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Tuesday, January 27, 2015

Migmatites and Ptygmatic Folding

         Let's examine ptygmatic folding in migmatites (huh?). Take a look first:

                                                         Migmatites are a mixture of metamorphic and igneous rock. The pink plagioclase feldspar in the rock below formed a ptygmatic fold after remelting of the lighter colored minerals:

           Thus, this remelting creates a mixture of the unmelted metamorphic part with the recrystallized igneous part. Migmatites tend to occur at very high-pressure and high-temperature zones and in very old rocks (such as Precambrian).

           The word ptygmatic was introduced into the geological literature by Jakob J. Sederholm in 1907 and originates from the ancient Greek word for “fold” or “anything folded.” The term “ptygmatic fold” is somewhat redundant, like saying “a folded fold.” However, the term “ptygmatic” in the geologic literature generally refers to tight folds that form when the folded material has a greater viscosity than the surrounding medium. In migmatites, ptygmatic folds generally form in the more viscous lighter layers.   

      A look at Bowen's Reaction Series:


          shows why the darker minerals such as olivine, pyroxene, amphibole, and biotite tend not to remelt as it takes higher temperatures for this to happen. The lighter-colored K-spar, muscovite and quartz melt at much lower temperatures forming those ptygmatic folds of newly igneous material.

      Sometimes, differentiating between migmatites and metamorphic gneisses can be difficult--but we'll leave that for a later, gneisser time.




  1. Scientific Steph,

    The photos make it appear as if the lighter-shaded “LeMans-curvelike” part of the migmatite juts out on a different plane that the rest of the rock, like a “snaky ruffly” fence (Just throw those metaphors in the blender, Lego!). Am I seeing it correctly? The photo above the Bowen’s chart resembles one of those layered prom dresses.

    Is the ptygmatic effect what makes the “hairpin turns” jutting from the migmatites so hairpinny? Is that where the “fold” happened, where the racecar (palindrome!) would be gingerly negotiating the turn at about 20 mph?

    Coincidently, David and the EAPOPS puzzle-puzzle constructor over at Puzzleria! have omelets on their minds. Omelets are normally served folded, like a PJ&B sandwich constructed from a non-divided bread slice.)

    Perhaps migmatites would make good amulets! I know meggmatites make good omelets.

    Is “magma” related to “magma,” etymologically or otherwise?


  2. MIGMA- and magma, I mean. Sorry,


    1. Here's the M-W scoop on magma's etymology: Middle English, from Latin magmat-, magma, from Greek, thick unguent, from massein to knead. They appear to share just 80% of their letters, nothing else.

      In the second photo, the lighter minerals in the ptygmatic fold have weathered out. I'd say that's not nearly as common. The wild folds are a result of a very liquidy band of stuff moving in the midst of less liquidy darker stuff.

      I gotta go with jan (below) on of what it reminds me. . .OK, that sounds too forced; "on what it reminds me of."

    2. Preposition at the end, be damned.

  3. You cannot fool me, jan. That is not migmatite. That is a Hostess Cupcake. A HOSTESS is a welcoming person, but if you add a "U" and rearrange, SHE OUSTS!
    (As Lorenzo might say, "Enough with the anagrams already!")

    Scientific Steph welcomes us all into her wonderful PEOTS blog. If I persist with my inane commentary, however, I may be subject to a "SHE OUSTS."


    1. Don't stop, Lego! We want s'more! Give us our just desserts!

    2. jam (sic),

      Oh, we could all endlessly spumoni bon mots (and bonbons) from our cyber-fountain pens, like lava from a volcano (obligatory PEOTS geological reference). But followers of this blog cannoli take so much!

      We mousse try not to fritter busy people’s time away with such buncombe, twaddle, gobbledygook, drivel, inanity, palaver, prattle, blather, bombast, twaddle (all good dessert names that, alas, are not dessert names!) and… Poppycock! Gelato irritation might well ensue and PEOTS readers could popover to Blainesville, AESAP, Puzzleria! or some other such less informative and entertaining blog! (Indeed, molasses and lads ought to visit PEOTS. They just donut know what they’re missing. They biscotti try it at least once. But I guess the sad fact that some don't is just parfait the course.)

      Once folks visit PEOTS, however, they have a truffle time not returning. Indeed, it’s a sherbet that they’ll be back.


    3. Lego, we knew you wouldn't (and yet would) des(s)ert us. Thanks!

    4. My son's 3rd grade class made an ice cream Earth, with different flavors for the core, mantle, and crust, that would have fit right in here.

    5. Those are fun.

      My new neighbor's wifi network name: TellMyWifiLoveHer.

  4. Replies
    1. Halfway through the 2nd paragraph, the possibility of a Fleming/bond joke hit me, so I actually felt a little disappointed when it appeared at the end.

    2. Disappointed? I was delighted.

  5. This may be just a matter of glass-half-empty/full, but I'm with jan on this one. I was disappointed but also depressed. I so much wanted to think, "Aha! I am brilliant! I made this clever verbal connection that maybe no one else notices. I like me. Right now, I like me!" Then, two sentences later, I discover the article's author, Amy Nordrum, is just as clever as I (and, let's be honest, likely cleverer).

    It's like when I create a puzzle for Puzzleria! and later discover that it has already been done... nothing original under the sun.

    It's not really a "competition thing" with me. I admire and revel in the creativity of others. It's just that, at least occasionally, I would also like to "admire and revel in" any sliver of creativity I might happen to muster.


    1. From the large survey of 2 XY and 1 XX, I must conclude, definitively, it's a guy thing ;-). Naw, I think we all like to be clever and witty. That's how we got here, right?

    2. Clever and witty? Hell, we don't even have to prove we're not robots any more!

  6. The 2015 "leader in the clubhouse" for "Straight-line Served up and easier to hit out of the park than a giant softball":

    “Here we actually hold a skull of a human being that was living next to the Neanderthals.” -- Israel Hershkovitz...

    "Israel, welcome to my neighborhood (or hometown, family, school, workplace, blog, etc.)"


    1. It would be kind of cool if you were a woman named Anne Anderthal who married Mr. John Smith. You could then be Anne Smith, Nee Anderthal. ;-)

      And live in the 'hood ;-).

      Thanks for your insights, Lego.

    2. And by "you" I mean "one," of course ;-).

    3. Which raises a serious question I had never pondered before... Maybe someone out there in PEOTSylvania knows the answer.

      Does one of the members of a same-sex marriage ever adopt the surname of his or her spouse?


    4. I imagine so. Likely lots of hyphenating also.

    5. Here's my question: What does "Freezable Inspect Upon Arrival" with a picture of a penguin mean? The image is set as my profile picture.

    6. Oh, it's a jolly 'oliday with Steph!

      The key is the diagonal slash. That image is used on "Refrigerate, Do Not Freeze" labels, for use on shipments containing stuff that needs to be cold, but not too cold. In this case, they want you to check to make sure.

    7. The Penguin clip was great. I'd forgotten how Dick Van Dyke pulled his pants down low to look like penguin bottoms (and then they cinch right back up, of course).

      Why not just say "Do Not Freeze" on the label. "Freezable" sounds like it's something you could happily freeze. . .or not.

      Anyway, Mary Poppins saved the day there.

    8. This comment has been removed by the author.

    9. Practicing my penguin walk. May neeed some Dick Van Dyke-esque pants, though.

      Hehe for the internal link, too. Go with the floe. . .

    10. New post is up . . .but limited internet here.