Tectonics of metamorphic crystallization

The chemical and physical properties of metamorphic minerals such as garnet and Al2SiO5 polymorphs (andalusite, kyanite, sillimanite) 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. These minerals are “rheologically insignificant” but their microstructures are nevertheless extremely useful for understanding the deformation conditions and mechanisms in the lithosphere.

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 recent, 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 microstructural study of lawsonite fabrics in blueschist and eclogite to understand the relationship of metamorphism and deformation at high-pressure conditions in subduction zones.

--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.

People: Donna Whitney, Christian Teyssier, Nick Seaton, Eric Goergen (PhD 2009)