Lead isotope evolution of the Central European upper mantle: Constraints
from the Bohemian Massif
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Abstract
The Pb isotope composition of the upper mantle beneath Central Europe is heterogeneous due to the subduction of
regionally contrasting material during the Variscan and Alpine orogenies. Late Variscan to Cenozoic mantlederived
melts allow mapping this heterogeneity on a regional scale for the last ca. 340 Myr. Late Cretaceous
and Cenozoic anorogenic magmatic rocks of the Bohemian Massif (lamprophyres, volcanic rocks of basanite/
tephrite and trachyte/phonolite series) concentrate mostly in the Eger Rift. Cretaceous ultramafic lamprophyres
yielded the most radiogenic Pb isotope signatures reflecting a maximum contribution from metasomatised lithospheric
mantle, whereas Tertiary alkaline lamprophyres originated from mantle with less radiogenic 206Pb/204Pb
ratios suggesting a more substantial modification of lithospheric source by interaction with asthenosphericderived
melts. Cenozoic volcanic rocks of the basanite/tephrite and trachyte/phonolite series define a linear
mixing trend between these components, indicating dilution of the initial lithospheric mantle signature by upwelling
asthenosphere during rifting. The Pb isotope composition of Late Cretaceous and Cenozoic magmatic
rocks of the Bohemian Massif follows the same Pb growth curve as Variscan orogenic lamprophyres and lamproites
that formed during the collision between Laurussia, Gondwana, and associated terranes. This implies that
the crustal Pb signature in the post-Variscan mantle is repeatedly sampled by younger anorogenic melts. Most
Cenozoic mantle-derived rocks of Central Europe show similar Pb isotope ranges as the Bohemian Massif.
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