Tectonic and Volcanic Controls on Hydrothermal Silicification in Marginal Zones of the Ohře Rift

Near-contact silicification as a product of hydrothermal alteration is associated with intrusive and effusive volcanic bodies in the marginal zones of the Ohře Rift. This process affects rocks of the sedimentary fill of Tertiary basins in this region (Oligocene to Miocene), rocks in their basement, as well as Upper Cretaceous sediments in shoulder blocks of the rift. Besides the near-contact zones, silicification also concentrates to tectonic structures functioning as transport paths for hydrothermal fluids. Elevated temperatures and alkalinity of the fluids resulted in dissolution and transport of silica, and its re-precipitation in the form of opal, chalcedony, moganite and quartz. Petrographic, chemical and isotope study of mineral successions related to silicification and other forms of coeval young mineralization (ferruginization, fluoritization, baritization) permits to determine the evolution of physico-chemical properties of the transport fluids in time. In a specific basin, hydraulic functions of different basinal structures can be thus deciphered. The project contributes to the understanding of factors controlling the cementation of detrital sediments in rift-basin settings.