Evolution of descending lithospheric slabs as inferred from assimilation of geophysical, geodetic and geological data
Final Report Abstract
The principal aim of the project E-SLAB was to study the evolution of thermal structures in the mantle by using geophysical, geological and geodetic data and by employing data assimilation techniques to model mantle dynamics. The evolution of two geological domains were the main subjects of the research: (i) gravitational descent of the Vrancea slab in the southeastern Carpathians and (ii) subduction of the Pacific plate beneath the Japanese island arc. A new approach for assimilation of data was developed accounting for temperature-pressure dependent rheology, phase transformations in the mantle, and plate movements. Two computer codes (based on the finite element/finite difference method and on the finite volume method) were developed to solve inverse (retrospective) problems of thermal evolution of a viscous inhomogeneous incompressible heat-conducting fluid, which describes dynamics of the Earth’s mantle. Prominent thermal states of the descending Vrancea slab were restored. In Miocene times the slab geometry clearly shows two portions of the sinking body. The northwest-southeast oriented portion of the body is located in the vicinity of the boundary between the East European and Scythian platforms, and this portion of the sinking body may be a relic of cold lithosphere that has travelled eastward. Another portion has a northeast-southwest orientation and is related to the present descending slab. Above a depth of 60 km the slab had a concave thermal shape, confirming the curvature of the Carpathian arc, and a convex surface below that depth. The slab maintained its convex shape until it split into two parts at a depth of about 220 km. This change in the slab geometry, which is likely to be preserved until the present, can cause stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region. The thermal states of the mantle beneath the Japanese islands and their surroundings were restored to the Middle Eocene times. The model shows that the hot mantle upwelling beneath the Pacific plate partly penetrated through the subducting plate into the mantle wedge and generated two smaller hot upwellings, which contributed to the Japan Sea basin evolution and to back-arc spreading. Another part of the hot mantle migrated upward beneath the Pacific lithosphere, and the present hot anomaly inferred from seismic tomography studies is likely to be a remnant part of this mantle upwelling. The results of the study may have an important implication for understanding back-arc spreading, tearing of subducting slabs, and geochemical mixing of mantle rocks. Although our principal finding is related to mantle dynamics beneath Japan and its surroundings, such a phenomenon (a linkage between the mantle beneath the slab and above it) may be rather ubiquitous in other subduction zones.
Publications
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Thermal evolution and geometry of the descending lithosphere beneath the SE-Carpathians: An insight from the past, Earth Planet. Sci. Lett., 273, 68-79, 2008
Ismail-Zadeh, A., Schubert, G., Tsepelev, I., and Korotkii, A.
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Numerical techniques for solving the inverse retrospective problem of thermal evolution of the Earth interior, Computers & Structures, 87, 802-811, 2009
Ismail-Zadeh, A., Korotkii, A., Schubert, G., and Tsepelev, I.
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Computational Methods for Geodynamics, Cambridge University Press, Cambridge, 313 p., 2010
Ismail-Zadeh, A. T., and Tackley, P. J.
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Three-dimensional numerical modeling of contemporary mantle flow and tectonic stress beneath the Central Mediterranean, Tectonophysics, 482, 226-236, 2010
Ismail-Zadeh, A., Aoudia, A., and Panza, G.
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Lithosphere-asthenosphere viscosity contrast and decoupling, Phys. Earth Planet. Inter., 189, 1-8, 2011
Doglioni, C., Ismail-Zadeh, A., Panza, G., and Riguzzi, F.
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Geodynamic and intermediate-depth seismicity in Vrancea (the south-eastern Carpathians): Current state-of-the-art, Tectonophysics, 530-531, 50-79, 2012
Ismail-Zadeh, A., Matenco, L., Radulian, M., Cloetingh, S., and Panza, G.
