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Mantle-crust interaction processes during the Variscan continental collision: insight into the diverse origin and complex evolution of heterogeneous mantle beneath Central Europe

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Year of publication 2021
Type Appeared in Conference without Proceedings
MU Faculty or unit

Faculty of Science

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Description The Gföhl Unit of the Moldanubian Zone (Bohemian Massif) hosts diverse ultrabasic rocks and thus represents an ideal site to study mantle-crust geodynamics beneath the Variscan Orogen. The genetically contrasting yet closely spatially associated mantle-derived assemblages comprise spinel or garnet peridotites, pyroxenites and subordinate eclogites. Garnet lherzolites, enclosed in HP granulites, correspond to fragments of the fertile subcontinental mantle (high Al2O3, TiO2, Yb, and Cr-rich spinels), dragged from shallow levels (?10 kbar) to great depths of the Variscan subduction zone (42 kbar, 1100 oC). The timing of the Variscan burial is recorded by Lu-Hf age of 338.4 ± 6.3 Ma. Spinel harzburgites, associated with HT anatectic gneisses, geochemically resemble refractory oceanic lithosphere (low Al2O3, CaO, and Cr-poor spinels), incorporated into the same subduction channel. Pyroxenites and eclogites, veining the host peridotites, were produced by partial melting of subducting slab beneath mantle wedge. These mildly evolved melts (87Sr/86Sr 0.7062–0.7076) infiltrated to the overlying mantle and triggered mantle refertilization, reflected by cryptic metasomatism of wall-rock peridotites (87Sr/86Sr ~0.7052, low Mg#, MgO/SiO2, high Al2O3/SiO2, TiO2). The rapid exhumation and juxtaposition of diverse mantle rocks within subduction-related tectonic mélange hence provide a unique insight into the history of the Earth mantle evolving during the formation of the European Variscides.
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