hydrothermal alteration of basalts beneath the bent hill massive sulfide deposit middle valley juan de fuca ridge burial of midocean ridges by clastic sediments particularly at continental margins profoundly affects the geometry and chemistry of hydrothermal circulation and mineralization in the upper crust middle valley the sediment covered northern extension of the bare rock endeavour segment of the juan de fuca ridge is host to the base metal rich cu zn bent hill massive sulfide deposit at a water depth of 2 400 m the 9 mt bent hill deposit is a steep sided body 200 m across and 100 m thick ocean drilling program odp hole 856h penetrates through the massive sulfide and underlying feeder zone extending to a total depth of 500 m below sea floor through the base of the strongly recrystallized quartz chlorite sediment pile and into the uppermost volcanic basement the basaltic rocks beneath the bent hill deposit include narrow sills intruded into indurated sediments a volcanic flow erupted on top of sediments and pillow lavas below the lowermost sediments recovered similar styles of alteration are present in both the sills and flows and alteration is dominated by the effects of large scale hydrothermal upflow rather than hydrothermal activity associated with individual eruptions or intrusions the basalts are slightly to completely altered to greenschist facies secondary minerals principally quartz chlorite and titanite with subsidiary epidote cu fe sulfides and rare actinolite there are steep mineralogical chemical and isotopic alteration gradients from the highly altered basalt sediment interfaces down to the less altered flow interiors suggesting the channeling of hydrothermal fluids along the basalt sediment boundaries alteration is reflected in intense metasomatic changes in the basalts assuming immobile tio 2 the most intensely altered basalts have undergone about 20 percent mass loss during recrystallization to chlorite quartz rocks with depletions in silica alumina and alkali alkali earth and base metals chloritized pillow margins with strongly light rare earth element enriched chondrite normalized patterns la sm n 1 5 cf fresh basalts 0 7 that mimic profiles for midocean ridge hydrothermal fluids require fluid rock exchange with large quantities of hydrothermal fluid w r 27 000 oxygen isotope compositions of chlorite quartz rocks 18 o 1 8 2 4 suggest that alteration occurred between 320 and 370 c strontium isotope compositions of the altered basalts and the chlorite quartz rocks are not homogeneous and range from 87 sr 86 sr ratio 0 7037 to 0 7046 there is a strong mode in 87 sr 86 sr ratio at 0 7038 suggesting that much of the alteration occurred by isotopic exchange with a hydrothermal fluid of that composition this ratio is significantly lower than that measured for 265 c fluids venting from the nearby odp mound 87 sr 86 sr 0 7044 the occurrence of epidote and isocubanite in the chloritized glassy pillow margins suggests that these rocks may retain a record of the high temperature 350 c hydrothermal fluid responsible for the formation of the overlying bent hill massive sulfide deposit the strontium isotope composition of the chloritized glassy pillow margins and hence the mineralizing fluid is slightly more radiogenic 87 sr 86 sr 0 7046 this composition could result from the addition of 15 percent of a pelagic or sedimentary component to the 87 sr 86 sr ratio 0 7038 fluid responsible for most of the sr isotope exchange with the upper basement the sediments beneath the bent hill deposit are also strongly recrystallized to quartz and chlorite although their strontium isotope compositions are much lower than those in pelagic or terrigenous sediments in the region 87 sr 86 sr 0 709 0 720 the range of compositions 87 sr 86 sr 0 7046 0 7060 has little overlap with that of the altered basalts and chlorite quartz rocks from the sills and uppermost basement this lack of overlap suggests that the sediments either retain some of their original sedimentary strontium or that there is a range of fluid compositions in the sediment pile beneath the bent hill deposit sediments from the margins of middle valley far from zones of active black smoker venting odp site 855 have 87 sr 86 sr ratios with a significant hydrothermal component 0 7059 0 7086 these ratios indicate that the subsurface hydrology of middle valley is dominated by evolved fluids rather than seawater and that recharge into this system is not through boundary faults or through the sedimentary blanket as suggested by previous models rather exposed basement rocks that form the flanks of middle valley are the most likely zones of regional seawater recharge to the deep high temperature hydrothermal systems

uranium thorium helium dating of apatite experience with samples from different geochemical environments abstract u he dating which during its history has been very problematic might find special application in the field of hydrothermal mineralizations where other methods generally fail the mineral apatite is a potential candidate for this method in order to shed light on various aspects of apatite dating by the u th he method two samples each from different geochemical environments plutonic pneumatolytic and hydrothermal were probed isotope dilution techniques were used for concentration analyses from which 4he model dates also called helium indices after n b keevil were calculated 4he diffusion measurements were carried out for comparison of the 4he retentivities between the samples comparisons of the apatite he indices with plausible reference ages of the sampling locations in combination with results obtained from diffusion experiments show that the u th he dating method applied to apatite yields an age of cooling rather than an emplacement age the calculated closure temperatures are similar to those obtained by the fission track method 100 c our results suggest that the high temperature apatites plutonic and pneumatolytic may be more suitable for he dating than hydrothermal apatite important criteria for the dating of apatite by u th he are the presence of moderate radionuclide concentrations tens of ppm and a minimum abundance of inclusions

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

polar lightning and decadal scale cloud variability on jupiter although lightning has been seen on other planets including jupiter polar lightning has been known only on earth optical observations from the new horizons spacecraft have identified lightning at high latitudes above jupiter up to 80 n and 74 s lightning rates and optical powers were similar at each pole and the mean optical flux is comparable to that at nonpolar latitudes which is consistent with the notion that internal heat is the main driver of convection both near infrared and ground based 5 micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 cassini flyby particularly in the turbulent wake of the great red spot and in the southern half of the equatorial region demonstrating that vertical dynamical processes are time varying on seasonal scales at mid and low latitudes on jupiter

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

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

new insights into the carrier phase s of extraterrestrial 3he in geologically old sediments to better understand the composition characteristics of helium diffusion and size distribution of interplanetary dust particles idps responsible for the long term retention of extraterrestrial 3he we carried out leaching stepped heating and sieving experiments on pelagic clays that varied in age from 0 5 ma to 90 myr the leaching experiments suggest that the host phase s of 3he in geologically old sediments are neither organic matter nor refractory phases such as diamond graphite al2o3 and sic but are consistent with extraterrestrial silicates fe ni sulfides and possibly magnetite stepped heating experiments demonstrate that the 3he release profiles from the magnetic and non magnetic components of the pelagic clays are remarkably similar because helium diffusion is likely to be controlled by mineral chemistry and structure the stepped heating results suggest a single carrier that may be magnetite or more probably a phase associated with magnetite furthermore the stepped outgassing experiments indicate that about 20 of the 3he will be lost through diffusion at seafloor temperatures after 50 myrs while sedimentary rocks exposed on the earth s surface for the same amount of time would lose up to 60 the absolute magnitude of the 3he loss is however likely to depend upon the 3he concentration profile within the idps which is not well known contrary to previous suggestions that micrometeorites in the size range of 50 100 m in diameter are responsible for the extraterrestrial 3he in geologically old sediments stuart f m harrop p j knott s turner g 1999 laser extraction of helium isotopes from antarctic micrometeorites source of he and implications for the flux of extraterrestrial 3he flux to earth geochim cosmochim acta63 2653 2665 our sieving experiment demonstrates that at most 20 of the 3he is carried by particles greater than 50 m in diameter the size distribution of the 3he bearing particles implies that extraterrestrial 3he in sediments record the idp flux rather than the micrometeorite flux

miocene crustal extension and uplift in southeastern nevada constraints from fission track analysis the gold butte block of southeastern nevada appears to be a cross section through the upper approximately 17 km of colorado plateau crust tilted eastward and tectonically denuded via top to the west normal faulting in tertiary time the east side of the block exposes a steeply dipping cratonic paleozoic section 2 to 3 km thick proterozoic basement to the west is continuously exposed for an apparent thickness of approximately 15 km structurally below the basal cambrian unconformity apatite fission track dating and confirmed track length distributions have been used to determine the time of unroofing of the gold butte block and hence the timing of one episode of extension in this part of the basin and range province samples collected in as east west transect along the block indicate an abrupt transition from a period of relative thermal and tectonic stability to the onset of rapid cooling the fission track data indicate that the unroofing of the gold butte block was rapid and that the crustal section was brought to within a few kilometers of the surface at ca 15 ma

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

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

measurements of martian dust devil winds with hirise 1 we report wind measurements within martian dust devils observed in plan view from the high resolution imaging science experiment hirise orbiting mars the central color swath of the hirise instrument has three separate charge coupled devices ccds and color filters that observe the surface in rapid cadence active features such as dust devils appear in motion when observed by this region of the instrument our image animations reveal clear circulatory motion within dust devils that is separate from their translational motion across the martian surface both manual and automated tracking of dust devil clouds reveal tangential winds that approach 20 30 m s 1 in some cases these winds are sufficient to induce a 1 decrease in atmospheric pressure within the dust devil core relative to ambient facilitating dust lifting by reducing the threshold wind speed for particle elevation finally radial velocity profiles constructed from our automated measurements test the rankine vortex model for dust devil structure our profiles successfully reveal the solid body rotation component in the interior but fail to conclusively illuminate the profile in the outer regions of the vortex one profile provides evidence for a velocity decrease as a function of r 1 2 instead of r 1 suggestive of surface friction effects however other profiles do not support this observation or do not contain enough measurements to produce meaningful insights

life cycles of spots on jupiter from cassini images using the sequence of 70 day continuum band 751 nm images from the cassini imaging science system iss we record over 500 compact oval spots and study their relation to the large scale motions the 100 spots whose vorticity could be measured the large spots in most cases were all anticyclonic we exclude cyclonic features chaotic regions because they do not have a compact oval shape but we do record their interactions with spots we distinguish probable convective storms from other spots because they appear suddenly grow rapidly and are much brighter than their surroundings the distribution of lifetimes for spots that appeared and disappeared during the 70 day period follows a decaying exponential with time constant mean lifetime of 3 5 days for probable convective storms and 16 8 days for all other spots extrapolating the exponential beyond 70 days seriously underestimates the number of spots that existed for the entire 70 day period this and other evidences size shape distribution in latitude suggest that these long lived spots with lifetime larger than 70 days are from a separate population the zonal wind profile obtained manually by tracking individual features this study agrees with that obtained automatically by correlating brightness variations in narrow latitude bands porco et al 2003 some westward jets have developed more curvature and some have developed less curvature since voyager times but the number of westward jets that violate the barotropic stability criterion is about the same in the northern hemisphere the number of spots is greatest at the latitudes of the westward jets which are the most unstable regions according to the barotropic stability criterion during the 70 day observation period the great red spot grs absorbed nine westward moving spots that originated in the south equatorial belt seb where most of the probable convective storms originate although the probable convective storms do not directly transform themselves into westward moving spots their common origin in the seb suggests that moist convection and the westward jet compose a system that has maintained the grs over its long lifetime

global context of the galileo e6 observations of jupiter s white ovals galileo solid state imaging ssi data taken during the e6 orbit on february 19 1997 offer a brief high resolution glimpse of jupiter s white ovals these data can be used to infer relative cloud heights and systematic rotations over a small area of latitude and longitude approximately 20 by 30 around the white ovals to fully understand the behavior of these cloud systems however a longer time span of global data is necessary in this paper we utilize ground based voyager and hubble space telescope data to interpret the galileo images we find that the white ovals translation rates have slowed from 0 39 deg day 1during the voyager era to 0 13 deg day 1in 1996 and they along with three smaller anticyclonic systems have coalesced into a system of alternating cyclonic and anticyclonic systems that has not been observed before the largest of the ovals bc is now impeding the eastward motion of the system causing more rapidly translating anticyclonic cells to catch the system and increase the westward extension of the equally spaced features rotational velocities for bc and a small anticyclonic system at 42 s have also been measured and peak at 120 m sec 1for both systems comparable to the mitchellet al j geophys res 86 8751 8757 measurements of bc and the great red spot grs from voyager data the motion of individual features and of the whole system in the ambient wind flow is discussed

quantifying the diffusion kinetics and spatial distributions of radiogenic 4he in minerals containing proton induced 3he apatite titanite and olivine samples were bombarded with a 150 mev proton beam to produce 10 8 atoms mg of spallation 3he high precision stepped heating experiments were then performed in which the artificial 3he and for apatite and titanite the natural radiogenic 4he were measured to characterize the diffusive behavior of each isotope helium 3 diffusion coefficients are in excellent agreement with concurrently and or previously determined he diffusion coefficients for each mineral our results indicate that proton induced 3he is uniformly distributed and that radiation damage associated with a proton fluence of 5 x 10 14 protons cm 2 does not cause noticeable changes in 4he diffusion behavior in at least apatite and titanite proton induced 3he can therefore be used to establish he diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural 4he distribution is inhomogeneous in addition step heating 4he 3he analysis of a mineral with a uniform synthetic 3he concentration provides a means by which a natural 4he distribution can be determined

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

color and the vertical structure in jupiter s belts zones and weather systems abstract radiative transfer analysis was performed with data taken by the galileo spacecraft solid state imager ssi during its nominal mission december 1995 to december 1997 the objective is to use the methane band 727 and 889 nm and color 410 and 756 nm sensitivities to identify the vertical position of cloud absorption that leads to coloration earlier work banfield et al 1998 icarus 135 230 250 with only the near ir continuum and methane band images yielded information about the vertical distribution of cloud scatterers but no information on the wavelength dependence of cloud absorption the new analysis employs the same parameter retrieval algorithm but adds the 410 nm wavelength under the assumption that the 410 nm absorption by cloud particles is indicative of spectrally broad blue absorption the new channel gives color information the primary color difference between the dark north equatorial belt neb and the brighter equatorial zone ez appears to be in the tropospheric haze layer s 410 nm single scattering albedo this layer extends through the stably stratified region approximately from 200 to 800 mbars the base of the haze layer is slightly deeper in the neb by about 200 mbars than in the ez and a variable thickness white cloud layer at the base of the haze exists in both regions but is about five times optically thicker in the ez within the ez slight color variation is seen with latitude again due to 410 nm single scattering albedo variation in the haze layer anomalous regions such as the great red spot and a 5 m hot spot are modeled showing additional variations in the structure and color of the tropospheric haze deeper clouds with pressures of 1 7 bars are seen in occasional clearings but their opacity and color are not well constrained by the data

spatial extent of rapid denudation in the glaciated st elias syntaxis region se alaska 1 the ongoing collision of the yakutat terrane with the north american plate formed the st elias range in southeastern alaska previously published detrital zircon fission track dating of sand size material detected very rapid rock denudation within the syntaxis region of the st elias range but the size and spatial extent of the rapid exhumation are elusive due to the glacial cover that inhibits direct bedrock studies two possible mechanisms were suggested to explain the rapid denudation occurring underneath the seward malaspina glacier which differ in their spatial extent of rapidly exhumed rocks this study evaluates the spatial extent of rapid denudation at the st elias syntaxis region we investigate the cobble sized material of the malaspina glacier petrological classifications are used as a provenance tool and combined with zircon and titanite u th he analysis to reveal cooling rates of the glacial detritus in total 1998 cobbles are classified in the field petrographic characterization is conducted on 91 thin sections and the u th he ages of 59 cobbles are measured fourteen cobbles reveal young cooling ages of 3 2 ma originating from various lithologies of undeformed and deformed magmatic and metamorphic rocks older age populations peak at 12 27 and 36 ma the cooling ages and the mapped known extent of the different lithologies suggest that a larger then previously assumed area of the st elias syntaxis region experienced rapid exhumation rapid rock exhumation extends beyond the contact fault and comprises most of the seward malaspina glacier catchment

a comparative study of jovian cyclonic features from a six year 1994 2000 survey abstract this work presents a six year study aimed at characterizing the morphology and properties of the atmospheric features present in jovian cyclonic regions it complements our previous analysis for the same period on the anticyclonic vortices morales juberias et al 2002 icarus 157 76 90 the main difference between cyclonic and anticyclonic regions in jupiter is that a variety of organized morphologies are present in the cyclonic areas although they can be grouped consistently into five different types filamentary turbulence related to the highest speed jets organized folded filamentary regions elongated areas with contours closed by a ribbon like feature discrete closed brown cyclones barges and peculiar transient structures such as short wave trains and cyclonic cells we present data on their color contrast size aspect ratio distribution lifetimes relation to the jet system and to the anticyclones and motions global and internal to the features most cyclonic features show a rapid evolution compared to the anticyclones and tend to be dispersed zonally although some survive for a few years we used the barges that are the most representative long lived and extended type of cyclonic features to show that there exists a linear relationship between their relative velocity and the mean zonal flow speed similar to that found in our previous work on the anticyclones there is also some evidence that the drift rate of barges is related to the planetary minus flow vorticity gradient

dating topography of the sierra nevada california using apatite u th he ages the upward motion of rock masses relative to the earth s surface has been documented for most of the main mountain belts using thermochronological and petrological techniques more fundamental to the physical processes of mountain building however is the motion of the earth s surface itself which remains elusive here we describe a technique for estimating the age of topographic relief by mapping the low temperature thermal structure imparted by river incision using the ages of apatites determined from their uranium thorium and helium contents the technique exploits horizontal variations in temperature in the shallow crust that result from range normal river drainages because cooling beneath ancient river valleys occurs earlier than beneath intervening ridges our results from the sierra nevada california indicate that two of the modern transverse drainages the kings and the san joaquin had developed deep canyons by the late cretaceous period suggesting that the high topography of the range is 50 60 million years older than generally thought

low temperature anisotropic diffusion of helium in zircon implications for zircon u th he thermochronometry abstract in the last decade the zircon u th he zhe thermochronometer has been applied to a variety of geologic problems although bulk diffusion coefficients for he in zircon are available from laboratory step heating experiments little is known about the diffusion mechanism s and their dependence on the crystallographic structure of zircon here we investigate the diffusion of he in perfectly crystalline zircon using atomistic simulation methods that provide insights into the structural pathways of he migration in zircon empirical force fields and quantum mechanical calculations reveal that the energy barriers for he diffusion are strongly dependent on structure the most favorable pathway for he diffusion is the 0 0 1 direction through the open channels parallel to the c axis e 001 13 4 kj mol 1 activation energy for tracer diffusion of a he atom along 0 0 1 in contrast energy barriers are higher in other directions where narrower channels for he diffusion are identified such as 1 0 0 1 0 1 and 1 1 0 e of 44 8 101 7 and 421 3 kj mol 1 respectively molecular dynamics simulations are in agreement with these results and provide additional insight in the diffusion mechanisms along different crystallographic directions as well as the temperature dependence below the closure temperature of he in zircon t c 180 c reiners p w spell t l nicolescu s and zanetti k a 2004 zircon u th he thermochronometry he diffusion and comparisons with ar 40 ar 39 dating geochim cosmochim acta 68 1857 1887 diffusion is anisotropic as he moves preferentially along the 0 0 1 direction and calculated tracer diffusivities along the two most favorable directions differ by approximately five orders of magnitude d 001 d 100 10 5 at t 25 c above this temperature he atoms start to hop between adjacent 0 0 1 channels along 1 0 0 and 0 1 0 directions perpendicular to the c axis the diffusion along 1 0 0 and 0 1 0 is thermally activated such that at higher temperatures he diffusion in zircon becomes nearly isotropic d 001 d 100 10 at t 580 c these results suggest that the anisotropic nature of he diffusion at temperatures near the closure temperature should be considered in future diffusivity experiments furthermore care should be taken when making geologic interpretations e g exhumation rates timing of cooling etc from this thermochronometer until the effects of anisotropic diffusion on bulk ages and closure temperature estimates are better quantified

hematite and mn oxide u th he dates from the buckskin rawhide detachment system western arizona gaining insights into hematite u th he systematics

the evolving flow of jupiter s white ovals and adjacent cyclones abstract we present results regarding the dynamical meteorology of jupiter s white ovals at different points in their evolution starting from the era with three white ovals fa bc and de galileo continuing to the post merger epoch with only one oval ba cassini and finally to oval ba s current reddened state new horizons we demonstrate that the dynamics of their flow have similarly evolved along with their appearance in the galileo epoch oval de had an elliptical shape with peak zonal wind speeds of 90 m s 1 in both its northern and southern peripheries during the post merger epoch oval ba s shape was more triangular and less elliptical than oval de in addition to widening in the north south direction its northern periphery was 20 m s 1 slower and its southern periphery was 20 m s 1 faster than oval de s flow during the galileo era finally in the new horizons era the reddened oval ba had evolved back to a classical elliptical form the northern periphery of oval ba increased in speed by 20 m s 1 from cassini to new horizons ending up at a speed nearly identical to that of the northern periphery of oval de during galileo however the peak speeds along the southern rim of the newly formed oval ba were consistently faster than the corresponding speeds in oval de and they increased still further between cassini and new horizons ending up at 140 150 m s 1 relative vorticity maps of oval ba reveal a cyclonic ring surrounding its outer periphery similar to the ring present around the great red spot the cyclonic ring around oval ba in 2007 appears to be moderately stronger than observed in 1997 and 2001 suggesting that this may be associated with the coloration of the vortex the modest strengthening of the winds in oval ba the appearance of red aerosols and the appearance of a turbulent cyclonic feature to oval ba s northwest create a strong resemblance with the great red spot from both a dynamical and morphological perspective in addition to the white ovals we also measure the winds within two compact cyclonic regions one in the galileo data set and one in the cassini data set in the images these cyclonic features appear turbulent and filamentary but our wind field reveals that the flow manifests as a coherent high speed collar surrounding relatively quiescent interiors our relative vorticity maps show that the vorticity likewise concentrates in a collar near the outermost periphery unlike the white ovals which have peak relative vorticity magnitudes near the center of the vortex the cyclones contain several localized bright regions consistent with the characteristics of thunderstorms identified in other studies although less studied than their anticyclonic cousins these cyclones may offer crucial insights into the planet s cloud level energetics and dynamical meteorology

oscillations and velocity structure of a long lived cyclonic spot dark brown cyclonic spots barges at 14 n were studied by using voyager 1 and 2 images of jupiter movie sequences were made to study the spots behavior over intervals of 50 days and longer these movies revealed that the length and width vary by 9 with a period of about 15 days while the area remains approximately constant the horizontal velocity field was investigated for an interval of about 1 day flow around the largest barge feature 6 occurs as a ring current the vorticity inferred is about 2 times that of the ambient cyclonic zonal circulation and about one half the value of the local planetary vorticity length and width variations appear to be associated with a nonzero horizontal divergence field if the oscillations are a natural mode of the system the 15 day period will provide an important datum for testing models of stable closed vortices

solving the production diffusion equation for finite diffusion domains of various shapes part i implications for low temperature u th he thermochronology abstract we propose an accurate fast and easy to use method to derive numerical solutions for production diffusion equations for finite diffusion domains of various shapes and arbitrary cooling histories previous studies provide solutions for spheres infinite cylinders and infinite sheets we extend this range and provide solutions for finite bodies i e finite cylinders and rectangular blocks of any aspect ratio this approach is important as recently it has become clear that for example the physical grain is the diffusion domain for he diffusion in apatite and titanite j geophys res 105 2000 2903 geochim cosmochim acta 63 1999 3845 we discuss the use of the new approach for forward modelling u th he production diffusion in apatite taking results with finite cylinders as a good approximation for apatite crystals it is found that approximating instead with spheres or infinite cylinders having the same radius yields differences in calculated ages that can easily be as large as 20 35 the relative differences are most pronounced in thermal histories that spend significant time at or near the closure temperature on the other hand reasonable agreement is found with spheres having the same surface to volume ratio

helium and argon thermochronometry of the gold butte block south virgin mountains nevada one of the largest exposures of precambrian crystalline rock in the basin and range province of the southwestern usa is the gold butte block of the south virgin mountains about 15 km west of the colorado plateau it has been interpreted as a largely continuous crustal cross section about 15 20 km thick that was exhumed by a deeply penetrating normal fault during miocene extension to test this interpretation as well as the use of the newly developed titanite u th he thermochronometer we examined the low temperature thermal history of the gold butte block with the apatite and titanite u th he and muscovite 40 ar 39 ar thermochronometers apatite he ages average 15 2 1 0 2 ma throughout the block indicating that the entire section was warmer than 70 c prior to miocene exhumation titanite he ages increase from 18 6 1 5 ma near the paleobottom west end of the block to 195 15 ma near the paleotop east end a rapid change from mid tertiary to increasingly older titanite he ages to the east is observed at about 9 3 km paleodepth and is interpreted as a fossil he partial retention zone for titanite assuming a pre exhumation geotherm of 20 c km consistent with earlier apatite fission track work this depth would have corresponded to 196 c prior to exhumation indicating that laboratory derived he diffusion characteristics for titanite that yield a closure temperature of about 200 c are applicable and correct muscovite 40 ar 39 ar ages are 1 0 1 4 ga near the paleotop of the block and 90 ma near the paleobottom together with 207 pb 206 pb ages on apatite and titanite and an earlier apatite fission track transect across the gold butte block our data indicate that the continental crust at the western edge of the colorado plateau resided at moderate geothermal gradients and slowly declined in temperature from 1 4 ga to about 100 200 ma a 90 ma cooling event clearly affected the mid crust deepest portions of gold butte which may reflect accelerated cooling or a brief heating and cooling cycle at this time after which gradients returned to about 20 c km prior to rapid exhumation in the miocene this work thus supports previous structural and thermochronologic studies that suggest that the gold butte block is the thickest largely continuous cross section of crust exposed in the southwestern usa

galileo imaging of jupiter s atmosphere the great red spot equatorial region and white ovals during the first six orbits of the galileo spacecraft s prime mission the solid state imaging ssi system acquired multispectral image mosaics of jupiter s great red spot an equatorial belt zone boundary a 5 m hot spot similar to the galileo probe entry site and two of the classic white ovals we present mosaics of each region approximating their appearance at visible wavelengths and showing cloud height and opacity variations the local wind field is derived by tracking cloud motions between multiple observations of each region with time separations of roughly 1 and 10 hr vertical cloud structure is derived in a companion paper by banfieldet al icarus135 230 250 galileo s brief high resolution observations complement earth based and voyager studies and offer local meteorological context for the galileo probe results our results show that the dynamics of the zonal jets and large vortices have changed little since voyager with a few exceptions we detect a cyclonic current within the center of the predominantly anticyclonic great red spot the zonal velocity difference between 0 s and 6 s has increased by 20 m sec 1 we measure a strong northeast flow approaching the hot spot this flow indicates either massive horizontal convergence or the presence of a large anticyclonic vortex southeast of the hot spot the current compact arrangement of two white ovals and a cyclonic structure greatly perturbs the zonal jets in that region

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

tracking eolian dust with helium and thorium impacts of grain size and provenance reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples more recently dust fluxes have been estimated from measurements of helium and thorium as rare isotopes of these elements he 3 and th 230 allow estimates of sediment flux and the dominant isotopes he 4 and th 232 are uniquely associated with the lithogenic fraction of marine sediments in order to improve the fidelity of dust flux reconstructions based on he and th we present a survey of he and th concentrations in sediments from dust source areas in east asia australia and south america our data show systematic relationships between he and th concentrations and grain size with he concentrations decreasing and th concentrations increasing with decreasing grain size we find consistent he and th concentrations in the fine fraction 5 m of samples from east asia australia and central south america puna central west argentina with th concentrations averaging 14 g g and he concentrations averaging 2 cc stp g we recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine grained and suggest that previous studies may have systematically overestimated th based dust fluxes by 30 source areas in patagonia appear to have lower he and th contents than other regions as fine fraction concentrations average 0 8 cc stp g and 9 g g for 4he and 232th respectively the impact of grain size on lithogenic he and th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably our data also have important implications for the hosts of he in long traveled dust and for the 3he 4he ratio used for terrigenous he in studies of extraterrestrial he in sediments and ice we also investigate the use of he th ratios as a provenance tracer our results suggest differences in fine fraction he th ratios between east asia australia central south america and patagonia with ratios showing a positive relationship with the geological age of source rocks he th ratios may thus provide useful provenance information for example allowing separation of patagonian sources from puna central west argentina or australian dust sources he th ratios in open ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas he th ratios in mid latitude south atlantic sediments suggest that dust in this region primarily derives from the puna central west argentina region 23 32 s rather than patagonia 38 s in the equatorial pacific he th ratios are much lower than in extratropical pacific sediments or potential source areas measured as a part of this study east asia south america australia for reasons that are at present unclear complicating their use as provenance tracers in this region

mesoproterozoic burial of the kaapvaal craton southern africa during rodinia supercontinent assembly from u th he thermochronology abstract we present the and zhe data for basement samples across the kaapvaal craton to investigate the cratonic burial and erosion history during the assembly and breakup of the rodinia supercontinent the and zhe dates vary from 1187 to 135 ma and 997 to 32 ma respectively both are negatively correlated with effective u concentration consistent with lower he retentivity at higher radiation damage dose the oldest the dates combined with volcanic rocks that document the basement was at the surface at 1 4 ga require heating to 130 c at 1 0 1 2 ga to cause complete he loss from the titanites we attribute this mesoproterozoic heating event to widespread burial of the craton during rodinia supercontinent assembly by sediments shed from the namaqua natal orogen on the craton s margin later neoproterozoic paleozoic erosion re exhumed the basement to the surface spatial variability in zhe data patterns can be explained by geologically reasonable differences in phanerozoic karoo basin burial and erosion the mesoproterozoic and karoo burial phases are analogous in that their detritus was derived from similarly located orogens during two different supercontinent cycles mesoproterozoic deposition across the kaapvaal craton may be part of a more global signal of burial and erosion during rodinia assembly and breakup our dataset illustrates the power of the and zhe thermochronology for detecting missing proterozoic depositional events in the rock record

conodont u th he thermochronology initial results potential and problems abstract we performed he diffusion experiments and u th he age determinations on conodonts from a variety of locations to explore the potential of conodont u th he thermochronology to constrain thermal and exhumation histories of some sedimentary rock dominated terrains based on two diffusion experiments and age results from some specimens he diffusion in conodont elements appears to be similar to that in durango apatite fragments of similar size and closure temperatures are approximately 60 70 c for cooling rates of 10 c m y u th he ages of conodonts from some locations yield reproducible ages consistent with regional thermal history constraints and in at least two cases require a closure temperature lower than 80 c other samples however yield irreproducible ages and in one case yield ages much younger than expected based on regional geologic considerations these irreproducible samples show inverse correlations between parent nuclides and age consistent with late stage open system u th behavior

influence of radiation damage on titanite he diffusion kinetics titanite is a common u th bearing accessory mineral that previous study suggested has a u th he closure temperature tc of 210 175 c although it has been recognized that radiation damage influences the he retentivity of apatite and zircon this effect has not been documented in titanite we acquired 51 the analyses from 11 archean basement samples across the kaapvaal craton south africa the the dates range from 20 to 1200 ma and are negatively correlated with their 10 970 ppm span of effective uranium concentration eu raman spectra acquired for 4 of these samples display peak broadening with increasing eu 4he diffusion experiments on the same 4 samples suggest tc values that vary by 175 c estimated alpha dose versus tc for our results and published the diffusion data document tc values of 150 210 c at alpha doses 50 1016 g with a sharp decrease in he retentivity above this threshold this damage diffusivity pattern is similar to zircon but the damage level at which the reduction in retentivity occurs appears to be lower for titanite because titanite typically has substantially lower eu than zircon for the same protracted thermal history the dates are likely to record higher temperature portions of the history than zircon u th he dates the results demonstrate that the dating can access a much larger temperature range and potentially be used to decipher more detailed time temperature paths than previously thought

prediction of a global climate change on jupiter jupiter s atmosphere as observed in the 1979 voyager space craft images is characterized by 12 zonal jet streams and about 80 vortices the largest of which are the great red spot and three white ovals that had formed1 in the 1930s the great red spot has been observed2 continuously since 1665 and given the dynamical similarities between the great red spot and the white ovals the disappearance3 4 of two white ovals in 1997 2000 was unexpected their longevity and sudden demise has been explained5 however by the trapping of anticyclonic vortices in the troughs of rossby waves forcing them to merge here i propose that the disappearance of the white ovals was not an isolated event but part of a recurring climate cycle which will cause most of jupiter s vortices to disappear within the next decade in my numerical simulations the loss of the vortices results in a global temperature change of about 10 k which destabilizes the atmosphere and thereby leads to the formation of new vortices after formation the large vortices are eroded by turbulence over a time of 60 years consistent with observations of the white ovals until they disappear and the cycle begins again

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

gold butte crustal section south virgin mountains nevada the gold butte block consists of a complex of proterozoic medium to high grade metamorphic and plutonic rocks unconformably overlain by steeply east dipping paleozoic sedimentary rocks on its east side this complex is one of the largest continuous exposures of crystalline rocks in the southwestern united states that lie structurally beneath a steeply tilted section of phanerozoic strata and it may represent part of an intact proterozoic miocene crustal section reaching paleodepths of approximately 15 km the section was exposed during tectonic denudation in miocene time at about 15 ma and lies directly adjacent to the colorado plateau to the east proterozoic and tertiary geological features support the hypothesis that the block represents a relatively intact crustal section a large exposure of proterozoic rapakivi granite the gold butte granite circa 1 45 ga crops out over most of the crystalline complex and displays strong zoning in phenocryst abundance which increases toward the top of a 10 to 12 km thick magma chamber the wallrocks of the granite are predominantly garnet bearing gneisses circa 1 7 ga which display increasing pressures of final equilibration westward away from the basal phanerozoic unconformity thermobarometry of gneisses immediately beneath the unconformity indicate pressures of 2 3 kbar whereas those 12 13 km west of the unconformity yield pressures of 5 6 kbar suggesting the crustal section was established by 1 7 ga the style of deformation displayed by denudation structures also varies from east to west with brittle faulting only in eastern portions of the block and retrograde metamorphism mylonitization and chlorite brecciation of the garnet gneiss observed in western areas

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

positioning the titanite fission track partial annealing zone abstract as part of the ktb kontinentale tiefbohrung programme in germany titanite sphene fission track data were acquired for samples to a depth of 9000 m where the host rock temperature is 265 c at this depth age and confined track length information suggest that the partial annealing zone for the fission tracks in titanite was not reached by reconstructing the thermal history and backstacking of an uplifted partial annealing zone it is suggested that the in situ partial annealing zone is likely to be found in the region 265 310 c this value is more precise than previous estimates of the titanite partial annealing zone and it is also higher than previous estimates microprobe analysis indicates that the chemical composition of the titanites is rather homogeneous throughout the whole drilled section

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

40ar 39ar and u th he 4he 3he geochronology of landscape evolution and channel iron deposit genesis at lynn peak western australia u th he geochronology of authigenic goethite cements from the lynn peak channel iron deposit cid hamersley province western australia reveals a history of mineral precipitation ranging from ca 33 to 14 ma massive goethites from nearby weathering profiles at roy hill north a possible source of detrital material during the aggradation of the lynn peak channels yield u th he results as old as ca 64 ma the combination of u th he geochronology with incremental outgassing 4he 3he studies on proton irradiated samples reveals that lynn peak goethites host radiogenic 4he in low retentivity lrd and high retentivity hrd domains and that the hrds account for most of the sample mass and have lost very little of their original 4he over geologic time such high retentivity is especially notable given the goethites were collected from the surface where they were subject to significant heating by solar irradiation minor contamination by detrital fragments of potentially 4he rich primary phases e g rutile ilmenite zircon occurs in some samples fortunately the 4he 3he method permits characterization of this extraneous 4he component which is small 10 wt of the total 4he in the goethite and can be corrected out in estimating the goethite formation age these results indicate that the lynn peak channel was already aggraded and undergoing goethite cementation by ca 33 ma the history of aggradation and channel cementation independently measured through 40 ar 39 ar geochronology is consistent with that obtained from the u th he and 4he 3he record laser incremental heating 40 ar 39 ar geochronology of detrital and authigenic mn oxides primarily cryptomelane kmn 8o 16 xh 2o from the same locality in the lynn peak channel reveals that detrital oxides are older than ca 44 ma and as old as ca 65 ma and authigenic oxides are younger than ca 35 ma and as young as ca 16 ma authigenic cryptomelane precipitation and channel cementation occurred throughout the miocene with a particularly strong period at around 20 ma the 40 ar 39 ar geochronological results suggest that regional weathering profiles developed before 44 ma and possibly as early as ca 65 ma were incised and partially eroded in the 44 35 ma interval semi arid conditions promoted the transport of large volumes of sediments aggrading the regional drainage system metasomatic reactions in the aggraded channels caused the ferruginization and in some places manganese replacement of the cids goethite and k mn oxide cementation continued throughout the oligocene and miocene post miocene aridification contributed to the preservation of the cemented channel sediments forming some of the largest readily mineable iron ore deposits on earth

helium diffusion in rutile and titanite and consideration of the origin and implications of diffusional anisotropy abstract diffusion of helium has been characterized in natural sphene titanite and synthetic rutile polished slabs of sphene and rutile were implanted with 100 kev 3he at a dose of 5 1015 3he cm2 and annealed in 1 atm furnaces 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in rutile we obtain the following arrhenius relations d a 2 26 1 0 1 0 exp 126 11 kj mol 1 rt m 2 sec 1 d c 1 75 1 0 8 exp 12 0 7 kj mol 1 rt m 2 sec 1 although activation energies for diffusion parallel to the c and a axes are comparable there is marked diffusional anisotropy with diffusion parallel to the c axis about 2 orders of magnitude faster than transport parallel to the a axis these diffusivities bracket the values determined for he diffusion in rutile in bulk release experiments stockli et al 2005 stockli et al 2007 wolfe 2009 although the role of anisotropy could not be directly evaluated in those measurements in titanite the following arrhenius relation was obtained over the temperature range 252 550 c for diffusion parallel to the a axis d 2 14 1 0 6 exp 148 8 kj mol 1 rt m 2 sec 1 in contrast to rutile and zircon cherniak et al 2009 titanite shows little evidence of anisotropy as diffusivities parallel to the a and c axes are similar and diffusivities for titanites from two different localities are similar he diffusion coefficients obtained in this study are similar to those measured through bulk release of he by step heating shuster et al 2003 over the investigated temperature range diffusion of he in titanite is similar to that of he diffusion in rutile parallel to the c axis but much faster than diffusion parallel to the a axis since the diffusion of he in rutile exhibits such pronounced anisotropy we model diffusional loss of he with a recently developed finite element code watson et al 2010 created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients we present example applications to evaluate helium losses from rutile grains as a function of grain size and length to diameter ratios in efforts to better understand the occurrence of pronounced anisotropy for he diffusion in some crystals e g rutile zircon but not in others e g apatite titanite we consider the density and distribution of interstitial apertures in the crystal structure that might permit he migration these determinations an extension of the concept of ionic porosity are consistent with observations of relative diffusivities and the existence or absence of significant anisotropy for the minerals rutile zircon apatite and titanite

cenozoic thermal evolution of the central sierra nevada california from uth he thermochronometry apatite u th he cooling ages are reported for igneous apatite samples from the central sierra nevada and compared to published apatite fission track ages and track length data from the same mineral separates helium ages are youngest at low elevations and increase systematically toward higher elevations ranging from 43 to 84 ma at yosemite valley 32 to 74 ma at kings river canyon and 23 to 75 ma at mt whitney helium ages from high elevation samples are generally concordant with corresponding fission track ages while lower elevation helium ages are substantially younger cooling histories inferred from present laboratory derived fission track annealing and helium diffusion models do not match well suggesting that either helium diffusion rates or fission track annealing rates are miscalibrated at temperatures below about 60 c for geologic exposure periods unlike the fission track results the helium data do not indicate a very low geothermal gradient in the sierra nevada during early to middle tertiary time

diffusion of helium in zircon and apatite abstract diffusion of helium has been characterized in natural zircon and apatite polished slabs of zircon and apatite oriented either normal or parallel to c were implanted with 100 kev 3he at a dose of 5 1015 3 he cm2 diffusion experiments on implanted zircon and apatite were run in pt capsules in 1 atm furnaces 3he distributions following experiments were measured with nuclear reaction analysis using the reaction 3he d p 4he for diffusion in zircon we obtain the following arrhenius relations d c 2 3 10 7 exp 146 11 kj mol 1 r t m 2 s 1 d c 1 7 10 5 exp 148 17 kj mol 1 r t m 2 s 1 although activation energies for diffusion normal and parallel to c are comparable there is marked diffusional anisotropy with diffusion parallel to c nearly 2 orders of magnitude faster than transport normal to c these diffusivities bracket the range of values determined for he diffusion in zircon in bulk release experiments although the role of anisotropy could not be directly evaluated in those measurements in apatite the following arrhenius relation was obtained over the temperature range of 148 449 c for diffusion normal to c d 2 10 10 6 exp 117 6 kj mol 1 r t m 2 s 1 in contrast to zircon apatite shows little evidence of anisotropy he diffusivities obtained in this study fall about an order of magnitude lower than diffusivities measured through bulk release of he through step heating and within an order of magnitude of determinations where ion implantation was used to introduce helium and he distributions measured with elastic recoil detection since the diffusion of he in zircon exhibits such pronounced anisotropy helium diffusional loss and closure cannot be modeled with simple spherical geometries and the assumption of isotropic diffusion a finite element code cylmod has recently been created to simulate diffusion in cylindrical geometry with differing radial and axial diffusion coefficients we present some applications of the code in evaluating helium lost from zircon grains as a function of grain size and length to diameter ratios and consider the effects of shape anisotropy where diffusion is isotropic as in the case of apatite but shapes of crystal grains or fragments may depart significantly from spherical geometry

an evaluation of low temperature apatite uth he thermochronometry abstract three studies have been conducted to test the usefulness of apatite u th he thermochronometry the first study compared u th he and fission track ages from quickly cooled plutonic rocks having concordant zircon and apatite fission track ages several samples analyzed show good helium retention the second experiment assessed the effect of compositional variations in apatite on closure temperature calculated closure temperatures agree with existing data and show no statistical dependence on composition arrhenius plots for all of the samples show linear trends at low temperatures representing volume diffusion that roll over to more shallowly sloping non linear paths at higher temperatures the roll over temperature appears to increase with increasing cl content in the apatite the third test focused on fluorapatites from the ktb borehole in germany to compare laboratory estimates with diffusion behavior in a natural setting the ktb apatites show a fair amount of scatter and record u th he ages that are younger than or equal to apatite fission track ages indicating a closure temperature less than or equal to that for the apatite fission track method closure temperatures predicted from the scattered data range from 80 120 c 1 c ma cooling rate or 95 135 c 10 c ma cooling rate the low end of this range agrees with our laboratory diffusion estimates for fluorapatite

uplift and erosion of the san bernardino mountains associated with transpression along the san andreas fault california as constrained by radiogenic helium thermochronometry apatite helium thermochronometry provides new constraints on the tectonic history of a recently uplifted crystalline mass adjacent to the san andreas fault by documenting aspects of the low temperature 40 100 c thermal history of the tectonic blocks of the san bernardino mountains in southern california we have placed new constraints on the magnitude and timing of uplift old helium ages 64 21 ma from the large big bear plateau predate the recent uplift of the range and show that only several kilometers of exhumation has taken place since the late cretaceous period these ages imply that the surface of the plateau may have been exposed in the late miocene and was uplifted only 1 km above the mojave desert in the last few myr by thrusting on the north and south a similar range in helium ages 56 14 ma from the higher san gorgonio block to the south suggests that its crest was once contiguous with that of the big bear block and that its greater elevation represents a localized uplift that the big bear plateau did not experience the structure of the san gorgonio block appears to be a gentle antiform based on the geometry of helium isochrons and geologic constraints young ages 0 7 1 6 ma from crustal slices within the san andreas fault zone indicate uplift of a greater magnitude than blocks to the north these smaller blocks probably experienced 3 4 km of uplift at rates 1 5 mm yr in the past few myr and would stand 2 5 km higher than the big bear plateau if erosion had not occurred the greater uplift of tectonic blocks adjacent to and within the san andreas fault zone is more likely the result of oblique displacement along high angle faults than motion along the thrust fault that bounds the north side of the range we speculate that this uplift is the result of convergence and slip partitioning associated with local geometric complexities along this strike slip system transpression thus appears to have been accommodated by both vertical displacement within the san andreas fault zone and thrusting on adjacent structures

forward modeling and interpretation of u th he ages soon after the initial studies on he diffusion in apatite pointed out the use of the u th he system for low temperature geochronology zeitler et al 1987 wolf et al 1996 warnock et al 1997 the potential value of forward modeling for refined interpretation of u th he dating was indicated wolf et al 1998 while the first studies provided evidence for the low closure temperature t c dodson 1973 of the u th he system in apatite for monotonously cooling systems the latter study investigated the sensitivity of the u th he system for a wide range of geologically feasible heating cooling scenarios forward modeling of he accumulation in minerals expanded the use of the u th he geochromometer to geological systems that do not fit one of the main conditions for the meaningful application of the closure temperature concept i e monotonous cooling at a constant rate through t c forward modeling can help to give a meaning to apparent u th he ages from rocks with cooling histories with protracted residence time in the helium partial retention zone heprz e g 40 85 c in apatite wolf et al 1998 where the closure temperature is undefined fig 1 figure 1 apatite he age evolution curves dotted lines for several representative time temperature paths solid lines forward modelling was conducted using the crank nicolson method for spheres of 60 m radius note that only for history 2 the closure temperature concept dodson 1973 is defined and the age obtained relates to passing through a point t c on the time temperature path for histories that are similar to 3 5 which know a protracted residence time in the heprz there is no direct geological meaning of he ages forward modelling is required to give a geological meaning to the apparent ages obtained from he and u th concentrations in samples used with permission of elsevier from wolf

potential vorticity and layer thickness variations in the flow around jupiter s great red spot and white oval bc layer thickness variations in jupiter s atmosphere are investigated by treating potential vorticity as a conserved tracer starting with the horizontal velocity field measured from voyager images fluid trajectories around the great red spot grs and white oval bc are calculated the flow is assumed to be frictionless adiabatic hydrostatic and steady in the reference frame of the vortex absolute vorticity is followed along each trajectory its magnitude is assumed to vary directly as the thickness which is defined as the mass per unit area between potential temperature surfaces to the accuracy of the observations the inferred thickness is a separable function of trajectory and latitude the latitude dependence has positive curvature near the grs and bc the relative variations of thickness with respect to latitude are generally larger than the relative variations of coriolis parameter with respect to latitude the beta effect the data are a useful diagnostic which will help differentiate between models of jovian vortices the present analysis employs a quasi geostrophic model in which a thin upper weather layer which contains the vortex is supported hydrostatically by a much deeper lower layer in this model the upper free surface does not contribute to the observed variation of thickness along trajectories such variations are due exclusively to bottom topography flow of the deep lower layer relative to the vortex the observation are used to infer the form of the deep zonal velocity profile vs latitude the magnitude of the profile depends on the unknown static stability the principal result is the existence of horizontal shear in the deep layer zonal velocity profile i e the lower layer is not in solid body rotation and does not act like a flat solid surface in this respect the data support the hypothesis of ingersoll and cuong concerning motions in the deep layer however at some latitudes the data violate ingersoll and cuong s criterion governing the compactness of the vortices at these latitudes the topography allows standing rossby waves wakes extending far downstream to the west observed wavelike features the filamentary regions are possibly formed by this mechanism

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

moist convection as an energy source for the large scale motions in jupiter s atmosphere jupiter s dominant large scale weather patterns dimensions 10 000 km are zonal jets and long lived ovals the jets have been flowing east and west at constant speeds of up to 180 m s 1 for over 100 years these jets receive energy from small scale eddies which pump eastward momentum into the eastward jets and westward momentum into the westward jets this momentum transfer was predicted by numerical models before it was observed on jupiter the large ovals roll between the jets in an anticyclonic direction clockwise in the northern hemisphere and counterclockwise in the southern hemisphere where they regularly assimilate small anticyclonic eddies but from where the eddies receive their energy has been an open question here we argue that the eddies which ultimately drive both the jets and the ovals receive their energy from moist convection this hypothesis is consistent with observations of jovian lightning which is an indicator of moist convection it also explains the anticyclonic rotation and poleward drift of the eddies and suggests patterns of upwelling and downwelling that resemble the patterns of large scale axisymmetric overturning in the earth s atmosphere

dating kimberlite emplacement with zircon and perovskite u th he geochronology kimberlites provide rich information about the composition and evolution of cratonic lithosphere accurate geochronology of these eruptions is key for discerning spatiotemporal trends in lithospheric evolution but kimberlites can sometimes be difficult to date with available methods we explored whether u th he dating of zircon and perovskite can serve as reliable techniques for determining kimberlite emplacement ages we obtained zircon and or perovskite u th he zhe phe dates from sixteen southern african kimberlites most samples with abundant zircon yielded reproducible zhe dates 15 dispersion that are in good agreement with published eruption ages the majority of dated zircon were xenocrystic zircons with reproducible dates were fully reset during eruption or resided at temperatures above the zhe closure temperature prior to entrainment in the kimberlite magma not dating hazy and radiation damaged grains can help avoid anomalous results for more shallowly sourced zircons that underwent incomplete damage annealing and or partial he loss during the eruptive process all seven kimberlites dated with phe yielded reproducible 15 dispersion and reasonable results we conducted two preliminary perovskite 4he diffusion experiments which suggest a phe closure temperature of 300 c perovskite in kimberlites is unlikely to be xenocrystic and its relatively high temperature sensitivity suggests that phe dates will typically record emplacement rather than post emplacement processes zhe and phe geochronology can effectively date kimberlite emplacement and provide useful complements to existing techniques this article is protected by copyright all rights reserved

quantitative constraints on the rate of landform evolution derived from low temperature thermochronology in recent years the nature of the complex interactions between the solid earth and the overlying atmosphere has been the subject of much debate england and molnar 1990 whipple et al 1999 braun et al 1999 does erosion play an important role in the dynamics of mountain building is there a strong feedback into the balance of forces at the crustal scale from mass transport by erosional and depositional processes at the earth s surface or does erosion passively react to changes in the earth s surface topography to shape mountains with tectonic forces originating in the underlying convecting mantle dominating the dynamics of plate interactions and crustal deformation at convergent plate margins the answers to these fundamental questions lie in our ability to determine the rate at which surface processes can react to tectonic forcing whipple et al 1999 where erosion is efficient the coupling will be strong as the rate of change of surface loading by mass transport will be similar to the rate of creation of topography by crustal deformation this may lead to a concentration of deformation and thus exhumation in regions of intense erosion koons 1990 willett et al 1993 beaumont et al 2001 koons et al 2002 2003 braun and pauselli 2004 where erosion is relatively inefficient mountain building is the result of a balance between internal driving forces and those originating from the deflection of an upper free surface there is no feedback from erosional processes low temperature thermochronology such as u th he he or fission track ft dating in apatite and zircon provides information on the rate at which rocks cool as they are exhumed towards the cold earth surface duddy et al 1988 warnock et al 1997 farley 2000 reiners and farley 1999 because the

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

a comparison of k ar and rb sr ages of rapidly cooled igneous rocks two points in the palaeozoic time scale re evaluated k ar and rb sr ages were measured on rapidly cooled igneous rocks from kinnekulle sweden ordovician bentonite the cerberean cauldron australia late devonian felsic volcanics mount dromedary australia cretaceous monzonite and cooma australia jurassic syenite no systematic bias was detected between the ages determined by the two techniques calculated using the constants recommended by the i u g s subcommission on geochronology the k ar and rb sr ages of the jurassic syenite also were indistinguishable from its zircon u pb age the kinnekulle a 1 bentonite gives a minimum age of 446 3 ma for the early caradocian diplograptus molestus zone the cerberean cauldron volcanics give a minimum age of 367 2 ma for the early frasnian these data are consistent with a small upwards revision of the ages in gale et al 9s 1979 time scale as proposed by gale et al 1980

the giant monazite crystals from manangotry madagascar abstract the manangotry area in the south east of madagascar is famous for its giant monazite crystals the studied occurrence is an outcrop near the manangotry pass were giant cm sized crystals have been found the crystals are embedded in biotitite levels also containing cm sized xenomorphic ilmenite and are associated with a 1 m thick layer of apatite besides giant crystals monazite is also present as abundant small mm sized grains the surrounding rocks are leucogranites and charnockites the monazite giant crystals are chemically homogeneous and thorium rich whereas small crystals tend to be heterogeneous both biotite and apatite are f rich temperature estimates from biotite and apatite yielded 750 to 800 c despite their high radioactivity the giant crystals preserve a high degree of crystallinity electron microprobe u th pb dating produced ages of 537 14 534 10 and 530 10 ma considered to be the age of the main monazite crystallization episode but some minor domains in small grains yielded 482 12 ma the enclosing biotites yielded 453 6 ma ar ar ages more than 98 of radiogenic helium have been retained in the studied monazite samples and kinetic experiments indicates the intrinsic diffusion parameters for high temperature to be ea 53 kcal mol and d0 3085 cm2 s the paragenesis monazite apatite ilmenite biotite is different from any other occurrences of larges monazite elsewhere based on the current data and literature the preferred genetic model for these giant monazites is crystallization from a high temperature fluorine rich fluid possibly originating from surrounding charnockites

u th he thermochronology of metallic ore deposits in the liaodong peninsula implications for orefield evolution in northeast china abstract the liaodong peninsula is an important region where polymetallic ores are mined in northeast china but precise thermochronological data needed to effectively constrain the evolution of this orefield are presently lacking for this study fifteen samples of granitoid rocks were collected from the qingchengzi and wulong orefields located in the liaodong peninsula to undertake u th he study of zircon and apatite single grain zhe and ahe ages from the qingchengzi orefield range from 73 to 166 ma and from 22 to 48 ma respectively whereas single grain zhe and ahe ages from the wulong orefield range from 42 to 88 ma and from 21 to 56 ma respectively some samples yield dispersed ages comprehensive analyses indicate that the main causes of the dispersion in the zhe ages are heterogeneous distribution of u and th within the crystals radiation damage and cooling rates whereas the dispersion in the ahe ages is primarily due to the first two factors based on the helium ages we calculate the average exhumation and cooling rates of the two orefields during different periods and the associated denudation which are 4 3 km for the qingchengzi orefield and 4 7 km for the wulong orefield the mineralization depths are estimated using homogenization temperature and the salinity of fluid inclusions and are calculated to be 1 5 3 2 km and 1 0 2 2 km for the qingchengzi pb zn and au ag deposits respectively and 2 1 3 1 km for the wulong au deposit these results are much less than the total denudation suggesting that the orebodies have been heavily eroded in conjunction with the distribution of the helium ages the modeled low t thermal histories of the two orefields reveal that the liaodong peninsula experienced three stages of relatively rapid cooling during the early cretaceous ca 135 115 ma from the end of the late cretaceous to the early eocene ca 70 50 ma and from the late eocene to the oligocene ca 38 26 ma the last stage of cooling affected both orefields and represents a period of relatively intense tectonic activity finally these results are compared with those of previous studies from the adjacent jiaodong peninsula this discussion shows that the cooling experienced by the orefields in the liaodong peninsula is largely consistent with that experienced by the jiaodong peninsula these data provide valuable information for further studies of the evolution of orefields in northeast china

a field based estimate of the zircon fission track closure temperature abstract a field based estimate of the zircon fission track closure temperature is proposed from 13 zircon fission track cooling ages of the gold butte block se nevada using previously published and new thermochronological data the thermal history of the gold butte block is re evaluated resulting in a geothermal gradient estimate of 20 3 c km and a slow cooling rate of 0 55 0 02 c m y from the late jurassic to the early miocene before onset of rapid miocene cooling the rapidly cooled part of the gold butte block provides a slip rate of 10 5 km m y of the hanging wall that caused the miocene exhumation of this crustal section assuming these thermal conditions are correct the closure temperature of the zircon fission track system is determined at 205 18 c which is in good agreement with previous field based estimates because of the variation in zircon fission track annealing behavior with radiation damage field studies are a suitable way to calibrate the closure temperature of the zircon fission track system

u th he thermochronometry constraints on unroofing of the eastern kaapvaal craton and significance for uplift of the southern african plateau the timing and causes of the 1 0 km elevation gain of the southern african plateau since paleozoic time are widely debated we report the first apatite and titanite u th he thermochronometry data for southern africa to resolve the unroofing history across a classic portion of the major escarpment that encircles the plateau the study area encompasses 1500 m of relief within archean basement of the barberton greenstone belt region of the eastern kaapvaal craton titanite dates are neoproterozoic apatite dates are cretaceous with most results clustering at ca 100 ma thermal history simulations confirm mesozoic heating followed by accelerated cooling in mid to late cretaceous time the lower temperature sensitivity of the apatite u th he method relative to previous thermochronometry in southern africa allows tighter constraints on the cenozoic thermal history than past work the data limit cenozoic temperatures east of the escarpment to 35 c and appear best explained by temperatures within a few degrees of the modern surface temperature these results restrict cenozoic unroofing to less than 850 m and permit negligible erosion since the cretaceous if substantial uplift of the southern african plateau occurred in the cenozoic as advocated by some workers then it was not responsible for the majority of post paleozoic unroofing across the eastern escarpment significant mesozoic unroofing is coincident with large igneous province activity kimberlite magmatism and continental rifting within and along the margins of southern africa compatible with a phase of plateau elevation gain due to mantle buoyancy sources associated with these events

the late quaternary diego hernandez formation tenerife volcanology of a complex cycle of voluminous explosive phonolitic eruptions abstract the diego hernandez formation dhf 600 ca 180 ka represents the products of the most recent complete cycle of phonolitic explosive volcanism on tenerife canary islands spain we provide a revised and detailed stratigraphy new 40ar 39ar and u th he age determinations for major eruptive units a summary of new chemical data and an overview of the key characteristics of the cycle including volume estimates dispersal patterns eruption styles phreatomagmatic influences and caldera collapse episodes the complex stratigraphy of the dhf is divided into 20 named members each representing a major eruption as well as numerous unnamed members of limited present day exposure the major eruptions are represented by the fortaleza 370 ka roque 347 ka 3 km3 aldea 319 ka 3 km3 fasnia 309 ka 13 km3 poris 268 ka 3 5 km3 arafo 4 km3 caleta 223 ka 3 5 km3 and abrigo between 196 and 171 ka 20 km3 members the aldea fasnia and poris members consist of highly complex successions of plinian fall surge and flow deposits and several of the eruptions produced widespread and internally complex ignimbrite sheets phreatomagmatism occurred most frequently in the opening phase of the eruptions but also recurred repeatedly throughout many of the sequences inferred sources of water include a shallow caldera lake and groundwater and intermittent phreatomagmatic activity was an important influence on eruption style another important factor was conduit and vent instability which frequently loaded the eruption column with dense lithic debris and occasionally triggered column collapse and ignimbrite formation most of the major dhf eruptions were triggered by injection of mafic magma into existing phonolitic magma bodies two phonolitic magma types were available for eruption during the lifetime of the dhf but each was dominant at different times the results presented here support a caldera collapse rather than a landslide model for the origin of the las canadas caldera although the evolution of the caldera is evidently more complex and incremental than first thought

jupiter s cloud structure from galileo imaging data the vertical structure of aerosols on jupiter is inferred from data obtained by the nasa galileo solid state imaging system during the first six orbits of the spacecraft images at 889 nm a strong methane band 727 nm a weaker methane band and 756 nm continuum taken at a variety of lighting and viewing angles are used the images are displayed and described in the companion paper by vasavada et al 1998 icarus 135 265 275 conservative scattering cloud particles with laterally uniform single scattering properties are assumed in the analysis and are shown to be consistent with the data at these wavelengths particles are bright and the darkest locations on jupiter correspond to the smallest optical thickness of aerosols optical depths and vertical positions of aerosol layers vary from place to place and are the retrieved quantities in the analysis only mid and low latitudes are sampled in this data set a stratospheric haze with an optical depth of roughly a tenth and an upper tropospheric haze with an optical depth of 2 to 6 exist over all regions both are consistent with previous conclusions based on data of lower spatial resolution e g west et al 1986 icarus 65 161 217 the new data show that these layers contain little lateral structure on scales smaller than the planetary jets on scales of the jets and ovals the top and bottom of the upper tropospheric haze vary in elevation the concentration of particles optical depth per pressure interval varies less than does the total optical depth near the base of the upper tropospheric haze is a third cloud component usually at pressure p 750 200 mb which is less than a scale height in geometric thickness its optical depth varies from zero to about 20 on regional scales and often varies by 50 on scales of a few tens of kilometers optical depth variations in this cloud are the principal cause of the features in jupiter s atmosphere seen at red and longer wavelengths it is probably composed of ammonia the expected nh 4sh cloud has not been identified in this work perhaps because it exists only at locations where it is concealed beneath higher clouds our retrievals also cannot rule out a pervasive deep haze without small scale structure finally in one region northwest of the great red spot a deeper cloud is identified parts of it lie at a pressure greater than four bars it is associated with a rapidly changing storm system with optical depth of several tens or more and a range of cloud heights between p 4 bars to p 400 mb it is probably composed of water

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

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

dynamics of saturn s great storm of 2010 2011 from cassini iss and rpws saturn s quasi periodic planet encircling storms are the largest convecting cumulus outbursts in the solar system the last eruption was in 1990 sanchez lavega a 1994 chaos 4 341 353 a new eruption started in december 2010 and presented the first ever opportunity to observe such episodic storms from a spacecraft in orbit around saturn fischer g et al 2011 nature 475 75 77 sanchez lavega a et al 2011 nature 475 71 74 fletcher l n et al 2011 science 332 1413 here we analyze images acquired with the cassini imaging science subsystem iss which captured the storm s birth evolution and demise in studying the end of the convective activity we also analyze the saturn electrostatic discharge sed signals detected by the radio and plasma wave science rpws instrument the storm s initial position coincided with that of a previously known feature called the string of pearls sops at 33 n planetocentric latitude intense cumulus convection at the westernmost point of the storm formed a particularly bright head that drifted at 26 9 0 8 m s 1 negative denotes westward motion on january 11 2011 the size of the head was 9200 km and up to 34 000 km in the north south and east west dimensions respectively rpws measurements show that the longitudinal extent of the lightning source expanded with the storm s growth the storm spawned the largest tropospheric vortex ever seen on saturn on january 11 2011 the anticyclone was sized 11 000 km by 12 000 km in the north south and east west directions respectively between january and september 2011 the vortex drifted at an average speed of 8 4 m s 1 we detect anticyclonic circulation in the new vortex the vortex s size gradually decreased after its formation and its central latitude shifted to the north the storm s head moved westward and encountered the new anticyclone from the east in june 2011 after the head vortex collision the rpws instrument detected that the sed activities became intermittent and declined over 40 days until the signals became undetectable in early august in late august the sed radio signals resurged for 9 days the storm left a vast dark area between 32 n and 38 n latitudes surrounded by a highly disturbed region that resembles the mid latitudes of jupiter using iss images we also made cloud tracking wind measurements that reveal differences in the cloud level zonal wind profiles before and after the storm

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

age and temperature of shock metamorphism of martian meteorite los angeles from u th he thermochronometry mineralogic features attributed to impact induced shock metamorphism are commonly observed in meteorites and terrestrial impact craters partly because the duration of shock metamorphism is very short constraining the timing and temperature of shock events has been problematic we measured u th he ages of single grains of merrillite and chlorapatite from the martian meteorite los angeles la merrillite and chlorapatite ages cluster at 3 28 6 0 15 ma 2s and 2 18 6 0 19 2s ma respectively the mean age of the merrillites which are larger than chlorapatites is indistinguishable from cosmic ray exposure ages 3 1 6 0 2 ma suggesting that impact induced shock metamorphism was coeval with ejection of the la precursor from mars to constrain the initial temperature of shock metamorphism in the la precursor body we modeled diffusive loss of he from merrillite as a function of diffusion domain size la precursor body size and ablation depth from these calculations we suggest that the metamorphic temperature of the shock event was higher than 450 8c these results support the idea that shock pressures of the martian meteorite shergotty were higher than 45 gpa as inferred from the presence of post stishovite sio2 polymorphs single grain u th he dating of phosphates may provide unique constraints on the timing and pressure temperature dynamics of shock metamorphism in a wide variety of extraterrestrial materials

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

on the interaction of jupiter s great red spot and zonal jet streams abstract in this paper jupiter s great red spot grs is used to determine properties of the jovian atmosphere that cannot otherwise be found these properties include the potential vorticity of the grs and its neighboring jet streams the shear imposed on the grs by the jet streams and the vertical entropy gradient i e rossby deformation radius the cloud cover of the grs which is often used to define the grs s area and aspect ratio is found to differ significantly from the region of the grs s potential vorticity anomaly the westward going jet stream to the north of the grs and the eastward going jet stream to its south are each found to have a large potential vorticity jump the jumps have opposite signs and as a consequence of their interaction with the grs the shear imposed on the grs is reduced the aspect ratio of the grs s potential vorticity anomaly depends on the ratio of the imposed shear to the strength of the anomaly the east west to north south aspect ratio is found to be 2 1

dynamical implications of jupiter s tropospheric ammonia abundance abstract groundbased radio observations indicate that jupiter s ammonia is globally depleted from 0 6 bars to at least 4 6 bars relative to the deep abundance of 3 times solar a fact that has so far defied explanation the observations also indicate that i the depletion is greater in belts than zones and ii the greatest depletion occurs within jupiter s local 5 m hot spots which have recently been detected at radio wavelengths here we first show that both the global depletion and its belt zone variation can be explained by a simple model for the interaction of moist convection with jupiter s cloud layer circulation if the global depletion is dynamical in origin then important endmember models for the belt zone circulation can be ruled out next we show that the radio observations of jupiter s 5 m hot spots imply that the equatorial wave inferred to cause hot spots induces vertical parcel oscillation of a factor of 2 in pressure near the 2 bar level which places important constraints on hot spot dynamics finally using spatially resolved radio maps we demonstrate that low latitude features exceeding 4000 km diameter such as the equatorial plumes and large vortices are also depleted in ammonia from 0 6 bars to at least 2 bars relative to the deep abundance of 3 times solar if any low latitude features exist that contain 3 times solar ammonia up to the 0 6 bar ammonia condensation level they must have diameters less than 4000 km

he diffusion in olivine helium diffusion in olivine dunite xenolith has been measured in the temperature range 1180 1460 c a linear arrhenius function was obtained with an activation energy of 120 27 32 kcal mole and a pre exponential factor d0 2 2 108 cm2 s diffusion mechanisms are not a viable means of degassing he from the mantle olivine phenocrysts can be expected to retain previously trapped he during cooling in extrusive basalts provided the flow units are thinner than 50 m xenoliths will retain mantle he signatures only if magma transport times are less than 50 years or if the he fugacity in the magma is high enough to prevent xenolith degassing the lower oceanic crust is probably substantially degassed of he trapped he will be qualitatively retained in quenched submarine basalt glass only if the cooling rate is faster than 5 1014 c m y glass at several centimeters depth in a basalt flow near the spherulite zone will have cooling rates lower than this so he loss may be significant in many basalt glass samples

vertical wind shear on jupiter from cassini images 1 multifilter images of jupiter acquired by the cassini imaging science subsystem iss are used to derive zonal winds at altitudes above and below the visible cloud deck small features unique to the ultraviolet images of iss are tracked to get the systematic high altitude zonal winds comparison between the zonal winds from ultraviolet images and the vertical profile of zonal winds from the cassini composite infrared spectrometer cirs shows that the zonal winds from the ultraviolet images are from a pressure level that is 0 2 scale heights higher than the pressure level of the zonal winds from continuum band images deeper zonal winds at different latitudes of the equatorial region are measured by tracking cloud features observed within hot spots on continuum band images the deeper zonal winds in this study extend the measurement of the galileo probe to different latitudes of the equatorial region comparison between the galileo probe and this study suggests that these fast moving clouds within hot spots are deeper than 3 bars and are therefore probably water clouds

incomplete retention of radiation damage in zircon from sri lanka a suite of 18 zircon gemstones from placers in the highland southwestern complex sri lanka were subjected to a comprehensive study of their radiation damages and ages the investigation included x ray diffraction raman and pl spectroscopy electron microprobe pixe and hrtem analysis as well as u th he and shrimp u th pb age determinations zircon samples described in this study are virtually homogeneous they cover the range from slightly metamict to nearly amorphous generally concordant u th pb ages averaging 555 11 ma were obtained late ordovician zircon u th he ages scattering around 443 9 ma correspond reasonably well with previously determined biotite rb sr ages for rocks from the hswc slightly to moderately metamict zircon has retained the radiogenic he whereas only strongly radiation damaged zircon calculated total fluences exceeding 3 5 10 18 events g has experienced significant he loss when compared to unannealed zircon from other localities sri lanka zircon is about half as metamict as would correspond to complete damage accumulation over a 555 m y lasting self irradiation period suggesting significant annealing of the structural radiation damage insufficient consideration of this has often resulted in significant underestimation of radiation effects in zircon we suggest to estimate effective doses for sri lanka zircon by multiplying total fluences which were calculated using the zircon u th pb age by a correction factor of 0 55 this conversion may be applied to literature data as well because all gem zircon samples from sri lanka this work and previous studies seem to reveal the same general trends of property changes depending on the radiation damage the use of effective doses for sri lanka zircon contributes to more reliable quantitative estimates of radiation effects and makes possible direct comparison between natural and synthetic radiation damaged zircon

exhumation patterns along shallow low angle normal faults an example from the altotiberina active fault system northern apennines italy a multi method approach palaeothermal and thermochronological analyses thermal modelling is applied to reconstruct the exhumation history of the altotiberina fault atf a representative example of crustal scale active low angle normal faulting in the northern apennines italy thermal maturity and thermochronological data yield similar burial histories but different exhumation patterns for the sedimentary successions in the hangingwall and the footwall of the atf since 3 8 ma the atf footwall has exhumed at rates of 0 90 mm a 1 exhumation led to bending and deactivation of the atf uppermost portion as a result of tectonic unloading and isostatic adjustment followed by migration of extension and the development of a set of domino like east dipping normal faults rooting on the buried portion of the atf atf activity and isostatic rebound exhumed triassic rock units from depths of about 4 km we suggest that isostatic instability is accommodated at shallow crustal levels in a similar way to what is observed on larger structures at mid low crustal levels

exotic pollen as an indicator of variable atmospheric circulation over the labrador sea region during the mid to late holocene variability in the abundance of exotic non native pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation but the difficulty of gaining sufficient total exotic pollen and the incomplete under standing of atmospheric pollen transport patterns has hindered its application in light of recent advances in the study of pollen transport we present an exotic pollen record from two fjord sediment cores taken from the west placentia bay newfoundland and east narsaq sund greenland labrador sea as a basis for studying variations in regional atmospheric circulation the two cores cover the last ca 5500 years and indicate a shift in dominant spring summer air masses at ca 2000 southern greenland and 3000 cal a bp newfoundland transporting reduced concentrations of pollen from southerly and south westerly vegetation zones this may suggest a shift away from more dominantly zonal atmospheric circulation a feature of positive north atlantic oscillation years to more frequent meridional circulation these results support sea ice sea surface temperature proxy reconstructions from newfoundland investigated as part of the same project which also suggest increased winter atmospheric circulation during the early part of the time period studied in this region more positive north atlantic oscillation years and therefore more zonal atmospheric circulation are associated with increased atmospheric circulation in both the winter and the summer seasons copyright 2011 john wiley sons ltd