SELECTED ELASTIC-MODULI AND THEIR TEMPERATURE DERIVATIVES FOR OLIVINEAND GARNET WITH DIFFERENT MG (MG+FE) CONTENTS - RESULTS FROM GHZ ULTRASONIC INTERFEROMETRY/

Selected P-wave acoustic travel times through single crystal samples o f olivine and garnet with different Mg/(Mg+Fe) ratios were measured at elevated temperatures (from 293 K to 363 K) using a newly developed G Hz ultrasonic interferometer. These high precision data allow us to ex amine aspects of the elasticity-composition systematics of olivine (fo rsterite-fayalite) and garnet (pyrope-almandine) solid solution series . For every 10% decrease in the Mg/(Mg+Fe) content, the P-velocity of olivine along the b-axis decreases about 3% and partial derivative lnC (22)/partial derivative T decreases about 7%; for garnet partial deriv ative lnright perpendicularC(44) + (C-11 + C-12)/2left perpendicular/p artial derivative T decreases about 6%. If such velocity-composition s ystematics are typical and hold at the P-T regime of the mantle, only a 3-4% variation in the Mg/(Mg+Fe) content of olivine is required to e xplain the lateral seismic velocity variation in the upper portion of the mantle within one tectonic region (dlnVp similar to 1%), and 7-8% variation in the Mg/(Mg+Fe) content to explain the 2% lateral seismic velocity variation of the upper mantle globally.