Relative strength of the pyrope-majorite solid solution and the flow-law of majorite containing garnets

Even though the garnet phase is the second most abundant phase in the upper-mantle and transition-zone, no previous studies have directly measured the effect of majorite content on the strength of garnet under mantle conditions. Here we report the results of constant strain-rate and stress-relaxation experiments on garnets in the pyrope-majorite solid solution which constrain the strength of majoritic containing garnets relative to pyrope as a function of majorite content and temperature. We find that at temperatures below 650 degrees C both pure pyrope and majoritic garnets have the same strength. Conversely, above 650 degrees C we find that majoritic garnets are initially stronger than pure pyrope but weaken with increasing temperature and majorite content and with significant majorite contents are weaker than pyrope above approximately 800 degrees C. We develop a flow law for the entire pyrope majorite solid solution as a function of temperature and majorite content. (C) 2010 Elsevier B.V. All rights reserved.