Mantle lithosphere control of crustal tectonics and magmatism of the western Ohře (Eger) Rift

Abstract

This paper summarizes our recent research on the relationship between tectonics of the mantle lithosphere and of the upper crust in the western Bohemian Massif. The rejuvenated Variscan junction of three mantle domains, the Saxothuringian, Moldanubian and Teplá-Barrandian, delimited by different orientation of seismic anisotropy reflecting a consistent fossil olivine orientation and belonging to originally separated microplates, plays important role in the crustal architecture of the region. The crust above the mantle junction is the most active part of the BM characterized by periodic earthquake swarms and mofettes emitting gases of mantle origin. Detected offsets of surface boundaries of the three units from their mantle counterparts indicate a detachment of the rigid upper crust from the mantle lithosphere. Locations of major tectonic features like the Ohře (Eger) Rift, the West Bohemian Shear Zone and the Mariánské Lázně Fault were probably predisposed by the boundaries of the mantle lithosphere domains. We have suggested that the sublithospheric mantle of the western BM acted as a major provider for heat and partial melts and the Variscan mantle boundaries served as magma conduits for the late-orogenic granitic magmatism and, after their rejuvenation, also for the Cenozoic volcanism. Similarly, the boundaries may have pre-determined the subsequent locations of sedimentary basins. It is possible that also in other regions some of these so called intra-plate phenomena can be related to partly healed up and later rejuvenated microplate boundaries.

Cenozoic volcanism in the Bohemian Massif in the context of P‐ and S‐velocity high‐resolution teleseismic tomography of the upper mantle

“…Babuška and Plomerová [] suggested that the sublithospheric mantle beneath the western BM acted as a major source for heat and partial melts. Variscan boundaries in the brittle lithospheric‐mantle domains served as magma conduits for the late‐orogenic granitic magmatism and, after rejuvenation of some of them, also for the Cenozoic volcanism.…”

Revision of Scheumann’s classification of melilitic lamprophyres and related melilitic rocks in light of new analytical data

“…Wilson et al (1995) proposed that olivine melilitites represent characteristic near-primary partial melts of the thermal boundary layer at the base of the lithosphere. The deep Saxothuringian-Moldanubian contact in the Bohemian Massif is marked by a lithospheric thinning to about 80-90 km beneath the (western) Ohře Rift (Babuška and Plomerová 2010;Geissler et al 2010). According to the model of the Hessian Depression of Wedepohl (1987) origin of the melilitic magma characterized by extreme silica undersaturation and high Ca content probably involved incongruent melting of clinopyroxene in presence of substantial amounts of H 2 O and CO 2 at P > 26 kbar (Morgan et al 1985).…”

Magmatic Evidence for Carbonate Metasomatism in the Lithospheric Mantle underneath the Ohře (Eger) Rift

“…We determine the conditions of melting and the magmatic evolution of the erupted lavas and present further insights into volcanic processes and the nature of the mantle beneath the Ohře Rift by combining major and trace element data with radiogenic (Sr-Nd-Hf) and stable O isotope data. ENE-WSW-trending extensional structure, about 25-30 km wide, that follows Variscan crustal lineaments between the Saxothuringian terrane in the NW, the Moldanubian terrane in the SE and the Tepla-Barrandian terrane between those two terranes (Malkovský , 1987;Babuš ka & Plomerová , 2010). In the region of the Cheb Basin, the crust is thinned to 25-28 km (e.g.…”

“…Quaternary volcanic rocks are present at Komorní hů rka (Kammerbü hl) and the volcanic system of the Mý tina Maar and Ž elezná hů rka ( Fig. 1a), both located roughly above the locus of crustal thinning (Babuš ka & Plomerová , 2010).…”