With the Spirit rover sitting in one spot, it's given me a chance to come up with an updated summary of the various Gusev and Columbia Hills rock types, geochemistry and latest geological interpretations. There have been several good papers but there hasn't been one comprehensive paper to put everything together (that I know of). And the one key component to interpreting the data that is still missing is a detailed structural model of the Columbia Hills. Nevertheless, I've tried my best to make sense of all the various information out there.

There are still a number of uncertainties and inconsistencies -- which are open to discussion here -- but in general terms I think this is the stratigraphic sequence we're looking at, with various alteration processes overprinting this stratigraphy:

ADIRONDACK basaltic flows related to the volcano Appollinaris Patera, 300 km to the north
BACKSTAY & IRVINE late stage mafic intrusive dikes cut through all Columbia Hills units
HOME PLATE maar type volcanism emplaced through Columbia Hills, interacting with groundwater
DESCARTES, CLOVIS & WATCHTOWER meteorite impact ejecta deposits mixing different rock types
INDEPENDENCE & WOOLY PATCH phyllosilicates derived from chemical weathering of volcaniclastics
WISHSTONE tuff or pyroclastic deposit (impact origin not fully discounted*)
PEACE sandstone produced by wind erosion of older ultramafic units
SEMINOLE mafic to ultramafic intrusive or extrusive rocks

The link to the summary is on my homepage.

aldo12xu: I've been remiss in not checking out your latest summary until now. They are always excellent, but this one exceeded my expectations.

Thanks Tom!

Does that stratigraphic sequence make sense to you? One of the uncertainties I have has to do with the source rocks for Clovis, which is described as ejecta material of basaltic glass chemistry. For Peace's ultramafic sand grains we have Seminole rocks as a possible source, but what about Clovis' basaltic glass? I think the basaltic source would lie between the Seminole and Wishtone units. I suppose the source unit may have been drift covered and easily missed by Spirit. I think if we ever get to McCool Hill we'd be able to get better constraints on the overall stratigraphy.

Still nice to see some of the pieces of the puzzle fitting together

Aldo,
You've produced and excellent summary of the geology of the region. Thanks for the effort. Your cross section of the Columbia Hills is a good integration of the geology as we know it so far.
Do you think that Seminole could have been the source for the grains in Clovis as well as Peace?

-gray

Everything I've read currently describes Clovis as having a basaltic glass compositon, whereas Seminole is ultramafic. The one possibility is that further analysis might change that. For instance, the earlier papers described the sand grains within Peace as being basaltic but the most recent paper by Squyres describes them as being ultramafic.

Have you seen this on MER website?
New Class of Igneous Rocks :
http://marsrovers.jpl.nasa.gov/gallery/pre.../20060823a.html
I'm not able to understand this but, I'm curious to get an explanation regarding the part of the graph called "Martian meteorites". I assume this show meteorites found on Earth and believed to come from Mars. Does it simply means that those metorites doesn't come from Gusev?

An interesting link directly relating to the new geo-chemistry chart mentioned in the previous post:
in this Lunar and Planetary
Science paper the authors discuss earthly analogues of the minerals found. They include a slightly-less-up-to-date Total Alkali-Silica diagram, which shows how the newer samples discovered by Spirit in the Columbia hills have expanded the bounds of what has been observed...

Click to view attachment

edit: I can't get the link to be clickable. Sorry, I don't know what I'm doing wrong. Lets try one more time: link

Aldo,

this is truly superb, thank you.

great map showing the location of different rock types. very helpful

as a chemist, I would be interested to see you add the approximate chemical composition/formula for the minerals where available

ken

The press release is telling us that the rocks making up the Columbia Hills are alkaline in composition, the Gusev plains basalts are borderline and all other Mars samples examined so far are subalkaline. I don't think it changes the current view that the Columbia Hills rocks consist of volcaniclastics and/or impact ejecta with localized intrusives like Backstay and Irvine......Or is there now an implication that the Seminole rocks may be intrusive as well?

Here's a paper discussing Irvine and Backstay:
H. Y. McSween, et al. (2006) Backstay And Irvine: Alkaline Volcanic Rocks From Guseve Crater, Mars [#1120], Planetary Science March 2006 Conference http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1120.pdf

And on the Seminole rocks:
D. W. Mittlefehldt, et al. (2006) Possible Ni-Rich Mafic-Ultramafic Magmatic Sequence in the Columbia Hills: Evidence From The Spirit Rover [#1505], Planetary Science March 2006 Conference http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1505.pdf

As for the Martian Meteorite plots, that was probably included for comparison purposes.

Just to elaborate on Aldo's reply, and in response to climber, I think, initially, people were surprised to find that the Martian basalts were so rich in silica. I'm really stretching my knowledge of igneous petrology here, but I think the higher silica igneous rocks are more often associated with magmas generated from rocks that have been "recycled" (read plate tectonics). Since almost all of the evidence suggests that plate tectonics has not occurred on Mars people expected the basalts to have a low silica content. The press release states that Mars does indeed have the low-silica igneous rocks also. The chart, I think, includes all the chemical data available for Martian igneous rocks (even the meteorites recovered on earth).

gray

So does this mean there was not a once a lake in Gustev Crater? Or was there a lake at one time, but any evidence for it is now buried under later, volcanic flows?

With the exception of Home Plate, it does not look like any evidence for sedmentary rocks were found.

Most of the rocks found in the Columbia Hills showed alteration by water. See Aldo's list here, particularly items 2-9 (except for 8).

Thats how I have interpreted the results from Gusev for a long time. That there have been a water there, for a brief or somewhat longer time but that the volcanic materials have blankeded almost all from the rover.

That some rocks show alteration by water as ToSeek correctly stated can also be one indication that at least some of those rocks have been part of eruptions that contained water vapour. So those might not neccesary be signs of a wet past in Gusev. Then again, im only quoting what have been said in publicaitons and press releases.

If you're interested in the stoichiometric chemical compositions for different minerals, a great resource is http://www.webmineral.com. This site is really nice because it also gives the mineral compositions in terms of major oxide phases, e.g. what APXS gives us on Mars.

Thanks for the link. tglotch. It's a very comprehensive resource and I've added it to my links page, which I've recently expanded. I assume you were referring to the Powder X-Ray Diffraction page that has "mineral compositions in terms of major oxide phases, e.g. what APXS gives us on Mars"