Petrology of the Taiheizan composite granitic rocks, Akita Prefecture, Northeast Japan

Fujimoto, Yukio

doi:10.2465/gkk.35.253

Cited by 3 publications

(1 citation statement)

References 16 publications

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“…The area is covered by Neogene volcanic and sedimentary rocks with a gently west‐dipping homoclinal structure. The Neogene rocks are in fault contact with the Cretaceous Taiheizan composite granitic pluton, exposed in the northeast of the area (Kano et al, 1964; Ohzawa et al, 1981; Fujimoto, 2006; Figure 2). The Oligocene Haginari Formation unconformably overlies the Taiheizan rocks and consists of pyroxene andesite lavas and pyroclastic flow deposits (Ohzawa et al, 1981; Tsuchiya and Yoshikawa, 1994).…”

Section: Geologymentioning

confidence: 99%

Late Miocene magmatic‐hydrothermal system and related Cu mineralization of the Arakawa area, Akita, Japan

Satori

Watanabe

Ogata³

et al. 2022

Resource Geology

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The Northeast Japan arc hosts a number of hydrothermal vein‐type copper deposits associated with Neogene felsic intrusions. The Arakawa area is underlain by Cretaceous granites and Tertiary sedimentary rocks, which were intruded by the Miocene Ushizawamata dacite. Zircon grains from the dacite intrusion yield a 206Pb/238U intercept age (laser ablation inductively coupled plasma mass spectrometry) of 8.10 ± 0.30 Ma, consistent with a previously reported K‐Ar illite age (8.1 ± 0.4 Ma) of the Ushizawamata lead and zinc prospect in the Arakawa area. The dacite intrusion and the surrounding Miocene sedimentary rocks were altered by hydrothermal activity on the surface, classified into four alteration zones: (1) biotite‐chlorite, (2) illite, (3) chlorite and (4) smectite, centered on the intrusion. About 20 major vertical sub‐parallel copper‐bearing quartz veins occur in the chlorite alteration zone on the west side of the dacite. The first vein stage is composed of chalcopyrite and chamosite with a minor amount of quartz in brecciated wall rocks, and the second‐stage is characterized by the presence of hematite in addition to the first‐stage mineral assemblage. The third‐stage consists of comb‐shaped quartz veins with a minor amount of chalcopyrite, sphalerite, galena and pyrite, and the fourth‐stage of barite and apatite present in druse in the third‐stage veins. Primary fluid inclusions in quartz of the first‐ and third‐stages are all liquid‐rich and two‐phase. Homogenization temperature and salinity of first‐stage quartz are 263–277°C and 5.7–7.5 wt% NaCl equivalent (eq.); in quartz of the third‐stage, 251–270°C and 2.7–4.2 wt% in the inner zone and 207–250°C and 2.7–3.7 wt% in comb‐shaped quartz on the vein margin. The fluid inclusions in quartz phenocrysts of the Ushizawamata dacite show two distinct assemblages, halite‐bearing polyphase inclusions that coexist with vapor‐phase inclusions and/or vapor‐rich two‐phase inclusions, and liquid‐rich two‐phase inclusions. Homogenization temperature and salinity of the polyphase inclusions are higher than 401°C and 46.7 wt%, respectively, and those of the vapor‐rich two‐phase inclusions report 393–419°C and 2.6–3.7 wt% NaCl, whereas the liquid‐rich two‐phase inclusions returned 344–403°C and 8.0–9.3 wt%, respectively. These results indicate that the ore forming fluid was slightly cooler and lower in salinity than the late‐stage hydrothermal fluid in the Ushizawamata intrusion. The spatial and temporal proximity between the Ushizawamata dacite and the hydrothermal veins indicates that the dacitic magma was genetically related to the vein copper mineralization in the Arakawa area.

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Section: Geologymentioning

confidence: 99%

Late Miocene magmatic‐hydrothermal system and related Cu mineralization of the Arakawa area, Akita, Japan

Satori

Watanabe

Ogata³

et al. 2022

Resource Geology

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秋田県太平山複合プルトンから得られたジルコンU-Pb年代

Nakajima,

Nagata,

Fukuda

et al. 2023

Jour. Geol. Soc. Japan

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Zircon U-Pb dating was carried out on granitic rocks from plutons in the Taiheizan Complex in Akita Prefecture, NE Japan. Two granodiorites from the Main Intrusive Rocks yielded weighted mean 206 Pb/ 238 U dates of 103.4±1.0 Ma and 115.6±1.1 Ma (1SE). Three porphyrygranite from the Young Intrusive Rocks yielded weighted mean 206 Pb/ 238 U dates of 11.4± 0.1 Ma, 4.7±Ma, and 4.8±0.1 Ma (1SE). The older and younger dates can be interpreted as the ages of early and later stages of granitic intrusion at the sampling locations. The Pliocene U-Pb dates suggest that the Nibetsu Body in the Young Intrusive Rocks is one of the youngest granitic plutons currently exposed on Earth.

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Physical properties of Cretaceous to Paleogene granitic rocks in Japan: Part 3. A case of the Ashio Belt (northern Kanto region)

弘¹,

茂雄²

2010

Bull. Geol. Surv. Japan

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About 300 granitic rocks exposed in the Ashio Belt (contains partially Jouetsu Belt) situated in the most eastern part of Southwest Japan were collected. And they were measured on density, porosity, magnetic susceptibility and Natural Remanent Magnetization. For more detailed observation, Ashio Belt was divided into three area, north Ashio area, south Ashio area and south-east Ashio area. The mean porosity shows about 0.83% and its mode 0.50%. Three areas show 0.75, 0.92 and 0.81 %, and its mode 0.40, 0.54 and 0.59. Magnetic susceptibilityAll the samples can be sectioned within a zone bounded by two straight lines in a density-magnetic susceptibility chart: The samples in the Ashio Belt lie mainly near the lower line (north Ashio area and south-east Ashio area) and partially middle zone (a part of south Ashio area). There is no sample along the upper line. Natural Remanent Magnetization (NRM)The relationship between the density and NRM could scarcely show the correlation, but the magnetic susceptibility and NRM show more correlative. Königsberger ratio (Q n ) s of the 90 percent rock sample show less than 0.4. These results are summarized in Table 1. (physical properties of the Cretaceous to Paleogene granitic rocks in the east Japanese Island). Oxidation ratioIn order to define the relationship between magnetic susceptibility and the oxidation state of iron, molecular ratio (2Fe 2 O 3 x100)/(2Fe 2 O 3 +FeO) termed the "oxidation ratio", was calculated for 1,200 Cretaceous to Paleogene granitic rocks exposed in the east Japanese Island. The plot Fe 2 O 3 (as total iron) against the magnetic susceptibility value divided into three groups (low magnetic susceptibility, intermediate magnetic susceptibility and high magnetic susceptibility), exhibits considerable scatter in these plots. It makes difficult to draw definitive conclusion about trends. But it is possible to find a slightly correlation trend. This fact means that several causes participate to decide the magnetic susceptibility value.

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Petrology of the Taiheizan composite granitic rocks, Akita Prefecture, Northeast Japan

Cited by 3 publications

References 16 publications

Late Miocene magmatic‐hydrothermal system and related Cu mineralization of the Arakawa area, Akita, Japan

Late Miocene magmatic‐hydrothermal system and related Cu mineralization of the Arakawa area, Akita, Japan

秋田県太平山複合プルトンから得られたジルコンU-Pb年代

Physical properties of Cretaceous to Paleogene granitic rocks in Japan: Part 3. A case of the Ashio Belt (northern Kanto region)

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