Impact crater or supervolcano caldera?

[Waspie_Dwarf]

Impact crater or supervolcano caldera?

21 May 2015 At first glance, the region covered by this latest Mars Express image release appears to be pockmarked with impact craters. But the largest structure among them may hold a rather explosive secret: it could be remains of an ancient supervolcano.

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[Doc Socks Junior]

I'm going with an "unlikely" that it's a supervolcano caldera. It would be unusual for the volcanic regime on Mars. But hey, they got it published in Nature, so what do I know.

Which brings us to a major problem with some aspects of planetary science. You can get informed shape matching, which is a little iffy.

[Zalmoxis]

The wider impression in the picture looks to my eyes like a sunken area because of material being removed underneath. If that were so then where did the resulting flow disappear to? Is this so long ago that all of the material is worn away through billions of years of erosion? I don't really know that much about craters or volcanos but that does look like the result of a collapse of some sort underneath the caldera.

[Waspie_Dwarf]

It would be unusual for the volcanic regime on Mars.

I don't claim to be an expert on volcanism but I don't understand how you can so easily dismiss the possibility out of hand. Volcanism was known to be common on Mars in the past. The Tharsis bulge containing the Thrasis Montes (Arsia Mons, Pavonis Mons, and Ascraeus Mons), Elysium and it's volcanoes (Hecates Tholus, Elysium Mons and Albor Tholus) or most famous of all, Olympus Mons are the largest known volcanoes in the solar system. Mars was extraordinarily volcanic in the past.

Siloe Patera is only one of SEVEN suspected calderas in the Arabia Terra region, so this is not a case of simply shape matching one feature, it is the result of extensive investigation of an entire region.

Given that Mars was so volcanically active in the past how can you possibly discount the possibility of another volcanic caldera as unlikely?

[Merc14]

I'm going with an "unlikely" that it's a supervolcano caldera. It would be unusual for the volcanic regime on Mars. But hey, they got it published in Nature, so what do I know.

Which brings us to a major problem with some aspects of planetary science. You can get informed shape matching, which is a little iffy.

Are you forgetting Olympus Mons, the largest volcano in the solar system?

Edited May 23, 2015 by Merc14

[S2F]

Thanks for sharing that Waspie. It is an interesting conundrum, how do you tell the difference between an impact crater or a volcanic caldera when a lot of the key features of both can overlap? The one interesting detail mentioned in the article is the valley cut through the edge of the crater. The article mentions that it could be caused by an oblique impact however the ejecta doesn't clearly indicate that is the case. Erosion could be obscuring that fact but I think it indicates a tick in a box on the volcanism side of the debate.

[Doc Socks Junior]

I don't claim to be an expert on volcanism but I don't understand how you can so easily dismiss the possibility out of hand. Volcanism was known to be common on Mars in the past. The Tharsis bulge containing the Thrasis Montes (Arsia Mons, Pavonis Mons, and Ascraeus Mons), Elysium and it's volcanoes (Hecates Tholus, Elysium Mons and Albor Tholus) or most famous of all, Olympus Mons are the largest known volcanoes in the solar system. Mars was extraordinarily volcanic in the past.

I'm also not an expert on volcanism by any means. But I'm not dismissing it out of hand either. I completely agree that Mars was (and is?) active volcanically. Very active volcanically indeed. Yep, the Tharsis province (and the Elysium province) are spectacular examples of volcanic activity. Extrusive basaltic volcanic activity.

We even see calderas on Mars, at Tharsis and Elysium. Think of the these provinces as hotspots...the Hawaiian Islands if they didn't move and simply stacked in a small geographic area. These were (are?) extraordinary active volcanic provinces. We must ask ourselves...does the Arabia province resemble these provinces? Do we have a preponderance of Mons? Clearly not.

So what is being proposed here is a province with a completely different mode of volcanism than what we see in other areas on Mars. The proposal is explosive volcanism, much different than what we see at Tharsis or Elysium.

SO.

Is it unlikely? I think so. Is that because we have a different province, without the same features other calderas on Mars, following a completely different eruptive style, that we don't (I'm fairly sure) see anywhere else on Mars? Yes, that's why I think so.

But, let's be real, I'm not a planetary geologist. And even if I was, my specialty wouldn't be volcanology. So. My thoughts are my own here.

Siloe Patera is only one of SEVEN suspected calderas in the Arabia Terra region, so this is not a case of simply shape matching one feature, it is the result of extensive investigation of an entire region.

Given that Mars was so volcanically active in the past how can you possibly discount the possibility of another volcanic caldera as unlikely?

I haven't completely discounted the possiblity. As I said. There are more weird hypotheses about what has gone on with Mars in the past. Plate tectonics, etc. Wild, wild. But honestly, a rather excellent planetary geologist who I admire was the first to tell me about the pitfalls of going solely based on geomorphic evidence. Sure, it's extensive shape-matching. But it's still shape-matching, to be simplistic about it.

[Doc Socks Junior]

Are you forgetting Olympus Mons, the largest volcano in the solar system?

Nope, not forgetting Olympus Mons. It's simply a completely different mode of volcanism than what is being proposed here at Arabia Terra. Which is part of my entire reason for caution here.

[Merc14]

Nope, not forgetting Olympus Mons. It's simply a completely different mode of volcanism than what is being proposed here at Arabia Terra. Which is part of my entire reason for caution here.

Just as super volcanoes are a completely different mode of volcanism than, say, Mt. Whitney. Understood though and I am no pro either but it definitely doesn't look like an impact crater. Edited May 23, 2015 by Merc14

[Doc Socks Junior]

Just as super volcanoes are a completely different mode of volcanism than, say, Mt. Whitney.

Mt Whitney? That's not volcanism at all, I would say. The Sierra Nevada batholith represents magmatic activity, sure.

Understood though and I am no pro either but it definitely doesn't look like an impact crater.

In doing my due diligence I pulled up the LPSC abstract on this topic:

http://www.hou.usra.edu/meetings/lpsc2014/pdf/2271.pdf

Figure 1, specifically, is of interest in the geomorphological classification of Siloe Patera.

[Merc14]

Mt Whitney? That's not volcanism at all, I would say. The Sierra Nevada batholith represents magmatic activity, sure.

In doing my due diligence I pulled up the LPSC abstract on this topic:

http://www.hou.usra....14/pdf/2271.pdf

Figure 1, specifically, is of interest in the geomorphological classification of Siloe Patera.

I don't know the difference but if you have the time I am willing to listen or would appreciate a civilian learning link. Any help appreciated. The older I get the less I know apparently. I think that is agood thing as long as I can find folks willing to explain things to my ignorant self. LOL

[Nnicolette]

Even if it looks like a caldera wouldnt there be more evidence in the form of igneous deposits?

[Waspie_Dwarf]

Nope, not forgetting Olympus Mons. It's simply a completely different mode of volcanism than what is being proposed here at Arabia Terra. Which is part of my entire reason for caution here.

Okay, I see what you are saying, however we have multiple modes of volcanism on Earth, why do you think it likely there would be only one mode of volcanism on the ancient Mars?

[Doc Socks Junior]

I don't know the difference but if you have the time I am willing to listen or would appreciate a civilian learning link. Any help appreciated. The older I get the less I know apparently. I think that is agood thing as long as I can find folks willing to explain things to my ignorant self. LOL

For the magmatism vs. volcanism? That's a question of where the igneous activity was occurring. Magmatism is igneous activity in the crust--if it reaches the surface its volcanism. Mt. Whitney is part of the Sierra Nevada batholith. A batholith is a large scale body of magma that solidifies below the surface. (It's also generally assembled via pulses, which is a fairly new concept in the literature. But it really makes a lot of sense.) Yellowstone, for example, is volcanism--but related to a large magma chamber (several actually) below ground. We can see shallow-crust emplacement of magma that does cause volcanism, and some that does not. All depends on the area.

Even if it looks like a caldera wouldnt there be more evidence in the form of igneous deposits?

They're positing it as an explanation for layered sulfate deposits in Arabia Terra and ridged lava deposits in the area. So there are definitely igneous deposits around the area. And the sulfur explanation, as they say, is nifty.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140011237.pdf

I like their work more and more as I read it more.

Okay, I see what you are saying, however we have multiple modes of volcanism on Earth, why do you think it likely there would be only one mode of volcanism on the ancient Mars?

Effusive basaltic volcanism is the major recognized mode of volcanism for Mars. And other planets in the System (besides Earth). (Venus has its pancake tholi I believe, so there's something different there though.) Earth also has a completely different geologic story than Mars. Plate tectonics, increased volatiles (I think, don't hold me to the second one), and we're still actually retaining inner heat pretty well. Which allows for magma evolution, and some nice interplay between differentiated layers which can lead to different chemistry magmas and therefore different modes of volcanism.

As it is, the paper mentions:

We suggest that a combination of regional extension and thermal erosion of the lower crust in the Late Noachian-Early Hesperian led to rapid ascent of magma in the northern Arabia Terra region. It is not necessary that the magmas were higher viscosity (more silicic) or had higher volatile content than other martian magmas. The lower gravity and atmospheric pressure on Mars lead to bubble nucleation at greater depths and greater gas expansion compared to Earth. As a result, pyroclastic eruptions would be more commonly associated with basaltic volcanoes on Mars than on Earth, particularly if the magma rapidly ascends and erupts, and is not stored in degassing magma chambers for long periods of time, as is thought to occur at younger, large shield volcanoes. In fact, it is possible that explosive volcanism was more prevalent on early Mars because the ancient crust was thinner, leading to less devolatilization of magmas during ascent. The result may have been the deposition of vast quantities of tephra early in Mars’ history.

I like this better and better. Still fairly unique. On the Moon, we see small-scale explosive cinder cone volcanism thanks to this process. But explosivity at this scale with this type of volcanism would be pretty unique, I believe. Which doesn't make it wrong, of course.

[Waspie_Dwarf]

We may still be retaining inner heat well, but let's not forget we are talking about a much earlier period in Martian history. How much heat the two planets retain today would seem to be irrelevant to me.

Also the argument that

Effusive basaltic volcanism is the major recognized mode of volcanism for Mars

would seem to be a circular argument.

Unless I have totally misunderstood your point, you argument seems to be of the form: We know that X occurs. Y has been suggested as well. Y is unlikely because we now X occurs.

such an argument would seem to preclude any new discoveries on the basis of it not being that same as that we already know.

[Doc Socks Junior]

We may still be retaining inner heat well, but let's not forget we are talking about a much earlier period in Martian history. How much heat the two planets retain today would seem to be irrelevant to me.

True. Good point.

Also the argument would seem to be a circular argument.

Unless I have totally misunderstood your point, you argument seems to be of the form: We know that X occurs. Y has been suggested as well. Y is unlikely because we now X occurs.

such an argument would seem to preclude any new discoveries on the basis of it not being that same as that we already know.

I think you're misunderstanding the argument. If that form is what is coming off, I'm not making myself clear I guess. Also, that's just a statement of fact. If something has been conclusively shown to occur in one way, it does make it less likely that it occurs in a completely different way. There's a reason why we don't hold the geosyncline up as a mechanism of equal validity to mantle convection as relates to plate tectonics.

That argument doesn't preclude new discoveries. It does preclude a lot of ill-supported and wildly improbable ideas however.

I am not saying this is an ill-supported or wildly improbable idea. However, it is a fairly new idea. As such, it must be compared to older ideas, and the current body of knowledge about the subject.