sequence of thrusting within a thick skinned tectonic wedge evidence from40ar 39ar and rb sr ages from the austroalpine nappe complex of the eastern alps the sequence of thrusting within a regional scale alpine thick skinned tectonic wedge has been constrained by rb sr and 40ar 39ar dating of whole rock constituent white mica and biotite from structural units of the austroalpine nappe complex eastern alps austria preservation of variscan and pre variscan isotopic signatures in pre alpine basement units indicates a non penetrative metamorphic alpine overprint alpine nappe assembly and accompanying ductile deformation occurred during maintenance of lower greenschist facies metamorphic conditions c 300 450 c analyses from greenschist facies metamorphic mylonites and penetratively ductile deformed cover sequences display decreasing 40ar 39ar plateau ages structurally downward thrusting and accompanied ductile deformation commenced at c 100 90 ma in the uppermost structural levels footwall fault propagation effected internal deformation and out of sequence thrusting within intermediate structural levels at c 95 80 ma this was contemporaneous wit

fluid inclusions reviews in mineralogy vol 12 edwin roedder 1984 mineralogical society of america 644 p u s 14

late cretaceous exhumation history of an extensional extruding wedge graz paleozoic nappe complex austria late cretaceous structures within the eastern graz paleozoic nappe complex define an extruding wedge with north eastward directed thrusting in eastern portions and strike slip shear along the margins stacking structures are overprinted by south westward directed extension with low grade metamorphic rocks in the hangingwall and high grade basement rocks in the footwall pressure temperature and structural data are obtained from successively opening quartz veins that record various stages of progressive deformation and metamorphism fluid inclusion data and related structures show that during extension isothermal decompression from ca 550 c and 8 kbar down to ca 450 c and 2 kbar was related to exhumation of rocks from deep crustal levels the data point to a high geothermal gradient and explain condensed paleo isotherms due to ductile normal faulting in the eastern areas of the graz paleozoic nappe complex the investigated late cretaceous structural elements suggest that the graz paleozoic nappe complex decoupled from the surrounding basement units and operated as a large scale extension extrusion corridor that evolved prior to miocene extrusion tectonics in the eastern alps

equilibria within the mineral assemblage quartz muscovite biotite garnet plagioclase and implications for the mixing properties of octahedrally coordinated cations in muscovite and biotite interaction parameters derived using empirical calibration methods indicate strong non ideality in the mixing of octahedrally coordinated cations in muscovite and biotite the data set used for calibration comprises mineral compositions from 49 samples containing quartz muscovite biotite garnet plagioclase and al2sio5 kyanite or sillimanite pressures and temperatures in the data set were determined through the simultaneous application of geothermometry based on the garnet biotite femg1 exchange equilibrium and geobarometry based on the anorthite breakdown equilibrium two equilibria yielded simple expressions from which binary interaction parameters for octahedrally coordinated cations in biotite could be directly determined a four component fe2 mg al ti regular symmetric mixing model was assumed for biotite one equilibrium yielded a simple expression from which an interaction parameter for the mixing of the mgal celadonite component in muscovite could be directly determined two sets of calculations were performed utilizing different calibrations of the garnet biotite geothermometer and the anothite breakdown geobarometer and different garnet activity models both placed samples within or near the stability field of the al2sio5 phase present in each sample and both yielded similar values for the interaction parameters within narrow uncertainties indicating that the values are insensitive to differences in the underlying methods using the derived interaction parameters activity models were formulated for the annite phlogopite eastonite and siderophyllite components of biotite and for the mgal celadonite component of muscovite these were utilized for the empirical calibration of 45 fluid independent equilibria involving unique combinations of phase components from the mineral assemblage garnet plagioclase biotite muscovite quartz forty three of the equilibria may be applied as geobarometers to equilibrium assemblages of quartz muscovite biotite garnet plagioclase when care is taken to insure that applications are restricted to valid compositional ranges for these the calibrations yielded multiple correlation coefficients ranging from 0 953 to 0 998 and standard deviations of the residuals ranging from 597 to 118 bars

synthetic fluid inclusions vii re equilibration of fluid inclusions in quartz during laboratory simulated metamorphic burial and uplift p t conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations these observations suggest that inclusions formed during early stages of regional metamorphism continue to re equilibrate during burial and subsequent uplift in response to differential pressure p t conditions accompanying burial and uplift were experimentally simulated by initially forming pure h2o inclusions in quartz at elevated temperatures and pressures and then re equilibrating the inclusions in the presence of a 20 wt nacl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re equilibration in all samples re equilibrated at confining pressures below the internal pressure some inclusions were formed that had compositions of 20 wt nacl and densities in accord with the final p t conditions additionally some inclusions were observed to contain fluids of intermediate salinities between 0 and 20 wt nacl densities of these inclusions were also consistent with formation at the re equilibration p t conditions the remainder of the fluid inclusions observed in these samples contained pure h2o and their homogenization temperatures corresponded to densities intermediate between the initial and final p t conditions in short term experiments 7 days where the initial internal overpressure exceeded 1 kbar no inclusions were found that contained the original density and none were found to have totally re equilibrated instead most h2o inclusions re equilibrated until their internal pressures were between 750 and 1500 bars above the confining pressure regardless of the initial pressure differential in a long term experiment 52 days inclusions re equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar i e total re equilibration and 1 2 kbar above the confining pressure in experiments where the confining pressure during re equilibration exceeded the initial internal pressure densities of pure h2o inclusions increased to values intermediate between the initial and final p t conditions additionally these inclusions were generally surrounded by a three dimensional halo of smaller inclusions also of intermediate density resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure in extreme cases where confining pressures were 4 5 kbar above the initial pressure the parent inclusion almost completely closed leaving only the three dimensional array of small 5 m inclusions the outline of which may be several times the volume of the original inclusion groups of such inclusions closely resemble textures commonly observed in medium to high grade metamorphic rocks inclusions containing 10 and 42 wt nacl solutions trapped at 600 c and 3 kbar were re equilibrated at 600 c and 1 kbar for 5 days in dry argon to evaluate the importance of h2o diffusion as a mechanism of lowering the inclusion bulk density salinities of re equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved density changes similar to those previously described were noted in these experiments in inclusions showing no visible microfractures therefore density variations observed in inclusions in this study re equilibrated under rapid deformation conditions are considered to result from a change in the inclusion volume without significant loss of contents by diffusion or leakage

extension in compressional orogenic belts the eastern alps extension in the eastern alps encompasses the following 1 extension accompanying simple shear crustal stacking subhorizontal stretching occurs along flat lying foliations and regionally consistent stretching lineations with associated high strains on a local scale stretching results from extrusion of ductile sediments squeezed between rigid basement blocks basement blocks during thrust sheet imbrication the overall geometric effect is crustal thickening 2 classical extensional tectonics extension first occurs as a consequence of accretion and underthrusting of continental and oceanic material and represents gravitational adjustment of an unstable orogenic wedge extension then occurs as a consequence of terminal continental collision and is accommodated by lateral extrusion of crustal of crustal blocks the overall geometric effect is crustal thinning extension is generally oriented subparallel to the strike of the orogen

effect of water on the rheology of experimentally deformed quartzite empirical flow laws have been determined for simpson quartzite samples deformed to mechanical steady state in the quartz stability field using griggs blacic solid medium deformation apparatus experiments were conducted on samples both as received dry and with water added via the dehydration of a talc confining medium wet best fits of the power law type yield a stress exponent of 2 72 0 19 an activation enthalpy of 134 32 kj mol 1 and a preexponential constant of 1 16 1 15 0 58 10 7 mpa 2 72 s 1 for the dry quartzite law and are 2 61 0 15 145 17 kj mol 1 and 5 05 5 00 10 6 mpa 2 61 s 1 for the wet quartzite the enhanced hydrolytic weakening of the wet experiments appears to affect the flow laws mostly in the preexponential constants possibly as a defect concentration term that is higher in the wet than in the dry law over the range of experimental conditions 750 900 c 10 7 to 10 4 s 1 and 1 0 1 25 gpa confining pressure dry specimens are 1 5 2 5 times stronger than wet samples deformed at the same conditions the microstructures produced are analogous to those observed in many natural quartz tectonites recrystallization is well developed in the wet but not the dry specimens at flow stresses below 500 mpa microstructures indicative of recovery are well developed a comparison of our creep activation enthalpies with those determined from diffusion experiments are consistent with deformation of wet simpson quartzite that is limited by oxygen self diffusion inconsistencies between the present study and previous studies are probably the result of differences in sample material sample treatment and sample assemblies chemical environment

calcite textures examples from nappes with strain path partitioning abstract strain path partitioning partitioning of deformation into components of pure and simple shear in two alpine nappes is qualitatively indicated by a variation in orientation of foliation microkinematic criteria quartz textures and a comparison with strain path partitioning in theoretical nappe models the degree of non coaxial deformation relative to the total deformation is quantified by using the asymmetry of textures in calcite tectonites the texture interpretation is based on both polycrystal plasticity models and experimental data calcite tectonites in the graz paleozoic thrust sheet austria and the morcles nappe switzerland were deformed in a strain path with both pure and simple shear components texture asymmetry supports the strain path derived from geological observations as an exception a high strain ultramylonite deformed nearly exclusively in pure shear it is suggested that this represents a softening instability since deformation in pure shear is energetically more favorable than in simple shear the incompatibilities caused by heterogeneous pure shear are accommodated by detachments and heterogeneous simple shear adjacent to the pure shear zone

seasonal temperature salinity changes and thermocline development in the mid atlantic bight as recorded by the isotopic composition of bivalves stable isotope records across annual growth increments in specimens of the surf clam spisula solidissima from the mid atlantic bight shelf from 10 m and 45 m depths reflect the changes in temperature and nutrient concentrations on the shelf over the year the 18 o and 13 c records from clams at the two depths record well mixed conditions in the water column during the winter months and the development of a thermocline during the summer spring high productivity and a transient salinity excursion in surface waters are also recorded reconstructing the paleoceanography of late cenozoic temperate continental shelves may be possible using stable isotope records from fossil spisula solidissima and other bivalves

tectonometamorphic evolution of the koralm complex eastern alps constraints from microstructures and textures of the plattengneis shear zone abstract lattice preferred orientations lpo of quartz have been investigated along a south north oriented section across the plattengneis of the koralm complex eastern alps the plattengneis forms an important shear zone within the austroalpine nappe complex of the eastern alps which has developed during the cretaceous evolution of the alpine orogen the quartz c axes form small circle distributions in the southernmost parts of the koralm complex which represent the uppermost structural level of the plattengneis further to the north two maxima between the y and z directions of the finite strain can be interpreted in terms of preferred slip on the rhomb planes these fabrics continuously grade into type i and type ii crossed girdle distributions in a northward direction a strong maximum near the y axis with the tendency to be distributed along a single girdle with three corresponding maxima of a axes near the margin of the pole figure can be observed in the central and northern parts such lpo are characteristic for both high grade metamorphic conditions and high finite strain the microstructures display that the deformation within the plattengneis shear zone was synmetamorphic a continuous increase of peak temperatures and pressure from approximately 550 c to approximately 750 c from the south to the central parts can be inferred from geothermometric calculations the temperatures then decrease to approximately 650 c from the central parts to the north the related pressures increase from 8 to 16 kbar and then decrease to 10 kbar the lpo changes that have been observed in the study area are best interpreted in terms of temperature dependence of the activation of glide systems within quartz aggregates the temperature and pressure evolution may indicate that the central parts of the koralm complex have been exhumed by larger amounts than the northern and southern parts this is also documented by the lpo evolution therefore we assume that the plattengneis shear zone formed during the exhumation of the koralm complex and is related to the exhumation of high pressure units in the footwall of this shear zone accordingly the kinematics of the plattengneis shear zone is rather extensional than thrust related the implications for the structural evolution of the eastern alps are shortly discussed

thermal evolution of an extensional detachment as constrained by organic metamorphic data and thermal modeling graz paleozoic nappe complex eastern alps abstract following early cretaceous nappe stacking the eastern alps were affected by late orogenic extension during the late cretaceous in the eastern segment of this range a late cretaceous detachment separates a very low to low grade metamorphic cover graz paleozoic nappe complex gpnc above a low to high grade metamorphic basement synchronously the kainach gosau basin kgb collapsed and subsided on top of the section metamorphism of organic material within this section has been investigated using vitrinite reflectance data and raman spectra of extracted carbonaceous material in the southern part of the gpnc vitrinite reflectance indicates a decrease in organic maturity towards the stratigraphic youngest unit the remaining part of the gpnc is characterized by an aureole of elevated vitrinite reflectance values and raman r2 ratios that parallels the margins of the gpnc vitrinite reflectance in the kgb shows a steep coalification gradient and increases significantly towards the western basin margin the observed stratigraphic trend in the southern gpnc is a result of deep paleozoic to early cretaceous burial this maturity pattern was overprinted along the margins by advective heat and convective fluids during late cretaceous to paleogene exhumation of basement rocks during shearing the fault zone was heated up to ca 500 c this overprint is explained by a two dimensional thermal model with a ramp flat fault geometry and a slip rate of 1 to 1 5 cm year during 5 ma fault movement the collapse basin above the detachment subsided in a thermal regime which was characterized by relaxing isotherms

are fluid inclusion planes useful in structural geology abstract quantification of deformation or stresses in structural geology is often difficult due to the uncertainity of the paleodepth or fluid pressure the best records of fluid percolation are paleofluids trapped as fluid inclusions in healed microcracks of the rock forming minerals fluid inclusion planes fip are mode i cracks which form in sets with a predominant orientation perpendicular to the least principle stress 3 however the repeated microfracturing and healing of the rock forming minerals yield complex superimposed patterns of healed microcracks such patterns are often difficult to interpret due to the lack of suitable chronological criteria these problems have been recently documented and solved by coupling deformation studies detailed examination at all scales of the relationships between trapped fluids and their host structures and studies of fluid inclusions this paper summarizes recent advancements in fip analysis and suggests further ways for research

late cretaceous synorogenic low angle normal faulting along the schlinig fault switzerland italy austria and its significance for the tectonics of the eastern alps abstract the schlinig fault at the western border of theotztal nappe eastern alps previously interpreted as a west directed thrust actually represents a late cretaceous top se to ese normal fault as indicated by sense of shear criteria found within cataclasites and greenschist facies mylonites normal faulting postdated and offset an earlier cretaceous age west directed thrust at the base of theotztal nappe shape fabric and crystallographic preferred orientation in completely recrystallized quartz layers in a mylonite from the schlinig fault record a combination of 1 top east southeast simple shear during late cretaceous normal faulting and 2 later north northeast directed shortening during the early tertiary also recorded by open folds on the outcrop and map scale offset of the basal thrust of theotztal nappe across the schlinig fault indicates a normal displacement of 17 km the fault was initiated with a dip angle of 10 to 15 low angle normal fault domino style extension of the competent late triassic hauptdolomit in the footwall was kinematically linked to normal faulting the schlinig fault belongs to a system of east to southeast dipping normal faults which accommodated severe stretching of the alpine orogen during the late cretaceous the slip direction of extensional faults often parallels the direction of earlier thrusting top w to top nw only the slip sense is reversed and the normal faults are slightly steeper than the thrusts in the western austroalpine nappes extension started at about 80 ma and was coeval with subduction of piemont ligurian oceanic lithosphere and continental fragments farther west the extensional episode led to the formation of austroalpine gosau basins with fluviatile to deep marine sediments west directed rollback of an east dipping piemont ligurian subduction zone is proposed to have caused this stretching in the upper plate

post collisional orogen parallel large scale extension in the eastern alps abstract large scale extension affected the eastern alps during post collisional lateral tectonic extrusion in early and middle miocene times the tauern window was mainly tectonically exhumed by the 160 km pullapart of the rigidly behaving austroalpine basement blocks forming the tectonic lid of the penninic contents of the window an evaluation of the syn extrusion fault pattern reveals displacements of several tens of kilometers along the low angle extensional shear zones at the western and eastern margins of the window and along the important strike slip fault zones north and south of the window large scale shear is reflected by discontinuities in mineral cooling patterns across important shear zones the cooling histories of the tectonic blocks show that the window boundaries during exhumation coincide only partly with the classical boundaries of the window defined by thrust units reconstruction of the exhumation history shows an asymmetric evolution of the tauern window we argue that the eastern and western low angle extensional shear zones formed in sequence which is reflected by different evolutions of the fragmentation and uplift history of the austraolpine tectonic blocks to the east and west of the window in the central and eastern alps three structural domes the lepontin dome in the central alps and the tauern and rechnitz domes in the eastern alps were formed by large scale extension in miocene times total e w stretch amounts to more than 300 km and results in 70 extension we propose that the central and eastern alps are part of an extensional province that also includes the pannonian basin and has a counterpart separated by the moesian indenter in the rhodope mountains the aegean sea and the menderes massif in asia minor in these regions a number of mainly tectonically exhumed domes or deep sedimentary basins formed by miocene large scale extension

kinematics of cretaceous nappe tectonics in the austroalpine basement of the koralpe region eastern austria krohe a 1987 kinematics of cretaceous nappe tectonics in the austroalpine basement of the koralpe region eastern austria tectonophysicz 136 171 196 the austroalpine basement of the koralpe area austria was affected by penetrative ductile deformation in the cretaceous three metamorphic events have been established ht lp metamorphism of unknown age a hercynian mt mp metamorphism and a cretaceous eo alpine mt mp metamorphism in the koralpe area cretaceous rb sr cooling ages of muscovite indicate temperatures of at least 500 o c during the eo alpine event the most intense deformation occurred along intracrustal shear zones plattengneis north to northeast directed thrusting is indicated by an inverted metamorphic gradient regional transposition of an older foliation s c fabrics and oblique quartz fabrics after development of high temperature mylonites low angle normal shear zones low temperature mylonites cut the uppermost parts of the austroalpine basement and indicate an extensional tectonic setting at about 85 to 90 ma s c and quartz fabrics indicate downdip movements of the hanging wall towards the northeast intracrystalline a slip in quartz caused strong preferred lattice orientation in high and low temperature mylonites during the e alpine deformation the basal a slip system is more pronounced at lower temperatures whereas a prism a system predominates at higher temperatures the overall kinematic history of the austroalpine nappe complex in the study area suggests a model in which an intracrustal south over north imbrication took place in an early stage of eo alpine collision these movements were outlasted by sinistral strike slip movement possibly due to oblique collision along irregular margins of the austroalpine and brianpnnais complexes the collision imbrication process resulted in crustal thickening isostatic uplift and thus extension of the higher parts of the crust low angle normal faulting initiated sedimentation in the intramontane c tic gosau basins of late cretaceous age

development of microcracks in granites during cooling and uplift examples from the variscan basement in ne bavaria germany abstract microcracks in two late variscan granites in ne bavaria provide information about regional paleostress directions and p t conditions during cooling and uplift in both granites three prominent generations of healed microcracks called ci cii ciii constitute an orthorhombic fabric the orientation of which is closely related to the mesoscopic joint pattern we present a model relating this orthorhombic crack fabric not only to external deviatoric stresses but also to internal stresses on the grain scale resulting from the strong thermal contraction of quartz relative to the feldspar framework at the deepest level 1 subvertical steep ci cracks developed normal to 3 and selectively in the quartz their formation caused a stress uncoupling of quartz aggregates from the external 3 direction so that further contraction of quartz produced steep cii cracks normal to 2 forming bridges between ci cracks at higher levels 2 subvertical the same process reactivated the ci cracks and now formed horizontal crack bridges ciii p t estimates based on fluid inclusion data and inferred geothermal gradients are 250 400 c at 1 5 3 kbar for ci cii cracks and 150 200 c at 1 2 kbar for ciii cracks the orientation of the younger open cracks which formed at higher crustal levels partly corresponds to the present regional stress field

density changes of fluid inclusions in high pressure low temperature metamorphic rocks from crete a thermobarometric approach based on the creep strength of the host minerals abstract the densities of fluid inclusions in quartz from high pressure low temperature metamorphic rocks are generally inconsistent with the p t conditions derived from solid phase equilibria therefore some process of change must regularly have occurred during exhumation however evidence of decrepitation is frequently lacking consideration of the rates of change of p and t in metamorphic rocks shows that very low strain rates are sufficient for volume adaptation dislocation creep appears to be a feasible deformation mechanism allowing for continuous ballooning driven by a small differential pressure during decompression down to temperatures of about 300 c in quartz decrepitation requires a higher differential pressure in natural rocks it is therefore restricted to relatively low temperatures this concept was tested on inclusions in the phyllite quartzite unit of crete in these rocks cooling to below ca 300 c at confining pressures of 3 to 4 kbar is indicated corresponding to depths of 10 to 13 km it is anticipated that in metamorphic rocks the isochores of all fluid inclusions in quartz that have been formed at higher temperatures and remain unaffected by decrepitation should intersect close to the 300 c isotherm thereby defining a point on the p t paths rarely accessible by other methods extension of this concept to other minerals with known mechanical properties is straightforward and can under favourable circumstances be used to fix several points on p t paths

synthetic fluid inclusions vi quantitative evaluation of the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure has been evaluated using pure h2o synthetic inclusions formed by healing fractures in natural quartz three different modes of non elastic deformation referred to as stretching leakage or partial decrepitation and total decrepitation have been observed the internal pressure required to initiate non elastic deformation is inversely related to inclusion size according to the equation internal pressure kbar 4 26 d 0 423 where d is the inclusion diameter in microns regularly shaped inclusions require a higher internal pressure to initiate non elastic deformation than do irregularly shaped inclusions of similar size heating inclusions through the quartz inversion results in mechanical instability in the quartz crystal and leads to mass decrepitation of inclusions owing to structural mismatches generated by pressure gradients in the quartz around each inclusion long term heating experiments 2 years suggest that the internal pressure required to initiate non elastic deformation does not decrease significantly with time and indicates that short lived thermal fluctuations in natural systems should not alter the inclusion density and homogenization temperature inclusions that do exhibit decreased density higher homogenization temperature are however always accompanied by a change in shape from irregular to that of a negative crystal observations of this study are consistent with elasticity theory related to fracture generation and propagation around inclusions in minerals these results indicate that an inclusion will not be influenced by a neighbouring inclusion or other defect in the host phase as long as the distance between the two is 2 4 diameters of the larger of the two inclusions

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

reconstructing past upwelling intensity and the seasonal dynamics of primary productivity along the peruvian coastline from mollusk shell stable isotopes 1 we present here a potential new method to evaluate past variations of the mean intensity of peruvian coastal upwelling and of the seasonal timing of phytoplankton blooms this method uses a combination of the monthly carbon and oxygen isotopic signals preserved in fossil mollusk shells and a series of corrections to extract the variations of the dissolved inorganic carbon dic 13c based on the analysis of five shell samples 85 shells in total from the southern peruvian coast we suggest that the mean coastal upwelling intensity can be determined from a linear relationship between average values of corrected shell 13c and 18o this new potential proxy would bring additional independent information valuable to interpret paleoproductivity changes reconstructed from marine sediment of the nearby continental shelf results obtained on fossil samples from the middle holocene show an increase in upwelling intensity during this period associated to a spatial reorganization of upwelling centers along the south peruvian coast at the seasonal scale corrected shell 13c enrichment indicates a phytoplankton bloom seasonal timing of phytoplankton blooms can be estimated by the lag with the annual temperature cycle reproduced by shell 18o monthly variations the results obtained with two modern shell samples indicate phytoplankton blooms occurring during summer and fall consistently with in situ productivity observations our method relies on revisited assumptions about the influence of temperature and metabolism in mollusk shell 13c we further discussed the validity of these assumptions and the potential implications for the interpretation of similar data sets

cold spots during the cenozoic evolution of the eastern alps thermochronological interpretation of apatite fission track data abstract the tectonical and morphological evolution of the eastern alps during the cenozoic is discussed in the light of sedimentary record and thermochronological data of crystalline basement rocks the regional distribution of apatite fission track data in the central eastern alps reveals the differential cenozoic exhumation in contrast to the penninic of the tauern window which has been strongly uplifted and eroded since the early miocene the amount of neogene denudation was much smaller in most areas east of the hohe tauern a sudden change in the regional cooling behaviour is observed at the katschberg fault system which must have been active in post oligocene times within the austroalpine only the schladming tauern have experienced a rather strong denudation the seckau core complex east of the pols line and the area of the northern koralpe cooled to below 100 c at the end of the cretaceous and in the early eocene respectively and have never been heated again during the cenozoic these parts of the austroalpine nappe pile were always near to the surface and therefore may be summarized under the term cold spots a major post cretaceous thickening of the austroalpine can be excluded because it would have produced more uplift and erosion any remnants of miocene or older landforms are certainly not preserved in the area of the tauern window the uppermost planation surfaces in the crystalline basement at the western border of the styrian basin koralpe probably developed in the late miocene

a new estimate of the conditions for transition from basal a to prism c slip in naturally deformed quartz abstract quartz c axis fabrics of naturally deformed quartz in metacherts from the ryoke metamorphic belt in the yanai district southwestern japan suggest that the prism c prism a and basal a slip systems were activated during the plastic deformation under high temperature metamorphic conditions with increasing temperature quartz c axis fabric patterns change from girdle type through x maximum with a faint crossed girdle to x maximum the dominant orientation of subgrain boundaries in the quartz also changes from prism to basal with increasing temperature closely correlated with the change in quartz c axis fabric the fabric transition is also accompanied by an abrupt increase of recrystallized quartz grain size moreover observations with transmission electron microscopy tem clearly identify the dominant activation of c slip through the presence of basal subgrain boundaries and free dislocations with the 0001 burgers vector in the quartz from the metachert samples exhibiting x maximum c axis fabric based on these observations it is concluded that the mechanism switch from basal a to prism c slip systems occurred with increasing temperature in the metacherts the transition temperature is petrologically estimated to be ca 550 600 c at the natural strain rate

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

rapid climate change in the north atlantic during the younger dryas recorded by deep sea corals research on global climate change has increasingly focused on rapid century scale and decadal changes one such climate shift the younger dryas cooling event1 took place during the last deglaciation from 13 000 to 11 700 years bp climate records from greenland ice cores and north atlantic sediment cores show high frequency fluctuations implying significant 5 c shifts in temperature at this time taking place within 50 100 years ref 2 the origin of the younger dryas has recently been attributed to a reduction or cessation of deep water production in the north atlantic and a concurrent lessening of the heat flux from low latitudes3 4 the role of intermediate waters 1 000 2 000 m depth is less certain however because climate proxies for this ocean reservoir are rare and ambiguous here we report on the use of a new climate archive deep sea corals from orphan knoll 1 600m depth in the northwestern atlantic ocean the oxygen isotope ratios in the coral skeletons accurately dated by the 230th 234u chronometric method change markedly coincident with the initiation of the younger dryas suggesting that there were profound changes in intermediate water circulation at this time

deformation induced resetting of rb sr and 40ar 39ar mineral systems in a low grade polymetamorphic terrane eastern alps austria a paradox in dating metamorphic events in low grade polymetamorphic terranes is exemplified by the eastern lower austroalpine nappes of the eastern alps here the last metamorphic event best recorded in post variscan cover rocks is dated as late cretaceous in age c 80 85 ma by white mica rb sr and 40 ar 39 ar systems within the underlying polymetamorphic basement 40 ar 39 ar and rb sr ages of phengitic white mica record only early and or late variscan ages 375 270 ma indicating that the alpine greenschist facies metamorphic overprint virtually caused no rejuvenation of variscan mineral ages based on these results the timing of a penetrative ductile top to wnw simple shear deformation recorded within both basement and cover rocks was contradictory deformation within the post variscan cover rocks had to be alpine in age whereas phengite 40 ar 39 ar ages from basement mylonites yield variscan ages to date this deformation directly we isolated different mineral size fractions 63 30 and 30 10 m from highly strained shearbands within the wechsel basement nappe a resulting rb sr errorchron pointed to an upper cretaceous age c 85 ma for the deformation consistent with the timing of alpine metamorphism in the cover rocks coarser grained white mica 150 300 im from similar basement mylonites do not reflect any alpine overprint of either k ar and or rb sr systems it follows that dynamic re and or neocrystallization induced by ductile deformation within the shearbands was the dominant process by which the rb sr system locally virtually re equilibrated this is valid even for overprinting metamorphic conditions below the temperatures required for ar diffusional loss in phengitic white mica c 40 ar 39 ar should be considered with caution

shifts in oxygen and carbon isotope signals in marine molluscs from the central paratethys europe around the lower middle miocene transition abstract stable isotope data of mollusc shells from two adjacent time slices karpatian badenian from the central paratethys were investigated to detect differences in environmental parameters and to depict shifts in the isotope signature of the paratethyan seawater around the early middle miocene transition altogether seventeen different gastropod species and one bivalve species from the karpatian korneuburg basin and the badenian northern alpine foreland basin were selected representatives of various ecological guilds yielded different isotope patterns especially in 13c reflecting different original habitats or nutrition although molluscs precipitate their shells in oxygen isotopic equilibrium we preferred to compare isotope data of shells of the same genus of the family turritellidae from the karpatian and badenian the badenian turritella shells from the northern alpine foreland basin yielded distinctly higher 18o and 13c values than the respective karpatian shells from the korneuburg basin as the main factors controlling 18o values in gastropod shells are temperature and 18o of the water during precipitation the differences between the oxygen isotope data of the two time slices can only be explained by these factors good independent palaeotemperature proxies exist for the early to middle miocene of central europe they do not indicate a significant temperature variation therefore different 18o values of the seawater in the different basins of the central paratethys must be responsible for the contrasting 18o values when calculated with commonly assumed 18o seawater values for the miocene badenian turritella shells indicate too cold temperatures these data clearly document the danger of palaeotemperature interpretations based solely on stable isotopes as smaller and marginal marine settings such as the paratethys sea can be seriously influenced by regional differences in the isotope composition of the seawater only a thorough consistent control by other climate proxies e g palaeoecology of molluscs as in this study allows a sensible interpretation

response of infaunal macrobenthos to the sediment granulometry in a tropical continental margin southwest coast of india abstract surficial sediment samples collected from the continental margin of the southwest coast of india in july 2004 were examined for the grain size and soft bottom macrobenthic fauna to understand the sediment granulometry and its effect on the faunal distribution samples were collected using smith mcintyre grab from 20 to 200 m depth range consisting of mid shelf outer shelf and slope fine grained sediment located in the mid shelf and supported low faunal abundance polychaetes constituted the bulk of the fauna feeding guild changed with depth and sediment granulometry coexistence of deposit feeders and carnivores in outer shelf and deposit feeders and filter feeders in the slope region indicated the effective utilization of different food resources in general richness and diversity were high in the southern region depth wise the diversity and abundance were relatively high in the 50 75 m depth range correlation and bio env analysis showed that combination of different factors such as sediment texture sediment sorting and depth were found to influence the distribution of macrobenthos hence spatial variations observed in benthic community were presumably linked to the variations in sediment granulometry and the energy level conditions prevailing in the area

fluid inclusions tectonic indicators abstract during the first half of the 20th century fluid inclusions have been studied in ore geology in order to determine the chemistry and physical parameters density of the mineralising fluids apart from a few pioneering works in the middle of the century fluid inclusions were not used as structural markers before the late 1980s during the same time experiments as well as observations of natural samples have shown that the volume shape and density of fluid inclusions may change when submitted to pressure temperature conditions different from their trapping isochores in view of these experiments and based on natural examples from the higher himalaya metamorphic rocks it is evident how fluid inclusions can be used as thermobarometric structural and tectonic markers points of interest for further studies on fluid inclusions in nature and experiments are also stressed

the use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual colorado river discharge abstract we describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river water seawater mixing zone of the colorado river estuary sclerochronological techniques are used to identify tidally induced fortnight scale bundles of daily growth increments within shell cross sections these fortnightly markers are used to establish a chronology for samples taken for 18 o analysis a composite seasonal 18 o profile derived from five shells that grew in the absence of river water flow is used as a baseline against which profiles of river influenced shells are compared because this comparison is between matched fortnights within a year the temperature of shell growth is likely to be very similar the difference in 18 o between the river influenced shell and the no flow composite shell therefore represents the change in the 18 o of the water due to the presence of river water in the mixing zone the river water end member is also determined within a fortnightly context so that the change in the 18 o of mixing zone water can be used to calculate the relative proportions of seawater and fresh water the fresh water end member is calculated from the 18 o of bivalves alive prior to the emplacement of dams and water diversions on the colorado river the marine end member is based on direct measurements of the 18 o of northern gulf of california water during times of no colorado river flow the system has been calibrated to absolute flow amounts using recent releases of known volume and rate

numerical modelling of the thermal history of the nw himalayas kullu valley india abstract this paper demonstrates two dimensional time dependent finite difference modelling of himalayan metamorphism illustrated by the kullu s lahul area himachal pradesh after the collision between india and asia and the over thrusting of the higher himalayas over the lesser himalayas it is shown that a one dimensional model with crustal thickening by a single thrust cannot satisfy the observations present in the section along the kullu valley a two dimensional solution demonstrates that during thrust sheet emplacement at geologically realistic strain rates of several centimetres a year a temperature inversion does not occur in contrast to the inversion assumed by the one dimensional instantaneous thrust models therefore the variability of two other model parameters were explicitly considered i there is a significant conductivity contrast between the different types of rocks as conductivity layers function as a barrier to the transport of heat the conductivity limit should be variable for different regions in the grid ii rocks in the higher himalayas record a phase of metamorphism that preceded the movements on the main central thrust this observation together with the knowledge that rocks with different radiogenic heat production and conductivity are not uniformly distributed in the crust emphasizes that there were considerable horizontal temperature variations across the whole region for that reason the initial temperature profile too has to be adapted for a realistic model

stable isotope profiles of last interglacial pelukian transgression mollusks and paleoclimate implications in the bering strait region abstract the marine paleoclimate during the last interglaciation in the bering strait region is inferred from the stable oxygen and carbon isotope profiles of fossil bivalve mollusks specimens were collected from the marine highstand deposits of the pelukian transgression from the arctic alaskan coastal plain the nome coastal plain st lawrence island and the val katlen suite on the chukotka peninsula as a calibration modern mollusks were obtained from the major water masses in the bering chukchi seas system and from coastal environments near the fossil localities the 18 o composition of the modern mollusks accurately reflects the seawater 18 o differences among the water masses and the ambient temperature range at each site seasonal paleotemperature ranges are estimated from the 18 o profiles of the fossils by comparison with those of the modern specimens a simple model is developed to correct the paleotemperature ranges for the influence of differences in seawater 18 o between water masses and seasonal variations caused by freshwater discharge paleotemperatures calculated for the skull cliff site alaskan arctic coastal plain are close to but slightly cooler than those of modern specimens from peard bay and icy cape the isotopic composition of a pelukian specimen collected near wainwright shows the obvious influence of locally reduced salinities with a correction for lower seawater 18 o this profile yields a summer temperature of 13 c which is 3 c warmer than that from the modern icy cape specimen the isotope records of two specimens from the nome coastal plain suggest salinities that were 3 5 psu lower than the modern eastern bering shelf the paleotemperature range of 0 15 c is consistent with modern conditions in norton sound the character of the isotope profiles of the pelukian specimens from st lawrence island is very different than that of modern specimens near the island but matches the 18 o values of shells from deeper sites in anadyr water this suggests that the fossil mollusks were living in anadyr strait and were transported by a glacial advance from the chukotka peninsula the last interglacial specimens from the val katlen suite have isotope profiles with large seasonal 18 o ranges and the clear influence of a reduced salinity coastal water mass calculated paleotemperatures from the val katlen specimens range from 0 to 13 c differences in the 13 c of shell carbonate between sites appears to reflect the regional distribution of the 13 c of sedimentary organic matter som which is a mixture between terrestrial organic matter mean 13 c of 24 and marine phytoplankton 21 partitioning of 13 c between shallow and deep waters by phytoplankton productivity and remineralization may also affect the regional distribution differences in shell 13 c between taxa may relate to feeding mode and the type and isotopic composition of ingested particles the filter feeders mya and astarte typically have 13 c values 1 2 more positive than the deposit feeders macoma and serripes this effect is attributed to a 13 c difference between marine phytoplankton and som with a component of terrestrial organic carbon

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

influence of the upwelling events on the δ13c and δ18o of the benthic bivalve shells of the south western continental margin of india in this study the influence of the spatial and temporal variability of upwelling intensity and the associated biological productivity observed during different phases of summer monsoon along the southwestern continental margin of india swcmi on the 13c and 18o of the inorganic biogenic carbonate shells was investigated multispecies benthic bivalve shells 1 5 mm separated from ten surface sediment samples of swcmi off 12 n 10 n and 9 n collected during the onset osm and peak psm phase of the summer monsoon of 2009 were analysed for 13c and 18o sea surface temperature along the study region indicates prominent upwelling in psm than in osm a comparison of analytical and predicted values for 18o in the bivalve shells confirmed their in situ origin during both the sampling periods during psm the 13c values in the benthic bivalve shells were more depleted in 13c than during osm which recorded lower values of 13c in dissolved inorganic carbon of bottom waters expected in the study region in psm due to the upwelled waters high surface productivity and the associated high degradation of the organic matter in the subsurface and bottom waters however this depletion of 13c was not observed in benthic bivalve shells obtained from 10 n since it is influenced by high export fluxes of carbon from the cochin estuary since early monsoon months

the development of flanking folds during simple shear and their use as kinematic indicators abstract we used a numerical finite element simulation to model the formation of flanking folds around rotating planar structures e g veins faults or dykes in a non linear viscous medium during ideal simple shear if the planar structure is much more viscous than its host it does not deform and flanking folds with no displacement along the structure develop their vergence is consistent with the overall sense of shear however if the planar structure is much less viscous than its host strain is concentrated within the structure and a secondary shear zone is developed in which slip is opposite to the overall sense of shear then flanking folds develop that have a vergence which is incompatible with the drag on structure if the deflection of markers is not clearly preserved then such flanking folds can be easily misinterpreted as shear bands indicating a wrong shear sense the deflection of the foliation in flanking folds is very similar to deformed asymmetric pull aparts and can therefore help to interpret these otherwise ambiguous shear sense criteria because our model ideal simple shear boundary conditions fails to describe back rotation of planar structures in rocks we speculate that shear band geometries are indicative for general shear

porphyroblast rotation eppur si muove in a number of recent papers the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates and can be used to determine the original orientation of older foliations complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis involving several alternating phases of horizontal shortening and extension critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws millipede structures used as proof for flow partitioning can also form by other flow geometries evidence quoted to support irrotational behaviour of porphyroblasts is unsound porphyrobl asts do occur in sets with a preferred orientation of the internal foliation trace but these cannot be shown to represent original orientations microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis they can however also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation finally porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations

paleostress directions from the preferred orientation of closed microfractures fluid inclusion planes in sandstone east texas basin u s a abstract closed extensional microfractures are useful indicators of paleostress directions in shallowly buried quartz cemented quartz arenites of the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 670 m thick that was deposited in the gradually subsiding northern gulf of mexico basin the closed microfractures are syndiagenetic fluid inclusion rich planes that have an ene strike that is subparallel to contemporary quartz filled extension veins and regional normal faults indicating that closed microfractures contain the maximum paleostress direction these microstructures are potentially useful for mapping paleostress trajectories in passive margin and platform settings particularly where samples are obtained from core previous experimental studies of microfracture closure suggest that microfractures evolved into fluid inclusion planes by dendritic quartz precipitation in east texas microfracture closure may have occurred at temperatures as low as 85 c and depths as shallow as 1500 m

evolution of veins and sub economic ore at strassegg paleozoic of graz eastern alps austria evidence for local fluid transport during metamorphism the north eastern part of the graz paleozoic thrust sheet at strassegg austria is characterised by metamorphic assemblages that reflect increasing temperature conditions from 3008c in hangingwall to around 5508c in footwall units the main quartz andror carbonate vein generation cuts the schistosity at moderate to low angles is folded with the schistosity and is commonly boudinaged there is a correlation between vein and the host rock mineralogy additionally the d 18 o and 13 d c signatures of vein minerals quartz andror carbonates vary systematically with the isotopic signature of the host rock and its minerals within individual units d 18 o of vein quartz has a narrow range of values in contrast with a larger variation in both with d 18 o and d 13 c of carbonates at strassegg the greenschist unit hosts an as au mineralisation arsenopyrite

massive methane release triggered by seafloor erosion offshore southwestern japan vast amounts of methane hydrate exist beneath continental margins but whether this methane releases from sediment on a large scale and affects the oceans and atmosphere remains unclear analysis of newly acquired three dimensional seismic images and drilling data from a large gas hydrate province reveal a recently eroded v shaped depression the depression sharply cuts through a relic bottom simulating reflection bsr and hydrate laden sediments the shape of the relic bsr indicates that the seafloor depression was once a large anticline that has recently been eroded and released an estimated 1 51 10 11 m 3 of methane we hypothesize that erosion of the seafloor via bottom water currents unroofed buoyant hydrate laden sediments and subhydrate overpressured free gas zones beneath the anticline once triggered gas driven erosion created a positive feedback mechanism releasing gas and eroding hydrate bearing sediment we suggest that erosive currents in deep water methane hydrate provinces act as hair triggers destabilizing kilometer scale swaths of the seafloor where large concentrations of underlying overpressured methane exist our analysis suggests that kilometer scale degassing events are widespread and that deep water hydrate reservoirs can rapidly release methane in massive quantities

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

textural evolution of synthetic fluid inclusions in quartz during reequilibration with applications to tectonic reconstruction experimental reequilibration of synthetic 10 wt nacl h2o inclusions in natural quartz reveals that reequilibration textures show distinct differences depending upon the p t path followed by the inclusion after formation these differences combined with other geological information may be used to determine whether the sample rock followed a dominantly isothermal or isobaricp t path following entrapment the intensity and style of inclusion reequilibration features is related to the direction and magnitude of the departure of thep t path from the original isochore for the inclusion thus fluid inclusion reequilibration textures not only permit inclusionists to determine whether the rocks followed an isothermal or isobaric retrogradep t path but also the magnitude of departure of this path from one that is isochoric

a model for interpreting continental shelf hydrographic processes from the stable isotope and cadmium calcium profiles of scallop shells abstract stable oxygen and carbon isotope and cadmium calcium profiles from the shells of scallops collected from the outer continental shelf of the south atlantic bight and the virginia bight appear to trace the hydrographic processes of the two regions a model is developed to distinguish two principal modes of nutrient and trace metal input to the outer shelf from the biogeochemical profiles of the shell the oxygen isotope profiles record bottom water temperature changes caused by seasonal temperature cycles and water mass movements nutrient input and subsequent phytoplankton blooms are recorded in the carbon isotope and cd ca profiles the shell profiles from the south atlantic bight record the dominant effect of upwelling caused by gulf stream meandering the shell profiles from the virginia bight show the influence of spring river runoff and summer water column stratification biogeochemical profiles in mollusk shells are potentially important tools for studying the dynamics of both modern and ancient continental shelf upwelling systems

multistage deformation of au quartz veins laurieras french massif central evidence for late gold introduction from microstructural isotopic and fluid inclusion studies abstract the relative chronology of fluid migration quartz and au deposition in a silicified fault from the main au district laurieras st yrieix district from northern french massif central has been determined from microstructural fluid inclusion isotopic and ore mineral evidences three main stages of fluid circulation microfracturing and quartz crystallization and ore deposition were distinguished on the basis of textural relationships and the pressure temperature and composition of the palaeo fluids 1 a series of early fluid events was responsible for the localized drainage of retrograde metamorphic fluids along the main fault and the subsequent sealing by milky and microcrystalline quartz preceeded the main au ore stages early fluids were aqueous carbonic trapped under lithostatic to sublithostatic pressures at temperatures in the range 350 500 c subsequently several types of microstructures were developed in the early quartz matrix 2 ns microfractures filled by clear quartz arsenopyrite and boulangerite i contain significant refractory gold concentrations clear quartz formed from aqueous carbonic fluids of lower densities than those of the earlier fluids significant pressure drops down to pressures around 55 mpa were responsible for a local immiscibility of the aqueous carbonic fluids at temperatures of 340 20 c 3 the main ore stage is characterized by the formation of dense sets of sub vertical ew microfractures healed fluid inclusion planes in quartz and filled by ore minerals native gold galena and boulangerite ii when they crosscut earlier sulfides the fluids are aqueous with low and decreasing salinity and probable trapping temperatures around 230 c isotopic data obtained on microfissured quartz indicate these dilute aqueous fluids may be considered as meteoric waters that deeply infiltrated the crust late microfissuring of a mesothermal quartz vein originally barren only with pyrite and arsenopyrite appears to be the main factor controlling gold enrichment it can be related to late hercynian deformational stages disconnected from the early fault formation and silicification these late stages which affected the hercynian basement during its uplift are of critical importance for the formation of au ores we concluded that this type of au ore formed under rather shallow conditions is distinct from those generally described in most mesothermal au veins