Twenty-six new 40 Ar/ 39 Ar plateau ages for 23 lavas and domes from the Uturuncu volcano in the Altiplano of SW Bolivia reveal a protracted eruptive history from 1050 + 5 to 250 + 5 ka. Eruptions have been exclusively effusive, producing some 50 km 3 of high-K dacites and silicic andesites. Bimodal mineral compositions, complex mineral textures, the presence of andesitic magmatic enclaves within dacites and linear chemical trends on binary element plots all indicate that magma mixing is an important petrogenetic process at Uturuncu. Post-458 ka, distinct high and low MgO-Cr magmas are resolved. These magmas erupt during similar times, suggesting that eruptions are tapping different parts of the magma system, albeit from the same vent system. Volcanic and petrological features are consistent with the existence of a vertically extensive magma mush column beneath Uturuncu, and calculated buoyancy forces are sufficient to drive effusive eruptions. Eruptive activity is episodic, with six eruptive periods separated by hiatuses of .50 kyr. Cumulative volume curves demonstrate that the majority of the edifice formed between 595 and 505 ka. The episodicity of eruptions is most likely to be related to fluctuations in the magma supply to the underlying Altiplano-Puno Magma Body.Supplementary material: Detailed 40 Ar/ 39 Ar data, and lava flow and dome areas, volumes and stratigraphic ages where absolute ages are lacking are available at www.geolsoc.org.uk/ SUP18815The tempo of crustal volcanism is a complex interplay of magma supply rate to the crust, magma storage within the crust, and the regional and local stress regime (Caricchi et al. 2014), as well as nonmagmatic factors, such as glaciations that affect crustal loading and magma generation (e.g. Maclennan et al. 2012). Unravelling the importance of these factors in a given magmatic province requires integration of geochronology, petrology, tectonics (e.g. Hawkesworth et al. 2004;Davidson et al. 2005) and climate. In the case of long-lived, potentially explosive silicic arc volcanoes, detailed geochronological studies are surprisingly scarce. Many investigations focus on the overall geochemical variation at a given volcano, but the temporal changes in chemistry, erupted volume or eruptive style are rarely quantified. Consequently, our understanding of the evolution of crustal arc magma systems over periods of thousands to hundreds of thousands of years is limited, and represents a significant impediment to modelling. Examples of continental stratovolcanoes with compositional and physical attributes such as mean output rate integrated with detailed, accurate geochronological data include Montserrat (Harford et al.
Uranium mononitride, UN, is considered a potential accident tolerant fuel due to its high uranium density, high thermal conductivity, and high melting point. Compared with the relatively inert UO 2 , UN has a high reactivity in water, however, studies have not considered the significant effect of radiation, which is known to cause corrosion of UO 2 . This study uses 0.1 M H 2 O 2 to simulate the effects of water radiolysis in order to compare the radiolytic corrosion rates of UO 2 , UN, and U 2 N 3 thin films at room temperature. X-ray reflectivity was used to investigate the changes in film morphology as a function of H 2 O 2 exposure time, allowing changes in film thickness and roughness to be observed on theÅngstrom length-scale. Results showed significant differences between UO 2 , UN, and U 2 N 3 , with corrosion rates of 0.083(3), 0.020(4), and 0.47(8)Å/s, respectively, showing that UN corrodes more slowly than UO 2 in 0.1 M H 2 O 2 .
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