Abstract
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.
Highlights
The European Variscan orogen originated in Upper Palaeozoic times (e. g. Kroner and Romer 2013), and was reactivated in the Cenozoic, when a system of rifts was formed due to stresses related to the Alpine orogeny (Dèzes et al 2004)
In this paper we present xenolith-based petrological data documenting peridotite variation in the subcontinental lithospheric mantle (SCLM) underlying the Variscan orogen in Central Europe from Lower
We show that large parts of the Variscan lithospheric mantle were metasomatically rejuvenated in the post-Variscan times and/or during Cenozoic rifting, but the slices of sub-oceanic mantle accreted to the growing Variscan orogen can be recognised in places
Summary
The European Variscan orogen originated in Upper Palaeozoic times (e. g. Kroner and Romer 2013), and was reactivated in the Cenozoic, when a system of rifts was formed due to stresses related to the Alpine orogeny (Dèzes et al 2004). Alkali basalt lavas entrained mantle xenoliths, which allows the lithospheric mantle root of the orogen to be studied. The study of Downes (2001) showed that the lithospheric mantle beneath Europe consists of spinel lherzolites grading to spinel harzburgites, which have been subjected to significant melting and subsequently modified by various metasomatic processes and events. The European subcontinental lithospheric mantle (SCLM) shows lithological variation. Two lithologically different SCLM domains beneath the Massif Central in France were recognized in the xenolith studies of Lenoir et al (2000) and Downes et al (2003). Puziewicz et al (2015) showed that the SCLM domain beneath Lower Silesia in Poland is dominated by harzburgites, which contain orthopyroxene that is significantly more Al-poor than those occurring to the west. A systematic study of SCLM variation at the European scale is missing
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