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International audience; A new model of the structure and composition of the Variscan crust in the Bohemian Massif is proposed based on 3D gravity modelling, geological data, seismic refraction (CEL09) and reflection (9HR) sections. The Bohemian Massif crust is characterized by a succession of positive and negative anomalies of about 6080 km wavelength for nearly constant Moho depths. The south-western part of the Bohemian Massif displays a large negative Bouguer anomaly corresponding to high grade rocks (granulites and migmatites) of the Palaeozoic crustal root represented by the Moldanubian domain. The adjacent Neo-Proterozoic Bruno-Vistulian microcontinent displays an important gravity high reflecting mafic and intermediate medium grade metamorphic and magmatic rocks. The deep crustal boundary between the root domain and the Bruno-Vistulian microcontinent is represented by a strong gradient located 50 to 70 km westwards from the surface boundary between these units indicating that the high density basement rocks are covered by a thin sheet of low density granulites and migmatites. North-west from the Moldanubian domain occurs an important gravity high corresponding to the Neo-Proterozoic basement of the Tepla-Barrandian Unit limited in the north by southeast dipping reflectors of the Tepla suture which is characterized by high density eclogites and ultramafics. The footwall of the suture corresponds to low density felsic crust of the Saxothuringian basement. The reflection and refraction seismics and gravity modelling suggest a complex lithological structure of the Moldanubian domain marked by a low density 5-10 km thick lower crustal layer located above the Moho, a 5-10 km thick heavy mafic layer, a 10 km thick mid-crustal layer of intermediate density and a locally developed 2-5 km thick low density layer at the surface. The low density lower crust correlates well with low P-wave velocities in the range 6.0-6.4 km s(-1) in the CEL09 section. This complex geophysical structure and surface geology are interpreted as a result of Carboniferous partial overturn of low density lower crust and high and intermediate density crust in the area of central root and by viscous extrusion of low density orogenic lower crust over the high density Bruno-Vistulian continent. Comparison of these data with geophysical profiling of the Andean and the Tibetan plateaus suggests that modern orogenic systems reveal comparable deep crustal geophysical pattern. Based on these similarities we propose that the Variscan root represents a deep crustal section of above mentioned plateaus, which may have develop by the same orogenic process. (C) 2010 Elsevier B.V. All rights reserved.

International audience; Reflection seismic section, field structural analysis and gravimetric modelling of orogenic lower crust in the core of a Carboniferous orogenic root reveal details of the polyphase process of exhumation. Subvertical amphibolite facies fabrics strike parallel to former plate margins that collided in the NW. The fabrics are developed in both mid-crustal and lower crustal high-pressure granulite units as a result of intensive NW-SE intraroot horizontal shortening driven probably by the west-directed collision. In granulites, the steep fabrics originated as a result of extrusion of orogenic lower crust in a similar to 20 km wide vertical ascent channel from lower crustal depths at 350-340 Ma. The large granulite bodies preserve older granulite facies fabrics documenting a two-stage evolution during the exhumation process. Surface exposures of granulites coincide with the absence of subhorizontal seismic reflectors at depth, suggesting preservation of the similar to 20 km wide subvertical tabular structure reaching Moho depths. Horizontal seismic reflectors surrounding the vertical channel structure corroborate a dominant flat migmatitic fabric developed in all tectonic units. This structural pattern is interpreted in terms of subhorizontal spreading of partially molten orogenic lower crust in mid-crustal levels (765 degrees C and 0.76 GPa) at 342-337 Ma. Large massifs of extruded and progressively dismembered felsic granulites disturbed mid-crustal fabrics in the surrounding horizontally flowing partially molten crust. The horizontal mid-crustal flow resulted in collapse of the supra-crustal Tepla-Barrandian Unit (interpreted as the orogenic lid) along a large-scale crustal detachment above the extruded lower crustal dome. The presence of felsic granulites at the bottom of the orogenic root is considered to be a key factor controlling the exhumation of orogenic lower crust in large hot orogens.

Internal sectors of the Alpine-Balkan-Carpathian-Dinaride (ABCD) orogen comprise fundamentally different, economically important ore deposits along strike in three temporally and spatially distinct belts. These were formed by several short-lived, late-stage collisional processes (including slab break-off or slab delamination) during the Late Cretaceous and Oligocene to Neogene times: (1) the Late Cretaceous “ Banatite” (magmatic) belt, which is associated mainly with porphyry Cu-Au, massive sulphide and Fe-Cu skarn mineralizations, and syn- and late-orogenic metasomatic and metamorphogenic ore and industrial mineral deposits in the Alpine-West-Carpathian sector ; (2) the Oligocene-Miocene Sebomacedonian-Rhodope magmatic/metallogenic zone comprising volcanic-hosted and vein-type Pb-Zn deposits, porphyry Cu-Au-Mo and epithermal Au mineralizations ; and (3) Oligocene-Neogene mineralization formed due to eastward extrusion of fault-bounded blocks into the Carpathian arc and exhumation of metamorphic core complexes and invasion of fault-bounded blocks into the Carpathian arc. This contribution is mainly aimed to put these mineralizations into the geodynamic context. The ABCD belt is a complex, arcuate, double-vergent orogen that formed during two independent stages of continent-continent collision during Mid/Late Cretaceous and Late Eocene/Oligocene. The present-day structure resulted from the final collision of the stable European/Moesian platform with the Adriatic hinterland, deforming a number of continental microplates in between. The Cretaceous orogen was heavily deformed during Tertiary microplate movements, as these moved towards the north against the stable European continent, due to southward subduction of the Penninic ocean and its expansion into the future Carpathian realm. Many different terms like Apuseni-Srednogrie magmatic/metallogenetic belt (or “ Banatite belt” ). The banatites (mainly calcalkaline shallow intrusions and subvolcanic rocks) are associated with various types of mineralization including porphyry copper, massive sulphide and replacement ores. Banatite magmatic rocks are exposed in an arcuate, L-shaped belt from the Apuseni Mountains to the Black Sea. Recent precise geochronological data from banatitic volcanic and plutonic rocks display ages from 92 to 75 Ma and seemingly proof (1) along-strike shift of magmatism from older magmatic activity in the south-east to younger magmatism in the present-day north and (2) across arc, inward shift, e.g. in the Panagyurishte region bezween 92 and 78 Ma. Banatite magmatism and mineralization took place contemporaneously with the formation post-collisional collapse basins, and may be interpreted to represent either a product of continuous northward subduction or post-collisional I-type magmatism due to break-off of the subducted lithosphere. In contrast, in the Eastern Alps and Western Carpathians many deposits of industrial minerals (talc, magnesite), siderite and vein-type Cu-siderite were formed or were remobilised during Cretaceous metamorphism. The formation of many collisional type ore deposits in veins (e. g. Cu, As-Au) and shear zones (Au) is related to the syn-collisional extension and exhumation of metamorphic core complexes which culminated at ca. 80 Ma. The Serbomacedonian-Rodopian belt is characterised by mostly andesitic to dacitic volcanic sequences, which range in age from ca. 35 to 19 Ma. The magmatism is largely calcalkaline, acidic, and in part highly potassic and is interpreted to represent collisional type magmatism formed, in part, by melting of continental crust. Pamic et al. recently proposed slab break for that magmatism although continued N-ward subduction along the Hellenic trench cannot be excluded. We distinguish two sub-belts with different types of deposits: (1) porphyry Cu-Mo-Au and subordinate epithermal Au deposits which are more common in the south-eastern sector ; and (2) Pb-Zn(-Ag) breccia- and vein deposits in volcanic rocks (e. g. Trepca), hydrothermal veins and fault-related breccias, the latter connected with metamorphic core complexes (e. g. Madan). The previous southern European continental margin has been subducted beneath the Alps and Carpathians. Oblique plate collision and associated stacking of lower plate continental units were followed by partitioning of convergence into northward thrusting along the northern leading edge of the orogen and emplacement of the entire Alpine nappe edifice onto European foreland units, and orogen-parallel strike-slip motions along wrench corridors due to ca. general NE– SW shortening. The latter stage was also governed by indentation of the rigid South Alpine indenter, which formed the northern extent of the Adriatic microplate. Post-collisional Late Oligocene to Early Miocene calc-alkaline plutons along southern sectors of the Eastern Alps has been interpreted as a result of slab break-off of the subducted continental lithosphere. A combination of slab roll-back of the remnant intra-Carpathian ocean and eastward extrusion of the Alps led to the closure of a remnant oceanic basin in the Carpathian arc. In Alps, mesothermal Au-quartz formed in the hangingwall of the Simplon detachment fault, the Lepontin gneiss dome and during exhumation of the Tauern metamorphic core complex due to oblique shortening. In the Western and Eastern Carpathians, several types of Neogene ore deposits are widespread and are intimately related to orogenic, subduction-related volcanism. Ore deposits include porphyry Cu along with high-sulphidation epithermal Au, intrusion-related base metal, Au mineralization and epithermal base metal and Au-Ag (-Sb) veins. The Baia Mare ore province is associated with the Drago Voda fault, the northern, sinistral, confining wrench corridor of the eastward extruding Tisia/Dacia block. The Brad ore province in the southern Apuseni Mountains is related to the emplacement of Neogene volcanic rocks mainly between 14.9 – 9 Ma. The ore deposits are of porphyry Cu- and related low-sulphidation epithermal type. Major ore deposits occur along a ESE-trending dextral strike-slip fault which is considered to represent a secondary fault zone that formed within the eastward moving Tisia– Dacia block during the Neogene. The data presented above mainly demonstrate two facts: (1) The Late Cretaceous and Late Paleogene/Miocene mineralization in the arcuate ABCD mountain belt is a discontinuous process that mostly relates to particular stages of syn- and post-collisional tectonic events. (2) The type of mineralization varies strongly along strike within both the Late Cretaceous and the Oligocene/Neogene orogenic belts. The data presented above allow to draw the following general conclusions for late-stage, orogenic mineralization within the ABCD belt: (1) Orogenic mineralization is limited to mainly two periods, Late Cretaceous and Late Paleogene/ Miocene, and represents therefore a discontinuous process which mostly relates to particular stages of syn-collisional tectonic events. (2) The type of mineralization varies strongly along strike within both the Late Cretaceous and the Oligocene/Neogene orogenic belts, with mainly magmatic-hosted mineralizations in Carpathian, Dinaride and Balkan/ Rhodopian sectors, and mainly metamorpho-genic mineralizations in Alps. (3) In the ABCD orogen, principal mineralization is syn- respectively post-collisional in respect to their country rocks. (4) The distinction of subduction-related magmatism and slab break-off magmatism is often ambiguous. Calcalkaline magmatism is in respect to the country rocks post-collisional arguing rather for a genesis by slab tear. (5) Post-collisional slab break-off and/or slab delamination are principal tectonic processes which are able to explain the post-collisional origin of magmatism and mineralization in eastern sectors of the ABCD belt, both during the Late Cretaceous, Oligocene-Neogene and Quaternary. (6) Locations of many Oligocene and Neogene ore deposits of Alps Inner Carpathians are controlled by the presence of large-scale faults due to the indentation process. Many ore veins are parallel to the principal motion direction of intruding and extruding blocks.