Lab Researchers
Prof. Carl B. Agee
Director, Institute of Meteoritics. Research interests include the origin and evolution of solar system bodies with specific interests in astromaterials, high-pressure mineral and magma physics, materials science, curation of extraterrestrial samples, and experimental petrology.
Dr. David S. Draper
Senior Research Scientist III and High Pressure Laboratory manager, Institute of Meteoritics. Research interests include formation and evolution of primitive basaltic magmas on Earth (especially arc- and extension-related settings) and on Mars; origins of small-degree silicate melts in terrestrial mantle xenoliths; role of fluids in arc and mantle processes; tectonomagmatic evolution of western North America.
Dave's Home Page
Dr. V. Rama Murthy
Research Professor, Institute of Meteoritics. Research interests include application of radiogenic isotope systematics to a variety of geological and geophysical problems, earliest history of the Earth during accretion and early differentiation, core forming processes, heat budget of the Earth.
In late 2000, Dave started an email group for experimental petrologists that's intended as a successor to the first incarnation of such a list organized by Henry Shaw back in the early 1990's. Take this link to join the group if you're interested.
Student Researchers
Karen H.
Ph. D. candidate, M.Sc. San Diego State University 2005. Experiments mimicking early magma ocean crystallization on Mars.
Karen's IOM page.Research Projects
Experimental work presently underway in our group, funded by both NASA and NSF, includes investigations of the conditions of formation of magmas that might be parents to the martian meteorites; constraining deep melting in the lunar mantle; and determining crystal-chemical controls on garnet-melt trace element partitioning.
In our Mars-related work, we have been studying trace element partitioning between chondritic silicate melt and coexisting garnet at pressures of 5 GPa and above, where garnet begins to undergo the transformation to the higher-pressure majorite form.
Briefly, we are examining the effect on element partitioning of the chemical and structural changes that occur as garnet begins to incorporate a significant majorite component. The diagram to the left plots our measured partition coefficients (Di) against ionic radii for the elements of interest, and the data fall on a parabola that can be fit to a mathematical relationship from which useful crystal-chemical information can be gleaned (see our recent paper in Physics of the Earth and Planetary Interiors for details and references on this method). In addition, we are using our measured D values to assess various petrologic models for the formation of magmas early in the history of Mars.
In another application of our melting experiments, we are assessing how well melts of candidate martian mantle compositions match proposed parent liquids for martian meteorites. It appears that our experimental melts can reproduce some of the important major element features of proposed martian parent liquids, but that a somewhat less Fe-rich mantle is required than what is commonly assumed for the martian interior.
Some of these results are shown on the figure below at right, and a recent paper in Earth and Planetary Science Letters (available from both the Agee and Draper IOM personnel pages) describes these inferences in more detail. New experiments melting a more Mg-rich (Mg# 80 instead of 75) candidate martian mantle composition are currently underway.
We also recently combined efforts with former IOM Research Scientist Lars Borg on constructing a petrological model for the origins of martian meteorites that combines results from our experimental work (to constrain major element features) and Lars's extensive work on trace element and isotopic systematics. The figure below left summarizes some of these results, which show how a model of an initial martian magma ocean can crystallize to give rise to source regions which, upon later melting, generate shergottite-like liquids. Our paper in Meteoritics and Planetary Science on this work shows the details of this model. This modeling yields the same inference as do our melting experiments, namely that the martian mantle should be slightly less Fe-rich than has been previously supposed, with an Mg# of ~80 instead of 75.
In other ongoing work, we are determining the liquidus mineralogy of a range of lunar picrite glasses in order to help constrain the depth at which melting took place to generate them. Geochemical evidence has suggested that garnet could be present in the source regions for some of these glasses, and our experiments on Apollo 15 green glass C show that although A15C is in fact saturated with garnet on its liquidus from ~3-5 GPa, this garnet does not partition trace elements in a way that allows garnet to be present in the residue from which this liquid was separated prior to eruption on the lunar surface. See our recent GCA paper from Dave's IOM page for more details on this project. A similar approach was also taken on another glass composition, Apollo 14 black, that, along with the composition of A15 green C, span the range of the entire set of pristine lunar glasses. This research formed a large part of the thesis work of recent M.Sc. graduate Rachel Dwarzski.
The projects on the martian mantle compositions and the lunar glasses are also being used to extend the compositional range over which garnet-melt partitioning data are available. This NSF-funded project aims to produce the data required to extend the predictive relationships of van Westrenen et al. (2001, 2002) to virtually any naturally-occurring garnet composition occurring in the solar system. This work has resulted in a pair of companion papers currently (mid-2007) in press in Contributions to Mineralogy and Petrology.