luhf geochronology applied to dating cenozoic events affecting lower crustal xenoliths from kilbourne hole new mexico abstract melt extraction or crystal accumulation events that affected garnet bearing granulite xenoliths from kilbourne hole new mexico have been dated using the lu hf isotope system two garnet bearing granulites from kilbourne hole have extreme 176 lu 177 hf ratios of 0 95 and 1 3 lu hf 28 and 39 chondritic but relatively normal hf values 5 and 12 necessitating either garnet accumulation or melt extraction from a garnet bearing protolith in the cenozoic hf isotope evolution curves for these two samples intersect those of depleted mantle and proterozoic crust at high angles and at similar times demonstrating the potential of hf isotope model ages to yield true age significance even if the initial hf isotope composition is not well constrained a third garnet granulite xenolith ckh63 176 lu 177 hf 0 025 contains zircon which buffered this sample against changes in lu hf during the cenozoic differentiation event the three garnet granulites lie closely about a 25 ma lu hf reference line demonstrating the potential of the lu hf system for detecting garnet controlled differentiation events in the cenozoic given the range in lu hf ratios measured events as young as 5 ma may be detected using the lu hf system conventional u pb zircon data from sample ckh63 reveal both a ca 1 4 ga inherited component and a component of recent pb loss or new zircon growth supporting the cenozoic event documented by hf isotope model ages

the source region and melting mineralogy of high titanium and low titanium lunar basalts deduced from lu hf isotope data five high ti basalts from the apollo 11 and 17 landing sites have been analyzed for their hafnium isotope composition these data serve to better constrain the hafnium isotope variation of the moon s mantle variations in initial hf and nd values of low and high ti basalts imply that the source region mineral assemblages of these lunar magma types are distinct low ti basalts have higher initial hf values at a given nd value than high ti basalts the differences in the hafnium and neodymium isotopic composition of low and high ti basalts reflect the fact that the source of low ti basalts had a lu hf n ratio approximately four times greater than its sm nd n ratio in contrast the high ti source region had subequal lu hf n and sm nd n ratios if it is assumed that mare basalts are partial melts of the moon s cumulate mantle the differences between low and high ti basalts can only be explained by these mare magma types being generated from melting sources with distinctly different mineral assemblages the large lu hf fractionations relative to sm nd fractionations of low ti basalts can best be produced by an assemblage of olivine and orthopyroxene with trace amount of clinopyroxene that crystallized early in the history of the lunar magma ocean lmo the subequal lu hf n and sm nd n fractionations of high ti basalts can be produced from a variety of ilmenite bearing mineral assemblages low and high ti basalts have similar lu hf ratios approximately 0 6 times chondrite the low lu hf ratios measured for these mare magmas contrast sharply with the high lu hf ratios greater than chondritic calculated for their sources from initial hf values and an assumed chondritic bulk moon initial hf value the difference between the measured lu hf of a lava vs the calculated lu hf of its source implies that during partial melting lu was preferentially retained in the residual source relative to hf in order to explain the extreme fractionation of measured lu hf ratios we suggest mare basalts can best be explained using a polybaric melting model initial melting of a garnet bearing source followed by continued melting in the spinel stability field can produce the required lu hf fractionations and produce a liquid that last equilibrated with a residuum of olivine and orthopyroxene

franciscan subduction off to a slow start evidence from high precision lu hf garnet ages on high grade blocks lu hf analyses of garnet from metabasic amphibolite glaucophane schist and eclogite facies blocks from the franciscan complex give highly precise ages that allow us to place new constraints on the early thermal history of the franciscan subduction zone garnets yield 176 lu 177 hf ratios ranging from 1 5 to 28 with the highest ratios from garnets with high spessartine pyrope ratio sulphuric acid leaching sal of garnets revealed the presence of inclusions with significantly higher lu hf ratios than those of garnet itself most likely apatite their removal by sal brings the 176 lu 177 hf ratios in garnets down by as much as 40 this suggests that 176 lu 177 hf ratios of apparently pure garnets can be greatly overestimated due to the presence of such inclusions sm nd garnet analyses were dominated by inclusions mainly sphene and failed to provide precise and accurate age information the oldest lu hf ages are 168 7f0 8 and 162 5f0 5 ma on plagioclase bearing garnet amphibolite from panoche pass and the berkeley hills respectively which suggests initiation of the subduction zone at about 169 ma coeval with the formation of the tectonically overlying coast range ophiolite relatively high temperature conditions persisted for about 14 ma as indicated by 153 4f0 8 ma garnet growth recorded in epidote amphibolite and 157 9f0 7 in eclogite from ring mountain and jenner respectively a 146 7f0 7 ma age was obtained from garnet glacuophane schist metamorphosed at around 400 jc the sequence of ages from central and northern california shows a younging trend with decreasing metamorphic grade which supports previous suggestions that the high grade metamorphic blocks and slices resulted from progressive underthrusting and underplating in a cooling subduction system combining geothermometry with geochronological data allow us to estimate cooling rate along the subduction zone interface from amphibolite to blueschist facies conditions as ca 15 jc ma the thermal history requires high initial geothermal gradients within both the footwall and the hangingwall of the subduction zone and a relatively slow subduction rate of the order of 10 km ma during the initial stages of franciscan subduction such conditions are consistent with initiation of the subduction zone at or close to an oceanic spreading centre the data also suggest slow exhumation rates and significant residence time at depth of the earliest franciscan rocks

zircon lu hf systematics and the evolution of the archean crust in the southern superior province canada a combined lu hf and u th pb isotopic study was made of 25 zircons and 2 whole rocks from the late archean crust 2 888 2 668 ma in the southern superior province canada the relative abundances of u th lu and hf in zircons from the low grade michipicoten and gamitagama greenstone belts show variable patterns which in part reflect the bulk compositional differences of their parent rocks zircons from the high grade lower crustal regions adjacent to these belts kapuskasing structural zone are distinguished from the low grade zircons by their strong depletions of lu and hf the low hf contents imply that the growth of metamorphic zircon involves a significant fractionation of the zr hf ratio

hafnium isotopes in zircon a tracer of fluid rock interaction during magnetite apatite kiruna type mineralization abstract in situ analyses of hafnium isotopes in zircon combined with u pb zircon ages and trace element data provide new information on the characterization and evolution of magnetite apatite kiruna type deposits and the tectonic environments in which they occur the lyon mountain granite in the adirondack mountains of new york is the host to numerous zircon bearing magnetite apatite deposits hafnium isotopic compositions and rare earth element contents in individual zircon crystals were measured in situ in both the host granites and the ore bodies by laser ablation inductively coupled plasma mass spectrometry hafnium isotopic compositions in the ore zircon can be divided into two groups those that have initial ehf t values that are indistinguishable from those of the host granites e g ehf t less than 7 and are typical of relatively juvenile proterozoic crust and those that have extremely radiogenic ehf t values as high 40 two models are proposed to explain the observed ehf t values in the zircon crystals 1 early formed ore bodies containing magnetite apatite and clinopyroxene were remobilized by secondary fluid alteration releasing zr and hf for the crystallization of new zircon or alternatively 2 fluids responsible for ore formation have interacted with garnet bearing rocks during retrograde metamorphism scavenging rare earth elements and radiogenic hf previous work done to determine the u pb ages from the same zircon crystals which were analyzed for the hf isotopic composition in this study revealed that ore bodies record a mineralizing event that is 20 to 60 m y younger than the age of granite emplacement this age discrepancy plus the highly radiogenic ehf t values in the ore zircon crystals suggests that the fluids responsible for this younger event could not have been derived from the granite hosts these data argue that magnetite apatite deposits in the lmg have multiple mineralizing events superimposed upon one another and that early formed deposits may be reworked modified and redeposited by fluids subsequent to magma crystallization

statistical analysis of an ionospheric parameter as a base for earthquake prediction 1 this paper is related to the use of ionospheric density variations to tentatively predict earthquakes the results of this statistical analysis are presented as a function of various parameters the ion density was recorded by the low altitude satellite demeter during more than 6 years and a search for anomalies was automatically conducted with the complete data set in a second time a software checked if each anomaly could correspond to an earthquake the search was conducted at less than 1500 km from the anomaly positions and until 15 days after the anomaly time the earthquakes have been classified depending on their magnitude depth and position below the sea or inland this attempt to predict earthquakes of course generates a lot of false alarms and wrong detections nevertheless it is shown that the number of good detections increases with the magnitude of the earthquakes in average the number of perturbations is higher the day of the earthquake and then smoothly decreases for the days before earthquakes below the sea are better detected there are seismic areas close to the south atlantic magnetic anomaly and at high latitudes where the number of natural perturbations is too important to expect a high number of good detections finally when there are several perturbations corresponding to a single earthquake it is possible to combine their positions to have a better estimation of the location of the future epicenter however uncertainties about the time and the magnitude are large

derivation of mesozoic adakitic magmas from ancient lower crust in the north china craton three mesozoic plutons were intruded into the archean granulite terrains in northern margin of the north china craton adjacent to the granulite xenolith bearing tertiary hannuoba basalts they are triassic guzuizi and honghualiang granites and early cretaceous zhuanzhilian diorite rocks of the three intrusions are characterized by high sr 576 1216 ppm and na2o 4 0 low y 18 ppm and heavy rare earth elements yb 1 8 ppm these features are similar to modern adakites siliceous rocks with high sodium aluminum and strontium and low heavy rare earth element and yttrium contents from island arcs and archean high al tonalite trondhjemite granodiorite ttg however they are distinctly potassium rich and their evolved strontium neodymium and hafnium isotopic compositions and inherited zircon ages coincide with those of the archean granulites and the hannuoba granulite xenoliths such features cannot readily be explained with previous models of the origin of adakites and ttgs we propose that these adakitic rocks are formed by partial melting of ancient lower crust and that the restites are represented by some of the hannuoba granulite xenoliths we further argue that this could be one major mechanism to generate voluminous mesozoic adakitic magmas in the eastern north china craton our hypothesis can also explain the discrepancies in ages and compositions between the granulite terrains and xenoliths and implies that crustal anatexis may be one of the major processes controlling the chemical differentiation of the continental crust

a statistical study on the characteristics of ionospheric storms in the equatorial ionization anomaly region gps tec observed over taiwan 1 positive and negative signatures of the ionospheric storms caused by the penetration electric field disturbance dynamo neutral wind neutral composition etc have been reported in this paper the ionospheric total electron content tec derived from the records of a network of ground based gps receivers in taiwan is used to statistically study the characteristics such as local time of appearance and duration of the storm signatures of various casuals in the equatorial ionization anomaly eia region during 1994 2003 a bias corrected accelerated bootstrap method and a z test are employed for the first time to detect each event and the overall storm signatures and characteristics respectively it is found that the positive signatures that appeared minutes to hours after the geomagnetic storm onset are pronounced on the storm day and the next day while the negative signatures that started hours after the geomagnetic storm onset can last for as long as the next 4 days the positive signature is statistically significant and most pronounced when the intense geomagnetic storm onset occurs during local afternoon which suggests that the signature may result from a combination of the prompt penetration electric field effect and mechanical effects of equatorward neutral wind additionally the negative signature that is statistically significant and most pronounced in the local afternoon of the storm onset day and or the next day may be produced by the disturbance dynamo or overshielding effects the long lasting negative signature occurred in local midnight noon period on days 2 4 after the storm onset may result from the neutral composition disturbances

a chemical method for hafnium separation from high ti whole rock and zircon samples abstract a chemical separation method of hf from rocks is presented a procedure involving three stages of ion exchange columns and sulfuric acid as an eluant produces consistent zr and ti free hf separations the methods described are well suited for high ti samples such as mafic rocks in addition the method provides a very efficient means for hf separation from zircons

garnetite xenoliths and mantle water interactions below the colorado plateau southwestern united states garnetite xenoliths from ultramafic diatremes in northeastern arizona provide insights into hydration and metasomatism in the mantle the garnetites contain more than 95 garnet some of which has complex compositional zonation related to growth in fractures within grains accessory minerals include rutile ilmenite chlorite clinopyroxene and zircon zircon grains in one rock were analyzed in situ to determine u pb ages and hf isotopic compositions most u pb analyses plot on or near concordia in the range 60 85ma but a few are discordant the range in 176 hf 177 hf is about 0 2818 0 2828 with grains zoned to more radiogenic hf from interiors to rims the garnetite protolith contained zircons at least 1 8ga in age and garnet and additional zircon crystallized episodically during the interval 85 60ma the garnetites are interpreted as mantle analogues of rodingites formed in metasomatic reaction zones caused by water rock interactions in proterozoic mantle during late cretaceous and cenozoic subduction of the farallon plate associated eclogite xenoliths may have been parts of these same reaction zones the rodingite hypothesis requires serpentinization in the mantle wedge 700km from the trench beginning 5 10myr before tectonism related to low angle subduction

a sediment budget for a small semiarid watershed in southeastern arizona usa article i nfo article history a sediment budget was developed for a 43 7 ha and a nested 3 7 ha semiarid shrub dominated watershed based on hydrologic geomorphic erosion and sediment data collected from 1963 through 2006 on the usda ars walnut gulch experimental watershed in the southwestern us sediment budgets based on such extensive and intensive field campaigns over several decades are rare the sediment budget was bal anced with a high degree of confidence because the study watershed is controlled by an earth dam at the out let although the channel network is well developed and incising in the steeper reaches of the watershed hillslopes are the dominant source of sediment contributing 85 of the overall total sediment yield erosion and sediment redistribution were driven by highly variable rainfall and runoff during july august and september sediment transfers are influenced by channel abstractions and the presence of the outlet dam which created conditions for deposition in the pond approach reach although earth dams are ubiquitous throughout the southwestern us and they can provide a measure of outlet sediment yield these outlet mea surements may be insufficient to interpret temporal and spatial variability in watershed sediment dynamics identification of dominant processes and sediment sources is critical for determining management actions that will improve rangeland conditions published by elsevier b v

combined high precision chronometry and geochemical tracing using accessory minerals applied to the central alpine bergell intrusion central europe abstract the behaviour of nd u th and pb isotopes in granitic rocks is usually controlled by accessory minerals in this study an approach is adopted which uses the initial 143 nd 144 nd as a geochemical tracer together with high precision u th pb geochronology for accessory phases and their respective whole rock this combination of techniques is applied to zircon allanite sphene apatite and thorite from both a tonalite and a granodiorite from the tertiary alpine bergell intrusion inherited isotopic signatures have been identified in bulk zircon fractions by inverse discordance in the u pb system in the case of the granodiorite the initial nd in the zircon is 1 77 units lower than the bulk rock this result indicates that nd isotopes in zircon may serve as a useful tool for tracing crustal precursors in silicic rocks all other accessories yield an initial nd equal to their respective whole rock and u th pb ages equal to or lower than the respective intrusion ages this indicates either the absence of inherited cores or that such cores have exchanged their nd and pb in the case of apatite also sr by diffusion where available experimental mineral melt equilibria and diffusion models are consistent with this behaviour u pb geochronology of carefully selected core free zircons yields a precise intrusion age of 31 88 0 09 ma for the tonalite in contrast granodioritic zircons are partially reset due to radiation damage caused by high u concentrations however an alternative means of dating young intrusions is to use 232th 208pb ages of allanite in the case of allanite the presence of a large excess of 206pb derived from 230th indicates that no total pb loss has occurred since crystallization and the nd isotopes indicate the absence of inheritance using both the allanite age and a 238u 206pb age for sphene an intrusion age of 30 13 0 17 ma is indicated for the granodiorite taken together with an allanite th pb age for the tonalite these results strongly support the high closure temperatures for the allanites studied here 700 800 c at high post magmatic cooling rates all other accessory mineral ages are reset to values similar to hornblende 39ar 40ar ages and reflect the effect of post magmatic cooling superimposed on post metamorphic cooling

hf zr and ree partition coefficients between ilmenite and liquid implications for lunar petrogenesis hf zr and ree partition coefficients between ilmenite and coexisting liquid were determined under near lunar conditions ilmenite was synthesized at 1125 c under low oxygen fugacity fo2 10 12 4 from glass of a high ti mare basalt composition doped with 50 100 g g of ree and hf and 500 1000 g g of zr the partition coefficients d of ilmenite for hf and zr obtained by isotope dilution analysis are 0 41 and 0 33 respectively these values are significantly lower than those of ilmenite 3 0 and 1 8 respectively from a kimberlite megacryst fujimaki et al 1984a dree for the synthesized ilmenite are slightly smaller than those of ilmenite from the kimberlite megacryst and the dlu is 0 056 these results suggest that ilmenite may have played an important role in the lu hf evolution of lunar mare basalts using newly determined dlu and dhf for ilmenite the lu hf evolution or lunar cumulates and the coexisting magma was examined for several different crystallization sequences by a model calculation the lu hf variation trend of most high ti mare basalts is well explained by a small degree less than 5 of partial melting of the cumulates however a higher degree of partial melting is required to explain the variation of very low ti basalts green glass and apollo 12 low ti basalts apollo 15 low ti basalts could not be produced by simple partial melting but may require chromite crystallization as well

high precision lu and hf isotope analyses of both spiked and unspiked samples a new approach 1 the functional form of instrumentally produced mass fractionation associated with mc icp ms analysis is not accurately known and therefore cannot be fully corrected by traditional approaches of internal normalization using power linear or exponential mass bias laws we present a method for robust correction of instrumentally produced mass fractionation of both spiked and unspiked samples that can be applied to mass analysis of hf as well as nd sr os etc correction of 176hf 177hf for unspiked samples follows a traditional approach of internal normalization using an exponential law followed by normalization to a standard of known composition such as jmc 475 for spiked samples standards are used to characterize a linear instrumental mass bias coefficient the mass bias coefficient is defined by the slope of a tie line between measured and true values of a standard this approximation results in identical precision and accuracy of measurements for spiked and unspiked samples 0 005 2 external reproducibility the effects of the spike on the 176hf 177hf ratio and calculation of the molar spike sample ratio is determined by a closed form solution modified from the double spike approach used for fe isotope analysis by tims johnson and beard 1999 the measured 176lu 175lu ratios are corrected by doping the sample with er and using the 167er 166er ratio to externally normalize the 176lu 175lu ratio using an exponential law finally spike sample equilibration is confirmed for our sample dissolution protocol through analysis of varying physical mixtures of 1 ga garnet and hornblende where all the data lie on a mixing line within error on a 176lu 177hf 176hf 177hf diagram precision of 176lu 177hf ratios is determined to be 0 2 2 for standards and for physical mixtures of garnet and hornblende

an investigation of dissolution methods for lu hf and sm nd isotope studies in zircon and garnet bearing whole rock samples 1 the distinct chemical behavior of lu and hf can limit complete sample dissolution and spike sample equilibration here we investigate the effects that four dissolution methods hotplate low temperature microwave high temperature microwave and steel jacketed parr bomb have on the sm nd and lu hf isotope compositions of rocks any of the dissolution methods produce high quality sm nd isotope data and hotplate dissolution of young volcanic rocks produces adequate lu hf data however low temperature microwave and hotplate dissolution methods produce significantly different lu hf and 176hf 177hf ratios as compared to parr bomb dissolution data for old samples or those that contain garnet rutile or zircon a characteristic feature of incomplete spike sample equilibration and sample dissolution for garnet bearing samples is anomalously high 176lu 177hf ratios relative to 176hf 177hf ratios our results show that for lu hf isotope studies of rocks of any significant age the errors in calculated initial hf values may exceed 10 hf units if complete dissolution and spike sample equilibration are not attained for garnet or zircon bearing rocks high temperature and pressure dissolution such as that which can be achieved through parr bomb dissolution is critical to ensure complete dissolution of refractory phases such as garnet or zircon

hf nd isotopic evolution of the lower crust we report hf isotopic data for over 50 well studied lower crustal samples from three proterozoic and phanerozoic regions in southwest europe eastern australia and southern mexico we use these data to characterize the lu hf isotopic composition of the lower crust and in combination with existing sm nd data to constrain coupled hf nd isotopic behavior and evolution within this reservoir although most of these samples have present day parent daughter p d ratios consistent with hf nd evolution within the terrestrial hf nd array some samples have divergent p d ratios that would evolve out of the terrestrial array in 1 ga or less the present day 176hf 177hf and 143nd 144nd isotopic compositions of all samples with one lone exception plot within the terrestrial array this indicates that 1 some present day p d ratios may be a relatively recently acquired characteristic through magmatic or metamorphic processes not related to the time integrated sm nd and lu hf ratios of their sources and or 2 the lu hf and sm nd p d variations exist on a small hand size scale but not necessarily on a larger scale the lower crust from this initial data set is broadly similar to the upper crust in terms of both its present day p d values and time integrated lu hf and sm nd evolution as a result the lower crust appears to have a hf and nd isotopic composition similar to that of all other crust and mantle reservoirs so far characterized

characteristics and timing of the cu mo mineralization in the kighal porphyry stock nw iran implications for the timing of porphyry cu related magmatism in iran and southern armenia abstract the quartz monzonite porphyry stock at kighal in northwestern iran intruded the upper eocene andesite to latite and basalt units and the resulted hydrothermal activities led to the development of hydrothermal alteration zones including potassic phyllic argillic and propylitic coupled with cu mineralization hypogene sulfide mineralization principally occurred within the potassic transitional potassic phyllic and phyllic alteration zones as disseminations stockwork veinlets and open space fillings these hypogene minerals include pyrite chalcopyrite and molybdenite along with lesser amounts of sphalerite and galena at the marginal parts of the porphyry stock by taking into account the development of hydrothermal alteration zones and their spatial distribution stockwork type mineralization of cu mo minerals and even the occurrence of mineralization zoning with cu mo rich ore within the stock and cu pb zn ore in the marginal parts mineralization at kighal in association with the quartz monzonite sub volcanic stock can be regarded as of porphyry copper type however its low cu and mo grade detracts its economic potential zircon u pb geochronology of the porphyry stock yielded early miocene ages of 20 0 0 2 to 18 8 0 2 ma with a weighted mean of 19 24 0 17 ma which correspond to the third porphyry cu metallogenic epoch in nw iran the age data show that it is a little younger than the quartz monzonite porphyry stock in the sungun porphyry copper deposit pcd and the porphyritic granodiorite stock in the niaz prospect while it is almost coeval with the porphyritic granodiorite stock in the haft cheshmeh pcd as well as with the mineralization at the masjed daghi pcd in nw iran the th u ratios of the zircons range between 0 37 and 0 59 corresponding to the values for magmatic zircons the analyzed zircons mainly possess initial ehf t values of 6 7 to 10 0 which suggest a juvenile and homogeneous magmatic source and the predominance of mantle derived magmas with limited crustal assimilation

chronology of the angrite parent body and implications for core formation in protoplanets abstract angrites formed by some of the earliest igneous activity in the solar system and provide insights into the early stages of planetary melting and differentiation moreover they are pivotal reference points for early solar system chronology in order to study the processes and timescales of metal segregation in early protoplanets and to assess the distribution of short lived radionuclides in the early solar system the 182 hf 182 w system was applied to a comprehensive suite of angrites 182 hf 182 w isochron ages for angrites are in excellent agreement with previously reported 207 pb 206 pb and 53 mn 53 cr results but are 1 myr older than ages obtained from 26 al 26 mg chronometry these inconsistencies probably reflect a disturbance of the al mg system in the angrite feldspars but could alternatively be explained by a heterogeneous distribution of 26 al in the early solar system based on the hf w results four texturally and temporally resolved groups of angrites can be identified that were derived from at least two distinct mantle sources these mantle sources are the result of separate events of core formation both of which took place within 2 myr of cai formation thus core formation in the angrite parent body did not occur as a single event of metal segregation from a global magma ocean but rather took place under varying conditions by several more local events the disparate hf w systematics of the two distinct angrite source regions indicate that convection in the magma ocean was inefficient in homogenizing the composition of the mantle possibly as a result of a continuous bombardment with small planetesimals during ongoing core formation such impacts could have constantly removed primordial and earlier formed crust facilitating rapid cooling of the magma ocean which solidified as early as 3 6 0 7 myr after cai formation

character and origin of deep arenaceous weathering mantles on the bega batholith southeastern australia summary arenaceous weathering mantles on the bega batholith southeastern australia are similar to those described from europe by millot as in europe they have been formed by hydrothermal alteration of the parent rock and later by chemical weathering of biotites and feldspars but comparisons with nearby torfields shows that their distribution is determined largely by mineralogical variations in the parent rock unlike the examples cited by millot in the bega mantles kaolinite is the dominant clay mineral nonetheless these mantles seem to be contemporary not relict features and apparently formed under a temperate climate

lu hf geochronology on cm sized garnets using microsampling new constraints on garnet growth rates and duration of metamorphism during continental collision menderes massif turkey abstract this study shows lu hf geochronology of zoned garnet crystals contained in mica schists from the southern menderes massif turkey selected samples are four 3 5 cm large garnet megacrysts of which several consecutive garnet shells have been sampled with a micro saw and analyzed for dating the results are used to extract growth rates of garnet and also to improve the time constraint for alpine aged overprint of the pan african basement in the menderes massif lu hf ages of the sampled garnet shells are determined by two point garnet only isochrons using the garnets lu depleted rim compositions this yields a consistent decrease of age information from core to rim segments of individual garnet crystals and the calculated isochron ages propose a time frame of growth between 42 6 1 9 and 34 8 3 1 ma major element profiles in the investigated garnets characterize zoning patterns indicative of prograde conditions rayleigh fractionated bell shaped mn and decreasing fe fe mg are recorded by the garnets core to rim compositions therefore the obtained lu hf ages record timing of early prograde growth for the cores of the garnets two of the large garnet crystals also yield isochron ages of 58 83 0 69 and 50 16 0 84 ma in their innermost cores which appear to record an early nucleation event this view however is not in concordance with the observed major element profiles of these garnets and therefore is interpreted with caution termination of the garnet growth period is determined through the calculation of radial growth rates based on the size of the garnets and the lu hf ages obtained for consecutive shells extrapolation of these rates potentially constrains the total duration for garnet growth terminating at 31 6 ma comparison of the growth rates calculated for individual crystals shows a variety of slow and fast growing garnets and similar results have been previously obtained with the rb sr and sm nd isotope systems the new data provides a precise age determination for prograde barrovian metamorphism in the southern menderes massif which so far was placed between 63 and 27 ma on the basis of mica rb sr and ar ar dating this study provides new constraints crucial to the understanding of the tectonic evolution of southwest anatolia and the aegean realm as it yields a shorter outline for alpine aged continental collision

additional attenuation of natural vlf electromagnetic waves observed by the demeter spacecraft resulting from preseismic activity 1 we use vlf electromagnetic wave data measured by the demeter detection of electro magnetic emissions transmitted from earthquake regions satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity due to signals from lightning related to preseismic activity all the relevant data acquired by demeter during almost 6 5 years of the mission have been analyzed using a robust two step data processing schema this enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole demeter mission and to evaluate the statistical significance of the observed effects we confirm previously reported results of a small but statistically significant decrease of the wave intensity by 2 db at frequencies of about 1 7 khz the effect is observed for a few hours before the times of the main shocks it occurs during the night the effect is stronger between march and august at higher latitudes and for the positions of hypocenters below the sea we suggest an explanation based on changed properties of the lower boundary of the ionosphere which leads to a decrease of the intensity of lightning generated whistlers observed at the spacecraft altitude this effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the earth s surface prior to earthquakes

partition coefficients of hf zr and ree between zircon apatite and liquid concentration ratios of hf zr and ree between zircon apatite and liquid were determined for three igneous compositions two andesites and a diorite the concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients those for the apatite in the diorite may deviate from the partition coefficients the hree partition coefficients between zircon and liquid are very large 100 for er to 500 for lu and the hf partition coefficient is even larger the ree partition coefficients between apatite and liquid are convex upward and large d 10 100 whereas the hf and zr partition coefficients are less than 1 the large differences between partition coefficients of lu and hf for zircon liquid and for apatite liquid are confirmed these partition coefficients are useful for petrogenetic models involving zircon and apatite

early cretaceous subduction modified lithosphere beneath the eastern qinling orogen revealed from the daying volcanic sequence in central china abstract new geochronological geochemical and sr nd hf isotopic data for the early cretaceous daying volcanic sequence eastern qinling orogen provides a probe into the nature of and tectonic process operating in the underlying mesozoic mantle the volcanic rocks in the sequence are composed of basaltic trachyandesite pyroxene andesite trachyandesite and trachyte they yield zircon u pb and whole rock 40ar 39ar plateau ages of 134 124 ma roughly synchronous with the cretaceous igneous rocks throughout the eastern qinling and dabie orogens clinopyroxene and plagioclase phenocrysts of the volcanic rocks exhibit simple normal zonation with higher mg number and an content in the core relative to the rim the amphibole is characterized by tschermakite and tschermakitic hornblende with mg number of 50 67 the daying volcanic rocks have variable sio2 54 27 63 44 wt al2o3 15 39 20 34 wt feot 5 23 9 94 wt and mgo 1 05 4 03 wt contents with low mg number 26 49 they exhibit arc like ree and pm normalized patterns with significant negative nb ta anomalies and highly enriched sr nd isotopic composition with 87sr 86sr i ratios of 0 7066 0 7078 and end t values of 15 5 11 0 their zircons exhibit strongly negative ehf t values ranging from 27 3 to 17 2 and two staged model ages from 2 90 ga to 2 28 ga such geochemical signatures suggest that the daying volcanic rocks were derived from a hybridized source of the north china craton enriched mantle with the input of some yangtze crustal materials created by triassic deep subduction digestion they also share similar eruption time as well as elemental and sr nd hf isotopic compositions with those in the southern margin of the north china craton suggesting a northward subduction of the yangtze block it is proposed that the volcanic rocks are petrogenetically related to an early cretaceous extensional event along the qinling dabie orogenic belt in response to unrooting of the thickened lithosphere

experimental investigation of the effect of vegetation on soil sediment erosion and salt transport processes in the upper colorado river basin mancos shale formation price utah usa abstract because of concerns about salinity in the colorado river this study focused on saline and sodic soils associated with the mancos shale formation with the objective of investigating mechanisms driving sediment yield and salinity loads and the role of vegetation in altering soil chemistry in the price san rafael river basin rainfall simulations using a walnut gulch rainfall simulator were performed at two study sites ferron and price utah across a range of slope angles and rainfall intensities to evaluate the relationship between sediment yield salinity transport processes and rainfall induced changes in soil chemistry soil at ferron had substantially greater salinity than price as expressed in evaluated sodium absorption ratio cation exchange capacity in soil sediment and total dissolved solids tds in runoff principal component analysis and t tests revealed that the two sites have different runoff and soil chemistry ions greater concentrations of k no3 and cl were present in soil under vegetation microsites compared to interspace soil areas soil soluble phase ions generally increased with depth and underwent vertical fluxes at rates proportional to rainfall intensity vegetation appears to have a protective effect on the soils from increasing rainfall intensity mat forming saltbush found at ferron was related most strongly to soil protection the dissolution of sediment particles in runoff may be a key component of salinity transport processes on the mancos shale plot averaged sediment and tds had a positive linear relationship the rangeland hydrology and erosion model successfully predicted tds in runoff derived from these upland rangelands in central utah

lu hf total rock age for the amitsoq gneisses west greenland abstract lu hf total rock data for the amitsoq gneisses of west greenland yield an age of 3 55 0 22gy 2 based on the decay constant 176lu 1 96 10 11y 1 and an initial176hf 177hf ratio of 0 280482 33 the result is in good agreement with rb sr total rock and u pb zircon ages in spite of severe metamorphism of the area at 2 9 gy zircons from two of the samples have remained on the total rock line and define points close to the initial hf ratio the initial176hf 177hf lies close to a chondritic hf isotopic evolution curve from 4 55 gy to present this is consistent with the igneous precursors to the amitsoq gneisses having been derived from the mantle at or shortly before 3 6 gy anomalous relationships between hf concentration and the176lu 177hf ratio may suggest that trace element abundances in the amitsoq gneisses are partly controlled by processes related to metamorphism

lu hf and sm nd evolution in lunar mare basalts lu hf and sm nd data for mare basalts combined with rb sr and total ree data taken from the literature suggest that the mare basalts were derived by small or 10 degrees of partial melting of cumulate sources but that the magma ocean from which these sources formed was light ree and hf enriched calculated source compositions range fromm lherzolite to olivine websterite nonmodal melting of small amounts of ilmenite or 3 in the sources seems to be required by the lu hf data a comparison of the hf and nd isotopic characteristics between the mare basalts and terrestrial oceanic basalts reveals that the epsilonhf epsilonnd ratios of low ti mare basalts are much higher than in terrestrial oceanic basalts the results are qualitatively consistent with the hypothesis that terrestrial basalt sources are partial melt residues whereas mare basalt sources are cumulates alternatively the results may imply that the terrestrial mantle has evolved in two or more stages of evolution and that the net effect was depletion of the mantle during the first approx 1 3 b y followed by enrichment during the last 1 2 b y or simply that there is a difference in lu hf crystal liquid partitioning relative to sm nd between the lunar and terrestrial mantles

decoupling of whole rock nd hf and zircon hf o isotopic compositions of a 284 ma mafic ultramafic intrusion in the beishan terrane nw china abundant permian mafic ultramafic intrusions in the beishan terrane nw china are parts of the tarim large igneous province among these intrusions luodong intrusion is composed of dunite wehrlite and gabbro these rocks have whole rock sr nd hf and zircon hf o isotope compositions that display significant decoupling the decoupling of these generally well correlated systems demonstrates contrasting evolving trends systematic compositional and mineralogical controls on decoupling have been investigated wehrlites and gabbros show morb like trace element patterns with negligible crustal contamination they have high initial 143nd 144nd end t 6 6 to 11 2 and 176hf 177hf ehf t 12 2 to 16 9 and low initial 87sr 86sr 87sr 86sr i 0 702949 0 704098 ratios and plot within the morb field indicating that their parental magmas were derived from a depleted mantle source the enrichment features are present in the zircon crystals separated from the gabbro these homogeneously unzoned zircon crystals have high u concentrations low th u ratios and a u pb age of 284 0 2 3 ma they are therefore interpreted as having formed rapidly in a highly fractionated evolved magma their ehf t and 18o values range from 9 3 to 6 7 and 10 25 to 11 42 respectively the decoupling is linked with crustal contamination by ancient crust probably proterozoic schist in the beishan terrane that occurred during zircon crystallization however the contamination signature in the whole rock composition was soon overprinted by magma mixing process the inference is evidenced by zoning textures preserved in plagioclase clinopyroxene spinel and particularly olivine and the presence of coeval diabase dykes cutting through the intrusion the isotope decoupling observed in this mantle plume related mafic ultramafic intrusion supports the idea that nd hf decoupling and lu hf and sm nd parent daughter variations exist only on a small hand size scale in a particular growth environment and prevailing kinetics

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

age of basement rocks from the maurice ewing bank and the falkland malvinas plateau abstract the maurice ewing bank is located east of the falkland malvinas islands and is one of the most intriguing regions of southern gondwana the interaction of several microplates with major cratonic areas resulted in complex displacements between paleozoic and cretaceous times here we present combined u pb and lu hf zircon isotopic analyses of the maurice ewing bank basement to constrain the age and tectonic setting to aid in paleogeographic reconstruction the high grade paragneisses in the bank present dominant late mesoproterozoic detrital zircon age distributions with populations at 1032 12 ma 1068 16 ma and 1233 8 ma and juvenile signature positive ehf t values the gneisses are cutting by anatectic pink granite crystallized at 1006 13 ma which formed after syn collisional high grade metamorphism and shows juvenile and some crustal component ehf t 1 6 to 3 the maurice ewing bank basement rocks have same stenian age and dominant juvenile signature as the arc related basement rocks from the falkland malvinas islands and are probably part of the same continental plateau of the south america continent this new finding enables future reconstructions in paleogeographic models where the basement of the falkland malvinas islands and the maurice ewing bank formed a single block during the mesoproterozoic and were partly separated by crustal stretching during the opening of the atlantic ocean in the late jurassic cretaceous the block played a major role in the deformation of the cape fold belt from the late paleozoic through the mesozoic

origin of meso proterozoic post collisional leucogranite suites kaokoveld namibia constraints from geochronology and nd sr hf and pb isotopes leucocratic granites of the proterozoic kaoko belt northern namibia now preserved as meta granites define a rock suite that is distinct from the surrounding granitoids based on their chemical and isotopic characteristics least evolved members of this 1 5 1 6 ga old leucogranite suite can be distinguished from ordinary calc alkaline granites that occur elsewhere in the kaoko belt by higher abundances of zr y and ree more radiogenic initial end values and unradiogenic initial 87sr 86sr the leucogranites have high calculated zircon saturation temperatures mostly 920 c for least fractionated samples suggesting that they represent high temperature melts originating from deep crustal levels isotope data i e endi 2 3 to 4 2 demonstrate that the granites formed from different sources and differentiated by a variety of processes including partial melting of mantle derived meta igneous rocks followed by crystal fractionation and interaction with older crustal material most fractionation corrected nd model ages tdm are between 1 7 and 1 8 ga and only slightly older than the inferred intrusion age of ca 1 6 ga indicating that the precursor rocks must have been dominated by juvenile material epsilon hf values of zircon separated from two granite samples are positive 11 and 13 and hf model ages 1 5 and 1 6 ga are similar to the u pb zircon ages again supporting the dominance of juvenile material in contrast the hf model ages of the respective whole rock samples are 2 3 and 2 4 ga demonstrating the involvement of older material in the generation of the granites the last major tectonothermal event in the kaoko belt in the proterozoic occurred at ca 2 0 ga and led to reworking of mostly 2 6 ga old rocks however the presence of 1 6 ga post collisional granites reflects addition of some juvenile mantle derived material after the last major tectonic event the results suggest that similar a type leucogranites are potentially more abundant in crustal terranes but are masked by afc processes in the case of the kaoko belt it is suggested that this rock suite indicates a yet unidentified period of mantle derived crustal growth in the proterozoic of south western africa

importance of late magmatic and hydrothermal fluids on the sm nd isotope mineral systematics of hypersolvus granites abstract despite the significant impact of the sm nd radiometric system in various fields of isotope geochemistry very few attempts have been made to use it at the mineral scale in granite studies this approach has been used on two granites from the anorogenic province of corsica se france two statistically acceptable alignments were obtained in an isochron diagram for the hypersolvus fayalite bearing granite of mantelluccio alkali feldspar amphibole inclusion free zircon fluorite and fergusonite give an age of 331 10 ma whereas allanite whole rock amphibole and inclusion free zircon yield a significantly younger age at 291 13 ma the latter is validated by a zircon u pb age of 283 1 ma as the magmatic emplacement date of the granite the other alignment giving a 50 ma older age can be interpreted either as being inherited or more likely as the result of hydrothermal convection interacting with the country rocks at the end of granite crystallization the sm nd systematics of epidote records a second fluid rock event which probably occurred at least 200 ma after the emplacement of the granite extremely low 143 nd 144 nd ratio indicates that the epidote crystallized from a fluid that carried lanthanides in the crust over a distance of at least 1 km zircons with inclusions have a lower initial 143 nd 144 nd ratio than inclusion free zircons this feature is attributed to apatite and or zircon core inheritance through contamination during the ascent of the granitic melt in the crust two isochrons have been also obtained for the hypersolvus peralkaline granite of evisa amphibole fluorite sphene and fergusonite yield an age of 259 6 ma whereas the whole rock alkali feldspar and metamict zircon give an age at 209 14 ma in this case the former value is roughly in agreement with a possibly slightly rejuvenated whole rock rb sr date of 249 3 ma suggesting that it documents the magmatic crystallization age of the granite sm nd isotope systematics of the alkali feldspar metamict zircon and possibly allanite were re equilibrated during an important hydrothermal event that affected western europe in early jurassic times in both examples however it appears that the whole rock nd isotopic signatures were not strongly affected by the various fluid rock events indicating that they can still be used for petrogenetic investigations in contrast these results show that like k ar and rb sr the sm nd systematics of minerals with weak resistance to post magmatic processes can be used to trace and date hydrothermal events

assessing the performance of structure from motion photogrammetry and terrestrial lidar for reconstructing soil surface microtopography of naturally vegetated plots soil microtopography is a property of critical importance in many earth surface processes but is often difficult to quantify advances in computer vision technologies have made image based three dimensional 3d reconstruction or structure from motion sfm available to many scientists as a low cost alternative to laser based systems such as terrestrial laser scanning tls while the performance of sfm at acquiring soil surface microtopography has been extensively compared to that of tls on bare surfaces little is known about the impact of vegetation on reconstruction performance this article evaluates the performance of sfm and tls technologies at reconstructing soil microtopography on 6 m 2 m erosion plots with vegetation cover ranging from 0 to 77 results show that soil surface occlusion by vegetation was more pronounced with tls compared to sfm a consequence of the single viewpoint laser scanning strategy adopted in this study on the bare soil surface elevation values estimated with sfm were within 5 mm of those from tls although long distance deformations were observed with the former technology as vegetation cover increased agreement between sfm and tls slightly degraded but was significantly affected beyond 53 of ground cover detailed semivariogram analysis on meter square scale surface patches showed that tls and sfm surfaces were very similar even on highly vegetated plots but with fine scale details and the dynamic elevation range smoothed out with sfm errors in the tls data were mainly caused by the distance measurement function of the instrument especially at the fringe of occlusion regions where the laser beam intersected foreground and background features simultaneously from this study we conclude that a realistic approach to digitizing soil surface microtopography in field conditions can be implemented by combining strengths of the image based method simplicity and effectiveness at reconstructing soil surface under sparse vegetation with the high accuracy of tls like technologies copyright 2015 john wiley sons ltd

hf isotope systematics in granitoids from the central and southern alps first initial hf isotopic compositions for samples from the alpine domain are presented and discussed the results are mainly based on zircons and a few whole rocks with ages between 30 and 450 ma of those so far analyzed the present day hf isotopic compositions of zircons from non metamorphic and metamorphic granitoid rocks vary between 0 2824 and 0 2829 zircon populations with concordant u pb ages have much higher initial 176hf 177hf than inversely discordant populations which have been contaminated with older zircons containing less radiogenic hf correlated nd hf crustal residence ages have been found involving model parameters of ehf end f lu hf f sm nd 1 6 for the depleted mantle and f lu hf f sm nd 1 2 for elemental fractionations in the crust the model implies 176lu 177hf of 0 017 for the bulk crust it is suggested that the granitoid rocks are the result of mixing of subcontinental mantle derived magmas with 1 7 ga old recycled and partially molten crustal material the continental mantle component mass ratio values for the granitoids range between 0 3 and 2

fluid zircon interaction during low temperature hydrothermal processes implications for the genesis of the banxi antimony deposit south china abstract fluid zircon interaction in hydrothermal systems may provide key information on fluid characterization and ore precipitation in this study in situ analyses of hf isotopes in zircon combined with u pb ages and major and trace element data provide new insights into fluid genesis at the banxi antimony deposit the zircons separated from typical quartz stibnite ores and altered wall rocks have undergone fluid modification to different degrees showing hydrothermal overprints in reflected transmitted light back scattered electron bse and cathodoluminescence cl images and variable concentrations of si zr hf u th pb ti nb ta p f y and rare earth elements they possess identical u pb ages to the banxi group and underlying lengjiaxi group clastic rocks but distinct 176hf 177hf 176lu 177hf and 176yb 177hf ratios indicating the possible changing of lu hf systematics during the hydrothermal alteration the evidence suggests a contribution of ore material from the banxi group and a deeper fluid source derived from the lengjiaxi group and the crystalline basement beneath it a fluid mixing model is proposed wherein the deep sourced high radiogenic hf fluid mixed with circulating near surface meteoric component dominated fluid triggering antimony precipitation the u pb chronometer was not reset during this low temperature mineralization event whereas the lu hf systematics in the fluid altered zircons show evidence of lattice breakdown of the old zircons during fluid mixing coupled with external input of highly radiogenic hf from the crystalline basement this research highlights the potential to use zircon structure and geochemistry in tracing complex fluid evolutionary processes

behavior of isotopic systematics during deformation and metamorphism a hf nd and sr isotopic study of mylonitized granite a combined compositional and hf nd and sr isotopic study was performed on a suite of samples of progressively deformed granite from a mylonite zone in the harquahala mountains western arizona to evaluate the effects of deformation and metamorphism on the isotopic systematics of typical continental crustal rocks the 1 4 ga harquahala granite was deformed during mesozoic thrusting along the harquahala thrust granite in the resulting 60 m wide shear zone ranges from protomylonite to ultramylonite in most of these mylonites the protolith is not megascopically recognizable and can be discerned only by the progressive transition to undeformed granite isotopic analyses of hf nd and sr from the shear zone document the immobility of the hf and nd isotopic systems relative to that of the sr isotopic system during deformation the rb sr isotopic data show considerable scatter on an isochron plot exhibiting both gains and losses of rb and sr from the whole rock systems in contrast the sm nd and lu hf isotopic systematics are mostly well behaved on isochron diagrams plotting mostly in tight clusters or along 1 4 ga isochrons these results show that while the sr isotopic system in crustal rocks is quite susceptible to later tectonic disturbance both hf and nd isotopic systems can provide reliable model age information in continental crustal terranes even when the rocks have been subjected to low to medium grades of deformation and metamorphism

burial rates during prograde metamorphism of an ultra high pressure terrane an example from lago di cignana western alps italy abstract estimation of burial rates and duration of prograde metamorphism of ultra high pressure uhp rocks t 590 630 c p 2 7 2 9 gpa of the zermatt saas ophiolite from lago di cignana italy may be made through combined lu hf and sm nd garnet geochronology in conjunction with petrologic estimates of the prograde p t path we report a lu hf garnet omphacite whole rock isochron age of 48 8 2 1 ma from the uhp locality at lago di cignana which stands in contrast to the sm nd age of 40 6 2 6 ma amato et al earth planet sci lett 171 1999 425 438 obtained from the same sample and mineral material the sm nd and lu hf ages as well as other ages determined on metamorphic garnet zircon and white mica amato et al earth planet sci lett 171 1999 425 438 mayer et al eur union geosci 10 1999 abstr 809 rubatto et al contrib mineral petrol 132 1998 269 287 dal piaz et al int j earth sci 90 2001 668 684 from lago di cignana and elsewhere in the zermatt saas ophiolite lie within a range of 50 38 ma which we interpret to encompass the duration of prograde metamorphism and possibly the duration of garnet growth the difference in measured sm nd and lu hf ages from cignana can be accounted for by expected core to rim variations in lu hf sm and nd the measured yttrium content in garnet which may be a proxy for lu is highest in garnet core and lowest in the mineral rim generally following a profile that is predicted by rayleigh fractionation preferential enrichment of lu in the core produces a lu hf age that is weighted toward the older garnet core sm nd ages as predicted by rayleigh fractionation of sm and nd during garnet growth however reflect later grown garnet as compared to lu hf ages the difference in sm nd and lu hf ages from a single sample should therefore be a minimum estimate for the duration of garnet growth and prograde metamorphism so long as sm nd and lu hf blocking temperatures were not exceeded for a long period of time based on the 12 myr duration of prograde garnet growth estimated in this study burial rates for rocks at lago di cignana were on the order of 0 23 0 47 cm yr these values correlate with continuous shortening rates of 0 4 1 4 cm yr between the european plate and the african adriatic promontory between 50 and 38 ma which is on the order of that calculated for plate velocities from plate reconstructions suggesting that the zermatt saas ophiolite may have remained well coupled to the down going slab to uhp conditions

importance of the lu hf isotopic system in studies of planetary chronology and chemical evolution the 176lu 176hf isotope method and its applications in earth sciences are discussed greater fractionation of lu hf than sm nd in planetary magmatic processes makes 176hf177hf a powerful geochemical tracer in general proportional variations of 176hf177hf exceed those of 143ndl44nd by factors of 1 5 3 in terrestrial and lunar materials lu hf studies therefore have a major contribution to make in understanding of terrestrial and other planetary evolution through time and this is the principal importance of lu hf new data on basalts from oceanic islands show unequivocally that whereas considerable divergences occur in 176hf177hf 87sr86sr and 143ndl44nd 87sr86sr diagrams 176hf177hf and 143nd144nd display a single linear isotopic variation in the suboceanic mantle these discordant 87sr86sr relationships may allow with the acquisition of further hf nd sr isotopic data a distinction between processes such as mantle metasomatism influence of seawater altered material in the magma source or recycling of sediments into the mantle in order to evaluate the hf nd isotopic correlation in terms of mantle fractionation history there is a need for measurements of hf distribution coefficients between silicate minerals and liquids and specifically for a knowledge of hf behavior in relation to rareearth elements for studying ancient terrestrial hf isotopic variations the best quality hf isotope data are obtained from granitoid rocks or zircons new data show that very u pb discordant zircons may have upwardly biased 176hf177hf but that at least concordant to slightly discordant zircons appear to be reliable carriers of initial 176hf177hf until the controls on addition of radiogenic hf to zircon are understood combined zircon whole rock studies are recommended lu hf has been demonstrated as a viable tool for dating of ancient terrestrial and extraterrestrial samples but because it offers little advantage over existing methods is unlikely to find wide application in pure chronological studies

martian mantle mineralogy investigated by the 176lu 176hf and 147sm 143nd systematics of shergottites abstract chemical heterogeneities in the martian mantle are believed to result from the crystallization of a magma ocean in the first 100 million years of its history shergottite meteorites from mars are thought to retain a compositional record of such early differentiation and the resulting mineralogy at different depths the coupled 176 lu 176 hf and 147 sm 143 nd isotope systematics in 9 shergottites are used here to investigate these issues three compositional groups in the shergottites display distinct isotope systematics one group commonly termed as depleted is characterized by positive 176 hf i from 46 2 to 50 4 and 143 nd i from 36 2 to 39 1 another termed as enriched has negative 176 hf i 16 5 to 13 2 and 143 nd i 7 0 to 6 5 the third group is intermediate between the depleted and enriched groups with positive 176 hf i 30 0 to 33 4 and 143 nd i 16 9 together they describe mixing curves between 176 hf 177 hf 143 nd 144 nd lu hf and sm nd implying that they sample two distinct sources in the martian mantle all shergottites are characterized by sm nd source sample but lu hf source lu hf sample this decoupling can be explained by two successive partial melting episodes in the depleted shergottite source and localized in the martian upper mantle the genesis of shergottites can be modeled using non modal equilibrium partial melting in a source initially composed of 60 olivine 21 clinopyroxene 9 orthopyroxene and 10 garnet with degrees of partial melting of 8 8 and 3 9 respectively for the two successive events the enriched end member of the shergottite mixing curve is best modeled by late stage quenched residual melt resulting from the crystallization of a magma ocean the depleted shergottite source may be modeled as a mixture of cumulates and residual melt as convection in the martian magma ocean is expected to reduce the incompatible trace element heterogeneity in the final solidified layers consequently equilibrium crystallization is preferred to model the crystallization of the martian magma ocean the models that best explain the shergottite data are those where the magma ocean is at a depth of at least 1350 km in mars

rapid exhumation of the zermatt saas ophiolite deduced from high precision smnd and rbsr geochronology sm nd isotope data from garnets in ultrahigh pressure coesite bearing eclogite from the western alps were obtained to determine the age of peak metamorphism and exhumation rates of deeply buried oceanic crust in the zermatt saas ophiolite complex we report an exceptionally well constrained sm nd isochron age of 40 62 6 ma from the lago di cignana eclogite difficulties in dating alpine eclogites using this method were overcome by using an hf acid leaching procedure on garnet to remove mineral inclusions the zermatt saas rocks reached greenschist facies conditions around 38 2m a on the basis of rb sr whole rock phengite isochrons these data combined with existing estimates of the pressure and temperature conditions of the eclogite give an estimate for the initial exhumation rate of 10 to 26 km m y depending on the inferred pressure for the recrystallization of phengite followed by slow exhumation of 0 3 km m y from 34 to 14 ma the initial exhumation rates at lago di cignana are among the highest yet determined for high pressure terranes and are well constrained because the age has been determined directly on the high pressure assemblage the rapid exhumation rates presented here place critical constraints on collisional tectonic models 1999 elsevier science b v all rights reserved

hafnium oxygen neodymium strontium and lead isotopic constraints on magmatic evolution of the supereruptive southern black mountains volcanic center arizona u s a a combined lass zircon whole rock study the 700 km 3 peach spring tuff pst erupted at 18 8 ma from the silver creek caldera in the southern black mountains volcanic center sbmvc of western arizona is the only supereruption scale ignimbrite in the northern colorado river extensional corridor the sbmvc contains pre and post caldera volcanic rocks and caldera related intrusions 19 17 ma that provide a detailed petrologic record of ignimbrite antecedence and aftermath whole rock sr nd pb hf isotopic data combined with complementary zircon o and hf isotopic data from a suite of pre through post pst samples provide robust constraints on 1 how the sbmvc evolved with respect to magmatic sources and processes throughout its 2 ma history and 2 the petrogenetic relationships between the pst and slightly younger intracaldera plutons both pre and post pst units have isotopic ranges nd 8 3 to 11 6 hf 8 2 to 14 0 87 sr 86 sr i 0 709 0 712 206 pb 204 pb 18 19 18 49 207 pb 204 pb 15 60 15 62 208 pb 204 pb 38 95 39 29 that fall within the spectrum of miocene colorado river extensional corridor rocks and are consistent with mixing of substantial fractions of proterozoic mojave crust and juvenile material derived from regional enriched mantle compared to the pst which has relatively uniform isotopic ratios nd 11 4 to 11 7 hf 13 8 to 14 3 87 sr 86 sr i 0 709 0 712 206 pb 204 pb 18 20 18 29 207 pb 204 pb 15 60 15 62 208 pb 204 pb 39 02 39 33 individual pre and post pst units are isotopically more variable and generally more primitive consistent with whole rock isotopes zircon hf 8 to 14 and oxygen 18 o 4 5 to 7 2 for most pre and post pst units also have wider ranges and more mantle like values than those of the pst 12 to 15 6 1 to 7 1 moreover zircon isotopic compositions decrease in post pst samples a few zircons from post pst intrusions have 18 o values lower than mantle values whole rock and zircon elemental and isotopic analyses indicate that 1 most pre and post pst units are less evolved and less homogenized than the pst itself 2 intrusions in the silver creek caldera are petrogenetically distinct from the pst and therefore represent discrete magmatic pulses not unerupted pst mush 3 enriched mantle input increased in the sbmvc following the paroxysmal pst eruption 4 post pst history of the sbmvc was characterized by periodic influx of magmas with varying juvenile fractions into pre existing mushy or solidified intrusions resulting in variable and incomplete hybridization and 5 melting and assimilation of hydrothermally altered crust played a relatively minor role in the generation and evolution of magmas in the sbmvc

high precision pb sr nd hf isotopic characterization of usgs bhvo 1 and bhvo 2 reference materials the recent development of multiple collector inductively coupled plasma mass spectrometry mc icp ms and increasing use of the technique have created the need for well characterized rock standards especially for isotopic systems where no internal fractionation correction can be applied this paper presents a careful leaching experiment on the u s geological survey usgs reference materials bhvo 1 and bhvo 2 hawaiian basalts and documents the evidence for contamination of the rock powders during processing this contamination accounts for the difference in pb isotopic ratios of bhvo 1 and bhvo 2 as well as for their lack of homogeneity both in pb isotopic compositions and in some trace element contents copyright 2005 by the american geophysical union

in situ measurement of hafnium isotopes in rutile by la mc icpms protocol and applications article i nfo this work presents a rigorous assessment of the accuracy and precision with which 176 hf 177 hf can be measured in rutile by laser ablation la mc icpms for rutile with 40 ppm hf we demonstrate that 176 hf 177 hf can be measured accurately and reproducibly with adequate precision for application to petrological problems we present an analytical and data reduction protocol tailored to the specific challenges of measuring hf isotope ratios in this low hf mineral precision and accuracy are optimised by interpolating between baselines measured every 10 analyses for many rutiles the advantages of determining the hf mass bias coefficient hf during analysis are negated by the low precision with which it can be measured at low hf contents hf mass bias is therefore monitored by regular analysis of a synthetic rutile doped with 5000 ppm hf sr 2 to facilitate an external mass bias correction because rutile contains negligible yb the yb mass bias coefficient yb must be inferred from yb hf measured on zircon in the same session to account for a systematic instrument bias of 0 5 1 ehf units rutile analyses are normalised to sr 2 for which 176 hf 177 hf has

dating subduction zone metamorphism with combined garnet and lawsonite lu hf geochronology studies of ancient and active subduction zones are critically important to understanding processes of interplate coupling crust mantle recycling and arc magmatism dating subduction metamorphism along prograde and retrograde paths in order to constrain such processes however has proved to be extremely difficult the complex thermal history of subduction systems poses significant challenges to low t geochronometers and subduction zone assemblages commonly lack suitable minerals for higher temperature geochronology garnet and lawsonite however are critical index minerals of high and low t subduction zone metamorphism and are well suited to lu hf geochronology in addition the closure temperature for lu hf in garnet and lawsonite should be sufficiently high that an age will date mineral crystallization and therefore the timing of subduction zone metamorphism the relative stability and timing of garnet and lawsonite formation will be controlled by the bulk composition peak metamorphic conditions and shape of the p t path experienced by a particular sample to test the influence of metamorphic conditions and p t path on lu hf geochronology garnet and lawsonite bearing samples were dated from rocks where lawsonite formed after garnet along a retrograde path stabilized prior to garnet along a prograde path and formed contemporaneously with garnet in the franciscan complex the ages of garnet epidote amphibolite garnet epidote blueschist garnet lawsonite blueschist and lawsonite blueschist range from c 166 130 ma and generally decrease with decreasing metamorphic grade consistent with previous studies garnet lawsonite blueschist eclogite formed along an apparent prograde path at ward creek records an apparent age of c 152 ma lower temperature lawsonite blueschist at ward creek however failed to provide a geologically significant date and likely reflects isotopic disequilibrium at low temperatures the apparent temperature time history from franciscan complex lu hf ages most likely reflects samples derived from various portions of the subduction zone or that were subducted and metamorphosed at different times in the thermal evolution of the subduction zone in the sivrihisar massif lawsonite eclogite and garnet lawsonite blueschist record distinctly different ages of 91 1 1 3 ma and 83 3 1 8 ma the different ages date the timing of high p metamorphism within each protolith and suggest that garnet lawsonite eclogite metamorphism pre dated garnet lawsonite blueschist metamorphism in these samples by c 8 ma the age of lawsonite eclogite metamorphism extends the timing of high p metamorphism and requires subduction initiation prior to 91 ma the results indicate that the lu hf system provides a reliable tool for dating the wide range in p t conditions of subduction zone metamorphism lawsonite dating in particular provides a reliable method by which to date low t retrograde and prograde metamorphism in the absence of garnet lawsonite may not be ideal for geochronology if sufficient garnet coexists in the mineral assemblage the lawsonite has very low t stability or if extremely fine grained hf phases such as zircon are present in lawsonite in poly metamorphic assemblages where the pressure and temperature can be estimated for separate garnet and lawsonite sub assemblages the age discrepancy between garnet and lawsonite may provide the ability to quantify the rates of heating or cooling and subduction or exhumation

history of crustal growth and recycling at the pacific convergent margin of south america at latitudes 29 36 s revealed by a u pb and lu hf isotope study of detrital zircon from late paleozoic accretionary systems detrital zircon provides a powerful archive of continental growth and recycling processes we have tested this by a combined laser ablation icp ms u pb and lu hf analysis of homogeneous growth domains in detrital zircon from late paleozoic coastal accretionary systems in central chile and the collisional guarguaraz complex in w argentina because detritus from a large part of w gondwana is present here the data delineate the crustal evolution of southern south america at its paleopacific margin consistent with known data in the source regions zircon in the guarguaraz complex mainly displays an u pb age cluster at 0 93 1 46 ga similar to zircon in sediments of the adjacent allochthonous cuyania terrane by contrast zircon from the coastal accretionary systems shows a mixed provenance age clusters at 363 722 ma are typical for zircon grown during the braziliano pampean famatinian and post famatinian orogenic episodes east of cuyania an age spectrum at 1 00 1 39 ga is interpreted as a mixture of zircon from cuyania and several sources further east minor age clusters between 1 46 and 3 20 ga suggest recycling of material from cratons within w gondwana the youngest age cluster 294 346 ma in the coastal accretionary prisms reflects a so far unknown local magmatic event also represented by rhyolite and leucogranite pebbles it sets time marks for the accretion history maximum depositional ages of most accreted metasediments are middle to upper carboniferous a change of the accretion mode occurred before 308 ma when also a concomitant retrowedge basin formed initial hf isotope compositions reveal at least three juvenile crust forming periods in southern south america characterised by three major periods of juvenile magma production at 2 7 3 4 ga 1 9 2 3 ga and 0 8 1 5 ga the 176hf 177hf of mesoproterozoic zircon from the coastal accretionary systems is consistent with extensive crustal recycling and addition of some juvenile mantle derived magma while that of zircon from the guarguaraz complex has a largely juvenile crustal signature zircon with pampean famatinian and braziliano ages 660 ma originated from recycled crust of variable age which is however mainly mesoproterozoic by contrast the carboniferous magmatic event shows less variable and more radiogenic 176hf 177hf pointing to a mean early neoproterozoic crustal residence this zircon is unlikely to have crystallized from melts of metasediments of the accretionary systems but probably derived from a more juvenile crust in their backstop system

hafnium isotope results from mid ocean ridges and kerguelen abstract 176hf 177hf ratios are presented for oceanic volcanics representing both extremes of the range of mantle hf nd sr isotopic variation hf from critical mid ocean ridgebasalts shows that 176hf 177hf does indeed have a greater variability than 143nd 144nd and 87sr 86sr in the depleted mantle this extra variation is essentially of a random nature and can perhaps be understood in terms of known rb sr sm nd lu hf fractionation relationships at the other extreme of mantle isotopic composition 176hf 177hf ratios for igneous rocks from the indian ocean island of kerguelen show a closely similar variation to published 143nd 144nd ratios for the same samples comparison of hf nd sr c relationships for tristan da cunha kerguelen and samoa reveals divergences in the mantle array for ocean island magma sources and perhaps suggests that these irregularities are largely the result of an extra component of 87sr 86sr variation

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

triassic granitoids of the qinling orogen central china genetic relationship of enclaves and rapakivi textured rocks abstract granitoids varying in composition from biotite amphibole granodiorite to monzogranite with rapakivi textures have recently been recognized in the qinling orogen central china the granitoids are magnesian calc alkalic and metaluminous a cnk 0 71 0 95 they contain many mafic to intermediate microgranular enclaves the enclaves are quenched mafic melts in granitic host magma as evidenced by fine grained sinuous margins against or transitional contacts with the host granitoids as well as disequilibrium textures and mineral assemblages u pb zircon dating of the granitoids yields 209 2 ma and 212 2 ma and the enclaves 210 2 ma and 211 2 ma respectively the host granitoids and enclaves show obvious silica gap but similar ree and trace element patterns the whole rock 87sr 86sr t end t and zircon ehf t values for the granitoids vary from 0 70516 to 0 70634 2 3 to 4 4 and 0 7 to 7 6 and for the enclaves from 0 70467 to 0 70600 1 1 to 4 0 and 1 2 to 8 8 respectively showing overlapped end t and zircon ehf t values all these suggest that the two magmatic systems represented by the host rock and enclave are probably derived from distinct sources with sufficient interaction or common origin but underwent different degrees of crustal contamination mineralogical and geochemical data point to enclave dissolution in silicic magma as a major process accounting for the origin of the rapakivi texture the possible bimodal magmatism suggested by the coeval granitoids and lamprophyre dykes combined with the structural pattern geochemical features and regional tectonics suggest a post collision setting for the qinling rapakivi textured granitoid plutons

empirical model of the thermospheric mass density based on champ satellite observations 1 the decadal observations from champ satellite have provided ample information on the earth s upper thermosphere reshaping our understandings of the vertical coupling in the atmosphere and near earth space an empirical model of the thermospheric mass density is constructed from these high resolution observations using the multivariable least squares fitting method it describes the density variation with latitude longitude height local time season and solar and geomagnetic activity levels within the altitude range of 350 420 km it represents well prominent thermosphere structures like the equatorial mass density anomaly ema and the wave 4 longitudinal pattern furthermore the empirical model reveals two distinct features first the ema is found to have a clear altitude dependence with its crests moving equatorward with increasing altitude second the equinoctial asymmetry is found to strongly depend on solar cycle with its magnitude and phase being strongly regulated by solar activity levels the equinoctial density maxima occur significantly after the actual equinox dates toward solar minimum which may signal growing influence from the lower atmosphere forcing this empirical model provides an instructive tool in exploring thermospheric density structures and dynamics it can also be easily incorporated into other models to have a more accurate description of the background thermosphere for both scientific and practical purposes

physical mechanisms of the ionospheric storms at equatorial and higher latitudes during the recovery phase of geomagnetic storms 1 the paper studies the physical mechanisms of the ionospheric storms at equatorial and higher latitudes which are generally opposite both during the main phase mp and recovery phase rp of geomagnetic storms the mechanisms are based on the natural tendency of physical systems to occupy minimum energy state which is most stable the paper first illustrates the recent developments in the understanding of the mechanisms during daytime mps when generally negative ionospheric storms in nmax and tec develop at equatorial latitudes and positive storms occur at higher latitudes including why the storms are severe only in some cases the paper then investigates the relative importance of the physical mechanisms of the positive ionospheric storms observed at equatorial latitudes within 15 during daytime rps when negative storms occur at higher latitudes using champ ne and gps tec data and sheffield university plasmasphere ionosphere model the results indicate that the mechanical effect of the storm time equatorward neutral winds that causes plasma convergence at equatorial f region could be a major source for the positive storms with the downwelling effect of the winds and zero or westward electric field if present acting as minor sources

a statistical study on elf whistlers emissions and m 5 0 earthquakes in taiwan 1 in this paper we conduct statistical approaches to study the potential relation between elf whistlers emissions below 100 hz and 20 m 5 0 earthquakes occurred in taiwan in the period from 26 august 2003 to 13 july 2004 occurrence ratios of the elf whistler and elf emission of the entire study period are computed as the reference backgrounds our study shows that the elf whistlers and elf emissions during the earthquake period appear less and more frequently than their associated backgrounds respectively for the elf emission the larger earthquakes generally yield the higher occurrence ratios the statistical analyses confirm that the occurrence ratios of the elf emission significantly enhance 5 7 days before the earthquakes and are proportional to the earthquake magnitude but inversely to the distance from the observatory to the epicenter

provenance of eclogitic metasediments in the north qilian hp lt metamorphic terrane western china geodynamic implications for early paleozoic subduction erosion abstract in this contribution we present new petrological geochemical zircon u pb and hf isotopic data for eclogitic metasediments from the north qilian orogenic belt in which early paleozoic ophiolitic sequences and hp lt metamorphic rocks have been previously recognized the studied metasediments contain eclogite facies assemblages reflecting p t conditions of 450 560 c and 1 9 2 4 gpa consistent with those of adjacent eclogites ree compositions of the eclogitic metasediments overlap those of average upper continental crust the shrimp and la mc icpms u pb data of zircons from metasediments demonstrate input from sources with major age components about 500 ma and 1600 1900 ma peak at 1800 ma with a smaller population at 660 800 ma peak at 750 ma and minor 1 9 ga zircon ages the youngest detrital zircons suggest a maximum depositional age of ca 475 ma and combined with p t conditions and previously determined metamorphic age suggest a burial rate of 0 6 0 7 cm yr zircon hf isotopic analyses show that 500 ma zircons have positive ehf t mainly between 8 and 16 by contrast meso to paleoproterozoic detrital zircons show a broad spectrum of ehf t mainly between 5 and 10 with t dm hf of 1800 2500 ma these data suggest that eclogitic metasediments are derived from a mixture of proterozoic continent crust and juvenile early paleozoic oceanic and or island arc crust and their protoliths likely were deposited in a terrigenous dominated continental margin basin rather than a pelagic oceanic crust environment the new results are consistent with subduction erosion of the active continental margin during south dipping subduction as these sediments formed in a fore arc environment close to the qilian block to the south were transported in the subduction zone to 60 70 km depth prior to their exhumation

straightforward reconstruction of 3d surfaces and topography with a camera accuracy and geoscience application topographic measurements for detailed studies of processes such as erosion or mass movement are usually acquired by expensive laser scanners or rigorous photogrammetry here we test and use an alternative technique based on freely available computer vision software which allows general geoscientists to easily create accurate 3d models from field photographs taken with a consumer grade camera the approach integrates structure from motion sfm and multi view stereo mvs algorithms and in contrast to traditional photogrammetry techniques it requires little expertise and few control measurements and processing is automated to assess the precision of the results we compare sfm mvs models spanning spatial scales of centimeters a hand sample to kilometers the summit craters of piton de la fournaise volcano with data acquired from laser scanning and formal close range photogrammetry the relative precision ratio achieved by sfm mvs measurement precision observation distance is limited by the straightforward camera calibration model used in the software but generally exceeds 1 1000 i e centimeter level precision over measurement distances of 10s of meters we apply sfm mvs at an intermediate scale to determine erosion rates along a 50 m long coastal cliff seven surveys carried out over a year indicate an average retreat rate of 0 70 0 05 m a 1 sequential erosion maps at 0 05 m grid resolution highlight the spatio temporal variability in the retreat with semivariogram analysis indicating a correlation between volume loss and length scale compared with a laser scanner survey of the same site sfm mvs produced comparable data and reduced data collection time by 80

lu hf isotope systematics of fossil biogenic apatite and their effects on geochronology abstract reliable methods for direct dating of biogenic apatite from pre pleistocene fossils are currently not available and recent attempts using the lu hf decay system yielded highly inaccurate ages for both bones and teeth the geological processes accounting for this poor accuracy of lu hf chronometry are not yet understood here we explore lu hf systematics in fossil bones and teeth in detail by applying five different sample digestion techniques that are tested on bones and composites of bone and sediment our current dataset implies that dissolution methods only slightly affect the resulting lu hf ages while clear differences between the individual digestion techniques became apparent for element concentrations by analysing the insoluble leftovers from incomplete sample dissolution four main reservoirs of hf in fossil bones were identified 1 a radiogenic end member associated with apatite 2 an unradiogenic end member represented by the authigenic minerals or the embedding sediment 3 a highly unradiogenic end member that can be attributed to detrital zircon and 4 a moderately soluble phase probably a zr hf phosphate that yielded very low lu hf but a highly radiogenic hf isotope composition at the same time this zr hf phase must have been precipitated within the fossil bone sample at a late stage of burial history thereby incorporating radiogenic 176 hf released from apatite surfaces over geological timescales a second focus of our study is the effect of different sediment matrices and of crystal size on the preservation of pristine lu hf isotope compositions in bioapatite because near depositional lu hf ages of phosphate fossils have previously been reported for the london clay england and a calcareous marl from tendaguru tanzania we herein investigate specimens fossilised in carbonate matrices calcareous marl from oker germany carbonate concretions from the santana formation brazil carbonate from the eifel germany and argillaceous matrices with low permeability oil shale of messel germany posidonienschiefer of holzmaden germany materials analysed from these localities include bones teeth conodonts as well as coproliths and diagenetic minerals siderite montgomeryite and messelite near depositional lu hf ages were obtained for a bony fish sample notelops brama encapsulated in an early diagenetic carbonate concretion from the early cretaceous santana formation brazil and for conodonts from a middle devonian carbonate from the eifel germany low 176 lu 177 hf ratios in all materials from the middle eocene messel oil shale e g bones fish scales sediment siderite result in poor age precision and an age that is near depositional due to this large analytical error in agreement with previous results all other ages determined here for both bones and teeth are by far younger than respective chronostratigraphic ages a model illustrating the behaviour of lu and hf over time with respect to the fossilisation process is presented which accounts both for the formation of a late diagenetic radiogenic zr hf phase and long term open system behaviour the continuous lu hf element exchange between the fossils and the embedding sediment is probably related to the nm scale crystal size of fossil bones dentine and also of enamel that generate large surface areas facilitating sorption desorption processes and open system behaviour

contribution of metapelitic sediments to the composition heat production and seismic velocity of the lower crust of southern new mexico u s a abstract granulite xenoliths erupted at kilbourne hole maar were recently extracted from the lower crust of southern new mexico garnet and sillimanite bearing quartzofeldspathic xenoliths had pelitic protoliths and were probably emplaced in the lower crust by tectonic underplating at a lower proterozoic subduction zone thus the kilbourne hole metapelitic xenoliths illustrate the potential role of tectonosedimentary processes at convergent margins in determining the ultimate composition of the crust average p wave velocities for metapelitic xenoliths from kilbourne hole are 7 km s at 6 kbar like those of mafic metagabbros and anorthosites however in contrast to mafic lithologies the major element composition of the representative pelitic paragneiss rpp described in this paper is relatively siliceous and like that of average upper crust except for depletions of u and cs the trace element characteristics of the rpp are like those of pelitic sediments and are 3 10 times higher than those typically estimated for the lower crust the heat production of the rpp is high 1 0 w m3 as are those of many granulite and amphibolite grade metapelites in general portions of the lower crust in which sediments are present may be high in light ion lithophile and rare earth element abundances heat production 18o and87sr 86sr moreover the high pb contents and unradiogenic pb isotope signatures of metapelites provide an important reservoir for unradiogenic pb in the earth as a whole

timescales and mechanisms of ree and hf uptake in fossil bones abstract rare earth element ree patterns of fossil bones and teeth are widely used as proxies for provenance taphonomy and palaeoenvironment in order to investigate if fossil bones behave as closed systems over geologic time ree profiles were analysed by la icpms along cross sections of 54 bones from various well characterised and well dated settings these include terrestrial and marine diagenetic environments covering early triassic to holocene ages in general all fossil bones exhibit the highest ree concentrations at the outer rim gradually decreasing by up to four orders of magnitude toward the inner bone cortex intra bone ree concentration gradients decrease significantly from quaternary via tertiary to mesozoic specimens suggesting long term ree uptake and open system behaviour of fossil bone this view is further corroborated by 176lu 176hf dating of selected samples all yielding significantly younger ages than the known chronostratigraphic ages hence there is clear evidence for long term open system behaviour of fossil bones with respect to ree which is in marked contrast to currently accepted models suggesting that ree uptake is only early diagenetic although unexpected statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one upper triassic mastodonsaurus tooth with mswds ranging from 0 083 to 4 5 notably mobility of lu alone cannot account for the observed age patterns assuming constant lu uptake rates over time the radiometric ages should only be as low as half of the chronostratigraphic age however a six point isochron defined by subsamples of a single upper triassic mastodonsaurus tooth yields an age of 65 2 1 1 ma mswd 0 68 much younger than half of the stratigraphic age ca 234 ma hence hf must also undergo late diagenetic exchange likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both ree and hf are diffusion adsorption and dissolution reprecipitation processes

granite related tin metallogenic events and key controlling factors in peninsular malaysia southeast asia new insights from cassiterite u pb dating and zircon geochemistry

occurrence rate of extreme magnetic storms 1 we investigate the occurrence rate of magnetic storms at the earth during the first part of our study the standard and integral distribution functions of magnetic storm value minimal dst index for the period 1963 2012 are analyzed and results show that the standard and integral distribution functions have power law tails with indexes 4 4 and 3 4 respectively during the second part statistical analysis of occurrence rate of magnetic storms induced by different types of interplanetary drivers is made using omni data for the period 1976 2000 using our catalog of large scale types of solar wind streams we study storms induced by interplanetary coronal mass ejections icmes separately magnetic clouds mcs and ejecta and both types of compressed regions corotating interaction regions cirs and sheaths for these types of drivers we calculate the integral probabilities of storms with minimum dst 50 70 100 150 and 200 nt the highest probability in this interval of dst is observed for mcs with the probabilities for other drivers being 3 10 times lower extrapolation of these results to extreme storms shows that a magnetic storm as large as the carrington storm in 1859 with dst 1760 nt is observed on the earth with frequency not higher than one event during 500 years