Tag Archives: igneous

Northwest Africa (NWA) 11119 is the oldest igneous meteorite recorded. Credit: University of New Mexico.

Unique 4.6-billion-year-old meteorite is a remnant of the early solar system

A never-before-seen space rock — older than Earth itself! — stands out among the 40,000 meteorites researchers have recovered so far. Scientists claim this is the oldest igneous meteorite found thus far and by studying it they hope to learn more about how the solar system formed and evolved.

Northwest Africa (NWA) 11119 is the oldest igneous meteorite recorded. Credit: University of New Mexico.

Northwest Africa (NWA) 11119 is the oldest igneous meteorite recorded. Credit: University of New Mexico.

About 4.6 billion years ago, a massive cloud of gas and dust collapsed under its own gravity, forming a spinning disk with a proto-sun at its center. Under the influence of gravity, material accreted into small chunks that got larger and larger, forming planetesimals. Many such objects likely broke back apart as they collided with each other, but others would have coalesced — eventually becoming planets and moons. However, the journey to building a planet was quite messy. One study published in Nature concluded that Earth lost nearly 40 percent of its mass as vapor during collisional growth.

The weird meteorite described by Carl Agee, the Director of the University of New Mexico’s Institute of Meteoritics, and colleagues provides chemical evidence that silica-rich crustal rocks were forming on planetesimals at least 10 million years before the assembly of the terrestrial planets.

At first, however, the space rock looked pretty unassuming. The researchers initially thought that the rock — called Northwest Africa 11119, as it was discovered in the sand dunes of Mauritania — was terrestrial in origin due to its light appearance and silica-rich content.

The rock, which was originally found by a nomad and later sourced by Agee via a meteorite dealer, was handed over to graduate student and lead author Poorna Srinivasan to study its mineralogy. Using an electron microprobe and a CT (computed tomography), Srinivasan started noticing unusual details in NWA 11119 and concluded it is extraterrestrial in origin, judging from its oxygen isotopes. What’s more, the silica-rich achondrite meteorite contains information involving the range of volcanic rock compositions (their ‘recipes’) within the first 3.5 million years of solar system creation.

“The age of this meteorite is the oldest, igneous meteorite ever recorded,” Agee said in a statement. “Not only is this just an extremely unusual rock type, it’s telling us that not all asteroids look the same. Some of them look almost like the crust of the Earth because they’re so light colored and full of SiO2. These not only exist, but it occurred during one of the very first volcanic events to take place in the solar system.”

Artist impression of NWA) 11119, seen in right bottom corner. Credit: University of New Mexico.

Artist impression of NWA) 11119, seen in right bottom corner. Credit: University of New Mexico.

According to Srinivasan, the mineralogy of the rock is unlike anything the researchers have worked on before. One of its most striking characteristics is that large silica crystals of tridymite — which are similar to quartz — comprise about 30 percent of the total meteorite. This kind of composition is unheard of in meteorites — which typically have ‘basaltic’ compositions with much lower abundances of silica — and can only be found in certain volcanic rocks from Earth.

Subsequent investigations using inductively coupled plasma mass spectrometry determined the precise formation age of the meteorite: 4.565 billion years.

But where exactly NWA 11119 formed is still a mystery.

“Based on oxygen isotopes, we know it’s from an extraterrestrial source somewhere in the solar system, but we can’t actually pinpoint it to a known body that has been viewed with a telescope,” said Srinivasan. “However, through the measured isotopic values, we were able to possibly link it to two other unusual meteorites (Northwest Africa 7235 and Almahata Sitta) suggesting that they all are from the same parent body – perhaps a large, geologically complex body that formed in the early solar system.”

It’s possible that this larger parent body was torn to pieces through the collision with some other asteroid or planetesimal, ejecting fragments that would eventually hit Earth at a yet unknown time in the past.

“The meteorite studied is unlike any other known meteorite,” says co-author and ASU School of Earth and Space Exploration graduate student Daniel Dunlap. “It has the highest abundance of silica and the most ancient age (4.565 billion years old) of any known igneous meteorite. Meteorites like this were the precursors to planet formation and represent a critical step in the evolution of rocky bodies in our solar system.”

The findings published in the journal Nature Communications are important because they help scientists piece together how the building blocks of planets formed in the early solar system. Specifically, this “missing part of the puzzle that we’ve now found that tells us these igneous processes act like little blast furnaces that are melting rock and processing all of the solar system solids,” Agee said.

“Ultimately, this is how planets are forged,” he added.

The types of rock: igneous, metamorphic and sedimentary

The three types of rocks

It’s the first thing you learn in a geology class — very briefly the three types of rocks are:

  • Igneous — they form from the cooling of magma deep inside the earth. They often have large crystals (you can see them with the naked eye).
  • Metamorphic — they are formed through the change (metamorphosis) of igneous and sedimentary rocks. They can form both underground and at the surface.
  • Sedimentary — they are formed through the solidification of sediment. They can be formed from organic remains (such as limestone), or from the cementing of other rocks.
    Now the long story, which is much more interesting, is this:

Now, the long story, which is much more interesting, is this:

Igneous Rocks

Lava flow on Hawaii. Lava is the extrusive equivalent of magma. Image via Wiki Commons.

Magma is the heart of any igneous rock. Magma is composed of a mixture of molten or semi-molten rock, along with gases and other volatile elements. As you go deeper underground, the temperature rises; go further and you’ll eventually reach the Earth’s mantle — a huge layer of solid rock surrounding the Earth’s core (which, in geologic time, behaves as a viscous liquid).

As you probably know, when magma cools, it turns into rock; if it cools while still underground at high temperatures (but at temperatures still lower than that of the magma), the cooling process will be slow, giving crystals time to develop. That’s why you see rocks such as granite with big crystals — the magma had time to cool off. The crystals are also differentiated, as you can see below.

Note the white, almost rectangular feldspar crystals, the grey virtually shapeless quartz crystals, and the black crystals, which can be either black mica or amphibole. Image modified from Eastern Illinois University.

Note the white, almost rectangular feldspar crystals, the grey virtually shapeless quartz crystals, and the black crystals, which can be either black mica or amphibole. Image modified from Eastern Illinois University.

However, if the magma erupts or is cooled rapidly, you instead get a volcanic rock – not really igneous, but also originating from lava. The classical example here is basalt, which can have many small crystals or very few large ones. Volcanic rocks are also called extrusive igneous rocks, as opposed to intrusive igneous rocks. Some volcanic rocks (like obsidian) don’t have any crystals at all.

Basalt — note the almost complete lack of visible crystals. Now compare it to the granite. Image via Georgia State University.

Pumice.

Not all magma is made equally: different magmas can have different chemical compositions, different quantities of gases and different temperature — and different types of magma make different types of rocks. That’s why you get incredible variety. There are over 700 hundred types of igneous rocks, and they are generally the hardest and heaviest of all rocks. However, volcanic rocks can be incredibly lightweight – pumice, for example, can even float, and was called by ancient sailors “the foam of the sea”. Pumice is created when a volcano violently erupts, creating pockets of air in the rock. The most common types of igneous rocks are:

  • andesite
  • basalt
  • dacite
  • dolerite (also called diabase)
  • gabbro
  • diorite
  • peridotite
  • nepheline
  • obsidian
  • scoria
  • tuff
  • volcanic bomb

Metamorphic Rocks

Here, the name says it all. These are rocks that underwent a metamorphosis; they changed. They were either sedimentary or igneous (or even metamorphic), and they changed so much, that they are fundamentally different from the initial rock.

Different types of metamorphism. Image via Tankon Yvtar.

There are two types of metamorphism (change) that can cause this:

  • contact metamorphism (or thermal metamorphism) — rocks are so close to magma that they start to partially melt and change their properties. You can have recrystallization, fusing between crystals and a lot of other chemical reactions. Temperature is the main driver here.
  • regional metamorphism (or dynamic metamorphism) — this typically happens when rocks are deep underground and they are subjected to massive pressure — so much so that they often become elongated, destroying the original features. Pressure (often times with temperature) is the main driver here.

Folded foliation in a metamorphic rock from near Geirangerfjord, Norway. Image via Wiki Commons.

Metamorphic rocks can have crystals and minerals from the initial rocks as well as new minerals resulting from the metamorphosis process. However, some minerals are clear indicators of a metamorphic process. Among these, the most usual ones are garnet, chlorite, and kyanite.

Equally as significant are changes in the chemical environment that result in two metamorphic processes: mechanical dislocation (the rock or some minerals are physically altered) and chemical recrystallization (when the temperature and pressure changes, some crystals aren’t stable, causing them to change into other crystals).

Marble is a non-foliated metamorphic rock.

They can be divided into many categories, but they are typically split into:

  • Foliated metamorphic rocks — pressure squeezes or elongates the crystals, resulting in a clear preferential alignment.
  • Non-foliated metamorphic rocks — the crystals have no preferential alignment. Some rocks, such as marble (the metamorphized version of limestone), are made of minerals that simply don’t elongate, no matter how much stress you apply.

Metamorphic rocks can form in different conditions, in different temperatures (up to 200 °C) and pressures (up to 1500 bars). By being buried deep enough for a long enough time, a rock will become metamorphic. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion; they can also form when the rock is heated up by the intrusion of magma from the Earth’s interior.

The most common metamorphic rocks are:

  • amphibolite
  • schist (blueschist, greenschist, micaschist, etc)

    MINOLTA DIGITAL CAMERA

    A micaschist. The dark brown rounded minerals are garnet, and everything you see with a whiteish tint is the mica. The reddish areas are rusty mica. Image modified from Willowleaf Minerals.

  • eclogite
  • gneiss
  • hornfels
  • marble
  • migmatite
  • phyllite
  • quartzite
  • serpentinite
  • slate

Sedimentary Rocks

Sedimentary rocks are named as such because they were once sediment. Sediment is a naturally occurring material that is broken down by the processes of weathering and erosion and is subsequently naturally transported (or not). Sedimentary rocks form through the deposition of material at the Earth’s surface and within bodies of water.

A conglomerate — a rock made from cemented gravel. Image via Earth Physics Teaching.

Sedimentary rocks are quite difficult to classify, as they have several different defining qualities (the chemical make-up, the sedimentation process, organic/inorganic material), but the most common classification is the following:

  • clastic sedimentary rocks — small rock fragments (many silicates) that were transported and deposited by fluids (water, bed flows). These rocks are further classified by the size and composition of the clastic crystals included in the sedimentary rocks (most often quartz, feldspar, mica and clay).
  • conglomerates (and breccias)  conglomerates are predominantly composed of rounded gravel, while breccias are composed of angular (sharper) gravel.
  • sandstones  as the name says, it’s a rock made from many-sand-sized minerals and rock grains. The most dominant mineral in sandstone is quartz because it is the most common mineral in the Earth’s surface crust.

    An old, red sandstone. Image via Ian Hopkinson.

  • mudrocks  again, the name says it all — they’re rocks made from solidified mud. They typically contain very fine particles and are transported as suspended particles by turbulent flow in water or air, depositing once the flow settles.
  • biochemical rocks — you’ll probably be surprised to find out that most limestone on the face of the Earth comes from biological sources. In other words, most limestone you see today comes from the skeletons of organisms such as corals, mollusks, and foraminifera. Coal is another example of biochemical rock.
  • chemical rocks — these rocks include gypsum and salt (halite) and are formed mostly through water evaporation

Yes, salt is a mineral — and it can be quite beautiful. In this context, it’s called halite and can be classified as a sedimentary rock.

There are also other types of specific sedimentary rocks for example, the ones formed in hot springs. Most of the solid surface of our planet (roughly 70%) is represented by sedimentary rocks, but if you go deep enough beneath the Earth’s surface, there are plenty of igneous and metamorphic rocks to be found.

As I mentioned with biochemical rocks, fossils can become rocks in time. You can actually have entire mountains made up from reefs like you can see below.

This entire mountain in Romania was formed based on a coral reef. Image via MP Interactiv

Some common sedimentary rocks are:

  • argillite
  • breccia
  • chalk
  • chert
  • claystone
  • coal
  • conglomerate
  • dolomite
  • limestone
  • gypsum
  • greywacke
  • mudstone
  • shale
  • siltstone
  • turbidite

This is just scratching the surface you could spend a lifetime studying rocks and still be surprised. But I hope that for your general knowledge or to impress some friends (or if you’re considering starting geology), the information here was useful and interesting to you. Feel free to send any questions and comments my way and I’ll do my best to answer them!

Curiosity finds water on Mars

After finding no methane in the Martian atmosphere, Curiosity has shown that the soil and dust on the surface of the Red Planet contain a few percent water, judging by weight. Yes, yes, I know, Curiosity has found signs that water flowed on Mars sometime during its past (1, 2, 3), but this time, it has found actual, direct evidence of water.

Water on Mars

curiosity-rocknest-closeup

The rover found that judging by weight, the surface of Mars contains some 2 percent water – this could mean that future, pioneer astronauts could extract 1 liter of water from 0.05 cubic meters. The sample Curiosity analyzed also revealed significant carbon dioxide and sulphur compounds.

“One of the most exciting results from this very first solid sample ingested by Curiosity is the high percentage of water in the soil,” said Laurie Leshin, lead author of one paper and dean of the School Science at Rensselaer Polytechnic Institute. “About 2 percent of the soil on the surface of Mars is made up of water, which is a great resource, and interesting scientifically.”

The results were part of a five-paper special edition on the Curiosity mission and were published today in Science. They don’t mention this, but some of you might find interesting to know that most of this water is probably frozen; in its warmest areas, Mars is about as cold as Alaska, and in its coldest areas, it’s like anything else on Earth.

The technical achievement in itself is huge. Curiosity is the first man-made equipment on Mars which can gather and process samples of soil. In order to do this, the rover employs the Sample Analysis at Mars (SAM) instrument suite, which includes a gas chromatograph, a mass spectrometer and a tunable laser spectrometer. These tools are able to identify a wide range of chemical compounds and also determine the ratios of different isotopes.

curiosity 2

“This work not only demonstrates that SAM is working beautifully on Mars, but also shows how SAM fits into Curiosity’s powerful and comprehensive suite of scientific instruments,” said Paul Mahaffy, principal investigator for SAM at NASA’s Goddard Space Flight Center in Greenbelt, Md. “By combining analyses of water and other volatiles from SAM with mineralogical, chemical and geological data from Curiosity’s other instruments, we have the most comprehensive information ever obtained on Martian surface fines. These data greatly advance our understanding surface processes and the action of water on Mars.”

Bad news for manned missions

SAM also detected some organic materials in the rock sample as well – carbon containing chemicals that are the building blocks of life on Earth; but don’t get your hopes up – these are simple, chlorinated organics that likely have nothing to do with Martian life. As a matter of fact, they are probably the result of forms of life which came from Earth and reacted with a toxic chemical called perchlorate. NASA’s Phoenix lander spotted perchlorate near the North Pole, and now Curiosity spotted it near the equator, so the substance is probably spread evenly across the planet. The presence of this chemical is an obstacle future missions will have to overcome.

“Perchlorate is not good for people. We have to figure out, if humans are going to come into contact with the soil, how to deal with that,” she said. “That’s the reason we send robotic explorers before we send humans — to try to really understand both the opportunities and the good stuff, and the challenges we need to work through,” Leshin added.

A very Earth-like igneous rock

igneous rock

Curiosity is more than a one-trick pony – it’s not only about analyzing the possibility of life on Mars, it’s also about understanding the geologic setting of the planet. Another one of the five papers detailed a rock found in October 2012 – an igneous type of rock, which was never before seen on Mars, but is rather common on Earth, on oceanic islands or where the crust is thinning out.

“Of all the Martian rocks, this one is the most Earth-like. It’s kind of amazing,” said Curiosity lead scientist John Grotzinger, a geologist at the California Institute of Technology in Pasadena. “What it indicates is that the planet is more evolved than we thought it was, more differentiated.”

Chemical tests conducted on the pyramid rock showed that it is highly enriched in sodium and potassium, making it chemically alkaline. Geologists are now fairly certain this is a type of basalt called mugearite. However, despite the massive implications this rock can carry, researchers don’t want to get carried away, as this is only one sample and may be an exception; still, if it isn’t, than this would put the entire Gale Crater in a new perspective, and would indicate that the inside processes and chemistry of Mars are far more similar to Earth than what was previously believed.

Ancient, long-lost continent found under the Indian Ocean

Evidence of drowned remnants of an ancient microcontinent have been found in sand grains from the beaches of a small Indian Ocean island, according to a new research.

Zircons and volcanoes

mauritia

This evidence was found in Mauritius, a volcanic island 900 kilometres east of Madagascar which serves as an exotic destination for many tourists. Basaltic rocks from the island have been dated to approximately 9 million years ago, but now, an international research team analyzed the beaches and found fragments of zircon that are much older, between 600 million and 2 billion years old.

Bjørn Jamtveit, a geologist at the University of Oslo explained that the zircons had crystallized within granites or other acidic igneous rocks (basalts being basic, non acidic). He believes that rocks containing these minerals came from a long-submerged landmass that was once wedged between India and Madagascar in a prehistoric supercontinent known as Rodinia; geologically recent volcanic eruptions brought the rocks up to the surface, where they were eroded, resulting in the shards they picked up. Most of the rocks were melted by the high temperatures, but some grains of zircons survived and were frozen into the lavas, rolling towards the Mauritian surface.

“When lavas moved through continental material on the way towards the surface, they picked up a few rocks containing zircon,” study co-author Bjørn Jamtveit, a geologist at the University of Oslo in Norway, explained in an email.

rodinia

The tectonic plates are mobile in geologic time – the surface of the Earth didn’t always look like this. As a matter of fact, the further down you go on the time scale, the more different it looks like. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago; virtually all of the Earth’s landmass was concentrated in this single supercontinent which started to split 3/4 billion years ago.

The study also analyzed the gravity field and as it turns out, something really interesting happened to the remains of Rodinia in that area. As India and Madagascar began to drift apart some 85 million years ago, the landmass just sinked, Atlantis style. The cause was tectonic rifting and sea-floor spreading sending the Indian subcontinent surging northeast, sinking the fragments of Mauritia (how the researchers named this microcontinent).

The variations in the gravitational field observed in some areas in Mauritius, the Seychelles, and the Maldives is pretty much a smoking gun suggesting a thick crust supporting the long-lost continent theory, with the continent being “tucked” under the Indian Ocean.

gravity

A non-geologic accident?

The only weak point, is that the study, thorough as it is, relies mostly on those zircons; couldn’t they be just some sort of non-geologic accident?

“There’s no obvious local source for these zircons,” says Conall Mac Niocaill, a geologist at the University of Oxford, UK, who was not involved in the research.

It also doesn’t look like they were brought there by winds.

“There’s a remote possibility that they were wind blown, but they’re probably too large to have done so,” adds Robert Duncan, a marine geologist at Oregon State University in Corvallis.

Also, the samples were picked up from remote sites, where it’s quite unlikely that humans would have brought them there. However, Jérôme Dyment, a geologist at the Paris Institute of Earth Physics in France, is not convinced. He believes that a number of non-geologic processes could have brought the minerals there, as part of ship ballast or modern construction material for example.

“Extraordinary claims require extraordinary evidence, which are not given by the authors so far,” said Dyment, who did not participate in the research. “Finding zircons in sand is one thing, finding them within a rock is another one … Finding the enclave of deep rocks that, according to the author’s inference, bring them to the surface during an eruption would be much more convincing evidence.”

He makes an even more convincing argument, explaining that if remains of such a continent were to exist, evidence for its existence should have been found as part of an ongoing experiment that installed deep-sea seismometers to investigate Earth’s mantle around Réunion Island, which is situated about 200 kilometers from Mauritius.

So is this compelling evidence, or is it more of an educated assertion? But Conall Mac Niocaill, a geologist at the University of Oxford in the U.K. who was also not involved in the study, is spot on: “the lines of evidence are, individually, only suggestive, but collectively they add up to a compelling story.”, he says. Particularly, the geophysic (gravimetric) evidence is highly consistent with the researchers’ claims. All in all, it paints a consistent picture which makes sense in a tectonic context, but as almost always in geology, you can’t just draw a line and say “This is so”; one thing’s for sure though: oceanic basins worldwide may very well host similarly submerged remains of “ghost continents”.

Via Nature Geoscience

Volcanic crystals might predict next big eruption

Analysis of crystal formed in the molten rocks of a volcano might predict volcanic eruptions with as much as a year in advance, researchers claim.

Mixing Seismology and Petrology

Different types of seismic recording; volcanic eruptions cause harmonic tremors, different from any other ones. Via USGS

Drawing data from the volcanic activity of Mount Helens from 1980 through 1986, geologists found that iron- and magnesium-rich crystals grow before an eruption, and by far, the most rapid growth of such crystals took place 12 months before an eruption.

Most active volcanoes, before erupting, display specific patterns of seismicity; monitoring these events, as well as, ground deformations, gas emissions and changes in water level are the best thing we have so far in terms of predicting volcanic eruptions. However, while these methods provide good indications, such a technique, if perfected, would dramatically improve the odds of predicting such an event.

“Volcanoes tend to erupt in a similar cycle and have similar trends,” said Kate Saunders, a study author and geologist at the University of Bristol in England, in a telephone interview. “If we can work out their behavior, it allows us to know what to look for. We can better evaluate the monitoring signals.”

Analyzing igneous rocks

Igneous rocks are one of the three major types of rocks (along with sedimentary and metamorphic), formed through the cooling and solidification of magma. When these rocks cool slowly, below the surface, they form visible, specific, crystals. Among the minerals form through this process are orthpyroxenes, silicate minerals comprising of single chains of chemical tetrahedra.

Dr Saunders and colleagues studied zoned crystals of orthpyroxenes, which grow concentrically like tree rings within the magma body. What happens is that these zones have slightly different chemical compositions, reflecting physical and chemical changes in the magmatic chamber where they were formed, thus giving a good indication of volcanic processes and the geological time setting when they occur, much like the rings on a tree.

Forensic mineralogy

Zoned orthopyroxene - not with its real color. The colors show the zones with different chemistries

Researchers used a technique called diffusion chronometry applied to orthopyroxene crystal rims, showing that episodes of magma intrusion correlate temporally with recorded seismicity, providing evidence that some seismic events are related to magma intrusion. Diffusion chronometry works in an almost forensic fashion, and it can must be applied to more volcanoes, in order to verify if this feature is present in all volcanoes, or if this was just a unlikely chance. If it isn’t then researchers have just struck gold.

“Such a correlation between crystal growth and volcanic seismicity has been long anticipated, but to see such clear evidence of this relationship is remarkable.”, explained Dr. Saunders.

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