Acid leaching of micas: Improved Rb-Sr geochronology of disequilibrated rocks from zones of alteration and deformation

Abstract

Rb-Sr dating of micas is commonly employed in reconnaissance geochronology of igneous and metamorphic rocks, and for dating fluid/rock interaction and deformation. High Rb/Sr-micas can be used to determine single mineral Rb-Sr model cooling ages, provided their 87Sr/86Sr is high enough to make the analysis insensitive to any errors in the choice of its initial 87Sr/86Sr (Sri). If the Rb/Sr ratio of the mica is low, e.g. due to low Rb or due to the presence of Sr-rich impurities, a second phase (host rock or another cogenetic mineral) is needed to constrain Sri. Problems may arise if the mica is not in isotopic equilibrium with other minerals in the rock, such as in ore-related alteration, in..