HR: 0830h
AN: S31E-0796    [PDF]
TI: Exceptional High Seismic P-wave Velocity of the Uppermost Mantle around the Mirny Kimberlite in Siberia
AU: Suvorov, V D
EM:
AF: Institute of Geophysics, Russian Academy of Sciences-Siberian Branch (RAS-SB), Prospect Koptuga 3, Novosibirsk, 630090 Russian Federation
AU: Melnik, E A
EM:
AF: Institute of Geophysics, Russian Academy of Sciences-Siberian Branch (RAS-SB), Prospect Koptuga 3, Novosibirsk, 630090 Russian Federation
AU: Thybo, H
EM: thybo@geol.ku.dk
AF: Geological Institute, University of Copenhagen, Oster Voldgade 10, Copenhagen, DK-1350 K Denmark
AU: * Perchuc, E
EM:
AF: Geophysical Institute, Polish Academy of Sciences, Ks. Janusza 64, Warsaw, PL-01452 Poland
AB: We present seismic velocity models along two perpendicular seismic profiles with their crosspoint 30 km to the south of the Mirny Kimberlite Pipe in Yakutia, Siberia. The data comprises recently digitized seismograms from vintage seismic sections that were acquired in 1981-1983 by use of Taiga analogue seismographs. 41 seismographs were deployed along the 370 km long, NW-striking profile I, which crosses the kimberlite pipe. 45 seismographs were deployed along the perpendicular 340 km long profile II. The sources were 20 chemical shots along each profile, loaded with between 1.5 and 6.0 ton of TNT distributed in individual charges of 100-200 kg in shallow water ($<$2 m deep). The data is of high quality with high signal/noise ratio to the furthest offsets. We have interpreted the data with seismic tomographic inversion of first arrivals and with 2D ray- tracing, forward modelling. The velocity models show normal cratonic structure of the ca. 45 km thick crust with only slight undulation of the Moho around Mirny. Low velocity anomalies are detected to 25 km depth in a ca. 60 km wide zone at the kimberlite pipe. Extremely high P-wave velocity ($>$8.7 km/s) of the sub-Moho mantle is interpreted along almost all of profile I, with an 80 km wide, low-velocity anomaly below the kimberlite. Profile II mainly shows Pn velocities of 8.0-8.2 km/s, with high velocity ($>$8.5 km/s) in two, ca. 100 km wide zones at its SW end. The nature of these exceptionally high, sub-Moho mantle velocities is not yet understood. The difference in velocity in the two profile directions indicate anisotropy, but the influence of unusual rock composition, e.g. from a high concentration of garnet, cannot be excluded.
DE: 7200 SEISMOLOGY
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8145 Physics of magma and magma bodies
SC: Seismology [S]
MN: 2003 Fall Meeting