a window into the lower crust trace element systematics and the occurrence of inclusions intergrowths in granulite facies rutile abstract rutile occurs as an accessory mineral in many high temperature metamorphic assemblages and has the potential to identify and investigate uht metamorphic terranes whilst the use of zr in rutile geothermometry to identify ultrahigh temperature terranes is appealing its application to granulites can be difficult owing to diffusional resetting of zr concentrations during cooling and decompression in order to provide constraints on p t conditions and trace element systematics during ultrahigh temperature metamorphism metamorphic rutile in granulites from the archean napier complex and the palaeozoic rauer group antarctica have been investigated for trace element composition and mineral inclusions intergrowths textural observations and zr in rutile temperatures show that unlike the large proportion of rutiles grains in the matrix rutile grains that are shielded by phases with low zr diffusivities e g orthopyroxene and or are in chemical isolation from zircon have the potential to retain zr concentrations that correspond to ultrahigh temperatures principal component analysis reveals that v cr nb mo ta and w are significantly enriched in rutile from archean and proterozoic ultrahigh temperature terranes high concentrations of elements such as cr and v indicate a spinel rich source demonstrating the effect of protolith bulk chemical composition on rutile trace element signatures rutile is shown to contain inclusions and intergrowths of aluminium silicate quartz corundum and feldspar including the first reported occurrence of prograde kyanite which provides direct evidence that the napier complex experienced a typical clockwise p t evolution

contrasting archaean crustal records in western part of the napier complex east antarctica new constraints from shrimp geochronology abstract u pb zircon geochronology of 6 samples collected from fyfe hills 2 felsic orthogneisses and 1 quartzo feldspathic gneiss and mt cronus 1 quartzo feldspathic gneiss and 2 quartzites in the western part of the napier complex east antarctica revealed an archaean proterozoic history ranging from 3128 to 1824 ma the absence of ancient evidence 3800 3600 ma indicates that these ages were not always dominant in these two areas the 3128 2580 ma protolith ages are similar to those of other areas e g mt riiser larsen tonagh island while the magmatic protolith age of 2741 ma obtained for the fyfe hills orthogneiss is a new component of the archaean magmatic protolith in the napier complex metamorphic overgrowth or recrystallized zircons yielded systematic disconformable ages for both fyfe hills 2518 ma and mt cronus 2490 ma the presence of 2580 ma inherited zircons provides important constraints that place the ultrahigh temperature metamorphic peak later than 2580 ma the post metamorphic ages suggest local fluid infiltration or local deformation event s

detrital rutile ages can deduce the tectonic setting of sedimentary basins abstract sedimentary sequences contain a detailed record of the evolution of the earth s surface detrital mineral grains provide for example evidence of source redox conditions insights into the age geochemistry and petrology of basement sources and can also be used to elucidate tectonic environments detrital zircon has been used as a means of analysing the tectonic setting of host sedimentary successions but with potentially ambiguous results it is important to find additional ways to discriminate depositional settings particularly in precambrian sequences where other proxies are either not available or have been lost in this contribution we provide a new way to discriminate between different sedimentary tectonic environments using the mineral rutile we present a large compilation of detrital rutile data to show that the u pb age distribution is sensitive to the tectonic setting of the basin in which the host sediments were deposited we then apply this new approach to two case studies where the depositional setting and age are well constrained siliciclastic units of nw scotland which were deposited in the neoproterozoic foreland of the grenville orogen and on the cambrian passive margin of the iapetus ocean and the brazilian sabara basin located within the palaeoproterozoic foreland of the minas orogen we compare the detrital rutile and zircon age distributions of these successions showing that in some cases they are different and that rutile is most sensitive to the youngest metamorphic events affecting the sources reinforcing the applicability of this tool by testing this new method on polyphasally deformed successions sabara basin we show that detrital rutile can still inform the tectonic setting even at medium grades of metamorphism

interpreting zirconium in rutile thermometric results at first sight experimental results and observations on rocks suggest that the zr content in rutile where equilibrated with quartz and zircon should be a useful thermometer for metamorphic rocks however diffusion data for zr in rutile imply that thermometry should not for plausible rates of cooling give the high temperatures commonly observed in high grade metamorphic rocks it is suggested here that such observations can be accounted for by high t diffusive closure of si in rutile causing the interior of rutile grains to become insensitive to the thermometer equilibrium well above the temperature of zr diffusive closure paired with comparatively slow grain boundary diffusion and problematic zircon nucleation this allows for cases of zr retention in rutile through temperatures where zr is still diffusively mobile within rutile grains other observations that may be accounted for in this context are large inter grain ranges of rutile zr contents uncorrelated with rutile grain size and flat zr profiles across individual rutile grains counter to what would be expected from diffusive closure a consequence is that it is unlikely that zr in rutile thermometry will be useful for estimating rock cooling rates

rutile as a pathfinder for metals exploration abstract the use of detrital rutile as an indicator of mineralisation is contingent on the identification of trace element signatures that uniquely distinguish rutile grains derived from mineralisation from those sourced from barren rocks in order to discriminate rutile sources principal component analysis was applied to a total of 3149 la icp ms analyses of rutile from ore environments au au cu pegmatites carbonatites lamprophyres vhms and barren igneous and metamorphic rocks hierarchical clustering of the results of principal component analysis pca determined sb and cr exhibit the most chemical variation in ore derived rutile rutile sourced from au deposits and enriched in sb can be distinguished from rutile from pegmatites which are enriched in nb ta and sn discriminating rutile from barren rocks can be done primarily using w and fe contents which can also provide insight on source rocks based on metamorphic grade and degree of crustal input clustering all rutile chemistries based on pca of 12 elements identified nine chemically distinct groups from ore mineralisation and barren igneous and metamorphic rocks primarily using variation in w and cr contents two groups are solely derived of rutile from au ores high versus low sb rutile of the remaining seven groups one group is comprised mainly of rutile from pegmatites high nb ta sn four groups are comprised solely of rutile from barren rocks and two groups are a mix of ore and non ore rutile rutile from au ore similar to the giant kalgoorlie and big bell au deposits is distinctive compared to rutile from all other rocks and can be distinguished from other ores and barren environments using multi element clustering of pca analysis thus rutile chemistry of detrital rutile grains is a valuable tool in au exploration

zr and hf diffusion in rutile abstract chemical diffusion of zr and hf under anhydrous conditions has been measured in synthetic and natural rutile the sources of diffusant used were hafnon or zircon powders or a hafnon rutile mixture experiments were run in crimped pt capsules in air or in sealed silica glass capsules with solid buffers to buffer at nno or qfm rutherford backscattering spectrometry rbs was used to measure zr and hf diffusion profiles from these measurements the following arrhenius relations were obtained for zr diffusion parallel to c over the temperature range 750 1100 c d zr c 9 8 10 15 exp 170 30 kj mol 1 rt m 2 s 1 for hf diffusion parallel to c over the temperature range 800 1000 c d hf c 9 1 10 15 exp 169 36 kj mol 1 rt m 2 s 1 for hf diffusion normal to c over the temperature range 750 1050 c d hf c 2 5 10 12 exp 227 62 kj mol 1 rt m 2 s 1 diffusivities for experiments buffered at qfm and nno are similar to those run in air diffusivities in synthetic and natural rutile are likewise similar indicating that these findings can be applied directly in determining zr diffusivities in rutile in natural systems these data indicate that rutile should be moderately retentive of zr chemical signatures with zr diffusivities within an order of magnitude of those for pb in rutile over most geologic conditions when applied in evaluation of the relative robustness of the recently developed zr in rutile geothermometer t zack r moraes a kronz temperature dependence of zr in rutile empirical calibration of a rutile thermometer contributions to mineralogy and petrology 148 2004 471 488 e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 these findings suggest that zr concentrations in rutile will be somewhat more likely to be affected by later thermal disturbance than the geothermometer based on zr concentrations in titanite l hayden e b watson d a wark a thermobarometer for sphene abstract 16th v m goldschmidt conference 2006 and much less resistant to diffusional alteration subsequent to crystallization than the ti in zircon geothermometer e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 e b watson t m harrison zircon thermometer reveals minimum melting conditions on earliest earth science 308 2005 841 844

deducing source rock lithology from detrital rutile geochemistry an example from the erzgebirge germany abstract this study evaluates the applicability of rutile trace element geochemistry to provenance studies the study area is the erzgebirge in eastern germany where metamorphic rocks ranging from lower greenschist facies conditions up to granulite facies conditions are exposed we collected sand and rock samples from small catchment areas for a comparative analysis of rutile geochemistry using wavelength dispersive electron microprobe our results show that rutile geochemistry is a powerful tool in provenance studies allowing for the identification of source lithologies and an evaluation of the host orogen s metamorphic history the log cr nb ratio has proven to be decisive in discriminating between mafic and metapelitic lithologies it is also useful for identifying different source rocks when plotted versus a third element or proxy furthermore our results suggest that rutile thermometry can be applied to a much wider range of lithologies than previously assumed a quantification of temperature populations within single sand samples shows that at high grade metamorphic conditions such as those found in the erzgebirge more than 65 of rutiles do not re equilibrate during retrograde metamorphism and thus retain their peak temperature chemistry such samples which have equilibrated at recent metamorphic conditions can be identified by their 2 standard deviations of less than 120 c below 550 600 c no complete equilibration is reached rutiles from greenschist facies and lower metamorphic conditions in the erzgebirge still inherit relict temperatures from a former metamorphic cycle they partly record very high temperatures 950 c and supposedly derive from erosion of the west african craton in ordovician time

discovery of a neoproterozoic basin in the prydz belt in east antarctica and its implications for gondwana assembly and ultrahigh temperature metamorphism abstract detrital zircon u pb age data from ultrahigh temperature metasedimentary rocks 950 c and 10 12 kbar in the rauer group and a granulite grade metasedimentary rock 850 c and 7 8 kbar in the bolingen islands in prydz bay east antarctica indicate the existence of a neoproterozoic ediacaran cover sequence that was deposited on basement ranging in age between approximately 2800 ma and 940 ma the neoproterozoic succession has a maximum depositional age of approximately 600 ma with derivation from igneous and metamorphic sources of archaean palaeoproterozoic and neoproterozoic age the minimum depositional age is constrained to be approximately 575 ma based on existing th u pb monazite metamorphic ages from the uht metasedimentary rocks the identification of late neoproterozoic protoliths to the uht granulites in the rauer group demonstrate that ultrahigh temperature metamorphism in prydz bay must be ediacaran to cambrian in age the timing of basin development ca 600 575 ma is coincident with the amalgamation of eastern gondwana the palaeogeography of the prydz bay region during the amalgamation of gondwana is uncertain but in our proposed reconstruction we suggest that inherited zircons were derived from indo antarctic crust ocean closure is inferred to have occurred along a suture zone to the southeast of prydz bay and the prince charles mountains our palaeogeographic model invites further work on the possibility of a shared history between india and a large portion of east antarctica prior to the final amalgamation of eastern gondwana during the ediacaran cambrian

a systematic evaluation of the zr in rutile thermometer in ultra high temperature uht rocks the zr in rutile geothermometer is potentially a widely applicable tool to estimate peak metamorphic temperatures in rocks from diverse geological settings in order to evaluate its usefulness and reliability to record and preserve high temperatures in granulite facies rocks rutile from uht rocks was investigated to assess different mechanisms of zr re distribution following cooling from high temperature granulite facies paragneisses from the lowermost part of the ivrea zone italy incorporated as thin sheets into the extensive basaltic body of the mafic complex were selected for this study the results show that zr in rutile thermometry if properly applied is well suited to identify and study uht terranes as it preserves a record of temperatures up to 1190 c although the thermometer is susceptible to partial post peak metamorphic resetting by zr diffusion texturally homogeneous rutile grains preserve zr concentrations corresponding to temperatures of prograde rutile growth diverse rutile textures and relationships between some rutile host grains and included or adjacent zr bearing phases bear testimony to varying mechanisms of partial redistribution and resetting of zr in rutile during cooling and link zr in rutile temperatures to different steps of the metamorphic evolution rutile grains that equilibrated their zr concentrations at temperatures above 1070 c i e 1 1 wt zr could not retain all zr in the rutile structure during cooling and exsolved baddeleyite zro2 by subsequent reaction of baddeleyite exsolution lamellae with sio2 zircon needles formed before the system finally closed at 650 700 c without significant net loss of zr from the whole host rutile grain by reintegration of zircon exsolution needles peak metamorphic temperatures of up to 1190 c are derived for the studied rocks which demonstrates the suitability of this solution thermometer to record uht conditions and also confirms the extraordinary geological setting of the lowermost part of the ivrea zone

multicycle slip distribution along a laboratory fault slip distribution along a laboratory fault which consists of eight spring connected blocks that are elastically driven to slide on a frictional surface has been examined for a long sequence of slip events to test the applicability of some conceptual models proposed recently in the literature the distributions of large slip events are found to be quite variable and do not fit the uniform slip or characteristic earthquake models the rupture initiation points are usually not near the corresponding maximum slip points in contrast to observations by thatcher 1990 and by fukao and kikuchi 1987 that earthquake hypocenters are commonly near corresponding regions of maximum slip in the fault planes this contrast may suggest that either the present observations or theirs are not representative or the teleseismically determined hypocenters may not always be true rupture initiation points as usually assumed large slip events are also found to be a stress roughening process they are triggered by some small events after the stresses have been adjusted by some earlier small to moderate events to be near the critical levels at most locations along the fault this suggests that earthquake prediction monitoring efforts should not be limited to a small region near an asperity but should be spread out to cover the entire fault segment in a seismic gap in order to detect the condition of simultaneous strain buildup

new constraints on metamorphism in the rauer group prydz bay east antarctica granulite facies metapelites of the mather and filla paragneisses within the rauer group east antarctica possess markedly different compositions the metamorphic evolution of the two metapelite types has been interpreted as temporally distinct with the rauer group preserving at least two distinct granulite facies tectonothermal episodes calculated p t pseudosections and orthopyroxene al content indicate the revised maximum preserved p t conditions within the mather paragneiss to lie in the vicinity of 950 975 c and 10 10 6 kbar less extreme than previous estimates the range of possible p t paths for the mather paragneiss consistent with mineral textural relationships and pseudosections contoured for mineral proportion are significantly shallower dp dt than previous estimates a near isothermal decompression p t path and extreme peak metamorphic conditions are not necessary to explain the development of preserved mineral reaction textures the filla paragneiss contains pelitic assemblages less amenable to rigorous quantitative analysis nevertheless possibilities for the shared or otherwise metamorphic evolution of the mather and filla paragneisses may be postulated on the basis of calculated pseudosections in the context of existing geochronology for the rauer group and preserved microstructures a shared evolution most likely during pan african granulite facies metamorphism is plausible and consistent with mineral assemblage development geochronology and microstructures a revised interpretation of the rauer group s preserved metamorphic evolution may warrant the revision of existing tectonic models applicable also to the remainder of prydz bay more generally the employed approach may incite a revision of peak p t and p t paths in other granulite facies terranes

ultrahigh temperature granulite metamorphism 1050 c 12 kbar and decompression in garnet mg70 orthopyroxene sillimanite gneisses from the rauer group east antarctica highly magnesian and aluminous migmatitic gneisses from mather peninsula in the rauer group eastern antarctica preserve ultrahigh temperature uht metamorphic assemblages that include orthopyroxene sillimanite quartz garnet sillimanite quartz and garnet orthopyroxene sillimanite garnet that ranges up to xmg of 71 5 coexists with aluminous orthopyroxene that shows zoning from cores with 7 5 8 5 wt al2o3 to rims with up to 10 6 wt al2o3 adjacent to garnet peak p t conditions of 1050 c and 12 kbar are retrieved from fe mg al thermobarometry involving garnet and orthopyroxene in very good agreement with independent constraints from petrogenetic grids in feo mgo al2o3 sio2 and related chemical systems sapphirine orthopyroxene and cordierite form extensive symplectites and coronas on the early phases the specific reaction textures and assemblages involving these secondary phases correlate with initial garnet xmg with apparent higher pressure reaction products occurring on the more magnesian garnet and are interpreted to result from an initial phase of ultrahigh temperature near isothermal decompression uht itd from 12 to 8 kbar at temperatures in excess of 950 c later textures that involved biotite formation and then partial breakdown along with garnet relics to symplectites of orthopyroxene cordierite or cordierite spinel may reflect hydration through back reaction with crystallizing melts on cooling below 900 850 c followed by itd from 7 to 8 kbar to c 5 kbar at temperatures of 750 850 c the tectonic significance of this p t history is ambiguous as the rauer group records the effects of archean tectonothermal events as well as high grade events at 1000 and 530 ma late stage biotite formation and subsequent itd can be correlated with the p t history preserved in the proterozoic components of the rauer group and hence with either 1000 or 530 ma collisional orogenesis however whether the preceding uht itd history reflects a temporally unrelated event e g archean or is simply an early stage of either the late proterozoic or pan african tectonism as recently deduced for similar uht rocks from other areas of the east antarctica remains uncertain

a cooling rate bias in paleointensity determination from volcanic glass an experimental demonstration 1 the suitability of volcanic glass for paleointensity determinations is the basis of many studies the dominant single domain sd magnetic remanence carriers the pristine character of volcanic glass and the possibility to correct paleointensity data for cooling rate dependence using relaxation geospeedometry are all arguments that have been made in favor of this technique in the present study the validity of cooling rate correction is tested using remelted volcanic glass to obtain a stable multicomponent glass with ideal magnetic properties a natural phonolitic glass from tenerife was remelted in air to avoid heterogeneity and degassing in later experiments further it was tempered for altogether 10 hours at 900 c to yield a sufficient concentration of magnetic remanence carriers to exclude nucleation or crystallization six samples were then heated to about 60 c above the calorimetric glass transition temperature 660 c and quenched at different rates from 0 1 to 15 k min rock magnetic measurements show that low titanium titanomagnetite in the sd range is the main remanence carrier after performing paleointensity experiments using a modified thellier method the dependence of the thermoremanence on cooling rate was investigated using the synthesis cooling rates and the experimentally determined magnetic cooling rate dependencies we were able to correct the data and obtained a mean paleointensity of 46 9 1 3 t which reflects the ambient field of 48 t within error the uncorrected mean paleointensity corresponds to a 18 larger value of 56 5 0 9 t therefore application of a cooling rate correction is essential to obtain the correct ancient magnetic field intensity from sd assemblages in volcanic glass

shrimp and electron microprobe chronology of uht metamorphism in the napier complex east antarctica implications for zircon growth at 1 000 c zircons in ultra high temperature uht metamorphosed paragneisses from mt riiser larsen in the napier complex east antarctica were dated by using ion microprobe shrimp and electron microprobe emp both shrimp and emp analyses yield consistent 2520 2460 ma age populations for garnet orthopyroxene bearing paragneiss and leucosomes enclosed within the peak uht event was dated at 2480 ma by shrimp analyses on metamorphic zircons from the garnet orthopyroxene paragneiss and those on magmatic zircons from the leucosomes which are interpreted to be formed at syn uht as obtained by shrimp the uht metamorphic event was terminated no later than 2460 ma minor 2520 ma shrimp age suggests either the onset of prograde metamorphism or another high grade metamorphic event unrelated to the uht emp analyses on metamorphic zircons from sapphirine quartz and osumilite bearing magnesian paragneisses give c 2500 2450 ma ages inherited igneous zircon cores of the magnesian paragneisses yield relatively scattered emp ages ranging over c 3000 2650 ma suggesting that igneous materials of these ages sourced the protoliths of the paragneisses and that they were deposited during the interval c 2650 2520 ma

al zoning in orthopyroxene in a sapphirine quartzite evidence for 1120 c uht metamorphism in the napier complex antarctica and implications for the entropy of sapphirine a unique sapphirine orthopyroxene quartz granulite from mt riiser larsen in the tula mountains of enderby land east antarctica preserves two generations of coarse and texturally equilibrated orthopyroxene and sapphirine coexisting with quartz initial subhedral orthopyroxene porphyroblasts retain core compositions enriched in al2o3 12 2 0 5 wt compared with their rims and finer orthopyroxene 9 6 0 5 wt al2o3 that forms granoblastic textures with sapphirine sapphirine and quartz also form symplectites on and along cleavage planes within orthopyroxene these compositional and textural features are consistent with the reaction 2mgal2sio6 mg2al4 sio10 sio2 leading to the formation of sapphirine quartz at the expense of aluminous orthopyroxene calculations in the mas and fmas systems and theoretical considerations involving the phases enstatite sapphirine sillimanite quartz and cordierite indicate that the reaction above progresses from left to right with decreasing temperature in the orthopyroxene sapphirine quartz field at pressures of ca 8 10 kbar the temperature difference required to account for the ca 2 5 3 wt decrease in al2o3 in orthopyroxene is at least 60 80 c and implies peak temperatures for the initial assemblage of at least 1120 c if the second granoblastic assemblage equilibrated at 1040 c the p t conditions required by the sapphirine quartz association and other p t sensitive assemblage indicators in the napier complex it is not possible to distinguish whether the two assemblages are simply related by cooling and re equilibration or reflect a polyphase evolution involving the superposition of a second uht event on an earlier even higher temperature uht metamorphism preliminary thermodynamic modelling of the reaction above incorporating the observed range in orthopyroxene al2o3 zoning indicates that present estimates for the entropy of high temperature sapphirine are potentially too high by 15 18 compared with sapphirine entropy estimates that are consistent with mas system experiments the mt riiser larsen sapphirine quartz rocks preserve the first definitive record of regional metamorphic temperatures in excess of 1120 c in the napier complex or indeed any uht granulite terrain worldwide similarly high peak temperatures may be retrieved from detailed studies of sapphirine quartz granulites from other regions further expanding the thermal realm of crustal metamorphism but progress will critically depend on the experimental acquisition of new entropy data for sapphirine

on the application of in situ monazite chemical geochronology to constraining p t t histories in high temperature 850 c polymetamorphic granulites from prydz bay east antarctica we present electron microprobe based in situ th u pb monazite chemical age data from granulite facies metapelites in prydz bay east antarctica the monazite age data define two distinct age populations late neoproterozoic to early palaeozoic c 570 520 ma and neoproterozoic c 950 820 ma that confirm the polytectonic nature of prydz bay our data suggest that similarity in lineation orientation along the prydz bay coast is not sufficient to necessarily indicate time equivalance the minimum duration of early palaeozoic tectonism spanning at least 60 ma is constrained from an mg al rich metapelite monazite hosted by coarse grained orthopyroxene defines the oldest early palaeozoic population whereas cordierite orthopyroxene symplectites define the youngest early palaeozoic population the spatial distribution of monazites and their ages is correlatable with the inferred mineral assemblage evolution we are able to characterize the evolution of early palaeozoic tectonism in quantitative p t t mineral assemblage space demonstrating that ultrahigh temperature tectono metamorphism in prydz bay is of early palaeozoic age the survival of neoproterozoic inheritance in fe al rich metapelites has implications for high pb retentivity in monazite when chemical and kinetic conditions are favourable the approach and logic applied herein are entirely and directly transferable to the interrogation of any other metamorphic terrane

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

th u pb monazite ages from al mg rich metapelites rauer group east antarctica the age of high temperature granulite facies metamorphism 800 850 c in the rauer group prydz bay east antarctica is relevant for establishing the metamorphic and temporal architecture of the prydz bay mobile belt monazites within al mg rich granulite facies metapelites give an overall tanh estimated pan african age of 511 4 ma 2r using in situ electron microprobe based th u pb chronology consistent with existing u pb zircon geochronology from the rauer group and prydz bay monazite occurs primarily within cordierite bearing coronae and symplectic min eral reaction textures and also within biotite pan african granulite facies metamorphism is preferred as responsible for the development of the cordierite bearing microstructures and probably peak coarse grained assemblages constrained using an integrated geologic geochronologic and metamorphic framework thus pan african granulite facies metamorphism affected the rauer group within the prydz bay mobile belt moreover integrated monazite geochronology may be used to decipher the temporal metamorphic histories of potentially complex high temperature terrains

trace element systematics in granulite facies rutile implications for zr geothermometry and provenance studies metamorphic rutile from granulite facies metapelitic rocks of the archean pikwitonei granulite domain pgd manitoba canada provides constraints on the systematics of trace elements in rutile during high temperature conditions and subsequent slow cooling compositional profiles and maps of the zr concentrations in rutile grains 120 600 m from three metapelitic gneisses were acquired by electron probe micro analysis using a spatial resolution of down to 2 m simultaneously profiles were analysed for nb cr and v which have significantly different diffusion characteristics in rutile the profiles of all elements show relatively homogeneous concentrations within most grains but significant inter grain differences even within a single thin section some rutile grains display a slight concentration decrease from a neighbouring garnet towards the matrix for all measured elements the lack of diffusion profiles for all analysed elements shows that these are highly immobile in rutile and that distributions of these elements are primary and preserve prograde information the nb and cr concentrations overlap with ranges that are ascribed to different provenances indicating that source discrimination based on these elements is not possible in all cases high retentiveness for zr implies that the zr in rutile geothermometer is highly robust to diffusive re equilibration even during very slow cooling 2 c ma 1 from granulite facies conditions most grains have high zr contents 3000 4600 ppm differences between high zr contents suggest that during growth under vapour absent conditions there may not be saturation of zr in rutile even if zircon is present therefore several rutile grains need to be analysed in a sample to obtain a useful minimum peak temperature the highest zr concentrations correspond to 900 c this is significantly higher than previous peak temperature estimates of 820 c based on two feldspar thermometry on a regional scale this implies that part of the pgd was affected by ultra high temperature uht metamorphism it also implies that rutile is able to preserve primary compositions even to uht conditions this study shows that if combined with textural information zr in rutile has the potential to be a very useful tool for estimating rutile crystallization temperatures and peak metamorphic conditions for granulite facies rocks zr in rutile yields more reliable peak metamorphic temperatures than most other exchange geothermometers which tend to partially re equilibrate by diffusion during cooling

nb and zr behavior in rutile during high grade metamorphism and retrogression an example from the ivrea verbano zone abstract detailed textural observations and in situ analyses emp sims and la icp ms are used to characterize trace element behavior during prograde and retrograde metamorphic reactions involving rutile the ivrea verbano zone is a classic granulite area and rocks from the strona and d ossola valleys are an example of the amphibolite to granulite facies transition although different rock types occur in the area detailed sampling and petrographic work show that rutile only occurs in granulite facies paragneisses these rocks show a rich inventory of textures that allow not only for the investigation of trace element behavior in response to prograde rutile growth but also for the effect of post peak processes on rutile chemistry nb concentrations in rutile from lower grade samples show a larger spread from 500 to 5000 ppm within one sample when compared to those from higher grades this pattern can be modeled using prograde rutile growth formed from biotite breakdown zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution maximum zr concentrations increase according to the general metamorphic gradient known for this area temperatures from zr in rutile thermometry although feasible are considerably higher than previous calculations increasing from ca 850 to 930 c a second cluster of zr concentrations in rutile occurs at rather constant concentrations ca 1000 ppm for all localities and is interpreted to be related to intense fluid influx at high temperature and or to post peak diffusional resetting favored by slow cooling rates alteration textures characterized by a complex network of micro veins are evidence for the late fluid influx the fluid strongly affected the rutiles which is evidenced by corrosion of older rutile grains and formation of rutile veinlets

rutile chemistry and thermometry as provenance indicator an example from chios island greece abstract in the present study we focused on detrital rutile separated from 12 psammitic samples that belong to three different sedimentary successions carboniferous permo carboniferous permo triassic occurring on chios island greece the ti cr al fe nb zr si and v contents of the rutiles were obtained by electron microprobe analyses to trace their provenance the cr and nb concentrations of the analysed rutile grains show a wide range and indicate that this mineral in the carboniferous succession is mainly derived from metamafic rocks whereas in the permo carboniferous and permo triassic successions stem from a metapelitic source the calculated formation temperatures using the zr in rutile thermometer range from ca 520 to 850 c with hotter rutile being encountered in the permo carboniferous and permo triassic successions this feature together with the rutile chemistry indicate a change in source rock lithology through time which could either reflect an increasing depth of erosion of an exhumed variscan nappe pile of heterogeneous composition in the hinterland or a change in the style of accretion and erosion of different terranes at the southern margin of laurussia during the subduction of a branch of the palaeotethys ocean in the late palaeozoic in general this study underscores the importance of rutile chemistry and thermometry in quantitative single mineral provenance analysis and in chemostratigraphic analysis of clastic sedimentary rocks

origin and evolution of granulites in normal and thickened crusts rocks buried in the upper part of a doubly thickened crust during orogeny can show prograde reactions with transitional features from lower grade rocks up to granulite facies they can be exposed at the earth9s surface within this one erogenic cycle for example the granulites exposed in british columbia have concordant u pb zircon ages of 65 85 ma in contrast rocks buried in the lower part of a thickened crust will crystallize granulites that typically show only retrograde relations with younger lower grade rocks at the cessation of orogeny such rocks will undergo near isobaric cooling from the peak metamorphism and can have very long residence times at the base of a crust of normal thickness these granulites require a second orogeny to uplift and expose them at the surface as an example the archean granulites of enderby land antarctica were metamorphosed at 3070 ma at 1000 c at 8 10 kbar pressure they then followed at least a 400 c isobaric cooling path they also had a prolonged residence time of 2000 m y near the base of the crust before uplift no doubt a continuum exists between these extremes but it is proposed that many intermediate and high pressure granulites form in the lower parts of thickened crust and therefore require a two stage cycle of tectonism to be uplifted and exposed at the earth9s surface although most granulites probably form in thickened crust at active plate margins underplating of normal 30 40 km thickness crust by mantle melts during extension can also produce granulites these granulites would also undergo isobaric cooling and require a later orogeny to expose them an example is the paleozoic lachlan fold belt of eastern australia which has undergone only minor uplift since the major ultrametamorphism at about 400 ma however isotopic petrologic and geochemical differences are to be expected between these extremes of granulite formation

pressure temperature evolution of metapelitic granulites in a polymetamorphic terrane the rauer group east antarctica distinctive lithological associations and geological relationships and initial geochronological results indicate the presence of an areally extensive region of reworked archaean basement containing polymetamorphic granulites in the rauer group east antarctica structurally early metapelites from within this reworked region preserve complex and varied metamorphic histories which largely pre date and bear no relation to a late proterozoic metamorphism generally recognized in this part of east antarctica in particular magnesian metapelite rafts from long point record extreme peak p t conditions of 10 12 kbar and 100 1050 c and an initial decompression to 8 kbar at temperatures of greater than 900 c initial garnet orthopyroxene sillimanite assemblages contain the most magnesian and pyrope rich garnets xmg 0 71 yet found in granulite facies rocks a high temperature decompressional p t history is consistent with reaction textures in which the phase assemblages produced through garnet breakdown vary systematically with the initial garnet xmg composition reflecting the intersection of different divariant reactions in rocks of varied composition as pressures decreased this history is thought to relate to archaean events whereas a lower temperature c 750 800 c decompression to 5 kbar reflects late proterozoic reworking of these relict assemblages the major late proterozoic c 1000 ma granulite facies metamorphism is recorded in a suite of younger fe rich metapelites and associated paragneisses in which syn to post deformational decompression through 2 4 kbar from maximum recorded p t conditions of 7 9 kbar and 800 850 c is constrained by geothermobarometry and reaction textures this p t evolution is thought to reflect rapid tectonic collapse of crust previously thickened through collision

an integrated microtextural and chemical approach to zircon geochronology refining the archaean history of the napier complex east antarctica integrated textural and chemical characterisation of zircon is used to refine the u pb geochronology of the archaean ultra high temperature napier complex east antarctica scanning electron microscope characterisation of zircon and the rare earth element compositions of zircon garnet and orthopyroxene are integrated to place zircon growth in an assemblage context thereby providing tighter constraints on the timing of magmatic and metamorphic events data indicate that magmatism occurred in the central and northern napier complex at ca 2 990 ma a regional relatively low pressure metamorphic event occurred at ca 2 850 2 840 ma mineral ree data from garnet bearing orthogneiss indicate that ca 2 490 2 485 ma u pb zircon ages provide an absolute minimum age for the ultrahigh temperature uht foliation preserved in this rock internal zircon zoning relationships and estimated zircon garnet dree values from paragneiss suggest that an absolute minimum age of ultra high temperature metamorphism is ca 2 510 ma but that it is more likely to be older than ca 2 545 ma we suggest that the high proportion of published zircon u pb data with ages between ca 2 490 2 450 ma reflects late post peak zircon growth and does not date the timing of peak uht metamorphism

mid to late archaean 3 3 2 5 ga tonalitic crustal formation and high grade metamorphism at mt riiser larsen napier complex east antarctica abstract the archaean napier complex consists of felsic orthogneiss mafic granulite and a variety of paragneisses metamorphosed in the granulite facies in part at ultrahigh temperature uht 900 c orthopyroxene bearing felsic orthogneiss of tonalitic granodioritic composition the highly recrystallized archaean tonalite trondhjemite granodiorite ttg crust is a major constituent of the complex especially at mt riiser larsen which is located within the uht region sensitive high resolution ion microprobe shrimp u pb analyses of zircon grains from three different layers of orthopyroxene bearing felsic orthogneiss were carried out two of the analyzed orthogneiss samples yield 3270 12 ma and 3267 5 ma concordia ages from igneous zircon cores another sample shows slightly scattered and discordant ages 3350 ma with a concordia age of 3073 12 ma these data suggest that the initial ttg crust of the mt riiser larsen was formed at 3270 ma and perhaps at 3070 ma these ages are considerably younger than the formation of tonalitic crust at mt sones gage ridge and at fyfe hills 3840 3770 ma but older than that at proclamation island 2980 ma and several other areas at 2840 ma two of the orthogneiss samples yield subordinate 2850 2790 ma zircon concordia ages that are considered to result from a high grade metamorphic event which may also relate to 2830 ma granitic magmatism recorded in the area zircon grains from the three analyzed orthogneiss samples yield an intense 2520 2450 ma age cluster that probably reflect the uht metamorphic event in the area the ca 3300 ma age for ttg magmatism and ca 2500 ma age for high grade metamorphism are comparable to the events in south india which is thought by some authors to have been continuous with the napier complex from the mid proterozoic until gondwana break up

u pb geochronology from tonagh island east antarctica implications for the timing of ultra high temperature metamorphism of the napier complex abstract ion microprobe u pb zircon geochronology of an orthopyroxene bearing felsic orthogneiss from central tonagh island enderby land east antarctica provides insight into the chronological metamorphic evolution of the archaean napier complex the details of which have been the source of debate for over two decades the orthogneiss crystallised at 2626 28 ma predating peak ultra high temperature uht metamorphism and development of an intense regional s1 gneissosity two subsequent episodes of zircon growth resetting can be identified a minor period of zircon growth occurred at 2546 13 ma the regional significance and geological nature of which is unclear this was followed by an episode of abundant zircon growth as mantles on 2626 ma cores and as anhedral grains partly characterised by high th u 1 2 at 2450 2480 ma this age coincides with both lower and upper concordia intercept ages from other u pb zircon studies and several rb sr and sm nd whole rock isochron ages from the napier complex we conclude that uht metamorphism occurred at 2450 2480 ma and find no compelling evidence that uht occurred much earlier as has been postulated the zircon u pb data from this study also indicates a lower intercept age of 500 ma which coincides with the emplacement of early palaeozoic pegmatite swarms and synchronous infiltration of aqueous fluids into the southwestern regions of the napier complex

application of zr in rutile thermometry a case study from ultrahigh temperature granulites of the khondalite belt north china craton zr in rutile thermometry was applied to ultrahigh temperature uht granulites from three localities dongpo tuguishan and dajing tuguiwula of the khondalite belt north china craton zr concentrations of analyzed rutiles were detected by la icp ms and emp which display a mutative composition zoning a large inter grain variation a bimodal distribution at around 1 500 and 6 000 ppm and no relationship with the textural setting matrix vs inclusion these characteristics were likely caused by post peak diffusional resetting associated with slow cooling rates and the presence of a co2 rich fluid the grains with lower zr concentrations 500 to 3 000 ppm and temperature estimates 650 to 850 c occur close to or in contact with zircon which was easily affected by post peak processes for example diffusion dissolution reprecipitation the lowest temperatures 650 to 700 c we obtained represent the closure temperature of zr in rutile rutiles with higher zr concentrations 3 000 to 8 000 ppm and calculated temperatures 850 to 1 000 c were least affected by late resetting giving near peak metamorphic temperatures these temperature results higher than 900 c even in excess of 1 000 c from the three localities reconfirm the presence of uht metamorphism our results also suggest that zr in rutile thermometry is valid for ultrahigh temperature estimates in addition there are positive correlations between concentrations of zr and hf nb and ta of the investigated rutiles but the correlations weaken as the concentrations increase especially for nb and ta implying fractionation of nb and ta