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1.90-1.88 Ga arcmagmatism of central Fennoscandia: geochemistry, U-Pb geochronology, Sm-Nd andLu-Hf isotope systematics of plutonic-volcanic rocks from southern Finland.
University of Turku.
University of Turku .
Swedish Museum of Natural History, Department of Geology.ORCID iD: 0000-0002-1598-5231
Geological Survey of Finland (GTK).
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2018 (English)In: Geologica Acta, ISSN 1695-6133, E-ISSN 1696-5728, Vol. 16, no 1, p. 1-23Article in journal (Refereed) Published
Abstract [en]

The earliest Svecofennian magmatism in southern Finland has been dated to 1.90-1.88Ga. As an example of this, the Orijärvi (ca. 1.89Ga) and Enklinge (ca. 1.88Ga) volcanic centres comprise bimodal plutonic batholiths surrounded by volcanic rocks of comparable ages and chemical compositions. The rock types range from gabbros to granites and indicate a subduction-related continental margin setting. The zircons from the Orijärvi granodiorite define an age of 1892±4Ma whereas the Enklinge granodiorite yields an age of 1882±6Ma. Several inherited ages of 2.25-1.95Ga as well as younger metamorphic ages of 1.86-1.80Ga were found in the Enklinge granodiorite. The initial εNd values of the mafic rocks from both locations fall in the range +1.1 to +2.9, whereas the felsic rocks exhibit initial εNd values of -0.4 to +1.2. The magmatic zircons from the Orijärvi and Enklinge granodiorites show average initial εHf values of -1.1 (at 1892Ma) and zero (at 1882Ma), respectively, both with a spread of about 7 ε-units. The initial εHf values for the inherited zircons from Enklinge range from +3.5 to +7.6 with increasing age. The Sm-Nd data indicate that the mafic rocks were derived from a “mildly depleted” mantle source while the felsi rocks show some crustal contribution. Also, the variation in ε Hf values indicates minor mixing between mildly depleted mantle-derived magmas and crustal sources. U-Pb ages and Hf isotopes for inherited zircons from the Enklinge granodiorite suggest the presence of juvenile Svecofennian “proto-crust” at depth

Place, publisher, year, edition, pages
2018. Vol. 16, no 1, p. 1-23
Keywords [en]
Fennoscandian shield. Svecofennian orogeny. Lu-Hf. U-Pb. Sm-Nd. Geochemistry
National Category
Geology
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-2779DOI: DOI: 10.1344/GeologicaActa2018.16.1.1.OAI: oai:DiVA.org:nrm-2779DiVA, id: diva2:1195630
Available from: 2018-04-06 Created: 2018-04-06 Last updated: 2018-04-06

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Publisher's full texthttp://revistes.ub.edu/index.php/GEOACTA/article/view/GeologicaActa2018.16.1.1/22435

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