"Crystal Tectonics"

 

 

The chemical and physical properties of metamorphic minerals such as garnet, Al2SiO5 polymorphs (andalusite, kyanite, sillimanite), and the Ca-Al hydrous silicates (epidote, lawsonite) have long been central to petrologic and structural studies of orogeny because these minerals may record the pressure, temperature, strain, and fluid histories of rocks through time.

Methods and applications that my research group has been involved with include field, analytical, and experimental study of metamorphic minerals. Our goals are to understand the rates and mechanisms of high-T geological processes (heating, burial/decompression, mineral growth, deformation), the record of mineral-fluid-deformation interactions in the Earth through time, the mechanical behavior of minerals during regional metamorphism, and the expressions of these processes at various rates in metamorphic textures.

Examples of ongoing and future work include studies of garnet, Al2SiO5, and reaction textures:

  • A microstructural study of garnets to determine garnet growth histories in relation to chemical zoning and mineral inclusion fabrics; this is an example of the application of electron backscattered diffraction (EBSD) to metamorphic petrology.
  • A study of the relationship between shape-preferred orientation and crystallographic-preferred orientation of mineral inclusions in garnet, to document the conditions and consequences of garnet-inclusion interactions.
  • A study of the conditions (rates, paths, temperatures) required to produce symplectite textures around Al2SiO5 phases and garnet (and other minerals).

A study of inclusions in minerals (garnet, zircon) using laser Raman spectroscopy.

 

 

Garnet X-ray maps showing concentric zoning of Mn and Ca (higher abundance of each element in garnet core, lower at rim), with a line (white/dashed) marked to show the location of a high-angle grain boundary detected by electron backscattered diffraction (EBSD) analysis. From Whitney & Seaton (2010)

 

 

This research has involved former graduate student Eric Goergen (PhD 2009 - now a research scientist at FEI) and research scientist Nick Seaton.