THE EFFECTS OF PRESSURE AND TEMPERATURE ON THE PARTITIONING OF TI, SR AND REE BETWEEN AMPHIBOLE, CLINOPYROXENE AND BASANITIC MELTS

An electron microprobe was used to measure partition coefficients (D-values) for Ti, Sr, La, Sm, Ho and Lu in amphiboles, clinopyroxenes and Sr- and REE-enriched basanitic melts. D-values were found to be negatively correlated with pressure at pressures from 0.5 to 3.0 GPa. This effect is greater for Ti and smallest for Lu. Changes in D-values accompanying changes in temperature are less apparent than those caused by changes in pressure. Only D-Ln for clinopyroxene shows a small but consistent increase as temperature increases from 1050 degrees to 1200 degrees C. D-values for amphibole are not noticeably affected by changes in f(O2). In contrast D-values for clinopyroxene become larger as f(O2) increases. The correlations between D-values and pressure may be related to changes in site volumes and electrostatic potentials accompanying shifts in the relative concentrations of Al-IV, Al-VI and Na+.