direct dating of mid crustal shear zones with synkinematic allanite new in situ u th pb geochronological approaches applied to the mont blanc massif dating the timing of motion on crustal shear zones is of tremendous importance for understanding the assembly of orogenic terranes this objective is achieved in this paper by combining petrological and structural observations with novel developments in in situ u th pb geochronology of allanite a greenschist facies shear zone within the mont blanc massif is documented allanite is synkinematic and belongs to the mylonitic assemblage la icp ms u th pb isotope analyses of allanite reveal high contents and highly radiogenic isotopic compositions of the common pb component the use of measured pb isotope compositions of associated minerals feldspars and chlorite is critical for accurate common pb correction and provides a powerful mechanism for linking allanite growth to the metamorphic assemblage a mean 208pb 232th age of 29 44 0 95 ma is accordingly taken for synkinematic allanite crystallisation under greenschist facies conditions this age reflects the timing of the mont blanc underthrusting below the penninic front and highlights the potential of directly dating deformation with allanite

time scales of deformation and exhumation in extensional detachment systems determined by high spatial resolution in situ uv laser 40ar 39ar dating abstract once dated with adequate precision intra grain recrystallization microstructures in deformed minerals provide valuable information about the tectonic and kinematic history of shear zones and entire orogens we present combined in situ uv laser 40ar 39ar geochronology and stable isotope data to decipher the relationships between intra grain recrystallization microstructures and 40ar 39ar ages in muscovite fish from extensional mylonite of the porsgrunn kristiansand shear zone southern norway texturally controlled uv laser 40ar 39ar dating of isotopically and compositionally distinct cores rims and tips of muscovite fish resolves intra grain age variations on the micrometer scale twenty eight in situ uv laser 40ar 39ar analyses from two muscovite cores yield a weighted mean age of 891 2 2 9 ma interpreted to date synkinematic neocrystallization of muscovite the integrated 880 2 2 8 ma n 30 analyses weighted mean age of rims and tips is in good agreement with observed recrystallization relationships which suggest that rims and tips of the muscovite fish record the final increments of the ductile deformation history diffusion considerations based on published argon diffusion rates and peak temperature estimates from oxygen isotope thermometry show that the 40ar 39ar ages are unlikely to be disturbed during cooling the 11 0 4 0 my core to rim age difference together with the stable isotope data are consistent with protracted ductile deformation extensional detachment faulting and meteoric fluid infiltration occurring over this time interval this approach combining x ray element mapping stable isotope geochemistry and in situ uv laser 40ar 39ar dating allows well characterized microstructures to be analyzed with high precision and permits direct determination of the time scales of deformation in crustal scale shear zones

aeolian silt contribution to soils on mountain slopes mt śleza southwest poland this paper evaluates the possible contribution of aeolian silt to soils of mt leza southwest poland silt loam textures are common across lower silesia and are often confused with silt clay loam especially at the outer boundaries with thin loess deposits eight study sites with different thicknesses of silt loam mantles that are covered and or mixed with underlying sediments were examined in the field to test our hypothesis we analyzed the particle size and geochemistry of representative horizons concentrations of major and trace elements as well as their cross ratios confirmed the aeolian origin of silt loam materials and clearly distinguished them from basal sediments there is a clear relationship between the presence and depth of aeolian mantles and mixing zones with the type of underlying material furthermore the incorporation of aeolian silt to regoliths soils was a main agent initiating and stimulating clay translocation leading to the formation of an argic horizon below the silt mantles mixing aeolian silt with acid granite regoliths and further illuviation resulted in the formation of alisols while silt contributions to serpentine sediments resulted in development of skeletic luvisols soils receiving very weak input of aeolian silts remain as leptosols cambisols

interpreting high pressure phengite 40 ar 39 ar laserprobe ages an example from saih hatat ne oman new single grain fusion and core rim 40ar 39ar laserprobe phengite data from the saih hatat high pressure terrane in ne oman show that individual samples yield a range of apparent ages which is similar to that previously reported from across the entire terrane the majority of the determined ages are older than the previously reported u pb zircon peak metamorphic age core to rim age variations within individual grains range from no discernible difference across the grain to grains with older cores or rarely older rims some samples manifest all three patterns numerical diffusion modelling shows that due to the peak temperature of ca 550 c the measured apparent ages cannot be explained by simple cooling or by partial retention of crystallisation or detrital ages in an open system the age variability is better explained by spatially and temporally variable open or closed system behaviour at the mm cm scale coupled with pervasive and heterogeneously distributed excess argon anomalously old eclogite phengite 40ar 39ar ages are due either to internally derived 40ar inherited from a k bearing precursor or externally derived 40ar distributed by grain boundary fluids mica rich schists within the eclogite boudins yield younger phengite ages suggesting excess argon was absent or diluted pelites hosting the eclogite appear to have been affected by later fluid ingress during deformation and greenschist facies overprint and yield very variable ages commonly with apparently older rims on younger cores the grain and sample scale age variations measured in saih hatat indicate that the grain boundary network in eclogite pods was not an efficient transfer pathway for argon transport whereas the grain boundary network in the surrounding pelites acted as a more efficient pathway on the timescale of the metamorphic cycle

dust flux estimates for the last glacial period in east central europe based on terrestrial records of loess deposits a review loess paleosol sequences are significant records of the mineral dust cycle of glacial interglacial periods as dust particles give rise to direct and indirect radiative forcing obtaining a reliable picture of the global and regional patterns of mineral dust fluxes during glacial periods can lead to a better understanding of the contribution of mineral dust to past climate changes recent progress in absolute dating of loess deposits in the carpathian basin in east central europe made it possible to provide correct aeolian flux estimates for the last glacial period marine isotope stage mis 2 mass accumulation rates mars from chronological data of 33 loess sites exhibited a wide range of values from 150 to 1422 g m 2 a 1 centered around median and mean values of 338 and 417 g m 2 a 1 marpm10marpm10 and marpm2marpm2 estimates have been also calculated using grain size measurements of many loess samples and loess mars in order to facilitate comparison with models and since particles larger than 10 m have a negligible radiative effect here we show that some previous model simulations of the dust cycle at the last glacial maximum lgm significantly underestimated the real aeolian flux ranges of our estimates marpm10 34 324marpm10 34 324 and marpm2 9 3 88 2gm 2a 1 in east central europe for this reason some simulations of dust induced direct radiative forcing of the lgm climate failed to yield reliable results for this mid latitude region as they have been based on three dimensional dust field models that are not capable of estimating the real aeolian fluxes in central europe a recent global model of top of the atmosphere toa radiative forcing by mineral aerosols at the lgm that has been based on more realistic parameterization of dust sources transport and deposition revealed zonally averaged surface cooling of 2 c for the latitudes of our study area this surface cooling and toa radiative forcing 2 to 3 w m 2 are greater than recognized in other models and draws our attention to the importance of further modeling the impact of mineral dust on lgm climate in order to gain insight into the spatial pattern of radiative forcing and better understand resulting climate response in mid latitude loess regions such as east central europe

indosinian deformation of the songpan garze fold belt northeast tibetan plateau abstract deformation of the songpan garze fold belt southwest china occurred progressively during the indosinian orogeny ca 230 200 ma two phases of south directed deformation are identified d 1 associated with pervasive thickening of the songpan garzi sedimentary pile and detachment of that portion of the fold belt onlapping the yangtze passive margin and d 2 a localized phase of deformation associated with transpressive shortening of the fold belt s southeast margin an arcuate form surface in the southeast fold belt reflects the distribution of d 1 and d 2 structural phases and the diachronous migration of these phases into the fold belt this migration accommodated lateral growth and cumulative sinistral transpression within the fold belt s eastern margin an enigmatic metamorphic complex the so called danba antiform is constrained to have formed during the early stages of the d 2 deformation this was associated with diapiric upwelling of buoyant migmatised basement and domal distortion of the overlying metasedimentary pile

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

loess palaeosol section in sarengrad croatia a qualitative discussion on the correlation of the geochemical and magnetic susceptibility data abstract the sarengrad loess section is located on the south bank of the danube river in the easternmost part of croatia the published lithostratigraphical results including grain size total organic content calcium carbonate content and luminescence dating results are complemented by geochemical content of major and trace elements and acidity and magnetic susceptibility studies throughout the section four palaeosols are intercalated in the loess the oldest hydromorphic one is covered by laminated alluvial sediments and loess the second palaeosol is an argillic dark brown soil with the highest value of the profile and the other two palaeosols are brownish and less developed geochemical characteristics and ms signals of the palaeosols explain both the main characteristics and degree of pedogenesis palaeosol horizons could be clearly distinguished from loess based on the content of major and trace elements and on weathering coefficients such as ba sr and cao na 2 o mgo k 2 o al 2 o 3 irsl age estimates of 86 6 8 6 and 55 3 5 5 ka indicate that most of the middle and upper pleniglacial loess record is missing at the sarengrad section however the loess palaeosol sequence at sarengrad has a very detailed record correlating with mis 4 5

recrystallization or cooling ages in situ uv laser 40ar 39ar geochronology of muscovite in mylonitic rocks the intra grain 40 ar 39 ar age distributions of muscovite from greenschist facies mylonite zones are shown to be sensors of metamorphic history textures compositions and in situ uv laser ablation 40 ar 39 ar data from two extensional shear zones demonstrate that cooling ages can be distinguished from neo or recrystallization ages deformed muscovite porphyroclasts and recrystallized shear band muscovite from the pogallo shear zone ivrea zone southern alps reveal variable intra grain 40 ar 39 ar ages with internal age variations of more than 65 ma the wide range of 40 ar 39 ar ages within compositionally homogeneous grains is consistent with diffusion dominated argon loss controlled by observable intra grain microstructures in contrast intra grain 40 ar 39 ar ages of muscovite fish from proterozoic mylonite of the porsgrunn kristiansand shear zone southern norway display only minor age dispersion and age variations are correlated with changes in muscovite composition the sympathetic age composition correlations in different muscovite microstructures directly relate to sequential neo and recrystallization of muscovite and ultimately provide insight into the protracted recrystallization history during extensional deformation along the porsgrunn kristiansand shear zone

metamorphic rates in collisional orogeny from in situ allanite and monazite dating the prograde sequence of rare earth minerals recorded in metapelites during regional metamorphism reveals a series of irreversible reactions among silicates and phosphates in individual samples from the northern lepontine central alps allanite is partly replaced by monazite at 560 580 c relic allanite retains its characteristic growth zoning acquired at greenschist facies conditions 430 450 c coexisting monazite and allanite were dated in situ to delimit in time successive stages of the barrovian metamorphism in situ sensitive high resolution ion microprobe shrimp u th pb dating of allanite 31 5 1 3 and 29 2 1 0 ma and monazite 18 0 0 3 and 19 1 0 3 ma constrains the time elapsed between 430 450 c and 560 580 c which implies an average heating rate of 8 15 c m y combined with new fission track ages zircon 10 9 ma apatite 7 5 6 5 ma metamorphic rates of the entire orogenic cycle from prograde to final cooling can be reconstructed

loess chronostratigraphy in eastern croatia a luminescence dating approach abstract in eastern croatia impressive loess palaeosol successions up to 30 m thick are exposed along the steep cliffs of the danube river between zmajevac and sarengrad the croatian loess record provides an excellent high resolution archive of climate and environmental change providing evidence for the interaction between accumulation and erosion of aeolian and fluvial sediments during the middle and late pleistocene sedimentological and pedological investigations including granulometry carbonate content and total organic carbon content and infrared optically stimulated luminescence irsl dating were carried out on samples collected from the loess sections at zmajevac erdut and sarengrad the loess successions are intercalated by at least four palaeosols or pedocomplexes which very likely correlate with middle and upper pleistocene interstadials and interglacials in all sediment successions investigated alluvial sediments are intercalated in the loess deposits indicating periods of fluvial activity the stratigraphically youngest alluvial sediments are exposed at the erdut section loess sandwiching these alluvial sediments yielded irsl age estimates of 61 5 6 2 and 53 8 5 4 ka the irsl age estimates give evidence for periods of increased accumulation of dust during the middle and late pleniglacial correlating with oxygen isotope stage ois 3 and ois 2 respectively during the penultimate glaciation and at least the antepenultimate glaciation however it is likely that irsl age estimates 60 ka are underestimated

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

an operational coupled hybrid wave prediction model gono is a numerical wave prediction model used for the preparation of forecasts as well as hind casts it is a hybrid model the wind sea is described in a parametric way but swell is treated in a spectral manner for the wind sea there are two prognostic parameters the zero moment wave height and the mean direction pure wind sea spectra are assumed to have a quasi universal shape above the spectral peak 5 behavior is assumed below the peak a linear frequency dependence is taken the directional dependence is of the cos2 type empirical relations are used to derive the full set of wind sea parameters from the prognostic variables and the wind vector the equations for the prognostic variables are solved on a discrete grid with the help of a simple finite difference scheme for the accurate propagation of swell possibly over large distances a ray technique is used the full two dimensional spectrum is reconstructed for selected grid points for which the results of the ray technique and the wind sea calculations are combined the model is a shallow water model because bottom dissipation effects are taken into account but effects of refraction are disregarded depending on wind speed these effects may be important in areas where the depth is less than about 100 m the model has not been applied in regions with depths less than 15 m therefore extreme shallow water effects are not considered the behavior of the model was studied in quite some detail during the recent sea wave modeling project swamp in a few idealized situations knowledge of the model behavior in more realistic situations stems from its routine operational application runs are made four times a day on a grid covering the north sea and the norwegian sea and the results are monitored continuously presently we have a data base containing about four years of observations and model predictions from this data base we discuss a few interesting storms and we present a statistical analysis of all of the available material as part of this analysis we consider the effect of the quality of the input winds on the model performance

crustal response to continental collisions between the tibet indian south china and north china blocks geochronological constraints from the songpan garze orogenic belt western china we report shrimp u th pb monazite conventional u pb titanite sm nd garnet and rb sr muscovite and biotite ages for metamorphic rocks from the danba domal metamorphic terrane in the eastern songpan garze orogenic belt eastern tibet plateau these ages are used to determine the timing of polyphase metamorphic events and the subsequent cooling history the oldest u th pb monazite and sm nd garnet ages constrain an early barrovian metamorphism m1 in the interval c 204 190 ma coincident with extensive indosinian granitic magmatism throughout the songpan garze orogenic belt a second higher grade sillimanite grade metamorphic event m2 recorded only in the northern part of the danba terrane was dated at c 168 158 ma by a combination of u th pb monazite and titanite and sm nd garnet ages it is suggested that m1 was a thermal event that affected the entire orogenic belt while m2 may represent a local thermal perturbation rb sr muscovite ages range from c 138 100 ma whereas rb sr biotite ages cluster at c 34 24 ma these ages document regional cooling at rates of c 2 3 c myr 1 following the m1 peak for most of the terrane however those parts of the terrane affected by the higher temperature m2 event e g the migmatite zone experienced initially more rapid c 8 c myr 1 cooling after peak m2 before joining the regional slow cooling path defined by the rest of the terrane at c 138 ma regional slow cooling between c 138 and c 30 ma is thought to be the result of post tectonic isostatic uplift after extensive crustal thickening caused by collision of the south and north china blocks the clustering of biotite rb sr ages marks the onset of rapid uplift across the entire terrane commencing at c 30 20 ma this cooling history is shared with many other regions of the tibet plateau suggesting that uplift of the tibet plateau including the songpan garze orogenic belt occurred predominantly in the last c 30 myr as a response to the continuing northwards collision of india with eurasia

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

the characteristics of cultivated soils developed from coastal paleosand korcula island croatia the problem of maintaining soil quality and fertility of soil developed from pleistocene eolian sand deposits arises from improper management and conservation of the highly fragile sandy soil environment the research was undertaken to determine howvarious aspects of cultivated soil fertility can be related to specific pedological and geological factors and which one of these relationships plays an essential role in lumbarda polje korcula island croatia soil survey was done by examining and sampling one hundred locations to the depth of 100 cm within 40 ha of the winegrowing site geostatistical analysis was applied to characterize the spatial variability and produce the soil map of the area soil profiles were sampled for laboratory analysis including physicochemical characteristics and mineralogy modal analysis and petrographic microscopy of soil concretions were conducted as well two soil units su were identified both containing more than 80 sand su1 hypoluvic arenosols and su2 haplic arenosols fao 2006 in su1 reddish brown color originated from fe oxide coatings on sand grains whereas su2 is characterized by the rise of ph with depth and the presence of calcite as a cementing material cation exchange capacity was significantly higher in su2 the documented variability of element content and distribution in the soil profiles indicates differentweathering stages of the sandy layers diagrams of cr v and co v ratios indicate different origin of sand deposits light mineral fraction is dominant in both su most of the sand grains are intensively weathered and well rounded indicating long transportation from the source area the results of mineralogical and geochemical characterization of lumbarda polje grapevine growing site are applicable and useful to future studies that involve fingerprinting regional wines

mesozoic cenozoic evolution of the danba dome songpan garze east tibet as inferred from la icpms u pb and fission track data abstract the eastern margin of the tibetan plateau is a key region to understand the formation and tectonic evolution of the plateau most studies concentrated on the longmen shan range that corresponds to the tectonically very active boundary between the tibetan plateau and the sichuan basin this work addresses the deformation and exhumation pattern in the poorly understood metamorphic danba dome situated at the conjunction between the southern longmen shan range and the major strike slip xian shui he fault the early mesozoic and cenozoic evolution of the dome are then compared to the regional evolution of eastern tibet the about 830 ma zircon u pb ages obtained on the gezong and gongcai gneiss as well as u pb ages on inherited zircons in the early mesozoic granites confirm the occurrence of neo proterozoic magmatic episodes in the danba basement at 800 900 ma and 650 750 ma following the closure of the palaeotethys ocean granitoids were emplaced in the danba metamorphic basement and triassic cover from about 230 ma to about 170 ma the western part of the lian he kau granitic massif emplaced between 210 and 200 ma within the triassic cover sequence of the dome was only slightly affected by the early mesozoic deformation however in the eastern deeper level compartment of the massif ductile deformation occurred between 200 and 190 ma contemporaneous with the onset of the barrovian type metamorphism dated at 200 180 ma that deformation is compatible with the early mesozoic deformation observed in the longmen shan range and with the development of the large scale decollement level in the songpan garze area apatite fission track data then indicate that following the oligocene middle eocene onset of eastward motion of the songpan garze terrane the danba dome developed as a crustal scale antiform during the late miocene early pliocene 10 4 ma the exhumation was controlled by the lian he kau fault a major transpressive structure parallel to the xian shui he fault and the associated manai thrust faults regionally while the oligocene middle miocene exhumation phase seems to have been of regional extent the late miocene to present day phase is localised along the longmen shan range thrusts as well as along the back thrusts formed by the lian he kau manai and associated faults

generation and emplacement of triassic granitoids within the songpan ganze accretionary orogenic wedge in a context of slab retreat accommodated by tear faulting eastern tibetan plateau china the eastern songpan ganze accretionary orogenic wedge northern tibetan plateau is characterized by extensive magmatism coeval with middle to upper triassic closure of the paleotethys ocean along a double subduction system traced by the kunlun anyemaqen suture to the north and the jinsha litang suture to the south new field petrographic and geochemical data on mesozoic plutons intrusive into triassic metasediments of the eastern songpan ganze wedge are presented and integrated in a review of available data for the region three types of granitoids are distinguished i high k calc alkaline granite to granodiorite yanggon maoergai markam sheng meng xue sheng taiyanghe menggu manai dusong xian tagong and jiulong plutons ii high k alkaline granite nyanbaoyeche and rilong plutons and the niuxingou shoshonitic syenite and iii peraluminous s type granite markam and manai leucogranites elemental and isotopic signatures of these granitoids are consistent with the implication of both crustal yangtze craton and songpan ganze metasediments and mantle asthenospheric mantle and metasomatised lithospheric mantle sources based on i the ages of the plutons that are concomitant with the end of the northern and southern subductions of the paleo tethys ii the position of the plutons intrusive in the crustal tectonically accreted units decoupled from the downgoing plate of this double subduction system iii the diversity of their petrological and geochemical signatures we propose that magma emplaced in the songpan ganze accretionary orogenic wedge were generated at the end of the paleotethys closure in a context of slab retreat accommodated by a tear fault along the passive margin of the south china block indeed we argue that this context is the most favourable to trigger synchronous partial melting of i the suprasubduction enriched mantle wedge owing to lowering of the mantle solidus by metasomatism ii the upwelled undepleted asthenospheric mantle into the tear fault owing to decompression iii the metasomatized lithospheric continental mantle of the yangtze craton owing to the temperature increase associated to the asthenospheric upwelling and iv the rocks of the songpan ganze accretionary wedge composed of metasediments and yangtze continental margin basement owing to the combined effects of increased radioactive heat production and mantle heat flux we propose that the concentration of plutons along the eastern margin of the songpan ganze results from focussed migration and emplacement of the granitic magmas guided by the development of a tear fault along the former passive eastern margin of the yangtze craton as a consequence of the paleotethys slab retreat

modelling wind generated surface gravity waves using similarity in a coupled discrete wave model in deep water there is a growing observational consensus that supports an 4 variation for the kitaigorodskii subrange of the high frequency energy spectra we therefore re examine and extend the tma texel marsen arsloe similarity and concepts for shallow water waves which were originally derived for an 5 phillips subrange the similarity for an 4 a subrange is found to closely resemble that of the 5 subrange the former exists when nonlinear transfer due to wave wave interactions dominates over other source terms such as wind input in the energy balance starting with a standard second generation deep water coupled discrete spectral wave model we implement the tma similarity to evaluate our modifications we perform the real and synthetic shallow water tests of the recent swim study thus we intercompare our model with hypas an analogously modified deep water coupled hybrid model and with other wave models which were not based on the tma similarity our model and hypas are found to behave quite similarly in the sloping and flat bottom swim tests compared to the other wave models of the swim intercomparison the more difficult and complex north sea swim hindcast extends this property in some regards

argon behaviour in an inverted barrovian sequence sikkim himalaya the consequences of temperature and timescale on 40ar 39ar mica geochronology abstract 40 ar 39 ar dating of metamorphic rocks sometimes yields complicated datasets which are difficult to interpret in terms of timescales of the metamorphic cycle single grain fusion and step heating data were obtained for rocks sampled through a major thrust sense shear zone the main central thrust and the associated inverted metamorphic zone in the sikkim region of the eastern himalaya this transect provides a natural laboratory to explore factors influencing apparent 40 ar 39 ar ages in similar lithologies at a variety of metamorphic pressure and temperature p t conditions the 40 ar 39 ar dataset records progressively younger apparent age populations and a decrease in within sample dispersion with increasing temperature through the sequence the white mica populations span 2 9 ma within each sample in the structurally lower levels garnet grade but only 0 3 ma at structurally higher levels kyanite sillimanite grade mean white mica single grain fusion population ages vary from 16 2 3 9 ma 2 to 13 2 1 3 ma 2 from lowest to highest levels white mica step heating data from the same samples yields plateau ages from 14 27 0 13 ma to 12 96 0 05 ma biotite yield older apparent age populations with mean single grain fusion dates varying from 74 7 11 8 ma 2 at the lowest structural levels to 18 6 4 7 ma 2 at the highest structural levels the step heating plateaux are commonly disturbed temperatures 600 c at pressures of 0 4 0 8 gpa sustained over 5 ma appear to be required for white mica and biotite ages to be consistent with diffusive open system cooling at lower temperatures and or over shorter metamorphic timescales more 40 ar is retained than results from simple diffusion models suggest diffusion modelling of ar in white mica from the highest structural levels suggests that the high temperature rocks cooled at a rate of 50 80 c ma 1 consistent with rapid thrusting extrusion and exhumation along the main central thrust during the mid miocene

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

on the loss of 40ar from muscovite during polymetamorphism abstract recent laser studies have documented 40ar concentration gradients in micas that correspond to age variations of tens to hundreds of millions of years a fundamental problem to interpretation of such variations is to evaluate whether they represent loss via lattice diffusion or alternatively loss during chemical reactions and deformation new data of this study and comparisons with previous work suggest that muscovite is far less prone to lose accumulated 40ar via lattice diffusion during overprinting events than has been inferred previously kyanite muscovite assemblages in proterozoic schist along the eastern flank of the green mountain massif central vermont appalachians formed during proterozoic metamorphism at ca 1 1 ga and were remetamorphosed in the greenschist facies during both taconian ca 465 ma and acadian ca 390 ma events the overprinting events resulted in deformation of earlier kyanite and muscovite growth of chemically and isotopically distinct rims on earlier muscovite and growth of neoblastic muscovite and chloritoid with each event at inferred minimum temperatures of ca 425 c laser spot analyses of the grenville muscovite range from 988 11 ma in the centers of porphyroclasts to 397 7 ma along rims ages younger than 750 ma occur only on the deformed edges of porphyroclasts and in highly deformed areas within crystals parts of early formed muscovite that escaped late deformation and chemical reaction seem remarkably retentive of accumulated 40ar laser spot analyses along the outer 100 m of an undeformed growth face yield ages close to the timing of proterozoic metamorphism and cooling the present study suggests episodic heating events are ineffective for producing measurable diffusive argon loss along the edges of large muscovite crystals ca 1 mm in diameter particularly in comparison with deformation and reaction mechanisms and are unlikely to result in complete 40 ar 39 ar age resetting of such crystals the results of this study further emphasize that the argon diffusivity in muscovite is lower than commonly considered in previous work

the effects of retrograde reactions and of diffusion on 40ar 39ar ages of micas the effects of metamorphic reactions occurring during decompression were explored to understand their influence on the ar ar ages of micas monometamorphic metasediments from the lepontine alps switzerland reached lower amphibolite facies during the barrovian metamorphism related to the collision between european and african adria continental plates mineral assemblages typically composed of garnet plagioclase biotite muscovite and paragonite or margarite were screened for petrological equilibrium to focus on samples that record a minimum degree of retrogression x ray diffraction data indicate that some mineral separates prepared for ar ar stepwise heating analysis are monomineralic whereas others are composed of two white micas muscovite with paragonite or margarite or biotite and chlorite in monomineralic samples ar ar and ar ar proportional to ca k and cl k ratios did not change and the resulting ages can be interpreted unambiguously in mineral separates containing two white micas ca k and cl k ratios were variable reflecting non simultaneous laboratory degassing of the two heterochemical ar reservoirs these ratios were used to identify each ar reservoir and to unravel the age in a chlorite margarite biotite calcschist equilibrated near 5608c and 0 65 gpa biotite margarite and muscovite all yield ages around 18ma at slightly higher grade 560 5808c 0 8 0 9 gpa the assemblage muscovite paragonite plagioclase is in equilibrium and remains stable during retrogression in this case muscovite and paragonite yield indistinguishable ages around 16 5ma above 5908c paragonite was mostly consumed to form plagioclase 45908c whereby the relict mica yields an age up to 5 6 ma younger than muscovite this partial or total resetting of the ar clock in paragonite is interpreted to reflect plagioclase growth during decompression where biotite is present within this same assemblage it systematically yields a younger age than muscovite by 0 5 2 ma however these biotites all show small amounts of retrograde chlorite formation we conclude that even very minor chloritization of biotite is apparently a more effective process than temperature in resetting the ar clock as is the formation of plagioclase from paragonite decomposition multi equilibrium thermobarometry is an excellent means to ensure that equilibrium in investigated samples is preserved and this helps to obtain geologically meaningful metamorphic ages however even samples passing such equilibrium tests may still show retrograde effects that affect the ar retention of micas a more robust interpretation of such ar ar results may require use of a second geochronometer such as u pb on monazite

complex structural pattern of the alpine dinaridic pannonian triple junction due to the political boundaries between the central european countries on one hand and the thick tertiary cover in the pannonian basin on the other the eastward continuation of the alpine and dinaridic units has been ambiguous and poorly documented based on comparative analyses the aim of the present paper is to define the pre tertiary structural units in the junction area of the alpine dinaridic and pannonian regions in the sw part of the pannonian basin and to draw conclusions on the continuation of the alpine and dinaridic units according to diagnostic characteristics of the periadriatic lineament system the balaton lineament system may be considered as its direct eastern continuation north of the periadriatic balaton lineament system the transdanubian range unit due to its pre tertiary paleogeographic setting shows mainly south alpine facies relations however its present structural position is identical to that of the upper austroalpine nappes between the periadriatic balaton and zagreb zemplin lineament systems heterogeneous structural units are juxtaposed forming the sava composite unit in the northern part of this composite unit non metamorphosed nappes occur which can be considered the eastern continuation of the south alpine units these nappes are overthrust onto internal dinaridic units in the tertiary the zagreb zemplin mid hungarian lineament separates the sava unit from the tisza unit showing close affinity to the tethyan margin of the eurasian plate during the early stage of the alpine evolution

late quaternary tephra derived paleosols in central italy s carbonate apennine range stratigraphical and paleoclimatological implications abstract detailed stratigraphical pedological and geochronological 14c dating research was carried out on numerous sections located in the carbonate apennine range of central italy two paleosols late pleistocene pedomarker a and holocene pedomarker b in age were recognized as having developed from air fall pyroclastic material given their special properties and widespread distribution both soils represent valuable markers in the late quaternary stratigraphy of central italy information about the climatic conditions that have influenced their pedogenesis through time has been obtained pedomarker a formed under temperate wet conditions related to the last interstadial fluctuations of the pleniglacial its development ceased after ca 30 ka because of the onset of last glacial maximum dry cold conditions pedomarker b formed at the beginning of the holocene under udic and perudic soil moisture regimes its development ceased in some localities because of a change towards a drier climate after ca 4 5 ka petrographic and geochemical characteristics of the parent materials are discussed and correlations with the campanian ignimbrite pedomarker a and neapolitan yellow tuff pedomarker b both related to activity in the phlegrean fields are proposed

graphitization in a high pressure low temperature metamorphic gradient a raman microspectroscopy and hrtem study the graphitization of carbonaceous material cm in a high pressure metamorphic gradient is characterized along a cross section in the schistes lustres formation western alps along this 25 km cross section both the cm precursor and the host rock lithology are homogeneous and the prograde evolution of the pressure temperature metamorphic conditions from the lower blueschist facies 13 kbar 330 c to the eclogite facies 20 kbar 500 c is tightly constrained by literature data raman microspectroscopy shows that at the micrometre scale this process is progressive and continuous with increasing metamorphic grade and that the structure of cm is very sensitive to temperature variations at the nanometre scale hrtem the cm is composed of a mixture of a microporous phase and an onion ring like phase both known as non graphitizing under the effect of temperature at ambient pressure the hp lt graphitization produces structurally and microtexturally heterogeneous cm with increasing metamorphic grade the graphitization of the two types of cm proceeds up to the triperiodic graphite stage because of microtextural and structural changes that are specific to each type of cm the microporous material is progressively transformed into graphite through a macroporous transitional stage in this case graphitization mainly occurs on the pore walls as a result of pore growth in the case of concentric onion ring like material graphitization occurs in the regions with the largest radius of curvature i e on the outer part of the ring in comparison with 1 bar experiments pressure seems to induce microtextural changes which allows the subsequent structural modifications of the starting material

dating polygenetic metamorphic assemblages along a transect across the western alps multichronometric analyses were performed on samples from a transect in the french italian western alps crossing nappes derived from the brianconnais terrane and the piemonte liguria ocean in an endeavour to date both high pressure hp metamorphism and retrogression history twelve samples of white mica were analysed by 39ar 40ar stepwise heating complemented by two samples from the monte rosa nappe 100 km to the ne and also attributed to the brianconnais terrane one sm nd and three lu hf garnet ages from eclogites were also obtained white mica ages decrease from c 300ma in the westernmost samples zone houille re reaching c 3008c during alpine metamorphism to 548ma in the internal units to the east which reached c 5008c during the alpine orogeny the spatial pattern of eocene k ar ages demonstrates that si rich hp white mica records the age of crystallization at 47 48ma and retains ar at temperatures of around 5008c paleocene early eocene lu hf and sm nd ages recording prograde garnet growth before the hp peak confirm eclogitization in eocene times petrological and microstructural features reveal important mineralogical differences along the transect all samples contain mixtures of detrital syn d1 and syn d2 mica and retrogression phases d3 in greatly varying proportions according to local variations in the evolution of pressure temperature fluid activity deformation p t a d conditions samples from the zone houille re mostly contain detrital mica the abundance of white mica with si46 45 atoms per formula unit increases eastward across the whole traverse phengitic mica grown during hp metamorphism defines the d1 foliation syn d2 mica is more si poor and associated with nappe stacking exhumation and hydrous retrogression under greenschist facies conditions syn d1 phengite is very often corroded overgrown by or intergrown with syn d2 muscovite most importantly syn d2 recrystallization is not limited to s2 schistosity domains micrometrescale chemical fingerprinting reveals muscovite pseudomorphs after phengite crystals which could be mistaken for syn d1 mica based on microstructural arguments alone the cl k ratio in white mica is a useful discriminator as d2 retrogression was associated with a less saline fluid than eclogitization as petrology exerts the main control on the isotope record constraining the petrological and microstructural framework is necessary to correctly interpret the geochronological data described in both the present study and the literature our approach which ties geochronology to detailed geochemical petrological and microstructural investigations identifies 47 48ma as the age of hp formation of syn d1 mica along the studied transect and in the monte rosa area cretaceous apparent mica ages which were proposed to date eclogitization by earlier studies based on conventional thermochronology are due to ar inheritance in incompletely recrystallized detrital mica grains the inferred age of the probably locally diachronous greenschist facies low si syn d2 mica ranges from 39 to 43ma coexistence of d1 and d2 ages and the constancy of non reset d1 ages along the entire transect provides strong evidence that the d1 white mica ages closely approximate formation ages volume diffusion of ar in white mica activation energy e 250 kj mol 1 pressure adjusted diffusion coefficient d 050 03 cm2 s 1 has a subordinate effect on mineral ages compared with both prograde and retrograde recrystallization in most samples

subduction related origin of the 750 ma xuelongbao adakitic complex sichuan province china implications for the tectonic setting of the giant neoproterozoic magmatic event in south china abstract the xuelongbao plutonic complex in the eastern margin of the tibetan plateau is dated at 748 7 ma using the shrimp zircon u pb method and represents part of the neoproterozoic igneous assemblage of south china rocks in the complex include tonalite and granodiorite and have sio2 ranging from 62 0 to 74 8 wt and al2o3 from 14 3 to 20 9 wt their na2o contents range from 4 2 to 6 7 wt and k2o from 0 47 to 1 96 wt indicating that they belong to the na series these rocks show chondrite normalized ree patterns depleted in hree and variably enriched in lree they have positive sr and negative nb and ti anomalies in the primitive mantle normalized trace elemental spider diagram their sr contents range from 320 to 780 ppm and y contents are lower than 10 ppm resulting in high sr y ratios 52 320 characteristic of typical adakites their end t and initial sr isotopic compositions range from 0 36 to 2 88 and from 0 7033 to 0 7054 respectively the geochemical features of the xuelongbao plutonic complex are consistent with an origin from adakitic magmas that were likely derived from partial melting of a subducted oceanic slab together with arc signatures of other granites and mafic intrusions in the region the 750 ma xuelongbao adakitic complex provides evidence for a major subduction related neoproterozoic magmatic event of south china

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

deformation partitioning and foliation reactivation during transpressional orogenesis an example from the central longmen shan china progressive localization of strain within the songpan garze fold belt at the eastern margin of the tibetan plateau has resulted in the formation of the wenchuan maowen shear zone and preservation of excellent overprinting relationships between three major phases of ductile and semi ductile deformation these relationships show that deformation in the eastern songpan garze fold belt evolved from crustal thickening during sw directed compression d1 to localized sinistral transcurrent shear d2 and finally to increasingly localized high temperature d3p and retrograde d3r reverse shear in response to se directed compression both d2 and d3 deformations were co planar and reactivation of the s2 foliation led to the formation of a composite s2 3 fabric however inclusion trails in garnet porphyroblasts preserve evidence of a transition between these strike slip and reverse shear end members indicating that d2 and d3 were part of an episode of progressive transpressional shear metamorphic grade increases from chlorite to kyanite zone within the wenchuan maowen shear zone reaching syn d3p peak conditions of 600 c and 10 kbar the d3p and d3r reverse shears were responsible for tectonic exhumation of the shear zone and resulted in the formation of retrograde d3r high strain zones along the margins of the xuelongbao granite and adjacent to the wenchuan maowen fault

a shallow water intercomparison of three numerical wave prediction models swim three operational shallow water wave models are intercompared for two artificial experiments and verified for a severe storm hindcast with the objectives of further understanding the effects of the parametrization of shallow water wave processes in numerical models the models used are the hypas max planck institute and gono knmi coupled hybrid models and the bmo meteorological office coupled discrete model which are all briefly described in the first case depth dependent fetch limited wave growth in a steady wind is examined in the second case a steady onshore wind is specified over an idealized constant slope coastal shelf and the stationary wave spectra at various depths are intercompared for the third case the wind fields for the north sea storms of 18 26 november 1981 were accurately reconstructed and used by each model in its operational configuration to produce a wave hindcast for this period in case 1 the gono and bmo models exhibit similar behaviour in the evolution of energy and peak frequency whereas hypas displays less depth attenuation and little variation in peak frequency in case 2 the energy values at different shelf depths are approximately as predicted in case 1 for hypas though rather higher for bmo and gono however gono and hypas show little change in peak frequency with depth here whereas bmo wave spectra become double peaked with a wind sea peak migrating to higher frequencies in shallower waters in case 3 the hindcasts all models produce qualitatively similar results the time series of wave height and period agree well with measurements bmo and hypas predicting correct energy levels except at storm peaks and gono generally overpredicting both at lower energy levels and in a duration limited strong wind case the r m s error in wave height at the southern shallow water verification site is 0 5 m for all models and varies between 0 9 m gono and 1 5m hypas at the northern deep water site some wave spectra are presented and the directional relaxation of wind sea in each model is illustrated the results of cases 1 and 2 are readily explained by the formulation of shallow water processes adopted in each model but it is difficult to isolate and identify these mechanisms in the measured or modelied spectra from the hindcast it is suggested that future studies involving detailed verification and intercomparison of wave models should be confined to more carefully designed wave measuring experiments so that less ambiguous results are obtained

eolian contribution to geochemical and mineralogical characteristics of some soil types in medvednica mountain croatia abstract six pedological profiles were analyzed above five typical lithological units in medvednica mountain to determine the effect of eolian additions to the soil composition as well as the possible influence of relief vegetation cover and anthropogenic input on the dynamics of pedogenesis bedrock composition was defined using petrographic thin sections and chemical analyses major and trace element contents whereas pedological sedimentological and geochemical characteristics of six cross sections were determined by chemical major and trace element contents mineralogical modal analysis and grain size analysis soils developed on sedimentary bedrock mollic rendzic leptosols calcaric and albic luvisol sceletic mostly originate from weathering of siliciclastic detritus that was exposed to oxidization before diagenesis furthermore soils on metasiltstone marble and lithothamnium limestone exhibit similar modal and geochemical composition and element distribution across the soil profile in contrast soils developed on igneous bedrock originate mostly from weathering of minerals of the first weathering cycle and thus abound with chemically less resistant minerals and less mobile elements however all profiles contain higher concentrations of lead with respect to bedrock indicating airborne contamination

tectonic activity in the croatian part of the pannonian basin abstract three main stages in structural development of the sw pannonian basin are differentiated the onset of extensional tectonics between the oligocene and the early miocene main extensional processes in the early and middle miocene and prevailing transpression in the pliocene and quaternary the neotectonic phase is given special attention in this paper structural fabrics allow to subdivide the area into three large structural zones corresponding to the western southern and central marginal part of the pannonian basin in croatia these zones are bounded by important faults the periadriatic drava fault the medvednica fault zone and the southern marginal fault of the pannonian basin the recent displacements within the dinarides and the eastern alps form the boundary conditions for active transpressional deformation in the western marginal part of the pannonian basin dextral transcurrent displacement is evident in the zone of the periadriatic drava wrench fault the formation of the new types of structures is observed especially in zones of compression along the faults narrowing of the area between the sava and drava rivers causes structural changes in the marginal parts of the corresponding basins i e in the areas close to the slavonian mts recent tectonic activity is marked by the occurrence of earthquakes which are most common in the northwestern part of croatia the spatial distribution of hypocentres and of seismotectonically active zones is used to reconstruct probable displacements and the structural style of deformation in depth the earthquake sources in the vicinity of the medvednica fault and the periadriatic drava fault are given special attention

using white mica 40ar 39ar data as a tracer for fluid flow and permeability under high p conditions tauern window eastern alps new single grain fusion muscovite and paragonite 40ar 39ar data from eclogite and blueschist units exposed in the tauern window eastern alps yield a range of apparent ages from 90 to 23 ma these apparent ages are generally older than expected for 40ar 39ar cooling ages given constraints from other geochronological systems such as rb sr and u pb numerical ar in muscovite diffusion models for tauern window nappe p t paths in an open system suggest that 40ar 39ar ages should lie between 29 and 24 ma and that they should constrain cooling and decompression following the post high pressure barrovian overprint the measured ranges of apparent 40ar 39ar dates suggest that the assumption of open system behaviour is not valid for this region the local and or regional generation of fluid during exhumation promoted pervasive recrystallization of high pressure lithologies throughout the tauern window to greenschist and amphibolite facies assemblages the old apparent 40ar 39ar white mica dates in all lithologies are therefore interpreted as being due to inefficient removal of grain boundary ar by the grain boundary fluids during the barrovian overprint due to high ar concentrations or limited connectivity or both this caused spatially mm scale and temporally variable fluxes of ar out of and probably into white mica in both metasedimentary and metabasic lithologies

mineralogical and geochemical indicators of the polygenetic nature of terra rossa in istria croatia abstract terra rossa in istria is situated on the jurassic cretaceous paleogene carbonate plain and is considered a polygenetic reddish soil which bears typical terra rossa fe oxide characteristics e g fe d and fe d fe t the difference in particle size mineralogy and geochemistry observed between terra rossa and the insoluble residue of limestones and dolomites clearly indicates that the additions of external materials might have diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in istria terra rossa is clay and silty clay composed of quartz plagioclase k feldspar micaceous clay minerals illitic material and mica kaolinites kl d and kl chlorite vermiculite low charge vermiculite or high charge smectite mixed layer clay minerals other than illitic material hematite goethite and xrd amorphous inorganic compound calcite dolomite and boehmite are sporadically present and are of local importance kaolinites and illitic material are dominant clay mineral phases in the clay fraction of all terra rossa from istria kaolinite which does not form intercalation compounds with dimethylsulfoxide dmso is the dominant mineral phase in fine clay and is considered predominantly authigenic rather then inherited from parent materials neither the content and particle size distribution nor the bulk and clay mineralogy of the insoluble residue of limestone and dolomite support development of terra rossa entirely by dissolution of carbonate rock if terra rossa has developed only from the insoluble residue of limestone and dolomite its clay content due to weathering should be higher than that in the insoluble residues which is not the case plagioclase was found only in one insoluble residue while all terra rossa samples contain this mineral moreover insoluble residues do not contain vermiculite which was observed in small amounts in clay fraction of all terra rossa samples na 2 o k 2 o 100 zr nb and zr ti 1000 ratios in the majority of terra rossa samples are much higher than in the insoluble residue of limestones and dolomites which also supports external material influence in the genesis of terra rossa materials other than the insoluble residue of limestones and dolomites which might have contributed to terra rossa are loess sediments whose deposition was very important recurrent process in istria probably since the early middle pleistocene and flysch sediments which extended much more southwards from its present position analyses performed indicate that both loess older than that of the upper pleistocene age and flysch might have contributed in the genesis of terra rossa

air ice ocean momentum exchange part ii ice drift a model was constructed to estimate ice floe trajectories the model considers the balance of atmosphere and ocean drag forces on ice floes including skin and body drag forces from wind waves and currents discussion of air ice and water ice skin stresses water ice form stress and wave radiation stress is presented estimates are presented for the ice drift in a variety of hypothetical situations i as a function of ice floe diameter thickness and concentration ii in wave and no wave situations and iii in constant wind forcing and time varying wind forcing situations the model is shown to be consistent with wave and ice observations collected during the labrador ice margin experiment 1987 on the grand banks during relatively high wind situations combining this model with the wave scattering model of part i allows estimation of 1 the effect of wave scattering attenuation on ice floe trajectories and the ice edge and 2 the effect of ice floe drift on the wave spectra thus an enhanced modeling of wave and ice dynamics is achieved

spatial variation in meso cenozoic exhumation history of the longmen shan thrust belt eastern tibetan plateau and the adjacent western sichuan basin constraints from fission track thermochronology abstract the ne trending longmen shan thrust belt marking the eastern margin of the tibetan plateau adjacent to the sichuan basin is characterized by the paradox of high topographic gradients but low convergence rates and thus critical for understanding of geodynamic processes involved in the eastward growth of the plateau many low temperature thermochronological studies focused on the central and southern portions of the longmen shan and western sichuan basin to investigate the cenozoic exhumation history of the eastern tibetan plateau but little work has been done on their northern portions furthermore the spatial variation in both cenozoic and mesozoic thermal histories of this region has been poorly documented in this paper zircon zft and apatite aft fission track analyses for samples collected from three transects and three boreholes covering the northern central and southern longmen shan and the western sichuan basin provide new data demonstrating several cooling events in this region since the indosinian deformation they occurred during the late triassic 200 ma at the end of early cretaceous 100 ma during the early cenozoic 60 40 ma the early miocene 20 25 ma and the late miocene 9 14 ma respectively on regional scale the longmen shan experienced a slow cooling between the mesozoic and early cenozoic followed by a rapid cooling during the late cenozoic when the rapid regional exhumation began at 10 ma with a sharp increase in exhumation rate from 0 2 mm yr up to 0 9 mm yr locally comparison of zft and aft ages shows that during the mesozoic the northern segment of the longmen shan belt cooled more rapidly than the central and southern segments while younger aft ages indicate more rapid exhumation in central and southern segments of the belt during the late cenozoic similar trend is demonstrated within the western sichuan basin where the onset of exhumation changes from 45 ma in the northern portion to 20 25 ma in the central and southern portions of the basin the thermochronological data reveal that the yingxiu beichuan and guanxian anxian faults have accommodated significant differential exhumation by thrusting activity and associated denudation with a greater amount of differential exhumation from north to south we propose that the major cause for the rise in topography and rapid exhumation in the longmen shan thrust belt during the late cenozoic is the thrusting activities integrated with the regional uplift of the eastern tibetan plateau a process unrelated to the channel flow within the lower crust

tracing the origin of loess in hungary with the help of heavy mineral composition data abstract heavy mineral composition of the fine sand fraction in the hungarian loess sediments provides important data about the closer sources of the loess in the carpathian basin quantitative detrital heavy mineral compositions of 216 loess loess like sediment and paleosol samples were compared to each other and to recent fluvial sands and different cenozoic sands and sandstones of hungary using statistical methods cluster analysis principal component analysis and discriminant analysis usually garnet is the most frequent detrital heavy mineral in the studied loess sections followed by chlorite magnetite epidote and amphiboles old loess and young loess have similar compositions indicating uniform or similar sources based on the similarities the garnet rich loess sediments could originate from aeolian reworking of the floodplain sediments of the danube and other rivers of transdanubia and the local cenozoic sands of the uplifting transdanubian central range and transdanubian hilly region the biotite and tourmaline rich loess in south transdanubia and the loess with high pyroxene content in the north hungarian range had some material from nearby sources weathered granitoids and volcanic rocks respectively or sediments of local rivers which carried detritus of these rocks the new results presented in this paper confirm numerous earlier ideas about the origin of loess in the carpathian basin but also suggest newly identified sources of the loess particles at several locations

geochemical characterization and origin of southeastern and eastern european loesses serbia romania ukraine abstract the loess paleosol sections of batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine were geochemically characterized based on discriminant analysis of major and trace elements the ratios of al ti fe ti and al fe the a cn k ternary plot and element enrichment depletion relative to the average composition of the upper continental crust the origin of the loess material in the southern pannonian basin vojvodina the lower danube basin dobrudja and the dnieper area was evaluated by comparison with the representative element composition of possible source areas and by considering the geomorphodynamic setting also the background values of the initial magnetic susceptibility of the loesses were taken into account for the lower danube basin dobrudja and the ukraine paleowind direction was reconstructed based on the geographic distribution of sandy soil texture and dunes related to river systems finally loesses were evaluated as possible samples of the average upper continental crust our results show that danube and dnieper loess areas can be clearly distinguished the former reveal higher al and fe contents the latter higher si zr hf content and indications of effective mineral and grain size sorting we can confirm that vojvodina loess originated from danube alluvial material and loess of the dnieper area from glaciofluvial sediments of the fennoscandinavian ice sheet the dobrudja loess derived also predominantly from danube alluvium but shows significant contribution of a second loess source probably the glaciofluvial sediments of the ukraine this was forced by northerly katabatic winds from the fennoscandinavian ice sheet whereas wnw winds prevailed in the western walachian plain the studied loesses reflect the average composition of the upper continental crust yet biases exist due to selective mineral element enrichment and depletion in the course of previous sedimentary recycling phases respectively material of all studied loess deposits seems to derive originally from sedimentary rocks

considerations regarding the definition of a geochemical baseline of elements in the surficial materials in areas differing in basic geology abstract the problem of a geochemical baseline in areas differing in basic geology was studied by comparing the results of regional geochemical mapping programmes undertaken in finland and lithuania using different sample media and a variety of analytical methods the authors discuss issues relevant to the definition of a geochemical baseline most of the differences in geochemical baselines between lithuania and finland are due to the dissimilarities in basic geology which in lithuania is controlled by palaeozoic and mesozoic sedimentary rocks but in finland by archaean and proterozoic metamorphic and intrusive rocks other important factors are the geological processes that after the last glaciation created the present surficial materials in finland for instance the abundances of potentially harmful elements derived from crystalline bedrock tend to be higher than in lithuania however in both countries element concentrations are higher in finely grained marine and lacustrine sediments than in glacial till and they are also higher in the finer grain size fractions than in the coarser fractions of till samples only a small proportion of the total heavy metal concentrations is bioavailable thus the baseline concentrations depend not only on the basic geology but also on sample material collected its grain size and the extraction method

when can muscovite 40ar 39ar dating constrain the timing of metamorphic exhumation abstract metamorphic cooling rates determined using muscovite 40 ar 39 ar ages underpin many tectonic models but are based on several simplifying approximations we demonstrate that a number of these approximations especially those relating to the assignment of a single closure temperature might not hold for certain metamorphic scenarios and particularly for metamorphism during rapid orogenic cycles using numerical diffusion models that include a recently reported significant pressure dependence of ar diffusion in muscovite we systematically interrogate the approximations associated with linking 40 ar 39 ar dates to pressure temperature histories the results of the simulations are presented in a simple graphic form allowing evaluation of the pressure temperature pt regions in which ar diffusion is efficient and hence those in which the muscovite may yield true 40 ar 39 ar cooling ages we suggest that a robust method for determining whether metamorphic muscovite 40 ar 39 ar ages relate to the timing of cooling involves 1 the determination of the pt conditions and relative timing of muscovite crystallisation during the metamorphic cycle 2 the collection of high precision and high spatial resolution 40 ar 39 ar data from muscovite grains and 3 the comparison between analytical data and numerical diffusion models which test different post crystallisation pressure temperature histories

diffusion in mineral geochronometers present and absent abstract in solid state physics and materials science fick s law diffusion is a well established process in earth sciences laboratory experiments on garnet olivine and other anhydrous minerals do document the intra grain element concentration gradients that follow the functional form required by fick s law natural gradients in minerals have rarely been analyzed with the necessary spatial resolution reports of actual observations of diffusion profiles of element concentrations are rare in the literature and diffusion profiles of isotope ratios in minerals used for geochronology are absent an in depth re examination of recent and older literature suggests that isotope transport in minerals is instead often dominated by fluid mediated retrogression reactions imaging microtextures by cathodoluminescence or back scattered electron maps provides ubiquitous evidence of patchy or dendritic replacement structures which correspond to multiple growth stages in zircon monazite muscovite biotite k feldspar etc the u pb k ar and rb sr systems in these partly retrogressed minerals show isotopic inheritance that survived the retrograde reactions at least in part in close correspondence with the petrologic relicts depending on the relative rates of the petrological processes relevant for isotope transport geochronometers can be grouped in two classes class i thermochronometers are those for which the diffusivity of a given radiogenic isotope is faster than the rate of dissolution and or reprecipitation and class ii hygrochronometers are those for which aqueous dissolution reprecipitation is the faster process all of the abovementioned geochronometers for which patchy dendritic textures formed by diachronous mineral generations and isotopic inheritance were observed must be assigned to class ii class ii samples in petrologic equilibrium can but need not record purely thermal diffusion of daughter isotopes the isotope record of class ii minerals in petrologic disequilibrium being controlled by inheritance and retrogression reactions depends chiefly on the reaction promoting factors water activity and strain the dependence of class ii mineral ages on thermal diffusion is subordinate and never unique

the relationship between k ar mineral ages mica grainsizes and movement on the moine thrust zone nw highlands scotland muscovite and biotite separated from moine schists close to the moine thrust zone yield a range of k ar ages incompatible with the simple cooling regime previously proposed for the caledonides of northern scotland differences of only 1 ma between muscovite and biotite of the same grainsize contrast with differences of 12 13 ma between the 125 200 m and 250 500 m grainsize fractions this is contrary to the normally accepted dominance of mica type over grainsize effects dynamic recrystallization of the micas during early deformation associated with the moine thrust zone is thought to play a role as important as temperature in determining the k ar ages the conclusions drawn have important implications for the use of uplift and cooling rates derived from the absolute k ar closure temperatures of micas close to thrust zones although the k ar ages from micas with diameters greater than 200 m are not reproducible the data can be used to show that deformation associated with thrusting commenced between c 443 ma and c 435 ma and that the thrust zone was active until at least 422 ma ago

k ar dating of an early middle pleistocene distal tephra in the interglacial varved succession of pianico sellere southern alps italy abstract a distal tephra has been discovered in the varved lacustrine succession of pianico sellere one of the best preserved interglacial sedimentary assemblages south to the italian alps the k ar dating of the juvenile glass fraction gives an age of 779 13 ka this age is supported by the observation of a reverse paleomagnetic direction probably recorded before the matuyama brunhes transition dated at 780 ka the tephra belongs to the shoshonite series and the volcanic source is likely located in southern italy the age of 779 13 ka is much older than that of the riss wurm interglacial which was previously suggested on the basis of geological setting and macroflora studies the pianico tephra represents the first stratigraphical marker of an interglacial so far unsettled in the southern alps

p t t estimation of deformation in low grade quartz feldspar bearing rocks using thermodynamic modelling and 40ar 39ar dating techniques example of the plan de phasy shear zone unit brianconnais zone western alps pressure temperature time p t t estimates of the syn kinematic strain at the peak pressure conditions reached during shallow underthrusting of the brianconnais zone in the alpine subduction zone was made by thermodynamic modelling and 40ar 39ar dating in the plan de phasy unit se of the pelvoux massif western alps the dated phengite minerals crystallized syn kinematically in a shear zone indicating top to the n motion by combining x ray mapping with multi equilibrium calculations we estimate the phengite crystallization conditions at 270 50 c and 8 1 2 kbar at an age of 45 9 1 1 ma combining this p t t estimate with data from the literature allows us to constrain the timing and geometry of alpine continental subduction we propose that the brianconnais units were scalped on top of the slab during ongoing continental subduction and exhumed continuously until collision

influence of dissolution reprecipitation reactions on metamorphic greenschist to amphibolite facies mica 40 ar 39 ar ages in the longmen shan eastern tibet linking ages to metamorphic stages in rocks that have experienced low to medium grade metamorphism can be particularly tricky due to the rarity of index minerals and the preservation of mineral or compositional relicts the timing of metamorphism and the mesozoic exhumation of the metasedimentary units and crystalline basement that form the internal part of the longmen shan eastern tibet sichuan china are for these reasons still largely unconstrained but crucial for understanding the regional tectonic evolution of eastern tibet in situ core rim 40ar 39ar biotite and u th pb allanite data show that amphibolite facies conditions 10 11 kbar 530 c to 6 7 kbar 580 c were reached at 210 180 ma and that biotite records crystallization rather than cooling ages these conditions are mainly recorded in the metasedimentary cover the 40ar 39ar ages obtained from matrix muscovite that partially re equilibrated during the post peak p metamorphic history comprise a mixture of ages between that of early prograde muscovite relicts and the timing of late muscovite recrystallization at c 140 120 ma this event marks a previously poorly documented greenschist facies metamorphic overprint this latest stage is also recorded in the crystalline basement and defines the timing of the greenschist overprint 7 1 kbar 370 35 c numerical models of ar diffusion show that the difference between 40ar 39ar biotite and muscovite ages cannot be explained by a slow and protracted cooling in an open system the model and petrological results rather suggest that biotite and muscovite experienced different ar retention and resetting histories the ar record in mica of the studied low to medium grade rocks seems to be mainly controlled by dissolution reprecipitation processes rather than by diffusive loss and by different microstructural positions in the sample together our data show that the metasedimentary cover was thickened and cooled independently from the basement prior to c 140 ma with a relatively fast cooling at 4 5 0 5 c ma between 185 and 140 ma since the lower cretaceous the metasedimentary cover and the crystalline basement experienced a coherent history during which both were partially exhumed the mesozoic history of the eastern border of the tibetan plateau is therefore complex and polyphase and the basement was actively involved at least since the early cretaceous changing our perspective on the contribution of the cenozoic geology

mesozoic cenozoic tectonothermal evolution of the eastern part of the tibetan plateau songpan garze longmen shan area insights from thermochronological data and simple thermal modelling we present a synthesis of the tectonic and thermochronological evolution of the eastern tibet since the triassic the long term cooling histories obtained on magmatic and metamorphic rocks of the south songpan garze kunlun and yidun blocks are similar showing a very slow and regular cooling during late jurassic and cretaceous confirming the suspected lack of major tectonic events between c 150 and 30 ma the exhumation linked to the tertiary growth of the tibetan plateau initiated around 30 ma and concentrates at the vicinity of the major tectonic structures exhumation rates increased again from about 7 ma in the longmen shan to interpret this very slow cooling rate between late jurassic and early cenozoic from granites of this area we use a simple 1d thermal model that takes into account the thermal properties of both sediments and crust the results suggest that 1 high temperature 500 8c can be kept over a long period of time 2 during cretaceous cooling is mostly controlled by the thermal properties of sediments of continental origin and 3 the initial late triassic rapid cooling rate was caused by the large thermal contrast between the granite body and the sedimentary rocks rather than by a high exhumation rate

dehydration of dioctahedral aluminous phyllosilicates thermodynamic modelling and implications for thermobarometric estimates we propose a solid solution model for dioctahedral aluminous phyllosilicates accounting for the main compositional variations including hydration observed in natural smectites interlayered illite smectite illites and phengites from diagenetic to high grade metamorphic conditions the suggested formalism involves dehydrated micas and hydrated pyrophyllite like thermodynamic end members with these end members the equilibrium conditions of quartz water k bearing mica like phyllosilicates of fixed 2 1 composition are represented by a line in p t space along which the interlayer water content varies the relevant thermodynamic properties required for the calculation of equilibrium conditions were derived using a set of 250 natural data of known maximal temperature and pressure conditions which covers a range between 25 c and few mpa to 800 c and 5 gpa the temperatures calculated at fixed pressure with our model are in fair agreement with those reported in the literature for the 250 natural data at low temperature and pressure the amount of interlayer water in k deficient phengite and illite is predicted to reach 100 of the apparent vacancies which is consistent with previous values reported in the literature although the amount of interlayer water is predicted to decrease with pressure and temperature it is calculated to be significant in k deficient phengite from lt hp pelites metamorphosed at about 350 c 10 kbar the presence of molecular water in the interlayer site of such phengites has been confirmed by ftir mapping its implications for p t estimates are discussed

emplacement of the longmen shan thrust nappe belt along the eastern margin of the tibetan plateau abstract the topographic descent from the eastern margin of the tibetan plateau to the sichuan basin passes through the longmen shan thrust nappe belt which is sub divided by six nw dipping major listric thrusts with accompanying duplexes and imbricate fans into five large scale nappes each nappe has its own stratigraphic and deformational features in the inner longmen shan longmen mountains allochthonous nappe units have incorporated both mesoproterozoic basement and sinian neoproterozoic to triassic cover sequences as thick skinned horses whereas in the frontal longmen shan sinian cretaceous cover sediments have been stripped from the basement as thin skinned fold and thrust sheets including the extensively distributed klippen structures pre thrusting extension during devonian to middle late triassic times resulted in syn depositional normal faults structural inversion of these faults initiated the peng xian guan xian basement complex jiuding shan and tangwangzhai nappes during the early episode of the indosinian orogeny norian to rhaetian this was followed by episodic thrusting during latest triassic to early cretaceous times to develop the guan xian an xian and southeastern marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the thrust nappe belt during a late miocene reactivation of the pre existing thrusts differential thrusting occurred across the thrust nappe belt

heterogeneous 40ar distributions in naturally deformed muscovite in situ uv laser ablation evidence for microstructurally controlled intragrain diffusion abstract micas are commonly used in 40 ar 39 ar thermochronological studies of variably deformed rocks yet the physical basis by which deformation may affect radiogenic argon retention in mica is poorly constrained this study examines the relationship between deformation and deformation induced microstructures on radiogenic argon retention in muscovite a combination of furnace step heating and high spatial resolution in situ uv laser ablation 40 ar 39 ar analyses are reported for deformed muscovites sampled from a granitic pegmatite vein within the siviez mischabel nappe western swiss alps penninic domain brianconnais unit the pegmatite forms part of the variscan 350 ma alpine basement and exhibits a prominent alpine s c fabric including numerous mica fish that developed under greenschist facies metamorphic conditions during the dominant tertiary alpine tectonic phase of nappe emplacement furnace step heating of milligram quantities of separated muscovite grains yields an 40 ar 39 ar age spectrum with two distinct staircase segments but without any statistical plateau consistent with a previous study from the same area a single 3 5 mm muscovite porphyroclast fish was investigated by in situ uv laser ablation a histogram plot of 170 individual 40 ar 39 ar uv laser ablation ages exhibit a range from 115 to 387 ma with modes at approximately 340 and 260 ma a variogram statistical treatment of the 40 ar 39 ar results reveals ages correlated with two directions a highly correlated direction at 310 and a lesser correlation at 0 relative to the sense of shearing using the highly correlated direction a statistically generated kriging method age contour map of the 40 ar 39 ar data reveals a series of elongated contours subparallel to the c surfaces which where formed during tertiary nappe emplacement similar data distributions and slightly younger apparent ages are recognized in a smaller mica fish the observed intragrain age variations are interpreted to reflect the partial loss of radiogenic argon during alpine 35 ma greenschist facies metamorphism one dimensional diffusion modelling results are consistent with the idea that the zones of youngest apparent age represent incipient shear band development within the mica porphyroclasts thus providing a network of fast diffusion pathways during alpine greenschist facies metamorphism the incipient shear bands enhanced the intragrain loss of radiogenic argon the structurally controlled intragrain age variations observed in this investigation imply that deformation has a direct control on the effective length scale for argon diffusion which is consistent with the heterogeneous nature of deformation

a wave prediction system for real time sea state forecasting the considerable increase in requirements for sea state forecasts in recent years has led to development of a numerical wave forecasting system in the meteorological office this is based on a wave prediction model which combines the advantages of the parametric technique in predicting a growing wind sea with those of a discrete spectral model in the swell regime this is done using a discrete model by parametrizing the nonlinear interactions term in the energy balance equation in a way that reproduces the behaviour of the parametric model the main difficulty with the method is in the separation of wind sea and swell required to do this propagation of wave energy is performed using an accurate form of the lax wendroff integration scheme a two term representation of wave growth is used whilst dissipation is modelled by an explicit whitecapping mechanism shallow water effects are included by representations of shoaling refraction and bottom friction the operational numerical atmospheric model at the meteorological office provides the wind input an extensive program of evaluation has shown that the results provide high quality guidance with 24 hour forecasts of wave height having a r m s error ranging from 0 6 m in the southern north sea to 1 0 m east of the shetlands

timing of granite emplacement and cooling in the songpan garze fold belt eastern tibetan plateau with tectonic implications abstract new u pb and rb sr geochronology on syn and post orogenic granites provide constraints on the timing of major tectonic events in the songpan garze fold belt west sichuan china the ma nai granite was probably syn kinematic with the main deformation and yields an age of 197 6 ma that is interpreted as an upper age limit of the indosinian event zircons and apatites from the post kinematic rilonguan granite also yield jurassic ages 195 6 and 181 4 ma the post orogenic markam massif gives two ages of 188 1 and 153 3 ma both granites are undeformed and cut structures in the triassic sedimentary rocks these results demonstrate that the major deformation and decollement tectonics in the songpan garze fold belt occurred prior to the early jurassic the wide range of ages obtained for post kinematic granites from early jurassic to late jurassic suggests that locally magmatic activity persisted for a long time at least 50 ma after the indosinian compressional tectonism no tertiary ages have been obtained suggesting that these granites were not affected strongly by the india asia collision

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision

origin weathering and geochemical composition of loess in southwestern hungary abstract loess geochemistry generally reflects paleo weathering conditions and it can be used to determine the average composition of the upper continental crust ucc in this study major and trace element concentrations were analyzed on loess samples from southwestern hungary to determine the factors influencing their chemical compositions and to propose new average loess compositions all studied loess samples had nearly uniform chemical composition suggesting similar alteration history of these deposits chemical index of alteration values 58 69 suggested a weak to moderate degree of weathering in a felsic source area typical non steady state weathering conditions were shown on the al 2 o 3 cao na 2 o k 2 o patterns indicating active tectonism of the alpine carpathian system during the pleistocene whole rock element budgets were controlled by heavy minerals derived from a felsic magmatic or reworked sedimentary provenance geochemical parameters indicated that dust particles must have been recycled and well homogenized during fluvial and eolian transport processes

differential exhumation in response to episodic thrusting along the eastern margin of the tibetan plateau abstract thermochronological data from the songpan ganze fold belt and longmen mountains thrust nappe belt on the eastern margin of the tibetan plateau in central china reveal several phases of differential cooling across major listric thrust faults since early cretaceous times differential cooling indicated by distinct breaks in age data across discrete compressional structures was superimposed upon a regional cooling pattern following the late triassic indosinian orogeny 40ar 39ar data from muscovite from the central and southern longmen mountains thrust nappe belt suggest a phase of differential cooling across the wenchuan maouwen shear zone during the early cretaceous the zircon fission track data also indicate differential cooling across a zone of brittle re activation on the eastern margin of the wenchuan maouwen shear zone during the mid tertiary between 38 and 10 ma apatite fission track data from the central and southern longmen mountains thrust nappe belt reveal differential cooling across the yingxiu beichuan and erwangmiao faults during the miocene forward modelling of apatite fission track data from the northern longmen mountains thrust nappe belt suggests relatively slow regional cooling through the mesozoic and early tertiary followed by accelerated cooling during the miocene beginning at ca 20 ma to present day regional cooling is attributed to erosion during exhumation of the evolving longmen mountains thrust nappe belt lmtnb following the indosinian orogeny differential cooling across the wenchuan maouwen shear zone and the yingxiu beichuan and erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults thermochronological data from the longmen mountains thrust nappe belt reveal a greater amount of differential exhumation across thrust faults from north to south this observation is in accord with the prevalence of proterozoic and sinian basement in the hanging walls of thrust faults in the central and southern longmen mountains the two most recent phases of reactivation occurred following the initial collision of india with eurasia suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the lmtnb

u th pb dating of collision in the external alpine domains urseren zone switzerland using low temperature allanite and monazite article i nfo dating metamorphism in external domains of orogenic belts is a challenging task due to the few chronometers available and common inheritance or disturbance of the isotopic systems at low temperature metamorphic con ditions in the external domains of the central alps urseren zone the occurrence of distinct populations of monazite and allanite in one single outcrop offers a unique chance to evaluate the potential of these two ree minerals to date successive metamorphic stages within a collisional cycle the studied outcrop locality of garvera exposes mesozoic metasediments that were metamorphosed under greenschist facies conditions t b 450 c under these conditions ree mineral grains or domains are typically small 5 50 m and in this case also occur as porphyroblast in pelites at the contact with carbonate layers or veins allanite grains n200 m based on the texture and mineral assemblages ree mineral growth conditions were attributed to be detrital mnz1 syn kinematic mnz2 and aln1 post kinematic at the thermal peak aln2 and retrograde during late stage deformation mnz3 to constrain temporally the successive crystallisation conditions ree minerals have been dated using shrimp ion microprobe u th pb analyses show that the alpine ree minerals have a high th u and while most of the 206 pb is non radiogenic f206 that can reach up to 99 for allanite th pb ages can be obtained using 206 pbc corrected th pb isochron the age of different generations of allanite and monazite constrains the timing of successive collisional stages for the prograde accretion at 22 5 1 5 ma mnz1 and aln1 thermal peak at 19 3 2 0 ma aln2 and late stage hydrothermal veining at13 6 1 4 ma mnz3 these novel geochronological data confirmtheregional diachroneity throughthe cen tral alps with younger ages burial thermal peak and exhumation toward the external domains the similarity betweenmetamorphicagesofsamplestakenintheurserenzoneandthenearbycrystallinemassifssuggeststhat themetasedimentarycoveroftheurserenzoneremainedcloselyjuxtaposedtotheexternalcrystallinebasement during the alpine collision cycle the monazite age of the late stage vein testifies for active tectonic deformation at 13 6 1 5 ma which likely played a crucial control on the exhumation of the external massifs in the middle miocene

multiple discriminant analysis of the drava river alluvial plain sediments three discriminant function models are raised and cross compared in order to distinguish geochemical patterns characteristic for the drava river floodplain sediments based on data representing total element concentrations in samples collected from alluvium a terrace t and unconsolidated bedrock b at the border of a floodplain four element clusters emerged accounting for discrimination between the referred groups of sediments the most prominent is contaminant carbonate cluster characteristic for alluvium the other two are silicate cluster typical for unconsolidated geological substrate neogene sedimentary rocks and naturally dispersed heavy metal cluster separating terrace from the former two groups models introducing depth intervals and single profiles as grouping criteria reveal identical sediment heavy metal matrices the second important issue of this paper is possibility of reclassification of samples originally assigned to one of the a priori defined groups of sediments based on established geochemical pattern the mapped geological units can be reconsidered by the post hoc assignments to a different group if geological border between alluvium and terrace or between terrace and bedrock can not be established geologically with absolute certainty