a reporting protocol for thermochronologic modeling illustrated with data from the grand canyon apatite u th he and fission track dates as well as 4he 3he and fission track length data provide rich thermal history information however numerous choices and assumptions are required on the long road from raw data and observations to potentially complex geologic interpretations this paper outlines a conceptual framework for this path with the aim of promoting a broader understanding of how thermochronologic conclusions are derived the tiered structure consists of thermal history model inputs at level 1 thermal history model outputs at level 2 and geologic interpretations at level 3 because inverse thermal history modeling is at the heart of converting thermochronologic data to interpretation for others to evaluate and reproduce conclusions derived from thermochronologic results it is necessary to publish all data required for modeling report all model inputs and clearly and completely depict model outputs here we suggest a generalized template for a model input table with which to arrange report and explain the choice of inputs to thermal history models model inputs include the thermochronologic data additional geologic information and system and model specific parameters as an example we show how the origin of discrepant thermochronologic interpretations in the grand canyon can be better understood by using this disciplined approach

chemical influence on α recoil damage annealing in apatite implications for u th he dating article apatite u th he ahe ages reflect the influence of several parameters such as grain size thermal history and diffusion kinetics previous work has suggested that recoil damage produced by the u th decay chains can have a significant effect on he diffusion kinetics models taking into account damage production and annealing via a parameterization similar to that for apatite fission tracks aft have been proposed comple mentary to these models in this work we demonstrate that grain chemistry influences the annealing rate of diffusivity altering damage in the same manner as for aft and thus is not constant across all apatites the key parameter of the annealing law rmr0 is examined and its theoretical impact on ahe age is tested in cer tain situations the ahe age can be significantly affected by changes in the damage annealing rate for sam ples having undergone a long stay in the ahe partial retention zone 50 80 c ahe ages can diverge by more than 15 over a reasonable range of annealing rates in addition this hypothesis is tested on a geolog ical case well samples of triassic sandstones at 67 5 1 5 c at depth in the paris basin france aft data and ahe ages have been measured on detrital apatite in addition to chemical analysis of the grains dated for aft ages for both thermochronometers present similar histogram distributions with younger ages for ahe aft 14 208 ma n 117 ahe 4 76 ma and one grain at 120 ma n 36 the apatite grains are character ized by dpar values from 1 2 m to 2 9 m and cl content ranging from 0 05 to 0 9 wt using a thermal his tory reconstruction based on aft data and geological evidence it is shown that the non correlation observed between ahe age and eu content can be simply explained by changing the rmr0 value we conclude that to fully access the ahe age meaning in terms of temperature sensitivity the parameters of the annealing law stemming from the grain chemistry need to be considered

upper crustal emplacement and deformation of granitoids inside the uppermost unit of the cretan nappe stack constraints from u pb zircon dating microfabrics and paleostress analyses the present study is dealing with the emplacement and deformation of diorite and quartz diorite exposed along new road cuts between agios nikolaos and sitia uppermost unit eastern crete mingling of both melt types is indicated by enclaves of diorite inside quartz diorite and vice versa the diorite and quartz diorite intruded into coarse grained white marble which is in lateral contact to but also forms the roof of the intrusive body evidence for contact metamorphism is indicated by increasing grain size of calcite in the marble with decreasing distance from the diorite u pb tims dating of zircons separated from quartz diorite yielded a concordant age at 74 0 0 25 ma which is interpreted as emplacement age as this age is close to published k ar cooling ages of hornblende and biotite the melt should have intruded and cooled down rapidly at upper structural levels which is not common for granitoids of the uppermost unit of crete upper crustal melt emplacement is also documented by stoped blocks and by the lack of any ductile viscous deformation the diorite and quartz diorite however are affected by strong post oligocene brittle faulting paleostress analysis based on these faults revealed a change in stress field from n s and nnw sse shortening by thrusting convergence between african and european plates to nne ssw and ne sw shortening accommodated by strike slip sw ward extrusion of the anatolian microplate calcite twin density indicates high differential stress 260 20 mpa related to these phases of crustal shortening

the influence of burial heating on the u th he system in apatite grand canyon case study article history thermochronological data can constrain the cooling paths of rocks exhumed through the uppermost 1 2 km of earth s crust and have thus been pivotal in illuminating topographic development over timescales 0 1 ma however in some cases different methods have led to conflicting conclusions about timing of valley scale exhumation here we investigate the case of western grand canyon usa where different thermochronological datasets have been interpreted to record very different timings of canyon incision 70 ma versus 5 ma we present a method to assess key assumptions in these constraints and demonstrate that burial heating conditions of basement rocks in the mesozoic can result in incomplete annealing of radiation damage in apatite in turn this has a dramatic effect on the temperature sensitivity of the apatite u th he system and its ability to record post burial exhumation the possibility of incomplete annealing resolves the apparent conflict in time temperature paths inferred over the last 70 ma although it requires temperatures during burial that are lower than predicted by apatite fission track data a refinement of parameters that prescribe the kinetics of damage annealing and related control on 4 he diffusivity in apatite would account for this discrepancy specifically if alpha recoil damage anneals at a lower rate than fission tracks at a given temperature these effects will be important for any application of the apatite u th he system in geologic settings that experienced prolonged residence 10 ma between 50 150 c the approaches developed here provide means to assess these effects

6 ma age of carving westernmost grand canyon reconciling geologic data with combined aft u th he and 4he 3he thermochronologic data conflicting hypotheses about the timing of carving of the grand canyon involve either a 70 ma old or 6 ma young grand canyon this paper evaluates the controversial westernmost segment of the grand canyon where the following lines of published evidence firmly favor a young canyon 1 north derived paleocene hindu fanglomerate was deposited across the present track of the westernmost grand canyon which therefore was not present at 55 ma 2 the 19 ma separation point basalt is stranded between high relief side canyons feeding the main stem of the colorado river and was emplaced before these tributaries and the main canyon were incised 3 geomorphic constraints indicate that relief generation in tributaries and on plateaus adjacent to the westernmost grand canyon took place after 17 ma 4 the late miocene pliocene muddy creek formation constraint shows that no river carrying far traveled materials exited at the mouth of the grand canyon until after 6 ma interpretations of previously published low temperature thermochronologic data conflict with these lines of evidence but are reconciled in this paper via the integration of three methods of analyses on the same sample apatite u th he ages ahe 4he 3he thermochronometry 4he 3he and apatite fission track ages and lengths aft hefty software was used to generate time temperature t t paths that predict all new and published 4he 3he ahe and aft data to within assumed uncertainties these t t paths show cooling from 100 c to 40 60 c in the laramide 70 50 ma long term residence at 40 60 c in the mid tertiary 50 10 ma and cooling to near surface temperatures after 10 ma and thus support young incision of the westernmost grand canyon a subset of ahe data when interpreted alone i e without 4he 3he or aft data are better predicted by t t paths that cool to surface temperatures during the laramide consistent with an old grand canyon however the combined aft ahe and 4he 3he analysis of a key sample from separation canyon can only be reconciled by a young canyon additional new aft 5 samples and ahe data 3 samples in several locations along the canyon corridor also support a young canyon this inconsistency which mimics the overall controversy of the age of the grand canyon is reconciled here by optimizing cooling paths so they are most consistent with multiple thermochronometers from the same rocks to do this we adjusted model parameters and uncertainties to account for uncertainty in the rate of radiation damage annealing in these apatites during sedimentary burial and the resulting variations in he retentivity in westernmost grand canyon peak burial conditions temperature and duration during the laramide were likely insufficient to fully anneal radiation damage that accumulated during prolonged near surface residence since the proterozoic we conclude that application of multiple thermochronometers from common rocks reconciles conflicting thermochronologic interpretations and the data presented here are best explained by a young westernmost grand canyon samples spread along the river corridor also suggest the possibility of variable mid tertiary thermal histories beneath north retreating cliffs

apatite u th sm he thermochronology on the wrong side of the tracks abstract despite the increasing application of apatite u th sm he thermochronology in a range of settings the technique suffers from two major unresolved problems which preclude reliable thermal history interpretations on a routine basis one problem is the common but unexplained over dispersion of single grain ages compared to predictions based on accepted models of diffusion systematics including enhanced he retentivity due to the buildup of radiation damage in the apatite crystal lattice a second related problem is that the widely adopted rdaam model does not provide an accurate representation of the degree to which helium retentivity is enhanced as a result of the accumulation of radiation damage until these problems are resolved and eliminated thermal history interpretations derived from this method cannot be regarded as reliable routine application of the technique requires a more rigorous quantitative understanding of these factors further experimental studies are required to identify all significant sources of variation in measured ages and to develop more accurate models of the thermal response of the system combined with rigorous calibration and validation against independent methods in well constrained natural settings only once this is achieved will the technique be capable of producing robust and reliable interpretations

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

4he 3he thermochronometry theory practice and potential complications thermochronometry most often involves the determination of a cooling age from parent and daughter abundances within an entire crystal or population of crystals dodson 1973 complementary information exists in the spatial concentration distribution of the daughter c x y z within a single crystal by combining a bulk cooling age with c x y z on the same sample it is possible to place tight limits on the sample s time temperature t t path techniques for this kind of analysis have been developed for several different parent daughter systems including u th pb and k ar harrison et al 2005 here we describe how this approach is applied to the u th he system the particular attraction of the u th he method is its sensitivity to uniquely low temperatures for example the nominal 4he closure temperatures at 10 c myr for apatite zircon and titanite are 70 c 180 c and 200 c respectively reiners and farley 1999 2001 farley 2000 reiners et al 2002 2004 in the case of apatite we will show that significant diffusive mobility of 4he occurs at temperatures just slightly higher than those of the earth s surface in this chapter we present an overview of the 4 he 3 he thermochronometry technique in which the natural spatial distribution of 4he is constrained by stepwise degassing 4he 3he analysis of a sample containing synthetic proton induced 3he we present the fundamental theory assumptions practical aspects of proton irradiation and stepwise 4he 3he analyses as well as several example applications of 4he 3he thermochronometry in particular we illustrate how the 4he 3he technique can be used to determine the helium diffusion kinetics and constrain the natural 4he distribution within an individual crystal or a small population of crystals and how this information can be

is apatite u th zonation information necessary for accurate interpretation of apatite u th he thermochronometry data abstract new u th and ce concentration maps were acquired by la icpms for 70 apatites from 18 cratonic basement samples from the canadian shield to characterize the nature and variability in apatite u th zonation all apatites are zoned in effective u concentration eu with 80 exhibiting modest zoning that varies from a factor of 1 2 to 2 4 zonation patterns include those with a general eu decrease from core to rim 25 a core to rim eu increase 35 and patchy or irregularly shaped eu distributions 40 most samples consist of individual apatites with markedly different and opposing eu profiles cathodoluminescence cl images were obtained for 258 apatites in 25 samples comparison of eu and cl patterns reveals no consistent relationships suggesting that cl is not a reliable proxy for apatite eu zonation we explore the implications of eu zonation for the interpretation of apatite u th he ahe data by comparing the age predictions for representative and endmember apatite eu profiles with those for unzoned apatites we focus on thermal histories that should magnify eu zonation effects including slow monotonic cooling extended he partial retention zone heprz residence and protracted reheating and cooling application of incorrect ejection correction f t factors different he concentration gradients and variable intracrystalline retentivity due to heterogeneous radiation damage may cause the ahe dates for zoned and unzoned apatites to differ in our dataset the magnitude of the f t effect is by simulating zoned apatite suites from representative and endmember samples we find that eu zoning adds modest age dispersion to most samples the commonly opposing eu profiles for individual apatites in most samples have different effects on the predicted age and partially cancel each other out to reduce the predicted age difference at the sample level higher predicted age differences between zoned and unzoned samples generally correlate with greater sample scatter the age deviations generally fall within the 15 uncertainty range that we commonly apply for sample ahe dates except in unusual circumstances it appears unlikely that the unzoned apatite assumption will lead to misinterpretation of ahe datasets thus precluding the need to routinely acquire apatite eu zonation information as part of ahe dating studies

unroofing incision and uplift history of the southwestern colorado plateau from apatite u th he thermochronometry the source of buoyancy for the uplift of cratonic plateaus is a fundamental question in continental dynamics the 1 9 km uplift of the colorado plateau since the late cretaceous is a prime example of this problem we used apatite u th he thermochronometry 230 analyses 36 samples to provide the fi rst single system regional scale proxy for the unroofi ng history of the southwestern quadrant of the plateau the results confi rm overall southwest to northeast unroofi ng from plateau margin to plateau interior a single phase of unroofi ng along the plateau margin in late cretaceous to early tertiary sevierlaramide time contrasts with multiphase unroofi ng of the southwestern plateau interior in early and mid to late tertiary time the early cretaceous was characterized by northeastward tilting and regional erosion followed by aggradation of 1500 m of upper cretaceous sediments along the eroded plateau margin sevier laramide denudation affected the entire southwestern plateau was concentrated along the plateau margin and migrated from northwest to southeast following a period of relative stability of the landscape from ca 50 30 ma signifi cant unroofi ng of the southwestern plateau interior occurred between ca 28 and 16 ma additional denudation north of the grand canyon took place in latest tertiary time mid tertiary dates from the grand canyon basement at the bottom of the upper granite gorge limit signifi cant incision of the modern grand canyon below the kaibab surface to 1500 m difference in vertical structural position if these models are correct they indicate that a proto grand canyon of kilometer scale depth had incised post paleozoic strata by the early eocene evidence for kilometerscale mid tertiary relief in northeast fl owing drainages along the plateau margin as well as the mid tertiary episode of plateau interior unroofi ng imply that the southwestern plateau interior had attained substantial elevation by at least 25 20 ma if not much earlier these observations are inconsistent with any model calling for exclusively late tertiary uplift of the southwestern plateau sevier laramide plateau surface uplift and incision thus result from one or more processes that enhanced the buoyancy of the plateau lithosphere expanding the cordillera s orogenic highlands into its lowstanding cratonic foreland the onset of the laramide slab s demise at ca 40 ma and the major pulse of extension in the basin and range from ca 16 10 ma appear to have had little infl uence on the denudation history of the southwestern plateau in contrast the post laramide unroofi ng episodes may be explained by drainage adjustments induced by rift related lowering of regions adjacent to the plateau without the need to otherwise modify the plateau lithosphere our data do not preclude a large component of post early eocene elevation gain or the geodynamic mechanisms it may imply but they do point toward laramide age buoyancy sources as the initial cause of signifi cant surface uplift ending more than 500 m y of residence near sea level

chronology of miocene pliocene deposits at split mountain gorge southern california a record of regional tectonics and colorado river evolution late miocene to early pliocene deposits at split mountain gorge california preserve a record of basinal response to changes in regional tectonics paleogeography and evolution of the colorado river the base of the elephant trees formation magnetostratigraphically dated as 8 1 0 4 ma provides the earliest well dated record of extension in the southwestern salton trough the oldest marine sediments are ca 6 3 ma the nearly synchronous timing of marine incursion in the salton trough and northern gulf of california region supports a model for localization of pacifi c north america plate motion in the gulf ca 6 ma the fi rst appearance of colorado river sand at the miocene pliocene boundary 5 33 ma suggests rapid propagation of the river to the salton trough and supports a lake spillover hypothesis for initiation of the lower colorado river

westernmost grand canyon incision testing thermochronometric resolution the timing of carving of grand canyon has been debated for over 100 years with competing endmember hypotheses advocating for either a 70 ma old or 6 ma young grand canyon several geological constraints appear to support a young canyon model but thermochronometric measures of cooling history and corresponding estimates of landscape evolution have been in debate in particular 4he 3he thermochronometric data record the distribution of radiogenic 4he from the 238u 235u and 232th decay series within an individual apatite crystal and thus are highly sensitive to the thermal history corresponding to landscape evolution however there are several complicating factors that make interpreting such data challenging in geologic scenarios involving reheating here we analyze new data that provide measures of the cooling of basement rocks at the base of westernmost grand canyon and use these data as a testbed for exploring the resolving power and limitations of 4he 3he data in general we explore a range of thermal histories and find that these data are most consistent with a young grand canyon a problem with the recovered thermal history however is that burial temperatures are under predicted based on sedimentological evidence a solution to this problem is to increase the resistance of alpha recoil damage to annealing thus modifying he diffusion kinetics allowing for higher temperatures throughout the thermal history this limitation in quantifying radiation damage and hence crystal retentivity introduces non uniqueness to interpreting time temperature paths in rocks that resided in the apatite helium partial retention zone for long durations another source of non uniqueness is due to unknown u and th distributions within crystals we show that for highly zoned with a decrease in effective u of 20 ppm over the outer 80 of the radius of the crystal the 4he 3he data could be consistent with an old canyon model to reduce this non uniqueness we obtain u and th zonation information for separate crystals from the same rock sample through la icp ms analysis the observed u and th distributions are relatively uniform and not strongly zoned thus supporting a young canyon model interpretation of the 4he 3he data furthermore we show that for the mapped zonation the difference between predicted 4he 3he data for a uniform crystal and a 3d model of the crystal are minimal highlighting that zonation is unlikely to lead us to falsely infer an old grand canyon

continental scale landscape evolution a history of north american topography the generation and evolution of continental topography are fundamental geologic and geomorphic concerns in particular the history of landscape development might contain useful information about the spatiotemporal evolution of deep earth processes such as mantle convection a significant challenge is to generate observations and theoretical predictions of sufficient fidelity to enable landscape evolution to be constrained at scales of interest here we combine substantial inventories of stratigraphic and geomorphic observations with inverse and forward modeling approaches to determine how the north american landscape evolved first stratigraphic markers are used to estimate postdepositional regional uplift present day elevations of these deposits demonstrate that 2 km of long wavelength surface uplift centered on the colorado rocky mountain plateaus occurred in cenozoic times second to bridge the gaps between these measurements an inverse modeling scheme is used to calculate the smoothest spatiotemporal pattern of rock uplift rate that yields the smallest misfit between 4 161 observed and calculated longitudinal river profiles our results suggest that cenozoic regional uplift occurred in a series of stages in agreement with independent stratigraphic observations finally a landscape evolution model driven by this calculated rock uplift history is used to determine drainage patterns denudation and sedimentary flux from late cretaceous times until the present day these patterns are broadly consistent with stratigraphic and thermochronologic observations we conclude that a calibrated inverse modeling strategy can be used to reliably extract the temporal and spatial evolution of the north american landscape at geodynamically useful scales

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

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

badly behaved detrital u th he ages problems with he diffusion models or geological models dispersion in apatite u th he ages makes extracting thermochronological information challenging this is particularly problematic for constraining the thermal history of sedimentary basins as the total amount of heating during burial can be small and at the limits of the sensitivity of the apatite u th he system in apatite but undetectable with other thermochronometric systems here we explore the importance of the differences in predepositional thermal histories for individual crystals and the effect of radiation damage related diffusion during both the predepositional and postdepositional thermal history on the dispersion of apatite u th he ages different predepositional thermal histories can lead to a large spread of detrital ages due to radiation damage and its effect on he diffusivity the resulting ages may appear scattered and relationships between age and eu a conventional proxy for accumulated radiation damage may be nonexistent or nonsensical furthermore other variables that are expected to control he diffusivity could vary as a function of source region resulting in false conclusions about controls on he diffusivity and the applicability of the apatite u th he system in general we suggest that in some situations in which detrital apatite u th he age does not correlate with eu it is not because of problems with the thermochronometric system but problems with the assumed geological model

eruptive history and petrologic evolution of the albano multiple maar alban hills central italy a comprehensive volcanological study of the albano multiple maar alban hills italy using i 40ar 39ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and ii petrographic observations phase analyses of major and trace elements and sr and o isotopic analyses of the pyroclastic deposits shows that volcanic activity at albano was strongly discontinuous with a first eruptive cycle at 69 1 ka producing at least two eruptions and a second cycle with two peaks at 39 1 and 36 1 ka producing at least four eruptions contrary to previous studies we did not find evidence of magmatic or hydromagmatic eruptions younger than 36 1 ka the activity of albano was fed by a new batch of primary magma compositionally different from that of the older activity of the alban hills moreover the ree and 87sr 86sr data indicate that the albano magma originated from an enriched metasomatized mantle according to the modeled liquid line of descent this magma differentiated under the influence of magma limestone wall rock interaction our detailed eruptive and petrologic reconstruction of the albano maar evolution substantiates the dormant state of the alban hills volcanic district

cretaceous eocene laramide landscape development and oligocene pliocene drainage reorganization of transition zone and colorado plateau arizona landscape development of central and northern arizona can no longer be ascribed mainly to events of miocene and pliocene age new information on the age and distribution of older cenozoic deposits has led to the recognition of a regional cretaceous paleocene surface of erosion that conforms to major elements of the present topography and to the recognition that a formerly thick deposit of gravel accumulated on this regional surface of erosion these relations cast new light on the history of evolution of the landscape and indicate a much greater age for the main landscape elements and a more complicated and prolonged history of erosion and deposition than has been previously supposed the timing of events postulated for development of drainage on the colorado plateau can now be compared and partly reconciled with events recognized in the adjacent closely related mountain region transition zone of central arizona as a consequence of late cretaceous paleocene laramide compression central and northern arizona underwent at least 1200 m of uplift documented by paleochannels cut into erosionally truncated paleozoic strata on the hualapai plateau of the southwestern colorado plateau during this time a highly irregular erosion surface was developed on proterozoic rocks across the transition zone south of the mogollon rim the scarp of the mogollon rim was eroded to its present height 600 900 m and an extensive stripped surface was developed on resistant upper paleozoic strata north of the rim deposition of several hundred meters of paleocene eocene rim gravels derived from highlands south and west of the region followed covering much of the cretaceous paleocene erosion surface nearly complete burial of the rim is suggested by the distribution of remnants of the rim gravels across the erosional scarps and on high plateau areas north of the rim a second increment of uplift apparently occurring in late eocene time and apparently recorded by a series of fission track cooling ages from the marble and grand canyons is inferred to have been responsible for ending deposition of the rim gravels for initiating differential uplift of contemporaneous deposits canaan peak and claron formations to their positions in the high plateaus of central utah and for causing the drainage reorganization required to explain the extensive removal of rim gravels from much of the region a southerly flowing ancestral verde river related to the drainage reorganization removed much of the older gravel cover from the transition zone of central arizona resulting in a younger regional erosion surface having 600 900 m of relief a surface closely approximating the cretaceous paleocene erosion surface late oligocene and early miocene rocks locally rest unconformably on remnants of rim gravels in the transition zone indicating that the second episode of regional erosion had been completed by late oligocene time north of the mogollon rim a west flowing ancestral colorado river is inferred to have become established on the rim gravels draining the interior parts of the colorado plateau and transporting detritus off the plateau exhumation of the mogollon rim and development of 600 900 m of topographic relief in the transition zone by an ancestral verde river system suggests the potential for a comparable coeval entrenchment of an ancestral colorado river in paleozoic strata north of the mogollon rim regional extension and volcanic activity ensued in late oligocene to pliocene time the oligocene erosion surface in the extensional basins of central arizona became largely concealed by miocene and pliocene deposits as the neogene climate became drier in late miocene and pliocene time perennial streams appear to have been lacking transport of detritus appears to have been principally by flash flooding little or no detritus appears to have been removed from the region and much of the precipitation presumably moved by groundwater flow through the deposits of aggradation a coeval episode of aggradation in the grand canyon is suggested by deposits that appear to have once choked much of the canyon if this event parallels the episode of late miocene and pliocene aggradation recorded east south and west of the grand canyon the colorado river could have been incised to its present level by late miocene time a return to wetter conditions in late pliocene time presumably was responsible for renewed erosion and reexcavation of older drainages and basins an understanding of this tertiary structural erosional and depositional history can be important for the geological analysis of geophysical transects across the region

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

the influence of natural radiation damage on helium diffusion kinetics in apatite abstract stepwise degassing diffusion experiments on 39 different apatite samples using radiogenic 4he and proton induced 3he reveal a range in closure temperature tc from 50 to 115 c for a cooling rate of 10 c myr there is no correlation between helium diffusion and apatite chemistry including f cl ratio but the closure temperature is positively correlated with the radiogenic 4he concentration 4he in each sample we argue that 4he is a proxy for a sample s natural exposure to actinide radioactivity below the closure temperature and that helium diffusion in apatite is impeded by radiation induced damage to the apatite structure the kinetics must therefore be an evolving function of time measured diffusivities thus reflect a snapshot in time and cannot alone be applied to the thermochronometric interpretation of a given sample the effect of radiation damage on helium diffusion appears to far exceed other known controls on helium diffusivity including grain size our diffusion data are well described by a previously proposed quantitative model that consists of two arrhenius relations one for volume diffusion through undamaged mineral structure and one for release of helium from radiation damage traps the unknown parameters in this trapping model were determined from the diffusion experiments and allow us to develop a tentative mathematical function that relates diffusivity to temperature and 4he by inserting this function into a 4he production diffusion model we have explored how these results affect the interpretation of apatite u th he thermochronometry the model predicts that the effective 4he closure temperature of apatite will vary with cooling rate and effective u concentration eu and may differ from the commonly assumed tc of 70 c by up to 15 c the 4he partial retention zone will look similar to previous expectations but its depth will depend on accumulation time and on eu most notably samples subjected to reheating after accumulation of substantial radiation damage will be more retentive than previously expected these predictions are consistent with recent observations of unexpected apatite u th he ages in some settings

apatite 4he 3he and u th he evidence for an ancient grand canyon the grand canyon is one of the most dramatic features on earth yet when and why it was carved have been controversial topics for more than 150 years here we present apatite 4he 3he thermochronometry data from the grand canyon basement that tightly constrain the near surface cooling history associated with canyon incision 4he 3he spectra for eastern grand canyon apatites of differing he date radiation damage and u th zonation yield a self consistent cooling history that substantially validates the he diffusion kinetic model applied here similar data for the western grand canyon provide evidence that it was excavated to within a few hundred meters of modern depths by 70 million years ago ma in contrast to the conventional model in which the entire canyon was carved since 5 to 6 ma

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

response to comments on apatite 4he 3he and u th he evidence for an ancient grand canyon we reiterate that geological observations do not require grand canyon carving coeval with colorado river integration u th he data from the western canyon totaling 29 reproducible analyses from six samples and two labs compellingly support an ancient canyon three dispersed analyses from one anomalous sample do not refute this conclusion nor do the claimed shortcomings of our modeling have validity