Distribution of REE between amphibole and pyroxenes in the lithospheric mantle: An assessment from the lattice strain model

Abstract

23 Amphibole and pyroxenes are the main reservoirs of rare earth elements (REEs) in 24 lithospheric mantle that has been affected by hydrous metasomatism. In this study, we 25 developed semi-empirical models for REE partitioning between orthopyroxene and 26 amphibole and between clinopyroxene and amphibole. These models were formulated on 27 the basis of parameterized lattice strain models of mineral–melt REE partitioning for 28 orthopyroxene, clinopyroxene, and amphibole, and they were calibrated using major 29 element and REE data of amphibole and pyroxenes in natural mantle samples from 30 intraplate setting. The mineral–melt REE partitioning models suggest that amphibole is 31 not in equilibrium with coexisting pyroxenes in the mantle samples, and that the 32 amphibole crystallized at a lower temperature than that of the pyroxenes. We estimated 33 the apparent amphibole crystallization temperature using major element compositions of 34 the amphibole and established temperature-and composition-dependent models that can 35 be used to predict apparent pyroxene–amphibole REE partition coefficients for 36 amphibole-bearing peridotite and pyroxenite from intraplate lithospheric mantle. 37 Apparent pyroxene–amphibole REE partition coefficients predicted by the models can be 38 used to infer REE contents of amphibole from REE contents of coexisting pyroxenes. 39 This is especially useful when the grain size of amphibole is too small for trace element 40 analysis. 41