fluid inclusions and hydrothermal alteration on the dixie valley fault nevada footwall rocks of the 1954 rupture segment of the dixie valley fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages an early biotite feldspar assemblage is followed by later fe chlorite and epidote both chlorite and epidote are replaced by hydrothermal sericite and cross cut by calcite hematite and quartz calcite veins biotite is partially replaced by prehnite the latest hydrothermal minerals are stilbite laumontite kaolinite alunite smectite illite and pervasive replacement of rock units with fine grained quartz chalcedony and opal secondary fluid inclusions trapped in healed microfractures in igneous quartz include type i inclusions that contain a moderate salinity aqueous liquid and vapor type ii inclusions that contain a moderate salinity aqueous liquid and co2 type iii inclusions that show eutectic melting temperatures below the nacl h2o eutectic and contain substantial cacl2 and type iv inclusions containing halite and other daughter minerals microthermometric measurements on these inclusions yield variable compositions and homogenization temperatures salinities of type i inclusions vary from 0 1 to 12 9 wt nacl with the mode in the interval 0 to 1 salinities of type ii co2 bearing inclusions range from 0 62 to 6 81 wt nacl relative to h2o and salinities of type iii inclusions with low eutectic melting temperatures are 12 9 to 25 3 nacl equivalent wt salinities of halite bearing inclusions are 30 1 to 39 2 wt nacl homogenization temperatures span the range 120 to 400 c the processes of isochemical cooling with upward displacement of the footwall mixing of cool low salinity water with hotter components and mixing of cool evaporite brine with hotter components could be responsible for variable fluid inclusion compositions homogenization temperatures and densities the p t path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics the path includes a lithostatic fluid pressure at 305 c and 1570 bars along with cooling and escape of co2 from fluids the fluid p t path probably approaches hydrostatic pressure conditions at lower temperatures hydrothermal alteration product minerals fluid temperatures pressures and compositions in the footwall of the dixie valley fault constrain minimum fault age to 20 to 25 ma displacement to 6 km with about 3 km of pre 10 to 13 ma and 3 km of post 10 ma uplift fluid compositions and p t data suggest the following mechanism for rupture initiation and arrest ruptures may be initiated as a result of high fluid pressures then opening of dilatant fractures causes drastic decrease in fluid pressure separation of steam and co2 the drastic reduction in fluid bulk modulus that accompanies volatile phase separation permits propagation of the ruptures even though fluid pressure is reduced in areas where fluid pressure reduction is not accompanied by phase separation fractures are arrested by dilatant hardening

origin of siderite veins in the western carpathians abstract siderite barite veins of the rud any ore field have precipitated from nacl cacl 2 h 2 o co 2 solutions with cacl 2 weight fractions between 0 05 and 0 38 total salinities between 17 and 35 wt and up to 1 8 mol co 2 homogeneous and heterogeneous trapping modes have been distinguished according to volumetric phase ratios of the fluid inclusions which have been trapped at 175 205 c in veiny siderite at 200 230 c in siderite and quartz from drusy cavities and at 90 180 c in the siderite postdating quartz sulfidic assemblage a sequential re equilibration technique has been developed to locate precisely vapour saturated halite liquidus of individual brine inclusions which normally homogenise by halite dissolution slopes of the vapour unsaturated halite liquidi constrained by isochores of coexisting two phase aqueous inclusions have been approximately three to five times steeper in natural polycomponent brines than those in the experimental nacl h 2 o system fluid pressures between 1 and 2 kbar have been determined using this method in drusy quartz associating with siderite crystals oxygen isotope variations 16 8 19 9 v smow in siderite result from a temperature increase from 175 to 230 c whereas nearly constant 13 c values 3 9 to 4 6 v pdb indicate absence of co 2 devolatilisation carbon isotope composition of the parental fluid changed from 9 5 to 8 8 v pdb while the oxygen isotope ratios remained essentially fixed at 7 7 0 3 v smov during formation of siderite the calculated 18 o fluid value is attributed to formation water enriched in 18 o during isotopic exchange with crustal rocks at low fluid rock ratios the 13 c fluid values probably correspond to a mixture of co 2 from dissolved matrix carbonates and that liberated by thermal decarboxylation of organic acids acetates which normally occur in formation waters leachate chemistry data have corroborated high concentrations of cacl 2 and mgcl 2 in the ore forming brines high br concentrations are similar to halite fractionated basinal brines ca 2 and k concentrations in excess of those in normal basinal brines reflect extensive cation exchange with surrounding low to medium grade metamorphites coincidental with calcite and k feldspar dissolution dolomitisation and albitisation of plagioclases high pressures of the siderite forming fluids 1 2 kbar must be linked with a deep circulation 4 8 km of the basinal brines derived primarily from marine water but significantly modified by interaction with low to medium grade paleozoic rocks at low fluid to rock ratios an anti clockwise crystallisation pt path inferred from fluid inclusion and stable isotope data is inconsistent with the siderite precipitation during extensional tectonic regime coincidental with permian triassic rifting suggested in previous models more likely the progressively increasing fluid pressures and temperatures could be attributed to compression and crustal thickening triggered by jurassic subduction in the meliatic hallstatt oceanic suture the superimposed quartz ankerite sulfidic ores have likely crystallised from brines expelled during compression associated with a continental collision during early to middle cretaceous times

mechanisms of flexural flow folding of competent single layers as evidenced by folded fibrous dolomite veins abstract flexural flow is thought unlikely to occur in naturally deformed competent isotropic single layers in this study we discuss a particular case of folded bedding parallel fibrous dolomite veins in shale in which the internal strain pattern and microstructural deformation features provide new insights in the mechanisms enabling flexural flow folding strain in the pre folding veins is accommodated by two main mechanisms intracrystalline deformation by bending and intergranular deformation with bookshelf rotation of dolomite fibres the initially orthogonal dolomite fibres allowed a reconstruction of the strain distribution across the folded veins this analysis shows that the planar mechanical anisotropy created by the fibres causes the veins to approximate flexural flow during folding synkinematic veins overgrow the pre folding fibrous dolomite veins microstructures and dolomite growth morphologies reflect growth during progressive fold evolution with evidence for flexural slip at fold lock up homogeneous flattening as evidenced by disjunctive axial planar cleavage subsequently modified these folds from class 1b to 1c folds our study shows that the internal vein fabric has a first order influence on folding kinematics moreover the fibrous dolomite veins show high viscosity contrasts with the shale matrix essential in creating transient permeability for subsequent mineralising stages in the later synkinematic veins during progressive folding

scanning anisotropy parameters in horizontal transversely isotropic media the horizontal transversely isotropic model with arbitrary symmetry axis orientation is the simplest effective representative that explains the azimuthal behaviour of seismic data estimating the anisotropy parameters of this model is important in reservoir characterisation specifically in terms of fracture delineation we propose a travel time based approach to estimate the anellipticity parameter and the symmetry axis azimuth of a horizontal transversely isotropic medium given an inhomogeneous elliptic background model which might be obtained from velocity analysis and well velocities this is accomplished through a taylor s series expansion of the travel time solution of the eikonal equation as a function of parameter and azimuth angle the accuracy of the travel time expansion is enhanced by the use of shanks transform this results in an accurate approximation of the solution of the non linear eikonal equation and provides a mechanism to scan simultaneously for the best fitting effective parameters and without the need for repetitive modelling of travel times the analysis of the travel time sensitivity to parameters and reveals that travel times are more sensitive to than to the symmetry axis azimuth thus is better constrained from travel times than the azimuth moreover the two parameter scan in the homogeneous case shows that errors in the background model affect the estimation of and differently while a gradual increase in errors in the background model leads to increasing errors in inaccuracies in on the other hand depend on the background model errors we also propose a layer stripping method valid for a stack of arbitrary oriented symmetry axis horizontal transversely isotropic layers to convert the effective parameters to the interval layer values

synorogenic hydrothermal origin for giant hamersley iron oxide ore bodies geologic mapping basin analysis and calculated fluid compositions indicate that giant orebodies of microplaty hematite and possibly martite goethite in the hamersley province of western australia were formed by heated fluids driven by early paleoproterozoic orogenesis detrital grains of microplaty hematite in the mcgrath trough a foreland basin in front of the northward advancing ophthalmian fold belt constrain the age of the earliest microplaty hematite ore formation to 200 c and locally up to 400 c were involved regional circulation of hydrothermal fluids including heated surface water through reduced banded iron formations occurred during or soon after the ophthalmian orogeny we speculate that martite goethite orebodies previously considered mesozoic cenozoic could also be related to heated paleoproterozoic meteoric fluids migrating northward away from the ophthalmian fold belt

fault valve action and vein development during strike slip faulting an example from the ribeira shear zone southeastern brazil abstract fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of neoproterozoic cambrian age in the ribeira river valley area southeastern brazil geometric and microstructural constraints indicate that foliation parallel and extensional veins were formed during dextral strike slip faulting both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates and were crystallized in the presence of co2 ch4 and h2o co2 ch4 nacl immiscible fluids following unmixing from a homogeneous parental fluid contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels foliation parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values 319 397 c and 47 215 mpa which is compatible with predicted fluid pressure cycle curves derived from fault valve action growth of extensional veins occurred in shallower structural levels under pressure fluctuating from near hydrostatic to moderately subhydrostatic values 207 218 c and 18 74 mpa which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone fluid immiscibility and precipitation of quartz in foliation parallel veins resulted from fluid pressure drop immediately after earthquake rupture fluid immiscibility following a local pressure drop during extensional veining occurred in pre seismic stages in response to the development of fracture porosity in the dilatant zone late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity 0 2 to 44 wt equivalent nacl h2o nacl cacl2 fluid inclusions trapped in healed fractures mainly in foliation parallel veins which also exhibit subordinate h2o nacl cacl2 co2 ch4 and h2o co2 ch4 nacl fluid inclusions trapped under subsolvus conditions in single healed microcracks recurrent circulation of aqueous carbonic fluids and aqueous fluids of highly contrasting salinities during veining and post veining stages suggests that fluids of different reservoirs were pumped to the ruptured fault zone during faulting episodes a fluid evolution trending toward ch4 depletion for co2 ch4 bearing fluids and salinity depletion and dilution approximation of the system h2o nacl for aqueous saline fluids occurred concomitantly with decrease in temperature and pressure related to fluid entrapment in progressively shallower structural levels reflecting the shear zone exhumation history

fault valve behaviour in optimally oriented shear zones an example at the revenge gold mine kambalda western australia abstract quartz vein systems developed in and adjacent to shear zones host major gold deposits in the kambalda region of the norseman wiluna greenstone belt at the revenge mine two groups of mineralised reverse shear zones formed as conjugate near optimally oriented sets during ese subhorizontal shortening adjacent to a major transpressional shear system the shear zones developed at temperatures of about 400 c in a transitional brittle ductile regime deformation was associated with high fluid fluxes and involved fault valve behaviour at transiently near lithostatic fluid pressures during progressive evolution of the shear system early brittle and ductile deformation was overprinted by predominantly brittle deformation brittle shear failure was associated with fault dilation and the formation of fault fill veins particularly at fault bends and jogs a transition from predominantly brittle shear failure to combined shear along faults and extension failure adjacent to faults occurred late during shear zone evolution and is interpreted as a response to a progressive decrease in maximum shear stress and a decrease in effective stresses the formation of subhorizontal stylolites locally subvertical extension veins and minor normal faults in association with thrust faulting indicates episodic or transient reorientation of the near field maximum principal stress from a subhorizontal to a near vertical attitude during some fault valve cycles local stress re orientation is interpreted as resulting from near total shear stress release and overshoot during some rupture events previously described fault valve systems have formed predominantly in severely misoriented faults the shear systems at revenge mine indicate that fault valve action and associated fluctuations in shear stress and fluid pressure can influence the mechanical behaviour of optimally oriented faults

quartz veining in slates and variscan deformation insights from the luarca sector nw spain abstract a structural and geochemical analysis of quartz veins is made in order to determine their evolution and the physical chemical conditions that enabled their development in this sector of the variscan belt westasturian leonese zone three phases of deformation have been described however only the first and third phases are represented in the study sections the first phase d 1 resulted in tight or closed folds f 1 verging towards the foreland and associated slaty cleavage s 1 the third phase d 3 resulted in approximately upright asymmetric folds f 3 with associated crenulation cleavage s 3 the veins are hosted in slates and approximately follow the slaty cleavage s 1 the veins started their development at the beginning of the deformation phase d 3 as a result of s 1 near parallel shortening through a process of progressive deformation this compression gave rise to the folding of the cleavage and eventually of the veins the f 3 folds have associated crenulation cleavage parallel to the axial planes in some cases the location of the veins was controlled by irregularities in the bedding due to sedimentary structures the quartz of the veins underwent notable intracrystalline plastic deformation and the contact zone between the veins and the host rock was affected by pressure solution the microstructures produced by the latter mechanism indicate the greatest compressive stress forming a high angle with the vein walls at a time post dating vein generation quartz precipitated from an aqueous carbonic fluid at temperatures between 350 c and 375 c under fluid pressure fluctuations of up to 140 mpa at constant depth maximum values of fluid pressure of 220 mpa and minimum values of 75 mpa were recorded by fluid inclusion assemblages in quartz of the veins under study pressure fluctuation from lithostatic to infralithostatic at constant depth was caused by the opening and sealing of the dilatant fractures

reflection seismology over azimuthally anisotropic media recent surveys have shown that azimuthal anisotropy due most plausibly to aligned fractures has an important effect on seismic shear waves previous work had discussed these effects on vsp data the same effects are seen in surface recording of reflections at small to moderate angles of incidence the anisotropic effects one different polarization components of vertically traveling shear waves permit the recognition and estimation of very small degrees of azimuthal anisotropy of order 2 1 percent as in an interferometer anisotropic effects on traveltime yield estimates of anisotropy which are averages over large depth intervals often raw field data must be corrected for these effects before the reflectors may be imaged two variations of a rotational algorithm to determine the principal time series are derived anisotropic effects on moveout lead to abnormal moveout unless the survey line is parallel to the fractures anisotropic effects on reflection amplitude permit the recognition and estimation of anisotropy hence fracture intensity differences at the reflecting horizon i e with high vertical resolution

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

ore lead and sulphur isotope pattern from the low temperature veins of the catalonian coastal ranges ne spain the lead isotopic composition of galenas from low temperature veins of the catalonian coastal ranges ne spain displays a small but distinct range of values 18 318 206pb 204pb 18 678 15 678 207pb 204pb 15 767 and 38 534 208pb 204pb 39 189 the data define a linear trend in the 208pb 204pb versus 206pb 204pb diagram that can be interpreted in terms of mixing of lead from different reservoirs the lead appears to be derived from a solution that preferentially leached granites of late hercynian age sulphur isotopic compositions of the galenas range from 8 5 to 7 3 but variations in a single deposit are small 1 2 pointing to different sources of sulphur in a 34s versus 206pb 204pb plot no clear correlation trends appear lead isotope data from deposits of similar characteristics situated within the hercynian orogenic belt as the linares la carolina district s spain and the inglesiente sulcis area sardinia show slight differences indicating a source area of similar lead isotopic composition in the ccr and linares la carolina districts the main source of lead is related to the hercynian granites of each area although small contributions from metasediments cannot be ruled out the contribution of lead from metasedimentary rocks is particularly seen in the sardinian hercynian vein type ores

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

development of fluid conduits in the auriferous shear zones of the hutti gold mine india evidence for spatially and temporally heterogeneous fluid flow abstract the gold mineralization of the hutti mine is hosted by nine parallel n s trending steeply dipping 2 10 m wide shear zones that transect archaean amphibolites the shear zones were formed after peak metamorphism during retrograde ductile d 2 shearing in the lower amphibolite facies they were reactivated in the lower to mid greenschist facies by brittle ductile d 3 shearing and intense quartz veining the development of a s 2 s 3 crenulation cleavage facilitates the discrimination between the two deformation events and contemporaneous alteration and gold mineralization ductile d 2 shearing is associated with a pervasively developed distal chlorite sericite alteration assemblage in the outer parts of the shear zones and the proximal biotite plagioclase alteration in the center of the shear zones d 3 is characterized by development of the inner chlorite k feldspar alteration which forms a centimeter scale alteration halo surrounding the laminated quartz veins and replaces earlier biotite along s 3 the average size of the laminated vein systems is 30 50 m along strike as well as down dip and 2 6 m in width mass balance calculations suggest strong metasomatic changes for the proximal biotite plagioclase alteration yielding mass and volume increase of ca 16 and 12 respectively the calculated mass and volume changes of the distal chlorite sericite alteration ca 11 ca 8 are lower the decrease in 18 o values of the whole rock from around 7 5 for the host rocks to 6 7 for the distal chlorite sericite and the proximal biotite plagioclase alteration and around 5 for the inner chlorite k feldspar alteration suggests hydrothermal alteration during two stage deformation and fluid flow the ductile d 2 deformation in the lower amphibolite facies has provided grain scale porosities by microfracturing the pervasive steady state fluid flow resulted in a disseminated style of gold sulfide mineralization and a penetrative alteration of the host rocks alternating ductile and brittle d 3 deformation during lower to mid greenschist facies conditions followed the fault valve process ductile creep in the shear zones resulted in a low permeability environment leading to fluid pressure build up strongly episodic fluid advection and mass transfer was controlled by repeated seismic fracturing during the formation of laminated quartz gold veins the limitation of quartz veins to the extent of earlier shear zones indicate the importance of pre existing anisotropies for fault valve action and economic gold mineralization

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

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

reflection moveout inversion for horizontal transverse isotropy accuracy limitation and acquisition horizontal transverse isotropy hti is the simplest azimuthally anisotropic model used to describe vertical fracturing in an isotropic matrix assuming that the subsurface is laterally homogeneous and using the elliptical variation of p wave nmo velocity with azimuth measured in at least three different source to receiver orientations we can estimate three key parameters of hti media the vertical velocity anisotropy and the azimuth of the symmetry axis such parameter estimation is sensitive to the angular separation between the survey lines in 2 d acquisition or equivalently to source to receiver azimuths in 3 d acquisition and the set of azimuths used in the inversion procedure the accuracy in estimating the azimuth in particular is also sensitive to the strength of anisotropy while the accuracy in resolving vertical velocity and anisotropy is about the same for any strength of anisotropy to maximize the accuracy and stability in parameter estimation it is best to have the azimuths for the

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

titaniq recrystallized experimental confirmation of the original ti in quartz calibrations several studies have reported the p t dependencies of ti in quartz solubility and there is close agreement among three of the four experimental calibrations new experiments were conducted in the present study to identify potential experimental disequilibrium and to determine which ti in quartz solubility calibration is most accurate crystals of quartz rutile and zircon were grown from sio2 tio2 and zrsio4 saturated aqueous fluids in an initial synthesis experiment at 925 c and 10 kbar in a piston cylinder apparatus a range of quartz crystal sizes was produced in this experiment both large and small examples were analyzed by electron microprobe to determine whether ti concentrations are correlated with crystal size cathodoluminescence images and epma measurements show that intercrystalline and intracrystalline variations in ti concentrations are remarkably small regardless of crystal size the average ti in quartz concentration from the synthesis experiment is 392 1 ppmw ti which is within 95 confidence interval of data from the 10 kbar isobar of wark and watson contrib mineral petrol 152 743 754 2006 and thomas et al contrib mineral petrol 160 743 759 2010 as a cross check on the ti in quartz calibration we also measured the concentration of zr in rutile from the synthesis experiment the average zr in rutile concentration is 4337 32 ppmw zr which is also within the 95 confidence interval of the zr in rutile solubility calibration of ferry and watson contrib mineral petrol 154 429 437 2007 the p t dependencies of ti solubility in quartz and zr solubility in rutile were applied as a thermobarometer to the experimental sample the average ti in quartz isopleth calculated from the calibration of thomas et al contrib mineral petrol 160 743 759 2010 and the average zr in rutile isopleth calculated from the calibration of tomkins et al j metamorph geol 25 703 713 2007 cross at 9 5 kbar and 920 c which is in excellent agreement with the p t conditions of the synthesis experiment separates of the high ti quartz from the initial synthesis experiment described above were used as starting material in subsequent experiments at 20 kbar at which pressure the solubility of ti in quartz is expected to be significantly lower in the recrystallized quartz these recrystallization experiments were conducted under wet and dry conditions at 925 c and under wet conditions at 850 c both wet and dry recrystallization experiments produced polycrystalline quartzites rutile occurs as inclusions in quartz and as individual crystals dispersed along quartz grain boundaries quartz that grew during the recrystallization experiments has dark cathodoluminescence indicating substantially lower ti concentrations the average ti concentrations in quartz from the recrystallization experiments are within the 95 confidence interval of a linear fit to the 20 kbar data of thomas et al contrib mineral petrol 160 743 759 2010 collectively the results from the synthesis and recrystallization experiments confirm that the ti in quartz concentrations used to calibrate the p t dependencies of ti in quartz solubility in thomas et al s contrib mineral petrol 160 743 759 2010 calibration represent the equilibrium concentrations of ti in quartz

single layer folding in simple shear abstract despite the common occurrence of simple shear deformation laboratory and numerical simulations of folding have so far been almost exclusively in pure shear here we present a series of finite element simulations of single layer folding in simple shear up to high shear strains 4 and up to 75 shortening of the folding layer in the simulations we vary the viscosity contrast between layer and its surroundings 25 100 the stress exponent 1 or 3 and the kinematics of deformation pure versus simple shear in simple shear fold trains do not show a clear asymmetry axial planes form perpendicular to the developing fold train and rotate along with the fold train differences in geometries between folds formed in simple and pure shear folds are thus difficult to distinguish visually with simple shear folds slightly more irregular and with more variable axial plane orientation than in pure shear asymmetric refraction of an axial planar cleavage is a clearer indication of folding in simple shear the main effect of an increase in stress exponent is an increase in effective viscosity contrast with only a secondary effect on fold geometry naturally folded aplite dykes in a granodiorite are found in a shear zone in roses ne spain comparison of the folded dykes with our numerical simulations indicates a viscosity contrast of around 25 and a stress exponent of 3 the natural folds confirm that at this moderate viscosity contrast a significant amount of shortening 20 30 is achieved by layer thickening instead of folding

enechelon sigmoidal vein arrays hosted by faults abstract the morphology of enechelon sigmoidal veins generally supports an extension fracture origin for host fractures nevertheless a shear fracture origin has been proposed in some cases mainly on geometric arguments often without morphological support this study describes a system of sigmoidal enechelon quartz veins in a deformed greywacke which displays morphological evidence that the veins are hosted by faults the veins occur in the hinge zone of an upright horizontal antiform and their configuration is consistent with both faulting and vein opening occurring during folding the formation of close spaced vertical dextral faults transformed thick massive greywacke beds into a discontinuous multilayer structure of rock bridges between faults as the length to thickness ratio of the multilayer structure increased the deformation mechanism changed to one of rotation and bending of rock bridges along sinistral shear displacement zones resulting in sigmoidal openings between rock bridges morphological features which indicate that the host fractures are faults include 1 continuity of host fractures well past the tips of the sigmoidal veins and shear displacement of markers by unopened host fractures 2 pinnate extension veins emanating from host fractures particularly near terminations and 3 shear quartz fibres on host fractures basic kinematic analysis shows that shear displacement with opposite shear sense to the array must occur before sigmoidal forms develop as the curvature produces contractional jogs which are incompatible with vein opening recognition of these features may assist in determining the role of shear displacement on host fractures of sigmoidal enechelon vein arrays

the bronzewing lode gold deposit western australia p t x evidence for fluid immiscibility caused by cyclic decompression in gold bearing quartz veins abstract the bronzewing lode gold deposit is located in the yandal greenstone belt in the yilgarn craton of western australia gold mineralization is hosted in tholeiitic basalt that is metamorphosed to greenschist facies individual ore bodies are controlled by a complex gold bearing quartz vein system that comprises shear and extension veins formed during a progressive d2 deformation event gold is localized in quartz along fractures and deformed grain boundaries and is interpreted to have formed late in the formation of the veins detailed petrography and microthermometry on primary pseudosecondary and secondary fluid inclusions trapped in gold bearing shear and extension veins revealed five types of fluid inclusions 1 co2 ch4 h2o nacl inclusions of variable salinity 0 1 to 17 5 eq wt nacl containing between 10 and 99 mol co2 and molar volumes that range from 22 to 76 cm3 2 h2o nacl inclusions of variable salinity 0 4 to 22 1 eq wt nacl 3 co2 ch4 inclusions with up to 58 mol ch4 and molar volumes between 54 and 73 cm3 4 ch4 h2o inclusions with ch4 ranging from 80 to 90 mol and 5 ch4 inclusions with low molar volumes of 19 to 23 cm3 types 1 2 and 3 constitute a fluid inclusion assemblage that occurs consistently in primary pseudosecondary and secondary trails and clusters within the gold bearing quartz vein system these co existing fluids are interpreted to have formed by fluid immiscibility of a low salinity homogeneous parent fluid at about 300 c and 1500 bars locally type 2 fluid inclusions exhibit total homogenization temperatures that are on average 100 c less than the co genetically trapped type 1 aqueous carbonic inclusions this discrepancy is interpreted to have involved co2 effervescence in response to fluid pressure fluctuations types 4 and 5 fluid inclusions are rare and are only present locally in secondary trails and clusters in extension veins significant pressure fluctuations but relatively constant homogenization temperatures for types 1 2 and 3 fluid inclusions suggest that cyclic decompression of the hydrothermal fluids due to seismic activity along the shear zones that host the gold bearing veins triggered fluid immiscibility the process of fluid immiscibility and subsequent lowering of gold solubility is interpreted to be the most efficient precipitation mechanism for gold in the d2 shear zone hosted vein system at bronzewing

saw tooth structures and curved veins related to folds in the south central pyrenees spain two generation of folds f1 and f2 and associated structures developed in the eocene turbidites of the south central pyrenees are analyzed in this paper f1 folds are close have sub horizontal axes and southwards vergence they have an associated cleavage s1 competent layers were folded by layer parallel shortening tangential longitudinal strain some possible flexural flow and an obliquely superimposed homogeneous strain due mainly to simple shear flexural slip is also an important mechanism in the whole multilayer f2 folds are gentle and scarce they fold the s1 cleavage among the structures associated with f1 folds there are sets of veins with curved form in the competent layers the displacement of each vein gave rise usually to a step in the layer boundary so that a set of veins produces a structure that is named saw tooth structure the veins initiated as small faults that made flexural slip difficult and gave rise to a concentration of stress on the steps leading to an opening of the fractures and a propagation of them along a curved path as suggested by a simple mechanical model this propagation agrees with finite element models developed by other authors

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

veins and hydrothermal fluid flow in the mt whaleback iron ore district eastern hamersley province western australia abstract with the advent of recent hydrothermal models for genesis of giant microplaty hematite ore deposits of the hamersley province we have undertaken regional scale analysis of veins and rocks surrounding the mt whaleback deposit with an aim to characterize the nature of fluid flow before during and after ore formation at least five groups of veins formed in the brockman iron formation in deformational events associated with the paleoproterozoic interaction between the yilgarn and pilbara cratons in a 600 km 2 area around the mt whaleback microplaty hematite orebody the five main veining events most likely correspond to the collisional d 2 and extensional collapse d 3 phases of the ca 2300 2200 ma ophthalmian orogeny with one or two later phases probably associated with the waning stages of the ca 1700 1650 ma capricorn orogeny d 4 and or later proterozoic events the abundance of veins associated with d 2 contraction and d 3 extensional fabrics and the composition up to 15 wt nacl equivalent and pressure corrected homogenisation temperatures of primary fluid inclusions 200 400 c indicate that the temperature salinity and likely volume of fluid reached a peak during the last stages of the ophthalmian orogeny and the first stages of post ophthalmian extension paragenesis of veins relative to the deformation history and localization of highest vein densities in the dales gorge member provides circumstantial evidence that the peak of hydrothermal activity in the district was synchronous with the main phase of microplaty hematite ore formation at mt whaleback we propose that the veins record part of the fluid flow system related to the genesis of this giant ore deposit

fluid history of the blue ridge anticlinorium in the central appalachians abstract analysis of fluid inclusions in quartz veins of the blue ridge anticlinorium in the central appalachians was undertaken to determine the relationship between the fluid history and structural evolution of the anticlinorium samples were collected from three generations of veins defined by their age relative to the alleghanian cleavage associated with formation of the anticlinorium and from different stratigraphic units on both limbs of the fold all fluid inclusions observed were two phase l v aqueous inclusions they were separated into four types based on their homogenization temperatures t h salinity and salt composition modal t h varies from 235 c for the oldest group to 135 c for the youngest corresponding salinities decrease progressively from 19 to 6 5 wt nacl equivalent predominant salt compositions are nacl cacl 2 mgcl 2 for older inclusions and nacl for the youngest based on the characteristics of these inclusion types along with the age of the vein and stratigraphic unit in which they occur four fluids were defined that were present in different parts of the anticlinorium at different times during its development the primary control on the occurrence of the different fluids was temporal with different fluids occurring in different age veins a secondary control was the stratigraphy with most of the fluid flow being focused in the catoctin and harpers formations structural location position on the fold and location relative to major faults played minor roles the temporal and stratigraphic controls on fluid occurrence along with an absence of ch 4 and co 2 which are common in fluids in the adjacent piedmont and valley and ridge provinces indicate that the fluids in the blue ridge were locally derived and not part of the late paleozoic regional fluid migration recorded elsewhere in the appalachians

retrieving a common accumulation record from greenland ice cores for the past 1800 years 1 in the accumulation zone of the greenland ice sheet the annual accumulation rate may be determined through identification of the annual cycle in the isotopic climate signal and other parameters that exhibit seasonal variations on an annual basis the accumulation rate in different greenland ice cores is highly variable and the degree of correlation between accumulation series from different ice cores is low however when using multiyear averages of the different accumulation records the correlation increases significantly a statistical model has been developed to estimate the common climate signal in the different accumulation records through optimization of the ratio between the variance of the common signal and of the residual using this model a common greenland accumulation record for the past 1800 years has been extracted the record shows significant 11 9 years periodicity a sharp transition to very dry conditions is found just before a d 1200 and very dry conditions during the 13th century together with dry and cold spells during the 14th century may have put extra strain on the norse population in greenland and may have contributed to their extinction accumulation rates gradually decrease from a distinct maximum in a d 1394 to very dry conditions in the late 17th century and thus reflect the little ice age

shear veins observed within anisotropic fabric at high angles to the maximum compressive stress some faults seem to slip at unusually high angles 45 relative to the orientation of the greatest principal compressive stress1 2 3 4 5 this implies that these faults are extremely weak compared with the surrounding rock6 laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre existing frictionally weak surface7 8 9 weakening from chemical reactions10 elevated fluid pressure11 12 13 or dissolution precipitation creep14 15 here we describe shear veins within the chrystalls beach accretionary melange new zealand the melange is a highly sheared assemblage of relatively competent rock within a cleaved anisotropic mudstone matrix the orientation of the shear veins compared with the direction of hydrothermal extension veins that formed contemporaneously indicates that they were active at an angle of 80 5 to the greatest principal compressive stress we show that the shear veins developed incrementally along the cleavage planes of the matrix thus we suggest that episodic slip was facilitated by the anisotropic internal fabric in a fluid overpressured heterogeneous shear zone a similar mechanism may accommodate shear at high angles to the greatest principal compressive stress in a range of tectonic settings we therefore conclude that incremental slip along a pre existing planar fabric coupled to high fluid pressure and dissolution precipitation creep may explain active slip on severely misoriented faults

elastic anisotropy due to aligned cracks in porous rock all theoretical expressions which relate the characteristics of saturated aligned cracks to the associated elastic anisotropy are restricted in some important way for example to the case of stiff pore fluids or of the absence of equant porosity or of a moderately high frequency band because of these restrictions previous theory is not suitable for application to the upper crust where the pore fluid is brine kf k820 the equant porosity is often substantial p 0 1 and the frequency band is sonic to seismic this work removes these particular restrictions recognizing in the process an important mechanism of dispersion a notable feature of these more general expressions is their insensitivity at low frequency to the aspect ratio of the cracks only the crack density is critical an important conclusion of this more general model is that many insights previously achieved concerning the shear wave splitting due to vertical aligned saturated cracks are sustained however conclusions on crack orientation or crack aspect ratio which were derived from p wave data or from shear wave critical angles may need to be reconsidered further the non linear coupling between pores and cracks due to pressure equalization effects means that the linear schoenberg muir calculus may not be applied to such systems the theory receives strong support from recent data by rathore et al on artificial samples with controlled crack geometry

inter array and intra array kinematics of en echelon sigmoidal veins in cross bedded sandstone merimbula southeastern australia abstract the kinematics of en echelon arrays of quartz veins hosted by sandstone of the upper devonian worange point formation are strongly influenced by bedding and cross bedding bulk deformation recorded by the vein arrays inter array kinematics was influenced by the anisotropy of the host rock such that three types of arrays are observed 1 east verging arrays parallel to bedding 2 east verging arrays oblique to bedding with veins parallel to cross bedding and 3 west verging arrays parallel to cross bedding with veins parallel to bedding these three array types correspond to flats ramps and backthrusts respectively and represent the earliest stages of thrust fault formation flat and ramp arrays form a staircase geometry and conjugate ramp and backthrust arrays form pop up structures the interpretation of the morphology of veins and wall rock intra array kinematics indicates rotation of bridges was the primary kinematic process in the arrays the opening of vein space by rotation of bridges which maintain constant thickness is predicted from measurements of the orientations of vein wall rock interfaces at vein tips and at the array centre comparison of the predictions with direct measurement of the proportion of vein to wall rock along the centreline of arrays demonstrates the applicability of the bridge rotation model which has been generalised to include the thickening or thinning of bridges during rotation

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

waveform tomography of two dimensional three component seismic data for hti anisotropic media reservoirs with vertically aligned fractures can be represented equivalently by horizontal transverse isotropy hti media but inverting for the anisotropic parameters of hti media is a challenging inverse problem because of difficulties inherent in a multiple parameter inversion in this paper when we invert for the anisotropic parameters we consider for the first time the azimuthal rotation of a two dimensional seismic survey line from the symmetry of hti the established wave equations for the hti media with azimuthal rotation consist of nine elastic coefficients expressed in terms of five modified thomsen parameters the latter are parallel to the thomsen parameters for describing velocity characteristics of weak vertical transverse isotropy media we analyze the sensitivity differences of the five modified thomsen parameters from their radiation patterns and attempt to balance the magnitude and sensitivity differences between the parameters through normalization and tuning factors which help to update the model parameters properly we demonstrate an effective inversion strategy by inverting velocity parameters in the first stage and updates the five modified thomsen parameters simultaneously in the second stage for generating reliably reconstructed models

formation of voids and veins during faulting abstract we have developed a quantitative model of void and vein development in fault zones based on observations of fault roughness and the contact characteristics of rough directionally anisotropic fractal surfaces this model includes progressive dilation of the fault during slip events and the elastic deformation of the surfaces normal to the fault plane closure as new void space develops the model predicts vein geometries that are qualitatively similar to those observed in fault controlled mineral deposits the statistics of the vein system are described and strategies for sampling of such structures by drilling are developed the results have significant implications for evaluation of ore reserves and evaluating the fluid transport properties of faults

provenance interpretation of quartz by scanning electron microscope cathodoluminescence fabric analysis we used a cathodoluminescence cl detector attached to a scanning electron microscope sem to study patterns of variable intensity cl in quartz grains from a variety of igneous metamorphic sedimentary and shock deformed meteorite impact rocks distinctive fabrics in quartz grains revealed by sem imaged differential cl include zoning healed fractures complex shears planar features shocked quartz dark cl streaks and patches indistinct mottled texture and nondifferential low contrast cl zoning is common in volcanic quartz and some plutonic quartz zoned plutonic quartz is distinguished from volcanic quartz by the presence of closed fractures and dark cl streaks and patches metamorphic quartz displays either an indistinct mottled texture or nearly uniform nondifferential cl quartz from rocks severely deformed by tectonism displays a complex pattern of multiple small scale shears quartz from meteorite impact sites and some system boundaries is characterized by intricate patterns of planar features presumably created by shock metamorphism thus the sem cl fabric analysis technique provides a rapid method for distinguishing quartz from a variety of source rocks

continental basinal origin of ore fluids from southwestern massif central fluorite veins albigeois france evidence from fluid inclusion and stable isotope analyses the most important fluorspar mining district in france is located in the palaeozoic basement of the albigeois in southwestern french massif central the massive fluorite is hosted within large e w striking fractures crosscutting cambro ordovician clastics associated with large zones of hypersilicified tectonic breccia which form the wall of the mined deposits fluid inclusion data for pre fluorite and fluorite stage fluids have salinities between 20 26 wt nacl equiv with homogenisation temperatures between 85 170 c furthermore low first ice melting temperatures around 50 c indicates the presence of significant cacl2 and possibly mgcl2 together with nacl calculated fluid 18o for pre fluorite quartz ranges from 9 1 to 5 2 with d between 55 to 64 placing the data directly on the present day meteoric water line fluorite stage fluids have 18o between 0 1 to 3 2 and d ranging from 53 to 75 indicating an interacted meteoric fluid origin combining the fluid inclusion and stable isotope data illustrates that the main fluorite depositing fluid has characteristics typical of a basinal brine the authors have no evidence that a magmatic system was involved in the deposit genesis the proposed model highlights that mineralisation was related to major mesozoic extensional events coinciding with the gradual opening of the atlantic and tethys oceans in order to account for the chemistry of the fluids and the siting of the deposits the authors postulate a genetic relationship with local continental evaporite bearing basins coincident with and controlled by the e w fractures

fluid pressure transients on seismogenic normal faults abstract fluid inclusions in hydrothermally altered footwall rocks of the dixie valley fault nevada and the wasatch fault utah indicate that pore fluid pressure fluctuated minimum entrapment pressures for fluid inclusions consisting of h2o co2 nacl ranged from 295 mpa to 60 mpa in the temperature range 350 to 170 c on the wasatch fault and from 158 to 35 mpa in the temperature range 350 to 200 c on the dixie valley fault scatter in the pressure estimates at constant temperature is interpreted as paleo fluid pressure transients at depths of up to 11 km on the wasatch fault and 3 to 5 km on the dixie valley fault observed pressure transients range from 5 mpa within the limits of error in pressure determination to 120 mpa on the wasatch fault and 7 to 126 mpa on the dixie valley fault the pressure transients are greatest on both faults in the temperature range 270 to 310 c the fluids represented by fluid inclusions play a key role in nucleation and propagation of earthquake ruptures high fluid pressures may initiate rupture then dilatancy pore pressure reduction and dilatant hardening may arrest the rupture however decompression of the fluids and phase separation produces a decrease in fluid bulk modulus of 41 to 90 which reduces the dilatant hardening effect and may permit ruptures to propagate

palaeoseismic events recorded in archaean gold quartz vein networks val d or abitibi quebec canada archaean gold quartz vein deposits are commonly hosted in high angle reverse shear zones and are interpreted to have formed in a regime of horizontal compression and high fluid pressure environment this paper presents the results of a combined structural and fluid inclusion study on three gold quartz vein deposits of the val d or area abitibi quebec consisting of subhorizontal extensional veins and e w steeply dipping shear veins crack seal structures tourmaline fibres stretched quartz crystals and open space filling textures indicate that the subhorizontal veins formed by hydraulic fracturing under supralithostatic fluid pressure co2 rich and h2o nacl fluid inclusions interpreted as two coexisting immiscible fluids occur typically in microcracks of different orientations interpreted to have formed in the 1 2 plane horizontal co2 rich fluid inclusion planes are contemporaneous with the opening of these veins 3 vertical vertical h2o nacl fluid inclusion planes as well as some microstructures such as deformed minerals indicate that the same extensional veins have experienced episodic vertical shortening 3 horizontal alternating with the opening events deformation and slip opening also occurred in shear veins in which preferred orientation of fluid inclusion planes is not clear except that the h2o nacl fluid inclusion planes tend to be oriented at high angles to the slip direction the successive opening and collapse events in subhorizontal extensional veins are correlated with deformation and slip opening events in shear veins respectively and are attributed to cyclic fluid pressure fluctuations in the system they are thus consistent with the fault valve model sudden drop in fluid pressure from supralithostatic to lower values induces fluid unmixing and occurs immediately post failure following seismic rupturing along the shear zone sealing of the shear veins allows the fluid pressure to build up again and the subhorizontal extensional veins to form the intermittent change in orientation of 3 in horizontal extensional veins is ascribed to a total shear stress release along the neighbouring shear veins after rupture the complex internal structures of the gold quartz veins provide an excellent record of archaean seismic activity along high angle reverse faults

pressure fluctuation during uplift of the northern apennines italy a fluid inclusions study abstract p t conditions existing after the main syn collision tectonic phase in the western part of the northern apenninic chain italy e g in the tuscan nappe outcropping in the la spezia area were estimated on the basis of a detailed microstructural structural petrographic and fluid inclusion study of quartz of syn tectonic d2 veins developed in the tertiary flysch at the top of the tuscan nappe macigno formation three main fluid events have been distinguished as follows during retrograde metamorphism d1 to d2 phase fluids in equilibrium with turbidites from the tuscan nappe were h2o ch4 mixtures issued from water organic matter interactions in temperatures conditions that may have reached at least 260 c or more 280 c depending on the considered depth estimates and maximum pressures around 210 250 mpa evidence of strong fluid pressure fluctuation between lithostatic and hydrostatic within the metamorphic formations up to 100 150 mpa possibly linked to fault valve activity at the beginning of the uplift triggered phase separation of the water methane fluids and production of methane rich and water rich fluids fluctuations in pressure during these events played a crucial role in quartz crystallization especially in extensional fissures formed perpendicular to the d2 folds axial foliation changes in the fluid regime and sources with time are evidenced by the input of brines which mix to distinct degrees and are trapped in healing microfissures during retrograde fluid evolution such mixing processes are an indication of the connection between separate fluid reservoirs with different temperature conditions consequently mass and heat transfer have to be taken into account as the downward percolation of cooler fluids probably accelerated the rate of cooling of the exhumed formations these processes are certainly common to most orogenic terrains and can be quantitatively studied through p v t x reconstruction using fluid inclusion data on the drainage zones where the mixing processes occurred this work confirms that fluid inclusion studies can provide accurate quantitative estimates of fluid pressure variations during the evolution of orogenic terrains and could therefore constitute a useful tool in tectonic interpretations at the light of the models developed for pressure variations in the upper crust

characterization and timing of the different types of fluids present in the barren and ore veins of the w sn deposit of panasqueira central portugal the panasqueira w sn deposit is the largest quartz vein type deposit of the iberian peninsula and the most important wolframite deposit in western europe the ore veins are almost exclusively sub horizontal besides ore bearing sub horizontal veins the panasqueira mine also contains barren quartz veins there are essentially two generations of barren quartz quartz contemporaneous with the earliest regional metamorphism qi and recrystallized quartz contemporaneous with the thermal metamorphism related to the granite intrusion qii fluid inclusion studies microthermometry and raman were undertaken in order to distinguish fluids contemporaneous with the barren quartz from those contemporaneous with the ore bearing quartz qiii fluid inclusion data indicate that the barren and ore bearing quartz fluids are dominantly aqueous 93 to 98 mol h2o with a nearly constant bulk salinity 8 to 12 wt eq nacl with the quantity of volatile component determined by raman spectrometry higher in qiii but never greater than 5 mol however the co2 ch4 n2 ratio is different for each type of quartz volatiles are dominated by ch4 10 to 96 mol zch4 and or n2 3 to 87 mol zn2 in the barren quartz and by co2 60 to 73 mol zco2 in ore bearing quartz the bulk chemical composition of the fluids in qiii is comparable to that found commonly in hydrothermal fluids associated with wolframite mineralization where na k ca and hco3 cl so4 a dispersion in th 226 to 350 c found in qiii together with a variation in the degree of filling 0 5 to 0 7 and with the consequent variation of fluid densities 0 70 to 0 79 may result from changes in the fluid pressure regime below lithostatic pressure suggesting vein filling related to tectonic events

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

sigmoidal wall rock fragments application to the origin geometry and kinematics of en echelon vein arrays abstract wall rock fragments found within en echelon vein arrays may provide valuable information on the origin of vein systems shear zone kinematics and vein geometry these fragments are sigmoidal and comprise intact rock between adjacent veins or fragments enclosed within individual veins we present field examples of sigmoidal rock fragments within en echelon veins that grew as opening mode fractures in response to an applied simple shear by virtue of their unique shape and alignment of pre existing fabric we demonstrate how small wall rock fragments may be used as kinematic indicators as well as to predict geometries of individual veins and entire vein arrays such a tool may be especially useful in mining exploration where the precise boundaries of large veins are unknown or in stockworks where the rock is composed primarily of vein material

azimuth preserved local angle domain prestack time migration in isotropic vertical transversely isotropic and azimuthally anisotropic media conventional prestack migration does not preserve local directional information of the seismic waves at the image points new attempts such as sectored migration of azimuth limited or common offset vector data only concern source receiver azimuth and offset on the surface which can be poor representation of subsurface wavepath direction moreover they could result in inaccurate imaging because they do not account for the energy propagation between azimuths or offset vectors in the past decade local angle domain seismic imaging has been highly advocated to avoid migration artifacts and to improve velocity estimation in complex media considering prestack time migration pstm is still widely used in seismic imaging and seismic data preconditioning for amplitude variations with offset or incident angle avo ava analysis fracture detection and reservoir characterization we present an azimuth preserved local angle domain kirchhoff pstm approach for such purposes we apply a seismic imaging condition i

an analysis of avo inversion for postcritical offsets in hti media abstractazimuthal variations of wavefield characteristics such as traveltime or reflection amplitude play an important role in the identification of fractured media a transversely isotropic medium with a horizontal symmetry axis hti medium is the simplest azimuthally anisotropic model typically used to describe one set of vertical fractures there exist many techniques in industry to recover anisotropic parameters based on moveout equations and linearized reflection coefficients using such a model however most of the methods have limitations in defining properties of the fractures due to linearizations and physical approximations used in their development thus azimuthal analysis of traveltimes based on normal moveout ellipses recovers a maximum of three medium parameters instead of the required five linearizations made in plane wave reflection coefficients pwrcs limit the amplitude versus offset avo analysis to small incident angles and weak contrast interfaces inversion based on azimuthal