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Geologist Abroad: Tungurahua, Ecuador

After nearly a week, the unrest of “Mama” Tungurahua has become evident in the city of Quito, in the form a a thin film of volcanic ash. It’s most visible on cars, not unlike the road salt that covers cars back in Ohio. But this accumulation come comes from the thick haze across the valleys of the Inter Andean region of Ecuador.

Dissapating ash cloud near sunset

Dissipating ash cloud near sunset

There are few countries more interesting than Ecuador for a Geology student like myself. I’m spending the second semester of my Junior year studying at a University in Quito, Ecuador’s capital and second largest city. Surrounded by 5000 m mountains and numerous active volcanoes, the city provides the perfect vantage point for observing earth’s tectonic forces and taking in nature’s beauty. Both of these became very evident last week, when Volcàn Tungurahua began another phase of heightened activity.

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In the Field at Mineral King

(From left) Dr. Greene, Cory, and Conner after summiting the 11,947 ft. Vandever Mountain at Mineral King, with Mt. Whitney in the distance.

After nineteen days in sunny California, Dr. Greene, Cory, and I have returned to Ohio. Our field session was a great success, giving us scores of samples to begin analyzing in the coming weeks. Dr. Greene was an excellent field leader for us new geologists, and a big thanks goes out to him and his parents for hosting us during our days in San Francisco. The trip was a tremendous learning experience, and what better location than the beautiful Sierra?

The Mineral King Valley is located within Sequoia National Park, a few hours east of Visalia, California. We drove the six or so hours from Daly City (near San Fran), at sea level, to the campground at over 7,000 ft. in elevation. From there, our hiking and field work ranged from 8,000 ft. to nearly 12,000. Never before had I done such strenuous hiking at such a high elevation. There’s no room to write all of the awesome things (geological or otherwise) that we saw, but the highlights ranged from seeing abundant wildlife, a bear, and the stunning views of mountain lakes and panoramas of the Southern Sierra from the tops of high peaks.

Conner and Cory in Mineral King Valley, Timber Gap and the colorful pendant rocks in the background.

Then, of course, there’s the geology. Cory and I had some time to develop our “elevator speech” through talking to the various hikers curious about our astoundingly heavy packs and our rock hammers. Most hikers were genuinely interested in the rocks of the beautiful valley. Our speech went a little something like this:

The Sierra Nevada most people think of is made up of gray-white granite, the same granite that rock climbers love. Granite comes from deep within the crust essentially as a liquid magma. It bubbles up in large plutons that wipe away most of the previously existing crust. The red and brown rocks seen throughout Mineral King (see above) are remnants of the sedimentary and volcanic rocks that the granitic magma intruded into. When the granite was emplaced, these older rocks were stretched, squeezed, heated, and sheared into the metamorphic rocks present today, and all this happened many kilometers beneath the earth’s surface. Over millions of years, the rock on top was weathered away, exposing the mountains that tower over the landscape now. Our research is focused primarily on the metamorphic remnants left between the classic granite mountains.

I am working with Dr. Erik Klemetti to analyze the ages of these older rocks (roughly 100-130 million years old) in order to understand that magmatic systems that both formed the Sierra and existed previously. Cory and Dr. Greene are studying the structure of the metamorphic rocks to analyze the strain and stress that deformed them during the intrusive process. All of this will give us a better picture of what happened at Mineral King and how mountains like the Sierra Nevada form. We hope to take geologic knowledge of the Mineral King Pendant to the next level, based on the important research of other geologists who have been working on this area for the past few decades.

Sheared granitoid in mylonitic zone. This is one of the samples now ready to date this week.

The field session was a lot of fun, and more importantly, my geological knowledge in this area increased immensely. I’m looking forward to what data arises and how that compares to the data that we have now. I can’t wait to see what the rocks tell us.

For more pictures from the trip, check out my web album!

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Zircon Fever: How Gold Mining Helps Us Study Zircon

Though we aren’t searching for gold, some of here in the Geo department do “rush” to California, but in search of a different mineral. Zircon is the keystone to much of the petrographic and volcanological research going on this summer. As Liz wrote earlier, there are different ways to get from a chunk of outcrop to the tiny zircon crystals that we can date. Both of us have used the “heavy liquids” in the lab for a density separation, but there is also another interesting method. That’s where gold comes in.

One method we have been experimenting with to separate zircon uses a “gold table”, the same thing that bearded prospectors use to get placer gold out of fine sediment. It works on the same principles as heavy liquids, but without the effects of those “nasty” chemicals. The crushed and sieved rock gets put into the top of a channel with water flowing through it.

Surface of the gold table, with crushed rock flowing downward. Zircon will concentrate at the top (left) of the sediment flow.

The particles get washed down over a set of grooves as the table shakes and vibrates. As the material moves down the table, the vibrations and flow cause the denser crystals (like zircon!) to sink and get trapped in the shallow grooves while the finer and lighter stuff continues to wash away. This leaves a concentration of heavier, albeit tiny, crystals that we can then sort out under a microscope, just like we would with the heavy liquids. The whole table is essentially a large-scale, modern version of the ubiquitous gold pan. With a table, gold miners would simply let the gold concentrate flow off the table into a designated bucket, but to be more precise, we arm ourselves with a blacklight and pipette to selectively extract the luminescent zircon. When seen under UV light, zircon glow (appropriately) gold, making them easier to spot on the table.

Luminescent zircon crystals in a pipette glow gold under a mineralogical blacklight.

Finely tuning the table is still a work in progress, but we were still able to extract a separate chock full of zircon quickly and without toxic (and expensive) chemicals. But with every benefit, there are drawbacks. A gold table separation requires much more sample due to a lack of comparable efficiency to chemicals, and also carries a slightly higher risk of contamination with zircon from other sample. If one is careful and cleans thoroughly, however, a much greater amount of sample can be processed in a shorter amount of time, with less waiting. Such qualities are ideal for samples to be run on a Laser Ablation Inductively Coupled Plasma-Mass Spectrometer, which Erik and I will be doing this week.

Samples from the gold table getting ready to be dried in funnels. Next they will go through the “Frantz” magnetic separator before mounting. One of the many steps to take before we actually gather data.

A lot of work, from crushing and grinding, to sieving and magnetically separating, to extracting and mounting, goes into the samples, but the data acquired in the end will surely be worth the hard work. Stay tuned for updates!

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Teeny Tiny Zircon

Zircon, or zirconium silicate, is a hardy mineral that typically forms in igneous systems like volcanoes. It is hardy because it is not easily broken down by weathering processes but can remain intact for billions of years. In fact, the oldest mineral so far discovered on Earth is a zircon mineral that is 4.4 billion years old. For reference, the Earth is 4.56 billion years old so zircon minerals are capable of being heated and squeezed repeatedly for many years without breaking down. This convenient property of zircon as well as the abundance of radioactive elements incorporated in its structure such as Uranium and Thorium allows researchers to date magmatic systems of all ages. Uranium is an element that decays over time. More specifically, Uranium gives off pieces of its atom, i.e. radioactivity, and transforms into other elements like Thorium or Lead depending on how long the zircon has to sit around. In our case, the part of this decay chain that is most helpful is the transformation from Uranium to Thorium. This process does not take billions of years, and allows us to date relatively young volcanic processes like those that we find at Lassen. In fact, the rocks that we are concerned with range from 67 million years to only a hundred years old.

So what does zircon look like?

The grain in the red circle is a zircon mineral. Zircon can be elongated like this one or stubbier. One of the defining features of zircon is the double pyramidal termination. This means that the ends of the mineral end in a point which, in a 3D view, creates a pyramid. In the picture above, you can get an idea of this shape although the points are rather rounded. Another diagnostic feature is the faceted nature of the crystal faces which means that if you were to rotate the grain you would run into flat surfaces like you see with a prism or rectangle. In the 2D view of this microscope this can be difficult to see but you can see hints of this along the vertical edges of the grain. These edges are slightly thicker than the other sides, implying a faceted shape. Lastly, see the small circles within the crystal? Those are inclusions of various elements within the crystal structure. This particular grain is about 150 by 40 microns- small enough that you need a microscope to see it.

Zircon is not the only thing that we extracted from that pile of rock. There are also glass fragments such as the grain just to the left of the circled zircon.

This next picture has a nice mix of both.

While we would ideally like only zircon in our sample, it is relatively easy to differentiate between zircon and glass. Here, the grains in the yellow circles are zircons and you can see the sharp point of that pyramidal termination better. There are suspect grains in this view but otherwise it is mostly glass which is comparatively shapeless and does not have nice facets. Why do we get all of this glass in our sample? It is possible that the glass had inclusions of denser elements that let it pass through the heavy liquids with the zircon. Expertimental error is another possibility. Whatever the reason, there are plenty of zircons here to analyze.

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Zircon Sighting

At last we have gotten to the zircon! This last step requires mad-scientist lab gear and some heavy liquids. They’re called heavy liquids because they are relatively dense- and this is what we are using for the final type of separation to get to the teeny tiny zircon. Zircon is a dense mineral (about 4.6 g/cm3) and will sink to the bottom of the slightly less dense heavy liquid, methylene iodine (3.3 g/cm3), while the majority of the other grains will float. (For reference, water has a density of 1 g/cm3).

Did I mention that methylene iodine (MEI) is a carcinogen? That’s why I get to wear this lovely getup (see below).

Like I mentioned above, we are trying to get to the zircon by separating the material based on density. For that we use a seperatory funnel in which we mix up some of the grains in the methylene iodine. The dense stuff sinks and the less dense grains float, leaving a nice boundary between the two. The funnel has a stopper that releases the bottom portion of the liquid including the zircon into one funnel. The rest of the liquid and floating material is collected in a different beaker and we have a separated sample!

A peak into the fume hood where this process takes place. The seperatory funnel full of MEI sits suspended above the beaker that will collect the dense zircon. What’s all the newspaper for? There’s zircon drying under there.

Once dried, we pop the funnel paper with the nearly invisible zircon under a microscope to double check that we have enough good zircon grains. And so far all the samples have produced lots of the tiny crystals!

Next time- maybe a look at the zircon under the microscope.

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Mr. Frantz

We tried to put it off but we could not avoid it- it is time to tackle the Frantz. The Frantz is a rather noisy machine that separates the magnetic and nonmagnetic components of our sample by running the grains between two electrically charged magnets. The point of all this is to further isolate the zircon minerals that we will be analyzing.

The crushed samples is fed into a funnel at the top right of the machine and travels between the magnets where it is separated into two buckets.

The only problem is that the machine has not been working properly. However, after fiddling with it for some time, I came across a video that made us a little less wary of the Frantz’s performance. In the video, the machine is doing what it should be- separating the grains- but they are being deposited in the wrong buckets based on what we know about how the magnets work. Fortunately, this has been what our machine has been doing so we decided to try it- and it works! Although still rather finicky, Mr. Frantz is churning out a separated sample and soon we will be able to move on to more separations- this time with some nasty liquids.

A peak at the video we found and how the Frantz “works”.

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Summer in Granville

Mineral King Samples

Summer has arrived in Granville. Warm winds suddenly change to thunder, and the Bluecoats’ music rumbles through campus. For some of us geoscientists, this signals the time to become enthralled in summer research. My second week of research work is coming to a close, and I’m not getting down to the nitty-gritty of why I’m here. Though I had never done summer research at Denison before, a semester of Directed Study led right in to crushing rocks on day one.

My summer will be all about zircon, the tiny crystals in many igneous rocks whose composition and structure allows scientists to gather data like ages and formation environments from isotopes within each crystal. My advisor, Erik Klemetti, will be studying zircons from various units in the Mineral King metamorphic pendant in Sequoia National Park, California. Our primary goal will be to better constrain the ages of some of the plutonic and volcanic rocks of the pendant, giving us a more complete picture of the geologic history of that area and more broadly, the Sierra Nevada as a whole.

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Summer Crushing

Hello all! This summer I am back at Denison working on a project with Professor Erik Klemetti involving the magmatic evolution of the Lassen volcanic system in Northern California. Lassen is the southernmost volcano in the Cascades Range and has had eruptions as recently as 1915. Our goal is to analyze the zircon minerals that we extract from various samples representing different eruptions and phases of the system. We hope to have a better understanding of the composition, interactions, and overall evolution of Lassen’s magmatic system from this project. To get to the zircon, however, much pounding, sorting, and separating must take place.

The lab.

Thus far, I have been focusing on samples from Eagle Peak which are 66 ka (thousand years old) and are relatively young. Using a stainless steel mortar and pestle I have crushed the rhyolite and sorted the grains by size using sieves- and a fair amount of physical labor. I then cleaned the portion of grains that contain the accessible zircons using water, ethanol, and pure water in varying stages. These samples were then left to dry whereupon I began to remove the heavy magnetic material, particularly the stainless steel fragments from the crushing process, using a hand magnet used by prospectors. The next step involves a rather persnickety piece of equipment called the Frantz (more magnets) and then on to separation of the zircon by either heavy liquids- a more efficient and clean but time consuming process- or the gold table which is less efficient but produces high yields quickly. Ultimately these zircons will be dated and analyzed by the SHRIMP-RG ion microprobe at Stanford.

http://shrimprg.stanford.edu/

The separation process: the magnet picks up large magnetic fragments (left sheet of paper) from the sample (right sheet of paper).

In the meantime, I have been crushing, sieving, washing, and separating samples from Chaos Crag and the 1915 Lassen eruptions. While these samples have been previously analyzed, we wish to do a rim analysis on them to better understand the magmatic environment during their last stages of growth before eruption. Check back for more updates!

 

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Summer Research Students Show Off Their Work

The 2012-13 school year has begun here at Denison, and tradition dictates that all the hardworking research students get to show off the science they’ve done. This year three Geoscience majors presented their summer research at the annual Summer Research Symposium. Check them out:

Mariann Bostic, presenting on stratigraphy of the earliest stages of the Kungurian Stage in the Pequop Mountains, Nevada(advisor: Kate Tierney)

April Strid presenting on models for carbon cycling in soils due to land use (advisor: Tod Frolking)

Amy Williamson presenting on pressure and temperature determinations for the Eagle Lake Pluton, California (advisor: Erik Klemetti)

Job well done … and now onto their senior year!

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GEOS-240: El Niño’s React to Global Warming (II)

Even though several groups of scientists hold different opinions on the prediction of the ENSO’s frequency in the future, they all agree that the predictions depend on many other complicated processes such as cloud feedback, etc. Therefore, so far no one can give a comprehensive answer to the future ENSO’s frequency. In this post, I will explain two extreme theories of the prediction.

Figure 1. Predicted temperature anomaly along the Pacific Ocean. The east shows a large increase of temperature, while the west warms up relatively in a small degree.

Timmermann et al. demonstrate that El Niño’s frequency would possibly increase due to the increasing carbon dioxide concentration (Timmermann et al., 1999). The model, developed by Roeckner in 1996, shows sea surface temperature is characterized by a strong warming in the east equatorial Pacific, with westerly winds blowing to the east. This procedure creates a condition that is similar to the current El Niño events (Figure 1). In the present climate system, west Pacific is so warm that even a small rise of temperature will result in cloud shielding effect, which will develop high cirrus clouds and reduce the solar radiation coming in to the surface; on the other hand, east Pacific receives more solar radiation. As a result, a large temperature difference will exist between west and east Pacific (Ramanathan et al. 1991). The model also predicts that the thermocline will become sharpening, with more frequent cold La Niño events (Stone et al., 1998).

Figure 2. Vertical temperature anomaly at tropical Pacific. The positive anomaly happens at the surface and below the thermocline.

Meehl et al., on the other hand, give the opposite prediction that the amplitude of El Niño will decrease because of global warming (Meehl et al. 2001). Instead of considering horizontal transport of heat, Meehl’s model illustrates the heat conduction vertically. One of his models shows that the temperature gets warmer at both upper surface and below the thermocline (Figure 2). This change of the water column temperature eventually weakens the circulation of the subtropical cells (STC). As a result, thermocline becomes more diffuse and deeper, which contributes to reduce El Niño’s frequency (McPhaden et Zhang, 2002).

 

Reference:

McPhaden MJ, Zhang D. (2002) Slowdown of the meridional overturning circulation in the upper Pacific Ocean. Nature 415:603–608

Meehl, G. A., H. Teng, G. Branstator, 2006, Future changes of El Niño in two global cou- pled climate models. Climate Dynamic. no. 26, pp. 549-566

Ramanathan, V. & Collins, W. (1991) Thermodynamic regulation of ocean warming by cirrus clouds deduced from observations of the 1987 El NinÄo. Nature 351, 27-32

Roeckner, E., Oberhuber, J. M., Bacher, A., Christoph, M. & Kirchner, I. (1996) ENSO variability and atmospheric response in a global atmosphere-ocean GCM. Clim. Dynam. 12, 737-754

Timmermann, A., M. Latif, A. Bacher, J. Oberhuber, E. Roeckner, 1999, Increased El Nin ̃o frequency in a climate model forced by future greenhouse warming. Nature, no. 398, pp. 694–696