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I. The heterogeneities at the core-mantle and inner-core boundaries from PKP phases. II. The static and dynamic behavior of silica at high pressures

Citation

Luo, Sheng-Nian (2003) I. The heterogeneities at the core-mantle and inner-core boundaries from PKP phases. II. The static and dynamic behavior of silica at high pressures. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-05302003-174154

Abstract

Waveform and differential travel-time (DTT) of various PKP phases have been utilized to study the velocity variations at the core-mantle boundary (CMB) and the inner-core boundary (ICB). The spatial concentration of events and stations, and the significant variations in PKPab-PKPdf DTT and waveform of PKPab, indicate localized sharp lateral variation of velocity at the CMB as supported by simulations. Modeling of DTT's among PKiKP, PKIKP and PKP-B-diffracted ($B_{diff}$) phases, and waveform of $B_{diff}$ supports that the ratio of relative velocity variations of S- and P-wave at the CMB is larger than 2, and that hemispheric P-wave velocity variations exist at the top of the inner core, and that D' structure is related to the ICB via core dynamics. The equation of state of stishovite is obtained by direct shock wave loading up to 235 GPa as $K_{0T}=306pm 5$ GPa and $K_{0T}^{'}=5.0pm 0.2$ where $K_{0T}$ is ambient bulk modulus and $K_{0T}^{'}$ its pressure derivative. Phase diagram of silica (including melting curve) up to megabar pressure regime is established based on molecular dynamics (MD) simulations and dynamic and static experiments. Calculations show that perovskite is thermodynamically stable relative to the stishovite and periclase assemblage at lower mantle conditions. A detailed and quantitative examination is conducted on the thermodynamics and phase change mechanisms (including amorphization) that occur upon shock wave loading and unloading of silica. The systematics of maximum undercooling and superheating, are established by incorporating normalized energy barrier for nucleation and heating (cooling) rate, and validated at the atomic level with systematic MD simulations. By considering superheating in shock wave experiments, high-pressure melting curves for silica, alkali halides and transition metals are constructed based on the Lindemann law and the $ln2$ rule for the entropy of melting.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:high pressure; melting; molecular dynamics; PKP phases; shock wave; silica; superheating and undercooling
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geological and Planetary Sciences
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Ahrens, Thomas J. (advisor)
  • Helmberger, Donald V. (co-advisor)
Thesis Committee:
  • Clayton, Robert W. (chair)
  • Helmberger, Donald V.
  • Ravichandran, Guruswami
  • Asimow, Paul David
  • Ahrens, Thomas J.
Defense Date:21 April 2003
Record Number:CaltechETD:etd-05302003-174154
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-05302003-174154
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2300
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:10 Jun 2003
Last Modified:26 Dec 2012 02:49

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