Two Hundredth Post: More Continental Crust on South America's Andean Plateau

       This is our 200th blog post and our 48th month of publishing Partial Ellipsis of the Sun! Thanks for your support over the past four years!

      "Seismologists investigating how earth forms new continental crust have compiled more than 20 years of seismic data from a wide swath of South America's Andean Plateau and determined that processes there have produced far more continental rock than previously believed.


     "When crust from an oceanic tectonic plate plunges beneath a continental tectonic plate, as it does beneath the Andean Plateau, it brings water with it and partially melts the mantle, the layer below earth's crust," said Rice University's Dr. Jonathan Delph, co-author of the new study published this week. "The less dense melt rises, and one of two things happens: It either stalls in the crust to crystallize in formations called plutons or reaches the surface through volcanic eruptions."

     Dr. Delph said the findings suggest that mountain-forming regions like the Andean Plateau, which geologists refer to as "orogenic plateaus," could produce much larger volumes of continental rock in less time than previously believed.

     Co-author Dr. Kevin Ward, a researcher at the University of Utah, said, "When we compared the amount of trapped plutonic rock beneath the plateau with the amount of erupted volcanic rock at the surface, we found the ratio was almost 30:1. That means 30 times more melt gets stuck in the crust than is erupted, which is about six times higher than what's generally believed to be the average. That's a tremendous amount of new material that has been added to the crust over a relatively short time period."

     The Andean Plateau covers much of Bolivia and parts of Peru, Chile, and Argentina. Its average height is more than 12,000 feet, and though it is smaller than Asia's Tibetan Plateau, different geologic processes created the Andean Plateau. The mountain-building forces at work in the Andean plateau are believed to be similar to those that worked along the western coast of the U.S. some 50 million years ago. Dr. Delph said it's possible that similar forces were at work along the coastlines of continents throughout Earth's history.


     Most of the rocks that form Earth's crust initially came from partial melts of the mantle. If the melt erupts quickly, it forms basalt, which makes up the crust beneath the oceans on Earth; but there are still questions about how continental crust, which is more buoyant than oceanic crust, is formed. Drs. Delph and Ward spent several months combining public datasets from seismic experiments. Seismic energy travels through different types of rock at different speeds, and by combining datasets that covered a 500-mile-wide swath of the Andean Plateau, Ward and Delph were able to resolve large plutonic volumes that had previously been seen only in pieces.



     Over the past 11 million years, volcanoes have erupted thousands of cubic miles' worth of material over much of the Andean Plateau. Ward and Delph calculated their plutonic-to-volcanic ratio by comparing the volume of regions where seismic waves travel extremely slowly beneath volcanically active regions, indicating some melt is present, with the volume of rock deposited on the surface by volcanoes.

     "Orogenic oceanic-continental subduction zones have been common as long as modern plate tectonics have been active," Dr. Delph said. "Our findings suggest that processes similar to those we observe in the Andes, along with the formation of supercontinents, could have been a significant contributor to the episodic formation of buoyant continental crust."


Happy 200th!
Steph

Failure to Launch: Andes, Lava Coulée, and Chao Baby!

       Geologists from

Heidelberg University have discovered deposits of magma in the Andes sufficient to have set off a super-eruption but which, in fact, did not. 

     Researchers discovered that magma volumes of supervolcanic proportions have been continuously accumulating in the Altiplano-Puna region of the Andes since the last super-eruption nearly 2.9 million years ago. 

     These magmas, however, did not reach the surface to trigger a catastrophic eruption but instead slowly cooled at depth and hardened into plutonic rock, similar to the area we discussed in Russia two weeks ago. The results of the research were published in the journal Geology.

       
      Unlike the pluton they describe, the Chao volcano in northern Chile with a lava coulée (or flow) approximately 14.5 km long in the center of the image above flowed at the surface. The composition of the lava matches that of deposits of adjacent supervolcanic calderas. Chao erupted about 75,000 years ago, but zircon crystals in the lava were already forming in a subterranean magma reservoir for nearly three million years.

     "A supervolcanic eruption spews out more than 1,000 cubic kilometers of magma, which accumulated over time in reservoirs close the earth's surface," explains Dr. Axel Schmitt.

       "In turn, these reservoirs are fed from deeper layers in the earth's crust and the underlying mantle. During an eruption, the overlying rock layers collapse into the empty magma chamber and form depressions, known as calderas, of up to 100 kilometers in diameter." Schmitt indicates that there have been at least seven super-eruptions in the Altiplano-Puna region within the last ten million years, the most recent one about 2.9 million years ago. We don't understand why no further major eruptions have occurred since then and whether the region can now be considered inactive for such events.

      Using samples from five small lava domes in northern Chile and southeast Bolivia, the researchers investigated the most recent eruptions whose chemical composition matches the supervolcanic magmas from the region. They determined the age of very small zircon crystals from these lava flows with the aid of a high-spatial-resolution mass spectrometer. 

      "The mineral zircon forms almost exclusively in magmas, so its age reveals when those magmas were present under the volcano," explains Schmitt. "The astonishing result was that the ages of the zircons measured from all five of the smaller volcanoes extended continuously from the time of the eruption 75,000 years ago back to the last supervolcanic eruption."

     Dr. Schmitt reports that model calculations demonstrated that zircon formation is only possible over such long durations if the inflow of magma amounted to approximately one cubic kilometer over 1,000 years, which is unusually high for a relatively small volcano. The volcanologist explains that the lack of a major volcanic eruption does not necessarily indicate that magmatic activity has come to a complete halt. Perhaps the rise in magma from deeper regions merely slowed during the last 2.9 million years, forming a pluton.

      "However, our results also show that a relatively small increase in the long-term magma recharge from about one to five cubic kilometers in 1,000 years would recreate conditions favoring a catastrophic supervolcanic eruption. A new super-eruption in the Altiplano-Puna region would be possible, but only after a long lead time," said Dr.Schmitt.

Have you ever seen anything so (lava) coulée?
Steph

ATLASGAL: Celebrating Holding Up New Images AND "Cool" ACRONYMS

         Researchers associated with ATLASGAL, the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) have just released this image of the Milky Way:

      "The APEX telescope has mapped the full area of the galactic plane visible from the southern hemisphere for the first time at sub-millimeter wavelengths and in finer detail than space-based surveys. The APEX telescope allows the study of the cold universe, a few tens of degrees above absolute zero" according to an article released today.

       "APEX, the Atacama Pathfinder EXperiment telescope, is located at 5100 meters above sea level on the Chajnantor Plateau in Chile's Atacama region. The ATLASGAL survey took advantage of the unique characteristics of the telescope to provide a detailed view of the distribution of cold dense gas along the plane of the Milky Way galaxy. The new image includes most of the regions of star formation in the southern Milky Way."

       "At the heart of APEX are its sensitive instruments. One of these, LABOCA (the LArge BOlometer Camera) was used for the ATLASGAL survey. LABOCA measures incoming radiation by registering the tiny rise in temperature it causes on its detectors and can detect emission from the cold dark dust bands obscuring the stellar light." LABOCA, "the mouth" in Spanish, for measuring tiny rises in temperature? {That works, according to my endodontist ;-).}

      [La Boca is also a colorful neighborhood in Buenos Aires, Argentina. The universe is a cold, colorful place :-).]

     And Atlas, of course, was charged with holding up the universe (not the earth as often depicted):

       Wonder what ATLASGAL will hold for the universe?

   

STARRILY (Have a go at it ;-),

Steph

P.S. And, speaking of acronyms, also noted today >>> "Acronyms kill, ma'am!"

Llareta in the Andes, Corn in Kaua'i, and GMOs: Slow Versus Fast Growth

     Llareta is the extremely slow-growing evergreen plant featured on yesterday's NPR Science Friday blog:

     Yes, llareta is real. The photo above is not a poorly photoshopped creation (for you bloggers resizing and reshaping your images ;-)). Azorella compacta is a perennial evergreen and grows close to rocks or soil in order to conserve heat at elevations of 14,000 to over 17,000 feet. Llareta is related to parsley and is quite slow-growing, adding only 1-1.5 centimeters per year. Some of these dense mats of llareta in the Andes Mountains of Chile, Peru, and Argentina have been carbon-dated as being over 3,000 years old. [Alternate carbon-dating definition: chemists getting together for dinner and a movie.]

     The complete article about these dense mats that have, unfortunately, been used in South America as non-renewable fuel is linked here:

               LLARETA OR YARETA


     In comparison, the fast-growing, 3-crop-per-year corn crop in Kaua'i, Hawaii, takes a mere 3-4 months for the entire life cycle. The genetically modified organisms (or GMOs) are pushed to a level of ever-faster change in growth so that modifications to the corn seeds can be made in just 3 years (or, by some accounts, 7 years) instead of at least 13 years in a one-crop-per-year acrigulture. In any case, it's rapid, push it out to market food. In between every corn cycle, the fields are sprayed with Roundup herbicide which kills every broadleaf. Seed agriculture is now Hawaii's number one agricultural business, ahead of cane sugar, pineapples, and other native plants.

     

     More on GMOs here from earlier this month (the photo credit is in the link below):

GMO Seed Agriculture Growth in Hawaii

     Slow-growing, ancient organisms that have been around for thousands of years or fast-growing corn that has been genetically modified every few months, treated with three rounds a year of Roundup? Which seems safer for animals, including humans, to be around or, in the case of the corn, to actually eat?

       This week's blog honors my mom, June, who has been active in getting people to understand what corporations like Monsanto and its product, Roundup, in their GMO research, are doing with our food. (Over 90 % of U.S. corn is now a GMO product).

        Her best suggestion for us? Plant our own gardens!

         And a final, favorite photo of another very old friend, the bristlecone pine (nearly 5,000 years of very slow growth in CA and other high elevations):

Looking forward to hearing your thoughts on the slow and the fast, the unchanged and the modified, llareta and GMOs (I can wait...),

Word Woman (aka Scientific Steph)