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Journal Articles

Micropores and mass transfer in the formation of myrmekites

Yuguchi, Takashi*; Yuasa, Haruka*; Izumino, Yuya*; Nakashima, Kazuo*; Sasao, Eiji; Nishiyama, Tadao*

American Mineralogist, 107(3), p.476 - 488, 2022/03

 Times Cited Count:0 Percentile:0.05(Geochemistry & Geophysics)

The methodology and interpretations in this study provide new insights into the mechanism of myrmekite formation in a granitic system. The presence of micropores in the myrmekites and this study clarified that the genesis of micropores is related to the formation of myrmekites in the Toki granite. The results led to an increased understanding of (1) an estimate of mass transfer between the reactant and product minerals, and the inflow and outflow of components with consideration of the volume change due to micropore formation, (2) the factor controlling the formation of micropores during myrmekitization, and (3) the sequential variations in the hydrothermal fluid chemistry during sub-solidus conditions. The micropores act as a migration pathway for hydrothermal fluid and thus enhance the mass transfer within a granitic body starting with the myrmekite formation and continuing through the present day and into the future.

Journal Articles

Mass transfer associated with chloritization in the hydrothermal alteration process of granitic pluton

Yuguchi, Takashi*; Matsuki, Takanobu*; Izumino, Yuya*; Sasao, Eiji; Nishiyama, Tadao*

American Mineralogist, 106(7), p.1128 - 1142, 2021/07

 Times Cited Count:0 Percentile:0.02(Geochemistry & Geophysics)

This study reveals the hydrothermal alteration processes in a pluton, with a focus on the mass transfer between minerals and hydrothermal fluid. Hydrothermal alteration of the Toki granite in Tono area, central Japan, progressed through the successive processes of chloritization, plagioclase alteration, and precipitation of a carbonate mineral. This paper describes the alteration process of hornblende chloritization, K-feldspar chloritization, and the formation of fracture-filling chlorite through petrography and mineral chemistry. Several types of chloritization reactions (including biotite chloritization) can be characterized by their reaction with the inflow of Al$$^{3+}$$, Fe$$^{2+}$$, Mn$$^{2+}$$, and Mg$$^{2+}$$ and the outflow of H$$_{4}$$SiO$$_{4}$$, Ca$$^{2+}$$, K$$^{+}$$+, and F$$^{-}$$. The reactions of chloritization and plagioclase alteration represent the sequential variations in fluid chemistry at temporal conditions from 68 Ma to 51 Ma as the temperature decreased from 350$$^{circ}$$C to 180$$^{circ}$$C.

Journal Articles

Genesis and development processes of fractures in granite; Petrographic indicators of hydrothermal alteration

Yuguchi, Takashi*; Izumino, Yuya*; Sasao, Eiji

PLOS ONE (Internet), 16(5), p.e0251198_1 - e0251198_17, 2021/05

 Times Cited Count:0 Percentile:0(Multidisciplinary Sciences)

This study analyzes the relationships among alteration indicators, areal microvoid fractions in chloritized biotite, and macroscopic fracture frequencies in the Toki granite, central Japan, to establish the genesis and development processes of fractures in granite. Petrographic alteration indicators using biotite chloritization as innovative methods are proposed to evaluate the extent of hydrothermal alteration and fracture frequency within granites. Samples with high macroscopic fracture frequencies correspond to a high number of areal microvoid fractions and large alteration indicators. The alteration indicators contribute to the characterization of present and future distributions of macroscopic fracture frequencies.

Journal Articles

Position-by-position cooling paths within the Toki granite, central Japan; Constraints and the relation with fracture population in a pluton

Yuguchi, Takashi*; Sueoka, Shigeru; Iwano, Hideki*; Izumino, Yuya*; Ishibashi, Masayuki; Danhara, Toru*; Sasao, Eiji; Hirata, Takafumi*; Nishiyama, Tadao*

Journal of Asian Earth Sciences, 169, p.47 - 66, 2019/01

AA2018-0254.pdf:5.48MB

 Times Cited Count:8 Percentile:52.73(Geosciences, Multidisciplinary)

This study presents position-by-position $$t-T$$ paths within a granitic pluton based on thermochronological data, and describes their constraints and their relationship with fracture frequency, as an example from the Toki granite, central Japan. The cooling paths have position-specific characteristics; a single $$t-T$$ path does not represent the cooling behavior of the entire pluton. Such position-specific $$t-T$$ paths enable us to evaluate three-dimensional thermal evolution within the granitic pluton, and thus can clarify the detailed formation history of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust. This study reveals the relationship between position-specific $$t-T$$ paths and fracture frequency, and thus provides a criterion for evaluating the fracture population in terms of thermal stress.

Oral presentation

Position-by-position cooling paths within the Toki granite, central Japan; Constraints and the relation with fracture population in a pluton

Yuguchi, Takashi*; Sueoka, Shigeru; Iwano, Hideki*; Izumino, Yuya*; Ishibashi, Masayuki; Danhara, Toru*; Sasao, Eiji; Hirata, Takafumi*; Nishiyama, Tadao*

no journal, , 

This study presents position-by-position $$t-T$$ paths within a granitic pluton based on thermochronological data, including zircon U-Pb, biotite K-Ar, ZFT, and AFT ages, FT length characterization, and FT inverse calculation, and describes their constraints and their relationship with fracture frequency, as an example from the Toki granite, central Japan. The cooling paths have position-specific characteristics; a single $$t-T$$ path does not represent the cooling behavior of the entire pluton. Such position-specific $$t-T$$ paths enable us to evaluate three-dimensional thermal evolution within the granitic pluton, and thus can clarify the detailed formation history of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust. This study reveals the relationship between position-specific $$t-T$$ paths and fracture frequency, and thus provides a criterion for evaluating the fracture population in terms of thermal stress.

Oral presentation

Genesis and development processes of fractures in granite; Petrographic indicators of hydrothermal alteration

Yuguchi, Takashi*; Izumino, Yuya*; Sasao, Eiji

no journal, , 

This study analyzes the relationships among alteration indicators, areal microvoid fractions in chloritized biotite and altered plagioclase, and macroscopic fracture frequencies in the Toki granite, central Japan, to establish the genesis and development processes of fractures in granite. Petrographic alteration indicators as innovative methods are proposed to evaluate the extent of hydrothermal alteration and fracture frequency within granites. Samples with high macroscopic fracture frequencies correspond to a high number of areal microvoid fractions and large alteration indicators. Microvoids are the source of macroscopic fractures and can be evaluated by intrinsic factors, such as alteration indicators.

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