Zhigang Han Title of Thesis: Correlations
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University of Alberta Library Release Form Name of Author: Zhigang Han Title of Thesis: Correlations between seismic and magnetic susceptibility anisotropy in serpentinized peridotite Degree: Master of Science in Geophysics Year this Degree Granted: 2004 Permission is hereby granted to the University of Alberta Library to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copy- right in the thesis, and except as herein before provided, neither the thesis nor any sub- stantial portion thereof may be printed or otherwise reproduced in any material form whatever without the author’s prior written permission. Zhigang Han 602 Avadh Bhatia Physics Building University of Alberta Edmonton, Alberta Canada, T6G 2J1 [email protected] Date: University of Alberta CORRELATIONS BETWEEN SEISMIC AND MAGNETIC SUSCEPTIBILITY ANISOTROPY IN SERPENTINIZED PERIDOTITE by Zhigang Han A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Geophysics. Department of Physics Edmonton, Alberta Fall 2004 University of Alberta Faculty of Graduate Studies and Research The undersigned certify that they have read, and recommend to the Faculty of Graduate Studies and Research for acceptance, a thesis entitled Correlations between seismic and magnetic susceptibility anisotropy in serpentinized peridotite submitted by Zhigang Han in partial fulfillment of the requirements for the degree of Master of Science in Geophysics. Dr. D. Schmitt (Co-supervisor) Dr. V. Kravachinsky (Supervisor) Dr. R. Luth (Earth and Atmospheric Sciences) Dr. A. Meldrum (Chair and examiner) Date: To my parents, my wife Ruth, and my daughter Martha. Abstract Rock fabrics deduced from either the anisotropy of magnetic susceptibility or of seis- mic anisotropy have been widely discussed; on this basis one might expect there to be some correlation between their characteristics. However, whether a general relationship exists between magnetic susceptibility and seismic anisotropy and what its significance might be remains unknown and there remains room for future studies. Pindos and Vouri- nos ophiolite with its high magnetic susceptibility is a good candidate for comparison between the anisotropy of magnetic susceptibility (AMS) studies and seismic anisotropy. Laboratory measurements on these materials include compressional and shear-wave ve- locities at confining pressures to 300 MPa, density, velocity anisotropy, and shear-wave splitting, which all generally decrease with increasing degree of serpentinization . In- versely, the Vp/Vs ratio and the Poisson’s ratio display a continuous increment with the serpentinization degree. Magnetic fabrics, sensitive indicators of low-intensity strain, were further obtained from AMS measurements on the same samples. The directions of acoustic and magnetic anisotropy compare favorably. A possible reason for this cor- relation is that the magnetic fabrics are thought to be representative of the secondary magnetite produced during serpentinization and also from the primary paramagnetic minerals assemblage. The bulk magnetic fabric of a few secondary magnetite originated from serpentinization along fractures that crosscut olivine grains might mimic the prin- cipal rock texture to some extent. The experimental seismic velocities offer the average calculations of anisotropies, elasticity, and symmetries for the whole mineral assembly of rocks. Comparing the AMS and seismic anisotropy indicates that generally both direc- tions and intensities of the magnetic susceptibility anisotropy and the seismic anisotropy coincide. These results motivate the development of additional method to use the fabric, as deduced from simple and fast AMS measurements, as a proxy for finding the direc- tions of elastic anisotropy in traditional ultrasonic laboratory methods. Acknowledgements First of all, I should express my sincere gratitude to my supervisors, Dr. Douglas R. Schmitt and Dr. Vadim A. Kravchinsky, for their guidance, intelligent advice, and support. Both their mentorship and friendship make my last two years in University of Alberta exciting and enjoyable. I wish to thank all my committee members for their revision and suggestion for my thesis, which significantly enhanced the quality of the present dissertation. I also want to thank the staff of the physics department for their help, special thanks to Lynn Chandler and Sarah Derr for their hard work for the graduate students in our department. I also like to extend my appreciations to my friends and follow students in the Univer- sity of Alberta for their kindness, support, and encourage. Needless to say, I will express my gratitude to M. Welz, J. Havestock, J. Mackinnon, O. Catuneanu, D. Rokosh and D. Caird for their technical assistances. I should specially mention L. Tober. He is very patient and ready to help all the time. He always knows how to solve the unexpected questions in the experiment with his experience and knowledge. I am grateful to my wife Ruth, who has undertaken many of the family chores during the past few years. She has dedicated her love to our success now and in the future. Finally, I should sincerely appreciate my parents and brother for all their spiritual encouragement and love, even far away, which always give me courage and confidence during my study in Canada. Contents 1 Introduction 1 1.1 Background . 1 1.2 Why elastic anisotropy measurements are important . 4 1.3 Causes of magnetic anisotropy . 9 1.4 Objective of the work . 11 1.5 Geological background . 13 2 Elastic-wave velocity and anisotropy 16 2.1 Introduction . 16 2.2 Brief review of elasticity theory . 18 2.3 Relationship between anisotropic velocities and elastic stiffness . 24 2.4 Laboratory measurement of elastic-wave velocity and anisotropy . 27 2.4.1 Sample preparation . 28 2.4.2 Experiment and Measurement . 31 2.4.3 Error analysis . 34 2.5 Results and Discussion . 34 2.5.1 Compressional wave results . 35 2.5.2 Shear wave results . 42 2.5.3 Elastic stiffness and symmetry . 49 2.5.4 Conclusion . 52 3 Magnetic Susceptibility and AMS 59 3.1 Introduction . 59 3.2 Theory and method of determining AMS . 60 3.2.1 Classes of Magnetic Materials . 60 3.2.2 Domain Theory . 61 3.2.3 Anisotropy of magnetic susceptibility . 62 3.2.4 Theory and method of determining AMS . 63 3.3 Magnetic susceptibility measurement . 67 3.3.1 Sample preparation . 67 3.3.2 AMS calculation and illustration . 68 3.4 Results and discussion . 70 3.5 Conclusion . 73 4 Comparison between seismic anisotropy and AMS 77 4.1 Introduction . 77 4.2 Serpentinization influences AMS and seismic anisotropy . 77 4.2.1 Serpentinization and magnetite . 78 4.2.2 AMS influenced by rock-forming minerals . 81 4.2.3 Seismic anisotropy influenced by serpentinization . 82 4.3 Comparison between magnetic fabric and seismic anisotropy . 83 4.4 Conclusion . 88 5 Future work 91 Bibliography 94 A Thin section 101 B Velocity Data 112 C X-ray diffraction 119 List of Tables 1.1 Earlier laboratory seismic measurements in ultramafic and mafic rocks . 9 1.2 The sampling location of Pindos and Vourinos ophiolites . 15 2.1 The cyclical recipe for transformation from full to Voigt notation . 19 2.2 Symmetries and the number of elastic constants required . 22 2.3 Elastic stiffnesses of minerals at room P / T . 24 2.4 Density, symmetry, and chemical formula of minerals . 25 2.5 The chemical composition and orientation of plugs . 30 2.6 The density and porosity of plugs . 30 2.7 P-wave velocities at various pressures for samples in the Pindos and Vouri- nos ophiolite (Greece) . 55 2.8 S-wave velocities at various pressures for samples in the Pindos and Vouri- nos ophiolite (Greece) . 56 2.9 Poisson’s and Vp / Vs ratio at 200 MPa . 58 2.10 Calculated elastic stiffnesses (GPa) for samples in the Pindos and Vourinos ophiolite (Greece) at 300 MPa . 58 2.11 Parameters of velocity anisotropy at 300 MPa . 58 3.1 The AMS measurement Data at room temperature and low field for sam- ples in the Pindos and Vourinos ophiolite (Greece) . 71 3.2 Parameters of describing AMS ellipsoid (Parameters defined in 3.3.3) . 76 4.1 P-wave velocities and magnetic susceptibilities along Z-axis and within XY plane . 87 B.1 P- and S- wave velocities at various confining pressure in sample P 03-1 . 113 B.2 P- and S- wave velocities at various confining pressure in sample P 04-2 . 113 B.3 P- and S- wave velocities at various confining pressure in sample P 08-3 . 114 B.4 P- and S- wave velocities at various confining pressure in sample P 08-4 . 114 B.5 P- and S- wave velocities at various confining pressure in sample P 11-1 . 115 B.6 P- and S- wave velocities at various confining pressure in sample P 12-1 . 115 B.7 P- and S- wave velocities at various confining pressure in sample P 13-1 . 116 B.8 P- and S- wave velocities at various confining pressure in sample P 13-2 . 116 B.9 P- and S- wave velocities at various confining pressure in sample P 16-3 . 117 B.10 P- and S- wave velocities at various confining pressure in sample V 03-11 117 B.11 P- and S- wave velocities at various confining pressure in sample V 03-7 . 118 List of Figures 1.1 P-wave velocity anisotropy and shear wave splitting (km/s) of single crys- tal olivine. Modified from Weiss et al. (1999) . 5 1.2 Schematic showing the magnetic susceptibility ellipsoid of rocks. (K min, K int, and K max correspond to the minimum, intermediate, and maxi- mum principal axes of the ellipsoid) . 12 1.3 Top: Sample location map in Greece.