Seismic anisotropy and mantle creep in young orogens

��������� � �� ���������� SUMMARY Seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere. We discuss the origin of anisotropy at various depths, and relate it to tectonic stress, geotherms and rheology. The anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine, and may result from ductile deformation, dynamic recrystallization or annealing. Anisotropy beneath young orogens has been measured for the seismic phase Pn that propagates in the uppermost mantle. This anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event, and thus provides information on the process of mountain building. Whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts, Pn anisotropy is aligned parallel to the structural axis. We interpret this to indicate mountainparallel ductile (i.e. creeping) deformation in the uppermost mantle that is a consequence of mountain-perpendicular compressive stresses. The preferred orientation of the fast axes of some anisotropic minerals, such as olivine, is known to be in the creep direction, a consequence of the anisotropy of strength and viscosity of orientated minerals. In order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal ‘escape’ (or ‘extrusion’) tectonics to the uppermost mantle. We present rheological model calculations to support this hypothesis. Mountain-perpendicular horizontal stress (determined in the upper crust) and mountain-parallel seismic anisotropy (in the uppermost mantle) require a zone of ductile decoupling in the middle or lower crust of young mountain belts. Examples for stress and mountain-parallel Pn anisotropy are given for Tibet, the Alpine chains, and young mountain ranges in the Americas. Finally, we suggest a simple model for initiating mountain parallel creep.

[1]  C. Fowler.  The Solid Earth: Introduction , 2004 .

[2]  Walter D. Mooney,et al.  Thermal thickness and evolution of Precambrian lithosphere: A global study , 2001 .

[3]  R. Meissner,et al.  Southern Tibet: its deep seismic structure and some tectonic implications , 2001 .

[4]  T. Wallace,et al.  Subduction and collision processes in the Central Andes constrained by converted seismic phases , 2000, Nature.

[5]  Wenjin Zhao,et al.  Seismic polarization anisotropy beneath the central Tibetan Plateau , 2000 .

[6]  R. Porth.  A strain‐rate‐dependent force model of lithospheric strength , 2000 .

[7]  G. Ranalli.  Rheology of the crust and its role in tectonic reactivation , 2000 .

[8]  H. Wenk,et al.  Modeling dynamic recrystallization of olivine aggregates deformed in simple shear , 1999 .

[9]  T. Bohlen,et al.  Seismic Velocities and Anisotropy of the Lower Continental Crust: A Review , 1999 .

[10]  W. Rabbel,et al.  Nature of Crustal Reflectivity along the DEKORP Profiles in Germany in Comparison with Reflection Patterns from Different Tectonic Units Worldwide: A Review , 1999 .

[11]  Y. Makovsky,et al.  Measuring the seismic properties of Tibetan bright spots: Evidence for free aqueous fluids in the Tibetan middle crust , 1999 .

[12]  I. Dricker,et al.  Upper‐mantle flow in eastern Europe , 1999 .

[13]  A. Vauchez,et al.  Upper mantle tectonics: three-dimensional deformation, olivine crystallographic fabrics and seismic properties , 1999 .

[14]  Sobolev,et al.  Seismic Evidence for a Detached Indian Lithospheric Mantle Beneath Tibet. , 1999, Science.

[15]  M. Savage.  Seismic anisotropy and mantle deformation: What have we learned from shear wave splitting? , 1999 .

[16]  G. Ekström,et al.  A global study of Pn anisotropy beneath continents , 1999 .

[17]  M. Grad,et al.  Seismic velocity structure across the Fennoscandia-Sarmatia suture of the East European Craton beneath the EUROBRIDGE profile through Lithuania and Belarus , 1999 .

[18]  L. Lliboutry.  Quantitative geophysics and geology , 1999 .

[19]  T. Bohlen,et al.  Shear wave anisotropy of laminated lower crust beneath Urach (SW Germany): a comparison with xenoliths and with exposed lower crustal sections , 1998 .

[20]  P. Silver,et al.  Apparent shear-wave splitting parameters in the presence of vertically varying anisotropy , 1998 .

[21]  A. Vauchez,et al.  Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere , 1998 .

[22]  W. Mooney,et al.  Weakness of the lower continental crust: a condition for delamination, uplift, and escape , 1998 .

[23]  W. B. Ismail,et al.  An olivine fabric database: an overview of upper mantle fabrics and seismic anisotropy , 1998 .

[24]  D. Marquer,et al.  Subduction and obduction processes in the Swiss Alps , 1998 .

[25]  D. Mainprice,et al.  A joint study of experimental deformation and experimentally induced microstructures of pretextured peridotites , 1998 .

[26]  Göran Ekström,et al.  The unique anisotropy of the Pacific upper mantle , 1998, Nature.

[27]  Walter D. Mooney,et al.  Crustal structure of China from deep seismic sounding profiles , 1998 .

[28]  R. Liebermann,et al.  Geodynamics of Lithosphere and Earth’s Mantle: Seismic Anisotropy as a Record of the Past and Present Dynamic Processes , 1998 .

[29]  A. Hirn,et al.  Variation of Shear-wave Residuals and Splitting Parameters from Array Observations in Southern Tibet , 1998 .

[30]  J. Montagner.  Where Can Seismic Anisotropy Be Detected in the Earth’s Mantle? In Boundary Layers... , 1998 .

[31]  G. Mele.  Pn Anisotropy in the Northern Apennine Chain (Italy) , 1998 .

[32]  D. Kohlstedt,et al.  High‐temperature deformation of dry diabase with application to tectonics on Venus , 1998 .

[33]  E. Sandvol,et al.  Lithospheric and upper mantle structure of southern Tibet from a seismological passive source experiment , 1997 .

[34]  M. Bostock.  Anisotropic upper-mantle stratigraphy and architecture of the Slave craton , 1997, Nature.

[35]  A. Vauchez,et al.  Why do continents break‐up parallel to ancient orogenic belts? , 1997 .

[36]  T. J. Owens,et al.  Upper mantle velocity structure beneath the Tibetan Plateau from Pn travel time tomography , 1997 .

[37]  Handong Tan,et al.  Partially Molten Middle Crust Beneath Southern Tibet: Synthesis of Project INDEPTH Results , 1996, Science.

[38]  M. Wysession,et al.  Slicing into the earth , 1996 .

[39]  R. Meissner.  Faults and folds, fact and fiction , 1996 .

[40]  M. Cocco,et al.  Seismic anisotropy beneath the Northern Apennines (Italy) and its tectonic implications , 1996 .

[41]  G. Grünthal,et al.  Upper mantle anisotropy beneath central Europe from SKS wave splitting: Effects of absolute plate motion and lithosphere-asthenosphere boundary topography? , 1996 .

[42]  H. Kern,et al.  Fabric-related seismic anisotropy in upper-mantle xenoliths: evidence from measurements and calculations , 1996 .

[43]  G. Ranalli,et al.  Thermal and rheological constraints on the earthquake depth distribution in the Charlevoix, Canada, intraplate seismic zone , 1996 .

[44]  P. Silver.  SEISMIC ANISOTROPY BENEATH THE CONTINENTS: Probing the Depths of Geology , 1996 .

[45]  J. Avouac,et al.  Seismic anisotropy beneath Tibet: evidence for eastward extrusion of the Tibetan lithosphere? , 1996 .

[46]  S. Siegesmund,et al.  The Significance of rock fabrics for the geological - interpretation of geophysical anisotropies , 1996 .

[47]  D. Kohlstedt,et al.  RHEOLOGY OF PARTIALLY MOLTEN MANTLE ROCKS , 1996 .

[48]  W. Rabbel,et al.  Seismic anisotropy of the crystalline crust: what does it tell us? , 1996 .

[49]  R. Westaway.  Crustal volume balance during the India‐Eurasia collision and altitude of the Tibetan Plateau: A working hypothesis , 1995 .

[50]  A. Nercessian,et al.  Seismic anisotropy as an indicator of mantle flow beneath the Himalayas and Tibet , 1995, Nature.

[51]  T. Jordan,et al.  Lehmann Discontinuity as the Base of an Anisotropic Layer Beneath Continents , 1995, Science.

[52]  G. Barruol,et al.  Anisotropy beneath the Pyrenees Range from teleseismic shear wave splitting: Results from a test experiment , 1995 .

[53]  Xiaoou Zhao,et al.  Calibration of shear-wave splitting in the subcontinental upper mantle beneath active orogenic belts using ultramafic xenoliths from the canadian cordillera and alaska , 1994 .

[54]  J. Viramonte,et al.  Young mafic back arc volcanic rocks as indicators of continental lithospheric delamination beneath the Argentine Puna Plateau, central Andes , 1994 .

[55]  P. Silver,et al.  The Interpretation of Shear‐Wave Splitting Parameters In the Presence of Two Anisotropic Layers , 1994 .

[56]  Richard G. Gordon,et al.  Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions , 1994 .

[57]  W. Rabbel.  Seismic anisotropy at the continental deep drilling site (Germany) , 1994 .

[58]  E. Lüschen.  Crustal “bright spots” and anisotropy from multi-component P- and S-wave measurements in southern Germany , 1994 .

[59]  C. Walther,et al.  The POLAR Profile revisited: combined P- and S-wave interpretation , 1993 .

[60]  Yvan Chastel,et al.  Anisotropic convection with implications for the upper mantle , 1993 .

[61]  Patrick Wu,et al.  Rheology of the Upper Mantle: A Synthesis , 1993, Science.

[62]  B. Isacks,et al.  Lithospheric structure of Tibet and western North America: Mechanisms of uplift and a comparative study , 1993 .

[63]  A. Milev,et al.  Global patterns of azimuthal anisotropy and deformations in the continental mantle , 1992 .

[64]  M. Zoback.  First‐ and second‐order patterns of stress in the lithosphere: The World Stress Map Project , 1992 .

[65]  W. Mooney.  Multi-genetic origin of crustal reflectivity: a review of seismic reflection profiling of the continental lower crust and Moho. , 1992 .

[66]  Paul G. Silver,et al.  Shear wave splitting and subcontinental mantle deformation , 1991 .

[67]  M. Cara,et al.  Seismic Anisotropy in the Earth , 1991 .

[68]  C. Doglioni,et al.  A proposal for the kinematic modelling of W-dipping subductions - possible applications to the Tyrrhenian-Apennines system , 1991 .

[69]  Peter Bird,et al.  Lateral extrusion of lower crust from under high topography , 1991 .

[70]  R. Meissner,et al.  Continental collisions and seismic signature , 1991 .

[71]  A. Vauchez,et al.  Mountain building: strike-parallel motion and mantle anisotropy , 1991 .

[72]  E. Rutter,et al.  Lithosphere rheology - a note of caution , 1991 .

[73]  N. Christensen,et al.  Seismic anisotropy due to preferred mineral orientation observed in shallow crustal rocks in southern Alaska , 1990 .

[74]  H. Wenk,et al.  Fabric‐related velocity anisotropy and shear wave splitting in rocks from the Santa Rosa Mylonite Zone, California , 1990 .

[75]  S. Siegesmund,et al.  Velocity anisotropy and shear-wave splitting in rocks from the mylonite belt along the Insubric Line (Ivrea Zone, Italy) , 1990 .

[76]  A. Hirn,et al.  Lithospheric wedging in the western Alps inferred from the ECORS-CROP traverse , 1990 .

[77]  C. Fowler,et al.  The Solid Earth: An Introduction to Global Geophysics , 1990 .

[78]  David Mainprice,et al.  A FORTRAN program to calculate seismic anisotropy from the lattice preferred orientation of minerals , 1990 .

[79]  A. Hirn,et al.  ECORS-CROP traverse and deep structure of the western Alps : a synthesis , 1990 .

[80]  D. L. Anderson.  Theory of Earth , 2014 .

[81]  Philip England,et al.  Extension during continental convergence, with application to the Tibetan Plateau , 1989 .

[82]  S. Crampin.  SUGGESTIONS FOR A CONSISTENT TERMINOLOGY FOR SEISMIC ANISOTROPY , 1989 .

[83]  O. Stephansson,et al.  Global patterns of tectonic stress , 1989, Nature.

[84]  L. Ratschbacher,et al.  Extension in compressional orogenic belts: The eastern Alps , 1989 .

[85]  N. Ribe.  Seismic anisotropy and mantle flow , 1989 .

[86]  R. Meissner.  Rupture, creep, lamellae and crocodiles: happenings in the continental crust , 1989 .

[87]  G. Nolet,et al.  Mantle, upper: Structure , 1989 .

[88]  Ecors Team.  The ECORS deep reflection seismic survey across the Pyrenees , 1988, Nature.

[89]  U. Christensen.  Some geodynamical effects of anisotropic viscosity , 1987 .

[90]  W. J. Morgan,et al.  Injection of Indian crust into Tibetan lower crust: A two‐dimensional finite element model study , 1987 .

[91]  D. Yuen,et al.  Injection of Indian crust into Tibetan lower crust: A temperature‐dependent viscous model , 1987 .

[92]  S. Kirby,et al.  Rheology of the lithosphere: Selected topics , 1987 .

[93]  A. Green,et al.  A quantitative approach to bedrock velocity resolution and precision: The Lithoprobe Vancouver Island Experiment , 1987 .

[94]  R. Schönenberg,et al.  Einführung in die Geologie Europas , 1987 .

[95]  H. Nataf,et al.  A simple method for inverting the azimuthal anisotropy of surface waves , 1986 .

[96]  David S. Chapman,et al.  Thermal gradients in the continental crust , 1986, Geological Society, London, Special Publications.

[97]  M. Paterson,et al.  The role of water in the deformation of olivine single crystals , 1985 .

[98]  B. Drummond.  Seismic P‐wave anisotropy in the subcrustal lithosphere of north‐west Australia , 1985 .

[99]  A. Şengör,et al.  Strike-Slip Faulting and Related Basin Formation in Zones of Tectonic Escape: Turkey as a Case Study , 1985 .

[100]  A. Nur,et al.  The nature of seismic reflections from deep crustal fault zones , 1984 .

[101]  K. Helbig.  Anisotropy and dispersion in periodically layered media , 1984 .

[102]  N. Pavlenkova,et al.  Crustal heterogeneity and velocity anisotropy from seismic studies in the USSR , 1984 .

[103]  S. Crampin.  Effective anisotropic elastic constants for wave propagation through cracked solids , 1984 .

[104]  P. R. Cobbold,et al.  Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine , 1982 .

[105]  R. Sibson.  Fault zone models, heat flow, and the depth distribution of earthquakes in the continental crust of the United States , 1982 .

[106]  R. Meissner,et al.  Limits of stresses in continental crusts and their relation to the depth-frequency distribution of shallow earthquakes , 1982 .

[107]  V. Babuška.  Anisotropy of vp and vs in rock-forming minerals , 1982 .

[108]  J. Minster,et al.  Pn velocity anisotropy in southern California , 1981 .

[109]  I. Jackson,et al.  Upper mantle seismic anisotropy and lithospheric decoupling , 1981, Nature.

[110]  J. Byerlee.  Friction of rocks , 1978 .

[111]  A. Lachenbruch,et al.  9: Models of an extending lithosphere and heat flow in the Basin and Range province , 1978 .

[112]  Robert B. Smith,et al.  Cenozoic tectonics and regional geophysics of the western Cordillera , 1978 .

[113]  W. Durham,et al.  Plastic flow of oriented single crystals of olivine: 1. Mechanical data , 1977 .

[114]  C. Willaime.  Crystalline Plasticity and Solid State Flow in Metamorphic Rocks, par A. Nicolas et J.-P. Poirier, 1976 , 1977 .

[115]  A. Nicolas,et al.  Crystalline plasticity and solid state flow in metamorphic rocks , 1976 .

[116]  B. Budiansky,et al.  Elastic moduli of a cracked solid , 1976 .

[117]  P. Molnar,et al.  Cenozoic Tectonics of Asia: Effects of a Continental Collision: Features of recent continental tectonics in Asia can be interpreted as results of the India-Eurasia collision. , 1975, Science.

[118]  M. A. Lauffer.  The Role of Water , 1975 .

[119]  A. Nicolas,et al.  Velocity anisotropy in a mantle peridotite from the Ivrea Zone: Application to upper mantle anisotropy , 1974 .

[120]  M. F. Ashby,et al.  On the rheology of the upper mantle , 1973 .

[121]  J. Weertman.  The creep strength of the Earth's mantle , 1970 .

[122]  J. C. Jaeger,et al.  Fundamentals of rock mechanics , 1969 .

[123]  G. Backus.  Long-Wave Elastic Anisotropy Produced by Horizontal Layering , 1962 .

[124]  R. Hill.  The mathematical theory of plasticity , 1950 .

[125]  G. M.,et al.  A Treatise on the Mathematical Theory of Elasticity , 1906, Nature.