Statistics – Methodology
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p11a0954w&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P11A-0954
Statistics
Methodology
5410 Composition, 5420 Impact Phenomena (Includes Cratering), 5470 Surface Materials And Properties, 5494 Instruments And Techniques, 3944 Shock Wave Experiments
Scientific paper
An abundance of impact craters on the martian surface and shock effects in the martian meteorites indicate that the surface of Mars has been shocked. The thermal infrared (TIR) spectra of plagioclase feldspars experimentally shocked to various pressures have enabled the amount of shock to be correlated with changes in the TIR spectra [Johnson et al., 2002, 2003]. With these, estimates on the amount of shocked plagioclase feldspar on the martian surface has been investigated [Johnson et al., in press]. However, in relation to the use of shocked plagioclase feldspars as end-members for the deconvolution of remote TIR data, similar work need to be performed on the laboratory spectra of shocked rocks and subsequent deconvolutions with these shocked mineral end-members. In this work, laboratory TIR spectra of a shocked terrestrial basalt and it unshocked counterpart are deconvolved and compared to assess the possibility of removing the spectral contribution of shocked plagioclase feldspar from a shocked martian basalt spectrum. It has been suggested that the modal abundances of martian meteorite Los Angeles [Rubin et al., 2000] are similar to mineral abundances derived from the deconvolution of Thermal Emission Spectrometer (TES) Surface Type 1 (ST1) [Bandfield, 2002]. TIR spectra of shocked basalt from Lonar Crater, India were collected and deconvolved with an end-member library containing experimentally shocked calcic plagioclase feldspars [Johnson et al., 2002]. The deconvolution-derived mineral abundances were compared to those from deconvolutions of unshocked basalt, and it was determined that the spectrum of the original, unshocked bulk rock could be replicated by removing from the spectrum of a shocked basalt the shocked plagioclase end-member spectrum (scaled by its abundance). The same methodology was performed on another shocked basalt, martian meteorite Los Angeles. The TIR spectra of Los Angeles was deconvolved with an end-member library containing shocked plagioclase feldspar (An75), revealing an abundance of maskelynite (~46%) that closely matches modal abundances from petrographic studies (~45%) [Rubin et al., 2000]. TIR spectra of shocked intermediate calcic plagioclase feldspars such as those found in Los Angeles (An56-38) do not exist and therefore are not contained within the spectral library used here. A mean percentage of 46% of the shocked plagioclase feldspar end-member was removed from the bulk rock spectra of Los Angeles and replaced with unshocked labradorite. Similar to the Lonar Crater basalts, this should recreate the spectra of the pre-impact, unshocked basalt. This end-member replacement results in a TIR spectrum of a basalt with a Christiansen feature moved to lower wavenumbers, agreeing with previous work that suggested the position of this feature varies with the amount of shock [Johnson et al., 2002]. The new "unshocked" Los Angeles TIR spectrum is not an exact match for ST1, but it is more similar to TES spectra than a shocked Los Angeles spectrum is. Whereas laboratory TIR spectra of shergottites provide poor matches to orbital TES data [Hamilton et al., 2003], using this unshocked basalt spectrum as an end-member might provide additional constraints on the source region of Los Angeles. Further, it is suggested here that TIR spectra be acquired for various experimentally shocked end members of plagioclase feldspar solid solution series for better deconvolutions of shocked rocks.
Bandfield Joshua L.
Christensen Per Rex
Johnson Jay Robert
Wright Shawn P.
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