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Yuguchi, Takashi*; Endo, Kyoka*; Suzuki, Satoshi*; Ogita, Yasuhiro; Sakata, Shuhei*; Yokoyama, Tatsunori; Imura, Takumi*; Ono, Takeshi*; Sasao, Eiji
Lithos, 494-495, p.107909_1 - 107909_14, 2025/02
Times Cited Count：0 Percentile：0.00(Geochemistry & Geophysics)This study described the growth characteristics of zircon crystals in the Kuki granite from the Kitakami Mountains in northeastern Japan as the key for elucidating granitic magma chamber processes. Using two approaches, analyses based on multiple sections of separated zircon crystals and thin-section-based zircon crystal analyses, we determined the characteristics of the 3D internal structure of the crystals, variations in U-Pb age, Ti concentrations, and Th/U in relation to crystal texture, and the crystallization sequence between zircon crystals and other minerals within the magma chamber. The textures, which occupy a large proportion of zircon, comprise low luminescence homogeneous cores (LLCs) and oscillatory zoning (OZ). The 3D distribution of the zircon internal structure can be classified into three types: Type 1 zircon comprising LLCs and the surrounding OZ and Types 2 and 3 zircon crystals composed entirely of OZ from the cores to the rims and characterized by brightness and darkness cores, respectively. LLC and OZ grew at temperatures from approximately 900 to 800
C and 850 to 700C, respectively, and LLC has a higher Th/U than that of OZ, indicating that fractional crystallization progression as the magma chamber cooled resulted in the transition from LLC to OZ. In the progression of fractional crystallization, the diffusion rate deceleration with decreasing magma temperatures triggered the transition from interfacial reaction-controlled growth producing LLC to diffusion-controlled growth producing OZ. In the thin-section analysis, zircon crystals which contained in different minerals are characterized by different Th/U values. The variation in Th/U and the crystallization temperature of zircon crystals considering the surrounding minerals can be used to elucidate the differentiation and mineral crystallization in magma chamber processes over a wide range of temperature conditions.
Yuguchi, Takashi*; Ito, Daichi*; Yokoyama, Tatsunori; Sakata, Shuhei*; Suzuki, Satoshi*; Ogita, Yasuhiro; Yagi, Koshi*; Imura, Takumi*; Motai, Satoko*; Ono, Takeshi*
Lithos, 440-441, p.107026_1 - 107026_14, 2023/03
Times Cited Count：2 Percentile：21.32(Geochemistry & Geophysics)We propose a new method for elucidating zircon growth in granitic plutons, based on variations in three-dimensional 3D cathodoluminescence (CL) patterns, U-Pb ages, titanium concentration, and Th/U ratios. We focused on the zircon growth processes in the Okueyama granite (OKG) in central Kyushu, Japan, to obtain interpretations of magma chamber processes that result in the formation of granitic plutons. The OKG consists of three lithofacies: biotite granite (BG), hornblende granite (HG), and hornblende granodiorite (HGD). To determine the 3D internal structure and growth pattern of a zircon crystal, we performed CL observations for multi-sections of the samples. Simultaneously, we also determined the zircon U-Pb age and titanium concentration of the center sections of the samples. The 3D distribution of the oscillatory zoning can be used to determine the crystal nucleus. The simultaneous determination of zircon U-Pb ages and Ti concentrations of the granite samples indicates the time-temperature (t-T) history of granitic magma before its solidification. The t-T histories of the BG, HG, and HGD represented similar cooling behaviors within the magma chamber: rapid cooling from the zircon crystallization temperature to the closure temperature of the biotite K-Ar system between 16 Ma and 10 Ma. The variations in the Th/U ratios against temperature also demonstrate a different trend at the boundary of approximately 670 C. Fractional crystallization in the magma chamber progressed significantly at temperatures above 670 C; below 670 C, crystallization progressed slowly, indicating only minimal changes in the magma composition. The variations in the Th/U ratio against temperature in the BG, HG, and HGD portrayed common tendencies, indicating the same behavior in the progression of fractional crystallization among the three lithofacies, which in turn, represented the same behavior within the entire magma chamber.
Yuguchi, Takashi*; Ishibashi, Kozue*; Sakata, Shuhei*; Yokoyama, Tatsunori; Ito, Daichi*; Ogita, Yasuhiro; Yagi, Koshi*; Ono, Takeshi*
Lithos, 372-373, p.105682_1 - 105682_9, 2020/11
Times Cited Count：8 Percentile：36.91(Geochemistry & Geophysics)Simultaneous determination of zircon U-Pb age and titanium concentration for a single analysis spot gives both the crystallization age and temperature. The crystallization age and temperature pairs in granitic zircons map the time-temperature (
) path of granitic magma before its solidification. In laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis, it is challenging to quantitatively analyse a low level of titanium concentration. This study employed two approaches using a Quadrupole mass spectrometer equipped with a collision/reaction cell (CRC). The methods were applied to zircon samples of the Kurobegawa granite (KRG), the Okueyama granite (OKG), the Toki granite (TKG), and the Tono plutonic complex (TPC) and provided U-Pb ages and titanium concentrations consistent with previous studies. The crystallization ages and temperatures collected from individual analysis spots of zircon samples in the KRG, OKG, TKG, and TPC are plotted in the diagrams and enable us to characterize the rapid cooling paths at thermal conditions of zircon crystallization at the sampling sites.
Umeda, Koji; Ninomiya, Atsushi; Shimada, Koji; Nakajima, Junichi*
Lithosphere; Geochemistry, Geology and Geophysics, p.141 - 169, 2008/10
A linear zone with high strain rates along the Sea of Japan coast, the Niigata-Kobe Tectonic Zone (NKTZ), is considered to be associated with rheological heterogeneity in the lower crust and/or upper mantle, which may be caused by the upwelling of aqueous fluid and/or melt related to subduction of the Philippine Sea and Pacific Plates. In order to elucidate the geographic distribution of 
He/
He ratios along the NKTZ, new helium isotope data from hot spring gases and water samples were determined. Our study reinforces the clear relationship between helium isotope variations on the surface and the seismicity and resistivity structure of the crust and upper mantle along the Niigata-Kobe Tectonic Zone, Central Japan. In addition, the helium isotopes in hot spring gases may be recognized as a useful geochemical indicator of the presence of concealed active faults with compressional tectonics.
Nagao, Hiromichi; Nakajima, Takahiro; Kunitomo, Takahiro; Kumazawa, Mineo; Nagao, Toshiyasu*; Sayanagi, Keizo*; Noda, Yoichi*; Harada, Makoto*
Proceedings of 2nd International Workshop Active Geophysical Monitoring of the Earth Lithosphere (AMSEG 2005), p.18 - 22, 2005/09
We have carried out an operation test of the EM-ACROSS at Tono, Japan. The EM-ACROSS signals were detected at a geomagnetic observatory 40km away from the transmitter located at Tono mine. The mean resistivity of the Toki granite formation is estimated to be 100 Ohm-m.
Hasada, Yoko; Kumazawa, Mineo; Tsuruga, Kayoko; Kunitomo, Takahiro; Kasahara, Junzo
Proceedings of 2nd International Workshop Active Geophysical Monitoring of the Earth Lithosphere (AMSEG 2005), p.35 - 37, 2005/09
The Sompi event analysis is a basic analysis method for ACROSS system, in which a set of time-localized events contained in the transfer function is extracted. Sompi is the Japanese word to mean existence or absence. We have established the fundamental algorithm and made revisions on the basis of Maximum Likelihood estimation (Hasada et al., 2004). To analyze numerous data acquired by continuous monitoring using ACROSS, automatic processing is necessary. We have attempted to improve the Sompi event analysis by using some additional techniques and examine the possibility of automatic travel time determination.
