Anne M. Hofmeister

Research Professor
Ph.D., California Institute of Technology, 1984

The Thermal State of the Earth

The first successful model for temperature, pressure, and compositional dependence of thermal conductivity was recently developed here at Washington U. The thermal conductivity (k) plays an crucial role anywhere heat is exchanged, such as mantle convection and planetary evolution. Some of the work is basic physics. Applications to the Earth are being made in collaboration with Dave Yuen (U. Minnesota).

The new model predicts that k for olivine is doubled upon its high-pressure transformation to the spinel structure, which subsequently was confirmed by experimental work of Xu et al. (Pepi 2005). Modeling the slab with this information yielded higher internal temperatures than previously thought, significantly reducing the likelihood of metastable olivine or of kinetics being important for deep earthquakes (Hauck et al. GRL 1999).

Pressure derivatives for k are straightforward to predict, but temperature derivatives are not. Fortunately, the latter (actually thermal diffusivity at T) can be accurately measured using a laser flash apparatus (in the picture above). A current focus is garnet and the high-pressure variety majorite, due to its volumetric importance to the transition zone, and on the radiative contribution, due to a misunderstanding in the geologic literature of the differences between direct and diffusive radiative transfer processes.

The model for radiative transfer in the solid earth was revised to account for grain size and applied to olivine near-IR to UV spectra at temperature (article).

Application has been made to revising the global heat flux (article | reply), which has already drawn a comment and reply, see above sites (link to pdf). In my view, the comment did not address the paper, but rather is a diatribe supporting the paradigm. This paper led to the realization that layered convection can be inferred from the pattern of trenches and ridges which result from coupling of the rotational and gravitational distortions of the Earth with locations of hot upwellings from the lower mantle convection cell [Hofmeister, A.M and Criss, R.E., 2005. Mantle convection and heat flow in the triaxial Earth. In: Melting anomalies: Their Nature and Origin, edited by G. R. Foulger, J.H. Natland, D.C. Presnall, and D.L. Anderson (Geological Society of America) pp 289-302], pdf provided upon request.

A new focus is thermal diffusivity of melts, glasses, and related minerals and rocks, in collaboration with Alan G. Whittington (U. Missouri, Columbia).

Washington U personel essential to research in heat transport are post-doctoral associate Maik Pertermann and gradute student Joy Branlund.

Dust in Space

Astronomical measurements of infrared spectra show signatures of dust superimposed upon stellar emissions. A first step in understanding the development of protoplanetary nebula is simply identification of the dust that exists in space. To achieve this end, my research group is collecting IR reflectivity spectra and thin film data of about 100 minerals thought to be part of the condensation sequence, or identified in meteorites, and various simple chemical compounds. Quantitative analyses of these data provide optical functions and emission spectra, which can be used to infer grain sizes, in addition to chemistry and structure. Application to the stars is made through collaborations with Angela Speck (University of Missouri) and Janet Bowey (University College London) and post-doctoral associate Karly Pitman. Much of the laboratory data were gathered by Erin Keppel, a middle-school teacher in St. Louis, during her summer break. Future plans include low temperature emissions and reflection spectra, and study of organic compounds.

In parallel, through collaboration with R.E. Criss in this department, we are examining the implications of thermodynamics and IR physics on the Big Bang.