Abstract
Journal of the Geological Society of Sri Lanka is a peer-reviewed and open access journal published by the Geological Society of Sri Lanka. It aims to publish the most topical and highest quality papers, summarizing the results of recent research across all sub-disciplines of the Earth Science. Papers are frequently interdisciplinary covering both pure and applied fields of Geology. Contributions often refer to local, regional and/or international studies and emphasize the development of the understanding of fundamental geological processes.
Highlights
Since 1940s isochron method of dating has been used to find geological ages of terrestrial and extraterrestrial materials (Hahn et al, 1943, Lugmair et al, 1975)
They are, the number of samples collected, the layer arrangement, length-scale of isotopic resetting, the 2σ percentage errors used in the calculations, the main controlling factor being the level of isotopic homogenization achieved at a given step of resetting
The simulated whole-rock Rb-Sr and Sm-Nd systems suggest that Mean Square of Weighted Deviates (MSWD) and Probability of Fit (PoF) of Best-Fit Line (BFL) for randomly collected data, (a) rely on too many factors, (b) improve towards ≤ 1 and 1.0, respectively, as isotopic homogenization progresses within stage 3 of isochron translation, (c) may give values ≤ 1 for both the parameters for samples representing the stage 1 of isochron translation
Summary
Since 1940s isochron method of dating has been used to find geological ages of terrestrial and extraterrestrial materials (Hahn et al, 1943, Lugmair et al, 1975). Before making inferences on the geological evolution on the basis of initial isotopic ratios and geological ages, the BFLs have to undergo a close scrutiny to ascertain the co-genesis of samples, if the material is metamorphic. Without such scrutiny, an uncertainty inevitably surrounds every isochron despite the perfectness of the line-fit on an isochron diagram. Since isotopic resetting has not been investigated in its true perspective, a geological criterion did not emerge to positively identify an isochron. Simulations were performed on computer to investigate whether isochrons rotate or translate in isochron diagrams during isotopic resetting. The procedures and notations used in the simulations are given in the Appendix
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