DOI: 10.1016/j.tecto.2020.228708
论文题名: Structural and chemical resetting processes in white mica and their effect on K-Ar data during low temperature metamorphism
作者: Akker I.V. ; Berger A. ; Zwingmann H. ; Todd A. ; Schrank C.E. ; Jones M.W.M. ; Kewish C.M. ; Schmid T.C. ; Herwegh M.
刊名: Tectonophysics
ISSN: 00401951
出版年: 2021
卷: 800 语种: 英语
中文关键词: K-Ar
; Metamorphism
; Microstructure
; Phyllosilicates
; Recrystallization
英文关键词: Deformation
; Dissolution
; Fluorescence microscopy
; Grain size and shape
; Isotopes
; Mica
; Precipitation (chemical)
; Recrystallization (metallurgy)
; Scanning electron microscopy
; Silicates
; Temperature
; Accretionary wedge
; Dissolution precipitations
; Dissolution-precipitation process
; Low temperature metamorphism
; Metamorphic conditions
; Physicochemical process
; Synchrotron x-ray fluorescences
; Thermally activated
; Potassium compounds
; accretionary prism
; deformation
; low temperature
; metamorphism
; mica group
; microstructure
; potassium-argon dating
; recrystallization
; resetting
; Europe
英文摘要: White mica has been widely used to date microstructures and tectonic events in faults, shear-zones and folds because of its suitability for radiogenic dating. However, complex (i) microstructural evolution, (ii) individual chemical evolution of the K-bearing phases, (iii) mixing of ‘detrital grains’ with newly formed and/or recrystallized or chemically reset grains as well as (iv) volume diffusion may result in apparent K-Ar ages. Here, specimens from a prograde sediment sequence of the exhumed fossil European Alpine accretionary wedge were used to investigate resetting processes of white mica by the type and intensity of deformation as well as peak metamorphic conditions. We combine the K-Ar system with mass and mineral quantities from grain size fractions to calculate the amount of recrystallized white mica in each grain size fraction along the metamorphic gradient. Increasing recrystallization with increasing metamorphic grade is related to thermally activated pressure solution and dissolution-precipitation creep, as seen by the formation of a spaced cleavage of recrystallized phyllosilicates documented through Synchrotron X-ray Fluorescence Microscopy and Scanning Electron Microscope imaging techniques. Increasing recrystallization by dissolution-precipitation processes induces chemical resetting of the isotopic system, resulting in a prograde decrease of apparent K-Ar ages. We demonstrate that Ar volume diffusion does not play a significant role for the low-temperature samples, promoting recrystallization as the important physico-chemical process for age resetting. However, white mica chemistry reveals that no simple relation between isotopic resetting and grain size exists along the prograde path. Reliable age information can therefore only be obtained in the case of (nearly) complete resetting, which accounts only for the smallest grain size fraction at the highest metamorphic temperature. These findings could shed new light on accurate dating of mica-rich fault rocks, where the time constraints depend not only on the temperature, but also on the amount and type of deformation. © 2021 Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/170763
Appears in Collections: 气候变化与战略
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作者单位: Institute of Geological Sciences, University of Bern, Bern, Switzerland; Division of Earth and Planetary Sciences, Graduate School of Science Kyoto University, Kyoto, Japan; Commonwealth Scientific and Industrial Research Organisation (CSIRO), Earth Science and Resource Engineering, Bentley, Australia; School of Earth and Atmospheric Sciences, Queensland University of TechnologyQueensland 4000, Australia; Central Analytical Research Facility, Institute of Future Environments, Queensland University of TechnologyQueensland 4000, Australia; Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe UniversityVictoria 3086, Australia; Australian Nuclear Science and Technology Organisation, Australian SynchrotronVictoria 3168, Australia
Recommended Citation:
Akker I.V.,Berger A.,Zwingmann H.,et al. Structural and chemical resetting processes in white mica and their effect on K-Ar data during low temperature metamorphism[J]. Tectonophysics,2021-01-01,800