Geological mapping of Norway’s least explored mountains
Research notes:
Four geologists participated last winter in the Norwegian Polar Institute’s expedition to Norway’s Troll research station in central Dronning Maud Land, Antarctica. The main goal of the expedition was a geological mapping of the region’s nunataks – mountain peaks completely surrounded by glacier ice.
The nunataks of Hochlinfjella consist of granite that intruded during a late stage of the Pan-African orogeny. Note the dark weathering colour. Photo: Joachim Jacobs / University of Bergen
By: Synnøve Elvevold and Per Inge Myhre // Norwegian Polar Institute, Ane K. Engvik // Geological Survey of Norway and Joachim Jacobs // University of Bergen
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The mountain range of Dronning Maud Land is an exposed row of nunataks that runs roughly parallel to the edge of the East Antarctica ice sheet, about 200 km inland. The barren nunataks of Fimbulheimen are Norway’s least explored mountains, and probably the most spectacular. The steep rock faces lack vegetation and is polished by the ice. The excellent quality of the exposures provides a unique opportunity to study the various geological processes that have affected and formed the bedrock in Dronning Maud Land.
The purpose of the 2017-2018 expedition was to produce a new geological map of the area surrounding the Norwegian Troll station in central Dronning Maud Land.
Mapping and thematic surveys in a claimed territory are considered a fundamental obligation for the claiming country. It is thus important to follow up geoscientific activities in Antarctica by taking an active role in geological mapping and research.
Geological maps communicate vast amounts of geological information. The maps show the distribution of different geological features, including rock types and structural features such as faults, folds and foliations. The maps also contain information about the relative age of the rocks, as well as the relative order of geological events such as deformation, metamorphism, intrusion of magma, erosion, and many others. Geological mapping is an interpretive, scientific process and involves several disciplines including petrology, geochemistry, structural geology, geochronology and stratigraphy. The new results from the expedition will increase our knowledge on the geology of Dronning Maud Land, and will thus be an important contribution to management-related research and mapping in the Norwegian polar regions.
Reconstructing ancient supercontinents
During the Precambrian period, most or all of the earth’s continental blocks assembled as “supercontinents”, then dispersed again.
During the Precambrian period, most or all of the earth’s continental blocks assembled as “supercontinents”, then dispersed again. This happened several times. The formation of large continental masses by plate collision has resulted in major mountain ranges and high erosion rates, and each supercontinent has marked the start of significant global climate change. The bedrock of Dronning Maud Land has a long and complex geological evolution and preserves evidence of being part of two supercontinent configurations: Rodinia and Gondwana. The oldest rocks in the area formed about 1100-1200 million years ago during the assembly of Rodinia. In the area around Troll, these rocks are present as migmatites and granitoid gneiss es. The older (Precambrian) gneisses underwent a new episode of orogeny (mountain-building) during the assembly of the supercontinent Gondwana 500 600 million years ago. Various continental blocks were assembled in Gondwana along a network of mountain ranges that are known as the Pan-African mountain belt. The mountain range that went through East Africa and Dronning Maud Land was probably one of the largest orogens[1] on Earth and has been compared to today’s Himalayas.
During this period, the bedrock of Dronning Maud Land underwent deformation, high-temperature transformation (metamorphism), partial melting and formation of a new crust. Thermodynamic modelling of equilibrium phase diagrams, based on observed mineral assemblages and geochemical analyses, demonstrate that metamorphism of the gneisses took place at temperatures between 750-850°C and at pressures corresponding to crustal depths of about 25-30 km. In other words, the high-temperature crust exposed at the surface today in Dronning Maud Land reveals a deeply eroded section through the central part of the 500-600 million year old Pan-African orogen.
[1] An orogen develops when a continental plate crumples and is pushed upward to form one or more mountain ranges.
Large volumes of granitoid magmas intruded the gneisses at a later stage of the Pan-African orogeny. The magma crystallised to form new rocks such as granite, charnockite, syenite and monzonite. These magmatic intrusions are massive and often form the spectacular, jagged peaks and alpine ranges that are so characteristic of the landscape in the central part of Dronning Maud Land. Another distinctive feature of the granitoid rocks is the dark-brown weathering colour, which often makes them recognisable at a great distance.
Towards the end of the Pan-African mountain-building event, the thickened crust became unstable. Extension of the crust in Dronning Maud Land caused rocks from deeper crustal levels to be carried to more shallow levels. The extension (stretching) continually occurred from crustal depths where ductile (plastic) deformation of the rock mass takes place, towards higher crustal levels where the rocks deform in a brittle fashion. Structures formed at the different crustal levels can be observed as folds, shear zones and faults.
Gondwana began to break up 180 million years ago. The different crustal fragments drifted apart, and most of the continents, subcontinents and islands we now recognise, like Africa, India and Madagascar, began to drift north towards their present location.
Today, Antarctica lies isolated around the South Pole. The geographical isolation led to climatic cooling and ultimately to glaciation of the southernmost continent on Earth.
The geology team. Left to right Joachim Jacobs from the University of Bergen, Synnøve Elvevold from the Norwegian Polar Institute, Ane K Engvik from the Geological Survey of Norway and Per Inge Myhre from the Norwegian Polar Institute. Photo: Christina Pedersen / Norwegian Polar Institute
Norway in Antarctica
Dronning Maud Land comprises nearly one-sixth of the Antarctic continent and is seven times larger than Norway. This part of Antarctica was annexed by Norway in January 1939 and is now one of Norway’s three dependencies in the southern hemisphere.
Since 1959, the entire Antarctic, including Dronning Maud Land, is managed under the Antarctic Treaty. The Norwegian Polar Institute has managing authority for all Norwegian activity in the Antarctic and is also the national mapping authority in Dronning Maud Land.
Dronning Maud Land is home to Norway’s Troll research station, which is located in Jutulsessen, 1275 metres above sea level at 72°S. The Norwegian Polar Institute also operates Troll Airfield which is a 3000 m long airfield on blue ice, a few kilometres from Troll station.
