Palaeo-thermal history of the Blanice Graben (the Bohemian Massif, Czech Republic): The origin of anthracite in a late-Variscan strike-slip basin

0565004 - ÚJF 2023 RIV NL eng J - Journal Article
Suchý, Václav - Zachariáš, J. - Sýkorová, Ivana - Kořínková, Dagmar - Pešek, J. - Pachnerová Brabcová, Kateřina - Luo, Q. -Y. - Filip, Jiří - Světlík, Ivo
Palaeo-thermal history of the Blanice Graben (the Bohemian Massif, Czech Republic): The origin of anthracite in a late-Variscan strike-slip basin.
International Journal of Coal Geology. Roč. 263, NOV (2022), č. článku 104129. ISSN 0166-5162. E-ISSN 1872-7840
R&D Projects: GA MŠMT EF16_019/0000728
Institutional support: RVO:61389005 ; RVO:67985891 ; RVO:67985831
Keywords : Coalification * Heat flow * Palaeofluids * Frictional heating * Hydrothermal alteration * Chlorite thermometry
OECD category: Geology; Geology (USMH-B); Geology (GLU-S)
Impact factor: 5.6, year: 2022
Method of publishing: Limited access
https://doi.org/10.1016/j.coal.2022.104129

Coal petrology data and vitrinite reflectance modelling were combined with micro-geochemical and fluid inclusion analyses of coal mineralization and apatite fission track analysis (AFTA) of coal-bearing sediments to constrain the thermal history of the Blanice Graben, a narrow, nearly 150-km long, late-Variscan strike-slip basin filled with Permo-Carboniferous continental coal-bearing deposits. The vitrinite reflectance modelling and the ranking of coals, which increased along the meridional axis of the graben from bituminous coals (Rr - 0.70%) to high-rank anthracites (Rr = 2.85-4.77%), provide evidence of maximum palaeo-temperatures ranging from about 120-145 degrees C to 310-390 degrees C. This corresponds to the diagenetic realm in the north of the graben that graded to high-grade anchizonal to low-epizonal metamorphic conditions in the south. The present level of coalification resulted from the Permian burial, 2500-5000 m thick, which aggregated under a high geothermal gradient (90 degrees C/km). In central and southern relics of the graben, however, specific microscopic features of coals and fluid inclusion and chlorite thermometry suggest that the anthracite rank was attained by the combined effect of a stratigraphic burial, a regional discharge of -300 degrees C hot, mineralized fluids that ascended along faults into buried coal-bearing strata and an intense Permian faulting and shearing of coal seams, which collectively contributed to the anthracitization process. The heat source, promoting high geothermal gradient and circulation of hot fluids through the coal-bearing sediments, was probably associated with a mantle magma chamber hidden deeply below the graben and manifested at current errosional level by -303 and - 270 Ma old microdiorite dykes. Similar dramatic geothermal settings, characterized by elevated geothermal gradients, localized faultcontrolled incursions of hot hydrothermal solutions, and rapid coalification of peat layers at relatively shallow depths of burial, dominated in many late Variscan coal-bearing basins during a period of post-collisional extension at -315-280 Ma. The AFTA method, applied to sedimentary apatites, provides evidence that following the climax of the Variscan orogeny, the Blanice Graben coal-bearing deposits were rapidly uplifted and, throughout the Mesozoic and Cenozoic times, they experienced only prolonged slow cooling (0.46-0.54 degrees C/My) and moderate burial temperatures of 50-70 degrees C. Its final ascent towards the present-day erosional surface occurred during a period of accelerated uplift that has affected the Bohemian Massif since the Oligocene.
Permanent Link: https://hdl.handle.net/11104/0336572