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° C both pure pyrope and majoritic garnets have the same strength. Conversely, above 650° 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° C. We develop a flow law for the entire pyrope-majorite solid solution as a function of temperature and majorite content. textcopyright 2010 Elsevier B.V. All rights reserved.