development of a one month long westward propagating subtropical low in boreal summer abstracta strong mjo event produced an upper tropospheric jet streak in northeast asia and repeated wave breaking in the jet exit region along 150 e during july 1988 a midlatitude low moved equatorward and intensified in the presence of bandpass filtered 15 100 day q vector forcing for upward motion associated with the wave breaking this forced ascent helped to moisten the atmosphere enough to increase the column water vapor to above 55 mm this value was sufficiently large to support a self sustaining low even after the upper forcing weakened the horizontal scale of the q vector forcing was about 1500 km consistent with the scale of most favorable convective response to quasigeostrophic forcing in the subtropics described by nie and sobel the low lasted one month as it moved southwestward then westward while remaining north of 20 n maximum precipitation along the track of the low exceeded 700 mm with an anomaly more than 400 mm a climatology of long lasting lows was carried out for the monsoo

monsoon gyres of the northwest pacific influences of enso the mjo and the pacific japan pattern abstractan objective definition of monsoon gyres in the northwest pacific was developed in order to construct a gyre climatology over a 31 yr period 53 gyres were identified with a median formation location at 16 5 n 135 e more than 80 formed during july september more than half of gyres developed during el nino periods at a median location 1200 km farther to the east southeast than during la nina cyclonic winds at 850 hpa extended across a diameter of more than 4000 km with maximum tangential wind near the 1000 km radius a precipitation maximum extended westward for several thousand kilometers south of the gyre typhoons were most common north and east of the gyre centers more than 70 of gyres developed during large amplitude mjo events with a strong preference for real time multivariate mjo rmm phases 5 7 in boreal summer these phases contain circulation and convective anomalies that coincide most closely with those of the climatological monsoon trough gyres are most likely to form when

a polycyclic two stage corona growth in the iforas granulitic unit mali retrograde and prograde mineral assemblages from metapelitic and metabasic rocks of the iforas granulitic unit mali were generated by the superimposition of two granulite facies metamorphic events they clearly result from a polycyclic evolution and can be related to a late eburnean unroofing followed by a pan african burial thermobarometry on pan african garnet bearing assemblages yields p t estimates of 620 50 c and 5 ikbar the nearly anhydrous conditions produced in the eburnean appear to be the direct cause of the unusually lowtemperature granulite facies metamorphism in the pan african these p t estimates are compared with those obtained on the underlying unit kidal assemblage upon which the iforas granulitic unit was thrust a p t t path during the pan african orogeny is proposed and discussed for both the iforas granulites and kidal assemblage

a comparison of microstructural and chemical patterns in garnet from the fleur de lys supergroup newfoundland this study uses compositional analyses of garnet porphyroblasts to test a previously published microstructure based model of garnet growth in the fleur de lys supergroup x ray maps reveal significant compositional anomalies within garnet including zoning reversals and steepened compositional gradients these anomalies occur at the margin of the proposed first stage of garnet growth g1 and coincide with truncations of inclusion trails and changes in the inclusion assemblage intervals of reversed composition zoning and steepened compositional gradients across this boundary are interpreted to represent a hiatus in garnet growth possibly accompanied by garnet consumption during which changes in the garnet forming reaction p t conditions and deformation kinematics occurred the junction of the proposed second and third stages of garnet growth g2 and g3 coincides with the transition between successive crenulation cleavages without substantial microstructural truncations or changes in the inclusion assemblage the g2 g3 boundary is generally marked by uninterrupted normal zoning with subtle compositional anomalies in some samples this boundary may in fact record continuous garnet growth or alternatively mark a relatively short intra orogenic pause in garnet growth with minimal affect on zoning patterns individual porphyroblasts with contrasting inclusion trail microstructures also have different zoning patterns and this supports the previous recognition of contrasting growth histories between individual porphyroblasts a combined structural metamorphic model is presented that integrates the timing of garnet growth and foliation development reaction history and the p t t path in the fleur de lys supergroup

polyphase metamorphism and the development of the main central thrust along a cross section through the lesser and higher himalayan units at the kishtwar window area north west india a polyphase barrovian type metamorphism has been delineated in relation to the development of the main central thrust mct in the metapelitic mineral assemblages three metamorphic phases have been distinguished a conditions up to amphibolite grade at moderate to high pressures alm rut ilm kya qtz characterize the m1 phase b pressure release and or temperature increase as a result of movement along the mct and the formation of gneiss domes in the higher himalaya as expressed by oriented n70 100 e fibrolite defines the m2 phase and c finally during uplift of the kishtwar window area a retrogressive m3 phase is characterized by the assemblage quartz muscovite chlorite both optically zoned and single stage garnets have been examined with the electron microprobe to determine their element partitioning normal zoning has been found in samples below the mct in the lesser himalaya indicating prograde growth during the m2 phase whereas tectonically above in the higher himalaya unit the garnets reveal double stage growth with a complex zoning pattern due to reaction partitioning during m1 and m2 and reverse zoning at their rims during the retrogressive m3 phase geothermometry on metapelites along a cross section through the mct zone and the higher himalaya imply distinct readjustments of garnet biotite exchange equilibria and indicate isothermal conditions 500 600 c throughout the section during the m3 retrogression pressure calculations gro an kya qtz and alm rut ilm kya qtz suggest a decrease in pressure towards the top of the section 6 7 5 to 4 5 5 kbar as corroborated by fibrolite replacing kyanite the spatially inverse metamorphism exposed within the lesser himalaya of the kishtwar window is regarded as a product of polyphase metamorphism combined with ongoing thrusting and shearing and is reflected by condensed m2 isograds around the kishtwar window

orogen parallel tectonic transport in the variscan belt of northeastern sardinia italy implications for the exhumation of medium pressure metamorphic rocks a transpressive crustal scale dextral shear zone is documented in the variscan basement of northeastern sardinia it indicates the presence of a shear deformation parallel to the belt overprinting previous d1 structures related to nappe stacking and top to the s and sw thrusting the l2 stretch ing lineation points to an orogen parallel stretching and to a general change in the tectonic transport from d1 to d2 phase d1 developed during initial frontal collision whereas the d2 deformation was characterized by dextral shearing during the increasing curvature of the ibero armorican arc transpressional deformation developed in a regime of decreasing pressure it caused telescoping of the barrovian isograds and the exhumation of the low to medium grade metamorphic rocks in this sector of the variscan belt exhumation is due to continuing compression with an increasing compo nent of horizontal displacement the overall change of the shortening direction in a large sector of an orogenic belt with the occurrence of increasing orogen parallel displacement may be regarded as a general mechanism affecting the exhumation of rocks and preventing the thickened collisional crust from undergoing a generalized gravitational collapse

progressive metamorphism in a crustal scale shear zone an example from the leon region north west brittany france this paper describes the progressive metamorphism and deformation of a series of metasediments le conquet schists and their higher grade equivalents which occur as tectonically emplaced screens within a sequence of foliated gneisses the gneiss de brest and gneiss de lesneven the sequence exhibits a steep south to north increase in metamorphic grade from garnet staurolite schist to sillimanite gneiss and sillimanite k feldspar migmatite the relationship of mineral growth to foliation development has been established for individual screens at least five phases of deformation d1 d5 are preserved analysis of porphyroblast inclusion trails is used to demonstrate sequential mineral growth during the successive development of orthogonal foliations s1 s4 porphyroblasts continued to grow during the subsequent development of c s mylonite fabrics and extensional crenulation cleavages which are genetically related to a series of high strain zones d5 mineral assemblages phase relations and mineral chemistry are consistent with porphyroblast growth being the result of continuous reactions microstructure porphyroblast relations are used to show that although mineral growth proceeded during continuous reactions these only operated episodically phase relations mineral chemistry and p t estimates are used to constrain p t trajectories and these are linked to the deformation histories within individual screens a comparison between the resulting pressure temperature deformation paths is used to demonstrate that the metamorphic peak occurred progressively later and at successively lower pressures with increasing metamorphic grade it is suggested that the early evolution of the belt is the result of crustal thickening by overthrusting the subsequent history is one of progressive heating and unroofing of the higher grade rocks in a dextral strike slip transtensional shear zone

seasonal variations of tropical intraseasonal oscillations a 20 25 day oscillation in the western pacific abstract spectral analysis within a movable time window is used to investigate the frequency and intensity of tropical oscillations with intraseasonal time scales surface and rawinsonde time series from several locations in the western pacific and indian oceans are used evidence is provided that the madden julian oscillation mjo in the indian ocean region shows a seasonal variation in its preferred period from 50 days during northern hemisphere winter to about 35 days during summer though this evidence is weak and stretches the limits of our ability to define a precise period for the oscillation in the western tropical pacific during the september december season a pronounced spectral peak with a central frequency between 20 and 25 days is observed this spectral peak appears to reveal an oscillation that is distinct from the mjo but may also result from coupling between the large scale motion and latent heat release on much smaller scales a relationship between the oscillation and the occurrence

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

empirical garnet biotite plagioclase quartz gbpq geobarometry in medium to high grade metapelites on the basis of the net transfer reactions among garnet biotite plagioclase and quartz for both mg and fe end member models the garnet biotite plagioclase quartz gbpq geobarometer was empirically calibrated under physical conditions of p 1 0 11 4 kbar and t 515 878 c based on the input garnet biotite temperatures and garnet aluminosilicate plagioclase quartz gasp pressures of 224 natural aluminosilicate bearing metapelitic samples collated from the literature the calibrations are internally consistent with the asymmetric quaternary solid solution model of garnet the symmetric quaternary solid solution model of biotite and the al avoidance ternary solid solution model of plagioclase in calibrating the garnet biotite geothermometer and the gasp geobarometer the resulting two gbpq barometer formulae reproduce the input gasp pressures well within 1 0 kbar mostly within 0 5 kbar for both aluminosilicate bearing and aluminosilicate absent metapelites the two gbpq barometry formulae yielded identical pressures whether the sample was included or not included in calibrating the gbpq barometry the random error of the gbpq barometry may be expected as 1 2 kbar the dp dt slopes of these two gbpq formulae are close to that of the gasp barometer in p t space applications of the gbpq barometry of aluminosilicate absent metapelites to the rocks within a thermal contact aureole or rocks within a limited geographical area without post metamorphic structural discontinuity show no obvious pressure change it may be concluded that the two gbpq barometry formulae derived in this study may be used as practical tools for metamorphic pelites under the conditions of 515 878 c and 1 0 11 4 kbar in the composition range of xgros 3 in garnet xan 17 in plagioclase and x bio 3 in biotite application of the gbpq barometer beyond the calibration range should be undertaken with caution

adiabatic westward drift of indian monsoon depressions a large fraction of the rain received by continental india is produced by cyclonic vortices with outer radii of about 1000 km that are contained within the larger scale south asian monsoon flow the more intense occurrences of these vortices are called monsoon depressions these consist of bottom heavy columns of relative vorticity that propagate to the northwest in time mean low level eastward flow previous studies have argued that this apparent upstream propagation is caused by dynamical lifting west of the vortex centre with the resulting ascent producing vortex stretching that shifts the vortex to the west here analysis of over 100 indian monsoon depressions is used to show that low level vortex stretching has a spatial structure inconsistent with the observed propagation and is balanced by other terms in the low level vorticity budget instead monsoon depressions are shown to consist of potential vorticity maxima that have peak amplitude in the middle troposphere and propagate westward by nonlinear horizontal adiabatic advection i e beta drift the precipitating ascent in monsoon depressions makes a more minor contribution to the total storm motion and primarily acts to maintain the upright structure of the vortex these results suggest a new view of indian monsoon depressions as potential vorticity columns that propagate primarily by adiabatic dynamics

eclogites and polyphase p t cycling in the caledonian uppermost allochthon in troms northern norway eclogites in the tromso area northern norway are intimately associated with meta supracrustals within the uppermost allochthon of the scandinavian caledonides the tromso nappe complex the whole sequence which includes pelitic to semipelitic schists and gneisses marbles and calc silicate rocks quartzofeldspathic gneisses metabasites and ultramafites has undergone three main deformational metamorphic events d1 m1 d2 m2 and d3 m3 detailed structural microtextural and mineral chemical studies have made it possible to construct separate p t paths for these three events chemically zoned late syn to post d1 garnets with inclusions of bt pl and qtz in ky bearing metapelites indicate a prograde evolution from 636 c 12 48 kbar to c 720 c 14 15 kbar this latter result is in agreement with grt cpx geothermometry and grt cpx pl qtz geobarometry on eclogites and trondhjemitic to dioritic gneisses maximum pressures at c 675 c probably reached 17 18 kbar based on cpx pl qtz inclusions in eclogitic garnets and grt ky pl qtz and jd ab qtz in trondhjemitic gneisses post d1 pre d2 decompressional breakdown of the high p assemblages indicates a substantial drop in pressure at this stage inclusions and chemical zoning in syn to post d2 garnets from metapelites record a second episode of prograde metamorphism from 552 c 7 95 kbar passing through a maximum pressure of 10 64 kbar at 644 c with final equilibration at c 665 c 9 10 kbar the corresponding apparently co facial paragenesis grt cpx pl qtz in metabasites yields c 635 c 8 10 kbar in the metapelites post d3 grt in apparent equilibrium with bt phe and pl yield c 630 c 9 kbar the d1 m1 and d2 m2 episodes are exclusively recorded in the tromso nappe complex and must thus pre date the emplacement of this allochthonous unit on top of the underlying lyngen nappe while the d3 m3 episode is common for the two units a previously published sm nd mineral isochron grt cpx am on a partly retrograded and recrystallized ecologite of 598 107 ma represents either the timing of formation of the eclogites or the post eclogite pre d2 decompression stage while a rb sr whole rock isochron of an apparently post d1 pre d2 granite of 433 11 ma is consistent with a k ar age of post d1 pre d2 amphiboles from a retrograded eclogite of 437 16 ma which most likely record cooling below the 475 500 c isotherm after the m3 metamorphism

guano derived δ 13 c based paleo hydroclimate record from gaura cu musca cave sw romania the 13c values of 23 unevenly spaced guano samples from a 17 cm long clay sediment profile in gaura cu musc cave gm in sw romania made it possible to preliminarily characterize the medieval warm period summer hydroclimate regime the beginning of the sequence ad 990 was rather wet for more than a century before becoming progressively drier after a brief yet distinct wet period around ad 1170 drier conditions with a possible shift from c3 to a mixed c3 dominated c4 type vegetation 2 lower 13c values prevailed for almost half a century before the climate became colder and wetter at the onset of the little ice age when bats left the cave the guano inferred wet and dry intervals from the gm cave are mirrored by changes in the color and amount of clay accumulated in the cave they also agree well with reconstructions based on pollen and charcoal from peat bogs and 13c and 18o on speleothems from other romanian sites overall these results indicate that the 13c of bat guano can provide a sensitive record of the short term coupling between local regional climate and the plant insect bat guano system

evaluating chemical equilibrium in metamorphic rocks using major element and sm nd isotopic age zoning in garnet townshend dam vermont usa abstract a quantitative assessment of metamorphic chemical equilibrium derived from correlation of spessartine content and garnet sm nd ages suggests that major element matrix equilibrium was maintained to a first order throughout a ca 40 cm wide rock sample during garnet growth however cm scale sm nd isotopic heterogeneity limits the sm nd age precision required to evaluate more subtle age differences within individual garnet crystals central wafers from 1 3 cm diameter garnet grains within a 1 21 104 cm3 block of pelitic schist were used to document concentric growth zoning of major elements with decreasing mn and ca and increasing fe and mg from cores to rims garnets also preserve growth zoning patterns for hree and mree and show evidence for resorption and partial recrystallization of the outermost rims similar garnet core compositions and identical garnet rim compositions for large like sized porphyroblasts throughout the sample suggest that garnet growth occurred at near equilibrium p t x conditions for major elements over the sample volume comparison of 28 rock sm nd isotope values from the sample indicates substantial cm scale heterogeneity which precludes meaningful use of local garnet rock isotope pairs for isochron age calculation therefore sm nd isotopic compositions of thirty eight concentric core to rim garnet segments from ten large 1 3 cm garnets and two small 1 4 mm bulk garnets with narrow ranges of mn content are paired with sixteen matrix whole rock sm nd isotopic compositions collected over the rock volume to define a range of isochron ages from 383 1 6 8 ma to 324 5 3 3 ma four of the garnets have anomalously young rims that likely result from post growth alteration chlorite quartz and xenotime haloes around garnet suggest that anomalously young garnet rim ages reflect post growth resorption recrystallization effects excluding these young rims yields a range of ages from 383 1 6 8 oldest core to 374 9 1 8 ma youngest rim sm nd age precisions 1 5 m y and high mswd result primarily from isotopic heterogeneity in the finely layered metasedimentary rock matrix however garnet cores with high mn n 7 mantles with intermediate mn n 14 and rims with low mn n 8 including the 2 smaller bulk garnet analyses define three distinct multi grain isochrons of 380 3 2 0 ma n 23 mswd 14 377 3 1 4 ma n 30 mswd 18 and 376 5 1 0 ma n 24 mswd 18 respectively yielding an average garnet growth duration of 3 8 2 2 m y these three composite mn age zones define a mn vs age relationship that reflects depletion of mn in the rock matrix as it is sequestered by growing garnet correlation of garnet major element compositions throughout the sample suggests that major element matrix equilibrium was generally maintained to a first order throughout the ca 4 m y duration of garnet growth

the significance of intergranular diffusion to the mechanisms and kinetics of porphyroblast crystallization the spatial disposition compositional zoning profiles and size distributions of garnet crystals in 11 specimens of pelitic schist from the picuris range of new mexico usa demonstrate that the kinetics of intergranular diffusion controlled the nucleation and growth mechanisms of porphyroblasts in these rocks an ordered disposition of garnet centers and a significant correlation between crystal radius and near neighbor distances manifest suppressed nucleation of new crystals in diffusionally depleted zones surrounding pre existing crystals compositional zoning profiles require diffusionally controlled growth the rate of which increases exponentially as temperature increases with time an acceleration factor for growth rate can be estimated from a comparison of compositional profiles for crystals of different sizes in each specimen crystal size distributions are interpreted as the result of nucleation rates that accelerate exponentially with increasing temperature early in the crystallization process but decline in the later stages because of suppression effects in the vicinity of earlier formed nuclei simulations of porphyroblast crystallization based upon thermally accelerated diffusionally influenced nucleation kinetics and diffusionally controlled growth kinetics quantitatively replicate textural relations in the rocks the simulations employ only two variable parameters which are evaluated by fitting of crystal size distributions both have physical significance the first is an acceleration factor for nucleation with a magnitude reflecting the prograde increase during the nucleation interval of the chemical affinity for the reaction in undepleted regions of the rock the second is a measure of the relative sizes of the porphyroblast and the diffusionally depleted zone surrounding it crystal size distributions for the picuris range garnets correspond very closely to those in the literature from a variety of other localities for garnet and other minerals the same kinetic model accounts quantitatively for crystal size distributions of porphyroblastic garnet phlogopite sphene and pyroxene in rocks from both regional and contact metamorphic occurrences these commonalities indicate that intergranular diffusion may be the dominant kinetic factor in the crystallization of porphyroblasts in a wide variety of metamorphic environments

fluid present melting of meta igneous rocks and the generation of leucogranites constraints from garnet major and trace element data lu hf whole rock garnet ages and whole rock nd sr hf o isotope data pan african high grade metamorphism in the proterozoic damara orogen namibia led to formation of garnet bearing leucosomes in potassic meta igneous gneisses producing a meta igneous migmatite in addition the migmatite gneiss mesosome plus leucosome was intruded by small scale leucogranitic melts with a high amount of accumulated biotite and garnet u pb zircon ages obtained on the mesosome and the leucosome indicate late proterozoic ca 850 ma concordia upper intercept ages which are interpreted as minimum ages of the precursor rock of the migmatite u pb monazite ages obtained on the leucogranite give a concordant age of 512 1 ma and two reversely discordant ages with pb 207 u 235 ages of 544 1 and 534 1 ma indicating the growth of monazite before or close to the age of high grade metamorphism in the damara orogen high precision lu hf garnet whole rock dating gave ages of 492 6 1 7 ma for the mesosome 497 6 1 7 ma for the leucosome and 494 0 1 7 ma for the garnet and biotite bearing leucogranite indicating that the growth of garnet postdates the growth of monazite during high grade metamorphism in addition it is suggested that melting and intrusion was coeval and occurred probably shortly after the main peak of metamorphism which occurred at c 512 1 ma p t estimates obtained by conventional thermobarometry c 690 720 degrees c and accessory mineral dissolution thermometry on the leucogranite c 730 degrees c suggest that partial melting occurred through limited fluid present melting of biotite via the reaction bt kfs pig qtz h2o double left right arrow grt melt outcrop evidence diffuse relationship between the gneiss domain and the leucosomes similar size of the leucosomes homogeneous distribution of leucosomes on the sample scale suggests that minor melt segregation had occurred whole rock sr nd hf and o isotope data of the mesosome indicate that it belongs to basement rocks from this area geochemical and isotope data obtained on the leucosomes argue for derivation by in situ melting of the mesosome both leucosome and leucogranite originated from the same source rock but the leucogranite represents an accumulated melt that was able to segregate and to intrude the gneiss domain the similar isotope features of the mesosome leucosome and leucogranite indicate a direct relationship for the gneiss and the melts chemical and mineral data favour a derivation of both types of melt through fluid present melting of isotopically and chemically comparable biotite plagioclase k feldspar quartz bearing gneisses c 2008 elsevier b v all rights reserved

a 2500 yr late holocene multi proxy record of vegetation and hydrologic changes from a cave guano clay sequence in sw romania we provide sedimentological geochemical mineral magnetic stable carbon isotope charcoal and pollen based evidence from a guano clay sequence in gaura cu musc cave sw romania from which we deduced that from 1230 bc to ad 1240 climate oscillated between wet and dry from 1230 bc to ad 1000 the climate was wetter than the present prompting flooding of the cave preventing bats from roosting and resulting in a slow rate of clay accumulation the second half of the medieval warm period mwp was generally drier the cave experienced occasional flash flooding in between which maternity bat roosts established in the cave one extremely wet event occurred around ad 1170 when fe mn and ti zr ratios show the highest values coincident with a substantial increase of sediment load in the underground stream the mineral magnetic characteristics for the second part of the mwp indicate the partial input of surface sourced sediments reflecting agricultural development and forest clearance in the area pollen and microcharcoal studies confirm that the overall vegetation cover and human land use have not changed much in this region since the medieval times

inverted metamorphic zonation and variscan thrust tectonics in the rouergue area massif central france p t t record from mineral to regional scale

propagation and maintenance mechanism of the tc submonthly wave pattern and tc feedback in the western north pacific abstractpropagation and maintenance mechanisms of the tropical cyclone submonthly wave pattern in the western north pacific are explored the wave pattern exhibited an equivalent barotropic structure with maximum vorticity and kinetic energy in the lower troposphere and propagated northwestward in the philippine sea in the intraseasonal oscillation iso westerly phase and north northeastward near the east asian coast in the easterly phase the mean flow advection played a dominant role in the propagation in both phases barotropic energy conversion is the dominant process in maintaining the kinetic energy of the pattern the wave pattern tended to occur in the confluent zone between the monsoon trough and the anticyclonic ridge where the kinetic energy could be efficiently extracted from the westerly mean flow associated with the monsoon trough the individual circulation circuit embedded in the pattern was oriented northeast southwest east west to have optimal growth and propagation during the iso wes

trace element mapping by la icp ms assessing geochemical mobility in garnet a persistent problem in the study of garnet geochemistry is that the consideration of major elements alone excludes a wealth of information preserved by trace elements particularly the rare earth elements rees this is despite the fact that trace elements are generally less vulnerable to diffusive resetting and are sensitive to a broader spectrum of geochemical interactions involving the entire mineral assemblage including the growth and or dissolution of accessory minerals we outline a technique for the routine acquisition of high resolution 2d trace element maps by la icp ms and introduce an extension of the software package xmaptools for rapid processing of la icp ms data to visualise and interpret compositional zoning patterns these methods form the basis for investigating the mechanisms controlling geochemical mobility in garnet which are argued to be largely dependent on the interplay between element fractionation mineral reactions and partitioning and the length scales of intergranular transport samples from the peaked hill shear zone reynolds range central australia exhibit contrasting trace element distributions that can be linked to a detailed sequence of growth and dissolution events trace element mapping is thus employed to place garnet evolution in a specific paragenetic context and derive absolute age information by integration with existing u pb monazite and sm nd garnet geochronology ultimately the remarkable preservation of original growth zoning and its subtle modification by subsequent re equilibration is used to see through multiple superimposed events thereby revealing a previously obscure petrological and temporal record of metamorphism metasomatism and deformation

trace element zoning in pelitic garnet of the black hills south dakota trace element ree cr ti y y and zr analysis of garnet from the garnet staurolite and lower sillimanite zones of an aluminous schist of the black hills south dakota indicates that ree zoning varies as a function of grade garnet zone garnet has high concentrations of rees cr ti y y and zr in the cores and low concentrations in the rims profiles of heavy rees contain inflections between the cores and rims which are approximately symmetric about the cores staurolite zone garnet contains cores enriched with y and heavy rees which decrease toward the rim and increase again at the rim edges but to lower concentrations than in the cores cr y ti zr and light ree zoning is less pronounced than heavy ree zoning and is less symmetric about the garnet cores almandine rich garnet of the lower sillimanite zone displays no major element zonation trace element ti cr y and zr concentrations are minimal and the zoning is irregular and not symmetric about the garnet cores garnet from all three zones has core to rim fe fe mg profiles that suggestgarnet growth was uninterrupted with respect to major element components and that mn zoning formed by a fractionation process analysis of trace element zoning in this garnet reveals that the major element zoning was relatively unaffected by volume diffusion reequilibration trace element zonation of all samples of garnet is best explained by a fractionation mechanism in conjunction with limited intergranular diffusion and changing partition coefficients during garnet growth heavy ree partitioning is especially dependent on the major element composition of garnet this research complements previous research by others on the use of trace elements as metamorphic petrogenetic indicators which demonstrated the importance of bulk rock composition and phase assemblage on trace element partitioning

recalibration of the garnet muscovite gm geothermometer and the garnet muscovite plagioclase quartz gmpq geobarometer for metapelitic assemblages the garnet muscovite gm geothermometer and the garnet muscovite plagioclase quartz gmpq geobarometer have been simultaneously calibrated under conditions of t 1 4 450 760 c and p 1 4 0 8 11 1 kbar using a large number of metapelitic samples in the compositional ranges x grt fe 1 4 0 53 0 81 x grt mg 1 4 0 05 0 24 x grt ca 1 4 0 03 0 23 in garnet x pl ca 1 4 0 17 0 74 in plagioclase and fe 1 4 0 04 0 16 mg 1 4 0 04 0 13 al 1 4 1 74 1 96 in muscovite on the basis of 11 oxygens the resulting gm thermometer yielded similar temperature estimates mostly within 50 c to that of the garnet biotite thermometer and successfully discerned the expected systematic temperature change of prograde sequences thermal contact zones and an inverted metamorphic zone the resulting gmpq barometer yielded similar pressure estimates mostly within 1 0 kbar to the garnet aluminum silicate plagioclase quartz gasp barometer and placed the aluminosilicate bearing samples in the appropriate aluminosilicate stability fields application of the gmpq barometer to thermal contact aureoles or rocks within limited geographical areas confirmed the expected constant pressures that should exist in these settings the random errors of the gm thermometer and the gmpq barometer are estimated to be 16 c and 1 5 kbar respectively when biotite or aluminosilicate is absent in metapelites metamorphic p t conditions may be determined by simultaneously applying the gm thermometer and the gmpq barometer

a climatology of central american gyres abstractcentral american gyres cags are large closed cyclonic circulations that occur during the rainy season may november which can yield exceptional rainfall leading to catastrophic flooding and large societal impacts a reanalysis based climatology of cags is developed from an algorithm that distinguishes cag cases from other systems this algorithm identified cag cases based on circulation intensity a broad radius of maximum winds and the existence of closed earth relative cyclonic flow based on these criteria 47 cag cases were identified from 1980 to 2010 featuring a bimodal distribution of cases with maxima in may june and september november cag cases are composited into two categories based on their upper tropospheric pv structure nonbaroclinic cags are more common n 42 and characterized by an upper tropospheric anticyclone while baroclinic cags are less common n 5 and characterized by an upper tropospheric trough whereas a nonbaroclinic cag has anomalous moisture and preci

valid garnet biotite gb geothermometry and garnet aluminum silicate plagioclase quartz gasp geobarometry in metapelitic rocks abstract at present there are many calibrations of both the garnet biotite gb thermometer and the garnet aluminum silicate plagioclase quartz gasp barometer that may confuse geologists in choosing a reliable thermometer and or barometer to test the accuracy of the gb thermometers we have applied the various gb thermometers to reproduce the experimental data and data from natural metapelitic rocks of various prograde sequences inverted metamorphic zones and thermal contact aureoles we have concluded that the four gb thermometers perchuk l l lavrent eva i v 1983 experimental investigation of exchange equilibria in the system cordierite garnet biotite in saxena s k ed kinetics and equilibrium in mineral reactions springer verlag new york berlin heidelberg pp 199 239 kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 model 6av kaneko y miyano t 2004 recalibration of mutually consistent garnet biotite and garnet cordierite geothermometers lithos 73 255 269 model b are the most valid and reliable of this kind of thermometer more specifically we prefer the holdaway holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 and the kleemann and reinhardt kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 calibrations due to their small errors in reproducing the experimental temperatures and good accuracy in successfully discerning the systematic temperature changes of the different sequences in addition after applying the gasp barometer to 335 natural metapelitic samples containing one kind of aluminosilicate and 33 natural metapelitic samples containing two kinds of aluminosilicate as well as to rocks in limited geographic areas and thermal contact aureoles we propose that the calibrations of holdaway holdaway m j 2001 recalibration of the gasp geobarometer in light of recent garnet and plagioclase activity models and versions of the garnet biotite geothermometer american mineralogist 86 1117 1129 and newton and haselton newton r c haselton h t 1981 thermodynamics of the garnet plagioclase al2sio5 quartz geobarometer in newton r c navrotsky a wood b j eds thermodynamics of minerals and melts new york springer verlag 131 147 based on kleemann and reinhardt s kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 thermometer are the most valid gasp barometers other gb thermometers and gasp barometers are not recommended

empirical garnet muscovite geothermometry in metapelites abstract two empirical garnet muscovite geothermometers assuming no ferric iron model a and 50 ferric iron model b in muscovite respectively were calibrated under the physical conditions of p 3 0 14 0 kbar and t 530 700 c the input temperatures and pressures were determined by simultaneously applying the garnet biotite thermometer am mineral 85 2000 881 and the gasp geobarometer am mineral 86 2001 1117 to natural metapelites to confirm internal thermodynamic consistency holdaway s am mineral 85 2000 881 garnet mixing properties were adopted muscovite was treated as a symmetric fe mg al vi ternary solid solution and its margules parameters were derived in this work the resulting two formulae reproduced the input garnet biotite temperatures well within 50 c and gave identical results for a great body of natural samples moreover they successfully distinguished the systematic changes of temperatures of different grade rocks from a prograde sequence inverted metamorphic zone and thermal contact aureole pressure estimation has almost no effect on the two formalisms of the garnet muscovite geothermometer assuming analytical error of 5 for the relevant components of both garnet and muscovite the total random uncertainty of the two formulations will generally be within 5 c the two thermometers derived in this work may be used as practical tools to metamorphic pelites under the conditions of 480 to 700 c low to high pressure in the composition ranges xalm 0 51 0 82 xpyr 0 04 0 22 and xgros 0 03 0 24 in garnet and fe tot 0 03 0 17 and mg 0 04 0 14 atoms p f u in muscovite

stable isotope composition of cave guano from eastern borneo reveals tropical environments over the past 15 000 cal yr bp abstract insular southeast asia is a key driver for global atmospheric and oceanic circulation is a hotspot for biodiversity and conservation and is likely to have played a unique and important role in early human dispersals despite this partially due to its vast size and remote tropical location very few continuous palaeoenvironmental records exist especially in eastern borneo therefore we investigated 13 c and 15 n values and geochemistry of two cave guano deposits to reconstruct palaeoenvironments in eastern borneo firstly a profile was recovered from gomantong caves sabah reflecting a continuous deposit over 15 cal kyr bp secondly a profile was recovered from bau bau cave east kalimantan that ranged from 15 5 cal kyr bp the geochemical signature of each deposit confirmed the material to be ancient guano 13 c values revealed that a continuous dense rainforest persisted over at least the last 15 cal kyr bp around the gomantong site that was relatively insensitive to regional climate change by contrast 13 c values at bau bau indicate that although rainforest remained dominant in the record a significant drying occurred between 7 7 and 6 3 cal kyr bp with up to 25 grasses present although most regional models suggest that sea level rise and increased holocene insolation led to an increase in monsoonal moisture we find some evidence of more regional variability and that a reduction in monsoonal precipitation could have occurred however we cannot discount the implementation of an anthropogenic fire regime that opened the canopy allowing more grasses to occur

a high resolution temporal record of environmental changes in the eastern caribbean guadeloupe from 40 to 10 ka bp abstract in neotropical regions fossil bat guano accumulated over time as laminated layers in caves hence providing a high resolution temporal record of terrestrial environmental changes additionally cave settings have the property to preserve such organic sediments from processes triggered by winds deflation abrasion and sandblasting and intense rainfall leaching away this study reports both stable carbon and nitrogen isotope compositions of frugivorous bat guano deposited in a well preserved stratigraphic succession of blanchard cave on marie galante guadeloupe these isotopic data are discussed with regard to climate changes and its specific impact on eastern caribbean vegetation during the late pleistocene from 40 to 10 ka cal bp guano 13 c values are higher than modern ones suggesting noticeable vegetation changes this provides also evidence for overall drier environmental conditions during the pleistocene compared to today meanwhile within this generally drier climate shifts between wetter and drier conditions can be observed large temporal amplitudes in both 13 c and 15 n variations reaching up to 5 9 and 16 8 respectively also indicate these oceanic tropical environments have been highly sensitive to regional or global climatic forcing stable isotope compositions of bat guano deposited from 40 to 35 ka bp the last glacial maximum and the younger dryas reveal relatively wet environmental conditions whereas at least from the end of the heinrich event 1 and the bolling period the region experienced drier environmental conditions nevertheless when considering uncertainties in the model age the isotopic record of blanchard cave show relatively similar variations with known proxy records from the northern south america and central america suggesting thus that the blanchard cave record is a robust proxy of past itcz migration teleconnections through global atmospheric pattern suggest that islands of the eastern caribbean basin could be also under the influence of a bipolar temperature gradients that impact the mean location of the itcz with a southern hemisphere imprint during the glacial period and a more significant role of northern hemisphere during the last deglaciation

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

assessing detrital garnet chemical composition as a quantitative provenance tool a multivariate statistical approach abstract chemical analysis of detrital garnet is a widely utilized quantitative tool for determining the provenance of sediments the goal of this study is to investigate the ability of the compositions of detrital garnet to provide a direct linkage to the specific source rocks from which the garnet was derived to achieve this goal we analyzed detrital garnet isolated from alluvial samples collected from the french broad river and several of its tributaries a watershed that drains portions of the multiply deformed southern appalachian orogen usa to test whether potential linkages between detrital and potential source rock garnet could be achieved garnet crystals were chemically characterized from a wide variety of lithologies that crop out in the french broad watershed and thus are the most likely local sources of detrital garnet mahalanobis distances measured on canonical discriminant functions successfully differentiated garnet compositions among the 18 analyzed source rocks these metrics were then applied to 2 300 detrital garnet compositions to link each grain to its potential source rock approximately 94 of the detrital garnet crystals were linked to their potential source regions thus only 6 of the detrital crystals were treated as unclassified we interpret the unclassified high ca garnets to have been derived from minor sub map scale lenses and boudins of calc silicate or skarns from exposed ocoee or ashe metaclastic units within the french broad river watershed the unclassified high mn detrital garnet grains are interpreted to have been derived from the various felsic granitiods and pegmatites that intrude the region of study

geothermobarometry and development of inverted metamorphism in the darjeeling sikkim region of the eastern himalayan abstract the darjeeling sikkim region provides a classic example of inverted himalayan metamorphism the different parageneses of pelitic rocks containing chlorite biotite garnet staurolite kyanite sillimanite plagioclase and k feldspar are documented by a variety of textures resulting from continuous and discontinuous reactions in the different zones microprobe data of coexisting minerals show that xmg varies in the order garnet staurolite biotite chlorite white mica is a solid solution between muscovite and phengite garnet is mostly almandine rich and shows normal growth zoning in the lower part of the main central thrust mct zone and reverse zoning in the upper part of the zone chemographical relations and inferred reactions for different zones are portrayed in afm space in the low grade zones oriented chlorites and micas and rolled garnets grew syntectonically and were succeeded by cross cutting chlorites and micas and garnet rims in the upper zones sillimanite kyanite and staurolite crystallized during a static inter kinematic phase p t contitions of metamorphism estimated through different models of geothermobarometry are estimated to have been 580 c for the garnet zone to a maximum of 770 c for the sillimanite zone the preferred values of pressure range from 5 0 kbar to 7 7 kbar models to explain the inverted metamorphism include overthrusting of a hot high himalayan slab along a c 5 km wide ductile mct zone and the syn or post metamorphic folding of isograds

mixed rossby gravity waves and western pacific tropical cyclogenesis part i synoptic evolution abstract a large amplitude mixed rossby gravity wave packet is identified in the western pacific using 6 10 day bandpass filtered winds individual disturbances of 2300 3000 km wavelength propagated westward as the packet moved slowly eastward the packet first appeared and subsequently amplified within a region of active convection associated with the madden julian oscillation mjo which was isolated by low pass filtered outgoing longwave radiation the packet lasted about 5 weeks then rapidly dispersed as the active mjo moved away from it to the east west of 150 e individual disturbances within the packet turned northwestward away from the equator indicating an apparent transition from mixed rossby gravity waves to off equatorial tropical depression td type disturbances cyclones filled with cloud and anticyclones cleared during the transition nevertheless convective structure consistent with mixed rossby gravity waves remained outside the circulation centers and three tropical cyclones for

tropical cyclogenesis within an equatorial rossby wave packet a packet of equatorial rossby er waves that lasted 2 5 months is identified in the lower troposphere of the northwest pacific waves within the packet had a period of 22 days a wavelength of 3600 km a westward phase speed of 1 9 m s 1 and a near zero group speed the wave properties followed the er wave dispersion relation with an equivalent depth near 25 m the packet was associated with the development of at least 8 of the 13 tropical cyclones that formed during the period a composite was constructed around the genesis locations tropical cyclones formed east of the center of the composite er wave low in a region of strong convection and a separate 850 hpa vorticity maximum the background flow during the life of the packet was characterized by 850 hpa zonal wind convergence and easterly vertical wind shear wave amplitude peaked at the west end of the convergent region suggesting that wave accumulation played a significant role in the growth of the packet the presence of easterly vertical wind shear provided an environment that trapped energy in the lower troposphere each of these processes increases wave amplitude and thus the likelihood of tropical cyclone formation within the waves the initial low pressure region within the wave packet met lander s definition of a monsoon gyre it developed to the west of persistent localized convection that followed the penetration of an uppertropospheric trough into the subtropics it is argued that the monsoon gyre represented the initial er wave low within the packet

granulite facies metamorphism and retrogressive evolution of the monts du lyonnais metabasites massif central france abstract garnet bearing pyriclasites have been found within the monts du lyonnais formation near st andrela cote in the eastern part of the massif central the rocks appear to have differentiated from a tholeiitic magma of continental affinity and they may be genetically related to quartzofeldspathic granulites considered to be the products of crustal melts by means of electron microprobe analyses the consistent pressure and temperature estimates based essentially on pyroxene garnet equilibria show that the peak of metamorphism was at about 860 c and 10 kbar furthermore this study tends to confirm the affiliation of monts du lyonnais granulites to the early variscan granulite eclogite facies metamorphism which extends from bohemia to spain through central europe this event may be expected in the vicinity of an ancient suture zone where a continental collision followed a subduction

a comparative study of diffusion profiles in himalayan and dalradian garnets constraints on diffusion data and the relative duration of the metamorphic events cation diffusion rates at 690 30 c have been calculated by inverse modelling of observed manganese mn zonation profiles in 40 garnets from two kyanite bearing metapelite samples from the high himalayan crystalline series zanskar northwest india knowledge of the initial growth profile of mn in garnet is a pre requisite for this technique following previous workers we model mn partitioning into growing garnet in terms of a rayleigh fractionation process and demonstrate that the mngarnet whole rock partition coefficient is 60 100 three dimensional zonation profiles were obtained by successively grinding and polishing 1 cm slabs of each sample at 0 1 0 2 mm intervals and analysing the garnets at each stage thus ensuring that core sections were measured the diffusion model assumes that garnet has a spherical geometry and behaves as a closed system and simulates diffusive modification of the hypothetical mn rayleigh growth profile for each garnet the derived measure of the time integrated diffusion history for each garnet is then combined with radiometric and field relation constraints for the duration of the himalayan metamorphic event to calculate cation diffusion rates the average cation interdiffusion rate calculated for garnets in the two samples examined is 6 3 2 10 23 m2s 1 this interdiffusion rate pertains to a temperature of 690 30 c which is 0 97 t peak the peak temperature conditions experienced by the samples estimated using standard thermobarometric techniques garnet compositions are py2 17alm65 77gro6 16sp1 17 these new diffusion data are consistent with and more precise than existing high temperature 1000 c experimentally determined diffusion data although some uncertainties remain difficult to constrain qualitative comparison between diffusively modified mn growth profiles in garnets from the scottish dalradian and the himalayan garnets suggests that the duration of metamorphism affecting the dalradian garnets was 10 20 times longer than that endured by the himalayan garnets

geochronology and geological evolution of metamorphic rocks in the field islands area east antarctica detailed geochronological structural and petrological studies reveal that the geological evolution of the field islands area east antarctica was substantially similar to that of the adjacent archaean napier complex though with notable differences in late and post archaean times these differences reflect the area s proximity to the proterozoic rayner complex and consequent vulnerability to tectonic process involved in the formation of the latter distinctive structural features of the field islands are 1 consistent development of a discordant pervasive s3 axial plane foliation 2 re orientation of s3 axial planes to approximate to the subsequent e w tectonic trend of the nearby rayner complex 3 selective retrogression by a post d3 static thermal overprint and 4 relatively common development of retrogressive e w trending mylonitic shear zones peak metamorphic conditions in excess of 800 c at 900 100 m pa 9 kbar were attained at one locality following but probably close to the time of d2 folding d3 took place in late archaean times when metamorphic temperatures were about 650 c and pressures were about 600 mpa 6 kbar later temperatures of 600 50 c and pressures of 700 mpa 7kbar were attained in an amphibolite facies event presumably associated with the widespread granulite to amphibolite facies metamorphism and intense deformation involved in the formation of the rayner complex at about 1100 ma the area was subsequently subjected to near isothermal uplift rb sr isotopic data indicate that the pervasive d3 fabric developed at about 2400 2500 ma and this age can be further refined to 2456 8 5 ma by concordant zircon analyses from a syn d3 pegmatite all zircons were affected by only minor 7 10 pb loss and or new zircon growth during the rayner event at about 1100ma thus the 450 850 g gu concentrations of these zircons were too low to cause sufficient lattice damage over the 1350 ma from 2450 ma for excessive pb to be lost during the 1100 ma event the emplacement of pegmatite at 522 10 ma substantially changed the rb sr systematics of the only analysed rock that developed a penetrative fabric during the 1100 ma event monazite in this pegmatite contains an inherited pb component which probably resides in small opaque inclusions a good correlation is found between rb sr total rock ages and rock fabric u pb zircon intercepts with concordia also mostly correspond to known events however in one example a near perfect alignment of zircon analyses probably developed by mixing of unrelated components produced concordia intercepts that appear to have no direct geochronological significance

a garnet population in yellowknife schist canada data are presented on a garnet population in a specimen of garnet biotite plagioclase quartz schist from the cordierite zone of an archaean thermal dome in the southern slave province of the canadian shield garnet crystals are bounded by planar dodecahedral faces and by trapezohedral faces which on the 10 m scale are corrugated crystal distribution as revealed by dissection of a small cubic volume of rock is random the size distribution is normal with a mean diameter of 0 81 mm and a standard deviation of 0 32 mm in the largest crystal of the population mean radius 0 83 mm mn 100 mn fe mg mn ca decreases from 14 5 at the centre to 7 5 and then increases in the outer margin to 8 5 fe increases continuously from 67 at the centre to 77 at the surface mg increases from 12 5 to 13 5 and then falls sharply to 11 ca remains unchanged at 4 0 and then drops to 3 3 progressively smaller crystals have progressively lower mn and higher fe concentrations at their centres while all crystals have the same margin composition growth vectors extending from given concentration contours to crystal surfaces are of equal length regardless of the size of the crystal in which the vector is located a garnet forming model is presented in which reaction was initiated by a rise in temperature nucleation sites were randomly selected the nucleation rate increased with time and then declined crystal faces advanced at a constant linear rate which implies an increase in volume proportional to surface area initially the composition of garnet deposited on crystal surfaces was determined by van laar equations of equilibrium which demanded the withdrawal of mn and fe from within chlorite crystals this transfer reaction was then accompanied by an ion exchange reaction which moved mn and fe to garnet surfaces from biotite in exchange for mg the exchange reaction provides an explanation for the high overall concentration of mn and fe in garnet and for the observed mn and mg reversals in the margins of crystals the increase of garnet volume in the garnet population is found to be parabolic i e v 5

effects of low frequency wave interactions on intraseasonal oscillations abstract intraseasonal oscillations isos control much of the large scale variability of convection in the tropics on time scales of about 15 100 days these disturbances are often thought to be dominated by eastward propagating modes especially during austral summer but disturbances that propagate westward are also important this work demonstrates by means of a multiple linear regression model and a brief case study that eastward and westward moving intraseasonal modes often cooperatively interact with one another to produce many of the characteristics of the observed southern hemisphere summer iso these interactions appear to be facilitated by topography and or by the convective anomalies that are cooperatively induced by the eastward and the westward moving components of the oscillations these interactions do not occur during every period of intraseasonal convective activity but they do commonly occur during periods of high amplitude convective anomalies this analysis shows that eastward and

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

metamorphism of high grade gneisses from the moldanubian zone austria with particular reference to the garnets gneisses from the southern part of the bunte series have been studied in order to determine their metamorphic evolution they all belong to the paragenetic facies type bt sil kfs qtz grt the garnets of these rocks generally exhibit typical features of garnets from this high temperature facies type diffusional homogenization throughout the bulk of the garnet and retrograde zoning patterns at the outer rim ca and mn richer relict cores in some garnets are evidence of the early metamorphism these cores are enveloped by the high temperature homogenized garnet the element distribution curves of the relict cores show evidence of partial element specific modification by volume diffusion paragenetic and textural relations as well as temperature and pressure calculations suggest the following conditions of the main metamorphism 700 770 c at 7 9 kbar and ph2o ptot despite the uncertainty due to the incomplete equilibration among garnet rims and other matrix minerals an attempt is made to model the cooling and uplift history of the rocks using textural paragenetic chemical and literature data zusammenfassung gneise aus dem sudlichen teil der bunten serie wurden im hinblick auf ihre metamorphoseentwicklung untersucht sie gehoren allgemein dem faziestyp bt sil kfs qtz grt an die granate weisen alle fur diesen faziestyp charakteristischen merkmale auf weitgeheride homogenisierung durch diffusion und abkuhlungserscheinungen am au eren rand ca und mn reiche reliktische kerne mancher granate weisen auf ein alteres ereignis hin diese relikte werden im homogenisierten granat hoherer bildungstem peratur eingeschlossen ihre element verteilungskurven sind teilweise durch die intrakristalline diffusion dem kationenradius entsprechend abgeflacht paragenetische beziehungen und t und p berechnungen ergeben folgende bedingungen fur die hauptmetamorphose 700 770 c bei 7 9 kbar und ph2optot trotz der unsicherheit die auf eine unvoll standige einstellung des gleichgewichtes zwischen granatrandern und den ubrigen matrixmineralen zuruckzufuhren ist wurde ver sucht ein modell uber die abkuhlungs und hebungsgeschichte der untersuchten gesteine zu erstelleu

effect of diet anthropogenic activity and climate on δ 15 n values of cave bat guano abstract few studies have attributed 15n values of guano to a factor other than diet a 15n record obtained from a 1 5 m core of bat guano deposit from zidit cave western romania provides a record of anthropogenic and climatic influence on the regional nitrogen pool nitrogen content is nearly constant n 9 for over 1 m of the core indicating limited diagenesis the 15n and 13c time series are compared and the 15n is also interpreted in light of previously published pollen assemblage from the same core using these comparisons the influence of anthropogenic activity and water availability is interpreted although some 15n variation can be attributed to major changes in anthropogenic activities additional variation implies an alternative control the correlation between 15n and 13c values is significant p

cluster analysis of typhoon tracks part i general properties a new probabilistic clustering technique based on a regression mixture model is used to describe tropical cyclone trajectories in the western north pacific each component of the mixture model consists of a quadratic regression curve of cyclone position against time the best track 1950 2002 dataset is described by seven distinct clusters these clusters are then analyzed in terms of genesis location trajectory landfall intensity and seasonality both genesis location and trajectory play important roles in defining the clusters several distinct types of straight moving as well as recurving trajectories are identified thus enriching this main distinction found in previous studies intensity and seasonality of cyclones though not used by the clustering algorithm are both highly stratified from cluster to cluster three straight moving trajectory types have very small withincluster spread while the recurving types are more diffuse tropical cyclone landfalls over east and southeast asia are found to be strongly cluster dependent both in terms of frequency and region of impact the relationships of each cluster type with the large scale circulation sea surface temperatures and the phase of the el nino southern oscillation are studied in a companion paper

trace element fractionation during high grade metamorphism and crustal melting constraints from ion microprobe data of metapelitic migmatitic and igneous garnets and implications for sm nd garnet chronology abstract rare earth element ree and other trace element y sr ti cr v na abundances in garnet from a garnet bearing metapelite a pelitic migmatite a syn tectonic granite and a post tectonic leucogranite were measured by secondary ion mass spectrometry sims in order to identify the effective variables on the trace element distribution between garnet and the host rock garnet from the garnet bearing metapelite the pelitic migmatite and the syn tectonic granite is zoned with respect to ree the cores are enriched by a factor of 2 3 relative to the rims for the garnets from the garnet bearing metapelite equilibrium distribution following a simple rayleigh fractionation is responsible for the decreasing concentrations in ree from core to rim garnet from the pelitic migmatite shows a more complex trace element pattern following distinct enrichment and depletion patterns for ti v cr and ree from core to rim these features suggest disequilibrium between garnet and the associated melt in which the enrichment of trace elements probably correspond to a period of open system behaviour in these rocks at a time when the garnet originally nucleated in the metamorphic environment was incorporated into the melt the garnet from the syn tectonic granite shows stepwise decreasing concentrations in ree from core to rim a ree rich core can be distinguished from a broad ree depleted rim notably from core to rim an inflection of the yb er and yb dy ratios is visible whereas the decrease of hree abundance in the core region of the garnet from the syn tectonic granite may arise from equilibrium partitioning during garnet growth the inflection can be interpreted as a result of partial melting garnet cores with high yb er and yb dy 1 nucleated in the metamorphic environment without the presence of a melt whereas the rims with lower yb er and yb dy

empirical garnet muscovite plagioclase quartz geobarometry in medium to high grade metapelites abstract based on the net transfer reactions among garnet muscovite plagioclase and quartz for both mg and fe end member models the garnet muscovite plagioclase quartz gmpq geobarometry was empirically calibrated under the physical conditions of p 1 0 11 4 kbar and t 505 745 c for 128 natural metapelitic rock samples collected from the literature the input temperatures and pressures were simultaneously determined by the garnet biotite thermometer and the garnet aluminosilicate plagioclase quartz gasp barometer the gmpq calibrations adopted the same asymmetric quaternary solid solution model of garnet and the same al avoidance asymmetric ternary model of plagioclase as the calibrations of the garnet biotite geothermometer and the gasp geobarometer a symmetric fe mg al vi ternary solid solution model of muscovite was adopted and the margules parameters of muscovite were obtained through regression the mg and fe model reactions along with the assumption of whether the ferric iron content in muscovite is 0 or 50 resulted in four gmpq barometry formulae the gmpq barometry formulae reproduce the input gasp pressures well within 1 0 kbar mostly within 0 5 kbar for both aluminosilicate bearing and aluminosilicate absent samples the gmpq barometry formulae yield identical pressures for every sample whether the sample was included or not in calibrating the barometers for each of the mg or fe model reaction the formulae gave identical pressures within 40 bars the random error of the gmpq barometry may be expected as 1 4 kbar the d p d t slopes of these gmpq formulae are close to that of the gasp barometer in the p t space applications of the gmpq barometry to aluminosilicate absent metapelites within a limited geographic area without postmetamorphic structural discontinuity generally show no pressure difference it may be concluded that the gmpq barometry formulae derived in this work may be used as practical tools for metamorphic pelites under the conditions of 505 745 c and 1 11 4 kbar in the composition range of x gros 3 in garnet and x an 17 in plagioclase

the alpine geodynamic evolution of penninic nappes in the eastern central alps the eastern central alps consist of several pennine nappes with different tectonometamorphic histories the tectonically uppermost units oceanic avers bundnerschiefer continental suretta and tambo nappes oceanic vals bundnerschiefer show cretaceous early tertiary w directed thrusting with associated blueschist facies metamorphism related to subduction of the pennine units beneath the austroalpine continental crust this event caused eclogite facies metamorphism in the underlying continental adula nappe the gross effect was crustal thickening the tectonically lower continental simano nappe is devoid of any imprint from this event in the course of continent continent collision high t metamorphism and n directed movements occurred both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions crustal thinning commenced during the regional temperature peak a final phase is related to differential uplift under retrograde p t conditions further thinning of the crust was accommodated by e to ne directed extensional deformation

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

calibration of a ti in muscovite geothermometer for ilmenite and al2sio5 bearing metapelites abstract the ti in muscovite geothermometer was empirically calibrated as ln t oc 7 258 0 289 ln ti 0 158 mg fe mg 0 031 ln p kbar using ilmenite and al2sio5 bearing assemblages in metapelites under p t conditions of 450 800 c and 0 1 1 4 gpa the calibration was conducted for muscovites containing ti 0 01 0 07 fe 0 03 0 16 mg 0 01 0 32 and mg fe mg 0 05 0 73 respectively on the basis of 11 oxygen per formula unit such compositional range covers more than 90 natural muscovites and the random error of this thermometer is estimated to be of 65 c the geothermometer was validated against a set of independently determined temperature conditions between different degrees in samples from different prograde inverted and contact metamorphic terranes application of this thermometer beyond the calibration conditions is not encouraged

a global climatology of monsoon low pressure systems the first global climatology of monsoon low pressure systems is presented here based on the era interim reanalysis low pressure systems are classified into three intensity categories and particular focus is given to systems in the category corresponding to a traditional definition of monsoon depressions vortex tracks are identified using an automated algorithm applied to the distributions of 850 hpa relative vorticity sea level pressure and surface wind speed for 1979 2012 roughly two to three times as many monsoon low pressure systems form in the northern hemisphere as in the southern hemisphere during local summer the frequency of genesis typically peaks in local summer but low pressure systems form throughout the year in every monsoon region interannual variability is weak with standard deviations of summer counts typically being below 10 of the long term summer mean regional composites reveal that monsoon depressions in india the western pacific and northern australia share a common structure consisting of a warm over cold core and a top heavy column of potential vorticity that extends from the surface to the upper troposphere a separate class of monsoon low pressure systems develops over dry regions of west africa and western australia with a shallow composite structure having a warm core in the lower troposphere and cyclonic potential vorticity confined to a thin near surface layer low pressure systems in nearly all monsoon regions are estimated to account for a large fraction from about 40 to more than 80 of summer precipitation on the poleward edge of the climatological mean precipitation maxima

empirical evaluation of solution models for pelitic minerals and their application to thermobarometry one of the major sources of uncertainty for thermobarometry in pelitic rocks is the inability of solution models to represent accurately the non ideal behavior of important pelitic minerals in particular garnet biotite and plagioclase in recent years a large number of different solution models have been proposed for these phases the purpose here is to test the effects on the overall uncertainty of the most commonly used solution models using the garnet muscovite annite plagioclase gmap barometer and the empirical calibration technique the gmap reaction has been empirically calibrated several times with varying results due in large part to the choice of solution models the method s dependence on the choice of solution model makes it an excellent was in which to address the quality of specific models by repeating the calibration exercise for different combinations of solution models it is possible to determine which set of solution models results in the lowest uncertainties using a sample set of 72 published electron microprobe analyses of pelitic rocks containing the assemblage garnet muscovite biotite plagioclase aluminum silicate quartz as an independent test of the suitability of solution models we compare the fit of the sample set to the kyanite sillimanite equilibrium curve obtaining thermobarometric estimates by simultaneous solution of the garnet biotite exchange thermometer and gmap calibrated from thermochemical data

the metamorphic characteristics of metapelites of the mashan group in mashan area eastern heilongjiang province china constraint on the crustal evolution of the jiamusi massif abstract mashan complex in the southeastern margin of the jiamusi massif has traditionally been interpreted to be the oldest stratigraphic sequence in eastern ne china here we investigated the mashan complex in the ximashan area and present lots of new la icp ms zircon u pb petrological and mineralogical chemical data in addition with phase equilibria modeling to constrain the timing of metamorphism p t conditions and the p t path of the mashan complex and furthermore to deduce the crustal evolution of the jiamusi massif the protoliths of the metapelites from the mashan complex in the ximashan area are clay rocks and sandstones whose provenance is dominantly felsic rocks which formed from a continental island arc three metamorphic generation assemblages m2 m4 are recognized in the studied samples a peak granulite facies stage a post peak near isothermal decompression stage and a late near isobaric cooling stage which together define a clockwise p t path it reveals important information related to the collision orogeny subsequent uplift and post collision process zircon u pb dating of two metapelitic samples yielded metamorphic ages of the older group varying from 535 6 to 480 5 ma which can be perfectly correlated with the age range 501 6 to 498 6 ma of magmatic activities recorded by the gneissic granite sample the data presented here together with those published allow us to preliminarily infer that the peak of the granulite facies metamorphism in the ximashan area of the jiamusi massif might have occurred at 530 500 ma the younger of the metamorphic ages 476 453 ma should be regarded as the age of late stage therefore a collision orogeny regime is favored to interpret the metamorphic evolution of metapelites of the mashan group in the mashan area

the effect of reaction overstep on garnet microtextures in metapelitic rocks of the ilesha schist belt sw nigeria garnet bearing assemblages of k rich and k poor metapelites from the ilesha schist belt sw nigeria are investigated k rich samples contain the assemblages a garnet staurolite muscovite chlorite magnetite b andalusite garnet staurolite muscovite chlorite magnetite and c sillimanite andalusite garnet muscovite chlorite magnetite k poor samples contain the assemblages d garnet staurolite cordierite chlorite and e garnet cordierite chlorite staurolite all assemblages contain quartz plagioclase biotite and ilmenite p t pseudosections calculated in the system cao na2o k2o tio2 mno feo mgo al2o3 sio2 h2o o2 suggest peak metamorphism at 590 20 c at 5 0 5 kbar followed by retrogression to 550 c at 3 0 kbar in agreement with field evidence domain assemblages mineral compositions modes and geothermobarometry the absence of compositional zonation shows that garnet in all investigated rocks nucleated and grew at constant p t x in equilibrium with associated minerals on the thin section scale however the garnet in reaction did not begin until the establishment of a significant temperature overstep of 80 c with consequent rapid dehydration of chloriteand muscovite bearing assemblages resulting in interface controlled garnet growth under locally hydrostatic pressure conditions garnet in rock types a and b formed with a characteristic pattern of biotite and quartz inclusions a house of cards texture additionally clusters and aggregates of unzoned garnet grains formed in rock types a and d garnet resorption in rock types a c resulted from prograde stauroliteand retrograde andalusite forming reactions

a new metamorphic constraint for the eburnean orogeny from paleoproterozoic formations of the man shield aribinda and tampelga countries burkina faso abstract progressive metamorphic zones developed in pelites around the aribinda granite burkina faso indicate contact metamorphism at 5 6 kbar biotite chloritoid staurolite kyanite zones are distributed concentrically around the aribinda pluton on its northern margin but are displaced by later thrust faults in the south of the aribinda area and in the nearly tampelga area these metamorphic and structural characteristics provide new constraints for the geodynamical evolution of the eburnean orogeny in the north part of the baoule mossi domain they show the leading part of the granitoid emplacement in the thermic structuration of the greenstone belts and the post metamorphic character of the tangential tectonic in burkina faso the eburnean orogeny underwent 1 initial greenschist facies metamorphism 2 emplacement of granitoids at mid deep crustal levels leading to unusual medium pressure metamorphism 3 later thrusting

iso modulation on the submonthly wave pattern and recurving tropical cyclones in the tropical western north pacific abstract this study demonstrates the multiscale nature from synoptic to intraseasonal time scales of the atmospheric flow in the tropical western north pacific the multiscale features include intraseasonal oscillations iso northwestward propagating submonthly wave patterns and recurving tropical cyclones tcs in the iso westerly phase the wave pattern was better organized and the tcs were clustered near the cyclonic circulation of the wave pattern during the genesis development and propagation on the other hand the wave pattern and tcs were weak and poorly organized in the iso easterly phase the distinct characteristics between the westerly and easterly phases could be attributed to the iso modulation on the monsoon trough and the subtropical anticyclonic ridge the iso in the westerly phase provided a favorable background e g enhanced monsoon trough and moisture confluent zone for the wave tc pattern development while the iso in the easterly phase provided a less favorable environment

plagioclase relations in pelites central menderes massif turkey i the peristerite gap with coexisting kyanite in pelites of the central menderes massif albite and oligoclase with only slight chemical zoning coexist in apparent textural equilibrium in the garnet zone staurolite zone and staurolite kyanite transition zone the metamorphic temperature range is estimated as approximately 440 550 c from the hodges spear calibration of the garnet biotite geo thermometer or 440 500 c ganguly saxena calibration while oligoclase composition at the peristerite gap changes from an22 to an14 albite also becomes more sodic an1 5 an0 6 the slope of the albite limb is thus the reverse of that reported in other areas and may not be a true equilibrium feature occurrence of kyanite at temperatures below the crest of the gap is due to low water activity in the presence of graphite ah2o is estimated at approximately 0 1 0 2 from the na content of muscovite coexisting with albite kyanite quartz

a subtropical cyclonic gyre associated with interactions of the mjo and the midlatitude jet abstractthis paper describes a large cyclonic gyre that lasted several days in the northwest pacific during july 1988 cyclonic winds at 850 hpa extended beyond the 2000 km radius with a radius of maximum winds of 700 800 km the gyre exhibited clear skies within and north of its center active convection extended 4000 km in longitude to its south the madden julian oscillation mjo was in its active phase in the indian ocean prior to gyre formation consistent with earlier studies diabatic heating in the mjo was associated with an anomalous upper tropospheric westerly jet over the northeast asian coast and a jet exit region over the northwest pacific repeated equatorward wave breaking events developed downwind of the jet exit region one such event left behind a region of lower tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation a second wave breaking event produced strong subsidence north of the mature gyre that contributed to its convective a

metamorphic and structural evolution of the early proterozoic puolankajrvi formation finland ii the pressure temperature deformation composition path the paragenetic relationships between sillimanite andalusite kyanite chlorite cordierite biotite garnet and staurolite in the early proterozoic puolankajarvi formation pjf together with mineral compositions are used to construct a partial petrogenetic grid for metapelites with significant mn content mno 0 1 0 5 by adding a six phase invariant point over the garnet absent invariant point for mn free amf phases the grid and textural relations of the pjf are used to construct part of the p t deformation path for the pjf relatively short deformation pulses and associated flow of oxidizing fluid along shear zones were responsible for the paragenetic and compositional changes during cooling and decompression at 600 500 c and 6 0 2 5 kbar oxidation led to decreased fe2 and further stressed the importance of mn increased mn divalent cations a tectonothermal evolution of the kainuu schist belt is presented which includes crustal thinning and steepening of a previously established thermal gradient this was followed by thrusting and folding of the isotherms into a thermal antiform on the western side of the belt

trace element zoning in garnet from the kwoiek area british columbia disequilibrium partitioning during garnet growth trace element zoning in garnets from two contact metamorphosed rocks from the kwoiek area british columbia hollister 1969a was measured with an ion microprobe zoning profiles have three distinct parts with chemical breaks defined by co variation of major and trace elements important features of the trace element zoning profiles are 1 roughly bell shaped zoning profiles for y and the hrees 2 an abrupt increase in ti at a point midway through each garnet with inflections in the zoning profiles of other elements li na cr v y zr and the hree and 3 irregular cr and v profiles unlike mn zoning the zoning profiles of most other trace elements cannot be easily modeled using simple rayleigh fractionation models ti activity in the two samples is buffered by phase relations with ilmenite garnets from a continuously heated contact metamorphic environment should display continuous ti zoning profiles if equilibrium was maintained and provided the ti buffering assemblage did not change during garnet growth the irregular ti profiles suggest disequilibrium behavior several elements cr v may indicate breakdown of a phase enriched in trace elements during metamorphism the source for the mass excess of these elements is probably the refractory cores of ilmenite grains either differing matrix transport rates of trace lements or interface kinetic controlled segregation could explain the unusual trace element behavior at the element inflection point the preferred explanation involves segregation of elements at the interface of the garnet that were trapped during episodes of rapid garnet growth

high temperature clockwise p t paths and melting in the development of regional migmatites an example from southern brittany france the southern brittany migmatite belt sbmb which evolved through the metamorphic peak between c 400 ma and c 370 ma ago consists of a heterogeneous suite of high grade gneisses and anatectic migmatites both metatexites and diatexites rare garnet cordierite gneiss layers record evidence of an early prograde p t path in these rocks growth zoned garnet cores and a sequence of included mineral assemblages in garnet from core to rim of qtz ilm ky pl ky st rt bt and pl sil st rt bt constrain a prograde evolution during which the reactions ilm ky qtz aim rt ms chl st bt qtz v and st qtz grt sil v were crossed parts of this prograde evolution are preserved as inclusion assemblages in garnet in all other rock types in all rock types garnet has reverse zoned rims and garnet replacement by cordierite and or biotite and plagioclase suggests the following reactions have occurred grt sil qtz crd hc ilm bt sil qtz crd hc ilm kfs v and na ca k ti grt bt pl qtz microstructural analysis of reaction textures in conjunction with a petrogenetic grid has enabled the construction of a tightly constrained clockwise p t path for the sbmb the high temperature part of the path has a steep dt dp slope characteristic of near isothermal decompression it is proposed that the p t path followed by the sbmb is the result of the inversion by overthrusting of a back arc basin and that such a tectonic setting may be applicable to other high temperature migmatite terranes the near isothermal decompression is at least partly driven by the upward diapiric movement of the diatexite anatectic granite core of the sbmb

crystal growth and the formation of chemical zoning in garnets a crystal growth model is developed which generalizes the rayleigh fractionation process the new growth model allows some insight into the interpretation of nonequilibrium behavior of minerals primarily the chemical zoning profiles exhibited by metamorphic minerals a nonlinear equilibrium term for exchange of constituents between a growing mineral and a reservoir is initially incorporated into the usual isothermal fractionation model criteria are established to decide when a simple distribution term is sufficient to describe the growth and exchange process the model is then extended to allow for temperature changes during a cooling or heating event finally an exact solution is obtained for the temperature dependent case incorporating a time dependent growth rate the growth models are successfully used to obtain growth rates of 0 01 to 0 09 cm million year and describe the magnesium and iron zoning profiles of garnets from phillipston massachusetts the generalized model confirms the development of zoning during the retrograde growth of garnet in the late stages of the acadian orogeny

evaluation of tropical cyclone center identification methods in numerical models abstractidentifying the center of a tropical cyclone in a high resolution model simulation has a number of operational and research applications including constructing a track calculating azimuthal means and perturbations and diagnosing vortex tilt this study evaluated several tropical cyclone center identification methods in a high resolution weather research and forecasting wrf model simulation of a sheared intensifying asymmetric tropical cyclone the simulated tropical cyclone tc contained downshear convective cells and a mesovortex embedded in a broader tc vortex complicating the identification of the tc vortex center it is shown that unlike other methods the pressure centroid method consistently 1 placed the tc center within the region of weak storm relative wind 2 produced a smooth track 3 yielded a vortex tilt that varied smoothly in magnitude and direction and 4 was insensitive to changes in horizontal grid resolution based on these results the authors recommend using the pr

staurolite producing reactions and geothermobarometry of a high pressure thermal aureole in the french massif central biotite garnet staurolite and kyanite isograds in pelitic metasedimentary rocks are developed as a result of thermal metamorphism around syntectonic granitoids in eastern rouergue france temperature estimates range between 400 c and 650 c at about 6 5 kbar geothermobarometry shows a steep isobaric t gradient which is consistent with the interpretation that the metamorphic highs are thermal aureoles high grade rocks show evidence of two staurolite forming reactions in the presence of plagioclase and the absence of chlorite that have not been described previously in the literature the reaction that occurs in the middle staurolite zone alm rich ga ca rich pla na rich mu gro rich ga na rich pla st na poor mu is considered to be prograde whereas the reaction that occurs in the kyanite zone alm rich ga ca rich pla w st ca rich ga na rich pla qz is retrograde the topology of these reactions is illustrated in terms of end member compositions for the systems knafash and kcafash respectively

regional shear variation in relation to diapirism and folding abstract regional structural trends in the levezou area southern massif central france delineate an antiformal structure deformed granitoids display changes along strike in s c plane relationships and therefore in sense of shear these variations are interpreted to be strain accommodation features that developed during the diapiric emplacement and folding of the granitoid sheets and so cannot be used as kinematic indicators on a regional scale

a climatology of rossby wave breaking along the subtropical tropopause ten years 1986 95 of global analyses from the european centre for medium range weather forecasts are used to investigate the temporal and spatial distributions of rossby wave breaking rwb at 350 k along the tropopause herein defined by the 61 5 potential vorticity pv unit 10 26 km 2 s21 kg21 contours though many studies acknowledge rwb as an important contributor to the complex of mixing processes in the atmosphere there exists no prior climatological study of its distribution near the tropopause as in previous studies rwb is identified in the global analyses by southward directed pv gradients at 350 k rwb along the tropopause occurs preferentially during summer over the midoceans in relative proximity to the planetary scale high pressure systems in the subtropics isentropic trajectories at 350 k show that outflow from the tops of these subtropical highs directly participates in rwb over the adjacent downstream oceanic regions two regions are highlighted in this study the north pacific during boreal summer and the south atlantic during austral summer synoptic maps of breaking rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane which characteristically accompanies rwb the rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere as expected from theoretical considerations the locations where rwb occurs most frequently known as surf zones are shown to coexist with regionally weak time mean wind speeds and horizontal gradients of pv at 350 k

what percentage of western north pacific tropical cyclones form within the monsoon trough abstractit is frequently stated that 70 80 of western north pacific tropical cyclones form within the monsoon trough but without an objective definition of the term several definitions are tested here when the monsoon trough mt is defined as the contiguous region where long term 1988 2010 mean july november 850 hpa relative vorticity is positive 73 of all july november tropical cyclones form within the mt this percentage varies interannually however from as low as 50 to nearly 100 the percentage correlates with the nino 3 4 index with more storms forming within the mt during warm periods when the mt is defined instead using long term monthly mean 850 more than 80 of tropical cyclones form within the mt in all months except july and august when more than 30 of storms form poleward of the mt it is hypothesized that the known peak in the frequency of upper tropospheric midlatitude wave breaking in july and august is responsible it is argued that any long term mean provides a suita

textural and isotopic variations in graphite from plutonic rocks south central new hampshire graphite occurs in two distinct textural varieties in syntectonic granitoids of the new hampshire plutonic series and in associated metasedimentary wall rocks textural characteristics indicate that coarse graphite flakes were present at an early stage of crystallization of the igneous rocks and thus may represent xenocrystic material assimilated from the wall rocks the range of 13c values determined for flake graphite in the igneous rocks 26 5 to 13 8 overlaps the range for flake graphite in the wall rocks 26 0 to 16 7 and spatial correlation of some 13c values in the plutons and wall rocks supports the assimilation mechanism the textures of fine grained irregular aggregates or spherulites of graphite on the other hand indicate that they formed along with secondary hydrous silicates and carbonates during retrograde reactions between the primary silicates and a carbon bearing aqueous fluid phase relative to coexisting flake graphite spherulitic graphite shows isotopic shifts ranging from 1 9 higher to 1 4 lower in both igneous and metasedimentary samples