Material transportation and fluid-melt activity in the subduction channel: Numerical modeling
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The subduction channel is defined as a planar to wedge-like area of variable size, internal structure and composition, which forms between the upper and lower plates during slab subduction into the mantle. The materials in the channel may experience complex pressure, temperature, stress and strain evolution, as well as strong fluid and melt activity. A certain amount of these materials may subduct to and later exhume from >100 km depth, forming high to ultra-high pressure rocks on the surface as widely discovered in nature. Rock deformation in the channel is strongly assisted by metamorphic fluids activities, which change composition and mechanical properties of rocks and thus affect their subduction and exhumation histories. In this study, we investigate the detailed structure and dynamics of both oceanic and continental subduction channels, by conducting high-resolution petrological-thermomechanical numerical simulations taking into account fluid and melt activities. The numerical results demonstrate that subduction channels are composed of a tectonic rock melange formed by crustal rocks detached from the subducting slab and the hydrated mantle rocks scratched from the overriding plate. These rocks may either extrude sub-vertically upward through the mantle wedge to the crust of the upper plate, or exhume along the subduction channel to the surface near the suture zone. Based on our numerical results, we first analyze similarities and differences between oceanic and continental subduction channels. We further compare numerical models with and without fluid and melt activity and demonstrate that this activity results in strong weakening and deformation of overriding lithosphere. Finally, we show that fast convergence of orogens subjected to fluid and melt activity leads to strong deformation of the overriding lithosphere and the topography builds up mainly on the overriding plate. In contrast, slow convergence of such orogens leads to very limited deformation of the overriding lithosphere and the mountain building mainly occurs on the subducting plate.
Keywordssubduction channel fluid activity partial melting topography numerical modeling
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