HR: 1340h
AN: V43C-1439    [Abstracts]
TI: Evolution of High Temperature Early Atmosphere Under the Interaction of H$_{2}$O-CO$_{2}$ Super-critical Fluid With Minerals
AU: * Isobe, H
EM: isobe@sci.kumamoto-u.ac.jp
AF: Faculty of Science, Kumamoto Univ., Kurokami, Kumamoto, 860-8555 Japan
AU: Tomita, T
EM: tomita@sci.kumamoto-u.ac.jp
AF: Faculty of Science, Kumamoto Univ., Kurokami, Kumamoto, 860-8555 Japan
AU: Ikeda, K
EM: kuru@es.sci.kumamoto-u.ac.jp
AF: Graduate School of Science and Technology, Kumamoto Univ., Kurokami, Kumamoto, 860-8555 Japan
AB: The evolution of atmosphere-lithosphere system of the early Earth is controlled by mutual interaction of high temperature atmosphere with rocks and minerals. It is assumed that the total pressure of the early atmosphere and the surface temperature above initial magma ocean are 26MPa (H$_{2}$O 20MPa, CO$_{2}$ 6MPa) and $130-330\deg$C, respectively. This composition, temperature and pressure are very close to an azeotropic critical point of the H$_{2}$O-CO$_{2}$ system. Cooling of the hot H$_{2}$O-CO$_{2}$ atmosphere brings the first precipitation of liquid phase at above $300\deg$C. During the early period, hot rain of the Earth should be a supercritical acid rain. Cooling rate of the hot atmosphere is regulated by energy transportation capacity among the surface, atmosphere and radiation of the early Earth. In this study, we discuss evolution of the early atmosphere-lithosphere system based on the results of the alteration experiments of minerals simulated early crust with the H$_{2}$O-CO$_{2}$ fluid and the cooling rate estimation of the high temperature atmosphere. The H$_{2}$O-CO$_{2}$ fluid easily reacts with silicate minerals at around critical point of the fluid to produce carbonate and hydrous minerals. Consumption of CO$_{2}$ increases up to approximately 80% at around $250\deg$C for olivine starting material. This means that most of Mg and Fe in the olivine starting material react with CO$_{2}$. The Formation of carbonate minerals reduces the CO$_{2}$ composition of fluid in the capsule to approximately one fifth. The fixation of CO$_{2}$ by carbonate formation should be very effective to reduce CO$_{2}$ pressure from the early atmosphere in cooling through $250\deg$C. The first sediment of the primitive ocean should contain dolomite and hydrous silicate. The CO$_{2}$ and H$_{2}$O fixed in the first sediment should take an important role in the evolution of the early crust. Composition of the early atmosphere, or partial pressures of CO$_{2}$ and H$_{2}$O and temperature gradient of the atmosphere are essential factors controlling cooling history of the high temperature early atmosphere. We discuss evolution of the early atmosphere including effects of precipitation of super-critical H$_{2}$O-CO$_{2}$ fluid and atmosphere-rock interaction.
DE: 8125 Evolution of the Earth
DE: 5400 PLANETOLOGY: SOLID SURFACE PLANETS
DE: 5407 Atmospheres--evolution
DE: 5455 Origin and evolution
DE: 3630 Experimental mineralogy and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting