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

Abstract:

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 (D_k(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 Al^VI in the stoichiometric formula of omphacite is limited, the content of the end-member NaAl^VISi₂O₆ should be decreased with increasing pressure, because K substitutes for Al^VI to produce the end-member KAl^VISi₂O₆. 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.