Numerical modeling of metamorphic core complex formation: Implications for the destruction of the North China Craton

Gang Lu,Liang Zhao,Jianfeng Yang,Ziqi Ma

doi:10.26464/epp2022016

Abstract

Widespread magmatism, metamorphic core complexes (MCCs), and significant lithospheric thinning occurred during the Mesozoic in the North China Craton (NCC). It has been suggested that the coeval exhumation of MCCs with uniform northwest-southeast shear senses and magmatism probably resulted from a decratonization event during the retreat of the paleo-Pacific Plate. Here we used two-dimensional finite element thermomechanical numerical models to investigate critical parameters controlling the formation of MCCs under far-field extensional stress. We observed three end-member deformation modes: the MCC mode, the symmetric-dome mode, and the pure-shear mode. The MCC mode requires a Moho temperature of ≥700 °C and an extensional strain rate of ≥5 × 10<sup>−16</sup> s<sup>−1</sup>, implying that the lithosphere had already thinned when the MCC was formed in the Mesozoic. Considering that the widespread MCCs have the same northwest-southeast extension direction in the NCC, we suggest that the MCCs are surface expressions of both large-scale extension and craton destruction and that rollback of the paleo-Pacific slab might be the common driving force.

Highlights

Metamorphic core complex (MCC) is a domal or arched structure characterized by three main features (Brun et al, 2018; Lin W & Wei W, 2020; Platt et al, 2014; Whitney et al, 2013): 1) a large-offset low-angle (< 30°) detachment fault, 2) direct contact of the brittle upper crust and ductile lower crust, 3) domal structure of the metamorphic core exhumed at the surface
Three end-member deformation modes are observed: i) metamorphic core complexes (MCCs) mode characterized by the formation of a low-angle detachment fault and fast exhumation of the lower crust material; ii) symmetric-dome mode characterized by the slow uplift of the lower crustal material without detachment fault; iii) pure-shear mode with uniform crustal extension
We suggest that far-field extensional stress resulting from trench retreat of the paleo-Pacific slab is a plausible mechanism for MCC formation and magmatism during the Mesozoic and a reasonable driving force for the North China Craton (NCC) destruction

Summary

Introduction

Metamorphic core complex (MCC) is a domal or arched structure characterized by three main features (Brun et al, 2018; Lin W & Wei W, 2020; Platt et al, 2014; Whitney et al, 2013): 1) a large-offset low-angle (< 30°) detachment fault, 2) direct contact of the brittle upper crust and ductile lower crust, 3) domal structure of the metamorphic core exhumed at the surface. Since their identification in Cordillera (Coney, 1980; Davis & Coney, 1979), MCCs soon caught geologists’. Various factors responsible for MCC formation have been proposed: (1) strain localization that accounts for the low-angle deflection of the detachment fault (Lavier et al, 1999, 2000); (2) temperature rise and partial melting (Buck, 1991; Rey et al, 2009b, 2009a; Tirel et al, 2008; Wang K et al, 2015); (3) thickened crust (Buck, 1991; Tirel et al, 2008);

Results

Discussion

Conclusion