sector trilling in cordierite and equilibrium overstepping in metamorphism the origin of sector trilling in cordierite is due to the hexagonal orthorhombic al si ordering transformation which under non equilibrium conditions proceeds via a short range ordered modulated structure the growth of these distortion waves associated with progressive ordering produces a strain field which is minimized by a cyclic distribution of symmetrically equivalent modulations sector and complexly trilled cordierites in metamorphic rocks grew as the hexagonal polymorph with a considerable degree of al si disorder the enthalpy and entropy of disorder are evaluated from recent experimental work the implication is that in metamorphic rocks substantial overstepping of stable equilibrium phase boundaries is required to nucleate hexagonal cordierite moreover its composition coexisting with other phases will also be significantly different from that of the stable ordered form

from granulites to eclogites in the sesia zone italian western alps a record of the opening and closure of the piedmont ocean the sesia zone italian western alps offers one of the best preserved examples of pre alpine basement reactivated under eclogite facies conditions during the alpine orogenesis a detailed mineralogical study of eclogitized acid and basic granulites and related amphibolites is presented in these rare weak to undeformed rocks microstructural investigations allow three main metamorphic stages to be distinguished a a medium to low p granulite stage giving rise to the development of orthopyroxene garnet plagioclase brown amphibole ilmenite biotite in basic granulites and garnet k feldspar plagioclase cordierite sillimanite biotite ilmenite in acid granulites b a post granulite re equilibration associated with the development of shear zones producing discrete amphibolitization of the basic granulites and widespread development of biotite sillimanite cordierite spinel in the acid rocks c an eo alpine eclogite stage giving rise to the crystallization of high p and low t assemblages in an effort to quantify this evolution independent well calibrated thermobarometers were applied to basic and acid rocks for the granulite event p t estimates are 7 9 kbar and 700 800 c and for subsequent retrograde evolution p t was 4 5 kbar and 600 c for the eo alpine eclogite metamorphism pressure and temperature conditions were 14 16 kbar and 550 c the inferred p t path is consistent with an uplift of continental crust produced by crustal thinning prior to the subduction of the continental rocks in the light of the available geochronological constraints we propose to relate the pre alpine granulite and post granulite retrograde evolution to the permo jurassic extensional regime the complex granulite eclogite transition is thus regarded as a record of the opening and of the closure of the piedmont ocean

defect microstructures of minerals as a potential indicator of extremely rapid and episodic exhumation of ultrahigh pressure metamorphic rock implication to continental collision orogens exhumation of subducted continental crust to the earth s surface was presumably rapid though at an uncertain rate to retain coesite diamond and pbo2 type tio2 here we report unique defect microstructures of minerals as a potential indicator of a rapid and episodic exhumation process in a fossil fracture zone of coesite eclogite from the sulu terrain eastern china having the most negative 18o value ever reported for eclogite facies metamorphic rock analytical electron microscopy indicates that semi brittle deformation occurred in kyanite omphacite spinel with extensive and unusual fine scale twin lamellae and that brittle deformation occurred in garnet with hardly healed 110 microcleavages these unique defect microstructures can be rationalized by a high strain rate at local weakening and deep faulting of continental collision orogens

the formation of modified zircons in f rich highly evolved granites an example from the shuangji granites in eastern tianshan china abstract two populations of zircons are present in the f rich highly evolved 300 ma shuangji granites xinjiang eastern tianshan china zircon i comprise a very small proportion of the population they show characteristics of primary igneous zircons and yield an age of ca 300 ma zircon ii are the dominant type and are weakly luminescent under cathodoluminescence cl but show a range of complex textures in back scattered electron bse images zircon ii are characterized by th u rich mineral inclusions not seen in zircon i and can be divided into zircon iia and zircon iib autometasomatism during the magmatic hydrothermal phase of the highly evolved shuangji granites fluids rich in f interacted with zircon i through a coupled dissolution reprecipitation process forming pores and cracks in the zircon grains the simultaneous alteration of u rich euxenite released high amounts of u and th into the fluids interaction of these fluids with porous zircon i resulted in the precipitation of u and th rich inclusions in the zircon i grains radiation damage resulted in the formation of metamict zircons later hydrothermal alteration affected the metamict zircons forming nanoscale baddeleyite in the amorphous zone subsequent radiation damage accumulated continuously resulting in the final textures of zircon ii

the dislocation substructures of naturally deformed omphacites abstract a transmission electron microscopy study of naturally deformed omphacite has revealed twins antiphase boundaries and a variety of dislocation substructures consisting of curved free dislocations loops isolated nodal points and networks both free dislocations and dislocation boundaries contain nodes that involve dislocations with the following burgers vectors 001 1 2 110 and 1 2 112 this implies a reaction of the type 001 1 2 110 1 2 112 by analogy with quartz and olivine the dislocation substructures in the omphacites are considered to be indicative of dislocation creep mechanisms and responsible for most of the optical defect structures using microstructural and geochemical data the metamorphic conditions during the creep deformation are estimated to be minimum 8 kbar 550 c maximum 15 kbar 625 c

bbe systematics in subduction related metamorphic rocks characterization of the subducted component the mobility of b and be in h2o rich fluids and felsic silicate liquids produced during metamorphism of subducted oceanic slab and sediments has been investigated through analysis of subduction zone metamorphic rocks of the catalina schist california in metasedimentary rocks b be and the range in b be decrease with increasing metamorphic grade mean 72 std dev 41 for lowest grade lawsonite albite fades rocks mean 21 std dev 11 for higher grade greenschist and epidote amphibolite facies equivalents this decrease to more uniformly low b be may be attributed to the preferential removal of b in h2o rich fluids produced by devolatilization reactions over the approximate temperature interval of 350 600 c metamafic rocks do not show pronounced decrease in b be with increasing metamorphic grade however all metamafic samples have b be 30 lower than values for many altered seafloor basalts in amphibolite grade exposures felsic leucosomes and pegmatites reflecting partial melting have low b be similar to their metasedimentary and metamafic hosts which presumably experienced prior reduction in b be during lower temperature devolatilization this evidence for b and be mobility during high p t metamorphism complements studies of b be systematics in arc volcanic rocks in further characterizing mechanisms by which slab derived elements can be added to the source regions of arc lavas before subducted mafic and sedimentary rocks reach wadati benioff zone depths beneath arcs 80 150 km the b be of these rocks is likely to have decreased to 30 thus highly fractionated slab derived hydrous fluids may be necessary to generate the high b be signatures observed in many arcs b be of up to 200 the b be data together with previously presented stable isotope data for the catalina schist demonstrate that subduction zone metamorphic processes are capable of homogenizing presubduction variability in the concentrations of particularly fluid mobile elements in rocks and may through mixing produce fluids which trend toward uniform trace element and isotopic compositions these homogeneous fluids could infiltrate parts of the mantle wedge and contribute to the characteristic trace element and isotopic signatures of arc magma source regions in hotter subduction zones e g involving subduction of young hot oceanic lithosphere silicate melts derived from previously devolatilized sedimentary and mafic rocks may contribute relatively low b be signatures to arc source regions thus significant variations among arcs in the ranges of b be observed in front rank volcanoes e g for the bismarck arc b be 20 190 for the cascades arc b be 5 may be related in part to varying thermal structure which could govern both the b be of hydrous fluids and the relative proportions of hydrous fluid and silicate melt derived from the subducted slab and sediments

eclogite from the ultrahigh pressure metamorphic unit at lago di cignana western alps a process oriented transmission electron microscope study abstract in the western alps the ocean derived lago di cignana unit of the piemonte zone has experienced ultrahigh pressure metamorphism we have studied the minerals of two eclogite samples from this unit using transmission electron microscopy tem in order to characterise their microstructures these microstructures are the result of deformation phase transformation and reactions and allow conclusions on the processes that had generated them the goal of this process oriented paper is to contribute to the knowledge of the formation and exhumation of ultrahigh pressure eclogites in our tem study we found omphacite amphibole barroisite glaucophane hornblende clinozoisite garnet albite and thin layers of chlorite and mica in amphibole the omphacite is well ordered and has the space group p2 n we observed antiphase domains apds dislocations that are organised in small angle grain boundaries and very rare crystallographic shear planes parallel to 010 and 110 deformation twin lamellae on 100 have not been observed most interesting is the first observation of faults parallel to 110 in a natural omphacite they are due to deformation chain multiplicity faults are common in the amphibole grains in one case the orientation of crystallographic shear planes was not only parallel to 010 but also parallel to 130 and 110 clinozoisite showed deformation twin lamellae on 100 with widths of a few nm up to about 50 nm dislocations organised into a small angle grain boundary have been found which have not been described before the garnet is almost free of dislocations while there are differences regarding the deformation microstructures from the uhp lago di cignana eclogite and other hp occurrences it is unlikely that these are due to higher pressures it is much more likely that the whole formation and exhumation history of the different geological units and the individual positions of the collected rocks within them are reflected in their microstructures a tentative correlation of the omphacite microstructures with the p t path of the lago di cignana unit is presented an important point is the early crystallisation of c2 c omphacite at a temperature below 500 c perhaps around 400 c the low temperature prevents rapid diffusion controlled ordering to p2 nomphacite and thus enables deformation of the metastable c2 c omphacite since c2 c omphacite is more easily to deform than p2 n omphacite this may influence the interplate coupling the onset of the transition to p2 n omphacite however will increase the shear strength of eclogite and the coupling with the overriding plate which may slow down the subduction and finally stop it

zircon solubility in alkaline aqueous fluids at upper crustal conditions field evidence and thermodynamic data at ambient conditions suggest that complexing of zr with hydroxyl ions at high ph enhances the solubility of zircon we tested this hypothesis by measuring the solubilities of the assemblages zircon zrsio 4 baddeleyite z b and zircon quartz z q in neutral to alkaline fluids at 0 2 gpa and 450 750 c in neutral to alkaline fluids 0 0 1 1m naoh zircon dissolved incongruently in quartz undersaturated fluids to form baddeleyite at 450 c various na zr silicates precipitated from fluids saturated and undersaturated in quartz we observed no significant dependence of solubility on temperature the measured solubilities of zircon in pure h 2o at 600 and 750 c are only slightly higher than the procedural blank of 3 3 10 7 m zr however the measured solubility of zircon increases with increasing aqueous silica suggesting that zirconium complexes with silica in the fluid at 600 c linear regression of experimental results yielded ln zr 0 25 2 9 ln si where terms in parentheses represent molal concentrations zircon solubility also seems to increase with increasing hydroxyl concentration in the fluid enhanced solubility in silica rich alkaline fluids may cause dissolution reprecipitation of zircon and resetting of its isotopic clocks suggesting that some zircon u pb ages may correspond to fluid events

omphacite microstructures as time temperature indicators of blueschist and eclogite facies metamorphism omphacites from a wide range of geological environments have been examined by transmission electron microscopy their microstructures are sufficiently variable as to be potential indicators of thermal history for blueschist and eclogite metamorphism in particular the average size of equiaxed antiphase domains apd s arising from cation ordering appears to be a characteristic feature of each environment and increases in the sequence franciscan blueschist 1 turkey blueschist 2 guatemala jadeitic blocks in serpentinite 3 syros blueschist 9 red wine complex canada amphibolite 1 maksyutov complex urals blueschist 3 zermatt saas blueschist 5 allalin metagabbro 4 tauern eclogite 1 franciscan eclogite 5 nybo norway eclogite 2 numbers in brackets indicate the number of hand specimens for which omphacite microstuctures are known a relationship between apd size annealing time and temperature has been derived by analogy with the known apd coarsening behaviour in other systems where apd size n text apd size text n propto text e text text q rt cdot text time text most omphacites fit into a self consistent scheme with n 8 2 if the activation energy q is assumed to be that of cation disordering 75 kcal mole 1 available estimates of peak metamorphic temperature t are used and a reasonable geological time scale is taken as 104 108 years according to this model apd sizes are set in a relatively short interval of the total history of a rock when its temperature is close to its peak value apd sizes are much more sensitive to temperature than to time and may be used as a geothermometer which has the advantage of not being reset by re equilibration at low temperatures petrological implications arising from the model are that allalin metagabbros were metamorphosed at a similar peak temperature to zermatt saas blueschists franciscan eclogites reached higher temperatures than has been previously supposed and that the microstructures in some sesia lanzo omphacites are consistent with a high temperature pre blueschist origin deviation from an ideal coarsening law with n 2 implies that the apd s are not simply stacking mistakes but have some associated structural or compositional modification locally excess titanium concentrated at apd s in red wine complex omphacites may account for their anomalously low observed apd size

relative geobarometry from high pressure rocks of quartzofeldspathic composition from the sesia zone western alps italy in the sesia zone of the western alps italy early alpine blueschist to eclogite facies metamorphism of rocks of quartzofeldspathic composition has produced the same high pressure assemblage of quartz na pyroxene na amphibole paragonite phengite zoisite garnet magnetite sphene and fe sulphide the qfs assemblage over an area 150 km2 relative gradients in pressure and temperature over this region are reflected in the variations in mineral chemistries of the individual phases of the quartzofeldspathic assemblage through continuous reactions mineralogical discontinuities do not occur in the qfs assemblage of this region increases in the jadeite content of the pyroxenes xjd 0 48 to xjd 0 93 and in the glaucophane content of the amphiboles xgl 0 89 to xgl 0 96 occur from the southwest to the northeast of the region studied analysis of coexisting garnets and pyroxenes indicate that the compositional variation of amphiboles and pyroxenes is associated with a decrease in the grossular component of the coexisting garnet zoned pyroxenes and garnets together with the regional trends in mineral chemistries suggest that the evolution of the qfs assemblage with increasing pressure may be modelled by pressure sensitive continuous reactions in which amphibole zoisite and the more jadeitic pyroxene constitute the high pressure assemblage chemographic constraints permit the positioning in pressure temperature space of the compositional isopleths of those model continuous reactions involving these phases which meet the textural and chemical criteria observed in the natural assemblages the low dp dt slope 20 bars c of these isopleths causes the continuous reactions to be useful for geobarometric calculations at pressures above the absolute breakdown of albite to jadeite plus quartz in addition the pseudobinary loops for the other continuous reactions which are potentially useful geobarometers and involve either the naalca 1mg 1 exchange or the mgca 1 exchange are calculated comparison of mineral chemistries with the isopleths yields a relative barometric scheme for the localities studied with these barometric observations it is possible to show that the p t path which the sesia body travelled towards the final recorded state was one of increasing pressure other blueschist and eclogite occurrences from syros and sifnos which contain rocks of quartzofeldspathic composition are also examined

zircon textures and composition refractory recorders of magmatic volatile evolution zircon textures and composition have been used to infer magmatic processes including closed system fractional crystallization magma mixing or replenishment and country rock assimilation here we propose that zircon textures and composition may also be refractory recorders of magmatic volatile evolution we present field whole rock chemical textural mineral chemical and u pb age data from evolved fine to coarse grained granite intrusions on melville peninsula nunavut canada zircon forms two main populations in these granites type 1 and type 2 zircon type 1 zircon is present in all samples but predominant in fine grained granite crystals are euhedral and inclusion rich and show periodic fine scale oscillatory zoning comparatively low concentrations of u 2 200 ppm and hf 1 6 wt high zr hf 40 62 and pervasive alteration type 2 zircon is predominant in coarse grained granite crystals form overgrowths on type 1 zircon and individual crystals they are subhedral and inclusion poor and show weak irregular large scale oscillatory zoning high u up to 7 250 ppm and hf 1 5 2 0 wt low zr hf 37 44 and only local alteration compatible trace element concentrations and zr hf change sharply across the boundary of type 1 to type 2 zircon 207pb 206pb ages preclude a significant hiatus between crystallization of the two types we argue against magmatic versus hydrothermal crystallization country rock assimilation or magma mixing as causes for the crystallization of type 1 and type 2 zircon we propose instead that type 1 zircon formed from volatile undersaturated magmas and that type 2 zircon formed from volatile saturated magmas magmas fractionated by volatile driven filter pressing into crystal rich mush and crystal poor magma crystal rich mush with abundant type 1 zircon crystallized to fine grained granite volatile rich magma crystallized to type 2 zircon and coarse grained granite while type 1 zircon was pervasively altered by exsolving magmatic volatiles type 2 zircon was only locally affected by subsolidus hydrothermal alteration

tectonic evolution of the south tianshan orogen and adjacent regions nw china geochemical and age constraints of granitoid rocks geochemical and geochronological evidence was obtained from granitoids of the south tianshan orogen and adjacent regions which consist of three individual tectonic domains the kazakhstan yili plate the central tianshan terrane and the tarim plate from north to south the central tianshan terrane is structurally bounded by the early paleozoic nikolaev line north nalati fault and late paleozoic atbashy inyl chek south nalati qawabulak fault zones against the kazakhstan yili and tarim plates respectively the meta aluminous to weakly peraluminous granitic rocks which are exposed along the kekesu river and the bikai river across the central tianshan terrane have a tholeiitic calc alkaline or high potassium calc alkaline composition i type geochemical trace element characteristics and the y versus rb nb or y versus nb discrimination diagrams favor a continental arc setting for these granitoid rocks shrimp u pb and la icp ms u pb zircon age data indicate that the magmatism started at about 480 ma continued from 460 to 330 ma and ended at about 275 ma the earlier magmatism 470 ma is considered to be the result of a simultaneous southward and northward subduction of the terskey ocean beneath the northern margin of the tarim plate and the kazakhstan yili plate respectively the later magmatism 460 330 ma is related to the northward subduction of the south tianshan ocean beneath the southern margin of the kazakhstan yili central tianshan plate the dataset presented here in conjunction with previously published data support a late paleozoic tectonic evolution of the south tianshan orogen not a triassic one as recently suggested by shrimp u pb zircon dating for eclogites

implications to garnet clinopyroxene geothermometry of non ideal solid solution in jadeitic pyroxenes garnet clinopyroxene geothermometry has been applied to numerous rock types from the blueschist and eclogite terrain of the sesia zone in the western alps discrepancies in apparent temperatures of up to 600 c have been found suggesting substantial deviation from ideal behaviour of the garnet clinopyroxene equilibria in certain assemblages assemblages containing jadeitic pyroxenes rather than omphacitic or diopsidic pyroxenes yield very low kd 2 0 values and correspondingly high apparent temperatures 1 000 c the garnets coexisting with high na pyroxenes have compositions similar to those coexisting with omphacitic pyroxenes departure from ideal behaviour of these garnets is likely to be minor and is accomodated in the formulation of the geothermometer numerous examples of coexisting garnet clinopyroxene pairs indicate that there is no obvious relationship of kd with jadeite content in pyroxenes with jadeite content less than 70 but at higher values kd varies inversely with the jadeite content the dependence of kd upon the jadeite content in the high na pyroxenes is believed to be due to the preference of m2 sites for fe2 in the enstatite jadeite substitution fe2 mgna 1al 1 this substitution is usually very limited and has no demonstrable effect upon x fe cpx when the m1 fe2 mg content of the pyroxenes is high as in omphacitic and diopsidic pyroxenes however when the m1 fe2 mg content is low as in jadeitic pyroxenes the non ideality of the enstatite type exchange has a marked effect on x fe cpx and consequently on garnet clinopyroxene calculations

cation ordering in omphacite and effect on deformation mechanism and lattice preferred orientation lpo we present microstructural data and lattice preferred orientations lpos of omphacites from a suite of eclogites from the adula cima lunga nappe central alps our work shows a surprisingly strong correlation between the measured lpo and the ordering state of cations in omphacite estimates of deformation temperature from metamorphic petrology together with measured omphacite compositions and lpos determine the field ordering state on the omphacite phase diagram into which each sample falls lpos dominated by l type and s type signatures are developed in samples that fall in the p2 n field ordered structure and c2 c field disordered structure respectively dislocations with b 1 2 110 or b 001 are observed in the transmission electron microscope tem in all samples the former change from a perfect dislocation in the c2 c structure to a partial in p2 n any movement of a partial dislocation requires the formation or growth of a stacking fault furthermore in order to pass an obstacle a partial dislocation has to constrict to a unit dislocation the energy to form a constriction is high in omphacite due to the large separation width thus the activity of the b 1 2 110 dislocation is hindered in the p2 n structure relative to the c2 c structure which change the balance between the two and might give rise to the different lpos

time temperature relation of mineral isochrons a thermodynamic model and illustrative examples for the rbsr system abstract we have developed a thermodynamic model for the determination of the closure temperature t c at which the minerals defining an internal isochron in rb sr or similar geochronological system were set with a geochronological clock it is shown that the equilibrium fractionation of 87 rb and 87 sr between a pair of minerals at t c k d 87 rb 87 sr c is given by the ratio of the quantity 87 rb 86 sr in the two minerals as measured at the present time k d 87 rb 87 sr which equals the element distribution coefficient k d rb sr under equilibrium condition can be calibrated as a function of temperature and compared with the retrieved value of k d 87 rb 87 sr c in a natural pair to obtain t c the various mineral pairs defining an internal isochron will yield concordant or discordant values of t c depending on whether or not they closed simultaneously with respect to the diffusion of rb and sr both types of results are expected and are important in the analyses of the evolutionary history of the host rocks preliminary analyses of the published data in the rb sr system suggest a fairly wide range of t c even for the same mineral pair reflecting differences in the cooling rates and physico chemical environments of the host rocks

microstructural criteria for reliable thermometry in low temperature eclogites abstract two alpine eclogite bodies sampled in metaophiolitic complexes of the piemonte zone have been studied for geothermometry it is demonstrated that temperature estimates by both exchange thermometry and sizes of antiphase domains in omphacites give rise to erratic results when the defect structures of the minerals are not taken into account microstructural criteria by means of both optical and tem microscopy for reliable thermometry in low temperature eclogites are disscussed the dynamically recrystallized grains are the more suitable sites for the application of exchange thermometry while only low strained omphacites can be used for thermometry based on apd s

grain scale variations in trace element composition of fluid altered zircon acasta gneiss complex northwestern canada sem back scattered electron images of zircon separates from a 2 9 ga granitic dyke from the acasta gneiss complex slave province reveal primary igneous oscillatory zoning which is transgressively overprinted by irregular alteration domains electron microprobe analyses show that altered zircon domains are depleted in zr and si relative to unaltered zircon while retaining a constant zr si ratio sims trace element analyses indicate that lree are preferentially enriched in the altered domains altered zircon contains elevated concentrations of ba up to 580 ppm ca up to 2 weight of the element and common pb 50 ppb the presence of lree ca ba and common pb in the zircons is interpreted to be the result of secondary alteration by an aqueous fluid and not by primary incorporation during crystallization we propose that the alteration related elements are located in amorphous zircon domains

kinematics of ductile shearing from outcrop to crustal scale in the monte rosa nappe western alps significant ductile deformation has produced widespread mylonitic structures in the basement orthogneisses and the mesozoic cover quartzites and marbles of the monte rosa nappe in the inner part of the western alps we summarize here the results of a detailed microstructural study at several scales of observation in the northern part of the nappe and discuss the kinematic significance and compatibility of such results most of the observed deformations can be accounted for by progressive wnw vergent shearing during and after the late eocene within a ductile shear zone of crustal scale the displacement of the hanging wall may have been in excess of several tens of kilometers however some ese vergent shear criteria cannot be reconciled with this general picture and suggest that local backthrusting occurred later near the toe of the monte rosa nappe

the clinopyroxene plagioclase symplectite in retrograde eclogites a potential geothermobarometer the retrograde p t t path of intermediate and high temperature eclogites t 500 50 c is characterized by the transformation of omphacite into a symplectitic intergrowth of clinopyroxene and plagioclase lamellae often this symplectite shows a two stage microstructural evolution i e a coarse lamellar width symplectite s1 followed by a thinner lamellar width symplectite s2 each symplectite may also evolve independently into a final globular microstructure sg

amorphization in natural omphacite and its implications abstract high resolution transmission electron microscopic data have revealed the existence of nanoscale intragranular amorphous phase in omphacite of eclogite from the dabieshan uhp metamorphic belt eastern china the results of profiles in the omphacite across the amorphous phase and micro fractured regions indicate variations in compositions and oh band intensity respectively this implies that the occurrence of amorphization in the omphacite appears to be pressure induced and controlled by kinetics oh may diffuse outward and further react with the atom at m2 site during more distorted plastic deformation which occurs as the omphacite crystalline structure collapses to a denser amorphous phase the reported propensity to amorphization and the strong influence on the outcome of the initial structure and of the pressurization protocol indicate the presence of metastability and large kinetic barriers

magmatic to hydrothermal crystallization in the w sn mineralized mole granite nsw australia part i crystallization of zircon and ree phosphates over three million years a geochemical and u pb geochronological study abstract zircon monazite and xenotime crystallized over a temperature interval of several hundred degrees at the magmatic to hydrothermal transition of the sn and w mineralized mole granite magmatic zircon and monazite thought to have crystallized from hydrous silicate melt were dated by conventional u pb techniques at an age of 247 6 0 4 and 247 7 0 5 ma respectively xenotime occurring in hydrothermal quartz is found to be significantly younger at 246 2 0 5 ma and is interpreted to represent hydrothermal growth from associated fluid inclusions it is concluded that it precipitated from a hydrothermal brine 600 c which is below the accepted closure temperature for u pb in this mineral these data are compatible with a two stage crystallization process precipitation of zircon and monazite as magmatic liquidus phases in deep crustal magma followed by complete crystallization and intimately associated sn w mineralization after intrusion of the shallow sill like body of the mole granite later hydrothermal formation of monazite in a biotite fluorite topaz reaction rim around a mineralized vein was dated at 244 4 1 4 ma which distinctly postdates the mole granite and is possibly related to a younger hidden intrusion and its hydrothermal fluid system obtaining precise age data for magmatic and hydrothermal minerals of the mole granite is hampered by uncertainties introduced by different corrections required for multiple highly radiogenic minerals crystallising from evolved hydrous granites including 230 th disequilibrium due to th u fractionation during monazite and possibly xenotime crystallization variable th u ratios of the fluids from which xenotime was precipitating elevated contents of common lead and post crystallization lead loss in zircon enhanced by the fluid saturated environment the data imply that monazite can also survive as a liquidus phase in protracted magmatic systems over periods of 10 6 years the outlined model is in agreement with prominent chemical core rim variation of the zircon