- Email: [email protected]
Evidence from core-reflected shear waves for anisotropy in the Earth's mantle
880
D. SubmarineGeologyand Geophysics
before reaching the core-mantle boundary and extensive mixing would be expected. With the present uncertainties about the physical nature of the 650-kin discontinuity, a variety of convective styles appears possible on dynamical grounds. Inst. fur Meteorol. und Geophys., Univ. of Frankfurt, FRG.
84:6155 Fukao, Yoshio, 1984. Evidence from core-reflected shear waves for anisotropy in the Earth's mantle. Nature, Lond., 309(5970):695-698. On entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases. The split SoS shear waves travel with different velocities in the anisotropic zone. The time delay between their arrival at stations and the azimuth of polarization were determined using the ScS records of two horizontal components from Japan for a deep shock beneath the Sea of Okhotsk. Of 41 stations, 34 show a polarization of the maximum velocity phase in the NNW-SSE direction with an average time advance of ~0.8 s from the minimum velocity phase. The relevant anisotropic zone seems to be deep-seated. Dept. of Earth Sci., Nagoya Univ., Chikusa, Nagoya 464, Japan. 84:6156 Giardini, Domenico, 1984. Systematic analysis of deep seismieity: 200 centroid-moment tensor solutions for earthquakes between 1977 and 1980. Geophys. Jl R. astr. Soc., 77(3):883-914. Dept. of Geol. Sci., Harvard Univ., Cambridge, Mass. 02138, USA.
84:6157 Girardeau, Jacques, Jean Marcoux and Zao Yougong, 1984. Lithologic and tectonic environment of the Xlgaze OphioUte (Yarlung Zangbo suture zone, Southern Tibet, China), and kinereties of its emplacement. Eclog. geol. Helv., 77(1):153-170. A swath of the Xigaze ophiolite a few kilometers wide has been mapped for 250 km from east to west. The northern contact with the Gangdise plutonic unit is probably tectonic; southern contact with a sedimentary series is marked by a major tectonic breccia. The tectonic history of the ophiolite is reconstructed from the observed field relationships and 'the kinematics of the thrusting of the ophiolite sheet is deduced from the analysis of the deformation in strongly deformed peridotites and in
OLR(1984)31 (12)
quartzites.' Inst. de Phys. du Globe, 4, place Jussieu, F-75230 Paris Cedex 05, France. (amt) 84:6158 Neprochnov, Iu.P. and P.N. Kuzmin, 1984. On the dependence of seismic parameters of the Earth's crust and upper mantle on the age of lithosphere in the Pacific Ocean. Dokl. Akad. Nauk SSSR, 275(3):704-706. (In Russian.) 84:6159 Pasteris, J.D., 1984. Kimherlites: complex mantle melts. A. Rev. Earth planet. Sci., 12:133-153. This review addresses the question: What do kimberlites and their eclogite and peridotite xenoliths reveal about mantle physicochemical and melting phenomena? Topics covered include kimberlite characterization, geologic and geographic locations, forms of intrusions, etc. Fluid movement seems 'essential to mantle melting and metasomatism,' and kimberlites may provide important insights for understanding such movement. Much of kimberlite history remains a conundrum. Dept. of Earth and Planetary Sci., Washington Univ., St. Louis, Mo. 63130, USA. (ihz)
84:6160 Rogers, J.J.W., 1984. Evolution of continents. Tectonophysics, 105(1/4):55-69. Continents evolve from ocean basins through a complex series of events. Early stages involve development of greenstone belts, island arcs, marginal basins, etc. These diverse assemblages are swept together during orogenic events; during this process continental fragments and other exotic blocks may be incorporated. Stabilization (cratonization) is caused by intrusion of post-orogenic, silicic, plutonic rocks, which weld the various fragments into a shield. Uplift commonly occurs a few tens of millions of years after stabilization. Four examples of places currently at different stages in the evolutionary pattern are discussed. Dept. of Geol., Univ. of North Carolina, Chapel Hill, NC 27514, USA.
84:6161 Smith, A.G. and D.J. Drewry, 1984. Delayed phase change due to hot asthenesphere causes Transantarctic uplift? Nature, Lond., 309(5968):536538. Dept. of Earth Sci., Univ. of Cambridge, Downing St., Cambridge CB2 3EQ, UK.
D. SubmarineGeologyand Geophysics
before reaching the core-mantle boundary and extensive mixing would be expected. With the present uncertainties about the physical nature of the 650-kin discontinuity, a variety of convective styles appears possible on dynamical grounds. Inst. fur Meteorol. und Geophys., Univ. of Frankfurt, FRG.
84:6155 Fukao, Yoshio, 1984. Evidence from core-reflected shear waves for anisotropy in the Earth's mantle. Nature, Lond., 309(5970):695-698. On entering an anisotropic zone a plane shear wave splits into two orthogonally polarized phases. The split SoS shear waves travel with different velocities in the anisotropic zone. The time delay between their arrival at stations and the azimuth of polarization were determined using the ScS records of two horizontal components from Japan for a deep shock beneath the Sea of Okhotsk. Of 41 stations, 34 show a polarization of the maximum velocity phase in the NNW-SSE direction with an average time advance of ~0.8 s from the minimum velocity phase. The relevant anisotropic zone seems to be deep-seated. Dept. of Earth Sci., Nagoya Univ., Chikusa, Nagoya 464, Japan. 84:6156 Giardini, Domenico, 1984. Systematic analysis of deep seismieity: 200 centroid-moment tensor solutions for earthquakes between 1977 and 1980. Geophys. Jl R. astr. Soc., 77(3):883-914. Dept. of Geol. Sci., Harvard Univ., Cambridge, Mass. 02138, USA.
84:6157 Girardeau, Jacques, Jean Marcoux and Zao Yougong, 1984. Lithologic and tectonic environment of the Xlgaze OphioUte (Yarlung Zangbo suture zone, Southern Tibet, China), and kinereties of its emplacement. Eclog. geol. Helv., 77(1):153-170. A swath of the Xigaze ophiolite a few kilometers wide has been mapped for 250 km from east to west. The northern contact with the Gangdise plutonic unit is probably tectonic; southern contact with a sedimentary series is marked by a major tectonic breccia. The tectonic history of the ophiolite is reconstructed from the observed field relationships and 'the kinematics of the thrusting of the ophiolite sheet is deduced from the analysis of the deformation in strongly deformed peridotites and in
OLR(1984)31 (12)
quartzites.' Inst. de Phys. du Globe, 4, place Jussieu, F-75230 Paris Cedex 05, France. (amt) 84:6158 Neprochnov, Iu.P. and P.N. Kuzmin, 1984. On the dependence of seismic parameters of the Earth's crust and upper mantle on the age of lithosphere in the Pacific Ocean. Dokl. Akad. Nauk SSSR, 275(3):704-706. (In Russian.) 84:6159 Pasteris, J.D., 1984. Kimherlites: complex mantle melts. A. Rev. Earth planet. Sci., 12:133-153. This review addresses the question: What do kimberlites and their eclogite and peridotite xenoliths reveal about mantle physicochemical and melting phenomena? Topics covered include kimberlite characterization, geologic and geographic locations, forms of intrusions, etc. Fluid movement seems 'essential to mantle melting and metasomatism,' and kimberlites may provide important insights for understanding such movement. Much of kimberlite history remains a conundrum. Dept. of Earth and Planetary Sci., Washington Univ., St. Louis, Mo. 63130, USA. (ihz)
84:6160 Rogers, J.J.W., 1984. Evolution of continents. Tectonophysics, 105(1/4):55-69. Continents evolve from ocean basins through a complex series of events. Early stages involve development of greenstone belts, island arcs, marginal basins, etc. These diverse assemblages are swept together during orogenic events; during this process continental fragments and other exotic blocks may be incorporated. Stabilization (cratonization) is caused by intrusion of post-orogenic, silicic, plutonic rocks, which weld the various fragments into a shield. Uplift commonly occurs a few tens of millions of years after stabilization. Four examples of places currently at different stages in the evolutionary pattern are discussed. Dept. of Geol., Univ. of North Carolina, Chapel Hill, NC 27514, USA.
84:6161 Smith, A.G. and D.J. Drewry, 1984. Delayed phase change due to hot asthenesphere causes Transantarctic uplift? Nature, Lond., 309(5968):536538. Dept. of Earth Sci., Univ. of Cambridge, Downing St., Cambridge CB2 3EQ, UK.