Chemical Mass Balance Equations for Open-system Magma Chamber Processes under Equilibrium Crystallization Conditions

A mass balance model is developed to describe the behavior of trace elements and isotopes during open-system magma chamber processes under equilibrium crystallization conditions.The model incorporates the effects of melt influx (recharge or mixing), equilibrium crystallization, magma extraction, assimilation of anatectic wallrock melt, and partial settling of crystals.The analytical solution of the mass-balance differential equations gives a quantitative account of the evolution of trace elements and isotopes.The chemical trends of the magma differ markedly from those predicted by a recently developed open-system magma chamber model under disequilibrium crystallization (crystal zoning) conditions.These two end-member models provide the upper and lower limits for the compositional variations expected during open-system magma chamber processes under natural conditions.