Tasha L. Dunn

PhD Candidate, Graduate Teaching Assistant

Department of Earth and Planetary Sciences

University of Tennessee

Knoxville, TN 37996

Email: tdunn@utk.edu          

Office: 316 EPS

Research

PhD

Understanding Thermal Metamorphism in Asteroidal Parent Bodies of Ordinary Chondrites

       Because it is difficult to distinguish some minerals by traditional optical point counting techniques, the actual modal proportions of minerals in ordinary chondrites are not well known. However, quantified mineral modes can directly address three long-standing problems that have hindered our understanding of thermal metamorphism in ordinary chondrite apparent bodies. To address the questions, we will use a microsource XRD technique to determine modal mineralogy of a suite ordinary chondrites whose spectral characteristics have previously been determined. This XRD technique employs a position-sensitive detector (PSD), which allows for simultaneous collection of diffraction patterns at all angles. The microsource X-ray generator produces a more highly collimated beam than conventional XRDs, allowing for analysis of smaller sample volumes. This XRD-PSD technique has been shown to determine mineral abundances in multi-phase chondrites with an accuracy of ~1%.

The modal mineralogy of the chondrites will be used to address three fundamental questions in ordinary chondrite metamorphism:

1. Hypothesized changes in redox state during metamorphism

2. Peak metamorphic conditions for the formation of feldspar

3. Spectral calibration for determining mineral proportions in chondrites and asteroids

Master's

Identification of Terrestrial Alkalic Rocks Using Thermal Emission Spectroscopy: Applications to Martian Remote Sensing

Abstract

        We present a detailed study examining the ability of laboratory thermal emission spectra (5-25 µm at 2 cm-1 spectral sampling) to identify and classify alkalic volcanic rocks.  Modal mineralogies and derived bulk rock chemistries of a suite of terrestrial alkali basalts, trachyandesites, trachytes, and rhyolites were determined using linear spectral deconvolution.  Model-derived mineral modes were compared to modes measured using an electron microprobe mapping technique to access the accuracy of linear deconvolution in determining mineral abundances.  1σ standard deviations of absolute differences between measured and modeled mineral abundances range from 0.68 to 15.02 vol %, with an average of 5.67 vol %.  Bulk rock chemistries were derived by combining modeled end-member compositions (wt %) in proportion to their abundances (recalculated to wt %).  Derived oxide data compare well with measured oxide data, with 1σ standard deviations ranging from 0.12 to 2.48 wt %.  Modeled mineralogies, derived mineral chemistries, and derived bulk chemistries were examined to access their accuracy in classifying alkalic rocks.  Derived bulk chemistry is the most effective classification tool, modal mineralogy is the least, and basalts and rhyolites are typically more accurately classified than trachyandesites and trachytes.  However, no single classification scheme can accurately identify all rock samples, indicating that a combination of classification schemes is necessary to distinguish alkalic volcanic rocks using thermal emission spectra.  To examine the accuracy of volcanic rock classification at lower spectral resolutions, thermal emission spectra were resampled to the resolution of the Thermal Emission Spectrometer (TES) instrument (10 cm-1) and a second series of linear deconvolutions was performed.  Results from modeled mineralogies and derived bulk rock chemistries at 10 cm-1 are similar to results at 2 cm-1 spectral sampling, indicating that degradation of spectral data does not adversely affect modal mineralogies and chemistries derived from linear deconvolution.  Data from 10 cm-1 spectral sampling were applied to derived mineral and bulk chemistry classification schemes with high degrees of success.  Often, samples that were misclassified at 2 cm-1 spectral sampling were classified correctly at 10 cm-1 spectral sampling.  Overall, results suggest that linear deconvolution of thermal emissivity spectra can be successfully applied to the identification and classification of alkalic volcanic rocks on Mars.

 

Education

Work Experience

Teaching Experience

Professional Affiliations  

Awards and Recognitions

Community Outreach

Publications

Dunn, T. L., H. Y. McSween, Jr., and P. R. Christensen (2007), Thermal emission spectra of terrestrial alkaline volcanic rocks: Applications to Martian remote sensing, J. Geophys. Res., 112, E05001, doi:10.1029/2006JE002766.
Abstracts

T.L. Dunn and H.Y. McSween Jr. (2007) Revisiting the Question of Redox Changes in Ordinary Chondrites Using XRD-Derived Mineral Abundances, 70th Meteoritical Society Meeting, Abstract 5038

T.L Dunn, H.Y. McSween Jr., G. Cressey, P.A. Bland, and T.J. McCoy (2007) Quantification of the Mineralogy of Ordinary Chondrites Using Position Sensitive X-ray Diffraction, LPSC XXXVIII, Abstract 1137, Lunar and Planetary Institute, Houston (CD-ROM)

T.L. Dunn and H.Y. McSween Jr. (2006) Is Martian Surface Type 1 Mildly Alkaline?: Results from New Linear Deconvolutions of Surface Types 1 and 2, 69th Meteoritical Society Meeting, Abstract 5008

T.L. Dunn and H.Y. McSween Jr. (2006) New Linear Deconvolutions of Martian Surface Types 1 and 2 Using Alkalic Mineral Endmembers, LPSC XXXVII, Abstract 1291, Lunar and Planetary Institute, Houston (CD-ROM)

T.L. Dunn and H.Y. McSween Jr. (2005) Identification of Alkalic Rocks Using Thermal Emission Spectroscopy: Applications to Mars, 68th Meteoritical Society Meeting, Abstract 5354

T.L. Dunn, H.Y. McSween Jr., and K.A. Milam (2005) Using Thermal Emission Spectra to Model Modal Mineralogies of  Alkalic Rocks: Application for Mars, LPSC XXXVI, Abstract 1776, Lunar and Planetary Institute, Houston (CD-ROM)

 Last Updated 08/27/2007