The post-spinel transformation in Mg2SiO4 and its relation to the 660-km seismic discontinuity

Citation
Sh. Shim et al., The post-spinel transformation in Mg2SiO4 and its relation to the 660-km seismic discontinuity, NATURE, 411(6837), 2001, pp. 571-574
Citations number
31
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Multidisciplinary,Multidisciplinary,Multidisciplinary
Journal title
NATURE
ISSN journal
0028-0836 → ACNP
Volume
411
Issue
6837
Year of publication
2001
Pages
571 - 574
Database
ISI
SICI code
0028-0836(20010531)411:6837<571:TPTIMA>2.0.ZU;2-Y
Abstract
The 660-km seismic discontinuity in the Earth's mantle has long been identi fied with the transformation of (Mg,Fe)(2)SiO4 from gamma -spinel (ringwood ite) to (Mg,Fe)SiO3-perovskite and (Mg,Fe)O-magnesiowustite. This has been based on experimental studies of materials quenched from high pressure and temperature(1-3), which have shown that the transformation is consistent wi th the seismically observed sharpness and the depth of the discontinuity at expected mantle temperatures(4). But the first in situ examination of this phase transformation in Mg2SiO4 using a multi-anvil press(5) indicated tha t the transformation occurs at a pressure about 2 GPa lower than previously thought (equivalent to similar to 600 km depth) and hence that it may not be associated with the 660-km discontinuity. Here we report the results of an in situ study of Mg2SiO4 at pressures of 20-36 GPa using a combination o f double-sided laser-heating and synchrotron X-ray diffraction in a diamond -anvil cell. The phase transformation from gamma -Mg2SiO4 to MgSiO3 perovsk ite and MgO (periclase) is readily observed in both the forward and reverse directions. In contrast to the in situ multi-anvil-press study(5), we rnd that the pressure and temperature of the post-spinel transformation in Mg2S iO4 is consistent with seismic observations(4,6) for the 660-km discontinui ty.