the ktb apatite fission track profiles building on a firm foundation abstract deep boreholes serve as natural laboratories for testing thermochronometers under geological conditions the kontinentale tiefbohrung ktb is an interesting candidate because the geological evidence suggests that approximate isothermal holding since the last documented exhumation in the late cretaceous to palaeocene is a reasonable assumption for the thermal histories of the ktb samples we report 30 new apatite fission track ages and 50 new mean confined track lengths determined on cores from the 4 km deep pilot hole the and external detector ages are consistent with the population ages from earlier studies and together define a clear age profile the mean track lengths from this and earlier studies reveal the effects of experimental factors the measured age and length profiles are compared with the predictions of 24 annealing models for isothermal holding there are clear discrepancies between the measured and calculated profiles down to 1 5 km depth the measured mean track lengths are shorter than the predicted the balance of methodological evidence indicates that this is due to seasoning i e a shortening of the fossil confined tracks without attendant age reduction from 2 5 to 4 0 km depth the mean track lengths are longer than the predictions this suggests that the bias model that weights the probabilities of observing tracks of different length and which is based on experiments relating surface track densities to mean track lengths is not appropriate for confined tracks experimental and methodological factors are sometimes difficult to disentangle but present a sufficient margin for there to be no need to go against the independent geological evidence unknown geological events cannot be ruled out but their existence cannot be inferred from the fission track data alone much less can the nature or magnitude of such events be specified

toward understanding the post collisional evolution of an orogen influenced by convergence at adjacent plate margins late cretaceous tertiary thermotectonic history of the apuseni mountains 1 the relationship between syn to post collisional orogenic shortening and stresses transmitted from other neighboring plate boundaries is important for understanding the kinematics of mountain belts but has received little attention so far the apuseni mountains are an example of an orogen in the interference zone between two other subduction systems located in the external carpathians and dinarides this interference is demonstrated by the results of a combined thermochronological and structural field study that quantifies the post collisional latest cretaceous tertiary evolution the exhumation history derived from apatite fission track and u th he thermochronology indicates that the present day topography of the apuseni mountains originates mainly from latest cretaceous times modified by two tectonic pulses during the paleogene the latter are suggested by cooling ages clustering around 45 ma and 30 ma and the associated shortening recorded along deep seated fault systems paleogene exhumation pulses are similar in magnitude 3 5 km and are coeval with the final collisional phases recorded in the dinarides and with part of the carpathian rotation around the moesian promontory these newly quantified paleogene exhumation and shortening pulses contradict the general view of tectonic quiescence subsidence and overall sedimentation for this time interval the miocene collapse of the pannonian basin did not induce significant regional exhumation along the western apuseni flank nor did the subsequent carpathian collision this is surprising in the overall context of pannonian basin formation and its subsequent inversion in which the apuseni mountains were previously interpreted as being significantly uplifted in both deformation stages

fundamentals of fission track thermochronology fission track ft analysis has developed into one of the most useful techniques used throughout the geologic community to reconstruct the low temperature thermal history of rocks over geological time the ft method is based on the accumulation of narrow damage trails i e fission tracks in uranium rich mineral grains e g apatite zircon titanite and natural glasses which form as a result of spontaneous nuclear fission decay of 238u in nature price and walker 1963 fleischer et al 1975 the time elapsed since fission tracks began to accumulate is estimated by determining the density of accumulated tracks in a particular material in relation to the uranium content of that material chemical etching can be used to enlarge fission tracks that have formed within a mineral in order to make them readily observable under an ordinary optical microscope price and walker 1962 if a host rock is subjected to elevated temperatures fission tracks that have formed up to that point in time are shortened progressively and eventually erased by the thermal recovery i e annealing of the damage fleischer et al 1975 because thermal diffusion basically governs the annealing process the reduction in ft length is a function of heating time and temperature importantly fission tracks are partially annealed over different temperature intervals within different minerals this characteristic allows for the construction of time temperature paths of many different rock types by a plotting ft and other isotopic ages from different minerals versus their closure temperatures which is applicable in the case of a monotonous cooling history e g wagner et al 1977 zeilter et al 1982 and or by b the inverse modeling of observed ft age and confined track length data e g corrigan 1991 lutz and omar 1991 gallagher 1995 ketcham et al 2000 see also ketcham 2005

evidence for unetchable gaps in apatite fission tracks abstract the apparent shape of etched confined fission tracks in apatite depends on their crystallographic orientation on the direction of observation and on the distribution of longitudinal etching velocities along the track overetched blade like tracks which are approximately perpendicular to the c axis sometimes exhibit an extremely discontinuous etching behaviour resulting from the existence of so called unetchable gaps the full length of such tracks might not be revealed under normal etching conditions in the context of thermal history analysis the occurrence of unetchable gaps is very important for the understanding of the relationship between measured track length distributions and areal track densities in contrast to previous statements concerning durango apatite it can be shown that the phenomenon of fragmentation is not restricted to short tracks with a length of proportionality between the reductions of the areal track density and the etchable track length as has been assumed in some models dealing with projected track length distributions does not describe the true behaviour of strongly annealed apatites

inter laboratory comparison of fission track confined length and etch figure measurements in apatite apatite fission track length and etch figure data are powerful tools for obtaining thermal history information but both require human analysts making manual measurements and reproducibility is not assured we report the results of an inter laboratory study designed to clarify areas of congruence and divergence for these measurements and provide a basis for evaluating best practices to enhance intercompatibility of data sets four samples of megacrystic apatite from durango mexico with induced tracks one unnannealed and three thermally annealed by varying amounts were distributed internationally in all 55 analysts in 30 laboratory groups participated in the experiment relative mean track lengths among the samples were consistent across all analysts but measurements for each sample showed scatter among labs and analysts considerably in excess of statistical expectation normalizing measurements of annealed samples using the unannealed sample improved consistency as did normalizing for track angle using c axis projection etch figure data also showed variability beyond statistical expectation and consistency was improved by normalizing based on these data we recommend rigorous analyst training for length and etch figure measurement that includes measurement of standards and that each analyst s data on unknowns be normalized by that analyst s own measurements on standards when using thermal history inverse modeling as part of the interpretation process

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

reconstruction of low temperature 100 c burial in sedimentary basins a comparison of geothermometer in the intracontinental paris basin abstract the thermal evolution of sediments in the shallowest part of sedimentary basins is challenging to investigate as most of the geothermometers are at their application limits this is typically the case of the callovian oxfordian claystones at the eastern border of the paris basin a recent 2000 m deep well penetrated the entire jurassic and triassic sedimentary series and permitted coring of sediments never reached by previous drilling in this part of the basin thanks to the use of several independent geothermometers apatite fission track thermochronology fluid inclusion microthermometry clay mineralogy and sedimentary organic matter evolution the burial history of the mesozoic series has been reconstructed modeled and calibrated using kinetic algorithms relevant to the various paleothermometers used in addition to these conventional methods an innovative approach was developed using the temperature dependence of the magnetic mineral assemblage within clay rich sediments mageval thermal modeling indicates that the callovian oxfordian and the lower triassic experienced maximum burial temperatures of 50 5 c and 90 10 c respectively i e about 25 c higher than present day this temperature offset implies the erosion of several hundred meters of sediments which depending on the thermal flux and conductivity considered most likely constituted upper cretaceous chalk deposits falling sea level resulted in the exposure and subsequent dismantling of the chalk cover at the beginning of cenozoic times the eastern border of the basin was then subjected to slow erosion and discrete tectonic deformation

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

late and post variscan cooling and exhumation history of the northern rhenish massif and the southern ruhr basin new constraints from fission track analysis apatite fission track analyses were carried out on outcrop and core samples from the rhenish massif and the carboniferous ruhr basin germany in order to study the late and post variscan thermal and exhumation history apatite fission track ages range from 291 15 ma lower permian to 136 7 ma lower cretaceous and mean track lengths vary between 11 6 m and 13 9 m mostly displaying unimodal distributions with narrow standard deviations all apatite fission track ages are younger than the corresponding sample stratigraphic age indicating substantial post depositional annealing of the apatite fission tracks this agrees with results from maturity modelling which indicates 3500 7000 m eroded devonian and carboniferous sedimentary cover numerical modelling of apatite fission track data predicts onset of exhumation and cooling not earlier than 320 ma in the rhenish massif and 300 ma in the ruhr basin generally followed by late carboniferous triassic cooling to below 50 60 c rapid late variscan cooling was followed by moderate mesozoic cooling rates of 0 1 0 2 c ma converting into denudation rates of 1 mm a assuming a stable geothermal gradient of 30 c km modelling results also give evidence for some late triassic and early jurassic heating and or burial which is supported by sedimentary rocks of the same age preserved at the rim of the lower rhine basin and in the subsurface of the central and northern ruhr basin cenozoic exhumation and cooling of the rhenish massif is interpreted as an isostatic response to former erosion and major base level fall caused by the subsidence in the lower rhine basin

an inverse method of modeling thermal histories from apatite fission track data abstract apatite fission track ft ages and track length distributions are important sources of information about the thermal histories of rocks recent advances in the understanding of track annealing in apatite provide a solution to the forward problem of predicting ft ages and track length distributions that result from a given thermal history in this paper a method is presented to address the inverse problem estimation of the thermal history from ft data the inverse method uses an iterative approach the downhill simplex to systematically modify a starting thermal history to achieve satisfactory statistical agreement between the predicted and observed ft age and track length distribution however because of analytical uncertainties a unique thermal history does not exist monte carlo simulations are used to take into account the uncertainties in the data and yield a spectrum of possible thermal histories the results are based on the isothermal annealing model of laslett et al 1 chem geol isot geosci sect vol 65 but because the method uses forward predictions and not an analytical formula specific to a single annealing model alternative annealing models could be used within the same framework this method is an improvement in interpreting fission track data because the range of thermal histories permitted by the data can be evaluated to demonstrate the method it is applied to several sets of test data created by forward modeling of idealized thermal histories the results show that the age at which the sample cooled through its closure temperature and the most general features of the thermal history are revealed however data from partially annealed samples have wide spectra that reflect large uncertainties in the form of the thermal history for such samples ft data alone are not likely to provide strong tests of geologic hypotheses conversely geologic information may play a crucial role in constraining the thermal history spectrum in application to uplift related cooling this inverse method can provide much more realistic assessments of the cooling rate and its uncertainty than are otherwise possible

the denudation history of the onshore continental margin of se brazil inferred from apatite fission track data a suite of 68 new apatite fission track analysis results from the onshore rift margin in southeast brazil are presented some of the results reflect resetting related to the eruption of the parana continental flood basalt 130 ma and four others are directly related to late cretaceous magmatism 80 ma the majority of the results were obtained from precambrian basement rocks and sediments from the parana basin the fission track ages broadly increase inland from 60 90 ma on the coastal plain to 300 ma in the continental hinterland the track length distributions show a characteristic trend being negatively skewed at the coast and showing increasing bimodality inland except for the oldest samples which are more unimodal these trends do not reflect rift related heating and resetting but are the result of protracted denudation since the opening of the south atlantic the results are consistent with more than 3 km of exhumation on the coastal plain but little more than 1 km in the hinterland the topographic morphology in the northern region of the study area is complex and is clearly influenced by structure and bedrock lithology for the region further south model calculations of the isostatic response to the denudation suggest that isostatic rebound makes a minor contribution to the long wavelength topography unless the flexural rigidity is more than 1025 n m in this case the initial elevation of the rift margin would need to be 2 5 km in order to accommodate the amount of denudation inferred from the fission track data however it is possible that the effective flexural rigidity varies across the margin becoming greater in the continental interior alternatively the broad scale wavelength topography may be the result of magmatic underplating related to the parana continental flood basalt event if so estimates of the volume of magma generated would need to be revised upward by as much as a factor of 5

paleosols from the groups of burial mounds provide paleoclimatic records of centennial to intercentennial time scale a case study from the early alan cemeteries in the northern caucasus russia abstract buried soil chronosequences under a series of early alan kurgans burial mounds in the vladikavkazkaya depression of the northern caucasus russia were studied to derive a high resolution paleoclimatic record from the variations of the selected paleosol properties haplic chernozems occur under kurgans and on the actual land surface three kurgan cemeteries brut 1 brut 2 and beslan dated from the end of the second to the beginning of the seventh centuries ad have been studied the cemeteries are situated close to each other under similar lithological and geomorphological conditions but differed in the paleosols preservation the brut 2 site has been recently altered due to annual ploughing and intensive irrigation for more than 30 years the background soils and paleosols of the brut 2 site have been compared with synchronous soils of non irrigated brut 1 and beslan sites to detect pedogenic properties that are less changed by irrigation and thus comprise the soil memory stronger black color of humus horizon increase of humus content and decrease of humus 13c values clear signs of biological activity absence of morphological and analytical signs of solonetz properties diffused carbonate white soft spots in the bca horizon and decreasing carbonate content are thought to be related to the comparatively humid climatic conditions in the region on the contrary relatively low humus content tongue like lower boundary of humus horizon increase of humus 13c values morphological signs of solonetz properties together with high content of exchangeable na relatively large and clearly shaped carbonate white soft spots in the paleosols of the brut 2 site as well as increase of density thickness of the carbonate pseudomicellium and high carbonate content in the upper part of profiles in the paleosols of the non irrigated brut 1 site are assumed to be xeromorphic features indicating comparatively drier climatic conditions the paleosols of the earliest chronointerval of burial the end of the second to the beginning of the third centuries ad demonstrate clear xeromorphic properties which indicate a relatively dry climate with a mean annual precipitation 50 100 mm less than today the estimated duration of the period with such climatic conditions is thought to be not less than 100 years in addition those paleosols have some weak signs of humid conditions indicating that between the end of the first and the middle of the second centuries ad the climate was getting more moist mean annual precipitation became equal or slightly higher than today the paleosols buried in the first half of the fifth century ad again demonstrate the gradual enhancement of xeromorphic properties reflecting the next stage of droughts thus the period with favourable humid climate when the early alan culture flourished in the northern caucasus was relatively short about 400 years studying the detailed chronosequence in the non irrigated brut 1 site the records of intercentennial time scale soil properties variability produced by comparatively fast pedogenic processes typical for the steppe zone i e humus formation and accumulation bioturbation carbonate accumulation and transformation and solonetzization have been provided

the relationship between track shortening and fission track age reduction in apatite combined influences of inherent instability annealing anisotropy length bias and system calibration abstract the relationship between reduced track density 0 and reduced mean confined track length l l 0 during annealing has been studied for both spontaneous and induced tracks in four apatite samples with different chemical composition compositional range and origin and with spontaneous tracks giving mean confined track lengths varying from 14 5 m down to 12 3 m in all four apatites induced tracks show a relationship between l l 0 and 0 composed of two regions at higher values the two appear to be equal while at lower values l l 0 is greater than 0 this can be understood qualitatively in terms of the anisotropy of annealing and the bias against revelation of short tracks data from three apatites of uniform composition show near identical relationships in a sample showing a range of apatite compositions the point of divergence from the 1 1 relationship is somewhat higher than in the uniform composition apatites because individual grains anneal at different rates and the presence of highly annealed grains affects the track density more strongly than the mean track length spontaneous tracks show similar relationships to those observed for induced tracks in each sample when the data are renormalised to allow for the natural annealing present in the spontaneous tracks previous studies which led to the idea of length reduction without density reduction for spontaneous tracks did not renormalise density data as well as length data thereby distorting the apparent relationship data for the multi compositional apatite sample where annealing has taken place in geological conditions also agrees with the laboratory annealing data for both spontaneous and induced tracks this consistency suggests that a single process is responsible in all three cases implying that a laboratory based description of annealing can be applied to geological conditions with confidence recognition that spontaneous tracks in apatite are commonly annealed suggests that in general the fission track age should be interpreted as a reflection of both the time over which tracks have been retained and the distribution of etchable track lengths since the latter is a manifestation of the thermal history the fission track age should be interpreted in similar terms

mesozoic exhumation history and palaeolandscape of the iberian massif in eastern galicia from apatite fission track and u th he data apatite fission track aft and u th he ahe data combined with time temperature inverse modelling reveal the cooling and exhumation history of the iberian massif in eastern galicia since the mesozoic the continuous cooling at various rates correlates with variation of tectonic boundary conditions in the adjacent continental margins the data provide constraints on the 107 timescale longevity of a relict paleolandscape aft ages range from 68 to 174 ma with mean track lengths of 10 7 2 6 to 12 6 1 8 m and ahe ages range from 73 to 147 ma fastest exhumation 0 25 km ma occurred during the late jurassic to early cretaceous main episode of rifting in the adjacent western and northern margins exhumation rates have decreased since then and have been approximately one order of magnitude lower across inland galicia the aft data are consistent with early cretaceous movement on post variscan ne trending faults this is coeval with an extensional episode offshore the ahe data in this region indicate less than 1 7 km of denudation in the last 100 ma this low exhumation suggests the attainment of a mature landscape during late cretaceous post rift tectonic stability whose remains are still preserved the low and steady rate of denudation prevailed across inland galicia despite minor n s shortening in the northern margin since 45 ma ago in north galicia rock uplift in response to nw strike slip faulting since early oligocene to early miocene has caused insufficient exhumation 3 km to remove the mesozoic cooling signal recorded by the aft data

variation in apatite fission track length measurement implications for thermal history modelling abstract predictive thermal history modelling using apatite fission track ft data is dependent on an algorithm to describe the time and temperature dependency of ft annealing which in turn relies on the empirical determination of ft length as a measure of the annealing process assessment of variation in ft length measurement is poorly described with few comparisons between analysts and little interlaboratory standardisation using apatites of various compositions containing induced tracks annealed to differing degrees this study has assessed variation in horizontal confined track length measurement for a variety of procedural conditions replicate analysis by a single observer is typically within 3 but increases inversely with track length comparison between observers on the same samples shows significant generally nonsystematic variation between observers for a complex length distribution variation is 12 sources of variation are identified as a variation from track revelation including etching track in track tint vs track in cleavage tincle measurement and use of 252 cf irradiation to produce additional etching channels b bias in measurement including equipment analytical procedures and sample size and c observer bias principally differences in and consistency of personal technique 5 m hno 3 is preferred to weaker etchants although more anisotropic tracks are better defined permitting more rigorous measurement while c axis parallel sections where 2 4 geometry is better defined are more easily identified for all but the longest length distributions tincles are significantly longer than tints with few short tincles at high angles measurement of tincles effectively masks the anisotropy of annealing 252 cf irradiation is effective in increasing the number of tints sampled and measured variation between values measured for unirradiated and cf irradiated aliquots does not exceed that found for a single analyst although a slight systematic shift to longer lengths for cf irradiated samples is seen as reported by other workers track length distributions are anisotropic anisotropy increasing with annealing level track angle exerts a major influence on measured length summing affects from annealing and etching anisotropies with observer bias track angle should be accommodated within the annealing algorithm it is recommended that similar track revelation observation and measurement conditions are used for the analysis of field samples as are used in annealing experiments and subsequently employed in numerical models to predict thermal history a parallel argument can be advanced for using samples of similar composition further we recommend that the ft community should seek as a matter of some urgency a programme of interlaboratory comparison of track length measurement using standard apatite samples containing artificial length distributions typifying various levels of complexity such comparisons would provide a more rigorous baseline for thermal history prediction in geological case studies

a bayesian approach to calibrating apatite fission track annealing models for laboratory and geological timescales abstract we present a new approach for modelling annealing of fission tracks in apatite aiming to address various problems with existing models we cast the model in a fully bayesian context which allows us explicitly to deal with data and parameter uncertainties and correlations and also to deal with the predictive uncertainties we focus on a well known annealing algorithm laslett g m green p f duddy i r gleadow a j w 1987 thermal annealing of fission tracks in apatite 2 a quantitative analysis chem geol 65 1 1 13 and build a hierachical bayesian model to incorporate both laboratory and geological timescale data as direct constraints relative to the original model calibration we find a better in terms of likelihood model conditioned just on the reported laboratory data we then include the uncertainty on the temperatures recorded during the laboratory annealing experiments we again find a better model but the predictive uncertainty when extrapolated to geological timescales is increased due to the uncertainty on the laboratory temperatures finally we explictly include a data set vrolijk p donelick r a quenq j cloos m 1992 testing models of fission track annealing in apatite in a simple thermal setting site 800 leg 129 in larson r lancelet y eds proceedings of the ocean drilling program scientific results vol 129 pp 169 176 which provides low temperature geological timescale constraints for the model calibration when combined with the laboratory data we find a model which satisfies both the low temperature and high temperature geological timescale benchmarks although the fit to the original laboratory data is degraded however when extrapolated to geological timescales this combined model significantly reduces the well known rapid recent cooling artifact found in many published thermal models for geological samples

uplift and denudation of the central alaska range a case study in the use of apatite fission track thermochronology to determine absolute uplift parameters apatite fission track thermochronology aftt on granitic samples collected in the central alaska range in conjunction with geologic constraints from basins to the north nenana basin and south cook inlet of the range is used to constrain the timing amount rate and pattern of surface uplift rock uplift and denudation since the late miocene the conversion from a thermal frame of reference apatite fission track data to an absolute frame of reference with respect to mean sea level which requires constraining the paleoland surface elevation the paleomean annual temperature and the paleogeothermal gradient is evaluated and shown to be viable in the context of an exhumed apatite partial annealing zone paz apatite ages at denali mount mckinley range from 16 ma near the summit 6 km elevation to 4 ma at 2 km elevation a distinctive break in slope in the apatite age profile at an elevation of 4 5 km also marked by a change in confined track length distributions marks the base of an exhumed apatite paz rock uplift and denudation are greatest at denali decreasing southward away from the mckinley strand of the denali fault system as shown by progressively older apatite ages 7 35 ma from a suite of samples along the kahiltna glacier a correlative decrease in topography occurs southward from the fault the central alaska range lies within an arc defined by the denali fault with the highest peaks including denali concentrated at the arc apex patterns of rock uplift and denudation within the central alaska range mimic topography between early and late miocene and possibly earlier the central alaska range was most likely an area of relative tectonic and thermal stability rock uplift denudation and mean surface uplift of the denali region began by the late miocene 5 6 ma being 8 5 km 5 7 km and 2 8 km respectively at average rates of 1 5 km m y 1 km m y and 0 5 km m y the amount of rock uplift denudation and surface uplift decreases to 3 km 2 km and 1 km at little switzerland some 45 km south of the denali fault we conclude that the topographic and rock uplift patterns of the central alaska range the shape and proximity of the mckinley strand of the denali fault to these patterns the timing of the onset of rock uplift and denudation at 5 6 ma and a significant change in relative plate motion between north america and the pacific plates circa 5 6 ma are all inherently related

mesozoic and cenozoic tectonics of the northeastern edge of the tibetan plateau evidence from modern river detrital apatite fission track age constraints abstract thermochronometry of modern river sands exploits the natural sampling of detritus in a river catchment to infer plausible regional exhumation patterns when combined with available bedrock thermochronometric information apatite fission track age distributions for six detrital samples are reported in this study to resolve the exhumation history of the upper reaches of the heihe river draining north qilian shan and tuole shan the northeastern margin of the tibetan plateau the apatite fission track aft ages include four major populations late paleozoic 300 55 293 43 ma early mesozoic 223 15 205 17 ma late jurassic cretaceous 112 6 2 84 8 5 6 ma and cenozoic 63 8 5 9 19 3 1 7 ma the ages of these populations correspond well with the deformation and cooling history of the study area the late paleozoic and early mesozoic aft age populations record cooling events resulting from continental collision between the qiantang and kunlun blocks the late jurassic cretaceous aft age populations are interpreted to record cooling events associated with exhumation of north qilian shan and tuole shan due to the collision of the lhasa block with asian continent the cenozoic aft age populations record several cooling events a cooling event is recorded corresponding to exhumation of north qilian shan and tuole shan due to late stress from the lhasa asia collision causing deformation nearly synchronous with the india asia collision another cooling event is recorded corresponding to uplift and exhumation in oligocene time due to ongoing india asia convergence north qilian shan and tuole shan were constructed as a distal effect of india asia convergence in the early miocene while approaching their present mountain river basin distributions thermochronometry applied to heihe river sediments provide convinced evidence of multi stage exhumation of most northeastern margin of the tibetan plateau in the late paleozoic cenozoic

on the occurrence of anomalous fission tracks in apatite and titanite in annealing experiments on natural crystals of apatite and titanite two types of fission track were observed that had not been identified previously 1 stable tracks and 2 tracks through fluid inclusions stable tracks do not shorten significantly even when heated to temperatures well above those normally sufficient for complete annealing of fission tracks tracks through fluid inclusions owe their excessive length to the fact that one fission fragment traveled through a fluid inclusion without appreciable energy loss if they go undetected both types of track can distort the temperature time paths constructed on the basis of confined fission track length measurements simple measures are proposed to avoid these pitfalls

tectono thermal history of an exhumed thrust sheet top basin an example from the south pyrenean thrust belt this paper presents a new balanced structural cross section of the jaca thrust sheet top basin of the southern pyrenees combined with paleo thermometry and apatite fission track aft thermochronology data the cross section based on field data and interpretation of industrial seismic reflection profiles allows refinement of previous interpretations of the south directed thrust system involving the identification of new thrust faults and of the kinematic relationships between basement and cover thrusts from the middle eocene to the early miocene aft analysis shows a southward decrease in the level of fission track resetting from totally reset paleozoic rocks and lower eocene turbidites indicative of heating to tmax 120 c to partially reset middle eocene turbidites and no very weak resetting in the upper eocene lower oligocene molasse tmax 60 c aft results indicate a late oligocene early miocene cooling event throughout the axial zone and jaca basin paleo maximum temperatures determined by vitrinite reflectance measurements and raman spectroscopy of carbonaceous material reach up to 240 c at the base of the turbidite succession inverse modelling of aft and vitrinite reflectance data with the qtqt software for key samples show compatibility between vitrinite derived tmax and the aft reset level for most of the samples however they also suggest that the highest temperatures determined in the lowermost turbidites correspond to a thermal anomaly rather than burial heating possibly due to fluid circulation during thrust activity from these results we propose a new sequential restoration of the south pyrenean thrust system propagation and related basin evolution

a scenario for late neogene andean shortening transfer in the camisea subandean zone peru 12 s implications for growth of the northern andean plateau precise knowledge of the timing of deformation in the subandean zone of the andean plateau is a prerequisite for deciphering the late neogene growth of the andean plateau in this paper we report new apatite fission track aft and vitrinite reflectance ro data for a regional balanced cross section of the camisea basin in the central peruvian subandean zone adjacent to the northern andean plateau the balanced cross section shows that the structure of this basin is characterized by a broad internal passive roof duplex and external thrust related anticlines the balanced cross section restoration shows 53 km 39 of total horizontal shortening we sampled paleozoic to cenozoic sedimentary strata for aft and ro analyses along the 4 km thick vertical profile of the mainique back thrust passive roof thrust the innermost preserved subandean structure young components of aft ages are spread between ca 6 ma and ca 24 ma a break in the slope in the aft ages determines the geometry of the miocene partial annealing zone and the exhumation of the mainique back thrust at ca 6 ma sequential restoration calibrated by aft and ro data indicates that the last 23 km horizontal shortening were accommodated by the camisea thrust system over the past 6 m y giving a mean shortening rate of 3 8 mm yr using this shortening rate for the first 30 km horizontal shortening we calculate that the andean shortening transfer into the peruvian subandean zone initially started at ca 14 ma this result suggests that the transfer of shortening from the northern andean plateau to the subandean zone occurred prior to the removal of dense lithosphere previously reported to have occurred between ca 10 ma and ca 7 ma we rather propose that the late neogene growth of the northern andean plateau mostly resulted from a continuous crustal shortening combined with lower crustal flow

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

unraveling the mesozoic and cenozoic tectonothermal evolution of the eastern basque cantabrian zone western pyrenees by low temperature thermochronology this is a contribution of the geotec group idi 2018 000216 and projects misterios cgl2013 48601 c2 2 r consolider ingenio 2010 topo iberia csd2006 00041 and esf topoeurope project pyrtec sv pa 10 03 ip2 pyrtec we thank additional financial support by the university of oviedo banco santander the government of the principality of asturias through the science technology and innovation plan pcti the european union through feder funds and the spanish ministry of education culture and sport through the training programme for academic staff fpu grant for idf

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

comparison of experimental techniques to increase the number of measurable confined fission tracks in zircon abstract we compared three experimental techniques for increasing the number of measurable horizontal confined fission tracks hcts in annealed and unannealed zircon these techniques are irradiation of 252 cf spontaneous fission fragments irradiation of heavy ions 58 ni 11 using a tandem van de graaff accelerator and artificial fracturing of the zircon grains all these techniques increased the number of measurable hcts and they introduced no significant change in the measured length of annealed hcts for the samples with low track density 10 5 cm 2 heavy ion irradiation was far more effective than irradiation of 252 cf fission fragments because relatively long artificial tracks could be formed by the heavy ion irradiation the artificial fracturing method is recommended when an accelerator facility is not easily available because its effect was comparable to heavy ion irradiation and it is practicable in ordinary laboratories using these techniques a preliminary comparison of annealing characteristics was performed for three zircon samples with different spontaneous track densities of 4 10 5 4 10 6 and 2 10 7 cm 2 with fission track ages of 3 1 22 8 and 367 6 ma respectively the length reduction due to the thermal annealing of these zircons appeared to be different with the possibility that the thermal stability of spontaneous fission tracks depends on the initial spontaneous track density i e the higher the initial spontaneous track density of a sample the slower the rate of track annealing

reproducibility of apatite fission track length data and thermal history reconstruction abstract the ability to derive detailed thermal history information from apatite fission track analysis is predicated on the reliability of track length measurements however insufficient attention has been given to whether and how these measurements should be standardized in conjunction with a fission track workshop we conducted an experiment in which 11 volunteers measured 50 track lengths on one or two samples one mount contained durango apatite with unannealed induced tracks and one contained apatite from a crystalline rock containing spontaneous tracks with a broad length distribution caused by partial resetting results for both mounts showed scatter indicative of differences in measurement technique among the individual analysts the effects of this variability on thermal history inversion were tested using the hefty computer program to model the spontaneous track measurements a cooling only scenario and a reheating scenario more consistent with the sample s geological history were posed when a uniform initial length value from the literature was used results among analysts were very inconsistent in both scenarios although normalizing for track angle by projecting all lengths to a c axis parallel crystallographic orientation improved some aspects of congruency when the induced track measurement was used as the basis for thermal history inversion congruency among analysts and agreement with inversions based on data previously collected was significantly improved further improvement was obtained by using c axis projection differences among inversions that persisted could be traced to differential sampling of long and short track populations among analysts the results of this study while demonstrating the robustness of apatite fission track thermal history inversion nevertheless point to the necessity for a standardized length calibration schema that accounts for analyst variation

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

late cretaceous extension and exhumation of the stong and taku magmatic and metamorphic complexes ne peninsular malaysia fragmentation of large continental areas by post orogenic extension requires favourable geodynamic conditions and frequently occurs along pre existing suture zones or nappe contacts as exemplified by the stong and taku magmatic and metamorphic complexes of northern peninsular malaysia for this case we have employed a field and microstructural kinematic study combined with low temperature thermo chronology to analyse the tectonic and exhumation history the results show that the late palaeozoic triassic indosinian orogeny created successive phases of burial related metamorphism shearing and contractional deformation this orogenic structure was subsequently dismembered during a cretaceous thermal event that culminated in the formation of a large scale late santonian early maastrichtian extensional detachment genetically associated with crustal melting the emplacement of syn kinematic plutons and widespread migmatisation the emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range represented by amphibolite and greenschist facies mylonites and as well as brittle structures such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment the formation of this detachment and a first phase of late cretaceous cooling was followed by renewed eocene oligocene exhumation as evidenced from our fission track ages we infer that an initial cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and rotation of normal faults these cretaceous processes played a critical role in the establishment of the presently observed crustal structure of peninsular malaysia

reply to comment on compositional and structural control of fission track annealing in apatite by j barbarand a carter i wood and a j hurford chemical geology 198 107 137 2003

improved measurement of fission track annealing in apatite using c axis projection apatite fission track length data are used extensively for thermal history inversion however several studies have documented instances of poor reproducibility of length data we address this problem by using c axis projection to normalize track lengths for crystallographic angle in the extensive laboratory annealing data set acquired by barbarand et al 2003a 2003b a new simplification reduces the c axis projection model from six to four fitted parameters normalizing for track angle using c axis projection improves every aspect of length measurement reproducibility examined it accelerates convergence of mean length in single analyses increases consistency among replicate measurements by a single analyst enhances consistency of measurements of the same mounts by different analysts and improves the match between analyses conducted with and without cf irradiation c axis projection is also shown to enhance the thermal sensitivity of length data based on these results we assert that c axis projection is a good means of compensating for observer bias although it does not overcome differences caused by experimental error