the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part ii xenotime xenotime from a geochemically heterogeneous series of mildly to strongly peraluminous granites of the erzgebirge germany displays extended compositional variability with respect to abundances of hree y u and th with few exceptions the maximum and minimum concentrations for the lanthanides and actinides exceed those noted for this mineral from other geologic environments xenotime chemistry is dominated by the theoretical end members hree po 4 and ypo 4 90 mol in total typical xenotime grains from the erzgebirge granites and from other granites worldwide contain 70 80 mol ypo 4 and 16 25 mol hree po 4 this study documents the occurrence of xenotime abnormally rich in hree in place of y with up to 45 mol hree po 4 substitutions of thorite coffinite th u pb sio 4 brabantite ca th u po 4 2 and monazite la sm po 4 are of minor importance reaching maximum levels of 5 6 mol each with a total contribution typically th u super 4 ca super 2 the total lanthanide and actinide contents in xenotime and host granite are not strongly correlated however formation of xenotime unusually rich in hree occurs only in the a type limica granites that are strongly enriched in these elements the shapes of hree patterns of xenotime and host rock are similar which combined with mass balance calculations indicate the importance of this mineral in affecting the hree as well as y evolution of late stage granitic melts late xenotime may show strong y ho fractionation thus recording the decoupling of y and the hree which can occur in the latest stages of crystallization of evolved granites and which may be associated with deuteric alteration

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

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

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

mineral chemical study of u bearing minerals from the dominion reefs south africa the neo archean dominion reefs 3 06 ga are thin meta conglomerate layers with concentrations of u and th bearing heavy minerals higher than in the overlying witwatersrand reefs ore samples from uranium one africa s rietkuil and dominion exploration areas near klerksdorp south africa were investigated for their mineral paragenesis texture and mineral chemical composition the ore and heavy mineral assemblages consist of uraninite other uraniferous minerals fe sulphides ni co sulfarsenides garnet pyrite pyrrhotite monazite zircon chromite magnetite and minor gold sub rounded uraninite grains occur associated with the primary detrital heavy mineral paragenesis u ti u th minerals pitchblende colloform uraninite and coffinite are of secondary re mobilised origin as evidenced by crystal shape and texture most of the uranium mineralisation is represented by detrital uraninite with up to 70 2 wt uo2 and up to 9 3 wt tho2 re crystallised phases such as secondary pitchblende without th coffinite u ti and u th phases are related to hydrothermal overprint during low grade metamorphism and are of minor abundance

modeling non steady state radioisotope transport in the vadose zone a case study using uranium isotopes at pena blanca mexico current models using u and th series disequilibria to study radioisotope transport in groundwater systems mostly consider a steady state situation these models have limited applicability to the vadose zone uz where the concentration and migratory behavior of radioisotopes in fluid are often transitory we present here as a first attempt of its kind a model simulating the non steady state intermittent fluid transport in vadose layers it provides quantitative constraints on in situ migration of dissolved and colloidal radioisotopes in terms of retardation factor and rock water interaction or water transit time for uranium the simulation predicts that intermittent flushing in the uz leads to a linear relationship between reciprocal u concentration and 234u 238u ratio in percolating waters with the intercept and slope bearing information on the rates of dissolution and recoil of u isotopes respectively the general validity of the model appears to be borne out by the measurement of uranium isotopes in uz waters collected at various times over a period during 1995 2006 from a site in the pena blanca mining district mexico where the nopal i uranium deposit is located enhanced 234u 238u ratios in vadose zone waters resulting from lengthened non flushing time as prescribed by the model provide an interpretative basis for using 234u 238u in cave calcites to reconstruct the regional changes in hydrology and climate we also provide a theoretical account of the model s potential applications using radium isotopes

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

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

alteration and breakdown of xenotime y and monazite ce in granitic rocks of the western carpathians slovakia abstract in the granitic rocks of the western carpathians xenotime y occurs both as a late stage magmatic mineral and as a secondary post magmatic phase magmatic xenotime occurs with monazite and displays minor compositional zonation involving si th and u the source of elements for the formation of secondary xenotime y in the granitic rocks results from leaching of p and y ree mainly from zircon and apatite both xenotime y and monazite ce are unstable during fluid activated overprinting low temperature alteration of monazite in s type granites leads to the formation of apatite enriched in the britholite component but low to medium grades of metamorphism result in the formation of apatite and lree enriched epidote partly allanite as a corona enclosing the monazite ce core xenotime y shows a similar alteration pattern but with different ree distributions within the products at greenschist amphibolite facies rims of secondary y rich apatite and y rich epidote form around xenotime y in low ca granites however apatite is missing from this alteration assemblage as xenotime y breaks down directly to y enriched epidote the relative mobilities of the heavy and light ree are different during breakdown of monazite and xenotime the fluid responsible for the breakdown of monazite and xenotime contains elements released from alteration of anorthite ca and biotite si al and f

electron microprobe dating of monazites from western carpathian basement granitoids plutonic evidence for an important permian rifting event subsequent to variscan crustal anatexis accessory monazites from 35 granitoid samples from the western carpathian basement have been analysed with the electron microprobe in an attempt to broadly constrain their formation ages on the basis of their th u and pb contents the sample set includes representative granite types from the tatric veporic and gemeric tectonic units in most cases lower carboniferous variscan ages have been obtained however a much younger mid permian age has been recorded for the specialised s type granites of the gemeric unit and several small a and s type granite bodies in the veporic unit and the southern tatric unit this distinct permian plutonic activity in the southern part of the western carpathians is an important although previously little considered geological feature it appears to be not related to the variscan orogeny and is interpreted here to reflect the onset of the alpine orogenic cycle with magma generation in response to continental rifting the voluminous carboniferous granitoid bodies in the tatric and veporic units comprise s and i type variants which document crustal anatexis accompanying the collapse of a compressional variscan orogen sector the variscan magmas were most likely produced through the remelting of a subducted precambrian volcanic arc type crust which included both igneous and sedimentary reworked volcanic arc material although the 2 errors of the applied dating method are quite large and typically 10 20 ma for single samples it would appear from the data that the variscan s type granitoids 333 367 ma are systematically older than the variscan i type granitoids 308 345 ma this feature is interpreted in terms of a prograde temperature evolution in the deeper parts of the post collisional variscan crust in accordance with recently published zircon ages this study shows that the western carpathian basement must be viewed as a distinct eastern tectonomagmatic province in the variscan collision zone where the post collisional crustal melting processes occurred 20 ma earlier than in the central sector south bohemian batholith hohe tauern batholith

monazite xenotime miscibility gap thermometry i an empirical calibration rare earth element ree and yttrium concentrations of coexisting monazite and xenotime were determined from a suite of seven metapelites from the variscan fold belt in ne bavaria germany the metapelites include a continuous prograde mainly low p 3 5 kbar metamorphic profile from greenschist c 400 c to lower granulite facies conditions c 700 c the lree la sm are incorporated preferentially in monoclinic monazite reo9 polyhedron whereas the hree plus y are concentrated in tetragonal xenotime reo8 polyhedron the major element concentrations of both phases in all rocks are very similar and do not depend on metamorphic grade monazite consists mainly of la ce and nd la0 20 0 23 ce0 41 0 45 nd0 15 0 18 po4 all other elements are below 6 mol likewise xenotime consists mainly of ypo4 with some dy and gd solid solutions y0 76 0 80 dy0 05 0 07 gd0 04 0 06 in contrast the minor hree concentrations in monazite increase strongly with increasing metamorphic grade y dy and gd increase by a factor of 3 5 from greenschist to granulite facies rocks monazite crystals often show zonation with cores low in hree and rims high in hree that is interpreted as growth zonation attained during prograde metamorphism similarly sm and nd in xenotimes increase by a factor of 3 4 with increasing metamorphic grade prograde zonation in single crystals of xenotime was not observed the xhree y in monazite and xlree in xenotime of the seven rocks define two limbs along the strongly asymmetric miscibility gap from c 400 c to 700 c the empirical calibration of the monazite miscibility gap limb coexisting with xenotime is appropriate for geothermometry due to its contents of u and th monazite has often been used for u pb age determination the combination of our empirical thermometer on prograde zoned monazite along with possible age determination of zoned single crystals may provide information about prograde branches of temperature time paths

prograde metamorphism strain evolution and collapse of footwalls of thick thrust sheets a case study from the mesozoic sevier hinterland u s a abstract analysis of prograde metamorphic fabrics in the exhumed footwall of the mesozoic windermere thrust northeast nevada reveals fabrics and style of ductile flow developed during tectonic burial metamorphism of a sedimentary footwall of a thick thrust sheet in response to structural burial footwall strata underwent barrovian metamorphism synchronous with development of bedding parallel or near parallel s and s l tectonites footwall rocks range from unmetamorphosed at high structural levels and progressively increase in metamorphic grade to upper amphibolite facies at deep levels attenuation of footwall stratigraphic units accompanied tectonite development whereby the amount of attenuation varies with metamorphic grade from 0 in lower greenschist facies to 30 50 in upper amphibolite facies rocks microstructures in metacarbonate metapsammite and metapelite and analysis of crystallographic preferred orientations of quartz c axes in quartzite suggest a dominantly coaxial strain path with flattening strain predominating at lower metamorphic grade and plane strain more dominant at higher metamorphic grade the microstructural data indicate that dominantly coaxial deformation during metamorphism accommodated extension of the footwall ductile extension most likely records footwall collapse induced by a loss of strength due to relative upward migration of isotherms during and or following burial extension may act as a mechanism that in part facilitates isostatic accommodation or sinking of the overlying load resulting in a reduction of topography attenuation of footwalls of thick thrust sheets and production of predominantly coaxial layer parallel or near parallel fabrics may be an intrinsic process once sufficient structural overburden is developed and thermal relaxation and prograde metamorphism ensues

dehydration melting and devolatilization during exhumation of high grade metapelites the tatra mountains western carpathians partial melting and retrogression related to variscan tectonic exhumation have been recognized in the high grade metapelites of the tatra mountains western carpathians staurolite and kyanite relics document an early stage of the prograde metamorphism at c 600 c and 9 10 kbar an increase in temperature to 730 c at 11 12 kbar resulted in partial melting and incipient migmatization in the stability field of kyanite further heating at decreasing pressure during the earliest stage of exhumation led to the dehydration melting of muscovite and biotite at 750 800 c and 6 10 kbar producing garnet bearing granite as leucosomes in migmatite subsequent cooling is documented by garnet resorption by biotite and sillimanite a reversal of the prograde biotite dehydration melting reaction this was followed by nearly isothermal decompression to c 4 5 kbar producing cordierite and some melt due to biotite decomposition later nearly isobaric cooling led to cordierite pinitization and formation of orthoamphibole chlorite and carbonates densities of primary monophase co2 n2 inclusions 0 69 1 06 g cm 3 from the migmatite leucosome are consistent with the near peak and retrograde conditions highly varying n2 contents 5 30 mol are thought to result from the nitrogen uptake in retrograde k bearing minerals or dilution by co2 liberated during interaction of melt derived water with metapelite graphite the relatively high nitrogen content not observed until now in migmatites could have been inherited from the high pressure metamorphism stage it is assumed that the water absent composition of fluid inclusions is not representative of the bulk water content xh2o 0 7 which was masked by mechanical separation of the co2 and h2o dominated immiscible phases and or by post entrapment modifications of the fluid inclusions decompression and the final stage of exhumation were accomplished by top to the south thrusting as well as west east orogen parallel extension they were most probably related to regional uplift and gravitational collapse of thermally weakened variscan crust

metamorphic evolution and fluid composition of garnet clinopyroxene amphibolites from the tatra mountains western carpathians relics suggesting an early high pressure eclogite facies stage have been identified in the garnet and clinopyroxene bearing amphibolites of the tatra mountains in the variscan basement of the western carpathians slovakia in these rocks primary omphacite cpx i has been wholly converted to symplectites of diopside cpx ii and plagioclase apart from minor inclusions in the garnet cores amphibole and plagioclase are secondary minerals formed in the kelyphitic rims between garnet and clinopyroxene several generations of amphibole pargasite hornblende cummingtonite actinolite are evidence of a transformation down to greenschist facies conditions thermobarometric calculations from mineral inclusions in the garnet cores yield 670 700 c and 10 15 kbar recording the initial path from upper amphibolite to eclogite facies conditions the attainment of the eclogite facies stability field is inferred from the composition of a reconstructed omphacite jd36 implying a minimum peak pressure of 15 16 kbar conditions of around 650 c and 8 10 kbar record the post eclogite breakdown and partial re equilibration in the amphibolite facies region the earliest fluid inclusions contain high density nitrogen dominated water absent fluid younger are polyphase brines and two phase h2o n2 ch4 inclusions with signs of heterogeneous entrapment of coexisting gas rich and water rich immiscible phases pure nitrogen 0 5 mol ch4 is considered to have been the major component during the high pressure metamorphism in contrast the later aqueous inclusions are interpreted to represent retrogression related fluids the brines have originated by leaching and re entrapment of saline melt inclusions observed in tonalitic trondhjemitic layers of the amphibolite enclosing the eclogitic relics a similar mechanism is assumed for the origin of the h2o n2 ch4 inclusions these represent relics of the primary eclogite facies related n2 inclusions re equilibrated and re entrapped during retrogression under increasing water activity a possible source of n2 and cl rich fluids was primary amphibole which decomposed during the prograde metamorphism from the amphibolite to the eclogite facies the metamorphic pt path is generally clockwise reflecting a steep increase in pressure and temperature during burial followed by decompression and cooling the retrograded eclogites occur in boudins within an allochthonous unit of an inverted metamorphic sequence their exhumation was facilitated by tectonic transport along a ductile shear zone during the variscan orogeny

incongruent dissolution of ree and sr rich apatite in peraluminous granitic liquids differential apatite monazite and xenotime solubilities during anatexis the relative solubilities of monazite mnz xenotime xno and apatite ap ree and sr rich and ree and sr poor have been studied in peraluminous granitic liquids in month long experiments at 750 c and 200 mpa ph20 in contrast with the high solubility of the apatite 0 7 wtojop205 in strongly peraluminous liquids monazite and xenotime have much lower solubilities 0 05 wt jop205 in mildly to strongly peraluminous compositions p205 in the liquid is 0 03 0 04 wt joat xenotime saturation and 0 02 0 05 wt jo at monazite saturation in keeping with the low p in the glasses re203 contents are below emp detection thresholds 50 08 wt jo for all conditions of experiments saturation of liquid at equilibrium and local saturation around apatite apatite dissolves incongruently crystallizing ree rich monazite on its surface 1 4 m iong grains resulting in similar low ree contents in liquids monazite precipitation occurs along the margins of dissolving apatite crystals even though the bulk liquid is not monazite saturated the abundance of monazite microcrystals increases with the ree content of the apatite and the degree of apatite dissolution the reaction relationship ap liqi mnz liq2 stemming from differences in relative solubilities greater than an order of magnitude between apatite and monazite results in the dissolution of much smaller amounts of ree into peraluminous liquids than expected by simple evaluation of apatite ree contents the amount of ree contributed from apatite directly to peraluminous granitic liquid is related to the amount of apatite dissolved by simple mass balance only if the total ree content of the apatite is sufficiently low that monazite saturation in liquid 50 100 ppm re203 at 750 c is avoided during dissolution of sr rich apatite the sr partitions into the liquid and at 750 c and 200 mpa ph20 the diffusion coefficient of sr in liquid is 2 x 10 10 cm2js r2 0 659 the reaction relationships described above may have application to some textural features observed in natural igneous rocks for example clusters of monazite microcrystals might be indicators of dissolved apatite monazite morphology can be used to distinguish the source of its ree and the general petrological process rock anatexis or magma crystallization under which the monazite formed in addition monazite microcrystals could serve as nucleation sites for other minerals which might explain their common inclusion in biotite and amphibole within granitoids

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

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

an empirical garnet yag xenotime thermometer a pronounced negative correlation between the yttrium concentration in garnet y grt and temperature has been observed in xenotime ypo4 bearing metapelites from central new england usa the y grt decreases roughly two orders of magnitude 5500 to less than 100 ppm y over a 150 c interval a regression of ln y grt against estimated reciprocal temperature yields the following relationship

the geochemistry of phosphorus in different granite suites of the western carpathians slovakia the role of apatite and p bearing feldspar the geochemical behaviour of phosphorus in granites coupled with compositional variations in apatite discriminate the different genetic suites of variscan granitic rocks in the west carpathian orogenic belt meso variscan granites mostly of stype affinity show a good correlation between sio2 and p2o5 with decreasing amounts of p in the poorly and moderated fractionated granites and increasing phosphorus in the most evolved and late differentiation products the aluminium saturation index asi correlates negatively with bulk p contents in i type granites and positively with p in s type granites the phosphorus content of alkali feldspar mainly kfs is usually very low typically 0 05 wt p2o5 or not detected in the slightly differentiated granites in the latevariscan i s type granitoids phosphorus is hosted mainly in the early magmatic apatite but is present also in the late k feldspar up to 0 15 wt of p2o5 that formed from the residual melts in the postorogenic s type granites the bulk of the phosphorus occurs in alkali feldspar f0 3 wt p2o5 with a minor proportion present in primary early magmatic apatite clusters of small secondary apatite grains with a distinctive composition are distributed in alkali feldspar grains of the post orogenic s type granites this apatite has formed post magmatically from p released from p rich alkali feldspar during decreasing temperature by reaction with a fluid rich in volatiles including f and b and alkali and alkali earth metals a type granites have the lowest bulk phosphorus contents consequently phosphate minerals are relatively rare in this granite type and the alkali feldspar has negligible p2o5 contents except for sr the minor element contents in apatite partly correlate with the bulk composition of their host rocks and partly reflect some thermodynamic properties of melt the mn contents of apatite increase with the peraluminous character of the melt and with decreasing fo2 and so apatite from the s type granites has significantly higher mn contents than apatite from the i type granites apatite from a type granites is enriched in fe and hree reflecting the higher bulk fe and hree content of this granite type apatite from specialized s type granites is enriched in yand hree in general the cl and s content of apatite is higher in the basic members of the i type affinity granitic rocks d 2004 elsevier b v all rights reserved

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