University of Oulu

Kärenlampi, K., Kontinen, A., Huhma, H., Hanski, E. (2019). Geology, geochronology and geochemistry of the 2.05 Ga gneissic A1-type granites and related intermediate rocks in central Finland: implication for the tectonic evolution of the Karelia craton margin. Bulletin of the Geological Society of Finland, 91(1), 35–73. https://doi.org/10.17741/bgsf/91.1.002

Geology, geochronology and geochemistry of the 2.05 Ga gneissic A1-type granites and related intermediate rocks in central Finland : implication for the tectonic evolution of the Karelia craton margin

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Author: Kärenlampi, Kimmo1; Kontinen, Asko2; Huhma, Hannu2;
Organizations: 1Oulu Mining School, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland
2Geological Survey of Finland, P.O. Box 1237, 70211 Kuopio, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 9.7 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2019070222540
Language: English
Published: The Geological Society of Finland, 2019
Publish Date: 2019-07-02
Description:

Abstract

The 2.05 Ga Otanmäki suite represents a globally rare occurrence of Paleoproterozoic non-orogenic A1-type magmatism. It consists of a broad variety of A-type felsic and intermediate igneous rocks including monzodiorites, monzonites, syenites and peralkaline to peraluminous granites, containing both plutonic and subvolcanic members. The suite has chemical characteristics similar to those of A1-type suites formed in intraplate hotspots or continental rifts by differentiation of variably crustally contaminated, mafic mantle-derived magmas. However, compared to the Otanmäki rocks, most A1-type suites are considerably younger.

Unraveling the original geologic setting of the Otanmäki suite is challenging because the suite was disintegrated, deformed and metamorphosed under amphibolite facies conditions (T ~550–600 ºC, P ~4 kbar) during the Svecofennian collisional orogeny (ca. 1900 Ma), i.e., 150–200 Ma after its initial emplacement. As a result, Otanmäki suite rocks are now found as pervasively foliated rocks within two nappe units sandwiched between Archean granitoid gneiss complexes and Paleoproterozoic supracrustal belts. The occurrence of slivers of 1950 Ma ocean-continent-transition ophiolitic rocks in the same thrust belt and the proximity of the Otanmäki suite to the Karelia-Svecofennia margin suggest that the suite records an early stage of a slow, ca. 100-Ma-long extension-rifting process which, at ca. 1950 Ma, eventually led to the final break-up of the Karelia craton and formation of the nascent ocean basin witnessed by the Jormua ophiolite complex.

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Series: Bulletin of the Geological Society of Finland
ISSN: 0367-5211
ISSN-E: 1799-4632
ISSN-L: 0367-5211
Volume: 91
Issue: 1
Pages: 35 - 73
DOI: 10.17741/bgsf/91.1.002
OADOI: https://oadoi.org/10.17741/bgsf/91.1.002
Type of Publication: A1 Journal article – refereed
Field of Science: 1171 Geosciences
Subjects:
Funding: Financial support for this study was provided by the Advanced Materials Doctoral Programme (ADMA-DP) of the University of Oulu, K.H. Renlund Foundation and Tauno Tönning Foundation.
Dataset Reference: Supplementary data
  http://www.geologinenseura.fi/bulletin/Volume91/Karenlampi_etal_Electronic_Appendix_A.xlsx
http://www.geologinenseura.fi/bulletin/Volume91/Karenlampi_etal_Electronic_Appendix_B.xlsx
http://www.geologinenseura.fi/bulletin/Volume91/Karenlampi_etal_Electronic_Appendix_C.xlsx
http://www.geologinenseura.fi/bulletin/Volume91/Karenlampi_etal_Electronic_Appendix_D.docx
http://www.geologinenseura.fi/bulletin/Volume91/Karenlampi_etal_Electronic_Appendix_E.pdf
http://www.geologinenseura.fi/bulletin/Volume91/Karenlampi_et_al_Electronic%20Appendix_F.xlsx
Copyright information: All published content of BGSF is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
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