regime? Finding hydrogen in even these unsuspecting rocks would substantiate just how pervasive hydrogen formation and migration can be. We would be unraveling much deeper mineral reactions and controls inevitably tied to the search for hydrogen at Earth’s surface.
From the southernmost part of the islands in the town of Å (pronounced like the letter “o”) to the shores of Ramberg about 30km north, we joined our colleagues and two videographers from the University of Oslo. In tandem with our search for traces of fluid, their team looks for evidence of deep crustal deformation in the form of pseudotachylites, or “fossil earthquakes”. While they focus on mechanisms occurring in a nearly dry crust, we dive into the fact that nearly dry means there are fluids (i.e fluid-reactions) to be investigated. These research questions require vastly different approaches but are undoubtedly part of the same lower crustal story–the perfect opportunity for collaboration.
However, this also means the likelihood of finding evidence of hydrogen in these rocks is slim, especially in contrast to sites with anomalously high rates of hydrogen outgassing recently reported, like the Samail ophiolite in Oman, or the Bourakebougou field in Mali. Hydrogen molecules are incredibly small and light, such that they diffuse rapidly through solids. On geologic timescales, traces of hydrogen at depth are then more likely to be lost to the surface or atmosphere. This is why we also turn to carbon. Whether in the form of CO2 or CH4 or other hydrocarbons, carbon is incorporated into heavier molecules that are often found in association with hydrogen and easier to chemically “fingerprint”. From the 1.8 Ga intrusive anorthosites and even older host paragneiss, to quartz veins and graphite-bearing micaschists, we sampled these target lithologies first in the south, making our way north to Sortland.
With the exception of an unfortunate flat tire, the Norwegian terrain treated us well. Driving between sites, we saw countless tall, wooden racks with hundreds of tørrfisk (stockfish) and skrei (cod) hanging to dry, just a small window into the fishing industry that has sustained the people of Lofoten for generations. In fact, thanks to a kind Norwegian fisherman and his boat, we were able to venture even further south to explore the formations of Hellsanden. It was much like a mom dropping off her kids at school and picking them up later in the afternoon–except that “mom” is a burly expert of the seas and her “kids” are equipped with hammers, chisels, canned mackerel, and every type of biscuit imaginable.
Each day brought new roadcuts, marshy coastlines, rocky beaches, ridge lines, and quarries. Being just above the arctic circle, the nighttime essentially never came. Unfortunately, the end of our ten-day expedition did. With over one hundred samples already back in Bologna, we left the cold mornings and mountains of Lofoten behind and are eager to see what 1.8 billion years was able to preserve in the lab.
Hanh-Tu Ella Do
Photography by Jacopo Pasotti
(This expedition was supported by Karpos, POC, Polar, and Midland)