HR: 1340h
AN: V53A-1528 [Abstracts]
TI: Experimental determination of water diffusion from hydrous basalt to nominally anhydrous
rhyolite
AU: * Lui, D K
EM: danielklui@yahoo.ca
AF: Univ. Western Ontario, Dept. Earth Sci., London, ON N6A 5B7
Canada
AU: King, P L
EM: penny.king@uwo.ca
AF: Univ. Western Ontario, Dept. Earth Sci., London, ON N6A 5B7
Canada
AB:
Chemical diffusion of total water from a molten hydrous basalt and nominally anhydrous rhyolite was examined using diffusion
couple experiments from 950 - 1350°C, 0.87 - 3.06 wt.% H2Ototal, at 0.5 GPa. Experiments were conducted in a
19 mm non-end-loaded piston-cylinder apparatus. Experiments were designed to simulate the transfer of H2Ototal
from hydrous basalt to relatively less hydrous rhyolite in a bimodal volcanic system. Apparent diffusivities of SiO2,
FeO, CaO, K2O and H2Ototal were estimated using an effective binary diffusion model. Concentration profiles
of H2Ototal were acquired by micro-reflectance Fourier Transform infrared spectroscopy.
Transfer of H2Ototal from the basalt to rhyolite over a 6 hr duration was not observed at 1000°C (below the
basalt's estimated liquidus), but was observed in runs at 1200°C and higher. In general, the rate at which
H2Ototal is transferred from the basalt to rhyolite is greater than that of interdiffusing major elements. For
example, at 70 wt.% SiO2, 0.73 wt.% H2Ototal, the effective diffusivity of SiO2 and H2Ototal
are 6.9 x 10-9 cm2/s and 3.3 x 10-8 cm2/s, respectively. However, this relationship is less obvious at
higher temperatures.
In comparison with previous studies of H2Ototal diffusion in felsic and intermediate melts, our results for the
effective diffusivity of H2Ototal between molten basalt and rhyolite are approximately an order of magnitude less
at comparable temperatures. In some experiments the concentration profile of H2Ototal diffusing from the basalt
into rhyolite is complementary to alkalies diffusing from the rhyolite into basalt. We infer that this relationship
represents charge-compensation of H-species and alkalis between the basalt and rhyolite. This exchange relationship may
account for an apparent negative correlation observed between H2Ototal effective diffusivities and
H2Ototal concentrations in our experiments.
DE: 8412 Reactions and phase equilibria (1012, 3612)
DE: 8430 Volcanic gases
DE: 8439 Physics and chemistry of magma bodies
DE: 8445 Experimental volcanism
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005