The Fen complex in Nome

Nome, Norway

Nome is a municipality in Telemark county, Norway. It is part of the traditional region of Midt-Telemark. The administrative centre of the municipality is the village of Ulefoss....

, Telemark

Telemark

is a county in Norway, bordering Vestfold, Buskerud, Hordaland, Rogaland and Aust-Agder. The county administration is in Skien. Until 1919 the county was known as Bratsberg amt.-Location:...

, Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

 is a region noted for an unusual suite of igneous rocks. Several varieties of carbonatite

Carbonatite

Carbonatites are intrusive or extrusive igneous rocks defined by mineralogic composition consisting of greater than 50 percent carbonate minerals. Carbonatites may be confused with marble, and may require geochemical verification....

 are present in the area as well as lamprophyre

Lamprophyre

Lamprophyres are uncommon, small volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks and small intrusions...

, ijolite

Ijolite

Ijolite , is an igneous rock consisting essentially of nepheline and augite. Ijolite is a rare rock type of considerable importance from a mineralogical and petrological standpoint...

 and other highly alkalic rocks. It is the type locality for fenite, a metasomatic

Metasomatism

Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...

 rock commonly found around carbonatite and alkali intrusives.

The Fen complex is a roughly circular area about three kilometres in diameter. It is located just west of the Oslo graben

Oslo Graben

The Oslo Graben or Oslo Rift is a graben formed during a geologic rifting event in Permian time, the last phase of the Variscan orogeny. The main graben forming period began in the late Carboniferous, which culminated with rift formation and volcanism, with associated rhomb porphyry lava flows...

. Radiometric age dating on the carbonatites gave an age of 539 +/- 14 Myr. The host rocks for the intrusions are middle Proterozoic

Proterozoic

The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...

 granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

s and gneiss

Gneiss

Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...

 and the complex was associated with the Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 rift

Rift

In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....

ing of the craton

Craton

A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

ic rocks.

The complex is a protected location because of the rare minerals and rock types found there. The rocks were first described by Waldemar Christofer Brøgger in 1921.