Abstract
AbstractThe upper boundary of the mantle transition zone, known as the “410-km discontinuity”, is attributed to the phase transformation of the mineral olivine (α) to wadsleyite (β olivine). Here we present observations of triplicated P-waves from dense seismic arrays that constrain the structure of the subducting Pacific slab near the 410-km discontinuity beneath the northern Sea of Japan. Our analysis of P-wave travel times and waveforms at periods as short as 2 s indicates the presence of an ultra-low-velocity layer within the cold slab, with a P-wave velocity that is at least ≈20% lower than in the ambient mantle and an apparent thickness of ≈20 km along the wave path. This ultra-low-velocity layer could contain unstable material (e.g., poirierite) with reduced grain size where diffusionless transformations are favored.
Funder
Alexander von Humboldt-Stiftung
National Scientific Foundation of China
National Science Foundation
Startup fund of Min Chen at Michigan State University
Publisher
Springer Science and Business Media LLC
Subject
General Earth and Planetary Sciences,General Environmental Science
Reference56 articles.
1. Anderson, D. L. Phase changes in the upper mantle. Science 157, 1165–1173 (1967).
2. Ringwood, A. E. Composition and Petrology of the Earth’s Mantle. MacGraw-Hill 618 (1975).
3. Niazi, M. & Anderson, D. L. Upper mantle structure of western North America from apparent velocities of P waves. J. Geophys. Res. 70, 4633–4640 (1965).
4. Johnson, L. R. Array measurements of P velocities in the upper mantle. J. Geophys. Res. 72, 6309–6325 (1967).
5. Flanagan, M. P. & Shearer, P. M. Global mapping of topography on transition zone velocity discontinuities by stacking SS precursors. JGR Solid Earth 103, 2673–2692 (1998).