P-wave anisotropy in eclogites and relationship to the omphacite crystallographic fabric |
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| Institution: | 1. Department of Physics and Geosciences, Texas A&M University-Kingsville, Kingsville, TX 78363, USA;2. School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8W 2Y2, Canada;3. Ocean Networks Canada, University of Victoria, Victoria, BC V8W 2Y2, Canada;4. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, Kiel 24105, Germany;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;3. Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China;4. Department of Geophysics, Faculty of Science, Cairo University, Giza, Egypt;5. Physics of the Earth, University of Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain |
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| Abstract: | Measurements of P-wave velocity at room temperature and confining pressures up to 500 MPa were carried out on three eclogite mylonites collected from a shear zone in the Monviso area (Western Alps). P-wave velocities at a pressure of 400 MPa range from 7.7 km/s to 7.9 km/s, yielding to a maximum anisotropy of 6%. From the CPO of omphacite we estimated a maximum contribution of omphacite to the P-wave anisotropy of only 1.3%. These results suggest that primarily the compositional layering and secondary the fabric of minor constituent minerals significantly contribute to the seismic anisotropy. Because of the anisotropy, the seismic reflectivity of subduction zones may vary with the direction of observation. |
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