OH-defects in quartz: application to igneous bodies and surface processes (2016-2021, FWF 29145)
Quartz is the second most abundant mineral in the Earth’s crust and an important constituent of many rock types. Primarily, quartz often crystallizes in water-bearing granitic systems, where the nominally anhydrous quartz incorporates water as defects in the crystal lattice. As the environmental conditions (e.g., pressure, temperature) change, the defects tend to adjust to the new conditions and, therefore, can be regarded as monitor/archive for the equilibration conditions. Although the water incorporation at elevated pressures (corresponding to 15-75 km depth) has partly been studied, detailed investigations at more relevant pressures (corresponding to 3-15 km depth) are hitherto missing and their performance is planned for this project. Different types of defects and their abundance will be characterised by structural (spectroscopic) and chemical analysis methods. In this respect, the chemical characterisation is of enormous importance, since traces of some specific metals foster the generation of defects.
Results from the experimental part of the project will be compared with quartz grains from two important rock types (granites and sandstones). Granitic bodies can reach a considerable size (up to many kilometres in all dimensions). In the course of the crystallisation its composition is modified, and with this the defects in the quartz crystals. Theses changes follow patterns that mirror the evolution of the granitic melt and potentially define characteristic trends. When the weathered material of granitic bodies is transported away by gravity, wind and water, quartz exhibits the highest chemical and mechanical resistivity amongst the abundant minerals, and, therefore, becomes one of the most abundant minerals in sedimentary rocks. Thus, with help of the knowledge gained from the experimental work and the findings from granites, the investigation of defects in quartz grains from sandstones can be applied as novel tool for provenance analysis.
Results:
Left: High pressure experiments show high concentrations of defect water at low pressure, with a local maximum around 5 kbar (corresponding to 15 km depth) and a tendency towards lower concentrations at higher pressure.
Right: OH-defects in young (0.3 Gyr) Variscan granites are one order of magnitude higher than in old (0.9-1.8 Gyr) Proterozoic granites from Scandinavia . The OH-content is reflected in recent sediments and Post-Variscan sedimentary rocks, showing a SW-NE gradation. In the 1.4 Gyr old sandstone from Dalarna/Sweden higher OH contents are preserved.
Publications:
Stalder, R. (2021) OH point defects in quartz – a review. European Journal of Mineralogy 33, 145-163
Potrafke, A., Breiter, K., Ludwig, T., Neuser, R.D., Stalder, R. (2020) Variations of OH defects and chemical impurities in quartz within igneous bodies. Physics and Chemistry of Minerals 47, 24
Potrafke, A., Stalder, R., Schmidt, B., Ludwig, T. (2019) OH-defect contents in quartz in a granitic system at 1-5 kbar. Contributions to Mineralogy and Petrology 174, 98
Stalder, R., von Eynatten, H., Costamoling, J., Potrafke, A., Dunkl, I., Meinhold, G. (2019) OH in detrital quartz grains as tool for provenance analysis: case studies on various settings from Cambrian to Recent. Sedimentary Geology 389, 121-126
Jaeger, D., Stalder, R., Masago, H., Strasser, M. (2019) OH defects in quartz as a provenance tool: Application to fluvial and deep marine sediments from SW Japan. Sedimentary Geology 388, 66-80
Stalder, R., Potrafke, A., Billström, K., Skogby, H., Meinhold, G., Gögele, C., Berberich, T. (2017) OH-defects in quartz as monitor for igneous, metamorphic and sedimentary processes. American Mineralogist 102, 1832-1842