Sedimentary record of Variscan unroofing of the Bohemian Massif

Abstract

The Bohemian Massif in the eastern Variscan Orogen is the host of globally significant ultrahigh-pressure metamorphic rock suites that experienced enigmatic unroofing processes. In the eastern Bohemian Massif, the Moravosilesian Culm Basin (The Czech Republic) with ≤7.5 km thick Lower Carboniferous siliciclastic turbidities has recorded crustal unroofing associated with the late Paleozoic amalgamation of Gondwana and Laurussia. This study presents data from sandstone petrography, heavy mineral assemblages, and detrital zircon U-Pb geochronology from Moravosilesian Culm sediments. Sandstone modal compositions imply continental/recycled orogen affinities. High-grade metamorphic lithic fragments and high garnet contents in upper Culm sediments indicate the exhumation of the middle to lower crustal materials, consistent with those of the Bohemian Massif. Detrital zircon U-Pb data constrain maximum depositional ages of sediments in the Drahany Upland to 335–326 Ma (late Viséan–middle Serpukhovian). Detrital, igneous and metamorphic zircon U-Pb data compiled from surrounding regions support that source regions for lower Culm sediments (Moldanubian Unit and Sudetes) remained the same. Whereas, upper Myslejovice sediments might have derived from exhumation and erosion of the root of the Moldanubian Unit and/or Moravosilesian Nappes. Rapid exhumation of the Moldanubian Unit within the Bohemian Massif during the deposition of upper Culm sediments is inferred.