Quartzite units in the Simplon Fault,Switzerland

Titanium in deforming quartz and the thermomechanics of extensional detachment and thrust systems

This research is an investigation of naturally and experimentally deformed quartz-rich samples to study the role of deformation in the distribution of Ti and other trace elements in quartz over a wide range of temperature and deformation/recrystallization processes. The mobility of Ti in deforming quartz is addressed directly by a set of high-pressure/high-temperature deformation experiments performed in the SiO2 -TiO2 system. This research targets a wide range of temperature conditions as well as zones of diverse microstructures. Two groups of tectonic settings are investigated:

(1) Thrust systems, in which rocks typically deform at low differential stress and strain rates during prograde metamorphism; microstructures equilibrate in a relatively narrow range of temperatures (300-450°C) but display a wide range of dislocation creep regimes involving various types of recrystallization dominated by bulging of grain boundaries and subgrain rotation at high stress, and grain boundary migration at lower stress.

(2) Extensional detachments that bound metamorphic core complexes; deformation fabrics form at high differential stress and strain rates in a wide temperature range (300 to 700°C), leading to subgrain rotation-dominated recrystallization.

In experiments as well as in natural examples from exhuming (detachment) and prograde (thrust) systems, our research focuses on how inherited Ti is redistributed as a function of deformation and recrystallization as well as T conditions.

People: Will Nachlas, Nick Seaton, Christian Teyssier, Donna Whitney, Greg Hirth (Brown), Sarah McKnight & Michelle Markley (Mt Holyoke College), Marty Grove (Stanford)