Appendix Geochronology in Myanmar (1964–2017)

This Appendix summarizes the published isotopic age data for Myanmar up to early 2017. It is intended as a resource for geoscientists to stimulate future investigations. A variety of age dating methods have been applied in Myanmar since the mid-1960s, when Searle & Ba Than Haq (1964) published ages of rocks from the Mogok area data based on their uranium contents. During the 1970s the K–Ar and Rb–Sr methods were applied to date biotite, muscovite and amphibole and aggregates of these minerals (‘whole-rock method’), mainly of granitic rocks. In the K–Ar dating method the original sample was split into two halves. One half of the sample was analysed for K and the second half of the sample for Ar. Ideally the K–Ar isotope data document the closure temperatures when the magmatic minerals stabilized, such as biotite (250–350°C), muscovite (300–400°C) and hornblende (450–500°C), the results being used to date the solidification of an igneous rock. In practice K–Ar age data were often ambiguous due to resetting of the magmatic Ar and K isotope system by later tectonic and metasomatic events. However, it was found that the isotopes of Rb and Sr in magmatic minerals were more stable and not so affected by later events. Dating of intrusion of magma could be derived from the linear plot of the ratios of 87Sr/86Sr v. 87Rb/86Sr from a collection of related igneous rock types from a locality to plot an ‘isochron age’. In addition, the initial 87Sr/86Sr ratios gave an indication of the source of an igneous rock. 87Sr/86Sr ratios less than 0.705 suggested a mantle origin, while higher 87Sr/86Sr ratios indicated crustal contaminations of some nature. The analysis of Rb and Sr isotopes, major oxides and trace elements …