lithosphere
; lower mantle
; marine environment
; numerical model
; slab
; subduction zone
; viscosity
英文摘要:
Subduction of oceanic lithosphere is the main process by which material from Earth's surface and atmosphere is recycled back into the deep mantle. Seismic images indicate that subducting slabs of oceanic lithosphere can stagnate and broaden in the shallow lower mantle. The main phases of the lower mantle, bridgmanite and ferropericlase, do not show any structural transitions at these depths, so only moderate and smooth viscosity variations are expected with depth to at least ∼2,500 km. The reason for slab stagnation, which may also lead to the formation of chemically distinct reservoirs in Earth's deep mantle, is therefore unclear. Here we use synchrotron radial X-ray diffraction to measure in situ the deformation behaviour of ferropericlase at pressures of up to 96 GPa. We find that the strength of ferropericlase increases by a factor of three at pressures from 20 to 65 GPa. Modelling based on our experimental data shows that the viscosity in the region surrounding the subducting slabs could increase by 2.3 orders of magnitude throughout the upper 900 km of the lower mantle. Such a strong increase in viscosity can lead to the stagnation of slabs that are sinking through the shallow lower mantle.
GFZ German Research Centre for Geosciences, Telegrafenberg, Potsdam, Germany; University of Utah, 115 So. 1460 E., Salt Lake City, UT, United States; Bayerisches Geoinstitut BGI, University of Bayreuth, Bayreuth, Germany
Recommended Citation:
Marquardt H.,Miyagi L.. Slab stagnation in the shallow lower mantle linked to an increase in mantle viscosity[J]. Nature Geoscience,2015-01-01,8(4)