Fractionation line
A fractionation line is a straight line in a three isotope diagram along the isotope ratios of an element (which has at least three stable isotopes), which can shift due to chemical or geochemical processes (mass-dependent isotope fractionation ).
For example, earthly rocks and lunar rocks lie on one line in the oxygen three- isotope diagram , while Martian meteorites lie on a different line. Other meteorite classes in turn define their own line. On the one hand, this shows that the oxygen from the earth and moon must come from a common, well-mixed reservoir . On the other hand, from the fact that not all solar oxygen is on a single fractionation line, one can conclude that the protoplanetary nebula from which the planetary system formed could not have been completely mixed and that at least two oxygen reservoirs with different isotopic compositions must have existed. Another possible explanation would be mass-independent isotope fractionation, which does not necessarily have to be on a fractionation line, but this rarely occurs.