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

intercalibration of astronomical and radioisotopic time the 40ar 39ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in earth s history but the accuracy of this method is limited by the accuracy with which the ages of neutron fluence monitors dating standards are known calibrating the ages of standards by conventional means has proved difficult and contentious the emerging astronomically calibrated geomagnetic polarity time scale apts offers a means to calibrate the ages of 40ar 39ar dating standards that is independent of absolute isotopic abundance measurements seven published 40ar 39ar dates for polarity transitions nominally ranging from 0 78 to 3 40 ma are based on the fish canyon sanidine standard and can be compared with apts predictions solving the 40ar 39ar age equation for the age of the fish canyon sanidine that produces coincidence with the apts age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27 78 to 28 09 ma with an inverse variance weighted mean of 27 95 0 18 ma normalized residuals are minimized at an age of 27 92 ma indicating the robustness of the solution

intercalibration of 40ar39ar dating standards a number of standards used for k ar and 40ar39ar dating have been intercalibrated multiple splits 15 40 mg each of mmhb 1 sb 3 biotite lp 6 biotite 40 60 ga1550 biotite fish canyon tuff 3 biotite taylor creek rhyolite sanidine bern 4 muscovite bern 4 biotite and pennsylvania state university orthoclase 1a were irradiated in capsules fused and analyzed in replicate analyses most of these standards proved to be homogeneous in 40ar 39ark ratio age k ca and 36ar contents mmhb 1 is inhomogeneous in age at the 15 mg level indicating it is unsuitable for use as an interlaboratory standard using material taken straight from the bottle the orthoclase sample is also inhomogeneous at the 30 mg level quoted relative to an age of 162 9 ma for the sb 3 biotite standard total fusion ages are lp 6 biotite 40 60 128 1 ma ga1550 biotite 97 8 ma fish canyon tuff 3 biotite 27 95 ma taylor creek rhyolite sanidine 28 0 ma bern 4 muscovite 18 51 ma bern 4 biotite 17 21 ma these ages are in good agreement with the absolute k ar ages of these minerals different preparations of biotite and sanidine standards from a welded tuff such as the fish canyon tuff may not be of identical ages tests on submilligram splits reveals that sb 3 biotite ga1550 biotite fish canyon tuff 3 biotite and taylor creek rhyolite sanidine are suitable for use as monitors in laser work the sanidine specimen appears to be the most suitable for use as the primary monitor for 40ar39ar dating

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

helium chronometry of apatite and titanite using nd yag laser heating we developed a technique for extracting 4he from apatite and titanite using laser heating that permits measurement of u and th and hence u th he ages on a single sample aliquot unlike direct laser heating quantitative he extraction and u th retention can be achieved when samples are indirectly laser heated to temperatures below their melting point resulting he ages are consistent with those obtained from conventional furnace heating of larger samples the major advantages of this technique include faster analysis and far lower more reproducible he blanks that permit single crystal analyses single crystal dating opens a variety of new avenues for u th he chronometry

standardless fission track ages of the iugs age standards abstract standardless fission track ages for four zircon two titanite and three apatite age standards most of them recommended by the fission track working group of the iugs subcommission on geochronology were redetermined the age calculations used the decay constant for spontaneous fission of 238u f 8 5 0 1 10 17 a 1 recommended by the iupac the ratio of etchable to latent track length in both the dated minerals zircon titanite and apatite and mica detectors and the 187 track counts with the external detector and population methods we found the resulting standardless fission track ages are in line with results from more recent high precision geochronology including zircon u pb dating these results confirm that standardless fission track dating of zircon titanite and apatite with the external detector method is feasible as well as dating of apatite with the population method and that calibration can be based on the zircon u pb ages of the current standard samples on the other hand there is no room for an age correction for partial annealing of the fossil tracks based on their mean confined track lengths of the apatite titanite and zircon age standards

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

thermal and exhumation history of sakhalin island russia constrained by apatite u pb and fission track thermochronology abstract sakhalin island represents a key locality to study the tectonic evolution of the western pacific the island is located at the amur okhotsk plate margin and records a complex thermotectonic history apatite double dating u pb and fission track and thermal history modelling were applied to three late eocene granitoid massifs within central and southern sakhalin the aniva okhotsk and langeri complexes apatite u pb results yield consistent late eocene 40 37 ma ages suggesting rapid post magmatic cooling apatite fission track results reveal bimodal age distributions with late eocene early oligocene 38 33 ma and early miocene 20 17 ma age populations that can be correlated with variations in uranium and chlorine concentrations thermal history modelling translates the aft age bimodality into two phase cooling histories the timing of the early cooling phase 38 33 ma corresponds with the apatite u pb ages indicating rapid cooling to at least 100 c during the late oligocene the second cooling phase at 20 17 ma cooled the samples to near surface temperatures both cooling phases correspond with regional unconformities and subsequent accelerations in sedimentation rate suggesting that cooling was a response to rapid exhumation in addition our data suggests that the studied terranes record differential exhumation with respect to the structural architecture the miocene exhumation pulse is coeval with the timing of transpressional fault displacement and the subsequent opening of the kuril basin

uplift and denudation history of the akaishi range a thrust block formed by arc arc collision in central japan insights from low temperature thermochronometry and thermokinematic modeling fission track ft u th he he and u pb data were used to identify the denudation history of the akaishi range central japan the northern akaishi range is bounded on the east by the itoigawa shizuoka tectonic line fault zone istl fz the thermochronometric ages progressively decreases with the decreasing distance to the istl fz thermo kinematic calculations suggest that the age pattern observed can be explained by a 5 7 5 mm yr reverse slip on the istl fz that dips 34 45 west and soles onto detachment at a20 22 5 km depth by assuming the same geometry and slip rate of the fault thebedrock uplift rates and denudation rates are estimated at 4 mm yr thus the uplift and denudation style of the northern akaishi range is well explained asa simple tilted thrust block that has been exhumed along the listric istl fz on the other hand considering both the difference in apatite ft age and the active fault distribution the southern akaishi range might be different in uplift origin and timing although the difference in apatite ft ages between them may be attributable to the chlorine content variation in apatite the inferred total denudation is larger than several kilometers and likely exceeds 10 km since the beginning of the northern akaishi range uplift suggesting that the low relief surfaces on the ridges and the relatively constant elevations of the summits reflect post uplift denudation rather than pre existing low relief landforms

the low temperature thermo tectonic evolution of the western tian shan uzbekistan abstract the kyzylkum nurata region represents a key area in understanding the tectonic evolution of the western tian shan in this study we present new thermochronological data apatite fission track and apatite u th sm he and associated thermal history models for 45 igneous samples from the kyzylkum nurata segment of south tian shan on the territory of uzbekistan and tajikistan our data show that the kyzylkum nurata segment experienced a multi phase mesozoic thermal history that differs from previously studied segments of the tian shan a triassic 220 200 ma cooling signal is widespread throughout the tian shan and is interpreted as being associated with exhumation following the closure of the palaeo asian ocean following this period of fast cooling the kyzylkum nurata segment experienced a period of slow cooling and erosion in the early jurassic 190 160 ma however in contrast to other parts of the tian shan our study area preserves evidence for rapid cooling during the late jurassic early cretaceous 160 120 given that this rapid cooling signal was only recorded for samples in association with major structures e g relic suture shear zones we interpret this event as a period of fault reactivation related with tectonic processes at the eurasian margin of the tethys ocean subsequently the late cretaceous early palaeogene 100 50 ma is characterised by slow cooling and erosion since the late palaeogene the basement of the tian shan experienced cooling related to the india eurasia collision the thermal signal of this collision has been extensively recorded in the high altitude kyrgyz tian shan within the low relief kyzylkum nurata segment this cenozoic overprint is not recorded allowing for a detailed assessment of the mesozoic thermal and landscape evolution of the western tian shan our study demonstrates that the cretaceous uzbek tian shan was characterised by a series of parallel linear mountain belts that formed along suture zones during fault reactivation

laser ablation u th sm he dating of detrital apatite abstract laser ablation u th sm he dating of apatite la ahe is an emerging technique that presents a number of advantages over conventional whole grain methods increased analytical efficiency through the elimination of he re extractions and acid digestion increases sample throughput and facilitates larger datasets the spatially resolved selection of helium extraction locations eliminates the need for alpha ejection corrections and allows for imperfect grains with inclusions fractures unusual morphologies rounding and surface frosting or coatings to be measured these advantages allow the effective analysis of detrital samples which opens new avenues for geologic applications time resolved parent isotope concentration data collected by la icp ms enables the screening of grains for chemical zonation a commonly cited cause of over dispersion in u th sm he dates simultaneous collection of other chemical e g anion or trace element compositions or isotopic u pb age information for the grain may enhance provenance interpretations we demonstrate the accuracy and uncertainty of the measurement method using two measurement sessions we determine the age of the fish canyon tuff apatite reference material to be 27 9 0 6 ma n 45 mswd 1 5 which is in agreement with previous determinations our data reveal that zonation is a common feature in fish canyon tuff apatite and can be resolved by la ahe methods to reduce dispersion la ahe methods are ideally suited to detrital studies where a large number of measurements and a reduction in grain selection bias compared to whole grain methods should result in the sample better reproducing the source population the utility of the method is demonstrated using a modern sand from the wenatchee river washington usa previously characterized by conventional whole grain ahe methods our la ahe dataset n 74 better reproduces the ahe ages of bedrock samples within the drainage in comparison to the age distribution derived from conventional ahe dating

voluminous lava like precursor to a major ash flow tuff low column pyroclastic eruption of the pagosa peak dacite san juan volcanic field colorado abstract the pagosa peak dacite is an unusual pyroclastic deposit that immediately predated eruption of the enormous fish canyon tuff 5000 km3 from the la garita caldera at 28 ma the pagosa peak dacite is thick to 1 km voluminous 200 km3 and has a high aspect ratio 1 50 similar to those of silicic lava flows it contains a high proportion 40 60 of juvenile clasts to 3 4 m emplaced as viscous magma that was less vesiculated than typical pumice accidental lithic fragments are absent above the basal 5 10 of the unit thick densely welded proximal deposits flowed rheomorphically due to gravitational spreading despite the very high viscosity of the crystal rich magma resulting in a macroscopic appearance similar to flow layered silicic lava although it is a separate depositional unit the pagosa peak dacite is indistinguishable from the overlying fish canyon tuff in bulk rock chemistry phenocryst compositions and 40ar 39ar age the unusual characteristics of this deposit are interpreted as consequences of eruption by low column pyroclastic fountaining and lateral transport as dense poorly inflated pyroclastic flows the inferred eruptive style may be in part related to synchronous disruption of the southern margin of the fish canyon magma chamber by block faulting the pagosa peak eruptive sources are apparently buried in the southern la garita caldera where northerly extensions of observed syneruptive faults served as fissure vents cumulative vent cross sections were large leading to relatively low emission velocities for a given discharge rate many successive pyroclastic flows accumulated sufficiently rapidly to weld densely as a cooling unit up to 1000 m thick and to retain heat adequately to permit rheomorphic flow explosive potential of the magma may have been reduced by degassing during ascent through fissure conduits leading to fracture dominated magma fragmentation at low vesicularity subsequent collapse of the 75 35 km 2 la garita caldera and eruption of the fish canyon tuff were probably triggered by destabilization of the chamber roof as magma was withdrawn during the pagosa peak eruption

building the pamir tibetan plateau crustal stacking extensional collapse and lateral extrusion in the central pamir 1 geometry and kinematics asian deep crust exposed in the pamir permits determination of the amount sequence and interaction of shortening extension and lateral extrusion over 30 km of crustal section during the india asia collision in the central pamir gneiss domes and their hanging walls record paleogene tripling of the 7 10 km thick phanerozoic upper crustal strata total crustal thickness may have amounted to 90 km two thrust sheets comprising cambro ordovician respectively carboniferous to paleogene strata straddle the domes amphibolite facies metamorphic rocks within the domes equivalent to lower grade rocks outside the domes form fold nappes with dome scale wavelengths e w stretching occurred contemporaneously with top to n imbrication and folding at 22 12 ma bivergent top to n and top to s normal sense shear zones exhumed the crystalline rocks most of the extension occurred along the northern dome margins shortening resumed at 12 ma with opposite sense thrusting and folding focused along the dome margins throughout the building of the central and south pamir dominant n s shortening interacted with e w extension along mostly dextral shear fault zones in the neogene shear is concentrated along a dextral wrench corridor south of the domes we interpret the paleogene shortening to record thickening and northward growth of the pamir tibetan plateau and short lived miocene crustal extension as gravitational adjustment i e collapse of the thickened asian crust to indian slab breakoff synconvergent paleogene lateral extrusion thickened the afghan hindu kush crust west of the india asia collision and the miocene recent dextral shear and e w extension have accommodated collapse of the pamir plateau into the tajik depression

an intercalibration study of the fish canyon sanidine and biotite 40ar 39ar standards and some comments on the age of the fish canyon tuff the age of the fish canyon tuff fct has been the subject of intense study due to its potential significance as a geochronological test to establish age concordance between the k ar and u pb isotopic systems minerals from the fct notably sanidine and biotite are in widespread use as 40ar 39ar fluence monitors standards and have been employed as both primary and intercalibrated standards in attempting to constrain the true age of fct the distinction between primary vs intercalibrated ages is important as only the primary age determinations are valid an investigation of both fish canyon sanidine fcs and fish canyon biotite fct 3 was undertaken to assess the chemical and isotopic homogeneity of the minerals on a grain to grain scale electron microprobe results show that fcs is chemically homogeneous verifying previous studies although there are some very small zones of minor k depletion fct 3 biotite commonly contains numerous and small mineral inclusions 40ar 39ar experiments further show that fcs is remarkably homogeneous confirming previous observations whereas fct 3 shows much greater isotopic variability due to contamination from the mineral inclusions by setting the age of fcs equal to 27 98 0 15 ma 2 as intercalibrated to the u pb system by villeneuve et al 2000 the resultant intercalibration factor between fcs and fct 3 is 1 005 0 017 yielding an age of 28 13 0 47 ma 2 for fct 3 although the significant intragrain chemical and isotopic variability precludes its use as an effective 40ar 39ar fluence monitor the true age of the fct is problematic a survey of all primary ages for fct shows that mean k ar ages for plagioclase hornblende biotite and sanidine are consistently younger than mean u pb ages from titanite and zircon in conjunction with recently published petrological results which indicate that the fct contains material from multiple crystallization events this significant discrepancy between the k ar and u pb data sets demonstrates that the fish canyon tuff cannot serve as a golden standard between the k ar and u pb systems

hydrochemical properties of transition zone between fresh groundwater and seawater in karst environment of the adriatic islands croatia eastern coast of the adriatic sea consists of karstified carbonates it belongs to the well known dinaric karst region the coast is extremely indented and there are 718 islands with numerous rock crags and reefs some of the inhabited islands use their own water resources for public water supply or plan to do it in the future since karst rocks are extremely permeable the seawater intrudes into underground water resources thereby forming the wedge a wide transition zone occurs between this seawater wedge and fresh water aquifers consequently island groundwater reserves turn brackish to a certain extent in this study 77 water samples were collected from a wide variety of water resources comprehensive statistical and mathematical multivariate analysis of these data was performed simple statistical approach showed several useful correlations among some parameters and more complex multivariate techniques extracted three factors in connection with three natural processes 1 mixing with the seawater 2 carbonate dissolution and 3 human influence pollution and nitrogen transformation processes the results of this study demonstrate that in situ measurement of electrical conductivity is adequate for the very rough field estimation of numerous parameters

mesozoic and cenozoic tectono thermal reconstruction of the western bohai bay basin east china with implications for hydrocarbon generation and migration abstract studies on the tectono thermal evolution of the western bohai bay basin wbbb including the jizhong sub basin and cangxian uplift are important for further petroleum exploration and exploitation this study aims to reconstruct the tectono thermal history of the wbbb based on a combination of 125 vitrinite reflectance ro data and seven apatite fission track aft and nine apatite u th he ahe ages the effective aft ages range from 60 3 to 97 0 ma with mean track lengths of 10 86 12 64 m the variable single grain aft ages are explained to be due to the parameter dpar the effective ahe ages range from 21 1 ma to 75 0 ma two rapid cooling events revealed by the thermal modeling results occurred during the early late cretaceous 130 90 ma and late eocene early miocene 40 18 ma respectively the fuping complex which is located in the western margin of the wbbb and mainly composed of the paleo proterozoic high grade gneisses experienced the intensive extension detachment during the early late cretaceous along with the subduction of the izanagi plate that was probably responsible for the first cooling event the second cooling event was caused by the subduction of the pacific plate during the middle eocene early miocene 43 23 ma as well as the collision of the indian and eurasian plates and the rollback of the subducting pacific plate during the early miocene 23 18 ma the wbbb experienced two heat flow peaks of 75 and 80 mw m2 during the early cretaceous and the late eocene respectively during the late eocene early miocene rapid subsidence in the baxian depression one secondary tectonic unit of the jizhong sub basin coupled with the rapid uplift in the cangxian uplift caused the shahejie formation of the middle upper eocene to generate gas during the early miocene meanwhile tectonic movement during the early miocene also caused faults to become migration paths as revealed by the homogenization temperature of the fluid inclusion this study provides new insights regarding the tectonic and hydrocarbon evolution of the wbbb

rapid cooling and exhumation as a consequence of extension and crustal thinning inferences from the late miocene to pliocene palu metamorphic complex sulawesi indonesia abstract metamorphic complexes forming high mountains of 1 5 2 km in western sulawesi were previously considered to be mesozoic or older basement of gondwana crust however many of the metamorphic rocks are much younger than previously thought some have eocene sedimentary protoliths new geothermobarometric and geochronological data from metamorphic rocks of the palu metamorphic complex pmc and associated granitoids provide information on the timing and mechanisms of neogene metamorphism and contemporaneous rapid exhumation the metamorphic rocks are strongly deformed and some were partially melted to form migmatites schists contain relict andalusite cordierite staurolite and mn rich garnet which are wrapped by a pervasive fabric 40ar 39ar dating of biotite white mica and amphibole from strongly deformed mylonitic schists and recrystallised amphibolites reveals cooling occurred in the early pliocene c 5 3 4 8 ma in the northern part and during the late pliocene c 3 1 2 7 ma in the southern part of the pmc u pb 40ar 39ar and u th he analyses of various minerals from pmc metamorphic and s type magmatic rocks give very similar mid to late pliocene ages indicating very fast cooling and rapid exhumation and show the high speed at which tectonic processes including magmatism exhumation and reworking into a sediment must have occurred the high rates could be unique to this area but we suggest they record the true speed of metamorphic complex exhumation in a very young orogenic belt rates in older orogens appear lower because they are averages measured over longer periods of time contemporaneous magmatism and deformation are interpreted as a consequence of decompressional melting due to extension and thinning of the crust promoted by possible detachment faults and normal faulting at the major nw trending palu koro and tambarana faults in contrast i type magmatic rocks separated from the pmc by the palu koro fault were exhumed from upper crustal levels by erosion at moderate rates

rapid exhumation of the upper siang valley arunachal himalaya since the pliocene abstract the work presents in situ low temperature thermochronological apatite fission track aft and u th he zircon zhe ages from the siang valley in the ne himalayan syntaxial zone our results highlight the unique spatial erosion along the axial regions of the siang antiform all the zhe cooling ages from the region range between 14 and 9 ma except for a northernmost sample that is distinctly younger 3 8 ma results from aft data 2 4 ma to present record pleistocene cooling along the siang river valley in the siang antiform and reveal a general northward younging trend of ages with rapid cooling

re evaluation of the ages of 40ar 39ar sanidine standards and supereruptions in the western u s using a noblesse multi collector mass spectrometer abstract the rewards from resolving the tempo of magmatic paleobiologic paleoclimatic and tectonic processes at better than the per mil level of precision have spurred a quest within the geochronology community to improve the precision accuracy and calibration of several chronometers including the 40 ar 39 ar variant of the k ar clock a new generation of multi collector mass spectrometers for 40 ar 39 ar geochronology provides the means to address these issues as well as to evaluate the ages of 40 ar 39 ar standards and key marker horizons deposited by large volume caldera forming supereruptions in the western u s at unprecedented temporal resolution we highlight the utility of a 5 collector noblesse mass spectrometer that has a sufficiently high mass resolving power to distinguish 36 ar h 35 cl from a 36 ar h 35 cl 12 c 3 sum peak at m e 36 maintains a remarkably low and stable background and thus yields 40 ar 39 ar dates of exceptionally high precision we have calibrated a reference gas and developed a simple analytical routine involving one peak hop both of which are used to evaluate detector bias correction factors because the 40 ar 39 ar chronometer is a relative dating technique that relies on calibration against mineral standards of known age precise and accurate determination of the ages of these standards and verification of isotopic composition and homogeneity is essential we present results from both total fusion and incremental heating experiments on single crystals of the widely used alder creek acs and fish canyon fcs sanidine standards several recent independent measurements of acs using multi collector mass spectrometers including those presented herein favor an age of 1 1864 0 0003 0 0012 ma 95 confidence analytical full external uncertainty that is 1 younger than the widely used value obtained by nomade et al 2005 using a single collector mass spectrometer incremental heating experiments on single crystals of fcs most commonly do not yield plateau ages instead many crystals appear to be affected by ar loss or excess ar our findings obtained using ion counters independently confirm those recently obtained using a multiple faraday detectors or a combination of faraday and ion counting detectors thus careful consideration must be given to using fcs in future high precision 40 ar 39 ar calibrations of the geologic timescale notwithstanding 40 ar 39 ar dating of sanidine using the 5 collector noblesse can now provide leverage critical to interpreting the large range of u pb zircon dates commonly found in rhyolitic lavas and tuffs

the alichur dome south pamir western india asia collisional zone detailing the neogene shakhdara alichur syn collisional gneiss dome complex and connection to lithospheric processes neogene syn collisional extensional exhumation of asian lower middle crust produced the shakhdara alichur gneiss dome complex in the south pamir the 1 km thick mylonitic brittle top nne normal sense alichur shear zone asz bounds the 125 25 km alichur dome to the north the shakhdara dome is bounded by the 4 km thick mylonitic brittle top sse south pamir normal sense shear zone spsz to the south and the dextral gunt wrench zone to its north the alichur dome comprises cretaceous granitoids gneisses cut by early miocene leucogranites its hanging wall contains non weakly metamorphosed rocks the 22 17 ma alichur dome injection complex leucogranites transition from foliation parallel centimeter to meter thick sheets within the asz into discordant intrusions that may comprise half the volume of the dome core secondary fluid inclusions in mylonites and mylonitization temperature constraints suggest alichur dome exhumation from 10 15 km depth thermochronologic dates bracket footwall cooling between 410 130 c from 16 4 ma tectonic cooling exhumation rates 42 c myr 1 1 km myr contrast with erosion dominated rates in the hanging wall 2 c myr 0 1 km myr dome scale boudinage oblique divergence of the asz and spsz hanging walls and dextral wrenching reflect minor approximately e w material flow out of the orogen we attribute broadly southward younging extensional exhumation across the central south pamir between 20 4 ma to i mostly northward foreland directed flow of hot crust into a cold foreland during the growth of the pamir orocline and ii contrasting effects of basal shear related to underthrusting indian lithosphere enhancing extension in the underthrust south pamir and inhibiting extension in the non underthrust central pamir

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

precise k ar 40ar 39ar rb sr and u pb mineral ages from the 27 5 ma fish canyon tuff reference standard the accuracy of ages measured using the 40ar 39ar technique is affected by uncertainties in the age of radiation fluence monitor minerals at present there is lack of agreement about the ages of certain minerals used as fluence monitors the accuracy of the age of a standard may be improved if the age can be measured using different decay schemes this has been done by measuring ages on minerals from the oligocene fish canyon tuff fct using the k ar 40ar 39ar rb sr and u pb methods k ar and 40ar 39ar total fusion ages of sanidine biotite and hornblende yielded a mean age of 27 57 0 36 ma the weighted mean 40ar 39ar plateau age of sanidine and biotite is 27 57 0 18 ma a biotite feldspar rb sr isochron yielded an age of 27 44 0 16 ma the u pb data for zircon are complex because of the presence of precambrian zircons and inheritance of radiogenic pb zircons with 207pb 235u 0 4 yielded a discordia line with a lower concordia intercept of 27 52 0 09 ma evaluation of the combined data suggests that the best age for fct is 27 51 ma

post collisional exhumation of the indus yarlung suture zone and northern tethyan himalaya saga sw tibet abstract the cretaceous eocene sedimentary sequences of the sangdanlin section at saga sw tibet within the india asia collisional zone have been studied in detail for constraining the timing of initial collision however the post depositional history has not been investigated here we report new low temperature thermochronology data along the classic sangdanlin section to reveal the cooling exhumation history of the indus yarlung suture zone iysz and northern tethyan himalaya samples from the iysz all yield latest oligocene miocene ages with most zircon u th he ages ranging between 18 and 27 ma and apatite fission track aft ages of 12 9 ma thermal history modelling indicates a consistent middle late miocene cooling episode related to post great counter thrust gct incision of the yarlung river to the south samples from the northern tethyan himalaya mesozoic sequences yield older zhe ages of 32 36 ma signifying activity of the tethyan himalayan fold thrust zone while two granites linked to formation of the north himalayan gneiss domes yield late miocene aft ages the regional low temperature thermochronology data reveal different cooling patterns for tributaries on the northern and southern sides of the yarlung river this points to the strong influence of early miocene tectonism along the gct as a major controlling factor on river drainage reorganization at this time

conditions for shallow geothermal energy utilization in dinaric karst terrains in croatia hydrogeological and thermogeological properties of the shallow subsurface in the dinaric karst area of croatia were investigated in the context of its utilization for ground and water source heat pumps gshps and wshps the research encompassed four 100 m deep boreholes with gshp installations in both coastal and inland dinaric karst different limestones and evaporitic rocks at one location and a set of six exploratory boreholes abstraction and reinjection wells for wshp heating and cooling using seawater on the coast fractured and karstified limestones it was determined that rock thermal conductivities are favourable for gshp utilization but dependent on the wider rock mass characteristics which are hard to predict size of karst voids and their saturation status in addition wells with high enough yield and stabile seawater or groundwater temperatures for wshp utilization can be designed in appropriate structural settings tensional fractures and fracture set intersections advantages and disadvantages of the utilized methodology have been pointed out as well as methods which should prove useful in the future especially if larger systems are planned hydrogeological geotechnical and thermal risks expected during the drilling installation and operational phases have also been identified presented case studies have given the insight into heat pump installation options and conditions in croatian part of the dinarides but can be useful to other researchers and engineers both in the dinarides and in similar karst regions

low temperature thermochronology of francolite insights into timing of dead sea transform motion cambrian siliciclastic sequences along the dead sea transform dst margin in southern israel and southern jordan host both detrital fluorapatite d apatite and u rich authigenic carbonate fluorapatite francolite a apatite d apatite and underlying neoproterozoic basement apatite yield fission track ft data reflecting paleozoic mesozoic sedimentary cycles and epeirogenic events and dispersed u th sm he ahe ages a apatite which may partially or completely replace d apatite yields an early miocene ft age suggesting formation by fracturing hydrothermal fluid ascent and intra strata recrystallisation linked to early dst motion the dst separating the african and arabian plates records 105 km of sinistral strike slip displacement but became more transtensional post 5 ma helium diffusion measurements on a apatite are consistent with thermally activated volume diffusion indicating tc 52 56 10 c cooling rate 10 c myr a apatite ahe data record pliocene cooling 35 40 c during the transtensional phase of movement this suggests that timing of important milestones in dst motion can be discerned using a apatite low temperature thermochronology data alone

tracking the evolution of large volume silicic magma reservoirs from assembly to supereruption the most voluminous silicic volcanic eruptions in the geological past were associated with caldera collapses above giant silicic magma reservoirs the thermal evolution of these subcaldera magma reservoirs controls the volume of eruptible magma and eruptive style here we combine high precision zircon u pb geochronology trace element analyses of the same mineral grains and mass balance modeling of zircon trace element compositions allowing us to track the thermal and chemical evolution of the oligocene fish canyon tuff magma reservoir colorado united states as a function of absolute time systematic compositional variations in u pb dated zircons record 440 k y of magma evolution an early phase of volumetric growth was followed by a period of cooling and crystallization during which the fish canyon magma approached complete solidifi cation subsequent remelting due to underplated andesitic recharge magmas began 219 45 k y prior to eruption and led to the generation of 5000 km3 of eruptible crystal rich 45 vol dacite age equivalent but compositionally different zircons in an andesite enclave from late erupted fish canyon tuff tie the growth and thermal evolution of the upper crustal reservoir to a lower crustal magma processing zone our results demonstrate that the combination of high precision dating and trace element analyses of accessory zircons can reveal invaluable information about the chemical and thermal histories of silicic magmatic systems and provides critical input parameters for fl uid dynamic modeling

comment on the joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by paul r renne et al 2010

standardless fission track dating of the durango apatite age standard abstract five dating strategies were used for determining the standardless fission track age of the durango apatite these use the same fossil track densities but differ in the manner in which the induced track densities are determined a conventional age calculation without correction for experimental factors gives inconsistent ages with method related differences 15 correcting for these factors brings the ages in line with each other and with the reference age but leaves no room for a partial annealing correction based on the confined track lengths three further reasons suggest that a length correction is not appropriate 1 the evidence for length based corrections is inconclusive 2 the plateau age of the durango apatite is consistent with its apparent fission track age to within 1 3 the calculated effective etchable length of the fossil tracks agrees within error with that of the induced tracks both are further consistent with the measured mean length of confined induced tracks the circumstance that the u th he ages of the accepted and proposed apatite age standards are consistent with their reference ages leaves no margin for a lowered fission track age resulting from partial annealing although the case of the durango apatite itself is inconclusive because of its exceptional crystal size it is conjectured that the shortening of the fossil tacks in the durango apatite is due to a lowering of the track etch rate over time in this case annealing equations fitted to induced track data underestimate the extent of confined track length reduction in geological samples

parameter estimation for a karst aquifer with unknown thickness using the genetic algorithm method the thickness of an aquifer b is a critical hydrogeologic parameter in understanding groundwater system especially in a karst aquifer where the high heterogeneity in this parameter brings more uncertainty to the evaluation of groundwater resources in this study the genetic algorithm ga method was used to estimate b as well as five other parameters including k r horizontal hydraulic conductivity k z vertical hydraulic conductivity s storativity s y specific yield and delayed coefficient of a karst aquifer based on a pumping test the search bounds of the six parameters for the ga method were obtained from numerous hypothetic numerical tests the feasibility of the ga method for parameter estimation was verified by the results obtained from the gradient method in terms of a pumping test conducted in the platte river valley in nebraska then this approach was used to estimate the hydraulic parameters in a karst aquifer with unknown aquifer thickness based on a pumping recovery test conducted in the houzhai karst basin southwestern china the results show that the k r k z and the anisotropy ratio of k r to k z are strongly affected by b the differences between the estimated parameter values at two observation wells indicate the existence of high heterogeneity in the karst aquifer the parameter b has the highest absolute normalized sensitivity among these variables implying that the estimated b may be more reliable as compared to other parameters this study demonstrates that the ga method is an alternative method of parameter estimation with the unknown aquifer thickness

mid late miocene deformation of the northern kuqa fold and thrust belt southern chinese tian shan an apatite u th sm he study abstract the kuqa fold and thrust belt developed in response to cenozoic southward shortening between the chinese tian shan and the tarim basin this study aims to constrain the timing of the late cenozoic deformation by determining the onset time of enhanced rock cooling using apatite u th sm he thermochronometry eight sedimentary samples were collected from triassic to cretaceous strata exposed along a 17 km n s transect cross cutting the northern kuqa fold and thrust belt single grain ahe ages from these samples mostly cluster around 8 16 ma and are younger than their depositional ages older ahe ages show a positive relationship with eu a proxy for radiation damage modelling of the observed age eu relationships suggest a phase of enhanced cooling and erosion initiated at mid late miocene time 10 20 ma in the northern kuqa fold and thrust belt this result is consistent with a coeval abrupt increase of sedimentation rate in the foreland kuqa depression south of the study area indicating a mid late miocene phase of shortening in the northern kuqa fold and thrust belt

late cretaceous to oligocene burial and collision in western papua new guinea indications from low temperature thermochronology and thermal modelling abstract recent field and analytical work have considerably improved our understanding of the structure of the muller range along the frontal trend of the papuan fold and thrust belt pftb in western papua new guinea png however numerous questions remain unresolved concerning the geological evolution of the region in particular the late cretaceous to oligocene history of the region is largely unknown due to the absence of a continuous stratigraphic record here we use both new and existing low temperature thermochronology data to investigate the geological history of the muller range thermal history models based on these data suggest two major cenozoic cooling episodes the youngest and best constrained is clearly recorded in the stratigraphic record and relates to neogene collision at the northern margin of the australian continent an older episode of comparable or greater magnitude occurred in the eocene to oligocene and may relate to the removal of 1500 3000 m of late cretaceous to eocene section across the muller range prior to the widespread deposition of the shelfal darai limestone we suggest that extension along major faults beneath the muller range accommodated sedimentation from the late cretaceous to the eocene consistent with long lived extensional structures observed in neighbouring regions in contrast to the muller range area an almost continuous late cretaceous to eocene stratigraphic sequence is preserved in the hinterland

estimating recharge in a tropical karst aquifer unique constraints on seasonal and spatial variations in recharge to the pleistocene limestone aquifer of barbados are obtained from the analysis of oxygen isotopic compositions of groundwater and rainwater conventional methods of estimating recharge are based on groundwater chloride variations coastal groundwater discharge and potential evapotranspiration these methods typically yield estimates of recharge for barbados that range from 9 to 20 of average annual rainfall with significant uncertainties that arise from poorly constrained model input parameters owing to the low relief and tropical climate of barbados variations in rainwater and groundwater 18o values are primarily influenced by the amount of rainfall with negligible temperature or altitude effects composite monthly rainwater 18o values are inversely related to rainfall while groundwater 18o values show little seasonal variability rainwater 18o values are equivalent to groundwater values only at the peak of the wet season by using mass balance the difference between groundwater and weighted mean rainwater 18o values gives recharge values these values are in general agreement with estimates by conventional methods 10 20 and provide unique additional information including the following 1 recharge is restricted to the wettest 1 3 months of the year and 2 there is less recharge at higher elevations the effective shift in 18o values between contemporaneous rainwater and groundwater via recharge is a useful tool for estimating temporal and spatial variability in recharge and must be considered in paleoclimatic studies where climate inferences are based on groundwater 18o values preserved in the geologic record

a review of possible eustatic isostatic and tectonic contributions in eight late holocene relative sea level histories from the mediterranean area abstract this paper consists of a comparison between eight late holocene sea level histories investigated by the author in different mediterranean areas and sea level predictions in the same areas made by global isostatic models the areas include three regions that are generally considered as tectonically relatively stable 1 the southern coast of france 2 sardinia and 3 the southern coasts of tunisia where late holocene evidence may be either of submergence or of emergence also considered are 4 a subsidence region in the northern adriatic and actively uplifting areas 5 in calabria and 6 in nisyros island greece lastly case studies in areas affected by repeated coseismic vertical displacements include 7 western crete and antikythira island in the hellenic arc and 8 the levant coasts of turkey syria and the lebanon in each case the question of whether the evidence available may or may not be consistent with gradual isostatic or eustatic displacements has been explored it appears that in non tectonic areas the hydro isostatic effects have been overestimated sardinia or underestimated southern tunisia by the same models in the northern adriatic the closest mediterranean area to the former scandinavian ice sheet glacio eustatic effects are suspected to be almost absent our analysis failed to quantify isostatic effects in areas of rapid tectonic uplift calabria and nisyros but rejected predictions of significant isostatic subsidence in the hellenic arc and on the levant coast finally several data from tectonic and non tectonic areas are consistent with nearly stable global eustasy since 6000 bp thus challenging the assertion of significant additional melting of antarctica after the complete melting of the former northern hemisphere ice caps

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

u pb and u th sm he double dating of detrital apatite by laser ablation a critical evaluation abstract paired u pb and u th sm he dating of individual detrital apatite crystals has potential as a valuable tool for constraining the high and low temperature thermal evolution of sediment source terrains here we present the results of exploratory applications of the laser ablation double dating ladd method originally developed for detrital zircon research to the widely available durango fluorapatite standard in order to evaluate the practicality of the method sixty two laser ablation analyses of a single large crystal of durango fluorapatite yielded an inverse variance weighted mean 206pb 238u date of 31 46 0 48 ma and an inverse variance weighted mean u th sm he date of 31 75 0 60 ma both of which are in good agreement with previously published conventional dates while these results are encouraging several factors suggest that ladd may be less useful for detrital apatites than for detrital zircons given widely available analytical instrumentation these principally reflect the propensity for apatites to have comparatively lower u th concentrations and thus lower radiogenic he and pb concentrations as well as high concentrations of common pb these factors contribute to substantially higher analytical imprecision for most ladd u pb dates for apatite occasionally too high for the dates to be geologically useful reasonably precise laser ablation u th sm he dating of detrital apatites requires relatively large crystal sizes 100 m in the shortest dimension with the minimum useful size increasing with decreasing u th sm he apparent age in contrast to the geological interpretation of ladd datasets for detrital zircons the interpretation of datasets for detrital apatites is less straightforward in particular researchers should consider carefully the possibility that u th sm he apparent age distributions are biased by the need to analyze only larger apatites

new 40ar 39ar and u th he dating for the zhunuo porphyry cu deposit gangdese belt southern tibet implications for pulsed magmatic hydrothermal processes and ore exhumation and preservation understanding the magmatic hydrothermal cooling and exhumation history is fundamental for investigating porphyry deposit formation and preservation in the zhunuo porphyry copper deposit of southern tibet hydrothermal biotite related to early potassic alteration likely formed from 14 7 0 3 ma zircon u pb age to 14 23 0 13 ma molybdenite re os age and cooled below the closure temperature for 40ar 39ar system at 13 91 0 05 ma hydrothermal biotite 40ar 39ar plateau age the 40ar 39ar spectra of another hydrothermal biotite sample that was selectively replaced by chlorite record the timing of late phyllic alteration at 13 53 0 08 ma zhunuo hydrothermal alteration and mineralization likely ceased at 13 09 0 07 ma based on the 40ar 39ar plateau age of the fresh magmatic biotite crystals the biotite 40ar 39ar systematics have not been reset by 12 0 ma post mineralization granite porphyry within ore district which is likely due to rapid cooling and or absence of fluid exsolution for the granite porphyry in combination with previous zircon u pb and molybdenite re os data two pulses of magmatic hydrothermal activity from 14 78 0 11 to 14 44 0 05 ma and from 14 23 0 13 to 13 53 0 08 ma can be recognized at zhunuo u th he thermochronological data on zircon and apatite from the inter mineralization monzogranite porphyry suggest three cooling events characterized by first stage magmatic cooling at a rate of 1850 c m y and two later phases of uplift and exhumation at 70 c m y and 10 c m y approximately 1 4 km thickness of materials have been removed from the zhunuo miocene monzogranite porphyry during uplift and erosion including a large volume of ore

estimating recharge thresholds in tropical karst island aquifers barbados puerto rico and guam the hydrology and geochemistry of groundwater in tropical island aquifers such as barbados guam and puerto rico are significantly influenced by tropical climatic conditions recharge to these aquifers is the product of regional and local climate patterns that control rainfall oxygen isotopes can be used to estimate the amount and timing of recharge on these islands because seasonal fluctuations of rainwater oxygen isotopic compositions are related to the amount of rainfall the karst aquifers on barbados guam and puerto rico have similar rainwater and groundwater oxygen isotopic compositions comparison of groundwater and rainwater oxygen isotopic compositions in the three aquifers indicates that 1 recharge occurs by rapid infiltration with little evaporation prior to recharge and 2 recharge is associated with similar monthly rainfall thresholds of 190 200 mm these rainfall thresholds are remarkably similar for three aquifers in different geographic locations differences between the spatial variations of groundwater oxygen isotopic compositions on barbados and puerto rico can be attributed to the more complex groundwater flow system on puerto rico the surprising similarities of hydrologic conditions under which recharge will take place can be attributed to similarities in climate and geologic conditions such as soils and limestone bedrock that exist on the three islands we therefore speculate that similar recharge rainfall thresholds may be observed in other tropical karst aquifers q 2003 elsevier science b v all rights reserved

the relationship between submarine canyon fill and sea level change an example from middle miocene offshore gabon west africa abstract a series of middle miocene submarine canyons has been mapped in offshore gabon west africa using a combination of seismic facies analysis and well information three distinct seismic facies are recognized in the canyon fill the evolution of these facies is inferred to be related to sea level change during sea level lowstand deposition was characterized by lateral accretion on the southern canyon wall whilst progressive erosion occurred on the northern wall this depositional pattern was controlled by a local coast parallel current that flowed northwestwards along west africa during the middle miocene as relative sea level rose the erosion on the northern wall ceased and the canyons were filled by sediments showing an aggradational stratal pattern finally during the early part of the transgression the canyons were filled with horizontal or subhorizontal sedimentary strata the sedimentary fill is thought to consist of alternating sands and mud within its lower part but as relative sea level rose clayey sediments gradually dominated the canyon fill

an assessment of hydrogeological parameters on the karstic island of dugi otok croatia summary extensive explorations have been performed in the northern part of the island of dugi otok in the adriatic sea croatia with the purpose of extraction of fresh and or brackish water the island is predominantly composed of karstified carbonate rocks of the cretaceous age the explorations included geological and hydrogeological mapping of the area geophysical surveys by means of the geoelectric tomography method electrical resistivity sounding and surface seismic refraction exploratory core drilling hydrochemical in situ and laboratory explorations and the pumping test with the calculation of rock mass parameters based on the obtained results it was concluded that it is possible to exploit the groundwater with a pumping quantity of 5 l s without intrusion of salt water into the fresh water lens choosing a pumping regime based on the parameters of the aquifer rock mass hydraulic conductivity order of magnitude 10 4 10 6 m s and knowing the parameters of the well as well as the tidal efficiency should reduce the possibility of intrusion to the minimum because of the systematic quality of the performed explorations and obtained results the island of dugi otok can serve as a typical example for such kinds of exploration works on other karstic islands hydrogeological composition behaves partly according to ghyben herzberg s law but because of the nature of the karstic hydrogeological system such a statement needs to be accepted approximately because of the highly complicated relationships

india asia convergence insights from burial and exhumation of the xigaze fore arc basin south tibet the composite fore arc syncollisional xigaze basin in south tibet preserves a key record of india asia collision new apatite fission track and zircon u th he data from an n s transect across the preserved fore arc basin sequence near xigaze show a consistent northward late cretaceous to middle miocene younging trend while coexisting apatite u th sm he ages are all miocene corresponding detrital zircon u pb data are also reported for constraining the cretaceous depositional ages of the xigaze basin sequence in the region thermal history modeling indicates that the basin experienced northward propagating episodic exhumation along with a northward migration of the depocenter and a pre existing cenozoic syncollisional basin sequence which had been removed in the southern part fore arc exhumation commenced in the late cretaceous 89 2 ma following transition to a syncollisional basin in the paleocene sedimentation in the central and northern xigaze basin continued until the latest eocene 34 4 ma ongoing folding and thrusting e g great counter thrusts caused by progressive plate convergence during late oligocene early miocene time resulted in regional uplift and considerable basin denudation which fed two fluvial basins along its northern and southern flanks and exposed the basement ophiolite subsequent incision of the yarlung river resulted in miocene cooling in the region different episodes in the exhumation history of the xigaze basin caused by thrusting of an accretionary wedge and ophiolitic basement can be linked to changes in india asia convergence rates and the changing subduction pattern of the indian and neo tethyan slabs

engineering characterization of hydraulic properties in a pilot rock cavern for underground lng storage abstract feasibility of storing lng in a lined rock cavern was evaluated using a pilot cryogenic rock cavern constructed in daejeon korea the pilot program included hydrogeological and engineering characterization of the rock mass around the cavern design and construction of a drainage system and pilot operation of the cryogenic cavern an appropriate drainage system is most important to protect the containment system of lng from thermal shocks due to ice lenses and hydrostatic pressure of groundwater as a part of the pilot program this study focused on the evaluation of hydraulic and engineering properties of the rock mass around the cavern for this purpose engineering logging of the rock cores single and cross hole hydraulic tests and recharge drainage tests were performed using seven drilled holes with different trends and plunges three main joint sets were found from the logging of the rock cores acoustic borehole televiewer and window mapping the orientations of the three major joint sets were 60 209 40 171 and 29 331 which can provide the main groundwater flow paths mean rqd values ranged from 56 to 88 which were classified as fair and good although varying with depth along single boreholes hydraulic conductivity from the single and cross hole hydraulic tests estimated in the order of 10 6 or 10 7 m s and corresponding transmissivity ranged between 10 5 and 10 6 m2 s permeable intervals identified from the hydraulic tests were mostly located above the cavern roof below the roof the permeable zone was difficult to observe according to the hydraulic communication tests performed for some designated intervals hydraulic connection between boreholes was highly varied with depth or location which indicated a very different distribution of water conducting joint sets along the boreholes when water was injected at r1 with constant or varying flow rates monotonous and stable seepage was observed at observation boreholes from this some stable drainage was expected even in relatively heavy rainfalls when designing the drainage system of the cavern the drainage holes should be orientated to maximize frequency of encountering the major joint sets and the permeable intervals identified from this study

is low temperature fission track annealing in apatite a thermally controlled process we report a new series of experiments to explore the phenomenon of low temperature annealing of fission tracks in apatite that feature a number of improvements over previous work grain mounts were

u th he geochronology of single zircon grains of known tertiary eruption age we performed a systematic study of u th he ages of volcanic zircons of known eruption age to establish a reliable protocol for zircon he dating and to validate the resulting ages using laser he extraction and dissolution by lithium borate flux melting we analyzed many aliquots of single zircon grains separated from four rapidly cooled rocks fish canyon tuff accepted age 27 8 0 7 ma buluk tuff 16 3 0 2 ma tardree rhyolite 58 4 0 7 ma and utaosa rhyolite 2 52 0 02 ma he ages of fish canyon tuff buluk tuff and utaosa rhyolite zircons are in good agreement with their reference ages mean emission corrected ages were 28 6 1 4 1 16 1 0 8 and 2 61 0 18 ma respectively however the zircon he ages of tardree rhyolite are irreproducible and consistently too old with a mean he age of 78 8 7 0 ma spontaneous fission track densities of tardree rhyolite zircons indicate that about 80 of these zircons are strongly zoned in u with high track density i e high u content in the core and low density on the rim this causes an overestimation of the ejection correction that likely explains the erratic and excessively high he ages from these zircons assessment of the degree and style of u zonation within a zircon population is thus prudent before application of the u th he method step heating experiments indicate that for most zircons he extraction is 99 complete after 1 h at 1300 c however for as yet unknown reasons occasional grains seem to retain substantial amounts of he under these conditions

wildfire thermochronology and the fate and transport of apatite in hillslope and fluvial environments 1 wildfire heating of the outer few centimeters of exposed rock or soil generates shortduration high temperature thermal events that produce characteristic thermochronologic signatures in minerals contrasting activation energies of fission track annealing and he diffusion in apatite lead to a kinetic crossover whereby wildfire heating resets fission track ft ages much faster than u th he ages resulting in inverted ft he ages in single grains this can be used to trace wildfire affected detritus at the earth s surface we show that in exposed bedrock inverted apatite ft he ages vary systematically with depth to 3 cm and detrital clasts on hillslopes also show strong but heterogeneous wildfire resetting signatures in soils colluvium and low order channel sediments strongly wildfire reset apatite grains are abundant and in some cases dominate the population of detrital apatite to depths at least as great as 10 cm wildfire reset apatite is rare however in fluvial sediments sampled from larger basins indicating a strong fractionation of apatite populations from hillslopes to rivers characteristic dissolution features in hillslope apatite and slower relative dissolution rates of other common minerals suggest that wildfire reset apatite grains are rare or absent in rivers because they dissolve relatively rapidly in soil profiles apatite that does contribute to fluvial sediments is likely to be dominantly derived from bedrock landslides in steep regions or from large clasts containing grains protected from both wildfire heating and dissolution this means that apatite in fluvial sediment is spatially fractionated with respect to its sources in the catchment even if catchment erosion rates are spatially uniform

the fish canyon tuff a new look at an old low temperature thermochronology standard abstract the fish canyon tuff fct has served as an important source for geochronology standards particularly for fission track k ar and 40 ar 39 ar dating even though efforts to establish precise ages for its constituent minerals have proved to be unexpectedly complex to evaluate the suitability of fct apatite as a standard for apatite u th sm he ahe thermochronometry and to test underlying assumptions about its suitability for apatite fission track aft thermochronometry we analysed samples from a series of sites throughout the vertical and lateral extent of the host ignimbrite sheet samples were collected from the relatively lithic rich classic sampling location in the lower part of the thick proximal ignimbrite and a 330 m vertical section of fct immediately above it average weighted mean ahe ages from multiple analyses at five sites in this profile range from 20 8 0 4 ma from the classic site at the base to an average of 28 4 0 2 ma all 1 in the upper part of the section the ahe age at the classic site is substantially reduced at 20 8 0 4 ma relative to a reference age for ignimbrite emplacement of 28 2 ma corresponding zircon u th he zhe ages for these samples are all concordant at 28 3 0 4 ma by contrast apatite fission track aft ages from the same vertical section are all concordant at 27 4 0 7 ma with the central age of 28 8 0 8 ma at the classic site except for the uppermost sample 23 2 1 7 ma for which clear evidence for local probably fire disturbance is seen in the track length distribution the ahe data at the classic site thus provide evidence for substantial post eruptive early miocene cooling of the tuff consistent with its position at the bottom of a deeply incised valley with 800 m of local relief and probably 1000 m of removed section above it the aft age of the classic sampling site however is indistinguishable from ignimbrite emplacement and thus continues to be a useful standard for aft but not for ahe geochronology apatites from this site have the highest measured cl concentrations 0 82 wt of any of the fct apatites analysed contributing to this suitability aft and ahe ages at three distal localities some 35 45 km to the east of the classic site where the thickness of the fct is reduced to 100 m all yielded concordant ages with a weighted mean of 28 5 0 11 ma with no evidence for post emplacement thermal disturbance one of the distal sites a quarry in the upper part of the fct appears to be an ideal locality for a standard reference material that would be suitable for both aft and ahe low temperature thermochronometers u pb ages for zircons and 40 ar 39 ar step heating age spectra for sanidine at this new distal site are essentially identical to those found at the classic site

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

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

u pb zircon and titanite systematics of the fish canyon tuff an assessment of high precision u pb geochronology and its application to young volcanic rocks a large data set of single and multi grain zircon and titanite analyses from a sample of the oligocene fish canyon tuff fct a voluminous ash flow from the san juan mountains of colorado and widely used 40ar 39ar geochronological standard has been used to evaluate the influence of various sources of analytical and geological uncertainty on the calculated age of this tuff by the isotope dilution u pb zircon method twenty three single zircon grains and seven small multi grain fractions of the fct yield an inverse variance weighted mean 206pb 238u date of 28 402 0 023 ma 2 mswd 0 93 and a slightly older weighted mean 207pb 235u date of 28 529 0 030 ma mswd 0 74 which are insensitive to common pb corrections initial 230th disequilibria calculated from a newly measured th u 2 2 for fct pumice shards indicate th deficiency for these zircons its correction brings the weighted mean 206pb 238u date to 28 478 0 024 mswd 0 97 minimizing the discordance of the fct zircon analyses these calculations culminate in concordia ages ludwig 1998 for the crystallization of the fct zircons of 28 476 0 029 ma mswd 1 50 without propagating decay constant errors or 28 498 0 035 ma mswd 1 03 with propagated decay constant errors these results are in close agreement with a previous single grain 206pb 238u zircon date of 28 41 0 05 ma for the fct oberli et al 1990 however they do not corroborate the discordia lower intercept date of 27 52 0 09 put forth by lanphere and baadsgard 2001 the 28 476 0 064 ma concordia age for fct zircons including systematic decay constant errors and uncertainty in pb u tracer calibration is substantially older than all published 40ar 39ar sanidine ages which range from 27 5 to 28 05 ma lanphere and baadsgaard 1997 renne et al 1998 a lengthy period 400 k y of zircon residence in the magma chamber before eruption is commonly called upon to explain the age discrepancy however fct titanite which may remain open to pb diffusive exchange until quenching upon eruption yield a minimum 230th disequilibrium corrected weighted mean 206pb 238u age of 28 395 0 049 ma 0 078 with tracer uncertainty weakening residence time arguments and supporting recent calls for re evaluation of the 40k decay constant and the accepted ages for commonly used 40ar 39ar mineral standards the fct zircon concordia age also provides an empirical constraint on the decay constants of the u isotopes indicating the relative accuracy of the currently accepted decay constants to within the original counting statistic errors of jaffey et al 1971

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

apatite fission track chronometry using laser ablation icp ms abstract comparison is made of apatite fission track ft ages measured by using conventional thermal neutron irradiation and laser ablation inductively coupled plasma mass spectrometry la icp ms to determine sample uranium content spontaneous track densities were determined on specified apatite grains from the durango fish canyon tuff and mount dromedary complex age standards neutron induced track densities and icp ms uranium values were determined for the same specified grains ages determined using the two approaches show reasonable consistency indicating the possibility of routine fission track analysis using la icp ms uncertainties and assumptions in the la icp ms approach include the laser ablation of chemically etched mineral surfaces the suitability of reference materials for calibration and the derivation of ft ages using the alternatives of selection of a f value or a revised zeta comparative approach the use of la icp ms in ft chronometry would dramatically increase the speed of analysis and hence sample throughput as well as avoiding the need for neutron irradiation and the production transport and handling of radioactive samples with the acknowledged dependency of ft annealing in apatite on composition such grain by grain multi element analysis could provide a more robust definition of the specific track annealing characteristics of each apatite crystal

ultra high precision 40ar 39ar ages for fish canyon tuff and alder creek rhyolite sanidine new dating standards required abstract the 40 ar 39 ar dating technique is a high precision 40 ar 39 ar standards include sanidine from the ca 28 ma fish canyon tuff fct and the ca 1 2 ma alder creek rhyolite acr despite common usage the ages of fct and acr sanidine have proven contentious with reported values varying by 2 well outside the 0 1 aspiration of earthtime www earth time org the current study presents ultra high precision multi collector 40 ar 39 ar results for fct and acr sanidine using a new generation argusvi mass spectrometer these analyses demonstrate the significantly higher by a factor of 10 level of precision achievable using the argusvi system compared to most previous studies significantly 40 ar 39 ar step heating analyses resolve distinct age gradients for both fct and acr sanidine possible explanations for these gradients include combinations of recoil loss of 39 ar instrumental bias isotopic fractionation during step heating thermally induced argon loss and or extraneous argon contamination minor recoil loss of 39 ar and partial retention of inherited argon during extended magma residence are deemed the most plausible causes of the age discordance given this assumption we calculate revised maximum eruption ages of 28 01 0 04 ma 2 for fct and 1 178 0 002 ma 2 for acr relative to the astronomically calibrated age of a1 tephra sanidine crete rivera et al 2011 earth planet sci lett 311 420 426 nonetheless the argusvi data demonstrate that fct and acr sanidine are non ideal as high precision 40 ar 39 ar standards with different heating protocols likely to induce inter laboratory bias the current findings account for at least some of the scatter in inter calibration ages reported previously for various 40 ar 39 ar standards in broader terms the results mandate a re evaluation of the astronomically calibrated ages for these and other sanidine samples while the new generation of multi collector mass spectrometers provides the means to further evaluate 40 ar 39 ar ages used to define new decay constants and standard ages

reply to comment on precise k ar 40ar 39ar rb sr and u pb mineral ages from the 27 5 ma fish canyon tuff reference standard by m a lanphere and h baadsgaard

helium diffusion and u th he thermochronometry of titanite we have explored the diffusivity characteristics of radiogenic he in titanite sphene and have developed analytical techniques for u th he dating of this mineral results of incremental he outgassing experiments performed on titanites from a variety of geological environments suggest a thermally activated volume diffusion mechanism with an activation energy of 44 6 3 4 2 kcal mol and a frequency factor of 60 cm 2 s diffusivity is highly linearly correlated with the inverse square of the grain size indicating that the he diffusion domain in titanite is the crystal itself for typical titanite grains of 200 to 800 m minimum dimension the he closure temperature is in the range 191 to 218 c for a cooling rate of 10 c myr there is no indication in the titanites we studied that radiation damage plays a major role in he diffusion u th he ages of titanites from quickly cooled rocks yield ages with 5 8 1 reproducibility that are concordant with known ages and u th he ages of titanites from slowly cooled rocks are consistent with independently established cooling paths supporting the closure temperature estimates these experiments suggest that titanite u th he ages may be useful for constraining cooling histories at temperatures near the lower limit of those accessed by feldspar 40 ar 39 ar dating but higher than apatite fission track or u th he dating

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

rejuvenation of the fish canyon magma body a window into the evolution of large volume silicic magma systems voluminous unzoned phenocryst rich pyroclastic deposits considered as erupted batholiths provide a unique opportunity to investigate magmatic processes in silicic magmas the fish canyon tuff a well documented example of these monotonous ignimbrites displays evidence for simultaneous dissolution of feldspars 1 quartz and crystallization of hydrous phases during gradual near isobaric reheating from 720 to 760 8c these observations along with a high crystallinity 45 and near solidus mineral assemblage suggest that the fish canyon magma cooled to a rigid crystal mush before being partly remelted prior to eruption rejuvenation was triggered by intrusion of water rich mafic magmas at the base of the fish canyon mush but the mechanisms of heat transfer remain poorly understood the growth of amphibole during reheating requires addition of mafic components but the absence of any measurable gradients and the paucity of mafic enclaves in the fish canyon magma rule out a reheating event dominated by convective mixing with a mafic magma closed system processes such as heat conduction and convective self mixing could not account for the transport of externally derived mafic components we performed numerical simulations of upward percolation of a hot low density h2o co2 fluid phase gas sparging through a crystalline framework saturated with rhyolitic melt to assess the efficiency of such a process in rejuvenating silicic mushes in open systems sparging by 20 40 km 3 of gas extracted from 3000 km 3 of mafic magma is capable of reheating 7500 km 3 of silicic crystal mush by 40 8c in 150 200 k y moreover the vertical thermal gradient after 150 k y in most of the mush is small 25 8c in the upper 65 gas sparging also produces an increase in the internal pressure of silicic crystal mushes and may lead to the formation of crystal poor rhyolites by expelling interstitial melt however our simulations predict that filter pressing driven by sparging of externally derived gas could not solely account for the generation of the most voluminous rhyolites

hydrological modeling in the karst area rižana spring catchment slovenia karst aquifers are known for their heterogeneity and irregular complex flow patterns which make them more difficult to model and demand specific modeling approaches this paper presents one such approach which is based on a conceptual model the model was applied in a karst area of the catchment of ri ana spring 200 km it is based on the mike she code and incorporates the main hydrological processes and geological features of the karst aquifer diffuse and concentrated infiltration allogenic recharge quick and slow groundwater flow shifting groundwater divides and groundwater outflow from the catchment area modeling of evapotranspiration and flow in the upper part of the unsaturated zone is more detailed for the modeling of groundwater flow in the karst aquifer a conceptual model was applied which uses drainage function for the simulation of groundwater flow through large conduits karst channels and large fissures the model was calibrated and validated against the observed ri ana spring discharge which represents a measured response of the aquifer the results of validation show that the model is able to adequately simulate temporal evolution of the spring discharge measured by nash sutcliffe coefficient 0 82 as well as overall water balance

comment on precise k ar 40ar 39ar rb sr and u pb mineral ages from the 27 5 ma fish canyon tuff reference standard by m a lanphere and h baadsgaard

thermochronological insights into the thermotectonic evolution of mishmi hills across the dibang valley ne himalayan syntaxis abstract eastern himalayan syntaxis ehs that forms the northeastern termination of the himalaya consists of three broad zones namche barwa massif siang antiform and mishmi hills the present work provides new in situ apatite fission track aft zircon u th he zhe and 40ar 39ar multi thermochronometric ages across the dibang valley in the mishmi hills the study constrains the structure emplacement time of major thrusts and initiation of lesser himalayan duplex lhd biotite 40ar 39ar ages of the lohit batholith suggest late oligocene cooling zhe ages indicate late miocene 8 9 ma foreland directed duplex initiation in the dibang valley the aft cooling ages 5 3 ma suggest lhd continued into mid pliocene confined track lengths and thermal modelling indicate that the northeastern samples from the study area underwent a phase of rapid exhumation around 10 ma followed by slow cooling it is in contrast to the south western samples from the dibang valley that have cooled and uplifted rapidly only after around 4 ma due to accelerated phase of lhd our 3d thermo kinematic modelling of the data indicates less mass removal around hunli than other parts of dibang valley the result is in contrast to previously estimated 16 km uplift near hunli and mass removal aft ages from the hunli window indicate that the region witnessed modest uplift of 4 5 km since ca 4 ma brittle duplexing of the lower lhs at hunli and mayodia caused the warping of the overlying litho units hunli duplex alone accommodated 86 of the total shortening

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

comagmatic granophyric granite in the fish canyon tuff colorado implications for magma chamber processes during a large ash flow eruption the 27 8 ma fish canyon tuff a vast ash flow sheet 5000 km 3 of uniform phenocryst rich dacite is representative of monotonous intermediate eruptions from a magma chamber that lacked compositional gradients sparse small fragments of comagmatic granophyre in late erupted tuff and postcaldera lava having mineral compositions indistinguishable from phenocrysts in the tuff and precaldera lava like rocks record complex events in the fish canyon chamber just prior to eruption sanidine phenocrysts in the granophyre preserve zoning evidence of mingling with andesitic magma then shattering by decompression and volatile loss accompanying early fish canyon eruptions before overgrowth by granophyre the textural and chemical disequilibria indicate that the eruption resulted from batholith scale remobilization of a shallow subvolcanic chamber contrary to previous interpretations of magma storage and phenocryst growth in the lower crust