THEMIS Multi-spectral Views of Compositional Heterogeneity in Nili Patera Caldera

Details THEMIS Multi-spectral Views of Compositional Heterogeneity in Nili Patera Caldera THEMIS Multi-spectral Views of Compositional Heterogeneity in Nili Patera Caldera

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p11b..10r&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P11B-10

Physics

5410 Composition, 5464 Remote Sensing, 5480 Volcanism (8450), 5494 Instruments And Techniques, 6225 Mars

Scientific paper

THEMIS infrared data provide remarkable multi-spectral views of the compositional variations in and around Nili Patera, the caldera at the summit of the Syrtis Major shield volcano. It was with TES spectra that these compositional variations were first observed and now THEMIS images show their distribution in great detail . Two spectral units dominate the scene. One also is a thermal inertia anomaly that was detected using TES data but is dramatically displayed in nighttime THEMIS images. It likely results from the presence of exposed bedrock. TES spectra of this surface resemble the Syrtis-type spectrum of Bandfield et al. [2000] but with notably enhanced spectral contrast. This is consistent with the effect of viewing bedrock rather than a particulate surface like that which presumably makes up the majority of Syrtis Major. The second spectral unit occurs in two very distinct settings. The first is associated with a small (~5 km diameter) knob on the floor of the caldera that appears to be a breached volcanic cone. The spectral unit fans out from the cone in a manner similar to a lava flow and cross-cuts the contact with the Syrtis-type spectral unit. The second occurrence of this spectral unit is ~50 km to the south of the caldera. In this location the unit clearly is structurally controlled, bounded on two sides of its roughly rectangular shape by wrinkle-ridge-like scarps. TES spectra of this unit display features similar to those of the Acidalia-type spectrum of Bandfield et al. [2000], indicative of a more glassy, silica-rich composition than the plagioclase-pyroxene Syrtis-type basalt. The cross-cutting relationship observed to the north suggests a more recent eruption of this unit than that of the Syrtis-type. The apparently more silica-rich composition may be indicative of late stage differentiation. The adjacency of these two compositional units and their apparent age relationship tend to support the idea that Acidalia-type spectral character is attributable to primary volcanic mineralogy rather than secondary alteration products, at least in this location.

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