低速区

低速区(LVZ)是上地幔接近岩石圈软流圈边界处,地震波横波速度显著偏低、电导率显著偏高的区域。深度从80km至300km。其中部分区域的地震波纵波缺失。[2][2][3][4]

地震波速度与深度的关系。[1] 在靠近地表 (≲ 220±30 km)的波速显著低,称为低速区。

另外一个地震波速显著降低的区域在核幔邊界的不超过50km的薄层,称为超低速区英语Ultra low velocity zone(ULVZ)。[3]

低速区可以用部分熔化英语partial melting(约1%)解释。[2]水可以降低熔点,扮演了重要角色。[4][5]

1959年,賓諾·古登堡在研究地震波的波速时指出在距离震中1-15°的区域内,纵波振幅会呈现突然增加然后呈指数下降的现象。[6][7]

地震横波在3个地质省的差别:TNA=北美板块;SNA= 北美地盾; & ATL =北大西洋。[8]

地震波的横波在低速区下降了3–6%,比纵波波速变化更显著。[9]雷氏不連續面是低速区的下界。

只需要0.05–0.1 %的水就可导致1%的熔融,产生低速区。地盾下缺乏低速区可解释为地热梯度太小,阻止了部分熔融。[10]

参见编辑

参考文献编辑

  1. ^ GR Helffrich & BJ Wood. The Earth's Mantle (PDF). Nature (Macmillan Magazines). 2002, 412 (2 August): 501; Figure 1. doi:10.1038/35087500. [失效連結]
  2. ^ 2.0 2.1 2.2 L Stixrude & C Lithgow-Bertolloni. Mineralogy and elasticity of the oceanic upper mantle: Origin of the low-velocity zone (PDF). Journal of Geophysical Research. 2005, 110: B03204 [2018-12-16]. Bibcode:2005JGRB..11003204S. doi:10.1029/2004JB002965. (原始内容 (PDF)存档于2011-08-30). 
  3. ^ 3.0 3.1 EJ Garnero, MS Thorne, A McNamara & S Rost. Chapter 6: Fine-scale ultra-low-velocity zone layering at the core-mantle boundary and superplumes. David A Yuen; Shigenori Maruyama (编). Superplumes: beyond plate tectonics. Springer. 2007: 139. ISBN 1-4020-5749-0. 
  4. ^ 4.0 4.1 Philip Kearey; Keith A. Klepeis; Frederick J. Vine. Global tectonics 3rd. Wiley-Blackwell. 2009: 32. ISBN 1-4051-0777-4. 
  5. ^ It is hypothesized that the absence of plate tectonics on the planet Venus is due to the absence of water in its crust and upper mantle. Cooling occurs largely through mantle plumes. See Gillian R. Foulger. Plates, plumes, and paradigms; Volume 388 of Special papers. Geological Society of America. 2005: 857. ISBN 0-8137-2388-4. 
  6. ^ Gutenberg, B. Physics of the Earth's Interior. New York: Academic Press. 1959: 240. ISBN 0-12-310650-8. 
  7. ^ Anderson, D.L. 3. The Crust and Upper Mantle. Theory of the Earth (PDF). Boston: Blackwell Scientific Publications. 1989 [2010-02-20]. ISBN 0-521-84959-4. (原始内容 (PDF)存档于2010-06-23). 
  8. ^ Figure patterned after Don L Anderson. New theory of the earth 2nd. Cambridge University Press. 2007: 102, Figure 8.6. ISBN 0-521-84959-4. ; Original figure attributed to Grand & Helmberger (1984)
  9. ^ Brown, G.C.; Mussett A.E. The inaccessible earth. Taylor & Francis. 1981: 235 [2010-02-20]. ISBN 978-0-04-550028-4. 
  10. ^ Condie, K.C. Plate tectonics and crustal evolution. Butterworth-Heinemann. 1997: 282 [2010-02-20]. ISBN 978-0-7506-3386-4.