Formation of elongated granite–migmatite domes as isostatic accommodation structures in collisional orogens
Abstrakt
The mid-Carboniferous Pelhrimov core complex, Bohemian Massif, is a crustal-scale elongated granite-migmatite dome interpreted to have formed by gravity-driven diapiric upwelling of the metapelitic middle crust. The vertical diapiric flow is evidenced by outward-dipping foliation and lineation patterns, deformation coeval with the widespread presence of melt, rapid exhumation of the dome center from depths corresponding to pressure of about 0.6 GPa to shallow levels (pressure less than 0.2 GPa) within 2 M.y., and kinematic indicators of downward return flow of the mantling rocks.
As compared to common diapirs, however, the Pelhrimov complex exhibits a more complicated inferred strain pattern with two perpendicular, irregularly alternating directions of horizontal extension in what is interpreted as the diapir head. Comparison of structural data from migmatites with anisotropy of magnetic susceptibility (AMS) data in granites also reveals that only final increments of strain are recorded in the granites.
The map dimensions and gravity image of the, complex suggest that the diapiric upwelling affected a large portion of the orogen's interior between two microplates brought together during continental collision.