Oskarshamn Jönköping belt

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The Oskarshamn-Jönköping Belt (short: OJB, from English Oskarshamn-Jönköping belt ) is a craton (small continent) and a tectonic unit of the Baltic Shield . This relatively small unit is located within the Trans-Scandinavian Magmatite Belt and differs in its lithology.

Map of the Baltic Shield. The OJB ( ) is located within the Trans-Scandinavian Magmatite Belt ( ). It extends roughly from Lake Vättern to Oskarshamn. For orientation purposes, the northern tip of Öland can be taken as the southeastern end .

Regional geological overview

The Baltic Shield can be divided into four groups of different ages. On the North Sea and in East Karelia are the archaic Saamids with an age of approximately 3–2.5 Ga. Between the Saamids are the Belmorids on the White Sea, which consist of highly metamorphic gneiss that were overprinted 2  Ga . Most of the Baltic Shield belongs to the Svekofennids, which were consolidated by orogeny 1.8 Ga ago. This unit stretches from Lake Ladoga to Sweden at the geographic height of Gotland. The youngest part of the shield are the Svekonorwegids. The last orogenesis took place about 1 Ga ago.

Genesis, Lithology and Tectonics

The unit of the OJB was integrated into the TIB by accretion and intrusion. The contact between the OJB and the TIB cannot be established in the field, as it is either covered by the granites and volcanic rocks of the TIB or separated by shear zones. The latter run mainly NW-SE. The OJB stands out from the surrounding granites , rhyolites and andesites by the composition of metasedimentites and metavolcanites.

The origin of the OJB probably lies in an arch of the islands, which grew over time through accretion (Andersson et al., 2004).

This belt was deformed before the TIB's magmatites intruded 1.81–1.77 Ga. Following the OJB magmatism, magmatism took place in TIB1 (1813–1766 Ma), the lithologies of which, together with those of TIB2 (1723–1691 Ma) and TIB3 (1681–1657 Ma), partially covered the OJB.

Later on, new magmatites formed occasionally, the youngest being 1,450 Ma old.

The magmas of the TIB come from the melting of rocks on destructive plate edges. These magmas led to volcanic and plutonic phenomena of the Andean type.

Deposits

Due to its lithology and the intrusion of acid igneous rocks, the OJB contains several formerly important ore deposits, such as the Kleva gruva copper deposit . Historically more important is the former gold deposit of Ädelfors , which was the first gold mine in Sweden and, due to its importance, was directly subordinate to the Swedish state. Mining began here around 1739 and lasted with interruptions until 1898 (Thorin and Lennart, 2008). Despite the high gold content of up to 140 ppm in the core area, mining became unprofitable due to the changed technical possibilities.

There are also over a hundred small mines or pings in the area around Kleva gruva and Ädelfors .

Individual evidence

  1. ↑ a b Peter Faupl: Historical Geology. An introduction (= UTB . 2149). 2nd, improved edition. facultas wuv, Vienna 2003, ISBN 3-8252-2149-0 .
  2. ↑ a b Annakaisa Korja, Pekka Heikkinen: The accretionary Svecofennian orogen-insight from the BABEL profiles. In: Precambrian Research . Vol. 136, No. 3/4, 2005, pp. 241-268, doi: 10.1016 / j.precamres.2004.10.007 .
  3. ↑ Andersson, Ulf B, Roland Gorbatschev, A. Wikström, Karin Högdahl, m. Ahl, J.-O. Nyström, Håkan Sjöström, Stefan Bergmann, Olav Eklund, Dick Claeson, Joakim Mansfeld, Mikael B. Stephens, Carl-Henric Wahlgren, T. Lundqvist, S.-A. Smeds, K. Sundblad, Björn Öhlander: The Transscandinavian Igneous Belt in Sweden: a review of its character and evolution. In: Geological Survey of Finland. Special Paper 37, 2004.
  4. ↑ Raimo Lahtinen, Mikko Nironen: Paleoproterozoic lateric paleosol-ultra-mature / mature quarzite-meta-arkose succsessions in southern Fennoscandia-intra-orogenig stage during the Svecofennian orogen. In: Precambrian Research. Vol. 183, No. 4, 2010, pp. 770-790, doi: 10.1016 / j.precamres.2010.09.006 .
  5. ↑ a b Jan Lundqvist, Thomas Lundqvist, Maurits Lindström, Mikael Calner, Ulf Sivhed: Sveriges Geologi från urtid till nutid. 3. Edition. Student literature, Lund 2011, ISBN 978-91-44-05847-4 .
  6. ↑ Lennart Thorin: Bergsbruket i Kleva, Ädelfors, Sunnerskog och Lessebo. In: Bergsverkrelation. No. 5, Författares Bokmaskin, Stockholm 2008.

See also