The generation of voluminous S-type granites in the Moldanubian unit, Bohemian Massif, by rapid isothermal exhumation of the metapelitic middle crust
Abstract
This paper presents new structural, anisotropy of magnetic susceptibility (AMS), petrological, and geochronological data to examine the link between LP-HT metamorphism and S-type granite formation in the Moldanubian unit, Bohemian Massif. We first describe the intrusive relationships of an S-type granite to its host cordierite-bearing migmatites, superbly exposed in the Racov locality, northeastern Moldanubian batholith.
The knife-sharp contacts and rectangular stoped blocks establish that the migmatites cooled and were exhumed above the brittle-ductile transition prior to the granite emplacement. The U-Pb monazite geochronology combined with P-T estimations constrain the age and depth of migmatization at similar to 329 Ma and similar to 21 km (T approximate to 730 degrees C).
The migmatite complex was then exhumed at a rate of 6-7 mm y(-1) to a depth of {9 km where it was intruded by the granite at similar to 327 Ma. These data indicate that the hot fertile metapelitic middle crust in this part of the Moldanubian unit, newly defined as the Pelhrimov complex, underwent rapid isothermal decompression at similar to 329-327 Ma, giving rise to biotite melting and generation of large volumes of S-type granite magma.