HR: 1330h
AN: T43B-01    [Abstracts]
TI: Modeling Low-Angle Subduction Initiation by Ductile Deformation
AU: * Goren, L
EM: liran.goren@weizmann.ac.il
AF: Department of Environmental Sciences and Energy Research,, Weizmann Institute of Science, Rehovot, 76100 Israel
AU: Aharonov, E
EM: einat.aharonov@weizmann.ac.il
AF: Department of Environmental Sciences and Energy Research,, Weizmann Institute of Science, Rehovot, 76100 Israel
AU: Mart, Y
EM: y.mart@research.haifa.ac.il
AF: Recanati Institute for Marine Studies University of Haifa, University of Haifa, Haifa, 31905 Israel
AB: The concept that new subduction systems are initiated repeatedly arises from the absence of oceanic crust older than ~200 Ma. Passive margins are considered a favorable site for subduction nucleation due to the existence of Andean type convergence margins. However, the force constellation and mechanisms that enable the development of a subduction system from a passive margin remain unclear. The difficulty arises when comparing the sum of the driving forces to the sum of the resisting forces. Such a calculation suggests that subduction cannot initiate spontaneously at passive margins, despite geological observations that indicate otherwise. To further investigate the subduction onset problem, we conduct scaled analogue experiments under the enhanced gravity of a centrifuge, and no other external force. We aim to study the conditions and processes by which the instability emerging from lateral density differences between the oceanic and continental lithospheres may lead to initiation of a low-angle subduction system. Furthermore, we analytically study the evolution of the interface between two juxtaposed high viscosity fluids, with lateral density contrast, simulating passive margin configuration. Our analogue experiments show that low-angle subduction may develop by ductile deformation and rotation of the ocean-continent interface (OCI), driven by lateral density variations. Hence we conclude that frictional resistance between the plates need not be overcome throughout the whole lithospheric profile, contrary to previous scenarios of subduction initiation. Our experiments also demonstrate that the force induced by the negative buoyancy of the oceanic plate with respect to the asthenosphere, which is widely considered a main force in driving incipient subduction, is in some cases irrelevant to subduction nucleation. The analytical formulation shows that the evolution of the OCI is a function of √ t, where t is the age of the oceanic plate, and the velocity field is expected to take the form of a convection cell. The results of both the analogue models and the analytical formulation are compared to south-east Australia passive margin, and show excellent fitting to its geometry and stress distribution.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8122 Dynamics, gravity and tectonics
SC: Tectonophysics [T]
MN: 2005 Joint Assembly