Experimental evidence for the survival of augite to transition zone depths, and implications for subduction zone dynamics

摘要: (Ca,Mg)-rich clinopyroxenes are abundant in Earth’s upper mantle and subduction zones. Experimental studies on the thermoelastic properties of these minerals at simultaneous high pressure temperature important for constraining composition structure Earth. Here, we present a synchrotron-based single-crystal X-ray diffraction study natural diopside-dominated augite [(Ca 0.89 Na 0.05 Mg 0.06 )(Mg 0.74 Fe 0.11 Al 0.14 Ti 0.01 )(Si 1.88 0.12 )O 6.00 ] P T to ~27 GPa 700 K. The experiment simulates conditions cold subducting slabs, results indicate that is stable over this range. A third-order high-temperature Birch-Murnaghan equation was fit with pressure-volume-temperature data, yielding following parameters: K T0 = 111(1) GPa, ′ 4.1(1), (∂ 0 /∂ ) −0.008(5) GPa/K α 4(1)×10 −5 −1 +2(3)×10 −8 −2 T. strain analysis shows compression along three principal stress directions highly anisotropic ɛ1:ɛ2:ɛ3 1.98:2.43:1.00. Additionally, high-pressure structural refinements room-temperature polyhedral geometry, bond lengths O3-O3-O3 angle were investigated ambient temperature. Pressure dependences volumes distortion substitution 3+ Si 4+ significantly changes compressional behavior O 4 -tetrahedron augite. Density calculations slab geotherm suggest as well other common would promote stagnations transition zone depths if they metastably preserved significant quantities.