Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the 40Ar/39Ar Method: A Review

The 40Ar/39Ar method applied to K-feldspars and muscovite has been often used construct continuous thermal history paths between ~150–600 °C, which are usually structural tectonic questions in many varied geological settings. However, other authors contest the use of thermochronology because they argue that assumptions rarely valid. Here we review evaluate key assumptions, (i) 40Ar is dominantly redistributed by thermally-driven volume diffusion, (ii) laboratory experiments (high temperatures short time scales) can accurately recover intrinsic diffusion parameters apply settings (lower over longer scales). Studies do not entirely negate application theory histories, although reveal paramount importance first accounting for fluid interaction secondary reaction products via a detailed textural study single crystals. Furthermore, an expanding database experimental evidence shows step-heating induce changes, thus extreme caution must be made when extrapolating derived rate loss constants past. We conclude with set recommendations include minimum sample characterisation prior degassing, assessment mineralogical transformations during degassing situ dating.