a climatological study of short period gravity waves and ripples at davis station antarctica 68 s 78 e during the austral winter february october period 1999 2013 a scanning radiometer deployed at davis station antarctica 68 s 78 e has been recording infrared 1 10 1 65 m images of a small region 24 km 24 km of the zenith night sky once per minute each austral winter night since february 1999 these images have been processed to extract information on the passage of gravity waves gws horizontal wavelength h 15 km and ripples h 15 km over the observing station phase speeds periods horizontal wavelengths and predominant propagation directions have been deduced observed speeds were found to be highly correlated with horizontal wavelengths as has been reported in previous studies reverse ray tracing of the detected gws only enabled us to identify four distinct groups on average only 15 of waves detected can be traced back to the troposphere and a large proportion 45 were not successfully reverse traced substantially below the airglow layer two smaller groups were found to reach a termination condition for reverse ray tracing at altitudes near 50 km and 75 km of those that reached the termination altitude in the troposphere 10 km most of the end points fell within a radius of 300 km of the station with a very pronounced concentration of wave initiation to the north west at approximately of the observing point the predominant direction of propagation was southward and they were observed throughout the year recent reports suggest the interaction of planetary waves with the background wind field as a potential source for these waves

inertia gravity waves observed in the lower stratosphere over macquarie island abstract this study examines the properties of inertia gravity waves observed in the lower stratosphere over macquarie island how these properties vary with season and the likely source of the waves the waves are observed in high resolution upper air ozonesonde soundings of wind and temperature released from macquarie island during the 1994 ashoe maesa program the properties of the inertia gravity waves observed in the soundings are quantified using hodograph and rotary spectral analyses the analyzed waves have horizontal wavelengths between 100 and 1000 km vertical wavelengths between about 1 and 7 km intrinsic frequencies between f and 2f and horizontal trace speeds between 50 and 30 m s 1 there appears to be a seasonal cycle in the inertia gravity wave activity in the lower stratosphere the minimum being in the austral winter when the background zonal flow is strong and westerly and its vertical shear is positive in contrast the variance of the horizontal perturbation winds does not show a

a high precision u pb age of metamorphic rutile in coesite bearing eclogite from the dabie mountains in central china a new constraint on the cooling history this paper first reports a high precision u pb age of 218 1 2 ma for rutile in coesite bearing eclogite from jinheqiao in the dabie mounteins east central china this work shows that the u pb mineral rutile omphacite isochron age of 218 2 5 ma and conventional rutile u pb concordia age of 218 1 2 ma obtained by common pb correction based on the pb isotopic composition of omphacite in the same eclogite sample are consistent proving that the omphacite with low u pb ratio 2 8 can be used for common pb correction in u pb dating of rutile oxygen isotope analysis of rutile aliquots gave the consistent 18o values of 6 1 0 1 demonstrating oxygen isotope homogenization in the rutile of different grains as inclusion in garnet and grain in matrix oxygen isotope thermometry yields temperatures of 695 35 and 460 15 c for quartz garnet and quartz rutile pairs respectively these oxygen isotopic observations suggest that the diffusion of oxygen in rutile as inclusion in garnet is not controlled by garnet according to field based thermochronological studies of rutile an estimate of the tc of about 460 c for u pb system in rutile under rapid cooling conditions 20 c ma was advised based on this u pb age as well as the reported chronological data with their corresponding metamorphic and or closure temperature an improved t t path has been constructed the t t path confirms that the uhpm rocks in south dabie experienced a rapid cooling following the peak metamorphism before 220 ma and a long isothermal stage from 213 to 180 ma around 425 c

inertia gravity waves associated with deep convection observed during the summers of 2005 and 2007 in korea 1 characteristics of inertia gravity waves associated with convection are investigated in the lower stratosphere using high resolution radiosonde data observed from 18 june to 15 july of 2005 and 2007 in korea three dimensional ray tracing model and reanalysis data are used to investigate the propagation and the sources of the observed waves the observed waves associated with convections are discriminated based on the existence of convections when and where the rays reach the average height range of convective clouds waves observed in 2005 and 2007 show similar spectral characteristics but wave energy in 2007 is significantly larger than in 2005 the observed waves propagate from three source regions the northeastern southeastern and western regions around korea they show preferential propagation directions based on their sources and convections from the western region generate larger amplitude gravity waves than the other two regions the spectral characteristics of the observed waves are determined largely by those of the convective forcing along with the wave propagation condition associated with background wind and stability the significantly larger mean wave energy in 2007 occurs because more observed waves originate from the western region of korea in 2007 than in 2005 where convective forcing is much larger than in the other source regions

variation in peak p t conditions across the upper contact of the uhp terrane dabieshan china gradational or abrupt the southern dabieshan terrane sdt has previously been divided into high pressure hp and ultrahigh pressure uhp terranes and its regional extent and the tectonic nature of its boundaries are hotly debated topics in this study an eclogite bearing area of 100 km2 near taihu is mapped in detail and divided into northern middle and southern zones on the basis of lithological characteristics the northern zone consists of epidote biotite gneiss and eclogite blocks the middle zone includes granitic gneiss biotite gneiss eclogites and amphibolite and the southern zone is composed mainly of garnet bearing mica schist the eclogites occur mainly as lens or blocks in the northern and middle zones the peak p t conditions for 61 eclogite samples across the area are estimated using the grt cpx fe2 mg thermometers and the grt cpx phe barometers the results indicate three different p t regions 2 82 4 09 gpa 759 942 c in the northern zone and 2 00 3 54 gpa 641 839 c in the granitic gneiss and 1 38 2 36 gpa 535 768 c in the biotite gneiss from the middle zone combined with the spatial distribution of eclogites across the area the p t values for eclogites increase continuously from the south to the north defining a reference geotherm of 5 c km 1 however some unreasonable apparent gradients can be established along two south north profiles across the area and display a p t difference between the northern and middle zones on the basis of the average p t data for eclogites across the area a gap of at least 0 3 gpa 20 c exists between the northern and middle zones by contrast the p t values of eclogites from the middle zone show a coherent pattern with transitional characteristics from hp in the south to uhp in the north we suggest that the sdt was a coherent slab during subduction and was broken up by a major fault during exhumation which was formed under uhp metamorphic conditions

tectonic evolution of a composite collision orogen an overview on the qinling tongbai hong an dabie sulu orogenic belt in central china abstract the formation of collisional orogens is a prominent feature in convergent plate margins it is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision the paleozoic convergence between the south china block scb and the north china block ncb is associated with a series of tectonic processes such as oceanic subduction terrane accretion and continental collision resulting in the qinling tongbai hong an dabie sulu orogenic belt while the arc continent collision orogeny is significant during the paleozoic in the qinling tongbai hong an orogens of central china the continent continent collision orogeny is prominent during the early mesozoic in the dabie sulu orogens of east central china this article presents an overview of regional geology geochronology and geochemistry for the composite orogenic belt the qinling tongbai hong an orogens exhibit the early paleozoic hp uhp metamorphism the carboniferous hp metamorphism and the paleozoic arc type magmatism but the three tectonothermal events are absent in the dabie sulu orogens the triassic uhp metamorphism is prominent in the dabie sulu orogens but it is absent in the qinling tongbai orogens the hong an orogen records both the hp and uhp metamorphism of triassic age and collided continental margins contain both the juvenile and ancient crustal rocks so do in the qinling and tongbai orogens in contrast only ancient crustal rocks were involved in the uhp metamorphism in the dabie sulu orogenic belt without involvement of the juvenile arc crust on the other hand the deformed and low grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late permian to early triassic along the northern margin of the dabie sulu orogenic belt and it was developed on the passive oceanic margin during subduction in the early paleozoic along the northern margin of the qinling orogen three episodes of arc continent collision are suggested to occur during the paleozoic continental convergence between the scb and ncb the first episode of arc continent collision is caused by northward subduction of the north qinling unit beneath the erlangping unit resulting in uhp metamorphism at ca 480 490 ma and the accretion of the north qinling unit to the ncb the second episode of arc continent collision is caused by northward subduction of the prototethyan oceanic crust beneath an andes type continental arc leading to granulite facies metamorphism at ca 420 430 ma and the accretion of the shangdan arc terrane to the ncb and reworking of the north qinling erlangping and kuanping units the third episode of arc continent collision is caused by northward subduction of the paleotethyan oceanic crust resulting in the hp eclogite facies metamorphism at ca 310 ma in the hong an orogen and low p metamorphism in the qinling tongbai orogens as well as crustal accretion to the ncb the closure of backarc basins is also associated with the arc continent collision processes with the possible cause for granulite facies metamorphism the massive continental subduction of the scb beneath the ncb took place in the triassic with the final continent continent collision and uhp metamorphism at ca 225 240 ma therefore the qinling tongbai hong an dabie sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc type magmatism to arc continent and continent continent collision

observations and numerical modelling of mountain waves over the southern alps of new zealand a detailed case study of mountain waves observed over the south island of new zealand during the southern alps experiment is presented the purpose of the study is to document the waves generated over this region to explore the extent to which high resolution radiosonde data can be used to determine gravity wave parameters and to estimate the vertical flux of horizontal momentum produced by flow over the southern alps organized wave clouds were observed in a visible satellite image on 20 october 1996 and are thought to have been produced by partially trapped lee waves using background flow fields derived from a radiosonde sounding the theoretical horizontal wavelength of the partially trapped mode is calculated and agrees well with that measured from the satellite image a technique called the horizontal projection method is developed to analyse radiosonde soundings for mountain waves specifically the technique determines the dominant horizontal wavelength over the entire depth of a radiosonde sounding this method uses a coordinate transformation to take account of vertical changes in the background flow and hence vertical variations in the vertical wave number as well as changes in the path of the radiosonde this method is applied to a radiosonde sounding to identify the dominant wave mode and emphasizes that radiosonde soundings should not in general be treated as instantaneous vertical profiles when analysing mountain waves the mountain waves observed are simulated using a high resolution numerical model and the results are used to check the consistency of the analysis the numerical model produces a horizontally averaged value of momentum flux in the lower stratosphere of 0 02 n m 2 although this value is probably underestimated by at least a factor of four

mjo related intraseasonal variation in the stratosphere gravity waves and zonal winds previous work has shown eastward migrating regions of enhanced temperature variance due to long vertical wavelength stratospheric gravity waves that are in sync with intraseasonal precipitation and tropopause wind anomalies associated with the madden julian oscillation mjo here the origin of these intraseasonal gravity wave variations is investigated with a set of idealized gravity wave resolving model experiments the experiments specifically test whether tropopause winds act to control gravity wave propagation into the stratosphere by a critical level filtering mechanism or play a role in gravity wave generation through an obstacle source effect all experiments use identical convective latent heating variability but the large scale horizontal wind profile is varied to investigate relationships between stratospheric gravity waves and zonal winds at different levels results show that the observed long vertical wavelength gravity waves are primarily sensitive to stratospheric zonal wind variations while tropopause wind variations have only a very small effect thus neither the critical level filter mechanism nor the obstacle source play much of a role in the observed intraseasonal gravity wave variations instead the results suggest that the stratospheric waves follow the mjo precipitation sources and tropopause wind anomalies follow the same sources we further find evidence of intraseasonal wave drag effects on the stratospheric circulation in reanalyzed winds the results suggest that waves drive intraseasonal stratospheric zonal wind anomalies that descend in altitude with increasing mjo phases 3 through 7 eastward anomalies descend further than westward suggesting that mjo related stratospheric waves cause larger eastward drag forces

the flow during toga coare as diagnosed by the bmrc tropical analysis and prediction system abstract the evolution of the large scale flow through the four month intensive observing period of toga coare is documented from large scale numerical analyses and gms cloud imagery produced by the australian bureau of meteorology and transmitted to the field stations during the experiment the evolution of the flow is dominated by the following phenomena 1 the normal seasonal evolution of the tropical flow over this region including a southward and eastward progression of the tropical convective heat source as the southern hemisphere monsoon developed and matured 2 a more eastward than normal progression of this monsoon circulation associated with a warm event of the enso phenomenon 3 the existence of a major westerly easterly westerly cycle of the madden julian low frequency wave occurring during the latter half of the experimental period and 4 the development and subsequent movement of tropical cyclones in both northern and southern hemispheres the madden julian event consisted of two eas

gravity wave and equatorial wave morphology of the stratosphere derived from long term rocket soundings fluctuations in vertical profiles of atmospheric temperature and horizontal wind in the 20 60 km altitude range have been isolated from meteorological rocket measurements during 1977 87 at 15 widely separated sites the seasonal geographical and vertical variability of the variance of horizontal velocities u 2 2 and relative temperature perturbations t 2 were studied the bulk of the variance of both quantities in the 2 10 km and 2 20 km vertical wavelength bands was associated with gravity wave motions although in depth study of the wave polarization shows that planetary scale equatorial wave modes contribute to the variance at equatorial sites annual mean variances varied widely among the 15 stations suggesting appreciable geographical variability in stratospheric wave activity

young eclogite from the greater himalayan sequence arun valley eastern nepal p t t path and tectonic implications abstract garnet geochronology was used to provide the first direct measurement of the timing of eclogitization in the central himalaya lu hf dates from garnet separates in one relict eclogite from the arun river valley in eastern nepal indicate an age of 20 7 0 4 ma significantly younger than ultra high pressure eclogites from the western himalaya reflecting either different origins or substantial time lags in tectonics along strike four proximal garnet amphibolites from structurally lower horizons are 14 15 ma similar to post eclogitization ages published for rocks along strike in southern tibet p t calculations indicate three metamorphic episodes for the eclogite i eclogite facies metamorphism at 670 c and 15 kbar at 23 16 ma ii a peak t granulite event at 780 c and 12 kbar and iii late stage amphibolite facies metamorphism at 675 c and 6 kbar at 14 ma the garnet amphibolites were metamorphosed at 660 c three models are considered to explain the observed p t t evolution the first assumes that the main himalayan thrust basal thrust of the himalayan thrust system cuts deeper at arun than elsewhere while conceptually the simplest this model has difficulty explaining both the granulite facies overprint and the pulse of exhumation between 25 and 14 ma a second model assumes that aborted subduction slab breakoff and ascent of india s leading edge occurred diachronously 50 ma in the western himalaya 25 ma in the central himalaya of nepal and presumably later in the eastern himalaya this model explains the p t t path particularly heating during initial exhumation but implies significant along strike diachroneity which is generally lacking in other features of the himalaya a third model assumes repeated loss of mantle lithosphere first by slab breakoff at 50 ma and again by delamination at 25 ma this model explains the p t t path but requires geographically restricted tectonic behavior at arun the p t t history of the arun eclogites may imply a change in the physical state of the himalayan metamorphic wedge at 16 25 ma ultimately giving rise to the main central thrust by 15 16 ma

a study of the dynamics of the equatorial lower stratosphere by use of ultra long duration balloons 2 gravity waves in the late southern winter of 1998 centre national d etudes spatiales cnes the french space agency released six 10 m diameter superpressure balloons from a location near quito ecuador three balloons collapsed soon after launching but the remaining three drifted westward for a few weeks at altitudes between 19 and 20 km two of those balloons crossed the pacific ocean before falling above the maritime continent while the other completed a revolution around the earth and crossed the pacific for a second time before its final fall despite the small number and the relatively short duration of the flights the balloons provided a unique in situ data set for the lower equatorial stratosphere this part 1 of a two part paper describes this data set and analyzes outstanding features in the planetary scales part 2 focuses on gravity wave scale it is argued that balloon trajectories over the pacific are primarily determined by the westward drift during the easterly phase of the equatorial quasi biennial oscillation qbo and the meridional velocity field of a mixed rossby gravity yanai wave with an apparent period of 4 days and zonal wave number 4 this wave appears to have two episodes of amplification during the balloon flights it is also argued that the balloons show evidence of oscillations with periods between 2 and 4 days and of a kelvin wave with an apparent period close to 10 days and zonal wave number 1 in this way the balloon behavior provided a pictorial view of air parcel trajectory in the equatorial lower stratosphere it is stated that larger balloon campaigns can provide excellent in situ data sets for studies on the dynamics and composition of the middle atmosphere

evidence for protracted prograde metamorphism followed by rapid exhumation of the zermatt saas fee ophiolite major and trace element zoning in garnet in combination with rb sr sm nd and lu hf geochronology provide evidence for a protracted garnet growth history for the zermatt saas fee zsf ophiolite western alps four new lu hf ages from pfulwe c 52 46 ma and one from chamois c 52 ma are very similar to a previously published lu hf age from lago di cignana overall the similarity of geochronological and garnet zoning patterns suggests that these three localities had a similar prograde tectonic history commensurate with their similar structural position near the top of the zsf samples from the lower part of the zsf at saas fee and st jacques however produced much younger lu hf ages c 41 38 ma neither differences in whole rock geochemistry which might produce distinct garnet growth histories nor rare earth element zoning in garnet can account for the age differences in the two suites this suggests a much later prograde history for the lower part of the zsf supporting the idea that it was subducted diachronously such a model is consistent with changes in subduction vectors based on plate tectonic reconstructions where early oblique subduction which produced long prograde garnet growth changed to more orthogonal subduction which corresponds to shorter prograde garnet growth six new rb sr phengite ages range from c 42 to 39 ma and in combination with previously published rb sr ages constrain the timing of the transition from eclogite to upper greenschist facies p t conditions the proximity of the zsf in the saas fee region to the underlying continental monte rosa unit and the similarity of peak metamorphic ages suggest these two units were linked for part of their tectonic history this in turn indicates that the monte rosa may have been partly responsible for rapid exhumation of the zsf unit

a multiple sounding technique for the study of gravity waves radiosondes released in rapid succession with a time separation of a few minutes were launched during a field experiment in central wales u k to study orographic gravity waves rate of ascent fluctuations were used to infer the existence of vertical velocity fluctuations associated with orographic gravity waves and differences between consecutive ascents provided information on the steadiness and phase line slope of the waves the potential of the multiple sounding technique is examined here and an analysis strategy proposed three triple sounding cases from the field experiment are used to illustrate the strengths and weaknesses of the technique in one case it was possible to estimate a phase line tilt with height and this combined with the inferred vertical velocity amplitude allowed the estimation of the vertical momentum flux it is suggested that the near simultaneous release of between three and five sondes upstream of mountainous terrain could provide a useful method for calculating the vertical flux of momentum due to gravity waves

a large amplitude gravity wave in the lower stratosphere detected by radiosonde temperature profiles in the lower stratosphere commonly show fluctuations typical peak to peak amplitude of a few degrees on a vertical scale of a few kilometres the routine operational radiosonde launched from shanwell 56 43 n 2 87 w at 2318 gmt on 12 december 1986 recorded very large amplitude excursions in temperature 15 9 k change over a vertical distance of 2 km in the lower stratosphere which were identified as being exceptional by the staff at the radiosonde station the temperature fluctuations were accompanied by strong shear in the horizontal wind and large variations in the rate of ascent of the balloon the disturbance is argued to be due to a quasi stationary gravity wave with vertical momentum flux about 3 or 4 n m 2 averaged over a horizontal scale of at least 20km these observations their meteorological context and their interpretation are described in detail

fluid flow during exhumation of deeply subducted continental crust zircon u pb age and o isotope studies of a quartz vein within ultrahigh pressure eclogite quartz veins in high pressure to ultrahigh pressure metamorphic rocks witness channelized fluid flow that transports both mass and heat during collisional orogenesis this flow can occur in the direction of changing temperature pressure during subduction or exhumation shrimp u pb dating of zircon from a kyanite quartz vein within ultrahigh pressure eclogite in the dabie continental collision orogen yields two age groups at 212 7 and 181 13 ma which are similar to two groups of la icpms age at 210 4 and 180 5 ma for the same sample these ages are significantly younger than zircon u pb ages of 224 2 ma from the host eclogite thus the two age groups from the vein date two episodes of fluid flow involving zircon growth the first due to decompression dehydration during exhumation and the second due to heating dehydration in response to a cryptic thermal event after continental collision laser fluorination o isotope analyses gave similar 18o values for minerals from both vein and eclogite indicating that the vein forming fluid was internally derived synchronous cooling between the vein and eclogite is suggested by almost the same quartz mineral fractionation values with regularly decreasing temperatures that are in concordance with rates of o diffusion in the minerals while the quartz veining was caused by decompression dehydration at 700 650 c in a transition from ultrahigh pressure to high pressure eclogite facies retrogression the postcollisional fluid flow was retriggered by heating dehydration at 500 c without corresponding metamorphism in either case the kyanite quartz vein formed later than the peak ultrahigh pressure metamorphic event at the middle triassic pointing to focused fluid flow during exhumation rather than subduction the growth of metamorphic zircon in the eclogite appears to have depended on fluid availability so that their occurrence is a type of geohygrometer besides geochronological applicability to dating of metamorphic events in orogenic cycles

unraveling the magnetic carriers of igneous cores from the atlantic pacific and the southern indian oceans with rock magnetic characterization previous rock magnetic investigations of oceanic basement samples have been mainly restricted by single drill holes of dredge collections in this study we present new and published data on the rock magnetic properties of igneous rock samples recovered during seven ocean drilling program odp legs in the atlantic pacific and the southern indian oceans the recovered igneous rocks from these legs are mainly basaltic flows both submarine and subaerial diabase sills and serpentinized peridotites with approximate ages of 140 000 years 10 12 34 69 100 108 and 110 121 ma which offers an opportunity to investigate magnetic properties and mineral changes attending alteration of basement rocks over a wide range of ages from variable tectonic settings titanomagnetite and titanomaghemite are commonly present in igneous rock samples of the ontong java plateau the kerguelen plateau broken ridge the eastern equatorial pacific the middle atlantic ridge trans atlantic geotraverse area and the newfoundland iberia rifted margins for basaltic rock samples three general groups a b and c respectively can be divided in terms of rock magnetic properties samples from group a have a single phase of ti poor titanomagnetite with curie temperatures ranging between 480 and 580 degrees c and exhibit a strong verwey transition in the vicinity of 110 k basalts from this group are most likely good paleomagnetic recorders and probably have preserved original and stable magnetic remanences group b is mainly observed in pillow lavas and is characterized by a curie temperature of 260 280 degrees c which is typical of low temperature oxidized titanomaghemite or titanium rich titanomagnetite the low temperature curves for group b do not show the verwey transition group c has more than one curie temperature which suggests the presence of multiple magnetic phases the thermomagnetic signature indicates the inversion of titanomaghemite to a strongly magnetized magnetite as shown by the irreversible cooling curves for the serpentinized peridotites recovered from both sides of the newfoundland iberia rifted margins results from low temperature measurements show that titano magnetites are present in the dark colored peridotites with a strong verwey transition in the vicinity of 110 k and with field and frequency dependent susceptibility curves that resemble those of synthetic tmo in contrast to the magnetic properties observed from the dark colored peridotites the low temperature curves for the yellow brown colored peridotites did not show any verwey transition thermomagnetic analysis also failed to show evidence for titanomagnetites the remanent magnetization is carried by a thermally unstable mineral that breaks down at about 420 degrees c probably maghemite the magnetic signatures of the serpentinized peridotites recovered from both sides of the newfoundland iberia rift appear not in conflict with the notion that conjugate margins will have generally similar crustal structure and evolution history our rock magnetic data indicate that the differences in the rock magnetic properties of basaltic rocks are mainly a function of mineralogy and alteration there is no apparent coincidence between the age of the rocks and the degree of low temperature alteration as suggested by the presence of nearly unoxidized titanomagnetite in the cretaceous aged basalts and by an examination of curie temperature versus sample age that does not unambiguously show a positive relationship between the degree of low temperature oxidation and crust ages c 206 elsevier b v all rights reserved less

constraints on timing of peak and retrograde metamorphism in the dabie shan ultrahigh pressure metamorphic belt east central china using u th pb dating of zircon and monazite abstract the dabie shan ultrahigh pressure metamorphic uhpm belt occupies the suture between the yangtze and sino korean blocks in east central china the timing of uhpm in the dabie belt is controversial and most recent data come from dating of zircons monazite has recently been recognized as useful for dating of multiple tectonic events due to its preservation of multiple growth zones and monazite growth has been documented to occur during prograde peak and retrograde metamorphism zircons and monazites from uhp mafic rocks from maowu and a uhp jadeite quartzite from shuanghe were imaged in thin sections and in mineral separates and dated using a high resolution ion microprobe maowu mafic rocks are unique in that they contain high light rare earth element concentrations and therefore contain abundant monazite maowu eclogites and garnet pyroxenites contain zircons with mean 206 pb 238 u age of 230 4 ma and monazites from a clinopyroxenite have 208 pb 232 th ages of 209 4 ma multiple lines of evidence suggest that the measured ages represent the timing of new growth and recrystallization and are not cooling ages i e they do not correspond to the cessation of diffusional pb loss as rocks cooled below the closure temperature during exhumation shuanghe jadeite quartzites contain zircons with cores that define a discordia with an upper intercept age 1921 22 ma and lower intercept age of 236 32 ma interpreted to represent the ages of the source rocks and of peak metamorphism respectively zircon rims contain jadeite inclusions that restrict growth to pressures greater than 1 5 gpa their pooled age of 238 3 ma agrees well with the lower intercept defined by cores suggesting that pb loss from cores and growth of new rims occurred during uhpm at 235 240 ma monazite records multiple events during retrograde metamorphism maowu clinopyroxenite and shuanghe jadeite quartzite experienced monazite growth at 209 ma interpreted to reflect regional amphibolite facies overprinting resulting from pervasive retrograde fluid infiltration only the jadeite quartzite records growth at 223 1 ma estimated exhumation rates for maowu are 7 8 km ma

self reversed magnetization carried by titanomaghemite in oceanic basalts abstract self reversal the remarkable ability of some rocks to acquire a magnetization antiparallel to the earth s magnetic field was of great interest in the 1950s and 1960s but it was subsequently found to be rare limited to a few hemoilmenite bearing igneous rocks here we show through thermal demagnetization experiments that pillow basalts from the northwestern pacific ocean lacking hemoilmenite contain two nearly antiparallel components of natural remanent magnetization partial thermoremanent magnetization experiments indicate that the component isolated at lower temperatures is a self reversal of the primary magnetization the self reversal is carried by titanomaghemite formed by low temperature oxidation because maghemitization of oceanic crust is ubiquitous self reversals may be an important factor contributing to the decrease with age in marine magnetic anomaly amplitudes observed for crust formed during the last 30 million years

origin of atoll garnets in eclogites and implications for the redistribution of trace elements during slab exhumation in a continental subduction zone detailed electron and ion microprobe analyses were carried out on atoll shaped and normal garnets in ultrahigh pressure uhp metamorphic eclogite from dabie east central china compositional profiles of both normal garnets and rings of atoll garnets show well preserved growth zoning with a decrease in mn ca and heavy rare earth elements hrees and an increase in mg toward rims manganese and middle rare earth element mree enrichments are observed near garnet rims island and peninsula shaped garnet inside atolls are homogeneous in major elements and show the same composition as garnet rims whereas the hree concentrations are similar to those of the normal garnet cores electron back scatter diffraction ebsd analyses show that the island and peninsula shaped garnet fractions inside atolls have crystallographic orientations identical to that of the atoll rings these observations suggest that the atoll garnets were formed by the consumption of earlier formed cores by fluid released from both hydroxyl exsolution from the nominally anhydrous minerals nams and lawsonite decomposition at the onset of exhumation i e garnet breakdown was from the inside and re growth from outside to inside though somewhat restricted this study reveals that because garnet and zircon act as sinks for hrees and zr respectively the majority of released hrees and zr were likely re incorporated into newly grown garnet and zircon during the dabie uhp metamorphic slab exhumation

multiple zircon growth during fast exhumation of diamondiferous deeply subducted continental crust kokchetav massif kazakhstan diamondiferous rocks from the kokchetav massif kazakhstan represent deeply subducted continental crust in order to constrain the age of ultra high pressure uhp metamorphism and subsequent retrogression during exhumation zircons from diamondiferous gneisses and metacarbonates have been investigated by a combined petrological and isotopic study four different zircon domains were distinguished on the basis of transmitted light microscopy cathodoluminescence trace element contents and mineral inclusions mineral inclusions and trace element characteristics of the zircon domains permit us to relate zircon growth to metamorphic conditions domain 1 consists of rounded cores and lacks evidence of uhp metamorphism domain 2 contains diamond coesite omphacite and titanian phengite inclusions providing evidence that it formed at uhp metamorphic conditions p 43 kbar t 950 c domain 3 is characterised by low pressure mineral inclusions such as garnet biotite and plagioclase which are common minerals in the granulite facies overprint of the gneisses p 10 kbar t 800 c this multi stage zircon growth during cooling and exhumation of the diamondiferous rocks can be best explained by zircon growth from zr saturated partial melts present in the gneisses domain 4 forms idiomorphic overgrowths and the rare earth element pattern indicates that it formed without coexisting garnet most probably at amphibolite facies conditions p 5 kbar t 600 c the metamorphic zircon domains were dated by shrimp ion microprobe and yielded ages of 527 5 528 8 and 526 5 ma for domains 2 3 and 4 respectively these indistinguishable ages provide evidence for a fast exhumation beyond the resolution of shrimp dating the mean age of all zircons formed between uhp metamorphic conditions and granulite facies metamorphism is 528 3 ma indicating that decompression took place in less than 6 ma hence the deeply subducted continental crust was exhumed from mantle depth to the base of the crust at rates higher than 1 8 cm year we propose a two stage exhumation model to explain the obtained p t t path fast exhumation on top of the subducted slab from depth 140 to 35 km was driven by buoyancy and facilitated by the presence of partial melts a period of near isobaric cooling was followed by a second decompression event probably related to extension in a late stage of continental collision

diffusion limited ree uptake by eclogite garnets and its consequences for lu hf and sm nd geochronology garnets from the zermatt saas fee eclogites contain narrow central peaks for lu yb tm er and at least one additional small peak towards the rim the ree sm eu gd tb dy are depleted in the cores but show one prominent peak close to the rim these patterns cannot be modeled using rayleigh fractionation accompanied by mineral breakdown reactions instead the patterns are well explained using a transient matrix diffusion model where ree uptake is limited by diffusion in the matrix surrounding the porphyroblast observed profiles are well matched if a roughly linear radius growth rate is used the secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to temperature increase during prograde metamorphism the model predicts anomalously low 176lu 177hf and 147sm 144nd ratios in garnets where growth rates are fast compared to diffusion of the ree and these results have important implications for lu hf and sm nd geochronology using garnet

radiosonde observations of partially trapped lee waves over tasmania australia a well defined family of lee waves over southern tasmania australia is analyzed using a routine radiosonde sounding released from hobart at 1100 utc june 18 1991 pronounced fluctuations in the ascent rate of the radiosonde are analyzed using a new technique called the horizontal projection method the dominant horizontal wavelength is found to be 8249 m an advanced very high resolution radiometer avhrr infrared satellite image at 1554 utc is used to check this calculation and gives a horizontal wavelength of 8 9 1 4 km the horizontal projection method takes account of the vertical variation of background flow and the trajectory of the radiosonde when the scorer parameter is a strong function of height as is the case with the 1100 utc sounding it is inappropriate to assume that the vertical wavenumber is constant with height in particular the vertical wavelength at low levels is about 4 5 km the waves become evanescent between the heights of 2 5 km and 9 km and above that the vertical wavelength is typically 10 15 km as a consistency check linear wave theory is used to calculate the resonant wave modes supported by the background profiles of wind and potential temperature these are the wave modes that are most likely responsible for the lee wave clouds seen in the avhrr satellite image the horizontal wavelength for the resonant wave mode is 8188 m in agreement with the estimates based on the avhrr satellite image and from the horizontal projection method the paper highlights the dangers of interpreting radiosonde soundings as vertical snapshots of the atmosphere and assuming that the vertical wavenumber can be characterized by a single value it is shown that treating the radiosonde sounding as a vertical profile and analysing wave like structures in the ascent rate using standard spectral methods gives an incorrect vertical wavelength of 1906 238 m the paper concludes that operational radiosonde soundings can be used to make accurate quantitative measurements of orographically generated waves provided that the vertical variation in the background flow and the motion of the radiosonde through the wave field are taken into account

regional ultrahigh pressure coesite bearing eclogitic terrane in central china evidence from country rocks gneiss marble and metapelite the dabie mountains represent a fault bounded coesite bearing eclogite gneissic terrane within the collisional belt between the sino korean and yangtze cratons the following geologic evidence indicates that this terrane has been subjected to regional ultrahigh pressure metamorphism 1 the country rocks have a metamorphic pressure temperature evolution compatible with that of the eclogites on the basis of the occurrence of quartz pseudomorphs after coesite calcite pseudomorphs after aragonite relict high pressure assemblages in different rock types of the country rocks and consistent comparable compositional zonations of garnets in both country rocks and eclogites 2 peak metamorphic pressure temperature conditions consistently decrease both from east to west in the collisional belt and from north to south in the dabie mountains and clockwise pressure temperature paths are common for eclogites over the region 3 layered eclogites interbedded with gneisses and amphibolites contain omphacite kyanite and garnet indicating a minimum pressure of 20 kbar at 600 c for formation of these rocks

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

coesite bearing eclogite from the dabie mountains in central china coesite and coesite pseudomorphs are recognized in eclogite from the dabie mountains a collision zone between the sino korean and yangtze cratons in central china this third known occurrence of coesite in deep crustal rocks is within an archean gneiss terrane and is the first locality where coesite has been identified as an inclusion in both omphacite and garnet crystals at the same location coesite bearing eclogite is estimated to form at pressures of 28 kbar and temperatures from 600 to 710 c the dabie mountains eclogite underwent retrograde metamorphism to amphibolite facies after its formation the preservation of coesite in eclogite is found to be strongly controlled by the pressure temperature time path that coesite bearing eclogite followed during its uplift and retrograde metamorphism

falling sphere observations of anisotropic gravity wave motions in the upper stratosphere over australia a study of inertial scale gravity wave motions in the region of the atmosphere between 30 and 60 km has been undertaken using wind and temperature data derived from rocket borne falling sphere density experiments performed over woomera australia between 1962 nad 1976 the gross features of the wave field compare favorably with those found in similar northern hemispheric studies wave propagation is found to be both vertically and horizontally anisotropic a rotary spectral analysis indicates predominately upgoing wave energy suggesting that the majority of sources of these waves lie below 30 km a detailed statistical investigation of the waves made using the stokes parameters technique reveals that phase progression is also highly directional in the horizontal with a significant zonal component in summer but with a strong meridional component in winter propagation towards the southeast is inferred in summer with the waves possibly emanating from tropospheric sources in equatorial regions to the north of australia the technique also shows that on average the waves appear to have mean ellipse eccentricities f around 0 4 0 45 indirect estimates of a number of important wave parameters are made in particular v andw flux estimates are made over several height intervals the vertical gradient of density weighted flux implies wave induced mean flow accelerations of the order 0 1 1 ms 1day 1 this suggests that dissipating gravity waves are a significant source of the momentum residuals that are encountered in studies of satellite data from this region

partial self reversal in basalts containing mildly low temperature oxidized titanomagnetite abstract oligocene basalt samples cored from yarraman creek in the liverpool range new south wales australia have been found to contain two remanence components with opposing directions the self reversed component has been clearly identified in several samples subjected to detailed thermal demagnetization moreover through af demagnetization results alone some unheated specimens display consistent multicomponent behavior several flows under investigation were extruded during what appears to have been an excursion of the geomagnetic field each possessing a magnetization direction far from the full polarity state the possibility that the self reversed moments are simply secondary components acquired in an opposing field direction is therefore ruled out optical examinations and thermomagnetic curves indicate that the samples contain from nearly unoxidized to moderately low temperature oxidized titanomagnetite the self reversed component is most clearly removed during thermal demagnetization between about 230 and 290 c above the observed curie point of the titanomagnetite and is believed to be associated with titanomaghemite consistently the role of the self reversed moment is seen to be most dramatic in samples showing the highest degree of low temperature oxidation moreover thermal demagnetization of samples from varying depths below the creek bed provide strong evidence that the self reversed component in some if not all of the samples investigated develops at room temperature the relevant self reversal mechanism is currently under investigation

sm nd and rb sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at shuanghe in the dabie mountains central china abstract ultrahigh pressure metamorphic uhpm rocks at shuanghe area in the dabie mountains occur as a uhpm block within the regional granitic gneiss a sm nd isochron defined by garnet omphacite rutile from coesite bearing eclogite yield an age of 226 3 3 2 ma another sm nd isochron defined by garnet two phengites form uhp gneiss yield a similar age of 226 5 2 3 ma the two consistent sm nd ages defined by three uhpm minerals suggest that nd isotopic equilibrium between uhpm minerals in these rocks during uhp metamorphism has been achieved this may correspond to the age of peak metamorphism with an average metamorphic temperature of 800 c it is demonstrated that the retrograde metamorphism of uhpm rocks occurred in an open chemical system whereas the nd and sr isotopic systematics of uhpm minerals may have remained closed nd and sr isotopic disequilibrium between uhpm minerals and retrograde metamorphic minerals has been observed therefore the tie line of garnet or phengite and whole rock containing retrograde metamorphic minerals gives an old sm nd age and a young rb sr age respectively with no geologic significance however a rb sr ages of 219 0 6 6 ma defined by phengite garnet from a uhpm gneiss indicates that the uhpm rocks at shuanghe cooled down to 500 c at that time it suggests that the uhpm rocks at shuanghe experienced the first rapid cooling during 226 219 ma on the other hand the rb sr ages of 174 7 8 to 169 2 3 3 ma defined by retrograde minerals amphibole or biotite with closure temperature ranging from 450 to 300 c and intensely retrograded metamorphic rocks reflect a second rapid cooling during this time interval this is consistent with the rapid cooling time of 190 170 ma of the orthogneiss in the dabie su lu uhpm belt obtained by ar ar dating method in contrast to uhpm rocks the nd isotopic composition of the garnet in granitic gneiss has been reset during retrograde metamorphism and is in equilibrium with those of retrograde epidote and biotite which yields a sm nd isochron age of 213 5 ma indicating the retrometamorphic time corresponding to amphibolite facies in addition the biotites from the granitic gneiss yield rb sr ages of 171 173 ma similar to those of the uhpm rocks these data suggest that the country rocks granitic gneiss may have a similar cooling history to the uhpm rocks at shuanghe two stages of rapid cooling of uhpm rocks at shuanghe may correspond two stages of fast uplift the initial rapid uplifting and cooling of uhpm rocks during 226 219 ma may be caused by compression tectonics during subducting time of the continental crust whereas the later rapid cooling may reflect the exhumation of the entire subducted continental crust by extension during the early middle jurassic

isotopic chronometry of zoned garnets growth kinetics and metamorphic histories basic information on the chronological and pressure temperature evolution of regional metamorphic terrains may in principle be derived from metamorphic garnets because of the similarly low diffusivities of sm nd and major cations in this mineral we report here smnd and rbsr isotopic and major element data on prograde garnets from regionally metamorphosed pelites from newfoundland the garnets preserve a prograde major element zonation as well as a sympathetic variation in sm nd ratio smnd data for separated portions of the garnet from core to rim provide both upper limits on the time for garnet growth and demonstrate synchronous growth of different garnet grains on a hand specimen scale the rbsr data on the same garnet fractions are in general agreement with these results but in some cases cannot be interpreted in terms of growth a minimum heating rate of 3k ma 1 is derived by combining the estimates for garnet growth time with the apparent temperature interval over which the garnet grew deduced from the major element zonation this value is similar to the minimum suggested by theoretical models for the thermal evolution of thickened continental crust the growth rate is within the range of 1 3 19 mm ma 1 set respectively by the isotopic data and the likely upper limit for heating rate during regional metamorphism these growth rates appear too slow to be controlled by surface reaction and suggest that other factors such as transport may be rate limiting in this case the limits set on the effective diffusion coefficient for material transport to the growth site 0 4 6 1 10 17 m2 s 1 suggest that grain boundary diffusion is probably the transport mechanism for supply of material to the growing garnet

large variations in balloon ascent rate over hawaii 1 a sequence of nine weather balloons were launched recently over the island of hawaii during the nights of 12 13 and 17 december 2002 providing measurements of ascent rate horizontal wind speed and direction temperature and other quantities the measurements show short intervals of altitude with a large increase in ascent rate occurring only near the tropopause indicating regions of strong upward air velocity at this location the large ascent rates correlate well to the strength of a jet stream and with the presence of a local critical level indicating mountain waves as the primary cause no corresponding decreases in ascent rate were measured suggesting strong three dimensional effects

alteration and self reversal in oceanic basalts 1 we report on magnetic properties and compositions of titanomaghemites from moderately to highly oxidized basalts recovered at nine drilling sites in the pacific ocean these new data together with similar data sets allow us to test compositional fields of titanomaghemite that could carry self reversed components of natural remanent magnetization above room temperature these compositions have been proposed on the basis of theoretical considerations of cation distributions during ionic reordering associated with low temperature oxidation maghemitization the data indicate that very high oxidation states z 0 9 and relatively high ti contents x 0 6 are needed to produce natural self reversed components this compositional range is much more limited than predicted the severe restrictions on compositions and oxidation state strongly suggest that self reversed magnetizations should not be a general feature of the magnetization carried by oceanic basalt instead the formation of self reversed components may signify unusual conditions such as extreme fluid flow and iron removal which could result in the required oxidation states while maintaining stability of the cation deficient titanomaghemite lattice structure

thermally induced inversion of al substituted titanomagnetite in basalts evidence for partial self reversal 1 we report properties of laboratory induced thermoremanence combined with detailed rock magnetic experiments on basaltic samples which contain aluminum substituted titanomagnetite fe2 24ti0 64al0 12o4 prior to thellier coe paleointensity experiments specimens were first demagnetized using an alternating field with a peak field of 90 mt and were then imparted an anhysteretic remanent magnetization arm to represent a natural remanent magnetization nrm results show that the partial thermal remanent magnetization ptrm gain and arm remaining are linearly correlated up to 300 c between 300 and 460 c specimens acquire thermoremanence with a direction antiparallel to the external field direction leading to intensity decreases this coincides with the onset of the mineral transformation from al titanomagnetite to a magnetic phase with higher tc our results support that phase interaction with distinct tc values in partially oxidized titanomagnetite can produce partial self reversal thermoremanence in rocks

numerical modeling of gravity wave generation by deep tropical convection although convective clouds are known to generate internal gravity waves the mechanisms responsible are not well understood the present study seeks to clarify the dynamics of wave generation using a high resolution numerical model of deep convection over the tiwi islands australia the numerical calculations presented explicitly resolve both the mesoscale convective cloud cluster and the gravity waves generated as the convective clouds evolve they excite gravity waves which are prominent features of the model solutions in both the troposphere and stratosphere the source location is variable in time and space but is related to the development of individual convective cells the largest amplitude gravity waves are generated when the cloud tops reach the upper troposphere a new analysis technique is introduced in which the nonlinear terms in the governing equations are taken as the forcing for linear gravity waves the analysis shows that in the present calculation neither the shear nor the diabatic heating are the dominant forcing terms instead the wave source is most easily understood when viewed in a frame of reference moving with the wind at the level of neutral buoyancy whereupon the source may be described as a vertically oriented oscillating convective updraft this description is consistent with the properties of the modeled stratospheric waves

the interaction between the tropopause inversion layer and the inertial gravity wave activities revealed by radiosonde observations at a midlatitude station the interaction between the tropopause inversion layer til and the inertial gravity wave igw activities is first presented by using a high vertical resolution radiosonde data set at a midlatitude station boise idaho 43 57 n 116 22 w for the period 1998 2008 the tropopause based vertical coordinate is used for the til detection and for meticulously studying the igw variation around the til the broad spectral method is used for the igw extraction generally the til at the midlatitude station is stronger and thicker in winter and spring which is consistent with previous studies our study confirmed the intense interaction between the til and igw it is found that the til not only could inhibit the upward propagation of igws from below but also imply the possible excitation links between the til and igw the results also indicate that the enhanced wind shear layer just 1 km above the tropopause may result in instability and finally leads to the igw breaking and intensive turbulence subsequently the igw induced intensive turbulence leads to strong wave energy dissipation and a downward heat flux this downward heat transportation could significantly cool the tropopause while it has only negligible thermal effect on the atmosphere above the tropopause then the igw induced cooling at the tropopause makes the tropopause colder and sharper and finally forms the til these suggest besides previously proposed mechanisms that igws also contribute greatly to the formation of til which is consistent with a recent related simulation study

the growth interval of garnet in the uhp eclogites from the dabie orogen china zircon inclusions extracted from garnet from an ultrahigh pressure eclogite in the eastern part of the dabie orogen were investigated with high spatial resolution u pb geochronology the unzoned zircon rims have garnet and omphacite inclusions and show weak cathodoluminescence low th u ratios 0 02 0 18 flat high rare earth elements patterns and an absence of eu anomalies which suggest metamorphic growth in the presence of garnet and in the absence of feldspar dispersed concordia u pb ages ranging from 205 1 3 3 to 255 3 6 1 ma defined a weighted mean 206 pb 238 u age of 223 8 ma mean square of weighted deviation mswd 38 which is significantly younger than the lu hf garnet whole rock age of 242 2 2 6 ma the u pb age probability distribution indicates two age populations at ca 241 and ca 216 ma the zircon rims with younger ages are distinguished from those with older ages by the occurrence of garnet and omphacite inclusions well preserved prograde major and trace element zoning in garnet and the significant contribution of older garnet cores in bulk isotopic digestion suggest that the lu hf age mostly reflects an early phase of garnet growth likely at amphibolite facies conditions the new lu hf age combined with the u pb ages of the zircon inclusions in garnet suggest that garnet growth was sustained over a time interval of 25 m y

gravity wave activity associated with tropical convection detected in toga coare sounding data upper air sounding data collected at santa cruz 10 s 165 e in the western tropical pacific ocean during november 1992 february 1993 have been used to estimate the gravity wave activity in the upper troposphere and lower stratosphere large amplitude gravity waves with vertical wavelengths of 2 5 km were found in almost all the soundings time series describing the wave activity in two height ranges 10 17 km the upper troposphere and 17 24 km the lower stratosphere are presented and compared to simple measures of the convective cloud activity there is enhanced gravity wave activity associated with increased convection on intraseasonal timescales

vertical fluctuation energy in united states high vertical resolution radiosonde data as an indicator of convective gravity wave sources 1 convectively generated internal gravity waves at extratropical latitudes are difficult to identify by climatological analysis of the temperature and horizontal wind fields from radiosonde profiles using traditional analysis methods here we show that by analyzing ascent rate profiles we define a new variable vertical fluctuation energy ve we can identify convection sources in climatological analyses analysis of a 9 year time series 1998 2006 of united states high vertical resolution radiosonde data shows that ve maximizes in summer in midlatitudes within the troposphere 2 8 9 km and peaks at local afternoon early evening during the summer over most of the contiguous united states furthermore the apparent dominant vertical wavelength based on fourier analysis of the low pass filtered ascent rate fluctuations also increase and decrease with ve both on diurnal and seasonal timescales ve in the lower stratosphere however does not show this same relationship to convection but analysis of the vertical wavelength does show some of the features seen in tropospheric ve unlike midlatitude stations ve within both the troposphere and the lower stratosphere over tropical western pacific island stations is highly correlated with convective precipitation and inversely correlated with outgoing longwave radiation we interpret this difference by using the 4 d gravity wave regional or global ray tracer ray tracing model with a source spectrum representative of a convection source

high altitude 0 100 km global atmospheric reanalysis system description and application to the 2014 austral winter of the deep propagating gravity wave experiment deepwave abstracta data assimilation system das is described for global atmospheric reanalysis from 0 to 100 km altitude we apply it to the 2014 austral winter of the deep propagating gravity wave exper

convectively generated gravity waves observed from radiosonde data taken during mctex the properties of gravity waves generated by deep tropical convective systems are analysed from radiosonde soundings taken during the maritime continent thunderstorm experiment and the results compared against recent cloud scale numerical modelling of convectively generated waves fluctuations in the ascent rate of the radiosonde are used to characterize the high frequency waves whereas the zonal wind fluctuations are used to determine the properties of the inertia gravity waves the density weighted vertical velocity variance shows a pronounced diurnal cycle with the largest amplitude gravity waves developing during the early afternoon following the development of deep convection in contrast the density weighted horizontal velocity variance and by implication the inertia gravity wave activity shows no diurnal variation simple theoretical analysis shows that the observations on 27 november 1995 are consistent with a westward propagating gravity wave with a horizontal wavelength of 17 km and a source frequency equal to 0 007 rad s 1 these findings are consistent also with a high resolution numerical model simulation for the same day nonetheless the character of the high frequency gravity waves cannot be uniquely determined from a single radiosonde sounding copyright 2003 royal meteorological society

tropospheric turbulence over the tropical open ocean role of gravity waves a large set of soundings obtained in the indian ocean during 3 field campaigns is used to provide statistical characteristics of tropospheric turbulence and its link with gravity wave gw activity the thorpe method is used to diagnose turbulent regions of a few hundred meters depth above the mixed layer turbulence frequency varies from 10 in the lower troposphere up to 30 around 12km heights gw are captured by their signature in horizontal wind normalized temperature and balloon vertical ascent rate these parameters emphasize different parts of the wave spectrum from longer to shorter vertical wavelengths respectively composites are constructed in order to reveal the vertical structure of the waves and their link with turbulence the relatively longer wavelength gw described by their signature in temperature gwt are more active in the lower troposphere where they are associated with clear variations in moisture turbulence is then associated with minimum static stability and vertical shear stressing the importance of the former and the possibility of convective instability conversely the short waves described by their signature in balloon ascent rate gww are detected primarily in the upper troposphere and their turbulence is associated with a vertical shear maximum suggesting the importance of dynamic instability furthermore gww appear to be linked with local convection whereas gwt are more active in suppressed and dry phases in particular of the madden julian oscillation these waves maybe associated with remote sources such as organized convection or local fronts such as those associated with dry air intrusions

two types of strong local wind captured by simultaneous multiple site radiosonde soundings across a mountain range abstracta radiosonde observation method is presented consisting of simultaneous radiosonde observations at closely spaced multiple sites using balloons with varied buoyancies this method was employed during a strong wind event suzuka oroshi on the lee side of the suzuka mountain range japan to derive the detailed structure of the wind as it crossed the mountains batches of six radiosondes were launched simultaneously from a line of four sites using balloons with three different degrees of buoyancy the four sites were 13 km apart along a 35 km long transect roughly aligned with the prevailing wind the observations documented two flow regimes a downslope flow perpendicular to the mountain range similar to a windstorm and an unexpectedly strong low level jet flowing parallel to the mountain range the method was more successful at delineating the first regime than the second the first regime was well simulated by a numerical experiment but the second regime was not the vertical wind associate

the gravity wave response above deep convection in a squall line simulation abstract high frequency gravity waves generated by convective storms likely play an important role in the general circulation of the middle atmosphere yet little is known about waves from this source this work utilizes a fully compressible nonlinear numerical two dimensional simulation of a midlatitude squall line to study vertically propagating waves generated by deep convection the model includes a deep stratosphere layer with high enough resolution to characterize the wave motions at these altitudes a spectral analysis of the stratospheric waves provides an understanding of the necessary characteristics of the spectrum for future studies of their effects on the middle atmosphere in realistic mean wind scenarios the wave spectrum also displays specific characteristics that point to low physical mechanisms within the storm responsible for their forcing understanding these forcing mechanisms and the properties of the storm and atmosphere that control them are crucial first steps toward developing

burial rates during prograde metamorphism of an ultra high pressure terrane an example from lago di cignana western alps italy abstract estimation of burial rates and duration of prograde metamorphism of ultra high pressure uhp rocks t 590 630 c p 2 7 2 9 gpa of the zermatt saas ophiolite from lago di cignana italy may be made through combined lu hf and sm nd garnet geochronology in conjunction with petrologic estimates of the prograde p t path we report a lu hf garnet omphacite whole rock isochron age of 48 8 2 1 ma from the uhp locality at lago di cignana which stands in contrast to the sm nd age of 40 6 2 6 ma amato et al earth planet sci lett 171 1999 425 438 obtained from the same sample and mineral material the sm nd and lu hf ages as well as other ages determined on metamorphic garnet zircon and white mica amato et al earth planet sci lett 171 1999 425 438 mayer et al eur union geosci 10 1999 abstr 809 rubatto et al contrib mineral petrol 132 1998 269 287 dal piaz et al int j earth sci 90 2001 668 684 from lago di cignana and elsewhere in the zermatt saas ophiolite lie within a range of 50 38 ma which we interpret to encompass the duration of prograde metamorphism and possibly the duration of garnet growth the difference in measured sm nd and lu hf ages from cignana can be accounted for by expected core to rim variations in lu hf sm and nd the measured yttrium content in garnet which may be a proxy for lu is highest in garnet core and lowest in the mineral rim generally following a profile that is predicted by rayleigh fractionation preferential enrichment of lu in the core produces a lu hf age that is weighted toward the older garnet core sm nd ages as predicted by rayleigh fractionation of sm and nd during garnet growth however reflect later grown garnet as compared to lu hf ages the difference in sm nd and lu hf ages from a single sample should therefore be a minimum estimate for the duration of garnet growth and prograde metamorphism so long as sm nd and lu hf blocking temperatures were not exceeded for a long period of time based on the 12 myr duration of prograde garnet growth estimated in this study burial rates for rocks at lago di cignana were on the order of 0 23 0 47 cm yr these values correlate with continuous shortening rates of 0 4 1 4 cm yr between the european plate and the african adriatic promontory between 50 and 38 ma which is on the order of that calculated for plate velocities from plate reconstructions suggesting that the zermatt saas ophiolite may have remained well coupled to the down going slab to uhp conditions

sm nd dating of spatially controlled domains of garnet single crystals a new method of high temperature thermochronology ganguly and tirone meteorit planet sci 36 2001 167 175 recently presented a method of determining the cooling rates of rocks from the difference between the core and bulk ages of a crystal as determined by a single decay system here we present the first application of the method using the core and bulk ages of garnet single crystals according to the sm nd decay system in two rock samples with contrasting cooling rates which can be constrained independently the samples belong to the metamorphic core complex valhalla british columbia and the mid crustal magmatic arc exposure of the salinian terrane california we have micro sampled the garnet crystals over specific radial dimensions and measured the nd isotopes of these small sample masses as ndo via solid source mass spectrometry to determine the sm nd age difference between the core and bulk crystals using a peak metamorphic p t condition of 8 1 kbar 820 30 c spear and parrish j petrol 37 1996 733 765 the core 67 3 2 3 ma and bulk 60 9 2 1 ma ages of the british columbian garnet sample yield a cooling rate of 2 13 c myr which is in very good agreement with the cooling rates that we have derived by modeling the retrograde fe mg zoning in the same garnet and assuming the same peak metamorphic p t condition considering earlier cooling rate data derived from closure temperature vs age relation of multiple geochronological systems spear and parrish j petrol 37 1996 733 765 a cooling rate of v15 20 c myr seems most reasonable for the valhalla complex diffusion kinetic analysis shows that the sm nd core age of the selected garnet crystal could not have been disturbed during cooling consequently the core age of the garnet crystal 67 3 2 3 ma corresponds to the peak metamorphic age of the valhalla complex the salinian sample on the other hand yields indistinguishable core 78 2 2 7 ma and bulk 77 9 2 9 ma ages as expected from its fast cooling history which can be constrained by the results of earlier studies the sm nd decay system in garnet has relatively high closure temperature usually s 650 c therefore the technique developed in this paper fills an important gap in thermochronology since the commonly used thermochronometers are applicable only at lower temperatures simultaneous modeling of the retrograde fe mg zoning in garnet spatially resolved sm nd ages of garnet single crystals and resetting of the bulk garnet sm nd age

gravity waves generated by convection during twp ice 2 high frequency gravity waves high frequency gravity waves are analyzed using radiosonde soundings taken during the tropical warm pool international cloud experiment twp ice the intrinsic periods of these waves are estimated to be between 10 and 50 min the high frequency wave activity in the stratosphere defined by mass weighted variance of the vertical motion of the sonde has a maximum following the afternoon local convection indicating that these waves are generated by local convection the wave activity is the strongest in the lower stratosphere below 22 km and during the suppressed monsoon period is modulated with a 3 4 day period the concentration of the wave activity in the lower stratosphere is consistent with the properties of the environment in which these waves propagate whereas its 3 4 day modulation is explained by the variation of the convection activity in the twp ice domain for shallow convection the wave activity has a weak tendency to increase as the rainfall intensity increases the wave activity associated with deep convection which typically occurs at high rainfall intensities is larger and has more spread than that associated with shallow convection

on the compositional field of self reversing titanomaghemite constraints from deep sea drilling project site 307 1 in 1956 verhoogen proposed that ionic reordering during low temperature oxidation of titanomagnetite could result in self reversal of natural remanent magnetization later in 1966 o reilly and banerjee concluded that 1 the compositional field of self reversing titanomaghemite was restricted to very high oxidation states and 2 that high oxidation temperature 250 c would be required to reach these oxidation levels which would in turn be inconsistent with stability of the cation deficient structure of titanomaghemite in nature however an example of the process has been reported in some altered pillow basalt lavas of late cretaceous age from detroit seamount ocean drilling program odp sites 883 1203 and 1204 in the northwestern pacific ocean here we present new paleomagnetic rock magnetic and compositional data from mid ocean ridge tholeiitic basalts of late jurassic age collected at deep sea drilling project dsdp site 307 although severely oxidized the dsdp site 307 basalt samples lack the clear self reversed magnetizations seen in some samples from detroit seamount these data constrain the compositional field of self reversing titanomaghemite to extremely high oxidation states z 0 95 consistent with the first conclusion of o reilly and banerjee the comparison of results from odp sites 883 1203 and 1204 on detroit seamount and those from the dsdp site 307 basalts suggests that the presence of self reversed magnetizations may signify unusually vigorous and sustained fluid flow that resulted in very efficient removal of fe from titanomaghemite producing the extremely high oxidation states required for self reversal

plate movements ductile deformation and geochronology of the sanbagawa belt sw japan tectonic significance of 89 88 ma lu hf eclogite ages prograde p t paths and thermal modelling suggest metamorphism in the sanbagawa belt represents unusually warm conditions for subduction type metamorphic belts and these likely reflect conditions of a convergent margin a few million years before the arrival of an active spreading ridge radiometric age data and kinematic indicators of ductile deformation suggest the sanbagawa belt formed in a cretaceous convergent margin associated with a plate movement vector that had a large sinistral oblique component with respect to the belt the east asian margin plate reconstructions for the cretaceous to tertiary for this region show that the only plausible plate compatible with such motion at this time is the izanagi plate these reconstructions also show that progressively younger sections of the izanagi plate were subducted beneath eastern asia i e a spreading ridge approached until 85 83 ma when the izanagi plate ceased to exist as an independent plate the major reorganization of plates and associated movements around this time is likely to be the age of major interaction between the ridge and convergent margin the ridge approach model for the sanbagawa metamorphism therefore predicts that peak metamorphism is a few million years older than this age range new lu hf dating of eclogite in the sanbagawa belt gives ages of 89 88 ma in excellent agreement with the prediction combining this estimate for the peak age of metamorphism with published p t t results implies vertical exhumation rates of greater than 2 5 cm yr 1 this high rate of exhumation can explain the lack of a significant thermal overprint in the sanbagawa belt during subduction of the ridge

models of garnet differential geochronology abstract rayleigh distillation models are developed to describe theoretical growth zoning of lu hf rb sr sm and nd in typical garnet crystals from metapelites and metabasites effects of diffusion limited transport within the matrix and intracrystalline diffusion are also considered qualitatively theoretical zoning profiles show strong depletions of lu in garnet rims compared to cores but virtually invariant hf rb sr sm and nd profiles generally consistent with natural profiles for lu and hf and previously published models theoretical isochron diagrams for lu hf exhibit distinctive arcuate distributions and high mswds consistent both with himalayan data and with expectations that garnet growth durations exceed chronologic resolution by as much as an order of magnitude predicted isochron diagrams for sm nd and rb sr exhibit vertical arrays for garnet and high mswds that are generally lower than for lu hf in metapelites inherent chronologic resolution for bulk separates is best for lu hf in metapelites and rb sr but analytical considerations favor rb sr or sm nd for chronologic zoning studies diffusion limited transport in the rock matrix strongly influences zoning profiles but does not change the main trends on isochron diagrams intracrystalline diffusion will initially rotate lu hf isochrons to steeper slopes giving older apparent ages the natural himalayan data indicate growth of garnet in one rock from the greater himalayan sequence at 34 ma consistent with previously measured monazite ages from the same rock data from another himalayan rock suggest polymetamorphism that includes a paleozoic component

is the hp uhp hong an dabie sulu orogen a piercing point for offset on the tan lu fault abstract the tan lu fault is a major strike slip fault in eastern china that appears to offset the high grade rocks of the hong an dabie sulu orogen left laterally 540 km we evaluate models for the collision between the south and north china blocks published radiometric dates recording hp uhp metamorphism and exhumation in the hong an dabie and sulu terranes and the timing of sinistral motion on the tan lu fault to evaluate whether uhp rocks provide a piercing point for offset on the tan lu fault uhp metamorphism in hong an dabie was concurrent with sulu based on u pb dating of coesite bearing domains of zircon at 244 5 226 2 ma for hong an dabie and 243 4 225 2 ma for sulu retrograde metamorphism began c 220 ma for both hong an dabie and sulu but retrograde zircon growth ended c 214 ma in hong an dabie and continued until c 202 ma in sulu based on u pb dating of zircon domains external to coesite bearing domains structures in sulu are rotated 25 counter clockwise from but are broadly similar to hong an dabie suggesting the two areas have a common triassic orogenic history that pre dates motion on the tan lu fault and that is consistent with paleomagnetic studies we constructed a pre cretaceous restoration of the hong an dabie sulu belt that moves the sulu terrane south aligning the suture and the eclogite facies isograd and rotates sulu c 25 clockwise to re align structures with hong an dabie our restoration is supported by published data and shows that the hong an dabie sulu orogen is a piercing point for post collisional offset on the tan lu fault and that these regions shared a common subduction exhumation history the tan lu fault did not play a significant role in the hong an dabie sulu collision and likely developed later in the early cretaceous

mesoscale disturbances in the tropical stratosphere excited by convection observations and effects on the stratospheric momentum budget abstract the importance of the momentum flux of topographically generated mesoscale gravity waves to the extratropical middle atmosphere circulation has been well established for over a decade estimates of the zonal forcing due to tropical mesoscale gravity waves however are hampered by lack of data on their primarily convective sources the advent of aircraft measurements over tropical convective systems now makes such estimates possible without the use of ad hoc assumptions about amplitudes and phase speeds aircraft measurements from nasa s 1980 panama and 1987 step australia missions show that convectively generated disturbances observed just above the tropopause have horizontal scales comparable to those of the underlying anvils about 50 100 km with peak to peak isentropic surface variations of about 300 400 m satellite imagery of tropical anvil evolution indicates a typical lifetime of about five hours assuming that each convective system s impact on the stratosphere can be modeled as a time

slow subduction of a thick ultrahigh pressure terrane 1 high precision lu hf and sm nd ages reported here cover a large portion of the western gneiss region wgr ultrahigh pressure uhp terrane norway and range from 413 9 3 7 to 397 1 4 8 ma collectively new and existing geochronologic data for eclogites demonstrate that eclogite facies metamorphism occurred over a large area 60 000 km2 for an unexpectedly long period of 20 ma a thermal model using slow subduction 2 4 mm a 1 of a relatively warm and thick slab can reproduce the observed p t t history of the wgr uhp terrane indicating that large uhp terranes with protracted peak or near peak histories probably reflect slow subduction of relatively thick crustal sections

radiosonde observations of equatorial atmosphere dynamics over indonesia 2 characteristics of gravity waves this paper discusses the characteristics of gravity waves in the equatorial region revealed by analyzing radiosonde measurements of wind velocity and temperature fluctuations at 0 35 km with a height resolution of 150 m made every 5 7 hours between february 27 and march 22 1990 in east java indonesia we conducted hodograph analysis to delineate vertical and horizontal propagation characteristics and found that most gravity waves were generated in the middle of the troposphere and that they propagated upward into the stratosphere the amplitudes of wind velocity and temperature fluctuations due to gravity waves were larger in the stratosphere than in the troposphere the direction of horizontal propagation of gravity waves was rather uniformly distributed in the troposphere but it became eastward in the lower stratosphere being opposite to that of the mean winds because of quasi biennial oscillation the vertical wavenumber spectra of wind velocity were described fairly well by a saturated model spectrum although their amplitudes were smaller in the stratosphere a typical vertical wavelength was 2 2 5 km while the horizontal phase velocities were 5 7 and 12 m s in the troposphere and stratosphere respectively the amplitudes of small scale gravity waves were significantly larger in the equatorial stratosphere than at middle latitudes time height variation of the wind velocity variance due to gravity waves showed a clear correlation with that for high relative humidity which implies that cloud convection is an important mechanism of gravity wave generation in the equatorial region

ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern dabie shan u pb zircon geochronology the dabie shan contains two rare geologic features one the occurrence of ultra high pressure metamorphic rocks peak p 2 7 gpa uhp in the east central part of this belt and two some of these uhp rocks are characterized by anomalously 18o depleted oxygen isotopic compositions geochronological data are presented that constrain the age of the uhp metamorphism the ages of protoliths and potentially the age of hydrothermal alteration believed to be responsible for the anomalous oxygen isotopic compositions the age of uhp metamorphism in the eastern dabie shan is dated at 218 5 1 7 ma using u pb in zircon separated from host gneisses this age is identical within uncertainty with a less precise age using u pb in zircon separated from uhp eclogite 225 5 3 6 ma and with previously published ages from uhp eclogites of the dabie shan map relationships strongly support an in situ as opposed to exotic orgin of the uhp eclogites in this region the identical ages of uhp metamorphism in the gneisses and eclogites provides additional support for this interpretation the age of the protolith gneisses is dated as 772 5 9 5 ma based on the upper intercept of the zircons which accords well with other dates of granitic gneisses in the qinling belt the association of mafic and felsic magmatism is interpreted to reflect rifting along the northern margin of the yangtze block at this time these upper intercept ages may date the hydrothermal circulation of 18o depleted meteoric water which gave rise to the anomalously 18o depleted uhp protoliths of the dabie shan and sulu region the coincidence of these protolith ages with the early sinian glaciation of south china is consonant with the suggestion that the highly anomalous oxygen isotopic compositions in this region date from this time the upper intercept age of the eclogite is imprecisely determined at 447 82 79 ma but is younger than the host gneisses and is not characterized by anomalous oxygen isotopic compositions

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

radiosonde observations of equatorial atmosphere dynamics over indonesia 1 equatorial waves and diurnal tides this paper describes the characteristics of the mean winds equatorial waves with periods ranging from 4 to 20 days and diurnal tides determined by analyzing the profiles of wind velocity temperature and humidity obtained every 5 7 hours in the height range up to about 35 km with a height resolution of 150 m during an observation campaign conducted february 27 to march 22 1990 in east java indonesia the structures of the mean winds in the troposphere and lower stratosphere seemed to be affected by the australian monsoon and the quasi biennial oscillation respectively frequency spectra indicated that the equatorial waves as well as the diurnal tides were dominant below about 25 km while gravity waves with periods shorter than 4 days became more significant above 25 km a 7 day oscillation showing an antiphase relation between the eastward and northward components and exhibiting large amplitudes was observed in the lower troposphere the time height variations of the activity of this 7 day oscillation were clearly correlated with a region of high relative humidity perturbations in the zonal wind and temperature with wave periods varying from 15 to 17 days were also enhanced in the troposphere while kelvin waves with periods of about 7 and 20 days were detected in the lower stratosphere and activity near the tropopause was conspicuously enhanced we found that the 20 day kelvin wave greatly modified the structure of the tropopause such as the minimum temperature the tropopause height and the values of the brunt vaisala frequency squared n2 which further suggests the effects of kelvin waves on the transportation of tropospheric water vapor into the stratosphere and on the downward mixing of stratospheric minor constituents into the troposphere the observed profiles of the diurnal oscillation were compared with those of a numerical model assuming only migrating tides which reasonably agreed above about 25 km below 25 km however the observed amplitudes were 1 1 5 m s exceeding those of the model about 10 times moreover the phase profiles involved fluctuations with small vertical scales suggesting interference by many nonmigrating tides with short vertical wavelengths