Numerical modeling of magmatism and metamorphic core complex formation in the North China Craton

Abstract:

The widespread magmatism, development of metamorphic core complexes (MCCs), together with significant lithospheric thinning in the North China Craton (NCC) during Mesozoic, is indicative of craton destruction or decratonization. It has been suggested that the coeval exhumation of MCCs is probably linked to the decratonization event during paleo-Pacific Plate retreat. An outstanding analogy is the Aegean MCCs which is contributed to Hellenic slab roll-back. Therefore, the understanding of MCCs is an important clue to decipher the mechanism of decratonization. Here we implement finite element thermomechanical numerical models to systematically study the lithospheric deformation and MCC formation at the back-arc extension resulting from the rollback of the paleo-Pacific Plate. Our first-stage models focus on the development of MCCs and the detachment faults. The results show that asymmetric MCC with low-angle normal faults develop with strong strain weakening mechanism. Furthermore, the presence of lower crustal melting could facilitate the rolling hinge expressed MCC and promote the rotation of the detachment fault that decreases its angle down to nearly horizontal over time. The development of detachment fault is also shown to depend critically on background extension rate and Moho temperature in the absence of melt. Higher extension rate and Moho temperature leads to faster exhumation of lower crust and high-dip faults. The involvement of asthenosphere partial melting to the lower crust probably supplies the major heat source. The far-field extension further promotes decompression melting, lithosphere thinning and MCC exhumation. Thereby the destruction of the NCC likely results from asthenospheric melting due to dehydration of paleo-Pacific Plate and its slab rollback.