Jung, Haemyeong1, L.F Dobrzhinetskaya2, and H.W. Green1,2
1Institute of Geophysics and Planetary Physics, and 2Department
of Earth Science,
University of California, Riverside, California 92521, U.S.A.
Earthquakes at depths greater than ~50 km cannot occur by unassisted brittle
failure but could be triggered by embrittlement accompanying dehydration of
hydrous minerals. Here we show that dehydration of an extensively serpentinized
peridotite under a differential stress displayed faults and localized shear
zones, delineated by ultra fine-grained solid reaction products, formed as byproducts
of antigorite dehydration. This phenomenon was observed under all conditions
tested (P = 1 - 6 GPa; T = 925 – 1100K), independent of the sign of the
net volume change (DV) of reaction. These observations
confirm that dehydration embrittlement is a viable mechanism for triggering
earthquakes independent of depth, so long as there are hydrous mineral breaking
down under a differential stress. In addition, some of the puzzling observations
of aseismicity in subduction zones may be attributable to “superplastic”
slip along ultra-fine-grained dehydration products in fault zones under low
stresses.