the nilgiri enderbites south india nature and age constraints on protolith formation high grade metamorphism and cooling history abstract the trident shaped nilgiri highland massif represents the deepest level exposure 9 10 kbar c 35 km palaeo depth of granulite grade lower crust in southern peninsular india the crustal section is essentially composed of garnetiferous enderbitic granulites with minor kyanite bearing gneisses quartzites and banded magnetite quartzites its deeper northern part is intruded by intermediate and basic magmatic rocks now represented by non garnetiferous enderbites garnetiferous basic granulites gabbroic to anorthositic two pyroxene granulites and pyroxenites the garnetiferous enderbitic granulites are tonalitic in composition displaying a typical calc alkaline trend and exhibit chemical features of both i type as well as s type granitoids they show moderate enrichment of lree la n 35 70 no to weakly negative eu anomalies and fairly constant levels of hree yb n 6 5 13 0 and resemble the ree spectra of tonalitic trondhjemitic granitoids and greywackes of late archaean to palaeoproterozoic age sedimentary protoliths are indicated by negative df values ranging from 1 to 4 al 2 o 3 cao na 2 o k 2 o molar ratios 1 1 high 18 o whole rock values 10 12 which match the values reported for greywackes whole rock isotope data for garnetiferous enderbites define linear arrays in the rb sr and sm nd evolution diagrams rb sr system 2460 81 ma with sr i 0 7030 5 sm nd system 2506 70 ma with nd i 0 509363 60 implying a provenance of the sedimentary precursors that was dominated by felsic volcanic rocks or tonalitic trondhjemitic granitoids of uniform isotopic composition and early proterozoic age the u pb systematics of composite zircon grains with detrital cores and metamorphic overgrowths in accord with the sm nd and rb sr errorchron ages and sm nd garnet whole rock data suggest that formation of the provenance deposition of the sedimentary precursors and subsequent high grade tectono metamorphic processes must have occurred in the short time span between 2600 and 2500 ma based on the regional geological framework the petrological geochemical and isotopic data the nilgiri granulite terrain is interpreted as a metasedimentary allochthonous unit that was thrust onto the dharwar craton during palaeoproterozoic collisional tectonics

carbonate silicate inclusions in garnet as evidence for a carbonate bearing source for fluids in leucocratic granitoids associated with granulites of the southern marginal zone limpopo complex south africa abstract we present a study of carbonate bearing polyphase inclusions in garnets from leucocratic granitoids intruding metapelitic granulites of the southern marginal zone smz of the neoarchean limpopo high grade complex south africa during the post peak stage 2710 2650 ma u pb ages for zircons and monazites ternary feldspar thermometry suggests that the granitoid magma cooled from temperatures 800 900 c at a pressure of ca 6 5 kbar abundant co2 fluid inclusions in quartz and t xco2 phase equilibria modeling via perple x imply action of an essentially carbonic fluid in the granitoids cores of almandine rich garnet grains from the granitoids contain polyphase carbonate bearing inclusions with a distinct negative crystal shape the major carbonate in the inclusions is a strongly zoned magnesite siderite variety whereas pyrophyllite is the predominant silicate phase raman spectra of unexposed inclusions revealed a presence of co2 as well as ch4 and h2o the carbonate bearing inclusions coexist with larger polyphase inclusions composed of biotite quartz k feldspar plagioclase sillimanite which are interpreted as relics of granitic melts modeling the mineral assemblage preserved within the carbonate bearing inclusions shows that their present mineral and chemical compositions are a product of interaction of the trapped aqueous carbonic fluid with host garnet during cooling below 400 c despite strong modifications the inclusions bear evidence for initial saturation of the fluid with mg carbonate this is taken as an evidence for an origin of the fluids by devolatilization of the mg rich carbonate bearing ultrabasic greenstone rocks of the kaapvaal craton that were buried under the smz being generated at temperatures between 650 and 700 c the fluid subsequently participated in anatexis and coexisted with the granite magma during exhumation and interaction of the smz granulites with cratonic rocks

statistical microthermometry of synthetic fluid inclusions in quartz during decompression reequilibration fluid inclusion microthermometric data are often reported as homogenization temperature frequency histograms interpretation of such histograms for a single fluid inclusion assemblage fia of non reequilibrated fluid inclusions is usually straightforward and provides an accurate determination of the original density th of that fia however interpretation of such histograms for reequilibrated inclusions is more problematic decompression experiments using synthetic inclusions in natural quartz and conducted at 2 5 kbar and 600 700 c with a maximum internal overpressure of 2 kbar indicate that histogram shape reflects the sample s p t history our results further indicate that the mean mode range standard deviation extreme values etc all have a significance with respect to the p t history of the sample thus a mound shaped unimodal histogram with low range is indicative of a nearly isochoric cooling p t path a unimodal histogram that is slightly skewed to the right and with a low standard deviation but high range results from inclusion deformation in the plastic regime high temperature low strain rates fluid inclusions deformed plastically show no correlation between size and density histogram outliers should not be ignored and may be used to determine an isochore that passes close to the conditions of entrapment minimum th or close to the final reequilibration conditions maximum th the histogram mean th value corresponds to an isochore that represents the internal overpressure about 1 kbar that can be maintained over geologic time by a majority of reequilibrated fluid inclusions a multimodal histogram with high range and high standard deviation indicates inclusion brittle deformation low temperature high strain environments fluid inclusions deformed in a brittle manner show strong positive correlation between size and density histograms produced in the laboratory show many similarities to histograms for natural samples offering the hope that laboratory results may be used to interpret p t histories of natural samples

low density co2 rich fluid inclusions from charnockites of southwestern madurai granulite block southern india implications on graphite mineralization abstract characterization of fluid inclusions in graphite bearing charnockites from the southwestern part of the madurai granulite block in southern india reveals a probable relation with the formation and break down of graphite during the high grade metamorphism the first generation monophase pure co 2 inclusions the composition of which is confirmed by laser raman spectroscopy recorded moderate density 0 77 0 87 g cc corresponding to low tapping pressure around 2 kb than that of the peak granulite facies metamorphism the precipitation of graphite as inferred from graphite inclusions and 13 c values of the graphite from the outcrops is interpreted as the cause of this lowering of fluid density an intermediate generation of pseudosecondary inclusions resulted from the re equilibration or modification of the first generation fluids and the co 2 formed is interpreted to be the oxidation product from graphite the youngest generation of fluids which caused widespread retrogression of the granulites is a low temperature 350 c high saline 32 4 52 0 wt nacl equivalent brine carbon isotope data on the graphite from the charnockites show 13 c values ranging from 11 3 to 19 9 suggesting a possibility of mixing of carbon sources relating to earlier biogenic and later co 2 fluid influx combining the information gathered from petrologic fluid inclusion and carbon stable isotope data we model the fluid evolution in the massive charnockites of the southwestern madurai granulite block

synmetamorphic high density carbonic fluids in the lower crust evidence from the nilgiri granulites southern india high density co2 inclusions occur abundantly in granulite facies rocks age of metamorphism approximately 2 5 b y of the nilgiri massif southern india the chronology of carbonic inclusions in the widespread enderbitic granulites studied in relation to the development of micro textures and mineral assemblages indicates that randomly oriented negative crystal shaped co2 inclusions 4 20 mu m in garnet and quartz grains qtz i armoured by garnet entrap syn peak metamorphic pore fluids the more abundant trail bound co2 inclusions in the deformed polygonized and partially recrystallized matrix quartz grains qtz ii and iii and plagioclase grains were formed in connection with a stage of compressional deformation and subsequent annealing related to the development of the late proterozoic bhavani shear zone these inclusions resulted from local re equilibration of the former peak granulitic carbonic inclusions and re entrapment of released fluids the presence of pure co2 in all the inclusions is confirmed by microthermometric data and laser excited raman microspectrometry temperatures of homogenization liquid phase are in the range of 50 to 20 degrees c and the corresponding co2 densities are between 1 154 and 0 807 g cm3 mineralogical thermobarometry on the enderbitic granulites documents a continuous gradient of near peak metamorphic conditions from 750 degrees c 9 10 kb in the northern part to 730 degrees c 7 kb in the southwestern part of the nilgiri massif uniform p t estimates 600 650 degrees c 6 7 kb for late coronitic garnet quartz assemblages in enderbites and metadolerites indicate that differential uplift of the massif to mid crustal levels was accomplished before late compressional deformation in conformity carbonic inclusions in quartz ii and iii are characterized by uniformly high density 1 154 1 08 g cm3 in contrast early carbonic inclusions in garnet and quartz i preserve the density contrast reflecting the regional p t gradient during near peak metamorphic fluid entrapment the fluid inclusion systematics indicate near isochoric uplift of the northern high p domain but near isobaric cooling of the southwestern low p domain the carbonic fluids are thought to have been derived either from internal sources during dehydration melting processes or from freezing synmetamorphic intrusives into the lower crust

neoarchean continental growth through arc magmatism in the nilgiri block southern india the formation and growth of continental crust in the archean have been evaluated through models of subduction accretion and mantle plume the nilgiri block in southern india exposes exhumed neoarchean lower crust uplifted to heights of 2500 m above sea level along the north western margin of the peninsula major lithologies in this block include charnockite with or without garnet anorthosite gabbro suite pyroxenite amphibolite and hornblende biotite gneiss ttg all these rock types are closely associated as an arc magmatic suite with diffuse boundaries and coeval nature the charnockite and hornblende biotite gneisses ttg show sio2 content varying from 64 to 73 wt the hornblende biotite gneisses ttg are high al type with al2o3 15 wt whereas the charnockites show al2o3 15 wt the composition of charnockite is mainly magnesian and calcic to calc alkaline the mafic ultramafic rocks show composition close to that of tholeiitic series the low values of k 2 o 3 wt k rb k2o 500 zr ti and trace element ratios like la yb n sr y y nb y nb rb y ta rb yb ta indicate a volcanic arc signature for these rocks the geochemical signature is consistent with arc magmatic rocks generated through oceanic plate subduction the primitive mantle normalized trace element patterns of these rocks display enrichment in large ion lithophile elements lile and comparable high field strength elements hfse in charnockite and hornblende biotite gneisses ttg consistent with subduction related origin primitive mantle normalized ree pattern displays an enrichment in lree in the chamockite and hornblende biotite gneisses ttg as compared to a flat pattern for the mafic rocks the chondrite normalized ree patterns of zircons of all the rock types reveal cores with high hree formed at ca 2700 ma and rims with low hree formed at 2500 2450 ma log transformed la th nb th sm th yb th discrimination diagram for the mafic and ultramafic rocks from nilgiri displays a transition from mid oceanic ridge basalt morb to island arc basalt iab suggesting a morb source the u pb zircon data from the charnockites mafic granulites and hornblende biotite gneisses ttg presented in our study show that the magma generation during subduction and accretion events in this block occurred at 2700 2500 ma together with the recent report on neoarchean supra subduction zone ophiolite suite at its southern margin the nilgiri block provides one of the best examples for continental growth through vertical stacking and lateral accretion in a subduction environment during the neoarchean c 2014 elsevier b v all rights reserved

fluid inclusions of the high pressure granulites from the namche barwa complex of the eastern himalayan syntaxis tibet fluid composition and evolution in the continental subduction zone abstract the namche barwa complex in the eastern himalayan syntaxis has experienced high medium pressure granulite facies and amphibolite facies metamorphism the high pressure granulites contain complex fluid inclusion assemblages including h 2 o co 2 ch 4 carbonic co 2 ch 4 n 2 co 2 solid brine medium to low salinity aqueous inclusions and low density gaseous inclusions textural evidence suggests that the isolated h 2 o co 2 ch 4 inclusions occurring in quartz blebs enclosed in garnet porphyroblasts were trapped in the peak metamorphic stage whereas isolated and trail bound co 2 inclusions along intragranular fractures in quartz plagioclase and garnet were mainly trapped during the early decompression stage of the high pressure granulites although some co 2 rich inclusions have formed by selective leakage of h 2 o out of h 2 o co 2 inclusions this together with wide variations in homogenization temperatures indicates modifications and density resetting of the fluid inclusions during exhumation in contrast to the common presence of high density co 2 fluid inclusions in granulite terrains worldwide the high pressure granulites in the namche barwa complex contain dominantly medium to low density h 2 o co 2 ch 4 and co 2 inclusions this may be explained as that the high pressure granulites occur in the continental subduction zone tectonic setting

a noble gas study of a granulite sample from the nilgiri hills southern india implications for granulite formation the he and ar isotopic composition of several mineral separates from a 2 5 ga old enderbite sample from the nilgiri hills southern india were analyzed the sample contains abundant high density carbonic fluid inclusions which have been well characterized in previous studies 1 2 on this particular sample garnet contains synmetamorphic primary fluid inclusions while quartz and plagioclase contain re equilibrated secondary inclusions the noble gases were extracted by crushing or heating of the minerals all measured 3he 4he ratios are above the typical value of old crustal rocks which is about 0 01 0 02 times the atmospheric ratio ra fluid inclusions from the crushed garnet sample contain helium with the highest 3he 4he ratio of 2 34 0 36 ra the he excess is mantle derived and cannot be explained by a cosmogenic or nucleogenic 3he rich component the elemental and isotopic ratios of he ne and ar in all minerals can be explained by a combination of elemental fractionation during diffusional loss of noble gases production of radiogenic nucleogenic4he 21ne 22ne and40ar and atmospheric contamination depending on the assumptions made for the evolution of the he trapped in the garnet fluid inclusions we obtain mixing ratios between mantle derived he and crustal he ranging from 1 5 5 to essentially pure mantle he however probably pure mantle he was trapped in the minerals 2 5 ga ago these data suggest that the enderbite sample represents a former mantle derived tonalitic magma which exsolved its volatiles upon crystallization in the lower crust liberation of a huge amount of co2 by similar intrusions together with the heat provided by them might be responsible for the dehydration of the former amphibolite facies rocks to the north bordering the nilgiri hills

differentiation of late archean crust in the eastern dharwar craton krishnagiri salem area south india the late archean crust south of krishnagiri tamil nadu consists of tonalitic trondhjemitic granodioritic ttg gneisses with mafic and sedimentary enclaves formed between 2 7 and 2 5 ga and metamorphosed at amphibolite facies in the north to granulite facies in the south close to 2 5 ga migmatization occurred at all grades and numerous small granite bodies were emplaced near the amphibolite to granulite facies horizon this nearly syn accretion meta morphism affected the entire crust and left a chemically differentiated section later exposed by uplift and erosion detailed chemical and petrographic study of 60 samples across a 90 km traverse provides evidence for an essentially unbroken crustal cross section paleopressures range from 4 kbar corresponding to 12 14 km paleodepth in the north to 8 kbar corresponding to 24 28 km paleodepth to the south corresponding paleotemperatures vary between 650 and 800 c across the section mineralogic grade monitors particularly increasing tio 2 con

palaeopressures of south indian two pyroxene garnet granulites from thermochemically calibrated cmas barometers the enthalpy of reaction of plagioclase and pyroxene to produce garnet and quartz has been a major source of error in granulite geobarometry because of relatively uncertain enthalpy values available from high temperature solution calorimetry and compiled indirectly from experimental phase equilibria recent improved calorimetric measurements of hr are shown to yield palaeopressures which are internally consistent between orthopyroxene and clinopyroxene calibrations for many south indian granulites from the archaean high grade terranes of southern karnataka and northern tamil nadu this represents a considerable improvement over previous calibrations which gave disparate results for the two independent barometers involving orthopyroxene and clinopyroxene requiring a 2 kbar empirical adjustment to force agreement palaeopressures thus calculated for 30 well documented two pyroxene garnet granulites from south india give internally consistent pressures with a mean of 8 1 1 1 kbar at 750 c consistent with the presence of both kyanite and sillimanite in many areas those samples for which garnet pyroxene exchange thermometers give plausible granulite range temperatures and whose minerals are minimally zoned give the best agreement of the two barometers samples which yield low palaeotemperatures and different rim and core compositions of minerals yield pressures for the orthopyroxene assemblage as much as 2 kbar lower than for the assemblage with clinopyroxene this disparity probably represents post metamorphic peak re equilibration we conclude that considerable confidence may be placed in geobarometry of two pyroxene granulites where apparent palaeotemperatures are in the granulite facies range 700 c and where mineral zonation is minimal of the several possible sets of activity composition relations in use those constructed from analysis of phase equilibria give slightly higher palaeopressures and appear more consistent with analytical data from the nilgiri hills uplift where kyanite is the only aluminium silicate reported to be stable in peak metamorphic assemblages the present results support a palaeopressure gradient increasing generally from south to north across the nilgiri hills as inferred by previous geobarometry

primary carbonate co2 inclusions in sapphirine bearing granulites from central sri lanka high density co2 rich fluid inclusions from a sapphirine bearing granulite hakurutale sri lanka have been studied by microthermometry raman spectrometry and sem analysis based on textural evidence two groups of inclusions can be identified primary negative crystal shaped inclusions group i and pseudo secondary inclusions which experienced a local limited post trapping modification group ii both groups contain magnesite as a daughter mineral occurring in a relatively constant fluid solid inclusion volume ratio volsolid 0 15 total volume co2 densities for group i and ii differ only slightly both groups contain a fluid which was initially trapped at peak metamorphic conditions as a homogeneous co2 mgco3 mixture thermodynamic calculations suggest that such a fluid co2 15 vol mgco3 is stable under granulite facies conditions after trapping magnesite separated upon cooling while the remaining co2 density suffered minor re adjustments a model isochore based on the integration of the magnesite molar volume in the co2 fluid passes about 1 5 2 kbar below peak metamorphic conditions this remaining discrepancy can be explained by the possible role of a small quantity of additional water

fluid evolution and exhumation path of the trivandrum granulite block southern india in charnockites and host garnet biotite gneis ses of the trivandrum granulite block tgb southern india fluid inclusions are mainly represented by co2 rich categories aqueous inclusions with low salt concentration 0 33 13 5 wt nacl equiv occur sub ordinately we recognize three generations of co2 rich inclusions which have contrasting fluid densities that correlate with the different stages of metamorphic evo lution established from mineral phase equilibria studies although some of these inclusions show variable depression in melting temperatures laser raman spec troscopic studies revealed no volatiles other than co2 we report here the occurrence of high density co2 rich inclusions for the first time from this region with homogenization temperatures in the range of 21 9 to 15 6 c q 1 041 1 012 g cm 3 the marked secondary character of these high density inclusions and their tex tural association with late brittle deformational features indicate their entrapment at low temperature conditions 250 300 c post dating charnockite formation regional metamorphism in tgb stage m1 took place at ca 700 c and 5 36 kbar although higher tempera tures prevailed in the northern part of the terrain a subsequent period of decompression of the order of 6 7 km was accompanied by partial recrystallization of host rocks and intensive processes of charnockite for mation m2 that extended to subisobaric cooling from 785 805 to 680 700 c the relatively small population of aqueous inclusions in charnockites and their low salinity preclude any major role for metasomatic pro cesses involving increase of potassium activity and confirm the important role of co2 rich fluids in stabi lizing low water activities during the final phase of exhumation of the region ca 9 km in depth additional heat input resulted in mineralogical alterations corre lated to stage m3 while the source of heat and fluids involved in charnockite formation is postulated to be magmas derived from sublithospheric sources the late heat and fluid transfer are correlated to late pan african ultrabasic and alkaline intrusives emplaced at shallow depths

fluid influence on mineral reactions in ultrahigh pressure granulites a case study in the śnieznik mts west sudetes poland small tectonic slices of undeformed eclogites and ultrahigh pressure granulites occur in three tectonic units of the nieznik mts sw poland ultrahigh pressure granulite eclogite transitions with peak metamorphic conditions between 21 and 28 kbar at 800 to 1000 c occur only in the zlote unit conventional u pb multigrain analyses of zircons from a mafic granulite provided 207pb 206pb ages between 360 to 369 ma which are interpreted to approximate timing of original crystallisation from a melt diffusion kinetics and the restricted availability of a fluid phase mainly controlled the conversion from granulite to eclogite although some bulk chemical differences were also recognised the ultrahigh pressure granulites from the zlote unit exclusively contain h2o rich inclusions with variable salinities which distinguishes them from high temperature ht granulites world wide this is also in contrast to the fluid regime h2o n2 co2 recognised in the lower temperature eclogites 600 800 c from the closely associated miedzygorze and nieznik units the variation in fluid composition between the lower temperature eclogites and ultrahigh pressure granulites on the one hand and ultrahigh pressure granulites and ht granulites on the other hand probably indicates contrasting p t t paths as a result of different tectonic environments

numerical simulations of co2 migration during charnockite genesis charnockite is considered to be generated either through the dehydration of granitic magma by co2 purging or by solid state dehydration through co2 metasomatism during granulite facies metamorphism to understand the extent of dehydration co2 migration is quantitatively modeled in silicate melt and metasomatic fluid as a function of temperature h2o wt pressure basal co2 flux and dynamic viscosity numerical simulations show that co2 advection through porous and permeable high grade metamorphic rocks can generate dehydrated patches close to the co2 flow path as illustrated by the occurrences of incipient charnockites co2 reaction front velocity constrained by field observations is 0 69 km m y a reasonable value which matches well with other studies on the other hand temperature rate of cooling and basal co2 flux are the critical parameters affecting co2 diffusion through a silicate melt co2 diffusion through silicate melt can only occur at temperature greater than 840 degrees c and during slow cooling 3 7 x 10 5 degrees c yr features that are typical of magma emplacement in the lower crust stalling of co2 fluxing at similar to 840 degrees c explains why some deep level plutons contain both hydrous and anhydrous charnockitic mineral assemblages co2 diffusion through silicate melt is virtually insensitive to pressure addition of co2 basal flux facilitates episodic dehydrated melt migration by generating fracture pathways

co2transfer between the upper mantle and the atmosphere temporary storage in the lower continental crust the co2 atmospheric content has shown large variations over geological times high contents up to one order of magnitude more than present day values ultimately correspond to discrete episodes of mantle degassing either juvenile or subduction related carbon recycling a number of arguments e g the continuous volume increase of carbonate bearing sediments with time suggest that throughout the earth s history juvenile co2 has formed a major contribution to the global carbon budget of the earth the absence of a direct relationship between major volcanic episodes and the average co2 atmospheric content suggests that volcanoes might not be the only way by which mantle co2 is transported to the surface it is proposed that large quantities of juvenile co2 could temporarily be stored in the lower continental crust during major episodes of granulite formation these are primarily caused by magmatic underplating and they result in a vertical accretion of the crust by accumulation of co2 bearing mantle derived magmas most of the co2 migrates through the crust during post metamorphic evolution and isostatic restoration of the normal continental thickness however large quantities of co2 can still be present in some areas notably as high density fluids enclosed in minerals

metamorphic reactions between fluid inclusions and mineral hosts i progress of the reaction calcite quartz wollastonite co 2 in natural wollastonite hosted fluid inclusions at the bufa del diente contact metamorphic aureole brine infiltration through metachert layers embedded in limestones produced thick wollastonite rims according to cc qz wo co2 fluid inclusions trapped in recrystallized quartz hosts include 1 high salinity four phase inclusions th v l 460 573 c td salts 350 400 c na k cleq 64 73 wt x co 2 0 02 2 low density vapour rich co2 bearing inclusions th l v 500 100 c x co 2 0 22 0 44 x nacl 0 01 corresponding to densities of 0 27 0 05 gcm 3 petrographical observations phase compositions and densities show that the two fluids were simultaneously trapped in the solvus of the h2o co2 salts system at 500 600 c and 700 200 bars the low density fluid was generated during brine infiltration at the solvus via the wollastonite producing reaction identical fluid types were also trapped as inclusion populations in wollastonite hosts 3 cm adjacent to quartz crystals at room temperature both fluid types additionally contain one quartz and one calcite crystal generated by the back reaction wo co2 cc qz of the host with the co2 proportion of the fluid during retrogression all of the co2 was removed from the fluid on heating in the microstage the reaction progress of the prograde reaction was estimated via volume loss of the calcites in vapour rich fluids 50 progress is reached at 490 530 c 80 at 520 560 c and 100 at 540 590 c the latter representing the trapping temperatures of the original fluid at the two fluid solvus the progress is volume controlled with knowledge of compositions and densities from unmodified inclusions in quartz and using the equation of state of duan et al 1995 for h2o co2 nacl along with f co 2 values extracted from it the reaction progress curve was recalculated in the p t x space the calculated progress curve passes through the two fluid solvus up to 380 c 210 bars continues in the one fluid field and meets the solvus again at trapping conditions the p t slope is steep most of the reaction occurs above 450 c and there is high correspondence between calculated and measured reaction progress we emphasize that with the exception of quartz back reactions between inclusion fluids and mineral hosts is a common process for almost any prograde metamorphic mineral that was formed by a devolatilization reaction and that trapped the equilibrium fluid or any peak metamorphic fluid as an inclusion a fluid host back reaction exists which must occur somewhere along the retrograde path such retrograde reactions may cause drastic changes in density and composition of the fluid in most cases however evidence of the evolving mineral assemblages is not given for they might form submicroscopical layers at the inclusion walls

fluid inclusion studies on the koraput alkaline complex eastern ghats province india implications for mid neoproterozoic granulite facies metamorphism and exhumation abstract following ultrahigh temperature granulite metamorphism at 1 ga the eastern ghats province of india was intruded by the koraput alkaline complex and was subsequently re metamorphosed in the granulite facies in the mid neoproterozoic time fluid inclusion studies were conducted on silica undersaturated alkali gabbro and syenites in the complex and a pre metamorphic pegmatitic granite dyke that intrudes it high density 1 02 1 05 g cc pseudo secondary pure co2 inclusions are restricted to metamorphic garnets within the gabbro and quartz within the granite whereas moderate 0 92 0 95 g cc and low density 0 75 g cc secondary inclusions occur in garnet magmatic clinopyroxene plagioclase hornblende and quartz the isochores calculated for high density pseudo secondary inclusions pass very close to the peak metamorphic window 8 kbar 750 c and are interpreted to represent the fluid present during peak metamorphism that was entrapped by the growing garnet microscopic round inclusions of undigested relict calcite in garnet suggest that the co2 present during metamorphism of the complex was internally derived through carbonate breakdown pure to low salinity 0 00 10 1 wt nacl equivalent aqueous intra intergranular inclusions showing unimodal normal distribution of final ice melting temperature tm and temperature of homogenization th are present only in quartz within the granite these represent re equilibrated inclusions within the quartz host that were entrapped at the metamorphic peak rare chemically precipitated graphite along the walls of carbonic inclusions is interpreted as a post entrapment reaction product formed during decompression the fluid inclusion evidence is consistent with rapid exhumation of a thickened lower crust following the mid neoproterozoic granulite facies metamorphic event the study suggests that mantle co2 transported by alkaline magma into the crust was locked up within carbonates and released during granulite metamorphism

high density early co2 fluids in the ultrahigh temperature granulites of ihouhaouene in ouzzal algeria abstract fluid inclusion studies in rocks from the lower proterozoic granulites from western hoggar algeria provide new evidence for the hypothesis that a co 2 rich h 2 o poor fluid was present during the high grade metamorphism co 2 inclusions represent the main fluid trapped in the ihouhaouene ultrahigh temperature over 1000 c and high pressure 10 to 14 kbar granulites the microthermometric and raman microspectrometric measurements indicate that the carbonic fluid is mainly composed of co 2 with minor amounts of ch 4 and n 2 detected in some inclusions 4 carbonic fluid densities range from 1 18 to 0 57 g cm 3 the highest densities are recorded in superdense carbonic inclusions presenting evidence of the earliest trapping and they correspond to the fluid densities expected for the p t conditions of the peak of metamorphism in the area previously determined from mineral geothermobarometers lower densities of carbonic fluids mainly result from the reequilibration of earlier trapped fluid inclusions during retrograde metamorphism and final uplift of the metamorphic terrane but a new influx of carbonic fluids during the retrograde event remains possible carbonic fluids can be produced in situ from decarbonation reactions in interlayered impure marbles during the prograde event or derived from co 2 flushing from underlying basic intrusions the aqueous fluids present large variations of composition 0 5 to 30 wt nacl equivalent and densities 1 16 to 0 57 g cm 3 they clearly correspond to post metamorphic fluids because they mainly occur along microfractures they do not show any evidence of immiscibility with the carbonic fluids and mixed aquo carbonic inclusions have not been observed the percolation of aqueous fluids is related to the pan african tectonometamorphic event

graphite bearing co2 fluid inclusions in granulites insights on graphite precipitation and carbon isotope evolution graphite in deep crustal enderbitic orthopyroxene garnet plagioclase quartz granulites 740 c 8 9 kb of nilgiri hills southern india were investigated for their spectroscopic and isotopic characteristics four types of graphite crystals were identified the first type gri which is interstitial to other mineral grains can be grouped into two subtypes gria and grib gria is either irregular in shape or deformed and rough textured with average 13c values of 12 7 0 4 n 3 a later generation of interstitial graphite grib shows polygonal crystal shapes and highly reflecting smooth surface features these graphite grains are more common and have 13c values of 11 9 0 3 n 14 both subtypes show well defined raman shifts suggesting a highly crystalline nature cores of interstitial graphite grains have on average lower 13c values by 0 5 compared to that of the rim the second type of graphite grii occurs as solid inclusions in silicate minerals commonly forming regular hexagonal crystals with a slightly disordered structure the third type of graphite griii is associated with solid inclusions up to 100 m that have decrepitation halos of numerous small 15 m satellite fluid inclusions of pure co2 with varying density 1 105 to 0 75 g cm3 the fourth type of graphite griv is found as daughter crystals within primary type co2 fluid inclusions in garnet and quartz these fluid inclusions have a range of densities 1 05 to 0 90 g cm3 but in general are significantly less dense than graphite free primary pure co2 fluid inclusions 1 12 g cm3 raman spectral characteristics of graphite inside fluid inclusions suggest graphite crystallization at low temperature 500 c the precipitation of graphite probably occurred during the isobaric cooling of co2 rich peak metamorphic fluid as a result of oxyexsolution of oxide phases the oxyexsolution process is evidenced by the magnetite ilmenite granular exsolution textures and the systematic presence of numerous micron sized rutile and other oxide inclusions in association with fluid inclusions within garnet plagioclase and quartz the carbon isotope compositions of coexisting co2 in fluid inclusions and graphite show a fractionation co2 gr co2 gr of 6 in garnet consistent with the existing theoretical estimates of co2 gr co2 gr at 800 c a subsequent generation of co2 inclusions trapped in matrix quartz and quartz segregation have higher 13c values 4 and 2 9 respectively graphite in quartz segregations also has higher 13c values 9 8 than those in enderbite 12 7 micro graphite crystals included in garnet quartz enderbite and quartz segregation have average 13c values of 11 1 10 4 and 8 7 respectively indicating progressive enrichment in 13c with a decrease in temperature of recrystallization of respective minerals this progressive enrichment is also observed in carbon isotope compositions of fluid inclusion co2 suggesting isotopic equilibrium during graphite precipitation from co2 fluids thus the carbon isotope record preserved in these rocks by the interstitial graphite co2 fluid in enderbite graphite microcrystals graphite in quartz segregation and co2 fluid in quartz segregation suggests a temperature controlled isotopic evolution this evolution is in accordance with a closed system rayleigh type graphite precipitation process which progressively enriched residual co2 in 13c

evidence in archaean alkali feldspar megacrysts for high temperature interaction with mantle fluids growth and regrowth textures trace element and oxygen isotope compositions and water content or species have been studied in alkali feldspars from the late archaean closepet igneous bodies feldspar crystals grew from mixed magmas that are characterized by a high degree of homogenization the 3d depiction of trace element distribution indicates that the crystallization process was followed by interaction with fluids the magmatic system involved in feldspar formation shows non linear dynamics the interaction with fluids is also deterministic but in contrast to magmatic crystallization it shows an increasing persistency in element behaviour the degree of persistency of the element activities in both processes has been calculated using the hurst exponent the recrystallization regrowth process induced by fluids proceeded along crystal fractures and cleavages causing selective enrichment in large ion lithophile elements light rare earth elements pb y and in various water species it did not change the feldspar oxygen isotope signature in turn the incorporation of hydrogen species into feldspar domains reduced al o al defect densities in the structure decreasing their luminescence water speciation shows persistent behaviour during heating the process being reversible at least up to 600 c carbonate crystals with a mantle isotope signature are associated with the re equilibrated feldspar domains the feldspar compositions the abundance of water species in them and the refractory nature of the residuum after heating the unchanged oxygen isotopes and the mantle signature of co precipitated carbonates testify that the observed recrystallization has taken place at temperatures above 600 c with h 2 o co 2 fertile mantle derived fluids the paper draws special attention to some methodological aspects of the problem the multi method approach used here major element trace element and isotope geochemistry infra red cathodoluminescence 3d depiction of geochemical data and fractal statistics may help to recognize and separate the various processes throughout the alteration history of the pluton

metamorphism and isotopic evolution of granulites of southern india reference to neoproterozoic crustal evolution abstract granulites are important component of high grade metamorphic rocks reflecting intense conditions observed for crustal rocks in terms of temperature and pressure this review paper demonstrates how these high grade granulites are critical to understanding the evolution of the lower continental crust with special reference to southern india geothermobarometric traverse across different granulite blocks in southern india shows wide ranging p t conditions of metamorphism 700 1000 c and 5 10 kbar the sapphirine orthopyroxene sillimanite and spinel bearing quartz deficient granulites recognised from parts of southern granulite terrain ganguvarpatti kiranur and palani hill ranges etc show oriented sillimanite aggregates pseudomorph after course twinned kyanite staurolite kyanite assemblages and corroded blebs of gedrite within orthopyroxene suggesting a prograde stage of a clockwise p t evolution evidence of itd history comes from the textures in which an early mg rich garnet xmg 52 60 with orthopyroxene up to 10 al2o3 involving sillimanite breakdown forming variety of symplectites having combinations of orthopyroxene sapphirine cordierite and spinel these spectacular reaction textures and mineralogic sensors from the high grade rocks establish a prograde clockwise p t t path with notable decompressive history itd in the southern granulite terrain the inferred p t t paths have been further integrated with the recent geochronological and isotopic data to constrain the timing and duration of metamorphism emplacement of the magmatic protolith for characterising the evolution of the granulites and their bearing on the geodynamic implications based on the emerging evidence for neoproterozoic tectonothermal imprints in the southern granulite terrain history of the assembly of dispersed fragments is also addressed within the east gondwana framework

extent and duration of the 2003 cascadia slow earthquake 1 inversion of continuous gps measurements from the pacific northwest show the 2003 cascadia slow earthquake to be among the largest of ten transients recognized here twelve stations bracketing slow slip indicate transient slip propagated bi directionally from initiation in the southern puget basin reaching 300 km along strike over a period of seven weeks this event produced for the first time resolvable vertical subsidence and horizontal displacement reaching six mm in southern washington state inverted for non negative thrust slip a maximum of 3 8 cm of slip is inferred centered at 28 km depth near the sharp arch in the subducting juan de fuca plate nearly all slip lies shallower than 38 km inverted slip shows a total moment release equal to mw 6 6 and a high degree of spatial localization rather than near uniform slip this suggests rupture concentrated along asperities holds for slow earthquakes as well as conventional events

coarse muscovite veins and alteration in porphyry systems abstract coarse muscovite veins and alteration occur in porphyry copper and porphyry molybdenum copper systems within the laramide arc in arizona as well as at the yerington district in nevada this work describes coarse muscovite in veins and altered wall rock in porphyry systems in this region and documents mineral assemblages mineral compositions spatial and temporal relationships and hydrogen isotopic compositions coarse hydrothermal muscovite is documented in the roots of porphyry cu mo systems as well as in and above the ore bodies in porphyry mo cu systems and it is compared to coarse hydrothermal muscovite greisen in lode sn w mo systems basin and range extension has exposed coarse hydrothermal muscovite in several laramide and jurassic porphyry cu mo systems at paleodepths of 3 to 12 km miami inspiration sierrita esperanza copper basin crown king granite mountain roots of the ray porphyry system gunnison texas canyon stock grayback kelvin riverside district sycamore canyon the new cornelia mine ajo district and two systems in the yerington district muscovite is the dominant mica in these coarse muscovite veins and associated alteration with common k feldspar and albite an00 06 common accessory hematite rutile pyrite and apatite and rare accessory chalcopyrite fluorite molybdenite wolframite and scheelite coarse hydrothermal muscovite yields d compositions that suggest formation from fluids that are dominantly magmatic hydrothermal in origin whole rock compositions of coarse hydrothermal muscovite show common gains in k and loss of ca na coarse muscovite veins and alteration in porphyry copper systems postdate mineralized potassic veins and form too deeply to overlap with shallower acidic forms of alteration sericitic advanced argillic variation in mineral assemblage mineral compositions and mineralization of coarse hydrothermal muscovite correlate with the composition of laramide stocks porphyry mo cu systems contain coarse muscovite alteration assemblages with the highest mineral diversity and trace element enrichment coarse muscovite veins and alteration in porphyry mo cu systems related to stocks ranging from quartz monzonite to granite in composition form at shallower paleodepths and occur within and above the associated orebodies in contrast coarse muscovite veins and alteration associated with subalkaline porphyry copper systems occur at deeper levels in some cases overlapping with the bottom of potassic alteration and the ore body but extending well into the roots of the system in the underlying granitoid cupola in these latter systems zones of coarse muscovite alteration typically are poorly mineralized and mineral assemblages are less varied these characteristics suggest that coarse muscovite forming fluids are predominately of magmatic hydrothermal origin and exsolved from late stage fractionated magmas of the larger pluton that sourced porphyry stocks and dikes responsible for porphyry copper mineralization in some instances however the exposed coarse muscovite alteration is associated with a petrologically unrelated commonly more felsic later intrusion rather than being related to late exsolution of fluid from the same crystallizing stock or batholith

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

high density carbonic fluid inclusions in charnockites from eastern ghats india petrologic implications abstract charnockite rocks a significant litho unit in eastern ghats granulite belt eggb are characterized by the presence of dry mineral assemblage the anhydrous conditions required for the formation of ganulites are believed to be controlled by the lowering of water activity through the influx of co2 bearing fluids here we present the results of systematic petrographic and microthermometric studies characterizing the nature composition and density of co2 rich fluid inclusions in charnockitic rocks from gangarajumadugula in this study we have combined mineralogic thermobarometry with microthermometric data of the carbonic fluid inclusion population of high density in the charnockite samples from gangarajumadugula area to substantiate desiccation of lower crustal environment producing anhydrous conditions in the eastern ghats granulite belt close to peak pressure temperature calculations for core composition using convergence technique in present study indicate that these charnockites have experienced maximum p t around 860 c at 9 kbar which is broadly consistent with independent p t estimates inferred for gangarajumadugula area the reaction textures preserved by these charnockites and the thermobarometric data characterize decompression followed by cooling history high density carbonic fluid inclusions 1 08 g cm3 in quartz provide potential evidence for the involvement of co2 rich fluid during granulite facies metamorphism in eggb occurrence of co2 rich inclusions and elevated p t conditions open up the possibility favoring the mechanism of vapour deficient dehydration melting accompanied by co2 infiltration to account for charnockite formation from precursor crustal rocks our study documents that fluid inclusions in high grade metamorphic rocks have enormous potential in retaining worthwhile information of peak metamorphic conditions and understanding the metamorphic processes

fluid characteristics of high to ultrahigh temperature metamorphism in southern india a quantitative raman spectroscopic study abstract we report the first quantitative compositional data on fluid inclusions in late neoproterozoic to cambrian ultrahigh temperature uht granulites from major crustal blocks and shear zones in southern india fluid inclusions in various high grade minerals such as garnet orthopyroxene plagioclase cordierite and quartz from these rocks were studied in terms of petrography microthermometry and laser raman spectroscopy measured melting temperatures of the inclusions indicate that the trapped fluid phase is dominantly carbonic raman analyses confirmed a co2 rich composition with only minor dilutants such as n2 5 0 mol h2o 0 50 mol and ch4 0 47 mol the range of most co2 isochores computed from density measurements in fluid inclusions from the uht granulites pass below the peak pressure temperature conditions of metamorphism indicating considerable resetting of fluid densities during decompression in contrast garnetiferous granulites from the salem area along the palghat cauvery shear zone system which underwent high pressure prograde metamorphism contain very high density syn metamorphic pure co2 inclusions such dense carbonic fluid inclusions in garnet and plagioclase coexist with carbonate minerals calcite or dolomite indicating probable derivation from deep seated primary magmatic sources although models on the origin of co2 are debatable the ubiquitous association of carbonic fluids in the uht mineral assemblages is in favour of large scale infiltration of co2 rich fluids during extreme crustal metamorphism associated with collisional orogeny and subsequent extensional collapse at the final stage of amalgamation of the gondwana supercontinent

thermobarometry and fluid evolution of enderbites within the magondi mobile belt northern zimbabwe abstract metamorphic conditions within arenaceous calcareous and argillaceous supracrustal rocks of the magondi mobile belt zimbabwe range from greenschist to granulite facies within the high grade segment basement gneisses of early proterozoic age and argillaceous rocks of the mid proterozoic piriwiri group are intruded by charnockites and enderbites metamorphic mineral assemblages and thermobarometric data for enderbitic granulites of nyaodza show temperatures of 700 800 c and pressures of 5 7 kbar for the peak of granulite facies metamorphism microthermometry and raman microspectroscopy reveal that co 2 associated with minor n 2 has been the dominant fluid phase during granulite facies metamorphism the chronology of the co 2 inclusions and the development of microtextures and mineral assemblages in the enderbites indicates that isolated negative crystal shaped co 2 inclusions in quartz and plagioclase porphyroclasts entrap syn metamorphic fluids of medium high densities 0 88 0 90 g cm 3 lower density 0 71 0 77 g cm 3 co 2 inclusions in trails and clusters within the same minerals were formed from local re equilibration and re entrapment of the former near peak granulitic co 2 inclusions as in many other granulites syn metamorphic co 2 is associated with intrusives emplaced near the peak of metamorphism

temperatures of granulite facies metamorphism constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange this study assesses temperatures of formation of common granulites by combining experimental constraints on the p t stability of granulite facies mineral associations with a garnet orthopyroxene grt opx thermobarometry scheme based on al solubility in opx corrected for late fe mg exchange we applied this scheme to 414 granulites of mafic intermediate and aluminous bulk compositions our findings suggest that granulites are much hotter than traditionally assumed and that the p t conditions of the amphibolite granulite transition portrayed in current petrology textbooks are significant underestimates by over 100 c for aluminous and intermediate granulites mean corrected temperatures based on our method are 890 17 and 841 11 c respectively uncertainties reported as 95 confidence limits on the mean consistent with minimum temperatures for orthopyroxene production by fluid absent partial melting in these bulk compositions in contrast mean temperatures based on grt opx fe mg exchange equilibria using the same thermodynamic data are 732 22 and 723 11 c respectively well below the minimum temperatures for opx stability for mafic granulites the mean corrected temperature using our method is 816 12 c similar to the mean temperature of 793 13 c from fe mg exchange reasons for the differences between the mafic granulites and aluminous intermediate granulites are unclear but may be due to the lower al concentrations in opx in the mafic rocks and possible deficiencies in the thermodynamic modelling of these low concentrations we discuss a number of well known granulite terrains in the context of our findings including the adirondacks the acadian granulites of new england the incipient charnockites of southern india and sri lanka and the kerala khondalite belt our findings carry implications for thermotectonic models of granulite formation a computer program to perform our thermobarometry calculations rclc is available from the journal of petrology website at http www petrology oupjournals org or from the authors at http www geo ucalgary ca pattison drm pattison rclc htm

fluids and h2o activity at the onset of granulite facies metamorphism abstract evidence is accumulating from experimental petrology and thermodynamic calculations based on detailed descriptions of key natural occurrences that h2o activity at the regional amphibolite facies granulite boundaries in high grade precambrian gneiss terranes coincident with the orthopyroxene isograd is considerably higher 0 3 0 6 than previously thought 0 15 0 3 this revision provides insight into the significance of fluid inclusions in minerals of the incipient charnockites characteristic of the granulite facies transitions in several precambrian gneiss terranes observations on nacl dominated brine inclusions in minerals including some new data in this paper in rocks from such places as the kabbal satnur halagur area of the archean shield of south india have salt concentrations consonant with the stabilization of orthopyroxene relative to calcic amphibole and biotite closely associated co2 dominated fluid inclusions can have substantial h2o contents at typical incipient granulite facies conditions 700 750 c and 0 5 0 7 gpa and can thus have been in equilibrium with the associated brines as immiscible metamorphic fluids observed densities of the best preserved co2 rich fluid inclusions in quartz are consistent with those expected from the equation of state of co2 at incipient granulite facies pressure temperature conditions it seems likely that the role of fluids in granulite facies metamorphism of the deep crust has been considerably underemphasized in discussions still prevalent which concentrate on the role of fluid deficient partial melting as the primary agent to the exclusion of a possible role of metamorphic fluids and metasomatism

the lower crust of the dharwar craton southern india patchwork of archean granulitic domains u pb geochronological major and trace element and isotope geochemical data identify crustal domains of contrasted petrological origins and histories in the lower crust of the dharwar craton all affected by granulite facies metamorphism and deformation in the neoarchean four lower crustal domains have been identified and investigated across the neoarchean amphibolite to granulite facies transition zone 1 in the southern part of the western dharwar craton wdc high grade metamorphism affects rocks formed before 3 0 ga high grade metamorphism is recorded at ca 2 51 ga followed by possible complex cooling and resetting until 2 2 ga 2 the br hills mm hills domain represents the lower crust of the central dharwar province cdp which is here defined as a transitional crust between the old 3 ga wdc and the eastern dharwar province edp not older than 2 7 ga this granulitic domain contains the oldest rocks of the dharwar craton with ttg suites formed at ca 3 4 ga and ca 2 6 ga suites of probable crustal recycling origin both suites are involved in 2513 5ma granulite facies metamorphism 3 the nilgiri granulitic domain is tectonically juxtaposed with the deepest level of the wdc as a consequence of neoarchean dextral slip along the moyar shear zone the massif consists of rocks of orogenic affinities formed between 2 70 and 2 56 ga and overprinted by granulite facies metamorphism at 2518 10 ma 4 the krishnagiri domain exposes the deepest levels of the eastern dharwar craton it is composed of ttg and calc alkaline igneous protoliths formed between 2 55 and 2 53 ga migmatization in the upper part of the domain took place at 2507 6ma and granulite facies overprint in the deepest parts of the domain is constrained at 2516 5 ma the krishnagiri domain was magmatically accreted to the lower crust of both the cdp and edp by interaction with mafic magmatism inducing reworking of the 2 7 2 6 ga or older overlying crust the nilgiri granulites share several temporal and petrological properties with the madras granulites that make the easternmost outcrop of the dharwar craton we tentatively suggest that the nilgiri and madras granulites evolved as parts of a common madras domain in the lower crust of the edp before activation of the moyar shear zone in this sense the nilgiri massif may be considered as an allochtonous unit in a context of neoarchean ultra hot orogeny in south india

silicate oxide and sulphide trends in neo archean rocks from the nilgiri block southern india the role of fluids during high grade metamorphism the nilgiri block southern india represents an exhumed section of lower late archean 2500 ma crust the northern highlands of the nilgiri block are characterized by metagabbros with pyroxenite inlayers a two pyroxene granulite zone acts as a transition between the metagabbros and charnockites which are exposed in the central and southern part of the nilgiri highlands thermobarometry results indicate a sw ne regional trend both in temperature similar to 650 800 degrees c and in pressure 700 1100 mpa over the nilgiri highlands in the charnockites composite rutile ilmenite grains are the dominant oxide assemblage in the two pyroxene granulites hemo ilmenite magnetite is dominant with coexisting rutile ilmenite composite grains in a few samples in the vicinity of the boundary with the charnockites in the metagabbros hemo ilmenite magnetite is the dominant oxide assemblage the principal sulphide mineral in the charnockite is pyrrhotite with minor pyrite chalcopyrite exsolution lamellae or blebs in the two pyroxene granulites and the metagabbros the principal sulphide assemblage consists of discrete pyrite grains with magnetite rims and pyrite pyrrhotite chalcocopyrite associations from these observations a specific oxidation trend is seen the northern granulite facies metagabbros and two pyroxene granulites of the nilgiri highlands are highly oxidized compared with the charnockites from the central and southern regions this higher oxidation state is proposed to be the result of highly oxidizing agents probably as so3 in low h2o activity grain boundary nacl saline fluids with a dissolved caso4 component present during granulite facies metamorphism of the metagabbros and two pyroxene granulites eventually these agents became more reducing owing to the inherent buffering of the original tonalite granodiorite granitoids at the graphite co2 buffer such that s took the form of h2s during the granulite facies metamorphism of the charnockites at the same time these saline fluids were also responsible the solid state conversion of biotite and amphibole to orthopyroxene and clinopyroxene in the metagabbro two pyroxene granulite and charnockite

primary co2 bearing fluid inclusions in granulitic garnet usually do not survive abstract co2 bearing fluid inclusions fi from granulites have been the main advocate for an active role of fluids during high temperature metamorphism yet the fluid regime of the deep crust and the role of fluids remain largely debated topics in this dispute one of the most controversial issues is the timing of fi entrapment relative to peak metamorphic conditions here we investigate three world renowned high to ultra high temperature metamorphic terranes to evaluate the fate of primary co2 and coh fluid inclusions certainly trapped during the prograde path fluid inclusions coexist along with nanogranitoids in peritectic garnet combination of cutting edge techniques indicates that the fi are composed of fluid and aggregates of solid phases the latter usually comprises siderite ferroan magnesite pyrophyllite calcite corundum quartz and in some cases kaolinite dolomite biotite and muscovite in the fluid phase low density co2 is the most common component and no free h2o has been detected methane and n2 may be also present the high proportion of solids in the fi with carbonates and oh bearing phases cannot have precipitated as daughter phases directly from a simple coh fluid as daughter phases these minerals require additional cations e g fe mg ca al si which may be dissolved in very small amounts in crustal fluids and yet are very abundant in the host the solids therefore imply that the initial composition of high density carbonic inclusions must have been changed by the interaction with the host garnet during cooling thermodynamic modelling of such fluid garnet interaction demonstrates that the assemblages found in fi are metastable and that whatever retrograde path is followed by the host rock primary c bearing fi must change their nature to a multiphase assemblage of stepdaughter minerals as a natural consequence of cooling it follows that supposed primary unmodified fi in garnet previously reported in the literature are in most cases secondary retrograde features whose low temperature of entrapment inhibited fluid host interaction our finding undermines the main pillar of the theory of carbonic fluid assisted metamorphism the presence of superdense co2 inclusions in granulites but at the same time it offers a novel perspective to identify prograde coh fluids in the deep hot crust

arrested charnockite formation at kottavattam southern india at kottavattam southern kerala india late proterozoic homogeneous leptynitic garnet biotite gneisses of granitic composition have been transformed on a decimetric scale into coarse grained massive charnockite sensu stricto along a set of conjugate fractures transecting the gneissic foliation charnockitization post dates the polyphase deformation regional high grade metamorphism and anatexis and evidently occurred at a late stage of the pan african tectonothermal history geothermobarometric and fluid inclusion data document textural and chemical equilibration of the gneiss and charnockite assemblages at similar p lith t conditions 650 700 degrees c 5 6kbar in the presence of carbonic fluids internally buffered by reaction with graphite and opaque mineral phases x co2 0 7 0 6 x h2o 0 2 0 3 x n2 0 1 logf o2 l7 5 mineralogical zonation indicates that charnockitization of the leptynitic gneiss involved first the breakdown of biotite and oxidation of graphite in narrow outward migrating transition zones adjacent to the gneiss followed by the breakdown of garnet and the neoblastesis of hypersthene in the central charnockite zone compared to the host gneiss the charnockite shows higher concentrations of k na sr ba and zn and lower concentrations of mg fe ti v y zr and the hree with a complementary pattern in the narrow transition zones of biotite breakdown the p lith t x h2o data and chemical zonation patterns indicate charnockitization through subsolidus dehydration reaction in an open system subsequent residence of the carbonic fluids in the charnockite resulted in low grade alteration causing modification of the syn charnockitic elemental distribution patterns and the properties of entrapped fluids we favour an internally controlled process of arrested charnockitization in which during near isothermal uplift the release of carbonic fluids from decrepitating inclusions in the host gneiss into simultaneously developing fracture zones led to a change in the fluid regime from fluid absent in the gneiss to fluid present in the fracture zones and to the development of an initial fluid pressure gradient triggering the dehydration reaction