In spite of their importance in constraining the petrogenetic processes at subduction zones, solid/liquid partitioning data for Light Lithophile (Li, Be and B; LLE) and Volatile (H2O, F and Cl; VE) elements at upper mantle conditions are still scarce in the literature. In particular, very little is know about the partitioning behaviour of VE. On the contrary, partitioning models for LLE and VE in the major mineral phases involved in mantle wedge metasomatic processes such as cpx, amph and phl are crucial for petrogenetic studies. We present new partitioning data for LLE and VE between pargasitic/kaersutitic amphiboles and silicate melt. In some of the experimental runs, equilibrium between clinopyroxene and glass or phlogopite and glass was also established. Therefore, the proper mineral/liquid and mineral/mineral partition coefficients (D) could be determined. Results indicate that all LLE are from moderately to highly incompatible in amphibole, clinopyroxene and mica. Whereas Li and B have nearly the same preference for amphibole and clinopyroxene, Be is preferentially hosted in amphibole. On the contrary, both Be and B are preferentially hosted in amphibole than in phlogopite. E Li? Amph/LDF are generally higher than unity, with maximum values exceeding 5. The measured values of Amph/LDCl are comparable to those of the exchange coefficient for H2O, but are much more variable (0.04-0.4). The exchange coefficients for H2O in phlogopite (0.51-0.77) are approximately twice those measured in amphiboles, whereas Phl/LDF (1.7-1.9) and Phl/LDCl (0.08-0.11) are similar to those in amphiboles. As a consequence, migration from an amphibole-free slab into the overlying mantle wedge is more likely for B and Be than for Li. On the contrary, migration from an amphibole-rich slab is more likely for Li than for B, in good agreement with previous findings.
Light lithophile (Li, Be and B) and Volatile (H2O, F, Cl) Elements. Mineral/liquid and mineral/mineral partitioning at upper mantle conditions
MASSIMO TIEPOLO;ALBERTO ZANETTI;
2004
Abstract
In spite of their importance in constraining the petrogenetic processes at subduction zones, solid/liquid partitioning data for Light Lithophile (Li, Be and B; LLE) and Volatile (H2O, F and Cl; VE) elements at upper mantle conditions are still scarce in the literature. In particular, very little is know about the partitioning behaviour of VE. On the contrary, partitioning models for LLE and VE in the major mineral phases involved in mantle wedge metasomatic processes such as cpx, amph and phl are crucial for petrogenetic studies. We present new partitioning data for LLE and VE between pargasitic/kaersutitic amphiboles and silicate melt. In some of the experimental runs, equilibrium between clinopyroxene and glass or phlogopite and glass was also established. Therefore, the proper mineral/liquid and mineral/mineral partition coefficients (D) could be determined. Results indicate that all LLE are from moderately to highly incompatible in amphibole, clinopyroxene and mica. Whereas Li and B have nearly the same preference for amphibole and clinopyroxene, Be is preferentially hosted in amphibole. On the contrary, both Be and B are preferentially hosted in amphibole than in phlogopite. E Li? Amph/LDF are generally higher than unity, with maximum values exceeding 5. The measured values of Amph/LDCl are comparable to those of the exchange coefficient for H2O, but are much more variable (0.04-0.4). The exchange coefficients for H2O in phlogopite (0.51-0.77) are approximately twice those measured in amphiboles, whereas Phl/LDF (1.7-1.9) and Phl/LDCl (0.08-0.11) are similar to those in amphiboles. As a consequence, migration from an amphibole-free slab into the overlying mantle wedge is more likely for B and Be than for Li. On the contrary, migration from an amphibole-rich slab is more likely for Li than for B, in good agreement with previous findings.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
