MIGRATION OF FLUIDS AND MELTS IN SUBDUCTION ZONES AND GENERAL ASPECTS OF THERMOPHYSICAL MODELING IN GEOLOGY
N.L. Dobretsov1,2, V.A. Simonov3,2, I.Yu. Koulakov1,2, A.V. Kotlyarov3
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Fluid, melt, subduction zone, mantle wedge, magma reservoir, peridotite, melt inclusion, seismic tomography, Avacha Volcano, Kamchatka
Abstract
Modeling of fluid-magmatic systems in a suprasubduction mantle wedge is considered for the case of Kamchatka with reference to data on peridotites from other known subduction and oceanic rock complexes. This modeling has to take account of magma storage in several intermediate reservoirs at different depths, up to six such reservoirs, as in the case of Avacha Volcano. Comparison of available data on melt inclusions in spinels indicates crystallization of the Avacha peridotites in magmatic systems progressively decreasing in temperature (>1200 °C → >1100 °C → >900 °C) and pressure (from 13.8 to 4.5 kbar) in intermediate reservoirs at depths of 30-40 and 15-20 km. The Avacha harzburgites do not belong to primary oceanic mantle as they lack both signatures of high-temperature plastic flow and effects of mantle melts known for sheared mantle peridotites from ophiolite suites. The vP / vS ratio estimated from jointly analyzed P - and S -wave velocities ( vP and vS , respectively), an important indicator for seismic tomographic reconstructions of subduction zones, allows discriminating between regions saturated mainly with liquid (melts) and gas phases beneath volcanoes. Only specially tested tomographic data can provide reliable reference for modeling of mantle wedge processes.
|
