contrasting provenance and timing of metamorphism from paragneisses of the aracuai ribeira orogenic system brazil hints for western gondwana assembly abstract the aracuai orogen and the ribeira belt make up a complex neoproterozoic cambrian orogenic system the aracuai ribeira orogenic system aros located from the eastern to southeastern brazil along the aros the ediacaran rio doce magmatic arc represents a geotectonic connection between the aracuai and the ribeira orogenic domains although the nature and evolution of the rio doce plutonic rocks is regionally well established it lacks detailed studies on the paragneisses found along the western and central regions of this magmatic arc besides information on the nature and provenance of their sedimentary protoliths the paragneisses provide data to unravel the palaeogeographic scenario from the precursor to arc related basins six samples of al rich gneisses covering a large aros region were selected for electron microprobe emp mineral analyses in order to obtain geothermobarometric data and monazite ages as well as for laser ablation inductively coupled plasma mass spectrometry la icp ms isotopic analyses on zircon u pb lu hf and monazite u pb the different age spectra from detrital zircon grains and contrasting hf isotopic signatures suggest a complex sedimentary history located in the western sector of the study region the samples rc 02 and rc 34 with an 80 age peak of detrital zircon grains from 2158 ma to 1830 ma e hf t from 2 2 to 22 7 and hf t dm model ages from 3530 ma to 2440 ma suggest sediment sources located in the sao francisco craton basement the samples rc 03 also from the western sector and rc 46 from the southern sector have a more complex assemblage of detrital zircon grains with an 87 age peak from 987 ma to 592 ma e hf t from 14 9 to 2 9 and hf t dm model ages from 2220 ma to 720 ma indicating provenance from mainly juvenile sources of distinct ages candidates to be juvenile sources for rc 03 and rc 46 sedimentary protoliths are the rhyacian juiz de fora and pocrane complexes in the basement of the rio doce arc the neoproterozoic rio negro arc system of the ribeira belt and aros ophiolite complexes samples rc 30 and rc 38 from the eastern sector of the study region with most detrital zircon ages between 650 ma and 552 ma and very negative e hf t 25 3 to 16 5 suggest main sediment sources in the rio doce arc by extending u pb analyses on metamorphic zircon and monazite we have identified a complex timing of metamorphism represented by metamorphic ages ranging from 621 ma to 480 ma with the main collisional activity between 580 ma and 540 ma geothermobarometric studies on garnet porphyroblasts syn kinematic to the d 2 regional foliation show a retrograde metamorphic path typical of continental collision belts starting with p t conditions of t max 733 c and p max 6 43 kbar our data also suggest i the studied paragneisses represent distinct neoproterozoic basin stages shifting from passive to active margin settings ii if the rio negro arc system really provided sediments for the basin stage represented by the rc 03 and rc 46 paragneisses it would have amalgamated with the aros before 614 ma iii the final amalgamation of western gondwana took place around 540 ma in the focused region iv an important re heating period 520 480 ma can be related to the aros gravitational collapse after western gondwana assembly

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

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

microprobe monazite geochronology understanding geologic processes by integrating composition and chronology abstractmonazite is a light rare earth element lree bearing phosphate mineral that is present in a wide variety of rock types has an extremely variable composition reflecting host rock conditions and is a robust geochronometer that can preserve crystallization ages through a long history of geological events monazite crystals typically contain distinct compositional domains that represent successive generations of monazite which in turn can provide a detailed record of the geologic history of its host rocks the electron microprobe can be used to characterize the geometry of compositional domains analyze the composition of each domain and when carefully configured determine the u th total pb age for domains as small as 5 m in width these data allow the monazite to be linked with and place timing constraints on silicate processes in the host rocks current applications span a broad range of geologic processes in igneous metamorphic hydrothermal and sedimentary rocks

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

kinematics strain pattern and geochronology of the salem attur shear zone tectonic implications for the multiple sheared salem namakkal blocks of the southern granulite terrane india abstract structural mapping strain analysis and a variety of geochronological studies were carried out to determine the tectonothermal evolution of the salem attur shear zone in the southern granulite terrane of south india the salem namakkal blocks containing the shear zone consisted of quartzofeldspathic gneiss charnockite and mafic granulite and had undergone multiple phases of magmatism spanning over a period of 3 2 0 5 ga the rocks were deformed by four phases of deformation d1 d4 the d1 deformation was characterized by isoclinal and recumbent ne sw trending f1 fold with a pervasive subhorizontal axial planar granulitic fabric s1 and associated quartzofeldspathic leucosomes granulite metamorphism was dated at ca 2 5 2 3 ga the f1 fold and s1 fabric were coaxially refolded by tight to isoclinal upright to steeply inclined ne sw trending f2 folds during d2 deformation the d2 deformation was associated with f2 axial planar shear zones crenulations and leucosomes s2 fabric large scale d2 shear zones characterized by high temperature ductile shear fabric with a vertical flow host syntectonic syenite pluton which was dated at ca 2 5 2 4 ga a p t condition of 7 kb 600 c was inferred for the d2 deformation the d3 deformation was characterized by nw se to e w trending f3 folds and the salem attur shear zone the shear zone was a greenschist to amphibolite facies shear zone being characterized by mylonitic foliation and dominantly down dip stretching lineation defined by quartz biotite and hornblende minerals and dated at ca 2 0 ga it indicated n nne vergence of thrusting with the mean kinematic vorticity number wm as 0 7 suggesting general simple shear strain with 50 pure shear component the d4 deformation was manifested as nne ssw striking strike slip faults and nw se striking extensional normal faults pseudotachylite veins having an age of 1 9 ga injected during strike slip faulting and granite pegmatite veins showing age of 0 8 0 5 ga intruded during normal faulting the salem namakkal blocks thus recorded a long lived shearing history we suggest that the salem attur shear zone and other shear zones such as palghat cauvery moyar bhavani karur kambam painavu trichur and achankovil shear zones were paleoproterozoic intraterrane shear zones which were overprinted by meso neoproterozoic cambrian ductile and brittle deformations

origins of wind driven intraseasonal sea level variations in the north indian ocean coastal waveguide 1 in this paper we show that a linear continuously stratified ocean model reproduces observed wind driven intraseasonal sea level variability in the coastal waveguide of the northern indian ocean nio sensitivity experiments with intraseasonal wind forcing selectively applied in the equatorial region bay of bengal and arabian sea show that a large part of the basin scale sea level variations are driven by zonal wind fluctuations along the equator within the nio coastal waveguide the contribution of remote equatorial forcing decreases from 80 90 in the andaman sea to 50 northeast of sri lanka and then increases to 60 70 along the west coast of india during the southwest monsoon intraseasonal wind variations become stronger over the nio resulting in a larger contribution of local wind forcing to sea level variability along the west up to 60 and east up to 40 coasts of india

an assessment of monazite from the itambe pegmatite district for use as u pb isotope reference material for microanalysis and implications for the origin of the moacyr monazite abstract large quantities of monazite from different pegmatite bodies of the itambe pegmatite district were investigated to assess their suitability as u pb and sm nd isotope reference materials for la icp ms and to track the origin of a piece of the moacyr monazite termed here itambe a widely used reference material for la icp ms u pb geochronology monazite from the largest pegmatite bodies in the district the bananeira coqueiro and paraiso pegmatites are ce monazite with negligible amounts of the huttonite and brabantite components they are homogeneous in major and trace elements which makes them potential candidates as compositional reference materials u pb la icp ms and id tims analyses yielded identical ages within error although the id tims ages 507 7 1 3 207 pb 235 u and 513 6 1 2 ma 206 pb 238 u were reversely discordant spot ages determined by la icp ms geochronology were concordant at ca 508 ma the bananeiro monazite was assessed as a la icp ms u pb primary reference material against other known reference materials treated as unknowns this approach successfully reproduced the previously published ages of the reference materials mree hree fractionation ie la gd n and gd lu n values eu eu and the chondrite normalized ree patterns suggest that the itambe monazite aliquot is very similar to that from the coqueiro pegmatite this similarity is likewise apparent in their sm nd isotope compositions moreover the endi values of the itambe monazite fragment endi 4 2 and those from all the major pegmatites in the district are distinct from other reference materials eg managountry endi 22 3 as well as gem quality monazite from c 490 520 ma pegmatites from the aracuai orogen further to the south the endi can provide a further distinction for tracing brazillian gem quality monazite reference materials

neodymium isotopic compositions of the standard monazites used in u th pb geochronology abstract as an important carrier of thorium uranium and trace elements monazite is widely used in u th pb geochronology and sm nd isotopic studies the combination of u th pb age and sm nd isotopic composition makes monazite one of the most versatile minerals in the study of crustal evolution nevertheless most monazites are small and have complex internal textures that require isotopic measurements with high spatial resolution the widely utilized in situ analyses such as secondary ion mass spectrometry sims and inductively coupled plasma mass spectrometry icp ms have emphasized the importance for uniform and homogeneous monazite standards for external calibration here we performed in situ simultaneous measurement of u th pb and sm nd isotopes as well as trace element determinations of several monazite standards using a 193 nm excimer laser ablation system coupled with an agilent 7500a quadruple q icp ms and a neptune multi collector mc icp ms for u th pb isotopic analysis instrumental mass bias and elemental fractionation were corrected by calibrating against a homogeneous monazite standard 44069 which makes it possible to precisely and accurately date other monazite grains in terms of the sm nd isotopes the interference of 144 sm on 144 nd was corrected by using the interference free 147 sm 149 sm for the sm mass fractionation and the fractionation between 144 sm and 144 nd was corrected by calibrating against an external monazite standard manangoutry which is homogeneous in sm nd isotopic composition the obtained sm nd isotopic compositions for synthetic lree glass and natural monazite samples are all consistent with the values obtained by isotope dilution thermal ionization mass spectrometry id tims which indicates the reliability and robustness of our method our results demonstrate that the manangoutry monazite from madagascar and the namaqualand monazite from south africa are relatively uniform and homogeneous in their sm nd isotopic compositions and hence can serve as standards for external calibration during in situ sm nd isotopic analysis

resetting monazite ages during fluid related alteration abstract fluid related coupled dissolution reprecipitation processes can modify the composition of monazite and other orthophosphate minerals at temperatures well below diffusional closure temperatures it is critical to evaluate the effects of alteration processes on th u pb dates especially because incomplete removal of pb during alteration could lead to spurious dates either older or younger than the actual age of the monazite formation experimental alteration of monazite at 450 mpa and 450 c has resulted in the production of altered domains in the vicinity of the grain rim as well as in the vicinity of inclusions and microfractures without any obvious structural control within grains the composition of the altered domains is relatively constant from domain to domain and from grain to grain thorium was reduced from ca 7 wt tho 2 to ca 2 wt uranium and pb were almost entirely removed from the altered domains while unaltered areas of the monazite grains as well as the original monazite grains before the experiment yield very consistent dates of ca 350 ma dates from the altered domains are consistently near zero the implication is that fluid aided alteration of monazite for the conditions of this experiment has resulted in a near complete resetting of the monazite age at temperatures well below the closure temperature because alteration textures in monazite are relatively common in nature careful analysis of such textures offers a means of recognizing and potentially dating fluid rock interactions

late neoproterozoic cambrian granitic magmatism in the aracuai orogen brazil the eastern brazilian pegmatite province and related mineral resources

u pb single zircon pb evaporation and sm nd isotopic study of a granulite domain in se madagascar madagascar is a poorly known precambrian domain at the eastern border of the mozambique belt strongly affected by the pan african orogeny this large island represents a key part of gondwanaland and the accurate dating of the major metamorphic event is critical for the reconstruction of that supercontinent in the southeastern zone of the island metamorphism has reached high temperature and low pressure conditions 850 c and 5 kbar with moderate retrogression a u pb conventional multigrain single zircon stepwise pb evaporation and sm nd geochronological study on meta felsic rocks has shown that basement of at least lower proterozoic age was strongly metamorphosed around 570 580 ma this tectometamorphic event nearly obliterated any pre pan african zircon isotopic memory the granulite facies metamorphism is associated with the syn metamorphic emplacement of the anosyan charnock ites and granites a strong channelized fluid contribution at 545 ma has produced the re crystallization of biotite apatite

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

neodymium isotope equilibration during crustal metamorphism revealed by in situ microanalysis of ree rich accessory minerals radiogenic isotopes are widely used to investigate crustal evolutionary processes however recent claims of nd and sr isotope disequilibrium during anatexis question the reliability of such information we have conducted an in situ sm nd isotope study of apatite allanite titanite xenotime and monazite in metasedimentary rocks of different metamorphic grade to test nd isotope equilibrium during metamorphism our results show that apatite retains an original probably detrital highly variable nd isotopic signature until at least 500 c before being isotopically homogenised irrespective of textural context within the rock once equilibrated apatite retains its nd isotope signature throughout anatexis in contrast allanite and titanite are equilibrated at temperatures as low as 350 400 c ree rich accessory minerals in high grade rocks 600 c show very similar initial end values at the time of metamorphism we conclude that under these metamorphic conditions nd isotope disequilibrium between crustal melts and metasedimentary sources is unlikely intra grain nd isotope zoning of monazite indicates that partial melting was open system involving the injection of externally derived melt into migmatites this process likely to be common in anatectic terranes but not always obvious at hand specimen scale or from bulk rock geochemical data can produce isotope variation that could potentially be misinterpreted as disequilibrium between the melt and its protolith

measurement of in situ oxygen isotope ratios in monazite by shrimp ion microprobe standards protocols and implications abstract monazite forms at sub solidus conditions in a variety of metamorphic rocks and has been proven to be reactive to fluids and thus is a potential monitor of fluid rock interaction as monazite can preserve multiple growth zones in order to explore the potential of monazite as a fluid tracer in metamorphic conditions microbeam analysis is required we performed oxygen isotope analysis of monazite using the shrimp ion microprobe and newly characterized standards for which we obtained laser fluorination 18o values usgs 44069 monazite 7 67 0 26 and itambe monazite 0 46 0 20 reproducibility of 18o ion microprobe analyses for usgs 44069 and itambe monazites is in the order of 0 4 0 6 standard deviation at 95 c l similar to what is routinely obtained for silicates this reproducibility is comparable to that of the analyses of experimental p rich glasses which are assumed to be homogeneous and free of geological imperfections the variable composition of natural monazite has the potential to produce matrix effects during ion microprobe measurements monazite grains from the malagasy syenite madagascar and the dora maira whiteschists italy display a scatter in 18o values that show a negative correlation with th content and is related to the huttonite thsio4 and cheralite cath po4 2 substitutions in monazite the matrix effect on oxygen isotope measurements can be significant and is estimated to produce a shift in 18o of circa 0 85 or 1 9 for every 10 wt th introduced by the huttonite and cheralite components respectively corrections for this matrix effect are proposed on the basis of the natural samples investigated oxygen isotope fractionation factors for monazites of different compositions cheralite and huttonite were calculated with the increment method the results suggest that the substitution of trivalent lree by tetravalent ce and th results in consistent enrichment of 18o in the monazites whereas the substitution of tetravalent th by divalent ca results in the depletion of 18o in cheralite rich monazite monazites from high grade metasediments mount stafford central australia preserve inherited cores but are homogeneous in oxygen composition this suggests that diffusion may efficiently erase the oxygen isotope signature in monazite that experienced 800 c metamorphism

in situ trace element analysis of monazite and other fine grained accessory minerals by epma abstract trace element analysis of high z accessory phases by electron probe micro analysis offers unique access to data unattainable by other analytical techniques but also presents great challenges the intimate relationships between beam conditions voltage current spatial resolution precision and spectral complexity require the careful examination of all analytical parameters and their consequences at a level commensurate with the sensitivity of the desired analysis the high ree and actinide content and resulting high z of monazite allows high direct analytical resolution below 500 nm at 10 kv depending on the realized beam diameter due to limited electron range but the high concentration of these elements will also produce significant fluorescence at a distance the use of high accelerating potential in an effort to improve counting statistics is injudicious in most cases as direct analytical resolution decreases and high overvoltage on rees and th in monazite results in efficient production of energetic ionizing radiation l series capable of fluorescing elements of interest or interfering elements at remarkable distances at least several 10 s of microns from the beam boundary fluorescence is a very significant problem in trace element analysis and in geochronologic analysis of monazite as grains are commonly complex with micro domains that differ considerably in composition especially th ree in such instances a 15 kv beam can produce fluorescence at a distance leading to errors of 10 s of ppm within 5 m of a compositional boundary for trace element analysis effects such as background curvature and minor interferences can result in very large errors 50 or more for curvature alone for concentrations at or below 100 ppm strong background curvature is observed for all makes and varieties of spectrometers in the pb m region in addition for ree and actinide bearing phases such as monazite the wavelength regions available for background determination are very limited requiring routine high precision scanning and regression modeling to determine reasonably accurate background intensities two point background interpolation methods are inappropriate for high sensitivity analysis in all cases without a direct means to verify the accuracy of low concentration analyses great attention must be paid to analytical protocol and very detailed spectral analysis the use of consistency standards to monitor changes is important but caution must be exercised in the use of secondary age standards in the case of monazite epma because systematic error can result in cancellation effects when concentrations of both parent and daughter are proportionally incorrect in all cases caution in interpretation and integration of all available information is necessary if the potential of the method is to be realized

spatiotemporal structure of the east india coastal current from satellite altimetry we use a newly processed altimeter data set to present a hitherto unprecedented description of the spatiotemporal structure of the east india coastal current eicc the data set resolves timescales ranging from a few months to a few years and the high along track resolution yields the first description of the cross shore structure of the current the seasonal cycle dominates the variability but the nonannual timescales have similar energy levels all along the eicc path there are short lived intense intraseasonal bursts in contrast to the seasonal cycle the interannual and intraseasonal components are decorrelated along the coast and possible mechanisms for the decorrelation discontinuity in the flow are discussed in the cross shore direction the current is highly correlated at all timescales the eicc is trapped against the shelf with the current offshore flowing in the opposite direction at most locations the eicc appears as an inherently discontinuous flow taking the form of a few recirculating loops along the eicc path with a typical cross shore spatial scale of 150 200 km the loops are highly variable in direction at all timescales from intraseasonal to interannual this discontinuity of the eicc in space and time implies that the basic pathways and advective timescales for the interbasin exchange of water masses between the bay of bengal and the arabian sea are not robust when the full spatiotemporal variability of the eicc is considered

precise and accurate determination of 147sm 144nd and 143nd 144nd in monazite using laser ablation mc icpms abstract the 147sm 143nd radioactive decay system has been widely used in the earth sciences as a geochronometer and isotopic tracer recent studies have shown that laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icpms is capable of precise and rapid 143nd 144nd measurements with high spatial resolution but its ability to measure 147sm 144nd accurately is still poorly constrained a critical analytical issue is the fractionation effects between 147sm and 144nd in la mc icpms which must be carefully corrected to determine robust initial 143nd 144nd particularly for ancient geological samples here we show that la mc icpms can produce substantial 5 147sm 144nd fractionation during analysis of monazite and that the fractionation can be corrected with uncertainty of 1 by using an independently defined 147sm 143nd isochron for an archean monazite standard in addition we describe a method for improving the precision and accuracy of la mc icpms isotopic measurements by calibration of faraday amplifier response and isotopic ratio normalization using a synthetic standard this method has been applied to one neogene and two archean monazites which were also analyzed by isotope dilution thermal ionization mass spectrometry id tims the la mc icpms data were acquired from 16 37 m single spots the la mc icpms determinations of the 145nd 144nd for all samples and 143nd 144nd for the neogene monazite compare well with the id tims results indicating the robustness of our method to measure nd isotopic ratios for the archean monazites the method yields initial 143nd 144nd values identical to the id tims values with reproducibilities 2 s d of 39 and 58 ppm analytical precisions of individual spot analyses for initial 143nd 144nd were calculated by taking into account the uncertainty in i the nd isotopic normalization to the synthetic monazite ii the correction factor for 147sm 144nd fractionation and iii the age which results in 2 of 45 87 ppm these results clearly demonstrate the capabilities of the la mc icpms technique applied to monazite sm nd isotope systematics for early crustal evolution studies

electron microprobe dating of monazite because monazite is extremely rich in u and th radiogenic pb pb accumulates very quickly and reaches in about 100 ma a level where it is possible to analyse it with the electron probe assuming that common pb is negligible and that partial loss of pb has not occurred the simultaneous measurement of u th and pb allows to obtain a geologically meaningful age from a single electron probe analysis here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method a specific statistical method to deal with the large number of data which can be obtained on a single sample is described and several guidelines illustrated by examples are suggested to optimize the method electron probe measurements carried out on samples of known age from 200 ma to 3 1 ga yield ages that always fall inside the confidence interval of the isotopically determined age demonstrating that this method is reliable the younger age limit is approximately 100 ma although it can be younger in some favourable cases in old monazites extremely high pb contents have been found up to 5 wt indicating that monazite can tolerate high radiation doses without experiencing lead loss the final precision on the age for a normal monazite is 30 50 ma for a total counting time of 600 s a complete dating procedure can be completed in less than 1 h first results indicate that old ages can be preserved in monazite either in small relict cores in crystals or by the coexistence of several generations of monazites in a sample this method has all the advantages of the electron probe it is non destructive has an excellent spatial resolution monazites as small as 5 i m can be dated and because it is possible to work on normal polished thin sections the petrographical position of the dated crystal is known this method offers a large number of geologists access to an in situ dating technique at moderate cost

mathematical models of vegetation pattern formation in ecohydrology 1 highly organized vegetation patterns can be found in a number of landscapes around the world in recent years several authors have investigated the processes underlying vegetation pattern formation patterns that are induced neither by heterogeneity in soil properties nor by the local topography are generally explained as the result of spatial self organization resulting from symmetry breaking instability in nonlinear systems in this case the spatial dynamics are able to destabilize the homogeneous state of the system leading to the emergence of stable heterogeneous configurations both deterministic and stochastic mechanisms may explain the self organized vegetation patterns observed in nature after an extensive analysis of deterministic theories we review noise induced mechanisms of pattern formation and provide some examples of applications relevant to the environmental sciences

electron microprobe dating of monazite the story abstract this paper is a testimony of how electron microprobe dating of monazite was developed in the early days of this technique in the 90 s five contributions have been collected from nagoya clermont ferrand orleans salzburg and amherst the technique was designed in nagoya by professor suzuki using an old jxa 5a jeol electron microprobe the first results were published in 1991 with great difficulty professor suzuki also created the isochron like pb th diagram to present the data progressive improvement of the method finally allowed the nagoya team to date cenozoic monazite the technique was re discovered in clermont ferrand using a cameca camebax microprobe this team demonstrated the accuracy of the method and proposed statistical tools to improve the precision and to handle multimodal populations the first results were published in 1993 in orleans the french geological survey brgm developed the method with a cameca sx50 to support mapping projects they developed a new method for calculating the age and showed that this technique was very efficient for dating monazite in migmatites in salzburg the first results were obtained in 1996 using a jeol jx 8600 it proved to be very efficient in the alps to distinguish cadomian ordovician variscan and alpine events it allowed this team to directly date a monazite allanite reaction they described for the first time finally the amherst team investigated in detail the technical issues of electron microprobe monazite dating they showed that the best analytical procedures must include at least detailed chemical mapping several interference corrections and special care for background measurements with the help of cameca they designed a specific microprobe for dating named ultrachron with this machine high precision ages can be obtained on well characterized individual grains in thin section giving birth to a new era in geochronology of complex metamorphic rocks

laser ablation split stream analysis of the sm nd and u pb isotope compositions of monazite titanite and apatite improvements potential reference materials and application to the archean saglek block gneisses abstract continued improvements in both icpms inductively coupled plasma mass spectrometry and laser ablation technologies are fueling advancements in accessory mineral investigations and their related isotope systems of interest and are now being applied to a wide range of geological applications in this contribution we present an updated methodology for laser ablation split stream lass analysis of the light rare earth element lree enriched minerals monazite titanite and apatite for simultaneous analysis of the u th pb age or trace element content and the sm nd isotope system the data were collected with the current generation of high sensitivity icpms and laser systems thermofinnigan neptuneplus mc icpms and element xr sf icpms coupled to a resolution 193 nm arf excimer laser system the increased sensitivity of these icpms instruments allows for improved spatial resolution and the ability to target minerals which previously contained insufficient concentrations of elements of interest e g sm nd in apatite making their analysis difficult if not impossible using less sensitive instruments furthermore the higher sensitivity allows less aggressive ablation parameters that facilitate thin section sampling and reduces inter element and isotopic fractionation to assess and improve the accuracy precision and efficiency of the technique three new potential lass reference materials rms are evaluated for dual u pb and sm nd analysis tory hill apatite tory hill titanite and steenskralkamp monazite the homogeneity of these materials was first assessed using reconnaissance laser ablation analyses with final characterization of u pb age and sm nd isotope composition using isotope dilution thermal ionization mass spectrometry id tims the precision and accuracy of the lass method is explored using secondary mineral reference materials of known age and sm nd isotope composition the utility of the technique is evaluated with a case study of monazite and apatite from the eoarchean uivak gneiss complex of labrador canada finally we suggest that there is a wide variety of geological applications for this methodology such as multi mineral detrital provenance crustal growth and petrogenic studies

eddy dynamics in a primitive equation model sensitivity to horizontal resolution and friction a primitive equation model of an idealized ocean basin driven by simple study wind and buoyancy forcing at the surface is used to study the dynamics of mesoscale eddies model statistics of a six year integration using a fine grid 1 6 0 2 with reduced coefficients of horizontal friction are compared to those using a coarser grid 1 3 0 4 but otherwise identical configuration eddy generation in both model cases is primarily due to the release of mean potential energy by baroclinic instability horizontal reynolds stresses become significant near the midlatitude jet of the fine grid case with a tendency for preferred energy transfers from the eddies to the mean flow using the finer resolution eddy kinetic energy nearly doubles at the surface of the subtropical gyre and increases by factors of 3 4 over the jet region and in higher latitudes the spatial characteristics of the mesoscale fluctuations are examined by calculating zonal wavenumber spectra and velocity autocorrelation functions with the higher resolution the dominant eddy scale remains approximately the same in the subtropical gyre but decreases by a factor of 2 in the subpolar areas the wavenumber spectra indicate a strong influence of the model friction in the coarse grid case especially in higher latitudes using the coarse grid there is almost no separation between the energetic eddy scale and the scale where friction begins to dominate leading to steep spectra beyond the cutoff wavenumber using the finer resolution an inertial subrange with a k 3 power law begins to emerge in all model regions outside the equatorial belt despite the large increase of eddy intensity in the fine grid model effects on the mean northward transport of heat are negligible strong eddy fluxes of heat across the midlatitude jet are almost exactly compensated by changes of the heat transport due to the mean flow

simultaneous in situ determination of u pb and sm nd isotopes in monazite by laser ablation icp ms results are presented for the in situ simultaneous determination of u pb and sm nd isotopes in monazite using the laser ablation split stream lass method this method uses a laser ablation system coupled to both a magnetic sector inductively coupled plasma mass spectrometer hr icp ms for measuring u pb isotopes and multicollector mc icp ms for measuring sm nd isotopes the ablated material is split using a glass y connector and transported simultaneously to both mass spectrometers in addition to sm and nd isotopes the mc icp ms is configured also acquire ce nd sm gd and eu elemental abundances this approach provides age tracer isotope and trace element data in the same ablation volume thus reducing but not eliminating sampling problems associated with fine scale zoning in accessory minerals the precision and accuracy of the u pb method along with the precision of the sm nd method is demonstrated by analysis of six well characterized monazite reference materials the lass results agree within uncertainty with previously determined isotope dilution thermal ionization mass spectrometry id tims ages accuracy of the sm nd method is assessed by comparing the la mc icp ms results with id tims determinations on a well characterized in house monazite reference material the lass method is then applied to monazite from the birch creek pluton bcp in the white mountains of southeastern california as a case study to illustrate the utility of this method for solving geologic problems the u pb ages and sm nd isotopic data determined using the lass method support the conclusions drawn from previous results that monazite can record both timing and potential sources of hydrothermal fluids

probing the depths of the india asia collision u th pb monazite chronology of granulites from nw bhutan 1 rocks metamorphosed to high temperatures and or high pressures are rare across the himalayan orogen where peak metamorphic conditions recorded in the exposed metamorphic core the greater himalayan sequence ghs are generally at middle to upper amphibolite facies however mafic garnet clinopyroxene assemblages exposed at the highest structural levels in bhutan eastern himalaya preserve patchy textural evidence for early eclogite facies conditions overprinted by granulite facies conditions monazite hosted within the leucosome of neighboring granulite facies orthopyroxene bearing felsic gneiss yields la mc icp ms u th pb ages of 13 9 0 3 ma monazite associated with sillimanite grade metamorphism in granulite hosting migmatitic gneisses yields u th pb rim ages between 15 4 0 8 ma and 13 4 0 5 ma monazite associated with sillimanite grade metamorphism in gneiss at structurally lower levels yields u pb rim ages of 21 17 ma these data are consistent with miocene exhumation of ghs material from a variety of crustal depths at different times along the himalayan orogen we propose that these granulitized eclogites represent lower crustal material exhumed by tectonic forcing over an incoming indian crustal ramp and that they formed in a different tectonic regime to the ultrahigh pressure eclogites in the western himalaya their formation and exhumation in the miocene therefore do not require diachroneity in the timing of the initial india asia collision

interpretation of monazite ages obtained via in situ analysis abstract monazite grains from nepal and vietnam were compositionally analyzed with an electron microprobe and dated th pb with an ion microprobe five sources of uncertainty explain age distributions from single samples that appear inconsistent with a single population 1 pb loss due to diffusion 2 dissolution reprecipitation reactions along a retrograde path 3 analytical uncertainties 4 analyses of overlapping age domains and 5 episodic monazite growth the influence of these factors is sample dependent but can be evaluated 1 using peak metamorphic conditions and x ray element maps to assess potential polymetamorphism or retrogression 2 obtaining other geochronologic data including previous work or dating other minerals in the sample 3 evaluating any method related uncertainty including counting statistics for electron microprobe analyses or calibration reproducibility for ion microprobe analyses and 4 ascertaining the potential growth mechanism of the monazite grain including dissolution of detrital grains or production from rare earth element ree oxide or allanite chemical contents of monazite grains analyzed in this study fail to reflect timing information or mineral growth mechanisms instead of relying on monazite chemical composition major mn fe mg ca and minor y element garnet zoning patterns and peak p t conditions should be used to facilitate age interpretation this thermobarometric data records the sample s thermal history changes in garnet growth rate and mechanisms and accessory mineral breakdown

detection of inherited monazite in the manaslu leucogranite by 208pb232th ion microprobe dating crystallization age and tectonic implications abstract although leucogranites are among the least petrologically variable of all igneous rocks ironically they are among the most difficult to reliably date the high himalayan leucogranites have been the subject of numerous geochronological investigations because of their interrelationship with the most significant tectonic features of that mountain belt for a variety of reasons linked to the minimum melt composition of these leucogranites these dating studies have not been entirely successful we report results of a new ion microprobe dating method based on the decay of 232 th to 208 pb in monazite that has directly revealed the presence of inherited pb in monazite from the manalsu granite casting doubt on its previously accepted age monazite ages obtained from this leucogranite yield two distinct populations a large number of ages with a normal distribution and mean age of 22 4 0 5 ma 2 s e that we interpret to be the crystallization age and a smaller inherited fraction with an age of ca 600 ma because formation of the granite is thought to be related to slip on the main central thrust both this date and a second less precise result from a structurally similar pluton near mt everest indicate that the main central thrust was active in the interval 24 22 ma but do not constrain its initiation together with crosscutting relationships these data require that movement on the north himalayan fault occurred prior to 22 ma at both locations

the araa uaa west congo orogen in brazil an overview of a confined orogen formed during gondwanaland assembly abstract the neoproterozoic adamastor brazilide ocean was generated during the breakup of the rodinia supercontinent and remnants of its oceanic lithosphere have been found in the brasiliano pan african orogenic system that includes the aracuai west congo brasilia ribeira kaoko dom feliciano damara and gariep belts the aracuai and the west congo belts are counterparts of the same neoproterozoic orogen the first belt comprises two thirds of the aracuai west congo orogen this orogen is rather unique owing to its confined nature within the embayment outlined by the sao francisco and congo cratons in spite of this the presence of ophiolitic remnants and a calc alkaline magmatic arc indicate that the basin orogen evolution comprise both oceanic spreading and consumption it is assumed that coeval paramirim and sangha aulacogens played a key role by making room for the aracuai west congo basin sedimentary successions record all major stages of a basin that evolved from continental rift when glaciation related sedimentation was very significant to passive margin rifting started around 1 0 0 9 ga the oceanic stage is constrained by an ophiolitic remnant dated at 0 8 ga if the cratonic bridge that once linked the sao francisco and congo palaeocontinental regions did not hinder the opening of an ocean basin it certainly limited its width as a consequence only a narrow oceanic lithosphere was generated and it was subducted afterwards this is also suggested by orogenic calc alkaline granitoids occuping a small area of the orogen geochronological data for pre syn and late collisional granitoids indicate that the orogenic stage lasted from 625 ma to 570 ma a period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535 500 ma the features of the aracuai west congo orogen suggest the development of a complete wilson cycle in a branch of the adamastor ocean which can be interpreted as a gulf with limited generation of oceanic lithosphere

insights from the salinity origins and interconnections of aquifers in a regional scale sedimentary aquifer system adour garonne district sw france contributions of δ34s and δ18o from dissolved sulfates and the 87sr 86sr ratio abstract the multi layered eocene aquifer is a regional scale sedimentary aquifer system occupying 120 000 km 2 within the adour garonne district france local authorities have recently identified the aquifer as being at risk from extensive irrigation abstractions threatening the sustainability of this key resource because large water abstractions for human activities can significantly influence the natural functioning of such aquifer systems e g with leakage between aquifer layers which can lead to water quality degradation the characterization of such large systems constitutes a key point to protect and prevent further deterioration of aquatic ecosystems this study provides further insight on this large aquifer through a geochemical approach which addresses the limited number of groundwater wells where sampling is possible for that purpose a geochemical analysis combining two isotope systems 34 s so4 18 o so4 and 87 sr 86 sr has been applied the eocene sedimentary aquifer system detrital to carbonate deposits is made up of four aquifer layers eocene infra molassic sand early eocene middle eocene and late eocene and has a mineralized area north of the aquitaine basin where groundwater shows strong mineralization and anomalous levels of critical substances so 4 f etc increasing the difficulty of resource exploitation the extreme heterogeneity of the geochemical composition of the groundwater between the aquifers and within a single aquifer is discussed in terms of the lithological control induced by the lateral variation of facies and interconnections between aquifer layers geochemical tools especially the 34 s and 18 o from dissolved sulfates and the 87 sr 86 sr ratio suggest that evaporite dissolution both sulfate and halite is the main process controlling the high salinity levels observed in the groundwater explaining the spatial variations observed at the aquifer system scale isotopic tools also provide new information regarding the interconnections between aquifer layers supporting the hypothesis that the eocene aquifer system integrates groundwater from the oligocene miocene aquifer through leakage effects these new insights will likely help decision makers adjust their choices when managing quality problems in particular in the mineralized area of the entre deux mers where targeted groundwater wells used for drinking water display anomalous levels of critical substances

does strong tropospheric forcing cause large amplitude mesospheric gravity waves a deepwave case study the deepwave deep propagating wave experiment campaign was designed for an airborne and ground based exploration of gravity waves from their tropospheric sources up to their dissipation at high altitudes it was performed in and around new zealand from 24 may till 27 july 2014 being the first comprehensive field campaign of this kind a variety of airborne instruments was deployed onboard the research aircraft nsf ncar gulfstream v gv and the dlr falcon additionally ground based measurements were conducted at different sites across the southern island of new zealand including the dlr rayleigh lidar located at lauder 45 04 s 169 68 e we focus on the intensive observing period iop 10 on the 4 july 2014 when strong wsw winds of about 40 m s at 700 hpa provided intense forcing conditions for mountain waves at tropopause level the horizontal wind exceeded 50 m s and favored the vertical propagation of gravity waves into the stratosphere the dlr rayleigh lidar measured temperature fluctuations with peak to peak amplitudes of about 20 k in the mesosphere 60 km to 80 km msl over a period of more than 10 hours two research flights were conducted by the dlr falcon falcon flight 04 and 05 during this period with straight transects mt aspiring 2a over new zealand s alps at three different flight levels around the tropopause approx 11 km msl these research flights were coordinated with the gv research flight 16 where the largest mountain wave amplitudes at flight level approx 13 km msl were measured during deepwave additionally a first analysis of falcon s in situ flight level data revealed amplitudes in the vertical wind larger than 4 m s at all altitudes in the vicinity of the highest peaks of the southern alps here we present a comprehensive picture of the gravity wave characteristics and propagation properties during this interesting gravity wave event we use the airborne observations combined with a comprehensive set of ground based measurements consisting of 13 radiosoundings 1 5 hourly interval together with the dlr rayleigh lidar to cover the altitude range from the troposphere to the mesosphere high resolution 1 hourly ecmwf analyses and forecasts are used to estimate the propagation conditions of the excited mountain waves the goal of our investigation is to find out whether the large amplitude mesospheric gravity waves are caused by the strong tropospheric forcing

sm nd isotope systematics of high ree accessory minerals and major phases id tims la icp ms and epma data constrain multiple permian triassic pegmatite emplacement in the koralpe eastern alps abstract detailed sm nd mineral id tims empa and la icp ms analysis of meta pegmatite minerals from the koralpe stubalpe area austria involving single crystal separation step wise dissolution and acid leaching techniques yielded i information about the partitioning of ree between accessory and major mineral phases in meta pegmatites and ii age constraints on the long lasting permian triassic event in the austroalpine basement units of the eastern alps internal sm nd mineral isochrons performed on porphyroclast domains from the three localities rostockbach kuppergrund and wildbachgraben including garnet xenotime apatite monazite and feldspar indicate multiple emplacement of pegmatoid melts between 273 2 and 258 3 ma other localities yielded younger ages indicating that magmatic garnet crystallisation persisted from 251 7 to c 230 ma ages calculated between high ree accessories monazite apatite xenotime and the low ree major phases feldspar and garnet are largely consistent zircon however plots clearly off the internal regression line h 2 so 4 leaching experiments on meta pegmatite garnet rich in micron sized xenotime and apatite inclusions locally affected by dynamic recrystallisation yielded information about the behaviour of the sm nd system during strong tectono metamorphic overprinting the data suggest multiple injections of pegmatite melts at distinctly different times during protracted crustal thinning and heating in the permian triassic ky paramorphs after andalusite and micro inclusions of kyanite staurolite and sillimanite in magmatic garnet indicate crystallisation of the garnet at moderately high but variable pressure conditions during subsequent eclogite facies overprinting peak pt c 700 c 2 2 gpa and intense deformation in cretaceous time the magmatic chemical and isotopic signatures of porphyroclasts were largely preserved except for localized within grain micro shear zones and outermost rim domains whereas part of the feldspar rich matrix recrystallised during pervasive mylonitisation along the eclogite to amphibolite facies grade exhumation path

high resolution 5 μm u th pb isotope dating of monazite with excimer laser ablation ela icpms abstract monazite lree po 4 a common accessory mineral in magmatic and metamorphic rocks is complementary to zircon in u th pb geochronology because the mineral can record successive growth phases it is useful for unravelling complex geological histories a high spatial resolution is required to identify contrasted age domains that may occur at the crystal scale bulk mineral techniques such as id tims applied to single monazite grains recording multiple overgrowths or isotope resetting can result in partly scattered discordant analytical points that produce inaccurate intercept ages laser ablation la icpms has been demonstrated to be a useful technique for u th pb dating of zircons and this study tests its analytical capabilities for dating monazite a sector field high resolution icpms coupled with a 193 nm arf excimer laser ablation microprobe is capable of achieving a high spatial resolution and producing stable and reliable isotope measurements the u th pb systematic was applied to monazite grains from several samples a lower palaeozoic lens from high grade terrains in southern madagascar neogene hydrothermal crystals from the western alps a palaeoproterozoic very high temperature granulite from central madagascar and a variscan leucogranite from spain directly on a polished thin section the major aim was to compare and or reproduce tims and emp ages of monazite from a variety of settings and ages the three independent 206 pb 238 u 207 pb 235 u and 208 pb 232 th ratios and ages were calculated isotope fractionation effects mass bias laser induced fractionation were corrected using a chemically homogeneous and u pb concordant monazite as external standard this study demonstrates that excimer laser ablation ela icpms allows u th pb dating of monazite with a high level of repeatability accuracy and precision as well as rapidity of analysis a spatial resolution almost comparable to that of emp in terms of crater width 5 m produced precise 208 pb 232 th 206 pb 238 u and 207 pb 235 u ratios for dating palaeozoic to precambrian monazites the advantages of ela icpms isotope dating are precision accuracy and the ability to detect discordance in the case of late miocene hydrothermal monazites from the alps a larger spot size of 25 m diameter is required and precise and accurate ages were obtained only for 208 pb 232 th systematics results from the variscan granite show that in situ u th pb dating of monazites with ela icpms is possible using a 5 m spot directly on thin sections so that age data can be placed in a textural context

pb diffusion in monazite a combined rbs sims study abstract we report measurements of pb diffusion in both synthetic cepo4 and natural monazites run under dry 1 atm conditions powdered mixtures of prereacted cepo4 and pbzro3 were used as the source of pb diffusant for in diffusion experiments conducted in sealed pt capsules for durations ranging from a few hours to several weeks following the diffusion anneals pb concentration profiles were measured with rutherford backscattering spectroscopy rbs and supplemented by measurements with secondary ion mass spectrometry sims in order to evaluate potential compositional effects upon pb diffusivity and simulate diffusional pb loss that might occur in natural systems we also conducted out diffusion experiments on pb bearing natural monazites in these experiments monazite grains were surrounded by a synthetic zircon powder to act as a sink monazites from these experiments were analyzed with sims over the temperature range 1100 to 1350 c the arrhenius relation determined for in diffusion experiments on synthetic monazite is given by d 0 94 exp 592 39 kj mol 1 rt m 2 s 1 diffusivities for synthetic and natural monazites are similar as are results of measurements made on the same samples using both rbs and sims the activation energy for pb diffusion we determined is more than three times that for natural monazite reported previously with pb diffusivities at

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part i the monazite ce brabantite solid solution series peraluminous granites of the erzgebirge fichtelgebirge germany are hosts of various members of the monazite group of minerals that display an unprecedented compositional diversity the eibenstock s type granite constitutes the third reported occurrence worldwide of brabantite and the first occurrence of this mineral in a granite many new occurrences of cheralite ce as well as a monazite group mineral intermediate between monazite ce and huttonite for which the term huttonitic monazite is proposed were discovered even common monazite ce may show extreme ranges of actinide and lanthanide element concentrations the granites that host brabantite and cheralite ce are highly differentiated strongly peraluminous low temperature residual melts of s type affinity which are rich in fluorine and other volatile constituents but depleted in thorium and the light rare earth elements such highly evolved volatile rich compositions resemble rare element pegmatites and appear favorable for the precipitation of cheralite ce and brabantite but not of monazite with large amounts of huttonitic substitution instead these minerals occur preferentially in f poor biotite and f rich li mica granites of a type affinity irrespective of the level of uranium in silicate melts which may exceed that of thorium the substitution of uranium in monazite remains limited the compositional data reported here are consistent with complete miscibility in the monazite ce brabantite solid solution series under magmatic conditions these granites contain monazites that span almost the entire compositional range reported for monazite group minerals worldwide and therefore granites appear to be ideal rocks in which to study the crystal chemistry of this mineral group in general

dynamics of andaman sea circulation and its role in connecting the equatorial indian ocean to the bay of bengal circulation in the bay of bengal bob is driven not only by local winds but are also strongly forced by the reflection of equatorial kelvin waves ekws from the eastern boundary of the indian ocean the equatorial influence attains its peak during the monsoon transition period when strong eastward currents force the strong ekws along the equator the andaman sea lying between the andaman and nicobar island chains to its west and indonesia thailand and myanmar to the south east and north is connected to the equatorial ocean and the bob by three primary passages the southern 6 n middle 10 n and northern 15 n channels we use ocean circulation models together with satellite altimeter data to study the pathways by which equatorial signals pass through the andaman sea to the bob and associated dynamical interactions in the process the mean coastal circulation within the andaman sea and around the islands is primarily driven by equatorial forcing with the local winds forcing a weak sea level signal on the other hand the current forced by local winds is comparable to that forced remotely from the equator our results suggest that the andaman and nicobar islands not only influence the circulation within the andaman sea but also significantly alter the circulation in the interior bay and along the east coast of india implying that they need to be represented accurately in numerical models of the indian ocean

crystal chemistry of the monazite and xenotime structures monazite and xenotime the re p04 dimorphs are the most ubiquitous rare earth re minerals yet accurate structure studies of the natural phases have not been reported here we report the results of high precision structure studies of both the natural phases and the synthetic re p04 phases for all individual stable rare earth elements monazite is monoclinic p2 n and xenotime is isostructural with zircon space group 14 amd both atomic arrangements are based on 001 chains of intervening phosphate tetrahedra and re polyhedra with a reogpolyhedron in xenotime that accommodates the heavy lanthanides tb lu in the synthetic phases and a re09 polyhedron in monazite that preferentially incorporates the larger light rare earth elements la gd as the structure transforms from xenotime to monazite the crystallographic properties are comparable along the 00i chains with structural adjustments to the different sizes of re atoms occurring principally in 00i there are distinct similarities between the structures that are evident when their atomic arrangements are projected down 001 in that projection the chains exist in 100 planes with two planes per unit cell in monazite the planes are offset by 2 2 a along 010 relative to those in xenotime in order to accommodate the larger light re atoms the shift of the planes in monazite allows the re atom in that phase to bond to an additional 02 atom to complete the re09 polyhedron

fluid mediated partial alteration in monazite the role of coupled dissolution reprecipitation in element redistribution and mass transfer monazite ce lree th u ca p si o4 with complex zoning in th and other elements is commonly observed in metamorphic and igneous rocks the hypothesis that this alteration is a product of fluid mediated element mass transfer has been tested in the piston cylinder press caf2 assembly cylindrical graphite oven at 1 000 mpa and 900 c and in cold seal autoclaves on a hydrothermal line at 500 mpa and 600 c experiments included a relatively homogeneous monazite ce 7 8 wt tho2 from a heavy mineral sand plus a series of alkali bearing fluids including 2n naoh 2n koh and na2si2o5 h2o experiments were conducted using bse imaging emp analysis and both tem and hrtem a subset of monazite grains from each experiment show evidence of partial alteration in the form of areas enriched in th si with sharp curvilinear compositional boundaries extending from the grain rim into the monazite interior these thsio4 enriched textures are similar to those commonly seen in natural examples of metasomatised monazite in both magmatic and metamorphic rocks in the na2si2o5 h2o experiments scarce inclusions of britholite formed in the altered monazite the altered monazite is also characterised by strong depletion in pb ca and y thorium and si mobility coupled with the formation of britholite inclusions during partial alteration in the monazite grain is considered to be the product of fluid aided coupled dissolution reprecipitation as opposed to solid state diffusion since other fluids including nacl and kcl brines do not result in the formation of these textures the experimental replication of thsio4 enriched areas in the monazite strongly suggests that similar textures in monazite observed in nature are fluid induced specifically by alkali bearing fluids if true complex metasomatically induced textures in monazite could yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of the metasomatic event presuming that all the original radiogenic pb has been removed

the giant monazite crystals from manangotry madagascar abstract the manangotry area in the south east of madagascar is famous for its giant monazite crystals the studied occurrence is an outcrop near the manangotry pass were giant cm sized crystals have been found the crystals are embedded in biotitite levels also containing cm sized xenomorphic ilmenite and are associated with a 1 m thick layer of apatite besides giant crystals monazite is also present as abundant small mm sized grains the surrounding rocks are leucogranites and charnockites the monazite giant crystals are chemically homogeneous and thorium rich whereas small crystals tend to be heterogeneous both biotite and apatite are f rich temperature estimates from biotite and apatite yielded 750 to 800 c despite their high radioactivity the giant crystals preserve a high degree of crystallinity electron microprobe u th pb dating produced ages of 537 14 534 10 and 530 10 ma considered to be the age of the main monazite crystallization episode but some minor domains in small grains yielded 482 12 ma the enclosing biotites yielded 453 6 ma ar ar ages more than 98 of radiogenic helium have been retained in the studied monazite samples and kinetic experiments indicates the intrinsic diffusion parameters for high temperature to be ea 53 kcal mol and d0 3085 cm2 s the paragenesis monazite apatite ilmenite biotite is different from any other occurrences of larges monazite elsewhere based on the current data and literature the preferred genetic model for these giant monazites is crystallization from a high temperature fluorine rich fluid possibly originating from surrounding charnockites

yanai waves in the western equatorial indian ocean 1 observations and models have shown the presence of intraseasonal fluctuations in 20 30 day and 10 20 day bands in the equatorial indian ocean west of 60 e weio their spatial and temporal structures characterize them as yanai waves which we label low frequency lfyw and high frequency hfyw yanai waves respectively we explore the dynamics of these intraseasonal signals using an ocean general circulation model modular ocean model and a linear continuously stratified model yanai waves are forced by the meridional wind y everywhere in the weio most strongly during the monsoon seasons they are forced both directly in the interior ocean and by reflection of the interior response from the western boundary interference between the interior and boundary responses results in a complex surface pattern that propagates eastward and has nodes yanai waves are also forced by instabilities primarily during june july in a region offshore from the western boundary 52 55 e at that time eddies generated by barotropic instability of the southern gyre are advected southward to the equator there they generate a westward propagating cross equatorial flow field veq with a wave number frequency spectrum that fits the dispersion relation of a number of yanai waves and these waves are efficiently excited typically yanai waves associated with several baroclinic modes are excited by both wind and eddy forcing and typically they superpose to create beams that carry energy vertically and eastward along ray paths the same processes generate lfyws and hfyws and hence their responses are similar differences are traceable to the property that hfyws have longer wavelengths than lfyws for each baroclinic mode

numerical simulation of the observed near surface east india coastal current on the continental slope we simulate the east india coastal current eicc using two numerical models resolution 0 1 circ times 0 1 circ an oceanic general circulation model ogcm called modular ocean model and a simpler linear continuously stratified lcs model and compare the simulated current with observations from moorings equipped with acoustic doppler current profilers deployed on the continental slope in the western bay of bengal bob we also carry out numerical experiments to analyse the processes both models simulate well the annual cycle of the eicc but the performance degrades for the intra annual and intraseasonal components in a model resolution experiment both models run at a coarser resolution of 0 25 circ times 0 25 circ simulate well the currents in the equatorial indian ocean eio but the performance of the high resolution lcs model as well as the coarse resolution ogcm which is good in the eicc regime degrades in the eastern and northern bob an experiment on forcing mechanisms shows that the annual eicc is largely forced by the local alongshore winds in the western bob and remote forcing due to ekman pumping over the bob but forcing from the eio has a strong impact on the intra annual eicc at intraseasonal periods local equatorial forcing dominates in the south north because the kelvin wave propagates equatorward in the western bob a stratification experiment with the lcs model shows that changing the background stratification from eio to bob leads to a stronger surface eicc owing to strong coupling of higher order vertical modes with wind forcing for the bob profiles these high order modes which lead to energy propagating down into the ocean in the form of beams are important only for the current and do not contribute significantly to the sea level

gangdese retroarc thrust belt and foreland basin deposits in the damxung area southern tibet abstract geologic mapping and u pb detrital zircon geochronologic studies of meta sedimentary rocks in the damxung area 90 km north of lhasa of the southern lhasa terrane in tibet provide new insights into the history of deformation and clastic sedimentation prior to late cenozoic extension cretaceous nonmarine clastic rocks 10 km southeast of damxung are exposed as structural windows in the footwall of a thrust fault the damxung thrust that carries paleozoic strata in the hanging wall to the north of damxung in the southern part of the northern nyainqentanglha range nnqtl metaclastic rocks of previously inferred paleozoic age are shown to range in depositional age from late cretaceous to eocene the metaclastic rocks regionally dip southward and are interpreted to have been structurally buried in the footwall of the damxung thrust prior to being tectonized during late cenozoic transtension along the northern flank of the nnqtl lower eocene syncontractional redbeds were deposited in a triangle zone structural setting all detrital zircon samples of cretaceous eocene strata in the damxung area include early cretaceous grains that were likely sourced from the gangdese arc to the south we suggest that the that newly recognized late cretaceous to early eocene meta clastic deposits and thrust faults represent the frontal and youngest part of a northward directed and propagating gangdese retroarc thrust belt and foreland basin system that led to significant crustal thickening and elevation gain in southern tibet prior to india asian collision

signature of la nina in interannual variations of the east india coastal current during spring we have investigated interannual variations of the spring february april average east india coastal current eicc magnitude between 2000 and 2018 using oscar ocean surface current analysis real time current and a linear continuously stratified lcs model interannual variability of the eicc shows significant decrease in magnitude during spring of 2000 2008 and 2011 the years when high negative oni oceanic nino index for sea surface temperature value has been observed due to dominance of strong la nina events our lcs model also successfully simulates these interannual variability of the spring average eicc between 2000 and 2018 we carried out numerical experiments using lcs model related to local and remote forcing response on eicc dynamics of the eicc during spring are dominated by four different forcing processes local wind along east coast of india remote forcing response from the eastern and northern boundary of the bob including islands interior bob and the equatorial indian ocean eio during el nino and normal spring years strong poleward interannual eicc are due to very weak negligible order of 0 5 cm s 1 eicc from eio remote response and in phase poleward eicc formation using other three forcings however during la nina spring years weak order of 0 10 cm s 1 poleward interannual eicc are formed due to destructive interference between equatorward current order of 10 25 cm s 1 from eio forcing and in phase poleward current from other three forcings we have also found propagation of interannual upwelling downwelling favorable kelvin wave from eio via eastern and western boundary of the bob during spring in the el nino la nina years the interannual variations in the propagation of eio kelvin wave are associated with the changes in the eio zonal wind direction by climate mode like enso el nino southern oscillation

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