Diversity of Origin and Geodynamic Evolution of the Mantle Beneath the Variscan Orogen Indicating Rapid Exhumation within Subduction-Related Mélange (Moldanubian Zone, Bohemian Massif)

2021 ◽  
Author(s):  
Martin Kubeš ◽  
Jaromír Leichmann ◽  
Jana Kotková ◽  
Renata Čopjaková ◽  
Markéta Holá ◽  
...  
Keyword(s):  
Bohemian Massif ◽  
Geodynamic Evolution ◽  
Moldanubian Zone ◽  
Variscan Orogen

Suture zones and importance of strike-slip faulting for Variscan geodynamic reconstructions of the External Crystalline Massifs of the western Alps

2009 ◽  
Vol 180 (6) ◽  
pp. 483-500 ◽  
Author(s):  
Stéphane Guillot ◽  
Silvia di Paola ◽  
René-Pierre Ménot ◽  
Patrick Ledru ◽  
Maria Iole Spalla ◽  
...  
Keyword(s):  
Shear Zone ◽  
Bohemian Massif ◽  
Western Alps ◽  
Alkaline Magmatism ◽  
Calc Alkaline ◽  
Geodynamic Evolution ◽  
Central European ◽  
Back Arc ◽  
Eastern Domain ◽  
Geodynamic Reconstructions

Abstract This paper reviews the geodynamic evolution of the Belledonne, Grandes Rousses and Oisans massifs in the western Alps from Early Ordovician to Permian times. Three domains are distinguished. The eastern domain, which includes the NE Belledonne massif and the inner Oisans massif, records the subduction of the Central-European ocean along a NW dipping subduction zone. The western domain is marked by Cambro-Ordovician back-arc rifting (Chamrousse ophiolite) initiating the opening of the Rheic ocean. It was followed by Mid-Devonian obduction of the back-arc Chamrousse ophiolite, towards the NW in relation with the SE dipping subduction of the Saxo-Thuringian ocean. The central domain, including the SW part of the Belledonne massif, the Grandes Rousses massif and the outer Oisans massif, records the Devonian to Carboniferous orogenic activity that produced calc-alkaline magmatism, Mg-K granite intrusions and syn-collisional sedimentation related to Visean nappe stacking that we relate to the closure of the Saxo-Thuringian ocean. Based on tectonostratigraphic correlations we propose that these domains initially correspond to the northeastward extension of the Bohemian massif. During the late Carboniferous, the External Crystalline Massifs including Sardinia and Corsica were stretched towards the SW along the > 600 km long dextral External Crystalline Massifs shear zone. Offset of the Saxo-Thuringian and eo-Variscan suture zones from the Bohemian massif to the ECM suggests a possible dextral displacement of about 300 km along the ECM shear zone.

Deciphering the petrogenesis of deeply buried granites: whole-rock geochemical constraints on the origin of largely undepleted felsic granulites from the Moldanubian Zone of the Bohemian Massif

2004 ◽  
Vol 95 (1-2) ◽  
pp. 141-159 ◽  
Author(s):  
Vojtěch Janoušek ◽  
Fritz Finger ◽  
Malcolm Roberts ◽  
Jiří Frýda ◽  
Christian Pin ◽  
...  
Keyword(s):  
Bohemian Massif ◽  
Granitic Rocks ◽  
Granitic Magma ◽  
Moldanubian Zone ◽  
Trace Element Contents ◽  
High Grade Metamorphism ◽  
Early Palaeozoic ◽  
High Level ◽  
Geochemical Constraints ◽  
Variation Trends

ABSTRACTThe prominent felsic granulites in the southern part of the Bohemian Massif (Gföhl Unit, Moldanubian Zone), with the Variscan (∼340 Ma) high-pressure and high-temperature assemblage garnet+quartz+hypersolvus feldspar ± kyanite, correspond geochemically to slightly peraluminous, fractionated granitic rocks. Compared to the average upper crust and most granites, the U, Th and Cs concentrations are strongly depleted, probably because of the fluid and/or slight melt loss during the high-grade metamorphism (900–1050°C, 1·5–2·0 GPa). However, the rest of the trace-element contents and variation trends, such as decreasing Sr, Ba, Eu, LREE and Zr with increasing SiO2 and Rb, can be explained by fractional crystallisation of a granitic magma. Low Zr and LREE contents yield ∼750°C zircon and monazite saturation temperatures and suggest relatively low-temperature crystallisation. The granulites contain radiogenic Sr (87Sr/86Sr340 = 0·7106–0·7706) and unradiogenic Nd ( = − 4·2 to − 7·5), indicating derivation from an old crustal source. The whole-rock Rb–Sr isotopic system preserves the memory of an earlier, probably Ordovician, isotopic equilibrium.Contrary to previous studies, the bulk of felsic Moldanubian granulites do not appear to represent separated, syn-metamorphic Variscan HP–HT melts. Instead, they are interpreted as metamorphosed (partly anatectic) equivalents of older, probably high-level granites subducted to continental roots during the Variscan collision. Protolith formation may have occurred within an Early Palaeozoic rift setting, which is documented throughout the Variscan Zone in Europe.

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