RCN Proposal

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This page contains the work-in-progress proposal for the Research Coordination Network, and the different sections written by the committee. As more changes are made and sections are added, the individual sections will be broken off into their own linked pages to reduce overall chaos, clutter, and confusion.


DRAFT Outline of RCN Proposal:

Rationale

  • Communities (PPEM email list, MSA list, and COMPRES list)
  • Research Opportunities
  • Science
  • Synchrotron Timing
  • Technical Developments

Plan

  • What Workshops are needed?
  • Beamline visits
  • What science can be done with what Technology

Management Plan

  • P.I.
  • Steering Committee


Why synchrotron-based mineral-rock physics?

Composition and structure of Earth (and other planets) can be studied based on the combination of various observations (gravity, composition of various planetary materials (e.g., mantle rocks, meteorites), seismic velocities, etc.) and the results of studies on materials properties under extreme conditions. There have been major progress in both fields, and we now have a good model of composition of Earth and other planets.

However, Earth and other planets are not static bodies but they are dynamic and evolving. Presence of earthquakes (on Earth) and volcanism and geochemical observations on some isotopes demonstrate this for a broad range of time scales. Consequently, many key questions on Earth (and other planets) can be addressed only through the studies on the dynamics and evolution of these planets. For example, one may ask how has Earth maintained temperate climate for billions of year that allowed life to emerge and evolve. One may also ask why plate tectonics operates on Earth but not on Venus. From more societal point of view, one may ask why fault motion is unstable causing earthquakes in some cases, while it is stable or nearly stable in other cases (slow earthquakes versus “normal” earthquakes). And as we will show later, when properties or processes related to the dynamics and evolution of Earth are to be studied, one will need to characterize heterogeneous and evolving properties that requires a use of a large volume apparatus combined with high resolution probes such as high intensity x-ray provided by a synchrotron facility.

A wide range of geological, geophysical and geochemical observations provides hints (constraints) on how these dynamic and processes might occur or have been occurring on Earth and on other planets. They include the distribution and frequency of earthquakes, the distribution of seismic wave velocities, attenuation and electrical conductivity, and the chemical composition of various materials including basaltic rocks and mantle rocks. In addition, geodetic measurements of crustal motion after the melting of ice sheets or after an earthquake provide constraints on rheological properties of Earth’s interior that control the nature of materials circulation.

However, understanding the evolution and dynamics of Earth and other planets through these observations is not straightforward. For example, deformation of rocks is often time-dependent and non-uniform. Strength of rocks at short time scales (e.g., deformation after the melting of ice sheets) and that at longer time scales (e.g., deformation associated with plate motion) can be largely different. Localized deformation is often found and plays a critical role in various geological processes, but charactering the processes of localization from these observations is difficult. In addition, chemical reactions or phase transformations may influence the nature of deformation potentially leads to localized unstable deformation. But a laboratory study of such a process is challenging for the same reasons. Furthermore, most of geodetic observations involve small strain (comparable to or less than elastic strain) and the connection of these observations to the flow properties in geological time scale (i.e., large strain deformation) is unclear.

The richness of mechanical behavior is caused by the complexities in rock structure that leads to evolving heterogeneous stress-strain inside of a deforming rock. Studying the role of evolving structure and evolving internal stress-strain is difficult if one uses a conventional method where only macroscopic stress-strain relationship is measured and the microstructure was studied only after an experiment (post mortem observations).

Similarly, constraining the processes of melt generation and migration from geochemical observations is difficult because the relation between these observations and the processes of melt generation and transport is non-unique. In addition, experimental studies on melt generation and transport is challenging because these processes are controlled by the geometry of melt and internal stress at the melt-mineral boundaries both of which evolve and most likely they depend on the stress level (or the time scale in which these processes occur) that differ substantially between the lab and Earth.

Common to these processes is the fact that they are affected largely by the microstructures and by the internal stress-strain in a rock with a variety of scales that evolve with time (strain). Synchrotron facilities provide an excellent opportunity to study these properties by providing the key information on microstructural and internal stress-strain evolution during an experiment (i.e., in-situ observations). Synchrotron produces high intensity and highly collimated x-rays. Consequently, one can investigate various properties with high spatial resolution. When combined with a theoretical model, one can also investigate the distribution of internal stress (and strain) including the variation of stress among crystals with different orientations from diffracted x-rays. Since the x-ray intensity is strong, most of these measurements can be done in a short period, and therefore in many cases, one can trace the evolution of properties of a sample during an experiment.

We note that most of these properties are highly sensitive to temperature and to chemical environment including water and oxygen fugacity. Also many of these properties or processes involve a variety of space scale from crystal dislocations to grain-boundaries, cracks and boundaries of different phases. For these reasons, a relatively large volume apparatus will be best suited to conduct these experimental studies combined with a synchrotron facility.

In the following, we will --------.

-- Shun-ichiro Karato; updated 12pm, 03 October, 2018