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Relationship between 1.90–1.85 Ga accretionary processes and 1.82–1.80 Ga oblique subduction at the Karelian craton margin, Fennoscandian Shield
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0003-3879-3897
Swedish Museum of Natural History.
Swedish Museum of Natural History.
Uppsala University.
2002 (English)In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 124, no 3, p. 163-180Article in journal (Refereed) Published
Abstract [en]

The three main intrusive suites: early calc-alkaline, late I/Atype, and late S-type intrusive rocks in relation to the Svecokarelian orogeny (1.9–1.8 Ga) have been dated at the Archaean craton margin in the Palaeoproterozoic Skellefte district and surrounding areas in northern Sweden. In addition, new SIMS data have been obtained on a calcalkaline intrusion for which unusually young TIMS ages existed, compared to similar calc-alkaline intrusions elsewhere in the region. Titanite and zircon from a subvolcanic intrusion affected by a major N–S trending shear zone have also been dated to constrain the last ductile deformation in the area. The 1895+14–12 Ma zircon age for a calc-alkaline intrusion is interpreted as the crystallisation age and is significantly older than the existing 1825 Ma age on titanite from a pyroxene skarn in a marble horizon close to the contact. The latter age is instead interpreted as the age of peak metamorphism in this area. The 1798±4 Ma age for the S-type granite confirms that the S-type magmatism is largely coeval with the I/A type magmatism previously dated at 1803±6 Ma. At a larger scale, a zoned belt over 2000 km long with A/I-type magmatism in the west and S-type magmatism in the east can be inferred. Either mafic underplating or Cordilleran type settings can explain the magmatic belt, which trends oblique to the roughly NE-directed subduction that led to the accretion of volcanic arcs onto the older craton between 1.95 and 1.87 Ga. An intimate temporal relationship between the extensive 1.80 Ga magmatism and regional N–S-trending shear zones in the area is confirmed by the titanite age of c. 1.80 Ga from one such shear zone. Kinematics on this shear zone suggest E–W shortening. SIMS data from a calc-alkaline intrusion at Sikträsk indicate that the previously obtained conventional zircon ages of 1.85–1.86 Ga are actually mixed ages of 1.88 Ga magmatic zircons, and c. 1.80 to 1.82 Ga metamorphic overgrowths. This shows that the 1.80 Ga event was not only constrained to shear zones. It is argued that both the 1.80 to 1.82 Ga deformation and metamorphism discussed here is related to E-W shortening and the voluminous magmatism at 1.82–1.80 Ga. This is in contrast to the older c. 1.88 Ga deformation identified to the north and east within the Karelian craton that was related to Svecokarelian accretionary processes.

Place, publisher, year, edition, pages
2002. Vol. 124, no 3, p. 163-180
National Category
Geology
Research subject
Ore Geology
Identifiers
URN: urn:nbn:se:ltu:diva-4738DOI: 10.1080/11035890201243163Local ID: 2bab15f0-7b34-11db-8824-000ea68e967bOAI: oai:DiVA.org:ltu-4738DiVA, id: diva2:977612
Note
Validerad; 2002; 20061123 (bajo)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-03-15Bibliographically approved

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Publisher's full texthttp://www.gff-online.se/site/article.asp?articleID=780

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Weihed, Pär

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