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In the present work, the α decay half-lives for even-even polonium–uranium nuclei, including three isotopes 214 - 218 U Zhang et al. (in Phys Rev Lett 126:152502, 2021), are studied within the generalized liquid drop model with the total α decay energy-dependent α -particle preformation factors. The α -particle preformation factors extracted from the experimental α decay half-life are also investigated. The calculated α decay half-lives can reproduce the experimental data within a factor of 1.74. The systematics of α decay half-lives and α -particle preformation factors suggest that the shell effect of N = 126 closed-shell also exists in the Z = 92 uranium isotopes, although its robustness is weakening as the polonium isotope evolves towards the more proton-rich uranium isotope. [ABSTRACT FROM AUTHOR]

Quartz veins in high-pressure (HP) to ultrahigh-pressure (UHP) rocks are the products of fluid-rock interaction, and thus provide insight into fluid processes in subduction zones. In this paper, we report an integrated study of mineral inclusion, trace-element, U-Pb age, and Lu-Hf isotope compositions of hydrothermal zircon grains from a quartz vein within an UHP eclogite outcrop from the Hong'an area, western Dabie Mountains. These data are used to decipher the age, conditions of formation, and source of fluid for zircon formation during the exhumation of UHP rocks. Zircon grains from the vein have perfect euhedral shape, and show sector zoning or weak zoning, indicating that they precipitated from the aqueous fluid responsible for the vein formation. Raman spectroscopy analysis reveals that the zircon grains contain inclusions of garnet, omphacite, rutile, quartz, and [H.sub.2]O, implying that they crystallized from aqueous fluid under HP eclogite-facies conditions. The zircon grains show low Th/U and Lu/Hf ratios, nearly flat HREE patterns, absent Eu anomalies and low LREE contents. These characteristics are consistent with their precipitation in the presence of garnet and epidote, and absence of feldspar, and thus suggest that trace-element concentrations in hydrothermal zircon are controlled by co-precipitation of mineral assemblages. Crystallization temperatures of 670 to 712[degrees]C, which were calculated using the Ti content of zircon, are consistent with their formation under eclogite-facies conditions and may correspond to the temperature of the infiltrating fluid. The weighted mean [sup.206]Pb/[sup.238]U age of 224.7 [+ or -] 1.3 Ma is taken as the best estimate for the age of quartz-vein formation and records aqueous fluid flow during the early exhumation stage of UHP rocks. The zircon grains in the quartz-vein have Hf compositions similar to those in the host eclogite, which demonstrates isotopic equilibrium between fluid and rocks and that the fluid-rock ratio was likely low. Keywords: Hydrothermal zircon, trace element, Lu-Hf isotope, U-Pb age, HP-UHP metamorphism, quartz vein, western Dabie Mountains

There is lively debate on whether Asian plate material was involved in southward flow of mid-lower crust in a ductile channel beneath southern Tibet. One argument against such involvement is the apparent absence of material derived from Asian lithosphere within the High Himalayan Series (Indian plate) that could represent the putative channel. A north-south--trending mid-Miocene dike swarm that intrudes the Tethyan sedimentary cover of the Sakya gneiss dome (Indian plate) yields new Sr-Nd isotopic data ([sup.87]Sr/[sup.86]Sr = 0.7071-0.7079;[[epsilon].sub.Nd]-4 to-6) indicating that these melts share the same source as Miocene dacitic dikes from north of the Indus-Tsangpo suture. Moreover, dikes on both sides of this suture represent crustal melts derived largely from mid-lower crust of the Asian plate, exposed today as the Nyainqentanglha gneisses that underlie the Gangdese batholith. We infer that melting of the Asian lithosphere extended south of the surface trace of the suture, requiring southward propagation of anatectic Asian middle crustal material during the Miocene. The emplacement ages of the southern dike swarm (12-9 Ma) thus delimit the timing of active southward ductile flow of Asian material. Keywords: Himalaya, isotope geochemistry, tectonics, channel flow.