Flat Subduction Versus Big Mantle Wedge: Contrasting Modes for Deep Hydration and Overriding Craton Modification

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Abstract
Subduction‐induced deep hydration and water cycling may strongly control the modification of overriding cratonic lithosphere. Two contrasting modes are generally proposed: (1) flat subduction (FS) regime with slab subducting subhorizontally beneath the overriding lithosphere and (2) big mantle wedge (BMW) regime with slab flattening at the bottom of mantle transition zone. Here, systematic numerical models are built to study the subduction‐induced deep hydration processes in the contrasting FS and BMW regimes as well as their effects on the modification of overriding lithosphere. The model results indicate that the dehydration process in the FS regime can significantly modify the overriding lithosphere for a region of about 600 km from the trench. During the progressive flat subduction, the partial melting and magmatism migrate toward the inner land of the overriding plate, which will be reversed and backward to the trench during the transition from flat to steep slab subduction. On the other hand, the deep hydration in the BMW regime is strongly dependent on the subcrustal serpentinite layer in the subducting slab, whereas the oceanic crust cannot carry water to the transition zone. The modification of the overriding lithosphere in the BMW regime occurs in a larger region of >1,000 km from trench, which is, however, generally slower and weaker. Thus, the flat subduction of Izanagi plate may play a more significant role in the modification of North China Craton in the late Jurassic to early Cretaceous, which could be accompanied by the effects of deep water cycling in the BMW regime.
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Funding Information
  • Innovative Research Group Project of the National Natural Science Foundation of China (41688103)

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