Microstructures, Deformation Mechanisms and Seismic Properties of Synkinematic Migmatite from Southeastern Tibet: Insights from the Migmatitic Core of the Ailao Shan-Red River Shear Zone, Western Yunnan, China

Abstract

Seismic anisotropy originating within the continental crust is commonly used to determine the deformation and kinematic flow within active orogens and is attributed to regionally oriented mica or hornblende grains. However, naturally deformed rocks usually contain compositional layers (e. g., parallel compositional banding). It is necessary to understand how both varying mineral contents and differing intensities of compositional layering influence the seismic properties of the deep crust. In this study, we analyzed the seismic response of migmatitic amphibolite with compositional banding structures. We present the microstructures, fabrics, calculated seismic velocities, and seismic anisotropies of mylonitic amphibolite from a horizontal shear layer preserved within the Ailao Shan-Red River shear zone, southwestern Yunnan, China. The investigated sample is characterized by pronounced centimeter-scale compositional banding. The microstructures and fabrics suggest that migmatitic amphibolite rocks within deep crust may delineate regions of deformation-assisted, channelized, reactive, porous melt flow. The origin of compositional banding in the studied migmatitic amphibolite is attributed primarily to partial melting together with some horizontal shearing deformation. The microfabrics and structures investigated in this study are considered to be typical for the base of active horizontal shear layers in the deep crust of southeastern Tibet. Seismic responses are modeled by using crystal preferred orientations for minerals of the migmatitic amphibolite by applying the Voigt-Reuss-Hill homogenization method. Calculated P-wave and S-wave velocities are largely consistent in the various layers of the migmatite. However, seismic anisotropies of P-wave (AV _p) and S-wave (AV _s) are higher in the melanosomes (AV _p = 5.6%, AV _s = 6.83%) than those in the leucosomes and the whole rock (AV _p = 4.2%–4.6%, AV _s = 3.1%–3.2%). In addition, there is pronounced, S-wave splitting oblique to the foliation plane in the migmatitic amphibolite. The multiple parallel compositional layers generate marked variation in the geometry of the seismic anisotropy (V _s1 polarization) in the whole rock. Combined with the macroscale geographical orientation of fabrics in the Ailao Shan-Red River shear zone, these compositional banding effects are inferred to generate significant variations in the magnitude and orientation of seismic anisotropy, especially for shear-wave anisotropy (AV _s) in the deep crust. Hence, our data suggest that layering of various origins (e.g., shear layers, partial-melting layers, and compositional layers) represents a new potential source of anisotropy within the deep crust.

Keywords

deformation-assisted melt flow / seismic anisotropy / microstructure / compositional banding / migmatite / deep crust / southeastern Tibet

References

[] Abers G A, Hacker B R. A MATLAB Toolbox and Excel Workbook for Calculating the Densities, Seismic Wave Speeds, and Major Element Composition of Minerals and Rocks at Pressure and Temperature. Geochemistry, Geophysics, Geosystems, 2016, 17(2): 616-624

[] Backus G E. Long-Wave Elastic Anisotropy Produced by Horizontal Layering. Journal of Geophysical Research, 1962, 67(11): 4427-4440

[] Baker D W, Carter N L, et al.. Heard H C, Borg I Y, Carter N L, et al.. Seismic Velocity Anisotropy Calculated for Ultramafic Minerals and Aggregates. Flow and Fracture of Rocks, 1972 Washington, D. C. American Geophysical Union 157-166

[] Bhagat S S, Bass J D, Smyth J R. Single-Crystal Elastic Properties of Omphacite-C2/c by Brillouin Spectroscopy. Journal of Geophysical Research: Solid Earth, 1992, 97(B5): 6843-6848

[] Brown J M, Abramson E H, Angel R J. Triclinic Elastic Constants for Low Albite. Physics and Chemistry of Minerals, 2006, 33(4): 256-265

[] Brown M. Orogeny, Migmatites and Leucogranites: a Review. Journal of Earth System Science, 2001, 110(4): 313-336

[] Burlini L, Arbaret L, Zeilinger G, et al.. High-Temperature and Pressure Seismic Properties of a Lower Crustal Prograde Shear Zone from the Kohistan Arc, Pakistan. Geological Society, London, Special Publications, 2005, 245(1): 187-202

[] Caldwell W B, Klemperer S L, Rai S S, et al.. Partial Melt in the Upper-Middle Crust of the Northwest Himalaya Revealed by Rayleigh Wave Dispersion. Tectonophysics, 2009, 477(1/2): 58-65

[] Cao S Y, Neubauer F, Liu J L, et al.. Exhumation of the Diancang Shan Metamorphic Complex along the Ailao Shan-Red River Belt, Southwestern Yunnan, China: Evidence from ⁴⁰Ar/³⁹Ar Thermochronology. Journal of Asian Earth Sciences, 2011, 42(3): 525-550

[] Chai M, Brown J M, Slutsky L J. The Elastic Constants of a Pyrope-Grossular-Almandine Garnet to 20 Gpa. Geophysical Research Letters, 1997, 24(5): 523-526

[] Christoffel E B. Sur Une Classe Particulière de Fonctions Entières et de Fractions Continues. Annali Di Matematica Pura Ed Applicata, 1877, 8(1): 1-10 1867–1897)

[] Collins M D, Brown J M. Elasticity of an Upper Mantle Clinopyroxene. Physics and Chemistry of Minerals, 1998, 26(1): 7-13

[] Cyprych D, Piazolo S, Almqvist B S G. Seismic Anisotropy from Compositional Banding in Granulites from the Deep Magmatic Arc of Fiordland, New Zealand. Earth and Planetary Science Letters, 2017, 477: 156-167

[] Faccenda M, Ferreira A M G, Tisato N, et al.. Extrinsic Elastic Anisotropy in a Compositionally Heterogeneous Earth’s Mantle. Journal of Geophysical Research Solid Earth, 2019, 124(2): 1671-1687 [PubMed]

[] Ferri F, Burlini L, Cesare B. Effect of Partial Melting on V_p and V_s in Crustal Enclaves from Mazarrón (SE Spain). Tectonophysics, 2016, 671(7): 139-150

[] Fusseis F, Regenauer-Lieb K, Liu J, et al.. Creep Cavitation Can Establish a Dynamic Granular Fluid Pump in Ductile Shear Zones. Nature, 2009, 459: 974-977

[] Hacker B R, Ritzwoller M H, Xie J. Partially Melted, Mica-Bearing Crust in Central Tibet. Tectonics, 2014, 33(7): 1408-1424

[] Hasalová P, Schulmann K, Lexa O, et al.. Origin of Migmatites by Deformation-Enhanced Melt Infiltration of Orthogneiss: A New Model Based on Quantitative Microstructural Analysis. Journal of Metamorphic Geology, 2008, 26(1): 29-53

[] Hielscher R, Schaeben H. A Novel Pole Figure Inversion Method: Specification of theMTEXalgorithm. Journal of Applied Crystallography, 2008, 41(6): 1024-1037

[] Hill R. The Elastic Behaviour of a Crystalline Aggregate. Proceedings of the Physical Society Section A, 1952, 65(5): 349-354

[] Hrstka T, Gottlieb P, Skála R, et al.. Automated Mineralogy and Petrology-Applications of TESCAN Integrated Mineral Analyzer (TIMA). Journal of Geosciences, 2018, 63(1): 47-63

[] Huang Z C, Zhao D P, Wang L S. Seismic Heterogeneity and Anisotropy of the Honshu Arc from the Japan Trench to the Japan Sea. Geophysical Journal International, 2011, 184(3): 1428-1444

[] Imon R, Okudaira T, Kanagawa K. Development of Shape- and Lattice-Preferred Orientations of Amphibole Grains during Initial Cataclastic Deformation and Subsequent Deformation by Dissolution–Precipitation Creep in Amphibolites from the Ryoke Metamorphic Belt, SW Japan. Journal of Structural Geology, 2004, 26(5): 793-805

[] Jackson J M, Sinogeikin S V, Bass J D. Sound Velocities and Single-Crystal Elasticity of Orthoenstatite to 1073K at Ambient Pressure. Physics of the Earth and Planetary Interiors, 2007, 161(1/2): 1-12

[] Ji S C, Shao T B, Michibayashi K, et al.. Magnitude and Symmetry of Seismic Anisotropy in Mica- and Amphibole-Bearing Metamorphic Rocks and Implications for Tectonic Interpretation of Seismic Data from the Southeast Tibetan Plateau. Journal of Geophysical Research: Solid Earth, 2015, 120(9): 6404-6430

[] Jolivet L, Beyssac O, Goffé B, et al.. Oligo-Miocene Midcrustal Subhorizontal Shear Zone in Indochina. Tectonics, 2001, 20(1): 46-57

[] Jones T, Nur A. Seismic Velocity and Anisotropy in Mylonites and the Reflectivity of Deep Crystal Fault Zones. Geology, 1982, 10(5): 260-263

[] Kelemen P B, Shimizu N, Salters V J M. Extraction of Mid-Ocean-Ridge Basalt from the Upwelling Mantle by Focused Flow of Melt in Dunite Channels. Nature, 1995, 375(6534): 747-753

[] Kim J, Jung H. New Crystal Preferred Orientation of Amphibole Experimentally Found in Simple Shear. Geophysical Research Letters, 2019, 46(22): 12996-13005

[] Klepeis K A, Schwartz J, Stowell H, et al.. Gneiss Domes, Vertical and Horizontal Mass Transfer, and the Initiation of Extension in the Hot Lower-Crustal Root of a Continental Arc, Fiordland, New Zealand. Lithosphere, 2016, 8(2): 116-140

[] Ko B, Jung H. Crystal Preferred Orientation of an Amphibole Experimentally Deformed by Simple Shear. Nature Communications, 2015, 6: 6586

[] Kono Y, Ishikawa M, Harigane Y, et al.. P- and S-Wave Velocities of the Lowermost Crustal Rocks from the Kohistan Arc: Implications for Seismic Moho Discontinuity Attributed to Abundant Garnet. Tectonophysics, 2009, 467(1/2/3/4): 44-54

[] Lee A L, Walker A M, Lloyd G E, et al.. Modeling the Impact of Melt on Seismic Properties during Mountain Building. Geochemistry, Geophysics, Geosystems, 2017, 18(3): 1090-1110

[] Leloup P H, Arnaud N, Lacassin R, et al.. New Constraints on the Structure, Thermochronology, and Timing of the Ailao Shan-Red River Shear Zone, SE Asia. Journal of Geophysical Research: Solid Earth, 2001, 106(B4): 6683-6732

[] Li W J, Zhang J F, Wang X, et al.. Petrofabrics and Seismic Properties of Himalayan Amphibolites: Implications for a Thick Anisotropic Deep Crust beneath Southern Tibet. Journal of Geophysical Research (Solid Earth), 2020, 125(8): e2019JB018700

[] Liu J L, Cao S Y, Zhai Y F, et al.. Rotation of Crustal Blocks as an Explanation of Oligo-Miocene Extension in Southeastern Tibet—Evidenced by the Diancangshan and nearby Metamorphic Core Complexes. Earth Science Frontiers, 2007, 14(4): 40-48

[] Liu J L, Chen X Y, Tang Y, et al.. The Ailao Shan-Red River Shear Zone Revisited: Timing and Tectonic Implications. GSA Bulletin, 2020, 132(5/6): 1165-1182

[] Lloyd G E, Butler R W H, Casey M, et al.. Mica, Deformation Fabrics and the Seismic Properties of the Continental Crust. Earth and Planetary Science Letters, 2009, 288(1/2): 320-328

[] Lloyd G E, Butler R W H, Casey M, et al.. Constraints on the Seismic Properties of the Middle and Lower Continental Crust. Geological Society, London, Special Publications, 2011, 360(1): 7-32

[] Mainprice D. Gerald S. Seismic Anisotropy of the Deep Earth from a Mineral and Rock Physics Perspective. Treatise on Geophysics, 2007 Amsterdam Elsevier 437-491

[] Mainprice D. Gerald S. Seismic Anisotropy of the Deep Earth from a Mineral and Rock Physics Perspective. Treatise on Geophysics, 2015 Amsterdam Elsevier 487-538

[] Mainprice D, Nicolas A. Development of Shape and Lattice Preferred Orientations: Application to the Seismic Anisotropy of the Lower Crust. Journal of Structural Geology, 1989, 11(1/2): 175-189

[] Mainprice D, Silver P G. Interpretation of SKS-Waves Using Samples from the Subcontinental Lithosphere. Physics of the Earth and Planetary Interiors, 1993, 78(3/4): 257-280

[] Meek U, Piazolo S, Daczko N R. The Field and Microstructural Signatures of Deformation-Assisted Melt Transfer: Insights from Magmatic Arc Lower Crust, New Zealand. Journal of Metamorphic Geology, 2019, 37(6): 795-821

[] Michibayashi K, Mainprice D. The Role of Pre-Existing Mechanical Anisotropy on Shear Zone Development within Oceanic Mantle Lithosphere: An Example from the Oman Ophiolite. Journal of Petrology, 2004, 45(2): 405-414

[] Moschetti M P, Ritzwoller M H, Lin F, et al.. Seismic Evidence for Widespread Western-US Deep-Crustal Deformation Caused by Extension. Nature, 2010, 464: 885-889

[] Naus-Thijssen F M J, Goupee A J, Johnson S E, et al.. The Influence of Crenulation Cleavage Development on the Bulk Elastic and Seismic Properties of Phyllosilicate-Rich Rocks. Earth and Planetary Science Letters, 2011, 311(3/4): 212-224

[] Naus-Thijssen F M J, Goupee A J, Vel S S, et al.. The Influence of Microstructure on Seismic Wave Speed Anisotropy in the Crust: Computational Analysis of Quartz-Muscovite Rocks. Geophysical Journal International, 2011, 185(2): 609-621

[] Ozacar A A, Zandt G. Crustal Seismic Anisotropy in Central Tibet: Implications for Deformational Style and Flow in the Crust. Geophysical Research Letters, 2004, 31(23): L23601

[] Reuss A. Berechnung Der Fließgrenze von Mischkristallen Auf Grund Der Plastizitätsbedingung Für Einkristalle. ZAMM-Journal of Applied Mathematics and Mechanics, 1929, 9(1): 49-58

[] Sanderson D J, Marchini W R D. Transpression. Journal of Structural Geology, 1984, 6(5): 449-458

[] Schulte-Pelkum V, Monsalve G, Sheehan A, et al.. Imaging the Indian Subcontinent beneath the Himalaya. Nature, 2005, 435: 1222-1225

[] Searle M P. Role of the Red River Shear Zone, Yunnan and Vietnam, in the Continental Extrusion of SE Asia. Journal of the Geological Society, 2006, 163(6): 1025-1036

[] Searle M P, Noble S R, Cottle J M, et al.. Tectonic Evolution of the Mogok Metamorphic Belt, Burma (Myanmar) Constrained by U-Th-Pb Dating of Metamorphic and Magmatic Rocks. Tectonics, 2007, 26(3): 623-626

[] Shao, Y. L., Piazolo, S., Liu, Y. J., et al., 2019. EBSD (Electron Backscatter Diffraction) Data of Tonalitic Migmatites [Dataset]. Pangaea. https://doi.org/10.1594/pangaea.907560

[] Shao Y L, Piazolo S, Liu Y J, et al.. Deformation Behavior and Inferred Seismic Properties of Tonalitic Migmatites at the Time of Pre Melting, Partial Melting, and Post Solidification. Geochemistry, Geophysics, Geosystems, 2021, 22(2): e2020GC009202

[] Shapiro N M, Ritzwoller M H, Molnar P, et al.. Thinning and Flow of Tibetan Crust Constrained by Seismic Anisotropy. Science, 2004, 305(5681): 233-236

[] Sherrington H F, Zandt G, Frederiksen A. Crustal Fabric in the Tibetan Plateau Based on Waveform Inversions for Seismic Anisotropy Parameters. Journal of Geophysical Research: Solid Earth, 2004, 109(B2): B02312

[] Silver P G. Seismic Anisotropy Beneath the Continents: Probing the Depths of Geology. Annual Review of Earth and Planetary Sciences, 1996, 24: 385-432

[] Solano J M S, Jackson M D, Sparks R S J, et al.. Melt Segregation in Deep Crustal Hot Zones: a Mechanism for Chemical Differentiation, Crustal Assimilation and the Formation of Evolved Magmas. Journal of Petrology, 2012, 53(10): 1999-2026

[] Stuart C A, Meek U, Daczko N R, et al.. Chemical Signatures of Melt – Rock Interaction in the Root of a Magmatic Arc. Journal of Petrology, 2018, 59(2): 321-340

[] Tatham D J, Lloyd G E, Butler R W H, et al.. Amphibole and Lower Crustal Seismic Properties. Earth and Planetary Science Letters, 2008, 267(1/2): 118-128

[] Tavarnelli E, Holdsworth R E. How Long do Structures Take to Form in Transpression Zones? a Cautionary Tale from California. Geology, 1999, 27(12): 1063-1066

[] Vanderhaeghe O. Migmatites, Granites and Orogeny: Flow Modes of Partially-Molten Rocks and Magmas Associated with Melt/Solid Segregation in Orogenic Belts. Tectonophysics, 2009, 477(3): 119-134

[] Vel S S, Cook A C, Johnson S E, et al.. Computational Homogenization and Micromechanical Analysis of Textured Polycrystalline Materials. Computer Methods in Applied Mechanics and Engineering, 2016, 310(1): 749-779

[] Vergne J, Wittlinger G, Farra V, et al.. Evidence for Upper Crustal Anisotropy in the Songpan-Ganze (Northeastern Tibet) Terrane. Geophysical Research Letters, 2003, 30(11): 1552

[] Voigt W. . Lehrbuch Der Kristallphysik: (Mit Ausschluss der Kristalloptik), 1928 Leipzig Teubner Verlag

[] Walker A M, Wookey J. MSAT—A New Toolkit for the Analysis of Elastic and Seismic Anisotropy. Computers & Geosciences, 2012, 49: 81-90

[] Wang F, Liu F L, Liu P H, et al.. Petrology, Geochemistry, and Metamorphic Evolution of Meta-Sedimentary Rocks in the Diancang Shan-Ailao Shan Metamorphic Complex, Southeastern Tibetan Plateau. Journal of Asian Earth Sciences, 2016, 124: 68-93

[] Wang X, Zhang J F, Tommasi A, et al.. Microstructure and Seismic Properties of Amphibole-Rich Rocks from the Deep Crust in Southern Tibet. Tectonophysics, 2021, 811(20): 228869

[] Ward D, Mahan K, Schulte-Pelkum V. Roles of Quartz and Mica in Seismic Anisotropy of Mylonites. Geophysical Journal International, 2012, 190(2): 1123-1134

[] Weinberg R F, Veveakis E, Regenauer-Lieb K. Compaction-Driven Melt Segregation in Migmatites. Geology, 2015, 43(6): 471-474

[] Xu L L, Rondenay S, van der Hilst R D. Structure of the Crust beneath the Southeastern Tibetan Plateau from Teleseismic Receiver Functions. Physics of the Earth and Planetary Interiors, 2007, 165(3/4): 176-193

[] Yan J X, Zhang T Y, Liu J L, et al.. Lateral Subhorizontal Middle to Lower Crustal Flow in Response to Continental Collision: Evidence from the Diancang Shan Complex along the Ailao Shan-Red River Belt, Southeastern Tibetan Plateau. Journal of Structural Geology, 2021, 143: 104234

[] Zhang B, Chen S Y, Wang Y, et al.. Crustal Deformation and Exhumation within the India-Eurasia Oblique Convergence Zone: New Insights from the Ailao Shan-Red River Shear Zone. Geological Society of America Bulletin, 2022, 134(5/6): 1443-1467

[] Zhang B, Yin C Y, Zhang J J, et al.. Midcrustal Shearing and Doming in a Cenozoic Compressive Setting along the Ailao Shan-Red River Shear Zone. Geochemistry, Geophysics, Geosystems, 2017, 18(1): 400-433

[] Zhang B, Zhang J J, Liu J, et al.. The Xuelongshan High Strain Zone: Cenozoic Structural Evolution and Implications for Fault Linkages and Deformation along the Ailao Shan-Red River Shear Zone. Journal of Structural Geology, 2014, 69: 209-233

[] Zhang J J, Zhong D L, Sang H Q, et al.. Structural and Geochronological Evidence for Multiple Episodes of Tertiary Deformation along the Ailaoshan-Red River Shear Zone, Southeastern Asia, since the Paleocene. Acta Geologica Sinica: English Edition, 2006, 80(1): 79-96

[] Zhao D P, Pirajno F, Dobretsov N L, et al.. Mantle Structure and Dynamics under East Russia and Adjacent Regions. Russian Geology and Geophysics, 2010, 51(9): 925-938