People

Frank M. RichterSewel L. Avery Distinguished Service Professor

Research Focus:
Experimental geochemistry, cosmochemistry
Email:
richter@geosci.uchicago.edu
Phone:
(773) 702-8118
Office:
Hinds 549

Research Interests

The common theme to my recent research involves laboratory experiments to determine the degree of kinetic isotope fractionation associated with mass transport processes within a phase (i.e., chemical diffusion in a silicate melt or water) or between phases as in the case of mass transfer from a condensed phase to a gas (i.e., evaporation).   The point is to find diagnostic isotopic fingerprints of particular transport processes, which would allow us to confirm and quantify their operation in a natural setting.

The degree of isotopic fractionation of lithium, calcium, magnesium and iron associated with the diffusion of these elements between molten basalt and rhyolite was found to be large compared to measure these fractionations [Richter F.M., Davis A.M., DePaolo D.J. and Watson E.B. (2003) Isotope fractionation by chemical diffusion between molten basalt and rhyolite.  Geochim. Cosmochim. Acta, 67, 3905-3923; Richter F.M., Watson E.B., Mendybaev R.A., Teng F-Z., Janney, P.E. (2008) Magnesium isotope fractionation in silicate melts by chemical and thermal diffusion. Geochim. Cosmochim. Acta 72, 206-220].  These fractionations are being used by one of our graduate students to test whether the chemical gradients he has measured in the boundary between basalts intruding rhyolites from Maine are due to diffusion (which would have associated isotopic fractionations) or mechanical mixing (which would not fractionate isotopes).

We have also determined the isotopic fractionations associated with the diffusion of salts such as LiCl, KCl, MgCl2, and CaCl2 dissolved in water [Richter F.M., Mendybaev R.A., Christensen J.N., Hutcheon I.D., Williams R.W., Sturchio N.C. and Beloso Jr. A.D. (2006) Kinetic isotope fractionation during diffusion of ionic species in water. Geochim. Cosmochim. Acta, 70, 277-289].  Except for potassium, these fractionations are much smaller than in a silicate melt reflecting the fact that water is a polar liquid that form hydration spheres around the dissolved ions.  Molecular dynamics calculations by a postdoctoral fellow - Ian Bourg - have been remarkably successful at reproducing the experimentally observed isotopic fractionations of lithium and magnesium.  The molecular calculations predicted that the isotopic fractionation of potassium would be found to be significantly larger that that of lithium, which is exactly what we found in a recent set of laboratory experiments motivated by the molecular calculations.

The laboratory experiments for measuring the isotopic fractionation of evaporation residues are motivated by the long known fact that the most primitive inclusions in meteorites dating back to the very start of our solar system (CAIS: calcium-aluminum-rich inclusions) often have correlated enrichments in the heavy isotopes of silicon and magnesium.  We use vacuum evaporation experiment to demonstrate and quantify how evaporation of SiO2 and MgO from molten silicates of CAI-like composition produces residues with the same sort of isotopic fractionation seen in the actual CAIs. We recently published an extensive study of magnesium isotopic fractionation by evaporation [Richter F.M., Janney P.E., Mendybaev R.A., Davis A.M. and Wadhwa M. (2007) Elemental and isotopic fractionation of Type B CAI-like liquids by evaporation. Geochim. Cosmochim. Acta 71, 5544-5564] and a companion paper involving silicon isotopes has been submitted [Knight K.B., Kita N.T., Mendybaev R.A., Richter F.M., Davis A.M. and Valley J.W. (2007) Silicon isotope fractionation in CAI-like evaporation residues. Submitted to Geochim. Cosmochim. Acta].

We are very excited by our recent results with another type of kinetic isotope fractionation involving isotope fractionation by a temperature gradient (i.e., isotope fractionation by thermal diffusion, also called Soret diffusion).  Isotope fractionation by temperature differences across a gas have been known for a long time, but that similarly large effects occur in molten silicates came as a surprise - especially that the fractionation that we have measured in molten basalt are in some cases larger than what happens in a gas.  In a recent paper [Richter F.M., Watson E.B., Mendybaev R.A., Teng F-Z., Janney, P.E. (2008) Magnesium isotope fractionation in silicate melts by chemical and thermal diffusion. Geochim. Cosmochim. Acta 72, 206-220] we reported extraordinarily large magnesium isotopic fractionations of 1% in the 26Mg/24Mg ratio by a temperature difference of only 100˚C. We have preliminary results showing that all the isotopes of all major elements of basalt are similarly fractionated by temperature differences.  I expect these preliminary results will stimulate a broad range studies exploring the effect of temperature gradients on chemical and isotopic fractionations in both laboratory and natural settings.

Selected Publications

  • Richter, Frank, et al. "Reassessing the cooling rate and geologic setting of Martian meteorites MIL 03346 and NWA 817." Geochimica et Cosmochimica Acta 182 (2016): 1-23.
  • Davis A.M., Richter F.M., Mendybaev R.A., Janney P.E., Wadhwa, M., and Mckeegan K.D. ( 2015) Isotopic mass fractionation laws for magnesium and their effect of Al-26-Mg-26 systematics in solar system materials. Geochim. Cosmochim. Acta. 158, 245-261.
  • Richter F., Watson B., Chaussidon M., Mendybaev R., and Ruscitto D. (2014) Lithium Isotope Fractionation by Diffusion in Minerals. Part 1: Pyroxenes. Geochim. Cosmochim. Acta. 126, 352- 370.

Courses

Geosci 131 - Introductory course in Geology
Geosci  342-  Modeling in the Geophysical Sciences

Curriculum Vitae

Frank M. Richter
Department of the Geophysical Sciences
The University of Chicago

Place of birth:  Dominican Republic  (naturalized U.S. citizen 1974)

Education

Prof. Eng.    1965    Colorado School of Mines
M.S.    1971    University of Chicago
Ph.D.        1972             University of Chicago

Professional Experience

1994-        Sewell Avery Distinguished Service Professor
Geophysical Sciences, The University of Chicago
1985-1994    Chairman, Department of the Geophysical Sciences
The University of Chicago
1981-    Professor, Department of the Geophysical Sciences
The University of Chicago
1978-1981    Associate Professor, Department of the Geophysical Sciences
The University of Chicago
1975-1978    Assistant Professor, Department of the Geophysical Sciences
The University of Chicago
1972-1974    Research Associate, Department of Earth and Planetary Science Massachusetts Institute of Technology

Honors

2007    Fellow, Geological Society of America
2006    Arthur L. Day Medal of the Geological Society of America
2001    Member, National Academy of Sciences
1999      George Woollard Award of the Geological Society of America
1995    Norman L. Bowen Award of the American Geophysical Union
1993    Fellow, American Academy of Arts and Sciences
1983    Fellow, American Geophysical Union
1981    Royal Society Research Fellow
1979    Green Scholar, Institute for Geophysics and Planetary Physics, La Jolla, CA.
1978    Fairchild Distinguished Scholar, California Institute of Technology
1974    John Simon Guggenheim Fellow