نتایج جستجو برای: mantle boundary

تعداد نتایج: 174924  

2004
Thorne Lay Edward J. Garnero

The past two decades have witnessed tremendous progress in seismological, geodynamical, geomagnetic, and mineral physics efforts to quantify deep Earth processes. Our understanding of structures and processes in the lowermost mantle has advanced accordingly, and there is now widespread agreement that some form of major thermo-chemical boundary layer (TCBL) exists on the mantle side of the core-...

Journal: :Science 2014
Denis Andrault Giacomo Pesce Mohamed Ali Bouhifd Nathalie Bolfan-Casanova Jean-Marc Hénot Mohamed Mezouar

The geological materials in Earth's lowermost mantle control the characteristics and interpretation of seismic ultra-low velocity zones at the base of the core-mantle boundary. Partial melting of the bulk lower mantle is often advocated as the cause, but this does not explain the nonubiquitous character of these regional seismic features. We explored the melting properties of mid-oceanic ridge ...

2006
H.-R. Wenk A. K. McNamara

A model is presented that simulates anisotropy development in a subducting slab from the upper–lower mantle boundary (661 km) to the core–mantle boundary (2891 km). Two phases are considered: orthorhombic MgSiO3-perovskite and cubic magnesiowuestite (Mg,Fe)O. Single crystal elastic properties at mantle conditions are obtained from existing density functional theory calculations and quasiharmoni...

2017
Paula Koelemeijer Arwen Deuss Jeroen Ritsema

Advances in our understanding of Earth's thermal evolution and the style of mantle convection rely on robust seismological constraints on lateral variations of density. The large-low-shear-wave velocity provinces (LLSVPs) atop the core-mantle boundary beneath Africa and the Pacific are the largest structures in the lower mantle, and hence severely affect the convective flow. Here, we show that ...

Journal: :فیزیک زمین و فضا 0
عبدالرحیم عسکری استادیار، گروه فیزیک، دانشگاه حکیم سبزواری، سبزوار، ایران براتعلی فیض آبادی استادیار، گروه فیزیک، دانشگاه حکیم سبزواری، سبزوار، ایران وحید ابراهیم زاده اردستانی دانشیار، گروه فیزیک زمین، موسسه ﮊئوفیزیک دانشگاه تهران، ایران

the mapping of the crust-mantle boundary surface is an important geophysical task, which the method of seismic profiling has dealt with profitably. there are, however, areas where the crustal structure is not known up to the present, and where the moho has as yet not been determined by geophysical sounding. in such areas the isostatic theory may be applied to give a first estimate of the depths...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2005
Wendy L Mao Yue Meng Guoyin Shen Vitali B Prakapenka Andrew J Campbell Dion L Heinz Jinfu Shu Razvan Caracas Ronald E Cohen Yingwei Fei Russell J Hemley Ho-kwang Mao

High-pressure experiments and theoretical calculations demonstrate that an iron-rich ferromagnesian silicate phase can be synthesized at the pressure-temperature conditions near the core-mantle boundary. The iron-rich phase is up to 20% denser than any known silicate at the core-mantle boundary. The high mean atomic number of the silicate greatly reduces the seismic velocity and provides an exp...

Journal: :Science 2010
G Fiquet A L Auzende J Siebert A Corgne H Bureau H Ozawa G Garbarino

Interrogating physical processes that occur within the lowermost mantle is a key to understanding Earth's evolution and present-day inner composition. Among such processes, partial melting has been proposed to explain mantle regions with ultralow seismic velocities near the core-mantle boundary, but experimental validation at the appropriate temperature and pressure regimes remains challenging....

2002
Eh Tan Michael Gurnis Lijie Han

[1] Numerical mantle convection models indicate that subducting slabs can reach the core-mantle boundary (CMB) for a wide range of assumed material properties and plate tectonic histories. An increase in lower mantle viscosity, a phase transition at 660 km depth, depth-dependent thermal expansivity, and depth-dependent thermal diffusivity do not preclude model slabs from reaching the CMB. We fi...

Journal: :Nature communications 2014
Motohiko Murakami Alexander F Goncharov Naohisa Hirao Ryo Masuda Takaya Mitsui Sylvia-Monique Thomas Craig R Bina

The possible presence of dense magmas at Earth's core-mantle boundary is expected to substantially affect the dynamics and thermal evolution of Earth's interior. However, the thermal transport properties of silicate melts under relevant high-pressure conditions are poorly understood. Here we report in situ high-pressure optical absorption and synchrotron Mössbauer spectroscopic measurements of ...

2014
Colton Lynner Maureen D. Long

Shear wave splitting of SK(K)S phases is often used to examine upper mantle anisotropy. In specific cases, however, splitting of these phases may reflect anisotropy in the lowermost mantle. Here we present SKS and SKKS splitting measurements for 233 event-station pairs at 34 seismic stations that sample D′′ beneath Africa. Of these, 36 pairs show significantly different splitting between the tw...

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