HR: 1340h
AN: T53B-0496    [Abstracts]
TI: Dynamic Development of the Europe/Adria Plate Boundary During the Transition from Oceanic Subduction to Continental Collision in the Northern Apennines: a Case History for Subduction Erosion
AU: Bettelli, G
EM: bettelli.giuseppe@unimore.it
AF: Universita' di Modena e Reggio Emilia, Dipartimento di Scienze della Terra Largo S.Eufemia, 19, Modena, 41100 Italy
AU: Vannucchi, P
EM: paolav@geo.unifi.it
AF: Universita' di Firenze, Dipartimento di Scienze della Terra via La Pira, 4, Firenze, 50121 Italy
AU: * Remitti, F
EM: remitti.francesca@unimore.it
AF: Universita' di Modena e Reggio Emilia, Dipartimento di Scienze della Terra Largo S.Eufemia, 19, Modena, 41100 Italy
AB: In the Northern Apennines the dynamic of the margin frontal wedge during the Oligo-Miocene transition from oceanic subduction to continental collision is preserved in a chaotic complex called the Sestola Vidiciatico Unit. There, oceanic sedimentary rocks accreted and deformed within the Late Cretaceous to Late Eocene accretionary prism have been successively involved in the plate boundary through underthrusting in a process of rock recycling. The Sestola Vidiciato Unit is a less than 1 km thick rock unit containing both gravitational and tectonic components: the first being massive debris flows accumulated at the frontal part of the prism and the second slivers of the inactive accretionary prism usually disrupted and occurring as broken formations. The boundary between the debris flows and the broken formations are always tectonic. Also, the debris flows are typically in stratigraphic contact with the foredeep turbidites representing the incoming, continental plate, indicating that the decollement is not located at the frontal prism/incoming sediment boundary. The older deformation phase recorded in this complex unit is of widespread extension: the same structures are present at the top of the foredeep turbidites indicating how the Sestola Vidiciatico Unit has been deformed together with the rocks of the incoming plate and both have been involved in the footwall of the megathrust fault representing the plate boundary. As deeper parts of the system are approached the deformation changes from widespread extension to compression. At the same time of the Late Cretaceous to Late Eocene accretionary prism development and Oligo-Miocene formation of the Sestola Vidiciatico Unit, sediments had been accumulated on the upper plate slope. These sequences testify a general, stable deep water environment during the accretionary prism development. In the Early Miocene the slope basins are characterised by a regional unconformity, after which the sedimentation starts again with deepening upwards sequences (i.e. the Bismantova Group) testifying the occurrence of long term subsidence. The long term subsidence of the margin and the concomitant entrance of progressively thicker continental crust in the subduction zone may be compared to modern subduction zones where the entrance of aseismic ridges, for example, caused the switch from tectonic accretion to tectonic erosion. So, we interpret the Sestola-Vidiciatico Unit as the best candidate to represent the first case history of a fossil subduction channel formed in a tectonically erosive convergent margin.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting