exploration for gas hydrates in the deepwater northern gulf of mexico part i a seismic approach based on geologic model inversion and rock physics principles this article presents the results of applying a five step process for using high quality seismic data to locate marine gas hydrates the process involved 1 reprocessing of seismic data for higher resolution 2 detailed stratigraphic evaluation and interpretation to locate possible hydrate bearing zones 3 seismic attribute analysis to further delineate these zones 4 seismic inversion to obtain appropriate elastic parameters of these zones in 3d and 5 quantitative estimation of gas hydrate saturation from seismic data using inversion and rock physics principles we used seismic data from keathley canyon 151 and atwater valley 14 in the northern gulf of mexico although careful analysis did indicate the presence of a bottom simulating reflector bsr our study mainly relied on a host of other seismic attributes e g gas chimneys seismically transparent zones other features associated with the petroleum system to characterize the occurrence of gas hydrates in these areas we tested and verified a viable rock model for hydrate bearing sediments using data from the mallik mckenzie delta canada and blake ridge odp leg 164 southeast u s atlantic margin wells and modified it for application in the current area we then used this model to estimate gas hydrate saturation in the host sediments of the northern gulf of mexico focus areas using estimates of p wave and s wave velocities from inversion of reflection seismic data in this paper we present the gas hydrate saturations predicted from the seismic processing methodology prior to 2005 drilling in the focus areas in frontier areas where no well data are available and lithologic heterogeneities are poorly understood implementing a seismic based technique like the one described here to identify potential gas hydrates can provide valuable pre drill information for site selection and for planning future characterization studies of gas hydrate bearing sediments

pre alpine history of the pennine zone in the tauern window austria u pb and rb sr geochronology zircon ages from major lithologies of the zentralgneis suggest that much of the variscan magmatism in the tauern window is older than previously suggested in the southeast tauern window a tonalite has been dated at 314 7 m y and a granodioritic biotite augen gneiss at 313 10 m y two granodiorites from the granatspitzkern yielded zircon data consistent with a similar age these zircon data require re interpretation of some previously published rb sr whole rock ages and raise the possibility that alpine metamorphism caused more widespread disturbance of rb sr whole rocks than commonly supposed

miocene rotations in the eastern alps palaeomagnetic results from intramontane basin sediments a palaeomagnetic study of late early miocene to late middle miocene sediments from the eastern alpine intramontane basins revealed counterclockwise rotations in the ennstal in the western part of the noric and in the lavanttal depressions for the basal strata of the basins declinations are between 273 and 315 while for the younger strata they are between 321 and 333 in perfect agreement with observations from the klagenfurt basin the results suggest synsedimentary rotation during the lateral tectonic extrusion of the eastern alps ca 17 13 ma which was also responsible for the formation of the mostly transtensional basins we propose a model in which domino shaped blocks separated by nnw sse trending dextral faults rotated counterclockwise due to faster eastward motion in the south relative to areas further north the protrusion of the bohemian spur inhibited eastward motion in the northern part of the study area thus creating a sinistral wrench corridor after lateral extrusion had ceased the counterclockwise rotation continued probably as en bloc rotation of ca 30 clockwise rotation was observed in the eastern part of the noric depression which appears to belong to a limited area with complex rotation pattern near the eastern margin of the alps this area is wedged between the counterclockwise rotated eastern alps and the similarly rotated north pannonian area in hungary 2000 elsevier science b v all rights reserved

in situ gas hydrate hydrate saturation estimated from various well logs at the mount elbert gas hydrate stratigraphic test well alaska north slope abstract in 2006 the u s geological survey usgs completed detailed analysis and interpretation of available 2 d and 3 d seismic data and proposed a viable method for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area of northern alaska to validate the predictions of the usgs and to acquire critical reservoir data needed to develop a long term production testing program a well was drilled at the mount elbert prospect in february 2007 numerous well log data and cores were acquired to estimate in situ gas hydrate saturations and reservoir properties gas hydrate saturations were estimated from various well logs such as nuclear magnetic resonance nmr p and s wave velocity and electrical resistivity logs along with pore water salinity gas hydrate saturations from the nmr log agree well with those estimated from p and s wave velocity data because of the low salinity of the connate water and the low formation temperature the resistivity of connate water is comparable to that of shale therefore the effect of clay should be accounted for to accurately estimate gas hydrate saturations from the resistivity data two highly gas hydrate saturated intervals are identified an upper 43 ft zone with an average gas hydrate saturation of 54 and a lower 53 ft zone with an average gas hydrate saturation of 50 both zones reach a maximum of about 75 saturation

palinspastic reconstruction and topographic evolution of the eastern alps during late tertiary tectonic extrusion this paper presents a new palinspastic restoration of the eastern alps for neogene time and an attempt to reconstruct the neogene palaeogeology palaeotopography and palaeohydrography in connection with the structural evolution the eastern alps underwent radical horizontal displacement during the neogene due to large strike slip systems and formation of structural windows our palinspastic reconstruction considers a the rearrangement of tectonic units dismembered during tectonic extrusion b the tectonic denudation driven by displacement of the crystalline blocks c geochronological arguments and d the sedimentary record of the syn extrusion basins the rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre miocene unstretched pattern of the eastern alps reduced to 65 of its present day e w elongation using this structural frame and considering the sedimentary record a set of palaeogeologic and palaeotopographic sketch maps with the palaeo river systems is presented for three time slices pre syn and post extension situation in late oligocene and early miocene times the western eastern alps were already mountainous whereas the eastern part of the orogen formed lowlands or hilly areas enhanced block movement in the course of the extrusion process around the early middle miocene boundary led to the formation of intramontane sedimentary basins and a fault induced reorientation of the drainage pattern which forms the basis of the modern river system in the area east of the tauern window this region where pre miocene land surfaces are preserved probably became a mountainous area not before late miocene time and never reached the elevations of the areas further west

mechanical and electromagnetic properties of northern gulf of mexico sediments with and without thf hydrates using an oedometer cell instrumented to measure the evolution of electromagnetic properties small strain stiffness and temperature we conducted consolidation tests on sediments recovered during drilling in the northern gulf of mexico at the atwater valley and keathley canyon sites as part of the 2005 chevron joint industry project on methane hydrates the tested specimens include both unremolded specimens as recovered from the original core liner and remolded sediments both without gas hydrate and with pore fluid exchanged to attain 100 synthetic tetrahydrofuran hydrate saturation at any stage of loading test results demonstrate the extent to which the electromagnetic and mechanical properties of hydrate bearing marine sediments are governed by the vertical effective stress stress history porosity hydrate saturation fabric ionic concentration of the pore fluid and temperature we also show how permittivity and electrical conductivity data can be used to estimate the evolution of hydrate volume fraction during formation the gradual evolution of geophysical properties during hydrate formation probably reflects the slow increase in ionic concentration in the pore fluid due to ion exclusion in closed systems and the gradual decrease in average pore size in which the hydrate forms during hydrate formation the increase in s wave velocity is delayed with respect to the decrease in permittivity consistent with hydrate formation on mineral surfaces and subsequent crystal growth toward the pore space no significant decementation debonding occurred in 100 thf hydrate saturated sediments during unloading hence the probability of sampling hydrate bearing sediments without disturbing the original sediment fabric is greatest for samples in which the gas hydrate is primarily responsible for maintaining the sediment fabric and for which the time between core retrieval and restoration of in situ effective stress in the laboratory is minimized in evaluating the impact of core retrieval on specimen properties it is also important to consider how far removed hydrate bearing samples are from hydrate stability conditions

lu hf and pbsl geochronology of apatites from proterozoic terranes a first look at lu hf isotopic closure in metamorphic apatite abstract the mineral apatite is characterized by elevated and highly variable lu hf ratios that in some cases allow for single crystal dating by the lu hf isotopic system apatites from the adirondack lowlands and otter lake area in the grenville province and from the black hills south dakota yield lu hf ages that are consistently older than their respective pb step leaching ages isotopic closure for the lu hf system therefore occurs before u pb system closure in this mineral in the adirondack lowlands where h2o activity was low lu hf systematics of cm sized apatite crystals remained undisturbed during upper amphibolite facies metamorphism 700 to 675 c at 1170 1130 ma the relatively old lu hf ages of 1270 and 1230 ma observed for these apatites correlate with decreasing crystal size in contrast apatite from the fluid rich otter lake area and black hills yields unrealistically low apparent lu hf closure temperatures implying that in these apatites fluids facilitated late exchange the lu hf ages for the metamorphic apatites were thus controlled either by the prevailing temperature and grain size or by fluid activity

u pb isotopic dating of fluid infiltration and metasomatism during dalradian regional metamorphism in connemara western ireland a metasomatic diopside rock occurs at the top of the dolomitic connemara marble formation of western ireland and contains titanite and k feldspar in addition to around 90 diopside xmg 0 90 0 97 u pb isotopic measurements on this mineral assemblage show that the titanite is both unusually uranium rich and isotopically concordant with the result that a precise u pb age of 478 2 5 ma can be determined the age is identical within error to a less precise rb sr age of diopside k feldspar of 483 6 ma petrological evidence indicates that the assemblage crystallized at c 620 c close to or below the closure temperature of titanite the age thus provides a precise estimate of the time of metamorphism this age is 11 3 ma younger than the 490 ma age for nearby gabbroic plutons which has previously been used to constrain the peak metamorphic age this difference accords well with geological evidence that the gabbros were emplaced prior to the metamorphic peak analysis of minerals with high closure temperature from assemblages whose crystallization is unambiguously associated with a specific episode of fluid infiltration at the peak of metamorphism provides the basis for a new approach to dating metamorphism the success of this approach is demonstrated by the results from connemara

changing patterns of exhumation and denudation in front of an advancing crustal indenter tauern window eastern alps the changing shape of indenting crustal blocks during northward motion of the adriatic microplate induced migration of miocene doming and orogen parallel extension of orogenic crust in the tauern window new structural and kinematic data indicate that initial shortening of the penninic nappe pile in the tauern window by upright folding and strike slip faulting was transitional to coeval north south shortening and east west extension the latter was accommodated by normal faulting at the eastern and western margins of the window retrodeforming these post nappe structures in map view yields a map view reconstruction of the orogenic crust back to 30 ma including the onset of pronounced indentation at 21 ma this model supports the notion that indentation involved approximately equal amounts of north south shortening and orogen parallel stretching and extrusion toward the pannonian basin as measured from the indenter tip to the european foreland in the north and austroalpine units in the east comparison of areal denudation of the orogenic crust before and after indentation indicate that erosion associated with upright folding was the primary agent of denudation whereas extensional unroofing and limited erosion along normal faults at the eastern and western ends of the tauern window accounted for only about a third of the total denudation

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

marine controlled source electromagnetic method used for the gas hydrate investigation in the offshore area of sw taiwan abstract bottom simulating reflectors bsrs high methane flux shallow sulfide methane interfaces fluids venting from the seafloor authigenic carbonates within sediments methane reefs and self biomes are common seafloor features in the area off southwest taiwan the geophysical and geochemical signatures of these features suggest a high potential for gas hydrate gh reservoirs in the region the bsrs are typically interpreted as the boundary between free gases and solid hydrate whereas the upper reaches of the hydrate stability zone and the distribution of gas hydrate in shallow sediments are not well understood this study shows the first results of a marine controlled source electromagnetic survey conducted in the offshore area of sw taiwan in 2010 the survey aimed to provide electrical resistivity information of the shallow sediments three target areas were surveyed 1 an area to the southeast of the xiaoliuchiu island gas seep g96 2 an area in the west of the yung an ridge yar and 3 an area in the northwest of the good weather ridge gwr in total fourteen survey lines with a total length of 72 km were completed our preliminary results show that relatively high resistivity anomalies occur within pockmarks and at gas seepage sites the apparent resistivity is estimated to be about 1 ohm m higher than background in g96 and yar sites while an anomaly up to 2 ohm m is found in the gwr at gas seep site g96 the high resistivity anomaly may be due to the existence of authigenic carbonates whereas the high resistivity anomaly in the nw of the gwr site may also be due to the existence of gas hydrate in the shallow seabed based on the resistivity anomaly the gas hydrate saturation is about 16 in the shallow sediments below the pockmark area in the northwest side of the gwr site

characterization of in situ elastic properties of gas hydrate bearing sediments on the blake ridge during ocean drilling program leg 164 shear sonic velocity and other geophysical logs were acquired in gas hydrate bearing sediments on the blake ridge to characterize the very distinct seismic signature of such formations anomalous low amplitudes overlying a strong bottom simulating reflector bsr a comparison of the bulk moduli derived from the logs to standard elastic consolidation models shows that the sediments are overconsolidated above the bsr at 440 meters below seafloor mbsf because of the presence of hydrates below the bottom of the thermodynamic hydrate stability zone at 520 mbsf the high compressibility of the formation and the attenuation of the monopole sonic waveforms are typical of sediments partially saturated with free gas between these two depths gas hydrate and free gas seem to coexist within the gas hydrate stability zone we estimate the amount of gas hydrates using different models based on theories for wave scattering in multiphase media and for grain cementation in close agreement with measurements made on discrete in situ samples the latter describes most accurately the interactions between the matrix the pore fluids and the hydrates this model indicates that 5 to 10 of the pore space is occupied by hydrates deposited uniformly on the surface of the grains the comparison with gassmann s model also show that the amount of free gas below the bsr never exceeds 5 of the pore space but is high enough to generate the bsr the coexistence of free gas and gas hydrates below the bsr may be explained by capillary effects in the smaller pores or by remaining crystalline structures after partial hydrate decomposition

estimate of gas hydrate saturations in the krishna godavari basin eastern continental margin of india results of expedition nghp 02 abstract a total of 25 drill sites were established in the krishna godavari kg and mahanadi basins along the eastern margin of india during the india national gas hydrate program expedition 02 nghp 02 with the goal to identify and characterize gas hydrate occurrences in sand rich reservoir systems the objective of this study is to characterize the gas hydrate bearing zones linked with two seismic inferred horizons r1 and r2 and estimate gas hydrate saturations at two sites in area b of the kg basin sites nghp 02 22 and nghp 02 23 the upper seismic imaged reservoir section reflector r1 contains both pore filling and fracture filling gas hydrate while the lower seismic imaged reservoir section reflector r2 has only pore filling gas hydrate since electrical resistivity seems to be the most pronounced physical response to the presence of gas hydrate we have analyzed the resistivity log data using archie s empirical equation from two sites based on an isotropic reservoir model in order to assess the gas hydrate saturation we have also performed isotropic velocity modelling using the three phase biot equation tpbe and density log derived sediment porosities at site nghp 02 22 the average gas hydrate saturation estimated using the resistivity log data and p wave velocity modelling are 29 and 17 respectively in the depth interval of 207 290 mbsf whereas at site nghp 02 23 the average gas hydrate saturation obtained from resistivity log data and p wave velocity modelling are 25 and 60 respectively in the depth interval of 271 288 mbsf estimated results are further validated with the pressure core derived gas hydrate saturations to ensure their reliability at the respective drill sites it was found that p wave velocity log inferred gas hydrates show a slight mismatch with the pressure core derived hydrate saturations while the electrical resistivity log based result depicts a major mismatch with the pressure core derived hydrate saturations the reason for this discrepancy is likely due to isotropic resistivity analysis of the reservoir section having anisotropic properties

combining impedance inversion and seismic similarity for robust gas hydrate concentration assessments a case study from the krishna godavari basin east coast of india abstract gas hydrate saturations were calculated based on archie s relation and rock physics modeling utilizing log measurements of electrical resistivity and p wave velocity through the gas hydrate stability zone ghsz at two sites in the krishna godavari kg basin off the east coast of india acoustic impedance inversion was then performed around the well sites for regional extrapolation of the borehole data well log based gas hydrate concentration estimates and core data are in general agreement with the seismic impedance inversion results at the individual well sites however the correlation with seismic data and thus the confidence in the extrapolation decreases with distance from the well site to address the general problem of unknown regional confidence limits in the extrapolation and aid in regional gas hydrate assessment analyses a new approach is introduced by calculating the running sum of the seismic similarity attribute across the gas hydrate stability zone the running sum of the similarity attribute can be used locally on a 2d seismic line or 3d seismic volume for defining the limit of well data extrapolation around a given well site by normalizing the running sum of the similarity attribute from all available 2d seismic data in the kg basin a regional map was generated yielding effective confidence limits for extrapolation of well log data such maps of regional confidence limits can be used strategically in basin wide gas hydrate assessments as they provide a measure of probability to find a given gas hydrate concentration and may also offer a guide for defining a minimum regional spacing between well sites to address the overall structural complexity of the basin which is reflected in the similarity of the seismic data

characterization and rheology of krishna godavari basin sediments abstract the krishna godavari offshore basin to the east of india is a proven reserve rich in natural gas hydrate the impact of sediment characteristics on the hydrate formation has already been well established in open literature in the present study we have attempted to investigate the mineralogy of sediments collected from kg basin by elemental analysis energy dispersive spectroscopy and x ray diffraction various physicochemical characteristics of the clayey sediments such as tds salinity ph conductivity and resistivity were analysed at various concentrations and compared together also this paper highlights the rheological behavior of the sediment samples with concentrations of 20 35 and 50 wt at different experimental temperatures 278 15 k 283 15 k and 288 15 k viscosity measurements were performed for a wide range of shear rates for all concentrations and comparative studies have been conducted on their exhibited behavior the viscosity of sediment sample were found to be varying from 76 3 to 0 003 pa s depending on the sediment concentration temperature and shear rate in addition viscoelastic measurements were carried out at various angular frequencies for all the sediment samples the work aims to characterise the sediments of kg basin and analyse the rheological behavior of sediment solution which has not yet been reported in open literature this will provide vital information for possible methane recovery from kg basin hydrate reservoir by manipulating the host sediment behavior

from source terrains of the eastern alps to the molasse basin detrital record of non steady state exhumation fission track cooling ages of detrital apatite aft in the east alpine molasse basin display age groups corresponding to geodynamic events in the orogen since jurassic times these age groups are typical of certain thermotectonic units which formed a patchwork in the swiss and eastern alps by a combination of petrographic and thermochronologic data progressive erosion of source terrains is monitored in different catchments since the oligocene the aft cooling ages show a decrease in lag time until when rapidly cooled debris derived from tectonically exhumed core complexes became exposed after termination of tectonic exhumation lag times of debris derived from the core complexes increased neither on the scale of the entire eastern alps or on the scale of individual catchments steady state exhumation is observed due to the highly dynamic changes of exhumation rates since late eocene collision d 2005 elsevier b v all rights reserved

extending nmr data for permeability estimation in fine grained sediments abstract we combine nuclear magnetic resonance nmr transverse relaxation time data and gamma ray data to estimate lithology dependent permeability in silt and clay rich sediments this approach extends the utility of the schlumberger doll research sdr permeability equation from reservoirs to aquicludes and seals and thus improves the value and robustness of nmr data data from keathley canyon northern gulf of mexico show that nmr data can be used to define permeability from 10 18 to 10 14 m 2 0 001 10 millidarcies as calibrated and tested by direct measurements on core samples we performed uniaxial constant rate of strain consolidation experiments on sediments from keathley canyon to determine core scale permeability permeabilities from these experiments were compared to permeabilities calculated from logging while drilling data a better fit between log derived permeability and laboratory measured permeability was obtained using the sdr equation with a variable coefficient a rather than a constant a as is typically used we show how a is a function of lithology and can be modeled from gamma ray data the relationship between a and gamma ray values suggests that variations in a are caused by platy clay minerals and the effect they have on the pore system our results provide improved means for permeability estimation for application in basin flow modeling hydrocarbon migration modeling and well completion design

post collisional sediment budget history of the alps tectonic versus climatic control based on the sediment budget of the eastern swiss and western alps since the oligocene the regional tectonic evolution has been identified as the dominant factor it is superimposed on the influence of both regional and global climate change and global sea level change during late pliocene and pleistocene times climate became the dominant factor because of cyclic glaciations the early post collisional history of the alps is characterized by a doubling of sediment discharge rates around the rupelian chattian boundary this increase is attributed to isostatic re adjustment either after large scale thermal reorganization of the lithosphere related to slab break off or to crustal thickening as continental crust became subducted from middle oligocene to late miocene times the overall trend of sediment discharge rates in the entire alps was modified only during relatively short lived phases these are characterized by an increase in aquitanian ca 23 21 ma and late burdigalian times ca 18 16 4 ma and a decrease in early to middle burdigalian 21 19 ma and langhian to serravalian times 16 4 12 ma an important still ongoing period of uplift reflected by rapidly increasing sediment discharge rates started in latest miocene times in the swiss and western alps and affected the eastern alps some 2 million years later the reason for this uplift is not clear but deep seated lithospheric processes appear to be likely

the crystal chemical basis for ar retention in micas inferences from interlayer partitioning and implications for geochronology cation partitioning data for coexisting muscovite and biotite are shown to be useful indicators of relative interlayer bond length strength in these minerals these data therefore provide a useful crystal chemical perspective on relative mass transfer kinetics of radiogenic isotopes and account for the observation that biotite is generally less retentive of 40ar and 87sr than coexisting muscovite partitioning behavior of trace elements underscores three reasons why overall interlayer bonding in biotite is weaker than in muscovite first the preferences of large rb cs in biotite and of small la3 and na in muscovite indicate a relatively spacious interlayer volume in biotite suggesting a longer mean k o bond second the preference of interlayer vacancies in biotite with some all possibly h2o h3o filled suggests that its adjacent 2 1 sheets are connected by fewer interlayer bonds per unit cell than those of muscovite third the relative exclusion of large ba2 from biotite despite its large interlayer sites is attributed to o h bonds pointing into the interlayer cavity sub normal to 001 k ba2 h repulsion thereby induced by the bare proton both destabilizes ba2 and weakens k o bonds in contrast muscovite offers a more favorable electrostatic environment for ba2 substitution since its o h bonds are directed into the vacant m1 octahedral site sub parallel to 001 this hypothesis is supported by the observation that progressive f oh 1 exchange enhances ba2 partitioning into biotite phlogopite relative to coexisting muscovite these crystal chemical differences between biotite and muscovite are mirrored in calculated values of ionic porosity z i defined here as the percentage of their interlayer unit cell volume not occupied by ions a monitor of ionic packing density and geometry z i is inversely correlated with k o bond strength which appears to be the rate determining kinetic common denominator for a variety of processes affecting micas including those responsible for loss of radiogenic isotopes in biotite and muscovite accordingly the relatively longer weaker k o bonds of biotite are envisioned as being more easily stretched during volume diffusion or broken during recrystallization or retrograde alteration this in turn accounts for common observations of enhanced radiogenic ar sr loss and younger 40ar 39ar and rb sr ages in natural biotite high z i relative to coexisting muscovite lower z i significantly this pattern may arise irrespective of isotopic loss mechanism diffusion or recrystallization etc and it follows that any age discordance observed between muscovite and biotite cannot be ascribed uniquely to one mechanism or the other without appropriate field petrographic and petrologic constraints extension of this partitioning porosity based synthesis leads to prediction of corollary age retentivity composition effects among chemically diverse trioctahedral and dioctahedral micas which are best field tested in terranes that cooled slowly under dry static conditions pressure effects on argon retention are also inferred from the porosity model

thermal effects of exhumation of a metamorphic core complex on hanging wall syn rift sediments an example from the rechnitz window eastern alps the removal of overburden by tectonic processes displaces the rock masses and their temperature with respect to the surface consequently high cooling rates and increased heat flow have been reported from rapidly exhuming terrains previous studies were mainly focused on the greenschist and amphibolite facies tectono thermal evolution of the footwall a two dimensional numerical thermal model presented in this study concentrates on the thermal history of the hanging wall and the footwall blocks and evaluates the variation of the near surface heat flow above an evolving metamorphic core complex based on structural thermobarometric and geochronological constraints from the rechnitz core complex of the eastern alps the modelling suggests that rapid movement along the extensional fault took place between 22 and 17 ma during this period the heat flow reached values of 140 150 mw m 2 in the hanging wall in a 10 15 km wide zone parallel to the fault trace the increased heat flow caused the high coal rank in the miocene syn rift sediments deposited on the hanging wall apatite fission track geochronology of the thermally overprinted sedimentary deposits gives the time at which the bottom of the syn rift sediment pile passed through 110oc 13 6 0 9 ma the vitrinite reflectance data rr 0 67 1 04 suggest significant burial of the margin of the hanging wall at the time of core complex formation considering the coal rank data and the thermal conductivity of the sedimentary deposits by modelling of the organic maturation we calculate syn rift early middle miocene burial of the hanging wall margin of the rechnitz core complex to be 1100 1600 m this value shows the importance of the post middle miocene erosion of the region which was related to the inversion of the pannonian basin 1998 elsevier science b v all rights reserved

orogeny and metamorphism a model for deformation and pressure temperature time paths with applications to the central and southern appalachians a model is presented for deformation uplift and exhumation in convergent orogens based on the following premises 1 foreland basin subsidence monitors the distribution in time and space of overthrust loads added to an orogen 2 the presence of an inherited rifted margin plays an important role in the subsequent history of an orogen by forming a basement ramp or buttress that must be surmounted in order for thrusts to advance on the craton on the seaward side of this transition up to 20 km of overthrusts can be accumulated without creating topography 3 critical shape theory can be applied to orogens as a whole allowing predictions to be made concerning dynamic balance between mass addition and loss uplift exhumation and growth of topography and 4 pressure temperature time p t t data can be used to reconstruct particle paths within the deforming orogen three states of overthrust orogens can be defined based on the relative rates of mass loss and mass addition as monitored by the foreland rapid exhumation of metamorphic terranes is most likely in the steady state where erosion balances accretion a constructive state where mass addition is greater than mass loss results in crustal thickening and initially little exhumation a destructive state where mass loss outweighs mass addition results in slow exhumation or subsidence of metamorphic rocks in the orogen depending on whether mass is removed by erosion or by extension p t t data on peak metamorphism pluton emplacement uplift exhumation and cooling can be used in conjunction with data from the foreland to distinguish among these various states the topography and strength of the inherited rifted margin play an important role in localizing zones of exhumation and uplift within the orogen application of this model to the central and southern appalachians suggests that during the constructive phases of the taconian and acadian orogenies overthrust loads accumulated mainly on the seaward side of the ocean continent transition as marked by the bouguer gravity gradient between the acadian and alleghanian orogenies the appalachian orogen was probably in a steady state with uplift and exhumation of rocks in the orogen but little subsidence of the foreland or advance of thrusts toward the craton the constructive stage of the alleghanian orogeny achieved the critical topography necessary to drive crystalline thrust sheets over the craton this resulted in widespread uplift and westward transport of older metamorphic rocks post orogenic unroofing of the southern appalachians is compatible with the predictions of flexural models the post orogenic unroofing history of the central appalachians and ouachitas probably reflects mesozoic extension in these areas

lateral extrusion in the eastern alps revisited refining the model by thermochronological sedimentary and seismic data 1 this study comprises a reassessment of the classical model of lateral extrusion in the eastern alps by using recently published geochronological data sedimentary ages from intramontane basins ages and distribution of magmatic rocks and information from seismic profiles extrusion related faulting continuously propagated from the western toward the central eastern part of the eastern alps during oligocene to middle miocene times this is confined by oblique convergence between the adriatic and european plates during middle miocene times extrusion became not only lateral in terms of parallel to the trend of the eastern alps but was characterized by a displacement vector at a high angle to the strike of the orogen this resulted in the exhumation of the schladming and pohorje blocks that were exhumed within extensional bridges at the northern and southern terminations of the pols lavanttal fault system respectively from middle miocene to recent times extrusion was controlled by overall extension between the dinaric and carpathian subduction zones the influence of north directed compression triggered by the northward moving adriatic plate diminished and the influence of the retreating carpathian subduction zone increased this gave rise to miocene volcanism that is exclusively found east of the dinaric subduction zone we therefore consider that lateral extrusion in the eastern alps can be subdivided into distinct tectonic phases with less pronounced eastward extension related displacement between late oligocene and middle miocene times as soon as the eastern alps passed the dinaric subduction zone the entire domain became highly extensive

modes of orogen parallel stretching and extensional exhumation in response to microplate indentation and roll back subduction tauern window eastern alps the tauern window exposes a paleogene nappe stack consisting of highly metamorphosed oceanic alpine tethys and continental distal european margin thrust sheets in the eastern part of this window this nappe stack eastern tauern subdome etd is bounded by a neogene system of shear the katschberg shear zone system kszs that accommodated orogen parallel stretching orogen normal shortening and exhumation with respect to the structurally overlying austroalpine units adriatic margin the kszs comprises a 5 km thick belt of retrograde mylonite the central segment of which is a southeast dipping low angle extensional shear zone with a brittle overprint katschberg normal fault knf at the northern and southern ends of this central segment the kszs loses its brittle overprint and swings around both corners of the etd to become subvertical dextral and sinistral strike slip faults the latter represent stretching faults whose displacements decrease westward to near zero the kinematic continuity of top east to top southeast ductile shearing along the central low angle extensional part of the kszs with strike slip shearing along its steep ends combined with maximum tectonic omission of nappes of the etd in the footwall of the knf indicates that north south shortening orogen parallel stretching and normal faulting were coeval stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the kszs to have begun at 23 21 ma leading to rapid cooling between 21 and 16 ma this exhumation involved a combination of tectonic unroofing by extensional shearing upright folding and erosional denudation the contribution of tectonic unroofing is greatest along the central segment of the kszs and decreases westward to the central part of the tauern window the kszs formed in response to the indentation of wedge shaped blocks of semi rigid austroalpine basement located in front of the south alpine indenter that was part of the adriatic microplate northward motion of this indenter along the sinistral giudicarie belt offsets the periadriatic fault and triggered rapid exhumation of orogenic crust within the entire tauern window exhumation involved strike slip and normal faulting that accommodated about 100 km of orogen parallel extension and was contemporaneous with about 30 km of orogen perpendicular north south shortening of the etd extension of the pannonian basin related to roll back subduction in the carpathians began at 20 ma but did not affect the eastern alps before about 17 ma the effect of this extension was to reduce the lateral resistance to eastward crustal flow away from the zone of greatest thickening in the tauern window area therefore we propose that roll back subduction temporarily enhanced rather than triggered exhumation and orogen parallel motion in the eastern alps lateral extrusion and orogen parallel extension in the eastern alps have continued from 12 to 10 ma to the present and are driven by northward push of adria

gas hydrate saturation in the krishna godavari basin from p wave velocity and electrical resistivity logs abstract during the indian national gas hydrate program nghp expedition 01 a series of well logs were acquired at several sites across the krishna godavari kg basin electrical resistivity logs were used for gas hydrate saturation estimates using archie s method the measured in situ pore water salinity seafloor temperature and geothermal gradients were used to determine the baseline pore water resistivity in the absence of core data arp s law was used to estimate in situ pore water resistivity uncertainties in the archie s approach are related to the calibration of archie coefficient a cementation factor m and saturation exponent n values we also have estimated gas hydrate saturation from sonic p wave velocity logs considering the gas hydrate in frame effective medium rock physics model uncertainties in the effective medium modeling stem from the choice of mineral assemblage used in the model in both methods we assume that gas hydrate forms in sediment pore space combined observations from these analyses show that gas hydrate saturations are relatively low s h 15 20 in two zones between 168 and 198 mbsf site nghp 01 05 s h 35 38 in two discrete zone between 70 and 90 mbsf and site nghp 01 07 shows the gas hydrate saturation more than 25 in two zones between 75 and 155 mbsf a total of 10 drill sites and associated log data regional occurrences of bottom simulating reflectors from 2d and 3d seismic data and thermal modeling of the gas hydrate stability zone were used to estimate the total amount of gas hydrate within the kg basin average gas hydrate saturations for the entire gas hydrate stability zone seafloor to base of gas hydrate stability sediment porosities and statistically derived extreme values for these parameters were defined from the logs the total area considered based on the bsr seismic data covers 720 km 2 using the statistical ranges in all parameters involved in the calculation the total amount of gas from gas hydrate in the kg basin study area varies from a minimum of 5 7 trillion cubic feet tcf to 32 1 tcf

exploration for gas hydrates in the deepwater northern gulf of mexico part ii model validation by drilling this study examines the accuracy of the predictions of gas hydrate saturations made based on five step analysis of 3d seismic data prior to 2005 drilling logging conventional coring and pressure core sampling through the gas hydrate stability zone at two focus sites in the northern gulf of mexico these predictions are detailed in part i 2008 here we conduct a detailed analysis of the gas hydrate saturation using both resistivity and p wave velocity log data and analyze the pre drilling predictions which were made almost exclusively on the basis of seismic data with no local logging control well log measurements core data analysis and pressure core degas experiments all indicated general agreement with the pre cruise analysis regarding the location and approximate concentration of gas hydrates in the sediments we find that seismic predictions are generally consistent with log based estimates after upscaling to seismic frequencies we recalibrated the pre drill model based on the new field data so that a refined version of the model could be used for future work

local attenuation in western nagano central japan estimated from seismograms recorded in three boreholes 1 seismic attenuation parameters three borehole stations in western nagano central japan based on the difference in attenuation between combinations of two boreholes the local attenuation qp 1 is 1 23 10 3 s in the frequency range of 80 to 250 hz obtained qp 1 is consistent with the trend estimated by grid search with the assumption of the 2 source model even though the boreholes are located on the fracture area of the 1984 nagano ken seibu earthquake the estimated qp 1 is low the result is not completely consistent with a previous study and a result of qs 1 obtained from the twofold spectral ratio but the difference can be interpreted as the difference of frequency ranges the differences of station corrections of attenuation between boreholes are much smaller than the difference between borehole and surface and the result shows the advantage of borehole seismometers

isotopic constraints on the cooling history of the nanga parbat haramosh massif and kohistan arc western himalaya nineteen 40ar 39ar and 22 rb sr mineral ages are presented for metamorphic rocks and granites collected from the northern part of the nanga parbat haramosh massif nphm and adjacent parts of the kohistan arc western himalaya the majority of these ages are interpreted as exhumation related cooling ages and they therefore place important constraints on the exhumation history of the region the 40ar 39ar and rb sr mica cooling ages for areas of the nphm to the north of the indus river lie in the range 2 8 ma and are similar to previously published ages from the indus gorge itself cooling histories for these areas show little systematic variation from east to west suggesting that the basement may have been exhumed as a relatively rigid block after the main stages of folding mica ages increase dramatically from the nphm westward into the kohistan arc where ages lie in the range 13 30 ma the contrast in both cooling ages and the age differential between mineral pairs between the two terranes indicates rapid cooling of the nphm in the last 10 m y compared with the kohistan arc the relationship between rates of cooling and exhumation is poorly constrained in regions of rapid uplift where the characteristics of the evolving geotherm are not well understood however the results are consistent with an anomalously rapid exhumation history of the nphm during the last 10 m y compared with the adjacent kohistan arc the interpretation of some of the ages documented in this study is problematical two biotite samples from contrasting lithologies within the nphm have yielded higher 87sr 86sr ratios than the corresponding whole rocks but the cause of this isotopic disequilibrium remains unclear other biotite samples from the region have consistently yielded younger rb sr ages than 40ar 39ar ages which may be a reflection of either preferential leaching of 87sr during fluid infiltration on a regional scale or the presence of excess argon alternatively the relative ages indicate slightly lower closure temperature for strontium diffusion in biotite than for argon diffusion in biotite where samples have undergone rapid cooling

u pb and rb sr geochronology of magmatism and metamorphism in the dalradian of connemara western ireland new geochronological data which clarify the timing of syn orogenic magmatism and regional metamorphism in the connemara dalradian are presented u pb zircon data on four intermediate to acid foliated magmatic rocks show important inherited components but the most concordant fractions demonstrate that major magmatism continued until 465 ma whereas the earliest basic magmatism has been dated previously at 490 ma a fine grained fabric cutting granite contains discordant zircons which also appear to be 465 ma old arc magmatism in connemara therefore spanned a period of at least 25 ma recent u pb data on titanite from central connemara which gave a peak metamorphic age of 478 ma are supplemented by u pb data on titanite and monazite from metamorphic veins in the east of connemara which indicate that low p high t regional metamorphism continued there to 465 ma i e at least 10 ma later than in the central region dated previously new rb sr data on muscovites from coarse grained segregations in different structural settings range from 475 to 435 ma in part this range probably also reflects differences in age from west to east with three ages close to 455 ma from the eastern area which is also the site of the lowest pressure metamorphism thermal modelling indicates that at any one locality the duration of metamorphism was probably as little as 1 2 ma the new dates emphasize the complexity in the spatial and temporal distribution of high level regional metamorphism caused by magmatic activity the relatively simple overall distribution of mineral appearance isograds revealed by regional mapping masks the complexity of a prolonged but punctuated metamorphic history related to multiple intrusions primarily in the southern part of connemara the later stages of magmatic activity followed progressive uplift and erosion after the onset of magmatism and were localized in the eastern part of the region

40ar 39ar muscovite ages from the penninic austroalpine plate boundary eastern alps the radstadt mountains eastern alps expose the tectonic boundary between the base of the austroalpine continental plate hanging wall and the penninic oceanic units foot wall parts of the austroalpine basement were penetratively deformed because of ongoing rifting of the continental crust during the permian 290 250 ma austroalpine permo mesozoic cover rocks were deformed during the cretaceous 80 ma and the paleogene 55 50 ma these ages are interpreted as representing two distinct events of nappe stacking the younger ages represent the collision of austroalpine and penninic tectonic units the penninic nappe complex displays a successive decrease of ages from 37 to 25 ma from high to deep tectonic levels a second age group of 22 ma was found both in low temperature release steps and as plateau ages close to the penninic austroalpine boundary it is attributed to a thermal overprint due to ductile extension of the overthickened orogenic wedge

geochemical constraints on the origin of the pore fluids and gas hydrate distribution at atwater valley and keathley canyon northern gulf of mexico abstract pore fluids from atwater valley at 13 14 and keathley canyon kc 151 in the northern gulf of mexico are surprisingly similar with respect to ionic concentrations and oxygen and strontium isotope values as well as hydrocarbon geochemistry suggesting that these widely separated localities share common deep subsurface fluid origins seafloor mounds with focused fluid migration pathways and inferred near seafloor gas hydrates characterize the at 13 14 region whereas the kc 151 region has a bottom simulating reflector bsr at 310 mbsf which is rather uncommon in the gulf of mexico gom at these sites seafloor gas hydrates were not observed but the sediment surface in the vicinity and particularly at the mounds is populated with chemosynthetic communities that are commonly associated with seafloor gas emission the geochemical results together with the pressure core data suggest that at the at region methane hydrate mostly occurs in near surface sediments at mounds consistent with focused migration pathways in the kc region methane hydrate mostly occurs deeper in the section in highly fractured silty clayey sediments from 220 to 300 mbsf the pore fluids at the at mounds and kc 151 are characterized by higher than seawater salinity the more saline pore fluids at the at mound and at kc151 sites located 350 km apart are almost chemically indistinct ionic ratios indicate that this distinct high salinity fluid is not from in situ salt dome halite dissolution rather this fluid is a subsurface brine derived from jurassic or cenozoic evaporite formation modified by fluid sediment reactions and migrated to the two sites analyzed despite porewater salinities elevated above that of seawater the sediment temperatures are within the range of methane hydrate stability for each of the sites based on cl dilutions the maximum gas hydrate pore volume occupancy at the at mound sites would be 9 at kc cl concentrations in pressure cores imply that in situ hydrate is unevenly distributed with pore volume occupancy of 1 12 significant variations in sulfate gradients were observed with the sulfate to methane transition zone smtz at or near the seafloor at the at mound sites at at 13 2 the well defined smtz is at 8 mbsf and at kc 151 3 it is at 9 mbsf there is no coincidence between the steepness of the sulfate gradients and the presence or depth of a bsr suggesting that the smtz interfaces are measuring different aspects of the subsurface methane hydrology at both at and kc the 13 c dic values clearly indicate that anaerobic oxidation of methane aom is the dominant reaction responsible for sulfate reduction and the increased alkalinities observed the most negative 13 c dic values obtained are 46 3 and 49 6 at the smtzs at at 13 2 and kc 151 3 respectively

isotopic dating in metamorphic belts isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions of these temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed the central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated in order to illustrate the factors which control closure temperatures and limit their application in practice the possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined taking examples involving k ar rb sr sm nd and u pb analyses the indirect dating of metamorphism via structurally dated plutons is briefly considered and the problems of interpreting both discordant u pb zircon ages and rb sr whole rock isochrons in metamorphosed granites are discussed the value of near concordant zircon ages is emphasized the extent of isotopic equilibration during metamorphism specifically of sr isotopes in metasediments is shown not to be a simple function of metamorphic grade the flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently the concluding discussion briefly examines existing data for the dalradian and indicates the potential for further progress using both well established and novel approaches

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

origin and evolution of fracture hosted methane hydrate deposits 1 fracture hosted methane hydrate deposits exist at many sites worldwide these sites often have hydrate present as vein and fracture fill as well as disseminated through the pore space we estimate that thousands to millions of years are required to form fracture systems by hydraulic fracturing driven by occlusion of the pore system by hydrate this time scale is a function of rates of fluid flow and permeability loss low permeability layers in a sedimentary column can reduce this time if the permeability contrast with respect to the surrounding sediments is of order 10 or greater additionally we find that tensile fracturing produced by hydrate heave around hydrate lenses is a viable fracture mechanism over all but the lowermost part of the hydrate stability zone with our coupled fluid flow hydrate formation model we assess fracture formation at four well studied hydrate provinces blake ridge offshore south carolina hydrate ridge offshore oregon keathley canyon block 151 offshore louisiana and the krishna godavari basin offshore india we conclude that hydraulic fracturing due to pore pressure buildup is reasonable only at hydrate ridge and the krishna godavari basin owing to sediment age constraints and that hydrate filled fractures observed at blake ridge and keathley canyon block 151 are formed either by hydrate heave or in preexisting fractures our findings offer new insight into the processes and time scales associated with fracture hosted hydrate deposits which help further our understanding of hydrate systems

trace element incorporation in titanite constraints from experimentally determined solid liquid partition coefficients titanite liquid partition coefficients for most of the trace elements relevant in petrogenetic studies are provided for titanite saturated liquids equilibrated at 1 5 gpa and 850 c starting from lamproitic compositions the high compatibility observed for ree hfse sr v and sc and the strong incompatibility observed for actinides large ion lithophile and light elements are discussed in terms of available crystal chemical mechanisms for incorporation and crystal structure control the exchange vectors na1ca 1 and al1ti 1 allow local charge balance to be achieved after incorporation of ree3 and r5 at the ca and ti site respectively the significant amounts of h measured are also relevant in this regard the exchange mechanism being oh 1o 1 at the o1 site the incorporation of u4 and th4 at the ca site is scarce and is likely balanced by that of mg2 at the ti site both these substitutions are responsible for strong structural strain titanite can thus be considered an important repository for ree and hfse in metamorphic and igneous rocks and its role must be accounted for when modelling trace element residence during metamorphic reactions and late magmatic crystallisation history due to the measured differences in compatibility titanite crystallisation increases the values of nb ta and lree hree ratios in residual liquids the similar compatibility of u and pb makes titanite suitable for u pb geochronology of igneous rocks only after common pb correction finally this study confirms that the titanite end member is not suitable for radioactive waste disposal due to the discussed crystal chemical constraints and that titanite based waste forms should contain high amounts of na and mg2

on uplift and exhumation during convergence a simple kinematic model is used to illustrate the vertical motions of rocks during convergent deformation and erosion at the surface it is shown that rocks may move upward or downward in the crust depending on the relative rates of erosion and thickening and depending on their initial depth in the crust exhumation during thickening can only occur if rapid denudation accompanies the thickening process during homogeneous thickening with erosion that is elevation dependent the initial depth from which rocks can be exhumed is only determined by the density distribution in the column and is independent of erosion or thickening rates the maximum initial depth from which rocks can be exhumed is of the order of 30 km or less there is therefore no conflict in the observation of synchronous exhumation and convergent deformation if the peak pressure of rocks is equivalent to no more than 30 km of burial it is also shown that uplift defined as vertical motion of the surface with respect to a reference level for example the geoid and exhumation defined as vertical motion of rocks with respect to the surface may follow different patterns in time and that the difference between the two evolutions may be a useful indicator of the exhumation process the model serves to emphasize the important differences between uplift and exhumation which are often not distinguished in the literature

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

eclogite meso and microfabrics implications for the burial and exhumation history of eclogites in the tauern window eastern alps from p t d paths abstract the eclogite zone of the central southern tauern window comprises eclogites and associated high pressure metasediments that are intercalated between penninic basement units in the foot wall and an imbricate stack in the hanging wall this nappe stack consists of continental basement units cover sequences of a distal continental slope and the main part of the ophiolitic glockner nappe textures and microfabrics of eclogites from the central southern tauern window allow the establishment of the eclogitic and post eclogitic deformation histories from burial by subduction to subsequent exhumation the metamorphic evolution of the eclogites is documented by 1 initial greenschist to blueschist facies 2 eclogite facies at ca 550 630 c and 20 kbar 3 a second blueschist facies overprint ca 450 c 10 15 kbar and 4 exhumation to pressures of ca 6 7 kbar at 500 550 c upper greenschist to lower amphibolite facies an eclogitic penetrative foliation s 1 and s dipping stretching lineation l 1 formed during the final stages of subduction of the eclogite bearing unit the p t evolution of the eclogites during d 1 documents the final increment of the prograde p t path later blueschist facies metamorphism is contemporaneous to top to the n emplacement of the eclogite bearing unit onto continental basement units within a subduction zone we discuss two models of eclogite emplacement most probably emplacement is achieved by a thrust along the base of the eclogite bearing unit alternatively the p t path of the eclogite facies rocks suggests an emplacement model similar to corner flow subsequent to eclogite and nappe emplacement the nappe stack is entirely affected by a penetrative deformation d 2 that resulted in the development of a mylonitic foliation s 2 and an e w oriented stretching lineation l 2 within lower amphibolite to upper greenschist facies this deformation is related to a crustal scale detachment zone that formed during the exhumation of the penninic units

peak temperature patterns of polyphase metamorphism resulting from accretion subduction and collision eastern tauern window european alps a study with raman microspectroscopy on carbonaceous material rscm raman microspectroscopy on carbonaceous material rscm from the eastern tauern window indicates contrasting peak temperature patterns in three different fabric domains each of which underwent a poly metamorphic orogenic evolution domain 1 in the northeastern tauern window preserves oceanic units glockner nappe system matrei zone that attained peak temperatures tp of 350 480 c following late cretaceous to palaeogene nappe stacking in an accretionary wedge domain 2 in the central tauern window experienced tp of 500 535 c that was attained either within an exhumed palaeogene subduction channel or during oligocene barrovian type thermal overprinting within the alpine collisional orogen domain 3 in the eastern tauern subdome has a peaktemperature pattern that resulted from eo oligocene nappe stacking of continental units derived from the distal european margin this pattern acquired its presently concentric pattern in miocene time due to post nappe doming and extensional shearing along the katschberg shear zone system kszs tp values in the largest hochalm dome range from 612 c in its core to 440 c at its rim the maximum peak temperature gradient 70 c km 1 occurs along the eastern margin of this dome where mylonitic shearing of the katschberg normal fault knf significantly thinned the subpenninic and penninic nappe pile including the pre existing peak temperature gradient

late stage differential exhumation of crustal blocks in the central eastern alps evidence from fission track and u th he thermochronology thermal history modelling based on zircon and apatite fission track and apatite u th he data constrain and refine the near surface exhumation of the south eastern tauern window penninic units and neighbouring austroalpine basement units in the eastern alps fast exhumation on both sides of the penninic austroalpine boundary coincides with a period of lateral extrusion and tectonic denudation of the penninic units in miocene time 22 12 ma the jump to older ages occurs within the austroalpine unit along the polinik fault which therefore defines the boundary between the tectonically denuded units and the hangingwall at that time according to the different u th he ages between the penninic hochalm and sonnblick domes we demonstrate a differential cooling history of these two domes in the latest miocene and early pliocene

heat sources of cretaceous metamorphism in the eastern alps a discussion abstract the alpine orogenic cycle is characterised by a series of early metamorphic events that occurred in the cretaceous the eoalpine events a collection of data on peak metamorphic conditions pt paths and on relationships between structure and metamorphism for these events in the eastern alps shows that 1 eoalpine metamorphism occurred largely simultaneously with pervasive deformation 2 the eoalpine thermal peak was reached near the pressure peak 3 lower grade structurally higher rocks reached their metamorphic peak earlier than higher grade structurally lower rocks and there is a wide spread of metamorphic ages 4 low grade metamorphic conditions are probably more perturbed than high grade conditions and 5 there is a conspicuous regional distribution of metamorphic grade with amphibolite and eclogite facies metamorphism occurring predominantly in two regions located symmetrically west and east of the tauern window possible heating mechanisms are discussed that can satisfy these observations and a review of previous thermal models is provided it is shown that models which rely on conductive heat transfer cannot account for all of these observations in order to assess other heat sources the effects of shear heating are evaluated here with simple model calculations and a straightforward comparison of length and time scales of dissipative heat production the results suggest that shear heat episodically released during the stacking of the austroalpine nappe pile may be a significant contributor to the observed thermal perturbation

u pb zircon and sm nd geochronology of mafic and ultramafic rocks from the central part of the tauern window eastern alps geochronological and geochemical analyses were carried out in order to identify the pre variscan basement of the tauern window eastern alps maficultramafic rocks from the central part of the tauern window have been studied by ree analysis and u pb and sm nd isotopic analyses on whole rock zircons garnets and sphene u pb and sm nd zircon dating define both magmatic pan african and cambro ordovician events from 650 ma to 486 ma within the alpine fold belt this indicates a time span of 150 ma for magmatic activities in the tauern window of the eastern alps the ages of 657 ma u pb zircon and 644 sm nd zireon obtained from an amphibolite are the oldest dates of the eastern alps they may be related to the pan african orogeny and imply an early cycle of magmatic intrusion before major activity started at around 500 ma sm nd whole rock analyses of the precambrian rocks do not define an isochron reflecting heterogenities within the mantle source the initial end values 1 2 to 4 7 are very low implying an enrichment of the magma source the second main phase of magmatic activity 539 486 ma is characterized by the emplacement of mafic ultramafic rock sequences as no ophiolitic relies are observed in these domains the early paleozoic magmatism was likely associated with extensional tectonics obtained ages of 301 3 and 314 4 3 ma point to a variscan metamorphism the first combined u pb zircon sm nd zircon data for an amphibolite from the basal amphibolite formation baf favoured the sm nd zircon isochron age as a magmatic age whereas the low initial end value point to an enriched magma source as well as to heterogenities within the magma source the obtained ages suggest that parts of the pre variscan basement within the alpine fold belt were formed during the pan africa cycle the detection of pre variscan ages within the alpine basement must reffect a complex history involving significant pre variscan activity

quantifying tectonic versus erosive denudation by the sediment budget the miocene core complexes of the alps abstract the denudation budget of the alps is quantified for the main period of lateral extrusion between 22 and 12 ma the relative importance of tectonic denudation increases from w to e from 70 in the lepontine window in the swiss alps to 80 in the tauern window and to more than 95 in the rechnitz window the driving mechanism of tectonic denudation was eastward extrusion due to an unconstrained orogenic margin in the pannonian basin tectonic denudation in the alps was responsible for about 30 of the total exhumation between 22 and 12 ma

l eclogite de faratsiho madagascar un cas exceptionnel de metamorphisme de haute p basse t au proterozoique superieur abstract a low t proterozoic eclogite group c from madagascar was sampled the rock contains omphacite garnet amphiboles paragonite clinozoisite epidote quartz rutile pyrite and sphene textural and chemical variations of five successive generations of amphiboles permit deduction of the p t path of this rock the conditions of the possible final portion of the prograde p t path are estimated using garnet omphacite pairs pmin 9 kbar at 420 c mineral cores and pmin 11 kbar at 500 c mineral rims this rock is similar to alpine eclogites and precludes a significant secular decrease in the subduction geotherm since at least the proterozoic the scarcity of group c eclogites and blueschists in the precambrian is related to the difficulties of preservation of such rocks rather than the absence of an appropriate geothermal gradient low t high p rocks have been either heated if they resided in the lower crust or eroded if they had been rapidly uplifted

coalification and thermal histories of tertiary basins in relation to late alpidic evolution of the eastern alps the thermal histories of tertiary basins situated around and within the eastern alps are examined using coalification data waples method is used to estimate paleogeothermal conditions the data suggest that the basins thermal histories are intimately related to late alpidic geodynamics of the eastern alps

decoupling along plate boundaries key variable controlling the mode of deformation and the geometry of collisional mountain belts the consequences of decoupling between weak orogenic wedges and strong adjacent foreland plates are investigated by means of lithospheric scale analogue modeling decoupling is implemented in the three layer models by lubrication of the inclined boundary between a strong foreland and a weak orogenic wedge plate boundaries are orthogonal to the convergence direction experimental results show that strong decoupling between the foreland and the orogenic wedge leads to underthrusting of the former underneath the orogenic wedge and deformation of the orogenic wedge by folding shearing and minor backthrusting shortening is mainly taken up along the main overthrust the decoupled boundary and within the orogenic wedge leaving the indenter devoid of deformation in contrast strong coupling between the foreland and the orogenic wedge favors buckling involving both the weak zone and the strong plates the results of these end member models have implications for collision zones for example the eastern alps in europe such that the switch from localized deformation within the orogenic wedge during the oligocene middle miocene to orogen scale uplift and deformation during the late miocene pliocene involving the foreland and indenter plates respectively is interpreted as reflecting a change from a decoupled to a coupled system

cooling and uplift histories of the crystalline thrust stack of the indian plate internal zones west of nanga parbat pakistan himalaya abstract amphibole and mica k ar ar ar and rb sr geochronology for the crystalline internal zones of the indian plate define both an extensive pre himalayan thermal history and a post himalayan metamorphism cooling history south of the main mantle thrust near besham hornblende ar ar ages from basement gneisses record an ca 1850 ma mid proterozoic thermal event hornblende muscovite and biotite cooling ages from cover sequences metamorphosed during the himalayan orogeny are 35 4 30 to 24 and 29 to 22 ma respectively the mica ages together with those derived from zircon and apatite fission track data zeitler 1985 demonstrate a rate of cooling of about 30 c ma during the late oligocene to early miocene that was greater than that either before or since this rapid cooling was initiated during the post metamorphic evolution of the indian plate south verging crustal scale thrust stack during which cover sequences metamorphosed during the himalayan orogeny were imbricated with basement rocks thermally unaffected during that event most of the cooling which happened during the stripping of some 10 2 km of overburden reflects exhumation due to a combination of erosion recorded in the miocene molasse sediments of the foreland basin and major crustal extension within the mmt zone both erosion and extension were the direct consequence of the evolution of the thrust stack

quantitative characterization of gas hydrate bearing sediment using elastic electrical rock physics models abstract successful evaluation of reservoir resources in gas hydrate bearing sediments depends on the accurate estimation of reservoir parameters such as hydrate saturation porosity and clay content elastic and electrical measurements are affected by several rock and fluid properties and their joint interpretation can provide complementary information and improve the accuracy of reservoir characterization results in this work we propose a new rock physics inversion workflow based on 3d rock physics template of elastic and electrical attributes for the direct estimation of reservoir parameters we first conduct a quantitative analysis of the available well log data and core data to understand the morphology of gas hydrate within the marine sediment and choose the appropriate elastic rock physics model then we construct the 3d rock physics template by discretizing the 3d space of reservoir parameters and implementing the suitable elastic and electrical models to calculate the poisson s ratio p wave impedance and electrical resistivity for each combination of values of rock and fluid properties finally we superimpose the measurements on the templates and use a grid searching method to find the nearest gridded node to the data point and minimize the objective function of the mismatch between data and model predictions to investigate the feasibility of our proposed inversion scheme we test a rock physics model based on effective medium theory and a modified archie s equation and invert for reservoir parameters of gas hydrate bearing sediments at well 1250f and 1247b in hydrate ridge the good match between inversion results and core data suggests that the proposed inversion scheme is applicable to real data and allows combining elastic and electrical data for reservoir parameter estimation of gas hydrate bearing sediments

a new approach for deriving pseudovelocity logs from resistivity logs1 this paper describes a method of generating pseudovelocity logs using measurements of electrical resistivity a theoretical relation between electrical resistivity and transit time which is applicable to a wide range of lithologies has been developed the application of this relation using a method which defines lithoresistivity zones as lithological intervals related to the same formation and showing small resistivity variations has been tested in the reconcavo sedimentary basin in bahia brazil a comparison of derived pseudovelocity logs with actual sonic logs for five wells shows the validity of the present approach

alpine metamorphism in the south east tauern window austria 1 p t variations in space and time the pennine rocks exposed in the south east tauern window austria contain mineral assemblages which crystallized in the mid tertiary late alpine regional metamorphism the pressure and temperature conditions at the thermal peak of this event have been estimated for rocks at four different structural levels using a variety of published and thermochemically derived geobarometers and geothermometers the results are a in the garnet chlorite zone 2 5 km structurally above the staurolite biotite isograd t 490 50 c p 7 1 kbar b within 0 5 km of the staurolite biotite isograd t 560 300c p 7 1 kbar c in the staurolite biotite zone c 2 5 km structurally below the staurolite biotite isograd t 610 30 c p 7 6 1 2 kbar d in the staurolite biotite zone 3 4 km structurally below the staurolite biotite isograd t 630 40 c p 6 6 1 2 kbar the pressure estimates imply that the total thickness of overburden above the basement cover interface in the mid tertiary was c 26 4 km this overburden can only be accounted for by the austro alpine units currently exposed in the vicinity of the tauern window if the altkristallin the middle austro alpine nappe was itself buried beneath an upper austro alpine nappe or nappe pile which was 7 4 km thick at that time the occurrence of epidote margarite quartz pseudomorphs after lawsonite in garnet indicates that part of the mesozoic pennine cover sequence in the south east tauern experienced blueschist facies conditions t 450 c p 12 kbar in early alpine times evidence from the central tauern is used to argue that the blueschist facies imprint post dated the main phase of tectonic thickening d1a and was thus a direct consequence of continental collision combined oxygen isotope and fluid inclusion studies on late stage veins thought to have been at lithostatic pressure and in thermal equilibrium with their host rocks during formation suggest that they crystallized from aqueous fluids at 1 1 0 4 kbar and 420 20 c early alpine late alpine and vein formation p t constraints have been used to construct a p t path for the base of the mesozoic cover sequence in the south east tauern window the prograde part of the p t path between early and late alpine metamorphic imprints is unlikely to have been a smooth curve and may well have had a low dp dt overall the decompression presumably due to erosion which occurred immediately before the thermal peak and possibly also earlier in the tertiary was probably partly or completely cancelled by the effects of early to mid tertiary d2a tectonic thickening the thermal peak of metamorphism was followed by a phase of almost isothermal decompression which implies a period of rapid uplift in the middle tertiary the peak metamorphic p t estimates are compared with the solutions of england s 1978 one dimensional conductive thermal model of the eastern alps and are shown to be consistent with the idea that the late alpine metamorphism was caused by tectonic burial of the pennine zone beneath the austro alpine nappes in the absence of extraneous heat sources such as large intrusions at depth

microstructural and textural development of calcite marbles during polyphase deformation of penninic units within the tauern window eastern alps abstract the evolution of calcite microstructures and crystallographic preferred orientations cpos is well understood due to well constrained experimental studies however the interpretation of naturally deformed calcite marbles is more difficult because of less constrained strain paths a multiphase deformation history and variable p t conditions the penninic units within the tauern window eastern alps have been affected by several deformation events and metamorphic overprint generally three major deformational events can be distinguished d 1 is related to underthrusting of penninic units beneath the austroalpine nappe complex and top to the n nappe stacking within the penninic continental units deformation stage d 2 is interpreted as reflecting the subsequent continent collision between the penninic continental units and the european foreland d 3 is related to the formation of the dome structure of the tauern window this polyphase deformation history can be partly reconstructed by the evolution of calcite microfabrics and cpos three types of calcite fabrics are distinguished within the penninic units of the tauern window and the lower austroalpine unit d 1 fabrics are characterized by equilibrated microstructures and lt cpos the cpos are generally strong and symmetric with one well developed cluster near the z axis of the finite strain ellipsoid these fabrics have locally been overprinted by subsequent amphibolite to greenschist facies metamorphism generally the occurrence of lt fabrics coincides with the occurrence of amphibolite facies metamorphic mineral assemblages in the central part of the tauern window while ht fabrics have been observed outside this area fabrics from the central part of the tauern window have likely been strengthened during subsequent thermal equilibration while the fabrics that have been observed at the peripheral parts have been less affected by subsequent metamorphic overprint therefore d 1 fabrics do not reflect d 1 conditions but subsequent thermal equilibration similar observations have been made for the evolution of d 2 fabrics lt fabrics dominate inside the amphibolite facies isograde ht fabrics occur outside greenschist facies metamorphic conditions the fabrics are characterized by high finite strains near the margins of the tauern window the intensity of which decreases towards the central parts where microstructures are characterized by recrystallization and thermal equilibration due to amphibolite facies metamorphic overprint the strong cpos document this influence the ht fabrics and microstructures within peripheral areas indicate that they have less been affected by this thermal event and therefore are more indicative for the deformational conditions during d 2 d 3 is restricted to distinct shear zones along the tectonic boundaries of the tauern window from the central parts to the shear zone boundaries a clear evolution of microfabrics can be observed in internal parts microstructures are characteristic for intracrystalline plasticity with a dominating activity of r glide twinning was less important during the final phases of deformation on approaching the shear zone boundaries the grain size decreases due to dynamic recrystallization and secondary grain size reduction until ultramylonites are formed within these domains grain boundary sliding seems to have been dominant in conclusion calcite cpos from polyphase areas do not only include information on the deformation conditions but also bear information about the thermal overprint subsequent to the main deformational event

geothermobarometry in metasediments of the southern grossvenediger area tauern window austria metasediments in the southern grossvenediger area tauern window austria were studied along a cross section through rocks of increasing metamorphic grade from the margin of the tauern window in the south to the base of the upper schieferhulle including the eclogite zone in the north in the southern part of the cross section there is no evidence for a pre late alpine metamorphic history in the form of high pressure relics or pseudomorphs mineral assemblages are characterized by the stability of tremolite calcite biotite calcite and biotite chlorite calcite in the northern part a more complete alpine metamorphic evolution is preserved primary high pressure assemblages are dolomite quartz tremolite zoisite zoisite dolomite quartz phengite i and probably tremolite dolomite phengite i secondary post kinematic assemblages tremolite calcite talc calcite phengite ii chlorite calcite quartz biotite chlorite calcite biotite zoisite calcite formed as a result of the dominant late alpine metamorphic overprint the occurrence of biotite zoisite calcite is confined to the northernmost area and defines a biotite zoisite calcite isograd p t estimates based on standard thermobarometric techniques and on stability relationships of tremolite calcite dolomite quartz and zoisite give consistent results p t conditions of the main tertiary metamorphic overprint were 525 c p 7 5 1 kbar in the northern part of the cross section the southern part was metamorphosed at lower temperatures of 430 470 c the si content of phengites from this area is almost as high as that of phengites from the eclogite zone simax 3 4 pfu pressures 10 kbar at 420 c are suggested by phengite barometry according to massone schreyer 1987 in the absence of high pressure relics or pseudomorphs these phengites which lack late alpine re equilibration are the only record that rocks of the southern part probably also experienced an early non eclogitic high pressure metamorphism

elastic velocities of partially gas saturated unconsolidated sediments abstract fluid in sediments significantly affects elastic properties of sediments and gas in the pore space can be identified by a marked reduction of p wave velocity or a decrease of poisson s ratio the elastic properties of gas saturated sediments can be predicted by the classical biot gassmann theory bgt however parameters for the bgt such as the biot coefficient or moduli of dry frame of unconsolidated and high porosity sediments are not readily available dependence of velocities on differential pressure or porosity for partially gas saturated sediments is formulated using properties derived from velocities of water saturated sediments laboratory samples for unconsolidated and consolidated sediments and well log data acquired for unconsolidated marine sediments agree well with the predictions however because the p wave velocity depends highly on how the gas is saturated in the pore space such as uniform or patch the amounts of gas estimated from the p wave velocity contains high uncertainty the modeled vp vs ratio of partially gas saturated sediment using the patch distribution is usually greater than 1 6 whereas the ratio modeled assuming a uniform distribution is about 1 6 thus poisson s ratio or vp vs ratio may be used to differentiate patch from uniform saturation but differences between various models of patch saturation cannot be easily identified

far field effects of late miocene subduction in the eastern carpathians e w compression and inversion of structures in the alpine carpathian pannonian region kinematic and paleostress data constrain a late miocene e w compressional event that affected the entire alpine carpathian pannonian system after 9 ma and prior to 5 3 ma the maximum horizontal compression directions obtained from 110 stations show a mean 1 orientation of 083 deformation is mainly strike slip e w directed compression followed early to middle miocene upper plate extension in the pannonian basin which was caused by the retreating subduction boundary in the outer carpathians this compressional event terminated early to middle miocene eastward lateral extrusion of the eastern alps and reverted strike slip faults which bounded earlier extruded wedges such as the salzachtal ennstal fault the periadriatic fault the mur murz vienna basin fault system and strike slip faults in the western carpathians e w compression caused the reorientation of the extension direction of the alpine crustal stack east directed tectonic unroofing of the metamorphic domes in the central eastern alps terminated between 9 and 6 ma and early to middle miocene orogen parallel e w extension switched to late miocene n s extension which parallels modern topographic slopes in the pannonian basin the change from synrift extension to late miocene compression during the postrift phase caused the pronounced postrift subsidence by stress induced downward flexure of the loaded lithosphere we relate late miocene e w compression to coeval late stage west directed subduction of the european plate below the eastern carpathians slab pull of the subducted plate caused subduction roll back and upper plate extension of the pannonian area up to the middle miocene subduction slowed down and ceased when up to 60 km thick buoyant continental crust entered the subduction zone during the short period of continued convergence e w directed compressive stress was transmitted across the subduction boundary into the upper plate compressive stress was transferred through the uppermost brittle crust of the earlier extended pannonian region into the eastern alps up to 1400 km behind the subduction zone e w compression terminated during the pliocene when the pliocene to recent nnw sse compressive stress field was established in central europe

localized ductile shear below the seismogenic zone structural analysis of an exhumed strike slip fault austrian alps 1 the miocene salzachtal ennstal mariazell puchberg semp strike slip fault in austria allows study of the internal structure of a fault zone from the near surface to 30 km depth as it enters the tauern window along the rinderkarsee shear zone the semp fault passes from a dominantly brittle to a dominantly ductile structure the shear zone consists of three 1 to 100 m wide zones of brittle ductile and ductile deformation separated by 500 m wide zones of less deformed rocks the southern shear zone is mylonitic with ductile amphibole and plagioclase weak crystal preferred orientations imply that the main deformation mechanism was dislocation accommodated grain boundary sliding the northern and central shear zones are characterized by discrete millimeter wide shear zones with ductile quartz muscovite and biotite and brittle feldspar shear zone nucleation at the grain scale involved dislocation creep and the transformation of plagioclase to muscovite strain then localized in muscovite rich grain boundary shear zones that linked to form throughgoing shear zones

mantle lithospheric deformation and crustal metamorphism with some speculations on the thermal and mechanical significance of the tauern event eastern alps changes in the thickness of the mantle lithosphere beneath convergent orogens through processes such as the pervasive thickening of the lithosphere and the convective thinning of the thermal boundary layer dictate the heat flow through the base of the crust and thus may profoundly influence the thermal evolution of crustal metamorphic terrains calculations based on one dimensional thermal energy balances show that when mantle lithosphere is substantially thickened and remains intact through the orogenic cycle then low temperature facies series including blueschist and eclogite facies may be preserved throughout the crust in contrast crust thickened above attenuated mantle lithosphere will develop much higher temperature facies series potential energy arguments suggest that changes in the thickness in the mantle lithosphere induce changes in the elevation and the potential energy stored within the lithosphere therefore the response to mantle lithospheric deformation observable in crustal metamorphic terrains should not only be recorded in the thermal regime but also in changes in the incremental strain history in as much as it reflects the force balance operating within the orogen for example mantle lithospheric thinning beneath thickened crust may cause an increase in crustal temperatures synchronous with the termination of convergent strain or for large reductions in mantle lithospheric thickness with the onset of extensional deformation such histories are recorded in a number of young metamorphic terrains for example the eastern alps which may provide an important thermal and isostatic record of the mantle lithospheric response to convergent deformation here we show how application of these ideas may lead to new insights into some outstanding problems concerning the thermal and mechanical evolution of the eastern alps during the tertiary tauern metamorphic event

p t fluid regimes of metamorphism and related magmatism with specific reference to the granulite facies sharyzhalgay complex of lake baikal

transition from orogen perpendicular to orogen parallel exhumation and cooling during crustal indentation key constraints from 147sm 144nd and 87rb 87sr geochronology tauern window alps abstract the core of the alpine orogen in the eastern alps tauern window experienced a change from orogen normal shortening and post nappe doming to predominantly orogen parallel extension and tectonic unroofing during late oligocene to miocene northward indentation of the adriatic microplate a new 147 sm 144 nd isochron age of 25 7 0 9 ma on a garnet bearing assemblage from the lowest nappe complex forming a dome in the eastern part of the tauern window indicates that high temperatures related to post nappe barrovian type metamorphism overlapped in time with the onset of doming new 87 rb 87 sr biotite ages from this same complex combined with previously published 87 rb 87 sr white mica ages suggest that doming and exhumation began no later than 28 ma immediately in front of indenting austroalpine crustal blocks then migrated laterally to the ese during rapid exhumation and orogen parallel stretching beginning at about 23 ma rapid cooling ended at approximately 17 ma in the footwall of the katschberg normal fault which delimits the eastern margin of the tauern window a similar pattern of migrating doming orogen parallel extension and cooling is recognized in the western part of the tauern window where rapid exhumation began at about 20 ma some 2 3 ma later than in the eastern part this difference in the onset of rapid exhumation as well as the overall migration of doming from the center to the ends of the tauern window are attributed to fragmentation of the aforementioned austroalpine blocks along the leading edge of the main adriatic indenter southern alps as this indenter advanced to the north

integrated analysis of well logs and seismic data to estimate gas hydrate concentrations at keathley canyon gulf of mexico abstract accurately detecting and quantifying gas hydrate or free gas in sediments from seismic data require downhole well log data to calibrate the physical properties of the gas hydrate free gas bearing sediments as part of the gulf of mexico joint industry program a series of wells were either cored or drilled in the gulf of mexico to characterize the physical properties of gas hydrate bearing sediments to calibrate geophysical estimates and to evaluate source and transport mechanisms for gas within the gas hydrates downhole acoustic logs were used sparingly in this study because of degraded log quality due to adverse wellbore conditions however reliable logging while drilling lwd electrical resistivity and porosity logs were obtained to tie the well log information to the available 3 d seismic data in this area a velocity log was calculated from the available resistivity log at the keathley canyon 151 2 well because the acoustic log or vertical seismic data acquired at the nearby keathley canyon 151 3 well were either of poor quality or had limited depth coverage based on the gas hydrate saturations estimated from the lwd resistivity log the modified biot gassmann theory was used to generate synthetic acoustic log and a synthetic seismogram was generated with a fairly good agreement with a seismic profile crossing the well site based on the well log information a faintly defined bottom simulating reflection bsr in this area is interpreted as a reflection representing gas hydrate bearing sediments with about 15 saturation overlying partially gas saturated sediments with 3 saturation gas hydrate saturations over 30 40 are estimated from the resistivity log in two distinct intervals at 220 230 and 264 300 m below the sea floor but gas hydrate was not physically recovered in cores it is speculated that the poor recovery of cores and gas hydrate morphology are responsible for the lack of physical gas hydrate recovery

permeability and porosity of hydrate bearing sediments in the northern gulf of mexico abstract hydrate bearing sands are being actively explored because they contain the highest concentrations of hydrate and are the most economically recoverable hydrate resource however relatively little is known about the mechanisms or timescales of hydrate formation which are related to methane supply fluid flux and host sediment properties such as permeability we used logging while drilling data from locations in the northern gulf of mexico to develop an effective medium theory based model for predicting permeability based on clay sized sediment fraction the model considers permeability varying between sand and clay endpoint permeabilities that are defined from laboratory data we verified the model using permeability measurements on core samples from three boreholes and then used the model to predict permeability in two wells drilled in walker ridge block 313 during the gulf of mexico gas hydrate joint industry project leg ii expedition in 2009 we found that the cleanest sands clay sized fraction

balancing lateral orogenic float of the eastern alps abstract oligocene to miocene post collisional shortening between the adriatic and european plates was compensated by frontal thrusting onto the molasse foreland basin and by contemporaneous lateral wedging of the austroalpine upper plate balancing of the upper plate shortening by horizontal retrodeformation of lateral escaping and extruding wedges of the austroalpine lid enables an evaluation of the total post collisional deformation of the hangingwall plate quantification of the north south shortening and east west extension of the upper plate is derived from displacement data of major faults that dissect the austroalpine wedges indentation of the south alpine unit corresponds to 64 km north south shortening and a minimum of 120 km of east west extension lateral wedging affected the eastern alps east of the giudicarie fault west of the giudicarie fault north south shortening was compensated by 50 to 80 km of backthrusting in the lombardian thrust system of the southern alps the main structures that bound the escaping wedges to the north are the inntal fault system ca 50 km sinistral offset the konigsee lammertal traunsee klt fault 10 km and the salzach ennstal mariazell puchberg semp fault system 60 km these faults as well as a number of minor faults with displacements less than 10 km root in the basal detachment of the alps the thin skinned nature of lateral escape related structures north of the semp line is documented by industry reflection seismic lines crossing the northern calcareous alps nca and the frontal thrust of the eastern alps complex triangle zones with passive roof backthrusts of middle miocene molasse sediments formed in front of the laterally escaping wedges of the northern eastern alps the aim of this paper is a semiquantitative reconstruction of the upper plate of the eastern alps most of the data is published elsewhere

alpine metamorphism in the south east tauern window austria 2 rates of heating cooling and uplift existing geochronological data are reviewed and new rb sr k ar and 39ar 40ar ages are presented including a suite of 33 mica ages from a 20 km north south tunnel section these data are discussed in relation to the thermal history from the overthrusting of the autroalpine nappes c 65 myr ago to the present the earliest phase of metamorphism involving lawsonite crystallization is associated with emplacement of these nappes subsequently temperatures in the rocks beneath rose at a mean rate of 3 6 c myr until the climax of metamorphism at high structural levels published data indicate an age 35 myr for the metamorphic climax in contrast a new 39ar 40ar step heating age of 23 8 0 8 myr on amphibole from near the base of peripheral schieferhulle closely approximates the age of metamorphism and provides the first clear indication that the climax of metamorphism occurred later at deeper structure levels following the climax near isothermal uplift and erosion reduced pressure to c 1 kbar before white mica closure at 19 myr this implies uplift at 3 mm yr along the tunnel section white mica k ar ages vary systematically from 24 myr to 16 5 myr with position relative to a late 4 km amplitude dome whereas biotite rb sr ages are uniform at 16 5 myr across the whole profile doming is thus dated at 16 5 myr with transient uplift rates 5 mm yr at other times uplift rates were 1 mm yr

dating deformation using rb sr in white mica greenschist facies deformation ages from the entrelor shear zone italian alps ages of deformation have been obtained by rb sr analysis of white micas whose microstructural and chemical characteristics indicate that they crystallized or recrystallized during shear fabric formation since white micas commonly define deformation fabrics in medium grade metamorphic rocks these ages can be directly related to structural geometries with regional context this direct method contrasts with estimates of midcrustal deformation ages derived from cooling histories because it does not rely on assumptions about the thermal structure of the crust it does require that the dated minerals attained isotopic equilibrium with the dominant sr reservoir at temperatures lower than the closure temperature this resetting was apparently achieved during dynamic recrystallization of white micas in greenschist facies metasediments and metagranitoid units in the western alps the results suggest that the sr isotopic composition of the new mica is buffered by the coexisting high sr phases calcite feldspar or epidote via the grain boundary network high strain rocks from the entrelor shear zone system of the western alps have yielded indistinguishable white mica rb sr ages along 30 km of individual and kinematically linked shear zones the age of the back thrusting event is constrained at 34 1ma the age yielded by the younger generation of synkinematically crystallized white micas this event was short lived involving at least 20 km of shortening in 1 m y or less an earlier variably overprinted component dating from 38 to 37 ma has been identified in the mica fabric but its kinematic significance is uncertain this method of dating strain fabrics offers a powerful tool for tectonic studies since isotopic resetting can be directly linked to structural geometries microstructural textures and pt conditions it allows testing of kinematic models in orogens and can provide important information on the rates of geological processes in the crust

erratum invasion of drilling mud into gas hydrate bearing sediments part i effect of drilling mud properties fulong ning 1 2 keni zhang 3 4 nengyou wu 2 ling zhang 1 gang li 2 guosheng jiang 1 yibing yu 1 li liu1 and yinghong qin1 1faculty of engineering china university of geosciences wuhan hubei 430074 china e mail nflzx cug edu cn 2guangzhou center for gas hydrate research chinese academy of sciences guangzhou 510640 china 3earth system division lawrence berkeley national laboratory berkeley ca 94720 usa 4college of water sciences beijing normal university beijing 100875 china

argon retentivity and argon excess in amphiboles from the garbenschists of the western tauern window eastern alps 22 hornblende k ar ages and 10 39ar 40ar spectra were obtained for hornblende garbenschists from the western tauern window the post kinematic amphiboles were produced during the late alpine prograde metamorphism 6 10 kb and 500 570 c two nearly potassiumfree cummingtonites rimming hornblende yield k ar ages of 120 ma while the 20 tschermakitic hornblendes scatter between 17 and 37 ma the reason for this scatter is excess ar possibly incorporated into amphiboles during healing of fractures now traceable by trails of fluid inclusions excess ar is semiquantitatively corrected for by combining cogenetic hornblende and cummingtonite with k ar isochrons it can be quantified in 4 out of 10 hornblendes by 39ar 40ar stepwise heating experiments ages of 18 20 ma result for corrected hornblendes the retentivity of 40ar after correction for excess shows no correlation with chemistry within the narrow compositional range observed rather it shows intriguing correlations with irregularities in ca k spectra pointing to a microstructurally controlled mechanism for ar loss this observation leads to a critical evaluation of the closure temperature constant which apparently depends on an incompletely known number of mineralogical and environmental parameters in particular those 39ar 40ar release spectra which yield low temperature steps with younger ages than the plateaus are not interpretable in terms of a synchronous closure this gives evidence that loss of radiogenic isotopes proceeds by a more complex mechanism than simple volume diffusion through isotropic media

models for relative motion of crustal blocks within the carpathian region based on restorations of the outer carpathian thrust sheets details of the oligocene present day motion of the adriatic block with respect to europe can be determined by palinspastic restorations of the outer carpathians thrust sheets the arcuate nature of the carpathians poses problems for simple restorations of sections because they create converging restoration paths which require large amounts of strike parallel extension 40 50 such large amounts of extension are not seen on maps or in the field a combination of thrust transport directions changing with time between and within thrust sheets and divergent transport directions helps minimise the arc parallel extension necessary 18 25 the pannonian basin can be treated either as an area dominated by strike slip motion rigid block movements or as an area of back arc extension the differences in restoration geometry produced by these two scenarios help to indicate which of the two mechanisms was dominant the consequences of the rigid block restoration indicate the model is inappropriate because it requires approximately 20 clockwise rotation of the adriatic block during the late tertiary it also indicates at least 300 km strike slip motion distributed among the late tertiary faults of the dinaride balkanide and hellenide mountain belts the back arc extension model alleviates the the 20 clockwise rotation of the adriatic block and requires about 200 km distributed strike slip motion in yugoslavia and bulgaria

imaging methane hydrates growth dynamics in porous media using synchrotron x ray computed microtomography commercial scale methane ch4 extraction from natural hydrate deposits remains a challenge due to among other factors a poor understanding of hydrate host sediment interactions under low temperature and high pressure conditions that are conducive to their existence we report the use of synchrotron x ray computed microtomography cmt to image for the first time time resolved pore scale methane ch4 hydrate growth from an aqueous solution containing 5 wt barium chloride bacl2 and pressurized ch4 hosted in glass beads all contained in an aluminum cell with an effective volume of 3 5 ml multiple two dimensional 2 d cross sectional images show ch4 hydrates with 7 5 m resolution distributed in patches throughout the system without dependence on distance from the cell walls the time resolved three dimensional 3 d images constructed from the 2 d slices exhibited pore filling hydrate formation from dissolved ch4 gas similar to natural ch4 hydrates si in the marine environment furthermore the 3 d images show that the aqueous phase was the wetting phase of the glass beads i e the host and the formed hydrate were separated by an aqueous layer these results provide some fundamental understanding of the nucleation phenomenon of gas hydrate formation at the pore scale pore filling ch4 hydrate growth is likely to result in a reduced bulk modulus and thus could affect seafloor stability during the reverse phenomenon i e dissociation of natural hydrate deposits

role of topography in isotherm perturbation apatite u th he and fission track results from the malta tunnel tauern window austria 1 apatite u th he and fission track age determinations of samples from a 20 km long near horizontal tunnel in the hochalm ankogel dome eastern tauern window austria are presented in order to determine the role of paleo topography in perturbing isotherms in the shallow crust apatite fission track ages 26 8 ma show no systematic correlation with distance along the tunnel or elevation two age components in the fission track data indicate cooling through 120 c at approximately 20 ma and 80 c at approximately 6 ma surface and tunnel u th he ages 17 9 ma and 13 5 ma respectively are consistently younger than the equivalent fission track ages u th he ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section geological factors faulting lithology appear to have had little effect on this age distribution the u th he age pattern is inconsistent with rock cooling underneath the present day hochalm ankogel dome topography the age minimum is interpreted to coincide with a paleotopographic maximum in the hochalm ankogel dome and suggests that the 40 60 c isotherms were warped sufficiently to affect apatite u th he ages the tunnel apatite u th he ages match synthetic he ages derived from a two dimensional numerical model of landscape evolution integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present day hochalm ankogel dome topography was formed at 7 to 10 ma

timing of metamorphism in the tauern window eastern alps rb sr ages and fabric formation the peripheral schieferhulle of the tauern window of the eastern alps represents post hercynian penninic cover sequences and preserves a record of metamorphism in the alpine orogeny without the inherited remnants of hercynian events that are retained in basement rocks the temperature time deformation history of rocks at the lower levels of these cover sequences have been investigated by geochronological and petrographic study of units whose p t evolution and structural setting are already well understood the eclogite zone of the central tauern formed from protoliths with penninic cover affinities and suffered early alpine eclogite facies metamorphism before tectonic interposition between basement and cover it then shared a common metamorphic history with these units experiencing blueschist facies and subsequent greenschist facies conditions in the alpine orogeny the greenschist facies phase associated with penetrative deformation in the cover and the influx of aqueous fluids reset sr isotopes in metasediments throughout the eclogite zone and cover schists recording deformation and peak metamorphism at 28 30 ma the peripheral schieferhulle of the south east tauern window yields rb sr white mica ages which can be tied to the structural evolution of the metamorphic pile early prograde fabrics pre date 31 ma and were reworked by the formation of the large north east vergent sonnblick fold structure at 28 ma peak metamorphism post dated this deformation but by contrast to the equivalent levels in the central tauern peak metamorphic conditions did not lead to widespread homogenization of the sr isotopes localized deformation continued into the cooling path until at least 23 ma partially or wholly resetting sr white mica ages in some samples these isotopic ages may be integrated with structural data in regional tectonic models and may constrain changes in the style of crustal deformation and plate interaction however such interpretations must accommodate the demonstrable variation in thermal histories over small distances

pore water sulfate alkalinity and carbon isotope profiles in shallow sediment above marine gas hydrate systems a numerical modeling perspective 1 both the concentration and the carbon isotope composition of dissolved inorganic carbon dic vary considerably across the sulfate methane transition smt in shallow marine sediment at locations with gas hydrate this variability has led to different interpretations for how carbon including ch4 cycles within gas charged sediment sequences over time we extend a one dimensional model for the formation of gas hydrate to account for downhole changes in dissolved ch4 so42 dic and ca2 and the 13c of dic the model includes advection diffusion and two reactions that consume so42 degradation of particulate organic carbon poc and anaerobic oxidation of methane aom using our model and site specific parameters steady state pore water profiles are simulated for two sites containing gas hydrate but different carbon chemistry across the smt site 1244 hydrate ridge dic 38 mm 13c of dic 22 5 pdb and site keathley canyon kc 151 3 gulf of mexico dic 16 mm 13c of dic 49 6 pdb the simulated profiles for ch4 so42 dic ca2 and 13c of dic resemble those measured at the sites and the model explains the similarities and differences in pore water chemistry at both sites an upward flux of ch4 consumes most net so42 at a shallow smt and calcium carbonate removes a portion of dic at this horizon however a large flux of 13c enriched hco3 enters the smt from depth at site 1244 but not at site kc151 3 this leads to a high concentration of dic with a 13c much greater than that of ch4 even though aom causes the smt the addition of hco3 from depth impacts the slope of certain concentration crossplots crucially neither the dic concentration nor its carbon isotope composition at the smt can be used to discriminate between sulfate reduction pathways

thermal history of the sonnblick dome south east tauern window austria implications for heterogeneous uplift within the pennine basement the sonnblick dome is one of several domal structures affecting the interface between basement and cover within the pennine zone of the tauern window in the eastern alps rb sr isotopic data comprising 19 biotite and 22 white mica ages from variably deformed granitic gneisses provide new evidence of the thermal and tectonic history of the dome and its relationships with other parts of the south east tauern window white mica ages generally cluster between 26 and 30 ma although there are values up to 82 ma which appear to reflect incomplete equilibration during tertiary metamorphism under low amphibolite facies conditions six closely spaced samples from an intensely sheared gneiss lamella are more tightly grouped between 26 and 27 6 ma and provide the best estimate of the age of syntectonic crystallization biotite ages are systematically younger ranging from 19 to 23 5 ma reflecting closure during post metamorphic cooling sonnblick dome and the hochalm dome approximately 20 km further east where closure of rb sr in biotite did not occur until 16 5 ma the metamorphic peak here is also probably younger possibly as late as 22 ma the sonnblick dome was formed before 27 ma and the deformation style had changed to extension before biotite closure by 19 ma in contrast rapid updoming in the hochalm dome was previously dated at 16 5 ma and the differences in thermal history can be linked to differences in deformation history overall the geochronological data from the south east tauern window demonstrate the heterogeneity of thermal history on a geographical scale of 10 km and emphasize the importance of tectonic displacements in controlling temperature within orogenic belts