13:45 〜 14:00
[MIS17-01] RockEvalによる有機物の熱分解・酸化を用いた短時間発熱の検出
キーワード：黄鉄鉱、ロックエバル
To examine the dynamics of earthquakes and/or magma-intrusion processes, it is important to have methods that can detect short-time heating generated by frictional heating along faults and/or caused by the metamorphic aureoles of igneous intrusions. During the last decade, frictional heating within fault zones was mainly examined by measurements of vitrinite reflectance, which in turn were understood using models of thermal maturation developed for oil exploration. However, short-duration heating phenomena within fault zones occurs at much higher temperatures (~1000℃ cf. 120℃) and generally over a much shorter time (a few to 106 seconds compared to 106 years). Thus, models of thermal maturation are being applied far outside of the ranges used for oil exploration and the ranges in which the models are most-tested. New-types of geothermometers developed for short-duration and high-temperature are required. Here, we present preliminary results from trials, that indicate that both the pyrolysis and oxidation measurements made by RockEval can detect short-duration heating as well as more typical longer duration heating environments. Especially, S2 (hydrocarbon parameter), S4CO2 (residual organic carbon), and total sulfur should be promising candidates. A major update of this presentation is measurement of organic/inorganic sulfur using RockEval-7S (Vinci Technologies).
To examine the feasibility of these parameters especially for short-duration heating, we applied the RockEval measurements for (1) the samples collected from the outcrop representing a minor diorite dykes (1.5 m width) and (2) the samples heated up in the laboratory experiments.
(1) was taken from the uppermost Miocene to Pliocene trench-fill sediments central Japan, allowed the demarcation of a thermal aureole around minor diorite dykes. Measurements along transects normal to the dyke showed varied trends in which S2, S4CO2, and total sulfur decreased with increased proximity to the contact.
(2) To understand field observations, unaltered samples of mudstone and samples of IFP 160000 standard were subjected to thermal decomposition by pyrolysis or oxidation. Samples for pyrolysis were enclosed in copper tubes under a nitrogen atmosphere and sealed, oxidation was done in open copper containers. Experiments were performed under isothermal conditions with varied durations of heating (300℃ and 102 to 106 seconds) or heated at temperatures ranging from 200-600℃ for 103 seconds. Based on experiments S2 was observed to rapidly decrease on heating, S4CO2 only decreased under oxidation. Interestingly, under heating to 300℃, total sulfur only decreased under pyrolysis when the duration is longer than 104 seconds while no change under oxidation since oxygen prevents reduction of sulfur. However, on the other hand, when the samples were heated up >~400-500℃ for 103 seconds, total sulfur was decreased under both pyrolysis and oxidation.
Therefore, decrements of S2 and total sulfur with constant S4CO2 for short-time laboratory heating at high temperature infers heating in an oxygen-free environment where only pyrolysis occurs. On the other hand, for short-time heating in the outcrop, decrements of S4CO2 indicates heating in the presence of oxygen (>~400℃). Oxygen within mudstones adjacent to intrusions may be released by breakdown of porewater leading to formation of hydrogen. For the next vision, we are now conducting the heating experiments under supercritical water condition, because “supercritical underwater combustion” is one of the candidates which may occur around the intrusion in the outcrop.
To examine the feasibility of these parameters especially for short-duration heating, we applied the RockEval measurements for (1) the samples collected from the outcrop representing a minor diorite dykes (1.5 m width) and (2) the samples heated up in the laboratory experiments.
(1) was taken from the uppermost Miocene to Pliocene trench-fill sediments central Japan, allowed the demarcation of a thermal aureole around minor diorite dykes. Measurements along transects normal to the dyke showed varied trends in which S2, S4CO2, and total sulfur decreased with increased proximity to the contact.
(2) To understand field observations, unaltered samples of mudstone and samples of IFP 160000 standard were subjected to thermal decomposition by pyrolysis or oxidation. Samples for pyrolysis were enclosed in copper tubes under a nitrogen atmosphere and sealed, oxidation was done in open copper containers. Experiments were performed under isothermal conditions with varied durations of heating (300℃ and 102 to 106 seconds) or heated at temperatures ranging from 200-600℃ for 103 seconds. Based on experiments S2 was observed to rapidly decrease on heating, S4CO2 only decreased under oxidation. Interestingly, under heating to 300℃, total sulfur only decreased under pyrolysis when the duration is longer than 104 seconds while no change under oxidation since oxygen prevents reduction of sulfur. However, on the other hand, when the samples were heated up >~400-500℃ for 103 seconds, total sulfur was decreased under both pyrolysis and oxidation.
Therefore, decrements of S2 and total sulfur with constant S4CO2 for short-time laboratory heating at high temperature infers heating in an oxygen-free environment where only pyrolysis occurs. On the other hand, for short-time heating in the outcrop, decrements of S4CO2 indicates heating in the presence of oxygen (>~400℃). Oxygen within mudstones adjacent to intrusions may be released by breakdown of porewater leading to formation of hydrogen. For the next vision, we are now conducting the heating experiments under supercritical water condition, because “supercritical underwater combustion” is one of the candidates which may occur around the intrusion in the outcrop.