survival of ancient landforms in a collisional setting as revealed by combined fission track and u th he thermochronometry a case study from corsica france abstractthe age of high elevation planation surfaces in corsica is constrained using new apatite u th he data field observations and published work zircon fission track apatite fission track aft data and landform stratigraphical analysis thermal modeling results based on aft and u th he data and the eocene sediments uncomformably overlapping the variscan crystalline basement indicate that present day elevated planation surfaces in corsica are the remnants of an erosion surface formed on the basement between 120 and 60 ma during the alpine collision in the paleocene eocene the variscan crystalline basement was buried beneath a westward thinning wedge of flysch and the eastern portion was overridden by the alpine nappes resetting of the apatite fission track thermochronometer suggests an overburden thickness of 4 km covering variscan corsica protected by soft sediment the planation surface was preserved in the latest oligocene to miocene times the surface was re exposed and offset by

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

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

on the development of electron microprobe zircon fission track geochronology abstract the fission track method has been applied for decades to quantify rates and timing of processes in the shallow crust the most widely used approach the external detector method involves counting fission tracks a decay product resulting from the spontaneous fission of 238 u and a paired set of induced tracks parent proxy from the thermal neutron irradiation of 235 u we propose an alternate method of dating zircons that utilizes an electron microprobe to directly measure uranium concentration u and image the number of spontaneous fission tracks or etch figures that intersect the surface of the crystal using an electron backscatter detector the electron microprobe fission track ep ft method is used to date six zircon samples four of which are widely used as standards fish canyon tuff peach springs tuff buluk member of the bakata formation tuff tardee rhyolite mt dromedary complex hypabyssal granite and browns park formation tuff all samples yield ages that overlap within two standard deviations of published reference ages determined using other radiometric techniques i e k ar 40 ar 39 ar and u pb and also by the traditional fission track external detector method to correct for poorly constrained parameters such as the spontaneous fission decay constant weight to volume percent conversions etching efficiency and selection bias we calculate a preliminary z proportionality factor of 4469 661 1 the ep ft technique avoids the hazard and expense of thermal neutron irradiation allows simultaneous chemical compositions to be determined removes the step of counting an external detector manually and will likely allow much higher track densities to be counted than would be normally possible with optical microscopy the technique is ideal for dating moderate to high u zircons 100 ppm u

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

pre observational evolution of surface temperature in romania as inferred from borehole temperature measurements temperature data from nine boreholes in the carpathian orogen in romania were used to obtain information on the ground surface temperature history gsth in the last 250 years the temperature measurements were taken with a thermistor probe sensitivity in the 10 mk range using the stop and go technique at 10 m intervals in the depth range of 20 580 m the least squares inverse modelling approach of tarantola and valette j geophys 50 159 170 1982 was used to infer the gsth long term air temperature records available from the romanian weather station network were used as a comparison term for the first 100 150 years of the gsth and as a forcing function in a pom sat model that combines borehole temperature profiles btps and meteorological time series surface air temperature sat to produce information on the so called pre observational mean pom results from a global circulation model for the romanian area are incorporated in the discussion as well

low temperature constraints on the cenozoic thermal evolution of the southern rhodope core complex northern greece the south rhodope core complex srcc of northern greece is probably the most studied metamorphic core complex of the rhodope massif and yet its geological evolution has not yet been fully unravelled especially the later stages of its thermotectonic evolution we applied the fission track method on apatite and zircon and the u th sm he method on apatite in order to reconstruct the low temperature thermal history the main detachments responsible for the unroofing of the core complex are the kerdilion and the strymon valley detachments the kerdilion detachment initiated the exhumation of the srcc at the latest at 42 ma and controlled it until about 24 ma between 24 and 12 ma the strymon valley detachment accommodated the exhumation since 12 ma brittle normal faults some of them cutting the strymon valley detachment were responsible for the final cooling of the basement rocks in the studied area and the formation of syn tectonic sedimentary basins activity along these brittle normal faults lasted until 6 ma or probably even until today as indicated by recent seismic activity in the area

geodynamic evolution of southern costa rica related to low angle subduction of the cocos ridge constraints from thermochronology abstract the late tertiary shallow subduction of the cocos ridge under the caribbean plate controlled the evolution of the cordillera de talamanca in southeast costa rica which is a mountain range that consists mainly of granitoids formed in a volcanic arc setting fission track thermochronology using zircon and apatite as well as 40ar 39ar and rb sr age data of amphibole and biotite in granitoid rocks constrain the thermal history of the cordillera de talamanca and the age of onset of subduction of the cocos ridge shallow intrusion of granitoid melts resulted in fast and isobaric cooling a weighted mean zircon fission track age 13 analyses and rb sr biotite ages of about 10 ma suggest rapid cooling and give minimum ages for granitoid emplacement in some cases 40ar 39ar and rb sr apparent ages of amphibole and biotite are younger than the zircon fission track ages which can be attributed to partial resetting by hydrothermal alteration apatite fission track ages range from 4 8 to 1 7 ma but show no correlation with the 3090 m elevation span over which they were sampled the apatite ages seem to indicate rapid exhumation caused by tectonic and isostatic processes the combination of the apatite fission track ages with subduction parameters of the cocos plate such as subduction angle plate convergence rate and distance of the cordillera de talamanca to the trench implies that the cocos ridge entered the middle america trench between 5 5 and 3 5 ma

can fission track annealing in apatite be described by first order kinetics abstract it is becoming commonplace to suggest that fission track annealing in apatite can be described by first order kinetics that is the decrease in track density and or length with time during isothermal annealing can be described by a single exponential equation a review of the literature reveals that there is no convincing evidence for such an assertion but more than ample evidence to the contrary simple graphical analysis of available annealing data from the literature clearly shows that the single exponential fails to adequately describe the data more rigorous statistical model fitting is not attempted due to the generally inadequate specification of annealing data in the literature most published annealing data suffer from flaws in experimental design that render them of limited value in defining viable kinetic models for the annealing process consideration of the processes taking place during annealing suggests that there is no good reason why first order kinetics would be expected to describe fission track annealing and more complex models should be considered in order to provide reliable data capable of yielding practically useful kinetic models laboratory annealing experiments should be designed to meet a number of strict criteria in identifying viable models the need is for those which adequately describe the data rather than for physically meaningful models although models should preferably be kept as simple as possible

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

thermotectonic evolution of an extensional dome the cenozoic osogovo lisets core complex kraishte zone western bulgaria the kraishte region of bulgaria is located at the junction of the balkanides and hellenides dinarides tectonic belts fission track analysis on both apatites and zircons documents the cenozoic exhumation of a precambrian basement bounded by low angle detachments late eocene oligocene extension began prior to 47 ma and was dominantly in a top to the southwest direction confirmed by the sense of younging of apatite and zircon ages this crustal extension controlled the formation of half graben sedimentary basins on the hanging walls of the detachments thermal modelling of these hanging wall units provides evidence for heat transfer across the detachments from a relatively warm rising footwall from 32 to 29 ma pervasive magmatic activity resulted in the emplacement of rhyolitic to dacitic subvolcanic bodies and dykes along with intrusion of the osogovo granite the results give evidence for extension in the southern balkan older than and separated from the miocene to quaternary aegean extension this might reflect transtension during northeastward extrusion and rotation of continental fragments around the western boundary of moesia eocene oligocene extension seems to have been controlled by the distribution of earlier thickening all around the carpatho balkanic orocline which is reflected by the cretaceous emplacement of the morava nappe in the kraishte

thermochronologic constraints on evolution of the linglong metamorphic core complex and implications for gold mineralization a case study from the xiadian gold deposit jiaodong peninsula eastern china abstract the nne trending linglong metamorphic core complex hosts the majority of the gold deposits in the jiaodong peninsula of eastern china many of the deposits are hosted by the 163 155 ma linglong granite in the footwall of the linglong detachment fault argon thermochronology suggests that the granite had cooled to 400 c by 143 1 5 ma possibly as a result of normal movement on the detachment nine zircon fission track zft ages from samples collected along a nw se transect perpendicular to the central part of the linglong detachment fault at the 652 m level in the xiadian deposit constrain the subsequent thermal evolution of linglong metamorphic core complex which overlapped the period of major gold deposition the zft ages vary from 136 9 3 3 ma 1 to 130 1 2 2 ma 1 the unaltered linglong granite in the footwall and amphibolite in the hangingwall have similar ages at 136 9 3 3 ma 1 and 135 0 3 0 ma 1 whereas ages for the disseminated and stockwork style ores appear to be younger at ca 131 130 ma although there is an overlap of ages when considering the 1 precision interestingly zft ages show no marked differences between the hangingwall and footwall of the linglong detachment fault although significant movement along the fault occurred the results are best interpreted to indicate that the linglong granite was emplaced at 160 ma and cooled to 240 50 c at 135 ma as recorded by unaltered rocks in the footwall hydrothermal alteration along the linglong detachment fault led to annealing of zircon fission tracks and the consistent younger ages of 131 ma quartz aggregates associated with gold mineralization show evidence of recrystallization suggesting that the hydrothermal event was initiated at temperatures of at least 300 350 c near the brittle ductile transition but cooled rapidly to zft closure temperatures within a country rock environment that was already relatively cool therefore these zft ages suggest that the timing of mineralization at the xiadian deposit was post 135 ma and likely very close to 131 ma the mineralization and cooling occurred in the footwall of a major detachment fault under an extensional regime possibly related to the progressive slab rollback of the paleo pacific plate and controlled by the linglong metamorphic core complex

exhumation in a convergent orogen the western tauern window unroofing of the western tauern window involved both low angle detachment faulting brenner fault and enhanced footwall erosion contemporaneous with upright antiformal folding this combination reflects orogen parallel e w extension during continued n s alpine convergence new fission track ages establish the relative chronology of folding and faulting and demonstrate that displacement was not always accommodated on the same surface during exhumation some units migrated from the footwall to the hanging wall of the main detachment fault due to the interplay between folding and faulting the region can effectively be divided into 3 distinct domains 1 the penninic units of the western tauern window were always in the footwall to the fault with maximum exhumation in the core of the dome due to folding and erosion 2 the lower austroalpine unit north of the tauern window was first part of the hanging wall to the brenner fault at a later stage this unit was exhumed by a further 4 5 km as part of the footwall to a more discrete through going fault the silltal fault 3 the middle and upper austroalpine units west of the tauern window were always within the hanging wall exhumation of the footwall from an initial depth of 25 km led to a transition in mechanical behaviour the curviplanar folded ductile shear zone marking the boundary to the tauern window was eventually transected by a more planar discrete brittle fault silltal fault with unit 2 now in the footwall along which the pre existing mylonites were passively exhumed to the surface

cooling exhumation and deformation in the hindu kush nw pakistan new constraints from preliminary 40ar 39ar and fission track analyses abstract asian crust in the hindu kush region in northern pakistan records a protracted history of rifting subduction and collision not commonly preserved within the himalaya because of this it is key to understanding the development of the southern eurasian margin both prior to and after collision with india new mica 40ar 39ar and apatite fission track geochronologic data from this region provide constraints on the kinematics of the hindu kush 40ar 39ar muscovite and biotite ages from the late cambrian kafiristan pluton are 379 7 1 7 ma and 47 2 0 3 ma respectively the muscovite age may record cooling or partial resetting while the biotite age is interpreted to record a thermal disruption associated with the early stages of continental collision in the himalayan system a 111 0 0 6 ma muscovite age from the northern part of the tirich mir pluton 123 ma old u pb is interpreted to indicate a recrystallization event 12 myrs after its intrusion in addition a younger muscovite age of 47 5 0 2 ma was derived from the opposite side of the same pluton in the immediate hanging wall of the tirich mir fault this eocene age is interpreted to represent the time of recrystallization during fault re activation in the early stages of india asia continent continent collision 40ar 39ar biotite analysis from the buni zom pluton yields an age of 61 6 1 1 ma and is interpreted to reflect cooling at mid upper crustal levels subsequent to the pluton s emplacement in the middle cretaceous finally 17 1 21 3 ma 40ar 39ar ages from the garam chasma pluton and surrounding metapelites indicate cooling immediately following crystallization of the leucogranite body in the earliest miocene latest oligocene the younger cooling history is resolved by fission track dating of apatite aft in the vicinity of the bounding tirich mir fault the tirich mir pluton yields an aft age of 1 4 0 3 ma which is consistent with active exhumation associated with the surface uplift of the 7700 m tirich mir peak the garam chasma pluton has a young age of 3 5 0 2 ma which also records rapid rock uplift and exhumation in the area finally an aft age of 9 1 2 1 ma was extracted from a metapelite in the footwall of an east verging thrust fault separating it from the garam chasma pluton to the west the difference in ages pliocene vs late miocene reflect differential cooling exhumation paths across that structure

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

thermochronological analysis of the dynamics of the southern alps new zealand the isotopic ages of material exposed close to the alpine fault in the southern alps new zealand vary in a consistent fashion along the orogen for the k ar system muscovite and biotite ages display two distinct spatial trends that meet in the area of fox glacier where a strong relationship is observed between k ar age and altitude excess argon is present in samples between mount kinnaird and haast pass in the southwest of the southern alps giving unrealistically old inconsistent k ar ages across this region incorporation of excess argon appears to be highly variable however and minimization of its influence on dynamical interpretations of thermochronology is possible through considering only the youngest age from a given area such treatment indicates that excess argon contamination does not play an important role in the systematic k ar age variation identified along the southern alps the observed age distribution is consistent with estimates of the modern rapid uplift and exhumation of the southern alps beginning ca 5 ma k ar mica ages older than this south of the copland valley indicate that substantial late cenozoic exhumation occurred along the southern alps prior to the development of the modern tectonic regime but at rates lower than at present total exhumation during the current phase of tectonism in the southern alps decreases from the whataroa river southward north of fox glacier the southern alps have attained a dynamical steady state such that the observed distribution of exhumation will not change significantly with further deformation and denudation under current conditions

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

an insight into the breakup of gondwana identifying events through low temperature thermochronology from the basement rocks of madagascar 1 fission track analysis was applied to the precambrian suites of madagascar in order to identify the lower temperature cooling histories and their relationships to the phanerozoic events that affected the island apatite ages range from 431 to 68 ma and zircon ages range from 452 to 238 ma thermochronologically the island can be divided into a southern central and northern region each with a subdivision on an east west basis the southern region is sharply separated from the central region by strongly contrasting apparent apatite ages over the northwest southeast striking ranotsara shear zone rsz the change in apparent ages over the rsz is indicative of later reactivation along younger brittle faults the central region has the oldest ages of the island and has a diffuse contact to the third region northward along the entire western margin of the precambrian basement initial paleozoic exhumation was followed by heating burial by sediments during jurassic and cretaceous times a decrease in ages along the eastern margin from 119 to 68 ma coincides with the predicted positions of the marion hot spot after effects of erosion are considered on the other hand these ages may represent progressive opening of the margin in a southward direction together with associated denudation of the rift shoulder the eastern part of the central region has remained very stable since at least devonian times undergoing only long term very slow exhumation at rates of 1 5 m myr

the stonyford volcanic complex a forearc seamount in the northern california coast ranges jurassic age volcanic rocks of the stonyford volcanic complex sfvc comprise three distinct petrological groups based on their whole rock geochemistry 1 oceanic tholeiites 2 transitional alkali basalts and glasses 3 high al low ti tholeiites major and trace element and sr nd pb isotopic data indicate that the oceanic tholeiites formed as low degree partial melts of normal mid ocean ridge basalt n morb source asthenosphere similar in isotope composition to the east pacific rise today the alkalic lavas were derived from an enriched source similar to that of e morb the high al low ti lavas resemble second stage melts of a depleted morb source asthenosphere that formed by melting spinel lherzolite at low pressures trace element systematics of the high al low ti basalts show the influence of an enriched component which overprints generally depleted trace element characteristics tectonic discrimination diagrams show that the oceanic tholeiite and alkali suites are similar to present day basalts generated at mid oceanic ridges the high al low ti suite resembles primitive arc basalts with an enriched alkali basalt like overprint isotopic data show the influence of recycled components in all three suites the sfvc was constructed on a substrate of normal coast range ophiolite in an extensional forearc setting the close juxtaposition of the morb like olivine tholeiites with alkali and high al low ti basalts suggests derivation from a hybrid mantle source region that included morb source asthenosphere enriched oceanic asthenosphere and the depleted supra subduction zone mantle wedge we propose that the sfvc formed in response to collision of a mid ocean ridge spreading center with the coast range ophiolite subduction zone formation of a slab window beneath the forearc during collision allowed the influx of ridge derived magmas or the mantle source of these magmas continued melting of the previously depleted mantle wedge above the now defunct subduction zone produced strongly depleted high al low ti basalts that were partially fertilized with enriched alkali basalt type melts and slab derived fluids

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

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

zircon la icpms u pb ages and hf isotopes of huayu penghu islands volcanics in the taiwan strait and tectonic implication abstract huayu the only non basalt islet in the penghu islands consists mainly of andesite lavas intruded by some intermediate dacite granodiorite and felsic rhyolite granite dikes the la icpms u pb zircon age determination yields 437 13 ma n 16 mswd 6 9 for the andesite lava and 63 3 1 5 ma n 7 mswd 2 9 for its potassic altered zone and 58 7 0 8 ma n 14 mswd 2 5 for one rhyolite dike the old and young groups of zircon show distinctive hf isotope compositions ehf t 9 for 437 ma zircons vs ehf t 9 to 6 and 9 to 1 for 63 ma and 59 ma zircons on the other hand sr and nd isotopic compositions of the andesite lava isr 0 7034 and end t 3 9 if t 437 ma are more depleted than the alteration zone and rhyolite dike isr 0 7051 and end t 1 3 to 1 9 decoupling of zircon ehf t and whole rock end t values of the andesite lava rules out the possibility of 437 13 ma to be the eruption time alternatively based on the similarity between the published zircon fission track ages 65 3 ma for the andesite lava and 61 2 ma for the rhyolite dike yang h c chen w s huang j c wang lee c m 2008 volcanic lithofacies of the huayu island bulletin of central geological survey 21 143 164 in chinese with english abstract and our u pb zircon ages of the altered andesite zone and rhyolite dike the span of 65 63 ma is suggested to be the formation time of huayu andesites since huayu is situated in a ne sw trending high magnetic anomaly belt which has been generally interpreted as a remnant magmatic terrain these data along with the geochemical results provide insights of this belt as a split part of the southeast coast magmatic belt in which huayu volcanics represent the younger arc volcanism comparable with those appeared in southern fujian

dating brittle tectonic movements with cleft monazite fluid rock interaction and formation of ree minerals 1 two millimeter sized hydrothermal monazites from an open fissure cleft that developed late during a dextral transpressional deformation event in the aar massif switzerland have been investigated using electron microprobe and ion probe the monazites are characterized by high th u ratios typical of other hydrothermal monazites deformation events in the area have been subdivided into three phases d1 main thrusting including formation of a new schistosity d2 dextral transpression and d3 local crenulation including development of a new schistosity the two younger deformational structures are related to a subvertically oriented intermediate stress axis which is characteristic for strike slip deformation the inferred stress environment is consistent with observed kinematics and the opening of such clefts therefore the investigated monazite bearing cleft formed at the end of d2 and or d3 and during dextral movements along nnw dipping planes interaction of cleft filling hydrothermal fluid with wall rock results in rare earth element ree mineral formation and alteration of the wall rock the main newly formed ree minerals are y si y nb ti minerals and monazite despite these mineralogical changes the bulk chemistry of the system remains constant and thus these mineralogical changes require redistribution of elements via a fluid over short distances centimeter low grade alteration enables local redistribution of ree related to the stability of the accessory phases this allows high precision isotope dating of cleft monazite 232th 208pb ages are not affected by excess pb and yield growth domain ages between 8 03 0 22 and 6 25 0 60 ma monazite crystallization in brittle structures is coeval or younger than 8 ma zircon fission track data and hence occurred below 280 c

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

statistical modelling of annealing kinetics of fission tracks in zircon reassessment of laboratory experiments abstract we remodel the annealing kinetics of fission tracks fts in zircon to fit data from 43 laboratory experiments in three earlier publications using spontaneous ft lengths in zircon from the nisatai dacite heating temperature and time are in the ranges of 350 912 c and 10 3 104 h respectively the data sets illustrate a transition in annealing process at a certain temperature zone in order to express the annealing behavior involving the possible transitional process with improved goodness of fit two types of models are constructed the hybrid linear model that consists of the fanning linear model at high temperature and the parallel linear model at low temperature connected with a transitional temperature zone and the parallel curvilinear model that approximates smoothly the transition in the annealing process the validity of the extrapolation of the model to geological time scale is confirmed by comparison with some deep borehole core data the length estimates by the hybrid linear model agree well with the borehole data whilst the estimates by the parallel curvilinear model show a significant disagreement with highly annealed borehole samples although this model provides good agreement with the experimental data for the hybrid linear model estimates of the partial annealing zone corresponding to isothermal heating for 106 and 107 years are 281 352 c and 262 330 c where the top and bottom of the partial annealing zone are defined by the mean length reduction ratio of 0 4 and 0 8 respectively

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

the role of extension in the miocene denudation of the nevado filabride complex betic cordillera se spain the internal zone of the betic cordillera se spain consists of a nappe stack of three complexes the deepest of which is the nevado filabride complex the zone is separated from the overlying alpujarride complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment a suite of 74 new apatite and zircon fission track results have been obtained from the nevado filabride complex and these have been used to define regional cooling patterns for the complex rapid cooling 105 c 200 c ma 1 is spatially related to the tectonic contact with the overlying alpujarride complex cooling to near surface temperatures occurred first in the east sierra de los filabres during the mid serravallian 12 1 ma and was completed by the early tortonian 9 8 ma in the west sierra nevada there is no correlation between fission track age and sample elevation these results are consistent with tectonic unroofing of this complex a finding that favors extension as the mechanism by which the two complexes were brought into contact extension spans the middle and earliest upper miocene 12 8 ma in the study area and therefore lasted much longer than previously documented a hypothesis is advanced which links oblique convergence between the iberian plate and the betic internal zones resulting in crustal contraction at depth with orogen parallel extension in the middle and upper crust

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

diverse sources for igneous blocks in franciscan melanges california coast ranges igneous blocks in franciscan melanges are of three chemical petrologic types 1 tholeiitic basalts of both arc and spreading center origin with depletions in light relative to heavy rare earth elements 3 tio 2 1 high y zr and y ti ratios and relict augites that generally have low al and ti and well defined iron enrichment trends 2 basalts of probable seamount origin with marked enrichments in light relative to heavy rare earth elements 5 tio 2 1 lower y zr and y ti than 1 and ti al rich augites showing little if any iron enrichment trends and 3 hypabyssal intrusives having sio 2 52 tio 2 1 flat or only slightly fractionated rare earth abundance patterns and diopsidic augites that are very low in ti and al and show no iron enrichment trends all of the blocks are metamorphosed most are undeformed pumpellyite bearing greenstones and a few contain sodic amphibole lawsonite sodic pyroxene the melanges are probably olistostromal in origin deriving the

k ar dating of synkinematic clay gouges from neoalpine faults of the central western and eastern alps abstract with ongoing alpine convergence and deformation during exhumation there is a general progression from ductile to brittle behaviour on the periadriatic fault and kinematically related faults farther north e g the simplon rhone fault and a diffuse discontinuous zone of generally dextral strike slip movement on the southern boundary of the aar massif k ar dating of fine grained illite from clay fault gouges provides a reliable method for establishing the maximum age of this transition to brittle faulting and for short lived faults the approximate time of faulting itself the new results establish that brittle faulting on the northeastern segment of the canavese fault i e the part of the periadriatic fault southwest of lago maggiore occurred around 20 ma with south side up kinematics a k ar age of ca 17 ma for the crosscutting giudicarie fault in the eastern alps is effectively identical with an already published pseudotachylyte age and places a lower limit on major and continuous strike slip movements of the periadriatic fault the age of brittle faulting farther north on the southern border of the aar massif is from 13 6 0 3 to 8 3 1 1 ma consistent with the younger cooling and exhumation in this area the dominantly dextral brittle faulting becoming younger to the north reflects the continued indentation and anticlockwise rotation of adria as alpine units become exhumed and progressively welded to the southern block in contrast to the eastern alps there is no field evidence for westward lateral extrusion of alpine units relative to adria and the european foreland

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

orogen parallel extension in the southern carpathians a structural study including a kinematic analysis based on sense of shear criteria recorded in fault rocks is combined with fission track dating a two stage alpine tectonic evolution is proposed for the major tectonic units which constitute the southern carpathians of the parang mountains area upper cretaceous top to the sse nappe stacking was followed by wsw ene orogen parallel extension in the eocene top to the ene shearing in lower greenschist facies mylonites from the eastern part of the danubian window parang mountains is associated with a low angle detachment at the base of the brittlely deformed getic nappe the getic detachment below the dome shaped getic detachment east dipping at the eastern termination of the danubian window the danubian units were rapidly exhumed hence the eastern part of the danubian window represents a greenschist facies core complex as a working hypothesis it is proposed that this orogen parallel stretch was originally n s oriented and that it formed when the rhodopean fragment which includes the getic and supragetic nappes moved northward into an oceanic embayment past the western margin of moesia this eocene extension was part of a process of oroclinal bending in the area of the southern carpathians and their continuation into the balkan mountains extension was followed by about 50o clockwise rotation of the southern carpathians associated with dextral wrenching along the northern boundary of moesia and compression in the moldavides of the eastern carpathians 1998 elsevier science b v all rights reserved

late oligocene neogene evolution of europe adria collision new structural and geochronological evidence from the giudicarie fault system italian eastern alps the giudicarie fault system giudicarie sensu stricto meran mauls passeier thurnstein and jaufen faults represents a sharp break in the generally e w strike direction of the orogen scale periadriatic fault system and is a key element for understanding the late oligocene neogene evolution of the alpine chain the kinematics timing and magnitude of movements on the giudicarie fault system are presented here on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples two main tectonic phases are established 1 back thrusting of the austroalpine units over the southern alps around 32 ma recorded by basement and limestone mylonites along the giudicarie and meran mauls faults with transport directions toward 100 110 and 2 later sinistral transpressive displacement characterized by structures at the ductile brittle transition which overprinted the top to e ese thrust related mylonites but also partitioned into a major system of transcurrent faults in the southalpine domain it was during this later event that the periadriatic fault attained its present day geometry however the amount of sinistral displacement along the giudicarie system was only 15 20 km the magnitude is established here from the 15 km sinistral offset of the jaufen mylonites across the passeier brittle fault and the 20 km long gap in the otherwise continuous distribution of oligocene tonalitic lamellae along the giudicarie fault a direct structural connection is also established between the brenner and the jaufen faults this constrains the timing of the second phase since it must postdate the main exhumation phase of the tauern window at 20 18 ma the results of this study argue against an originally straight periadriatic fault the giudicarie fault formed a restraining bend in this part of the periadriatic fault system since at least the late miocene and probably since the late oligocene

jurassic volcanic glass from the stonyford volcanic complex franciscan assemblage northern california coast ranges hyaloclastite breccias that occur near the top of the stonyford volcanic complex contain abundant volcanic glass and rare basaltic clasts that have not been altered significantly by hydrothermal processes or by subsequent metamorphism they resemble hyaloclastites observed in the summit regions of young pacific seamounts and appear to have formed by submarine fire fountains during which globules of the erupting lava were fragmented by thermal shock from contact with seawater these breccias contain the first reported occurrence of unaltered olivine fo 86 and plagioclase an 63 80 in volcanic rocks of the franciscan complex the glasses are rich in k 2 o nb zr rb and sr relative to both normal and enriched mid ocean ridge basalt morb and low in y v and sc pillow lavas intercalated with the hyaloclastites and a crystalline basalt clast have similar compositional characteristics these magmas are similar to alkalic and transitional basalts that are common in intraplate seamounts and along oceanic spreading centers associated with large ion lithophile element lile enriched mantle plumes other volcanic rocks of the stonyford complex are lile rich tholeiitic basalts and ferrobasalts characteristic of intraplate seamounts a heterogeneous source region that has at least two distinct end members is suggested by the zr nb systematics depleted suboceanic asthenosphere normal morb type source and enriched asthenosphere

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

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

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

cenozoic granitoids in the dinarides of southern serbia age of intrusion isotope geochemistry exhumation history and significance for the geodynamic evolution of the balkan peninsula two age groups were determined for the cenozoic granitoids in the dinarides of southern serbia by high precision single grain u pb dating of thermally annealed and chemically abraded zircons 1 oligocene ages kopaonik drenje eljin ranging from 31 7 to 30 6 ma 2 miocene ages golija and polumir at 20 58 20 17 and 18 06 17 74 ma respectively apatite fission track central ages modelling combined with zircon central ages and additionally local structural observations constrain the subsequent exhumation history of the magmatic rocks they indicate rapid cooling from above 300 c to ca 80 c between 16 and 10 ma for both age groups induced by extensional exhumation of the plutons located in the footwall of core complexes hence miocene magmatism and core complex formation not only affected the pannonian basin but also a part of the mountainous areas of the internal dinarides based on an extensive set of existing age data combined with our own analyses we propose a geodynamical model for the balkan peninsula the late eocene to oligocene magmatism which affects the adria derived lower plate units of the internal dinarides was caused by delamination of the adriatic mantle from the overlying crust associated with post collisional convergence that propagated outward into the external dinarides miocene magmatism on the other hand is associated with core complex formation along the southern margin of the pannonian basin probably associated with the w directed subduction of the european lithosphere beneath the carpathians and interfering with ongoing dinaridic hellenic back arc extension

crustal thermal regime prior to during and after rifting a geochronological and modeling study of the mesozoic south alpine rifted margin an approximately 15 km thick segment of the mesozoic passive continental margin of adria was involved in alpine shortening and is now exposed in the lake como lake lugano area southern alps northern italy and southern swit zerland the segment comprises the monte generoso basin a deep 9 km extensional basin controlled by the activity of the lugano val grande normal fault the paleosurface and mesozoic geometric relations are well preserved so that the kinematics of fault blocks prior to during and after extension are well constrained rb sr 4oar 39ar and zircon fission track data from basement rocks underlying at various the generoso basin depths provide independent estimates on the thermal evolution of the crustal segment during and after rifting most rb sr and 4oar 39ar ages are contemporaneous with the initial stages of rifting late triassic to early jurassic documenting 1 strongly altered thermal conditions before the onset of ex tension and 2 cooling throughout rifting thermal gradients decreased from 60oc km at the onset of extension to 20oc km 4 shortly after breakup zircon fission track ages are juras sic to early cretaceous providing evidence for continued cooling until the beginning of alpine shortening thermoki nematic numerical modeling of the considered crustal segment provides a full two dimensional description of synrift and postrift evolution synthetic time versus temperature curves are extracted from the model and compared with those derived from absolute ages

mechanisms of radon loss from zircon microstructural controls on emanation and diffusion abstract understanding how radon escapes from minerals is important for many fields in earth science yet few studies have focused on the mechanisms for radon escape we measured radon emanation rate and radon loss upon heating for crushed aliquots of three large zircon crystals from three localities mud tank australia bancroft canada and malawi africa our study in conjunction with published data shows that the room temperature radon emanation coefficient rec varies over 5 orders of magnitude in zircon for low u zircon mud tank there are variations in rec that appear to be related to annealing at different temperatures possibly due to annealing of fission tracks however all rec values for mud tank zircon are within error of one another bancroft and malawi zircons have higher u content and do not show any systematic relationship of rec to annealing temperature results from mud tank zircon suggest that partial annealing of fission tracks decreases rec but when all fission tracks are annealed rec reaches a maximum rec in zircons with high u content bancroft and malawi is slightly higher than in zircon with lower u although results are within error results of measurements of radon loss upon heating suggest that radon diffusion is slow 30 of the radon is lost during heating at 975 c for 48 h samples heated a second time yield less fractional radon loss 10 suggesting that diffusion parameters are changed during heating at temperatures 975 c which is likely the result of annealing of radiation damage diffusion parameters calculated from the fractional loss experiments reflect diffusion in highly radiation damaged or metamict zircons our results indicate that internal microstructures in zircon such as fission tracks and alpha radiation damage influence radon escape for diffusion and recoil mechanisms and hence if these effects can be further characterized measurements of 222rn escape have the potential to be useful for probing the internal structure of zircon and other u bearing minerals

a thermomechanical wedge model of taiwan constrained by fission track thermochronometry abstract we present 31 new apatite fission track aft ages for the island of taiwan that when combined with existing aft and zircon fission track zft data provide regional spatial coverage of the island with respect to low temperature thermochronometry the overall pattern of zft and aft ages in taiwan exhibits unreset ages in the southern and western portions of the island and reset ages predominantly in the central range and eastern taiwan this pattern supports interpretations of the orogen kinematics as reflecting a crustal scale wedge with a southward propagating collision zone in this model new material is accreted to the wedge from the west and is transferred to the east with the greatest exhumation occurring along the eastern margin as recorded in the reset ages in the east and unreset ages in the west the southward propagating collision is consistent with reset ages in the north where erosional exhumation has been ongoing for longer and unreset ages in the south where the younger collision implies less time for erosional exhumation despite the variation in the age of the collision along the strike of the island the widths of the aft and zft reset age zones remain nearly constant between 23 00 n to 24 00 n and 23 20 n to 24 00 n respectively suggesting that the orogen is in an exhumational steady state over these regions with respect to the aft and zft thermochronometers we use the fission track data in conjunction with observations of crustal structure crustal fabric and heat flow measurements to constrain a time dependent two dimensional thermomechanical model of orogen evolution by accounting for the heat transfer tectonic and erosion processes needed to predict aft and zft ages we are able to investigate the relationship between the measured ages and the tectonic characteristics of the orogen with our model we conclude that 1 roughly half of the material accretion in taiwan occurs through underplating over an approximately 40 km wide region 2 current average erosion rates are 3 3 mm yr in the eastern central range and 2 3 mm yr over the whole island 3 the collision has been propagating southward at a rate between 20 and 51 km ma over the past 2 3 ma and 4 central taiwan is in a topographic thermal and exhumational steady state

mineralogy and petrology of the haiti cretaceous tertiary section abstract the cretaceous tertiary sections in haiti consist of a sequence of graded beds of turbidity current or gravity flow origin each section may consist variously of five major constituents 1 black glass 2 brown globules veinlets and blobs 3 argillaceous limestone clasts 4 white clasts and shards and 5 a fine grained matrix rich in smectite zeolites and calcite in addition there are trace amounts of a high calcium yellow glass the black glass particles are vesicular apparently unaltered with an andesitic to dacitic composition and in sharp contact with the secondary matrix and veinlet alteration products the brown globules veinlets and blobs consist of a palagonite smectite mix of a distinctly different composition than the black glasses white clasts and shards of a still different more hydrated composition are also present all of these materials are sometimes associated with accretionary lapilli the hydration or alteration products brown globules white clasts and shards and matrix amount to something in excess of 95 of the total deposits the sedimentology mineralogy and petrology of the haiti sections has provided a record of a sequence of probable volcanic events

geochemistry and tectonic setting of the ophiolitic ingalls complex north cascades washington implications for correlations of jurassic cordilleran ophiolites abstract this study synthesizes new and existing chemical data to interpret the tectonic setting of the late jurassic ingalls complex of the northwest cascades washington and to compare it with other cordilleran ophiolites of similar age mafic rocks of the ingalls complex represent a spectrum of magma types including normal type and enriched mid ocean ridge basalt within plate basalt and island arc basalt based on mafic magma chemistry compositions of cr spinels in associated peridotite and field relations the ingalls complex is a suprasubduction zone ophiolite formed in a back arc basin cut by an oceanic fracture zone regional tectonic relations also support this hypothesis our synthesis of available chronologic geochemical and stratigraphic data for all jurassic cordilleran ophiolites shows that the ingalls complex has similarities and differences with each the most compelling likeness is between the ingalls complex and josephine ophiolite both of which exhibit a wide range of magmatic af

exhumation of the sierra de cameros iberian range spain constraints from low temperature thermochronology we present new fission track and u th he data from apatite and zircon in order to reconstruct the exhumation of the sierra de cameros in the northwestern part of iberian range spain zircon fission track ages from samples from the depocentre of the basin were reset during the metamorphic peak at approximately 100 ma detrital apatites from the uppermost sediments retain fission track age information that is older than the sediment deposition age indicating that these rocks have not exceeded 110 c apatites from deeper in the stratigraphic sequence of the central part of the basin have fission track ages of around 40 ma significantly younger than the stratigraphic age recording the time of cooling after peak metamorphic conditions apatite u th he ages in samples from these sediments are 31 40 ma and record the last period of cooling during alpine compression the modelled thermal history derived from the uppermost sediments indicates that the thermal pulse associated with peak metamorphism was rapid and that the region has cooled continuously to the present the estimated palaeogeothermal gradient is around 86 c km 1 and supports a tectonic model with a thick sedimentary fill c 8 km and explains the origin of the low grade metamorphism observed in the oldest sediments

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

glassy microspherules microtektites from an upper devonian limestone the properties of microspherules recovered from an upper devonian marine limestone immediately overlain by a geochemical anomaly of siderophile and chalcophile elements are similar to those of impact derived microtektites these microspherules are glass have splash form shapes contain spherical vesicles and lechatelierite inclusions and show oxide compositional variations similar to those in known microtektites these characteristics suggest that these upper devonian microspherules have an impact origin a bolide impact may have occurred about 365 million years ago on the south china plate and caused a faunal extinction on eastern gondwana

late mesozoic and cenozoic tectono thermal history and geodynamic implications of the great xing an range ne china abstract the mesozoic cenozoic tectonics of northeastern china involves complex multistage interaction of different tectonic domains and has long been controversial the tectono thermal evolutionary history recorded by the widespread outcropped granitoids in the great xing an range gxr may provide significant constraints on the tectonics illuminating the deep geodynamic process here we present new low temperature thermochronology data from the gxr and thus reconstruct the detailed thermal history zircon fission track dating yielded a group of central ages ranging from 80 4 to 185 10 ma while apatite fission track ages range from 55 3 to 75 5 ma the modeled time temperature paths of all the samples reveal two relatively rapid cooling events at 100 60 ma and 50 0 ma and one intervening reheating episode at 60 50 ma the initial uplift exhumation and induced cooling events which represent strong orogenic activity are related mainly to closure of the mongol okhotsk ocean in the north and were subsequently influenced by the paleo pacific plate subduction in the east the evolution of the basin mountain system consisting of the songliao basin and gxr as well as the accretion metamorphism and magmatism at the northeast asian continental margin are all dominated or indirectly influenced by the paleo pacific subduction this indicates that the paleo pacific subduction had affected the evolution of the gxr to the west since the jurassic the significant reheating episode during the late paleocene to eocene may be related to the heat flux derived from asthenosphere upwelling and igneous activity

statistical modelling of thermal annealing of fission tracks in zircon abstract we re analyse the data of yamada et al 1995b which represent the first substantial published experiments on thermal annealing of fission tracks in zircon we use an improved approach to the statistical modelling of the relation between track length temperature and time that has recently been developed for fission tracks in apatite there are several advantages to our new approach we distinguish between unannealed and induced tracks we partition the residual variance into within and between components corresponding to sampling error and extraneous sources of variation we allow for different numbers of tracks in the experiments and we use the information even in those cases where no tracks are seen our conclusions differ somewhat from those of yamada et al 1995b in that we find that the data are not extensive enough to distinguish clearly between competing models there is a need for further experiments to be planned and carried out and we make some recommendations on their design

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

fission track analysis of the footwall of the catalina detachment fault arizona tectonic denudation magmatism and erosion new apatite and zircon fission track ages obtained from the footwall of the catalina metamorphic core complex record a complicated cooling history associated with mid tertiary extension zircon fission track ages record the progressive unroofing of the catalina metamorphic core complex along the catalina detachment fault zircon fission track ages range from 31 9 to 19 4 ma generally decrease in the hanging wall slip direction and yield slip rates along the catalina detachment fault ranging from 1 2 to 12 km myr 1 in contrast apatite fission track ages increase in the hanging wall slip direction samples from the main range of the santa catalina mountains yield apatite fission track ages of 20 5 to 14 6 ma samples from the santa catalina mountain forerange located closer to the detachment fault yield apatite fission track ages of 21 4 to 18 8 ma rapid cooling 40 to 60 c myr 1 related to detachment faulting is best recorded by zircon fission track ages and higher temperature thermochronometers in the main range and by nearly concordant zircon and apatite fission track ages in the forerange slower cooling 3 7 c myr 1 of the footwall is recorded by shortened mean confined fission track lengths 14 m and is related to erosional unroofing approximately 2 km of late tertiary erosion played a significant role in the unroofing of the footwall of the catalina metamorphic core complex in contrast to metamorphic core complexes in western arizona where detachment faulting is the dominant unroofing mechanism

radioisotopic and biostratigraphic age relations in the coast range ophiolite northern california implications for the tectonic evolution of the western cordillera the coast range ophiolite cro in northern california includes two distinct remnants the elder creek ophiolite is a classic suprasubduction zone ophiolite with three sequential plutonic suites layered gabbro wehrlite pyroxenite quartz diorite a mafi c to felsic dike complex and mafi c felsic volcanic rocks the entire suite is cut by late mid oceanic ridge basalt morb dikes and overlain by ophiolitic breccia the stonyford volcanic complex sfvc comprises three volcanic series with intercalated chert horizons that form a submarine volcano enclosed in sheared serpentinite structurally below this seamount are melange blocks of cro similar to elder creek u pb zircon ages from plagiogranite and quartz diorites at elder creek range in age from 165 ma to 172 ma u pb zircon ages obtained from cro melange blocks below the sfvc are similar 166 172 ma 40 ar 39 ar ages of alkali basalt glass in the upper sfvc are all younger at 164 ma radiolarians extracted from chert lenses intercalated with basalt in the sfvc indicate that the sedimentary strata range in age from bathonian unitary association zone 6 6 of baumgartner et al 1995a near the base of the complex to late callovian to early kimmeridgian unitary association zones 8 10 in the upper part the sfvc sedimentary record preserves evidence of a major faunal change wherein relatively small sized polytaxic radiolarian faunas were replaced by very robust oligotaxic nassellarian dominated faunas that included praeparvicingula spp we suggest that cro formation began after the early middle jurassic 172 180 ma collision of an exotic or fringing arc with north america and initiation of a new or reconfi gured east dipping subduction zone the data show that the cro formed prior to the late jurassic nevadan orogeny probably by rapid forearc extension above a nascent subduction zone we infer that cro spreading ended with the collision of an oceanic spreading center ca 164 ma coincident with the oldest high grade blocks in the structurally underlying franciscan assemblage we further suggest that the classic nevadan orogeny represents a response to spreading center collision with shallow subduction of young lithosphere causing the initial compressional deformation and with a subsequent change in north american plate motion to rapid northward drift j2 cusp causing sinistral transpression and transtension in the sierra foothills these data are not consistent with models for late jurassic arc collision in the sierra foothills or a back arc origin for the cro

direct dating of archean microbial ichnofossils well preserved archean pillow lavas from the ca 3 35 ga euro basalt of the pilbara craton western australia contain micron sized tubular structures mineralized by titanite catisio 4 with residual organic carbon preserved along their margins direct u pb dating of titanite in the tubular structures demonstrates an archean age these tubular microstruc tures are identical to microbial ichnofossils in modern basalts ophiolites and greenstone belts and are interpreted as a biogenic signature in these ancient rocks microbial colonization of basaltic glass thus appears to have been part of a deep subsurface biosphere established early in earth s history

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

experimental study on hydrothermal annealing of fission tracks in zircon abstract increasing temperature causes fading of fission tracks fts in minerals which has been quantified by many laboratory heating experiments in atmosphere in order to elucidate whether or not ft annealing at hydrothermally pressured conditions is the same as that at atmospheric condition we performed zircon heating experiments using a hydrothermal synthetic apparatus for reliable comparison we annealed the same zircon samples using the same temperature monitor and analyzed them using the same experimental procedure as the previous experiment at atmosphere yamada et al chem geol isot geosci sect 122 1995 249 the observed ft annealing characteristics are indistinguishable between atmospheric and hydrothermally heating it is therefore implied that the annealing kinetics of ft in zircon previously established can be applied to thermal history analysis of rocks that were subjected to hydrothermal conditions in nature such as those in fault and subduction zones

thermal and unroofing history of a thick tilted basin and range crustal section in the tortilla mountains arizona we estimate here a geothermal gradient of only 17 5 c km 1 for the tilted grayback fault block in southeastern arizona when extension began 25 ma this gradient is lower than preextension gradients estimated elsewhere in the basin and range is only about 50 of typical gradients in the basin and range today and needs to be accounted for in models of continental extension the grayback block exposes a 12 km thick crustal section of proterozoic and cretaceous granitoids which was tilted 90 during extension between 25 and 15 ma zircon fission track ages decrease structurally downward westward across the block and were all within a zone of partial track annealing prior to tilting and quenching the zircon age gradient suggests that the 220 240 c isotherm migrated downward 5 6 km during paleogene erosion and regional cooling apatite fission track ages decrease westward from 83 ma in the structurally highest crystalline rocks to 24 ma at 6 km paleodepth and then to 15 ma another 6 km farther west track length analysis confirms that apatites above the break in slope in age at 5 7 km paleodepth resided in a zone of partial annealing prior to tilting and deeper apatites record rapid cooling upon tilting and unroofing beginning 25 ma at that time the 110 10 c isotherm determined by the depth at which tracks in apatite were fully erased was at a basement paleodepth of 5 7 km and the 220 30 c isotherm as estimated from zircon data resided at a pretilting basement depth of 12 15 km from consistent values of paleogeothermal gradient for two depth intervals we estimate the pretilt gradient was 17 5 c km 1 from 25 to 15 ma the rotating grayback block cooled rapidly as higher westward moving blocks unroofed it tectonically at a rate of 1 km m y 1

low temperature thermochronology of the yakutat plate corner st elias range alaska bridging short term and long term deformation abstract this study investigates the long term deformation and rock exhumation of the subducting yakutat microplate corner at the st elias syntaxis region with a special focus on the area east and west of yakutat bay where major coseismic surface uplift occurred during a mw 8 2 earthquake in 1899 we use low temperature thermochronology to quantify the long term activity of thrust and reverse faults we present new apatite and zircon u th sm he ages from 35 bedrock samples collected along profiles crossing major faults that compose a one sided flower structure at the northern end of the fairweather fault the cooling ages reveal that rapid rock exhumation is accommodated by the eastern esker creek fault and the yakutat fault with rates of 2 3 mm yr and slower rates of

radon emanation coefficients of several minerals how they vary with physical and mineralogical properties the escape rates of radon gas from rocks and minerals are of great relevance to many branches of geosciences and it is thus important to understand the physical and mineralogical properties that control radon emanation rates mechanisms of radon loss from minerals have direct bearing on the reliability of u pb and u th he geochronology fourteen minerals from three different mineral groups and with localities spanning three continents were selected for this study the radon emanation coefficients rec for each mineral were measured as a function of grain size temperature 238 u and 232 th activities total absorbed dose density and mineral melting temperature the measured 238 u and 232 th activities ranged from 0 01 to 6487 bq g and from below detection limit to 776 bq g respectively the rec values for unheated pulverized samples ranged from 0 083 to 7 0 which is comparable to previously reported ranges except for zircon an inverse correlation between grain size and rec was observed full annealing of fission tracks resulted in an overall decrease in rec values suggesting that nuclear tracks could possibly act as conduits for radon release while activity dose density and melting temperatures are not strongly correlated with rec values it was observed that minerals with high melting points 1400 c have lower rec values most likely due to inhibition of radon release by compact crystal lattice structures this is the first attempt to our knowledge to correlate rec values with melting temperature and this study reports six minerals for which no rec values have been previously reported

phanerozoic history of the mahanadi region india the mahanadi basin is a nw se stretching gondwana basin perpendicular to the east coast of india the metamorphic basement to the basin mainly comprises rocks of the eastern ghats mobile belt egmb which experienced a complex thermotectonic evolution involving several episodes of deformation and magmatism it can be inferred from 40ar 39ar ages on hornblende 845 ma and biotite 622 and 593 ma from basement rocks that the last high grade metamorphism in the western part of the egmb i e the western khondalite zone occurred during the late grenvillian with any pan african overprint only reaching anchimetamorphic conditions only pseudotachylite intrusions and their related thermal imprint with ages around 515 ma display a direct pan african signature fission track analyses on nine zircon 419 313 ma and 49 apatite 443 119 ma samples indicate a rift related formation of the mahanadi basin as an asymmetrical half graben in two stages during the permo carboniferous and the middle triassic moreover the gondwana breakup in eastern india is signified by dyke intrusions and the thermal overprint of thrusts and faults in the mahanadi region and the onset of ocean floor production in the mahanadi offshore basin at around 120 ma

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

precambrian temperature and pressure system of gaoshiti moxi block in the central paleo uplift of sichuan basin southwest china abstract recently trillions of cubic meters gas resources have been found in sinian reservoirs of gaoshiti moxi region in the central uplift of sichuan basin which is the first commercial discovery of primary gas field in precambrian anywhere in the world to obtain a great breakthrough in precambrian hydrocarbon exploration it is necessary to find out the evolution process of temperature and pressure reconstructing the thermal history and pore pressure evolution in carbonate reservoirs are challenging problems especially in deep old layers without available samples and methods to study the temperature and pressure system we conducted a comprehensive analysis combining the paleo thermal indicators and inclusions pressure volume temperature pvt simulation with basin modeling the results showed that the thermal history of the gaoshiti moxi area could be divided into three stages from the late sinian to late paleozoic the thermal regime was stable with low heat flow value

constraining the timing of brittle deformation and faulting in the toki granite central japan abstract constraining of the timing of fault zone formation is of fundamental geotectonic importance to understand structural evolution and brittle fault processes here we present authigenic illite k ar age data from brittle fault zones comprising two gouges within the toki granite central japan the gouge samples were collected at depths of 252 9 and 403 7 m from a shaft at the mizunami underground research laboratory and were separated into five grain size fractions

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

timing of brittle deformation within the nojima fault zone japan abstract k ar ages from clay fault gouges of outcrop and core samples ug500 well from the nojima fault zone awaji island japan are consistent internally with established field constraints and with apatite and zircon fission track ages demonstrating the suitability of this method for dating of brittle deformation six unspiked and thirty conventional k ar data of clay minerals separated from gouge zones were analysed characterized by protoliths of high grade metamorphic and magmatic rocks the samples from the nojima fault zone offer the opportunity to distinct identify newly grown illite in the fault planes all dated sample fractions were characterized by xrd sem and tem k ar ages of 29 separates have an age range from 63 4 1 3 ma early palaeocene danian to 42 2 1 0 palaeogene middle eocene lutetian some

transition from orogen perpendicular to orogen parallel exhumation and cooling during crustal indentation key constraints from 147sm 144nd and 87rb 87sr geochronology tauern window alps abstract the core of the alpine orogen in the eastern alps tauern window experienced a change from orogen normal shortening and post nappe doming to predominantly orogen parallel extension and tectonic unroofing during late oligocene to miocene northward indentation of the adriatic microplate a new 147 sm 144 nd isochron age of 25 7 0 9 ma on a garnet bearing assemblage from the lowest nappe complex forming a dome in the eastern part of the tauern window indicates that high temperatures related to post nappe barrovian type metamorphism overlapped in time with the onset of doming new 87 rb 87 sr biotite ages from this same complex combined with previously published 87 rb 87 sr white mica ages suggest that doming and exhumation began no later than 28 ma immediately in front of indenting austroalpine crustal blocks then migrated laterally to the ese during rapid exhumation and orogen parallel stretching beginning at about 23 ma rapid cooling ended at approximately 17 ma in the footwall of the katschberg normal fault which delimits the eastern margin of the tauern window a similar pattern of migrating doming orogen parallel extension and cooling is recognized in the western part of the tauern window where rapid exhumation began at about 20 ma some 2 3 ma later than in the eastern part this difference in the onset of rapid exhumation as well as the overall migration of doming from the center to the ends of the tauern window are attributed to fragmentation of the aforementioned austroalpine blocks along the leading edge of the main adriatic indenter southern alps as this indenter advanced to the north

bioalteration of basaltic glass in the oceanic crust 1 bioalteration of quaternary to early cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in deep sea drilling project ocean drilling program dsdp odp samples from shallow to deep drill holes from the north to central atlantic ocean lau basin and costa rica rift a wide range of marine settings biogenerated textures are rooted in fractures and occur as two main types a granular type and a tubular type the granular type common at all depths within the volcanic pile appears as solid bands semicircles or irregular patches of individual and or coalesced spherical bodies mostly 0 2 0 6 m in diameter with irregular protrusions into the fresh glass the tubular type is more common at deeper levels in the crust and consists of thin tubes sometime branching bodies mostly 20 30 m long and are more common at deeper levels the upper crust displays a large variability in the relative importance of biotic to abiotic alteration and the degree of bioalteration appears to decrease with depth thus the fraction of bioalteration of the total alteration of the glass ranges from 20 90 in the upper 300 m down to a maximum of 10 at about 500 m depth this might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust the proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust thus bioalteration lasts as long as abiotic alteration i e for as long as water is available to the hydration of the oceanic crust evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least 70 ma and thus the deep biosphere is likely to expand at least into crust of this age

burial and exhumation of corsica france in the light of fission track data 1 the mesozoic and cenozoic exhumation and cooling history of corsica is reconstructed by fission track ft data on basement and sedimentary rocks apatite ages are 105 16 ma zircon ages are 160 145 ma the jurassic and cretaceous ages show that parts of the variscan basement escaped alpine influence the basement was thermally affected by rifting prior to jurassic opening of the ligurian piedmont ocean then it cooled to near surface temperatures in paleocene eocene times subduction buried parts of the basement and overlying flysch to greater depth in the oligocene both collapse of the nappe stack and rifting prior to opening of the ligurian provencal basin affected the apatite ft system of the basement in different partly overlapping areas causing a complex age pattern the study shows that thorough analysis of ft data and thermal modeling allow to assign age populations to distinct cooling processes even when several thermotectonic events contributed to generate an intricate age pattern

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