Transition zone (Earth)

The mantle transition zone is defined by geophysical significant jumps in velocity of seismic waves and is on average 410-660 km depth. The transition zone is characterized by an increase in the density of 3.42 g / cm ³ in the lowermost upper mantle to 3.9 g / cm ³ at the top lower mantle.

Phase transitions

The change of the shaft speeds can be reduced to essentially three phase transitions of certain minerals, which are presented in the following oversimplified today. The depth data is global averages. The stable in the upper mantle olivine goes from 410 km depth in wadsleyite and later from about 520 km depth in ringwoodite over. The lower edge of the transition zone is formed by the phase transition from ringwoodite to Mg - perovskite and magnesiowüstite in an average of 660 km depth.

Significance for geodynamics

The mantle transition zone is due to the phase transitions and the occurring here denser rocks initially an obstacle for further subduction and thus a Ganzmantelkonvektion represents, according to recent findings, however, a descent of the plate remains up to the core - mantle boundary seems very likely.

According to one study, it could also lead to partial melting and / or drainage of former oceanic crust in the transition zone, which Manteldiapire might arise. Found inclusions of majorite in diamonds prove an origin of rocks at least from the mantle transition zone ( sometimes also a deeper origin occupied).

Swell

  • Kearey P. (2008): Global Tectonics. 3rd Edition. S.32f
  • T. Stachel: inclusions in diamonds - " holes " in the deep mantle. http://www.uibk.ac.at/mineralogie/oemg/bd_145/145_031-037.pdf
  • Dapeng Zhao: Global tomographic images of mantle plumes and subducting slabs: insight into deep Earth dynamics, Physics of the Earth and Planetary Interiors, Volume 146, Issues 1-2, 16 August 2004 Pages 3-34, ISSN 0031-9201, 10.1016 / j.pepi.2003.07.032. ( http://www.sciencedirect.com/science/article/pii/S0031920104001086 )
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