Publication Date:
2018-07-05
Description:
Publication date: 15 September 2018 Source: Earth and Planetary Science Letters, Volume 498 Author(s): Johannes Buchen, Hauke Marquardt, Sergio Speziale, Takaaki Kawazoe, Tiziana Boffa Ballaran, Alexander Kurnosov Earth's transition zone at depths between 410 km and 660 km plays a key role in Earth's deep water cycle since large amounts of hydrogen can be stored in the nominally anhydrous minerals wadsleyite and ringwoodite, ( Mg,Fe ) 2 SiO 4 . Previous mineral physics experiments on iron-free wadsleyite proposed low seismic velocities as an indicative feature for hydration in the transition zone. Here we report simultaneous sound wave velocity and density measurements on iron-bearing wadsleyite single crystals with 0.24 wt-% H 2 O . By comparison with earlier studies, we show that pressure suppresses the velocity reduction caused by higher degrees of hydration in iron-bearing wadsleyite, ultimately leading to a velocity cross-over for both P-waves and S-waves. Modeling based on our experimental results shows that wave speed variations within the transition zone as well as velocity jumps at the 410-km seismic discontinuity, both of which have been used in previous work to detect mantle hydration, are poor water sensors. Instead, the impedance contrast across the 410-km seismic discontinuity that is reduced in the presence of water can serve as a more robust indicator for hydrated parts of the transition zone.
Print ISSN:
0012-821X
Electronic ISSN:
1385-013X
Topics:
Geosciences
,
Physics
