contact metamorphism and depth of emplacement of the manaslu granite central nepal implications for himalayan orogenesis abstract the manaslu massif central nepal provides a well exposed example of a deeply eroded pluton its contact aureole can be followed from the base to the top along medium to low grade mesozonal to anchizonal tethyan metasediments contact metamorphic mineral assemblages and thermobarometric estimations suggest that the granite was emplaced at 18 21 km for the base and 9 13 km for the roof calculated temperatures within the aureole at 550 40 c are compatible with the intrusion temperature of a leucogranitic magma microstructural evidence shows that the temperature remained high 500 c at the base of the massif during and after granite emplacement whereas towards the top of the granite deformation proceeded rapidly at lower temperature heating of the abundant calcareous rocks in the contact aureole released a local co2 rich fluid whereas a h2o and boron rich fluid seems to have pervaded the whole zone this fluid is probably exsolved from the granitic melt during its crystallization the depth of emplacement of the massif has an important implication for the reconstruction of the himalayan geodynamic evolution implying a burial of the tethyan metasediments by a major refolding of the sedimentary cover or more probably by extensive development of the north himalayan nappes towards the south for more than 70 km before granite emplacement i e before the miocene the young age of the granite and its depth of emplacement suggest a rapid tectonic denudation in the order of 1 mm a 1 probably by normal faulting north of the massif during its cooling

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

migration of brines in the basement rocks of the athabasca basin through microfracture networks p patch u deposit canada abstract the unconformity type uranium deposits of the athabasca basin saskatchewan canada are hosted near the unconformity between a middle proterozoic intracratonic sedimentary basin and an archean to paleo proterozoic metamorphic and plutonic basement these deposits which are considered to be the richest u deposits in the world are the result of massive basinal fluid migrations in the basement rocks this study shows that basinal brines have strongly penetrated into the basement not only through faults and major pathways but also by way of dense networks of microfractures which favoured the percolation of fluids down to considerable depths hundred metres below the unconformity and their chemical modification salinity increase by interaction with basement lithologies these processes are one of the major causes of uranium mobility within the basement rocks and the formation of unconformity type mineralization microfracture networks which opened during the basinal brine stage ca 1600 1400 ma are interpreted as sets of mode i cracks corresponding to a specific stage of deformation and occur as fluid inclusion planes after healing the stress field at that stage 1 n130 150 e subvertical partly reopened the earlier microcrack networks 1 n80 110 e and n130 150 e subvertical issued from the trans hudson orogeny late retrograde metamorphic stage ca 1795 1720 ma the circulation of the two types of fluids carbonic and brines occurs thus at two distinct events trans hudson orogeny late retrograde metamorphism for carbonic fluids and maximal burial diagenesis for brines but the same main microfissure geometry was used by the fluids this demonstrates the existence of a similar stress field direction acting before and after the basin formation moreover the brine circulations in the basement acted in a wider volume than the clay rich alteration halo surrounding the u ores generally considered as the main envelope of fluid percolation outside the fault systems the data on the chemistry of the fluids and on the geometry of their migration at various scales emphasise the fundamental role of the basement in the chemical evolution of highly saline brines linked to unconformity related uranium mineralization in the athabasca basin

etude petro structurale des chevauchements ductiles himalayens sur la transversale de l everest makalu nepal oriental tectonic and microtectonic data in eastern nepal indicate that the major observed thrusting 100 km on the main central thrust mct postdates the barrovian metamorphism of the high himalaya gneisses this result at variance with the famous reverse metamorphism model better explains the abnormal metamorphic superpositions in the himalayas and accounts for the lack of high pressure assemblages under the thick allochtonous high himalaya tibetan slab pressure and temperature estimates by microprobe analysis on plagioclase biotite garnet kyanite sillimanite and cordierite assemblages are presented for samples collected along the mct shear zone and across the gneiss slab in the everest makalu area since there is very little difference in pressure at the front of the slab kathmandu klippe and its root these estimates support the existence of important late metamorphic thrusting the decrease of pressure towards the top of the gneiss pile combined with a small temperature increase explains the k

correlation between melting deformation and fluid interaction in the continental crust of the high himalayas langtang valley nepal combined metamorphic stable isotope and structural studies from the high himalayan crystalline sequence in the langtang valley of north central nepal reveal a strong positive correlation between distance above the base of the section the main central thrust the amount of melt material and evidence of prolonged fluid and deformation histories thus suggesting that these processes are strongly interdependent kyanite grade rocks at the base of the section are unmelted and have undergone little syn or post metamorphic internal deformation and little prograde or retrograde fluid rock interaction by contrast sillimanite grade rocks higher in the section contain progressively larger volumes of melt have suffered increasingly complex syn and post metamorphic deformation and show increasing evidence for the presence of fluids although the factors that initiated these processes remain problematic it is suggested that fluid distributions within the langtang section have been passively controlled by the movement of melts these melts may have provided a primary control on deformation during both the magmatic stage and subsequently through the exsolution of exsolved aqueous fluids

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

relations between fluid inclusion trails and regional stress field a tool for fluid chronology an example of an intragranitic uranium ore deposit northwest massif central france abstract episyenites within the uranium ore bearing le bernardan granite northwest french massif central were formed through the dissolution of quartz by hydrothermal solutions these solutions may now be found fossilized as fluid inclusions f i the f i form rectilinear trails along microcracks which trapped the percolating fluids simultaneous study of the orientations of the trails and the chemistry of the inclusions shows that 1 1 the trails may be grouped according to direction each related to successive regional stress fields 2 2 the fluids of each group are compositionally distinct marking different stages of the hydrothermal event this example shows that the geometric relations between secondary f i trails and regional stress fields may be used to establish the chronology of both during a region s geological evolution

fluid record of rock exhumation across the brittle ductile transition during formation of a metamorphic core complex naxos island cyclades greece fluid inclusions trapped in quartz veins hosted by a leucogneiss from the southern part of the naxos metamorphic core complex attic cycladic massif greece were studied to determine the evolution of the fluid record of metamorphic rocks during their exhumation across the ductile brittle transition three sets of quartz veins v m2 v bd v b are distinguished the v m2 and v bd are totally or respectively partially transposed into the foliation of the leucogneiss they formed by hydrofracturing alternating with ductile deformation accommodated by crystal plastic deformation the v b is discordant to the foliation and formed by fracturing during exhumation without subsequent ductile transposition fluids trapped during crystalplastic deformation comprise two very distinct fluid types namely a co2 rich fluid and a high salinity brine that are interpreted to represent immiscible fluids generated from metamorphic reactions and the crystallization of magmas respectively they were initially trapped at approximate to 625 degrees c and 400mpa and then remobilized during subsequent ductile deformation resulting in various degrees of mixing of the two end members with later trapping conditions of approximate to 350 degrees c and 140mpa in contrast brittle microcracks contain aqueous fluids trapped at 250 degrees c and 80mpa all veins display a similar 13c pointing to carbon that was trapped at depth and then preserved in the fluid inclusions throughout the exhumation history in contrast the d signature is marked by a drastic difference between i v m2 and v bd veins that are dominated by carbonic aqueous carbonic and high salinity fluids of metamorphic and magmatic origin characterized by d between 56 parts per thousand and 66 parts per thousand and ii v b veins that are dominated by aqueous fluids of meteoric origin characterized by d between 40 parts per thousand and 46 parts per thousand the retrograde pt pathway implies that the brittle ductile transition separates two structurally chemically and thermally distinct fluid reservoirs namely i the ductile crust into which fluids originating from crystallizing magmas and fluids in equilibrium with metamorphic rocks circulate through a geothermal gradient of 30 degrees c km1 at lithostatic pressure and ii the brittle upper crust through which meteoric fluids percolate through a high geothermal gradient of 55 degrees c km1 at hydrostatic pressure

high co2 content of fluid inclusions in gold mineralisations in the ashanti belt ghana a new category of ore forming fluids a reply fluid inclusions were studied in samples from the ashanti konongo southern cross prestea abosso damang and ayanfuri gold deposits in the ashanti belt ghana primary fluid inclusions in quartz from mineralised veins of the ashanti prestea konongo southern cross and abosso damang deposits contain almost exclusively volatile species the primary setting of the gaseous i e the fluid components co2 ch4 and n2 fluid inclusions in clusters and intragranular trails suggests that they represent the mineralising fluids microthermometric and raman spectroscopic analyses of the inclusions revealed a co2 dominated fluid with variable contents of n2 and traces of ch4 water content of most inclusions is below the detection limits of the respective methods used aqueous inclusions are rare in all samples with the exception of those from the granite hosted ayanfuri mineralisation here inclusions associated with the gold mineralisation contain a low salinity co2 and low salinity 6 eq wt nacl however fluid inclusions in quartz from the gold mineralisations in the ashanti belt point to distinctly different fluid compositions specifically the predominance of co2 and co2 h2o have to be emphasized fluid systems with this unique bulk composition were apparently active over more than 200 km along strike of the ashanti belt fluids rich in co2 may present a hitherto unrecognised new category of ore forming fluids

fluid inclusions in granulite facies metapelites of the hercynian ancient lower crust of the serre calabria southern italy investigations of fluid inclusions in granulitefacies metapelites of southern calabria enable characterization of the fluid composition of these lower crustal rocks and constrain the petrologically deduced retrograde p t path characterized by isothermal uplift prior to isobaric cooling in middle crustal levels fluid inclusions in cordierite garnet and sillimanite have a co2 rich composition inclusions in cordierite rarely contain minor amounts of n2 and h2o and in garnets some co2 ch4 n2 inclusions have been analyzed by raman microprobe quartz reveals the most complex fluid melusion compositions 1 co2 rich 2 co2 ch4 n2 3 ch4 n2 4 h2o mgcl2 cacl2 nacl 5 h2o nacl and 6 h2o co2 the earliest fluid inclusions after peak metamorphism are rich in co2 with minor amounts of n2 and h2o an early co2 h2o n2 fluid composition has been confirmed by detection of co2 h2o and n2 in the channels of the cordierite structure most of the early co2 rich fluid inclusions were modified during the uplift from the lower to the middle crustal level resulting in a density decrease with co2 still dominant the subsequent isobaric cooling led to further modifications of the fluid inclusions high density inclusions around implosion textures or scattered amongst lower density ones must have formed during this cooling episode aqueous inclusions in quartz are mostly formed late and are consistent with trapping during retrograde rehydration

some aspects of the variation with time of katabatic flow over a simple slope features of the variations in katabatic flow along a simple slope in athens greece are examined both observationally and from a simplified theoretical basis when undisturbed periods of established flows are selected it is observed that the velocity and temperature fluctuations reveal characteristics which are in agreement with the theory proposed by fleagle interesting implications of the theory are discussed such as the effects of prescribing a decreasing cooling rate throughout the night or of taking into account the vertical structure of the katabatic layer

fluid inclusion constraints on the kinematics of footwall uplift beneath the brenner line normal fault eastern alps dynamic models of isostatic footwall uplift in response to normal faulting can be divided into those in which uplift is accomplished by flexural failure and those in which uplift occurs via subvertical simple shear each class of model predicts a different incremental strain history that should be recorded in the footwall in the tauern window eastern alps postmylonitic structures in the footwall of the brenner line normal shear zone predominantly consist of closely spaced steep west down and east down microfaults formation of the west down faults before and at greater depths than the east down faults would be consistent with unroofing via subvertical simple shear in contrast formation of the two fault types as a conjugate set would be more indicative of unroofing via elastic processes the field data alone do not provide a sufficient test of the two hypotheses because crosscutting relations are only rarely observed and there is no control on the depth at which the structures formed however both depth and timing constraints on the formation of the late structures can be obtained by correlating the orientations of fluid inclusion lined microfaults with the macroscopic west down and east down faults obtaining density data for the inclusions and correlating these data with previously obtained geochronologic data the results indicate that the west down structures formed at depths of 10 20 km and temperatures 450 c in the mid to late oligocene and that the east down structures formed at 2 to 10 km depth and temperatures of 300 50 c in the mid miocene these data support the hypothesis that a rolling hinge was present in the footwall of the brenner line and that isostatically driven footwall deformation was accomplished predominantly by subvertical simple shear the depths at which west down and east down faulting occurred coupled with the angle of dip of the brenner line yield a minimum lateral displacement on the fault of 15 26 km approximately coeval ductile shearing and brittle faulting at depths of 15 20 km and temperatures in excess of 400 c may reflect local variations in strain rate as the footwall rocks entered the zone of rolling hinge deformation

fluid inclusion evidence for progressive folding during decompression in metasediments of the voltri group western alps italy abstract quartz veins syntectonic to distinct folding events in metasediments from the voltri group ligurian alps were studied in order to compare fluid and structural evolution studied veins vs1 vs2 vs3 pertain to three distinct generations of folds f 1 f 2 f 3 that formed during the retrograde metamorphic evolution two types of fluids characterize the different generations of veins and are represented essentially by aqueo carbonic mixtures of moderate salinity with decreasing densities 1 01 0 41 g cm 3 the chemical evolution is characterised by a progressive decrease of h 2 o from early fluids associated with opening of vs1 and vs2 xco 2 0 08 to fluids related to vs3 formation xco 2 0 3 the close match between the fluids in vs1 and vs2 suggests that the development of two superimposed systems of folds f 1 and f 2 folds occurs under very similar p t conditions during a progressive and continuous deformational event at glaucophanic and or barroisitic metamorphic grade a different evolution is outlined for the formation of vs3 during low greenschist grade successive isochores allow us to define a retrograde decompression path for the voltri group present results indicate that fluid inclusions are powerful markers to constrain the p t t conditions of different folding events

fluid circulation related to deformation in the zabargad gneisses red sea rift abstract a fluid inclusion study in relation to textures has been performed on pan african granulite facies gneisses from zabargad island red sea rift egypt the gneiss samples were collected at a maximum distance of 60 m above the contact with mantle peridotites with which they are co structured by a high t plastic deformation during an isothermal decompression starting from conditions estimated at 35 km depth and 850 c base of the pan african crust a first metasomatism of the crustal section during decompression is represented by co2 fluid inclusions trapped at minimum conditions of 15 km depth and 800 c the co2 fluid inclusion planes are controlled in orientation by the high t plastic flow structures but have been subsequently deformed during medium t plastic deformation in quartz the second metasomatism is represented by solid rich aqueous fluid inclusions which were trapped at minimum p t conditions of 3 7 km depth and 450 c corresponding to a very high thermal gradient they trace the introduction either of seawater or of fluids resulting from leaching of the middle miocene evaporites within the gneisses during their residence at a shallow depth below the seafloor two models are proposed in the literature in order to reconstruct the geodynamic history of zabargad island one brueckner h k elhaddad m a hamelin b hemming s kroner a reisberg l seyler m 1995 a pan african origin and uplift for the gneisses and peridotites of zabargad island red sea a nd sr pb and os isotope study j geophys res 100 22283 22297 suggests that most of the decompression p t path is pan african in age and only the aqueous metasomatism is related to the rifting history of the red sea the second nicolas a boudier f montigny r 1987 structure of zabargad island and early rifting of the red sea j geophys res 92 461 474 boudier f nicolas a ji s kienast j r mevel c 1988 the gneiss of zabargad island deep crust of a rift tectonophysics 150 209 227 supposes the existence of an asthenospheric diapir intrusive through the deep pan african crust leading to a continuous deformation event during early rifting of the red sea although it is impossible to date trapping of fluid inclusions and to know with certainty the origin of the fluids our preference is for the second model but slightly modified the high t decompression path traced by co2 fluid inclusions relayed by solid rich aqueous inclusions traces a continuous process of crustal thinning such a continuous path would assign to a single event the thinning and uplift of the deep crust and uppermost lithosphere to shallow basin bottom during the red sea early rifting in such an interpretative model the northern and central peridotite bodies are representative of the uppermost continental lithosphere and only the southern body could belong to an ascending asthenospheric diapir centred on the southeast of zabargad island

manaslu leucogranite a collision signature of the himalaya a model for its genesis and emplacement the manaslu pluton is one of 10 leucogranites that formed in the overthrusted higher himalaya after the indo eurasian collision field and analytical data indicate that the underlying migmatites of the tibetan slab may be where the leucogranitic melts were generated the himalayan crustal thrusting of a hot slab over a rather cold volcano sedimentary pile le fort 1975a provides the necessary release of fluids these fluids cross the main central thrust mct induce the partial anatexis of the overheated tibetan slab and produce a leucogranitic magma the emplacement of the magma at first is located along the main disharmonic plane above the mct between the infrastructure and the superstructure there it generates a convective hydrothermal system extending very far laterally according to the stratification of permeabilities progressive emplacement of the granite proceeds as the convected fluids including the fluids released by the saturated magma dissolve the mainly calcareous host rocks of tibetan sedimentaries a frozen image of this caving out progression is given by the extensive network of granitic dikes outside the pluton the two quite independant fluid cycles of the generation and of the emplacement were triggered or guided by the tectonics due to collision this two fold model dominated by fluid activity may be of importance for other leucogranites and granites

zanskar shear zone northeast southwest extension within the higher himalayas ladakh india a complete geologic section through the northwestern himalayas is well exposed in ladakh india the collision between the indian shield and the tibetan platform caused large scale intracrustal thrusting and piling up of the himalayan nappes this compressional event was accompanied by prograde regional metamorphism the metamorphism ranges from low grade anchimetamorphism in the indus suture zone in the northeast to upper amphibolite grade in the higher himalaya tectonic unit in the southwest in the zanskar area a well exposed and morphologically prominent shear zone 2 25 to 6 75 km wide can be followed from the northwest to the southeast for at least 80 km in contrast to the main compressional tectonics this shear zone indicates an extensional event within the higher himalaya tectonic unit the zanskar shear zone involves granitic rocks leucogranites of miocene age and various metasediments and in general separates the late precambrian early cambrian sedimentary sequence phe formation from the underlying crystalline basement zanskar crystalline unit a normal sense of shear has been determined by using asymmetric macroscopic and microscopic structures such as pegmatite boudins feldspar augen and crystallographic fabrics the metamorphic isograds are very close within this shear zone as a result of shear deformation a gradual transition from upper amphibolite to lower greenschist facies occurs within 200 m movement in this zone occurred late in the metamorphic history under greenschist or lower metamorphic conditions the minimum horizontal extension and vertical displacement are on the order of 16 and 19 km respectively

structure and tectonics of the himalaya constraints and implications of geophysical data the himalayan range is a product of continental collision between india and eurasia and for several reasons it is a logical place to examine the physical causes and mechanisms of mountain building the exceptionally high mountains and the great length of the range alone single the himalaya out as a major structural feature the convergence rate between india and eurasia of about 50 mm yr 1 minster jordan 1978 requires rapid rates of slip and the occurrence of four major earthquakes with magnitudes in excess of 8 4 in the last 100 years attests to a high level of seismicity and a rapid rate of active deformation e g richter 1958 seeber armbruster 1981 the exposures of high grade metamorphic rocks in the greater himalaya may suggest large vertical transport of lower crustal rocks e g valdiya 1980a b and the occurrences of young postcollision granites imply recent large perturbations of the temperature structure of the range e g lefort 1981 moreover as sediments derived from the himalaya fill the broad ganga basin south of the range the mountain belt simul taneously seems to override the basin e g g d johnson et al 1979 n m johnson et al 1982 as such the processes occurring now and since the collision began in the early tertiary as well as the present structure of the himalayan belt are probably similar to those at different stages of collision and mountain building in other older orogenic belts such as the appalachians the scottish and scandinavian caledonides the alps and

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

stress state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein types high ardenne slate belt germany abstract in the frontal part of the rhenohercynian fold and thrust belt high ardenne slate belt germany two successive types of quartz veins oriented normal and parallel to bedding respectively are interpreted to reflect the early variscan compressional tectonic inversion of the ardenne eifel sedimentary basin fracturing and sealing occurred in lower devonian siliciclastic multilayers under very low grade metamorphic conditions in a brittle upper crust a geometrical and microthermometric analysis of these veins has helped to constrain the kinematic and pressure temperature conditions of both vein types allowing the reconstruction of the stress state evolution in a basin during tectonic inversion it is demonstrated that bedding normal extension veins which developed under low differential stresses and repeatedly opened and sealed crack seal under near lithostatic fluid pressures reflect the latest stage of an extensional stress regime bedding parallel veins which developed at differential stresses that were still low enough to allow the formation of extension veins cross cut the bedding normal veins and preceded the regional fold and cleavage development these veins show a pronounced bedding parallel fabric reflecting bedding normal uplift and bedding parallel shearing under lithostatic to supra lithostatic fluid pressures during the early stages of a compressional stress regime this kinematic history corroborates that fluid overpressures are easy to maintain during compressional tectonic inversion at the onset of orogeny

crystallization conditions and evolution of magmatic fluids in the harney peak granite and associated pegmatites black hills south dakota evidence from fluid inclusions abstract a microthermometric study of inclusions in granites and pegmatites in the proterozoic harney peak granite system identified four types of inclusions type 1 inclusions are mixtures of co2 and h2o and have low salinities on average 3 5 wt nacleq type 2 inclusions are aqueous solutions of variable salinities from 0 to 40 wt nacleq type 3 inclusions are carbonic dominated by co2 with no detectable water and type 4 inclusions consist of 20 to 100 solids with the remaining volume occupied by a co2 h2o fluid many inclusions have a secondary character however a primary character can be unambiguously established in several occurrences of the type 1 inclusions these inclusions were trapped above the solidus and represent the exsolved magmatic fluid the secondary populations of types 1 2 and 3 probably formed as a result of reequilibration and unmixing of the type 1 fluid that progressively changed composition and density with decreasing temperature and pressure and was finally trapped along healed microfractures under subsolidus conditions type 4 inclusions are primary and are interpreted to be trapped fluid bearing complex silicate melts that subsequently solidified or underwent other posttrapping changes it is demonstrated that primary type 1 fluid inclusions that coexist with crystallized melt inclusions in the complex li bearing tin mountain pegmatite were trapped along the two fluid phase boundary in the system co2 h2o nacleq consequently the temperature and pressure conditions of trapping are identical to the bulk homogenization conditions on average 340 c and 2 7 kbar these conditions indicate that this li cs rb p and b rich pegmatite crystallized at some of the lowest known temperatures for a silicate melt in the crust an internally consistent empirical solvus surface in p t xco2 coordinates was generated for the pseudobinary co2 h2o 4 3 wt nacleq pegmatite fluid system distribution coefficients for the major species co2 h2o nacl and ch4 between the immiscible co2 rich and h2o rich fluid phases as a function of pressure and temperature were extracted from data for the two cogenetic fluid inclusions types

hypersaline fluids generated by high grade metamorphism of evaporites fluid inclusion study of uranium occurrences in the western zambian copperbelt in the pan african lufilian belt western zambian copperbelt uranium mineralizations preferentially scattered in kyanite talc micaschists metamorphosed evaporitic sediments or concentrated along transposed quartz veins provide an opportunity to 1 understand the time space relationship between the ore minerals and the deformation of the host rocks 2 identify the different fluid events associated with specific stages of quartz deformation and 3 characterize the ore fluid geochemistry in terms of fluid origin and fluid rock interactions in the u occurrences studied in lolwa and mitukuluku domes region western zambian copperbelt two mineralizing stages are described the first generation of ore fluids 53 59 wt cacl2 13 15 wt nacl n2 h2 in the gas phase of fluid inclusions circulated during the high temperature quartz recrystallization at 500 700 c this temperature is in agreement with the p t conditions recorded during the crustal thickening related to continental collision at ca 530 ma la icpms analyses show the presence of uranium within this fluid with a concentration mode around 20 ppm the second generation of ore fluid 21 32 wt nacl 19 21 wt cacl2 co2 co in the gas phase of fluid inclusions percolated at lower temperature conditions at the brittle ductile transition between 200 and 300 c this temperature could be related to the exhumation of the high grade metamorphic rocks at ca 500 ma the formation of h2 and co is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions finally a late fluid 14 16 wt naclequiv circulated in the brittle domain but seems unrelated to u re mobilization event

fluid inclusions in crack seal veins at dugald river mount isa inlier implications for palaeostress states and deformation conditions during orogenesis abstract an integrated geometrical investigation and microthermometric analysis of fluid inclusion trails in fibrous crack seal veins at dugald river mount isa inlier allowed distinction of two general types of fluid inclusions a co 2 ch 4 rich variety and a h 2 o rich variety at least three stages of fluid percolation are identified to be related to the vein formation trails of pseudosecondary inclusions have a constant orientation relative to the direction of the regional maximum principal shortening direction 3 this relationship allows the trails to be regarded as potential structural markers however trails of secondary inclusions generally show a deviation from the established bulk shortening direction and possibly reflect the overprinting of a later deformation event microthermometric data combined with knowledge of metamorphic reactions suggest that the p t path of crackseal deformation started at about 450 c and 2 8 kbar then crossed 340 c and 1 2 kbar and possibly terminated around 130 c and at near surface pressure corresponding to the regional crustal uplift this study shows the importance of combined geometrical and microthermometric studies of fluid inclusions for understanding the physical conditions of crack seal deformation a common phenomenon in low grade metamorphic terrains

fluid evolution during uplift of the annapurna himal central nepal abstract fluid inclusions from post metamorphic quartz show that there has been considerable co 2 rich fluid flux during uplift of greenschist amphibolite facies rocks along the main central thrust mct maximum fluid co 2 content increased with metamorphic grade of the host rock ranging from 20 30 mole in the greenschist facies to both the north and south of the mct to 70 mole in the amphibolite facies the highest co 2 content is in late stage veins which cross cut uplift related schistosity in the sillimanite zone this contrasts with the syn metamorphic fluid which was probably dominantly aqueous fluid immiscibility occurred in quartz veins near the brittle ductile transition at 280 310 c and 700 300 bar fluid pressure an upper limit of 1600 bar lithostatic pressure was determined from a co 2 rich isochore the high thermal gradient implied by p t data is due to rapid uplift along the mct mct movement ceased in the miocene and the rocks have experienced slower uplift along a lower thermal gradient during this slower uplift ca na brines some with freezing point depression below 20 c have traversed the rock at first the brines mixed with co 2 then brines dominated until diluted by incursion of lowsalinity presumably meteoric water near the surface brines and co 2 may be reaching the surface today in diluted from as numerous warm and ambient springs brines were probably derived from connate fluids in the tibetan carbonate clastic sedimentary succession to the north of the mct co 2 was derived from metamorphosed equivalents of these sediments and perhaps from similar sediments beneath the mct

the gangotri granite garhwal himalaya laccolithic emplacement in an extending collisional belt the gangotri miocene leucogranite is composed of several laccoliths 6 7 km long 1 5 2 km thick which can be divided into two sets of lenses the southern lenses intruded in the lower part of the high himalaya sedimentary cover and the northern lenses intruded in an older porphyritic biotite bearing granite in both cases the magmatic fabric is commonly weak with no dominant stretching direction although a rough e w trend is present in the northern lenses the magnetic fabric is characterized by the fact that drastic changes in the direction in the magnitude of the magnetic parameters or in the fabric type planar or linear may take place over very short distances measurements of preferred orientations in thin sections indicate that the strain regime was largely dominated by a coaxial component for both sets of lenses in agreement with the large dispersion observed in both the field and magnetic lineations the comparison of the granite and host rock structures shows that the leucogranite emplacement dates the onset of the extensional tectonism in the high himalaya range and is not related to a southward directed thrust event associated with the main central thrust this is exemplified by the vertical attitude of the feeder dikes that intrude the metasedimentary rocks beneath die southern lenses the presence of these dikes indicates in turn that magma ascent occurred by fracture propagation the spatial disposition of the southern lenses could have resulted either from the disruption of a single laccolithic intrusion by crustal scale boudinage due to a northern gravity backslide of the top of the tibetan slab or from the intrusion of independent laccoliths the use of the elastic bending theory of pollard and johnson 1973 shows that in both hypotheses the current laccolith sizes are compatible with a laccolithic mode of magma emplacement however neither the density contrast between the magma and its enclosing rocks nor the lithological boundary between the tibetan slab and the overlying tibetan metasedimentary series controlled the level of magma emplacement rather flat lying collapse structures which intersected the upward propagating magma dikes are the most likely causes of magma arrest such a mechanism was favored by the schist rich lithology of the metasedimentary host rocks in addition field relationships indicate that the melt supply through the dike system was a continuous rather than pulsed process existing numerical treatments on the rates of magma transport through fractures show that in such a case the laccoliths could have been built in less than 100 years this short time of emplacement the small size of the laccoliths and their peripheral disposition relative to the badrinath granite suggest that the gangotri lenses may represent the initial stage of pluton accretion in the high himalaya which ultimately gave rise to a much larger massif such as the manaslu granite

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

deformation of leucogranites of the crystalline main central sheet in southern tibet china abstract towards the top of the main central sheet in southern tibet china leucogranites intrude metamorphic rocks related to rocks of the main central thrust in the himalayas our study shows that the leucogranites suffered a northward shear deformation the significance of this event is discussed in terms of gravity driven decollement of the 10 000 m thick tethyan sedimentary pile over its crystalline basement

thermobarometric constraints on the thermal history of the main central thrust zone and tibetan slab eastern nepal himalaya the main central thrust mct south of mt everest in eastern nepal is a 3 to 5km thick shear zone separating chlorite bearing schist in the lower plate from sillimanite bearing migmatitic gneiss in the overlying tibetan slab the metamorphic grade increases through the mct zone toward structurally higher levels previous workers have suggested that either post or synmetamorphic thrust movement has caused this inversion of metamorphic isograds in an effort to quantify the increase in grade and to constrain proposed structural relations between metamorphism and slip on the fault four well calibrated thermobarometers were applied to pelitic samples collected along two cross strike transects through the mct zone and tibetan slab results show an increase in apparent temperature up section in the mct zone from 778 k to 990 k and a decrease in temperature to 850 k in the lower tibetan slab which is consistent with synmetamorphic thrust movement a trend in calculated pressures across this section is less well defined but on average decreases up section with a gradient of 28mpa km resembling a lithostatic gradient pressure temperature paths for zoned garnets from samples within the mct zone modelled using the gibbs method show a significant decrease in temperature and a slight decrease in pressure from core to rim which might be expected for upper plate rocks during synmetamorphic thrust movement samples from the uppermost tibetan slab yield higher temperatures and pressures than those from the lower tibetan slab which may be evidence for later resetting of thermobarometers by intrusion of the large amounts of leucogranite at that structural level

hydrogen and oxygen isotope variations in the high himalaya peraluminous manaslu leucogranite evidence for heterogeneous sedimentary source abstract the manaslu granite belongs to the high himalaya leucogranitic belt which was produced by melting of the crust during postcollisional thrusting d and 18o values have been determined for whole rock and coexisting minerals from the 8 km thick manaslu massif and its 50 km long dyke sheet its country rocks and the formation 1 f1 paragneisses which are the source of the granite for the granite dmusc range from 70 to 85 and 18o w r from 10 9 to 12 8 h and o isotope fractionations among minerals are consistent with high temperature equilibrium and for oxygen closed system evolution a few samples coming mainly from the dyke swarm have very low d values down to 188 and biotite muscovite h isotope fractionations indicative of disequilibrium the d h ratios of associated magmatic tourmaline are essentially unmodified from the distribution of d values in the granite and its country rocks circulation of very low deuterium meteoric hydrothermal waters was extremely localized because these waters are depleted in deuterium by up to 50 relative to modern meteoric waters the manaslu area was either at an altitude substantially higher than that of today 2500 6000 m for the analyzed samples or a mountain chain once existed to the south the f1 gneisses have 18oquartz between 12 and 14 3 which confirms that the granite was generated from f1 but d values are 20 higher than in the granite such a difference can be a result of degassing of the magma and or introduction of fluid in the melting zone infiltration of low d fluid 90 into the hot but dry f1 probably triggered partial melting these fluids could have come from the dehydration of the midlands sediments which are separated from the overlying f1 by the main central thrust the correlations among 18o 87 sr 86 sr 20 ma and nd values in both f1 and the granite indicate that the variations of these isotopic ratios in the manaslu are inherited from those in f1 at the time of melting in turn these ratios in f1 are related to the proportion of quartz and phyllosilicates for the isotopic ratios of nd and o and to the quantity of radiogenic sr generated within the sediment which is a function of age and rb content amount of phyllosilicate some other himalayan leucogranites require either other crustal source rocks or the 18o and 87 sr 86 sr ratios of f1 vary along the himalaya

deformation by solution deposition and re equilibration of fluid inclusions in crystals depending on temperature internal pressure and stress abstract changes of shape and density of fluid inclusions in crystals were demonstrated when these crystals were subjected to temperatures and internal pressures greater than those of their growth experimental relations have been established between the rate of length change of the inclusions and the different parameters of the experiment nature of the crystal temperature and internal pressure state of stress on the crystal geometric characters of the inclusion length width orientation of the inclusion with respect to the optical axes of host mineral it is essentially the effect of the variation of surface energy with the curvature around the cavity which causes a mass transfer of the host crystal by diffusion through the fluid under pressure the rate of length change is limited by the rate of dissolution at the median part of elongate inclusions this change of shape and density is known to occur in naturally deformed crystals an example of such a behaviour is given which allowed us to use the inclusions as markers of the conditions of temperature and pressure subsequent to the growth of crystal

primary to re equilibrated fluids and geochemical signatures for the evolution of the nagthat siliciclastics in the tons valley lesser himalaya india abstract medium to coarse grained neo proterozoic nagthat siliciclastic rocks form a part of the krol formation in the lesser himalayan geotectonic zone fluid inclusion and geochemical studies have been carried out on the nagthat siliciclastics from the tons valley to determine their provenance during the proterozoic and their recrystallisation during maximum burial to uplift fluid inclusion studies have been carried out on detrital recrystallised quartz grains and quartz overgrowths major and trace element analyses of the siliciclastics the relationships of sio 2 with various trace elements and the association of various trace elements with mineral species suggest a granitic source for these siliciclastics primary q1 aqueous brine inclusions and q3 h 2 o co 2 fluid with 0 9 gm cm 3 co 2 density in detrital quartz grains characterised the protolith of the sandstone as granite or metamorphic rocks h 2 o nacl fluids participated in the cementation history temperatures of quartz overgrowth from 198 to 232 c show the effect of maximum burial the re equilibration of the primary fluid due to elevated internal pressure confining pressure is evident from features like c shaped cavities stretching of the inclusions their migration decrepitation clusters etc during recrystallisation these inclusions were equilibrated at 187 and 235 c in a restricted fluid of aqueous moderately saline composition the observed inclusion morphology is attributed to a decrease in external pressure related to isothermal decompression uplift

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

deformation of granitoid plutons in the dongshan area southeast china constraints on the physical conditions and timing of movement along the changle nanao shear zone the ne trending changle nanao shear zone has affected several granitoid plutons in the dongshan area southeast china microstructures in the granitoids range from undeformed to solid state lineations and foliation migmatitic textures are common in some units microprobe analysis of total al has been carried out on hornblende rims in four samples of gneiss from various points across the shear zone confining pressures calculated fall into range of 4 2 4 9 kb the average pressure 4 5 kb suggests that the shear zone may have reached at least 16 km depth fluid inclusion studies referred from the correspondent p t isochores indicate that the temperature of ductile deformation in the shear zone was 740 c observations on intrusive relations between the various granitic phases and their relative degrees of deformation suggest that emplacement of the different magma phases may be closely related in time and to movement along the changle nanao shear zone zircon from one deformed pluton yielded a crystallization u pb age of 121 5 2 8 ma field and microstructural data suggest the dated pluton is syntectonic which constrains the upper age of high temperature deformation in the orthogneiss along the changle nanao shear zone at that locality

microfracturing and regional stress field a study of the preferred orientations of fluid inclusion planes in a granite from the massif central france abstract a study of the deformation of a granitic massif indicates a relationship between palaeostress fields and the geometry of microfractures as defined by fluid inclusion trails that is healed microfractures a statistical study of the distribution of the trails leads to the following conclusions trails exhibit several distinct preferred orientations on the scale of a grain which may be observed in many samples the orientations of the trails are similar to those of micro and mesoscale fractures in the granite and the dominant trail direction is parallel to the main direction of regional shortening thus fluid inclusion trails are mode i cracks which can be used as excellent markers of palaeostress fields

thermal evolution of the greater himalaya garhwal india the hanging wall of the main central thrust mct in garhwal india roughly 79 n 80 e 30 n 31 n exhibits an inverted metamorphic gradient sillimanite potassium feldspar assemblages near the top of the hanging wall or greater himalayan sequence are underlain by kyanite grade rocks near the fault textural relationships in pelitic samples from the alaknanda and dhauli river valleys indicate that the inversion is the product of two distinct metamorphic events an early harrovian event m1 which affected the entire greater himalayan sequence and a later buchan event m2 the effects of which are most obvious in the upper part of the sequence rim thermobarometry garnet inclusion thermobarometry and thermodynamic modeling of garnet zoning reveal that the basal portions of the metamorphic sequence experienced peak m1 conditions of 900 k and 960 mpa roughly 36 km depth before following an erosion controlled uplift path e g england and richardson 1977 m2 metamorphic temperatures in the upper part of the sequence also exceeded 900 k but maximum pressures 317 523 mpa indicate paleodepths of only 12 19 km calculated pressure temperature paths indicate that m2 was characterized by temperature increases of 80 k and roughly 5 km of tectonic burial we attribute m1 to tectonic burial of the greater himalayan sequence during the early stages of india eurasia collision we believe that the uplift and cooling path of the sequence was interrupted in late oligocene miocene time by a second burial and heating event m2 related to thrust imbrications in southern tibet this burial was coincident with the generation of leucogranites which are abundant near the top of the greater himalayan sequence but are virtually absent near the mct field relations do not constrain whether the leucogranites were derived from some presently unexposed portion of the greater himalayan sequence and were injected at their present structural level or were melted in situ if the granites were injected then they may have provided some of the heat necessary for m2 metamorphism although our data suggest no direct relationship between the main central thrust as mapped in garhwal and metamorphism in the greater himalaya anatectic melting of an unexposed portion of the greater himalayan sequence could have been associated with movement along a blind thrust with characteristics similar to the mapped mct in central nepal cf le fort 1981 if the granites were produced by in situ m2 melting then we must appeal to a heat source within the upper part of the greater himalayan sequence such as locally high concentrations of heat producing elements cf pinet and jaupart 1987

a fluid inclusion study of blueschist facies lithologies from the indus suture zone ladakh india implications for the exhumation of the subduction related sapi shergol ophiolitic melange abstract the best occurrence of blueschist facies lithologies in himalaya is that of the shergol ophiolitic melange along the indus suture zone in ladakh region of north western india these lithologies are characterized by well preserved lawsonite glaucophane garnet quartz assemblages this paper presents for the first time the results of a detailed fluid inclusion study on these lithologies in order to understand the fluid p t evolution and its tectonic implications the blueschist rocks from shergol ophiolitic melange record metamorphic peak conditions at 19 kbar 470 c several types of fluid inclusions are trapped in quartz and garnet most of them being two phase at room temperature three types of fluid inclusions have been recognised basing on microtextures and fluid composition type i are primary two phase carbonic aqueous fluid inclusions v co2 l h2o type ii are two phase l h2o v h2o aqueous fluid inclusions either primary type iia or secondary type iib type iii are re equilibrated fluid inclusions in the type i primary carbonic aqueous inclusions h 2 o is strongly predominant with respect to co 2 the homogenization temperature of co 2 range from 7 to 2 c the clathrate melting temperature in such inclusions varies in between 7 1 and 8 6 c type ii two phase aqueous fluid inclusions show a wide range of salinity from 7 8 14 wt nacl eq type iia to 1 65 6 37 wt nacl eq type iib with accuracy 0 4 wt nacl eq type i and type iia primary fluid inclusions are hosted in peak minerals garnet and quartz included in garnet therefore they were likely entrapped at or near to peak p t conditions the dominantly aqueous fluid of both type i and type iia inclusions was most likely produced through metamorphic devolatilization reactions occurring in the subducting slab despite their primary nature the isochores of type i and type iia inclusions do not intersect the peak metamorphic conditions of the blueschist mineral assemblage suggesting that these inclusions stretched or re equilibrated during nearly isothermal decompression from 19 kbar to 3 kbar or less at t 290 c this conclusion is further supported by their large variability in shapes and sizes which range from irregular inclusions c arc shaped hook shape and satellite type this decompression stage was followed by nearly isobaric cooling testified by the occurrence of dendritic networks of decrepitated and imploded fluid inclusions

the geochemistry of germanium in deep sea cherts nineteen chert samples from a continuous core of the dsdp leg 17 hole 167 were analysed for ge in addition we analysed five samples from other cores the ages range between late jurassic and late eocene the concentration of ge changes with age from 0 87 ppm in the oldest samples to 0 23 ppm in the youngest equivalent to a gesi decrease from 0 72 10 6 to 0 19 10 6 the decrease in gesi is well correlated with the 87sr86sr ratio in sea water of the relevant age the interpretation of this trend may reflect a different levels of gesi in sea water as a result of a different ratio between hydrothermal and riverine input b a diagenetic trend in siliceous sediments c recording by radiolaria a transition between a radiolaria dominated ocean with relatively high gesi ratios in sea water and diatom domination or d a combination of the above

tectonically driven fluid flow and gold mineralisation in active collisional orogenic belts comparison between new zealand and western himalaya abstract hydrothermal activity and mesothermal styled gold mineralisation occurs near the main topographic divide of most active or young collisional mountain belts the southern alps of new zealand is used in this study as a model for the mineralising processes the collisional tectonics results in a two sided wedge shaped orogen into which rock is transported horizontally upper crustal rocks pass through the orogen and leave the orogen by erosion whereas lower crustal rocks are deformed into the mountain roots high relief drives meteoric water flow to near the brittle ductile transition lower to upper greenschist facies metamorphic reactions driven by deformation at the crustal decollement and in the root release water rich fluids that rise through the orogen intimate chemical interaction between fluid and rock results in dissolution and later precipitation of gold arsenic and sulphur fluid flow and mineralisation in the topographic divide region is facilitated by a network of steeply dipping faults and associated rock damage zones where oblique strike slip faults intersect the thrust faults that strike subparallel to the main mountain range the nanga parbat massif of the western himalaya is an example of an active collisional zone which hosts hydrothermal activity but no gold mineralisation the lack of gold mineralisation is due to the following factors co 2 dominated rising metamorphic fluid in dehydrated amphibolite granulite facies metamorphic rocks does not dissolve gold and arsenic hot up to 400 c meteoric water confined to fractures in the gneiss limits dissolution of gold and arsenic low density of hot water dry steam and low reduced sulphur content of fluid restrict solubility of gold and arsenic absence of fracture networks in the core of the massif and the small volumes of circulating fluid limit metal concentration and lack of reactive rock compositions limits chemically mediated metal deposition

exhumation history of a shear zone constrained by microstructural and fluid inclusion techniques an example from the satluj valley nw himalaya india abstract the regional structures rock microstructures and fluid inclusion trail patterns have been employed to determine the evolution of the jakhri thrust zone jtz the jtz is a break back thrust cutting across the folded lesser himalayan crystalline nappe and is best exposed in the kulu rampur window zone of the nw himalaya the microstructures in the jtz suggest sw directed ductile shearing and a progressively decreasing finite strain away from the thrust in the footwall the quartz recrystallization microstructures and presence of chlorite in the thrust zone indicate lower greenschist facies p t conditions during deformation the microstructures and fluid inclusion trails secondary show analogous patterns suggesting that the latter would have formed by the healing of microfractures during shearing in the footwall the microthermic studies on these fluid inclusions suggest that the co2 h2o inclusions have been emplaced and reequilibrated during peak deformation whereas the h2o nacl inclusions reequilibrated during footwall exhumation the density and salinity of fluid inclusions were also reset during the same exhumation the isochores of co2 h2o and h2o nacl inclusions in the greenschist facies suggest an isothermal exhumation path from a depth of 15 to 17 km assuming lithostatic pressure conditions these results in the jtz emphasize the utility of fluid inclusions in tectonic studies

petrology and fluid inclusions of a quartz kyanite segregation in the main thrust zone of the himalayas fluid inclusion data are compared to p t estimates from coexisting minerals in a quartz kyanite segregation and in the surrounding garnet bearing micaschist mineral assemblages notably plagioclase garnet kyanite quartz record a retromorphic evolution from 550 600 c 7 8 kb to 450 500 c 3 4 kb the density of the early fluid in the segregation h2o 9 to 15 mole co2 is compatible with this last set of values it suggests a continuity of the evolution in the metamorphic rock and in the segregation and an early separation of the during postmetamorphic uplift

estimation of volume changes by comparative chemical analyses in heterogeneously deformed rocks folds with mass transfer abstract this paper presents a method for calculating the volume change between the various sectors of the same heterogeneously deformed layer fold shear zone by comparing the chemical composition of deformed sectors with that of a reference sector the principle consists of considering some minerals as being insoluble illite chlorite and passively concentrated in deformed zones because of the loss of more soluble minerals quartz calcite dolomite by pressure solution simple observations can be used to test the validity of the assumptions required to calculate volume change in the analysis of a slaty matrix around a ptygmatic fold a map of values is drawn and these values are shown to be compatible with the general strain pattern for several limb hinge pairs of straight limbed folds the relations between volume change elongation parallel to limb layering l l o and the angle between limb and hinge are determined the influence of various parameters such as temperature pressure initial composition and structure of the rock on these relations is also pointed out

structural evolution of orogenic wedges interplay between erosion and weak decollements orogenic wedges commonly display an inner wedge where crystalline units have been exhumed and an outer wedge formed by imbricated sedimentary units detached from the basement analog experiments have shown that similar structures can emerge naturally in the presence of weak decollements due to the interplay between erosion and deformation in this study we further investigate this hypothesis using two dimensional visco elasto plastic numerical models our experiments assume a basal and an intermediate decollement within the wedge experiments with a frictional strength of the basal decollement lower or equal to that of the intermediate decollement show a structural evolution of fold and thrust belts dominated by out of sequence thrusting conversely when the intermediate decollement is weaker than the basal decollement distinct outer and inner wedges are formed this process leads to episodic migration of midcrustal ramps tectonic underplating and antiformal stacking facilitated by erosion comparison between our models and the himalayan wedge suggests a low effective friction 0 10 which is probably due to dynamic weakening during large m8 himalayan earthquakes the deeper decollement along which the lower plate thrusts beneath the high himalaya must be a thermally activated ductile shear zone with an apparent friction of 0 18 fold and thrust belts worldwide exhibit various architectures in which different decollement levels might be activated thus our study provides a framework to help assess under which conditions a variety of structures observed in orogenic systems can arise

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

linked fluid and tectonic evolution in the high himalaya mountains nepal fluid inclusions were studied in a quartz lens from the structurally highest unit of the himalaya mountains in nepal from a textural geometrical chemical and isotopic point of view six types of fluid inclusions were distinguished one of these types consists of annular inclusions this shape is attributed to a confining pressure increase in a non isotropic stress field two successive stress fields were deduced from the orientation of the inclusion planes relative to the schistosity the bulk composition of the fluid was dominated by co2 84 mol and h2o the composition remained constant during the whole history of the sample indicating that it was buffered by the carbonaceous host rock and or that one single fluid was reworked in situ by decrepitation stable isotope of fluids and minerals indicate 1 that fluids were buffered by surrounding rocks for o and c and 2 that at least two types of water metamorphic and meteoric were involved finally a p t t e path is proposed for the sample taking into account the southward thrusting along the main central thrust the northward tectonic denudation of the himalaya mountains inducing tectonic burying below the annapurna range and lastly rapid uplift

the use of fluid inclusions to constrain fault zone pressure temperature and kinematic history an example from the alpi apuane italy the alpi apuane is a tectonic window that exposes ductilely deformed greenschist facies metaigneous and metasedimentary rocks beneath relatively unmetamorphosed brittlely deformed sedimentary rocks of the tuscan nappe the brecciated fault zone the window fault separating the two tectonic units was originally described as a simple thrust fault but has recently been interpreted to have been reactivated as a later extensional detachment although evidence for extensional faulting is seen above and below the window fault the amount of extensional displacement along this fault is unclear fluid inclusions from veins cementing the fault breccia were used to estimate the pressures and temperatures during the last fault movement minimum pressure estimates obtained from these inclusions range from 105 to 240 mpa pressure corrected trapping temperatures for these fluids range from about 300 to 345 c these pressures and temperatures indicate that the fault was last active at a depth of about 10 km assuming a geothermal gradient at the time of 31 c km 1 this rules out complete extensional unroofing of the alpi apuane by movement along the window fault fluid salinities increase abruptly from the footwall into the fault zone this pattern suggests that fluids rose from the footwall entered the fault zone and were channeled within it leaching salt from the overlying evaporite the lack of quartz veins above the fault zone indicates that these fluids did not circulate into the overlying tuscan nappe

the metamorphism in the central himalaya all along the himalayan chain an axis of crystalline rocks has been preserved made of the higher himalaya crystalline and the crystalline nappes of the lesser himalaya the salient points of the metamorphism as deduced from data collected in central himalaya central nepal and kumaun are 1 the higher himalaya crystalline also called the tibetan slab displays a polymetamorphic history with a first stage of barrovian type overprinted by a lower pressure and or higher temperature type metamorphism the metamorphism is due to quick and quasi adiabatic uplift of the tibetan slab by transport along an mct ramp accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover the resulting metamorphic pattern is an apparent diachronic inverse zonation with the sillimanite zone above the kyanite zone 2 conversely the famous inverted zonation of the lesser himalaya is basically a primary pattern acquired during a one stage prograde metamorphism its origin must be related to the thrusting along the mct with heat supplied from the overlying hot tibetan slab as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust 3 thermal equilibrium is reached between units above and below the mct far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the tibetan slab during the second metamorphic stage but closer to the mct front the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the tibetan slab

the himalayan main central thrust pile and its quartz rich tectonites in central nepal as a consequence of the india asia collision a deeply rooted crustal slice has been moved southwards over the northern boundary of the indian plate at the present level of observation the main central thrust pile a rock pile of several kilometers thickness is affected by shear deformation which imprinted a flat foliation and a constant n s trending lineation these tectonites were deformed under a wide range of metamorphic conditions grading from lower greenschists up to the sillimanite field the m c t shear zone is studied from the view point of the quartz rich rocks over 100 samples helped to define a microstructural zonation roughly parallel to the thermal one 35 samples particularly rich in quartz have been used for the preferred orientation study of their c axes and a few of them for their a axes strong lattice orientations when undisturbed by mainly secondary recrystallization attest to large plastic strains in quartz the c axes are mostly distributed along unequally populated crossed girdles which may evolve into an inclined single girdle the a axes concentrate perpendicular to the more populated girdle concerning quartz the following is suggested 1 1 the deformation has a dominant shear component responsible for the dominant stretching lineation it could be simple shear in case of inclined single girdles 2 2 one set of a axes line up parallel to the shear direction slip on various planes in the a direction may be an important deformation mechanism 3 3 asymmetry in the lattice preferred orientations could be used to predict the sense of shear for the himalayan thrusting in more than 80 of cases

the p v t x f o2 evolution of h2o co2 ch4 bearing fluid in a wolframite vein reconstruction from fluid inclusion studies aqueous carbonaceous and later pure aqueous fluid inclusions in quartz from a ferberite fe 95mn 05 wo4 vein within the low grade metamorphic aureole of the borne granite french massif central have been studied by microthermometry and raman spectrometry the bulk v x properties of the aqueous carbonaceous inclusions have been derived using the equation of state of heyenet al 1982 for the low temperature co2 ch4 system a p t path has been proposed for their trapping using the equations of state of jacobs and kerrick 1981a for the h2o co2 ch4 system two main episodes were reconstructed for the history of the aqueous carbonaceous fluid 1 primary h2o co2 ch4 vapourrich inclusions in quartz indicated the early circulation of a low density fluid 65 mole h2o 34 mole co2 1 mole ch4 and traces of n2 d 0 35 gcm 3 at around 550 50 c and 700 100 bar fluid cooled approximately isobarically to 450 400 c and was progressively diluted by h2o with a concomitant increase in density the fo2 of the h2oco2 ch4 fluid estimated from the equilibrium co2 2h2o ch4 2o2 first ranged from 10 22 to 10 27 bar close to the q f m buffer within analytical errors these values were consistent with the presence of graphite in equilibrium with the fluid 2 a drop in pco2 and therefore a drop in fo2 was recorded by the secondary liquid rich inclusions in quartz the inclusions formed at and below 400 c were composed of h2o and ch4 only and fo2 at that stage was below that fixed by the graphite fluid equilibrium this second episode in the fluid rock system could be explained by the drop of temperature below the blocking temperature of the graphite fluid equilibrium according to this interpretation the blocking of the graphite fluid equilibrium occurred at t 370 c and probably at 400 c on account of the pressure correction mass spectrometric data show that ferberite contains h2o co2 and ch4 in fluid inclusions which lie in the gap of the v x properties of the aqueouscarbonaceous fluid in quartz deposition of ferberite probably occurred at around 400 c the previously inferred blocking temperature resulting from either the drop in pco2 the drop fo2 and or the related ph increase it is concluded that the existence of a blocking temperature for the graphite fluid chemical equilibrium may be a critical factor for maintaining a stable fluid pressure gradient in geothermal systems occurring under greenschist facies conditions in graphite bearing rocks

styles of footwall uplift along the simplon and brenner normal fault systems central and eastern alps the simplon and brenner extensional shear zones of the central and eastern alps respectively are low angle detachments that accommodated orogen parallel extension and unroofed midcrustal rocks in their footwalls an integrated field and fluid inclusion study of the simplon low angle shear zone reveals several postmylonitic structure types that are consistent with passage of a complex rolling hinge through the simplon footwall including synthetic west down and antithetic east down semibrittle and brittle structures and strike slip extensional and contractional structures all of which are consistent with southwest directed extension along the main detachment zone fluid inclusion analysis of kinematically referenced inclusion arrays indicates that west down semibrittle and brittle shears were active at conditions above 300 450 c and 14 26 km antithetic deformation along brittle faults occurred at much shallower conditions of 300 c and 3 7 km deformation along these structures accommodated footwall uplift by a subvertical simple shear mechanism in the southern part of the simplon region these results are strikingly similar to those from the brenner shear zone in contrast with the brenner region however the northern simplon footwall shows strike slip dominated postmylonitic deformation related to slip along the rhone line the footwalls of these detachment systems define a unique class of core complex characterized by the development of a midcrustal synthetic lower hinge that acts to steepen the detachment system and accommodate footwall uplift by a subvertical simple shear mechanism both systems have poorly developed upper hinges that flatten the middle to upper crustal ramp by only a few degrees of dip which is in contrast to detachment fault systems of the western united states where evidence of a deep hinge is rarely observed and the upper hinge acts to deactivate the flattened updip part of the detachment our results emphasize the role of tectonic setting buoyancy forces and synkinematic fluids in controlling the observed style and mechanisms of large magnitude extension during collision between continental masses

experimental decrepitation and re equilibration of fluid inclusions in synthetic quartz abstract strong discrepancies between densities of the fluids trapped in fluid inclusions f i and p tp couples deduced from other geological considerations are common so it was decided to test experimentally the possible f i re equilibrations when bringing the host crystal in p tp conditions different from trapping conditions runs were conducted on synthetic quartz in a gas apparatus and in a griggs solid medium apparatus the following modifications of the f i were observed 1 1 drastic shape changes of the primary f i and appearance of clusters or trails of small secondary inclusions sometimes related to a crack 2 2 lowering of the fluid densities such a re equilibration is a decrepitation phenomenon first hydraulic fracturing then sealing of the cracks with appearance of secondary inclusions when using the gas apparatus the new measured densities are in very good accordance with the nominal p tp conditions when using the solid medium apparatus the new densities are surprisingly low relative to the nominal p t conditions probably due to a strongly anisotropic stress state in the apparatus

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

high density co2 inclusions in the colorado front range a fluid density in an inclusion is commonly observed to be too low for the p t estimates for the postulated time of trapping and is generally attributed to a fluid loss during the uplift process it is more difficult to explain a fluid density which is too high in the 1700 m y front range migmatites such high densities occur in some of co2 inclusions which were deduced to have formed during the migmatization episode the peak p t estimates for migmatization in the front range are 4 6 kb and 650 700 c in sillimanite field but pressures required to form the most dense inclusions are 7 6 kb in kyanite field the high density is not likely to be a relic of a higher pressure condition earlier than the main migmatization episode for the following reasons a no kyanite or any other relic high pressure phase has been found in the precambrian front range b the high density inclusions are rare in zones with least signs of deformation and melting paleosomes and quartz inclusions within feldspar grains which instead contain relatively undisturbed early inclusions c high density inclusions with th 30 c are associated with heavily altered plagioclase caused by hydrothermal activity which was a late event in leucosome formation further there is evidence for post entrapment change s in density an intragranular trail in quartz contains co2 inclusions that exhibit almost the whole range in th 40 to 24 c as displayed by the entire population of the early co2 inclusions 66 to 30 c the density of an inclusion in the trail is not related to inclusion size but to the position of the inclusion relative to apparent micro shear zones crossing the co2 trail a change to a higher density a smaller volume could have resulted from an initially isobaric cooling path which intersects co2 isochores with increasingly higher densities additional excess pressure may have resulted from overthrusting however because high density inclusions occur selectively in the zones in which plagioclase shows alteration indicating a high a h 2 o and because there is a correlation between shear zones and high density inclusions it is postulated that local hydrolytic weakening of quartz was necessary for the decrease of inclusion volume which occurred during deformation the localized deformation may also result in an excess pressure however the introduction of a small amount of h2o into these inclusions as a possible cause of high density inclusions cannot be ruled out