Quantitative structural analyses and numerical modelling of ...

Author's personal copy272K. Schulmann et al. / C. R. Geoscience 341 (2009) 266–286conditions to the magmatic emplacement of granuliteprotoliths at moderate depth of c. 7–13 kbar, followed bycooling and prograde metamorphic overprint anddecompression occuring at temperatures lower than850 8C [128,129]. The granulite-facies overprint isprobably Visean in age as shown by a number of zirconages [1,84,122,131,153] but recent studies indicatepossible Devonian age of 370 Ma [2].Based on existing pressure-temperature (P–T)estimates two NW–SE trending belts of HP rocks(granulites, eclogites and peridotites) are distinguished,one located close to the Barrandian–Moldanubianboundary (the western belt of Finger et al. [29]) andthe other rimming the eastern margin of the BohemianMassif. These belts alternate with MP units, representedby the Varied and Monotonous groups, which also formNW–SE trending wide belts.The deformation history in the Moldanubian Zonereveals early vertical NNE–SSW trending fabrics,associated with crystallization of HP mineral assemblages[31,113,131,142,151]. These are reworked byflat deformation fabrics that are associated with MP tolow-pressure (LP) and high-temperature (HT) mineralassemblages [50,133,142,143,151]. The flat fabricsshow intense NE–SW trending mineral lineation that iscommonly associated with generalized ductile flowtowards northeast and this kind of deformation is typicalof the whole eastern margin of the Bohemian Massif.The early steep fabrics are dated at 350 to 340 Ma [122],while the ages of the flat ones cluster generally around335 Ma [123]. In the southwestern part of theMoldanubian domain, younger set of steep NW–SEmetamorphic fabrics reworks the flat foliation, havingbeen associated with LP metamorphic conditions ataround 325–315 Ma [29,138].The HP granulites are spatially, structurally andtemporally associated with (ultra-)potassic melasyenitesto melagranites, which can be divided into twogroups differing in modal mineralogy and textures: coarsely porphyritic K-feldspar melasyenites tomelagranites of the so-called durbachite group/serieswith a ‘‘wet’’ mineral assemblage Mg-biotite plusactinolitic hornblende (e.g., Čertovo břemeno andTřebíč intrusions); even-grained melasyenites–melagranites (Tábor andJihlava intrusions), containing a variously retrogressed,originally almost ‘‘dry’’, assemblage oftwo pyroxenes plus Mg-biotite [29,53,59,149].For the most basic ultra-potassic rocks, the highcontents of Cr and Ni with high melting point toderivation from an olivine-rich source (i.e., Earth’smantle). On the other hand, elevated concentrations of U,Th, LREE and LILE, pronounced depletion in HFSE aswell as high K/Na and Rb/Sr ratios seem to contradict themantle origin. This dual geochemical character andcrustal-like Sr–Nd isotopic compositions require meltingof anomalous lithospheric mantle sources, metasomatisedand contaminated by mature crustal material ([59]and references therein), and interaction of these maficmelts with crustally-derived leucogranitic magmas.The Moldanubian metamorphic units were penetratedby numerous and voluminous anatectic plutons looselygrouped into the Moldanubian (or South Bohemian)Plutonic Complex [26,45,46,54]. These are mostlyfelsic–intermediate, two-mica granitic to granodioriticintrusions with either S- or transitional I/S type character[26,88,148]. High-resolution conventional U–Pb zirconand monazite dating showed that the bulk of theMoldanubian Plutonic Complex (c. 80%) was emplacedat 331–323 Ma. The fine-grained granodiorites associatedwith minor diorites followed in a second, lessimportant event at 319–315 Ma [47]. The post-tectonicintrusions of the Moldanubian Plutonic Complexpostdated shortly the thermal peak of the regionalmetamorphism, but were significantly younger than theemplacement of both the Central Bohemian PlutonicComplex and (ultra-)potassic plutonic rocks scatteredthroughout the Moldanubian domain.Granitic rocks in the southwestern sector of theBohemian Massif (Bavarian Forest) have largelyindependent position. Here, large-scale crustal anatexiswas connected with a significant reheating (LP–HTregional metamorphism) and a tectonic remobilisation ofthe crust (Bavarian Phase sensu [29]). The intrusionsnortheast of the Bavarian Pfahl Zone are dated between328 and 321 Ma, whereas ages between 324 and 321 Maare obtained southwest of this zone. It apparentlyrepresents an important terrane boundary and the graniticintrusions sampled distinct basement units [124].2.6. The Moldanubian–Brunia continentaltransition zoneThis boundary was defined by Suess [136,137] as azone of severe deformation and metamorphism ofcontinental rocks (the so-called Moravo-Silesian Zone,Fig. 1). In his seminal work, Suess [136] defined the deepthrusting of the Moldanubian Zone over more externaland shallower Moravo-Silesian Zone, the latter emergingthrough Moldanubian nappe in a form of several tectonicwindows. The contact between these units is marked by aparticular unit, the Moravian ‘‘micaschist zone’’, which165