17th GRC International Frontier Seminar
Electronic Spin Transition of Iron
in the Earth’s Deep Mantle
Dr. Jung-Fu Lin
Lawrence Livermore National Laboratory, USA
30 March 2007 17:0-18:00
Room 101, Kogi-to Bldg, Faculty of Science, Ehime University
Mineralogical models of the planet indicate that the lower mantle, the
most voluminous layer of the Earth, consists of approximately 20% ferropericlase
[(Mg,Fe)O] and approximately 80% silicate perovskite [(Mg, Fe)SiO3] containing
minor amounts of aluminum, in addition to a small amount of calcium silicate
perovskite (CaSiO3). Iron (Fe) is the most abundant 3d transition metal
in the mantle, substituting for magnesium (Mg) at a level of about 20%
in ferropericlase and about 10% in silicate perovskite. The unique properties
of iron give rise to complex physical and chemical properties of Earth’s
lower mantle. Iron exhibits two main valence states in silicates and oxides:
ferrous iron (Fe2+) with six 3d electrons and ferric iron (Fe3+) with five
3d electrons. The electronic configuration of iron therefore depends on
its oxidation state, that is, the number of valence electrons. Under ambient
conditions, ferrous iron in the lower-mantle ferropericlase, for example,
is in the high-spin state with four unpaired and two paired 3d electrons,
i.e., the maximum number of unpaired electrons possible. To the astonishment
of mineral physicists, pressure-induced electronic spin-pairing transitions
of iron and associated effects on the physical properties of host phases
have been recently reported in lower-mantle minerals including ferropericlase,
silicate perovskite, and possibly in post-silicate perovskite at high pressures
(Ref. 1-3). These mineral physics studies have prompted geophysicists and
geodynamicists to re-evaluate the state of the lower mantle, and in particular
the possible sources of seismic heterogeneity, as well as the thermal stability
of massive upwellings in terms of spin-pairing phenomena. Here I will discuss
what is known about the nature of the spin transition, focusing on the
possible effects on the physical properties of the deep mantle such as
seismic velocities and transport properties, as well as on the effects
of pressure and temperature on the spin transitions. Future challenges
and opportunities in the studies of the spin transitions will also be addressed
so as to stimulate experimentalists and theorists to explore this new frontier
collaboratively.
1. J. F. Lin, V. V. Struzhkin, S. D. Jacobsen, M. Hu, P. Chow, J. Kung, H. Liu, H. K. Mao, and R. J. Hemley, Spin transition of iron in magnesiowustite in Earth’s lower mantle, Nature, 436, 377-380, 2005.
2. J. F. Lin, S. D. Jacobsen, W. Sturhahn, J. M. Jackson, J. Zhao, and C. S. Yoo, Sound velocities of ferropericlase in Earth’s lower mantle, Geophys. Res. Lett., 33,?L22304, doi:10.1029/2006GL028099, 2006.
3. J. F. Lin, S. D. Jacobsen, and R. M. Wentzcovitch, Electronic spin transition of iron in the Earth's deep mantle, Eos. Trans. American Geophysical Union, 88, 2, pages 13,17, 2007.
お問い合わせ先： irifune@dpc.ehime-u.ac.jp TEL 089-927-9645
詳細情報：http://www.ehime-u.ac.jp/~grc/
主催：愛媛大学地球深部ダイナミクス研究センター
