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Mantle Geochemistry

  1. Sep 14, 2011 #1
    Does anybody have any resources on MANTLE GEOCHEMISTRY as I would like to do some reading. I'm reading Don Anderson's http://authors.library.caltech.edu/25018/" [Broken], although apparently he has some slightly odd views as to the nature of the mantle's 660 km deep discontinuity.

    An excellent starting point if you want to get up to speed with this is the following review paper:

    http://seismo.berkeley.edu/~rallen/teaching/F04_GEO302_PhysChemEarth/Lectures/HellfrichWood2001.pdf" [Broken]


    Please feel free to start some discussion if there is an area that particularly interests you -- I am interested in understanding the bigger picture. Although I happily admit my bias is towards the deeper mantle.
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 14, 2011 #2
    Have you come across

    Physics and Chemistry of Earth Materials

    Navrotsky

    Cambridge University Press

    There is a chapter "High pressure phase transitions in the Earth's interior" - she gives lots of references.

    go well
     
  4. Sep 14, 2011 #3
    Hi studiot, I haven't seen it yet, I will see if it is in the library.

    I think the task of talking about "mantle geochemistry" is overly daunting. Where can we begin?

    Perhaps it would be useful to try to break it down into some of the key sub-areas and questions:

    1) Geochemistry methods: What elements are used to study the mantle? How do these methods work?

    2) Grand structure of the mantle: Phase transformations in the mantle and their relationship to seismic velocities.

    3) The upper mantle -- relationship to overlying crust: Formation of continental crust -- Large Igneous Provinces -- (other sources). Oceanic crust -- mid-ocean ridge basalts. The Moho -- a change in chemistry? The lithosphere asthenosphere boundary -- a change in chemistry?

    4) The lowermost mantle -- source of mantle plumes?

    5) Earth evolution through time. How do geochemical data tell us about the evolving Earth?

    6) Piecing it together. What is the picture of the Earth that we get from geochemistry?

    7) ?

    8) ?

    I'm sure there are more we can add.
     
  5. Sep 14, 2011 #4
    Hard to see into it

    Petrology: Igneous, Sedimentary and Metamorphic by Blatt and others did a good job explaining things like lherzolites, thoelites, and all that other good stuff. Just a general petrology book from my days in college.

    Lherzolite, that's what I was taught and what I can remember. Wikipedia (without citation) says garnet lherzolite is the main constituent in the upper mantle. Not sure how accurate or on track that is with what you are after.

    Studying the mantle's chemistry? You can study mantle chemistry with xenoliths as well as mantle plumes by determing the depth and cause of mantle plumes, but there ought to be crustal contamination along the way. I suppose the later method is done by tomographic surveying, but wait aren't you the geophysicist?

    And meteorites, can't forget those. Most important may be the carbonaceous chondrites.

    So there are three rocks to study:

    1. Mantle xenoliths
    2. Mantle plumes
    3. Carbonaceous Chondrites

    Hope that helps
     
    Last edited by a moderator: Sep 14, 2011
  6. Sep 14, 2011 #5
    I'm not sure what edition you have, but it is an old book and a lot has changed. I'm not up on what are the best books, but if you have it in your library you try http://www.sciencedirect.com/science/referenceworks/9780444527486#ancv0020". The first few chapters should give you an overview.

    DrClapeyron (what is in a name...?) has some good advice about the source of info on mantle composition and is right about lherzolite, or more generally peridotite. Peridotites are primarily composed of high magnesium olivine and pyroxene (lherzolite is a type of peridotite).

    In general, the seismic discontinuities are related to solid-solid phase transformations and not compositional changes. At 410 km olivine takes on a spinel structure to become what is known as wadsleyite. At ~510 km wadsleyite transforms to ringwoodite. This phase change is not so pronounced, which is why this is no distinct seismic anomaly. Then at 660 km ringwoodite transforms to a combination of perovskite and magnesiowustite. Then even further down ~2600 km at the core mantle boundary there is the post-perovskite phase, which is likely to be the cause of the seismic anomalies associated with the D'' layer.

    This topic and some of the questions that you are asking are at the frontiers of Earth science so you may not get all the answers you are looking for, but I hope I can help a little.
     
    Last edited by a moderator: Apr 26, 2017
  7. Sep 14, 2011 #6
    Adding further on the meteorites is that the chemistry of carbonaceous chondrites is believed to be the undiffirentiated mantle chemsitry. That is to say, the chemistry of a mantle that has not undergone fractionation where heated portions have risen to the surface along mid-ocean ridges, hot spots and other places within the crust (eclogites).

    Some of the more rare elements within these rocks are used as a normalizations (?) to compare the abundances of such rare elements in mafic and ultramafic rocks. That is to say the trends in the relative abundances (PPB) of these elements are similar in both carbonaceous chondrites and such mafic and ultramafic rocks. Studying the pre-solar nebula, its chemical reactions and physical processes may be good way to understand what lies beneath.

    There are some otherthings which I can't remember much about that would seem important like the Sm-Nb and Rb-Sr isotope ratios in igneous rocks and the role that subducting crustal slabs play in mantle convection.

    I looked for sources in my old petrology book and was able to find the following two most recent books:

    The Earth's Mantle: Composition, Structure and Evolution edited by I. Jackson (1998)
    Deep Interior of the Earth by J.A. Jacobs (1992)
     
  8. Sep 16, 2011 #7
    Thanks for the contributions.

    I have always been impressed by the geochemist's ability to infer tectonic settings from the presence, absence, or ratios of various elements and isotopes in a sample. It would seem that geochemists are good at telling you about things that they can actually sample, except, moreover, they have theories which they use to infer things about places that they don't even have samples...(?!)

    I often wonder how well constrained all the stuff they come out with really is. It is difficult for a geophysicist to understand the significance of a geochemist's data. Obviously it is hugely important. We both study the same Earth and so ultimately our results must not be contradictory, we can use this fact to guide us in our interpretations, which is why I am interested in learning what the geochemists have to say.

    For example a geophysicist might see a patch of slow velocities in the mantle from their new super-duper high resolution full-waveform inversion tomography and come to the immediate ad hoc conclusion that the Earth is abnormally hot in that region. The geochemist, meanwhile, might have predicted that we should find regions in the earth that are chemically distinct and calculate that these regions should exhibit slow velocities. Perhaps the geophysicist is seeing what the geochemist has predicted?
     
  9. Sep 28, 2011 #8
  10. Sep 28, 2011 #9

    davenn

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  11. Sep 29, 2011 #10
    Looks a good addition to my existing library.

    :approve:
     
  12. Sep 29, 2011 #11
    Indeed. Seismology. That's where the good stuff is.

    What kind of seismology do you do?

    I've done quite a bit of reservoir imaging in a past life, but now I'm looking at the deep earth for my PhD. In particular I am looking at the anisotropy of D".
     
  13. Oct 4, 2011 #12
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