Magma accumulation underneath Laacher See volcano from detrital zircon in modern streams

Posted on 29.07.2022 - 13:45
Abstract: Detrital zircon grains from two catchments in the East Eifel Volcanic Field comprise crystals sourced from proximal deposits of Quaternary trachytic-phonolitic volcanic centers, Hocheifel Paleogene trachytic rocks, and Paleozoic basement. Outcrop patterns indicate derivation of a significant detrital zircon population from deposits of the c. 13 ka Lower and Upper Laacher See Tephra. Intercalated Middle Laacher See Tephra, comprising valley-filling ignimbrites, by contrast, is a minor zircon source despite thick ignimbrite deposits in one of the catchments. This reflects zircon undersaturation in hotter and less evolved phonolite tapped from deeper parts of the magma reservoir as the eruption unfolded, as well as fewer antecrysts recycled from the plutonic carapace. A previously unrecognized zircon age population of c. 63 ka, mostly derived from Lower Laacher See Tephra, marks the onset of evolved magma presence at the reservoir top. Correlative Hf and O isotopic analysis reveals significant crustal interaction during phonolite differentiation in a shallow reservoir, with assimilation of cogenetic, but hydrothermally modified plutonic margins. Raman spectra indicate that magmatically heated crustal zircon xenocrysts are absent. Detrital zircon thus can provide more integrated insights into the evolution of Quaternary magma systems than punctuated sampling of volcanic or cogenetic plutonic rocks.

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Schmitt, Fabian H.; Schmitt, Axel K.; Gerdes, Axel; Harvey, Janet C. (2022): Magma accumulation underneath Laacher See volcano from detrital zircon in modern streams. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.6123823.v1
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