Abstracts Earth and Environmental Sciences

An exploratory survey of the experimental determination of the activity of jadeite component in binary (jadeite-hedenbergite) pyroxene: Implications for geothermo-barometry of eclogites

by Kristopher Edwin Kerry

The study of jadeite-hedenbergite binary pyroxenes has profound implications for interpreting the P/T history of eclogites and, in particular, ultra high pressure metamorphic rocks. Because binary pyroxenes are extremely rare in nature, a synthesis method was developed, and various compositions along the jadeite-hedenbergite join were produced. Synthesis products were analyzed using an X-ray diffractometer and microprobe to verify purity and homogeneity. Synthesized binary pyroxene was then mixed with quartz and albite and subjected to eclogitic conditions in order to determine the equilibrium reaction Ab <=> Jd + Qtz as a function of pressure, temperature, and X(jd). Two methods of reaction have been developed; one employs a graphite sample cup, and the other requires the use of welded gold sample cups, which reduce the temperature of reaction and allow for better pyroxene growth. All experiments were performed in a 1/2" or 3/4" piston cylinder apparatus at pressures from 15-39 kbar and temperatures from 650-1300°C.