Crystal chemistry and partitioning of halogens in hydrous silicates

Understanding how halogens are distributed among usual hydrous silicates in the lithosphere is important to constrain their deep geochemical cycle and fluid-rock interactions subduction zones. This article presents first-principles modelling of halogen (F−, Cl−, Br−) incorporation including mica, chlorite, serpentine, amphibole, epidote carpholite. The approach allows studying impact crystal chemistry on partitioning by quantification energetic cost minerals. Calculations carried out large systems where minor trace concentrations. Estimations show that F-bearing defects must be separated at least 9 Å from one another reproduce element behaviour, this value increasing 10 for Cl Br. Results highlight competition between effects electrostatic steric hindrance halogens, has greater importance heavy particular Interaction with alkalis a major control F incorporation, especially mica. Other parameters such as octahedral site occupancy, Si/Al ratio tetrahedral sites nature amphibole mica (K or Na) appear play subordinate roles. Partition coefficients have been estimated mineral assemblages an effort representative zone metamorphism. pargasite, biotite lizardite favoured hosts all three followed clinochlore, tremolite incorporating into dioctahedral phyllosilicates comparatively higher, predicted unfavourable these Fractionation zones evolution partition coefficients, consequence influence over silicates.