HR: 1340h
AN: V43A-1420    [Abstracts]
TI: Interaction Between Magma Fluids and Lithosphere Rocks Under Crest Zone of MAR: Mineralogical and Petrophysical Consequences
AU: * Sharapov, V N
EM: vik@uiggm.nsc.ru
AF: Institute of Geology, Koptyug Pr.3, Novosibirsk, 630090 Russian Federation
AU: Mazurov, M P
AF: Institute of Geology, Koptyug Pr.3, Novosibirsk, 630090 Russian Federation
AU: Mysov, V M
AF: Institute of Catalysis, Lavrentyeva 5, Novosibirsk, 630090 Russian Federation
AB: Using numerical and physical experiments dynamics of mass-change in the lithosphere under the zones joining rift valleys of MAR and transform faults was modeled. `Black smokers', methane gas flows, and bubbly carbon deposits, as products of hydrocarbon condensation, present in these zones. Numerical experiments were completed using flow-reactor scheme of PC Selector Win for gas flows of compositions: C (0.1-4), O (0-2), H (0.5-4), Cl (0.05-0.5), F (0.01-1), S (0.01-0.1), and N (0.02-0.1). Weight fraction of gas mixture in rocks was 1.5-0.01%, P from 45-10 kbar to 30-100 bar, T=$1200-400\deg$C. The fluid-rock interaction time was t=1-100 steps. Density change for new-formed rock in the lithosphere profile was estimated by virtual mineral composition recounting for each time step. Verification of physicochemical model was carried out by comparison of changed rocks and numerically obtained condensates, as well as minerals and solid, gas and liquid carbon phases, obtained experimentally using the equipment to study catalytic conversion of synthesis-gas flow (H$_{2}$=65%, CO=34.8%, N$_{2}$=0.2% vol.). It was shown that above the boiling boundary of basic liquids a field of convective mass transfer should form in the lithosphere. This field includes a number of zones of initial rock change with regions of solid phase depleting and condensing. The ranges of rock composition change due to `reduced' and oxidized' gas mixtures were studied. The density change for ultra-basic rock in the lithosphere is related to spatial and time change of oxygen potential, which current values at the beginning of the interaction process are buffering by rocks, and then - by the values at the system input. In the case when reduced gas mixtures exist, an oxidation roll is forming in the flow, for oxidized mixtures - a reduction roll. At the fluid output at the sea bottom their composition is the most oxidized. When fluids and initial rocks of the lithosphere interact, changed rock mixtures of anomalously high density appear (30-60% higher as compared to the initial value). These mixtures appear under the temperatures t$_{55-100}$=$750-650\deg$C (reduced) and $675-500\deg$C (oxidized). For complex mineral columns the densities of rocks appearing when interacting with the reduced fluids are higher than those due to oxidized (not less than 3-4%). Rock densities for t$_{0}$, when interacting with the reduced fluids for the temperature interval $1100-900\deg$C, are 2-4% higher. For the temperature interval $900-750\deg$C the density inversion for changed rocks was found, the density being decreased to 5-8% for t$_{5-35}$ and increased to 2-4% for t $>$ t$_{50}$ relative to t$_{0}$. Relative densities of the rocks due to interaction with the reduced fluids for the above-mentioned temperature range are 2-4% less than the initial ones. The least densities were found for the temperature range $900-750\deg$C. Above the boundary of the magma fluid source within the depleting field the density changes are orthogonal for both reduced and oxidized fluids. Here the reduced fluid influence causes first the density decrease, and then its anomalous increase, with the transition though zero for the time range t$_{5-55}$. For the oxidized fluids the density decreases to about 4-5% relative to zero from high to low temperatures. This work has been completed with the financial support of the RFBR (Grant N 04-05-64107), the Integration Project of the Presidium of SB RAS (Grant N 6.1.1).
DE: 1025 Composition of the mantle
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting