IS THE PROPAGATION OF ARC-CONTINENT COLLISION A LINEAR PROCESS? INSIGHTS FROM 3D THERMO-MECHANICAL ANALOGUE EXPERIMENTS
Abstract
3D thermo-mechanical laboratory experiments of arc-continent collision are performed to investigate how this process propagates along the convergent plate boundary. We explore two scenarios that have proposed for this process when the continental subduction is in the high compression regime. In the first one, the collision is expected to propagate linearly along the subduction zone after an initial collision stage. The deformation of the upper plate is confined to the magmatic arc area where the lithosphere is thinned and weak. The magmatic arc lithosphere progressively fails as the collision propagates because of the convergence obliquity (of either the passive or active margin) and the fore-arc block is progressively subducted without large internal deformation. In the second scenario, the collision also generates the failure of the lithosphere in the arc area but this fault zone crosses the fore-arc, reaches the main subduction thrust and only a piece of the fore-arc is subducted at a time. As collision propagates laterally another piece of the fore-arc detaches and subducts. In this second scenario the propagation mechanism is therefore non-linear. Our 3D thermo-mechanical modeling allows testing these two hypotheses. The experimental results show that subduction of an oblique continental margin always produces the first scenario if the lithosphere in the magmatic arc is weaker than fore-arc block. Failure in the arc does not cut this lithospheric block but rather propagates along the weak arc where collision is not yet fully developed. This corresponds to the early failure observed in previous isothermal experiments. When the obliquity of the passive margin is 90°, the collision does not propagate laterally, but the failure of the magmatic arc lithosphere does spread outside the collision zone. It follows that the failure of the arc lithosphere just outside the collision zone is not driven by the frontal push but rather the lateral drag exerted by the fore-arc subducting in the collision zone. Experiments thus reveal that the failure in the arc and its subduction is fundamentally a three-dimensional process and therefore, 3D modeling technique is required to further investigate this process. However, the propagation of the deformation in the arc is linear after the initial collision stage and therefore, the space for time substitution remains valid.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T54B..08B
- Keywords:
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- 8104 TECTONOPHYSICS / Continental margins: convergent;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general