Recapitulating, any suiteofcomagmaticrocks with anage defines an isochron if its members all had the same initial ratio and if it was closed to both and since crystallization occurred and neither element was introduced from any extraneous source.[…]In this way, whole-rock isochrons can produce rather reliable age data for rock samples.
(mathematics, dynamical systems) A collection of points (such as a manifold), each point representing a set of initial conditions for a given dynamical system, such that every set results in the same long-term behaviour of the system.
2007, Eugene M. Izhikevich, Dynamical Systems in Neuroscience, The MIT Press, page 446: