compressional and extensional tectonics in low medium pressure granulites from the larsemann hills east antarctica meta sediments in the larsemann hills that preserve a coherent stratigraphy form a cover sequence deposited upon basement of mafic felsic granulite their outcrop pattern defines a 10 kilometre wide east west trending synclinal trough structure in which basement cover contacts differ in the north and the south suggesting tectonic interleaving during a prograde d 1 thickening event subsequent conditions reached low medium pressure granulite grade and structures can be divided into two groups d 2 and d 3 each defined by a unique lineation direction and shear sense d 2 structures which are associated with the dominant gneissic foliation in much of the larsemann hills contain a moderately east plunging lineation indicative of west directed thrusting d 2 comprises a colinear fold sequence that evolved from early intrafolial folds to late upright folds d 3 structures are associated with a high strain zone to the south of the larsemann hills where s 3 is the dominant gneissic layering and folds sequences resemble d 2 folding outside the d 3 high strain zone occurs a low strain d 3 window preserving low strain d 3 structures minor shear bands and upright folds that partly re orient d 2 structures all structures are truncated by a series of planar pegmatites and parallel d 4 mylonite zones recording extensional dextral displacements d 2 assemblages include coexisting garnet orthopyroxene pairs recording peak conditions of 7 kbar and 780 c subsequent retrograde decompression textures partly evolved during both d 2 and d 3 when conditions of 4 5 kbar and 750 c were attained this is followed by d 4 shear zones which formed around 3 kbar and 550 c it is tempting to combine d 2 4 structures in one tectonic cycle involving prograde thrusting and thickening followed by retrograde extension and uplift the available geochronological data however present a number of interpretations for example d 2 was possibly associated with a clockwise p t path at medium pressures around 1000 ma by correlation with similar structures developed in the rauer group whilst d 3 and d 4 events occurred in response to extension and heating at low pressures at 550 ma associated with the emplacement of numerous granitoid bodies thus decompression textures typical for the larsemann hills granulites maybe the combined effect of two separate events

shrimp zircon age constraints from the larsemann hills region prydz bay for a late mesoproterozoic to early neoproterozoic tectono thermal event in east antarctica this paper reports a geochronological study of granulite facies rocks from the larsemann hills of prydz bay east antarctica shrimp zircon ages were obtained for a total of 14 samples that cover various rock types including felsic gneiss mafic gneiss paragneiss enderbite granitic gneiss and leucogneiss these age results combined with zircon geochemical data and cathodoluminescence images enable us to explore the morphological complexity in zircons that record polytectonic events features of multiple age zoning for example were observed in zircon separates from three felsic gneiss samples studied which contain magmatic cores of ca 1 13 ga and metamorphic mantles and rims of ca 1 0 and 0 53 ga respectively this suggests a period of magmatism and crust formation in the late mesoproterozoic and two subsequent phases of high grade metamorphism during the early neoproterozoic and early paleozoic respectively similar phenomena of zircon overgrowth were also observed in other rock types although early paleozoic tectonic activity has been considered as most significant in antarctic crustal evolution our study provides the first convincing age evidence for the existence of a prydz bay late mesoproterozoic mobile belt the ca 1 0 ga metamorphic record preserved in diverse rocks from the study area furthermore supports the proposal of a continuous circum east antarctica late mesoproterozoic grenville age orogenic belt within this framework the prydz bay orogen is proposed to have been located in the central part of the rodinia assembly that brought the eastern ghats of india together with antarctica at ca 1 0 ga

air sea interactions over terra nova bay during winter simulation with a coupled atmosphere polynya model a preliminary simulation of the terra nova bay polynya has been performed with a coupled atmosphere polynya model the atmospheric model is a hydrostatic primitive equations model that has been validated previously by a simulation of the strong katabatic winds observed in that area the polynya model includes a representation of the free drift of frazil ice and simple sea ice dynamics and thermodynamics two and three dimensional experiments have been performed under polar night conditions two dimensional experiments show that an open warm water area influences significantly the atmospheric circulation in the antarctic coastal zone an additional ice breeze effect is simulated and is responsible for the strenghthening of the katabatic winds near the coast because of the important temperature difference between the continental air and the ice free ocean up to 40 c strong surface heat fluxes are simulated over the polynya finally a three dimensional experiment has been performed the integration domain includes terra nova bay the polynya observed in that region is well simulated it is found that heat losses from the polynya surface are stronger than previously thought but are probably constrained by the idealized representation of frazil ice which is assumed to be uniform in each grid box this stresses the need for having a better knowledge of frazil ice evolution in large polynyas

surface airflow around windless bight ross island antarctica ross island antarctica is located along the transantarctic mountains and is subjected to a strong southerly mountain parallel wind regime despite this windless bight on the island s southern coast is a region of anomalous calm the atmospheric boundary layer dynamics that gives rise to this phenomenon is analysed both theoretically and observationally it is the strong static stability of the boundary layer air encountering the high steep topography of ross island that causes a stagnation zone resulting in the calm conditions of windless bight direct and proxy observations of boundary layer winds provide a detailed description of airflow around the island the anomalous with respect to the synoptic pressure field but persistent north easterly winds at scott base are due to the deflection of highly stable low level air around hut point peninsula by contrast the less frequent strong southerly winds which override the peninsula are associated with the influx of warm maritime air from cyclonic systems to the east it is inferred that flow of air around the terrain of ross island gives rise to locally strong winds these are responsible for the ice breakout and polynya occurrences in mcmurdo sound the surface airflow past ross island can be modelled by a two dimensional steady frictionless irrotational incompressible flow past an obstacle with a shape based on an island height contour the flow is assumed to separate from the eastern and western sides of the island and form a wake downstream a solution for this flow is presented based on potential theory for streaming motion past an obstacle the streamline and isobar patterns clearly depict the stagnation region in windless bight for approaching winds of 20 ms 1 the local pressure field is perturbed by several millibars

partial melting during tectonic exhumation of a granulite terrane an example from the larsemann hills east antarctica anatectic migmatites in medium to low pressure granulite facies metasediments exposed in the larsemann hills east antarctica contain leucosomes with abundant quartz and plagioclase and minor interstitial k feldspar and assemblages of garnet cordierite spinel ilmenite sillimanite qualitative modelling in the system k2o feo mgo al2o3 sio2 h2o tio2 o2 in conjunction with various p t calculations indicate that the high grade retrograde evolution of the terrane was dominated by decompression from peak conditions of c 7 kbar at c 800 c to 4 5 kbar at c 750 c extensive partial melting during decompression involved the replacement of biotite by the assemblage cordierite garnet spinel within the leucosomes these leucosomes represent the site of partial melt generation the cordierite garnet spinel ilmenite assemblage representing the solid products and excess reactants from the melting reaction the extraction and accumulation of this decompression generated melt led to the formation of syntectonic pegmatites and extensive granitic plutons leucosome development and terrane decompression proceeded during crustal transpression synchronous with upper crustal extension during a progressive early palaeozoic collisional event subsequent retrograde evolution was characterized by cooling as indicated by the growth of biotite replacing spinel and garnet thin mantles of cordierite replacing spinel and quartz within metapelites and garnet replacing orthopyroxene and hornblende within metabasites p t calculations on late mylonites indicate lower grade conditions of formation of c 3 5 kbar at c 650 c consistent with the development of late cooling textures

the confluence zone of the intense katabatic winds at terra nova bay antarctica as derived from airborne sastrugi surveys and mesoscale numerical modeling the surface wind field inland of the intense coastal kataba c wind regime at terra nova bay antarctica has been studied both observationally and numerically airborne surveys of windinduced features on the snow surface have been used to construct the time averaged winter surface airflow pattern the surface motion field has also been simulated by a mesoscale primitive equation model using terrain slopes with a horizontal resolution of 32 km both methods of analys s demonstrate that the intense katabatic airstream at terra nova bay is forced by converging air currents in the continental interior the broadscale confluence zone becomes organized into two regions within about 180 km of the coast the primary route for katabatic mass transport into the terra nova bay area is reeves glacier valley but an important secondary source is provided by airflow down david glacier the former is generated by the coriolis induced concentration of mass transport on the left side looking downwind of the broadscale confluence zone as well as by the near coastal mountain deflection of airflow into the valley head the confluence zone feeding into david glacier valley stretches over 100 km into the interior and is forced by the broadscale terrain configuration of the ice sheet source areas for the two airstreams differ with reeves glacier valley being fed by cold air formed well into the interior whereas the airflow down david glacier is sustained by radiative cooling over lower parts of the ice sheet which are much closer to the ross sea evaluation of the observational and modeling results reveals both the strengths and weaknesses of each approach airborne surveys of sastrugi orientations are a highly successful method for establishing the detailed pattern of surface airflow however a systematic examination of sastrugi dimensions suggests that such work could also be carried out using spot type satellite observations which is a more cost effective approach than aircraft surveying the double jet structure of katabatic airflow into the terra nova bay area is well represented by the primitive equation modeling but much finer grids are needed to resolve the near coastal drainage details

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

on the forcing of planetary scale rossby waves by antarctica the propagation of rossby waves forced at high latitudes into middle and low latitudes is studied using the barotropic vorticity equation on the sphere ray tracing theory indicates that fundamental differences exist between the response of an atmosphere initialized with typical northern hemisphere winter flow and typical southern hemisphere winter flow to such a forcing with a substantial response more likely for the southern hemisphere case integrations with a fully nonlinear barotropic model confirm this suggestion and indicate that away from the local forcing region linear theory provides a good description of the response the most notable feature in the steady solutions is a split of the mid latitude jet close to new zealand the location of this split coincides well with a region where blocking is observed to be prevalent in the southern hemisphere

origin and significance of tourmaline rich rocks in the broken hill district australia tourmaline rich rocks are widespread minor lithologies within the early proterozoic willyama supergroup in the broken hill district australia tourmaline concentrations occur in strata bound and local stratiform tourmalinites clastic metasedimentary rocks quartz gahnite lode rocks stratiform pb zn ag sulfide ores garnet quartzites strata bound scheelite deposits quartz tourmaline nodules discordant quartz veins and granitic pegmatites most of the tourmaline rich rocks are within the broken hill group that hosts the main pb zn ag ores at the globe mine along the northeast end of the main lodes tourmalinites are closely associated with pb zn ag mineralization and in places are interbedded with mn rich garnet quartzites galena and other ore minerals occur locally in the cores of recrystallized tourmaline grains in these tourmalinites indicating that tourmaline and sulfides were present together prior to deformation and high grade metamorphism electron microprobe analyses of tourmalines intergrown with fe sulfides at the globe mine show mg rich compositions relative to tourmalines in sulfide free assemblages from the same area suggesting early premetamorphic introduction of boron and mg enrichment of tourmaline by sulfide silicate reactions during metamorphism combined field and geochemical data indicate that the district tourmalinites represent normal clastic sediments that were metasomatically altered by boron rich hydrothermal fluids at or below the sediment water interface whole rock chemical analyses of 33 tourmaline rich rocks show linear trends of data for major and trace elements that closely resemble the trends observed for unmineralized elastic metasedimentary rocks of the district average fe al mg al na al and ti al molar ratios of the tourmaline rich rocks and clastic metasediments are very similar the average k al molar ratio of the tourmaline rich rocks is significantly lower than that of the clastic metasediments reflecting the loss of k during tourmalinite formation chondrite normalized patterns of rare earth elements ree in the quartz rich tourmalinites are generally similar to those of the clastic metasediments except for minor depletions of light ree local positive and negative ce anomalies suggest tourmalinite formation in the presence of seawater or a seawater derived pore fluid the geochemical data imply relative immobility of al ti cr and heavy ree during hydrothermal alteration and later metamorphism boron isotope analyses of 52 tourmaline separates show a total range of delta 11 b values from 26 8 to 17 0 per mil fine grained euhedral nonpoikilitic tourmalines from tourmalinites in the andalusite muscovite zone in the northern part of the district e g black prince mine have delta 11 b values from 21 to 17 per mil whereas coarse granoblastic and poikilo blastic tourmalines from the sillimanite and two pyroxene granulite zones in the southern part of the district e g globe mine have delta 11 b values of 24 to 19 per mil tourmalines in strongly retrogressed tourmalinites have delta 11 b values from about 27 to 20 per mil the observed variations in delta 11 b are consistent with prograde and retrograde metamorphic fractionation of boron isotopes in which the fluid phase is preferentially enriched in the heavier isotope 11 b premetamorphic hydrothermal fluids that deposited the black prince tourmalinites had delta 11 b values of 8 to 5 per mil at 200 degrees to 300 degrees c suggesting a boron source from nonmarine evaporite borates tourmalinites in the broken hill district apparently formed by the same submarine hydrothermal processes as the main pb zn ag lodes and the siliceous ferromanganese protoliths of the garnet quartzites in our model the hydrothermal system s acquired abundant boron by leaching evaporitic borates within the thackaringa group the stratigraphic sequence that underlies the broken hill group and most of the tourmaline concentrations we suggest that evaporites of the thackaringa group provided a source of readily extractable boron for formation of the tourmalinites and also the source of the fluoride sulfur and perhaps the carbonate in the main lodes such evaporites may have been critical for increased metal chloride complexing and transport necessary for deposition of the high grade pb zn ag ores the broken hill deposit may have formed contemporaneously with the mount isa and mcarthur river pb zn ag deposits in similar evaporite bearing sequences during widespread early proterozoic continental rifting

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

analysis of gravity waves generated at the top of a drainage flow abstract drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near surface air masses in sloping terrain the initial irruption of these flows with sudden shifts in wind speed and direction may result in vertical displacements of air parcels from their equilibrium position which prove to be a common source of internal gravity waves this paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the stable atmospheric boundary layer experiment in spain 2006 sables2006 field campaign pressure differences measured by microbarometers set at different levels of a tower help to interpret the evolution of other atmospheric variables provide a detailed picture of the irruption of a drainage current and reveal the formation of gravity waves at its top the main parameters of the waves are derived from wavelet cross correlation of p

boron recycling in the continental crust of the central andes from the palaeozoic to mesozoic nw argentina whole rock chemical composition and 11b 10b isotope ratios in tourmaline was investigated to study the geochemical recycling of boron during the evolution of the andean basement from the palaeozoic to mesozoic in the basement cambrian to ordovician high grade paragneisses migmatites and orthogneisses the eocambrian puncoviscana formation and paleozoic mesozoic granitoid igneous rocks whole rock b contents are generally below 100 ppm but b contents of 1 wt are found in cogenetic aplite and pegmatite dikes and in tourmaline quartz rocks in the metasedimentary rocks no systematic variation in b content because of metamorphic grade and no correlation of b with other incompatible elements are apparent tourmalines from the high grade metamorphic basement yield 11b values ranging from 11 2 to 6 8 and isotope fractionation during migmatisation was small metamorphic tourmalines from the puncoviscana formation have 11b values between 6 3 and 5 8 the calculated corrected for fractionation 11b values of 6 to 2 for the sedimentary protolith of the metamorphic basement indicate a continental b source with subordinate marine input tourmalines from palaeozoic and mesozoic granitoids display an identical range of 11b values from 12 to 5 3 and indicate a similarly homogeneous b source throughout time tourmalines from pegmatites and tourmaline quartz rocks record the average 11b values of the parental granitic magma we assume that b in the palaeozoic and mesozoic granitoids is derived from the local metamorphic basement supporting the hypothesis that recycling of the lower palaeozoic crust is the dominant process in granitic magma formation from palaeozoic to mesozoic

a numerical study of strong katabatic winds over antarctica abstract certain coastal sections of antarctica most notably adelie land and terra nova bay experience anomalously intense persistent katabatic winds the forcing of such katabatic outflow is believed to originate several hundred kilometers upslope in the interior of the continent where cold air drainage currents from a large area converge into a relatively narrow zone focused on the steeply sloping ice terrain near the coastline numerical simulations with a three dimensional hydrostatic model incorporating terrain features representative of adelie land reveal a significant topographical channeling of the surface airflow katabatic wind speeds as depicted by the model are greatly enhanced downslope of the convergence channel these results emphasize the importance of topography in the continental interior in shaping the character of coastal katabatic flow

boron isotope evidence for the involvement of non marine evaporites in the origin of the broken hill ore deposits identifying the palaeogeographic setting and mode of origin of stratabound ore deposits can be difficult in high grade metamorphic terranes where the effects of metamorphism may obscure the nature of the protoliths here we report boron isotope data for tourmalines from the early proterozoic broken hill block in australia which hosts giant lead zinc silver sulphide deposits with one exception the 11b 10b ratios are lower than those for all other tourmalines from massive sulphide deposits and tour malinites elsewhere in the world we propose that these low ratios reflect leaching of boron from non marine evaporitic borates by convecting hydrothermal fluids associated with early proterozoic continental rifting a possible modern analogue is the salton sea geothermal field in california

a numerical study of open water formation in sea ice 1 a multicategory sea ice model that explicitly takes into account redistribution of undeformed ice into categories of ridged and rafted ice is introduced with the intention of investigating the simulation of the open water fraction within sea ice the performance of this model is compared with that of a reduced model that accounts for only two categories the latter type of sea ice model being most widely used in global climate models two idealized scenarios are considered polynya formation along a coastline under offshore winds and a low pressure system passing over an ice field furthermore the two models are compared under more real world forcing conditions as they exist in the weddell sea in simplified situations both models produce identical results upon introduction of more realistic ambient conditions however the multicategory model produces larger open water fractions than the two level model concomitantly and consistently with earlier findings the multicategory model produces thicker ice this is a result of the larger horizontal gradients of ice motion which in turn are due to the weaker ice strength that arises from a higher abundance of thinner ice this leads to more open water as well as increased dynamical growth of ice the open water fraction is of relevance in global ocean circulation models where the amount of open water influences the deep and bottom water formation rates such as in conjunction with antarctic coastal polynyas

a rare garnet tourmaline sillimanite biotite ilmenite quartz assemblage from the granulite facies region of south central massachusetts a rare lithology consisting of garnet tourmaline sillimanite biotite ilmenite quartz has been found within the granulite facies region of south central massachusetts the homogeneous ti rich oxy dravitic tourmaline x mg mg mg fe 0 72 0 77 falls into the alkali group and is similar in composition to lower grade tourmaline found in corresponding metapelitic rocks in maine charge balancing calculations and binary diagrams suggest that like biotite in the region tourmaline has undergone deprotonation by means of the exchange vectors alor 1 oh 1 and tio 2 r 1 oh 2 where r represents fe mg the restriction of a concordant tourmaline rich horizon in otherwise tourmaline free rocks of this granulite facies region suggests that either 1 b released during prograde fluid absent dehydration reactions of muscovite and biotite was locally available in a fluid phase or melt for later crystallization near the peak of granulite facies metamorphism along pathways that provided a conduit for fluid migration or 2 that this is simply a b rich compositional horizon tourmalinite that survived anatexis and granulite facies metamorphism and that records the incipient conditions of tourmaline breakdown and subsequent recrystallization near or post peak metamorphism

femtosecond lasers in fluid inclusion analysis three dimensional imaging and determination of inclusion volume in quartz using second harmonic generation microscopy abstract optical second harmonic generation microscopy was used to generate three dimensional images of fluid inclusions in quartz because the exciting light was focused with a high numerical aperture microscope objective phase matching conditions in the quartz led to the generation of frequency doubled light only at the surfaces of the fluid inclusions and not in the bulk material providing an axial resolution of approximately 1 m the volume of synthetic two phase water inclusions was determined from second harmonic images the bubble volume was measured using brightfield microscopy the sample was heated to ensure a smaller bubble that could take on a spherical shape inside the inclusion the bulk molar volume was then calculated from the vapor liquid ratio the values obtained for the bulk molar volume were found to be in good agreement with values calculated from measurements of the homogenization temperature

quasi stationary waves in the southern hemisphere part i observational data abstract this part i presents selected major features of the quasi stationary monthly mean wave field in the troposphere and stratosphere of the southern hemisphere it is confirmed that the quasi stationary wave with zonal wavenumber 1 qs wave 1 is by far the dominant component of the geopotential height field at tropospheric and stratospheric levels the amplitude of this wave is largest at about 60 s all year round and reaches a maximum during september and october in the upper troposphere and stratosphere analysis of the elliasen palm flux vector suggests that at high latitudes the quasi stationary wave field is primarily forced from lower latitudes most prominently from the indian ocean region during june and october orographic and thermal forcing from antarctic regions seem to also be important sources of wave activity in polar and high latitudes particularly over southern south america and the atlantic ocean the contribution to the quasi stationary flow by the transient component of the fl

melt biotite 11b 10b isotopic fractionation and the boron local environment in the structure of volcanic glasses abstract this paper is focused on the role of boron coordination in determining the 11b 10b isotopic fractionation between melt glass and biotite at magmatic temperatures for this purpose three evolved volcanic rocks from roccastrada mt amiata and mt cimini belonging to the neogene quaternary magmatism of central italy were studied in these samples the measured boron biotite glass partition coefficient ranges between 0 004 and 0 011 indicating that boron behaves as an incompatible element during biotite crystallization the 11b magic angle spinning nuclear magnetic resonance nmr spectra reveal the presence of trigonal bo3 2 units tetrahedral bo4 2 sites and three coordinated bo2 2o species containing one nonbridging oxygen the relative contributions of these different boron sites were estimated by spectral deconvolution and it was observed that the fraction of trigonally coordinated boron decreases with increasing k2o concentration in the glass the 11b 10b isotopic fractionation between biotite and melt glass was observed to be large even at magmatic temperatures and was found to be 1 0066 roccastrada sample 1 00535 mt amiata sample and 1 00279 mt cimini sample fractionation is mostly related to the relative amount of trigonal and tetrahedral boron sites in the glass network rather than to other processes including the speciation of hydrous species in the glass structure the measured values are significantly higher than the calculated ones obtained using the reduced partition function ratios rpfrs for b oh 3 and b oh 4 as reported by kakihana et al 1977 and the abundance of trigonal and tetrahedral boron obtained by 11b nmr spectra furthermore a nonlinear relationship is observed between the percentage of bo4 in the glass structure and the measured 1000ln suggesting that the approximation of monomeric b oh 3 and b oh 4 species contributions through ideal mixing in calculating the rpfrs in polyanions oi et al 1989 probably does not apply to silicate glasses the large b isotopic fractionation measured between glass and biotite and its dependence on the boron coordination in the glass are a limitation to the use of 11b in the mineral to characterize magmas nonetheless the high incompatible behavior of boron in the most common magmatic minerals rules out that fractional crystallization significantly modified the b isotopic composition of the melt

boron isotopic composition of marine and nonmarine evaporite borates abstract here we present the results of the boron isotopic analysis of borates from some well known marine and nonmarine evaporite deposits combining new analyses with analyses from the literature yields a mean 11 b value for nine marine evaporite borate analyses of 25 4 permil 11 b 10 b 4 15 0 02 and a mean for twenty five nonmarine evaporite borates of 7 10 permil 11 b 10 b 4 02 0 04 previous studies have shown that the boron isotopic composition of seawater 11 b 40 permil 11 b 10 b 4 20 is about four percent heavier than the boron isotopic composition of most crustal rocks and minerals we suggest that our results for marine and nonmarine evaporite borates reflect this difference thus it should be possible to use boron isotopic composition as a tracer for boron of marine evaporitic origin applications include borate bearing evaporite deposits and perhaps borate and or borosilicate bearing metamorphic rocks

boron isotopic composition of tourmaline prismatine and grandidierite from granulite facies paragneisses in the larsemann hills prydz bay east antarctica evidence for a non marine evaporite source a unique assemblage of b rich rocks 2 wt b containing the borosilicate minerals tourmaline tur prismatine prs and grandidierite gdd is exposed in the ca 1000 ma brattstrand paragneiss in the larsemann hills east antarctica the b isotope composition of these three minerals in 21 paragneisses and 6 anatectic pegmatites were measured in situ using secondary ion mass spectrometry 11b ranges from 2 8 to 14 4 in tourmaline from 9 6 to 17 8 in prismatine and from 2 8 to 8 7 in grandidierite weighted uncertainties mostly 1 2 per sample in most cases average 11b increases in a given sample prs tur gdd whether the observed b isotope distribution has attained equilibrium were assessed using two criteria microstructural equilibrium and regular distribution of mg and fe in samples for which the two criteria are met we assume the measured distribution of isotopes 11ba b 11ba 11bb represents equilibrium 11btur prs 5 0 1 4 5 of 12 pairs 11btur gdd 3 3 0 8 3 of 5 pairs and 11bgdd prs 7 2 1 3 2 of 2 pairs consistent with the preference of 10b for tetrahedral sites prismatine and 11b for trigonal sites tourmaline grandidierite ab initio computations of b isotope fractionation factors 11btur prs 6 4 1 3 11btur gdd 1 8 1 1 and 11bgdd prs 8 2 1 1 provide confirmation of the measured fractionations the computed relaxed ionic structure of grandidierite gave a shorter 1 368 a b o bond length than in case of dravite 1 385 a which explains the measured enrichment of grandidierite in 11b relative to tourmaline the precursor of the b rich rock least changed by metamorphism tourmaline metaquartzite 11b tur 8 6 to 5 9 is interpreted to be a product of pre metamorphic hydrothermal b metasomatism boron sources consistent with this 11b range include oceanic crust clastic sediments volcanic rocks and non marine evaporite borate but not marine evaporite however dominance of metasediments in the brattstrand paragneiss major and trace element compositions of the b rich rocks and presence of abundant b are consistent with non marine evaporite being the most important source of b for the b rich lithologies of the larsemann hills a possible scenario for precursors of these rocks is a succession of clastic sediments in part tuffaceous intercalated with b rich evaporite deposits in a continental rift basin in which circulating hydrothermal fluids leached b from the evaporite and precipitated it as tourmaline in the associated clastic rocks to form the precursors to the tourmaline metaquartzites

intraseasonal variability of katabatic wind over east antarctica and planetary flow regime in the southern hemisphere the intraseasonal variation 30 to 50 day period of katabatic wind has been found at mizuho plateau east antarctica as a predominant mode of the subseasonal time scale variability the atmospheric circulation in the southern middle and polar latitudes associated with this fluctuation of katabatic wind has been deduced by using the nmc gridded 500 mbar zonal wind and geopotential height field the axisymmetric circulation pattern to antarctica is noticeable in the anomalous zonal wind and height field that is the strong weak katabatic wind phase corresponds to the shallower and broadened deepened and narrowed tropospheric circumpolar vortex with weaker stronger westerlies over the surrounding oceans these results strongly suggest that the intraseasonal variation of katabatic wind regime over east antarctica is part of the modulation of planetary flow regime and meridional circulation in the southern middle and high latitudes i e part of the index cycle of the southern hemisphere

interaction of katabatic flow with local thermal effects in a coastal region of adelie land east antarctica katabatic flows largely dominate the climate of the adelie land coastal region a detailed climatological data analysis of dumont d urville has been conducted results of this study support the idea that katabatic flow can be locally enhanced by the diurnal cycle of solar insolation and the temperature contrast between the continent and the ocean the interaction between katabatic wind and local thermal effects is expressed in terms of scale analysis except for surface stress all terms in the momentum equation for a katabatic flow in a coastal region of antarctica can reach the same order of magnitude the local circulation then is the result of a relatively tenuous force balance which can be disrupted even by a weak perturbation of any term to estimate the effect of the temperature contrast between the ocean and the continent on the katabatic flow two numerical experiments have been conducted the simulations consider an ocean free of sea ice representative of the summer months and another winter case with the ocean covered by thick sea ice these simulations show that with the ocean free of sea ice the katabatic flows extend only a limited distance over the open ocean during the day due to the local thermal effects with the ocean covered by sea ice the katabatic winds are not constrained and extend a considerable distance offshore

boron in metapelites controlled by the breakdown of tourmaline and retrograde formation of borosilicates in the yanai area ryoke metamorphic belt sw japan tourmaline out isograd formed by the breakdown of tourmaline is defined in the upper amphibolite facies metapelites in the yanai area ryoke metamorphic belt sw japan the rim composition of tourmaline progressively becomes aluminous with ascending metamorphic grade and the chemical zoning of tourmaline is controlled by x alna 1mg 1 and mgtiyal 2 vectors in low to medium grade zones where muscovite is stable whereas it is controlled by mg oh yal 1o 1 camgox 1 yal 1 oh 1 and mgtiyal 2 vectors in further higher grade muscovite unstable zones the size of tourmaline increases drastically where breakdown of muscovite quartz takes place probably due to the growth of tourmaline during breakdown of muscovite on the high temperature side of the tourmaline out isograd depletion of whole rock boron is observed escape of boron bearing melt or the fluid evolved from the melt during its crystallization probably caused this depletion although locally trapped boron bearing melt or fluid formed irregularly shaped tourmaline and dumortierite during retrograde metamorphism

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

glacier winds in the rongbuk valley north of mount everest 1 meteorological modeling with remote sensing data 1 persistent glacier winds blowing from noon to midnight in summer are present in the rongbuk valley north of mount everest with a maximum speed of 10 m s 1 and a vertical thickness as high as 1 km these glacier winds may bring upper level atmosphere ozone to the surface having a significant impact on the atmospheric environment such phenomena may be typical of the tibetan plateau where most high mountains are covered by snow or glacier ice throughout the year the advanced regional prediction model was used to simulate the down valley flows using realistic topography but neglecting synoptic winds the modeling results agree well with the observations obtained in june 2002 revealing that the glacier winds are thermal flows primarily driven by the along valley temperature gradient between the colder air over the glacier surface and the warmer air over surface areas covered by rock debris which maintains air advection along the rongbuk valley downslope winds over the glacier slopes especially from the western valley side and the west rongbuk glacier were forced by their inertia farther down into the valley and would intensify the glacier winds the narrowing of the rongbuk valley could also speed up the glacier winds sensitivity tests showed that the detailed distribution of the rongbuk glacier delineated by data from the enhanced thematic mapper plus on landsat 7 plays an important role in glacier winds development the glacier winds could be much weaker in winter when the area is completely snow covered

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

isotopic and elemental partitioning of boron between hydrous fluid and silicate melt the fractionation of b and its isotopes between aqueous fluid and silicate melt has been studied from 550 to 1100 c and 100 500 mpa fluid melt partition coefficients are 1 for rhyolite melt this shows that b is not always strongly extracted from melts into hydrous fluids boron isotopic fractionation is large compared with the carbon and oxygen stable isotopic systems especially at high t and is most simply explained by differences in coordination trigonal vs tetrahedral among coexisting phases combined with earlier measurements on illite water 300 350 c b isotopic fractionation defines a temperature dependent trend from 300 to 1100 c because of the large magnitude and apparent low sensitivity to bulk composition b isotopic fractionation can be readily applied to studies of diagenesis hydrothermal alteration of planetary bodies subduction zone processing and arc magma generation and magma chamber evolution

characteristics of the ross ice shelf air stream as depicted in antarctic mesoscale prediction system simulations 1 streamlines of the mean annual near surface winds over the antarctic continent suggest a confluent channeling of the drainage flows off the ice sheets and onto the ross ice shelf a persistent cyclonic circulation to the north of the ice shelf supports a large scale pressure field that reinforces the continental drainage flows owing to these two processes an enhanced low level airflow is present along the southern and western sections of the ross ice shelf the resulting air stream known as the ross ice shelf air stream ras is one of the persistent and prominent low level wind features seen in the antarctic real time mesoscale simulations of the antarctic atmosphere and high southern latitudes using a modified version of the pennsylvania state university national center for atmospheric research mesoscale modeling system have been ongoing since the 1999 2000 austral field season model results from the 1 year period november 2001 to october 2002 have been analyzed to investigate the mean structure and modulation of the ross ice shelf air stream analyses of model results show the low level air stream over the western ross ice shelf has a wind speed maxima that is linked to the steep topography to the west individual cases of strong wind events appear to contain a significant barrier wind component that arises from cold air damming against the transantarctic mountains cyclones that frequently form in the ross sea are shown to establish conditions that promote barrier wind dynamics and thus significantly modulate the intensity of the ras

diagnosis of the katabatic wind influence on the wintertime antarctic surface wind field from numerical simulations abstract katabatic winds have long been recognized as one of the key climatic variables of the low level antarctic environment antarctic surface winds display a high degree of persistence with mean directions related to the local topographic configuration of the ice sheet consistent with katabatic forcing continental orography also constrains the atmospheric boundary layer motions through blocking and cold air damming finally the coastal rim about the antarctic continent is among the most active baroclinic zones on earth the establishment of the low level wind field over antarctica is thus potentially the result of a number of interacting processes to quantify the forcing of the wintertime surface wind field over the antarctic continent two numerical strategies are presented first idealized numerical simulations are conducted to illustrate the strong orographic control of the low level wind field second a series of daily numerical simulations using the fifth generation pennsylvania state unive

cenozoic boron isotope variations in benthic foraminifers the boron isotopic composition of seawater 11 b sw is a prerequisite for reliably estimating past variation of seawater ph from boron isotopes in marine carbonates 11 b c here we compose a 50 m y stack of 11 b c from atlantic and pacific ocean deep sea sediments and discuss the potential effects of deep sea ph and 11 b sw on our record using model based cenozoic ph values the inferred 11 b sw values suggest an 3 increase since the late eocene superimposed on oscillating variations with amplitudes of up to 2 our estimates match existing reconstructions of 11 b sw but call into question published fluid 11 b in halite as a recorder of 11 b sw

boron rich mud volcanoes of the black sea region modern analogues to ancient sea floor tourmalinites associated with sullivan type pb zn deposits large submarine mud volcanoes in the abyssal part of the black sea south of the crimean peninsula are similar in many respects to synsedimentary mud volcanoes in the mesoproterozoic belt purcell basin one of the belt purcell mud volcanoes directly underlies the giant sullivan pb zn ag deposit in southeastern british columbia footwall rocks to the sullivan deposit comprise variably tourmalinized siltstone conglomerate and related fragmental rock local thin pyrrhotite rich and spessartine quartz beds are interpreted as fe and fe mn exhalites respectively analogous fe and mn rich sediments occur near the abyssal black sea mud volcanoes massive pyrite crusts and associated carbonate chimneys discovered in relatively shallow waters 200 m depth west of the crimean peninsula indicate an active sea floor hydrothermal system subaerial mud volcanoes on the kerch and taman peninsulas 100 km north of the abyssal mud volcanoes contain saline thermal waters that locally have very high b contents to 915 mg l these data suggest that tourmalinites might be forming in or near submarine black sea mud volcanoes where potential may also exist for sullivan type pb zn mineralization

the dynamics of idealized katabatic flow over a moderate slope and ice shelf summary a non hydrostatic numerical weather prediction model has been employed to simulate idealized katabatic flows over a moderate slope and adjoining ice shelf the topography of coats land and the adjoining brunt ice shelf antarctica has been used this is typical of much of the antarctic coastline the regional atmospheric modeling system version 4 3 has been adapted for simulations over compacted snow most notably through changes to the multi layer soil model the simulations are initialized using clear sky conditions and at rest on the slope a shallow katabatic flow develops the winds becoming approximately steady on the slope by 12 h the peak downslope winds are about 7 m s 1 at 30 m above the snow surface the katabatic flow depth ranges from 50 to 100 m down the slope over the ice shelf the katabatic flow peters out while a pool of cold air develops primarily through sensible heat loss into the surface and partially balancing the net radiative heat loss to space near surface and sounding data from the model simulations compare well with archetypal and typical katabatic flow observations especially after some tuning of the model s turbulence parametrization an analysis of the downslope flow dynamics shows the buoyancy force is generally balanced by the inertial force except towards the foot of the slope where it is balanced by upslope forces related to gradients in the potential temperature deficit and katabatic layer height caused by the pool of cold air over the ice shelf over time the cooling of the ice shelf boundary layer leads to an apparent retreat of the katabatic flow from the ice shelf and some way up the slope the dynamical analysis explains the surface climatology observed such that the persistent katabatic winds of coats land rarely reach the brunt ice shelf the simulated katabatic flow moves from shooting to tranquil towards the foot of the slope this transition acts to trigger a train of internal gravity waves which propagate energy upwards away from the katabatic flow jump previous studies have also found shooting to tranquil katabatic flow transitions so to generalize these findings would suggest that internal gravitywave generation is ubiquitous around much of coastal antarctica and greenland

the role of eolian processes in forming surface features of the martian polar layered deposits abstract the major topographic features of the martian polar layered deposits include the conspicuous spiral troughs subtle undulations broad reentrants chasma steep arcuate scarps and dune fields a prominent role for eolian processes in the formation of all of these features is proposed strong katabatic winds occur on the north polar cap producing widespread frost streaks these cold drainage winds are analogous to those on the terrestrial antarctic cap in the chasmae convergent katabatic winds create yardangs and erode arcuate scarps in the layered deposits that are also the source for local dune fields migrating outward from the polar cap the chasmae are postulated to originate by long term erosion by katabatic wind wind plays a role in formation of the troughs and scarps primarily through removal of dust freed from exposed layered deposits by ablation of ice on defrosted equator facing slopes the undulations are created by interaction between surface erosion or deposition of perennial ice and standing waves in the shallow katabatic windflow the south polar layered deposits exhibit topographic features similar to those at the north polar cap but erosion and depositional processes creating these features may be inactive during the current epoch because of the lack of an extensive perennial ice cover and associated katabatic wind

marine evaporites from an oceanic island in the neoproterozoic adamastor ocean abstract we report a hitherto unknown occurrence of ancient neoproterozoic evaporite deposits from an allochthonous terrane in the pan african gariep belt in namibia low contents of rb cs ba zr hf th and u flat chondrite normalised rare earth element ree patterns 87 sr 86 sr ratios as low as 0 7075 na cl br systematics of fluid inclusion leachates and high 11 b values for stratiform tourmalinites together with geologic evidence such as association with oceanic basalt gabbro and stromatolitic dolomite point to a marine evaporitic origin an atoll environment on an oceanic island is envisaged as a likely depositional setting in the associated mafic sequence we found a diamictite with metre sized ice rafted detritus suggesting the presence of sea ice cover at relatively low latitude around the time of evaporite deposition based on chemostratigraphic 87 sr 86 sr 13 c comparison with passive continental margin sediments in the para autochthonous external part of the gariep belt a correlation of the mafic diamicitite with the global varangian 590 560 ma glaciation is proposed

climatic atmospheric outflow at the rim of the antarctic continent using gauss s divergence theorem we examine the role of the net radiative cooling and of the entrainment of potentially warm air from the free atmosphere into the surface layer in determining the intensity of the cold air outflow at the rim of the antarctic continent the result shows that a large amount of cold air significant at even a global climatological scale is exported through this process from high to low latitude regions the theory gives also the average intensity of the wind at the coast in the coastal regions of antarctica the wind exhibits a complex behavior observations show that katabatic winds in the near coastal region can be periodic or continuous or can stay a long time in a quiescent near critical state then burst in short and strong gusts we examine some aspects of these katabatic winds in terms of the mesoscale energy theory developed by dalu and green 1983 this complex behavior is described by a nonlinear system where the relevant parameter is the froude number of the inflow at a rossby radius distance from the coast the analytical theory developed agrees well with qualitative features observed

talc mineralisation associated with soft hematite ore gongo soco deposit minas gerais brazil petrography mineral chemistry and boron isotope composition of tourmaline talc mineralisation occurs as hematite talc schist between soft hematite ore and dolomitic itabirite at gongo soco quadrilatero ferrifero of minas gerais brazil the hematite talc schist and soft hematite have a prominent tectonic foliation of tabular hematite tabular hematite without preferential orientation is superimposed on the tectonic foliation the talcose schist is enriched in f and has a constant fe s ratio electron microprobe analyses indicate trace amounts of s in different generations of hematite the whole rock fe s ratio possibly represents sulfate s from hematite hosted fluid inclusions fluid inclusions in foliation overprinting hematite and chlorite geothermometry from talcose rocks suggest respectively temperatures from 200 c to 300 c tourmaline a rarely observed mineral in the hematite talc schist belongs to the alkali group and falls in the dravite compositional field boron isotope determinations of tourmaline crystals using secondary ion mass spectrometry vary from 20 to 12 11b this compositional isotopic range and the tourmaline chemical composition suggest a meta evaporitic origin a non marine evaporitic setting is the most likely source of acidic highly oxidising fluids which resulted in the abundant f bearing talc and the presence of otherwise immobile ti in hematite oxidising brines were channelled along shear zones and converted dolomitic itabirite into the gongo soco soft hematite and the talc mineralisation the latter is envisaged as the hydrothermal wall rock alteration of dolomitic itabirite which gave rise to the soft hematite ore

surface winds over the antarctic continent a review surface winds over antarctica often classified as katabatic are intimately related to the orientation and steepness of the underlying ice terrain such flows result primarily from the strong radiational cooling of the sloping ice surface which creates a downslope directed horizontal pressure gradient force it is possible to diagnose the time averaged near surface streamline patterns of cold air drainage currents using recently compiled detailed antarctic ice topography maps and appropriate estimates of the strength of the surface temperature inversion the resulting streamlines agree with available observations and illustrate the high degree of nonuniformity of gravity driven flows off the ice sheets in certain interior sections negatively buoyant air from a large catchment area drains through a restricted section of coastline such confluence zones represent regions of enhanced supplies of cold air and are shown to be related to anomalously strong katabatic winds implications for sea ice formation are discussed