apatite feldspar u pb thermochronometer a reliable mid range 450 c diffusion controlled system the u pb systematics of apatite are commonly dominated by simple volume diffusion without secondary growth and recrystallization that can affect u pb systematics of sphene monazite and zircon although apatite is a relatively low u mineral both u and pb are lattice bound and thus the u pb systematics are not controlled by micro inclusions as appears to be the case for other low u minerals such as garnet and staurolite closure temperature estimates from both experimental and empirical studies range from 425 c to as high as 500 c for typical diffusion radii 25 m and cooling rates 2 100 c ma respectively this range can be exploited to constrain cooling and exhumation histories of both igneous and metamorphic rocks in addition the closure temperature for pb diffusion in apatite fills a gap between that for pb diffusion in sphene 650 c and diffusion of ar in hornblende 500 c muscovite 350 c and biotite 300 325 c apatite is a common accessory phase in many rock types and u pb apatite dating can be a reliable and powerful thermochronometer as it combines mid range cooling ages with the strength of the u pb system in testing for isotopic closure precisions of u pb apatite dates can range from 1 2 to as low as 0 3 for proterozoic or archean dates the main limitation to accuracy of u pb apatite dates is a moderate to low ratio of u to pb and corresponding dependence of concordia coordinates on the choice of initial pb isotopic composition for proterozoic aged samples with measured 206pb 204pb of 100 the range of geologically reasonable initial pb isotopic compositions can shift the calculated u pb age by 60 ma fortunately even though the diffusion rate of pb in alkali feldspar is less than in apatite it appears that the isotopic composition of pb in coexisting feldspar is a good approximation of the initial isotopic composition in apatite for many geologic settings examples are given from an archean terrane in se wyoming that was unroofed and cooled during proterozoic uplift and from proterozoic terranes in sw us that have contrasting thermal histories

improving volcanic sulfur dioxide cloud dispersal forecasts by progressive assimilation of satellite observations forecasting the dispersal of volcanic clouds during an eruption is of primary importance especially for ensuring aviation safety as volcanic emissions are characterized by rapid variations of emission rate and height the generally high level of uncertainty in the emission parameters represents a critical issue that limits the robustness of volcanic cloud dispersal forecasts an inverse modeling scheme combining satellite observations of the volcanic cloud with a regional chemistry transport model allows reconstructing this source term at high temporal resolution we demonstrate here how a progressive assimilation of freshly acquired satellite observations via such an inverse modeling procedure allows for delivering robust sulfur dioxide so2 cloud dispersal forecasts during the eruption this approach provides a computationally cheap estimate of the expected location and mass loading of volcanic clouds including the identification of so2 rich parts

seismic images of the transition fault and the unstable yakutat pacific north american triple junction in southern alaska the pacific plate and yakutat terrane subduct beneath the north american plate along the aleutian trench and pamplona zone respectively and are sliding past each other at minimal rates along the transition fault as the deformation front of the pamplona zone stepped eastward during the pliocene pleistocene the pacific north american yakutat triple junction became unstable four recent seismic images reveal that the transition fault changes from a single strike slip boundary east of the deformation front to three strands that step increasingly seaward between the deformation front and the aleutian trench the southern two strands deform the pacific crust and the outermost of these became increasingly convergent sometime since 1 ma as demonstrated by young growth strata we propose that this internal deformation of the pacific plate is an attempt to re attain stability which can only be reached by creating a tectonic boundary collinear with the pamplona zone the plate reorganization will result in initiation of subduction such that a portion of former pacific crust will become accreted to the north american plate such accretion events caused by triple junction instability may be an important mechanism for transferring oceanic crust to continental margins

an evaluation of volcanic cloud detection techniques during recent significant eruptions in the western ring of fire we examined recent volcanic cloud events in the western pacific and indonesian area to validate the performance of remote sensing techniques used to support the international airways volcano watch iavw five events were considered during which eruptions from eight volcanoes injected ash into the upper troposphere or lower stratosphere for one of the eruptions at miyakejima japan at least five aircraft encountered volcanic ash clouds and the cost to three operators alone exceeded us 12 000 000 in aircraft repairs diversions and lost operating time we performed reverse absorption and pattern analysis using gms 5 vissr modis and avhrr data and we examined toms so2 and aerosol index data surface based observations pilot reports and dispersion model output our results verify that the introduction of reverse absorption using the geostationary gms 5 platform significantly enhanced our capacity to monitor volcanic ash clouds in the region in one case we tracked an eruption cloud for approximately 80 h the primary impediment to remote monitoring is the presence of overlying cloud or substantial amounts of ice within the volcanic clouds toms data showed success in identifying volcanic clouds during these conditions but was limited by the infrequency of observations more effective future operation of the iavw relies on developing complementary methods of volcanic cloud remote sensing and greatly increasing the amount and quality of available surface and air observations including observations of precursor activity an understanding of the likely future limitations of remote sensing techniques will aid in the refining of iavw procedures

relative sea level change in northeastern florida usa during the last 8 0 ka abstract an existing database of relative sea level rsl reconstructions from the u s atlantic coast lacked valid sea level index points from georgia and florida this region lies on the edge of the collapsing forebulge of the former laurentide ice sheet making it an important location for understanding glacio isostatic adjustment and the history of ice sheet melt to address the paucity of data we reconstruct rsl in northeastern florida st marys over the last 8 0 ka from samples of basal salt marsh sediment that minimize the influence of compaction the analogy between modern salt marsh foraminifera and their fossil counterparts preserved in the sedimentary record was used to estimate paleomarsh surface elevation sample ages were determined by radiocarbon dating of identifiable and in situ plant macrofossils this approach yielded 25 new sea level index points that constrain a 5 7 m rise in rsl during the last 8 0 ka the record shows that no highstand in sea level occurred in this region over the period of the reconstruction we compared the new reconstruction to earth ice models ice 6g c vm5a and ice 6g c vm6 there is good fit in the later part of the holocene with vm5a and for a brief time in the earlier holocene with vm6 however there are discrepancies in model reconstruction fit in the early to mid holocene in northeastern florida and elsewhere along the atlantic coast at locations with early holocene rsl reconstructions the most pronounced feature of the new reconstruction is a slow down in the rate of rsl rise from approximately 5 0 to 3 0 ka this trend may reflect a significant contribution from local scale processes such as tidal range change and or change in base flow of the st marys river in response to paleoclimate changes however the spatial expression local vs regional of this slow down is undetermined and corroborative records are needed to establish its geographical extent

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

pedogenic carbonate carbon isotopic constraints on paleoprecipitation evolution of desert in the pacific northwest usa in response to topographic development of the cascade range abstract the cascade range in the northwestern u s acts as an orographic barrier to the easterly movement of humid air masses from the pacific ocean producing a massive rain shadow with arid to semi arid climate conditions on the leeward side of the range pedogenic carbonates formed in the c3 dominated landscapes east of the range have 13ccarbonate that is enriched by approximately 4 relative to carbonates formed in sub tropical c3 dominated ecosystems we measured stable isotopic compositions of pedogenic carbonates preserved in the quaternary and neogene sedimentary rock units in the inland pacific northwest and examined the impact of long term aridification and paleohydrology on their isotopic compositions the determined 13ccarbonate record shows a gradual increase of 5 from approximately 10 in older pedogenic carbonates to 5 in younger ones whereas 18ocarbonate record indicates a decrease of approximately 4 in the late neogene in addition the quaternary 13ccarbonate and 18ocarbonate records indicate the highest 13c and 18o among the samples during the pleistocene and significant fluctuation over the time period the gradual increase in the 13ccarbonate and the decrease in the 18ocarbonate in the late neogene are interpreted by the development of the rain shadow as a result of topographic development of the cascade range changes in the quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation resulting from changes in large scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet the isotope record from pedogenic carbonates provides a direct record of climatic change suggesting that long term carbon isotope data can provide useful constraints on timing and intensity of regional desertification and its associated climate and topographic interaction

sea level records at 80 ka from tectonically stable platforms florida and bermuda studies from tectonically active coasts on new guinea and barbados have suggested that sea level at 80 ka was significantly lower than present whereas data from the atlantic and pacific coasts of north america indicate an 80 ka sea level close to that of the present we determined ages of corals from a shallow submerged reef off the florida keys and an emergent marine deposit on bermuda both localities are on tectonically stable platforms distant from plate boundaries uranium series ages show that corals at both localities grew during the 80 ka sea level highstand and geologic data show that sea level at that time was no lower than 7 9 m below present florida and may have been 1 2 m above present bermuda the ice volume discrepancy of the 80 ka sea level estimates is greater than the volume of the greenland or west antarctic ice sheets comparison of our ages with high latitude insolation values indicates that the sea level stand near the present at 80 ka could have been orbitally forced

separation of ash and sulfur dioxide during the 2011 grimsvotn eruption modeling the transport of volcanic ash and gases released during volcanic eruptions is crucially dependent on knowledge of the source term of the eruption that is the source strength as a function of altitude and time for the first time an inversion method is used to estimate the source terms of both volcanic sulfur dioxide so2 and ash it was applied to the explosive volcanic eruption of grimsvotn iceland in may 2011 the method uses input from the particle dispersion model flexpart flexible particle dispersion model a priori source estimates and satellite observations of so2 or ash total columns from infrared atmospheric sounding interferometer to separately obtain the source terms for volcanic so2 and fine ash the estimated source terms show that so2 was emitted mostly to high altitudes 5 to 13 km during about 18 h 22 may 00 18 utc while fine ash was emitted mostly to low altitudes below 4 km during roughly 24 h 22 may 06 utc to 23 may 06 utc flexpart simulations using the estimated source terms show a clear separation of so2 transported mostly northwestward and the fine ash transported mostly southeastward this corresponds well with independent satellite observations and measured aerosol mass concentrations and lidar measurements at surface stations in scandinavia aircraft measurements above iceland and germany confirmed that the ash was located in the lower atmosphere this demonstrates that the inversion method in this case is able to distinguish between emission heights of so2 and ash and can capture resulting differences in transport patterns key points ash and so2 source terms estimated using inverse techniques and satellite data the transport and separation of ash and so2 are modeled model simulations correspond well with a range of independent observations 2014 the authors

dating crystalline groundmass separates of altered cretaceous seamount basalts by the 40ar 39ar incremental heating technique abstract alteration of submarine basalts compromises geochronology using conventional k ar and 40 ar 39 ar techniques to help overcome these problems we re evaluated the potential of groundmass dating techniques incremental heating on acid leached groundmass samples following an overnight bakeout at 200 c and using high resolution heating schedules eliminated most of the low temperature alteration effects in the submarine basalts studied more than 75 of the groundmass analyses n 32 display accurate age plateaus consisting of 30 70 of the total amount of 39 ar k released more than 50 of the analyses have plateau ages concordant with their total fusion ages implying minor or proportional loss of radiogenic 40 ar and 39 ar k overall we could show a high degree of coherence between ages of groundmass separates and comagmatic phenocrysts this suggests that the dating of aphyric basalts which previously has proven problematic can be accomplished with increasing confidence as well adding these rock types to the list of datable submarine basalts significantly enhances our ability to understand the eruptive history of linear submarine volcanic chains

formation and paleoenvironment of rhizoliths of shiyang river basin tengeri desert nw china abstract rhizoliths found in bed of the late quaternary paleolake zhuyezhe minqin basin central tengeri desert nw china were studied vegetation coverage is present at some locations in the paleolake area although much of the bed area is covered with moving dunes rhizoliths are occasionally eroded out and exposed to the air the morphology of the rhizoliths resembles singular or branching carbonated tubules which are hollow in their central part the rhizoliths are black to grey and are broken and scattered randomly on the sand surface of the lake bed the lacustrine deposits are black greenish silt or silty clay with a large quantity of white petite lake snail shells the possible plant types sources and formation conditions of carbon dioxide and calcium the sedimentary and diagenetic environments and the process of rhizolith formation were discussed via examining rhizoliths macromorphology studying the micromorphology and mineralogy by microscopy cathodoluminescence and scanning electron microscope and studying the chemical compositions of cementing minerals and fragments by energy dispersive x ray spectra the original roots of the rhizoliths belong to hydrophytes such as typha latifolia scirpus maritimus and carex stenophylla lake snails and previous pollen data indicate that the rhizoliths formed in a sedimentary environment of shallow fresh water lake like marginal or palustrine areas during the holocene shallow lake water disturbance by desert wind above the loose sandy sediment or soil was favoring the rhizoliths formation a continuous supply of oxygen through water disturbance led to complete oxidation of roots and producing carbon dioxide dissolution of co2 in water and so carbonic acid production resulted in minerals weathering such as feldspar and primary carbonate particles and the release of k and ca2 ions at presence of co2 and ca2 saturated in the pore water around the roots of hydrophytes within the sediments or soil carbonate precipitation occurred around the root channel and led to rhizoliths formation as tubules the petrifaction process therefore has happened in margin of the paleolake with shallow water and weak redox condition which implies the suitability of rhizolith for reconstructing paleoenvironment

deciphering holocene sea level history on the u s gulf coast a high resolution record from the mississippi delta published holocene relative sea level rsl curves for the u s gulf coast are in mutual conflict with some characterized by a smooth rsl rise akin to widely accepted eustatic sea level curves versus others including several recent ones that are characterized by a conspicuous stair step pattern with prolonged millennium scale rsl stillstands alternating with rapid meter scale rises in addition recent work in texas and alabama has revitalized the notion of a middle holocene rsl highstand estimated at 2 m above present mean sea level an extensive sampling program in the mississippi delta louisiana focused on the collection of basal peats that accumulated during the initial transgression of the pre existing consolidated pleistocene basement we used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the 30 cm zone between mean spring high water and mean sea level and we selected plant macrofossils that were subjected to ams 14c dating nearly 30 sea level index points from a 20 km2 study area on the eastern margin of the delta suggest that rsl rise followed a relatively smooth trend for the time interval 8000 3000 cal yr b p thus questioning the occurrence of major rsl stillstands alternating with abrupt rises given the narrow error envelope defined by our data set any sea level fluctuations if present would have amplitudes of 1 m although a true middle holocene highstand never occurred in the mississippi delta the high level of detail of our time series enables a rigorous test of this hypothesis correction of our data set for a hypothetical tectonic subsidence rate of 1 1 mm yr 1 assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of texas leads to sea levels near 2 m above present during the time interval 6000 4000 cal yr b p however this model also implies a rsl position near 2 m around 8000 cal yr b p which is inconsistent both with data of this age from texas as well as with widely accepted sea level data from elsewhere we therefore conclude that a middle holocene highstand for the u s gulf coast is highly unlikely and that the entire area is still responding glacio isostatically by means of forebulge collapse to the melting of the laurentide ice sheet

early holocene sea level record from submerged fossil reefs on the southeast florida margin massive fossil outlier reefs are preserved seaward of the modern shelf and reef tract along the southeast florida margin thermal ionization mass spectrometric tims u th dating of 16 pristine acropora palmata and head corals cored from two transects document early holocene reef growth from 8 9 to 5 0 ka from approximately 13 5 to 7 m msl mean sea level these samples fill a gap in the florida keys sea level database and clarify the timing of a significant decrease in the rate of sea level rise a portion of this interval represented by a gap in the caribbean record of a palmata reefs has been interpreted as reef drowning during an inferred catastrophic sea level rise event of 45 mm yr or a 6 5 m rise between 7 6 and 7 2 ka attributed to west antarctic ice sheet instability and changes in marine ice extent between 8 and 7 ka continuous in situ shallow water reef growth in florida during this interval precludes the occurrence of exceedingly rapid rates of sea level rise and is consistent with the north atlantic record of deglaciation from 9 to 7 ka gaps in the early holocene sea level records for florida and the caribbean are thus more likely to be artifacts of limited sampling and or core coverage and not necessarily a result of drowning

seismically imaged relict slab from the 55 ma siletzia accretion to the northwest united states teleseismic tomography images a large high velocity curtain extending vertically beneath the ca 50 ma challis magmatic trend to maximum depths of 230 600 km we interpret this structure as subducted farallon ocean lithosphere that stalled with the ca 55 ma accretion of the siletzia microplate to north america within the columbia embayment and we consider the regional tectonic implications the abrupt switch ca 53 ma from laramide thrusting and magmatic quiescence to extension and vigorous magmatism in the northwestern united states is evidence for foundering of the fl at subducting farallon slab to account for the imaged curtain foundering apparently occurred by rollback after siletzia accretion terminated subduction within the columbia embayment the magnitude of the high seismic velocity curtain is approximately that expected for 20 50 m y old ocean lithosphere that stalled in the upper mantle ca 50 ma we suggest that the stalled slab became nearly neutrally buoyant as a result of removal of its basaltic crust the melting of which likely contributed to the short lived vigor of challis magmatism after siletzia accretion normal dip cascadia subduction initiated west of siletzia evidenced by arc volcanism in oregon and washington beginning ca 45 40 ma while continued quiescence of the sierra nevada arc suggests persistence of flsubduction to the south kinematically this requires a tear in the subducted farallon slab near the latitude of southern oregon we propose that north to south propagation of this torn slab edge propagated the ignimbrite fl are up across what now is the northern basin and range and ended the laramide orogeny

polygenetic topography of the cascade range washington state usa we evaluate models for the cenozoic topographic evolution of the cascade range of washington state by analyzing the topography geology and exhumation patterns across the range the models for topographic evolution include 1 post miocene surface uplift of the range from initially low relief topography 2 post miocene surface uplift of the range superimposed on pre existing high relief topography and 3 post miocene surface uplift of high relief cascades in northern washington and low relief cascades in southern washington the third model a polygenetic topographic history is most consistent with our analysis of topographic data and the previously contradictory geologic paleontologic and isotopic lines of evidence regarding the cascades physiographic history between snoqualmie pass and the columbia river the east derived 15 my old columbia river basalt crb reaches nearly as far west as the modern drainage divide and is warped upward to the crest of the range these observations require subdued relief on the east flank of the southern cascades during the late miocene in the northern cascades the crb does not extend into the range and crb deformation only reflects 30 to 60 percent of the total relief thus the northern cascades were likely already a topographic barrier to the west flowing flood basalts moreover a polygenetic topographic history appears most consistent with the geologic data and the paleontologic and isotopic evidence for rainshadow formation during the middle miocene despite differences in topographic history and rock type the maximum and mean altitudes of the cascade range decrease smoothly from northern to southern washington we suggest that post uplift erosion particularly glacial erosion has reduced the topographic distinctions between the northern and southern cascades resulting in a single mountain range with a polygenetic topographic history

cenozoic active margin and shallow cascades structure cocorp results from western oregon two deep seismic reflection profiles totaling 98 km were recorded by the consortium for continental reflection profiling cocorp in western oregon in 1984 providing some of the first onshore deep seismic reflection data from the forearc and arc of an active convergent margin these data are of lower quality than most cocorp data but when combined with other geological and geophysical data they provide some useful insights into the subduction zone beneath oregon and into extensional structures in the cascades line 1 crossed the eocene sediments and underlying pillow basalts of the coast range and western willamette valley reflections from the willamette valley clearly define the lower and western boundary of flat lying rhythmically bedded eocene sediments these sediments appear to be underlain by as much as 8 km of seismically transparent eocene pillow basalts layered reflections at depths of 8 16 km may indicate a remnant crust upon which the eocene pillow basalts were erupted east dipping reflections at depths of 35 40 km may represent the decollement above the subducting juan de fuca plate oregon line 2 crosses the cenozoic volcanic arc terrains of the western and high cascades interpretation of cocorp seismic data suggests modification of existing models for normal faulting that postulate a symmetric graben or grabens in the cascades of oregon in the high cascades along cocorp oregon line 2 reflections suggest a large gently west dipping half graben with major offset only on the west side of the range the seismic reflection data along with other geological and geophysical data suggest that the high cascades were built on a series of blocks rather than a single graben the blocks were differentially faulted during the pliocene seismic data from the western cascades indicate several normal faults with down to the east offset including a major previously unidentified fault of probable miocene age

the columbia river basalt group in the cascade range a middle miocene reference datum for structural analysis the distributional patterns of individual columbia river basalt group crbg unite and structures recorded in the crbg place the following constraints on neogene tectonics of the northern oregon cascade range 1 a north east trending topographic low of regional extent the columbia transarc lowland transected the miocene northern oregon cascade range the columbia transarc lowland existed prior to the eruption of the crbg and served to funnel crbg flows across the miocene cascade range the lowland was apparently devoid of active volcanic centers from before 17 to 14 5 ma after 15 ma volcanic centers began to develop in the southern and central parts of the lowland 2 folds and associated faults of the yakima fold belt extend through the western columbia plateau and far into the cascade range these structures were active between 16 5 and s ma and represent n s shortening 3 the portland hills clackamas river structural zone is a northwest trending dextral wrench fault zone that became active prior to the incursion of crbg flows 16 5 ma and limited the distribution of some crbg units this structural zone appears to mark the western termination of the yakima fold belt other similarly trending dextral strike slip faults are common in the northern oregon cascades but did not affect the distribution of crbg flows and therefore developed in post crbg time 4 mount hood is located near the axis of a major yakima fold belt syncline in the crbg in the general location of earlier major andesitic volcanic activity related to the rhododendron formation

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

oxygen isotope evidence for the late cenozoic development of an orographic rain shadow in eastern washington usa topographic development of the southern washington cascade range and its influence on regional climate on the leeward side of the range for the past 15 6 m y are evaluated using oxygen isotope ratios d 18 o of ancient meteoric water recorded in authigenic smec tites the d 18 o values of authigenic smectites from paleosols and altered tuffs on the east side of the range exhibit a temporal and continuous decrease of 3 4 from 15 6 ma to the present taking into account a regional temperature change in eastern washington since the middle miocene the calculated d 18 o values of regional meteoric water show a negative shift of 3 5 4 5 over the same interval such a decrease is similar to the change in the d 18 o values of modern precipitation from the coastal side to a region down wind of the washington cascades this negative shift of the calculated d 18 o values on the east side of the range is best explained by the development of a rain shadow due to the tectonic rock uplift of the cascades during the late cenozoic based on the empirically calculated relationship between change in elevation and change in the d 18 o value of pre cipitation paleorelief of the southern washington cascades since 15 6 ma is estimated to be 1 2 1 7 km

holocene millennial to centennial carbonate cyclicity recorded in slope sediments of the great bahama bank and its climatic implications a 38 m long sediment core md992201 retrieved from a water depth of 290 m from the leeward margin of the great bahama bank gbb 25 53 49 n 79 16 34 w has been investigated for changes in aragonite content the core covers the mid to late holocene the past 7230 yr sediment lightness l values was used as a proxy for aragonite content based on a high linear correlation r 0 93 between the x ray diffraction derived aragonite content and l values the resulting time resolution of the l values derived aragonite content ranges from 1 yr at the base of the core to 4 yr at the top detailed time series analysis using monte carlo singular spectrum analysis and spectral analysis lomb scargle fourier transform identifies the presence of seven signals with varying amplitudes and wavelengths that could be traced throughout the past 5500 yr during the first 1600 yr of sedimentation the aragonite record is dominated by the initial flooding of the flat topped gbb superimposed on a multimillennial signal related to holocene sea level changes a millennial scale fluctuation and five quasi periodic oscillations were detected 1 3 2 kyr 500 600 yr 380 yr 260 yr 200 yr and 100 yr period comparisons with other proxies e g tree ring 14c 10be and 18o in ice cores provides information on the origin and dynamics of the individual signals the analysis shows that the 200 yr and 100 yr signals can be attributed to solar forcing the 260 yr 380 yr and the 500 600 yr quasi periodic signals are found to be of climatic origin whereas the millennial scale fluctuations remain enigmatic although solar forcing mechanisms seem likely the data show that variability of solar output as well as past oceanographic and atmospheric changes have modulated the mid to late holocene climate which in turn controlled sediment input variations found in the holocene wedge leeward of the gbb although these periplatform sediments have a rather uniform appearance they still contain a large variety of subtle sedimentary variations

stratospheric volcanic ash emissions from the 13 february 2014 kelut eruption mount kelut indonesia erupted explosively around 15 50 ut on 13 february 2014 sending ash and gases into the stratosphere satellite ash retrievals and dispersion transport modeling are combined within an inversion framework to estimate the volcanic ash source term and to study ash transport the estimated source term suggests that most of the ash was injected to altitudes of 16 17 km in agreement with space based lidar data modeled ash concentrations along the flight track of a commercial aircraft that encountered the ash cloud indicate that it flew under the main ash cloud and encountered maximum ash concentrations of 9 3 mg m 3 mean concentrations of 2 1 mg m 3over a period of 10 11 min of the flight giving a dosage of 1 2 0 3 g s m 3 satellite data could not be used directly to observe the ash cloud encountered by the aircraft whereas inverse modeling revealed its presence

operational prediction of ash concentrations in the distal volcanic cloud from the 2010 eyjafjallajokull eruption 1 during the 2010 eruption of eyjafjallajokull improvements were made to the modeling procedure at the met office uk enabling peak ash concentrations within the volcanic cloud to be estimated in this paper we describe the ash concentration forecasting method its rationale and how it evolved over time in response to new information and user requirements the change from solely forecasting regions of ash to also estimating peak ash concentrations required consideration of volcanic ash emission rates the fraction of ash surviving near source fall out and the relationship between predicted mean and local peak ash concentrations unresolved by the model to validate the modeling procedure predicted peak ash concentrations are compared against observations obtained by ground based and research aircraft instrumentation this comparison between modeled and observed peak concentrations highlights the many sources of error and the uncertainties involved despite the challenges of predicting ash concentrations the ash forecasting method employed here is found to give useful guidance on likely ash concentrations predicted peak ash concentrations lie within about one and a half orders of magnitude of the observed peak concentrations a significant improvement in the agreement between modeled and observed values is seen if a buffer zone accounting for positional errors in the predicted ash cloud is used sensitivity of the predicted ash concentrations to the source properties e g the plume height and the vertical distribution of ash at the source is assessed and in some cases seemingly minor uncertainties in the source specification have a large effect on predicted ash concentrations

a simple inversion method for determining optimal dispersion model parameters from satellite detections of volcanic sulfur dioxide a simple inversion scheme for optimizing volcanic emission dispersion model parameters with respect to satellite detections is presented in this paper in this scheme multiple dispersion model simulations obtained by varying relevant model parameters are created and compared against satellite detections using pattern correlation as a measure of model agreement with observations it is shown that the scheme is successful in inferring emission source parameters such as those describing the vertical extent of the nascent sulfur dioxide emissions in the november 2010 mount merapi eruption in java indonesia these optimal parameter values then become a basis for improved forecasts of the transport of volcanic emissions

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

volcanic signature of basin and range extension on the shrinking cascade arc klamath falls keno area oregon 1 detailed geologic mapping of the klamath falls keno area revealed the complex relationship between subduction crustal extension and magmatic composition of the southern oregon cascade volcanic arc volcanism in the study area at 7 4 ma consisted of calc alkaline basaltic andesite and andesite lava flowing over a relatively flat landscape local angular unconformities are evidence that basin and range extension began at by at least 4 ma and continues today with fault blocks tilting at a long term rate of 2 ma to 3 ma minimum nw se extension is 1 5 km over 28 km 5 high alumina olivine tholeiite haot or low k low ti transitional high alumina olivine tholeiite lklt erupted within and adjacent to the back edge of the calc alkaline arc as the edge receded westward at a rate of 10 km ma at 2 7 0 45 ma the volcanic front migrated east much slower than the back arc migrated west 0 km ma for 6 0 4 ma calc alkaline rocks 0 7 km ma if 6 ma haot lklt is included and 1 km ma if highly differentiated 17 30 ma volcanic rocks of the early western cascades are included declining convergence probably decreased asthenospheric corner flow decreasing width of calc alkaline and haot lklt volcanism and the associated heat flow anomaly the margins of which focused on basin and range extension and leakage of haot lklt magma to the surface this declining corner flow combined with steepening slab dip shifted the back arc west compensation of extension by volcanic intrusion and extrusion allowed growth of imposing range front fault scarps only behind the trailing edge of the shrinking arc

daily monitoring of ecuadorian volcanic degassing from space we present daily measurements of sulfur dioxide so2 emissions from active volcanoes in ecuador and southern colombia between september 2004 and september 2006 derived from the ozone monitoring instrument omi on nasa s eos aura satellite omi is an ultraviolet visible spectrometer with an unprecedented combination of spatial and spectral resolution and global coverage that permits daily measurements of passive volcanic degassing from space we use non interactive processing methods to automatically extract daily so2 burdens and information on so2 sources from the omi datastream maps of monthly average so2 vertical columns retrieved by omi over ecuador and s colombia are also used to illustrate variations in regional so2 loading and to pinpoint sources the dense concentration of active volcanoes in ecuador provides a stringent test of omi s ability to distinguish so2 from multiple emitting sources our analysis reveals that tungurahua reventador and galeras were responsible for the bulk of the so2 emissions in the region in the timeframe of our study with no significant so2 discharge detected from sangay at galeras and reventador we conclude that omi can detect variations in so2 release related to cycles of conduit sealing and degassing which are a critical factor in hazard assessment the omi so2 data for reventador are the most extensive sequence of degassing measurements available for this remote volcano which dominated regional so2 production in june august 2005 at tungurahua the omi measurements span the waning stage of one eruptive cycle and the beginning of another and we observe increasing so2 burdens in the months prior to explosive eruptions of the volcano in july and august 2006 cumulative so2 loadings measured by omi yield a total of 1 16 tg so2 emitted by volcanoes on mainland ecuador s colombia between september 2004 and september 2006 as much as 95 of this so2 may originate from non eruptive degassing approximate apportionment of the total so2 loading indicates that 40 originated from tungurahua with 30 supplied by both reventador and galeras these measurements of volcanic so2 degassing in ecuador confirm omi s potential as an effective economical and risk free tool for daily monitoring of so2 emissions from hazardous volcanoes

tectonics and seismicity of the southern washington cascade range abstract geophysical geological and seismicity data are combined to develop a transpressional strain model for the southern washington cascades region we use this model to explain oblique fold and fault systems transverse faults and a linear seismic zone just west of mt rainier known as the western rainier zone we also attempt to explain a concentration of earthquakes that connects the northwest trending mount st helens seismic zone to the north trending western rainier zone our tectonic model illustrates the pervasive effects of accretionary processes combined with subsequent transpressive forces generated by oblique subduction on eocene to present crustal processes such as seismicity and volcanism

effect of alpha damage annealing on apatite u th he thermochronology recent data on he diffusion challenge the temperature sensitivity of apatite u th he thermochronology the damage induced by recoil of u and th decay series during emission of particles recoil damage has been proposed to modify he diffusion properties through time however we propose that annealing of these irradiation defects may be an important phenomenon and may be significant in case of slowly cooled or reheated basement rocks to test this hypothesis we developed a quantitative model including an explicit treatment of recoil damage annealing and their effect on he diffusion kinetics and calibrate it against literature data our model is based on two hypotheses 1 helium is in equilibrium between an apatite crystal and its defects and 2 alpha recoil damage annealing can be described analogously to fission track annealing this model has been embedded into a monte carlo simulation of helium production ejection diffusion and applied to data from the french massif central a complex slowly cooled terrain with burial reheating where the thermal history has been constrained by previous fission track ft data including ft length distributions u th he ages are close to the ft ages from the same samples and are generally reproducible among replicates but some samples present he age dispersion that is not correlated with crystal size our model reproduces the massif central data very well except for three samples where he ages are older than corresponding ft ages we show that annealing of irradiation damage has an important impact on retentivity of helium and that the he content he is only a rough approximation of the damage level in particular our results show that independence of he ages on crystal sizes in case of reheated samples is a clear indication of the higher he retentivity induced by recoil defects and that an explicit treatment of defect annealing is required for a correct interpretation of u th he ages in such a case more generally a correlation with the crystal size can bring information on the thermal path only if the age of defects well represented by the fission track age is available due to the dependence of the partial retention zone on damages conversely in case of rapid cooling or for samples having low u and th contents damage effects can be ignored without significant effects on he ages

thermochronometer record of central andean plateau growth bolivia 19 5 s 1 quantifying the timing magnitude and rates of exhumation and deformation across the central andes is a prerequisite for understanding the history of plateau rise we present 23 new apatite and zircon fission track thermochronometer samples to chronicle the exhumation and deformation across the entire 500 km andean fold thrust belt at 19 5 s in bolivia exhumation and deformation are constrained with inverse thermal modeling of the thermochronometer data regional stratigraphy geothermal gradients and mass deficits inferred from a balanced section results suggest the following 1 initial exhumation of the eastern cordillera ec fore thrust and back thrust belts began in the late eocene to early oligocene 27 36 ma and continued in a distributed manner in the late oligocene to early miocene 19 25 ma interandean zone ia exhumation began 19 22 ma followed by a third pulse of exhumation 11 16 ma in the ec back thrust belt and initial cooling in the westernmost subandes sa 8 20 ma finally exhumation propagated eastward across the sa during the late mio pliocene 2 8 ma 2 exhumation magnitudes are spatially variable and range from maximums of 8 km in the ec fore thrust belt to average values of 4 7 km across the ec 2 5 3 km in the altiplano 4 6 km in the ia and 3 km in the sa 3 exhumation rates range from 0 1 to 0 2 mm a in the ec from 0 1 to 0 6 mm a in the ia and from 0 1 to 0 4 mm a to locally 1 4 mm a or more in the eastern sa we synthesize similar constraints with sediments throughout bolivia and characterize plateau development by 1 distributed deformation throughout the altiplano and ec regions from 20 to 40 ma with minor deformation continuing until 10 ma 2 contemporaneous cessation of most ec deformation and exhumation of the ia 20 ma implying establishment of the modern plateau width with significant but unknown crustal thickness and elevation shortly thereafter by 15 20 ma and 3 dominantly eastward propagation of deformation from the ia since 20 ma with minor out of sequence deformation in the central to eastern sa

accounting for long alpha particle stopping distances in u th sm he geochronology 3d modeling of diffusion zoning implantation and abrasion in apatite u th he thermochronology the helium distribution in a crystal is a function of the simultaneous processes of radiogenic production thermally activated volume diffusion and the ejection of he caused by long alpha stopping distances these processes are further complicated by zonation of u th and sm within the grain and implantation of 4he from neighboring u th sm bearing minerals we use a refined version of the 3d monte carlo diffusion code of gautheron and tassan got 2010 to simulate the interplay between ejection and diffusion with or without zonation ejection and abrasion for a suite of thermal histories we examine the phenomenon of over correction produced by the alpha ejection correction parameter ft or fzac for homogeneous or heterogeneous eu repartition by comparing the raw measured and ft or fzac corrected ages for a number of scenarios to the ejection free age aef which we define as the age that would be obtained if alpha ejection had not occurred or equivalently if the stopping distance was zero we show that the use of ft or fzac corrected ages generally reproduces the ejection free age to within typical u th he uncertainties 8 even for zoned apatites we then quantify the effect of alpha implantation on u th he ages showing that implantation from a single external source with modest relative u or th enrichment can generate as much as 50 excess he for more extreme cases where an apatite is surrounded by multiple external sources the measured age can be 300 of that determined from an isolated crystal while abrasion of the outer 20 25 m can significantly reduce the age dispersion for rapidly cooled samples slowly cooled samples can still retain 10 30 excess he the removal of the rim of the crystal reduces the thermal information from very low temperatures 40 c and introduces additional technical complications and biases and should therefore be used with caution overall we demonstrate that although zonation and implantation may not be routinely determined we now have the 3d modeling capability to fully investigate and constrain the causes of age dispersion within a sample leading to significant improvement in our ability to interpret u th he data

palaeoenvironmental evolution of lake gacko southern bosnia and herzegovina impact of the middle miocene climatic optimum on the dinaride lake system in the early to middle miocene a series of lakes collectively termed the dinaride lake system dls spread out across the north western part of the dinaride anatolian continental block its deposits preserved in numerous intra montane basins allow a glimpse into the palaeoenvironmental palaeobiogeographic and geodynamic evolution of the region lake gacko situated in southern bosnia and herzegovina is one of the constituent lakes of the dls and its deposits are excellently exposed in the gracanica open cast coal mine a detailed study of the sedimentary succession that addresses facies sediment petrography geophysical properties and fossil mollusc palaeoecology reveals repetitive changes in lake level these are interpreted to reflect changes in the regional water budget first order chronologic constraints arise from the integration of radio isotopic and palaeomagnetic data 40ar 39ar measurements on feldspar crystals from a tephra bed in the upper part of the sedimentary succession indicate a 15 31 0 16 ma age for this level the reversed magnetic polarity signal that characterises the larger part of the investigated section correlates to chron c5br of the astronomically tuned neogene timescale guided by these chronologic data and a detailed cyclostratigraphic analysis the observed variations in lake level evident as two 40 m and seven 10 m scale transgression regression cycles are tuned to 400 kyr and 100 kyr eccentricity cycles from the tuning it can be inferred that the sediments in the gacko basin accumulated between 15 8 and 15 2 ma the economically valuable lignite accumulations in the lower part of the succession are interpreted to indicate the development of swamp forests in conjunction with lake level falls corresponding to 100 kyr eccentricity minima pedogenesis rhizoliths and palustrine carbonate breccias in the upper part of the section reveal long term aridity coinciding with a 400 kyr eccentricity minimum eccentricity maxima are interpreted to trigger lake level high stands these are accompanied by eutrophication events caused by enhanced denudation of the surrounding basement and increased detrital input into the basin the presented age model proves that lake gacko arose during the middle miocene climatic optimum and that the optimum climatic conditions triggered the formation of this long lived lake

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

influence of crystal size on apatite u th he thermochronology an example from the bighorn mountains wyoming near surface tectonic and geomorphic processes involve cooling of rocks through low temperatures 50 200 c because rates of helium diffusion in apatite titanite and zircon are sensitive to temperature variations in this range uranium thorium helium thermochronometry u th he dating is well suited to establishing the timing and rates of these processes in the geologic record however because fractional loss of he is controlled by crystal size such that larger crystals retain a larger fraction of radiogenic he u th he ages must vary not only with thermal history but also with crystal size here we present crystal size correlated he ages from co existing apatites from the bighorn mountains wyoming that range from 100 to 350 ma these correlations are a sensitive indicator of the rock s thermal history in a temperature range below the system s nominal closure temperature t c 70 c for apatite and are consistent with a thermal history involving residence in the upper 2 3 km of crust since the precambrian with maximum temperatures of 65 80 c just prior to laramide orogenic exhumation the influence of crystal size on he ages will be most apparent in rocks where temperatures have been in the range of partial he retention for long periods of time 30 70 c for 10 7 years in such cases accurate interpretation of u th he ages must incorporate the effect of crystal size and this method may provide insights to thermal histories of rocks in previously inaccessible low temperature ranges

oxygen isotope evidence for progressive uplift of the cascade range oregon oxygen isotope compositions of fossil equid teeth in the cascade rainshadow reveal a v5x decrease in mean n 18 o since 27 ma isotopic changes are inconsistent with expected effects from global climate change because a the expected isotopic shift to tooth n 18 o values due to global climate change v1x is much smaller than the observed shift b predicted and observed isotopic trends are opposite for oligocene vs miocene samples and c average compositions and ranges in compositions remained unchanged for samples from before and after major global cooling in the mid miocene accounting for a decrease in relative humidity of at least 15 we infer a topographically driven secular shift in the n 18 o value of rainwater of 6 8x since the late oligocene which is approximately equivalent to the modern day difference in n 18 o values of precipitation and surface waters across the central cascades rise of the central cascades apparently occurred monotonically over the last 27 ma with a hiatus between v15 4 and 7 2 ma possibly related to eruption of the columbia river basalts progressive volcanic accumulation over tens of millions of years best explains the data rather than a short lived uplift event paleoseasonality as inferred from isotope zoning and intertooth variability decreased dramatically from 7 9x at 15 4 7 ma to v3x at 3 ma then increased to 6 8x today the cause of the decrease in seasonality at 3 ma may reflect either brief warming during the mid pliocene within the context of global tectonic reorganization or consumption by equids of water from an isotopically buffered lake idaho 2002 elsevier science b v all rights reserved

merapi 2010 eruption chronology and extrusion rates monitored with satellite radar and used in eruption forecasting abstract despite dense cloud cover satellite borne commercial synthetic aperture radar sar enabled frequent monitoring of merapi volcano s 2010 eruption near real time interpretation of images derived from the amplitude of the sar signals and timely delivery of these interpretations to those responsible for warnings allowed satellite remote sensing for the first time to play an equal role with in situ seismic geodetic and gas monitoring in guiding life saving decisions during a major volcanic crisis our remotely sensed data provide an observational chronology for the main phase of the 2010 eruption which lasted 12 days 26 october 7 november 2010 unlike the prolonged low rate and relatively low explosivity dome forming and collapse eruptions of recent decades at merapi the eruption began with an explosive eruption that produced a new summit crater on 26 october and was accompanied by an ash column and pyroclastic flows that extended 8 km down the flanks this initial explosive event was followed by smaller explosive eruptions on 29 october 1 november then by a period of rapid dome growth on 1 4 november which produced a summit lava dome with a volume of 5 10 6 m 3 a paroxysmal vei 4 magmatic eruption with ash column to 17 km altitude destroyed this dome greatly enlarged the new summit crater and produced extensive pyroclastic flows to 16 km radial distance in the gendol drainage and surges during the night of 4 5 november the paroxysmal eruption was followed by a period of jetting of gas and tephra and by a second short period 12 h of rapid dome growth on 6 november the eruption ended with low level ash and steam emissions that buried the 6 november dome with tephra and continued at low levels until seismicity decreased to background levels by about 23 november our near real time commercial sar documented the explosive events on 26 october and 4 5 november and high rates of dome growth 25 m 3 s 1 an event tree analysis for the previous 2006 merapi eruption indicated that for lava dome extrusion rates 1 2 m 3 s 1 the probability of a large 1872 scale eruption was 10 consequently the order of magnitude greater rates in 2010 along with the explosive start of the eruption on 26 october the large volume of lava accumulating at the summit by 4 november and the rapid and large increases in seismic energy release deformation and gas emissions were the basis for warnings of an unusually large eruption by the indonesian geological agency s center for volcanology and geologic hazard mitigation cvghm and their volcano research and technology development center bpptk in yogyakarta warnings that saved thousands of lives

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

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

effects of u th rich grain boundary phases on apatite helium ages abstract single grain apatite u th sm he ages he ages from non detrital samples sometimes show larger dispersions than can be explained by known sources of age dispersion such as grain size radiation damage parent zonation fracturing or intracrystalline inclusions we present observations and model age bias effects of an additional source of apatite he age dispersion observed in some cases u th rich grain boundary phases gbps precipitated on apatite crystal surfaces apatite grains from several samples with dispersed apatite he ages are coated or partially coated by reddish orange gbps rich in fe u and th these gbps are heterogeneous in thickness grain coverage and composition and have effective u concentrations eu up to 1000 ppm these phases may have large effects on the bulk eu and 4he compositions of apatite grains and can produce significant he age biases the direction and magnitude of this age bias is primarily a function of four factors 1 the host grain s size 2 the gbps thickness and eu relative to the host grain 3 the timing of gbp formation relative to the cooling age of the host grain and 4 whether the gbps are preserved and analyzed with the grain during he dating some of the most severe effects occur when gbps formed before or near the time of the apatite cooling age but were lost just prior to analysis for example during mineral separation in this case gbps of commonly observed thicknesses 1 10 m with eu 2 10 times that of the host apatite grain implant enough 4he into typical sized apatite grains to produce hundreds of percent positive age biases in contrast when u th rich gbps are preserved and analyzed with apatite grains the resulting he ages can be negatively biased though the heterogeneity variable preservation and ambiguous formation ages of gbps preclude a general quantitative and practical solution to this problem our model demonstrates that observed age dispersions in some samples are consistent with the effects of u th rich grain boundary phases and illustrates the conditions under which and by how much they will bias he ages

origin of compound biogenic sedimentary structures in eocene strata of wadi el hitan universal heritage area fayum egypt mangrove roots or not abstract ichnological data are integrated with sedimentologic data and body fossil content to reconsider the origins of the biogenic sedimentary structures in upper middle eocene strata of wadi el hitan unesco universal heritage area in egypt three types of rhizoliths type 1 to 3 are recognized in addition to co occurrence of six common marine ichnogenera ophiomorpha skolithos thalassinoides palaeophycus teichichnus and taenidium fossil content comprises bivalves ostrea sp cardia sp cardium sp carditopsis sp and pinna sp gastropods turritella sp scaphopoda tusk shells arthropods crabs and balanus sp and the larger foraminifer nummulites sp as well as bony fossils of basilosaurus isis dorudon atrox crocodiles sharks rays and saw fish facies characteristics fossil content rhizoliths and invertebrate trace fossil suites imply a bay margin origin of the plant and animal associated biogenic sedimentary structures importantly characteristics such as downward tapering and or branching into smaller branches in addition to external and internal ornamentations are used to distinguish rhizoliths from burrows comparison between modern mangrove environments i e substrates fauna and flora with the examined biogenic sedimentary structures can be used to support the marginal marine mangrove swamp origin importantly living mangrove roots are characteristically associated with marine bioturbation which can be compared to the structures reported in the eocene bioturbated bed large vertical type 1 rhizoliths are interpreted as mangrove tree trunks type 2 rhizoliths correspond to prop stilt roots similar to those of living rhizophora sp and locally to pneumatophore anchor roots of living avicennia sp type 3 rhizoliths are ascribed to sea grasses roots and or tertiary roots and root hairs the examined compound biogenic sedimentary structures represent an excellent example for distinguishing previously misinterpreted plant roots rhizoliths from animal trace fossils burrows in marine setting as well as recognizing mangrove rhizoliths in the rock record

thermal and exhumation history of the eocene chumstick basin washington state usa this study investigates the cenozoic evolution of the cascades mountains usa by means of reconstructing the thermal history of the chumstick basin deposits that are located on the eastern flank of the orogen we present new detrital apatite u th sm he and detrital apatite fission track ages from the middle eocene 48 37 ma chumstick formation and modern river detritus these data are integrated with the published thermochronometric ages of the adjoining cascade mountains basement the new thermochronometer results are combined with existing vitrinite reflectance data for modeling of the basin s thermal history results suggest constant temperatures throughout the late oligocene to early miocene followed by rapid cooling since 17 10 ma results indicate that the middle to late miocene uplift of the cascades resulted in reactivation of the fault zones bounding the chumstick basin the structural reactivation and the weaker lithology of the basin strata in comparison to the harder and more resistant basement rocks of the cascades resulted in significant basin exhumation this interpretation is determined from younger apatite u th sm he cooling ages observed in the reset detrital bedrock of the chumstick formation than in the adjoining basement rocks these observations suggest a structural and lithological control on exhumation magnitudes in this region

estimation of optimal dispersion model source parameters using satellite detections of volcanic ash in this paper we demonstrate how parameters describing the geometry of the volcanic ash source for a particular volcanic ash dispersion model hysplit may be inferred by the use of satellite data and multiple trial simulations the areas of space likely to be contaminated by ash are identified with the aid of various remote sensing techniques and polygons are drawn around these areas as they would be in an operational setting dispersion model simulations are initialized either by a cylindrical source or a specified ash distribution depending on the context parameters of interest such as the base and top height diameter and optimal release time of the cylindrical source or the height of the specified ash distribution are inferred by forming a parameter grid and running multiple simulations for each parameter grid point value optimal values of the parameter values are identified by calculating spatial correlations between the model simulations and observations we demonstrate that the methodology can be used to correctly infer various model parameters and improves volcanic ash forecasts in various eruption case studies

fining upwards sedimentary sequences generated in seagrass beds shallow marine clastic and carbonate environments of southeast florida contain fining upwards sedimentary sequences being generated by beds of the seagrass thalassia testudinum lateral seaward migration of flute shaped sand pockets storm blowouts in the grass platform produces a lenticular fining upwards package 10 50 m in width 20 100 m in length and 0 3 2 m in thickness migration and vegetative restabilization of recurring blowouts on a grass platform can produce a composite sequence containing numerous complete or stacked incomplete fining upwards packages a complete fining upwards sequence consists of 1 an erosional base 2 a coarse basal shell layer representing the winnowed lag of the eroded preexisting grass stabilized platform 3 a ripple laminated well sorted medium grained sand zone representing the mobile sand on the leeward slope of the blowout and 4 a shelly bioturbated sand or silty sand having a strongly bimodal texture modes at 100 and 500 mu m in which the fine mode dominates upwards this upper portion records increased trapping of storm suspensions and decreased bedload transport as seagrasses are reestablished the mollusks chione cancellata and codakia orbicularis characterize the grass stabilized zone the distinctive textural sequence and molluscan assemblage serve to differentiate these biogenically induced fining upwards sequences from others in the geological record

holocene sea level changes along the north carolina coastline and their implications for glacial isostatic adjustment models abstract we have synthesized new and existing relative sea level rsl data to produce a quality controlled spatially comprehensive database from the north carolina coastline the rsl database consists of 54 sea level index points that are quantitatively related to an appropriate tide level and assigned an error estimate and a further 33 limiting dates that confine the maximum and minimum elevations of rsl the temporal distribution of the index points is very uneven with only five index points older than 4000 cal a bp but the form of the holocene sea level trend is constrained by both terrestrial and marine limiting dates the data illustrate rsl rapidly rising during the early and mid holocene from an observed elevation of 35 7 1 1 m msl at 11062 10576 cal a bp to 4 2 m 0 4 m msl at 4240 3592 cal a bp we restricted comparisons between observations and predictions from the ice 5g vm2 with rotational feedback glacial isostatic adjustment gia model to the late holocene rsl last 4000 cal a bp because of the wealth of sea level data during this time interval the ice 5g vm2 model predicts significant spatial variations in rsl across north carolina thus we subdivided the observations into two regions the model forecasts an increase in the rate of sea level rise in region 1 albemarle currituck roanoke croatan and northern pamlico sounds compared to region 2 southern pamlico core and bogue sounds and farther south to wilmington the observations show late holocene sea level rising at 1 14 0 03 mm year 1 and 0 82 0 02 mm year 1 in regions 1 and 2 respectively the ice 5g vm2 predictions capture the general temporal trend of the observations although there is an apparent misfit for index points older than 2000 cal a bp it is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid carolina platform high or a flaw in the gia model a comparison of local tide gauge data with the late holocene rsl trends from regions 1 and 2 support the spatial variation in rsl across north carolina and imply an additional increase of mean sea level of greater than 2 mm year 1 during the latter half of the 20th century this is in general agreement with historical tide gauge and satellite altimetry data

precise and accurate in situ pb pb dating of apatite monazite and sphene by laser ablation multiple collector icp ms to evaluate in situ pb dating by laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icp ms we analysed apatite sphene and monazite from paleoproterozoic metamorphic rocks from west greenland pb isotope ratios were also determined in the national institute of standards and technology nist 610 glass standard and were corrected for mass fractionation by reference to the measured thallium isotope ratio the nist 610 glass was used to monitor pb isotope mass fractionation in the low tl pb accessory minerals replicate analyses of the glass 1 to 2 min yielded ratios with an external reproducibility comparable to conventional analyses of standard reference material 981 by thermal ionisation mass spectrometry tims mineral grains were generally analysed with a 100 m laser beam although some monazite crystals were analysed at smaller spot sizes 10 and 25 m the common pb isotope ratios required for age calculations were either measured on coexisting plagioclase by la mc icp ms or could be ignored as individual crystals exhibit sufficient pb isotopic heterogeneity to perform isochron calculations on replicate analyses of single crystals mean mineral ages with the 204pb ion beam measured in the multiplier were as follows apatite 1715 23 m y sphene 1789 11 m y and monazite 1783 to 1888 m y with relative uncertainties on individual monazite ages of 0 2 but highly reproducible age determinations on single monazite crystals 1 isochron ages calculated from several mineral analyses without assumption of common pb also yield precise age determinations apatite and monazite pb ages determined by in situ pb isotope analysis are identical to those determined by conventional tims analysis of bulk mineral separates and the analytical uncertainties of these short laser analyses with no prior mechanical or chemical separation are comparable to those obtained by tims detailed examination of the sphene in situ age data does however show a small discrepancy between the la mc icp ms and tims ages 1 younger high resolution mass scans of the sphene during ablation clearly showed several small and as yet unidentified isobaric interferences that overlap with the 207pb peak at the resolution conditions for measurement of isotope ratios these might account for the age discrepancy between the la mc icp ms and tims sphene ages la mc icp ms is a rapid accurate and precise method for in situ determination of pb isotope ratios that can be used for geochronological studies in a manner similar to an ion microprobe albeit currently at a somewhat degraded spatial resolution further modifications to the la mc icp ms system such as improved sensitivity ion transmission and la methodology may lead to this type of instrument becoming the method of choice for many types of in situ pb isotope dating

stratigraphic sedimentologic and petrologic record of late miocene subsidence of the central oregon high cascades pliocene to holocene volcanics of the central oregon high cascades largely confined to an intra arc graben bury older volcanic centers early high cascade volcanism is recorded by late miocene volcanics and sediments of the deschutes formation that accumulated in a fluvial basin east of the cascades aggradation in the adjacent fluvial basin occurred episodically when pyroclastic debris choked streams deschutes basin aggradation commenced near 7 4 ma and was synchronous with extension influenced cascade magmatism dominated by basalts and basaltic andesites initial subsidence of the cascades occurred at about 5 4 ma in response to plate margin processes structural isolation of the basin from ignimbrites and volcanism induced sedimentation resulted in widespread development of superimposed paleosols in the basin subsequent mafic lavas erupted near the eastern margin of the initial depression were truncated by east stepping down to the west faults at about 5 3 ma

numerical investigations of apatite 4he 3he thermochronometry apatite 4he 3he thermochronometry has the potential to constrain cooling histories for individual samples provided that several presently untested assumptions are valid here we simulate the sensitivity of 4he 3he spectra to assumptions regarding geometric model crystallographic anisotropy broken grain terminations parent nuclide zonation and the accuracy of results obtained from analyses of aggregates of multiple crystals we find that 4he 3he spectra obtained from a cylinder with isotropic diffusion are almost indistinguishable from those obtained from an equivalent sphere with an equivalent initial 4he distribution under similar conditions anisotropic diffusion from the cylinder can greatly bias 4he 3he spectra but only if diffusion is 10 times faster in the axial than the radial direction existing data argue against anisotropy of this magnitude we find that analysis of apatites with broken terminations will also bias 4he 3he spectra but not greatly so in contrast we find that zonation of a factor of 3 in parent nuclide concentration produces 4he 3he spectra that deviate substantially from the homogeneous model when parent nuclides are highly concentrated near the grain rim and or cooling is fast the resulting 4he 3he spectra will be readily identified as aberrant however more subtle zonation higher concentrations in the grain interior or samples that have cooled slowly regardless of zonation style can yield 4he 3he spectra that look acceptable but will lead to inaccurate thermochronometric interpretation if parent homogeneity is assumed finally we find that analysis of an aggregate of crystals with identical 4he distributions can yield 4he 3he spectra and diffusion arrhenius arrays that are very different from those that would be obtained on the individual crystals if even small variations in he diffusion exist among the grains overall our observations suggest that modeling tools that assume spherical geometry and isotropic diffusion are appropriate for interpreting apatite 4he 3he spectra however it is essential to analyze only individual crystals and to assess the degree of parent nuclide zonation in those crystals

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

simultaneous retrieval of volcanic ash and so2 using msg seviri measurements 1 volcanic ash and sulphur dioxide masses from the november 2005 eruption of karthala volcano comoros islands are simultaneously retrieved using rapid scan multispectral infrared measurements from the spin enhanced visible and infrared imager on board the meteosat second generation geosynchronous satellite retrievals are made every 15 min which show that the ash and so2 separate in the vertically sheared atmosphere producing a fast moving upper level 12 km so2 cloud a slower moving middle level 8 km ash cloud and a boundary layer 3 km so2 plume the total mass of fine ash is 0 1 0 05 tg sio2 the upper level so2 mass is 0 19 0 01 tg s while the boundary layer so2 mass is 0 009 0 01 tg s these are the first simultaneous satellite measurements of ash and so2 from an erupting volcano and confirm previous ideas about vertical separation we suggest care must be exercised when using so2 as a tracer for volcanic ash in aviation hazard warning systems

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

magnitude and timing of episodic sea level rise during the last deglaciation a succession of elevated ridge deposits on the south florida margin was mapped using high resolution seismic and side scan sonar imaging in water depths ranging from 50 to 124 m the ridges are interpreted to be subtidal shoal complexes and paleoshorelines eolian dune or beach formed during the last sea level transgression oolitic and skeletal grainstones and mixed skeletal peloidal ooid packstones were recovered using a research submersible all of the grains are of shallow water or intertidal origin and both marine and nonmarine cements were identified formation and preservation of these features are attributed to episodic and rapid changes in the rate of the deglacial sea level rise at the onset of the termination 1a 18o excursion this high resolution record of sea level change appears to be related to deglacial processes operating on submillennial time scales and supports increasing evidence of rapid episodic fluctuations in ice volume climate and ocean circulation patterns during glacial interglacial transitions

the saddle mountains the evolution of an anticline in the yakima fold belt the saddle mountains uplift is an asymmetrical north vergent anticline with a length of about 110 km it varies from an open to tight fold and is divided into six segments based upon differences in geometry flows of the columbia river basalt group intercalated sedimentary deposits of the ellensburg formation and suprabasalt sediments thin over the uplift and thicken into the synclines variations in thickness are used to determine the timing of deformation and age of major and minor structures the close correlation of growth rate of the folds with rate of magma supply of the columbia river basalt group suggests that the yakima fold belt resulted from the same tectonic processes that produced eruption of the columbia river basalt modified journal abstract

new aeromagnetic data reveal large strike slip faults in the northern willamette valley oregon high resolution aeromagnetic data from the northern willamette valley oregon reveal large northwest striking faults buried beneath quaternary basin sediments several faults known from geologic mapping are well defined by the data and appear to extend far beyond their mapped surface traces the mount angel fault the likely source of the richter magnitude m l 5 6 earthquake in 1993 is at least 55 km long and may be connected in the subsurface with the gales creek fault 25 km farther northwest northeast of the mount angel fault a 60 km long northwest striking anomaly may represent a previously unrecognized dextral slip fault beneath the towns of canby and molalla vertical offsets along the mount angel fault increase with depth indicating a long history of movement for the fault dominantly northwest trending relatively straight faults consistent stepover geometries offset magnetic anomalies and earthquake focal mechanisms suggest that these faults collectively accommodate significant dextral slip the 1993 earthquake may have occurred on a left stepping restraining bend along the mount angel gales creek fault zone

steady rotation of the cascade arc displacement of the miocene cascade volcanic arc northwestern north america from the active arc is in the same sense and at nearly the same rate as the present clockwise block motions calculated from gps velocities in a north american reference frame migration of the ancestral arc over the past 16 m y can be explained by clockwise rotation of upper plate blocks at 1 0 m y over a linear melting source moving westward 1 4 5 km m y due to slab rollback block motion and slab rollback are in opposite directions in the northern arc but both are westerly in the southern extensional arc where rollback may be enhanced by proximity to the edge of the juan de fuca slab similarities between post 16 ma arc migration paleomagnetic rotation and modern gps block motions indicate that the secular block motions from decadal gps can be used to calculate long term strain rates and earthquake hazards northwest directed basin and range extension of 140 km is predicted behind the southern arc since 16 ma and 70 km of shortening is predicted in the northern arc the gps rotation poles overlie a high velocity slab of the siletzia terrane dangling into the mantle beneath idaho united states which may provide an anchor for the rotations

radiation damage control on apatite u th he dates from the grand canyon region colorado plateau individual detrital apatite grains from the esplanade coconino and moenkopi formations in the grand canyon region of the colorado plateau yield u th he dates from 104 to 5 ma the range of dates within each unit far exceeds analytical uncertainty but correlates with both he concentration he and effective u concentration eu these dates are all signifi cantly younger than the sandstone units indicating partial to complete he loss following deposition recently published laboratory diffusion data suggest that he retentivity in apatite increases with radiation damage forward models predict that the consequences of this effect will be manifested most clearly as a correlation between u th he dates and the he and eu in suites of apatites that 1 are characterized by a large span of eu and 2 had thermal histories in which suffi cient time elapsed for the apatite he diffusion kinetics to diverge prior to reheating and partial resetting apatites in the sedimentary units investigated fi t these cri teria using geologically reasonable deposition burial and unroofi ng histories simulations that include the effect of radiation damage on apatite he retentivity can reproduce the observed distributions of apatite dates and correlations with parent and daughter concentrations these results suggest that a span of u th he dates positively correlated with eu may provide important information regarding a sample s thermal history

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

faulting in a propagating continental rift insight from the late miocene structural development of the abert rim fault southern oregon usa abstract new geological mapping and 40ar 39ar ages reveal a temporal progression of faulting along a major extensional fault the abert rim fault at the active margin of the basin and range province in the western u s the onset of extensional deformation near lake abert coincided with widespread basaltic volcanism fault cross cutting relationships and tilt of volcanic layers demonstrate that nw striking faults formed between 8 9 and 7 5 ma and were subsequently cut by the nne striking abert rim fault sequential restoration of cross sections indicate that the abert rim fault south of 42 40 n latitude had 250 m of stratigraphic separation prior to deposition of the rattlesnake tuff at 7 ma low values of net extension 4 and long term rates of geologic deformation 1 mm yr suggest that regional extension since 10 ma has occurred primarily by diking we model province wide along and across strike expansion within the margin of the basin and range province as regional dilation accompanying northward propagation of the walker lane transform the growth of this extensional province is superimposed on a previously unrecognized early miocene volcanic landscape marked by volcanism between 21 4 and 22 3 ma dike orientations within one of these early miocene volcanoes and evidence for the existence of as much as 500 m of paleo topography prior to widespread deposition of the steens basalts at 16 ma suggests that late miocene faults near lake abert may reactivate an older structural fabric

effects of inherited cores and magmatic overgrowths on zircon u th he ages and age eu trends from greater himalayan sequence rocks mount everest region tibet previous constraints on the timing and rate of exhumation of the footwall of the south tibetan detachment system stds north of mount everest suggest rapid miocene cooling from 700 c to 120 c between 14 17 ma however 25 new single grain zircon he ages from leucogranites intruding greater himalayan sequence rocks in the footwall of the stds are between 9 9 and 15 ma with weighted mean ages between 10 and 12 ma zircon grains exhibit a positive correlation between age and effective uranium eu laser ablation zircon u pb geochronology detailed sem observations and laser ablation depth profiling of these zircons reveal low eu 0 5 2 5 ga inherited cores overgrown by high eu 17 22 ma rims this intragranular zonation produces ages as much as 32 too young when a standard alpha ejection correction assuming uniform eu distribution is applied modeling of the effects of varying rim thickness and rim eu concentration on the bulk grain eu and alpha ejection correction suggests that zonation also exerts the primary control on the form of the age eu correlation observed application of grain specific zonation dependent age corrections to our data yields zircon he ages between 14 and 17 ma in agreement with aft and 40ar 39ar ages growth of magmatic rims followed by cooling to 120 c within 1 6 million years supports rapid tectonic exhumation associated with slip along the stds in the miocene this study highlights the importance of characterizing parent nuclide zonation in zircon he studies which seek to understand the timing of exhumation along exhumed crustal blocks

holocene sea level database for the atlantic coast of the united states we have constructed a database of holocene relative sea level rsl observations for the atlantic coast of the united states the database contains 492 index points which locate the position of rsl in time and space and 344 limiting dates which constrain the minimum or maximum limit of former sea level the majority of the index points in the database are from 6 ka bp to present with only 7 older than 6 ka bp spatially index points are distributed between maine and south carolina but there is an absence of data from georgia and the atlantic coast of florida the database is sub divided into 16 regions based on the distance from the former laurentide ice sheet and are classified depending upon their susceptibility to compaction the index points and limiting data demonstrate that rsl did not exceed present 0 m during the holocene except potentially in regions 1 and 2 eastern maine and southern maine rates of rsl change were highest during the early holocene and have decreased over time due to the diminishing response of the earth s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input along the atlantic coast of the united states the linear rate of rsl rise prior to 4 ka bp ranged from 0 5 to 4 5 mm a 1 compared to 0 6 1 8 mm a 1 from 4 ka bp to ad 1900 the database suggests minimal 0 3 mm yr changes in these rates of rsl rise during the late holocene deglaciation of the laurentide ice sheet caused the spatial variability captured by the database the maximum rate of late holocene and ongoing rsl rise occurred in mid atlantic regions new jersey and inner delaware because of collapse of the peripheral forebulge

termination of the northwestern basin and range province into a clockwise rotating region of transtension and volcanism southeast oregon abstract new data indicate that northeast directed extensional faulting characterizes slip across the brothers fault zone bfz which marks the northern limit of the northwestern basin and range nwbr extensional province in southeastern oregon structural separation across individual north northeast striking nwbr faults decreases to zero south of the bfz field relationships and cross sections demonstrate limited kinematic linkage and independent evolution of the two fault systems since 7 ma west directed extension accumulated on nwbr faults at 0 01 mm yr and lengthened northward after 7 05 ma bfz faults accumulated northeast directed extension at rates of 0 01 mm yr since 5 68 ma deformation coincides with periods of heightened basaltic magmatism in the high lava plains implying that volcanism weakened the crust and promoted extension in the bfz in a new model we reconcile the observed northward diminishing rate and clockwise motion of the modern nwbr deformation field with regional geology the bfz defines a small circle about the pole of rotation and separates a stable block to the ne from the extending region to the south faults to the south are growing northward consistent with the northward decrease in rate and magnitude of extension in the nwbr

rhizolith evidence in support of a late holocene sea level highstand at least 0 5 m higher than present at key biscayne florida r fairbridge and f shepard proposed different sea level curves for the late holocene south florida as a tectonically stable platform provides a key locale from which late quaternary sea level measurements have been attempted previous studies supporting holocene sea level curves have focused on mangrove peat deposits barrier ridges and archaeological sites however in situ biological indicators provide the best evidence in support of varying sea level positions during the late holocene the northeastern side of key biscayne florida has two areas of rock reef where rhizoliths i e fossilized root casts are exposed within the intertidal zone they have previously been interpreted as the fossilized roots of a former black mangrove avicennia germinans forest however the morphology size orientation and areal extent of the rhizoliths is best understood if they are interpreted as the former root casts of turtle grass thalassia testudinum this interpretation would constitute in situ biological evidence of a late holocene sea level position at least 0 5 m higher than at present previously published 14c dating of the calcareous paste inside the rhizoliths suggests that they formed 1 2 k y before present this corresponds to a higher than present sea level highstand supported by independent evidence from other areas in south florida

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

two phase westward encroachment of basin and range extension into the northern sierra nevada 1 structural geophysical and thermochronological data from the transition zone between the sierra nevada and the basin and range province at latitude 39 n suggest 100 km westward encroachment of basin and range extensional deformation since the middle miocene extension accommodated primarily by east dipping normal faults that bound west tilted range forming fault blocks varies in magnitude from 150 in the wassuk and singatse ranges to the east geological and apatite fission track data from exhumed upper crustal sections in the wassuk and singatse ranges point to rapid footwall cooling related to large magnitude extension starting at 14 15 ma farther to the west geological and thermochronological data indicate a younger period of extension in the previously unextended pine nut mountains the carson range and the tahoe truckee depression initiated between 10 ma and 3 ma and incipient post 0 5 ma faulting to the west of the tahoe truckee area these data imply the presence of an extensional breakaway zone between the singatse range and the pine nut mountains at 14 15 ma forming the boundary between the sierra nevada and basin and range at that time in addition fission track data imply a miocene preextensional geothermal gradient of 27 5 c km 1 in the central wassuk range and 20 5 c km 1 in the singatse range much higher than the estimated early tertiary gradient of 10 5 c km 1 for the sierra nevada batholith this might point to a significant increase in geothermal gradients coupled with a likely decrease in crustal strength enabling the initiation of extensional faulting apatite fission track geophysical and geological constraints across the sierra nevada basin and range transition zone indicate a two stage coupled structural and thermal westward encroachment of the basin and range province into the sierra nevada since the middle miocene

interpretation of u th he single grain ages from slowly cooled crustal terranes a case study from the transantarctic mountains of southern victoria land low temperature thermochronologic techniques e g apatite fission track aft thermochronology and u th he dating constrain near surface t t paths and are often applied to uplift denudation and landscape evolution studies samples collected in vertical profiles from granitic walls on either side of the ferrar glacier southern victoria land antarctica were analyzed using aft thermochronology and apatite u th he dating to further constrain the lowest temperature thermal history of this portion of the transantarctic mountains aft central ages vary systematically with elevation and together with track length information define a multi stage cooling denudation history in the cretaceous and early tertiary apatite u th he single grain age variation with elevation is not as systematic with considerable intra sample age variation although many complicating factors e g u and th rich micro inclusions fluid inclusions variation in crystal size particle ejection correction zonation and particle ejection correction implantation of he into a crystal or impediment of he diffusion out of a crystal and 147sm derived particles may contribute to age dispersion we found that variation in single grain ages correlated with cooling rate samples that cooled relatively quickly have less variation in single grain ages whereas samples that cooled relatively slowly 3 c m y or resided within an u th he partial retention zone heprz prior to more rapid cooling have a comparatively greater variation in ages decay of u and th via particle emission creates a 4he concentration profile dependent upon the initial parent u th within a crystal variation of single grain ages for samples with non homogeneous u th distributions will be enhanced with long residence time in the partial retention zone i e slow cooling because of the relative importance of loss via volume diffusion and loss via particle ejection with respect to the u th zonation and the grain boundary correction of ages for particle ejection ft correction factor typically assumes uniform u and th distribution within the crystal and when applied to a population of crystals with different u and th distributions will enhance the variation in ages most complicating factors listed above for apatite u th he ages result in ages that are too old we propose that if considerable variation in u th he single grain ages exists that a weighted mean age is determined once outlier single crystal ages are excluded using the criterion of chauvenet or a similar approach we suggest that the true age or most representative age for that age population lies between the minimum u th he age and the weighted mean age we apply this approach coupled with composite age profiles to better constrain the t t history of the profiles along the ferrar glacier significant intra sample variation in single crystal apatite u th he ages and other minerals dated by the u th he method should be expected especially when the cooling rate is slow the variation of u th he single crystal ages is therefore another parameter that can be used to constrain low temperature thermal histories

petrology of the yerington batholith nevada evidence for evolution of porphyry copper ore fluids the jurassic yerington batholith western nevada is a composite pluton that contains several centers of porphyry copper mineralization and is exposed in structural cross section at paleodepths ranging from 0 to 8 km within these exposures the mcleod hill quartz monzodiorite bear quartz monzonite and luhr hill granite form successive intrusions that are in turn volumetrically smaller approximately 75 19 and 6 vol respectively more deeply emplaced tops at 65 km 3 luhr hill granite the low cu content approximately 10 ppm of the granite would allow extraction of approximately 50 ppm cu from it during crystallization these data suggest an orthomagmatic model in which both high and low density saline aqueous fluids formed during exsolution of water from the crystallizing luhr hill granite and from which salts cu fe and s strongly partitioned into the high density ore fluid low density fluids may have risen from the magma as a vapor plume mineralization occurred when fluid overpressures caused fracturing of wall rock and upward intrusion of granite porphyry dikes and high density saline ore fluids both the f sub o 2 path during subsolidus cooling and the deposition of most s as chalcopyrite pyrite in ore suggest that reduction of magmatic s to sulfide may have been a mechanism for oxidation of magmatic ferromagnesian silicate and fe ti oxide minerals