atmospheric fronts along the east coast of taiwan studied by ers synthetic aperture radar images the existence of quasi stationary alongshore atmospheric fronts typically located 30 70 km off the east coast of taiwan is demonstrated by analyzing synthetic aperture radar sar images of the sea surface acquired by the european remote sensing satellites ers 1 and ers 2 for the data interpretation cloud images from the japanese geostationary meteorological satellite gms 4 and the american terra satellite rain rate maps from ground based weather radars sea surface wind data from the scatterometer on board the quick scatterometer quikscat satellite and meteorological data from weather maps and radiosonde ascents have also been used it is shown that these atmospheric fronts are generated by the collisions of the two airflows from opposing directions one is associated with a weak easterly synoptic scale wind blowing against the high coastal mountain range at the east coast of taiwan and the other with a local offshore wind at the convergence zone where both airflows collide air is forced to move upward which often gives rise to the formation of coast parallel cloud bands there are two hypotheses about the origin of the offshore wind the first one is that it is a thermally driven land breeze katabatic wind and the second one is that it is wind resulting from recirculated airflow from the synoptic scale onshore wind air blocked by the mountain range at low froude numbers is recirculated and flows at low levels back offshore arguments in favor of and against the two hypotheses are presented it is argued that both the recirculation of airflow and land breeze katabatic wind contribute to the formation of the offshore atmospheric front but that land breeze katabatic wind is probably the main cause

remote trigger of deep convection by cold outflow over the taiwan strait in the mei yu season a modeling study of the 8 june 2007 case abstractin this study the heavy rainfall event over central taiwan during the mei yu season on 8 june 2007 is investigated with an emphasis on the triggering mechanism for the deep convection that produced the rain observations indicate that there existed two lines of forcing with convection prior to the rain one over the northern taiwan strait along the mei yu front and the other over the southern taiwan strait yet the convection in question developed over the central strait between these two lines in an unstable environment with strong westerly vertical wind shear this motivated the authors to carry out the present study the cloud resolving storm simulation cress of nagoya university was used and the event was reproduced at a horizontal grid size of 2 km including the initiation of new convection over the central strait at the correct location and time the model results suggest a crucial role played by the series of active persistent and propagating storms in the southern strait along the

composition and origin of intermediate solid solutions in the system thorite xenotime zircon coffinite abstract a comprehensive survey of the accessory mineral assemblages in variscan granites of the german erzgebirge and pan african granites from jordan revealed the occurrence of intermediate solid solutions of the tetragonal thorite xenotime zircon coffinite mineral group with partially novel compositions these solid solutions preferentially formed in evolved and metasomatically altered p poor leucogranites of either i or a type affinity thorite from the erzgebirge contained up to 18 8 wt y2o3 16 1 wt zro2 and 23 3 wt uo2 xenotime and zircon have incorporated th in abundances up to 36 3 wt and 41 8 wt tho2 respectively extended compositional gradation with only minor gaps is confined to hydrated members of this mineral group and is observed to exist between thorite and xenotime thorite and coffinite and y hree bearing thorite and zircon complex hydrous solid solutions containing elevated abundances of three or more of the endmembers are subordinate previously reported intermediate solid solutions between anhydrous zircon and xenotime and anhydrous zircon and thorite are not observed and are in conflict with experimental work demonstrating very limited miscibility between anhydrous species of endmember composition the majority of hydrous intermediate solid solutions in the th y zr u system are likely thermodynamically unstable instead they are probably metastable responses to unusual physico chemical conditions involving various parameters and conditions the relative importance of which is incompletely known leaching and dissolution of preexisting accessory phases during interaction with f bearing hydrous fluids enriched in th y hree zr and or u and common deposition of the various elements at disequilibrium supersaturation seems to play a key role but other processes may be of similar importance experimental work involving hydrous conditions and complex systems composed of more than two endmembers are needed to shed light into the stability relations of the chemically uncommon compositions treated in this study

importance of pressure solution and coble creep in the deformation of polymineralic rocks the theoretical framework for modeling pressure solution in polyphase rocks is presented it is often assumed that pressure solution is a deformation mechanism of secondary importance deep in the lithosphere it is shown here that the rheology of rock during pressure solution may be drastically reduced in a bimineralic and polymineralic rock relative to its monomineralic counterparts and therefore the importance of this deformation mechanism importance is perhaps underestimated this behavior contrasts with that of a polymineralic rock undergoing dislocation creep where existing models show that the rheology will be some average of the rheologies of individual phases for instance the rheology of a dunite in pressure solution is governed by the diffusion of both mgo and sio2 whichever is the slowest will control the viscosity of the rock conversely in a harzburgite with a specific texture flow will be governed by the fastest diffusing species thus its strength may be as low as that of a quartz rock of comparable grain size given the comparative strength of many phases undergoing dislocation creep relative to quartz this prediction implies a larger range of conditions under which pressure solution forms an important part of bulk rock deformation than inferred previously predictions on textural evolution of polymineralic aggregates are also made and it is shown that some minerals grains may become elongate parallel to the maximum principal stress during deformation even though the rock as a a whole shortens in this direction

in situ investigations of allanite hydrothermal alteration examples from calc alkaline and anorogenic granites of corsica southeast france allanite is with monazite the main repository for light rare earth elements ree in the continental crust and can be used in u th pb geochronology this mineral has been shown to be prone to alteration the geochemical exchanges occurring between allanite and hydrothermal fluids were explored using backscattered scanning electron microscopy electron microprobe and laser ablation inductively coupled plasma mass spectrometry la icp ms the alteration mechanisms found show the restricted role of metamictization and correspond to the allanite to epidote transformation or to the leaching of the allanite a crystallographic sites hence the ree are mostly removed from this phase during fluid mineral interactions although a heavy rare earth rich fluid may imprint its geochemical signature on the allanite altered zones it appears that even if this ree holder presents evidence of alteration the bulk mineral and whole rock ree and sm nd isotope signatures were not significantly affected in the cases studied alteration results mostly in the input of common lead thus restricting the usefulness of allanite for u th pb dating when alteration occurs finally the alteration mechanisms found here confirm the much more limited flexibility of silicates crystalline lattice as compared to phosphates

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

disturbance versus preservation of u th pb ages in monazite during fluid rock interaction textural chemical and isotopic in situ study in microgranites velay dome france monazite is extensively used to date crustal processes and is usually considered to be resistant to diffusive pb loss nevertheless fluid assisted recrystallisation is known to be capable of resetting the monazite chronometer this study focuses on chemical and isotopic disturbances in monazite grains from two microgranite intrusions in the french central massif charron and montasset petrologic data and oxygen isotopes suggest that both intrusions have interacted with alkali bearing hydrothermal magmatic fluids in the charron intrusion regardless of their textural location monazite grains are sub euhedral and cover a large domain of compositions u pb chronometers yield a lower intercept age of 297 4 ma an inherited component at 320 ma is responsible for the scattering of the u th pb ages the montasset intrusion was later affected by an additional f rich crustal fluid with crystallisation of ca ree fluorocarbonates fluorite calcite and chloritisation pristine monazite is chemically homogeneous and displays 208pb 232th and 206pb 238u concordant ages at 307 2 ma by contrast groundmass monazite shows dissolution recrystallisation features associated with apatite and thorite precipitation th silicate and strong chemical reequilibration 208pb 232th ages are disturbed and range between 270 and 690 ma showing that the th pb ratio is highly fractionated during the interaction with fluids apparent u pb ages are older due to common pb incorporation yielding a lower intercept age at 312 10 ma the age of the pristine monazite these results show that f rich fluids are responsible for th mobility and incorporation of excess pb which thus strongly disturbed the u th pb chronometers in the monazite

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

experimental resetting of the u th pb systems in monazite abraded fragments 200 400 m of a large chemically homogeneous and non metamict brazilian monazite crystal characterised by a concordant u pb ages of 474 1 ma 208pb 206pb 19 5 were hydrothermally treated at varying temperatures with solutions of different compositions product monazites were analysed with scanning electron microscope sem electron microprobe emp secondary ion mass spectrometer sims and isotope dilution thermal ionisation mass spectrometer id tims experiments with pure water over a temperature range of 800 1200 c at 700 mpa and durations ranging from 5 to 60 days showed that even at 1200 c any dissolution and recrystallization of new monazite is confined to the outermost surface of the grain neither pb diffusion at the emp scale nor significant discordancy were observed we performed experiments at 800 and 1000 c for different durations using different fluid compositions at quartz saturation a 10 wt cacl2 fluid a 10 wt srcl2 fluid a 10 wt nacl fluid and a fluid containing nbs 982 pb standard 208pb 206pb 1 for all runs emp traverses revealed no pb diffusion profiles significant overgrowths of newly formed monazite are documented by sem analyses they occurred only in the 1000 c experiments when either cacl2 or pb bearing fluids were present in the cacl2 experiment two zones could be distinguished within the crystal a core possessing the initial monazite composition and a rim consisting of newly formed monazite produced by dissolution precipitation which was enriched in ca and pb free id tims dating of single grains treated with srcl2 and cacl2 solutions at 1000 c are significantly discordant experiments employing the nbs pb standard produced sub concordant monazite for which the 207pb 206pb apparent age has become older than prior to the experiment 544 ma at 800 c and 495 ma at 1000 c the newly grown monazite rim had obviously incorporated pb from the fluid none of our reaction products contained a detectable diffusion profile the only resetting mechanism we detected involved dissolution precipitation the extent of the dissolution precipitation process depends on fluid composition and is a more efficient mechanism than diffusion for controlling the resetting of monazite in natural rocks

replacement of primary monazite by apatite allanite epidote coronas in an amphibolite facies granite gneiss from the eastern alps accessory monazite crystals in granites are commonly unstable during amphibolite facies regional metamorphism and typically become mantled by newly formed apatite allanite epidote coronas this distinct textural feature of altered monazite and its growth mechanism were studied in detail using backscattered electron imaging in a sample of metagranite from the tauern window in the eastern alps it appears that the outer rims of the former monazites were replaced directly by an apatite ring with tiny thorite intergrowths in connection with ca supply through metamorphic fluid around the apatite zone a proximal allanite ring and a distal epidote ring developed this concentric corona structure with the monazite core regularly preserved in the center shows that the reaction kinetics were diffusion controlled and relatively slow quantitative electron microprobe analyses suggest that the elements released from monazite breakdown p ree y th u were diluted and redistributed in the newly formed apatite allanite and epidote overgrowth rings and were unable to leave the corona this supports the common hypothesis that these trace elements are highly immobile during metamorphism furthermore microprobe data suggest that the preserved monazite cores lost little possibly none of their radiogenic lead during metamorphism thus metastable monazite grains from orthogneisses appear to be very useful for constraining u th pb protolith ages on the basis of these findings and a review of literature data it seems that monazite stability in amphibolite facies metamorphic rocks depends strongly on lithologic composition while breaking down in granitoids monazite may grow during prograde metamorphism in other rocks such as metapelites

allanite and other ree rich epidote group minerals epidote group minerals rich in rare earth elements ree in particular allanite are common accessory phases in igneous metamorphic metasomatic and sedimentary rocks small amounts of ree are present in most epidote group minerals but in allanite and the related minerals dissakisite ferriallanite dollaseite khristovite and androsite the ree are essential structural constituents an important characteristic of ree rich epidote group minerals is that their octahedrally coordinated m sites contain major amounts of divalent cations this paper summarizes literature data for these minerals and discusses their chemistry occurrence phase relations and petrologic and geologic significance the chapter emphasizes allanite because it is the most common and best studied of the ree rich epidote group minerals epidote group minerals contain isolated silicon tetrahedra and corner sharing groups of two tetrahedra and are thus assigned to the disilicate or sorosilicate structural family for a detailed description of the structure see franz and liebscher 2004 the epidote group structural formula is a2m3 sio4 si2o7 o f oh or in a simplified form a2m3si3o11 o f oh in which a ca sr pb2 mn2 th ree3 and u and m al fe3 fe2 mn3 mn2 mg cr3 and v3 deer et al 1986 there are two structurally different a sites a 1 and a 2 with different coordination numbers and there are three different m sites m 1 m 2 and m 3 which are all octahedrally coordinated ueda 1955 dollase 1971 in epidote group minerals trivalent ree are accommodated in the a sites which in endmember epidote both contain ca the incorporation of ree3 is commonly charge balanced by a divalent cation fe2 mn2 mg substituted for a trivalent one in the m sites table 1

partial high grade alteration of monazite using alkali bearing fluids experiment and nature recent advances in the dating of monazite using the electron microprobe indicate that thsio 4 and or cath po 4 2 enriched intergrowths in monazite can give ages younger than the original monazite the morphology of the intergrowths suggests that the original monazite grain has been partly altered by a fluid in which th si and ca are mobile this hypothesis has been tested in the piston cylinder apparatus at 1000 mpa and 900 c utilizing a natural unzoned th and pb bearing monazite ce and na 2 si 2 o 5 h 2 o during the experiment a subset of the monazite grains acquired thsi0 4 enriched areas with sharp compositional boundaries devoid of pb and show evidence of being a pseudomorphic partial replacement of the monazite rather than an overgrowth of the monazite these experiments support the hypothesis that similar th enriched or th depleted patches with sharp compositional boundaries observed in natural monazite could be the result of fluid induced alteration via coupled dissolution reprecipitation if so such altered regions would yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of single or multiple metasomatic events assuming that all pre existing radiogenic pb is removed during alteration

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

sensitivity of typhoon track to asymmetric latent heating rainfall induced by taiwan topography a numerical study of typhoon fanapi 2010 1 typhoon fanapi 2010 traveled westward across the central mountain range of taiwan on 19 september and its rainfall shifted from a symmetric to an asymmetric pattern with convection mostly to the south and southeast meanwhile the storm slowed down from 22 to 14 km h 1 for 12 h upon leaving taiwan and led to heavy rainfall 800 mm and serious flooding over the low lying southwestern plains through simulation and sensitivity tests using the cloud resolving storm simulator at 3 km grid size this study shows that the sudden and temporary speed reduction was caused by the asymmetric latent heating lh not the environmental flow specifically over a 9 h period the model storm moved westward at 16 km h 1 in the control run but increasingly faster and more toward the northwest when the moisture and thus the lh effect and its asymmetry is gradually reduced steering flow analysis and estimation using model results suggest an eastward motion vector of about 8 km h 1 consistent with the observation is produced by the asymmetric lh effect when the effects from the vertical wind shear and beta drift are both taken into account this result is further supported by the diagnosis on storm motion based on potential vorticity tendency although important such feedback to typhoon track from rainfall asymmetry that is induced by the blocking effect of topography have not been reported or studied

a numerical study on the effects of taiwan topography on a convective line during the mei yu season abstract during the morning hours on 23 may 2002 a convective line associated with a mei yu front brought heavy rainfall along the coast of central taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy cape of over 3000 m2 s 2 doppler radar observations indicated that deep convection was organized into a linear shape with a northeast southwest orientation along the front about 70 km offshore from taiwan over the northern taiwan strait the system then moved toward taiwan at a slow speed of about 4 m s 1 in the present study the effects of taiwan topography on this convective line and subsequent rainfall distribution were investigated through numerical modeling using the nagoya university cloud resolving storm simulator cress at a 2 km horizontal grid size experiments with different terrain heights of taiwan including full terrain ftrn half terrain htrn and no terrain ntrn were performed the control run using full terrain and co

u pb shrimp geochronology of th poor hydrothermal monazite an example from the llallagua tin porphyry deposit bolivia in situ u pb shrimp analysis of hydrothermal monazite virtually free of th and poor in u 0 2 ppm th 40 103 ppm u from the world class llallagua tin porphyry deposit in bolivia defines a mineralization age of 23 4 2 2 ma mswd 0 48 confirming earlier k ar sericite alteration age data these ages are however in contrast with a weighted mean single crystal 207pb 206pb evaporation age of 39 3 6 0 ma and a related pb pb inverse isochron age of 42 4 4 0 ma mswd 0 66 on zircon from a post porphyry dike as well as with an earlier single crystal sm nd apatite isochron age our data points to a significant time gap between emplacement of the ore hosting porphyry intrusion magmatism and its hydrothermal overprint tin mineralization suggesting long lived magmatic hydrothermal activity in this part of the andean back arc crust the decoupling of porphyry magmatism and hydrothermal activity may explain the unusual occurrence of relatively little fractionated felsic rocks together with extensive tin mineralization our study demonstrates the usefulness of the application of the u pb shrimp method to direct age determination of ore mineralization using th poor hydrothermal monazite even when dealing with geological young events the common assumption of synchronous magmatism and hydrothermal ore formation in porphyry systems may not always be warranted

a study of two propagating heavy rainfall episodes near taiwan during sowmex timrex iop 8 in june 2008 part i synoptic evolution episode propagation and model control simulation abstractthis paper is the first of a two part study to investigate two rain producing episodes in the longitude time hovmoller space upstream from taiwan during the eighth intensive observing period iop 8 12 17 june 2008 of the southwest monsoon experiment terrain influenced monsoon rainfall experiment sowmex timrex with a goal to better understand the mechanism and controlling factors for their organization and propagation both in a prefrontal environment the first episode moved eastward and the second was a rare westward moving event and each caused heavy rainfall in taiwan on 14 and 16 june respectively in part ii the roles played by synoptic conditions and terrain effects are further examined through sensitivity tests with the aid from a successful simulation with a grid spacing of 2 5 km the structure and organization of convection embedded in the two episodes are shown to be different with stronger low level vertical wind shear in its environment the first episode consisted of well

low temperature replacement of monazite in the ireteba granite southern nevada geochronological implications the ireteba pluton is a relatively homogeneous 64 ma zircon ion probe age two mica granite that was intruded by two 16 ma miocene plutons at depths ranging from 5 to 13 km deeper levels of the ireteba and miocene plutons were ductilely deformed at 15 16 ma at shallow levels remote from the miocene plutons the ireteba granite appears to have experienced little miocene heating and deformation monazites from different portions of the pluton reflect the different histories experienced by the host rock irregularly shaped patchy zones with high huttonite component thsio4 are widespread in monazite at deep levels adjacent to miocene plutons but less common in shallow level rock monazite grains with extensive replacement generally have irregular embayed surfaces in undeformed rocks distant from the miocene plutons monazites are less modified and more nearly euhedral though fine networks of replacement veins are common and irregular rims are evident in some grains secondary monazite from these samples is poorer in huttonite ion probe th pb dating yields 60 65 ma ages for magmatic and some replacement zones in monazite from the shallow samples and veins yield apparent ages as young as mid tertiary monazites from deep samples yield a few 55 65 ma ages for remnant magmatic zones and abundant miocene ages for replacement zones 14 18 ma these data demonstrate extensive miocene replacement of magmatic monazite especially at deep levels near miocene plutons and they suggest an early replacement episode as well both events were probably related to influxes of fluid the first may have been associated with initial solidification of the ireteba pluton and the second with the miocene plutons and or extensional deformation ambient temperatures at the time of replacement indicate that secondary monazite growth occurred at t as low as 400 c or less

metamorphic rates in collisional orogeny from in situ allanite and monazite dating the prograde sequence of rare earth minerals recorded in metapelites during regional metamorphism reveals a series of irreversible reactions among silicates and phosphates in individual samples from the northern lepontine central alps allanite is partly replaced by monazite at 560 580 c relic allanite retains its characteristic growth zoning acquired at greenschist facies conditions 430 450 c coexisting monazite and allanite were dated in situ to delimit in time successive stages of the barrovian metamorphism in situ sensitive high resolution ion microprobe shrimp u th pb dating of allanite 31 5 1 3 and 29 2 1 0 ma and monazite 18 0 0 3 and 19 1 0 3 ma constrains the time elapsed between 430 450 c and 560 580 c which implies an average heating rate of 8 15 c m y combined with new fission track ages zircon 10 9 ma apatite 7 5 6 5 ma metamorphic rates of the entire orogenic cycle from prograde to final cooling can be reconstructed

experimental determination of ree distributions between monazite and xenotime potential for temperature calibrated geochronology solid solutions of the ree y orthophosphates monazite and xenotime were synthesized hydrothermally between 300 c and 800 c at 2 and 5 kbar using ree y oxides and h3po4 as starting materials the ree bulk composition was similar to those found in metapelitic rocks all experiments produced two solid phases monoclinic monazite and tetragonal xenotime in volumetric ratios similar to relative abundances in metapelites ree concentrations of coexisting monazite xenotime pairs were determined by emp analysis and ree distribution coefficients dree xreemonazite xreexenotime were derived for the entire ree y suite values of dree depend strongly on ionic radii of the rees and on temperature the log dree vs ionic radius curve shows a nearly linear decrease from la to lu and comprises almost five orders of magnitude from dla 102 5 to dlu 10 2 between 450 and 800 c most dree values vary continuously by a factor of about 2 to 3 dnd decreases from 48 to 16 and dsm from 9 to 5 dtb increases from about 0 2 to about 0 4 ddy from 0 1 to 0 2 and dy from 0 06 to 0 12 along this temperature range experimentally determined values of dree are in close agreement with those derived from natural monazite xenotime pairs equilibrated between 400 and 700 c ree partitioning between monazite and xenotime is appropriate for geothermometry the most useful application is that equilibrium and disequilibrium partitioning of ree in metamorphic rocks are easily recognized in the case of equilibrium distributions u pb chronometry of single monazites or xenotimes provides a direct link to their growth conditions and information on temperature time paths equilibrium distributions of sm and nd expressed in molar fractions result in kd xsmmonazitexndxenotime xsmxenotimexndmonazite 0 2 to 0 3 from 600 to 800 c and sm nd chronometry should provide reasonable two mineral isochrons for such monazite xenotime pairs

detrital and newly formed metamorphic monazite in amphibolite facies metapelites from the motajica massif bosnia abstract the motajica massif in bosnia situated in the sava zone between the tisza unit and the dinarides hosts a late cretaceous flysch series which is partly preserved in an anchimetamorphic state partly affected by amphibolite facies overprint samples from both parts contain abundant accessory monazite which was investigated by means of the electron microprobe with reference to age and composition in the amphibolite facies samples new metamorphic monazite has formed chemical th u pb monazite ages indicate that the regional metamorphic event happened in the late cretaceous or the early palaeogene in addition inherited detrital monazite of permian age has been identified based on various observations it is argued that the detrital monazite was not the direct precursor to the metamorphic monazite the latter may rather have grown from other more reactive ree carrier minerals either detrital ones e g detrital allanite or such that formed during diagenesis and low grade metamorphism a later greenschist facies event that occurred in connection with a ca 27 ma old granodiorite intrusion led in some samples to the formation of late fluorapatite allanite coronas around both detrital and newly formed monazites the anchimetamorphic samples contain exclusively detrital monazite these are partly of permian as well as jurassic to early cretaceous age based on their compositional and textural features the jurassic to early cretaceous monazite relics are considered to be mainly derived from metamorphic rocks the permian monazite displays high yttrium content up to ca 3 5 wt y 2 o 3 indicating a high formation temperature 650 c and therefore probably a magmatic origin apart from almost ubiquitous permian high y monazite the motajica flysch also contains large permian xenotime with magmatic zoning patterns fluorapatite with parasitic monazite inclusions formerly ree rich fluorapatite and zircon with a type granite morphology this accessory mineral spectrum implies that among others rift related ree rich permian a type granites or rhyolites should be considered as a source for the sava zone flysch

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

contrasted monazite hydrothermal alteration mechanisms and their geochemical implications in spite of the major importance of monazite as a repository for the rare earths and th in the continental crust for u th pb geochronology and as a possible form for high level nuclear waste very little work has been carried out so far on the behaviour of this mineral during fluid rock events this contribution describes two contrasting examples of the hydrothermal alteration of monazite the first case comes from a sample of the carnmenellis granite cornwall southwest england chloritized at 284 16 c whereas the other occurs in the skiddaw granite lake district northwest england which underwent greisenization at 200 30 c an integrated study involving backscattered scanning electron microscopy electron microprobe analyses and laser ablation inductively coupled plasma mass spectrometry la icp ms reveals that the chloritization event was characterized by the coupled substitution 2ree3 th4 ca2 in the altered parts of the monazite thus leaving the p o framework of the crystal untouched in contrast greisenization led to the coupled substitution ree3 p5 th4 si4 and therefore involved a partial destruction of the phosphate framework the resulting rare earth element patterns are quite different for these two examples with a maximum depletion for dy and er in the altered parts of the carnmenellis monazite whereas the skiddaw monazite shows a light rare earth depletion but an yb and er enrichment during alteration this latter enrichment accompanied by an increase in u but roughly unchanged pb concentrations probably resulted from a decrease in the size of the 9 coordinated site in monazite thereby favouring the smaller rare earths these contrasted styles of monazite alteration show that the conditions of fluid rock interaction will not only affect the aqueous geochemistry of the lanthanides actinides and lead and the relative stability of the different minerals holding these elements variations in these conditions will also lead to various possible chemical exchanges between the crystalline phases and the hydrothermal fluids the occurrence of common lead along penetrative cracks in the carnmenellis monazite shows that only a leaching prior to the u pb analyses of the whole grain will permit an accurate determination of the magmatic crystallization age in contrast for the skiddaw case it may be possible to date the fluid rock event by in situ 207pb 206pb geochronology the observation that the altered parts of both monazite examples display nd leaching and no significant sm nd fractionation indicates that they should not affect the host whole rock nd isotopic signatures finally it appears that monazite like ceramics designed for the containment of high level nuclear wastes will retain th and the geochemically equivalent transuranic elements during fluid rock events similar to those documented in this study but may release nd u and the corresponding radionuclides to the environment

pre orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central pyrenees pre kinematic greenschist facies metamorphism is often observed in granites and basement units of mountain belts but rarely dated and accounted for in orogenic cycle reconstructions studying pre kinematic alteration is challenging because of its usual obliteration by subsequent syn kinematic metamorphism often occurring at conditions typical of the brittle ductile transition it is however to be expected that pre kinematic alteration has major implications for the rheology of the upper crust in the 305 ma old variscan basement of the bielsa massif located in the axial zone of the pyrenees successive fluid rock interaction events are recorded in granites below 350 c combined microstructural and petrographic analysis low t thermobarometry and in situ u th pb dating of anatase titanite and monazite show extensive pre orogenic pre alpine and pre kinematic alteration related to feldspar sericitization and chloritization of biotite and amphibole at temperatures of 270 350 c at 230 300 ma this event is followed by a second fluid rock interaction stage marked by new crystallization of phyllosilicates at 200 280 c and is associated with the formation of mylonitic shear zones and fractures parallel to the shear planes u pb anatase and monazite ages as well as the microtextural relationships of accessory minerals suggest an age for this event at 40 70 ma consistent with independent regional geology constraints the variscan basement was therefore softened at late to post variscan time at least 150 200 ma before the main alpine shortening while alpine age compression c 35 50 ma leads to the formation of a dense net of mylonites the associated deformation both distributed at the scale of the bielsa massif and localized at decametric scale in mylonitic corridors precedes the strain localization along the major thrusts of the axial zone the bielsa massif is a good example where inherited pre orogenic upper crustal softening controls the deformation patterns in granitic basement units through low grade metamorphic reactions

transmission electron microscope study of polyphase and discordant monazites site specific specimen preparation using the focused ion beam technique electron microprobe emp u th pb dating on polyphase and discordant monazites from polymetamorphic granulites of the andriamena unit north central madagascar reveals inconsistent chemical ages to explain these drastic variations transmission electron microscopy tem foils were prepared directly from thin sections by using the focused ion beam technique the most important result of the tem study is the demonstration of the presence of small 50 nm pb rich domains where large variations in emp ages occur we suggest that radiogenic pb was partially reincorporated in monazite during the recrystallization at 790 ma because the excited volume of emp is 4 m3 u th pb dating yielded various apparent older ages without geological significance in addition tem analysis of the foils revealed the presence of an 150 nm wide amorphous zone along the grain boundary of monazite and its host quartz this fe si al rich phase may have formed as a result of fluid activity at 500 ma and the phase s amorphous state may be due to the irradiation from u and th decay in the monazite this demonstrates for the first time the enormous potential of the tem investigations on site specific specimens prepared with the focused ion beam technique for the interpretation of geochronological data

a martian general circulation experiment with large topography abstract a three layer general circulation model used to simulate the martian atmosphere is described and results are presented the model assumes a dust free pure c02 atmosphere and allows for a diurnally varying convective boundary layer smoothed martian topography and albedo variations are incorporated the simulation described is for the period near southern winter solstice season of the viking landings the zonally averaged circulation mass heat and momentum balances and properties of stationary and transient waves are described in some detail and are compared with results of previous simulations of the martian general circulation with related features of the earth s general circulation and with observed characteristics of the martian atmosphere the principal conclusions are the following 1 the simulated zonally averaged circulation is not very sensitive to differences between this model and the earlier general circulation model of leovy and mintz 1969 and compares reasonably well wi

atmospheric front over the east china sea studied by multisensor satellite and in situ data 1 a frontal feature visible on a synthetic aperture radar sar image acquired by the radarsat satellite over the east china sea on 19 november 2000 is analyzed in conjunction with data acquired by quikscat topex poseidon tropical rain measurement mission trmm defense meteorological satellite program dmsp and national oceanic and atmospheric administration noaa satellites and with data obtained from ship measurements although this frontal feature is located close to the kuroshio front it is demonstrated that it is not a sea surface manifestation of an oceanic front but rather of an atmospheric front extending over 800 km from an area of the pacific ocean northeast of taiwan to the southern coast of korea it is a cold front moving in the southeast direction with a speed of approximately 45 50 km hour and associated with a 40 km wide rainband trailing the front the radarsat image which has a resolution of 50 m reveals fine scale structures of the atmospheric front in particular small scale convective rain cells embedded in the front conclusion is drawn that accurate interpretation of frontal features in sar images requires use of additional meteorological and remote sensing data and information

orographically forced oscillations in a dynamical model of the martian atmosphere abstract a single layer shallow water model with realistic topography and idealized zonal forcing is used to analyze barotropic orographically forced intraseasonal oscillations in the martian atmosphere a robust oscillation with a mean period near 85 martian days sols is observed in a time series of the model global atmospheric angular momentum aam its robustness with respect to changes of the model parameters is verified this oscillation is still present when an annual component is added to the forcing to account for seasonal variations in the sun s declination and for the redistribution of atmospheric mass in connection with condensation and sublimation of carbon dioxide in the polar caps composites of the surface height anomaly field keyed to filtered aam time series are examined to identify the spatial features associated with the 85 sol oscillation and its relation to the spatial distribution of the most prominent aspects of the martian mountain field the oscillation has a standing zonal component with centers of action located upstream and downstream of salient orographic features and a global meridional component a resemblance is detected between its northern hemisphere nh features and those of the terrestrial 40 day oscillation this resemblance is attributed to the similarity between the two planets nh orographic covers it is noted that interferences between the 85 sol oscillation and shorter timescale phenomena which cause a redistribution of the martian atmosphere s heat and momentum content such as global dust storms will have to be examined with a more complete model and or with long records from the imminent mars observer mission

pb and rare earth element diffusion in xenotime abstract diffusion of pb and the rare earth elements sm dy and yb have been characterized in synthetic xenotime under dry conditions the synthetic xenotime was grown via a na2co3 moo3 flux method the sources of diffusant for the rare earth diffusion experiments were ree phosphate powders with experiments run using sources containing a single ree for pb the source consisted a mixture of ypo4 and pbtio3 experiments were performed by placing source and xenotime in pt capsules and annealing capsules in 1 atm furnaces for times ranging from 30 min to several weeks at temperatures from 1000 to 1500 c the ree and pb distributions in the xenotime were profiled by rutherford backscattering spectrometry rbs the following arrhenius relations are obtained for diffusion in xenotime normal to 101 d sm 1 5 10 4 exp 441 12 kjmol 1 r t m 2 s 1 d dy 9 0 10 8 exp 349 16 kjmol 1 r t m 2 s 1 d yb 3 9 10 7 exp 362 13 kjmol 1 r t m 2 s 1 diffusivities among the ree do not differ greatly in xenotime over the investigated temperature range in contrast to findings for the ree in zircon cherniak d j hanchar j m watson e b 1997 rare earth diffusion in zircon chem geol 134 289 301 where the lree diffuse more slowly and with higher activation energies for diffusion than the heavier rare earths in zircon these differences among diffusion of the rare earths are attributed to the relatively large size of the ree with respect to zr for which they likely substitute in the zircon lattice with the systematic increase in ionic radius from the heavy to lighter ree this size mismatch becomes more pronounced and diffusivities of the lree are as consequence slower although xenotime is isostructural with zircon the ree are more closely matched in size to y so in xenotime this effect appears much smaller and the ree diffuse at similar rates in addition the process of diffusion in xenotime likely involves simple ree 3 y 3 exchange without charge compensation as needed for ree 3 zr 4 exchange in zircon this latter factor may also contribute to the large activation energies for diffusion of the ree in zircon i e 691 841 kj mol 1 cherniak d j hanchar j m watson e b 1997 rare earth diffusion in zircon chem geol 134 289 301 in comparison with those for xenotime for pb the following arrhenius relation is obtained also normal to 101 d pb 3 0 10 9 exp 382 64 kjmol 1 r t m 2 s 1 these measurements suggest that pb diffusion in xenotime is quite slow even slower than pb diffusion in monazite and zircon and considerably slower than diffusion of the ree in xenotime xenotime may therefore be even more retentive of pb isotope signatures than either monazite or zircon in cases where pb isotopes are altered solely by volume diffusion however because the activation energy for pb diffusion in xenotime is lower than those for monazite and zircon pb diffusion may be somewhat faster at many temperatures of geologic interest in xenotime than in monazite or zircon

monazite u pb dating of staurolite grade metamorphism in pelitic schists a study of the occurrence of and relations between rare earth element ree minerals in pelitic schists indicates that monazite forms at or near the p and t of the staurolite isograd samples at staurolite grade from the silurian perry mountain formation in the rumford quadrangle of maine yield monazite in sufficient quantities to permit accurate dating of the metamorphic events forming the monazites the bulk chemistry of the metapelites as seen in the major element abundances and ree patterns does not vary significantly across the study area thus the appearance and disappearance of ree phases is assumed to reflect changes in metamorphic grade in a sample from the biotite zone scanning electron microscope and microprobe studies show allanite and monazite intimately associated on a 10 m scale the texture suggest that metastable detrital monazite breaks down distributing its ree components to allanite from samples below staurolite grade in which monazite is not present our observations suggest that rees are partitioned into allanite at or near the staurolite isograd monazite forms as a metamorphic mineral initiating its role as a geochronometer garnet biotite geothermometry on samples at this grade from this and other studies places constraints on the minimum temperature necessary to form monazite 525 c 25 c at 3 1 0 25 kbar a total of 15 separates from nine schist samples ranging up to sillimanite grade have been dated each date is remarkably concordant even though petrologic and textural studies by previous workers have shown that the rocks in the area have been affected by at least three metamorphic episodes calculations indicate insignificant th disequilibrium in these monazites the conditions associated with the metamorphic events suggest that monazite remains closed to lead loss provided that subsequent metamorphisms are at or below sillimanite grade two distinct metamorphic events are resolved one at around 400 ma and one at about 370 ma the latter was due to thermal effects of a nearby pluton that yields concordant monazite ages of 363 ma this work suggests that in addition to dating plutonism and high grade metamorphism monazite should be viewed as a reliable geochronometer for moderate metamorphism of pelitic schists

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

arsenian monazite ce and xenotime y ree arsenates and carbonates from the tisovec rejkovo rhyolite western carpathians slovakia composition and substitutions in the ree y xo4 system x p as si nb s abstract a unique ree y th p as si nb s accessory assemblage was identified in a small body of lower triassic a type rhyolite of the silicic superunit near tisovec rejkovo central slovakia arsenian monazite ce phosphatian gasparite ce and arsenian xenotime y phosphatian chernovite y solid solutions in association with ree carbonates bastnasite parisite rontgenite synchysite and rare cerianite ce form anhedral to subhedral grains and aggregates 0 3 mm scattered in the groundass or as intergrowths with zircon and fe ti oxides compositions show a wide asp 1 substitution in monazite gasparite and xenotime chernovite solid solutions atom as as p 0 00 to 0 73 and 0 10 to 0 94 respectively the presence of s in monazite gasparite s s 0 14 apfu together with ca enrichment indicates clinoanhydrite substitution cas ree y 1 p as 1 rather than the incorporation of brabantite along the cath ree y 2 exchange vector moreover the th and nb rich members reveal thorite and fergusonite substitutions thsi y ree 1 p as 1 and nb p as 1 respectively the as rich ree phases originated probably during the post magmatic alteration of primary monazite ce and xenotime y by as rich high fo2 fluids whereas cerianite ce and the ree carbonates are products of a later hydrothermal overprint of the rhyolite by co2 rich solutions

rare earth element mineralogy and geochemistry in a laterite profile from madagascar abstract in this study rare earth element ree distribution has been investigated in a weathering profile from central madagascar combination of bulk rock geochemical data elements and isotopes with mineral characterization reveals a remarkable evolution of the ree abundances and ree minerals in the vertical weathering profile in the fresh tonalite bedrock ree y concentrations are typical of granitoids 299 363 ppm and the main ree minerals are allanite and chevkinite in the c horizon saprolite primary ree minerals disappear and rees are transported via fluid to precipitate rhabdophane group minerals in cracks and pores the presence of sulfate ligands produced by sulfide oxidation may be responsible for the ree speciation as suggested by the composition of the secondary ree minerals rhabdophane group minerals contain up to 9 wt so 3 and 7 wt cao indicating a mixture between rhabdophane sensu stricto ree po 4 h 2 o and tristamite ca u fe iii po 4 so 4 2h 2 o due to intense ca leaching rhabdophane disappears and al phosphates alunite jarosite group are found in the soil cerianite ce iv o 2 also precipitates in the b horizon of the soil mass transfer calculations based on immobile ti indicate significant ree leaching in a horizon with preferential leaching of the heavy ree rees accumulate partly in the b horizon the uniform nd isotope compositions and the constant proportion of immobile elements do not reveal external input in the b horizon total ree y reach 2194 ppm with high ce concentrations 1638 ppm 9 ce bedrock compared to other ree 3 4 ree bedrock tetravalent ce state is dominant in the b horizon and requires oxidizing conditions that likely account for the accumulation of redox sensitive elements in b horizon e g mn fe co under oxidizing conditions cerianite precipitation causes a ce fractionation from other trivalent ree in comparison to the ion adsorption clay of southern china preferential heavy ree enrichment was not observed in the weathering profile another remarkable peculiarity of the studied profile is the occurrence of gd 2 so 6 grains the discovery of this new mineral demonstrates that a natural process exists that that can fractionate ree to such an extent to produce a pure gadolinium end member mineral an understanding of such a mechanisms is crucial for the ree geochemistry of low temperature alteration processes as well as for the formation of ree ore deposits or industrial processing

fluid regimes during late stages of a continental collision physical chemical and stable isotope measurements of fluid inclusions in fissure quartz from a geotraverse through the central alps switzerland fluid evolution during neo alpine metamorphism during late stages of the continental collision between europe and africa was studied by analyzing fluid inclusions in alpine fissure quartz collected in forty nine localities along a geotraverse through the central alps switzerland the methods employed include microthermometry micro raman spectroscopy k na thermometry and stable isotope analysis early fluid inclusions provide evidence of close to peak metamorphic temperatures of the late tertiary or neo alpine metamorphic event fluid composition evolved along the geotraverse from north to south as follows higher hydrocarbons were dominant in the low and medium grade diagenetic zones methane was the main volatile in the high grade diagenetic and low grade anchizone water dominated in the highgrade anchizone and low grade epizone with co2 10 mol in the high grade epizone and in the mesozone higher hydrocarbons and ch4 were the products of kerogen maturation and cracking of preexisting petroleum large water supplies originated from the dehydration of cooler metasedimentary rocks that were overthrust by crystalline basements of the lepontines aar and gotthard massifs carbon isotope analyses suggest that the co2 component was derived from oxidation of graphitic matter especially in the vicinity of sulfate bearing metasediments and from decarbonation reactions in the aar and gotthard massifs as well as in the helvetic axen nappe and its underlying north helvetic flysch high fluid pressures prevailed and favored nappe transport by contrast in the southern lepontine area very low early fluid pressures were probably related to dry rocks and scarce metasediments and to high geothermal gradients that resulted from intense uplift and erosion between 26 and 18 ma retrograde fluid evolution was recorded by a succession of fluid inclusion populations in each alpine fissure it was controlled by uplift and cooling and characterized by decreasing contents of volatiles and an increase in 18o of host quartz tectonic activity led to episodic pressure drops of at least 0 5 to 2 kbar and promoted fluid unmixing channelized flow and rapid growth of skeletal quartz channelized rather than pervasive fluid migration at temperatures 450 c and under conditions of brittle deformation is documented by episodic increases in salinity and by fluid flushing through the massifs there is stable isotope evidence for involvement of meteoric water only in late crystallizing quartz formation of alpine fissures and fissure minerals was the result of a unique coincidence of late continental collision 450 c fluid expulsion from overthrust metasediments uplift and erosion

formation of monazite and rhabdophane at the expense of allanite during alpine low temperature retrogression of metapelitic basement rocks from crete greece microprobe data and geochronological implications abstract accessory lree bearing minerals have been investigated in a sequence of palaeozoic amphibolite facies metapelites in eastern crete greece which were overprinted by alpine low t metamorphism 300 c the series is dominated by al ca rich metapelite layers which contain palaeozoic allanite secondary alpine monazite with low y contents only in some quartz rich layers of metapelites which are allanite free is primary palaeozoic monazite to be found in such special variants alpine monazite or rhabdophane appear to be absent and the lrees remained trapped in the palaeozoic monazite not even the outermost rims of the old monazites experienced alteration during the alpine retrograde metamorphism and preserve undisturbed palaeozoic th u pb ages this observations made in this study confirm other recent work according to which in many cases monazite and not allanite is the stable lree phase under low grade metamorphic conditions rocks with primary allanite contents can be considered particularly fertile for the production of monazite at low metamorphic grades in contrast rocks without allanite but with primary monazite are unfertile for the growth of a secondary monazite generation a composite lithologically variable basement with a low temperature overprint will therefore often include both remnant and new monazite although the two monazite generations will commonly occur in different lithologies and rarely together in the same samples therefore if a cunning sampling strategy is applied monazite geochronology is capable of yielding the ages of both primary and secondary events in such settings

metasomatic thorite and uraninite inclusions in xenotime and monazite from granitic pegmatites hidra anorthosite massif southwestern norway mechanics and fluid chemistry thorite and uraninite inclusions are documented in metasomatized regions in three xenotime crystals and one monazite crystal collected from three granitic pegmatites hosted within an anorthosite intrusion located on the island of hidra southwestern norway formation of these inclusions is demonstrated to be the result of dissolution reprecipitation processes that occurred in an effectively closed chemical system the reaction was initiated by interaction between the early crystallizing orthophosphate minerals and the evolving pegmatite fluid this fluid was dominated by h 2 o but also contained f and minor amounts of cl and significant quantities of dissolved na and k this is an example of auto metasomatism and highlights a natural case where th u si enriched orthophosphate minerals have been partially altered such that the th u and si have been converted to secondary inclusions within the now th u si depleted orthophosphate via reaction with fluids rich in alkali elements

simultaneous observations of rain cells over the ocean by the synthetic aperture radar aboard the ers satellites and by surface based weather radars radar images acquired over the ocean by the c band synthetic aperture radar sar aboard the european remote sensing satellites ers 1 and ers 2 often show sea surface manifestations of rain cells we have searched the archives of several weather stations for weather radar data acquired concurrently with ers sar data and have found four concurrent data pairs one in the south china sea two in the baltic sea and one in the north sea the comparison of ers 1 2 sar images showing radar signatures of rain cells with weather radar images reveals that the radar signatures of rain cells on ers sar images vary considerably which makes it often difficult to distinguish them from radar signatures of other mesoscale or submesoscale atmospheric and oceanic phenomena the present analysis together with results obtained from previous analyses of spaceborne multifrequency sar data and laboratory data as well as results obtained from theoretical models on radar backscattering at the sea surface suggest the following c band radar signatures of rain cells with rain rates below 50 mm h are mainly caused by a modification of the sea surface roughness induced by 1 the raindrops impinging on the sea surface and thus modifying the sea surface roughness and by 2 local wind field variations associated with rain cells spreading downdrafts raindrops impinging on the sea surface generate ring waves as well as turbulence in the upper water layer depending on rain rate drop size distribution wind speed and temporal evolution of the rain event the net effect can be an increase or a reduction of the amplitude of the c band bragg waves and thus of the backscattered radar power thus ocean areas struck by rain can show up on ers sar images as areas with higher or lower image brightness than the surroundings

statistical location and timing of the convective lines off the mountainous coast of southeastern taiwan from long term radar observations in this study observations from the c band doppler radar on green island which is located off the southeastern coast of taiwan during 1998 2004 were analyzed to investigate the statistical characteristics of the convective lines occurring off the mountainous coast of southeastern taiwan with emphasis on their formative location and timing a total of 211 cases of the lines were identified during the study period it is shown that the lines were clearly a year round phenomenon and five cases occurred per month on average statistical analyses for all identified cases reveal that the formative area of the lines was extended substantially from nearshore regions to at least 100 km offshore with the region of the most frequent formation primarily confined to an elongated zone located 30 km off the coast along coast variations of line formation were also evident and were shown to be closely related to the nearshore terrain features the lines tended to form more frequently during the nighttime hours than the daytime hours with a formative peak between 2000 and 2200 lst minimum formation was found near noon between 1200 and 1400 lst however considerable cases still could be found during the late morning and late afternoon hours more than 70 of the lines 150 cases had a duration of less than 4 h and the mean duration for all lines was calculated to be 3 5 h in addition this study also documented statistical differences in the formative and flow characteristics between the nearshore and offshore lines which are distinguished by offshore distances of formative location that are less or greater than 40 km respectively of particular note the analyses presented strongly suggest that the physical mechanisms contributing to the initiation of the nearshore and offshore lines are fundamentally different

persistent anomalies blocking and variations in atmospheric predictability abstract we consider regimes of low frequency variability in large scale atmospheric dynamics the model used for the study of these regimes is the fully nonlinear equivalent barotropic vorticity equation on the sphere with simplified forcing dissipation and topography twenty five modes are retained in a spherical harmonics expansion of the streamfunction solutions are studied as a function of the nondimensional intensity of the forcing and dissipation multiple stationary solutions are obtained as a result of nonlinear interaction between waves mean flow and orography the number of modes retained in the analysis permits these multiple equilibria to appear for realistic values of the forcing the equilibria exhibit blocked and zonal flow patterns bearing a marked resemblance to synoptically defined zonal and blocked northern hemisphere midlatitude flows wave wave interactions influence strongly the stability properties of the equilibria and the time evolution of nonequilibrium solutions time depe

deformation mechanisms and reaction of hornblende examples from the bergell tonalite central alps abstract hornblendes in the bergell tonalite begin to crystallize relatively early during the crystallization history of the pluton and become resorbed during the late stages of crystallization during the crystallization of the magma deformation commences by magmatic flow in this stage the hornblendes behave as rigid particles in a viscous matrix melt the rotation and alignment of hornblende as elongate rigid particles have produced a strong preferred orientation of both particle long axes and crystallographic directions with progressive solidification of the melt there is a gradual transition from magmatic flow to solid state deformation in the bergell tonalite the crystallographic and shape preferred orientation that have developed during solid state deformation are identical to those of magmatic flow this identical fabric development during solid state and magmatic flow deformation can be explained by the same deformation mechanism that has prevailed in hornblends during both deformation periods i e hornblendes have always acted as rigid particles in a viscous matrix tem observations show no evidence for intracrystalline plasticity in hornblende grains the modal abundance of hornblende decreases progressively with increasing solid state deformation to yield more biotite epidote and quartz small hornblende matrix grains form by cataclastic processes the observed changes in grain size shape and abundance of hornblende occur mainly by fracturing dissolution and reaction so that the solid state deformation of the tonalite is a complex process to which fracturing dissolution of hornblende and metamorphic reactions all contribute the relationship between deformation and reaction represents an example of incongruous pressure solution or diffusive mass transfer involving reaction it is inferred that generally hornblende does not appear to deform significantly by intracrystalline plasticity at temperatures below 650 750 c in the presence of an aqueous fluid crystal plasticity could become dominant at higher temperatures and or lower aqueous fluid activities

evolution of the ree mineralogy in hp lt metapelites of the sebtide complex rif morocco monazite stability and geochronology abstract ree mineralogy was characterized at the micrometer scale using scanning electron microscopy in the four tectono metamorphic units of the beni mzala window sebtide complex internal rif morocco which sample a hp lt metamorphic gradient from subgreenschist to blueschist eclogite facies these tectonic units are composed of garnet free metapelites and associated synmetamorphic veins from the same homogeneous aluminium rich and calcium poor protolith in that context mineralogical differences between units are assumed to result from contrasted pressure and temperature histories light ree bearing al phosphates of the crandallite group with florencite rich composition and variable goyazite content are the dominant lree minerals in the lowest grade units tizgarine 300 c 3 kbar as peak conditions and boquete de anjera 350 c 10 kbar in the latter unit metamorphic florencite is associated with mree rich monazite in the schist of the highest grade units beni mzala 2 420 450 c 12 kbar and beni mzala 1 550 c 16 kbar associations of allanite rich epidote and synchisite a lree fluorocarbonate are found whereas florencite and monazite are no longer observed at the wall of the quartz kyanite veins retrograde monazite ce with grain size of 20 to 50 m is the only lree bearing mineral th pb and u pb sims data on some of these grains yield ages of 21 3 1 7 ma and 20 9 2 1 ma respectively consistent with previous k ar ages obtained on retrograde clay mica mixtures in rocks from the same locality the identification of a stability field for monazite in high pressure aluminous metapelites with an upper thermal limit below 450 c as well as the derivation of meaningful u pb and th pb sims ages demonstrates the monazite potential for dating hp lt metapelites however since under these conditions monazite growth occurs below its admitted closure temperature these ages must be interpreted on the basis of monazite textural relationships

high resolution simulation of a nocturnal narrow convective line off the southeastern coast of taiwan in the mei yu season 1 this study performed high resolution numerical simulation on a convective line that occurred roughly 10 30 km offshore of southeastern taiwan overnight of 14 15 may 1998 three experiments at successively higher resolution 10 2 and 0 5 km but smaller domain were carried out and the narrow line is eventually reproduced it is found that shallow offshore return flow along the coast appeared since daytime due to topographic blocking on the weak prevailing onshore south southeasterly wind producing convergence at their interface near shore during the night mountain breeze further strengthened the offshore flow and convergence and the line initiated once developed downdrafts and outflow boundaries from old clouds triggered new clouds and this was more active along the eastern boundaries against the undisturbed environmental flow thus repeated new cloud formation took place throughout the night and into the next morning

formation and composition of rhabdophane bastnasite and hydrated thorium minerals during alteration implications for geochronology and low temperature processes abstract an investigation of accessory minerals in plutonic rocks from central madagascar reveals local very low grade alteration of the primary ree and th bearing phases monazite lree th po4 allanite careefe2 al2 sio7 sio4 o oh and thorite thsio4 all examples are found in relatively fresh looking samples in which alteration occurs on the micron to submicron scale the alteration occurs associated with micro fissures and predominantly affects the accessory minerals one type of alteration is replacement of thorite and monazite by thorogummite th u sio4 oh 4 and rhabdophane reepo4 h2o some of these secondary phases grow topotactically on the original magmatic crystals during development of rhabdophane pb and th can be transferred from the monazite precursor to rhabdophane resulting in similar apparent ages for both phases a second type of alteration has been investigated in two granites where bastnasite reeco3f forms at the expense of allanite which requires a fluid containing h2o co2 and f in either type of alteration mass transport of pb is deduced from galena development in the vicinity of the altered mineral in other examples mass transport of ree is assumed based on ree fractionation in secondary phases th rich minerals th rich monazite thorite are more affected by alteration than th poor phases this may be due to chemical disequilibrium at low temperatures or partial metamictization before alteration overlooking such alterations can lead to pitfalls during dating

temperature and bulk composition control on the growth of monazite and zircon during low pressure anatexis mount stafford central australia the formation age and trace element composition of zircon and monazite were investigated across the prograde low pressure metamorphic sequence at mount stafford central australia three pairs of inter layered metapelites and metapsammites were sampled in migmatites from amphibolite facies t 600 c to granulite facies conditions t 800 c sensitive high resolution ion microprobe u pb dating on metamorphic zircon rims and on monazite indicates that granulite facies metamorphism occurred between 1795 and 1805ma the intrusion of an associated granite was coeval with metamorphism at 1802 3ma and is unlikely to be the heat source for the prograde metamorphism metamorphic growth of zircon started at t 750 c well above the pelite solidus zircon is more abundant in the metapelites which experienced higher degrees of partial melting compared with the associated metapsammites in contrast monazite growth initiated under sub solidus prograde conditions at granulite facies conditions two distinct metamorphic domains were observed in monazite textural observations petrology and the trace element composition of monazite and garnet provide evidence that the first metamorphic monazite domain grew prior to garnet during prograde conditions and the second in equilibrium with garnet and zircon close to the metamorphic peak ages from sub solidus prograde and peak metamorphic monazite and zircon are not distinguishable within error indicating that heating took place in less than 20 myr

physico chemical control on the ree minerals in chloritoid grade metasediments from a single outcrop central alps switzerland this study assesses the effects of fluid whole rock composition and oxygen fugacity on the texture and composition of monazite allanite and xenotime for this purpose these were investigated in 13 mono metamorphic metasediments from a single locality of the central alps switzerland which record greenschist facies conditions t 400 450 c two of the samples contain hydrothermal veins dominated by quartz and calcite quartz respectively in metasediments devoid of veins the light rare earth elements lree are concentrated in allanite in all samples except for one metamarl ga06 allanite formation is texturally coeval with apatite chloritoid and xenotime during the main tectono metamorphic stage allanite formation implies significant mass transfer of ca and p via a fluid phase which is not clearly related to advective transport in ga06 elongate monazite grains have a detrital core rimmed by newly formed monazite significant arsenic contents are found in newly formed monazite xenotime and apatite monazite texture and composition suggest re crystallization by pressure solution at an oxygen fugacity sufficient to partly oxidize as s u and fe whether or not monazite is preserved appears to be but weakly dependent on the ca al ratio and thus whole rock composition at greenschist facies conditions samples with veins show peculiar features along carbonate bearing veins allanite occurs as porphyroblasts overgrowing the main foliation of the host rock as similar allanite porphyroblasts occur in calcite bearing metamarl their formation is attributed to environments rich in co2 bearing fluid a new generation of monazite is found in and along retrograde quartz veins this study demonstrates that at least in metasediments up to chloritoid grade ree minerals record fluid rock interaction that occurred at different deformation stages arsenic concentrations in ree phosphates appear to reflect conditions of elevated oxygen fugacity in cases where such conditions are not inherited from the sedimentary protolith the oxidation reflects a hydrothermal event the age of which may be directly datable by u th pb of as rich monazite

dating diagenetic monazite in mudrocks constraining the oil window authigenic monazite nodules increasingly recognized in pre mesozoic mudrock successions provide a means for dating diagenesis by exploiting trace uranium within the monazite structure but dating is difficult in practice because of zonation and abundant host rock inclusions we report here a refined technique that has yielded a date of 419 14 ma 2 mswd 1 2 for a 17 point pb pb regression age from a telychian silurian late llandovery mudrock from central wales shrimp analyses of monazite nodules from the same horizon are consistent with this and additionally demonstrate concordance of the u pb and th pb systems these results open the door to providing robust dates for a phase of burial related diagenesis which in wales seems approximately coincident with and perhaps was related to hydrocarbon expulsion

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

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

low temperature alteration of monazite fluid mediated coupled dissolution precipitation irradiation damage and disturbance of the u pb and th pb chronometers abstract low temperature alteration of monazite is documented in three centimeter sized monazite crystals from norway arendal madagascar ambato and sri lanka the three crystals have different chemical compositions especially in their u th y and pb contents and have 208 pb 232 th ages ranging from 491 to 900 ma optical microscope om scanning electron microscope sem and transmission electron microscope tem images and electron microprobe analyses epma show that all three preserve a similar patchy texture this texture is interpreted as resulting from an alteration reaction in which unaltered monazite mnz1 reacts to form a secondary th u y depleted high th u monazite mnz2 accompanied by thorite huttonite thsio 4 thorianite tho 2 and xenotime ypo 4 the proportions of which are dependent upon the initial composition of the monazite mnz1 images reveal variably intense internal fracturing with cracks filled with th rich fe rich phases monazite xenotime thermometry demonstrates that the pristine monazites mnz1 interacted with a low temperature fluid the alteration process is interpreted to follow a mechanism of fluid mediated coupled dissolution precipitation chemical dating with the electron microprobe shows no th u pb age differences between primary and secondary monazites except in the case of the ambato monazite in which altered domains yield older 750 ma apparent ages than the pristine mnz1 domains u pb and th pb isotope dating using la icp ms yields ages consistent with electron probe dates for pristine mnz1 zones however disturbance of these systems in the altered monazite domains leads to variable age results for these depending on sample in the case of sri lanka and arendal only 208 pb 232 th dates provide a reasonable estimate of the age of alteration which are constrained to be 450 and 864 ma respectively u pb systems are disturbed due to common pb contamination up to 40 and u fractionation relative to th during alteration responsible for depletion of u in altered monazites and increase of th u in contrast for the ambato monazite both the u pb and th pb systems were affected and yield inconsistent older dates for altered zones this is attributed to significant common pb contamination up to 80 which affects all pb isotopes and explains why electron probe ages are erroneous th u silicate contamination during measurement resulting from the presence of a numerous nano phases and nano fractures filled with th u silicates that are visible only under tem also contributes to the anomalously old ages for these disturbed mnz2 domains these results demonstrate the important role of radiation damage effects in particular swelling induced fracturing and the essential role of porosity and cracks which allow fluid charged with elements migration through monazite during low temperature alteration

paleoarchean partial convective overturn in the singhbhum craton eastern india abstract analyses of fold superposition structures and kinematics of shear zones along a 120 km long e w corridor across the singhbhum craton eastern india are combined with u pb th chemical ages of texturally constrained monazites in supracrustals gneisses and granitoids to reconstruct the paleoarchean tectonic history of the western part of the craton metamorphic sub greenschist facies shallow marine to platformal sediments of the iron ore group iog and the accordantly deformed jagnnathpur meta lavas were accreted onto a basement composed of 3 4 ga amphibolite facies para amphibolites quartzites muscovite schists older metamorphic group omg and anatectic older metamorphic tonalite gneisses omtg crustal shortening was followed by emplacement ascent of the singhbhum granitoid pluton sgp 3 2 3 3 ga synchronous with sinking of supracrustal screens along n nne trending steep dipping sinistral normal ductile shear zones deformation microstructures indicate the bulk of the pluton responded to exhumation strain by low t 500 c ductile flow of quartz and k feldspar with plagioclase being largely unaffected but granitoids along the western margin of pluton emplaced concurrent with westward retreating exhumation of the thickened crust was deformed at t 650 c since all granitoids in the pluton share the same n nne trending tectonic fabric microstructural features imply phased emplacement of the pluton during exhumation strain the transition from crustal shortening to exhumation interrupted by phased granitoid emplacement between 3 2 and 3 4 ga is explained by a two stage partial convective overturn model involving structures typical of supracrustal down granitoid up sense of movement the tectonic restoration in the western part of the singhbhum craton is new and complements growing evidence that accretion and convective overturn may have operated during the paleoarchean

petrochronology based on ree minerals monazite allanite xenotime apatite ree minerals monazite xenotime and allanite are ree1 minerals sensu stricto because lanthanides la lu and yttrium are critical constituents in them apatite does not require ree but because it contains substantial ree in many rocks it is included in this review all four minerals also host unusually high radionuclide concentrations notably th and u forming the basis of their utility as geochronometers this quartet of accessory minerals is playing an increasingly important role in petrochronology because they provide ways to link robust spot ages to petrogenetic p t conditions so can lend petrogenetic context to chronology based on other minerals part i of this review assembles the basic requisites prior to integrative petrochronologic analysis individual characteristics of the four ree minerals are addressed first i e their crystal chemistry and stability relations thermobarometers and trace element geochemistry used for tracing petrogenesis are discussed next and finally their chronology is summarized part ii presents case studies to highlight the specific strengths of ree minerals used to resolve the dynamics of a broad range of processes from diagenetic to magmatic conditions finally a brief section at the end outlines a few of the current challenges and promising perspectives for future work to introduce the four ree minerals in style let us recall the origins of their names the three phosphates have well respected greek grandparents and allanite has solid scottish roots yet of all four of them show idiosyncracies in etymology or type material apatite had long puzzled naturalists as it shows great chemical and physical variability and can resemble other minerals once properly identified abraham gottlieb werner named it apatite his reasoning referred to the greek root and giving the precise latin translation decipio taken literally both mean i deceive or i mislead which sounds like an apt confession from this mineral for having fooled

experimental determination of stability relations between monazite fluorapatite allanite and ree epidote as a function of pressure temperature and fluid composition the experimental alteration of monazite to allanite ree epidote fluorapatite and or fluorapatite britholite was investigated at 450 to 610 mpa and 450 to 500 c experiments involved monazite albite k feldspar muscovite biotite sio 2 caf 2 and variety of fluids including h 2 o kcl h 2 o nacl h 2 o cacl 2 h 2 o na 2 si 2 o 5 h 2 o 1 m hcl 2 m naoh 2 m koh 1 m ca oh 2 2 m ca oh 2 and caco 3 h 2 o the reaction products or lack thereof clearly show that the stability relations between monazite fluorapatite and allanite or ree epidote are more dependent on the fluid composition and the ratio of silicate minerals than on the p t conditions a high ca content in the fluid promotes monazite dissolution and the formation of fluorapatite and allanite or ree epidote lowering the ca content and raising the na content in the fluid decreases the solubility of monazite but promotes the formation of allanite replacing na with k in the same fluid causes fluorapatite with a britholite component to form from the monazite however allanite and ree epidote are not formed monazite is stable in the presence of nacl brines in kcl brine monazite shows a very limited reaction to fluorapatite when the fluid is na 2 si 2 o 5 h 2 o strong dissolution of monazite occurs resulting in the mobilization of rees and actinides to form fluorapatite britholite and turkestanite these experimental results are consistent with natural observations of the partial to total replacement of monazite by fluorapatite ree epidote and allanite in fluid aided reactions involving the anorthite component in plagioclase at mid to high grade metamorphic conditions in contrast an alkali bearing environment with excess na prevents the growth of allanite and eventually promotes the precipitation of secondary monazite the results from this study provide implications for geochronology and for deducing fluid compositions in metamorphic rocks

katabatic wind fields in coastal areas studied by ers 1 synthetic aperture radar imagery and numerical modeling synthetic aperture radar sar images acquired over mediterranean coastal waters from the first european remote sensing satellite ers 1 showing sea surface manifestations of katabatic wind fields are presented in particular sea surface roughness patterns generated by katabatic winds blowing from 1800 in high mountains through a broad valley at the western coast of calabria southern italy into the gulf of gioia is investigated the ers 1 sar images show that their areal extent and shape vary strongly depending on the meteorological conditions the roughness pattern sometimes has the form of a mushroom an elongated tongue a broad blob or a narrow truncated band for one event september 8 1992 we have simulated the wind field at the sea surface by using a nonhydrostatic mesoscale atmospheric model and then compared it with the wind field derived from the ers 1 sar image by using the c band wind scatterometer model cmod4 the comparison shows that the atmospheric model reproduces quite well the mushroom like form of the wind field pattern while the wind speed is obtained somewhat lower than the one inferred from the sar image this study demonstrates that sar images acquired over coastal waters are well suited to study local wind fields in coastal areas and to test numerical models that describe local wind fields which extend from the coast onto the sea

mass transport and fractionation during monazite alteration by anisotropic replacement abstract the present experimental study investigates the causes of anisotropic replacement and its impact on the element mass transfer during monazite alteration by combining in situ characterization of solid and fluid products starting material of standard manangotry monazite was placed at 200 mpa with 18 o doped fluids at temperature t between 300 and 600 c for durations between 14 and 114 days in some cases with hematite magnetite buffer and in presence of pre fractured quartz crystals for all experiments with naoh at t 400 c monazite products show a replacement rim altered domain but with complex microstructures that are best explained by nanoscale observations at 400 c and 500 c replacement propagates anisotropically through the unaltered domain due to preferentially oriented dissolution and or fracturing at the reaction interface the altered domain corresponds to nanochannels of secondary monazite mnz2 intruding primary monazite mnz1 with nanopores filled by amorphous si rich inclusions at the reaction front interface at 600 c the altered domain increases in volume and becomes homogeneous and non porous due to textural and chemical reequilibration however nanoscale observations reveal an anisotropic propagation associated with dislocations and preservation of mnz1 relics within the apparently homogeneous altered domain textural equilibration leads to transient pores inclusions which preferentially move toward the reaction front in all experimental products the abundant porosity attests to significant mass transfer during monazite replacement nanomixture within altered domains hampers accurate determination of mnz2 composition and is assumed to be responsible for the pb measured in the rim due to mnz1 contribution however composition measurements indicate that mnz2 contains higher light rare earth elements lree higher th u ratio but lower y th u pb and ca contents compared to mnz1 elements released in the fluid by monazite replacement are mobilized from the reaction front toward the grain boundary and then redistributed between secondary th silicates and phosphates si rich gel like material and aqueous fluids at t 500 c analyses of inclusions trapped in replaced quartz confirm an efficient ree solubility in the alkaline solutions the si rich gel like inclusions contain high amounts of ree e g 950 4600 ppm ce th 4480 6170 ppm and u 30 110 ppm while aqueous fluid inclusions have high concentrations of ree and th around 100 s of ppm compared to common natural brines there is a fractionation of th and u during mnz1 replacement th u 70 with low th u ratios in the aqueous fluid 7 23 compared to the secondary solid products up to 150 independently of the initial presence of hematite magnetite buffer this accounts for a fractionation within the isotopic th pb and u pb ages within the altered domain in natural samples observed microscopically the complex anisotropic geometry of the replacement can lead to a nanomixture within apparently homogeneous altered domains with partial resetting of the u th pb geochronometer and to misleading interpretations of secondary inclusions within apparently unaltered domain

radar observations of the diurnally forced offshore convective lines along the southeastern coast of taiwan this study documents offshore convective lines along the southeastern coast of taiwan a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the taiwan mei yu season doppler radar and surface observations were gathered from a specially chosen period 11 15 may 1998 when the offshore convective lines were active off the southeastern coast of taiwan these observations were used to show the basic character structure and possible formative processes of offshore convective lines the synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly south southeasterly winds in the boundary layer with southwesterlies westerlies aloft examination of radar data during the study period indicates that the lines generally occurred 10 30 km offshore and were characterized by an elongated narrow zone 5 10 km wide of heavy precipitation the lines were oriented roughly parallel to the coastline and generally did not move significantly the intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night detailed analyses of an event on 14 15 may 1998 further show the important physical link between the offshore flow and the development of the line the offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow particularly a very narrow zone 2 km of low level heavy precipitation 40 45 dbz coincided with regions of strong updrafts and convergence where the prevailing southerly onshore flow encountered the cool offshore flow nearshore this offshore flow induced convergence given a stable thermodynamic condition in the lowest 1 km in the inflow region was a crucial low level forcing that provided lifting to trigger moist deep convection in this case the line s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line no consistent upshear tilt of updrafts throughout the storm layer was observed which is consistent with the presence of a strong westerly shear in the line s environment both of these observations explain a relatively strong weak modification of low level onshore offshore flow by precipitation additionally a combination of surface and doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0 7 m s 1 and possessed a frontal character with notable discontinuities in near surface wind and temperature instead of pressure and dewpoint temperature

geochronology of accessory allanite and monazite in the barrovian metamorphic sequence of the central alps switzerland abstract the formation of accessory allanite monazite and rutile in amphibolite facies rocks across the barrovian sequence of the central alps switzerland was investigated with a combination of petrography and geochemistry and related to the known structural and metamorphic evolution of the lepontine dome for each of these minerals a specific approach was adopted for geochronology taking into account internal zoning and u th pb systematics in situ u th pb dating of allanite and monazite by ion microprobe revealed systematic trends for the ages of main deformation and temperature in the lepontine dome isotope dilution tims dating of rutile returns dates in line with this picture but is complicated by inheritance of pre alpine rutile and possible pb loss during alpine metamorphism allanite is generally a prograde mineral that is aligned along the main foliation of the samples and found also as inclusions in garnet prograde allanite formation is further documented by rutile inclusions with formation temperatures significantly lower than the maximum t recorded by the rock mineral assemblage allanite ages vary from 31 3 1 1 ma in orthogneisses in the east to 31 7 1 1 ma for a bundnerschiefer and 28 5 1 3 ma for a metaquartzite in the central area to 26 8 1 1 ma in the western part of the lepontine dome these ages are interpreted to date the main deformation events nappe stacking and isoclinal deformation of the nappe stack close to peak pressure conditions the timing of the thermal peak in the lepontine dome is recorded in monazite that grew at the expense of allanite and after a main episode of garnet growth at temperatures of 620 c monazite in the central area yields an age of 22 0 0 3 ma which is indistinguishable from the age of 21 7 0 4 ma from a metapelite in the western part of the lepontine dome in the central area some of the classical kyanite staurolite garnet schists directly underlying the metamorphosed mesozoic sediments contain monazite that records only a pre alpine variscan metamorphic event of upper greenschist to lower amphibolite facies conditions dated at 330 ma the new age data provide evidence that nappe stacking at prograde amphibolite facies conditions and refolding of the nappe stack occurred between 32 and 27 ma only a few million years after eclogite facies metamorphism in the adula cima lunga unit amphibolite facies metamorphism lasted for about 10 my to 22 ma allowing for multiple ductile deformation and recrystallization events the long lasting amphibolite facies metamorphism requires fast cooling between 20 and 15 ma in the central alps this fast cooling was not related to an increase in sedimentation rates in the foreland basins suggesting that tectonic exhumation was responsible for termination of amphibolite facies metamorphism in the lepontine dome

testing ore deposit models using in situ u pb geochronology of hydrothermal monazite paleoproterozoic gold mineralization in northern australia the inability to establish absolute ages for gold deposition in the pine creek orogen of northern australia has led to conflicting ore deposit models ranging from intrusion related which predict that gold mineralization was synchronous with granite magmatism ca 1835 1820 ma to orogenic which place ore deposition nearly 100 m y later here we present ion microprobe u pb geochronology for a mineralized quartz reef from tom s gully mine mount bundey northern territory australia and nearby granitic rocks and associated contact aureoles isotopic dating of zircon and monazite indicates that intrusion and contact metamorphism occurred ca 1825 ma whereas hydrothermal monazite from the auriferous quartz reef gives a mean 207pb 206pb age of 1780 10 ma interpreted as the time of gold mineralization mineralization therefore postdated intrusion by 45 m y and preceded a postulated ca 1740 1730 ma cratonwide orogenic gold event by 50 m y hence neither the intrusion related model nor the recently proposed orogenic model is applicable combined with a reevaluation of age data from the nearby goodall gold deposit our data suggest that mineralization coincides with and may be related to an episode of regional low grade metamorphism deformation and fluid circulation shoobridge event our results demonstrate the importance of high precision in situ geochronology and detailed petrography for deciphering age relationships in ore deposits and of testing the veracity of models for ore formation

timing of diagenesis and very low grade metamorphism in the eastern sector of the sierra de cameros iberian range spain a u pb shrimp study on monazite the sierra de cameros is an intracontinental orogen and represents the north western part of the iberian range in northern spain it comprises a thick sequence of syn rift continental sediments mainly sandstones and carbonates deposited during lower cretaceous times a unique characteristic of the sierra de cameros in relation to the rest of the iberian range is the presence of low grade metamorphism in certain parts of the basin an event that predates basin inversion this paper describes the presence textural relationships and geochemical aspects of authigenic and or metamorphic monazite within different lithologies from the deepest parts of the basin sensitive high resolution ion microprobe shrimp u pb dating of monazite records the presence of two age populations the first with 206 pb 238 u ages ranging from 122 to 116 ma which is considered as diagenetic in origin whilst the second is dated at 99 2 ma and postdates the metamorphic climax

th pb ion microprobe dating of allanite allanite which is a common accessory mineral in a wide variety of rock types typically contains high concentrations of th and u thus an in situ method of u th pb dating of this phase would have broad application we describe a method to permit th pb ages of allanite to be determined with approximately 10 accuracy using a high resolution ion microprobe knowledge of the composition and substitution mechanisms of this complex mineral is key to understanding the relative ion ization efficiencies of th and pb the chemical compositions of three allanite samples used as age standards cima d asta pluton 275 5 1 5 ma atesina volcanic complex 276 3 2 2 ma la posta pluton 94 2 ma were determined using an electron microprobe permitting an assessment of matrix effects on ionization an ion microprobe calibration curve involving elemental and oxide species of th and pb i e 208 pb th vs tho 2 th yields highly scattered apparent ages when allanite age standards with different fe contents are used however a three dimensional plot of 208 pb th vs tho 2 th vs feo sio improves the accuracy of the calibration to about 10 even though this level of uncertainty is substantially greater than that expected for u th pb ion microprobe analyses of zircon or monazite th pb ages of allanite can still be used to address important geologic questions we used this method to date two metamorphic allanite grains from the footwall of the main central thrust nepal himalaya and an allanite grain from the pacoima canyon pegmatite california allanite inclusions in garnet from nepal yield significantly older ages than the coexisting monazite indicating that allanite formation in these rocks records a previous metamorphic cycle that predates slip along the fault the pacoima canyon allanite grain yields a younger age than that reported for zircon implying pb loss during cooling of the pegmatite

understanding geologic processes with xenotime composition chronology and a protocol for electron probe microanalysis abstract xenotime ypo 4 is iso structural with zircon group minerals and lies at one end of a compositional solid solution with monazite as with monazite and zircon naturally occurring xenotime may accommodate significant concentrations of rare earth elements as well as th and u making it an important repository for these valuable geochemical marker elements and a potential geochronometer xenotime grows in sediments during diagenesis in low to granulite grade metamorphic rocks in migmatites and is common in peraluminous igneous rocks xenotime can be a complement or indeed an alternative to monazite and or zircon in geochemical and geochronological studies to maximise the petrographic potential of xenotime a complete understanding of its composition and relationship to rock forming assemblages is essential electron beam techniques provide micron scale resolution of compositional and textural variation and yield precise dates for individual micro volumes in multi domain grains methods for collecting trace element data by electron probe microanalysis differ from those routinely employed to collect major element concentrations careful characterisation of background curvature and background interferences around the th u and pb peaks is required to avoid large overlap correction for y l 2 3 on pb m analysis of pb is made on the m peak a broad array of geochemical and geochronological applications can take advantage of the links between xenotime composition and texture and the evolution of silicate mineral assemblages in a diversity of environments one example of metasomatised xenotime from a pegmatite in sw norway demonstrates a practical application to dating geologic processes as well as the potential limitations that arise in compositionally heterogeneous xenotime

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

apatite monazite and xenotime in metamorphic rocks this chapter focuses on phosphates that are significant in metamorphic rocks a quick survey of phosphate mineral descriptions at a commercial mineral web site revealed over 500 phosphate mineral names remarkably only three are common in metamorphic rocks apatite monazite and xenotime and this chapter is restricted to discussion of these minerals apatite monazite and to a lesser extent xenotime have enjoyed intensive study during the previous half century following world war ii considerable study was made of minerals that contain fissionable materials and the sometimes large concentrations of u and th in monazite culminated in a number of seminal papers on the occurrence of that mineral e g overstreet 1967 during the 1970s and early 1980s the study of apatite and monazite turned towards their role as a sink for rees and other trace elements in rocks e g watson 1980 watson and capobianco 1981 throughout this period monazite and to some extent xenotime enjoyed attention as a geochronometer e g parrish 1990 and through today this attention has continued to grow accessory minerals such as monazite xenotime and apatite have come to the forefront of research in metamorphic petrology in recent years for two reasons first it has recently been recognized that trace elements in metamorphic rocks and especially trace element zoning in garnet and other major phases contain considerable detailed information about the reaction history a rock has experienced coupled with the fact that diffusion of many trace elements in metamorphic minerals is in general considerably slower than diffusion of major elements in those same minerals the possibility has recently emerged of recovering details of metamorphic petrogenesis that were previously unattainable inasmuch as accessory minerals play a dominant role in the mass budget of many trace elements attention has naturally turned to their paragenesis it has also recently been discovered that

formation and maintenance of a long lived taiwan rainband during 1 3 march 2003 abstracttaiwan rainbands trs defined here as convective lines which form off the mountainous eastern coast of taiwan under weakly synoptically forced weather conditions are a well known mesoscale phenomenon but their formative processes remain the subject of debate this study uses surface and radar observations within the coastal zone of eastern taiwan and ncep reanalysis data to document a long lived tr with a lifetime of 36 h during 1 3 march 2003 to advance the current general understanding of mechanisms responsible for the tr s formation and maintenance detailed analyses indicate that the rainband was initiated by convergence that was produced as low level environmental northeasterly easterly onshore flow encountered topographically blocked northerlies that developed nearshore the northerly blocked flow was observed to weaken and subsequently dissipate because of changing synoptic pressure patterns that caused prevailing southeasterlies southerlies at low levels however colder nearshore ai

u th pb dating of collision in the external alpine domains urseren zone switzerland using low temperature allanite and monazite article i nfo dating metamorphism in external domains of orogenic belts is a challenging task due to the few chronometers available and common inheritance or disturbance of the isotopic systems at low temperature metamorphic con ditions in the external domains of the central alps urseren zone the occurrence of distinct populations of monazite and allanite in one single outcrop offers a unique chance to evaluate the potential of these two ree minerals to date successive metamorphic stages within a collisional cycle the studied outcrop locality of garvera exposes mesozoic metasediments that were metamorphosed under greenschist facies conditions t b 450 c under these conditions ree mineral grains or domains are typically small 5 50 m and in this case also occur as porphyroblast in pelites at the contact with carbonate layers or veins allanite grains n200 m based on the texture and mineral assemblages ree mineral growth conditions were attributed to be detrital mnz1 syn kinematic mnz2 and aln1 post kinematic at the thermal peak aln2 and retrograde during late stage deformation mnz3 to constrain temporally the successive crystallisation conditions ree minerals have been dated using shrimp ion microprobe u th pb analyses show that the alpine ree minerals have a high th u and while most of the 206 pb is non radiogenic f206 that can reach up to 99 for allanite th pb ages can be obtained using 206 pbc corrected th pb isochron the age of different generations of allanite and monazite constrains the timing of successive collisional stages for the prograde accretion at 22 5 1 5 ma mnz1 and aln1 thermal peak at 19 3 2 0 ma aln2 and late stage hydrothermal veining at13 6 1 4 ma mnz3 these novel geochronological data confirmtheregional diachroneity throughthe cen tral alps with younger ages burial thermal peak and exhumation toward the external domains the similarity betweenmetamorphicagesofsamplestakenintheurserenzoneandthenearbycrystallinemassifssuggeststhat themetasedimentarycoveroftheurserenzoneremainedcloselyjuxtaposedtotheexternalcrystallinebasement during the alpine collision cycle the monazite age of the late stage vein testifies for active tectonic deformation at 13 6 1 5 ma which likely played a crucial control on the exhumation of the external massifs in the middle miocene

resolving poly metamorphic paleoarchean ages by chemical dating of monazites using multi spectrometer u th and pb analyses and sub counting methodology abstract chemical u th total pb dating method is a low cost and reliable technique to estimate the age of monazites of detrital and diagenetic origin or those found in low to high t metamorphic or magmatic rocks using electron microprobe emp analyses the method has been commonly applied for age estimation in phanerozoic and proterozoic rocks and less commonly in neoarchean rocks monazite dates from the paleoarchean era are rare and the associated error of spot age 2 error absolute age 100 is high i e between 2 and 26 the errors associated with chemical dating of monazite are significantly larger compared to isotope methods which impede precise age estimation and age resolution in polygenetic monazites of neoarchean and older rocks in this study simultaneous element analyses in multiple spectrometers and the sub counting method of analyses are employed to obtain precise estimates of u th and pb concentrations in monazite using vanadinite pb 5 vo 4 3 cl as the pb standard instead of pbs the method yields an age of 3118 28 ma with mount narryer mesoarchean monazite thermal ionization mass spectrometry tims age 3132 1 ma and 516 12 ma with moacyr monazite tims age 509 1 ma emp monazite age 497 10 ma as the reference samples the modifications led to 40 reduction in spot age errors in the mount narryer sample relative to those obtained by conventional monazite dating method the reduced errors in spot ages helped in resolving statistically un mixed age populations 3152 16 ma 3322 15 ma and 3420 140 ma in polygenetic monazites within muscovite quartz schists from the singhbhum craton eastern india the significance of these dates is briefly discussed