origin of ore forming brines in sediment hosted zn pb deposits of the basque cantabrian basin northern spain fluid inclusion data microthermometry and na k li cl br chemistry from mississippi valley type zn pb deposits in the basque cantabrian basin north iberian peninsula indicate that fluid mixing occurred during mineralization cl br ratios of the ore forming brines suggest that the high salinity was primarily acquired by evaporation of seawater only in deposits near salt domes orduna and murgia diapirs do the ore forming brines have halogen signatures indicative of halite dissolution mixing of fluids frequently cannot be detected using only microthermometry or halogen data although microthermometric data can indicate mixing where one of the end members is fresh water or a highly diluted fluid combining the two allows both the recognition of mixing and an estimation of the relative proportion of the different fluids involved the effects of mixing on the salinity and halogen ratios of the resulting mixture have been calculated using four types of fluids 1 seawater 2 evaporated seawater before the onset of halite precipitation 3 seawater evaporated past the point of halite precipitation and 4 a halite saturated brine at 25oc derived from halite dissolution the calculated cl br na br mixing curves have been compared to data from the zn pb deposits of the basque cantabrian basin and show that mixing between a residual brine and a halite dissolution brine can account for the deposits in the western biscay district txomin matienzo barambio most of the ore forming brines from the studied deposits around the orduna and murgia salt domes altube monteleon jugo originated by halite dissolution although there is also significant contribution 20 50 wt from a highly evaporated brine

dating of pore waters with 129 i relevance for the origin of marine gas hydrates pore waters associated with gas hydrates at blake ridge in the atlantic ocean were dated by measuring their iodine 129 iodine ratios samples collected from sediments with ages between 1 8 and 6 million years ago consistently yield ages around 55 million years ago these ages together with the strong iodine enrichment observed in the pore waters suggest that the origin of iodine is related to organic material of early tertiary age which probably is also the source of the methane in the gas hydrates at this location

scandinavian caledonide metallogeny in a plate tectonic perspective caledonian metallogeny has endowed scandinavia with abundant metalliferous mineral resources of several genetical and compositional types many of which have been exploited at various scales from the seventeenth century onwards because of this long history of exploration exploitation coupled with excellent exposures the caledonian orogen in scandinavia can be taken as a model to illustrate the relationship between metallogenic evolution and plate tectonics its orogenic and metallogenic development can be related to a period of plate movements which started about 700 600 ma ago with rifting and break up of a proterozoic megacontinent rodinia followed by the opening up of a wide ocean iapetus and ending with collision between the laurentian and baltic continents the climactic scandian phase of orogeny in silurian times fragments of this sedimentary magmatic and tectonic history are recorded in various autochthonous and allochthonous units which were ultimately thrusted eastwards above the baltic plate margin

the behavior of lithium and its isotopes in oilfield brines evidence from the heletz kokhav field israel twenty four brine samples from the heletz kokhav oilfield israel have been analyzed for chemical composition and li isotope ratios the chemical composition of the brines together with geological evidence suggests derivation from messinian seawater by evaporation that proceeded well into the gypsum stability field but failed to reach the stage of halite crystallization the present salinity of the samples 18 47 g cl l was achieved by dilution of the original evaporitic brine by local fresh waters like brines from other sedimentary basins the li cl ratios in the heletz kokhav samples show a prominent li enrichment five fold to eight fold relative to modern seawater the isotopic ratios of li expressed in the 6 li notation vary from 26 3 to 17 9 all values being significantly higher than that of modern seawater 32 irrespective of their corresponding li concentration 1 0 2 3 mg l the isotopic composition of li and the li cl ratio in the oilfield brines were acquired in two stages a the original evaporated seawater gained isotopically light li during the diagenetic interaction between the interstitial messinian brine and the basin sediments a parent brine with an elevated li cl ratio was formed the brine was later diluted in the oilfields b the 6 li values of the final brines were determined during epigenetic interaction with the heletz kokhav aquifer rocks at the same time the li cl ratio inherited from stage a remained largely unchanged this work represents the first use of lithium isotopic composition to elucidate the origin and evolution of formation waters in sedimentary basins copyright 2002 elsevier science ltd

paleogene seafloor spreading in the southeast tasman sea magnetic anomalies 11 18 have been identified in the southeast tasman sea the area of ocean crust southwest of fiordland new zealand west of the puysegur trench the present plate boundary and southeast of the older 80 58 ma ocean crust of the tasman sea basin structures associated with two changes in spreading direction are preserved in the area spreading between the australian and pacific plates began in the eocene about 40 ma in this area orthogonal to cretaceous paleocene spreading between them in the tasman sea the boundary between the two ages of ocean crust is abrupt and associated with what we have interpreted as marginal uplift blocks and rift basins of the resolution ridge system rifting appears to have propagated northeast along a fracture zone the northern blocks of the resolution ridge system may be isolated fragments of continental crust of the campbell plateau between anomalies 18 and 11 40 30 ma the spreading rate was about 1 5 cm yr swath mapping and satellite altimetry data show that a second change in relative plate motion direction began shortly after anomaly 11 about 30 ma and led to a change from tension to transcurrent motion along the plate boundary the timing of the changes in spreading direction agrees with tectonic events interpreted from onshore data

shear fracture pattern and microstructural evolution in transpressional fault zones from field and laboratory studies abstract zones of transpressional shear deformation accommodate strike slip and oblique slip displacements field work in a transpressive shear zone and transpressional analogue clay box modelling show that a p oriented foliation and associated p shears are preferentially developed over the more common r 1 riedel shears the carboneras fault system cfs in se spain is a left lateral transpressional shear zone with an internal geometry characterized by first order y oriented faults and widespread p oriented second order faults the mesoscopic to microscopic gouge fabric reflects the regional architecture of the shear zone being dominated by a pervasive poriented foliation and discrete y and p shears friction experiments carried out to investigate the textural evolution of gouge fabrics showed four textural stages of fabric development from foliation formation to extreme shear localization resulting in cross gouge failure transpression clay box models favoured the formation of secondary p oriented shear fractures and p oriented shear lenses further deformation caused differential shear lens rotation and shear lens orientations closer to the mean displacement direction our field studies and laboratory analogue experiments indicate that shear zones dominated by p shears are diagnostic of a transpressional deformation regime

effect of mechanical interaction on the development of strike slip faults with echelon patterns abstract the overlapping geometry of echelon strike slip faults is well known we have quantified this observation by measuring the amount of overlap and separation and plotting them against each other for over 120 examples although there is large scatter the data show a linear trend suggesting that the overlap increases proportionally with separation up to a limiting value we have analyzed this conspicuous relationship in terms of fault interaction by using a numerical model based on displacement discontinuity the results show that fault interaction is in fact an important factor in contributing to the overlapping geometry of echelon strike slip faults

hydrothermal dolomites in sw sardinia italy evidence for a widespread late variscan fluid flow event abstract epigenetic replacive and saddle dolomite frequently forming zebra structures geodic dolomite affected cambrian limestones and early diagenetic dolomites across large areas of the iglesiente sulcis mining district sw sardinia italy the dolomite crops out in an area of more than 500 km 2 and reaches a thickness of up to 600 m or even more this rock represents one of the most extensive dolomites of epigenetic origin yet documented prior to dolomitization the cambrian carbonates underwent ductile deformation and greenschist facies metamorphism the same is true for the overlying tectonic nappes fluid inclusion analysis combined with o and sr isotope data indicate that the dolomitizing fluid can be categorized as a basinal brine the spread in homogenization temperatures shows a gradient with values decreasing from east to west the higher temperatures mean of around 100 c have been measured in eastern parts of the iglesiente area whereas the lowermost temperatures mean of about 85 c have been found along the western coast of iglesiente this fluid certainly can neither have come directly from the low grade metamorphic lithotypes undergoing dolomitization nor from the low temperature metamorphic rocks within the overlying nappes it is assumed that a late variscan hydrothermal event which coincided with extensional tectonics set brine circulation into motion dolomitization may have occurred within circulation cells which were driven by high heat flow fluids originated in the underlying rocks and circulated upward to affect the overlying cambrian carbonates an alternative model is that the dolomitization was caused by hydrothermal brines that originated within basinal areas of the variscan orogenic pile circulating deep within the crust and ascended in the external zone iglesiente sulcis whatever the origin these reducing saline fluids which carried radiogenic sr dolomitized a large volume of early paleozoic rocks the many subhorizontal open cavities within the geodic dolomite only partly filled with cement might indicate fluid overpressure at the time of dolomitization

extension along the australian pacific transpressional transform plate boundary near macquarie island the australian pacific transform plate boundary fault zone along the macquarie and mcdougall segments of the macquarie ridge complex mrc south of new zealand is characterized by dominantly normal faults and pull apart basins in apparent conflict with the regional transpressional tectonic setting we propose that present day curvature of the transform is inherited from a preexisting divergent plate boundary and that the overall extensional kinematics shown by faults along the main plate boundary trace and exposed on macquarie island result from local stresses related to right lateral right stepping en echelon plate boundary faults and not to the current transpressional setting transpression along the australian pacific transform plate boundary has resulted in uplift along the 1500 km long macquarie ridge complex macquarie island the only subaerial exposure of the complex sits atop a 5 km high 50 km wide submarine ridge of oceanic crust and lies 4 5 km east of the major active plate boundary fault zone thus macquarie island and the surrounding seafloor provide a unique opportunity to study an active oceanic transform fault using complementary marine geophysical and land based geological data mapping of recent faults affecting the topography of macquarie island shows that the island is extensively cut by high angle normal faults forming pull apart basins furthermore evidence for reverse motion is rare using marine geophysical data including swath bathymetry reflectivity and seismic reflection data collected along the australian pacific plate boundary north and south of the island we have defined a 5 15 km wide plate boundary zone a series of right stepping en echelon faults within this zone lies along the main plate boundary trace at the right stepping fault terminations elongate depressions 10 km wide and 1 2 km deep parallel the plate boundary which we interpret as extensional relay zones or pull apart basins we propose that transpression is partitioned into en echelon strike slip faults at the plate boundary and a convergent component that flexes the crust causing the anomalous bathymetric ridge and trough morphology of the mcdougall and macquarie segments of the mrc

the oligocene miocene pacific australia plate boundary south of new zealand evolution from oceanic spreading to strike slip faulting abstract since the eocene the pacific australia plate boundary south of new zealand has evolved from a spreading system into a transform boundary swath data acquired in the southeast tasman oceanic crust between the macquarie ridge complex and the resolution ridge system show that the spreading fabric changes orientation southwards along the puysegur trench striking successively n60 e n85 e and n120 e this reflects the reorganisation of the plate boundary in response to changes in relative plate motion a comparison of these orientations with the positions of the pacific australia relative poles of rotation enables us to estimate the age of stoc where there are no identified magnetic anomalies the youngest age of the oceanic crust is ca 12 ma at the south end of the puysegur trench this age is consistent with spreading rates and the amount of crust generated since 31 ma curved fracture zones on either side of the macquarie ridge complex suggest a continuous reorientation of transform faults between 31 ma and ca 15 ma small scale seafloor morphology shows a 13 change of orientation in the l atalante fracture zone that indicates incremental rather than continuous changes in azimuth of the transform faults patterns of fanning ridges indicate that periods of asymmetric spreading accompanied the spreading segment reorientations using swath data and plate reconstruction models we infer that between 31 and 12 ma the plate boundary reorganisation resulted in a continuous increase in the ratio of the cumulative length of transform faults over the cumulative length of spreading segments along the whole plate boundary this indicates that since 14 15 ma the plate boundary has become progressively predominantly transcurrent allowing strike slip motion to develop along a line of merging transform faults that connected to the intracontinental alpine fault

structural and volcanic expression of a fast slipping ridge transform ridge plate boundary sea marc i and photographic surveys at the clipperton transform fault a high resolution near bottom survey has been conducted of the clipperton transform fault and adjoining segments of the east pacific rise epr using the sea marc i side looking sonar system and the lamont doherty geological observatory olympus based camera system the transform fault zone tfz is a narrow well defined belt of transform parallel lineaments which varies along strike from a single sharp edged notch to a complex band of subparallel lineaments up to 1 km wide the tfz is set within a 5 km wide band of unusually fine grained side scan texture which could indicate nonbasaltic seafloor and or pervasively sheared and mass wasted basaltic crust the fine grained swath is surrounded by constructional volcanic terrain with no hint of strike slip motion this observation puts an upper limit of 5 km on the extent of lateral migration of the tfz in the last 1 5 m y both ridge transform intersections rtis are dominated by bathymetric highs located on the old plate opposite the spreading center a mantling of fresh looking constructional volcanic terrain on side scan images suggests that the highs are built in part by recent extrusive and intrusive volcanism thermal expansion may also play a part the epr south of clipperton has recently experienced extrusion of high effusion rate basalts burial of faults and fissures by lava flows and development of vigorous hydrothermal circulation on the epr north of clipperton the axial zone of faults and fissures tapers toward the transform fault this may reflect a change in the shape or size of the underlying shallow level magma feeders as a function of distance from the site of magma upwelling or distance toward the transform fault

morphology and tectonics of the kane transform from sea beam bathymetry data high resolution sea beam data have been used to construct an accurate regional scale bathymetric map of the kane transform a large offset slowly slipping 30 mm yr central north atlantic transform the kane transform trends about 100 nearly orthogonal to the regional trend of the adjacent mid atlantic ridge mar rift valley the transform valley walls are composed of an alternating series of ridges and troughs which parallel the regional trend of the mar the ridges narrow and deepen toward the transform valley over distances of 10 20 km and the intervening troughs widen into distinct closed contour depressions that appear to be relict nodal basins the morphologic elements found on either side of the transform valley exhibit along strike continuity and represent undisrupted displacement markers the swath of terrain sandwiched between these markers is only several kilometers wide and is made up of elongate basins and ridges that integrate to create a distinctive transform parallel grain this interval the transform tectonized zone ttz marks the time averaged location of strike slip tectonism as parcels of crust move from each intersection along the transform interface the ttz is widest 6 km near the eastern ridge transform intersection rti and narrows to a strand less than 3 km wide along the central and western portions of the transform along the eastern portion of the transform valley a narrow 3 km median ridge several hundred meters high can be traced for more than 40 km along the valley floor and a similar but shorter feature is also present near the western rti at both rtis the neovolcanic zone from the adjacent rift valley can be traced as a series of constructional edifices across the entire intersection area to the opposing transform valley wall at the eastern rti the neovolcanic zone wraps around the eastern edge of the nodal basin while at the western rti it appears to bisect a paired nodal basin located in the intersection area a line drawn connecting the ends of each neovolcanic zone lies within the narrow ttz and has a strike of 098 using the bathymetric map of the kane transform as a record of the time integrated tectonic evolution of this large slowly slipping ridge transform ridge plate boundary we have constructed a simple model for the evolution of rtis our model emphasizes the interplay between temporal variations in crustal production rates i e variations in the volume of basaltic melt production along oceanic spreading centers and extensional tectonism this model can explain the existence of nodal basins at rtis and relict nodal basins along transforms and fracture zones as well as the occurrence of regularly spaced ridge and trough topography on the ridge flanks

sediment provenance and dispersal in a deep marine foreland basin the lower carboniferous culm basin czech republic the lower carboniferous culm basin of the czech republic represents the most easterly and southerly part of the european variscan foreland basin system the nne ssw trending basin is exposed along the eastern flank of the bohemian massif it contains up to 7 5 km of deep marine sediment deposited as an axial turbidite system sourced from south southwest of the basin heavy mineral data and clast types indicate that for much of the visean sediment was sourced from a predominantly low grade metamorphic terrane and visean limestones in the latest visean a progressive change in source material is recorded by an increase in high grade metamorphic detritus studies of variscan nappe pile emplacement along the eastern flank of the bohemian massif allow an assessment of the relationship between basin development and nappe emplacement basin initiation coincided with underthrusting of high grade metamorphic moldanubian nappes at 340 ma sedimentation was synchronous with nappe emplacement throughout the visean which resulted in uplift and erosion of a low grade metamorphic terrane moldanubian nappes were exhumed at approximately 330 ma when high grade metamorphic detritus entered the basin two phases of northward directed sediment progradation are recognized sediment progradation is considered to be related to changes in drainage basin size and or climatic fluctuations within the variscan orogen since sediment is inferred to have been supplied to the basin axially rather than laterally and subsidence curves show no significant change in subsidence rates in contrast to many models of foreland basin sediment distribution filling of the culm basin was largely independent of tectonic activity adjacent to the basin margin and or of subsidence rate changes sedimentation in the culm basin commenced 10 15 ma earlier than the rest of the variscan foreland and records the first impact of the northwardly propagating variscan orogen in northern europe

fluid transfers at a basement cover interface part ii large scale introduction of chlorine into the basement by mesozoic basinal brines significant fracture and porosity sealing characterizes the sedimentary cover basement interface in the northwestern margin of the aquitaine basin france dolomite and calcite and sometimes fluorite barite and quartz constitute most of the fracture fillings they contain primary inclusions of brines having chlorinities in the range of 3 3 to 5 5 mol cl kg solution with total homogenization temperatures in between 65 and 130 c for quartz and slightly lower for dolomite barite fluorite and calcite crush leach analyses indicate that brines are characterized by na k ratios of 5 to 40 na li ratios of 20 to 530 and cl br ratios of 200 to 1000 which are rather typical of deep basinal brines the fluid 18o signature is estimated to be 6 6 1 8 smow for a crystallization temperature of 100 20 c between 80 and 120 c and the d value is 30 10 smow the fluid source for the fracture filling mineral is interpreted as a deep sedimentary brine expelled during a period of maximum subsidence in the aquitaine basin which migrated along the sediment cover basement interface which is characterized by high permeabilities below the toarcian shales the sealing is likely to be linked to the mixing of the brines with dilute ascending hot waters these dilute waters infiltrated from emerged zones convected and heated at depth reaching temperatures of 100 c up to 150 c on the basis of cation geothermometry extensional activity of probable cretaceous age related to the gascogne gulf rifting could be considered as the most likely cause of a significant fluid migration event at the basement cover interface all along the margins of the french massif central these processes are large scale as shown by the similarities of mineral sequences fluid types and general features of most of the f ba pb zn deposits located at the basement sedimentary cover interface the mass transfer of cl linked to this stage is significant and accounts for the early introduction of large amounts of chlorine in the granitoid microporosity this probably explains the significant chlorine concentrations of the present day fluids recovered in the granitoid aquifer

evidence of transpression along the clipperton transform implications for processes of plate boundary reorganization abstract high resolution bathymetry data of the clipperton fracture zone and focal mechanisms of recent earthquakes along the active transform provide evidence for recent and ongoing transpression along the clipperton transform structural and morphological features observed in the bathymetry data include normal and strike slip faults oriented obliquely to the strike of the transform curved trends of abyssal hills produced by simple shear of the lithosphere bordering the transform fault abyssal hills offset by obliquely trending strike slip faults on lithosphere bordering the transform and lithospheric flexure and associated volcanism near the active transform all of these features can be explained by a transpression scenario in which a counter clockwise change in spreading direction of 5 began about 0 4 0 5 ma and subjected the right stepping clipperton transform to compression a comparison of the median ridge volume to calculated estimates of the convergent volume predicted by the transpression scenario indicates that the median ridge is likely to be a product of the brittle deformation associated with transpression the convergent volume estimates suggest that larger spreading direction changes 5 do not occur instantaneously instead spreading direction changes begin slowly and accelerate to the new spreading direction once compression across the transform has ceased many of the structures observed along the clipperton transform are very similar to features observed along other known convergent transforms such as the san andreas fault in california and may have important implications for understanding continental transforms the transpression scenario also indicates that transforms are very important in constraining the rate and character of global plate motion changes

oceanic broad multifault transform plate boundaries oceanic transform plate boundaries consist of a single narrow a few kilometers wide strike slip seismic zone offsetting two mid ocean ridge segments however we define here a new class of oceanic transform boundaries with broad complex multifault zones of deformation similar to some continental strike slip systems examples are the 750 km long 120 km wide andrew bain transform on the southwest indian ridge and the romanche transform where the mid atlantic ridge is offset by a lens shaped 900 km long 100 km wide sliver of deformed lithosphere bound by two major transform valleys one of the valleys is seismically highly active and constitutes the present day principal transform boundary however strike slip seismic events also occur in the second valley and elsewhere in the deformed zone some of these events may be triggered by earthquakes from the principal boundary numerical modeling predicts the development of wide multiple transform boundaries when the age offset is above a threshold value of 30 m y i e in extra long 500 km slow slip transforms multiple boundaries develop so that strike slip ruptures avoid very thick and strong lithosphere

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

relationship between fluid flow and faulting in the alpine realm austria germany italy abstract five carbonate cement generations in faults and associated fractures which precipitated during two major cementation phases were studied in permian to tertiary sedimentary rocks in the drau range in the southern alps and in different nappes of the northern calcareous alps nca the first major cementation phase is represented by clear saddle dolomite csd that can be further subdivided by cathodoluminescence cl into five cl zones a non carbonate zone consisting of chlinochlorite chlorite zone is intercalated between cl zones ii and iii cl zones i iv occur in rocks of permian to early jurassic age while cl zone v is also present in upper jurassic strata the second major cementation phase characterized by another saddle dolomite and three generations of blocky calcite is of miocene age dedolomitized csd which occurs in a synsedimentary normal fault of early jurassic age contains a zone of pyrite the trace element composition of this pyrite zone and of an upper hettangian fe mn crust marmorea crust were compared with the trace element composition of the chlorite zone similar trace element patterns within all three non carbonate zones suggest the same fluid source for these zones during upper hettangian time this fluid could be of hydrothermal origin as indicated by the geochemical characteristics of the fe mn crust hydrothermal activities started during the beginning of rifting in the alpine realm in the late triassic early jurassic fluid inclusion data reveal variable homogenization temperatures for the five cl zones in the clear saddle dolomite formation temperatures between 146 and 201 c were calculated considering the overburden pressure during the formation of the cl zones calculated equilibrium oxygen isotopic fluid compositions indicate 18 o values between 4 0 and 9 0 smow for the fluid from which the different saddle dolomite zones precipitated the origin of the fluid can be related to brines present in the hinterland vindelician high bohemian massif the stratigraphic occurrence of csd and its paragenetic relationship to the non carbonate zones enables a more exact dating of the cl zones cl zones i and ii precipitated between norian and late hettangian time and cl zones iii and iv are of early sinemurian age the formation period of cl zone v is late jurassic to early cretaceous the distribution of the carbonate cements was investigated within different fault sets and in associated subparallel fractures in the nca i e the allgau lechtal and inntal nappe which show a polyphase deformation history csd occurs in normal faults n s trending high angular faults and wnw trending strike slip faults indicating minimum an early jurassic age for these faults the only carbonate cements that are present within ne trending sinistral strike slip faults are of the second major cementation phase implicating a miocene age for these faults fibrous shaped crystals of the first calcite cement of the second major cementation phase preferentially occur within wnw trending strike slip faults reactivation of these faults as conjugated shear pairs in connection with the formation of ne trending strike slip faults is assumed

tectonic implications of fault scarp derived volcaniclastic deposits on macquarie island sedimentation at a fossil ridge transform intersection upper miocene to lower pliocene sedimentary rocks on macquarie island are dominantly volcaniclastic breccia sandstone and siltstone produced by the physical disintegration and tectonic abrasion of oceanic crust in fault zones and mass wasting of these tectonic features they represent small debris fans and small scale turbidites deposited at the base of active fault scarps related to late miocene to early pliocene seafloor spreading most of the sediment is derived from basalts but diabase and gabbro clasts in some sedimentary rocks indicate that middle and lower oceanic crust was exposed to erosion on the sea floor a lack of exotic clasts and a low degree of clast roundness are consistent with a local source for the sediment and no input from continental rocks spatial relationships between sedimentary rocks and major faults associated with seafloor spreading on the island and correlation between sedimentary clast and adjacent up thrown block compositions allow us to infer paleotectonic relief for macquarie island crust during deposition our data support a model involving the deposition of these rocks at the inside corner of a ridge transform intersection furthermore a tectonic reconstruction of the australian pacific plate boundary for the approximate time that macquarie island crust formed 10 9 ma also shows that macquarie island crust most likely formed near a ridge transform intersection this paper describes sedimentation associated with active faulting at a ridge transform intersection that has been uplifted in situ above sea level along with the surrounding oceanic crust and demonstrates that high angle faults have the most pronounced influence compared with low angle faults on sedimentation in this tectonic environment

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

carbon oxygen isotopic covariation in hydrothermal calcite during degassing of co 2 the effect of the outgassing of co2 from a hydrothermal fluid on the c and o isotopic compositions of calcite which is precipitated from this fluid is quantitatively modelled in terms of batch and rayleigh distillation equations both co2 degassing and calcite precipitation are considered to be the removal mechanisms for dissolved carbon species from the fluid combined degassing precipitation models are then developed by taking h2co3 and hco 3 respectively as the dominant dissolved carbon species a positive correlation array between 13c and 13o values of calcite can be yielded by the precipitation of calcite from a h2co 3 dominant fluid accompanied by a progressive decrease in temperature during co2 degassing whereas calcite precipitated from a hco 3 dominant fluid under the same conditions tends to display much smaller variation in 13c values than in 18o values the combined processes of co2 degassing and calcite precipitation result in lowering the 13c value of calcites with respect to those precipitated in a closed system simply due to temperature effect carbon and oxygen isotopic data for calcite from the kushikino gold mining area in japan illustrate the application of quantitative modelling and degassing of co2 is suggested as a more likely cause for the precipitation of the calcite and quartz in this mining area

a detrital record of lower oceanic crust exhumation within a miocene slow spreading ridge macquarie island southern ocean uplift exhumation and denudation of the lower oceanic crust are recorded by sedimentary rocks of macquarie island 54 30 s 158 54 e which were deposited within the slow spreading proto macquarie spreading ridge between ca 9 and 12 ma measured stratigraphic sections typically contain basal basaltic breccia lithofacies that are overlain by a thick sequence of enriched mid ocean ridge basalt e morb with thin intercalations of gabbroic sedimentary lithofacies basaltic detritus has zeolite to lower greenschist metamorphic grades typical of the upper oceanic crust and gabbroic detritus has upper greenschist to amphibolite metamorphic grades typical of the lower oceanic crust breccia clast counts and sedimentary structures indicate that basaltic lithofacies were locally derived from the footwalls of adjacent spreading related faults sedimentary structures detrital clinopyroxene major and trace element geochemistry and 206 pb 238 u zircon geochronology indicate that the gabbroic lithofacies were more distally derived from a paleogene aged tholeiitic morb source detrital zircon populations of ca 27 and ca 33 ma correspond to oceanic magnetic anomalies 8o and 13o respectively and exclude ca 8 5 ma gabbroic rocks of macquarie island as a potential source geodynamic reconstructions show that anomaly 8o crust from the southeast indian ridge was juxtaposed against the active proto macquarie spreading ridge when sedimentary rocks of macquarie island were deposited and was a likely source for the gabbroic lithofacies the proto macquarie spreading ridge and southeast indian ridge were connected by the jurru long offset transform which has undergone significant transpression since 27 ma this transpression formed a bathymetric transverse ridge that was composed of structurally isolated blocks of heterogeneously aged paleogene source crust which provided the source for macquarie island9s gabbroic sedimentary lithofacies

evolution of macquarie ridge complex seamounts implications for volcanic and tectonic processes at the australia pacific plate boundary south of new zealand abstract the macquarie ridge complex mrc coincides with the australia pacific plate boundary south of new zealand and is characterised by a rugged bathymetry that comprises numerous seamounts along its length tectonic plate reconstructions show that the australia pacific plate boundary evolved from a spreading centre to a transpressional boundary from ca 40 to 6 ma however limited sampling and high resolution mapping of the region have meant that the composition and morphology of the mrc remain relatively unknown here we present results from multibeam mapping photographic investigation and petrologic and geochemical analyses from 10 seamounts along the mrc dredge samples collected from the seamounts are alkaline to sub alkaline basalts containing 45 1 50 8 wt sio2 3 5 12 0 wt mgo and 1 9 4 9 wt total alkalis all samples are enriched mid ocean ridge basalts that have k ti 0 15 which originated as low degree partial melts during the late stages of mid ocean ridge volcanism this oceanic crust has been sheared and accreted along the plate boundary since ca 6 ma by cumulative transpressional relative plate motion such that lavas from distinct magma chambers have been juxtaposed at individual seamounts along the ridge mrc seamounts have formed as discrete elevations as a result of dip slip and strike slip faulting of the ridge axis three guyot type seamounts have flat top summit plateaux that were presumably formed by wave erosion via relative sea level lowering due to uplift of the ridge these seamounts have since subsided due to extension associated with the step over fault geometry of the transform plate boundary along the mcdougall and macquarie ridge segments while the seamounts are of volcanic origin they are manifestations of tectonic and geomorphic processes seamounts distal from the ridge axis however are not subjected to plate boundary deformation and instead have morphologies formed through volcanic processes

from ocean depths to mountain tops uplift of the troodos ophiolite cyprus constrained by low temperature thermochronology and geomorphic analysis the timing and mode of uplift of the troodos ophiolite are constrained by low temperature thermochronology combined with geomorphic analysis zircon u th he and apatite fission track cooling ages in the troodos plutonic sequence are all cretaceous 83 106 ma and within error of published zircon u pb crystallization ages this indicates early cooling of the oceanic crust and termination of spreading axis magmatism at 90 ma apatite u th he ages decrease with reconstructed crustal depths from 40 ma near the top of the sheeted dike complex to 4 ma within the mantle sequence a prominent inflection point in the age versus depth curve defines the bottom of the exhumed helium partial retention zone and records the onset of rapid exhumation of the main troodos massif at 6 2 ma inverse thermal modeling supports this conclusion indicating that the timing of uplift is earlier than previously estimated the boundaries of the mantle sequence exposed in the core of the troodos structure closely overlap the boundaries of a concentric zone delineated by high local relief and higher channel steepness indices indicating differential exhumation and uplift of this area relative to its surroundings this zone also overlaps with a prominent negative bouguer gravity anomaly the timing and pattern of the troodos ophiolite uplift suggest that it is driven by serpentinite diapirism possibly triggered by miocene reactivation of subduction along the cyprean arc the worldwide ubiquity of suprasubduction zone ophiolites may thus reflect the importance of extensive serpentinization at the overthrusting mantle wedge in obduction processes

influence of cumulative convergence on lithospheric thrust fault development and topography along the australian pacific plate boundary south of new zealand the development of faulting and topography resulting from initial convergence within oceanic lithosphere is largely unknown we explore relationships among convergence structural development and topography along 1500 km of the submarine australian pacific plate boundary south of new zealand the macquarie ridge complex mrc due to the variable orientation of the boundary and close proximity of the australian pacific poles of rotation individual segments of the plate boundary have experienced different convergence histories since 10 95 ma chron 5o because interaction along the oceanic extent of the boundary involves oceanic lithosphere of broadly the same age and therefore thermal structure structural and morphologic differences can be attributed primarily to variations in angles and rates of convergence with respect to the plate boundary orientation since 10 95 ma we relate plate boundary normal convergence determined from stage pole rotations to structural development focusing on transitions from purely strike slip faulting to partitioned thrust and strike slip faulting between 47 s and 60 s since 10 95 ma our results indicate that boundary normal convergence of 100 km marks the transition from strike slip dominated faulting to partitioned underthrusting and strike slip faulting incipient subduction establishment of subduction at the puysegur trench and incipient subduction at the hjort trench corresponds to convergence at rates between 2 and 4 cm yr angles 30 and with durations of at least 10 m y resulting in 100 km of boundary normal convergence anomalous topographic volumes resulting from tectonic deformation are quantified from swath bathymetry and compared to convergence history results from analysis of the central mrc suggest that prior to lithospheric scale thrust faulting 100 km of boundary normal convergence can be accommodated by crustal deformation 6 km relief from ridge crest to adjacent trough and strike slip faulting our research supports induced forced intraoceanic initiation of subduction

mapping of a segment of the romanche fracture zone a morphostructural analysis of a major transform fault of the equatorial atlantic ocean one square nautical degree within the active part of the romanche fracture zone was surveyed at about long 17 w during the 1988 equamarge ii cruise of the r v jean charcot to the equatorial atlantic seabeam mapping and seismic reflection profiles of the trench and adjacent northern and southern transverse ridges emphasize the contrast between the apparent simplicity of the major morphostructural lineaments and the complexity of the second order features the vertical displacement associated with the main strike slip movement of major oceanic transform faults is clearly illustrated by positive topographic anomalies of the transverse ridges the bathymetric map and samples collected confirm that the flat topped northern transverse ridge actually emerged at a time when peridesertic climate shaped basaltic basement into ventifact pebbles coated with desert varnish

evolution of nappes in the eastern margin of the bohemian massif a kinematic interpretation the entire pile of nappes in the eastern margin of the bohemian massif is characterized by two stages of variscan nappe emplacement each exhibiting a different kinematic and metamorphic evolution

intraplate thrusting near the easter microplate gloria long range sidescan sonar images from a region of the nazca plate immediately to the north of the easter microplate have revealed a prominent series of anomalous ridges these extend from lat 22 s long 114 w near the east pacific rise to 23 s 112 w near pito deep at the northeast corner of the microplate they are 20 to 50 km long and trend east west subparallel to the pacific nazca spreading direction swath bathymetric data indicate that the ridges dip steeply to the south and gently to the north and in places reliefs exceed 1 km earthquake focal mechanisms and predicted plate motions point to thrust faulting as the most likely mechanism for producing these ridges and their morphology suggests that the crust to the north has over ridden that to the south the nazca easter euler pole predicts a maximum present day convergence of about 50 km m y at the western end of the easter microplate9s northern boundary and we estimate that about one third of this has been taken up by the intraplate thrusts during the past 2 5 m y

seafloor slopes at mid ocean ridges from submersible observations and implications for interpreting geology from seafloor topography abstract observations from 145 submersible dives are used to create a database of mid ocean ridge scarp topography and lithology seafloor lithologies are classified into extrusives basaltic talus dykes gabbros and serpentinites and the dive locations are broadly classified according to whether they are close to transform valleys and as a function of ridge spreading rate the database is used to determine whether there is any difference in the maximum slope for each rock type which might relate to differences in rock jointing cohesion or friction properties there is a common perception that lower crustal rocks form steeper slopes than shallower crustal rocks but until now there has been little evidence to support or refute this idea from our analysis we find a tendency for gabbro and dykes to form steeper slopes than serpentinite the 90th percentile of each lithology slope distribution used as a measure of limiting slope is 43 39 and 32 for gabbro dykes and serpentinite respectively lithologic control on slope is weak however compared to overall slope variability in these mid ocean ridge settings so seafloor relief is likely to be a poor guide to underlying geology we speculate on the structure of eroding fault scarps outline the implications for attempts to infer active faults from talus ramp activity and discuss more generally factors affecting the geomorphology of mid ocean ridge slopes

determination of source ages and migration patterns of brines from the u s gulf coast basin using 129i abstract the long lived cosmogenic and fissiogenic isotope 129i has been applied to the study of source ages and migration patterns of oil field brines from the u s gulf coast basin 129 i i ratios were measured in sixty samples of saline formation water from depths of 660 4503 m in several oil fields in southeast texas south central louisiana and offshore louisiana comparisons between measured ratios and the decay curve for surface hydrospheric 129i result in minimum source ages much older than present host formation ages indicating vertical migration of brine from older deeper sources conservative corrections for a fissiogenic component due to spontaneous fission of 238u in the subsurface result in the following median source ages iberia field 55 ma port barre field 53 ma and eugene island blocks 316 and 330 55 ma pointing to wilcox group shales as source formations mesozoic sources cannot be ruled out due to the uncertainties in estimating the fissiogenic component some of the ratios measured in texas gulf coast brines show evidence of a greater fissiogenic component which indicates that the brines have resided in formations with locally high u concentrations

limist on the metal content of fluid inclusions in gangue minerals from the viburnum trend southeast missouri determined by laser ablation icp ms the hydrothermal fluids that deposited the ores of the viburnum trend of the southeast missouri district have long been recognized to be sedimentary basinal brines the major element composition of these brines has been well characterized however there have been no attempts to measure their metal content which is only loosely constrained by theoretical solubility relations the present study is an effort to assess the metal content of these mineralizing brines by analyzing fluid inclusions from gangue minerals in the viburnum trend using laser ablation inductively coupled plasma mass spectrometry la icp ms and microthermometry by focusing on gangue minerals instead of metal sulfide minerals interferences from the mineral matrix are avoided a high priority was to determine whether brines of anomalously high metal content were circulating through southeast missouri during the time of mississippi valley type mineralization fluid inclusions in dolomite quartz and calcite gangue from throughout the viburnum trend and representative of the entire paragenesis were analyzed none of the inclusions contained measurable quantities of pb zn or cu and only a few contained measurable quantities of ba which ranged from about 100 to 500 ppm where detection limits were not exceeded they indicated maximum possible concentrations of the element in the fluid inclusion maximum possible concentrations varied from inclusion to inclusion and were controlled by the mass of analyte within the fluid volume the larger or more saline the inclusion the lower the detection limit these results showed that the fluid that deposited quartz calcite and most of the dolomite gangue in the viburnum trend is unlikely to have had order of magnitude concentrations of pb and zn higher than 102 ppm or order of magnitude concentrations of cu higher than 101 ppm concentrations of pb and zn during deposition of stage 3 dolomite could not have been higher than 103 ppm and concentrations of cu could not have been higher than 102 ppm these upper limits on possible metal concentrations with the principal exception of those in stage 3 dolomite fluid inclusions are of magnitude similar to the highest measured concentrations of pb zn cu and ba found in typical sedimentary brines thus the brines responsible for depositing gangue minerals in the viburnum trend are unlikely to have had higher ore metal concentrations than typical basinal brines the lack of temporal overlap between gangue and metal sulfide deposition and the higher k na and lower ca mg ratios in fluid inclusions in the gangue minerals compared with fluid inclusions in the metal sulfides leaves open the possibility that the metal content of the fluid that deposited the sulfides was different from that responsible for depositing gangue however the data show that fluid entering the southeast missouri district was not pervasively metal rich throughout time and that if metal enriched fluid ever entered the district it did so at discrete intervals

origin of brines in the upper silesian coal basin poland inferred from stable isotope and chemical data brines in the miocene formations of the upper silesian coal basin have isotopic composition close to smow which identifies them as the connate marine water however controversies exist on the origin of brines in the carboniferous formations isotopic and hydrochemical data exclude any relationship to marine water and enrichment by evaporation the most common brine which occurs at great depths can be identified as the oldest infiltration in a very hot climate 18o 2 d 20 cl content 34 to 140 g l this brine is free of so42 and u and rich in ba2 and226ra its salinity is probably related to the leaching of evaporites and intensive weathering of rocks during the rotliegendes other brines are difficult to identify because their isotopic contents are within the range of mixing between the oldest brine and the quaternary waters 18o 10 d 70 isotopic and hydrochemical data allow identification of several occurrences of brine formed by meteoric water of a warm tertiary climate after the last marine transgression in the tortonian that brine is rich in so42 and contains moderate contents of226ra and u its salinity is thought to result from leaching of miocene evaporites two other identified types of brines can be related to some infiltration periods before the last marine transgression the sources in salinity of these 2 types remain unknown mining activity results in a common occurrence of mixed brines when the quaternary component dominates its identification is easy from the isotopic composition whereas the end brine component can ususally be identified by chosen ion ratios and the presence or lack of sulphates

origin and evolution of high salinity zn pb mineralising fluids in the variscides of belgium high salinity na ca cl rich fluids 20 wt salts in inclusions in gangue and ore minerals from mesozoic mississippi valley type mvt deposits in the verviers synclinorium eastern belgium and in cretaceous vein calcites at the variscan front were investigated by microthermometric and crush leach analysis the mvt deposits formed at temperatures of 110 c while the cretaceous vein calcites were precipitated at temperatures 50 c their cl br content cl br ratio between 246 and 458 suggests that the fluids probably originated by the evaporation of seawater during basin development at the southern margin of the caledonian brabant massif in the late palaeozoic the na ca k content na 29 700 49 600 ppm ca 25 700 46 200 ppm k 1 000 5 620 ppm is similar to that of the mineralising fluids in other pb zn districts interpreted to be of evaporative origin e g newfoundland east tennessee polaris furthermore comparison of the na ca k content of the fluids with that of an evolved evaporitic brine enables the recognition of major water rock interactions that modified the fluid composition it indicates that the ambient fluids participated in the early diagenetic dolomitisation of upper palaeozoic carbonates and also in the albitisation of plagioclase in lower palaeozoic siliciclastics of the caledonian basement illitisation of smectites or dissolution of k feldspar probably controlled the k content of the fluids a model is proposed where the bittern brines migrated down into the deep subsurface because of their density during extension after the variscan orogeny these fluids were finally expelled along extensional faults resulting in the formation of zn pb deposits

neotectonics of the macquarie ridge complex australia pacific plate boundary new marine geophysical data along the macquarie ridge complex the australia pacific plate boundary south of new zealand illuminate regional neotectonics we identify tectonic spreading fabric and fracture zones and precisely locate the australia pacific plate boundary along the macquarie ridge complex we interpret a 5 10 km wide macquarie fault zone between the two plates along a bathymetrie high that extends nearly the entire length of the australia pacific plate boundary south of new zealand we conclude that this is the active australia pacific strike slip plate boundary arcuate fracture zones become asymptotic as they approach the plate boundary a broad zone of less intense deformation associated with the plate boundary extends 50 km on either side of the macquarie fault zone marine geophysical data suggest that distinct segments of the plate boundary have experienced convergence and strike slip deformation although teleseismic evidence overwhelmingly indicates strike slip motion along the entire surveyed boundary today the mcdougall and southernmost puysegur segments show no evidence for past underthrusting whereas data from the macquarie and hjort segments strongly suggest past convergence the present day strike slip plate boundary along the macquarie ridge complex coincides with the relict spreading center responsible for australia pacific crust in the region our conceptual model for the transition from seafloor spreading to strike slip motion along the macquarie ridge complex addresses the decreasing length of spreading center segments and spacing between fracture zones as well as the arcuate bend of the fracture zones that become asymptotic to the current transform plate boundary

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

iodine 129 constraints on residence times of deep marine brines in the canadian shield canadian shield brines are characterized by high concentrations of both stable iodine and 1 2 9 i the former reflecting its concentrated but diagenetically modified seawater origin and the latter its long subsurface residence time within its host shield rocks stable iodine concentrations in the yellowknife brine are as high as 18 mg l requiring the contribution of iodine from an external marine reservoir this reservoir likely comprised organic rich marine sediments in the basin where the brine was produced diagenesis of these sediments released iodine to the brine during its infiltration into the subsurface 1 2 9 i concentrations in the yellowknife brine are as high as 3 4 x 10 8 atom l and are due to the fission of 2 3 8 u in the rock matrix and subsequent diffusion of the radiogenic 1 2 9 i into the fracture fluids this concentration is close to the predicted secular equilibrium concentration for a fluid in basaltic rock with a uranium concentration of 1 mg kg after the residence time of 80 m y required for secular equilibrium has been attained this time period is interpreted as the minimum residence time of the yellowknife brine in the shield but it may be much greater possibly dating back to middle devonian time when most of the present day shield was covered by seawater similarly high stable iodine and 1 2 9 i concentrations measured in the sudbury brine support a generic ancient marine hypothesis for the origin of shield brines stable iodine and 1 2 9 i concentrations in the shallower mine waters are the result of mixing between the brine and low iodine modern meteoric recharge that is enriched in 1 2 9 i due to global fallout from nuclear fuel waste reprocessing activities

geochemistry of highly saline fluids in siliciclastic sequences genetic implications for post variscan fluid flow in the moravosilesian palaeozoic of the czech republic ubiquitous post variscan dolomites occur in zn pb cu veins at the nizk jesenik mountains and the upper silesian basin lower and upper carboniferous siliciclastics at the eastern part of the bohemian massif crush leach stable isotope oxygen and carbon and microthermometry analysis of the fluid inclusions in dolomites enable understanding the geochemistry origin and possible migration pathways of the fluids homogenisation temperatures of fluid inclusions range between 66 and 148 c with generally higher temperatures in the nizk jesenik mountains area than in the upper silesian basin the highest homogenisation temperatures up to 148 c have been found near major regional faults and the lowest in a distant position or at higher stratigraphic levels highly saline 16 6 28 4 eq wt nacl h2o nacl cacl2 mgcl2 fluids occur in inclusions na cl br systematics of trapped fluids and a calculated oxygen isotopic fluid composition between 0 9 and 3 0 v smow indicate that the fluid was derived from evaporated seawater stable isotopic modelling has been used to explain stable isotopic trends isotopic values 13c 6 0 2 0 v pdb 18o 15 5 22 5 v smow of dolomites resulted from fractionation and crystallisation within an open system at temperatures between 80 and 160 c rock buffering explains the isotopic composition at low w r ratios organic matter maturation caused the presence of isotopically light carbon in the fluids and fluid rock interactions largely controlled the fluid chemistry k li br and na contents k cl i cl and li cl molar ratios the fluid chemistry reflects well the interaction between the fluid and underlying limestones as well as with clay and organic rich siliciclastics no regional trends in temperature or fluid geochemistry favour a fluid migration model characterised by an important vertical upward migration along major faults a permeable basement and fractured sedimentary sequence enhanced the general nature of the fluid system fluid characteristics are comparable with the main post variscan fluid flow systems in the polish cracow silesian ore district and german sedimentary basins

noble gas and halogen evidence for the origin of scandinavian sandstone hosted pb zn deposits abstract fluid origins in the sandstone hosted pb zn class of ore deposit have been investigated in three deposits from scandinavia laisvall vassbo and osen the deposits studied are hosted by autochthonous cambrian sandstones that preserve a near original structural relationship to the underlying precambrian basement enabling the role of basement interaction to be assessed mineral samples have been collected from across the paragenetic sequence sphalerite galena pyrite fluorite and barite of impregnation and related joint hosted mineralization fluid inclusion halogen cl br and i and noble gas isotope 40 ar 36 ar 84 kr compositions were determined simultaneously by noble gas mass spectrometry of irradiated sample splits complementary he isotope analyses are obtained from nonirradiated splits of the same samples 3 he 4 he values at laisvall and osen are highly radiogenic 0 02 ra and the 4 he 40 ar ratio extends to values greater than the crustal production value of 5 characteristic of low temperature crustal fluids at vassbo a slightly elevated 3 he 4 he ratio of 0 1 0 3 ra is compatible with a very minor mantle component 1 4 suggesting a distal source for the basinal brine dominated fluid br cl molar ratios 3 2 8 2 10 3 are greater than the present seawater value of 1 54 10 3 and correspond with i cl molar ratios in the range 64 1600 10 6 the upper limits of both the i cl and br cl values are amongst the highest measured in crustal fluids together the data indicate acquisition of salinity by the evaporation of seawater beyond the point of halite saturation and subsequent fluid interaction with i rich organic matter in the subsurface the data are compatible with the independent transport of sulfate and sulfide and indicate that fluids responsible for joint hosted mineralization were distinct to those responsible for impregnation mineralization all three deposits preserve fluids with 40 ar 36 ar in the range of 6 000 10 000 and fluid inclusion 40 ar concentrations of 0 02 0 05 cm 3 cm 3 fluid inclusion 4 he concentrations are also extremely elevated with maximum values of 0 1 cm 3 cm 3 in laisvall fluorite and sphalerite the high 40 ar 36 ar values together with the high 4 he and 40 ar concentrations result from a very long premineralization crustal residence time on the order of 100 200 ma together the noble gas and halogen data are compatible with a caledonian mineralization event 425 ma caused by mixing of two or more long lived hydrothermal basinal brines and pore fluids at the sites of mineralization the data suggest negligible recharge of the basinal brines by meteoric water and indicate extensive fluid basement interaction before mineralization the similar noble gas composition of each deposit suggests that similar processes operated at all three deposits and favors a single pass fluid flow model for mineralization

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

hydrothermal fluid origins in mississippi valley type ore districts combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the illinois kentucky fluorspar district viburnum trend and tri state districts midcontinent united states samples were selected from three of the classic mississippi valley type districts in the midcontinent area of north america the illinois kentucky fluorspar district belongs to the fluoritic subtype of mississippi valleytype districts and the ozark districts of the viburnum trend and tri state are representative of the pb rich and more typical zn rich subtypes of mississippi valley type mineralization respectively noble gas ar kr and halogen cl br i data have been obtained simultaneously by noble gas mass spectrometry of inclusion fluids released by in vacuo crushing of irradiated fluorite quartz carbonate and sphalerite samples additionally he analyses have been obtained from nonirradiated fluorite from the illinois kentucky fluorspar district fluorite from the illinois kentucky fluorspar district has a maximum 3 he 4 he ratio of 0 35 ra where ra atmospheric 3 he 4 he ratio of 1 4 10 6 higher than values typical of crustal fluids and confirming the presence of a minor mantle component equal to less than 6 percent of the total he in the fluids of the illinois kentucky fluorspar district the br cl mol ratios of all the deposits are with one exception higher than the value of seawater 1 54 10 3 ranging from 1 69 to 3 70 10 3 and indicating acquisition of salinity by the evaporation of seawater beyond the point of halite saturation late quartz from the tri state district contains a very minor component of halite dissolution water and has a br cl mol ratio of 1 46 10 3 the i cl mol ratios are typical of oil field brines and are ubiquitously higher than what is attainable by the evaporation of seawater alone i cl mol ratios are in the range of 6 to 270 10 6 indicating that the fluids have interacted with i rich organic matter present in sedimentary rocks in the ozark districts 40 ar 36 ar ratios vary between 320 and 345 in the tri state and between 350 and 420 in the viburnum trend in the illinois kentucky fluorspar district 40 ar 36 ar ratios reach values of 1 200 the corresponding concentrations of 40 arexcess 40 ar not attributable to radiogenic decay of 40 k or an atmospheric source are similarly elevated in the main stage fluorite mineralization of the illinois kentucky fluorspar district 6 8 18 2 10 4 cm 3 cm 3 h2o relative to the viburnum trend and tri state districts mostly 1 3 3 3 10 4 cm 3 cm 3 h2o and 0 3 1 4 10 4 cm 3 cm 3 h2o respectively together the noble gas and halogen data indicate the existence of three brine provinces 1 a regional tristate brine present throughout the ozark region 2 a viburnum trend brine and 3 an illinois kentucky brine furthermore in the viburnum trend the halogen composition of main stage dolomite is distinct from that of the main stage sphalerite but identical to the regional hydrothermal dolomite seen in the tri state district the data imply that mixing relationships in the viburnum trend are highly complex but are compatible with regional models in which the tri state brine present throughout the ozark region was sourced in the arkoma basin

macquarie island s finch langdon fault a ridge transform inside corner structure macquarie island consists of uplifted oceanic crust uniquely situated in the ocean basin where it formed thus allowing onshore structures to be placed into their regional oceanic tectonic context the finch langdon fault the most significant spreading related structure on the island juxtaposes upper crust rocks against lower crust and upper mantle rocks it consists of dominantly oblique strike slip northwest west northwest and north northeast striking fault segments that bear hydrothermal mineralization indicative of faulting during seafloor spreading talus breccias and graywackes overlain by volcanic flows proximal to the fault indicate a long lived submarine fault scarp that exposed diabase dikes and gabbros during volcanism swath reflectivity and bathymetry reveal ridge parallel spreading fabric and perpendicular fracture zones the closest 7 km east of the island on the basis of field and swath data we propose that this fault zone formed near the inside corner of a ridge transform intersection and that structures on the island are conformable with those in the surrounding seafloor

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

a sea beam investigation of the clipperton transform fault the morphotectonic expression of a fast slipping transform boundary a regional scale bathymetric map of the fast slipping 11 0 cm yr clipperton transform boundary and adjoining east pacific rise segments has been constructed using the high resolution capabilities of sea beam the transform domain is 85 km long varies in width from 10 to 20 km and is defined by an assemblage of transform parallel ridges and troughs the largest of which is a 40 km long median ridge that stands up to 700 m above the surrounding seafloor these major topographic elements of the transform domain are bisected by a very narrow 1 km swath of strongly lineated terrain composed of elongate depressions narrow lozenge shaped ridges and gullies that integrate spatially to create a narrow zone of disturbed topography this zone trends 082 and cuts like a knife across the grain of the clipperton transform domain linking one truncated ridge tip with the other we interpret this swath of disturbed terrain to be the product of strike slip tectonism thereby fixing the location of the present day plate boundary the present day structural geometry of the clipperton transform appears relatively simple and characterized by a narrow strike slip plate boundary linking two offset ridge axes

anatomy of the dead sea transform does it reflect continuous changes in plate motion a new gravity map of the southern half of the dead sea transform offers the first regional view of the anatomy of this plate boundary interpreted together with auxiliary seismic and well data the map reveals a string of subsurface basins of widely varying size shape and depth along the plate boundary and relatively short 25 55 km and discontinuous fault segments we argue that this structure is a result of continuous small changes in relative plate motion however several segments must have ruptured simultaneously to produce the inferred maximum magnitude of historical earthquakes

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

an examination of some enso mechanisms using interannual sea level at the eastern and western equatorial boundaries and the zonally averaged equatorial wind abstract theory suggests that the interannual equatorial kelvin wave sea level w in the western pacific should be directly proportional to the interannual western australian sea level and the interannual equatorial kelvin wave sea level e in the eastern pacific should be directly proportional to the equatorial interannual sea level at the south american coast forced equatorial kelvin wave dynamics implies approximately that e t t w t b t t where t b and are respectively a lag corresponding to equatorial kelvin wave propagation zonally averaged equatorial interannual eastward wind stress a forcing coefficient and a number between 0 and 1 a regression analysis of the sea level difference above using western australian and south american sea levels against shows that the correlation is high and is highest 0 83 when deltat 3 months and deltat 1 month the values for deltat and b are reasonable for they are appropriate for a signal dominated by the first

melting behavior of fluid inclusions in laboratory grown halite crystals in the systems naclh2o naclkclh2o naclmgcl2h2o and naclcacl2h2o abstract the chemical composition of aqueous fluid inclusions in crystals of halite can be accurately determined from observed melting behaviors of ice hydrohalite and sylvite some fluid inclusion melting behaviors observed in laboratory grown halite crystals systems nacl h 2 o nacl kcl h 2 o nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o differ from predicted stable equilibrium relations in the nacl h 2 o and nacl kcl h 2 o systems observed first melt temperatures are up to 15 c below the equilibrium eutectic temperatures of 21 2 and 22 9 c respectively the final melting temperature of ice in the presence of hydrohalite and the final melting temperature of hydrohalite are reproducible and match predicted melting temperatures the limit of detection of sylvite daughter crystals in the nacl kcl h 2 o system is approximately 5 wt 1 molal kcl final melting temperatures of sylvite match published equilibrium data to within 0 3 c in the nacl kcl h 2 o system at halite saturation m kcl can be determined from the final sylvite dissolution temperature or from the final melting temperature of hydrohalite fluid inclusions in the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems that form stable salt hydrates mgcl 2 12h 2 o and cacl 2 6h 2 o during freezing first melt within 3 c of predicted eutectic temperatures 37 and 52 c however fluid inclusions with mgcl 2 or cacl 2 may also start melting at temperatures as low as 80 c such low first melt temperatures indicate the presence of metastable salt hydrates presumably mgcl 2 8h 2 o mgcl 2 6h 2 o or cacl 2 4h 2 o the formation of metastable phases during freezing of fluid inclusions can lead to misinterpretation of the chemical composition of fluid inclusions in natural samples this is especially true for fluid inclusions with first melt temperatures below 37 c which may be erroneously interpreted as being rich in cacl 2 the final melting of ice in the presence of hydrohalite may vary by more than 15 c in fluid inclusions of different size but identical bulk composition and occurs at lower temperatures than predicted in fluid inclusions from the nacl mgcl 2 h 2 o and nacl cacl 2 h 2 o systems however the final melting temperature of ice in inclusions which fail to nucleate hydrohalite and the final melting temperature of hydrohalite are reproducible to within 0 1 c and can be used to determine mgcl 2 and cacl 2 molalities

ridge reorientation mechanisms macquarie ridge complex australia pacific plate boundary the macquarie ridge complex portion of the australia pacific plate boundary south of new zealand provides a unique complete record of a 60 90 change in spreading direction since 40 ma that resulted in the transition from a spreading center to a transform plate boundary marine geophysical data show that during reorientation most ridge segments completely disappeared and all shortened additionally modification of newly created crust caused differences in widths of correlative spreading segment corridors on the two plates we propose two models for ridge reorientation that explain the observed spreading fabric and arcuate fracture zone relationships nonrigid plate deformation was accommodated by failing and propagating spreading ridge segments rifts and transfer of crust between plates during the gradual reorientation of the spreading axes

massive hydrothermal dolomites in the southwestern cantabrian zone spain and their relation to the late variscan evolution abstract large scale massive burial dolomitization affected upper carboniferous carbonates of the southwestern variscan cantabrian zone spain replacive and void filling dolomites formed and were post dated by calcite cementation the process of dolomitization was due to the circulation of hypersaline and hydrothermal marine derived brines controlled by rock anisotropies the dolomites probably formed in early permian time during post thrusting orocline formation in an extensional setting lithospheric delamination induced increased heat flow and allowed thermal convection of the fluids the dolomites from the cantabrian zone are excellently exposed and represent an interesting outcrop analogue for hydrocarbon reservoirs elsewhere in comparable geotectonic settings of the european variscan orogen large masses of similar dolomites could have formed if mg rich brines were available

the morphology of strike slip faults examples from the san andreas fault california fault zones are seldom straight nor are fractures within them continuous permanent strain fields are imprinted near a fault of complex geometry as a result of continued slip these strain fields may be manifest as vertical deformation near the fault strain fields that increase area result in subsidence and strain fields that reduce area result in uplift although these effects are modified by erosion and deposition the general features of fault zone morphology are a consequence of the geometry and slip distribution along strike graphical views of strain fields associated with simple vertical strike slip faults are derived using boundary element methods if the fault is straight and parallel to the applied shear strain the hills and valleys resulting from finite fault rupture are separated by the fault trace this is rarely observed in nature instead strike slip faults cut through hills and valleys apparently of their own making we show this to be a consequence of segments of the fault being nonparallel to each other and to the overall applied shear strain coseismic strains are large but transient since they are substantially annulled by rupture on contiguous fault segments we test our theory with examples from parts of the san andreas fault system in california the morphologies of the parkfield region and the southern san andreas fault in the coachella valley are shown to be consistent with plausible distributions of slip on mapped surface faults the location of the salton sea appears to be a consequence of a reduction of slip on the san andreas fault toward the brawley seismic zone

fluid transfers at the basement cover interface part i subsurface recycling of trace carbonate from granitoid basement rocks france basement rocks usually contain trace amounts of disseminated carbonate minerals and sometimes also fractures veins filled with carbonates which may have a variety of origins extensive drilling has been performed of a granitoid body vienne western part of the french massif central overlain by a carbonate sedimentary sequence a situation which is representative of most of the variscan basement in western europe these unique samples provide the opportunity to investigate the behaviour of basement trace carbonate across the basin basement interface and the mass transfers throughout a series of fluid migration ranging from high ca 450 c to low down to 50 c temperature conditions study of quartz and carbonate found in fracture infillings reveals three major stages of fluid circulation namely 1 high to medium temperature late hercynian fluids which circulated in fractures developed during basement uplift 2 medium temperature mesozoic basinal brines migration laterally along the basement cover contact 3 late infiltration of diagenetic marine waters in the upper part of the granitoid body a majority of analyzed vein carbonates from the three stages displayed a rather restricted range of c isotopic compositions 13c between 14 and 9 pdb whatever the stage in which they were deposited and despite large variations of o isotopic ratios 18o in the range 3 to 30 smow carbon in pervasively altered rocks displays the same features and is distributed among the two broad groups defined using o isotopic ratios in veins and fluid inclusions data namely the hercynian and the mesozoic carbonates isotopic data argue that carbon was introduced as carbonates in the early stages of the retrograde hercynian metamorphism and was systematically reworked by subsequent fluids without any significant carbon introduction from external sources the only exception corresponds to the stage iii calcite veins which are located in the upper sections of the cores at depths lower than 350 m beneath the basement cover boundary and are the only witnesses of element transfer from the sediments towards the basement the present data show that trapping of carbon by ca rich plutonic rocks during their cooling history confers on these rocks an efficient self sealing capacity during later fracturing and fluid flow because carbonates possess high solubility and rapid dissolution precipitation kinetics fluid circulation occurred not only in the macroscopic system of fractures but also within some volumes of the granitic matrix in order to scavenge and redistribute the early granitic trace carbonate in the event of poly cyclic carbonate redistribution the use of carbon isotopic composition to unravel the fluid origins must be exercised with caution as early c could be easily redistributed during later fluid migration episodes

constraints on macquarie ridge tectonics provided by harvard focal mechanisms and teleseismic earthquake locations in this study we evaluate teleseismically determined focal mechanisms and epicenters for earthquakes along the macquarie ridge complex mrc from 45os to 61 os and 155oe to 168oe a region characterized by some previous investigators as undergoing subduction initiation from 65 centroid moment tensors reported by harvard we develop statistical guidelines for choosing 26 which represent better determined more reliable focal mechanisms for tectonic analysis although thrust mechanisms occur in the north near fiordland elsewhere along the mrc the better determined mechanisms virtually all indicate that present day motion along most of the mrc is strike slip this is consistent with sidescan sonar and multichannel reflection data collected between 50os and 57os on 1994 and 1996 cruises the active plate boundar3 zone appears to be quite narrow 5 km wide and no active compressional features can be observed on the seafloor if we determine a rotation pole for plate boundary motion using only slip vectors from better determined harvard mechanisms along the mrc the best fitting instantaneous pole is at 57 4os 179 4oe about 2 5 o north of the nuvel i australian pacific pole which averages motion over the last 3 0 my if the mrc pole was formerly farther south than at present this could explain the existence of relict features associated with crustal shortening such as bathymetric highs and troughs yet the absence of active features such as thrust faults etc suggests ongoing compression or subduction initiation we also carefully read arrival times for p phases for 53 earthquakes at 16 teleseismic stations selected to represent a range of azimuths surrounding the earthquakes we relocated these earthquakes using standard joint epicentral determination jed methods while most of the better quality relocations lie on or very close to the australia pacific boundar3 as determined on the 1994 cruise a few epicenters occur well away from the boundar3 apparently on cenozoic fracture zones thus on the macquarie ridge complex and other major strike slip boundaries e g in california it appears that the very largest earthquakes occur on the principal plate boundar3 fault but that other earthquakes some quite large may occur away from the boundary along zones of preexisting weakness