There was an explosive eruption on Mars! ??Estimated from tridymite found in lake bottom sediments | sorae Portal site to space

[▲ Figure 1: “Selfie” of Curio City taken on July 30, 2015. The whitish line at the bottom of the photo is a trace of sampling shown in Figure 2. (Credit Image: NASA, JPL-Caltech, MSSS)]

Mars is now a barren planet, but it is believed that it maintained an environment similar to Earth for some time after its birth. There used to be a significant amount of liquid water on the surface of Mars, and it is believed that volcanic activity was active. Nowadays, both water and volcanoes only leave traces on the surface, but research is continuing to analyze the substances on the surface and estimate the former environment.

NASA Mars RoverCuriosityIs a “running laboratory” that conducts Mars exploration with high accuracy.Curiosity is on the Elysium Planitia of Mars on August 6, 2012GaleLanded on a crater called.

The Gale Crater is believed to have been a water-filled lake for some time after it was formed 3.8 billion years ago. It was chosen as the landing site for Curio City because of presumed geological evidence of the time when Mars had liquid water. According to Rice University, Curiosity has found evidence that Gale craters seemed to have had liquid water up to a billion years ago. Then, in 2015, we dug up the Gale Crater deposits and analyzed what kind of minerals they contained.

[▲ Figure 2: Traces of Curiosity taking a sample of the Gale Crater. From this sample, tridymite, which is the main player in this study, was found. (Credit Image: NASA, JPL-Caltech, MSSS)]

Then, in the sedimentscale stone Scientists were surprised to find that a mineral called (tridymite) was contained in high concentrations of up to 15.6w% (weight percent).

Tridymite is a mineral of silicon dioxide, which has the same composition as quartz (a beautiful crystal is also called quartz), which is common in rocks, but has a different formation environment. Scientists were surprised because the environment for tridymite formation was unexpected on Mars.

The tridymite formation environment requires a high temperature of 870 ° C to 1470 ° C, andFelsic magmaWe also need magma rich in silicate. The siliceous magma volcano is known on Earth as a volcano with explosive eruptions and volcanic ash eruptions, such as Mount St. Helens and Satsuma Ioshima.

However, tridymite is a mineral that exists stably only at high temperatures, and when it cools slowly, it changes to quartz. For this reason, the conditions under which tridymite can be seen on the ground are limited, and it can only be found on Earth in limited places such as Japan, Italy, and Greenland.

On the other hand, most of the rocks found on MarsBasaltic magmaIt is derived from silicate-poor magma, and rocks derived from felsic magma are very scarce. Basaltic magma volcanoes, such as Kilauea and Izu Oshima, are characterized by the fact that they do not eject volcanic ash and allow magma to flow quietly.

Since the tridymite found in the Gale crater is concentrated in one layer of sediment, it is most likely that the volcanic ash was the origin of the tridymite. However, no evidence of such a volcano on Mars has been found so far. In addition, long-term interactions between silicon dioxide and water and the high temperature and high pressure that are temporarily generated by meteorite impacts can cause tridymite from sources other than magma, so it is necessary to distinguish them from these. Gale craters are just such an environment.

V. Payré and colleagues at Northern Arizona University investigated from various angles whether tridymite in the Gale crater originated from volcanic ash.

Payré et al. First analyzed how solid the crystal structure of tridymite is from the data of Curiocity’s X-ray diffractometer “XRD” used for mineral identification. As a result, it was found that the crystal structure of the tridymite of the Gale crater is very solid, and there are almost no parts with low crystallinity. This cannot be explained by very low crystallinity silicon dioxide such as opal. This excludes the possibility that tridymite may have arisen from its interaction with water.

[▲Figure3:ResultsofXRDanalysisoftridymiteThepeakrepresentingtridymite(red)isveryclearanditcanbeseenthatitisclearlydifferentfromtheamorphouscomponentwithlowcrystallinity(black)andtheopalCT(yellow)whichhasacrystalstructuresimilartotridymite(Credit:Payréetal)】

It was also found that the gale crater tridymite has a monoclinic crystal structure. This indicates that tridymite was formed at high temperature and then cooled rapidly. Studies of monoclinic tridymite found on Earth have shown that such an environment exists only in environments such as meteorite collisions or rocks being crushed to volcanic ash by an explosive eruption. I am.

Now that we’ve narrowed it down to this point, the next thing to look at is ingredients other than tridymite. More than half of the sediment samples in which tridymite was found in Gale Crater are silicon-rich amorphous components (materials with very low or no crystallinity), while the rest are ash feldspar, orthoclase, tridymite, porcelain, or Cristobas. It turned out that it was composed of stone and anhydrous gypsum.

In addition, when examining the concentration of elements, it was found that aluminum was less than the amount of silicon and titanium was relatively more. These components are relatively consistent with rhyolitic magma (a type of felsic magma). However, as I said relatively, that alone cannot explain everything.

Here, the lake that was once thought to have existed in the Gale Crater fills in the discrepancy. This is because water causes chemical weathering of volcanic ash. Aluminum, which is an element that easily accompanies silicon, easily dissolves in water, and the low concentration of aluminum can be explained by considering that it has dissolved in water.

Also, in the interaction with water, silicon dioxide with low crystallinity dissolves in water, but silicon dioxide with high crystallinity hardly dissolves in water. This can explain the state of the analyzed sediments by considering that low crystallinity opal silicon dioxide has dissolved in water, while high crystallinity tridymite has settled on the bottom of the lake at high concentrations. .. The situation at the site shows that the felsic magma ash makes the most sense, not the impact of a meteorite.

[▲Figure4:ThescenarioassumedinthisstudyMorethan3billionyearsagotherewasafelsicmagmavolcanothousandsofkilometersawayandanexplosiveeruptionproducedalargeamountofvolcanicashTheasheventuallyfellintothelakethatfilledtheGalecrateranddeposited(Credit:Payréetal)】

From the above, the following story can be considered about the eruption that occurred on Mars in the past.

There used to be a volcano on Mars with felsic magma with components similar to rhyolite. The volcano is estimated to have been thousands of kilometers away from the Gale Crater. In the magma chamber of this volcano, a phenomenon called fractional crystallization occurred, in which the components that remained dissolved in the magma and the components that did not dissolve in the magma and crystallized were separated. This fractional crystallization is thought to have occurred at least twice, once with orthoclase and once with tridymite and anorthite.

And at some point during the Hesperian period, 3.7 to 3.2 billion years ago, the volcano erupted explosively. At this time, tridymite was also contained in the volcanic ash generated from magma. It is probable that this volcanic ash fell and accumulated on the lake that filled the Gale crater, and then the chemical composition changed between the Gale crater and the water drying up, resulting in the currently observed sediments.

There is ample evidence of basaltic magma on Mars, but little evidence of felsic magma. However, this study of tridymite found in the Gale Crater shows that at least one explosive eruption of a volcano with felsic magma has occurred on Mars in the past.

In addition, the proportion of components other than tridymite indicates that the magma component changed significantly before the eruption. It shows the geological and chemical changes on the surface of Mars and is very interesting for measuring the planetary scientific evolution of Mars.

Past Mars rover may have missed the highly transparent felsic magma component, only by near-infrared component analysis. On the other hand, Curio City is equipped with XRD that analyzes with X-rays, which may have led to this discovery. NASA’s Perseverance Mars rover, Perseverance, which landed on the Jezero Crater in February 2021, is equipped with similar equipment, and new evidence may be found. Keep an eye on future Mars exploration and research.

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Source

• Image Credit: NASA/JPL-Caltech/MSSS; Payré et.al.
• V. Payré, et.al. – Tridymite in a lacustrine mudstone in Gale Crater, Mars: Evidence for an explosive silicic eruption during the Hesperian (Earth and Planetary Science Letters)
• Rice University – Study: Explosive volcanic eruption produced rare mineral on Mars
• Kazuhide KAWAI, et.al. – The first finding of monoclinic tridymite in terrestrial volcanic rocks (Mineralogical Journal)
• Richard V. Morris, et.al. – Silicic volcanism on Mars evidenced by tridymite in high-SiO2 sedimentary rock at Gale crater (Proceedings of the National Academy of Sciences)

Sentence / Aya Eri