Chondrites are believed to be the least modified most pristine material left over after the formation of the solar system. Geochemists make use chondrites as their ultimate reference and carryout a chondrite normalization of their analyses and isotope geochemists compare isotopic evolution of chondrites with that of their samples. I want to know the pros and cons of this practice and whether it is really meaningful.
Chondrite is chosen as the reference because Chondrite is considered to represent the initial condition (distribution at the formation of the solar system). The presumption is that the earth also had the same distribution at the time of formation, so any difference from that reference is the result of post-earth formation processes (ie. differentiation).
When REE fractionation is discussed, it is common to normalize the data to the values in shale which are thought to be representative of the REEs in the upper continental crust. The shale-normalization helps to eliminate the well-known distinctive even–odd variation in natural abundance (the Oddo–Harkins effect) of the REEs.
Anything can be used as a set against which to normalize, but terrestrial MORBs & chondritic abundances are the most common. Of these two, chondritic elemental abundances are the more commonly used, as already stated. They are the closest analog we possess to the actual original abundances in the solar system before any sorting process took place. As such, they provide an excellent starting place from which to compare very different rock groups such as those from different planets or from very different geological settings.
It should be emphasized however, that only the CI type of carbonaceous chondrites can really be considered as the most primitive compositions ( because of their strong correlation with the composition of the Sun). ALL other chondrites show some degree of differentiation from that composition. Ordinary chondrites, the most abundant meteorite types are significantly fractionated from CI.
Hi Tim, Thanks for the info, but could not access through doi. Give the title of the paper. Regards. LRK
Quantification of the elemental incompatibility sequence, and composition of the “superchondritic” mantle by Youxue Zhang
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