co2 depleted fluids from mid ocean ridge flank hydrothermal springs hydrothermal spring fluids were collected from baby bare a basement outcrop on the sediment covered eastern flank of the juan de fuca ridge overlying 3 5 ma old crust these waters are venting at 25 c but have cooled from 64 c within the upper 200 300 m of the upflow zone during their ascent unlike ridge axis hydrothermal vent fluids previously sampled the total co2 content of the endmember spring fluids 0 85 mol kg 1 is depleted with respect to bottom seawater the very low alkalinities 0 43 meq l 1 and high ca2 concentrations 55 mmol kg 1 of endmember spring fluids suggest that the removal of c in the spring fluids is associated with carbonate precipitation in the igneous basement assuming that 8 20 of the total ridge flank heat loss rate of 50 1018 cal yr 1 6 6 tw is removed by porewater advecting from the sediment at 25 c an upper limit dictated by the global input rate of mg 2 to the oceans mottl and wheat 1994 a maximum global carbon sink of 1 0 2 6 1011 mol yr 1 1 2 3 1 mton c yr 1 and a maximum global alkalinity sink of 140 340 109 eq yr 1 are calculated for warm 25 c ridge flank hydrothermal circulation this carbon flux is only 2 5 of current estimates of subaerial and submarine volcanic co2 emissions 50 1011 mol yr 1 indicating that hydrothermal alteration of oceanic crust on young mid ocean ridge flanks at temperatures of a few tens of degrees celsius is only a relatively minor sink for carbon on a global basis it is still possible however that ridge flank alteration at lower temperatures 25 c is an important component of the global carbon budget

carbon dioxide and carbon monoxide emission rates from an alkaline intra plate volcano mt erebus antarctica abstract this is the first report of co and co 2 flux from mt erebus antarctica an alkaline intra plate volcano with a convecting lava lake the co 2 flux from the mt erebus plume was measured by in plume infrared analysis during december 1997 december 1999 and january 2001 the co 2 emission rates were consistently close to the average of 22 3 kg s 1930 mg day for the three measurements conducted over a 4 year period even though the third measurement january 2001 was conducted at a time of elevated activity as co 2 is considered a good indicator of eruptive activity a more frequent type of monitoring system may be necessary to detect changes related to activity at mt erebus increased co 2 emissions lost via strombolian eruptions in the lava lake were not accounted for in our airborne measurements carbon monoxide flux determined by fourier transform infrared spectroscopy in december 1995 yielded a rate of 1 74 kg s 150 mg day and a high co co 2 ratio of 0 12

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

late cretaceous and cenozoic tectonics of the malay peninsula constrained by thermochronology abstract new thermochronological analyses of granites from the malay peninsula record the region s thermal history during the late mesozoic and cenozoic 40 ar 39 ar and u th sm he analyses are combined with existing fission track data to provide a comprehensive set of temperature and time data fully and partially reset k feldspar and biotite mica 40 ar 39 ar analyses indicate a significant period of thermal perturbation between 100 and 90 ma and a second lesser perturbation between 51 and 43 ma zircon u th sm he analyses and existing fission track data indicate exhumation of the malay peninsula in the cretaceous and renewed localised exhumation in the early paleogene apatite u th sm he and fission track data indicate rapid exhumation of the region in the late eocene and oligocene late cretaceous tectonism is linked to the reversal of a regional dynamic topographic low following the cessation of subduction along the sundaland margin in the late cretaceous causing regional uplift and exhumation and the addition of significant heat into the crust via mantle upwelling early paleogene exhumation may reflect the continuation of cretaceous tectonism or a discrete phase of paleocene exhumation linked to localised transpressional tectonics eocene tectonism is coincident with major subsidence offshore of the malay peninsula interpreted to reflect regional block faulting in response to north south compression driven by the resumption of subduction along the southern margin of sundaland in the eocene

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

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

past present and future of thermochronology in one form or another geochronologists have been practicing thermochronology 1 the use of radioisotopic dating to constrain thermal histories of rocks and minerals for over 40 years building from lessons learned over these four decades thermochronology continues to evolve due to technical developments increasingly sophisticated theoretical models and an expanding range of applications in geologic and planetary science most recently interest in earth surface processes and interactions between tectonics erosion and climate has drawn attention to techniques that can address the timing and rates of processes operating at temperatures below about 300 c the purpose of this rimg volume is to assess the current state of thermochronology as of circa 2005 which is coincidentally the 100th anniversary of the first radioisotopic date rutherford 1905 1906 excellent review papers and books on specific topics within this field have been published but no single volume has yet provided a comprehensive review of current practices basic theory and illustrative examples the motivation for this volume stems from these considerations knowing that in a fast developing field a book like this can quickly become dated we tried to include sufficient review of fundamentals and the literature to offer students and new users a useful introduction to thermochronology that may have some staying power in this chapter we first review the salient points of thermochronology s history before assessing our current capabilities and challenges and then taking the risk of suggesting where the field is headed we do not provide a comprehensive history of the method that does full justice to the work of the large and growing cohort of thermochronologists in this short space we instead opted to give our perspectives on where the intellectual and technological roots of the discipline lie which run deeper and go back farther than is sometimes appreciated

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

kimberlite u th he dating links surface erosion with lithospheric heating thinning and metasomatism in the southern african plateau documenting the surface response to processes at depth is a central challenge in continental tectonics kimberlites bear an unusual record of both surface and deep processes through their downrafted crustal clasts pipe erosion levels and mantle xenolith suites here we combine new apatite u th he ahe data from four south africa kimberlites ranging in emplacement age from ca 143 ma to ca 74 ma with a wealth of other geologic information from the pipes to resolve the timing patterns and causes of erosion across 200 km of the southern african plateau comparison of the ahe dates with the kimberlite eruption ages constrains a strong regional unroofing pulse ca 117 90 ma which was most intense from ca 100 to 90 ma this unroofing phase is synchronous with warming thinning and metasomatism of the mantle lithosphere recorded by xenocrysts and peridotite xenoliths within these same kimberlites these thermochemical changes could be related to still deeper dynamic mantle processes our ahe data appear to directly document the erosional response to surface uplift induced by these various events the ahe results also detect as much as 1 5 km of cenozoic unroofing that is spatially centered on a proposed mid tertiary paleotributary to the orange river suggesting drainage patterns as the cause our results not only tightly refine the surface history of the interior of the southern african plateau but show that kimberlite ahe dating can tie cratonic erosion phases with contemporaneous thermochemical changes in the mantle and thereby point to causative links

nonlinear seismo acoustic land mine detection and discrimination a novel technique for detection and discrimination of artificial objects such as land mines pipes containers etc buried in the ground has been developed and tested the developed approach utilizes vibration using seismic or airborne acoustic waves of buried objects remote measurements of soil surface vibration using laser or microwave vibrometers and processing of the measured vibration to extract mine s vibration signatures the technique does not depend upon the material from which the mine is fabricated whether it be metal plastic wood or any other material it depends upon the fact that a mine is a container whose purpose is to contain explosive materials and associated detonation apparatus the mine container is in contact with the soil in which it is buried the container is an acoustically compliant article whose compliance is notably different from the compliance of the surrounding soil dynamic interaction of the compliant container and soil on top of it leads to specific linear and nonlinear effects used for mine detection and discrimination the mass of the soil on top of a compliant container creates a classical mass spring system with a well defined resonance response besides the connection between mass soil and spring mine is not elastic linear but rather nonlinear due to the separation of the soil mine interface in the tensile phase of applied dynamic stress these two effects constituting the mine s vibration signature have been measured in numerous laboratory and field tests which proved that the resonance and nonlinear responses of a mine soil system can be used for detection and discrimination of buried mines thus the fact that the mine is buried is turned into a detection advantage because the seismo acoustic technique intrinsically detects buried containers it can discriminate mines from noncompliant false targets such as rocks tree roots chunks of metal bricks etc this was also confirmed experimentally in laboratory and field tests

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

miocene rise of the shillong plateau and the beginning of the end for the eastern himalaya abstract a common feature of convergent plate boundaries is the self organization of strain exhumation and topography along discrete arcuate boundaries deviations from this geometry can represent first order changes in stress applied at a plate boundary that must affect how strain is partitioned within the interior of an orogen the simplicity of the himalayan fold and thrust belt seen along its central portion breaks down along the eastern extremity of the arc where the 400 km long shillong plateau has developed this change in strain partitioning affects nearly 25 of the arc and has not previously been considered to be important to the orogen s development new low temperature thermochronometry data suggest this structure initiated in mid to late miocene time significantly earlier than was previously estimated from the sedimentary record alone development of the shillong plateau may be linked to a number of kinematic changes within the himalayan and burman collision zones that occur at the same time these events include the onset of e w extension in central tibet eastward expansion of high topography of the tibetan plateau onset of rotation of crustal fragments in southeastern tibet and re establishment of eastward subduction beneath the indo burman ranges we suggest that the coincidence of these tectonic events is related to the dismemberment of the eastern himalayan arc signifying a change in regional stress applied along the india eurasia burma plate boundaries discrepancies between vertical long term faulting rates and geodetically derived far field convergence rates suggest that the collisional boundary in the eastern himalayan system may be poorly coupled due to introduction of oceanic and transitional crust into the eastern plate boundary the introduction of dense material into the plate boundary late in the orogen s history may explain regional changes in the strain field that affect not only the himalaya but also the deformation field more than 1000 km into the tibetan plateau

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

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

rapid pliocene exhumation of the central greater caucasus constrained by low temperature thermochronometry 1 constraining the timing of onset and rates of deformation within the greater caucasus mountains is key to understanding their role in accommodating deformation across the arabia eurasia orogen we present new low temperature thermochronometric constraints on the cenozoic thermal evolution of the central greater caucasus that elucidate a three phase cooling history between 50 and 30 ma cooling within the range was negligible in oligocene time cooling rates throughout the range increased to 4 c myr these rates remained constant until the early pliocene time when they increased again reaching 25 c myr along the axial part of the range rates and timing of oligocene exhumation are consistent with previous results from the western greater caucasus and are proposed to result from onset of subduction of the greater caucasus back arc basin rapid exhumation of the greater caucasus beginning in pliocene time contrasts with previously reported thermal histories for other portions of the range pliocene exhumation of the central greater caucasus appears to be tectonically driven and coincides with widespread evidence for a major reorganization of the arabia eurasia plate boundary we hypothesize that this exhumation and regionally observed plate reorganization results from the collision of the lesser caucasus with eurasia completing the subduction of oceanic lithosphere across this segment of the arabia eurasia plate boundary

cenozoic denudation history of southern hainan island south china sea constraints from low temperature thermochronology abstract as a large block of continental crust hainan island located in the western south china sea forms a rift shoulder to the adjacent offshore yinggehai and qiongdongnan basins and lies in the footwall of their main boundary faults we present 11 apatite fission track aft data and 16 u th sm he ages to elucidate the island s cenozoic morphotectonic evolution our data indicate that much of southern hainan island experienced a well defined cooling episode commencing in late eocene oligocene time during this time most samples cooled from 110 c to 55 15 c at a rate of 4 0 c ma following which the cooling rate decreased to 2 5 c ma assuming a constant paleogeothermal gradient of 23 c km similar to that of the present day since oligocene time when most samples cooled into the base of the aft partial annealing zone the total eroded section is estimated at a minimum of 3 5 km about two thirds of which was removed during the oligocene rapid cooling phase this implies that elevation of southern hainan island has decreased since the oligocene and this is supported by independent paleobotanical evidence although a further cooling episode since 5 ma is also suggested by aft thermal history models cooling occurred from relatively low temperatures 45 50 c where annealing kinetics are not well understood so this cannot be rigorously assessed despite evidence for increased sedimentation in offshore basins at this time our data suggest that the no 1 fault of the adjacent offshore yinggehai basin to the west which is thought to be an offshore extension of the red river fault zone was mainly active from late eocene through much of the oligocene but declined rapidly after 22 ma the marked reduction of potential sediment supply rate from hainan island into neighboring basins after that time suggests that miocene to recent sedimentation in the yinggehai basin was mainly supplied by the red river

oligocene early miocene river incision near the first bend of the yangze river insights from apatite u th sm he thermochronology abstract the southeastern tibetan plateau is deeply incised by three parallel rivers the salween the mekong and the yangtze the river incision and surface uplift histories of this landscape are hotly debated this study presents bedrock apatite u th sm he data from a 1800 m vertical profile located near the first bend of the yangtze river ages range from 20 to 30 ma indicating an oligocene early miocene phase of moderate river incision at a rate of 0 10 0 18 mm yr this is considerably older than elsewhere in the region but consistent with a previously proposed phase of eocene surface uplift inferred from stable isotope geochemistry we consider the implications of the new data under two different tectonic models if the surface uplift and river incision resulted from lower crustal flow the new results require such flow to have commenced at oligocene early miocene time rather than during the previously proposed late miocene alternatively oligocene to early miocene plateau growth might have resulted from transpressional deformation in the southeastern tibetan plateau

thermotectonic history of the maranon fold thrust belt peru insights into mineralisation in an evolving orogen fold thrust belts along convergent margins around the world host major ore deposits the origin of such ore deposits is commonly episodic and so are the temporal and spatial variations in deformation styles in these fold thrust belts here we focus on the maranon fold thrust belt mftb of the peruvian andes and demonstrate a link between the spatio temporal distribution of ore deposits and thick skinned tectonics we present low temperature thermochronology results from the mftb that document the uplift exhumation history and timing of thick skinned tectonics and vergence reversal our results suggest that the thermal history of the mftb involved two discrete intervals of opposed vergence large scale crustal deformation since the late cretaceous an early interval at 80 20 ma was associated with folding and east vergent thin skinned tectonics and was followed by west vergent thick skinned deformation at 20 0 ma furthermore our findings suggest that thick skinned contraction was coincident with increased focusing of mineralising fluids and ore deposition in the mftb during the early miocene and in the mid miocene both mineralisation and deformation were enhanced by subduction of the nazca ridge underneath the south american plate

isobar free neon isotope measurements of flux fused potential reference minerals on a helix mc plus mass spectrometer abstract this work presents new analytical techniques for extraction and analysis of neon from a suite of different mineral phases including quartz pyroxene hematite apatite zircon topaz and fluorite neon was quantitatively extracted at 1100 c from all of these minerals using an in vacuum lithium borate flux fusion technique evolved neon was purified using a cryogenic method capable of separating ne from he present in abundances 8 orders of magnitude higher typical of samples carrying nucleogenic radiogenic noble gases the purified neon was measured on a helix mc plus10k mass spectrometer that permits isobar free measurement of all three neon isotopes when operated at its highest mass resolving power mrp of 10 300 the shoulder representing solely 22ne on the low mass side of the 22ne co2 2 doublet is wide enough to permit measurement of isobar free 22ne operating in this mode comes with the penalty of a 50 reduction in neon sensitivity coupled with a mathematical isobar stripping method this approach excludes 99 5 of the co2 2 while still collecting 99 of the 22ne beam routine edge centering on the dynamic co2 2 peak prior to introduction of a sample permits rapid and robust relocation of the desired measure point in the mass spectrum cosmogenic 21ne and 22ne concentrations obtained using these methods on the cronus a quartz and cronus p pyroxene international reference materials are in excellent agreement with previous work or expectations similarly the concentration of nucleogenic 21ne and 22ne in durango apatite and the cit hematite standard agree well with previous work durango apatite has notable heterogeneity in neon concentrations consistent with previous observations of heterogeneous he u and th concentrations in this apatite nucleogenic neon concentrations are also presented for previously unstudied minerals including a sri lanka zircon slc a topaz from the imperial topaz mine in brazil itp1 and a fluorite w 90 from new hampshire taken together this set of potential reference minerals and the associated dataset provide a starting point for intercalibration among multiple mineral phases carrying 21ne and 22ne of cosmogenic or nucleogenic origin

resonance frequency shift saturation in land mine burial simulation experiments in the field of acoustic land mine detection the mechanical resonant behavior of land mines has proven to be a feature key to this detection method s success land mines are often interred at depths ranging from several millimeters to tens of centimeters thus it is necessary to understand the effect of burial on the land mine s resonances theoretical works on burial s effects on land mine resonance frequency have reported varying results in this work burial simulation experiments in both water and sand using a land mine and a simulant have been performed to study the effect burial has on the resonance frequencies of a land mine saturation of the resonance frequency shift i e the resonance frequency becomes constant after shifting due to added mass is observed in both burial simulations the experimental observations are qualitatively explained by recent theoretical work on the subject

global co2 degassing and the carbon cycle comment on cretaceous ocean crust at dsdp sites 417 and 418 carbon uptake from weathering vs loss by magmatic outgassing

near field response to transpression along the southern san andreas fault based on exhumation of the northern san gabriel mountains southern california 1 near field mountain building is common along transpressive faults but how vertical deformation relates to oblique plate motion versus local structural complexity has not been universally established we have investigated the mechanisms of exhumation along the southern san andreas fault in the northern san gabriel mountains to examine the effects of pure shear dominated transpression obliquity 20 although rugged topography suggests near field uplift low temperature thermochronometry indicates minimal exhumation apatite u th he ages are 10 ma along narrow ridges within the fault zone implying near field rock uplift is not pervasive along this oblique plate boundary ages farther from the fault are younger 5 ma and suggest a deformation event occurred during the transition of activity from the san gabriel fault to the modern san andreas strand these results reveal a heterogeneous crustal response to transpression and imply that secondary structures or geometrical complexities play a primary role in near field bedrock uplift along transpressive faults

eocene arc continent collision and crustal consolidation in kamchatka russian far east the age and origin of high grade metamorphic rocks of the sredinnyi range kamchatka have been the subject of a long and controversial debate based on geochronologic data and its association with a collage of accreted oceanic terranes leading interpretations argue that the sredinnyi range metamorphic rocks represent an accreted precambrian or mesozoic microcontinent in this contribution we present new data that indicate that these metamorphic rocks were formed from the cretaceous paleocene sedimentary margin of northeast russia when it was overridden during eocene obduction of the olyutorsky arc a far travelled oceanic island arc our data include new mapping and structural observations along the northern and eastern flanks of the sredinnyi range and shrimp zircon and monazite u th pb age data from 15 key samples these new isotopic data demonstrate that paragneissic units were formed from sediments with depositional ages locally no older than late cretaceous to paleocene furthermore the statistical similarity of zircon u pb grain ages from the kamchatka schist with very low grade turbidite sandstones of the ukelayat and khozgon groups indicate that metasediments of the sredinnyi range are upgraded stratigraphic equivalents of northeast russian marginal strata shrimp u pb ages of zircon overgrowths and metamorphic monazite extracted from migmatite and gneiss indicate that peak metamorphism occurred at 52 ma which is synchronous with the onset of the olyutorsky arc continent collision heating and cooling occurred rapidly at rates approaching 80 c m y rapid heating is attributed to syn collisional subduction related magmatism thermochronology and structural observations indicate that exhumation was due to a combination of ductile and brittle thinning of the crust we speculate that this thinning was caused by diapiric ascent of a low density low viscosity continental material beneath a dense structural lid of the obducted island arc

evidence for middle eocene and younger land emergence in central panama implications for isthmus closure the rise of the isthmus of panama linked to a number of climatic paleoceanographic and biological events has been studied mostly from indirect often distal geochemical and biotic evidence we have upgraded existing geologic mapping in central panama with more than 2000 field stations over 40 petrographic analyses and more than 30 new geochronological and thermochronological analyses this data set suggests that the isthmus was an uninterrupted chain above sea level from late eocene until at least late miocene times the basement complex of central panama is a folded faulted 3 km thick arc sequence intruded by granitoid bodies and onlapped by mildly deformed upper eocene and oligocene strata six u pb zircon ages in the granitoids along with published geochronological data reveal intense late paleocene to middle eocene magmatism 58 39 ma a temporary cessation of magmatic activity between 38 and 27 ma and renewed magmatism between 25 and 15 ma in a position 75 km south of the former magmatic axis thermochronological analyses in zircon eight u th he ages and in apatite crystals four u th he ages and nine fission track ages obtained from a subset of 58 54 ma granitoid bodies record a concordant lutetian age 47 42 ma cooling from 200 c to 70 c in 5 m y and cooling below 40 c between 12 and 9 ma cooling is linked to exhumation by an angular unconformity that separates the deformed basement complex below from mildly deformed upper eocene to oligocene terrestrial to shallow marine strata above exhumation and erosion of the basement complex are independently confirmed by lower miocene strata that have a detrital zircon signature that closely follows the central panama basement complex age distribution these results greatly restrict the width and depth of the strait separating southern central america from south america and challenge the widely accepted notion that the central american seaway closed in late pliocene time when the ice age began

anomalous cosmogenic 3he production and elevation scaling in the high himalaya the production rate of cosmogenic 3he in apatite zircon kyanite and garnet was obtained by cross calibration against 10 be in co existing quartz in glacial moraine boulders from the nepalese himalaya the boulders have 10 be ages between 6 and 16 kyr and span elevations from 3200 to 4800 m in all of these minerals 3he correlates with 10 be and is dominantly cosmogenic in origin after modest correction for non cosmogenic components 3he 10 be systematics imply apparent sea level high latitude slhl apparent production rates for 3he of 226 atoms g 1 yr 1 in zircon 254 atoms g 1 yr 1 in apatite 177 atoms g 1 yr 1 in kyanite and 153 atoms g 1 yr 1 in gamet these production rates are unexpectedly high compared with rates measured elsewhere in the world and also compared with proposed element specific production rates for apatite and zircon the data are sufficient to conclude that the 3he 10 be ratio increases with elevation if this reflects different altitudinal scaling between production rates for the two isotopes then the slhl production rates estimated by our approach are overestimates we consider several hypotheses to explain these observations including production of 3he via thermal neutron capture on 6li altitudinal variations in the energy spectrum of cosmic ray neutrons and the effects of snow cover because all of these effects are small we conclude that the altitudinal variations in production rates of cosmogenic 3he and 10 be are distinct from each other at least at this location over the last last 10 kyr kyr this conclusion calls into question commonly adopted geographic scaling laws for at least some cosmogenic nuclides if confirmed this distinction may provide a mechanism by which to obtain paleoelevation estimates

is the wasatch fault footwall utah united states segmented over million year time scales the wasatch fault zone utah is a 370 km long segmented normal fault system with topographic salients depths of footwall exposure geomorphic properties and geophysical anomalies that suggest differential long term footwall uplift and exhumation on segments that are partitioned by long lived structural segment boundaries apatite u th he ages from footwall samples along the range front from the five central footwall segments av erage 5 3 6 1 0 ma coupled two dimensional thermokinematic and helium diffusion mod els suggest average long term 5 m y exhumation rates of 0 2 0 4 mm yr for most of the wasatch front the exception is the southern end of the salt lake city segment where exhumation rates are two times as great as elsewhere along the wasatch front the rel atively invariant he ages and exhumation rates imply that most of the wasatch did not behave kinematically as independent footwall segment blocks with differential exhumation amounts over the past 5 m y the structural boundaries such as salients and intrabasin highs that partially delineate segments may have persisted since the pliocene and con trolled the locations of the surface rupture segments

mesozoic and cenozoic tectonic history of the central chinese tian shan reactivated tectonic structures and active deformation 1 the present day topography of the tian shan range is considered to result from crustal shortening related to the ongoing india asia collision that started in the early tertiary in this study we report evidence for several episodes of localized tectonic activity which occurred prior to that major orogenic event apatite fission track analysis and u th he dating on apatite and zircon indicate that inherited paleozoic structures were reactivated in the late paleozoic early mesozoic during a cimmerian orogenic episode and also in the late cretaceous paleogene around 65 60 ma these reactivations could have resulted from the accretion of the kohistan dras arc or lithospheric extension in the siberia mongolia zone activity resumed in the late mesozoic prior to the major tertiary orogenic phase finally the ongoing deformation which again reactivates inherited tectonic structures tends to propagate inside the endoreic basins that were preserved in the range leading to their progressive closure this study demonstrates the importance of inherited structures in localizing the first increments of the deformation before it propagates into yet undeformed areas

apatite fission track and u th he ages from the higher himalayan crystallines kaghan valley pakistan implications for an eocene plateau and oligocene to pliocene exhumation abstract apatite fission track and apatite and zircon u th he ages were obtained from high and ultra high pressure rocks from the kaghan valley pakistan four samples from the high altitude northern parts of the valley yielded apatite fission track ages between 24 5 3 7 and 15 6 2 1 ma and apatite u th he ages between 21 0 0 6 and 5 3 0 2 ma these data record cooling of the formerly deeply subducted high grade metamorphic rocks induced by denudation and exhumation consistent with extension and back sliding along the reactivated normal acting main mantle thrust overlap at around 10 ma between fission track and u th he ages is recognised at one location besal showing that fast cooling occurred due to brittle reactivation of a former thrust fault widespread miocene cooling is also evident in adjacent areas to the west deosai plateau tso morari most likely related to uplift and unroofing linked to continued underplating of the indian lower crust beneath ladakh and kohistan in the late eocene to oligocene in the southernmost part of the study area near naran two significantly younger late miocene to pliocene apatite fission track ages of 7 6 2 1 to 4 0 0 5 ma suggest a spatial and temporal separation of exhumation processes these younger ages are best explained by enhanced late miocene uplift and erosion driven by thrusting along the main boundary thrust

lithium magnesium and uranium isotope behaviour in the estuarine environment of basaltic islands this study presents major and trace elements and uranium u lithium li and magnesium mg isotope data for dissolved and suspended particulate material from estuaries draining dominantly basaltic terrains in iceland borgarfjor ur and sao miguel povoacao in the azores archipelago the concentrations of dissolved sodium na calcium ca potassium k sulphate so4 mg and li and 7li 6li and 26mg 24mg isotope ratios vary directly as a function of the dissolved chloride concentration cl indicating that these species are non reactive in these estuaries however u appears to be affected either by colloid flocculation or the formation of fe oxyhydroxides in borgarfjor ur the major element composition of suspended particulate material in the estuary at borgarfjor ur shows that the detrital silicates delivered to the estuarine mixing zone are relatively unweathered accordingly the 26mg isotope composition of the suspended material is indistinguishable from that of the parent basalts however the 234u 238u activity ratios of the suspended material are significantly different from the parent basalt indicating rapid equilibration of the u isotopes between particles and seawater the li concentration and 7li isotope composition of the suspended load are also observed to increase with increasing cl consistent with ongoing weathering of detrital material and the formation of secondary minerals in seawater depending on the particle residence time in the estuary this process could remove as much as 15 25 of the global riverine input of li to the ocean

u th ne and multidomain u th he systematics of a hydrothermal hematite from eastern grand canyon a hydrothermal hematite from the redwall limestone in eastern grand canyon arizona usa was analyzed for u th he and u th ne systematics the dense polycrystalline aggregate has u and th concentrations of 16 ppm each neon produced by particle capture on 18 o is abundant in the sample it constitutes 90 of total 21 ne and indicates a u th ne age of 217 5 ma this value provides a lower bound for the formation age of the sample but detailed interpretation is not possible given the current absence of neon diffusion data for hematite the 130 2 ma u th he age is much younger than the ne age and therefore must be a cooling age highly reproducible step heating he release experiments reveal the existence of a spectrum of diffusion domain sizes spanning about 3 orders of magnitude in radius corresponding to he closure temperatures ranging from 0 to 150 c these domains may correspond to crystallites in the specimen which are observed to range from smaller than a few nm to a few m 4he 3he age spectra acquired from the same experiments define a distinctive sigmoidal shape with step ages increasing monotonically from 0 to 210 ma this pattern clearly records the presence of the multiple domains as the hematite acquired its radiogenic helium coupling of the 4he 3he spectra and the diffusion data allow modeling of permissible time temperature paths experienced by the hematite these paths can be compared with independent thermal history reconstructions for eastern grand canyon characterized by 170 m yr of sedimentary burial followed by regional unroofing and canyon incision beginning at 80 ma the unroofing portion of the path inferred from the hematite is in good agreement with apatite u th he and fission track data the results permit rapid cooling in late cretaceous early tertiary time suggest a subsequent period of slow cooling through temperatures of 50 70 c with accelerated cooling ensuing after 20 ma in contrast the hematite data demand temperatures in some part s of the mesozoic that are at least 100 c hotter than expected based on burial depth estimates this may indicate that the sample experienced a reheating event associated with the passage of fluids similar to those observed at nearby mineralized breccia pipes overall these data provide motivation for further work to understand he and ne behavior in hematite and their potential use in thermochronometry

constraining the long term evolution of the slip rate for a major extensional fault system in the central aegean greece using thermochronology the brittle ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary in this study we examine the slip history of the large scale naxos paros extensional fault system npefs cyclades greece by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime based on apatite and zircon fission track aft and zft and u th he dating we observe variable slip rates across the brittle ductile transition on naxos zft and aft ages range from 11 8 0 8 to 9 7 0 8 ma and 11 2 1 6 to 8 2 1 2 ma and u th he zircon and apatite ages are between 10 4 0 4 to 9 2 0 3 ma and 10 7 1 0 to 8 9 0 6 ma respectively on paros zft and aft ages range from 13 1 1 4 ma to 11 1 1 0 ma and 12 7 2 8 ma to 10 5 2 0 ma while the u th he zircon ages are slightly younger between 8 3 0 4 ma and 9 8 0 3 ma all ages consistently decrease northwards in the direction of hanging wall transport most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of 6 8 km myr 1 on the npefs across the brittle ductile transition even the intrusion of a large granodiorite body into the narrowing fault zone at 12 ma on naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate the data also show that the npefs accomplished a minimum total offset of 50 km between 16 and 8 ma

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

mass spectrometric 3he measurement in 4he rich phases techniques and limitations for cosmogenic 3he dating of zircon apatite and titanite recent calibration studies have expanded the range of target minerals suitable for cosmogenic 3he dating to include u and th rich phases such as zircon apatite and titanite these minerals often contain large amounts of radiogenic 4he that present several analytical challenges for precise and accurate 3he determinations in this paper we document the abundance sensitivity and changes in the absolute sensitivity and time evolution of the 3he signal over a wide range of 4he pressures in a map 215 50 noble gas mass spectrometer large 50 decreases in sensitivity with 4he amount arising from space charge effects were observed but can be corrected for using an isotope dilution like technique in which 3he spike is added to a sample midway through the mass spectrometric analysis large amounts of 4he also cause the time evolution of the 3he signal to become steeper degrading precision of the initial peak height determination from the intercept taken together we find that these effects preclude reliable analysis of samples with 4he 1 mol and that 3he 4he ratios of greater than 5 10 10 are required to routinely measure 3he to better than 20 precision we present some general considerations by which to assess the probability of success of measuring cosmogenic 3he in these phases as a function of elevation exposure age and helium cooling age

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

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

the first u th he thermochronology of pseudotachylyte from the median tectonic line southwest japan abstract to constrain the thermal and its spatial conditions of pseudotachylyte formation and cooling we dated zircons from a pseudotachylyte in the ryoke belt obtained about 100 m north from the median tectonic line in the taki area southwest japan and its host rock the hatai tonalite by the u th he method the ages obtained are 60 3 2 7 and 55 5 4 5 1se ma respectively which are essentially the same within the error this is the first u th he age directly measured for a pseudotachylyte the coincidence between these ages indicates that the pseudotachylyte formed at ca 60 ma under the ambient temperature of about 180 c the closure temperature of zircon u th he method the fish canyon tuff zircon one of the most well known geological age standards was also dated to confirm the validity of our analyses which yielded the weighted mean age of 29 6 1 5 1se ma consistent with other reported ages the average cooling rates and denudation rates of the host rock were calculated based on these ages reported zircon fission track ages ca 70 ma and apatite fission track ages ca 40 ma as about 12 c myr and about 0 6 mm yr from 70 to 60 ma and about 4 c myr and about 0 2 mm yr from 60 to 40 ma respectively assuming that the closure temperatures of zircon and apatite ft methods are 300 c and 110 c respectively and a geothermal gradient of 20 c km one possible reason of this slow down of denudation rates is the decrease of convergent rate and change in the movement direction of the pacific plate relative to the eurasian plate along the southwest japan in the paleogene

cosmogenic noble gas studies in the oldest landscape on earth surface exposure ages of the dry valleys antarctica extraordinarily high surface exposure ages have been determined for sirius group tillites of mt fleming and mt feather as well as at localities in the inner dry valleys using cosmogenic helium and neon ages of 10 ma at mt fleming 5 3 ma at mt feather and 6 5 ma at insel mountain are among the highest nominal exposure ages published so far these values are minimal ages as they are based on the assumption of zero erosion and uplift the mt feather sample independently confirms the pre pliocene age of the sirius group sediments in the dry valleys as previously determined at mt fleming the insel mountain samples provide evidence for a landscape formation of the inner dry valleys not later than late miocene time assuming conservatively low values of 2 5 cm ma 1 for erosion rate and 50 m ma 1 for uplift rate we infer that the sirius group tillites at mt fleming were deposited earlier than 20 ma ago this indicates that the overriding of the dry valleys block of the transantarctic mountains by the east antarctic ice sheet occurred not later than the early miocene maximum long term erosion rates in the inner dry valleys must be 15 cm ma 1 down to altitudes 1000 m since such low erosion rates require permanently cold and hyperarid conditions the response of antarctica to the pliocene warm climatic episode must have been small cosmogenic nuclide data from both the inner dry valleys and the sirius group sediment localities support the hypothesis of a stable east antarctic ice sheet since at least late miocene time implying that the climate of antarctica was decoupled from that of lower southern latitudes we present also new elemental 21ne production rates of p21 mg 196 atoms g 1 yr 1 and p21 al 55 atoms g 1 yr 1 at sea level and high geomagnetic latitude these figures are consistent with a 3he production rate of p3 110 atoms g 1 yr 1 similar to previously published values this consistency provides evidence that pyroxene is retentive for both helium and neon over at least 10 ma cosmogenic ne in quartz and pyroxene has a 22ne 21ne cos ratio of 1 266 0 040 and 1 159 0 040 respectively

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

u th ne chronometry abstract production of 21ne from the reaction 18o n 21ne in u and th rich minerals such as apatite zircon monazite and titanite can potentially be used for chronometry based on a review of the available cross section data we reevaluated the production of 21ne from this reaction using a thin target approach and compared the results against thick target situations the 21ne 4he production ratio in these minerals is about 4 10 8 but varies with oxygen content and th u ratio 21ne has a stopping range of about 1 m compared to about 20 m for particles thus the 21ne 4he production ratio also depends on crystal size when the crystals are small enough that ejection is important using a monte carlo model we computed the effects of ejection on the 21ne 4he ratio for various geometries and grain sizes we also present measurements of the 21ne 4he ratio on few mg aliquots of well dated volcanic apatites and zircons for which the duration of retention of 21ne and 4he is the same values of 4 4 1 1 10 8 and 3 5 1 2 10 8 for apatite and zircon respectively are in agreement with the theoretical values of 4 16 0 14 10 8 3 54 0 13 10 8 based on our production rate estimates the durango apatite and fish canyon tuff zircon give ne ages of 34 2 8 6 and 28 12 ma respectively which are in agreement with independently known ages our results demonstrate that the 21ne production is well understood and can be used to measure the neon retention time for slowly cooled minerals the 4he and 21ne content of zircons from the deeply exhumed crustal section in gold butte nevada crystallization age of 1 4 ga imply u th ne ages of 963 164 and 777 122 ma far older than their he ages of 16 7 1 3 and 19 1 1 5 ma respectively to explain the age difference a neon closure temperature for zircon between the values given by the thermochronometers u pb on apatite and ar ar on muscovite is derived probably 400 50 c

late palaeozoic and meso cenozoic tectonic evolution of the southern kyrgyz tien shan constraints from multi method thermochronology in the trans alai turkestan alai segment and the southeastern ferghana basin abstract in this paper we present new geochronological and thermochronological data from the turkestan alai segment of the southern kyrgyz tien shan the ferghana basin transition and the trans alai pamir foreland in the southern and central parts of the alai range towards the alai valley mainly post collisional granitoids were targeted for zircon u pb dating by laser ablation inductively coupled plasma mass spectrometry la icp ms apatite fission track aft and apatite u th sm he ahe thermochronology these granitoids and their thermally metamorphosed contact aureole yielded middle permian zircon crystallization ages of 284 4 to 264 5 ma aft ages both using the traditional external detector approach as well as using la icp ms for these samples are constrained to the miocene and range between 22 3 1 1 and 8 4 0 3 ma while the ahe ages are somewhat younger between 12 5 0 8 and 5 0 0 3 ma this low temperature thermochronological data suggests an early miocene onset of denudation in this area in the tien shan orogen continuing through the miocene and pliocene this denudation is interpreted as a response to reactivation of the mountain belt in the framework of india eurasia convergence and specific to this region of the pamir tien shan interaction on the northern slopes of the alai range at the edge of the ferghana basin a late palaeozoic conglomerate yielded a reset early cretaceous aft age of 118 7 ma pointing to an older denudation event with respect to those identified in the southern and central parts of the alai range a mesozoic sediment sample from the same region only contains a late triassic age component of 223 ma mesozoic and cenozoic age components on the other hand are all detected in the cenozoic sediments of the trans alai range at the transition between the southern alai valley and the pamirs revealing several meso cenozoic denudation events in the adjoining basement source rocks the age components in these detrital apatites are 207 ma 75 ma 18 ma and 3 ma

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

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

the effect of inherited paleotopography on exhumation of the central andes of nw argentina differential exhumation in the puna plateau and eastern cordillera of nw argentina is controlled by inherited paleostructures and resulting paleotopography related to the cretaceous salta rift paleomargins the ceno zoic deformation front related to the development of the andean retro arc orogenic system is generally associated with 4 km of exhumation which is recorded by cenozoic apatite fi ssion track aft and u th sm he ages he ages in the eastern cordillera of nw argentina new aft ages from the top of the nevado de cachi document oligocene ca 28 ma cooling which combined with existing data indicates exhumation of this range between ca 28 ma and ca 14 ma however some of the highest ranges in the eastern cordillera preserve cretaceous ages indicative of limited cenozoic exhumation samples collected from an similar to 3 km elevation transect along the northern part of the sierra de quilmes paleorift fl ank laguna brava show aft ages between ca 80 and ca 50 ma and he ages between ca 45 and ca 10 ma another set of samples from an similar to 1 km elevation transect farther to the southwest la quebrada shows cretaceous aft ages between ca 116 ma and ca 76 ma and mainly cretaceous he ages in agreement with aft data analysis of existing aft and he ages from the area once occupied by the salta rift reveals a pattern characterized by cretaceous ages along paleorift highs and cenozoic ages within paleorift hanging wall basins and later foreland basin depocenters this pattern is interrupted by the sierras pampeanas at similar to 28 degrees s which record mid cenozoic ages our data are consistent with a complex inherited pattern of pre andean paleostructures likely associated with paleotopography which was beveled by the cenozoic regional foreland basin and reactivated during the late neogene ca 10 ma strongly controlling the magnitude of cenozoic uplift and exhumation and thus cooling age distribution this combined with variable lithologic erodibility resulted in an irregular distribution of themochronological ages

wideband nonlinear time reversal seismo acoustic method for landmine detection acoustic and seismic waves provide a method to localize compliant mines by vibrating the top plate and a thin soil layer above the mine this vibration is mostly linear but also includes a small nonlinear deviation the main goal of this paper is to introduce a method of processing that uses phase inversion to observe nonlinear effects in a wide frequency band the method extracts a nonlinear part of surface velocity from two similar broadcast signals of opposite sign by summing and canceling the linear components and leaving the nonlinear components this phase inversion method is combined with time reversal focusing to provide increased seismic vibration and enhance the nonlinear effect the experiments used six loudspeakers in a wood box placed over sand in which inert landmines were buried the nonlinear surface velocity of the sand with a mine compared to the sand without a mine was greater as compared to a linear technique

empirical constraints on the titanite u th he partial retention zone from the ktb drill hole we analyzed u th he ages of titanite from both the initial pilot hole 4 km depth and the main drill hole 9 km depth of the german continental deep drilling project ktb to empirically evaluate the titanite u th he partial retention zone heprz and laboratory helium diffusion data laser u th he ages on single titanite fragments from the ktb drill hole uncorrected for emission range from 94 to 2 ma with reproducibility better than 9 nearly invariant titanite u th he ages concordant with reported apatite fission track data suggest that rocks from the upper 3 km of the ktb drill hole rapidly cooled from temperatures 200 to 110 c between 75 and 85 ma followed by protracted cooling below 3 km mean titanite u th he ages decrease systematically with increasing borehole depth and down hole temperature in a pattern similar to the titanite heprz predicted on the basis of laboratory determined he diffusivities our results demonstrate that experimental titanite he diffusion data are applicable in the natural setting and that titanite u th he thermochronometry provides a means to reliably reconstruct and quantify thermal histories between 100 and 180 c bridging the temperature ranges constrained by other techniques such as 40 ar 39 ar k feldspar multi diffusion domain modeling 350 150 c and apatite fission track dating 110 c

neogene rock uplift and erosion in northern borneo evidence from the kinabalu granite mount kinabalu thermochronological data from the kinabalu granite emplaced between c 7 2 and 7 8 ma provide a unique record of northern borneo s exhumation during the neogene biotite 40 ar 39 ar ages c 7 32 7 63 ma record rapid cooling of the granite in the late miocene as it equilibrated with ambient crustal temperatures zircon fission track ages c 6 6 5 8 ma and apatite u th sm he ages central age c 5 5 ma indicate rapid cooling during the late miocene early pliocene this cooling reflects exhumation of the granite uplift and erosion bringing it closer to the earth s surface thermochronological age versus elevation relationships suggest exhumation rates of more than 7 mm a 1 during the latest miocene and early pliocene neither the emplacement of the kinabalu granite nor its exhumation is related to the sabah orogeny which terminated in the early miocene instead granite magmatism was caused by extension related to subduction rollback of the sulu arc and mio pliocene exhumation of the kinabalu granite was driven either by lithospheric delamination or break off of a subducted slab beneath sabah plio pleistocene tectonism offshore and onshore northern borneo reflects continuing large scale gravity driven tectonics in the region supplementary material full 40 ar 39 ar fission track and u th sm he analytical data and 40 ar 39 ar age spectra plots can be found at www geolsoc org uk sup18613

exhumation of the west central alborz mountains iran caspian subsidence and collision related tectonics crystallization and thermal histories of two plutons in the west central alborz also elburz elburs mountains northern iran are combined with crosscutting relations and kinematic data from nearby faults to determine the cenozoic tectonic evolution of this segment of the youthful euro arabian collision zone u pb 40 ar 39 ar and u th he data were obtained from zircon biotite k feldspar and apatite the akapol pluton intruded at 56 2 ma cooled to 150 c by ca 40 ma and stayed near that temperature until at least 25 ma the nearby alam kuh granite intruded at 6 8 0 1 ma and cooled rapidly to 70 c by ca 6 ma these results imply tectonic stability of the west central alborz from late eocene to late miocene time consistent with miocene sedimentation patterns in central iran elevation correlated u th he ages from the akapol suite indicate 0 7 km m y exhumation between 6 and 4 ma and imply 10 km of alborz uplift that was nearly synchronous with rapid south caspian subsidence suggesting a causal relation uplift south caspian subsidence and subsequent folding reversal of alborz strike slip from dextral to sinistral and eastward extrusion of central iran coarse zagros molasse deposition dead sea transform reorganization red sea oceanic spreading and north and east anatolian fault slip all apparently began ca 5 2 ma suggesting a widespread tectonic event that we infer was a response to buoyant arabian lithosphere choking the neo tethyan subduction zone

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

new evidence on the neogene uplift of south tianshan constraints from the u th he and aft ages of borehole samples of the tarim basin and implications for hydrocarbon generation we identified a neogene rapid uplift denudation event of the south tianshan based on apatite u th he and apatite fission track aft ages in tertiary rocks of the tarim basin using borehole samples the u th he thermochronology can be used to reveal the tectono thermal events with lower temperature than that of aft thermochronology and has not been used previously to study the uplift of the tianshan mountain using these data we show the relationship between the uplift of the south tianshan and the subsidence deposition of the northern tarim basin during the neogene the apatite helium ages reveal the migration of uplift erosion and deposition in the northern tarim basin a rapid uplift of the south tianshan during the miocene and a corresponding rapid subsidence in the northern tarim basin occurred however in the pliocene the kuqa depression and south tianshan uplifted and eroded at the same time and in turn provided the detrital source rocks for the northern uplift of the tarim basin in contrast to earlier studies we arrive at the conclusion that the south tianshan experienced rapid uplift in the miocene based on u th he data of apatite obtained from borehole samples collected in the tarim basin itself and not from the bordering mountain chain combined apatite u th he and fission track thermochronometry enables reconstruction of thermal histories of sedimentary rocks between 40 and 120 c and this has implications for the generation of liquid hydrocarbon in the 65 120 c range in the basin thermal and burial histories of typical samples were also modelled to show the rapid uplift in our study our works not only provide a new evidence for the south tianshan uplift but also indicate that there is a coupling between uplift and subsidence in the south tianshan and adjacent northern part of the tarim basin which controlled hydrocarbon accumulation in the kuqa depression and northern uplift of the tarim basin

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

low temperature thermochronology of the southern east greenland continental margin evidence from apatite u th he and fission track analysis and implications for intermethod calibration abstract the southern coast of east greenland is characterized by high topographic relief and deep fjords but the evolution of the landscape and the low temperature thermochronology of the region is not well understood here we present apatite fission track and u th he ages that suggest several important features of the long term geomorphic history of this region but which also illustrate an important discrepancy in the thermal histories derived from each technique apatite from bedrock of the southern coast of east greenland between 62 n and 67 n has fission track ages ranging from 60 to 840 ma and u th he ages ranging from 21 to 250 ma the ages generally increase with elevation and distance from the coast and fission track analyses show significant differences in thermal histories for the different regions in the kangertittivatsiaq area c 66 67 n apatite fission track data and models suggest two separate periods of slow cooling prior to c 200 ma and between c 160 ma and the late cenozoic more recently than c 20 ma each of which was followed by a period of rapid cooling and inferred exhumation apatite he data in the kangertittivatsiaq region including crystal size age correlations in low elevation samples are most simply interpreted as recording an incision event of at least 1 5 km later than 20 ma near the coast this may have been caused by glacial erosion the u th he data also indicate an earlier phase of rapid exhumation at c 250 ma in the skjoldungen kap mosting area c 62 64 n approximately 200 km south of the kangertittivatsiaq apatite fission track data suggest slow exhumation from c 200 ma into the neogene followed by fast exhumation the similarity of fission track ages 200 ma at sea level in the fjords in the skjoldungen area c 62 64 n do not suggest tilting in the hinterland related to the breakup of the east greenland continental margin furthermore the cenozoic fission track ages and modeling fission track data suggest that pre breakup basins may have covered the outer coast despite the broadly similar topographic implications of the fission track and u th he data the thermal histories derived from these systems are inconsistent fission track data require thermal histories that predict he ages younger than observed and he data require thermal histories that predict fission track ages older than observed similar discrepancies have also been observed in other settings characterized by long term low temperature thermal histories and may reflect changes in annealing or diffusion behavior or both that either develop or become more apparent in such cases

thermal history of the unsaturated zone at yucca mountain nevada usa abstract secondary calcite silica and minor amounts of fluorite deposited in fractures and cavities record the chemistry temperatures and timing of past fluid movement in the unsaturated zone at yucca mountain nevada the proposed site of a high level radioactive waste repository the distribution and geochemistry of these deposits are consistent with low temperature precipitation from meteoric waters that infiltrated at the surface and percolated down through the unsaturated zone however the discovery of fluid inclusions in calcite with homogenization temperatures th up to 80 c was construed by some scientists as strong evidence for hydrothermal deposition this paper reports the results of investigations to test the hypothesis of hydrothermal deposition and to determine the temperature and timing of secondary mineral deposition mineral precipitation temperatures in the unsaturated zone are estimated from calcite and fluorite hosted fluid inclusions and calcite 18o values and depositional timing is constrained by the 207pb 235u ages of chalcedony or opal in the deposits fluid inclusion th from 50 samples of calcite and four samples of fluorite range from 35 to 90 c calcite 18o values range from 0 to 22 smow but most fall between 12 and 20 the highest th and the lowest 18o values are found in the older calcite calcite th and 18o values indicate that most calcite precipitated from water with 18o values between 13 and 7 similar to modern meteoric waters twenty two 207pb 235u ages of chalcedony or opal that generally postdate elevated depositional temperatures range from 9 5 to 1 9 ma new and published 207pb 235u and 230th uages coupled with the th values and estimates of temperature from calcite 18o values indicate that maximum unsaturated zone temperatures probably predate 10 ma and that the unsaturated zone had cooled to near present day temperatures 24 26 c at a depth of 250 m by 2 4 ma the evidence of elevated temperatures persisting in ash flow tuffs adjacent to parent calderas for as much as 8 ma is a new finding but consistent with thermal modeling simulations using the heat code demonstrate that prolonged cooling of the unsaturated zone is consistent with magmatic heat inputs and deep seated sub water table hydrothermal activity generated by the large magma body 8 km to the north that produced the 15 11 ma ash flows and ash falls that make up yucca mountain the evidence discussed in this and preceding papers strongly supports unsaturated zone deposition of the secondary minerals from descending meteoric waters although depositional temperatures reflect conductive and possibly vapor phase convective heating of the unsaturated zone related to regional magmatic sources until perhaps 6 ma depositional conditions similar to the present day unsaturated zone have prevailed for at least the past 2 4 ma

twenty million years of continuous deformation along the karakorum fault western tibet a thermochronological analysis the role of the karakorum fault zone kfz is debated south of 33 n ongoing dextral oblique slip along the sw edge of the gar basin exhumes metamorphic and magmatic rocks of the ayilari range minerals have recorded a continuum of deformation from temperatures 600 400 c down to 20 ma of deformation along the fault greenschist facies deformation superimposed upon the medium to high grade deformation marks a kinematic change from pure dextral to dextral normal motion associated with the onset of rapid cooling at the regional scale the coexistence of transtension in the gar basin with transpression documented along the pangong range farther north suggests another example of the zipper tectonics model developed along the red river fault the kinematic shift induced the rise of the ayilari range starting at 16 12 ma and the incision of major river courses the indus river might have become captive of the relief at this time the river s 120 km of apparent offset implies dextral motion at a long term rate of ca 8 5 1 5 mm yr

thermal evolution and maturation of lower paleozoic source rocks in the tarim basin northwest china the tarim basin is one of the richest basins in oil and gas resources in china the cambrian and middle upper ordovician strata are the most important source rocks previous early paleozoic thermal histories have led to varied hypotheses on the evolution of the lower paleozoic source rocks causing a significant impact on petroleum exploration in the basin a new paleozoic thermal history of the tarim basin was reconstructed in this article using the integrated thermal indicators of apatite and zircon uranium thorium helium ages apatite fission tracks and equivalent vitrinite reflectance data the modeled results indicate that different parts of the basin experienced widely differing early paleozoic thermal gradient evolution the eastern and central regions of the basin experienced a decreasing thermal gradient evolution from 37 to 39c km during the cambrian and ordovician to 35 to 36c km in the silurian whereas the northwestern region of the basin had an increasing early paleozoic thermal gradient evolution from 28 to 32c km in the cambrian to 30 to 34c km in the ordovician and silurian the lower cambrian thermal gradient resulted from the higher thermal conductivity of the 800 to 1000 m 2625 to 3280 ft thickness of gypsum and salt in the cambrian strata the basin experienced an intracratonic phase during the late paleozoic and a foreland basin phase during the mesozoic and cenozoic with the thermal gradient decreasing to the present day value of 20 to 25c km the sensitivity of thermal modeling by the best fit method is less than 5 in our study and the differences of the early paleozoic thermal gradient evolution in different regions of the basin may result in differential maturation of lower paleozoic source rocks the maturity histories of the source rocks modeled based on the new thermal histories indicate that the lower paleozoic source rocks in most areas of the basin matured rapidly and reached the late mature to dry gas stage during the paleozoic but experienced slower maturation during the mesozoic and cenozoic these new data on the paleozoic thermal history and lower paleozoic source rock maturity histories of the tarim basin provide new insights to guide oil and gas exploration of the basin

volatiles co2 s f cl br in the dike gabbro transition zone at iodp hole 1256d magmatic imprint versus hydrothermal influence at fast spreading mid ocean ridge abstract the dike gabbro transition zone of mid ocean ridges mors is a critical site for the accretion of oceanic crusts as it is the main zone of interactions between the hydrothermal and magmatic systems in this study volatiles contents of co 2 s f cl and br for a variety of lithologies from the dike gabbro transition zone of an intact oceanic crust were investigated in order to examine the magmatic imprint versus hydrothermal influence the studied samples include plutonic rocks gabbros diorites and tonalites hornfelses i e granoblastic dikes an amphibole rich vein and albitites these rocks were recently sampled by the iodp integrated ocean drilling program at site 1256 representing parts of an oceanic crust that formed at the fast spreading ridge of the east pacific rise the bulk co 2 contents 500 10 000 ppm show no lithological dependence and are similar to those of fresh lavas highly variable bulk s concentrations 3 900 ppm show significant depletions compared to undegassed morb melts which might be caused by exsolution of magmatic fluids during crystallization the plutonic samples have cl concentrations of 500 1000 ppm remarkably higher than the hornfelses 200 600 ppm cl and erupted lavas average 200 ppm cl except for the albitites that contain very low f 20 30 ppm and the hydrothermal amphibole rich vein that contains extremely high f 1000 ppm the other lithologies have similar f concentrations within 100 350 ppm the br concentrations of different lithologies are largely overlapping within 0 5 3 5 ppm petrological and mineralogical evidence indicates that bulk f concentrations are dominated by the presence of amphibole and apatite whereas cl and br are mainly hosted in fluid inclusions rather than in hydrous minerals the variation of f cl and br cl ratios may trace the mixing between morb magmas and seawater derived fluids crystallization of apatite and amphibole and or extraction of magmatic fluids our data support the current s budget of oceanic crust but indicate that the budgets of c and cl may have been underestimated

continental weathering following a cryogenian glaciation evidence from calcium and magnesium isotopes a marked ocean acidification event and elevated atmospheric carbon dioxide concentrations following the extreme environmental conditions of the younger cryogenian glaciation have been inferred from boron isotope measurements calcium and magnesium isotope analyses offer additional insights into the processes occurring during this time data from neoproterozoic sections in namibia indicate that following the end of glaciation the continental weathering flux transitioned from being of mixed carbonate and silicate character to a silicate dominated one combined with the effects of primary dolomite formation in the cap dolostones this caused the ocean to depart from a state of acidification and return to higher ph after climatic amelioration differences in the magnitude of stratigraphic isotopic changes across the continental margin of the southern congo craton shelf point to local influences modifying and amplifying the global signal which need to be considered in order to avoid overestimation of the worldwide chemical weathering flux

structural vibrations of buried land mines buried landmines exhibit complex structural vibrations which are dependent on interaction between soil and mines as well as on their respective properties this paper presents experimental and theoretical studies of multimodal vibrations of buried mines and discusses the effects of burial depth and soil properties on dynamics of the soil mine system the two dimensional model of the soil mine system that accounts for soil coupled mine s multiple vibration modes and spatial distribution of vibrations over the soil surface is introduced the model was tested using experiments with the plastic mine simulant the study reveals that the soil shear stiffness is one of the key governing parameters determining the resonance vibration frequency and the amplitude of the soil mine system burial depth soil moisture and consolidation are among factors leading to the increase of the soil shear stiffness therefore effectively influencing modal vibrations of buried mines

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

u th he dating of phosphates apatite monazite and xenotime the common phosphate minerals apatite ca 5 po 4 3 f oh cl monazite ce la th po 4 and xenotime ypo 4 have found widespread use in geochronology because they incorporate u and th into their structures for example apatite usually has a few tens of ppm of both u and th while monazite and xenotime usually have hundreds of ppm to weight percent levels of these elements as a consequence these phosphates can be dated using several fundamentally different isotopic techniques elsewhere in this volume harrison et al describe phosphate dating using ingrowth of radiogenic pb the final daughter of u and th series decay and gleadow et al describe dating based on damage tracks from the spontaneous fission of 238 u the most recently developed dating technique applied to phosphates described in this chapter uses the accumulation of particles from u and th series decay u th he dating while phosphate u th pb dating is usually used to date high temperature events such as crystallization of igneous rocks and the timing of prograde metamorphism fission track and u th he dating are more commonly used to establish cooling histories through low temperatures for example in the range 110 40 c in the case of apatite dating of minerals using radiogenic he was first explored shortly after the discovery of radioactivity strutt 1908 and was investigated extensively in the 1950s and 1960s mostly on very u and th rich minerals such as zircon and titanite hurley 1952 1954 damon and kulp 1957 damon and green 1963 apatite he dating was first investigated by zeitler et al 1987 who studied the diffusion rate of he from apatite and proposed that apatite he dating might provide a useful thermochronometer recording cooling through about 100 c further studies both in the laboratory lippolt et al 1994 wolf et al 1996b warnock et al 1997 farley 2000 and in the natural setting house et al 1999 stockli et al 2000 have confirmed this idea and the technique has now been applied to a range of tectonic geologic and geomorphologic problems e g house et al 1997 1998 spotila et al 1997 farley et al 2001 stockli et al 2000 monazite and xenotime have only recently come under scrutiny for he geochronology e g pik and marty 1999 and little is yet known of their potential for routine geo or thermochronometry

u th he dating of kimberlites a case study from north eastern kansas abstract dating kimberlite intrusive rocks by radiogenic isotope geochronology often is a difficult task complicated by both the lack of dateable minerals within kimberlite as well as significant sample alteration that can degrade samples and alter parent daughter ratios this study presents a new geochronologic tool for timing the emplacement of kimberlites using the u th he system to date the cooling of common kimberlite phenocrystic and xenocrystic minerals to demonstrate the use of this technique new apatite titanite zircon magnetite and garnet u th he ages constrain the timing of emplacement for the stockdale tuttle baldwin creek bala and leonardville kimberlite pipes located in riley county kansas zircon from the tuttle pipe and titanite from the stockdale pipe yield u th he ages of 108 6 9 6 ma and 106 4 3 1 ma respectively these data are consistent with new tuttle kimberlite rb sr analyses of phlogopite megacrysts that give a five point isochron age of 106 6 1 0 ma similarly an apatite u th he age of 85 3 2 3 ma from the baldwin creek kimberlite is in agreement with a rb sr phlogopite age of 88 4 2 7 ma these dates demonstrate that u th he thermochronometry provides reliable timing constraints on the cooling of common kimberlite xenocrystic phases thereby timing kimberlite emplacement in addition to the use of more commonly used apatite and zircon u th he thermochronometers we produced reliable emplacement ages of 103 0 7 5 ma for the bala kimberlite using u th he dating of phenocrystic magnetite and an age of 98 8 8 9 ma for the tuttle kimberlite using u th he dating of megacrystic garnet in contrast kimberlitic apatite u th he ages from the stockdale bala tuttle and leonardville kimberlites yield ages ranging from 67 3 4 4 ma to 64 3 5 6 ma suggesting a local possibly hydrothermal reheating event resulting in resetting of the apatite u th he clock in latest cretaceous to earliest tertiary time additional u th he analyses of apatite from nearby sandstone and basement rocks suggest regional cooling below 70 c at 165 ma these u th he and rb sr age data imply that the kimberlites were emplaced over a period of time from 85 110 ma with several pipes subjected to local reheating at 65 ma

miocene pliocene exhumation along the west salton detachment fault southern california from u th he thermochronometry of apatite and zircon 1 the salton trough is the northernmost segment of the active gulf of california oblique rift system the main rift related structure in the western salton trough is the low angle west salton detachment fault wsdf footwall and hanging wall apatite and zircon u th he ages record a significant contrast in thermal history across the wsdf confirming pliocene normal slip along the fault apatite u th he ages record rapid exhumational cooling from 5 to 2 ma consistent with the timing of accelerated tectonic subsidence recorded in wsdf hanging wall sedimentary strata and consistent with the initiation age of dextral plate boundary slip on the southern san andreas fault in the salton trough our results indicate that the wsdf caused at least 2 3 4 km of exhumation and 8 10 km of approximately e directed horizontal extension since 5 ma slip rate of the wsdf at yaqui ridge was likely in the range of 2 3 5 km ma from 7 to 2 ma the wsdf may have been active well before 5 ma middle miocene apatite u th he ages from samples at high elevations have steep age elevation gradients and suggest that exhumation may have initiated by 12 ma about when subduction ceased along a large segment of the baja california margin and consistent with the age of onset of extension in northeastern baja california

a simple method for in situ u th he dating this paper presents a significantly simplified method for in situ u th he dating removing the need to know any absolute concentrations this is done by calculating the normalised u th and he concentrations of a conventionally dated calibration standard from its measured th u ratio and known u th he age and scaling these concentrations to the raw u th and he signals of the sample the th u ratio of the standard can be determined from its measured 208pb 206pb ratio removing the need to use nist glass as a reference material we introduce an la icp ms based method to correct for variable ablation depths between the standard and the unknown using the strength of the ablated 29si signal finally we propose a pseudo depth profile method to assess the effects of compositional zoning on the accuracy of in situ u th he data the effectiveness of the proposed method has been demonstrated on three samples of gem quality sri lanka zircon which yield ages that are in agreement with previously published conventional u th he measurements

apatite u th sm he thermochronology of rapidly cooled samples the effect of he implantation apatite u th sm he ahe thermochronology is increasingly used for reconstructing geodynamic processes of the upper crust and the surface results of ahe thermochronology however are often in conflict with apatite fission track aft thermochronology yielding an inverted age relationship with ahe dates older than aft dates of the same samples this effect is mainly explained by radiation damage of apatite either impeding he diffusion or causing non thermal annealing of fission tracks so far systematic age inversions have only been described for old and slowly cooled terranes whereas for young and rapidly cooled samples too old ahe dates are usually explained by the presence of undetected u and or th rich micro inclusions we report apatite u th sm he results for rapidly cooled volcanogenic samples deposited in a deep ocean environment with a relatively simple post depositional thermal history robust age constraints are provided independently through sample biostratigraphy all studied apatites have low u contents 5 ppm on average while aft dates are largely in agreement with deposition ages most ahe dates are too old for leg 43 where deposition age of sampled sediment is 26 5 29 5 ma alpha corrected average ahe dates are up to 45 ma indicating overestimations of ahe dates up to 50 this is explained by he implantation from surrounding host u th rich sedimentary components and it is shown that ahe dates can be corrected by mechanically abrading the outer part of grains we recommend that particularly for low u th apatites the possibility of he implantation should be carefully checked before considering the degree to which the alpha ejection correction should be applied

radiometric dating and temperature history of banded iron formation associated hematite gogebic iron range michigan usa newly developed techniques were used to characterize the age origin and temperature history of coarse hematite contained in high grade iron ore three botryoidal specimens from two different mines in the gogebic iron range near ironwood michigan usa yielded u th 21 ne ages concordant with plateau 4he 3he ages these data reveal that while two of the specimens grew at ca 772 41 ma the third formed 300 m y later 453 14 ma 4he 3he polydomain thermochronometry indicates hematite formation at 80 c for the older specimens and 60 c for the younger fe mobilization and recrystallization in open cavities at 3 5 km subsurface has occurred episodically or possibly continuously over hundreds of millions of years despite a quiescent tectonic setting throughout this interval while the analyzed specimens are distinct from typical fe ore their ages along with structural relationships constrain the onset of iron enrichment to between 1060 and 770 ma cooling of 0 5 c m y ensued between ca 800 and ca 550 ma declining to 0 1 c m y for the last 550 m y these data suggest an erosion rate of 6 m m y and 5 km of total erosion of the superior upland province through the phanerozoic and limit unroofing associated with pleistocene glaciation to 1 km

mass spectrometric identification of cosmic ray produced neon in terrestrial rocks with multiple neon components studies of cosmic ray produced nuclides in terrestrial rocks are expected to provide important geomorphological and glaciological information such as surface exposure ages erosion rates and extent of glacial cover in the case of the stable nuclide21ne the cosmic ray produced component may represent but one of several components and a component resolution based on three isotope correlations is essential we developed analytical techniques which permit accurate corrections for all interfering ions we show for our modified nier source that corrections for doubly charged species based on constant charge state ratios are not satisfactory the improved techniques permit isotopic studies of 106 atoms of21ne the spallation ratio 22ne 21ne c from si was calibrated using a quartz separate from an allan hills sandstone and yields a value of1 243 0 022 this ratio is expected to be essentially constant for terrestrial quartz samples and should be useful in component resolutions the stepwise release of ne at increasing temperatures shows that cosmic ray produced ne is released from quartz at rather low temperatures this permits an estimate of the activation energy for ne diffusion in quartz 90 10 kj mol

refining the footwall cooling history of a rift flank uplift rio grande rift new mexico 1 apatite fission track aft and u th he data from the sandia mountains and hagan embayment provide new insights into the thermal and tectonic evolution of the eastern flank of the rio grande rift in northern new mexico aft and u th he data reveal rapid cooling in the sandia mountains between 22 and 17 ma followed by a decrease in cooling rate at 16 to 14 ma that temporally corresponds to a hiatus in deposition in the albuquerque basin a second increase in cooling rate at approximately 14 ma was followed by continued slow cooling until present cooling ages from jurassic to permian sandstones in the hagan embayment northeast of the sandia mountains are used to constrain the thermal conditions in oligocene time that are necessary to map cooling histories into exhumation histories thereby providing a limit on the amount of section removed during rift flank development thermal modeling geologic constraints and low temperature thermochronology are used to demonstrate that the heat flow in the sandia mountain region was at least 25 mw m2 higher during oligocene time compared to today furthermore at least 3 1 km of material has been exhumed from the sandia mountains and 2 4 km of rock uplift occurred during flexural tilting of the block since middle miocene time

fluid induced nucleation of y ree phosphate minerals within apatite nature and experiment part i chlorapatite this study investigates chlorapatite ideally ca10 po4 6cl2 from two spatially separated locations in the odegardens verk apatite mine bamble sector se norway which was partially metasomatized under amphibolite facies conditions relative to the original chlorapatite metasomatized areas in sample dl136 are enriched in oh and f depleted in na si and y ree and contain numerous inclusions 1 15 m of monazite and xenotime in contrast metasomatized areas in sample tn174 are enriched in f and si depleted in na show y ree abundances similar to the original chlorapatite and host only a few monazite and xenotime grains in order to define the role of fluids in the formation of y ree phosphate minerals associated with apatite a series of experiments covering wide ranges of temperature 900 300 c and pressure 1000 500 mpa for a series of fluid compositions pure h2o a 50 50 molar mix of h2o and caf2 and co2 with 1 2 wt h2o were conducted on unaltered chlorapatite from the odegardens verk in the h2o experiments features due to metasomatic alteration depletion in na si and y ree as well as numerous monazite and xenotime inclusions as observed in the natural sample dl136 were fully reproduced monazite and xenotime grains were also observed growing on the surface of the apatite in dissolution embayments in metasomatized areas in the 50 50 caf2 h2o experiments metasomatized regions are strongly enriched in f and si depleted in na show unchanged y ree abundances and contain only a very few small monazite and xenotime grains similar to what was observed in sample tn174 natural and experimental observation imply the presence of two coupled substitutions na y ree 3 2 ca2 and si4 y ree 3 p5 ca2 in the case of dl136 and h2o fluid experiments na and si4 went into solution whereas the released y ree contributed to the growth of monazite and xenotime within the metasomatized apatite structure for sample tn174 and the 50 50 caf2 h2o fluid experiments na in apatite became depleted but si was enriched thereby stabilizing the y ree in the now recrystallized fluor hydroxylapatite structure which retarded the growth of monazite or xenotime inclusions the basic conclusion of this study is that nucleation of monazite and xenotime in the metasomatized chlorapatite is principally a function of the composition of the infiltrating fluid and to a much lesser extent temperature and pressure

middle late miocene rapid exhumation of the southern qilian shan and implications for propagation of the tibetan plateau abstract the northeastern tibetan plateau is a key place to test several contrasting tectonic models regarding uplift of the plateau however our understanding of the cenozoic deformation history of the northeastern tibetan plateau is incomplete preventing a clear understanding of the uplift and deformation mechanisms of this plateau here we present new apatite u th he ages from the hanging wall of the qaidam shan fault which lies on the southern margin of the qilian shan our results reveal a phase of rapid exhumation during 15 10 ma driven by thrusting accompanied by southward growth of the qilian shan a review of the literature reveals that this phase of tectonic deformation is widespread in the northeastern tibetan plateau and some recent studies suggest 25 20 ma onset of sediment accumulation in the northern qaidam basin bounding the qilian shan these results challenge models arguing for early deformation of northeastern margin of the tibetan plateau