age of emplacement of the schistes lustres nappe alpine corsica abstract structural studies in the schistes lustres nappe west of bastia corsica demonstrate the existence of a tectonic melange in which km scale blocks and smaller lozenges of basement granite gneiss thick layered marble and dismembered mesozoic ophiolite are enveloped in a matrix of calc schist and blueschist the main s1 foliation is developed in both block and matrix and is concordant with lithologie contacts blueschist facies metamorphism was syn kinematic with the main foliation the s1 in the schistes lustres was refolded about ene wsw trending tight similar and monoclinal fold axes f2 these second folds verge to the southeast and show km scale axial culminations and depressions that are reflected by topography and residual bouguer gravity anomalies parautochthonous hercynian basement tenda corte complex beneath the western edge of the schistes lustres nappe contains a mylonitic foliation which is concordant with the main foliation in the schistes lustres the intensity of deformation in the basement decreases away from this contact and undeformed granites are found 3 km to the west whole rock samples of the deformed basement immediately beneath the schistes lustres yield an rb sr isochron diagram n 4 which has an age of 105 8 ma 1 and initial 87 sr 86 sr ratio of 0 7228 0 0005 1 this result is more precise than our preliminary age and initial ratio estimate of 98 14 and 0 7296 0 0068 respectively cohen et al 1979 it is similar to a recently published mid cretaceous 90 ma 40ar 39ar age from glaucophane mineral separates we interpret this date as the age of a metamorphic overprint related to the emplacement of the schistes lustres nappe and associated ophiolites the formation of the main foliation and blueschist facies metamorphism these results indicate that the mid cretaceous blueschist facies metamorphism documented in the western alps formerly extended farther south of its present terminus the data are consistent with mid cretaceous obduction of tethyan oceanic crust onto the present day eastern continental margin of corsica we postulate that during eocene early oligocene time a polarity flip occurred outboard of the obducted crust and a new southfacing subduction zone developed this change in polarity was responsible for the development of southeast vergent second folds and for the resetting of 40ar 39ar and k ar geochronologic clocks described in the literature

nonlinear frequency dependence of the effective seabottom acoustic attenuation from low frequency field measurements in shallow water hamilton s seabed geo acoustic model which is widely accepted predicts that the attenuation of sound in marine sediments increases linearly with frequency over the full frequency range of interest in ocean acoustics a few hertz to megahertz however biot stoll s physics based seabed geo acoustic model predicts that the bottom attenuation should exhibit non linear frequency dependence particularly in sandy bottoms since the publication of previous papers zhou j acoust soc am 78 1003 1009 1985 kibblewhite ibid 86 716 738 1989 more low frequency field data collected from different coastal zones around the world have shown inconsistencies with the often used linear frequency dependence this paper attempts to support the non linear frequency dependence of sea bottom attenuation through a review of shallow water acoustic field measurements with a special emphasis on the 50 1000 hz frequency range the relevant measurements include bottom reflection loss sound transmission loss dispersion analysis vertical coherence of both propagation and reverberation normal mode spatial filtering and optimum frequency and transition range of sound propagation a non linear frequency dependence of equivalent bottom acoustic attenuation derived from these measurements will be introduced work supported by onr and nnsf of china

the maritime alps arc in the ligurian and tyrrhenian systems abstract after late eocene meso alpine collision between the european and adria plates the maritime alps underwent further deformations linked to the apennine orogenesis and consistent with a stress field developed during anticlockwise rotation the western limit of the rotated sector is east of the argentera massif and to the southwest represents the northwestern margin of the post eocene ligurian sphenochasm the sinistral rotation of the maritime alps initially occurred contemporaneous with the opening of the ligurian basin about 30 19 ma and probably continued during the subsequent opening of the tyrrhenian basin about 10 0 ma the rotating block comprises the northwestern part of the adria indenter and a part of the paleo european plate namely the maritime alps corsica and sardinia if a convenient configuration is assumed for the moho of the adria margin and suitable poles are chosen for subsequent rotations then a simplified model of rigid body can explain the rotation structures in the maritime alps the apennines and po plain subsurface compressional arcs the late foreland directed transport of nappes in the western alps the presence of extensional and dextral transcurrent structures and the general uplift of the lithospheric mantle between the ligurian sea and the ivrea body as to the causes of rotation two alternatives subduction or asthenosphere uplift are discussed chronological and mechanical arguments seem to favour the latter

sequential inversion of modal data for sound attenuation in sediment at the new jersey shelf this paper presents a method for estimating bottom geoacoustic properties especially the sediment attenuation from information contained in normal modes of a broadband signal propagating modes are resolved using the time warping technique applied to signals from light bulb sound sources deployed at ranges of 5 and 7 km in the shallow water 06 experiment a sequential inversion approach is designed that uses specific features of the acoustic data that are highly sensitive to specific geoacoustic model parameters the first feature is the modal group speed which is inverted for seabed sound speed density and sediment thickness the second feature is the modal depth function for inverting receiver depths the third feature is related to the modal coefficient spectra and this is inverted for source depth and sediment attenuation in each subsequent stage estimates from the previous stage s are used as known values the sequential inversion is stable and generates estimates for the geoacoustic model parameters that agree very well with results from other experiments carried out in the same region notably the inversion obtains an estimated attenuation of 0 078 db in the band 120 180 hz for the de watered marine sediment characteristic of the continental shelf at the site

low frequency sound speed and attenuation in sandy seabottom from long range broadband acoustic measurements a joint china u s underwater acoustics experiment was conducted in the yellow sea with a very flat bottom and a strong and sharp thermocline broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57 2 km and a quarter circle with a radius of 34 km two inversion schemes are used to obtain the seabottom sound speed one is based on extracting normal mode depth functions from the cross spectral density matrix the other is based on the best match between the calculated and measured modal arrival times for different frequencies the inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods the first method involves measuring the attenuation coefficients of normal modes in the second method the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios the third method is based on finding the best match between the

provenance of oligocene synorogenic sediments of the ligurian alps nw italy inferences on belt age and cooling history mineral chemistry 40ar 39ar geochronology on white micas and apatite fission track thermochronology aftt are applied here to study the provenance of the synorogenic molare formation lowermost unit of the tertiary piedmont basin clastic sequence the molare formation was deposited during transgression onto the ligurian alps nappe stack in the early oligocene depositional facies show that clastic distribution remained transversal with local sources located just landward from the coastline phengite mineral chemistry together with 40ar 39ar data clearly shows two distinctive source areas each one mirroring the composition of the basement directly beneath the clastic sequence amphibole mineral chemistry allows second order provenance distinctions within each sector reflecting heterogeneous metamorphic evolution of the bedrock complexes integrated 40ar 39ar dating and aftt suggest that following a fast cooling exhumation episode of the ligurian alps during the oligocene very little net uplift has since occurred this is due to a period of general subsidence from the oligocene late miocene followed by comparable uplift from late miocene pliocene to the present in general our data provide an image of the ligurian alps during the oligocene which is very similar to the present day one

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

and mg fe si al2 compositional control on argon behaviour in high pressure white micas a continuous laser probe study from the dora maira nappe of the internal western alps italy abstract high pressure white micas from a restricted area in the dora maira nappe of the western alps italy were analyzed by the conventional 40 ar 39 ar bulk sample step heating method and by the step heating and the spot fusion 40 ar 39 ar continuous laser probe techniques on single grains high si ferich phengites from fine grained gneisses display homogeneous 35 40 ma plateau and spot fusion ages consistent with the upper eocene 40 ar 39 ar phengite ages documented over the whole internal western alps in contrast phengite separates and single grains of high si and mg rich to intermediate composition selected from metapelitic and mg rich mica schist samples yield older discordant apparent ages even when sampled in the same outcrop as the fine grained gneisses these local age variations are interpreted to reflect primarily an increasing ar retentivity with increasing mg content in phengites in metapelite derived white micas the isotopic discordance is marked by 1 1 a characteristic bulk sample upward convex spectrum shape 2 2 single grain disturbed age spectra 3 3 a systematic radially outward decrease in spot ages across individual mica cleavage planes and 4 4 strong grain to grain spot age variations in rock sections 1 1 in mg rich mica schists the isotopic discordance is observed as a reproducible upward convex bulk sample age spectrum with high 140 ma intermediate apparent ages 2 2 upward convex single grain age spectra and 3 3 irregular intra and intergrain age gradients on geochemical grounds it is argued that the isotopic discordance occurring in the metapelites is mainly controlled by the compositional changes introduced by the mg fe si al2 celadonitic re equilibration of the high pressure phengites during greenschist overprinting in mg rich phengites this chemical re equilibration may induce ar loss below their presumed higher blocking temperature a model of ar behaviour in high pressure white micas is proposed which explains the age variations recorded throughout the different lithologies in terms of a simple interaction between the mg fe compositional control on ar retentivity and the mg fe si al2 modifications occurring in phengites during progressive overprinting

estimating marine sediment attenuation at low frequency with a vertical line array this paper presents a method of determining the compressional wave attenuation in marine sediment from a short range measurement the data were collected on a vertical line array at a range of 230 m during the shallow water 2006 experiments the sediment attenuation is extracted from the signal strength ratio of the sea bottom reflection to a sub bottom reflection at different frequencies from 1 75 to 3 15 khz linear frequency dependence of the attenuation is found from the estimation the sediment attenuation estimate is lower than the values estimated from the inversions of acoustic field data previously done in the vicinity

excess argon in k ar and ar ar geochronology the k ar and ar ar dating techniques occasionally produce anomalously old ages attributed to excess argon and such data is often rejected as not offering any insight into the age thermal history or geochemistry of the rock however improvements in the quantification of argon geochemistry now provide a framework to model excess argon in both open and closed systems solubility data for argon in hydrous fluids melts and emerging data for minerals can be used to understand the behaviour of excess argon and provide valuable insights into the environment in which the samples cooled to their argon retention or closure temperature treating excess argon as a trace element also throws light on its behaviour in minerals above the closure temperature in deeply buried dry systems such as eclogites blueschists granulites and even in the lithospheric mantle extremely low partition coefficients between k feldspar and hydrous fluid phases predict lower excess argon susceptibility than micas and this is observed in fluid poor systems variation of partition coefficients can lead to excess argon in fluids being introduced into minerals or removed from minerals as grain boundary fluids change during flow through a rock however excess argon can also be introduced or removed from minerals by varying temperature without the need for fluid flow high mineral melt and mineral fluid partition coefficients are also the reason why excess argon is often concentrated in inclusions within minerals partition coefficients between minerals and hydrous fluids as low as 10 6 lead fluid inclusions to dominate the radiogenic argon budget particularly in low potassium minerals melt inclusions are less dominant but become critical in dating younger samples

middle eocene to early miocene sedimentary evolution of the western lombardian segment of the south alpine foredeep italy the main steps of the sedimentary evolution of the west lombardian south alpine foredeep between the eocene and the early miocene are described the oldest is a bartonian carbonate decrease in hemipelagic sediments linked with an increase in terrigenous input possibly related to a rainfall increase in the alps between the middle eocene and the early chattian a volcanoclastic input is associated with an extensional tectonic regime coeval with magma emplacement in the southern central alps and with volcanogenic deposits of the european foredeep and apennines suggesting a regional extensional tectonic phase leading to the ascent of magma during late eocene to early oligocene two periods of coarse clastic sedimentation occurred probably controlled by eustasy the first during late eocene fed by a local south alpine source the second earliest oligocene in age supplied by the central alps in the chattian a strong increase in coarse supply records the massive erosion of central alps coupled with a structures growth phase in the subsurface it was followed by an aquitanian rearrangement of the alpine drainage systems suggested by both petrography of clastic sediments and retreat of depositional systems while subsurface sheet like geometry of aquitanian turbidites marks a strong decrease in tectonic activity

inherited argon in a pleistocene andesite lava 40ar 39ar incremental heating and laser fusion analyses of plagioclase by using 40 ar 39 ar incremental heating and laser fusion techniques xenocrystic plagioclase was discovered in a late pleistocene andesitic lava that erupted through the andean cordillera inherited argon in the xenocrysts is as much as 450 times older than the host lava the age of which is independently known and is an obstacle to dating the lava by using a whole rock sample the xenocrysts are impossible to identify from petrography or chemical parameters such as their k ca ratios holocrystalline groundmass carefully separated from plagioclase and other phenocrysts gives an accurate 40 ar 39 ar age for the lava the xenocrysts could not have been degassed for more than several days in the magma and probably were assimilated from paleozoic rocks buried under kilometers of mesozoic and tertiary arc rocks composing the cordillera in central chile the required magma ascent velocity on the order of kilometers day is extraordinarily high compared to the 10 4 km day minimum implied by the 226 ra excess in continental arc lavas these data permit magma migration and storage in the mantle and lower crust for as much as thousands of years followed abruptly by rapid ascent to the surface

the early stages of the alpine collision an image derived from the upper eocene lower oligocene record in the alps apennines junction area the upper eocene lower oligocene sediments deposited in the eastern part of the tertiary piedmont basin in northern italy provide a complete record of the unroofing of the alpine orogenic prism during the early stages of exhumation in the ligurian sector from late priabonian till late rupelian time the sediments in the study area were derived from two different sources one characterised by white micas with sib6 5 pfu and permian 40 ar 39 ar ages 270 ma and the other characterised by white micas with sin7 pfu and eocene oligocene 40 ar 39 ar ages 32 50 ma the first source is considered to be indicative of low pressure metamorphic rocks that covered the hp rocks of the ligurian alps and were completely eroded by chattian time from this time on the study area started to record the first input from western alpine sources characterised by a larger span of ages with a more frequent eoalpine signal thus sediments deposited in the eastern part of the tertiary piedmont basin contain the only available evidence of rocks belonging to high crustal levels in the alpine orogenic prism that were not affected by the alpine overprint these data also provide time constraints to the poorly dated first conglomerates deposited in this area 40 ar 39 ar geochronology reveals a minimum age of 33f1 4 ma for the pianfolco conglomerates in the type locality and of 31 4f3 5 ma for the borbera conglomerates d 2004 elsevier b v all rights reserved

some constraints on the kinematics of the tertiary piemonte basin northwest italy abstract an analysis of fault slip data in oligocene and miocene sediments of the piemonte basin northwest italy shows that a nearly continous sweep of shortening directions exists between the northern apennines and the maritime alps transport directions change from n s to nw se near the western termination of the northern apennines through w e in the ligurian alps to sw ne in the maritime alps n nw directed thrusting along the front of the monferrato culmination fits within this general kinematic framework in addition basement thrusts and transform faults were not sealed by an oligocene transgression but remained active throughout the oligocene and miocene these data provide a distinct constraint on the tertiary kinematics and dynamics of the alps apennine system

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

40ar 39ar laserprobe direct dating of discrete deformational events a continuous record of early alpine tectonics in the pelagonian zone nw aegean area greece abstract the pelagonian zone of the hellenides which occurs in the northwestern aegean region of the eastern mediterranean contains remnants of a high pressure metamorphic belt which subsequently underwent localized reworking during low temperature deformational events formation of alpine deformational structures in the ossa massif northern pelagonian zone occurred at metamorphic temperatures which failed to reset most pre alpine 40ar 39ar cooling ages in muscovite porphyroclasts the low metamorphic temperatures at alpine times have preserved the argon isotopic signature in white mica bearing deformational structures which allows direct dating of these structures and refinement of the alpine tectonic history in the region after separation of carefully selected and characterized mica generations application of sensitive 40ar 39ar laserprobe dating has resulted in a continuous record of the early alpine tectonic history of the ossa massif from the early cretaceous well into the eocene the early alpine history of the ossa massif records cooling of basement thrust slices which are mostly hercynian granites and metamorphics below ca 350 c by 100 ma while lower tectonostratigraphic levels of the basement had already cooled below these temperatures at around ca 285 ma blueschist facies mylonite fabrics related to a top to ene direction of tectonic transport yield ages as old as 84 5 3 3 ma exhumation of the blueschist facies sequences was initiated at ca 54 ma and involved tectonic activity along blueschist facies and greenschist facies mylonites zones final wsw ward transport of the metamorphic sequence across the structurally lowest and supposed autochthonous series occurred at around 45 ma and resulted in termination of the ductile deformation history in the studied area this study confines the onset of high pressure metamorphism in the pelagonian zone to an interval between 100 ma and 85 ma and has shown that high pressure metamorphism had terminated by ca 54 ma the recognition of an early to middle alpine cycle lasting over 30 million years and involving crustal shortening high pressure metamorphism exhumation and subsequent crustal shortening is a key contribution to a better understanding of the early alpine tectonic history of the aegean region and eastern mediterranean

bayesian geoacoustic inversion in a dynamic shallow water environment this paper presents results for matched field bayesian geoacoustic inversion of multitonal continuous wave data collected on the new jersey continental shelf to account for effects of significant spatial and temporal variation of the water column sound speed the sound speed profile was represented by empirical orthogonal functions data error information for the inversion was estimated from multiple time windows of the data inversion results for the sediment sound speeds at three ranges are in excellent agreement with the ground truth

two stage erosion and deposition in a continental margin setting an 40ar 39ar laserprobe study of offshore detrital white micas in the norwegian sea detrital white micas from a restricted region of the norwegian sea have been analysed by the 40ar 39ar laserprobe examining the ages of individual white mica grains from offshore triassic jurassic and cretaceous sandstones reveals a narrow range of detrital white mica ages 369 424 ma moreover there is an inverse relationship between sediment age and detrital white mica age with the triassic sands containing a larger proportion of younger white micas and the cretaceous sands containing the oldest white micas in addition residence times of the detritus which is the age of the sediment subtracted from the age of the detrital white mica range from c 150 to c 300 ma for the triassic and cretaceous sands respectively the inverse age relationships combined with the large residence times for these stratigraphic levels can best be explained by an erosion deposition model involving at least two stages taking into account previous provenance studies in the lofoten region of the norwegian sea these new data suggest that detritus shed initially from the exhuming caledonian nappes of nw norway in late silurian early devonian times was deposited in intramontane basins that were themselves subsequently unroofed and re eroded from permo triassic times this caused the recycling of the caledonian detritus from the devono carboniferous basins and led to the inverted detrital age distribution ovserved in the triassic cretaceous sediments examined in this study while sedimentary recycling is not a surprising feature for mesozoic basins in the north and norwegian seas this study documents a previously untapped method 40ar 39ar laserprobe provenance studies by which to identify its effect and extent

uplift history of thrust belts an approach based on fission track data and thermal modelization abstract a tentative method to reconstruct the uplift history in thrust belts from fission tracks ft data is proposed as it is well established that the thermal gradient varies considerably both with time and depth in the evolution of mountains a time dependent thermal model is used to infer the temperature time history of sampled rocks given parameters such as the thrust thickness 7 t and the erosion v t randomly chosen in an acceptable range among a great number of trials monte carlo simulation this technique is applied to the corsican island which is a good example of alpine thrust belt the most striking result is that a large range of different possible erosion histories can explain the same set of ft data and that further geological constraints are required to give reasonable bounds in the case of corsica information on the minimum eroded thickness and on the relative amplitude of erosion phases gives sufficient constraints on the erosion uplift history since thrusting

40ar 39ar laser probe dating of detrital micas from the montgomery creek formation northern california clues to provenance tectonics and weathering processes generic provenance data from the montgomery creek formation northern california even in light of paleocurrent data and regional stratigraphic patterns do not uniquely establish its sediment source dating individual detrital mica grains mica with the sup 40 ar sup 39 ar laser probe shows that the source area for the upper montgomery creek included the idaho batholith unaltered muscovite grains yield data that provide limits on timing and rate of uplift of the batholith combined with paleocurrent data the inferred provenance constrains the timing of tectonic rotation in the southeastern klamath orogen dating variably altered biotite grains elucidates the age and environment of alteration and establishes a distinct source for some of the lower montgomery creek

quantifying the uncertainty of geoacoustic parameter estimates for the new jersey shelf by inverting air gun data this paper describes geoacoustic inversion of low frequency air gun data acquired during an experiment on the new jersey shelf hybrid optimization and bayesian inversion techniques based on matched field processing were applied to multiple shots from three air gun data sets recorded by a vertical line array in a long range shallow water geometry for the bayesian inversions full data error covariance matrix was estimated from a set of consecutive shots that had high temporal coherence and small spatial variation in source position the effect of different data error information on the geoacoustic parameter uncertainty estimates was investigated by using the full data error covariance matrix a diagonalized version of the full error covariance and a diagonal matrix with identical variances the comparison demonstrated that inversion using the full data error information provided the most reliable parameter uncertainty estimates the inversions were highly sensitive to the near sea floor geoacoustic parameters including sediment attenuation of a simple single layer geoacoustic model the estimated parameter values of the model were consistent with depth averaged values over wavelength scales of a high resolution geoacoustic model developed from extensive ground truth information the interpretation of the frequency dependence of the estimated attenuation is also discussed

seabed acoustics of a sand ridge on the new jersey continental shelf acoustic measurements were made on a sand ridge on the new jersey continental shelf data collected on two l arrays separated by 20km from a single multi frequency tow suggest small horizontal environmental variability values for the sound speed structure of the seabed are extracted by first applying a geo acoustic inversion method to broadband and narrowband acoustic data from short range sources then a parabolic equation algorithm is used to properly include the bathymetry and sub bottom layering finally the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long range transmission loss data in the 50 3000hz band

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

provenance of cretaceous synorogenic sandstones in the eastern alps constraints from framework petrography heavy mineral analysis and mineral chemistry abstract the detrital components of cretaceous sedimentary rocks in the northern calcareous alps reflect the early alpine geodynamic evolution of the austroalpine microplate two contrasting source areas are distinguished on the base of light and heavy mineral analysis the first source area is located at the southeastern margin of the austroalpine and is composed of palaeozoic sediments and metamorphic rocks mesozoic carbonate rocks and ultrabasic rocks derived from the suture zone of the vardar meliata ocean the second source area is located in the northwest in a lower austroalpine position near the transpressive plate margin that juxtaposes austroalpine and penninic units this source area comprises palaeozoic low grade metamorphic rocks including high pressure hp rocks late palaeozoic meta sediments mesozoic carbonate rocks and ultrabasic rocks from obducted slices of penninic oceanic crust chemical analyses of detrital white mica amphibole and garnet support the discrimination between the two source areas tourmaline chemistry calls for a significant amount of metasedimentary rocks in the source area granitoid rocks and high grade metamorphic rocks are rare blue amphibole phengite and chloritoid composition suggest the erosion of lower blueschist facies rocks in the northwestern source area we suggest a modified model of austroalpine valanginian to coniacian tectono sedimentary evolution which is based on 1 an onset of subduction of the penninic ocean no earlier than late cretaceous 2 deposition of the analyzed sedimentary rocks in piggyback basins and 3 a reconstruction of provenance as proposed in this study

the role of hydrodynamic forcing sediment transport processes and bottom substratum in the shoreward development of posidonia oceanica meadow abstract this paper investigates the combined role of hydrodynamic forcing sediment transport processes and sea bottom features in determining the location of the meadow upper limit of the endemic mediterranean seagrass posidonia oceanica for this purpose an approach including extreme wave analysis and numerical modelling is applied to two sandy beach systems located in southern sardinia italy information about bathymetry p oceanica meadow extension and bottom features has been made available by previous published studies based on the 30 year long noaa hindcast dataset a wave climate analysis is carried out to identify the incoming storm wave conditions 1 year return period to be simulated with the delft3d model package the simulation results extend the current knowledge highlighting the importance of wave induced hydrodynamic parameters as limiting factors for the survival of p oceanica meadows in particular the results suggest that on sandy substrata the meadow upper limit lies well offshore of the surf zone in areas with little morphological activity where the wave orbital velocities associated to storms are on the order of 0 8 m s and the mean current magnitude does not exceed 0 5 m s on rocky bottoms the p oceanica meadow can extend up to the outer surf zone of storms and is thus able to colonize shallow areas subject to stronger hydrodynamic forcings than those observed on sand this difference in the plant tolerance to wave forcing depending on the substratum type shows how both hydrodynamic and geological factors play a key role in defining the environmental conditions for the development of seagrass meadows

statistical analysis of sound transmission results obtained on the new jersey continental shelf experiments have been conducted near the site of amcor borehole 6010 on the new jersey shelf to evaluate propagation predictability in sandy shallow water environments the influence of a nonlinear frequency dependence of the sediment volume attenuation in the uppermost sediment layer at this location is examined previously it was determined that a frequency power law exponent of 1 5 was required for the best modeling of experimental results over the band 50 1000hz the approach here references the attenuation to an accepted value at 1khz and makes extensive comparisons between measurements and calculations to determine a power law exponent of 1 85 0 15

staircase 40 ar39ar spectra of fine grained white mica timing and duration of deformation and empirical constraints on argon diffusion staircase 40 ar 39 ar spectra of 2 to 6 m white micas in ductile carbonate mylonites morcles doldenhorn nappe switzerland record ages between 32 and 13 ma these ages are within independent geochronologic and biostratigraphic time limits for the beginning and ending of deformation of this fold thrust nappe we interpret these data to record protracted white mica neocrystallization and growth during low temperature ductile deformation such that the differences between the maximum and minimum ages in the 40 ar 39 ar spectra record the time span over which mica formed and grew we have modeled the argon concentrations in these micas taking into account the thermal history of the nappe mica growth and diffusional loss of argon our results indicate that available experimental data underestimate the activation energy for argon diffusion in muscovite and that the retentivity of argon in white mica is greater than generally thought

episodic rapid uplift in the himalaya revealed by 40ar 39ar analysis of detrital k feldspar and muscovite bengal fan detrital k feldspar and muscovite samples from ocean drilling program leg 116 cores have been dated by the sup 40 ar sup 39 ar technique and have depositional ages from 0 to 18 ma from 4 to 13 individual k feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels in every level at least one k feldspar and one muscovite yielded a minimum age identical within uncertainty to the age of deposition these results indicate that a significant portion of the material in the bengal fan is first cycle detritus derived from the himalaya therefore the substantial amount of sediment deposited in the distal fan in early to middle miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time moreover these data indicate that throughout the neogene some part of the himalayan orogen was undergoing rapid erosion 1 to 10 mm yr this erosion must have been less than or equal to uplift relative to sea level the lack of granulite facies rocks in the eastern himalaya and tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt these datamore are incompatible with tectonic models in which the himalaya and tibetan plateau are uplifted either uniformly over the past 40 m y or mostly within the past 2 to 5 m y less