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Tuesday, February 11, 2014

Icelandic Plate Tectonics: No Scree-ching Halt: Give It an Inch and It'll Take A Year



     At long last, we are ready for the trip to Iceland now that the Viking Sunstone (optical Iceland spar or calcite) has been found:


 

     Optical calcite is rhombohedral and refracts light in a way that Norse explorers of 900-1200 A. D. were likely able to locate the sun even after sunset and on cloudy days. In those pre-GPS days, the calcite rhomb was accurate to within 1 degree:




     Optical calcite is found in abundance in the scree of Iceland, though it is now a protected resource since Icelandic tourism has recently blossomed. You may read more about calcite here, but I want to get us to Iceland, the only place on earth (currently) where a mid-oceanic ridge occurs on land:


     To repeat, Iceland is the ONLY place on our planet where one may actually witness oceanic crust being created on land. All other parts of the global mid-oceanic ridges are deep beneath the surface of the ocean. These folks are walking between two tectonic plates, the North American plate and the Eurasian plate, in Iceland:






     The theory of plate tectonics
describes the large-scale motions of the lithosphere. A good, general overview of the theory may be found here:



     The divergent boundaries between plates, known as mid-oceanic ridges, are the places where oceanic crust is created. There is a particularly good color, animated graphic in the link below (and shared here) which shows the new basalt (nicknamed MORB for Mid-Oceanic Ridge Basalt) or gabbro being created:





     Oceanic crust is richer in iron and magnesium making it heavier than continental crust, which is richer in lighter silica. The very newest "skin of the earth"  is created at mid-oceanic ridges. As one moves away from the center of the ridge, the oceanic crust is progressively older on mirroring sides of the ridge. Almost all oceanic crust is 200 million years old or younger, fairly young in geologic terms. Then, at the margins with lighter continental crust, the oceanic crust dives beneath the lighter continental crust and is essentially recycled. The major plates and their current movements are shown below:



     In Iceland, one may witness this new "baby earth skin" creation directly. In the land of fire and ice, you can actually touch this brand new earth as the mid-oceanic Atlantic ridge runs right through Iceland:




       The Eurasian and North American plates are moving apart at the rate of about an inch a year. There is no scree-ching halt to the oceanic plate movement due to the convection currents in the earth. The convection is akin to heating up pudding on the stove. The rising hot pudding comes to the surface then plunges back down again as it cools at the surface. 

        To witness new earth being created is, for me, amazing. After seeing the volcanos, ice, spar, and other Icelandic delights, here's that optional side trip to the Lucky Leif bridge in southwestern Iceland. It's a moment to ponder the earth's dynamic nature while straddling the two tectonic plates. Our trip would have been unabridged without it. :-) Enjoy!

        I welcome your comments, insights, and any sparring. 





      Here's to MORB excitement with all of you gab-BRO and SIS enthusiasts,

      Word Woman (aka Scientific Steph) 

 



16 comments:

  1. I want to also describe the triple junction on Iceland. The point where three tectonic plates meet (see Iceland map) is called the triple junction. In this case, the Hengill Triple Junction is located where two ridge and one transform margin meet. Where three divergent margins meet, one of the three becomes a " failed arm " or aulacogen. These failed arm rift basins occur in the U. S. in both the Mississippi River embayment and the Rio Grande Rift Zone.

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    1. Is that bridge far enough north that, in the summer, the sun stays up all night at Leif Lucky? (A very daft, punk attempt at humor...)

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    2. I appreciate your attempt, jan (no snappy comeback though).

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  2. Okay, so this stuff coming up from the bowels of Gaea to make new crust -- is it hot, or cold, or what? I would suspect it's cooling rather quickly, which would make it ... what kind of rock? I'm totally lost.

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    1. Hot. Yes, fast-cooling, extrusive, fine-grained. Look for YouTube videos of the birth of Surtsey in 1963.

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    2. Ok, I see the confusion now, Paul (told you I needed coffee). The fast-cooling, extrusive fine-grained basalt does pour out of the mid-oceanic ridge. And slower-cooling, coarser grained intrusive gabbros come to the surface also. This article explains fairly well how those deeper, slower-cooling, intrusive rocks can rise to the surface as the overburden of rocks above keeps them from liquifying as they come to the surface:

      http://myweb.cwpost.liu.edu/vdivener/notes/MOR.htm

      I remember this same confused feeling from mineralogy and petrology. It's partly why I became a sedimentary geologist (Well, that and all the amazing fossils). Hope that make things clearer than mud. If not, perhaps go drink a green gabbro:

      http://greengabbro.net/



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    3. Iceland is also theorized to lie atop a mantle plume, the depth of which is unknown. This plume is somewhat similar to Hawaii (which lies within a tectonic plate) but also different in that this hot spot lies at a plate margin, intensifying the geothermal and volcanic activity. It's also likely why we are able to see the mid-Atlantic ridge on land. Iceland has tapped into these hot resources to heat water, warm sidewalks, etc.

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  3. And here I thought it was gravity pulling everything south that caused continental drip ;-)

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    1. Haha. I may need some continental drip coffee this morning as I am moving as fast as a tectonic plate.

      Ridge-push and slab pull inspired, I imagine. Thanks for sharing, jan.

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  4. So, should I get a "Reunite Gondwanaland!" t-shirt to go with my Native American "Homeland Security: Protecting America From Terrorists Since 1492" one?

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  5. Of course. I have one already.

    RoRo can also vouch for our "Smith College: A Century of Women on Top" t-shirts.

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  6. Heard a great story on NPR on the drive home today. Grist for a future blog post here, maybe? (Would that be karst grist? Is this a karst v car story?)

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    1. I heard that also. Karst is interesting stuff (and sedimentary ;-)).

      Love karst topography topo maps with those tic marks on topographic lines indicating decreasing elevation or sinkholes:

      KARST TOPOGRAPHY TOPO MAP

      I have a sinking feeling...it could work...Limestone rocks!

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  7. SS,
    Like Paul, I'm a little lost this week also, through no fault of your own. My geo-ignorance is showing and the subject matter feels like it's over my head (which, I suppose, situates mw somewhere near the Earth's core.

    I do remember decades ago reading/hearing about the continental shift, however, and being fascinated by the coincidence of the eastern South American coast and western African coast being like jigsaw pieces that could easily interlock across the vast Atlantic "cardboard table."

    I like the ideas of soapstone, too, a forgotten ancient discovery that does the work, and then some, of a subsequent more modern invention, the magnetic compass. Evolution takes a as step backwards, then two steps ahead.

    jan,
    They should have vetted the stability of that museum floor.

    Lego...

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    1. Thanks for the snappy 'vette comeback to Jan's comment, Lego. Obviously my coffee has worn off.

      Perhaps I tried to cover too much this week. I didn't want to leave out gabbros because they are an important part of the deeper oceanic crust. It might have been easier to just use the extrusive basalts to show the mirrored, matching stripy rocks on either side of the mid-oceanic ridge.

      And backing up to talk about the giant jigsaw puzzle pieces of South America and Africa across the Atlantic cardboard table is a good idea too. That is a great description, Lego, of what Alfred Wegner saw in 1912...but he had no proof.

      When I finished presenting my senior paper on the Nazca Tectonic Plate one of the professors said something like "Whoa, that's a whole lot of information about the Nazca Plate!" Some things don't change, I guess.

      Oh, also sorry to have been confusing about soap-bar-sized calcite which is different from soapstone (a talc-rich metamorphic rock). Talc has a hardness of 1 on Moh's Hardness Scale so it is easy to carve; Calcite has a hardness of 3.

      You may remember Moh's Hardness Scale from 1(softest) to 10 (hardest): talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, diamond with this little ditty: tall girls can flirt and other queer things can do.

      And that's a whole lot of information about a lot of geologic things. . .

      Steph

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  8. SS,
    No need to apologize. You've got loads of wisdom and knowledge to impart. I think of you as Walter Matthau in The Odd Couple (or was it Jack Lemon, playing out of character, no, it was Matthau) throwing the spaghetti and meatballs against the apartment wall. I am the wall. Now and then, a spaghetti noodle, or even a meatball or two, will stick, and eventually worm its way into my own noodle.

    And so, don't whoa! Don't even slow. And don't ever change. We like you just the way you are.

    I like the Moh's Scale mnemonic. Problem is, I'll remember the ditty and forget the substances. (Corundum has always been a conundrum for me.)

    Lego...

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