Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p51a..07l&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P51A-07
Mathematics
Logic
5420 Impact Phenomena (Includes Cratering), 5460 Physical Properties Of Materials, 5464 Remote Sensing, 6225 Mars
Scientific paper
Midinfrared spectral data received from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) have provided evidence for several equatorial, gray hematite (alpha-Fe2O3)-bearing deposits, including a large area in Sinus Meridiani, Mars. For this study, detailed laboratory spectroscopic investigation was conducted of twenty-four well-characterized hematite samples. These laboratory midinfrared analyses produced thermal emissivity spectra that show a strong spectral-shape dependence upon crystal axis orientation, as would be expected for the anisotropic mineral hematite. More importantly, this laboratory study shows that both unconsolidated platy hematite grains and schistose hematite rocks comprised of aligned platy grains exhibit axis-dependent spectral behavior similar to the behavior of single-crystal hematite. The comparison of the laboratory spectra to the hematite emissivity spectra from Sinus Meridiani, suggests that the Martian hematite spectra also show evidence for crystal-axis orientation. The hematite on Mars may consist of platy, aligned hematite grains. Interpretation of the crystal alignment exhibited in the emissivity spectra of the Mars hematite suggests that the hematite occurs either in outcrops bearing consolidated, specular hematite grains (schistose in texture) or as loose, well-aligned platy hematite particles. The platy hematite is interpreted to have resulted from burial metamorphism (of an iron-oxide chemical precipitate) rather than from orogeny. Crater density studies also included in this work show a bimodal population in the Sinus Meridiani hematite region. The first group consists of highly eroded large craters with population densities that approach the saturation equilibrium line and are thought to represent impacts on early Mars (prior to 3.8 Gy). The second group consists of a sparse population of fresh, sharp-rimmed craters that reflect a geologically young age (on the order of 10 My). This dichotomy is interpreted to suggests that after heavy bombardment, the surface was buried and protected for many millennia only much later to be exhumed and reexposed. Both the bimodal crater populations and the spectral evidence for platy hematite grains support the hypothesis that the Sinus Meridiani region of Mars has undergone significant burial. Burial would have acted to protect the oldest craters from being completely obliterated by erosion or impact gardening and also would have provided the overburden stress to induce the preferential alignment of the hematite grains.
Christensen Per Rex
Hartmann William K.
Lane Melissa D.
Morris Richard V.
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