paleogeography of the late cretaceous quadersandstein of central europe abstract thick sequences of cross bedded quartzose sandstones indicate paleogeographic circumstances favorable for their accumulation post variscan peneplanation of central europe relatively rapid subsidence of a level bottom where transport and deposition were ruled by non tidal and tidal currents and continuous uplift of two islands which yielded deeply weathered detrital material primarily derived from plutonic rocks the relatively narrow depositional area represented a connection between the extensive epicontinental sea in northern europe and the oceanic basin of the tethys the fluctuating share of non tidal and tidal currents was detected from rose diagrams constructed for three different stages

macrofabric fingerprints of late devonian early carboniferous subduction in the polish variscides the kaczawa complex sudetes we describe a remarkably preserved assemblage of sedimentary and tectonic fabrics in cores from the kaczawa complex sudetes sw poland these fabrics indicate a continuum of process from repeated remobilization of upper devonian lower carboniferous muddy flysch and volcaniclastic sediments as debris flows and olistostromes to fracturing fluid streaming and soft sediment injection triggered by high pore water pressures during the initial stages of tectonic deformation to contractional cleavage formation and local cataclasis while the sediment was still only partially consolidated these structures are similar to those described from odp cores through the toes of active accretionary prisms they indicate active subduction of oceanic crust during the late devonian suggesting that ophiolite obduction and significant overthrusting in the sudetes occurred as an integral part of the variscan orogeny

vestiges of saxothuringian crust in the central sudetes bohemian massif zircon evidence of a recycled subducted slab provenance abstract four detrital zircon concentrates from the metasediments and metavolcanics of the central sudetes bohemian massif have been dated using shrimp ii the wyszki paragneiss yielded precambrian age spectra similar to those characteristic of the cadomian terranes 1 archaean and palaeoproterozoic zircons are scattered between 2830 and 1867 ma and 2 there are abundant neoproterozoic zircons dated at 803 577 ma the estimated maximum sedimentation age for this rock is 566 4 ma the klodzko fortress pyroclastic metarhyodacite gave an igneous emplacement age of 536 2 ma the magmatic precursor to the subvolcanic gniewoszow metarhyolite was dated at 501 3 ma finally the cinawica subvolcanic rhyolite yielded an igneous emplacement age of 338 3 ma and a large population of inherited zircons dated at palaeoproterozoic neoproterozoic cambro ordovician and late devonian early carboniferous the dated samples come from two adjacent suspect terranes the orlica nieznik dome and the klodzko massif in the central sudetes that are characterised by contrasting timing of metamorphism and exhumation despite this difference the results obtained show in conjunction with earlier data a similar provenance of the studied units and their common affinity to the saxo thuringian terrane since the central sudetes are separated from saxo thuringia by a collisional suture the pre variscan rocks must represent the deformed and metamorphosed allochthonous equivalents to saxo thuringian lithologies they were probably subducted together with the saxo thuringian passive margin during a variscan collision and then exhumed within an accretionary wedge in front of brunia east avalonia the central sudetic suspected terranes must have been derived from a dismembered single accretionary complex and were then juxtaposed by strike slip faults

is there a relationship between magmatic fabrics and brittle fractures in plutons a view based on structural analysis anisotropy of magnetic susceptibility and thermo mechanical modelling of the tanvald pluton bohemian massif abstract the present study focuses on the thermal and mechanical aspects of cooling of plutonic systems with respect to their internal structure analysis of the tanvald pluton and the nearby liberec granite the krkonose jizera plutonic complex bohemian massif using the anisotropy of magnetic susceptibility ams method indicates the decoupled magnetic fabrics formed by different processes in these two plutons two regional sets of vertical fractures cut across the plutons and their host rocks they are interpreted as having been formed as opening mode fractures joints after emplacement and cooling our thermo mechanical finite element modelling indicates that the thermal stresses within the tanvald pluton were compressive and that fracture criteria were not met during pluton cooling these results imply that the emplacement depth and confining pressure significantly affect the state of stress within a pluton during cooling and may play a crucial role in the formation of early fractures in plutons consequently the formation of early fractures during pluton cooling is driven by external conditions overriding the role of internal magmatic fabrics we argue that no genetic geometric or temporal correlation can exist between magmatic fabrics and fractures in granitoid plutons and thus that the original concept of hans cloos based on fabric joints relationships should be reconsidered instead an alternative classification of fractures in plutons should include cooling fractures syntectonic fractures uplift fractures and post uplift fractures

records of precambrian early palaeozoic volcanic and sedimentary processes in the central european variscides a review of shrimp zircon data from the kaczawa succession sudetes sw poland abstract the early pre orogenic stages of evolution in the variscan belt i e rifting processes opening of sedimentary basins and associated igneous activities are often obscure because many successions have yielded little or no biostratigraphic data have a strong metamorphic overprint and are tectonically deformed and dislocated the increasing application of shrimp zircon dating has provided useful constraints on magmatic and metamorphic processes helped locate probable source areas for detritus within sedimentary successions and facilitated large scale palaeogeographic correlations this methodology has recently thrown considerable light on the age and relationships of the previously poorly constrained rock units of the kaczawa complex in the polish west sudetes thus recent shrimp studies in the kaczawa mountains have yielded early ordovician ages of the initial rift type bimodal volcanic suites at the bottom part of the kaczawa succession c 503 ma for metarhyodacites of crustal derivation and c 485 ma for alkaline metatrachytes of mantle signature these dates provide a firm temporal constraint on the initial rift magmatism interpreted as related to the continental break up of the northern peripheries of gondwana new shrimp data from metavolcaniclastic and metasedimentary rocks of the kaczawa complex have yielded results that have provided significantly changed interpretations on their age and relationships for instance a siliciclastic sequence interpreted as belonging to the lower part of the kaczawa complex the gackowa sandstones and seemingly sourced using an array of geochemical and mineralogical evidence from nearby early ordovician volcanic rocks has surprisingly yielded zircon ages not younger than precambrian and thus this unit has tentatively been reinterpreted as a possible correlative of the neoproterozoic lusatian graywackes felsic metavolcaniclastic rocks embedded in the carbonate succession of the wojcieszow limestone have yielded shrimp zircon ages of c 497 ma thus supporting a late cambrian early ordovician age for this shallow water limestone sequence which had been proposed to be late ordovician silurian or younger in age based on controversial foraminifera evidence and more recently assigned to the mid cambrian based on newly found archaeocyathid fragments and age spectra of zircon populations in the metamudstone sequence of the radzimowice slates of thus far enigmatic stratigraphic position indicate that these deposits may have accumulated during early palaeozoic rifting with source areas similar to those known from parts of gondwana e g nw africa overall the new shrimp zircon studies both in metavolcanic and metasedimentary sequences have considerably illuminated their affinities and should provide encouragement for further application of this technique in this region in general the results provide support and detail for interpretation of this rock complex as reflecting the early stages of development of the volcanic and sedimentary processes operating along north gondwana during latest precambrian and early palaeozoic times

ordovician passive continental margin magmatism in the central european variscides u pb zircon data from the se part of the karkonosze izera massif sudetes sw poland approximately 500 ma old orthogneisses are widespread in the eastern part of the variscan belt and are commonly interpreted to have intruded mica schist series of assumed neoproterozoic age new shrimp zircon ages of quartzofeldspathic metavolcanogenic rocks of the mica schist series in the eastern part of the karkonosze izera massif sw poland indicate that they are late cambrian early ordovician rather than neoproterozoic in age based on the zircon age spectra distributed mainly between ca 500 and 660 ma with a few proterozoic inherited minimum ages of ca 970 and 1 825 ma younger zircon dates dispersed between ca 412 and 464 ma are interpreted as a result of pb loss likely caused by subsequent metamorphism consequently the felsic metavolcanogenic rocks appear to be roughly contemporaneous with the intrusion of ca 500 ma old orthogneiss protoliths with the pooled concordia age of 487 8 ma interpreted as the best approximation of the protolith intrusive age field relationships petrological and geochemical features of the felsic and mafic rocks studied support a model in which the accompanying mica schist series are not the original country rocks to the ca 500 ma granite intrusions and indicate that their recent close proximity is the result of tectonic juxtaposition however both the mica schists enclosing the bimodal metavolcanic rocks and the orthogneisses are interpreted to represent a cambro ordovician passive continental margin sequence being part of the saxothuringian domain they are tectonically overlain to the east by hp t metamorphic units comprising morb type metaigneous rocks and delineating a tectonic suture separating the saxothuringian block in the west from an assumed continental block tepla barrandian to the south east

location of the rheic suture in the eastern bohemian massif evidence from detrital zircon data introductionthe variscan orogen of europe con tains a collection of terranes that weredispersed along the northern marginof west gondwana in the late neo proterozoic and early palaeozoic e g murphy et al 2002 linnemannet al 2007 nance et al 2008 theseperi gondwanan terranes show anumber of common features as 1 voluminous late neoproterozoic c 640 550 ma arc magmatism 2 extensive volcano sedimentary succes sions of cogenetic arc related basins 3 a widespread cadomian unconfor mity separating deformed precam brian rock units from their earlypalaeozoic cambro ordovician overstep sequence and 4 an overlyingearly middle cambrian shallow marine platform e g murphy andnance 1989 nance et al 1991 2002 the peri gondwanan terranesrepresent dismembered fragments ofthe avalonian cadomian orogenthat was formed in the late neoprote rozoic c 700 540 ma at the north ern edge of gondwana e g nanceet al 2002 linnemann et al 2007 in the early palaeozoic several peri gondwanan terranes were separatedfrom west gondwana e g avalonia while others including the cadomianterranes remained attached togondwana and were accreted intothe appalachian variscan orogenwith the closure of the rheic ocean inthe late palaeozoic e g linnemannet al 2004 nance et al 2008 pres ently the cadomian terranes areincluded within the variscan belt ofeurope as separate blocks that stretchout from the iberian massif to thesaxo thuringian and tepla barran dian zones fig 1 e g linnemannet al 2008 nance et al 2008 the occurrences of neoproterozoicrocks have long been known from thecentral sudetic segment of the easternvariscides fig 2 although their pre cise age and provenance remainedunclear e g aleksandrowski and ma zur 2002 only recently jastrze bskiet al 2010 reported from the orlica s nieznik dome in the central sudetes a metamorphosed volcano sedimen tary succession continuing from thelate neoproterozoic into the early pal aeozoicwithoutacadomianunconfor mity if uninterrupted sedimentationwas actually the case across theneoproterozoic palaeozoic boundary c 542 ma the orlica s nieznik dome would lack a cadomian a nity con sequently the central sudetes wouldrepresent an exotic terrane insertedbetween the cadomian terranesand east avalonia in such a case existing plate tectonic models for theclosure of the rheic ocean wouldrequiresubstantialrevision in this article we present new sen sitive high resolution ion micro probe shrimp u pb data fordetrital zircon grains to constrain theage and provenance of selectedmetasediments from the orlica s nieznik dome fig 2 these geo chronological data in combinationwith eld relations and publishedresults are used to identify the plate tectonic setting s of neoproterozoicto cambro ordovician rock units ofthe orlica s nieznik dome we then compare the new results with theneoproterozoic to early palaeozoicstratigraphy of the saxo thuringianzone to test the cadomian a nity ofthe central sudetes our goal is toconstrain the eastern extent of thecadomian terranes and the location ofthe rheic suture in central europe geological settingthe orlica s nie znik dome fig 2 isdominated by amphibolite grade or thogneiss locally containing lenses of u hp rocks alternating with belts ofstaurolite grade supracrustal rocks don et al 1990 the orthogneiss istraditionally subdivided into two maintextural varieties fig 2 the por phyric augen to banded s nieznik abstract

selective weathering of cross bedded layers forming shelters and small caves on akopan tepui venezuela field laboratory and experimental evidence about diagenesis and weathering of the mataui formation arenites roraima supergroup middle proterozoic abstract south american table top mountains tepuis are formed by quartzites and sandstones of mataui formation belonging to the roraima supergroup lower to middle proterozoic field observations in the northern part of akopan tepui in venezuela revealed that unlike the beds with flat bedding the cross bedded layers are commonly affected by selective weathering expressed by depressions shelters and even small caves all the arenites are fine grained most of them are likely of aeolian origin hardness measurements confirmed that the cross bedded layers are softer than the flat bedded or structureless beds occurring above and below them petrographic analysis showed that the rocks are mostly fine grained quartzites to quartz sandstones with original sand grains overgrown by syntaxial quartz cement and bearing signs of compaction manifested by local pressure solution some intergranular spaces are filled by newly formed phyllosilicates paragonite locally intergrown with muscovite in the overlying beds no porosity was observed by microscopic study and under sem whereas in the underlying rocks signs of slight weathering and etching of phyllosilicates was observed together with locally widened spaces along the grain to grain boundaries the samples from cross bedded layers display weathering the degree of which depends on the present access of flowing water where water has periodical access to the arenite it shows dissolution of quartz cement arenization together with complete leaching and removal of the phyllosilicates due to lateritization the intergranular spaces are considerably widened and quartz grains bear signs of strong skeletal etching and pitting samples from the sites where the water access ceased show mostly leaching of phyllosilicates with weak skeletal dissolution of quartz grains without pitting to imitate the origin of structures observed in the field experimental modelling was performed using artificially layered and compacted fine grained sands on which sodium silicate solution was dripped during soaking downward preferential penetration of the solution along the cross bedding laminae funnel flow was observed in the cross bedded layer the resulting structures display good lithification of horizontally layered sands and relatively poorer lithification of the cross bedded sediment between them showing triangular shaped overhangs and shelters which mimic those on the akopan tepui differential weathering of otherwise petrologically very similar arenites indicates that there had to be a difference in the initial porosity in the time of the rock denudation a preserved porosity in the cross bedded layers was necessary for the water rock contact to perform dissolution

thermotectonic evolution of the barrandian czech republic as revealed by apatite fission track analysis abstract a fission track ft study was carried out on apatite from upper proterozoic to upper carboniferous sedimentary and volcanic rocks in the barrandian czech republic apatite ft ages vary between 324 8 ma lower carboniferous and 196 14 ma lower jurassic mean confined track lengths range from 11 68 1 76 to 13 30 1 41 m the temperature time path of selected samples was simulated by applying the laslett annealing model and independent geological constraints from the barrandian the first stage of increased temperature that is recorded in nearly all samples occurred at the upper devonian lower carboniferous boundary the change in temperature is due to the thickening of the crust by increased sediment load and stacking of sedimentary rocks along thrusts ft data indicate a limitation of the extension of thrust sheets towards the west cooling during the carboniferous is attributed to exhumation of parts of the barrandian deposition of upper carboniferous to lower permian sediments caused a second increase in temperature in lower permian time variation in maximum temperature indicates variable thickness of the sedimentary cover the second cooling during the mesozoic is linked to the long term slow to medium exhumation process of the central variscan belt

thermochronological constraints on the long term erosional history of the karkonosze mts central europe abstract a combination of zircon u th he zhe apatite fission track aft and apatite u th sm he ahe thermochronology is used to constrain the long term exhumation and erosional history of the karkonosze mts in north eastern bohemian massif by analyzing samples from the highly elevated summit planation surface zhe ages from the south eastern part of the planation surface are 285 19 295 20 and 308 21 ma indicating that the area remained at temperatures below 190 c since the permian in contrast zhe ages in the western part of the planation surface are mid cretaceous proving that this part was residing at temperatures above 190 c prior to exhumation the exhumation occurred in the late cretaceous as evidenced by aft and ahe ages ranging from 82 5 to 90 8 ma and from 77 5 to 91 6 ma respectively modelled cooling trajectories are characterized by a two stage cooling history fast cooling through the apatite partial annealing zone and helium partial retention zone to surface conditions between 90 and 75 ma and slow cooling or even thermal stagnation from 75 ma to present although our data do not allow us to resolve the age of the planation surface completely we narrowed down the number of explanatory options and propose two alternative solutions for the formation of the planation surface i the planation surface represents the remnant of a permian peneplain which was buried by mesozoic sediments of the central european basin system and was re exposed in the late cretaceous or ii the planation surface formed after 75 ma after termination of a period of massive erosion documented by thermochronological data and by the sedimentary record in adjacent basins cenozoic relief production and uplift of the planation surface evident from regional landforms and the sedimentary record is not recorded by thermochronological data this shows that erosion on the uplifted planation surface since 75 ma was less than 1 2 km

u pb ages from sw poland evidence for a caledonian suture zone between baltica and gondwana faunal and palaeomagnetic evidence suggests the existence of a c 3000 km wide tornquist sea between gondwana and baltica in early ordovician times which narrowed to 50 2 ma an unmetamorphosed ophiolite gives a 420 20 2 ma age whilst in two other terranes amphibolite facies island arc lavas have fossiliferous lower ludlow 424 415 ma sequences all are unconformably overlain by unmetamorphosed upper devonian conglomerates a sinistral transpressive regime is observed in regionally extensive mylonite zones titanite and zircon ages 338 2 3 and 339 4 ma record variscan magmatism the data suggest considerable narrowing of the tornquist sea during the ordovician continuing ocean floor and island arc activity in the silurian and final sinistral transpressive closure by the mid devonian

fission track thermochronology of the ruhla crystalline complex new constraints on the post variscan thermal evolution of the nw saxo bohemian massif abstract to help clarify the relative and absolute timing of post variscan cooling and exhumation processes in the ruhla crystalline complex rcc situated in the nw part of the saxo bohemian massif eight zircon and eleven apatite fission track ages and nine apatite track length measurements have been obtained zircon fission track ages support an existing model of post variscan exhumation of the rcc as three discrete blocks the eastern and western blocks show cooling from peak metamorphic conditions to below 260 30 c by ca 300 ma and exposure by 296 ma the central block shows a later cooling to below 260 30 c by ca 270 ma and exposure at the surface by ca 256 ma apatite fission track data reveal late cretaceous accelerated cooling through the apatite partial annealing zone 120 to 60 c this can be correlated with tectonic inversion at this time the apatite data also indicate that the rocks of the rcc were at temperatures above 110 10 c before ca 85 ma this requires either an anomalously high palaeo geothermal gradient of ca 60 c km 1 during the late cretaceous or that the rcc region was originally covered by up to 1400 m of now eroded jurassic and cretaceous sedimentary rocks we favour a combination of both factors with accelerated erosion of missing overburden during a period of increased heat flow initiated at ca 85 ma

different modes of the late cretaceous early tertiary inversion in the north german and polish basins several selected seismic lines are used to show and compare the modes of late cretaceous early tertiary inversion within the north german and polish basins these seismic data illustrate an important difference in the allocation of major zones of basement thick skinned deformation and maximum uplift within both basins the most important inversion related uplift of the polish basin was localised in its axial part the mid polish trough whereas the basement in the axial part of the north german basin remained virtually flat the latter was uplifted along the sw and to a smaller degree the ne margins of the north german basin presently defined by the elbe fault system and the grimmen high respectively the different location of the basement inversion and uplift within the north german and polish basins is interpreted to reflect the position of major zones of crustal weakness represented by the wnw ese trending elbe fault system and by the nw se striking teisseyre tornquist zone the latter underlying the mid polish trough therefore the inversion of the polish and north german basins demonstrates the significance of an inherited basement structure regardless of its relationship to the position of the basin axis the inversion of the mid polish trough was connected with the reactivation of normal basement fault zones responsible for its permo mesozoic subsidence these faults zones inverted as reverse faults facilitated the uplift of the mid polish trough in the order of 1 3 km in contrast inversion of the north german basin rarely re used structures active during its subsidence basement inversion and uplift in the range of 3 4 km was focused at the elbe fault system which has remained quiescent in the triassic and jurassic but reproduced the direction of an earlier variscan structural grain in contrast n s oriented mesozoic grabens and troughs in the central part of the north german basin avoided significant inversion as they were oriented parallel to the direction of the inferred late cretaceous early tertiary compression the comparison of the north german and polish basins shows that inversion structures can follow an earlier subsidence pattern only under a favourable orientation of the stress field a thick zechstein salt layer in the central parts of the north german basin and the mid polish trough caused mechanical decoupling between the sub salt basement and the supra salt sedimentary cover resultant thin skinned inversion was manifested by the formation of various structures developed entirely in the supra salt mesozoic cenozoic succession the zechstein salt provided a mechanical buffer accommodating compressional stress and responding to the inversion through salt mobilisation and redistribution only in parts of the ngb and mpt characterised by either thin or missing zechstein evaporites thick skinned inversion directly controlled inversion related deformations of the sedimentary cover inversion of the permo mesozoic fill within the mid polish trough was achieved by a regional elevation above uplifted basement blocks conversely in the north german basin horizontal stress must have been transferred into the salt cover across the basin from its sw margin towards the basins centre this must be the case since compressional deformations are concentrated mostly above the salt and no significant inversion related basement faults are seismically detected apart from the basin margins this strain decoupling in the interior of the north german basin was enhanced by the presence of the elbe fault system which allowed strain localization in the basin floor due to its orientation perpendicular to the inferred late cretaceous early tertiary far field compression

timing of post collisional volcanism in the eastern part of the variscan belt constraints from shrimp zircon dating of permian rhyolites in the north sudetic basin sw poland the final stages of the variscan orogeny in central europe were associated with voluminous granitic plutonism and widespread volcanism four samples representative of the main rhyolitic volcanic units from the stephanian permian continental succession of the north sudetic basin in the eastern part of the variscan belt were dated using the sims shrimp zircon method three samples show overlapping 206 pb 238 u mean ages of 294 3 293 2 and 292 2 ma and constrain the age of the rhyolitic volcanism in the north sudetic basin at 294 292 ma this age corresponds to the early permian sakmarian stage and is consistent with the stratigraphic position of the lava units the fourth sample dated at 288 4 ma reflects a minor younger stage of sub volcanic activity in the artinskian the silicic activity was shortly followed by mafic volcanism the rhyolite samples contained very few inherited zircons possibly owing to limited contribution of crustal sources to the silicic magma or owing to processes involved in anatectic melting and magma differentiation e g resorption of old zircon by zr undersaturated melts the shrimp results and the stratigraphic evidence suggest that the bimodal volcanism terminated the early short lived 10 15 ma and vigorous stage of basin evolution the permian volcanism in the north sudetic basin may be correlated with relatively late phases of the regional climax of late palaeozoic volcanism in central europe constrained by 41 published shrimp zircon age determinations at 299 291 ma the permian volcanism and coeval plutonism in the ne part of the bohemian massif can be linked to late variscan post collisional extension

topographic relief driven by variations in surface rock density earth s surface topography is generated by tectonically induced variations in crustal thickness combined with erosion and to a lesser degree by vertical stresses caused by convection in the underlying mantle rock hardness and resistance to erosion are also commonly thought to influence topography because hard rocks such as granites and basalts usually form topographic highs in the landscape here we use analytical and numerical models to simulate the erosion induced isostatic rebound of rocks we find that the isostatic rebound that accompanies erosion causes denser rocks to occupy higher elevations in the landscape thereby creating topographic relief that is proportional to surface rock density differences rather than rock hardness we quantify this effect taking into account the flexural strength of the continental lithosphere we show that in a steady state erosional setting density dependent isostatic rebound can cause the densest rocks to be exhumed at double the rate of surrounding less dense rocks and has a stronger effect than typical rock hardness variations the results imply that denser rock formations should erode faster and therefore be characterized by younger thermochronological ages thermochronological data sets from the kinabalu granite in borneo and the shakhdara alichur gneiss domes in pamir confirm this counter intuitive result our findings imply that lateral variations in surface rock density have significant control on the shaping of the large scale features of earth s surface the high elevation in earth s topography of hard rocks such as granites and basalts was thought to be caused by their inherent resistance to erosion numerical modelling now demonstrates counterintuitively that erosion induced isostatic rebound of rocks which is density dependent causes granites and basalts to occupy high elevations because they are more dense than surrounding rocks

the 40ar 39ar ages from the west sudetes ne bohemian massif constraints on the variscan polyphase tectonothermal development

the tepla saxothuringian suture in the karkonosze izera massif western sudetes central european variscides the southern and eastern karkonosze izera massif northern bohemian massif exposes blueschist facies rocks and morb type magmatic complexes during late devonian to early carboniferous times these were overthrust within a nappe pile toward the nw onto the pre variscan saxothuringian basement composed of the izera kowary metagranitoids and their envelope the lowermost nappe or parautochthonous unit of the pile is the low grade metamorphosed jest d complex comprising a devonian to early carboniferous sedimentary succession of the saxothuringian passive margin this is tectonically overlain by the south karkonosze complex which represents ordovician silurian volcano sedimentary infill of the saxothuringian basin affected by late devonian hp metamorphism the uppermost nappe is the early palaeozoic epidote amphibolite grade leszczyniec morb like complex cropping out on the eastern margin of the karkonosze izera massif it probably represents a fragment of obducted saxothuringian basin floor the nappe pile was stacked beneath the overriding upper plate margin now concealed below the intra sudetic basin and hypothesized to represent a fragment of the tepla barrandian terrane the nappe stacking triggered by buoyancy controlled upward extrusion of the subducted continental slab was the main mechanism for the exhumation of hp rocks the final stages of the nw ward nappe stacking were accompanied and followed by se directed early carboniferous extensional collapse the lower plate of the suture zone was uplifted at that time and intruded by the 330 ma old nearly undeformed karkonosze granite pluton as a result of the collapse the tepla barrandian upper plate was downthrown on shear zones and brittle faults and buried under several km thick synorogenic late tournaisian through namurian and post orogenic late carboniferous early permian succession of the intra sudetic basin the south and east karkonosze suture most probably is a fragment of the tepla saxothuringian munchberg tepla suture belt known from the western bohemian massif

fission track dating of the south eastern bohemian massif waldviertel austria thermochronology and long term erosion apatite fission track thermochronology was applied to the outcropping variscan basement of the south eastern bohemian massif in order to resolve its post variscan cooling and denudation history nineteen samples could be dated by the grain population method the ages range from 235 to 90 ma middle triassic to middle cretaceous neglecting some local variations they show a decrease from the western edge of the moravian thaya window towards the west and the south fission track length histograms mainly exhibit broad distributions with arithmetic means between 12 3 and 13 4 m and standard deviations between 1 5 and 2 0 m thermochronological model calculations of the measured data demonstrate that the apatite fission track memory of the samples reaches back until the begin of the cretaceous and for some samples even until the permian the regional fission track cooling pattern is not related to the limitations and the internal structure of the moravian thaya window which appears to be an elder probably late carboniferous to permian tectonic feature also the vitis fault does not delimit areas of different thermochronological behaviour therefore significant vertical offset on that fault can be excluded for the cretaceous and cenozoic thermochronological model calculations of fission track ages and length data are consistent with the assumption of regional sedimentary reburial during the late cretaceous the amount of reburial could have attained 1 km the cenozoic bulk denudation was in the order of 1 to 3 km

post variscan cooling history of the central western sudetes ne bohemian massif poland constrained by apatite fission track and zircon u th he thermochronology abstract apatite fission track aft and zircon u th he zhe dating techniques were combined to reveal post orogenic history of the rudawy janowickie mts in the west sudetes bohemian massif permian to jurassic zhe ages of 271 2 24 8 171 3 11 5 ma obtained for crystalline basement rocks indicate post orogenic cooling and progressive unroofing of the ne bohemian massif on the other hand cretaceous zhe ages of 130 5 8 8 99 7 6 7 ma prove that the rudawy janowickie mts region remained under 190 c during the mid cretaceous suggesting a deep burial zhe ages from the cretaceous sediments located to the east of the rudawy janowickie mts range between 298 8 16 8 and 181 8 11 9 ma documenting that the burial did not exceed 6 km in the axial part of the intra sudetic through aft ages range from 105 9 6 1 to 51 1 4 3 ma the eocene aft ages revealed by the granite basement and the cretaceous aft age revealed by the metamorphic cover suggest the existence of at least two different thermo tectonic blocks experiencing different post variscan cooling and exhumation aft results strongly support 3 3 3 5 km exhumation for the rudawy janowickie mts since the cenomanian which in combination with zhe results clearly contradicts some of the previously proposed evolutionary scenarios for the sudetes

late cretaceous intraplate thrusting in central europe effect of africa iberia europe convergence not alpine collision a well established event of intraplate basin inversion and basement thrusting affected central europe in late cretaceous time it is widely accepted to have resulted from the collision of the alpine orogen with europe s margin at that time an early alpine orogen located on the leading edge of the adria microplate still lay far southeast of its present day position and had entered a phase of extension after a first orogenic event characterized by w to nw directed thrusting this configuration is not likely to have induced ssw nne directed thrusting and folding in the future european foreland that was still separated from the alpine wedge by a strip of oceanic lithosphere by contrast the onset of intraplate contraction coincides with an important change in relative motion between the european and african plates at ca 90 ma africa s sse directed sinistral transform motion relative to europe changed to ne directed convergence this agrees well with the timing and kinematics of intraplate thrusting in central europe structures of similar age and kinematics occurring in southern france spain and north africa suggest that the late cretaceous pulse of contraction was caused by pinching west central europe s thin lithosphere between baltica and africa only since the onset of n directed thrusting in the alps in paleocene or eocene time are the kinematics of the alps and their european foreland compatible indicating that mechanical coupling between africa europe and the adria microplate had been achieved

fission track dating of the western border of the bohemian massif thermochronology and tectonic implications since 1985 apatite fission track analysis was applied to more than 70 samples from surface outcrops and shallow boreholes at the western margin of the bohemian massif apatite ages were determined by the grain population method additional information from the frequency distributions of fully confined spontaneous tracks was used for modelling of t t paths in the low temperature range 120 c seven zircon samples were dated by the external detector method zircon ages between 283 and 215 ma indicate unroofing during the permian molasse stage and the triassic tectonic quiescence and slow subsidence prevailed from the jurassic until the middle cretaceous in the basement area south of weiden a mesozoic partial annealing zone for apatite fission tracks is now exposed at the surface farther north the basement was affected by stronger cretaceous and palaeogene erosion which yielded cooling ages between 110 and 49 ma this second period of post variscan denudation was correlated to reverse faulting along the franconian line

geochemical evidence for progressive rift related early palaeozoic volcanism in the western sudetes the volcanigenic rocks of the kaczawa mts western sudetes poland in the eastern variscides show changing geological and geochemical evolution during early palaeozoic time the lower part of the succession cambrian ordovician has three components 1 shallow marine to subaerial metabasalts associated with limestones and volcaniclastics the lavas are dominantly of a transitional tholeiitic alkaline type and their trace element patterns typically represent a rift related environment they pass laterally and upwards into more depleted basalts resembling enriched morb with nd isotopic characteristics indicating contamination by continental crust 2 interlayered rhyodacitic lavas and volcaniclastics which show negative nd values suggesting formation of the original magma by crustal melting 3 an overlying alkaline bimodal suite of lavas and volcaniclastic rocks as well as alkaline metabasites of shallow intrusive character the geochemistry of the latter resembles oceanic island volcanics but they may well have been emplaced in the same evolving rift environment the upper part of the kaczawa succession ordovician silurian in age comprises a thick and monotonous sequence of deep marine pillowed and massive metabasalts associated with black shales and cherts these lavas exhibit morb trace element characteristics with minor evidence of crustal contamination during this stage of rifting true oceanic crust probably formed it is thus suggested that the studied part of the kaczawa succession developed in a progressively evolving rift initially within an ensialic environment and finally reaching the stage of a basin underlain by oceanic type crust together with similar cambrian ordovician volcanic sedimentary associations widely distributed in western europe from portugal through france and germany they represent a record of the early palaeozoic rifting in the northern periphery of gondwana

weathering mantles and their significance for geomorphological evolution of central and northern europe since the mesozoic abstract weathering mantles saprolites are very widespread in central western and northern europe where they form thick near surface residual deposits often in excess of 50 m they vary in the type of weathering the bedrock lithology involved the topographic setting and the age and stratigraphic context this review paper provides information about the distribution and major characteristics of weathering mantles from a number of key areas including the british isles the central european belt of mid mountains and uplands the scandinavian mountains and the fennoscandian shield it also examines the evidence for weathering etched origin of various landforms including boulders tors inselbergs basins and some regional landforms assemblages major types of regionally important weathering mantles include ferrallitic lateritic saprolites kaolinite rich saprolites sandy to grus mantles and various residuals left after partial dissolution of carbonate rocks although dating of weathering mantles is often circumstantial it appears sufficiently precise to argue for various ages of deep weathering mesozoic pre late cretaceous mantles are particularly widespread but there are also early tertiary and miocene saprolites widely present whilst most grus weathering is likely to be of miocene to pleistocene age individual upland areas have been subjected to multiple episodes of weathering whose legacy is the present day co existence of different weathering products continental and shallow marine deposits around the uplands particularly in the north sea and intra continental graben structures are often dominated by quartz and kaolinite pointing to deeply weathered land surfaces as the source areas and extending the record of weathering on the geological time scale they demonstrate that weathering mantles repeatedly formed and were subjected to erosion and new cycles of weathering were initiated we suggest that deep unroofing of basement structures in many parts of europe has been mainly accomplished by deep weathering and stripping of pre weathered rock the phenomenon of deep weathering has been very important for geomorphology etched landforms vary in size from small residual boulders up to regional characteristic landscapes etchsurfaces such as joint valley landscapes of southern sweden or undulating multi convex and multi concave landscapes of many uplands in central europe deep weathering has played a major part in the geomorphological evolution of europe since at least the late triassic and the concept involving long term etching and stripping provides an appropriate framework to describe and explain both erosional landscapes and sediment features

the elbe fault system in north central europe a basement controlled zone of crustal weakness abstract the elbe fault system efs is a wnw striking zone extending from the southeastern north sea to southwestern poland along the present southern margin of the north german basin and the northern margin of the sudetes mountains although details are still under debate geological and geophysical data reveal that upper crustal deformation along the elbe fault system has taken place repeatedly since late carboniferous times with changing kinematic activity in response to variation in the stress regime in late carboniferous to early permian times the elbe fault system was part of a post variscan wrench fault system and acted as the southern boundary fault during the formation of the permian basins along the trans european suture zone sensu geol mag 134 5 1997 585 the teisseyre tornquist zone ttz most probably provided the northern counterpart in a pull apart scenario at that time further strain localisation took place during late mesozoic transtension when local shear within the elbe fault system caused subsidence and basin formation along and parallel to the fault system the most intense deformation took place along the system during late cretaceous early cenozoic time when the elbe fault system responded to regional compression with up to 4 km of uplift and formation of internal flexural highs compressional deformation continued during early cenozoic time and actually may be ongoing the upper crust of the elbe fault system which itself reacted in a more or less ductile fashion is underlain by a lower crust characterised by low p wave velocities low densities and a weak rheology structural seismic and gravimetric data as well as rheology models support the assumption that a weak stress sensitive zone in the lower crust is the reason for the high mobility of the area and repeated strain localisation along the elbe fault system

lu hf geochronology and trace element distribution in garnet implications for uplift and exhumation of ultra high pressure granulites in the sudetes sw poland combining lu hf garnet geochronology with in situ trace element analyses in garnet allowed its to gain new insight into the metamorphic evolution of uhp uht rocks in the stary gieraltow region in the polish sudetes prograde garnet growth recorded by rayleigh type heavy ree hree zoning in the felsic granulites indicates that the obtained 386 6 4 9 ma lu hf age represents the time of garnet crystallization on a prograde uhp metamorphic path the surrounding rocks were metamorphosed at the same time as indicated by 381 2 6 7 ma sm nd garnet age obtained for the mid crustal metapelites the second metamorphic episode which affected most of the lower crust in the orlica snieznik massif osm occurred at ca 340 ma as determined by u pb zircon and sm nd garnet dating of granulites in this and previous studies is interpreted as a high temperature event which took place on a retrograde path trace element distribution in garnets from the layered granulites showed significant differences in distribution of medium and hree in garnets from mafic and felsic protoliths over the course of the metamorphic evolution this had strong impact on the isotopic dating results and led to decoupling of the sm nd and lu hf clocks which recorded timing of the two different metamorphic episodes separated by as much as 40 ma moreover the preservation of the hree growth zonation profile in garnets from the felsic granulites whose minimum metamorphic temperature was established at 900 degrees c implies that the lu hf system under relatively dry conditions does not undergo significant diffusional re equilibration even at such extreme temperatures and therefore it sill provides the age of prograde garnet growth under hydrous conditions at least some resetting will take place as documented by the partially relaxed hree zonation profile in the amphibolitised mafic granulite which yielded a 10 ma younger age the hree distribution study appeared to be a particularly valuable and essential tool which allowed us to distinguish garnet growth from post growth complexities and hence provide improved age interpretation medium ree on the other hand did not show any obvious correlation with the isotopic signature of garnet two distinct metamorphic episodes recorded in the stary gieraltow region show that buoyancy driven uplift of uhp rocks can be arrested at the base of a continental crust if not supported by any additional force in our case study the uhp rocks would have never reached the surface if their uplift had not been resumed after a long pause under a different tectonic regime the multistage discontinuous uplift revealed by the uhp rocks of the osm provides a new scenario for the exhumation of continental crust from mantle depths distinct from the fast track exhumation histories recognized in uhp terranes elsewhere c 2006 elsevier b v all rights reserved