The degassing of Hawaiian tholeiite |
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| Authors: | Y Bottinga M Javoy |
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| Institution: | (1) Institut de Physique du Globe de Paris, 4, place Jussieu, F-75252 Paris Cédex 05, France |
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| Abstract: | Accepting the Gerlach and Graeber (1985) estimates of the initial CO2 and H2O concentrations, we have calculated the variation of the concentrations of these gases, dissolved and/or exsolved, in Hawaiian tholeiite from the moment it is generated until it solidifies at the Earth's surface. These computations are extensions of our previous work (Bottinga and Javoy 1989, 1990a, 1990b) on the nucleation, growth and ascent of bubbles in mid-oceanic ridge basalt. The present study is different in that we consider low-pressure (P>1 bar) bubble nucleation and the presence of H2O. Our results indicate that: (1) Hawaiian liquid tholeiite is supersaturated with respect to CO2 when it erupts; (2) degassing of the basaltic liquid takes place during different stages, each of which gives rise to a compositionally distinct bubble population, which to a large extent is lost before the formation of a new population; (3) fumarolic gas compositions are affected by the pressure and temperature at which gas bubbles are released from the lava and the velocity with which lava is ejected from the magma chamber. |
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