If it is not the flows' age, that is not a "problem" with isochron dating, and it is not relevant to the large number of Rb/Sr isochrons which were computed from mineral separations of a single object.At the GSA meeting, Austin discussed the inheritance of a mantle age.In fact, the resulting age in this case may well be meaningful and accurate.The problem is not the age itself but rather Austin's sleight-of-hand in trying to pass off the result as necessarily the age of the flows rather than a minimum age of their source.
The Cenozoic flows sampled by ICR thus are claimed to yield an age which is about 200 million years older than the Cardenas Basalt.
But the Cardenas Basalt cannot be younger than the plateau flows, due to the geological relationships discussed in the first section of this document.
Austin says that his isochron age is the result of a "" (1992, p. In other words, Austin claims that he has produced a seemingly reliable isochron age which must necessarily be wrong, and therefore the Rb-Sr isochron dating method, which is considered to be among the more reliable of radiometric dating methods, must be considered suspect.
The ICR's Grand Canyon Dating Project does not strike a telling blow against the reliability of isochron dating.
The conditions which caused the "false isochron" in this case are fairly well-understood, and easy to avoid by proper sample selection.
The canyon must be younger than the rock layers that it cuts into.