Kinematic interpretation of the 3D shapes of metamorphic core complexes

Metamorphic Core Complexes form dome shaped structures in which the ductile crust is exhumed beneath a detachment fault. The 3D dome geometry, inferred by mapping the schistosity in the exhumed crust, can be either elongated normal to the stretching direction or along it. In the first case, the domes are interpreted as having formed during extension. However, in the second case, they are interpreted either as strike‐slip, transpressive or constrictive extensional structures, depending on the geodynamic context. Numerical models of metamorphic core complexes published to date are all two‐dimensional and therefore, theoretically only apply to domes which are elongated normal to the stretching direction. Here, we explore by means of 3D thermomechanical modeling, the impact of 3D kinematic extensional boundary conditions on the shape of metamorphic core complexes. We examine the impact of a transtensional step over and of horsetail splay fault kinematics on the dynamics of exhumation, finite strain and P‐T paths, and compare them to cylindrical 3D models. We show, for the first time, that domes formed in transtensional step over, or at the tip of propagating strike‐slip faults, display a finite strain field which can be interpreted as characteristic of a transpressive domes, although no shortening was applied in the far‐field. Applying our models to the Cyclades, we propose that the coeval formation of domes elongated normal and parallel to the stretching during the Miocene can be the result of horsetail splay fault kinematics, which could correspond to the formation of a tear in the Aegean slab.