Physical Modeling of Arc-Continent Collision: A Review of 2D, 3D, Purely Mechanical and Thermo‐Mechanical Experimental Models
Résumé
In this chapter we present a review of 2D, and 3D, purely mechanical and thermo‐mechanical experimental models of arc-continent collision obtained using the modeling technique pioneered by A. Chemenda. Also presented are earlier models of oceanic and continental subduction which led to the development of the arc-continent collision experiments. Physical models of continental subduction revealed the existence of two principal subduction regimes defined by the interplate pressure, which is inversely proportional to the slab pull‐force. In both high and low compression regimes, the subduction of a continental passive margin generates a horizontal compression of the overriding plate that can produce failure of the overriding plate in the arc area or near the back‐arc basin spreading center if the arc-continent collision was preceded by oceanic subduction in the extension regime. Failure of the overriding plate can lead to subduction reversal or the subduction of either the fore‐arc block or the entire arc plate. Evolutionary scenarios including subduction of the fore‐arc block have been proposed for Taiwan and the Urals, where the fore‐arc block is presently subducting or is missing. The scenario including the subduction of the arc plate with total or partial subduction/accretion of the arc crust fits the geological data of the Oman Mountains, the western Variscan belt and Kohistan‐Ladakh arc in western Himalaya. Although these modeling results correspond well to the geological data, it was purely mechanical and did not consider any change in the mechanical properties during subduction. In nature, however, both pressure and temperature increase with depth causing the strength of the subducting crust and mantle to be reduced by about one order of magnitude when reaching 100 km‐depth. Thermo‐mechanical laboratory experiments revealed that such strong change deeply affect the subduction and exhumation processes. In the low compression regime, subduction of the continental passive margin does not produce failure of the overriding plate in the arc area and the continental crust can only subduct to ~120 km‐depth in the asthenosphere. By then, it has become too hot and weak and undergoes large deformation, including upward ductile flow of the deeply subducted portions and a localized failure of the upper crust at depth of a few tens of kilometers allowing the buoyancy‐driven exhumation of a crustal slice in between the plates. In the high compression regime, the subducted continental crust reaches greater depth (~150-200 km), remaining relatively cold due to the subduction of the fore‐arc block or the arc plate that occurs in this regime. However, the exhumation of the deeply subducted continental crust that reached UHP/LT conditions does not occur in 2D models in the high compression subduction regime. Such exhumation has been obtained in 3D thermo‐mechanical laboratory experiments where the geometry of the interplate zone causes a local reduction of the interplate pressure, which in turn allows a local buoyancy‐driven exhumation of UHP/LT material.