Frank M. RichterSewell Avery Distinguished Service Professor, Emeritus

Research Focus:

Geochemistry

Email:

richter@geosci.uchicago.edu

Phone:

(773) 702-8118

Office:

Hinds 549

Research Interests

The common theme of 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 minerals, silicate melts or water) or mass transfer from a condensed phase to a gas (i.e., evaporation). The goal is to find diagnostic isotopic fingerprints of particular transport processes that will allow one to confirm and quantify their operation in natural settings.

The degree of isotopic fractionation of Li, Ca, Mg and Fe associated with diffusion between molten basalt and rhyolite was found to be very large compared to the precision with which these fractionations can be measured (Richter et al. (2003) Isotope fractionation by chemical diffusion between molten basalt and rhyolite. Geochim. Cosmochim. Acta, 67, 3905-3923; Richter et al. (2008) Magnesium isotope fractionation in silicate melts by chemical and thermal diffusion. Geochim. Cosmochim. Acta 72, 206-220]. Even larger isotope fractionations than those in melts were found associated with diffusion in minerals (Richter et al. (2014) Lithium Isotope Fractionation by Diffusion in Minerals. Part 1: Pyroxenes. Geochim. Cosmochim. Acta. 126, 352- 370;  Richter et al. (2017) Lithium Isotope Fractionation by Diffusion in Minerals. Part 2: Olivine. In Press Geochim. Cosmochim. Acta). On the other hand, because of hydration effects of ions in water isotopic fractionations associated with the diffusion of salts such as LiCl, KCl, MgCl2, and CaCl2 in water are much smaller than that in silicate liquids (Richter et al. (2006) Kinetic isotope fractionation during diffusion of ionic species in water. Geochim. Cosmochim. Acta,70, 277-289).

The isotopic fractionations documented by the laboratory experiments have been used to constrain the rates of mass transfer and cooling in a number of natural settings. Rahul Chopra, as part of his PhD dissertation, was able to distinguish whether the chemical gradients at the boundary between basalts intruding rhyolites from Vinal Haven Island, Maine were due to diffusion, which has associated isotopic fractionations or mechanical mixing, which would not. The gradients identified as being due to diffusion were then used to constrain the cooling rate of this co-magmatic system. This work was published as Chopra R., Richter F.M., and Watson E.B. (2012) Isotope fractionation by chemical diffusion in natural settings and in their laboratory analogues. Geochim. Cosmochim. Acta. 88, 1-18.   Another example of how kinetic isotope fractionation due to diffusion can be used to constrain the processes affecting a set of natural samples is given in Richter et al. (2016) Reassessing the cooling rate and geologic setting of Martian meteorites MIL 03346 and NWA 817. Geochim. Cosmochim. Acta 182, 1-23.

Laboratory experiments were also used to determine the isotopic fractionation of Mg, Si, and O due to evaporation from molten silicate liquids. These studies were motivated by the long known fact that the most primitive inclusions in meteorites (CAIs: calcium-aluminum-rich inclusions) dating back to the very start of our solar system often have correlated enrichments in the heavy isotopes of silicon and magnesium. The evaporation experiments demonstrated that 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 (Richter et al. (2002) Geochim. Elemental and isotopic fractionation of Type B CAIs: experiments, theoretical considerations, and constraints on their thermal history. Geochim. Cosmochim. Acta, 66, 521-540; Richter (2007) Elemental and isotopic fractionation of Type B CAI-like liquids by evaporation. Geochim. Cosmochim. Acta 71, 5544-5564). A companion paper focused on the evaporation of silicon (Knight (2009) Si isotope fractionation of CAI-like vacuum evaporation residues. Geochim. Cosmochim. Acta. 73, 6390-6401.  Another study focused on evaporation of very fosterite-rich compositions to better understand the extraordinarily large isotopic fractionations of magnesium, silicon, and oxygen in a special class of CAIs called FUN inclusion (Mendybaev et al. (2013) Experimental evaporation of Mg- and Si-rich melts: Implications for the origin and evolution of FUN CAIs. Geochim. Cosmochim. Acta. 123, 368-364).

A detailed discussion of the main results of high-temperature laboratory evaporation experiments, theoretical considerations, and their use for understanding the processes and conditions in the early solar system are given in FMR Paris Evap. Notes:  Notes regarding evaporation of silicate materials and applications to cosmochemistry.

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