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King, G.*; Bartz, M.*; Bossin, L.*; Wen, X.*; 塚本 すみ子*; Herman, F.*; 小形 学; 末岡 茂
no journal, ,
Electron spin resonance dating of quartz minerals offers a significant advantage over luminescence dating because of its later signal saturation. We are seeking to exploit this to build upon earlier studies in the development of a thermochronometry system capable of resolving rock cooling rates throughout the Quaternary. In order to determine a rock cooling history, it is necessary to constrain both signal accumulation and signal thermal loss robustly within the laboratory. We have collated a series of geological samples including rocks from boreholes that have known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany). Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable.
King, G. E.*; Wen, X.*; Bartz, M.*; Anderson, L.*; Bossin, L.*; 塚本 すみ子*; Li, Y.*; Herman, F.*; 小形 学; 末岡 茂
no journal, ,
To determine a rock cooling history using ESR thermochronometry, signal accumulation and signal thermal loss must be robustly determined within the laboratory. We have collected a series of geological samples including rocks from boreholes that have known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany) as well as samples from Sion in the Western European Alps. Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable. Whereas the Al-centre of some samples exhibits linear dose response to laboratory irradiation up to 15 kGy, the Al-centre of other samples exhibits exponential, or double exponential growth and saturates at doses of 3-4 kGy. The Ti-centre of most samples is well described by a single saturating exponential function, however samples from the MIZ1 borehole exhibit pronounced sub-linearity in the low-dose response region. Furthermore, whereas for some samples the Al-centre is less thermally stable than the Ti-centre, for other samples the inverse is observed. These observations suggest that a uniform measurement protocol and data-fitting approach may not be appropriate for quartz ESR data. Inversion of two KTB samples yielded temperatures within uncertainty of borehole temperature, however results for the MIZ1 borehole are more variable and can only recover temperature at best within c.a. 10%. Investigations into the cause of the poor results for the MIZ1 borehole are ongoing (i.e. measurement protocol, data-fitting/numerical model) and will be discussed. Preliminary data from Sion are promising and reveal consistent cooling rates.
King, G. E.*; Wen, X.*; Bartz, M.*; Bossin, L.*; 塚本 すみ子*; Li, Y.*; Herman, F.*; 小形 学; 末岡 茂
no journal, ,
Whereas the luminescence thermochronometry system is limited to areas experiencing very rapid rock cooling (exhumation) of 10s of mm/yr, our data indicate that ESR thermochronometry can resolve rates of 1 mm/yr over Quaternary timescales. To determine a rock cooling history using ESR thermochronometry, signal accumulation and signal thermal loss must be robustly determined within the laboratory. We have collected a series of borehole samples with known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models by using the ESR-thermochronometry method to recover their known in-situ temperatures. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany). Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable. Whereas the Al-centre of some samples exhibits linear dose response to laboratory irradiation up to 15 kGy, the Al-centre of other samples exhibits exponential, or double-exponential growth and saturates at doses of 3-4 kGy. The Ti-centre of most samples is well described by a single saturating exponential function, however samples from the MIZ1 borehole exhibit pronounced sublinearity in the low-dose response region. Furthermore, whereas for some samples the Al-centre is less thermally stable than the Ti-centre, for other samples the inverse is observed. These observations suggest that a uniform measurement protocol and data-fitting approach may not be appropriate for quartz ESR data.