Andrzej Kozłowski

Oxfordian neptunian dykes with brachiopods from the southern part of the Kraków-Częstochowa Upland (southern Poland) and their links to hydrothermal vents

Neptunian dykes with abundant brachiopods, cf. Lacunosella sp. and fragments of echinoderms, occur in Oxfordian limestones in the southern part of the Kraków-Częstochowa Upland. The dykes fill fissures that have opened in the massive limestones due to local extension of the sedimentary basin located along the northern, passive margin of the Tethys Ocean. These fissures transmitted warm hydrothermal solutions that controlled the mass growth of free-living bacteria and microbial mats feeding the fauna, mostly brachiopods and echinoderms, settling the seafloor around the fissures. For some time, the fissures remained empty and their vertical walls were settled by stromatolites. Infilling of the fissures was an abrupt event related to faulting in the Oxfordian and to the rejuvenation of dislocations cutting through the Paleozoic basement. Then, in the Cretaceous, and primarily in the Cenozoic, tectonic discontinuities filled with neptunian dykes were penetrated by karst waters and by hydrothermal solutions, which partly silicified the carbonate material infilling the dykes. The formation of dykes is genetically related to the Late Jurassic, Pan-European stress-field reorganization caused by the opening of the Northern Atlantic and Tethys Oceans.

Fluid inclusion study of epigenetic veinlets from the Carboniferous rocks of the Fore-Sudetic Monocline (southwest Poland)

Abstract Thermobarogeochemical investigations have been conducted on abundant veinlets that cut Carboniferous rocks of the Fore-Sudetic Monocline. Temperatures of the veinlet formation have been found to be relatively high, ranging mainly from 150° to 300°C. The results suggest that the paleogeothermal field of the Fore-Sudetic Monocline was generally uplifted. The actually observed positive geothermal anomaly of southwestern Poland overlaps the paleogeothermal one and is caused by a deep thermal disturbance on the contact of lithosphere and the upper mantle. This disturbance, of Variscan age, still produces remnant heat.

Geochemistry and mineralogy of Rotliegend metavolcanic mafic rocks from Poland: pervasive low-grade metamorphism versus parent rock signature

Abstract Permian volcanic rocks from the Gorzów Wielkopolski region (NW Poland), although pervasively altered by low-grade metamorphism, still preserve the geochemical characteristics of continental mafic volcanic rocks formed by partial melting of an enriched mantle source. The metamorphic assemblage comprises corrensite, pumpellyite, laumontite, quartz and chalcedony, albite, calcite and solid bitumen (major components). Petrological studies combined with microthermometric determinations indicate a low-pressure zeolite-greenschist-facies transitional zone metamorphic grade with a clockwise (pressure-temperature) P-T path: earliest event 140–210 °C and 630–760 bar; metamorphic peak 220–300 °C and 950 bar; youngest episode: T ⩾ 130 °C and 630–760 bar. The metamorphism of the Rotliegend volcanic rocks is generally ascribed to penetration of upwelling fluids released from clastic rocks underlying the extrusive Permian unit. However, the ubiquitous occurrence of anhydrite in the altered volcanic rocks suggests an influence of pore water from the overlying Zechstein evaporite sequence. The source of metamorphic heat can be tentatively assigned to abnormal heat flow and/or exothermic reactions during magmatic mineral alteration processes. Dating of metamorphism in neighbouring areas suggests an Upper Jurassic thermal event related to the upwelling of a mantle diapir during the initiation and early evolution of the North Atlantic rift.