Evaluation of the corresponding isochron plot gave MSWD = 3.9 (Both the plateau and isochron approach statistics are unequivocal – a large amount of excess scatter is present in the data sets (“geological error”).
This mineral separate fails to yield either a plateau or an isochron age.
For BI (Lower lava) a descending age spectrum was used to arrive at a plateau age of 60.56 ± 0.29 Ma.
Thus low-temperature steps normally exhibit ages lower than, or equal to, those of the higher temerature steps.“Descending staircase” type age spectra may result from two totally different phenomena.The first is due to the presence of excess (1999) showed that almost all the ages were untenable as crystallization values.In this web page, I take a similar approach (but one that is somewhat easier to visualize) to evaluate these ages based on their age spectra. Elsewhere it will be shown that this conclusion is fully supported by critical examination of the individual age spectra.At the end of the series of experiments, the step ages (± one sigma errors are quoted herein) are plotted against the cumulative amount of ).
This approach is designed to look at the gas released from sites of increasing argon retentivity.Any two points in the universe lie on a straight line!In evaluating isochron “goodness of fit parameters”, the number of degrees of freedom for Chi Square Tables is N-2, and for two steps, this is zero.Note that the same value of MSWD (= 2.5), makes an isochron statistically acceptable for up to 5 points (nu = 3), but unacceptable when seven or more points are used (nu I begin by looking at a hypothetrical data set.Consider a case of five steps carrying equal quantities of gas giving rise to step ages of 99.0, 101.0, 100.0, 101.0 and 99.0 Ma, each with an error of ± 0.5 m.y.The plate motion model derived by (2001) reported a number of plateau/isochron ages for both rocks and mineral separates from the BTIP. BM67 and 64 (Ben More lavas) were said to yield plateau ages of 58.66 ± 0.25 Ma and 58.19 ± 0.26 Ma, respectively, although many step ages obviously do not overlap in each case.