what could be the most possible reason of being the trace elements particularly the REE in peridotites are below detection limit in the bulk rock composition??????
The concentration of trace elements will vary with the rock type; whereas Ni and Cr show higher concentrations in mafic and ultramafic rocks, Zr and Rb are more concentrated in acidic rocks.
Large ion lithophile elements (LILE) are characterized by large ionic radii, and low charges, and will therefore preferentially concentrate in the liquid until a particular phase with large enough sites to accommodate them begins to crystallize. These elements will therefore be largely "incompatible" particularly with respect to mantle phases (Ol, Opx, Cpx, Gt, .. etc). Examples include: K, Rb, Sr and Ba.
Similarly High field strength elements (HFSE) have large cations, but also large charges, and are also excluded from mantle phases and more concentrated in residual liquids (i.e. they will be more incompatible). These elements are concentrated in accessory phases as sphene, zircon, and apatite. Examples include Zr, Hf, Nb, Ta, Th and U.
Rare earth elements (REE): with atomic numbers between 57 (La) and 72 (Lu) characterized by relatively large ionic radii, and valences of either +2 or +3. These are again in minerals which are mostly late magmatic and acidic rocks, therefore not present much in ultramafic rocks.
Only Transition elements characterized by relatively small ionic radii, either bi- or tri-valent, are strongly partitioned in the solid phases that crystallize during the early stages of magmatic evolution, and are therefore "compatible" with mantle phases. Examples include Ni, Co, Cr, and Sc.
Thank You Ma'am for you nice explanation...But what best can be done to infer the tectonic environment..... when I have only these elements Ni, Sc, Co, V, W and also Zr......
To infer the tectonic environment you can analyse chromites and other spinels. You have to plot the Mg-number against the Cr-number. Then you can seperate between stratiform and podiform "tectonics".
Please refer to the following publications:
https://academic.oup.com/petrology/article/56/12/2395/2375694/Chromitite-Dykes-in-the-Monchegorsk-Layered
https://www.researchgate.net/publication/230015802_Ophiolitic_chromitites_from_the_Kahramanmaras_area_southeastern_Turkey_Their_platinum-group_elements_PGE_geochemistry_mineralogy_and_Os-isotope_signature
Article Ophiolitic chromitites from the Kahramanmaras area, southeas...
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