Subduction factory in an ampoule: Experiments on sediment–peridotite interaction under temperature gradient conditions

To better understand processes above subducted oceanic slabs, we have undertaken experiments with juxtaposed sediment and peridotite layers at pressures of 7.5 and 10.5 GPa at a controlled temperature gradient from ∼100 to ∼500 °C per a sample length of ∼3 mm. The sediment starting material contains H2O (6.9 wt%) and CO2 (5.9 wt%) and has a major-element composition similar to GLOSS (Plank and Langmuir, 1998) doped with trace elements at 10–100 ppm levels. Several experiments were conducted with ∼0.5 wt% Cl or F. The peridotite layer is composed of natural olivine (66 wt%), orthopyroxene (27 wt%) and garnet (7 wt%) mixed with ∼15 wt% graphite. Several experimental configurations were investigated, but the “basic” setup has the sediment layer at the bottom in the cold zone (400–1200 °C) overlain by peridotite at 900–1500 °C. The temperature distribution was determined by two thermocouples and orthopyroxene–garnet thermometry.