Experimental Divalent Element Partitioning between Anorthite and Cai Melt

Introduction: A quantitative description of crystal-liquid trace element partitioning is critical to understanding the igneous differentiation history of the terrestrial planets. Anorthitic plagioclase is the type mineral of terrestrial planet crusts, and for the Moon, specifically, quantitative understanding of trace element partitioning in anorthite is key to testing models of the lunar magma ocean. Although the partition coefficient, D, is expected to be independent of trace element concentration (Henry’s Law), it will vary with pressure (P), temperature (T), and the major element composition or structure of both mineral and melt. The relative contributions of melt and mineral structures to element partitioning between the phases have been debated at length. Over the past decade Blundy and Wood [1,2] have developed and utilized a compelling element partitioning model based entirely on considerations of energetics in the mineral phase, drawing on insights of numerous workers [e.g., 3]. This study focuses on the Blundy-Wood quantitative thermodynamic model of partitioning, which interprets D values in terms of crystal lattice strain theory [4]. D is parameterized as a function of mineral composition, pressure, and temperature: