Isochron-Plot of Short-Lived Decay Systems скачать в хорошем качестве

Isochron-Plot of Short-Lived Decay Systems

Short-lived decay systems are those in which the half-life of the parent is smaller than about 100 Ma. An example is the 182Hf to 182W system, with a half-life of 8.9 Ma. For an isochron plot it is required that a number of components, e.g., various minerals, had variable 180Hf/184W ratios, but the same 182W/184W ratios. An example would be a melt, in which these minerals crystallise at about the same time. 182Hf then decays to 182W. This, of course, does not change the 180Hf/184W ratios of the minerals, however their 182W/184W ratios increase. As a result, the compositions of the minerals move along lines parallel to the y-axis. The connection of the endpoints of these lines define the isochron. The slope of this isochron can then be used to back-calculate when the various minerals crystallised, i.e., how old the rock is – but only, and this is important to note, relative to another rock of which also an isochron has been determined.