The Fen Complex ( Norwegian : Fensfeltet ) in Nome , Telemark , Norway is a region noted for an unusual suite of igneous rocks . Several varieties of carbonatite are present in the area as well as lamprophyre , ijolite and other highly alkalic rocks. It is the type locality for fenite , a metasomatic rock commonly found around carbonatite and alkali intrusives.
6-514: The Fen Complex is a roughly circular area about three kilometres in diameter. It is located just west of the Oslo graben . Radiometric age dating on the carbonatites gave an age of 539 +/- 14 Myr. The host rocks for the intrusions are middle Proterozoic granites and gneiss and the complex was associated with the Cambrian rifting of the cratonic rocks. The complex is a protected location because of
12-539: A rare view of what goes on beneath a rift valley . Several of the old magma plumes are now quarried, the rich black larvikite (named from Larvik , a town south of Oslo) being one. The Särna alkaline complex in western Sweden, also of Late Carboniferous age, is thought to be related to the Oslo Graben as it is aligned to it. 59°48′04″N 10°33′23″E / 59.8011°N 10.5564°E / 59.8011; 10.5564 This Norway location article
18-513: 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. This activity was followed by uplifting , and ended with intrusions about 65 million years after the onset of the formation. It
24-516: Is located in the area around the Norwegian capital Oslo . The lava production was high when the rhomb porphyry lavas were deposited. The lavas reflect a period of abundant earthquake-related movements, when tectonic forces tore the crust apart. In the Vestfold district, one lava flow was deposited on average every 250,000 years, resulting in a 3000-metre thick sequence of mainly volcanic material. In
30-494: The Oslo area, lavas were deposited on average every 800,000 years. Only a few plant remains have been found between these lavas. The bedrock in this area, roughly from Skien to Oslo and Mjøsa , results in soil rich in nutrients important for plant growth. Since the Permian, erosion has removed the volcanic peaks and indeed most of the lava layer and laid bare the magma chambers and volcanic pipes deep below, allowing scientist
36-484: The rare minerals and rock types found there. The rocks were first described by Waldemar Christofer Brøgger in 1921. 59°16′04″N 9°16′40″E / 59.2677°N 9.2779°E / 59.2677; 9.2779 This article about a regional geological feature is a stub . You can help Misplaced Pages by expanding it . This Telemark location article is a stub . You can help Misplaced Pages by expanding it . Oslo graben The Oslo Graben or Oslo Rift
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