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Long story encrypted in a small grain – zircon from meta-andesite in the Lower Köli Nappes reveals a complex history of the Virisen Arc Terrane, Scandinavian Caledonides, Sweden

Katarzyna A. Walczak

Katarzyna A. Walczak

AGH University of Krakow, Faculty of Geology, Geophysics and Environmental ProtectionKraków, Poland
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Walczak, Katarzyna A.
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Adam Włodek

Adam Włodek

AGH University of Krakow, Faculty of Geology, Geophysics and Environmental ProtectionKraków, Poland
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Włodek, Adam
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Simon Cuthbert

Simon Cuthbert

AGH University of Krakow, Faculty of Geology, Geophysics and Environmental ProtectionKraków, Poland
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Cuthbert, Simon
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Isabel S. M. Carter

Isabel S. M. Carter

  • AGH University of Krakow, Faculty of Geology, Geophysics and Environmental ProtectionKraków, Poland
  • Department of Earth Sciences, Uppsala UniversityUppsala, Sweden
  • Geological Survey of NorwayTrondheim, Norway
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Carter, Isabel S. M.
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Grzegorz Ziemniak

Grzegorz Ziemniak

Institute of Geological Sciences, University of WrocławWrocław, Poland
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Ziemniak, Grzegorz
  
Apr 18, 2025
Long story encrypted in a small grain – zircon from meta-andesite in the Lower Köli Nappes reveals a complex history of the Virisen Arc Terrane, Scandinavian Caledonides, Sweden's Cover Image
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Article Category: Letter
Published Online: Apr 18, 2025
Page range: 34 - 43
Received: Oct 03, 2024
Accepted: Feb 24, 2025
DOI: https://doi.org/10.2478/mipo-2025-0005
Keywords
© 2025 Katarzyna A. Walczak et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.

Figure 1.

A) The whole U-Pb data set from Carter et al. 2023 (no selection) plotted on the Tera-Wasserburg concordia diagram. B) Zircon 206Pb/238U ages (Carter et al., 2023) versus their discordance (Disc [%] = (207Pb/206Pb age - 206Pb/238U age) ∙ (206Pb/238U age)−1 ∙ 100), analyses placed in mantles (m) and cores (c).
A) The whole U-Pb data set from Carter et al. 2023 (no selection) plotted on the Tera-Wasserburg concordia diagram. B) Zircon 206Pb/238U ages (Carter et al., 2023) versus their discordance (Disc [%] = (207Pb/206Pb age - 206Pb/238U age) ∙ (206Pb/238U age)−1 ∙ 100), analyses placed in mantles (m) and cores (c).

Figure 2.

Backscattered electron (BSE) images of studied zircon grains with visible inclusions of apatite (Ap), epidote (Ep), chlorite (Chl), albite (Ab), quartz (Qz), titanite (Ttn) and thorite (Thr). Image D represents magnified fragment from the frame on picture C. The white scale bars are 10 µm.
Backscattered electron (BSE) images of studied zircon grains with visible inclusions of apatite (Ap), epidote (Ep), chlorite (Chl), albite (Ab), quartz (Qz), titanite (Ttn) and thorite (Thr). Image D represents magnified fragment from the frame on picture C. The white scale bars are 10 µm.

Figure 3.

Representative cathodoluminescence (CL) images of analysed zircon grains showing variability of zircon internal structures.
Representative cathodoluminescence (CL) images of analysed zircon grains showing variability of zircon internal structures.

Figure 4.

Backscattered electron (BSE) images, Y, Hf and U distribution maps and concentration profiles for representative zircon grains. Yellow arrows indicate the course of the profile. Blue circles represent U-Pb analytical points from Carter et al. (2023). The coloured scale bar: warmer colours indicate higher relative abundance of element (higher signal intensity). In Fig. 3 you can find CL images of the analysed crystals: A = Fig. 3.F, B = Fig. 3.J, C = Fig. 3.E.
Backscattered electron (BSE) images, Y, Hf and U distribution maps and concentration profiles for representative zircon grains. Yellow arrows indicate the course of the profile. Blue circles represent U-Pb analytical points from Carter et al. (2023). The coloured scale bar: warmer colours indicate higher relative abundance of element (higher signal intensity). In Fig. 3 you can find CL images of the analysed crystals: A = Fig. 3.F, B = Fig. 3.J, C = Fig. 3.E.

Figure 5.

Examples of amphibolite-felsite mingling observed in the Ankarede Volcanite Formation of the Lower Köli Nappe Complex close to Ankarede (64.81717616° N, 14.21804096° E). The field photographs show mingled amphibolite–felsite (A), a close-up of mingled amphibolite-felsite (B) and mingled rock viewed perpendicular to a lineation - stretching direction (C).
Examples of amphibolite-felsite mingling observed in the Ankarede Volcanite Formation of the Lower Köli Nappe Complex close to Ankarede (64.81717616° N, 14.21804096° E). The field photographs show mingled amphibolite–felsite (A), a close-up of mingled amphibolite-felsite (B) and mingled rock viewed perpendicular to a lineation - stretching direction (C).

Figure 6.

The summary of zircon growth history: 1. High Y and HREE magmatic zircon growth (the cores; dark navy blue). 2. The abrupt change in magma chemistry due to magma mingling or the crystallisation of other minerals competing for Y and HREE. Further growth of low-Y zircon (the mantles; blue). 3. Formation of high-U rims (grey-blue). 4. The high-U rims and adjacent zones accumulate radioactive damage, their internal structure is partially damaged and pathways for fluid infiltration are created. 5. Hydrothermal fluid infiltrate metamict zones causing alterations; dissolution of zircon rim and precipitation of new, porous zircon rims. High U concentration is inherited by the newborn zircon. Yttrium is resorbed into a non-altered zircon forming a high-Y band (yellow).
The summary of zircon growth history: 1. High Y and HREE magmatic zircon growth (the cores; dark navy blue). 2. The abrupt change in magma chemistry due to magma mingling or the crystallisation of other minerals competing for Y and HREE. Further growth of low-Y zircon (the mantles; blue). 3. Formation of high-U rims (grey-blue). 4. The high-U rims and adjacent zones accumulate radioactive damage, their internal structure is partially damaged and pathways for fluid infiltration are created. 5. Hydrothermal fluid infiltrate metamict zones causing alterations; dissolution of zircon rim and precipitation of new, porous zircon rims. High U concentration is inherited by the newborn zircon. Yttrium is resorbed into a non-altered zircon forming a high-Y band (yellow).
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