A seismic refraction study of cretaceous oceanic lithosphere in the Northwest Pacific Basin
Tóm tắt
A seismic refraction study on old (≈110 Myr) lithosphere in the northwest Pacific Basin has placed constraints on crustal and uppermantle seismic structure of old oceanic lithosphere, and lithospheric aging processes. No significant lateral variation in structure other than azimuthally anisotropic mantle velocities was found, allowing the application of powerful amplitude modeling techniques. The anisotropy observed is in an opposite sense to that expected, suggesting the tectonic setting of the area may be more complex than originally thought. Upper crustal velocities are generally larger than for younger crust, supporting current theories of decreased porosity with crustal aging. However, there is no evidence for significant thickening of the oceanic crust with age, nor is there any evidence of a lower crustal layer of high or low velocity relative to the velocity of the rest of Layer 3. The compressional and shear wave velocities rule out a large component of serpentinization of mantle materials. The only evidence for a basal crustal layer of olivine gabbro cumulates is a 1.5 km thick Moho transition zone. In the slow direction of anisotropy, upper mantle velocities increase from 8.0 km s-1 to 8.35 km s-1 in the upper 15 km below the Moho. This increase is inconsistent with an homogeneous upper mantle and suggests that compositinal or phase changes occur near the Moho.
Tài liệu tham khảo
Anosov G. I., Argentov V. V., and Gnibidenko H. S., 1982, Crustal Low-velocity Zone South of Shatsky Rise, Northwest Pacific Ocean, Geo-Mar. Lett. 2, 17–21.
Arons A. B., 1948, Secondary Pressure Pulses due to Gas Globe Oscillation in Underwater Explosions. II. Selection of Adiabatic Parameters in the theory of Oscillation, J. Acous. Soc. America 20, 277–282.
Arons A. B., 1954, Underwater Explosion Shock Wave Parameters at Large Distances from the Charge, J. Acous. Soc. America 26, 343–346.
Arons A. B., Slifko J. P., and Carter A., 1948, Secondary Pressure Pulses due to Gas Globe Oscillation in Underwater Explosions. I. Expermental Data, J. Acous. Soc. America 20, 271–276.
Asada, T. and Shimamura, H., 1976, Observations of Earthquakes and Explosions at the Bottom of the Western Pacific: Structure of the Oceanic Lithosphere Revealed by Longshot Experiment, in G. H. Sutton, M. H. Manghnani, and R. Moberly (eds), The Geophysics of the Pacific Ocean Basin and its Margin, AGU, Geophys. Monogr. Ser. 19, Washington, D. C., 135–153.
Bibee L. D. and Shor G. G.Jr., 1976, Compressional Wave Anisotropy in the Crust and Upper Mantle, Geophys. Res. Lett. 3, 639–642.
Byrne D. A., Harris D., Duennebier F. K., and Cessaro R., 1987, The Ocean Sub-bottom Seismometer System Installed in Deep Sea Drilling Project Hole 581C, Leg 88: A Technical Review, Init. Repts. DSDP 88, 65–88.
Bratt S. R. and Purdy G. M., 1984, Structure and Variability of Oceanic Crust on the Flanks of the East Pacific Rise between 11°N and 13°N, J. Geophys. Res. 89, 6111–6125.
Carter J., Duennebier F. K., and Hussong D., 1984, A Comparison between a Downhole Seismometer and a Seismometer on the Ocean Floor, Bull. Seism. Soc. Am. 74, 763–772.
Chapman C. H., 1978, A New Method for Computing Synthetic Seismograms, Geophys. J. R. Astron. Soc. 54, 481–518.
Christensen N. I., 1974, Compressional Wave Velocities in Possible Mantle Rocks to Pressures of 30 kilobars, J. Geophys. Res. 79, 407–412.
Christensen N. I. and Salisbury M. H., 1975, Structure and Constitution of the Lower Oceanic Crust, Rev. Geophys. Space Phys. 13, 57–86.
Dorman L. M. and Jacobson R. S., 1981, Linear Inversion of Body Wave Data Part I: Velocity Structure from Traveltimes and Ranges, Geophysics 46, 138–151.
Duennebier F. K. and Blackinton G., 1983, The Ocean Subbottom Seismometer, in R. A. Geyer (ed), CRC Handbook of Geophysical Exploration at Sea, Boca Raton, Florida (CRC Press.), 317–332.
Duennebier F. K., Lienert B., Cessaro R., Anderson P., and Mallick S., 1987a, Controlled-source Seismic Experiment at Hole 581C, Init. Repts. DSDP 88, 105–125.
Duennebier F. K., McCreery C. S., Harris D., Cessaro R. K., Fisher C., and Anderson P., 1987b, OSS IV: Noise Levels, Signal-to-Noise Ratios, and Noise Sources, Init. Repts, DSDP 88, 89–103.
Duennebier F. K., Stephen R. A., Gettrust J. F. et al., 1987c, Site 581: Downhole Seismometer Experiment in the Northwest Pacific, Init. Repts. DSDP 88, 9–36.
Ewing J. I. and Purdy G. M., 1982, Upper Crustal Velocity Structure in the ROSE Area of the East Pacific Rise. J. Geophys. Res. 87, 8397–8402.
Fuchs K. and Müller G., 1971, Computation of Synthetic Seismograms with the Reflectivity Method and Comparison with Observations, Geophys. J. R. Astron. Soc. 23, 417–433.
Goslin J., Beuzart P., Francheteau J., and Le Pichon X., 1972, Thickening of the Oceanic Layer in the Pacific Ocean. Mar. Geophys. Res. 1, 418–427.
Grim M. S. and Gettrust J. F., 1987, Geophysical Site Survey Results: Leg 88, Init. Repts. DSDP 88, 39–53.
Heath G. R., Burckle L. H. et al., 1985, Site 581, Init. Repts. DSDP 86, 241–266.
Hilde, T. W. C., Isezaki, N., and Wageman, J. M., 1976, Mesozoic Seafloor Spreading in the North Pacific in G. H. Sutton, M. H. Manghnani, and R. Moberly (eds), The Geophysics of the Pacific Ocean Basin and its Margin, AGU, Geophys. Monogr. Ser. Vol. 19, Washington, D.C., 205–226.
Houtz R. and Ewing J., 1976, Upper Crustal Structure as a Function of Plate Age J. Geophys. Res. 81, 2490–2498.
Kempner W. C. and Gettrust J. F., 1982a, Ophiolites, Synthetic Seismograms, and Ocean Crustal Structure, 1. Comparison of Ocean Bottom Seismometer Data and Synthetic Seismograms for the Bay of Islands Ophiolite, J. Geophys. Res. 87, 8447–8462.
Kempner W. C. and Gettrust J. F., 1982b, Ophiolites, Synthetic Seismograms, and Oceanic Crustal Structure, 2. A Comparison of Synthetic Seismograms of the Samail Ophiolite, Oman, and the ROSE Refraction Data from the East Pacific Rise, J. Geophys. Res. 87, 8463–8476.
Kong L., Brocher T. M., and Stephen R. A., 1985, Spreading Rate Independence of Oceanic Seismic Layer 2, Geophys. Res. Lett. 12, 219–222.
Lewis B. T. R., 1978, Evolution of Ocean Crust Seismic Velocities, Ann. Rev. Earth Planet. Sci. 6, 377–404.
Purdy G. M., 1983, The Seismic Structure of 140 Myr Old Crust in the Western Central Atlantic Ocean, Geophys. J. R. Astron. Soc. 72, 115–137.
Raitt R. W., Shor G. G., Francis T. J. G. and Morris G. B., 1969, Anisotropy of the Pacific Upper Mantle, J. Geophys. Res. 74, 3095–3109.
Shearer P. M., Orcutt J. A., Jordan T. H., Whitmarsh R. B., Kim I. I., Adair R. G., and Burnett M. S., 1987, The Ngendei Seismic Refraction Experiment at Hole 595B-Ocean bottom Seismometer Data and Evidence for Crustal and Upper Mantle Anisotropy, Init. Repts. DSDP 91, 385–436.
Spudich P. and Orcutt J., 1980, A New Look at the Seismic Velocity Structure of the Oceanic Crust, Rev. Geophys. Space Phys. 18, 627–645.
Sutton, G. H., Maynard, G. L., and Hussong, D. M., 1971, Widespread Occurrence of a High Velocity Basal Layer in the Pacific Crust Found with Repetitive Sources and Sonobuoys, in J. G. Heacock (ed.), The Structure and Physical Properties of the Earth's Crust, AGU, Geophys. Monogr. Ser. 14, Washington, D.C., 193–209.
White R. S., 1979, Oceanic Upper Crustal Structure from Variable Angle Seismic Reflection-refraction Profiles, Geophys. J. R. Astron. Soc. 57, 683–726.
Whitmarsh R. B., Orcutt J. A., Jordan T. H., Adair R. G., and Shearer P. M., 1987, Velocity Bounds on the Seismic Structure of Mesozoic Crust and Upper Mantle in the Southwest Pacific Basin from Downhole Observations at DSDP Hole 595B, Init. Repts. DSDP 91, 437–444.