The geology of East Greenland

Eighty percent of Greenland is covered by ice and, in places, this is up to 3.4km thick. So, Greenland might not immediately spring to mind as a place to go to observe rocks. However, it is a huge country and the ice-free area, at 410,000km2, is nearly twice the size of the UK. This is generally sparsely vegetated, leaving the rocks beautifully exposed and the geology incredibly easy to see. The area of East Greenland around Scoresby Sund, Kong Oscar and Kejser Franz Joseph Fjords is the largest ice-free area in Greenland. It also has incredible geodiversity, with basement rocks as old as three billion years, an almost complete sedimentary record of the last 1.6byrs and huge volumes of flood basalts from the splitting of the Atlantic. If you were an alien and wanted to try to piece together the geological story of Planet Earth – but could only visit one area – East Greenland would be the place to go.

Fig 1
Fig 1. A simplified geological map of East Greenland.

The geological history of Greenland is vastly long and spans 3.8byrs. Its oldest rocks are the 3.8byr-old Isua Complex, situated in West Greenland, near the capital Nuuk. These rocks are the Earth’s oldest, most well-preserved sedimentary and volcanic rocks, and they contain carbon particles that most likely originate from the oldest known life on the planet. To put into perspective just how old these rocks are, try to imagine that the planet is only one year old. It would have formed on 1 January, with the earliest known life and these Greenlandic rocks forming in March. Multicellular life did not evolve until October, the dinosaurs a few days before Christmas (going extinct on Boxing Day) and humans only appeared 15 minutes ago, with all of civilisation being in the last 10 seconds.

At the time these rocks formed, our planet was a very different place and the continents were still forming, and there was less continental crust than there is now. However, plate tectonics were taking place. Broadly, when one oceanic plate collides with another, one is forced to slide under the other in a process called ‘subduction’. Minerals in the subducting slab dehydrate, causing the overlying mantle to melt and new rock types, like granites, to be produced. The early granites of East Greenland (and all subsequent granites) are continental crust and in all continental collisions, they are not subducted due to their relative buoyancy. Over time, the amount of continental crust increased and when pieces of continental crust collided, they welded together to form one block, and the immense forces involved thrust up chains of mountains. During this process, the rocks buckle and fold, with the intense heat and pressure causing them to transform into metamorphic rocks such as gneisses.

Fig 7
Fig 7. The 1,977m-high peak of Grundvigskirche in Øfjord. Most of the rock in the photograph is 1byr-old gneiss that was originally Krummedal sediments. The peak of the mountain is a pink granite and the dark stripe of rock rising from the bottom left corner is hypersthene monzonite, both of which were intruded during the Caledonian Orogeny.
Fig 9
Fig 8. A Caledonian intrusion of hypersthene monzonite is bounded by the red line. The surrounding rock is the remains of Krummedal Rocks that were metamorphosed 900mya in the building of Rodinia. The red layers are paragneiss, which are extremely rich in garnets; while the whiter layers are due to the complete melting of the original rock and are now augen granite. The photograph was taken in Øfjord. Figs. 9 and 10 show these bands more clearly.

A large proportion of the rock exposed in Greenland, particularly in the west and south, is made of these strongly folded gneissic rocks, which are the eroded roots of different mountain belts, now welded together to form a stable, coherent block. This block is commonly known as ‘the basement’. The coming together of the basement occurred over a huge period of time, spanning 3.8 to 1.75byrs. It was also not a simple process. For example, by 2.7bya, most of West, East and South Greenland had formed and were probably part of a theorised ancient continent referred to as Kenorland. Two billion years ago, this split up and parts of West Greenland rifted apart again, only to come back together 200myrs later. The final stages of basement building occurred from 1.8 to 1.725bya, when Greenland was part of another super continent referred to as Columbia. These youngest basement rocks are seen in South Greenland.

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