la icp ms monazite u pb age and trace element constraints on the granulite facies metamorphism in the tongbai orogen central china abstract granulite facies metamorphic rocks in the tongbai orogen have great implications for the evolution of the whole qinling tongbai dabie orogenic belt however the age and tectonic setting of the granulite facies metamorphism have not been well constrained yet in this contribution bse imaging trace element analysis and u pb dating of monazite were undertaken for three felsic granulites a gneiss and a leucosome from the tongbai orogen most monazite grains from the granulite and gneiss samples exhibit no zoning relatively low th u ratios significant depletion in hrees and y and negative eu anomalies indicating their formation under granulite facies metamorphic conditions their formation ages range from 423 2 to 430 3 ma with a weighted mean of 426 5 which is taken as the timing of the peak granulite facies metamorphism in the leucosome sample the monazite shows a euhedral to subhedral shape coupled with a core and rim structure besides being depleted in hrees and y both of them have significantly negative eu anomalies and variable u contents 1220 13323 ppm and th u ratios 7 2 136 7 this suggests that their formation was coeval with the crystallization of feldspar metamorphic zircon and garnet the monazites yield a weighted mean age of 426 3 ma suggesting nearly coeval partial melting during granulite facies metamorphism the relationship between metamorphic monazite and zircon within the same metamorphic sample is complex as revealed by metamorphic monazite and zircon u pb ages for the gneiss granulite and leucosome samples in the other two granulite samples the monazite yields u pb ages of 423 2 and 425 3 ma whereas only little overgrowth or recrystallization of metamorphic zircon this indicates that monazite is more sensitive than zircon in recording of metamorphic age even at the granulite facies conditions combined with previous metamorphic zircon u pb age results the prograde peak and retrograde stages of the granulite facies metamorphism in the tongbai orogen can be constrained at ca 440 426 and 415 ma respectively therefore the granulite facies metamorphism would have lasted for more than 20 myr the prolonged granulite facies metamorphism might result from the continuous northward subduction of the paleotethyan oceanic crust beneath the north qinling terrane

the tectonic significance of u th pb ages of monazite inclusions in garnet from the himalaya of central nepal abstract textural observations chemical zoning and 196 in situ la icp ms 232 th 208 pb and 238 u 206 pb dates of monazite inclusions in greater himalayan garnets demonstrate that inclusions are frequently composite grains composed of multiple generations of monazite cenozoic prograde and retrograde monazite are commonly intergrown and both of these components are frequently intergrown with lower paleozoic monazite because zones in most inclusions are too small to date and because some inclusions show little zoning of y and th chemical characterization alone is often insufficient to guide interpretation of the crystallization significance of th pb dates comparison of 238 u 206 pb and 232 th 208 pb dates thus is critical for interpreting the tectonic significance of dates derived from these composite inclusions most cenozoic monazite crystallized between 42 29 and 22 12 ma and these age ranges may record prograde and retrograde metamorphism of greater himalayan rocks respectively dates younger than 12 ma are discordant without exception the

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

pb diffusion in monazite constraints from a high t contact aureole setting abstract we report measurements of pb diffusion in natural monazite that was subjected to a static anhydrous high temperature overprint in the contact aureole of the makhavinekh lake pluton mlp northern labrador canada the 1850 ma monazite grains we studied were reheated to temperatures of 900 25 c during intrusion of mlp at 1322 ma ion microprobe depth profiling reveals the outermost 0 3 m of these grains to contain pb u gradients that can be modeled as a result of one dimensional concentration independent diffusion i e an error function profile at 1322 ma these gradients are combined with temperature time histories predicted by a numerical model of conductive heat flow in the contact aureole to calculate pb diffusion coefficients between 3 2 10 28 and 1 3 10 27 m2 s this range overlaps with the down temperature extrapolation of experimental pb diffusion data obtained under dry conditions confirming the slow diffusivity of pb in monazite at crustal temperatures and timescales

high frequency internal wave observations in the marginal ice zone three thermistor chains extending from 15 to 65 m were deployed from ice floes in the marginal ice zone north of svalbard in a triangle with sides of 500 800 m for a period of 7 days vertical displacement spectra indicate that the internal wave energy level is lower than the garrett and munk spectrum by a factor of 2 3 but higher than other observations in the arctic a group of internal waves a wave train with frequency of 2 3 cph was observed to propagate at 0 05 m s through the triangle in a west southwesterly direction during a 4 to 6 hour period a case study of this wave train where the horizontal phase differences between the three thermistor chains were analyzed showed wavelengths of 100 200 m and phase velocities of 0 10 0 15 m s observation of the density field and the velocity field indicated that stratification dominated over vertical shear consequently the dispersion relation was calculated by solving numerically the vertical mode equation for internal waves in a shearless ocean the estimated wavelengths and phase velocities agree with the dispersion relation for first mode internal waves the generating mechanisms may be tidal oscillations associated with a seamount located east of the triangle or ice keels moving in relation to the water creating lee waves in the pycnocline

very high temperature moderate pressure metamorphism in the new russia gneiss complex northeastern adirondack highlands metamorphic aureole to the marcy anorthosite discussion alcock and muller 1999 assert four inferences regarding grenville gneisses near new russia n y named new russia gneiss complex by them and the adjacent ca 1130 ma marcy anorthosite massif these four inferences follow 1 metamorphism and anatexis of the new russia complex were due to contact effects in the thermal aureole of the ca 1130 ma marcy anorthosite 2 pressure estimates in the gneiss suggest anorthosite emplacement pressures of 750 mpa 3 heat from intrusion of the marcy anorthosite and coeval anorthosite mangerite charnockite granite amcg plutons caused regional granulite facies metamorphism of the adirondack highlands and 4 the marcy anorthosite massif which commonly is only mildly deformed in its core is a postkinematic intrusion thus implying that the adirondacks experienced no post marcy ottawan orogenesis at ca 1090 1030 ma we consider all four assertions to be seriously flawed and we address these and related issues beginning with inference 4 above which is critical to their entire argument alcock and muller ignore or misrepresent two critical pieces of widely reported data based upon field relations and u pb zircon geochronology in addition their own most recent geochronological results contradict the model that they propose these critical issues are discussed below under three separate headings 1 alcock and muller cite the existence of only younger undeformed or mildly deformed granites following the ca 1150 1130 ma amcg plutonism of the adirondack highlands this ignores the existence of the well established hawkeye granitic suite of the highlands that is closely related to buddington s 1939 younger hornblende granite and has been dated six samples from across the region by u pb zircon at 1095 13 ma chiarenzelli and mclelland 1991 mclelland et al 1996 in press the hawkeye suite commonly exhibits intense ductile strain fig d1 and therefore predates high grade granulite facies t 700 850 c metamorphism and penetrative deformation of the ottawan orogeny ca 1090 1030 ma the age of which has

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

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

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

response of the u pb chronometer and trace elements in zircon to ultrahigh temperature metamorphism the kadavur anorthosite complex southern india abstract zircon from quartzites in the contact aureole and wider environs of the kadavur anorthosite complex se india was studied by laser ablation icp ms to assess the response of the u pb isotope system and trace element concentrations to ultrahigh temperature uht contact metamorphism 1000 c combined cathodoluminescence imaging and la icp ms analyses show that zircon grains contain detrital cores which yield ages between 3 4 ga and 1 8 ga and exhibit a large spread in ree concentrations these cores are associated with one or two rims that provide concordant age populations at 955 16 ma and 810 7 ma 2 and relatively uniform ree patterns the older ages of ca 955 ma record the imprints of regional early neoproterozoic metamorphism related to rodinia assembly the younger age is interpreted to date anorthosite emplacement and its associated contact metamorphism during a second regional metamorphic episode coeval with the intrusion of a type granites in the area zircon grains from the country rocks away from the anorthosite show additional rims yielding ages from 590 to 490 ma corresponding to regional pan african tectonometamorphism the zircon rims are either newly grown domains or represent recrystallized and re equilibrated parts of precursor zircon discordance is only observed in 25 of the detrital cores these cores have relatively high u concentrations 400 ppm which strongly suggests that pb loss occurred under u ht conditions by partial recrystallization annealing of zircon that had become metamict the preservation of old concordant ages and source ree characteristics by the low u i e weakly to non metamict detrital cores shows that pristine zircon is extremely robust to thermal disturbance and that its u pb systematics can remain unaffected despite multiple u ht metamorphic episodes these observations imply that u pb ages in zircon cannot be reset by volume diffusion under any crustal conditions disturbance of the u pb system in individual zircon crystals or parts thereof can only be achieved by recrystallization of radiation damaged zircon

pb isotopic composition colour and microstructure of monazites from a polymetamorphic rock in antarctica a moderate to high grade regionally metamorphosed paragneiss from antarctica contains monazites of several different colours brown yellow and grey each colour type has a distinctive u pb isotopic composition which appears to result from different proportions of radiogenic pb loss isotopic differences are neither related to la nd ce p ca ti and or ba nor to u or th content all colour types have similar structures at the submicron scale as determined by both conventional and high resolution transmission electron microscopy tem these show that the grains are essenttially non metamict but are composed of 100 a crystalline domains misoriented from each other by no more than 2 10 3 radians and separated by narrow confused boundary regions where misorientation is probably accommodated by imperfect atomic arrangements these regions of mismatch form potential zones of high permeability diffusivity which are believed to be fundamental to the isotopic and colour differences between grains colour type is apparently related to the capacity of different minerals to shield included monazite grains from fluids circulating in the rock system

an overview of the upb geochronology of the paleoproterozoic torngat orogen northeastern canada abstract the paleoproterozoic torngat orogen northern labrador and northeastern quebec canada is the result of oblique collision between the nain north atlantic and rae cratons a comprehensive set of u pb ages allows the chronology of events to be closely bracketed subduction occurred below the nain craton from ca 1910 1870 ma and collision between the cratons may have occurred between 1869 and 1844 ma sinistral deformation continued along the intervening abloviak shear zone until ca 1824 ma and convergence was ultimately impeded by the partial subduction of the southern rae craton post collisional isostatic uplift of the southern rae craton initiated deformation in the komaktorvik zone ca 1798 ma a prominent bend in the abloviak shear zone may be the result of differential uplift of the western side of the orogen in the south sinistral strike slip and east as well as west side up deformation continued episodically in the komaktorvik zone until at least 1710 ma the tectonic development of the orogen can be explained in terms of modern plate tectonic processes

40ar 39ar chronology of the nain anorthosites canada a hornblende 40ar 39ar age of 1328 8 ma has been obtained from the contact aureole of the bird lake massif confirming it as one of the oldest members of the nain plutonic suite this age constrains the timing of the early stage magma activity of the nain plutonic suite plagioclase samples from the intrusions yield either u shaped or staircase shaped 40ar 39ar age spectra and most of them have two isochrons of similar age but greatly different initial argon composition most plagioclase closure ages are 95 of either the hornblende age from a contact aureole or coexisting biotite ages and appear to reflect single cooling events for each intrusion two major stages of emplacement for the nain anorthosites are identified an older anorthosite event and a main anorthosite event in agreement with results from earlier field studies the port manvers run paul island and nukasorsuktokh island intrusions yield much younger plagioclase ages than any previously established intrusion ages probably reflecti

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

prograde peak and retrograde p t paths from aluminium in orthopyroxene high temperature contact metamorphism in the aureole of the makhavinekh lake pluton nain plutonic suite labrador static heating during intrusion of the makhavinekh lake pluton mlp caused replacement of garnet in the adjacent country rocks tasiuyak gneiss by coronal assemblages of orthopyroxene cordierite thermometry based on al solubility in orthopyroxene applied to relict garnet and neighbouring orthopyroxene preserves a temperature gradient from 700 to 900 c at distances between 5750 and 20 m from the intrusion reaffirming the robustness of this thermometry technique intracrystalline and intergranular variations of al zoning in orthopyroxene are well preserved suggesting that little diffusional modification of al growth zoning occurred maximum al2o3 in orthopyroxene ranges from c 2 0 wt at 5750 m from the intrusion to a maximum of 4 3 wt at the contact individual orthopyroxene grains show decreasing al from core to rim in samples 500 m from the intrusion while those at greater distances show an increase from core to rim these features are interpreted with the aid of numerical models for conductive heat flow in the aureole coronas in samples close to the intrusion grew at high temperatures and along t t paths dominated by cooling so maximum al content in orthopyroxene in these samples occurs in the cores of grains that grew during the earliest stages of garnet consumption in contrast the corona forming reactions in rocks further from the contact proceeded along prograde heating paths so maximum al content in orthopyroxene occurs in the rims of grains that grew during the final stages of garnet consumption these results document the ability of al in orthopyroxene thermometry to preserve a detailed record of thermal histories in contact metamorphic granulites they suggest that similar intracrystalline and intergranular variations of al zoning in orthopyroxene in regional granulites may also preserve portions of both the prograde and peak t evolution

monazite and xenotime petrogenesis in the contact aureole of the makhavinekh lake pluton northern labrador high temperature 700 900 c metamorphism in the contact aureole of the makhavinekh lake pluton mlp northern labrador led to the growth of monazite and xenotime during progressive replacement of regional garnet bearing assemblages m1 by lower pressure symplectitic coronas of orthopyroxene cordierite m2 in the inner aureole 500 m from the contact where m1 garnet is strongly resorbed high y hree monazite xy hree 0 14 0 18 occurs as small isolated grains and as discontinuous rims on partially resorbed pre m2 monazites that were liberated from garnet xenotime also occurs as small isolated grains within m2 coronas ion microprobe dating of thin high y rims indicates that new monazite growth occurred during m2 monazite xenotime miscibility gap temperatures are consistent with al solubility in orthopyroxene thermometry estimates indicating that peak temperatures in the inner aureole are accurately recorded and preserved by monazite m2 monazite records therefore the temperature and timing of m2 metamorphism two net transfer reactions modelled using singular value decomposition in the system p y hree lree are proposed to account for the growth of m2 phosphates 1 38 grt1 1 mnz1 1 13 mnz2 and 2 737 grt1 1 ap 1 mnz2 3 4 xno2 reaction 1 conserves p and gave rise to locally coronitic high y overgrowths on partially resorbed pre m2 monazite whereas reaction 2 accounts for the growth of small new monazite and xenotime grains both reactions were highly localized within individual m2 coronas due to slow intergranular diffusion accompanying fluid undersaturated metamorphism in the mlp aureole similar monazite forming reactions are expected in other polymetamorphosed granulites

applications and limitations of u pb thermochronology to middle and lower crustal thermal histories abstract volume diffusion of pb occurs over micron length scales in apatite and rutile at temperatures relevant to the evolution of the middle and lower crust continuous thermal history information can be resolved from inversion of intracrystalline u pb date profiles preserved within individual grains recent developments in microbeam analysis permit rapid measurement of these age profiles at sub micron spatial resolution thus heralding a new era for u pb thermochronology here we review the theoretical experimental and empirical basis for u pb thermochronology and show that rutile in particular presents an exceptional opportunity to obtain high resolution thermal history information from the deep crust we present a bayesian procedure that is well suited to the inversion of u pb date profile datasets and balances computational efficiency with a full search of thermal history coordinate space complications relevant to accurate application of u pb thermochronology are discussed i theoretically and ii empirically using a rutile u pb dataset from the lower crust of the grenville orogeny purely diffusive date profiles are shown to be the exception to uniform or step like young profiles suggesting that processes other than thermally activated volume diffusion may control u pb systematics in rutile residing in the lower crust however the data obtained from apparent diffusive profiles systematically match cooling histories inferred from other thermochronometers this result emphasises the importance of integrating microtextural observations and trace element concentrations with u pb age data in order to discriminate between diffusive and non diffusive pb transport mechanisms in accessory phases and thus minimize the risk of generating spurious thermal histories

on the interaction between infiltration and hortonian runoff abstract a model which couples the kinematic wave approximation for hortonian overland flow and the conceptual approach developed by corradini et al 1997 j hydrol 192 104 124 for local infiltration was used to investigate the effects of random spatial variability of saturated hydraulic conductivity k s on the outflow hydrograph at hillslope scale the model incorporates a representation of infiltration of overland flow running over pervious downstream areas run on process single rainfall pulses and complex storms over two soils representative of a silty loam and a sandy loam soil were considered our results suggest that for realistic values of the coefficient of variation of k s the run on process cannot be disregarded because it produces a significant decrease of overland flow during both the rising and the recession limb of the hydrograph furthermore the role of the level of spatial correlation of k s was found to be typically minor and the run on process concurred to this result the possibility of simplifying the stochastic problem by a deterministic approach based on the use of a uniform lumped value of k s was also examined and rainfall patterns adequate for this simplification were deduced in terms of scaled storm intensity and storm duration

texturally controlled u th pb monazite geochronology reveals paleoproterozoic uht metamorphic evolution in the khondalite belt north china craton

makhavinekh lake pluton labrador canada geological setting subdivisions mode of emplacement and a comparison with finnish rapakivi granites abstract makhavinekh lake pluton is an oval elsonian 1322 ma granitic intrusion within the nain plutonic suite of central coastal labrador the pluton comprises at least five textural mineralogical subdivisions dominated by quartz monzonite and granite and it is surrounded by a well defined pyroxene hornfels thermal aureole fayalite and clinopyroxene are common constituents of the eastern half of the makhavinckh lake pluton hornblende is present throughout the whole pluton and is the dominant mafic mineral in the western half of the intrusion the hornblende rich parts of the intrusion appear to be a consequence of late to post emplacement hydration of originally olivine bearing rocks textural mineralogical and geochemical features are similar to the rapakivi granites of finland the makhavinekh lake pluton has the morphology of a sheath separating an external gneissic country rock complex from an internal basic plutonic suite it is proposed that the makhavinekh lake pluton developed through cumulate processes and was emplaced as a hot dry crystal charged mush via a mechanism of cauldron subsidence block faulting that allowed ascent of the pluton may have been related to crustal bulging from an underlying mafic magma pond

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

age trends in garnet hosted monazite inclusions from upper amphibolite facies schist in the northern grouse creek mountains utah we performed in situ th pb dating of monazite in upper amphibolite facies pelitic schist from the grouse creek mountains in northwest utah sixty six ages from inclusions in four garnet grains range from 37 to 72 ma and decrease with radial distance from garnet cores the age range of 30 matrix monazite grains overlaps and extends to younger ages than inclusions 25 58 ma the monazite grains are not intersected by cracks in the garnets through which dissolution reprecipitation or pb loss might occur and are generally too small 20 lm to allow for more than one age determination on any one grain processes that might explain inclusion ages that decrease with radial distance from garnet cores include 1 pb diffusion in monazite 2 dissolution and reprecipitation of monazite and 3 co crystallization of monazite and garnet after consideration of these possibilities it is concluded that the co crystallization of monazite and garnet is the most plausible with monazite neoblasts deriving rees from the breakdown of muscovite garnet ages derived by regression of the inclusion ages and assuming a constant rate of volume increase during garnet growth yield model ages with a maximum difference between core and rim of 22 m y

mid late triassic metamorphic event for changhai meta sedimentary rocks from the se jiao liao ji belt north china craton evidence from monazite u th pb and muscovite ar ar dating abstract the precise constraints on the timing of metamorphism of the changhai metamorphic complex is of great importance considering the prolonged controversial issue of the north margin and the extension of the sulu dabie hp uhp belt while the monazite u th pb and muscovite 40 ar 39 ar techniques are widely accepted as two of the most powerful dating tools for revealing the thermal histories of medium low grade metamorphic rocks and precisely constraining the timing of metamorphism the changhai metamorphic complex at the se jiao liao ji belt north china craton consists of a variety of pelitic schist and grt ky bearing paragneiss and minor quartzite and marble analyses of mineral inclusions and back scattered electric bse images of monazites combined with la icp ms u th pb ages for monazites and 40 ar 39 ar ages for muscovites provide evidence of the origin and metamorphic age of the changhai metamorphic complex monazites separates from various grt mus schists and grt ky st mus paragneisses exhibit homogeneous bse images from cores to rims and contain inclusion assemblages of grt mus qtz ctd ky in schist and grt ky st mus pl kfs qtz inclusions in paragneiss these inclusion assemblages are very similar to matrix minerals of host rocks indicating they are metamorphic rather than inherited or detrital in origin la icp ms u th pb dating reveals that monazites of schist and paragneiss have consistent 206 pb 238 u ages ranging from 228 1 3 8 to 218 2 3 7 ma in contrast muscovites from various schists show slightly older 40 ar 39 ar plateau ages of 236 1 1 5 to 230 2 1 2 ma these geochronological and petrological data conclude that the pelitic sediments have experienced a metamorphic event at the mid late triassic 236 1 218 2 ma rather than the paleoproterozoic 1950 1850 ma commonly regarded as the precambrian basement for the jiao liao ji belt hence the changhai metamorphic complex should be considered as a discrete lithotectonic group this newly recognized mid late triassic metamorphic event 236 1 218 2 ma for the changhai metamorphic complex is coeval with the hp uhp metamorphic event 235 220 ma for sulu dabie rocks this leads us to speculate that the metamorphism of the changhai complex belt along the se margin of the north china craton was genetically related to the mid late triassic collision of the north china and south china cratons by the same token the sulu dabie hp uhp belt may have extended through yantai and the southern yellow sea and to the southern side of the changhai metamorphic complex

contour mapping of arctic basin ice draft and roughness parameters a data base of ice draft and roughness parameters has been constructed for selected portions of the arctic ocean based upon analysis of under ice draft distribution data acquired by inverted echo sounder systems on submarines from the voyages of 12 submarines which traversed the alaskan canadian and central arctic regions of the arctic ocean during the summer and winter seasons a series of mean ice draft and deep draft keel statistics was calculated for 50 km segments along each submarine track contour maps of the mean ice draft its standard deviation the mean keel draft and the spatial frequency of ice keels were constructed they show that the greatest ice drafts the roughest ice and the greatest number of deep draft keels are found off the north coasts of the canadian archipelago and greenland due to ice convergence on these land barriers

temporal moment analysis for stochastic advective vertical solute transport in heterogeneous unsaturated soils summary temporal moment analysis of solute transport in unsaturated soils subjected to rainfall events is typically achieved by the numerical solution of the flow field from the richards equation followed by a numerical solution of the advection dispersion equation before computing moments these numerical solutions are computationally very intensive and may not provide the insights that are possible from simpler analytical representations in this study temporal moments of solute transport for unsteady unsaturated flows under rainfall conditions at the soil surface are presented for the first time a local scale model for water movement is derived from a sharp front approximation and is combined with a model for transport of solute particles along the main characteristics of the flow field expressions for travel times from the local scale model are first presented for pre and post ponding conditions these local solutions are upscaled to field scale solute transport by adopting a log normally distributed spatial hydraulic conductivity field semi analytical expressions are developed for temporal moments of travel times these expressions are compared to 1 d monte carlo simulation results and to 3 d numerical results for model corroboration the model is used to investigate the behavior of macroscopic eulerian effective velocities and dispersion at the field scale expressions for asymptotic effective properties show that effective velocity achieves a constant value while effective dispersion increases linearly with depth the roles of pre ponding and post ponding conditions in determining field scale dispersion are described

constraints on the u pb systematics of metamorphic rutile from in situ la icp ms analysis abstract in situ laser ablation icp ms u pb dating of metamorphic rutile from granulite facies metapelitic rocks of the archaean pikwitonei granulite domain manitoba canada provides constraints on pb diffusion and characterizes the closure behavior of rutile the analysis of transects of 35 m spots across 15 rutile grains having a size of 120 to 280 m yielded concordant ages with core ages of ca 2450 ma and core to rim younging towards 2280 ma age profiles indicate that volume diffusion of pb occurs in rutile implying that the ages represent cooling ages to investigate the closure behavior of pb in rutile closure temperature profiles t c x were constructed based on different models combined with experimentally determined diffusion parameters the classical t c x model of dodson 1986 mat sci forum 7 145 154 indicates a rapid decrease of t c in the rims of grains providing unrealistic estimates for the cooling rate when combined with u pb ages a new t c x model was constructed based on the analyzed age profiles that are described by an error function this model shows a more steady decrease in t c throughout the grain from ca 640 c in the core depending on grain size to a rim intercept t c rim of 490 c 7 2 which is interpreted to be the extrapolated theoretical absolute temperature of insignificant pb diffusion in rutile the new model provides a better description of the relation between age and t c for the analyzed grains however both t c x models demonstrate that even in small grains the variations of t c can be significant making it impossible to derive one representative t c for pb in rutile the error function based t c x model allows the determination of cooling rates which show a decrease over time from ca 2 2 to 0 4 c ma agreeing well with previous estimates for the pikwitonei granulite domain this consistency supports the validity of our model and indicates that cooling rates can be estimated from single grains by la icp ms u pb dating of rutile providing constraints on the cooling history of a metamorphic terrane the slow cooling rates imply that exhumation was slow

country rock monazite response to intrusion of the searchlight pluton southern nevada we investigated how monazite grains in country rocks responded to the intrusion of the miocene searchlight pluton in southern nevada country rock samples were collected from the roof zone and along transects on the flanks wallrock of the 16 to 17 ma pluton deep wallrock ireteba granite monazite grains have patchy secondary growth zones of searchlight age overprinting primary growth zones of ireteba age 66 ma shallow wallrock proterozoic gneiss zircon grains define a discordia with an upper intercept age of 1 74 0 02 ga corresponding to crystallization of the protolith proterozoic gneiss monazite grains define a discordia with an upper intercept age of 1 64 0 02 ga and a poorly defined lower intercept age of 75 61 ma that may correspond to the ireteba intrusion emp analyses show that patchy secondary zones in proterozoic gneiss monazite grains were contemporaneous with intrusion of the ireteba granite not the searchlight pluton oxygen isotopes in ireteba monazite hydrogen and oxygen isotopes in whole rocks from the ireteba transect and oxygen isotopes in whole rocks from the proterozoic gneiss transect show no systematic pattern related to the contact no geochemical data support the hypothesis that hydrothermal fluids associated with intrusion of the searchlight pluton caused monazite in the proterozoic gneiss or ireteba granite wallrock to partially recrystallize ireteba samples with the most intensely altered monazite were at the greatest paleodepths at the time of searchlight intrusion and are the most deformed suggesting that strain caused ireteba monazite grains to partially recrystallize in proterozoic gneiss country rock monazite grains are present on the flanks but absent from the roof zone suggesting that high fluid fluxes in the roof may have destroyed monazite strong focusing of hydrothermal fluid and heat into the roof zone prevented the development of a well defined contact metamorphic aureole in ireteba granite and proterozoic gneiss wallrocks

internal wave generation by ice floes moving in stratified water results from a laboratory study a series of tests has been conducted to investigate the increased ice water drag exhibited by ice floes in two layer salinity stratified water scaled model tests are used to quantify the additional drag due to internal wave creation at the fresh water salt water interface this additional drag is shown to have a peak value five times the drag in similar unstratified conditions and to have a strong dependence on a few well defined nondimensional parameters describing the ice and water characteristics

monazite in situ 207pb 206pb geochronology using a small geometry high resolution ion probe application to archaean and proterozoic rocks this paper reports the application of secondary ion mass spectrometry sims using a small geometry cameca ims4f ion probe to provide reliable in situ 207pb 206pb ages on monazite populations of archaean and proterozoic age the reliability of the sims technique has been assessed on two samples previously dated by the conventional id tims method at 2661 1 ma for monazites extracted from a pelitic schist from the jimperding metamorphic belt yilgarn craton western australia and 1083 3 ma for monazites from a high grade paragneiss from the northampton metamorphic complex pinjarra orogen western australia sims results provide 207pb 206pb weighted mean ages of 2659 3 ma n 28 and 1086 6 ma n 21 in close agreement with id tims reference values for the main monazite growth event monazites from the northampton complex document a complex history the spatial resolution of about 30 m and the precision achieved successfully identify within grain heterogeneities and indicate that monazite growth and recrystallisation occurred during several events this includes detection of one inherited grain dated at ca 1360 ma which is identical to the age of the youngest group of detrital zircons in the paragneiss younger ages at ca 1120 ma are tentatively interpreted as dating a growth event during the prograde stages of metamorphism these results demonstrate that the closure temperature for lead diffusion in monazite can be as high as 800 c at last ages down to ca 990 ma are coeval with late pegmatitic activity and may reflect either lead losses or partial recrystallisation during the waning stages of metamorphism a third unknown sample was analysed to test the capability of the in situ method to date younger monazite populations the sample a pelitic metatexite from northwestern hoggar algeria contains rounded metamorphic monazites that provide a 207pb 206pb weighted mean age of 603 11 ma n 20 this age is interpreted as recording emplacement of a gabbronoritic body during amphibolite facies regional metamorphism and is representative of the late pulse of the pan african tectonometamorphic evolution in the western part of the tuareg shield in situ sims analyses using a widely available small geometry ion probe can thus be successfully used to accurately determine ages for complex precambrian monazite populations

monazite th pb age depth profiling the significant capabilities of the ion microprobe for thermochronometric investigations of geologic materials remain largely unexploited whereas sup 208 pb sup 232 th spot analysis allows approximately 10 mm scale imaging of pb loss profiles or overgrowths in sectioned monazite grains the spatial resolution offered by depth profiling into the surface region of natural crystals is more than two orders of magnitude higher the authors document here the ability of the high resolution ion microprobe to detect sup 208 pb sup 232 th age differences of 1 m y with better than 0 05 micro m depth resolution in the outer micron of tertiary monazites from the hanging wall of the himalayan main central thrust age gradients on this scale are inaccessible to ion microprobe spot analysis or conventional thermal ionization mass spectrometry interpretation of the near surface sup 208 pb distributions with available monazite pb diffusion data illustrates the potential of the approach for recovering continuous high temperature thermal history information not previously available

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

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

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

timing of magmatic crystallization and sn w mo greisen vein formation within the mount douglas granite new brunswick canada u pb geochronology was applied to a combination of magmatic and hydrothermal minerals to help constrain the timing of emplacement of three units in the mount douglas granite mdg and reveal their

a semidiscrete finite volume formulation for multiprocess watershed simulation 1 hydrological processes within the terrestrial water cycle operate over a wide range of time and space scales and with governing equations that may be a mixture of ordinary differential equations odes and partial differential equations pdes in this paper we propose a unified strategy for the formulation and solution of fully coupled process equations at the watershed and river basin scale the strategy shows how a system of mixed equations can be locally reduced to ordinary differential equations using the semidiscrete finite volume method fvm domain decomposition partitions the watershed surface onto an unstructured grid and vertical projection of each element forms a finite volume on which all physical process equations are formed the projected volume or prism is partitioned into surface and subsurface layers leading to a fully coupled local ode system referred to as the model kernel the global ode system is assembled by combining the local ode system over the domain and is then solved by a state of the art ode solver the unstructured grid based on delaunay triangulation is generated with constraints related to the river network watershed boundary elevation contours vegetation geology etc the underlying geometry and parameter fields are then projected onto the irregular network the kernel based formulation simplifies the process of adding or eliminating states constitutive laws or closure relations the strategy is demonstrated for the shale hills experimental watershed in central pennsylvania and several phenomena are observed 1 the enslaving principle is shown to be a useful approximation for soil moisture water table dynamics for shallow soils in upland watersheds 2 the coupling shows how antecedent moisture i e initial conditions can amplify peak flows 3 the coupled equations predict the onset or threshold for upland ephemeral channel flow and 4 the model shows how microtopographic information controls surface saturation and connectivity of overland flow paths for the shale hills site the open source code developed in this research is referred to as the penn state integrated hydrologic model pihm

very high temperature moderate pressure metamorphism in the new russia gneiss complex northeastern adirondack highlands metamorphic aureole to the marcy anorthosite the new russia gneiss complex in the northeastern adirondack highlands of new york includes meta anorthosite gneiss and anatectic gneiss derived from metagabbro mangerite and charnockite metamor

high temperature metamorphism and the role of magmatic heat sources at the rogaland anorthosite complex in southwestern norway the rogaland complex covers 1000 km in southwestern norway and consists mainly of anorthosite massifs and the layered bjerkreim sokndal lopolith bsl these rocks intrude charnockitic migmatites containing intercalated marbles and garnetiferous migmatites high temperature mineral isograds pigeonite osumilite and orthopyroxene in the metamorphic basement are subparallel to and increase in grade towards the intrusive complex p t estimates from the country rocks show a roughly linear increase in temperature towards the bsl consistent with the distribution of isograds the peak p t conditions at 20 and 2 5 km from the contact at 5 kbar range from 700 to 41000 c field relations and age determinations link the high t metamorphism and the magmatism the two dimensional thermal modelling indicates that heat from a single magmatic cooling unit is not sufficient to produce the array of isograds and the peak metamorphic temperatures two magmatic episodes separated by 3myr however can account for the high temperature metamorphism in this model the emplacement and crystallization of the anorthosite produces a regional thermal gradient from 750 to 600 c after a brief hiatus a second smaller body bsl provides an additional thermal input that results in an array of high temperature isograds and country rock temperatures 41000 c

u pb geochronology of deformation and metamorphism across a central transect of the early proterozoic torngat orogen north river map area labrador1 the early proterozoic torngat orogen resulted from the oblique collision of the archean nain and southeastern rae provinces and evolved in four stages 0 deposition of platformal supracrustal assemblages followed by subduction related arc magmatism in the margin of the rae province i crustal thickening and nappe tectonics ii sinistral transpression and formation of the abloviak shear zone iii uplift on steeply dipping east verging mylonites along the eastern orogenic front u pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca 1880 ma was followed by 40 ma of deformation and high grade metamorphism from ca 1860 to 1820 subsequent uplift and final cooling occurred ca 1795 1770 ma several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized 1 1858 1853 ma zircon and monazite dates are interpreted as the minimum age of stage i and peak metamorphic conditions 2

complexity in the behavior and recrystallization of monazite during high t metamorphism and fluid infiltration abstract a detailed study of monazite grains in silica undersaturated and quartz bearing mg al metapelite from the oygarden group of islands east antarctica reveals a complex history of growth and recrystallization during two separate events in the neoproterozoic and earliest cambrian monazite grains from garnet poor and garnet rich metapelite preserve core domains that have ages corresponding to growth and or recrystallization at granulite facies p 9 1 0 gpa t 850 900 c conditions during the rayner structural episode between 930 and 890 ma high th rims 22 wt tho 2 that are in textural equilibrium with sapphirine orthopyroxene symplectites formed after garnet during late rayner decompression occur on monazite grains in garnet rich assemblages and give electron microprobe ages 883 18 ma within error of core domains 903 14 ma these high th rim domains are interpreted to have formed through recrystallization of liberated inclusions via a process dominated by coupled dissolution reprecipitation reactions facilitated by transient fluid films on the large surface areas in the symplectite and not by new growth in garnet poor metapelite monazite grains that have grain boundaries in textural equilibrium with the granulite facies assemblage also show alteration to higher th compositions on rims and along vein like fractures this compositional shift is accompanied by partial to complete resetting of ages to 500 ma along with minor modification of core domain ages textures and patterns of chemical age resetting are interpreted to also be the result of a coupled dissolution reprecipitation reaction process but in contrast to garnet bearing assemblages this alteration occurred during a fluid influx at lower temperatures during regional pan african tectonism this study highlights the susceptibility of monazite to resetting with fluid present conditions dramatically increasing the potential for recrystallization

downward lee wave radiation from tropical instability waves in the central equatorial pacific ocean a possible energy pathway to turbulent mixing turbulent mixing in the equatorial pacific ocean is an important process that controls diapycnal heat transport and hence affects the air sea interactions and global climate it is recently shown that in the eastern equatorial pacific strong mixing is induced in the thermocline by enhanced vertical shear associated with tropical instability waves tiws which propagate westward along the equator at a speed of 0 5 m s 1 with a wavelength of 1000 km in this study using a high resolution ocean general circulation model we show that the tiws can play an important role in inducing turbulent mixing in the thermocline also in the central equatorial pacific although the thermocline is too deep to be directly affected by the vertical shear of the tiws the front of the tiw is clearly manifested as a narrow strip of strong convergence of horizontal surface flow from which area downward and westward propagating internal waves are intermittently emanated these internal waves can be interpreted as lee waves generated by the surface flow convergence zone which acts like an inverted obstacle moving along the stratified ocean surface by inducing downward flow the associated downward energy flux below the surface mixed layer increases as the tiw structure becomes deeper toward the central equatorial pacific so that the energy pathway to turbulent mixing in the thermocline can be created the downward energy flux integrated over the entire equatorial pacific and averaged during january 2011 amounts to 8 1 gw occupying a significant fraction of the energy input to the tiws

a finite element model for simulating surface run off and unsaturated seepage flow in the shallow subsurface this work introduces water air two phase flow into integrated surface subsurface flow by simulating rainfall infiltration and run off production on a soil slope with the finite element method the numerical model is formulated by partial differential equations for hydrostatic shallow flow and water air two phase flow in the shallow subsurface finite element computing formats and solution strategies are presented to obtain a numerical solution for the coupled model an unsaturated seepage flow process is first simulated by water air two phase flow under the atmospheric pressure boundary condition to obtain the rainfall infiltration rate then the rainfall infiltration rate is used as an input parameter to solve the surface run off equations and determine the value of the surface run off depth in the next iteration the pressure boundary condition of unsaturated seepage flow is adjusted by the surface run off depth the coupling process is achieved by updating the rainfall infiltration rate and surface run off depth sequentially until the convergence criteria are reached in a time step a well conducted surface run off experiment and traditional surface subsurface model are used to validate the new model comparisons with the traditional surface subsurface model show that the initiation time of surface run off calculated by the proposed model is earlier and that the water depth is larger thus providing values that are closer to the experimental results

surface subsurface flow modeling with path based runoff routing boundary condition based coupling and assimilation of multisource observation data received 21 october 2008 revised 2 september 2009 accepted 16 september 2009 published 13 february 2010 1 a distributed physically based model incorporating novel approaches for the representation of surface subsurface processes and interactions is presented a path based description of surface flow across the drainage basin is used with several options for identifying flow directions for separating channel cells from hillslope cells and for representing stream channel hydraulic geometry lakes and other topographic depressions are identified and specially treated as part of the preprocessing procedures applied to the digital elevation data for the catchment threshold based boundary condition switching is used to partition potential atmospheric fluxes into actual fluxes across the land surface and changes in surface storage thus resolving the exchange fluxes or coupling between the surface and subsurface modules nested time stepping allows smaller steps to be taken for typically faster and explicitly solved surface runoff routing while a mesh coarsening option allows larger grid elements to be used for typically slower and more compute intensive subsurface flow sequential data assimilation schemes allow the model predictions to be updated with spatiotemporal observation data of surface and subsurface variables these approaches are discussed in detail and the physical and numerical behavior of the model is illustrated over catchment scales ranging from 0 0027 to 356 km 2 addressing different hydrological processes and highlighting the importance of describing coupled surfacesubsurface flow

paleoproterozoic ultrahigh temperature granulite facies metamorphism in the sulu orogen eastern china evidence from zircon and monazite in the pelitic granulite abstract because of their essential information for constraining the timescales of high temperature processes zircon and monazite are the two most important minerals for understanding crustal processes zircon and monazite are common accessory minerals in pelitic granulites sulu orogen eastern china the pelitic granulites have a peak mineral assemblage of garnet sillimanite antiperthite plagioclase quartz rutile biotite zircons from the granulite have low th u ratios

monazite and xenotime solubility in granitic melts and the origin of the lanthanide tetrad effect the solubility of synthetic pure rare earth phosphates with monazite or xenotime structure lapo4 to lupo4 in hydrous haplogranitic melts was measured at 2 kbar and 800 1 100 c experiments were run for up to 2 months to attain equilibrium monazite and xenotime solubility decreases with increasing phosphorus concentration in the melt published equations for monazite solubility in felsic melts which do not explicitly include phosphorus concentration in the melt should therefore be treated with caution the effect of phosphorus can be quantitatively modeled if one assumes that monazite partially dissolves as ionic and molecular species in the melt ree3 and reepo4 equilibrium constants for the dissolution reactions as well as quantitative data on speciation were derived from the solubility data monazite and xenotime solubility strongly increases with the peralkalinity of the melt this effect is mostly due to an increase in the solubility of the ionic species which are probably stabilized by non bridging oxygen atoms in the melt in peraluminous melts the solubility of monazite and xenotime is nearly constant fluorine has no major effect on monazite and xenotime solubility in fact the solubility appears to slightly decrease with increasing fluorine content the solubility of rare earth phosphates is not a simple continuous function of atomic number or ionic radius rather the solubility shows a tetrad like pattern with several local maxima of solubility at individual rare earth elements the solubilities of neighboring rare earth elements sometimes differ by more than a factor of two these effects are far outside any analytical error the tetrad pattern is particularly clearly seen in some of the peralkaline melts and in the fluorine rich metaluminous melts some features however such as a solubility maximum at ytterbium are seen in virtually all melts the lanthanide tetrad effect in some highly evolved granites may therefore be a result of monazite and xenotime fractionation the solubility of monazite and xenotime in silicate melt probably shows the tetrad effect because of the very unusual coordination of the rare earth elements in these phosphate minerals which is different from the coordination of the melt and therefore causes different crystal field interactions with the partially filled f orbitals of the rare earths the tetrad effect in granites cannot be used as an indicator of fluid rock or fluid melt interaction since it can be experimentally reproduced in the absence of any fluids

geochronology of shear zones a review abstract shear zones play a major role in the deformation of the crust at a variety of scales as expressions of strain localization during orogeny and rifting and also as reactivated structures they influence the geometry and evolution of orogenic belts and rifts crustal rheology magma ascent and emplacement and fluid flow consequently assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere the interpretation of thermochronologic data from shear zones is however not straightforward in the first place closure temperatures depend on a number of factors grain size cooling rate mineral composition and pressure among others on the other hand deformation related processes such as dynamic recrystallization neocrystallization and fluid circulation seem to be crucial for isotopic systems and thus the obtained ages cannot be solely interpreted as a function of temperature in sheared rocks for this reason geochronologic data from shear zones might not only record cooling below closure temperature conditions but may also be affected by neo or recrystallization fluid assisted deformation and inheritance of the protolith age s in order to robustly reconstruct p t e t paths of long term crustal scale shear zones structural microstructural and petrologic data from mylonites need to be integrated with ages from different thermochronometric systems in addition geochronologic data from associated intrusions and adjacent blocks can provide further irreplaceable constraints on the timing of deformation and its regional implications one of the most challenging aspects that future lines of investigation should analyze is the quantitative evaluation of so far poorly explored aspects of isotopic diffusion particularly the coupling with deformation processes based on natural theoretical and experimental data future works should also investigate the role of strain partitioning and localization processes in order to constrain the timing of deformation in different parts of a shear zone or in different branches of anastomosing shear zone networks

versatile monazite resolving geological records and solving challenges in materials science generalizations about monazite implications for geochronologic studies with the advent of techniques that preclude mineral separation ages from specific compositional domains in monazite ce la th po 4 have provided a wealth of information regarding the timing of the geologic evolution of numerous regions however confusion can arise when single grains show large differences in age that fail to correlate to chemistry or location within the monazite generalizations that lead to incorrect age interpretations include that monazite zoning in y th and or the rare earth elements ree always identify 1 distinct tectonic events 2 environment of crystallization and 3 provenance of detrital grains increasing th contents in monazite do not always reflect 1 increasing grade in metamorphic grains 2 changes in silicate melt composition in igneous grains 3 make the mineral more susceptible to alteration nor 4 control the mineral s uptake of ree metamorphic monazites from himalayan garnet bearing rocks with coexisting allanite show no relationship between th content and ree instead chondrite normalized ree patterns of the allanite mirror those of the monazite indicating the variations are related to the reactant that formed the mineral generalizations about pb behavior in monazite remain problematic incorporation of pb into monazite has thus far been precluded by experimental studies yet common pb has been measured in many studies of natural monazite a clear understanding about controls of monazite composition and the role of the chemical and or pressure temperature p t environment of the rocks in which it forms is required to correctly interpret the meaning of the mineral s age s

generation of internal waves by sea ice observations in the greenland sea marginal ice zone suggest that when strong stratification occurs near the surface momentum flux into the internal wave field of the upper ocean can be a major component of the force balance that governs ice drift since energy is radiated away by the internal waves turbulent mixing and heat flux are also affected we investigate the downward flux of momentum and energy by internal waves in an ice covered ocean with an idealized model comprising a mixed layer overlying a deep uniformly stratified layer a buoyancy jump separates the mixed layer from the pycnocline drag from a single wave number component of the under ice roughness spectrum is derived as the product of a drag coefficient based on ice speed under ice roughness wave number and amplitude and uniform stratification to the ice ocean interface times an attenuation factor that depends additionally on mixed layer depth and the buoyancy jump at the base of the mixed layer the model is extended to a plausible spectrum of under ice roughness by integration over wave number space internal wave effects are parameterized in terms of the drag coefficient from the integrated spectrum and incorporated into an upper ocean turbulence model model calculations show that plausible values for the peak wave number of the idealized spectrum and roughness variance can account for 1 decreased ice velocity relative to the wind 2 decreased heat exchange coefficient between the ice and ocean and 3 lack of mixed layer deepening all of which were observed during the last week of the 1984 marginal ice zone experiment

infiltration and deep flow over sloping surfaces comparison of numerical and experimental results summary infiltration and deep flow on sloping surfaces were studied by combining controlled laboratory experiments with mathematical models experimental variables included soil types rainfall intensities and surface slopes preliminary analyses of the data indicated that increased slope has a positive influence on surface flow and that this influence increases relatively with decreasing rainfall rate however current theories could not adequately explain the observed behavior of deep and surface flows for varying slopes three mathematical models of varying complexity were employed to supplement the experimental results these models were i the 2 d hydrus numerical model ii numerical solution of 1 d saturated unsaturated flow equation on sloping surfaces and iii a simplified 1 d sharp front model for sloping surfaces for the latter two models a surface flow component based on the kinematic wave approximation for shallow flows was externally coupled to the subsurface flows to route water over the soil surface for each soil one experiment at the lowest slope and rainfall rate was utilized for estimation of model parameters that could not be measured independently while all the other results were used for model corroboration the hydrus model indicated that a 1 d analysis would be adequate as the water front moves essentially parallel to the slope to account for the influence of slope and soil type on experimental results an effective saturated conductivity was proposed model results were found to be in reasonable agreement with observations of surface flow deep flow and water contents in the soil profile with the use of the proposed effective saturated conductivity limitations on the applicability of the sharp front model in this context were discussed

diffusion obstacles and opportunities in petrochronology many of the approaches in petrochronology are rooted in the assumption of equilibrium diffusion is an expression of disequilibrium the movement of mass in response to chemical potential gradients and isotopes in response to isotopic gradients it is extremely important that we be aware of how the effects of diffusion can place obstacles across our path towards petrochronologic enlightenment conversely the effects of diffusion also provide opportunities for understanding rates processes and conditions experienced by rocks the enormity of the field does not permit us to provide a comprehensive review of either the mathematics of diffusion or quantitative data that have been obtained relevant to the interpretation of diffusive processes in rocks and minerals many resources cover these topics including rimg volume 72 diffusion in minerals and melts zhang and cherniak 2010 and several textbooks crank 1975 glicksman 2000 particularly relevant to the discussion of petrochronology are summaries of the theory and controls on diffusion brady and cherniak 2010 zhang 2010 as well as diffusion rates in feldspar cherniak 2010a accessory minerals cherniak 2010b garnet ganguly 2010 mica pyroxene and amphibole cherniak and dimanov 2010 and melts zhang and ni 2010 zhang et al 2010 rather than duplicate that material our goal is to explore the obstacles and opportunities presented by the effects of diffusion as they inform the rates of petrologic processes to achieve this goal we emphasize key principles and illustrative examples quantitative interpretation of the effects of diffusion assumes predictability of numerous factors that may affect chemical or isotopic transport including temperature initial and boundary conditions water and oxygen fugacities activities of other components multiple mechanisms of diffusion and crystal chemistry coupling of the substitution of elements into different crystallographic sites additionally the extraction of meaningful ages durations of events and temperatures requires

rates of fe mg mn and ca diffusion in garnet extraction of the thermal and chemical histories preserved by modified compositional zoning in garnet is compromised by large uncertainties in experimentally determined diffusion coefficients for principal divalent cations some of this uncertainty derives from long down temperature extrapolations but much of it arises from an inability to account accurately for large variations in diffusivity as a function of garnet composition numerical simulation of stranded diffusion profiles in partially resorbed natural garnets constrains diffusivities at low temperature and reveals a systematic dependence of diffusion rates on host garnet composition a comprehensive model incorporating a simple compositional dependence allows accurate prediction of diffusion rates for fe mg mn and ca for nearly all garnet compositions across the full range of geologically relevant temperatures pressures and oxygen fugacities

three dimensional model of heat flow in the aureole of the marcy anorthosite adirondack highlands new york implications for depth of emplacement the new russia gneiss complex occurs within a broad very high temperature 800 950 c metamorphic aureole against the eastern margin of the marcy anorthosite northeastern adirondack highlands of new york three dimensional models of heat flow from the anorthosite indicate that an aureole like that preserved in the new russia gneisses would form if the country rock were at high temperature 700 c and at depth prior to intrusion these findings are consistent with geobarometric evidence indicating that partial melting in the aureole occurred at 700 1000 mpa and support the hypothesis that the anorthosite intruded at a depth of 25 to 35 km

stability analysis of unsaturated soil slopes considering water air flow caused by rainfall infiltration abstract even though soil is a mixture of solids with voids that are filled by air and water most previous studies on rainfall infiltration and its influence on slope stability were based on a single phase water flow model by assuming that the pore air pressure was atmospheric the purpose of this study is to examine the effect of interactions between air and water flow due to heavy rainfall on the mechanical stability of an unsaturated soil slope water air two phase flow analyses were conducted to investigate the contribution of pore air pressure on infiltration by rainfall in order to study the infiltration behavior with respect to soil type flow analyses were performed with two types of soil under similar settings results obtained from the two phase infiltration analysis were then used as input to the stability analysis by the strength reduction method infiltration and stability analyses based on a single phase water flow model were also carried out which helped clarify the effects of air flow induced by rainfall infiltration on an unsaturated soil slope the results showed an increase in pore air pressure during infiltration because rainwater displaced the air in the unsaturated zone hence remarkable delaying effects on water flow were induced such water air interactions in the pore space of soil significantly affected the stability and behavior of the soil slope