This relative abundance is expressed as the Sr ratio, where strontium-86 is chosen to represent the stable isotopes strontium-88, strontium-86, and strontium-84, which occur in constant proportions in natural materials.
Thus, a precise measurement of the Sr ratio in a modern volcano can be used to determine age if recycled older crust is present.
Different minerals in a given geologic setting can acquire distinctly different ratios of radiogenic strontium-87 to naturally occurring strontium-86 (Sr as the parent melt.
However, because Rb substitutes for K in minerals and these minerals have different K/Ca ratios, the minerals will have had different Rb/Sr ratios.
The utility of the rubidium-strontium isotope system results from the fact that Sr with a half life of 48.8 billion years.
Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, including rapid oxidation in air.
Part or all of this report is presented in Portable Document Format (PDF).
For best results viewing and printing PDF documents, it is recommended that you download the documents to your computer and open them with Adobe Reader.
PDF documents opened from your browser may not display or print as intended.
Download the latest version of Adobe Reader, free of charge.