u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

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

sedfoam a multi dimensional eulerian two phase model for sediment transport and its application to momentary bed failure abstract a multi dimensional eulerian two phase model for sediment transport called sedfoam is presented the model was developed under the open source framework via the cfd toolbox openfoam with closures of particle stresses and fluid particle interactions the model is able to resolve processes in the concentrated region of sediment transport and hence does not require conventional bedload suspended load assumptions a modified k closure was adopted for the carrier flow turbulence the model was validated for reynolds averaged steady and oscillatory sheet flows and verified with empirical formulae for scour downstream of an apron the model was used to study momentary bed failure or plug flow under sheet flow conditions model results revealed the existence of instabilities of the near bed transport layer when momentary bed failure criteria was exceeded these instabilities evolved into 5 10 cm billows and were responsible for the large transport rate the instabilities were associated with a large erosion depth which was triggered by the combination of large bed shear stresses and large horizontal pressure gradients further numerical experiments confirmed the conjecture by previous studies that a criterion for onset of momentary bed failure in oscillatory sheet flow was a function of both the shields parameter and sleath parameter

petrography and provenance of the early permian fluvial warchha sandstone salt range pakistan abstract the warchha sandstone of the salt range of pakistan is a continental succession that accumulated as part of a meandering fluvial system during early permian times several fining upward depositional cycles are developed each of which is composed of conglomerate cross bedded sandstone and in their upper parts bioturbated siltstone and claystone units with distinctive desiccation cracks and carbonate concretions clast lithologies are mainly of plutonic and low grade metamorphic origin with an additional minor sedimentary component textural properties of the sandstone are fine to coarse grained poorly to moderately sorted sub angular to sub rounded and with generally loose packing based on modal analyses the sandstone is dominantly a feldspathoquartzose arkose to sub arkose detrital constituents are mainly composed of monocrystalline quartz feldspars more k feldspar than plagioclase and various types of lithic clasts xrd and sem studies indicate that kaolinite is the dominant clay mineral and that it occurs as both allogenic and authigenic forms however illite illite smectite mixed layer smectite and chlorite are also recognised in both pores and fractures much of the kaolinite was likely derived by the severe chemical weathering of previously deposited basement rocks under the influence of a hot and humid climate transported residual clays deposited as part of the matrix of the warchha sandstone show coherent links with the sandstone petrofacies thereby indicating the same likely origin illite smectite and chlorite mainly occur as detrital minerals and as alteration products of weathered acidic igneous and metamorphic rocks based primarily on fabric relationship the sequence of cement formation in the warchha sandstone is clay generally kaolinite iron oxide calcareous and siliceous material before iron rich illite and occasional mixed layer smectite illite and rare chlorite both petrographic analysis and field characteristics of the sandstone indicate that the source areas were characterised by uplift of a moderate to high relief continental block that was weathered under the influence of hot and humid climatic conditions the rocks weathered from the source areas included primary granites and gneisses together with metamorphic basement rocks and minor amounts of sedimentary rocks regional palaeogeographic reconstructions indicate that much of the warchha sandstone detritus was derived from the aravalli and malani ranges and surrounding areas of the indian craton to the south and southeast before being transported to and deposited within the salt range region under the influence of a semi arid to arid climatic regime

the p t deformation path for a mid proterozoic low pressure terrane the reynolds range central australia the proterozoic low pressure high temperature lpht terrane of the reynolds range occurs in a 130 km long nw trending belt in the central part of the arunta block central australia the reynolds range has been affected by two mid proterozoic tectonic cycles di and dii associated with two metamorphic events mi and mii di mi effects are restricted to the older of two sedimentary successions the lander rock beds which are separated from the younger reynolds range group by an angular unconformity the dominant structural metamorphic features formed during dii mii affected both sedimentary successions and the various granites that intruded them and reworked most di mi effects the dii deformation history can be subdivided into one prograde two peak and one retrograde stage average p t calculations in the southeastern half of the range indicate a peak metamorphic pressure of 4 1 0 3 kbar because the calculated values are derived from the same stratigraphic level corresponding to the base of the reynolds range group which is exposed throughout the area it is likely that pressures were similar in the entire range in fact however the peak metamorphic temperature shows a dramatic increase from greenschist facies c 400 c in the northwest to granulite facies 740 60 c in the southeast indicating that mii was associated with anomalously high heat flows the p t path is anticlockwise with isobaric cooling from the metamorphic peak indicated by corona textures however the evidence of a prograde increase in pressure is indirect and based on the compressional nature of the structures peak metamorphic mineral assemblages and retrograde mineral assemblages in amphibolite facies shear zones show the same metamorphic zonation suggesting they formed in response to the same thermal event if this is true the implication is that a thermal perturbation external to the crust was maintained for a considerable period of time 110 ma based on zircon dating as it is not clear whether proterozoic asthenosphere active thermal perturbations operated for this long the alternative interpretation must be considered namely that the peak metamorphic events are separate from the shear zone event associated with reheating of the area

experimental study of sheet flow sediment transport under nonlinear oscillatory flow over a sloping bed abstract the seabed is sloped in shallow coastal regions where strong nonlinear shoaling waves can generate sheet flow sediment transport both wave nonlinearity and bottom slope can lead to a wave averaged net sediment transport rate but the bottom slope effect is often overlooked in existing sediment transport models a full scale experimental study of sheet flow sediment transport under the oscillatory flows with nonlinear features skewness or asymmetry was conducted in an inclinable oscillatory water tunnel so the bottom slope induced net transport rate in the context of nonlinear waves was experimentally investigated the tests cover a variety of nonlinear wave shape bottom slope 0 to 2 5 and two sediment diameters 0 24 and 0 51 mm since the downslope direction is the offshore direction in our tests it is found that bottom slope reduces the net onshore transport rate due to wave nonlinearity the slope contribution to the net transport rate is evaluated by taking the difference between the measured net transport rate from a sloping bed experiment and the measured net transport rate from the corresponding horizontal bed experiment the results suggest that slope induced net transport rate is insensitive to wave nonlinearity and its variation with bottom slope can be considered linear in the context of predicting net transport rate comparisons between this study and a preceding sinusoidal flow study of yuan et al 2017b suggest that nonlinear waves can be approximated as sinusoidal flows for estimating the slope contribution to the net transport rate subsequently an empirical model for predicting net sheet flow transport rate due to bottom slope is established based on dimensional analysis this model can be simply added to existing sheet flow sediment transport models to improve their applicability in coastal regions

the notch peak contact metamorphic aureole utah petrology of the big horse limestone member of the orr formation the upper cambrian big horse limestone member of the orr formation is contact metamorphosed by the jurassic notch peak quartz monzonite in the central portion of the house range utah two lithologic types were sampled from specific stratigraphic horizons within the member over a lateral distance of 6 km at locations reflecting a range in metamorphic grades the rocks were metamorphosed at 2 kbar on the basis of estimates of stratigraphic overburden at the time of intrusion the lithologies are relatively pure dolomitic limestones and impure argillaceous limestones argillites the progressive metamorphism has resulted in the successive appearance of talc tremolite scapolite diopside and forsterite in the meta limestones and the appearance of biotite tremolite diopside plagioclase scapolite vesuvianite grossular and wollastonite in the argillites mineral assemblages of the limestones compared with isobaric 2 kbar phase equilibria in the cao mgo sio 2 h 2 o co 2 system suggest that 1 fluid buffering by metamorphic reactions has occurred 2 domains of equilibrium are small and 3 the limestones behaved as relatively closed systems during metamorphism maximum temperatures and x co 2 composition consistent with assemblages in the limestone are see pdf for table temperatures estimated by the calcite dolomite geothermometer are consistent with these temperature estimates temperatures estimated from limestone mineral assemblages are used to establish the sequence of prograde reactions in the multi component argillite system compositions of fluids in equilibrium with low grade argillites are poorly constrained but may have reached a maximum x co 2 of 0 75 fluid compositions in equilibrium with medium to high grade argillites were more h 2 o rich than x co 2 0 20 indicated primarily by the presence of wollastonite at temperatures between 475 and 600 c therefore the argillites were either initially more water rich than limestones at the same grade or they were more open to h 2 o rich fluids during metamorphism

vertical fluxes of sediment in oscillatory sheet flow time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves while the concentrations c z t vary very little with time for z 10d50 the measured vertical sediment fluxes qzs z t vary strongly with time in this vertical band and their time variation follows to some extent the variation of the grain roughness shields parameter 2 5 t thus sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements however the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow they are so far unable to model the following strong downward sediment fluxes which are observed during the periods of flow deceleration classical pickup functions which essentially depend on the shields parameter are also incapable of modelling the secondary entrainment fluxes which sometimes occur at free stream velocity reversal the measured vertical fluxes indicate that the effective sediment settling velocity in the high 0 3 c z t 0 4 concentration area is typically only a few percent of the clear water settling velocity while the measurements of richardson and jeronimo chem eng sci 34 1979 1419 from a different physical setting lead to estimates of the order 20 the data does not support gradient diffusion as a model for sediment entrainment from the bed that is detailed modelling of the observed near bed fluxes would require diffusivities that go negative during periods of flow deceleration an observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition

sediment transport in oscillatory flow over flat beds the motion of sediment in oscillatory flow over a flat bed is investigated both theoretically and experimentally the theory makes use of results for the relationship between stress and strain in steady flow the experiments were performed in two different oscillatory flow water tunnels with two different sediments they were designed to measure the variation of velocity with height in the moving layer of sediment under conditions of intense sediment transport although certainly not perfect the agreement between theory and experiment is reasonable provided the stress ratio is chosen correctly calculated values of the mean sediment transport rate during a half cycle are compared with the predictions of currently available formulas

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

lead isotopic compositions of the western dharwar craton southern india evidence for distinct middle archean terranes in a late archean craton abstract lead and sr isotopic compositions of whole rocks and feldspar separates from several fielddefined suites of rocks from the western dharwar craton of southern india elucidate a complex history of the area the evolution of the craton earlier than 3 0 ga is difficult to determine because of thermal and metasomatic overprinting at 3 0 ga many whole rocks were completely reset then but feldspar separates preserve some of the earlier history apparently a series of terranes evolved from the mantle over the period 3 4 to 3 0 ga to form the western dharwar craton in each case metamorphism and anatexis of older terranes accompanied extraction of juvenile material from the mantle the oldest gneisses 3 4 ga had radiogenic pb and sr isotopic compositions when they formed and were derived from older crustal protoliths that were plausibly accreted to the crust at or even before 3 8 ga the old gneisses were greatly depleted in rb probably at 3 4 ga when the protoliths of younger magmatic rocks may have separated from the mantle younger gneisses apparently formed from these mafic intermediate protoliths in the age range of 3 2 to 3 0ga the 3 0 ga event in the central part of the craton was accompanied by intrusion of small diapiric trondhjemites formed by melting of older crust and penecontemporaneous metasomatism of country rocks by hydrous fluids carrying u and other lithophilic elements the resultant deep crust was greatly depleted in heat producing elements and the craton has been inactive since 3 0 ga except for production of minor granites from depleted source regions at 2 5 2 6 ga the lack of activity at 2 5 ga contrasts strongly with extensive magmatism and metamorphism in surrounding areas that had not undergone depletion at 3 0 ga lower crustal depletion also has caused present day reduced heat flow to be very low

a semianalytical model for sheet flow layer thickness with application to the swash zone a new semianalytical model for the time dependent thickness of the sheet flow layer that includes the effects of pressure gradients bed slope boundary layer growth and bore turbulence is presented the shear stress and boundary layer growth are computed using the boundary layer integral method the model is expressed as two coupled ordinary differential equations that are solved numerically given a prescribed time series of free stream velocity horizontal pressure gradient and bore turbulence which together represent the hydrodynamic forcing the model was validated against two data sets of sheet flow layer thickness collected in oscillatory flow tunnels and one data set collected in the swash zone of a prototype scale laboratory experiment in the oscillatory flow tunnel data sets sheet flow is mostly generated by shear stress with pressure gradients providing an important secondary forcing around flow reversal in the swash zone pressure gradients and shear stresses alone are not sufficient to generate the large sheet flow layer thickness observed at the initial stages of uprush bore turbulence is most likely the dominant generation mechanism for this intense sheet flow

resetting of oxybarometers and oxygen isotope ratios in granulite facies orthogneisses during cooling and shearing adirondack mountains new york the petrography petrology and oxygenisotope geochemistry of granulite facies granitic and syenitic orthogneisses of the diana and stark complexes adirondack mountains new york show that the extent and nature of resetting of isotopic and mineralogic systems is highly variable there is a strong correlation between retrogression and shearing and the rocks may be divided texturally into 1 unsheared lithologies that preserve little retrogressed pyroxene or hornblendebearing peak metamorphic mineralogies and 2 sheared rocks that underwent retrogression marked by the growth of late biotite in centimetre to metre wide shear zones after the peak of metamorphism oxygen fugacities in the unsheared lithologies were estimated for reintegrated mineral compositions from magnetiteilmenite mt ilm and ferrosilite magnetic quartz fs mt qtz equilibria mt ilm yields logfo2mt ilm values of 15 9 to 17 6 0 6 to 1 3 log units below the fayalite magnetite quartz buffer fmq and temperatures of 670 745 c that agree with those from other geothermometry and phase equilibria studies these data suggest that aside from oxyexsolution of ilmenite from magnetite the fe ti system underwent only minor resetting during cooling and the fe ti oxides yield good estimates of peak metamorphic temperatures and fo2 in unsheared ilmenite magnetite orthopyroxene quartz assemblages values of logfo2mt ilm are lower than logfo2fs mt qtz by an average of 0 6 when the orthopyroxene activity model of sack and ghiorso is used minor resetting of the fe ti oxides analytical errors and errors in the placement of end member reactions probably account for this relatively small difference in fo2 values whole rock 18o values of unsheared diana and stark lithologies range from 4 0 to 10 3 reflecting pre regional metamorphic oxygen isotope ratios peak metamorphic minerals preserve high temperature oxygen isotope fractionations and in many samples the effective diffusion of oxygen in minerals ceased at higher temperatures than predicted from wet experimental diffusion data these data suggest that the rocks did not contain an aqueous fluid phase during cooling the combination of petrologic isotopic and textural data also permits a detailed study of shearing and retrogression ilmenites in the sheared lithologies underwent greater degrees of hematite loss than in the unsheared rocks resulting in logfo2mt ilm values as low as 24 1 3 1 log units below fmq and mt ilm temperatures that are up to 175 c below regional estimates sheared rocks also have higher 18o values up to 13 3 during shearing 18o values of biotite k feldspar and magnetite reset readily while the degree of isotopic resetting of quartz correlates with the intensity for recrystallization

late pleistocene holocene paleoclimatic history of the southern kerala basin southwest india abstract the south kerala sedimentary basin sksb constitutes one of the most significant landward extensions of the southwest offshore sedimentary basins of india and is situated between 8o45 and 10o15 n latitudes with a maximum width of about 20 km and incorporating a 700 m thick sedimentary succession ranging in age from early miocene to holocene this belt lies almost entirely under water or alluvium covered coastal plains in this study we use two continuously cored bore holes at eruva 7 25m deep and muthukulam 3m deep separated by a distance of about 7km to investigate the depositional environment as well as paleo ecology of the depocentre and climatic aspects during the late pleistocene and holocene results from c14 dating of shell fragments from eruva depth zone 2 10 6 64m yielded ages in the range of 36 2 to 42 5 kybp corresponding to the late pleistocene wood fragments in the muthukulam core sample depth zone 1 27 3 00m gave c14 ages in the range of 3 7 to 7 2 kybp indicating a holocene history the lower half of the eruva bore hole indicates a marginal marine environment with an abundant supply of terrestrial carbonaceous debris probably corresponding to a period of abnormally high rainfall recorded in many parts of the globe covered by the asian summer monsoon the sediments in the upper part of this bore hole indicate a continuation of this environment but with much less input of terrestrial organic carbon the lower part of the bore hole from this locality corresponding to the holocene transgression is similar to the lower part of eruva bore hole in the case of toc deposition took place in water bodies with considerable marine influence but receiving high amounts of terrestrial plant debris mostly in the form of finely divided particles mixed with mud this transgressive sequence was also deposited during a time when the asian summer monsoon was abnormally high in intensity as indicated by many examples in india africa madagascar and elsewhere it is significant that during the deposition of this part the sea level was probably the same as present or higher suggesting possible lowering of the stream velocities and resultant deposition of only muddy sediments laden with terrestrial organic material along the coast the upper part of the section shows a progressively reduced rainfall pattern culminating in a period of very low precipitation with the development of a paleosol which is traceable all over the sksb where late holocene sediments are available this period also witnessed aeolian activity modifying the sand ridges in the ridge runnel systems formed by the holocene regression

cordierite gneisses of southern kerala india petrology fluid inclusions and implications for crustal uplift history the cordierite bearing gneisses occurring as elongate patches in an 8 to 10 km wide zone along the achankovil fault lineament at the northern margin of the southern kerala crustal segment represent an important lithological unit in the archaean granulite terrane of south india the textural relationships in these rocks are consistent with the following main reactions 1 garnet quartz cordierite hypersthene 2 garnet sillimanite quartz cordierite 3 hypersthene sillimanite quartz cordierite 4 sillimanite spinel cordierite corundum and 5 biotite quartz sillimanite cordierite k feldspar many of the mineral associations and reaction textures including the remarkable preservation of symplectites are indicative of partial replacement of high pressure assemblages by cordierite bearing lower pressure ones during an event of rapid decompression temperature estimates from coexisting mineral phases show 710 garnet biotite 791 garnet cordierite and 788 c garnet orthopyroxene pressure estimates from mineral assemblages range from 5 4 to 7 kb detailed fluid inclusion studies in quartz associated with cordierite show high density co2 0 80 0 95 g cm3 as the dominant fluid phase with traces of probable ch4 in the sillimanite bearing rocks the isochore for the higher density fluid inclusions defines a pressure of 5 5 kb the fracture bound co2 and co2 h2o ch4 inclusions indicate simultaneous entrapment at 400 c and 1 7 kb in the cordierite hypersthene assemblage and 340 c and 1 2 kb in the cordierite sillimanite assemblage the p t path delineated from combined solid and fluid data corresponds to the piezothermic array of the gneisses and is characterized by t convex nature indicative of rapid and virtually isothermal crustal uplift probably aided by extensional tectonics

sediment suspension in oscillatory flow measurements of instantaneous concentration at high shear abstract different syphon type suspended load probes were used together with a specially developed carousel sampler for measurements of the instantaneous sediment concentration in turbulent oscillatory flow over a sand bed shields parameters were well above the ripple flat bed transition region resulting in intense sediment transport over a flat bed the measurements were performed at different levels in a large oscillating water tunnel they showed some characteristic features of the temporal concentration variation at fixed levels including a pronounced effect of the orientation of the suction tube relative to the flow the variation with height of the average concentration is reasonably well described assuming a constant turbulent diffusivity and the magnitude of this can be predicted relatively well using simple turbulence arguments two empirical formulae for the extrapolated bed concentration are also presented the analysis is partly based on wilson s finding that in sheet flow the equivalent bed roughness is nearly proportional with the shields parameter resulting in a roughness grain diameter ratio much larger than 2 5 the figure often adopted for a flat bed but without sheet flow

evidence for pre regional metamorphic fluid infiltration of the lower calcsilicate unit reynolds range group central australia grandite garnet rich calcsilicate rocks from the lower calcsilicate unit of the regionally metamorphosed reynolds range group central australia crop out along a strike parallel section in which a transition zone from m22 amphibolite to granulite facies rocks is exposed across this transition the grandite rich layers do not show systematic changes in mineral assemblages compositions and modes or stable isotope compositions these layers are deformed by f22 folds that are associated with the peak of regional low pressure high temperature metamorphism therefore the grandite rich layers appear to pre date regional metamorphism and to have acted as closed chemical systems during prograde m22 metamorphism mineral assemblages in the grandite rich layers are consistent with their formation through the infiltration of oxidized water rich fluids xco2 0 1 0 3 log fo2 16 to 14 the stable isotope values of calcite 13c 4 2 to 0 8 0 pdb 18o 10 5 14 0 0 v smow and bulk silicate fractions 18o 6 1 to 10 8 of the grandite rich layers are most consistent with the infiltrating fluid being from a magmatic source it is most likely that fluid infiltration occurred during the pre m22 contact metamorphism m21 that affected much of the reynolds range group the preservation of these assemblages is probably due to their high variance and little pervasive fluid rock interaction having occurred during m22 the clinopyroxene and feldspar rich calcsilicate rocks that host the grandite rich layers contain poikiloblastic grandite garnet that formed during prograde m22 metamorphism thin marbles that locally occur with the grandite rich layers contain a third garnet generation that is post or late m22 this grossular rich garnet occurs in coronas around calcite plagioclase clinopyroxene wollastonite and scapolite these coronas are consistent with cooling and or compression however because the marble assemblages are themselves overprinted by m21 grandite rich layers the development of coronal garnet does not reflect a continuous p t t path rather it more probably reflects the partial re equilibration of m21 contact metamorphic assemblages to post m22 conditions

lateritization cycles and their relation to the formation and quality of kaolin deposits in south kerala india abstract laterite occurs extensively over the crystalline and sedimentary rocks in the midland and lowland areas of south kerala india two lateritization cycles are identified in this area large good quality kaolin deposits composed mostly of kaolinite are characteristic of the sedimentary sequence in south kerala these deposits were formed on deposition of the weathering materials of the khondalites towards the first cycle of lateritization after deposition and uplift of the sedimentary rocks another lateritization cycle affected these as well as the khondalites during pre quaternary times with the formation of a planation surface at 25 125 m above sea level having thick laterite profiles the laterite profiles over the kaolin deposits show higher concentration of fe oxides mostly in the form of hematite and titania compared to their concentration in the kaolins higher contents of cr and ni are also characteristic of the laterite over kaolin deposits recrystallization of the kaolinite appearance of al fe and si amorphous phases in the kaolin clays and partial removal of fe and ti from them are attributed to the second lateritization cycle

how well established is isobaric cooling in proterozoic orogenic belts an example from the arunta inlier central australia orogenic pressure temperature paths can only be deduced from metamorphic textures if they formed during a single metamorphic event rather than recording the effects of two or more separate events erroneous tectonic models are likely to result if textures formed in several events are ascribed to one event we illustrate this problem for the arunta inlier in central australia which has been considered to be a good example of an isobarically cooled terrain rocks of the anmatjira range in the central arunta inlier which has been described in terms of isobaric cooling actually record the effects of two low pressure granulite facies metamorphic events of similar peak metamorphic grade m 1 and m 2 that are separated in time by a period of basin development and deposition of a succession of sedimentary rocks correlations of stratigraphic structural fabric and metamorphic texture data allow the effects of m 1 and m 2 to be distinguished without this fine control the textures formed by superposition of m 1 upon m 2 considered as a manifestation of one event could easily be interpreted as indicating isobaric cooling because the overprinting assemblages are of similar pressure but slightly lower temperature than the original assemblages we call this apparent isobaric cooling in fact we now recognize textures reflecting decompression that formed immediately following the peaks of both m 1 and m 2 it is now a matter for conjecture whether isobaric cooling is more apparent than real in other terrains for which it has been recorded

significance of early scapolite in greenschist facies marbles from the reynolds range group central australia marbles from the upper calcsilicate unit of the reynolds range group central australia experienced regional proterozoic greenschist facies metamorphism but preserve relicts of an earlier higher temperature assemblage the earlier assemblage is typified by intermediate scapolite that predates regional metamorphic fabrics and it is pseudomorphed by assemblages that were stable during regional greenschist facies metamorphism the scapolite was formed at temperatures in excess of 540 575 c far higher than the regional metamorphic temperatures 400 450 oc marbles and associated pelites display variable but lower i8 o values than are typical of greenschist facies metasediments scapolitization and lowering of isotope ratios probably resulted from pre regional metamorphic contact metamorphism around early granites

calculation of co 2 activities using scapolite equilibria constraints on the presence and composition of a fluid phase during high grade metamorphism thermodynamic and phase equilibrium data for scapolite have been used to calculate co2 activities aco2 and to evaluate the presence or absence of a fluid phase in high grade scapolite bearing meta anorthosite granulites calc silicates and mafix xenoliths the assemblage scapolite plagioclase garnet quartz may be used to calculate or limit aco2 by the reaction meionite quartz grossular anorthite co2 granulites from four high grade terranes grenville province canada sargut belt india furua complex tanzania bergen arcs norway yield aco2 0 4 1 with most 0 7 for scapolite bearing granulites from the furua complex in which aco2 0 9 calculated h2o activities ah2o based on phlogopite dehydration equilibria are uniformly low 0 1 0 2 the aco2 calculated for meta anorthosite from the grenville province ontario ranges from 0 2 to 0 8 for grenville meta anorthosite also containing epidote the ah2o calculated from clinozoisite dehydration ranges from 0 2 to 0 6 calc silicates from the grenville sargur and furua terranes mostly yield aco2 1 the calculated fluid activities are consistent with metamorphism 1 in the presence of a mixed co2 h2o fluid phase in which co2 is the dominant fluid species but other c o h s species are minor 2 in the absence of a bulk fluid phase fluid absent metamorphism or 3 in the presence of a fluid bearing melt phase the results for many granulites and grenville meta anorthosite are consistent with the presence of a co2 rich mixed co2 h2o fluid phase in contrast the relatively restricted and low values of aco2 for calc silicates require an h2o rich fluid or absence of a fluid phase during metamorphism the range of values for xenoliths are most consistent with absence of a fluid phase the primary implication of these results is that a co2 rich fluid accounts for the reduced ah2o in scapolite bearing granulites however scapolite may be stable with a wide range of fluid compositions or in the absence of a fluid phase and the presence of scapolite is not a priori evidence of a co2 rich fluid phase in addition close association of scapolite free mafic granulites with scapolite bearing granulites having identical mineral compositions in the furua complex and the absence of scapolite from most granulite terranes implies that a co2 rich fluid phase is not pervasive on an outcrop scale or common to all granulite terranes

sediment transport in oscillatory sheet flow motivated by an interest in high rates of sediment transport an experimental investigation was conducted to examine sediment motion in conditions of intense sediment transport fluid velocity and sediment concentration were measured simultaneously in a sheet flow regime generated in a u shaped oscillatory water tunnel for two types of noncohesive sediments a probe was developed to measure the instantaneous variations in sediment concentration based on the electrical conductivity of the fluid grain mixture unlike previous concentration devices this probe is nonintrusive and is capable of measuring a wide range of sediment concentrations from extremely dense concentrations within the bed to low concentration suspended load well above the moving layer of sediment horizontal fluid velocities were measured simultaneously using laser doppler anemometry in backscatter mode the sediment concentration measurements provide a comprehensive data set for sediment transport in sheet flow and near sheet flow regimes the temporal variation of sediment transport over the half cycle of oscillation was examined most of the sediment was transported within the moving bed layer with the total transport occurring between the stationary bed height and a distance about twice the thickness of the moving bed layer the temporal variation in sediment transport was found to be proportional to cos t the magnitude of the sediment transport increased with increasing bottom shear stress fluid velocity and sediment concentration measurements were used to calculate instantaneous and mean rates of sediment transport which were compared with predictions from existing models

fluid heterogeneity during granulite facies metamorphism in the adirondacks stable isotope evidence the preservation of premetamorphic whole rock oxygen isotope ratios in adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived hot co2 h2o fluids during granulite facies metamorphism this conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations the data suggest that these rocks were not an open system during metamorphism that fluid rock ratios were in many instances between 0 0 and 0 1 that externally derived fluids as well as fluids derived by metamorphic volatilization rose along localized channels and were not pervasive and thus that no single generalization can be applied to metamorphic fluid conditions in the adirondacks

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

a two phase approach to wave induced sediment transport under sheet flow conditions a numerical model for the general description of the sediment transport under oscillatory sheet flow conditions is developed based on a two fluid representation of the two phase turbulent flows the governing equations of the model are the reynolds averaged continuity equations and equations of motion for both the fluid and the sediment phases the two phases are coupled by the interphase forces including the resistance force the inertia force and the lift force turbulence closure of the fluid phase is based on a slightly modified k epsilon model while an algebraic particle turbulence model is applied to the sediment phase the numerical method is based on the modified simple scheme and an improved time stepping technique the model is validated by the published data for the symmetrical oscillatory sheet flows generated in an oscillatory flow tunnel at the university of tokyo and for both the symmetrical and the asymmetrical oscillatory sheet flows generated in an oscillatory flow tunnel at university of aberdeen the numerical results on the temporal and spacial variation of the sediment concentration the horizontal velocities of the two phases the horizontal and vertical fluxes of the sediment phase as well as the thickness of the sheet flow layer all show satisfactory agreement with the laboratory data the model is also shown to predict the net sediment transport rate with a reasonably good accuracy c 2011 elsevier b v all rights reserved

late archaean 2550 2520 ma juvenile magmatism in the eastern dharwar craton southern india constraints from geochronology nd sr isotopes and whole rock geochemistry the results of field geochronologic geochemical and isotopic studies are presented for the granitoids that occur east of the closepet batholith up to the kolar schist belt ksb field data such as common foliation strong shear deformation occasionally leading to mylonitization together with petrographic data including reduction in grain size with corroded borders show characteristics of the syn kinematic emplacement of the granitoids single zircon evaporation ages define a minimum age of 3127 ma for the tonalitic trondhjemitic granodioritic ttg basement and 2552 2534 ma plateau ages for the emplacement of the granitoids which slightly predate 20 30 ma the emplacement of the 2518 ma closepet batholith major and trace element data together with isotopic data suggest at least four magmatic suites from closepet batholith to the east which have independent magmatic evolution histories the observed data are compatible with magma mixing for the closepet batholith melting of ttg and assimilation fractional crystallization processes for bangalore granites either melting of heterogeneous source or different degree of melting of the same source for the granitoids of hoskote kolar and fractional crystallization for the western margin of the ksb isotopic nd sr and geochemical data lree and lil elements suggest highly enriched mantle and ancient ttg crust for the closepet batholith enriched mantle and ttg crust for the bangalore granites c a chondritic mantle source for the granitoids of hoskote kolar and the quartz monzonites of the western margin of the ksb and slightly depleted mantle for granodiorites of the eastern margin of the ksb we interpret all these geochronologic geochemical and isotopic characteristics of granitoids from the closepet batholith to the east up to the ksb in terms of a plume model the centre of the plume would be an enriched hot spot in the mantle that lies below the present exposure level of the closepet batholith melting of such an enriched mantle hot spot produces high temperature magmas closepet that penetrate overlying ancient crust where they strongly interact and induce partial melting of the surrounding crust these magmas cool very slowly as the hot spot maintains high temperatures for a long time thus they appear younger 2518 ma on the contrary to the east the plume induces melting of c a chondritic or slightly depleted mantle that produces relatively colder and less enriched magmas which show less or no interactions with the surrounding crust and cool rapidly and appear slightly older 2552 2534 ma this plume model can also account for late archaean geodynamic evolution including juvenile magmatism heat source for reworking inverse diapirism and granulite metamorphism in the dharwar craton

two phase flow modeling of sediment motion in sheet flows above plane beds most models of sediment transport are based on the hypothesis of a weak interaction between the fluid and the sediment phase where the main flow is subjected to the mass and momentum conservation of the fluid phase with small corrections due to the presence of the sediments these models usually give a correct answer for conditions where the concentration of sediment is really low in the case of high sediment transport some models analyze the two subdomains separately the high and the low concentration and employ different constitutive equations in the present model there is a two phase description of the whole domain the closure of the turbulence and the interaction between the sediments and the fluid introduce approximations but results are consistent with experiments and previous models

the application of single zircon evaporation and model nd ages to the interpretation of polymetamorphic terrains an example from the proterozoic mobile belt of south india the technique of single zircon dating from the thermal evaporation of 207pb 206pb kober 1986 1987 provides a means of dating successive periods of growth and nucleation of zircons in polymetamorphic assemblages in contrast nd model ages may provide a measure of the period of crustal residency for the sample or its protolith these two techniques have been combined to elucidate the tectonic history of the proterozoic mobile belt of southern india exposed south of the palghat cauvery shear zone that marks the southern boundary of the archaean craton of karnataka the two main tectonic units of this mobile belt comprise the madurai and trivandrum blocks both of which are characterised by massive charnockite uplands and low lying polymetamorphic metasedimentary belts that have undergone a complex tectonic history throughout the proterozoic evidence for early palaeoproterozoic magmatism is restricted to the madurai block where single zircon evaporation ages from a metagranite 2436 4 ma are similar to model nd ages from a range of lithologies suggesting crustal growth at that time the trivandrum block to the south of the achankovil shear zone is comprised of the kerala khondalite belt the nagercoil charnockites and the achankovil metasediments single zircon evaporation ages together with conventional zircon and garnet chronometry suggest that all three units underwent upper amphibolite facies metamorphism at 1800 ma an event unrecorded in the metagranite from the madurai block this implies that the madurai and trivandrum blocks represent distinct terrains throughout the palaeoproterozoic model nd ages from the achankovil metasediments are much younger 1500 1200 ma than those from the adjacent kerala khondalite belt and madurai blocks 3000 2100 ma but there is no evidence for zircon growth in these metasediments during the mesoproterozoic hence the comparatively young model nd ages of the metasediments are indicative of a mixed provenance rather than a discrete period of crustal growth zircon overgrowths from the madurai block 547 17 ma and achankovil metasediments 530 21 ma suggest that all tectonic units of the proterozoic mobile belt of south india shared the same metamorphic history from the early palaeozoic this event has been recognised in the basement lithologies of sri lanka and east antarctica confirming that the constituent terrains of east gondwana had assembled by this time

halogen rich scapolite and biotite implications for metamorphic fluid rock interaction abundant cl rich scapolite and biotite indicate high cl activities during greenschistthrough amphibolite facies regional metamorphism of metasedimentary rocks northwest of the idaho batholith biotite zone granofels contain up to 40 modal percent cl rich scapolite the strict stratigraphic control on the occurrence ofscapolite and the fine scale interlayering of cl rich and cl poor metasedimentary rocks suggest that scapolite was formed during regional metamorphism by reaction of plagioclase with calcite and halite mass balance constraints on the formation of scapolite show that prior to metamorphism sedimentary units containing l0 modal percent halite along restricted sedimentary horizons 0 5 to 20 cm thick would have been sufficient to form the most scapolite rich layers the abundance ofcl rich phases decreases abruptly with the appearance ofzoisite bearing assemblages in the metasedimentary rocks suggesting infiltration of low cl hro at higher grades scapolite compositions range from 32 to 62 equivalent anorthite eqan and 0 7 6 to 0 06 xo there is a general increase in eqan and decrease in x with increasing metamorphic grade however local variations in scapolite composition suggest hat metamorphic fluid compositions were heterogeneous and internally bufered biotites coexisting with scapolite contain up to 0 51 wto o cl biotite grade and 2 58 wto o f kyanite sillimanite grade biotite compositions indicate significant differences inlogffir fr values of fluids in equilibrium with low grade biotiteand carbonate rich granofels differences in the inferred metamorphic fluid compositions are observed in some cases down t o a s c a l e o f l c m cl is strongly partitioned into an aqueous fluid relative to solid phases and is removed by metamorphic devolatilization and infiltration by dilute fluids therefore the occurrence of bufered activity gradients in cl as indicated by scapolite and biotite compositions suggests that metamorphic fluid flow was highly channelized and aqueous fluid rock interaction was limited high and variable cl activities were not smoothed out by aqueous fluid rock interaction through two regional metamorphic events

proterozoic granulite facies metamorphism in the southeastern reynolds range central australia geological context p t path and overprinting relationships in the southeastern reynolds range central australia a low p granulite facies metamorphism affected two sedimentary sequences the lander rock beds and the reynolds range group in the context of the whole of the reynolds range and the adjacent anmatjira range this metamorphism is m3 in a sequence m1 4 that occurred over a period of 250 ma in particular m1 affected the lander rock beds prior to the deposition of the reynolds group m3 has an areally restricted high grade area in the southeastern reynolds range affecting both the reynolds range group and the underlying lander rock beds the effects of m3 are characterized by spinel quartz bearing peak metamorphic assemblages in metapelites which imply peak conditions of 750 c and 4 5 1 kbar and involved isobaric cooling or compression with cooling it is concluded that one of a series of thermal perturbations caused by thinning of mantle lithosphere contemporaneous with crustal thickening was responsible for m3 in the southeastern reynolds range evidence of both the unconformity between the two rock groups and previous metamorphism deformation has been completely erased by recrystallization during m3 d3

constraints on the application of carbon isotope thermometry in high to ultrahigh temperature metamorphic terranes nine marble horizons from the granulite facies terrane of southern india were examined in detail for stable carbon and oxygen isotopes in calcite and carbon isotopes in graphite the marbles in trivandrum block show coupled lowering of 13c and 18o values in calcite and heterogeneous single crystal 13c values 1 to 10 for graphite indicating varying carbon isotope fractionation between calcite and graphite despite the granulite facies regional metamorphic conditions the stable isotope patterns suggest alteration of 13c and 18o values in marbles by infiltration of low 13c 18o bearing fluids the extent of alteration being a direct function of the fluid rock ratio the carbon isotope zonation preserved in graphite suggests that the graphite crystals precipitated recrystallized in the presence of an externally derived co2 rich fluid and that the infiltration had occurred under high temperature and low fo2 conditions during metamorphism the onset of graphite precipitation resulted in a depletion of the carbon isotope values of the remaining fluid calcite carbon reservoir following a rayleigh type distillation process within fluid rich pockets pathways in marbles resulting in the observed zonation the results suggest that calcite graphite thermometry cannot be applied in marbles that are affected by external carbonic fluid infiltration however marble horizons in the madurai block where the effect of fluid infiltration is not detected record clear imprints of ultrahigh temperature metamorphism 800 1000 c with fractionations reaching 1000 c and would be consistent with uht metamorphism

occurrence and origin of marialitic scapolite in the humboldt lopolith n w nevada the occurrence and origin of marialitic scapolite in the humboldt lopolith was investigated in the field and in the laboratory using petrographic and experimental techniques scapolite occurs in three modes as a pervasive replacement of plagioclase and other minerals in gabbro diorite and extrusive rocks as a poikiloblastic mineral in scapolitite dikes and as a fracture filling mineral with analcime albite and sphene in scapolite veins additional secondary minerals associated with scapolite include epidote prehnite hornblende and diopside salite clinopyroxene relations with these minerals suggest that most marialitic scapolite grew at temperatures around 400 c scapolite composition varies from eqan12 to eqan37 containing from 72 to 96 atomic cl in the r position experiments on systems of similar compositions indicate that nacl h2o fluid having more than 40 mol nacl is needed to stabilize the scapolite

electron microprobe dating of monazites from high grade gneisses and pegmatites of the kerala khondalite belt southern india monazites of five samples one leptynitic garnet biotite gneiss one khondalite one augen gneiss and two pegmatites from the central and northern part ponmudi unit of the kerala khondalite belt kkb in southern india were analyzed with the electron microprobe dating technique monazites in the augen gneiss and the pegmatites yield grain sizes between 200 800 m th abundances are rather low 10 wt and the distribution of th u and pb within single grains is fairly homogeneous contrasting to this monazites in the leptynitic gneiss and the khondalite are small 150 m they often display very complex th u pb patterns and contain high th concentrations up to 20 wt the statistical treatment of individual ages from the investigated samples revealed three populations of lower proterozoic 1 9 ga upper proterozoic 580 ma and ordovician age 470 ma as well as mid proterozoic ages between 0 8 1 7 ga which are not regarded to be of geological significance lower proterozoic ages are preserved in the cores of monazites from leptynitic gneisses and khondalites they fairly agree with sm nd model ages for similar rocks of the kkb and give a minimum age for first monazite growth or complete homogenization the prominent pan african population with mean values between 540 and 580 ma is present in the leptynitic gneiss the khondalite and the augen gneiss and in line with published isotope ages for the kkb the ordovician population finally marks the emplacement of granitic pegmatites subsequent to the pan african high grade metamorphic event there is an obvious discrepancy between khondalites and leptynitic gneisses on the one hand and augen gneisses on the other concerning the presence of lower proterozoic ages while these are abundant in the former often rimmed by upper proterozoic ages they are completely absent in the latter it appears unlikely that lower proterozoic ages were completely reset during a pan african event exclusively in the augen gneisses while they were preserved in leptynitic gneisses and khondalites it is further concluded that the augen gneisses are of magmatic origin and were derived from porphyritic granites thus the upper proterozoic age of 605 37 ma calculated for the investigated sample approximates the time of magma emplacement which slightly precedes the peak stage of pan african high grade metamorphism in the kkb and of monazite crystallization from the granitic melt a characteristic feature of the investigated monazites is the resetting of lower proterozoic and pan african ages to significantly younger values due to partial pb loss monazites not shielded by other minerals e g garnet suffered selective mobilization of pb along fractures or at their rims while th and u concentrations remained almost unchanged the results presented in this study indicate that this was mainly due to fluid rock interaction it is concluded that thermal diffusion of pb even at the suggested temperatures of 900 c only had minor influence on the th u pb composition in monazite and that the closure temperature for this system must be significantly higher than previously assumed 750 c

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

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

a two phase numerical model for sediment transport prediction under oscillatory sheet flows to predict sediment transport under oscillatory sheet flow condition especially for fine sand is still a challenging research subject in coastal engineering this paper describes a newly developed numerical model based on two phase theory with the use of a one equation turbulence closure and its applications in predicting fine sediment suspension in near prototype oscillatory sheet flow conditions model results were compared with comprehensive laboratory measurements of flow velocity and sediment concentration under both symmetrical and asymmetrical oscillatory sheet flows from a large scale water tunnel good agreements between the model results and measurements were achieved and the results demonstrated that the model is capable of reproducing detailed characteristics of sediment entrainment process in the sheet flow regime the comparisons also revealed the fact that the concentration peaks at flow reversal is associated with the strong vertical sediment transport flux in the pickup layer which has been widely observed in many laboratory experiments the effects of flow reversal events on total sediment transport were also discussed

two phase model for sand transport in sheet flow regime 1 we introduce a two phase model for sand transport in sheet flow regime this model uses a collisional theory and a k fluid turbulence closure to respectively model the sediment and fluid phase stresses the sediment stress closure adopts a balance equation of sediment particle fluctuation energy based on kinetic theory that incorporates two way interactions between fluid and sediment phases the fluid turbulence closure also considers the two way interaction between fluid turbulence and sand particles model data comparisons for the sheet layer for oscillatory flows in a u tube and for open channel flows demonstrate the model s predictive skill for steady open channel flows the fluid phase velocity follows closely the law of wall i e the log profile in which the von karman constant is reduced and the equivalent roughness is increased compared to the clear fluid flow conditions the model also provides information in the near bed region where the transition from the solid like to the fluid like behavior of sediment particles is resolved and both the bed load layer thickness and bed load transport rate can be evaluated for unsteady flows this model can predict time evolutions for sediment transport throughout the water column

intense near bed sediment motions in waves and currents abstract in the past few years two phase models have been developed to describe the detail behaviour of fluid sediment interactions and transport under the sheet flow conditions due to the complexity of the governing equations and uncertainties in the formulations of various stress terms few complete solutions of these equations are known and the validations are thus far limited to only a few experimental data in this paper the numerical predictions of the behaviour of sheet flows using an improved version of an earlier two phase flow model coastal eng 36 2 1999 87 are described although the general structure of the model was retained a number of improvements had been made to give better account the underlying physics of the flow in areas very close to the stationary bed all key flow parameters have been predicted and analysed in order to gain insight into the processes calculated time dependent as well as time averaged concentrations are compared with experimental data from purely oscillatory flows and oscillatory flow plus a current good qualitative agreements between predictions and measurements were achieved for the time dependent concentrations while the time averaged concentrations are quantitatively accurate as well

channelled fluid infiltration and variation in permeability in reynolds range marbles australia strike parallel flow of h 2 o rich fluids through reynolds range marbles formed wollastonite bearing assemblages wollastonite abundance varies on a millimetre de from 10 to 66 modal the mineralogy of unmetasomatized marbles suggests that the formation of more than c 19 wollastonite requires silica metasomatism comparison with advective transport models suggests that the variable wollastonite contents may be explained by time integrated fluid fluxes and intrinsic permeability varying by up to two orders of magnitude on a millimetre scale fluids were probably focused through the marble within microfractures and the variations in intrinsic permeability may reflect variable fracture density

concentrations in oscillatory sheet flow for well sorted and graded sands in wave generated sheet flow conditions oscillatory near bed flow is large ripples are washed out and sand is mainly transported in a thin layer a few centimetres thick close to and below the no flow bed level new experiments in the aberdeen oscillatory flow tunnel have produced a comprehensive dataset of transport processes for well sorted and graded sands in large scale sinusoidal and asymmetric oscillatory sheet flow conditions in this paper detailed time and height varying concentration measurements are analysed the range and level of detail in the measurements make it possible to quantitatively analyse concentration behaviour more rigorously than before a new empirical equation is presented which characterises the time dependent concentration profile in the sheet flow layer the equation involves two time dependent parameters erosion depth and reference concentration the dependence of both parameters on flow and bed conditions is analysed new results are presented which make it possible to estimate time dependent erosion depth reference concentration and therefore concentration profile the effects of grading on sheet flow concentrations are analysed by comparing results from the large range of sand beds tested

metamorphic p t conditions of the kerala south india khondalite belt a granulite facies supracrustal terrain the khondalite belt of southernmost india is an immense section of granulite facies metasediments of probable early proterozoic age dominant rock types are migmatized khondalites garnet sillimanite pm cordierite metapelites acid biotite garnet graphitic gneisses and charnockites quartzofeldspathic gneisses with orthopyroxene throughout much of southern kerala the biotite gneisses are in a state of arrested conversion to charnockite partially decrepitated co 2 inclusions in quartz at the ponmudi mixed biotite gneiss charnockite quarry have significant ch 4 and or n 2 and are texturally late the probable sequence of events in metasediments was 1 migmatization 2 charnockite formation 3 symplectitic cordierite formation and 4 late co 2 entrapment phase equilibrium diagrams of anatexis in aluminous systems and fe mg exchange between garnet and biotite indicate metamorphic temperatures of 650 850 c for the khondalites temperatures based on garnet orthopyroxene

multiple tectonothermal events in the granulite blocks of southern india revealed from epma dating implications on the history of supercontinents abstract we report age data on zircon monazite uraninite and huttonite from a suite of 29 samples covering four major granulite blocks in southern india using an electron microprobe technique the rocks analysed in this study cover all of the major lithounits in these terrains and include garnet bearing and garnet free charnockites garnet biotite gneisses khondalites calc silicate rocks and a suite of orthogneisses biotite gneiss biotite hornblende gneiss two pink metagranites representing the magmatic phase were also analysed zircons from the madras block yield well defined isochrons at 2 5 2 6 ga core to rim analyses of single zircon grains show age zoning with 2 6 2 9 ga igneous cores mantled by 2 4 2 5 ga rims detrital zircons show age up to ca 3 2 ga monazites in this block have cores and rims with 2 5 2 3 ga a suite of 19 samples from the madurai block brings out the multiple tectonothermal events in this terrain zircons from an orthogneiss yield well defined isochrons at 1 7 0 1 ga 0 82 0 05 ga and 0 58 0 04 ga from core inner rim and rim portions respectively zircon grains in other rocks preserve either core or secondary growth ages at 0 8 1 0 ga zircons in a pink metagranite from this block show sharply defined isochrons of 0 68 0 03 ga for the core and 0 57 0 01 ga for the secondary portion a late pan african overprint is observed throughout this block with zircon rims monazite uraninite and huttonite yielding age values in the range of 0 45 0 60 ga zircons from both the trivandrum and nagercoil blocks show a major tectonothermal event at 0 55 ga with faint indications of previous tectonothermal events during 0 8 1 0 and 1 7 2 0 ga monazite data from both the trivandrum and nagercoil blocks are essentially similar to those from the madurai block except for presence of relic monazite in the former our study confirms the notion that the palghat cauvery shear zone marks the major terrain boundary between an archean craton in the north and proterozoic terrains in the south it also strengthens the view of paleoproterozoic accretion and pan african reworking of blocks south of this shear zone the ages of production accretion and reworking in the terrains of southern india yield important information for the histories of columbia 1 8 1 5 ga rodinia 1 1 1 0 ga and gondwana 0 6 0 5 ga supercontinents the southern indian terrains formed part of a worldwide network of orogenic belts that is centered around 1 8 ga and outlines the configuration of columbia accretion of terrains in the madurai block to archean rocks north of the palghat cauvery shear zone at this time is consistent with the ages suggested to be the oldest metamorphic event in the eastern ghats orogen of eastern india and the rayner belt of coastal east antarctica our data confirm earlier evidence that all of southernmost india underwent resetting of isotopic systems during the final accretion of gondwana at the time of the pan african orogeny 0 5 ga the possibility that the trivandrum and nagercoil terrains accreted to the madurai block after 0 7 ga suggests that this pan african zone may also have involved accretion and closure of ocean basins if that happened then this zone may be the long sought suture between east and west gondwana

middle precambrian provenance of jurassic sandstone in the mino terrane central japan th u total pb evidence from an electron microprobe monazite study precise electron microprobe analyses have been made on detrital monazites in jurassic sandstones of the mino terrane central japan and their th u pb relations are examined in terms of pbo and tho2 tho2 tho2 plus the equivalent of uo2 the pbo tho2 ratios of most detrital monazites 403 of 581 grains cluster in the range from 0 0763 to 0 0618 other grains show the ratio of about 0 0541 46 grains 0 0364 29 grains 0 0170 24 grains and 0 0116 79 grains the pbo tho2 ratio of 0 0763 0 0618 is nearly identical with that of monazites in a middle precambrian 1740 ma gneiss clast from the kamiaso conglomerate of the mino terrane this strongly suggests that the detrital monazites were derived from gneisses and or granitoids of middle precambrian age the ratio of 0 0116 is nearly the same as that of monazites in a permian 274 ma paragneiss of the hida terrane north to the mino terrane the pbo tho2 monazite data coupled with palaeocurrent analyses and petrological characteristics of sandstones show that middle precambrian high grade metamorphic rocks and granitoids were widespread both in the northern and southern source regions of the e w trending jurassic basin of the mino terrane the pbo tho2 ratio of detrial monazites is a useful new measure for the provenance analysis of clastic rocks

a two phase flow model for asymmetric sheetflow conditions abstract a newly developed two phase flow model was applied to simulate the sediment movement under 2nd order stokes wave sheetflow conditions with different sediment sizes and wave periods as for the distribution of eddy viscosity and sediment diffusion coefficient the difference between onshore and offshore phases was considered by using an equivalent sinusoidal velocity amplitude for the asymmetric velocity profile sophisticated comparisons between laboratory measurements o donoghue t wright s 2004b flow tunnel measurements of velocities and sand flux in oscillatory sheetflow for well sorted and graded sands coast eng 51 11 12 1163 1184 and the present numerical simulation were performed for sediment concentration sediment velocity sand flux and net transport rate four existing engineering models together with the present two phase flow model were introduced for net transport rate prediction taking both the net sand transport rate magnitude and direction into account the present process based two phase flow model provided the best estimations which can simulate both the onshore net transport for medium coarse sand cases and offshore net transport for fine sand cases with the agreement by a factor of 2 for almost all the considered cases

orogeny associated with anticlockwise p t t paths evidence from low p high t metamorphic terranes in the arunta inlier central australia low pressure high temperature metamorphic terranes from the proterozoic northern arunta inlier central australia are characterized by anticlockwise pressure temperature time paths the thermal peak was reached before or during the earliest folding and it was associated with abundant repeated intrusion of granite sheets we generalize our observations in the area to infer that low p high t metamorphism is induced principally by focusing of mid crustal heat from rapid repeated granite sheet intrusion which generates large metamorphic aureoles intrusion and associated metamorphism produce melting reactions which increase the fluid pressure and thermally soften the mid crust resulting in accelerated melt enhanced deformation shortening is accommodated generally by thrusting in the mid crust and by upright folding in the upper crust compression occurs during cooling of the terrane as indicated by near isobaric cooling paths and the preservation of upper crust sections the result is the production of discrete low p high t terranes that are localized around abundant granitoids show thin skinned deformation and have anticlockwise p t time paths continued granitoid intrusion produces posttectonic discordant plutons at high crustal levels within low p metamorphic belts

measurements of sheet flow transport in acceleration skewed oscillatory flow and comparison with practical formulations near bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water in order to isolate the effects of acceleration skewness on sheet flow sand transport new experiments are carried out in the aberdeen oscillatory flow tunnel the experiments have produced a dataset of net transport rates for full scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes the new data confirm previous research that net transport in acceleration skewed flow is non zero is always in the direction of the largest acceleration and increases with increasing acceleration skewness large transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive net transport a comparison of the new experimental data with a number of practical sand transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured net transport rates for both the fine and the coarser sands the new experimental data can be used to further develop practical sand transport formulations to better account for acceleration skewness

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

precambrian tectonics and crustal evolution in south india about 3 4 ga ago voluminous calc alkaline magmas represented by the granitoid gneisses of southern india were emplaced into a now poorly preserved non continental crust unstable ensialic basins initiated at about 3 0 ga were filled with volcanic and sedimentary rocks up to about 2 6 ga this basement cover sequence was deformed at the close of the archaean first by northward accretion and thickening of several crustal slabs formerly separated by prisms of stable shelf sediments structures produced by this episode were refolded and dislocated by large n s strike slip shear belts to impart intense steep planar fabrics to large volumes of the crust fluids rich in co possibly derived from sedimentary material driven beneath the crustal slabs by the thickening mechanism purged the deep crust of h o to form granulites upward migration of hot h o rich fluids encouraged partial melting at intermediate crustal levels these late archaean tectonic and thermal events began soon after the close of basin f

nd isotopic evidence for the position of southernmost indian terranes within east gondwana abstract sm nd model ages of orthopyroxene bearing massif charnockites from the cardamom hills massif and adjoining supracrustal rocks from the kerala khondalite belt in southernmost india are used to infer some of the relationships within these rocks and between them and neighboring areas most of these rocks have model ages of 2 1 2 8 ga with most charnockites in the range 2 2 2 6 ga thus 3 0 3 4 ga archean rocks to their north did not contribute material to either suite and the two suites may have been juxtaposed after formation of the supracrustal rocks the similarity of sm nd isotope systems in the two units studied here supports an argument that the massif charnockites were the primary sole source of the detritus incorporated into the supracrustal rocks a cordierite gneiss representative of a relatively minor lithology in the supracrustal belt has a model age of 1 3 ga the protolith of this gneiss not only formed from much younger material than the rest of the belt but also formed significantly after the other metasedimentary rocks the source material of the gneiss protolith may have been located in the wanni and vijayan complexes of sri lanka the overlap of the model ages of rocks in this area and those in the highland complex of sri lanka supports the notion that these two sets of rocks were joined to each other in gondwana they belong to a belt that ran from antarctica through sri lanka and india into madagascar this belt was involved in pan african tectono metamorphism as reflected in the 550 ma age of the last granulite forming event throughout the belt

middle precambrian detrital monazite and zircon from the hida gneiss on oki dogo island japan their origin and implications for the correlation of basement gneiss of southwest japan and korea abstract monazite and zircon from seven paragneiss samples of the upper amphibolite facies grade from oki dogo island in the hida terrane western japan were analyzed for th u and pb on an electron microprobe most monazite grains are chronologically unzoned and give unequivocal chime chemical th u total pb isochron ages of 250 ma but some grains show a distinct core overgrowth relationship the cores retain evidence of pre 250 ma ages and are interpreted to be of detrital origin suggesting that monazite can be more immune to diagenetic and low grade metamorphic decompositions than had been thought previously zircon grains rounded to nearly euhedral give chime ages ranging from 3000 to 350 ma of particular interest are several rounded 3000 ma recycled zircons which perhaps originated from an archean terrain in the sino korean craton the youngest age of detrital zircons constrains that the gneiss protolith deposited after the 350 ma event the chime monazite and zircon ages for the paragneisses from oki dogo island and from the main part of the hida terrane reveal that the gneisses formed from permo carboniferous clastic sediments during a single metamorphism at ca 250 ma the results are in marked contrast to the current view that 1 the hida gneiss is a polymetamorphosed precambrian complex 2 the central part hida gneiss region and the eastern marginal part unazuki schist region of the hida terrane are correlative with the precambrian kyonggi massif and the paleozoic okchon zone in the korean peninsula respectively instead we consider that the okchon zone alone can be correlatable with the paleozoic hida terrane

kaolin deposits at melthonnakkal and pallipuram within trivandrum block southern india abstract the kaolin deposits at melthonnakkal and pallipuram mines form part of the warkalli formation belonging to the tertiary sequence in southern kerala and occur at the boundary between the tertiary sequence and precambrian granulite facies metapelites khondalites the sedimentary clays are composed mainly of kaolinite quartz and gibbsite xrd and sem studies have revealed that kaolinite is well crystallized variety and the platy crystals are scarcely broken in the sedimentary clays these sedimentary kaolins are considered to have been formed by intense tropical weathering of the khondalites and subsequently transported and deposited with high organic input into lakes near the weathering crust over the basement rock besides the surficial parts of the sedimentary deposits are extensively lateritized with the formation of goethite and hematite by quaternary tropical weathering processes

ultrahigh temperature stability of sapphirine and kornerupine in ganguvarpatti granulite madurai block southern india

sediment flux based model of instantaneous sediment transport due to pure velocity skewed oscillatory sheet flow with boundary layer stream abstract velocity skewed oscillatory sheet flow transport is studied by an approximate model for instantaneous sediment transport resulting from exponential profiles of sediment concentration and velocity over a mobile bed the phase lag effect and asymmetry in wave friction factor oscillatory flow orbital amplitude roughness height bed shear stress and wave boundary layer thickness are modelled so that the net boundary layer stream of pure velocity skewed oscillatory flow can be obtained the proposed model is found consistent with the previous classical formulas and qualitatively refines a series of exponents of velocity power function for the approximation of instantaneous sediment transport rate under different flow conditions the sediment fluxes can be well predicted with accuracy as that of a two phase numerical model the net boundary layer stream and sediment transport rates are also well predicted especially the negative net stream and rates with large phase residual the phase residual is shown a useful but insufficient factor in the net sediment transport in pure velocity skewed flows in addition the net boundary layer stream resulting from velocity skewed wave boundary layer development difference between onshore and offshore flow durations is an essential factor as well

the geological evolution of the reynolds range central australia evidence for three distinct structural metamorphic cycles the reynolds range is affected by three distinct structural metamorphic cycles di mi dii mii anddiii miii which represent the local expressions of a series of orogenic events that affected large sections of the arunta block central australia the tectonic cycles recognized in the reynolds range correlate extremely well with similar events in the nearby anmatjira range di mi took place around 1820 ma and only affected the nw reynolds range dii mii occurred between 1760 and 1650 ma and involved ne sw shortening with identical timing relationships between the deformations and metamorphism along the entire reynolds range dii commenced with the formation of a fabric sii1 preserved as inclusion trails in porphyroblasts sii1 formed early during a progressive event dii1 2 which involved the formation and tightening of upright nw se trending isoclinal folds a penetrative subvertical nw se trending fabric sii2 developed axial planar to these folds the general symmetry of dii2 microstructures suggests that fii2 folds were formed during progressive coaxial deformation under plane strain conditions dii3 structures are associated with conjugate sets of crenulation bands within the macroscopic crenulation bands large sections of earlier folds and fabrics are rotated to a near recumbent position the dominant set of crenulation bands is upright and trends ene wsw while the conjugate to this set trends nw se no penetrative fabric formed during dii3 dii4 is associated with a system of amphibolite grade ne dipping thrusts interconnected by numerous smaller shear zones the sense of movement is ne over sw during dii essentially penetrative coaxial deformation dii2 evolved into essentially localized non coaxial deformation dii3 dii4 dii deformation occurred concomitant with a low pressure granulite facies metamorphic event mii 1730 ma peak metamorphic sillimanite cordierite orthopyroxene ilmenite spinel garnet k feldspar quartz assemblages define sii2 oriented sillimanite biotite assemblages that formed early during dii3 and unoriented andalusite chlorite muscovite assemblages that formed late during dii3 indicate that cooling of mii was initially isobaric during dii4 thrusting staurolite garnet biotite quartz and biotite kyanite quartz assemblages defining the mylonitic fabric overprint the late dii3 andalusite assemblages dii4 shear movement is therefore accompanied by a slight rise in pressure dii4 shear zones gradually increase in grade eastward along the reynolds range this trend coincides with the variation in peak metamorphic grade attained during mii indicating that the rocks had not yet fully cooled when dii4 thrusting commenced diii miii is late devonian to carboniferous in age and caused minor differential movement 100 m and retrogression along dii4 shear zones

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

crustal trajectory of sapphirine bearing granulites from ganguvarpatti south india evidence for an isothermal decompression path abstract ganguvarpatti is part of a precambrian terrane characterized by granulite facies rocks including charnockites mafic granulites sapphirine bearing granulites leptynites and gneisses a sequence of reactions deduced from the multiphase reaction textures provide information on the metamorphic history of this area as they formed in response to decompression during uplift geothermobarometry and constraints from reaction textures define a segment of a p t path traversed by the granulites of ganguvarpatti near peak metamorphic conditions of c 800 c and 8 kbar were succeeded by a symplectitic stage at a significantly lower pressure c 700 c and 4 5 kbar documenting a nearly isothermal decompression p t path and rapid uplift c 12 km followed by cooling the presence of many fluid inclusions of extremely low density in the charnockites is consistent with a nearly isothermal uplift path attainment of a maximum pressure of c 8 kbar indicates c 27 km depth of burial during metamorphism this would imply a total crustal thickness of c 65 70 km at 2 6 2 5 ga such a profound crustal thickness and a clockwise decompressive p t path is interpreted as a consequence of tectonic thickening of crust accomplished by collision tectonics of the southern granulite terrane against the dharwar craton along the palghat cauvery shear zone via northward subduction

two phase flow modelling of sediment motions in oscillatory sheet flow in this paper a two phase flow model is presented which simulates the fluid and sediment motions in the sheet flow regime on a flat bed under oscillatory flow conditions the model is developed based on the continuity equations and linearised momentum equations for the fluid and sediment phases respectively all major forcing terms such as the intergranular stresses and the turbulent stress are included in the model from the detailed computations and comparison with the available laboratory data it has been demonstrated that the model is capable of predicting fairly accurately both flow kinematics and sediment concentrations in particular the model predicts that the well known phenomenon of fluid velocity over shoot that exists in clear water also appears in the case of lighter sediments but vanishes when the materials are heavier which is in perfect accord with the experimental observations considered

late archaean crust mantle interactions geochemistry of lree enriched mantle derived magmas example of the closepet batholith southern india the closepet batholith in south india is generally considered as a typical crustal granite emplaced 2 5 ga ago and derived through partial melting of the surrounding peninsular gneisses 3 3 to 3 0 ga in the field it appears as a composite batholith made up of at least two groups of intrusions a an early sio2 poor group clinopyroxene quartz monzonite and porphyritic phyritic monzogranite is located in the central part of the batholith these rocks display a narrow range in both initial 87sr 86sr 0 7017 0 7035 and nd 0 9to 4 1 b a later sio2 rich group equigranular grey and pink granites is located along the interface between the sio2 poor group and the peninsular gneisses they progressively grade into migmatised peninsular gneisses thus indicating their anatectic derivation their isotopic characteristics vary over a wide range 87sr 86sr ratios 0 7028 0 7336 and nd values from 2 7 to 8 3 at 2 52 ga field and geochronological evidence shows that the two groups are broadly contemporaneous 2 518 2 513 ga and mechanically mixed this observation is supported by the chemical data that display well defined mixing trends in the sr vs nd and elemental variation diagrams the continuous chemical variation of the two magmatic bodies is interpreted in terms of interaction and mixing of two unrelated end members derived from different source regions enriched peridotitic mantle and peninsular gneisses it is proposed that the intrusion of mantle derived magmas into mid crustal levels occurred along a transcurrent shear zone these magmas supplied additional heat and fluids that initiated anatexis of the surrounding crust during this event large scale mixing occurred between mantle and crustal melts thus generating the composite closepet batholith the mantle derived magmatism is clearly associated with granulite facies metamorphism 2 51 0 01 ga ago both are interpreted as resulting from a major crustal accretion event possibly related to mantle plume activity

flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well sorted and graded sands oscillatory flow tunnel measurements of velocities and fluxes for sands in oscillatory sheet flow conditions are presented the experiments involved a range of well sorted and graded sands in two asymmetric flows velocities were measured using an ultrasonic velocity profiler uvp capable of measuring deep within the sheet flow layer velocity profiles are found to be similar for the same flow but different sand beds and display expected features of oscillatory boundary layer flow the near bed velocity leads the main flow velocity by approximately 21 and a small offshore directed current is generated near the bed measures of the boundary layer thickness are in good agreement with those predicted using an equation formulated for the boundary layer thickness over fixed beds velocity data have been combined with concentration data to produce time dependent sand flux profiles covering the sheet flow and suspension regions there are fundamental differences in the transport processes of sands of different size and grading caused by unsteady effects which dominate in the case of fine sand and are largely absent in the case of coarse sand 1 time averaged flux is onshore directed positive in the case of coarse sand and is confined to a region immediately above the bed in contrast time averaged flux in the case of fine sand extends high above the bed is offshore directed negative in the sheet flow layer and becomes onshore directed in the suspension layer 2 net transport in the case of coarse sand is directed onshore as the percentage of fine sand in the bed increases offshore transport becomes increasingly dominant as the percentage of fine sand increases 3 net transport in the suspension layer is onshore while net transport in the sheet flow layer may be onshore or offshore depending on sand size and grading

smnd isotopes and ree geochemistry of madras granulites india an introductory statement abstract major and trace elements including ree as well as sm nd isotope analyses of eight granulite samples from the madras area are presented the data provide evidence for the origin of some of the granulites but in other cases demonstrate metasomatic changes in major and trace element contents including lree the data furthermore demonstrate that the analysed granulites are not cogenetic however when plotted in a sm nd isochron diagram the samples yield a linear array which corresponds to an age t 2555 140 ma and nd t 1 1 4 this age of 2555 140 ma could represent the time of granulite facies metamorphism immediately preceded by the formation of the protolith the nd t 1 value may be indicative of a near chondritic mantle source or alternatively of mixing between a depleted mantle and a crustal component

lead diffusion in apatite and zircon using ion implantation and rutherford backscattering techniques abstract ion implantation was used to introduce pb into the minerals zircon and apatite diffusion profiles were obtained using rutherford backscattering and the results were fitted with a model to determine the diffusion coefficients this approach is both simple and useful in studying diffusion over a temperature range of geologic interest without inordinate annealing times results for apatite over the temperature range 600 900 c are in good agreement with earlier results obtained for higher temperatures watson et al 1985 and are described by the following arrhenius law d 1 27 10 4 cm 2 s 1 exp 54 6 1 7 kcl mol 1 rt this suggests that radiation damage induced by ion implantation has little effect on pb diffusion in this case due to rapid annealing of induced damage at low temperatures the activation energy stated above is somewhat smaller than that previously determined 70 kcal mol 1 reflecting the larger range in 1 t sampled by the present results closure temperatures calculated with these diffusion parameters are in good agreement with those inferred from geochronologic data diffusion coefficients for pb in zircon determined in this study are greater than those obtained from a single experimental measurement and estimates of pb diffusion based on geochronologic data and u pb zoning in natural zircons the differing results for zircon and apatite obtained in this study appear to be related to each mineral s ability to anneal the radiation damage induced by ion implantation

isobaric cooling of proterozoic high temperature metamorphites in the northern arunta block central australia implications for tectonic evolution abstract protoliths of metamorphites in the proterozoic reynolds range region northern arunta block central australia included mafic and felsic igneous rocks pelites calcareous rocks and quartzites metamorphism began with an early high t low p facies stage followed by early rehydration in higher grade areas isobaric cooling and late high t low p facies hydration in and near shear zones metamorphic grade increases southeastwards shown by the change from andalusite in metapelites in the northwest to sillimanite in the southeast and by the incoming of cordierite cordierite biotite cordierite k feldspar sillimanite and cordierite garnet migmatites kornerupine quartz spinel and orthopyroxene k feldspar assemblages occur in the highest grade rocks downwarping at near peak temperatures is shown by garnet sillimanite replacing cordierite and by sillimanite pseudomorphing andalusite early in the near isobaric cooling that followed peak temperatures freezing of partial melts released water and biotite formed the hydrated retrograde assemblages formed after temperatures had fallen considerably are also zoned from northwest to southeast with andalusite sillimanite or kyanite bearing assemblages developed in appropriate bulk compositions the early high t metamorphism is best explained by tectonic models based on extension crustal delamination and underplating the hydration and deformation were caused by processes unrelated to the early history occurring at least 200 ma later possibly as late as the mid palaeozoic

explicit approximation for velocity and sediment flux above mobile sediment bed beneath current and asymmetric wave abstract an explicit approximation is proposed for velocity distribution and sediment flux above mobile sediment bed beneath current and asymmetric wave the predicted velocity is decomposed into an oscillatory part and a current part such that the interaction between current and asymmetric wave can be performed directly the oscillatory part consists of a free stream velocity and a defect function which includes phase lead mobile sediment bed level and wave boundary layer thickness the oscillatory part is influenced by the current due to the changes of both mobile sediment bed level and wave boundary layer thickness the current part is influenced by a wave eddy viscosity in the wave boundary layer and by an apparent wave roughness of the combined wave current flow outside the wave boundary layer eight free variables are required for the approximation and iterative bottom shear stress and roughness height are applied for the wave boundary layer thickness and mobile sediment bed level the mobile sediment bed level takes account of the effects of phase lag phase shift and residual acceleration and flow asymmetry therefore the mobile bed effect instantaneous velocity net velocity and sediment flux in the wave boundary layer can be reasonably presented by the explicit approximation beneath current and asymmetric wave

dehydration and incipient charnockite formation a phase equilibria and fluid inclusion study from south india a 3 m traverse across a charnockite lens in a biotite garnet graphite gneiss quarry from southern india has provided mineral equilibria that indicate charnockite formation occurred under fluid conditions of x h 2 o 0 2 to 0 3 at p 5 5 pm 1 9 kb and t 700 to 750 c dehydration of biotite loss of garnet and growth of orthopyroxene are related to a decrease in x h 2 o in the fluid phase within the charnockite lens isotopic analysis of the fluid entrapped in quartz from the charnockite indicates delta 13 c 8 2 0 3 0 heavier than delta 13 c values from smaller volumes of co 2 entrapped in quartz from the gneiss although the increase in fluid inclusion abundance in the charnockite can be related to oxidation of graphite without influx of co 2 an external source of co 2 is required in order to account for the shift to heavier carbon isotope values observed in both graphite and entrapped co 2 within the charnockite carbon isotope data across the gne

metamorphic plumbing system in proterozoic calc silicates queensland australia a calc silicate rich terrain in northwest queensland exhibits spectacular examples of heterogeneous fluid rock interaction attending regional amphibolite facies metamorphism and deformation large areas of pristine calc silicate rocks show evidence for internal buffering of fluid composition and low fluid rock ratios f r as inferred from 18 o and 13 c signatures typical of metamorphosed marine carbonates the progress of calc silicate reactions and scapolite compositional variations between layers in contrast high variance assemblages are developed in pretectonic intrusive rocks as well as in metasomatic zones in calc silicates around their margins scapolitized metadolerites albitized calc silicates and large calcite pods and veins with 18 o and 13 c depleted values are typical of these regions and indicate localized throughput of predominantly externally derived fluid at high f r accompanying the metamorphic peak major competency contrasts between meta intrusive and calc silicate rock types influenced stress and strain patterns around the igneous bodies which in turn controlled fracture permeability and the focusing of the metamorphic fluid the relatively brittle behavior of the meta intrusive rocks favored the development of small scale fracture permeability and consequent pervasive alteration of these bodies calcite vein systems and intensely albitized calc silicate breccias are localized in shear zones and dilatant areas around the meta intrusions either where shear stresses were high or where all stresses were low resulting in shear and tensile failure respectively thus permeability enhancement and the development of major fluid pathways during regional metamorphism of the terrain are systematically related to variations in the stress field accompanying deformation similar factors may strongly influence the channeling of fluids during metamorphism of other terrains

fluid rock interaction during low pressure polymetamorphism of the reynolds range group central australia marbles and metapelites from the reynolds range group central australia were regionally metamorphosed at low pressure during m at 6 go m ranged in grade from gnenschist to granulite fades along the length of the reynolds range and overprinted l 78 ga granites and their contact aureoles in the reynolds range group metasediments at all m 2 grades the marbles and metapelites have highly variable oxygen isotope ratios marbles 5i8o carb 14 20 o metapelites b180 6 14 o similarly l 78 ga granites have highly variable oxygen isotope ratios 8i8o 5 13 o with the lowest values occurring at the granite margins in all rock types the lowest oxygen isotope values are consistent with the infiltration of channelled magmatic and or meteoric fluids the variable lowering of oxygen isotope values resulted from pre mi2 contact metamorphism and fluid rock interaction around the l 78 ga granites in contrast mineral assemblages in the marbles define a trend of increasing xco with increasing grade from 0 05 gnenschist fades to 0 71 0 granulite fades this together with the lack of regionally systematic resetting of oxygen isotope ratios implies that there was little fluid rock interaction during prograde regional metamorphism key word law pressure polymetamorphism fluids stable isotopes petrology