Microstructural evolution of deformation-modified primary halite from the Middle Triassic Röt Formation at Hengelo, The Netherlands |
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| Authors: | Zsolt Schléder János L Urai |
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| Institution: | (1) Geologie-Endogene Dynamik, RWTH Aachen, Lochnerstrasse 4-20, 52056 Aachen, Germany |
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| Abstract: | The microstructure of halite from the subhorizontal, bedded Main Röt Evaporite Member at Hengelo, The Netherlands (AKZO well 382, depth interval of 420–460 m), was studied by transmitted and reflected light microscopy of gamma-irradiation decorated samples. Primary microstructures compare favourably with those found in recent ephemeral salt pans. Large, blocky, fluid-inclusion-poor halite grains and elongated chevrons are interpreted to have formed in the saline lake stage, while void-filling clear halite is interpreted to have formed during the desiccation stage of the salt pan. In addition, in all layers the grains are rich in deformation-related substructures such as slip bands and subgrains indicating strains of a few percent. The study of gamma-irradiation decorated thin sections shows that the main recrystallization mechanism is grain boundary migration. Grain boundary migration removes primary fluid inclusions and produces clear, strain-free new grains. Differential stresses as determined by subgrain size piezometry were 0.45–0.97 MPa. The deformation of the salt layers is probably related to Cretaceous inversion in the area. |
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| Keywords: | Hengelo (The Netherlands) Triassic bedded rock salt Synsedimentary structures Deformation microstructures Recrystallization |
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