thermochronological investigation of fault zones abstract the timing of faulting episodes can be constrained by radiometric dating of fault zone rocks fault zone material suitable for dating is produced by tectonic processes such as 1 fragmentation of host rocks followed by grain size reduction and recrystallization to form mica and clay minerals 2 secondary heating melting of host rocks by frictional fault motions and 3 mineral vein formation as a result of fluid advection associated with the fault motions the thermal regime of fault zones consists primarily of the following three factors a regional geothermal structure across the fault zone and background thermal history of studied province bounded by fault systems b frictional heating of wall rocks by fault motions and c heating of host rocks by hot fluid advection in and around the fault zone thermochronological methods widely applied in fault zones are k ar 40ar 39ar fission track and u th methods for which methodological principles as well as analytical procedures are briefly described the thermal sensitivities of individual thermochronological systems are then reviewed which critically control the response of each method against the thermal processes based on the knowledge above representative examples as well as key issues are highlighted to date fault gouges pseudotachylytes mylonites and carbonate veins placing new constraints upon geological geomorphological and seismological frames finally the nojima fault is presented as an example for multiple applications of thermochronological methods in a complex fault zone

constraints on provenance of the central european triassic using detrital zircon fission track data the type of provenance information obtained from dating detrital grains will depend upon the thermal sensitivity of the isotopic dating method for detrital zircon the two methods fission track and u pb in routine use have widely different thermal sensitivities and therefore may provide quite different provenance information zircon fission track data are sensitive to thermal overprinting in the temperature range 200 300 c and therefore have the unique ability to provide source thermal history data the purpose of this study is to evaluate the suitability of zircon fission track data for provenance studies of the triassic siliciclastic sediments of central europe with an emphasis on testing proposed sediment pathways zircon fission track data obtained during this study are consistent with a sediment pathway linking fennoscandia with the central german basin in addition during carnian times there must also have been a pathway linking the schilfsandstein formation of the german basin with the lunzersandstein of the tethyan realm pointing to a european wide fluvial transport system detrital zircon fission track data are therefore a useful means for discerning sediment source and reconstructing sediment pathways

low temperature thermochronology of the northern cordillera real ecuador tectonic insights from zircon and apatite fission track analysis the post early cretaceous tectonic development of the northern andean segment north of 5 s is loosely constrained by a series of partially and fully reset k ar ages new apatite and zircon fission track data from three traverses across the cordillera real of ecuador reveal distinct periods of accelerated crustal cooling during the cenozoic fission track ages range from 65 to 14 ma zircon and 44 to 8 ma apatite with apatite mean track lengths ranging from 14 6 to 12 1 m these results record rapid cooling rates during 43 30 ma 23 15 ma and 10 0 ma occurring at temperatures below 275 c the events reflect up to 9 km of crustal exhumation in various regions of the cordillera in response to relative changes in the kinematics of the farallon nazca and south american plates the exhumation history of the cordillera real was not continuous but rather evolved during separate phases these phases persisted for 10 myr and are partly coincident with tectonic phases of the central andes although extend for longer time periods possibly as a result of isostatically driven crustal exhumation large spatial variations in the zircon and apatite fission track data within the cordillera real indicate that local fault bounded massifs have experienced different thermal histories since 43 ma major variations are not restricted to the regional scale and exist within individual terranes faulted slivers within terranes demonstrate highly variable exhumation histories suggesting that deformation was not dominated by terrane bounding faults additionally n s variations in exhumation depths suggest that ne sw trending faults have been active since 10 9ma

cretaceous to cenozoic thermal evolution of the southwestern south carpathians evidence from fission track thermochronology abstract the southwestern south carpathian orogen is composed of various nappe complexes which were assembled during the cretaceous cenozoic orogeny these are from footwall to hangingwall 1 the danubian nappe complex including a cadomian variscan basement 2 the arjana and severin units with jurassic to early cretaceous rift and oceanic sequences and 3 the getic nappe complex with variscan continental basement fission track ft thermochronology on apatite zircon and sphene from samples collected from various units of the south carpathians in conjunction with field constraints and previous geochronology is used to characterise the alpine tectonic events and to restore the pattern and amount of exhumation since the cretaceous zircon from the flysch unit and the danubian liassic cover sequence yields ft ages around 200 ma suggesting cooling of the rift flanks prior to the opening of the severin rift zircon and sphene from the getic and danubian basement units yield ft ages averaging 110 ma and indicating cooling under 240 c of the basement contemporaneous with or postdating thrusting apatite ft ages display a decreasing age trend from the hangingwall 65 ma to the footwall units 30 ma the age data and corresponding horizontal confined track length distributions suggest that exhumation of the nappe pile occurred in two stages the first is related to the late cretaceous nappe stacking and the second one to the final thrusting of the south carpathians onto the top of the moesian platform apatite ft ages along major brittle wrench faults indicate reheating above ca 120 c during fluid flow associated with fault re activation during oligocene and neogene times thus shear zone rocks experienced a higher temperature overprint during cenozoic time than rocks of the unaffected nappe pile temperatures of hydrothermal flow along these zones decreased below 100 c progressively starting with the late oligocene early miocene when the area began to override the moesian platform

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

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

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

mesozoic and cenozoic tectonics of the northern edge of the tibetan plateau fission track constraints abstract fission track analysis on zircons and apatites yields new information about the timing of deformation of the northern tibetan plateau ages on zircons ranging from 221 22 to 96 4 ma are indicative of a general late triassic early jurassic cooling probably driven by the collision between the qiantang and kunlun blocks mid jurassic slow cooling is recorded also in the apatites in regions not affected by later cenozoic deformation this jurassic denudation was followed by a period of sedimentation during the cretaceous except along the altyn tagh fault atf zone and in some restricted areas of the western and eastern qilian shan this long and relatively quiet period ended at about 40 10 ma along the major altyn tagh and kunlun strike slip fault zones which were activated by the india asia collision this first movement along lithospheric faults resulted in the eastward extrusion of the tibet plateau which was followed in late oligocene miocene times by a major compression event initiating the formation of the high relief of north tibet a final compressional event took place at 9 5 ma and is well correlated with high sedimentation rates in the basins of this region this compression induced continental subduction in the kunlun ranges the altun shan belt and possibly the qilian shan belt

can fossil bones and teeth be dated using fission track analysis the high proportion of crystallized apatite forming the bones and teeth should theoretically allow the use of fission track analysis to date vertebrate fossils when burying of the fossiliferous series did not subject them to temperatures exceeding 60 degrees c however several major obstacles arise such as the complexity of fossils internal structures diagenetic modifications and substitutions of the hydroxyapatite by other minerals and massive u uptake or loss during diagenesis in this work those various problems are addressed combining optical microscope observation of the fossils a systematic fission track analysis of the best samples alpha and gamma spectrometry and secondary ion mass spectrometry even if the problems caused by internal structures and mineral substitutions can be solved u movements in and out of the fossils are generally too complex to allow fission track analysis dating of the fossils

timing tectonic implications and genesis of gold mineralization in the xincheng gold deposit china c h o isotopes pyrite rb sr and zircon fission track thermochronometry abstract the xincheng gold deposit located at the northwestern edge of the jiaodong peninsula in the north china craton has a reserve of 96 t au and is among the largest in the jiaodong gold province here disseminated and stockwork style ores are hosted in mesozoic granitoids the mineralization and alteration are largely controlled by the regional jiaojia fault the c h o isotope values in the ores indicate that the ore forming fluids were derived mainly from magmatic sources new rb sr geochronological data on hydrothermal pyrite from the xincheng deposit presented in this study indicate that the main gold mineralization occurred between 126 ma and 122 ma the zircon fission track of convergent ages and decomposed divergent ages from the ores and altered rocks show four groups of ages 135 ma 124 ma 96 75 ma and 66 52 ma the 135 ma is related to the exhumation and cooling of the linglong granitoids the 124 ma is considered to represent the principal stage of gold mineralization and is consistent with the pyrite rb sr ages the younger ages of 96 75 ma and 66 52 ma resulted from subsequent annealing caused by later tectonic activity the timing of gold mineralization in the xincheng gold deposit broadly coincides with the switch in stress field in eastern china from extension to transpression resulting from the change in subduction direction of the pacific plate from ne sw to nw se and marked by extension related voluminous magmatism associated with the cretaceous giant igneous event in eastern china

low temperature thermochronology of the flanks of the southern upper rhine graben the upper rhine graben urg is the most perceptible part of the european cenozoic rift system uplifted variscan basement of the black forest and the vosges forms the flanks of the southern part of the graben apatite and zircon fission track ft analyses indicate a complex low temperature thermal history of the basement that was deciphered by inverse modelling of ft parameters the models were tested against the observed data and independent geological constraints the zircon ft ages of 28 outcrop samples taken along an e w trending transect across the black forest and the vosges range from 136 to 312 ma the apatite ft ages from 20 to 83 ma the frequency distributions of confined track lengths are broad and often bimodal in shape indicating a complex thermal history cooling below 120 c in the early cretaceous to palaeogene was followed by a discrete heating episode during the late eocene and subsequent cooling to surface temperature the modelled time temperature t t paths point to a total denudation of the flanks of urg in the range of 1 0 1 7 km for a paleogeothermal gradient of 60 c km and 1 3 2 2 km for a paleogeothermal gradient of 45 c km since the late eocene

timing duration and role of magmatism in wide rift systems insights from the jiaodong peninsula china east asia in east asia widespread extensional sedimentary basins together with the close association of metamorphic core complexes and magmatism are prominent features of the large scale wide rift system developed during late mesozoic times this region thus appears as a proper place to study continental extension as well as questions about the link between continental extension and magmatism this paper primarily provides pioneer exhumation time constraints on the linglong mcc jiaodong peninsula including cooling and deformation ages mcc cooling at mid crustal levels occurred at ca 143 ma besides last ductile deformation occurred at ca 134 ma while final exhumation stages under brittle 2 conditions occurred as late as ca 128 ma continuous crustal stretching were then recorded by the emplacement of a synkinematic pluton in the upper crust at ca 128 ma that cooled fast below an intracrustal shear zone crossing the ductile brittle transition at ca 123 ma the ca 120 118 ma age cluster is ascribed to the fast cooling of undeformed plutons marking the end of extension that lasted in the area over a minimum period of ca 30 my combining other mcc exhumation constraints and the onset of subsidence in the sedimentary basins total duration of late mesozoic extension in east asia could be estimated at ca 60 my related with a rather long process for extension from 160 to at least 100 ma east asian continental extension is heterogeneously distributed in space and time as revealed by fundamental differences between two end member classes of migmatite cored mcc already described in other wide rift systems extension seems to have first favoured partial melting which subsequently in turn maintained continental extension

late cenozoic geomorphic and tectonic evolution of the patagonian andes between latitudes 42 s and 46 s an appraisal based on fission track results from the transpressional intra arc liquine ofqui fault zone fission track ft thermochronology has been applied to investigate the low temperature cooling and denudation history of the patagonian andes along the southern part of the intra arc transpressional liquine ofqui fault zone between 42 and 46 s the liquine ofqui fault is shown to have been the focus of enhanced cooling and denudation initiated between ca 16 and 10 ma several fault blocks with different cooling histories are identified these are separated by major oblique or reverse slip faults proposed to form the eastern part of a major crustal scale dextral transpression zone local very fast rates of cooling and denudation between ca 7 and 2 ma were coeval with collision of the chile rise an active mid oceanic ridge with the peru chile trench between 47 and 48 s this location is close to the southern termination of the liquine ofqui fault implying that the collision of the ridge was a major force driving late cenozoic transpression the lack of significant cooling and denudation before ca 16 ma is indicative of pure strike slip or transtensional movement along the liquine ofqui fault before the collision of the ridge digital landscape analysis supports glacial and periglacial erosion as the main contributor to denudation since ca 7 ma leading to restriction of topographic development the combination of transpression induced rock uplift and glacial erosion is shown to be very effective at causing localized denudation anomalously young ft ages along the liquine ofqui fault are attributed to the existence of a late cenozoic localized heat flow anomaly along the fault

fission track dating of faulting events accommodating plastic deformation of biotites we performed fission track ft analyses to constrain the timing of fault slip events associated with plastic deformation of biotite grains formed at high temperature higher than 200 300 c apatite ft ages of 49 6 16 7 ma were obtained from late cretaceous granites near the fault with younger ages near a basaltic dike that intruded at 19 ma by comparing the distribution of apatite ft ages using forward thermal and ft annealing calculations we interpreted the younger ages as being explained by basaltic intrusion we concluded that the plastic deformation of the biotite grains could have occurred associated with the following events 1 primal cooling of the granitic body at 68 50 ma and or 2 basaltic intrusion at 19 ma a combination of detailed observation of microscale deformation structures and dense ft measurements successfully constrained timing of fault events distributed in bedrock without covering layers

natural long term annealing of the zircon fission track system in vienna basin deep borehole samples constraints upon the partial annealing zone and closure temperature abstract fission track ft analysis of zircon from cretaceous and tertiary sandstone samples in vienna basin boreholes has provided constraints for the thermal stability of the zircon ft system over a geological timescale confined track lengths and ages were measured for samples from depths of 1 5 7 5 km the deepest with a present environmental temperature of 200 c mean track lengths range from 10 3 to 10 8 m indistinguishable within error from the unannealed reference length of 10 7 0 1 m 1 standard error thus showing no sign of systematic downhole reduction central zircon ages are consistently older than stratigraphic ages of parent rocks with no single grain ages significantly younger than their respective stratigraphic ages such ft age and length evidence strongly suggests that the tracks have not been significantly annealed since sediment deposition because the present geothermal regime as well as sample burial depths have been near constant for at least the past 5 m y the lower temperature limit of the zircon ft partial annealing zone is 200 c for a heating duration of the order of 5 10 m y such evidence from long term natural annealing is compatible with a zircon ft partial annealing zone cf 200 350 c derived by the extrapolation of laboratory annealing results based on onfined track length measurements but cannot alone discriminate between different annealing models for the zircon ft closure temperature a perhaps over simplified concept these results are consistent with the oft quoted temperature of 250 c for cooling rates of 10 100 c m y

confined fission track length measurement of zircon assessment of factors affecting the paleotemperature estimate abstract we carried out a series of laboratory annealing experiments in order to understand the factors affecting observed confined track lengths in thermally annealed zircon the variation of confined fission track lengths according to both experimental and analytical conditions was determined on zircons from nisatai dacite it was found that etching temperature track etching criteria measurement criteria of horizontal confined tracks hct s and the orientation of hct s significantly control the observed track lengths if samples are highly annealed i e 600 c for 1 hr annealing the first three factors may be related to the presence of gap zones in an annealed track whilst the fourth is caused by anisotropic annealing and etching characteristics for reliable thermal history reconstruction therefore it should be the minimum requirement to document explicitly the experimental and analytical conditions of these factors in zircon fission track analysis

radiation damage in zircon a single zoned sri lankan zircon exhibits a range of microstructures from crystalline to nearly amorphous that are the result of radiation damage over a dose range of 2 1 10 1 1015 decay events mg 0 16 0 47 dpa the zones in the crystal were examined at a variety of length scales using optical microscopy micro raman spectroscopy electron microprobe analysis and transmission electron microscopy birefringence varies linearly with dose birefringence 4 71 10 18 g d 4 86 10 2 full width at half maximum fwhm measurements of the b1g 3 peak as determined by micro raman spectroscopy were used to estimate the extent of radiation damage in each zone the radiation dose calculated on the basis of u and th concentrations and sample age vs damage from the fwhm measurements of the b1g 3 peak relationship among zones was consistent with results for a suite of sri lankan single crystals suggesting that all of these zircon crystals have undergone a similar thermal history based on a comparison with zircon crystals that are considered to have undergone minimal annealing e g lunar zircon the sri lankan zircon crystals have accumulated less damage than is expected based on their calculated dose consistent with previous evidence for annealing to estimate the extent of annealing in sri lankan samples an equivalent damage dose i e the dose required to produce the same amount of damage in an unannealed sample was calculated for a given u and th concentration by determining the time of damage accumulation required to create an equivalent amount of damage in an unannealed zircon the dose vs damage relationship in sri lankan zircon crystals 560 ma is equivalent to that of a 375 ma unannealed zircon suggesting that approximately one third of the damage has been lost due to annealing the dose vs damage relationship is consistent with the direct impact model of damage accumulation transmission electron microscopy revealed zoning on a scale finer than could be identified optically 0 5 m and the presence of abundant zro2 nano particles at zone boundaries

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

new information on the thermal history of the southwestern lower saxony basin northern germany based on fission track analysis the southwestern part of the lower saxony basin lsb is characterized by gravity and magnetic anomalies and by an extremely high thermal maturity of organic matter this was for many years attributed to a late cretaceous intrusion but actually deep burial is being debated the complex thermal history of the area has been studied by fission track analysis zircon data provide evidence for widespread hydro thermal activity during the permian and upper jurassic lower cretaceous apatite ages indicate a major cooling event in the mid cretaceous 89 72 ma reflecting the time of inversion of the lsb during the cretaceous the cooling of the basin centre was rapid compared to the basin margins apatite fission track ages from borehole samples which are recently within the upper part of the apaz indicate a young heating of the sedimentary sequences until present

mesozoic cenozoic denudation history of the patagonian andes southern chile and its correlation to different subduction processes fission track ft analysis is applied to assess the mesozoic and cenozoic thermal and denudational history of the patagonian andes between 44 and 51 s and the geologic and geomorphic response of late cenozoic subduction of the active chile rise mid oceanic spreading center on the overriding plate seventy two ft ages from 43 samples are presented zircon ft ages indicate fast post intrusion cooling of cretaceous parts of the patagonian batholith and previously unreported miocene magmatic rocks south of 48 s metamorphic basement rocks to the east of the batholith are constrained as having been deposited and metamorphosed in the early carboniferous and late permian apatite ft data reveal initiation of accelerated cooling and denudation at ca 30 ma at the western margin of southern continental south america followed by an up to 200 km eastward migration of the locus of maximum denudation that ceased at ca 12 8 ma at the position of the present day main topographic divide this migration is proposed to be related to either coeval eastward migration of the retroarc deformation the effects of subduction erosion in the overriding plate at the peru chile trench or less likely shallowing of the angle of subduction east of the divide 3 km of denudation has occurred since the late cretaceous enhanced denudation is interpreted to be the result of increased tectonic uplift driven by a large increase in convergence rates at ca 28 26 ma that triggered orographically enhanced precipitation on the west side of the patagonian andes allowing increased erosion by fluvial incision and mass transport processes the actual process of spreading center subduction had remarkably little influence on denudation in the upper plate and indeed coincides with a slowdown in denudation

assessment of overetching factor for confined fission track length measurement in zircon abstract the effect of prolonged etching provides a fundamental bias in observed confined track lengths in minerals particularly those having highly anisotropic etching characteristics such as zircon in this paper the anisotropic prolonged etching factor around the ends of horizontal confined tracks hct s which are practically used for track length analysis was assessed quantitatively by step etch of spontaneous tracks in zircon the observed etching characteristics are two fold 1 the track etch rate for the direction perpendicular to the crystallographic c axis is significantly smaller than that parallel to it and 2 for a particular crystallographic direction the growth rate of track length is consistently greater than the bulk etch rate measured as the growth rate of track width for the direction perpendicular to that of interest to further constrain the etching characteristics of hct s the shape of their ends were compared and contrasted with that of track etch pits on a prismatic surface in contrast to the diamond shape of surface tracks the ends of hct s are generally convex outward with the core of etched track longest regardless of track orientation this suggests that at the ends of hct s the core of track has a growth rate greater than the surrounding bulk region probably with decreasing rate outward hence the traditional model of track etching dividing a latent track into the etchable and unetchable ranges should be refined etch rate of a latent track decreases rather continuously toward both ends this model is concordant with the ionization pattern in a mineral detector produced by nuclear fission and explains reasonably the experimental results because the correction of such a complicated overetching factor for an individual sample is extremely laborious for routine analysis it is recommended that hct s nearly perpendicular to the crystallographic c axis e g 70 should be used for track length measurement nevertheless the reduction in number of tracks to be measured may be rather small since hct s with smaller angles to the c axis are less detectable due to the etching anisotropy

towards zircon fission track thermochronology reference framework for confined track length measurements abstract horizontal confined track hct lengths and angles to the crystallographic c axis were measured for both unannealed spontaneous and induced fission tracks ft in zircons to establish a reference framework of hct length measurement induced track lengths were analysed on eleven zircon separates from various rock types including four age standards and spontaneous lengths on three zircon standards were analysed in general the observed hct lengths in each sample are slightly anisotropic with shorter tracks having greater angles to the c axis in addition all samples show large anisotropy in the number of observed hct s particularly for induced tracks as an observed mean hct length is controlled by the combined influence of these two anisotropies selective measurement of tracks that have specified azimuth angles to the c axis e g 60 90 is recommended in annealing studies or thermochronological applications mean spontaneous and induced hct lengths of 60 90 are approximately concordant for individual age standards although slightly controlled by the difference in overetching effects due to the different etching criteria adopted this indicates that natural track annealing at an ambient surface temperature at geological timescales is negligible in zircon in contrast to the case in apatite mean lengths of induced hct s do not differ significantly between the zircons analysed therefore the overall mean and standard deviation values of hct lengths for 60 90 azimuth angles i e 10 50 0 04 1 standard error m and 0 76 0 03 m for spontaneous tracks and 10 73 0 04 and 0 63 0 03 m for induced tracks respectively offer reliable references for hct length measurement in zircon ft thermochronology

the record from british quaternary river systems within the context of global fluvial archives data amassed in the past decade on quaternary fluvial archives has allowed comparison across widely separated regions of the world meanwhile there has been a new impetus for research on british sequences as a result particularly of the aggregates levy sustainability fund alsf in this context the key british records from the thames severn avon trent wash system and solent are described briefly with emphasis on the latest information in the case of the trent sedimentary evidence discovered during alsf funded work appears to confirm the existence of a middle pleistocene trent ancaster river in the case of the solent independent projects that sought to improve the age constraint for the sequence have produced complimentary results the first used luminescence dating whereas the second made use of palaeolithic evidence to calibrate numerical incision uplift modelling the overarching message is that the british fluvial archive can be readily understood within a global context it typifies records from areas with relatively young crust that has been uplifting during the quaternary and being in the temperate latitudes and close to the atlantic margin it reflects strong climatic forcing the combination of rich faunal and palaeolithic artefact contents means that certain british records are of international significance copyright 2010 john wiley sons ltd

natural long term annealing of the zircon fission track system around a granitic pluton we measured 24 ages and 14 length distributions of fission tracks in zircons separated from basement sandstones around a granitic pluton to investigate natural long term annealing behaviors of the zircon fission track zft system samples were collected from three cretaceous coherent units of the shimanto accretionary complex shikoku japan along an eastward traverse at distances of between 1 6 and 10 6 km from the intrusion contact of 15 ma takatsukiyama granite exposing about 5 km in diameter sampling was carried out around the expected position of the transition zone of track retention i e the fossil partial annealing zone fpaz based on previous regional zft age distributions approaching the contact original zft ages of 100 ma show a continuous reduction to 15 ma at 3 km distance their single grain age distributions accordingly change from widespread multimodal patterns reflecting provenance ages to unimodal ones characterizing the secondary heating by the granite intrusion mean and distributions of zft lengths also show notable variations within the fpaz as a result of mixing both preexistent tracks that were shortened by the miocene heating and unannealed ones having original long lengths that have been formed and accumulated after the cooling of the pluton these facts along with observed track segmentation and annealing anisotropy suggest that the shortening patterns of tracks in nature a heating duration of 105 106 years estimated from thermal modeling are indistinguishable from those previously demonstrated at laboratory timescales this basically validates the conventional approach of extrapolating laboratory based kinetic parameters to geologic timescales the observed fpaz and thermal modeling results in conjunction with laboratory heating data previously reported and recent constraints from an ultradeep borehole favor a relatively narrow temperature range for the partial annealing zone i e 230 to 330 c for a heating duration of 106 years

total exhumation across the beichuan fault in the longmen shan eastern tibetan plateau china constraints from petrology and thermobarometry the deep structure and deformation mechanisms of the longmen shan thrust belt sichuan china at the eastern border of the tibetan plateau were largely debated after the devastating mw 7 9 wenchuan earthquake 2008 recent geophysical studies and field investigations have been focused on the active motion of the major beichuan fault which ruptured during the earthquake however the total exhumation across the fault still remains unclear in the hanging wall of the beichuan fault the south china block is exhumed in the pengguan massif close to the beichuan fault the rocks of the pengguan massif underwent greenschist facies metamorphism associated with brittle ductile deformation no metamorphism is observed in the footwall of the fault in this study we characterize and date the metamorphic history recorded in the hanging wall of the beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the pengguan massif along the fault a high resolution petrological approach involving chemical analyses and x ray maps was used to analyze the micrometric metamorphic minerals the p t conditions of the greenschist facies metamorphic event were estimated by an inverse multi equilibrium thermodynamic approach the results 280 30 c and 7 1 kbar suggest that the rocks of the pengguan massif were exhumed from ca 20 km depth our results underline the importance of the thrusting component in the long term behavior of the beichuan fault and provide a minimal depth at which the fault is rooted in situ laser ablation 40ar 39ar dating of metamorphic white mica revealed that the greenschist overprint occurred at 135 140 ma the pengguan massif was therefore partially thrusted along the beichuan fault during the lower cretaceous long before the eocene miocene exhumation phase which is well constrained by low temperature thermochronology our results provide the first independent depth information for the exhumation history of the pengguan massif and reveal a previously undocumented lower cretaceous tectonic event that marks the onset of the thick skinned deformation in the external domain of the longmen shan east of the wenchuan fault

cretaceous cenozoic tectonic history of the jiaojia fault and gold mineralization in the jiaodong peninsula china constraints from zircon u pb illite k ar and apatite fission track thermochronometry the jiaojia fault jjf in the jiaodong area of eastern china is an important nne trending structure that is subsidiary to the regional tancheng lujiang tan lu fault zone and hosts 1200 t of gold reserves contained in disseminated and stockwork ore dominantly in the footwall of the fault we present new zircon u pb apatite fission track and illite k ar data along the jjf and have delineated its tectonic history focusing on its formation and reactivation zircon u pb dating shows that the shangzhuang granite is a composite body with ages between 132 1 and 127 1 ma illite k ar ages for the fault s gouge range from 83 2 to 68 2 ma and the measured apatite fission track ages for ores are between 55 and 21 ma previous zircon u pb geochronology and structural studies suggest that the jjf was originally activated in the jurassic during 160 150 ma as a sinistral fault the jjf was a normal fault in the early cretaceous due to nw se orientated tension and ne sw compression which lasted from 135 to 120 ma this was followed by sinistral strike slip faulting due to nw se compression and ne sw tension during 120 110 ma and it changed to normal displacement at ca 110 ma our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca 55 ma previous age data of ca 130 110 ma for gold mineralization along the jjf coincides with the early cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike slip faulting of the jjf in early cretaceous which is interpreted to be due to changing direction of the subducting pacific plate

temperature and age constraints on the metamorphism of the tethyan himalaya in central nepal a multidisciplinary approach abstract metasediments of devonian to triassic age of the tethyan himalaya th from several areas in central and western nepal between western dolpo and marsyandi valley were sampled for thermo metamorphic studies illite and chlorite crystallinity vitrinite reflectance calcite dolomite and chlorite chloritoid geothermometers k ar dating on illite rich fractions and zircon fission track thermochronology this paper reports for the first time the occurrence of chloritoid in the th out of the range of granite contact aureoles it also presents the first zircon fission track dating performed on th metasediments the peak temperatures of metamorphism have been around 250 300 c 320 350 c 330 370 c and 400 450 c in the western dolpo hidden valley manang and marpha areas respectively in the manang and hidden valley areas illite k ar data are interpreted as ages of recrystallized k white micas newly formed during metamorphism at around 25 30 ma in the marpha area illite k ar and zircon fission track ages 12 15 ma are consistent representing cooling ages after metamorphic overprinting of higher grade than in the other areas the joint investigation of the organic maturation and zircon ft chronology yields insight on the thermal calibration of zircon reset the rmax of 5 7 to 8 0 indicates a temperature range of ca 315 325 c which is in the partial annealing zone of the zircon ft thermochronometer our results might be explained by the presence of a thick thrust sheet once existing above the study area

cooling history of the upper cretaceous palgongsan granite gyeongsang basin se korea and its tectonic implication for uplift on the active continental margin abstract apatite and zircon fission track analyses were carried out to reconstruct the cooling and inferred uplift history of the cretaceous palgongsan granite gyeongsang basin korea the palgongsan granite is one of the bulguksa intrusive rocks that formed by arc related plutonism during late cretaceous to early tertiary time fission track dating of the palgongsan granite yielded nearly concordant ages of 53 and 65 ma for apatite and zircon respectively the palgongsan granite also shows a simple cooling pattern which suggests that it has not been affected by any thermal event after emplacement the cooling history derived from fission track data combined with other thermochronometric data indicates that the palgongsan granite experienced relatively rapid cooling in earlier stage 30 c ma the initial rapid cooling rate during the late cretaceous has been caused by the large thermal contrast between the granite body and the country rocks after reaching thermal equilibrium with the surrounding country rocks the cooling rate of the palgongsan granite was abruptly decreased in late stage in this late stage the decelerated cooling rate is interpreted to have been controlled by uplift and erosion processes and the average exhumation rate is calculated to be ca 50 m my over the temperature range from 100 c to the surface temperature the cooling history of the palgongsan granite is in good agreement with that of the ryoke granitic belt in southwest japan as well as those of the taebaeksan range and other bulguksa intrusive rocks in the gyeongsang basin this suggests that such cooling was probably caused by regional uplift and exhumation processes on the east asian active continental margin compared with the uplift rates of the andes the uplift rates on the eastern pacific margin appear to be higher than those on the western pacific margin

reconstruction of the differentiated long term exhumation history of fuerteventura canary islands spain through fission track and u th sm he data miocene intrusives and lower cretaceous siliciclastic sedimentary rocks from the basal complex in western fuerteventura were analyzed with low temperature thermochronometric methods such as fission track and u th sm he dating in order to reveal the evolution of the island s exhumation history the obtained thermochronometric data yields a very slow rate of cooling in the order of 1 5 3 c myr from 50 to 20 ma for the early cretaceous siliciclastic rocks these sedimentary units have never been heated significantly above 240 c after deposition and still record the submarine onset of the island s formation in the eocene intrusive bodies associated with the early miocene magmatic activity of the central volcanic complex of the island show rapid initial cooling rates of 50 70 c myr from 20 to 14 ma contemporaneous with the intrusions the cooling rate of the cretaceous sedimentary units increased to 25 35 c myr and it is inferred that this increase is associated with enhanced uplift and erosion of the central volcanic complex after 14 ma rates slowed down to 3 6 c myr palaeosols overlying the sedimentary units are themselves covered by pliocene basalt flows and reveal that the sedimentary rocks reached the surface before 5 ma the thermochronometric data obtained in this study for central fuerteventura is difficult to reconcile with the cooling history derived from previously obtained fission track and k ar data from the north western part of the island this inconsistency is likely to indicate that the exhumation history of fuerteventura is more complex and regionally subdivided than previously believed

post break up tectonic inversion across the southwestern cape of south africa new insights from apatite and zircon fission track thermochronometry the south west african margin is regarded as an example of a passive continental margin formed by continental rifting following a phase of lithospheric extension and thinning recent attention focused on this margin has included theoretical modelling studies of rift processes plate kinematic studies of the opening geometry and timing and empirical studies focused on documenting the crustal structure and offshore sedimentary record here we examine the onshore geomorphic and tectonic response to rifting and breakup with a specific focus on the sw cape of south africa we present 75 new apatite and 8 new zircon fission track analyses from outcrop samples and onshore borehole profiles along the western margin of south africa the data are used to derive robust thermal histories that record two discrete phases of accelerated erosional cooling during the early cretaceous 150 130 ma and late cretaceous 100 80 ma respectively both periods of enhanced erosion are regional in extent involved km scale erosion and extend well inland of the current escarpment zone albeit with spatially variable intensity and style the late cretaceous episode is also expressed more locally by tectonic reactivation and inversion of major faults causing km scale differential displacement and erosion the new aft data do not exclude the possibility of modest surface uplift occurring during the cenozoic but they restrict the depth of regional cenozoic erosion on the western margin to less than c 1 km the inferred pattern and chronology of erosion onshore is consistent with the key features and sediment accumulation patterns within the offshore orange and bredasdorp basins it is suggested that the late cretaceous event was triggered by a combination of regional dynamic uplift augmented along the western margin and in the sw cape by local tectonic forces arising from dextral displacement of the falkland plateau along the falkland agulhas fracture zone

neoproterozoic metamorphism and deformation at the southeastern margin of the east european craton uralides russia the eastern margin of the east european craton eec has a long lasting geological record of precambrian age archaean and proterozoic strata are exposed in the western fold and thrust belt of the uralides and are known from drill cores and geophysical data below the palaeozoic cover in the uralides and its western foredeep in the southern uralides sedimentary metamorphic and magmatic rocks of riphean and vendian age occur in the bashkirian mega anticlinorium bma and the beloretzk terrane in the eastern part of the bma yamantau anticlinorium and the beloretzk terrane k ar ages of the 2 m size fraction of phyllites potassic white mica and slates illite give evidence for a complex pre uralian metamorphic and deformational history of the precambrian basement at the southeastern margin of the eec interpretation of the k ar ages considered the variation of secondary foliation and the diagenetic to metamorphic grade in the yamantau anticlinorium the greenschist facies metamorphism of the mesoproterozoic siliciclastic rocks is of early neoproterozoic origin about 970 ma and the s1 cleavage formation of late neoproterozoic about 550 ma the second wide spaced cleavage is of uralian origin in the central and western part of the bma the diagenetic to incipient metamorphic grade developed in late neoproterozoic time in post uralian time proterozoic siliciclastic rocks with a cleavage of uralian age have not been exhumed to the surface of the bma late neoproterozoic thrusts and faults within the eastern margin of the eec are reactivated during the uralian deformation

architectural evolution of the nojima fault and identification of the activated slip layer by kobe earthquake 1 evolutionary history of nojima fault zone is clarified by comprehensive examinations of petrological geophysical and geochemical characterizations on a fault zone in deep drilled core penetrating the nojima fault on the basis of the results we reconstruct a whole depth profile of the architecture of the nojima fault and identify the primal slip layer activated by 1995 kobe earthquake the deepest part 8 to 12 km depth of the fault zone is composed of thin slip layers of pseudotachylite 5 to 10 mm thick each 10 cm in total middle depth 4 to 8 km depth of the fault zone is composed of fault core 6 to 10 m thick surrounded by thick 100 m thick damage zone characterized by zeolite precipitation the shallow part of the fault zone 1 to 4 km depth is composed of distributed narrow shear zones which are characterized by combination of thin 0 5 cm thick each 10 cm in total ultracataclasite layers at the core of shear zones surrounded by thicker 1 to 3 m thick damage zones associated with carbonate precipitation an extremely thin ultracataclasite layer 7 mm thick activated by the 1995 kobe earthquake is clearly identified from numerous past slip layers overprinting one of the shear zones as evidenced by conspicuous geological and geophysical anomalies the nojima fault zone was 10 to 100 times thicker at middle depth than that of shallower and deeper depths the thickening would be explained as a combination of physical and chemical effects as follows 1 thickening of fault core at middle depth would be attributed to normal stress dependence on thickness of the shear zone and 2 an extreme thickening of damage zone in middle depth of the crust would result from the weakening of the fault zone due to super hydrostatic fluid pressure at middle depths the high fluid pressure would result from faster sealing with low temperature carbonate at the shallower fault zone

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

resolution of the age structure of the detrital zircon populations of two lower cretaceous sandstones from the weald of england by fission track dating modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography a computer program has been written and used to identify modes in the zircon fission track age distribution within two lower cretaceous sandstone samples from the weald of southern england pronounced modes appear in one rock around 119 ma 160 ma 243 ma and 309 ma and in the other around 141 ma 175 ma 257 to 277 ma and 394 to 453 ma the geological implications of these quite dissimilar zircon age spectra are discussed it is concluded that they support the palaeogeographical models of allen 1981 and indicate that the provenance of the first sample from the top ashdown sandstone member at dallington in east sussex was almost entirely southerly while that of the second from the netherside sand member at northchapel in west sussex was more varied but predominantly westerly and northerly

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

35 ma old ultrahigh pressure metamorphism and evidence for very rapid exhumation in the dora maira massif western alps abstract ion microprobe shrimp data on zircons from various rock types of an ultrahigh pressure uhp metamorphic whiteschist type pyrope quartzite lens of the dora maira massif dmm consistently show domains giving a late eocene age of 35 4 1 0 ma which is taken as the age of uhp metamorphism these domains partially replace the older oscillatory zoning pattern of the zircons formed during primary magmatic crystallization at about 275 ma zircons of a metagranitic country rock next to the uhp metamorphic lens have these primary features best preserved all zircons measured also yield intermediate ages between 275 and 35 ma with a statistical concentration between 260 and 210 ma thus the uniformity of the initial zircon population both in the lens and the country rock evidences a common protolith that is a granite intruded during the late herynian while the intermediate ages are at least partly due to incomplete resetting of the zircons during uhp metamorphism those in the 260 210 ma range may be related to rifting episodes in the permotriassic the mg rich chemistry of the whiteschist lenses is due to local metasomatic alterations of the granite perhaps by fluids derived from evaporitic sediments dating as early as the permotriassic as well the more pervasive resetting of zircon ages during uhp metamorphism in the pyrope quartzite lenses is explained by the ubiquity of fluids and or melts produced during subduction by a series of dehydration reactions that occurred only in the more hydrous mg rich protoliths and not in their drier granitic neighborhood fission track ages determined partly on the same zircon samples yielding 29 9 1 4 ma mark the time when the uhpm unit had reached about 290 c at a shallow location within the crust thus exhumation over a vertical distance of about 120 km must have occurred within about 5 6 ma indicating an average uplift rate of about 20 24 km ma and an average cooling rate of about 85 100 c ma the radiometric data obtained do not lend any support to an eo alpine cretaceous subduction event so that deep subduction and immediately following exhumation all took place during early to mid tertiary time this scenario seems to apply to large portions of the western and central alps as well calling for drastic geodynamic reinterpretations of these parts of the alps

diagenesis and incipient metamorphism in the western fold and thrust belt sw urals russia in the western fold and thrust belt of the southern urals the kubler and arkai indices determined on shales slates and phyllites record an increase from lower late diagenetic to epizonal grade from west to east the metamorphic grade varies strongly within the different tectonic segments which are separated by major thrusts the increase of diagenetic and incipient metamorphic grade from the footwall to the hanging wall of all major upper palaeozoic thrusts indicates a pre permo triassic origin west of the avzyan thrust zone the diagenetic to incipient metamorphic grade is related to the palaeozoic basin development and reached the final grades in late carboniferous to early permian times east of the first avzyan thrust in the yamantau anticlinorium the diagenetic to lower greenschist metamorphic grade is possibly of neoproterozoic origin and might be related to the development of the neoproterozoic basin at the eastern margin of the east european craton the eastern part of the yamantau anticlinorium was exhumed below 200 c in the late carboniferous or early permian the diagenetic grade of the autochthonous palaeozoic sedimentary units increases toward the stack of palaeozoic nappes and might partly be caused by the deformational process due to the emplacement of the palaeozoic nappes within the timirovo thrust sheet the decrease of metamorphic grade with stratigraphic age developed prior to the emplacement of the nappes the upper anchizonal metamorphic grade of the upper devonian slates of the zilair nappe results from the deformation process related to the lower carboniferous nappe emplacement

the thermal evolution of corsica as recorded by zircon fission tracks abstract new zircon fission track zft ages from corsica record multiple thermal events that can be tied to the structural evolution of the western mediterranean region the corsican zircons have a wide scatter of zft grain ages 243 14 ma which together define several age domains western corsica consists largely of stable hercynian basement characterized by zft ages in the range 161 114 ma we interpret these ages late jurassic early cretaceous as the product of a long lived tethyan thermal event related to continental rifting and subsequent drifting during the separation of the european and african plates and the formation of the liguro piemontese ocean basin in contrast to hercynian corsica alpine corsica northeast corsica experienced widespread deformation and metamorphism in late cretaceous tertiary time dated samples from alpine corsica range in age from 112 to 19 ma and all are reset or partially reset by one or more alpine thermal events the youngest zft grain ages are from the northernmost alpine corsica and define an age population at 24 ma that indicates cooling after tertiary thermal events associated with the alpine metamorphism and the opening of the liguro provencal basin a less well defined zft age population at 72 ma is present in both alpine corsica and hercynian basement rocks the thermal history of these rocks is not clear one interpretation is that the zft population at 72 ma reflects resetting during a late cretaceous event broadly synchronous with the early alpine metamorphism another interpretation is that this peak is related to variable fission track annealing and partial resetting during the tertiary alpine metamorphic event across central to north eastern corsica this partial age resetting supports the presence of a fossil zft partial annealing zone and limits the peak temperature in this area below 300 c for both the affected pre alpine and alpine units

inversion of apatite fission track data for thermal history information apatite fission track length distributions and ages provide an integrated record of the low temperature 20 150 c thermal history of the host rock over geologic time scales the information content of these data is quantified by applying a stochastic optimization technique simulated annealing to determine the range of thermal histories compatible with synthetic apatite fission track data given a mathematical description of fission track annealing the goodness of fit between the observed and predicted data parameters and a slowly decreasing control parameter are treated as analogous to the free energy and temperature respectively of a thermodynamic system on this basis a boltzmann type probability distribution is defined and used to accept or reject random thermal history perturbations a priori information used to constrain the model space may include the temperature range in which the solutions are sought present day temperature the complexity of the thermal history and the maximum duration of the data sensitive thermal history this approach allows determination of the range of thermal histories compatible with an observed confined track length distribution and associated fission track age and it provides an estimate of the probability distribution of temperatures at a specific time results for synthetic data sets for diverse model thermal histories suggest that the resolution of thermal history is generally poor parts of the thermal history to which the data are most sensitive can be resolved to no better than about 10 c for ideal data bounds on acceptable time temperature space are sensitive to the assumed complexity of the thermal history but are relatively insensitive to typical uncertainties associated with the data application of this approach to real data is fundamentally limited by the uncertainty associated with extrapolating annealing models to geologic conditions

alpine orogenic evolution from subduction to collisional thermal overprint the 40ar 39ar age constraints from the valaisan ocean central alps 1 the investigated hp lt metasedimentary units of the valaisan and adjacent european domains occupy a key position in the alpine belt for understanding the transition from early subduction related hp lt metamorphism to collision related barrovian overprint and the evolution of mountain belts in general the timing of high pressure metamorphism subsequent retrogression and following barrow type overprint was studied by 40ar 39ar dating of biotite and several white mica generations that are well characterized in terms of mineral chemistry texture and associated mineral assemblages four distinct age populations of white mica record peak pressure conditions 42 40 ma and several stages of subsequent retrograde metamorphic evolution 36 25 ma biotite isotopic analyses yield consistent apparent ages that cluster around 18 16 ma for the barrow type thermal overprint the recorded isotopic data reveal a significant time gap in the order of some 20 ma between subduction related hp lt metamorphism and collision related barrovian overprint supporting the notion of a polymetamorphic evolution associated with a bimodal p t path

pre miocene palaeogeography of the los cabos block baja california sur geochronological and palaeomagnetic constraints the los cabos block lcb is located at the southern end of the baja california peninsula and is composed mainly of intrusive rocks that were emplaced into pre cretaceous heterogeneous metasediments and are partly covered by miocene volcanic and volcaniclastic rocks field observations provide evidence that the undeformed homogeneous gabbronorite of the sierra el novillo in the ne part of the lcb is the oldest crystalline unit which is intruded by undeformed to slightly deformed tonalitic quartz dioritic granitoids for these rocks an rb sr intrusion age of 129 15 ma and a biotite whole rock cooling age of 116 2 ma were obtained low initial 87sr 86sr and high e nd values of about 0 7036 and 5t o 6 respectively characterise the intrusives as primitive mantle derived granites further to the southeast and south granitoids are more silicic with abundant deformed sequences orthogneisses diatexites and migmatites among others from the southern part of the lcb an rb sr intrusion age for the undeformed granites of 115 4 ma and a biotite cooling age of 90 2 ma were determined initial 87sr 86sr was determined to be 0 7054 and e nd values fall between 2 and 0 the isotopic data do not clearly allow us to characterise the deformed granitoids of the lcb as being intruded by the undeformed unit deformation could have been partly due to syn intrusive tectonics palaeomagnetic data suggest minor if any northward displacement of the lcb with respect to continental mexico corresponding to the rifting in the gulf of california since the late miocene and significant 35 45 clockwise rotations possible tilting evects which may have occurred given the dip of tertiary volcanics on top of the intrusives would modify these values for rotation and to a lesser degree of northward displacement geochemical isotopic and palaeomagnetic results and the cooling history of the lcb are similar to those from the puerto vallarta batholith whereas other mexican continental margin plutons further to the se display lower intrusion ages more rapid cooling rates and generally more primitive magma compositions in the light of the data presented a common magmatic evolution of the lcb and the puerto vallarta batholith is strongly suggested 2000 elsevier science b v all rights reserved

new zircon fission track analysis constraints on tectonic mineralization epochs in the ganzi litang gold belt eastern qinghai tibet plateau abstract the ganzi litang gold belt as a part of the sanjiang tethys orogen is located between the yidun block and songpan ganzi block terrane in the eastern qinghai tibetan plateau and experienced oceanic slab subduction continent arc collision and intracontinental convergence since the indosinian orogeny a series of gold ore deposits have been found within the region this paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track ft thermochronology a total of 15 zircon ft analysis results were obtained that can be divided into four age groups 217 213 ma 190 160 ma 155 93 ma and 72 67 ma representing four distinct episodes of gold mineralization of which the middle two episodes predominate eruption of the auriferous volcanic rocks that comprise the belt started at 217 213 ma when the ganzi litang meso tethys ocean began to subduct the mineralization episode at 190 160 ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional convergence of the ganzi litang belt finally the episodes at 155 93 ma and 72 67 ma are respectively related to the closing times of the bangong nujiang and yarlung zangbu oceans corresponding to tectonic quiet episodes

zircon fission track thermochronology and applications to fault studies zircon is one of the most useful minerals used to unravel the earth s history recorded in rocks after the success of etching fission tracks in zircon fleischer et al 1964 naeser 1969 krishnaswami et al 1974 early studies focused primarily on dating young volcanic horizons for stratigraphic purposes e g naeser et al 1973 hurford et al 1976 seward 1979 gleadow 1980 kowallis et al 1986 kohn et al 1992 subsequently fission track analysis of zircon has been extensively employed along with other radiometric dating methods such as u pb and u th he techniques e g davis et al 2003 reiners 2005 to understand the thermochronology of rocks in a variety of geological settings i e thermal history analysis of basement rocks for orogenic studies e g zeilter et al 1982 hurford 1986 kamp et al 1989 sorkhabi 1993 seward and mancktelow 1994 hasebe and tagami 2001 spikings et al 2001 thermochronology using detrital zircon grains in sedimentary rocks for provenance analysis and thermal history analysis in or near faults which will be highlighted below in this present chapter the thermal sensitivity of the zircon fission track thermochronometry is reviewed in the context of laboratory and field studies then laboratory procedures of the zircon fission track analysis using the external detector method are outlined as practiced in the fission track laboratory of kyoto university for basic fundamentals of these fission track analyses including data analysis and graphical displays see the chapter by tagami and o sullivan 2005 finally as an example of recent geological applications of the technique the results of zircon fission track analysis of the nojima fault zone japan are presented these rocks were the target of systematic drilling of an active fault system using five boreholes and a trench applications to other geological settings and the