climatology and dynamics of the link between dry intrusions and cold fronts during winter part i global climatology cold fronts are a primary feature of the day to day variability of weather in the midlatitudes and feature in conceptual extratropical cyclone models alongside the dry intrusion airstream here the climatological frequency and spatial distribution of the co occurrence of these two features are quantified and the differences in cold front characteristics intensity size and precipitation when a dry intrusion is present or not are calculated fronts are objectively identified in the ecmwf era interim dataset for the winter seasons in each hemisphere and split into three sub types central fronts within a cyclone area trailing fronts outwith the cyclone area but connected to a central front and isolated fronts not connected to a cyclone these are then associated with dry intrusions identified using lagrangian trajectory analysis trailing fronts are most likely to be associated with a di in both hemispheres and this occurs more frequently in the western parts of the major storm track regions isolated fronts are linked to dis more frequently on the eastern ends of the storm tracks and in the subtropics all front types when co occurring with a di are stronger in terms of their temperature gradient are much larger in area and typically have higher average precipitation therefore climatologically the link with dis increases the impact of cold fronts there are some differences in the statistics of the precipitation for trailing and isolated fronts that are further investigated in part ii of this study from the front centred perspective

identification of inherited radiogenic pb in monazite and its implications for u pb systematics the simplest interpretation of uranium lead mineral ages in igneous rocks embodies the assumption that melting of pre existing rocks leads to homogenization of the lead isotopes thus resetting the radiometric clock zircons often violate this assumption by only partially dissolving and preserving a component of lead inherited from before the melting episode but until now such behaviour has not been observed in monazite here we report u pb data for zircons and monazites from a tertiary granite from the himalayas in which zircons and monazites contain inherited radio genic lead an analysis of a single entirely igneous zircon crystal plots on concordia at 19 5 0 4 myr eight monazite fractions lie on a line from an upper intercept of 471 10 myr to the youngest fraction which plots slightly above concordia at 21 myr the presence of excess 206pb in the youngest monazite fractions indi cates that the monazite data represent a mixing line between young magmatic monazite and an older inherited component rather than a resetting of 471 myr monazites at 20 myr these data suggest a closure temperature for pb in monazite significantly higher than previously published estimates

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

climatological characteristics of fronts in the western north pacific based on surface weather charts composite front climatology in the western north pacific is determined using a newly developed 1 0 gridded data set here we propose a research strategy for determining the spatiotemporal distribution of fronts using weather chart images published by the japan meteorological agency one of the major data providers in the region a preliminarily investigation of the internal data characteristics for the period of 2000 2010 is undertaken and the final 4 years of data are used for an analysis of front climatology to avoid the effect of any spurious trends this enables in depth analyses to be conducted which have not previously been possible in the region including the composites of cross sectional patterns for the thermal fields and precipitation near fronts front length seasonality and the significance of the thermal gradient near the fronts in addition to determining the frontal frequency and spatial distribution of frontal precipitation pixel wise analysis reveals that 56 of the local precipitation maximum is located on the warm side of a cold front caused by less tilted upward motion on the warm side with the intrusion of the upper level cold dry air into the warm side this new data set also enables a further analysis of the occluded fronts which are not correctly distinguished in the existing objective detection method

ground based array for tomographic imaging of the tropical forest in p band in this paper we discuss the design concepts and preliminary results relating to the european space agency s ground based campaign tropiscat whose main goal is to evaluate temporal coherence at p band in a tropical forest in quad polarization considering temporal lags ranging from hours to months and at different heights within the vegetation layer the experiment has been successfully set up and operated since october 2011 at the paracou field station french guiana where the equipment was installed on top of the 55 m high guyaflux tower to illuminate the forest below the system consists of a vector network analyzer connected to 20 antennas through a switchbox which allows the use of any of them either as a transmitter or as a receiver vertical imaging and fully polarimetric capabilities are achieved by operating the 20 antennas in a multistatic fashion resulting in an equivalent monostatic array consisting of 15 phase centers displaced along the vertical direction in each polarization such a design allows unambiguous imaging of the vegetation while yielding a minimum distance between nearby antennas on the order of 0 8 m so as to minimize coupling effects the equipment allows the gathering of signals with the tomographic array within a few minutes resulting in the possibility to produce a tomographic image of the forest with a temporal sampling of 15 min system calibration and validation was performed by employing a 2 m trihedral reflector and a rotating dihedral reflector this allowed the evaluation of the system pulse response in all polarizations and also assessment of the extent of tower motions as a result tomographic images have been generated from 500 p band to 900 mhz in all polarizations results from real data acquired in fall 2011 confirm the feasibility of carrying out reliable coherence measurements for the whole duration of the campaign

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

low pressure granulite facies metamorphism in the larsemann hills area east antarctica petrology and tectonic implications for the evolution of the prydz bay area thermobarometric studies on various granulite facies areas along the prydz bay coast east antarctica 73 79 e 68 70 s show that at around 1100 ma during a late proterozoic orogeny the rocks of the larsemann hills suffered a lower pressure metamorphic peak than the surrounding areas along the prydz bay coast the rocks affected by this event include parts of the vestfold hills block plus all of the rauer group the larsemann hills and the munro kerr mountains the dykes in the south west corner of the vestfold hills were recrystallized during this event with little deformation at temperatures not quite as high as in the areas further south west 650 c 6 5 kbar collerson et al 1983 the rauer group was metamorphosed at 800 c and 7 5 kbar harley 1987a the larsemann hills at 750 c and 4 5 kbar and the munro kerr mountains probably at around 850 c and 5 kbar retrograde equilibration in the different areas occurred during decompression to about 10 km depth in all areas followed by isobaric cooling at this depth this paper shows that the peak metamorphism in the larsemann hills occurred at a pressure which is too low to have been the consequence of thermal relaxation of overthickened crust with normal mantle heat flow although other areas in prydz bay were metamorphosed at sufficiently high pressures so that their decompression paths are not inconsistent with a continental collision model the inferred pre metamorphic peak histories and the requirement of consistency with the larsemann hills make it unlikely that collision followed by erosion driven decompression is an appropriate model we suggest that the thermal regime of the crust in the larsemann hills region was controlled by a perturbation in the asthenosphere with magma invasion of the crust we suggest that the 500 ma event represented in prydz bay by granitic outcrops at landing bluff and by several k ar ages from the larsemann hills area was responsible for the final excavation of the terrane

a global climatology of atmospheric fronts 1 atmospheric fronts in the lower troposphere often mark regions of significant weather and serve as an important conceptual tool that is frequently used and well understood by the public this study uses an objective method to identify fronts in the era 40 reanalysis and to compile a quantitative global climatology of their occurrence the climatology confirms the mid latitude storm tracks as the regions of highest front frequency and identifies slow moving frontal boundaries in the subtropics corresponding to major climate features such as the mei yu front the climatology also shows fronts to be common features of the south pacific convergence zone in the northern hemisphere fronts shift poleward in summer in the southern hemisphere this and other aspects of seasonal behavior are rather different

u pb monazite ages in amphibolite to granulite facies orthogneiss reflect hydrous mineral breakdown reactions sveconorwegian province of sw norway in the rogaland vest agder terrain of the sveconorwegian province of sw norway two main sveconorwegian metamorphic phases are reported a phase of regional metamorphism linked to orogenic thickening m1 and a phase of low pressure thermal metamorphism associated with the intrusion of the 931 2 ma anorthosite charnockite rogaland igneous complex m2 phase m1 reached granulite facies to the west of the terrane and m2 culminated locally at 800 850 c with the formation of dry osumilite bearing mineral associations monazite and titanite u pb geochronology was conducted on 17 amphibolite to granulite facies orthogneiss samples mainly from a suite of 1050 2 8 ma calc alkaline augen gneisses the feda suite in these rocks prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012 1006 ma in the feda suite and other charnockitic gneisses concordant to slightly discordant monazite at 1024 997 ma probably reflects breakdown of biotite during granulite facies m1 metamorphism a spread of monazite ages down to 970 ma in biotite hornblende samples possibly corresponds to the waning stage of this first event in the feda suite a well defined monazite growth episode at 930 925 ma in the amphibolite facies domain corresponds to major clinopyroxene formation at the expense of hornblende during m2 growth or resetting of monazite was extremely limited during this phase in the granulite facies domain up to the direct vicinity of the anorthosite complex the m2 event was shortly followed by cooling through ca 610 c as indicated by tightly grouped u pb ages of accessory titanite and titanite relict inclusions at 918 2 ma over the entire region a last generation of u poor monazite formed during regional cooling below 610 c in hornblende rich samples at 912 904 ma this study suggests 1 that monazite formed during the prograde path of high grade metamorphism may be preserved 2 that monazite ages reflect primary or secondary growth of monazite linked to metamorphic reactions involving redistribution of rees and th and or fluid mobilisation 3 that the u pb system in monazite is not affected by thermal events up to 800 850 c provided that conditions were dry during metamorphism

lewisian crustal history from in situ sims mineral chronometry and related metamorphic textures abstract a combination of detailed petrography and in situ sims 207 pb 206 pb micro chronometry of monazite has been carried out on samples from the lewisian high grade metamorphic terrain northwest scotland two episodes of granulite facies metamorphism have been recognized the thermal maxima of which are estimated at or before 2760 12 ma 2 and at 2526 8 ma respectively pegmatites at scourie crystallised at 2480 ma the amphibolite facies metamorphism of the main laxfordian event is estimated at 1752 12 ma and the formation of kyanite and staurolite is associated with this event the oldest ages of 2760 ma have been obtained from micro inclusions of monazite in garnet it appears that garnet which has a high closure temperature for the u pb system plays an important role in the behaviour of the monazite u pb system it serves to shield monazite from reaction with the other phases and to armour monazine from diffusive pb loss or from resetting

textural chemical and isotopic insights into the nature and behaviour of metamorphic monazite monazite is a mineral of choice for dating metamorphism in amphibolite and granulite grade metapelites however there exist a number of difficulties that complicate the interpretation of monazite geochronological data and prevent its application to many geological problems the two main obstacles addressed in this contribution are firstly the minor but significant e g 1 30 ma dispersal in duplicate isotope dilution thermal ionisation mass spectrometry id tims u pb age data commonly recorded from a single rock and secondly the difficulty of attaching monazite age data to pressure and temperature information through a multidisciplinary approach utilising tims and laser ablation multicollector inductively coupled plasma mass spectrometry la mc icpms isotope data quantitative and qualitative emp chemical analyses of monazite and textural studies we assess the significance of pb loss older components and continuous and episodic monazite growth in the generation of dispersed age data three samples from the canadian cordillera and one sample from the himalaya of pakistan are examined each sample exhibits an age dispersion of between 1 and 12 ma for single crystal and multi grain tims u pb monazite age determinations consideration of the closure temperature for pb diffusion in monazite and the metamorphic temperatures experienced by these samples suggests diffusive pb loss did not play a significant part in generating this age dispersal the la mc icpms study indicates that an older component 100 ma older than the tims ages contributed to the age dispersal in three of the four samples in all the samples however chemical analyses identified that the majority of monazites examined exhibited significant intra crystalline zoning in y content the la mc icpms analysis of one sample that was constrained to zones of distinct y content indicates that these zones are of distinct age we suggest that monazite grown before the appearance of garnet and during garnet breakdown is relatively rich in y whereas monazite grown after garnet is relatively poor in y a combination of these chemical data with textural observations suggests that once monazite had entered the mineral assemblage it grew or recrystallised episodically throughout the prograde and retrograde paths of the metamorphic event this behaviour contributes to and in one of the samples controls the observed age dispersal this recognition allows the generation of pressure temperature time points by combining textural and chemical information of monazite with in situ age determinations and pressure temperature information from garnet thus the episodic growth of compositionally distinct monazite throughout a metamorphic event provides the geochronologist with a very valuable chronological tool

chemical evolution of granitic rocks in the east antarctic shield with particular reference to post orogenic granites granitic intrusives of the east antarctic shield range in age from early archaean 3930 ma to cambrian and show systematic variations in chemical and isotopic characteristics many archaean orthogneisses are of tonalitic to granodioritic composition and represent new continental crust derived from the mantle by a two stage process involving hydrous melting of mafic crustal rocks syn orogenic granitic rocks are generally of more potassic composition and were derived by intracrustal melting under lower ph2o conditions they are mostly of more typical i type derived from igneous source materials but there is an increasing proportion of s types derived by melting of sedimentary materials with time late and post orogenic intrusives are mostly granites s s with a type anorogenic affinities and were derived by melting of relatively anhydrous granulite facies lower crustal rocks they are characterised by marked enrichment of y zr nb la and ce relative to p ti and sr and commonly have high f femg znfe and gaal plagioclase apatite and ti minerals were probably residual phases during partial melting as well as being involved in fractional crystallisation whereas other minor phases such as zircon were apparently relatively soluble in the high temperature melts emplacement of a type granites at about 500 ma may have been associated with internal fracturing of gondwanaland before eventual break up

post granulite facies monazite growth and rejuvenation during permian to lower jurassic thermal and fluid events in the ivrea zone southern alps u pb analyses of single monazite grains from two granulite facies metapelites in the ivrea zone southern alps reveal the presence in both samples of at least three different ages and prove that earlier interpretations of supposedly concordant monazite data as cooling ages are unwarranted one group of monazite data defines a subconcordant discordia line with an upper intercept age of 293 4 5 8 ma and a lower intercept age of 210 14 ma the upper intercept is interpreted as the real cooling age of the monazites the lower intercept is interpreted as an episode of fluid driven pb loss indicated by the presence of internal and external corrosion structures not only of the monazites but also of the zircons in the same samples that are also rejuvenated at 210 12 ma another group of monazite data lies above the concordia the presence of excess 206pb indicates that these crystals have grown below the monazite blocking temperature thus after the granulite facies metamorphism the age of growth of the new monazite crystals is approached by their 207pb 235u ages that range between 273 and 244 ma the two groups of post cooling age post 293 4 5 8 ma monazite data correspond to two distinct late and post variscan geotectonic regimes that affected the southern alps 1 permian transtension with decompression and anatectic melting 2 upper triassic to lower jurassic rifting with geographically dispersed hydrothermal activity and alkaline magmatism

an electron microprobe study of the u th pb systematics of metamorphosed monazite the role of pb diffusion versus overgrowth and recrystallization abstract an electron microprobe emp was used to obtain u th pb chemical ages from monazite that underwent an amphibolite facies metamorphic overprint in the monashee complex southern canadian cordillera u pb isotope dilution dating of single grains yielded discordant ages that plot in linear arrays on a concordia diagram upper intercepts of the arrays indicate primary growth in the proterozoic and cretaceous and lower intercepts are coeval with a tertiary metamorphic event the microprobe s high spatial resolution 2 m and ability to quickly differentiate between domains with greatly contrasting u th and pb concentrations made it the ideal tool for investigating the cause of the u pb isotopic discordance the microprobe dating shows that proterozoic monazite lies directly adjacent to generally small

generalized terrain topography in radar scattering models modeling of terrain topography is crucial for vegetated areas given that even small slopes impact and alter the radar wave interactions between the ground and the overlying vegetation current missions either exclude pixels with large topographic slopes or disregard the terrain topography entirely potentially accumulating substantial modeling errors and therefore impacting the retrieval performance over such sloped pixels the underlying terrain topography needs to be considered and modeled to obtain a truly general and accurate radar scattering model in this paper a flexible and modular model is developed the vegetation is considered by a multilayered multispecies vegetation model capable of representing a wide range of vegetation cover types ranging from bare soil to dense forests the ground is incorporated with the stabilized extended boundary condition method allowing the representation of an n layered soil structure with rough interfaces terrain topography is characterized by a 2 d slope with two tilt angles alpha beta simulation results for an evergreen forest show the impact of a 2 d slope for a range of tilt angles a 10 circ tilt in the plane of incidence translates to a change of up to 15 db in hh 10 db in vv and 1 5 db in hv for the total radar backscatter terrain topography is shown to be crucial for accurate forward modeling especially over forested areas

radar modeling of a boreal forest the authors report on the use of microwave modeling ground truth and synthetic aperture radar sar data to investigate the characteristics of forest stands a mixed coniferous forest stand has been modeled at sar frequencies p l and c bands the extensive measurements of ground truth and canopy geometry parameters were performed in a 200 m square hemlock dominated plot inside a forest hemlock trees in the forest are modeled by characterizing tree trunks branches and needles leaves with randomly oriented lossy dielectric cylinders whose area and orientation distributions are prescribed the distorted born approximation is used to compute the backscatter at p l and c sar frequencies

terrain influences on sar backscatter around mt taranaki new zealand an l band sar image from the japanese jers 1 satellite has been analyzed for the effects of local surface orientation relative to the radar illumination direction orthorectification of the sar imagery and determination of the local surface orientation is achieved with the aid of a high resolution digital terrain model an improved method of determining scatterer density for a surface in three dimensions is introduced and used to correct radiometrically the image for terrain variation residual radiometric effects due to surface orientation are shown to be dependent on the ground cover class backscatter from the indigenous forest was more isotropic than that from the farmland as accurate registration was required for this study a method for identifying control points in the rectified imagery is described which alleviated the difficulty of identifying them in the raw image

assessment of scattering mechanism of polarimetric sar signal from mountainous forest areas this study aims to understand the effects of the topographic slope variation on the vegetation backscattering characteristics of polarimetric imaging radar most of the previous studies in modeling microwave backscattering signatures of vegetated area have been carried out over relatively flat areas in order to model vegetation scattering mechanisms of mountainous forests this paper presents an improvement of the radiative transfer model that accounts for the tilted scattering surface beneath a forest canopy an l band polarimetric synthetic aperture radar sar data set acquired by the nasa jet propulsion laboratory airborne sar system was used to test and to assess the vegetation scattering model for a sloping forest area experimental result shows the proposed model to be adequate for evaluating slope induced changes in microwave scattering mechanisms

monazite u pb and th pb geochronology by ion microprobe with an application to in situ dating of an archean metasedimentary rock abstract monazite grains from nine different precambrian rock samples and having concordant isotope dilution u pb and th pb ages were used to develop and evaluate techniques for u pb th pb and pb pb isotopic dating using an ion microprobe operating at high mass resolution r 5500 1 an unidentified isobar at 203 960 amu complicated the determination of 204 pb in the monazites with higher th but it appeared to have been eliminated when using a slight energy offset the 207 pb 206 pb ratios of individual spots were determined in 10 min analyses to 0 3 0 5 1 of the true values using a 20 m wide o 2 primary beam whereas the uncertainty in the mean of several spots on a single generation of monazite was typically 0 1 0 4 2 instrumental bias in the measured pb uo and pb tho values of individual analyses was monitored using linear relationships between 206 pb uo vs uo 2 uo and 208 pb tho vs uo 2 uo the bias appears to vary somewhat with monazite th content requiring the use of compositionally matched standards individual spot measurements of the 206 pb 238 u and 208 pb 232 th ratios in unknown monazites of low to moderate th can be determined to 2 1 the dating technique was applied to in situ analysis of small monazite inclusions hosted in an amphibolite grade metapelite of archean origin both the contextual setting and the morphology of the monazite grains were found to be important factors in interpreting the timing of growth of the host metamorphic mineral e g garnet staurolite plagioclase euhedral monazite grains armoured in low cao garnet and matrix plagioclase yielded an age of 2548 17 ma interpreted as dating an early episode of low pressure metamorphism partially resorbed monazite within a high cao garnet rim yielded ages of ca 2500 ma but are interpreted as inherited from the first event rather than syn genetic with respect to the growth of this garnet an age of 1755 30 ma was obtained for anhedral monazite associated with late chlorite filled fractures apparently reflecting post tectonic retrogression

modeling and observation of the radar polarization signature of forested areas to understand radar measurements of forested areas the authors have developed a model of l band 25 cm microwave scattering from a forest the forest floor is layer of nearly vertical dielectric cylinders representing tree trunks above this layer is a second layer consisting of randomly oriented cylinders which represent branches the authors identify several scattering mechanisms and calculate the corresponding stokes matrices which combine to give the total stokes matrix and resulting polarization signature it is found that this simple model permits accurate prediction of the polarization of the scattered waves and that additional mechanisms including the effects of leaves and twigs are not required for the 25 cm observation of the forests studied the authors present measurements of the polarization signature acquired over a forested area and show comparisons with model calculations

proterozoic granulites from the rauer group east antarctica i decompressional pressure temperature paths deduced from mafic and felsic gneisses

the effect of topography on radar scattering from vegetated areas the ways in which radar scattering from vegetated areas is affected by the topography of the surface underneath the vegetation are discussed it is shown using a discrete scatterer model that the dominant scattering mechanism may change drastically when the ground surface is tilted relative to the horizontal for a horizontal ground surface for example the total scattering may be dominated by scattering off the tree trunks followed by a reflection off the ground surface for a relatively small tilt in the ground surface the ground trunk interaction term may be replaced by scattering from the branches alone as the dominant scattering mechanism the effect of the topography is more pronounced for scattering by longer wavelengths and the implications on algorithms designed to infer forest woody biomass and soil and vegetation moisture using polarimetric sar data are discussed the effect of the topography on the scattering behavior from forested areas is illustrated with images acquired by the nasa jpl three frequency polarimetric sar over the black forest in germany

new constraints on metamorphism in the rauer group prydz bay east antarctica granulite facies metapelites of the mather and filla paragneisses within the rauer group east antarctica possess markedly different compositions the metamorphic evolution of the two metapelite types has been interpreted as temporally distinct with the rauer group preserving at least two distinct granulite facies tectonothermal episodes calculated p t pseudosections and orthopyroxene al content indicate the revised maximum preserved p t conditions within the mather paragneiss to lie in the vicinity of 950 975 c and 10 10 6 kbar less extreme than previous estimates the range of possible p t paths for the mather paragneiss consistent with mineral textural relationships and pseudosections contoured for mineral proportion are significantly shallower dp dt than previous estimates a near isothermal decompression p t path and extreme peak metamorphic conditions are not necessary to explain the development of preserved mineral reaction textures the filla paragneiss contains pelitic assemblages less amenable to rigorous quantitative analysis nevertheless possibilities for the shared or otherwise metamorphic evolution of the mather and filla paragneisses may be postulated on the basis of calculated pseudosections in the context of existing geochronology for the rauer group and preserved microstructures a shared evolution most likely during pan african granulite facies metamorphism is plausible and consistent with mineral assemblage development geochronology and microstructures a revised interpretation of the rauer group s preserved metamorphic evolution may warrant the revision of existing tectonic models applicable also to the remainder of prydz bay more generally the employed approach may incite a revision of peak p t and p t paths in other granulite facies terranes

ultrahigh temperature granulite metamorphism 1050 c 12 kbar and decompression in garnet mg70 orthopyroxene sillimanite gneisses from the rauer group east antarctica highly magnesian and aluminous migmatitic gneisses from mather peninsula in the rauer group eastern antarctica preserve ultrahigh temperature uht metamorphic assemblages that include orthopyroxene sillimanite quartz garnet sillimanite quartz and garnet orthopyroxene sillimanite garnet that ranges up to xmg of 71 5 coexists with aluminous orthopyroxene that shows zoning from cores with 7 5 8 5 wt al2o3 to rims with up to 10 6 wt al2o3 adjacent to garnet peak p t conditions of 1050 c and 12 kbar are retrieved from fe mg al thermobarometry involving garnet and orthopyroxene in very good agreement with independent constraints from petrogenetic grids in feo mgo al2o3 sio2 and related chemical systems sapphirine orthopyroxene and cordierite form extensive symplectites and coronas on the early phases the specific reaction textures and assemblages involving these secondary phases correlate with initial garnet xmg with apparent higher pressure reaction products occurring on the more magnesian garnet and are interpreted to result from an initial phase of ultrahigh temperature near isothermal decompression uht itd from 12 to 8 kbar at temperatures in excess of 950 c later textures that involved biotite formation and then partial breakdown along with garnet relics to symplectites of orthopyroxene cordierite or cordierite spinel may reflect hydration through back reaction with crystallizing melts on cooling below 900 850 c followed by itd from 7 to 8 kbar to c 5 kbar at temperatures of 750 850 c the tectonic significance of this p t history is ambiguous as the rauer group records the effects of archean tectonothermal events as well as high grade events at 1000 and 530 ma late stage biotite formation and subsequent itd can be correlated with the p t history preserved in the proterozoic components of the rauer group and hence with either 1000 or 530 ma collisional orogenesis however whether the preceding uht itd history reflects a temporally unrelated event e g archean or is simply an early stage of either the late proterozoic or pan african tectonism as recently deduced for similar uht rocks from other areas of the east antarctica remains uncertain

monazite paragenesis and u pb systematics in rocks of the eastern mojave desert california u s a implications for thermochronometry abstract studies of the paragenesis and u pb systematics of monazite in rocks from the eastern mojave desert california corroborate its potential usefulness as a prograde thermochronometer and in dating granite inheritance unmetamorphosed latham shale and its equivalents at grades ranging from greenschist to upper amphibolite facies are virtually identical in composition monazite is absent in the shale and low grade schists but it is abundant in schists at staurolite and higher grades lower grade schists instead include minute th and ce oxides and unidentified ce poor lree phosphates that apparently are lower temperature precursors to monazite thus monazite originates when the pelite passes through lower amphibolite facies conditions monazites from three upper cretaceous granites yield ages that are strongly discordant upper intercepts of 1 6 1 7 ga are similar to those defined by u pb data for coexisting zircons and coincide with a period of copious magmatism in the mojave crust as the host upper cretaceous granitic magmas were all above 700 c effective closure of the restitic monazites to pb loss must be well in excess of this temperature u pb compositions of monazite from proterozoic granitoids and schist also indicate high pb retentivity taken together these studies support the suggestion that monazite can be an effective prograde thermochronometer at least in pelites it is not usually retained as a detrital mineral but rather forms during moderate temperature metamorphism its u pb system should not be reset by subsequent higher grade metamorphism

a radar backscatter model for discontinuous coniferous forests a radar backscattering model for low to medium density woodland in which each tree is treated as an individual backscatterer is described a forest stand viewed by radar is then an assemblage of scatterers standing on a background in a certain spatial pattern the backscattering components arising from the various intersections of radar beams with the forest stand are calculated separately and their stokes matrices are then added together to achieve the stokes matrix for total backscattering probabilities of radar beams intersecting tree crowns are introduced into the model

a simple model for the synoptic analysis of cold fronts a split cold front model with an over running upper front or humidity front ahead of a surface front or humidity front is shown to provide a useful representation of the principal characteristics of many katafronts the use of such a model leads to more consistent analyses especially of cloud and rain than are achieved using unmodified classical concepts

a crystal chemical basis for pb retention and fission track annealing systematics in u bearing minerals with implications for geochronology this study develops an empirical crystal chemical framework for systematizing the kinetics of pb loss and fission track annealing in u bearing minerals ionic porosity z the fraction of a mineral s unit cell volume not occupied by ions potentially accounts for kinetic behavior by monitoring mean metal oxygen bond length strength various tests of a general kinetics porosity relationship are presented based upon diverse mineral data including 1 pb diffusion parameters 2 measured closure temperatures tc for fission track annealing and 3 retentivities of both pb and fission tracks from apparent age data every kinetic parameter including tc and mineral age for both the u pb and fission track systems is inversely correlated with z within the sub assemblage zircon z 29 titanite 34 and apatite 38 assuming a diffusional closure model pb isotopic transport phenomena are described by a tc z scale calibrated with field based tc data for titanite 680 20 c and apatite 500 c extrapolation of this scale yields tc estimates for the following minerals staurolite tc 1060 c z 25 garnet 1010 c 26 5 zircon 900 c monazite xenotime and epidote 750 c 32 and ca clinopyroxene 670 30 c 34 1 depending on composition these empirical results imply that a u pb pb date for staurolite or garnet records the time of mineral growth not post growth isotopic closure as also concluded in recent field studies because z systematizes fission track annealing this recrystallization process like volume diffusion must also be rate limited by the strength of chemical bonds the extent to which other recrystallization processes are likewise rate limited is important to u pb geochronology because they potentially compete with diffusion as mechanisms for pb isotopic resetting in nature

zonation of monazite in metamorphic rocks and its implications for high temperature thermochronology a case study from the lewisian terrain abstract monazite is a valuable chronometer for many geological processes and a proper interpretation for the age derived from monazite requires an adequate understanding of the behaviour of this phase and its chemical and isotopic systems during geological processes this contribution reports the results of a detailed study on chemical and isotopic zonation of monazite in lewisian granulites which is of general significance for monazite geochronology in high grade metamorphic rocks detailed investigations on two lewisian granulite samples using sem epma and sims have revealed that lewisian monazites frequently show petrographic chemical and age zonation the petrographical zonation which reflects the chemical compositional variation can be characterised as follows on the basis of the bse images 1 concentric zoning 2 patchy zoning and 3 intergrowth like zoning the chondrite normalised ree distribution patterns are remarkably similar between different zones of single monazite grains this rules out the possibility that any portion of a zoned monazite in these two samples is detrital in origin some possible mechanisms are proposed for the formation of monazite zonation these include 1 intergrowth of monazite crystals with different composition 2 episodic growth or regrowth of monazite in response to the change of environment conditions during thermal event s which may involve recrystallisation or replacement of the original crystals in short the diversity of zoning patterns in monazites observed in this study cannot be explained assuming a single mechanism accordingly interpretation of the chemical and age information from any zoned monazite requires an adequate understanding of its formation mechanism line scans of th u pb la ce nd sm ca and si across monazite zones have been performed on two monazite grains which experienced granulite facies metamorphism the very sharp boundaries in these line scans indicate that the diffusive transport of these elements in monazite is low even at the temperature of granulite facies metamorphism the effective closure of monazite grains may also depend upon other factors such as the armouring effects of the host phase and recrystallisation of the mineral itself thus great care needs to be taken for geological application of the closure temperature concept

two stages of zircon and monazite growth in anatectic leucogneiss shrimp constraints on the duration and intensity of pan african metamorphism in prydz bay east antarctica

differential response of u pb systems in coexisting accessory minerals winnipeg river subprovince canadian shield implications for archean crustal growth and stabilization the u pb isotopic systems of zircon monazite titanite and some apatite and the pb isotopic composition of k feldspar have been investigated in three areas of the winnipeg river subprovince wrs of the superior province canada in order to define the timing of magmatic and metamorphic processes in this archean gneissic granitoid terrain

improving isochron calculations with robust statistics and the bootstrap typical isochron calculations involve using a least squares analysis of the data if the scatter about a line through the data is perfectly gaussian then least squares provides an optimal handling of the data however if the data are gaussian only in the centre of the distribution but depart from it only slightly in the tails of the distribution then least squares is not optimal and can easily degrade seriously for the size of datasets that are used in isochron calculations such non gaussian behaviour is impossible to test for this is important because there are numerous sources of uncertainty which might result in subtly non gaussian behaviour therefore to defend against degradation it is proposed that isochron calculations be modified by the use of a robust statistical method so that non gaussian tail behaviour can be accounted for for data that are actually gaussian distributed the new isochron calculation method will generally give identical results to least squares the improvement given by the new method is illustrated by the use of simulations

age mapping and dating of monazite on the electron microprobe deconvoluting multistage tectonic histories high resolution x ray mapping and dating of monazite on the electron microprobe are powerful geochronological tools for structural metamorphic and tectonic analysis x ray maps commonly show complex th u and pb zoning that reflects monazite growth and overgrowth events age maps constructed from the x ray maps simplify the zoning and highlight age domains microprobe dating offers a rapid in situ method for estimating ages of mapped domains application of these techniques has placed new constraints on the tectonic history of three areas in western canada age mapping has revealed multiphase monazite with older cores and younger rims included in syntectonic garnet microprobe ages show that tectonism occurred ca 1 9 ga 700 m y later than mylonitization in the adjacent snowbird tectonic zone in new mexico age mapping and dating show that the dominant fabric and triple point metamorphism occurred during a 1 4 ga reactivation not during the 1 7 ga yavapai mazatzal orogeny in norway monazite inclusions in garnet constrain high pressure metamorphism to ca 405 ma and older cores indicate a previously unrecognized component of ca 1 0 ga monazite in all three areas microprobe dating and age mapping have provided a critical textural context for geochronologic data and a better understanding of the complex age spectra of these multistage orogenic belts

an improved u th pb age calculation for electron microprobe dating of monazite abstract determination of u th pb ages using the electron probe microanalyser epma is an inexpensive alternative method for dating monazite the method is rapid and reliable both for simple monogenenetic monazite and for complex polygenetic monazite having undergone metamorphic events involving fluid interaction and recrystallization the main limitation of the method is its rather poor precision i e 45 to 120 ma for ages ranging from 300 to 3000 ma calculated on each spot the precision is limited by pb content and by counting statistics which cannot give precision better than 2 for individual determinations on u th and pb even at high levels a procedure that uses the new th pb vs u pb diagram to improve the calculated precision on u th pb ages gives results to within 5 to 15 ma for ages ranging from 300 to 3000 ma with complex polygenetic monazite in which either the points show large scattering indicated by a large mswd or the regression line exhibits a slope very different from neighbour theoretical isochrons the procedure must be applied separately on homogeneous domains only this makes it possible to distinguish between events separated by a gap of 20 to 60 ma according to the range of ages concerned i e 300 to 3000 ma several examples are given to illustrate these systematics

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

low vhf band backscatter from coniferous forests on sloping terrain low frequency synthetic aperture radar sar is a promising technique for stem volume retrieval particularly for dense forests due to the good penetration of forest canopies however it is well known that the dominant scattering mechanism the trunk ground dihedral interaction decreases rapidly on sloping terrain in this paper we use low vhf band sar data collected with carabas over dense coniferous forests in sweden to examine the effect of topography using flight passes with different headings the effect of slope and aspect angle on backscatter is characterized for tall trees spl sim 30 m on the steepest slopes in the test site up to spl sim 12 spl deg differences of up to 8 db are observed between images acquired with different look directions relative to the slope a physical model is developed to investigate the different scattering mechanisms and their sensitivity to terrain slopes the model shows that the trunk ground scattering still dominates the response for large trees on moderate slopes and a semiempirical model for the effect of topography on backscatter is proposed the model shows good agreement with measurements indicating the possibility of using it to compensate for the effects of sloping terrain when retrieving stem volume in coniferous forest

unsupervised classification of scattering behavior using radar polarimetry data the use of an imaging radar polarimeter data for unsupervised classification of scattering behavior is described by comparing the polarization properties of each pixel in an image to that of simple classes of scattering such as even number of reflections odd number of reflections and diffuse scattering for example when this algorithm is applied to data acquired over the san francisco bay area in california it classifies scattering by the ocean as being similar to that predicted by the class of odd number of reflections scattering by the urban area as being similar to that predicted by the class of even number of reflections and scattering by the golden gate park as being similar to that predicted by the diffuse scattering class it also classifies the scattering by a lighthouse in the ocean and boats on the ocean surface as being similar to that predicted by the even number of reflections class making it easy to identify these objects against the background of the surrounding ocean

estimation of near surface soil moisture in a sloping terrain of a himalayan watershed using envisat asar multi incidence angle alternate polarisation data soil moisture is one of the important input variables in hydrological and water erosion models the extraction of information on near surface soil moisture from synthetic aperture radar sar is well established mostly for flat terrain and using low incidence angle single polarisation data the envisat advanced sar asar data available in multiple incidence angles and alternate polarisation modes were investigated in this study for soil moisture estimation in sloping terrain the test site was sitla rao watershed in the lesser himalayas of northern india empirical models were developed to estimate near surface soil moisture in bare agricultural fields using alternate polarisation asar data both soil moisture and surface roughness field measurements were performed during the satellite passes backscatter from medium incidence angle is 4 and vertical vertical vv polarisation signal is correlated better with volumetric soil moisture content compared to other incidence angles the model parameters were further improved and soil moisture estimation was refined by combining medium incidence angle is4 vertical horizontal polarisation response as another variable along with vv polarisation response the effect of slope on the radar backscatter was minimized by incorporating local incidence angles derived from an aster dem copyright 2012 john wiley sons ltd

th u pb monazite ages from al mg rich metapelites rauer group east antarctica the age of high temperature granulite facies metamorphism 800 850 c in the rauer group prydz bay east antarctica is relevant for establishing the metamorphic and temporal architecture of the prydz bay mobile belt monazites within al mg rich granulite facies metapelites give an overall tanh estimated pan african age of 511 4 ma 2r using in situ electron microprobe based th u pb chronology consistent with existing u pb zircon geochronology from the rauer group and prydz bay monazite occurs primarily within cordierite bearing coronae and symplectic min eral reaction textures and also within biotite pan african granulite facies metamorphism is preferred as responsible for the development of the cordierite bearing microstructures and probably peak coarse grained assemblages constrained using an integrated geologic geochronologic and metamorphic framework thus pan african granulite facies metamorphism affected the rauer group within the prydz bay mobile belt moreover integrated monazite geochronology may be used to decipher the temporal metamorphic histories of potentially complex high temperature terrains

measurement of topography using polarimetric sar images a processing technique for polarimetric synthetic aperture radar sar data has been developed which produces profiles of terrain slopes and elevations in the azimuthal or along track direction this technique estimates the average shift in orientation angle of copolarization backscatter caused by azimuthal tilts of the scattering plane using p band data tests of this technique have been made for an area in the black forest near villingen schwenningen in baden wurttemberg germany the radar measured slope and derived elevation profiles have low rms errors and high correlation values when compared with a stereo photograph digital elevation map dem for the area this algorithm is capable of adaptively making transitions from the forested areas to nearby regions with open terrain subsequent tests of the algorithm have been conducted using polarimetric sar l band data for a mountainous nonforested region in the mojave desert ft irwin ca where an accurate dem also was available complete elevation and slope mapping of the terrain in two dimensions using this technique is possible when azimuthal elevation profiles are produced throughout the range extent of the sar image

the evolution of a layered metaigneous complex in the rauer group east antarctica evidence for a distinct archaean terrane abstract the rauer group in prydz bay east antarctica contains both archaean and proterozoic crustal components archaean geological relationships have been defined from the scherbinina layered complex slc a polydeformed and metamorphosed fe tholeiite intrusive cut by several generations of deformed metabasite dykes the slc and three of these dyke generations are intruded by tonalitic and trondhjemitic sheets representative of archaean felsic orthogneisses present outside the complex u pb shrimp dating of zircons precisely defines the magmatic age of the slc as 2844 6 ma a tonalite sheet that cuts the slc preserves a complex zircon isotopic array dominated by inherited grains derived from source rocks up to 3470 30 ma old but from field evidence was emplaced at ca 2800 2550 ma the presence of 3470 ma source rocks is unique in the east antarctic shield and this feature as well as the prominence of 2840 2800 ma orthogneisses establishes the rauer group as a distinct archaean terrane the archaean of the rauer group is not comparable with the nearby vestfold hills where ca 2520 2480 ma orthogneisses form the dominant rock units it is likely that the vestfold hills and rauer group terranes were amalgamated at either 1000 or 500 ma rather than at the end of the archaean a mid proterozoic tectonothermal event documented in the rauer group from syn metamorphic 1030 1000 ma intrusives kinny p d black l p and sheraton j w 1993 zircon ages and the distribution of archaean and proterozoic rocks in the rauer islands antarctic sci 5 193 206 has not been detected in the zircon u pb data obtained on the archaean gneisses examined here instead the slc and intrusive tonalite show resetting of zircon u pb systematics at ca 520 ma this resetting reflects pb loss within irregular compositional zones and healed cracks in older zircon and is attributed to the effects of fluid infiltration under greenschist to amphibolite facies conditions these effects correlate in time with ca 530 510 ma higher grade deformation and metamorphism evident in proterozoic paragneisses exposed in areas to the south west of the rauer group and may record amalgamation of the rauer group with these areas during the east gondwanian pan african orogeny

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

correction of sar imagery for variation in pixel scattering area caused by topography the radiometric correction of synthetic aperture radar sar imagery for topographically induced changes in the pixel scattering area is examined the relative significance of ground slope in the range and azimuth directions is compared and a widely used correction factor based on the sin of the local radar incidence angle is shown to be sufficiently accurate the importance of performing this correction in slant range rather than ground range is demonstrated

electron microprobe observations of pb diffusion in metamorphosed detrital monazites electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite sillimanite transition 620 15 c and sillimanite orthoclase 680 15 c zones of the cretaceous ryoke metamorphic belt southwest japan monazites from pelitic gneisses are of metamorphic origin euhedral to subhedral and chronologically homogeneous giving chemical th u total pb isochron chime ages of 98 8 3 3 98 0 3 2 ma two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca 1700 ma most detrital monazite grains are heterogeneous in the tho2 and uo2 concentrations and have multiple or single rims as young as ca 100 ma several detrital monazite grains are well rounded in form exhibit homogeneous th and u distributions and show a pb diffusion profile in the margin the width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss 18 22 m for 620 c and 48 58 m for 680 c assuming the isothermal diffusion of pb from homogeneous monazite spheres during a 5 ma duration of peak metamorphism we obtain diffusion coefficients of 1 9 0 3 10 21 and 1 5 0 3 10 20 cm2 s at 620 c and 680 c respectively these data derive an activation energy of 2 44 2 85 1 26 105 j mol and a frequency factor of 3 4 10 7 8 5 10 12 2 2 107 cm2 s taking account of uncertainties of 15 c in the temperatures and of 20 in the diffusion coefficients the diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for pb in monazite that has been poorly understood so far

identification and climatology of southern hemisphere mobile fronts in a modern reanalysis abstractpresented here is an objective approach to identify characterize and track southern hemisphere mobile fronts in hemispheric analyses of relatively modest resolution such as reanalyses among the principles in its design were that it should be based on broadscale synoptic considerations and be as simple and easily understood as possible the resulting eulerian scheme has been applied to the european centre for medium range weather forecasts ecmwf re analysis era interim and a climatology of frontal characteristics at both the 10 m and 850 hpa levels derived for the period 1 january 1989 28 february 2009 the knowledge of the character of these features is central to understanding weather and climate over the hemisphere in both summer and winter the latitude belt 40 60 s hosts the highest frequency of frontal points but there are significant zonal asymmetries within this band the climatology reveals that the longest fronts are in the indian ocean where mean lengths exceed 2000 km the me

backscatter model for the unusual radar properties of the greenland ice sheet a number of planetary objects exhibit large radar reflectivity and polarization ratios and more recently a similar behavior has been observed over a vast portion of the earth s surface the percolation facies of the greenland ice sheet surface based ranging radar data and snow stratigraphy studies demonstrated that the radar properties of that portion of greenland are caused by enhanced scattering from massive large solid ice bodies buried in the top few meters of the dry cold clean snowy surface of the ice sheet and created by seasonal melting and refreezing events from author

reaction textures in calc silicate granulites from the bolingen islands prydz bay east antarctica implications for the retrograde p t path calc silicate granulites from the bolingen islands prydz bay east antarctica exhibit a sequence of reaction textures that have been used to elucidate their retrograde p t path the highest temperature recorded in the calc silicates is represented by the wollastonite and scapolite bearing assemblages which yield at least 760 c at 6 kbar based on experimental results the calc silicates have partially re equilibrated at lower temperatures down to 450 c as evidenced by the successive reactions 1 wollastonite scapolite calcite garnet co2 2 wollastonite co2 calcite quartz 3 wollastonite plagioclase garnet quartz 4 scapolite plagioclase calcite quartz 5 garnet co2 h2o epidote calcite quartz and 6 clinopyroxene co2 h2o tremolite calcite quartz the reaction sequence observed indicates that aco2 was relatively low in the wollastonite bearing rocks during peak metamorphic conditions and may have been further lowered by local infiltration of h2o from the surrounding migmatitic gneisses on cooling fluid activities in the bolingen calc silicates were probably locally variable during the granulite facies metamorphism and large scale co2 advection did not occur a retrograde p t path from the sillimanite stability field c 760 c at 6 kbar into the andalusite stability field c 450 c at 3 kbar is suggested by the occurrence of secondary andalusite in an adjacent cordierite sillimanite gneiss in which sillimanite occurs as inclusions in cordierite

a physical optics model for double bounce scattering from tree stems standing on an undulating ground surface in this paper a model for prediction of radar backscatter from coniferous forests in the vhf and uhf band is proposed the model includes the double bounce scattering originating from vertical stems standing on an undulating ground surface and is based on a physical optics approach the model can be used to assess the importance of ground topography in synthetic aperture radar sar imagery of forests and it is applicable to sar systems using horizontally transmit and receive polarization hh the model was validated against data from the airborne sar systems carabas ii and lora precision measurements of ground topography and forest characterization at a single tree level were used as model input to simulate sar images the simulated images were compared to radar data in the frequency bands 22 82 and 225 470 mhz and it was found that the model could predict much of the variation in backscatter observed in images r2 0 44 and 0 65 at best for the lower and higher frequency band respectively which should be compared to r2 0 1 if the same model but assuming a flat ground was used the results thus indicate that ground topography must be considered when predicting the variations in backscatter in the sar images studied the model did however fail to predict the absolute values of the backscattered intensity the reason for the discrepancy is believed to be the value chosen for stem dielectric constant and unmodeled effects due to wave attenuation tilting stems and small scale surface roughness

polarimetric radar measurements of a forested area near mt shasta the authors present the results of an experiment using the nasa jpl dc 8 airsar aircraft synthetic aperture radar over a coniferous forest near mt shasta california in 1989 calibration devices were deployed in clearings and under the forest canopy and passes at 20 degrees 40 degrees and 55 degrees incidence angles were made with the airsar a total of eight images at differing incidence angles have been processed and calibrated the multipolarization multifrequency data were examined and it was found that the c band cross section averaged over like and cross polarizations is the best parameter for distinguishing between two stands with differing forest biomass the average cross section at p and l bands is useful only for smaller incidence angles parameters describing the polarization behavior of the scattering were primarily useful in identifying the dominant scattering mechanisms for forest backscatter

pressure temperature evolution of metapelitic granulites in a polymetamorphic terrane the rauer group east antarctica distinctive lithological associations and geological relationships and initial geochronological results indicate the presence of an areally extensive region of reworked archaean basement containing polymetamorphic granulites in the rauer group east antarctica structurally early metapelites from within this reworked region preserve complex and varied metamorphic histories which largely pre date and bear no relation to a late proterozoic metamorphism generally recognized in this part of east antarctica in particular magnesian metapelite rafts from long point record extreme peak p t conditions of 10 12 kbar and 100 1050 c and an initial decompression to 8 kbar at temperatures of greater than 900 c initial garnet orthopyroxene sillimanite assemblages contain the most magnesian and pyrope rich garnets xmg 0 71 yet found in granulite facies rocks a high temperature decompressional p t history is consistent with reaction textures in which the phase assemblages produced through garnet breakdown vary systematically with the initial garnet xmg composition reflecting the intersection of different divariant reactions in rocks of varied composition as pressures decreased this history is thought to relate to archaean events whereas a lower temperature c 750 800 c decompression to 5 kbar reflects late proterozoic reworking of these relict assemblages the major late proterozoic c 1000 ma granulite facies metamorphism is recorded in a suite of younger fe rich metapelites and associated paragneisses in which syn to post deformational decompression through 2 4 kbar from maximum recorded p t conditions of 7 9 kbar and 800 850 c is constrained by geothermobarometry and reaction textures this p t evolution is thought to reflect rapid tectonic collapse of crust previously thickened through collision

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

meteorological tower measurements of a surface cold front abstract measurements from the boulder atmospheric observatory meteorological research tower are used to describe the structure and physical processes of a strong surface cold front analysis reveals that the horizontal gradients in temperature and wind velocity at the front are concentrated within a 200 m distance and measured vertical velocities exceed 5 m s 1 at the leading edge of the front calculations with the miller frontogenesis equation show the magnitude and relative importance of cross frontal confluence versus differential vertical motion tilting in forcing frontogenesis

geochronology of polygenetic monazites constrained by in situ electron microprobe th u total lead determination implications for lead behaviour in monazite abstract monazite grains are generally concordant and with an electron microprobe give th u total pb isochron ages in agreement with conventional u pb data monazites from four samples of post archean migmatite from the ivory coast record two main ages an archean age at 2 80 ga partly overprinted by a late migmatization event at 2 03 ga the in situ electron microprobe determination has also shown a third event that systematically appears at 2 72 ga for all the monazites from two of the four studied rocks the three events at 2 80 2 72 and 2 03 ga recorded by the th u total pb system in monazite were each obtained on independent homogeneous parts of a single grain with no sign of pb diffusion thus the oldest monazite remained closed during a high grade resetting migmatization at a temperature estimated at around 700 c and also remained closed during the growth of secondary monazite conventional u pb data isotope dilution on monazite from the same rocks did not allow precise age determinations because the representative points were highly up to 83 discordant and did not fit well along a chord in the concordia diagram the u pb isotope dilution method gave a lower intercept age of 2029 25 ma in agreement with the electron microprobe age although with an unusually high uncertainty due to a poor fit of the data the pb evaporation method gave an old archean age at 2830 7 ma and proterozoic ages ranging from 2417 10 to 2074 7 ma thus although the oldest archean age obtained with the pb evaporation and electron microprobe methods is similar within the analytical error the proterozoic ages obtained by the pb evaporation method are significantly older than the th u total pb proterozoic age obtained with the electron microprobe this discrepancy is presumed to be due to the influence in the pb evaporation method of radiogenic lead contained within archean zones of the monazite grains in other words it means that migmatization took place later than 2074 7 ma and probably around 2030 ma the second archean event at 2 72 ga revealed by high spatial resolution of the electron microprobe could not be determined by other methods the th u total pb method appears to be an inexpensive alternative method for dating simple monazites with a precision close to 20 ma even if the u pb isotopic dilution technique remains the reference method moreover owing to the very high spatial resolution 1 m of the electron microprobe it appears to have no competitor for dating complex polygenetic monazites especially when more than two events are recorded homogeneous zones of different ages coexist in a single grain with no major indication of lead diffusion a procedure for age and error calculations is defined

global climatologies of fronts airmass boundaries and airstream boundaries why the definition of front matters abstractclimatologies of fronts airmass boundaries and airstream boundaries can be calculated using automated approaches on gridded data such approaches may require choices to define a front in

crustal evolution of the east antarctic mobile belt in prydz bay continental collision at 500 ma the east antarctic mobile belt as exposed in prydz bay presents an excellent example of a poly metamorphic terrain where complicated high grade structures can be grouped on the basis of lineation direction sense of shear and metamorphic grade in this way local intricacies resulting from truncating and interfering foliations and folds can be simplified by ordering structures with respect to their kinematic connotation the resulting deformation scheme is simple and facilitates regional correlations and simultaneously places metamorphic textures in a kinematic structural background the mobile belt in prydz bay is exposed along 200 km of coastline and consists of granulite facies gneiss in which low to mid crustal compressional d1 2 structures and mid to upper crustal extensional d3 6 structures and relateddecompression cooling textures are best explained in an exhumation model involving extensional collapse of upper crust in an overall compressional tectonic setting this implies that compression and extension structures are genetically related however d3 6 structures in the larsemann hills appear to have formed between 550 and 500 ma whilst d2 structures in the rauer group have been dated at 1100 1000 ma reinterpretation of the latter dates is possible implying that most high grade deformation in prydz bay is early palaeozoic

a metamorphic history from micron scale 207pb 206pb chronometry of archean monazite ion microprobe measurements of pb isotope ratios in monazites have been obtained in situ from thin sections using the cambridge isolab 120 molecular interferences are sufficiently resolved at an rp of 6500 to allow 2 7pb z 6pb dating of monazite with precisions as low as 4 5 ma 2 r the results presented here provide important information on the chronological history of the late archean metamorphism of the wind river range wyoming usa matrix monazites and monazite inclusions in garnets from a metapelite from the northern wind river range have been analysed by sims in a previous study peak metamorphic conditions t 800 c p 8 1 kb were estimated using inclusion assemblages in garnets from this same sample isolated monazite inclusions in garnet yield 2 7pb z 6pb age estimates of 2781 6 to 2809 10 ma those along fractures yield lower ages 2603 2687 ma which are similar to tims and sims ages of matrix monazites a single large 500 xm monazite grain locally preserves growth zoning but has a recrystallised core and a resorbed recrystallised rim age estimates for these three regions are 2788 9 ma 2663 4 and 2523 6 ma respectively thus the inclusion assemblages of sharp and essene may record peak metamorphic conditions at ca 2 8 ga and indicate a phase of metamorphism that predates by over 100 ma the emplacement of the bridget batholith the major lithologic component of the northern wind river range the analysed monazite grains appear to preserve ca 300 ma history even within a single grain monazite inclusions in garnet that are fully armoured may provide estimates for the time of garnet growth even in high grade terranes where most chronometers are reset the age pattern preserved by the large monazite grain cannot be simply related to diffusion controlled closure instead a chronology is preserved which can be related to the petrographic setting of individual grains through in situ analysis

chemical th u total pb dating by electron microprobe analysis of monazite xenotime and zircon from the archean napier complex east antarctica evidence for ultra high temperature metamorphism at 2400 ma abstract the chemical th u total pb isochron method chime of dating was carried out on monazite xenotime zircon and polycrase in six samples of ultra high temperature uht granulites and one of pegmatite from five localities in the napier complex enderby land east antarctica despite the chronological heterogeneity in many grains the chime ages overall show strong evidence for a major event near 2420 ma analyzed monazite and xenotime grains except monazite from mt riiser larsen have a narrow range of chime ages 2412 42 ma from beaver island and 2429 36 2421 18 and 2431 22 ma from reference peak these ages are indistinguishable from chime ages on zircon 2436 17 and 2420 20 ma and on central older domains of monazite 2404 54 ma from mt riiser larsen and on a zircon rim 2430 15 ma from mt cronus we conclude that the ca 2420 ma ages relate to the uht metamorphism but we do not exclude the possibility that lead loss has lowered the ages by some 50 ma this interpretation is consistent with a preponderance of ages obtained by other methods on the napier complex particularly the ca 2475 25 ma age for a generation of pegmatites coeval with the uht event and containing the uht mineral assemblage beryllian sapphirine khmaralite quartz events prior to 2500 ma and after 2420 ma have also left their imprint on the chime ages for example a 3646 ma chime age suggests that a zircon core is inherited whereas ca 2200 and 2000 ma chime ages in zoned monazite could be due to further lead loss during post uht activity the much younger chime age of 1094 67 ma for monazite from a pegmatite at zircon point casey bay confirms 1000 1100 ma lead loss ages reported for this region and could result from fluid activity in an outlier of rayner activity near the boundary between the rayner and napier complexes approximately 2500 ma ages have been reported from granulite facies but not uht rocks in the madras and nilgiri blocks in south india these blocks and the napier complex could have constituted a single structural unit by late archean time

u pb systematics of monazite and xenotime case studies from the paleoproterozoic of the grand canyon arizona monazite is accepted widely as an important u pb geochronometer in metamorphic terranes because it potentially preserves prograde crystallization ages however recent studies have shown that the u pb isotopic system in monazite can be influenced by a variety of processes that partially obscure the early growth history in this paper we attempt to interpret complex monazite and xenotime u pb data from three paleoproterozoic granite dikes exposed in the grand canyon single crystal monazite analyses from an unfoliated granite dike spread out along concordia from the crystallization age of the dike defined by u pb zircon data to be 1685 1 ma to 1659 2 ma a span of 26 million years back scattered electron bse imaging reveals that magmatic domains within most crystals from this sample are truncated by secondary domains associated with prominent embayments at the grain margin fragments of a single crystal yield contrasting concordant dates and fragments from the edges and tips of crystals yield the youngest dates based on these observations we suggest that the secondary domains formed at least 26 million years after the crystal formed monazite and xenotime dates from the second sample a sheared dike that cross cuts the previous dike spread out along concordia over 16 million years and range up to 2 4 normally discordant again bse imaging reveals secondary domains that truncate both magmatic zoning and xenocrystic cores fragments sliced from specific domains of a previously imaged monazite crystal demonstrate that the secondary domain is 13 million years younger than the core domain textures revealed in bse images suggest that the secondary domains formed by fluid mineral interaction normal discordance appears to result from both radiation damage accumulated at temperatures below 300 c and water mineral interaction monazite data from the third sample exhibit dispersion in both the 207pb 206pb dates 1677 1690 ma and discordance 1 6 to 3 1 reverse discordance in these monazites cannot be explained by incomplete dissolution or excess thorogenic 206pb sliced fragments from several crystals reveal dramatic intragrain u pb disequilibrium that does not correlate with either th or u concentration or position within the crystal we suggest that reverse discordance resulted from mechanisms that involve exchange or fractionation of elemental u or elemental pb and that neither the u pb dates nor the 207pb 206pb dates are reliable indicators of the rock s crystallization age given the large number of processes proposed in the recent literature to explain monazite u pb systematics from rocks of all ages our results can be viewed as another cautionary note for single crystal and multi crystal monazite geochronometry however we suggest that because individual crystals can preserve a temporal record of primary and secondary monazite growth micro sampling of individual monazite crystals may provide precise absolute ages on a variety of processes that operate during the prograde peak and or retrograde history of metamorphic terranes

phenomenology of ground scattering in a tropical forest through polarimetric synthetic aperture radar tomography this paper aims at characterizing the scattering mechanisms occurring at the ground level in a tropical forest illuminated by a p band synthetic aperture radar sar the analysis is carried out based on the multibaseline fully polarimetric data set collected by onera over paracou french guyana in the frame of the european space agency campaign tropisar the favorable baseline distribution of this data set results in the possibility of removing most contributions from the vegetation layer by tomographic techniques thus allowing the generation of a new fully polarimetric single look complex sar image relative to scattering contributions from the ground level only such a ground layer image is then analyzed by considering the variation of its polarimetric signature with respect to terrain local slope and radar look angle two major conclusions are drawn 1 double bounce scattering from trunk ground interactions is observed to be the dominant scattering mechanism at the ground level on flat terrains whereas it rapidly tends to vanish as the topographic slope increases and 2 the characteristic parameter that rules trunk ground scattering is not the tree height but rather the available free path facing the tree as a result of the presence of nearby trees undulating topography or understory preventing double bounce scattering from taking place whenever the ground bounce occurs too far away from the considered tree the mean free path length resulting from the analysis of this data set is found to be l 7 m finally we discuss how the concept of free path length can be accounted for in simple terms by assuming an equivalent extinction model characterized by a variation along the horizontal dimension

a decompressional p t path reinbolt hills east antarctica granulites exposed in the reinbolt hills east antarctica are part of the extensive late proterozoic granulite complex of east antarctica which includes the rauer group to the east and the northern prince charles mountains to the west the deformation history includes three pervasive deformation phases no chemical or mineralogical distinction between these phases has been detected and this is interpreted to be the result of complete re equilibration at the end of the third deformation phase two late deformation phases post date the metamorphism and record a medium temperature cooling path a short segment of the p t path of these rocks was inferred from mineral reactions that occurred during these late deformation phases the path passes from 800 c 7 kbar to 690 c 5 kbar indicating strong decompression which is typical of a thrust dominated crustal thickening followed by rapid erosion or extensional collapse