Organ orgam rock dating method

22-Jun-2014 16:09

As rubidium easily substitutes chemically for potassium, it can be found doing so in small quantities in potassium-containing minerals such as biotite, potassium feldspar, and hornblende.(The quantity will be small because there is much more potassium than rubidium in the Universe.) This means that if we wanted to date a rock, and if there was no Sr present initially.To see how we actually use this information to date rocks, consider the following: Usually, we know the amount, N, of an isotope present today, and the amount of a daughter element produced by decay, D*.

We can see how do deal with this if we take a particular case. For example the amount of Rb in mantle rocks is generally low, i.e. The mantle thus has a low If these two independent dates are the same, we say they are concordant.Then these different parts of the rock, when analyzed for their isotopic composition, will plot in a straight line on the isochron diagram; and the slope of this line, and the point at which it intercepts the vertical axis, will have nothing to do with the age of the rock, and everything to do with the compositions of X and Y.About half the time this will produce a straight line with negative slope: that is, it will slope down from left to right instead of up.There is, however, one potential source of error which will not show up on the isochron diagram, since it is expected to produce a straight line.Suppose that the original source of the rock was two different magmas (call them X and Y) imperfectly mixed together so that some parts of the rock will be all X, some all Y, some part X and part Y in varying proportions.

We can see how do deal with this if we take a particular case. For example the amount of Rb in mantle rocks is generally low, i.e. The mantle thus has a low If these two independent dates are the same, we say they are concordant.Then these different parts of the rock, when analyzed for their isotopic composition, will plot in a straight line on the isochron diagram; and the slope of this line, and the point at which it intercepts the vertical axis, will have nothing to do with the age of the rock, and everything to do with the compositions of X and Y.About half the time this will produce a straight line with negative slope: that is, it will slope down from left to right instead of up.There is, however, one potential source of error which will not show up on the isochron diagram, since it is expected to produce a straight line.Suppose that the original source of the rock was two different magmas (call them X and Y) imperfectly mixed together so that some parts of the rock will be all X, some all Y, some part X and part Y in varying proportions.When we produced the formula for K-Ar dating, it was reasonable enough to think that there was little to no argon present in the original state of the rock, because argon is an inert gas, does not take part in chemical processes, and so in particular does not take part in mineral formation.