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View Diary: DKos Special Supplement: Plate Tectonics And The World’s Changing Geography (Part 2 of 2) (68 comments)

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  •  good read - thanks! (7+ / 0-)

    question - has the amount of continental crust increased over the history of the earth?

    this stuff fascinates me all of a sudden.

    An ambulance can only go so fast - Neil Young

    by mightymouse on Tue Apr 16, 2013 at 07:31:29 AM PDT

    •  not sure . . . (3+ / 0-)
      Recommended by:
      Cliss, RiveroftheWest, mightymouse

      I hear the report both ways. . .seafloor spreading, of course, continues spewing basaltic oceanic stuff, like volcanoes, and of course volcanoes are being 'born' all the time, while continental crust are not forming new landscapes. But let me check on this and confirm so that I don't give you a 'rong answer, mightmouse. I'm moving this week and internet service is quite iffy. But I will contact you via your profile's email sooner than later. Meanwhile, thanks so much for your comment. This stuff fascinates me, too. I ma glad I didn't bore the community to tears with the writeup.

      Treat the world (yourself, and others) as part of a living organism. Everyone and everything will benefit.

      by richholtzin on Tue Apr 16, 2013 at 12:11:27 PM PDT

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      •  thanks! (1+ / 0-)
        Recommended by:
        RiveroftheWest

        this is something I've wondered but not asked to a knowledgeable person.

        An ambulance can only go so fast - Neil Young

        by mightymouse on Tue Apr 16, 2013 at 08:41:38 PM PDT

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      •  Thanks for posting these (1+ / 0-)
        Recommended by:
        RiveroftheWest

        Rich, thanks so much for taking the time to post these diaries. I took a Geology Field Course to Death Valley a few years ago and got to see some of these concepts on the ground (and in the rocks!).  Fascinating subject indeed for someone who lives on the Pacific Plate.

        Keep 'em coming!
        Faye

        •  a remarkable geologic setting... (1+ / 0-)
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          RiveroftheWest

          Death Valley and one of my favorite places on the planet. I took a course or two there, myself, having first learned the stuff and then finding a way to help make sense of all that mountain-building drama. Coming mainly from a sedimentary rock haven, the Colorado Plateau, which is mostly that, there is mountain-building going on so much as it's laccoliths and such. So, there in the Big Valley of granitic giants and such. . .it's another kind of geologic textbook altogther. Thanks for your comments, fiercefilms. I'll continue writing these diaries as long as their interesting folks out there, like you, who'll read 'em. Thanks for your support, too.  

          Treat the world (yourself, and others) as part of a living organism. Everyone and everything will benefit.

          by richholtzin on Wed Apr 17, 2013 at 04:13:44 PM PDT

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    •  Many of the continents have central areas of very (2+ / 0-)
      Recommended by:
      RiveroftheWest, mightymouse

      old rocks surrounded by younger rocks. The so-called "Precambrian Shield" of North America is one example. Younger rocks have been added to the continents in more recent times, so the continents appear to have grown over time.

      There is some evidence to suggest that the solid crust/mantle was probably thinner in the distant past with faster rates of plate motion. There may even have been different processes associated with plate tectonics 3-4 billion years back, but the modern model seems to work well for much of later geologic time.

      •  thanks! (1+ / 0-)
        Recommended by:
        janislav

        does continental crust ever disappear, once formed? I guess eroded continental material that finds its way to trenches would be recycled into the mantle ... is there a mass balance between that process and the creation of new continental crust as island arcs?

        it is fascinating to think of how the earth's tectonic process have changed over time.

        it's also fascinating that people have figured out so much based on the available clues.

        An ambulance can only go so fast - Neil Young

        by mightymouse on Tue Apr 16, 2013 at 08:45:09 PM PDT

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        •  A lot of stuff goes down the trenches, but as temp (2+ / 0-)
          Recommended by:
          mightymouse, RiveroftheWest

          rises, gasses and low temperature minerals become fluid and can return to the surface as magma/lava or rise, cool and add to the base of the continent (do a search on "continental underplating."

          Lavas derived from the mantle would be generally basaltic (gabbroic). Magmas/lavas with rhyolitic (granite) or andesitic (diorite) compositions that form adjacent to trenches may be in part recycled materials carried down by subduction.

          (It's more complicated than this, but I think this is basically an acceptable explanation.)

          •  your assessment. . . (3+ / 0-)
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            janislav, RiveroftheWest, mightymouse

            spot on. I'm thinking you must be an active geologist outside the shell oil trade. . .I mean, given your insights on volcanism and such. I'd be tempted to ask at what percentage do magma/lavas flow that is granitic based, that is, compared to basalt content that enriches continental underplating? We'll have to have a chat about this, too, I'm thinking.

            Treat the world (yourself, and others) as part of a living organism. Everyone and everything will benefit.

            by richholtzin on Wed Apr 17, 2013 at 06:22:37 AM PDT

            [ Parent ]

        •  both recycled and new. . . (2+ / 0-)
          Recommended by:
          mightymouse, RiveroftheWest

          this material that's worked, reworked, created and so on. The clues were always there; but sometimes the most important thing is not really knowing the answer, but asking the right question. That's also the tricky part: knowing how to frame the question so that it will ultimately produce an answer.

          Treat the world (yourself, and others) as part of a living organism. Everyone and everything will benefit.

          by richholtzin on Wed Apr 17, 2013 at 04:08:00 PM PDT

          [ Parent ]

      •  The thinner part. . . (2+ / 0-)
        Recommended by:
        janislav, RiveroftheWest

        of the question/answer which has been made thicker over time shows there is support for continental mass increasing, yet continents continuing growing and diminishing in size given the millions of years of plate migrations. I met an expert on the field one year, whose name I now stupidly forget, and it was his opinion the whole shebang is about even, a give or take proposition. And I am reluctant to argue one way or the other. But basaltic mass is obviously growing and I'm not sure just which part of the world is doing the biggest growth, but something tells me Iceland. Anyway, I am sure the different processes you mentioned has something to do with no firm answers in the community, albeit there are theories. And here I thought working out the Grand Canyon's "Muddy Creek" problem was the most serious matter to debate. HA! Thanks for posting your illuminating comment, janislav. (I"m still moving this week and Internet service/opportunity is spotty, at best. . .should be back in the driver's seat within a week, I'm hoping. . then I'd like to run a few theories by you and see what you think.)

        Treat the world (yourself, and others) as part of a living organism. Everyone and everything will benefit.

        by richholtzin on Wed Apr 17, 2013 at 06:20:02 AM PDT

        [ Parent ]

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