Rb-Sr dating relies on correctly measuring the Rb-Sr ratio of a mineral or whole rock sample, plus deriving an accurate One of the major drawbacks (and, conversely, the most important use) of utilizing Rb and Sr to derive a radiometric date is their relative mobility, especially in hydrothermal fluids.

Rb and Sr are relatively mobile alkaline elements and as such are relatively easily moved around by the hot, often carbonated hydrothermal fluids present during metamorphism or magmatism.

1982-1986 Dating guide In July 1986 the line symbols were discontinued and the lighters were then identified by a series of roman numerals.

These were placed to the left of the word Zippo, which left the space to the right free.

The Rb-Sr dating method has been used extensively in dating terrestrial and lunar rocks, and meteorites.

If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the Sr ratio.

Conversely, these fluids may metasomatically alter a rock, introducing new Rb and Sr into the rock (generally during potassic alteration or calcic (albitisation) alteration.

Rb-Sr can then be used on the altered mineralogy to date the time of this alteration, but not the date at which the rock formed.

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.

During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase.

The resulting Rb-Sr ratios and Rb and Sr abundances of both the whole rocks and their component minerals will be markedly different.

This, thus, allows a different rate of radiogenic Sr to evolve in the separate rocks and their component minerals as time progresses.

The ideal scenario according to Bowen's reaction series would see a granite melt begin crystallizing a cumulate assemblage of plagioclase and hornblende (i.e.; tonalite or diorite), which is low in K (and hence Rb) but high in Sr (as this substitutes for Ca), which proportionally enriches the melt in K and Rb.