constraints on early cenozoic underplating driven uplift and denudation of western scotland from low temperature thermochronometry apatite u th he and fission track data from profiles in western scotland constrain the timing and magnitude of denudation during the early cenozoic when the north atlantic region was the site of intense magmatic activity related to the proto icelandic plume apatite helium ages vary from 77 8 to 265 27 ma 2 at sgorr dhonuill ballachulish and from 104 10 ma to 166 17 ma at clisham outer hebrides at both locations apatite fission track aft ages are older than the corresponding he ages at clisham they vary from 189 28 ma to 242 26 ma and from 186 6 ma to 257 12 ma at sgorr dhonuill apatite he ages increase linearly with elevation suggesting that the cooling rate remained constant in the late mesozoic however the apatite he age profile requires a period of rapid cooling after 100 ma apatite he ages predicted from the aft derived thermal histories are indistinguishable from measured he ages for a rapid cooling event of 1 to 10 myr duration between 61 and 47 ma at sgorr dhonuill and 65 to 49 ma at clisham the combined apatite ft and he derived thermal histories constrain the early cenozoic geothermal gradient at 39 9 c km at sgorr dhonuill and 19 6 c km at clisham amounts of denudation related to the rapid cooling event vary from 1330 230 m at sgorr dhonuill to 2250 750 m at clisham in agreement with models that predict greater amounts of denudation where magmatic underplating is thicker however the direct correlation between underplating driven surface uplift and denudation may only be apparent and a more complex link between spatial variation of surface uplift and denudation is suggested the integration of results from multiple low temperature thermochronometers combined with inverse and forward modelling provides a convincing and quantitative method to deduce onshore erosional histories and provides critical information about the spatial distribution of erosion that cannot be derived from the offshore record

maturity of central madagascar s landscape low temperature thermochronological constraints abstract low temperature thermochronological data from two profiles across central madagascar give apatite fission track and apatite u th he ages ranging between 258 ma and 176 ma and from 239 ma to 48 ma respectively thermal models derived from these data as well as modelling of basement denudation and the sedimentary record indicate that first order topography of central madagascar developed mainly due to flexural uplift during mesozoic times this was in response to successive erosion and depositional loading associated with the sedimentation in the morondava and majunga basins both of which are now exposed along the western margin of madagascar our data suggest that the eastern margin of the island had a similar denudation history and was probably at a similar topographic level before the late cretaceous break up of madagascar and the india seychelles block cretaceous normal faulting without major amounts of denudation led to the development of the present east coast topography defined by a tectonically juvenile escarpment in the centre of the island cenozoic tectonics and volcanism has had a minor and localised influence on the landscape of central madagascar

ocean island densities and models of lithospheric flexure estimates of the effective elastic thickness te of the oceanic lithosphere based on gravity and bathymetric data from island loads are commonly significantly lower than those based on the wavelength of plate bending at subduction zones the anomalously low values for ocean islands have been attributed to the finite yield strength of the lithosphere to erosion of the mechanical boundary layer by mantle plumes to pre existing thermal stresses and to overprinting of old volcanic loads by younger ones a fifth possible contribution to the discrepancy is an incorrect assumption about the density of volcanic loads we suggest that load densities have been systematically overestimated in studies of lithospheric flexure potentially resulting in systematic underestimation of effective elastic thicknesses and overestimation of the effects of hotspot volcanism we illustrate the effect of underestimating load density with synthetic examples and an example from the marquesas islands this effect combined with the other effects listed above in many cases may obviate the need to invoke hotspot reheating to explain low apparent elastic thicknesses

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

incorporating 3 d parent nuclide zonation for apatite 4he 3he thermochronometry an example from the appalachian mountains the ability to constrain km scale exhumation with apatite 4he 3he thermochronometry is well established and the technique has been applied to a range of tectonic and geomorphic problems however multiple sources of uncertainty in specific crystal characteristics limit the applicability of the method especially when geologic problems require identifying small perturbations in a cooling path here we present new 4he 3he thermochronometric data from the appalachian mountains which indicate significant parent nuclide zonation in an apatite crystal using la icpms measurements of u and th in the same crystal we design a 3 d model of the crystal to explore the effects of intra crystal variability in radiation damage accumulation we describe a numerical approach to solve the 3 d production diffusion equation using our numerical model and a previously determined time temperature path for this part of the appalachians we find excellent agreement between predicted and observed 4he 3he spectra our results confirm this time temperature path and highlight that for complex u and th zonation patterns 3 d numerical models are required to infer an accurate time temperature history in addition our results provide independent and novel evidence for a radiation damage control on diffusivity the ability to exploit intra crystal differences in 4he diffusivity i e temperature sensitivity greatly increases the potential to infer complex thermal histories

thermal consequences of thrust faulting simultaneous versus successive fault activation and exhumation abstract when converting temperature time curves obtained from geochronology into the denudation history of an area variations in the isotherm geometry should not be neglected the geothermal gradient changes with depth due to heat production and evolves with time due to heat advection if the deformation rate is high furthermore lateral variations arise due to topographic effects ignoring these aspects can result in significant errors when estimating denudation rates we present a numerical model for the thermal response to thrust faulting which takes these features into account this kinematic two dimensional model is fully time dependent and includes the effects of alternating fault activation in the upper crust furthermore any denudation history can be imposed implying that erosion and rock uplift can be studied independently to each other the model is used to investigate the difference in thermal response between scenarios with simultaneous compressional faulting and erosion and scenarios with a time lag between rock uplift and denudation hereby we aim to contribute to the analysis of the mutual interaction between mountain growth and surface processes we show that rock uplift occurring before the onset of erosion might cause 10 to more than 50 of the total amount of cooling we applied the model to study the cenozoic development of the sierra de guadarrama in the spanish central system aiming to find the source of a cooling event in the pliocene in this region as shown by our modeling this temperature drop cannot be caused by erosion of a previously uplifted mountain chain the only scenarios giving results compatible with the observations are those incorporating active compressional deformation during the pliocene which is consistent with the ongoing nw se oriented convergence between africa and iberia

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

α emitting mineral inclusions in apatite their effect on u th he ages and how to reduce it u th rich mineral inclusions in apatite are often held responsible for erroneously old u th he ages because they produce parentless he three aspects associated with this problem are discussed here first simple dimensional considerations indicate that for small mineral inclusions the parentless helium problem might not be as serious as generally thought for example a mineral inclusion that is 10 the length width and height of its host apatite needs to be a thousand times more concentrated in u and th to produce an equal amount of he therefore single isolated inclusions smaller than a few m are unlikely to contribute significant helium for larger or more abundant inclusions the parentless helium problem can be solved by dissolution of the apatite and its inclusions in hot hf second besides creating parentless helium inclusions also complicate ejection corrections mathematical exploration of this latter problem for spherical geometries reveals that for randomly distributed inclusions the probability distribution of single grain ages is predicted to have a sharp mode at the mean age with tails towards younger and older ages multiple grain measurements will yield accurate and precise age estimates if 10 or more randomly distributed emitting mineral inclusions are present in a sample third thermal modeling indicates that mineral inclusions have a non trivial but minor 5 c effect on the closure temperature these predictions were tested on apatites from rapidly cooled migmatites of naxos greece which contain abundant u rich zircon inclusions thirty seven samples were subjected to two kinds of treatment the pooled age i e the synthetic multi grain age computed from a number of single grain analyses of four inclusion free samples 13 apatites prepared in hno3 is 10 9 ma close to apatite and zircon fission track ages from the same rock u th he ages of 14 inclusion bearing samples dissolved in hno3 range between 9 and 45 ma with a pooled age of 22 6 ma the ages of 19 hf treated samples range between 5 and 16 ma with 10 of 14 single grain samples between 9 and 13 ma and a pooled age of 10 9 ma these observations agree with the theoretical predictions and support the addition of hf treated apatite u th he dating to the thermochronological toolbox

combined apatite fission track and single grain apatite u th he ages from basement rocks of central dronning maud land east antarctica possible identification of thermally overprinted crustal segments abstract apatite fission track ft and single grain u th he ages from four vertical profiles in central dronning maud land east antarctica range from 312 20 ma to 135 11 ma and 304 28 ma to 104 8 ma respectively the combined age data allows to discriminate between undisturbed cooled due to exhumation and thermally overprinted crustal blocks profiles at the zwieselhohe and the conradgebirge revealed unusual apatite ft vs elevation relationships and u th he ages older than the corresponding central apatite ft ages possibly providing evidence for a jurassic thermal overprint most probably jurassic magmatism and associated advective heating led to total annealing of the apatite fission tracks but helium only partially diffused the model developed in this paper suggests that the u th he ages from the zwieselhohe and conradgebirge profiles are in part relicts of the pre jurassic cooling history two thermally undisturbed vertical profiles are used to record the long term cooling history of central dronning maud land time temperature paths derived from modelled apatite ft data of these profiles revealed two phases of accelerated cooling during the late carboniferous and the early jurassic both phases are followed by slow cooling which is also documented by the spread in apatite u th he single grain ages the cooling at the end of the carboniferous is most probably related to far field effects associated to the prevailing convergent tectonics during the initial separation between east antarctica and mozambique erosion along an evolving rift shoulder caused the jurassic cooling denudation of the basement was simultaneous with volcanism with both pre dating c 20 10 ma sea floor spreading in the riser larsen sea c 155 ma post jurassic cooling was restricted to the lowest temperature sensitivity of both methods combined inverse modelled apatite ft data and forward modelled u th he data suggest an eocene oligocene cooling step possibly related to the flexural isostatic response to the development of ice sheets

deciphering continental breakup in eastern australia using low temperature thermochronometers 1 first order topographical features at high elevation passive margins have the potential to store information about the early stages of continental rifting which are usually lost in the sediment record in this study we present a new combination of apatite fission track and u th he analyses from two coast perpendicular traverses to decipher the time of formation and evolution of the escarpment at the southeastern australian margin a combination of inverse and forward modeling of the apatite fission track aft and he data indicates that the coast experienced a rapid denudational event starting at 110 10 ma at least 15 myr before seafloor spreading 85 ma in agreement with the hypothesis that rifting at magma poor margins evolves slowly thus the enhanced denudation is not related to the synbreakup base level drop but it may have been related to a thermally driven transient surface uplift considerations on isostatic flexure and rigidity of the lithosphere indicate that unless significant synrift brittle movements are assumed to have occurred along margin parallel faults that are no more visible the coast must have experienced a higher geothermal gradient than normal the evolution of the rest of the coastal plain may have taken up to 90 myr in agreement with numerical models of passive margins evolution the u th he ages across the coastal plain are consistent with an in place excavation scenario of a high rift shoulder and they rule out the possibility of a constant retreat of the escarpment aft he data from the plateau indicate that the highlands remained stable throughout continental breakup experiencing rates of erosion of 5 10 m myr since at least 200 ma

tracking low temperature tectonism of the st lawrence platform and humber zone southern quebec appalachians through apatite and zircon u th he thermochronology the st lawrence platform slp and humber zone hz of the southern quebec appalachians have been the subject of extensive studies to resolve the degree of thermal maturation yet the timing of the thermal maximum is not well understood we have employed apatite ahe and zircon zhe u th he thermochronometry across a network of late cambrian to late ordovician siliciclastic and grenvillian basement outcrops to resolve the thermal history below 200 c single crystal dates from individual samples exhibit age dispersion by as much as 300 million years with a strong positive to negative correlation with increasing effective uranium eu concentration the data in the southwestern portion of the basin allow for thermal maxima of up to 200 c during the late ordovician or early devonian regional burial trends combined with local estimates of paleogeothermal gradients indicate that if sedimentation continued after the late ordovician there was no significant increase in burial in southwestern portions

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

low temperature thermal history and landscape development of the eastern adirondack mountains new york constraints from apatite fission track thermochronology and apatite u th he dating the adirondack mountains in northern new york state form an elongate domal exposure of mainly high grade metamor phic tectonites in a mountainous setting with topographic relief of 1 km the origin of the adirondack mountains and this relief has long been enigmatic since the adirondacks presently lie within an intracratonic setting inboard of the north american passive mar gin and far from any active plate boundaries through the application of apatite fi ssion track aft thermochronology and apatite u th he ahe dating within the eastern adirondack mountains this study provides constraints on both the thermal and ero sional effects of mesozoic passage near a hot spot and the timing of relief development aft thermochronology and ahe dating record relatively stable thermal conditions within the eastern adirondacks from the middle jurassic into the early cretaceous during the early cretaceous ca 130 120 ma the region underwent heating as sociated with progressive movement near the great meteor hotspot resulting in the temporary establishment of an elevated geo thermal gradient following regional heat ing cooling rates increased considerably ca 105 95 ma likely due to both thermal doming producing an increase in erosion rate and the relaxation of isotherms after passage near the hotspot the regional distribution of aft ages across the eastern adirondacks reveals no systematic age gradient from core to periph ery which would be expected under con ditions of persistent high relief during the decay of a crustal root over many tens to hun dreds of millions of years instead thermo chronological data suggest that the present relief developed during the late cretaceous cenozoic through plateau dissection during periodic base level changes

the thermal history of the western irish onshore we present here a low temperature thermochronological study that combines the apatite fission track and u th he dating methods with a pseudo vertical sampling approach to generate continuous and well constrained temperature time histories from the onshore irish atlantic margin the apatite fission track and u th he ages range from the late jurassic to early cretaceous and the mean track lengths are relatively short thermal histories derived from inverse modelling show that following post orogenic exhumation the sample profiles cooled to c 75 c a rapid cooling event to surface temperatures occurred during the late jurassic to early cretaceous and was diachronous from north to south it was most probably caused by c 2 5 km of rift shoulder related exhumation and can be temporally linked to the main stage of mesozoic rifting in the offshore basins a slow phase of reheating during the late cretaceous and early cenozoic is attributed to the deposition of a thick sedimentary sequence that resulted in c 1 5 km of burial our data imply a final pulse of exhumation in neogene times probably related to compression of the margin however it is possible that an early cenozoic cooling event compatible with our data but not seen in our inverse models accounts for part of the cenozoic exhumation supplementary material details on the apatite fission track and u th he methods are available at www geolsoc org uk sup18765

the exhumation history of collision related mineralizing systems in tibet insights from thermal studies of the sharang and yaguila deposits central lhasa abstract the large newly discovered sharang porphyry mo deposit and nearby yaguila skarn pb zn ag mo deposit reside in the central lhasa terrane northern gangdese metallogenic belt tibet multiple mineral chronometers zircon u pb sericite 40 ar 39 ar and zircon and apatite u th he reveal that ore forming porphyritic intrusions experienced rapid cooling 100 c ma during a monotonic magmatic hydrothermal evolution the magmatic hydrothermal ore forming event at sharang lasted 6 0 myr 1 8 myr for cooling from 900 to 350 c and 4 0 myr for cooling from 350 to 200 c whereas cooling was more prolonged during ore formation at yaguila 1 8 myr from 900 to 500 c and a maximum of 16 myr from 900 to 350 c all porphyritic intrusions in the ore district experienced exhumation at a rate of 0 07 0 09 mm yr apatite he ages between 37 and 30 ma combined with previous studies this work implies that uplift of the eastern section of the lhasa terrane expanded from central lhasa 37 30 ma to southern lhasa 15 12 ma at an increasing exhumation rate all available geochronologic data reveal that magmatic hydrothermal exhumation activities in the sharang yaguila ore district occurred within four periods of magmatism with related mineralization significant porphyry type mo mineralization was associated with late cretaceous eocene felsic porphyritic intrusions in the central lhasa terrane resulting from neotethyan oceanic subduction and india asia continental collision

u th he thermochronometry mapping 3d geometry using micro x ray tomography and solving the associated production diffusion equation u th he ages reflect the combined effects of he particles loss due to diffusion and he ingrowth due to radioactive decay of u and th series furthermore the particles are emitted with sufficient kinetic energy that they can travel in theory up to 20 m and as a result particles may be ejected beyond the crystal edges to circumvent this problem a correction factor must be applied which is essentially based on the geometry of the crystals farley k a wolf r and silver l 1996 the effect of long alpha stopping distances on u th he dates geochimica et cosmochimica acta 60 4223 4229 this strongly limits the application of the technique to crystals of appropriate geometries we present here a method to compute the effects of ejection for u th he dating by taking into account the 3d morphology of individual crystals determined with micro x ray tomography we also develop a model which solves the diffusion equation for the crystals that have been imaged we then couple this model with an inversion algorithm to extract the range of thermal histories that the rocks may have experienced this technique is applied to detrital samples from rocks collected in the southern alps of new zealand a region of high exhumation rate

accounting for long alpha particle stopping distances in u th sm he geochronology 3d modeling of diffusion zoning implantation and abrasion in apatite u th he thermochronology the helium distribution in a crystal is a function of the simultaneous processes of radiogenic production thermally activated volume diffusion and the ejection of he caused by long alpha stopping distances these processes are further complicated by zonation of u th and sm within the grain and implantation of 4he from neighboring u th sm bearing minerals we use a refined version of the 3d monte carlo diffusion code of gautheron and tassan got 2010 to simulate the interplay between ejection and diffusion with or without zonation ejection and abrasion for a suite of thermal histories we examine the phenomenon of over correction produced by the alpha ejection correction parameter ft or fzac for homogeneous or heterogeneous eu repartition by comparing the raw measured and ft or fzac corrected ages for a number of scenarios to the ejection free age aef which we define as the age that would be obtained if alpha ejection had not occurred or equivalently if the stopping distance was zero we show that the use of ft or fzac corrected ages generally reproduces the ejection free age to within typical u th he uncertainties 8 even for zoned apatites we then quantify the effect of alpha implantation on u th he ages showing that implantation from a single external source with modest relative u or th enrichment can generate as much as 50 excess he for more extreme cases where an apatite is surrounded by multiple external sources the measured age can be 300 of that determined from an isolated crystal while abrasion of the outer 20 25 m can significantly reduce the age dispersion for rapidly cooled samples slowly cooled samples can still retain 10 30 excess he the removal of the rim of the crystal reduces the thermal information from very low temperatures 40 c and introduces additional technical complications and biases and should therefore be used with caution overall we demonstrate that although zonation and implantation may not be routinely determined we now have the 3d modeling capability to fully investigate and constrain the causes of age dispersion within a sample leading to significant improvement in our ability to interpret u th he data

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

apatite u th he age constraints on the development of the great escarpment on the southeastern australian passive margin the southeast australian margin like other high elevation passive margins is characterised by a steep escarpment that separates a dissected coastal plain from a low relief inland plateau quantitative constraints on the generation of escarpments can be provided by apatite u th he ages here we use a coast perpendicular traverse across the coastal lowlands escarpment and plateau to test the three prevailing models of se australian escarpment formation namely retreat into a downwarped rift shoulder escarpment retreat and down wearing on high elevation rift shoulder with flexural rebound apatites from the coastal plain have he ages of between 87 and 112 ma suggesting that the coastal lowlands developed very rapidly after rifting and continental break up at 85 100 ma the he age data are inconsistent with the erosion of a downwarped rift margin and cannot be explained by a constant post break up rate of lateral escarpment retreat across the coastal plain or by constant down wearing the data require either rapid escarpment retreat or rapid in place excavation of the escarpment soon after break up in response to rifting and the lowering of base levels on the margin of the new continent at break up followed by a period of landscape stability and low erosion combined with the existing apatite fission track record the he data are consistent with erosion of 3 4 km within a maximum of 28 myr of break up at a minimum vertical erosion rate of 130 m myr 1 along the coast the rapid denudation period across the coastal plain in this region took less than 48 myr from the coast to the escarpment base which corresponds to an average vertical erosion rate of 45 m myr 1 this is equivalent to a mean escarpment retreat rate of 5 10 km myr 1 apatite he ages from the plateau 183 247 ma indicate that the highlands remained stable throughout continental break up experiencing average erosion rates of less than 10 m myr 1 since the late palaeozoic early mesozoic

quantifying exhumation at the giant pulang porphyry cu au deposit using u pb he dating the triassic pulang porphyry cu au deposit located in the south yidun terrane is the oldest and one of the largest porphyry deposits in the southeastern tibetan plateau the mineralization occurs mostly in the potassic alteration zone of the pulang intrusive complex u pb he triple dating namely apatite u th he zircon u pb and zircon u th he dating together with inverse thermal modeling reveals that the pulang complex was emplaced at a paleodepth of 5 0 to 6 5 km at 215 2 ma the deep level emplacement of the complex coupled with the episodic replenishment of the magma chamber gave rise to the establishment of a prolonged magmatic hydrothermal system at pulang although a range of single grain zircon and apatite u th he ages were obtained on each sample the weighted mean zircon and apatite u th he ages vary systematically with elevation defining a multistage cooling denudation history at pulang specifically three phases of cooling were recognized from inverse thermal modeling including rapid cooling 80 120 c m y in the late triassic moderate cooling 3 5 c m y from the late triassic to early cretaceous and a protracted slow cooling period 50 m y of extremely slow cooling and erosion at pulang could be related to the formation and preservation of a peneplain on the southeastern tibetan plateau since the late cretaceous a relict peneplain thus signifies a favorable tectonic environment for the preservation of ancient porphyry systems worldwide

spatial variation in the diversity and composition of the lower cambrian series 2 stage 3 chengjiang biota southwest china abstract strata hosting the lower cambrian series 2 stage 3 chengjiang biota maotianshan shale member yu anshan formation occur throughout the eastern part of yunnan province southwest china in this study literature based faunal inventories from 10 areas representing 34 localities together with 22 038 new specimens collected at three localities from three of the 10 areas were analyzed quantitatively to assess large scale spatial variation in taxonomic diversity and composition our analyses show substantial co variation between local paleoenvironmental settings and species diversity and suggest the presence of three general taphofacies in the maotianshan shale member from west to east low diversity 26 species characterizes the wuding area where fossiliferous strata have undergone extensive bioturbation high diversity 215 species characterizes the chengjiang haikou anning areas where fossiliferous strata consist of stacked couplets of thin event and background mudstone layers moderate diversity 55 species characterizes the malong area where fossiliferous strata consist of indistinctly bedded shale showing fewer single event layers but abundant background layers in spite of variations in sampling effort between sites spatial patterns in species diversity and community composition were controlled primarily by variation in depositional environments along a proximal offshore to lower shoreface gradient which influenced both ecological and taphonomic factors the offshore settings haikou chengjiang anning areas show relatively high species diversity and exceptional preservation of soft bodied fossils reflecting rapid burial in distal tempestites relatively high degrees of bioturbation time averaging and hydrodynamic disturbance caused a substantial decrease in the quality of preservation and number of soft bodied species in the wuding and malong areas arthropods are the most diverse group in most localities followed by priapulids poriferans brachiopods lobopods and hyoliths this study shows that the chengjiang biota lends itself very well to high resolution characterization of spatial variation in taxonomic diversity faunal composition and fossil preservation furthermore the chengjiang biota may provide a unique opportunity to assess the roles of environmental factors taphonomy and ecological controls on species diversity at local to regional spatial scales

dating constituent formation in soils to determine rates of soil processes a review abstract rates of soil processes are poorly known one approach to determine them could be through the radiogenic isotopic dating of soil constituents such methods have been recently used to date minerals in soils and weathering profiles thanks to the development of high resolution techniques such as 40ar 39ar u series of micro drilled samples u series by laser ablation and u th he and to the development of suitable methodology expanding application of the techniques to a variety of supergene minerals e g fe and mn oxihydroxides carbonates etc in this paper we identify i the main soil constituents that can be dated through these isotopic methods that are mainly fe oxides mn oxides pedogenic carbonates and organic matter ii the main pedogenic processes that leads to their formation in soils and iii the different soil settings that allow transforming soil constituent ages into rates of soil processes namely growth bands transformation fronts and chronosequences

helium diffusion in rutile and titanite and consideration of the origin and implications of diffusional anisotropy abstract diffusion of helium has been characterized in natural sphene titanite and synthetic rutile polished slabs of sphene and rutile were implanted with 100 kev 3he at a dose of 5 1015 3he cm2 and annealed in 1 atm furnaces 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in rutile we obtain the following arrhenius relations d a 2 26 1 0 1 0 exp 126 11 kj mol 1 rt m 2 sec 1 d c 1 75 1 0 8 exp 12 0 7 kj mol 1 rt m 2 sec 1 although activation energies for diffusion parallel to the c and a axes are comparable there is marked diffusional anisotropy with diffusion parallel to the c axis about 2 orders of magnitude faster than transport parallel to the a axis these diffusivities bracket the values determined for he diffusion in rutile in bulk release experiments stockli et al 2005 stockli et al 2007 wolfe 2009 although the role of anisotropy could not be directly evaluated in those measurements in titanite the following arrhenius relation was obtained over the temperature range 252 550 c for diffusion parallel to the a axis d 2 14 1 0 6 exp 148 8 kj mol 1 rt m 2 sec 1 in contrast to rutile and zircon cherniak et al 2009 titanite shows little evidence of anisotropy as diffusivities parallel to the a and c axes are similar and diffusivities for titanites from two different localities are similar he diffusion coefficients obtained in this study are similar to those measured through bulk release of he by step heating shuster et al 2003 over the investigated temperature range diffusion of he in titanite is similar to that of he diffusion in rutile parallel to the c axis but much faster than diffusion parallel to the a axis since the diffusion of he in rutile exhibits such pronounced anisotropy we model diffusional loss of he with a recently developed finite element code watson et al 2010 created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients we present example applications to evaluate helium losses from rutile grains as a function of grain size and length to diameter ratios in efforts to better understand the occurrence of pronounced anisotropy for he diffusion in some crystals e g rutile zircon but not in others e g apatite titanite we consider the density and distribution of interstitial apertures in the crystal structure that might permit he migration these determinations an extension of the concept of ionic porosity are consistent with observations of relative diffusivities and the existence or absence of significant anisotropy for the minerals rutile zircon apatite and titanite

an evaluation of low temperature apatite uth he thermochronometry abstract three studies have been conducted to test the usefulness of apatite u th he thermochronometry the first study compared u th he and fission track ages from quickly cooled plutonic rocks having concordant zircon and apatite fission track ages several samples analyzed show good helium retention the second experiment assessed the effect of compositional variations in apatite on closure temperature calculated closure temperatures agree with existing data and show no statistical dependence on composition arrhenius plots for all of the samples show linear trends at low temperatures representing volume diffusion that roll over to more shallowly sloping non linear paths at higher temperatures the roll over temperature appears to increase with increasing cl content in the apatite the third test focused on fluorapatites from the ktb borehole in germany to compare laboratory estimates with diffusion behavior in a natural setting the ktb apatites show a fair amount of scatter and record u th he ages that are younger than or equal to apatite fission track ages indicating a closure temperature less than or equal to that for the apatite fission track method closure temperatures predicted from the scattered data range from 80 120 c 1 c ma cooling rate or 95 135 c 10 c ma cooling rate the low end of this range agrees with our laboratory diffusion estimates for fluorapatite

post breakup tectonics in southeast brazil from thermochronological data and combined inverse forward thermal history modeling the continental margin of southeast brazil is elevated onshore tertiary basins and late cretaceous paleogene intrusions are good evidence for post breakup tectono magmatic activity to constrain the impact of post rift reactivation on the geological history of the area we carried out a new thermochronological study apatite fission track ages range from 60 7 1 9 ma to 129 3 4 3 ma mean track lengths from 11 41 0 23 mm to 14 31 0 24 mm and a subset of the u th he ages range from 45 1 1 5 to 122 4 2 5 ma results of inverse thermal history modeling generally support the conclusions from an earlier study for a late cretaceous phase of cooling around the onshore taubate basin for a limited number of samples the first detectable period of cooling occurred during the early tertiary the inferred thermal histories for many samples also imply subsequent reheating followed by neogene cooling given the uncertainty of the inversion results we did deterministic forward modeling to assess the range of possibilities of this tertiary part of the thermal history the evidence for reheating seems to be robust around the taubate basin but elsewhere the data cannot discriminate between this and a less complex thermal history however forward modeling results and geological information support the conclusion that the whole area underwent cooling during the neogene the synchronicity of the cooling phases with andean tectonics and those in ne brazil leads us to assume a plate wide compressional stress that reactivated inherited structures the present day topographic relief of the margin reflects a contribution from post breakup reactivation and uplift

natural age dispersion arising from the analysis of broken crystals part i theoretical basis and implications for the apatite u th he thermochronometer abstract over the last decade major progress has been made in developing both the theoretical and practical aspects of apatite u th he thermochronometry and it is now standard practice and generally seen as best practice to analyse single grain aliquots these individual prismatic crystals are often broken and are fragments of larger crystals that have broken during mineral separation along the weak basal cleavage in apatite this is clearly indicated by the common occurrence of only 1 or no clear crystal terminations present on separated apatite grains and evidence of freshly broken ends when grains are viewed using a scanning electron microscope this matters because if the 4 he distribution within the whole grain is not homogeneous because of partial loss due to thermal diffusion for example then the fragments will all yield ages different from each other and from the whole grain age here we use a numerical model with a finite cylinder geometry to approximate 4 he ingrowth and thermal diffusion within hexagonal prismatic apatite crystals this is used to quantify the amount and patterns of inherent natural age dispersion that arises from analysing broken crystals a series of systematic numerical experiments were conducted to explore and quantify the pattern and behaviour of this source of dispersion using a set of 5 simple thermal histories that represent a range of plausible geological scenarios in addition some more complex numerical experiments were run to investigate the pattern and behaviour of grain dispersion seen in several real data sets the results indicate that natural dispersion of a set of single fragment ages defined as the range divided by the mean arising from fragmentation alone varies from c 7 even for rapid c 10 c ma monotonic cooling to over 50 for protracted complex histories that cause significant diffusional loss of 4 he the magnitude of dispersion arising from fragmentation scales with the grain cylindrical radius and is of a similar magnitude to dispersion expected from differences in absolute grain size alone spherical equivalent radii of 40 150 m this source of dispersion is significant compared with typical analytical uncertainties on individual grain analyses c 6 and standard deviations on multiple grain analyses from a single sample c 10 20 where there is a significant difference in the u and th concentration of individual grains eu the effect of radiation damage accumulation on 4 he diffusivity assessed using the rdaam model of flowers et al 2009 is the primary cause of dispersion for samples that have experienced a protracted thermal history and can cause dispersion in excess of 100 for realistic ranges of eu concentration i e 5 100 ppm expected natural dispersion arising from the combined effects of reasonable variations in grain size radii 40 125 m eu concentration 5 150 ppm and fragmentation would typically exceed 100 for complex thermal histories in addition to adding a significant component of natural dispersion to analyses the effect of fragmentation also acts to decouple and corrupt expected correlations between grain ages and absolute grain size and to a lesser extent between grain age and effective uranium concentration eu considering fragmentation explicitly as a source of dispersion and analysing how the different sources of natural dispersion all interact with each other provides a quantitative framework for understanding patterns of dispersion that otherwise appear chaotic an important outcome of these numerical experiments is that they demonstrate that the pattern of age dispersion arising from fragmentation mimics the pattern of 4 he distribution within the whole grains thus providing an important source of information about the thermal history of the sample we suggest that if the primary focus of a study is to extract the thermal history information from u th he analyses then sampling and analytical strategies should aim to maximise the natural dispersion of grain ages not minimise it and should aim to analyse circa 20 30 grains from each sample the key observations and conclusions drawn here are directly applicable to other thermochronometers such as the apatite rutile and titanite u pb systems where the diffusion domain is approximated by the physical grain size

forward modeling and interpretation of u th he ages soon after the initial studies on he diffusion in apatite pointed out the use of the u th he system for low temperature geochronology zeitler et al 1987 wolf et al 1996 warnock et al 1997 the potential value of forward modeling for refined interpretation of u th he dating was indicated wolf et al 1998 while the first studies provided evidence for the low closure temperature t c dodson 1973 of the u th he system in apatite for monotonously cooling systems the latter study investigated the sensitivity of the u th he system for a wide range of geologically feasible heating cooling scenarios forward modeling of he accumulation in minerals expanded the use of the u th he geochromometer to geological systems that do not fit one of the main conditions for the meaningful application of the closure temperature concept i e monotonous cooling at a constant rate through t c forward modeling can help to give a meaning to apparent u th he ages from rocks with cooling histories with protracted residence time in the helium partial retention zone heprz e g 40 85 c in apatite wolf et al 1998 where the closure temperature is undefined fig 1 figure 1 apatite he age evolution curves dotted lines for several representative time temperature paths solid lines forward modelling was conducted using the crank nicolson method for spheres of 60 m radius note that only for history 2 the closure temperature concept dodson 1973 is defined and the age obtained relates to passing through a point t c on the time temperature path for histories that are similar to 3 5 which know a protracted residence time in the heprz there is no direct geological meaning of he ages forward modelling is required to give a geological meaning to the apparent ages obtained from he and u th concentrations in samples used with permission of elsevier from wolf

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

using gis to study palaeobiogeographic and macroevolutionary patterns in soft bodied cambrian arthropods abstract soft bodied cambrian arthropods from burgess shale type deposits are some of the most famous and extensively studied fossil invertebrates but global species level assessments of their biogeographic patterns have not previously been explored quantitatively here we use a newly developed occurrence database in conjunction with geographic information systems gis analysis and paleogis which allows fossil locality positions to be viewed in the context of cambrian palaeogeography to quantitatively reconstruct geographic distribution patterns of primarily soft bodied arthropod species further we compare these patterns with those of co occurring trilobite taxa soft bodied cambrian arthropods show both statistically larger geographic ranges and greater stratigraphic longevities than co occurring trilobites many of the most widely distributed soft bodied arthropods were likely capable of swimming and this may in part explain their extensive distributions

from orogen to passive margin constraints from fission track and u th he analyses on mesozoic uplift and fault reactivation in sw norway the post caledonian tectonic history and landscape evolution of southwestern norway are poorly understood primarily owing to the lack of onshore post devonian sediments to bridge this knowledge gap low temperature thermochronological techniques were applied to investigate vertical movements in the upper crust new apatite fission track and apatite and zircon u th he analyses on samples from southwestern norway yielded permian to jurassic triassic to cretac eous and carboniferous to triassic ages respectively thermal history modelling indicates rela tively high cooling rates 2 3 8 cm a 21 throughout permian to early jurassic times since the jurassic samples from coastal areas have remained close to the surface and were reheated to 30 50 8c during sedimentary burial in the cretaceous inland samples experienced lesser amounts of permo triassic exhumation continued to cool slowly 1 8 cm a 21 throughout the jurassic cretaceous and did not reach the surface until the cenozoic both fission track and u th he ages are offset across faults highlighting the importance of fault activity throughout the mesozoic in combination with previously published results the new data suggest that the geo morphological evolution of southwestern norway is closely connected to rift and post rift tec tonics related to north sea and north atlantic rifting the topographic relief was most likely repeatedly rejuvenated during periods of tectonic activity

an empirical test of helium diffusion in apatite borehole data from the otway basin australia we have analyzed helium ages of apatites from several boreholes in the otway basin australia to evaluate whether laboratory helium diffusivity can be accurately extrapolated to conditions relevant in nature downhole apatite helium ages define a broad swath of values from 78 71 ma at the surface 15 c to nearly zero at depths corresponding to ambient temperatures of 80 c the width of the swath results from uncertainties in corrected borehole temperatures differences in the thermal history experienced by the various boreholes and possibly from slightly different helium diffusivities among the detrital apatite grains studied in the eastern otway basin the shape and position of the helium age profile is in good agreement with predictions based on the extrapolation of laboratory diffusivity data for durango apatite coupled with published thermal histories for this part of the basin in contrast helium ages are much younger than predicted in the western otway basin based on measured ages from otway sediments which have been essentially isothermal over the last few million years an empirical diffusivity d 2 of 2 10 15 s 1 can be assigned to apatites residing at downhole temperatures of 67 97 c this empirical diffusivity is consistent with laboratory diffusion measurements demonstrating that such measurements are reasonably accurate and can be applied with confidence to natural geologic settings given this confirmation of the laboratory diffusivity data the discrepancy between the observed and modeled helium age profiles in the western otway basin suggests that these sediments recently experienced higher temperatures than presently supposed

the lower ordovician fezouata konservat lagerstatte from morocco age environment and evolutionary perspectives abstract the lower ordovician fezouata konservat lagerstatte from southern morocco has been one of the major palaeontological discoveries of the last decade it provides a unique insight into one of the most critical periods in the evolution of marine life the cambrian ordovician transition however its potential for deciphering key trends in animal diversification was hitherto largely limited by major uncertainties concerning its stratigraphic position age and environmental setting based on extensive fieldwork fossil evidence and facies recognition our study provides clarification on these three crucial issues exceptional preservation is limited to two intervals within the fezouata shale graptolites indicate a late tremadocian age for the fezouata konservat lagerstatte as a whole which is supported by biostratigraphical evidence provided by acritarchs sedimentological features and reconstructed patterns of relative sea level changes indicate relatively shallow water environmental conditions under distal storm influence in an offshore to lower shoreface siliciclastic ramp setting the fezouata biota represents a unique and exceptional window into the palaeobiodiversity in open marine conditions thus contrasting with the other ordovician konservat lagerstatten presently known in our analyses of this new set of data we pave the way for accurate temporal faunal and environmental comparisons with other lower palaeozoic konservat lagerstatten and unlock the full potential of the fezouata biota to better understand the processes and scenarios of early animal radiations

low temperature thermochronology of the southern east greenland continental margin evidence from apatite u th he and fission track analysis and implications for intermethod calibration abstract the southern coast of east greenland is characterized by high topographic relief and deep fjords but the evolution of the landscape and the low temperature thermochronology of the region is not well understood here we present apatite fission track and u th he ages that suggest several important features of the long term geomorphic history of this region but which also illustrate an important discrepancy in the thermal histories derived from each technique apatite from bedrock of the southern coast of east greenland between 62 n and 67 n has fission track ages ranging from 60 to 840 ma and u th he ages ranging from 21 to 250 ma the ages generally increase with elevation and distance from the coast and fission track analyses show significant differences in thermal histories for the different regions in the kangertittivatsiaq area c 66 67 n apatite fission track data and models suggest two separate periods of slow cooling prior to c 200 ma and between c 160 ma and the late cenozoic more recently than c 20 ma each of which was followed by a period of rapid cooling and inferred exhumation apatite he data in the kangertittivatsiaq region including crystal size age correlations in low elevation samples are most simply interpreted as recording an incision event of at least 1 5 km later than 20 ma near the coast this may have been caused by glacial erosion the u th he data also indicate an earlier phase of rapid exhumation at c 250 ma in the skjoldungen kap mosting area c 62 64 n approximately 200 km south of the kangertittivatsiaq apatite fission track data suggest slow exhumation from c 200 ma into the neogene followed by fast exhumation the similarity of fission track ages 200 ma at sea level in the fjords in the skjoldungen area c 62 64 n do not suggest tilting in the hinterland related to the breakup of the east greenland continental margin furthermore the cenozoic fission track ages and modeling fission track data suggest that pre breakup basins may have covered the outer coast despite the broadly similar topographic implications of the fission track and u th he data the thermal histories derived from these systems are inconsistent fission track data require thermal histories that predict he ages younger than observed and he data require thermal histories that predict fission track ages older than observed similar discrepancies have also been observed in other settings characterized by long term low temperature thermal histories and may reflect changes in annealing or diffusion behavior or both that either develop or become more apparent in such cases

conflicting u th he and fission track ages in apatite enhanced he retention not anomalous annealing behaviour while initial studies showed a high degree of consistency between afta and apatite u th he dating an increasing number of studies are reporting apatite u th he ages which are older than expected on the basis of apatite fission track data from the same region we present data from a range of geological settings to document a systematic discrepancy between the two systems which becomes more pronounced in samples with older fission track ages except for samples with very low uranium contents results from a granite pebble and enclosing volcanogenic sandstone provide a well controlled test case in which independent constraints are available on the underlying thermal history these demonstrate that the progressive discrepancy between the two techniques arises not from anomalous fission track annealing behaviour as has been suggested but as a result of a change in the he retention properties of apatite this change appears to be linked to the degree of accumulated radiation damage within the crystal lattice although underlying mechanisms remain unclear we suggest detailed experiments should be performed to delineate and quantify the processes responsible until this is achieved we suggest that apatite u th he studies should also incorporate apatite fission track data as well as other low temperature indicators in order to monitor the u th he system response and to guard against the anomalous behaviour described here

the emu bay shale konservat lagerstatte a view of cambrian life from east gondwana recent fossil discoveries from the lower cambrian emu bay shale ebs on kangaroo island south australia have provided critical insights into the tempo of the cambrian explosion of animals such as the origin and seemingly rapid evolution of arthropod compound eyes as well as extending the geographical ranges of several groups to the east gondwanan margin supporting close faunal affinities with south china the ebs also holds great potential for broadening knowledge on taphonomic pathways involved in the exceptional preservation of fossils in cambrian konservat lagerstatten ebs fossils display a range of taphonomic modes for a variety of soft tissues especially phosphatization and pyritization in some cases recording a level of anatomical detail that is absent from most cambrian konservat lagerstatten

role of topography in isotherm perturbation apatite u th he and fission track results from the malta tunnel tauern window austria 1 apatite u th he and fission track age determinations of samples from a 20 km long near horizontal tunnel in the hochalm ankogel dome eastern tauern window austria are presented in order to determine the role of paleo topography in perturbing isotherms in the shallow crust apatite fission track ages 26 8 ma show no systematic correlation with distance along the tunnel or elevation two age components in the fission track data indicate cooling through 120 c at approximately 20 ma and 80 c at approximately 6 ma surface and tunnel u th he ages 17 9 ma and 13 5 ma respectively are consistently younger than the equivalent fission track ages u th he ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section geological factors faulting lithology appear to have had little effect on this age distribution the u th he age pattern is inconsistent with rock cooling underneath the present day hochalm ankogel dome topography the age minimum is interpreted to coincide with a paleotopographic maximum in the hochalm ankogel dome and suggests that the 40 60 c isotherms were warped sufficiently to affect apatite u th he ages the tunnel apatite u th he ages match synthetic he ages derived from a two dimensional numerical model of landscape evolution integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present day hochalm ankogel dome topography was formed at 7 to 10 ma

low temperature thermal evolution of the azov massif ukrainian shield ukraine implications for interpreting u th he and fission track ages from cratons abstract the low temperature thermal evolution of the azov massif eastern part of the ukrainian shield ukraine is investigated by combined zircon fission track zft apatite fission track aft and apatite u th he ahe thermochronology the data help to better understand the geodynamic evolution of the azov massif and the adjacent intra cratonic rift basin dniepr donets basin as follows zft data reveal that the precambrian crystalline basement of the azov massif was heated to temperatures close to 240 c during the late palaeozoic the heating event is interpreted in terms of burial of the basement beneath a several kilometres thick pile of devonian and carboniferous sedimentary deposits of the adjacent dniepr donets basin during permo triassic times large parts of the basement were affected by a thermal event related to mantle upwelling associated magmatic activity and increased heat flow in the adjacent rift the major part of the basement cooled to near surface conditions in the early to middle triassic and since then was thermally stable as suggested by aft and ahe data further aft data confirm late triassic magmatic activity in the azov massif which however did not influence regional thermal pattern the northern part of the basement and its sedimentary cover record a cooling event in the jurassic which was probably related to erosion however although ar ar data of jurassic magmatic activity in the donbas foldbelt are about 20 my younger than the aft data thermal relaxation after elevated heat flow associated with this magmatic event cannot be completely ruled out our results reveal apparent inconsistencies between aft and ahe data the ahe ages corrected for alpha ejection according to the standard procedure farley k a wolf r a silver l t 1996 the effect of long alpha stopping distances on u th he ages geochim cosmochim acta 60 21 4223 4229 farley k a 2002 u th he dating techniques calibrations and applications mineral soc am rev mineral geochem 47 819 844 are older than corresponding aft ages in order to test the relevance of alpha ejection correction mechanical abrasion of several apatite grains was applied we found that in case of relatively slow cooling alpha ejection correction of raw u th he ages leads to erroneously high ages this shows that alpha ejection correction should be used with caution we propose that this correction should only be applied to samples with a fast cooling history whereas it should not be applied to slowly cooled samples and to samples whose thermal history is not constrained by other means

apatite u th sm he thermochronology of rapidly cooled samples the effect of he implantation apatite u th sm he ahe thermochronology is increasingly used for reconstructing geodynamic processes of the upper crust and the surface results of ahe thermochronology however are often in conflict with apatite fission track aft thermochronology yielding an inverted age relationship with ahe dates older than aft dates of the same samples this effect is mainly explained by radiation damage of apatite either impeding he diffusion or causing non thermal annealing of fission tracks so far systematic age inversions have only been described for old and slowly cooled terranes whereas for young and rapidly cooled samples too old ahe dates are usually explained by the presence of undetected u and or th rich micro inclusions we report apatite u th sm he results for rapidly cooled volcanogenic samples deposited in a deep ocean environment with a relatively simple post depositional thermal history robust age constraints are provided independently through sample biostratigraphy all studied apatites have low u contents 5 ppm on average while aft dates are largely in agreement with deposition ages most ahe dates are too old for leg 43 where deposition age of sampled sediment is 26 5 29 5 ma alpha corrected average ahe dates are up to 45 ma indicating overestimations of ahe dates up to 50 this is explained by he implantation from surrounding host u th rich sedimentary components and it is shown that ahe dates can be corrected by mechanically abrading the outer part of grains we recommend that particularly for low u th apatites the possibility of he implantation should be carefully checked before considering the degree to which the alpha ejection correction should be applied

the great appendage arthropod tanglangia biogeographic connections between early cambrian biotas of australia and south china abstract the cambrian great appendage arthropod tanglangia luo and hu in luo et al 1999 has until now been known from a single species from the chengjiang biota of southwest china cambrian series 2 stage 3 a new species from the emu bay shale konservat lagerstatte on kangaroo island south australia cambrian series 2 stage 4 tanglangia rangatanga sp nov extends the geographic and stratigraphic ranges of this genus and amplifies the biogeographic links between non biomineralised faunas from the early cambrian of australian east gondwana and the south china plate

tectono thermal evolution of the northwestern edge of the tarim basin in china constraints from apatite u th he thermochronology abstract the northwestern edge of the tarim basin which contains the kalpin uplift and the north bachu uplift lies between the south tianshan and tarim continental block and its tectonic evolution is closely correlated with the tianshan the pre mesozoic units are widely exposed in the northwestern edge of the tarim basin which allow detailed geological observation and sample collection in this paper the apatite u th he thermochronology was used to study the tectono thermal evolution of the northwestern edge of the tarim basin the sandstone samples from the upper neoproterozoic silurian devonian carboniferous and permian units etc on the northwestern edge of the tarim basin were collected and used to determine apatite u th he ages the apatite he ages in the kalpin uplift reveal the tectonic uplift events during the late cretaceous 96 70 ma and the miocene 22 20 ma these uplift events are linked to collisions of the lhasa block and the india plate with the southern eurasian continental margin respectively however apatite he ages in the north bachu uplift show only the eocene event at 40 ma because the west kunlun orogenic belt thrust over the southwestern edge of the tarim basin during the eocene the thermal modeling results reveal four cooling events in the kalpin uplift since the late neoproterozoic corresponding to 460 445 ma 350 320 ma 220 210 ma and 20 10 ma but only one episode with 220 210 ma in the north bachu uplift since the devonian based on the thermal modeling results the north bachu uplift did not experience the cooling events at 460 445 ma 350 320 ma and 20 10 ma shown in the kalpin uplift this paper provides a new insight into the tectonic evolution of the tianshan and the northwestern tarim basin

solving the production diffusion equation for finite diffusion domains of various shapes part i implications for low temperature u th he thermochronology abstract we propose an accurate fast and easy to use method to derive numerical solutions for production diffusion equations for finite diffusion domains of various shapes and arbitrary cooling histories previous studies provide solutions for spheres infinite cylinders and infinite sheets we extend this range and provide solutions for finite bodies i e finite cylinders and rectangular blocks of any aspect ratio this approach is important as recently it has become clear that for example the physical grain is the diffusion domain for he diffusion in apatite and titanite j geophys res 105 2000 2903 geochim cosmochim acta 63 1999 3845 we discuss the use of the new approach for forward modelling u th he production diffusion in apatite taking results with finite cylinders as a good approximation for apatite crystals it is found that approximating instead with spheres or infinite cylinders having the same radius yields differences in calculated ages that can easily be as large as 20 35 the relative differences are most pronounced in thermal histories that spend significant time at or near the closure temperature on the other hand reasonable agreement is found with spheres having the same surface to volume ratio

cenozoic uplift exhumation and deformation in the north kuqa depression china as constrained by u th he thermochronometry placing spatial and temporal constraints on deformation uplift and exhumation using thermochronology methods can shed light on cenozoic orogenic evolution in the kuqa foreland new apatite u th he and previously published apatite fission track thermochronology are combined with vitrinite reflectance data and modeling to compile a low temperature multi stage thermal history of tectonic uplift thrust and exhumation a rapid uplift and exhumation event originated in south tianshan during the eocene 46 ma with systematic younging of mean apatite u th he ages from north to south from the margin towards the interior uplift and exhumation south edge of the biyoulebaoguzi anticline in the northern monocline belt at 36 ma with more than 3400 m of stratum denuded subsequently deformation and uplift south edge of the biyoulebaoguzi anticline in the northern monocline belt at 36 ma with more than 3400 m of stratum denuded subsequently deformation and uplift extended to the northern edge of kelasu yiqikelike at 10 ma and then at 6 ma the kanyaken anticline formed and uplifted resulting in 3000 3700 m of overburden erosion the data support sequential southward propagating deformation and uplift inferred exhumation in the north kuqa depression during the cenozoic probably as a result of the collision of india with asia far to the south of the tianshan

natural age dispersion arising from the analysis of broken crystals part ii practical application to apatite u th he thermochronometry abstract we describe a new numerical inversion approach to deriving thermal history information from a range of naturally dispersed single grain apatite u th he ages the approach explicitly exploits the information about the shape of the 4he diffusion profile within individual grains that is inherent in the pattern of dispersion that arises from the common and routine practice of analysing broken crystals additional dispersion arising from differences in grain size and in u and th concentration of grains and the resultant changes to helium diffusivity caused by differential accumulation and annealing of radiation damage is explicitly included in this approach we calculate the ingrowth and loss due to both thermal diffusion and the effects of ejection of helium over time using a finite cylinder geometry broken grains are treated explicitly as fragments of an initially larger crystal the initial grain lengths l0 can be treated as unknown parameters to be estimated although this is computationally demanding a practical solution to the problem of solving for the unknown initial grain lengths is to simply apply a constant and sufficiently long l0 value to each fragment we found that a good value for l0 was given by the maximum fragment length plus two times the maximum radius of a given set of fragments currently whole crystals and fragments with one termination are taken into account a set of numerical experiments using synthetic fragment ages generated for increasingly complex thermal histories and including realistic amounts of random noise 5 15 are presented and show that useful thermal history information can be extracted from datasets showing very large dispersion these include experiments where dispersion arises only from fragmentation of a single grain length 400 m and radius 75 m c 6 50 dispersion including the effects of grain size variation for spherical equivalent grain radii between 74 and 122 m c 10 70 dispersion and the combined effects of fragmentation grain size and radiation damage for eu between 5 and 150 ppm c 10 107 dispersion additionally we show that if the spherical equivalent radius of a broken grain is used as a measure of the effective diffusion domain for thermal history inversions then this will likely lead to erroneous thermal histories being obtained in many cases the viability of the new technique is demonstrated for a real data set of 25 single grain u th he apatite ages obtained for a gabbro sample from the bk 1 bierkraal borehole drilled through the bushveld complex in south africa the inversion produces a well constrained thermal history consistent with both the u th he data and available fission track analysis data the advantage of the new approach is that it can explicitly accommodate all the details of conventional schemes such as the effects of temporally variable diffusivity zonation of u and th and arbitrary grain size variations and it works equally effectively for whole or broken crystals and for the most common situation where a mixture of both are analysed for the routine application of the apatite u th he thermochronometry technique with samples where whole apatite grains are rare our experiments indicate that 15 20 single grain analyses are typically required to characterise the age dispersion pattern of a sample the experiments also suggest that picking very short crystal fragments as well as long fragments or even deliberately breaking long crystals to maximise the age dispersion in some cases would ensure the best constraints on the thermal history models the inversion strategy described in this paper is likely also directly applicable to other thermochronometers such as the apatite rutile and titanite u pb systems where the diffusion domain is approximated by the physical grain size