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Rheology of Mg 2 GeO 4 olivine and spinel harzburgite: Implications for Earth's mantle transition zone
Author(s) -
Shi F.,
Zhang J.,
Xia G.,
Jin Z.,
Green H. W.
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl063316
Subject(s) - ringwoodite , olivine , transition zone , geology , mantle (geology) , spinel , pyroxene , rheology , mantle wedge , peridotite , discontinuity (linguistics) , mineralogy , geophysics , geochemistry , lithosphere , thermodynamics , seismology , tectonics , paleontology , mathematical analysis , mathematics , physics
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.