topographic inversion and changes in the sediment routing systems in the variscan orogenic belt as revealed by detrital zircon and monazite upb geochronology in post collisional continental basins abstract the basal alluvial and fluvial siliciclastic successions within the late carboniferous intracontinental basins of the west central bohemian massif provide an intriguing sedimentary record of changes in paleotopography and paleodrainage systems during and after orogenic collapse we analyze this record using the u pb laser ablation icp ms detrital zircon and monazite geochronology five distinct age groups have been identified across the examined stratigraphic succession i archean paleoproterozoic ii late neoproterozoic iii cambro ordovician iv late devonian and v mid to late carboniferous these age groups indicate mixing of both local and distal extra basinal sources and also point to a two stage post convergent geodynamic evolution of the variscan belt the first stage followed collapse of the central bohemian orogenic plateau at around 346 337 ma and involved rapid cooling at ca 340 320 ma and removal of ca 2 3 km of sedimentary overburden from the top of the plateau no sedimentary record of this erosional event suggests that the river systems transported detritus radially outwards from the inner part of the orogen to its forelands a paleorelief inversion and thus major reorganization of the sediment routing systems were then associated with uplift in the southerly and southwesterly peripheral domains of the orogen at ca 330 310 ma in turn these uplifted domains occupied by rapidly unroofed voluminous granite plutons shed detritus into the bohemian sink this was represented by the former plateau collapsed to relatively low elevations but still with significant internal paleorelief dominated by a system of tens of kilometers long nne ssw trending paleovalleys some of the material was further transported in extensive river systems crossing the former plateau to the northerly variscan foreland basin thus the radial sediment routing system changed into axial unidirectional finally we suggest that these major inversions of paleorelief and changes in the surface processes and paleodrainage systems may have been linked to distinct late orogenic lithospheric mantle delamination events first stage delamination occurred beneath the center of the bohemian massif to cause the plateau collapse denudation and radial sediment transport whereas the second stage delamination occurred along its periphery to cause uplift sourcing the intracontinental basins and unidirectional sediment transport end of deposition and magmatic shutdown at around 305 ma may then define the very cessation of late orogenic vertical movements and the transition to a post orogenic intra plate setting

creep strength of ringwoodite measured at pressure temperature conditions of the lower part of the mantle transition zone using a deformation dia apparatus abstract creep strength of ringwoodite is important for understanding complicated patterns of the mantle convection in and around the mantle transition zone to determine the creep strength of ringwoodite we expanded pressure temperature conditions of in situ stress strain measurements in a deformation dia apparatus combined with synchrotron x ray to those of the lower part of the mantle transition zone the expansion of the pressure temperature conditions was made by shrinking anvil truncation to 2 0 mm and the development of a cell assembly for in situ deformation experiments up to 1700 k utilizing the developed technique creep strength measurements on polycrystalline ringwoodite were performed at 16 9 18 0 gpa and 1300 1700 k during axial deformation with strain rates of 1 48 3 59 10 5 s 1 to strains of 13 2 24 9 based on mechanical and microstructural observations we infer that ringwoodite deformed by exponential dislocation creep through the peierls mechanism at 1300 1400 k and power law dislocation creep at 1500 1700 k the creep strength of ringwoodite is apparently lower than that of bridgmanite wadsleyite and olivine the present result implies the possibility that the lower mantle transition zone is a low viscosity layer further creep strength data of these minerals are necessary to be determined above 13 5 gpa and high temperatures to determine viscosity structure in and around the lower mantle transition zone at strain rates relevant to the mantle convection

p t t evolution of ultrahigh temperature granulites from the saxon granulite massif germany part ii geochronology the granulites of the saxon granulite massif equilibrated at high pressure and ultrahigh temperature and were exhumed in large part under near isothermal decompression this raises the question of whether p t t data on the peak metamorphism may still be retrieved with confidence felsic and mafic granulites with geochronologically useful major and accessory phases have provided a basis to relate p t estimates with isotopic ages presented in a companion paper the assemblage garnet clinopyroxene in mafic granulite records peak temperatures of 1010 1060 c consistent with minimum estimates of around 967 c and 22 3 kbar obtained from the assemblage garnet kyanite ternary feldspar quartz in felsic granulite multiple partial overprint of these assemblages reflects a clockwise p t evolution garnet and kyanite in the felsic granulite were successively overgrown by plagioclase spinel plagioclase sapphirine plagioclase and biotite plagioclase most of this overprinting occurred within the stability field of sillimanite garnet clinopyroxene in the mafic granulite were replaced by clinopyroxene amphibole plagioclase magnetite the high p t conditions and the absence of thermal relaxation features in these granulites require a short lived metamorphism with rapid exhumation the ages of peak metamorphism 342 ma and shallow level granitoid intrusions 333 ma constrain the time span for the exhumation of the saxon granulites to about 9 ma

age geodynamic setting and mantle enrichment processes of a k rich intrusion from the meissen massif northern bohemian massif and implications for related occurrences from the mid european hercynian the plutonic complex of the meissen massif northern margin of the bohemian massif comprises dioritic to mainly monzonitic and granitic rocks the diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series the chemical signatures of less crustally contaminated diorites are similar to arc related shoshonitic rocks derived from continental lithospheric mantle clm sources previously enriched by subduction of altered oceanic crust laser step heating 40ar 39ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329 1 1 4 to 330 4 1 4 ma and from 330 4 2 1 to 330 6 1 8 ma respectively these cooling ages are indistinguishable from sensitive highresolution ion microprobe shrimp 238u 206pb intrusion ages measured on magmatic zircon rims from the monzonite nasdala et al submitted this shows that the monzonite intrusion is probably not related temporally to active subduction because it postdates eclogites of the adjacent saxonian erzgebirge by approximately 20 ma the shoshonitic magmas intruded during strike slip tectonism along the elbe valley zone the enrichment of their mantle sources may be of upper devonian lower carboniferous age or older intrusions of shoshonitic to ultra potassic k rich rocks during the upper visean namurian are widespread in the moldanubian zone based on similar ages and structural relationships a similar post collisional setting to the meissen shoshonitic rocks can be demonstrated most of these occurrences cut high grade nappe units which were subducted during the upper devonian lower carboniferous in contrast to the meissen massif at least the ultra potassic members of the central and the south bohemian batholiths were derived from clm sources enriched by fluids or melts released from subducted oceanic crust and by greater portions of crustal material despite the similar post collisional geodynamic setting of the k rich intrusions different enrichment processes generated mid european hercynian clm sources with heterogeneous major and trace element and isotopic signatures

u pb zircon ages from volcanic and sedimentary rocks of the ediacaran bas draâ inlier anti atlas morocco chronostratigraphic and provenance implications abstract u pb la icp ms analyses on zircon extracted from felsic ignimbrites and sandstones of the bas dra succession bds constrain the post pan african evolution in the anti atlas aa at the northern margin of gondwana the 2000 m thick ediacaran bds consists of four volcanic units including i rhyolitic ignimbrite sheets ao i ii high silica andesitic and rhyolitic lavas ao ii iii silica poor lava and pyroclastics ao iii and iv rhyolitic lava dome complexes ao iv ao iii is dominated by basaltic and andesitic lava and it contains at least three sandstone lenses the bds is capped by an angular unconformity which is defined by sedimentary rocks of the adoudou formation of the taroudant group the u pb data set 99 zircon grains with 90 110 concordance from the ignimbrite yields an age of 565 6 ma 564 8 5 6 ma interpreted as the crystallization age which represents the early volcanic activity in the bds for the upper bds maximum ages of ca 552 and ca 541 ma are indicated by u pb ages of detrital zircons extracted from sandstone these age constraints confine the bds to the upper ouarzazate supergroup most detrital zircon ages three sandstone samples with 367 zircon grains analyzed fall in the range of ca 606 541 ma this main ediacaran peak is interpreted to have been derived from the post pan african magmatic complexes surrounding the west african craton wac secondary age peaks at ca 652 ma and ca 655 ma are inferred to originate from early to late pan african magmatism of the anti atlas region due to the complete absence of pre neoproterozoic zircon ages our data set is interpreted to indicate a large voluminous volcanic episode that covered the palaeoproterozoic and cryogenian basement or the river system was confined to the bds basin facies and provenance analyses of bds sandstones indicate that the detrital input was mostly locally derived with a minor amount from an external source in addition large peaks of older zircon ages are recognized only on the lower sandstone lens bd 86 aoiii thus the drainage system was large within the lower part and became more localized at the end of bds evolution the maximum depositional age for the zircons separated from the uppermost ao iii sandstone lens 541 ma shifts the precambrian cambrian boundary down from the lower adoudou formation as proposed by previous studies to the uppermost ouarzazate supergroup or to the hiatus between both units the volcanic activity within the bds is linked to a transtensional regime that operated along the gondwana margin during the ediacaran the bds volcanic activity is contemporaneous with the widespread volcanic volcanoclastic and siliciclastic rocks of upper ouarzazate supergroup

multiple sources for sea rafted loisels pumice new zealand sea rafted loisels pumice is one of the few stratigraphic markers used to correlate late holocene coastal deposits in new zealand along with underlying sea rafted products of the local taupo eruption of ca 1800 yr b p these events have been used to bracket the first arrival of humans at new zealand loisels pumice is dacitic to rhyolitic sio263 78 wt in composition but individual clasts are homogeneous sio2range 1 wt characteristics include very low k2o 0 5 1 75 wt and rb 25 ppm and a mineralogy dominated by calcic and mafic xenocrysts similar features are shared by pumices of the tonga kermadec arc suggesting a common tholeiitic oceanic source interclast diversity of loisels pumice suggests that it is the product of several eruptive events from different volcanoes the differences in glass and mineral compositions found at various sites can be explained if the deposits are from different events a multisource origin can also partially explain the discrepancy in reported14c ages ca 1500 600 yr b p from different localities therefore the value of loisels pumice as a stratigraphic marker is questionable and it does not constrain the arrival of humans the predominant westward drift of historic tonga kermadec arc pumices and prevailing ocean currents suggest a long anticlockwise semicircular transport route into the tasman sea before sea rafted pumice arrival in new zealand the diversity of the pumices indicates that silicic eruptions frequently occur from the predominantly basic oceanic volcanoes

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

internal structures and dating of complex zircons from meissen massif monzonites saxony abstract u pb zircon ages were determined for accessory zircons from two monzonites from the meissen massif northern bohemian massif germany by shrimp ion microprobe bse and cl imaging revealed that the monzonite zircons showing oscillatory growth zoning often contain inherited cores raman microprobe measurements showed that zoned rims u 277 1426 ppm th 144 910 ppm are slightly disordered to moderately metamict whereas cores have a wide spectrum of structural states from well crystallized to highly metamict the radionuclide u th content of cores varies from a few hundred to more than 20 000 ppm shrimp ion probe measurements on zoned rims interpreted as zircon growth during crystallization of the monzonite magma gave concordant carboniferous 206 pb 238 u ages of 326 6 ma monzonite from leuben and 330 5 ma monzonite from heidenschanze 95 confidence respectively these ages are consistent with recently published 40 ar 39 ar ages of 329 1 2 8 to 330 4 2 8 ma 2 on amphiboles from the same rocks in contrast shrimp measurements on cores range from slightly discordant proterozoic relic ages in low u and th cores to highly discordant data in the most metamict cores previously obtained 207 pb 206 pb ages single zircon evaporation technique in the range 340 16 to 357 16 ma 1 are probably mixed ages between magmatic and inherited zircon components the u pb ages of the monzonite zircons postdate the upper devonian lower carboniferous subduction and collision events in the area by about 20 ma due to their shoshonitic chemical signature which is typical of rocks from destructive plate boundary settings the meissen massif monzonites might be interpreted as originating during these 350 ma events and the earlier 207 pb 206 pb ages appeared to confirm this interpretation however both the 40 ar 39 ar ages and our current results show that only the enrichment of the lithospheric mantle source but not the monzonite intrusion itself was directly related to these events the monzonite intrusion itself took place 330 ma ago in the framework of strike slip tectonics in the elbe valley zone widely occurring zircon cores are indicative of crustal contamination of the magma causing considerable modification of chemical signatures trace element content of the monzonites

the cadomian orogeny in saxo thuringia germany geochemical and nd sr pb isotopic characterization of marginal basins with constraints to geotectonic setting and provenance abstract the cadomian basement and the cambro ordovician overstep sequence in saxo thuringia is characterized by clastic sedimentation from the late neoproterozoic to the ordovician magmatism in the avalonian cadomian arc preserved in saxo thuringia occurred between ca 570 and 540 ma peri gondwanan basin remnants with cadomian to early palaeozoic rocks are exposed as very low grade metamorphosed rocks in six areas schwarzburg anticline berga anticline doberlug syncline north saxon anticline lausitz anticline and elbe zone a hiatus in sedimentation between 540 and 530 ma cadomian unconformity is related to the cadomian orogeny a second gap in sedimentation occurred during the upper cambrian 500 to 490 ma and is documented by a disconformity between lower to middle cambrian rocks and overlying tremadocian sediments major and trace element signatures of the cadomian sediments reflect an active margin continental arc those of the ordovician sediments a passive margin the cambrian sediments have inherited the arc signature through the input of relatively unaltered cadomian detritus initial nd and pb isotope data from the six saxo thuringian areas demonstrate that there is no change in source area with time for each location but that there are minor contrasts among the locations 1 cadomian sediments from the lausitz anticline the doberlug syncline and the elbe zone have lower 207pb 204pb than all other areas 2 the core of the schwarzburg anticline which is overprinted by greenschist facies conditions and detached is isotopically heterogeneous one part of its metasedimentary units has less radiogenic nd than sediments from other low grade units of similar age in the same area 3 cadomian sediments from the schwarzburg anticline show an input of younger felsic crust 4 the rothstein group shows distinct input of young volcanic material also 5 cadomian sediments from the lausitz anticline the elbe zone and parts of the north saxon anticline are characterized by input from an old mafic crust nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1 5 1 9 ga which suggests derivation from an old craton as found for other parts of the iberian armorican terrane collage similarly the pb isotope data of all areas indicate sediment provenance from an old craton the rapid change of lithologies from greywacke to quartzite from the late neoproterozoic cadomian basement to the ordovician does not reflect changes in sediment provenance but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation this change in sediment maturity takes its chemical expression in lower overall trace element contents in the quartzite dilution effect by quartz and relative enrichment of some trace elements zr mree hree due to detrital zircon and garnet the rb sr systematics of the quartzites and one ordovician tuffite was disturbed most likely during the variscan orogeny which suggests a lithology controlled mobility of alkali and calc alkali elements by comparison with available data it seems unlikely that only nd tdm model ages are useful to distinguish between west african and amazonian provenance nd tdm model ages of 1 5 to 1 9 ga in combination with paleobiogeographic aspects age data from detrital zircon and palaeogeographic constraints especially through tillites of the saharan glaciation in the hirnantian strongly indicate a provenance of saxo thuringia from the west african craton

u pb ages of magmatic and detrital zircon of the dohlen basin geological history of a permian strike slip basin in the elbe zone germany the post orogenic evolution of variscan central europe is characterized by the formation of numerous basins the early permian dohlen basin is located in the elbe zone germany and is bordered by metamorphic rocks of the erzgebirge and numerous variscan magmatic complexes the nw se oriented basin is evidence for a major rearrangement of stress fields during the post variscan reactivation of fault zones in central europe eleven samples of magmatic rocks and sediments have been analyzed with respect to their u th pb isotope ratios and geochemical composition of three magmatic samples two tuffs one trachyandesite we analyzed 170 zircon grains the unkersdorf tuff of the unkersdorf formation gave an age of 294 3 ma upper asselian to sakmarian whereas a trachyandesite of the same formation was dated at 293 5 ma lower artinskian to lower asselian the wachtelberg ignimbrite upper bannewitz formation showed an age of 286 4 ma artinskian to lower kungurian as the first study we also analyzed 984 detrital zircon grains of nine late paleozoic central european sandstone and conglomerate samples of the niederhaslich formation and the bannewitz formation with respect to their u pb age composition all sediments but two yielded two distinct age groups between 295 and 340 ma and 530 750 ma as well as a minor amount of precambrian zircon ages geochemical data points to an active margin setting with developing strike slip basins the data suggests a c 10 ma lasting basin formation during the second culmination of volcano tectonic activity with basic to intermediate melts the second youngest formation niederhaslich formation consists predominantly of pre permian basement material which implies only minor volcanic activity and erosion from adjacent basement blocks on the contrary the uppermost and youngest bannewitz formation features strong evidence for volcanic activity in the neighboring area of the basin the present study strongly suggests a rapid basin development and further shows how the evolution of the dohlen basin is proof for several post variscan tectonic reactivation phases in sakmarian and lower kungurian of central europe finally our results exemplarily show how basin evolution may be characterized by radiometric data of detrital zircon grains

carboniferous permian volcanic evolution in central europe u pb ages of volcanic rocks in saxony germany and northern bohemia czech republic nine shrimp u pb ages on zircon and two pb pb single zircon ages have been determined from late paleozoic volcanic rocks from saxony and northern bohemia samples came from the teplice altenberg volcanic complex the meissen volcanic complex the chemnitz basin the dohlen basin the brandov olbernhau basin and the north saxon volcanic complex the teplice altenberg volcanic complex is subdivided into an early namurian phase mikulov ignimbrite 326 8 4 3 ma thus older than assumed by previous studies and a late caldera forming phase teplice ignimbrite 308 8 4 9 ma the age of the latter however is not well constrained due to a large population of inherited zircon and possible hydrothermal overprint the leutewitz ignimbrite product of an early explosive volcanic episode of the meissen volcanic complex yielded an age of 302 9 2 5 ma stephanian a volcanic rocks intercalated in the brandov olbernhau basin bob 302 2 8 ma chemnitz basin cb 296 6 3 0 ma dohlen basin db 296 3 0 ma and the north saxon volcanic complex nsvc c 300 290 ma yielded well constrained stephanian to sakmarian ages the largest late paleozoic ignimbrite forming eruption in central europe the rochlitz ignimbrite has a well defined middle asselian age of 294 4 1 8 ma ages of palingenic zircon revealed that the namurian westphalian magmatism assimilated larger amounts of crystalline basement that formed during previous paleozoic geodynamic phases the precambrian inherited ages support the chronostratigraphic structure assumed for the saxo thuringian zone of the variscan orogen the present results help to improve the chronostratigraphic allocation of the late paleozoic volcanic zones in central europe at the same time the radiometric ages have implications for the interbasinal correlation and for the geodynamic evolution of the variscan orogeny

the east variscan shear zone geochronological constraints from the capo ferro area ne sardinia italy abstract the exhumation of the variscan high grade metamorphic complex of sardinia was driven by large scale asymmetric shear zones which reached middle crustal levels at 325 1 3 u pb monazite ma exhumation was accompanied by heating and partial melting the migmatization process was followed by the emplacement of syntectonic granites dated with u pb on zircon at 318 3 ma and 317 2 ma which produced contact metamorphism at 315 1 3 ma u pb monazite in mylonitic silurian orthogneisses the nw se dextral shear zone of the capo ferro area ne sardinia is affected by partial melting by granite emplacement and shows remarkable petrotectonic analogies to and can thus be related to the east variscan shear zone a major intra continental shear zone which was active in the southern european variscides from 325 ma to 315 ma and that has been precisely dated with the u pb monazite system the emplacement of migmatitic gneisses along large shear zones within this time interval is not restricted to sardinia but has also been observed in southern corsica in the french massif central in the western alps and in central spain this pattern of shear zones is related to a complex geodynamic scenario linked to the oblique convergence of the gondwana and laurussia plates during the middle upper carboniferous

paired uraninite and molybdenite dating of the konigshain granite implications for the onset of late variscan magmatism in the lausitz block we present geochronological data for late variscan magmatism in the lausitz block of the saxo thuringian zone germany the th u total pb age of uraninite and the re os age of molybdenite from the composite biotite monzogranite pluton of konigshain overlap at the 2 confidence limit 328 6 1 9 ma uraninite and 327 0 1 3 ma and 327 6 1 3 ma molybdenite indicating that crystallization of magmatic uraninite and deposition of molybdenite were nearly contemporaneous these data imply that magmatic processes in this part of the variscan orogen already started in latest visean time about 10 ma earlier than previously assumed 315 320 ma the new ages correspond to ages for plutonic rocks in the elbe zone immediately west of the lausitz around 335 325 ma and the bulk of late variscan igneous rocks in the saxo thuringian zone 335 320 ma

a lifetime of the variscan orogenic plateau from uplift to collapse as recorded by the prague basin bohemian massif the ordovician to middle devonian prague basin bohemian massif represents the shallowest crust of the variscan orogen corresponding to c 1 4 km palaeodepth the basin was inverted and multiply deformed during the late devonian to early carboniferous variscan orogeny and its structural inventory provides an intriguing record of complex geodynamic processes that led to growth and collapse of a tibetan type orogenic plateau the northeastern part of the prague basin is a simple syncline cross cut by reverse thrust faults and represents a doubly vergent compressional fan accommodating c 10 19 nw se shortening only minor syncline axis parallel extension and significant crustal thickening the compressional structures were locally overprinted by vertical shortening kinematically compatible with ductile normal shear zones that exhumed deep crust in the orogen s interior at c 346 337 ma on a larger scale the deformation history of the prague syncline is consistent with building significant palaeoelevation during variscan plate convergence based on a synthesis of finite deformation parameters observed across the upper crust in the centre of the bohemian massif we argue for a differentiated within plateau palaeotopography consisting of domains of local thickening alternating with topographic depressions over lateral extrusion zones the plateau growth involving such complex three dimensional internal deformations was terminated by its collapse driven by multiple interlinked processes including gravity voluminous magma emplacement and thermal softening in the hinterland and far field plate boundary forces resulting from the relative dextral motion of gondwana and laurussia

lattice preferred orientations of late variscan granitoids derived from neutron diffraction data implications for magma emplacement mechanisms the lattice preferred orientation lpos of two late variscan granitoids the meissen monzonite and the podlesi dyke granite were determined from high resolution time of flight neutron diffraction patterns gained at the diffractometer skat in dubna russia the results demonstrate that the method is suitable for the lpo analysis of polyphase relatively coarse grained 0 1 6 mm rocks the meissen monzonite has a prominent shape preferred orientation spo of the non equidimensional minerals feldspar mica and amphibole whereas spo of the podlesi granite is unapparent at the hand specimen scale the neutron diffraction data revealed distinct lpos in both granitoids the lpo of the non equidimensional minerals feldspar mica and amphibole developed mainly during magmatic flow in the case of the meissen monzonite the magmatic flow was superimposed by regional shear tectonics which however had no significant effect on the lpos in both samples quartz shows a weak but distinct lpo which is atypical for plastic deformation and different in the syn kinematic meissen monzonite and the post kinematic podlesi granite we suggest that first of all the quartz lpo of the meissen monzonite is the result of oriented growth in an anisotropic stress field the quartz lpo of the podlesi granite which more or less resembles a deformational lpo in the flattening field of the local strain field developed during magmatic flow whereby the rhombohedral faces of the quartz crystals adhered to the 010 faces of aligned albite and to the 001 faces of zinnwaldite due to shape anisotropy of their attachments the quartz crystals were passively aligned by magmatic flow thus magmatic flow and oriented crystal growth are the major lpo forming processes in both granitoids for the meissen monzonite the solid state flow was too weak to cause significant crystallographic re orientation of the minerals aligned by magmatic flow finally the significance of our results for the evaluation of the regional tectonic environment during magma emplacement is discussed the discussion on the regional implications of the more methodologically oriented results provides the basis for future more regionally aimed studies in view of the fabric characteristics of such plutons and their developing mechanisms

polykinematic foreland basins initiated during orthogonal convergence and terminated by orogen oblique strike slip faulting an example from the northeastern variscan belt abstract an extensive early carboniferous foreland basin the moravosilesian culm basin mscb delineates the northeastern margin of the bohemian massif variscan orogenic belt the basin overlays a complex suture between the outer brunovistulia microplate forming a promontory previously accreted to laurussia and inner gondwana derived units that form the remainder of the bohemian massif our structural paleomagnetic and magnetic anisotropy data from the eastern portion of the mscb indicate that its depositional architecture internal fabric and deformation by folding and faulting record a major switch from orthogonal convergence to orogen oblique strike slip shearing first the brunovistulia microcontinent was subducted frontally towards w during 346 335 ma followed by a shift of the subduction vector towards ssw at around 335 330 ma from 330 ma onwards the underthrusting had ceased and the wnw ese dextral elbe shear zone related to the westward movement of gondwana with respect to laurussia controlled deformation of this region displacement of the northerly eastern sudetes block towards ese produced regional wnw ese pure shear shortening against the brunovistulia indentor and resulted in an overall doubly vergent structure of the mscb simultaneously the southerly moldanubian unit was translated towards wnw away from the brunovistulian microplate and likely contributed to an extensional regime related to orogenic collapse progressing outward from the internal domains of the bohemian massif on a larger scale we suggest that the mscb is an illustrative example of a polykinematic foreland basin where deposition syn to post sedimentary deformation and thus geodynamic processes changed significantly during basin evolution starting off with microplate impingement into a continental margin reentrant and terminated by strike slip shearing our data also do not support previous models for the tectonic development of the northeastern termination of the variscan belt which suggested either a large magnitude vertical axis oroclinal rotation of the foreland or its translation along an orogen perpendicular strike slip fault

biogeography of indo pacific larger foraminifera and scleractinian corals a probabilistic approach to estimating taxonomic diversity faunal similarity and sampling bias abstract the eastward decline in the diversity of indo pacific scleractinian corals and larger foraminifera is due primarily to the shallowing of the thermocline and significant cooling of the equatorial undercurrent in the eastern pacific the coral larvae carried eastward across the pacific encounter temperatures below 18 c which is lower than the optimum for the long term survival of reef building corals this thermal barrier to dispersal of the indo pacific fauna is particularly effective in an area within 2000 km west of the galapagos islands nevertheless trend surface analysis of faunal similarity based on the probabilistic index of raup and crick 1979 suggests that the modern scleractinian fauna of the eastern pacific region exhibits a high degree of similarity to that of the indo pacific region the newly assembled data on the generic occurrence of larger foraminifera and the results of the probabilistic analysis based on the method of henderson and heron 1977 indicate that the observed diversity of a fauna constituted on average 65 of the true diversity the remaining 35 can be viewed as a measure of the sampling bias last the maximum north south range of a genus belonging to modern scleractinian corals or larger foraminifera is 70 5 and its east west range never exceeds the distance that is four times the north south range the reason for a correspondence between the maximum latitudinal and longitudinal ranges of genera belonging to these two unrelated groups is believed to lie in the similarity of their dispersal capabilities which were largely controlled by temperature

from cadomian subduction to early palaeozoic rifting the evolution of saxo thuringia at the margin of gondwana in the light of single zircon geochronology and basin development central european variscides germany

careon ophiolite nw spain suprasubduction zone setting for the youngest rheic ocean floor the careon ophiolite galicia nw iberian massif shows lithological and geochemical features suggestive of an origin in a suprasubduction zone setting as with other devonian ophiolites in the european variscan belt it was generated within a contracting rheic ocean this setting and the general absence of large silurian devonian volcanic arcs on both of the rheic ocean margins strongly suggest that this ocean was closed by intraoceanic subduction directed to the north this subduction removed the older normal n mid oceanic ridge basalt morb oceanic lithosphere and gave rise to a limited volume of new suprasubduction zone oceanic lithosphere the careon ophiolite is a key element in understanding the evolution of the rheic ocean which was the main oceanic domain that closed during the paleozoic convergence of gondwana and laurussia preceding the assembly of pangea

timing of dextral strike slip processes and basement exhumation in the elbe zone saxo thuringian zone the final pulse of the variscan orogeny in the bohemian massif constrained by la sf icp ms u pb zircon data

transport of reef corals into the great barrier reef major submarine pumice eruptions have occurred repeatedly during the past 25 years in the tonga kermadec region1 3 pumice from this area drifts through fiji and new caledonia reaching australia roughly one year after an eruption1 2 coral larvae settle and grow on the floating pumice fragments fig 1 the geographic pattern of abundance and size distribution of rafted corals found on drift pumice in relation to the pumice source area suggests massive transport of corals into the great barrier reef from regions of lower diversity lying far to the east and southeast dispersal range is not limited by longevity of larvae and centres of diversity may be sites of species accumulation rather than sites of species origin

drift pumice at christmas island and hawaii evidence of oceanic dispersal patterns the use of pumice as a geological tracer for oceanic dispersal patterns was evaluated by comparing the elemental signatures of drift pumice collected from christmas island and hawaii in relation to prevailing oceanic currents and pumice source areas both sites lie in the middle of the pacific ocean far from sources of volcanic pumice hawaii lies in the persistent westward flowing north equatorial current christmas island in contrast is influenced by the highly variable westward flowing south equatorial current and the eastward flowing equatorial counter current pumice is very abundant at christmas island in the beach drift pumice from christmas island is derived from the western pacific ocean krakatau southwestern pacific ocean tonga trench east pacific ocean mexico south atlantic ridge and an unknown source in contrast pumice is rare in hawaii pumice from hawaii originates primarily from the south sandwich islands mexico isla san benedicto and krakatau the currents that control dispersal of pumice also control dispersal of larvae and rafted organisms christmas island has a higher coral diversity 31 genera 81 species than hawaii 17 genera 50 species hawaii receives only small amounts of pumice drift from a limited area to the east and has a more restricted coral diversity while christmas receives massive amounts of pumice and presumably larvae and rafted organisms from the area of high coral diversity to the west

deciphering the variscan tectonothermal overprint and deformation partitioning in the cadomian basement of the tepla barrandian unit bohemian massif the tepla barrandian unit tbu has long been considered as a simply bivergent supracrustal median massif above the saxothuringian subduction zone in the variscan orogenic belt this contribution reveals a much more complex style of the variscan tectonometamorphic overprint and resulting architecture of the neoproterozoic basement of the tbu for the first time we describe the crustal scale ne sw trending dextral transpressional krakovec shear zone ksz that intersects the tbu and thrusts its higher grade northwestern portion severely reworked by variscan deformation over a southeastern very low grade portion with well preserved cadomian structures and only brittle variscan deformation the age of movements along the ksz is inferred as late devonian 380 370 ma on the basis of structural microstructural and anisotropy of magnetic susceptibility data from the ksz we propose a new synthetic model for the deformation partitioning in the tepla barrandian upper crust in response to the late devonian to early carboniferous subduction and underthrusting of the saxothuringan lithosphere we conclude that the saxothuringian tepla barrandian convergence was nearly frontal during 380 346 ma and was partitioned into pure shear dominated domains that accommodated orogen perpendicular shortening alternating with orogen parallel high strain domains that accommodated dextral transpression or bilateral extrusion the synconvergent shortening of the tbu was terminated by a rapid gravity driven collapse of the thickened lithosphere at 346 337 ma followed by or partly simultaneous with dextral strike slip along the baltica margin parallel zones driven by the westward movement of gondwana from approximately 345 ma onwards