Lebedev Evgeny B, Kern Hartmut, Pavlenkova Ninely I, Lukanin Oleg A, Lobanov Konstantin V, Zharikov Andrey V, Popp Till
Vemadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, Kosygina Str. 19, Moscow, Russia, 119991.
Institut Fur Geowissenschaften der Universitat Kiel, Olshausenstrasse 40-60, 24098, Kiel, Germany.
Sci Rep. 2021 Jun 28;11(1):13424. doi: 10.1038/s41598-021-92248-2.
Deep seismic studies have revealed that low-velocity zones mainly occurred in the continental lithosphere at the depth of 100-150 km. Their origin has not been clearly explained yet. The article demonstrates the possible scale of Vp changes in crystalline rocks of different composition. The conclusions were made on the basis of the comprehensive analysis of the experimental data obtained by the authors. The compressional wave velocities in the temperature range from 20 to 800 °C, both in dry conditions (at pressure of 600 MPa) and in the presence of aqueous fluid (at pressure of 300 MPa) were measured. It is shown that the most significant decrease of velocities (by ~ 3 km/s) in the temperature range of 400-700 °C, corresponding to the deep waveguides of the lithospheric mantle, occurs under water pressure in ultramafic rocks enriched by olivine (dunites). Such decrease is due to rock structure changes caused by olivine serpentinization reactions. It is assumed that serpentinization and/or formation of similar hydrous minerals, which are stable in a wide range of PT-conditions in olivine-rich mantle rocks due to the influence of deep fluids, may cause low-velocities zones in the upper mantle at depths of about 100 km.
深部地震研究表明，低速带主要出现在大陆岩石圈深度100 - 150千米处。其成因尚未得到明确解释。本文展示了不同成分结晶岩中纵波速度变化的可能范围。这些结论是基于作者对所获实验数据的综合分析得出的。测量了在干燥条件下（600兆帕压力）以及存在含水流体时（300兆帕压力），温度范围从20到800摄氏度的压缩波速度。结果表明，在富含橄榄石的超镁铁岩（纯橄岩）中，对应于岩石圈地幔深部波导的400 - 700摄氏度温度范围内，在水压作用下速度出现最显著下降（约3千米/秒）。这种下降是由橄榄石蛇纹石化反应导致的岩石结构变化引起的。据推测，由于深部流体的影响，在富含橄榄石的地幔岩石中，在广泛的压力 - 温度条件下稳定的蛇纹石化和/或类似含水矿物的形成，可能导致上地幔深度约100千米处出现低速带。
