garnet orthopyroxene bearing granulites from enderby land antarctica metamorphic pressure temperature time evolution of the archaean napier complex

an improved set of a x parameters for fe mg ca garnets and refinements of the orthopyroxene garnet thermometer and the orthopyroxene garnet plagioclase quartz barometer

young high temperature granulites from the base of the crust in central mexico characterization of the lower continental crust is essential to understanding processes of crustal formation and evolution many workers have concluded that the lower crust is composed of granulite facies rocks see for example refs 1 2 but many exposed granulite facies terranes seem to have mid crustal rather than lower crustal origins3 5 here we present new data from direct samples of the lower continental crust in the form of metapelitic rock fragments brought to the surface by quaternary volcanism in central mexico these xenoliths contain exsolved ternary feldspars that record extremely high minimum metamorphic temperatures of 950 1 100 c the highest yet known to be preserved in deep seated metamorphic rocks the metamorphism seems to be the result of underplating by basaltic magma and to be regional in extent our barometry on these samples demonstrates that granulite facies metamorphic rocks are present in the lower crust and provides important constraints on tectonic models and interpretations of geophysical data chemical and text lira i evidence suggest that the xenoliths were not able to cool to below 850 900 c before being entrained in their host magmas indicating that the granulite facies metamorphism occurred no more than 30 myr ago

co 2 melts and granulite metamorphism the discovery that granulites contain co2 rich fluid inclusions while amphibolites in the same terrane contain h2o rich or mixed co2 h2o inclusions1 has led to a debate over the processes that produce granulite metamorphism one theory2 4 maintains that granulites form as the result of a massive influx of co2 from lower crustal or mantle sources such an influx could be responsible for the marked depletion many granulite terranes show in large ion lithophile elements2 5 others however maintain that granulite facies metamorphism is a necessary complement of crustal melt ing6 9 recently lamb and valley10 11 have argued that granulite metamorphism may be a product of any one of three processes co2 streaming partial melting or recrystallization of originally dry rocks here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust

application of vitrinite reflectance anisotropy in the evaluation of coal metamorphism measurement of the maximum plus either the minimum or mean vitrinite reflectance provides a method for quantification of anisotropy of the reflectance previous research has suggested that anisotropy of vitrinite reflectance may be a direct indicator of static pressure depth of burial at which coal metamorphism occurred the combination of thermal information from vitrinite reflectance and pressure information should therefore provide a means of evaluating the metamorphic history of a single coal seam or a series of coals in a sedimentary basin given the independent placement of coal rank parameters on a pressure temperature grid occurrence of coals in strata with diagnostic metamorphic minerals is rare therefore evaluation of coal metamorphic conditions can seldom proceed parallel to mineralogical evaluation of rock metamorphic conditions rather the coal petrologist has generally relied upon time temperature nomograms to estimate metamorphic temperature from coal rank in this study the level of organic metamorphism lom time temperature scale of hood and others 1975 was considered the most versatile nomogram for evaluation of metamorphic conditions coals from throughout the appalachians were studied but this study concentrates on coals from the allegheny plateau in western pennsylvania vitrinite maximum reflectance in oil at 546 nm and reflectance anisotropy r maximum r mean r maximum anisotropy were measured on pennsylvania coals in order to estimate rank gradients and subsequently paleogeothermal gradients however it was necessary to rely upon previously published volatile matter data from the lower kittanning upper freeport and pittsburgh seams from equivalent metamorphic temperatures from the lom time temperature scale and from vertical separation of the seams paleogeothermal gradients were calculated for somerset county adjacent to the allegheny front about 40 c km and for westmoreland county to the west about 33 c km past depths of burial for both localities were calculated to have been 3 5 to 4 km for the allegheny group coals calculated gradients are each in areas on the plateau where vitrinite reflectance is nearly constant within each area two similar areas for which geothermal gradient could not be calculated directly due to insufficient vertical exposure of coals lie immediately to the north the crustal blocks appear to be divided by the southwest to northeast chestnut ridge anticline which marks a major tectonic division on the plateau and by the southeast to northwest gwinn type lineament which marks a northward reduction in amplitude of the plateau folds coal rank is 1 6 r low volatile bituminous in the somerset county block associated with the 40 c km gradient 1 3 r medium volatile in the block northeast of the lineament centered in clearfield county 0 9 r high volatile a in the westmoreland county block associated with the 33 c km gradient west of chestnut ridge and 0 8 r high volatile a in the block northeast of the lineament clarion county the rank decrease west across chestnut ridge occurs in a zone about 50 km wide width of the zone of northeastward rank that decreases across the lineament is not as well defined but is probably of the same magnitude as burial depths of the blocks appear to have been similar the primary cause for rank variation was variation in geothermal gradients between blocks anisotropy did not change significantly across the region suggesting that it can be correlated with past depth of burial

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

the felsic complex of the vallehermoso caldera interior of an ancient volcanic system la gomera canary islands abstract a mid to upper miocene felsic cone sheet dike complex caldera collapse and dome intrusion located around the vallehermoso and tamargada areas north of la gomera island is described it constitutes one of the less known volcanic episodes in the canary archipelago and especially in la gomera island based on detailed field and structural evidence it is suggested that the cone sheet shows at the surface an almost circular geometry truncated to the nw sector after the cone sheet dike complex formed decompression of the interior of an assumed shallow magma chamber occurred due to the subsequent migration of felsic magma throughout the dikes of the cone sheet this last event caused the roof of the magma chamber to collapse leading to the formation of a 3 to 4 km wide caldera a breccia deposit formed during the collapse and filled a depressed central area which finally was affected by an episode of magmatic resurgence leading to a later almost circular dome intrusion the association of cone sheet breccia deposits and domes constitutes the so called trachytic phonolitic complex tpc and should be viewed as the root of an ancient intensely eroded volcanic edifice made of trachytes nepheline phonolites and minor hauyne phonolites as the dominant materials a description of the structural petrological and geochemical features of the trachytic phonolitic complex and a discussion about their origin are considered in this paper we also consider the correlation between another felsic intrusion of alkali gabbros and syenites called tamargada syenites that also crops out in the vallehermoso tamargada area with respect to the trachytic phonolitic complex our data suggest that this alkaline intrusion of alkali gabbros and syenites belongs to an earlier intrusive episode on the basis of petrological geochemical and detailed field studies both trachytes and nepheline phonolites included in the trachytic phonolitic complex most likely evolved from alkali mafic magmas from the upper old basalt formation through a dominant fractional crystallization process additionally hauyne phonolites could develop from local and later magmatic processes such as gas transfer that altered and changed a small part of the previously mentioned nepheline phonolites to hauyne phonolites

p t x relationships deduced from corona textures in sapphirine spinel quartz assemblages from paderu southern india the sapphirine sa spinel sp quartz qz bearing rocks from paderu occur as lenticular enclaves within the precambrian khondalitecharnockite terrane of southern india in addition these rocks contain orthopyroxene opx sillimanite sill garnet gt cordierite cd biotite potash feldspar kf plagioclase and symplectites of cd kf qz opx the symplectites may have formed from the breakdown of osumilite grain contacts of sapphirine and spinel with quartz are rarely observed and the incompatibility with quartz during later stages is displayed by the development of several types of polymineralic reaction coronas the coronas in the different rock types a b etc are minerals listed from core to rim of corona a 1 sapphirine bearing rock type without spinel sa sill opx sa sill cd sa cd opx a 2 sapphirine and spinel bearing sp sa sill opx qz sp sa sill sp sa opx sp sill opx sp sa sill gt qz sa sill opx sp sa sill opx sa sill opx gt sp sa opx gt sp sa sill gt and b spinel bearing but sapphirine free sp sill opx sp sill gt sp cd commonly the coronas in the rock type a 2 and b also contain ilmeno hematite corundum in the core in association with spinel these rock types also provide textural evidence for later crystallization of cd cd sa and gt qz from opx sill qz and gt sill qz sapphirine is aluminous near 7 mg fe 2 o 9 al fe 3 2 o 3 3sio 2 and contains up to 12 2 wt per cent iron as feo orthopyroxene is also aluminous containing up to 10 4 wt per cent al 2 o 3 sapphirine and spinel have relatively high contents of fe 2 o 3 x mg in the fe mg minerals increases from rock type b to a2 to a1 a sequence of reactions has been deduced from coronas and other reaction textures and from the phase compatibility relations in the feo mgo al 2 o 3 sio 2 h 2 o system the p t x relationships from geothermobarometry and petrogenetic grids viz fe 2 o 3 vs feo and h 2 o vs fe 2 o 3 suggest 1 a retrograde mildly decompressive trajectory from 900 60 c 65 0 7 kb core to 760 50 c 5 0 6 kb rim and 2 the observed mineralogy of the coronas and reactions deduced from them are dependent on the relative feo fe 2 o 3 and h 2 o contents of the rocks feo 3 fe 2 o 3 and h 2 o

garnet orthopyroxene plagioclase quartz barometry refinement and application to the english river subprovince and the minnesota river valley recent experimental theoretical and thermodynamic studies permit better calibration of two reactions for geobarometry grossular pyrope quartz anorthite enstatite grossular almandine quartz anorthite ferrosilite if both reactions are applied using the same thermodynamic data and activity models they should yield the same pressure for a given garnet pyroxene plagioclase quartz assemblage application to a variety of high grade terrains generally yielded excellent results however poor results have been obtained for high fe rocks which can be traced to errors in activity models for garnet and or pyroxene either a two site ideal mixing model for orthopyroxene cf wood and banno 1973 underestimates enstatite activity for high fe orthopyroxenes or the ganguly and saxena 1984 model overestimates pyrope activity in low mg garnets

the role of synmetamorphic igneous rocks in the metamorphism and partial melting of metasediments northwest adirondacks field and petrologic studies along the adirondack lowlands highlands boundary near harrisville ny indicate that heat from the synmetamorphic intrusion of the diana syenite complex intrusion temperature of 1 050 c played a major role in the local metamorphic thermal regime and was responsible for extensive partial melting of adjacent metasedimentary units major paragneiss of engel and engel metamorphic temperatures inferred from two feldspar and spinel quartz assemblages decrease from 850 950 c along the diana metasediment contact to 650 700 c 2 3 km away from the contact metamorphic pressures are 7 0 5 kb as determined from coexisting plagioclase garnet sillimanite quartz kyanite sillimanite and garnet rutile ilmenite sillimanite quartz grail in the paragneiss migmatites consisting of quartz microcline perthite sodic plagioclase leucosomes are generally concordant with the melanosome consisting of biotite sillimanite garnet spinel plagioclase corundum cordierite qualitatively the amount of partial melt and occurrences of corundum bearing assemblages decrease away from the diana contact activity of h2o inferred from coexisting biotite sillimanite quartz garnet k feldspar ranges from 0 01 to 0 17 and is five to ten times lower in corundum bearing rocks

theoretical phase relations involving cordierite and garnet revisited the influence of oxygen fugacity on the stability of sapphirine and spinel in the system mg fe al si o the theoreticalp t grid for stability relations of the phases cordierite cd sapphirine sa hypersthene hy garnet ga spinel sp sillimanite si and quartz qz of hensen 1971 has proved useful in the interpretation of metamorphic mineral assemblages formed at low oxygen fugacity both experimental data and evidence from natural rocks indicate that at high oxygen fugacity compatability relations change as a result of the enlargement of the stability field of spinel which causes a topological inversion and the stabilisation of the invariant points sa ga and cd this implies the stable existence of the univariant equilibria for f text o text 2 buffered conditions sp qz ga hy si o2 sa cd cd sp qz hy si o2 sa ga and sa sp qz hy si o2 ga cd and the divariant reaction sp qz hy si o2 sa ga cd these redox equilibria are restricted to conditions of high oxygen fugacity the proposed theoreticalp t grids for both low and high oxygen fugacity satisfactorily explain all experimental data and metamorphic mineral assemblages so far found in granulites

a geochemical and experimental study of the role of k feldspar during water undersaturated melting of metapelites abstract the production of s type granites has been related to the extraction of melts during water undersaturated melting of metasediments in the lower continental crust if this mechanism is of widespread applicability a chemically distinctive granulitic restite must be left behind with a positive eu anomaly and depleted incompatible element concentrations however little geochemical evidence has been found in support of this hypothesis the rare earth element geochemistry of lower crustal granulites and associated melts will depend on the behaviour of the phases in which ree and trace elements are concentrated i e zircon monazite and k rich feldspar new experimental data on synthetic metapelites show that k feldspar can be a product or a reactant during water undersaturated melting of biotite depending on the h2o k2o of the melt relative to biotite past confusion over the role of k feldspar during melting is due to the reaction being close to degeneracy and changing its stoichiometry in response to only small changes in bulk composition coherent interpretation of the role of k feldspar in different experimental studies requires a better knowledge of phase water contents than has commonly been available the leucosomes formed in some antarctic granulite facies migmatites are likely to have had low h2o k2o ratios which suggests that k feldspar would have been a reactant during melting this could cause the positive eu anomalies observed in the leucosomes through the disequilibrium melting of k feldspar during water undersaturated melting the undersaturation of trace elements and ree in the leucosomes strongly suggests that disequilibrium melting took place caused by the incomplete dissolution of accessory phases monazite and zircon these phenomena give the melts a distinctive geochemical character which has also been seen in the other granulite facies leucosomes analysed to date this geochemical character contrasts with that of s type granites and therefore the production of granulites in the lower crust may not necessarily be associated with this type of magmatism if lower crustal granulite facies migmatites are the source region for peraluminous s type granites then the melts generated must undergo considerable modification during ascent

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

silica undersaturated sapphirine spinel and kornerupine granulite facies rocks ne strangways range central australia small pods of silica undersaturated al rich and mg rich granulite facies rocks containing sapphirine pleonastic spinel kornerupine cordierite orthopyroxene corundum sillimanite and gedrite are scattered throughout the ne strangways range central australia these are divided into four distinct rock types namely orthopyroxene rich aluminous granofels and metapelitic gneisses containing sapphirine spinel or kornerupine two granulite facies metamorphic events are recognized of which only the first m1 is considered in this paper peak metamorphic mineral parageneses indicate that the m1 thermal maximum occurred at approximately 900 950 c and 8 9 kbar all samples are characterized by profuse and diverse coronitic and symplectic reaction textures these are interpreted as evidence for the sequential crossing of the following reactions in the system fmas cordierite spinel corundum sapphirine sillimanite cordierite spinel orthopyroxene sapphirine sillimanite sapphirine spinel sillimanite orthopyroxene corundum sapphirine sillimanite cordierite orthopyroxene corundum phase stability relationships in fmas and mash indicate an anticlockwise p t path terminated by isobaric cooling such a path is exemplified by early low p mineral parageneses containing spinel corundum and gedrite and the occurrence of both prograde and retrograde corundum reaction textures preserve evidence for an increase in ah2o and ab2o3 with progressive isobaric cooling this hydrous retrogression resulted from crystallization of intimately associated m1 partial melt segregations there is no evidence for voluminous magmatic accretion giving rise to the high m1 thermal gradient the m1 p t path may be the result of either lithospheric thinning after both crustal thickening and burial of the supracrustal terrane or concomitant crustal thickening and mantle lithosphere thinning

low pressure granulite facies metapelitic assemblages and corona textures from macrobertson land east antarctica the importance of fe2o3and tio2in accounting for spinel bearing assemblages low pressure granulite facies metasedimentary gneisses exposed in macrobertson land east antarctica include hercynitic spinel bearing metapelitic gneisses peak metamorphic mineral assemblages include spinel rutile ilmenite sillimanite garnet spinel ilmenite sillimanite garnet cordierite ortho pyroxene magnetite ilmenite garnet spinel cordierite biotite ilmenite and orthopyroxene cordierite biotite each with quartz k feldspar and melt the presence of garnet biotite and cordierite orthopyroxene bearing assemblages implies crossing tie lines in afm projection for the k2o feo mgo al2o3 sio2 h2o kfmash system this apparent contradiction and the presence of spinel rutile and ilmenite in the assemblages is acounted for by using the kfmash tio2 o2 system i e afm tio2 fe2o3 we derive a petrogenetic grid for this system applicable to low pressure granulite facies metamorphic conditions retrograde assemblages are interpreted from corona textures on hercynitic spinel and fe ti oxides the relative positions of the peak and retrograde metamorphic assemblages on the petrogenetic grid suggest that corona development occurred during essentially isobaric cooling

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

u pb data on granulite facies rocks from fold island kemp coast east antarctica abstract the northern tip of fold island 67 16 s 59 20 e on the kemp coast is composed largely of quartzofeldspathic gneisses charnockitic and enderbitic and pyroxene granulite garnet biotite sillimanite gneiss garnet clinopyroxene plagioclase calc silicate rock magnetite bearing rocks and ultramafic rocks are very subordinate the gneisses were deformed by the two phases of isoclinal folding and were subsequently intruded by mafic dikes a second stage of deformation involving tight ductile folding post dates the dikes this deformation culminated with the emplacement of hypersthene bearing pegmatites in discordant planar veins and irregular masses and with the hornblende granulite facies metamorphism that resulted in the present day mineral assemblages u pb isotope data on zircon and monazite from two pegmatites define a chord intersecting concordia at 0 94 0 08 ga and 0 21 0 21 ga the 0 94 ga age dates deformation granulite facies metamorphism and the pegmatite emplacement of stage ii u pb data on a total of five fractions of highly rounded zircons from two quartzofeldspathic gneisses define a chord with intersections at 3 08 0 17 ga and 0 82 0 48 ga our results suggest that the gneiss zircons are xenocrysts and do not provide any direct indication of the age of the host gneisses the fold island gneisses are interpreted to be older napier complex rocks that were reworked during the late proterozoic 1000 ma rayner event a similar sequence of events has been reported for a coastal portion of the eastern ghats province of south india suggesting that these two areas were part of the same metamorphic complex in gondwanaland

sm nd and rb sr ages and p t history of the archean sittampundi and bhavani layered meta anorthosite complexes in cauvery shear zone south india evidence for neoproterozoic reworking of archean crust sittampundi and bhavani archean layered meta anorthosite complexes occur as tectonic lenses within the cauvery shear zone csz a crustal scale shear dividing the precambrian granulite crust of south india into late archean 2 5 ga and proterozoic c 0 55 ga blocks they and their host supracrustal gneiss rocks record at least two stages of tectonometamorphic history the first is seen as regional scale refolded isoclinal folds and granulite metamorphism d1 m1 while the second stage is associated with dominantly e w dextral transcurrent shearing and metamorphic recrystallisation d2 mcsz whole rock sm nd isochrons for several comagmatic rocks of the layered complexes yield concordant ages sittampundi 2935 60 ma nd 1 85 0 16 and bhavani 2899 28 ma nd 2 18 0 14 2 errors our sm nd results suggest that 1 the magmatic protoliths of the sittampundi and bhavani layered complexes were extracted from similar uniform and lree depleted mantle sources 2 m1 metamorphism occurred soon after emplacement at c 3 0 ga ago p t estimates on garnet granulites from the sittampundi complex characterise the mcsz as a high p event with metamorphic peak conditions of c 11 8 kbar and 830 c minimum the mcsz is associated with significant isothermal decompression of the order of 4 5 3 5 kbar followed by static high temperature rehydration and retrogression around 600 c the timing of mcsz is inferred to be neoproterozoic at c 730 ma based on a whole rock garnet plagioclase hornblende sm nd isochron age for a garnet granulite from the sittampundi complex and its agreement with the 800 600 ma published age data on post kinematic plutonic rocks within the csz these results demonstrate that the cauvery shear zone is a zone of neoproterozoic reworking of archean crust broadly similar to the interface between the napier and rayner complexes of the east antarctic shield in a model proterozoic gondwana supercontinent

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

ultra high temperature metamorphism of metapelitic granulites from kondapalle eastern ghats belt implications for the indo antarctic correlation a suite of quartz and corundum bearing metapelitic granulites intruded by layered gabbronorite pyroxenite anorthosite at kondapalle eastern ghats belt preserves a multitude of reaction textures involving oxide and silicate minerals that attest to several prograde and retrograde reactions in the quartz bearing associations the reactions are a biotite sillimanite quartz garnet liquid b garnet sillimanite spinel magnetite quartz c fe2tio4 o2 ferrian ilmenite magnetite d reversal of reaction b e fe2o3 rich ilmenite plagioclase quartz fe2o3 poor ilmenite garnet o2 reactions in the corundum bearing associations are f spinel biotite sillimanite garnet liquid g biotite sillimanite garnet ti rich spinel corundum liquid h biotite sillimanite garnet corundum liquid i fe2tio4 feal2o4 o2 ferrian ilmenite fe3o4 al2o3 in ilmenite j garnet corundum spinel sillimanite to examine the paragenetic evolution of the metapelitic granulites a petrogenetic grid for the kfmash system at high temperatures and pressures involving quartz and corundum was constructed the sequence of inferred reactions documents an anticlockwise heating cooling path reintegrated compositions of spinel with 10 mol fe2tio4 and feldspars indicate ultra high temperature uht of metamorphism 1000 c comparable with the liquidus temperature of the enclosing magmatic rocks crystallization pressures inferred for the magmatic rocks and the pressure constraints imposed by the petrogenetic grid on the metapelite assemblages indicate that the emplacement of the igneous suite and the accompanying uht metamorphism occurred in the lower crust 8 kbar reported u pb cooling ages of monazite and allanite from a late pegmatite suggest the uht metamorphism to be older than 1600 ma the deduced p t history and the absence of grenvillian high grade metamorphism in the study area provide important constraints on the configuration of east gondwana in particular on the continuation of the napier rayner terrane boundary into the eastern ghats belt