DOI: 10.1016/j.tecto.2021.229005
论文题名: Seismic properties across an amphibolite- to greenschist-facies strain gradient (Neves area, eastern Alps, Italy): New considerations for shear zone imaging
作者: Leydier T. ; Goncalves P. ; Albaric J. ; Leclère H. ; Mahan K.H. ; Faulkner D.
刊名: Tectonophysics
ISSN: 00401951
出版年: 2021
卷: 816 语种: 英语
中文关键词: EBSD
; Seismic anisotropy
; Shear zone
; Ultrasonic measurements
英文关键词: Anisotropy
; Feldspar
; Mica
; Seismic prospecting
; Seismic waves
; Seismology
; Shear waves
; Silicates
; Structural geology
; Wave propagation
; Electron backscatter diffraction methods
; Further deformations
; Intrinsic parameters
; Mineral transformations
; Mineralogical changes
; Nonlinear evolutions
; Orthorhombic symmetry
; Pressure-temperature conditions
; Shear flow
; amphibolite facies
; greenschist facies
; P-wave
; S-wave
; seismic anisotropy
; seismic property
; seismic velocity
; shear zone
; strain analysis
; wave propagation
; wave splitting
; Alps
; Eastern Alps
; Italy
英文摘要: Detecting the presence and geometry of crustal shear zones by geophysical methods relies on our understanding of the intrinsic parameters controlling the seismic properties of these deformed rocks, over the range of pressure-temperature conditions expected in the Earth's crust. To this end, we aimed to track changes in P-wave propagation velocity (VP), anisotropy (AVP) and S-wave splitting (AVS) across a natural shear zone using experimental and electron backscatter diffraction methods. Five samples were collected across a meter-scale shear zone developed under amphibolite- to greenschist-facies in the Neves metagranodiorite (Tauern Window, Eastern Alps). With increasing strain, seismic properties show a non-linear evolution resulting from interactions among structural, textural and mineralogical changes. Geometry and magnitude of seismic anisotropy are controlled by the interference of strongly anisotropic phyllosilicates with less anisotropic but more abundant quartz and plagioclase. The amphibolite-facies shear zone margin (> 500 °C) is free of major mineral transformations, and rather characterized by the development of S-C structure, inducing an orthorhombic symmetry to the VP distribution and up to 12 % AVP, with the fast axis parallel to lineation. AVS is maximized (6 %) in the two directions parallel to the C-planes. Further deformation under greenschist-facies (450–500 °C) induces significant crystallization of muscovite, chlorite, and albite. A dominant hexagonal symmetry develops, with a fast VP plane and a fast S-wave polarization plane along the C-planes. AVP and AVS exceed 10 %. The computed elastic tensor of the whole shear zone emphasizes the importance of the strain gradient on the seismic signature of the overall structure. In our model, the bulk seismic properties are dominated by the orthorhombic symmetry of the protomylonitic zone rather than by the ultramylonite core with hexagonal symmetry (C-plane), which may explain why seismic studies of shear zones commonly involve a fast velocity plane oblique to the layer boundaries. © 2021 Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/170836
Appears in Collections: 气候变化与战略
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作者单位: Université de Bourgogne Franche-Comté, UMR-CNRS 6249 Laboratoire Chrono-Environnement, 16 route de Gray, Besancon, 25000, France; Department of Geological Sciences, University of Colorado Boulder, 2200 Colorado Ave, Boulder, CO 80309, United States; Department of Earth and Ocean Sciences, University of Liverpool, 4 Brownlow Street, Liverpool, L69 3GP, United Kingdom
Recommended Citation:
Leydier T.,Goncalves P.,Albaric J.,et al. Seismic properties across an amphibolite- to greenschist-facies strain gradient (Neves area, eastern Alps, Italy): New considerations for shear zone imaging[J]. Tectonophysics,2021-01-01,816