Moore, J, Beinlich, A, Porter, JK et al. (5 more authors) (2020) Microstructurally controlled trace element (Zr, U–Pb) concentrations in metamorphic rutile: An example from the amphibolites of the Bergen Arcs. Journal of Metamorphic Geology, 38 (1). pp. 103-127. ISSN 0263-4929
Abstract
As a common constituent of metamorphic assemblages, rutile provides constraints on the timing and conditions of rock transformation at high resolution. However, very little is known about the links between trace element mobility and rutile microstructures that result from syn‐metamorphic deformation. To address this issue, here we combine in situ LA‐ICP‐MS and SHRIMP trace element data with EBSD microstructural analyses to investigate the links between rutile lattice distortions and Zr and U–Pb systematics. Furthermore, we apply this integrated approach to constrain further the temperature and timing of amphibolite‐facies metamorphism and deformation in the Bergen Arcs of southwestern Norway. In outcrop, the formation of porphyroblastic rutile in dynamically hydrated leucocratic domains of otherwise rutile‐poor statically‐hydrated amphibolite provides key contextual information on both the ambient conditions of hydration and deformation and the composition of the reactive fluid. Rutile in amphibolite recorded ambient metamorphic temperatures of ~ 590–730°C during static hydration of the granulitic precursor. In contrast, rutile from leucocratic domains in the directly adjacent shear zone indicates that deformation was accompanied by a localized increase in temperature. These higher temperatures are recorded in strain‐free rutile (~600–860°C) and by Zr concentration measurements on low‐angle boundaries and shear bands (620–820°C). In addition, we also observe slight depletions of Zr and U along rutile low‐angle boundaries relative to strain‐free areas in deformed grains from the shear zone. This indicates that crystal‐plastic deformation facilitated the compositional re‐equilibration of rutile upon cooling to slightly below the peak temperature of deformation. Cessation of deformation at mid‐crustal conditions near ~ 600°C is recorded by late stage growth of small (< 150 µm) rutile in the high strain zones. U–Pb age data obtained from the strain‐free and distorted rutile grains cluster in distinct populations of 437.4 ± 2.7 Ma and c. 405–410 Ma, respectively. These different ages are interpreted to reflect the difference in closure for thermally‐induced Pb diffusion between undeformed and deformed rutile during post‐deformation exhumation and cooling. Thus, our results provide a reconstruction of the thermochronological history of the amphibolite‐facies rocks of the Lindås Nappe and highlight the importance of integration of microstructural data during application of thermometers and geochronometers.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2019 John Wiley & Sons Ltd. This is the peer reviewed version of the following article: Moore, J, Beinlich, A, Porter, JK et al. (5 more authors) (2020) Microstructurally controlled trace element (Zr, U–Pb) concentrations in metamorphic rutile: An example from the amphibolites of the Bergen Arcs. Journal of Metamorphic Geology, 38 (1). pp. 103-127, which has been published in final form at https://doi.org/10.1111/jmg.12514. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | amphibolite; deformation microstructures; high diffusivity pathways; U–Pb geochronology; Zr‐in‐rutile thermometry |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 13 Nov 2019 15:47 |
Last Modified: | 01 Nov 2020 01:38 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1111/jmg.12514 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:153407 |