ultrahigh temperature metamorphism and decompression history of sapphirine granulites from rajapalaiyam southern india implications for the formation of hot orogens during gondwana assembly sapphirine bearing mg al granulites from rajapalaiyam in the southern part of the madurai block provide critical evidence for late neoproterozoic cambrian ultrahigh temperature uht metamorphism in southern india poikiloblastic garnet in quartzo feldspathic and pelitic granulites contain inclusions of fine grained subidioblastic to xenoblastic sapphirine associated with quartz suggesting that the rocks underwent t 1000 c peak metamorphism quartz inclusions in spinel within garnet are also regarded as clear evidence for a uht condition inclusions of orthopyroxene within porphyroblastic garnet in the sapphirine bearing rocks show the highest al 2 o 3 content of up to 10 3 wt suggesting t 1050 1070 c and p 8 5 9 5 kbar temperatures estimated from ternary feldspar and other geothermometers t 950 1000 c further support extreme thermal metamorphism in this region xenoblastic spinel inclusions in sapphirine coexisting with quartz suggest that the spinel quartz assemblage pre dates the sapphirine quartz assemblage probably implying a cooling from t 1050 c or an anticlockwise p t path the fmas reaction sapphirine quartz garnet orthopyroxene sillimanite indicates a cooling from the sapphirine quartz stability field after the peak metamorphism corona textures of orthopyroxene cordierite sapphirine orthopyroxene sapphirine cordierite and cordierite spinel around garnet suggest subsequent near isothermal decompression followed by decompressional cooling toward t 650 750 c and p 4 5 5 5 kbar the sapphirine quartz association and related textures described in this study have an important bearing on the uht metamorphism and exhumation history of the madurai block as well as on the tectonic evolution of the continental deep crust in southern india our study provides a typical example for extreme metamorphism associated with collisional tectonics during the late neoproterozoic cambrian assembly of the gondwana supercontinent

discriminating between large mine collapses and explosions using teleseismic p waves some of the most suspicious seismic disturbances under the comprehensive nuclear test ban treaty ctbt are likely to be those associated with mining as they are shallow and at least some have an explosion like m b m s signature previous research highlighted the potential of broadband teleseismic p waves as a way of identifying large mine tremors broadband teleseismic p from two suspected large mine collapses one in germany 1302 ut 13 march 1989 5 4 m b and another in wyoming 1526 ut 3 february 1995 5 3 m b show differences in character despite the similarity of the reported ground failure and mine types we apply a full moment tensor analysis to the teleseismic p waves and show that the data are inconsistent with either a shallow explosion or an earthquake double couple at depth but this method is unable to distinguish between a shallow dip slip source and a closing crack moment tensor however three component surface wave seismograms recorded at regional distances fit the shallow closing crack model but are inconsistent with a shallow earthquake source because strong love waves expected from a double couple source are not observed at a number of stations well distributed in azimuth here we restate the equivalence for shallow sources of the closing crack model and a gravitational collapse model we use the latter to model the broadband p waves from these mine tremors and show that while non unique the differences in the observed broadband p waves from the two tremors can be attributed to the area amount of collapse depth and rate of collapse the collapse model predicts negative first motion for all p waves in contrast to the positive polarity expected from explosions thus the broadband teleseismic p waves have the potential to discriminate between large collapses and explosions

pressure temperature fluid history and exhumation path of a gondwana fragment the trivandrum granulite block southern india the trivandrum granulite block tgb southern india records evidence for three distinct stages of metamorphic evolution ml m2 m3 during the pan african orogeny with possible temperature gradient from south to north of the terrain as inferred from mineral phase equilibria thermobarometry in a number of classic localities nuliyam kunnanpara pandicherry and nellikkala fluid inclusions ei are mostly represented by c0 rich varieties in some cases with trace admixture of other gases brine inclusions are markedly rare several generations of carbonic inclusions occur in the charnockites and host rocks bt grt gneisses mostly with rare exception homogenizing into the liquid phase but yielding different homogenization temperatures th which translate into variable density p ranges the most common arrays of c0 rich inclusions have th values within the interval of 2 to 17 5 c p 0 9160 79 g cm3 and of 18 5 to f28 3 c p 0 790 0 649 g cm3 a denser variety of co inclusions with th within the range of 12 4 to 0 5 c p 0 996 0 931g cm3 also occur these th values and corresponding densities are generally comparable with those reported in previous fluid inclusion studies from this region we also report here the discovery of superdense c0 rich inclusions in a charnockite sample from nuliyam with th in the range of 15 6 to 21 9 c p 1 012 1 041 g cm3 this is by far the first report of such superdense inclusions from this granulite block a sketch of one of the arrays of these inclusions in nuliyam charnockite is shown in figure 1 although this array represents a group of synchronous inclusions the homogenization temperatures are not uniform and range from 15 6 to 1 8 c and even c such variations in th representing density reversals within ei during exhumation of rocks are not uncommon these groups of inclusions fill healed cracks in quartz often transecting grain boundaries and apparently showing a primary secondary pseudosecondary or even late secondary character the charnockites of the region formed during the decompression at the first metamorphic stage ml at temperatures 730k 35 c higher than for their host rocks 697k 40 c and at appreciably lower pressures 3 56 and 5 36 kbar respectively from textural relations the groups of synchronous c0 rich inclusions having th 8 1 13 6 c p 0 8760 834 g cm3 and probably also those with th 2 1 4 9t p 0 9150 897 g cm3 can be considered trapped at p t conditions of charnockite formation former group and during m1 metamorphism of the host rocks latter group

an investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the united states in the 0 5 4 hz band summary studies of teleseismic p and s wave amplitudes and spectra in the 0 5 4 hz band show large variations in the attenuative properties of the upper mantle under the united states the data indicate that attenuation is greatest under the south western united states including but not confined to the basin and range province the lowest attenuation prevails under the north central shield regions the north eastern part of the country consisting of new england and possibly including a larger area along the eastern seaboard is characterized by moderate attenuation in the mantle the level of the high frequency energy in short period seismic waves and the differences between q values derived from short and long period data indicate that q is frequency dependent the form of frequency dependence of t compatible with the data in the 0 5 4 hz range does not allow a rapid decrease of t with increasing frequency rather it supports a gradual decrease covering the broader 0 1 4 hz range the curves of t versus frequency for shield to shield and mixed shield to western united states type paths are parallel with an average difference of 0 2 s in t in the short period band but may diverge towards the long period band for both curves t p is below 1 s for shield to shield paths t p must be below 0 5 s at 1 hz

origin of paired high pressure ultrahigh temperature orogens a ridge subduction and slab window model introductionmetamorphism at elevated pressure temperature conditions and distinct uid regimes generates ultrahigh pres sure uhp high pressure hp andultrahigh temperature uht rocks harley 2004 brown 2006 2007 2009 kelsey 2008 santosh andomori 2008a b santos et al 2009 santosh et al 2009a zhang et al 2009 although previous studies havecorrelated these di erent orogens todistinct tectonic settings recent inves tigations record high pressure anduht conditions from the same tec tonic environment within the sameorogenic belt and in some cases evenwithin the same samples mostoftheseexamples come from major collisionalzones along which continental blocksweresuturedatdi erenttimesinearthhistory including from the neoarch ean hp uht rocks of the limpopobeltinsouthafrica tsunogaeandvanreenen 2006 the palaeoproterozoichp guo et al 2004 obrien et al 2005 and uht santosh et al 2007a b 2008 2009b belts in thenorth china craton and the hp uht belts in the neoproterozoiceastern ghats belt as well as thecambrian gondwana suture in south ern india shimpo et al 2006 tsuno gaeet al 2008a santoshet al 2009c notably the thermal regimes for thesepaired hp and uht rocks are similar 1000 c and they also share acommon uid history characterizedby co

extremely high density pure co2 fluid inclusions in a garnet granulite from southern india abstract a late archean 2 4 2 7 ga garnet granulite from the southern margin of the south indian craton preserves fluid inclusions with the highest density co2 yet reported from lower crustal rocks the rock comprises garnet clinopyroxene salite plagioclase amphibole pargasite orthopyroxene hypersthene biotite scapolite and quartz with accessory k feldspar ilmenite apatite and ankerite pressure temperature estimates of 9 11 kbar and 740 800 c are computed from electron microprobe data on equilibrium assemblages we report here detailed inclusion petrography and microthermometric data on fluids trapped in garnet feldspar and quartz from the granulite the dominant category in all these minerals are composed of monophase carbonic inclusions with melting temperatures close to 56 6 c indicating a co2 rich composition for the fluid laser raman microscopic studies confirm that the fluid is pure co2 with no traces of impurities such as n2 and or ch4 the inclusions homogenize into the l

fluids in high to ultrahigh temperature metamorphism along collisional sutures record from fluid inclusions abstract petrographic studies and microthermometric investigations on fluid inclusions associated with high to ultrahigh temperature metamorphic rocks in three major precambrian suture zones on the globe demonstrate the dominant occurrence of co 2 rich fluids these rocks form part of hot orogens developed along collisional plate boundaries the sapphirine quartz bearing mg al rich rock from the palghat cauvery suture zone a trace of the cambrian gondwana suture zone in southern india preserves evidence for a prograde high pressure event and subsequent peak ultrahigh temperature metamorphism along a clockwise path and contains abundant co 2 rich inclusions in corundum garnet and sapphirine most of the fluid inclusions are either primary or secondary and preserve low density co 2 rich fluids 0 569 0 807 g cm 3 similar low density co 2 rich fluid inclusions 0 853 0 953 g cm 3 are also present in pelitic granulites from the limpopo complex of southern africa a neoarchean granulite facies orogen formed by continent continent collision in contrast the garnet orthopyroxene granulite from tonagh island in the neoarchean napier complex in east antarctica contains very high density primary 1 095 1 129 g cm 3 and secondary 0 960 1 179 g cm 3 carbonic inclusions in garnet and quartz the calculated isochores for the fluid inclusions from the palghat cauvery suture zone and the limpopo complex yield significantly lower pressure estimates than those predicted from peak metamorphic conditions we interpret this as a result of significant density decrease due to rapid decompression along a clockwise p t trajectory in contrast the estimated isochores for primary inclusions in garnet orthopyroxene granulites from the napier complex are consistent with the peak p t conditions estimated from mineral phase equilibria for the tonagh island rocks suggesting that most of the fluid inclusions in these rocks did not undergo any marked effect of volume change and density decrease the contrasting fluid densities among the localities investigated in this study are probably related to the nature of the p t trajectory the tonagh island rocks had a near isochoric exhumation history whereas the metamorphic orogens in the other two sutures witnessed rapid decompression our results suggest that whereas the composition of the syn metamorphic fluids are preserved in all cases density reversal occurs within inclusions as a function of the tectonic history and exhumation style

carbonic fluids in ultrahigh temperature metamorphism evidence from raman spectroscopic study of fluid inclusions in granulites from the napier complex east antarctica

carbon isotope compositions of fluid inclusions in charnockites from southern india models for the formation of crustal granulites which include the metamorphism of anhydrous lithologies1 2 the extraction of hygroscopic granite melts3 4 and fluxing by co25 7 constrain the thermal and geochemical evolution of the lower crust and its interaction with mantle derived volatiles here we present abundances and carbon isotope compositions of co2 in fluid inclusions in quartz and garnet from gneiss granulite pairs from the incipient char nockite quarries of southern india determined by a stepped combustion thermal decrepitation carbon extraction technique which quantifies problematic sample contamination and allows precise lithological control the results show that the co2 in incipient charnockite is more abundant and isotopically heavier than the co2 in associated gneiss providing evidence for the influx of co2 rich fluids during their formation the inferred carbon isotope compositions of these fluids are consistent with a mantle source and at ponmudi the isotopic composition of coexisting graphite and co2 implies fluid rock volume ratios in excess of 0 15

sapphirine and corundum bearing granulites from karur madurai block southern india we report new occurrences of sapphirine and corundum bearing granulites intercalated within orthogneisses at lachmanapatti and malappatty in the northern part of madurai block sapphirine in these localities occurs either as needle like intergrowth with cordierite and corundum in symplectites and medium to fine grained euhderal to subhedral crystals associated with cordierite and corundum lachmanapatti or in association with plagioclase corundum and gedrite malappatty the sapphirine from lachmanapatti is highly magnesian xmg 0 87 0 94 with higher cr content up to 0 9 pfu as compared with those in other localities in the madurai block the sapphirine corundum association reported in this study has important bearing on the ultrahigh temperature metamorphism and exhumation history of the northern madurai block as well as on the tectonic evolution of the continental deep crust in southern india

modelling albedo and specific balance of the greenland ice sheet calculations for the sondre stromfjord transect glacio meteorological data obtained during the greenland ice margin experiment gimex investigations in west greenland the sondre stromfjord transect have been used to test and calibrate four energy balance mass balance models for the ice snow surface the region is characterised by the development of a wide zone of low surface albedo in the course of the melting season this zone was simulated in one of the energy balance models by including the effect of surficial meltwater on albedo observed mass balance and albedo data were used to constrain the models although all the models are capable of predicting the transect balance reasonably well only the model with the meltwater albedo coupling is able to reproduce the observed albedo pattern and mass balance profile along the transect by including the feedback between surficial meltwater and albedo in the model the sensitivity of the specific balance to changes in air temperature is found to be greatest just below the equilibrium line in contrast to what is generally found for valley glaciers a 1 k warming of the air temperature would increase the mean ablation along the transect by 0 5 m w e year 1

teleseismic spectral and temporal m0 and ψ estimates for four french explosions in southern sahara estimates for explosion moment m and reduced displacement potential are made for four french explosions at taourirt tan afella massif in southern french sahara using data from the long range seismic measurement network and the eka and yka arrays preparatory to determining moments attenuation t estimates are made for each station and the source region t values of 0 30 to 0 35 sec are found for the southern sahara test site this source region attenuation level is consistent with the hot spot hypothesis for the ahaggar plateau in northern africa consequently the attenuation bias between ahaggar and the nevada test site should be small both spectral estimation and broadband temporal deconvolution methods are used for estimation of the explosion moments the deconvolution estimates of static moment are found to be consistent with the spectral estimation methods deconvolved seismograms for the explosions emeraude rubis saphir and grenat show evidence of strong anisotropic free surface interaction that may be due to scattering or spall from the steep topography of the taourirt tan affela massif test site

fluid inclusions in adirondack granulites implications for the retrograde p t path investigation of fluid inclusions in granitic and calc silicate gneisses from the adirondack mountains new york has revealed the presence of various types including 1 co2 rich 2 mixed h20 c02 salt and 3 aqueous inclusions with no visible co2 many if not all of these inclusions were trapped or modified after the peak of granulite facies metamorphism as shown by textural relations or by the lack of agreement between the composition of the fluids found in some inclusions and the composition of the peak metamorphic fluid as estimated from mineral equilibria many fluid inclusions record conditions attained during retrograde cooling and uplift with minimum pressures and temper atures of 2 to 3 kbar and 200 to 300 c the tempera tures and pressures derived from the investigation of these inclusions constrain the retrograde p t path and the results indicate that a period of cooling with little or no decompression

fluid inclusions in granulites granulitized eclogites and garnet clinopyroxenites from the dabie sulu terranes eastern china minor granulites believed to be pre triassic surrounded by abundant amphibolite facies orthogneiss occur in the same region as the well documented triassic high and ultrahigh pressure hp and uhp eclogites in the dabie sulu terranes eastern china moreover some eclogites and garnet clinopyroxenites have been metamorphosed at granulite to amphibolite facies conditions during exhumation granulitized hp eclogites garnet clinopyroxenites at huangweihe and baizhangyan record estimated eclogite facies metamorphic conditions of 775 805 c and 15 kbar followed by granulite to amphibolite facies overprint of ca 750 800 c and 6 11 kbar the presence of na ca ba sr feldspars in garnet and omphacite corresponds to amphibolite facies conditions metamorphic mineral assemblages and p t estimates for felsic granulite at huangtuling and mafic granulite at huilanshan indicate peak conditions of 850 c and 12 kbar for the granulite facies metamorphism and 700 c and 6 kbar for amphibolite facies retrograde metamorphism cordierite orthopyroxene and ferropargasite plagioclase coronas and symplectites around garnet record a strong rapid decompression possibly contemporaneous with the uplift of neighbouring hp uhp eclogites carbonic fluid co2 rich inclusions are predominant in both hp granulites and granulitized hp uhp eclogites garnet clinopyroxenites they have low densities having been reset during decompression minor amounts of ch4 and or n2 as well as carbonate are present in the granulitized hp uhp eclogites garnet clinopyroxenites early fluids are high salinity brines with minor n2 whereas low salinity fluids formed during retrogression syn granulite facies carbonic fluid inclusions occur either in quartz rods in clinopyroxene granulitized hp garnet clinopyxeronite or in quartz blebs in garnet and quartz matrices uhp eclogite for hp granulites a limited number of primary co2 and mixed h2o co2 liquid inclusions have also been observed in undeformed quartz inclusions within garnet orthopyroxene and plagioclase which contain abundant low density co2 carbonate inclusions it is suggested that the primary fluid in the hp granulites was high density co2 mixed with a significant quantity of water the water was consumed by retrograde metamorphic mineral reactions and may also have been responsible for metasomatic reactions giant myrmekites occurring at quartz feldspar boundaries compared with the uhp eclogites in this region the granulites were exhumed in the presence of massive externally derived carbonic fluids and subsequently limited low salinity aqueous fluids probably derived from the surrounding gneisses

scattering from near source topography teleseismic observations and numerical simulations two dimensional linear elastic finite difference simulations of teleseismic p waveforms from point sources in two dimensional structure have been used to explore the variations that may be induced in event magnitude yield determination by the emplacement of explosive sources under mountainous topographic features the southern sahara french test site in algeria at taourirt tan afella massif on the ahaggar plateau has been used as a case study the topography of this test site is extreme and the event locations permit a test of the hypothesis that topography influences short period magnitudes of contained nuclear explosions the maximum expected variation is plus or minus 0 15 magnitude units from the network mean the magnitude variations are expected to change rapidly with take off angle and azimuth teleseismic observations of the explosions at the southern sahara test site are compared to predictions made from two dimensional linear finite difference simulations waveform data from the arrays eka and yka as well as lrsm data have been deconvolved to broadband displacement for inspection of the apparent far field p wave source qualitative comparisons are favorable that the topography above the explosions rubis and saphir defocused teleseismic pp at certain take off angles and azimuths long period positive polarity pulses can be seen at several sites that may indicate rayleigh to p scattering from topography near the source wwssn maximum likelihood magnitude data for the a ab and max p phases have been used to estimate that the magnitude variation due to topographic scattering is no more than 0 15 rms magnitude units across the wwssn for the southern sahara test site

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

co2 rich fluid inclusions in staurolite and associated minerals in a high pressure ultrahigh temperature granulite from the gondwana suture in southern india abstract we report the first detailed fluid inclusion study on mg al rocks from the gondwana suture zone along the palghat cauvery shear zone system in southern india these rocks underwent high pressure p 12 kbar and ultrahigh temperature t 990 c metamorphism during the late neoproterozoic associated with the collisional assembly of the gondwana supercontinent fluid inclusions of texturally primary and pseudosecondary categories occur in plagioclase staurolite and kyanite in these rocks inclusions of secondary nature are found in garnet and apatite all the trapped fluids show melting temperatures in the range of 58 6 to 56 6 c suggesting a dominantly pure co 2 composition the secondary inclusions show high homogenization temperatures t h of 12 9 to 30 0 c indicating low density of 0 59 0 83 g cm 3 although most of the primary and pseudosecondary inclusions also contain moderate to low density fluids 0 67 0 95 g cm 3 t h 3 5 to 27 4 c rare high density inclusions 1 00 1 06 g cm 3 t h 26 1 to 14 1 c were discovered in matrix plagioclase and porphyroblastic staurolite the estimated co 2 isochores for the high density primary and pseudosecondary inclusions intersect the clockwise p t trajectory of the rocks at around 8 3 9 0 kbar at 1000 c which broadly coincide with the peak metamorphic conditions of the area since these fluid inclusions show textural evidence for entrapment during the growth of the host high grade minerals we interpret the high density co 2 fluids to be traces of a co 2 rich synmetamorphic fluid that was present during the peak ultrahigh temperature metamorphism despite the preservation of high density co 2 inclusions in staurolite and plagioclase the primary and pseudosecondary inclusions in most of the other minerals show wide density variation which suggests the fluids in these inclusions underwent significant density reversal density decrease during decompression of the rocks from high pressure through the peak ultrahigh temperature stage along a clockwise p t trajectory the finding of pure co 2 inclusions in these mg al granulites conforms with similar observations from many other granulite facies terrains with the carbonic fluids probably derived from mantle reservoirs and transferred through deep seated shear zones that characterize this gondwana suture

frequency dependence of q in the mantle underlying the shield areas of eurasia part iii the q model summary a large set of teleseismic body wave data covering a broad range in frequency was analysed to determine the frequency arid depth dependence of q for p and s waves under the northern shield areas of eurasia based on numerous f estimates for p and s waves covering the seismic band between 0 02 and 8 hz a q model of the eurasian shield was constructed the data require a model in which q increases with frequency and which is characterized by q values in the upper mantle that are generally higher than those of global average models the model with the best fit includes a minimum in q between about 100 and 200 km depth and high q values on the order of thousands throughout most of the deeper mantle these results are generally consistent with proposed models of attenuation as a thermally activated process which is influenced by the temperature and pressure in the earth preliminary results suggest that t under tectonic regions is higher than t under shield regions for all frequencies over the 0 02 to 8 hz frequency range suggesting that q varies regionally as well as with frequency and depth

multi channel deconvolution of p waves at seismic arrays the results of a new multi channel deconvolution method applied to norsar and eka array recordings of teleseismic p waves are presented and interpreted in terms of possible surface reflections and other arrivals from the nevada test site and kazakh nuclear explosions the deconvolution method utilizes the well known fact that p wave spectra can be decomposed into source and receiver spectral factors for most events the source time functions appear to contain a pp arrival but they also show later unexplained arrivals the site functions are also complex in many cases about half of the late coda in p appears to be due to each source and receiver the recordings for a presumed kazakh cratering event show a distinctly different source function when compared to deeper buried explosions at the same test site from the deconvolved source time functions the cratering to noncratering mb bias is estimated to be between 0 09 and 0 22 magnitude units

age and sedimentary provenance of the southern granulites south india u th pb shrimp secondary ion mass spectrometry abstract southern india lies at a junction in the gondwana forming orogenic belts between the east african orogen and the kuunga orogen it contains voluminous high grade metasedimentary gneisses that make up an important component of the record of collision and amalgamation of gondwana here we present u pb secondary ion mass spectrometry sims isotopic data from detrital zircon cores from throughout southern india that demonstrate dominant neoarchaean to palaeoproterozoic age components that are incompatible with the known ages of potential southern and central indian source regions the original sediments to the trivandrum block gneisses were deposited between 1900 and 515 ma whereas a sample from the achancovil unit and possible also a sample from the madurai block were deposited in neoproterozoic times we speculate that these rocks broadly correlate with southern and western malagasy metasedimentary rocks including the itremo and molo groups and formed an extensive basin or basins that lay on the west side present orientation of the neoproterozoic continent azania in addition metamorphic zircon from four samples yielded an age of 513 6 ma that is interpreted as dating high grade metamorphism throughout much of the southern granulite terrane

spectral characteristics of p waves from nuclear explosions and yield estimation abstract spectra of teleseismic short period p waves from nuclear explosions show clear path related differences in their high frequency falloff rates p waves from kazakh explosions commonly show significant seismic energy above the frequency of 5 hz when recorded in shield regions peaceful nuclear explosions in the tectonically stable areas of the ussr have similar properties together with the amchitka explosions and salmon nuclear explosions in the western united states algeria and french polynesia show much less high frequency energy in their p wave spectra and signal energy above 5 hz is usually not seen we attribute these variations to lateral changes in the anelastic attenuation properties of the upper mantle for the events in the contiguous united states this interpretation is confirmed by the results of reciprocal measurements of q about 500 p wave spectra not including those utilized in the reciprocal measurements were used to estimate the contribution to t p of the upper mantle q structures under a number of nuclear test sites and observatories

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

attenuation and scattering of broadband p and s waves across north america differential attenuation deltat italic measurements of teleseismic p italic and s italic waves are made in the frequency range 0 05 5 0 hz across north america using broadband seismic data from the department of energy s regional seismic test network and lawrence livermore national laboratory s basin and range network data from four events have been analyzed by first assuming frequency independent q italic the observed regional variations for deltat italic are consistent with previous studies and show greater attenuation for stations in the basin and range relative to those in shield regions of north america

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

first report of sapphirine bearing rocks from the palghat cauvery shear zone system southern india abstract silica deficient mg al granulites from paramati within the palghat cauvery shear system contain sapphirine in association with corundum spinel and sillimanite gedrite which occurs commonly in this locality coexists with cordierite corundum and sillimanite mineral assemblages and reaction textures indicate peak metamorphism at ultrahigh temperature conditions this new locality provides evidence for extreme crustal metamorphism along the archean proterozoic collision boundary in southern india

the pwaves from the amchitka island explosions summary there is evidence that the equivalent seismic sources of the amchitka island explosions longshot milrow and cannikin depart significantly from the simple model of a point compressional source in a layered elastic medium consequently modelling the observed seismograms using standard source models may not be the most efficient method of determining source properties here an alternative to modelling is used to obtain information on the seismic sources due to the explosions broad band bb estimates of the p signals are obtained from the short period sp seismograms corrected for attenuation and interpreted in terms of p pp and radiation from secondary sources the main conclusions are i bb estimates of the radiated displacement from the explosions can be obtained with only a small reduction in the signal to noise ratio seen on sp seismograms ii observations of differences in pulse amplitudes and spectra are not necessarily due to differences in anelastic attenuation iii p and pp at a given station may differ in shape so that notches in the signal spectrum may not be related to source depth iv there is evidence of arrivals that others have identified as due to slapdown but which could be interpreted as an overshoot to pp v direct interpretation of the estimated ground displacement is a better procedure for determining the seismic source properties of explosions than modelling sp seismograms using idealised models as a starting point

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

post metamorphic co2 rich fluid inclusions in granulites in granulite facies samples from the adirondack mountains ny estimates of peak metamorphic co2 fugacities based on mineral equilibria are not consistent with estimates based on data for high density co2 rich fluid inclusions of the 21 adirondack samples investigated for this study all contain co2 rich inclusions inclusions occur in quartz apatite and garnet they range in size from 3 to 50 m and are without visible h2o in a few of the inclusions freezing point determinations and preliminary laser raman spectroscopy show the presence of small amounts 3 of other fluids n2 and h2s co2 liquid vapor homogenization temperatures are between 46 and 31 c corresponding to densities between 1 14 and 0 5 gm cc some of these densities are consistent with peak metamorphic entrapment 1 06 to 1 1 gm cc

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

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

regional carbonate alteration of the crust by mantle derived magmatic fluids tamil nadu south india regional carbonate alteration of the crust associated with major shear zones provides direct evidence for co 2 rich fluid mobility a good example occurs within the attur lineament one of numerous proterozoic shear zones which crosscut charnockitic gneisses and other lithologies of the southern indian craton at this locality widespread carbonate alteration of silicate rocks has involved growth of ankerite and other carbonate minerals which replace preexisting silicates some of the ankerite was subsequently recrystallized to fine grained calcite and iron oxide accompanied by sericitization of feldspar carbon oxygen and strontium isotope analyses of samples of ankerite and calcite together with some of the coexisting silicate minerals have been used to constrain the conditions of formation of the carbonate alteration and the origin of the fluids involved delta 13 c values of ankerite are relatively homogeneous ranging between 6 5 and 3 9 with a mean of 5 3 delta 18 o is also

three dimensional lithospheric electrical structure of southern granulite terrain india and its tectonic implications 1 the crustal as well as the upper mantle lithospheric electrical structure of the southern granulite terrain sgt is evaluated using the magnetotelluric mt data from two parallel traverses one is an 500 km long n s trending traverse across sgt and another a 200 km long traverse data space occam 3 d inversion was used to invert the mt data the electrical characterization of lithospheric structure in sgt shows basically a highly resistive several thousands of ohm meters upper crustal layer overlying a moderately resistive a few hundred ohm meters lower crustal layer which in turn is underlain by the upper mantle lithosphere whose resistivity shows significant changes along the traverse the highly resistive upper crustal layer is interspersed with four major conductive features with three of them cutting across the crustal column bringing out a well defined crustal block structure in sgt with individual highly resistive blocks showing correspondence to the geologically demarcated salem madurai and trivandrum blocks the 3 d model also brought out a well defined major crustal conductor located in the northern half of the madurai block the electrical characteristics of this south dipping conductor and its close spatial correlation with two of the major structural elements viz karur oddanchatram kodaikanal shear zone and karur kamban painavu trichur shear zone suggest that this conductive feature is closely linked to the subduction collision tectonic processes in the sgt and it is inferred that the archean dharwar craton neoproterozoic sgt terrain boundary lies south of the palghat cauvery shear zone the results also showed that the achankovil shear zone is characterized by a well defined north dipping conductive feature the resistive block adjoining this conductor on the southern side representing the trivandrum block is shown to be downthrown along this north dipping crustal conductor relative to the madurai block suggesting a northward movement of trivandrum block colliding against the madurai block the lithospheric upper mantle electrical structure of the sgt up to a depth of 100 km may be broadly divided into two distinctly different segments viz northern and southern segments the northern lithospheric segment over a major part is characterized by a thick resistive upper mantle while the southern one is characterized by a dominantly conductive medium suggesting a relatively thinned lithosphere in the southern segment

fluid absent melting and the roles of fluids in the lithosphere a slanted summary abstract the presence or absence nature and compositions of lithospheric fluids are crucial factors in the evolution of igneous and metamorphic rocks despite this confusion still surrounds perceptions of the degrees of fluid involvement in many geological settings however experimental and field investigations constrain these roles and we are able to make some valid generalizations studies of prograde metamorphism have highlighted the spatial heterogeneity of fluid concentrations in many crustal environments this commonly indicates internal lithological control of volatile activities under fluid present conditions crustal fluids do not appear to mix readily fluid flow is generally structurally or lithologically controlled the transition from amphibolite to granulite facies is characterized by a decrease in ah2o as well as a temperature increase in many terranes these phenomena correlate with the appearance of migmatites some granulites are not migmatitic but have chemical and mineralogical characteristics of melt depleted restites this indicates efficient extraction of melts incongruent melting reactions involving the breakdown of crystalline hydrates in crustal rocks produce granitoid melts plus denser restites that are nearly or actually anhydrous experimental and theoretical treatments of fluid absent melting show that micas and amphiboles decompose at 700 to 900 c for mid to lower crustal pressures the melts resemble the compositions of s and i type granitoids pervasive aqueous fluids could not generally have been present during this melting since exposed granulite terranes are not characterized by high melt proportions and the magmas themselves are water undersaturated likewise the general presence of very h2o poor pervasive fluids is unlikely since this would allow only subsolidus dehydration at normally attainable crustal temperatures in this case the amphibolite granulite transition is possible at relatively low temperatures and the resultant rocks would not contain evidence of in situ melting the granulite granite connexion and effective crustal differentiation seem viable only during high temperature fluid absent metamorphism data on continental geotherms show that the lower crust is not entirely granulitic granulites are produced in regions of anomalously high heat flow the mantle connexion thus inferences on the nature of the lower crust should not be entirely based on studies of exposed granulite terranes mineral assemblages in eclogites also indicate widespread internal buffering of volatile activities and probable fluid absent conditions mantle derived basaltic magmas too are volatile bearing and it is plausible that volatile fixing phases also occur in the mantle volatiles may largely be introduced into the mantle through subduction processes and only released during the melting attending the breakdown of hydrous minerals as in the crust

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

the nagercoil granulite block southern india petrology fluid inclusions and exhumation history abstract the nagercoil granulite block ngb constitutes the southernmost domain in the high grade metamorphic terrain of southern india and dominantly comprises orthopyroxene k feldspar plagioclase quartz biotite ilmenite bearing massive charnockites where they are mixed with aluminous supracrustals the charnockites contain garnet often displaying typical decompression textures with coronal orthopyroxene and plagioclase surrounding relict garnet grains orthopyroxene is preserved in near pristine state in the charnockite suggesting low water activity garnet orthopyroxene thermometry of ngb charnockites yields temperatures of 691 934 c garnet biotite thermometry yield values that broadly overlap 538 864 c with the above estimate although some lower values indicative of retrograde fe mg exchange are also obtained the presence of mesoperthite in the rock and high fluorine content in biotites also suggest high metamorphic temperatures charnockite barometry using garnet orthopyroxene plagioclase quartz assemblage yields 4 0 6 3 kbar an overall drop in pressure by over 2 kbar correlate with the isothermal decompression history inferred from textural criteria detailed fluid inclusion petrographic microthermometric and laser raman spectroscopic data presented here allow an evaluation of the fluid evolution history of ngb charnockites we distinguish four groups of inclusions with the earliest generation characterised by co2 with variable but minor proportion of h2o subsequent generations are dominated by co2 locally ch4 and n2 occur as trace components co2 rich inclusions dominate in all minerals garnet k feldspar plagioclase and apatite homogenisation temperatures assign densities of 0 92 0 93 g cm3 for the co2 involved in charnockite formation a close correspondence of the isochores for co2 h2o and co2 inclusions with p t data derived from mineral phase equilibria suggests fluid entrapment at peak metamorphic conditions the metamorphic evolution of ngb and its exhumation path characterised by isothermal decompression are comparable with those of charnockites from pan african terrains elsewhere in east gondwana

fluid evolution of indus basin ladakh north west himalaya india constraint from fluid inclusion and oxygen isotope thermometry fluid inclusions and oxygen isotope thermometry were carried out on quartz calcite veins of the indus basin in indus suture zone isz of northwest ladakh himalaya to constrain fluid evolution history of the basin three types of veins are identified as fault fill network and sigmoidal in the study area the fault fill veins microstructures of calcite and quartz suggest the deformation temperature of veins between 250 and 400 c and oxygen isotope thermometry provide the range between 192 and 359 c the network type veins microstructures of calcite revel deformation temperature in the range of 170 250 c and oxygen isotope thermometry indicate vein temperature range between 144 and 276 c stable isotopic values of sigmoidal and network type veins suggest the magmatic source of fluid the fault fill veins display magmatic to the marine fluid signature microstructures and isotope data set advocate the formation of veins from the wall rocks by leaching processes fluid inclusion microthermometric dataset indicates that veins were formed at a maximum depth of 20 km at 700 c the co2 fluids were trapped below 6 2 kbar at 700 c ch4 fluid was trapped at a shallower depth between 4 2 kbar 650 c and 2 3 kbar 381 c the primary aqueous fluids were trapped below 3 0 kbar up to 2 3 kbar at 594 to 382 c and secondary aqueous fluids were trapped between 2 9 and 1 5 kbar at 359 to 197 c the p t path for the entrapment defines an initial isothermal decompression itd itd is also supported by decrepitated and stretched inclusions texture as well as c shaped or hook like fluid inclusions morphology which collectively points towards fast basin uplift

very high density co2 associated with ultrahigh temperature metamorphism in the eastern ghats granulite belt india spinel bearing high mg al granulites of the vizianagram area in the eastern ghats granulite belt show textural features clearly establishing that the association spinel ss quartz fe ti oxide solid solution sillimanite porphyroblastic orthopyroxene was stable during peak metamorphic conditions pressure temperature p t conditions estimated from both mineralogical thermobarometry and phase equilibrium limitations indicate that the peak metamorphism occurred under ultrahigh t conditions 1000 c at 8 9 kbar pressure retrograde p t conditions of 750 800 c 6 7 kbar are deduced from the compositions of coronal garnet and orthopyroxene which have rims of spinel against quartz indicating significant cooling with slight lowering of pressure quartz associated with the ultrahigh t assemblage at vizianagram contains ubiquitous single phase carbonic inclusions as isolated clusters that belong to two categories group i shows extremely high density homogenization temperature 51 1 8 c density 1 15 g cm 3 and group ii trapped relatively lower density fluids homogenization temperature 18 4 2 4 c density 1 05 g cm 3 the iso chores for group i inclusions pass through the peak metamorphic p t conditions whereas those for group ii coincide with the p t conditions of the formation of coronal garnet and orthopyroxene our study is the first report of very high density co 2 associated with the eastern ghats granulite belt rocks and provides a strong case for the presence of co 2 rich fluids during ultrahigh t metamorphism at lower crustal levels

free air gravity over the hoggar massif northwest africa evidence for alteration of the lithosphere abstract analysis of the free air gravity field over the broadly elevated hoggar region in northwest africa suggests that the uplift is similar in origin to the midplate hotspot swells observed on the seafloor the hoggar massif is a dome of precambrian basement approximately 1 km high 1000 km wide and capped by late tertiary alkali basalt volcanos gravity measurements reveal a broad free air high with maximum amplitude of approximately 40 mgal which is coincident with the areal extent of the hoggar using the reasonable assumption that the hoggar is in local isostatic balance calculations indicate that the amplitude of the gravity anomaly is best explained if the isostatic root of the elevated area is 60 km below ground surface this root depth is similar to that observed for both the hawaiian swell in the pacific and the bermuda rise in the atlantic and is shallower than the expected base of the lithosphere the gravity data suggest that the lithosphere beneath the hoggar has been reduced in density perhaps by reheating as inferred for oceanic swells

carbonic metamorphism at ultrahigh temperatures evidence from north china craton abstract the north china craton ncc constitutes one of the fundamental precambrian nuclei of asia the paleoproterozoic khondalite belt along the northern margin of the ncc shows evidence for extreme crustal metamorphism at temperatures exceeding 1000 c and pressures of 10 12 kbar with the formation of diagnostic ultrahigh temperature uht mineral assemblages including sapphirine quartz high alumina orthopyroxene sillimanite and high temperature mesoperthites here we record for the first time the common occurrence of co2 rich fluid inclusions in peak uht minerals in the mg al granulites of ncc and trace the fluid evolution history from microthermometric and laser raman spectroscopic studies we show that the syn metamorphic fluid in the uht rocks was pure co2 while very high density carbonic fluids are preserved in some cases corresponding to entrapment at peak conditions many of the inclusions underwent density modification during the rapid and near isothermal exhumation of the rocks following peak uht metamorphism and initial cooling at depth the present study area within the northern margin of the ncc defines a collisional orogenic belt where continental collision and deep subduction were possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusions of paleoproterozoic age that are seen emplaced within the granulite facies supracrustals the thermal anomaly displayed by the uht granulites may thus correlate with asthenospheric upwelling and emplacement of mafic magmas possibly associated with plume activity which provided the heat and co2 input to achieve extreme crustal metamorphism and generation of dry granulite facies assemblages our study is the first report of syn metamorphic co2 rich fluids in uht granulites from a paleoproterozoic ca 1 92 ga terrane and provide evidence for carbonic metamorphism at ultrahigh temperatures as north china craton joined the columbia supercontinent amalgam

anticlockwise evolution of ultrahigh temperature granulites within continental collision zone in southern india abstract we report three new localities of corundum and sapphirine bearing hyper aluminous mg rich and silica poor ultrahigh temperature granulites formed during late neoproterozoic cambrian times within the palghat cauvery shear zone system in southern india from petrologic characteristics mineral chemistry and petrogenetic grid considerations the peak metamorphic conditions of these rocks are inferred to lie around 950 1000 c as suggested by al in orthopyroxene thermometer at pressures above 10 kbar as indicated by the equilibrium orthopyroxene sillimanite gedrite quartz assemblage these rocks preserve several remarkable reaction textures the most prominent among which is the triple corona of spinel sapphirine cordierite on corundum with the whole textural assembly embedded within the matrix of gedrite suggesting the reaction ged crn spl spr crd the formation of sapphirine sillimanite assemblage symplectite associated with relict corundum and porphyroblasitc cordierite is explained by the reaction crd crn spr sil the association of sapphirine cordierite symplectite with gedrite sillimanite assemblage as well as with aluminosilicate boundaries indicates the gedrite consuming reaction ged sil spr crd extensive growth of sapphirine cordierite observed on the rim of gedrite porphyroblasts with spinel occurring as relict inclusions within the sapphirine indicates the reaction ged spl spr crd the pressure temperature p t path defined from the observed mineral assemblages and reaction texture is characterized by anticlockwise trajectory with a prograde segment of initial heating and subsequent deep burial followed by retrograde near isothermal decompression such an anticlockwise trajectory is being reported for the first time from southern india and has important tectonic implications since these rocks were developed at the leading edge of the crustal block that was involved in collisional orogeny and subsequent extension during the final phase of assembly of the gondwana supercontinent we propose that the rocks were subjected to deep subduction and rapid exhumation and the extreme thermal conditions were attained either through input from underplated mantle derived magmas or convective thinning or detachment of the lithospheric thermal boundary layer during or after crustal thickening

carbonic fluid inclusions in south indian granulites evidence for entrapment during charnockite formation field evidence and fluid inclusion studies on south indian incipient charnockites suggest that charnockite formation occurred during a decompressional brittle regime following the peak of metamorphism and regional deformation the most abundant type of inclusions in quartz and garnet grains in these charnockites contain high density carbonic fluids although lower density fluids occur in younger arrays of inclusions discrete fluid inclusion generations optically are observed to decrepitate over well defined temperature intervals and quantitative measurements of co2 abundance released from these inclusions by stepped thermal decrepitation show up to a four fold increase by volume in the incipient charnockites relative to the adjacent gneisses from which they are derived studies based on optical thermometry visual decrepitation and stepped heating inclusion release together indicate that entrapment of carbonic fluids coincided with charnockite formation we confirm that an influx of carbon dioxide rich fluids is associated with the amphibolite granulite transition as recorded by the incipient charnockites the remnants of which are commonly preserved as the earliest generation of high density fluid inclusions