MR13B-2694
An Approach to Calculate Minerals´ Bulk Moduli KS from Chemical Composition and Density ρ

Monday, 14 December 2015
Poster Hall (Moscone South)
Simon Breuer, Frank R Schilling, Birgit Mueller and Kirsten Drüppel, Karlsruhe Institute of Technology, Applied Geosciences - Petrophysics, Karlsruhe, Germany
Abstract:
The elastic properties of minerals are fundamental parameters for technical and geotechnical applications and an important research topic towards a better understanding of the Earth´s interior.

Published elastic properties, chemical composition, and density data of 86 minerals (total of 258 data including properties of minerals at various p, T conditions) were collected into a database. It was used to test different hypotheses about relationships between these properties (e.g. water content in minerals and their Poisson's ratio). Furthermore, a scheme to model the average elastic properties, i.e. the bulk modulus KS, based on mineral density and composition was developed.

Birch´s law, a linearity between density ρ and wave velocity (e.g. vp.), is frequently used in seismic and seismology to derive density of the Earth´s interior from seismic velocities. Applying the compiled mineral data contradicts the use of a simple velocity-density relation (e.g. Gardner´s relation, 1974).

The presented model-approach to estimate the minerals´ bulk moduli Ks (as Voigt-Reuss-Hill average) is based on the idea of pressure-temperature (p-T) dependent ions´ bulk moduli. Using a multi-exponential regression to ascertain the ions´ bulk moduli and by applying an exponential scaling with density ρ, their bulk moduli could be modelled. As a result, > 88 % of the 258 bulk moduli data are predicted with an uncertainty of < 20 % compared to published values. Compared to other models (e.g. Anderson et al. 1970 and Anderson & Nafe 1965), the here presented approach to model the bulk moduli only requires the density ρ and chemical composition of the mineral and is not limited to a specific group of minerals, composition, or structure. In addition to this, by using the pressure and temperature dependent density ρ(p, T), it is possible to predict bulk moduli for varying p-T conditions.

References:

Gardner, G.H.F, Gardner, L.W. and Gregory, A.R. (1974). Geophysics, 39, No. 6, 770-780.

Anderson D.L., Anderson, O.L. (1970). JGR, 75, No. 17, 3494-3500

Anderson, O.L., Nafe, J.E. (1965). KGR, 70, No. 16, 3951-3962

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