Яндекс.Метрика

V.D. Suvorov, E.A. Melnik,H.Thybo,E.Perchuc,B.S.Parasotka

Выпуск: 1-2 , Том: 420 , Год издания: 2006
Сериальное издание: Tectonophysics
Страницы: 49-73

Аннотация

We present the first detailed seismic velocity models of the crust and uppermost mantle around the Mimyi kimberlite field in Yakutia, Siberia. We have digitized vintage seismograms that were acquired in 1981 and 1983 by use of Taiga analogue seismographs along two perpendicular seismic profiles. The 370-km long, northwest striking profile I across the kimberlite pipe was covered by 41 seismographs, which recorded seismic signals from 21 chemical shots along the line, including one off-end shot. The perpendicular, 340-km long profile II across profile I ca. 30km to the south of the Mimyi kimberlite field was covered by 45 seismographs, which recorded seismic signals from 22 chemical shots, including four off-end shots. Each shot involved detonation of between 1.5 and 6.0tons of TNT, distributed in individual charges of 100-200kg in shallow water (<2m deep). The data is of high quality with high signal/noise ratio to the farthest offsets. We present the results from two-dimensional ray tracing, forward modelling. Both velocity models show normal cratonic structure of the ca. 45-km-thick crust with only slight undulation of the Moho. However, relatively small seismic velocity is detected to 25-km depth in a ca. 60-km wide zone around the kimberlite pipe, surrounded by elevated velocity (>6.3 km/s) in the upper crust. The lower crust has a relatively constant velocity of 6.8-6.9km/s. It appears relatively unaffected by the presence of the kimberlite field. Extremely large P-wave velocity (> 8.7 km/s) of the sub-Moho mantle is interpreted along profile 1, except for a 70-km wide zone with a ''normal'' Pn velocity of 8.1 km/s below the kimberlite. Profile 11 mainly shows Pn velocities of 8.0-8.2km/s, with unusually large velocity (>8.5km/s) in two, ca. 100-km wide zones, at its southwestern end, one zone being close to the kimberlite field. The nature of these exceptionally large, sub-Moho mantle velocities is not yet understood. The difference in velocity in the two profile directions indicates anisotropy, but the effect of unusual rock composition, e.g. from a high concentration of garnet, cannot be excluded.
индекс в базе ИАЦ: 026909