HR: 1340h
AN: T13D-1980 INVITED [Abstracts]
TI: Continental Collision and the STEP-wise Evolution of Convergent Plate Boundaries: The Mediterranean Region
AU: * Wortel, M J
EM: wortel@geo.uu.nl
AF: Department of Earth Sciences, Utrecht University, PO Box 80021, Utrecht, 3508 TA,
Netherlands
AU: Govers, R
EM: govers@geo.uu.nl
AF: Department of Earth Sciences, Utrecht University, PO Box 80021, Utrecht, 3508 TA,
Netherlands
AU: Spakman, W
EM: wims@geo.uu.nl
AF: Department of Earth Sciences, Utrecht University, PO Box 80021, Utrecht, 3508 TA,
Netherlands
AB:
This contribution focusses on terminal stage subduction, often triggered by continent-continent or arc-
continent collision. The landlocked basin setting of the Mediterranean region provides unique opportunities
to study terminal stage subduction and its consequences.
We use seismic tomography results on lithosphere and upper mantle structure as a source of information on
plate boundary structure, and concentrate on the lithospheric scale aspects. Combining this structural
information with process-oriented numerical modelling studies and regional observations, we present a 3D
model for convergent plate boundary evolution after collision, in which slab detachment and the formation of
tear or STEP (Subduction-Transform-Edge-Propagator; see R. Govers and M.J.R. Wortel, EPSL, 236, 505-
523, 2005) faults are key elements. A STEP fault laterally decouples subducting lithosphere from non-
subducting lithosphere in a scissor type of fashion. It enhances the ability of a slab to retreat through the
mantle flow around the edge of the subducted slab. In this way collision and back-arc extension may occur in
close proximity. In our study area this specifically pertains to collision along the north African margin, STEP
formation in easterly direction, CCW rotation of the southern Apennines slab and the opening of the
Tyrrhenian Sea. Vertical tearing of subducted lithosphere may play an important role as well, but is probably
not crucial. Similar processes are likely to have occurred in the eastern Mediterranean. On the basis of the
good agreement between the Mediterranean-based model and the evolution of the Tonga-Fiji region we
expect that the model may shed light on other complex convergent plate boundary regions, as well.
In summary: Upon continental (or arc-continent) collision, along-trench variations in lithospheric properties of
the subducting lithosphere may lead to disruption and segmentation of the subduction system. Following slab
detachment along limited segments of a convergent plate boundary, the development of STEP faults is
expected. These faults contribute to an increase in arc curvature within plate boundary segments. This
contributes to the sinuous geometry of long subduction systems such as in the western and southwest Pacific.
DE: 8104 Continental margins: convergent
DE: 8106 Continental margins: transform
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2008 Fall Meeting