Home Plate Summary Options

[Phil Stooke]

The bomb sag images look very convincing... but presumably impact ejecta blocks falling into soft layered sediments - say groudwater-soaked aeolian bedded drifts - would look the same. The mere appearance isn't enough to prove a volcanic origin. We have to get the chemistry.

Phil

[Zeke4ther]

Well...
(i) to please all the Forum contributors ;
(ii) to thank its Administrators for all the work they are doing for us in keeping alive this wonderful tool of exchange ;
(iii) to honour the 2 discoverers of the Home Plate feature (Dr. Nathalie Cabrol and Dr. Edmond Grin at NASA/AMES + their student in Paris Gilles Dawidowicz who helped them map the Gusev crater and identify features inside),
here is the sol 758 fully calibrated mosaic (reduced 50% in size to fit in the Forum)
PLUS the same image as desktop wallpaper for you to enjoy !

1st desktop wallpaper

(2nd desktop wallpaper)

Excellent work! Thanks for the desktops.

[aldo12xu]

Works of beauty, Olivier!!

....and yes, it looks like the case for a maar or tuff cone is getting stronger.

And getting back to what Richard Trigaux said in Post #50, what's interesting is that in Squyre's Journal of Geophysical Research 2006 paper, he describes the Backstay class of rocks as basalt/trachybasalts and that Peace is comprised of ultramafic sand grains (komatiites??). Another paper mentioned that Clovis has basaltic glass as it's principal component.

[Bill Harris]

....and yes, it looks like the case for a maar or tuff cone is getting stronger.

And getting back to what Richard Trigaux said in Post #50, what's interesting is that in Squyre's Journal of Geophysical Research 2006 paper, he describes the Backstay class of rocks as basalt/trachybasalts and that Peace is comprised of ultramafic sand grains (komatiites??). Another paper mentioned that Clovis has basaltic glass as it's principal component.

Yes, crumbs have been dropped for us for some time now. Many of these little puzzle pieces are going to start coming together.

Here is something interesting from today's imagery: we have the contact of the lower part of the Homeplate formation with the underlying unit, and the unit below that is the "fractal spongebob" scoria. Looking at other images, we can see weathered outcrops of bedded after bedded unit.

This is going to be a productive Winter.

--Bill

[neb]

Bill: I have reviewed the images you refer to but my view differs somewhat.
I see steepening of the dip from the flat HP beds we have been on to fairly high dips at the edge of the outcrop in the foreground.including some of the basal HP unit. Mar 06 image 02075
I do not see any vescicular basalt in place which would represent a lower stratigraphic unit.
I did see several bomb -erratics in the x-bedded sediments which suggests ejected volcanic beds and a more convincing feature is the drape of HP eqivalent units over a small rise along the ridge immediately in front of us. This drape almost has to be associated with air-fall material.
I do agree that we are going to see more of these HP type beds at different elevations because they covered the topography at the time and have now been seperated by erosion into isolated patches.

[Guest_Richard Trigaux_*]

I somewhat agree and somewhat disagree with neb.

The scoriaced basaltic blocks we see could have been added here much afterwards by meteorites impacts, as much of the blocks we see everywhere. So it is difficult to conclude.


"my" paradigm about Homeplate and the overal surrounding hills, that I already explained in this discution, is that the hills would be large spans of ancient soil, expelled by the Gussev impact, and which fell back in place (eventually upside-down) and were broken, folded, crunched, while keeping a recognizable layer pattern. Such formation can be seen in the Ries crater, in Germany (Sorry for Bruce Moomaw, but the exploration of Ries crater was made by manned missions, not robotic ). It is a bit surprising, but the evidences are just under our feets.

So the hills would be remnants of very ancient terrains, dating back perhaps to the formation of the martian crust, no less.

We earthlings are accustomed to see ancient terrains heavily metamorphised or eroded. On Mars this don't seems to happen, and we look at four billions years old lava scorias which look as fresh as what we can pick on a recent Earth volcano, I even have some at home that I gathered in the chaîne des puys, France.

But martian holes are larger, hinting for a weaker atmosphere from the very beginning of Mars history.


Also in the image above, the leftermost big bomb looks a bit like if it was formed in a phreatomagmatic eruption. A close look would be interesting, as knowing for phreatomagmatic eruptions on Mars would be an evidence for past water.

[abalone]

Could it be that these layers in the distance and on the side of McCool hill are a continuation of the Home Plate sequence? I know its not new speculation but the evidence appears to be mounting

Attached thumbnail(s)

 

[neb]

Could it be that these layers in the distance and on the side of McCool hill are a continuation of the Home Plate sequence? I know its not new speculation but the evidence appears to be mounting

Abalone: I am confident the beds you refer to are equivalent to the HP section but possibly reduced in thickness. It will be interesting to see what their dip is.

[Shaka]

Abalone: I am confident the beds you refer to are equivalent to the HP section but possibly reduced in thickness. It will be interesting to see what their dip is.

Hmmm...well now. Do I get the drift from this discussion that HP may not represent a specific impact or volcanic structure, but perhaps just a chance residue of once continuous beds filling inner basin?

[Bob Shaw]

Hmmm...well now. Do I get the drift from this discussion that HP may not represent a specific impact or volcanic structure, but perhaps just a chance residue of once continuous beds filling inner basin?

Yup!

Though perhaps not all-enveloping - though any airfall could well be such.

Bob Shaw

[Guest_paulanderson_*]

Yup!

Though perhaps not all-enveloping - though any airfall could well be such.

Bob Shaw

But the MER team seems to be suggesting, almost with certainty now, that HP is a remnant maar / tuff cone. Airfall deposits would then be expected to be found, would they not? Couldn't the other nearby possible deposits be remains of other similar vents? Like others noted before, why is the ground around and near HP seemingly littered with the "sponge rocks"? Plus the imbedded (apparent) volcanic bombs in HP itself. All these things need to be taken into account. But again, I want to wait until they say more officially.

[Shaka]

Yup!

Though perhaps not all-enveloping - though any airfall could well be such.

Bob Shaw

Donnerwetter nochmal! I suppose this finding was always lurking off in the fringes of our imaginations, like a gray stormcloud threatening our bright postulates for Home Plate. And I suppose we needn't hope to rove into the extinct volcano that did all this, since it could be far away or deep beneath the plains lavas. Sad, if true, but at least it will salve our regret if Spirit never returns to the Ballpark.

Side note: I got very confused by the latest batch of MIs at Exploratorium: http://qt.exploratorium.edu/mars/spirit/mi...ger/2006-03-07/
until I figured out that they were over six months old! How can relics of the past like this suddenly show up? Surely these were not languishing in the deep recesses of Spirit's memory all this time! (I am unavoidably reminded of a Woody Allen seasickness joke about "a lunch he had in 1956".) sorry

[imipak]

Hmmm...well now. Do I get the drift from this discussion that HP may not represent a specific impact or volcanic structure, but perhaps just a chance residue of once continuous beds filling inner basin?

Surely HP-liked layers on McCool and/or Michaeltree Ridge doesn't disprove the volcanic vent theory. (I may not know much* geology but I seem to recall that there are large areas of Siberia and the Indian subcontinent covered by lava flows from one location, albeit a very large one with a completely different aetiology Another factor -- presumably gravity 33% of that on earth would tend to mean that volcanic ejecta would tend to go higher and further from the source.

And some have mentioned the possibility that the vent was actually submerged in a shallow sea or lake (rather than just occuring through water-soaked sediments) -- in which case explosive ash and other sediment would presumably be distributed by any currents or even just convection from the heat of the vent.

* s/much/any/

[odave]

How can relics of the past like this suddenly show up? Surely these were not languishing in the deep recesses of Spirit's memory all this time!

It all depends on the image priority. Images that deal with the next sol's drive/sequence planning always have higher priority than other data products. Some of them may in fact be parked in flash for a long time, simply because other images need to get down first, and there isn't enough time in the pass to get to lower priority items. Check out the transcript from the 1/31/06 pancam update, 3rd DE question

[tty]

Surely HP-liked layers on McCool and/or Michaeltree Ridge doesn't disprove the volcanic vent theory. (I may not know much* geology but I seem to recall that there are large areas of Siberia and the Indian subcontinent covered by lava flows from one location, albeit a very large one with a completely different aetiology Another factor -- presumably gravity 33% of that on earth would tend to mean that volcanic ejecta would tend to go higher and further from the source.

And some have mentioned the possibility that the vent was actually submerged in a shallow sea or lake (rather than just occuring through water-soaked sediments) -- in which case explosive ash and other sediment would presumably be distributed by any currents or even just convection from the heat of the vent.

* s/much/any/

The deposits You are thinking of (the Siberian and Deccan traps) are plateau basalts which is a completely different type of deposit (and eruption).

If the eruption actually occurred underwater there should be pillow lavas around somewhere.

tty