Temporal–spatial evolution of low-SiO2 volcanism in the Pleistocene West Eifel volcanic field (West Germany) and relationship to upwelling asthenosphere

Abstract

The temporal–spatial evolution of low-SiO2 lavas from the Pleistocene West Eifel volcanic field (Central European Volcanic Province) and linked petrogenetic variations are evaluated using 40Ar/39Ar age and geochemical data. Geochronological and petrological evidence is related to the physical structure of the previously established seismologically anomalous asthenosphere interpreted as thermally upwelling mantle (Eifel Plume).Lava flows >480ka (Middle Pleistocene) occur exclusively in the NW of the volcanic field. After a time span of ca. 400ka lacking significant activity, volcanism has migrated to the SE generating flows <80ka (Late Pleistocene). Middle Pleistocene occurrences form a bilaterally structured, SE-striking zone comprising an internal domain of intense activity between ca. 560 and 480ka and an external domain of less intense preceding activity initiated at ca. 720ka. The tectonic pattern corresponds to recent stress field conditions probably analogous to the Pleistocene setting, which may have reactivated major transverse structures of Hercynian origin providing preferred pathways for melt transfer through the brittle crust.At melting depth >70km of parental asthenospheric melts in garnet–spinel peridotite the surface-projected contour of the low-velocity P-wave anomaly coincides with the geographical boundary separating >480ka volcanism in the NW from <80ka volcanism in the SE. Thus, the melting zones of <80ka and >480ka volcanism reside within and beyond the P-wave velocity anomaly, respectively. The coupling between time-space pattern of volcanism and seismological contrast in the mantle sources indicates that volcanic activity is linked to a highly dynamic low-velocity anomaly with lateral and vertical motion rates of 4–5cm/year and up to 6cm/year, respectively. The change in seismological contrast is accompanied by a transition in the petrogenetic style resulting from differently intense thermal erosion of multiply metasomatized lithosphere by upwelling asthenosphere. Asthenosphere-lithosphere interaction is widespread in the NW and subordinate in the SE of the volcanic field, where melts ascended through a more refractory lithosphere which has been affected by preferential melting of hydrous portions by pre-80ka thermal exposure.