Accelerated subduction of the western Pacific Plate promotes the intracontinental uplift and magmatism in late Jurassic South China

Widespread fold and thrust belt and magmatism that occurred in the Mesozoic South China Block (SCB) have generated much debate on their dynamic mechanism related to the western Pacific Plate. Unlike a delayed Andean orogen, the SCB contains large areas of magmatic rocks coinciding with the absence of Upper Jurassic strata, which is not consistent with a flat-slab subduction geometry, and no consensus model has been suggested. To obtain more general insight into the effects of paleo-Pacific Plate subduction on the SCB, thermal-fluid-solid simulations of the subduction process are conducted. The models involved varied subduction rates and lithospheric viscosities to investigate their effect on the subduction style, mantle flow and overriding plate deformation. Low-rate subduction easily forms a subduction geometry with a higher angle, while high-rate subduction causes the slab to break off and drip downward. Fast subduction produces a quasi-horizontal mantle flow and a poloidal flow at the front of the mantle wedge, whereas slow subduction produces two poloidal flows developed on both sides of the subducting slab. The strain tensor of the overriding plate coincides well with the gradient of the horizontal mantle flow rate. A high subduction rate and low lithospheric viscosity promote the deformation of the overriding plate and are further attributed to mantle flow. Combining these results with global plate reconstructions, we find that accelerated subduction of the paleo-Pacific Plate resulted in the Late Jurassic uplift of the SCB. The low viscosity of the overriding plate caused by multiphase orogenic deformation promoted the thinning of the lithosphere due to induced mantle flow, which was associated with the intrusion of magmas and foundering of the subducted slab in a compressional regime. At the end of the Late Jurassic, subduction-induced mantle flow transformed from westward to eastward. Concurrently, the subducted slab began to steepen, and widespread Cretaceous magmatism occurred.

Automated summary

The accelerated subduction of the paleo-Pacific Plate resulted in the Late Jurassic uplift of the South China Block and widespread magmatism. The subduction rate and lithospheric viscosity affected mantle flow, overriding plate deformation, and the intrusion of magmas. Low-rate subduction formed a higher angle subduction geometry, while high-rate subduction caused slab break-off. Different subduction rates and lithospheric viscosities influenced mantle flow, overriding plate deformation, and magmatic activity.