HR: 09:15h
AN: T51E-06    [Abstracts]
TI: Subduction Zone Dynamics and the Recent Evolution of the Hellenic Subduction System
AU: * Royden, L H
EM: lhroyden@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, M.I.T., MIT 54-826, Cambridge, MA 02139 United States
AU: Papanikolaou, D
EM: lhroyden@mit.edu
AF: Department of Geology/ University of Athens, Panepistimioupoli Zografou, Athens, non 157 84 Greece
AB: The Hellenic subduction system of western Greece and Albania accommodates northeastward subduction of both oceanic and continental lithosphere and offers an excellent opportunity to study the relationship among subduction rate, trench retreat and density of subducted lithosphere. The Hellenic system can be divided into a northern and a southern segment across a ~100 km dextral discontinuity corresponding to the west-southwest trending Kephalonia Transform. To the north, continental crust ~25 km thick is subducted at 5-10 mm/yr; to the south, oceanic crust is subducted at 35-40 mm/yr. A broad zone of dextral shear (the Central Hellenic Shear Zone) divides the over-riding lithosphere into northern and southern segments. Geological reconstructions show that the Hellenic system formed a continuous thrust belt until late Miocene time and shallow water, presumably continental, lithosphere was subducted beneath the belt from ~30-10 Ma, at an average rate of 5-10 mm/yr. Atfter ~10 Ma, oceanic lithosphere entered the southern Hellenic trench while continental lithosphere continued to be subducted in the north. From ~10-0 Ma, the subduction rate increased to ~40 mm/yr in the southern Hellenides but remained largely unchanged in the north. Over the same period, the southern trench migrated 100 km southwest relative to the northern segment of the Hellenides, while the Kephalonia transform and the Central Hellenic Shear Zone experienced ~100 km of dextral shear, continuing today at ~25 mm/yr. Dynamic modeling shows that the increase in rate and magnitude of trench retreat in the southern Hellenides is consistent with entry of dense oceanic lithosphere into the southern trench at ~10 Ma, with the increased rate of retreat being due to the increasing density of the subducted slab. Thus the Hellenic system exhibits exhibits a spatial and a temporal variability in subduction that correlates closely with the density of subducting lithosphere and strongly indicates the major role of slab density in driving the subduction process and upper plate deformation.
DE: 8105 Continental margins and sedimentary basins
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting