A project of the Theoretical Chemical and Quantum Physics Group

Team

Mr. Tim DuBois, Prof. Salvy Russo

Collaborators

Dr Nick Wilson & Dr Colin McRae: Division of Minerals, CSIRO.

Brief Project Outline 

Geodynamic processes are extremely difficult to investigate with current technologies. Rheology in the lithosphere and asthenosphere is highly nonlinear and elasticity causes complications near the surface when the ambient temperature is less than approximately 600°C. The current contention between Geologists and Geophysicists is that the Earth's main geodynamic process is that of Mantle Convection; exerting plate tectonics to organise the system. Considering that plate tectonics is only a kinematic description of observations though, and not a fully dynamic description of plate motion, this and other approximations and assumptions continue to build upon one another yielding incomplete and inconsistent models. Geothermobarometry is the science of measuring temperature and pressure histories of intrusive igneous or metamorphic rock in an attempt to understand these processes in a limited fashion.

The recent work complied on a Titanium-in-Quartz geothermometer by Wark & Watson concluded with an empirical formula generated from the cathodoluminescence of a synthesised Quartz system in the presence of Rutile. The absence of a major pressure effect on the calibration is suggested, but could not be verified.

Generation of an ab initio model of a Ti defect in a SiO2 crystal was undertaken to assist in validating the Ti/Quartz relationship at pressure and temperature over ranges of 0 - 11 GPa and 0 - 1500 K respectively. A Molecular Mechanics model was also constructed due to issues pertaining to the construction of the former. An analysis and comparison of the two models conclude that the Titanium-in-Quartz defect investigated showed a pressure dependence of less than 0.2% over the pressure range.

Atomic structure of a titanium defect in a SiO2 crystal.

For more information about this project, please contact Salvy Russo.