Journal articles: 'K-Ar and 40Ar'

1

Lanphere, Marvin A. "Comparison of Conventional K–Ar and 40Ar/39Ar Dating of Young Mafic Volcanic Rocks." Quaternary Research 53, no. 3 (May 2000): 294–301. http://dx.doi.org/10.1006/qres.1999.2122.

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AbstractK–Ar and 40Ar/39Ar ages have been measured on nine mafic volcanic rocks younger than 1 myr from the Snake River Plain (Idaho), Mount Adams (Washington), and Crater Lake (Oregon). The K–Ar ages were calculated from Ar measurements made by isotope dilution and K2O measurements by flame photometry. The 40Ar/39Ar ages are incremental-heating experiments using a low-blank resistance-heated furnace. The results indicate that high-quality ages can be measured on young, mafic volcanic rocks using either the K–Ar or the 40Ar/39Ar technique. The precision of an 40Ar/39Ar plateau age generally is better than the precision of a K–Ar age because the plateau age is calculated by pooling the ages of several gas increments. The precision of a plateau age generally is better than the precision of an isotope correlation (isochron) age for the same sample. For one sample the intercept of the isochron yielded an 40Ar/36Ar value significantly different from the atmospheric value of 295.5. Recalculation of increment ages using the isochron intercept for the composition of nonradiogenic Ar in the sample resulted in much better agreement of ages for this sample. The results of this study also indicate that, given suitable material and modern equipment, precise K–Ar and 40Ar/39Ar ages can be measured on volcanic rocks as young as the latest Pleistocene, and perhaps even the Holocene.

2

Clauer, Norbert, and Abraham Lerman. "A Kinetic Explanation for Combined Potassium Gains and Radiogenic 40Argon Losses of Diagenetic Illite-Rich Clay Separates." Geosciences 12, no. 5 (April 25, 2022): 186. http://dx.doi.org/10.3390/geosciences12050186.

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In this study, a kinetic model sketches the concomitant K gain and radiogenic 40Ar loss of clay separates recovered from progressively buried sediments. Published K-Ar ages of clay separates from the Mahakam Delta, the Texas Gulf Coast, and the North Sea were used to constrain the modeling. As compared with analytical results, the model simulates changes relative to depth or to deposition time of the K-Ar ages from fine- and coarse-grained clay crystals. The decrease in the K-Ar ages of detrital-rich coarse-grained fractions (>2 μm) is bracketed with depth by K addition rates between 0.2 and 3.5%/Ma and slightly higher 40Ar release rates between 0.5 and 4.5%/Ma. The former rate varies from 3.5 to 6%/Ma in the fine-grained fractions (<0.4 μm) and the latter rate varies from 0.7 to 6%/Ma in the same fractions. In fact, the K addition and the radiogenic 40Ar release rates record independent processes on different material sizes and types. Small K addition and 40Ar escape rates of about 1%/Ma also simulate analytical cases in which the mean K-Ar ages of the finer grained fractions remain about constant with increasing depth, confirming that the relationship between K-Ar age and stratigraphic depth cannot represent a temporary “steady state”, but a continuing dynamic process at a smaller rate. In turn, the modeled results help quantifying the illitization reactions in size separates consisting of authigenic and detrital clay materials from sediments covering stratigraphic intervals from 10 to 1000 Ma.

3

Clauer, Norbert, and Abraham Lerman. "A Kinetic Explanation for Combined Potassium Gains and Radiogenic 40Argon Losses of Diagenetic Illite-Rich Clay Separates." Geosciences 12, no. 5 (April 25, 2022): 186. http://dx.doi.org/10.3390/geosciences12050186.

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In this study, a kinetic model sketches the concomitant K gain and radiogenic 40Ar loss of clay separates recovered from progressively buried sediments. Published K-Ar ages of clay separates from the Mahakam Delta, the Texas Gulf Coast, and the North Sea were used to constrain the modeling. As compared with analytical results, the model simulates changes relative to depth or to deposition time of the K-Ar ages from fine- and coarse-grained clay crystals. The decrease in the K-Ar ages of detrital-rich coarse-grained fractions (>2 μm) is bracketed with depth by K addition rates between 0.2 and 3.5%/Ma and slightly higher 40Ar release rates between 0.5 and 4.5%/Ma. The former rate varies from 3.5 to 6%/Ma in the fine-grained fractions (<0.4 μm) and the latter rate varies from 0.7 to 6%/Ma in the same fractions. In fact, the K addition and the radiogenic 40Ar release rates record independent processes on different material sizes and types. Small K addition and 40Ar escape rates of about 1%/Ma also simulate analytical cases in which the mean K-Ar ages of the finer grained fractions remain about constant with increasing depth, confirming that the relationship between K-Ar age and stratigraphic depth cannot represent a temporary “steady state”, but a continuing dynamic process at a smaller rate. In turn, the modeled results help quantifying the illitization reactions in size separates consisting of authigenic and detrital clay materials from sediments covering stratigraphic intervals from 10 to 1000 Ma.

4

Plint, H. E., and M. R. McDonough. "40Ar/39Ar and K–Ar age constraints on shear zone evolution, southern Taltson magmatic zone, northeastern Alberta." Canadian Journal of Earth Sciences 32, no. 3 (March 1, 1995): 281–91. http://dx.doi.org/10.1139/e95-023.

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New 40Ar/39Ar analyses of hornblende, muscovite, biotite, and K-feldspar constrain the timing of deformation and cooling of the southern Taltson magmatic zone, which underwent lower granulite to upper amphibolite grade deformation, in part synchronous with voluminous 1.99–1.92 Ga magmatism. New data are combined with existing K–Ar dates into a regional cooling framework to provide thermotemporal constraints on the deformational history. 40Ar/39Ar hornblende ages of ca. 1900 Ma are interpreted to record relatively rapid cooling following ductile thrusting on the Andrew Lake shear zone, and younger anatectic magmatism. These data, with published K–Ar and U–Pb data, support relatively rapid cooling of the Taltson magmatic zone from monazite closure temperature of 725 °C at ca. 1930 Ma to 525 °C at ca. 1900 Ma. Cooling rate estimates are about 7 °C/Ma, which suggests moderate exhumation rates during the high-grade part of the deformational history. A muscovite 40Ar/39Ar plateau age of 1803 ± 11 Ma is consistent with the mean muscovite K–Ar age of 1792 Ma, indicating regional cooling through about 350 °C at ca. 1800 Ma. 40Ar/39Ar ages from magmatic biotite of 1856 and 1799 Ma also suggest slow cooling during greenschist grade deformation, which can be no older than ca. 1860 Ma. A K-feldspar 40Ar/39Ar age of 1681 Ma provides a lower limit for the time of greenschist grade deformation. Cooling rate estimates during amphibolite to greenschist grade deformation are 1.75–2.25 °C/Ma.

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Carter, Jack, Ryan B. Ickert, Darren F. Mark, Marissa M. Tremblay, Alan J. Cresswell, and David C. W. Sanderson. "Production of 40Ar by an overlooked mode of 40K decay with implications for K-Ar geochronology." Geochronology 2, no. 2 (November 26, 2020): 355–65. http://dx.doi.org/10.5194/gchron-2-355-2020.

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Abstract. The decay of 40K to the stable isotopes 40Ca and 40Ar is used as a measure of time for both the K-Ca and K-Ar geochronometers, the latter of which is most generally utilized by the variant 40Ar∕39Ar system. The increasing precision of geochronology has forced practitioners to deal with the systematic uncertainties rooted in all radioisotope dating methods. A major component of these systematic uncertainties for the K-Ar and 40Ar∕39Ar techniques is imprecisely determined decay constants and an incomplete knowledge of the decay scheme of 40K. Recent geochronology studies question whether 40K can decay to 40Ar via an electron capture directly to ground state (ECground), citing the lack of experimental verification as reasoning for its omission. In this study, we (1) provide a theoretical argument in favor of the presence of this decay mode and (2) evaluate the magnitude of this decay mode by calculating the electron capture to positron ratio (ECground/β+) and comparing calculated ratios to previously published calculations, which yield ECground/β+ between 150–212. We provide support for this calculation through comparison of the experimentally verified ECground/β+ ratio of 22Na with our calculation using the theory of β decay. When combined with measured values of β+ and β− decay rates, the best estimate for the calculated ECground/β+ for 40K yields a partial decay constant for 40K direct to ground-state 40Ar of 11.6±1.5×10-13 a−1 (2σ). We calculate a partial decay constant of 40K to 40Ar of 0.592±0.014×10-10 a−1 and a total decay constant of 5.475±0.107×10-10 a−1 (2σ), and we conclude that although omission of this decay mode can be significant for K-Ar dating, it is minor for 40Ar∕39Ar geochronology and is therefore unlikely to have significantly biased published measurements.

6

Sato, Megumi, Hironobu Hyodo, Kei Sugiura, Tatsuki Tsujimori, and Tetsumaru Itaya. "Regional-Scale Paleoproterozoic Heating Event on Archean Acasta Gneisses in Slave Province, Canada: Insights from K–Ar and 40Ar/39Ar Chronology." Minerals 14, no. 4 (April 12, 2024): 397. http://dx.doi.org/10.3390/min14040397.

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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.

7

Jeans, C. V., J. G. Mitchell, M. J. Fisher, D. S. Wray, and I. R. Hall. "Age, origin and climatic signal of English Mesozoic clays based on K/Ar signatures." Clay Minerals 36, no. 4 (December 2001): 515–39. http://dx.doi.org/10.1180/0009855013640006.

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AbstractThe K/Ar characteristics of 53 clay assemblages (Triassic–Cretaceous), representing the detrital, volcanogenic and arid-facies clay mineral associations, are interpreted in relation to their mineralogy, chronostratic age and geological origins. The K-bearing mineral components of the 1–2 μm, 0.2–1 μm and <0.2 μm fractions of each clay assemblage together display one of two characteristic patterns of K2O and 40Ar values (the K/Ar signature of the assemblage) on a 40Ar/K2O correlation diagram. Interpretation of the K/Ar signatures indicates that: (1) all of these clay assemblages are apparently unaffected by burial diagenetic illitization; (2) the Jurassic and Cretaceous detrital clay assemblages are derived from the reworking of weathered Caledonian metasediments (420 500 Ma) and weathered kaolin-bearing sediments of Upper Devonian/ Carboniferous age; and (3) the role played by palaeoclimate in developing the pattern of clay minerals in the Mesozoic sediments of England is much less significant than previously believed.

8

Renne, Paul R. "Progress and Challenges in K-Ar and40Ar/39Ar Geochronology." Paleontological Society Papers 12 (October 2006): 47–66. http://dx.doi.org/10.1017/s1089332600001340.

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K-Ar and more recently the40Ar/39Ar variant are well established dating methods. The40Ar/39Ar method requires irradiation with neutrons, posing some complications that are greatly outweighed by the benefits. The40Ar/39Ar method is particularly powerful due to the availability of internal reliability criteria, the ability to analyze single crystals, and the amenability of the analyses to automation.40Ar/39Ar dating has the capability for unsurpassed precision and is applicable to the broadest range of geologic environments and time scales of any radioisotope dating technique. For chronostratigraphic applications,40Ar/39Ar is most important in the Cenozoic, becoming progressively less useful into the early Phanerozoic due to alteration and loss of radiogenic argon. Precision and accuracy of40Ar/39Ar dating have been improved considerably in recent years, but an uncertainty of about 1% in the decay constant for40K, probably mainly in the electron capture decay branch, still limits accuracy at about this level. Inconsistent use of standards (neutron fluence monitors) and attribution of variable ages to standards is still a source of confusion, but straightforward recalculation procedures can overcome the underlying problems provided that appropriate standards are used.

9

Yudin, Denis, Nikolay Murzintsev, Alexey Travin, Taisiya Alifirova, Egor Zhimulev, and Sofya Novikova. "Studying the Stability of the K/Ar Isotopic System of Phlogopites in Conditions of High T, P: 40Ar/39Ar Dating, Laboratory Experiment, Numerical Simulation." Minerals 11, no. 2 (February 12, 2021): 192. http://dx.doi.org/10.3390/min11020192.

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Typically, 40Ar/39Ar dating of phlogopites from deep-seated xenoliths of kimberlite pipes produces estimates that suggest much older ages than those when these pipes were intruded. High-pressure (3 GPa) laboratory experiments enabled the authors to explore the behaviour of argon in the phlogopite structure under the conditions that correspond to the mantle, at the temperatures (from 700 to 1000 °С), far exceeding closure temperature of the K/Ar isotopic system. “Volume diffusion” remains foremost for describing the mobility of argon in phlogopite at high pressures. The mantle material age can be estimated through the dating of the phlogopites from deep-seated xenoliths of kimberlites, employing the 40Ar/39Ar method, subject to correction for a partial loss of radiogenic 40Ar when xenolith moves upwards to the Earth’s surface. The obtained data served as the basis for proposing the behaviour model of the K/Ar isotopic system of minerals in conditions of great depths (lower crust, mantle), and when transporting xenoliths in the kimberlite melt.

10

KANEOKA, Ichiro. "Age Determinations by the K-Ar and 40Ar-39Ar Methods." Journal of Geography (Chigaku Zasshi) 94, no. 7 (1986): 676–81. http://dx.doi.org/10.5026/jgeography.94.676.

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11

MARASCHIN, Anderson, Ana Maria MIZUSAKI, Paulo VASCONCELOS, Ruth HINRICHS, Luiz DE ROS, and Sylvia Dos ANJOS. "DEFINIÇÃO DA IDADE DEPOSICIONAL DA FORMAÇÃO AÇU (BACIA POTIGUAR, NORDESTE DO BRASIL) 40 39 ATRAVÉS DA DATAÇÃO." Pesquisas em Geociências 37, no. 2 (August 31, 2010): 85. http://dx.doi.org/10.22456/1807-9806.22649.

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Crescimentos autigênicos precoces de K-feldspato são abundantes nos arenitos fluviais cretácicos da Formação Açu (Bacia Potiguar), um dos mais importantes reservatórios onshore de hidrocarbonetos do Brasil. Estes crescimentos foram formados diretamente ao redor de K-feldspatos detríticos, em condições superficiais (eodiagênese inicial). A continuidade física entre crescimentos e grãos detríticos impossibilitou sua separação visando a aplicação do método convencional 40K- 40Ar. Assim, optou-se em aplicar o método 40 39 Ar- Ar diretamente nos crescimentos autigênicos de K-feldspato. Como resultado, foi obtida uma idade mínima de 120 Ma, muito próxima à idade bioestratigráfica previamente estabelecida para os arenitos da Formação Açu, o que demonstra a viabilidade da aplicação do método 40Ar- 39Ar na determinação de idades deposicionais de arenitos-reservatório. Entretanto, para fins de aprimoramento do método e melhor precisão nas idades, é sugerido o uso de equipamentos que utilizam sonda a laser ultravioleta (UV), o que reduz a possibilidade de contaminação por diferentes fases minerais.

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Bounliyong, Patthana, Hirochika Sumino, and Antonio Arribas. "Large Amount of Excess Argon in Hydrothermal Quartz from the Vangtat Orogenic Gold Belt, Southern Laos: New In-Sight from K-Ar and Noble Gas Isotope Analyses." Minerals 12, no. 10 (September 24, 2022): 1205. http://dx.doi.org/10.3390/min12101205.

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K-Ar dating and 3He/4He and 40Ar/36Ar analyses were conducted on samples of hydrothermal quartz from the Thongkai-Ok Au deposit in the Vangtat orogenic Au belt of southern Laos to study the presence of excess argon in hydrothermal quartz and to better understand the origin of the ore-forming fluids. The K-Ar age of two hydrothermal quartz separates yielded apparent dates of 1040 and 1385 Ma. These ages are significantly older than the estimated age of Vangtat Au mineralization (~200 Ma) and other regional geologic events, indicating the presence of an extraordinary amount of excess argon in the hydrothermal quartz crystals. In vacuo crushing analyses of the Thongkai-Ok hydrothermal vein quartz delivered 3He/4He ≈ 0.2–0.3 R/Ra and 40Ar/36Ar ≈ 455–725, suggesting the ore-forming fluid is mainly derived from a crustal component with a minor contribution of mantle and meteoric fluids.

13

Zhang, Wan-Feng, De-Wen Zheng, Guo-Qing Liu, Yi-Gang Xu, and Ying-De Jiang. "Optimization of irradiation parameters for 40Ar/39Ar dating by Argus VI multi-collector mass spectrometry." Journal of Analytical Atomic Spectrometry 36, no. 7 (2021): 1374–80. http://dx.doi.org/10.1039/d1ja00055a.

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In ⁴⁰Ar/³⁹Ar dating, ³⁹Ar_K generated is dependent on irradiation conditions, and the accumulation fast neutron fluence is a critical parameter for ⁴⁰Ar/³⁹Ar dating.

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Hemming, Sidney R., Tanzhuo Liu, Paul Northrup, Sarah Nicholas, E. Troy Rasbury, Heng Chen, Alice Warden, et al. "Synchrotron Microanalytical Characterization and K/Ar Dating of the GL-O-1 Glauconite Reference Material at the Single Pellet Scale and Reassessment of the Age of Visually Mature Pellets." Minerals 13, no. 6 (June 5, 2023): 773. http://dx.doi.org/10.3390/min13060773.

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The K/Ar chronology of glauconite pellets is a long-used method for directly dating marine sedimentary deposits. Many papers have explored the processes that form glauconite and the factors that lead to greater reliability in the ages. Although K/Ar ages of glauconite are generally in agreement with other measures of stratigraphic age, there are examples of occurrences with ages too old and examples with ages too young. This paper seeks to build on the accumulated knowledge of glauconite, using synchrotron radiation to non-destructively characterize individual pellets and then consecutively measure the argon and potassium to obtain a K/Ar age. This strategy provides the advantage of measurements on a single aliquot while avoiding recoil loss of 40Ar in the nuclear reactor during irradiation for 40Ar/39Ar dating. We have used the glauconite reference material GL-O-1 to showcase several non-destructive methods for evaluating the maturity of individual pellets. In our argon measurements, we have found that the radiogenic argon concentration of large bulk samples underestimates the values for individual visually mature pellets, and we determined a K/Ar age of 101.0 ± 0.3 Ma (1σ SEM), M.S.W.D. 0.54 from 15 of 16 visually mature individual pellets. This age is 6% older than the reference value of 95.03 ± 1.11 Ma (1σ), and it is in good agreement with constraints from the U-Pb dating of volcanic minerals near the Albian–Cenomanian boundary.

15

Richards, Lachlan, Fred Jourdan, Alan Stephen Collins, and Rosalind Clare King. "Deformation recorded in polyhalite from evaporite detachments revealed by 40Ar ∕ 39Ar dating." Geochronology 3, no. 2 (December 13, 2021): 545–59. http://dx.doi.org/10.5194/gchron-3-545-2021.

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Abstract. The Salt Range Formation is an extensive evaporite sequence in northern Pakistan that has acted as the primary detachment accommodating Himalayan orogenic deformation from the north. This rheologically weak formation forms a mylonite in the Khewra Mine, where it accommodates approximately 40 km displacement and is comprised of intercalated halite and potash salts and gypsiferous marls. Polyhalite [K2Ca2Mg(SO4)4⚫2H2O] grains taken from potash marl and crystalline halite samples are used as geochronometers to date the formation and identify the closure temperature of the mineral polyhalite using the 40Ar/39Ar step-heating laser and furnace methods. The diffusion characteristics measured for two samples of polyhalite are diffusivity (D0), activation energy (Ea), and %39Ar. These values correspond to a closure temperature of ca. 254 and 277 ∘C for a cooling rate of 10 ∘C Myr−1. 40Ar/39Ar age results for both samples did not return any reliable crystallisation age. This is not unexpected as polyhalite is prone to 40Ar* diffusion loss and the evaporites have experienced numerous phases of deformation resetting the closed K/Ar system. An oldest minimum heating step age of ∼514 Ma from sample 06-3.1 corresponds relatively well to the established early Cambrian age of the formation. Samples 05-P2 and 05-W2 have measured step ages and represent a deformation event that partially reset the K/Ar system based on oldest significant ages between ca. 381 and 415 Ma. We interpret the youngest measured step ages, between ca. 286 and 292 Ma, to represent the maximum age of deformation-induced recrystallisation. Both the youngest and oldest measured step ages for samples 05-P2 and 05-W2 occur within the time of a major unconformity in the area. These dates may reflect partial resetting of the K/Ar system from meteoric water infiltration and recrystallisation during this non-depositional time. Otherwise, they may result from mixing of Ar derived by radiogenic decay after Cambrian precipitation with partially reset Ar from pervasive Cenozoic deformation and physical recrystallisation.

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Singer, Brad S., Robert P. Ackert,, and Hervé Guillou. "40Ar/39Ar and K-Ar chronology of Pleistocene glaciations in Patagonia." Geological Society of America Bulletin 116, no. 3 (2004): 434. http://dx.doi.org/10.1130/b25177.1.

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Wang, Fei, Ri-Xiang Zhu, Lie-Kun Yang, Huai-Yu He, and Ching-Hua Lo. "40Ar/39Ar analyses on Quaternary K–Ar standard BB-24: Evaluations." International Journal of Mass Spectrometry 270, no. 1-2 (February 2008): 16–22. http://dx.doi.org/10.1016/j.ijms.2007.11.002.

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Holm, Paul Martin. "Radiometric age determinations in the Kærven area, Kangerdlugssuaq, Bast Greenland Tertiary igneous Province: 40Ar/39 Ar, Kl Ar and Rb/Sr isotopic results." Bulletin of the Geological Society of Denmark 38 (February 18, 1991): 183–201. http://dx.doi.org/10.37570/bgsd-1990-38-18.

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The Kærven syenite complex was emplaced as part of the magmatic activity related to continental rifling in the Paleogene. Radiometric age determinations have been carried out on samples from selected parts of the complex, which consists of more !han 10 significant units. Five amphiboles and two alkali feldspar have been analysed by the 40Arl'9Ar method with stepwise heating, five amphiboles and one biotite K/Ar analyses are presented together with Rb/Sr isotope analysis of 6 amphiboles, 2 biotites, 3 alkali feldspars and 32 whole rocks. The results reveal that a Iate, probably 36 Ma, thermal event caused Ar-loss in the alkali feldspars and excess 40Ar-gain in variable amounts in the analysed minerals. Also the Sr isotopes were disturbed by the secondary heating. Crystallisation ages for parts of the Kærven complex can be established as 58 ± 1 Ma, while other units have younger ages of 56.1 ± 0.8 Ma and 50.4 ± 0.8 Ma. The age for the early Kærven rocks is significantly older than other recorded syenites in the Kangerdlugssuaq area and is comparable only to the estimated age of the initiation of basaltic volcanism along the East Greenland coast at 57 Ma. An Rb/Sr isochron for four nordmarkite whole rocks and a 40Ar/39 Ar age plateau of an amphibole from one nordmarkite date the part of the Kangerdlugssuaq alkaline intrusion adjacent to the Kærven complex as 54.6 ± 2.4 Ma. This is older than other parts of the Kangerdlugssuaq intrusion, and indicate that this intrusion was multiple and emplaced over several million years

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Uysal, I. Tonguç, Claudio Delle Piane, Andrew James Todd, and Horst Zwingmann. "Precambrian faulting episodes and insights into the tectonothermal history of north Australia: microstructural evidence and K–Ar, 40Ar–39Ar, and Rb–Sr dating of syntectonic illite from the intracratonic Millungera Basin." Solid Earth 11, no. 5 (September 4, 2020): 1653–79. http://dx.doi.org/10.5194/se-11-1653-2020.

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Abstract. Australian terranes concealed beneath Mesozoic cover record complex Precambrian tectonic histories involving a successive development of several Proterozoic to Palaeozoic orogenic systems. This study presents an integrated approach combining K–Ar, 40Ar–39Ar, and Rb–Sr geochronologies of Precambrian authigenic illites from the recently discovered Millungera Basin in north-central Australia. Brittle deformation and repeated fault activity are evident from the sampled cores and their microstructures, probably associated with the large-scale faults inferred from interpretations of seismic surveys. Rb–Sr isochron, 40Ar–39Ar total gas, and K–Ar ages are largely consistent in indicating late Mesoproterozoic and early Proterozoic episodes (∼1115±26, ∼ 1070±25, ∼1040±24, ∼1000±23, and ∼905±21 Ma) of active tectonics in north-central Australia. K–Ar results show that illites from fault gouges and authigenic matrix illites in undeformed adjacent sandstones precipitated contemporaneously, indicating that advection of tectonically mobilized fluids extended into the undeformed wall rocks above or below the fracture and shear (fault gouge) zones. Isotopic age data clearly indicate a Mesoproterozoic minimum age for the Millungera Basin and thus previously unrecorded late Mesoproterozoic–early Neoproterozoic tectonic events in north-central Australia. This study provides insight into the enigmatic time–space distribution of Precambrian tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant energy and mineral resources.

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Balogh, Kadosa, and Imre Kádár. "Changes in the structure and formal K-Ar age of soil minerals in response to mineral fertilization." Agrokémia és Talajtan 62, no. 1 (June 1, 2013): 81–98. http://dx.doi.org/10.1556/agrokem.62.2013.1.6.

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Ismeretes, hogy trágyázás hatására a talaj agyagásványai megváltoztatják szerkezetüket. Továbbá az is, hogy az Alföld fiatal üledékein mérhető formális K-Ar „korok” legtöbbször mezozoosak. Azaz lényegében megőrizték képződésük korát, mely a lepusztulás, elszállítódás és lerakódás folyamán csak nagyon keveset változhatott. Következésképpen a talajműveléssel járó ásványátalakulás megváltoztatja a formális K-Ar korokat is. Ennek a valószínűsíthető effektusnak a kimutatására tettünk kísérletet annak reményében, hogy a K-Ar módszer alkalmassá tehető azoknak az elváltozásoknak az integrális mérésére, melyeket az agyagásványok képződésük óta elszenvedtek. E munka során biztató eredményeket értünk el, és sikerült körvonalaznunk a további megoldandó feladatokat. Kimutattuk, hogy:A soha nem trágyázott erdő talaj agyagásványainak K-Ar „kora” idősebb a szomszédos, trágyázott nagyüzemi szántó agyagásványainak „koránál”. Az ismert mennyiségű NPK-val trágyázott talajok agyagásványai közül a nagyobb mennyiségű K-műtrágyát kapott talaj agyagásványain mutatható ki fiatalodás, mintha az effektusnak küszöbértéke lenne. A K-műtrágyát nem kapott talajok közül azok kora az „idősebb”, amelyek NP-trágyázásban részesültek. Ez a növényzet K-felvételével lenne magyarázható: ha a NP-trágyázás hatására a növényzet több káliumot vesz fel úgy, hogy a felvett kálium részben a rétegszilikátokból származik. Ebben az esetben a K-Ar kor akkor növekedhet, ha a kálium a 40Ar(rad)-nál nagyobb arányban távozik az agyagásványokból. Ez lehetséges, mivel a 40Ar(rad) keletkezésekor a bomlás visszalökődési energiájának segítségével a 40Ar(rad) átjuthat az oktaéderes rétegbe.A bemutatott 2. táblázat adatai szerint a K-Ar „kor” függ a szemcsemérettől, a kisebb szemcsék „fiatalabbak”. Ez a függés rendkívül hasonló a kisfokú metamorfitokon megfigyelthez. A fiatal üledékek nemcsak a kort, hanem annak a szemcsemérettől való függését is megőrizték a kisfokú metamorfózistól a talajképződésig eltelt idő alatt. A szemcseméret függés oka az illitesedés folyamatának elhúzódása az átalakuláshoz szükséges kálium lassú diffúziója miatt. Az üledékes kőzeten kialakult talaj szemcseméretét a szállítás és talajképződés során végbement aprózódás és mállás ugyanakkor tovább alakítják. Ha tehát a trágyázás hatására bekövetkezett változást kívánjuk vizsgálni, akkor alapvető követelmény, hogy a referenciának használt és a hozzá hasonlított talajból ugyanazt a szemcseméretet vizsgáljuk. Emiatt, a szemcsék összetapadását elkerülendő, kísérletet tettünk a szemcsék karbonátmentesítésére, továbbá a humuszsavak elroncsolására is.A 3. táblázatban együtt tanulmányozhatók a kezeletlen mintákból és a karbonát- és humuszmentesített mintákból elválasztott ásványokon mért K, 40Ar(rad) és koradatok. A karbonát- és humuszmentesítés hatására minden mintában dúsult a Kkoncentráció, a formális K-Ar kor szintén emelkedett, ami azt mutatja, hogy a minták illittartalma nőtt. Emellett azonban a kontrollhoz képest „fiatalodott kort” csak a 4. és 7. minta esetén észleltünk, e két minta közös vonása a K-tartalom nagyobb növekedése és a műtrágyaként hozzáadott kálium magas értéke; ez az eddigiek fényében nem meglepő. Érdekes viszont, hogy a káliumban leggazdagabb 10. minta kora nem csökkent érdemben. Ennek oka vélhetően az, hogy ez a talaj volt a legnagyobb mennyiségű NP-műtrágyával kezelve, ami megnövelhette a növényzet Kfelvételét is (vagy az NH4-ion K-iont szorított ki), így az agyagásványok átalakítására kevesebb kálium maradt.A módszer alkalmazása olyan referencia talaj használatát kívánja meg, ami eredetileg azonos volt a vizsgált talajjal, de trágyázásban nem részesült. Ezt a feltételt egy öreg erdő talaja teljesíti. Az öreg erdők ritkasága az Alföldön azonban korlátozza a módszer alkalmazhatóságát. Felvetődött a kérdés, hogy mivel a kálium nagyon gyorsan megkötődik, a mélyebb talajréteg nem használható-e referencia talajként? A formális K-Ar kor mélységfüggését a 4. táblázatban foglalt adatok egyértelműen mutatják, a mélységgel a formális kor nő. Ebben az esetben viszont nem különböztethető meg a K-műtrágya és az ősi növényzet feltalajban akkumulált K-hatása. A feltételezett effektus kimutatása után a mérési módszer kidolgozása további vizsgálatokat igényel, mindenekelőtt a mintaelőkészítés területén. A továbblépéshez nélkülözhetetlennek látszik az agyagásványminták XRD módszeres vizsgálata. Továbbá a szmektit, az I/S és az illit szétválasztásának, illetve dúsításának megkísérlése eltérő peptizálódásuk alapján, esetleg a kisebb méretű ásványok elválasztása centrifugálással.Az alkalmazási lehetőségek közül fontos lehet az ásványátalakulás mértékének tanulmányozása a talajtípus és a művelés történetének függvényben; a növényzet milyenségének hatása az ásványátalakulásra; továbbá az alföldi folyók gátjai között a folyószabályozás óta leülepedett, azonos fekün képződött talajon a kor mélységfüggésének tanulmányozása, ami ebben az esetben lehetővé tenné a növényzet által felszínre szállított kálium mennyiségének és ásványátalakító hatásának elkülönített tanulmányozását.

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Guan, Yao, Yingzhi Ren, Xiaoming Sun, Zhenglian Xiao, and Zhengxing Guo. "Helium and Argon Isotopes in the Fe-Mn Polymetallic Crusts and Nodules from the South China Sea: Constraints on Their Genetic Sources and Origins." Minerals 8, no. 10 (October 22, 2018): 471. http://dx.doi.org/10.3390/min8100471.

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In this study, the He and Ar isotope compositions were measured for the Fe-Mn polymetallic crusts and nodules from the South China Sea (SCS), using the high temperature bulk melting method and noble gases isotope mass spectrometry. The He and Ar of the SCS crusts/nodules exist mainly in the Fe-Mn mineral crystal lattice and terrigenous clastic mineral particles. The results show that the 3He concentrations and R/RA values of the SCS crusts are generally higher than those of the SCS nodules, while 4He and 40Ar concentrations of the SCS crusts are lower than those of the SCS nodules. Comparison with the Pacific crusts and nodules, the SCS Fe-Mn crusts/nodules have lower 3He concentrations and 3He/4He ratios (R/RA, 0.19 to 1.08) than those of the Pacific Fe-Mn crusts/nodules, while the 40Ar/36Ar ratios of the SCS samples are significantly higher than those of the Pacific counterparts. The relatively low 3He/4He ratios and high 40Ar concentrations in the SCS samples are likely caused by terrigenous detrital input with high radiogenic 4He and 40Ar contents. The SCS crusts and nodules have shorter growth periods, implying that in situ post-formation radiogenic 3He, 4He and 40Ar produced by decay of U, Th and K have no effect on their isotope compositions. Thus, the SCS crusts/nodules inherited the noble gases characteristics of their sources. Helium and Ar isotope compositions in the SCS Fe-Mn crusts and nodules reflect the product of an equilibrium mixture between air-saturated seawater and radiogenic components during their growth, while the partial 3He excess in some SCS samples may represent a little mantle-derived origin. The different He and Ar isotope compositions of the Fe-Mn crusts and nodules between the South China Sea and the Pacific Ocean are due to their different sources and genetic processes. The characteristics of He and Ar isotope compositions in the SCS polymetallic crusts and nodules are similar to the properties of hydrogenetic Fe-Mn oxide/hydroxide precipitates, which reflects mainly the product of an equilibrium mixture between air-saturated seawater and radiogenic components.

22

Guillou, Herve. "Combined K-Ar and 40Ar/39Ar dating of the top Jaramillo boundary." Quaternary International 279-280 (November 2012): 180–81. http://dx.doi.org/10.1016/j.quaint.2012.08.277.

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23

McDougall, Ian, and Peter Wellman. "Calibration of GA1550 biotite standard for K/Ar and 40Ar/39Ar dating." Chemical Geology 280, no. 1-2 (January 2011): 19–25. http://dx.doi.org/10.1016/j.chemgeo.2010.10.001.

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24

Hart, Craig JR, and Mike Villeneuve. "Geochronology of Neogene alkaline volcanic rocks (Miles Canyon basalt), southern Yukon Territory, Canada: the relative effectiveness of laser 40Ar/39Ar and K-Ar geochronology." Canadian Journal of Earth Sciences 36, no. 9 (September 1, 1999): 1495–507. http://dx.doi.org/10.1139/e99-049.

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Miles Canyon basalt is an informal term used to describe numerous exposures of young alkaline olivine basalt flows in southern Yukon. The volcanic rocks are part of the Northern Cordilleran volcanic province. K-Ar and Ar-Ar whole-rock dates indicate that the Miles Canyon succession of flows at the Whitehorse Rapids are clearly Late Miocene in age (ca. 8.4 Ma). The largest exposure of the Miles Canyon basalt occurs at the Alligator Lake volcanic complex where two nearly concordant Pliocene Ar-Ar dates indicate eruption at ca. 3.2 Ma. K-Ar analyses from other sites yield dates of 2.4 and 7.1 Ma and indicate an episodic Neogene volcanic history for the region. There is no evidence of Quaternary or postglacial volcanism. The dates are older than assumed by previous workers, and in some cases the K-Ar dates are strongly discordant from Ar-Ar determinations. More accurate Ar-Ar determinations may result from the method's ability to select smaller amounts of better material for analysis. Excess 40Ar was not encountered. As a result, the accuracy of any single or several discordant K-Ar determinations for Neogene subaerial volcanic rocks, particularly low-K rocks such as basalts, should be questioned and resulting interpretations made with caution. Models accounting for the eruption of the Northern Cordilleran volcanic province lavas have typically relied upon extension along north-trending faults that were generated by stresses along the continental margin. However, we consider a slab window model which better accounts for the initiation and distribution of northern Cordilleran Neogene volcanic activity.

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Clauer, Norbert. "The K-Ar and 40Ar/39Ar methods revisited for dating fine-grained K-bearing clay minerals." Chemical Geology 354 (September 2013): 163–85. http://dx.doi.org/10.1016/j.chemgeo.2013.05.030.

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Dunlap, W. James, Christian Teyssier, Ian McDougall, and Suzanne Baldwin. "Ages of deformation from K/Ar and 40Ar/39Ar dating of white micas." Geology 19, no. 12 (1991): 1213. http://dx.doi.org/10.1130/0091-7613(1991)019<1213:aodfka>2.3.co;2.

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Clauer, N., J. Środoń, J. Francu, and V. Šucha. "K-Ar dating of illite fundamental particles separated from illite-smectite." Clay Minerals 32, no. 2 (June 1997): 181–96. http://dx.doi.org/10.1180/claymin.1997.032.2.02.

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AbstractFundamental particles of illite-smectite from bentonites were separated into classes by high-speed centrifugation after infinite osmotic swelling of mixed-layer crystals, achieved by Na-exchange and dispersion in distilled water. In samples free of detrital contamination, the thinnest fundamental particles yield older K-Ar ages than the thicker fundamental particles. This implies that they do not preferentially lose radiogenic 40Ar due to size, and that the illitization process is a crystal growth mechanism (not nucleation plus growth). As a result, any K-Ar age of fundamental illite particles from bentonites is an integral over longer or shorter periods of time, depending on the thermal history of the rocks. In thick bentonite beds, the measured age difference between the beginning of the illitization process at the contact with the host rocks and the end in the centre of the bed records extremely slow K diffusion in these well compacted rocks. These data explain why measured K-Ar ages of illite-smectite from bentonites are younger than the corresponding age of shale illitization, inferred from the burial history of the basin. The finest technically separable size-fractions of associated shales (<0.02 μm) yield K-Ar dates* greater than the stratigraphic age. This observation points to incomplete recrystallization of detrital illite during burial diagenesis.

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Cogliati, Simone, Sarah C. Sherlock, Alison M. Halton, Alena Ebinghaus, Simon P. Kelley, David W. Jolley, and Tiffany L. Barry. "Expanding the toolbox for dating basaltic lava sequences: 40Ar–39Ar dating of silicic volcanic glass from interbeds." Journal of the Geological Society 178, no. 1 (September 10, 2020): jgs2019–207. http://dx.doi.org/10.1144/jgs2019-207.

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40Ar–39Ar dating of glass shards from silicic tuffs of the Ellensburg Formation (NW, USA) interbedding basaltic lavas yielded accurate, precise, reproducible plateau and isochron ages that are within error at the 2σ level. The age-spectra have flat plateaus and the inverse isochrons have atmospheric 40Ar/36Ar at the 2σ level. Ages of 12.00 ± 0.24, 11.37 ± 0.15, 10.67 ± 0.21 and 10.70 ± 0.18 Ma are consistent with the stratigraphy of four of the dated layers; the age of 10.77 ± 0.18 Ma for a fifth layer is at odds with the stratigraphy. This discrepancy arises due to the effect of glass alteration that induced K- and Ar-loss. There is no evidence of excess 40Ar or 39Ar recoil. The new ages indirectly constrain the timing of eruption of the lavas above and below the ash beds. This demonstrates that volcanic glass from interbeds can be used as an additional tool for indirectly dating basaltic lava sequences, which is independent of the lavas and complementary to other materials. Considering the numerous studies in which volcanic glass failed to provide reliable 40Ar–39Ar ages, additional and supportive constraints are still needed to assess the validity of the ages from glass shards.Supplementary material: A1 – sample location, stratigraphic position and depositional environments; A2 – electron microprobe information with calibration and sample data; A3 – Ar isotopic data of blanks and samples, data reduction software, J values, criteria for age calculation and images of age spectra and inverse isochrons are available at https://doi.org/10.6084/m9.figshare.c.5077705

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Gilbert, Lisa A., and K. A. Foland. "The Mont Saint Hilaire plutonic complex: occurrence of excess 40Ar and short intrusion history." Canadian Journal of Earth Sciences 23, no. 7 (July 1, 1986): 948–58. http://dx.doi.org/10.1139/e86-096.

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Mont Saint Hilaire is an approximately 10 km2 alkaline plutonic complex in the Monteregian petrographic province of Quebec. The complex consists of an older, western half of alkali gabbros and an eastern portion of nepheline syenites and magmatic breccias. The intrusives were emplaced at depths of no more than a few kilometres into Paleozoic sedimentary rocks through the underlying Grenville basement. 40Ar/39Ar analyses of amphibole yield complex age spectra in which the apparent ages decrease with increasing heating temperature. Conventional K–Ar analyses of amphibole, pyroxene, and feldspar yield anomalously old dates. These data indicate the presence of small yet significant amounts (up to 8 × 10−11 mol/g) of excess 40Ar. The quantities of excess argon are variable between rocks and minerals from the same rock. In contrast, biotites yield concordant plateaus and consistent ages ranging only from 124.1 to 124.6 Ma. These data define the age of the complex (124.4 ± 1.2 Ma) and imply a short time span of emplacement of about 0.5 Ma or less. The restricted time interval suggests the various lithologies are cogenetic. The nature of the amphibole 40Ar/39Ar spectra indicates that excess 40Ar was acquired after crystallization. The 40Ar could have been present in the initial magma either from crustal assimilation or from a mantle source. Alternatively, it could have been derived from outgassing of older crustal rocks. The occurrence of excess 40Ar in epizonal plutons may be a more widespread phenomenon than commonly recognized.

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Franz, Gerhard, Masafumi Sudo, and Vladimir Khomenko. "40Ar/39Ar dating of a hydrothermal pegmatitic buddingtonite–muscovite assemblage from Volyn, Ukraine." European Journal of Mineralogy 34, no. 1 (January 12, 2022): 7–18. http://dx.doi.org/10.5194/ejm-34-7-2022.

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Abstract. We determined 40Ar/39Ar ages of buddingtonite, occurring together with muscovite, with the laser-ablation method. This is the first attempt to date the NH4-feldspar buddingtonite, which is typical for sedimentary–diagenetic environments of sediments, rich in organic matter, or in hydrothermal environments, associated with volcanic geyser systems. The sample is a hydrothermal breccia, coming from the Paleoproterozoic pegmatite field of the Korosten Plutonic Complex, Volyn, Ukraine. A detailed characterization by optical methods, electron microprobe analyses, backscattered electron imaging, and IR analyses showed that the buddingtonite consists of euhedral-appearing platy crystals of tens of micrometers wide, 100 or more micrometers in length, which consist of fine-grained fibers of ≤ 1 µm thickness. The crystals are sector and growth zoned in terms of K–NH4–H3O content. The content of K allows for an age determination with the 40Ar/39Ar method, as well as in the accompanying muscovite, intimately intergrown with the buddingtonite. The determinations on muscovite yielded an age of 1491 ± 9 Ma, interpreted as the hydrothermal event forming the breccia. However, buddingtonite apparent ages yielded a range of 563 ± 14 Ma down to 383 ± 12 Ma, which are interpreted as reset ages due to Ar loss of the fibrous buddingtonite crystals during later heating. We conclude that buddingtonite is suited for 40Ar/39Ar age determinations as a supplementary method, together with other methods and minerals; however, it requires a detailed mineralogical characterization, and the ages will likely represent minimum ages.

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Isava, V., M. Grove, J. B. Mahoney, and J. W. Haggart. "Testing local and extraregional sediment sources for the Late Cretaceous northern Nanaimo basin, British Columbia, using 40Ar/39Ar detrital K-feldspar thermochronology." Geosphere 17, no. 6 (November 8, 2021): 2234–61. http://dx.doi.org/10.1130/ges02395.1.

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Abstract Detrital K-feldspar 40Ar/39Ar thermochronology was conducted on clastic sedimentary rock samples collected from northern exposures of the Upper Cretaceous Nanaimo Group on Vancouver Island and adjacent Gulf Islands of British Columbia to constrain the denudation history of the local Coast Mountains batholith source region and determine the origin of extraregional sediment supplied to the basin. Strata of the northern Nanaimo Group deposited between 86 and 83 Ma (Comox and Extension formations) exhibit a 130–85 Ma age distribution of detrital K-feldspar 40Ar/39Ar ages that lack age maxima. These are interpreted to have been sourced from the southwestern Coast Mountains batholith. Younger strata deposited between 83 and 72 Ma (Cedar District and De Courcy formations) yield a broader age range (150–85 Ma) with an age maximum near the depositional age. These results indicate focused denudation of deeper-seated rocks east of the Harrison Lake fault. The youngest units deposited after 72 Ma (Geoffrey, Spray, and Gabriola formations) primarily yield younger than 75 Ma detrital K-feldspar ages with pronounced age maxima near the depositional age. This sediment was sourced extraregionally relative to the Coast Mountains batholith. We sought to constrain the origin of the extraregional sediment by measuring the thermal histories of 74 samples of basement rocks from throughout the Pacific Northwest, and by compiling a database of over 2400 biotite 40Ar/39Ar and K/Ar cooling ages from predominantly Cretaceous batholiths along the western North American margin. This analysis focused upon two previously proposed source regions: the Idaho batholith and the Mojave-Salina margin of southern California. The Nanaimo detrital K-feldspar 40Ar/39Ar age distributions favor the peraluminous Late Cretaceous Idaho batholith and its Proterozoic Belt-Purcell Supergroup sedimentary wall rock as the more likely source of the extraregional sediment and disfavor the Baja–British Columbia hypothesis for 2000–4000-km-scale translation of rocks along the margin during the Late Cretaceous.

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Kaufman, Darrell S., Robert C. Walter, Julie Brigham-Grette, and David M. Hopkins. "Middle Pleistocene age of the Nome River glaciation, northwestern Alaska." Quaternary Research 36, no. 3 (November 1991): 277–93. http://dx.doi.org/10.1016/0033-5894(91)90003-n.

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AbstractDuring the middle Pleistocene Nome River glaciation of northwestern Alaska, glaciers covered an area an order of magnitude more extensive than during any subsequent glacial intervals. The age of the Nome River glaciation is constrained by laser-fusion 40Ar/39Ar analyses of basaltic lava that overlies Nome River drift at Minnie Creek, central Seward Peninsula, that average 470,000 ± 190,000 yr (±1σ). Milligram-size subsamples of the lava were dated to identify and eliminate extraneous 40Ar enrichments that rendered the mean of conventional K-Ar dates on larger bulk samples of the same flow too old (700,000 ± 570,000 yr). While the 40Ar/39Ar analyses provide a minimum limiting age for the Nome River glaciation, maximum ages are provided by a provisional K-Ar date on a basaltic lava flow that underlies the Nome River drift at nearby Lave Creek, by paleomagnetic determinations of the drift itself at and near the type locality, and by amino acid epimerization analysis of molluscan fossils from nearshore sediments of the Anvilian marine transgression that underlie Nome River drift on the coastal plain at Nome. Taken together, the new age data indicate that the glaciation took place between 580,000 and 280,000 yr ago. The altitude of the Anvilian deposits suggests that eustatic sea level during the Anvilian transgression rose at least as high as and probably higher than during the last interglacial transgression; by correlation with the marine oxygen-isotope record, the transgression probably dates to stage 11 at 410,000 yr, and the Nome River glaciation is younger still. Analyses of floor altitudes of presumed Nome River cirques indicate that the Nome River regional snowline depression was at least twice that of the maximum late Wisconsin. The cause of the enhanced snowline lowering appears to be related to greater availability of moisture in northwestern Alaska during the middle Pleistocene.

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di Brozolo, Filippo Radicati, Pio Di Girolamo, Bruno Turi, and Massimo Oddone. "40Ar-39Ar and K-Ar dating of K-rich rocks from the Roccamonfina Volcano, Roman comagmatic Region, Italy." Geochimica et Cosmochimica Acta 52, no. 6 (June 1988): 1435–41. http://dx.doi.org/10.1016/0016-7037(88)90213-x.

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34

Glasmacher, Ulrich A., Alain Tremblay, and Norbert Clauer. "K-Ar dating constraints on the tectonothermal evolution of the external Humber zone, southern Quebec Appalachians." Canadian Journal of Earth Sciences 40, no. 2 (February 1, 2003): 285–300. http://dx.doi.org/10.1139/e02-105.

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In the external Humber zone, the emplacement episodes of allochthonous nappes and related low-grade metamorphism are mainly based on paleontological ages from the St. Lawrence Lowlands. In fact, Late Ordovician flysches are affected by thrusting, and it is not clear if the nappe imbrication is the result of the Taconian or the Acadian deformation. Along the Chaudière River transect, fourteen shales and phyllites of Cambrian to Ordovician age were sampled for determination of the KAr values of their < 2 µm-size fractions. To interpret the KAr data, mineral composition and clay mineral crystallinity of the < 2 µm-size fractions and maturation of the organic matter were determined. In addition, the intensity of deformation was characterized by describing the rock texture at macroscopic and microscopic scale. The combined approach used in this study emphasized that nearly all KAr dates are mixed or partly reset values. However, it can be stated that in the Quebec Promontory nappe and part of the Chaudière nappe, a Cretaceous thermal overprint might have occurred on the basis of a low KAr value at 256 Ma. Furthermore, the KAr dates of 491467 Ma obtained in the Chaudière nappe to the southeast, most probably represent mixed values of detrital material affected by diagenetic or tectonic processes. It might also be stated that the base of the Sainte-Hénédine nappe appears to be characterized by southeast-dipping thrust sheets with KAr dates of 439418 Ma, which may represent either a late-stage emplacement of the nappe or a yet unrecognized structural effect of hinterland-directed deformation that characterizes the internal Humber zone. In the southeastern part of the Sainte-Hénédine nappe, the thermal grade increases to epizonal conditions and the KAr dates that, in this case, could be of meaningful geological significance increase to 455445 Ma. Such ages are consistent with Ordovician 40Ar/39Ar metamorphic ages attributed to the Taconian orogeny in the internal Humber zone.

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Strutinski, Carol, Adrian Puște, and Rodica Stan. "The metamorphic basement of Romanian Carpathians: a discussion of K-Ar and 40Ar/39Ar ages." Studia Universitatis Babes-Bolyai, Geologia 51, no. 1-2 (April 2006): 15–21. http://dx.doi.org/10.5038/1937-8602.51.1.2.

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Radhakrishna, T., H. Maluski, J. G. Mitchell, and M. Joseph. "40Ar/39Ar and K/Ar geochronology of the dykes from the south Indian granulite terrain." Tectonophysics 304, no. 1-2 (March 1999): 109–29. http://dx.doi.org/10.1016/s0040-1951(98)00288-1.

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Smith, P. E., D. York, R. M. Easton, Ö. Özdemir, and P. W. Layer. "A laser 40Ar–39Ar study of minerals across the Grenville Front: investigation of reproducible excess Ar patterns." Canadian Journal of Earth Sciences 31, no. 5 (May 1, 1994): 808–17. http://dx.doi.org/10.1139/e94-074.

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Abstract:

40Ar–39Ar ages have been determined on single grains of biotite and amphibole from rocks on a 40 km traverse across the Grenville Front (GF) in the Temagami area, Ontario. Minerals in the vicinity of the GF contain excess Ar in varying amounts characterized by both anomalously high integrated and plateau ages. The excess Ar in biotite varies with distance from the GF, such that the overall age distribution along the GF forms an asymmetric wave-like pattern (an argonami) with two age maxima, one on either side of the GF. The integrated age maxima are 2.34 Ga for biotite and 3.21 Ga for amphibole located 6 and 0.2 km north of the GF, respectively, whereas maxima are 1.33 Ga for biotite and 1.50 Ga for amphibole 7 km south of the GF. This wave-like pattern of apparent ages shows a remarkable similarity with that seen in an earlier K–Ar study across the GF at Chibougamau, Quebec, and also with a small-scale pattern of excess Ar associated with the emplacement of a dyke. Variations in the magnitude of excess Ar in minerals can be interpreted in terms of the interaction of variable mineral blocking trajectories with the ambient partial pressure of Ar, and their patterns may also provide clues to underlying tectonic structures associated with the anomalies.The time–temperature relationships for minerals geographically located beyond the effects of significant excess Ar suggest that the crust in the Temagami area was subjected to more rapid cooling relative to gneisses of the interior of the Grenville Province.

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Stuart, F. M. "The exhumation history of orogenic belts from 40Ar/39Ar ages of detrital micas." Mineralogical Magazine 66, no. 1 (February 2002): 121–35. http://dx.doi.org/10.1180/0026461026610017.

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AbstractThe exhumation history of mountain belts can be derived from radiometric dating of detrital mineral grains in proximal and distal post- and synorogenic sediments. The application of single-crystal dating techniques avoids the averaging effect that characterizes multi-grain and whole-rock techniques and allows the identification of populations of grains with distinct thermal histories. Of the major single crystal dating methods available, 40Ar/39Ar dating of detrital K-bearing minerals, in particular white mica, is perhaps the most versatile and widely applied technique. For a closure temperature of Ar of 350–400°C, muscovite 40Ar/39Ar ages record the time a rock mass passed through 8–10 km beneath actively eroding mountain belts. Detrital muscovit ages eroded from orogenic mountain belts have been used extensively to identify the provenance of sediments from source regions with distinct thermal histories, determine the history and rate of exhumation of the source region, and provide an upper limit on the sediment age. Here I review the principles of 40Ar/39Ar dating of detrital muscovite and illustrate the method with examples showing how the provenance and the thermal history of sediment source regions derived from such studies can be used to constrain the exhumation and tectonic history of orogenic belts.

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Webster, Ewan R., Douglas A. Archibald, David R. M. Pattison, Jessica A. Pickett, and Joel C. Jansen. "Tectonic domains and exhumation history of the Omineca Belt in southeastern British Columbia from 40Ar/39Ar thermochronology." Canadian Journal of Earth Sciences 57, no. 8 (August 2020): 918–46. http://dx.doi.org/10.1139/cjes-2019-0131.

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Abstract:

A large geochronological data set comprising 40Ar/39Ar and K–Ar (hornblende, muscovite, biotite, and K-feldspar), Rb–Sr (muscovite), fission track (zircon and apatite) and U–Pb (zircon and monazite) dates has been compiled for the southern Kootenay Arc and western Purcell anticlinorium in the Omineca Belt of the Canadian Cordillera in southeastern British Columbia. New 40Ar/39Ar data for hornblende, muscovite, biotite, and alkali feldspar are presented and combined with data from other studies. We integrate these data with recent advances in the geology of the region to define three partially fault-bounded domains with differing geological and exhumation histories, here termed the western, central, and eastern domains. The western domain is characterized by (1) late synkinematic Jurassic plutons with hornblende, muscovite, and biotite 40Ar/39Ar plateau dates between 170 and 165 Ma, some of which are within error of the U–Pb zircon dates for these plutons, and (2) late Early Cretaceous (118–102 Ma) plutons commonly with concordant mica 40Ar/39Ar plateau dates of a similar age range, indicating rapid cooling following emplacement of both suites. The central domain is bounded by regional-scale normal faults (Gallagher and Midge Creek faults, Blazed Creek/Next Creek faults, and Purcell Trench fault) and contains superposed Early and Late Cretaceous zones of Barrovian metamorphic rocks and several mid- to Late Cretaceous, post-kinematic plutons. The transition from the western domain into the central domain is characterized by 40Ar/39Ar mica age spectra showing a progression of increasing thermal overprinting. Along the north–south length of the central domain, biotite and muscovite yield Paleocene to Eocene K–Ar and 40Ar/39Ar plateau dates between 66 and 40 Ma. The eastern domain consists of (1) a southern portion that occurs in the hanging wall of the Purcell Trench fault, comprising mid-Cretaceous intrusions of the Bayonne magmatic suite emplaced into biotite zone metasedimentary rocks of the Mesoproterozoic Belt-Purcell Supergroup in the western Purcell anticlinorium, and (2) a northern portion that shows a continuous transition with the northern part of the central domain north of the terminus of the Purcell Trench fault. Cretaceous igneous rocks in the southern portion of the eastern and western domains have 40Ar/39Ar mica plateau dates that are <9 Myr younger than U–Pb zircon dates, indicating rapid cooling shortly after emplacement. 40Ar/39Ar step-heating reveals that there was a mid- to Late Cretaceous thermal disturbance in the eastern domain, possibly related to emplacement of younger plutons at deeper crustal levels and the Late Cretaceous Barrovian metamorphic event recorded in rocks of the central domain, such that biotite with dates <ca. 73 Ma yield plateau age spectra but those with older dates are disturbed. The new geochronology, combined with recent mapping and metamorphic studies, leads to the conclusion that the exhumation of the Barrovian metamorphic rocks of the central domain was a multi-stage process. The central domain experienced rapid tectonic decompression and minor pluton emplacement in the Late Cretaceous to early Paleocene (76–61 Ma) when the Cordilleran orogen was under regional contraction during which most of the exhumation occurred. Final exhumation in the footwall of Eocene normal faults was less significant and occurred between 53 and ca. 46 Ma when the Cordilleran orogen had transitioned to regional extension, by which time the three domains had attained a similar crustal level. These episodes of exhumation are similar to those found in other core complexes in the southern Canadian Cordillera and contiguous northern Idaho and Washington. The earlier episode is coincident with regional-scale, Late Cretaceous thrust faulting in the Foreland Belt of the Rocky Mountains. Eocene normal faulting and final exhumation of core complexes in the Omineca Belt mark the end of contraction in the Foreland Belt.

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Rogers, Raymond R., Carl C. Swisher III, and John R. Horner. "40Ar/39Ar age and correlation of the nonmarine Two Medicine Formation (Upper Cretaceous), northwestern Montana, U.S.A." Canadian Journal of Earth Sciences 30, no. 5 (May 1, 1993): 1066–75. http://dx.doi.org/10.1139/e93-090.

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The age of the nonmarine Two Medicine Formation of northwestern Montana is currently based upon correlations with K–Ar-dated Western Interior ammonite zones. 40Ar/39Ar dating of biotite and plagioclase separated from four bentonites and one crystal-rich tuff permits for the first time direct determination of the age of Two Medicine strata. Biotite and plagioclase from a bentonite 10 m below the top of the Two Medicine Formation yield concordant 40Ar/39Ar ages of 74 Ma, while biotite and plagioclase from two bentonites and a crystal-rich tuff from approximately 100 m above the base of the formation cluster in age around 80 Ma. The total duration of Two Medicine deposition is estimated using these new radio-isotopic ages via extrapolation of an average rock accumulation rate.The new 40Ar/39Ar ages facilitate regional correlation of the dinosaur-dominated paleofauna recovered from the Two Medicine Formation, and help constrain the timing of the Claggett and Bearpaw transgressions. The ages support correlation of the richly fossiliferous upper lithofacies suite of the Two Medicine Formation with exposures of the Judith River Formation in Dinosaur Provincial Park, Alberta, Canada. Radioisotopically dated exposures of the Judith River Formation within Montana that include important Judithian "age" mammal localities correlate approximately with middle and lower parts of the middle lithofacies suite of the Two Medicine Formation. The new 40Ar/39Ar ages further indicate that the transgressions of the Claggett and Bearpaw seas culminated within northwestern Montana at ca. 79.6 and 74.0 Ma, respectively.

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SAITO, Kazuo, Soichi OSOZAWA, and Ken-ichi ISHIKAWA. "40Ar-39Ar and K-Ar ages of the igneous blocks in the Setogawa and Mikasa Groups." JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY 87, no. 7 (1992): 255–64. http://dx.doi.org/10.2465/ganko.87.255.

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Uto, Kozo, and Osamu Ishizuka. "The current state and the future of K-Ar and 40Ar/39Ar dating of volcanic rocks." Journal of the Japanese Association for Petroleum Technology 64, no. 1 (1999): 63–71. http://dx.doi.org/10.3720/japt.64.63.

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TAKAGI, Tetsuichi, and Atsushi KAMEI. "40Ar-39Ar and K-Ar geochronology for plutonic rocks in the central Abukuma Plateau, northeastern Japan." Journal of Mineralogical and Petrological Sciences 103, no. 5 (2008): 307–17. http://dx.doi.org/10.2465/jmps.071120.

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Reuter, A., and R. D. Dallmeyer. "K-Ar and 40Ar/39Ar dating of cleavage formed during very low-grade metamorphism: a review." Geological Society, London, Special Publications 43, no. 1 (1989): 161–71. http://dx.doi.org/10.1144/gsl.sp.1989.043.01.10.

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Guillou, Hervé, Sébastien Nomade, Juan Carlos Carracedo, Catherine Kissel, Carlo Laj, Francisco José Perez Torrado, and Camille Wandres. "Effectiveness of combined unspiked K–Ar and 40Ar/39Ar dating methods in the 14C age range." Quaternary Geochronology 6, no. 6 (December 2011): 530–38. http://dx.doi.org/10.1016/j.quageo.2011.03.011.

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Rouchon, Virgile, Jean-Claude Lefèvre, Xavier Quidelleur, Gilles Guérin, and Pierre-Yves Gillot. "Nonspiked 40Ar and 36Ar quantification using a quadrupole mass spectrometer: A potential for K–Ar geochronology." International Journal of Mass Spectrometry 270, no. 1-2 (February 2008): 52–61. http://dx.doi.org/10.1016/j.ijms.2007.11.009.

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Kligfield, Roy, Johannes Hunziker, R. D. Dallmeyer, and Steven Schamel. "Dating of deformation phases using K-Ar and 40Ar/39Ar techniques: results from the northern apennines." Journal of Structural Geology 8, no. 7 (January 1986): 781–98. http://dx.doi.org/10.1016/0191-8141(86)90025-8.

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Berry, R. F., and Ian McDougall. "Interpretation of 40Ar/39Ar and K/Ar dating evidence from the Aileu Formation, East Timor, Indonesia." Chemical Geology: Isotope Geoscience section 59 (January 1986): 43–58. http://dx.doi.org/10.1016/0168-9622(86)90056-4.

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Bai, Xiu-Juan, Rong-Guo Hu, Ying-De Jiang, Xiao Liu, Bin Tang, and Hua-Ning Qiu. "Refined insight into 40Ar/39Ar progressive crushing technique from K–Cl–Ar correlations in fluid inclusions." Chemical Geology 515 (June 2019): 37–49. http://dx.doi.org/10.1016/j.chemgeo.2019.03.037.

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Jourdan, Fred, and Paul R. Renne. "Age calibration of the Fish Canyon sanidine 40Ar/39Ar dating standard using primary K–Ar standards." Geochimica et Cosmochimica Acta 71, no. 2 (January 2007): 387–402. http://dx.doi.org/10.1016/j.gca.2006.09.002.

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Journal articles on the topic 'K-Ar and 40Ar'

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