Department of Earth and Planetary Sciences


Geochemistry

Chemical, thermodynamic, and kinetic characterization of geologic materials in high- and low-temperature systems, using radiogenic and stable isotopes, organic geochemistry, experimental mineralogy, and elemental analysis. Some examples of current research by our faculty in Geochemistry are shown below. Visit the faculty members’ pages through the above links to get more information about research in Geochemistry at UT.

Meteorite analysisCosmochemistry

Hap McSween is involved with on-going studies of the chemistry of Martian rocks and soils, as determined by the APXS instrument on the Mars Exploration Rovers and by the Gamma-Ray Spectrometer on the Mars Odyssey orbiter, as well as from Martian meteorites.  The figure below is taken from a recent Science paper summarizing these data.  He has also been investigating how ratios of elements that can be analyzed with the Gamma-Ray and Neutron Detector on the Dawn spacecraft can be used to identify various kinds of HED meteorites.  This information will be critical in interpreting GRaND spectra from the Dawn mission to asteroid Vesta.  Dr. McSween is also involved in studies of the chemical compositions of chondritic meteorites.

Mineral Alteration

Dr. Labotka, in collaboration with Dr. D. Cole, Oak Ridge National Laboratory, has been studying experimentally the combined cation exchange of K and Na and the isotope exchange of O18 and O16 in alkali feldspar to determine the mechanism of mineral alteration. The image at left shows both the O-isotope–exchanged (nanoSIMS ion image) and K-exchanged (EMP x-ray image) rim on a grain of Amelia albite. The feldspar was reacted with a 2 m KCl solution, in which the solvent was H2O18.

Images

sill sillWhole-rock and Isotope Geochemistry;
P-T Conditions in Metamorphic Rocks

Bob Hatcher studies the geochemistry of major, minor, trace, and rare-earth elements in metamorphosed basalts and granitic rocks to provide clues about the tectonic environments in which they formed.  Using the USGS-Stanford Sensitive High-Resolution Ion Microprobe (SHRIMP) instrument, he is able to determine  the U-Pb ages of complex zircons from granitic and unmetamorphosed to metamorphosed sedimentary rocks.  In addition, Bob employs various thermometers on the UTK electron microprobe to determine the P-T conditions of metamorphism also entails.

Low Temperature Aqueous Geochemistry and Geomicrobiology

Annette Engel conducts interdisciplinary research that includes cave and karst aquifer evolution and speleogenesis, the role of natural organic matter in karst, geochemical controls on microbial metabolism, oil degradation and trajectories following environmental disturbances, the biodiversity of cave systems and coastal marine habitats, and symbiotic associations between bacteria and clams, invertebrates, and alligators. Her research falls broadly within the discipline of geomicrobiology, the study of the interactions between microorganisms and their geological and geochemical surroundings. Research involves a range of classical inorganic and organic geochemistry, stable isotope geochemistry, and molecular genetics methods within a microbial systems biology approach. Much of the instrumentation is available in Dr. Engel's laboratory. To quantify inorganic and organic compounds in water and gases, she applies basic wet and dry chemistry methods, ion chromatography, UV-Vis and fluorescence spectroscopy, Fourier transform infrared spectroscopy, gas chromatography, gas chromatography-mass spectrometry, and inductively coupled plasma mass spectrometry. She also uses X-ray diffraction and X-ray absorption spectroscopy using synchrotron radiation to understand mineralogical and elemental composition of natural materials. She uses stable isotope geochemistry, specifically of carbon, nitrogen, and sulfur, to characterize microbial signatures in water and sediment. For systems biology, she applies genomics and bioinformatics approaches that include DNA amplification protocols for PCR and quantitative PCR, and different gene sequencing methods, including next-generation high-throughput 454 and Illumina platform sequencing technologies to obtain DNA-based gene sequences and metagenomes ("who is there?") and also RNA-based transcriptomes ("what are they doing?") from environmental samples. To investigate metabolic potential directly from a sample, she routinely uses classical culturing methods and enzymatic assays. She also examines samples microscopically using gene probes for a full-cycle approach, where she can obtain genetic information and then probe material with specially designed probes to target specific microbes.

Andrew Steen's research focuses on better understanding the function, environmental controls, and geochemical effects of enzymes in aquatic environments. Many key geochemical processes – especially oxidation of organic carbon to CO2 – are performed by environmental microorganisms. All life relies on enzymes to catalyze chemical processes, so the precise way that microbial enzymes work can have major effects on geochemical cycles.

Steen Lab Research Areas:

  1. Kinetics of aquatic extracellular enzymes
  2. Functional variation among heterotrophic microbial communities
  3. Novel methods for marine organic geochemistry


 

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