Modelización geoquímica de los procesos de diferenciación por cristalización

Abstract

During crystallization processes, major and trace elements and stable isotopes fractionate, whereas radiogenic isotopes do not change. The different equations proposed allow us to reproduce the variation in major and trace elements during these differentiation processes. In the case of simple fractional crystallization, the residual liquid is impoverished in compatible elements faster than it is enriched in incompatible elements as crystallization proceeds. During in situ crystallization the highly incompatible elements evolve in a similar way to the case of simple fractional crystallization but the enrichment rate of the moderately incompatible elements is slower and the compatible element; do not suffer a depletion as strong as the one observed during simple fractional crystallization, even for higher f values. In a periodically replenished magma chamber if all the liquid present is removed at the end of each cycle, the magma follows patterns similar to those generated by simple fractional crystallization. On the contrary, if the liquid fraction that crystallizes during each cycle and the one that is extruded at the end of the cycle are small, the residual liquid shows compositions similar to those that would be obtained by equilibrium crystallization. Crystallization processes modelling is in general less difficult than (or partial melting. If a rock series is the result of simple fractional crystallization, a el Cⁱ_L - C^j_L plot in which i is a compatible element and j is highly incompatible, allows us to obtain a good approximation to the initial liquid composition. Additionally, log Cⁱ_L -log C^j_L diagrams in which i is a highly incompatible element, allow us to identify steps in the process and to calculate the bulk distribution coefficients of the trace elements during each step.