Abstract
AbstractThe Quaternary volcanic fields of the Eifel (Rhineland‐Palatinate, Germany) had their last eruptions less than 13,000 years ago. Recently, deep low‐frequency (DLF) earthquakes were detected beneath one of the volcanic fields showing evidence of ongoing magmatic activity in the lower crust and upper mantle. In this work, seismic wide‐ and steep‐angle experiments from 1978/1979 and 1987/1988 are compiled, partially reprocessed and interpreted, together with other data to better determine the location, size, shape, and state of magmatic reservoirs in the Eifel region near the crust‐mantle boundary. We discuss seismic evidence for a low‐velocity gradient layer from 30–36 km depth, which has developed over a large region under all Quaternary volcanic fields of the Rhenish Massif and can be explained by the presence of partial melts. We show that the DLF earthquakes connect the postulated upper mantle reservoir with the upper crust at a depth of about 8 km, directly below one of the youngest phonolitic volcanic centers in the Eifel, where CO2 originating from the mantle is massively outgassing. A bright spot in the West Eifel between 6 and 10 km depth represents a Tertiary magma reservoir and is seen as a model for a differentiated reservoir beneath the young phonolitic center today. We find that the distribution of volcanic fields is controlled by the Variscan lithospheric structures and terrane boundaries as a whole, which is reflected by an offset of the Moho depth, a wedge‐shaped transparent zone in the lower crust and the system of thrusts over about 120 km length.
Highlights
Quaternary volcanism in the western part of Germany is limited to the Eifel region in the Rhenish Massif (RHM)
We show that the deep low‐frequency (DLF) earthquakes connect the postulated upper mantle reservoir with the upper crust at a depth of about 8 km, directly below one of the youngest phonolitic volcanic centers in the Eifel, where CO2 originating from the mantle is massively outgassing
We find that the distribution of volcanic fields is controlled by the Variscan lithospheric structures and terrane boundaries as a whole, which is reflected by an offset of the Moho depth, a wedge‐shaped transparent zone in the lower crust and the system of thrusts over about 120 km length
Summary
Quaternary volcanism in the western part of Germany is limited to the Eifel region in the Rhenish Massif (RHM). Independent of the existence of a deep lower mantle plume, the magmatism in the RHM is a product of the interaction of upper mantle upwelling, tectonic stressing, and preexisting lithospheric structures and slab suture zones/terrane boundaries developed during the Variscan collision, where several minor continental terranes and basins (Saxo‐Thuringian, Mid‐German Crystalline Zone, Rheno‐Hercynian, Figure 1) were successfully accreted and shortened by 52% (Franke et al, 2017; Koenigshof et al, 2016; Oncken et al, 1999) Their geological records, faults, and folds indicate trends parallel to the distribution of Cenozoic volcanoes (Figure 1). We discuss this information in the context of mushy melt reservoirs in the upper mantle and lower crust beneath the Eifel and estimate possible melt fractions in low velocity zones
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