Noble gas isotopes suggest deep mantle plume source of late Cenozoic mafic alkaline volcanism in Europe

Late Cenozoic mafic alkaline volcanism associated with lithospheric thinning is a widespread phenomenon in Europe. However, there is no consensus about its geodynamical causes, e.g., if active shallow or deep mantle-derived plume upwelling has driven this activity. Seismic tomography demonstrated 400-500 km deep plume-like structures under the Massif Central and Eifel volcanic fields, but cannot prove compellingly a lower mantle root. Here, we present high-precision helium, neon and argon isotope data on ultramafic xenoliths from mafic alkaline volcanic formations from the Pannonian basin and the Eifel region. Noble gas extraction by stepwise crushing allowed a successful separation of variably fractionated atmosphere- and mantle-derived components, and the detailed evaluation of helium-neon and neon-argon isotope mixing relationships. The mantle xenoliths trapped mantle fluids with two distinct noble gas components: one component is derived from the local lithospheric and/or a HIMU mantle source with Ne-21/Ne-22(mantle)=0.07 and He-4/He-3 of about 120,000, and dominates helium and part of the neon. The second component is similar to hot spot-type noble gases, e.g., Hawaii or Reunion. It is clearly resolvable in neon isotopes and dominates the argon budget. Its isotopic structure is determined to Ar-40/Ar-36=15,000+/-1200, Ne-21/Ne-22(mantle)=0.042+/-0.005 and He-4/He-3 of about 36,000. Our results are consistent with previous suggestions that a deep mantle component is involved in European intraplate volcanism. (C) 2004 Elsevier B.V. All rights reserved.