Rubidium strontium dating example

20-Oct-2016 04:15 by 3 Comments

Rubidium strontium dating example

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.

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The Rb-Sr dating method has been used extensively in dating rocks.

The Sr87/Sr86 ratio for each sample is plotted against its Rb87/Sr86 ratio on a graph called an isochron.

If these form a straight line then the samples are consistent, and the age probably reliable.

The slope of the line dictates the age of the sample.

Rb-Sr dating relies on correctly measuring the Rb-Sr ratio of a mineral or whole rock sample, plus accurately 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.

The application of Sr isotope stratigraphy is generally limited to carbonate samples for which the Sr seawater curve is well defined.

This is well-known for the Cenozoic time-scale but, due to poorer preservation of carbonate sequences in the Mesozoic and earlier, it is not completely understood for older sequences.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.The dates indicate the true age of the minerals only if the rocks have not been subsequently altered.During fractional crystallization, Sr tends to be come concentrated in plagioclase, leaving Rb in the liquid phase.Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Typically, Rb/Sr increases in the order plagioclase, hornblende, K-feldspar, biotite, muscovite.This, thus, allows a different rate of radiogenic Sr to evolve in the separate rocks and their component minerals as time progresses.

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