rare earth thhfta and large ion lithophile element variations in metabasites from the proterozoic amphibolite granulite transition zone at arendal south norway abstract the proterozoic arendal metabasites are minor intrusions which possess wholly metamorphic textures and mineral assemblages data are presented for eight selected samples chondrite normalised ree patterns are relatively flat between 10 and 20 chondrite abundances they are characterised by 1 ce n yb n n nd n 1 normalised to primordial mantle values the incompatible elements reveal variable enrichment in the large ion lithophile elements except th and low ta they are similar to many destructive plate margin basalts on a th hf ta diagram the rocks plot in a sub linear trend reflecting variation in th hf samples with high th hf ratios come from the zone of highest metamorphic grade where the host gneisses are deficient in th consequently the patterns in the metabasites could not have been produced by any secondary metamorphic fractionation or by bulk contamination by the country rocks there is no evidence for any post magmatic mobility of any of the elements except rb which is depleted in the highest grade rocks relative to their lower grade counterparts the trace element distributions are largely reflecting those of the parental magmas but consideration of bulk distribution coefficients shows how they may have been modified in some aspects e g ce n nd n by the imposition of the metamorphic mineralogies the data are consistent with a model involving a derivation from a mantle source region which had been affected by subduction related hydrous metasomatism or partial melting and b crystallisation of the magmas directly under the high grade conditions

u and th zonation in fish canyon tuff zircons implications for a zircon u th he standard the inability to accurately determine the distribution of u and th in zircon crystals analysed using u th he is a major source of error and limits the confidence in subsequent data interpretation the fish canyon tuff fct zircon standard shows u th he age reproducibility in excess of 10 we have tested the extent to which this is due to u and th zonation using a combination of cathodoluminescence and ion probe analysis of a population of fct zircons primarily we find that fct zircons exhibit extreme u and th zonation and the population has large inter crystalline variability furthermore the net cathodoluminescence intensity from the fct zircons is negatively correlated with u and th concentration allowing cathodoluminescence emission to be used as a proxy for u and th zonation this correlation was exploited to constrain the u and th zonation within the crystal population and to show that the poor age reproducibility of the fct zircons is consistent with the observed zonation

environmental memory and a possible seasonal bias in the stable isotope composition of u th he dated goethite from the canadian arctic abstract goethite ax 2 from axel heiberg island 80 n on the margin of the arctic ocean is the dominant mineral in a sample of petrified eocene wood but u th and he measurements suggest that the goethite feooh crystallized in the latest miocene pliocene ca 5 5 to 2 8 ma measured d and 18 o values of ax 2 are 221 6 and 9 6 0 5 respectively the inferred d and 18 o values of the ancient water were about 139 and 18 6 respectively with a calculated temperature of crystallization of 3 5 c which compares with the modern summer j j a temperature of 3 c and contrasts with a modern mat of 19 c published results from various biological proxies on nearby ellesmere island indicate a pliocene 4 ma mat of either 6 or 0 4 c and corresponding seasonal amplitudes of about 18 or 13 c a conductive heat flow model suggests that a temperature of 3 c could represent goethite crystallization at depths of 100 200 cm for mat 6 c or 250 450 cm for mat 0 4 c over seasonally restricted intervals of time the 18 o value of the ax 2 water 18 6 is more positive than the modern j j a precipitation 22 in combination the paleotemperatures and 18 o values of ancient waters from ax 2 and published results from three eocene or pliocene proxy sites on axel heiberg and ellesmere islands are consistent with a warm season bias in those isotopic proxies the results are also consistent with higher proportions of j j a precipitation in the annual total if so this emphasizes the importance of seasonality at high latitudes even in times of warmer global climates and suggests that the arctic hydrologic cycle as expressed in the seasonal distribution and isotopic composition of precipitation perhaps modified by a warmer arctic ocean differed from modern the 13 c value of the fe co 3 oh component in the ax 2 goethite is 6 6 which is much more positive than expected if crystallizing goethite incorporated co 2 derived primarily from oxidation of relict eocene wood with 13 c values of about 24 this apparent paradox may be resolved if the goethite is a product of oxidation of 13 c rich siderite which had previously replaced wood in an eocene methanogenic burial environment thus the goethite retains a carbon isotope memory of a diagenetic eocene event but a d and 18 o record of the latest miocene pliocene arctic climate

formation of al rich titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2 abstract reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite facies metapelites and amphibolites namely the tamil nadu area southern india the val strona area of the ivrea verbano zone northern italy the bamble sector southern norway and the northwestern austroalpine otztal complex the titanite rims and hence the stability of titanite catisio4o and al oh titanite i e vuaganatite hypothetical end member caalsio4oh are discussed in the light of fh2o and fo2 buffered equilibria involving clinopyroxene amphibole biotite ilmenite magnetite and quartz in the systems cao feo fe2o3 tio2 sio2 h2o o2 cftsh and cao feo fe2o3 al2o3 sio2 h2o o2 cfash present in each of the examples textural evidence suggests that titanite reaction rims on ilmenite in rocks from tamil nadu val strona and the bamble sector originated most likely due to hydration reactions such as clinopyroxene ilmenite quartz h2o amphibole titanite and oxidation reactions such as amphibole ilmenite o2 titanite magnetite quartz h2o during amphibolite facies metamorphism or as in the case of the otztal complex during a subsequent greenschist facies overprint overstepping of these reactions requires fh2o and fo2 to be high for titanite formation which is also in accordance with equilibria involving al oh titanite this study shows that in addition to p t bulk rock composition and composition of the coexisting fluid fo2 and fh2o also play an important role in the formation of al bearing titanite during amphibolite and greenschist facies metamorphism

the sveconorwegian orogeny reamalgamation of the fragmented southwestern margin of fennoscandia abstract the sveconorwegian orogeny encompasses magmatic metamorphic and deformational events between ca 1140 and 920 ma at the southwestern margin of fennoscandia in recent years the tectonic setting of this nearly 200 myr long evolution has been debated with some workers arguing for collision with an unknown continent off the present day southwest coast of norway and others advocating accretionary processes inboard of an active margin recently it has been suggested that orogeny may have been gravity driven by delamination and foundering of heavy subcontinental lithospheric mantle in an intraplate setting in some ways similar to proposed sagduction processes in the archaean resolving the tectonic setting of the sveconorwegian orogen has implications for correlation with other orogens and rodinia supercontinent reconstructions and for assessments of the evolution of plate tectonics on earth from the archaean to the present here we present new mapping and geochronological data from the bamble and telemark lithotectonic units in the central and western sveconorwegian orogen the former representing a critical region separating western parts of the orogen that underwent long lived high to ultrahigh temperature metamorphism and magmatism from parts closer to the orogenic foreland that underwent episodic high pressure events the data show that the units constituting the sveconorwegian orogen most likely formed at the southwestern margin of fennoscandia between ca 1800 and 1480 ma followed by fragmentation during widespread extension between ca 1340 and 1100 ma marked by bimodal magmatism and sedimentation a summary of sveconorwegian magmatic metamorphic and depositional events in the different units shows disparate histories prior to their assembly with adjacent units the most likely interpretation of this record seems to be that episodic sveconorwegian metamorphic and deformational events in the central and eastern parts of the orogen represent accretion and assembly of these units this process most likely took place behind an active margin to the southwest that sustained mafic underplating in the proximal back arc resulting in high to ultrahigh temperature metamorphism in the western parts in this interpretation all features of the sveconorwegian orogen are readily explained by modern style plate tectonic processes and hypotheses involving some form of vertical intraplate tectonics are not supported

solving the production diffusion equation for finite diffusion domains of various shapes part 2 application to cases with alpha ejection and non homogeneous distribution of the source abstract in this paper numerical methods derived in part i chem geol 2002 are expanded to accommodate the effects of emission and zonation of u and th as relevant for u th he thermochronology expressions for the required coefficients are derived for spheres finite and infinite cylinders and rectangular blocks for parent nuclide distributions which are either uniform or have stepwise zoning we show that the effects of emission and zonation on the he retention in a nonspherical crystal of modest aspect ratio can be approximated by a sphere of identical surface to volume ratio s v if the zonation is transposed on to the sphere the currently usual correction method is to perform first a diffusive calculation without considering emission and zonation and to multiply afterward with a correction factor that has been derived originally for nondiffusive calculations our results demonstrate that more accurate calculations yield different results and that the differences are often too large to be ignored in practice especially for thermal histories that include a protracted residence in the partial retention zone the difference between the usual correction and our correction can be as high as 20 for homogeneous sources for zoned crystals the difference can be even larger

age relationships in the proterozoic high grade gneiss regions of southern norway reply to discussion and comment by weis and demaiffe

backstacking apatite fission track stratigraphy a method for resolving the erosional and isostatic rebound components of tectonic uplift histories measuring tectonic uplift of the mean surface of earth using thermochronological data to document uplift histories is often plagued by confusion arising from the independent nature of the thermal and sea level frames of reference the technique of backstacking apatite fission track stratigraphy differentiates between vertical movement of rocks toward earth9s surface due to erosional or tectonic denudation and tectonic uplift of earth9s surface apatite fission track analysis can also be used to identify episodes of erosion where no other evidence for the erosional event exists in addition to providing information about the timing magnitude and geographic distribution of erosion

anomalously low temperature orthopyroxene spinel and sapphirine occurrences in metasediments from the bamble amphibolite to granulite facies transition zone south norway possible evidence for localized action of saline fluids a reply the question has been raised whether isolated granulite facies islands which occur throughout the amphibolite facies of the regional amphibolite to granulite facies transition zone in the central part of the bamble sector southern norway are the result of prograde or retrograde metamorphism we have studied one of these islands the sapphirine granulites at hauglandsvatn despite the preponderance of amphibolite facies assemblages in the surrounding rocks and the small scale of distribution of the granulite facies assemblages the current assemblage is considered to be prograde and has developed at the expense of biotite in the regional main foliation leaving relict biotite separated from quartz by a continuous corona of orthopyroxene and k feldspar other high temperature low ah2o reactions resulted in the formation of spinel corundum albite oligoclase symplectites at the expense of biotite and sillimanite the symplectites have partially been replaced by symplectites of tiny blue sapphirine

what controls partial melting in migmatites the layers of six stromatic migmatites from northern western and central europe display small but systematic chemical and mineralogical differences at least five of these migmatites do not show any signs of largescale metamorphic differentiation metasomatism or segregation of melts it is concluded therefore that the compositional layering observed in most of the investigated migmatites is due to compositional differences inherited from the parent rocks almost isochemical partial melting seems to be the most probable process transforming layered paragneisses metavolcanics or schists into migmatites the formation of neosomes is believed to be caused by higher amounts of partial melts formed due to higher amounts of water moving into these layers the neosomes have less biotite and more k feldspar if k feldspar is present at all than the adjacent mesosomes these differences are small but systematic and seem to control the access of different amounts of water to the various rock portions petrographical observations chemical data and theoretical considerations indicate a close relationship between rock composition rock deformation transport of water partial melting and formation of layered migmatites

is apatite u th zonation information necessary for accurate interpretation of apatite u th he thermochronometry data abstract new u th and ce concentration maps were acquired by la icpms for 70 apatites from 18 cratonic basement samples from the canadian shield to characterize the nature and variability in apatite u th zonation all apatites are zoned in effective u concentration eu with 80 exhibiting modest zoning that varies from a factor of 1 2 to 2 4 zonation patterns include those with a general eu decrease from core to rim 25 a core to rim eu increase 35 and patchy or irregularly shaped eu distributions 40 most samples consist of individual apatites with markedly different and opposing eu profiles cathodoluminescence cl images were obtained for 258 apatites in 25 samples comparison of eu and cl patterns reveals no consistent relationships suggesting that cl is not a reliable proxy for apatite eu zonation we explore the implications of eu zonation for the interpretation of apatite u th he ahe data by comparing the age predictions for representative and endmember apatite eu profiles with those for unzoned apatites we focus on thermal histories that should magnify eu zonation effects including slow monotonic cooling extended he partial retention zone heprz residence and protracted reheating and cooling application of incorrect ejection correction f t factors different he concentration gradients and variable intracrystalline retentivity due to heterogeneous radiation damage may cause the ahe dates for zoned and unzoned apatites to differ in our dataset the magnitude of the f t effect is by simulating zoned apatite suites from representative and endmember samples we find that eu zoning adds modest age dispersion to most samples the commonly opposing eu profiles for individual apatites in most samples have different effects on the predicted age and partially cancel each other out to reduce the predicted age difference at the sample level higher predicted age differences between zoned and unzoned samples generally correlate with greater sample scatter the age deviations generally fall within the 15 uncertainty range that we commonly apply for sample ahe dates except in unusual circumstances it appears unlikely that the unzoned apatite assumption will lead to misinterpretation of ahe datasets thus precluding the need to routinely acquire apatite eu zonation information as part of ahe dating studies

thermal history of an early paleozoic epithermal deposit constraints from 40ar 39ar and u th he thermochronology at zhengguang eastern central asian orogenic belt abstract the zhengguang epithermal au zn deposit located in heilongjiang province ne china is an early paleozoic intermediate sulfidation epithermal deposit which is adjacent to the duobaoshan and tongshan porphyry cu deposits in the duobaoshan magmatic arc eastern central asian orogenic belt caob our new 40ar 39ar dating presents plateau ages of 276 9 1 2 ma mswd 1 5 for adularia and 265 7 1 2 ma mswd 3 5 for illite these ages are clearly younger than the mineralization age of zhengguang 480 ma and therefore represent a post ore event which reset the adularia and illite argon systems the resetting event could be related to post collision of xing an block and songliao xilinhot block the weighted mean of zircon u th he ages zhe and apatite u th he ages ahe from the same dacite porphyry with illite dating sample are 192 10 ma mswd 2 2 and 98 8 5 3 ma mswd 2 1 respectively the zhe age 190 ma indicates a tectonothermal resetting event possibly related to the development of tongshan fault whereas the ahe age 100 ma likely reflects 3 km deep burial at zhengguang the intra sample variations of u th he ages for zircon grains are mainly due to radiation damage while those for apatite are unknown we argue that the post ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the paleo pacific plate could facilitate burial and preservation of the epithermal and by inference porphyry deposits in ne china considering the complex collisional and amalgamation history in this area we believe that there is exploration potential for ancient porphyry and epithermal deposits within the eastern section of the caob

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

the influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic napperby gneiss central australia in the napperby gneiss central australia a distinctive group of elongate leucosomes occurs along the axial planes of mesoscopic crenulations that have harmonic two dimensional kink band like geometries the leucosomes truncate a fabric defined by biotite quartz k feldspar plagioclase sillimanite and are chiefly composed of k feldspar and quartz with or without plagioclase they are characterized by accessory garnet or aggregates of intergrown ilmenite and magnetite produced during the melting reactions bi plag q sill g ksp melt and bi plag q ru ilm mt ksp melt the absence of garnet and intergrown ilmenitemagnetite aggregates in the gneiss surrounding the crenulation zones indicates that these melting reactions preferentially occurred in the deformation zones in spite of a homogeneous distribution of reactant phases in the gneiss this means that strain partitioning and partial melting are coupled processes in which the garnet and ilmenite magnetite producing melt reactions initially occurred in high strain zones where the melting reaction activation energy was first overstepped this was a consequence of an additional strain induced matrix free energy component on top of the temperature effect once reaction product nucleation had occurred the deformation zones became the sites for continued melting which was energetically favoured over nucleating garnet and ilmenite magnetite elsewhere the melt reactions producing garnet and ilmenite magnetite resulted in the formation of grain supported leucosomes with a higher melt component than the surrounding gneiss and the leucosomes were therefore relatively incompetent in a differential stress field diffusional processes will cause elongation of the leucosome in a plane normal to 1 parallel to the axial planes of folds if sufficient melting has occurred an interconnected leucosome network will result creating a potentially important buoyancy driven melt drainage system in the napperby gneiss interconnected leucosome bearing crenulation zones are mostly vertical which is an ideal orientation for buoyancy driven diffusive melt migration however melt segregations remained small due to a melt impermeable lithological boundary overlying the gneiss

constraining the long term evolution of the slip rate for a major extensional fault system in the central aegean greece using thermochronology the brittle ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary in this study we examine the slip history of the large scale naxos paros extensional fault system npefs cyclades greece by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime based on apatite and zircon fission track aft and zft and u th he dating we observe variable slip rates across the brittle ductile transition on naxos zft and aft ages range from 11 8 0 8 to 9 7 0 8 ma and 11 2 1 6 to 8 2 1 2 ma and u th he zircon and apatite ages are between 10 4 0 4 to 9 2 0 3 ma and 10 7 1 0 to 8 9 0 6 ma respectively on paros zft and aft ages range from 13 1 1 4 ma to 11 1 1 0 ma and 12 7 2 8 ma to 10 5 2 0 ma while the u th he zircon ages are slightly younger between 8 3 0 4 ma and 9 8 0 3 ma all ages consistently decrease northwards in the direction of hanging wall transport most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of 6 8 km myr 1 on the npefs across the brittle ductile transition even the intrusion of a large granodiorite body into the narrowing fault zone at 12 ma on naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate the data also show that the npefs accomplished a minimum total offset of 50 km between 16 and 8 ma

precambrian multi stage crustal evolution in the bamble sector of south norway pb isotopic evidence from a sveconorwegian deep seated granitic intrusion abstract the precambrian ubergsmoen augen gneiss in the bamble sector of south norway is a dry syntectonic charnockitic intrusion which was emplaced at amphibolite to granulite facies conditions in the sveconorwegian orogeny 1120 ma the present day 206 pb 204 pb and 207 pb 204 pb ratios show restricted variation 206 pb 204 pb 17 566 17 938 207 pb 204 pb 15 459 15 590 in whole rocks and 206 pb 204 pb 17 159 17 350 207 pb 204 pb 15 451 15 487 in feldspar whereas the 208 pb 204 pb ratio has a wider range of variation in whole rocks 36 571 42 200 but not in feldspars 36 487 37 054 these values reflect a 238 u 204 pb of 2 6 since the sveconorwegian and a variable th u ratio 2 20 at the time of final u pb differentiation homogenization of the pb isotopes was imperfect the data therefore do not allow pb pb isochron dating but are well suited for model calculations the isotopic evolution of pb can be reproduced by a three stage model involving 1 a mantle stage ending at 1 9 1 6 ga 2 extraction of a crustal precursor at 1 9 1 6 ga and differentiation of a lile enriched component 14 22 and 3 anatexis igneous differentiation emplacement and subsequent metamorphism at 1 12 ga the granitic intrusion acquired its low u pb ratio by magmatic differentiation processes rather than by fluid induced u loss at high grade metamorphic conditions

helium irradiation study on zircon synthetic zrsio4 and mildly to strongly radiation damaged natural zircon samples were irradiated with 8 8 mev 4he2 ions fluences in the range 1 1013 5 1016 ions cm2 for comparison an additional irradiation experiment was done with 30 mev 16o6 ions fluence 1 1015 ions cm2 the light ion irradiation resulted in the generation of new synthetic zrsio4 or additional mildly to strongly metamict natural samples damage the maximum extent of the damage is observed in a shallow depth range approximately 32 33 m 8 8 mev he and 12 m 30 mev o below the sample surface i e near the end of the ion trajectories these depth values and the observed damage distribution correspond well to defect distribution patterns as predicted by monte carlo simulations the irradiation damage is recognised from the notable broadening of raman active vibrational modes lowered interference colours i e decreased birefringence and changes in the optical activity i e luminescence emission at very low damage levels a broad band yellow emission centre is generated whereas at elevated damage levels this centre is suppressed and samples experience a general decrease in their emission intensity most remarkably there is no indication of notable structural recovery in pre damaged natural zircon as induced by the light ion irradiation which questions the relevance of alpha assisted annealing of radiation damage in natural zircon

exhumation of the central wasatch mountains utah 2 thermokinematic model of exhumation erosion and thermochronometer interpretation 1 the wasatch fault is a 370 km long normal fault in utah that marks the boundary between the stable colorado plateau to the east and the extending basin and range to the west understanding the thermokinematic evolution of this fault can provide insights into intracontinental extensional tectonics and deformation processes in other rift zones e g east africa rift transantarctic mountains we explore the thermokinematics of footwall exhumation and erosion in the cottonwood intrusive belt of the central wasatch mountains emphasis is placed on using low temperature thermochronometers to quantify 1 the spatial and temporal variability of exhumation and erosion rates 2 the geometry of footwall tilt 3 the fault dip angle and 4 the magnitude and duration of exhumation these processes are investigated using two dimensional 2 d thermal kinematic models coupled with cooling rate dependent kinetic models which predict exhumed apatite fission track aft and u th he ages the range of model parameters considered includes footwall exhumation and erosion rates at the fault between 0 2 and 2 0 mm yr 1 footwall tilt hinge positions between 15 and 40 km distance from the fault a single planar normal fault with dip angles of 45 and 60 and exhumation magnitudes of up to 15 km at the fault simulations include the formation of a low thermal conductivity sedimentary basin and erosion of heat producing layers erosion maintains a constant topographic profile the kinematic and exhumation history of the wasatch mountains is investigated by comparing model predicted thermochronometer ages to observed aft zft and u th he ages predicted and observed ages are compared using a reduced chi square analysis to determine a best fit kinematic model for the wasatch mountains the preferred model includes exhumation occurring on either a 45 or 60 dipping fault a footwall hinge located a minimum of 20 25 km from the fault and a step decrease deceleration in the footwall exhumation rate at the fault from 1 2 to 0 8 mm yr 1 at around 5 ma the model also suggests an exhumation duration of 12 myr 2 myr index terms 1035 geochemistry geochronology 8010 structural geology fractures and faults 8015 structural geology local crustal structure 8109 tectonophysics continental tectonics extensional 0905 8130 tectonophysics heat generation and transport keywords exhumation erosion normal faults numerical modeling heat flow thermochronometers

episodes of dormancy and eruption of the late pleistocene ciomadul volcanic complex eastern carpathians romania constrained by zircon geochronology abstract ciomadul is the youngest volcanic system in the carpathian pannonian region recording eruptive activity from ca 1 ma to 30 ka based on combined zircon u th and u th he geochronology ciomadul volcanism is divided into two main eruptive periods old ciomadul 1 ma 300 ka ocep and young ciomadul eruptive period 160 30 ka ycep ocep activity comprises eruptive epochs 1 3 whereas new ages for eight lava domes and four pyroclastic units belonging to the ycep lead to its further subdivision into two eruptive epochs eruptive epochs 4 and 5 the extrusion of most of the lava domes occurred between 160 and 90 ka eruptive epoch 4 during three eruptive episodes at ca 155 ka 135 ka and 95 ka eruptive episodes 4 1 4 2 and 4 3 respectively along a ne sw lineament which is perpendicular to the regional nw se trend of the c limani gurghiu harghita volcanic chain eruptive epoch 5 occurred after a ca 40 kyr of quiescence at ca 55 30 ka and is mainly characterized by explosive eruptions with a minor lava dome building activity all of the dated pyroclastic outcrops together with the lava dome of piscul pietros belong to the older eruptive episode 5 1 with an eruption age of 55 45 ka the eruption centers of eruptive epoch 5 are located at the junction of the conjugated nw se and ne sw lineaments defined by the older eruptive centers the whole rock geochemistry of all studied samples is fairly homogeneous sio2 63 69 wt k2o 3 4 wt it also overlaps with the composition of the lava domes of the old ciomadul eruptive period implying a monotonous geochemical characteristic for the past 1 myr the eruption rates for the ciomadul volcanism were determined based on the erupted lava dome volume calculations supplemented with the eruption ages the activity peaked during the eruptive epoch 4 160 90 ka having an eruption rate of 0 1 km3 kyr in comparison these values are 0 05 km3 kyr for the ycep 160 30 ka and 0 01 km3 kyr for the overall ciomadul volcanism 1 ma 30 ka based on the geochemical characteristics the quiescence periods and the lifetime of the complex as well as the relatively small amount of erupted material this volcanic system can be placed in a subduction related post collisional geodynamic setting which shows strong chemical similarities to continental arc volcanism the commonly found long repose times between the active phases suggest that the nature of a volcano cannot be understood solely based on the elapsed time since the last eruption instead comprehensive geochronology coupled with the understanding of the magma storage behavior could be a base of hazard assessment for volcanic fields where the last eruptions occurred several 10 s of thousand years ago and therefore they are not considered as potentially active

post triassic multiple exhumation of the taihang mountains revealed via low t thermochronology implications for the paleo geomorphologic reconstruction of the north china craton abstract to better define the uplift and denudation process of the taihang mountains and its uplift subsidence coupling with the western bohai bay basin the zircon and apatite u th he thermochronology and apatite fission track thermochronology of samples from the taihang mountains trans north china orogen were examined in this study the weighted averages of single grain zircon and apatite u th he ages were 70 3 79 9 ma and 15 1 26 8 ma respectively the apatite fission track ages ranged from 41 8 ma to 51 9 ma with mean track lengths of 11 68 13 3 m three distinct episodes of cooling at 100 45 ma at 38 30 ma and after 20 ma revealed via joint inverse modeling were related to compression from the subduction of the kula plate during the late cretaceous the rapidly changing differential elevation and subsidence between the taihang mountains and the western bohai bay basin from the late eocene to early oligocene and the combined distant effects of the collision of the indian and eurasian plates and the rollback of the subducting pacific plate during late cenozoic respectively this paper presents the cooling histories of the shallow crust below 200 c in the taihang mountains and provides new insights into the geodynamic mechanism of the uplift events that occurred in the different areas of the north china craton understanding these events is very important to comprehend the differential uplift in the north china craton basin mountain coupling and its tectonic morphological evolution since the mesozoic

halogen geochemistry of fluid during amphibolite granulite metamorphism as indicated by apatite and hydrous silicates in basic rocks from the bamble sector south norway abstract the halogen chemistry of apatites biotites amphiboles and titanites from metabasites in the proterozoic bamble sector amphibolite granulite facies transition zone norway has been studied to gather data on the behaviour of halogens during original magmatism and subsequent metamorphism three groups of apatites could be recognized 1 f oh apatites with more than 50 mole f and virtually no cl 2 f oh apatites with up to 15 mole of cl 3 cl rich apatites with up to 6 73 wt cl the latter are the most cl rich metamorphic apatites ever reported the f contents of coexisting biotite do not follow this division but their cl contents do log z sfnc hf z sfnc h 2 o values for the coexisting fluid phase calculated from biotite are slightly lower than those calculated from apatite log z sfnc hcl z sfnc h 2 o values in the coexisting fluid phase calculated from biotite are substantially higher than those calculated from apatite the log z sfnc hf z sfnc h 2 o reflects the composition of the peak metamorphic fluid phase the apatites show three types of patterns of f contents 1 w shaped 2 rimward increasing and 3 rimward decreasing pattern 2 reflects progressive metamorphism pattern 3 is thought to reflect growth starting near peak metamorphism and going on during retrograde dilution of the peak metamorphic fluid by a newly introduced aqueous one some apatites show local resorption effects along cracks no regional trend in calculated log z sfnc hf z sfnc h 2 o values is present as different from other granulite terrains the bamble biotites and amphiboles from granulite facies samples do not have higher halogen contents as those from the amphibolite facies area the samples show that halogen bearing fluids were controlled at a very restricted scale during peak as well as retrograde metamorphism

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

diffusion of helium in zircon and apatite abstract diffusion of helium has been characterized in natural zircon and apatite polished slabs of zircon and apatite oriented either normal or parallel to c were implanted with 100 kev 3he at a dose of 5 1015 3 he cm2 diffusion experiments on implanted zircon and apatite were run in pt capsules in 1 atm furnaces 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in zircon we obtain the following arrhenius relations d c 2 3 10 7 exp 146 11 kj mol 1 r t m 2 s 1 d c 1 7 10 5 exp 148 17 kj mol 1 r t m 2 s 1 although activation energies for diffusion normal and parallel to c are comparable there is marked diffusional anisotropy with diffusion parallel to c nearly 2 orders of magnitude faster than transport normal to c these diffusivities bracket the range of values determined for he diffusion in zircon in bulk release experiments although the role of anisotropy could not be directly evaluated in those measurements in apatite the following arrhenius relation was obtained over the temperature range of 148 449 c for diffusion normal to c d 2 10 10 6 exp 117 6 kj mol 1 r t m 2 s 1 in contrast to zircon apatite shows little evidence of anisotropy he diffusivities obtained in this study fall about an order of magnitude lower than diffusivities measured through bulk release of he through step heating and within an order of magnitude of determinations where ion implantation was used to introduce helium and he distributions measured with elastic recoil detection since the diffusion of he in zircon exhibits such pronounced anisotropy helium diffusional loss and closure cannot be modeled with simple spherical geometries and the assumption of isotropic diffusion a finite element code cylmod has recently been created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients we present some applications of the code in evaluating helium lost from zircon grains as a function of grain size and length to diameter ratios and consider the effects of shape anisotropy where diffusion is isotropic as in the case of apatite but shapes of crystal grains or fragments may depart significantly from spherical geometry

sveconorwegian granulite facies metamorphism of polyphase migmatites and basic dikes south norway migmatites in the nelaug krossvatnet ubergsmoen area in the amphibolite facies part of the bamble sector were intruded by the ubergsmoen augen gneiss uag and by younger basic dikes both are critical time markers and show that the area underwent two phases of deformation and migmatization during the gothian orogeny 1600 1500 ma before emplacement of the augen gneiss and four subsequent phases of deformation during the sveconorwegian event 1200 950 ma accompanied by amphibolite facies metamorphism and a minor third migmatization mineral assemblages in the basic dikes and in the migmatites indicate local granulite facies conditions resulting from lowered ah 2 o at nearly constant temperature of approx 750 circ c at 8 7 kb it is suggested that this sveconorwegian granulite facies overprinting was due to the introduction of fluids released during the crystallization of another charnockitic magma at a deeper level

improved accuracy of zircon u th he ages by rectifying parent nuclide zonation with practical methods abstract a major limitation in the accuracy of zircon u th he thermochronometry zhe is the alpha ejection correction the standard alpha ejection correction f t assumes a homogeneous u th distribution in the host crystal here two approaches are used to address parent nuclide heterogeneity often observed in natural zircons 1 a new methodology where offending zonation is mechanically removed and 2 custom alpha ejection corrections informed by a la icp ms depth profile f zac we present an empirical test of these methodologies on a suite of bedrock zircons from variscan orthogneisses of the central aegean which display marked parent nuclide zonation which has impacted the ability to obtain accurate and precise thermochronometric data during the progressive mechanical abrasion of enriched u th and he zones the change in grain diameter exhibits a parabolic relationship with respect to the apparent age where the youngest age should represent the true age of the sample the abrasion corrected weighted mean age for sample 08pa01 is 8 8 0 7 ma f t 1 a too young age possibly the result of parent nuclide enriched cores the findings also show that using f zac instead of f t may change single sample zhe aliquots up to 29 using f zac increases the weighted mean age 17 for sample 08pa01 from 9 2 0 7 ma f t to 10 8 0 9 ma f zac and 6 for sample 08pa71 from 10 9 0 8 f t ma to 11 5 0 9 ma f zac in this case the f zac correction improves the overall accuracy of the zhe data but does not impact the problem of over dispersed ages suggesting they may be separate issues the increase in zhe age brings the dataset into agreement with previous thermochronometric studies indicating that cooling of the paros footwall below 180 c may have occurred earlier than hitherto thought

comparative oxygen barometry in granulites bamble sector se norway oxygen fugacities have been estimated for the high grade portion of the bamble granulite facies terrane se norway using both titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers the two oxygen barometers show good agreement for samples indicating high titaniferous magnetite ilmenite temperatures whereas agreement is poor for low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably lower than those estimated from orthopyroxene titaniferous magnetite quartz this discrepancy increases with a decrease in temperature which appears to reflect preferential resetting of the hematite content in the ilmenite grains without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains the mean temperature for the non reset samples 795 60 c 1 agrees well with temperatures obtained from garnet orthopyroxene k d exchange thermometry in the same region 785 60 c 1 most non reset o

rapid extension recorded by cooling age patterns and brittle deformation naxos greece the metamorphic core complex exposed as the island of naxos in the aegean sea records an unusually complete sequence of structures developed as a result of continental extension the structures formed during miocene rise and cooling from ductile upper amphibolite facies and anatectic conditions to brittle near surface conditions beneath the naxos detachment fault top to the north ductile fabrics in the footwall which initially developed during amphibolite facies prograde metamorphism were overprinted by a succession of north directed normal sense lower temperature brittle structures as the footwall was tectonically unloaded and unroofed pseudotachylite and cataclasite formation brittle faulting alteration and erosion of the footwall occurred during continued slip and tectonic denudation neogene conglomerate and megabreccia in part derived from exhumation of this footwall lie structurally above the peripheral naxos fault published k ar and 40ar 39ar ages for hornblende white mica and biotite in the footwall decrease northwestward apparent ages 17 50 ma in the southeast correspond to areas of low metamorphic grade where preextension argon was partially retained published ages 16 10 ma in higher grade rocks of the domal core in the north are cooling ages that for each of the three minerals show a component of younging in the nne direction of extension assuming this is the direction of unroofing we interpret the rate of this younging as the fault slip rate as the footwall rocks moved 20 km ssw relative to their hanging wall along the base of the naxos detachment fault the calculated rates of slip average 5 8 mm yr comparable to maximum rates reported in the basin and range province

zircon 4he 3he fractional loss step heating and characterization of parent nuclide distribution abstract the radiogenic ingrowth and diffusive loss of 4he in accessory minerals is used to determine the timing of low temperature thermal processes such as shallow tectonic magmatic hydrothermal and geomorphic events while the thermal history experienced by a sample cannot be directly constrained by a single u th he total gas age 4he concentration profiles normalized against irradiation induced spallogenic 3he have been shown to reliably recover continuous thermal history constraints if the parent nuclide distribution is either spatially uniform or can be determined as such 4he 3he thermochronometry has been successfully applied to apatite however individual zircon grains can contain complex parent nuclide zonation using moderately zoned euhedral zircon grains from the rapidly cooled distal fish canyon tuff we investigated the potential of the zircon 4he 3he thermochronometer through combining 4he 3he diode laser fractional loss step heating with detailed analysis of parent element zonation we present a routine method for the quantitative characterization of parent nuclide zonation by la icp ms depth profiling this study also demonstrates the importance of thermal control and avoidance of intra sample thermal gradients during laser step heating fractional loss experiments accurate and stable thermal control was achieved with an optimized sample holder design laser defocusing and pid control loops to minimize temperature overshoot failure to reach set point and temperature drop offs these analytical developments illustrate both the pitfalls and promise of zircon 4he 3he thermochronometry and create a reproducible methodology for 4he 3he thermochronometric applications to zoned and slowly cooled zircon

emplacement of polygeneration pegmatites in relation to sveco norwegian contractional tectonics examples from southern norway abstract recent studies have demonstrated that there is a strong link between sites of concentrated magmatism and crustal deformation zones magmatism is often described as being syn kinematic where one or more increments of intrusion punctuate deformation with successive generations of injections being progressively deformed pegmatite formation in the mesoproterozoic of south norway has been considered as post kinematic in nature relative to sveconorwegian grenvillian deformation 1 13 ga to 0 85 ga during accretion of the sw margin of baltica this paper presents structural observations from mapping of some pegmatites in the bamble terrane of south norway demonstrating that the pegmatites are structurally related to sveconorwegian fold geometries associated with peak metamorphism at approximately 1 14 ga and are kinematically related to overthrust geometries associated with the initial overthrusting phase of the porsgrunn kristiansand fault when the bamble terrane docked with the underlying telemark terrane local fold geometries suggest a strain regime where the maximum contractional axis is sub horizontal and oriented nw se consistent with the regional kinematics the pegmatites display a systematic deformation pattern consistent with deformation in the isoclinal fold limbs pegmatites are also deformed into asymmetric antiformal folds above reverse shear structures and are also cut by these structures thus showing a thrust geometry the undeformed pegmatites are emplaced in sub horizontal fractures and suggests sub horizontal contractional axis related to overthrusting which is identical to the strain regime of the folding the evidence suggests that the pegmatites are syn tectonic and were injected into reverse shear related fractures deformation was progressive and incremental with longer periods of ductile deformation at low strain rate punctuated by shorter periods of fracturing and pegmatite injection at high strain rate this work therefore implies an intimate spatial and temporal relationship between deformation and magmatism during crustal accretion on the western margin of fennoscandia

timing of exhumation wheeler pass thrust sheet southern nevada and california late jurassic to middle cretaceous evolution of the southern sevier fold and thrust belt zircon u th he zhe thermochronologic data for 46 samples from the wheeler pass thrust sheet which carries thick passive margin strata and is discontinuously exposed across the southern part of the sevier fold and thrust belt record late jurassic cooling related to exhumation during early thrust slip and local middle cretaceous cooling related to footwall basement imbrication within the frontal part of the wheeler pass sheet exposed in the northwest spring mountains zhe ages decrease from ca 160 to 140 ma over a paleodepth interval of 6 to 9 km in devonian to lower cambrian strata interpreted to record exhumation and enhanced cooling above a frontal ramp followed by slow cooling a similar pattern of zhe ages occurs over a more limited paleodepth range exposed within the resting spring range to the south in the nopah range zhe ages of ca 140 ma in lower cambrian strata record early cooling followed by slow cooling until ca 100 ma zhe ages in underlying paleoproterozoic basement rocks decrease from ca 100 to 85 ma over a paleodepth interval of 9 to 12 km interpreted to record uplift exhumation and cooling during footwall basement imbrication as slip was transferred eastward onto the keystone thrust system late jurassic slip on the wheeler pass thrust overlapped with deformation along the nw trending east sierran thrust system early hinterland crustal thickening and growth of the sierra magmatic arc and may have been correlative with early deformation in the central nevada thrust belt slip on the wheeler pass thrust preceded major slip on other thrust sheets that carried thick passive margin strata in more northern parts of the sevier belt probably reflecting the influence of different initial widths and tapers of the passive margin sedimentary wedge

radiation damage control on apatite u th he dates from the grand canyon region colorado plateau individual detrital apatite grains from the esplanade coconino and moenkopi formations in the grand canyon region of the colorado plateau yield u th he dates from 104 to 5 ma the range of dates within each unit far exceeds analytical uncertainty but correlates with both he concentration he and effective u concentration eu these dates are all signifi cantly younger than the sandstone units indicating partial to complete he loss following deposition recently published laboratory diffusion data suggest that he retentivity in apatite increases with radiation damage forward models predict that the consequences of this effect will be manifested most clearly as a correlation between u th he dates and the he and eu in suites of apatites that 1 are characterized by a large span of eu and 2 had thermal histories in which suffi cient time elapsed for the apatite he diffusion kinetics to diverge prior to reheating and partial resetting apatites in the sedimentary units investigated fi t these cri teria using geologically reasonable deposition burial and unroofi ng histories simulations that include the effect of radiation damage on apatite he retentivity can reproduce the observed distributions of apatite dates and correlations with parent and daughter concentrations these results suggest that a span of u th he dates positively correlated with eu may provide important information regarding a sample s thermal history

radiation damage and uranium concentration in zircon as assessed by raman spectroscopy and neutron irradiation radiation damage of natural and synthetic zircon grains is evaluated by raman spectroscopy to understand annealing and stability of fission tracks analyses focus on a suite of 338 paleozoic detrital zircon grains from metamorphosed strata in the hellenic forearc that were variably annealed by a miocene thermal event as well as a suite of 97 synthetic zircon grains the raman wavenumber shift of v 3 si0 4 reveals that radiation damage and damage distribution in this suite mainly depends on uranium concentration in zircon with similar uranium concentration the raman wavenumber shift allows for the determination of radiation damage in different crystals which is a function of effective accumulation time nine detrital zircons grains with moderate radiation damage were stepwise annealed at 1000 and 1400 c which resulted in progressive removal of radiation damage revealed in an increase of 3 si0 4 peak positions for a partly reset sample that was brought to temperatures of 350 c in a geologic setting hellenic forearc we use the raman measurements and uranium determination to estimate a zircon damage discrimination factor z rdd which is our attempt to estimate only radiation damage in single grains by accounting for affects of the uranium atom in the raman wavenumber this discrimination allows for a separation of zircon fission track zft ages of single ages based on grains that have a low track retention high damage fully reset grain thus refining the age determination of cooling in a rock that shows variable resetting

improving sparse network seismic location with bayesian kriging and teleseismically constrained calibration events monitoring the comprehensive nuclear test ban treaty will require improved seismic location capability for small magnitude events the international monitoring system ims is well suited to locate events that are large enough to be recorded at teleseismic distances however small events are likely to be recorded on a sparse subset of ims stations at regional to upper mantle distances less than 30 and sparse network locations can be strongly effected by travel time errors that result from path specific velocity model inaccuracies in an effort to improve sparse network location capability we outline a procedure that applies empirical corrections to travel times determined with an appropriate velocity model more specifically bayesian kriging and calibration events constrained with a global network are used to estimate epicenter specific travel time corrections for a test sparse network of stations we calculate travel time residuals for the calibration events relative to the ak135 velocity model travel time residuals are assigned to the respective calibration epicenter forming a set of spatially varying travel time correction points the spatial set of correction points is declustered to reduce the dimension of the observations with minimal reduction in accuracy of the travel time corrections we then use the declustered set of calibration points and bayesian kriging to form continuous travel time correction surfaces for each station of the test network the effectiveness of travel time correction surfaces is evaluated by locating with and without corrections a subset of the 1991 racha earthquake sequence caucasus mountains for which we have accurate locations that were independently determined with a dense local network when no travel time correction is applied the mean horizontal distance between the local and test network locations is 42 km and there is a distinct bias in sparse network locations toward the north northwest the mean difference between local and sparse network locations is cut to 13 km when corrections are applied and the bias in location is significantly reduced when calibration events in the racha vicinity are not used to make the correction surfaces there is still a significant improvement in location with mean mislocations of 15 km when corrections are not applied only one of the locally determined locations lies within the associated 90 coverage ellipse determined with the test sparse network however by using travel time corrections and estimates of model uncertainty determined using kriging representative error ellipses are obtained this study demonstrates that kriging correction surfaces based on global network constrained calibration events can improve the ability to accurately locate lower magnitude events while providing representative coverage ellipses

the influence of natural radiation damage on helium diffusion kinetics in apatite abstract stepwise degassing diffusion experiments on 39 different apatite samples using radiogenic 4he and proton induced 3he reveal a range in closure temperature tc from 50 to 115 c for a cooling rate of 10 c myr there is no correlation between helium diffusion and apatite chemistry including f cl ratio but the closure temperature is positively correlated with the radiogenic 4he concentration 4he in each sample we argue that 4he is a proxy for a sample s natural exposure to actinide radioactivity below the closure temperature and that helium diffusion in apatite is impeded by radiation induced damage to the apatite structure the kinetics must therefore be an evolving function of time measured diffusivities thus reflect a snapshot in time and cannot alone be applied to the thermochronometric interpretation of a given sample the effect of radiation damage on helium diffusion appears to far exceed other known controls on helium diffusivity including grain size our diffusion data are well described by a previously proposed quantitative model that consists of two arrhenius relations one for volume diffusion through undamaged mineral structure and one for release of helium from radiation damage traps the unknown parameters in this trapping model were determined from the diffusion experiments and allow us to develop a tentative mathematical function that relates diffusivity to temperature and 4he by inserting this function into a 4he production diffusion model we have explored how these results affect the interpretation of apatite u th he thermochronometry the model predicts that the effective 4he closure temperature of apatite will vary with cooling rate and effective u concentration eu and may differ from the commonly assumed tc of 70 c by up to 15 c the 4he partial retention zone will look similar to previous expectations but its depth will depend on accumulation time and on eu most notably samples subjected to reheating after accumulation of substantial radiation damage will be more retentive than previously expected these predictions are consistent with recent observations of unexpected apatite u th he ages in some settings

cenozoic exhumation of the ailaoshan red river shear zone new insights from low temperature thermochronology continental scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the ailaoshan red river shear zone asrrsz in the se tibetan plateau this study presents 13 apatite u th he 11 zircon u th he and three apatite fission track dates together with thermal modeling in the ailaoshan and xuelongshan segments alsz and xlsz of the shear zone to investigate its cenozoic exhumation history and mechanism which are critical for understanding its tectonic and landscape evolution our results combined with published chronologic data reveal that shear zone rocks along the alsz experienced prominent and rapid cooling from high temperature 500 c to 120 60 c at a rate of 75 100 c myr during 29 17 ma with northwestward younging onset a second lower magnitude accelerated cooling occurred at 14 10 ma along the alsz at a rate of 20 30 c myr with a later initiation on the xlsz at 5 ma and continuing to present with a cooling rate of 20 c myr thermal modeling reveals a single rapid cooling phase with a rate of 17 14 c myr in the eocene to early oligocene for samples outside the shear zones these three fast cooling episodes are directly related to deformation stages including crustal shortening across the se plateau sinistral ductile shearing along the asrrsz and dextral faulting with a dip slip component on the red river and weixi qiaohou faults along the shear zone flanks furthermore the northward migration of kinematic reversal and associated cooling along strike since the mid late miocene likely reflects the northward advance of the eastern himalayan syntaxis

incomplete retention of radiation damage in zircon from sri lanka a suite of 18 zircon gemstones from placers in the highland southwestern complex sri lanka were subjected to a comprehensive study of their radiation damages and ages the investigation included x ray diffraction raman and pl spectroscopy electron microprobe pixe and hrtem analysis as well as u th he and shrimp u th pb age determinations zircon samples described in this study are virtually homogeneous they cover the range from slightly metamict to nearly amorphous generally concordant u th pb ages averaging 555 11 ma were obtained late ordovician zircon u th he ages scattering around 443 9 ma correspond reasonably well with previously determined biotite rb sr ages for rocks from the hswc slightly to moderately metamict zircon has retained the radiogenic he whereas only strongly radiation damaged zircon calculated total fluences exceeding 3 5 10 18 events g has experienced significant he loss when compared to unannealed zircon from other localities sri lanka zircon is about half as metamict as would correspond to complete damage accumulation over a 555 m y lasting self irradiation period suggesting significant annealing of the structural radiation damage insufficient consideration of this has often resulted in significant underestimation of radiation effects in zircon we suggest to estimate effective doses for sri lanka zircon by multiplying total fluences which were calculated using the zircon u th pb age by a correction factor of 0 55 this conversion may be applied to literature data as well because all gem zircon samples from sri lanka this work and previous studies seem to reveal the same general trends of property changes depending on the radiation damage the use of effective doses for sri lanka zircon contributes to more reliable quantitative estimates of radiation effects and makes possible direct comparison between natural and synthetic radiation damaged zircon