Materials Theory and Mineral Physics erview of methods orphization of quartz under pressure ructural transitions in ruby and the ruby pressure ermoelasticity of LM minerals and the problem f LM temperature and composition ilog Renata Wentzcovitch CEMS, U of MN
Materials Theory and Mineral Physics. Renata Wentzcovitch CEMS, U of MN. • Overview of methods • Amorphization of quartz under pressure • Structural transitions in ruby and the ruby pressure scale • Thermoelasticity of LM minerals and the problem - PowerPoint PPT Presentation
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Materials Theory and Mineral Physics
• Overview of methods
• Amorphization of quartz under pressure
• Structural transitions in ruby and the ruby pressure scale • Thermoelasticity of LM minerals and the problem of LM temperature and composition
• Nature of the intermediate phase of silica seems to be understood • Properties: produced by a soft mode structure consists of 6-, and 5-fold Si at 33 GPa it is 10% denser than quartz (H ~ 0.1 eV/atom)
• Amorphous could be the result of a generalized phonon stability
Optical transitions in ruby across the corundum to Rh2O3 (II) phase transformation
Collaborators: W. Duan (U. of MN), G. Paiva (USP), & A. Fazzio (USP)Support: NSF, CNPq, and FAPESP
Structural Transition in Ruby (Al2O3:Cr)
• PIB (Cynn et al.-1990 and Bukowinski – 1994). Between 4 and 148 GPa
Thermal expansivity of MgO & MgSiO3-pv(Karki, Wentzcovitch, Gironcoli and Baroni, GRL in press)
(1
0-5 K
-1)
(1
0-5 K
-1)
MgSiO3-perovskite and MgO
(gr/cm-3)
V (A3)
KT
(GPa) d KT/dP d KT
2/dP2
(GPa-1) d KT/dT (Gpa K-1)
10-5 K-1
3.580 18.80 159 4.30 -0.030 -0.014 3.12 Calc. MW
3.601 18.69 160 4.15 ~ -0.0145 3.13 Exp. MW
4.210 164.1 247 4.0 -0.016 -0.031 2.1 Calc. Pv
4.247 162.3 246 | 266
3.7 | 4.0
~ -0.02 | -0.07
1.7 | 2.2
Exp. Pv
Exp.: [Ross & Hazen, 1989; Mao et al., 1991; Wang et al., 1994; Funamori et al., 1996; Chopelas, 1996; Gillet et al., 2000; Fiquet et al., 2000]
Elastic moduli of MgO at high P and T(Karki et al. 1999, 2000)
KS at Lower Mantle P-T
300 K 1000 K 2000 K 3000 K
LM Geotherms
1000
2000
3000
4000
5000
6000
500 1000 1500 2000 2500 3000
T (
K)
Depth (km)
Pv
Solidus
Isentropes
Pyrolite
CMB |
Tc
Me
“…At depths greater than 1200 km, the rate of rise of the bulk modulus is too small for the lower mantle to consist of an adiabatic and homogeneous layer of standard chondritic or pyrolitic composition. Superadiabatic gradients, or continuous changes in chemical composition, or phase, or all are required to account for the relatively low bulk modulus of the deeper part of the LM ,….” (Wentzcovitch, 2001)