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Petrophysics Annual Report 2001 - Introduction

The Group's research centres on investigation of the physical behaviour of geological materials under controlled laboratory conditions and application of the resulting insights to the structure and processes of the Earth.

Measurements of macroscopic physical properties such as strength, permeability or seismic wave speeds and attenuation, are interpreted through microstructural studies centred around light and electron microscopy. Often it is necessary to prepare, from either natural or synthetic precursors, simpler synthetic materials whose properties are amenable to more detailed interpretation than those of complex natural rocks. Our interest in Earth materials is shared by members of the School's Petrochemistry and Experimental Petrology Group, who focus primarily upon the chemical aspects of their behaviour.

Geological and geophysical observations of the response of the Earth to naturally applied stresses, which vary widely in intensity and timescale, provide much of the motivation for the Group's work. In the laboratory, ultrasonic wave propagation and lower frequency forced-oscillation methods are used to probe the elastic/anelastic behaviour which determines seismic wave speeds and attenuation. On longer time scales and at higher stresses, the mechanical behaviour of synthetic faults and fault gouge is studied with particular interest in the complex interaction between chemical reaction, crustal deformation and fluid flow. The fact that all but the simplest elastic behaviour of geological materials is controlled by microscopic defects such as dislocations and processes operative at grain boundaries, places a premium on the complementary microstructural studies involving light and electron microscopy.

Major achievements for 2001 include

  • Demonstration of the capability for accurate high-temperature (to 1600 K) measurement of elastic wave speeds by ultrasonic interferometry
  • Identification of a melt-related dissipation peak in an exploratory study of the influence of partial melting on seismic wave attenuation in fine-grained polycrystalline olivine.

Members of the group collaborate widely within the School and beyond. Natural links with the Seismology Group are based on a common interest in the interpretation of seismological models for the Earth's interior. Preparation of synthetic rock specimens and their precursors and investigations of melt distribution within partially molten upper mantle rocks involve intensive collaboration between the Petrophysics and Petrochemistry and Experimental Petrology Groups. The field-based observations of the structures and microstructures in naturally deformed rocks, and fluid-chemical studies by members of the Centre for Advanced Studies of Ore Systems (RSES and Geology Department, Faculty of Science), complement the experimental program in rock deformation.

Within the wider ANU community, the influence of the Petrophysics Group is felt in a variety of forums. The ANU's flagship TEM serving the needs of the campus materials science community, is housed within the School and operated by Dr. Fitz Gerald and Mr. D. Llewellyn on behalf of the ANU Electron Microscope Unit. In this capacity, Dr Fitz Gerald collaborates intensively in microstructural aspects of various materials science programs particularly those of the Research School of Physical Sciences and Engineering. Maintaining the group's longstanding commitment to the enrichment of undergraduate teaching, Dr. Jackson this year contributed a condensed matter continuum mechanics segment to the undergraduate physics unit PHYS2016.

The successful operation of novel equipment, and the further development and timely exploitation of associated experimental techniques, depend heavily'upon the skill and commitment of research support staff Messrs H. Kokkonen and J. Carr and Ms. L. Weston along with the staff of the School's Mechanical and Electronics Workshops. Mrs K. Provins provides invaluable administrative support for the activities of the Petrophysics and Ore Genesis Groups, including responsibility for website development and maintenance. With the arrival of School-funded post-doc Eric Tenthorey from Columbia University, New York and the funding this year of two new ARC proposals, the Group is well positioned to pursue the ambitious research agenda outlined below. It is with regret that we farewell Joshua Carr after just two productive years with the Group as a trainee technical officer and wish his well in his new career.

Seismic wave attenuation in polycrystalline olivine: the influence of grain size and partial melting Ian Jackson, John Fitz Gerald, Uli Faul, Harri Kokkonen and Joshua Carr

A test of an alternative finite-strain equation-of-state for the lower mantle Ian Jackson

Fluid flow, vein formation and permeability evolution in the Earth's Crust Eric Tenthorey, Stephen Cox and Christoph Hilgers