Hazai képződményekből szeparált kvarcok jellemzői az OSL kormeghatározás szempontjából

The Optically Stimulated Luminescence (OSL) dating started in 2004 in the Geological Institute of Hungary, then continued in the successor Geological and Geophysical Institute of Hungary, and the Mining and Geological Survey of Hungary. Our OSL ages have contributed to the reconstructions of palaeohydrography and palaeomorphology as well as the timing of neotectonic movements and archaeological sites among others. Principally, quartz is used for dating because it is an abundant and resistant mineral of the sediments and it serves as a natural retrospective dosimeter that is trapping and storing charges in the point defects of its crystal lattice. During the dating of Upper Pleistocene and Holocene sediments, it has been recognised that the luminescence properties of quartz and its suitability for OSL dating show local differences. For example, in some places of Hungary, quartz has much dimmer luminescence than in other areas of the country, or it is saturated due to lower radioactive radiation, which makes OSL dating challenging. The aim of this study was to find the causes of these local differences. Quartz was separated from some plutonic, volcanic, metamorphic and older sedimentary rocks and sediments of Hungary, which can be source of some Upper Pleistocene and Holocene sediments in Hungary. Beside OSL measurements, for the detection of the chemical impurities that can cause defects in the crystal lattice, Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Micro-Fourier Transform Infrared Spectrometry (Micro-FTIR) and Infrared Spectrometry were applied. Thermal Analysis and X-Ray Diffraction were applied for the characterization of the quartz separates. The concentration of the radioactive elements in the studied formations was also determined based on laboratory High-Resolution Gamma-Ray Spectrometry. The results of the OSL measurements indicated that sediments, sedimentary rocks and some volcanic tuffs give brighter or more intensive luminescence than the quartz of the studied metamorphic and plutonic rocks. The quartz grains of only a few formations are appropriate for OSL dating if they get into the Pleistocene or Holocene sediments. They are solely sediments and sedimentary rocks, certain Upper-Miocene, Upper-Miocene–Pliocene and Upper-Oligocene sands of Kalla Gravel, Zagyva and Torokbalint Sandstone formations. The results of the LA-ICP-MS measurements indicated Li, Na, Al, P, K, Ti and Ba impurities in the quartz grains, while Micro-FTIR analysis detected coupled substitution of Al3++ H+ at the position of Si4+ incorporated as AlOH structural hydroxyl, and molecular water as well. These impurities partly are present in mineral phases, as clay minerals or smectite, and mica, according to the results of XRD, Thermal Analysis and Infrared Spectrometry. The causes of the local differences in luminescence properties of quartz grains and their suitability for OSL dating are probably their different source rocks, and diverse thermal and sedimentary history. The quartz grains that are originated directly from metamorphic and plutonic rocks by erosion show unfavourable OSL properties, probably because, during their long cooling period, they relax most of the point defects in their crystal lattice that were formed during their formation on high temperature. The OSL properties of the quartz grains of the sediments and sedimentary rocks are more favourable due to the repeated cycles of radioactive irradiation and the zeroing of the OSL in sunshine which increase the sensitivity of quartz.