Sealing of fluid pathways in overpressure cells: a case study from the Buntsandstein in the Lower Saxony Basin (NW Germany) |
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| Authors: | Sofie Nollet Christoph Hilgers Janos Urai |
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| Institution: | (1) Geologie-Endogene Dynamik, RWTH Aachen, Lochnerstr. 4-20, 52056 Aachen, Germany |
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| Abstract: | We studied veins in the Triassic Buntsandstein of the Lower Saxony Basin (NW Germany) with the aim of quantifying the evolution
of in-situ stress, fluids and material transport. Different generations of veins are observed. The first generation formed
in weakly consolidated rocks without a significant increase in fracture permeability and was filled syntectonically with fibrous
calcite and blocky to elongate-blocky quartz. The stable isotopic signature (δ18O and δ13C) indicates that the calcite veins precipitated from connate water at temperatures of 55–122°C. The second vein generation
was syntectonically filled with blocky anhydrite, which grew in open fractures. Fluid inclusions indicate that the anhydrite
veins precipitated at a minimum temperature of 150°C from hypersaline brines. Based on δ34S measurements, the source of the sulphate was found in the underlying Zechstein evaporites. The macro- and microstructures
indicate that all veins were formed during subsidence and that the anhydrite veins were formed under conditions of overpressure,
generated by inflation rather than non-equilibrium compaction. The large amount of fluids which are formed by the dehydrating
gypsum in the underlying Zechstein and are released into the Buntsandstein during progressive burial form a likely source
of overpressures and the anhydrite forming fluids. |
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| Keywords: | Veins Lower Saxony Basin overpressure |
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