the incorporation of pb into zircon abstract the incorporation of pb into zircons grown from pb rich solutions was evaluated using three different approaches 1 high temperature growth of large crystals from pb silicate melts 2 hydrothermal overplating of thin epitaxial layers on substrates of natural zircon and 3 growth of small homogeneously nucleated crystals from aqueous fluids the melt grown zircons 50 400 m were crystallized from pbo sio2 zro2 p2o5 liquid at atmospheric pressure by cooling from 1430 to 1350 c in the p2o5 free system despite 66 wt pbo in the melt these zircons contain 3 atom pb with apparent zircon fluid partition coefficients of 4 2 and 2 6 respectively for pb4 and pb2 in contrast to the case of melt grown zircons available p is excluded from the aqueous epitaxial zircon suggesting that charge balance is accomplished by h instead small 2 5 m zircons grown by cooling aqueous solutions pbo sio2 zro2 p2o5 from 800 c or 900 c contain 0 25 0 5 atom pb 2 4 wt pbo yielding apparent dpb values of 0 2 0 3 available p5 is incorporated in a 2 1 ratio with pb2 suggesting a specific charge balance mechanism 2p5 pb2 2si4 zr4 however pb enters the zircon even when p is unavailable so h may again play a charge balancing role because of the rapid polythermal modes of zircon growth and the high pb content of the experimental systems the apparent partition coefficients should not be viewed as equilibrium values but as qualitative indicators of pb compatibility under various growth circumstances the overall results are consistent with the low but variable levels of non radiogenic common pb in natural zircons the increased compatibility of pb in fluid grown low temperature zircons suggests a possible fingerprint for zircons from hydrothermal and wet metamorphic rocks i e high concentrations of common pb

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

zircon radiation damage ages abstract the suggestion that the accumulation of radiation damage in zircons could be used as a dating method was first proposed in the 1950s in the original technique radiation damage was determined by x ray diffraction however this is not suitable for the small sample analysis needed in modern geochronology it is now possible to measure radiation damage and u and th contents on micron sized areas on the polished surface of zircon grains using raman spectroscopy and sims mass spectrometry this opens the way for a reassessment of the potential of radiation damage ages and the purpose of this contribution is to re examine the technique through its application to zircons from two granitoids from the archean yilgarn craton and ancient detrital zircons from the jack hills in western australia the three examples show internally consistent radiation damage ages that are also in accord with independent geochronological evidence the 420 110 ma radiation damage age for the darling range granite is coincident with 500 400 ma biotite rb sr ages in the same region of the yilgarn craton likewise a tonalite from the youanmi terrane in the craton with a 1650 150 ma zircon radiation damage age lies within the domain of a 1600 ma event recorded by biotite rb sr ages the jack hills zircons have a 1120 130 ma radiation damage age that is explained by a complex damage accumulation and annealing history culminating in a mild heating event indicated by biotite ar ar ages of about 1140 ma the positive results for the three case histories suggest that radiation damage ages could play a useful role in dating low temperature thermal events

constraints on the timing of multiple thermal events and re equilibration recorded by high u zircon and xenotime case study of pegmatite from pilawa gorna gory sowie block sw poland abstract the application of zircon and xenotime geochronometers requires knowledge of their potential and limitations related to possible disturbance of the age record the alteration of the intergrown zircon and xenotime in pegmatite from the gory sowie block sw poland was studied using the electron microprobe analysis x ray wds compositional mapping micro raman analysis and la icp ms u pb dating of zircon and xenotime as well as the u th total pb dating of uraninite these microanalytical techniques were applied to understand the formation mechanisms of the secondary textures related to post magmatic processes in the zircon and xenotime intergrowth and to constrain their timing textural and compositional features combined with u pb data indicate that the pegmatite related crystallization of the zircon and xenotime intergrowth occurred ca 2 09 ga 2086 35 ma for zircon and 2093 52 ma for xenotime followed by the re equilibration of zircon and xenotime ca 370 ma 373 18 ma and 368 6 ma respectively during the formation of the younger pegmatite the zircon and xenotime were most likely derived from precambrian basement rocks and emplaced in the pegmatite as a restite the zircon preserved textures related to diffusion reaction processes that affected its high u core up to ca 9 6 wt uo2 which underwent further metamictization and amorphization due to self radiation damage the zircon rim and xenotime were affected by coupled dissolution reprecipitation processes that resulted in patchy zoning age disturbance and sponge like textures xenotime was also partially replaced by fluorapatite or hingganite y and y enriched allanite ce the termination of the low temperature alteration was constrained by the u th total pb age of the uraninite inclusions that crystallized in zircon at 281 2 ma which is consistent with the age of 278 15 ma obtained from the youngest cluster of u pb ages in the re equilibrated high u zircon domains this study demonstrates the importance of the careful examination of compositional microtextural and geochronological data obtained using microanalytical techniques to reconstruct the complex thermal histories recorded by accessory minerals

nanoscale processes of trace element mobility in metamorphosed zircon several examples of zircon grains from high to ultrahigh pressure uhp and ultrahigh temperature uht metapelites exhibit a characteristic yet atypical core rim interface domain 5 m wide observed in cathodoluminescence cl imaging the interface domain is located immediately against the magmatic core and is comprised of an irregular 0 2 m wide cl dark domain that is rimmed by a complex 0 5 m wide cl bright domain with cuspate margins the outer margin of the interface domain is rimmed by intermediate cl zircon with low contrast zoning to characterize the nature of the interface domain and to identify mechanisms of trace element mobility in metamorphosed zircon we analyzed several specimens prepared from zircon from the rhodope metamorphic complex eastern greece and the goshen dome western massachusetts usa via atom probe tomography apt the data reveal three types of geochemical anomalies each with a unique morphology 1 toroidal clusters with high concentrations of pb y al are found exclusively within the core of the rhodope grain these clusters are interpreted as decorated dislocation loops that formed during metamorphism and annealing of radiation damage to the lattice geochronological and geochemical data support this interpretation 2 complex cross cutting planar and linear features with anomalous concentrations of y p yb or u are spatially restricted to the core rim interface domain these features do not correlate with inherited geochemical variation oscillatory zoning or deformation induced microstructures instead the planar features likely formed in response to an interface coupled dissolution reprecipitation reaction that propagated into the crystal during metamorphism the observed cross cutting relationships are the product of either multiple events or complexity of the process that originally formed the domains 3 ellipsoidal features with high concentrations of y p yb al are found exclusively within the high y p yb planar features these features are interpreted as the product of spinodal decomposition that occurred during exhumation as the zircon passed the solvus where local equilibria favored nm scale exsolution to minimize the gibbs free energy the presence of multiple types of geochemical features in these examples indicates that trace element mobility in zircon is driven by multiple processes over the course of orogenesis given that these atypical domains are apparently restricted to zircon metamorphosed at uht and u hp conditions their presence may represent a marker of metamorphism at very high grade conditions

nanoscale occurrence of pb in an archean zircon abstract we report for the first time a direct atomic scale characterization of pb in zircon 4 4 3 1 ga from the early archean yilgarn craton in australia using high resolution haadf stem two forms of pb have been identified pb concentrated at 3 atom as a nanoscale patch in zircon structure and pb concentrated within the amorphous domain created by fission fragment damage the first result suggests that the pb atoms directly substitute for zr4 in the zircon structure and the latter observation demonstrates that pb diffusion can occur through amorphous regions created by radiation damage although volume diffusion is typically considered to be the dominant mechanism for pb diffusion beyond the first percolation point i e when the amorphous domains overlap and form a fully interconnected network of amorphous domains there is a new pathway for the diffusion of pb that is faster than volume diffusion through crystalline zircon

relationships between environmental conditions and the diagenetic evolution of organic matter derived from higher plants in a modern mangrove swamp system guadeloupe french west indies abstract the sedimentary organic matter content of a series of 2 m deep cores was investigated along a sea land transect at five sites representing five species of mangrove and salt marsh vegetation the vegetation was settled at the same place for at least 1000 years and therefore sedimentary organic matter deriving from the decay of higher plants has accumulated in large amounts the global morphological and chemical preservation of the organic matter attested by various sedimentary parameters including the proportions of cellulose bearing tissues the toc contents the c n ratios the total sulphur contents and the 13 c compositions reveals that the sedimentary organic matter is less degraded when it has been under the influence of the marine water table for a long time this is indicated by a good correlation between the salinities of interstitial waters the redox potentials measured in the wet sediments and the chemical composition of the organic matter moreover the concentration of organic sulphur shows a positive correlation with the hydrogen index hi only under the marine water table influence suggesting the very local presence of sulphur hc compounds

micron to nanoscale characterisation and u pb geochronology of zircon from granites of the samphire pluton south australia abstract zircons from three distinct granites within the samphire pluton south australia are characterised at the micron to nanoscale sensitive high resolution ion microprobe shrimp u pb zircon dating generated 207pb 206pb weighted average ages of 1586 9 3 ma 1583 2 8 5 ma and 1578 9 5 ma respectively although zircons from all three granites display evidence of hydrothermal overprinting this is most strongly expressed in a distinct red colored granite referred to here as granite c alteration is expressed as variation in the concentrations of hree y th and pb whereby grain margins are relatively enriched in these elements and both zr and si are depleted altered zircon cores have high u contents relative to grain margins which are appreciably poorer in this element whereas th is strongly enriched within crosscutting microfractures coupled with the relative enrichment in non formula elements and marked disturbance of u th pb isotope ratios the nanoscale observations of pb bearing nanoparticles galena implying mobility of pb and other elements nanofractures and structural defects demonstrate that zircon in granite c has undergone multi stage alteration impacting upon accurate dating importantly and with implications for analogous systems elsewhere our results confirm nanoscale open system u pb behaviour in hiltaba suite zircon shrimp u pb zircon geochronology cannot confidently resolve any statistical differences in the age of the three granites despite their distinct appearance suggesting they might represent temporally distinct phases of a larger magmatic system zircons within the most altered granite c directly underlying the blackbush uranium prospect contain convincing micron to nanoscale evidence for an alteration event that triggered a remobilisation of uranium from granite into the cover sequence

decoding a protracted zircon geochronological record in ultrahigh temperature granulite and persistence of partial melting in the crust rogaland norway this contribution evaluates the relation between protracted zircon geochronological signal and protracted crustal melting in the course of polyphase high to ultrahigh temperature uht t 900 c granulite facies metamorphism new u pb oxygen isotope trace element ion imaging and cathodoluminescence cl imaging data in zircon are reported from five samples from rogaland south norway the data reveal that the spread of apparent age captured by zircon between 1040 and 930 ma results both from open system growth and closed system post crystallization disturbance post crystallization disturbance is evidenced by inverse age zoning induced by solid state recrystallization of metamict cores that received an alpha dose above 35 1017 g 1 zircon neocrystallization is documented by cl dark domains displaying o isotope open system behaviour in uht samples o isotopic ratios are homogenous 18o 8 91 0 08 pointing to high temperature diffusion scanning ion imaging of these cl dark domains did not reveal unsupported radiogenic pb the continuous geochronological signal retrieved from the cl dark zircon in uht samples is similar to that of monazite for the two recognized metamorphic phases m1 1040 990 ma m2 940 930 ma a specific zircon forming event is identified in the orthopyroxene and uht zone with a probability peak at ca 975 ma lasting until ca 955 ma coupling u pb geochronology and ti in zircon thermometry provides firm evidence of protracted melting lasting up to 110 my 1040 930 ma in the uht zone 85 my ca 1040 955 ma in the orthopyroxene zone and some 40 my ca 1040 1000 ma in the regional basement these results demonstrate the persistence of melt over long timescales in the crust punctuated by two uht incursions

mobilization of radiogenic pb in zircon revealed by ion imaging implications for early earth geochronology zircon is arguably the most commonly used geochronometer but the reliability of ages obtained requires a full understanding of processes that might compromise the integrity of its u pb systematics here we present the results of a multifaceted ion microprobe study of zircon grains from the napier complex east antarctica a region affected by pervasive high temperature metamorphism at 2 5 ga and from which previous zircon geochronological interpretations have been problematic both u pb spot analysis 15 m and high spatial resolution 2 m scanning ion imaging of pb isotopes have been applied in an attempt to quantify the effects of metamorphism spot analyses spread along concordia yielding 207 pb 206 pb ages from 2 5 ga to 3 9 ga with the oldest grains reversely discordant ion images of uranogenic pb reveal a surprising micrometer scale patchy distribution that is unrelated to crystal morphology or damage the 207 pb 206 pb ratios within these subdomains correspond to apparent zircon ages as old as 4 2 ga these are interpreted as artifacts of ancient redistribution of radiogenic pb a process that can generate meaningless ages and are not relicts of ancient including hadean zircon scanning ion imaging thus facilitates identification of unsupported radiogenic pb and enables testing of the validity of old ages from zircon known to have a long and complicated history

erratum to metamictisation of natural zircon accumulation versus thermal annealing of radioactivity induced damage annealing of the radiation damage generated in decay events is a common phenomenon in natural zircons we have studied relationships between radiation damage age and radionuclide content of natural zircons on a micro scale the degree of metamictisation was estimated by means of confocal laser raman spectroscopic measurements raman band broadening in well ordered to moderately metamict zircons that have not experienced significant healing of the radiation damage since the time of their growth shows a nearly linear dependence on the fluence this dependence is proposed as a calibration line for examining unknown zircons in order to consider complete or incomplete damage storage which may contribute to the understanding of the low t thermal history of their host rocks seven examples for the application are presented radiation damage may anneal heterogeneously with preferred re ordering in more damaged micro areas results suggest that single point defects do not anneal continuously over geologic periods of time but are in contrast a comparably stable type of radiation damage in contrast to recrystallisation processes structural recovery due to simple thermal annealing is not necessarily connected with loss of radiogenic pb the most prominent example for this are concordant zircons from sri lanka although they are excellent standards for u pb dating sri lankan zircons should not be used as standards for structural radiation damage the experimental work is completed by monte carlo simulations of decay events in zircon

al zoning in orthopyroxene in a sapphirine quartzite evidence for 1120 c uht metamorphism in the napier complex antarctica and implications for the entropy of sapphirine a unique sapphirine orthopyroxene quartz granulite from mt riiser larsen in the tula mountains of enderby land east antarctica preserves two generations of coarse and texturally equilibrated orthopyroxene and sapphirine coexisting with quartz initial subhedral orthopyroxene porphyroblasts retain core compositions enriched in al2o3 12 2 0 5 wt compared with their rims and finer orthopyroxene 9 6 0 5 wt al2o3 that forms granoblastic textures with sapphirine sapphirine and quartz also form symplectites on and along cleavage planes within orthopyroxene these compositional and textural features are consistent with the reaction 2mgal2sio6 mg2al4 sio10 sio2 leading to the formation of sapphirine quartz at the expense of aluminous orthopyroxene calculations in the mas and fmas systems and theoretical considerations involving the phases enstatite sapphirine sillimanite quartz and cordierite indicate that the reaction above progresses from left to right with decreasing temperature in the orthopyroxene sapphirine quartz field at pressures of ca 8 10 kbar the temperature difference required to account for the ca 2 5 3 wt decrease in al2o3 in orthopyroxene is at least 60 80 c and implies peak temperatures for the initial assemblage of at least 1120 c if the second granoblastic assemblage equilibrated at 1040 c the p t conditions required by the sapphirine quartz association and other p t sensitive assemblage indicators in the napier complex it is not possible to distinguish whether the two assemblages are simply related by cooling and re equilibration or reflect a polyphase evolution involving the superposition of a second uht event on an earlier even higher temperature uht metamorphism preliminary thermodynamic modelling of the reaction above incorporating the observed range in orthopyroxene al2o3 zoning indicates that present estimates for the entropy of high temperature sapphirine are potentially too high by 15 18 compared with sapphirine entropy estimates that are consistent with mas system experiments the mt riiser larsen sapphirine quartz rocks preserve the first definitive record of regional metamorphic temperatures in excess of 1120 c in the napier complex or indeed any uht granulite terrain worldwide similarly high peak temperatures may be retrieved from detailed studies of sapphirine quartz granulites from other regions further expanding the thermal realm of crustal metamorphism but progress will critically depend on the experimental acquisition of new entropy data for sapphirine

annealing radiation damage and the recovery of cathodoluminescence the structural recovery upon heat treatment of a highly metamict actinide rich zircon u 6000 ppm has been studied in detail using a range of techniques including x ray powder diffraction raman spectroscopy shrimp ion probe electron microprobe transmission electron microscopy and cathodoluminescence analysis the structural regeneration of the amorphous starting material depends on random nucleation it starts between 800 and 950 c when amorphous zrsio4 decomposes to form crystalline zro2 and amorphous sio2 at around 1100 c well crystallised zrsio4 grows at the expense of the oxides u has been retained in the newly grown zircon whereas pb was evaporated during the heat treatment this process is in marked opposition to the reconstitution of moderately metamict minerals which experience a gradual recovery controlled by the epitaxial growth at the crystalline amorphous boundaries both of these recovery processes are not the direct inverse of metamictisation the structural regeneration was found to be connected with a significant increase in the emission of cl in all cases annealing heavily damaged zircon and moderately damaged zircon and monazite we observe that the final wellcrystallised annealing products emit more intense cl than their radiation damaged starting minerals although having almost identical elemental composition our observations are taken as evidence that the cl is not only determined by the chemical composition of the sample but is also strongly controlled by structural parameters such as crystallinity or the presence of defect centres

mechanisms and consequences of intra crystalline enrichment of ancient radiogenic pb in detrital hadean zircons from the jack hills western australia abstract the recent discovery of pb radiogenic lead enriched domains peds in zircon using high resolution scanning ion imaging atom probe tomography and transmission electron microscopy indicates that the u pb isotopic system in zircon can be affected not only by pb loss but also by intra crystalline pb enrichment however the formation mechanism of peds and the consequences for in situ u pb dating remain elusive to further understand these issues scanning ion imaging and u pb dating were carried out on 51 hadean detrital zircon grains from the jack hills western australia of these 8 grains were found to contain micrometer scale peds with elevated 207pb and 206pb in the ion images isotope profiles across these peds confirm that they represent unsupported pb resulting from intra grain mobilization and local enrichment of pb during ancient overprinting events the peds are rare in most grains with only 1 3 pb hotspots present in any 70 m 70 m imaged area and are located either in dark cl high u growth zones or associated with bright cl low th recrystallized domains suggesting that they were likely formed by local scale processes the peds located in dark cl high u growth zones likely resulted from pb trapped in local interconnected pathways produced by radiation damage during thermal overprinting events those associated with bright cl low th domains are interpreted as pb concentrated in nanoscale pores formed during fluid present recrystallization of non metamict zircon our interpretations therefore imply that intra crystalline enrichment of pb in zircon can occur at various scales and through diverse mechanisms age calculations based on the ion images demonstrate that incorporation of peds in conventional in situ sims spots produces spuriously old ages that are either reversely discordant or concordant depending on the time of pb mobilization and the analytical precision the implication is that careful investigation of intra grain distribution of u th pb isotopes is required in order to better understand the u pb isotopic system and to obtain reliable crystallization ages for ancient zircons affected by complex pb mobilization and redistribution

diffusion in zircon despite its low abundance in most rocks zircon is extraordinarily useful in interpreting crustal histories the importance of u th pb isotopic dating of zircon is well and long established davis et al this volume parrish et al this volume zircon also tends to incorporate trace elements useful as geochemical tracers such as the ree y and hf a number of characteristics of zircon encourage the preservation of internal isotopic and chemical variations often on extremely fine scale which provide valuable insight into thermal histories and past geochemical environments the relative insolubility of zircon in crustal melts and fluids as well as its general resistance to chemical and physical breakdown often result in the existence of several generations of geochemical information in a single zircon grain the fact that this information is so frequently retained as evidenced through backscattered electron or cathodoluminescence imaging that often reveal fine scale zoning down to the sub micron scale has long suggested that diffusion of most elements is quite sluggish in zircon in this chapter we present an overview of the findings to date from laboratory measurements of diffusion of cations and oxygen in zircon because of its importance as a geochronometer attempts have been made to measure diffusion especially of pb for over 30 years but only in the last decade or so have profiling techniques with adequate depth resolution been employed in these studies resulting in a plethora of new diffusion data these findings have important implications for isotopic dating interpretation of stable isotope ratios closure temperatures and formation and preservation of primary chemical composition and zoning in zircon efforts have been made for some time to quantify and characterize diffusion in zircon most notably of pb in deference to its significance in interpreting pb isotopic signatures and refining understanding of thermal histories as is evident from

zircon the metamorphic mineral a mineral that forms under conditions as variable as diagenesis to deep subduction melt crystallization to low temperature alteration and that retains information on time temperature trace element and isotopic signatures is bound to be a useful petrogenetic tool the variety of conditions under which zircon forms and reacts during metamorphism is a great asset but also a challenge as interpretation of any geochemical data obtained from zircon must be placed in pressure temperature deformation fluid context under which condition and by which process zircon forms in metamorphic rocks remains a crucial question to answer for the correct interpretation of its precious geochemical information in the last 20 years there has been a dramatic evolution in the use of zircon in metamorphic petrology with the advent of in situ dating techniques zircon became relevant as a mineral for age determinations in high grade metamorphic rocks since then there has been incredible progress in our understanding of metamorphic zircon with the documentation of growth and alteration textures its capacity to protect mineral inclusions zircon thermometry trace element patterns and their relation to main mineral assemblages solubility of zircon in melt and fluids and isotopic systematics in single domains that go beyond u pb age determinations metamorphic zircon is no longer an impediment to precise geochronology of protolith rocks but has become a truly indispensable mineral in reconstructing pressure temperature time fluid paths over a wide range of settings an obvious consequence of its wide use is the rapid increase of literature on metamorphic zircon and any attempt to summarize it can only be partial in this chapter reference to published works are intended as examples and not as a compilation this chapter approaches zircon as a metamorphic mineral reporting on its petrography and texture deformation structure and mineral chemistry including trace element and isotopic systematics linking this information together highlights the potential of zircon as a key mineral in petrochronology

nanosims study of seismically deformed zircon evidence of y yb ce and p redistribution and resetting of radiogenic pb lattice defects in zircon can cause trace elements redistribution and disturbance of isotopic systems this study investigates in detail how seismically induced deformation microstructures in zircon correlate with trace element and isotope re equilibration felsic mylonites with pseudotachylyte veins from the ivrea verbano zone in northern italy were studied with special focus on deformed zircon we have revealed the following post growth deformation microstructures planar deformation bands pdbs planar fractures pfs non planar fractures both healed and open and finite strain patterns pdbs are planar portions of crystal lattice that are strictly parallel to 100 crystallographic planes and are rotated to up to 3 with respect to the host grain they are from 0 5 to 1 m wide and have average spacing of 5 m pdbs originate in seismically active environment at elevated differential stress strain rate and temperature several grains in which pdbs are observed were analyzed with ion microprobe ion maps indicate redistribution of radiogenic pb isotopes associated with pdb formation isotopic redistribution preferably occurs in pdbs with larger crystallographic misorientation profiling demonstrated clear spatial correlation of pdbs with variations of ree abundances both gain and loss and possible correlations with increased and decreased hf ti and p abundances trace elements can be depleted or enriched compared to the abundance in surrounding matrix in deformed domains depending on the spacing of pdbs and the proximity of the analyzed volume to grain boundary or to detrital core 207 pb 206 pb ratio demonstrates systematic pb loss in the pdb bearing lattice domains with respect to pdb free domains in some cases pb gain is observed where the pdbs source radiogenic pb from older detrital cores our study has important implications for geochronology and microchemistry of zircon from seismically deformed sections of ivrea verbano zone and from other paleo seismic zones of the world zircon found in seismically deformed rocks near pseudotachylyte veins may demonstrate distorted and even reset isotopic ages and altered trace element abundances enhanced trace element exchange between deformed zircon and host mylonite can influence mass balance calculations for the bulk rock

late palaeoproterozoic depositional age for khondalite protoliths in southern india and tectonic implications abstract shrimp dating of detrital zircons from garnet sillimanite cordierite paragneisses khondalites of the trivandrum block southern india revealed nanometer scale pb isotopic inhomogeneity in most grains that we ascribe to annealing processes during ultra high temperature metamorphism at ca 570 ma our age data for zircons from six representative khondalite samples do not document any neo or mesoproterozoic detrital grains and we conclude from the concordant ages and discordant minimum 207pb 206pb ages that the khondalite precursor sediments were deposited more than 2 1 ga ago and were subsequently intruded by granitoid rocks at ca 1765 2100 ma some detrital zircons in the khondalites contain late palaeoproterozoic metamorphic domains suggesting that these grains are derived from an unknown crustal source that most likely experienced late palaeoproterozoic high grade metamorphism both the metasedimentary assemblage and granitoids were severely ductilely deformed metamorphosed and migmatized during the pervasive pan african event at ca 550 580 ma this caused many detrital zircons in the khondalites to become variably recrystallized and to develop metamorphic rims proper interpretation of cathodoluminescence images and zircon morphology is important in interpreting detrital populations the southern indian khondalites were part of an extensive palaeoproterozoic metasedimentary assemblage that may have extended from southern madagascar via the trivandrum block to the highland complex of sri lanka and seems to reflect a continental margin sequence that was deposited on an archaean to early palaeoproterozoic continental terrane possibly the southern margin of the indian dharwar craton the tectonic history of this terrane remains obscure due to the pervasive overprint during the pan african event

petrochronology of zircon and baddeleyite in igneous rocks reconstructing magmatic processes at high temporal resolution zircon zrsio4 and baddeleyite zro2 are common accessory minerals in igneous rocks of felsic to mafic composition both minerals host trace elements substituting for zr among them hf th u y rees and many more the excellent chemical and physical resistivity of zircon makes this mineral a perfect archive of chemical and temporal information to trace geological processes in the past utilizing the outstanding power and temporal resolution of the u pb decay schemes baddeleyite is a chemically and physically much more fragile mineral it preserves similar information only where it is shielded from dissolution and physical fragmentation as an inclusion in other minerals or in a fine grained or non reactive rock matrix it offers the potential for dating the solidification of mafic rocks with high precision through its crystallization in small pockets of zr enriched melt after extensive olivine and pyroxene fractionation zircon and baddelelyite u pb dates are for an overwhelming majority of cases and where we can assume a closed system considered to reflect the time of crystallization the development of the u pb dating tool ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry since 2005 has led to unprecedented precision of better than 0 1 in 206pb 238u dates bowring et al 2005 increased sensitivity of mass spectrometers and low laboratory blanks due to reduction of acid volumes allow routine u pb age determinations of micrograms of material at sufficiently high radiogenic common lead ratios see schoene and baxter 2017 this volume in situ u pb age analysis using laser ablation or primary ion beam sputtering allows analysis of sub microgram quantities of zircon material from polished internal sections or zircon surfaces with spot diameters ranging from 30 m for laser ablation inductively coupled plasma mass spectrometry la icp ms to 10 m for secondary ion mass spectrometry sims lateral resolutions of 2 5 m for nanosims

chondritic lu hf in the early crust mantle system as recorded by zircon populations from the oldest eoarchean rocks of yilgarn craton west australia and enderby land antarctica abstract a persistent question in early earth investigations is the depletion history of the mantle as recorded in the isotopic compositions of the oldest rocks and minerals here we present new in situ sensitive high resolution ion microprobe shrimp u th pb geochronology and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icpms lu hf tracing data for individual zircons extracted from the oldest rocks of the antarctic and australian continents these are 3 88 and 3 85 ga orthogneisses from the gage ridge and mt sones in enderby land and a 3 73 ga meeberrie gneiss from the yilgarn craton the zircons from each sample show complex u th pb systematics due to the mobile behaviour of pb resulting in several age populations with discordant to reversely discordant arrays on concordia plots in contrast measured 176hf 177hf compositions from the same analysis sites show narrowly defined compositional ranges with 3 or fewer groups for each sample reflecting the resistance of 176hf 177hf in zircons to disturbance even under high temperature granulite conditions the initial 176hf 177hf calculated for the most primitive hf population for each sample using the best age estimate yields near chondritic weighted mean compositions of 1 6 0 5 1 6 0 4 and 0 6 0 7 epsilon units deviations in parts per 10 000 from a chondritic uniform reservoir chur reference at 3877 62 3850 50 and 3731 4 ma respectively these results provide no evidence for significant lu hf fractionation on the early earth expected to result from processes including accretion intra mantle differentiation or massive hadean crustal growth

zircon and monazite petrochronologic record of prolonged amphibolite to granulite facies metamorphism in the ivrea verbano and strona ceneri zones nw italy abstract in order to improve the understanding of thermal tectonic evolution of high grade terranes we conducted a systematic study of textures ree content and u pb ages of zircon and monazite grains extracted from migmatitic metapelites across the amphibolite to granulite facies metamorphic gradient exposed in the ivrea verbano and strona ceneri zones italy this study documents the behaviour of these accessory minerals in the presence of melt the absence of relict monazite grains in the metasediments and the gradual decrease in the size of inherited zircon grains from amphibolite to granulite facies cores indicate partial to total dissolution of accessory minerals during the prograde path and partial melting the retrograde path is marked by i growth of new zircon rims r1 and r2 around inherited cores in the mesosome ii crystallisation of stubby zircon grains in the leucosome especially at granulite facies and iii crystallisation of new monazite in the mesosome stubby zircon grains have a distinctive fir tree zoning and a constant th u ratio of 0 20 together these features reflect growth in the melt conversely the new zircon grains with r1 rims have dark prismatic habits and th u ratios in the ivrea verbano zone the interquartile range iqr of u pb ages on zircon and monazite are interpreted to represent the length of zircon and monazite crystallisation in the presence of melt accordingly they provide an indication on the minimum duration for high temperature metamorphism and partial melting of the lower crust 20 ma and 30 ma in amphibolite and granulite facies respectively in amphibolite facies zircon crystallisation between 310 and 294 ma iqr is interpreted to reflect metamorphic peak condition and earlier retrograde history conversely monazite crystallisation between 297 and 271 ma iqr reflects cooling under 750 c to a temperature close to the solidus in granulite facies zircon crystallisation between 295 and 265 ma iqr is interpreted to reflect high temperature conditions which were attained after peak of metamorphism during isothermal decompression and subsequent cooling under 850 950 c the observed decrease of u pb ages in metamorphic zircon and monazite from amphibolite to granulite facies i e from the middle to the lower crust is interpreted to record slow cooling and crystallisation of the variscan orogenic root at the transition from orogenic collapse to opening of the tethys ocean

similarity between c n and s stable isotope profiles in european spruce forest soils implications for the use of δ34s as a tracer abstract stable isotope systematics of c n and s were studied in soils of 5 european forest ecosystems the sites were located along a north south transect from sweden to italy mean annual temperatures from 1 0 to 8 5 c atmospheric deposition from 2 to 19 kg n ha 1 a 1 and from 6 to 42 kg s ha 1 a 1 in picea stands the behavior of c n and s isotopes was similar in 3 aspects 1 assimilation favored the lighter isotopes 12 c 14 n and 32 s 2 mineralization in the soil profile left in situ residues enriched in the heavier isotopes 13 c 15 n and 34 s and 3 no 3 n as well as so 4 s in soil solution was isotopically lighter compared to the same species in the atmospheric input in this study emphasis was placed on s isotope profiles which so far have been investigated to a much lesser extent than those of c and n sulfate in monthly samples of atmospheric input had systematically higher 34 s ratios than total soil s at the 0 5 cm depth on average by 4 0 sulfate in the atmospheric input had higher 34 s ratios than in deep 50 cm lysimeter water on average by 3 2 organic s constituted more than 50 of total soil s throughout most of the profiles 0 20 cm below surface there was a tendency to isotopically heavier organic s and lighter inorganic so 4 s with ester so 4 s heavier than c bonded s at 3 of the 5 sites with an increasing depth 0 to 20 cm below surface 13 c 15 n and 34 s ratios of bulk soil increased on average by 0 9 4 2 and 1 6 respectively reflecting an increasing degree of mineralization of organic matter the isotope effects of c n and s mineralization were robust enough to exist at a variety of climate conditions and pollution levels in the case of s the difference between isotope composition of the upper organic rich soil horizon lower 34 s and the deeper sesquioxide rich soil horizons higher 34 s can be used to determine the source of so 4 in streams draining forests this application of 34 s as a tracer of s origin was developed in the jeze i catchment czech republic a highly polluted site suffering from spruce die back in 1996 1997 the magnitude and 34 s of atmospheric input 20 kg s ha 1 a 1 5 8 and stream discharge 56 kg s ha 1 a 1 3 5 was monitored export of s from the catchment was 3 times higher than contemporary atmospheric input more than 50 of s in the discharge was represented by release of previously stored pollutant s from the soil stable isotope systematics of jeze i soil s mean of 2 5 in the o a horizon 4 8 in the b horizon and 5 8 in the bedrock suggests that most of the soil derived s in discharge must come from the isotopically light organic s present in the upper soil horizon and that mineralized organically cycled s is mainly flushed out during the spring snowmelt the fact that a considerable proportion of incoming s is organically cycled should be considered when predicting the time scale of acidification reversal in spruce die back affected areas

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

paleoproterozoic sedex type stratiform mineralization overprinted by mesozoic vein type mineralization in the qingchengzi pb zn deposit northeastern china abstract the qingchengzi pb zn deposit is located in the northeastern jiao liao ji belt jljb north china craton ncc field observation and age dating indicate that the deposit was formed from paleoproterozoic sedimentary exhalative sedex stratiform mineralization overprinted by late triassic hydrothermal vein type mineralization five types of fluid inclusions fis are identified in the quartz grains based on petrography and laser raman spectroscopy liquid rich two phase type 1 vapor rich two phase type 2 co2 bearing types 3a and 3b and co2 pure type 4 quartz from the sedex stratiform ores contains only type 1 fis and hydrogen oxygen isotopic compositions indicate that the ore forming fluids were magmatic water derived the ore forming fluids were likely of medium temperatures and low salinity and belonged to a nacl h2o hydrothermal system quartz from the vein types contains all five types of fis and the ore forming fluids may have belonged to a medium temperature low salinity nacl h2o co2 hydrothermal system hydrogen oxygen isotopes indicate that the vein type ore forming fluids were derived from magmatic meteoric mixed source rare earth element ree and sulfur lead isotopic compositions indicate that ore forming materials of the sedex stratiform mineralization were derived from the wall rocks and magma wheres those of the vein type mineralization were derived from late triassic granitic magma wall rocks and the paleoproterozoic sedex ores based on field geological and geochronological data we propose the following regional metallogenic model 1 sedex mineralization occurred during the paleoproterozoic post collisional extension in the jljb 2 vein type mineralization was generated by the north dipping subduction of the yangtze craton beneath the ncc which led to continent continent collision and slab break off in the late triassic

an integrated microtextural and chemical approach to zircon geochronology refining the archaean history of the napier complex east antarctica integrated textural and chemical characterisation of zircon is used to refine the u pb geochronology of the archaean ultra high temperature napier complex east antarctica scanning electron microscope characterisation of zircon and the rare earth element compositions of zircon garnet and orthopyroxene are integrated to place zircon growth in an assemblage context thereby providing tighter constraints on the timing of magmatic and metamorphic events data indicate that magmatism occurred in the central and northern napier complex at ca 2 990 ma a regional relatively low pressure metamorphic event occurred at ca 2 850 2 840 ma mineral ree data from garnet bearing orthogneiss indicate that ca 2 490 2 485 ma u pb zircon ages provide an absolute minimum age for the ultrahigh temperature uht foliation preserved in this rock internal zircon zoning relationships and estimated zircon garnet dree values from paragneiss suggest that an absolute minimum age of ultra high temperature metamorphism is ca 2 510 ma but that it is more likely to be older than ca 2 545 ma we suggest that the high proportion of published zircon u pb data with ages between ca 2 490 2 450 ma reflects late post peak zircon growth and does not date the timing of peak uht metamorphism

metallic lead nanospheres discovered in ancient zircons zircon zrsio4 is the most commonly used geochronometer preserving age and geochemical information through a wide range of geological processes however zircon u pb geochronology can be affected by redistribution of radiogenic pb which is incompatible in the crystal structure this phenomenon is particularly common in zircon that has experienced ultra high temperature metamorphism where ion imaging has revealed submicrometer domains that are sufficiently heterogeneously distributed to severely perturb ages in some cases yielding apparent hadean 4 ga ages from younger zircons documenting the composition and mineralogy of these pb enriched domains is essential for understanding the processes of pb redistribution in zircon and its effects on geochronology using high resolution scanning transmission electron microscopy we show that pb rich domains previously identified in zircons from east antarctic granulites are 5 30 nm nanospheres of metallic pb they are randomly distributed with respect to zircon crystallinity and their association with a ti and al rich silica melt suggests that they represent melt inclusions generated during ultra high temperature metamorphism metallic pb is exceedingly rare in nature and previously has not been reported in association with high grade metamorphism formation of these metallic nanospheres within annealed zircon effectively halts the loss of radiogenic pb from zircon both the redistribution and phase separation of radiogenic pb in this manner can compromise the precision and accuracy of u pb ages obtained by high spatial resolution methods

impact triggered nanoscale pb clustering and pb loss domains in archean zircon zircon microcrystals are found in many planetary crustal rocks and nanoscale research on grains from well characterized impact environments on earth provide a baseline for reconstructing extreme shock and thermal histories elsewhere however using zircon to date large impact events can be challenging given that shock related isotopic re setting of u pb ratios when measured at micrometre scale is often incomplete and difficult to interpret as the underlying pb migration mechanisms are unclear to better understand shocked zircon u pb systematics we performed atom probe tomography and electron microscopy with the previous sims analyses of two shock metamorphosed mesoarchean zircon grains from deep 15 km beneath the centre of the 2 020 ga giant vredefort impact structure we find evidence of two types of impact related nanoscale pb mobility in one grain clustering has produced 10 nm diameter bodies of radiogenic pb unsupported by u and co located with al with an average 207pb 206pb ratio of 0 50 n 4 the value extant in the grain at the time of impact conversely nearby nanodomains exhibit randomly distributed radiogenic pb u and al and yield 206pb 238u dates consistent with 100 loss of pre impact radiogenic pb atoms during shock metamorphic processes notably domains with multiple pb clusters occur within micrometres of domains that experienced 100 pb loss precluding a uniform radial pattern of thermally driven pb diffusion at the grain scale these cases of broadly coeval clustering and outward pb mobility during geologically instantaneous shock metamorphism point to unusually rapid multi path diffusion processes within sub micrometre volumes which when averaged yield normally discordant u pb dates the isolation of spatially variable styles of pb retention and loss at nanoscale amidst classical grain scale shock microstructures shows promise for recognizing and resolving bombardment histories in planetary crusts using zircon

four zircon ages from one rock the history of a 3930 ma old granulite from mount sones enderby land antarctica ion microprobe u th pb analyses of zircons from a granulite grade orthogneiss from mount sones enderby land antarctica record the ages of four principal events in the history of the gneiss three of which already have been recognized through previous isotopic dating of other samples the structure of the zircons indicates at least four different stages of growth the several zircon ages were obtained by grouping the analyses according to the stage they represented in the observed stratigraphic succession of growth and thereby defining separate u pb discordance patterns for each stage the stratigraphically oldest zircon rare discrete cores is indistinguishable in age from the most common euhedrally zoned zircon both crystallized when the tonalitic precursor of the orthogneiss was emplaced into the crust 3927 10 ma ago making the orthogneiss currently the oldest known terrestrial rock the outer parts of most grains and some whole grains recrystallized at 2948 31 17 ma during or immediately after possibly 100 ma of high granulite grade metamorphism the recrystallized zircon was isotopically disturbed by tectonism associated with reactivation of the southern margin of the napier complex at 1000 ma in the intervening time at 2479 23 ma the cores and zoned zircon suffered a major isotopic disturbance involving movement of radiogenic pb which left most of the crystals with radiogenic pb deficiencies but produced local radiogenic pb excesses in others a new generation of zircon characterized by very high th u and low u grew at that time that event deformation and possibly a minor rise in temperature produced widespread perturbations of other isotopic systems throughout the napier complex

a 4463 ma apparent zircon age from the jack hills western australia resulting from ancient pb mobilization hadean 4 0 ga zircon grains provide the only direct record of the first half billion years of earth s history determining accurate and precise crystallization ages of these ancient zircons is a

unsupported radiogenic pb in zircon a cause of anomalously high pb pb u pb and th pb ages ion microprobe u th pb isotopic analyses of zircons from a granodioritic orthogneiss from the napier complex mount sones enderby land antarctica have identified an unambiguous example of unsupported radiogenic pb in a 3 950 ma old crystal at one 40 m spot on the crystal an unusually large heterogeneity in pb content was found the concentration of radiogenic pb ranging from 5 to 50 percent higher than could have been generated in 3 950 ma by radioactive decay of the co existing u and th this relative excess of radiogenic pb is attributed to pb gain rather than to u and th loss because first the pb content varied by more than the u or th contents and secondly changes in the pb u pb th and pb isotopic composition correlated directly with changes in the pb concentration the individual 207pb 206pb apparent ages ranged from 4 000 ma to 4 145 ma all greater than the inferred age of the crystal a correlation between 207pb 206pb and pb u shows that the pb excess has not resulted from recent pb movement the spot apparently gained radiogenic pb about 2 500 ma ago at the same time as the majority of the other zircons in the rock suffered substantial pb loss the pb movement occurred in response to a discrete geologic event reverse discordance is a phenomenon that must be considered when interpreting zircon u pb ages especially 207pb 206pb ages of single crystals or portions of crystals

hadean age for a post magma ocean zircon confirmed by atom probe tomography the only physical evidence from the earliest phases of earth s evolution comes from zircons ancient mineral grains that can be dated using the u th pb geochronometer 1 oxygen isotope ratios from such zircons have been used to infer when the hydrosphere and conditions habitable to life were established 2 3 chemical homogenization of earth s crust and the existence of a magma ocean have not been dated directly but must have occurred earlier 4 however the accuracy of the u pbzirconagescanplausiblybebiasedbypoorlyunderstood processes of intracrystalline pb mobility 5 7 here we use atomprobe tomography 8 to identify and map individual atoms in the oldest concordant grain from earth a 4 4 gyr old hadean zircon with a high temperature overgrowth that formed about 1gyrafterthemineral score isolatednanoclusters measuring about 10nm and spaced 10 50nm apart are enriched in incompatible elements including radiogenic pb with unusually high 207 pb 206 pbratios wedemonstratethatthelengthscales of these clusters make u pb age biasing impossible and that they formed during the later reheating event our tomography data thereby confirm that any mixing event of the silicate earth must have occurred before 4 4gyr ago consistent with

radiation damage in zircon and monazite monazite and zircon respond differently to ion irradiation and to thermal and irradiation enhanced annealing monazite cannot be amorphized by 800 kev kr ions at temperatures greater than 175 c whereas zircon can be amorphized at temperatures up to 740 c the damage process i e elastic interactions leading to amorphization in radioactive minerals metamictization is basically the same as for the ion beam irradiated samples with the exception of the dose rate which is much lower in the case of natural samples the crystalline to metamict transition in natural samples with different degrees of damage from almost fully crystalline to completely metamict is compared to the sequence of microstructures observed for ion beam irradiated monazite and zircon the damage accumulation process representing the competing effects of radiation induced structural disorder and subsequent annealing mechanisms irradiation enhanced and thermal occurs at much higher temperatures for zircon than for monazite the amorphization dose expressed as displacements per atom is considerably higher in the natural samples and the atomic scale process leading to metamictization appears to develop differently ion beam induced amorphization data were used to calculate the decay event dose required for amorphization in terms of a critical radionuclide concentration i e the concentration above which a sample of a given age will become metamict at a specific temperature this equation was applied to estimate the reliability of u pb ages to provide a qualitative estimate of the thermal history of high u natural zircons and to predict whether actinide bearing zircon or monazite nuclear waste forms will become amorphous metamict over long timescales

evidence for neoarchean ni cu bearing mafic intrusions along a major lithospheric structure a case study from the south rae craton canada abstract deformed and metamorphosed mafic to ultramafic intrusive rocks are common along and adjacent to the snowbird tectonic zone a major paleoproterozoic structure separating the rae and hearne cratons on the rae side of this major lithospheric structure we investigated a series of mafic bodies that intrude high grade paragneiss and are associated with ni cu pge mineralization by linking field observations geochronology and metamorphic petrology our results indicate archean 2 63 ga crystallization ages for these mafic intrusions over a minimum along strike extent of 500 km and a later high temperature 820 c and 7 5 kbar paleoproterozoic metamorphic overprint at t