middepth flow near hydrothermal venting sites on the southern juan de fuca ridge long term moored current measurements around the southern end of the juan de fuca ridge show that flow parallels the ridge and may be intensified by its presence the mean flow is northward on the west side and southward on the east thus plumes emanating from the ridge probably are advected along the ridge before flowing away from the ridge other topographic features may be responsible for westward or eastward turning along the west side of the ridge we hypothesize a regional flow pattern with southward flow north of axial seamount northward flow south of axial and a convergence somewhere south of axial resulting in westward flow along the east side the flow may be southward everywhere above the ridge crest the long term mean flow is weaker and more variable and it includes tidal inertial and a dominant broadband 4 day oscillation this 4 day energy is maximum in the rift valley where the inertial is least decreases upward and away from the ridge and is more energetic in winter this oscillation is predominately a clockwise rotating feature which along with the presence of inertial oscillations suggests that it may be storm induced from the sea surface these observations along with those by cannon and pashinski 1990 suggest northward propagation flow variations across the ridge lasting one to a few months have mean speeds of 1 3 cm s and are capable of transporting plumes off axis to the west or east into the northerly or southerly flows respectively

pt paths from modal proportions application to the koralm complex eastern alps thermodynamic pseudosections portray those parts of a petrogenetic grid that are relevant to a given bulk composition and the reactions appearing on them can therefore be used directly to infer the pt path that the rock followed however for many normal bulk compositions the use of pseudosections is hampered by the fact that they display only few large fields of high thermodynamic variance in the pt range of interest here it is discussed how modal information on reaction progress within these fields can be used to determine pt path information for thermodynamically high variant metamorphic assemblages we use this information on reaction progress to contour pseudosections for modal proportions of minerals using the software package thermocalc the approach is applied to di tri and quadrivariant assemblages from the koralm complex in the eastern alps a pt path for these rocks is derived from modal considerations and compared with interpretations of mineral composition contours on the same pseudosection and with conventional thermobarometry it is shown that at least part of the complex must have cooled initially near isobarically from prevalent peak conditions around 700 c and 14 kbar before the rocks commenced a barroviantype decompression path

fabric analysis by orientation distribution functions abstract crystalline materials natural or artificial may consist of several phases minerals the crystal structures and relative amounts of which will generally be known in order to fully characterize such a material also the form and spatial distribution of the phases the grain structure and lattice defects and their distribution must be specified by appropriate distribution functions among these the orientation distribution function texture fabric structure plays an important role it can be deduced from experimental pole figures by series expansion methods in textured materials two different symmetries can be distinguished the crystal symmetry and the statistical sample symmetry special consideration must be given to the inversion centre as an element of either of these symmetries and in friedels law a complete description of all possible sample symmetries can be given in terms of black white symmetry groups the determination of the odd part of the texture function is strongly related to these groups and the various kinds of the inversion centre each combination of a certain crystal symmetry group with a certain sample symmetry group induces a certain space group in the orientation space the proper consideration of which minimizes the required amount of numerical calculations the texture function odf is the most important factor in the relation between anisotropic properties of single crystals and the polycrystalline material changes of the odf can be used as a sensitive indicator for solid state processes having occurred in the material

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

the first measurements of hydrothermal heat output at 9 50 n east pacific rise abstract despite the importance of the heat output of seafloor hydrothermal systems for the earth s energy budget hydrothermal heat output measurements have been very limited in this paper we report the first measurements of hydrothermal heat output at the ridge 2000 integrated study site on the east pacific rise we focused our work on the bio 9 complex situated at 9 50 n where there has been an extensive measurement and sampling program since 1991 this site is located along the eruptive fissure of the 1991 1992 event and the site of the 1995 earthquake swarm we made direct measurements of advective heat output at several individual vents and at one site of diffuse flow tica although these data do not describe the complete heat flux picture at this vent field the data yield a total hydrothermal heat output of 325 160 mw with 42 21 mw coming from high temperature vents along this 2 km segment of ridge this result assumes a diffuse flux similar to that measured at tica occurs at each high temperature vent site our initial measurements thus suggest that the heat output of the low temperature diffuse venting is approximately 10 times that of the high temperature vents but may also be one or two orders of magnitude greater

simple shear deformation and quartz crystallographic fabrics a possible natural example from the torridon area of nw scotland ln this paper the microstructures and crystallographic fabrics of a 30 cm wide deformed quartz vein from the torridon area of nw scotland are described the vein which lies along a joint separating two blocks of proterozoic gneiss was deformed by crystal plastic processes when the rigid joint blocks moved in opposite directions parallel to the vein margins mylonitic foliation within this quartzose ductile shear zone locally displays the classic orientation variation expected for heterogeneous simple shear deformation in thin section the vein is a mylonite composed of dynamically recrystallized elongate quartz grains aligned oblique to the mylonitic foliation fabrics within the central part of the vein have been examined by optical and x ray texture goniometry methods together with orientation distribution function odf analysis the a axis fabric consists of a dominant single point maximum orientated within the xz plane at 9 to the lineation x this point maximum occupies a pole position to the corresponding single girdle c axis fabric for individual positions on the c axis fabric skeleton the orientations of potential crystallographic slip systems slip plane and direction relative to shear zone co ordinates have been calculated by odf analysis the calculation of relative resolved shear stresses schmidfactors for the potential slip systems assuming a simple shear kinematic framework reveals an elegantly simple relationship between individual grain c axis orientation and correspond ing orientations of potential slip systems these results are readily interpreted in terms of bulk simple shear deformation

heterogeneous sub simple deformation in the gol e gohar shear zone zagros sw iran insights from microstructural and crystal fabric analyses petrofabrics and microstructural characteristics of the quartz rich mylonites were investigated in the nw se trending gol e gohar shear zone with length of ca 25 km within the zagros transpression zone sw iran the semi quantitative vorticity analysis using quartz c axis fabric rxz method and rigid porphyroclast geometry rigid grain net method reveals that mean kinematic vorticity number wm increases towards the baghat thrust fault displaying the occurrence of spatial and temporal variations of flow during progressive deformation the wm values show pure shear dominated flow progressively was changed to a simple shear dominated flow toward to the late stages of ductile deformation implying that the accelerating flow path was accompanied with progressive cooling and strain localization at the lower parts of the zone the measured vertical thinning dip parallel elongation suggests that thrust emplacement and metamorphic rock extrusion likely occurred by a combination of simple shear with a pure shear component of deformation i e general shear the estimated deformation temperatures based on the quartz c axis fabric patterns and their opening angles highlight greenschist to amphibolite facies conditions

microscopic anatomy of a hot on cold shear zone insights from quartzites of the main central thrust in the alaknanda region garhwal himalaya

temporal and spatial variability of hydrothermal manganese and iron at cleft segment juan de fuca ridge a unique data set for hydrothermal mn and fe was collected at cleft segment on the juan de fuca ridge between 1983 and 1991 the data set includes observations of focused and diffuse venting fluids and neutrally buoyant plumes formed by chronic and episodic venting manganese heat and iron heat ratios for plumes from the north end of the cleft segment were combined with independently determined estimates of plume heat flux to yield annually averaged chronic venting fluxes for mn of 0 36 0 17 mol s 1 and for fe of 0 61 0 34 mol s 1 over 6 years of plume measurements at north cleft segment observed episodic hydrothermal discharge accounted for 15 of the total vented mn and 35 of vented fe the chronic fluxes for mn and fe at a second venting center located at the south end of the cleft segment were estimated to be approximately equal to the fluxes at north cleft segment chronic plumes at north cleft segment are mixtures of focused and diffuse discharge that contribute heat mn and fe in variable proportions similar examination of south cleft segment data strongly suggests the presence of an as yet unobserved venting source relatively depleted in mn and fe but contributing substantially to the overall heat temporal and spatial variations in the concentrations of mn and fe and in mn heat and fe heat ratios for focused seafloor vents were difficult to resolve within complex chronic plumes manganese heat and iron heat ratios of megaplumes suggest they may have derived from reservoirs of diffuse fluids while smaller event plumes may have formed by different processes and have properties similar to chronic plumes the accurate assessment of segment scale hydrothermal fluxes of mn and fe requires coordinated measurements of representative seafloor sources and the neutrally buoyant plume that integrates all seafloor discharge

metamorphosed and dismembered ophiolite suites in the basement units of the eastern alps abstract the pre alpine basement of the eastern alps contains several ultramafic mafic rock complexes four of which have been investigated although polyphase deformation and metamorphism obscures much of the primary features field petrographical and geochemical evidence favours ophiolitic origins in mid ocean ridge and back arc tectonic settings the stubach complex belongs to the penninic basement of the tauern window and is interpreted as an obducted back arc ophiolite with ultramafic cumulates gabbro and minor amounts of basalt which shows the geochemistry of subduction related magma generation the rating complex belongs to a group of strongly dismembered basement slices carrying the palaeozoic austroalpine sequence of the northern greywacke zone basaltic rocks are accompanied by former metamorphic peridotite containing chromite concentrations nearly all members of an ophiolite suite are present in the speik complex in the austro alpine crystalline basement the source rocks are metamorphic peridotite harzburgite with chromite occurrences cumulate ultramafic and mafic rocks isotropic gabbro basalt and or dolerite and oceanic sediments the plankogel complex also part of the austro alpine crystalline basement represents a tectonic melange blocks of serpentinite and amphibolite derived from metamorphic peridotites and mid ocean ridge basalts together with marble and quartzite are contained in a micaschist matrix admixed is a rock assemblage with alkali basaltic amphibolites interpreted as a seamount environment the ritting plankogel and possibly parts of the speik complexes contain relict high pressure minerals and therefore went through a stage of subduction the inferred ages of all complexes is late precambrian to early palaeozoic the ophiolite suites have their distinct characteristics and contrasting tectonic settings and are therefore considered to be genetically unrelated to each other

hydrothermal cooling of midocean ridge axes do measured and modeled heat fluxes agree abstract accurate estimates of near axis hydrothermal cooling are keys to understanding many geological chemical and biological processes at midocean ridges at present however field observations h heat flux vent field are few and imprecise and model results h m heat flux km of axis vary widely depending on assumptions about crustal formation crustal composition and the cooling efficiency and spatial and temporal extent of hydrothermal circulation in this paper i compare all published vent field scale measurements of h to a range of published h m for slow 40 mm yr and fast 40 mm yr ridges to assess the present state of knowledge about the magnitude of near axis hydrothermal cooling h has been evaluated 28 times either by point measurements using inventories of individual sources 362 552 mw n 12 measurements or by integrated measurements using water column observations 876 1011 mw n 16 comparable estimates of mean vent field expected h at any spreading rate can be derived by merging h m from various models with the predicted global inventory of active vent sites these estimates range from 1 1 5 gw field and are approximately constant for all spreading rates this range agrees with the best constrained results of h from slow ridge vent fields 1669 1354 mw but is considerably higher than those from fast ridges 245 170 mw inferences about the spatial and temporal variability of h can be gained by defining the parameter l h h m equivalent to the axis length needed to continuously power a hydrothermal field the resultant large l values 13 333 km for slow ridges 1 32 km for fast demand punctuated cooling where for short periods h h m the percentage of time that a given vent field might be active can be speculatively estimated by dividing l by the length of axis the field cools examples of this percentage range from a low of 50 for some fast ridge fields

garnet sm nd data from the saualpe and the koralpe eastern alps austria chronological and p t constraints on the thermal and tectonic history abstract garnets from recrystallized staurolite and kyanite bearing mica schists from the central saualpe base ment representing the host rocks of the type locality eclogites give concordant sm nd garnet whole rockisochronagesbetween88 5 1 7and90 9 0 7ma themillimetre sized mostly inclusion freegrainsshowfairlyhomogeneouselement pro les withpyropecontentsof25 27 narrowrims withanincreasein fe and mn and a decrease in mg document minor local re equilibration during cooling accordingto phengite geothermobarometry peak metamorphic conditions at 90 ma were close to 20kbar and680 c and similar to those recorded by the eclogites the garnet rims record about 575 c 7kbar forthe nal stages of metamorphism a phengitic garnet mica schist sampled at the immediate contact withthe gertrusk eclogite gave a garnet whole rock sm nd age of 94 0 2 7 ma garnet porphyroclasts separated from a pegmatite mylonite of the koralpe plattengneiss near stainzare unzoned and show spessartine contents of 15 composition and sm nd ages of close to 260 mapoint to a magmatic origin for these garnets the garnet data from the saualpe document an intense alpine metamorphism for this part of theaustroalpine basement the mica schists recrystallized during decompression and rapid exhumation atthe nal stages of and immediately following a high p event the koralpe data show that high alpinetemperatures did not reopen the sm nd isotope system implying a closure temperature in excess of c 600 c for this isotopic system in garnet key words alpine orogenesis closure temperature eastern alps high p metamorphism metamorphicand magmatic garnets p t t paths saualpe koralpe basement sm nd geochronology

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

heterogeneous deformation and quartz crystallographic fabric transitions natural examples from the moine thrust zone at the stack of glencoul northern assynt quartz crystallographic fabric transitions in well exposed mylonites immediately beneath the moine thrust at the stack of glencoul nw scotland have been investigated by optical microscopy x ray texture goniometry and orientation distribution function analysis a progressive change is observed from asymmetrical kinked single girdle c axis fabrics at 0 5 cm beneath the moine thrust through asymmetrical type i cross girdle fabrics to symmetrical type i cross girdle fabrics at 30 cm beneath the thrust this c axis fabric transition is accompanied by a transition from asymmetrical single a axis maximum fabrics 0 5 cm beneath the thrust through asymmetrical two maxima fabrics to essentially symmetrical two maxima a axis fabrics odf analysis of these s l and l s tectonites indicates that c axis positions on the leading edge of the fabric skeleton are related by a common a direction oriented within the xz plane at a moderate angle to the lineation x in contrast c axis positions on the peripheral trailing edge are related by a positive r rhomb pole oriented close to z a directions lying within this common rhomb plane progressively change through 180 in orientation traced around the c axis fabric skeleton such contrasting single crystal rhomb a preferred orientations on the leading and trailing edges of the fabric skeleton are interpreted as indicating localized grain scale plane strain and flattening deformation respectively they result in tectonites with essentially symmetrical c and a axis fabrics which display strongly asymmetrical positive r and negative z rhomb pole figures the observed transition in quartz c and a axis fabrics is interpreted as indicating an increasing importance of non coaxial plane strain deformation as the moine thrust is approached even immediately 1 cm beneath the thrust however flow has still significantly departed from bulk simple shear and involved an important heterogeneous component of contemporaneous flattening deformation

salt marsh aggradation in response to late holocene sea level rise at amherst point nova scotia canada a radiocarbon 14c chronology determined for plant macrofossils in exposed salt marsh sediments at amherst point nova scotia canada shows that the edge of the high salt marsh aggraded 7 5 m since 900 bc equivalent to a mean rate of 25 9 cm 100 yr 1 four phases of rapid aggradation 900 600 bc 100 bc ad 200 ad 700 1100 and ad 1600 to present were interspersed with three phases of slower aggradation 600 100 bc ad 200 700 and tentatively ad 1100 1600 the stepped pattern of marsh aggradation probably resulted from eustatic sea level fluctuations superimposed on background signals of crustal subsidence and tidal range expansion because the rate of high salt marsh aggradation lagged or exceeded the rate of higher high water hhw increase at various times the high salt marsh aggradation trend only approximates the trend of hhw increase the eustatic sea level fluctuations are estimated to have a range of at least 0 8 m

kinematics of austro alpine cover nappes changing translation path due to transpression upper and middle austro alpine nappes of the eastern alps the structural uppermost subunits of the alps suffered two major superposed deformations d1 d2 during the eo alpine cretaceous orogeny d1 is characterized by nw to w directed thrusting and nappe internal rock flow d2 by large scale folding and imbrication toward the north and northeast structures strain metamorphic history microfabrics and stretching trajectories indicate that the superposition of d2 over d1 structures can be interpreted as a progressive deformation it is concluded that the emplacement of the nappes follows a curved translation path a model which emphasizes non coaxial deformation structures explains the detachment of the nappes the configuration of the separating thrust planes and the distribution of intense deformation zones the overall kinematic history of the austro alpine nappes fits a model in which strike slip shearing horizontal shortening and vertical lengthening act together continuously over a finite deformation zone transpressional model this model emphasizing a gradually changing strain regime eliminates the space problems encountered in models which consider simple south over north imbrication during the alpine orogeny the study stresses two interpretations 1 1 stretching lineations indicate nappe transport directions 2 2 transpression may be a common feature of orogenic belts

long term monitoring of hydrothermal heat flux using moored temperature sensors cleft segment juan de fuca ridge heat flux from submarine vent fields can vary gradually on interannual scales or nearly instantaneously in response to volcano tectonic events in the underlying crust neither case is well documented because measurements of vent field scale heat flux are scarce we report here a new approach to hydrothermal plume monitoring sensitive to both progressive changes and hydrothermal events from june 1991 to may 1992 we moored 35 self contained temperature sensors and six current meters on seven moorings located in and around the plume from a vent field on the cleft segment juan de fuca ridge the hydrothermal plume was identified by a local temperature anomaly of 0 01 to 0 03 c in the lowermost 200 m of the water column plume heat flux defined as the net advection of this temperature anomaly averaged about 250 mw during the deployment this flux is less than previous estimates and thus supports speculation that the heat flux is declining after a sudden reinvigoration triggered by a seafloor rifting event in 1986

a 6 year time series of hydrothermal plumes over the cleft segment of the juan de fuca ridge the causal links between magmatic tectonic processes and hydrothermal venting along the mid ocean ridge axis will be difficult to discern without broadband observations of the temporal variability of hydrothermal activity i report here on temporal variability in the intensity and distribution of chronic and event plumes generated by continuous and episodic hydrothermal discharge at two vent fields on the cleft segment of the juan de fuca ridge hydrothermal temperature and light attenuation c anomalies were comprehensively mapped between 1 and 4 times per year during nine cruises from 1986 to 1991 intensity of and c in the chronic plume overlying the north cleft vent field showed more variability between years than within a given year both and c were exceptionally high in 1986 fell to moderate levels during 1988 to 1990 and declined to minimum values in 1991 the chronic plume over the south cleft vent field varied similarly superimposed on the chronic plumes were brief and intense releases of hydrothermal fluid that created event plumes distinguishable by their symmetry and exceptional rise height event plumes at the north cleft field ranged from the 1986 megaplume with a rise height exceeding 1000 m to smaller events in 1987 and 1989 with rise heights of 400 m chronic hydrothermal heat 660 277 1 mw and mass 204 86 1 g s 1 fluxes from the north cleft field were determined by assuming these fluxes were equivalent to the long term net advection of a mean cross section of the vertically integrated and c in the plume this 6 year history of hydrothermal plumes indicates that episodic discharge has been an important component of the recent hydrothermal flux and that the aggregate heat and mass fluxes declined significantly though not consistently between 1986 and 1991

late cretaceous exhumation of the metamorphic gleinalm dome eastern alps kinematics cooling history and sedimentary response in a sinistral wrench corridor abstract the metamorphic gleinalm dome eastern alps was uplifted and exhumed within a releasing structure in a sinistral wrench corridor during the late cretaceous the dome is confined by a system of ductile shear zones including low angle normal faults and steep sinistral tear faults which define a large releasing structure with the metamorphic dome in its center the fabrics developed within all ductile shear zones record processes which were operating during decreasing temperatures from initial epidote amphibolite upper greenschist facies conditions with crystal plastic fabrics in quartz to temperatures below ca 300 c with predominantly cataclastic fabrics a cooling path based on 40ar 39ar amphibole 95 4 1 2 ma and muscovite ages 87 6 0 6 84 3 0 7 ma together with sphene zircon and apatite fission track data indicate cooling through ca 500 c at ca 94 ma to below ca 250 200 c at 65 ma subsidence of the adjacent late cretaceous kainach gosau basin occurred synchronously with cooling and uplift of the gleinalm dome internal depositional patterns record rapid subsidence at the time of cooling with internal synsedimentary block rotation above an intra crustal ductile normal fault the sinistral wrench corridor of the eastern alps developed by sinistral displacement of the austroalpine units against a relatively stable europe during the late cretaceous

characteristics of 4 day oscillations trapped by the juan de fuca ridge current meter observations from different studies along the crest of the juan de fuca ridge have been combined to show new features of the relatively large broad spectral peak centered near a period of about 4 days the coherence range of the 4 day oscillations has been extended to the extreme ends of the ridge and the trapped waves appear to propagate northward along the entire length of the ridge at about 1 m s spectral amplitudes are about double on the south end compared to the north end and a recent model for bottom trapped subinertial waves over topography shows this may be due to variations in ridge width allen and thomson 1993 new observations show coherence between temperatures and currents near the south cleft vent field and suggest 4 day oscillations can play a major role in the local advection of hydrothermal plumes these observations combined with earlier results demonstrate that 4 day oscillations are a significant ridge trapped feature and they suggest that other ridges may be important in transmitting energy over much longer distances

a model of an atlantic and pacific hydrothermal plume a turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields owing to the stably stratified salinity field in the pacific relatively warm salty water spreads at an equilibrium level where the plume density equals the ambient density in contrast the unstable salinity profile in the atlantic gives the plume added buoyancy and it continues to rise to an equilibrium level where it is relatively cool and fresh these attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer the equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient the net entrainment of surrounding seawater is greater in the atlantic plume model than in the pacific plume model for the same buoyancy flux recent data from the tag hydrothermal field at 26 n on the mid atlantic ridge and data from a vent field on the endeavor segment of the juan de fuca ridge are compared to model results the model predicts the penetration height and s characteristics of the atlantic plume and it explains some of the differences between the observed atlantic and pacific hydrothermal plumes

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

bulk properties of hot smoker plumes the hot buoyant fluid from a submarine vent rises as a plume entraining fluid from the stratified ocean until a height is reached where the driving buoyant force vanishes and shortly thereafter the diluted plume fluid intrudes into the ocean interior at its equilibrium depth while a large positive heat flux issues from the vent the potential temperature anomaly of the horizontally spreading fluid at the equilibrium height depends on the oceanic stratification of both salinity and potential temperature and on the salinity of the source fluid at the vent for example in the atlantic ocean the oceanic stratification causes the spreading plume fluid to be cooler and fresher than the surrounding seawater of the same density while in the pacific the spreading fluid is relatively warm here the well known solution for a turbulent plume rising in a linearly stratified environment is used to obtain simple formulae for 1 the potential temperature anomaly of the horizontally spreading fluid 2 the heat flux associated with this injection of diluted vent water at this density level and 3 the nondimensional solution for the evolution of tracer properties e g salinity and potential temperature in the rising plume

evidence for volcanic eruption on the southern juan de fuca ridge between 1981 and 1987 the formation of new ocean crust at mid ocean ridges is known to be a discontinuous process in both space and time but little is known about the frequency and duration of eruptions along an active ridge segment here we present evidence from sea beam surveys and underwater photography for the eruption of lavas along a segment of the juan de fuca ridge between 1981 and 1987 although previous studies have inferred volcanic activity on ridges in areas where recent seismicity or young lava flows have been observed1 4 none has yet had direct evidence to date such a recent submarine eruption the temporal coincidence between this eruptive episode and the megaplumes huge sudden emissions of hot mineral laden water observed over this part of the ridge5 6 in 1986 and 1987 supports previous suggestions5 10 that megaplumes are caused by sea floor spreading events

abundance and isotopic composition of helium in hydrothermal sulfides from the east pacific rise at 13 n abstract the helium isotopes composition of fluids trapped in hydrothermal sulfides from the east pacific rise 13 n were measured two extraction techniques i e crushing and heating were tested and sulfldes of different mineralogical types were studied the comparison between the two extraction methods suggests that both should give similar results provided the crushing efficiency is sufficiently high sulfides 3 he 4 he ratio for crushed samples are in the range 6 85 8 10 times the atmospheric ratio r a 1 38 10 6 and the measured helium concentration is of the order of 5 5 10 5 cm 3 stp per gram of trapped fluid comparison with the helium isotope composition of the hydrothermal vent fluids themselves shows that the mineral phases formed at the highest temperature i e with less dilution by the ambient seawater retain the helium information most effectively with values almost indistinguishable from the endmember vent fluid

transpressional collision structures in the upper crust the fold thrust belt of the northern calcareous alps abstract two major structural events characterize the tectonic evolution of the northern calcareous alps nca 1 late early cretaceous to late eocene nw directed dextral transpressional stacking of nappes as an expression of the formation of the austroalpine orogenic wedge and 2 miocene sinistral wrenching due to eastward lateral extrusion of crustal wedges along the central eastern alps three first order detachment horizons are defined by differences of competence within areas of facies transition preexisting normal faults control the thrust architecture transpressional contraction in the nca is indicated by a nw directed thrusting oblique to both the long axis of the nca and the edge of the orogenic foreland b the occurrence of en echelon arrays of thrusts and folds laterally displaced by dextral strike slip faults the thrusts and strike slip faults are kinematically connected to each other and dissect the nca into rhomboidal blocks c ne directed extension parallel to fold and ramp axes and the internal strike of the nca and d clockwise rotation 30 of the entire nca around a vertical axis kinematic and dynamic analysis of mesoscale fault striae data related to transpressional stacking indicates a nw trend of contraction directions and in general a ne trend of the extension directions parallel to fold axes and branch lines of thrusts before rotation the average contraction direction was probably parallel to the generally w directed shear direction recorded in the crystal plastically deformed central part of the eastern alps three balanced cross sections across the nca yield a minimum of 54 65 total shortening

decay of hydrothermal output following the 1998 seafloor eruption at axial volcano observations and models 1 observations of the decay of heat and particle discharge following the reinvigoration of a hydrothermal field by a dike intrusion and eruption can provide insights about subsurface hydrothermal circulation in january 1998 a lava eruption at the summit of axial volcano juan de fuca ridge created numerous new vents along a 5 km length of the caldera boundary five cruises over the next 3 5 years found the inventory of hydrothermal heat and particles determined by optical backscattering in the overlying plume decaying as time t 0 9 these results are consistent with the 1993 coaxial eruption where the heat flux decayed as t 1 2 and t 0 7 at the flow and floc sites respectively all three eruption sites decayed significantly faster than t 0 5 the rate attributable to cooling only by simple conduction through the impermeable layer separating magma from hydrothermal circulation we present a more realistic model of hydrothermal cooling that adds conductive heat loss by ascending fluid to the surrounding rock walls increasing the theoretical loss rate to t 0 75 we suggest that variability in the observed decay rates are not sampling variations but reflect real differences in the local heat supply and cooling processes the decay rate was slowest and matched our model result where no seafloor eruption occurred and a long lasting heat source was likely present floc the rate was fastest where a shallow source erupted a thick lava pavement flow the axial eruption where a substantial magma chamber emplaced only a thin sheet flow may be intermediate between these extremes

thermometrically inferred cooling rates from the plattengneis koralm region eastern alps abstract closure of fe mg exchange between garnet and biotite is used to estimate cooling rates from the koralm region of the austro alpine nappe complex east of the tauern window in the eastern alps maximum cooling rates for a 700 m thick mylonitic shear zone the plattengneis are at least an order of magnitude higher than those of surrounding country rocks the cooling rate history inferred for the plattengneis suggests exponentially decreasing cooling rates whilst the cooling history of the surrounding country rocks is inferred to involve an approximately constant cooling rate the fast cooling rates in the shear zone are interpreted as evidence for an additional energy input from an internal heat source which may have been heat that was released during deformation related to the alpine nappe stacking processes

physical characteristics of the endeavour ridge hydrothermal plume during july 1988 abstract we conducted ctd transmissometer tows from 8 to 26 july 1988 within 15 km of the central hydrothermal vent site 47 57 n 129 06 w on the endeavour segment of juan de fuca ridge anomalies of temperature salinity and light attenuation reveal possible new vent sites 4 and 8 km northeast and 6 km south of the central vent site as a result of widespread plume dispersion background values of potential temperature salinity and light attenuation below the 1900 m depth exceeded those for pristine ambient waters by 0 05 c 0 05 psu and 0 03 m 1 respectively maximum plume anomalies relative to the background waters were of the order of 0 10 c 0 010 psu and 0 10 m 1 at core depths of 2000 2050 m heat and salt anomalies were detectable more than 5 km from the central vent site whereas light attenuation particle anomalies were confined to within 2 5 km of the vent site based on the background water property anomalies and moored current meter records the mean time averaged heat fluxes for the survey region were 2 3 1 5 10 8 w in the along ridge direction 20 t and 7 7 4 7 10 8 w in the cross ridge direction 110 t mean along and cross ridge salt fluxes were 7 5 and 25 15 kg s 1 mean particle fluxes were 0 09 0 06 and 0 29 0 18 kg s 1 estimates of the instantaneous fluxes derived from coincident current and plume measurements indicate that heat fluxes from the central vent field may have been as high as1 2 0 6 10 10 w and corresponding particulate fluxes as high as6 3 kg s 1

the spodumene deposit at weinebene koralpe austria the weinebene spodumene deposit is located in carinthia about 270 km southwest of vienna it is hosted by the medium to high grade metamorphic rocks of the koralpe the spodumene bearing pegmatites form unzoned dikelike bodies in eclogitic amphibolites and kyanite bearing micaschists with concordant foliations their lateorogenic emplacement is probably of variscan age a younger probably alpine metamorphic event affected the pegmatites it caused extensive recrystallization of the micaschist hosted pegmatites but had only a minor impact on the amphibolite hosted ones the spodumene bearing pegmatites have been traced over a length of 1 5 km along strike and to about 450 m down dip their average thickness is 2 m with a maximum of 5 5 m emplacement of the pegmatites caused an alteration halo of several dm in the hosting amphibolites characterized by biotitization and formation of holmquistite an aplitic spodumene free seam of about 10 cm symmetrically borders the pegmatites no contact phenomena are observed along the micaschist hosted dikes spodumene is the only lithium bearing mineral its average content is 22 vol equivalent to 1 68 wt li2o in the amphibolite hosted pegmatites and 15 vol equivalent to 1 13 wt li2o in the micaschist hosted dikes such a significant difference is also shown by rubidium 1 100 ppm vs 880 ppm and cesium 60 ppm vs 25 ppm beryllium and tin are the only other significant trace elements they show average contents of about 100 ppm and 120 ppm respectively with maxima of 1 690 ppm beryllium and 1 500 ppm tin no correlation is found between lithium tin and beryllium niobium and tantalum are very low a na k ratio of 1 2 emphasizes the predominance of albite over microcline there is no discernable correlation between spodumene and albite contents or between lithium and any other alkalies the average k rb ratio is 20 pointing to the high degree of fractionation spodumene contains 7 4 li2o and 0 45 feo there is no difference in the spodumene chemistry between the amphibolite hosted and the micaschist hosted pegmatites strong structural and textural evidence mineral zoning bulk composition corresponding to thermal minima in relevant experimental systems and trace element signature support an igneous derivation of the pegmatites however no granitic intrusion is exposed in the area and the pegmatites could have been displaced from their source by tectonic events

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

preliminary investigation results on fabrics and related physical properties of an anisotropic gneiss abstract in order to evaluate the fabric dependent anisotropy of a particular gneiss type we assessed the quartz lattice and shape preferred orientations as well as the microcrack pattern statistics in the rock mechanics laboratory several strength and deformability tests on drilled rock samples were run and the seismic wave propagation properties along the rock s principal strain axes were determined in the mechanical tests it turned out that despite a distinct stretching lineation with initially extreme grain elongation the rock performs for the larger part as a transversely isotropic material with the schistosity as plane of isotropy the anisotropy in seismic wave propagation within the plane of schistosity is attributed primarily to a highly anisotropic microcrack pattern the distinct gneissose banding and to a lower degree to the lpo of quartz

hydrothermal vent alvinellid polychaete dispersal in the eastern pacific 1 influence of vent site distribution bottom currents and biological patterns deep sea hydrothermal vent habitats are typically linear discontinuous and short lived some of the vent fauna such as the endemic polychaete family alvinellidae are thought to lack a planktotrophic larval stage and therefore not to broadcast release their offspring the genetic evidence points to exchanges on a scale that seems to contradict this type of reproductive pattern however the rift valley may topographically rectify the bottom currents thereby facilitating the dispersal of propagules between active vent sites separated in some cases by 10s of kilometers or more along the ridge axis a propagule flux model based on a matrix of intersite distances long term current mete data and information on the biology and ecology of alvinellidae was developed to test this hypothesis calculations of the number of migrants exchanged between two populations per generation n allowed comparisons with estimates obtained from genetic studies n displays a logarithmic decrease with increasing dispersal duration and reaches the critical value of 1 after 8 d when the propagule flux model was run in standard conditions at most propagule traveling time cannot reasonably exceed 15 30 d according to the model whereas reported distances between sites would require longer lasting dispersal abilities two nonexclusive explanations are proposed first some aspects of the biology of alvinellidae have been overlooked and long distance dispersal does occur second such dispersal never occurs in alvinellidae but the spatial temporal dynamics of vent sites over geological timescales allows short range dispersal processes to maintain gene flow deep sea hydrothermal vent habitats are characterized by temperatures higher than ambient for the deep sea lower oxygen concentration higher levels of toxic compounds metals sulfide and extreme spatial and temporal variability tunnicliffe 1991 the biology and life history of the vent fauna are closely linked with these features which are stable over geological time on a large spatial scale in contrast vent sites seem to be ephemeral on short temporal scales lalou 199 1 hydrothermal activity indeed shifts along the ridges generating numerous short lived spots and consequently forcing the endemic fauna to colonize new vents as they appear in the eastern pacific hydrothermally active venting areas are restricted to a few portions of oceanic ridges the continuity between the sediment covered ridge in the gulf of california guaymas basin the east pacific rise epr and the galapagos rift is of particular interest to biologists segmentation of the ridge by transform faults and the great distance separating the main hydrothermal areas raise the question of dispersal processes this

variations in mean currents affecting hydrothermal plumes on the juan de fuca ridge a summary of current meter observations near the juan de fuca ridge shows new features of topographic steering of flow that determine the fate of plumes from hydrothermal vents an anticyclonic circulation exists over the ridge with north and south mean flows along the west and east flanks speeds are up to 2 3 cm s 1 near the ridge and decrease to zero about 25 km from the crest contributions from hydrothermal forcing and tidal rectification may generate the along ridge flows average anomalous heat fluxes associated with the north and south flows were estimated at 1400 and 2600 mw respectively and they are larger than previous estimates based on single point current measurements variability of flow occurs on several time scales and space scales daily average currents over a 4 day period can rotate over the entire ridge with sufficient cross axis speeds to move plumes away from the vents into the stronger north south flows over the flanks currents along the west side of north cleft diverge with near ridge flow 10 km from the ridge turning eastward around the north end of the segment and offshore flow turning westward farther west in winter off axis currents can be several times as large as the long term mean and could advect plume water relatively long distances significant cross axis flow occurs on the north side of axial volcano that may be the result of interaction between the general circulation and topography generating eddy circulations around or near axial or the entire axial cobb massif

estimation of heat and chemical fluxes from a seafloor hydrothermal vent field using radon measurements the circulation of seawater through newly formed ocean crust at mid ocean ridge spreading centres is important in the oceanic heat and chemical budgets the heat transfer in submarine hydrothermal systems accounts for 25 of the total global heat loss1 the transfer of mass resulting from basaltic alteration affects the geochemistry of seawater2 and is responsible for the formation of ore deposits on and beneath the seafloor3 various geophysical techniques have been employed in efforts to determine the heat output from hydrothermal vent fields4 9 however the magnitudes of the heat and chemical fluxes through these systems remain uncertain here we introduce a geochemical approach for estimating the flux from a vent field based on radon 222rn measurements in the overlying effluent plume this method was applied successfully in september 1986 during a 23 day expedition to an active vent field on the 170 km endeavour segment of the juan de fuca ridge fig la we estimate the heat flux from this site to be l 5 l09 w

characteristics of hydrothermal plumes from two vent fields on the juan de fuca ridge northeast pacific ocean deep ctd transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally buoyant plumes emanating from each of two major vent fields on the southern symmetrical segment sss and endeavour segment es of the juan de fuca ridge at both vent fields emissions from point and diffuse hydrothermal sources coalesced into a single 200 m thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0 02 0 05 c and light attenuation anomalies of 0 01 0 08 m 1 10 80 g l above background temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped 10 15 km downcurrent light attenuation trends were non uniform and differed between plumes apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates vent fluids from the sss are metal dominated and mostly precipitate very fine grained hydrous fe oxides that remain suspended in the plume vent fluids from the es are sulfur dominated and precipitate a high proportion of coarser grained fe sulfides that rapidly settle from the plume the integrated flux of each vent field was estimated from measurements of the advective transport of each plume heat flux was 1700 1100 mw from the es and 580 351 mw from the sss particle flux varied from 546 312 g s to 204 116 g s at the es depending on distance from the vent field and was 92 48 g s from the sss

geology of the northern cleft segment juan de fuca ridge recent lava flows sea floor spreading and the formation of megaplumes geologic mapping and lava sampling were carried out after the discovery of large bursts of hydrothermal fluids megaplumes over the southern juan de fuca ridge in 1986 and 1987 our investigations of the northernmost section of the cleft segment have discovered 1 semicontinuous low temperature venting and one major high temperature vent site along 17 km of the neovolcanic zone and 2 very glassy lightly sedimented sheet flows and pillow mounds superimposed on older terrain over about 24 km along the northern most part the pillow mounds are documented to have erupted between 1981 and 1987 the occurrence of the megaplumes during this same time period strengthens the hypothesis that megaplumes are caused by sea floor extension events although the basalts from the entire length of the neovolcanic zone of the cleft segment appear to have been derived from the same mantle source a systematic northward increase in mg number along the segment within the neovolcanic zone indicates less shallow level differentiation to the north possibly related to the development of new magma chambers during the recent phase of sea floor spreading that has occurred there

eo alpine eclogitisation of permian morb type gabbros in the koralpe eastern alps austria new geochronological geochemical and petrological data new petrological geochemical and isotopic data sm nd rb sr from meta gabbros eclogites and metapelites from the southern koralpe are presented pl cpx gabbros mostly olivine free that have preserved their magmatic minerals to varying extent occur as relics within eclogites transformation of gabbro into eclogite is documented in different stages ranging from macro to microscale based on textural characteristics the eclogites are classified into four groups types 1 4 typical eclogite parageneses are grt omp zo ky qtz amp phe rut the metapelitic eclogite host rocks are composed of qtz ms bt pl grt ky p t estimates for both metabasites and metapelites range at 1 8 2 0 gpa 600 650 c sm nd mineral isochrons pl cpx for the gabbroic eclogite precursors give ages of between 247 16 and 255 9 ma their initial nd and sr isotopic compositions are clearly within the range of modern depleted mantle values minerals from type 1 metagabbroic eclogites are in clear nd isotopic disequilibrium pervasively recrystallized type 3 eclogites yield grt wr or grt omp zo amp wr ages of 97 5 101 7 and 109 8 ma the metapelitic eclogite host rocks mica schists yield nd dm depleted mantle model ages of 1 44 1 63 ga grt wr isochron ages from these rocks are 86 1 87 4 and 89 3 ma the new data further support the permian early mesozoic rifting event for this part of the austroalpine basement which is related to initial oceanization at the western end of the alpine tethys during alpine plate convergence pre alpine continental basement and oceanic crustal fragments where subducted to depths of c 60 km the most likely time span for the high pressure peak is c 100 10 ma rapid exhumation in the upper cretaceous is inferred from mineral cooling ages between 80 and 60 ma

locating hydrothermal vents by detecting buoyant advected plumes an improved method of detecting buoyant hydrothermal plumes and locating their source vents is introduced plumes are detected by computing fluid stability from conductivity temperature and depth measurements acquired during navigated towed vertically oscillating casts over the endeavour segment of the juan de fuca ridge for each instability detected the maximum range to its hydrothermal source is estimated by multiplying a theoretical plume equilibration time by a measured current velocity using an estimate of current direction the method reliably locates plume sources where they are known to exist in all of the focused vent fields mapped by submersible and in several isolated diffuse flow sites the method generates a distribution of hydrothermal sources that is more consistent with variations in surface permeability than with circulation cells spaced evenly along a uniformly permeable axis axial instabilities are nearly continuous along the heavily fissured and fractured western wall of the axial valley beyond the axial valley instabilities evidence that hydrothermal upflow penetrates the outer slopes of the ridge crest probably along a boundary between sheet and pillow flows