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Thread: Isn't there a way to know where a rock originated.

  1. #1 Isn't there a way to know where a rock originated. 
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    I thought I read somewhere, there is a test that can be done to figure out which part of the the earth a stone originated. Like a drop stone? Filix.


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    WYSIWYG Moderator marnixR's Avatar
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    basically you try and match the petrography of the dropstones with areas where similar types of rock are known to occur
    + there's always a possibility to confirm the identification using Sm or Nd isotope ratios

    e.g. PROVENANCE OF PLIOCENE-PLEISTOCENE ICE-RAFTED DEBRIS, LEG 145, NORTHERN PACIFIC OCEAN


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    That depends on from which stones you want to know this, and what you exactly want to know. By drop stones there isn't such complicated technology like isotope ratios (normally you take 2 ratios of isotops and not "or") necesary.
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    Very cool stuff. I remember reading something on drop stones in north Austrialia. Where it is very hot. Continential drift? I saw this erratic personaly. Filix. Madison, New Hampshire - Wikipedia, the free encyclopedia
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    Quote Originally Posted by filix View Post
    Very cool stuff. I remember reading something on drop stones in north Austrialia. Where it is very hot. Continential drift? I saw this erratic personaly. Filix. Madison, New Hampshire - Wikipedia, the free encyclopedia
    Australia is big. I would rather guess not, when you look at the ages of glacial erratics they are usually to young for continental drift. Erratics like you think of would be gone because of erosion.
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    WYSIWYG Moderator marnixR's Avatar
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    Quote Originally Posted by The Geographer View Post
    By drop stones there isn't such complicated technology like isotope ratios (normally you take 2 ratios of isotops and not "or") necesary.
    i went to a talk of the local Geologist's Assocation branch last saturday, where the occurrence of early Pleistocene episodes in Britain were recognised from dropstones, and isotope ratios WERE used to pinpoint their source with greater accuracy
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    Quote Originally Posted by marnixR View Post
    Quote Originally Posted by The Geographer View Post
    By drop stones there isn't such complicated technology like isotope ratios (normally you take 2 ratios of isotops and not "or") necesary.
    i went to a talk of the local Geologist's Assocation branch last saturday, where the occurrence of early Pleistocene episodes in Britain were recognised from dropstones, and isotope ratios WERE used to pinpoint their source with greater accuracy
    if you have the equipment you will do this, but for 5-10 years not every institute had this (and I'm not sure if really every institute has this today the technological equipment costs about 100.000-200.000 Euros in Dollar it's even a bit more)
    Last edited by The Geographer; January 30th, 2012 at 03:16 PM.
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    In special I thought of a case in canada where diamonds were found in glacial sediments, they traced the flow back to find the kimberlit pipe, without any isotope data.
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    If the rock has a distinctive mineralogy then its source could likely be determined on that alone. Where there are several possible candidate sources then isotope chemistry would be appropriate solution. Typically one will not entertain the thought that a granitic rock found in northern France came from a similar source in the Southern Hemispher, when there is a good match in Sweden.
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    Quote Originally Posted by John Galt View Post
    Typically one will not entertain the thought that a granitic rock found in northern France came from a similar source in the Southern Hemispher, when there is a good match in Sweden.
    I don't want to contradict you in general but the grain size at glacial sediments depends on the transport distance, even in northern germany there are grain sizes of those sediments is sand, so very hard to see the minerals in this material.
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  12. #11  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by The Geographer View Post
    Quote Originally Posted by John Galt View Post
    Typically one will not entertain the thought that a granitic rock found in northern France came from a similar source in the Southern Hemispher, when there is a good match in Sweden.
    I don't want to contradict you in general but the grain size at glacial sediments depends on the transport distance, even in northern germany there are grain sizes of those sediments is sand, so very hard to see the minerals in this material.
    As far as I can see this discussion is about dropstones. i.e. glacial erratics, not boulder clay or moraines.

    A further point of clarification. I am equating dropstones and erratics. I suspect if I were using the terms strictly then an erratic is carried by a glacier far from its source and deposited upon melting of the ice on land. A dropstone is also ice-transported, but is deposited at sea. However, in terms of origin and identification of origin this distinction seems minor.
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