Archive | 2021
Model-derived uncertainties in the calculation of geological phase equilibria
Abstract
<p>Phase equilibrium modelling offers a welcome window onto rock-forming processes. It underpins the principles of geothermobarometry, which today is commonly carried out via pseudosection calculations in software such as THERMOCALC and Perple_X. Increasingly, phase equilibrium modelling is combined with complementary approaches such as diffusion or geodynamical calculations, in order to simulate Earth processes.</p><p>However, as anyone with experience of pseudosection calculations will know, it is not always easy to make sense of a rock through phase equilibrium modelling. Problems may relate to: (1) in what way the assumption of thermodynamic equilibrium may, or may not, be applied; (2) uncertainties in compositional analysis; and (3) uncertainties in the composition-dependent equations of state (<em>x</em>-eos). The <em>x</em>-eos are the building blocks of the modelling – one <em>x</em>-eos is needed to represent each of the mineral and fluid phases in the calculation. </p><p>Of the problems listed above, (3) is the most opaque for the user. In this talk I will discuss the uncertainties associated with the <em>x</em>-eos, and the implications of those uncertainties for thermobarometry and the simulation of Earth processes. I will describe two tools, currently in development, for investigating <em>x</em>-eos-derived uncertainty in thermobarometry.</p>