Noriyoshi Tsuchiya

Petrography and uplift history of the Quaternary Takidani Granodiorite: could it have hosted a supercritical (HDR) geothermal reservoir?

Abstract The Quaternary Takidani Granodiorite (Japan Alps) is analogous to the type of deep-seated (3–5 km deep) intrusive-hosted fracture network system that might support (supercritical) hot dry/wet rock (HDR/HWR) energy extraction. The I-type Takidani Granodiorite comprises: porphyritic granodiorite, porphyritic granite, biotite-hornblende granodiorite, hornblende-biotite granodiorite, biotite-hornblende granite and biotite granite facies; the intrusion has a reverse chemical zonation, characterized by >70 wt% SiO2 at its inferred margin and 600°C, hypersaline (∼35 wt% NaCleq) fluids of magmatic origin, with inferred minimum pressures of formation being ∼600–750 bar, which corresponds to fluid entrapment at ∼2.4–3.0 km depth. Al-in-hornblende geobarometry indicates that hornblende crystallization occurred at about 1.45 Ma (7.7–9.4 km depth) in the (marginal) eastern Takidani Granodiorite, but later (at ∼1.25 Ma) and shallower (∼6.5–7.0 km) near the core of the intrusion. The average rate of uplift across the Takidani Granodiorite from the time of hornblende crystallization has been 5.1–5.9 mm/yr (although uplift was about 7.5 mm/yr prior to ∼1.2 Ma), which is faster than average uplift rates in the Japan Alps (∼3 mm/yr during the last 2 million years). A temperature–depth–time window, when the Takidani Granodiorite had potential to host an HDR system, would have been when the internal temperature of the intrusive was cooling from 500°C to ∼400°C. Taking into account the initial (7.5 mm/yr) rate of uplift and effects of erosion, an optimal temperature–time–depth window is proposed: for 500°C at 1.54–1.57 Ma and ∼5.2±0.9 km (drilling) depth; and 400°C at 1.36–1.38 Ma and ∼3.3±0.8 km (drilling) depth, which is within the capabilities of modern drilling technologies, and similar to measured temperature–depth profiles in other active hydrothermal systems (e.g. at Kakkonda, Japan).

Velocity of vertical fluid ascent within vein-forming fractures

Quartz-albite-calcite veins in metamorphic rocks of the Sanbagawa belt, Japan, contain sugary mosaics of equant quartz grains <0.01–1.6 mm in size (blocky texture). The quartz crystals show euhed ral to subhedral double-terminated crystal shape, and concentric growth zoning, indicating suspension in aqueous fluid during crystal growth until formation of a framework within the crack. Such a crystallization process is only possible when downward crystal settling is balanced by upward fluid flow. Application of crystal settling theory to the crystal size distributions within the veins reveals an extremely high rate of fluid ascent during blocky vein formation (10−2 to 10−1 m/s) due to the low viscosity of the hydrothermal fluid (~10−4 Pa·s). Such a high rate of ascent suggests the injection of fluids from mobile hydrofractures within deeper levels of the subduction zone.

Determination of total contents of bromine, iodine and several trace elements in soil by polarizing energy-dispersive X-ray fluorescence spectrometry

A non-destructive analysis method for total bromine (Br) and iodine (I) contents in soil was established using polarizing energy-dispersive X-ray fluorescence (EDXRF) spectrometry. The matrix-corrected intensity of Br and I Kα X-rays from pressed pellets of soil powder samples was calibrated with their contents measured by inductively coupled plasma (ICP)-mass spectrometry after pyrohydrolysis preparation. The calibration curves for Br and I were successfully obtained in the concentration ranges 3.8–223 mg kg−1 and 0.91–54 mg kg−1 respectively. Repeated analyses of the same sample with polarizing EDXRF spectrometry within one day and after approximately 1.5 years showed good reproducibility of the measurement results. The lower limits of detection for Br and I were 0.14 mg kg−1and 0.34 mg kg−1 respectively. The established analytical method for total Br and I contents in soil is non-destructive, simple and rapid, and is suitable for routine analysis. Trace elements such as rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), cadmium (Cd), tin (Sn), antimony (Sb), caesium (Cs), barium (Ba), light rare earth elements and lead (Pb) were also measurable simultaneously under the identical operational conditions as those for Br and I measurements.

Rapid simultaneous multi-element determination of soils and environmental samples with polarizing energy dispersive X-ray fluorescence (EDXRF) spectrometry using pressed powder pellets.

Abstract A rapid simultaneous multi-element analysis method for soils and environmental samples has been established using polarizing energy dispersive X-ray fluorescence (EDXRF) spectrometry. The pressed powder pellet technique was adopted because it is simple and requires no specialized skills for sample preparation. The analytes examined were: Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, MnO, Fe2O3, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Pb and Th. Twenty-six reference samples were used for the calibrations. Compton scatter radiation was used as an internal standard to compensate for variations in the sample matrix, particle size, packing density and operating characteristics of the instrument. The correlation coefficients of the linear regression lines were >0.98, with the exception of Na2O, MgO, Al2O3, SiO2, P2O5, Co, Pr and Nd. The values obtained using the proposed EDXRF spectrometry were compared with the values obtained using other methods. Out of the 31 analytes examined, the results for 12 compounds (CaO, K2O, TiO2, MnO, Fe2O3, Ni, Zn, Rb, Sr, Cs, Ba and Ce) obtained by the proposed EDXRF spectrometry compared favorably with those determined through conventional wet chemical methods. In contrast, the results for eight compounds (Na2O, MgO, Cr, Co, Zr, Sn, Sb and Pr) obtained by the proposed EDXRF spectrometry exhibited poor agreements with those obtained using chemical methods. Among these analytes, the poor agreements of Cr, Zr and Sn were attributable to incomplete dissolution and/or volatilization losses during the chemical treatments based on an acid attack. It can be concluded, therefore, that there is a high possibility of underestimating the concentrations of these elements if wet chemical methods are used. Although the results of the other 11 analytes were not as good as those of the first group, they still appeared to be of practical use, considering the time consuming and potentially hazardous wet chemical pretreatment.

Machine-learning techniques for geochemical discrimination of 2011 Tohoku tsunami deposits

Geochemical discrimination has recently been recognised as a potentially useful proxy for identifying tsunami deposits in addition to classical proxies such as sedimentological and micropalaeontological evidence. However, difficulties remain because it is unclear which elements best discriminate between tsunami and non-tsunami deposits. Herein, we propose a mathematical methodology for the geochemical discrimination of tsunami deposits using machine-learning techniques. The proposed method can determine the appropriate combinations of elements and the precise discrimination plane that best discerns tsunami deposits from non-tsunami deposits in high-dimensional compositional space through the use of data sets of bulk composition that have been categorised as tsunami or non-tsunami sediments. We applied this method to the 2011 Tohoku tsunami and to background marine sedimentary rocks. After an exhaustive search of all 262,144 (= 218) combinations of the 18 analysed elements, we observed several tens of combinations with discrimination rates higher than 99.0%. The analytical results show that elements such as Ca and several heavy-metal elements are important for discriminating tsunami deposits from marine sedimentary rocks. These elements are considered to reflect the formation mechanism and origin of the tsunami deposits. The proposed methodology has the potential to aid in the identification of past tsunamis by using other tsunami proxies.

Parallelepiped cooling joint and anisotropy of P-wave velocity in the Takidani granitoid, Japan Alps

Correlations between anisotropy of joint systems and physical rock properties, particularly P-wave velocities, were investigated. Characterization of fracture networks in the Takidani granitoid (Japan Alps) was obtained by field observation and laboratory measurement of P-wave velocities. Three preferred joint sets with no shear displacement were identified, and their directions change and spacing progressively increases from the margin to the center of the pluton. The azimuthal variation of P-wave velocity (Vp) is minimal perpendicular to one of the preferred joint orientations. The orientation of microcracks observed at grain scale and joints at outcrop scale show a good correlation. Vp and the preferred orientation of microcracks are in harmony with anisotropy of the joint system, allowing reconstruction of the joint structure in the Takidani granitoid. Thus we were able to evaluate joint anisotropy in terms of Vp anisotropy.

Distribution coefficients (K d) of stable iodine in estuarine and coastal regions, Japan, and their relationship to salinity and organic carbon in sediments

The sediment–water distribution coefficient, Kd, is one of the most important parameters in radionuclide assessment models. In this study, we determined Kds of stable iodine (I) in estuarine and coastal regions. We studied 16 estuarine and coastal regions of Japan and obtained I data on water and sediments. Data on salinity, pH, dissolved organic carbon and dissolved oxygen in water, and organic carbon (OC) in sediments were also obtained as estuarine variables. Determined Kds of I in the Sagami River estuary decreased along the salinity gradient (salinity range, 0.1–33.8), indicating that salinity is one of the important factors controlling the Kd values; however, when the Kd values were compared among all the estuaries, the difference between minimum and maximum Kd values varied by about two orders of magnitude in a narrow salinity range of 30.0–34.4. A significant correlation between Kd value and OC content in sediments was observed in all the stations with a salinity of ≥30 except for stations in the Ishikari and Onga River estuaries. The exceptions are probably due to different sources of the sediments, which are explained by the results of relatively low I/OC ratios in sediments in those two estuaries, compared to the other estuaries. Thus, OC in sediments as well as salinity may be responsible for the variation of Kds of I in the estuarine and coastal regions.

Thermoluminescence as a new research tool for the evaluation of geothermal activity of the Kakkonda geothermal system, Northeast Japan

Abstract The thermoluminescence glow-curve of quartz in volcanic and pyroclastic rocks of the Miocene and Quaternary in the Kakkonda geothermal field was divided into L (low), M (medium) and H (high) peaks in order of increasing temperature. Thermoluminescence emission is independent of stratigraphic boundaries but it is closely related to surface geothermal manifestations. Thermally stimulated processes of thermoluminescence caused by natural annealing occurred in the Quaternary after the eruption of the Tamagawa Welded Tuffs; radiation storage processes then began, as a consequence of the temperature drop. Thermoluminescence behavior indicates natural temperature manifestations, together with the paleo-temperature history. The H peak was thermally stable compared to the L and M peaks, and the area within which the relative intensity of the H peak is less than 5% coincides with the surface zone where dominant fluid flow is convective. In addition, L and M peaks indicate that a relatively low-temperature fluid mixes with the hot upflow around the western margin of the ascending flow zone. Thermoluminescence characteristics reflect paleo-temperature history and are related to geothermal fluid flow. Thermoluminescence is an effective exploration technique for evaluating natural temperature manifestations and subterranean heat flow in geothermal systems.

Effects of soil erosion and anoxic-euxinic ocean in the Permian-Triassic marine crisis.

The largest mass extinction of biota in the Earth’s history occurred during the Permian–Triassic transition and included two extinctions, one each at the latest Permian (first phase) and earliest Triassic (second phase). High seawater temperature in the surface water accompanied by euxinic deep-intermediate water, intrusion of the euxinic water to the surface water, a decrease in pH, and hypercapnia have been proposed as direct causes of the marine crisis. For the first-phase extinction, we here add a causal mechanism beginning from massive soil and rock erosion and leading to algal blooms, release of toxic components, asphyxiation, and oxygen-depleted nearshore bottom water that created environmental stress for nearshore marine animals. For the second-phase extinction, we show that a soil and rock erosion/algal bloom event did not occur, but culmination of anoxia–euxinia in intermediate waters did occur, spanning the second-phase extinction. We investigated sedimentary organic molecules, and the results indicated a peak of a massive soil erosion proxy followed by peaks of marine productivity proxy. Anoxic proxies of surface sediments and water occurred in the shallow nearshore sea at the eastern and western margins of the Paleotethys at the first-phase extinction horizon, but not at the second-phase extinction horizon. Our reconstruction of ocean redox structure at low latitudes indicates that a gradual increase in temperature spanning the two extinctions could have induced a gradual change from a well-mixed oxic to a stratified euxinic ocean beginning immediately prior to the first-phase extinction, followed by culmination of anoxia in nearshore surface waters and of anoxia and euxinia in the shallow-intermediate waters at the second-phase extinction over a period of approximately one million years or more. Enhanced global warming, ocean acidification, and hypercapnia could have caused the second-phase extinction approximately 60 kyr after the first-phase extinction. The causes of the first-phase extinction were not only those environmental stresses but also environmental stresses caused by the soil and rock erosion/algal bloom event.

Red soils derived from limestone contain higher amounts of trace elements than those derived from various other parent materials

Abstract The concentrations of 48 trace elements (Li, Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, As, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, In, Cd, Sn, Sb, I, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Tl, Pb, Bi, Th and U) in 14 soils derived from limestone, sampled at three sites, are compared with the concentrations in 500 soil samples derived from a variety of other parent materials. The 500 samples were collected from 75 sites nationwide in order to include the wide range of common soil types in Japan. Most analytical results were obtained by inductively coupled plasma mass spectrometry (ICP-MS), but Cr, As, Br, Zr, Sn, and I concentrations were determined by energy dispersive X-ray fluorescence spectrometry (EDXRF), because the acid dissolution techniques employed in this study were found to be incapable of recovering these elements completely. In order to examine the reliability of analyses, the concentrations of many elements were also determined by EDXRF, inductively coupled plasma-atomic emission spectrometry (ICP-AES), and atomic absorption spectrometry (AAS). Box and whisker diagrams (Tukey plots), constructed using log-transformed values of each element, show clearly that geometric means of nearly all the trace elements in soils derived from limestone are higher than those in soils derived from other parent materials. The only exceptions are Sr, Ag and Eu, though statistical analysis (Student’s t-test) shows that the differences for these three elements were not significant at p < 0.05. Similarly, the observed differences of geometric means for Sc, Br and Ba between limestone soils and other types of soils were also not significant at p < 0.05. It can be concluded, therefore, that the concentrations of the above-mentioned 48 trace elements in soils derived from limestone are significantly higher than those in other types of soils, with the exception of Sc, Br, Sr, Ag, and Ba, though it was necessary to exclude 81 soil samples, developed on scoriaceous (basaltic) volcanic ash from Mt. Fuji, as an exceptional group for comparisons of V and Cu, as these soils contain higher levels of these two elements. The above results can be attributed to the gradual accumulation of trace elements in the limestone soils due to the intense weathering processes.