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

a diode laser system for heating minerals for u th he chronometry we have developed a diode laser 25 w 808 nm system for he extraction from minerals for u th he chronometry the laser beam is delivered via a 600 m fiber cable and focused using a binocular microscope temperatures necessary for he release from apatite 500 600 c and zircon 1100 1300 c encapsulated in pt foil tubes are attained by heating to 0 5 w for 30 s and 1 25 2 5 w for 20 min respectively using a defocused beam heating at these powers does not result in measurable u and or th loss from apatite as noted by the preservation of the distinct th u in multiple splits of two different durango apatite crystals analyses of durango and the california institute of technology internal standard apatite 97mr22 yield u th he ages of 32 8 1 8 ma 1 n 11 and 4 6 0 5 1 n 5 respectively well within accepted ages the u th he age and th u of five fish canyon tuff zircon aliquots yield 29 3 2 2 ma 1 and 0 6 0 03 respectively and are indistinguishable from ages produced by resistance furnace he extraction heating of unencapsulated minerals shows that the diode laser couples well with optically opaque minerals e g hornblende biotite muscovite garnet and basalt groundmass suggesting that diode lasers offer a cheap small low maintenance alternative to nd yag and ar ion lasers for 40ar 39ar cosmogenic noble gas and stable isotope studies

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

reorientation and faulting of pluto due to volatile loading within sputnik planitia the location of sputnik planitia on pluto is shown to result from volatiles sequestered within the basin forcing the reorientation of the dwarf planet as supported by the planet wide fault network james keane et al report that the location of sputnik planitia the approximately 1 000 kilometre diameter topographic basin that dominates the surface of pluto is a natural consequence of the infill of volatile ices within the basin and the resulting reorientation true polar wander of the dwarf planet as sputnik planitia slowly loaded with volatiles the pull of tidal torques from charon would have resulted in the eventual alignment of the basin with the pluto charon tidal axis sputnik planitia probably formed northwest of its present location and was loaded with volatiles over million year timescales as a result of volatile transport cycles this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context pluto is an astoundingly diverse geologically dynamic world the dominant feature is sputnik planitia a tear drop shaped topographic depression approximately 1 000 kilometres in diameter possibly representing an ancient impact basin1 2 the interior of sputnik planitia is characterized by a smooth craterless plain three to four kilometres beneath the surrounding rugged uplands and represents the surface of a massive unit of actively convecting volatile ices n2 ch4 and co several kilometres thick1 2 3 4 5 this large feature is very near the pluto charon tidal axis here we report that the location of sputnik planitia is the natural consequence of the sequestration of volatile ices within the basin and the resulting reorientation true polar wander of pluto loading of volatile ices within a basin the size of sputnik planitia can substantially alter pluto s inertia tensor resulting in a reorientation of the dwarf planet of around 60 degrees with respect to the rotational and tidal axes the combination of this reorientation loading and global expansion due to the freezing of a possible subsurface ocean generates stresses within the planet s lithosphere resulting in a global network of extensional faults that closely replicate the observed fault networks on pluto sputnik planitia probably formed northwest of its present location and was loaded with volatiles over million year timescales as a result of volatile transport cycles on pluto6 7 pluto s past present and future orientation is controlled by feedbacks between volatile sublimation and condensation changing insolation conditions and pluto s interior structure

long term evolution of the west african transform margin estimates of denudation from benin using apatite thermochronology the benin continental margin was formed during the breakup of gondwana through oblique rifting along transform faults the evolution of topography following breakup directly affects the evolution of sedimentary basins which has major implications for hydrocarbon exploration in the region quantitative constraints on erosion across benin are limited to the cenozoic based on analysis of dissected lateritic palaeolandscapes to resolve the mesozoic erosion history we have obtained apatite fission track and single grain u th sm he data from 18 samples collected across a 600 km long transect through benin we invert these data including available geological and geomorphological constraints to obtain time temperature paths which are used to estimate magnitudes of denudation over the last 200 myr our study suggests that denudation was focused over a c 300 km long seaward sloping limb of the marginal upwarp and at the southern margin of the interior iullemmeden basin from 140 to 100 ma with lower magnitudes of denudation characterizing the continental interior and post cretaceous evolution of the margin models are consistent with modest burial c 1 km of the iullemmeden basin between 120 and 85 ma and of the continental margin between 85 and 45 ma by the eocene the first order relief of benin had developed with regional erosion rates supplementary information full details of the analytical data and modelling results including the various constraints and further data on denudation and burial magnitudes and rates are available at https doi org 10 6084 m9 figshare c 4220804

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

mesozoic and cenozoic exhumation history of the sw iberian variscides inferred from low temperature thermochronology abstract the post paleozoic tectonothermal evolution of the sw iberian variscides is poorly known mainly due to the scarce low temperature geochronological data available we have obtained new apatite fission tracks and apatite u th he ages to constrain the mesozoic and cenozoic tectonic evolution of this portion of the iberian massif located just north of the betic rif alpine orogen we have obtained nine apatite fission track ages on samples from variscan and pre variscan granitoids these ages range from 174 4 10 8 to 54 1 4 9 ma with mean track lengths between 10 3 and 13 9 m we have also performed 5 u th he datings on some of the same samples obtaining ages between 74 6 1 6 and 18 5 1 4 ma time temperature path modeling of these low temperature geochronological data leads us to envisage four post paleozoic tectonically controlled exhumation episodes in the sw iberian variscides three of these episodes occurred in mesozoic times middle triassic to early jurassic early cretaceous and late cretaceous at rates of 1 1 to 2 5 c ma 1 separated by periods with almost no cooling we relate these mesozoic cooling events to the formation of important marginal reliefs during the rifting and opening of the central and northern atlantic realm the fourth exhumation episode occurred in cenozoic times at rates of 3 2 to 3 6 c ma 1 being only recorded in samples next to faults with topographic escarpments these samples cooled below 80 c at 20 ma at rates of 3 13 c ma 1 due to roughly n s oriented compressional stresses affecting the whole iberian plate which in the particular case of sw iberia reactivated some of the previous late paleozoic thrusts

k ar and ar ar dating the aim of this chapter is to present the k ar and ar ar dating techniques in the context of noble gas studies since there are already several recent texts on k ar and ar ar dating dickin 1995 mcdougall and harrison 1999 the focus of this section will be aspects of argon transport and storage in the crust which affect k ar and ar ar dating including ar loss from minerals by diffusion and ar gain by minerals or excess argon the k ar dating technique was one of the earliest isotope dating techniques developed soon after the discovery of radioactive potassium and provided an important adjunct to u pb and u he dating techniques the ease of measurement and ideal half life 1250 million years see table 2 below for dating geological events has made this the most popular of isotopic dating techniques aldrich and nier 1948 first demonstrated that 40ar was the product of the decay of 40k and soon after k ar ages were being measured in several laboratories most often using an absolute method such as a mcleod gauge to measure argon concentrations the first published k ar results by such a technique were those of smits and gentner 1950 who analyzed sylvite from the buggingen oligocene evaporite deposits obtaining an age of 20 million years mass spectrometers which simultaneously measured very small amounts of gas and the isotope ratios necessary to make corrections for atmospheric contamination quickly replaced manometric techniques crucially the use of static vacuum techniques pioneered by john reynolds at the university of california berkeley meant that mass spectrometers were sufficiently sensitive to analyse the small amounts of gas released from common rocks and minerals although the earliest mass spectrometers were built in house the introduction of the commercially available ms10 farrar et al 1964 a small 180 metal mass spectrometer built for

cooling history of the chapedony metamorphic core complex central iran implications for the eurasia arabia collision abstract new apatite and zircon u th he thermochronometry is used to constrain the late stage cooling history of the chapedony metamorphic core complex in the saghand region of central iran providing new constraints on the cenozoic tectonic evolution of this segment of the euro arabian collision zone zircon and apatite he ages from the footwall indicate that it cooled to near surface temperatures by 30 ma combined with previous high temperature thermochronology the new data require that the chapedony metamorphic core complex cooled from 750 c to 60 c in less than 20 million years at 80 c myr cooling of the complex occurred through tectonic exhumation at a rate of 1 2 1 5 km myr exhumation of the core complex occurred during the main phase of subduction of the distal arabian margin beneath the central iranian plate at 49 to 30 ma zircon he ages from the hangingwall units of the complex suggest an earlier pulse of exhumation in middle late cretaceous apatite he ages from the hangingwall 22 30 ma are significantly younger than the core complex exhumation but is consistent with the regional timing of initial eurasia arabia collision

u th he dating of apatite a potential thermochronometer abstract we found a gem quality crystal of durango fluorapatite to have a 4he content consistent with complete retention of radiogenic helium since its formation at about 31 ma isothermal heating and step heating analysis reveal 4he loss to occur systematically by volume diffusion at low temperatures the linear low temperature portion of the diffusion data yields an activation energy of 38 5 8 1 kcal mol and a frequency factor of in d 0 a 2 16 4 2 8 sec 1 corresponding to a closure temperature of 105 c 30 c cooling rate 10 c m y it appears that u th he dating of apatite might represent a useful new thermochronometer with a range similar to that of fission track dating of apatite from these results we infer that a number of the too young u th he dates reported in the literature on minerals such as zircon and magnetite may in fact represent valuable records of the low temperature thermal history of their host rocks

post orogenic evolution of the dabie shan eastern china from u th he and fission track thermochronology the dabie shan of eastern china is a 200 kilometers wide mountain range with nearly 2 kilometers of relief and is an archetype of deep ultrahigh pressure metamorphic rock exhumation despite its regional and petrologic importance little is known about the low temperature and post orogenic evolution of the dabie shan here we present apatite and zircon u th he ahe and zhe respectively and apatite fission track aft cooling ages from the dabie shan that constrain the patterns and history of exhumation over the last 115 myr on the scale of the whole orogen zhe and ahe ages are inversely correlated with mean elevation and are systematically younger in the core of the range these cooling ages were converted to exhumation rates assuming steady state erosion and accounting for topographic effects these results indicate that since the eocene flanks of the range have eroded at rates as low as 0 02 km myr while the range core has eroded at about 0 06 km myr even in the core of the range these recent exhumation rates are at least 10 to 20 times slower than those estimated for the initial stages of exhumation in the triassic jurassic in a 1 4 kilometer vertical transect in the core of the range all ages are positively correlated with elevation with zhe ages increasing from 76 to 112 ma aft from 44 to 70 ma and ahe from 24 to 43 ma we present a simple model for topographic correction of thermochronometric ages in vertical transects using the admittance ratio ratio of isotherm relief to topographic relief applied to the ahe age elevation relationship this yields tertiary exhumation rates of 0 05 to 0 07 km myr in the core of the dabie shan in good agreement with regional exhumation rate patterns finally age elevation relationships for all three chronometers in the vertical transect are consistent with a constant exhumation rate of 0 06 0 01 km myr since the creta ceous with a possible modest increase in exhumation rates as high as 0 2 km myr between 80 to 40 ma these data show no evidence for significant variations in exhumation rates over the last 115 myr as might be expected for decay of old topography or tectonic reactivation of old structures

geomorphic development of the escarpment of the eritrean margin southern red sea from combined apatite fission track and u th he thermochronometry apatite u th he and fission track thermochronometers are combined to constrain models of denudation and escarpment development of the high elevation eritrean margin along the southern red sea u th he ages have been determined for apatites from two coast perpendicular transects that were previously used for apatite fission track analysis e abbate m l balestrieri g bigazzi morphostructural development of the eritrean rift flank southern red sea inferred from apatite fission track analysis j geophys res 107 b11 doi 10 1029 2001jb001009 2002 in central eritrea near asmara he ages increase from c 7 ma at the coast to 152 ma on the plateau along a transect further south he ages from the margin border to the base of the escarpment span a narrower range 7 to 12 ma one sample from the top of a marginal high 2950 m yields older ages 22 43 ma forward modeling suggests that the he age distribution across the margin should allow scarp retreat and downwearing mechanisms to be distinguished in the case of a margin formed in the last twenty million years the distribution of he ages suggests that the escarpment evolved by downwearing and that post break up erosion of the escarpment was facilitated by in situ excavation rather than parallel retreat this implies the existence of an inland drainage divide located seaward of the present day escarpment rim we envisage that the inland divide formed during or immediately after continent break up and that the eastern marginal belt represents a remnant of the apex structure the short distance between the eastern marginal belt and the rim c 10 km represents the total retreat of the escarpment comparison of the measured he ages from the coastal plain with those predicted from forward modelling indicates that the main phase of post break up erosion started at about 15 ma closer to the initiation of seafloor spreading in the red sea than was thought previously

tectono thermal evolution of a distal rifted margin constraints from the calizzano massif prepiedmont brianconnais domain ligurian alps the thermal evolution of distal domains along rifted margins is at present poorly constrained in this study we show that a thermal pulse most likely triggered by lithospheric thinning and asthenospheric rise is recorded at upper crustal levels and may also influence the diagenetic processes in the overlying sediments thus representing a critical aspect for the evaluation of hydrocarbon systems the thermal history of a distal sector of the alpine tethys rifted margin preserved in the ligurian alps case tuberto calizzano unit is investigated with thermochronological methods and petrologic observations the studied unit is composed of a polymetamorphic basement and a sedimentary cover providing a complete section through the prerift synrift and postrift system zircon fission track analyses on basement rocks samples suggest that temperatures exceeding 240 25 c were reached before 150 160 ma upper jurassic at few kilometer depth neoformation of green biotite stable at temperatures of 350 to 450 c was synkinematic with this event the tectonic setting of the studied unit suggests that the heating cooling cycle took place during the formation of the distal rifted margin and terminated during late jurassic 150 160 ma major crustal and lithospheric thinning likely promoted high geothermal gradients 60 90 c km and triggered the circulation of hot deep seated fluids along brittle faults causing the observed thermal anomaly our results suggest that rifting can generate thermal perturbations at relatively high temperatures between 240 and 450 c at less than 3 km depth in the distal domains during major crustal thinning preceding breakup and onset of seafloor spreading

exhumation history of the tatry mountains western carpathians constrained by low temperature thermochronology this study tests alternative models for the growth of the tatry mountains central western carpathians by the application of low temperature thermochronology zircon u th he ages from the north of the range are mostly between 48 to 37 ma and indicate cooling prior to the onset of forearc sedimentation in the region 42 39 ma in contrast zircon u th he ages in the south of the range are around 22 ma apatite fission track ages across the sampled sites range from 20 to 15 ma apatite u th he ages range from 18 to 14 ma with little variation with elevation or horizontal location based on thermal modelling and tectonic reconstructions these miocene ages are interpreted as cooling in the hanging wall of a northward dipping thrust ramp in the current location of the sub tatric fault with cooling rates of 20 c myr at 22 14 ma modeled cooling histories require an abrupt deceleration in cooling after 14 ma to 5 c myr this is associated with termination of deformation in the outer carpathians and is synchronous with the transition of the pannonian basin from a syn rift to a post rift stage and with termination of n s compression in the northern part of the central western carpathians overall the timing of shortening and exhumation is synchronous with the formation of the outer carpathian orogen and so the miocene exhumation of the tatry record retro vergent thrusting at the northern margin of the alcapa microplate

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

dating the cooling of exhumed central uplifts of impact structures by the u th he method a case study at manicouagan abstract forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the manicouagan impact structure were dated by the u th he technique a u th he central age of 207 1 6 4 ma 2 standard error se n 40 has been determined with 4 outlier ages removed the central age is refined to 208 9 5 1 ma 2 se both of these ages are within error of the previously determined u pb zircon age of 214 1 ma 2 derived from the impact melt manicouagan s central uplift formed due to rapid elevation from 7 10 km depth as part of the modification stage of the impact process which has facilitated the dating of its emplacement due to resulting rapid exhumation and cooling and closure of the u th he system in titanite correlation with the previous u pb zircon 214 1 ma impact melt crystallization age indicates that the u th he titanite dating technique offers a new approach to dating complex impact structures in the absence of viable melt sheets or other melt products the youngest ca 195 ma u th he dates preserved in some titanite fragments are synchronous with early jurassic rift induced lithospheric thinning and associated igneous activity that defines the central atlantic magmatic province camp the u th he titanite data from manicouagan indicate that the influence of this regional event may extend west of the previously proposed limit of camp activity

characterization of helium release from apatite by continuous ramped heating abstract knowledge of the kinetic behavior of he in apatite and other u and th bearing minerals comes largely from detailed step heating experiments yet such experiments are time consuming and are rarely performed during routine thermochronological studies using the u th he method we propose a new analytical method for measuring both the bulk 4he abundance and the kinetics of he release in apatite using this method he is extracted from samples by continuous heating using a ramped temperature schedule under static vacuum conditions and the evolved he is measured periodically as it accumulates in the extraction system continuous ramped heating crh experiments can be conducted using instrumentation available in most noble gas thermochronology labs but require particular attention to temperature control measurement linearity and dynamic range and suppression of active gases co evolved with he crh experiments require little more time than conventional single step heating measurements but yield a detailed record of he release not provided by conventional methods kinetic parameters for he diffusion in durango apatite derived from continuous heating data agree well with those obtained from published step heating studies the continuous record of he release obtained from crh experiments also provides important information about the siting of he and the presence of multiple he components in apatite some of which may be responsible for anomalous u th he ages and high age dispersion as such the crh method shows promise as a useful sample screening tool for apatite u th he thermochronology

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

measuring plume related exhumation of the british isles in early cenozoic times mantle plumes have been proposed to exert a first order control on the morphology of earth s surface however there is little consensus on the lifespan of the convectively supported topography here we focus on the cenozoic uplift and exhumation history of the british isles while uplift in the absence of major regional tectonic activity has long been documented the causative mechanism is highly controversial and direct exhumation estimates are hindered by the near complete absence of onshore post cretaceous sediments outside northern ireland and the truncated stratigraphic record of many offshore basins two main hypotheses have been developed by previous studies epeirogenic exhumation driven by the proto iceland plume or multiple phases of cenozoic compression driven by far field stresses here we present a new thermochronological dataset comprising 43 apatite fission track aft and 102 u th sm he ahe dates from the onshore british isles inverse modelling of vertical sample profiles allows us to define well constrained regional cooling histories crucially during the paleocene the thermal history models show that a rapid exhumation pulse 1 2 5 km occurred focused on the irish sea exhumation is greatest in the north of the irish sea region and decreases in intensity to the south and west the spatial pattern of paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies and the timing of uplift and exhumation is synchronous with emplacement of the plume related british and irish paleogene igneous province bipip prior to the paleocene exhumation pulse the mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long lived rifting history of the neighbouring offshore basins the extent of neogene exhumation is difficult to constrain due to the poor sensitivity of the ahe and aft systems at low temperatures we conclude that the cenozoic topographic evolution of the british isles is the result of plume driven uplift and exhumation with inversion under compressive stress playing a secondary role

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

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

unexpected jurassic to neogene vertical movements in stable parts of nw africa revealed by low temperature geochronology in morocco it is generally considered that post hercynian vertical movements were limited to the atlas system the passive continental margin and the rif apatite ft and he ages from the moroccan meseta rehamna and zaer massif document instead two episodes of subsidence and exhumation in jurassic early cretaceous and during the late cretaceous to neogene the meseta subsided to 3 km depth during the late triassic to middle jurassic and was exhumed to the surface before the late cretaceous during the rift and post rift stages of central atlantic opening erosion of the exhuming rocks is responsible for a thick package of terrigenous sands found in the moroccan offshore and elsewhere along the nw africa margin about 1 km of subsidence affected the meseta during the late cretaceous to eocene during the neogene these areas were brought back to the surface in association with bimodal folding with wavelengths of 100 150 km and 500 km

inversion of thermochronological age elevation profiles to extract independent estimates of denudation and relief history ii application to the french western alps abstract thermochronologic data collected along age elevation profiles are commonly interpreted as recording temporally variant but spatially constant exhumation rates however thermochronologic age elevation relationships are known to be perturbed by topographic effects and potential changes in relief which are neglected in the inherently 1 d interpretation commonly applied such data thus potentially record both the denudation and relief history of the sampled region but extracting this information is challenging in a companion paper we develop a methodology for rigorously interpreting thermochronologic age elevation profiles in terms of exhumation rates and relief development through time and to independently quantify the resolution of these constraints here we test this approach using a thermochronological dataset consisting of apatite and zircon fission track and u th he data collected at la meije peak in the pelvoux ecrins massif french western alps our data and models suggest a three phase exhumation history in the pelvoux ecrins massif including a pulse of rapid exhumation at 6 5 5 ma preceded and followed by more moderate rates of denudation in the order of 0 3 0 4 km myr 1 this rapid exhumation event appears to occur coevally in other external crystalline massifs in the alps but is not detected by qualitative inspection of the age elevation relationships both our synthetic results and inversion of the la meije data strongly suggest that apatite fission track age elevation relationships alone cannot resolve both denudation and relief histories independently and that multiple thermochronometers are required combining apatite fission track and u th he ages and particularly including fission track length data greatly improves the resolution of the inferred exhumation histories although denudation rates through time and the timing of rate changes are generally well resolved our data have insufficient resolution to satisfactorily constrain the relief history synthetic results reported in the companion paper suggest that the reason for this limitation is that relief increase through valley carving has been insufficient with respect to the regional denudation rates to be unambiguously extracted from the data

laser extraction of helium isotopes from antarctic micrometeorites source of he and implications for the flux of extraterrestrial 3he to earth helium isotopes have been measured in 45 putative micrometeorites in the size range 50 to 400 m that were extracted from antarctic ice forty of the antarctic micrometeorites amms are irregular in shape and display varying degrees of partial melting whereas five are spherical and thought to represent completely melted particles of the 30 50 to 100 m suspected micrometeorites only 8 released neither 3he or 4he sixteen released 3he and 4he 0 004 3 5 10 3 cm3 stp g having 3he 4he in the range 1 5 10 4 to 4 1 10 4 six particles released only 3he yielding minimum 3he 4he of 1 6 to 10 6 10 4 5 of which fall in the range of values for amms that had measurable 3he and 4he only 2 of the 15 100 to 400 m amms released measurable 4he 4 44 10 7 cc g 1 these have 3he 4he of 6 10 4 and 20 10 4 respectively significantly higher than the majority of the ratios of 50 to 100 m amms implanted solar energetic particles are the dominant source of he in the 50 to 100 m amms with small contributions of solar wind and or spallogenic he present in 10 particles the absence of sw he is likely due to the loss of the outermost layers of the micrometeorites by ablation during atmospheric entry and abrasion during residence in ice and sampling spallation he is most important in the 100 to 400 m amms consistent with their smaller surface area to volume ratio maximum spallation 3he exposure ages of six particles are close to that predicted from poynting robertson spiral in times of asteroidal micrometeorites the two terrestrial particles identified by chemical composition and mineralogy released only 4he yielding radiogenic he isotope compositions an inverse relationship between particle sizes and solar he abundance is explained by he loss during entry helium loss is likely controlled by phyllosilicate breakdown where present and diffusion controlled bubble growth and rupture rather than melting the 50 to 100 m micrometeorites deliver 8 10 8 cm3 stp 3he g to earth this is more than 100 times less than transported by 20 m particles 2 10 5 cm3 stp 3he g but because 50 to 100 m micrometeorites deliver approximately 20 times more extraterrestrial matter to earth than 20 m particles the larger particles may contribute 5 of the total flux of extraterrestrial 3he to terrestrial sediments the mean he concentrations of the 50 to 100 m amms antarctic micrometeorites and the five spherules 2 1 10 9 cm3 stp 3he g 1 overlap those of the magnetic fraction of deep sea sediments 0 8 68 10 9 cm3 stp g a combination of this material could provide the extraterrestrial 3he measured in ancient deep sea sediments without calling upon the survival of friable 20 m chondritic interplanetary dust particles for tens of millions of years

the laser microprobe and its application to the study of c and o isotopes in calcite and aragonite abstract laser probe microsampling of c and o from carbonate minerals for isotopic analysis was achieved by focussing a nd yag high power laser through microscope optics onto a sample situated in a vacuum chamber the laser beam about 10 m in diameter was used to ablate an area on the sample a slab or a thin section liberating co 2 gas the co 2 was purified and led directly into a mass spectrometer for isotopic analysis fractionation effects and reproducibility were assessed by analyzing homogenized natural and synthetic carbonate standards that had been well characterized using conventional acid digestion techniques the data indicated that 13 c was not significantly fractionated during laser ablation however the 18 o of the evolved co 2 was 1 7 lighter than o in the original caco 3 in the case of calcite 2 5 lighter for aragonite this fractionation was not dependent on laser operating conditions although the operating conditions were important for efficient co 2 production optimal reproducibility in carbonates was in the order of 0 2 for both 13 o

assessment of u th he thermochronometry the low temperature history of the san jacinto mountains california u th he ages have been measured on igneous apatites from the san jacinto mountains a high region at the junction of the peninsular and transverse ranges to investigate the potential of this technique for thermochronometry of slowly cooled rocks helium ages from 79 to 17 ma are younger than ages obtained by other dating techniques including apatite fission track counting and are consistent with laboratory experiments that indicate this system has a uniquely low closure temperature helium ages are strongly correlated with elevation and record the latest low temperature thermal evolution of the range they suggest relative tectonic quiescence in the latest cretaceous through mid tertiary and provide no evidence for rapid unroofing of the block during this period nor do they obviously require a large degree of uplift associated with convergence between the transverse and peninsular ranges in the last few million years helium ages document modest westward tilting of the block 7 and a significant vertical component of motion on the block s bounding faults after helium retention began this work suggests that apatite helium ages record low temperature tectonic and thermal histories that are not apparent from other dating techniques

multi aliquot method for determining u th he ages of hydrothermal hematite returning to elba abstract we have used a multi aliquot method to obtain precise u th he ages of hydrothermal hematite and to assess the extent to which he loss from fine grained hematite caused by diffusion and recoil hematite n 6 from the rio marina mine elba italy yields u th he ages that range from 5 36 0 33 to 5 64 0 11 ma giving a weighted mean age of 5 53 0 14 ma and an isochron age of 5 25 0 20 ma 40ar 39ar data from cogenetic adularia yield flat age spectra with analytically indistinguishable plateau ages 5 575 0 008 and 5 583 0 013 ma an additional adularia has a more complex spectrum and yields an interpreted age of 5 64 0 03 ma the hematite u th he ages overlap the 40ar 39ar ages albeit they are less precise 2 6 vs 0 2 0 5 this indicates that the loss of in situ radiogenic 4he from complex fine grained hematite either by diffusion and recoil is insignificant the study shows that multi aliquot method has the potential to reliably deliver precise and accurate ages for iron oxide mineralisation that has not suffered significant post crystallisation thermal perturbation

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

tertiary cooling and exhumation history in the maramures area internal eastern carpathians northern romania thermochronology and structural data the tertiary kinematic history of the maramures area is constrained by integrating thermochronological fission track and uth he analysis data with field based structural investigations this study focuses on the tectonic evolution of the northern rim of the tisza dacia block during collision with the european margin cretaceous nappe stacking related metamorphism as well as late cretaceous exhumation are evidenced by zircon fission track data subsequent palaeogene to early miocene sedimentation led to burial heating and annealing of fission tracks in apatite final tectonic uplift was initiated during the convergence of tisza dacia with the european margin associated with transpressional deformation 16 to 12 ma this led to mid miocene exhumation recorded by apatite fission track cooling ages in the western part of the study area transtension between 12 and 10 ma caused brittle deformation along ew trending strike slip faults and swne trending normal faults delimiting blocks that were tilted towards the sw this fragmentation of the crust led to enhanced exhumation at rates of 1 mm a in the central part of the study area as is documented by middle to late miocene cooling ages 13 to 7 ma the outside estimate for the total amount of exhumation since middle miocene times is 7 km

appraisal of u th he apatite thermochronology as a thermal history tool for hydrocarbon exploration an example from the taranaki basin new zealand the taranaki basin contains most of new zealand s commercial hydrocarbon reserves the southern parts of the taranaki basin underwent inversion during the late miocene with published afta apatite fission track analysis and vitrinite reflectance data suggesting approximately 2 5 3 km of section eroded from the structure on which the fresne 1 well was drilled consistent with estimates from reconstructions based on seismic sections the well constrained tectonic and thermal history framework for this well section established by earlier studies provides an ideal test bed for the thermochronological technique of apatite u th he dating helium ages determined in apatites from the earlier afta study decrease from about 6 ma at about 400 m depth to about 1 ma at 2465 m although these results are qualitatively consistent with late miocene cooling quantitative modeling of u th he ages based on best fit thermal histories derived from new afta analyses using improved methods suggests that cooling was protracted involving accelerated cooling during the pliocene possibly indicating a discrete pliocene inversion phase integration of afta and u th he dating can provide improved thermal history constraints in sedimentary basins particularly on cooling rates and or resolution of multiple thermal events by independently defining the timing of peak maturation in relation to formation of potential trapping structures this information offers the potential for improved assessment of hydrocarbon prospectivity and reduced exploration risk

long term low latitude cosmogenic 3he production rate determined from a 126 ka basalt from fogo cape verdes an ankaramite lava from fogo cape verdes has been used to determine the long term cosmogenic 3he 3hecos production rate at low latitude 14 9 n 40ar 39ar incremental heating yield an eruption age of 125 8 7 ka cosmogenic 3he abundances yield local production rates of 75 6 7 0 atoms g year in olivine 1 n 10 and 70 1 2 9 atoms g yr in pyroxene 1 n 11 the lower 3hecos production rate in pyroxene is consistent with compositional control on production when scaled to sea level high latitude using available algorithms the olivine 3hecos production rate ranges from 86 109 atoms g yr these values overlap the long term production rate determined at the canary islands 99 atoms g yr they are however lower than previously reported long term production rates from hawaii and southern south america 129 152 atoms g yr and the range of 20 ka calibration sites 110 130 atoms g yr erosion burial and high atmospheric pressure appear to be of negligible importance the likeliest explanation is that the geomagnetic field strength was higher in the past the agreement between the fogo geomagnetic field strength corrected production rate scaled using various published scaling algorithms suggests that differences in incorporation of the non dipole component of the earth magnetic field in the scaling algorithms are negligible for long term production rate determinations at low elevation and low latitude longitudinal variation in long term cosmogenic nuclide production rates between the central atlantic ocean and the americas hawaii and patagonia may exist this has implications for exposure dating of old surfaces it will require that locally determined production rates should be used where available and that scaling schemes incorporating longitudinal variations should be used if nearby calibration sites are not available furthermore if long term longitudinal production rate variations exist it implies that variation in the geomagnetic field may not average out after around 20 ka but may require significantly longer periods up to 100 ka

thermochronological constraints on the timing and magnitude of miocene and pliocene extension in the central wassuk range western nevada apatite fission track and u th he thermochronological data provide new constraints on the timing of faulting and exhumation of the wassuk range western nevada where east dipping normal faults have accommodated large magnitude ene wsw oriented extension extensional deformation has resulted in the exhumation of structurally coherent fault blocks that expose sections of preextensional mostly granitic upper crust in the grey hills and central wassuk range these fault blocks display westward tilts of 60 and expose preextensional paleodepths of up to 8 5 km based on the structural reconstruction of tilted preextensional tertiary andesite flows that unconformably overlie mesozoic basement rocks apatite fission track and u th he thermochronological data from the fault blocks constrain the onset of rapid footwall exhumation at 15 ma fission track modeling results indicate rapid fault block exhumation occurred between 15 and 12 ma which is in agreement with miocene volcanic rocks that bracket the tilting history in addition fission track and u th he data suggest reduced rates of cooling following major extension as well as renewed cooling related to active high angle faulting along the present day range front starting at 4 ma thermochronological data from structurally restored fault blocks indicate a preextensional miocene geothermal gradient of 27 5 c km the thermochronological constraints on the timing of extensional faulting and the eruptive history in the wassuk range imply a model for extension where crustal heating and volcanism precede the onset of rapid large magnitude extension and where synextensional magmatism is suppressed during the highest rates of extension

near fault peak ground velocity from earthquake and laboratory data we test the hypothesis that peak ground velocity pgv has an upper bound independent of earthquake magnitude and that this bound is controlled primarily by the strength of the seismogenic crust the highest pgvs ranging up to several meters per second have been measured at sites within a few kilometers of the causative faults because the database for near fault pgv is small we use earthquake slip models laboratory experiments and evidence from a mining induced earthquake to investigate the factors influencing near fault pgv and the nature of its scaling for each earthquake slip model we have calculated the peak slip rates for all subfaults and then chosen the maximum of these rates as an estimate of twice the largest near fault pgv nine slip models for eight earthquakes with magnitudes ranging from 6 5 to 7 6 yielded maximum peak slip rates ranging from 2 3 to 12 m sec with a median of 5 9 m sec by making several adjustments pgvs for small earthquakes can be simulated from peak slip rates measured during laboratory stick slip experiments first we adjust the pgv for differences in the state of stress i e the difference between the laboratory loading stresses and those appropriate for faults at seismogenic depths to do this we multiply both the slip and the peak slip rate by the ratio of the effective normal stresses acting on fault planes measured at 6 8 km depth at the ktb site germany deepest available in situ stress measurements to those acting on the laboratory faults we also adjust the seismic moment by replacing the laboratory fault with a buried circular shear crack whose radius is chosen to match the experimental unloading stiffness an additional less important adjustment is needed for experiments run in triaxial loading conditions with these adjustments peak slip rates for 10 stick slip events with scaled moment magnitudes from 2 9 to 1 0 range from 3 3 to 10 3 m sec with a median of 5 4 m sec both the earthquake and laboratory results are consistent with typical maximum peak slip rates averaging between 5 and 6 m sec or corresponding maximum near fault pgvs between 2 5 and 3 m sec at seismogenic depths independent of magnitude our ability to replicate maximum slip rates in the fault zones of earthquakes by adjusting the corresponding laboratory rates using the ratio of effective normal stresses acting on the fault planes suggests that the strength of the seismogenic crust is the important factor limiting the near fault pgv

late miocene to present exhumation in the ligurian alps southwest alps with evidence for accelerated denudation during the messinian salinity crisis detrital apatite u th he and fission track thermochronometry are applied to constrain the exhumation history of the ligurian alps southwest alps exhumation of the ligurian alps is recorded from ca 11 ma and continues until present more than 4 km of exhumation is recorded at an average rate of 0 4 0 2 mm yr exhumation is accommodated along a north dipping thrust at the foot of the ligurian margin combined u th he and fission track thermal modeling show a phase of accelerated denudation between 7 and 5 ma associated with the base level drop during the messinian salinity crisis

constraining the post emplacement evolution of the hebridean igneous province hip using low temperature thermochronology how long has the hip been cool abstract the thermal history of the hebridean igneous province has been determined through the application of low temperature thermochronology to the four central complexes in the province the zircon u th he age 59 4 3 3 ma 1 n 18 and the ages from each complex 60 7 2 3 ma for skye 58 0 0 4 ma for mull 55 9 3 2 ma for ardnamurchan 55 6 2 7 ma for rum are indistinguishable from the crystallization ages apatite fission track ages 61 2 57 2 ma mean of 59 3 3 4 ma from the major plutonic units also overlap crystallization ages implying that on a regional scale the hebridean igneous province cooled rapidly to near surface temperatures immediately after emplacement however apatite fission track ages and track lengths and apatite u th he ages from some small volume intrusions in the skye and rum central complexes identify localized mid eocene 45 47 ma cooling forward and inverse modelling suggests a discrete heating cooling event at c 47 ma which may have been caused by structurally controlled localized advection of heat above shallow emplacement this is the first suggestion of eocene magmatism in the hebridean igneous province

u and th zoning in cerro de mercado durango mexico fluorapatite insights regarding the impact of recoil redistribution of radiogenic 4he on u th he thermochronology abstract fluorapatite from cerro de mercado durango mexico has been used in several important diffusion studies aimed at calibrating the closure temperature of the u th he apatite thermochronometer and has become a de facto standard for u th he laboratories nevertheless replicate laser fusion analyses of small crystal fragments of the durango fluorapatite typically yield a range of u th he dates that cannot be explained by reported analytical imprecision alone laser ablation icpms measurements of u and th of a section cut through a representative crystal of durango fluorapatite perpendicular to the c axis reveal the existence of significant zoning in these elements since alpha stopping distances in apatite are comparable to the scale of this zoning the ejection of radiogenic 4he from one zone to another may explain some of the reported fragment to fragment variation in u th he dates two dimensional numerical models of the recoil redistribution of 4he in a crystal with the zoning we observed lead to predicted age variations of several percent for fragments with sizes and aspect ratios typical of those used for laser fusion of durango fluorapatite it is likely that large crystals or large aliquots of small fragments of zoned materials may be acceptable as bulk interlaboratory standards however the current trend is toward the use of smaller and smaller sample sizes including broken crystals for u th he thermochronology our work indicates that heterogeneities in the u and th concentrations of such samples are a serious concern so much so that high precision u th he geochronologic studies should include a concerted effort to characterize the extent of u and th zoning in analyzed crystals

tectonic response of the central chilean margin 35 38 s to the collision and subduction of heterogeneous oceanic crust a thermochronological study along strike geological segmentation in the andean chain has been recognized at various scales and is usually attributed to changes in plate motion vectors as well as the upper plate expression of differing subducted slab age strength and composition we present new multi phase 40ar 39ar apatite fission track and zircon and apatite u th he data from a north south oriented traverse between 35 and 38 s along the principal andean cordillera of chile that reveal 1 rapid cooling at 18 and 15 ma which can be attributed to both thermal relaxation following magmatic intrusion and regional scale exhumation and 2 along strike differences in the extent of exhumation since 7 5 ma that may be a consequence of the subduction of the juan fernandez ridge above the flat slab segment at 32 since 10 ma a comparison of the response of the south american plate to the collision of the carnegie nazca and juan fernandez ridges suggests that slab flattening is not the dominant driving force that exhumes the upper plate in these settings rather the extent of exhumation is controlled by pre existing structural weaknesses the time duration of the dynamically supported topography and climate

testing models of orogen exhumation using zircon u th he thermochronology insight from the ligurian alps northern italy testing models of orogen exhumation requires precise constraint of the time temperature paths of the exhumed rocks the zircon u th he zhe thermochronometer has a closure temperature of 140 210 c and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen we performed zhe analyses to test the existing contradictory models for the exhumation of the ligurian alps the zhe ages indicate a very rapid 1 3 6 8 mm yr and southward migrating exhumation of the orogen between 32 and 25 ma these high exhumation rates are unique within the alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the ligurian alps we propose a model of tectonic denudation via detachment accomplished in the shallowest crust 5 km as a result of the last orogenic phase of extension

kinematic and thermal evolution of the haymana basin a fore arc to foreland basin in central anatolia turkey abstract gondwana tauride kirsehir blocks and eurasia pontides derived continental blocks delimit the haymana basin central turkey to the south and the north respectively the boundaries of these blocks define the izmir ankara erzincan and intra tauride suture zones which are straddled by a number of late cretaceous to oligocene marine to continental basins the haymana basin is located at the junction of the iaesz and itsz and comprises upper cretaceous to middle eocene basin infill deposited in response to the interaction of these blocks the basin provides a unique opportunity to unravel spatio temporal relationships related to the timing of late stage subduction history of neo tethys ocean and subsequent collision of the intervening continental blocks we have conducted a multidisciplinary study in the region that includes mapping of major structures combined with fault kinematic analyses e w striking folds dominate the basin cross section balancing of these structures indicates around 25 roughly n s shortening in the region paleostress studies indicate that the basin was initially subjected to n s to nne ssw extension until the middle paleocene phase 1 and then n s directed syn depositional compression and coeval e w directed extension until the middle miocene phase 2 implying strike slip deformation and pure shear shortening in the basin these different deformation phases are attributed to first fore arc subduction basin development then foreland collision stages of the basin apatite u th he dating of 5 samples indicate that exhumation of the se segment of the basin started in early oligocene whereas the nw segment of the basin exhumed in the early miocene the differential uplift is possibly related to progressive north westwards movement of derekoy basin bounding fault at the north we propose that the haymana basin evolved from extensional forearc basin during the late cretaceous to early paleocene and foreland basin after the terminal subduction and subsequent collision of tauride and pontide blocks

from source to sink in central gondwana exhumation of the precambrian basement rocks of tanzania and sediment accumulation in the adjacent congo basin apatite fission track aft and u th he ahe thermochronometry data are reported and used to unravel the exhumation history of crystalline basement rocks from the elevated 1000 m a s l but low relief tanzanian craton coeval episodes of sedimentation documented within adjacent paleozoic to mesozoic basins of southern tanzania and the congo basin of the democratic republic of congo drc indicate that most of the cooling in the basement rocks in tanzania was linked to erosion basement samples were from an exploration borehole located within the craton and up to 2200 m below surface surface samples were also analysed aft dates range between 317 33 ma and 188 44 ma alpha ft corrected ahe dates are between 433 24 ma and 154 20 ma modelling of the data reveals two important periods of cooling within the craton one during the carboniferous triassic 340 220 ma and a later less well constrained episode during the late cretaceous the later exhumation is well detected proximal to the east african rift 70 ma thermal histories combined with the estimated geothermal gradient of 9 c km constrained by the aft and ahe data from the craton and a mean surface temperature of 20 c indicate removal of up to 9 2 km of overburden since the end paleozoic the correlation of erosion of the craton and sedimentation and subsidence within the congo basin in the paleozoic may indicate regional flexural geodynamics of the lithosphere due to lithosphere buckling induced by far field compressional tectonic processes and thereafter through deep mantle upwelling and epeirogeny tectonic processes

cenozoic unroofing history of the ladakh batholith western himalaya constrained by thermochronology and numerical modelling abstract the ladakh batholith is part of the transhimalayan plutonic belt which crops out north of the indus suture zone we propose that the exhumation history of the ladakh batholith is linked to the tectonic magmatic and erosion history of the karakoram terrane and sw tibet we present new multiple low temperature thermochronometry data zircon u th he apatite fission track and apatite u th he to gain insight into the cooling history of the ladakh batholith and recognize key periods in the evolution of the region from the indus valley northwards the ages decrease across the batholith for all three thermochronometers applied a model is proposed in which magmatism in the ladakh batholith ceased in the late eocene and initial denudation was driven by topographic uplift caused by collision southward tilting of the batholith occurred in the late palaeogene this tilting resulted in an asymmetric topography with increasing elevation to the north strong erosion occurred in this northern region whereas the southern margin was affected by northwards thrusting of the indus molasse for the first time clear temporal and spatial variations in exhumation rate are identified in this region highlighting why sampling strategy is critical in documenting exhumation changes in active tectonic settings supplementary material sample co ordinates from the ladakh batholith sample preparation and fission track age measurements of apatite grains and grain size dimensions are available at http www geolsoc org uk sup18350

from nappe stacking to out of sequence postcollisional deformations cretaceous to quaternary exhumation history of the se carpathians assessed by low temperature thermochronology 1 apatite fission track aft and u th he ahe thermochronology have been combined to constrain the exhumation history of the se carpathians cooling ages generally decrease from cretaceous for the internal basement nappes aft ages to miocene quaternary aft and ahe respectively for the external sedimentary wedge the aft and ahe data show a paleogene age cluster which confirms a suspected but never demonstrated tectonic event the new data furthermore suggest that the se carpathians have been affected by a middle miocene exhumation phase related to continental collision which occurred at rates of 0 8 mm yr similar to the one previously inferred for the east carpathians the se carpathian tectonic evolution however is overprinted by two younger exhumation events in the pliocene pleistocene the first exhumation phase latest miocene early pliocene occurred at high exhumation rates 1 7 mm yr and is interpreted as a tectonic event and or associated with a sea level drop in the paratethys basins during the messinian low stand the youngest recorded tectonic phase suggests rapid pleistocene exhumation 1 6 mm yr and is interpreted to represent crustal scale shortening different in mechanics from collisional processes the data suggest that the se carpathians did not develop as a typical double vergent orogenic wedge instead exhumation was related to a foreland vergent sequence of nappe stacking during collision and was subsequently followed by a large out of sequence shortening event truncating the already locked collisional boundary

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

a precise 40ar 39ar reference age for the durango apatite u th he and fission track dating standard the distinctive durango apatite is widely distributed as a reference material for mineralogy geochemistry and thermochronology the apatite occurs within the cerro de mercado open pit iron mine located in the northern portion of durango city mexico it is largely confined to vugs and open fractures within the lower portion of the ore deposit apatite and iron ore formed in situ and concurrently along with emplacement of small felsic intrusions along the southern margin of the chupaderos caldera complex this activity occurred between eruptions of two major ignimbrites from the caldera complex four single crystal sanidine anorthoclase 40 ar 39 ar ages from these ignimbrites and from a conformable older unit have been used to compute a reference age of 31 44 0 18 ma 2 for the apatite itself four additional multi crystal measurements are in general agreement with this age also in agreement are a set of 24 u th sm he ages recently determined directly on the apatite which have a mean of 31 02 1 01 ma 1 with a standard error s e of 0 22 ma

post rift reactivation of the onshore margin of southeast brazil evidence from apatite u th he and fission track data abstract on the continental margin of southeast brazil there is good geological evidence for post rift tectonic reactivation in the form of onshore tertiary basins up to 800 m deep and cretaceous to paleocene alkaline intrusive bodies at the surface with the aim of constraining the mesozoic and cenozoic exhumation history of this region we present new apatite u th he ages on basement samples which one of us previously used for apatite fission track aft analysis the new he ages range from 115 5 2 2 ma to 47 0 6 4 ma whereas the aft ages range from 330 3 22 ma to 64 5 3 ma inverse thermal history modelling of all the data provides more detail on the post rift cooling history than do the aft data alone furthermore models incorporating radiation damage effects on he diffusion produce thermal histories that are more consistent with independent geological evidence than models without these effects the results imply that only a few samples record an early cooling phase around the time of opening of the south atlantic ocean the new u th he data also imply a late cretaceous phase of exhumation between 90 and 60 ma subsequently the region underwent slow cooling i e erosion rate two or three samples seem to indicate a period of rapid cooling during the neogene although this is at the limit of resolution of the methods the post rift cooling phases imply exhumation from depths between 2 and 5 km this activity we attribute to compression in the south american plate between the andean subduction zone and the mid atlantic ridge in southeast brazil compression acted on a crust that was thermally or mechanically susceptible to reactivation during the late cretaceous deformation in the study area was of regional extent whereas during the tertiary it concentrated along pre existing shear zones of the precambrian brasiliano orogeny

variable late neogene exhumation of the central european alps low temperature thermochronology from the aar massif switzerland and the lepontine dome italy 1 several recent studies proposed an important increase in exhumation rate in the western european alps since circa 5 4 ma in order to assess potential spatial differences in exhumation histories we present new apatite fission track aft and apatite u th he ahe ages from the central aar massif guttannen area switzerland and the western lepontine dome formazza area italy internal u th zoning in apatites explains alpha ejection corrected ahe ages that are older than the corresponding aft ages in this study a qualitative interpretation of aft and ahe age elevation relationships suggests a two phase 9 7 and 5 3 ma exhumation scenario affecting the central alps with a stronger expression of the pliocene signal in the formazza area however a quantitative evaluation of exhumation scenarios using the 3 d heat equation solver pecube highlights the existence of several other likely scenarios casting doubt on the validity of a qualitative interpretation of the age elevation relationships in formazza scenarios suggested by quantitative modeling include continuous denudation at a rate of 750 m ma and a one step exhumation rate change from 300 to 1000 m ma at 5 ma in guttannen they include continuous denudation at a rate of 400 m ma with valley deepening and two periods of higher exhumation rate increasing from 300 to 700 m ma repeatedly at 9 7 and at 5 3 ma contingent upon further flexural isostatic modeling the magnitude of exhumation recorded in the axial region of the alps since circa 5 ma does not appear sufficient to solely explain the denudation recorded in the north alpine foreland basin

quantitative constraints on mid to shallow crustal processes using the zircon u th he thermochronometer despite the potential of zircon he thermochronometry for constraining rock thermal histories it remains less commonly exploited than the apatite he chronometer in part this is due to the more challenging analytical techniques required to extract he u and th here we present a new method for the routine determination of zircon u th he ages and demonstrate how it can be used to constrain thermal histories and to quantify cooling in different tectonic settings we present zircon u th he ages that place a firm upper limit on the extent of denudation induced cooling c 3 km on the se australian passive margin a region where synrift apatite fission track and apatite u th he ages have previously prevented quantitative constraint we have also used the zircon u th he thermochronometer to quantify the cooling of early tertiary mafic plutons from skye scotland where the rate and timing of cooling cannot be determined using other thermochronometers