Compositional analyses of meteorites
Using the facilities of the plasma mass spectrometry laboratory a student would analyze meteoritic samples for their chemical and or isotopic compositions. Bulk solution analyses, in-situ, spatially resolved analyses, or both can be carried out; the choice will be dictated by the hypothesis to be tested. A number of specific experiments are on offer, including but not limited to (1) element partitioning between phases in meteorites, (2) element fractionation in the early cosmos, and (3) Li isotopic composition of phases in a meteorite. Students are encouraged to contact Bill McDonough for further info.
Compositional analyses of peridotites/basalts
Using the facilities of the plasma mass spectrometry laboratory a student would analyze samples for their chemical and or isotopic compositions. Bulk solution analyses, in-situ, spatially resolved analyses, or both can be carried out; the choice will be dictated by the hypothesis to be tested. A number of specific experiments are on offer, including but not limited to (1) compositional analyses of sulfides in basalts and peridotites, (2) analyses of olivines from the Archean, Proterozoic and Phanerozoic, and (3) Li isotopic studies of recent basalts or minerals from peridotites. Students are encouraged to contact Bill McDonough for further info.
Compositional analyses of water
Using the facilities of the plasma mass spectrometry laboratory a student would analyze water samples for their chemical and or isotopic composition. These projects would be designed to test specific hypotheses; for example, one could examine the levels of trace metal in ground waters, river waters, domestic waters, etc, or the source of waters based on its Li isotopic composition. A number of factors can be considered in this project, including but not limited to (1) time dependent variations in water composition, (2) spatial variation in water composition, and (3) effectiveness of filtration systems. Students are encouraged to contact Bill McDonough for further info.
Gold in Ellicott City Granodiorite
The Ellicott City granodiorite (ECG) is famous as an example of an epidote-bearing granite. Magmatic epidote forms only at high pressures, indicating that this magma intruded and cooled deep within the Earth's crust. The ECG also contains magmatic sulfides. Gold and other water-soluble metals partition into the magmatic vapor phase, which typically exsolves from granites at low pressures after sulfide saturation. Because the ECG crystallized at high pressures, it is possible that Au was incorporated into the magmatic sulfides before it was lost to the vapor phase. This project will entail understanding the field relations of the ECG, detailed petrography of the sulfides in the ECG , characterization with by electron microprobe and measurement of their Au concentrations by laser ablation ICP-MS in order to determine whether the sulfides incorporated significant Au, hence crystallized before saturation of a vapor phase.
Supervisors: Roberta Rudnick, Philip Piccoli, Bill McDonough, Philip Candela
High-Mg andesites from the North China craton - melts of slab or delaminated lower continental crust?
The eastern block of the North China craton breaks the rule that "cratons are forever". Whereas the North China craton formed in the Archean and remained an island of stability through the Paleozoic (as expected of cratons), a fundamental change in its structure occurred during the Mesozoic, when the crust was intruded by volumninous melts. The big question is - what caused the transformation of this stable craton into a tectonically and magmatically active region and exactly when did this occur? The key may lie in understanding the origin of some very interesting lavas that erupted in the Jurassic. These high Mg andesites have the chemical characteristics of melts from subducted slabs, yet it remains unknown whether subduction occurred in this region during the Mesozoic. In order to unravel the origin of these unique rocks, the project will entail detailed petrographic, electron microprobe and laser-ablation ICP-MS characterization of the lavas, their phenocrysts and melt inclusions trapped within the phenocrysts.
Supervisors: Roberta Rudnick, Bill McDonough and Philip Piccoli
Refractory element variations in chondritic meteorites
It is widely held that the Earth's composition matches that of chondritic meteorites for refractory elements. However, new data for the concentrations of highly refractory elements have demonstrated that significant variation in refractory element ratios exists within the chondritic meteorite groups. In particular, the Nb/Ta ratio in CV chondrites is lower than that of most other chondrite types. Münker et al. (2003, Science) have attributed this to the presence of Ta-rich calcium-aluminum inclusions (CAI's) in CV's. This project would test this hypothesis by measuring the refractory element compositions of CAIs as well as chondrules using the laser ablation ICP-MS.
Supervisors: Bill McDonough, Roberta Rudnick, Richard Walker, Richard Ash
Topics in compositional analyses of samples
393/394 students are encouraged to contact Bill McDonough with more specific projects that seeks to use the facilities of the plasma mass spectrometry laboratory for their research project.
What caused melting at Great Falls?
At the highest grades of metamorphism exposed along the Great Falls section of the Potomac River, migmatite is juxtaposed against amphibolite. Deformation has obscured the original igneous contact relationships. This project would use laser ablation ICP-MS to determine the igneous and metamorphic ages of the rocks types and thus determine whether the amphibolite could represent intrusive basaltic magma that heated the metapelitic country rocks and caused their melting.
Supervisors: Roberta Rudnick, Bill McDonough