A nearly water-saturated mantle transition zone inferred from mineral viscosity

作者：Fei Hongzhan^*; Yamazaki Daisuke; Sakurai Moe; Miyajima Nobuyoshi; Ohfuji Hiroaki; Katsura Tomoo; Yamamoto Takafumi

来源：Science Advances, 2017, 3(6): e1603024.

DOI：10.1126/sciadv.1603024

An opesn question for solid-earth scientists is the amount of water in Earth's interior. The uppermost mantle and lower mantle contain little water because their dominant minerals, olivine and bridgmanite, have limited water storage capacity. In contrast, the mantle transition zone (MTZ) at a depth of 410 to 660 km is considered to be a potential water reservoir because its dominant minerals, wadsleyite and ringwoodite, can contain large amounts of water [up to 3 weight % (wt %)]. However, the actual amount of water in the MTZ is unknown. Given that water incorporated into mantle minerals can lower their viscosity, we evaluate the water content of the MTZ bymeasuring dislocationmobility, a property that is inversely proportional to viscosity, as a function of temperature and water content in ringwoodite and bridgmanite. We find that dislocation mobility in bridgmanite is faster by two orders of magnitude than in anhydrous ringwoodite but 1.5 orders ofmagnitude slower than inwater-saturated ringwoodite. To fit the observed mantle viscosity profiles, ringwoodite in the MTZ should contain 1 to 2 wt % water. The MTZ should thus be nearly water-saturated globally.

• 出版日期2017-6