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[SCG54-02] Effect of frictional heat on OSL signal of quartz: verification by short time heating experiments
Keywords:optically-stimulated luminescence, heating experiments, thermal annealing, friction heat, active fault
Recent studies have investigated to adapt optically stimulated luminescence (OSL) dating methods to the dating of faults. The conditions for resetting the OSL signal of quartz are being determined by friction experiments, and they noted that frictional heating affects the OSL signal decrease (Kim et al., 2019; Yang et al., 2019; Oohashi et al., 2020). However, in addition to frictional heating, physical factors such as friction and crushing occur in friction experiments. We investigated the effect of heat on the OSL signal behavior of quartz by short heating experiment.
The starting material is quartz particles with a grain size of 150-250 μm separated from beach sand near Maruo Port in Ube City, Yamaguchi Prefecture, with gamma rays of about 200 Gy accumulated. Quartz was heated using a graphite furnace (cuvette) in a polarized Zeeman atomic absorption spectrophotometer; this method is an improvement on the method proposed in Murakami. First, 0.005 g of quartz particles (equivalent to 250 particles) were dropped inside the cuvette, and then it was set in the instrument and heated. The temperature inside the cuvette was measured with an infrared thermography camera (NEC Avio Infrared Tecnologies Co, Ltd). The heating conditions were set to 200-500℃ for 3-75 s, based on the frictional heating temperatures, experimental times, and changes in the OSL signal in previous friction experiments. Although it takes a certain amount of time (approximately 10 seconds each) to raise and lower the temperature of the cuvette, the aforementioned experimental time does not include the time for raising and lowering the temperature.
OSL measurements were performed with 10 particles per aliquot, 4-10 aliquots for each heating condition. Changes in the OSL signal were compared using the OSL intensity Ln/Tn, where the main OSL intensity Ln is normalized by the OSL intensity Tn at the test dose of 10 Gy. The Ln/Tn of the unheated starting quartz was an average value of 9.70, with a minimum value of 2.39 and a maximum value of 15.51. The Ln/Tn average value of quartz heated at 200℃ decreased predominantly compared to that of the starting quartz, but there was little difference depending on the experimental time. The Ln/Tn average values of quartz heated at 250℃ and 350℃ became almost zero at experimental times of 10 seconds or longer. The Ln/Tn average value for quartz heated at 400℃ or higher was almost zero at all experimental time (3-10 s). A complete reset was determined when the main luminescence peak was predominantly lower than the starting quartz and the Ln/Tn mean value was almost zero within a standard deviation, while a partial reset was determined when the Ln/Tn mean value was not zero but predominantly lower than the starting quartz.
As a general trend, the OSL signal decreased with increasing heating temperature and heating time. A comparison of the temperature-time conditions for complete and partial resetting between the heating and friction experiments showed that the resetting conditions for both experiments were approximately the same. From these results, we concluded that frictional heating is the main cause of the OSL signal decrease in faulting. Therefore, if an OSL signal reset is observed in quartz sampled from a natural fault, the frictional heating temperatures of the fault can be estimated. When collecting quartz from natural faults, it is important to select coarse particles that are less affected by fracturing.
References
Kim, J.H., Ree, J.H., Choi, J.H., Chauhan, N., Hirose, T. and Kitamura, M. (2019) Experimental investigations on dating the last earthquake event using OSL signals of quartz from fault gouges. Tectonophysics, 769, 228191.
Murakami, M., Tagami, T. (2020) term heating experiments of mineral samples using graphite furnace. Fission Track News Letter, 33, 1-10.
Oohashi, K., Minomo, Y., Akasegawa, K., Hasebe, N., and Miura, K. (2020) Optically stimulated luminescence signal resetting of quartz gouge during subseismic to seismic frictional sliding: A case study using granite derived quartz. Journal of Geophysical Research: Solid Earth, 125, e2020JB019900.
Yang,H.L., Chen,J.,Yao,L.,Liu,C.R., Shimamoto,T. and Jobe,J.T.A. (2019) Resetting of OSL/TL/ESR signals by frictional heating in experimentally sheared quartz gouge at seismic slip rates. Quaternary Geochronology, 49, 52-56.
The starting material is quartz particles with a grain size of 150-250 μm separated from beach sand near Maruo Port in Ube City, Yamaguchi Prefecture, with gamma rays of about 200 Gy accumulated. Quartz was heated using a graphite furnace (cuvette) in a polarized Zeeman atomic absorption spectrophotometer; this method is an improvement on the method proposed in Murakami. First, 0.005 g of quartz particles (equivalent to 250 particles) were dropped inside the cuvette, and then it was set in the instrument and heated. The temperature inside the cuvette was measured with an infrared thermography camera (NEC Avio Infrared Tecnologies Co, Ltd). The heating conditions were set to 200-500℃ for 3-75 s, based on the frictional heating temperatures, experimental times, and changes in the OSL signal in previous friction experiments. Although it takes a certain amount of time (approximately 10 seconds each) to raise and lower the temperature of the cuvette, the aforementioned experimental time does not include the time for raising and lowering the temperature.
OSL measurements were performed with 10 particles per aliquot, 4-10 aliquots for each heating condition. Changes in the OSL signal were compared using the OSL intensity Ln/Tn, where the main OSL intensity Ln is normalized by the OSL intensity Tn at the test dose of 10 Gy. The Ln/Tn of the unheated starting quartz was an average value of 9.70, with a minimum value of 2.39 and a maximum value of 15.51. The Ln/Tn average value of quartz heated at 200℃ decreased predominantly compared to that of the starting quartz, but there was little difference depending on the experimental time. The Ln/Tn average values of quartz heated at 250℃ and 350℃ became almost zero at experimental times of 10 seconds or longer. The Ln/Tn average value for quartz heated at 400℃ or higher was almost zero at all experimental time (3-10 s). A complete reset was determined when the main luminescence peak was predominantly lower than the starting quartz and the Ln/Tn mean value was almost zero within a standard deviation, while a partial reset was determined when the Ln/Tn mean value was not zero but predominantly lower than the starting quartz.
As a general trend, the OSL signal decreased with increasing heating temperature and heating time. A comparison of the temperature-time conditions for complete and partial resetting between the heating and friction experiments showed that the resetting conditions for both experiments were approximately the same. From these results, we concluded that frictional heating is the main cause of the OSL signal decrease in faulting. Therefore, if an OSL signal reset is observed in quartz sampled from a natural fault, the frictional heating temperatures of the fault can be estimated. When collecting quartz from natural faults, it is important to select coarse particles that are less affected by fracturing.
References
Kim, J.H., Ree, J.H., Choi, J.H., Chauhan, N., Hirose, T. and Kitamura, M. (2019) Experimental investigations on dating the last earthquake event using OSL signals of quartz from fault gouges. Tectonophysics, 769, 228191.
Murakami, M., Tagami, T. (2020) term heating experiments of mineral samples using graphite furnace. Fission Track News Letter, 33, 1-10.
Oohashi, K., Minomo, Y., Akasegawa, K., Hasebe, N., and Miura, K. (2020) Optically stimulated luminescence signal resetting of quartz gouge during subseismic to seismic frictional sliding: A case study using granite derived quartz. Journal of Geophysical Research: Solid Earth, 125, e2020JB019900.
Yang,H.L., Chen,J.,Yao,L.,Liu,C.R., Shimamoto,T. and Jobe,J.T.A. (2019) Resetting of OSL/TL/ESR signals by frictional heating in experimentally sheared quartz gouge at seismic slip rates. Quaternary Geochronology, 49, 52-56.