Mathematics – Logic
Scientific paper
May 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993e%26psl.117..279b&link_type=abstract
Earth and Planetary Science Letters, Volume 117, Issue 1-2, p. 279-294.
Mathematics
Logic
22
Scientific paper
In order to assess the efficacy of fluid-assisted chemical transport in deep-seated, pyroxene-rich rocks, two types of experiment involving synthetic clinopyroxenites were performed at 900°-950°C and 1.5 GPa: (1) annealing of ferrosalite (CaMg0.4Fe0.54Mn0.06Si2O6) or diopside (CaMg0.94Fe0.06Si2O6) powder in the presence of aqueous fluids (water NaCl, CaCl2 or CO2) to produce near-equilibrium fluid/crystal dihedral angles (θs), and (2) diffusion-couple experiments in which an H2O-bearing cylinder of Fe-rich clinopyroxenite (ferrosalite) was placed against one of Mg-rich clinopyroxenite (diopside). `Control' diffusion experiments on fluid-free clinopyroxenite and on single clinopyroxene crystals were also carried out. The dihedral angle experiments consistently yielded median apparent θ values (i.e., in 2D section) of 65-69°, well above the `pinch-off' value of 60° and independent of additives NaCl, CaCl2 and CO2. In all cases, however, the θ frequency distributions were broad enough to suggest a range of real θs on either side of the median. The textures were also complicated by frequent crystal faceting at pore margins. The diffusion-couple experiments, carried out with 0, 0.6, 1.3, 2.7, 4.0 and 8.0 vol% H2O (at run P and T) showed no Fe = Mg interdiffusion for all but the most fluid-rich (8%) couple. This result is consistent with the determinations in showing that, for geologically realistic fluid abundances, aqueous fluids in clinopyroxenite form isolated (noninterconnected) pores. This conclusion implies that aqueous fluids play no role in larger-than-grain-scale chemical transport in pyroxene-rich rocks under conditions of mechanical equilibrium. The results also allow the possibility that water can be deeply subducted as a separate (but trapped) phase beyond the stability limit of amphibole.
Bruce Watson E.
Lupulescu Afina
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