Tracing arclogites in the Paleoproterozoic Era - A shift from 1.88 Ga calc-alkaline to 1.86 Ga high-Nb and adakite-like magmatism in central Fennoscandian Shield

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Kara , J , Väisänen , M , Heinonen , J S , Lahaye , Y , O'Brien , H & Huhma , H 2020 , ' Tracing arclogites in the Paleoproterozoic Era - A shift from 1.88 Ga calc-alkaline to 1.86 Ga high-Nb and adakite-like magmatism in central Fennoscandian Shield ' , Lithos , vol. 372 , 105663 . https://doi.org/10.1016/j.lithos.2020.105663

Title: Tracing arclogites in the Paleoproterozoic Era - A shift from 1.88 Ga calc-alkaline to 1.86 Ga high-Nb and adakite-like magmatism in central Fennoscandian Shield
Alternative title: Paleoproterotsooisten arclogiittien jäljillä - Muutos 1.88 Ga kalkkialkalisesta magmatismista 1.86 Ga korkean Nb:n ja adakiitti-tyyppiseen magmatismiin Fennoskandian kilven keskiosissa
Author: Kara, Jaakko; Väisänen, Markku; Heinonen, Jussi S.; Lahaye, Yann; O'Brien, Hugh; Huhma, Hannu
Contributor organization: Petrology and Geochemistry
Department of Geosciences and Geography
Date: 2020-11-01
Language: eng
Number of pages: 21
Belongs to series: Lithos
ISSN: 0024-4937
DOI: https://doi.org/10.1016/j.lithos.2020.105663
URI: http://hdl.handle.net/10138/346369
Abstract: Arclogites, i.e., lower crustal gamet-pyroxenite cumulates, are suggested to play an important role in controlling magma differentiation in modem continental arcs. Until now, arclogite-related magmatism has only been described from the Phanerozoic Era. The Svecofennian orogen in the central Fennoscandian Shield hosts a rare association of 1.86 Ga igneous rocks geochemically distinct from the surrounding and much more abundant 1.90-1.87 Ga subduction-related talc-alkaline magmatism. The 1.86 Ga magmatic rocks are divided into three groups: 1) high-Nb gabbros (HNB) which are enriched in Fe2O3T, TiO2, P2O5, F. LILE, and HFSE (especially Nb: 18.9-44 ppm), show positive initial epsilon(Nd) value, and near-chondritic but variable initial zircon epsilon(Hf) values; 2) high-Mg gabbros (HMG) which are characterised by high MgO, CaO, Cr and Ni contents, slight enrichment in LILE, positive epsilon(Hf), and positive but variable zircon epsilon(Hf) values; 3) adakite-like rocks showing high Al2O3 and Na2O contents, slight enrichment in LILE, relative depletion in some HFSE, positive CNd value, and chondritic to negative zircon epsilon(Nd) values. The three groups yield zircon U-Pb ages of similar to 1.86 Ga and exhibit undeformed textures in contrast to the surrounding supracrustal rocks metamorphosed at similar to 1.88 Ga. The ages and compositions are dearly different from the adjacent 1.90-1.87 Ga arc-related igneous rocks suggesting a distinct origin. Despite similar ages and close spatial relationship, separate sources are required for each of the different 1.86 Ga rock groups. Trace element modelling of partial melting suggests that arclogites, with compositions similar to pyroxenite xenoliths found in the kimberlite pipes of eastern Finland, are the source for the HNB rocks. In contrast, subduction-modified mantle peridotite is the source for the HMG rocks, and a mafic lower crustal source is suggested for the adakite-like rocks. The following geodynamic model is suggested: (rutile-bearing) arclogite formation at 1.90-1.87 Ga followed by arclogite delamination and partial melting during extension of the thickened Svecofennian crust at 1.86 Ga. (C) 2020 Elsevier B.V. All rights reserved.
Subject: 1171 Geosciences
Arclogite
High-Nb gabbro
Svecofennian orogen
Geochemistry
Sm-Nd isotopes
Zircon U-Pb-Hf isotopes
FINLAND GRANITOID COMPLEX
PB ZIRCON AGES
U-PB
VOLCANIC-ROCKS
SIERRA-NEVADA
ELEMENT FRACTIONATION
BASALTIC MAGMATISM
CONTINENTAL-CRUST
GARNET PYROXENITE
HF ISOTOPES
Peer reviewed: Yes
Rights: cc_by_nc_nd
Usage restriction: openAccess
Self-archived version: acceptedVersion


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