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Central European Basin system · Rift-related silicic volcanism · Tectonic setting · Superheated magma · Zircon
saturation
Abstract:
The late Carboniferous/early Permian post-collisional rhyolites (305–285 Ma) that formed in Central Europe have generally
similar whole rock compositions to that of older Late-Variscan rhyolites (330–310 Ma). However, data compilation
combining zircon age with the chemical composition of rhyolites from 20 units shows a trend of increasing zircon saturation
temperature with decreasing age. This trend is particularly well identified in rhyolites from the Central European Lowlands
(CEL)—consisting of the NE German and NW Polish Basin—and also correlates their location with the zircon saturation
temperature increasing from SE to NW from 750°C to 850°C. We infer that these higher temperatures of zircon saturation
reflect a contemporaneous change in the tectonic setting from collisional to divergent, reflecting the onset of the Central
European continental rifting. This interpretation is further corroborated by the trace element compositions of the CEL zircons,
which resembles zircon crystallized in a divergent setting. Interestingly, the zircon formed globally in this type of setting is
chemically diverse, especially considering uranium concentration. For example, zircon from locations dominated by mafic
magma fractionation, such as rhyolites from Iceland, have low U concentrations and low U/Yb ratios. On the other hand,
zircon formed in rhyolites in rifted margins, like western North America, tends to have much higher U and U/Yb ratios. Such
high concentrations are not observed in zircon from the CEL, suggesting that the mantle input could be higher and residence
times within continental crust shorter than those for rhyolites from the Cenozoic western USA. This may, in turn, suggest that
the region might have been affected by a hot spot, similar to that responsible for rhyolite formation of the Snake River Plain.
