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Challenges and Future Trends in K–Ar (40Ar/39...
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Challenges and Future Trends in K–Ar (40Ar/39Ar) Geochronology, 2nd Edition

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Geochemistry and Geochronology".

Deadline for manuscript submissions: closed (30 August 2024) | Viewed by 3500

Special Issue Editors

Dr. Tetsumaru Itaya

E-Mail Website
Guest Editor
Institute of GeoHistory, Japan Geochronology Network (NPO), Akaiwa 701-2503, Japan
Interests: K–Ar (40Ar/39Ar) geochronology; field geology; petrology; mineralogy; opaque mineralogy; graphitization
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Tatsuki Tsujimori

E-Mail Website
Guest Editor
Department of Earth Science, Tohoku University, Aoba Ku, Sendai, Miyagi 9808578, Japan
Interests: orogenic belts; HP-UHP metamorphism; blueschist; serpentinite; jadeitite
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Radiogenic 40Ar was discovered from natural minerals in 1948, and the K–Ar dating method has been developed since the 1950s. Subsequently, in the 1960s, the 40Ar/39Ar dating method was established, and further developments in its applications led to improvements in the in situ dating technique. Thus far, this K–Ar (40Ar/39Ar) method has been applied to many varieties of geological materials as the most approachable radiometric dating method. However, the method often yields certain geological inconsistencies and/or anomalously old ages, especially for high- and ultrahigh-pressure (HP–UHP) metamorphic rocks in collisional orogenic belts. For example, some micas in UHP-metamorphosed granite give unusual K–Ar (40Ar/39Ar) ages which are significantly older than the host granite. Such an observation infers the presence of extremely high excess argon. This problem has been discussed by many geochronologists over the last 40 years. Although the reconnaissance of radiogenic argon loss or gain is difficult, multidisciplinary approaches have the potential to uncover the physicochemical behavior of argon in nature and to improve the reliability of the K–Ar (40Ar/39Ar) dating of metamorphic processes.

Understanding the behavior of argon also enables more accurate K–Ar (40Ar/39Ar) dating for young volcanic rocks which have experienced Ar isotope mass fractionation and for fluid-induced gold mineralization with excess argon. Moreover, it would further improve authigenic illite and smectite K–Ar (40Ar/39Ar) dating for fault-gouge rocks, which has been applied to determine fault movements. Recently, the possibility of the in situ 40Ar/39Ar dating of planetary surfaces using cosmogenic 39Ar was proposed; this may be also possible by in situ K-Ar dating.

This Special Issue invites submissions on K–Ar (40Ar/39Ar) geochronology and geochemistry with a multidisciplinary scope, including field observations, petrology, mineralogy, structural geology, and numerical modeling. Studies that help to better understand argon’s behavior in nature are particularly encouraged. Challenging studies on the in situ dating of planetary surfaces will be also welcome.

Dr. Tetsumaru Itaya
Prof. Dr. Tatsuki Tsujimori
Guest Editors

Manuscript Submission Information

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Keywords

  • K–Ar (40Ar/39Ar) geochronology
  • excess argon and wave
  • argon release by deformation
  • exhumation of metamorphic units
  • argon behavior in nature
  • accurate and reliable dating
  • in situ dating of planetary surfaces

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Related Special Issue

Published Papers (3 papers)

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Research

13 pages, 13174 KiB  
Article
Peak Height Comparison K-Ar Method Applied to Zao Volcano Bomb Samples Younger than ca. 35 ka
by Mirai Takebe, Keiko Sato, Hidenori Kumagai, Naoyoshi Iwata and Masao Ban
Minerals 2024, 14(10), 979; https://doi.org/10.3390/min14100979 - 28 Sep 2024
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Abstract
The peak height comparison K-Ar dating method was applied to very young (younger than ca. 35 ka) vesiculated bombs from three pyroclastic units (Komakusadaira Pyroclastics, Kattadake Pyroclastics, and Umanose Agglutinate) from Zao Volcano in northeast Japan. Because the 38Ar/36Ar ratios [...] Read more.
The peak height comparison K-Ar dating method was applied to very young (younger than ca. 35 ka) vesiculated bombs from three pyroclastic units (Komakusadaira Pyroclastics, Kattadake Pyroclastics, and Umanose Agglutinate) from Zao Volcano in northeast Japan. Because the 38Ar/36Ar ratios differed from 0.187, the mass fractionation was corrected for all measurement data. The obtained K-Ar ages are 30.0 ± 32.2 ka (no. 1-1, weakly vesiculated), 37.4 ± 64.8 ka, and 33.0 ± 58.0 ka (nos. 2-1, 2-2, weakly vesiculated) for the samples from Komakusadaira Pyroclastics; 12.6 ± 46.7 ka (no. 3-1, highly vesiculated) for a sample from Kattadake Pyroclastics; and 5.3 ± 44.9 ka, 5.7 ± 14.3 ka (no. 4-1, 4-2, weakly vesiculated), and 17.3 ± 79.3 ka (no. 5-1, moderately vesiculated) for the samples from Umanose Agglutinate on a 1σ error basis. For all cases, the obtained ages’ errors exceed 100%, with none involved within the error range. Therefore, the following age value upper limits are considered statistically significant: no. 1-1 is ≤94.4 ka, 2-1 is ≤167.0 ka, 2-2 is ≤149.0 ka, 3-1 is ≤106.0 ka, 4-1 is ≤95.1 ka, 4-2 is ≤34.3 ka, and 5-1 is ≤175.9 ka, considering 2σ errors. The obtained ages are generally consistent with those previously estimated using 14C dating. Full article
(This article belongs to the Special Issue Challenges and Future Trends in K–Ar (40Ar/39Ar) Geochronology, 2nd Edition)
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63 pages, 48747 KiB  
Article
Petrogenesis of an Episyenite from Iwagi Islet, Southwest Japan: Unique Li–Na Metasomatism during the Turonian
by Teruyoshi Imaoka, Sachiho Akita, Tsuyoshi Ishikawa, Kenichiro Tani, Jun-Ichi Kimura, Qing Chang and Mariko Nagashima
Minerals 2024, 14(9), 929; https://doi.org/10.3390/min14090929 - 11 Sep 2024
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Abstract
A unique Li–Na metasomatic rock from Iwagi Islet in Southwest (SW) Japan is an episyenite that contains new Li-rich minerals, including sugilite, katayamalite, murakamiite, and ferro-ferri-holmquistite. We present petrographical, mineralogical, and geochronological data for the protoliths and episyenite. We classified the metasomatic rocks [...] Read more.
A unique Li–Na metasomatic rock from Iwagi Islet in Southwest (SW) Japan is an episyenite that contains new Li-rich minerals, including sugilite, katayamalite, murakamiite, and ferro-ferri-holmquistite. We present petrographical, mineralogical, and geochronological data for the protoliths and episyenite. We classified the metasomatic rocks based on the mineral assemblages, from the protolith biotite granite to albitized granite, quartz albitite, hedenbergite albitite, aegirine albitite, sugilite albitite, and katayamalite albitite. The protolith of hedenbergite albitites may have been metasomatic granite that has been subjected to calcic skarnization. Albitites are formed related to fractures and shear zones that focused the fluid flow and metasomatism. Extensive albitization and formation of abundant Li minerals requires involvement of external Li-Na-Cl-rich fluids, which might be related to deep high-temperature Arima-like brines derived from dehydration of the subducted oceanic slab. Formation of the albitites began with quartz dissolution and vug formation, and record interface-coupled dissolution–reprecipitation processes in an open system. The 40Ar/39Ar age of 91.5 ± 0.3 Ma determined for the katayamalite is slightly younger than the protolith zircon U–Pb age of 93.5 ± 1.7 Ma (Turonian), reasonably explaining the timing of Li–Na metasomatism after the petrogenesis of host granites. Full article
(This article belongs to the Special Issue Challenges and Future Trends in K–Ar (40Ar/39Ar) Geochronology, 2nd Edition)
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24 pages, 8380 KiB  
Article
Regional-Scale Paleoproterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology
by Megumi Sato, Hironobu Hyodo, Kei Sugiura, Tatsuki Tsujimori and Tetsumaru Itaya
Minerals 2024, 14(4), 397; https://doi.org/10.3390/min14040397 - 12 Apr 2024
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Abstract
Slave Province in Canada is an Archean granite–supracrustal terrane at the northwestern corner of the Canadian Shield. It is bordered by the Thelon–Taltson orogen (2.0 to 1.9 Ga) to the southeast and the Wopmay orogen (1.9 to 1.8 Ga) to the west. Acasta [...] Read more.
Slave Province in Canada is an Archean granite–supracrustal terrane at the northwestern corner of the Canadian Shield. It is bordered by the Thelon–Taltson orogen (2.0 to 1.9 Ga) to the southeast and the Wopmay orogen (1.9 to 1.8 Ga) to the west. Acasta gneisses, exposed in the westernmost Slave Province, and the Wopmay rocks, located close to the gneisses, were systematically collected for K–Ar and laser step-heating 40Ar/39Ar single-crystal analyses of the biotite and amphibole. The K–Ar biotite ages of the four Wopmay samples range from 1816 ± 18 Ma to 1854 ± 26 Ma. The 40Ar/39Ar biotite analyses of the three Wopmay samples yield plateau ages of 1826 ± 21 Ma, 1886 ± 13 Ma, and 1870 ± 18 Ma. These ages fall within the reported U–Pb zircon age range of the Wopmay orogen. The K–Ar biotite ages of the fifteen Acasta gneisses range from 1779 ± 25 Ma to 1877 ± 26 Ma, except for one younger sample (1711 ± 25 Ma). The 40Ar/39Ar analyses of the biotite crystals from three samples give the plateau ages of 1877 ± 8 Ma, 1935 ± 14 Ma, and 1951 ± 11 Ma. The K–Ar amphibole ages from twelve samples range from 1949 ± 19 Ma to 1685 ± 25 Ma. Two samples of them give ages older than the zircon U-Pb age of Hepburn plutons. The 40Ar/39Ar analyses of the amphibole crystals show varied age relations. The two samples give plateau ages of 1814 ± 22 Ma and 1964 ± 12 Ma. Some samples exhibit apparent old ages of ~2000 Ma in the middle temperature fractions. These old fractions result from the amphibole crystals, originally formed in the Archean, being affected by the thermal events during the Wopmay orogeny but not fully resetting. These observations suggest that the K–Ar system ages of the biotite and amphibole in the Archean Acasta gneiss were rejuvenated during the Paleoproterozoic ages. The Discussion explores the possibility that the heat source rejuvenating the K–Ar system ages may have arisen due to asthenospheric extrusion into the wedge mantle, a process likely triggered by subduction rollback. Full article
(This article belongs to the Special Issue Challenges and Future Trends in K–Ar (40Ar/39Ar) Geochronology, 2nd Edition)
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