Three major types of subcontinental lithospheric mantle beneath the Variscan orogen in Europe

Petrographic observations as well as new and published mineral major and trace element compositions, in part complemented by electron backscatter diffraction, evidence that representative mantle xenolith suites from several Cenozoic basalt locations in the European Variscan orogen can be grouped into three main types. Each type is derived from parts of the sub-continental lithospheric mantle which have experienced a different geological history. The oldest type, referred to as orogenic mantle, is dominated by strongly depleted harzburgites, which represent a fossil Variscan mantle wedge with slices of mantle of continental and oceanic plates attached to it during collision. This mantle lithosphere has been overprinted by Cenozoic carbonated alkali basalt melts, and clinopyroxene, if present, is LREE-enriched and re-introduced. This type of mantle is exemplified by xenoliths from Lower Silesia (Poland) and the northern Massif Central (France). The second type of lithospheric mantle lies beneath parts of the Variscan orogen which experienced Cenozoic rifting. This mantle is dominated by harzburgites and lherzolites formed by multiple episodes of reactive percolation of basaltic melts generated at various stages of continental rifting. The clinopyroxene REE patterns range from flat to LREE-enriched. The xenoliths from Vogelsberg (Germany) are an example of such a lithospheric mantle. The third mantle type consists of lherzolites which originated by refertilization of a harzburgitic protolith by melts derived from upwelled asthenosphere. Lherzolites contain primary clinopyroxene characterized by LREE-depleted-patterns. The xenoliths from south Massif Central (France) are an example of that third type. The xenoliths in Cenozoic basalts considered so far show that the mantle root of the Variscan orogen in Central Europe consists of various domains which in part conserve their characteristics from the time of the Variscan collision, and in part are overprinted by metasomatism caused by late-orogenic asthenosphere upwelling or by Cenozoic rifting. The metasomatically affected domains are decoupled from the Variscan structure of the orogen.