New maps provide a detailed picture of the geology north of Qaanaaq (Thule)

Overlying these are the spectacular late Proterozoic sediments of the so-called Thule Basin, which was formed as a result of a continental breakup that occurred about 1,300 million years ago. The Thule Basin’s deposits include fluvial plains, shallow marine sediments, and volcanic rocks, which were deposited in a series of fault-bounded geological blocks (half-grabens) orientated WNW–ESE. The formation of these half-grabens was a consequence of extensional tectonics, which also affected neighbouring Arctic regions.

Volcanism plays a central role in the basin, where Neoproterozoic basaltic sills, known as the Steensby Land Sill Complex, and the Thule Dyke Swarm represent magmatic events associated with the Franklin magmatic event around 670 million years ago. This event also has geological parallels in the Canadian Arctic region.

The area is known for occurrences of minerals such as copper, ilmenite and iron-rich sulphides and has potential for gold and other minerals. Magnetite belts in the region span over 400 km and are related to similar occurrences on Baffin Island, Canada. The basin is therefore not only geologically significant but also important if we want to understand the area’s resources and tectonic history.

The new maps are the result of decades of geological studies and fieldwork, building on field maps prepared in the 1980s by Peter R. Dawes, now Emeritus at GEUS. These maps also formed the foundation for the 1:500 000 geological map of the Thule area, published in 1991, with an accompanying map sheet description released in 2006.

From the 1960s to the 1980s, Peter R. Dawes coordinated his investigations along Nares Strait – which stretches from Baffin Bay to the Arctic Ocean – with geologists from the Arctic Division of the Geological Survey of Canada (GSC). Their focus was the geological evolution of the Thule Basin, which extends across the southern part of the strait. Dawes mapped the Greenlandic part of the basin, while GSC geologists Robert L. Christie and later Thomas Frisch mapped the western part on Ellesmere Island.

The geology detailed on the two new maps is based on fieldwork conducted by Peter R. Dawes during the 1970s. This mapping was later compiled with photo interpretation in 1988–1989 and revised in some areas based on fieldwork in 2001. Coastal areas were examined by boat with traverses on foot, supported by helicopter.

The final maps were produced by geologists and GIS staff at GEUS with ongoing assistance and quality assurance from Peter R. Dawes. The remaining four map sheets in the Thule map series will be published throughout 2025.

Together, the six new maps at a scale of 1:100 000 will provide a comprehensive and detailed picture of the complex and spectacular geology of this area.

Dawes, P.R. 2025: Geological map of Greenland 1:100 000 Siorapaluk 77 V.1 Nord. Copenhagen: Geological Survey of Denmark and Greenland.

Citation: Dawes, P.R. & Nutman, A.P. 2025: Geological map of Greenland 1:100 000 Quinisut 77 V.2 Nord. Copenhagen: Geological Survey of Denmark and Greenland.