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1. Radiogenic Power and Geoneutrino Luminosity of the Earth and Other Terrestrial Bodies Through Time

   https://doi.org/10.1029/2019GC008865  

   McDonough, W. F. ; Šrámek, O. ; Wipperfurth, S. A. ( July 2020 , Geochemistry, Geophysics, Geosystems)

   We report the Earth's rate of radiogenic heat production and (anti)neutrino luminosity from geologically relevant short‐lived radionuclides (SLR) and long‐lived radionuclides (LLR) using decay constants from the geological community, updated nuclear physics parameters, and calculations of theβspectra. We track the time evolution of the radiogenic power and luminosity of the Earth over the last 4.57 billion years, assuming an absolute abundance for the refractory elements in the silicate Earth and key volatile/refractory element ratios (e.g., Fe/Al, K/U, and Rb/Sr) to set the abundance levels for the moderately volatile elements. The relevant decays for the present‐day heat production in the Earth (19.9 ± 3.0 TW) are from⁴⁰K,⁸⁷Rb,¹⁴⁷Sm,²³²Th,²³⁵U, and²³⁸U. Given element concentrations in kg‐element/kg‐rock and densityρin kg/m³, a simplified equation to calculate the present‐day heat production in a rock isurn:x-wiley:ggge:media:ggge22244:ggge22244-math-0001

   The radiogenic heating rate of Earth‐like material at solar system formation was some 10³to 10⁴times greater than present‐day values, largely due to decay of²⁶Al in the silicate fraction, which was the dominant radiogenic heat source for the first∼10 Ma. Assuming instantaneous Earth formation, the upper bound on radiogenic energy supplied by the most powerful short‐lived radionuclide²⁶Al (t_1/2= 0.7 Ma) is 5.5×10³¹ J, which is comparable (within a factor of a few) to the planet's gravitational binding energy.

    

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2. Reference Models for Lithospheric Geoneutrino Signal

   https://doi.org/10.1029/2019JB018433  

   Wipperfurth, S. A. ; Šrámek, O. ; McDonough, W. F. ( February 2020 , Journal of Geophysical Research: Solid Earth)

   Debate continues on the amount and distribution of radioactive heat producing elements (i.e., U, Th, and K) in the Earth, with estimates for mantle heat production varying by an order of magnitude. Constraints on the bulk‐silicate Earth's (BSE) radiogenic power also places constraints on overall BSE composition. Geoneutrino detection is a direct measure of the Earth's decay rate of Th and U. The geoneutrino signal has contributions from the local (40%) and global (35%) continental lithosphere and the underlying inaccessible mantle (25%). Geophysical models are combined with geochemical data sets to predict the geoneutrino signal at current and future geoneutrino detectors. We propagated uncertainties, both chemical and physical, through Monte Carlo methods. Estimated total signal uncertainties are on the order of20%, proportionally with geophysical and geochemical inputs contributing30% and70%, respectively. We find that estimated signals, calculated using CRUST2.0, CRUST1.0, and LITHO1.0, are within physical uncertainty of each other, suggesting that the choice of underlying geophysical model will not change results significantly, but will shift the central value by up to15%. Similarly, we see no significant difference between calculated layer abundances and bulk crustal heat production when using these geophysical models. The bulk crustal heat production is calculated as 7  2 TW, which includes an increase of 1 TW in uncertainty relative to previous studies. Combination of our predicted lithospheric signal with measured signals yield an estimated BSE heat production of 21.5  10.4 TW. Future improvements, including uncertainty attribution and near‐field modeling, are discussed.

    

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3. Post-spreading Basalts from the Nanyue Seamount: Implications for the Involvement of Crustal- and Plume-Type Components in the Genesis of the South China Sea Mantle

   https://doi.org/10.3390/min9060378  

   Zheng, Hao ; Zhong, Li-Feng ; Kapsiotis, Argyrios ; Cai, Guan-Qiang ; Wan, Zhi-Feng ; Xia, Bin ( June 2019 , Minerals)

   Fresh samples of basalts were collected by dredging from the Nanyue intraplate seamount in the Southwest sub-basin of the South China Sea (SCS). These are alkali basalts displaying right-sloping, chondrite-normalized rare earth element (REE) profiles. The investigated basalts are characterized by low Os content (60.37–85.13 ppt) and radiogenic 187Os/188Os ratios (~0.19 to 0.21). Furthermore, 40Ar/39Ar dating of the Nanyue basalts showed they formed during the Tortonian (~8.3 Ma) and, thus, are products of (Late Cenozoic) post-spreading volcanism. The Sr–Nd–Pb–Hf isotopic compositions of the Nanyue basalts indicate that their parental melts were derived from an upper mantle reservoir possessing the so-called Dupal isotopic anomaly. Semiquantitative isotopic modeling demonstrates that the isotopic compositions of the Nanyue basalts can be reproduced by mixing three components: the average Pacific midocean ridge basalt (MORB), the lower continental crust (LCC), and the average Hainan ocean island basalt (OIB). Our preferred hypothesis for the genesis of the Nanyue basalts is that their parental magmas were produced from an originally depleted mantle (DM) source that was much affected by the activity of the Hainan plume. Initially, the Hainan diapir caused a thermal perturbation in the upper mantle under the present-day Southwest sub-basin of the SCS that led to erosion of the overlying LCC. Eventually, the resultant suboceanic lithospheric mantle (SOLM) interacted with OIB-type components derived from the nearby Hainan plume. Collectively, these processes contributed crustal- and plume-type components to the upper mantle underlying the Southwest sub-basin of the SCS. This implies that the Dupal isotopic signature in the upper mantle beneath the SCS was an artifact of in situ geological processes rather than a feature inherited from a Southern Hemispheric, upper mantle source. 

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4. Himalayan-like Crustal Melting and Differentiation in the Southern North American Cordilleran Anatectic Belt during the Laramide Orogeny: Coyote Mountains, Arizona

   https://doi.org/10.1093/petrology/egad075  

   Chapman, James B. ; Pridmore, Cody ; Chamberlain, Kevin ; Haxel, Gordon ; Ducea, Mihai ( October 2023 , Journal of Petrology)

   The southern US and northern Mexican Cordillera experienced crustal melting during the Laramide orogeny (c. 80–40 Ma). The metamorphic sources of melt are not exposed at the surface; however, anatectic granites are present throughout the region, providing an opportunity to investigate the metamorphic processes associated with this orogeny. A detailed geochemical and petrochronological analysis of the Pan Tak Granite from the Coyote Mountains core complex in southern Arizona suggests that prograde metamorphism, melting, and melt crystallization occurred here from 62 to 42 Ma. Ti-in-zircon temperatures (TTi-zr) correlate with changes in zircon rare earth elements (REE) concentrations, and indicate prograde heating, mineral breakdown, and melt generation took place from 62 to 53 Ma. TTi-zr increases from ~650 to 850 °C during this interval. A prominent gap in zircon ages is observed from 53 to 51 Ma and is interpreted to reflect the timing of peak metamorphism and melting, which caused zircon dissolution. The age gap is an inflection point in several geochemical-temporal trends that suggest crystallization and cooling dominated afterward, from 51 to 42 Ma. Supporting this interpretation is an increase in zircon U/Th and Hf, a decrease in TTi-zr, increasing zircon (Dy/Yb)n, and textural evidence for coupled dissolution–reprecipitation processes that resulted in zircon (re)crystallization. In addition, whole rock REE, large ion lithophile elements, and major elements suggest that the Pan Tak Granite experienced advanced fractional crystallization during this time. High-silica, muscovite± garnet leucogranite dikes that crosscut two-mica granite represent more evolved residual melt compositions. The Pan Tak Granite was formed by fluid-deficient melting and biotite dehydration melting of meta-igneous protoliths, including Jurassic arc rocks and the Proterozoic Oracle Granite. The most likely causes of melting are interpreted to be a combination of (1) radiogenic heating and relaxation of isotherms associated with crustal thickening under a plateau environment, (2) heat and fluid transfer related to the Laramide continental arc, and (3) shear and viscous heating related to the deformation of the deep lithosphere. The characteristics and petrologic processes that created the Pan Tak Granite are strikingly similar to intrusive suites in the Himalayan leucogranite belt and further support the association between the North American Cordilleran anatectic belt and a major orogenic and thermal event during the Laramide orogeny.

    

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5. Oxygen and Al‐Mg isotopic compositions of grossite‐bearing refractory inclusions from CO 3 chondrites

   https://doi.org/10.1111/maps.13282  

   Simon, Steven B. ; Krot, Alexander N. ; Nagashima, Kazuhide ( April 2019 , Meteoritics & Planetary Science)

   The distribution of the short‐lived radionuclide²⁶Al in the early solar system remains a major topic of investigation in planetary science. Thousands of analyses are now available but grossite‐bearing Ca‐, Al‐rich inclusions (CAIs) are underrepresented in the database. Recently found grossite‐bearing inclusions inCO3 chondrites provide an opportunity to address this matter. We determined the oxygen and magnesium isotopic compositions of individual phases of 10 grossite‐bearingCAIs in the Dominion Range (DOM) 08006 (CO3.0) andDOM08004 (CO3.1) chondrites. All minerals inDOM08006CAIs as well as hibonite, spinel, and pyroxene inDOM08004 are uniformly¹⁶O‐rich (Δ¹⁷O = −25 to −20‰) but grossite and melilite inDOM08004CAIs are not; Δ¹⁷O of grossite and melilite range from ~ −11 to ~0‰ and from ~ −23 up to ~0‰, respectively. Even within this small suite, in the two chondrites a bimodal distribution of the inferred initial²⁶Al/²⁷Al ratios (²⁶Al/²⁷Al)₀is seen, with four having (²⁶Al/²⁷Al)₀≤1.1 × 10⁻⁵and six having (²⁶Al/²⁷Al)₀≥3.7 × 10⁻⁵. Five of the²⁶Al‐richCAIs have (²⁶Al/²⁷Al)₀within error of 4.5 × 10⁻⁵; these values can probably be considered indistinguishable from the “canonical” value of 5.2 × 10⁻⁵given the uncertainty in the relative sensitivity factor for grossite measured by secondary ion mass spectrometry. We infer that the²⁶Al‐poorCAIs probably formed before the radionuclide was fully mixed into the solar nebula. All minerals in theDOM08006CAIs, as well as spinel, hibonite, and Al‐diopside in theDOM08004CAIs retained their initial oxygen isotopic compositions, indicating homogeneity of oxygen isotopic compositions in the nebular region where theCOgrossite‐bearingCAIs originated. Oxygen isotopic heterogeneity inCAIs fromDOM08004 resulted from exchange between the initially¹⁶O‐rich (Δ¹⁷O ~−24‰) melilite and grossite and¹⁶O‐poor (Δ¹⁷O ~0‰) fluid during hydrothermal alteration on theCOchondrite parent body; hibonite, spinel, and Al‐diopside avoided oxygen isotopic exchange during the alteration. Grossite and melilite that underwent oxygen isotopic exchange avoided redistribution of radiogenic²⁶Mg and preserved undisturbed internal Al‐Mg isochrons. The Δ¹⁷O of the fluid can be inferred from O‐isotopic compositions of aqueously formed fayalite and magnetite that precipitated from the fluid on theCOparent asteroid. This and previous studies suggest that O‐isotope exchange during fluid–rock interaction affected mostCAIs in CO ≥3.1 chondrites.

    

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