the composition and role of the fluid in migmatites a fluid inclusion study of the front range rocks monophase negative crystal shaped co2 inclusions occurring isolated in small clusters or in well healed intragranular fractures are common in the leucosome quartz of the 1700m y old migmatites from the east central colorado front range they are however quite rare in the mafic selvage and paleosome host rock quartz the mode of occurrence suggests that these are the earliest inclusions to form in addition to the difference in abundance of the inclusions there is a difference in co2 density distribution between migmatitic zones the temperatures of homogenization for the leucosome inclusions range and l c from 67 c to 20 c with two maxima at 21 c while those for the paleosome and selvage inclusions are 37 c to 20 c with a single maximum at 5 c these differences between the migmatitic zones which occur on the scale of a few centimeters suggest that the formation of these inclusions was related to the migmatization process the densities corresponding to the th maxima are appropriate for the p t conditions for migmatization estimated from the mineral geobarometer geothermometer these inclusions must contain nearly pure co2 as their final melting temperatures 56 5 to 57 2 c are very close to that of the triple point of co2 their composition also was confirmed by raman spectroscopic analyses

geology and geochemistry of archaean granites in the kalgoorlie region of the eastern goldfields western australia a syn collisional tectonic setting abstract granites in the kalgoorlie region of the archaean yilgarn craton are predominantly biotite granodiorite and monzogranite with some hornblende bearing varieties granites are divided on the basis of field relationships petrography and chemical composition into five supersuites an older supersuite containing four suites pre dates regional folding and four supersuites post date regional folding the potassic composition of the mainly silica rich granites 68 sio2 suggest that the most appropriate source for the majority of supersuites is continental crust with a composition in the range tonalite to granodiorite most supersuites evolved by fractional crystallization mainly of biotite and plagioclase some suites contain synplutonic dykes and microgranite xenoliths that crystallized from enriched mantle derived magmas there was only limited and local chemical interaction between granite and mantle derived magmas geometric and temporal relationships between regional structures and granites indicate that the granites were emplaced during a major orogenic event however s type granites which are widespread in some modern syn collision settings are absent in the kalgoorlie region the predominance of high fo2 i type granites in the study area probably reflects the absence of large graphite bearing metasedimentary accumulations in the lower crustal source regions the distribution of suites and supersuites implies a common source region beneath the kalgoorlie and gindalbie granite greenstone terranes suggesting that they shared a common geological history dating back to late greenstone deposition

retrograde methane dominated fluid inclusions from high temperature granulites of rogaland southwestern norway non aqueous inclusions in the high grade 800 1 000c 4kbar metamorphic rogaland region southwestern norway consist of mixtures of co sub 2 ch sub 4 n sub 2 in particular the fluid inclusions in quartz veins in migmatites are characterized by high ch sub 4 concentrations and they were re equilibrated at temperatures below 500c during isobaric cooling observations by microthermometry demonstrated several complicated sequences of phase transitions including partial and metastable homogenization at lower temperature than melting and s l or s v transitions the phase behavior reflects a wide variation in composition and molar volume fluid compositions were measured by raman microspectrometry by this method also small amounts of graphite have been detected in co sub 2 ch sub 4 inclusions the instantaneous formation of graphite in a co sub 2 ch sub 4 inclusion by induction of the argon laser beam has been observed which points to the metastability of the co sub 2 ch sub 4 mixture the calculated densities of the observed fluid mixtures are relatively low necessitating a revision of the earlier interpretation of these inclusions as containing pure high density fluids inclusions in quartz trapped after the peak of metamorphism record fluid heterogeneity which may present evidence for fluid deficient metamorphism during the retrograde m2 m3 metamorphism

a fluid inclusion and isotopic study of an intrusion related gold deposit irgd setting in the 380 ma south mountain batholith nova scotia canada evidence for multiple fluid reservoirs a set of sheeted quartz veins cutting 380 ma monzogranite at sandwich point nova scotia canada provide an opportunity to address issues regarding fluid reservoirs and genesis of intrusion related gold deposits the quartz veins locally with arsenopyrite 5 and elevated au bi sb cu zn occur within the reduced south mountain batholith which also has other zones of anomalous gold enrichment the host granite intruded p 3 5 kbars lower paleozoic metaturbiditic rocks of the meguma supergroup well known for orogenic vein gold mineralization relevant field observations include the following 1 the granite contains pegmatite segregations and is cut by aplitic dykes and zones 1 2 m of spaced fracture cleavage 2 sheeted veins containing coarse comb textured quartz extend into a pegmatite zone 3 arsenopyrite bearing greisens dominated by f rich muscovite occur adjacent the quartz veins and 4 vein and greisen formation is consistent with riedel shear geometry although these features suggest a magmatic origin for the vein forming fluids geochemical studies indicate a more complex origin vein quartz contains two types of aqueous fluid inclusion assemblages fia type 1 is a low salinity 3 wt equivalent nacl with minor co2 2 mol and has th 280 340 c in contrast type 2 is a high salinity 20 25 wt equivalent nacl ca rich fluid with th 160 200 c pressure corrected fluid inclusion data reflect expulsion of a magmatic fluid near the granite solidus 650 c that cooled and mixed with a lower temperature 400 c wall rock equilibrated ca rich fluid evidence for fluid unmixing an important process in some intrusion related gold deposit settings is lacking stable isotopic o d s analyses for quartz muscovite and arsenopyrite samples from vein and greisens indicate the following 1 18oqtz 11 7 to 17 8 and 18omusc 10 7 to 11 2 2 dmusc 44 to 54 and 3 34saspy 7 8 to 10 3 these data are interpreted in conjunction with fluid inclusion data to reflect contamination of a magmatic derived fluid delta 18 hbox o rm h 2 rm o 10 by an external fluid delta 18 hbox o rm h 2 rm o 15 the latter having equilibrated with the surrounding metasedimentary rocks the 34s data are inconsistent with a direct igneous source based on other studies for the host intrusion delta 18 hbox o rm h 2 rm o 5 and are instead consistent with an external reservoir for sulphur based on 34sh2s data for the surrounding metasedimentary rocks divergent fluid reservoirs are also supported by analyses of pb isotopes for pegmatitic k feldspar and vein arsenopyrite collectively the data indicate that the vein and greisen forming fluids had a complex origin and reflect both magmatic and non magmatic reservoirs thus although the geological setting suggests a magmatic origin the geochemical data indicate involvement of multiple reservoirs these results suggest multiple reservoirs for this intrusion related gold deposit setting and caution against interpreting the genesis of intrusion related gold deposit mineralization in somewhat analogous settings based on a limited geochemical data set

interpretation of fluid inclusions in quartz deformed by weak ductile shearing reconstruction of differential stress magnitudes and pre deformation fluid properties abstract a well developed theoretical framework is available in which paleofluid properties such as chemical composition and density can be reconstructed from fluid inclusions in minerals that have undergone no ductile deformation the present study extends this framework to encompass fluid inclusions hosted by quartz that has undergone weak ductile deformation following fluid entrapment recent experiments have shown that such deformation causes inclusions to become dismembered into clusters of irregularly shaped relict inclusions surrounded by planar arrays of tiny new formed neonate inclusions comparison of the experimental samples with a naturally sheared quartz vein from grimsel pass aar massif central alps switzerland reveals striking similarities this strong concordance justifies applying the experimentally derived rules of fluid inclusion behaviour to nature thus planar arrays of dismembered inclusions defining cleavage planes in quartz may be taken as diagnostic of small amounts of intracrystalline strain deformed inclusions preserve their pre deformation concentration ratios of gases to electrolytes but their h2o contents typically have changed morphologically intact inclusions in contrast preserve the pre deformation composition and density of their originally trapped fluid the orientation of the maximum principal compressive stress 1 at the time of shear deformation can be derived from the pole to the cleavage plane within which the dismembered inclusions are aligned finally the density of neonate inclusions is commensurate with the pressure value of 1 at the temperature and time of deformation this last rule offers a means to estimate magnitudes of shear stresses from fluid inclusion studies application of this new paleopiezometer approach to the grimsel vein yields a differential stress 1 3 of 300 mpa at 390 30 c during late miocene nnw sse orogenic shortening and regional uplift of the aar massif this differential stress resulted in strain hardening of the quartz at very low total strain 5 while nearby shear zones were accommodating significant displacements further implementation of these experimentally derived rules should provide new insight into processes of fluid rock interaction in the ductile regime within the earth s crust

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

a new empirical calibration of the quartz c axis fabric opening angle deformation thermometer abstract the opening angle of quartz c axis fabrics oa is strongly temperature dependent and has proven to be a powerful deformation thermometer for natural metamorphic rocks previous considerations of empirical data have identified a linear correlation between oa and temperature between 250 and 650 c and no correlation above 650 c however possible effects of pressure have not been investigated we expanded the data set of oa versus temperature including data from rocks deformed over 300 1050 c and 2 5 15 kbar disregarding possible effects of pressure the oa temperature relationship can be described by two linear correlations for the intervals 250 650 c and 650 1050 c t c 6 9 o a degrees 48 250 c t 650 c and o a 87 t c 4 6 o a degrees 258 650 c t 1050 c and o a 87 the change on the curve slope of the oa temperature relationship correlates approximately to the low to high quartz transition and to changes in the dynamic recrystallization mechanism from subgrain rotation to grain boundary migration the available data suggest that pressure has a secondary effect accompanying the major temperature dependence of oa which is particularly important for temperatures above 650 c where the correlation between oa and temperature is less pronounced for fixed pressures the oa has logarithmic relationships with temperature over the range 250 1050 c the following thermometer equation is formulated from a multiple regression t c 410 44 ln oa degrees 14 22 p kbar 1272 an uncertainty of 50 c is inherited from the petrological temperature estimates of the natural samples the data suggest the gradual increasing importance of prism c slip relative to slip in quartz with rising temperature under conditions of average geological strain rate and water weakening prism c slip dominates for deformation above 700 c

pressure temperature and evolution of fluid compositions of al 2 sio 5 bearing rocks mica creek b c in light of fluid inclusion data and mineral equilibria metamorphosed pelitic rocks from mica creek british columbia contain sillimanite kyanite with minor fibrolite and andalusite bearing quartz pods mineral equilibria were used to infer peak p t conditions and fluid compositions in equilibrium with the solid phases fluid inclusions in three schist samples appear to be good indicators of conditions affecting those rocks during and after peak metamorphic conditions in samples from two localities fluid inclusions from schist and quartz rich segregations have densities appropriate to the peak metamorphic conditions the observed compositions for these fluids low salinity with 12 mole dissolved co2 agree with calculated text x text h text 2 text o values of 0 84 to 0 85 based upon paragonite quartz albite al2sio5 equilibria the fluids unmixed as the schists were uplifted and cooled fluid inclusions trapped during this stage outline a solvus in the co2 h2o nacl system a later influx of fluids containing ch4 and n2 accompanied formation of andalusite bearing plagioclaserich segregations the restricted association of andalusite bearing pods and low density fluids suggest a localized but pervasive fluid influx during uplift preservation of high density fluid inclusions during uplift and erosion coupled with evidence for unmixing of h2o and co2 rich fluids on the solvus provide constraints on the p t uplift path

modification of fluid inclusions in quartz by deviatoric stress iii influence of principal stresses on inclusion density and orientation extraction of useful geochemical petrologic and structural information from deformed fluid inclusions is still a challenge in rocks displaying moderate plastic strain in order to better understand the inclusion modifications induced by deviatoric stresses six deformation experiments were performed with a griggs piston cylinder apparatus natural nacl h2o inclusions in an oriented quartz crystal were subjected to differential stresses of 250 470 mpa at 700 900 c and at 700 1 000 mpa confining pressure independently of the strain rate and of the crystallographic orientation of the quartz the inclusions became dismembered and flattened within a crystallographic cleavage plane subperpendicular to 1 the neonate newly formed inclusions that result from dismemberment have densities that tend towards equilibrium with pfluid 1 at tshearing these results permit ambiguities in earlier deformation experiments on co2 h2o nacl to be resolved the results of the two studies converge indicating that density changes in neonate inclusions are promoted by high differential stresses long periods at high p and high t and fluid compositions that maximize quartz solubility neonates spawned from large precursor inclusions show greater changes in density that those spawned from small precursors these findings support the proposal that deformed fluid inclusions can serve as monitors of both the orientation and magnitude of deviatoric stresses during low strain ductile deformation of quartz bearing rocks

mobility and h2o loss from fluid inclusions in natural quartz crystals petrographic observations on quartz crystals from the mole granite australia and other localities shed new light on the mechanisms of post entrapment modification of fluid inclusions these modifications include migration away from pseudosecondary trails changes in fluid salinity and density shape distortion and the formation of sweat haloes around strongly deformed inclusions increases in fluid salinity which usually are associated with inclusion migration indicate water losses of up to 50 however la icp ms analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged ratios of major and trace element cations with the exception of li which seems to be incorporated into the crystal lattice during migration despite the fact that all these modifications are closely related to deformation processes they occur not only in mechanically deformed quartz but also in free standing crystals in the latter samples stress has been generated internally as a result of brazil twinned growth and compositional zonation these observations and their interpretation leads to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other samples

fluid inclusions in hydrated granulite facies rocks southern marginal zone of the limpopo belt south africa abstract the archean granulite terrane of the southern marginal zone of the limpopo belt south africa was rapidly uplifted and thrust over a low grade granite greenstone terrane van reenen et al 1987 during cooling the granulites were rehydrated in a zone parallel to the contact with the low grade terrane a sharply defined retrograde orthoamphibole isograd at conditions of 6 kbar 625 650 c x co 2 0 8 van reenen 1986 was established we made microthermometric analyses of over 1000 fluid inclusions in four samples representing a traverse across the isograd with the goal of characterizing the hydrating fluid we found patterns of composition and density of inclusions to be similar to those reported from other granulite facies terranes a few apparently pure co 2 inclusions with densities appropriate for the p t conditions many co 2 inclusions with lower densities and aqueous inclusions of variable salinity and containing no detectable co 2 the results suggest that the hydrating fluid may be represented by secondary co 2 rich fluid inclusions because of their small size most between 5 and 10 m and equant shapes h 2 o contents of the co 2 rich inclusions of up to 0 3 mole fraction may not be detectable a model for hydration of the granulites includes infiltration of a fluid into the partially cooled overthrust granulites with a temperature gradient decreasing towards the underthrust greenstone terrane the fluid was probably generated by devolatilization of the greenstones as they were heated by the overthrust granulites the high co 2 content of the calculated fluid and of the fluid inclusions suggests the hydrating fluid was co 2 rich at the p t conditions of the retrograde isograd

postmetamorphic unroofing history deduced from petrology fluid inclusions thermochronometry and thermal modeling an example from southwestern new england nonlinear unroofing rates from 10 to 2 and h 2 o rich fluid inclusions require nearly isothermal decompression followed by more isobaric cooling from these conditions comparison of this observed path to those generated by thermal models suggests that decompression was characterized by initial rapid upward en bloc velocity 1 cm yr of brief duration followed by much slower unroofing rates 0 3 mm yr published geochronologic ages in this region constrain the rapid uplift to the middle devonian and uplift slowed dramatically by the end of the devonian this differential uplift has major implications for interpretation of devonian igneous activity and sedimentation in southwestern new england

new constraints on the genesis and geodynamic setting of the wulong gold deposit liaodong peninsula northeast china evidence from geology geochemistry fluid inclusions and c h o s pb isotopes the wulong lode gold deposit is located in the liaoning province northeast part of north china craton gold ore bodies are mainly hosted in the late jurassic granite and structurally controlled by

evidence for externally derived vein forming and mineralising fluids an example from the magdala gold mine stawell victoria australia abstract mineralogical and microfabric studies of the magdala gold deposit together with isotopic and fluid inclusion studies have shown that the mineralising fluid is externally derived the host rocks to the quartz veins do not possess any significant amounts of gold whereas the quartz veins can contain 7 g t gold the walls to the quartz veins possess alteration haloes in the form of stilpnomelane porphyroblasts attesting to the fact that the fluid in the veins was out of equilibrium with the host rocks the distribution of alteration haloes that occur parallel to the quartz vein margins necessitates that a subvertical fluid gradient be more or less constant during the deposition process in order to produce the observed architecture of the alteration haloes quartz lodes possess 18 o values that range from 15 8 to 17 3 per mil while associated host rocks range between 9 7 to 12 per mil in the metabasalts and 10 2 to 14 1 per mil in the volcanogenic and metasedimentary rocks the dissimilarity of 18 o values between host rocks and quartz veins suggests that there has been a high fluid influx in the veins implying external buffering four types of fluid inclusions were distinguished on the basis of spatial arrangement and composition using the laser raman spectroscopy method the salinity of the fluid inclusions range from 0 7 to 8 4 wt nacl equivalent suggesting that gold was deposited due to the influx of different external fluids the association of pyrite arsenopyrite pyrrhotite with gold and with pges suggests that these fluids have a lower crustal origin and may have originated from the upper mantle and mixed with fluids derived from deep seated metasediments

origin and evolution of ore fluid and gold deposition processes at the giant taishang gold deposit jiaodong peninsula eastern china abstract the early cretaceous taishang gold deposit is the largest deposit in the linglong goldfield jiaodong peninsula with a pre mining endowment of 326 t of gold it is hosted in the 165 150 ma linglong biotite granite and controlled by the nee to ne trending potouqing fault near the northern end of the regional zhaoping fault system hydrothermal alteration is well developed in the footwall of the potouqing fault and is characterized by a narrow zone of sericitization followed by a wider zone of silicification and an even wider zone of potassic alteration the main orebodies no i orebody comprise disseminated and stockwork veinlet systems although about 5 of the resources are in larger quartz veins no ii orebody four stages have been identified for both styles of mineralization on the basis of cross cutting relationships and mineralogical and textural characteristics pyrite quartz sericite stage 1 quartz pyrite stage 2 quartz pyrite base metal sulfide stage 3 and quartz carbonate stage 4 gold was mainly deposited in stages 2 and 3 with minor amounts in stage 1 petrographical microthermometric and laser raman spectroscopic studies on fluid inclusion assemblages in quartz and calcite from the four stages reveal three types of primary fluid inclusions type 1 h 2 o rich aqueous carbonic type 2 co 2 rich aqueous carbonic and rare type 3 carbonic inclusions stage 1 quartz primary inclusions are only type 1 inclusions with an estimated composition of 88 h 2 o 10 co 2 4 5 wt nacl equiv and 0 5 ch 4 with trapping at 336 c and 1 7 kbars the gold rich stages 2 and 3 from both orebodies typically contain primary fluid inclusion assemblages with both type 1 and 2 inclusions which show similar phase transition temperatures and were trapped between 246 and 294 c the stage 4 quartz and calcite contain only primary type 1 inclusions which are estimated to have a composition of 93 h 2 o 6 0 co 2 3 6 wt nacl equiv and trace amount of ch 4 and were trapped at temperatures of 236 c the 34 s values of hydrothermal pyrite from the four stages have a narrow range from 4 5 to 8 0 and are within the ranges for whole rock sulfides from the archean jiaodong group and magmatic pyrite from mesozoic granitoid and intermediate basic dikes the 18 o values of hydrothermal quartz range mainly from 10 9 to 12 5 and remain constant for all four stages calculated fluid 18 o values are 1 3 10 0 the d water values calculated from hydrothermal sericite range from 60 to 45 considering the fluid inclusion compositions 18 o and d compositions of ore forming fluids and regional geological events the most likely ultimate potential fluid and metal reservoirs would be the paleo pacific oceanic slab and its overlying sediments which were thrust below the high grade metamorphic rocks of the jiaodong peninsula the initial ore forming fluids were medium high temperature co 2 rich and low salinity h 2 o co 2 nacl ch 4 homogeneous fluids over the duration of the hydrothermal system the fluid remained fairly consistent in p t x although becoming slightly more water rich during final post ore activity fluid immiscibility occurred during stages 2 and 3 ore deposition at pressures that fluctuated strongly from 1700 to 580 bars during hydrofracturing the hs 2 ion was the most probable gold transporting complex at taishang wall rock sulfidation and episodic pressure drops with associated fluid unmixing and other chemical changes were the two main mechanisms of ore deposition

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

tectono metamorphic evolution of the karakoram terrane constrained from p t t fluid history of garnet bearing amphibolites from trans himalaya ladakh india abstract this study presents new data sets on the petrological fluid inclusion and u pb zircon geochronological aspects of the garnet bearing amphibolites from the eastern karakorum pangong tso ladakh to delineate the p t t fluid evolution and its tectonic implications the calculated phase equilibria in the model system nckfmashto reveal that the peak metamorphism occurred at 8 5 9 5 kbar 630 655 c and retrograde metamorphism crossed a stage at 5 5 5 7 kbar 620 630 c monophase primary and secondary carbonic and carbonic aqueous fluid inclusions occur in garnet and quartz trapping of the primary inclusion occurred at pressures lower than the estimated peak p t conditions 5 8 6 1 kbar 629 638 c indicative of partially re equilibrated fluid inclusions during exhumation the primary inclusions were original as carbonic aqueous fluid derived from prograde decarbonation of the amphibolite s protolith or adjacent carbonate rich rocks and h2o leached out during deformation leaving a pure co2 fluid u pb dating of zircons yielded two age groups i at 128 to 131 ma interpreted as the age of detrital zircons of sedimentary derivation and constrain the maximum depositional age of the sedimentary protolith at 131 ma and ii at 114 0 38 ma is interpreted as the age of peak metamorphism remarkably similar to the metamorphic age of the surrounding metapelites this metamorphic stage corresponds to the well known cretaceous phase of crustal thickening and heating along the active continental margin of south asia

raman spectroscopic characterization of h2o in co2 rich fluid inclusions in granulite facies metamorphic rocks abstract water h2o has been identified during raman analyses at 150 200 c of fluid inclusions from granulites that were previously thought to contain pure co2 at room temperature h2o in a co2 rich fluid inclusion forms an optically unresolvable liquid wetting the inclusion walls during heating the h2o phase evaporates into the co2 phase to produce a homogeneous h2o co2 fluid throughout the inclusion volume and the h2o raman peak at 3640 cm 1 is clearly resolvable at elevated temperatures to test and confirm the method synthetic h2o co2 fi of known composition 87 5 mol and 95 mol co2 were also analyzed previously studied granulite samples from the adirondack mountains usa and from the kerala khondalite belt sittampundi complex and sevitturangampatti india were tested for the presence of h2o in co2 rich fluid inclusions traces of h2o were found in co2 rich fluid inclusions in quartz crystals from the adirondacks and from the kerala khondalite belt h2o was not detected in co2 rich secondary fluid inclusions in garnet from the sittampundi complex and from sevitturangampatti rather hydrogarnet was detected along the walls of inclusions in garnet as evidenced by a peak at 3661 cm 1 the hydrogarnet is interpreted to be a step daughter phase that formed by reaction of the h2o in the fluid inclusion with the garnet host during retrogression these observations confirm the presence of an h2o bearing co2 rich fluid at some time during granulite petrogenesis but do not resolve the question of whether these co2 rich fluids were trapped at peak metamorphic conditions or during retrogression or whether the fluid inclusions have reequilibrated following entrapment

oxygen and hydrogen isotopic ratios of water in precipitation beyond paleothermometry paleoclimatologists face a dilemma no sedimentary proxy is a pure recorder of quantitative climate information yet climate modelers and policy makers increasingly seek quantitative comparisons between instrumentally documented possibly anthropogenic climate changes and those produced naturally in the past in the second edition of his influential book bradley 1999 p 6 discussed the calibration of proxy records to learn past climate changes calibration involves using modern climatic records and proxy materials to understand how and to what extent proxy materials are climate dependent it is assumed that the modern relationships observed have operated unchanged throughout the period of interest the principle of uniformitarianism in other words one relates the characteristics of sediment to climate at different places for one time or at a place for short times and then uses that relation plus characteristics of older sediments to estimate the climatic conditions that produced those sedimentary characteristics bradley 1999 then extensively discussed the difficulties in applying this methodology in a complex world with imperfect recorders nonetheless the goal of using calibrated proxies for quantitative as well as qualitative paleoclimatic reconstruction is clear a prominent recent use of calibrated paleoclimatic data is the assessment of whether the probably anthropogenic warming of the latter 20th century moved beyond the band of natural variability of the prevailing climate bradley 2000 combined recent instrumental records with several longer proxy based reconstructions of surface temperature including that of mann et al 1999 based on this composite data set bradley 2000 argued that temperatures in the late 20th century were unique in the context of the entire millennium the proxy records were primarily based on tree ring data but included isotopic and major element geochemistry of corals and occurrence of melt layers and isotopic ratios of water in ice cores however broecker 2001 questioned the basis for the reconstruction of

are stable isotopic trends in amphibolite to granulite facies transitions metamorphic or diagenetic an answer for the arendal area bamble sector southeastern norway from mid proterozoic carbon bearing rocks the isotopic 3 i3 c and 3 18 0 compositions of primary marbles and secondary veins calcites and primary fahlbands and metapelites and secondary veins graphites sampled across the am phibolite to granulite facies transition in the bamble sector southeast ern norway have been investigated the primary calcites display a regional trend in a 3 i3c 3i80 plot which is the reverse of the expected trend the granulite grade primary calcites essentially preserved most of their initial sedimentary compositions whereas the amphibolite grade calcites have increasingly lower 3 i3 c values the 3 18 0 composi tions of amphibolite grade primary calcites and of some vein tlpes appear to be buffered by the o reservoir of the country rock the 3 1 c of graphite of different types is specific for a certain lithology but not spatially related to the metamorphic zoning reaction progress calculations and rayleigh fractionation model ling prove that prograde metamorphic decarbonation reactions alone cannot be held responsible for the isotopic trend in the marbles the reversed isotopic trend in the marbles themselves combined with the lack of any trend in the primary graphites is not compatible with pervasive flushing with a homogeneous mantle derived co2 rich fluid at granulite facies metamorphism the marble trend and the constant 3 i3 c composition of j rimary graphite throughout the metamorphic zoning are best explamed by low grade processes that did affect the stable isotopic compositions of the marbles but left the graphites unaffected the processes may even occur under diagenetic conditions later amphibolite granulite facies metamorphism preserved the trend despite the production of calcsilicates subsequent retrograde hydro thermal action produced graphite quartz veins and several types of calcite veins without resetting stable isotope systematics on a regional scale

on the origin of co2 rich fluid inclusions in migmatites nearly pure co2 fluid inclusions are abundant in migmatites although h2o rich fluids are predicted from the phase equilibria processes which may play a role in this observation include 1 the effects of decompression on melt 2 generation of a co2 bearing volatile phase by the reaction graphite quartz biotite plagioclase melt orthopyroxene co2 rich vapour 3 selective leakage of h2o from co2 h2o inclusions when the pressure in the inclusion exceeds the confining pressure during decompression and 4 enrichment of grain boundary vapour in co2 by subsolidus retrograde hydration reactions

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

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

post granulite facies fluid infiltration in the adirondack mountains granulite facies lithologies from the adirondack mountains of new york contain alteration assemblages composed dominantly of calcite chlorite sericite these assemblages document fluid infiltration at middle to upper crustal levels cathodoluminescence of samples from the marcy anorthosite massif indicates that the late fluid infiltration is more widespread than initially indicated by transmitted light petrography alone samples that appear unaltered in transmitted light show extensive anastomosing veins of calcite 0 05 mm wide along grain boundaries in crosscutting fractures and along mineral cleavages the presence of the retrograde calcite documents paleopermeability in crystalline rocks and is related to the formation of high density co sub 2 rich fluid inclusions recognition of this process has important implications for studies of granulite genesis and the geophysical properties of the crust

development of sigmoidal en echelon microfractures in beryl and the role of strain localization evidenced by fluid inclusions abstract a combined fluid inclusion and microstructural study was carried out in beryl crystals from the san cayetano nb ta bearing pegmatite san luis argentina primary aqueous carbonic fluids t0 were subsequently re trapped during shearing resulting in en echelon microfractures the more brittle behaviour of beryl compared to quartz makes this mineral more suitable for the preservation of fluid inclusions and microstructures the primary inclusions t0 are preserved in strain free domains whereas the pseudo secondary t1 to t3 type inclusions occur in domains showing intracrystalline deformation co2 was relatively immobile or reacted to form carbonate in early t1 type inclusions whereas h2o preferentially migrated along microfractures and was trapped as t2 and t3 type inclusions short intragranular trails of fluid inclusions representing en echelon healed microfractures resulted from progressive strain localization contrary to previous proposals this new model implies the progressive thickness reduction of intracrystalline micro shear zones besides hydrolytic weakening linked to dislocation glide is the most likely mechanism to explain the evolution of fluid inclusions with intracrystalline deformation enhancing anisotropic diffusion this study highlights the potential of combined fluid inclusion and microstructural studies in order to understand the interaction between fluid activity and deformation in this way valuable insights can be provided into the progressive development of overprinted fabrics and low to medium temperature deformation mechanisms of minerals

fluid inclusions in rocks from the amphibolite facies gneiss to charnockite progression in southern karnataka india direct evidence concerning the fluids of granulite metamorphism fluid inclusion studies of rocks from the late archaean amphibolite facies to granulite facies transition zone of southern india provide support for the hypothesis that co2 rich h2o poor fluids were a major factor in the origin of the high grade terrain charnockites closely associated leucogranites and quartzo feldspathic veins contain vast numbers of large co2 rich inclusions in planar arrays in quartz and feldspar whereas amphibole bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed facies quarries contain no large fluid inclusions inclusions in the northernmost incipient charnockites as at kabbal karnataka occasionally contain about 25 mol of immiscible h2o lining cavity walls whereas inclusions from the charnockite massif terrane farther south do not have visibile h2o microthermometry of co2 inclusions shows that miscible ch4 and n2 must be small probably less than 10mol combined densities of co2 increase steadily from north to south across the transitional terrane entrapment pressures calculated from the co2 equation of state range from 5 kbar in the north to 7 5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750 c in quantitative agreement with mineralogic geobarometry this agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions calculations on the stability of the charnockite assemblage biotite orthopyroxene k feldspar quartz show that an associated fluid phase must have less than 0 35 h2o activity at the inferred p and t conditions which agrees with the petrographic observations high tio2 content of biotite stabilizes it to lower h2o activities and the steady increase of biotite tio2 southward in the area suggests progressive decrease of ah2o with increasing grade oxygen fugacities calculated from orthopyroxene magnetite quartz are considerably higher than the graphite co2 o2 buffer which explains the absence of graphite in the charnockites the present study quantifies the nature of the vapours in the southern india granulite metamorphism it remains to be determined whether co2 flushing of the crust can by itself create large terranes of largeion lithophile depleted granulites or whether removal of h2o bearing anatectic melts is essential

genesis and mobility of the h2o co2 fluid phase during regional greenschist and epidote amphibolite facies metamorphism a petrological and stable isotope study in the scottish dalradian during high pressure low temperature greenschist and epidote amphibolite facies metamorphism in dalradian rocks of the sw scottish highlands mineral assemblages in metabasites and calcareous metasediments were dominantly controlled by infiltration of hydrous fluids consequently mineral assemblages capable of buffering the fluid phase composition were rare equilibrium prograde h 2 o co 2 fluids usually contained less or much less than about 1 2 mol co 2 three fluid infiltration events are recognized during prograde greenschist facies metamorphism metabasic sills were infiltrated by large volumes of co 2 bearing hydrous fluid carbon isotope studies indicate that the co 2 was locally derived by widespread oxidation of graphite or other organic carbon in adjacent metasediments this may have occurred under approximately lower greenschist facies conditions as a result of mixing of fluids of varying f o 2 initiated by thermal expansion of water during heating decompression and consequent hydraulic fracturing in the epidote amphibole facies garnet zone dehydration reactions in metabasites generated large quantities of water which removed carbonate from metabasites on a regional scale and infiltrated calcareous metasediments to produce assemblages containing grossular diopside k feldspar amphibole clinozoisite and sphene a late retrograde infiltration of co 2 bearing hydrous fluid under lower greenschist facies conditions generated assemblages containing k feldspar chlorite rutile dolomite in calcareous rocks and albite prophyroblast schists in zones of intense secondary deformation large scale infiltration of fluid into greenschist facies metadolerite sills was intimately related to and possibly controlled by penetrative deformation and in the absence of a penetrative deformation grain boundary diffusion by itself was an ineffectual mechanism of fluid transport

mechanical re equilibration of fluid inclusions in san carlos olivine by power law creep fluid inclusions in san carlos olivine stretch via plastic mechanisms when heat treated at 1400 c and 0 1 mpa in controlled f o 2 atmospheres for several days measurable changes in both inclusion dimensions and fluid densities occur densities decrease from 1 0 to 0 7 g cc stretching is fastest along 100 and slower along 001 and 010 the dislocation microstructure around the inclusions suggests that creep mechanisms operate uncertainties in the experimental determinations of stretching rates result from optical resolution limits errors inherent in measuring homogenization temperatures uncertainties in the fluid equation of state and changes in fluid chemistry during the heat treatment inclusion stretching by dislocation creep can be treated using a model developed for hot isostatic pressing in this model we assume spherical symmetry of plastic flow that the material yields by steady state power law creep and that the parameters for the constitutive law and fluid equation of state are known stretching rates are predicted to depend on the difference between the fluid pressure and the external pressure the temperature the constitutive law governing power law creep and geometry predicted stretching rates show fair but not exact agreement with experimentally measured rates the amount of stretching predicted by the model is in rough agreement with estimates based on dislocation microstructures around natural inclusions if xenolith ascent rates are of the order of 1 cm s or faster

the interaction of migrating grain boundaries and fluid inclusions in naturally deformed quartz a case study of a folded and partly recrystallized quartz vein from the hunsruck slate germany abstract we studied the microstructure of a folded and partly recrystallized quartz vein from the hunsruck slates in germany focusing on the morphology and distribution of fluid inclusions in the old and new grains and along the different types of grain boundaries blocky vein quartz grains show undulose extinction and develop subgrains new grains form by subgrain rotation and grain boundary migration with a bimodal size distribution the old deformed grains contain numerous complex h2o co2 graphite inclusions with significant differences in fluid inclusion setting along subgrain boundaries the new grains have a lower content of h2o rich inclusions than the old grains and do not contain graphite and there is a significant difference in volume and density of fluid inclusions between the large and small new grains grain boundaries between old and new grains are irregular containing similar fluid inclusions as the old grains but no enrichment in graphite while grain boundaries between new grains are smooth and can be inclusion free or contain arrays of fluid inclusions we interpret these structures to have formed by a series of complex interactions between grain boundaries migrating at different velocity and the fluid inclusions differences in mobility and grain boundary velocity can result in different variations of drag and drop interaction while chemical differences lead to phase separation during grain boundary fluid interaction migration of grain boundaries into the old grains was accompanied by significant redistribution of fluids and graphite along the grain boundary together with oxidation of graphitic inclusions to co2

the gounkoto au deposit west africa constraints on ore genesis and volatile sources from petrological fluid inclusion and stable isotope data the loulo gounkoto complex in the kedougou kenieba inlier hosts three multi million ounce orogenic gold deposits situated along the senegal mali shear zone this west malian gold belt represents the largest west african orogenic gold district outside ghana the gounkoto deposit is hosted to the south of the gara and yalea gold mines in the kofi series metasedimentary rocks the ore body is structurally controlled and is characterised by sodic and phyllic alteration as and fe rich ore assemblages with abundant magnetite and overall enrichment in fe as cu au ag w ni co ree minor te pb se cd fluid inclusion analysis indicates that the deposit formed at p t conditions of approximately 1 4 kbar and 340 c and that two end member fluids were involved in mineralisation 1 a moderate temperature 315 340 c low salinity 10 wt nacl equiv low density 1 g cm 3 h2o co2 nacl h2s n2 ch4 fluid 2 a high temperature up to 445 c hypersaline 40 wt nacl equiv high density 1 3 g cm 3 h2o co2 nacl fecl2 fluid partial mixing of these fluids within the jog zone at gounkoto enhanced phase separation in the aqueo carbonic fluid and acted as a precipitation mechanism for au these findings demonstrate the widespread if heterogeneously distributed nature of fluid mixing as an ore forming process in the loulo gounkoto complex operating over at least a 30 km strike length of the shear zone stable isotope analyses of ore components at gounkoto indicate a dominant metamorphic source for h2o h2s and co2 and by extension au it thus can be reasoned that both the aqueo carbonic and the hypersaline fluid at gounkoto are of metamorphic origin and that the high levels of salinity in the brine are likely derived from evaporite dissolution

fluid immiscibility in natural processes use and misuse of fluid inclusion data abstract many occurrences of fluid immiscibility in natural geologic systems have been reported recently most often from fluid inclusion studies however the interpretation of fluid inclusion data in terms of immiscibility sometimes suffers from ambiguity of the vocabulary insufficient knowledge of the immiscibility constraints and insufficient knowledge of the topology in the tpx space of natural fluid systems for such reasons some authors have been misled to erroneous interpretations the term chemical immiscibility is unambiguously redefined as a multiphase multicomponent equilibrium the consequences of this definition are directly derived from the phase rule and concern the possible equations that relate the various parameters temperature pressure volumes compositions to each other these equations already put constraints on the topology of the phase equilibria in fluid systems a particular expression of the phase rule is proposed which takes into account the multiphase constant bulk volume constant bulk composition constraints in fluid inclusions the consequences of such an expression are of major importance in fluid inclusion studies the phase relations of some simple systems that approximate quite efficiently the natural complex fluids are then detailed h2o nacl co2 ch4 h2o co2 h2o co2 nacl the effects of these topologies and of the supplementary constraints constant bulk composition and constant bulk volume assumed for fluid inclusions isopleth isochoric systems are discussed

a comparison of jiaojia and linglong type gold deposit ore forming fluids do they differ abstract the jiaodong peninsula contains the most important concentration of gold deposits in china which can be divided into jiaojia type and linglong type deposits based on mineralization style the former is characterized by disseminated and stockwork style mineralization hosted in first order regional faults with relatively larger tonnages and lower gold grades the latter is characterized by massive auriferous quartz veins commonly hosted in subsidiary second or third order faults with smaller tonnage but higher grade orebodies despite these differences both groups of deposits have the same alteration assemblages mineral paragenesis element concentrations and ore forming ages the mainly jiaojia type luoshan gold deposit and the mainly linglong type fushan gold deposit are characterized by h o s pb isotope data that indicate the ore forming fluids have a dominantly metamorphic source the fluids were derived during the yanshanian orogenic event and were most likely associated with dehydration and decarbonization processes near the top of the subducting paleo pacific plate the linglong type ores have relatively lighter calculated 18 o compositions 3 9 to 2 3 than the jiaojia type ores 0 3 8 0 possibly because of a greater degree of mixing with meteoric water petrographic cathodoluminescence microthermometric and laser raman spectroscopic analyses of fluid inclusion assemblages in quartz from the two types of ores indicate fluids were similar in both cases characterized by medium high homogenization temperatures 211 393 c significant co 2 15 mol minor ch 4 18 in the carbonic phase and low salinity 11 2 wt nacl eq the linglong type ores however have a wider range of co 2 and ch 4 concentration and salinity than the jiaojia type ores fluid immiscibility occurred in main ore stage of both ore types with the trapping conditions of 77 185 mpa and 284 328 c although the unmixing is more intense and widespread in the linglong type ores both fluid wallrock interaction and fluid immiscibility are important gold deposition processes in the two types but immiscibility is more important in the linglong type ores and that has led to the typical higher gold grade in general there is little geochemical differences between the ore forming fluids for jiaojia and linglong type gold deposits both jiaojia and linglong type ores can exist in a single deposit and form in the same metallogenic event the linglong type ores developed as more massive veins because of their location in zones of more extensive extension and they lack significant post ore cataclastic deformation

genesis of the wulong gold deposit northeastern north china craton constraints from fluid inclusions h o s pb isotopes and pyrite trace element concentrations abstract the wulong vein type gold deposit located along the northeastern margin of the north china craton ncc contains 80 tonnes of gold at an average grade of 5 35 g t a total of 380 auriferous quartz veins are hosted in late jurassic gneissic two mica granite and early cretaceous granodiorite a paragenetic sequence representing three hydrothermal stages has been identified 1 quartz pyrite 2 quartz polymetallic sulfide and 3 quartz calcite pyrite petrography fluid inclusion microthermometry and laser raman spectroscopy revealed three types of fluid inclusions co2 ch4 type i h2o co2 ch4 type ii and h2o nacl type iii fluid inclusion data indicate that during mineralization fluid temperatures evolved from 283 to 395 c to 219 328 c to 144 255 c and salinities varied from 0 70 to 8 95 wt to 0 18 7 86 wt to 0 18 4 96 wt nacl equivalent quartz yielded 18oh2o smow and dsmow values of 0 9 7 3 and 65 to 48 respectively indicating that the ore forming fluids were derived from magmatic water and mixed with meteoric water during the later stages of mineralization sulfides have 34scdt sulfur isotopic compositions ranging from 0 9 to 3 9 suggesting that the s was derived from a magmatic source pb isotopic compositions of sulfides 206pb 204pb 17 488 17 718 207pb 204pb 15 565 15 631 and 208pb 204pb 38 190 38 766 indicate that the pb was derived primarily from the upper crust with minor input from the mantle in situ laser ablation inductively coupled plasma mass spectrometry la icp ms trace element analyses of three generations of pyrite py1 py2 and py3 reveal that gold concentrations in py2 are higher than those in py1 and py3 which indicates that gold mineralization occurred primarily during the middle stage high co ni ratios of pyrite are consistent with a hydrothermal origin we suggest that the wulong gold deposit formed during lithospheric thinning associated with destruction of the ncc this process was triggered by subduction of the paleo pacific plate during the early cretaceous

water in nominally anhydrous minerals implications for partial melting and strain localization in the lower crust low concentrations tens to hundreds of parts per million of water in nominally anhydrous minerals nams of the mantle have been shown to significantly affect the rheology depth of depressurization melting and many other properties of the mantle in this contribution we evaluate the effect of trace concentrations of water in nams on melting of lower continental crust water locked in structural sites and in fluid inclusions in nominally anhydrous minerals in lower crustal granitoids may act as a flux for partial melting of these source rocks water concentrations of 3000 ppm in minerals that make up large volumes of crustal rocks k feldspar plagioclase quartz would lower the dry solidus of granite by 273 c at 1 gpa measurements and maps of water concentration in variably deformed samples of the stevenson granite from northern saskatchewan canada show that during deformation and recrystallization of k feldspar megacrysts water migrated from the interior of megacrysts to finer grained matrix material dark fine grained water richer matrix material consisting of quartz plagioclase alkali feldspar and fine iron oxides are interpreted to be former melt films that resulted at least in part from fluxing by nam derived water deformation may play a role in moving water from nams to phase boundaries where generation of partial melt may lead to further rock weakening and further release of water from nams

secondary siderite oxide sulphide and carbonate andalusite assemblages in cordierite granulites from sri lanka post granulite facies fluid evolution during uplift we report here that some of the pelitic rocks from the wanni and highland complexes of sri lanka reacted with co2 rich fluids to produce a wide range of unusual secondary carbonate silicate oxide sulphide assemblages these enable the depth temperature and fluid compositions of co2 reactions to be calculated more rigorously than is generally possible for the patches of arrested charnockite that have been described from sri lanka magnesite andalusite quartz has partially replaced primary cordierite and siderite rutile replaced ilmenite paragenetic sequences involving primary pyrrhotite ilmenite and magnetite and secondary pyrite siderite rutile magnetite hematite demonstrate the control which carbonate equilibria have upon evolving fluid compositions during cooling direct evidence for the role of graphite as a source of co2 is found in the highland complex where primary graphite partially reacted with silicates to form secondary siderite assemblages it is proposed that following peak metamorphism continued uplift along a clockwise p t t path was accompanied by a series of devolatilization reactions involving breakdown of graphite and the continuous production of secondary co2 rich fluids the limited extent of disseminated secondary carbonate reflects the small amount of graphite inferred to have been present in the source rocks these rocks demonstrate that co2 rich fluids as found in disseminated fluid inclusions need not form during peak granulite metamorphism but may be an inevitable consequence of continued uplift along a clockwise p t t path the arrested charnockite which overprinted some of the hornblende bearing felsic intermediate composition rocks in sri lanka most likely formed by the same process

petroleum and aqueous inclusions from deeply buried reservoirs experimental simulations and consequences for overpressure estimates abstract synthetic hydrocarbon and aqueous inclusions have been created in the laboratory batch reactors in order to mimic inclusion formation or re equilibration in deeply buried reservoirs inclusions were synthesized in quartz and calcite using pure water and mexican dead oil or n tetradecane c14h30 at a temperature and pressure of 150 c and 1 kbar one phase hydrocarbon inclusions are frequently observed at standard laboratory conditions leading to homogenization temperatures between 0 and 60 c uv epifluorescence of mexican oil inclusions is not uniform blue and green yellow colored inclusions coexist however no clear evidence of variations in fluid chemistry were observed homogenization temperatures were recorded and the maxima of th plotted on histograms are in good agreement with expected th in a range of 6 c broad histograms were reconstructed showing non symmetrical th distributions over a 20 c temperature range centered on the expected th this histogram broadening is due to the fragility of the fluid inclusions that were created by re filling of pre existing microcavities such th histograms are similar to th histograms recorded on natural samples from deeply buried carbonate reservoirs th values lower than those expected were measured for hydrocarbon inclusions in quartz and calcite and for aqueous inclusions in calcite however the results confirm the ability of fluid inclusions containing two immiscible fluids to lead to pt reconstructions even in overpressured environments

a comparative fluid inclusion study of the waterville and sangerville vassalboro formations south central maine petrologic and oxygen isotope data indicate that water rich fluids infiltrated metasedimentary rocks of the waterville and sangerville formally vassalboro formations south central maine during peak metamorphism and depleted sangerville rocks in alkalis but not equivalent waterville rocks fluid inclusion data from two outcrops 1 km apart one of the waterville and the other of the sangerville formations suggest a cause for the geochemical difference between the two units postulated peak metamorphic inclusions the texturally earliest of aqueous inclusions in the metasediments approximate the water rich compositions of peak fluids predicted by mineral fluid equilibria and have average salinity in the sangerville formation three times that of equivalent waterville inclusions the higher salinity in the sangerville fluids could explain the greater alkali depletion in these rocks probable pre peak or prograde inclusions are preserved in metasediments as the texturally earliest carbonic inclusions which contain co2 ch4 n2 h2o as determined by microthermometry and raman spectrometry they may have formed by breakdown of organic matter probable retrograde inclusions occur as texturally late aqucous inclusions in healed fractures with salinity ranges indistinguishable between the two formations synmetamorphic granitic dikes present in the two outcrops were ruled out as a source for fluids in metasediments because composition and density ranges of inclusions in dikes and metasediments are fundamentally different and because there is no correlation between the abundance or composition of inclusions in a sample and proximity to dikes isochores for many of the inclusions in both metasediments and dikes are not consistent with the inferred p t conditions of their trapping but intersect at 300 to 400 c and 1 to 2 kbar the intersections probably resulted because inclusion densities continued to equilibrate during uplift and cooling until quartz became rigid the present densities are those at the last equilibration not the time of trapping in contrast the clear distinctions in inclusion compositions between dikes and between dike and country rock show that the original compositional differences generally have been preserved

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