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The geology in Magma Geopark
Igneous rocks belonging to the Rogaland Anorthosite Province were intruded into gneisses of the Sveconorwegian orogenic belt in southern Norway, The granites and gneisses of Rogaland.
The province comprises:
- Three major anorthosite massifs (Egersund-Ogna, Åna Sira and Håland-Helleren),
- Norway’s largest layered intrusion (Bjerkreim-Sokndal),
- two smaller anorthosite bodies,
- several broadly mangeritic (=hypersthene monzonite) intrusions, charnockites,
- many minor intrusions of jotunite (=hypersthene monzonorite)
- and Egersund dykeswarm
The igneous activity took place over a surprisingly short period of time (at 931±3 Ma) at a depth of ~16-20 km. Contact metamorphism influenced gneisses that had previously reached granulite facies regional metamorphism and produced very high temperature mineral assemblages in the inner aureole. There is a long history of exploitation of iron-titanium ores in the province and it contains the largest active titanium mine in Europe at Tellnes.
The Rogaland Anorthosite Province forms the most important part of the Magma Geopark. The landscapes here are unique with bare, rounded, rocky outcrops stretching for as far as the eye can see. The mining history can be studied at several locations, including Blåfjell (titanium), Gursli, Liland (molybdenum) and Ørsdalen (tungsten and molybdenum). The landscape was strongly influenced by the Ice Age and many glacial features are well preserved, including chatter marks, glacial striations, perched erratics, end moraines, an esker (the superbly exposed St. Olav´s Orm) and many rock falls (including the huge block field in Gloppedal).
The granites and gneisses of Rogaland
The granites and gneisses of Southern Norway are commonly thought to have formed in the process of two continental plates colliding during the creation of the supercontinent Rodinia (about 1000 million years ago) (Figure 1). This continuous collision folded up a mountain chain that was once similar to the Himalayas today, but now is long gone. However, new research suggests a more likely hypothesis for the geological evolution of the area during the creation of Rodinia.
The rocks surrounding the Rogaland Igneous Complex comprise a variety of gneisses and granites, formed between 1500 and 920 million years ago. Intrusion of the Rogaland Igneous Complex marks the end of this nearly 600 million year-long history. Most of the continental crust in south Norway formed during this time interval. The gneisses originally formed as magmatic and sedimentary rocks between 1500 and 1200 million years ago.
During the Sveconorwegian orogeny (orogeny = mountain building), between 1100 and 920 million years ago, these rocks were metamorphosed at very high temperatures and turned into gneisses. At the same time, they were intruded by large volumes of granite. The granites form a more than 50 km-wide belt that runs from the southern tip of Norway and all the way up along the coast of western Norway. Recent studies of the Sveconorwegian orogeny suggest that if formed in much the same way as the Andes mountain chain (Figure 2). Here, the oceanic crust underlying the Pacific ocean sinks beneath the west coast of South America, triggering massive volcanism and mountain building along the South American margin. The oceanic crust that sank under the western margin of Norway roughly a billion years ago is long gone, but the effects can still be observed in the rocks in Rogaland and the rest of south Norway.