Thursday, September 14, 2017

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

85 comments:

  1. Congratulations on your landmark post and blogoversary! Coincidentally, I just wrote a post about my fourth blogoversary over at Top of JC's Mind! https://topofjcsmind.wordpress.com/2017/09/14/fourth-blogoversary/

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  2. "When crust from an oceanic tectonic plate plunges beneath a continental tectonic plate, it brings water with it and partially melts the mantle." -- I don't follow the logic here. Isn't the crust cooler than the mantle? Why does the crust cause mantle melting?

    Congrats on your 200th! I like "blogoversary", Joanne.

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    1. jan, that statement had me scratching my head a bit, too. I believe the addition of water makes the melt occur at a lower temperature in the mantle. Density differences come into play then, too. Here's the original research.

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  3. A friend who researches at Microsoft sent along this NYT article about computers taking design cues from human brains.

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  4. Replies
    1. I would have said zeros had been found much sooner than the article indicates.

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    2. I think it may be the oldest stand-alone zero. Or maybe the oldest one that can be traced to our zero. It's unclear to me.

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  5. Congrats Steph on four great years and 200 wonderful episodes of PEOTS. Quite an accomplishment. Great quality every week without fail.
    Congrats too to Joanne on her blogoversary. (Nice coinage!)

    (I dreamt last night that I was at Rice University. There, when I sat in on a lecture by Dr. Jonathan Delph I was sure I was listening to God's mouthpiece. Mirroracularous!)

    LegoWhoWonders"AndeanPlateau?Really?I'veAlwaysHeardThatItWasMickey'N'Pluto"

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  6. Replies
    1. That story is from her talk at The Moth. If you're not familiar with that site/podcast/radio program, consider giving it a try. Moth stories are true, told without notes in front of a live audience. I tend to save them up and listen on long plane/car trips.

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    2. Sorry, here's the correct link to The Moth.

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    3. Thanks for that corrected link, jan!

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  7. Replies
    1. A pee-test of sorts. It's pretty wild but I am willing to go with the flow.

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    3. Hmmmmm, no doubt that article will make a big splash. Your innate (say it fast) sense may be to agree with it, but gee whiz, I doubt that's the number one reason boys do more than a wee bit better with projectile motion. [Rim shot!] So let me float another theory.

      In my very unscientific observations of the diaper crowd (young, not old) boys seem more interested in throwing things, and not just fits. There was a BBC show that tested people's spatial abilities, and they found it had a stronger correlation to testosterone levels in both genders. And males, on average, do have more testo.

      That doesn't preclude the notion in the motion of teaching with other aspects of physics first.

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    4. When training our son to use the toilet while standing, we bought a packet of little cut-out paper warships (I think they were called "Pee Shooters"), which we floated in the bowl and let him sink. He went on to excel in math. QED.

      Speaking of point-and-shoot, that's the mnemonic our med school physiology prof taught us to remember which part of the autonomic nervous system controlled which male sexual function. Erection is the parasympathetic, ejaculation the sympathetic. (He only confided this after class; amazingly, he had been reprimanded for including in in the lecture.)

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    5. We had no pee shooters for our son and he went on to excel in math. . .

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    6. Maybe that explains why I flunked math. I always thought was due to Miss Catheter's poor teaching abilities.

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  8. Replies
    1. Yikes! Hard to get that hanging hummingbird image out of my head.

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    2. And who wants to put a collar with a bell around their necks?

      One of those little green monsters got its claw around my brother's finger, and even though he killed it, we had to use pliers to pull the claw apart.

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  9. Replies
    1. I can't figure out your new thumbnail image, eco. Is it a swamp?!

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    2. I thought you might try to figure that out - it's a closeup of a tide pool. Aren't too many swamps in the west, and I don't have any good photos of swamps, best I could do is channels in New Orleans.

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    3. Ah, I see. Maybe live-streaming next ;-)?

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    4. But not, definitely not, of the call of nature.

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    5. eco, we appreciate your restraint. This is the sort of
      live-streaming, I was considering.

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    6. Brrrr. Now that I've seen that I don't believe your claim Maizie is "really" poodle. The one I grew up with would have been in the creek come hell or cold water!

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    7. Great live-stream, eco. Is that your design?

      We think Maizie is part poodle, part bichon frise. She'll go in water spring, summer, and autumn.

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    8. I was only teasing about Maizie, she has much more common sense than my dog did. I spent many youthful hours ridding his matted hair of chunks of snow and ice. Have you ever seen a Coton du Tulear? I first saw one in Idaho last month, related to the bichons, hairy, and very sweet and quiet small dogs.

      I could only dream that was my design.

      It's the Salk Institute in La Jolla, near San Diego, designed by Louis Kahn. Though not so well known by the general public (save for the movie "My Architect"), architects around the world consider him one of the greatest modernists.

      His early work can be a little brutal and lifeless, but his later work, including Salk, the Kimbell Art Museum in Fort Worth, and Exeter Library in New Hampshire are renowned masterpieces.

      Kahn went far beyond architecture into the realms of philosophy and spirit. Once in a while I still turn to the book "Between Silence and Light", which is almost entirely of almost poetic quotes and writings by Kahn, set to wonderful images, some of his buildings, most not. Though much is about architecture, a lot is not, highly recommended. Alibris and Abebooks probably have the best prices.

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  10. I've not seen a Coton du Tulear, as far as I know. They look sweet.

    Louis Kahn sounds ethereal and flowing. I will check out "Between Silence and Light." Glimpses of Waldorf/Rudolf Steiner?

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    1. Hmmm, you raise an interesting comparison. Over many years I've had the privilege of working with one of the world's leading "Anthroposophical" architects, who are inspired by the teaching of Steiner. We've worked on a few Waldorf Schools in California and Rhode Island, as well as other projects. My first strawbale building was for a Waldorf School.

      Like Steiner, Kahn was certainly very spiritual, with mystical tendencies even. And both believed in a higher consciousness that could be understood through nature.

      But the manifestations of Steiner's Anthroposophical approach are very different from the disciplined purity, with overtones of historical reference, that Kahn strove for.

      Steiner only designed a few buildings, but in them the forms and space are flowing, "organic", derived from perceptions of the natural world. More of an expressionist style. Nature has very few (virtually none) right angles and corners, and those are rare in Steiner and Steiner inspired buildings. In seeking a unity with nature, Steiner was looking for an architecture that comes from nature and is outside of "Architecture".

      Kahn, on the other hand, seems guided by the need for an almost purification of nature, an architecture that embraces the natural world by combining it with the geometry and mathematics of the built form - that perhaps underlies nature but is not necessarily visibly manifest in its creations. And Kahn, likely from his Beaux-Arts training, still believed in the importance of the historic reflection in buildings, something Steiner sought to break. Perhaps Kahn thought of the human experience as inspired by, but not derived from, the natural world.

      I'd have to think about that more. Has the makings of a good thesis paper, not late night blog ramblings.

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    2. To the Coton du Tulear, you might say they are real bichon'! The one I met was indeed very sweet, took to hand licking almost immediately, and was very quiet and at ease. Something I don't see that often in small dogs - I'd be nervous too if all I saw was ankles. They're also popular with folks who suffer dog allergies.

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    3. Looking forward to that thesis, eco. I am a neophyte in the worlds of both Steiner and architecture.

      Maizie is at ease almost all the time. She is not a yapper, though she will bark at the mail carrier.

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  11. Pluto's penitentes.
    I couldn't find a picture of the Disney dog with his hackles up, unfortunately.

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    1. Fascinating stuff, Paul. Thanks. Trying to make a connection between penitentes and penitent but not seeing a link. . .Do the penitentes look penitent, perhaps?

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    2. According to Wikipedia, "The name comes from the resemblance of a field of penitentes to a crowd of kneeling people doing penance. The formation evokes the tall, pointed habits and hoods worn by brothers of religious orders in the Processions of Penance during Spanish Holy Week. In particular the brothers' hats are tall, narrow, and white, with a pointed top."

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    3. Thanks, jan. Taking a knee on this one. . .

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  12. In space, no one can hear you chirp. But they can pick it up on earth, and share in the Nobel Prize in Physics. an award with gravity.

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    1. But what is the sound of one black hole colliding? (Somebody had to ask.)

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    2. Wonderful question, Paul.

      Awards with gravity, awards with gravy, awards with the it factor. . .;-)

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  13. Anyone been following Austin Rogers on Jeopardy? What fun . . .and a Macalester College grad to boot!

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    1. I watched it last night, noticed he unkindly crushed the other contestants. Macalaster? I thought you were a Smithy? Or do you live in the multiverse?

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    2. My daughter, Zoë, who I've mentioned here, is a Macalester '15 grad. Mac is a great place.

      That $34,000 final Jeopardy wager was pretty bold. He might have wagered just a wee bit and safely won.

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    3. I caught Friday's show while exercising this evening (last night's show was preempted by Las Vegas coverage; tonight's will be seen in the future, maybe). He's smart and personable, but I think the Final Jeopardy questions have been pretty easy lately.

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    4. Agreed, jan. They have been easy.

      He's quirky, bright, and irreverent, much like PEOTS folks (at times, eh?).

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    5. Wait, did you just post a spoiler? They're only in Double Jeopardy on the west coast now....

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    6. Gaack, sorry, eco. Don't watch!

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    7. Too late, I did watch.

      And yes, I know of (Out In Africa) Zoë, but I don't think I knew she went to Macalester. For what it's worth, one of my early clients (and 20 years later still friend) was in the Peace Corps in Africa in the 1960's, and he's still in touch with the people he knew there, including one US Congressman. Her friendships there can last a lifetime.

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    8. I am certainly hoping those lifelong friendships will materialize for Zoë. She had a wonderful experience in St. Paul (except for the cold).

      Again, oops for the early post. Jeopardy is on at 6:30-7:00 p.m. here so I figured west coast would be over by 8:00 p.m., our time.

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    9. They show Jeopardy at 7-7:30 here, but no worries.

      Isn't St Paul's weather comparable to Colorado? Maybe a little colder, but not of a magnitude?

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    10. Jan and Feb in St. Paul are appreciably colder and it's a bone-chilling cold with the humidity. Here's a cool site comparing any two cities .

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    11. ***Correction, 6-630 p.m. here for Jeopardy time.

      Still waiting for jan to appear on the program. . .

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    12. Me, too. Don't hold your breath.

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    13. Fun city comparison website; my little town does well on the weather, but is awful for cost of living.

      I see your point about St. Paul's weather, much colder than Denver. It's misery index is closer to Ithaca - my college days - St Paul is sunnier but colder. I don't know much about the twin cities, though a friend is a leading contender for Minneapolis mayor in their election next month.

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  14. Replies
    1. No words (even though it's The Onion ).

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    2. It's what happens when you've got rocks in your head.

      And since you ask, the photo is "Bison Jump" in Idaho. Apparently the Shoshoni [sic], with horses from the Spanish, would drive the buffalo herds off the edge of the cliff, the first drive-through dinner spot.

      Dave Barry wrote a hilarious article (if you like his humor) about a similar place in Alberta.

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    3. Hilarious Dave Barry article about the Head Smashed-In Bison Jump. Oh those Canadians!

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  15. New post on "Geologic Mélange: A Mixed Bag of Lithologies" is now up.

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