Publication Date:
2015-03-14
Description:
Geophysical modeling requires an upper mantle low-viscosity zone (LVZ); recent results suggest that the LVZ could be within the mantle transition zone (MTZ) or above it, depending on boundary conditions. The rheology of the olivine-dominated uppermost mantle is well constrained experimentally but not the MTZ. Here we report first-time measurement of the rheology of Mg 2 GeO 4 spinel (analogue of ringwoodite, the dominant mineral of the lower MTZ) in the dislocation creep regime and compare it with that of Mg 2 GeO 4 olivine. In both cases, we incorporate 15-20% pyroxene, the second-most abundant mineral in the upper mantle to provide a realistic comparison of rock rheologies. Under similar conditions, spinel-dominated material is about twice as strong as olivine-dominated material. Our results suggest that unless H 2 O weakening of ringwoodite or phase-transformation-induced grain size reduction occurs in the lower MTZ, it will be more viscous than above the 410 km discontinuity.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
