Baltic Shield
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The Baltic Shield (or Fennoscandian Shield) is a segment of the Earth's crust belonging to the East European Craton, representing a large part of Fennoscandia, northwestern Russia and the northern Baltic Sea. It is composed mostly of Archaean and Proterozoic gneisses and greenstone which have undergone numerous deformations through tectonic activity. It contains the oldest rocks of the European continent with a thickness of 250-300 km.
The Baltic Shield is divided into five provinces: the Svecofennian and Sveconorwegian (or Southwestern gneiss) provinces in Fennoscandia, and the Karelian, Belmorian and Kola provinces in Russia. The latter three are divided further into several blocks and complexes and contain the oldest of the rocks, at 2500-3100 Ma (million years) old. The youngest rocks belong to the Sveconorwegian province, at 900-1700 Ma old. Sometimes included as part of the Baltic Shield is the East European Platform (or Russian Platform), an area of western Russia covered by 3 km of sedimentary rock.
Thought to be formerly part of an ancient continent, the Baltic Shield grew in size through collisions with neighbouring crustal fragments. The mountains created by this tectonic processes have since been eroded to their bases, the region being largely flat today. Through five successive Pleistocene glaciations and subsequent retreats, the Baltic Shield has been scoured clean of its overlying sediments, leaving expansive areas (most within Scandinavia) exposed. It is therefore of importance to geophysicists studying the geologic history and dynamics of eastern Europe.
The scouring and compression of the Baltic Shield by glacial movements created the area's many lakes and streams, the land retaining only a thin layer of sandy sediment collected in depressions: Vast forests of pine dominate, clearly demarcating its boundaries.
The Baltic Shield yields important industrial minerals and ores, such as those of iron, nickel, copper and platinum group metals. Because of its similarity to the Canadian Shield and cratons of southern Africa and Western Australia, the Baltic Shield had long been a suspected source of diamonds and gold. Currently, especially the Central Lapland Greenstone Belt in the north is considered to be an unexplored area that has the potential to hold exploitable gold deposits.
Recent exploration by De Beers and others has revealed a significant number of diamond-bearing kimberlites in the Kola Peninsula, and (possibly extensive) deposits of gold in Finland. In Sweden, Alcaston Diamond NL is presently conducting a diamond exploration project, claiming some 9,550 square kilometres.
See also
External links
- Rb-Sr Data for Diamond-Bearing Kimberlite and Alkaline Massives in NE Fennoscandia (http://www.the-conference.com/JConfAbs/4/426.html)
- Precambrian evolution of the major Archaean blocks of the Baltic Shield (http://www.google.ca/search?q=cache:hKH5el0IIkwJ:www.student.oulu.fi/~pevins/Archaean.html+%22the+baltic+shield+is%22&hl=en&ie=UTF-8) (Google cached file)
- Geology of Fennoscandia (http://www.nrm.se/lig/fennmap.html.en)
- Why does the East European Platform has (sic) 3 km of sediments? Insights from lithospheric structure, thermal regime, and composition (http://www.cosis.net/abstracts/EAE03/02239/EAE03-J-02239.pdf) (PDF file)sv:Fennoskandia