In situ X-ray diffraction studies of dense hydrous magnesium silicates at mantle conditions

摘要

Lizardite was pressurized up to about 28 and 20 GPa and heated at 1310 (±50) and 1100 (±100) ℃; antigorite was pressurized at about 25 and 22 GPa and heated at ～1000 ℃, with a Nd:YAG laser using the double-side laser heating technique. Samples were then examined in situ by energy dispersive synchrotron X-ray diffraction. Our results show that phase E, superhydrous phase B, and phase D are indeed dense silicate phases that are stable at high P-T conditions and quenchable to ambient conditions. Some unidentified peaks observed in our runs indicate the existence of unknown hydrous phases. The lattice parameter and bulk modulus of phase E are in good agreement with previous measurements. The linear moduli of the three axes of superhydrous phase B are k_(ao) = 482 (±36) GPa, k_(bo) = 544 (±62) GPa, and k_(co) = 472 (±66) GPa and the bulk modulus of superhydrous phase B is 156 (±2) GPa. The linear moduli of the three axes of Fe-bearing phase D (phase D_(ant)) are k_(ao) = 422 (±8) GPa and k_(co) = 404 (±4) GPa and the bulk modulus is 134 (±5) GPa, which is ～19% smaller than the Fe-free phase D reported previously. Our results indicate that phase E, superhydrous phase B, and phase D are indeed thermodynamically stable phases at mantle conditions.