Trace-Element Partitioning Between Amphibole and Silicate Melt

Abstract

Knowledge of the partitioning behavior of trace elements between solid and liquid is a prerequisite for modern igneous and mantle petrology. Most of the mathematical models simulating melt generation, migration and evolution within the mantle and/or the crust require the availability of reliable solid/liquid partition coefficients for the mineral phases involved in the process. Calcic amphiboles are extremely important for the understanding of lithospheric processes because of both their common occurrence in a variety of igneous and metamorphic rocks types and their capability of hosting a large number of geochemically important trace elements. A series of studies on the partitioning behavior of trace elements between calcic amphibole and silicate melt have therefore been carried out at different pressures, temperatures and system compositions during the last 15 years. However, due to the complex crystal chemistry of amphiboles, only few studies focused on the role of crystal structure and composition on amphibole-liquid partition coefficients (Amph/LD). In this chapter, present knowledge of the solid/ liquid trace element partitioning between calcic amphiboles and silicate melt is summarized and the role played by the crystal structure and melt composition on Amph/LD variations is highlighted in addition to the effects of pressure and temperature. The dataset used in this chapter includes only the results of experimental studies performed under well constrained P - T conditions for which trace element determinations were carried out with highly sensitive in situ microanalytical techniques. The available dataset considered in this work are listed in Table 1⇓. Although far less common than the calcic amphiboles, potassic-richterites are potentially important in the generation of potassic magmatic rocks and in re-enrichment processes occurring in the subcontinental mantle lithosphere sampled as xenoliths in kimberlites. A comprehensive experimental study of trace element partitioning between synthetic potassic richterites and silicate melts has …