velocity structure of the kapuskasing uplift northern ontario from seismic refraction studies a crustal scale seismic refraction experiment was conducted over the kapuskasing structural zone northern ontario in 1984 the zone cuts obliquely across the east west structural grain of the superior province in the canadian shield and has been proposed as a cross section of archean crust exposed by thrust faulting along the ivanhoe lake cataclastic zone during early proterozoic time five seismic refraction lines of 360 450 km were shot over the area there were 18 profile shots and two fan shots with a recorder spacing of 2 5 km we have modeled the travel times and amplitudes of the data from the profile lines and analyzed reflections from the crust mantle boundary on the fan shots we have imaged a low velocity zone under the abitibi greenstone belt ranging from 4 5 to 9 12 km depth that is underlain by a highly reflective zone there is a considerable deepening of the moho from 40 43 km to 50 53 km under and to the west of the southern end of the kapuskasing structural zone a high velocity anomaly of 6 6 6 7 km s has been imaged in the upper crust down to 20 km depth beneath the kapuskasing structure with a suggested dip of 15 2 to the west this corresponds well to the proposed location of a granulite zone thrust up from the middle or lower crust in the early proterozoic

constraints from 40ar 39ar geochronology on the tectonothermal history of the kapuskasing uplift in the canadian superior province the kapuskasing uplift ku in the superior province of the canadian shield has been interpreted as an oblique cross section through the archean mid crust however the time of juxtaposition of the granulites of the ku against the lower grade rocks of the abitibi greenstone belt agb along the ivanhoe lake fault zone is problematic to constrain the postmetamorphic tectonothermal history of the ku we have conducted 57 40ar 39ar step heating analyses on mineral and rock samples collected in a transect across the southern ku and adjacent agb the age spectra record a complex thermal history amphiboles from the agb in the footwall of the ivanhoe lake fault zone have ca 2 66 ga dates similar to closure ages for amphiboles from farther east in the agb amphibole dates of 2 46 2 52 ga from the deepest structural levels of the ku place an upper limit on the time of major uplift of the granulites and their juxtaposition with the agb biotite and muscovite dates from the transect cluster into three age groups

evidence from aeromagnetics on the configuration of matachewan dykes and the tectonic evolution of the kapuskasing structural zone ontario canada by digital image processing of federal provincial aeromagnetic survey data for the south central superior province we have obtained an improved picture of the distribution of dykes in the huge matachewan mafic dyke swarm 2454 ma we deduce from it a picture of post emplacement deformation in the vicinity of the uplifted granulite gneisses of the kapuskasing structural zone ksz matachewan dykes are emplaced in three subswarms the two easterly subswarms are clearly truncated by the ksz s eastern boundary faults the western subswarm shows an open z bend as it crosses the ksz but it does not reveal any major fault offset on the plausible assumption supported by paleomagnetic data that the subswarms were originally intruded radially the horizontal strain suffered by the ksz since emplacement of the dykes is mainly a northeast southwest trending band of dextral transcurrent deformation which in the northeast is discontinuous and concentrated in a fault horizontal offset 60 80 km and in the south

the structure of seismogenic strike slip faults in the eastern part of the reykjanes peninsula oblique rift sw iceland abstract a considerable part of the seismic risk to the capital area of iceland is provided by a series of strike slip faults at the mid atlantic plate boundary within a distance range of 15 35 km about two thirds of the icelandic population lives within this distance range from the source areas of m 6 6 5 earthquakes the structure of the plate boundaries in sw iceland is relatively complex three branches meet in the hengill triple junction the oblique rift of the reykjanes peninsula the south iceland seismic zone a transform zone and the western volcanic zone a rift zone the reykjanes peninsula oblique rift has an over all trend of 70 highly oblique with respect to the spreading direction 101 in this region it contains both volcanic systems and seismogenic strike slip faults the fissure swarms of individual volcanic systems contain normal faults and fissures with a ne trend also quite oblique to the plate boundary the fissure swarms fade out towards the ne and sw as they extend into the plates on either side overprinting this pattern of volcano tectonic structures are sets of parallel northerly striking transcurrent faults that generate the largest earthquakes in this zone their surface expressions are en echelon fracture arrays and push up structures the sense of displacement is right lateral in the 15 km long section of the rift studied here we find evidence for at least six faults of this type the length of individual faults may exceed 12 km the distance between them varies from 1 to 5 km and together they form a bookshelf type fault system taking up the left lateral component of plate movements across the oblique rift zone

high precision u pb ages for granulite metamorphism and deformation in the archean kapuskasing structural zone ontario implications for structure and development of the lower crust abstract precise u pb isotopic ages for two subhorizontal granulite gneisses in the kapuskasing structural zone indicate that formation and emplacement occurred more than 50 m y after cessation of volcanism in the steeply folded nearby greenstone belts by successive stages of ductile underplating across a zone of crust mantle delamination volcanism and batholith formation had ceased by 2700 and 2680 ma respectively while granulite formation occurred between 2660 and 2640 ma and ductile deformation continued until 2585 ma emplacement of the oldest granulite caused the development of shear planes and melting in the older overlying tonalite while emplacement of the younger granulite caused rupturing and rehydration of the overlying older granulite widespread tectonic underplating is implied since all superior province granulites have similar young ages anomalous ar ages that post date accretion by about 150 m y and scrambled pb pb and rb sr whole rock systems also suggest that late low temperature alteration accompanied this event temporal relationships and the presence of post volcanic 2670 ma conglomerate cobbles at granulite grade support a model of ductile underplating of a post accretion thermally softened back arc fore arc complex with components welded onto an overlying volcanic plutonic complex at successively deeper levels multistage deformation in active fault zones and hydrothermal emplacement of major gold deposits in greenstone belts are coeval with ductile underplating with ages between 2670 and 2585 ma anomalously abundant gold production from archean rocks may indicate that shallow underplating granulitization and devolatization was a widespread phenomenon at this time post accretion ductile underplating must be considered as a primary cause of seismic reflectors in archean terrains

boron and lithium in high grade rocks and minerals from the wawa kapuskasing region ontario there is no preferential partitioning of boron among the principal rock forming minerals in high grade rocks of the kapuskasing structural zone ksz and the wawa domal gneiss region wdg lithium is strongly concentrated in biotite and other ferromagnesian minerals but does not show consistent partitioning between these and the sialic minerals the distribution of b and li within a rock may be studied using an alpha track image which shows that the inconsistencies in partitioning may be largely attributed to disturbance of mineral equilibria by postmetamorphic low grade alteration that deposited b and li boron has similar concentrations in all the rock types studied although it is an incompatible element that elsewhere accumulates in pegmatites lithium concentrations are low in the anorthositic rocks but are otherwise very variable in some but not all rocks higher than usual b and li can be attributed to introduction during alteration boron occurs at low concentrations 2 3 ppm throughout both the k

anisotropic changes in p wave velocity and attenuation during deformation and fluid infiltration of granite fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes yet for most damaging earthquakes with nucleation zones below a few kilometers depth direct measurements of fluid pressure variations are not available instead pore fluid pressures are inferred primarily from seismic wave propagation characteristics such as v p v s ratio attenuation and reflectivity contacts we present laboratory measurements of changes in p wave velocity and attenuation during the injection of water into a granite sample as it was loaded to failure a cylindrical sample of westerly granite was deformed at constant confining and pore pressures of 50 and 1 mpa respectively axial load was increased in discrete steps by controlling axial displacement anisotropic p wave velocity and attenuation fields were determined during the experiment using an array of 13 piezoelectric transducers at the final loading steps 86 and 95 of peak stress both spatial and temporal changes in p wave velocity and peak to peak amplitudes of p and s waves were observed p wave velocity anisotropy reached a maximum of 26 transient increases in attenuation of up to 483 db m were also observed and were associated with diffusion of water into the sample we show that velocity and attenuation of p waves are sensitive to the process of opening of microcracks and the subsequent resaturation of these cracks as water diffuses in from the surrounding region symmetry of the orientation of newly formed microcracks results in anisotropic velocity and attenuation fields that systematically evolve in response to changes in stress and influx of water with proper scaling these measurements provide constraints on the magnitude and duration of velocity and attenuation transients that can be expected to accompany the nucleation of earthquakes in the earth9s crust

saline minewaters of the keweenaw peninsula northern michigan their nature origin and relation to similar deep waters in precambrian crystalline rocks of the canadian shield

synthetic fluid inclusions viii vapor saturated halite solubility in part of the system nacl cacl2 h2o with application to fluid inclusions from oceanic hydrothermal systems abstract halite solubility along part of the vapor saturated liquidus in the system nacl cacl 2 h 2 o has been determined using the synthetic fluid inclusion technique data allow the construction of liquidus isotherms for temperatures up to 500 c and bulk compositions containing 60 wt total salt and as much as 25 wt cacl 2 combined with previous data for the binary system nacl h 2 o and for the ternary system nacl cacl 2 h 2 o in the low salinity low temperature region a preliminary ternary phase diagram can be constructed that remains incomplete only in the cacl 2 rich region results are applied to the interpretation of saline fluid inclusions from quartz veins in oceanic metagabbros and can be applied to many other natural inclusions containing aqueous solutions with nacl and cacl 2 the dominant solutes microthermometric measurements at equilibrium of the melting temperature of ice tm ice and of the dissolution temperature of halite tm halite are sufficient to determine the bulk composition of the nacl cacl 2 h 2 o fluid

vapour loss boiling as a mechanism for fluid evolution in metamorphic rocks the calculation of fluid evolution paths during reaction progress is considered for multicomponent systems and the results applied to the ternary system co2 h2o nacl fluid evolution paths are considered for systems in which a co2 rich phase of lesser density vapour is preferentially removed from the system leaving behind a saline aqueous phase liquid such boiling leads to enrichment of the residual aqueous phase in dissolved components and for certain reaction stoichiometries to eventual saturation of the fluids in salt components distinctive textures particularly radiating growths of prismatic minerals such as tremolite or diopside are associated with saline fluid inclusions and solid syngenetic salt inclusions at a number of field localities the most thoroughly studied of these localities is campolungo switzerland where metasomatic rocks have developed in association with fractures and veins at 500 c and 2 000 bars of pressure the petrography of these rocks suggests that fluid phase separation into liquid and vapour has been an important process during metasomatism fracture systems with fluids at pressure less than lithostatic may facilitate the loss of the less dense vapour phase to conditions of the amphibolite facies

sampling of brine in cores of precambrian granite from northern illinois the composition of groundwater in deep seated rocks is of great interest both geochemically and in connection with the disposal of radioactive waste however sampling of deep seated groundwater is expensive and often difficult we describe here a simple technique for the elution of pore fluid groundwater from cores of igneous rocks and we describe brine eluted from a core of precambrian granite from northern illinois drill hole uph 3 the brine is predominantly nacl and cacl2 with a ca na mole ratio of about 0 05 to 0 1 from analysis of soluble chloride in a crushed sample the chloride concentration in the pore water is estimated as 2 3 m the brine is similar to brine in the illinois basin and it was probably derived from the overlying sediments

repetitive hydraulic fracturing and shear zone inflation in an archean granitoid hosted ribbon banded au quartz vein system renabie area ontario canada abstract economically significant tonalite 2722 ma and trondhjemite 2728 ma hosted archean au quartz vein mineralization in the renabie area ontario located in a marginal part of the 10 15 km thick wawa domal gneiss terrane shows strong structural control major ore zones occur in e w and nw nnw striking ductile brittle high strain zones that are superimposed on an earlier regional foliation mineralized zones are up to 20 30 m wide mineable to a depth of 1300 vertical metres and dip typically at 60 80 angles production and reserves for the renabie mine totalled 6 million tonnes at 6 6 g t au and 2 g t ag net shear from kinematic indicators is oblique reverse south side up sinistral on e w structures e g nudulama renabie main zone depth 2475 level and west side up sinistral on nw nnw structures e g braminco 21 zone the strain features of the shear zone hosted mineralization together with evidence of reaction enhanced ductility associated with hydrothermal fluid wallrock interaction indicate that mineralization and hydrothermal alteration occurred synchronously with shear deformation the characteristic banded appearance book ribbon structure of the renabie veins which is typical of many archean and cordilleran au quartz vein systems is interpreted to be the result of inflationary vein formation by repeated increments of hydraulic fracturing and mineral deposition 250 750 associated with hydrothermal fluid overpressuring within and below the actively deforming ductile brittle shear zones crack seal type process fracture orientation was largely controlled by the anisotropy in rock tensile strength associated with the approximately planar shear fabric the element mineral association of renabie is typical of oxidized archean au quartz vein systems containing anhydrite hematite carbonate and tourmaline with a chalcophile association consisting of mos 2 cu pb sulphides native au ag and pb bi au ag tellurides key factors in the development of significant mineralization at renabie as compared with other usually small low grade archean granitoid hosted au quartz vein systems include the repetitive nature of the mineralizing process and the focusing of au bearing fluids within the actively deforming shear zones a specific and sufficiently large reservoir of overpressured hydrothermal archean au bearing fluid was generated at some location not yet identified in the archean crustal structure represented by the kapuskasing section

thermobarometry of garnet clinopyroxene hornblende granulites from the kapuskasing structural zone amphibole mixing properties and standard state properties for the end members tremolite tschermakite pargasite ferrotremolite ferrotschermakite and ferropargasite have been refined through analysis of relevant phase equilibrium experiments coexisting cummingtonite hornblende pairs and natural mineral parageneses when merged with the mineral properties given by r g berman these amphibole properties allow the calculation of numerous equilibria suitable for thermobarometry in a wide range of bulk compositions at amphibolite to granulite metamorphic grades the method was applied to texturally equilibrated garnet pyroxene hornblende gneisses and compared both to results based on anhydrous assemblages and to those for garnet biotite gneisses from the kapuskasing structural zone thermometer resetting is apparent only in garnet biotite gneisses whereas touching garnet pyroxene pairs in mafic gneiss show little evidence of retrograde fe mg exchange computed metamorphic temperatures garnet clinopyrox

water saturation effects on elastic wave attenuation in porous rocks with aligned fractures summary elastic wave attenuation anisotropy in porous rocks with aligned fractures is of interest to seismic remote sensing of the earth s structure and to hydrocarbon reservoir characterization in particular we investigated the effect of partial water saturation on attenuation in fractured rocks in the laboratory by conducting ultrasonic pulse echo measurements on synthetic silicacemented sandstones with aligned penny shaped voids fracture density of 0 0298 0 0077 chosen to simulate the effect of natural fractures in the earth according to theoretical models our results show for the first time contrasting variations in the attenuation q 1 o fp and s

retrograde fluids in the archean shawmere anorthosite kapuskasing structural zone ontario canada the archean shawmere anorthosite lies within the granulite facies portion of the kapuskasing structural zone ksz ontario and is crosscut by numerous linear alteration veins containing calcite quartz dolomite zoisite clinozoisite margarite paragonite chlorite these veins roughly parallel the trend of the ivanhoe lake cataclastic zone equilibria involving clinozoisite margarite quartz calcite plagioclase show that the vein minerals were stable at t 0 9 thus vein formation while clearly retrograde spanned a range of temperatures and fluid compositions evolved from h2o rich to co2 rich the calcite in the retrograde veins has 18o values that range from 8 4 to 11 2 average 9 7 0 9 and 13c values that range from 3 9 to 1 6 average 3 1 0 6 these values indicate that the fluids from which calcite precipitated underwent extensive exchange with the anorthosite and other crustal lithologies the fluids may have been initially derived either from devolatilization of metamorphic rocks or crystallization of igneous rocks in the adjacent abitibi subprovince vein quartz contains co2 rich fluid inclusions final melting t 57 0 to 58 7 c that range in size from 5 to 17 m measured homogenization temperatures t h range from 44 0 to 14 5 c however for most inclusions 46 of s1 t h 44 0 to 21 1 c co2 1 13 to 1 05 g cm3 at 400 to 600 c these densities correspond to pressures of 3 5 to 7 kbar which is the best estimate of pressures of vein formation it has been argued that some high density co2 rich fluid inclusions found in the ksz were formed during peak metamorphism and thus document the presence of a co2 rich fluid during peak granulite facies metamorphism rudnick et al 1984 the association of high density co2 rich fluid inclusions with clearly retrograde veins documents the formation of similar composition and density inclusions after the peak of metamorphism thus the coincidence of entrapment pressures calculated from fluid inclusion density measurements with peak metamorphic pressures alone should not be considered strong evidence for peak metamorphic inclusion entrapment all fluid inclusion results are consistent with an initially semi isobaric retrograde p t path

synopsis of paleomagnetic studies in the kapuskasing structural zone this paper summarizes results from paleomagnetic studies sponsored by lithoprobe on the kapuskasing structural zone ksz data from archean rocks outside the ksz indicate that the wawa subprovince has not been significantly rotated or translated 5 relative to the abitibi subprovince results from the granulites and amphibolites indicate that the ksz underwent several kilometres of uplift at ca 2 51 ga and then 10 5 west northwest tilt with several kilometres of further uplift between 2 04 and 1 88 ga from thrust faulting on the ivanhoe lake fault zone localized chemical remagnetization occurred at 1 1 ga along the west side of the shawmere anorthosite paleomagnetic data from the 2 45 ga matachewan diabase dike swarm indicate that it was emplaced within one reversed to normal polarity interval of less than 5 ma their polarity pattern indicates major north trending faults with several kilometres of dip slip displacement their remanence confirms that the superior province was deformed around th

a comparative 40ar 39ar study of the kapuskasing structural zone and the wawa gneiss terrane thermal and tectonic implications 40ar 39ar studies were performed on rocks from two traverses within the southern superior province of the canadian shield the racine traverse across the wawa gneiss terrane and the shawmere traver

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

metamorphism in archaean greenstone belts calculated fluid compositions and implications for gold mineralization an inescapable consequence of the metamorphism of greenstone belt sequences is the release of a large volume of metamorphic fluid of low salinity with chemical characteristics controlled by the mineral assemblages involved in the devolatilization reactions for mafic and ultramafic sequences the composition of fluids released at upper greenschist to lower amphibolite facies conditions for the necessary relatively hot geotherm corresponds to those inferred for greenstone gold deposits xco2 0 2 0 3 this result follows from the calculation of mineral equilibria in the model system cao mgo feo al2o3 sio2 h2o co2 using a new expanded internally consistent dataset greenstone metamorphism cannot have involved much crustal over thickening because very shallow levels of greenstone belts are preserved such orogeny can be accounted for if compressive deformation of the crust is accompanied by thinning of the mantle lithosphere in this case the observed metamorphism which was contemporaneous with deformation is of the low p high t type for this type of metamorphism the metamorphic peak should have occurred earlier at deeper levels in the crust i e the piezothermal array should be of the deeper earlier type however at shallow crustal levels the piezothermal array is likely to have been of deeper later type as a consequence of erosion thus while the lower crust reached maximum temperatures and partially melted to produce the observed granites mid crustal levels were releasing fluids prograde into shallow crustal levels that were already retrograde we propose that these fluids are responsible for the gold mineralization thus the contemporaneity of igneous activity and gold mineralization is a natural consequence of the thermal evolution and does not mean that the mineralization has to be a consequence of igneous processes upward migration of metamorphic fluid via appropriate structurally controlled pathways will bring the fluid into contact with mineral assemblages that have equilibrated with a fluid with significantly lower xco2 these assemblages are therefore grossly out of equilibrium with the fluid in the case of infiltrated metabasic rocks intense carbonation and sulphidation is predicted if as seems reasonable gold is mobilized by the fluid generated by devolatilization then the combination of processes proposed most of which are an inevitable consequence of the metamorphism leads to the formation of greenstone gold deposits predominantly from metamorphic fluids

paleomagnetism of the clay howells carbonatite complex constraints on proterozoic motion in the kapuskasing structural zone superior province canada abstract the clay howells complex is located approximately 130 km east of hearst ontario at 49 50 n 82 05 w near the north end of the kapuskasing structural zone ksz of the superior province in the canadian shield the pluton is a large oviform pluton of about 16 km2 that is composed dominantly of syenite with minor carbonatite it was emplaced into an archean gneissic terrain of amphibolite to granulite facies with middle precambrian diabase dikes the complex is unmetamorphosed and late precambrian in age rb sr 1075 15 ma multistep alternating field af and thermal demagnetization was carried out on 194 specimens from 18 sites in the intrusion and three sites in the host rock dikes and gneisses the 18 syenite sites give a unit mean direction of 294 2 27 1 n 18 k 26 95 7 0 which yields a pole position of 178 8 e 26 5 n p 4 1 m 7 6 for the clay howells complex a crude contact test using the three host rock sites proved inconclusive the pole for the intrusion is concordant falling at about 1080 10 ma on the keweenawan apparent polar wander path which agrees with the rb sr age thus the complex has an untilted primary remanence that indicates that there has been no significant uplift

high grade metamorphism in the chapleau foleyet area ontario archean rocks superior province kapuskasing structural zone in migmatitic mafic gneiss paragneiss dioritic and tonalitic rocks a lower grade garnet clinopyroxene plagioclase gt cpx pl zone and patchy higher grade orthopyroxene zones are distinguished based on mineral melt equilibria minimum conditions for the gt cpx pl zone are 750 degrees c 6 kbar a h 2 o 0 5 0 7 and for the orthopyroxene zone 770 degrees c 6 kbar a h 2 o 800 degrees c pressure values are 5 4 8 4 kbar and define a nne trending area of relatively high p in the kapuskasing zone supporting the interpretation of a tilted crustal section modified journal abstract

quantification of lower crustal synmetamorphic fluid fluxes in the kapuskasing structural zone based on oxygen isotope profiles across two paragneiss mafic gneiss contacts detailed oxygen isotope profiles were measured across two very similar amphibolite grade paragneiss mafic gneiss contacts located 2 km apart within the kapuskasing structural zone the first profile is asymmetrical about die contact 18 o values for whole rocks and minerals are homogeneous in the paragneiss whole rock 18 o 10 4 to 11 4 smoothly decrease by about 2 over 2 5 m moving into the mafic gneiss and are homogeneous in the remainder of the mafic gneiss whole rock 18 o 7 0 to 7 4 the second profile is flat with homogeneous whole rock and mineral 18 o values in bom lithologies and mafic gneiss values whole rock 18 o 8 7 to 9 8 that are higher by about 3 relative to typical mafic gneiss values mineral mineral isotopic fractioations are fairly constant in all samples and are typical of high grade metamorphic rocks despite their differences both profiles can be explained by the advection of a mixed h 2 o co 2 fluid in equilibrium with the paragneiss across the contact into the mafic gneiss coupled with diffusion of oxygen in the fluid modeling constrains the net fluid flux required to form me first profile to be 1 3 m 3 m 2 and for me second profile to be 10 m 3 m 2 thus the net fluid flux during metamorphism varied probably by at least a factor of five over 2 km these fluxes could have been generated locally within the kapuskasing structural zone during metamorphism either by metamorphic devolatilization reactions or by the release of volatiles from crystallizing magmas

co 2 brine immiscibility at high temperatures evidence from calcareous metasedimentary rocks study of fluid inclusions in quartz segregations and in the rock matrix of a calcareous psammite and a carbonate schist suggests that brines containing 23 24 weight percent salt nacl equivalent are immiscible with co2 at the metamorphic conditions of approximately 600 and 6 5 kb the presence of a high temperature solvus between saline brine and co2 is supported by other fluid inclusion studies as well as experimental measurements from the literature as saline brines are common in metamorphic and hydrothermal systems co2 brine immiscibility should play an important role in petrogenesis the fluid inclusions preserved in the quartz segregations probably represent the fluids generated by prograde metamorphic reactions whereas the compositions of the fluids trapped in the rock matrix quartz suggest they have reequilibrated with the matrix minerals during incipient retrograde reactions the isochores from the densest inclusions observed in this study pass close to the inferred peak metamorphic conditions other isochores suggest an episode of deformation and recrystallization at 275 c and 1 4 kb using the density information preserved in all the inclusions a convex downward uplift path on a p t diagram is inferred for these rocks

ultrasonic properties of sedimentary rocks effect of pressure saturation frequency and microcracks seismic velocities and attenuations are influenced by lithology porosity and permeability as well as the kind and quantity of the pore fluids the microstructure of rocks is another important factor influencing seismic properties this influence can be used to investigate the pressure dependent closure of microcracks for this purpose velocities and attenuations of p and s waves have been determined at ultrasonic frequencies in three different rocks vacuum dry and partially saturated with water as a function of hydrostatic pressure up to 200 mpa a new combined model has been developed with this model an explicit description of the microstructure local fluid flow lf and macrostructure gassmann effect global fluid flow is possible assuming a patchy saturation i e inhomogeneous distribution of the fluid in the pores and modulus reduction both the saturation dependent measurements and the pressure dependent data can be explained the modelling and the phenomenological interpretation of the data gained under increasing hydrostatic pressure yields consistent results concerning the amount of crack closure as well as the range in which crack closure appears in high porosity sandstones bentheimer and obernkirchner sandstone a strong closure of cracks already with a small increase of pressure must be concluded in a low porosity harzer greywacke a significantly lower closure of cracks can be concluded within the pressure range of 0 100 mpa it is shown however that there must be open cracks in all rocks even under elevated hydrostatic pressure resulting in a measurable effect due to lf

geochemistry of late 1 1 ga fluid inclusions in rocks of the kapuskasing archean crustal section three outcrops well constrained by geochronological and structural studies and representing a traverse running from tonalite dominated outcrops in the eastern wawa gneiss terrane to high grade granulites of the kapuskasing structural zone were mapped and sampled in detail in order to study the trapped fluids all fluid inclusions in quartz are secondary and consist mostly of co2 dominated type ii and saline aqueous type iiia fluids usually occurring on separate healed fractures but also coexisting on some fractures healed fractures in quartz contain fluid inclusions but are associated with carbonate sericite alteration where they pass into adjacent mineral grains homogeneous h2o co2 salt fluid inclusions type ia in carbonate rich veins of probable keweenawan 1 1 ga age were trapped at 400 550 c and ambient pressures of 1 5 2 kbar 1 kbar 100 mpa as these fluids cooled on penetration into cool 200 c country rocks along fractures they underwent open system h2o co2 phase separation f

thin thrust sheet formation of the kapuskasing structural zone revealed by lithoprobe seismic reflection data regional and high resolution seismic reflection data across the kapuskasing structural zone in ontario canada image at least three significant thrust faults that are low angle merge into a flat detachment on the west and together were responsible for the uplift of amphibolite and granulite facies rocks their geometry resembles a ramp and flat style of deformation that results in a thin upper plate above the 10 12 km about 4 0 s detachment northwest southeast horizontal shortening is estimated to be at least 55 km this large amount of shortening implies that much of the superior province was detached during the formation of the kapuskasing structural zone

immiscible fluids in metamorphism implications of two phase flow for reaction history fluid immiscibility between a co 2 rich fluid and brine has been described from several medium to high grade marbles and calcsilicates here we also report evidence for ch 4 h 2 o immiscibility in low grade metamorphic rocks from wales and suggest that the flow of such immiscible fluids may be comparable to that of water oil or water gas mixtures in petroleum reservoirs this analogy implies that where one fluid is being produced by reaction it will flow out of the rock while the other remains immobile except insofar as it is soluble in the more abundant fluid phase hence extensive reaction may take place in the presence of coexisting immiscible fluids each having high activities it is proposed that this type of flow behavior not only accounts for the development of salt saturated fluids in marbles but also may be responsible for the elimination of carbonate and extensive loss of graphite from pelites in the lower part of the greenschist facies

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

saline ground waters and brines in the canadian shield geochemical and isotopic evidence for a residual evaporite brine component abstract saline ca na cl type groundwaters and brines sampled in deep mines over an extensive area of the canadian precambrian shield have elevated br cl ratios which may indicate that the chlorinity of these waters was derived from the infiltration of residual evaporitic brines remnants of the great marine incursions of the paleozoic era boron concentrations in these waters are generally low i e 11 b 10 b ratios of these waters are significantly greater than the average value for continental crustal rocks with the highest values 4 19 approaching that of present day seawater 4 20 moreover the boron isotopic ratios generally trend to higher values with increasing chlorinity which supports the conclusion from the br cl relationship that most of the chloride in shield brines is of marine origin rather than a product of water rock interactions if this is correct crystalline rocks must then be sufficiently permeable on a regional scale to have allowed the brine to infiltrate to depths of several kilometers where it now resides

spatial and temporal variation of seismic attenuation during hydraulic fracturing of a sandstone block subjected to triaxial stress q factors estimated with spectral ratios describe the attenuation experienced by seismic arrivals in their travel from the source s to the receiver s when q is not the same along the travel path of each arrival the formulation must incorporate two q factors making the problem indeterminate here we show that by assuming that q is a random variable the parameters of its probability distribution can be recovered through a mapping workflow using the spectral ratios an advantage of such a workflow is that uncertainties in source location and velocity model can also be incorporated by representing these elements as random variables we apply such a methodology to an acoustic emission ae dataset from a laboratory experiment of hydraulic fracturing in a colton sandstone block we assume that the probability distribution of q is normal anisotropic mean q values correlate with the triaxial stress conditions imposed at the boundaries of the block with higher stress corresponding with less attenuation the q values estimated within time intervals in the direction perpendicular to the hydraulic fracture plane correlate with stress build up at the borehole during fracture propagation and borehole pressure relaxation or drop during fracture closure the standard deviations q reflect the attenuation heterogeneity within the sampled regions an increase in heterogeneity is correlated with pressure build up at the borehole which we interpret to reflect a dynamic stress gradient formed from the hydraulic fracture towards the surroundings

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

the role of fluids during formation and evolution of the southern superior province lithosphere an overview models for fluid flow and hydrothermal alteration for the abitibi greenstone belt are reviewed in the light of lithoprobe results in the region in the abitibi greenstone belt eruption of volcanic sequences over 2750 2700 ma was accompanied by pervasive low temperature hydrothermal alteration at high water rock ratios giving systematic 18o enrichment archean ambient ocean water bottom temperatures were likely ca 30 c and 18o 0 1 chert iron formations precipitated from low temperature hydrothermal discharge base metal massive sulphide deposits formed at or near the seafloor from focussed discharge of high temperature 300 400 c fluids in convective cells sited above subvolcanic intrusions the ore fluids were evolved seawater that had undergone compositional and isotopic evolution by high temperature low water rock exchange with the volcanic pile to nacl 3 7 wt or cacl2 nacl up to 30 wt brines of 18o 0 8 these volcanic associated hydrothermal deposits are associated with greenst