First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

Several magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU). The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44–0.27) and for the Nb/U ratio at (9.55–4.18), which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new 206U–238Pb zircon ages (concordia age at 269 ± 7 Ma) confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle

Light-driven nanoperiodical modulation of alkaline cation distribution inside sodium silicate glass

Chemical differentiation of atoms in the nanoscale by femtosecond laser treatment enabling the formation of periodical nanostructures (nanogratings) is demonstrated for the first time in sodium silicate glass. We report periodical redistribution of Na+ cations in SiO2 matrix related to the formation of nanogratings in 15Na2O·85SiO2 glass. They are shown to be similar to nanogratings in silica glass but their inscription is a much longer process taking 105–107 laser pulses. SEM, TEM and EDXA analysis revealed substantial migration of Na+ from the laser-irradiated area. Na+ cations remaining in nanogratings are accumulated at the boundaries or inside the 20–30 nm thick nanoplanes whereas the chemical composition of regions between the nanoplanes approaches to pure SiO2 making a drastic chemical differentiation on a nanoscale. Thus, the opportunity of optically driven nanoperiodical modulation of alkaline cation distribution inside the glass changing its properties in the nanoscale has been shown. This cation redistribution is expected to stimulate the search for new approaches to the design of complex nanostructured architectures in a glassy matrix.</p

Refined geological history of the polyphase plutonometamorphic complex in the Thala Hills area (Enderby Land, East Antarctica) from zircon SHRIMP dating and implications for Neoproterozoic amalgamation of Gondwanaland

Trace element compositions of zircons and whole-rock chemical compositions obtained by previous studies

Substitution-induced internal strain and high disorder in weakly radiation damaged hydrothermal zircon from Mt. Malosa, Malawi

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Geochronological constraints on the evolution of the southern Dom Feliciano Belt (Uruguay)

<p>New U–Pb sensitive high-resolution ion microprobe, K–Ar and Ar–Ar data from the southernmost Dom Feliciano Belt allow the identification of four major events. Orthogneisses from the Punta del Este Terrane indicate a magmatic episode at <em>c</em>. 770 Ma and high-grade metamorphism at 641 ± 17 Ma. Granitoid emplacement at 627 ± 23 Ma was roughly coeval with peak metamorphism. Volcaniclastic rocks of the Las Ventanas Formation dated at 573 ± 11 Ma can be correlated with the peripheral foreland basin (571 ± 8 Ma). Transpression and coeval high-K calc-alkaline magmatism is recorded in the Maldonado granite dated at 564 ± 7 Ma. The following events are postulated: (1) magmatism at 850–750 Ma related to rifting; (2) metamorphism and granite emplacement at 650–600 Ma; (3) molasse sequences and foreland basins at <em>c</em>. 573 Ma; (4) late magmatism at 580–560 Ma associated with transpression. The data indicate that (1) the Punta del Este Terrane could be a portion of the Coastal Terrane of the Kaoko Belt, (2) granitoid emplacement at 650–600 Ma in the Punta del Este and Nico Pérez terranes favours westward subduction, and (3) widespread post-collisional synkinematic magmatism occurred in the Dom Feliciano and Kaoko belts between 580 and 550 Ma. </p

Magmatic evolution of the ultramafic-mafic Kharaelakh intrusion (Siberian Craton, Russia): insights from trace-element, U-Pb and Hf-isotope data on zircon

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