Sr method (Schreiner, 1958), was the analysis of co-genetic whole-rock sample suites, as an alternative to separate minerals. Redistribution of strontium and rubidium isotopes during metamorphism, World Beater complex, Panamint Range, California.
Each mineral composition remains on the isochron as its slope increases with time.
In practice, the y axis is usually very much expanded to display rocks of geological age in a suitable format, and the growth lines are then nearly vertical.
Such determinations are called model ages because the initial ratio is predicted by a model rather than measured directly.
Sr method was extended to less exotic rock-forming minerals such as biotite, muscovite and K-feldspar, with lower Rb/Sr ratios.
On a diagram where the two axes have the same scale (Fig.
3.3), the points move up straight lines with a slope of Sr by the same amount. Therefore it is more convenient to convert this number to an isotope ratio by dividing through by Sr method was first used in geochronology, the poor precision attainable in mass spectrometry limited the technique to the dating of Rb-rich minerals such as lepidolite.These minerals develop such high Sr ratio of 0.712 could be assumed in all dating studies without introducing significant errors.In order to make this determination, Papanastassiou et al. analysed whole-rock samples from seven different basaltic achondrites, yielding an isochron (Fig. Testing models of large-scale crustal fluid flow using direct dating of sulfides: Rb Sr evidence for early dewatering and formation of Mississippi Valley-type deposits, Hodell, D. However, discordant dates were often generated by assuming an initial ratio of 0.712 when the real initial ratio was higher.