transition from an eastern pacific upper level mixed rossby gravity wave to a western pacific tropical cyclone 1 the ancestor of unseasonal typhoon nanmadol 2004 over the western north pacific is traced back to the eastern pacific near 120 w as an upper tropospheric counter clockwise rotating mixed rossby gravity mrg wave the temporal and spatial evolution from an equatorial trapped mrg wave type disturbance to an off equatorial tropical depression is documented by utilizing nogaps navy s operational global atmospheric prediction system analysis data it is found that the mrg wave moved away from the equator after a dramatic reduction in its zonal dimension and downward development and amplification in the lower troposphere these dramatic changes in mrg wave properties are attributed to the modulation of the easterly vertical shear low level westerly easterly confluence in the large scale background flows and convective coupling as well as underlying high sea surface temperature sst the boundary layer convergence associated with asymmetric pressure field of the mrg wave is likely responsible for the transition from an equatorial mrg to an off equatorial tropical disturbance this case study addresses the possibility that upper tropospheric mrg waves over the far eastern pacific may provide seeds for tropical cyclogenesis over the western north pacific

geobarometry geothermometry and late archean geotherms from the granulite facies terrain of south india geobarometry and geothermometry of garnet bearing chamockitic and metapelitic assemblages from the high grade terrain from south india indicate three fields of equilibration high pressure granulites p 8 3 pm 1 0 kb t 760 pm 40 circ c are restricted to the charnockites and mafic granulites of the north slopes of the nilgiris these place a minimum constraint of 30 km on the maximum thickness of late archean crust medium pressure granulites p 6 4 pm 1 0 kb t 735 pm 40 circ c characterize the charnockites of the central nilgiris and the madras granulites to the east low pressure granulites p 5 0 pm 1 0 kb t 700 pm 20 circ c characterize the charnockites and metapelites south of the bhavani shear zone although migmatites from the kodaikanal massif may reflect somewhat higher temperatures all three granulite fields lie on a metamorphic geotherm piezothermic array which is strongly convex to the temperature axis and characteristic of convective heat transfer

the structure and annual variation of antisymmetric fluctuations of tropical convection and their association with rossby gravity waves abstract the signature of 4 5 day period rossby gravity waves is searched for in the tropical convection field across the indian pacific oceans the convergence divergence field of these waves in the lower troposphere is anticipated to produce an antisymmetric fluctuation in tropical convection antisymmetric fluctuations of tropical convection are shown to exhibit a pronounced spectral peak at a 4 5 day period only during boreal fall and only within about 30 longitude of the date line the peak amplitude occurs around 7 5 latitude these fluctuations propagate westward at 15 20 m s 1 with zonal wavelength of about 7000 9000 km the fluctuations of convection are coherent and out of phase with the equatorial meridional wind which also exhibits a pronounced spectral peak at a 4 5 day period in the lower troposphere near the date line the antisymmetric zonal wind also is strongly coherent with the antisymmetric convective fluctuations in this region the horizontal distributions of the 4 5 day power an

stability analysis of the north eastern slope of daralou copper open pit mine against a secondary toppling failure abstract secondary toppling failures have complicated mechanisms in these instabilities some natural or manmade external factors motivate and overturn a rock mass one of the most common types of secondary toppling failures is slide toe toppling mode when a blocky or layered rock mass is overlaid by a soil or weak rock mass the combination of a toppling failure in the rock at the toe and a circular or non circular sliding in the soil or weak rock in the top leads to this hybrid failure in 2015 such failure occurred in north eastern slope of daralou copper open pit mine during this instability the slope consisted mainly of two 10 m benches and one 4 m semi bench since it was supposed to excavate the slope to the depth of 54 m experts were worried about the project facing a similar larger failure in the future hence a widespread investigation was carried out on the failure firstly the mechanism of this instability was clarified with geological and geotechnical surface and subsurface investigations next existing analytical solution which had been presented for analysis of static slide toe toppling failure was modified and some new equations were obtained for analysis of the failure under dynamic condition then a computer code was developed based on the new equations for evaluation of the instability in the next step the failed slope was analyzed using the code and finite element method and outcomes of these analyses were compared with real conditions the comparison showed that there was satisfactory agreement between the analytical numerical and actual results therefore these methods were used to predict the behavior of the final slope in static and dynamic conditions these evaluations indicated that if displaced materials are completely excavated and removed from the mine and overall dip of the slope is reduced the final slope will be stable against slide toe toppling failure this paper summarizes the results and concludes that both the modified analytical approach and finite element method are able to analyze a slope against the secondary toppling mode furthermore the research proves that re sloping and unloading are two adequate methods which can be used for stabilization of the failure

analysis of a complex toppling circular slope failure abstract this technical note describes a complex failure that occurred in an open pit mine in valencia spain the failure which was analysed and interpreted in accordance with the local geology occurred in a slope comprised of a limestone rock mass in the upper part and a claystone sandstone sedimentary formation in the lower part the failure mechanism which was interpreted as complex toppling combining toppling and circular failure was back analysed using analytical and numerical techniques

effects of zonal flows on equatorially trapped waves abstract linear shallow water equations are employed to study the effects of basic zonal flows on equatorially trapped waves analytical solutions are obtained for constant basic zonal flows it is shown that changes in the wave structures due to the non doppler effect of the basic zonal flow are considerable for the rossby wave moderate for the westward propagating mixed rossby gravity wave but negligible for the other equatorial waves the rossby wave and the westward propagating mixed rossby gravity wave possess greater eigenfrequencies and are less trapped in westerlies than in easterlies the dependence of the rossby wave structure upon the basic zonal flow is interpreted in terms of potential vorticity conservation in basic zonal flows with meridional shears the eigenfrequencies are found to be larger in equatorial easterlies than in equatorial westerlies for the westward propagating waves but smaller for the eastward propagating waves while the meridional structures of the eastward propagating

cross equatorial response to middle latitude forcing in a zonally varying basic state abstract a nonlinear model based on the shallow water equations is used to study cross equatorial propagation of forced waves in the presence of a longitudinally varying time mean basic state zonal wind field it is found that global scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes however if the longitudinally asymmetric basic state includes a duet in which the zonal winds are westerly waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally symmetric mean zonal wind remains easterly in the equatorial region the amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct the existence and annual variations of a westerly duct region in the upper troposphere in the eastern pacific appear to account for some features of the low frequency variability in the no

synoptic scale disturbances near the equator abstract a spectral analysis of winds analyzed and initialized at the european centre for medium range weather forecasts reveals an abundance of power in the 850 mb meridional wind along the equator with periods near four days the power is mostly in the westward propagating component using high pass filtered data it is shown that the waves have westward phase and eastward group propagation relative to the mean wind the longest wavelengths are found over the pacific ocean while the shortest are found over the convectively variable regions of indonesia south america and africa mean phase speeds at 850 mb are positively correlated with the mean wind on the equator at 500 mb and below and negatively correlated with the mean wind above that level the effective advecting zonal wind of the disturbances seems to be the density weighted average of the lower troposphere the structure of the disturbances bears resemblance to the expected structure of an equatorially trapped mixed rossby gravity wave over t

an analytical solution for analysis of toppling slumping failure in rock slopes abstract when a slope consists of a horizontal weak rock or soil overlaid by some vertical strong slender rock columns the slope is prone to a secondary toppling failure which is known as toppling slumping failure in the slope rock columns impose pressure on the lower continuous weak rock or soil mass which leads to a differential settlement at the base of each rock column or a circular shear failure in the continuous mass if the differential settlements reach a special threshold rock column overturn and toppling slumping will happen however the circular shear failure of the soil or weak rock mass which is a well recognized failure mechanism will occur when shear stress in the slope exceeds its shear strength in this paper an attempt has been made to better understanding of the toppling slumping failure mechanism through developing an analytical solution for this purpose first an airy stress function is acquired for the lower continuous soil mass and its stress distribution and displacement are accordingly determined analytically due to the overlaid rock columns loads then differential settlements at the base of all rock columns and shear stresses in the soil or weak rock mass are computed and compared with the toppling and shear failure criteria to assess slope failure finally several design charts are developed that determine the stability of a slope against toppling slumping failure mechanism based on geometric characteristics of the slope and shear strength of its constituent material also a mathematica package code was developed to evaluate the stress distribution within the slope and the safety factor the results show that the vertical stress distribution plays a significant role in the settlement of the rock columns results also manifested that at a certain distance from the slope crest the set of rock columns will act like a single column on a half plane the shear or toppling failure of the slope not only depends on the material s strength but also on the geometry and the normalized column distance

ultrahigh temperature metamorphism in madurai granulites southern india evidence from carbon isotope thermometry abstract ultrahigh temperature uht metamorphism in the madurai block of the southern indian granulite terrain has been verified using the calcite graphite isotope exchange thermometer carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 c the 13c and 18o values of calcite are homogenous implying equilibration of the isotopes during metamorphism however the 13c values of single graphite crystals show variations in the order of 1 within a hand specimen detailed isotopic zonation studies indicate that graphite preserves either the time integrated crystal growth history or reequilibrium fractionation during its cooling history the graphite cores preserve higher 13c values than the rims the fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 c which matches the petrologically inferred temperature estimates in the high

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

an observational study of easterly waves over the eastern pacific in the northern summer using fgge data abstract fgge revel iii b data provided by the european centre for medium range weather forecasts and the outgoing longwave radiation data measured by satellites are used to investigate observationally relationships between deep cloud activity and large scale meteorological fields during the northern hemisphere summer may september of 1979 over the eastern pacific aside from the summer monsoon area over southern and eastern asia the eastern pacific is the area where strong deep convection frequently develops in the northern summer this is also one of the tropical ocean areas that have been least explored meteorologically a power spectral analysis using the maximum entropy method is made for the meridional wind component at 850 mb at various grid points in the analysis domain for each mouth from may through september the waves with a period of 4 6 days are not only stronger in july and august than those of other months but active in the regions of 100 130 w in the eastern pacific and 130 160 e i

geochemistry of high grade supracrustal rocks from the kerala khondalite belt and adjacent massif charnockites south india abstract the kerala khondalite belt kkb comprises a suite of supracrustal rocks of probable proterozoic age that was metamorphosed to the granulite facies the kkb consists of an interlayered sequence of 1 garnet biotite orthopyroxene graphite gneisses 2 khondalites graphite garnet biotite sillimanite cordierite gneisses and 3 cordierite gneisses garnet biotite cordierite orthopyroxene as well as less abundant mafic granulites calc silicates and quartzites petrologic and geochemical data suggest that these rocks were originally arkosic and argillaceous sediments possibly accompanied by felsic volcanic rocks along with minor intercalations of basalts carbonates and quartz rich sandstones the ree patterns of the metasediments are typically lree enriched with large negative eu anomalies indicating a continental provenance the major and trace element compositions of some of the arkosic rocks of the kkb resemble those of the massif charnockites that bound the kkb to the north which suggests that the massif charnockites may have been the source of some of the kkb sediments modern day analogues of the pelite arkose lithologic association observed in the kkb occur in intracratonic rifts and rifted continental margins this association is clearly distinct from the graywacke mafic volcanic association found in the southern indian greenstone belts and many other lower grade archean sedimentary sequences the kkb supracrustals show both lithologic and chemical similarities to many proterozoic supracrustal successions

carbon isotopic equilibrium between calcite and graphite in skallen marbles east antarctica evidence for the preservation of peak metamorphic temperatures abstract carbon isotope thermometry between calcite and graphite has been applied to the granulite facies marble assemblages in the skallen region of the lutzow holm bay east antarctica the carbon and oxygen isotope values of calcite from five samples which are interlayered with pelitic and charnockitic assemblages suggest within layer isotopic equilibrium textural studies of graphite crystals indicate two types one smooth highly reflecting regular shaped graphite and the other rough dull and irregular shaped graphite the 13 c values of the dull surfaced graphite are lower by about one per mil than the high reflecting graphite carbon isotopic compositions suggest that graphite with lower 13 c values is confined to the surface layer of the graphite crystal this is indicative of a later stage overgrowth during retrograde metamorphism 13 c of dull graphite was excluded in calculating the temperature of peak metamorphism temperatures of 850 c correspond to the peak metamorphic temperatures for the region this temperature estimate is consistent with the regional metamorphic conditions based on cation exchange thermometry in pelitic granulites and is interpreted to be more precise

quasi biennial oscillation and tropical waves in total ozone westward and eastward propagating tropical waves in total ozone are investigated in 13 years 1979 1991 of version 6 total column ozone data from the nimbus 7 total ozone mapping spectrometer toms satellite instrument a clear synchronization between the stratospheric quasi biennial oscillation qbo zonal winds and the fast periods 15 days propagating waves in tropical toms data is detailed largest total ozone wave amplitudes 3 6 dobson units occur when their phase propagation direction is primarily opposite the singapore qbo lower stratospheric winds this effect is most apparent in meridionally symmetric components examination of specific episodes including cross spectral calculations with singapore rawinsonde wind data 10 70 hpa reveals signatures of tropically confined eastward propagating kelvin waves of zonal wavenumbers 1 2 during the descending eastward qbo phase consistent with acceleration of that qbo phase by kelvin waves the toms results are also consistent with possible forcing of the westward qbo wind phase by episodes of both meridionally symmetric and asymmetric westward waves w events in the text however in contrast to the case of eastward kelvin waves the strongest westward events w events in the text appear to be filtered by rather than forcing the westward phase of the stratospheric qbo wind these dominant westward episodes are interpreted as meridionally symmetric westward global normal modes and tropically confined equatorial rossby waves 2 6 the events exhibit phase and group speeds characteristic of wave dynamics rather than simple wind advection these results underscore the utility of the long time series and excellent horizontal coverage of toms data for dynamical investigations in the relatively observation poor tropical stratosphere

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

theoretical and numerical study on the block flexure toppling failure of rock slopes abstract block flexure toppling failure is frequently encountered in rock slopes in this paper we first proposed two theoretical models to calculate the factor of safety against block flexure toppling namely step by step analysis model lem ssam and overall analysis model lem oam then we developed two special matlab codes for a quick stability estimation based on the proposed methods respectively next the universal distinct element code udec was used to study the failure mechanisms of block flexure toppling in order to realistically simulate the excavation of slope and obtain the detailed damage information of joints we developed two fish functions in udec finally we conducted a comparative analysis of the limit equilibrium method and the numerical simulations through twelve theoretical models the results show that many aspects of block flexure toppling failure have been captured using udec combined with the developed fish functions the lem oam and udec agree well while a larger factor of safety is obtained using the lem ssam it is found that the dip angles and friction angles of the joints dipping steeply into face have a great influence on block flexure toppling failure while the influence of the cross joint spacing is less significant

strategies for high temperature oxygen isotope thermometry a worked example from the laramie anorthosite complex wyoming usa abstract an understanding of the factors that affect the magnitude and direction of isotopic exchange is fundamental to the application of oxygen isotope geothermometers this is particularly true in high temperature rocks where retrograde exchange between minerals commonly results in the calculation of spurious isotopic temperatures herein we present an approach to isotope thermometry that combines numerical modelling techniques with a directed sampling strategy to retrieve peak or near peak temperature information from rocks that have behaved as closed systems on the hand sample scale during cooling the isotopic composition of minerals in such samples changes in predictable fashion on cooling these so called isotope exchange trajectories iet can be calculated for any mineral given the whole rock isotopic composition the modal abundance of each mineral in the rock and the fractionation factors between the minerals model temperatures can be obtained for both single and multiple hand samples through the calculation of iets temperatures for single samples are determined by locating the intersection between a mineral s calculated iet and its measured isotopic composition on plots of 18 o vs 1 t 2 the resulting temperature represents either the closure temperature of the mineral or the maximum temperature attained by the rock whichever is lower the multiple sample method relies on the premise that at high temperatures isotopic equilibrium is effectively achieved over a large area typically on the scale of meters or larger this method permits the retrieval of temperatures that are significantly higher than the closure temperature of any individual mineral multiple sample temperatures are calculated by determining the intersection of the iets of a given mineral in two or more samples the intersection of these iets represents the temperature at which the isotopic composition of the mineral was the same in both samples i e the last temperature of large scale isotopic equilibrium our methods allow for a rigorous determination of uncertainties in the calculated temperatures these numerical techniques can be used on any samples precise temperature estimates however require samples with specific mineralogic and modal characteristics the best samples for use with the single sample method are those that contain small amounts of a slow diffusing mineral and large fractionation factors between this mineral and the other minerals in the rock the multiple sample method requires two or more samples with widely different modal proportions of a mineral that strongly fractionates oxygen isotopes such samples are present in many terrains but are commonly overlooked because their mineral assemblages are not well suited for conventional thermobarometry these methods yield excellent results when applied to rocks from the sybille fe ti oxide quarry a late magmatic segregate of the laramie anorthosite numerical modelling of single sample and multiple samples from this quarry yield temperatures of 1000 and 1080 c respectively the single sample temperatures record the closure temperature of ilmenite whereas the multiple sample temperatures correspond closely to the experimentally determined solidus for these rocks these model temperatures are higher than any other conventional oxygen isotope temperatures yet reported from slowly cooled rocks

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

calcite graphite isotope thermometry a test for polymetamorphism in marble tudor gabbro aureole ontario canada graphitization and coarsening of organic material in carbonate bearing metasedimentary rocks is accompanied by carbon isotope exchange which is the basis of a refractory pressure independent geothermometer comparison of observed isotopic fractionations between calcite and graphite a13ccal gr with independent petrological thermometers provides the following empirical calibration over the range 400 800 c a13ccal gr 5 81 x lo6 x t k 2 61 this system has its greatest potential in marbles where calcite graphite is a common assemblage and other geothermometers are often unavailable the temperature dependency of this empirical calibration differs from theoretical calibrations reasons for this are unclear but the new empirical calibration yields temperature estimates in better agreement with independent thermometry from several terranes and is preferred for geological applications both calcite graphite isotopic thermometry and calcite dolomite solvus thermometry are applied to marble adjacent to the tudor gabbro in the grenville province of ontario canada the marble has undergone two metamorphic episodes early contact metamorphism and later regional metamorphism values of a13cca gr decrease regularly from c 8 0 in samples over 2 km from the pluton to values of 3 4 within 200m of the contact these samples appear to preserve fractionations from the early thermal aureole with the empirical geothermometer and indicate temperatures of 450 500 c away from the intrusion and 700 750 c near the gabbro this thermal profile around the gabbro is consistent with conductive heat flow models in contrast the distribution of mg between calcite and dolomite has been completely reset during later regional metamorphism and yields uniform temperatures of c 500 c even at the contact graphite textures are important for interpreting the results of the calcite graphite thermometer coarsening of graphite approaching the tudor gabbro correlates with the decrease in isotopic fractionations and provides textural evidence that graphite crystallization took place at the time of intrusion in contrast to isotopic exchange during prograde metamorphism which is facilitated by graphitization retrogressive carbon isotopic exchange appears to require recrystallization of graphite which is sluggish and easily recognized texturally resistance of the calcite graphite system to resetting permits thermometry in polymetamorphic settings to see through later events that have disturbed other systems

phase speed spectra of transient eddy fluxes and critical layer absorption abstract tropospheric zonal mean eddy fluxes of heat and momentum and the divergence of the eliassen palm flux are decomposed into contributions from different zonal phase speeds data analyzed are ecmwf operational global analyses covering 1980 87 eastward moving medium scale waves zonal waves 4 7 dominate the spectra of lower tropospheric heat fluxes in both hemispheres and all seasons upper tropospheric wave flux spectra are similar to the low level spectra in midlatitudes but shift to slower zonal phase speeds as low latitudes are approached the cause of this shift is the selective absorption of faster moving components in midlatitudes as the waves propagate meridionally latitude phase speed distributions of eddy fluxes are constructed and compared to the zonal mean wind structure these results demonstrate that upper tropospheric eddies break and decelerate the zonal mean flow approximately 10 20 in latitude away from their critical line where phase speed equals zonal wind speed compari

upper tropospheric equatorial waves in ecmwf analyses tropical wind fields from the european centre for medium range weather forecasts operational analyses are analysed to search for equatorially trapped waves in the upper troposphere data are studied for 1980 87 zonal wind spectra show a predominance of power at low zonal wave numbers and low frequencies these data do not show distinct spectral peaks corresponding to eastward propagating kelvin waves or westward propagating equatorially trapped rossby waves the zonal wind spectra do show episodic evidence for westward propagating 5 day zonal wave 1 features with maxima over the equator these are likely related to rossby normal mode oscillations previously reported meridional wind spectra show a predominance of westward propagating power in the 6 to 10 day period range primarily concentrated in zonal waves 4 7 enhanced meridional wind activity at the equator occurs episodically in time with events persisting for one to several months duration wave packets are longitudinally localized with preferred occurrence over the eastern pacific ocean most cases show evidence of meridional wind maxima in the tropics suggesting a degree of equatorial trapping the horizontal structure of these oscillations is that of mixed rossby gravity waves although they are not necessarily centred directly over the equator these waves have largest amplitudes in the upper troposphere showing weak coherence with the surface they appear to be fundamentally distinct from fast 4 to 5 day rossby gravity waves observed in the western pacific a detailed study of a group of intense rossby gravity waves observed over the eastern pacific during august september 1985 is presented the reality of these features is confirmed in direct rawinsonde observations correlations are found between bursts of equatorial wave activity and enhanced meridional momentum fluxes from the subtropics suggesting extratropical forcing as at least one mechanism for their generation the waves are also strongly coupled to the upper tropospheric zonal wind field which likely accounts for their longitudinal and temporal confinement

microscale isotopic zoning in calcite and graphite crystals in marble chemical and isotopic zoning in minerals is a clear indication of disequilibrium and provides an important key for elucidating metamorphic processes here i present carbon and oxygen isotope data from calcite and graphite crystals in a marble from the hida metamorphic belt central japan showing isotopic zoning within individual crystals within 100 m of the calcite graphite grain boundary the 13c contents gradually decrease from the constant values of the crystal core to values 1 lower 18o contents in calcite decrease by up to 7 within 200 300 jim of the boundary at a calcite calcite grain boundary similar patterns of 13c and 18o depletions were found whereas the 13c contents of graphites remained constant except in a narrow zone at the calcite contact these isotopic patterns are interpreted as reflecting isotopic exchange with metamorphic fluids that were relatively depleted in 13c and 18o these results strongly suggest that the most accurate geothermometry will be obtained if only the cores of crystals are used and that isotopic zoning may provide another way to elucidate polymetamorphic processes

fluid rock history of granulite facies humite marbles from ambasamudram southern india an extensive humite bearing marble horizon within a supracrustal sequence at ambasamudram southern india was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics at peak metamorphic temperatures of 775 73 c based on calcite graphite carbon isotope thermometry the mineral assemblages suggest layer by layer control of fluid compositions clinohumite calcite bearing assemblages suggest xco2 0 9 at 790 c and local wollastonite scapolite grossular bearing zones formed at xco2 of c 0 3 retrograde reaction textures such as scapolite quartz symplectites after feldspar and calcite and replacement of dolomite diopside or tremolite dolomite after calcite forsterite or calcite clinohumite are indicative of retrogression under high xco2 conditions calcite preserves late proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting isotopic zonation of calcite and graphite grains was likely produced by localized co2 fluid infiltration during retrogression contrary to the widespread occurrence of humite marbles related to retrograde aqueous fluid infiltration the ambasamudram humite marbles record a prograde to peak metamorphic humite formation and retrogression under conditions of low xh2o

rossby wave propagation into the tropics in two gfdl general circulation models during the northern winter the eastern pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres theoretical and simple modeling studies suggest that such a region should favor the penetration of rossby waves into the tropics from higher latitudes observational results by kiladis and weickmann using 200 mb data indicate that rossby waves do indeed propagate freely into the tropical eastern pacific during the northern winter from the asian jet exit region they also confirmed that cross equatorial dispersion of energy from the northern into the southern hemisphere occurs frequently the present study examines these interactions in climatological runs of two gfdl gcms the northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical pacific despite the relative weakness of the asian jet and wave activity with respect to observations propagation of rossby waves into the tropics is present in both models and these waves are strongly positively tilted as seen in the observations a momentum budget of the zonal wind and e vector diagnostics over the tropical pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models

carbon isotope thermometry in marbles of the adirondack mountains new york carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the adirondack mountains new york eighty nine calcite graphite pairs from the amphibolite grade nw adirondacks change systematically in temperature north westwards from 680 to 640 to 670 c over a 30 km distance reflecting transitions from amphibolite facies towards granulite facies to the north west and to the south east temperature contours based on calcite graphite thermometry in the nw adirondacks parallel mineral isograds with the orthopyroxene isograd falling above 675 c and indicate that regional metamorphic temperatures were up to 75 c higher than temperatures inferred from isotherms based on cation and solvus thermometry bohlen et al 1985 fifty five calcite graphite pairs from granulite grade marbles of the central adirondacks give regional metamorphic temperatures of 670 780 c in general agreement with cation and solvus thermometry data for amphibolite and granulite grade marbles show a 12 oo range in 13ccal and 13cgr a strong correlation between carbon isotopic composition and the abundance of graphite cgr crock indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism the trends seen in 13c vs cgr crock and 13ccal vs 13cgr could not have been preserved if significant amounts of co2 rich fluid had pervasively infiltrated the adirondacks at any time the close fit between natural data and calculated trends of 13c vs cgr crock indicates a biogenic origin for adirondack graphites even though low 13c values are not preserved in marble delamination of 17 graphite flakes perpendicular to the c axis reveals isotopic zonation with higher 13c cores these isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite samples located 2km from anorthosite show a decrease of 0 5 0 8 oo in the outer 100 of the grains while samples at distances over 8 km show smaller core to rim decreases of c 0 2 oo correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism core graphite compositions indicate contact metamorphic temperatures were 860 890 c within 1 km of the marcy anorthosite massif if samples with a significant contact metamorphic effect cal gr 3 2 oo are not included then the remaining 38 granulite facies samples define the relation 13c cal gr 3 56 106t 2 k

climatology of the equatorial lower stratosphere abstract twenty years of radiosonde data have been analyzed in an attempt to develop a latitudinal structure climatology of winds temperature and geopotential at 30 and 50 mb in the equatorial stratosphere the fine latitudinal resolution provided by the wmo station network reveals several interesting features in the latitudinal structure of the annual and quasi biennial cycles which dominate this region for example the westerly and easterly acceleration phases of the quasi biennial oscillation are markedly different westerly accelerations appear first at the equator spreading outward with time to higher latitude and an more intense on average than the easterly accelerations the easterly accelerations are more uniform in latitude but leer uniform in time sometimes occurring in two stages the quasi biennial wind and temperature oscillations are symmetric about the equator while the annual harmonic in zonal wind is antisymmetric about the equator but is not proportional to the coriolis paramete

oxygen self diffusion in calcite dependence on temperature and water fugacity oxygen self diffusion in natural calcite single crystals was studied hydrothermally at 400 800 c and 10 350 mpa confining pressure diffusion coefficients d were determined from18o concentration profiles measured with an ion microprobe at 100 mpa confining pressure the arrhenius parameters yield an activation energy q 173 6 kj mole and pre exponential factor d0 7 10 9 m2 s over the temperature range 400 800 c and there is no measurable anisotropy constant temperature experiments at 700 c indicate that there is a strong linear correlation slope 0 9 of d with water fugacity over the range 4 240 mpa consistent with the interpretation that in the presence of water the dominant oxygen bearing transport species in calcite is molecular water a sample containing 1180 ppm mn shows a marked increase in observed d values at temperatures below 600 c however when pre annealed at 700 c the d values obtained at 550 c are within a factor of four of the value obtained for the low 100 ppm mn sample the results of this study confirm that in contrast to carbon oxygen diffusion rates in calcite are greatly enhanced when water is present the difference in the effect of water on doxygen and dcarbon in calcite may provide valuable information for evaluating the role of fluids in the thermal histories of calcite bearing rocks

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

carbon isotopic thermometry calibrated by dolomite calcite solvus temperatures abstract the temperature dependence of carbon isotopic fractionations between calcite and graphite and between dolomite and graphite are calibrated by the calcite dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the kasuga area central japan the carbon isotopic fractionations 13ccc gr and 13cdo gr systematically decrease with increasing metamorphic temperature the concordant relationships between the fractionations and solvus temperatures are approximately linear with t 2 over the temperature range 400 to 680 c 13ccc gr 5 6 106 t 2 k 2 4 13cdo gr 5 9 106 t 2 k 1 9 these systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases the equation for the calcite graphite system has a slope steeper than bottinga s 1969 results it is however in good agreement with that of valley and o neil 1981 in the temperature range from 600 to 800 c because of the relatively high sensitivity to temperature these isotopic geothermometers are useful for determining the temperatures in moderate to high grade metamorphosed carbonate rocks

general circulation model simulation of the semiannual oscillation of the tropical middle atmosphere abstract a study has been made of the evolution of the zonal mean zonal wind and temperature in a multiyear integration of the 40 level 3 3 6 resolution skyhi general circulation model gcm that has been developed at gfdl in the tropical upper stratosphere the mean wind variation is dominated by a strong semiannual oscillation sao the peak sao amplitude in the model is almost 25 m s 1 and occurs near the 1 mb level the phase of the sao near the stratopause is such that maximum westerlies occur shortly after the equinoxes these features are in good agreement with the available observations in addition the meridional width of the stratopause sao in the gcm compares well with observations a diagnostic analysis of the zonal mean momentum balance near the tropical stratopause was performed using the detailed fields archived during the gcm integration it appears that the easterly accelerations in the model sao are provided by a combination of i divergence of the meridional component of the el

laterally forced equatorial perturbations in a linear model part ii mobile forcing abstract impacts of atmospheric mean zonal flows on equatorial perturbations laterally forced by extratropical mobile sources in a linear model are examined an analytical solution of the model with a constant mean zonal flow reveals that amplitudes of forced waves can be significantly modulated by the mean zonal flow through its doppler shift effect on the forcing frequency in general amplitudes of westward propagating waves such as the rossby and mixed rossby gravity waves tend to be larger in mean westerlies than in mean easterlies for low frequency forcing but smaller in mean westerlies for high frequency forcing the opposite dependence on the mean zonal flow applies to eastward propagating waves such as the kelvin wave the model numerical solutions show that the spatial structure of the laterally forced equatorial perturbation as a whole is sensitive to the mean zonal flow particularly a substantial zonal variation in the equatorial perturbation occurs when the mean zonal flow varies in long

stability analysis of slopes against combined circular toppling failure abstract circular failure is one of the most probable instabilities on slopes with severely crushed rock or soil slopes another type of instability is block flexural toppling which is the most common type of toppling failure in this type of failure some rock blocks are broken by bending and other topples due to their weight in some slopes a soil mass has direct contact with the rock mass with the potential of block flexural failure if so the total slope failure potential is the combination of circular toppling failure this instability can be called secondary toppling failure for which there is no solution available in the literature studies on circular and toppling failure are reviewed then the interaction between soil mass and rock blocks is studied considering the interaction between soil and rock this study proposes a theoretical model for stability analysis for the combination of circular toppling failure and the required equations are developed solving these equations manually is time consuming thus a special computer code is programmed to analyze the combination failure the code receives slope s information from the user and calculates the factor of safety subject to combination failure circumstances finally a real case instability of a slope in vana village along haraz road in northern iran is analyzed with this code and results are compared with the observed data

preservation of oxygen isotope compositions in granulites from northwestern canada and enderby land antarctica implications for high temperature isotopic thermometry preservation of high temperature mineral isotopic compositions is necessary for successful high temperature isotopic thermometry other requirements include large fractionations between constituent minerals well calibrated equilibria carefully designed sampling strategies and data handling techniques that quantitatively account for retrograde exchange here we apply isotopic thermometry and data handling techniques to calculate and contrast mineral pair apparent temperature data and observed closure temperature data tc observed cf farquhar et al 1993 for the very high temperature 900 c dry granulites of the taltson magmatic zone of northwestern canada and the napier complex of enderby land antarctica the isotopic compositions of garnet grains from both terrains reflect high temperature conditions 950 c and point to this mineral as an excellent candidate for isotopic thermometry the isotopic compositions of quartz pyroxene ilmenite and magnetite indicate that they equilibrated to lower temperature conditions 900 c due to faster rates of oxygen diffusion in these minerals possibly enhanced by exsolution and ductile deformation compared with garnet our temperature data for garnet and pyroxene are 200 c higher than is possible to explain by existing wet diffusion data but is consistent with dry diffusion data suggesting that the extremely dry nature of these rocks may have played a significant role in the preservation of high temperature isotopic compositions both quartz and magnetite exhibit subgrain features indicative of ductile deformation quartz magnetite temperatures from the napier complex are similar to those inferred for a late d3 deformation and are lower than those predicted by dry diffusion data we infer that the quartz magnetite isotopic fractionations reflect deformation enhanced exchange that accompanied d3 garnet in these same samples did not undergo ductile deformation and did not exchange oxygen with coexisiting phases during cooling this may reflect strain partitioning between less easily deformed low abundance garnet and more easily deformed matrix quartz and magnetite the resistance of garnet to ductile deformation in these rocks is a second reason why garnet is suitable for isotopic thermometry

evidence for equatorial kelvin modes in nimbus 7 lims abstract eastward propagating disturbances over the equator are diagnosed in two independent nimbus 7 lims limb infrared monitor of the stratosphere data sets they are evident consistently at several pressure levels throughout the stratosphere and account for much of the temperature variance in the tropics the disturbances which can be seen in wavenumbers 1 3 are in phase and symmetric about the equator latitudinally evanescent and have short moderate vertical phase structure 10 40 km which progresses downward wavenumber 1 has spectral components which propagate eastward at periods of 6 7 8 6 days 54 69 m s 1 and 3 5 4 0 days 115 135 m s 1 wavenumber 2 exhibits eastward propagating variance at periods of 6 0 7 5 days 31 39 m s 1 and 3 8 4 3 days 55 62 m s 1 the faster waves appear principally in the upper stratosphere these features are in reasonable agreement with the structure and dispersion characteristics of simple quasi separable kelvin modes with the exception of the slower w

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

the calcite graphite isotope thermometer data on graphite bearing marbles from naxos greece abstract graphite bearing marbles occur in the regional metamorphic complex of naxos over a continuous temperature range of 380 to 670 c the graphite is of biogenic origin and changed its original isotopic composition towards values in equilibrium with the calcite partial isotope exchange took place at temperatures as low as 380 c but near equilibrium values were generally not reached below 550 c the data agree better with the theoretically derived fractionation curve of bottinga 1969 than with the empirical curve proposed by valley and o neil 1981 we believe that the system will not provide a good thermometer

carbon isotope exchange during polymetamorphism in the panamint mountains california usa carbon isotope fractionations between calcite and graphite in the panamint mountains california usa demonstrate the importance of mass balance on carbon isotope values in metamorphosed carbon bearing minerals while recording the thermal conditions during peak regional metamorphism interbedded graphitic marbles and graphitic calcareous schists in the kingston peak formation define distinct populations on a 13c gr 13c cc diagram the 13c values of both graphite and calcite in the marbles are higher than the values of the respective minerals in the schists 13c values in both rock types were controlled by the relative proportions of the carbon bearing minerals calcite the dominant carbon reservoir in the marble largely controlled the 13c values in this lithology whereas the 13c values in the schists were largely controlled by the dominant graphite this is in contrast to graphite poor calcsilicate systems where carbon isotope shifts in carbonate minerals are controlled by decarbonation reactions the marbles record a peak temperature of 531 30 c of a jurassic low pressure regional metamorphic event above the tremolite isograd in the schists there is a much wider range of recorded temperatures however there is a mode of temperatures at c 435 c which approximately corresponds to the temperatures of the principal decarbonation metamorphic reactions in the schists suggesting that the carbon exchange was set by loss of calcite and armouring of graphite by newly formed silicate minerals the armouring may explain the relatively large spread of apparent temperatures although the modal temperature also corresponds to the approximate temperature of the cretaceous retrograde event retrograde exchange is thought less likely due to very slow exchange rates involving well crystallized graphite armouring of graphite by silicates during the earlier event and because of other barriers to retrograde carbon exchange thus only the calcite graphite carbon isotope fractionations recorded by the marbles demonstrate the high temperature conditions of the low pressure jurassic metamorphic event that was associated with the emplacement of granitic plutons to the west of the panamint mountains

one to two month oscillations in the stratosphere during southern winter abstract stratospheric disturbances on the 35 60 day time scale are investigated with particular emphasis on the southern hemisphere the data used are stratospheric brightness temperatures from 90 to 1 5 hpa covering seven 6 month southern winter periods from april 1980 to march 1987 global time lag correlation plots are constructed from which tropical extratropical connections three dimensional wave structure and propagation characteristics are studied horizontal correlation patterns at 90 hpa reveal a strong connection between the indonesian tropics and the winter extratropics vertical correlation patterns in the southern winter extratropics reveal westward tilt with height and vertical propagation of 35 60 day zonal wavenumber 1 perturbations from tropospheric regions up to great heights at least as high as the stratopause region disturbances are found to propagate from 90 hpa to 1 5 hpa in generally 6 to 9 days in contrast the vertical correlation plots in the tropics indicate little or n

intensity variation and coherence of 3 6 day equatorial waves meridional wind oscillations of 3 6 day period are common in the equatorial lower stratosphere upper air data obtained from 32 equatorial stations 1973 87 show that 70 mb wave intensity over the maritime continent varied annually with largest amplitude in nh late winter and spring but the seasonal cycle of intensity was not uniform in the tropics time series of meridional velocity and its spatial coherence suggest that 70 mb wave packets were local in longitude and episodic in time

stability analysis of slopes with a potential of slide head toppling failure abstract toppling is a mode of slope instability that may occur in a wide range of layered or blocky rock masses if this instability is caused by some natural or man made external factors it is termed a secondary toppling failure one of the important modes of toppling instability is the slide head toppling failure when a layer of soil or weak rock is overlaid by a blocky or layered rock mass the combination of a toppling failure in the rock at the top and a circular sliding in the soil or weak rock in the bottom leads to this hybrid failure the mechanism of this hybrid failure is extremely complicated and it may occur in some special geological conditions in civil engineering and mining projects in this paper the mechanisms of toppling failures in general and the mechanism of slide head toppling failure in particular are presented and described then the outcomes of seven physical models which were constructed with base friction materials and conducted under static loading conditions by a tilting table apparatus are summarized to investigate this hybrid failure mechanism subsequently a new step by step theoretical approach is proposed for assessment of this failure mode and a typical example is analyzed to better demonstrate the results finally the results of the physical modeling are compared with the outcomes of the proposed theoretical method and an existing analytical approach this comparison shows that there are acceptable agreements between the physical and analytical results hence both proposed and existing analytical approaches can be used for the analysis of the slide head toppling slope failure

modelling and back analysing failures in steep limestone cliffs abstract the observation of 12 rock fall scars in steep limestone cliffs has shown that the fallen masses were stable as a result of relatively small rock bridges these results demonstrate that consideration of rock bridges is necessary for a realistic evaluation of stability limit equilibrium methods of analysis are presented for sliding and toppling for both isostatic and hyperstatic conditions these methods are illustrated with four case histories the results of nine back analyses of rock falls with volumes between 24 and 3500 m 3 are presented the rock cohesion obtained from back analysis appears to be significantly lower than the cohesion obtained from classical laboratory tests this discrepancy can be attributed to several factors including a spatial and temporal scale effect the oversimplified modelling two dimensional limit equilibrium and some uncertainties affecting the geometrical data when analysing the stability of a cliff with a limit equilibrium method the authors suggest dividing the cohesion by a scale and method factor of 3

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

rossby gravity waves in tropical total ozone randel 1992 has recently reported evidence for rossby gravity waves in tropical data fields produced by the european centre for medium range weather forecasts ecmwf the purpose of this paper is to show that similar features are observable in fields of total column ozone from the total ozone mapping spectrometer toms satellite instrument the observed features are episodic have zonal east west wavelengths of approximately 6 000 10 000 km and oscillate with periods of 5 10 days the modes exhibit westward phase progression and eastward group velocity a simple linear model is used to estimate the magnitude of total ozone perturbations induced by rossby gravity waves the model is able to account for the magnitude of observed toms features as well as their asymmetry about the equator the significance of finding rossby gravity waves in total ozone fields is that 1 the report of similar features in ecmwf tropical fields is corroborated with an independent data set and 2 the toms data set is demonstrated to possess surprising versatility and sensitivity to relatively smaller scale tropical phenomena

carbon isotopic study on coexisting calcite and graphite in the ryoke metamorphic rocks northern kiso district central japan carbon isotope fractionation between coexisting calcite and grpahite 13ccc gr has been determined in metamorphosed limestones and calc silicate rocks from the ryoke metamorphic belt in the northern kiso district in this district the ryoke metamorphic rocks ranging from the lower greenschist facies to the upper amphibolite facies are widely distributed the fractionation of 13c 12c between calcite and graphite decreases regularly with increasing metamorphic grade and is independent of absolute 13c values of calcite this evidence suggests that carbon isotopic exchange equilibrium has been attained during metamorphism even in the greenschist facies and isotopic modification possibly caused by retrogressive metamorphism is not distinguished for t 270 650 c the fractionation is expressed by the following equation 13ccc gr 8 9 106t 2 7 1 t in k

dextral pan african shear along the southwestern edge of the achankovil shear belt south india constraints on gondwana reconstructions a discussion achankovil shear zone acsz figure 1a intering charnockites garnet biotite gneiss biotite gneiss calc gneiss and granite as revealed in the preted as a major nw trending strike slip shear zone of probable proterozoic age drury et al 1984 lithological mapping carried out as part of this study figure 2 a preliminary structural assesshas prominently figured in gondwana correlative studies e g windley et al 1994 although it is ment reveals the presence of a distinctive assemblage of asymmetric structures in the gneissic exclear that there is a major lithologic change across acsz figure 1b detailed studies indicating the posures indicating a consistent sinistral sense of shear gneissosity forming the secondary compoprobable sense of shear are lacking across this 10 20 km wide and 100 km long shear zone resitional banding strikes wnw ese to nw se dipping moderately toward sw with relatively rare cently sacks et al 1997 reported field observations bearing on the probable sense of shear of the ne dip and is conformable in all the rock types of the area in conformity with the general nw se acsz after combining field criteria and kinematic analysis of asymmetric features along the sw trend of the acsz structurally the terrain has undergone four phases of deformation summarized in edge of the acsz known as the tenmala shear zone they concluded that the acsz indicated prirajesh and santosh 1997 open to isoclinal intrafolial folds encountered in marily dextral shear with a minor component of reverse shear the authors illustrate their discusthe study area are invariably asymmetric fold limbs are zones of transposed gneissosity that consion with examples of kinematic indicators including shear bands asymmetric folds stretched and tain indicators of a probable sinistral sense of shear and well developed mineral elongation lineation asymmetric garnet feldspar and quartz porphyroclasts hook folds and lineations thus they appardefined by quartz ribbons trails of xenoblastic garnet grains and the alignment of the long axes of kently question the correlation of the dextral achankovil shear zone rather tenmala shear zone with feldspar augen pinch and swell structures and boudins commonly show rotation with respect to the sinistral bongolava ranotsara shear zone brsz in the india madagascar gondwana enfoliation tight s asymmetric f2 folds and synkinematic pegmatite veins are seen in the western semble we focus the present discussion on the probable part of the study area the development of a refold structure by superposed buckling is illustrated in sense of shear of acsz in the light of new data our study area falls around punalur and its adjoinfigure 3a there are smaller asymmetric sand zfolds congruent with the larger f1 with one limb ing areas within the quilon district southern kerala south india and is located between longitudes striking e w while the other strikes n50 e showing negative extension during the development of 76 55 and 76 59 e and latitudes 9 1 and 9 3 n figure 2 represented in the survey of india topo f2 on the traces of preserved axial planar cleavage the simple shear is dextral on the left limb and sisheet no 58c 16 outcrops within the study area expose a strongly deformed suite of rocks comprisnistral on the right limb asymmetrically folded veins figure 3b the bulk asymmetry of which represents a sinistral sense of shear have been found 1 manuscript received may 14 1997 in a few locations elongate quartz lenticles and 2 centre for earth science studies pb 7250 trivandrum 695 031 india garnet and biotite aggregates define penetrative lin

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