Geomorphology of Gale Crater, Rock on! |
Geomorphology of Gale Crater, Rock on! |
Sep 26 2012, 10:22 PM
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#31
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
I'd like a discussion thread about the geology detatched from the time limits of current MSL threads. We had a 'Geomorphology of Cape York' thread that attracted a lot of interesting posts. How about 'Geomorphology of Gale Crater'? I have one or two ideas but many more questions, and I'd like to post them in a longer-running thread away from the day to day imaging discussion. Any other takers?
For starters, does anybody have a contour map of this place like the one at Meridiani with 5m intervals? ADMIN: You have your wishes fulfilled on UMSF (sometimes) |
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Dec 2 2012, 09:15 PM
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#32
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Junior Member Group: Members Posts: 94 Joined: 11-August 12 Member No.: 6536 |
I still like the spring mound idea.
The rover is currently seeing a lot of rocks which look spongy and porous. What if there is a thick layer of such rock underlying Gale Crater? In wet, high atmospheric pressure climates these rocks would fill up with water, creating a large aquifer. Then the atmospheric pressure drops quickly, due to carbon dioxide freezing out at the poles. The drop in pressure reduces the boiling point of water, and the water in the aquifer starts to boil. The porous beds slope upwards towards the center of the crater, so the warmer less dense fluids migrate in that direction. They erupt from Mt Sharp, leaving behind an evaporite deposit. The chemistry of the evaporite depends on the chemistry of Martian water and the atmosphere at the time. When the atmosphere was rich in sulfur dioxide, sulphates were formed. More recently, another mineral, maybe carbonates was deposited. Martian winds have eroded Mt Sharp over time, giving the deposits an aeolian appearance. The lowest clay bearing layers might be old lakebed deposits which were covered and protected from erosion by later materials. Mt Sharp could be the result of a long history of oscillations in atmospheric pressure which alternately filled an aquifer and then dropped the pressure enough to boil it. |
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Dec 18 2012, 02:10 PM
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#33
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
The rover is currently seeing a lot of rocks which look spongy and porous. What if there is a thick layer of such rock underlying Gale Crater? I think, the spongy-looking surface of those rocks may be explained by conglomerates similar to those at Bradbury Landing. Easily weatherable rounded stones might be embedded in a more resistant material. As soon as the conglomerate is exposed to the acidic and oxidizing environment, embedded stones fall out of their holes or weather rapidely. To an explanation of the embedded stones being more weatherable might contribute acidity: Embedded stones are older than embedding rock. So they probably will be more basic (alkaline) due to increasing acidity of the Marsian surface over time; they might be more basic, if they are of magmatic or plutonic origin (basalt), as well. Alkaline rocks will tend to weather more easily today than acidic ones. Then the atmospheric pressure drops quickly, due to carbon dioxide freezing out at the poles. Water will freeze out first, before carbon dioxide. Freezing produces warmth. So a runaway freezing at the poles looks to me rather unlikely. The drop in pressure reduces the boiling point of water, and the water in the aquifer starts to boil. The porous beds slope upwards towards the center of the crater, so the warmer less dense fluids migrate in that direction. They erupt from Mt Sharp, leaving behind an evaporite deposit. Some water might evaporate or sublimate; boiling might have occurred in the context of vulcanism. Capillar forces are too weak to drive water upward more than a few hundred meters, I think. Pressure from shrinking rocks will erupt surface water at most once, thereafter the pores will allow less water contents. Repeated formation of new pores by solvents probably leads to a net shrinkage of the mountain. The only way, I can imagine, able to change this may be periodic hot vulcanism. The other question is: Why doesn't the water flow sideward as ground water on a layer of clay and form springs at the laterals of Mt. Sharp? When the atmosphere was rich in sulfur dioxide, sulphates were formed. More recently, another mineral, maybe carbonates was deposited. Normally carbonates will tend to be more alkaline than sulfates. So I guess, that carbonates might have formed in the Noachian, i.e. early in Marsian history, together with clay minerals. Later, in the Hesperian, sulfur oxides might have transformed some of the carbonates and clay minerals to sulfates or sulfites. Many sulfates are more water-solvable than the corresponding carbonates or clay minerals. So acidic weathering sounds rather plausible to me. Acidic weathering, together with acidic deposites in riverbeds, might also contribute to the inverted river and pool beds, because acidic beds within more alkaline surrounding rock will tend to be more resistant under the present acidic conditions. Same with reduced stuff under oxidizing conditions. I could imagine an ice cap or permafrost helping prevent Mt. Sharp from fast erosion, much the same as mountains on Earth. |
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