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Part 1. Dynamic Response of Phase Boundaries in the Earth to Surface Loading. Part 2. Pleistocene Glaciation and the Viscosity of the Lower Mantle


O'Connell, Richard John (1969) Part 1. Dynamic Response of Phase Boundaries in the Earth to Surface Loading. Part 2. Pleistocene Glaciation and the Viscosity of the Lower Mantle. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3JGM-5Q68.


Part 1. Analytic approximate solutions have been found for the response of a phase change to pressure loading. These solutions allow the behavior of the system to be analyzed in terms of simple parameters of the system. Different characteristic types of behavior are shown to obtain for short times and long times, and criteria for defining these characteristic time scales are given in terms of known parameters. The distribution of heat sources and convective heat transport are shown to generally have only minor influence on the solution, and may be neglected in many cases. The important parameters are the latent heat of the phase change, and the difference between the Clapeyron slope and the temperature gradient at the phase boundary; in addition the long term behavior is governed by the boundary conditions at the surface and at depth, and the relative positions of the surface, the phase boundary, and the lower boundary. The effect of thermal blanketing from sediments is included in the solution, and it depends primarily on the depth of the phase boundary and the average temperature gradient in the sediments. The effect of isostasy in conjunction with a phase change is shown to be of major importance; the existence of instabilities where the water depth increases with sedimentation are demonstrated. These solutions allow the history of a sedimentary basin to be calculated, and characterized in terms of certain types of behavior. The existence of oscillatory behavior is demonstrated, where repeated cycles of sedimentation and erosion take place. These oscillations can either decay or grow in amplitude, and expressions are given for their frequency and damping or growth constants. A phase change mechanism can account for thicknesses of sediments which exceed the depth of the basin in which they were deposited by a factor of twenty or more. These solutions allow the discussion of the geological implications of phase changes in a quantitative manner. The consequences of a phase change can be accurately calculated. This will allow the more complete investigation of the role of phase changes in geologic processes.

Part 2. The non-tidal acceleration of the earth, revealed by astronomical observations and records of eclipses in antiquity, is attributed to the change in the earth's moment of inertia resulting from isostatic response to the most recent deglaciation and rise in sea level. The isostatic response time for a spherical harmonic deformation of degree two is calculated on this basis to be either ~2000 years or ~100,000 years. A correlation of the geopotential with the potential that would have existed following de glaciation indicates that any large scale anomalies resulting from deglaciation have already decayed. This rules out the 100,000 relaxation time; thus the relaxation time of the earth is ~2000 years for degree two. Calculations of the relaxation time spectrum of a layered, gravitating spherical viscous earth model indicates that a model with a uniform mantle viscosity of ~10^(22) poise, except for fine structure in the upper few hundred kilometers, can satisfy the relaxation time of 3000 years for degree two as well as the relaxation time of ~4000 years for degree twenty which results from studies of uplift in Fennoscandia. A zone of high viscosity in the lower 800 km. of the mantle has a significant effect on the degree two relaxation time. This rules out any substantial increase in viscosity in the lower mantle. The calculated viscosity permits rapid polar wandering and convection in the lower mantle.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Geophysics
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Wasserburg, Gerald J. (advisor)
  • Anderson, Don L. (co-advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:19 May 1969
Funding AgencyGrant Number
NASANGL 05-002-069
Record Number:CaltechTHESIS:04052018-084913740
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10792
Deposited By: Tony Diaz
Deposited On:09 Apr 2018 17:12
Last Modified:21 Dec 2019 01:52

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