Behavior of K in Eclogite from Subducted Slab at Pressures from 4 to 10 GPa

Monday, 15 December 2014
Lei Han1,2, Yingwei Fei1 and Lifei Zhang2, (1)Carnegie Institution for Science, Washington, DC, United States, (2)Peking University, Beijing, China
The behavior of potassium (K) in eclogite from deep subducted slab is rarely studied, even though there have been many experimental studies in basalt or clinopyroxene systems at high pressure and temperature. We have performed high P-T sub-solidus experiments in the eclogite system with excess K up to 10 GPa, using the multi-anvil press. From 4 to 10 GPa, there is a systematic increase of K2O content in omphacite from ~0.4 wt% to ~4.4 wt%. Therefore, eclogitic omphacite could be an important carrier to transfer K into the deep mantle. The partitioning coefficient of K (Dk(Grt/Omp)) between garnet and clinopyroxene has a negative trend with increasing pressure, indicating that K is preferred to be incorporated into omphacite when the slab is subducted to deep interior. As the amount of AlVI in the stoichiometric formula of omphacite is limited, the content of the end-member NaAlVISi2O6 should be decreased with increasing pressure, because K substitutes for AlVI to produce the end-member KAlVISi2O6. The end-member substitution of diopside (CaMgSi2O6) by K-jadetie (KAlSi2O6) in omphacite results in the increases of Ca, Mg in garnet and of K, Al in omphacite. The K content in clinopyroxene is strongly depended on the mineral composition and pressure.