styles of failure in late holocene highstand prodelta wedges on the adriatic shelf on the continental shelves of the northern mediterranean basin the late holocene highstand systems tract hst prograded un der the influence of major rivers after the attainment of the present sea level highstand about 5 5 cal kyr bp on the adriatic shelf the thickness distribution of the late holocene hst reflects the location of major deltas on the western side of the basin and the geostrophic cir culation which prevents a more uniform sediment dispersal toward the center of the basin very high sediment accumulation rates 1 to 10 cm year resulted in the construction of a hst depocenter up to 35 m thick this shore parallel depocenter is affected by failure of limited displacement over as much as 40 of its extent gas impregnation is common in the topset region and occurs at very shallow levels a few meters below the sea floor five areas are characterized by a variety of sea floor and subsurface crenulations although locally some of these crenulations have an intriguingly regular geometry sediment failure is the most plausible mechanism for their formation sediment failure better explains the large variety of geometries that characterizes the coastal mud prism of the late holocene hst furthermore we observe that these crenulations occur only where the downlap surface at the base of the hst is disrupted and affected by geometries that are con sistent with fluid escape processes this relationship suggests that the basal surface acts as a weak layer for sediment failure failure occurred in variable water depths from the northern slope of the modern po prodelta 10 20 m water depth to the narrow shelf offshore bari 40 110 m water depth in all these areas the proximal part of the hst prodelta wedge is intensely gas charged the thickness and age of the sediment sections affected by failure are slightly differ ent from place to place but appear everywhere younger than 5 5 cal kyr bp where failure affects the entire hst the detachment occurs on the downlap surface at its base failure geometries characterize the head region whereas compressional features such as pressure ridges and mud diapirs dominate in the toe region ranging in depth between 70 and 110 m where failure is limited to the upper few meters of the hst there is a clear lithologic change decrease in carbonate fraction and grain size across the basal surface this lithological change reflects a switch in sediment supply from local apennine rivers below to po derived mud this change occurred at the onset of the little ice age documenting the indirect control of short term climate change and hu man impact on sediment architecture the deformations affecting the late holocene hst in the various areas show differences in internal geometry but appear everywhere to be characterized by limited downward displacement and can be attri buted to shear dominated retrogressive failure it is suggested that some degree of consolidation occurred immediately after mobilization possibly induced by the escape of fluids nowhere has failure evolved into disintegration and flow likely because the type of cyclic loading that triggered it was not prolonged over a long enough interval short lived radionuclides in the uppermost stratigraphic layers which postdate the failure in the area offshore ortona allowed us to quantify systematic changes in sediment accumulation rates as a func tion of the underlying deformed sea floor in areas of wavy sea floor troughs show sediment accumulation rates of greater than 16 mm yr a figure that is fourfold the rate measured on the flanks of the troughs

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

geochemical facies analysis of fine grained siliciclastics using th u zr rb and zr rb sr ratios abstract abundance of the trace elements zr rb sr th and u may provide insight into the sedimentological origin of fine grained siliciclastic sediments provided that the units are derived from similar source areas as demonstrated here with suites of the fine grained jurassic and cretaceous rocks from the barents sea and svalbard zr rb ratios can be interpreted to indicate grain size variations while zr rb sr values reflect variations in the siliciclastic versus carbonate contents the th u ratio can be applied as an indicator of the redox conditions in 3d plots such as presented here the interplay between these geochemical factors can be interpreted in terms of the sedimentological evolution of the depositional basin the geochemical facies analyses show that similar depositional conditions existed on the jurassic shelf in the two studied localities the succeeding prodeltaic cretaceous beds were generally coarser grained and deposited in ventilated depositional conditions

la icp ms depth profile analysis of apatite protocol and implications for u th he thermochronometry abstract heterogeneous concentrations of producing nuclides in apatite have been recognized through a variety of methods the presence of zonation in apatite complicates both traditional ejection corrections and diffusive models both of which operate under the assumption of homogeneous concentrations in this work we develop a method for measuring radial concentration profiles of 238 u and 232 th in apatite by laser ablation icp ms depth profiling we then focus on one application of this method removing bias introduced by applying inappropriate ejection corrections formal treatment of laser ablation icp ms depth profile calibration for apatite includes construction and calibration of matrix matched standards and quantification of rates of elemental fractionation from this we conclude that matrix matched standards provide more robust monitors of fractionation rate and concentrations than doped silicate glass standards we apply laser ablation icp ms depth profiling to apatites from three unknown populations and small intact crystals of durango fluorapatite accurate and reproducible durango apatite dates suggest that prolonged exposure to laser drilling does not impact cooling ages intracrystalline concentrations vary by at least a factor of 2 in the majority of the samples analyzed but concentration variation only exceeds 5x in 5 grains and 10x in 1 out of the 63 grains analyzed modeling of synthetic concentration profiles suggests that for concentration variations of 2x and 10x individual homogeneous versus zonation dependent ejection corrections could lead to age bias of 5 and 20 respectively however models based on measured concentration profiles only generated biases exceeding 5 in 13 of the 63 cases modeled application of zonation dependent ejection corrections did not significantly reduce the age dispersion present in any of the populations studied this suggests that factors beyond homogeneous ejection corrections are the dominant source of overdispersion in apatite u th he cooling ages

u pb geochronology of zircon and polygenetic titanite from the glastonbury complex connecticut usa an integrated sem empa tims and shrimp study abstract u pb ages for zircon and titanite from a granodioritic gneiss in the glastonbury complex connecticut have been determined using both isotope dilution thermal ionization mass spectrometry tims and the sensitive high resolution ion microprobe shrimp zircons occur in three morphologic populations 1 equant to stubby multifaceted colorless 2 prismatic dark brown with numerous cracks and 3 elongate prismatic light tan to colorless cathodoluminescence cl imaging of the three populations shows simple concentric oscillatory zoning the zircon tims age weighted average of 207pb 206pb ages from group 3 grains 450 5 1 6 ma mswd 1 11 and shrimp age composite of 206pb 238 u age data from all three groups 448 2 2 7 ma mswd 1 3 are interpreted to suggest a relatively simple crystallization history titanite from the granodioritic gneiss occurs as both brown and colorless varieties scanning electron microscope backscatter bse images of brown grains show multiple cross cutting oscillatory zones of variable brightness and dark overgrowths colorless grains are unzoned or contain subtle wispy or very faint oscillatory zoning electron microprobe analysis empa clearly distinguishes the two populations brown grains contain relatively high concentrations of fe2o3 ce2o3 up to 1 5 wt nb2o5 and zr cerium concentration is positively correlated with total ree y concentration which together can exceed 3 5 wt oscillatory zoning in brown titanite is correlated with variations in ree concentrations in contrast colorless titanite both as discrete grains and overgrowths on brown titanite contains lower concentrations of y ree fe2o3 and zr but somewhat higher al2o3 and nb2o5 uranium concentrations and th u discriminate between brown grains typically 200 400 ppm u all analyses but one have th u between about 0 8 and 2 and colorless grains 10 60 ppm u th u of 0 0 17 in contrast to the zircon u pb age results shrimp u pb data from titanite indicate multiple growth episodes in brown grains oscillatory zoned cores formed at 443 6 ma whereas white in bse cross cutting zones are 425 9 ma colorless grains and overgrowths on brown grains yield an age of 265 8 ma using the total pb method or 265 5 ma using the weighted average of the 206pb 238u ages however empa chemical data identify zoning that suggests that this colorless titanite may preserve three growth events oscillatory zoned portions of brown titanite grains are igneous in origin white cross cutting zones probably formed during a previously unrecognized event that caused partial dissolution of earlier titanite and reprecipitation of a slightly younger generation of brown titanite colorless titanite replaced and grew over the magmatic titanite during the permian alleghanian orogeny these isotopic data indicate that titanite like zircon can contain multiple age components coupling shrimp microanalysis with empa and sem results on dated zones as presented in this study is an efficient and effective technique to extract additional chronologic data to reveal the complexities of igneous crystallization and metamorphic growth

thermochronologic record of pluton emplacement deformation and exhumation at courtright shear zone central sierra nevada california thermochronology and thermobarometry of two plutons and a ductile shear zone at their contact in the central sierra nevada california as defined over the range 700 to 300 c by 40 ar 39 ar dating of hornblende and biotite and u pb dating of zircon indicate that ductile shear coincided closely with dramatically increased cooling and possible decompression of both plutons deformation occurred as the younger 90 ma mount givens pluton was emplaced against the older 102 ma dinkey creek pluton which was softened by conductive heating during extension these events coincided with significant regional exhumation possibly a result of crustal inflation recorded by a major pulse of rapid sediment accumulation in contemporaneous fore arc strata of the great valley sequence

composition and geochemistry of clay sediments offshore the northeastern sicilian coast southeastern tyrrhenian sea italy abstract grain size mineralogical and chemical analyses were carried out on fine fraction of sediments collected in the gulfs of patti and milazzo two borderland basins in the southern tyrrhenian extending offshore the northeastern sicilian coast results of granulometric analyses on size fractions smaller than 63 m showed that the investigated samples can be classified mainly as clayey silts the coarse fractions 63 m examined by optical microscopy consist of a terrigenous component representing in some samples about 98 99 of the total sediment and by a biogenic component this latter is mainly made up of benthic foraminifera the mineralogical composition of the fine fraction determined by x ray diffractometry is represented by muscovite quartz clay minerals carbonates calcite and in some samples by calcium and sodium rich plagioclases the method of saturation with k and mg followed by ethylene glycol solvation and heating are used for a qualitative determination of the clay minerals clay mineralogical composition is characterized by the dominance of clinochlore and illite with minor amounts of smectite especially montmorillonite and vermiculite the chemical data reflect the main mineralogical composition showing a uniform quantitative composition with high al 2 o 3 and sio 2 values and very few variations in the relative abundance of the other components the cr th th sc th co and la sc ratios suggest a felsic nature of the source rocks finally the geochemical parameters such as v cr u th ni co and cu zn ratios indicate that examined sediments were deposited under oxic environments

provenance of lower paleogene strata in the huerfano basin implications for uplift of the wet mountains colorado u s a abstract sedimentary basins throughout the western interior of north america preserve a record of late cretaceous through latest eocene sedimentation derived from flanking laramide uplifts and sevier hinterland in northern and western basins the strata contain a well documented record of laramide style exhumation however the tectonic histories of more southerly basins such as the huerfano basin studied herein are comparatively poorly known despite being key for understanding the spatiotemporal evolution of laramide tectonism in this study we address this issue with a comprehensive analysis of provenance for the poison canyon cuchara and huerfano formations in the huerfano basin south central colorado u s a as part of our provenance analysis we characterized gravel clast composition petrographic compositions of sandstone bodies n 31 thin sections and u pb detrital zircon age spectra n 848 age determinations from fluvial sandstone units in each of the three formations the results are used to construct a new unroofing and source history for the sediments in the basin that contradicts previous hypotheses diagnostic zircon peaks at 516 517 ma 1423 1430 ma and 1678 1687 ma show that sediment delivered to the huerfano basin did not originate in the san luis highlands or the incipient sangre de cristo mountains but from the precambrian crystalline core and associated cambrian plutons of the wet mountains which were exposed by the time laramide deposition began in the basin there are no detected provenance shifts upsection indicating a largely stable or lithologically uniform sediment source from the paleocene through at least 51 ma this suggests that the major changes recorded in the rock record were more likely related to variations in tectonic and climatic conditions rather than changes in lithology of the rocks being eroded

a total electron content space weather study of the nighttime weddell sea anomaly of 1996 1997 southern summer with topex poseidon radar altimetry this paper reports on a total electron content space weather study of the nighttime weddell sea anomaly overlooked by previously published topex poseidon climate studies and of the nighttime ionosphere during the 1996 1997 southern summer to ascertain the morphology of spatial tec distribution over the oceans in terms of hourly geomagnetic longitudinal and summer winter variations the topex tec magnetic and published neutral wind velocity data are utilized to understand the underlying physical processes the tec results are combined with inclination and declination data plus global magnetic field line maps to investigate spatial and temporal tec variations geographic magnetic latitudes and local times are computed as results show the nighttime weddell sea anomaly is a large 1 600 2 22 million km2 estimated for a steady ionosphere space weather feature extending between 200 e and 300 e geographic it is an ionization enhancement peaking at 50 s 60 s 250 e 270 e and continuing beyond 66 s it develops where the spacing between the magnetic field lines is wide medium easterly declination is large medium 20 50 and inclination is optimum 55 s its development and hourly variations are closely correlated with wind speed variations there is a noticeable 43 reduction in its average area during the high magnetic activity period investigated southern summer nighttime tecs follow closely the variations of declination and field line configuration and therefore introduce a longitudinal division of four indian western eastern pacific atlantic northern winter nighttime tecs measured over a limited area are rather uniform longitudinally because of the small declination variation topex maps depict the expected strong asymmetry in tec distribution about the magnetic dip equator

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

identification and characterization of the encrusting materials in a coastal liquefied petroleum gas storage cavern an examination was carried out of the encrusting materials on the seepage removal pumps in a bottom sump of an undersea liquefied petroleum gas lpg cavern the studied cavern constructed at 8 km off the western coast of korea facing the yellow sea is at 130 150 m below the seabed since the first filling of the lpg into the cavern it has suffered from the unexpected problem of a thick encrustation of unknown materials on the seepage removal pumps of the cavern the xrd and xrf analyses revealed that the encrustation materials were mainly iron hydro oxides and carbonate mineral aragonite based on the geological setting below the cavern site it was inferred that iron oxides found in the pleistocene sandy sediment and the precambrian gneiss might be supplying ferrous iron to the cavern waters under an anaerobic condition evidenced by low dissolved oxygen and negative redox potential in the cavern water a significant change in the hydraulic condition near the pump intake and mixing the cavern water with oxic waters supplied through re circulated seawater and terrestrial groundwater discharge would precipitate the dissolved iron precipitation of the carbonate mineral is thought to have occurred due to over saturation of calcium and bicarbonate which may have resulted from the dissolution of cement grouting materials used during the undersea cavern construction and submarine groundwater discharge sgd this study reports the iron and carbonate precipitation in the man made undersea cavern which is affected by the surrounding hydrogeological condition and the sgd

geochemical and mineralogical variations as indicators of provenance changes in late quaternary deposits of se po plain combined geochemical and mineralogical characterisation of mudstone prone successions can provide suitable indicators of sediment provenance a case study from the late quaternary depositional sequence of southeastern po plain shows that major changes in geochemical and mineralogical composition can be ascribed to changes in sediment dispersal patterns occurring during the last 30 ka in response to fluctuating sea level the po river with a mixed contribution from the alpine and apenninic chains and its southern tributaries flowing from the apennines acted as the major feeders for the study area during the late quaternary chromium and nickel among trace elements and serpentine and dolomite among minerals appear as the major provenance indicators for the study succession allowing distinction of an apenninic chromium and serpentine poor province from a mixed alpine apenninic po related chromium and serpentine rich province the relatively low cr al2o3 and serpentine silicate ratios recorded in sediments of late pleistocene age 30 ka bp which accumulated at the last glacial maximum suggest that during lowstand times and early stages of transgression the southeastern po plain was beyond the po river influence being fed uniquely by rivers of apenninic provenance increasing cr al2o3 and serpentine silicate ratios recorded within back barrier transgressive deposits 8 10 ka bp in the comacchio and ravenna sectors reflect a major change in sediment supply taking place during the holocene when partially barred environments largely connected with the open sea became established in the study area and po derived detritus was delivered to estuaries and lagoons by littoral drift maximum chromium and serpentine values are recorded at peak transgression and during the following sea level highstand 6 ka bp present when sediment supply exceeded the rate at which new accommodation space was created leading to extensive po delta progradation the drop in cr al2o3 and serpentine silicate ratios recorded in some cores at top of the holocene succession reflects the local reestablishment behind the prograding po delta complexes of an alluvial plain drained by rivers of apenninic provenance as a result of distributary channel switching and delta lobe abandonment geochemical and mineralogical analyses show negligible compositional variations between pleistocene and holocene deposits landward of the line of maximum marine incursion especially close to the basin margin in these instances sample composition throughout the entire stratigraphic succession clearly suggests an ongoing supply from the adjacent apenninic chain comparison with sand compositional analyses from major sand bodies of the same stratigraphic succession highlights the complementary but fundamental role of geochemical and mineralogical characterisation of clays for provenance research

pre 3000 ma thermal history of the archean kaap valley puton south africa the kaap valley pluton is one of several early archean 3200 3500 ma tonalitetrondhjemite plutons that surround the barberton greenstone belt southern africa precise dating using single grain 207 pb 206 pb evaporation of zircon and 40 ar 39 ar laser step heating of hornblende and biotite indicates that in its interior the kaap valley pluton preserves a memory of its initial intrusion and cooling which spanned a time from 3225 to 3142 ma the pluton also records the effect of a low temperature thermal event at its margin as seen by a 40 ar 39 ar biotite age of 3035 ma which is perhaps related to hydrothermal activity and gold mineralization in the adjacent barberton greenstone belt these pre 3000 ma ages are not in agreement with results of dating studies from sedimentary rocks in the barberton greenstone belt and plutons south of the belt which show evidence of having been overprinted by late archean events 2650 2700 ma and the bushveld complex intrusion 2050 ma these events have been interpreted as affecting most of the kaapvaal craton that the kaap valley pluton has escaped these and all other events since 3035 ma with temperatures never reaching 250 c implies that these large scale events did not affect the entire craton and the overprinting seen elsewhere is of a more local nature thus it is possible to determine the intrusive and cooling history of the pluton these data can be used in developing models of heat flow paleomagnetic remanence acquisition and deformation events

a study of stratospheric gw fluctuations and sporadic e at midlatitudes with focus on possible orographic effect of andes 1 longitudinal dependences of stratospheric gravity wave gw fluctuations and lower ionospheric irregularities sporadic e at midlatitudes are studied by means of radio occultation data of the global positioning system meteorology experiment gps met satellite mission the zonal average of temperature variance of gw fluctuations with vertical scales less than 7 km at northern midlatitudes is observed to be similar to that at southern midlatitudes but there is a significant interhemispheric difference in the longitudinal dependence of gw fluctuations the gps met data at northern midlatitudes show a rapid change of the gravity wave distribution from 25 to 35 km height resulting in a broad maximum of temperature variance located over the atlantic and eurasia we only find in the wave distribution at h 25 km some weak traces of possible orographic effects on the other hand the distribution of gw fluctuations at southern midlatitudes has a strong and sharp maximum over andes which is obviously due to orographic wave generation by the interaction of surface wind with the andean mountain ridge this observation of the new gps radio occultation technique is in agreement with previous measurements of spaceborne microwave and infrared limb sounders the amplitude of the average wave field increases with height over andes while the amplitude maximum moves westward against the prevailing wind the temperature fluctuations have an apparent dominant vertical wavelength of around 6 km in situ measurements by a balloon borne rawinsonde at ushuaia argentina 54 7 s 68 1 w are compared to a simultaneous gps met temperature profile the balloon observations of temperature and horizontal wind are interpreted by a large amplitude mountain wave propagating to the upper stratosphere wave characteristics and atmospheric background conditions are investigated in detail for this mountain wave observation finally the gps met experiment indicates enhanced sporadic e in the lower ionosphere over southern andes we assume that these plasma irregularities are generated by enhanced upward wave flux due to the possible orographic effect of andes

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

distribution and phase association of some major and trace elements in the arabian gulf sediments twenty four sediment samples were collected from the arabian gulf ropme sea and analysed for their grain size distribution and carbonate contents as well as the major elements ca mg fe and al and macro and trace elements mn sr ba zn cu cr v ni and hg concentration of trace elements are found comparable to previous data published for samples taken before and after the gulf war and reflect the natural background level grain size analyses aluminium and carbonate measurements support the presence of two major sediment types 1 a terrigenous fine grained and al rich type predominating along the iranian side and 2 a coarse grained and carbonate rich type predominating along the arabian side of the gulf investigation of the correlation of the elements analysed with the sediment type indicates that they could be grouped under two distinct associations 1 carbonate association including ca and sr and 2 terrigenous association comprising al fe mg ba mn zn cu cr v ni and hg element al ratios calculated for the mud non carbonate fraction indicate that the euphrates and tigris rivers have minor importance as sediment sources to the gulf most of the elements have exceptionally high aluminium ratios in sediments containing more than 85 90 carbonate these sediments are restricted to the southern and south eastern part of the area where depth is shallow and temperature and salinity are high both biological accumulation and chemical and biochemical coprecipitation could be responsible for this anomaly

geochemistry and particle size of surface sediments of gulf of manfredonia southern adriatic sea abstract in this study we describe mechanisms influencing the spatial distribution of the surface sediments in the gulf of manfredonia seventy three samples were collected on a regional grid and analyzed for grain size major and trace elements and organic matter content sediments contain marine derived carbonate as well as terrigenous fractions indicating highly heterogeneous sediment composition dictated by different provenance and complex transport processes principal component analysis provides information about processes involved in the formation and dispersal of the sediments the regional sediment distribution is function of the gulf s morphology and sedimentary inputs from fluvial sources mainly from the ofanto river and from the north and central adriatic basin biogenic carbonate reefs identified in two restricted coastal areas add complexity to sediment shelf dispersal the north adriatic current flowing southward transports and deposits sediments from the northern basin in the offshore area of the gulf while an inner anticyclonic current distributes and mixes northern and fluvial sediment with a clockwise pattern in order to better assess the fluvial contribution also bedload samples from the main river debouching into the gulf were sampled enabling the identification of geochemical indexes to distinguish the role of both fluvial inputs and hydrodynamic processes affecting solid particles dispersion within the gulf this study provides a contribution to a qualitative estimate of the sediment supply entailed in the southwestern adriatic basin

argon diffusion in plagioclase and implications for thermochronometry a case study from the bushveld complex south africa plagioclase is not only the most abundant mineral in the earth s crust but is present in almost all terrestrial tectonic settings and is widespread in most extraterrestrial material applying the k ar system to this common mineral would provide a powerful tool for quantifying thermal histories in a wide variety of settings nonetheless plagioclase has rarely been used for thermochronometry largely due to difficulties in simultaneously acquiring precise geochronologic data and quantifying argon diffusion kinetics from a mineral with low k concentration here we describe an analytical technique that generates high precision 40 ar 39 ar data and quantifies ar diffusion kinetics of low k minerals we present results of five diffusion experiments conducted on single crystals of plagioclase from the bushveld complex south africa the observed diffusion kinetics yield internally consistent thermochronological constraints indicating that plagioclase is a reliable thermochronometer individual grains have activation energies of 155 178 kj mol and ln d0 a 2 varies between 3 5 and 6 5 these diffusion parameters correspond to closure temperatures of 225 300 c for a 10 c ma cooling rate age spectra generally conform to single domain diffusive loss profiles suggesting that grain scale diffusion dominates argon transport in this fairly simple plagioclase conjointly examining several single grain analyses enables us to distinguish episodic reheating from slow cooling and indicates that the bushveld complex cooled rapidly and monotonically from magmatic temperature to 300 c over 3 ma followed by protracted cooling to ambient crustal temperatures of 150 200 c over 600 ma 2009 elsevier ltd all rights reserved

mls observations of atmospheric gravity waves over antarctica 1 stratospheric gravity waves over antarctica are studied with the radiance variances observed by upper atmosphere research satellite microwave limb sounder uars mls strong wave activities are found during august and september in 1992 1994 over the drake passage region 290 315 longitude and 50 s 70 s latitude where the enhancement seems associated with the topography of both south america and antarctic peninsula tips during the same period significant gravity wave activities are also evident along the antarctic coastal region the vertical growth of the wave variance shows a scale height of 14 km at low altitudes for both drake passage and the coastal regions but reduces substantially at high altitudes the growth rate transition occurs at a lower altitude in the drake passage region where the variance is larger the gravity wave activities observed near the antarctic may contribute significantly to the formation of polar stratospheric clouds psc because of the overlapping with the vortex edge and with the psc activities as observed by claes cryogenic limb array etalon spectrometer

chemical and mineralogical comparison of the pennsylvanian fountain formation colorado u s a an uplifted continental block to sedimentary rocks from other tectonic environments the mineralogic and chemical composition of composites of cobble and pebble sized rock clasts clay stones siltstones fine sandstones and size fractions of two sandstones of the fountain formation near beulah colorado were determined the sandstones are arkosic and most plot in the basement uplift or transitional continental fields of qfl diagrams the mineralogic composition of the sandstones is similar to that of the composite of rock clasts at a given location al mg fe ti mn sc th ree and cs are concentrated in the clay minerals or heavy minerals and are diluted by quartz or feldspar consequently they are inversely correlated with si cr hf k rb ba and sr are poorly correlated with si cr is concentrated in clay and in heavy minerals in the silts k rb ba and sr are correlated with k feldspar mica or clay mineral abundances sedimentary rocks from the fountain formed from an uplifted continental block the element concentrations plot in the fields of active or passive continental margins in many tectonic discrimination diagrams probably as a result of derivation from granitoid sources of similar composition the ree patterns eu anomaly size k and rb concentrations of the fine sandstones are mostly similar to those of the corresponding composite of rock clasts at a given location suggesting that these parameters might be the most reliable in distinguishing sources the most reliable discrimination diagram for uplifted tectonic blocks like the fountain may be a plot of k2o vs eu anomaly size since both of these parameters were very similar in concentration in both the sedimentary rocks and presumed source of the fountain most sedimentary rocks in this study have larger negative eu anomalies than those from the nasc north american shale composite or mcps midcontinent platform sediment this suggests a more evolved source for the fountain than that for average platform sediment

nb and ta diffusion in titanite abstract chemical diffusion of nb and ta under anhydrous po 2 buffered conditions has been measured in natural titanite the source of diffusants were mixtures of casio 3 tio 2 and al 2 o 3 powders with either nb or ta oxides added experiments were run in evacuated sealed silica glass ampoules with solid buffers buffered at nno rutherford backscattering spectrometry rbs was used to measure nb and ta concentration profiles the following arrhenius parameters were obtained for nb and ta diffusion parallel to c over the temperature range 850 1252 c under nno buffered conditions d n b 3 23 10 9 exp 299 12 kj mol 1 r t m 2 s 1 d t a 4 34 10 10 exp 281 10 kj mol 1 r t m 2 s 1 in contrast to the findings of marschall et al 2013 for rutile there do not appear to be large differences between ta and nb diffusivities in titanite so the likelihood of diffusive fractionation of these elements will not be great values for diffusion coefficients measured parallel to the a axis for both elements are similar to those parallel to c indicating that nb and ta diffusivities in titanite do not exhibit significant anisotropy nb and ta diffusion in rutile is faster than diffusion of these elements in titanite at higher temperatures by about 2 and 1 5 orders of magnitude at 700 c for nb and ta respectively but because of the higher activation energies for diffusion of nb and ta in rutile they will approach values for titanite with decreasing t these diffusion data indicate that titanite should be moderately retentive of nb and ta chemical signatures with diffusivities slower than those for zr o and pb in titanite but faster than those for the ree under most geologic conditions these differences among diffusivities suggest that information derived from zr thermometry u pb geochronology and geochemical tracers such as ta nb and the ree may be decoupled in titanite under some conditions

extraction studies of heavy metal pollutants in surficial sediments from the southern baltic sea off poland surficial sediment samples from the gulf of gdansk and the southern baltic sea were analyzed for cu zn cd pb ag cr co ni mn cs rb fe ca mg k na li sr al and p extraction techniques were used to establish the association of the elements with specific phases in the sediments elimination of grain size effects was achieved by analyzing the size fraction 60 of the total zn cd pb and na 60 of the cu cr mn sr ca and mn and 50 of the ag co ni cs rb li fe al k and p in the sediment up to 45 of the total cu was extracted from the sediments by 0 1 m naoh and appears to be associated with the humic acid fraction areal variations of element contents were observed most elements in total and hcl leachates were enriched in sediments from near the mouth of the vistula river correlation studies indicated that the trace elements are partitioned among several phases such as fe and mn oxyhydroxides and clay minerals in the sediments

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

theoretical study of the ionospheric weddell sea anomaly using sami2 1 the ionospheric weddell sea anomaly wsa was first reported more than five decades ago based on ionosonde data near the antarctica peninsula the wsa is an ionospheric structure characterized by a larger nighttime electron density than daytime density recent satellite observations indicate that the wsa can extend from south america and antarctica to the central pacific the major physical mechanisms that have been suggested for the wsa formation are an equatorward neutral wind an electric field the photoionization and the downward diffusion from the plasmasphere on the basis of the theoretical modeling performed in this study using the sami2 model an equatorward neutral wind is identified as the major cause of the wsa while the downward flux from the plasmasphere provides an additional plasma source to enhance or maintain the density of the anomalous structure

erratum to metamictisation of natural zircon accumulation versus thermal annealing of radioactivity induced damage annealing of the radiation damage generated in decay events is a common phenomenon in natural zircons we have studied relationships between radiation damage age and radionuclide content of natural zircons on a micro scale the degree of metamictisation was estimated by means of confocal laser raman spectroscopic measurements raman band broadening in well ordered to moderately metamict zircons that have not experienced significant healing of the radiation damage since the time of their growth shows a nearly linear dependence on the fluence this dependence is proposed as a calibration line for examining unknown zircons in order to consider complete or incomplete damage storage which may contribute to the understanding of the low t thermal history of their host rocks seven examples for the application are presented radiation damage may anneal heterogeneously with preferred re ordering in more damaged micro areas results suggest that single point defects do not anneal continuously over geologic periods of time but are in contrast a comparably stable type of radiation damage in contrast to recrystallisation processes structural recovery due to simple thermal annealing is not necessarily connected with loss of radiogenic pb the most prominent example for this are concordant zircons from sri lanka although they are excellent standards for u pb dating sri lankan zircons should not be used as standards for structural radiation damage the experimental work is completed by monte carlo simulations of decay events in zircon

fine sediment mass balance in the western adriatic continental shelf over a century time scale abstract to obtain a quantitative estimate of the sediment accumulating on the muddy belt extending along the western adriatic continental shelf a budget was calculated based on the mass accumulation rates measured from more than one hundred activity depth profiles of 210 pb 137 cs depth distributions were used when possible to support 210 pb results 210 pb profiles show quasi monotonic declines in the foreset region of the central adriatic clinoform in the prodelta of the rivers po and isonzo 210 pb profiles are characterized by intervals of low and uniform activity which are thought to be produced by flood deposition since the north adriatic is shallow and occasionally affected by storms from bora wind sediments are not in steady state and their accumulation is the net result of recurring deposition resuspension and winnowing events in the western adriatic mass accumulation rates range between 0 04 and 6 6 g cm 2 yr 1 peak values were recorded in the po and isonzo prodeltas and along a narrow belt between pescara and the gargano promontory furthermore the latter depocentre is located immediately seaward of the offlap break 40 50 m water depth and parallels that of the most recent sigmoid of the hst the integration of mass accumulation rates throughout the mud wedge of the north and central adriatic gave a value of 42 0 tg yr 1 of sediment accumulating along the italian coast the balance between sediment accumulation and riverine sediment supply 46 6 tg yr 1 suggests an export of 4 6 tg yr 1 to the south adriatic basin and or the mediterranean sea the along shore sediment transport is very effective and in particular 16 2 tg yr 1 of sedimentary material 35 of the riverine supply is transferred from north to central adriatic through the ancona section

traveling ionospheric disturbances in the weddell sea anomaly associated with geomagnetic activity we present observations from the falkland islands super dual auroral radar network radar of the propagation of hf radio waves via the weddell sea ionospheric anomaly wsa a region of enhanced austral summer nighttime ionospheric electron densities covering the southern pacific and south americas region this anomaly is thought to be produced by uplift of the ionosphere by prevailing equatorward thermospheric winds of particular interest are perturbations of the wsa supported propagation which suggest that during periods of geomagnetic disturbance the ionospheric layer can be lowered by several tens of kilometers and subsequently recover over a period of 1 to 2 h perturbations can appear singly or as a train of two to three events we discuss possible causes of the perturbations and conclude that they are associated with equatorward propagating large scale atmospheric waves produced by magnetospheric energy deposition in the auroral or subauroral ionosphere changes in high middle latitude electrodynamics during geomagnetic storms may also account for the perturbations but further modeling is required to fully understand their cause

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

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

differential response of u pb systems in coexisting accessory minerals winnipeg river subprovince canadian shield implications for archean crustal growth and stabilization the u pb isotopic systems of zircon monazite titanite and some apatite and the pb isotopic composition of k feldspar have been investigated in three areas of the winnipeg river subprovince wrs of the superior province canada in order to define the timing of magmatic and metamorphic processes in this archean gneissic granitoid terrain

icp ms a powerful tool for high precision trace element analysis in earth sciences evidence from analysis of selected u s g s reference samples abstract inductively coupled plasma mass spectrometry icp ms is a powerful analytical technique with considerable application to geochemistry in this paper we demonstrate the power of icp ms as a tool in petrogenetic studies data for 28 elements in seven u s g s basalt and andesite reference samples agv 1 bcr 1 bhvo 1 bir 1 dnc 1 w 1 and w 2 are presented accuracy and precision standard deviation for 26 of these elements is either excellent a detailed description of the icp ms technique we have developed is given a simple hf hno 3 dissolution in screwtop teflon bombs was used for sample preparation icp ms instrumental sensitivity was measured by external solutions with surrogate calibration for 4 elements matrix correction was made by use of standard addition naturally occurring internal standards rb y ce and pb were used to correct for instrumental drift between sample and spiked sample measurements we report data for the elements li cs rb sr ba zr hf nb ta y sc u th pb and all 14 of the ree in addition the procedure acquired data for be mo w tl and bi many elements in this array are crucial for the evaluation of petrogenetic models and source tracing herein lies the real power of icp ms one technique one dissolution small sample size good limits of detection good to excellent accuracy and good precision for many geochemically important elements

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

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

goose bay radar observations of earth reflected atmospheric gravity waves in the high latitude ionosphere in the late fall and early winter the johns hopkins university hf radar at goose bay labrador observes the effects of atmospheric gravity waves on radar transmissions that are obliquely reflected from the ionosphere and subsequently backscattered from the earth s surface the waves exist under a wide variety of geomagnetic conditions however they are particularly noticeable under quiet conditions o le kp le 1 the clearest signatures of the waves are spatially localized enhancements in the backscattered power and quasi periodic fluctuations in the backscatter powers doppler velocities and reflection heights the waves are generally observed during daylight hours and propagate equatorward from regions of high latitude ionospheric backscatter that are located near the ionospheric convection reversal boundary the gravity waves appear to be generated just equatorward of the dayside flow reversal boundary in the vicinity of the auroral electrojet at altitudes of 115 to 135 km and propagate approximately perpendicular to the boundary along azimuths ranging from 156 degree to 180 degree the waves propagate obliquely downward through the lower atmosphere until they are reflected by the earth s surface back into the upper atmosphere the frequencies associated with these gravity waves cover the range of 0 3 to 0 6 mhz with wavelengths of 300more to 500 km and with average phase velocities of 110 to 180 m s the maximum phase speeds are 270 to 300 m s which is slightly less than the speed of sound in the lower atmosphere poleward propagating gravity waves are sometimes observed under disturbed conditions when the polar cap and convection reversal boundary have expanded equatorward less

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

preserved zr temperatures and u pb ages in high grade metamorphic titanite evidence for a static hot channel in the himalayan orogen abstract titanite grains from 800 c gneisses of the c 6 km thick greater himalayan sequence of central nepal were analyzed for zr in titanite temperatures and u pb ages to investigate the formation and evolution of a former weak mid crustal channel in the himalaya laser ablation icp ms depth profiles and spot analyses of titanite zr and u pb isotopic compositions are inconsistent with diffusional reequilibration on scales greater than 1 2 m and instead data appear to faithfully record both temperature and age titanite records protracted heating from 700 750 c at 37 ma to 775 c at 24 ma and possibly slight cooling to 765 c at 20 ma such temperatures exceed partial melting reactions in associated metapelites and imply profoundly weak rheologies i e a hot channel yet predate initiation of the bounding main central thrust and south tibetan detachment systems by as much as 15 myr evidently thick but weak crustal channels may remain stationary with respect to the convergence direction for 10 myr even during one of earth s biggest continent continent collisions

on the densities of etchable fission tracks in a mineral and co irradiated external detector with reference to fission track dating of minerals abstract the ratio r of the densities of etchable fission tracks in a mineral and co irradiated external detector is shown to depend on the length ratios of the latent l f l f and etched fission tracks l e l e in the two media calculations of l f for apatite titanite zircon and l f for muscovite external detectors allow a precise determination of r and confirm that neglecting r could constitute the most significant source of systematic error in fission track dating with the external detector method the ratios of the measured fission track densities in an external and internal surface of apatite and a muscovite external detector are calculated from r and the track counting efficiencies q the fact that the results are consistent with the experiment supports the accuracy of r and of the q factors the external detector ages of a basal and prismatic section of durango apatite are consistent with its reference age without the need for a length correction a critical examination of the uncertainties related to the thermal neutron fluence measurements fission decay constant calculated r value independently determined q factors and the reference age of the standard demonstrates that the assumption that a reduction of the confined track length of the spontaneous tracks in durango apatite necessitates a proportional correction of its apparent fission track age is the element most in question published u th he ages lend support to the conclusion that such a correction is not required the significance of r and of the ratio q of the q factors for the induced and spontaneous track counts leads us to propose a formalisation of the age equation in which these are included as well as a formal length correction l which is however not set equal to the ratio of the confined track lengths of the induced and spontaneous tracks the accuracy of the thermal neutron fluence and the decay constant leads us to propose a possible deconvolution of the calibration factor if for suitable age standards l 1 the proposed deconvoluted calibration factor 0 is a function of r and q which can be determined in ways that are independent of the reference ages of the standards this can either be interpreted as a multiple calibration or as establishing the fission track method as an independent dating method

unraveling the mesozoic and cenozoic tectonothermal evolution of the eastern basque cantabrian zone western pyrenees by low temperature thermochronology this is a contribution of the geotec group idi 2018 000216 and projects misterios cgl2013 48601 c2 2 r consolider ingenio 2010 topo iberia csd2006 00041 and esf topoeurope project pyrtec sv pa 10 03 ip2 pyrtec we thank additional financial support by the university of oviedo banco santander the government of the principality of asturias through the science technology and innovation plan pcti the european union through feder funds and the spanish ministry of education culture and sport through the training programme for academic staff fpu grant for idf

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

the significance of rb sr ages of biotite and phlogopite for the thermal history of the central and southern marginal zones of the limpopo belt of southern africa and the adjacent portions of the kaapvaal craton abstract generally rb sr biotite and phlogopite ages range from 2050 ma to 1950 ma between the murchison thabazimbi and triangle tuli sabi shear zones of southern africa in the rocks comprising the central and southern marginal zones of the limpopo belt and adjacent portions of the kaapvaal craton in some shear zones however similar ages ocurr as young as 800 ma in contrast within the kaapvaal craton south of the murchison thabazimbi shear zone rb sr biotite ages range between 3150 ma and 2100 ma and show no regular distribution in all cases the ages are interpreted to indicate the time elapsed since the biotite last cooled below its closure temperature approximately 320 c the regular pattern of 2050 ma to 1950 ma rb sr biotite ages north of the murchison thabazimbi shear zone suggests that the present erosional surface approximates a paleo isothermal surface this surface was exposed by uplift and erosion which was completed by 1900 ma to 1800 ma ago when the sedimentary and volcanic rocks of the soutpansberg group were deposited the regional uplift was accommodated by motion on the murchison thabazimbi and triangle tuli sabi shear zones and probably was related to tectonism associated with the emplacement of the anorogenic bushveld and phalaborwa complexes other anorogenic granitic magmatism accompanied uplift the depth represented by the paleo isothermal surface and the magnitude of the uplift that exhumed it cannot be constrained precisely it is suggested however that the majority of the 10 to 15 km by which crust in this area is thinner than that of the adjacent cratons is the manifestation of this uplift

large scale observations of a subauroral polarization stream by midlatitude superdarn radars instantaneous longitudinal velocity variations 1 we present simultaneous measurements of flow velocities inside a subauroral polarization stream saps made by six midlatitude high frequency superdarn radars the instantaneous observations cover three hours of universal time and six hours of magnetic local time mlt from velocity variations across the field of view of the radars we infer the local 2d flow direction at three different longitudes we find that the local flow direction inside the saps channel is remarkably constant over the course of the event the flow speed however shows significant temporal and spatial variations after correcting for the radar look direction we are able to accurately determine the dependence of the saps velocity on magnetic local time we find that the saps velocity variation with magnetic local time is best described by an exponential function the average velocity at 00 mlt was 1 2 km s and it decreased with a spatial e folding scale of two hours of mlt toward the dawn sector we speculate that the longitudinal distribution of pressure gradients in the ring current is responsible for this dependence and find these observations in good agreement with results from ring current models using tec measurements we find that the high westward velocities of the saps are as expected located in a region of low tec values indicating low ionospheric conductivities

the glacial interglacial transition and holocene environmental changes in sediments from the gulf of taranto central mediterranean abstract an extensive high resolution sedimentological geochemical survey was done using geo acoustics xrf core scans icp aes ams 14c dating and grain size analyses of sediments in 11 cores from the gulf of taranto the southern adriatic sea and the central ionian sea spanning the last 16 cal ka bp comparable results were obtained for cores from the gallipoli shelf eastern gulf of taranto and the southern adriatic sea suggesting that the dominant provenance of gallipoli shelf sediments is from the western adriatic mud belt the 210pb and 14c dated high accumulation rate sediments permit a detailed reconstruction of climate variability over the last 16 cal ka bp although the glacial interglacial transition is generally dry and stable these conditions are interrupted by two phases of increased detrital input during the bolling allerod and the late younger dryas the event during the younger dryas period is characterized by increased sediment inputs from southern italian sources this suggests that run off was higher in southern compared to northern italy at approximately 7 cal ka bp increased detrital input from the adriatic mud belt related to sea level rise and the onset of deep water formation in the adriatic sea is observed and is coincident with the end of sapropel s1 formation in the southern adriatic sea during the mid to late holocene we observed millennial scale events of increased detrital input e g during the roman humid period and of decreased detrital input e g medieval warm period these dry wet spells are consistent with variability in the north atlantic oscillation nao a negative state of the nao and thus a more advanced penetration of the westerlies into the central mediterranean that result in wet conditions in the research area concord with events of high detrital input e g during the roman humid period in contrast a positive state of the nao resulting in dry conditions in the mediterranean dominated during events of rapid climate change such as the medieval warm period and the bronze age

denudational history along a transect across the drakensberg escarpment of southern africa derived from apatite fission track thermochronology 1 the denudational history of a 500 km long transect across the drakensberg escarpment on the high elevation passive margin of se africa is quantified on the basis of thermal history modeling of apatite fission track data for 15 deep borehole samples supplemented by an additional 10 outcrop samples a minimum of 4 5 km of denudation since formation of the margin 130 myr ago is estimated for the coastal zone with a marked early cretaceous episode of accelerated denudation broadly coincident with continental breakup samples from the swartberg borehole sw 1 67 located 30 km seaward of the present position of the drakensberg escarpment indicate a total depth of denudation of 3 1 1 2 km since 91 myr with a phase of accelerated denudation of 2 1 0 9 km at a mean rate of 95 43 m myr between 91 and 69 myr samples from the ladybrand borehole la 1 68 west of the lesotho highlands indicate 1 7 0 5 km of denudation since 78 myr with a phase of accelerated denudation at 82 43 m myr from 78 to 64 myr average denudation rates declined to about 10 m myr during much of the tertiary although the apatite fission track data do not provide any direct constraints on the denudational history of the lesotho highlands interpolation between the two boreholes constrained by geological evidence and extrapolated in situ produced cosmogenic 36cl derived denudation rate estimates suggests a pattern of denudation compatible with numerical modeling studies of escarpment evolution involving rapid river incision seaward of a preexisting inland drainage divide these patterns of denudation are incompatible with constant retreat of the drakensberg escarpment from an initial position near the present coast we suggest that the drakensberg escarpment formed by rapid post breakup river incision seaward of a preexisting drainage divide located just east of the present escarpment location and became pinned at this divide with subsequent retreat rates of only 100 200 m myr

paleoceanographic changes in the ulleung basin east japan sea during the last 20 000 years evidence from variations in element composition of core sediments a millennial scale paleoceanographic record of the ulleung basin in the southern part of the east japan sea es for the last 20 000 years was reconstructed based on variations in the element compositions of core sediment most of the elements showed relatively wide content ranges throughout the core largely because of different sediment types their grain size spectra biological components and geochemical conditions i e redox conditions in particular biogenic components ca sr ba and caco 3 and some minor elements cu mn mo u cd zn and v revealed three distinct intervals of major paleoceanographic changes interval 1 similar to 18 9 3 kyr bp is characterized by a rhythmic alternation of dark and light colored sediment bands distinctive differences in the abundance of organic carbon carbonate and redox elements between the dark and light colored sediment layers are probably attributable to especially those associated with bottom water redox variations combined with the enhanced primary productivity and water stratification in the ulleung basin

geochemistry of alkaline earth elements mg ca sr ba in the surface sediments of the yellow sea abstract the concentrations of alkaline earth elements were measured in the surface sediments of the yellow sea in an attempt to establish their sources from horizontal distributions the maximum concentrations of mg are found in the central yellow sea and its horizontal distribution is mainly controlled by quartz dilution the concentrations of ca and sr increase toward the southeastern yellow sea region the relatively higher enrichment of ca and sr in the southeastern yellow sea with sr ca ratios of 0 0053 suggests the presence of carbonates which are comprised of foraminifera and or coccoliths like deep sea carbonates on the other hand the concentrations of ba increase toward the northeastern yellow sea the higher ba enrichment in the sandy region of the northeastern yellow sea is associated with the presence of feldspar as evidenced by excellent correlations among ba mg al mg and sr ca ratios our results suggest that the transgressive and relict sand occurring in the eastern parts of the yellow sea contains al sr and ba enriched feldspars which originated from arprock river korea and thus can be distinguished from sand occurring in the western parts of the yellow sea which originated from yellow and yangtze rivers

response to comment on a reporting protocol for thermochronologic modeling illustrated with data from the grand canyon we suggested a reporting protocol for thermochronologic modeling with which to arrange and explain the choice of thermal history modeling inputs and emphasized the need to fully depict model outputs flowers et al 2015 our goals were to improve transparency and reproducibility in thermochronologic data interpretation and motivate a broader discussion of this topic we welcome the contribution by gallagher 2016 and agree that clearly conveying how well a preferred thermal history model outcome honors the data is essential to allow evaluation of the derived conclusions and how they can be tested however in our view how this goal is best achieved depends largely on the modeling approach rather than posing a one size fits all scheme in this case we suggest that the developers of the modeling software and their user communities should define best practices to which users should adhere

super dual auroral radar network observations of meteor echoes radar echoes from ranges less than 500 km are routinely observed by the super dual auroral radar network superdarn on most days many of these echoes have properties which are markedly different from what one would expect from e or f region irregularities we show that these unusual short range hf echoes are due to scattering off meteor trails this explains why among other things the doppler shift from the short range echoes taken from the superdarn saskatoon antenna are consistent with the mesospheric winds observed by the saskatoon mf radar this means that the superdarn radars can be used to study neutral winds at meteor heights a result which is especially interesting since it opens up the capability for a global coverage of mesospheric winds using the worldwide distribution of superdarn radars

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

geochemical variability induced by entrainment sorting quantified signals for provenance analysis abstract a substantial part of the mineralogical and chemical heterogeneity of clay poor sands at the bed scale results from tractive redistribution of the grains in the bedload since coarse and light particles are more easily entrained than denser and smaller heavy minerals the latter commonly concentrate in grain scale lags that alternate with sand depleted in these minerals when sampled and analysed at the centimetre scale this primary heterogeneity translates into nice geochemical covariations between the minor trace elements that concentrate in some heavy minerals zr ti p cr v y ce among others regressing these variations allow us to derive two chemical fingerprints of the sand one records the proportions between some heavy minerals the other the average composition of framework grains i e a sand composition corrected from the contribution of heavy minerals both relate to provenance and allow different sand beds to be compared in appropriate spider diagrams the construction of these diagrams their potential use and their limitations are discussed using two contrasting examples continental channel sandstones from the ravenscar group middle jurassic yorkshire uk illustrate how these geochemical fingerprints vary from the local to the group scales and how robust they are against diagenetic overprint at ravenscar the zr vs ti v cr covariations record the presence of ti oxides and magnetite together with zircon and of volcanic lithoclasts at the deposition stage despite a high degree of diagenetic alteration overbank sandstones lateral to channels from the deep marine gres d annot formation eocene oligocene alps illustrates how apatite and monazite delivered by a dominantly granitic source generate covariations between zr and p y ce and th contents with characteristically steep slopes

geochemistry of sediments in the northern and central adriatic sea abstract major minor and trace elements loss of ignition specific surface area quantities of calcite and dolomite qualitative mineralogical composition grain size distribution and organic micropollutants pah pcb ddt were determined on surficial marine sediments sampled during the 1990 ascop adriatic scientific cooperative program cruise mineralogical composition and carbonate content of the samples were found to be comparable with data previously reported in the literature whereas geochemical composition and distribution of major minor and trace elements for samples in international waters and in the central basin have never been reported before the large amount of information contained in the variables of different origin has been processed by means of a comprehensive approach which establishes the relations among the components through the mathematical statistical calculation of principal components factors these account for the major part of data variance loosing only marginal parts of information and are independent from the units of measure the sample descriptors concerning natural components and contamination load are discussed by means of a statistical model based on an r mode factor analysis calculating four significant factors which explain 86 8 of the total variance and represent important relationships between grain size mineralogy geochemistry and organic micropollutants a description and an interpretation of factor composition is discussed on the basis of pollution inputs basin geology and hydrodynamics the areal distribution of the factors showed that it is the fine grain size fraction with oxides and hydroxides of colloidal origin which are the main means of transport and thus the principal link between chemical physical and granulometric elements in the adriatic

development of anoxia during the holocene fresh brackish water transition in the baltic sea one of the most pronounced environmental changes during the holocene baltic sea history was the transition from the freshwater ancylus lake to the brackish water litorina sea the establishment of

exploiting radiation damage control on apatite u th he dates in cratonic regions abstract apatites from four pairs of samples of precambrian basement from the western canadian shield were analyzed by u th he thermochronometry to test for the influence of radiation damage on apatite u th he dates in this cratonic region recent studies have demonstrated that the accumulation of radiation damage increases the apatite he retentivity so that apatites with a span of effective u concentrations eu that experienced the same thermal history may be characterized by a range of closure temperatures in this investigation each sample pair consisted of a mafic dike cross cutting felsic gneisses from a single outcrop or nearby outcrops that contained apatites with a span of eu the apatites yielded u th he dates from 846 to 123 ma and were positively correlated with eu within each sample pair these results can be explained using a model that tracks the evolution of he mobility in response to the accumulation of radiation damage when coupled with regional geological constraints the data appear to require partial to complete he loss due to burial and reheating in phanerozoic time new apatite fission track dates and length data were obtained for five of these samples the apatite fission track dates are proterozoic regardless of apatite eu thermal history simulations indicate that the apatite fission track data are compatible with the u th he results although the thermal histories are not identical in detail and the fission track results alone do not require phanerozoic heating together the data are consistent with burial of this region by 1 km of phanerozoic strata that were subsequently denuded thus pointing toward significant phanerozoic deposition in the north american cratonic interior hundreds of kilometers east of where previously documented the results suggest that exploiting radiation damage control on apatite u th he dates through investigation of surface sample apatites with a span of closure temperatures can impose tighter restrictions on thermal histories in low relief cratonic landscapes than was previously possible

u pb zircon and titanite systematics of the fish canyon tuff an assessment of high precision u pb geochronology and its application to young volcanic rocks a large data set of single and multi grain zircon and titanite analyses from a sample of the oligocene fish canyon tuff fct a voluminous ash flow from the san juan mountains of colorado and widely used 40ar 39ar geochronological standard has been used to evaluate the influence of various sources of analytical and geological uncertainty on the calculated age of this tuff by the isotope dilution u pb zircon method twenty three single zircon grains and seven small multi grain fractions of the fct yield an inverse variance weighted mean 206pb 238u date of 28 402 0 023 ma 2 mswd 0 93 and a slightly older weighted mean 207pb 235u date of 28 529 0 030 ma mswd 0 74 which are insensitive to common pb corrections initial 230th disequilibria calculated from a newly measured th u 2 2 for fct pumice shards indicate th deficiency for these zircons its correction brings the weighted mean 206pb 238u date to 28 478 0 024 mswd 0 97 minimizing the discordance of the fct zircon analyses these calculations culminate in concordia ages ludwig 1998 for the crystallization of the fct zircons of 28 476 0 029 ma mswd 1 50 without propagating decay constant errors or 28 498 0 035 ma mswd 1 03 with propagated decay constant errors these results are in close agreement with a previous single grain 206pb 238u zircon date of 28 41 0 05 ma for the fct oberli et al 1990 however they do not corroborate the discordia lower intercept date of 27 52 0 09 put forth by lanphere and baadsgard 2001 the 28 476 0 064 ma concordia age for fct zircons including systematic decay constant errors and uncertainty in pb u tracer calibration is substantially older than all published 40ar 39ar sanidine ages which range from 27 5 to 28 05 ma lanphere and baadsgaard 1997 renne et al 1998 a lengthy period 400 k y of zircon residence in the magma chamber before eruption is commonly called upon to explain the age discrepancy however fct titanite which may remain open to pb diffusive exchange until quenching upon eruption yield a minimum 230th disequilibrium corrected weighted mean 206pb 238u age of 28 395 0 049 ma 0 078 with tracer uncertainty weakening residence time arguments and supporting recent calls for re evaluation of the 40k decay constant and the accepted ages for commonly used 40ar 39ar mineral standards the fct zircon concordia age also provides an empirical constraint on the decay constants of the u isotopes indicating the relative accuracy of the currently accepted decay constants to within the original counting statistic errors of jaffey et al 1971

dynamic subauroral ionospheric electric fields observed by the falkland islands radar during the course of a geomagnetic storm ion drift said located between 53 and 58 magnetic south and lasting 6 5 hours was observed by the falkland islands radar in the pre midnight sector coincident flow data from the dmsp satellites and the magnetically near conjugate northern hemisphere blackstone hf radar reveal that the said was embedded within the broader subauroral polarization streams saps dmsp particle data indicate that the said location closely followed the equatorward edge of the auroral electron precipitation boundary while remaining generally poleward of the equatorward boundary of the ion precipitation the latitude of the said varied throughout the interval on similar timescales to variations in the interplanetary magnetic field and auroral activity while variations in its velocity were more closely related to ring current dynamics these results are consistent with said electric fields being generated by localized charge separation in the partial ring current but suggest that their location is more strongly governed by solar wind driving and associated large scale magnetospheric dynamics

magma evolution at mount vulture southern italy the vulture complex is made up of foiditic tephritic phonolitic trachytic and phonolitic products new rock analyses have been performed in order to ascertain whether the various rock types derive from a unique parental magma and if so to define its nature the data presented support that the vulture suite originated from a foiditic melt which had differentiated at low pressures the main process determining the foidite tephrite phonolitic trachyte evolution seems to be the crystal fractionation of mainly clinopyroxenes and opaques with the contribution of plagioclases and hauyne too in the tephrite trachyte evolution additionary role must have been played by a mixing of melts at different evolution stages occurred in a shallow seated magma chamber

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

provenance of surface sediments along the southeastern adriatic coast off italy an overview multi proxy studies are necessary to understand sediment composition and related provenance on continental shelfs here it is shown that the spatial distribution of geochemical composition and grain size for surface sediments along the southeastern italian coast is related to provenance and mechanisms influencing sediment pathways a northern adriatic italian provenance can be distinguished from a southern apennine river source this is done independent of grain size using the element ratios ce ni and zr cr furthermore the origin of organic matter is determined using bulk carbon isotopes and the c n ratio integrating these results with those from complementary studies on 18o and 13c of globigerinoides ruber white the bit index stable isotopes of plant waxes and dinoflagellate cyst distribution from the same set of samples reveals that sediments from the northwestern adriatic are transported as far southward as the gallipoli shelf eastern gulf of taranto by the western adriatic current wac along the wac there is a consistent southward decrease in po river northern apennines provenance and a concomitant decrease in terrestrial soil organic matter om whereas the percentage of marine om increases the provenance for gallipoli shelf sediments is for 80 attributed to po river northern apennines sources and for 20 to southern italian sources om in the eastern gulf of taranto contains more marine om than other areas within the wac whereas om and sediments from the western part of the gulf of taranto have a more local riverine provenanc

isotopic and ree characteristics of the intrusive charnoenderbite and enderbite geographically associated with the matok pluton limpopo belt southern africa abstract intrusive charnoenderbite and enderbite in the southern marginal zone of the limpopo belt are genetically linked with peak metamorphism m1 during the 2700 ma to 2650 ma limpopo orogeny they occur geographically associated with and are intruded by the granodiorite and granite of the matok pluton which were emplaced between the response phase m2 and the rehydration phase m3 of that orogeny rb sr pb ree and sm nd elemental and isotopic data for whole rock samples and u pb data for populations of zircon suggest that the charnoenderbite and enderbite were intruded 2671 ma ago and were derived from a crustal precursor the granodiorite and granite of the matok pluton were intruded at approximately the same time between 2667 ma and 2664 ma ago they also were derived from a crustal precursor nd model ages and ree patterns for the charnoenderbite and enderbite and the granodiorite are distinct this relationship may imply that they are not cogenetic alternatively these rock types could be cogenetic if the magma from which they were derived was assimilating older crustal material as it evolved nd isotopic data indicate that the magma giving rise to the charnoenderbite and enderbite formed by partial melting of rocks compositionally similar to some portions of the baviaanskloof gneiss data for the granodiorite are consistent with the possibility that this unit formed in a similar manner from rocks compositionally similar to other portions of the baviaanskloof gneiss the close temporal relationship between the emplacement of the charnoenderbite and enderbite and the granitic rocks of the matok pluton indicates that the retrograde portion of the limpopo orogeny beginning 2670 ma ago occurred rapidly perhaps over 7 ma

cyclic variations in the chemical composition of eastern mediterranean pliocene sediments a key for understanding sapropel formation abstract two pliocene mediterranean sediment cores from ocean drilling program odp leg 160 sites 964 pisano plateau ionian basin and 967 lower northern slope of eratosthenes seamount south of cyprus have been analyzed for major and minor elements si ti al fe mg ca k ba cr ni v zn zr by x ray fluorescence analysis at a depth resolution of 3 to 4 cm a total of 430 samples core 964c 9h comprises five sapropels with up to 9 7 total organic carbon toc one 2 5 m thick turbidite and a 50 cm segment of a second turbidite whereas core 967b 9h contains eight sapropels with toc contents of up to 6 7 cyclic variations in carbonate content and detrital matter composition are evident at both sites at site 964 pisano plateau terrigenous detrital matter chemistry reflects periods of stronger saharan dust input higher si al and zr al ratios alternating with fluvial input from the northern borderlands higher mg al ratios cyclicity is not well expressed at this location because turbidites and winnowing occur site 967 eratosthenes seamount sediments are strongly influenced by discharge from the nile river during humid periods low k al and mg al ratios at site 967 sapropels occur only during periods of enhanced nile discharge with correspondingly lower si al ti al mg al k al and zr al ratios accumulation rates of carbonate and terrigenous detrital matter were 30 lower during such episodes because of the reduction in eolian input and carbonate production and or carbonate dissolution periodical ba enrichments which are not only seen in the sapropels but in every k al minimum document the association of enhanced bioproductivity and sapropel formation as calculated from excess ba concentrations productivity increased by up to a factor of five during intervals of intensified nile runoff fluviatile discharge seems to be responsible for an enhanced input of nutrients and suspended matter containing low mg al and k al ratios based on organic carbon concentrations episodes of sapropel formation lasted at least from 1000 to 4000 years at site 964 and from 2000 to 6000 years at site 967 periods of enhanced bio productivity as defined by ba enrichments lasted from 8000 to 12 000 years at site 967 episodes of high river discharge and corresponding nutrient input as well as conditions of sapropel formation seem to have lasted longer in the eastern part of the basin site 967 than at the pisano plateau site 964

geochemistry of surface sediments off the southern and western coasts of korea abstract the continental shelf off the southern and western side of the korean peninsula is part of a modern epicontinental sea and is an effective sediment trap for clastic material derived from china and korea we have analyzed 179 surface sediment samples from this shelf for al fe na k mg ca ti p mn sr ba v cr co ni cu zn organic carbon and calcium carbonate in order to determine the geochemical characteristics of these sediments results showed a wide range of element contents which are mainly related to the textural variability of sediments exceptions to this were found in the contents of ca k sr and ba the ca and sr contents were largely determined by the amounts of carbonate present the k content on the other hand appeared to be influenced by both the contents of illite and feldspar and ba of potassium feldspar for muds i e sediments deposited under present day conditions it is possible to distinguish those in the central yellow sea from those in the keum estuary the former are characterized by high contents of fe na k mg ca and v and the latter by high contents of mn ba and co these differences become more apparent when these elements are normalized relative to al in order to minimize grain size effects the distribution of v al ratios is different from that of other elements the highest v al values occur in muds from the central yellow sea derived from the huanghe the yellow river in china whereas the highest values of mn al are found in the nearshore area adjacent to the korean peninsula based on these results it is suggested that the sources of fine sediments in the yellow and south seas can be distinguished from the geochemical characteristics of the surface sediments in the yellow sea two different sources of fine grained sediments can be seen the huanghe and the keum river the former is characterized by higher v contents and the latter by higher mn contents using the v al ratio as an end member component of the two source materials the dispersal patterns of the fine sediments 6o were also derived

first observations of the midlatitude evening anomaly using super dual auroral radar network superdarn radars 1 under geomagnetically quiet conditions the daytime midlatitude ionosphere is mainly influenced by solar radiation typically electron densities in the ionosphere peak around solar noon previous observations from the millstone hill incoherent scatter radar isr have evidenced the presence of evening electron densities higher than daytime densities during the summer the recent development of midlatitude super dual auroral radar network superdarn radars over north america and japan has revealed an evening enhancement in ground backscatter during the summer superdarn observations are compared to data from the millstone hill isr confirming a direct relation between the observed evening enhancements in electron densities and ground backscatter statistics over a year of data from the blackstone radar show that the enhancement occurs during sunset for a few hours from april to september the evening enhancement observed by both superdarn and the millstone hill isr is shown to be related to recent satellite observations reporting an enhancement in electron densities over a wide range of longitudes in the northern hemisphere midlatitude sector during summer time finally global results from the international reference ionosphere iri and the horizontal wind model hwm07 are presented in relation with previously published experimental results and proposed mechanisms of the evening enhancement namely thermospheric horizontal winds and geomagnetic field configuration it is shown that the iri captures the features of the evening enhancement as observed by superdarn radars and satellites

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

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

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

comment on distinguishing slow cooling versus multiphase cooling and heating in zircon and apatite u th he datasets the case of the mcclure mountain syenite standard by weisberg metcalf and flowers

emplacement and crystallization time for the bushveld complex the bushveld complex formed by the crystallization of successive basaltic magmatism may be of the order of several million years for example the columbia river basalts hooper injections of magma which were sufficiently closely spaced in time that each previous magma had not cooled and differentiated 1988 were erupted in the period 17 12 ma with minor eruptions for a further 5 my although most outpouring significantly before the addition of the next one to constrain the emplacement and crystallization times a thermal model is presented occurred within the first 2 my it is now recognized that large intrusions were not emplaced in a single pulse but which permits the investigation of the rate of cooling of magma in an intrusion repeatedly subjected to magma addition and subresult from multiple magma injection the question is how rapidly were magma chambers such as the bc traction such modelling indicates that magmas injected into the bushveld complex were emplaced within 75 000 years at that filled and how much magma was involved answers are relevant to the dynamics of melt production storage and time injection into the complex ceased the volume of rock in the eastern and western limbs is 370 000 600 000 km however transport in the mantle and crust this paper describes a thermal modelling technique not previously applied a quantitative evaluation of the cr budget in the formation of chromitite layers indicates that large volumes of magma cannot be to magma chambers which can be used to analyse this process and to obtain an estimate of the emplacement accounted for in the preserved rock sequence similarly an evaluation of the incompatible trace element abundances such as those for zr time to present this model it is necessary to discuss the stratigraphy size and connectivity of the different limbs and k suggests that the chamber was open and that large volumes of differentiated magma escaped the volume of magma therefore of the bushveld complex and to consider the extent of tapping of the magma chamber as well as its filling greatly exceeded the preserved volume of cumulate rocks giving an estimated magma volume of over 1 10 km an average the term bushveld complex has been given several meanings in the literature and according to the south emplacement rate of 13 km year is indicated by these calculations african commission on stratigraphy 1980 includes not only the ultramafic mafic layered rocks but also the sills beneath the intrusion volcanic rocks which pre date the

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

the adriatic sea general circulation part ii baroclinic circulation structure abstract in the second part of the paper dedicated to the adriatic sea general circulation the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the adriatic sea which at the surface is associated with the major dilution effects of river runoff the density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation winter is dominated by compensation effects between temperature and salinity fronts along the western coastline the resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin scale gyres and current systems which have been classified in a schematic representation of the circu

multielement geochemistry of offshore sediments in the southeastern yellow sea and implications for sediment origin and dispersal abstract in total 116 surface sediments were collected from an offshore area of the southeastern yellow sea including a large mud belt southeastern yellow sea mud seysm and analyzed for grain size and geochemical composition organic carbon and 42 elements principal component analysis revealed that elemental compositions of the offshore sediments were mostly controlled by common aluminosilicate clay minerals and quartz most elements heavy minerals hf zr u th rare earth elements rees biogenic calcium carbonates ca sr feldspar and mica k ba pb and mn oxides mn oxide coatings on sand grains notably total ree concentrations may be associated with heavy minerals possibly zircon and monazite especially in silty grains even though heavy ree hrees concentrations are more strongly controlled by clay minerals in muddy sediments the diagnostic discrimination plots of geochemical compositions e g fe vs al mg vs al light ree vs hree and la lu ucc vs la y ucc suggested that the offshore sediments especially in seysm deposits were composed of a mixture of korean river derived silts and chinese river derived clays this demonstrated that chinese river sediments especially clay particles largely contributed to the formation of the giant mud belt in the korean coastal area furthermore the observed geochemical end members provide new markers of sediment provenance which can be used to track dispersal patterns and sediment limits from chinese and or korean rivers

natural age dispersion arising from the analysis of broken crystals part ii practical application to apatite u th he thermochronometry abstract we describe a new numerical inversion approach to deriving thermal history information from a range of naturally dispersed single grain apatite u th he ages the approach explicitly exploits the information about the shape of the 4he diffusion profile within individual grains that is inherent in the pattern of dispersion that arises from the common and routine practice of analysing broken crystals additional dispersion arising from differences in grain size and in u and th concentration of grains and the resultant changes to helium diffusivity caused by differential accumulation and annealing of radiation damage is explicitly included in this approach we calculate the ingrowth and loss due to both thermal diffusion and the effects of ejection of helium over time using a finite cylinder geometry broken grains are treated explicitly as fragments of an initially larger crystal the initial grain lengths l0 can be treated as unknown parameters to be estimated although this is computationally demanding a practical solution to the problem of solving for the unknown initial grain lengths is to simply apply a constant and sufficiently long l0 value to each fragment we found that a good value for l0 was given by the maximum fragment length plus two times the maximum radius of a given set of fragments currently whole crystals and fragments with one termination are taken into account a set of numerical experiments using synthetic fragment ages generated for increasingly complex thermal histories and including realistic amounts of random noise 5 15 are presented and show that useful thermal history information can be extracted from datasets showing very large dispersion these include experiments where dispersion arises only from fragmentation of a single grain length 400 m and radius 75 m c 6 50 dispersion including the effects of grain size variation for spherical equivalent grain radii between 74 and 122 m c 10 70 dispersion and the combined effects of fragmentation grain size and radiation damage for eu between 5 and 150 ppm c 10 107 dispersion additionally we show that if the spherical equivalent radius of a broken grain is used as a measure of the effective diffusion domain for thermal history inversions then this will likely lead to erroneous thermal histories being obtained in many cases the viability of the new technique is demonstrated for a real data set of 25 single grain u th he apatite ages obtained for a gabbro sample from the bk 1 bierkraal borehole drilled through the bushveld complex in south africa the inversion produces a well constrained thermal history consistent with both the u th he data and available fission track analysis data the advantage of the new approach is that it can explicitly accommodate all the details of conventional schemes such as the effects of temporally variable diffusivity zonation of u and th and arbitrary grain size variations and it works equally effectively for whole or broken crystals and for the most common situation where a mixture of both are analysed for the routine application of the apatite u th he thermochronometry technique with samples where whole apatite grains are rare our experiments indicate that 15 20 single grain analyses are typically required to characterise the age dispersion pattern of a sample the experiments also suggest that picking very short crystal fragments as well as long fragments or even deliberately breaking long crystals to maximise the age dispersion in some cases would ensure the best constraints on the thermal history models the inversion strategy described in this paper is likely also directly applicable to other thermochronometers such as the apatite rutile and titanite u pb systems where the diffusion domain is approximated by the physical grain size