Usually whole rock plots in between the minerals in isochrom.. Is there any published literature where it was shown that the whole rock is plotting at the lower end of isochron.. Just need some material..
hi, if I am not mistaken, this can only happen if the minerals, which are not at the lower end of the isochron, are not analyzed. In Rb-Sr isochrons, often the wr analysis plots at the lower end of the isochron but if you analyze apatite or epidote (which contain a lot of Sr but no Rb), these minerals would plot almost at Rb/Sr = 0.
Sir, I have understood your concern.. Do you have any literature available with you where it has been shown that the WR is coming at the lowermost end in the isochron..
The position of a whole-rock in a Sm-Nd isochron plot depends on the relative modal percentages of low and high 147Sm/144Nd minerals in the rock, because it represents the average of the Sm and Nd isotopic compositions of the minerals that constitute the rock. If the modal percentage of low 147Sm/144Nd minerals is very high and only a few percent of high 147Sm/144Nd minerals are present in a rock, then the whole-rock isotopic composition will plot very close to the lower end of a Sm-Nd isochron. If the modal percentages low and high 147Sm/144Nd minerals are reversed, then the whole-rock will plot close to the high 147Sm/144Nd end of the isochron. In case, a whole-rock plots at the extreme low or high 147Sm/144Nd end of an isochron, it only suggests that one has failed to analyze some very low 147Sm/144Nd or very high 147Sm/144Nd minerals in the rock, respectively.
Dear Saha
1.Nd/Sm is best studied to dating of mafic igneous rocks ( more variation in Sm/Ndthan felsic rocks)
2. Nd/Sm remained closed during different metamorphism conditions and effective hydrothermal metamorphic events.
3. During partial melting:
Because Nd is more incompatible than Sm, melts are enriched in Nd (Lower Sm/Nd) therefore melts have lower present-day 143Nd/144Nd than CHUR (Chondritic Uniform Reservoir) residual material has higher 143Nd/144Nd.
Best wishes
Leyla Kalender
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