Lab_4__Isotopes

39 x 1011 yr1 t age in ma this is an equation of the

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Unformatted text preview: e Sr in these sulphides was derived from leaching of underlying basement do you think that these rocks were mantle ­ or crustally ­derived? Explain. Rb-Sr Isotopes: Basic Equations and Terminology Rb Sr Decay Equation and Isochron Age Calculations Rb ­Sr system is based on the decay of 87Rb to 87Sr from the following equation: (87Sr/86Sr)m = (87Sr/86Sr)o + (87Rb/86Sr)m(e t 1) (1) where: (87Sr/86Sr)m = measured 87Sr/86Sr ratio of the sample (87Sr/86Sr)o = initial 87Sr/86Srratio of the sample (or source) when the rock formed (87Rb/86Sr)m = measured 87Rb/86Sr ratio of the sample λ = decay constant (1.39 x 10 ­11 yr ­1) t = age in Ma. This is an equation of the form y = mx + b, by obtaining the slope of this line we can calculate the age of the sample/rock by using: m = e t –1 (2) and rearranging this we have: t = ln(m+1) / λ (3) Since we are often dealing with multiple datapoints for an isochron we must calculate the “least squares” regression line for the multi...
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This document was uploaded on 03/06/2014 for the course ES 4211 at Memorial University.

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