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Academic literature on the topic 'K-Ar and 40Ar'

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Published: 7 July 2024

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  2. Dissertations / Theses
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Journal articles on the topic "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.
5

Carter, Jack, Ryan B. Ickert, Darren F. Mark, Marissa M. Tremblay, Alan J. Cresswell, and David C. W. Sanderson. "Production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K 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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You might also be interested in the extended bibliographies on the topic 'K-Ar and 40Ar' for particular source types:
Journal articles

Dissertations / Theses on the topic "K-Ar and 40Ar":

1

Gaylor, Jonathan. "40Ar/39Ar Dating of the Late Cretaceous." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-01017165.

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As part of the wider European GTS Next project, I propose new constraints on the ages of the Late Cretaceous, derived from a multitude of geochronological techniques, and successful stratigraphic interpretations from Canada and Japan. In the Western Canada Sedimentary Basin, we propose a new constraint on the age of the K/Pg boundary in the Red Deer River section (Alberta, Canada). We were able to cyclostratigraphically tune sediments in a non-marine, fluvial environment utilising high-resolution proxy records suggesting a 11-12 precession related cyclicity. Assuming the 40Ar/39Ar method is inter-calibrated with the cyclostratigraphy, the apparent age for C29r suggests that the K/Pg boundary falls between eccentricity maxima and minima, yielding an age of the C29r between 65.89 ± 0.08 and 66.30 ± 0.08 Ma. Assuming that the bundle containing the coal horizon represents a precession cycle, the K/Pg boundary is within the analytical uncertainty of the youngest zircon population achieving a revised age for the K/Pg boundary as 65.75 ± 0.06 Ma. The Campanian - Maastrichtian boundary is preserved in the sedimentary succession of the Horseshoe Canyon Formation and has been placed ~8 m below Coal nr. 10. Cyclostratigraphic studies show that the formation of these depositional sequences (alternations) of all scales are influenced directly by sea-level changes due to precession but more dominated by eccentricity cycles proved in the cyclostratigraphic framework and is mainly controlled by sand horizons, which have been related by autocyclicity in a dynamic sedimentary setting. Our work shows that the Campanian - Maastrichtian boundary in the Western Canada Sedimentary Basin coincides with ~2.5 eccentricity cycles above the youngest zircon age population at the bottom of the section and ~4.9 Myr before the Cretaceous - Palaeogene boundary (K/Pg), and thus corresponds to an absolute age of 70.65 ± 0.09 Ma producing an ~1.4 Myr younger age than recent published ages. Finally, using advances with terrestrial carbon isotope and planktonic foraminifera records within central Hokkaido, Northwest Pacific, sections from the Cretaceous Yezo group were correlated to that of European and North American counterparts. Datable ash layers throughout the Kotanbetsu and Shumarinai section were analysed using both 40Ar/39Ar and U-Pb methods. We successfully dated two ash tuff layers falling either side of the Turonian - Coniacian boundary, yielding an age range for the boundary between 89.31 ± 0.11 Ma and 89.57 ± 0.11 Ma or a boundary age of 89.44 ± 0.24 Ma. Combining these U-Pb ages with recent published ages we are able to reduce the age limit once more and propose an age for the Turonian - Coniacian boundary as 89.62 ± 0.04 Ma.
2

Hevia, Cruz Francisco. "Climatic and landscape evolution of the Azores over the past million years." Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASJ035.

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L'évolution des îles volcaniques résulte d'interactions complexes entre croissance des volcans et processus de destruction (éruptions explosives, glissements de terrain, érosion fluviale, altération). Les changements climatiques peuvent influencer ces processus sur des échelles variées. A l’échelle événementielle, des précipitations intenses peuvent engendrer des épisodes érosifs extrêmes. Sur le long-terme, des variations des taux d'altération, sensibles aux précipitations et à la température, peuvent impacter la fertilité des sols et le cycle global du carbone.Les îles volcaniques des Açores offrent un cadre idéal pour étudier ces interactions, avec une grande importance scientifique et sociétal, en particulier dans le contexte actuel du réchauffement climatique. Au centre de l'Atlantique Nord, elles sont influencées par des facteurs climatiques majeurs. Ces îles ont eu des pulses d'activité volcanique au cours du dernier million d'années (Ma), une période marquée par d’importants changements climatiques liés aux cycles glaciaires-interglaciaires. Si les variations des conditions globales ont été bien documentées sur cette période, la reconstruction paléoclimatique aux échelles locales/régionales reste un défi. Les paléosols (PSs) sont des anciens sols inclus dans le registre géologique. Leur géochimie fournit des informations précieuses sur les conditions paléo-environnementales, et la géochronologie des produits volcaniques les encadrant permet leur contrainte temporelle.Dans ce travail, nous avons reconstruit les conditions moyennes annuelles de précipitation (MAP) et de température de l’air (MAAT) aux Açores au cours du dernier Ma. Deux proxies basés sur la composition en éléments majeurs des PSs ont été utilisés : l’indice d'altération CIA-K et l’argilosité, tous deux validés dans d'autres milieux volcaniques. La datation précise des unités volcaniques par K-Ar sur mésostase séparée (laves) et par ⁴⁰Ar/³⁹Ar sur monocristaux de feldspath potassique (dépôts pyroclastiques), révèle des «pulses» d‘altération sur quelques milliers d’années, notamment après les terminaisons glaciaires (MIS 21, 19, 11, 9e, 5e et 1). La géochimie des PSs montre des changements environnementaux rapides et des MAATs (12-28 ᵒC) en accord avec les données de température marine de surface établies à partir d’archives océaniques. Cette concordance indique une étroite relation océan-atmosphère. Ces «pulses» suggèrent en outre des phases d'affaiblissement de l'anticyclone des Açores, permettant aux courants d'air humides d'atteindre des secteurs plus au sud.Les taux moyens de formation des sols (3-180 mm/kyr) ont été influencés par la structure et la texture du substrat rocheux. Des PSs se sont formés lors de MAPs plus faibles dans les dépôts pyroclastiques que dans les coulées de lave (seuils de ~500 et ~800 mm/an). Cette différence supporte une cinétique favorisée par la fragmentation et une surface spécifique élevée. L’altération accrue en surface et le long des discontinuités géologiques de sub-surface peut avoir favorisé l'érosion par glissements de terrain. Des MAPs élevées (jusqu'à 1500 mm/an) sont notamment obtenues autour du stade interglaciaire de l’Eemien, qui coïncide avec l’initiation d’un glissement complexe sur le flanc Sud de Pico. Des MAPs intenses ont pu accélérer l’infiltration des eaux et favoriser les interactions hydromagmatiques. L’augmentation associée de pression interstitielle a ainsi pu déclencher la mise en mouvement du flanc le long de failles listriques toujours actives. Les conditions actuelles aux Açores sont plus humides et légèrement plus chaudes qu’au cours du dernier Ma, ce que pourrait favoriser le détachement du flanc externe de Pico, avec des conséquences potentiellement drastiques.Plus généralement, l’altération accrue favorise l’évolution rapide du paysage sur de telles îles et engendre des flux élémentaires et une absorption de CO₂ atmosphérique croissantes, ce qui a impacts locaux, régionaux et globaux
Landscape evolution on volcanic islands is driven by complex interactions between volcano growth and destruction by a variety of processes (explosive eruptions, landslides, riverine erosion, weathering). Major climate changes, may impact the dynamics of degradation processes at different spatial and temporal scales. For example, extreme rain can produce an immediate hydrological response causing important destruction. Changes in weathering rates, sensitive to precipitation and temperature, can trigger changes in soil fertility but also modify global carbon cycling.The Azores volcanic islands provide an ideal setting to study these interactions, with both scientific and societal significance, especially in the context of ongoing global warming. Located in the Central North Atlantic, they are under the influence of major climatic drivers. Most of them had pulses of volcanic activity over the past 1 Myr, a period characterized by high-amplitude glacial-interglacial transitions with major climatic changes. While global climatic variations have been relatively well-studied for this period, reconstructing the atmospheric paleoclimate and its effects at local/regional scales remains challenging. Paleosols (PSs) are fossil soils formed by weathering at surface, and later incorporated into the geological record. Their geochemistry provides valuable insights into past environmental conditions, while the geochronology of volcanic products “bracketing” PSs allows their temporal constraint.In this work, we reconstructed mean annual precipitations (MAP) and air temperature (MAAT) over the last 1 Myr in the Azores region through a combined geochemical-geochronological study of PSs. Two proxies based on PSs’ major element were used: the weathering index (CIA-K) and the Clayeyness, both validated in other volcanic settings. The precise dating of volcanic units by either unspiked K-Ar on lava flow groundmass separates or ⁴⁰Ar/³⁹Ar on single K-feldspar of trachytic fallout evidence “pulses” of soil-formation within only a few kyr. This occurred especially after glacial terminations (MIS 21, 19, 11, 9e, 5e and 1), under wet and warm conditions. Fast paleoenvironmental changes were recorded in PSs’ geochemistry, and MAAT reconstructions (12-28 ᵒC) agree with previously published Sea Surface Temperatures, pointing to a tight ocean-atmosphere teleconnection. Those “pulses” suggest sustained weakening phases for the Azores High, allowing humid air currents (Westerlies) to reach further to the south.Our data also show contrasted rates of vertical soil development (3-180 mm/kyr). Weathering was favored by the structure and texture of parental materials, as PSs formed under lower MAP in pyroclastic deposits than in lava flows (~500 and ~800 mm/yr thresholds). This highlights the influence of fragmentation on weathering’s kinetics due to higher specific surface area. Enhanced weathering at surface and along geological discontinuities may have promoted mechanical weakening, favoring erosion and landslides. Notably, high MAPs (up to 1500 mm/yr) obtained around the Eemian interglacial stage are coincident in time with the initiation of a large slide complex on the southern flank of Pico. Intense precipitation may have led to increased water infiltration favoring enhanced hydromagmatic interactions. Drastic increase in pore pressure may then have triggered the initiation of the flank movement along listric faults that are still active. Current conditions in the Azores are wetter and slightly warmer than during the last Myr. Increased infiltration along faults could partly control subsequent movement and yield to detachment of the outer flank of Pico, with potentially dramatic consequences.More generally, present temperature and humidity increase on volcanic islands points to intense weathering, resulting in fast landscape evolution, increased lixiviation and elementary export and high atmospheric CO₂ uptaking, with local, regional and global impacts
3

Coulié, Emmanuel. "Chronologie 40Ar/39Ar et K/Ar de la dislocation du plateau éthiopien et de la déchirure continentale à la corne de l'Afrique depuis 30 Ma." Paris 11, 2001. http://www.theses.fr/2001PA112284.

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Ce travail de thèse présente le développement et la mise au point d'un procédé original pour la datation par la technique 40_Ar/39_Ar. Le cœur de ce système, un spectromètre de masse utilisant la collection simultanée des cinq isotopes de l'argon, est aujourd'hui unique à l'échelle internationale. Tout d'abord testé et validé sur des échantillons géologiques standard, ce système a permis de réaliser, dans sa configuration actuelle, des analyses de grande qualité sur les roches volcaniques de l'Ethiopie, avec une reproductibilité analytique de l'ordre de 0. 2%. Il est maintenant communément admis que les grands traps basaltiques sont en étroite relation avec les grandes déchirures continentales. C'est notamment le cas du point chaud Afar localisé dans un contexte extensif de point triple. Un des objectifs de cette thèse est d'apporter, à la lumière de 28 et 68 nouvelles données acquises, respectivement, en 40_Ar/39_Ar et K/Ar, des contraintes temporelles sur l'épanchement du point chaud et sur les prémices de l'ouverture continentale. Pour cela, des laves et des granites d'ouverture ont été échantillonnées sur les trois zones géographiques aujourd'hui désunies, c'est-à-dire sur les hauts plateaux éthiopiens, yéménites et somaliens, ainsi que le long de leurs escarpements aux marges de la dépression Afar. Nos résultats attestent de l'édification rapide des grands traps (en moins de 1 Ma, pour l'essentiel de la pile volcanique) et d'une initiation du volcanisme autour de 30. 2 Ma. Les prémices de l'ouverture apparaissent en conséquence totalement synchrones de cette phase, comme l'indique la mise en place de granites, dès 30 Ma. Les résultats de cette étude sont repris et discutés de manière plus générale, afin de préciser et de proposer un schéma global d'évolution depuis 30 Ma
We present here a new analytical system for 4O_Ar/39_Ar dating that relies onto an original 180ʿ sector multiple collection mass spectrometer with five faraday cups. Results of preliminarily experiments undertaken on geological standard minerals highlight the good behavior of this new instrument for step heating analyses. The age reproducibility of successive steps lead to analytical errors lower than 0. 2 %. Such a system appears today unique on the international plan for 40_Ar/39_Ar routine dating. This new penta-collector MS enabled us to perform highly reproducible 40_Ar/39_Ar dating of Ethiopian volcanics. It is now admitted that continental flood basalt volcanism has a strong relationship with continental break-up. The Ethiopian-Afar plume has been linked to the early opening of the Afar depression, where the propagation of Red Sea and Gulf of Aden within the depression is still an ongoing process. The purposes of this study are to constrain the emplacement and duration of the trap series, and to reconstruct the eruptive chronology of the earlier opening stages, since the initiation of the fracturation. Twenty-eight 40_Ar/39_Ar and 68 K/Ar new ages data have been performed on volcanic series and granitic bodies, sampled on the plateaus (Ethiopian, Yemenite, Somalian) and along their boundaries on the Afar margin. Our results support that the onset of traps volcanism took place around 30 Ma, with a duration lower than 1 Myr. The emplacement of granitic bodies as early as 30 Ma argues for a synchronous initiation of the opening. Finally, all results obtained in this study on both plateau and rifted margin areas helped us to propose a global scheme for the evolution of the Afar depression since 30 Ma
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Most, Thomas. "Geodynamic evolution of the Eastern Pelagonian zone in north-western Greece and the Republic of Macedonia implications from U/Pb, Rb/Sr, K/Ar, 40Ar/39Ar geochronology and fission track thermochronology /." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=96650268X.

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5

Favier, Alexiane. "Évolution spatio-temporelle de l'hydrothermalisme dans la plaque supérieure de l'arc des Petites Antilles en Guadeloupe : applications aux systèmes géothermaux." Thesis, Antilles, 2019. http://www.theses.fr/2019ANTI0401.

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Pour poursuivre le développement de la géothermie de haute-enthalpie dans l’arc insulaire des Petites Antilles il faut d’une part identifier de nouvelles zones potentielles et d’autre part mieux comprendre le fonctionnement des réservoirs géothermaux. Dans ce cadre, l’objectif de cette thèse est de caractériser l’évolution spatio-temporelle de l’hydrothermalisme au niveau de la plaque supérieure de l’arc en Guadeloupe au travers d’une analyse pluridisciplinaire (études structurales, géochimiques, minéralogiques, pétrologiques et géochronologiques) des complexes volcaniques les plus anciens de l’archipel. Au Nord de la Basse-Terre nous identifions un métamorphisme d’arc de type sub-Schistes Verts. L’état thermique standard de la croûte d’arc en Guadeloupe ainsi établit indique une transition fragile-ductile située à 3-4 km de profondeur. Un paléo-réservoir exhumé, identifié au Sud de l’île de la Basse-Terre, illustre un métamorphisme hydrothermal de type Schistes-Verts synchrone du développement de couloirs de schistosité et révèle la présence d’horizons verticaux et latéraux de transfert de fluides hydrothermaux situés à 2-3 km de profondeur. En comparant l’âge du volcanisme et la datation Ar-Ar des phases hydrothermales de haute-température, nous estimons une durée maximale de fonctionnement du paléo-réservoir à 650 ka. Enfin, la découverte, l’analyse et la datation K-Ar d’une nouvelle brèche hydrothermale, au coeur du système géothermal actif, met en évidence un système épithermal distal relié à l’activité volcanique de la Soufrière. Nos résultats conduisent à un modèle conceptuel de fonctionnement d’un réservoir géothermal de haute-énergie en contexte d’arc actif
To further develop high-enthalpy geothermal energy in Lesser Antilles arc, it is necessary to identify possible new key targets, and to better understand the modes of fluids and heat transfers in geothermal reservoirs. The objective of this work is thus to characterize the spatio-temporal evolution of hydrothermalism at the upper plate of the arc in Guadeloupe with a multidisciplinary approach (combined structural, geochemical, mineralogical, petrological and geochronological analyses) focussed on the oldest volcanic complexes of the archipelago. In the north of Basse-Terre Island reveals an arc metamorphism developed under sub-Greenschist facies. The standard thermal state of the arc crust in Guadeloupe thus established shows a brittle-ductile transition located at depths of 3 to 4 km. An exhumed geothermal paleo-reservoir, identified at the south of Basse-Terre Island, indicates a hydrothermal metamorphism developed under Greenschist facies synchronous with the development of schistose corridors and attests for both vertical and lateral hydrothermal fluid transfers at depths between 2 and 3 km. Comparison of the age of the volcanic activity and Ar-Ar dating of the high-temperature hydrothermal phases allows us to estimate a maximum operating time of the paleo-reservoir at 650 ka. Finally, the discovery, the analysis and the K-Ar dating of a new hydrothermal breccia, within the active geothermal system, reveals a link between current geothermal activity and volcanic activity of the Soufrière, interpreted as a distal epithermal system. Our results lead to a conceptual model for the operation of a high-energy geothermal reservoir in the context of an active arc
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Most, Thomas [Verfasser]. "Geodynamic evolution of the Eastern Pelagonian zone in north-western Greece and the Republic of Macedonia : implications from U/Pb, Rb/Sr, K/Ar, 40Ar/39Ar geochronology and fission track thermochronology / vorgelegt von Thomas Most." 2003. http://d-nb.info/96650268X/34.

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Books on the topic "K-Ar and 40Ar":

1

1952-, Burton William C., and Geological Survey (U.S.), eds. 40Ar/39 Ar age-spectrum data for amphibole, muscovite, biotite, and K-feldspar samples from metamorphic rocks in the Blue Ridge anticlinorium, northern Virginia. [Denver, CO]: U.S. Geological Survey, 1999.

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1952-, Burton William C., and Geological Survey (U.S.), eds. 40Ar/39 Ar age-spectrum data for amphibole, muscovite, biotite, and K-feldspar samples from metamorphic rocks in the Blue Ridge anticlinorium, northern Virginia. [Denver, CO]: U.S. Geological Survey, 1999.

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1952-, Burton William C., and Geological Survey (U.S.), eds. 40Ar/39 Ar age-spectrum data for amphibole, muscovite, biotite, and K-feldspar samples from metamorphic rocks in the Blue Ridge anticlinorium, northern Virginia. [Denver, CO]: U.S. Geological Survey, 1999.

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1952-, Burton William C., and Geological Survey (U.S.), eds. 40Ar/39 Ar age-spectrum data for amphibole, muscovite, biotite, and K-feldspar samples from metamorphic rocks in the Blue Ridge anticlinorium, northern Virginia. [Denver, CO]: U.S. Geological Survey, 1999.

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1952-, Burton William C., and Geological Survey (U.S.), eds. 40Ar/39 Ar age-spectrum data for amphibole, muscovite, biotite, and K-feldspar samples from metamorphic rocks in the Blue Ridge anticlinorium, northern Virginia. [Denver, CO]: U.S. Geological Survey, 1999.

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Book chapters on the topic "K-Ar and 40Ar":

1

Morgan, Leah E. "40Ar/39Ar and K–Ar Geochronology." In Encyclopedia of Geoarchaeology, 27–32. Dordrecht: Springer Netherlands, 2016. http://dx.doi.org/10.1007/978-1-4020-4409-0_45.

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Wijbrans, Jan R. "Metamorphic Terranes (K–Ar/40Ar/39Ar)." In Encyclopedia of Scientific Dating Methods, 1–8. Dordrecht: Springer Netherlands, 2013. http://dx.doi.org/10.1007/978-94-007-6326-5_44-1.

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Wijbrans, Jan R. "Metamorphic Terranes (K–Ar/40Ar/39Ar)." In Encyclopedia of Marine Geosciences, 542–47. Dordrecht: Springer Netherlands, 2015. http://dx.doi.org/10.1007/978-94-007-6304-3_44.

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Renne, Paul R. "K-Ar and 40Ar/39Ar Dating." In AGU Reference Shelf, 77–100. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/rf004p0077.

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Morgan, Leah E. "40Ar/39Ar and K–Ar Geochronology." In Encyclopedia of Geoarchaeology, 1–6. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-030-44600-0_45-1.

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McDougall, Ian. "Volcanogenic Sedimentary Rocks (K/Ar, 40Ar/39Ar)." In Encyclopedia of Scientific Dating Methods, 950–55. Dordrecht: Springer Netherlands, 2015. http://dx.doi.org/10.1007/978-94-007-6304-3_265.

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Scaillet, Stéphane. "K-Ar (40Ar/39Ar) Geochronology of Ultrahigh Pressure Rocks." In When Continents Collide: Geodynamics and Geochemistry of Ultrahigh-Pressure Rocks, 161–201. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-015-9050-1_7.

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Dallmeyer, R. D., A. Reuter, N. Clauer, and N. Liewig. "Chronology of Caledonian tectonothermal activity within the Gaissa and Laksefjord Nappe Complexes (Lower Allochthon), Finnmark, Norway: Evidence from K—Ar and 40Ar/39Ar ages." In The Caledonide Geology of Scandinavia, 9–26. Dordrecht: Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-2549-6_2.

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Wijbrans, J. R., and K. F. Kuiper. "K/AR AND 40AR/39AR DATING." In Encyclopedia of Quaternary Science, 477–82. Elsevier, 2013. http://dx.doi.org/10.1016/b978-0-444-53643-3.00040-6.

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McDougall, Ian, and T. Mark Harrison. "Basis of the 40Ar/39Ar Dating Method." In Geochronology and Theromochronology By The 40 Ar/39 Ar Method, 9–43. Oxford University PressNew York, NY, 1999. http://dx.doi.org/10.1093/oso/9780195109207.003.0002.

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Abstract:
Abstract The 40Ar/39 Ar method of dating rocks has its foundations in the potassium-argon (K/Ar) isotopic dating method, a widely used technique for measuring numerical ages on minerals and rocks. Since the K/Ar method was developed more than 40 years ago, it has been applied to a diverse range of geological samples to help elucidate many important geological problems of local, regional, or global significance. Particularly notable successes, dependent largely upon dating by the K/Ar method, include the development of the geomagnetic polarity time scale and the numerical calibration of the Phanerozoic geological or relative time scale.

Conference papers on the topic "K-Ar and 40Ar":

1

Mercer, C. M., and K. V. Hodges. "ARAR — SOFTWARE TO ACCOUNT FOR DISCREPANCIES BETWEEN K/AR AND 40AR/39AR DATASETS PUBLISHED WITH DIFFERENT DECAY, ISOTOPIC, AND MONITOR-AGE PARAMETERS." In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-286929.

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Reports on the topic "K-Ar and 40Ar":

1

Hunt, P. A., and J. C. Roddick. A compilation of K-Ar and 40Ar-39Ar ages: Report 23. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1993. http://dx.doi.org/10.4095/193342.

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Hunt, P. A., and J. C. Roddick. A compilation of K-Ar and 40Ar-39Ar ages: Report 24. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1994. http://dx.doi.org/10.4095/195178.

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Hunt, P. A., and J. C. Roddick. A compilation of 40Ar-39Ar and K-Ar ages: Report 25. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 1996. http://dx.doi.org/10.4095/207763.

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Kellett, D., S. Pehrsson, D. Skipton, D. Regis, A. Camacho, D. Schneider, and R. Berman. Thermochronological history of the northern Canadian Shield: a synthesis. Natural Resources Canada/CMSS/Information Management, 2024. http://dx.doi.org/10.4095/332507.

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This contribution examines the current state of knowledge regarding the postmetamorphic cooling of most Archean to Paleoproterozoic tectonic elements of the northern Canadian Shield. This was achieved by building an extensive data set of over 2000 combined K-Ar and 40Ar/39Ar cooling ages. The Churchill Province (amalgamated Rae and Hearne cratons) shows a general west to east cooling pattern illustrated by two large-scale thermochronological profiles.
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Age of tephra beds at the Ocean Point dinosaur locality, North Slope, Alaska, based on K-Ar and 40Ar/39Ar analyses. US Geological Survey, 1992. http://dx.doi.org/10.3133/b1990c.

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