Magma evolution of the East Eifel volcanic field from a perspective based on detrital zircon in modern river sediment

• Applicant: Professor Dr. Axel Karl Schmitt, Ph.D.
• Subject Area: Mineralogy, Petrology and Geochemistry ; Palaeontology
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 461405636

With the eruption of Laacher See volcano ca. 13,000 years ago, the Quaternary East Eifel volcanic field ranks among the youngest and most dynamic volcanically active areas in Central Europe. Earthquakes, uplift, and gas emissions occur focused in this region, suggesting persistent migration of magmatic fluids from anomalously hot upper mantle zones to the present day. Geodetic and geophysical methods, however, can only image the current conditions in the crust and mantle underneath the volcanic cover. To improve the understanding of the long-term processes and timescales of magma transfer from the mantle to the surface, investigations of past eruptions are therefore essential. Conventionally, samples of lava, pyroclastic fragments or xenoliths from volcanic deposits are collected for such investigations. This punctuated sampling, however, is labor intensive and prone to bias. Instead, it is proposed here to investigate modern stream sediments from the East Eifel, from which zircon can be extracted as a particularly resistant and datable index mineral at relative ease. In the liquid line of descent, zircon crystallizes in evolved melts, which for the East Eifel were tapped predominantly in the phonolitic‒trachytic volcanic centers of Rieden, Wehr, and Laacher See. In addition, mafic volcanics occasionally contain zircon megacrysts which represent xenocrysts entrained from plutonic bodies at depth during magma ascent. In this project, stream sediment of the Nette and Brohlbach catchments will be sampled to extract zircon using in-situ hydraulic separation. Both stream systems drain an area that encompasses nearly all East Eifel volcanic centers and thus can yield a complete picture of all zircon-bearing sources in regional volcanic deposits. A representative number (n = 300) of volcanic detrital zircon crystals will be dated using uranium-thorium and uranium-lead geochronology, and their oxygen-hafnium isotopic compositions will be determined. Results will aid in clarifying critical questions regarding the causes for spatially focused episodes in volcanic activity, which are known from existing eruption ages and volumes for the East Eifel. The analysis of detrital components in modern streams located in young volcanic areas allows rapid and comprehensive sampling, which can also include minerals of already weathered and eroded volcanic edifices. This novel approach has potential to be widely applied to other volcanic regions worldwide.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Axel Gerdes