Odyssey Unveils A 'New Mars'
"James Garvin, Mars Exploration Program Scientist at NASA Headquarters in Washington, D.C., shares the same view as Saunders regarding first-look images by THEMIS. 'It's a whole new Mars,' he told SPACE.com."
http://www.space.com/scienceastronomy/solarsystem/odyssey_update_020226.html

Planetary Society president and Caltech geologist Bruce Murray in an interview also described the results from Mars Global Surveyor as revealing a new Mars:

Mars, Old and New: A Personal View
by Dr. Bruce Murray
"The Planetary Report: Clearly, a 'New Mars' seems to be emerging from Mars Global Surveyor [MGS] data. How have your views of Mars changed?
"Bruce C. Murray: Mars Global Surveyor has, for me, renamed Mars the land of broken paradigms. MGS not only produced stunning results but also revealed that we can't explain them, as we thought we would be able to."
http://www.planetary.org/html/society/advisors/murray/tprarticle.html

The spatial resolution of the infrared imager on Mars Global Surveyor TES is about an order of magnitude better than that of the IRTM imager on the Viking orbiters:

Mars surface rock abundance from thermal emission spectrometer(TES) mapping data.
"The spatial resolution of TES data is an order of magnitude greater than IRTM, with a 3 km pixel at nadir, as compared to 30 km resolution in the IRTM observations."
http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6191.pdf

Several new minerals were found by MGS that were not previously observed by the Viking orbiters, such as hematite, olivine and andesitic volcanic rock.
The THEMIS spectrometer on Mars Odyssey will provide an improvement in spatial resolution over TES by a factor of 30. I expect then there will also be new minerals observed by THEMIS not seen by TES.

Since there is abundant evidence of subglacial volcanism on Mars one key mineral I expect to be observed is rhyolite:

Iceland
http://perseus.geology.ubc.ca/projects/subglacial/pages/Iceland.html

Subglacial rhyolite volcanoes
http://www.es.lancs.ac.uk/vgrg/People/hugh/rhy.html

The recent report of hydrovolcanism in Cerberus Fossae for example might be modeled as due to subglacial volcanism. This is supported by the huge floods that were argued to arise from the volcanism in the region, which might be analogous to jokulhlaups and the numerous mesas seen, which might be analogous to tuyas, or table mountains.

At the upcoming LPSC conference there will be presented another report suggesting subglacial volcanism on Mars in Cavi Angusti:

Cavi Angusti: evidence for volcanic activity, ice sheet melting, and basal drainage of water.
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1054.pdf

Also it is sometimes said that mineral indications of hydrous weathering has not been seen on Mars. This has been true of carbonates which so far have not been observed. There have been conflicting reports on the ability of THEMIS to detect carbonates on Mars. However, one mineral I do expect to be detected by THEMIS is palagonite. Palagonite is due to volcanic rock weathered by liquid water. Both the Viking landers and Viking orbiters provided spectrographic evidence that has been modeled as being close to palagonite, but so far this has not been shown definitively. My expectation is that THEMIS will confirm palagonite on Mars.

Bob Clark