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: 30 August 2024 | Viewed by 1129

Special Issue Editors


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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
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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

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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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Published Papers (1 paper)

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Research

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
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Title: K-Ar and 40Ar/39Ar Analyses of Biotite and Hornblende from Acasta Gneisses in Slave Province

    Authors: Tetsumaru Itaya et al.

2. Title: Cooling of Southern Granulite Terrane, India: Evidence from K-Ar Biotite Ages

    Authors: Sajeev Krishnan et al.

3. Title: Excess 40Ar in Biotite Revealed by Conventional K-Ar Method Example of the Matsumae Plutonic Complex

    Authors: Nobutaka Tsuchiya et al.

4. Title: Exploration Implications of Gajah Tidur, An Older Cu-Mo-(Au) Deposit below the Main Grasberg Porphyry Cu-Au Deposit

    Authors: Reza Al Furqan et al.

5. Title: K-Ar Age Mapping of Cordilleran Orogenic Belt including the Cretaceous High-Pressure Metamorphic Franciscan Belt

    Authors: Yukio Isozaki et al.

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