HR: 10:50h
AN: T32A-03 INVITED     [Abstracts]
TI: Numerical modeling of volcanic arc development
AU: * Gerya, T
EM: taras.gerya@erdw.ethz.ch
AF: Department of Earth Sciences, Swiss Federal Institute of Technology (ETH - Zürich), ETH- Hoenggerberg, HPP , Zurich, CH-8093, Switzerland
AU: Gorczyk, W
EM: weronika.gorczyk@erdw.ethz.ch
AF: Department of Earth Sciences, Swiss Federal Institute of Technology (ETH - Zürich), ETH- Hoenggerberg, HPP , Zurich, CH-8093, Switzerland
AU: Nikolaeva, K
EM: nikolaeva@erdw.ethz.ch
AF: Department of Earth Sciences, Swiss Federal Institute of Technology (ETH - Zürich), ETH- Hoenggerberg, HPP , Zurich, CH-8093, Switzerland
AB: We have created a new coupled geochemical-petrological-thermomechanical numerical model of subduction associated with volcanic arc development. The model includes spontaneous slab bending, subducted crust dehydration, aqueous fluid transport, mantle wedge melting and melt extraction resulting in crustal growth. Two major volcanic arc settings are modeled so far: active continental margins, and intraoceanic subduction. In case of Pacific-type continental margin two fundamentally different regimes of melt productivity are observed in numerical experiments which are in line with natural observations: (1) During continuous convergence with coupled plates highest amounts of melts are formed immediately after the initiation of subduction and then decrease rapidly with time due to the steepening of the slab inclination angle precluding formation of partially molten mantle wedge plumes; (2) During subduction associated with slab delamination and trench retreat resulting in the formation of a pronounced back arc basin with a spreading center in the middle melt production increases with time due to shallowing/stabilization of slab inclination associated with upward asthenospheric mantle flow toward the extension region facilitating propagation of hydrous partially molten plumes from the slab. In case of spontaneous nucleation of retreating oceanic subduction two scenarios of tecono-magmatic evolution are distinguished: (1) decay and, ultimately, the cessation of subduction and related magmatic activity, (2) increase in subduction rate (to up to ~12 cm/yr) and stabilization of subduction and magmatic arc growth. In the first case the duration of subduction correlates positively with the intensity of melt extraction: the period of continued subduction increases from 15,4 Myrs to 47,6 Myrs with the increase of melt extraction threshold from 1% to 9%. In scenario (1) the magmatic arc crust includes large amounts of rocks formed by melting of subducted crust atop the thermally relaxing slab. In contrast, in case of stable self-sustaining subduction, magmatic rocks produced by partial melting of hydrated mantle wedge clearly dominate the crust. In several numerical experiments an intra-arc extension is observed during subduction. This process results in splitting of previously formed magmatic arc crust by a newly formed spreading center. In all conducted numerical experiments the loci of magmatic activity and intensity of crustal growth is strongly dependent on the dynamics of hydrous partially molten upwellings (cold plumes) rising from the slab. The material forming these plumes can be homogenous (composed of hydrated mantle) or heterogeneous (composed of both hydrated mantle and subducted crustal rocks). In case of heterogeneous plume growth material mix chaotically resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges.
DE: 0560 Numerical solutions (4255)
DE: 1037 Magma genesis and partial melting (3619)
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3619 Magma genesis and partial melting (1037)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly