Ice-VII inclusions in diamonds: 

Evidence for water-saturated regions in the mantle transition zone

Tschauner O., Huang S., Greenberg E., Ma C., Rossman G., Shen A.H. Bechtel H., Chen B., Zhang D., Dera P., Mewville M., Lanzirotti A., Kait K.

1Department of Geoscience, University of Nevada Las Vegas, Las Vegas, Nevada 89154, USA.
2 Center of Advanced Radiation Sources, University of Chicago, Illinois 60632, USA.
3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA.
4Gemological Institute, China University of Geosciences, Wuhan 430074, China
5Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, California 94720 USA.
6School of Ocean and Earth Science and Technology, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA.
7Royal Ontario Museum, 100 Queen’s Park, Toronto, ON  M5S 2C6, Canada.


We show that ice-VII occurs as inclusions in natural diamond. As the residue of aqueous fluid present during growth of diamond, ice-VII crystallized upon obduction of the host diamonds and remained at pressures around 10 to 23 GPa, much higher than any previously known inclusion in diamonds. Ice-VII (now approved as a mineral species - IMA2017-029) appears to be common in diamonds and serves as a very accurate geobarometer. We report thirteen occurrences, nine of which correspond to encapsulation at or below 410 km depth, two at or below 660 km, and two in the range 130-180 km.  These inclusions bear witness of water-saturated conditions near the 410 and 660 km boundaries and provide strong support for the presence of water-rich layers in these regions.