When doing my analysis all my rock( amphibolites, gneiss and mylonites)showed a negative anomaly in Nd. I wish to know if there is an element which consumes Nd to have such a result.
Hello Sobze,
I think there isn't a specific element that "consumes" Nd to produce negative anomalies. It will be better to provide more details on the geological context... However, the negative Nd anomalies in your samples could be to a crustal contamination or were assimilation during the emplacement of the original magmas from which your samples were derived. Moreover, metamorphic reactions could have caused redistribution and incorporation of Nd into specific minerals, such as apatite, monazite, and allanite (because they incorporate REEs, including Nd.
It is possible to have a negative anomaly in Nd when normalized to MORB and this can occur for a number of reasons.
One possible case is that the sample being analyzed has experienced some degree of continental crust contamination, which can result in a depletion of Nd relative to other elements. This can be particularly pronounced in samples from old and evolved continental crust, which may have undergone multiple cycles of partial melting and crustal assimilation.
Another possibility is that the sample represents an extreme or unusual type of mantle source that is not well represented by MORB. For example, some mantle plumes or hotspot-related magmas may have distinct geochemical signatures that can result in a negative Nd anomaly when normalized to MORB.
Presence of a negative Nd anomaly when normalized to MORB does not mean that there is a problem with the data or analysis. It may provide important insights into the source and evolution of the sample being analyzed.
I am aware of negative Nd "anomalies" in granites only. Bau:
M. Bau (1996) Controls on the fractionation of isovalent trace elements in magmatic and aqueous systems: evidence from Y/Ho, Zr/Hf, and lanthanide tetrad effect. Contrib. Mineral. Petrol. 123, 323–333, doi: 10.1007/s004100050159
has called this the tetrad effect and ascribed it to mineral/fluid or mineral/aqueous solution partitioning in highly differentiated granites.
Later it has been found that the effect can also be accounted for by phosphate/melt partitioning in the absence of fluids in peralkaline granite systems:
Q. Duc-Tin & H. Keppler (2015) Monazite and xenotime solubility in granitic melts and the origin of the lanthanide tetrad effect. Contrib. Mineral. Petrol. 169, 8, doi: 10.1007/s00410-014-1100-9
Regarding amphibolites I am not aware of similar observations. Have you considered analytical artifacts? How big are your "anomalies"?
Heinz-G. Stosch
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