[X] My Assistant

[djellison]

http://www.unmannedspaceflight.com/doug_im...aving_larry.jpg (476kb)

Larry is the outcropping to the right - Methuselah is the layered rock on the left.

As an interesting point to judge distances - assuming zero slip the marks made by the hold-down-brackets on the wheel tread are 80cm apart - or about 2ft 7inches

Doug

[Guest_Edward Schmitz_*]

Good discussion. Let me jump in here. There are a few things I would like to bring up.

1) Gusev has a number of compression faults that are generally aligned north-south and perpendicular to the direction to the tharis bulge. In fact the tharis bulge is ringed by compression faults in all directions. This is most likely due to the relaxing of the bulge. Picture a cone on a desk. As you push down on the cone, the sides either have to compress or they split. It seems that tharis is doing both. And it seems to have occured as far out as Gusev.

Further, this could have been active before the lava flows embayed the hills. Thus the hills could easily be formed by thrust faulting.

2) Sedimentary rocks can form at an angle. These rocks need not have tilted at all. Air born ash falling on a hill side or the rim of a crater will have angled layers. Think of snow falling in the mountains.

3) On the point of active volcanism, it is posible that Mars has seen it's last eruption. However, some very good studies have pegged the ages of lava flows in the tharis and elisium region at less than a million years old. This means that the last flows occured in the last 0.025 percent of the planets age. It is highly unlikely that we would get there and miss the volcanic age of Mars by just a tad. It is more likely that there is still molten magma in the mantle and that future reruptions will occure.

[dvandorn]

Good discussion.  Let me jump in here.  There are a few things I would like to bring up. 

1) Gusev has a number of compression faults that are generally aligned north-south and perpendicular to the direction to the tharis bulge.  In fact the tharis bulge is ringed by compression faults in all directions.  This is most likely due to the relaxing of the bulge.  Picture a cone on a desk.  As you push down on the cone, the sides either have to compress or they split.  It seems that tharis is doing both.  And it seems to have occured as far out as Gusev.

Further, this could have been active before the lava flows embayed the hills.  Thus the hills could easily be formed by thrust faulting.

2) Sedimentary rocks can form at an angle.  These rocks need not have tilted at all.  Air born ash falling on a hill side or the rim of a crater will have angled layers.  Think of snow falling in the mountains.

3) On the point of active volcanism, it is posible that Mars has seen it's last eruption.  However, some very good studies have pegged the ages of lava flows in the tharis and elisium region at less than a million years old.  This means that the last flows occured in the last 0.025 percent of the planets age.  It is highly unlikely that we would get there and miss the volcanic age of Mars by just a tad.  It is more likely that there is still molten magma in the mantle and that future reruptions will occure.

In re your point 1) -- really? I'm not disputing, certainly, I've just never seen compressional stress features when I've looked at all the various images of Gusev and its surrounding region. I would assume the features we're talking about look, at the surface, like low ridges as opposed to graben?

On point 2), yeah, sedimentary rock does form at angles (people *do* need to remember that sedimentary rock forms in all sorts of ways, and water deposition is only one of those ways). I just think that Gusev's features, taken at a gross level, really do suggest that it was a lake at some point in the past, and applying Occam's Razor, it's simply more likely that layered sediments were water-deposited. But, of course, we'll be able to tell a lot better when we've gotten a really good look at the rocks in this outcrop.

And on point 3), I'm also of the opinion that we haven't seen the last of Martian volcanism. After all, we really don't have a complete understanding of the process of core/mantle cooling in rocky planets. And as for Marsquakes, we also have to remember that the Tharsis bulge may yet be in the active process of deformation as it settles, which can drive quake activity. And billions of tons of dry ice get deposited on, and removed from, alternate poles every Martian year, which has to have *some* impact on the overall flexing of the Martian crust.

About the only thing I would think is pretty certain about Martian crust/mantle interactions is that there seems to be no sign, whatsoever, that active plate tectonics are happening on the planet currently. Other than that, I think the door is wide open for most other processes.

-the other Doug

[Guest_Edward Schmitz_*]

In re your point 1) -- really?  I'm not disputing, certainly, I've just never seen compressional stress features when I've looked at all the various images of Gusev and its surrounding region.  I would assume the features we're talking about look, at the surface, like low ridges as opposed to graben?

-the other Doug

Here is a great example of a thrust fault in Gusev. It seems quite posible that the hills are the result of thrust faulting and later embayment by lava flows. The hills have more than a passing resemblance to the thrust fault hills in the other image. That would be consistant with layers being sedimentary and the angle that they now sit at. But they could easily be ash fall on the hill after it was thrust / embayed. The plains are volcanic (we know that) so why not ash fall as well.

Lots of senarios are open. That's what makes this exporation. It is really exciting. So far, the hills have been quite difficult to interpret. I wouldn't be surprised if this doesn't clear up the mistery.

Thrust Fault
http://themis-data.asu.edu/img/V06798003.html

Colubia Hills
http://themis-data.asu.edu/img/V00881003.html

[dvandorn]

In re your point 1) -- really?  I'm not disputing, certainly, I've just never seen compressional stress features when I've looked at all the various images of Gusev and its surrounding region.  I would assume the features we're talking about look, at the surface, like low ridges as opposed to graben?

-the other Doug

Here is a great example of a thrust fault in Gusev. It seems quite posible that the hills are the result of thrust faulting and later embayment by lava flows. The hills have more than a passing resemblance to the thrust fault hills in the other image. That would be consistant with layers being sedimentary and the angle that they now sit at. But they could easily be ash fall on the hill after it was thrust / embayed. The plains are volcanic (we know that) so why not ash fall as well.

Lots of senarios are open. That's what makes this exporation. It is really exciting. So far, the hills have been quite difficult to interpret. I wouldn't be surprised if this doesn't clear up the mistery.

Thrust Fault
http://themis-data.asu.edu/img/V06798003.html

Colubia Hills
http://themis-data.asu.edu/img/V00881003.html

Interesting... it always looked to me like these thrust faults were very similar to the wrinkle ridges on the lunar maria, and that, as such, they were a result of the (relatively) heavy lavas compressing under their own weight. In other words, that they were an artifact of the lava fill and not pre-existing of them.

But yes, I do see the orientation of the north-south trending faults, and in fact the one main fault line does extend beyond Gusev into the non-lava-filled ancient cratered terrain to the north.

I stand corrected... *smile*...

-the other Doug