Distribution coefficients of major and trace elements; fractional crystallization in the alkali basalt series of Chaîne des Puys (Massif Central, France)

The mass balance equations, Di=∑;xjDjii where Di and Dji are the bulk and mineral/liquid distribution coefficients respectively, and xj the weight fractions of the fractionating phases, are solved by least square resolution of the overdetermined system, taking into account the analytical errors on data. The solution applied to the Chaîne des Puys suite leads to a coherent and quantitative model of the fractional crystallization process. The suite has apparently evolved in three stages. Each stage is characterized by constant bulk distribution coefficients and a specific mineral assemblage. Amphibole fractionation plays an important role in the early stages. Some intensive parameters (T, ƒ ƒO2, PH2O) as well as f (weight fraction of residual liquid) are also estimated.