Sm nd dating method
Nd isochron, there are two problems with the sample selection.Firstly, the sample suite combined amphibolite- and granulite-facies gneisses, and secondly it contained a bimodal petrological suite, including tonalitic gneisses and basic rocks from the Drumbeg layered complex. (1979) apparently does correctly date the time of protolith formation, but only the basic rocks remained closed systems during the Badcallian event.Nd isotope ratios are affected by the choice of normalising factor for mass fractionation. However, the isotopic composition of the chondrites is a critical benchmark for the evolution of solar system bodies such as the Earth, because chondrites are believed to represent the nearest approach to the primordial solar nebula.De Paolo and Wasserburg (1976a) coined the acronym CHUR (chondritic uniform reservoir) for this benchmark, but in the absence of isotopic data for chondrites had to use Lugmairs (1975) Nd ratios determined from elemental analysis, compared with the value from Fig. Ordinary chondrites are sub-divided into compositional classes (H, L, LL). The analysis of separated minerals provided a much greater range of Sm/Nd ratios than whole-rock samples, but raised the possibility that Sm Nd mineral systems might have been opened by the event that disturbed Rb Sr systems.However, because Sm and Nd have very similar chemical properties (unlike Rb and Sr), large ranges of Sm/Nd in whole-rock systems are rare, and in particular, low Sm/Nd ratios near the y axis are very rare.Therefore, because of the difficulty of obtaining a wide range of Sm/Nd ratios from a single rock body, and because of the greater technical demands of Nd isotope analysis, the Sm Sr isochrons had proved unsatisfactory.were transformed to an eclogite mineralogy (garnet and omphacite), but retained a relict igneous texture.
However, they were forced to combine analyses from komatiites and basalts in order to achieve a good spread of Sm/Nd ratios (Fig. After the exclusion of one komatiite point from Kambalda and a suite of basalt lavas from Bluebush (40 km south of the main Kambalda sequence), ten data points gave an age of 3262 Nd data.
For example, garnet and clinopyroxene (cpx) have mirror-image distribution coefficients for rare-earth elements (REE), giving rise to a large range of Sm/Nd ratios, and hence allowing precise age determinations.
The classic example of a garnet Nd method to date metamorphism.
In contrast, nearby country-rocks which had been transformed to eclogite generated a mineral isochron with very low scatter (MSWD = 0.1) and a typical Caledonian metamorphic age of 400 16 Myr.
The contrasting behaviour of the two eclogite types cannot be attributed to variable P, T conditions, since they are from within 1 km of each other.