microstructural deformation record of an orogen parallel extension in the vepor unit west carpathians abstract deformation microstructures of quartzo feldspathic rocks have been used to analyse the orogen parallel stretching of the vepor unit in the west carpathians during cretaceous convergence this process occurs contemporaneously with the burial of the vepor basement related to the overthrusting palaeozoic volcano sedimentary sequences of the gemer unit the microstructures develop along a metamorphic gradient indicating an increase of pressure and temperature towards the structural footwall the recrystallization of quartz occurs in the field of subgrain rotation recrystallization sgr while the plagioclase and k feldspar disintegrate into a neocrystallized muscovite albite matrix palaeopiezometry of the recrystallized quartz in conjunction with p t estimates yield strain rates of 9 10 12 to 6 10 14 s 1 depending on temperature 380 480 c and choice of piezometer and flow law calibration strain analysis of the recrystallized quartz aggregates and quartz texture analysis indicate an overprint of the variscan magmatic and high grade fabrics by a cretaceous plane strain deformation resulting in vertical shortening and horizontal orogen parallel east west stretching spatial distribution and conflicting sense of shear of the asymmetrical quartz lattice preferred orientation patterns indicate that the large scale pure shear deformation of the vepor unit is locally accommodated by simple shear zones observed metamorphic gradients across the vepor unit are interpreted to result from later large scale folding and heterogeneous exhumation of the orogen parallel deformation fabric

intercalibration of astronomical and radioisotopic time the 40ar 39ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in earth s history but the accuracy of this method is limited by the accuracy with which the ages of neutron fluence monitors dating standards are known calibrating the ages of standards by conventional means has proved difficult and contentious the emerging astronomically calibrated geomagnetic polarity time scale apts offers a means to calibrate the ages of 40ar 39ar dating standards that is independent of absolute isotopic abundance measurements seven published 40ar 39ar dates for polarity transitions nominally ranging from 0 78 to 3 40 ma are based on the fish canyon sanidine standard and can be compared with apts predictions solving the 40ar 39ar age equation for the age of the fish canyon sanidine that produces coincidence with the apts age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27 78 to 28 09 ma with an inverse variance weighted mean of 27 95 0 18 ma normalized residuals are minimized at an age of 27 92 ma indicating the robustness of the solution

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

how many oceans meliata vardar and pindos oceans in mesozoic alpine paleogeography the timing of rifting and subduction in the meliata vardar and pindos zones of the hellenic dinaric carpathian region indicates that they cannot be considered remnants of a single ocean basin in contrast to several recently published mesozoic paleogeographies sea floor spreading in the meliata zone culminated in middle triassic ladinian time and ceased in the late triassic and subduction occurred from this time until late jurassic closure in contrast sea floor spreading in the vardar zone began in early jurassic time and culminated in the middle jurassic and subduction occurred from latest jurassic time in the pindos zone sea floor spreading was initiated in the early triassic with late jurassic and early tertiary subduction

rainfall runoff properties of tephra simulated effects of grain size and antecedent rainfall abstract rain triggered lahars rtls are a significant and often persistent secondary volcanic hazard at many volcanoes around the world rainfall on unconsolidated volcaniclastic material is the primary initiation mechanism of rtls the resultant flows have the potential for large runout distances 100 km and present a substantial hazard to downstream infrastructure and communities rtls are frequently anticipated in the aftermath of eruptions but the pattern timing and scale of lahars varies on an eruption by eruption and even catchment by catchment basis this variability is driven by a set of local factors including the grain size distribution thickness stratigraphy and spatial distribution of source material in addition to topography vegetation coverage and rainfall conditions these factors are often qualitatively discussed in rtl studies based on post eruption lahar observations or instrumental detections conversely this study aims to move towards a quantitative assessment of rtl hazard in order to facilitate rtl predictions and forecasts based on constrained rainfall grain size distribution and isopach data calibrated simulated rainfall and laboratory constructed tephra beds are used within a repeatable experimental set up to isolate the effects of individual parameters and to examine runoff and infiltration processes from analogous rtl source conditions laboratory experiments show that increased antecedent rainfall and finer grained surface tephra individually increase runoff rates and decrease runoff lag times while a combination of these factors produces a compound effect these impacts are driven by increased residual moisture content and decreased permeability due to surface sealing and have previously been inferred from downstream observations of lahars but not identified at source water and sediment transport mechanisms differ based on surface grain size distribution a fine grained surface layer displayed airborne remobilisation accretionary pellet formation rapid surface sealing and infiltration excess overland flow generation whilst a coarse surface layer demonstrated exclusively rainsplash driven particle detachment throughout the rainfall simulations this experimental protocol has the potential to quantitatively examine the effects of a variety of individual parameters in rtl initiation under controlled conditions

detrital zircon u pb geochronology of pennsylvanian permian sandstones from the turnaicum and meliaticum western carpathians slovakia provenance and tectonic implications the blueschist bearing borka nappe regarded as a part of the meliaticum unit s l and the turnaicum unit in its hanging wall were thrusted together to the north on the inner western carpathians basement during the orogenic events of the late jurassic early cretaceous a new u pb sensitive high resolution ion microprobe shrimp magmatic as well as detrital zircon ages were used to constrain provenance and paleogeography the detrital zircon age spectrum of the studied metasediments contains mainly ages of the ediacaran cryogenian 550 720 ma and tonian stenian 0 9 1 1 ga which correspond to the pan african belt and saharan metacraton subordinate archean ages were likely derived from the saharan metacraton of north gondwana 1 7 2 2 and 2 5 2 7 ga the 273 2 ma zircon age of a metarhyolite along with the youngest detrital zircon of 265 4 ma from the associated metasediments specify the maximum depositional age of the bucina fm from the borka nappe to the guadalupian the rhyolite olistoliths from the middle late jurassic meliaticum olistostrome yielded the latest cambrian earliest ordovician 488 6 ma and middle ordovician 465 ma zircon ages this is consistent with the u pb zircon ages from the foot walling southern gemericum basement metavolcanites which are therefore regarded as a potential source the obtained zircon ages confirm the provenance from the southern gemericum basement and its permian envelope for the meliaticum borka nappe and turnaicum sedimentary embayment

the schneeberg normal fault zone normal faulting associated with cretaceous se directed extrusion in the eastern alps italy austria abstract the cretaceous eo alpine collisional event in the european eastern alps is generally accepted to induce w nw directed thrusting both in basement and in sedimentary cover units this study presents the first evidence of eo alpine w nw directed normal kinematics along the schneeberg normal fault zone which separates eo alpine high pressure rocks in a footwall position from pre alpine basement rocks in a hanging wall position new garnet sm nd data indicate that exhumation of the high pressure rocks along the normal fault zone started around 95 ma ago and continued up to low greenschist brittle conditions at 76 ma as indicated by a rb sr age from a low temperature mylonite the occurrence of pre alpine basement rocks both in the hanging wall and the footwall of eo alpine high pressure rocks suggests exhumation by extrusion processes despite the displacement or removal of parts of the lower portion of the high pressure unit by tertiary strike slip faults eo alpine top to ese thrusting as expected for the structurally lower part of an extruding wedge was found at and below the base of the eo alpine high pressure rocks a rb sr age of 77 ma from a greenschist facies mylonite in this thrust shear zone shows the contemporaneity of deformation at the base and the top of the wedge the tectonic transport direction within the extruding wedge was e se opposite to the w nw direction so far reported for the eo alpine event in the eastern alps the contemporaneity of opposite tectonic transport directions during continental subduction may be explained by a double vergent wedge model with a narrow zone of ductile flow where the high pressure rocks were exhumed

exhumation of the schistes lustres complex in situ laser probe 40ar 39ar constraints and implications for the western alps the schistes lustres sl suture zone occupies a key position in the alpine chain between the high pressure hp brianconnais domain and the ultrahigh pressure uhp dora maira massif and reached subduction depths ranging from c 40 65 km cottian alps in order to constrain the timing of hp metamorphism and subsequent exhumation several phengite generations were differentiated on the basis of habit texture paragenesis and chemistry as belonging to the first or second exhumation episode respectively d2 or d3 or to earlier stages of the tectono metamorphic evolution ten carefully selected samples showing d2 d3 d2 d3 or earlier mostly peak temperature phengite population s were subjected to laser probe 40ar 39ar analysis the data support the results of the petrostructural study with two distinct age groups crystallization ages for d2 and d3 phengite at 51 45 and 38 35 ma respectively the data also reveal a coherent age cluster at 62 55 ma for peak temperature phengite associated with chloritoid which were preserved in low strain domains the age of the d3 event in the sl complex appears very similar to ages recently obtained for greenschist facies deformation on the border of most internal crystalline massifs exhumation rates of the order of 1 2 mm yr 1 are obtained for the sl complex which are compatible with velocities documented for accretionary wedge settings similarly cooling velocities are only moderate c 5 c myr 1 which is at variance with recent estimates in the nearby uhp massifs

the oligocene miocene tectonic evolution of the northern outer carpathian fold and thrust belt insights from compression and rotation analogue modelling experiments this paper presents the different analogue scenarios of the tectonic evolution of the northern outer carpathians i e the western and northern eastern outer carpathians which formed as an accretionary wedge in front of the east alpine carpathian pannonian alcapa block during oligocene miocene times currently this fold and thrust belt forms an arc which is asymmetrically convex to the north and wider in its eastern part palaeomagnetic investigations have suggested that the rocks of the arc underwent counter clockwise rotation along almost the whole arc which is difficult to explain as an effect of simple indentation of the triangular indenter in this case two branches of the arc should be rotated in the opposite directions the structural evolution of the western outer carpathians is characterized by superposition of two successive tectonic shortening events directed n s and ne sw the results of the presented analogue modelling suggest that two scenarios of the geodynamic evolution of the studied belt could explain the occurrence of such differently oriented shortening events 1 two phases of differently directed indentation first to the n then to the ne and 2 indenter movement to the ne with simultaneous counter clockwise rotation however the experiment in which the moving indenter is simultaneously rotated produces the most suitable model the counter clockwise rotation of the material is only possible in front of both sides of the convex indenter in this model the results of the analogue modelling also prove that rotation of the alcapa block started after formation of the magura nappe the innermost nappe of the western outer carpathians

sources and distribution of late quaternary silt in the surficial sediment of the northeastern continental shelf of the united states abstract the sources and distribution of silt in the surficial sediment of the northeastern continental shelf of the united states and the gulf of maine were determined by the analysis of quartz grain roundness and surface textures three distinct populations of silt are present in the surficial sediment of the continental shelf and the gulf of maine each population is represented by a suite of quartz silt grains with distinctive roundness and surface texture characteristics is derived from a different source and is distributed throughout different parts of the study area the first population is represented by rounded and subrounded quartz silt grains with weathered surfaces quo end member 1 quo it was apparently derived from the cretacious tertiary and quaternary sdiments of the atlantic coastal plain and is most abundant on the continental shelf between cape cod and cape hatteras which is underlain and bordered by coastal plain strata and on the western and eastern rims of the gulf of maine which are also underlain by coastal plain strata the second population is represented by very angular quartz silt grains with microfractures and fracture faces quo end member 2 quo it was apparently derived from the late wisconsin glacial and periglacial deposits of the northeast united states and is most abundant within and downdrift from the glaciated part of the study area and in the modern depocenters of rivers which drain glaciated terranes in new york and new england the third population is represented by subangular and subrounded quartz silt grains with crystalline nodes grain embayments and secondary quartz overgrowths quo end member 3 quo it was apparently derived from precambrian paleozoic and early mesozoic crystalline and sedimentary rocks of the appalachian mountains and is most abundant in the modern and ancient depocenters of the appalachian rivers of the eastern united states

eastern alpine tectono metamorphic evolution constraints from two dimensional p t t modeling we use two dimensional 2 d p t t modeling to constrain the thermal and rheological aspects of different scenarios for the late mesozoic and cenozoic tectonic evolution of the eastern alps inferred from excellent data sets from the tauern window tw models invoking subduction of the south penninic sp oceanic lithosphere during thrusting and subsequent erosion of the austro alpine aa upper plate nappe stack are inconsistent with the observed thermal evolution within the aa and penninic units in these models predictions for the aa peak thermal conditions are lower than observed after exhumation and cooling to midcrustal levels and subduction of the continental middle penninic mp block the aa undergoes a phase of renewed heating to almost the previous peak temperatures simultaneously the penninic units experience a phase of heating upon subduction followed by cooling after onset of subduction of the north penninic np basin the model predictions are inconsistent with the observed nearly isothermal uplift path of the sp after subduction and cannot explain observed inverted metamorphic peak conditions in the deeper aa amphibolite facies down to the higher penninic unit greenschist facies a model with the beginning of subduction of the sp occurring after crustal thickening of the aa and subsequent return to normal crustal thicknesses is compatible with the p t t data in this model peak temperature conditions are higher in the aa followed by a phase of strong cooling in the aa upper plate with the onset of underthrusting this model also explains successfully nearly isothermal exhumation of the mp and inverted metamorphic peak conditions in the deeper aa material accreted to the hanging wall from the oceanic crust sp experiences a phase of cooling during ongoing subduction of oceanic lithosphere and begins to heat up to its thermal climax after the subduction of trailing continental lithosphere the subsequent pt path of the penninic units strongly depends on the timing and rates of underthrusting by the foreland observed pt paths in the mp within the tw require continuous subduction of the np and the trailing european foreland under the exhuming mp block documented rapid cooling in the final uplift phase of the penninic units in the tw requires exhumation rates up to approximately 4 mm yr predictions of slightly elevated present day geothermal gradients in the tw area are consistent with available heat flow data as a result of mesozoic rifting followed by late mesozoic crustal thickening of the aa paleorheological reconstructions are characterized by a contrast between relatively strong oceanic lithosphere and adjacent weak continental lithosphere predicted decoupling of weak continental and oceanic lithosphere during subsequent subduction of the penninic units can explain observed late cretaceous crustal extension in the aa units in terms of gravitational spreading ongoing subduction leads to an overall strength increase due to underthrusting of cool oceanic lithosphere whereas subduction of continental lithosphere causes a strength decrease in the upper levels of the lithosphere continuous crustal thickening and relaxation of the depressed isotherms reduce the strength of the lower lithospheric mantle beneath the central orogen further enhanced by rapid late stage uplift predictions for the present day rheological structure of the eastern alps support the existence of a strong upper crustal layer two wedge shaped strong upper mantle layers to the north and the south of the orogen and a weak upper mantle underlying the central orogen

multi temporal uav data for automatic measurement of rill and interrill erosion on loess soil the fragile landscape of the north european loess belt is prone to soil erosion due to soil properties and intense land use of the fertile region exact measurement of surface changes with high temporal and spatial resolution over large areas is necessary to quantify and understand rill and interrill erosion processes high resolution aerial imagery acquired by an unmanned aerial vehicle uav is used to automatically generate precise digital surface models dsms of high spatial resolution by applying structure from motion image processing tools during an investigation period of ten months a 600 m2 field plot is observed during four field campaigns a stable reference system is established for multi temporal comparison the overall accuracy of the dsms generated from uav images is less than 1 cm verified by comparison with terrestrial laser scanner tls data furthermore a method for automatic rill extraction and rill parameter calculation is developed which enables objective rill description with cm accuracy and resolution soil surface roughness and rill development as well as volumetric quantifications are analysed for multi temporal change detection surface changes during winter season are controlled by soil consolidation crusting and sheet erosion during rainy spring season sheet erosion and rill incision occur two thunderstorms in summer season cause dominant rill erosion erosion rills are more dominantly deepening than widening from to 2 to 4 cm depth and from 17 to 23 cm width resulting in average per rill erosion values of 0 03 and 0 07 m3 respectively an orientation dependent lateral rill shift is revealed implying rill widening in eastern direction due to dominant winds from the west volumetric quantifications indicate high erosion volumes reaching up to 121 tha 1 during the summer events highest erosion volumes are due to rill erosion rather than interrill erosion copyright 2014 john wiley sons ltd

textural and age relations of polymetamorphic rocks in the hp meliata unit western carpathians abstract slices and tectonic blocks of amphibolite facies crustal rocks overprinted by blueschist facies metamorphism occur in the middle jurassic meliata high pressure unit of the western carpathians the early paleozoic age for relic muscovite is known from some micaschists with blueschist facies overpint in the eastern sector of the meliata unit based on lithology some amphibolite facies rocks are comparable with the early paleozoic basement rocks in the gemeric unit in this work we present results of petrology and ar ar and rb sr geochronology from blueschist facies rocks with relicts of hornblende muscovite garnet and rutile the older amphibolite facies metamorphism was followed by retrogression prior to the blueschist facies overprint the blueschist facies metamorphic minerals are ca rich garnet glaucophane phengite and albite the coarse grained relict muscovite indicates an early paleozoic age using the ar ar method and a middle jurassic age using the rb sr technique the presence of amphibolite facies rocks within the meliata unit is interpreted as involvment of variscan pre variscan basement unit rocks in the middle jurassic subduction of the meliata hallstatt oceanic basin

a long flume study of the dynamic factors affecting the resistance of a loamy soil to concentrated flow erosion experiments were carried out in a 20 m long flume to assess the variation of the runoff erosion resistance of a loamy soil as a function of initial moisture content and compaction the results of seven experimental runs show that the runoff erosion resistance of a loamy material is extremely sensitive to variations in initial moisture content and to a somewhat lesser extent in bulk density the very low resistance to runoff erosion of initially dry material is explained by structural changes which take place at the time of wetting slaking and microfissuration cause a considerable decrease of the soil s shear strength and therefore of its resistance to runoff erosion a first analysis shows that during a given rainfall event initially dry soils may well show significantly more erosion than initially wet soils despite the increase of infiltration with decreasing initial moisture content

origin of shape changes of sand and silt in a high gradient stream system abstract changes in shape of sand and silt in streams may be a reflection of changes in source rock rather than the progressive effects of transport if so shape characteristics should change as the stream crosses geologic contacts to clarify the problem stream sediment samples were collected in two drainage basins on the west flank of the bighorn mountains wyoming three size fractions fine sand very fine sand and coarse silt were studied using fourier analysis and the scanning electron microscope provenance discrimination improves with increasing grain size in all three size ranges sediment derived from a glaciated crystalline rock source can be differentiated from that derived from sedimentary rock sources sand from sedimentary rock sources can be subdivided into shape families according to the extent of diagenesis in very fine sand and fine sand sediment from the flathead sandstone is distinguishable from that derived from other sedimentary rocks in fine sand the tensleep and darwin sandstones are also distinguishable as separate sources along tensleep creek changes in the shape composition of sediment occur rather continuously due to transport of sediment by past glacial processes along paintrock creek however shape proportions do not change in a continuous manner but instead change by abrupt discrete jumps which occur where additional sources provide sediment the shape changes are due to the dilution of upstream sediment by sediment from adjacent sources this suggests that downstream sources provide sediment at a greater rate than the upstream sources even though the gradient decreases with distance this can be explained by the fact that the younger downstream sedimentary rocks are more friable than the upstream rocks

low temperature constraints on the alpine thermal evolution of the western carpathian basement rock complexes abstract the cretaceous to palaeogene alpine exhumation of previously buried variscan basements is recorded in the southern portion of the western carpathians in the gemeric and veporic units the meso cenozoic collisional processes resulted in basement exhumation of the tatric unit from palaeogene to neogene times according to zircon and apatite fission track data the gemeric unit an uppermost thick skinned thrust sheet cooled from depth levels of 10 up to 2 5 km temperature interval of 250 60 c about 88 64 ma ago after the collapse of overlying meliata tur a silica mesozoic accretionary prism the middle and lower thick skinned thrust sheets veporic and tatric units cooled from the depths of 10 up to 2 5 km 110 40 ma ago the process was controlled by unroofing of footwall from beneath the gemeric unit about 50 20 ma ago the internal zone of tatric unit gradually exhumed to depth of

pre metamorphic 40ar 39ar and u pb ages in hp metagranitoids from the hercynian belt france in most orogenic belts the age of hp metamorphism and subsequent exhumation events still remain open to debate since geochronology can yield results which appear to conflict with the closure temperature concept dodson m h 1973 contrib mineral petrol 40 259 274 and because the behaviour of daughter radiogenic isotopes under hp to uhp conditions is poorly constrained to obtain new data on isotope migration under high pressure conditions two undeformed hp metagranites with partially preserved magmatic assemblages from the french variscan belt were investigated using the 40ar 39ar laser probe and u pb ion probe methods in both cases 40ar 39ar biotite and u pb zircon ages are consistent and could be related to the emplacement of pre orogenic granites despite petrological evidence of a strong metamorphic overprint during the variscan orogeny temperatures experienced by the granites during subduction and exhumation events were more than 400 c above that normally estimated for argon retention in biotite but failed to cause significant resetting of the mica 40ar 39ar chronometer only a weak intragrain redistribution of argon is evidenced with the laser probe up to the contact with metamorphic garnet fringing biotite by contrast a complete resetting of biotite ages occurs in gneisses enclosing the metagranites these results suggest that in these dry undeformed hp metagranites the thermally activated diffusion was relatively ineffective and that recrystallisation is the main process which controlled isotopic exchanges of ar and pb it is likely that the absence of pervasive deformation and fluid circulation has also exercised some control on the preservation of pre metamorphic isotopic signature in the studied rocks the possible influence of several other parameters is also discussed this example reveals that recovering thermochronological information in high pressure metamorphic rocks is not straightforward and that great caution must be paid in the use of ages for the reconstruction of p t t paths

ordovician and cretaceous tectonothermal history of the southern gemericum unit from microprobe monazite geochronology western carpathians slovakia the southern gemericum basement in the inner western carpathians experienced a polyphase regional deformation differences in the pre alpine and alpine events have been constantly discussed to address this monazites from metapelites and acid metavolcanic rocks were dated using the th u pb electron microprobe method three monazite generations such as precambrian early paleozoic and alpine have been recognized in the greenschist facies pelites and acid metavolcanic rocks of the southern gemericum basement both inherited magmatic monazite grains in metavolcanites and rare relics of detrital monazites within the polyphase monazite grains in metapelites yielded the precambrian age in the time span of 550 660 ma they prove the provenance and derivation from deeper crustal cadomian fragments high y magmatic monazites of early paleozoic age 444 13 and 477 7 ma have been recorded in the acid metavolcanites and their metavolcaniclastics these ages roughly fit within the previously published magmatic zircon age determinations at 494 1 7 and 464 1 7 ma that clearly indicate two phase volcanic activity in the early paleozoic southern gemericum basin the early paleozoic magmatic monazites were partly overprinted by the low y alpine monazites 133 5 and 184 16 ma at their rims in al rich metapelites the newly formed low y monazites of alpine age commonly occur reflecting the polystage compression geodynamic evolution with three distinct peaks at 100 8 133 5 and 190 16 ma respectively no data as the evidence of the pre alpine metamorphic events were observed in metapelites only some monazites yield the age indications for the permian extensional thermal re heating 260 290 ma the monazite age data from the southern gemericum basement indicate the strong overprinting due to the polyphase alpine deformation at least in the greenschist facies conditions

geochronological evidence for the alpine tectono thermal evolution of the veporic unit western carpathians slovakia abstract tectono thermal evolution of the veporic unit was revealed by multiple geochronological methods including 87rb 86sr on muscovite and biotite zircon and apatite fission track and apatite u th he analysis based on the new data the following alpine tectono thermal stages can be distinguished the eo alpine cretaceous nappe stacking 135 95 ma resulted in burial of the veporic unit beneath the northward overthrusting gemeric unit and overlying jurassic meliata accretionary wedge during this process the veporic unit reached metamorphic peak of greenschist to amphibolite facies accompanied by orogen parallel flow in its lower and middle crust the subsequent evolution of this crust is associated with two distinct exhumation mechanisms related to collision with the northerly tatric fatric basement the first mechanism 90 80 ma is associated with internal subhorizontal shortening of the veporic unit reflected by large scale upright folding and heterogeneous exhumation of the veporic lower crust in the cores of crustal scale antiforms this led to juxtaposition of the higher and lower grade parts of basement all cooled down to 350 c by 80 ma the second mechanism is associated with the overthrusting of the veporic unit over the attenuated fatric crust this led to a passive en block exhumation of the veporic crust from 350 c to 60 c between 80 and 55 ma followed by erosion 55 35 ma the erosion processes resulted in formation of planation surface before the late eocene transgression after erosion and planation a new sedimentary cycle of the central carpathian palaeogene basin was deposited with the sedimentary strata thickness of 1 5 2 0 km 21 17 ma the early to middle miocene is characterised by destruction tectonic disintegration and erosion of this basin 20 13 ma and formation of the neogene vepor stratovolcano 13 ma the final shaping of the area has been linked to erosional processes of the volcanic structure since the late sarmatian with accelerated processes during the plio quaternary

late cambrian ordovician magmatic arc type volcanism in the southern gemericum basement western carpathians slovakia u pb shrimp data from zircons the low grade crystalline basement of the southern gemeric unit inner western carpathians consists mainly of siliciclastic deep water turbidite sequence associated with a huge mass of redeposited rhyolite dacite volcanics and their volcaniclastics in situ u pb shrimp zircon dating applied to metavolcanic rocks contributed to specification of the southern gemeric crystalline basement stratigraphy the gelnica group zircon populations from ten samples of three lithostratigraphic units of the gelnica group rock complex have been analysed the zircons presented significant magmatic zoning part of the magmatic zircons contained inherited older cores the vlachovo formation gives the 494 1 6 ma zircon average age the bystr potok formation gives 465 8 1 5 ma and the drnava formation 463 9 1 7 ma average age the geochemical data are compatible with an orogenic geodynamic setting dominant rhyolite dacite volcanites belong to the peraluminous calc alkaline high k magmatic series the age data let us presume two phase longlasting magmatic activity starting in the late cambrian and continuing to the middle late ordovician thus the studied late cambrian volcanic sequence of the gelnica group reflects the active continental margin setting the second middle ordovician volcanic phase documents an assumed rifting stage accompanied by a strong volcanic activity with inherited features of the late cambrian magmatic arc the inherited cores of magmatic zircons have proterozoic 600 760 1 000 1 400 2 000 2 700 ma and archean 3 099 3 164 ma ages

physical changes in the lithosphere associated with thermal relaxation after rifting we define the terms modem rift and paleorift with respect to the thermal state of the lithosphere the former being rifted lithosphere not in thermal equilibrium and the latter being thermally stabilized rifted lithosphere a comparison of the physical characteristics of modern rifts with paleorifts shows that they share many of the same geomorphic structural and magmatic features but have important differences in their geophysical signatures using a simple model for the thermal relaxation of the lithosphere in the transition from modern rift to paleorift we show that differences in upper mantle seismic velocities and density surface heat flow thermal structure and curie point depth and magnetotelluric properties of the lithosphere between modern and paleorifts can be explained by lithospheric cooling cooling alone cannot explain the complex subsidence histories associated with and following rifting however nor the presence of high velocity crustal layers and sometimes thickened crust in paleorifts these features can be explained by consideration of lithospheric flexural strength and magmatic thickening of the crust associated with rifting we speculate that the anomalous upper mantle beneath many modern rifts may be associated with the process of magmatic thickening of the rifted crust

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

analysis of fault populations in western spitsbergen implications for deformation partitioning along transform margins mesoscale faults expressed in the paleogene central basin and cretaceous basement along the west spitsbergen orogenic belt are used to define the history of continental deformation associated with the development of the transform system that accompanied the opening of the eurasian basin and the norwegian greenland sea a fundamental change in the orientation of faults from dominantly north south in the basal part of the basin to northeast striking in the upper units broadly correlates with a major shift in plate motion during late paleocene early eocene time the two main populations of faults are interpreted as extension fractures that were variably reactivated as shear fractures and formed in response to north south compression followed by northeast southwest compression paleostress stratigraphy or the analysis of striated faults measured in successive stratigraphic units of the central basin corroborates this interpretation and allows a time sequence of paleostress tensors to be defined results show that a late cretaceous early paleocene north south compression consistent with plate motion was followed by three relatively short lived and regionally limited faulting events leading up to a change in plate motion during late paleocene time post chron 25 major transpressive tectonism followed producing northeast trending fractures that were reactivated as dextral and sinistral faults defining a prolate shape paleostress ellipsoid with a horizontal 1 this regionally reproducible tensor consistent with the prediction of dextral transpression along the paleotransform was probably initiated at approximately the paleocene eocene boundary finally a post early eocene deformation pervasively recorded in the study area by an oblate shape paleostress ellipsoid with horizontal 3 is tentatively correlated with the dextral transtension that characterized the post chron 13 opening of the norwegian greenland sea and eurasian basin this study offers documentation of deformation partitioning during the evolution of a transform margin the late cretaceousearliest paleocene compression associated with the prototransform did not involve substantial partitioning and a north south maximum principal stress pervaded the continental crust away from the transform in contrast the late paleocene eocene transpression reflects total partitioning of deformation along the evolved mature transform margin oblique plate motion was presumably partitioned into a strikeslip zone s offshore whereas the onshore central basin recorded only the orthogonal component of oblique convergence and divergence a pattern similar to modern orogenic belts developed in zones of oblique plate motion

cretaceous collision and indentation in the west carpathians view based on structural analysis and numerical modeling 1 a model of indentation of a rigid promontory into weak metasedimentary rocks during cretaceous convergence is suggested for tectonic evolution of southern part of west carpathians an early arcuate cleavage fan has developed in front of northward moving southern rigid basement block the interaction of the moving indenter with western stationary basement promontory is responsible for development of the boundary parallel shear zone along which the main southern indenter is shifted to the east this results in development of a new steep transpressional cleavage overprinting the early fabric eastward displacement of the southern indenter causes the development of a thrust zone parallel to the margin of the eastern stationary promontory a proposed numerical model of the deformation of a thin viscous sheet in front of oval rigid indenter reliably simulates the development of the observed deformation pattern modeled discrete partitioning between the western promontory and the indenting block fully agrees with the observed secondary cleavage associated with the transpressional shear zone our numerical model interconnects this complex kinematic frame with finite strain pattern which was to date possible only for simple boundary conditions in addition the model explains the polyphase cleavage patterns in terms of complex shapes of promontories and changes in movements of indenting blocks

kinematics of the alpine west carpathian orogen and palaeogeographic implications we present the euler rotations of the plates involved in the alpine west carpathian orogen the rotations are defined to a large extent by the magnetic anomalies of the atlantic ocean a few extra rotations occurred during two collisions and a mid cretaceous event at variance with earlier reconstructions we additionally control the rotations by the orientation of palaeomagnetic declinations the plate rotations are integrated into a model illustrated by palaeogeographical maps special features of the model are 1 subdivision of the northern margin of adria into the two plates pelso and austroalpine west carpathia on the basis of palaeomagnetic data 2 eohellenic obduction of meliata units onto the eastern margins of pelso and austroalpine west carpathia from the tethys side 3 first eoalpine collision of the marginal plates of adria with tisza far off the west european plate margin 4 a 80 90 rotation of austroalpine west carpathia during the eoalpine collision 5 subdivision of the neoalpine collision into a palaeogene stage of predominantly strong se nw shortening and a neogene stage of predominantly lateral extrusion westward and eastward in principle the maps show quantitative ocean spreading subduction and plate rotations however possible modifications of the model discussed in this paper limit the quantitative evaluation

apparent shear band geometry resulting from oblique fold sections abstract small scale shear zones inclined at intermediate angles to an earlier anisotropy are often observed in deformed rocks they are traditionally described as shear bands c bands extensional crenulation cleavage or normal kink bands formed as a result of extension along the anisotropy their asymmetries are widely used to describe the large scale kinematics of deformation and the deformational history of a given area we demonstrate that when various three dimensional fold structures are observed on two dimensional outcrop surfaces or in thin section they can appear geometrically identical we have developed a simple technique that allows the geometrical evaluation of any section across a cylindrical fold of arbitrary geometry the ranges of planar sections on which a fold exhibits shear band like geometry are presented on a stereographic projection in order to simplify the determination of critical orientations we demonstrate that for any fold geometry there are two distinct groups of sections showing shear band like geometry with opposite senses of shear criteria systematically arranged around the axial plane and which are inclined at a high angle to the major anisotropy we provide a field example from western carpathians where kinematic analysis mainly based on apparent extensional shear bands led to overemphasis of the role of post orogenic extension on the final structural pattern of the belt

continuity and episodicity in the early alpine tectonic evolution of the western carpathians how large scale processes are expressed by the orogenic architecture and rock record data

superdense co 2 inclusions in cretaceous quartz stibnite veins hosted in low grade variscan basement of the western carpathians slovakia co2 inclusions with density up to 1 197 kg m 3 occur in quartz stibnite veins hosted in the low grade palaeozoic basement of the gemericum tectonic unit in the western carpathians raman microanalysis corroborated co2 as dominant gas species accompanied by small amounts of nitrogen 7 3 mol and methane 2 5 mol the superdense co2 phase exsolved from an aqueous bulk fluid at temperatures of 183 237 c and pressures between 1 6 and 3 5 kbar possibly up to 4 5 kbar low thermal gradients 12 13 c km 1 and the co2 ch4 n2 fluid composition rule out a genetic link with the subjacent permian granites and indicate an external either metamorphogenic oxidation of siderite dedolomitization or lower crustal mantle source of the ore forming fluids

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

new evidence of blueschist facies rocks and their geotectonic implication for variscan suture s in the bohemian massif blueschist facies rocks exposed within consolidated continental blocks provide some of the best evidence for the existence of previous suture s they usually occur as lenses or layers embedded within greenschist or amphibolite facies rocks and indicate reequilibration at medium to low pressure conditions in the bohemian massif a few occurrences of blueschists have been reported and here new evidence of high pressure hp metamorphism in various lithologies is presented that suggests a larger extent of blueschist facies rocks along the northern border of this massif an earlier blueschist facies metamorphism is documented by inclusions of glaucophane in garnet epidote and titanite from metabasites along with zoned white mica having a phengitic core and a muscovite rim in metapelites and orthogneisses the estimated p t conditions obtained using pseudosections and mineral isopleths correspond to blueschist and low temperature eclogite facies conditions 1 1 2 0 gpa at 350 550 c together with medium temperature eclogites from different units in the bohemian massif they indicate a geothermal gradient of 8 10 c km 1 which is typical for cool subduction radiometric dating on phengite from metapelites confirms an early palaeozoic cooling age of c 360 ma for this hp metamorphic event the presence of blueschist facies rocks their p t relations and age constraint together with those from eclogite facies rocks allows us to locate the variscan suture which straddles the se margin of saxothuringian zone from erzgebirge to sudetes and its possible continuation to the moldanubian zone where eclogite facies and uhpm rocks are abundant

fourier grain shape analysis of antarctic marine core the relative influence of provenance and glacial activity on grain shape abstract grain shape is useful as a depositional environmental diagenetic and provenance proxy here we conduct the first study of down core grain shape variation in antarctica this study further examines the utility of grain shape as a depositional proxy namely of glacial influence in the james ross basin and joinville plateau of the antarctic peninsula from the eocene to the present fourier grain shape analysis was used to quantify the grain shape of 31 samples spanning the glacial history of the antarctic peninsula ice sheet a total of 6 442 quartz grain peripheries were digitized and described through the twenty first fourier harmonic sediment provenance has a greater influence on grain roughness than glacial activity in the study area however provided a similar sedimentary source secondary changes in roughness correlate with changes in the extent of the antarctic peninsula ice sheet since the late oligocene grain roughness increased with increased glacial influence during the middle miocene after an early pliocene warm period and just above a pliocene regional glacial unconformity conversely grain roughness decreased with less glacial influence during the late oligocene and during an early pliocene warm period this study further illustrates the usefulness of grain shape in distinguishing sediment provenance and environmental conditions in antarctic settings

petrological and kar and40ar39ar age constraints for the tectonothermal evolution of the high pressure meliata unit western carpathians slovakia abstract the meliata high pressure unit exposed in the southern part of the western carpathians consists of four groups of rocks which are characterized by different lithologies and metamorphic histories 1 the most common are triassic marbles intercalated with metabasalts and glaucophane bearing phyllites phengite from metabasalts and phyllites record k ar and40ar 39ar plateau ages of 152 155 ma which are interpreted to date the high pressure metamorphism 2 blueschist facies mafic rocks and subordinate glaucophane bearing micaschists devoid of marbles which contain relic low si muscovite and newly formed high si phengite the40ar 39ar data obtained for the micas indicate palaeozoic ages of 375 380 ma for the early amphibolite facies muscovite and a 250 ma age for the secondary blueschist facies phengite 3 glaucophane free phyllites and phengite quartzite with low si and high si micas respectively textural features indicate a polyphase evolution characterized by a greenschist facies metamorphism followed by a blueschist facies overprint the high si micas provide evidence for an early middle jurassic age 172 ma of the high pressure metamorphism 4 amphibolite facies slices and blocks overprinted by blueschist facies metamorphism represent old basement rocks regarding the differences in lithologies metamorphic conditions and radiometric ages of high pressure micas older age for continental vs younger age for oceanic rocks subduction of a continental wedge prior to that of oceanic crust can be assumed this interpretation is based also on palaeogeographical reconstruction of the mesozoic western tethys between the apulian promontory and the tisza bihor continental block

geometric morphometrics and geological shape classification systems abstract many areas of geological inquiry involve the description and or comparison of shapes while various morphometric tools have long been available to facilitate these types of comparisons by far the most common approach to such form classification has been via the creation of a semiquantitative scale of morphological exemplars type specimens etc to which unknown structures objects or specimens can be compared such form scales are ubiquitous either in terms of text based descriptions or illustration sets throughout the geological literature however students and even experienced geologists often have difficulty using such scales and achieving consistent results investigations of three such scales drawn from the fields of sedimentology paleontology and geomorphology using the analytical tools of geometric morphometrics suggests that one reason for this difficulty is that the exemplars drawn from sets of real objects 1 often exhibit shape differences other than those under nominal consideration or 2 are used to represents object classes whose boundaries are insufficiently documented or described herein strategies are developed that employ the ordination and modeling capabilities of eigenshape analysis to correct these deficiencies and devise sets of new more representative and easier to use shape classification systems by employing these approaches augmented where necessary with formal statistical analyses geologists can improve the sophistication accuracy and reproducibility of their morphological inferences in doing this they will also improve the reliability of their hypotheses tests

correction to a thin viscous sheet model for continental deformation summary the governing equation derived by england mckenzie for the deformation of a thin viscous shell contains an error we give the correct derivation here and correct those figures where the change makes a visible difference the correct results differ quantitatively from those of england mckenzie but their conclusions are not affected

deep crustal structure beneath the central and inner west carpathians abstract the 150 km long deep seismic transect 2t crossing the central part of the slovakian west carpathians has revealed an important whole crustal seismic suture zone dipping to the south this zone is dominated by six large and several minor reflection events because of our good knowledge of the surface geology and a large number of comparative studies of the eastern alps it is clear that the upper reflections are due to overthrust sheets that originated during compression of the apulian passive margin tectonically deeper reflections are interpreted as being due to ligurian oceanic igneous and sedimentary rocks sheared in ductile domain during continental collision with the brianconnais passive margin and continental masses north of the central apulian west carpathians cwc behind a significant strike slip fault are the cenozoic structures of the pieniny klippen belt and the magura rhenodanubian flysch south of the cwc the inner tethyan west carpathians iwc are thrust over the cwc the iwc originated during the late jurassic early cretaceous closure of the tethyan ocean and the seismic image of the iwc is different from the highly reflective cwc suture these three pre neogene nappe systems amalgamated as one overthrust system during the neogene subduction of the moldavian sea as the moldavian accretionary wedge the vepor gemer block of the west carpathians where the cretaceous suture is observed has been untouched by any major cenozoic deformation and has remained relatively rigid this unique structure therefore enables us to observe seismically the cretaceous suture zone which elsewhere in the european alpine belt has been almost completely destroyed more general data about the beginning of subduction and subsequent collision processes are presented significant compression and partial subduction of the apulian upper plate passive margin lasted from the hauterivian to the beginning of the turonian for about 25 30 ma subduction of the ligurian ocean occurred from turonian to campanian times after the early campanian the collision of the apulian and brianconnais plates took place

thermomechanical structure of european continental lithosphere constraints from rheological profiles and eet estimates summary the eet equivalent elastic thickness of the lithosphere is a measure of the integrated lithospheric strength it is directly related to the mechanical thickness and rheology of the crustal and mantle lithosphere we present a comparison of eet estimates and strength profiles based on the extrapolation of rock mechanics data for different parts of the european and eurasian continental lithosphere we discuss the temporal and spatial variations in the mechanical thickness and strength inferred from data for precambrian segments of europe s lithosphere variscan europe and the alpine collision belt this analysis demonstrates important spatial and temporal variations in lithospheric rigidity for orogenic belts and sedimentary basins in eastern and western europe and asian parts of eurasia the eet estimates based on synthetic rheological profiles constrained by newly available geophysical data are consistent with the estimates of eet derived from flexural studies of sedimentary basins forelands and orogenic belts these rheological profiles suggest weakening of the major parts of the european and eurasian continental lithosphere by decoupling of the crustal and upper mantle parts a comparison with the seismicity depth distribution for some selected sites suggests that the intra plate seismicity is essentially restricted to the upper crustal parts of europe s lithosphere providing additional support to the notion of the decoupled lithosphere the presence of intra plate stress fields can explain a significant part of the observed variations in eet estimates within individual thermotectonic age groups a comparison of wavelengths of crustal and lithospheric folding with observations shows these wavelengths to be consistent with estimates of eet inferred from the rheological response of basins and orogens at more moderate levels of intra plate stress

the original shapes of quartz silt grains a test of the validity of the use of quartz grain shape analysis to determine the sources of terrigenous silt in marine sedimentary deposits abstract the results of a study of the original shapes of quartz silt grains that are released from plutonic metamorphic and sedimentary rocks of varied age origin and lithology are reported the purpose of the study is to demonstrate the validity of quartz grain shape analysis as a technique for determining the sources of terrigenous silt within marine sedimentary deposits by showing that different sources of terrigenous silt release quartz silt grains with different shapes there are four major types of sources that release quartz silt grains with different and distinctive shapes crystalline rocks release a mixture of crystalline grains with subrounded and subangular outlines crystalline nodes and grain embayments and fractured grains with angular outlines microfractures deformation sheets and fracture faces quartz cemented sedimentary rocks release overgrown grains with subangular to angular outlines and quartz overgrowths and lesser numbers of rounded grains with rounded and subrounded outlines and abraded grain surfaces glacial deposits release fractured grains with angular outlines microfractures deformation sheets fracture faces micro blocks and comminution debris lastly quartzose multicyclic sediments release abundant rounded grains with rounded or subrounded outlines and abraded and weathered surfaces therefore the results indicate that quartz grain shape analysis is generally a valid technique for determining the sources of silt however there are exceptions to this generalization for there are some sediment sources e g first cycle coastal plain sediments that inherit and release grain shape types which are released from other sediment sources e g crystalline rocks thus the application of quartz grain shape analysis to the study of the sources of terrigenous silt for a given study area requires some knowledge about the major sediment sources which are available to that study area for this knowledge will define the limitations of this sourcing technique

high density nitrogen inclusions in barite from a giant siderite vein implications for alpine evolution of the variscan basement of western carpathians slovakia contrasting compositions and densities of fluid inclusions were revealed in siderite barite intergrowths of the dro diak polymetallic vein hosted in variscan basement of the gemeric unit central european carpathians primary two phase aqueous inclusions in siderite homogenized between 101 and 165 c total salinity ranged between 18 and 27 wt and cacl2 nacl cacl2 weight ratios were fixed at 0 1 0 3 by contrast mono and two phase aqueous inclusions in barite exhibited total salinities between 2 and 22 wt and the cacl2 nacl ratios ranged from nacl to cacl2 dominated compositions the aqueous inclusions in barite were closely associated with very high density 0 55 0 745 g cm 3 nitrogen inclusions in some cases containing up to 16 mol co2 crystallization p t conditions of siderite 175 210 c 1 2 1 7 kbar constrained by the vertical oxygen isotope gradient along the studied vein isochores of fluid inclusions and the k na exchange thermometer corresponded to minimal palaeodepths between 4 3 and 6 3 km assuming lithostatic load and average crust density of 2 75 g cm 3 maximum fluid pressure during barite crystallization attained 3 6 4 4 kbar at 200 300 c and the most dense nitrogen inclusions maintained without decrepitation the residual internal pressure of 2 2 kbar at 25 c contrasting fluid compositions increasing depths of burial 4 14 km and decreasing thermal gradients 40 15 c km 1 during initial mineralization stages of the dro diak vein reflect alpine orogenic processes rather than an incipient permian rifting suggested in previous metallogenetic models siderite crystallized at rising p t in a closed rock buffered hydrothermal system developed in the variscan basement during the north vergent cretaceous thrusting and thickening of the gemeric crustal wedge variable salinities of the barite hosted inclusions reflect a fluid mixing in open hydrothermal system and re equilibration textures lengths of decrepitation cracks proportional to fluid inclusion sizes correspond to retrograde crystallization trajectory coincidental with transpression or unroofing maximum recorded fluid pressures indicate 12 km thick pile of imbricated nappe units accumulated over the gemeric basement during the cretaceous collision

distribution and significance of extraneous argon in uhp eclogite sulu terrain china insight from in situ 40ar 39ar uv laser ablation analysis in situ 40ar 39ar uv laser ablation analyses of garnet omphacite epidote phengite barroisite and symplectite in a sample of uhp eclogite from qinglongshan sulu terrain china reveal extremely heterogeneous argon isotopic ratios results from the 220 240 ma eclogite indicate a significant and variable extraneous argon signature that is restricted to the early formed phengite and epidote and later formed barroisite individual compositionally zoned phengite grains record a large variation in 40ar 39ar dates 300 1100 ma that are positively correlated with celadonite content these data are consistent with retrograde chemical exchange and argon isotopic repartitioning in response to decreasing partial pressures of argon during decompression consistent with the observation of atmospheric argon ratios in garnet omphacite and symplectite these data support an interpretation that the extraneous ar was incorporated early in the crystallization history of the eclogite and not from a late infiltrating fluid the ultimate source of the extraneous argon remains speculative however on the basis of supporting stable oxygen and hydrogen isotope data from this locality which support a closed isotopic system it is inferred to have been inherited from the protolith of the uhp eclogite

erosion induced exposure of soc to mineralization in aggregated sediment during slope scale erosion events re distribution of eroded soil and the associated soil organic carbon soc is not always uniform but very often affected by preferential transport and deposition under given flow conditions the site of soc deposition depends on the transport distances of sediment particles containing the soc very often soil and soc erosion risk are assessed by applying mineral particle specific soc distributions to erosion models however soil is not always eroded as individual mineral particles but mostly in a form of aggregates aggregates are likely to increase settling velocities of individual mineral particles which may considerably reduce the transport distance of sediment fractions and the associated soc skewing soc redistribution and its subsequent fate yet little is known about the potential effects of aggregation on the movement and fate of eroded soc to assess the effect of preferential deposition a simulated rainfall was applied to two soils in this study with the movelier silty clay having greater soc content and aggregate stability than the mohlin silty loam the eroded sediments of the two soils were fractionated by a settling tube apparatus according to their potential transport distances the co2 emissions of the fractionated and incubated sediments were then measured for 50 days enabling the assessment of the bioactivity of eroded soc for weeks after deposition our results show that 1 the re deposition of eroded soc into terrestrial systems increased by 64 if considering the actual aggregate specific rather than the mineral particle specific soc distribution 2 the co2 emission rates differed across settling fractions with the most pronounced rates in the finest fractions from the mohlin silty loam sediment and in the medium size fractions from the movelier silty clay sediment 3 over 50 day incubation the co2 emissions from the mohlin silty loam sediment was 114 greater than that from the non eroded mohlin soil whereas co2 emissions were roughly equivalent for the movelier sediment and non eroded movelier silty clay these data demonstrate that erosion and preferential deposition of soc enriched aggregates can enhance terrestrial soc deposition this can further result in greater co2 efflux than commonly applied mineral particle size specific soc distribution would suggest the different performances of deposition and co2 emissions between the two soils also suggest that these effects can vary with soil type our observations certainly illustrate that sediment aggregation requires further investigation to assess the redistribution and subsequent fate of eroded soc appropriately

metamorphic evolution and fluid composition of garnet clinopyroxene amphibolites from the tatra mountains western carpathians relics suggesting an early high pressure eclogite facies stage have been identified in the garnet and clinopyroxene bearing amphibolites of the tatra mountains in the variscan basement of the western carpathians slovakia in these rocks primary omphacite cpx i has been wholly converted to symplectites of diopside cpx ii and plagioclase apart from minor inclusions in the garnet cores amphibole and plagioclase are secondary minerals formed in the kelyphitic rims between garnet and clinopyroxene several generations of amphibole pargasite hornblende cummingtonite actinolite are evidence of a transformation down to greenschist facies conditions thermobarometric calculations from mineral inclusions in the garnet cores yield 670 700 c and 10 15 kbar recording the initial path from upper amphibolite to eclogite facies conditions the attainment of the eclogite facies stability field is inferred from the composition of a reconstructed omphacite jd36 implying a minimum peak pressure of 15 16 kbar conditions of around 650 c and 8 10 kbar record the post eclogite breakdown and partial re equilibration in the amphibolite facies region the earliest fluid inclusions contain high density nitrogen dominated water absent fluid younger are polyphase brines and two phase h2o n2 ch4 inclusions with signs of heterogeneous entrapment of coexisting gas rich and water rich immiscible phases pure nitrogen 0 5 mol ch4 is considered to have been the major component during the high pressure metamorphism in contrast the later aqueous inclusions are interpreted to represent retrogression related fluids the brines have originated by leaching and re entrapment of saline melt inclusions observed in tonalitic trondhjemitic layers of the amphibolite enclosing the eclogitic relics a similar mechanism is assumed for the origin of the h2o n2 ch4 inclusions these represent relics of the primary eclogite facies related n2 inclusions re equilibrated and re entrapped during retrogression under increasing water activity a possible source of n2 and cl rich fluids was primary amphibole which decomposed during the prograde metamorphism from the amphibolite to the eclogite facies the metamorphic pt path is generally clockwise reflecting a steep increase in pressure and temperature during burial followed by decompression and cooling the retrograded eclogites occur in boudins within an allochthonous unit of an inverted metamorphic sequence their exhumation was facilitated by tectonic transport along a ductile shear zone during the variscan orogeny

cretaceous evolution of a metamorphic core complex the veporic unit western carpathians slovakia p t conditions and in situ40ar 39ar uv laser probe dating of metapelites alpine metamorphism related to the development of a metamorphic core complex during cretaceous orogenic events has been recognized in the veporic unit western carpathians slovakia three metamorphic zones have been distinguished in the metapelites 1 chloritoid chlorite garnet 2 garnet staurolite chlorite 3 staurolite biotite kyanite the isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system k2o feo mgo al2o3 sio2 h2o kfmash the isograds are roughly parallel to the north east dipping foliation related to extensional updoming along low angle normal faults thermobarometric data document increasing p t conditions from c 500 c and 7 8 kbar to c 620 c and 9 10 kbar reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies 40ar 39ar data obtained by high spatial resolution in situ ultraviolet uv laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the late cretaceous mean dates are between 77 and 72 ma however individual white mica grains record a range of apparent 40ar 39ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous the reconstructed metamorphic p t t path is clockwise reflecting post burial decompression and cooling during a single alpine orogenic cycle the presented data suggest that the veporic unit evolved as a metamorphic core complex during the cretaceous growth of the western carpathian orogenic wedge metamorphism was related to collisional crustal shortening and stacking following closure of the meliata ocean exhumation was accomplished by synorogenic orogen parallel extension and unroofing in an overall compressive regime

degradation of soil structure by welding a micromorphological study abstract in 1985 a plot study was started on sloping cultivated loess soils in south limbourg the netherlands to evaluate the effects of various cropping systems of fodder maize on runoff soil loss and crop yield under natural rainfall to monitor degradation of soil structure including crust formation undisturbed vertical samples 15 7 cm for soil micromorphological analysis were taken of the top 7 cm of soil at ten dates chosen in relation to times of tillage and sowing crop stage harvest and winter frost wheel marks if present were also sampled contrary to accepted views no disintegration of structural elements by slaking or dispersion was observed freshly tilled soil exhibited a loss of its original granular structure by coalescence of the aggregates into larger units eventually leading to a structureless state of part of the top soil processes held responsible for this are mainly welding of wet aggregates and seldom fusion by silt infillings in vertical inter aggregate pores the two layer model of soil crust formation of mcintyre could not be confirmed as no important vertical translocation of fines or washed in layers were observed horizontal cracks developed in the structureless soil giving rise to a platy structure in part of the top soil transitional stages of loss of soil structure were observed characterized by the progressive reduction of compound packing voids to vughs which ultimately disappeared completely and sometimes were replaced by planar voids besides structural crusts sedimentary crusts including splash deposits were observed

size shape and orientation of grains in sands and sandstones image analysis applied to rock thin sections abstract a computer based image analysis system is used to determine the grain size distribution grain shape and grain orientation from rock thin sections a monte carlo simulation allows correction of the grain size distribution for the corpuscle effect grains cut marginally in the thin section plane have smaller apparent diameters thin section derived grain size distributions of modern and ancient samples have been compared with distributions obtained from sieving of the same samples different grain shape parameters have been compared with the wadell formula the grain orientation can be easily and reliably measured in thin sections from different cuts of a sample grain orientation data can help to determine paleocurrent directions

first permian early triassic zircon ages for tin bearing granites from the gemeric unit western carpathians slovakia connection to the post collisional extension of the variscan orogen and s type granite magmatism this study presents the first preliminary u pb zircon data on tin bearing s type granites from the gemeric unit of the western carpathians slovakia u pb single zircon dating controlled by cathodoluminescence suggests crystallization of the gemeric granites during permian to early triassic 303 241 ma time post crystallization low temperature metamorphic overprint is reflected by partial pb loss in zircons these gemeric granites are younger than the highly fractionated s type tin and rare element bearing leucogranites in the european variscides they may have resulted from partial melting triggered by increased heat flow from the mantle below the continental crust and most probably intruded during the post collisional extension and initial rifting of the variscan orogenic belt during alpine orogeny the gemeric granites were affected by a low temperature deformation and metamorphism

rb sr record of fluid rock interaction in eclogites the marun keu complex polar urals russia abstract rb sr internal mineral isochrons in the eclogite facies marun keu metamorphic complex polar urals russia date periods of fluid rock interaction and record the metamorphic reaction history the marun keu complex consists of late proterozoic to early ordovician mostly igneous rocks that experienced a subduction related non pervasive eclogite facies metamorphism followed by a local decompression related amphibolite facies overprint during the uralian orogeny field observations show that metamorphic reactions as well as ductile deformation are controlled by local availability of a free fluid phase isotopic data reveals that availability of fluids similarly exerts control on isotope distribution from a relic gabbro which has never been infiltrated by free fluids a premetamorphic rb sr age of 467 39 ma was obtained rb sr isochron ages for 14 samples of eclogite and amphibolite facies assemblages sampled from within or close to metamorphic fluid veins range from 352 5 ma to 360 3 ma a sm nd isochron for a metagranite yields an age of 354 4 ma taken together the ages for both prograde and retrograde metamorphic assemblages overlap within analytical uncertainty and yield an average value of 355 5 1 4 ma indicating that the metamorphic evolution and incipient exhumation of the marun keu complex proceeded rapidly the results demonstrate that assemblages preserve their rb sr isotopic signatures as long as they remain devoid of free fluids and that only fluid rock interaction may cause sr isotope redistribution in addition the data suggest local fluid rock equilibrium low fluid rock ratios with overall fluid deficiency and limited fluid mobility at depth however some fluids must have been mobile on the km scale since they can be traced into the suprasubduction zone mantle wedge metasomatic veins in the rai iz ophiolite yield a rb sr mineral isochron age of 373 1 5 4 ma they are interpreted as evidence for suprasubduction zone metasomatism in an oceanic setting prior to subduction of the east european margin and associated formation of eclogites in the marun keu complex we propose that rb sr mineral isochron ages provide hygrochronological rather than thermochronological constraints they define the cooling history only in combination with zircon and apatite fission track data the straightforward interpretation of rb sr mineral ages as cooling ages is obsolete

transected folds and transpression how are they associated abstract folds transected by cleavage are a distinctive structural feature in the caledonian appalachian orogenic belt with the advent of a tectonic model of transpression for this belt there has been an assumption that transected folds are a symptom of transpressive deformation in particular that clockwise transection signifies sinistral transpression we examine this tenet and conclude that there is no unique explanation for folds transected by a synchronous cleavage explanations can be found for either clockwise or anticlockwise transection for sinistral or dextral transpression each requiring assumptions about the inclination of bedding to the transpression vector or requiring that cleavage does not track the finite xy plane a further explanation which may fit the regional data best requires a non constant transpressive deformation with initial pure shear dominated deformation giving way to increasing transcurrent movement in time none of these models can be assumed to be right without supporting data on the incremental and finite strain histories of such regions

interrill erosion of carbon and phosphorus from conventionally and organically farmed devon silt soils abstract globally between 0 57 and 1 33 pg of soil organic carbon soc may be affected by interrill processes also a significant amount of phosphorus p is contained in the surface soil layer transformed by raindrop impact runoff and crust formation in the eu the p content of a crusted 2 mm surface layer corresponds to 4 to 40 kg ha 1 of p on arable land 1 094 mil km2 therefore the role of interrill processes for nutrient cycling and the global carbon cycle requires close attention interrill erosion is a complex phenomenon involving the detachment transport and deposition of soil particles by raindrop impacted flow resistance to interrill erosion varies between soils depending on their physical chemical and mineralogical properties in addition significant changes in soil resistance to interrill erosion occur during storms as a result of changes in surface roughness cohesion and particle size as a consequence erosion on interrill areas is selective moving the most easily detached small and or light soil particles this leads to the enrichment of clay phosphorous p and carbon c such enrichment in interrill sediment is well documented however the role of interrill erosion processes on the enrichment remains unclear enrichment of p and c in interrill sediment is attributed to the preferential erosion of the smaller lighter soil particles in this study the p and organic c content of sediment generated from two devon silts under conventional cs and organic os soil management were examined artificial rainfall was applied to the soils using two rainfall scenarios of differing intensity and kinetic energy to determine the effects on the p and c enrichment in interrill sediment interrill soil erodibility was lower on the os irrespective of rainfall intensity sediment from both soils showed a significant enrichment in p and c compared to the bulk soil however sediment from the os displayed a much greater degree of p enrichment this shows that the net p export from organically farmed soils is not reduced by a similar degree than soil erosion compared to conventional soil management the enrichment of p and c in the interrill sediment was not directly related to soc p content of the soil and soil interrill erodibility a comparison of soil and sediment properties indicates that crusting p and c content as well as density and size of eroded aggregate fragments control p and c enrichment due to complex and dynamic interactions between p soc and interrill erosional processes the nutrient and c status of sediments cannot be predicted based on soil p content soc or interrill erodibility alone clearly further research on crust formation and the composition of fragments generated by aggregate breakdown and their transport in raindrop impacted flow under different rainfall conditions is required attaining this critical missing knowledge would enable a comprehensive assessment of the benefits of organic farming on nutrient budgets off site effects of interrill erosion and its role in the global c cycle

complex growth textures in a polymetamorphic metabasite from the kraubath massif eastern alps zoned garnet and amphibole occur in metabasites of the kraubath massif eastern alps that contain relic magmatic clinopyroxene the amphibole composition gradually changes from core xmg 1 4 0 83 to rim xmg 1 4 0 6 0 7 a number of compositional varieties of garnet occur in the metabasite an older porphyroblastic garnet py23 27 alm41 43 grs29 33 has two different compositional domains one relatively rich in mg py27 30 and the other rich in ca grs35 38 with a low mg py20 25 content the youngest variety which forms rims on or microveins in the porphyroblastic garnet has high ca and low mg grs40 57 py2 7 alm46 51 the amphibole cores and garnet porphyroblasts are interpreted to represent minerals formed during variscan regional metamorphism under amphibolite facies conditions alpine metamorphism is represented by the most recent ca rich and mg poor variety of garnet that coexists with the amphibole rims epidote and chlorite fracturing in the porphyroblastic garnet probably originated during retrogression of the variscan amphibolite facies assemblages textural relations suggest that the garnet in the microveins formed by dehydration of hydrous phases during an alpine metamorphic overprint that reached p t conditions of 550 583 c at 1 0 gpa

arcuate fold and cleavage patterns in the southeastern part of the anglo brabant fold belt belgium tectonic implications abstract the brabant massif belgium is situated at the southeastern extremity of the anglo brabant fold belt the predominantly concealed eastern branch of the british belgian caledonides in contrast to the other parts of this caledonian slate belt the deformation history in the brabant massif has to date never been constrained properly in this paper a synthesis is presented of the structural observations in the limited outcrop area of the brabant massif in particular with respect to cleavage and fold trajectories and mutual cleavage fold relationships arcuate fold and cleavage patterns as well as the presence of cleavage transected folds are demonstrated similar to the other parts of the belt moreover the arcuate trajectories are considered to reflect the trace of the caledonian deformation front once obscured by the variscan ardenne allochthon combined with interpretations of the aeromagnetic and bouguer anomaly maps an overall kinematic model is proposed for the acadian deformation event in the brabant massif with the proposed model calling upon processes of indentation by promontories and lateral escape of lithostructural domains as well as on the control exerted by rigid granitoid basement blocks the strong similarities with the other parts of the british belgian caledonides become apparent by defining an overall shortening direction and proposing a trace for the caledonian deformation front in this southeastern extremity of the anglo brabant fold belt an integrated tectonic image is obtained for the entire british belgian caledonides

crustal influx indentation ductile thinning and gravity redistribution in a continental wedge building a moldanubian mantled gneiss dome with underthrust saxothuringian material european variscan belt 1 the contribution of lateral forces vertical load gravity redistribution and erosion to the origin of mantled gneiss domes in internal zones of orogens remains debated in the orlica snieznik dome moldanubian zone european variscan belt the polyphase tectono metamorphic history is initially characterized by the development of subhorizontal fabrics associated with medium to high grade metamorphic conditions in different levels of the crust it reflects the eastward influx of a saxothuringian type passive margin sequence below a tepla barrandian upper plate the ongoing influx of continental crust creates a thick felsic orogenic root with hp rocks and migmatitic orthogneiss the orogenic wedge is subsequently indented by the eastern brunia microcontinent producing a multiscale folding of the orogenic infrastructure the resulting kilometre scale folding is associated with the variable burial of the middle crust in synforms and the exhumation of the lower crust in antiforms these localized vertical exchanges of material and heat are coeval with a larger crustal scale folding of the whole infrastructure generating a general uplift of the dome it is exemplified by increasing metamorphic conditions and younging of 40ar 39ar cooling ages toward the extruded migmatitic subdomes cored by hp rocks the vertical growth of the dome induces exhumation by pure shear dominated ductile thinning laterally evolving to non coaxial detachment faulting while erosion feeds the surrounding sedimentary basins modeling of the bouguer anomaly grid is compatible with crustal scale mass transfers between a dense superstructure and a lighter infrastructure the model implies that the moldanubian orlica snieznik mantled gneiss dome derives from polyphase recycling of saxothuringian material

magnetic fabric overprints in multi deformed polymetamorphic rocks of the gemeric unit western carpathians and its tectonic implications abstract in the gemeric unit of the central west carpathians the magnetic fabric was investigated in early palaeozoic metasediments and metavolcanics permian to early triassic granites and late palaeozoic molasse metasediments in addition to variscan greenschist facies metamorphism in the early palaeozoic basement all rocks underwent cretaceous alpine low grade metamorphism which significantly modified their mineral composition and fabric original magnetic minerals were destroyed at least partially and new mostly paramagnetic minerals were created in the early palaeozoic metasediments the magnetic fabric is entirely metamorphic deformational in origin in metavolcanics the magnetic foliations are partly parallel to the alpine metamorphic foliations developed in relatively incompetent lithologies such as tuffs and tuffites and partly to disjunctive foliations developed in competent rhyolites and its subvolcanic members their magnetic fabrics probably represent gradual transition from variscan to alpine fabrics in the permian granites the magnetic foliations are near the alpine mesoscopic disjunctive foliations crosscutting metamorphic schistosity in contact aureoles of granite in the late palaeozoic molasse metasediments the magnetic foliations are near the alpine metamorphic foliations that are mostly parallel to the original bedding on regional scale the magnetic fabrics show curved pattern indicating complex interactions between the gemeric and underlain veporic units in the final stages of intendation and collision the magnetic fabric pattern in the gemeric unit roughly resembles that in the veporic unit this results from similar tectonic movements operating at least during cretaceous collision in both the units this tectonic process occurred subsequent to the closure of the meliata ocean and was responsible for creation of the final structure of the central western carpathians nevertheless in contrast to the veporic unit where dominantly alpine type of magnetic fabrics is present in the gemeric unit the alpine overprint had variable degrees of modification of ams fabrics ranging from relatively weak to totally obliterated

length scales for continental deformation in convergent divergent and strike slip environments analytical and approximate solutions for a thin viscous sheet model the deformation of a thin viscous layer that has a moving boundary is investigated for comparison with zones of deformation in the continental lithosphere exact analytical solutions for the case of a newtonian fluid and approximate solutions for the case of fluid with power law rheology show that when the imposed velocity vector is normal to the boundary congressional or extensional regime the deformation field decays away from the boundary with a characteristic length scale 1 3 to 1 10 the wavelength of the imposed boundary velocity distribution for n between 1 and 10 where n is the stress strain exponent in the rheology in contrast when the imposed velocity vector is parallel to the boundary transcurrent regime the length scale of the deformation field is approximately 4 times smaller in each case these length scales decrease approximately as n the difference in length scales arises even in the absence of any buoyancy forces acting on thickened or thinned crust such forces would modify the ratio of length scales but not sufficiently to affect this result

35 ma old ultrahigh pressure metamorphism and evidence for very rapid exhumation in the dora maira massif western alps abstract ion microprobe shrimp data on zircons from various rock types of an ultrahigh pressure uhp metamorphic whiteschist type pyrope quartzite lens of the dora maira massif dmm consistently show domains giving a late eocene age of 35 4 1 0 ma which is taken as the age of uhp metamorphism these domains partially replace the older oscillatory zoning pattern of the zircons formed during primary magmatic crystallization at about 275 ma zircons of a metagranitic country rock next to the uhp metamorphic lens have these primary features best preserved all zircons measured also yield intermediate ages between 275 and 35 ma with a statistical concentration between 260 and 210 ma thus the uniformity of the initial zircon population both in the lens and the country rock evidences a common protolith that is a granite intruded during the late herynian while the intermediate ages are at least partly due to incomplete resetting of the zircons during uhp metamorphism those in the 260 210 ma range may be related to rifting episodes in the permotriassic the mg rich chemistry of the whiteschist lenses is due to local metasomatic alterations of the granite perhaps by fluids derived from evaporitic sediments dating as early as the permotriassic as well the more pervasive resetting of zircon ages during uhp metamorphism in the pyrope quartzite lenses is explained by the ubiquity of fluids and or melts produced during subduction by a series of dehydration reactions that occurred only in the more hydrous mg rich protoliths and not in their drier granitic neighborhood fission track ages determined partly on the same zircon samples yielding 29 9 1 4 ma mark the time when the uhpm unit had reached about 290 c at a shallow location within the crust thus exhumation over a vertical distance of about 120 km must have occurred within about 5 6 ma indicating an average uplift rate of about 20 24 km ma and an average cooling rate of about 85 100 c ma the radiometric data obtained do not lend any support to an eo alpine cretaceous subduction event so that deep subduction and immediately following exhumation all took place during early to mid tertiary time this scenario seems to apply to large portions of the western and central alps as well calling for drastic geodynamic reinterpretations of these parts of the alps

effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events the effect of antecedent conditions and specific rock fragment coverage on precipitation driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6 m 1 m flumes with 2 2 slope four sequential experiments denoted e1 e2 e3 and e4 involved 2 h precipitation rates of 28 74 74 and 28 mm h 1 respectively and 22 h without rainfall were conducted in each experiment one flume was bare while the other had 40 rock fragment coverage the soil was hand cultivated and smoothed before the first event e1 only and left untouched subsequently sediment yields at the flume exit reached steady state conditions over time scales that increased with sediment size experiments were designed such that both steady and non steady effluent sediment yields were reached at the conclusion of e1 results from subsequent experiments showed that short time soil erosion was dependent on whether steady state erosion was achieved during the preceding event although consistent steady state effluent sediment yields were reached for each sediment size class steady state erosion rates were however dependent on the rainfall intensity and its duration if steady state sediment yields were reached for a particular size class that class s effluent sediment yield peaked rapidly in the next rainfall event the early peak was followed by a gradual decline to the steady state condition on the other hand for size classes in which steady state was not reached at the end of the rainfall event i e e1 in the following event e2 the sediment yields for those classes increased gradually to steady state i e the sharp peak was not observed the effect of rock fragment cover 40 on the soil surface was also found to be significant in terms of the time to reach steady state i e their presence reduced the time for steady conditions to be attained effluent sediment yields for the bare and rock fragment covered flumes e1 showed steady conditions were reached for the latter in contrast to the former we used the hairsine rose h r model to simulate the experimental data as it explicitly models soil particle size classes experiments e1 and e2 involved soil compaction by raindrops and in this case the model predictions were found to be unsatisfactory however compaction was effectively completed by the end of experiment e2 and the model provided reasonable predictions for experiments e3 and e4

phase petrology and p t conditions of mafic blueschists from the meliata unit west carpathians slovakia blueschists occurring as layers in calcite marbles of the meliata unit occur along the so called roznava tectonic line situated in the southern part of the gemericum slovakia mineral assemblages and compositions from seven blueschists localities and one occurrence of amphibolite facies rocks overprinted by blueschist metamorphism were investigated the most common minerals in the blueschists are blue amphibole epidote and albite some fe2 and al rich rocks also contain garnet and chloritoid respectively na pyroxene with a maximum 50 jadeite component was also found the blue amphiboles correspond mostly to crossite and also to glaucophane and ferroglaucophane in some samples almandine and spessartine rich garnet has very low mgo content 3 wt the si content in phengite ranges between 3 3 and 3 5 pfu calculated on the basis of 11 oxygens the zoning patterns of blue amphibole garnet and chloritoid suggest their formation during a prograde stage of metamorphism the p t conditions of metamorphism are estimated to be about 380 460 c and 10 13 kbar pressures of 7 5 8 5 kbar and temperatures of 350 370 c were obtained for some actinolite and aegirine rich rocks apart from chlorite other mafic minerals formed during retrograde metamorphism are biotite and occasionally also actinolite

sequential porphyroblast growth and crenulation cleavage development during progressive deformation abstract six stages of crenulation cleavage development during a single deformation event d2 can be recognised in both matrix and porphyroblast inclusion trails in the robertson river formation n e australia these stages progress from undeformed to crenulation and differentiated crenulation of s1 through development of differentiated crenulation cleavage s2 and differentiated schistosity s2 to homogeneous foliation s2 these rocks underwent prograde metamorphism during d2 and chloritoid garnet staurolite andalusite and sillimanite isograds have been mapped most rocks are rich in porphyroblasts which commonly contain well defined inclusion trails the geometry of these trails varies from one mineral type to the next depending on the timing of porphyroblast growth relative to the stage of crenulation cleavage development in the schistose matrix the deformation history involved progressive bulk inhomogeneous shortening and the strain is very heterogeneous on all scales partly as a consequence of this hence each of the six stages of crenulation cleavage development formed locally at various times during d2 therefore if a porphyroblast grew late in the deformation it could overgrow all stages of crenulation cleavage development including the very early ones the temperature increased during metamorphism in any one locality and consequently some porphyroblasts overgrew others that were unstable in the new conditions preserving them from destruction hence the precise timing of mineralogical reactions deduced from isograds and mineral chemistry relative to the stages in schistosity development can also be determined in the andalusite zone the sequence of porphyroblasts in decreasing order of age is biotite garnet biotite staurolite andalusite dissolution of garnet occurred during growth of staurolite and especially andalusite and dissolution of staurolite accompanied andalusite growth

strain partitioning and metamorphism in a deformable orogenic wedge application to the alpine belt abstract various processes have been proposed in the literature to explain the exhumation and preservation of blueschist and eclogitic facies rocks among these processes corner flow circulation within an accretionary wedge is frequently advocated in the alpine collisional belt geological petrological and chronological evidences indicate that high pressure low temperature metamorphic rocks have been generated in the subduction zones which existed before the collisional event indeed the internal part of the alps have been compared to the inner zone of modern accretionary prisms in order to discuss the corner flow circulation model and its applications to the internal part of the alps taking into account the metamorphic and structural data we have numerically explored in a deformable orogenic wedge 1 the possible generation of hp lt metamorphism in this context and the ptt paths related to the exhumation process 2 the duration of the exhumation and 3 the strain partitioning and the related geometries imposed by this circulation the velocity field is computed from mass conservation law no attempt has been made to include variable viscosity we show that 1 hp lt metamorphism can be achieved in the computed conditions ptt paths differ according to the velocity of subduction 2 the exhumation process lasts less than 15 ma and generates high strains which erase the initial deformation phases and 3 metamorphic and structural data from the internal part of the alps are compatible with the numerical constraints

continental rifting parallel to ancient collisional belts an effect of the mechanical anisotropy of the lithospheric mantle analysis of major rift systems suggests that the preexisting structure of the lithosphere is a key parameter in the rifting process rift propagation is not random but tends to follow the trend of the orogenic fabric of the plates systematically reactivating ancient lithospheric structures continental rifts often display a clear component of strike slip deformation in particular in the early rifting stage moreover although the close temporal and spatial association between flood basalt eruption and continental breakup suggests that mantle plumes play an important role in the rifting process there is a paradox between the pinpoint thermal and stress perturbation generated by an upwelling mantle plume and the planar geometry of rifts these observations suggest that the deformation of the lithosphere especially during rifting is controlled by its preexisting structure on the other hand 1 the plasticity anisotropy of olivine single crystal and aggregates 2 the strong crystallographic orientation of olivine observed in mantle xenoliths and lherzolite massifs and 3 seismic anisotropy data which require a tectonic fabric in the upper mantle coherent over large areas suggest that preservation within the lithospheric mantle of a lattice preferred orientation lpo of olivine crystals may induce a large scale mechanical anisotropy of the lithospheric mantle we use a polycrystal plasticity model to investigate the effect of a preexisting mantle fabric on the continental breakup process we assess the deformation of an anisotropic continental lithosphere in response to an axi symmetric tensional stress field produced by an upwelling mantle plume by calculating the deformation of textured olivine polycrystals representative of the lithospheric mantle at different positions above a plume head model results show that a lpo induced mechanical anisotropy of the lithospheric mantle may result in directional softening leading to heterogeneous deformation during continental rifting this mechanical anisotropy may induce strain localisation in domains where extensional stress is oblique 30 55 to the preexisting mantle fabric this directional softening associated with olivine lpo frozen in the lithospheric mantle may also guide the propagation of the initial instability that will follow the preexisting structural trend the preexisting mantle fabric also controls the deformation regime imposing a strong strike slip shear component a lpoinduced mechanical anisotropy may therefore explain the systematic reactivation of ancient collisional belts during rifting structural inheritance the plume rift paradox and the onset of transtension within continental rifts fl 2001 elsevier science b v all rights reserved

inverse ductile thinning via lower crustal flow and fold induced doming in the west carpathian eo alpine collisional wedge 1 continental core complexes are generally interpreted to result from extensional doming due to gravity driven upflow of lower crust in contrast the vepor dome is characterized by the lack of inverted density profile and relatively cold metamorphic field gradient which precludes an activation of rayleigh taylor instability instead the crustal structure of the vepor unit is marked by dense and weak metapelitic lower crust and light and strong granitoid upper crust inherited from variscan nappe stacking it is shown that the cretaceous eo alpine tectonic evolution of the vepor dome is controlled by the dynamics of two neighboring mechanically strong continental blocks i e the overthrusting of the suprastructural gemer unit from the south and the underthrusting of the fatric basement from the north structural metamorphic and geochronological data from the vepor unit imply two main phases of the convergent process 1 lower cretaceous crustal thickening due to overthrusting and internal deformation of the gemer unit together with upper crustal folding in the vepor unit led to the progressive development of the orogenic front parallel pressure gradient the instantaneous response of the lower crustal and low viscosity metapelites led to an along strike lower crustal flow accompanied by prograde barrovian type metamorphism 2 as the south vergent underthrusting of the fatric basement propagated to greater depths during the upper cretaceous the convergent process switched from top driven to bottom driven and the exhumation of the lower crust occurred via polyharmonic folding overall doming of the vepor unit induced upper crustal detachment faulting and eastward unroofing of the dome

sources and dispersal of late quaternary silt on the northern gulf of mexico continental shelf abstract the surficial sediments of the northern gulf of mexico continental shelf consist of large volumes of silt and clay and lesser amounts of sand of late quaternary age a study of the roundness and surface textures of quartz silt grains in these surficial sediments was conducted to determine the sources and dispersal patterns of this size fraction and to gain a better understanding of late quaternary sedimentation on this shelf the results indicate that there are six distinct silt provinces within the study area that can be distinguished on the basis of grain roundness and surface textures three of the provinces are characterized by relatively angular quartz silt grains on the average and an abundance of first cycle crystalline quartz grains the remaining three provinces are characterized by relatively rounded quartz silt grains and an abundance of multicyclic sedimentary rounded grains the dispersal patterns of these six provinces are partly controlled by the late wisconsinian paleogeography thus a comparison of the dispersal patterns with the locations of the modern and ancient fluviodeltaic depocenters allows the identification of these six provinces as deposits of the rio grande the coastal plain streams of south texas the brazos and colorado river the mississippi the mobile river and the rivers of the southeastern united states however the dispersal patterns have also been modified by the prevailing shelf and longshore currents and there is up to 400 km of downcurrent displacement of silt from its late wisconsinian sites of deposition on some parts of the shelf

drying soil surface condition and interrill erosion on two ontario soils abstract interrill erodibility summarizes the resistance of soil to rainsplash sheetwash and rainflow erosion and incorporates changes in infiltration roughness and resistance to detachment and transportation resistance to interrill erosion varies during storms reflecting the effect of wetting sealing crusting and erosion on surface conditions significant changes in soil conditions also occur as a result of progressive drying between storms producing considerable uncertainty in event based erosion prediction however a clear link between drying primary soil properties and soil condition as well as interrill erosion during subsequent storms has not been established in this study soil condition and interrill erosion of soils from southern ontario were examined in detail during a sequence of simulated rainstorms and linkages between primary soil properties drying surface soil structure and interrill erosion were established interrill erosion after drying differed depending on the persistence of the changes in soil structure caused by drying pronounced stabilization of aggregates on drying led to an increase of erodibility indicating a transition from a coherent to granular structure requiring lower stresses for particle detachment the sensitivity of soil erodibility to drying appears to be determined by the tendency of a soil to form aggregates the results show that a better understanding of the linkages between primary soil properties rainfall and drying history soil condition and interrill erosion is required for effective event based erodibility assessment however the wide range of possible initial soil conditions and the complex nature of soil climate interaction are likely to limit the effectiveness of erodibility assessment

40ar 39ar dating of the inner carpathians variscan basement and alpine mylonitic overprinting abstract the 40ar 39ar dating method has been applied to mylonitic rocks from the carpathian mountains these are variscan metamorphic and magmatic rocks that were overprinted during the alpine orogeny the inner western carpathians are conventionally described as a nappe pile formed by northward movement and then subjected to intense strike slip and normal faulting resulting in the formation of mylonitic rocks precise stratigraphie ages provide clear constraints for the geodynamic interpretation related to the succession of alpine events such as the pre gosauian phase during the turonian 90 ma the 40ar 39ar method allows to define the age of the ancient variscan basement and the ages of the alpine overprinting in the high and low tatras mineral ages of around 340 350 ma are yielded by gneisses micaschists and amphibolites providing a younger limit for the variscan metamorphism the emplacement cooling of the variscan granites is defined between 305 and 335 ma these rocks are overprinted by several alpine tectonothermal events the major events are dated at 65 and 86 88 ma during which the mylonites were generated an older event around 140 ma earlier defined by the rb sr method is now confirmed by the 40ar 39ar method dating of phengites extracted from high pressure metamorphic triassic rocks from the kosice area yields new data for the age of this event at 155 ma