Geodynamic setting of Upper Miocene to Quaternary alkaline basalts from Harrat al ‘Uwayrid (NW Saudi Arabia): Constraints from K Ar dating, chemical and Sr-Nd-Pb isotope compositions, and petrological modeling

Altherr, Rainer; Mertz‐Kraus, Regina; Volker, F.; Kreuzer, H. J.; Henjes‐Kunst, Friedhelm; Lange, Ulrich

doi:10.1016/j.lithos.2019.02.007

Cited by 23 publications

(57 citation statements)

References 105 publications

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“…We posit that northward asthenospheric flow of plume material from Afar has reached Harrat Ithnayn and then extended to Harrat Lunayyir west of the MMN line guided along thin lithosphere as a natural channel (Figures 10 and 11). However, this asthenospheric flow likely does not extend to Harrat Uwayrid and Harrat Hutaymah, which is consistent with geochemical studies that found no plume signal there (Altherr et al, 2019; Konrad et al, 2016). Due to thin lithosphere, plume material may have risen and caused decompression melting, leading to the formation of Harrat Lunayyir.…”

Section: Discussionsupporting

confidence: 82%

Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

et al. 2020

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Widespread Cenozoic volcanism in the Arabian Peninsula has been attributed to mantle plume activity and/or lithospheric thinning due to rift‐related extension. However, there is discrepancy between geochemical and geophysical studies about which mechanism is dominant over the other for post‐12 Ma volcanism. Plume signals in some volcanic fields in the Arabian shield are not evident in isotope analyses, but low‐velocity anomalies connected to Afar are found beneath the Arabian shield in tomographic studies and interpreted as asthenospheric flow from the Afar plume. To resolve this contradiction, we investigate the upper mantle beneath the Arabian Peninsula and northeastern Africa by inverting relative S and SKS wave arrival times recorded at dense seismic networks to derive a high‐resolution S wave velocity model. Our results clearly show a narrow, elongated low‐velocity anomaly along the Makkah‐Madinah‐Nafud (MMN) volcanic line beneath the Arabian shield at 100–300 km depth which extends northward to Harrat Ithnayn and Harrat Lunayyir, but most likely not further north. The limited extent of the low‐velocity anomaly and variations in lithospheric thickness of the Arabian shield may explain why geochemical studies did not find plume signals in some harrats. Therefore, the timing and plume signals of volcanism in western Arabia may not be age progressive from Afar. We also find a possible connection between the low‐velocity anomalies beneath Harrat Lunayyir and the MMN line, suggesting that the 2007–2009 seismic swarm may be associated with northward asthenospheric flow of plume material from Afar.

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Section: Discussionsupporting

confidence: 82%

Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

et al. 2020

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“…This decay mode is also included in the widely used Evaluated Nuclear Structure Data File (ENSDF) and Decay Data Evaluation Project (DDEP) evaluations (Chen, 2017;Mougeot and Helmer, 2009, respectively). However, evaluations by Endt andVan der Leun (1973, 1978), Endt (1990), and Audi et al (2003) do not explicitly include this decay mode, with Audi et al (2003) giving a transition intensity that is the combined EC* and β + intensities. Min et al (2000) have questioned its validity because there is no experimental verification and therefore do not include EC ground in their estimates.…”

Section: Historical Overviewmentioning

confidence: 99%

“…Both processes are types of β decay and result in the transformation of a proton to a neutron to conserve charge, and they both also emit a neutrino in order to conserve lepton number and energy. These two processes are typically paired: coupled electron capture-β + is the second most abundant decay type on the chart of the nuclides, after β − decay (Audi et al, 2003). The electron capture (EC) and positron (β + ) decay modes are linked because both processes have the same initial and final nuclear states.…”

Section: Why There Must Be An Ec Ground Decay Modementioning

confidence: 99%

“…The early but influential review of 40 K decay by Beckinsale and Gale (1969) included these decay modes and also included a prediction of a second electron capture decay directly to the ground state of 40 Ar that would add an additional ∼ 2 % to the rate of decay from 40 K to 40 Ar. Many workers in geochronology (e.g., those who use the Min et al, 2000, decay constants) have ignored this prediction, and some nuclear physics tabulations do not clearly include it (Endt, 1990;Audi et al, 2003). The influential review by Min et al (2000) described this decay mode as "unverified" and having a "questionable" existence.…”

Section: Introductionmentioning

confidence: 99%

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Production of 40Ar by an overlooked mode of 40K decay with implications for K-Ar geochronology

et al. 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.

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“…Overall, the effects of an EC ground decay mode are unlikely to be significant for most current applications of 40 Ar/ 39 Ar geochronology. However, given the levels of analytical precision attainable by the K-Ar dating approach when dating geologically recent materials by K-Ar (e.g., Altherr et al 2019), the EC ground decay mode will impact the accuracy of this chronometer. 320 https://doi.org/10.5194/gchron-2020-9 Preprint.…”

Section: Relevance For Geochronology 285mentioning

confidence: 99%

Percent-level production of 40Ar by an overlooked mode of 40K decay

Carter¹,

Ickert²,

Mark³

et al. 2020

Preprint

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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 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 favour 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&#8201;/&#8201;&#946;+) and after combining it with other estimates, provide a best estimate of 175&#8201;&#177;&#8201;65 (2&#963;). We provide support for this calculation through comparison of the experimentally verified ECground&#8201;/&#8201;&#946;+ ratio of 22Na with our calculation using the theory of &#946; decay.When combined with measured values of &#946;+ and &#946;- decay rates, this yields a partial decay constant for 40K direct to ground state 40Ar of 9.6&#8201;&#177;&#8201;3.8&#8201;&#215;&#8201;10&#8722;13&#8201;a&#8722;1 (2&#963;). We calculate a partial decay constant of 40K to 40Ar of 0.590&#8201;&#177;&#8201;0.014&#8201;&#215;&#8201;10&#8722;10&#8201;a&#8722;1, total decay constant of 5.473&#8201;&#177;&#8201;0.107&#8201;&#215;&#8201;10&#8722;10&#8201;a&#8722;1 (2&#963;), and 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.

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Geodynamic setting of Upper Miocene to Quaternary alkaline basalts from Harrat al ‘Uwayrid (NW Saudi Arabia): Constraints from K Ar dating, chemical and Sr-Nd-Pb isotope compositions, and petrological modeling

Cited by 23 publications

References 105 publications

Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

Production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay with implications for K-Ar geochronology

Percent-level production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay

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Geodynamic setting of Upper Miocene to Quaternary alkaline basalts from Harrat al ‘Uwayrid (NW Saudi Arabia): Constraints from K Ar dating, chemical and Sr-Nd-Pb isotope compositions, and petrological modeling

Cited by 23 publications

References 105 publications

Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

Production of &lt;sup&gt;40&lt;/sup&gt;Ar by an overlooked mode of &lt;sup&gt;40&lt;/sup&gt;K decay with implications for K-Ar geochronology

Percent-level production of &lt;sup&gt;40&lt;/sup&gt;Ar by an overlooked mode of &lt;sup&gt;40&lt;/sup&gt;K decay

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Production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay with implications for K-Ar geochronology

Percent-level production of <sup>40</sup>Ar by an overlooked mode of <sup>40</sup>K decay