The role of inherited orogenic structures on metamorphic core complex formation: a 3D numerical investigation

Continental metamorphic core complexes (MCCs) are almost exclusively found within orogens where both pervasive compression and extension processes occur. Previous 2-D models usually implement heterogeneities (e.g., thermal anomaly, preexisting faults, compositional variation) to investigate the formation of MCCs. However, these models fail to explain some intrinsically 3D structures, for example, the extensional orientation revealed by MCCs is not always perpendicular to the mountain trending. Although it is generally in agreement that orogenic imprints plays an important role in the architecture of lithospheric deformation, the influence of the inheritance on the formation of MCCs is not yet well understood. Here we apply high resolution visco-elasto-plastic numerical models to study the MCC formation during the late- to post-orogenic extension, emphasizing on the inherited structural influence. We found that the extensional mode is greatly affected by the strike and dip angle of the preexisting structural anomaly. Wide rift is favored by the scenario of mountain trending paralleled to extensional direction, in contrast, MCC is favored by orthogonal scenario. The domiform geometrical relationship between MCC elongation and the warping detachment is also controlled by the strike of this inheritance. Steep dipping fault/shear zone leads to the rolling-hinge detachment whereas gently dipping forms domino faulting. The model results highlight the key role of tectonically inherited heterogeneities on the formation of metamorphic core complex.