Parent zonation in thermochronometers - resolving complexity revealed by ID-TIMS U-Pb dates and implications for the application of decay-based thermochronometers

NASA Astrophysics Data System (ADS)

Navin Paul, Andre; Spikings, Richard; Chew, David; Daly, J. Stephen; Ulyanov, Alexey

2017-04-01

High temperature (>350℃) U-Pb thermochronometers primarily use accessory minerals such as apatite, titanite and rutile, and assume that daughter isotopes are lost by thermally activated volume diffusion while the parent remains immobile. Studies exploiting such behaviour have been successfully used to reconstruct thermal histories spanning several hundred million years (e.g. Cochrane et al., 2014). However, outliers in date (ID-TIMS) vs diffusion length space are frequently observed, and grains are frequently found to be either too young or too old for expected thermal history solutions using the diffusion data of Cherniak et al. (2010). These deviations of single grain apatite U-Pb dates from expected behaviour could be caused by a combination of i) metamorphic (over-)growth, ii) fluid-aided Pb mobilisation during alteration/recrystallization, iii) parent isotope zonation, iv) metamictisation, and v) changes in diffusion length with time (e.g. fracturing). We present a large data set from the northern Andes of South America, where we compare apatite U-Pb ID-TIMS-(TEA) data with LA-ICP-MS element maps and in-situ apatite U-Pb LA-(MC)-ICP-MS dates. These are combined with U-Pb zircon and 40Ar/39Ar (muscovite) data to attempt to distinguish between thermally activated volume diffusion and secondary overgrowth/recrystallization. We demonstrate that in young (e.g. Phanerozoic) apatites that have not recrystallized or experienced metasomatic overgrowths, U-Pb dates are dominantly controlled by volume diffusion and intra-crystal uranium zonation. This implies that ID-TIMS analyses of apatites with zoned parent isotope distributions will not usually recover accurate thermal history solutions, and an in-situ dating method is required. Recovering the uranium distribution during in-situ analysis provides a means to account for parent zonation, substantially increasing the accuracy of the modelled t-T-paths. We present in-situ data from apatites where scatter in date v diffusion length scale is observed and compare t-T-paths from single grain and in-situ modelling. Modelling of in-situ data will further show if all apatites from a single hand specimen record the same thermal history using Cherniak et al. (2010) diffusion data, or if the Pb-in-apatite diffusion parameters are a function of composition. U zonation is ubiquitous in the studied rocks (Triassic apatites extracted from peraluminous leucosomes), implying that these conclusions may also apply to lower temperature thermochronometers that are based on uranium decay, such as (U-Th)/He dating.

Is 137Cs Dating Becoming Obsolete in North America?

NASA Astrophysics Data System (ADS)

Drexler, J. Z.; Fuller, C.; Salas, A.

2016-12-01

Dating of wetland sediments and peat is routinely carried out using 137Cs and 210Pb analysis. Unlike 210Pb, 137Cs is an anthropogenic radionuclide with a history of fallout from nuclear weapons testing. 137Cs is used as a single time marker; its peak is coincident with the height of atmospheric nuclear testing in 1963/4. During its use in the 1970s-90s, 137Cs peaks were usually highly distinct in wetland sediments (e.g., see 137Cs peaks from Louisiana marshes in Feijtel et al., 1988). This enabled its use as a check for dates assigned to a profile by 210Pb and other methods. However, recently, the efficacy of 137Cs dating in North America has deteriorated. In this presentation, we will provide specific examples of 137Cs as well as 210Pb dating in wetland sediments/peats we collected between 2005 and 2015 in Maine, California, Virginia, North Carolina, South Carolina, and Washington. Two main reasons exist for this decline. First, 137Cs activities in our recent cores are 30-40 % of the original activities in 1963/4 due to decay of the original 137Cs in situ (half-life = 30.17 years) and no major new sources. This manifests in lower signal to noise ratio, with some peaks barely recognizable above the noise. Second, 137Cs peaks are much less distinct due to 137Cs migration through time independent of substrate (or sediment) particles. Migration of peaks has resulted in estimated accretion rates being systematically lower or higher than those derived from 210Pb dating. These issues with 137Cs dating have important implications because 137Cs is used with 210Pb dating or even alone to determine rates of recent wetland carbon accumulation. Such rates are required to enter wetland restoration projects into carbon markets and to document IPCC mandated reductions in carbon pollution. Our analysis shows that, although dating by 137Cs alone has always been highly tenuous, now it is especially contraindicated and should be disallowed for the purposes of carbon accounting.

Dating human skeletal remains using a radiometric method: biogenic versus diagenetic 90Sr and 210Pb in vertebrae.

PubMed

Schrag, Bettina; Uldin, Tanya; Mangin, Patrice; Froidevaux, Pascal

2012-07-10

In forensic science, there is a strong interest in determining the post-mortem interval (PMI) of human skeletal remains up to 50 years after death. Currently, there are no reliable methods to resolve PMI, the determination of which relies almost exclusively on the experience of the investigating expert. Here we measured (90)Sr and (210)Pb ((210)Po) incorporated into bones through a biogenic process as indicators of the time elapsed since death. We hypothesised that the activity of radionuclides incorporated into trabecular bone will more accurately match the activity in the environment and the food chain at the time of death than the activity in cortical bone because of a higher remodelling rate. We found that determining (90)Sr can yield reliable PMI estimates as long as a calibration curve exists for (90)Sr covering the studied area and the last 50 years. We also found that adding the activity of (210)Po, a proxy for naturally occurring (210)Pb incorporated through ingestion, to the (90)Sr dating increases the reliability of the PMI value. Our results also show that trabecular bone is subject to both (90)Sr and (210)Po diagenesis. Accordingly, we used a solubility profile method to determine the biogenic radionuclide only, and we are proposing a new method of bone decontamination to be used prior to (90)Sr and (210)Pb dating. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

In situ location and U-Pb dating of small zircon grains in igneous rocks using laser ablation-inductively coupled plasma-quadrupole mass spectrometry

NASA Astrophysics Data System (ADS)

Sack, Patrick J.; Berry, Ron F.; Meffre, Sebastien; Falloon, Trevor J.; Gemmell, J. Bruce; Friedman, Richard M.

2011-05-01

A new U-Pb zircon dating protocol for small (10-50 μm) zircons has been developed using an automated searching method to locate zircon grains in a polished rock mount. The scanning electron microscope-energy-dispersive X ray spectrum-based automated searching method can routinely find in situ zircon grains larger than 5 μm across. A selection of these grains was ablated using a 10 μm laser spot and analyzed in an inductively coupled plasma-quadrupole mass spectrometer (ICP-QMS). The technique has lower precision (˜6% uncertainty at 95% confidence on individual spot analyses) than typical laser ablation ICP-MS (˜2%), secondary ion mass spectrometry (<1%), and isotope dilution-thermal ionization mass spectrometry (˜0.4%) methods. However, it is accurate and has been used successfully on fine-grained lithologies, including mafic rocks from island arcs, ocean basins, and ophiolites, which have traditionally been considered devoid of dateable zircons. This technique is particularly well suited for medium- to fine-grained mafic volcanic rocks where zircon separation is challenging and can also be used to date rocks where only small amounts of sample are available (clasts, xenoliths, dredge rocks). The most significant problem with dating small in situ zircon grains is Pb loss. In our study, many of the small zircons analyzed have high U contents, and the isotopic compositions of these grains are consistent with Pb loss resulting from internal α radiation damage. This problem is not significant in very young rocks and can be minimized in older rocks by avoiding high-U zircon grains.

U-Pb SHRIMP dating of uraniferous opals

USGS Publications Warehouse

Nemchin, A.A.; Neymark, L.A.; Simons, S.L.

2006-01-01

U-Pb and U-series analyses of four U-rich opal samples using sensitive high-resolution ion microprobe (SHRIMP) demonstrate the potential of this technique for the dating of opals with ages ranging from several tens of thousand years to millions of years. The major advantages of the technique, compared to the conventional thermal ionisation mass spectrometry (TIMS), are the high spatial resolution (???20 ??m), the ability to analyse in situ all isotopes required to determine both U-Pb and U-series ages, and a relatively short analysis time which allows obtaining a growth rate of opal as a result of a single SHRIMP session. There are two major limitations to this method, determined by both current level of development of ion probes and understanding of ion sputtering processes. First, sufficient secondary ion beam intensities can only be obtained for opal samples with U concentrations in excess of ???20 ??g/g. However, this restriction still permits dating of a large variety of opals. Second, U-Pb ratios in all analyses drifted with time and were only weakly correlated with changes in other ratios (such as U/UO). This drift, which is difficult to correct for, remains the main factor currently limiting the precision and accuracy of the U-Pb SHRIMP opal ages. Nevertheless, an assumption of similar behaviour of standard and unknown opals under similar analytical conditions allowed successful determination of ages with precisions of ???10% for the samples investigated in this study. SHRIMP-based U-series and U-Pb ages are consistent with TIMS dating results of the same materials and known geological timeframes. ?? 2005 Elsevier B.V. All rights reserved.

Laser Ablation in situ (U-Th-Sm)/He and U-Pb Double-Dating of Apatite and Zircon: Techniques and Applications

NASA Astrophysics Data System (ADS)

McInnes, B.; Danišík, M.; Evans, N.; McDonald, B.; Becker, T.; Vermeesch, P.

2015-12-01

We present a new laser-based technique for rapid, quantitative and automated in situ microanalysis of U, Th, Sm, Pb and He for applications in geochronology, thermochronometry and geochemistry (Evans et al., 2015). This novel capability permits a detailed interrogation of the time-temperature history of rocks containing apatite, zircon and other accessory phases by providing both (U-Th-Sm)/He and U-Pb ages (+trace element analysis) on single crystals. In situ laser microanalysis offers several advantages over conventional bulk crystal methods in terms of safety, cost, productivity and spatial resolution. We developed and integrated a suite of analytical instruments including a 193 nm ArF excimer laser system (RESOlution M-50A-LR), a quadrupole ICP-MS (Agilent 7700s), an Alphachron helium mass spectrometry system and swappable flow-through and ultra-high vacuum analytical chambers. The analytical protocols include the following steps: mounting/polishing in PFA Teflon using methods similar to those adopted for fission track etching; laser He extraction and analysis using a 2 s ablation at 5 Hz and 2-3 J/cm2fluence; He pit volume measurement using atomic force microscopy, and U-Th-Sm-Pb (plus optional trace element) analysis using traditional laser ablation methods. The major analytical challenges for apatite include the low U, Th and He contents relative to zircon and the elevated common Pb content. On the other hand, apatite typically has less extreme and less complex zoning of parent isotopes (primarily U and Th). A freeware application has been developed for determining (U-Th-Sm)/He ages from the raw analytical data and Iolite software was used for U-Pb age and trace element determination. In situ double-dating has successfully replicated conventional U-Pb and (U-Th)/He age variations in xenocrystic zircon from the diamondiferous Ellendale lamproite pipe, Western Australia and increased zircon analytical throughput by a factor of 50 over conventional methods.Reference: Evans NJ, McInnes BIA, McDonald B, Becker T, Vermeesch P, Danisik M, Shelley M, Marillo-Sialer E and Patterson D. An in situ technique for (U-Th-Sm)/He and U-Pb double dating. J Analytical Atomic Spectrometry, 30, 1636 - 1645.

Capability of U-Pb dating of zircons from Quaternary tephra: Jemez Mountains, NM, and La Sal Mountains, UT, USA

NASA Astrophysics Data System (ADS)

Krautz, Jana; Hofmann, Mandy; Gärtner, Andreas; Linnemann, Ulf; Kleber, Arno

2018-01-01

Two Quaternary tephras derived from the Jemez Mountains, New Mexico - the Guaje and Tsankawi tephras - are difficult to distinguish due to their similar glass-shard chemical composition. Differences in bulk chemical composition are small as well. Here we examine the feasibility to assign an age to a distal tephra layer in the La Sal Mountains, Utah, by U-Pb dating of zircons and to correlate it with one of the two Jemez eruptions. We also dated original Jemez tephras for comparison. Even though the tephras are very young, we obtained reasonable age determinations using the youngest cluster of zircon grains overlapping in age at 2σ. Thereafter, the Guaje tephra is 1.513 ± 0.021 Myr old. The La Sal Mountains tephra is correlated with the Tsankawi tephra. Three samples yielded a common age range of 1.31-1.40 Myr. All ages are in slight disagreement with published age determinations obtained by 40Ar / 39Ar dating. These findings indicate that distal Jemez tephras can be distinguished by U-Pb dating. Furthermore, we encourage giving this method a try for age assignments even of Quaternary volcanic material.

Possibility of wine dating using the natural Pb-210 radioactive isotope.

PubMed

Hubert, Ph; Pravikoff, M S; Gaye, J

2015-04-01

To control the authenticity of an old wine without opening the bottle, we developed a few years ago a method based on the measurement of the (137)Cs activity. However, for recent vintages, the (137)Cs activity drops to far too low values (most of the time less than 10 mBq/L for a 10-year-old wine) for this method to perform correctly. In this paper we examine the possibility to date wines using the natural radio-element (210)Pb which has a 22-year period. This new method we propose implies the opening of the bottle and the follow-on destruction of the wine itself, which means that it can only be used for investigating non-expensive bottles or wine lots where there are multiple bottles of the same provenance. Uncertainties on the resulting (210)Pb radioactivity values are large, up to more than 50%, mainly due to local atmospheric variations, which prevents us to carry out precise dating. However it can be used to discriminate between an old wine (pre-1952) and a young wine (past-1990), an information that cannot be obtained with the other techniques based on other isotopes ((137)Cs, (14)C or tritium). Copyright © 2015 Elsevier Ltd. All rights reserved.

Dating human skeletal remains: investigating the viability of measuring the equilibrium between 210Po and 210Pb as a means of estimating the post-mortem interval.

PubMed

Swift, B

1998-11-30

Estimating the post-mortem interval in skeletal remains is a notoriously difficult task; forensic pathologists often rely heavily upon experience in recognising morphological appearances. Previous techniques have involved measuring physical or chemical changes within the hydroxyapatite matrix, radiocarbon dating and 90Sr dating, though no individual test has been advocated. Within this paper it is proposed that measuring the equilibrium between two naturally occurring radio-isotopes, 210Po and 210Pb, and comparison with post-mortem examination samples would produce a new method of dating human skeletal remains. Possible limitations exist, notably the effect of diagenesis, time limitations and relative cost, though this technique could provide a relatively accurate means of determining the post-mortem interval. It is therefore proposed that a large study be undertaken to provide a calibration scale against which bones uncovered can be dated.

210Pb dating

USGS Publications Warehouse

Swarzenski, Peter W.

2014-01-01

Roughly fifty years ago, a small group of scientists from Belgium and the United States, trying to better constrain ice sheet accumulation rates, attempted to apply what was then know about environmental lead as a potential geochronometer. Thus Goldberg (1963) developed the first principles of the 210Pb dating method, which was soon followed by a paper by Crozaz et al. (1964), who examined accumulation history of Antarctic snow using 210Pb. Shortly thereafter, Koide et al. (1972, 1973) adapted this technique to unravel sediment deposition and accumulation records in deep-sea environments. Serendipitously, they chose to work in a deep basin off California, where an independent and robust age model had already been developed. Krishanswami et al. (1971) extended the use of this technique to lacustrine deposits to reconstruct depositional histories of lake sediment, and maybe more importantly, contaminant inputs and burial. Thus, the powerful tool for dating recent (up to about one century old) sediment deposits was established and soon widely adopted. Today almost all oceanographic or limnologic studies that address recent depositional reconstructions employ 210Pb as one of several possible geochronometers (Andrews et al., 2009; Gale, 2009; Baskaran, 2011; Persson and Helms, 2011). This paper presents a short overview of the principles of 210Pb dating and provides a few examples that illustrate the utility of this tracer in contrasting depositional systems. Potential caveats and uncertainties (Appleby et al., 1986; Binford, 1990; Binford et al., 1993; Smith, 2001; Hancock et al., 2002) inherent to the use and interpretation of 210Pb-derived age-models are also introduced. Recommendations as to best practices for most reliable uses and reporting are presented in the summary.

UPb ages of zircon rims: A new analytical method using the air-abrasion technique

USGS Publications Warehouse

Aleinikoff, J.N.; Winegarden, D.L.; Walter, M.

1990-01-01

We present a new technique for directly dating, by conventional techniques, the rims of zircons. Several circumstances, such as a xenocrystic or inherited component in igneous zircon and metamorphic overgrowths on igneous cores, can result in grains with physically distinct age components. Pneumatic abrasion has been previously shown by Krogh to remove overgrowths and damaged areas of zircon, leaving more resistant and isotopically less disturbed parts available for analysis. A new abrader design, which is capable of very gently grinding only tips and interfacial edges of even needle-like grains, permits easy collection of abraded material for dating. Five examples demonstrate the utility of the "dust-collecting" technique, including two studies that compare conventional, ion microprobe and abrader data. Common Pb may be strongly concentrated in the outermost zones of many zircons and this Pb is not easily removed by leaching (even in weak HF). Thus, the benefit of removing only the outermost zones (and avoiding mixing of age components) is somewhat compromised by the much higher common Pb contents which result in less precise age determinations. A very brief abrasion to remove the high common Pb zones prior to collection of material for dating is selected. ?? 1990.

New age data on the geological evolution of Southern India

NASA Technical Reports Server (NTRS)

Taylor, Paul N.; Chadwick, B.; Friend, C. R. L.; Ramakrishnan, M.; Moorbath, Stephen; Viswanatha, M. N.

1988-01-01

The Peninsular Gneisses of Southern India developed over a period of several hundred Ma in the middle-to-late Archaean. Gneisses in the Gorur-Hassan area of southern Karnataka are the oldest recognized constituents: Beckinsale et al. reported a preliminary Rb-Sr whole-rock isochron age of 33558 + or - 66 Ma, but further Rb-Sr and Pb/Pb whole-rock isochron determinations indicate a slightly younger, though more precise age of ca 3305 Ma (R. D. Beckinsale, Pers. Comm.). It is well established that the Peninsular Gneisses constitute basement on which the Dharwar schist belts were deposited. Well-documented exposures of unconformities, with basal quartz pebble conglomerates of the Dharwar Supergroup overlying Peninsular Gneisses, have been reported from the Chikmagalur and Chitradurga areas, and basement gneisses in these two areas have been dated by Rb-Sr and Pb/Pb whole-rock isochron methods at ca 3150 Ma and ca 3000 Ma respectively. Dharwar supracrustal rocks of the Chitradurga schist belt are intruded by the Chitradurga Granite, dated by a Pb/Pb whole-rock isochron at 2605 + or - 18 Ma. These results indicate that the Dharwar Supergroup in the Chitradurga belt was deposited between 3000 Ma and 2600 Ma.

U-Pb Dating of Zircons and Phosphates in Lunar Meteorites, Acapulcoites and Angrites

NASA Technical Reports Server (NTRS)

Zhou, Q.; Zeigler, R. A.; Yin, Q. Z.; Korotev, R. L.; Joliff, B. L.; Amelin, Y.; Marti, K.; Wu, F. Y.; Li, X. H.; Li, Q. L.;

Matrix effects for elemental fractionation within ICPMS: applications for U-Th-Pb geochronology

NASA Astrophysics Data System (ADS)

Chen, W.

2016-12-01

Recent development in instruments provides significant technical supports for daily, quick, money saving geochemical analyses. Laser ablation ICPMS stands out due to these reasons, especially for the U-Th-Pb isotopic dating. Matrix-matched external standardization is by far the most common approach used in U-Th-Pb dating via LA-ICPMS. However, matrix-effects between standard and sample for in-situ dating have shown to be both significant and insignificant. It remains mysterious whether a well matrix-matched standard is needed for U-Th-Pb dating by LA-ICPMS. This study provides an experimental framework for the understanding of matrix effects induced elemental fractionation for U-Th-Pb associated with ICPMS. A preliminary study on the influence of varied U, Th and Pb amounts on their fractionations has been carried out. Experimental data show that different U, Th and Pb contents result in varied 238U/206Pb and 232Th/208Pb ratios. The fractionations of U/Pb and Th/Pb increase with the increasing contents (1 ppb to 100 ppb) with a strong positive anomaly at 10 ppb. Matrixes representing minerals frequently used in dating have been investigated for the influences on U/Pb and Th/Pb fractionations, which suggest a complicated effect. Little fractionations observed between mineral pairs (e.g., monazite and apatite; zircon and perovskite; rutile and perovskite; xenotime and baddeleyite), whereas large fractionations identified for other minerals (e.g., zircon and baddeleyite; monazite and sphene; rutile and baddeleyite). Single element matrix (i.e., Si, P, Ca, Zr, Ti) has been studied to identify their effects on the fractionations. U/Pb ratio increases with the increasing Si and P contents, whereas it decreases for Zr, Ca and Ti. Th/Pb ratio increases with increasing Si contents, decreases for P and Zr, and increases first then decreases for Ca and Ti. Above all, different matrix and U, Th and Pb amounts show distinct U/Pb and Th/Pb fractionations within ICPMS. The minerals with matrix indicating similar fractionations in ICPMS can be used as suitable reference standards for each other with proper laser ablation settings via LA-ICPMS. Moreover, matched U, Th and Pb contents should be considered when using a matrix-matched standard in laser ablation analysis.

Lead Selenide Colloidal Quantum Dot Solar Cells Achieving High Open-Circuit Voltage with One-Step Deposition Strategy.

PubMed

Zhang, Yaohong; Wu, Guohua; Ding, Chao; Liu, Feng; Yao, Yingfang; Zhou, Yong; Wu, Congping; Nakazawa, Naoki; Huang, Qingxun; Toyoda, Taro; Wang, Ruixiang; Hayase, Shuzi; Zou, Zhigang; Shen, Qing

2018-06-18

Lead selenide (PbSe) colloidal quantum dots (CQDs) are considered to be a strong candidate for high-efficiency colloidal quantum dot solar cells (CQDSCs) due to its efficient multiple exciton generation. However, currently, even the best PbSe CQDSCs can only display open-circuit voltage ( V oc ) about 0.530 V. Here, we introduce a solution-phase ligand exchange method to prepare PbI 2 -capped PbSe (PbSe-PbI 2 ) CQD inks, and for the first time, the absorber layer of PbSe CQDSCs was deposited in one step by using this PbSe-PbI 2 CQD inks. One-step-deposited PbSe CQDs absorber layer exhibits fast charge transfer rate, reduced energy funneling, and low trap assisted recombination. The champion large-area (active area is 0.35 cm 2 ) PbSe CQDSCs fabricated with one-step PbSe CQDs achieve a power conversion efficiency (PCE) of 6.0% and a V oc of 0.616 V, which is the highest V oc among PbSe CQDSCs reported to date.

Linking sedimentary total organic carbon to 210Pbex chronology from Changshou Lake in the Three Gorges Reservoir Region, China.

PubMed

Anjum, Raheel; Gao, Jinzhang; Tang, Qiang; He, Xiubin; Zhang, Xinbao; Long, Yi; Shi, Zhonglin; Wang, Mingfeng

2017-05-01

The influences of total organic carbon (TOC) and total nitrogen (TN) on Lead-210 ( 210 Pb) dating have recently been of increasing concern in lacustrine research. Sediment core from Changshou Lake in the Longxi catchment was investigated for influence of TOC on 210 Pb dating. Lead-210 excess ( 210 Pb ex ), Cesium-137 ( 137 Cs) activities, TOC, TN, and particle size were measured. We proposed a dating index based on 137 Cs chronology and particle size distribution of the lake sediment profile and rainfall erosivities calculated from Longxi catchment metrological records. Increasing trends in TOC and TN were specifically caused by commercial cage fish farming after 1989. The statistically significant correlation between 210 Pb ex activity, TOC (0.61, p = 0.04) and TN (0.51, p = 0.04), respectively explained post-1989 210 Pb scavenging. The 210 Pb ex activity was closely related with coupled peaks of TOC and TN from mass depth 5-10 g cm -2 . Higher TOC/TN ratio (8.33) indicated submerged macrophytes and native aquatic algal growth as main source of carbon from enhanced primary productivity because of massive fertilizer use and coherent climate warming. The study supported key hypothesis on vital role of fertilizer usage and algal derived TOC in controlling sedimentary 210 Pb ex activity at Changshou Lake sediment. 137 Cs profile and erosive events as time markers provided reliable and consistent sedimentation rate of (1.6 cm y -1 ). 210 Pb ex activity decayed exponentially after peak at mass depth 5.68 g cm -2 . Therefore, violation of 210 Pb dating primary assumptions made it inappropriate for sediment dating at Changshou Lake. TOC content must be considered while using 210 Pb as dating tool for lake sediment profiles. Copyright © 2017 Elsevier Ltd. All rights reserved.

High-resolution age modelling of peat bog profiles using pre and post-bomb 14C, 210Pb and cryptotephra data from six Albertan peat bogs

NASA Astrophysics Data System (ADS)

Davies, L. J.; Froese, D. G.; Appleby, P.; van Bellen, S.; Magnan, G.; Mullan-Boudreau, G.; Noernberg, T.; Shotyk, W.; Zaccone, C.

2016-12-01

Age modelling of recent peat profiles is frequently undertaken for high-resolution modern studies, but the most common techniques applied (e.g. 14C, 210Pb, cryptotephra) are rarely combined and used for testing and inter-comparison. Here, we integrate three age-dating approaches to produce a single age model to comprehensively investigate variations in the chronometers and individual site histories since 1900. OxCal's P_Sequence function is used to model dates produced using 14C (pre- and post-bomb), 210Pb (corroborated with 137Cs and 241Am) from six peat bogs in central and northern Alberta. Physical and chemical characteristics of the cores (e.g. macrofossils, humification, ash content, dry density) provide important constraints for the model by highlighting periods with significant changes in accumulation rate (e.g. fire events, permafrost development, prolonged surficial drying). Sub-cm resolution output shows there are consistent differences in how the 14C and 210Pb signals are preserved in peat profiles, with 14C commonly showing a slight bias toward older ages at the same depth relative to 210Pb data. These methods can successfully be combined in a Bayesian model and used to produce a single age model that more accurately accounts for the uncertainties inherent in each method. Understanding these differences and combining the results of these methods results in a stronger chronology at each site investigated here despite observed differences in ecological setting, accumulation rates, fire events/frequency and permafrost development.

Precise and accurate in situ Pb-Pb dating of apatite, monazite, and sphene by laser ablation multiple-collector ICP-MS

NASA Astrophysics Data System (ADS)

Willigers, B. J. A.; Baker, J. A.; Krogstad, E. J.; Peate, D. W.

2002-03-01

To evaluate in situ Pb dating by laser ablation multiple-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS), we analysed apatite, sphene, and monazite from Paleoproterozoic metamorphic rocks from West Greenland. Pb isotope ratios were also determined in the National Institute of Standards and Technology (NIST) 610 glass standard and were corrected for mass fractionation by reference to the measured thallium isotope ratio. The NIST 610 glass was used to monitor Pb isotope mass fractionation in the low Tl/Pb accessory minerals. Replicate analyses of the glass (1 to 2 min) yielded ratios with an external reproducibility comparable to conventional analyses of standard reference material 981 by thermal ionisation mass spectrometry (TIMS). Mineral grains were generally analysed with a 100-μm laser beam, although some monazite crystals were analysed at smaller spot sizes (10 and 25 μm). The common Pb isotope ratios required for age calculations were either measured on coexisting plagioclase by LA-MC-ICP-MS or could be ignored, as individual crystals exhibit sufficient Pb isotopic heterogeneity to perform isochron calculations on replicate analyses of single crystals. Mean mineral ages with the 204Pb ion beam measured in the multiplier were as follows: apatite, 1715 ± 23 m.y.; sphene, 1789 ± 11 m.y.; and monazite, 1783 to 1888 m.y., with relative uncertainties on individual monazite ages of <0.2% but highly reproducible age determinations on single monazite crystals (≪1%). Isochron ages calculated from several mineral analyses without assumption of common Pb also yield precise age determinations. Apatite and monazite Pb ages determined by in situ Pb isotope analysis are identical to those determined by conventional TIMS analysis of bulk mineral separates, and the analytical uncertainties of these short laser analyses with no prior mechanical or chemical separation are comparable to those obtained by TIMS. Detailed examination of the sphene in situ age data does, however, show a small discrepancy between the LA-MC-ICP-MS and TIMS ages (˜1% younger). High-resolution mass scans of the sphene during ablation clearly showed several small and as yet unidentified isobaric interferences that overlap with the 207Pb peak at the resolution conditions for measurement of isotope ratios. These might account for the age discrepancy between the LA-MC-ICP-MS and TIMS sphene ages. LA-MC-ICP-MS is a rapid, accurate, and precise method for in situ determination of Pb isotope ratios that can be used for geochronological studies in a manner similar to an ion microprobe, albeit currently at a somewhat degraded spatial resolution. Further modifications to the LA-MC-ICP-MS system, such as improved sensitivity, ion transmission, and LA methodology, may lead to this type of instrument becoming the method of choice for many types of in situ Pb isotope dating.

Connecting the U-Th and U-Pb Chronometers: New Algorithms and Applications

NASA Astrophysics Data System (ADS)

McLean, N. M.; Smith, C. J. M.; Roberts, N. M. W.; Richards, D. A.

2016-12-01

The U-Th and U-Pb geochronometers are important clocks for separate intervals of the geologic timescale. U-Th dates exploit disequilibrium in the 238U intermediate daughter isotopes 234U and 230Th, and are often used to date corals and speleothems that are zero age through 800 ka. The U-Pb system relies on secular equilibrium decay of 238U to 206Pb and 235U to 207Pb over longer timescales, and can be used to date samples from <1 Ma to 4.5 Ga. Disequilibrium plays a role in young U-Pb dates, but only as a nuisance correction. Both chronometers can produce dates with uncertainties <0.1% near the center of their applicable age ranges, but become less precise at their intersection, when the 238U decay chain approaches secular equilibrium and there has been little time for ingrowth of radiogenic Pb. However, if measurements or assumptions about both chronometers can be made, then they can be combined into a single, more informed date. Coupling the datasets can improve their precision and accuracy and help interrogate the assumptions that underpin each. Working with this data is difficult for two reasons. The Bateman equations are long and cumbersome for U decay chains that include 238U, 234U, 230Th, 226Ra, 206Pb and 235U, 231Pa, and 207Pb. Also, Pb measurements often comprise varying amounts of radiogenic Pb from locally heterogeneous U concentrations mixed with varying amounts of common Pb. At present there is no established, flexible computational framework to combine information from measurements and/or assumptions of these parameters, and no way to visualize and interpret the results. We present new algorithms to quickly and accurately solve the system of differential equations defined by both of the uranium decay chains and the linear regression through the U-Pb isochron. The results are illustrated on a new concordia diagram, where the concordia curve is determined by measured and/or assumed U-series disequilibrium and can have unfamiliar topologies. We demonstrate this approach using data collected by solution and laser ablation ICPMS on carbonates with measurable 230Th and 234U disequilibrium, measurable disequilibrium for only 234U, and when only assumptions can be made about initial U-series disequilibrium. Potential applications include refining chronologies at ca. 1 Ma, an important period in Earth history.

Modeling Peat Ages Using 7Be Data to Account for Downwash of 210Pb

NASA Astrophysics Data System (ADS)

Manies, K.; Fuller, C.; Jones, M.

2016-12-01

In order to determine the amount of peat, and thus carbon, which has accumulated since the last thaw event, we are interested in dating the surface layers of boreal thermokarst bogs. However, there can often be a mismatch by several decades between dates obtained using 210Pb, 14C, or 137Cs. We found that 210Pb-based dates were almost always younger than 14C-based dates. One of the limitations often cited regarding the use of 210Pb dating for peatlands is the potential for this radionuclide to be transported down the soil profile, biasing the mean accumulation rate (MAR) towards higher values which, in turn, results in younger ages at a specific horizon. 7Be, which has similar depositional behaviors as 210Pb but a much shorter half-life (53.22 days), can be used to help determine if there is movement of 210Pb through surface layers and the depths to which 210Pb-bearing particles are transported (over the mean life of 7Be). These data can then be used in new models, such as the Linked Radionuclide aCcumulation model (LRC; Landis et al., 2016, http://dx.doi.org/10.1016/ j.gca.2016.02.2013), which account for 210Pb downwash when calculating soil horizon ages. To this end, we measured 7Be within a bog four times over the growing season. 7Be was found to 4 cm in May, reached its maximum depth of penetration in July (7 cm), and then receded again to 4 cm. The maximum integrated 7Be activity was also found in July. This pattern is similar to other studies which found 7Be deposition decreased over the rainy season. Next, we will calculate peat ages with models that include downwash of 210Pb, the depths of which will be based on the penetration depth of 7Be. These ages will be compared to 210Pb ages obtained with both the Constant Rate of Supply (CRS) and Constant Flux - Constant Sedimentation (CF:CS) models and to 137Cs- and 14C-derived ages. We anticipate that dates based on models that include some transport of 210Pb into the soil profile will provide more accurate peat formation dates and allow for more accurate carbon accumulation rates.

Marine Chemistry in the People’s Republic of China.

DTIC Science & Technology

1984-08-01

Eh, Fe, Al, Mn, Cu, Pb, Zn, Cd, Hg, Cr, and also the sedimentation rate by Pb- 210 method. (2) The effects of flow rate, eddy diffusion, axial length of...sediments, distribution, determination, radium-226, uranium-238, radon-222, polonium - 210 , bismuth- 210 , lead-206, particulates, adsorption, polonium ...sediments, distribution, radium-226, uranium-238, radon-222, polonium - 210 , bismuth- 210 , lead-206, particulates, adsorption, polonium , dating, Zhujiang

Analytical and sampling constraints in ²¹⁰Pb dating.

PubMed

MacKenzie, A B; Hardie, S M L; Farmer, J G; Eades, L J; Pulford, I D

2011-03-01

²¹⁰Pb dating provides a valuable, widely used means of establishing recent chronologies for sediments and other accumulating natural deposits. The Constant Rate of Supply (CRS) model is the most versatile and widely used method for establishing ²¹⁰Pb chronologies but, when using this model, care must be taken to account for limitations imposed by sampling and analytical factors. In particular, incompatibility of finite values for empirical data, which are constrained by detection limit and core length, with terms in the age calculation, which represent integrations to infinity, can generate erroneously old ages for deeper sections of cores. The bias in calculated ages increases with poorer limit of detection and the magnitude of the disparity increases with age. The origin and magnitude of this effect are considered below, firstly for an idealized, theoretical ²¹⁰Pb profile and secondly for a freshwater lake sediment core. A brief consideration is presented of the implications of this potential artefact for sampling and analysis. Copyright © 2011 Elsevier B.V. All rights reserved.

Late Permian volcanic dykes in the crystalline basement of the Považský Inovec Mts. (Western Carpathians): U-Th-Pb zircon SHRIMP and monazite chemical dating

NASA Astrophysics Data System (ADS)

Pelech, Ondrej; Vozárová, Anna; Uher, Pavel; Petrík, Igor; Plašienka, Dušan; Šarinová, Katarína; Rodionov, Nikolay

2017-08-01

This paper presents geochronological data for the volcanic dykes located in the northern Považský Inovec Mts. The dykes are up to 5 m thick and tens to hundreds of metres long. They comprise variously inclined and oriented lenses, composed of strongly altered grey-green alkali basalts. Their age was variously interpreted and discussed in the past. Dykes were emplaced into the Tatricum metamorphic rocks, mostly consisting of mica schists and gneisses of the Variscan (early Carboniferous) age. Two different methods, zircon SHRIMP and monazite chemical dating, were applied to determine the age of these dykes. U-Pb SHRIMP dating of magmatic zircons yielded the concordia age of 260.2 ± 1.4 Ma. The Th-U-Pb monazite dating of the same dyke gave the CHIME age of 259 ± 3Ma. Both ages confirm the magmatic crystallization at the boundary of the latest Middle Permian to the Late Permian. Dyke emplacement was coeval with development of the Late Paleozoic sedimentary basin known in the northern Považský Inovec Mts. and could be correlated with other pre-Mesozoic Tethyan regions especially in the Southern Alps.

Progress integrating ID-TIMS U-Pb geochronology with accessory mineral geochemistry: towards better accuracy and higher precision time

NASA Astrophysics Data System (ADS)

Schoene, B.; Samperton, K. M.; Crowley, J. L.; Cottle, J. M.

2012-12-01

It is increasingly common that hand samples of plutonic and volcanic rocks contain zircon with dates that span between zero and >100 ka. This recognition comes from the increased application of U-series geochronology on young volcanic rocks and the increased precision to better than 0.1% on single zircons by the U-Pb ID-TIMS method. It has thus become more difficult to interpret such complicated datasets in terms of ashbed eruption or magma emplacement, which are critical constraints for geochronologic applications ranging from biotic evolution and the stratigraphic record to magmatic and metamorphic processes in orogenic belts. It is important, therefore, to develop methods that aid in interpreting which minerals, if any, date the targeted process. One promising tactic is to better integrate accessory mineral geochemistry with high-precision ID-TIMS U-Pb geochronology. These dual constraints can 1) identify cogenetic populations of minerals, and 2) record magmatic or metamorphic fluid evolution through time. Goal (1) has been widely sought with in situ geochronology and geochemical analysis but is limited by low-precision dates. Recent work has attempted to bridge this gap by retrieving the typically discarded elution from ion exchange chemistry that precedes ID-TIMS U-Pb geochronology and analyzing it by ICP-MS (U-Pb TIMS-TEA). The result integrates geochemistry and high-precision geochronology from the exact same volume of material. The limitation of this method is the relatively coarse spatial resolution compared to in situ techniques, and thus averages potentially complicated trace element profiles through single minerals or mineral fragments. In continued work, we test the effect of this on zircon by beginning with CL imaging to reveal internal zonation and growth histories. This is followed by in situ LA-ICPMS trace element transects of imaged grains to reveal internal geochemical zonation. The same grains are then removed from grain-mount, fragmented, and analyzed by U-Pb TIMS-TEA. In situ trace element transects are used to model predicted TIMS-TEA trace element concentrations to test whether complicated trace element profiles undermine U-Pb TIMS-TEA data. We find good agreement between predicted and measured TIMS-TEA data, and can argue that the measured ID-TIMS U-Pb date corresponds to the time at which the geochemical signature measured by TIMS-TEA was acquired. Thus, in a hypothetical magma that is differentiating through AFC processes on timescales resolvable by geochronology, U-Pb TIMS-TEA should usually be a robust indicator of magma evolution through time. We present data from two ca. 40-30 Ma alpine intrusions from northern Italy: the southern Adamello batholith and the Bergell intrusion. The relatively young age of these intrusions permits uncertainties on individual zircon or zircon fragments as good as 10 ka, while zircon populations from individual hand samples often record zircon growth of >200 ka. Using the methodologies described above, we explore whether these zircons record in situ magmatic differentiation or introduction of antecrystic zircon to magma batches, and integrate these data to gain a better understanding of magma storage, differentiation and emplacement as a function of pressure, temperature, and time. These methods are a promising step towards interpreting complicated geochronologic data in ashbed samples as well through a better understanding of magmatic processes that precede eruption.

Reliance on (210)Pb chronology can compromise the inference of preindustrial Hg flux to lake sediments.

PubMed

Cooke, Colin A; Hobbs, William O; Michelutti, Neal; Wolfe, Alexander P

2010-03-15

Lake sediments are frequently used to reconstruct the rate and magnitude of human impacts on the biogeochemical cycle of mercury (Hg). The vast majority of these studies rely on excess (210)Pb inventories in short cores to temporally constrain recent trends in Hg deposition, revealing an approximately 3-fold increase in Hg deposition since preindustrial times. However, the exhaustion of unsupported (210)Pb and the onset of widespread global Hg pollution converge temporally in the late 19th century, raising the possibility that preindustrial Hg fluxes are poorly constrained. Here, we combine (210)Pb and accelerator mass spectrometry (AMS) (14)C dated lake sediment records from arctic and Andean lakes to assess the reliability of (210)Pb-derived chronologies in the estimation of preindustrial Hg fluxes. For all four studied lakes, relying on (210)Pb chronologies results in an overestimate of preindustrial Hg fluxes, because extrapolated basal (210)Pb sedimentation rates are systematically overestimated in comparison to accumulation models that include (14)C dates. In the Andes, the use of (14)C dates is critical toward assessing the full history of Hg pollution, which extends beyond the industrial era. In the Arctic, (14)C dating suggests that Hg deposition may have increased >10-fold since the Industrial Revolution, rather than the commonly quoted 3-fold increase. The incorporation of (14)C dates may therefore be necessary if accurate Hg flux histories are sought from oligotrophic lake sediments.

Implications of Bishop Tuff zircon U-Pb ages for rates of zircon growth and magma accumulation

NASA Astrophysics Data System (ADS)

Reid, M. R.; Schmitt, A. K.

2012-12-01

Rates of geologic processes obtained from natural studies rely on accurate geochronologic information. An important benchmark in geochronology as well as a valuable source of insights into the evolution of voluminous explosive eruptions is the >600 km3 Bishop Tuff (BT). A recently determined weighted mean 206Pb/238U date of 767.1±0.9 ka for a BT zircon population [1] is indistinguishable from the recalibrated 40Ar/39Ar sanidine date of 767.4±2.2 ka [2], potentially providing a key intercalibration point between astronomical and radio-isotopic dating approaches. Consequences of these results are linear zircon growth rates of >1×10-14 cm/sec and magma accumulation rates of >200 km3/ka. In contrast, spatially selective SIMS U-Pb dating of BT zircons yielded mean pre-eruption ages of 850 ka [3], a difference that raises questions about the validity of intercalibration between U-Pb and K-Ar dating methods and the history of magma accumulation. We obtained new SIMS analyses of the BT zircons using more spatially and analytically sensitive methods and verifying our accuracy against the TIMS dated Quaternary zircon 61.308A (2.488±0.002 Ma). Analyses were performed on zircon rims and on oriented cross-sections exposed during optical interferometry-calibrated serial sectioning removing the outermost ~31 μm. Sputtering by a 100 nA ion beam versus the normally employed 10-12 nA beam resulted in enhanced radiogenic Pb yields and analytical uncertainties for Quaternary zircon approaching the U-Pb age reproducibility of the primary zircon standard (~1-2 % for AS3). Ages obtained at ~31 μm depth (representing <5% of crystal growth in most cases) average 892±26ka (MSWD=0.29), corroborating previous evidence for residence times of several tens of ka. Rim ages average 781±22 ka (MSWD=0.61), overlapping Ar/Ar determinations of eruption age and corroborating the importance of near-eruption aged zircon growth. Our results confirm the presence of BT zircon domains that predate eruption by tens of ka, domains that could be difficult to detect by single crystal analyses. SIMS analyses can selectively sample more interior portions of grains whereas whole grain TIMS analyses will be volumetrically biased towards the outermost ~20% of the BT zircons. Spots centered on BT zircon cores sample a domain representing only a few volume percent of the crystal; if mantled completely by eruption-aged growth, single crystal zircon ages are predicted to be <5 ka older than eruption, extrapolating from the SIMS dates. When, compared to grain interiors, the greater average near-rim U concentrations are factored into this mass balance, the influence of these older domains is further diminished. A scenario that can at least partially reconcile the disparate zircon dates in the context of evolution of the BT and the dynamics of zircon crystallization is as follows: (1) zircon nucleation and relatively rapid growth an average of ~100 ka before eruption; (2) significant decay in zircon growth rates as temperatures and Zr melt gradients relax; and, finally, (3) mantling of earlier zircon cores by rejuvenation and renewed BT zircon growth during the lead-up to eruption. Comparisons between spot and single grain dating show that most zircon growth likely occurred close to eruption. [1] Crowley et al., 2007.Geology 35, 1123. [2] Rivera et al., 2011. Earth Planet. Sci. Lett. 311, 420. [3] Simon and Reid, 2005. Earth Planet. Sci. Lett. 235, 123.

U-Pb Geochronology of Grandite Skarn Garnet: Case Studies From Jurassic Skarns of California

NASA Astrophysics Data System (ADS)

Gevedon, M. L.; Seman, S.; Barnes, J.; Stockli, D. F.; Lackey, J. S.

2016-12-01

We present 3 case studies using a new method for U-Pb dating grossular-andradite (grandite) skarn garnet via LA-ICP-MS (Seman et al., in prep). Grandite is commonly rich in U, with high Fe3+ contents generally correlating with higher U concentrations. Micron-scale non-radiogenic Pb heterogeneities allow for regression of age data using Tera-Wasserberg concordia. Although others have dated accessory skarn minerals, garnet U-Pb ages are powerful because garnet grows early and is nearly ubiquitous in skarns, resists alteration, and provides a formation age independent of that of the causative pluton. The Darwin stock (Argus range, eastern CA) was likely a short-lived, single pulse of magmatism, genetically related to the Darwin skarn. A robust skarn garnet U-Pb age of 176.8 ± 1.3 Ma agrees well with the pluton U-Pb zircon age of 175 Ma (Chen and Moore, 1982). Furthermore, zircon separated from, and in textural equilibrium with, exoskarn garnetite yields a U-Pb age of 176.8 ± 1 Ma. Such agreement between plutonic and skarn zircon ages with a skarn garnet age in a geologically simple field area is the ideal scenario for establishing grandite U-Pb as a viable tool for directly dating skarns. The Black Rock skarn (BRS; eastern CA) is more complex: multiple plutons and ambiguous field relations complicate determination of a causative pluton. A skarn garnet U-Pb age of 172.0 ± 3 Ma confirms a middle Jurassic BRS formation age. Investigation of 4 local plutons yield zircon U-Pb ages of 222 ± 3 Ma, 213 ± 4 Ma, 207 ± 4 Ma and 176.2 ± 2 Ma. Comparison of the skarn garnet U-Pb and pluton ages suggest the BRS is genetically related to the youngest pluton, providing basis for further field and geochemical investigation. The Whitehorse skarn (WS; Mojave Desert, CA) lies in an important region for studying the changing tectono-magmatic regime of the Jurassic North American Cordillera; basin fill suggests a tectonically-controlled oscillating regional shoreline (Busby, 2012). Values of δ18O of WS garnet are strongly negative, —9.8‰ to 1.2‰, and can only be the result of access to meteoric water. A grandite U-Pb age of 162.3 ± 2 Ma requires the region of the WS not be submerged below the sea at this time. Future work coupling grandite U-Pb and δ18O may be vital in establishing the timing of Jurassic Cordilleran tectonic changes in the Mojave Desert.

Sm-Nd dating of the giant Sullivan Pb-Zn-Ag deposit, British Columbia

USGS Publications Warehouse

Jiang, Shao-Yong; Slack, John F.; Palmer, Martin R.

2000-01-01

We report here Sm and Nd isotope data for hydrothermal tourmalinites and sulfide ores from the giant Sullivan Pb-Zn-Ag deposit, which occurs in the lower part of the Mesoproterozoic Purcell (Belt) Supergroup. Whole-rock samples of quartz-tourmaline tourmalinite from the footwall alteration pipe yield a Sm-Nd isochron age of 1470 ± 59 Ma, recording synsedimentary B metasomatism of clastic sediments during early evolution of the Sullivan hydrothermal system. Data for variably altered (chloritized and/or albitized) tourmalinites from the hanging wall of the deposit, which are believed to have formed originally ca. 1470 Ma, define a younger 1076 ± 77 Ma isochron because of resetting of Sm and Nd isotopes during Grenvillian metamorphism. HCl leachates of bedded Pb-Zn ore yield a Sm-Nd isochron age of 1451 ± 46 Ma, which is consistent with syngenetic-exhalative mineralization ca. 1470 Ma; this age could also reflect a slightly younger, epigenetic hydrothermal event. Results obtained for the Sullivan deposit indicate that the Sm-Nd geochronometer has the potential to directly date mineralization and alteration in stratabound sulfide deposits that are not amenable to dating by other isotope methods.

Problems of geological and isotopic age of the Okhotsk-Chukotsk Volcanogenic Belt (OCVB)

NASA Astrophysics Data System (ADS)

Belyi, V. F.

2008-12-01

The working stratigraphic chart accepted for the Okhotsk-Chukotsk Volcanogenic Belt (OCVB) at the 3rd Interdepartmental Regional Stratigraphic Conference (IRSC) integrated data of the medium-scale geological survey, the established succession of endemic floras of the developing volcanic highland, and the results of palynological and magnetostratigraphic study ( Resolutions of the 3rd…, 2003). The OCVB was formed during the middle Albian-Santonian (and initial Campanian probably). Sequences of the belt are attributed to the Buor-Kemyus (early-middle Albian), Arman (late Albian), Amka (Cenomanian), and Arkagala (Turonian-Santonian) phytostratigraphic horizons. The lack of data on relations between the horizons and fauna-bearing marine deposits is a serious obstacle for correlation of regional subdivisions with the general stratigraphic scale. The problem can be solved using geological methods of palynological and tephrochronological research. Isotopic ages of the OCVB rocks were determined applying the K-Ar and Rb-Sr isotopic dating in the early period and the Ar-Ar and U-Pb (SHRIMP) methods in recent years. The subdivision scheme of the OCVB volcanics based on the K-Ar relict and Rb-Sr isochron dates, which is accepted as addendum to the working stratigraphic chart, confirms in general the geological inferences concerning the OCVB age. The Ar-Ar and U-Pb dates (less than 100 determinations in total) obtained for the Okhotsk, Central Chukotsk, and Anadyr sectors of the OCVB external zone provoked opinions that the belt age should be radically revised. Analysis of new isotopic dates showed that they contradict in variable extent to geological data on the Okhotsk and Central Chukotsk sectors, whereas there is no significant discordance between isotopic and geological data on the Anadyr sector. Consequently, it can be empirically concluded that geological factors influenced the isotopic systems (“clock”). There is also a considerable discordance between the Ar-Ar and U-Pb isotopic dates. These uncertainties of the isotopic dating imply prematurity of idea to revise age of the OCVB.

210Pb-dating of a lake sediment core from Lough Carra (Co. Mayo, western Ireland): use of paleolimnological data for chronology validation below the 210Pb dating horizon.

PubMed

O'Reilly, J; Vintró, L León; Mitchell, P I; Donohue, I; Leira, M; Hobbs, W; Irvine, K

2011-05-01

The chronologies and sediment accumulation rates for a lake sediment sequence from Lough Carra (Co. Mayo, western Ireland) were established by applying the constant initial concentration (CIC) and constant rate of supply (CRS) hypotheses to the measured (210)Pb(excess) profile. The resulting chronologies were validated using the artificial fallout radionuclides (137)Cs and (241)Am, which provide independent chronostratigraphic markers for the second half of the 20th century. The validity of extrapolating the derived CIC and CRS dates below the (210)Pb dating horizon using average sedimentation rates was investigated using supplementary paleolimnological information and historical data. Our data confirm that such an extrapolation is well justified at sites characterised by relatively stable sedimentation conditions. Copyright © 2010 Elsevier Ltd. All rights reserved.

Constraining Metamorphic Timing and Processes by Dating Garnet, Zircon, Titanite and Monazite in UHP and HP Rocks from Weihai, Sulu UHP Terrane, Eastern China

NASA Astrophysics Data System (ADS)

Wang, D.; Vervoort, J. D.; Fisher, C. M.; Cao, H.

2016-12-01

The Sulu UHP terrane is the extension of the Dabie orogenic belt to the east, offset 500 km to the northeast by the Tanlu fault [1]. The focus of this study, the Weihai area, is located at the northernmost part of the Sulu UHP terrane, and consists mainly of gneisses overprinted by amphibolite-facies assemblages, in addition to minor eclogite, granulite, and some ultramafic rocks [1]. Time constrains are critical to our understanding of the processes of UHP metamorphism, as well as the tectonic evolution of the region. In the last decade, U-Pb dating of metamorphic domains of zircons has been widely applied to determine the history of the UHP metamorphism (240 - 220 Ma) [1]. Recent garnet Lu-Hf dating from the Dabie terrane (240 - 220Ma) suggests the initiation of prograde metamorphism to be prior to ca. 240 Ma [2]. In-situ U-Pb dating of accessary minerals using LA-ICPMS (i.e. monazite, titanite, rutile, etc.), can provide important information to augment and complement the zircon U-Pb metamorphic dates. In this study, we collected samples throughout the Weihai area. Protolith ages of these samples range from Paleoproterozoic to Neoproterozoic ( 1850 - 700 Ma) as indicated by U-Pb dating of zircon cores. Zircon metamorphic rims yield U-Pb ages of 240 - 220 Ma, likely indicating the UHP stage of the Sulu terrane [3]. Four eclogites yield Lu-Hf garnet isochrons with dates between 239 and 224 Ma, consistent with garnet Lu-Hf dates from Dabie UHP terrane [2]. Sm-Nd isochrons indicate systematic younger dates (220 - 210 Ma) interpreted as cooling ages. Titanites extracted from four samples give U-Pb ages ranging from 220 to 200 Ma, in agreement with the titanite dates from the southern Sulu terrane [4]. Monazites from three samples give precise dates between 214 and 211 Ma. Collectively, monazite and titanite U-Pb ages are broadly consistent with the garnet Sm-Nd isochrons, and thus we interpret these as cooling ages. Based on the dates of different systems/minerals presented above, we suggest the prograde metamorphism of Weihai UHP terrane likely took place prior to 240 Ma, and the peak of the UHP stage is likely between 240 and 220 Ma. [1] Zhang et al., Gondwana Res., 16 (2009) 1-26 [2] Cheng et al., J. Metamorphic Geol., 26 (2008), 741-758 [3] Liou et al., J. Asian Earth Sci., 35 (2009), 199-231 [4] Chen and Zheng, GCA, 150(2015), 53-73

Quantifying the timescales of Archean UHT metamorphism through U-Pb monazite and zircon petrochronology

NASA Astrophysics Data System (ADS)

Guevara, V.; MacLennan, S. A.; Schoene, B.; Dragovic, B.; Caddick, M. J.; Kylander-Clark, A. R.; Couëslan, C. G.

2016-12-01

Unraveling the timescales of metamorphism is crucial to understanding the mechanisms behind mass/heat transfer through Earth's crust. Though such mechanisms and their durations are becoming well constrained in modern (Phanerozoic) settings, the drivers of metamorphism in the ancient geologic record remain more enigmatic. The development of accessory phase petrochronology has allowed metamorphic evolution to be closely linked to isotopic dates, ultimately improving quantification of metamorphic durations. While in-situ petrochronological methods preserve textural and spatial context, they often lack the temporal resolution required to accurately quantify metamorphic duration in Archean terranes. Here we combine in-situ U-Pb monazite (mnz) and zircon (zrn) laser ablation split-stream (LASS) and high-precision ID-TIMS-TEA petrochronology of distinct grain domains to resolve the timescales of ultrahigh temperature (UHT) metamorphism in the Archean Pikwitonei granulite domain (PGD). The PGD encompasses >1.5x105 km2 of granulite-facies rocks on the NW edge of the Superior Province. Themodynamic modelling of a pelite from the western part of the PGD suggests peak P-T conditions of >8 kbar, 900-940 °C and UHT decompression to 8 kbar followed by cooling. LASS analysis of zrn inclusions in garnet (grt) yields a date of 2701 Ma, with Ti in zrn thermometry yielding T of 800-900 °C. LASS analysis of mnz yields dates of 2720-2680 Ma for low HREE domains with no to shallow negative Eu anomalies, suggestive of growth during plagioclase (plg) breakdown and grt stability. ID-TIMS analysis of a mnz fragment with a strong negative Eu anomaly, suggestive of growth during plg stability, gives a concordant 207Pb/206Pb date of 2666 Ma, consistent with LASS results of 2660-2640 Ma for chemically similar domains. ID-TIMS analyses of zrn rims yield a range of 207Pb/206Pb dates from 2671 to 2656 Ma (±<1 Ma). Ti in zrn yields 800 °C for these rims, indicating they grew at similar T. Together, these data indicate a metamorphic cycle in the PGD to/from UHT over a minimum of 35 Ma, with at least 12 Ma of slow cooling near 800 °C in the lower crust following UHT decompression. This evolution is inconsistent with punctuated thermal pulses due to focused fluid flow or magmatism, instead requiring a long-lived source of crustal heating.

Heterogeneity in the 238U/235U Ratios of Angrites.

NASA Astrophysics Data System (ADS)

Tissot, F.; Dauphas, N.; Grove, T. L.

2016-12-01

Angrites are differentiated meteorites of basaltic composition, of either volcanic or plutonic origin, that display minimal post-crystallization alteration, metamorphism, shock or impact brecciation. Because quenched angrites cooled very rapidly, all radiochronometric systems closed simultaneously in these samples. Quenched angrites are thus often used as anchors for cross-calibrating short-lived dating methods (e.g., 26Al-26Mg) and the absolute dating techniques (e.g, Pb-Pb). Due to the constancy of the 238U/235U ratio in natural samples, Pb-Pb ages have long been calculated using a "consensus" 238U/235U ratio, but the discovery of resolvable variations in the 238U/235U ratio of natural samples, means that the U isotopic composition of the material to date also has to be determined in order to obtain high-precision Pb-Pb ages. We set out (a) to measure at high-precision the 238U/235U ratio of a large array of angrites to correct their Pb-Pb ages, and (b) to identify whether all angrites have a similar U isotopic composition, and, if not, what were the processes responsible for this variability. Recently, Brennecka & Wadhwa (2012) suggested that the angrite-parent body had a homogeneous 238U/235U ratio. They reached this conclusion partly because they propagated the uncertainties of the U isotopic composition of the various U double spikes that they used onto the final 238U/235U ratio the sample. Because this error is systematic (i.e., it affects all samples similarly), differences in the δ238U values of samples corrected by the same double spike are better known than one would be led to believe if uncertainties on the spike composition are propagated. At the conference, we will present the results of the high-precision U isotope analyses for six angrite samples: NWA 4590, NWA 4801, NWA 6291, Angra dos Reis, D'Orbigny, and Sahara 99555. We will show that there is some heterogeneity in the δ238U values of the angrites and will discuss the possible processes by which different angrite samples can acquire different U isotopic compositions. The U isotope data will then be used to correct Pb-Pb ages of angrites estimated using an assumed 238U/235U ratio. These ages will be used to discuss the degree of concordance between short-lived nuclides systems and the absolute Pb-Pb clock in early Solar System materials.

Atmospheric lead deposition to Okefenokee Swamp, Georgia, USA

USGS Publications Warehouse

Jackson, B.P.; Winger, P.V.; Lasier, P.J.

2004-01-01

'Capsule:' Coal combustion emissions appear to be a major source of Pb in the Okefenokee wetland. Contamination of the environment from atmospheric deposition during the twentieth century is pervasive even in areas ostensibly considered pristine or remote from point sources. In this study, Pb concentrations in a Pb-210-dated peat core collected from the Okefenokee Swamp, GA were used to assess historical contaminant input via atmospheric deposition. Lead isotope ratios were determined by dynamic reaction cell ICP-MS (DRC-ICP-MS). Increases in Pb concentration occurred in the late nineteenth century and a marked rise in Pb concentrations pre-dated the widespread use of leaded gasoline within the US. The Pb-206/Pb-207 ratios of 1.19 during this period were consistent with coal combustion emissions. A later increase in Pb concentration, concurrent with a trend toward more radiogenic Pb-206/Pb-207 ratios in gasoline is consistent with an increased input of Pb from leaded gasoline emissions. However, it appears that coal combustion emissions remain a major source of Pb to the Okefenokee.

U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand - A new report of Early Paleozoic granite

NASA Astrophysics Data System (ADS)

Kawakami, T.; Nakano, N.; Higashino, F.; Hokada, T.; Osanai, Y.; Yuhara, M.; Charusiri, P.; Kamikubo, H.; Yonemura, K.; Hirata, T.

2014-07-01

In order to understand the age and tectonic framework of Eastern to Peninsular Thailand from the viewpoint of basement (metamorphic and plutonic) geology, the LA-ICP-MS U-Pb zircon dating and the chemical Th-U-total Pb isochron method (CHIME) monazite dating were performed in the Khao Chao, Hub-Kapong to Pran Buri, and Khanom areas in Eastern to Peninsular Thailand. The LA-ICP-MS U-Pb zircon dating of the garnet-hornblende gneiss from the Khao Chao area gave 229 ± 3 Ma representing the crystallization age of the gabbro, and that of the garnet-biotite gneisses gave 193 ± 4 Ma representing the timing of an upper amphibolite facies metamorphism. The CHIME monazite dating of pelitic gneiss from the Khao Chao gneiss gave scattered result of 68 ± 22 Ma, due to low PbO content and rejuvenation of older monazite grains during another metamorphism in the Late Cretaceous to Tertiary time. The U-Pb ages of zircon from the Hua Hin gneissic granite in the Hub-Kapong to Pran Buri area scatter from 250 Ma to 170 Ma on the concordia. Granite crystallization was at 219 ± 2 Ma, followed by the sillimanite-grade regional metamorphism at 185 ± 2 Ma. Monazite in the pelitic gneiss from this area also preserves Early to Middle Jurassic metamorphism and rejuvenation by later contact metamorphism by non-foliated granite or by another fluid infiltration event in the Late Cretaceous to Tertiary time. The Khao Dat Fa granite from the Khanom area of Peninsular Thailand gave a U-Pb zircon age of 477 ± 7 Ma. This is the second oldest granite pluton ever reported from Thailand, and is a clear evidence for the Sibumasu block having a crystalline basement that was formed during the Pan-African Orogeny. The Khao Pret granite gives U-Pb zircon concordia age of 67.5 ± 1.3 Ma, which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite-grade contact metamorphism against surrounding metapelites and gneisses. Metamorphic rocks in the Doi Inthanon area also share the similar plutono-metamorphic history with the Khanom and the Hub-Kapong to Pran Buri areas. This suggests that these three areas belong to the Sibumasu block, and the Sibumasu block records similar plutono-metamorphic history from Northern to Peninsular Thailand. Relative abundance of oceanic components in the Khao Chao gneiss, their Late Triassic magmatic ages, and the Early Jurassic metamorphic ages prefer the interpretation that the Khao Chao gneiss belongs to the Sukhothai Arc.

Radium and radium-daughter nuclides in carbonates: a brief overview of strategies for determining chronologies.

PubMed

Schmidt, Sabine; Cochran, J Kirk

2010-07-01

Radium isotopes have been used extensively to trace the movement of groundwater as well as oceanic water masses, but these radionuclides (and their daughters) are also useful chronometers for the determination of the time scales of other Earth and environmental processes. The purpose of this overview is to present the application of Ra and Ra daughters in the dating of carbonates. We show that the choice of dating method (decay of excess radionuclide or ingrowth of daughter) depends strongly on the parent/daughter activity ratios in the water in which the carbonate was precipitated. Thus freshly precipitated carbonates uniformly show excesses of 226Ra relative to its parent 230Th, and 226Ra decay can provide ages of carbonates over Holocene time scales. In contrast, carbonates are precipitated in waters of greatly varying 210Pb/226Ra. Corals, deep-sea hydrothermal vent clams and the shelled cephalopod Nautilus live in waters with significant dissolved 210Pb and all show excesses of 210Pb in their carbonate. Bivalve molluscs from nearshore and coastal waters, and carbonates deposited from groundwater environments (e.g. travertines) in which 210Pb is efficiently scavenged from solution, show deficiencies of 210Pb relative to 226Ra. In contrast, fish otoliths strongly discriminate against 210Pb regardless of the environment in which the fish lives. Deficiencies of 228Th relative to 228Ra are common in all carbonates. Useful time ranges for the 210Pb/226Ra and 228Th/228Ra chronometers are approximately 100 y and approximately 10 y, respectively. 2009 Elsevier Ltd. All rights reserved.

210Pb as a tool for establishing sediment chronologies: examples of potentials and limitations of conventional dating models.

PubMed

Kirchner, Gerald

2011-05-01

For aquatic sediments, the use of (210)Pb originating from the decay of atmospheric (222)Rn is a well-established methodology to estimate sediment ages and sedimentation rates. Traditionally, the measurement of (210)Pb in soils and sediments involved laborious and time-consuming radiochemical separation procedures. Due to the recent development of advanced planar ('n-type') semi-conductors with high efficiencies in the low-energy range which enable the gamma-spectrometric analysis of the 46.5 keV decay line of (210)Pb, sediment dating using this radionuclide has gained renewed interest. In this contribution, potentials and limitations of the (210)Pb methodology and of the models used for estimating sediment ages and sedimentation rates are discussed and illustrated by examples of freshwater and marine sediments. Comparison with the use of (137)Cs shows that the information which may be gained by these two tracers is complementary. As a consequence, both radionuclides should be used in combination for dating of recent sediments. It is shown that for various sedimentation regimes additional information from other sources (e.g. sediment lithology) may be needed to establish a reliable chronology. A strategy for sediment dating using (210)Pb is recommended. Copyright © 2010 Elsevier Ltd. All rights reserved.

210Pb sediment dating in coastal transition zones: tropical saltmarshes.

NASA Astrophysics Data System (ADS)

Ruiz-Fernandez, A. C.; Sanchez-Cabeza, J. A.; Carnero-Bravo, V.; Perez-Bernal, L. H.

2016-12-01

Sea level rise (SLR) is one of the climate change effects expected to have the largest impact on coastal environments. SLR rates are not uniform around the planet and, therefore, local and regional data and trends are needed for proper adaptation plans. As long term monitoring stations of SLR are very scarce in most of the world, SLR trends obtained from 210Pb-dated sediment cores from tropical saltmarshes have become a practical alternative to obtain SLR trends within the past century, under the assumption that these ecosystems accrete at a similar rate to SLR. However, tropical saltmarshes are challenging environments for 210Pb dating: they are regularly dry, intermittently covered by seawater only during the highest tides, and sedimentary records often reflect the transition between terrestrial and marine environments (e.g. changes in grain size distribution, organic matter content and elemental composition) with all these factors contributing for atypical 210Pb depth profiles. In addition, 137Cs, the chronostratigraphic marker most commonly used to corroborate 210Pb dating, fails to be preserved in the sedimentary record in tropical areas, owing to its solubility in marine waters, if at all detectable. The present study describes the challenges and proposed solutions for 210Pb dating saltmarsh sediment cores from two saltmarsh areas (southern Gulf of California and Yucatan Peninsula) including the use of plutonium isotopes for corroboration purposes. Acknowledgements: projects CONACYT CB2010/153492 and PDCPN201301/214349; UNAM PAPIIT-IN203313 and the PRODEP network "Aquatic contamination: levels and effects" (year 3).

Correlating rates of magmatic arc unroofing and sedimentation using detrital zircon U/Pb and (U-Th)/He thermochronology

NASA Astrophysics Data System (ADS)

Fosdick, J. C.

2017-12-01

Double and triple dating of minerals using multiple geo-thermochronometers has revolutionized efforts to evaluate complex thermotectonic histories of orogens, isolate unique sedimentary sources, and quantify basin burial reheating. A persisting challenge is to distinguish volcanic sources from rapidly exhumed sources, with the simplistic premise that coincident cooling dates among high- to low-temperature thermochronometers are diagnostic of volcanic sources. Coupled zircon U/Pb and (U-Th)/He geo-thermochronometry from the Miocene Bermejo foreland basin in the southern Central Andes reveals a high temporal resolution of unroofing signatures of the Choiyoi Group, a Permian-Triassic silicic volcanic and plutonic complex, and the Pennsylvanian-Permian Colangüil batholith. Both units are important sediment sources within the High Andes for the Cenozoic east-flowing sediment routing systems. Results show fluvial sourcing of Colangüil detrital zircons with progressively greater partial loss of He (<8% to 12-23% fractional loss from 9.5 Ma to 6 Ma), as indicated by upsection younging of zircon He dates for a given U/Pb age cluster. These findings suggest erosion of increasingly deeper levels of the Colangüil arc during late Miocene development of the High Andes. This progression of higher He loss and thus younger He dates during sedimentation for a given U/Pb age cluster is analogous to the magmatic arc unroofing trend revealed by undissected to dissected arc provenance fields in sandstone petrography. Multi-method thermochronometry of detrital minerals may reveal an added level of information regarding rates of cooling, unroofing, and thermal evolution of magmatic systems as preserved in the detrital record.

Problems with the dating of sediment core using excess (210)Pb in a freshwater system impacted by large scale watershed changes.

PubMed

Baskaran, Mark; Nix, Joe; Kuyper, Clark; Karunakara, N

2014-12-01

Pb-210 dating of freshwater and coastal sediments have been extensively conducted over the past 40 years for historical pollution reconstruction studies, sediment focusing, sediment accumulation and mixing rate determination. In areas where there is large scale disturbance of sediments and the watershed, the vertical profiles of excess (210)Pb ((210)Pbxs) could provide erroneous or less reliable information on sediment accumulation rates. We analyzed one sediment core from Hendrix Lake in southwestern Arkansas for excess (210)Pb and (137)Cs. There is no decrease in excess (210)Pb activity with depth while the (137)Cs profile indicates sharp peak corresponding to 1963 and the (137)Cs penetration depth of (137)Cs corresponds to 1952. The historical data on the accelerated mercury mining during 1931-1944 resulted in large-scale Hg input to this watershed. Using the peak Hg activity as a time marker, the obtained sediment accumulation rates agree well with the (137)Cs-based rates. Four independent evidences (two-marker events based on (137)Cs and two marker events based on Hg mining activity) result in about the same sedimentation rates and thus, we endorse earlier suggestion that (210)Pb profile always needs to be validated with at least one another independent method. We also present a concise discussion on what important factors that can affect the vertical profiles of (210)Pbxs in relatively smaller lakes. Copyright © 2014 Elsevier Ltd. All rights reserved.

Prospects for Practical Laser Ablation U/Pb and (U-Th)/He Double-Dating (LADD) of Detrital Apatite

NASA Astrophysics Data System (ADS)

Horne, A.; Hodges, K. V.; Van Soest, M. C.

2017-12-01

A laser ablation micro-analytical technique for (U-Th)/He dating has been shown to be an effective approach to the thermochronologic study of detrital zircons (Tripathy-Lang et al., J. Geophys. Res., 2013), while Evans et al. (J. Anal. At. Spectrom., 2015) and Horne et al. (Geochim. Cosmochim. Acta, 2016) demonstrated how the technique could be modified to enable laser ablation U/Pb and (U-Th)/He double-dating (LADD) of detrital zircon and titanite. These successes beg the question of whether or not LADD is viable for another commonly encountered detrital mineral: apatite. Exploratory LADD studies in Arizona State University's Group 18 Laboratories - using Durango fluorapatite, apatite from the Fish Canyon tuff, and detrital apatite from modern fluvial sediments in the eastern Sierra Nevada of California - illustrate that the method is indeed viable for detrital apatite. However, the method may not be appropriate for all detrital samples. For example, many apatite grains encountered in detrital samples from young orogenic settings have low concentrations of U and Th and small crystal sizes. This can lead to imprecise laser ablation (U-Th)/He dates, especially for very young grains potentially obscuring or inhibiting relevant interpretations of the data set.

Assessing Chronology and Mantle Evolution In-Situ with CODEX

NASA Astrophysics Data System (ADS)

Anderson, F. S.; Levine, J.; Whitaker, T.

2017-12-01

Understanding lunar bombardment history is crucial to understanding the dynamic evolution of the Moon. Using an instrument called CODEX (Chemistry, Organics, and Dating Experiment) intended for in-situ dating [1-5], we have obtained Pb-Pb dates for Martian meteorites Zagami and Northwest Africa (NWA) 7034, and lunar meteorites Miller Range 05035, LaPaz Icefield 02205, and NWA 032. In conjunction with our previous Rb-Sr success, these measurments demonstrate the potential for in-situ measurements of the Moon. Some of these Pb dates are consistent with young age estimates, however, many are consistent with previous anomalously old Pb measurements for lunar and SNC meteorites. Proposed explanations for this paradox include terrestrial Pb contamination, that the SNC's are actually ancient and reset in Rb/Sr, that there are multiple isotopic reservoirs sampled by the impact process, or that multiple reservoirs are sampled during the volcanic emplacement. In the future, we plan to use CODEX to test these hypotheses by making measurements on outcrops in-situ on Mars or the Moon, avoiding terrestrial or impact mixing. If in-situ Rb-Sr and Pb-Pb measurements are not concordant, then we are likely constraining the common Pb signature, and hence mantle evolution, of the Moon or Mars. Alternatively, we are likely obtaining a robust age estimate. References: [1] F. S. Anderson et al. LPSC 1246, 2 (2017); [2] F. S. Anderson et al. LPSC 2957, 2 (2017); [3] S. Beck et al., LPSC, 3001, 2 (2017); [4] T. J. Whitaker et al. LPSC 2328, 2 (2017); [5] F. S. Anderson et al. RCMS 29, 191 (2015);

Direct U-Pb dating of Cretaceous and Paleocene dinosaur bones, San Juan Basin, New Mexico: COMMENT

USGS Publications Warehouse

Koenig, Alan E.; Lucas, Spencer G.; Neymark, Leonid A.; Heckert, Andrew B.; Sullivan, Robert M.; Jasinski, Steven E.; Fowler, Denver W.

2012-01-01

Based on U-Pb dating of two dinosaur bones from the San Juan Basin of New Mexico (United States), Fassett et al. (2011) claim to provide the first successful direct dating of fossil bones and to establish the presence of Paleocene dinosaurs. Fassett et al. ignore previously published work that directly questions their stratigraphic interpretations (Lucas et al., 2009), and fail to provide sufficient descriptions of instrumental, geochronological, and statistical treatments of the data to allow evaluation of the potentially complex diagenetic and recrystallization history of bone. These shortcomings lead us to question the validity of the U-Pb dates published by Fassett et al. and their conclusions regarding the existence of Paleocene dinosaurs.

Dating of sediments from four Swiss prealpine lakes with (210)Pb determined by gamma-spectrometry: progress and problems.

PubMed

Putyrskaya, V; Klemt, E; Röllin, S; Astner, M; Sahli, H

2015-07-01

In this paper the most important problems in dating lake sediments with unsupported (210)Pb are summarized and the progress in gamma-spectrometry of the unsupported (210)Pb is discussed. The main topics of these studies concern sediment samples preparation for gamma-spectrometry, measurement techniques and data analysis, as well as understanding of accumulation and sedimentation processes in lakes. The vertical distributions of artificial ((137)Cs, (241)Am, (239)Pu) and natural radionuclides ((40)K, (210,214)Pb, (214)Bi) as well as stable trace elements (Fe, Mn, Pb) in sediment cores from four Swiss lakes were used as examples for the interpretation, inter-comparison and validation of depth-age relations established by three (210)Pb-based models (CF-CSR, CRS and SIT). The identification of turbidite layers and the influence of the turbidity flows on the accuracy of sediment dating is demonstrated. Time-dependent mass sedimentation rates in lakes Brienz, Thun, Biel and Lucerne are discussed and compared with published data. Copyright © 2015 Elsevier Ltd. All rights reserved.

Radiometric dates from Alaska: A 1975 compilation

USGS Publications Warehouse

Turner, D.L.; Grybeck, Donald; Wilson, Frederic H.

1975-01-01

The following table of radiometric dates from Alaska includes published material through 1972 as well as some selected later data. The table includes 726 mineral and whole-rock dates determined by the K-Ar, Rb-Sr, fission-track U-Pb, and Pb-alpha techniques.The data are organized in alphabetical order of the 1:250,000 scale quadrangles in which the dated rocks are located. The latitude and longitude of each sample are given. In addition, each sample is located on a 1:250,000 quadrangle map by a grid system. The initial point of the grid is taken as the southwest corner of the quadrangle and the location of the sample is measured in inches east and inches north from that corner, e.g., "156E 126N" indicated 15.6 inches east and 12.6 inches north of the southwest corner of the quadrangle. Zeroes in the location columns for some dates indicate that accurate locations are not available.Rock type, dating method, mineral dated, radiometric age, sample identification number, and reference are also listed where possible. Short comments, mostly geographic locality names, are given for some dates. These comments have been taken from the original references.Sample identification numbers beginning with "AA" or "BB" have been assigned arbitrarily in cases where sample numbers were not assigned in the original references. Abbreviations are explained in the appendix at the end of table 1.

Comparative use of TIMS and SHRIMP for U Pb zircon dating of A-type granites and mafic tholeiitic layered complexes and dykes from the Corsican Batholith (France)

NASA Astrophysics Data System (ADS)

Cocherie, A.; Rossi, Ph.; Fanning, C. M.; Guerrot, C.

2005-05-01

The Corsica-Sardinia batholith in the southern realm of the Hercynian belt of Europe shows evidence for gravitational collapse of this part of the mountain belt, causing major felsic and mafic magmatism. The latest intrusions are composed of leucomonzogranite and late metaluminous and alkaline granite, associated with tholeiitic layered complexes and dykes. Three dating methods on zircon (Pb-evaporation, ID-TIMS and SHRIMP) were used to unravel the chronology of these felsic and mafic rocks. Dating of zircons by the conventional U-Pb method, using TIMS after zircon dissolution, achieved an analytical uncertainty of 1 Ma for favourable cases. The TIMS Pb-evaporation technique resulted in ages with an uncertainty range of 4 to 8 Ma. After 15 to 20 analyses with the SHRIMP method, a precision ranging from 2 to 5 Ma was obtained (all at 2 σ). The three methods applied to the same zircon population extracted from four A-type granites, show that the uncertainty ranges within 2-5 Ma according to the sample. This error seems to correspond to the real geochronological uncertainty that can be achieved. The results obtained show that all six tested alkaline granites were emplaced during a very short interval of about 3-5 Ma at about 288 Ma, almost contemporaneous with the leucomonzogranite emplacement (291-287 Ma) that ended the batholith formation. In addition, there is no significant gap with the age of emplacement of the mafic tholeiitic magmatism (around 286 Ma) crosscutting the "A-type" granites. The late alkaline granites definitely do not show up here as precursors of the Tethyan rifting that began at about 170 Ma, i.e. some 100 Ma after their emplacement. It is thus necessary to examine if alternative hypotheses to the anorogenic model of the A-type Younger Granite province better fit the new geochronological data. A model involving depleted continental-crust derived magma should be compatible with the timing and geodynamical constraints as far as isotopic data are concerned.

High-precision Temporal Calibration of the Early Cambrian Biotic and Paleoenvironmental Records: New U-Pb Geochronology from Eastern Yunnan, China.

NASA Astrophysics Data System (ADS)

Tsukui, K.; Ramezani, J.; Zhu, M.; Maloof, A. C.; Porter, S.; Moore, J.; Eddy, M. P.; Bowring, S. A.

2016-12-01

The Terreneuvian Epoch of the early Cambrian marks the global diversification of early animal life, as well as major perturbations to Earth's geochemical cycles. Understanding possible links between biotic evolution (e.g., emergence of skeletal animals) and the recognized changes in ocean chemistry requires a high fidelity chronostratigraphic framework for the early Cambrian records. One such chronostratigraphy was built by mapping local early Cambrian carbon isotope profiles onto a U-Pb age-calibrated marine carbonate δ13C record from Morocco, assuming global synchroneity of the observed δ13C trends. Here we present a direct test of this assumption using high-precision U-Pb geochronology (CA-ID-TIMS method) of ash beds from key lower Cambrian horizons throughout eastern Yunnan Province in South China. Preliminary age results from ash beds near the top of the Dengying Formation (Fm.) and the basal Daibu Member (Mb.) of the Zhujiaqing Fm. in multiple sections place the basal Cambrian negative δ13C excursion (BACE) in China at ca. 540.7-539.6 Ma. Our new U-Pb dates from the overlying Zhongyicun Mb. at the Meishucun and nearby sections improve significantly upon previous in situ U-Pb geochronology and constrain the onset of high-frequency δ13C oscillations in some sections to between 533.5 and 532.9 Ma. Most importantly, a new U-Pb date of ca. 526 Ma from the basal Shiyantou Fm. in the Xiaotan Section marks the termination of a >1 million year-long period of consistently positive (≥+4‰) δ13C values (ZHUCE) that is characteristic of many early Cambrian records worldwide. This date establishes a robust time correlation between ZHUCE in South China and its equivalent 5p excursion in Morocco and Siberia, and constrains the timing and duration of the largest positive δ13C anomalies in the Cambrian.

Development of a petrochronology laboratory in Russia

NASA Astrophysics Data System (ADS)

Yavryan, M.; Powerman, V.; Nourgaliev, D. K.

2017-12-01

Each year more and more U-Pb detrital zircon studies are coming from Russia. However, the latest developments in zircon studies, namely combining U-Pb age with the measurements of REE concentrations and Lu-Hf isotopy on the same grain, have been unavailable in Russia. Kazan Federal U. has undertaken certain efforts in order to develop Russia's first petrochronology laboratory. The following equipment was recently purchased, installed and put into operation: Neptune Plus HR MC ICPMS, with jet-interface and RPQ filter. iCAP-Qc quadruple ICPMS. 2 x NWR213 laser ablation systems; one of them equipped with the TwoVol2 ablation chamber. Helium gas is used to flush the ablation chamber; 5 ml/min. of nitrogen is mixed downstream before plasma in order to increase the signal. The following methods have been set up at KFU on the Neptune Plus ICPMS: (1) U-Pb geochronology on zircons. A set of standards have been dated (R33, 91500, Plesovice, Mudtank, GJ-1, AS-3); (2) U-Pb geochronology on perovskites. We have collected, separated and analyzed Baikal Tazheran 463 Ma perovskite, previously dated on TIMS (e.g., Ireland et al., 1990; Li et al., 2010), using 91500 zircon as a primary standard. We intend to start using Tazheran perovskite as an in-house standard for dating perovskites. (3) Lu-Hf isotopy on a set of standard zircons. All results will be presented during the poster session. Our next steps will include setting the (a) U-Pb geochronology and (b) REE measurements on the quadruple MS; (c) splitting the ablation stream into two and directing them to Neptune for Lu-Hf measurements and to iCAP for either U-Pb, or REE, or both types of measurements; (d) experimenting with pre-ablation in order to diminish common lead, with (e) rastering during ablation to diminish downhole fractionation, with (f) squid signal smoothing device.

I-Xe Dating: Comparison of I-Xe and Pb-Pb Ages of Richardton Chondrules and Separated Mineral Phases

NASA Technical Reports Server (NTRS)

Pravdivtseva, O. V.; Amelin, Y.; Hohenberg, C. M.; Meshik, A. P.

2002-01-01

I-Xe and Pb-Pb ages of individual Richardton chondrules and different mineral phases were compared in order to test the absolute I-Xe age normalization. Additional information is contained in the original extended abstract.

Application of U-Pb ID-TIMS dating to the end-Triassic global crisis: testing the limits on precision and accuracy in a multidisciplinary whodunnit (Invited)

NASA Astrophysics Data System (ADS)

Schoene, B.; Schaltegger, U.; Guex, J.; Bartolini, A.

2010-12-01

The ca. 201.4 Ma Triassic-Jurassic boundary is characterized by one of the most devastating mass-extinctions in Earth history, subsequent biologic radiation, rapid carbon cycle disturbances and enormous flood basalt volcanism (Central Atlantic Magmatic Province - CAMP). Considerable uncertainty remains regarding the temporal and causal relationship between these events though this link is important for understanding global environmental change under extreme stresses. We present ID-TIMS U-Pb zircon geochronology on volcanic ash beds from two marine sections that span the Triassic-Jurassic boundary and from the CAMP in North America. To compare the timing of the extinction with the onset of the CAMP, we assess the precision and accuracy of ID-TIMS U-Pb zircon geochronology by exploring random and systematic uncertainties, reproducibility, open-system behavior, and pre-eruptive crystallization of zircon. We find that U-Pb ID-TIMS dates on single zircons can be internally and externally reproducible at 0.05% of the age, consistent with recent experiments coordinated through the EARTHTIME network. Increased precision combined with methods alleviating Pb-loss in zircon reveals that these ash beds contain zircon that crystallized between 10^5 and 10^6 years prior to eruption. Mineral dates older than eruption ages are prone to affect all geochronologic methods and therefore new tools exploring this form of “geologic uncertainty” will lead to better time constraints for ash bed deposition. In an effort to understand zircon dates within the framework of a magmatic system, we analyzed zircon trace elements by solution ICPMS for the same volume of zircon dated by ID-TIMS. In one example we argue that zircon trace element patterns as a function of time result from a mix of xeno-, ante-, and autocrystic zircons in the ash bed, and approximate eruption age with the youngest zircon date. In a contrasting example from a suite of Cretaceous andesites, zircon trace elements record crystallization in a differentiating magma over ~200 ka. This new tool can lead to more robust ages for the deposition of volcanic rocks and therefore aids in calibrating the stratigraphic record. Our new U-Pb geochronology shows that the end-Triassic extinction and a concomitant negative spike in organic carbon isotopes and sea level occurred in far less than 300 ka and that these events coincided within 150 ka to the onset of CAMP volcanism in North America. These data substantially tighten the correlation between extinction and the CAMP, though more high-precision age constraints from sections that record these events, coupled with ongoing bio-, chemo- and magnetostratigraphic efforts, are needed to substantiate and understand causality. The post extinction recovery in ammonite diversity occurred in 2.0±0.2 Ma, coinciding with the duration of the Hettangian stage. Recovery of numerous ash beds from within the Hettangian allow determination of the absolute rates of ammonite diversification at the sub-zone level, constraining the interaction between volcanism, animal evolution and global environment in the wake of catastrophe.

Bayesian integration of radioisotope dating (210Pb, 137Cs, 241Am, 14C) and an 18-20th century mining history of Brotherswater, English Lake District

NASA Astrophysics Data System (ADS)

Schillereff, Daniel; Chiverrell, Richard; Macdonald, Neil; Hooke, Janet; Welsh, Katharine; Piliposyan, Gayane; Appleby, Peter

2014-05-01

Lake sediment records are often a useful tool for investigating landscape evolution as geomorphic changes in the catchment are reflected by altered sediment properties in the material transported through the watershed and deposited at the lake bed. Recent research at Brotherswater, an upland waterbody in the Lake District, northwest England, has focused on reconstructing historical floods from their sedimentary signatures and calculating long-term sediment and carbon budgets from fourteen sediment cores extracted from across the basin. Developing accurate chronological control is essential for these tasks. One sediment core (BW11-2; 3.5 m length) from the central basin has been dated using artificial radionuclide measurements (210Pb, 137Cs, 241Am) for the uppermost sediments and radiocarbon (14C) for lower sediments. The core appears to span the past 1500 years, however a number of problems have arisen. We present our explanations for these errors, the independent chronological techniques used to generate an accurate age-depth model for this core and methods for its transferral to the other 13 cores extracted from the basin. Two distinct 137Cs markers, corresponding to the 1986 Chernobyl disaster and 1960s weapons testing, confirm the 210Pb profile for sediment deposition since ~1950, but calculations prior to this appear erroneous, possibly due to a hiatus in the sediment record. We used high-resolution geochemical profiles (measured by XRF) to cross-correlate with a second 210Pb-dated chronology from a more distal location, which returned more sensible results. Unfortunately, the longer 14C sequence exhibits two age-reversals (radiocarbon dates that are too old). We believe the uppermost two dates are erroneous, due to a shift in inflow location as a flood prevention method ~1900 A.D., dated using information from historical maps. The lower age-reversal coincides with greater supply of terrigenous material to the lake (increased Zr, K, Ti concentrations), pointing to a hillslope clearance event. A widespread concurrent hillslope gullying phase in northwest England triggering enhanced soil erosion is thus the most likely explanation, as the presence of old carbon is a known issue for lakes in the region at this time. Applying a Bayesian age-depth modelling protocol is able to account for these age-reversals with some success. However, the greatest uncertainty in the model occurs across the 1700 -1900 A.D. time window as the radiocarbon percentages offer multiple age solutions due to fluctuating atmospheric 14C concentrations from fossil fuel emissions. We address this issue by incorporating into the model geochemical markers in the sediment core related to local point-source Pb mining of known-age; the most-likely age-depth curve is subsequently much more definitively resolved. Usefully, these mining-derived chronological markers bridge the temporal gap between artificial radionuclide and conventional radiocarbon dating which is a common problem in palaeolimnology. These distinctive geochemical mining profiles (Pb, Zn, Cu) have been mapped across all cores, enabling precise core correlation and confident transferral of the age-depth model, and reveal highly spatially variable sediment accumulation rates. This has enabled more accurate sediment and carbon budgets to be calculated and some insight into palaeoflood frequency to be obtained from the Brotherswater sediment sequence.

Quantifying time in sedimentary successions by radio-isotopic dating of ash beds

NASA Astrophysics Data System (ADS)

Schaltegger, Urs

2014-05-01

Sedimentary rock sequences are an accurate record of geological, chemical and biological processes throughout the history of our planet. If we want to know more about the duration or the rates of some of these processes, we can apply methods of absolute age determination, i.e. of radio-isotopic dating. Data of highest precision and accuracy, and therefore of highest degree of confidence, are obtained by chemical abrasion, isotope-dilution, thermal ionization mass spectrometry (CA-ID-TIMS) 238U-206Pb dating techniques, applied to magmatic zircon from ash beds that are interbedded with the sediments. This techniques allows high-precision estimates of age at the 0.1% uncertainty for single analyses, and down to 0.03% uncertainty for groups of statistically equivalent 206Pb/238U dates. Such high precision is needed, since we would like the precision to be approximately equivalent or better than the (interpolated) duration of ammonoid zones in the Mesozoic (e.g., Ovtcharova et al. 2006), or to match short feedback rates of biological, climatic, or geochemical cycles after giant volcanic eruptions in large igneous provinces (LIP's), e.g., at the Permian/Triassic or the Triassic/Jurassic boundaries. We also wish to establish as precisely as possible temporal coincidence between the sedimentary record and short-lived volcanic events within the LIP's. Precision and accuracy of the U-Pb data has to be traceable and quantifiable in absolute terms, achieved by direct reference to the international kilogram, via an absolute calibration of the standard and isotopic tracer solutions. Only with a perfect control on precision and accuracy of radio-isotopic data, we can confidently determine whether two ages of geological events are really different, and avoid mistaking interlaboratory or interchronometer biases for age difference. The development of unprecedented precision of CA-ID-TIMS 238U-206Pb dates led to the recognition of protracted growth of zircon in a magmatic liquid (see, e.g., Schoene et al. 2012), which then becomes transferred into volcanic ashes as excess dispersion of 238U-206Pb dates (see, e.g., Guex et al. 2012). Zircon is crystallizing in the magmatic liquid shortly before the volcanic eruption; we therefore aim at finding the youngest zircon date or youngest statistically equivalent cluster of 238U-206Pb dates as an approximation of ash deposition (Wotzlaw et al. 2013). Time gaps between last zircon crystallization and eruption ("Δt") may be as large as 100-200 ka, at the limits of analytical precision. Understanding the magmatic crystallization history of zircon is the fundamental background for interpreting ash bed dates in a sedimentary succession. Ash beds of different stratigraphic position and age my be generated within different magmatic systems, showing different crystallization histories. A sufficient number of samples (N) is therefore of paramount importance, not to lose the stratigraphic age control in a given section, and to be able to discard samples with large Δt - but, how large has to be "N"? In order to use the youngest zircon or zircons as an approximation of the age of eruption and ash deposition, we need to be sure that we have quantitatively solved the problem of post-crystallization lead loss - but, how can we be sure?! Ash bed zircons are prone to partial loss of radiogenic lead, because the ashes have been flushed by volcanic gases, as well as brines during sediment compaction. We therefore need to analyze a sufficient number of zircons (n) to be sure not to miss the youngest - but, how large has to be "n"? Analysis of trace elements or oxygen, hafnium isotopic compositions in dated zircon may sometimes help to distinguish zircon that is in equilibrium with the last magmatic liquid, from those that are recycled from earlier crystallization episodes, or to recognize zircon with partial lead loss (Schoene et al. 2010). Respecting these constraints, we may arrive at accurate correlation of periods of global environmental and biotic disturbance (from ash bed analysis in biostratigraphically or cyclostratigraphically well constrained marine sections) with volcanic activity; examples are the Triassic-Jurassic boundary and the Central Atlantic Magmatic Province (Schoene et al. 2010), or the lower Toarcian oceanic anoxic event and the Karoo Province volcanism (Sell et al. in prep.). High-precision temporal correlations may also be obtained by combining high-precision U-Pb dating with biochronology in the Middle Triassic (Ovtcharova et al., in prep.), or by comparing U-Pb dates with astronomical timescales in the Upper Miocene (Wotzlaw et al., in prep.). References Guex, J., Schoene, B., Bartolini, A., Spangenberg, J., Schaltegger, U., O'Dogherty, L., et al. (2012). Geochronological constraints on post-extinction recovery of the ammonoids and carbon cycle perturbations during the Early Jurassic. Palaeogeography, Palaeoclimatology, Palaeoecology, 346-347(C), 1-11. Ovtcharova, M., Bucher, H., Schaltegger, U., Galfetti, T., Brayard, A., & Guex, J. (2006). New Early to Middle Triassic U-Pb ages from South China: Calibration with ammonoid biochronozones and implications for the timing of the Triassic biotic recovery. Earth and Planetary Science Letters, 243(3-4), 463-475. Ovtcharova, M., Goudemand, N., Galfetti, Th., Guodun, K., Hammer, O., Schaltegger, U., Bucher, H. Improving accuracy and precision of radio-isotopic and biochronological approaches in dating geological boundaries: The Early-Middle Triassic boundary case. In preparation. Schoene, B., Schaltegger, U., Brack, P., Latkoczy, C., Stracke, A., & Günther, D. (2012). Rates of magma differentiation and emplacement in a ballooning pluton recorded by U-Pb TIMS-TEA, Adamello batholith, Italy. Earth and Planetary Science Letters, 355-356, 162-173. Schoene, B., Latkoczy, C., Schaltegger, U., & Günther, D. (2010). A new method integrating high-precision U-Pb geochronology with zircon trace element analysis (U-Pb TIMS-TEA). Geochimica Et Cosmochimica Acta, 74(24), 7144-7159. Schoene, B., Guex, J., Bartolini, A., Schaltegger, U., & Blackburn, T. J. (2010). Correlating the end-Triassic mass extinction and flood basalt volcanism at the 100 ka level. Geology, 38(5), 387-390. Sell, B., Ovtcharova, M., Guex, J., Jourdan, F., Schaltegger, U. Evaluating the link between the Karoo LIP and climatic-biologic events of the Toarcian Stage with high-precision U-Pb geochronology. In preparation. Wotzlaw, J. F., Schaltegger, U., Frick, D. A., Dungan, M. A., Gerdes, A., & Günther, D. (2013). Tracking the evolution of large-volume silicic magma reservoirs from assembly to supereruption. Geology, 41(8), 867-870. Wotzlaw, J.F., Hüsing, S.K., Hilgen, F.J.., Schaltegger, U. Testing the gold standard of geochronology against astronomical time: High-precision U-Pb geochronology of orbitally tuned ash beds from the Mediterranean Miocene. In preparation.

Mercury contamination history of an estuarine floodplain reconstructed from a 210Pb-dated sediment core (Berg River, South Africa).

PubMed

Kading, T J; Mason, R P; Leaner, J J

2009-01-01

Mercury deposition histories have been scarcely documented in the southern hemisphere. A sediment core was collected from the ecologically important estuarine floodplain of the Berg River (South Africa). We establish the concentration of Hg in this (210)Pb-dated sediment core at <50 ng g(-1) Hg(T) throughout the core, but with 1.3 ng g(-1) methylmercury in surface sediments. The (210)Pb dating of the core provides a first record of mercury deposition to the site and reveals the onset of enhanced mercury deposition in 1970. The ratio of methylmercury to total mercury is relatively high in these sediments when compared to other wetlands.

Constraints on a Late Cretaceous uplift, denudation, and incision of the Grand Canyon region, southwestern Colorado Plateau, USA, from U-Pb dating of lacustrine limestone

NASA Astrophysics Data System (ADS)

Hill, Carol A.; Polyak, Victor J.; Asmerom, Yemane; P. Provencio, Paula

2016-04-01

The uplift and denudation of the Colorado Plateau is important in reconstructing the geomorphic and tectonic evolution of western North America. A Late Cretaceous (64 ± 2 Ma) U-Pb age for the Long Point limestone on the Coconino Plateau, which overlies a regional erosional surface developed on Permo-Triassic formations, supports unroofing of the Coconino Plateau part of Grand Canyon by that time. U-Pb analyses of three separate outcrops of this limestone gave ages of 64.0 ± 0.7, 60.5 ± 4.6, and 66.3 ± 3.9 Ma, which dates are older than a fossil-based, early Eocene age. Samples of the Long Point limestone were dated using the isotope dilution isochron method on well-preserved carbonates having high-uranium and low-lead concentrations. Our U-Pb ages on the Long Point limestone place important constraints on the (1) time of tectonic uplift of the southwestern Colorado Plateau and Kaibab arch, (2) time of denudation of the Coconino Plateau, and (3) Late Cretaceous models of paleocanyon incision west of, or across, the Kaibab arch. We propose that the age of the Long Point limestone, interbedded within the Music Mountain Formation in the Long Point area, represents a period of regional aggradation and a time of drainage blockage northward and eastward across the Kaibab arch, with possible diversion of northward drainage on the Coconino Plateau westward around the arch via a Laramide paleo-Grand Canyon.

Examining (239+240)Pu, (210)Pb and historical events to determine carbon, nitrogen and phosphorus burial in mangrove sediments of Moreton Bay, Australia.

PubMed

Sanders, Christian J; Santos, Isaac R; Maher, Damien T; Breithaupt, Joshua L; Smoak, Joseph M; Ketterer, Michael; Call, Mitchell; Sanders, Luciana; Eyre, Bradley D

2016-01-01

Two sediment cores were collected in a mangrove forest to construct geochronologies for the previous century using natural and anthropogenic radionuclide tracers. Both sediment cores were dated using (239+240)Pu global fallout signatures as well as (210)Pb, applying both the Constant Initial Concentration (CIC) and the Constant Rate of Supply (CRS) models. The (239+240)Pu and CIC model are interpreted as having comparable sediment accretion rates (SAR) below an apparent mixed region in the upper ∼5 to 10 cm. In contrast, the CRS dating method shows high sediment accretion rates in the uppermost intervals, which is substantially reduced over the lower intervals of the 100-year record. A local anthropogenic nutrient signal is reflected in the high total phosphorus (TP) concentration in younger sediments. The carbon/nitrogen molar ratios and δ(15)N values further support a local anthropogenic nutrient enrichment signal. The origin of these signals is likely the treated sewage discharge to Moreton Bay which began in the early 1970s. While the (239+240)Pu and CIC models can only produce rates averaged over the intervals of interest within the profile, the (210)Pb CRS model identifies elevated rates of sediment accretion, organic carbon (OC), nitrogen (N), and TP burial from 2000 to 2013. From 1920 to 2000, the three dating methods provide similar OC, N and TP burial rates, ∼150, 10 and 2 g m(-2) year(-1), respectively, which are comparable to global averages. Copyright © 2015 Elsevier Ltd. All rights reserved.

Natural radionuclide mobility and its influence on U-Th-Pb dating of secondary minerals from the unsaturated zone at Yucca Mountain, Nevada

USGS Publications Warehouse

Neymark, L.A.; Amelin, Y.V.

2008-01-01

Extreme U and Pb isotope variations produced by disequilibrium in decay chains of 238U and 232Th are found in calcite, opal/chalcedony, and Mn-oxides occurring as secondary mineral coatings in the unsaturated zone at Yucca Mountain, Nevada. These very slowly growing minerals (mm my-1) contain excess 206Pb and 208Pb formed from excesses of intermediate daughter isotopes and cannot be used as reliable 206Pb/238U geochronometers. The presence of excess intermediate daughter isotopes does not appreciably affect 207Pb/235U ages of U-enriched opal/chalcedony, which are interpreted as mineral formation ages. Opal and calcite from outer (younger) portions of coatings have 230Th/U ages from 94.6 ?? 3.7 to 361.3 ?? 9.8 ka and initial 234U/238U activity ratios (AR) from 4.351 ?? 0.070 to 7.02 ?? 0.12, which indicate 234U enrichment from percolating water. Present-day 234U/238U AR is ???1 in opal/chalcedony from older portions of the coatings. The 207Pb/235U ages of opal/chalcedony samples range from 0.1329 ?? 0.0080 to 9.10 ?? 0.21 Ma, increase with microstratigraphic depth, and define slow long-term average growth rates of about 1.2-2.0 mm my-1, in good agreement with previous results. Measured 234U/238U AR in Mn-oxides, which pre-date the oldest calcite and opal/chalcedony, range from 0.939 ?? 0.006 to 2.091 ?? 0.006 and are >1 in most samples. The range of 87Sr/86Sr ratios (0.71156-0.71280) in Mn-oxides overlaps that in the late calcite. These data indicate that Mn-oxides exchange U and Sr with percolating water and cannot be used as a reliable dating tool. In the U-poor calcite samples, measured 206Pb/207Pb ratios have a wide range, do not correlate with Ba concentration as would be expected if excess Ra was present, and reach a value of about 1400, the highest ever reported for natural Pb. Calcite intergrown with opal contains excesses of both 206Pb and 207Pb derived from Rn diffusion and from direct ??-recoil from U-rich opal. Calcite from coatings devoid of opal/chalcedony contains 206Pb and 208Pb excesses, but no appreciable 207Pb excesses. Observed Pb isotope anomalies in calcite are explained by Rn-produced excess Pb. The Rn emanation may strongly affect 206Pb-238U ages of slow-growing U-poor calcite, but should be negligible for dating fast-growing U-enriched speleothem calcite.

Provenance implications of Th U Pb electron microprobe ages from detrital monazite in the Carboniferous Upper Silesia Coal Basin, Poland

NASA Astrophysics Data System (ADS)

Kusiak, Monika Agnieszka; Kędzior, Artur; Paszkowski, Mariusz; Suzuki, Kazuhiro; González-Álvarez, Ignacio; Wajsprych, Bolesław; Doktor, Marek

2006-05-01

This paper reports the results of CHIME (chemical Th-U-Pb isochron method) dating of detrital monazites from Carboniferous sandstones in the Upper Silesia Coal Basin (USCB). A total of 4739 spots on 863 monazite grains were analyzed from samples of sandstone derived from six stratigraphic units in the sedimentary sequence. Age distributions were identified in detrital monazites from the USCB sequence and correlated with specific dated domains in potential source areas. Most monazites in all samples yielded ca. 300-320 Ma (Variscan) ages; however, eo-Variscan, Caledonian and Cadomian ages were also obtained. The predominant ages are comparable to reported ages of certain tectonostratigraphic domains in the polyorogenic Bohemian Massif (BM), which suggests that various crystalline lithologies in the BM were the dominant sources of USCB sediments.

Precise U-Pb Zircon Constraints on the Earliest Magmatic History of the Carolina Terrane.

PubMed

Wortman; Samson; Hibbard

2000-05-01

The early magmatic and tectonic history of the Carolina terrane and its possible affinities with other Neoproterozoic circum-Atlantic arc terranes have been poorly understood, in large part because of a lack of reliable geochronological data. Precise U-Pb zircon dates for the Virgilina sequence, the oldest exposed part, constrain the timing of the earliest known stage of magmatism in the terrane and of the Virgilina orogeny. A flow-banded rhyolite sampled from a metavolcanic sequence near Chapel Hill, North Carolina, yielded a U-Pb zircon date of 632.9 +2.6/-1.9 Ma. A granitic unit of the Chapel Hill pluton, which intrudes the metavolcanic sequence, yielded a nearly identical U-Pb zircon date of 633 +2/-1.5 Ma, interpreted as its crystallization age. A felsic gneiss and a dacitic tuff from the Hyco Formation yielded U-Pb zircon dates of 619.9 +4.5/-3 Ma and 615.7 +3.7/-1.9 Ma, respectively. Diorite and granite of the Flat River complex have indistinguishable U-Pb upper-intercept dates of 613.9 +1.6/-1.5 Ma and 613.4 +2.8/-2 Ma. The Osmond biotite-granite gneiss, which intruded the Hyco Formation before the Virgilina orogeny, crystallized at 612.4 +5.2/-1.7 Ma. Granite of the Roxboro pluton, an intrusion that postdated the Virgilina orogeny, yielded a U-Pb upper intercept date of 546.5 +3.0/-2.4 Ma, interpreted as the time of its crystallization. These new dates both provide the first reliable estimates of the age of the Virgilina sequence and document that the earliest known stage of magmatism in the Carolina terrane had begun by 633 +2/-1.5 Ma and continued at least until 612.4 +5.2/-1.7 Ma, an interval of approximately 25 m.yr. Timing of the Virgilina orogeny is bracketed between 612.4 +5.2/-1.7 Ma and 586+/-10 Ma (reported age of the upper Uwharrie Formation). The U-Pb systematics of all units studied in the Virgilina sequence are simple and lack any evidence of an older xenocrystic zircon component, which would indicate the presence of a continental-type basement. This observation, together with the juvenile Nd isotopic character of the Virgilina volcanic arc sequence, suggests that the oldest part of the Carolina terrane was built on oceanic crust away from a continental crustal influence.

Finding the "true" age: ways to read high-precision U-Pb zircon dates

NASA Astrophysics Data System (ADS)

Schaltegger, U.; Schoene, B.; Ovtcharova, M.; Sell, B. K.; Broderick, C. A.; Wotzlaw, J.

2011-12-01

Refined U-Pb dating techniques, applying an empirical chemical abrasion treatment prior to analysis [1], and using a precisely calibrated double isotope Pb, U EARTHTIME tracer solution, have led to an unprecedented <0.1% precision and accuracy of obtained 206Pb/238U dates of single zircon crystals or fragments. Results very often range over 10e4 to 10e6 years and cannot be treated as statistically singular age populations. The interpretation of precise zircon U-Pb ages is biased by two problems: (A) Post-crystallization Pb loss from decay damaged areas is considered to be mitigated by applying chemical abrasion techniques. The success of such treatment can, however, not be assumed a priori. The following examples demonstrate that youngest zircons are not biased by lead loss but represent close-to-youngest zircon growth: (i) coincidence of youngest zircon dates with co-magmatic titanite in tonalite; (ii) coincidence with statistically equivalent clusters of 206Pb/238U dates from zircon in residual melts of cogenetic mafic magmas; (iii) youngest zircons in ash beds of sedimentary sequences do not violate the stratigraphic superposition, whereas conventional statistical interpretation (mean or median values) does; (iv) results of published inter-laboratory cross-calibration tests using chemical abrasion on natural zircon crystals of the same sample arrive at the same 206Pb/238U result within <0.1% (e.g., [2]); (v) Youngest crystals coincide in age with the astronomical age of hosting cyclic sediments. Residual lead loss may, however, still be identified in the case of single, significantly younger dates (>3 sigma), and are common in many pre-Triassic and hydrothermally altered rocks. (B) Pre-eruptive/pre-intrusive growth is found to be the main reason for scattered zircon ages in igneous rocks. Zircons crystallizing from the final magma batch are called autocrystic [3]. Autocrystic growth will happen in a moving or stagnant magma shortly before or after the rheological lockup by the crystals. Last crystallizing zircons in the interstitial melt may therefore postdate emplacement of the magma. The range of 206Pb/238U ages may yield a time frame for the cooling of a given magma batch, which could be added to quantitative thermal models of magma emplacement and cooling. Hf isotopes and trace elements of the dated zircon are used to trace the nature of the dated grains [4], specifically for identification of crystals that form earlier at lower crustal levels (antecrysts). Autocrystic zircons typically show, e.g., distinctly different (higher or lower) Th/U ratios. Cautiously interpreted high-precision U-Pb data of chemically abraded zircons may resolve the evolution of a magmatic system from its roots to final emplacement or eruption, trace fractional crystallization of zircon and other accessory and major phases in a magma batch, and add quantitative temporal constraints to thermal models. The proposed interpretation scheme thus adds significant information compared to conventional statistics. [1] Mattinson J., 2005, Chem. Geol. 200, 47-66; ; [2] Slama et al., 2008, Chem. Geol. 249, 1-35; [3] Miller et al., 2007, J. Volc. Geotherm. Res. 167, 282-299; [4] Schoene et al., 2010, Geochim. Cosmochim. Acta 74, 7144-7159

Historical reconstruction of atmospheric lead pollution in central Yunnan province, southwest China: an analysis based on lacustrine sedimentary records.

PubMed

Liu, Enfeng; Zhang, Enlou; Li, Kai; Nath, Bibhash; Li, Yanling; Shen, Ji

2013-12-01

Atmospheric lead (Pb) pollution during the last century in central Yunnan province, one of the largest non-ferrous metal production centers in China, was reconstructed using sediment cores collected from Fuxian and Qingshui Lakes. Lead concentrations and isotopic ratios ((207)Pb/(206)Pb and (208)Pb/(206)Pb) were measured in sediment cores from both lakes. The operationally defined chemical fractions of Pb in sediment core from Fuxian Lake were determined by the optimized BCR procedure. The chronology of the cores was reconstructed using (210)Pb and (137)Cs dating methods. Similar three-phase variations in isotopic ratios and enrichment factors of Pb were observed in the sediment cores from both lakes. Before the 1950s, the sediment data showed low (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios and enrichment factors (EFs=~1), indicating that the sedimentary Pb was predominantly of lithogenic origin. However, these indices were increased gradually between the 1950s and the mid-1980s, implying an atmospheric Pb deposition. The EFs and isotopic ratios of Pb reached their peak during recent years, indicating aggravating atmospheric Pb pollution. The average anthropogenic Pb fluxes since the mid-1980s were estimated to be 0.032 and 0.053 g m(-2) year(-1) recorded in Fuxian and Qingshui cores, respectively. The anthropogenic Pb was primarily concentrated in the reducible fraction. Combining the results of Pb isotopic compositions and chemical speciations in the sediment cores and in potential sources, we deduced that recent aggravating atmospheric Pb pollution in central Yunnan province should primarily be attributed to regional emissions from non-ferrous metal production industries.

Lead contamination and source in Shanghai in the past century using dated sediment cores from urban park lakes.

PubMed

Li, H B; Yu, S; Li, G L; Deng, H

2012-08-01

Lead contamination becomes of importance to urban resident health worldwide, especially for child health and growth. Undisturbed lake sediment cores are increasingly employed as a useful tool to backdate environmental contamination history. Five intact sediment cores collected from lakes in five urban parks were dated using (210)Pb and analyzed for total Pb content and isotope ratio to reconstruct the Pb contamination history over the last century in Shanghai, China. Total Pb content in the sediment cores increased by about 2- to 3-fold since 1900s. The profile of Pb flux in each sediment core revealed a remarkable increase of Pb contamination in Shanghai over the past century, especially in the latest three decades when China was experiencing a rapid economic and industrial development. Significant correlations were found between Pb fluxes in sediment cores and Pb emission from coal combustion in Shanghai. Coal combustion emission dominated anthropogenic Pb sources during the past century contributing from 52% to 69% of total Pb in cores, estimated by a three-end member model of Pb isotope ratios. Leaded gasoline emission generally contributed <30% of total Pb, which was banned by 1997 in the Shanghai region. Our results implicate that coal combustion-based energy consumption should be replaced, or at least partially replaced, to reduce health risks of Pb contamination in Shanghai. Copyright © 2012 Elsevier Ltd. All rights reserved.

LA-ICP-MS Pb-U Dating of Young Zircons from the Kos-Nisyros Volcanic Centre, SE Aegean Arc (Greece)

NASA Astrophysics Data System (ADS)

Guillong, M.; Von Quadt, A.; Peytcheva, I.; Bachmann, O.

2014-12-01

Zircon Pb-U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos-Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay. Guillong, M. et al., 2014, JAAS, 29, p. 963-967; doi: 10.1039/c4ja00009a.

Sedimentation rates and erosion changes recorded in recent sediments of Lake Piaseczno, south-eastern Poland

NASA Astrophysics Data System (ADS)

Tylmann, Wojciech; Turczyński, Marek; Kinder, Małgorzata

2009-10-01

This paper presents the dating results and basic analyses of recent sediments from Lake Piaseczno. The age of sediments was determined using the 210Pb method and constant flux: constant sedimentation (CF: CS) model. The estimated timescale was in agreement with the AMS14C date from the base of the core. The mean sediment accumulation rate during the last 100 years was calculated as 0.025 g cm-2 a-1. Based on the radiocarbon date, the rate of sediment accumulation below the 210Pb dating horizon was estimated as 0.066 g cm-2 a-1. The variability of main physical properties and sediment components along the core was analysed as well. The sediments were characterised by a very high water content (>80%). Carbonates were either not present or at a very low level (<1%). However, organic and minerogenic matter variability represents an interesting record of increasing erosion intensity in the catchment area. Analysis of archival cartographic materials demonstrated that the most likely reason for the enhanced transport of minerogenic matter to the lake was deforestation caused by human activity in the beginning of the 20th century.

Exploring the U-Pb systematics of titanite from the Archean Stillwater Complex

NASA Astrophysics Data System (ADS)

Friedman, R. M.; Wall, C. J.; Scoates, J. S.; Weis, D. A.; Meurer, W. P.

2011-12-01

The Stillwater Complex is a large mafic-ultramafic layered intrusion in the Beartooth Mountains of Montana (USA) and host to the world-class J-M Reef platinum group element deposit. The size and geologic/economic importance of this igneous complex make it an important target for high-precision U-Pb dating. As a part of a comprehensive U-Pb study of the Stillwater Complex, we present ID-TIMS U-Pb titanite data, including new single grain results produced using the EARTHTIME ET535 spike, for very low-volume, relatively felsic granophyric and pegmatitic rocks associated with Stillwater layered rocks. Four samples studied include a pegmatitic ksp-qtz core to a gabbroic pegmatoid in the Lower Banded Series (N1), an alaskite (quartz diorite) and an amphibole-rich reaction zone between the alaskite and anorthosite (AN1) in the Middle Banded Series, and an amphibole-bearing granophyre from the Upper Banded Series (GN3). CA-TIMS U-Pb dating of zircon from these samples yielded concordant results only for the pegmatitic rock (weighted 207Pb/206Pb: 2709.65 ± 0.80 Ma, n = 5), which agrees with new zircon ages from Stillwater layered rocks. Results for high-U (up to 1438 ppm) metamict zircon that occurs in the other three rocks were highly discordant and did not yield precise ages. Titanite U-Pb results for the pegmatite are about -1% to +1% discordant with two groupings of 207Pb/206Pb dates: one with a weighted average of 2708.1 ± 2.0 Ma (n = 2), which overlaps in age with zircon from the same sample and the crystallization age of the Stillwater Complex, and a second, younger grouping of 2701.1 ± 1.3 Ma (n = 5). Younger dates record an early Pb-loss event, possibly related to intrusion of cross-cutting quartz monzonites. The alaskite data also shows two groupings of 207Pb/206Pb dates, although more subtle: a weighted average of 2709.3 ± 1.8 Ma (n = 3) and a single result of 2706.5 ± 1.7 Ma. Titanite from the other two samples has undergone significant Pb-loss. Results for four analyses from the reaction zone sample are 1.74-54.3% discordant and lie in a quasi-linear array with intercepts at ca. 2700 Ma and 325 Ma. Data for the granophyre in the Upper Banded Series also have a wide range of discordance (1.5-3.4%, 21.4% and 61.3%). Titanites from these samples appear to have undergone a two stage Pb-loss history: an early, relatively minor event as suggested for the pegmatite, and a subsequent episode, which for some grains resulted in significant discordance. Concordant U-Pb titanite data from two of the Stillwater Complex granophyres confirms nearly synchronous crystallization with that of the layered rocks in the intrusion. For the pegmatite, the ages and overlap of zircon and titanite suggest a direct relationship between the granophyres and the layered rock and relatively rapid cooling of the complex through titanite closure temperature. Titanite from the alaskite yields useful age information, whereas coexisting zircon are highly discordant and not age diagnostic.

Determination of heavy metals in the fruit of date palm growing at different locations of Riyadh.

PubMed

Aldjain, Ibrahim M; Al-Whaibi, Mohamed H; Al-Showiman, Salim S; Siddiqui, Manzer H

2011-04-01

Exposure of heavy metals to human beings has risen dramatically in the last 50 years. In today's urban and industrial society, there is no escaping from exposure to toxic chemicals and heavy metals. Humans are more likely to be exposed to heavy metal contamination from the dust that adheres to edible plants than from bioaccumulation. This is because it is very difficult to wash off all the dust particles from the plant material before ingesting them. The objectives of this experiment were to determine the concentrations of lead (Pb) and cadmium (Cd) in washing residues and in the tissues of fruits of date palm growing in 14 sites of Riyadh and also to assess whether the fruits were safe for human consumption. The washing residues and tissue of date palm fruits collected from different sites showed the presence of significant amounts of the Pb and Cd. The concentration of Pb in the dust and fruit tissue increased with increasing anthropogenic sources. Therefore, fruits of date palm might be used as a pollution indicator; it might be recommend that fruits of date palm could be safe for human consumption after washing. The mean concentration of Pb and Cd in all the samples collected from different sites is within the safe limits recommended by FAO/WHO.

Comparing pre- and post-chemical abrasion ages for Miocene Peach Springs Tuff zircon from ID-TIMS and SIMS analyses

NASA Astrophysics Data System (ADS)

Lidzbarski, M. I.; Mundil, R.; Miller, J. S.; Vazquez, J. A.

2012-12-01

The Miocene Peach Spring Tuff (PST) is a voluminous (>600 km3), zoned ignimbrite (trachyte to high-SiO2 rhyolite) that is exposed widely in eastern California, western Arizona, and southernmost Nevada, which was erupted from the Silver Creek caldera in the southwestern Black Mountains, AZ. PST serves as a regionally widespread marker unit and its eruption age has been determined to 18.8 to 18.9 Ma by 40Ar/39Ar methods, when corrected for systematic bias and normalized to the U-Pb system (Renne et al., 2010,). We performed ion-microprobe (SIMS) U-Pb dating of zircon from individual pumice clasts from PST to evaluate the growth history of zircon in the PST magma system. Sectioned, polished zircon from conventional epoxy mounts allows dating of internal growth domains (e.g. cores, interiors, and near-rim), whereas mounting unpolished zircon in indium and analyzing unpolished crystal faces provides a means to selectively sample the final increments of crystal growth (Reid and Coath, 2000). Combining U-Pb ages of unpolished zircon rims with near-rim interior analyses on sectioned grains yields a mean age of ca. 18.3 Ma, whereas ages of cores of sectioned crystals yield a mean of ca. 18.9 Ma. Several zircons have rim and/or core ages that are several hundred thousand years older or younger than these means (up to 1 m.y. total spread), although the uncertainties for individual SIMS ages are 2 to 5% (2 sigma uncertainty). Therefore, the distribution of ages is challenging to resolve. A modest number of the older grains are plausibly recycled antecrysts, but we suspect that the youngest zircons may have experienced Pb-loss. Failure to account for the possibility of inheritance and Pb-loss may lead to erroneous interpretations about crystallization in the PST system. In order to evaluate and mitigate the effects of Pb-loss, we employed the chemical abrasion (CA) technique of Mattinson (2005), which effectively eliminates domains in zircon that have suffered Pb-loss, and removes micro-inclusions that typically contain common Pb. Thermal annealing followed by CA techniques were used for ID-TIMS dating of a sub-set of zircon crystals previously analyzed by SIMS. Prior to TIMS analyses, zircon crystals were imaged by scanning electron microscopy (SEM) to evaluate the effects of CA on crystal domains sampled by SIMS. SEM images reveal that whole portions of crystals were removed by the CA technique, and a heterogeneous pattern of etching that was not confined to specific compositional zones visible in cathodoluminescence. Most of the SIMS sputter pits that yield spurious ages, are associated with etching and/or preferential annealing by the combined annealing and CA technique, suggesting that the young ages relative to the 40Ar/39Ar age may be due to Pb loss. ID-TIMS yields a coherent U-Pb age population of 18.8 Ma, with several older and younger crystals that might reflect xenocrysts, Pb-loss, and/or younger crystallization. In order to maintain spatial resolution and further evaluate the effects of Pb-loss in PST zircon, the annealing and CA-technique will be applied to zircon prior to SIMS dating. References: Reid and Coath, 2000, Geology 28: 443 Renne et al., 2010, GCA 78: 5349

Effective LA-ICP-MS dating of common-Pb bearing accessory minerals with new data reduction schemes in Iolite

NASA Astrophysics Data System (ADS)

Kamber, Balz S.; Chew, David M.; Petrus, Joseph A.

2014-05-01

Compared to non-destructive geochemical analyses, LA-ICP-MS consumes ca. 0.1 μm of material per ablation pulse. It is therefore to be expected that the combined analyses of ca. 200 pulses will encounter geochemical and isotopic complexities in all but the most perfect minerals. Experienced LA-ICP-MS analysts spot down-hole complexities and choose signal integration areas accordingly. In U-Pb geochronology, the task of signal integration choice is complex as the analyst wants to avoid areas of common Pb and Pb-loss and separate true (concordant) age complexity. Petrus and Kamber (2012) developed VizualAge as a tool for reducing and visualising, in real time, U-Pb geochronology data obtained by LA-ICP-MS as an add-on for the freely available U-Pb geochronology data reduction scheme of Paton et al. (2010) in Iolite. The most important feature of VizualAge is its ability to display a live concordia diagram, allowing users to inspect the data of a signal on a concordia diagram as the integration area it is being adjusted, thus providing immediate visual feedback regarding discordance, uncertainty, and common lead for different regions of the signal. It can also be used to construct histograms and probability distributions, standard and Tera-Wasserburg style concordia diagrams, as well as 3D U-Th-Pb and total U-Pb concordia diagrams. More recently, Chew et al. (2014) presented a new data reduction scheme (VizualAge_UcomPbine) with much improved common Pb correction functionality. Common Pb is a problem for many U-bearing accessory minerals and an under-appreciated difficulty is the potential presence of (possibly unevenly distributed) common Pb in calibration standards, introducing systematic inaccuracy into entire datasets. One key feature of the new method is that it can correct for variable amounts of common Pb in any U-Pb accessory mineral standard as long as the standard is concordant in the U/Pb (and Th/Pb) systems after common Pb correction. Common Pb correction can be undertaken using either the 204Pb, 207Pb or 208Pb(no Th) methods. After common Pb correction to the user-selected age standard integrations, the scheme fits session-wide model U-Pb fractionation curves to the time-resolved U-Pb standard data. This down hole fractionation model is next applied to the unknowns and sample-standard bracketing (using a user specified interpolation method) is used to calculate final isotopic ratios and ages. 204Pb- and 208Pb(no Th)-corrected concordia diagrams and 204Pb-, 207Pb- and 208Pb(no Th)-corrected age channels can be calculated for user-specified initial Pb ratio(s). All other conventional common Pb correction methods (e.g. intercept or isochron methods on co-genetic analyses) can be performed offline. Apatite, titanite, rutile and very young zircon data will be presented, obtained using a Thermo Scientific iCAP-Qc (Q-ICP-MS) coupled to a Photon Machines Analyte Excite 193 nm ArF Excimer laser with a novel signal smoothing device Chew, D.M., Petrus, J.A., and Kamber, B.S. (2014); Chemical Geology, 363, 185-199. Paton C., Woodhead J.D., Hellstrom J.C., Hergt J.M., Greig A. and Maas R. (2010); Geochemistry Geophysics Geosystems, 11, 1-36. Petrus, J.A. and Kamber, B.S. (2012): Geostandards and Geoanalytical Research, 36, 247-270.

Titanite chronology, thermometry, and speedometry of ultrahigh-temperature (UHT) calc-silicates from south Madagascar: U-Pb dates, Zr temperatures, and lengthscales of trace-element diffusion

NASA Astrophysics Data System (ADS)

Holder, R. M.; Hacker, B. R.

2017-12-01

Calc-silicate rocks are often overlooked as sources of pressure-temperature-time data in granulite-UHT metamorphic terranes due to the strong dependence of calc-silicate mineral assemblages on complex fluid compositions and a lack of thermodynamic data on common high-temperature calc-silicate minerals such as scapolite. In the Ediacaran-Cambrian UHT rocks of southern Madagascar, clinopyroxene-scapolite-feldspar-quartz-zircon-titanite calc-silicate rocks are wide-spread. U-Pb dates of 540-520 Ma from unaltered portions of titanite correspond to cooling of the rocks through upper-amphibolite facies and indicate UHT metamorphism occurred before 540 Ma. Zr concentrations in these domains preserve growth temperatures of 900-950 °C, consistent with peak temperatures calculated by pseudosection modeling of nearby osumilite-bearing gneisses. Younger U-Pb dates (510-490 Ma) correspond to fluid-mediated Pb loss from titanite grains, which occurred below their diffusive Pb-closure temperature, along fractures. The extent of fluid alteration is seen clearly in back-scattered electron images and Zr-, Al-, Fe-, Ce-, and Nb-concentration maps. Laser-ablation depth profiling of idioblastic titanite grains shows preserved Pb diffusion profiles at grain rims, but there is no evidence for Zr diffusion, indicating that it was effectively immobile even at UHT.

Onset of industrial pollution recorded in Mumbai mudflat sediments, using integrated magnetic, chemical, 210Pb dating, and microscopic methods.

PubMed

Blaha, U; Basavaiah, N; Deenadayalan, K; Borole, D V; Mohite, R D

2011-01-15

The onset and rise of urban and industrial pollution in the Mumbai region was reconstructed from an anthropogenically contaminated mudflat sediment profile from the adjacent Thane creek using magnetic parameters, polycyclic aromatic hydrocarbon (PAH) data, metal contents, and the (210)Pb dating technique. The 1.8 m vertical section at Airoli (Navi Mumbai) reveals an increase of magnetic susceptibility (χ) from background values of (20-50) to (75-100) × 10(-8) [m(3) kg(-1)] in the anthropogenically affected zone above ∼93 cm. A sharp rise of χ from (75-100) to (130-215) × 10(-8) [m(3) kg(-1)] subdivides the anthropogenically affected zone at a depth of ∼63 cm. Characterization with rock magnetic parameters (SIRM, Soft IRM, and S-ratio) reveals a significant contribution of ferri(o)magnetic phases in the upper zone. Based on the magnetic classification sampling intervals for cost-intensive PAH and metal analyses were determined. Steadily increasing contents of PAH and metals of anthropogenic origin are observed above the boundary depth at ∼93 cm. A sediment accumulation rate of 1.2 ± 0.3 cm/yr provided by (210)Pb dating dates the ∼63 cm boundary to 1951. Increasing industrial activity, including the establishment of a coal-fired power plant in 1956, and refineries between 1955 and 1960, correlates well with the substantial increase of χ, PAH, and metal contents. Scanning electron microscopy (SEM) investigation on magnetic extracts from the contaminated zone reveals the presence of magnetic spherules derived from industrial high-temperature processes.

Fission track dating of kimberlitic zircons

NASA Astrophysics Data System (ADS)

Haggerty, Stephen E.; Raber, Ellen; Naeser, Charles W.

1983-04-01

The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206Pb and 238U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ± 6.5 m.y.), Orapa (87.4 ± 5.7 and 92.4 ± 6.1 m.y.), Nzega (51.1 ± 3.8 m.y.), Koffiefontein (90.0 ± 8.2 m.y.), and Val do Queve (133.4 ± 11.5 m.y.). In addition we report the first radiometric ages (707.9 ± 59.6 and 705.5 ± 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption.

Fission track dating of kimberlitic zircons

USGS Publications Warehouse

Haggerty, S.E.; Raber, E.; Naeser, C.W.

1983-01-01

The only reliable method for dating kimberlites at present is the lengthy and specialized hydrothermal procedure that extracts 206Pb and 238U from low-uranium zircons. This paper describes a second successful method by fission track dating of large single-crystal zircons, 1.0-1.5 cm in dimension. The use of large crystals overcomes the limitations imposed in conventional fission track analysis which utilizes crushed fragments. Low track densities, optical track dispersion, and the random orientation of polished surfaces in the etch and irradiation cycle are effectively overcome. Fission track ages of zircons from five African kimberlites are reported, from the Kimberley Pool (90.3 ?? 6.5 m.y.), Orapa (87.4 ?? 5.7 and 92.4 ?? 6.1 m.y.), Nzega (51.1 ?? 3.8 m.y.), Koffiefontein (90.0 ?? 8.2 m.y.), and Val do Queve (133.4 ?? 11.5 m.y.). In addition we report the first radiometric ages (707.9 ?? 59.6 and 705.5 ?? 61.0 m.y.) of crustal zircons from kimberlites in northwest Liberia. The fission track ages agree well with earlier age estimates. Most of the zircons examined in this study are zoned with respect to uranium but linear correlations are established (by regression analysis) between zones of variable uranium content, and within zones of constant uranium content (by analysis of variance). Concordance between the fission track method and the U/Pb technique is established and we concluded that track fading from thermal annealing has not taken place. Kimberlitic zircons dated in this study, therefore, record the time of eruption. ?? 1983.

Thermal and exhumation history of the central Tianshan (NW China): Constraints by U-Pb geochronology and Ar-Ar and (U-Th)/He thermochronology

NASA Astrophysics Data System (ADS)

Yin, J.; Chen, W.; Hodges, K. V.; Xiao, W.; Van Soest, M. C.; Cai, K.; Zhang, B.; Mercer, C. M.; Yuan, C.

2015-12-01

Geochronology and thermochronology using multiple mineral-isotopic chronometers reveals the thermo-tectonic history of the central Tianshan (NW China) from emplacement to exhumation. Granites from the central Tianshan, which are associated with the southward subduction of the northern Tianshan Ocean, have been dated at 362-354 Ma using the LA-ICP-MS Zircon U-Pb method. A younger diorite sample (282 ± 1 Ma, Zircon U-Pb method by LA-ICP-MS) from northern Tianshan formed during the final closure of the Northern Tianshan Ocean when the Junggar Block collided with the Yili-Central Tianshan Block. 40Ar/39Ar step-wise heating plateau dates (biotite Ar/Ar: 312-293 Ma; Plagioclase Ar/Ar: 270-229 Ma) from the Central Tianshan show rapid post-magmatic cooling during the Late Carboniferous-Early Permian followed by a more modest rate of cooling from the middle Permian to the middle Jurassic. The northern Tianshan diorite (biotite Ar/Ar: 240 ± 1 Ma) also reveals a middle Jurassic cooling. Apatite (U-Th )/He dates from the central Tianshan samples range from ca. 130 Ma to ca. 116 Ma. The Apatite (U-Th )/He date for the northern Tianshan sample is ca. 27 Ma. Previous studies also reported Apatite (U-Th)/He ages of ca. 44 Ma-11 Ma in the Baluntai area of the southern Central Tianshan[1]. Two episodes of cooling are distinguished by thermal history modelling: (1) Mesozoic cooling occurred as the result of the exhumation and tectonic reactivation of the central Tianshan; and (2) The Tianshan orogenic belt has been rapidly exhumed since the Middle Cenozoic. References [1] Lü, H.H., Chang, Y., Wang, W., Zhou, Z.Y., 2013. Rapid exhumation of the Tianshan Mountains since the early Miocene: Evidence from combined apatite fission track and (U-Th)/He thermochronology. Science China: Earth Sciences, 43(12): 1964-1974 (in Chinese).

U Pb ages of angrites

NASA Astrophysics Data System (ADS)

Amelin, Yuri

2008-01-01

Precise U-Pb ages, determined with double spike ( 202Pb- 205Pb) thermal ionization m1ass spectrometry, are reported for angrites Angra dos Reis (AdoR), Lewis Cliff 86010 (LEW), and D'Orbigny. Nineteen of 23 acid-washed pyroxene fractions from these meteorites and whole rock fractions from D'Orbigny contain between 0.5 and 1.3 pg of total common Pb, indistinguishable from analytical blank. Measured 206Pb/ 204Pb ratios in these fractions are between 6300 and 14,100 for AdoR, 1160-4500 for LEW, and 608-8500 for D'Orbigny. Blank-corrected 206Pb/ 204Pb ratios for all three meteorites vary from 2160 to over 100,000. These fractions yielded precise and reproducible 207Pb ∗/ 206Pb ∗ dates with the average values of 4557.65 ± 0.13 Ma for AdoR, 4558.55 ± 0.15 Ma for LEW, and 4564.42 ± 0.12 Ma for D'Orbigny. Pb-Pb isochrons including data with slightly elevated common Pb, and U-Pb upper concordia intercepts, yield similar dates. The implications of these new Pb-isotopic ages of angrites are threefold. First, they demonstrate that AdoR and LEW are not coeval, and the group of "slowly cooled" angrites is therefore genetically diverse. Second, the new age of LEW suggests an upward revision of 53Mn- 53Cr "absolute" ages by 0.7 Ma. Third, a precise age of D'Orbigny allows consistent linking of the 53Mn- 53Cr and 26Al- 26Mg extinct nuclide chronometers to the absolute lime scale.

Radiogenic Isotopes As Paleoceanographic Tracers in Deep-Sea Corals: Advances in TIMS Measurements of Pb Isotopes and Application to Southern Ocean Corals

NASA Astrophysics Data System (ADS)

Wilson, D. J.; van de Flierdt, T.; Bridgestock, L. J.; Paul, M.; Rehkamper, M.; Robinson, L. F.; Adkins, J. F.

2014-12-01

Deep-sea corals have emerged as a valuable archive of deep ocean paleoceanographic change, with uranium-series dating providing absolute ages and the potential for centennial resolution. In combination with measurements of radiocarbon, neodymium isotopes and clumped isotopes, this archive has recently been exploited to reconstruct changes in ventilation, water mass sourcing and temperature in relation to millennial climate change. Lead (Pb) isotopes in both corals and seawater have also been used to track anthropogenic inputs through space and time and to trace transport pathways within the oceans. Better understanding of the oceanic Pb cycle is emerging from the GEOTRACES programme. However, while Pb isotopes have been widely used in environmental studies, their full potential as a (pre-anthropogenic) paleoceanographic tracer remains to be exploited. In deep-sea corals, challenges exist from low Pb concentrations in aragonite in comparison to secondary coatings, the potential for contamination, and the efficient elemental separation required for measurement by thermal ionisation mass spectrometry (TIMS). Here we discuss progress in measuring Pb isotopes in coral aragonite using a 207Pb-204Pb double spike on a ThermoFinnigan Triton TIMS. For a 2 ng NIST-981 Pb standard, the long term reproducibility (using 1011 Ω resistors) is ~1000 ppm (2 s.d.) on 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios. We now show that using a new 1012 Ω resistor to measure the small 204Pb beam improves the internal precision on these ratios from ~500 ppm (2 s.e.) to ~250 ppm (2 s.e.) and we envisage a potential improvement in the long term reproducibility as a consequence. We further assess the internal precision and external reproducibility of our method using a BCR-2 rock standard and an in-house coral standard. Preliminary evidence on the application of this method to natural samples is derived from cleaning experiments and replication tests on deep-sea corals from the Southern Ocean.

Air abrasion experiments in U-Pb dating of zircon

USGS Publications Warehouse

Goldich, S.S.; Fischer, L.B.

1986-01-01

Air abrasion of zircon grains can remove metamict material that has lost radiogenic Pb and zircon overgrowths that were added during younger events and thereby improve the precision of the age measurements and permit closer estimates of the original age. Age discordance that resulted from a single disturbance of the U-Pb isotopic decay systems, as had been demonstrated by T.E. Krogh, can be considerably reduced, and, under favorable conditions, the ages brought into concordancy. Two or more events complicate the U-Pb systematics, but a series of abrasion experiments can be helpful in deciphering the geologic history and in arriving at a useful interpretation of the probable times of origin and disturbances. In east-central Minnesota, U.S.A., Penokean tonalite gneiss is dated at 1869 ?? 5 Ma, and sheared granite gneiss is shown to have been a high-level granite intrusion at 1982 ?? 5 Ma in the McGrath Gneiss precursor. Tonalite gneiss and a mafic granodiorite in the Rainy Lake area, Ontario, Canada, are dated at 2736 ?? 16 and 2682 ?? 4 Ma, respectively. The tonalitic phase of the Morton Gneiss, southwestern Minnesota, is dated at 3662 ?? 42 Ma. ?? 1986.

3.1 Ga crystallization age for magnesian and ferroan gabbro lithologies in the Northwest Africa 773 clan of lunar meteorites

NASA Astrophysics Data System (ADS)

Shaulis, B. J.; Righter, M.; Lapen, T. J.; Jolliff, B. L.; Irving, A. J.

2017-09-01

The Northwest Africa (NWA) 773 clan of meteorites is a group of paired and/or petrogenetically related stones that contain at least six different lithologies: magnesian gabbro, ferroan gabbro, anorthositic gabbro, olivine phyric basalt, regolith breccia, and polymict breccia. Uranium-lead dates of baddeleyite in the magnesian gabbro, ferroan gabbro, and components within breccia lithologies of paired lunar meteorites NWA 773, NWA 3170, NWA 6950, and NWA 7007 indicate a chronologic link among the meteorites and their components. A total of 50 baddeleyite grains were analyzed and yielded weighted average 207Pb-206Pb dates of 3119.4 ± 9.4 (n = 27), 3108 ± 20 (n = 13), and 3113 ± 15 (n = 10) Ma for the magnesian gabbro, ferroan gabbro, and polymict breccia lithologies, respectively. A weighted average date of 3115.6 ± 6.8 Ma (n = 47/50) was calculated from the baddeleyite dates for all lithologies. A single large zircon grain found in a lithic clast in the polymict breccia of NWA 773 yielded a U-Pb concordia date of 3953 ± 18 Ma, indicating a much more ancient source for some of the components within the breccia. A U-Pb concordia date of apatite and merrillite grains from the magnesian gabbro and polymict breccia lithologies in NWA 773 is 3112 ± 33 Ma, identical to the baddeleyite dates. Magnesian and ferroan gabbros, as well as the dated baddeleyite and Ca-phosphate-bearing detritus in the breccia lithologies, formed during the same igneous event at about 3115 Ma. These data also strengthen proposed petrogenetic connections between magnesian and ferroan gabbro lithologies, which represent some of the youngest igneous rocks known from the Moon.

Determination of heavy metals in the fruit of date palm growing at different locations of Riyadh

PubMed Central

Aldjain, Ibrahim M.; Al-Whaibi, Mohamed H.; Al-Showiman, Salim S.; Siddiqui, Manzer H.

2010-01-01

Exposure of heavy metals to human beings has risen dramatically in the last 50 years. In today’s urban and industrial society, there is no escaping from exposure to toxic chemicals and heavy metals. Humans are more likely to be exposed to heavy metal contamination from the dust that adheres to edible plants than from bioaccumulation. This is because it is very difficult to wash off all the dust particles from the plant material before ingesting them. The objectives of this experiment were to determine the concentrations of lead (Pb) and cadmium (Cd) in washing residues and in the tissues of fruits of date palm growing in 14 sites of Riyadh and also to assess whether the fruits were safe for human consumption. The washing residues and tissue of date palm fruits collected from different sites showed the presence of significant amounts of the Pb and Cd. The concentration of Pb in the dust and fruit tissue increased with increasing anthropogenic sources. Therefore, fruits of date palm might be used as a pollution indicator; it might be recommend that fruits of date palm could be safe for human consumption after washing. The mean concentration of Pb and Cd in all the samples collected from different sites is within the safe limits recommended by FAO/WHO. PMID:23961121

Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14C "bomb pulse curve"

NASA Astrophysics Data System (ADS)

Shotyk, W.; Goodsite, M. E.; Roos-Barraclough, F.; Frei, R.; Heinemeier, J.; Asmund, G.; Lohse, C.; Hansen, T. S.

2003-11-01

Mercury concentrations are clearly elevated in the surface and sub-surface layers of peat cores collected from a minerotrophic ("groundwater-fed") fen in southern Greenland (GL) and an ombrotrophic ("rainwater-fed") bog in Denmark (DK). Using 14C to precisely date samples since ca. AD 1950 using the "atmospheric bomb pulse," the chronology of Hg accumulation in GL is remarkably similar to the bog in DK where Hg was supplied only by atmospheric deposition: this suggests not only that Hg has been supplied to the surface layers of the minerotrophic core (GL) primarily by atmospheric inputs, but also that the peat cores have preserved a consistent record of the changing rates of atmospheric Hg accumulation. The lowest Hg fluxes in the GL core (0.3 to 0.5 μg/m 2/yr) were found in peats dating from AD 550 to AD 975, compared to the maximum of 164 μg/m 2/yr in AD 1953. Atmospheric Hg accumulation rates have since declined, with the value for 1995 (14 μg/m 2/yr) comparable to the value for 1995 obtained by published studies of atmospheric transport modelling (12 μg/m 2/yr). The greatest rates of atmospheric Hg accumulation in the DK core are also found in the sample dating from AD 1953 and are comparable in magnitude (184 μg/m 2/yr) to the GL core; again, the fluxes have since gone into strong decline. The accumulation rates recorded by the peat core for AD 1994 (14 μg/m 2/yr) are also comparable to the value for 1995 obtained by atmospheric transport modelling (18 μg/m 2/yr). Comparing the Pb/Ti and As/Ti ratios of the DK samples with the corresponding crustal ratios (or "natural background values" for preanthropogenic peat) shows that the samples dating from 1953 also contain the maximum concentration of "excess" Pb and As. The synchroneity of the enrichments of all three elements (Hg, Pb, and As) suggests a common source, with coal-burning the most likely candidate. Independent support for this interpretation was obtained from the Pb isotope data ( 206Pb/ 207Pb = 1.1481 ± 0.0002 in the leached fraction and 1.1505 ± 0.0002 in the residual fraction) which is too radiogenic to be explained in terms of gasoline lead alone, but compares well with values for U.K. coals. In contrast, the lowest values for 206Pb/ 207Pb in the DK profile (1.1370 ± 0.0003 in the leached fraction and 1.1408 ± 0.0003 in the residual fraction) are found in the sample dating from AD 1979: this shows that the maximum contribution of leaded gasoline occurred approximately 25 yr after the zenith in total anthropogenic Pb deposition.

New data for paleoprotherozoic PGE-bearing anorthosite of Kandalaksha massif (Baltic shield): U-Pb and Sm-Nd ages

NASA Astrophysics Data System (ADS)

Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel

2015-04-01

The aims of this researches were to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) on Kandalaksha anorthosite massif due to study of polimetamorphic history. In marginal zone firstly have been obtained the presence of sulphide mineralization with PGE (Chashchin, Petrov , 2013). Kandalaksha massif is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate polymetamorphism. Two fractions of single grains from anorthosite of the massif gave precise U-Pb age, which is equal to 2450± 3 Ma. Leucocratic gabbro-norite were dated by U-Pb method, with age up to 2230 ± 10 Ma. This age reflects the time of granulite metamorphism according to data of (Mitrofanov, Nirovich, 2003). Two fractions of rutile have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile is 400-450 ° C (Mezger et.al., 1989), thus cooling processes of massif rocks to these temperatures was about 1.7 Ga. These data reflect one of the stages of metamorphic alteration of the massif. Three stages of metamorphism are distinguished by Sm-Nd method. Isotope Sm-Nd dating on Cpx-WR line gives the age of 2311 Ma which suggested of high pressure granulite metamorphism. Moreover Cpx-Pl line reflect the age 1908 Ma of low pressure granulite metamorphism. Also two-points (Grt-Rt) Sm-Nd isochrone yield the age 1687 Ma of the last metamorphic alterations in Kandalaksha anorthosite massif. Model Sm-Nd age of the leucocratic gabbro-norite is 2796 Ma with positive ɛNd (+0.32). It means that the source of gabbro-norite was mantle reservoir. All investigations are devoted to memory of academician PAS F. MItrofanov which was a leader of scientific school for geology, geochemistry and metallogenesis of ore deposits. The studies are contribution by RFBR OFI-M 13-05-12055, 13-05-00493, Department of Earth Sciences RAS (programs 2 and 4), and IGCP-SIDA 599.

Status Report on the 40Ar/39Ar and U/Pb Dating of Tuffs in the Dewey Lake Formation of West Texas Towards Constraining the Permo-Triassic Magnetostratigraphic Time Scale

NASA Astrophysics Data System (ADS)

Chang, S.; Renne, P. R.; Mundil, R.

2007-12-01

A detailed magnetic polarity time scale for the Permo-Triassic Boundary interval, critical for correlating events in marine and terrestrial paleoenvironments, is not yet well-established. Recently, late Permian magnetostratigraphic studies have been reported for non-marine sections in Europe and South Africa (Szurlies et al., 2003; Nawrocki, 2004; Ward et al., 2005). However, these sections are devoid of index fossil suitable for correlation with marine successions and also lack age constraints from radioisotopic dating methods. In other words, it is dubious to correlate these magnetostratigraphic data with the GSSP Permo-Triassic boundary and mass extinction. The Dewey Lake red beds formation of West Texas, believed to be the youngest Permian formation in North America, has yielded high-quality paleomagnetic data (Molina-Garza et al., 1989; Steiner, 2001) and contains several silicic tuffs potentially enabling high-resolution calibration of the magnetic polarity time scale in this critical age range. The tuffs have yet to be placed into a regional stratigraphic or magnetostratigraphic framework, and it is unclear exactly how many distinct eruptive units are represented by the 7 distinct samples collected to date from widely separated (>160 km) localities. 40Ar/39Ar (sanidine and biotite) and U/Pb (zircon) studies reveal that all 7 sampled tuffs were probably erupted within several hundred ka of the Permo-Triassic boundary as dated at the Meishan GSSP section (Renne et al., 1995; Mundil et al., 2004) but results thus far are inadequate to convincingly resolve age differences between the various samples. U/Pb dating of some samples is severely challenged by Pb-loss from the zircons despite application of the Mattinson (2005) annealing/chemical abrasion technique. 40Ar/39Ar data have been obtained from as many as four different irradiations in order to reduce neutron fluence related error. We observe the familiar ~1% bias between U/Pb and 40Ar/39Ar ages. Biotite microprobe data, zircon U/Th TIMS data, and the absence of sanidine from some samples serve to help correlate or distinguish some samples despite irresolvable age differences; existing data suggest that 4 distinct tuffs are present in the Dewey Lake Formation. Resolving their ages convincingly will require further work, but it is clear from our results combined with previous magnetostratigraphic data that magnetic polarity reversals were relatively frequent in the latest Permian. Thus the uniqueness of correlations elsewhere with the Permo-Triassic boundary based on magnetostratigraphy alone are not well-founded.

Preface

NASA Astrophysics Data System (ADS)

Hart, Stan; Basu, Asish

Publication of this monograph will coincide, to a precision of a few per mil, with the centenary of Henri Becquerel's discovery of "radiations actives" (C. R. Acad. Sci., Feb. 24, 1896). In 1896 the Earth was only 40 million years old according to Lord Kelvin. Eleven years later, Boltwood had pushed the Earth's age past 2000 million years, based on the first U/Pb chemical dating results. In exciting progression came discovery of isotopes by J. J. Thomson in 1912, invention of the mass spectrometer by Dempster (1918) and Aston (1919), the first measurement of the isotopic composition of Pb (Aston, 1927) and the final approach, using Pb-Pb isotopic dating, to the correct age of the Earth: close—2.9 Ga (Gerling, 1942), closer—3.0 Ga (Holmes, 1949) and closest—4.50 Ga (Patterson, Tilton and Inghram, 1953).

Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

USGS Publications Warehouse

Matthews, Naomi E.; Vazquez, Jorge A.; Calvert, Andrew T.

2015-01-01

The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff. Tephra from the Lava Creek eruption is a key Quaternary chronostratigraphic marker, in particular for dating the deposition of mid Pleistocene glacial and pluvial deposits in western North America. To resolve the timing of eruption and crystallization history for the Lava Creek magma, we performed (1) 40Ar/39Ar dating of single sanidine crystals to delimit eruption age and (2) ion microprobe U-Pb and trace-element analyses of the crystal faces and interiors of single zircons to date the interval of zircon crystallization and characterize magmatic evolution. Sanidines from the two informal members composing Lava Creek Tuff yield a preferred 40Ar/39Ar isochron date of 631.3 ± 4.3 ka. Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 626.5 ± 5.8 ka, and have trace element concentrations that vary with the eruptive stratigraphy. Zircon interiors yield a mean 206Pb/238U date of 659.8 ± 5.5 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high U concentration cores that likely grew from highly evolved melt. The occurrence of distal Lava Creek tephra in stratigraphic sequences marking the Marine Isotope Stage 16–15 transition supports the apparent eruption age of ∼631 ka. The combined results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103−104 year interval before eruption.

Datation U_Pb : âge de mise en place du magmatisme bimodal des Jebilet centrales (chaîne Varisque, Maroc). Implications géodynamiquesU_Pb dating: emplacement age of the bimodal magmatism of central Jebilet (Variscan Belt, Morocco). Geodynamic implications

NASA Astrophysics Data System (ADS)

Essaifi, Abderrahim; Potrel, Alain; Capdevila, Ramon; Lagarde, Jean-Louis

2003-01-01

The bimodal magmatism of central Jebilet is dated to 330.5 +0.68-0.83 Ma by UPb dating on zircons. This age, similar to that of the syntectonic Jebilet cordierite-bearing granitoids, corresponds to the age of the local major tectonometamorphic event. The syntectonic plutonism of the Jebilet massif, composed of tholeiitic, alkaline, and peraluminous calc-alkaline series, is variegated. Magmas emplacement was favoured by the local extension induced by the motion along the western boundary of the Carboniferous basins of the Moroccan Meseta. The Jebilet massif exemplifies the activation of various magmas sources during an episode of continental convergence and crustal wrenching.

Enhanced provenance interpretation using combined U-Pb and (U-Th)/He double dating of detrital zircon grains from lower Miocene strata, proximal Gulf of Mexico Basin, North America

NASA Astrophysics Data System (ADS)

Xu, Jie; Stockli, Daniel F.; Snedden, John W.

2017-10-01

Detrital zircon U-Pb analysis is an effective approach for investigating sediment provenance by relating crystallization age to potential crystalline source terranes. Studies of large passive margin basins, such as the Gulf of Mexico Basin, that have received sediment from multiple terranes with non-unique crystallization ages or sedimentary strata, benefit from additional constraints to better elucidate provenance interpretation. In this study, U-Pb and (U-Th)/He double dating analyses on single zircons from the lower Miocene sandstones in the northern Gulf of Mexico Basin reveal a detailed history of sediment source evolution. U-Pb age data indicate that most zircon originated from five major crystalline provinces, including the Western Cordillera Arc (<250 Ma), the Appalachian-Ouachita orogen (500-260 Ma), the Grenville (1300-950 Ma) orogen, the Mid-Continent Granite-Rhyolite (1500-1300 Ma), and the Yavapai-Mazatzal (1800-1600 Ma) terranes as well as sparse Pan-African (700-500 Ma) and Canadian Shield (>1800 Ma) terranes. Zircon (U-Th)/He ages record tectonic cooling and exhumation in the U.S. since the Mesoproterozoic related to the Grenville to Laramide Orogenies. The combined crystallization and cooling information from single zircon double dating can differentiate volcanic and plutonic zircons. Importantly, the U-Pb-He double dating approach allows for the differentiation between multiple possible crystallization-age sources on the basis of their subsequent tectonic evolution. In particular, for Grenville zircons that are present in all of lower Miocene samples, four distinct zircon U-Pb-He age combinations are recognizable that can be traced back to four different possible sources. The integrated U-Pb and (U-Th)/He data eliminate some ambiguities and improves the provenance interpretation for the lower Miocene strata in the northern Gulf of Mexico Basin and illustrate the applicability of this approach for other large-scale basins to reconstruct sediment provenance and dispersal patterns.

Recent changes in Red Lake (Romania) sedimentation rate determined from depth profiles of 210Pb and 137Cs radioisotopes.

PubMed

Begy, R; Cosma, C; Timar, A

2009-08-01

This work presents a first estimation of the sedimentation rate for the Red Lake (Romania). The sediment accumulation rates were determined by two well-known methods for recent sediment dating: (210)Pb and (137)Cs methods. Both techniques implied used the gamma emission of the above-mentioned radionuclides. The (210)Pb and (137)Cs concentrations in the sediment were measured using a gamma spectrometer with a HpGe detector, Gamma-X type. Activities ranging from 41+/-7 to 135+/-34Bq/kg were found for (210)Pb and from 3+/-0.5 to 1054+/-150Bq/kg for (137)Cs. The sediment profile indicates acceleration in sedimentation rate in the last 18 years. Thus, the sedimentation process for the Red Lake can be divided in two periods, the last 18 years, and respectively, the period before that. Using the Constant Rate of (210)Pb Supply method values between 0.18+/-0.04 and 1.85+/-0.5g/cm(2) year (0.32+/-0.08 and 2.83+/-0.7cm/year) were obtained. Considering both periods, an average sedimentation rate of 0.87+/-0.17g/cm(2) year (1.17cm/year) was calculated. Considering an average depth of 5.41m for the lake and the sedimentation rate estimated for the last 18 years, it could be estimated that the lake will disappear in 195 years.

The Approaching Obsolescence of 137Cs as a Means of Dating Wetland Soils and Sediments in North America

NASA Astrophysics Data System (ADS)

Drexler, J. Z.; Fuller, C.

2017-12-01

137Cesium is an anthropogenic radionuclide whose maximum fallout occurred in 1963/4 at the height of above-ground nuclear weapons testing. The presence of this fallout peak in core profiles has been used widely to estimate vertical accretion and carbon accumulation rates in wetlands. 137Cs dating has long been applied with little attention to uncertainty of peak position or measurement error. Initially, this caused few problems as activities were high and peaks were generally clear; however recently the clarity of peaks has deteriorated, raising questions of method efficacy. We quantified uncertainty in 137Cs dating in 52 wetland sediment/peat cores collected from 2005 - 2015 in Maine, California, Virginia, North Carolina, South Carolina, and Washington and compared the position of each peak to the date obtained with 210Pb. We found that the two dating methods matched within 5 years for only 20% of cores with a distinct 137Cs peak. We attribute this to a decline in 137Cs efficacy for three main reasons: (1) mobility of 137Cs resulting from diffusion independent of sediments, downwashing, and/or physical/biotic perturbation, (2) on-going decay of the original 137Cs in situ (half-life = 30.17 years), which manifests in lower signal to noise ratios, and (3) 137Cs inputs from watershed/tidal sources, which have confounded the 137Cs pattern in sediments. Such reduced efficacy is of concern because carbon accumulation rates determined with 137Cs are used for informing national-scale carbon assessments and for determining the carbon storage potential of wetlands restored as offsets for the carbon market. We conclude that 137Cs dating alone has sufficient uncertainty that it should be disallowed for carbon accounting and that any use of 137Cs should be accompanied by an uncertainty analysis of peak position. Our results suggest that soon the common practice of using 137Cs to corroborate 210Pb dating will likely be obsolete in much of North America.

Testing the age calibration of the Newark-Hartford APTS by magnetostratigraphic correlation of U-Pb zircon-dated tuffaceous beds in the Late Traissic Chinle Formation in core PFNP-1A from the Petrified Forest National Park (Arizona, USA)

NASA Astrophysics Data System (ADS)

Kent, D. V.; Olsen, P. E.; Mundil, R.; Lepre, C. J.

2017-12-01

The Newark-Hartford APTS extends over 27 Myr according to cycle stratigraphy of the Norian and Rhaetian of the Late Triassic and Hettangian and Sinemurian of the Early Jurassic and an additional 6 Myr by extrapolation into the Carnian; the entire sequence is anchored by U-Pb zircon dating of CAMP activity that provides a calibration date of 201.6 Ma for Chron E23r just below the end-Triassic extinction and the earliest CAMP basalts in the Newark basin (Blackburn+2013 Science; Kent+2017 ESR). The developing APTS has been successfully used for global correlations in marine and non-marine facies but there have been ongoing suggestions that millions of years of Rhaetian time are missing in a cryptic unconformity that supposedly occurs just above E23r in the Newark Supergroup basins. Testing the continuity of the APTS by magnetostratigraphic correlation of U-Pb zircon-dated tuffaceous beds in the Chinle Formation was a prime scientific objective for core PFNP-1A. Paleomagnetic results were obtained using stepwise thermal demagnetization to 680°C from >150 samples of finer-grained red lithologies from the upper 250 m of the cored section of the Chinle (upper Sonsela, Petrified Forest including the Black Forest Bed, and lower Owl Rock Members). Characteristic directions isolated in 2/3 of the samples showed antipodal directions that were shallow with respect to reference directions (flattening factor 0.5), consistent with early acquisition of remanence. Seven polarity magnetozones produce a distinctive pattern correlated to Chrons E17r to E14r of the APTS. The Black Forest Bed at 209.93±0.26 Ma (Ramezani+2011 GSAB), confirmed by our new U-Pb dates from core PFNP-1A, occurs in a reverse polarity magnetozone correlated to E16r (209.95-210.25 Ma), which puts the U-Pb zircon date(s) in excellent agreement with the inferred APTS age. Rather than a 'missing Rhaetian', the apparent regional differences in appearances and disappearances of palynoflora, conchostracans, and other endemic taxa in continental deposits are more likely a reflection of demonstrated continental drift across climate belts and the misinterpretation of ecostratigraphy as chronostratigraphy. A suite of new U-Pb dates in conjunction with paleomagnetic analyses in PFNP-1A is expected to calibrate much of Triassic succession of the Colorado Plateau.

Geochronology of recent sediments from the Cariaco Trench (Venezuela) by Alpha Spectrometry of {sup 210}Pb ({sup 210}Po)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arriojas, A.; Barros, H.; Palacios, D.

2010-08-04

210Pb concentration in marine sediments of the Cariaco Trench (North-East of Venezuela) was measured through the analysis of 210Po alpha emissions, which can be assumed to be in secular equilibrium with 210Pb. The analysed sediment core has a length of 1.9 m. The results allowed to apply the CF:CS dating model (Constant Flux and Constant Supply). The sedimentation rate was estimated to be 0.25 cm/y. As far as we know this is the first {alpha}- dating carried out in the country, performed with an alpha spectrometer recently funded by the IAEA.

Characterization and expression of the ABC family (G group) in 'Dangshansuli' pear (Pyrus bretschneideri Rehd.) and its russet mutant.

PubMed

Hou, Zhaoqi; Jia, Bing; Li, Fei; Liu, Pu; Liu, Li; Ye, Zhenfeng; Zhu, Liwu; Wang, Qi; Heng, Wei

2018-01-01

The plant genes encoding ABCGs that have been identified to date play a role in suberin formation in response to abiotic and biotic stress. In the present study, 80 ABCG genes were identified in 'Dangshansuli' Chinese white pear and designated as PbABCGs. Based on the structural characteristics and phylogenetic analysis, the PbABCG family genes could be classified into seven main groups: classes A-G. Segmental and dispersed duplications were the primary forces underlying the PbABCG gene family expansion in 'Dangshansuli' pear. Most of the PbABCG duplicated gene pairs date to the recent whole-genome duplication that occurred 30~45 million years ago. Purifying selection has also played a critical role in the evolution of the ABCG genes. Ten PbABCG genes screened in the transcriptome of 'Dangshansuli' pear and its russet mutant 'Xiusu' were validated, and the expression levels of the PbABCG genes exhibited significant differences at different stages. The results presented here will undoubtedly be useful for better understanding of the complexity of the PbABCG gene family and will facilitate the functional characterization of suberin formation in the russet mutant.

Absolute timing of sulfide and gold mineralization: A comparison of Re-Os molybdenite and Ar-Ar mica methods from the Tintina Gold Belt, Alaska

USGS Publications Warehouse

Selby, D.; Creaser, R.A.; Hart, C.J.R.; Rombach, C.S.; Thompson, J.F.H.; Smith, Moira T.; Bakke, A.A.; Goldfarb, R.J.

2002-01-01

New Re-Os molybdenite dates from two lode gold deposits of the Tintina Gold Belt, Alaska, provide direct timing constraints for sulfide and gold mineralization. At Fort Knox, the Re-Os molybdenite date is identical to the U-Pb zircon age for the host intrusion, supporting an intrusive-related origin for the deposit. However, 40Ar/39Ar dates from hydrothermal and igneous mica are considerably younger. At the Pogo deposit, Re-Os molybdenite dates are also much older than 40Ar/39Ar dates from hydrothermal mica, but dissimilar to the age of local granites. These age relationships indicate that the Re-Os molybdenite method records the timing of sulfide and gold mineralization, whereas much younger 40Ar/39Ar dates are affected by post-ore thermal events, slow cooling, and/or systemic analytical effects. The results of this study complement a growing body of evidence to indicate that the Re-Os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems.

The age of universe

NASA Astrophysics Data System (ADS)

Ali, Zeeshan

The presence of short-lived isotope Curium-247 in the early Solar System complicates the job of dating the earliest events in the solar nebula. Primitive components in meteorites contain a detailed record of the conditions and processes in the solarnebula, the cloud of dust and gas surrounding the infant Sun. Determining accurately when the first materialsformed re-quires the lead-lead (Pb-Pb) dating method, a method based on the decay of uranium (U) isotopes toPb isotopes. The initial ratio of U-238 to U-235 is critical to determining theages correctly, and many studies have concluded that the ratio is constant for any given age. How-ever, my colleagues at Arizona State University(Frankfurt, Germany), and the Senckenberg Forschungsinstitut und Naturmuseum (also in Frankfurt) and I have found that some calcium-aluminum-rich inclusions (CAIs) in chondritic meteorites deviate from the conventional value for the U-238/U-235 ratio. This could lead to inaccuracies of up to 5 million years in the age of these objects, if no correction is made.Variations in the concentrations of thorium and neodymium with the U-238/U-235 ratio suggest that the ratio may have been lowered by the decay of curium-247, which decays to U-235 with a half-life of 15.6 million years. Curium-247 is created in certain types of energetic supernovae, so its presence suggests that a supernova added material to the pre-solar interstellar cloud between 110 and 140 million years before theSolar System began to form.

Algorithms and software for U-Pb geochronology by LA-ICPMS

NASA Astrophysics Data System (ADS)

McLean, Noah M.; Bowring, James F.; Gehrels, George

2016-07-01

The past 15 years have produced numerous innovations in geochronology, including experimental methods, instrumentation, and software that are revolutionizing the acquisition and application of geochronological data. For example, exciting advances are being driven by Laser-Ablation ICP Mass Spectrometry (LA-ICPMS), which allows for rapid determination of U-Th-Pb ages with 10s of micrometer-scale spatial resolution. This method has become the most commonly applied tool for dating zircons, constraining a host of geological problems. The LA-ICPMS community is now faced with archiving these data with associated analytical results and, more importantly, ensuring that data meet the highest standards for precision and accuracy and that interlaboratory biases are minimized. However, there is little consensus with regard to analytical strategies and data reduction protocols for LA-ICPMS geochronology. The result is systematic interlaboratory bias and both underestimation and overestimation of uncertainties on calculated dates that, in turn, decrease the value of data in repositories such as EarthChem, which archives data and analytical results from participating laboratories. We present free open-source software that implements new algorithms for evaluating and resolving many of these discrepancies. This solution is the result of a collaborative effort to extend the U-Pb_Redux software for the ID-TIMS community to the LA-ICPMS community. Now named ET_Redux, our new software automates the analytical and scientific workflows of data acquisition, statistical filtering, data analysis and interpretation, publication, community-based archiving, and the compilation and comparison of data from different laboratories to support collaborative science.

Modern U-Pb chronometry of meteorites: advancing to higher time resolution reveals new problems

USGS Publications Warehouse

Amelin, Y.; Connelly, J.; Zartman, R.E.; Chen, J.-H.; Gopel, C.; Neymark, L.A.

2009-01-01

In this paper, we evaluate the factors that influence the accuracy of lead (Pb)-isotopic ages of meteorites, and may possibly be responsible for inconsistencies between Pb-isotopic and extinct nuclide timescales of the early Solar System: instrumental mass fractionation and other possible analytical sources of error, presence of more than one component of non-radiogenic Pb, migration of ancient radiogenic Pb by diffusion and other mechanisms, possible heterogeneity of the isotopic composition of uranium (U), uncertainties in the decay constants of uranium isotopes, possible presence of "freshly synthesized" actinides with short half-life (e.g. 234U) in the early Solar System, possible initial disequilibrium in the uranium decay chains, and potential fractionation of radiogenic Pb isotopes and U isotopes caused by alpha-recoil and subsequent laboratory treatment. We review the use of 232Th/238U values to assist in making accurate interpretations of the U-Pb ages of meteorite components. We discuss recently published U-Pb dates of calcium-aluminum-rich inclusions (CAIs), and their apparent disagreement with the extinct nuclide dates, in the context of capability and common pitfalls in modern meteorite chronology. Finally, we discuss the requirements of meteorites that are intended to be used as the reference points in building a consistent time scale of the early Solar System, based on the combined use of the U-Pb system and extinct nuclide chronometers.

A European lead isotope signal recorded from 6000 to 300 years BP in coastal marshes (SW France)

NASA Astrophysics Data System (ADS)

Alfonso, S.; Grousset, F.; Massé, L.; Tastet, J.-P.

Cores covering the last 6000 years were recovered from two marshes from south-western France. They were studied in an attempt to build a reliable regional record of heavy metal pollution. The cores were dated using 14C and historical data. Both Pb concentrations and Pb isotopic composition ( 206Pb/ 207Pb and 208Pb/ 206Pb) were measured in bulk sediment samples using the inductively coupled plasma-mass spectrometer technique. The evolution of the 206Pb/ 207Pb ratio recorded in both marshes reveals a good correlation with the worldwide Pb production during the last 5000 years. The lead isotopic records reveal some general trends, along with a few typical events such as the imprints of the pre-anthropogenic background between 6000 and 2300 years BP, the mining activity during the Roman and Greek periods from 2300 to 1700 years BP, the fall of the Roman Empire and the mining activity in Central Europe since the 11th century AD. These results are also consistent with records obtained in other European environments. Consequently, the European atmospheric signal is recorded in these marshes, hiding expected local riverine contributions. Thus, such records may contribute to the construction of a chronological standard curve for continental environments. However, it will be necessary to study other records more accurately dated to obtain an adequate precision before such a reference curve can be set-up.

Earth Processes: Reading the Isotopic Code

NASA Astrophysics Data System (ADS)

Basu, Asish; Hart, Stan

Publication of this monograph will coincide, to a precision of a few per mil, with the centenary of Henri Becquerel's discovery of "radiations actives" (C. R. Acad. Sci., Feb. 24, 1896). In 1896 the Earth was only 40 million years old according to Lord Kelvin. Eleven years later, Boltwood had pushed the Earth's age past 2000 million years, based on the first U/Pb chemical dating results. In exciting progression came discovery of isotopes by J. J. Thomson in 1912, invention of the mass spectrometer by Dempster (1918) and Aston (1919), the first measurement of the isotopic composition of Pb (Aston, 1927) and the final approach, using Pb-Pb isotopic dating, to the correct age of the Earth: close—2.9 Ga (Gerling, 1942), closer—3.0 Ga (Holmes, 1949) and closest—4.50 Ga (Patterson, Tilton and Inghram, 1953).

The isotopic record of atmospheric lead fall-out on an Icelandic salt marsh since AD 50.

PubMed

Marshall, William A; Clough, Robert; Gehrels, W Roland

2009-04-01

We report a record of atmospheric Pb deposition at a coastal site in western Iceland that spans the last two millennia. The elemental concentrations of Pb, Al, Li and Ti are determined using ICP-MS from a sediment monolith collected from a salt marsh. Multicollector (MC) ICP-MS analysis is used to obtain isotopic ratios of stable Pb. The Pb/Ti and Pb/Li ratios are used to separate natural Pb background concentrations from Pb derived from remote anthropogenic sources. The pollution record in western Iceland is subdued in comparison with Pb records from the European mainland, but the isotopic character, profile and timing of Pb deposition show good agreement with the atmospheric Pb fall-out reported from sites in Scandinavia and northwestern Europe. At the bottom of the sequence we isolate a low-level (0.1-0.4 mg kg(-1)) Pb enrichment signal dated to AD 50-150. The isotopic signature and timing of this signal suggest Roman metal working industries as the source. In the subsequent millennium there was no significant or very low (i.e. elemental concentrations<0.01 mg kg(-1)) anthropogenic Pb deposition at the site up to, and including, the early Medieval period. Above a pumice layer, dated to AD 1226-1227, a small increase in Pb deposition is found. This trend is maintained until a more substantive and progressive increase is signalled during the late 1700s and early 1800s. This is followed by a substantial enrichment signal in the sediments (>3.0 mg kg(-1)) that is interpreted as derived from industrial coal burning and metal working during the 19th and 20th centuries in northern Europe. During the late 20th century, significant fall-out from European fuel additives reached Iceland.

New dating evidence of the early presence of hominins in Southern Europe.

PubMed

Michel, Véronique; Shen, Chuan-Chou; Woodhead, Jon; Hu, Hsun-Ming; Wu, Chung-Che; Moullé, Pierre-Élie; Khatib, Samir; Cauche, Dominique; Moncel, Marie-Hélène; Valensi, Patricia; Chou, Yu-Min; Gallet, Sylvain; Echassoux, Anna; Orange, François; de Lumley, Henry

2017-08-30

The first "Out of Africa" migrations represent a seminal event in the history of humankind. At the gates of Europe, the first appearance of Hominins is recorded in Georgia, 1.8 million years ago (Ma); however, the picture of migration across the continent remains incomplete. Vallonnet Cave (France) is a Lower Paleolithic prehistoric site with traces of hominin activities including lithic remains and cut-marks on mammal bones. Here, we apply the uranium-lead (U-Pb) methods to two flowstones to date the intervening archaeological levels. The U-Pb data, coupled with paleomagnetic constraints, provide an age range from 1.2 to 1.1 Ma. The results conclusively demonstrate that Vallonnet Cave is one of the oldest European prehistoric sites in France with early hominin occupations associated with an Epivillafranchian fauna. Combined with data from other archaeological sites, the new precise chronology suggests a widespread occupation the Northern Mediterranean to Southwestern Europe at ~1.2 Ma.

Precise U/Pb zircons dates of bentonites in Upper Ordovician and Lower Silurian reference sections in North America and Britain.

NASA Astrophysics Data System (ADS)

Suarez, S. E.; Brookfield, M. E.; Catlos, E. J.; Stockli, D. F.; Batchelor, R. A.

2016-12-01

The end of the Ordovician marks one of the greatest of the Earth's mass extinctions. One hypothesis explains this mass extinction as the result of a short-lived, major glaciation preceded by episodes of increased volcanism brought on by the Taconic orogeny. K-bentonites, weathered volcanic ash, provide evidence for increased volcanism. However, there is a lack of modern precise U-Pb dating of these ashes and some confusion in the biostratigraphy. The aim of this study is to obtain more precise U-Pb zircon ages from biostratigraphically constrained bentonites which will lead to better correlation of the Upper Ordovician and Lower Silurian relative time scales, as well as time the pulses of eruption. Zircon grains were extracted from the samples by heavy mineral separation and U-Pb dated using the Laser Ablation-Inductively Coupled Plasma-Mass Spectrometer at the University of Texas-Austin. We report here 3 precise U-Pb zircon ages from the Trenton Group, Ontario, Canada, and Dob's Linn, Scotland. The youngest age from the top of the Kirkfield Formation in Ontario is 448.0 +/- 18 Ma, which fits with existing late Ordovician stratigraphic ages. At Dob's Linn, Scotland, the site of the Ordovician/Silurian Global Boundary Stratigraphic Section and Point (GSSP), the youngest age for DL7, a bentonite 5 meters below the GSSP is 402.0 +/- 12.0 Ma, and for DL24L, a bentonite 8 meters above the GSSP is 358.2 +/- 7.9 Ma. These are Devonian ages in current timescales - the current age for the GSSP is 443.8 +/- 1.8 Ma, based on an U/Pb dates from a bentonite 1.6 meters above the GSSP at Dob's Linn. We are confident that our techniques rule out contamination and the most likely explanation is that the small zircons we analyzed either suffered Pb loss, or grew overgrowths during low grade hydrothermal metamorphism of the sediments during the intrusion of the Southern Upland Devonian granites during the Caledonian orogeny. These Devonian ages suggest that the 443.8 +/- 1.8 Ma age may also be suspect. The Dob's Linn site is therefore unsuitable for calibrating the biostratigraphic horizons. Work in progress will provide more U-Pb dating of bentonites from around the Ordovician-Silurian boundary in Canada, United States, Britain and Scandinavia with the aim of calibrating the local series and stages in order to help in International correlations.

Advantages of conducting in-situ U-Pb age dating of multiple U-bearing minerals from a single complex: Case in point - the Oka Carbonatite Complex

NASA Astrophysics Data System (ADS)

Chen, W.; Simonetti, A.

2012-12-01

A detailed radiometric investigation is currently underway focusing on U-bearing accessory minerals apatite, perovskite, and niocalite from the Oka Carbonatite Complex (Canada). One of the main objectives is to obtain a comparative chronology of melt crystallization for the complex. Unlike other commonly adopted U-bearing minerals (e.g., zircon, monazite) for in-situ dating investigations, apatite, perovskite, and niocalite contain relatively high contents of common Pb. Hence, careful assessment of the proportion and composition of the common Pb, and usage of appropriate matrix-matched external standards are imperative. The Madagascar apatite was utilized as the external standard for apatite dating, and the Emerald Lake and Durango apatites were adopted as secondary standards; the latter yield ages of 92.6 ±1.8 and 32.2 ±1.1 Ma, respectively, and these are identical to their accepted ages. Pb/U ages for apatite from Oka were obtained for different rock types, including 8 carbonatites, 4 okaites, 3 ijolites and 3 alnoites, and these define a range of ages between ~105 and ~135 Ma; this result suggests a protracted crystallization history. In total, 266 individual analyses define two peaks at ~115 and ~125Ma. For perovskite dating, the Ice River perovskite standard was utilized as the external standard. The perovskites from one okaite sample yield an age of 112.2 ±1.9 Ma, and is much younger than the previously reported U-Pb perovskite age of 131 ±7 Ma. Hence, the combined U-Pb perovskite ages also suggest a rather prolonged time of melt crystallization. Niocalite is a rare, accessory silicate mineral that occurs within the carbonatites at Oka. The international zircon standard BR266 was selected for use as the external standard and rastering was employed to minimize the Pb-U fractionation. Two niocalite samples give young ages at 110.6 ±1.2 and 115.0 ±1.9 Ma, and are identical to their respective apatite ages (given associated uncertainties) from the same sample. The niocalite for a carbonatite sample Oka153 defines a bimodal age distribution, with weighted average 206Pb/238U ages of 110.1 ±5.0 and 133.2 ±6.1 Ma. Apatite from the same sample also records a similar bimodal age distribution of 111.4 ±2.8 and 126.9 ±1.8 Ma. The combined in situ U-Pb dating results for apatite, pervoskite, niocalite from Oka clearly support a protracted history of magmatic activity (~30 Myr) for this carbonatite complex. Of importance, the U-Pb results from this study clearly indicate the significance of conducting a thorough geochronological investigation rather than defining the age of any one alkaline complex solely on the basis of a single radiometric age determination.

Lead (Pb) National Ambient Air Quality Standards (NAAQS) Implementation Guidance Documents

EPA Pesticide Factsheets

This page contains implementation guidance documents for the 1978 and 2008 Lead (Pb) NAAQS. Some of the topics covered are: RACM/RACT, RFP, new source review, designations, emissions inventories, attainment dates, and transition policy

Publications - GMC 198 | Alaska Division of Geological & Geophysical

Science.gov Websites

, Alaska Authors: O'Sullivan, P.B., and Murphy, John Publication Date: 1992 Publisher: Alaska Division of publication sales page for more information. Bibliographic Reference O'Sullivan, P.B., and Murphy, John, 1992

Provenance of Marine Sediment in the Gulf of Alaska, IODP Expedition 341: Links Between Sediment Derivation, Glacial Systems, and Exhumation of the Coastal Mountain Belts

NASA Astrophysics Data System (ADS)

Allen, W. K.; Dunn, C. A.; Enkelmann, E.; Ridgway, K.; Colliver, L.

2015-12-01

Provenance analysis of Neogene sand and diamict beds from marine boreholes drilled by the IODP Expedition 341 provides a marine sedimentary record of the interactions between tectonics, climate and sediment deposition along a glaciated convergent margin. The 341 boreholes represent a cross-margin transect that sampled the continental shelf, slope, and deep sea Surveyor Fan of the Gulf of Alaska. Our dataset currently consists of ~ 650 detrital zircons selected for double dating method utilizing both detrital zircon fission track (FT) and U-Pb analysis from sand and diamict beds, as well as zircon U-Pb geochronology and apatite FT from igneous and gneissic clasts. Detrital zircon U-Pb geochronology of sand records dominant peak ages of 53, 62, 70, and 98 Ma with minor populations of 117, 154, and 170 Ma. Most of these ages can be correlated to primary igneous sources in the Coast Plutonic Complex, the Chugach Metamorphic Complex, the plutonic rocks of Wrangellia, and the Sanak-Baranoff plutonic belt. All samples analyzed to date, covering a 10 Myr range, share nearly identical detrital zircon populations suggesting similar primary sediment sources and reworking of sediment in thrust belts and accretionary prisms along this convergent margin. Plutonic and gneissic clasts collected from the boreholes on the shelf have already been double dated. These clasts have general U-Pb zircon crystallization ages of 52-54 Ma and apatite fission track cooling ages of 10-12 Ma. These results, along with previous published studies, indicate that these clasts were derived from the Chugach Metamorphic Complex and were eroded and transported by the Bagley Ice Field and Bering Glacier. Future results using this approach should allow us to pinpoint which parts of the exhumed onshore ranges and which glacial systems provided sediment to marine environments in the Gulf of Alaska.

CL-imaging and ion microprobe dating of single zircons from a high-grade rock from the Central Zone, Limpopo Belt, South Africa: Evidence for a single metamorphic event at ˜2.0 Ga

NASA Astrophysics Data System (ADS)

Mouri, H.; Brandl, G.; Whitehouse, M.; de Waal, S.; Guiraud, M.

2008-02-01

The combination of ion microprobe dating and cathodoluminescence (CL) imaging of zircons from a high-grade rock from the Central Zone of the Limpopo Belt were used to constrain the age of metamorphic events in the area. Zircon grains extracted from an orthopyroxene-gedrite-bearing granulite were prepared for single crystal CL-imaging and ion microprobe dating. The grains display complex zoning when using SEM-based CL-imaging. A common feature in most grains is the presence of a distinct core with a broken oscillatory zoned structure, which clearly appears to be the remnant of an original grain of igneous origin. This core is overgrown by an unzoned thin rim measuring about 10-30 μm in diameter, which is considered as new zircon growth during a single metamorphic event. Selected domains of the zircon grains were analysed for U, Pb and Th isotopic composition using a CAMECA IMS 1270 ion microprobe (Nordsim facility). Most of the grains define a near-concordant cluster with some evidence of Pb loss. The most concordant ages of the cores yielded a weighted mean 207Pb/ 206Pb age of 2689 ± 15 (2 σ) Ma, interpreted as the age of the protolith of an igneous origin. The unzoned overgrowths of the zircon grains yielded a considerably younger weighted mean 207Pb/ 206Pb age of ˜2006.5 ± 8.0 Ma (2 σ), and these data are interpreted to reflect closely the age of the ubiquitous high-grade metamorphic event in the Central Zone. This study shows clearly, based on both the internal structure of the zircons and the data obtained by ion microprobe dating, that only a single metamorphic event is recorded by the studied 2.69 Ga old rocks, and we found no evidence of an earlier metamorphic event at ˜2.5 Ga as postulated earlier by some workers.

Apatite U-Pb thermochronolgy applied to complex geological settings - insights from geo/thermochronology and geochemistry

NASA Astrophysics Data System (ADS)

Paul, Andre; Spikings, Richard; Ulyanov, Alexey; Chew, David

2016-04-01

Application of high temperature (>350oC) thermochronology is limited to the U-Pb system of accessory minerals, such as apatite, under the assumption that radiogenic lead is lost to thermally activated volume diffusion into an infinite reservoir. Cochrane et al. (2015) have demonstrated a working example from the northern Andes of South America. Predictions from volume diffusion theory were compared with measured single grain U-Pb date correlated to shortest diffusion radius and in-situ profiles measured by LA-ICP-MS. Results from both techniques were found to be in agreement with predictions from thermally activated, volume diffusion. However, outliers from the ID-TIMS data suggested some complexity, as grains were found to be too young relative to their diffusion radius. Interaction of multiple processes can be responsible for the alteration of apatite U-Pb dates such as: (1) metamorphic (over)growth, (2) fluid aided alteration/recrystallization and (3) metamictization and fracturing of the grain. Further, predictions from volume diffusion rely on the input parameters: (a) diffusivity, (b) activation energy and (c) shortest diffusion radius. Diffusivity and activation energy are potentially influenced by the chemical composition and subsequent changes in crystal structure. Currently there is one value for diffusion parameter and activation energy established for (Durango) apatite (Cherniak et al., 1991). Correlation between diffusivity/activation energy and composition has not been established. We investigate if correlations exist between diffusivity/activation energy and composition by obtaining single grain apatite U-Pb date and chemical compostion and correlating these to their diffusion radius. We test the consistency of apatite closure temperature, by comparing the apatite U-Pb dates with lower temperature thermochronometers such as white mica and K-feldspar Ar/Ar and by petrographic observations. We test if chemical information can be a proxy to identify metamorphic (over)growth and fluid aided alteration/recrystallization. We seek to evaluate if apatite U-Pb thermochronology can be applied to a broad range of rock types and geological environments or if limitations must be drawn.

Recent atmospheric lead deposition recorded in an ombrotrophic peat bog of Great Hinggan Mountains, Northeast China, from 210Pb and 137Cs dating.

PubMed

Bao, K; Xia, W; Lu, X; Wang, G

2010-09-01

Radioactive markers are useful in dating lead deposition patterns from industrialization in peat archive. Peat cores were collected in an ombrotrophic peat bog in the Great Hinggan Mountains in Northeast China in September 2008 and dated using (210)Pb and (137)Cs radiometric techniques. The mosses in both cores were examined systematically for dry bulk density, water and ash content. Lead also was measured using atomic emission spectroscopy with inductively coupled plasma (ICP-AES). Both patterned peat profiles were preserved well without evident anthropogenic disturbance. Unsupported (210)Pb and (137)Cs decreased with the depth in both of the two sample cores. The (210)Pb chronologies were established using the constant rate of supply model (CRS) and are in good agreement with the (137)Cs time marker. Recent atmospheric (210)Pb flux in Great Hinggan Mountains peat bog was estimated to be 337 Bq m(-2)y(-1), which is consistent with published data for the region. Lead deposition rate in this region was also derived from these two peat cores and ranged from 24.6 to 55.8 mg m(-2)y(-1) with a range of Pb concentration of 14-262 microg g(-1). The Pb deposition patterns were consistent with increasing industrialization over the last 135-170 y, with a peak of production and coal burning in the last 50 y in Northeast China. This work presents a first estimation of atmospheric Pb deposition rate in peatlands in China and suggests an increasing trend of environmental pollution due to anthropogenic contaminants in the atmosphere. More attention should be paid to current local pollution problems, and society should take actions to seek a balance between economic development and environmental protection. Copyright 2010 Elsevier Ltd. All rights reserved.

Variable microstructural response of baddeleyite to shock metamorphism in young basaltic shergottite NWA 5298 and improved U-Pb dating of Solar System events

NASA Astrophysics Data System (ADS)

Darling, James R.; Moser, Desmond E.; Barker, Ivan R.; Tait, Kim T.; Chamberlain, Kevin R.; Schmitt, Axel K.; Hyde, Brendt C.

2016-06-01

The accurate dating of igneous and impact events is vital for the understanding of Solar System evolution, but has been hampered by limited knowledge of how shock metamorphism affects mineral and whole-rock isotopic systems used for geochronology. Baddeleyite (monoclinic ZrO2) is a refractory mineral chronometer of great potential to date these processes due to its widespread occurrence in achondrites and robust U-Pb isotopic systematics, but there is little understanding of shock-effects on this phase. Here we present new nano-structural measurements of baddeleyite grains in a thin-section of the highly-shocked basaltic shergottite Northwest Africa (NWA) 5298, using high-resolution electron backscattered diffraction (EBSD) and scanning transmission electron microscopy (STEM) techniques, to investigate shock-effects and their linkage with U-Pb isotopic disturbance that has previously been documented by in-situ U-Pb isotopic analyses. The shock-altered state of originally igneous baddeleyite grains is highly variable across the thin-section and often within single grains. Analyzed grains range from those that preserve primary (magmatic) twinning and trace-element zonation (baddeleyite shock Group 1), to quasi-amorphous ZrO2 (Group 2) and to recrystallized micro-granular domains of baddeleyite (Group 3). These groups correlate closely with measured U-Pb isotope compositions. Primary igneous features in Group 1 baddeleyites (n = 5) are retained in high shock impedance grain environments, and an average of these grains yields a revised late-Amazonian magmatic crystallization age of 175 ± 30 Ma for this shergottite. The youngest U-Pb dates occur from Group 3 recrystallized nano- to micro-granular baddeleyite grains, indicating that it is post-shock heating and new mineral growth that drives much of the isotopic disturbance, rather than just shock deformation and phase transitions. Our data demonstrate that a systematic multi-stage microstructural evolution in baddeleyite results from a single cycle of shock-loading, heating and cooling during transit to space, and that this leads to variable disturbance of the U-Pb isotope system. Furthermore, by linking in-situ U-Pb isotopic measurements with detailed micro- to nano-structural analyses, it is possible to resolve the timing of both endogenic crustal processes and impact events in highly-shocked planetary materials using baddeleyite. This opens up new opportunities to refine the timing of major events across the Solar System.

U-Th-Pb zircon dating of the 13.8-Ma dacite volcanic dome at Cerro Rico de Potosi, Bolivia

USGS Publications Warehouse

Zartman, R.E.; Cunningham, C.G.

1995-01-01

The temporal relationship between the extrusion of the Miocene dacite volcanic dome at Cerro Rico de Potasi, Bolivia, and the associated Ag-Sn mineralization has an important bearing on the heat and metal sources for this world class mineral deposit. The present study uses U-Th-Pb dating of sparse zircon contained in the dacite to demonstrate that, at most, only several hundred thousand years separate dome emplacement from main stage mineralization. -from Authors

Towards Synthesis and Usage of Actinide-Bearing REE Phosphate age Standards: A Progress Report

NASA Astrophysics Data System (ADS)

Pyle, J. M.; Cherniak, D. J.

2006-05-01

Electron microprobe (EMP) dates result from a concentration-time unit conversion, so use of a concentration- based (rather than isotope-ratio based) fictive age standard is warranted. This observation has motivated our mineral synthesis program, aimed at producing actinide-doped REE phosphate EMP dating standards that meet the following criteria: 1) known concentrations of U, Th, and Pb; 2) homogeneous intragrain distribution of all components; 3) of suitable size, either as a single-crystal or polycrystalline sintered ceramic. Single-crystal synthesis of actinide-doped LaPO4 by flux-growth methods results in disproportionation of lanthanide and flux, alkali, and actinide components into phosphate and oxide phases, respectively, and flux- growth methods were abandoned. Actinide-doped La phosphate is successfully prepared by high-T annealing and hydrothermal processing of microcrystalline phosphate; both homogeneity and charge-balance of (Ca, Th, Pb)-bearing LaPO4 increase with increasing solvent acidity during cold-seal hydrothermal synthesis. A combination of pressing and high-T (1400° C) sintering transforms fine-grained (0.1-10 μm) run- products to ceramic pellets with 90-95% theoretical density. Our most recent runs focused on a target composition of La80(CaTh)17(CaU)2(PbTh)1PO4 processed with 6% 2M HCl at 820° C, 0.75 kbar for 1 week. The run products are 0.1-2 μm crystals identified by XRD as La-actinide phosphate solid solution. 2 μm grains (N=16) give a composition (mean±2 sd) of La79.77(1.26)(CaTh)17.87(1.00)(CaU)1.53(0.42)(PbTh)0.82(0.09)PO4. Th (8.07-9.13 wt. %) is homogeneous at the level of analytical precision, and the Pb concentration range (3500-4350 ppm) is restricted relative to untreated precipitate. Uranium concentration values are more variable (6500-10000 ppm). This run yields a fictive age of 702±4 Ma (mean±2 se), compared to the fictive age of 794 Ma for the target composition.

206Pb-230Th-234U-238U and 207Pb-235U geochronology of Quaternary opal, Yucca Mountain, Nevada

USGS Publications Warehouse

Neymark, Leonid A.; Amelin, Yuri V.; Paces, James B.

2000-01-01

U–Th–Pb isotopic systems have been studied in submillimeter-thick outermost layers of Quaternary opal occurring in calcite–silica fracture and cavity coatings within Tertiary tuffs at Yucca Mountain, Nevada, USA. These coatings preserve a record of paleohydrologic conditions at this site, which is being evaluated as a potential high-level nuclear waste repository. The opal precipitated from groundwater is variably enriched in 234U (measured 234U/238U activity ratio 1.124–6.179) and has high U (30–313 ppm), low Th (0.008–3.7 ppm), and low common Pb concentrations (measured 206Pb/204Pb up to 11,370). It has been demonstrated that the laboratory acid treatment used in this study to clean sample surfaces and to remove adherent calcite, did not disturb U–Th–Pb isotopic systems in opal. The opal ages calculated from 206Pb∗/238U and 207Pb∗/235U ratios display strong reverse discordance because of excess radiogenic 206Pb∗ derived from the elevated initial 234U. The data are best interpreted using projections of a new four-dimensional concordia diagram defined by 206Pb∗/238U, 207Pb∗/235U, 234U/238Uactivity, and 230Th/238Uactivity. Ages and initial 234U/238U activity ratios have been calculated using different projections of this diagram and tested for concordance. The data are discordant, that is observed 207Pb∗/235U ages of 170 ± 32 (2σ) to 1772 ± 40 ka are systematically older than 230Th/U ages of 34.1 ± 0.6 to 452 ± 32 ka. The age discordance is not a result of migration of uranium and its decay products under the open system conditions, but a consequence of noninstantaneous growth of opal. Combined U–Pb and 230Th/U ages support the model of slow mineral deposition at the rates of millimeters per million years resulting in layering on a scale too fine for mechanical sampling. In this case, U–Pb ages provide more accurate estimates of the average age for mixed multiage samples than 230Th/U ages, because ages based on shorter-lived isotopes are nonlinearly biased by younger mineral additions. Use of the combined U–Th–Pb technique to date Yucca Mountain Quaternary opals significantly extends the age range beyond that of the 230Th/U dating method and shows that selected fracture pathways in the unsaturated zone felsic tuffs of Yucca Mountain have been active throughout the Quaternary.

210Pb dating of sediments in a heavily contaminated drainage channel to the La Plata estuary in Buenos Aires, Argentina.

PubMed

Di Gregorio, D E; Fernández Niello, J O; Huck, H; Somacal, H; Curutchet, G

2007-01-01

Concentrations of (210)Pb and (137)Cs in sediment samples collected from two cores at a drainage channel to the La Plata river estuary in Buenos Aires, Argentina, were measured using ultralow-background detection systems. The (210)Pb data were used to determine the rate of sediment accumulation of the sites. These results were correlated with some heavy metal (chromium and lead) concentrations of the samples in an attempt to characterize the historical input of contaminants due to the industrial development, which has taken place in this area over the last century. The (137)Cs measurements demonstrate that cesium dating is not adequate in regions of the southern hemisphere.

Thermochronological modeling of the age of Vologda crystalline basement of the Russian platform

NASA Astrophysics Data System (ADS)

Gerasimov, V. Yu.; Petrov, D. B.; Lebedev, V. A.

2010-05-01

The results of the complex petrological and isotope-geochronological study of the crystalline rock from the deep drilling hall of the south of Vologda segment are presented in this work. The crystalline basement of the platform in Vologda region lie in a depth 2.5 km and represented by high alumina mica schist. The thick sedimentary cover consists of vendian and phanerozoic sediments. Upper level covered by quaternary glacial deposits up to 50 m. A core sample from the borehole of Fedotovo village was obtained from the depth 2600 m. It is fine-medium grained metamorphic mica schist with sillimanite. The mineral assemblage represented by association: Pl-Bt-Ms-Sil-Qtz-Mag +Zrn +Mnz. The metamorphic schist of the crystalline basement contains several radio isotope sensors. There are two rock forming potassium reach mica, - biotite (Bt) and muscovite (Ms) and accessories monazite (Mnz), - the phosphate of REE enriched by Th and U. It was a reason why traditional K-Ar isotope dating method in the combination with electron microprobe U-Th-Pb dating method CHIME [Suzuki et al. 1991] was used for Vologda metapelite rocks dating. In addition to geochronology, the detailed petrological investigation using electron microprobe allowed also to determine thermodynamic parameters of metamorphic system with a help of the mineral thermobarometry and finally estimate the age of the metamorphic thermal event using experimental diffusion data of Ar and Pb in minerals [Gerasimov et al. 2004]. The temperature of the regional metamorphism was estimated using Bt+Mag+Qtz and Bt+Ms geothermometers [Glassley 1983, Hoisch 1989]. Taking into account the field of the sillimanite P-T stability it is possible to conclude that the peak of metamorphism was reached at temperature about ТоС=550+/-30° C and pressure Р=4+/-1 kbar. Isotope thermochronology of the sample demonstrate nearly Svecofenian age 1.7-1.8 Ga of Vologda crystalline basement. K-Ar isotope dating of black and white mica demonstrates regular progression of ages in a concordance with closure temperature of each mineral. The apparent Bt age is about 1670 Ma and Ms age is 1710 Ma. The estimation of closure temperature (Tc) for each of the minerals using Dodsn's theory [Dodson 1973] and DCT computer program with concordance procedure of cooling rate simulation for the two coexisting minerals demonstrate value 340° C and и 460° C for Bt and Ms respectively. The rate of cooling in this temperature range is about 3° C/Ma and time span between closure temperatures of the two micas is about 40 Ma. The value of the cooling rate is a very typical for regional metamorphism conditions. The linear extrapolation of the simulated time-temperature trend to the thermal peak of the regional metamorphism (estimated by mineral equilibriums at 550° C) demonstrates that cooling of the metamorphic system from the thermal peak to 460° C(closure temperature of Ms) takes about 30-40 Ma. It is a value of systematic thermochronological correction to the muscovite apparent K-Ar age which has to be added to estimate the age of regional metamorphism, after that we finally receive the age 1750+/-40 Ma. U-Th-Pb system of monazite grains was tested by electron microprobe JEOL 8200 in IGEM RAS using CHIME method. The analysis of 8 grains demonstrated averaged value of age 1790+/-55 Ma. It is in a very good agreement with K-Ar isotope dating results. Moreover, the estimation of monazite closure temperature using experimental data of Pb diffusion [Smith & Giletti 1997] shows the value Tc=540-560° C which almost exactly corresponds to the peak temperature of regional metamorphism. It is also an explanation of the very close results of dating in different isotope systems (conservative U-Th-Pb system of monazite and flexible K-Ar system) in the condition of slow cooling and demonstrates the thermochronological modeling effectiveness.

Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

NASA Astrophysics Data System (ADS)

Vazquez, J. A.; Matthews, N. E.; Calvert, A. T.

2015-12-01

The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff (LCT). Tephra from the eruption blanketed much of the western United States, and is a key Quaternary chronostratigraphic marker, in particular for dating deposition of mid-Pleistocene glacial and pluvial deposits in western North America. We performed 40Ar/39Ar dating of single sanidines to delimit eruption age, and ion microprobe U-Pb and trace-element analyses of crystal faces on single zircons to characterize magmatic evolution and date near-eruption crystallization, as well as analyses of crystal interiors to date the interval of zircon crystallization. Sanidines from the two LCT members A and B yield an 40Ar/39Ar isochron date of 631 ± 4 ka (2σ). Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 627 ± 6 ka (2σ) and have trace element concentrations that vary with eruptive stratigraphy. Zircon interiors yield a weighted mean 206Pb/238U date of 660 ± 6 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high-U concentrations and dark cathodoluminescence (CL) cores. These crystals with high-U cores are possibly sourced from 'defrosting' of melt-impregnated margins of the growing subvolcanic reservoir. LCT sanidines mirror the variation of zircon composition within the eruptive stratigraphy, with crystals from upper LCT-A and basal LCT-B having bright-CL rims with high Ba concentrations, suggesting late crystallization after addition of less evolved silicic magma. The occurrence of distal LCT in stratigraphic sequences marking the Marine Isotope Stage 16-15 transition supports the apparent eruption age of ca. 631 ka. These results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103-104 year interval before eruption.

From opening to subduction of an oceanic domain constrained by LA-ICP-MS U-Pb zircon dating (Variscan belt, Southern Armorican Massif, France)

NASA Astrophysics Data System (ADS)

Paquette, J.-L.; Ballèvre, M.; Peucat, J.-J.; Cornen, G.

2017-12-01

In the Variscan belt of Western Europe, the lifetime and evolution of the oceanic domain is poorly constrained by sparse, outdated and unreliable multigrain ID-TIMS U-Pb zircon dating. In this article, we present a complete in situ LA-ICP-MS dataset of about 300 U-Pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of Southern Brittany, comprising new dating of previously published zircon populations and newly discovered rock samples. In situ dating and cathodo-luminescence imaging of each zircon grain yields new absolute time-constraints on the evolution of the Galicia-Moldanubian Ocean. The new results confirm that the opening of this oceanic domain is well defined at about 490 Ma. In contrast, the generally-quoted 400-410 Ma-age for the high-pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites. In light of these new data, we propose that the obduction of oceanic rocks occurred at about 370-380 Ma while the high-pressure event is recorded at 355 Ma in only a few zircon grains of some eclogite samples. Additionally, this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their U-Pb systems do not record that metamorphism systematically. These zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith. Another example of an eclogite sample from the French Massif Central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism.

Magmatic Longevity Constrained by ID-TIMS U-Pb Dating of Zircon and Titanite

NASA Astrophysics Data System (ADS)

Szymanowski, D.; Wotzlaw, J. F.; Ellis, B. S.; Bachmann, O.; Von Quadt, A.

2016-12-01

Clues about the timescales and thermal conditions associated with the growth and evacuation of large silicic magma reservoirs are frequently drawn from radiometric dating, diffusion modelling, or thermomechanical modelling. A growing amount of petrological and geochronological evidence, supported by thermal modelling, suggests that many silicic magma reservoirs may exist for some 104-106 years in the form of high-crystallinity mushes at relatively low temperatures ( 700-750°C; [1-3]). Geochronological studies addressing this issue typically utilise the U-Pb system in zircon capable of recording extended periods of crystallisation, particularly in evolved calc-alkaline systems that spend most of their lifetime zircon-saturated. In this study, we integrate U-Pb dating of zircon and titanite to investigate the longevity of the magma reservoir that produced the Kneeling Nun Tuff, a 35 Ma, >900 km3 crystal-rich rhyolitic super-eruption from the Mogollon-Datil volcanic field in New Mexico (USA). High-precision ID-TIMS U-Pb dates of single crystals of both zircon and titanite independently record a continuous crystallisation history over >400,000 years. We combine the dating of both accessory phases with textural, major, trace element and isotopic studies of single crystals, placing tight constraints on the thermal conditions of magma accumulation and storage while recording differentiation and rejuvenation processes within the magma reservoir. The results suggest a protracted `cool' upper-crustal storage of magma prior to the Kneeling Nun Tuff eruption followed by a melting event which reduced the magma crystallinity and conditioned it for eruption. [1] Bachmann & Bergantz (2004), J. Petrol. 45, 1565-1582. [2] Gelman et al. (2013), Geology 41, 759-762. [3] Cooper & Kent (2014), Nature 506, 480-483.

High spatial resolution U-Pb geochronology and Pb isotope geochemistry of magnetite-apatite ore from the Pea Ridge iron oxide-apatite deposit, St. Francois Mountains, southeast Missouri, USA

USGS Publications Warehouse

Neymark, Leonid; Holm-Denoma, Christopher S.; Pietruszka, Aaron; Aleinikoff, John N.; Fanning, C. Mark; Pillers, Renee M.; Moscati, Richard J.

2016-01-01

The Pea Ridge iron oxide-apatite (IOA) deposit is one of the major rhyolite-hosted magnetite deposits of the St. Francois Mountains terrane, which is located within the Mesoproterozoic (1.5–1.3 Ga) Granite-Rhyolite province in the U.S. Midcontinent. Precise and accurate determination of the timing and duration of oreforming processes in this deposit is crucial for understanding its origin and placing it within a deposit-scale and regional geologic context. Apatite and monazite, well-established U-Pb mineral geochronometers, are abundant in the Pea Ridge orebody. However, the potential presence of multiple generations of dateable minerals, processes of dissolution-reprecipitation, and occurrence of micrometer-sized intergrowths and inclusions complicate measurements and interpretations of the geochronological results. Here, we employ a combination of several techniques, including ID-TIMS and high spatial resolution geochronology of apatite and monazite using LA-SC-ICPMS and SHRIMP, and Pb isotope geochemistry of pyrite and magnetite to obtain the first direct age constraints on the formation and alteration history of the Pea Ridge IOA deposit. The oldest apatite TIMS 207Pb*/206Pb* dates are 1471 ± 1 and 1468 ± 1 Ma, slightly younger than (but within error of) the ~1474 to ~1473 Ma U-Pb zircon ages of the host rhyolites. Dating of apatite and monazite inclusions within apatite provides evidence for at least one younger metasomatic event at ~1.44 Ga, and possibly multiple superimposed metasomatic events between 1.47 and 1.44 Ga. Lead isotop analyses of pyrite show extremely radiogenic 206Pb/204Pb ratios up to ~80 unsupported by in situ U decay. This excess radiogenic Pb in pyrite may have been derived from the spatially associated apatite as apatite recrystallized several tens of million years after its formation. The low initial 206Pb/204Pb ratio of ~16.5 and 207Pb/204Pb ratio of ~15.4 for individual magnetite grains indicate closed U-Pb system behavior in this mineral and are consistent with derivation of the Pb from a mantle-like source.

In situ SIMS U-Pb dating of hydrothermal rutile: reliable age for the Zhesang Carlin-type gold deposit in the golden triangle region, SW China

NASA Astrophysics Data System (ADS)

Pi, Qiaohui; Hu, Ruizhong; Xiong, Bin; Li, Qiuli; Zhong, Richen

2017-12-01

The contiguous region between Guangxi, Guizhou, and Yunnan, commonly referred to as the Golden Triangle region in SW China, hosts many Carlin-type gold deposits. Previously, the ages of the gold mineralization in this region have not been well constrained due to the lack of suitable minerals for radiometric dating. This paper reports the first SIMS U-Pb age of hydrothermal rutile crystals for the Zhesang Carlin-type gold deposit in the region. The hydrothermal U-bearing rutile associated with gold-bearing sulfides in the deposit yields an U-Pb age of 213.6 ± 5.4 Ma, which is within the range of the previously reported arsenopyrite Re-Os isochron ages (204 ± 19 to 235 ± 33 Ma) for three other Carlin-type gold deposits in the region. Our new and more precise rutile U-Pb age confirms that the gold mineralization was contemporaneous with the Triassic W-Sn mineralization and associated granitic magmatism in the surrounding regions. Based on the temporal correlation, we postulate that coeval granitic plutons may be present at greater depths in the Golden Triangle region and that the formation of the Carlin-type gold deposits is probably linked to the coeval granitic magmatism in the region. This study clearly demonstrates that in situ rutile U-Pb dating is a robust tool for the geochronogical study of hydrothermal deposits that contain hydrothermal rutile.

Mercerized mesoporous date pit activated carbon-A novel adsorbent to sequester potentially toxic divalent heavy metals from water.

PubMed

Aldawsari, Abdullah; Khan, Moonis Ali; Hameed, B H; Alqadami, Ayoub Abdullah; Siddiqui, Masoom Raza; Alothman, Zeid Abdullah; Ahmed, A Yacine Badjah Hadj

2017-01-01

A substantive approach converting waste date pits to mercerized mesoporous date pit activated carbon (DPAC) and utilizing it in the removal of Cd(II), Cu(II), Pb(II), and Zn(II) was reported. In general, rapid heavy metals adsorption kinetics for Co range: 25-100 mg/L was observed, accomplishing 77-97% adsorption within 15 min, finally, attaining equilibrium in 360 min. Linear and non-linear isotherm studies revealed Langmuir model applicability for Cd(II) and Pb(II) adsorption, while Freundlich model was fitted to Zn(II) and Cu(II) adsorption. Maximum monolayer adsorption capacities (qm) for Cd(II), Pb(II), Cu(II), and Zn(II) obtained by non-linear isotherm model at 298 K were 212.1, 133.5, 194.4, and 111 mg/g, respectively. Kinetics modeling parameters showed the applicability of pseudo-second-order model. The activation energy (Ea) magnitude revealed physical nature of adsorption. Maximum elution of Cu(II) (81.6%), Zn(II) (70.1%), Pb(II) (96%), and Cd(II) (78.2%) were observed with 0.1 M HCl. Thermogravimetric analysis of DPAC showed a total weight loss (in two-stages) of 28.3%. Infra-red spectral analysis showed the presence of carboxyl and hydroxyl groups over DPAC surface. The peaks at 820, 825, 845 and 885 cm-1 attributed to Zn-O, Pb-O, Cd-O, and Cu-O appeared on heavy metals saturated DPAC, confirmed their binding on DPAC during the adsorption.

210Po/210Pb Activity Ratios as a Possible `Dating Tool' of Ice Cores and Ice-rafted Sediments from the Western Arctic Ocean - Preliminary Results

NASA Astrophysics Data System (ADS)

Krupp, K.; Baskaran, M. M.

2016-02-01

We have collected and analyzed a suite of surface snow samples, ice cores, ice-rafted sediments (IRS) and aerosol samples from the Western Arctic for Po-210 and Pb-210 to examine the extent of disequilibrium between this pair to possibly use 210Po/210Pb activity ratio to date different layers of ice cores and time of incorporation of ice-rafted sediments into the sea ice. We have earlier reported that the activity concentrations of 210Pb in IRS vary over an order of magnitude and it is 1-2 orders of magnitude higher than that of the benthic sediments (1-2 dpm/g in benthic sediments compared to 25 to 300 dpm/g in IRS). In this study, we have measured 210Po/210Pb activity ratios in aerosols from the Arctic Ocean to constrain the initial 210Po/210Pb ratio at the time of deposition during precipitation. The 210Po activity concentration in recent snow is compared to surface ice samples. The `age' of IRS incorporation can be calculated as follows: [210Po]measured = [210Po]initial + [210Pb] (1 - exp(-λt)) (1) where λ is the decay constant of 210Po, 138.4 days, and `t' is the in-growth time period. From this equation, `t' can be calculated as follows: t = (-1/λ) [ln (1- ((210Po/210Pb)measured - (210Po/210Pb)initial)] (2) The assumption involved in this approach are: i) there is no preferential uptake of 210Po (highly biogenic - S group); and iii) both 210Po and 210Pb remain as closed system. The calculated age using equation (2) will be discussed and presented.

Provenance of the lower Miocene of the Gulf of Mexico from detrital zircon double dating

NASA Astrophysics Data System (ADS)

xu, J.

2013-12-01

The lower Miocene interval of the Gulf of Mexico (GOM) has recently gained increasing attention from oil and gas industry due to its hydrocarbon potential below the salt canopy. However, it has been less well studied than both the underlying Oligocene and overlying middle Miocene strata. The lower Miocene worldwide is a transitional period of tectonic, climatic, and oceanographic change. In particular, it is a period of major tectonic reorganization in the western interior of North America (Rocky Mountains), involving a shift from the Oligocene thermal phase, with abundant volcanic activity recorded in the thick Frio/Vicksburg succession of the GOM, to the Miocene Basin-Range extensional phase. Climatic conditions also changed from a relatively arid Oligocene to wetter Miocene, resulting in increased sediment yields from exhumed tectonic structures. Previous provenance studies used proportions of quartz, feldspar and lithic fragments and consideration of likely river courses through known paleogeomorphological elements. Only limited detrital zircon (DZ) U-Pb studies on Paleocene strata have been undertaken and there has been no previous U-Pb and (U-Th)/He double dating in the GOM. In this study we apply the latest analytical approaches, such as DZ U-Pb dating to gain robust source terranes ages and more fully elucidate the complex sediment provenance and dispersal history of GOM. We also employ DZ (U-Th)/He (ZHe) dating, combined with DZ U-Pb, to not only define sedimentary provenance but also the exhumation histories of detrital source regions. Samples of lower Miocene outcrop exposures in Texas and Louisiana have been collected to discriminate the varied tectonic and drainage system changes across the basin in lateral. In addition, samples from the Eocene, Oligocene and middle Miocene have been obtained to reveal vertical shift of source terranes contributions. Our initial age data show detrital zircons of lower Miocene sediments come from a wide range of source terranes including a large populations from the western interior of North America (Rocky Mountains), Grenville, Mid-Continent, and Yavapai-Mazatzal provinces, with smaller populations from the Appalachian-Ouachita, Wyoming or Superior regions. Based on U-Pb dating results, we will carry out (U-Th)/He dating on selected zircons to reveal the detailed exhumation histories of the sediment source regions. Using the dual criteria of DZ crystallization age (U-Pb) and cooling age (U-Th/He) to constrain provenance will enable us to generate rigorous reconstructions of the lower Miocene depositional systems from source terrane to deep-water sink for this key transitional period in geologic history.

Cr-rich rutile: A powerful tool for diamond exploration

NASA Astrophysics Data System (ADS)

Malkovets, V. G.; Rezvukhin, D. I.; Belousova, E. A.; Griffin, W. L.; Sharygin, I. S.; Tretiakova, I. G.; Gibsher, A. A.; O'Reilly, S. Y.; Kuzmin, D. V.; Litasov, K. D.; Logvinova, A. M.; Pokhilenko, N. P.; Sobolev, N. V.

2016-11-01

Mineralogical studies and U-Pb dating have been carried out on rutile included in peridotitic and eclogitic garnets from the Internatsionalnaya pipe, Mirny field, Siberian craton. We also describe a unique peridotitic paragenesis (rutile + forsterite + enstatite + Cr-diopside + Cr-pyrope) preserved in diamond from the Mir pipe, Mirny field. Compositions of rutile from the heavy mineral concentrates of the Internatsionalnaya pipe and rutile inclusions in crustal almandine-rich garnets from the Mayskaya pipe (Nakyn field), as well as from a range of different lithologies, are presented for comparison. Rutile from cratonic mantle peridotites shows characteristic enrichment in Cr, in contrast to lower-Cr rutile from crustal rocks and off-craton mantle. Rutile with Cr2O3 > 1.7 wt% is commonly derived from cratonic mantle, while rutiles with lower Cr2O3 may be both of cratonic and off-cratonic origin. New analytical developments and availability of standards have made rutile accessible to in situ U-Pb dating by laser ablation ICP-MS. A U-Pb age of 369 ± 10 Ma for 9 rutile grains in 6 garnets from the Internatsionalnaya pipe is consistent with the accepted eruption age of the pipe (360 Ma). The equilibrium temperatures of pyropes with rutile inclusions calculated using Ni-in-Gar thermometer range between 725 and 1030 °C, corresponding to a depth range of ca 100-165 km. At the time of entrainment in the kimberlite, garnets with Cr-rich rutile inclusions resided at temperatures well above the closure temperature for Pb in rutile, and thus U-Pb ages on mantle-derived rutile most likely record the emplacement age of the kimberlites. The synthesis of distinctive rutile compositions and U-Pb dating opens new perspectives for using rutile in diamond exploration in cratonic areas.

Zircon U-Pb and molybdenite Re-Os geochronology and Sr-Nd-Pb-Hf isotopic constraints on the genesis of the Xuejiping porphyry copper deposit in Zhongdian, Northwest Yunnan, China

NASA Astrophysics Data System (ADS)

Leng, Cheng-Biao; Zhang, Xing-Chun; Hu, Rui-Zhong; Wang, Shou-Xu; Zhong, Hong; Wang, Wai-Quan; Bi, Xian-Wu

2012-10-01

The Xuejiping porphyry copper deposit is located in northwestern Yunnan Province, China. Tectonically, it lies in the southern part of the Triassic Yidun island arc. The copper mineralization is mainly hosted in quartz-dioritic and quartz-monzonitic porphyries which intruded into clastic-volcanic rocks of the Late Triassic Tumugou Formation. There are several alteration zones including potassic, strong silicific and phyllic, argillic, and propylitic alteration zones from inner to outer of the mineralized porphyry bodies. The ages of ore-bearing quartz-monzonitic porphyry and its host andesite are obtained by using the zircon SIMS U-Pb dating method, with results of 218.3 ± 1.6 Ma (MSWD = 0.31, N = 15) and 218.5 ± 1.6 Ma (MSWD = 0.91, N = 16), respectively. Meanwhile, the molybdenite Re-Os dating yields a Re-Os isochronal age of 221.4 ± 2.3 Ma (MSWD = 0.54, N = 5) and a weighted mean age of 219.9 ± 0.7 Ma (MSWD = 0.88). They are quite in accordance with the zircon U-Pb ages within errors. Furthermore, all of them are contemporary with the timing of the Garzê-Litang oceanic crust subduction in the Yidun arc. Therefore, the Xuejiping deposit could be formed in a continental margin setting. There are negative ɛNd(t) values ranging from -3.8 to -2.1 and relatively high initial 87Sr/86Sr ratios from 0.7051 to 0.7059 for the Xuejiping porphyries and host andesites. The (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t values of the Xuejiping porphyries and host andesites vary from 17.899 to 18.654, from 15.529 to 15.626, and from 37.864 to 38.52, respectively, indicative of high radiogenic Pb isotopic features. In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS exhibit that there are quite uniform and slightly positive ɛHf(t) values ranging from -0.2 to +3.2 (mostly between 0 and +2), corresponding to relatively young single-stage Hf model ages from 735 Ma to 871 Ma. These isotopic features suggest that the primary magmas of the Xuejiping porphyries and their host andesites were mainly derived from a metasomatized mantle, with contamination of about 5-10% crustal rocks during ascending. Comparing with typical porphyry Cu deposits, the Xuejiping porphyry Cu deposit is distinct by strong silicific and phyllic alteration and major stockwork veining mineralization in the ore-bearing porphyries, but lack of pervasive potassic alteration and disseminated mineralization. This indicates that there could be more prospective Cu resources in the Xuejiping ore district.

NanoSIMS U-Pb dating of hydrothermally altered monazite: Constraints on the Timing of LaoZaiWan Carlin-type gold deposit in the golden triangle region, SW China

NASA Astrophysics Data System (ADS)

PI, Q.

2017-12-01

Abstract: Direct dating of Carlin-type Au deposits was restricted due to the absence of a geochronometer. Back-scattered electron (BSE) imaging and X-ray element mapping of monazite in gold-rich ore samples from the LaoZaiWan Au deposit in SW China, reveal the presence of distinct, high-Th cores surrounded by low-Th, inclusion-rich rims. The monazite grain is considered to be the product of fluid-aided coupled dissolution-reprecipitation during Au mineralization via prograde metamorphic reactions. We present results of in situ NonSIMS U-Pb dating applied to the rims of monazite . NonSIMS U-Pb age of hydrothermal monazite gave ages of 228 ± 9 Ma(2σ) and 230 ± 16 Ma(2σ) for LaoZaiWan Au deposit. These ages are interpreted as Au mineralization ages, which consistent with the Re-Os age of arsenopyite for JinYa Au deposit, the U-Pb age of rutile for and 40Ar-39Ar age of sericite for Zhesang Au deposit. We postulate that the formation of the Carlin-type Au deposits in the Golden Triangle region was triggered by the Indosinian Orogen, related to collision of the Indochina Block with South China Block.

Concordant ages for the Lava Creek Tuff from high-spatial-resolution U-Pb dating of zircon rim faces and single-crystal sanidine 40Ar/39Ar dating

NASA Astrophysics Data System (ADS)

Matthews, N. E.; Vazquez, J. A.; Calvert, A. T.

2013-12-01

The last great explosive supereruption from the Yellowstone Plateau formed present-day Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff (LCT). The LCT eruption blanketed much of the western United States in ash, and consequently is a key chronostratigraphic marker bed for delimiting Quaternary uplift rates, the age of middle Pleistocene glacial and pluvial deposits, and tephra correlation in North America. Previous 40Ar/39Ar dating of the two mineralogically distinct LCT members (A & B) yield ages ranging from ca. 600 ka (Gansecki et al., 1998) to ca. 640 ka (Lanphere et al., 2002). To resolve the timing of eruption and crystallization timescale for the LCT magma, we dated both LCT members using a dual-method approach as follows: (1) ion microprobe (SHRIMP-RG) U-Pb dating and trace-element characterization of the final few micrometers of zircon crystallization by analysis of unpolished rims on indium-mounted crystals, and dating of the onset of zircon crystallization by traditional analysis of sectioned crystal interiors, and (2) laser-fusion 40Ar/39Ar dating of single sanidine crystals from bulk LCT ignimbrite and pumice. The unpolished rims of zircon from LCT members A & B yield indistinguishable ages, with a mean age of 621.8 × 2.5 ka (1σ) after correction for initial 230Th disequilibrium as constrained by ion-probe analyses of LCT melt inclusions. Single sanidine crystals from LCT-B yield a mean age of 624.9 × 2.6 ka (FCT=28.17 Ma) that is indistinguishable from the zircon rim ages for both members. These results indicate that LCT members A & B erupted over a geologically brief interval, which is supported by the direct and gradational contact of their equivalent fallout in distal lacustrine deposits and a lack of field evidence for a significant time-break between the LCT A & B in proximal deposits (Christiansen, 2001), but contrasts with older Yellowstone ignimbrite (e.g., Huckleberry Ridge) that may have erupted as multiple pulses over tens of kyr (Ellis et al., 2012). Both LCT members contain zircon whose interiors yield U-Pb ages that are mostly ca. 40 kyr older than their rims, suggesting a short timescale for assembly of the LCT magma chamber relative to some other voluminous bodies of silicic magma (e.g., Fish Canyon). Trace-element concentrations in zircon from Members A and B appear diagnostic, with the former containing higher U and REE concentrations. Our concordant results from U-Pb and 40Ar/39Ar dating indicating a ca. 625 ka age for the LCT eruption are supported by the stratigraphic position of LCT-B tephra at or near the top of Great Basin pluvial lake bed sequences associated with Marine Isotope Stage 16, whose termination is astronomically dated at 621 ka. Christiansen, 2001, USGS Prof. Pap. 729-G; Ellis et al., 2012, Quat Geochron 9: 31-41; Gansecki et al., 1998, Geology 26(4): 343-346; Lanphere et al., 2002, GSA Bull. 114(5): 559-568.

Late Proterozoic charnockites in Orissa, India: A U-Pb and Rb-Sr isotopic study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aftalion, M.; Bowes, D.R.; Dash, B.

1988-11-01

Charnockite formation in the Angul district of Orissa took place between 1088 + 26/ -17 Ma, the U-Pb zircon upper intercept crystallization age of a leptynite neosome, and 957 +8/ -4-956 {plus minus} 4 Ma, the U-Pb zircon-monazite upper intercept and U-Pb monazite crystallization ages of a granite. Confirmation of the Proterozoic age of the charnockites is given by (1) a U-Pb zircon upper intercept 1159 + 59/ -30 Ma age and a Rb-Sr whole-rock 1080 {plus minus} 65 Ma age for an augen gneiss which pre-dates the leptynite, and (2) U-Pb monazite ages of 973 {plus minus} 5,964 {plusmore » minus} 4, and 953 {plus minus} 4 Ma for a gray quartzofeldspathic gneiss, the augen gneiss, and the leptynite, respectively: these late Proterozoic dates are interpreted as representing ages recorded during charnockitization. The ca. 950-980 Ma charnockite- and granite-forming events are related to the evolution of mantle-derived, CO{sub 2}-bearing basic magma emplaced into the deeper levels of an extensional tectonic-transcurrent fault regime. The ca. 1100-1150 Ma tectonothermal and igneous events represent compressional tectonism in reactivated crystalline basement in the late mid-Proterozoic Eastern Ghats orogenic belt.« less

A combined geochronological approach to investigating long lived granite magmatism, the Shap granite, UK

NASA Astrophysics Data System (ADS)

Miles, A. J.; Woodcock, N. H.

2018-04-01

With the advent of more precise dating methods, it has become apparent that zircon dates from granite plutons frequently indicate older emplacement ages than other dating methods. Here we attempt to reconcile a number of dating methods from the c. 5 km2 Caledonian Shap granite, Northern England. The results reveal a more complex and protracted evolution than indicated by application of any single dating method. Zircon U-Pb dates give a weighted mean age of 415.6 ± 1.4 (2σ) Ma. A mafic enclave, dated at 412 ± 2 (2σ) Ma (revised Rb-Sr feldspar age from Davidson et al., 2005), contains resorbed K-feldspar and zircon crystals scavenged from the host crystal mush. These ages are at odds with field relations in the thermal aureole that suggest final emplacement at approximately 404 Ma or later during Acadian deformation. Previously reported Re-Os ages on molybdenites associated with magmatic fluids, have given ages of 405.2 ± 1.8 (2σ) Ma (Selby et al., 2008) and confirm the overlap of at least some magmatic activity with Acadian deformation. A similar emplacement age is supported by Rb-Sr whole-rock-mineral and biotite K-Ar dates when adjusted for revised decay constants (402 ± 3 Ma and 401 ± 7 Ma, respectively, Wadge et al., 1978). The lower closure temperatures of these systems relative to the U-Pb system in zircon means that they are more likely to record the timing of final granite emplacement. These data suggest that most zircons grew before final granite emplacement, by about 10 Ma on average. We suggest that the majority of zircon crystals record pre-emplacement magmatic activity within a deeper part of the system. Mafic enclaves and their scavenged cargo of crystals record the assembly of a mid-crustal batholith where crystals remained at least locally mobile at 412 Ma. Gravity data support the existence of an extensive, 1500 km2 intrusive body, originally at about 15 km depth beneath Shap. This batholith is likely to have remained below the granite solidus for much of its existence due to conductive heat loss, but episodic influxes of silicic magma between c. 412 and 405 Ma are thought to have enabled periods of rejuvenation. These influxes are recorded by complex compositional zoning patterns within K-feldspar megacrysts. The Shap granite itself is likely to represent a rejuvenated crystal slurry, emplaced as a cylindrical cupola above the main magma body during Acadian transpression. This study highlights the importance of integrating different dating techniques and that final emplacement of granites can only be indicated by the youngest zircon ages.

New uppermost Cambrian U-Pb date from Avalonian Wales and age of the Cambrian-Ordovician boundary

USGS Publications Warehouse

Davidek, K.; Landing, E.; Bowring, S.A.; Westrop, S.R.; Rushton, A.W.A.; Fortey, R.A.; Adrain, J.M.

1998-01-01

A crystal-rich volcaniclastic sandatone in the lower Peltura scarabaeoides Zone at Ogof-odi near Criccieth, North Wales, yields a U-Pb zircon age of 491 ?? 1 Ma. This late Late Cambrian date indicates a remarkably young age for the Cambrian-Ordovician boundary whose age must be less than 491 Ma. Hence the revised duration of the post-Placentian (trilobite-bearing) Cambrian indicates that local trilobite zonations allow a biostratigraphic resolution comparble to that provided by Ordovician graptolites and Mesozoic ammonites.

Elemental and Molecular Segregation in Oil Paintings due to Lead Soap Degradation.

PubMed

Chen-Wiegart, Yu-Chen Karen; Catalano, Jaclyn; Williams, Garth J; Murphy, Anna; Yao, Yao; Zumbulyadis, Nicholas; Centeno, Silvia A; Dybowski, Cecil; Thieme, Juergen

2017-09-14

The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques. X-ray fluorescence (XRF) microscopy, quantified with elemental correlation density distribution, showed Pb and Sn segregation in the soap-affected areas. X-ray absorption near edge structure (XANES) around the Pb-L3 absorption edge showed that Pb pigments and Pb soaps can be distinguished while micro-XANES gave further information on the chemical heterogeneity in the paint film. The advantages and limitations of these synchrotron-based techniques are discussed and compared to those of methods routinely used to analyze paint samples. The results presented set the stage for improving the information extracted from samples removed from works of art and for correlating observations in model paint samples to those in the naturally aged samples, to shed light onto the mechanism of soap formation.

Advances and limitations on interpreting the erosional record from isotopic analysis of single detrital mineral grains

NASA Astrophysics Data System (ADS)

Parrish, Randall

2010-05-01

The analysis of provenance of clastic sediments is useful for reconstructing the characteristics and rates of exhumation of source areas, and sometimes placing minimum age constraints on depositional age. Due largely to increased availability and ease of access to LA-ICP-MS instrumentation, the analysis of provenance using single detrital accessory minerals has grown very rapidly over recent years. With this however is a culture of casual users who may not fully appreciate subtleties of measurement and isotope interpretation. The isotopic provenance literature is dominated by zircon-centric studies that use U-Pb dating and Hf isotope measurements of single zircons, but unfortunately an increasing number of these studies appear to lack sufficient understanding of U-Pb and Hf systematics; misleading interpretations are increasingly common. The inherent information contained in detrital accessory minerals is potentially immense, scientifically, but comprehensive interpretations attempting to reconstruct the geological make-up and evolution of sources require dating of multiple types of accessory minerals (i.e. zircon, titanite, monazite, garnet inclusions, micas, allanite, rutile, apatite) by various methods (U-Pb, fission track, Ar-Ar…) at times accompanied by isotope geochemical data (Lu-Hf, Sm-Nd, Rb-Sr) of phases where Sr, Hf, or REE comprise a major element (≥0.5%). Many approaches have been demonstrated but the mix of methodologies needs to be tailored to the problem, in view of the variable effort and expense needed to acquire good datasets. To date there are few comprehensive multi-mineral, multi-isotope system applications, and too many studies that follow a prescriptive cookbook that lacks innovation and fails to address a problem. The field needs to focus effort on the approaches that can solve a problem well rather than doing either just the easy methods or too many methods only moderately well. Zircon studies require strategies that reduce or eliminate discordance, collect sufficient data on each grain to make a robust age interpretation, improve accuracy of data by more attention to standards and uncertainties, can analyze thin overgrowths that reveal the magmatic or metamorphic age, and minimize sample consumption, not an easy task for the vast majority of laboratories doing provenance applications. Detrital monazite, monazite-in garnet, titanite and rutile can reveal much of the higher temperature metamorphic time-temperature path, and coupled U-Pb and fission track studies of single zircon and apatite grains can be useful for determining lower temperature exhumation rates. Isotope geochemistry (Hf-Nd-Sr-O) is more time consuming but can be pivotal to distinguish subtle differences in sources and to test specific hypotheses. Examples of improved methods and applications will be presented to illustrate the presentation.

Dating High Temperature Mineral Fabrics in Lower Crustal Granulite Facies Rocks

NASA Astrophysics Data System (ADS)

Stowell, H. H.; Schwartz, J. J.; Tulloch, A. J.; Klepeis, K. A.; Odom Parker, K.; Palin, M.; Ramezani, J.

2015-12-01

Granulite facies rocks may record strain that provides a record of compressional and/or extensional crustal events in hot orogenic cores and the roots of magmatic arcs. Although the precise timing of these events is important for constructing tectonic histories, it is often difficult to determine due to uncertain relationships between isotopic signatures, mineral growth, and textural features that record strain. In addition, there may be large uncertainties in isotope data due to intracrystalline diffusion and multiple crystallization events. L-S tectonites in lower crustal rocks from Fiordland, NZ record the early stages of extensional collapse of thickened magmatic arc crust. The precise age of these fabrics is important for constraining the timing of extension that led to opening of the Tasman Sea. High temperature granulite facies L-S fabrics in garnet reaction zones (GRZ) border syn- to post-deformational leucosomes. U-Pb zircon, Lu-Hf garnet, and Sm-Nd garnet ages, and trace elements in these phases indicate the complexity of assigning precise and useful ages. Zircon have soccer ball morphology with patchy and sector zoned CL. Zircon dates for igneous host and adjacent GRZ range over ca. 17 Ma. 236U-208Pb LA-ICP-MS are 108-125 Ma, N=124 (host & GRZ); however, chemical abrasion (CA) shifts GRZ dates ca. 2 Ma older. 236U-208Pb SHRIMP-RG dates cluster in 2 groups: 118.5±0.8 Ma, N=23 and 111.0±0.8 Ma, N=6. CA single crystal TIMS dates also fall into 2 groups: 117.6±0.1 Ma, N=4 and 116.6±0.2 Ma N=4. Garnet isochron ages determined from coarse garnet selvages adjacent to leucosomes range from 112.8±2.2 (147Sm-143Nd, 10 pts.) to 114.8±3.5 (177Lu-176Hf, 6 pts.) Ma. Zircon dates from all methods show ranges (>10 Ma) and 2 distinct populations. Host and GRZ zircon cannot be readily distinguished by age, lack younger rims, but have distinct Th/U trends and Eu/Eu* vs. Hf ratios. Difference in zircon trace element composition indicates either early leucosome emplacement or xenocrystic zircon in leucosomes. We conclude that the small number of oldest zircon grains are inherited, older zircon age populations (CA LA-ICP-MS, SHRIMP-RG and TIMS) are near identical ca. 118 Ma and date intrusion, and that the youngest zircon and indistinguishable garnet ages (113-116 Ma) date syn-deformational granulite facies metamorphism.

Baddeleyite in PGE paleoproterozoic layered intrusions on Fennoscandian Shield (Arctic region): significance for timing, duration and continental reconstraction

NASA Astrophysics Data System (ADS)

Bayanova, Tamara; Korchagin, Aleksey; Chachshin, Viktor; Nerovich, Ludmila; Drogobuzhskaya, Svetlana

2017-04-01

Baddeleyite was firstly found and U-Pb dating in PGE layered intrusions of the Fennoscandian Shield in the rock-forming orthopyroxene (Lukkulaisvaara intrusion in Karelia region) and in magmatic zircon from gabbronorite Mt. Generalskaya (Kola region). Real crystals of baddeleyite were separated and U-Pb measured from Fedorovo-Pansky complex in gabbronorites lower part of the Pt-Pd reef intrusion (as first phase 2.50 Ga) and in upper part of Pt-Pd reef in anorthosites (second phase -2.45 Ga) and reflect time interval about 50 Ma of magmatic complex activity. In basite dykes from Cr-Ti-V Imandra lopolith baddeleyite were dating by U-Pb with 2.40 Ga. Therefore total duration time of Kola LIP and magmatic origin of the multimetal deposits are estimated as 100 Ma [1]. New additional isotope Nd-Sr-He data for the WR of the layered PGE intrusions in the Kola-Karelia-Finland big belt more than 500 km reflect EM-1 mantle reservoir. New REE (ELAN- 9000) distributions in the WR and dykes complexes of the Fedorovo-Pansky and Monshegorck Cu-Ni and PGE ore deposits gave OIB, N-MORB and E-MORB primary plume mantle source due to Re-Os data [2]. LA-ICP-MS data of REE investigations in baddeleyite crystals from Monchegorsk ore region yielded 1000 C forming of the grains and high U-Pb closure temperatures compared with zircon. Baddeleyite also primary magmatic minerals in the layered PGE intrusions and dykes complexes from Fennoscandian Shield and U-Pb precise data using artificial 205 Pb spike of the crystals together with time data for different continents gave new important information concerning break up and super continental reconstruction of geological history in paleoproterozoic time [3]. Acknowledgements: Many thanks to G.Wasserburg for 205 Pb artificial spike, J. Ludden, F. Corfu, V. Todt and U. Poller for assistance in the establishing of the U-Pb for single zircon and baddeleyite. All studies are supported by RFBR 16-05-00305. All investigations are devoted to memory of academician RAS F.P. Mitrofanov due to whom baddeleyite was found, separation and studied by U-Pb (ID-TIMS and LA-ICP-MS) methods. References: [1] Bayanova et al. (2014), INTECH, 143-193; [2] Yang Sheng-Hong et. al. (2016), Mineralium Deposita 51, 1055-1073; [3] Ernst R. Large igneous provinces. (2016), London, 500

A comparison of lead pollution record in Sphagnum peat with known historical Pb emission rates in the British Isles and the Czech Republic

NASA Astrophysics Data System (ADS)

Novak, Martin; Erel, Yigal; Zemanova, Leona; Bottrell, Simon H.; Adamova, Marie

Vertical Pb concentration gradients and isotope ratios ( 206Pb/ 207Pb, 208Pb/ 207Pb) are reported for five 210Pb-dated Sphagnum peat profiles. The studied peat bogs are in the British Isles (Thorne Moors, England; Mull, Scotland; and Connemara, Eire) and central Europe (Ocean, northern Czech Republic; Rybarenska slat, southern Czech Republic). Both the U.K. and the Czech Republic experienced maximum Pb emissions from Ag-Pb smelting around 1880. Pb emissions from coal burning peaked in 1955 in the U.K. and in the 1980s in the Czech Republic. In both countries, use of alkyl-lead additives to gasoline resulted in large Pb emissions between 1950 and 2000. We hypothesized that peaks in Pb emissions from smelting, coal burning and gasoline burning, respectively, should be mirrored in the peat profiles. However, a more complicated pattern emerged. Maximum annual Pb accumulation rates occurred in 1870 at Ocean, 1940 at Thorne Moors, 1988 at Rybarenska slat, and 1990 at Mull and Connemara. Atmospheric Pb inputs decreased in the order Thorne Moors ≥ Ocean > Rybarenska slat > Mull > Connemara. The Ocean bog was unique in the central European region in that its maximum Pb pollution dated back to the 19th century and coincided with maximum Pb smelting at Freiberg and Pribram. In contrast, numerous previously studied sites showed no Pb accumulation maximum in the 19th century, but increasing pollution until the 1980s. It remains unclear why Ocean did not record the regional peak in Pb emissions caused by high coal and gasoline burning around 1980, while an array of nearby bogs studied previously did record the 1980 coal/gasoline peak, but no 1880 smelting peak. Mean 206Pb/ 207Pb ratios of potential pollution sources were 1.07 and 1.11 for gasoline, 1.17 and 1.17 for local ores, and 1.18 and 1.19 for coal in the U.K. and the Czech Republic, respectively. The calculated percentages of gasoline-derived Pb in peat (≤55% for the British Isles and ≤63% for the Czech Republic) were surprisingly low. An explanation for the low percentage of gasoline-derived Pb in peat can be more easily found for the Czech sites (until 1989 Czechoslovakia was the third largest lignite producer in the world). Regional differences in deposition rates of gasoline-derived Pb in the U.K. need further study.

Allanite age-dating: Non-matrix-matched standardization in quadrupole LA-ICP-MS

NASA Astrophysics Data System (ADS)

Burn, M.; Lanari, P.; Pettke, T.; Engi, M.

2014-12-01

Allanite Th-U-Pb age-dating has recently been found to be powerful in unraveling the timing of geological processes such as the metamorphic dynamics in subduction zones and crystallization velocity of magmas. However, inconsistencies among analytical techniques have raised doubts about the accuracy of allanite age data. Spot analysis techniques such as LA-ICP-MS are claimed to be crucially dependent on matrix-matched standards, the quality of which is variable. We present a new approach in LA-ICP-MS data reduction that allows non-matrix-matched standardization via well constrained zircon reference materials as primary standards. Our data were obtained using a GeoLas Pro 193 nm ArF excimer laser ablation system coupled to an ELAN DRC-e quadrupole ICP-MS. We use 32 μm and 24 μm spot sizes; laser operating conditions of 9 Hz repetition rate and 2.5 J/cm2 fluence have proven advantageous. Matrix dependent downhole fractionation evolution is empirically determined by analyzing 208Pb/232Th and 206Pb/238U and applied prior to standardization. The new data reduction technique was tested on three magmatic allanite reference materials (SISSb, CAPb, TARA); within error these show the same downhole fractionation evolution for all allanite types and in different analytical sessions, provided measurement conditions remain the same. Although the downhole evolution of allanite and zircon differs significantly, a link between zircon and allanite matrix is established by assuming CAPb and TARA to be fixed at the corresponding reference ages. Our weighted mean 208Pb/232Th ages are 30.06 ± 0.22 (2σ) for SISSb, 275.4 ± 1.3 (2σ) for CAPb, and 409.9 ± 1.8 (2σ) for TARA. Precision of single spot age data varies between 1.5 and 8 % (2σ), dependent on spot size and common lead concentrations. Quadrupole LA-ICP-MS allanite age-dating has thus similar uncertainties as do other spot analysis techniques. The new data reduction technique is much less dependent on quality and homogeneity of allanite standard reference materials. This method of correcting for matrix-dependent downhole fractionation evolution opens new possibilities in the field of LA-ICP-MS data acquisition, e.g. the use of a NIST standard glass to date all material types given a set of well constrained reference materials.

Sediment radioisotope dating across a stratigraphic discontinuity in a mining-impacted lake.

PubMed

McDonald, C P; Urban, N R

2007-01-01

Application of radioisotope sediment dating models to lakes subjected to large anthropogenic sediment inputs can be problematic. As a result of copper mining activities, Torch Lake received large volumes of sediment, the characteristics of which were dramatically different from those of the native sediment. Commonly used dating models (CIC-CSR, CRS) were applied to Torch Lake, but assumptions of these methods are violated, rendering sediment geochronologies inaccurate. A modification was made to the CRS model, utilizing a distinct horizon separating mining from post-mining sediment to differentiate between two focusing regimes. (210)Pb inventories in post-mining sediment were adjusted to correspond to those in mining-era sediment, and a sediment geochronology was established and verified using independent markers in (137)Cs accumulation profiles and core X-rays.

Ion-probe U–Pb dating of authigenic and detrital opal from Neogene-Quaternary alluvium

USGS Publications Warehouse

Neymark, Leonid; Paces, James B.

2013-01-01

Knowing depositional ages of alluvial fans is essential for many tectonic, paleoclimatic, and geomorphic studies in arid environments. The use of U–Pb dating on secondary silica to establish the age of Neogene-Quaternary clastic sediments was tested on samples of authigenic and detrital opal and chalcedony from depths of ∼25 to 53 m in boreholes at Midway Valley, Nevada. Dating of authigenic opal present as rinds on rock clasts and in calcite/silica cements establishes minimum ages of alluvium deposition; dating of detrital opal or chalcedony derived from the source volcanic rocks gives the maximum age of sediment deposition.Materials analyzed included 12 samples of authigenic opal, one sample of fracture-coating opal from bedrock, one sample of detrital opal, and two samples of detrital chalcedony. Uranium–lead isotope data were obtained by both thermal ionization mass spectrometry and ion-microprobe. Uranium concentrations ranged from tens to hundreds of μg/g. Relatively large U/Pb allowed calculation of 206Pb/238U ages that ranged from 1.64±0.36 (2σ) to 6.16±0.50 Ma for authigenic opal and from 8.34±0.28 to 11.2±1.3 Ma for detrital opal/chalcedony. Three samples with the most radiogenic Pb isotope compositions also allowed calculation of 207Pb/235U ages, which were concordant with 206Pb/238U ages from the same samples.These results indicate that basin development at Midway Valley was initiated between about 8 and 6 Ma, and that the basin was filled at long-term average deposition rates of less than 1 cm/ka. Because alluvium in Midway Valley was derived from adjacent highlands at Yucca Mountain, the low rates of deposition determined in this study may imply a slow rate of erosion of Yucca Mountain. Volcanic strata underlying the basin are offset by a number of buried faults to a greater degree than the relatively smooth-sloping bedrock/alluvium contact. These geologic relations indicate that movement on most faults ceased prior to erosional planation and burial. Therefore, ages of the authigenic opal from basal alluvium indicate that the last movement on buried faults was older than about 6 Ma.

CONCH: A Visual Basic program for interactive processing of ion-microprobe analytical data

NASA Astrophysics Data System (ADS)

Nelson, David R.

2006-11-01

A Visual Basic program for flexible, interactive processing of ion-microprobe data acquired for quantitative trace element, 26Al- 26Mg, 53Mn- 53Cr, 60Fe- 60Ni and U-Th-Pb geochronology applications is described. Default but editable run-tables enable software identification of secondary ion species analyzed and for characterization of the standard used. Counts obtained for each species may be displayed in plots against analysis time and edited interactively. Count outliers can be automatically identified via a set of editable count-rejection criteria and displayed for assessment. Standard analyses are distinguished from Unknowns by matching of the analysis label with a string specified in the Set-up dialog, and processed separately. A generalized routine writes background-corrected count rates, ratios and uncertainties, plus weighted means and uncertainties for Standards and Unknowns, to a spreadsheet that may be saved as a text-delimited file. Specialized routines process trace-element concentration, 26Al- 26Mg, 53Mn- 53Cr, 60Fe- 60Ni, and Th-U disequilibrium analysis types, and U-Th-Pb isotopic data obtained for zircon, titanite, perovskite, monazite, xenotime and baddeleyite. Correction to measured Pb-isotopic, Pb/U and Pb/Th ratios for the presence of common Pb may be made using measured 204Pb counts, or the 207Pb or 208Pb counts following subtraction from these of the radiogenic component. Common-Pb corrections may be made automatically, using a (user-specified) common-Pb isotopic composition appropriate for that on the sample surface, or for that incorporated within the mineral at the time of its crystallization, depending on whether the 204Pb count rate determined for the Unknown is substantially higher than the average 204Pb count rate for all session standards. Pb/U inter-element fractionation corrections are determined using an interactive log e-log e plot of common-Pb corrected 206Pb/ 238U ratios against any nominated fractionation-sensitive species pair (commonly 238U 16O +/ 238U +) for session standards. Also displayed with this plot are calculated Pb/U and Pb/Th calibration line regression slopes, y-intercepts, calibration uncertainties, standard 204Pb- and 208Pb-corrected 207Pb/ 206Pb dates and other parameters useful for assessment of the calibration-line data. Calibrated data for Unknowns may be automatically grouped according to calculated date and displayed in color on interactive Wetherill Concordia, Tera-Wasserburg Concordia, Linearized Gaussian ("Probability Paper") and Gaussian-summation probability density diagrams.

Intercomparison of Pb-210, Cs-137, Pu-239,240 and C-14-Based Chronologies of Recent Sediments - Problems and Challenges

NASA Astrophysics Data System (ADS)

Baskaran, M. M.

2016-12-01

Short-lived naturally-occurring Pb-210 and anthropogenically-delivered Cs-137 are the two most extensively utilized chronometers over the time scale of less than a decade to 60 (Cs-137) to 120 yrs (Pb-210) in a variety of environment including terrestrial and aqueous systems and glaciers. Despite all the advances in the field, still major issues, we confront several issues on the robustness of their applications in these environments. Those include: i) how does the temporal and spatial variations of Pb-210 input to an aqueous environment affect the Pb-210 chronology? ii) how well we are able to quantify the multiple source inputs (atmospheric fallout, watershed erosional input, production of Pb-210 from the decay of SGD-derived Rn-222 and Ra-226, etc); iii) How well are we able to sort out a number of processes that affect the vertical profiles of both Cs-137 and Pb-210 which include sediment mixing (biological and/or physical), sediment focusing/erosion due to bottom currents and transport of sediments in subsurface environment and post-depositional mobility of Cs-137 and Pb-210. In this presentation, the following case studies will be discussed: 1) where there is excellent as well non-agreement between Pb-210 and Cs-137-based chronologies; 2) agreement between Cs-137-based chronology with historical time-marker from Hg mining, while no chronology obtainable from Pb-210; 3) agreement between five different methods of dating in a reservoir; 4) evidence of Cs-137 diffusion in some of the sediment cores, but not in all cores in a small reservoir; and 5) evidence of long-term remineralization based on a comparison of C-14-based ages with those of Pb-210, Cs-137 and Pu-239,240-based methods. We also show evidence Cs-137 diffusion based on a set of laboratory-based diffusion experiments under different pore water chemical conditions. A brief discussion on time resolution and error estimation on ages will be discussed. The challenges in the field of `Anthropocene geochronology' will be discussed. In view of the recent technological developments in gamma-ray spectrometry and ICPMS and analytical methodology for Pu analysis, the new opportunities to move forward this research area will be presented.

The 230Th correction is the 1st priority for accurate dates of young zircons: U/Th partitioning experiments and measurements

NASA Astrophysics Data System (ADS)

Krawczynski, M.; McLean, N.

2017-12-01

One of the most accurate and useful ways of determining the age of rocks that formed more than about 500,000 years ago is uranium-lead (U-Pb) geochronology. Earth scientists use U-Pb geochronology to put together the geologic history of entire regions and of specific events, like the mass extinction of all non-avian dinosaurs about 66 million years ago or the catastrophic eruptions of supervolcanoes like the one currently centered at Yellowstone. The mineral zircon is often utilized because it is abundant, durable, and readily incorporates uranium into its crystal structure. But it excludes thorium, whose isotope 230Th is part of the naturally occurring isotopic decay chain from 238U to 206Pb. Calculating a date from the relative abundances of 206Pb and 238U therefore requires a correction for the missing 230Th. Existing experimental and observational constraints on the way U and Th behave when zircon crystallizes from a melt are not known precisely enough, and thus currently the uncertainty in dates introduced by they `Th correction' is one of the largest sources of systematic error in determining dates. Here we present preliminary results on our study of actinide partitioning between zircon and melt. Experiments have been conducted to grow zircon from melts doped with U and Th that mimic natural magmas at a range of temperatures, and compositions. Synthetic zircons are separated from their coexisting glass and using high precision and high-spatial-resolution techniques, the abundance and distribution of U and Th in each phase is determined. These preliminary experiments are the beginning of a study that will result in precise determination of the zircon/melt uranium and thorium partition coefficients under a wide variety of naturally occurring conditions. This data will be fit to a multidimensional surface using maximum likelihood regression techniques, so that the ratio of partition coefficients can be calculated for any set of known parameters. The results of this study will reduce the largest source of uncertainty in dating young zircons and improve the accuracy of U-Pb dates, improving our ability to tell time during geologic processes. The attainment of more accurate timing of the geologic timescale is important to geologists of all disciplines, from paleontology to planetary cosmochemistry to geobiology.

Complex Histories of Two Lunar Zircons as Evidenced by their Internal Structures and U-Pb Ages

NASA Technical Reports Server (NTRS)

Pidgeon, R. T.; Nemchin, A. A.; Meyer, Charles

2006-01-01

The U-Pb dating of lunar zircon by ion-microprobe provides a robust technique for investigating the timing of lunar events [1,2]. However, we have now identified two cases where the U-Pb systems in a single zircon show more than one age. These complex zircons provide new opportunities for extending our knowledge on the timing of events in the early history of the Moon.

New zircon (U-Th)/He and U/Pb eruption age for the Rockland tephra, western USA

USGS Publications Warehouse

Coble, Matthew A.; Burgess, Seth; Klemetti, Erik W.

2017-01-01

Eruption ages of a number of prominent Quaternary volcanic deposits remain inaccurately and/or imprecisely constrained, despite their importance as regional stratigraphic markers in paleo-environment reconstruction and as evidence of climate-altering eruptions. Accurately dating volcanic deposits presents challenging analytical considerations, including poor radiogenic yield, scarcity of datable minerals, and contamination of crystal populations by magma, eruption, and transport processes. One prominent example is the Rockland tephra, which erupted from the Lassen Volcanic Center in the southern Cascade arc. Despite a range in published eruption ages from 0.40 to 0.63 Ma, the Rockland tephra is extensively used as a marker bed across the western United States. To more accurately and precisely constrain the age of the Rockland tephra-producing eruption, we report U/Pb crystallization dates from the outermost ∼2 μm of zircon crystal faces (surfaces) using secondary ion mass spectrometry (SIMS). Our new weighted mean 238U/206Pb age for Rockland tephra zircon surfaces is 0.598 ± 0.013 Ma (2σ) and MSWD = 1.11 (mean square weighted deviation). As an independent test of the accuracy of this age, we obtained new (U-Th)/He dates from individual zircon grains from the Rockland tephra, which yielded a weighted mean age of 0.599 ± 0.012 Ma (2σ, MSWD = 5.13). We also obtained a (U-Th)/He age of 0.628 ± 0.014 Ma (MSWD = 1.19) for the Lava Creek Tuff member B, which was analyzed as a secondary standard to test the accuracy of the (U-Th)/He technique for Quaternary tephras, and to evaluate assumptions made in the model-age calculation. Concordance of new U/Pb and (U-Th)/He zircon ages reinforces the accuracy of our preferred Rockland tephra eruption age, and confirms that zircon surface dates sample zircon growth up to the time of eruption. We demonstrate the broad applicability of coupled U/Pb zircon-surface and single-grain zircon (U-Th)/He geochronology to accurate dating of Quaternary tephra, and highlight the challenges and opportunities of this technique.

New zircon (U-Th)/He and U/Pb eruption age for the Rockland tephra, western USA

NASA Astrophysics Data System (ADS)

Coble, Matthew A.; Burgess, Seth D.; Klemetti, Erik W.

2017-09-01

Eruption ages of a number of prominent Quaternary volcanic deposits remain inaccurately and/or imprecisely constrained, despite their importance as regional stratigraphic markers in paleo-environment reconstruction and as evidence of climate-altering eruptions. Accurately dating volcanic deposits presents challenging analytical considerations, including poor radiogenic yield, scarcity of datable minerals, and contamination of crystal populations by magma, eruption, and transport processes. One prominent example is the Rockland tephra, which erupted from the Lassen Volcanic Center in the southern Cascade arc. Despite a range in published eruption ages from 0.40 to 0.63 Ma, the Rockland tephra is extensively used as a marker bed across the western United States. To more accurately and precisely constrain the age of the Rockland tephra-producing eruption, we report U/Pb crystallization dates from the outermost ∼2 μm of zircon crystal faces (surfaces) using secondary ion mass spectrometry (SIMS). Our new weighted mean 238U/206Pb age for Rockland tephra zircon surfaces is 0.598 ± 0.013 Ma (2σ) and MSWD = 1.11 (mean square weighted deviation). As an independent test of the accuracy of this age, we obtained new (U-Th)/He dates from individual zircon grains from the Rockland tephra, which yielded a weighted mean age of 0.599 ± 0.012 Ma (2σ, MSWD = 5.13). We also obtained a (U-Th)/He age of 0.628 ± 0.014 Ma (MSWD = 1.19) for the Lava Creek Tuff member B, which was analyzed as a secondary standard to test the accuracy of the (U-Th)/He technique for Quaternary tephras, and to evaluate assumptions made in the model-age calculation. Concordance of new U/Pb and (U-Th)/He zircon ages reinforces the accuracy of our preferred Rockland tephra eruption age, and confirms that zircon surface dates sample zircon growth up to the time of eruption. We demonstrate the broad applicability of coupled U/Pb zircon-surface and single-grain zircon (U-Th)/He geochronology to accurate dating of Quaternary tephra, and highlight the challenges and opportunities of this technique.

New geochronological history of the Mbuji-Mayi Supergroup (Proterozoic, DRC) through U-Pb and Sm-Nd dating

NASA Astrophysics Data System (ADS)

François, Camille; Baludikay, Blaise K.; Storme, Jean-Yves; Baudet, Daniel; Paquette, Jean-Louis; Fialin, Michel; Debaille, Vinciane; Javaux, Emmanuelle J.

2016-04-01

The Mbuji-Mayi Supergroup, DRC is located between the Archean-Paleoproterozoic Kasai Craton and the Mesoproterozoic Kibaran Belt. This sedimentary sequence, unaffected by regional metamorphism, preserves a large diversity of well-preserved acritarchs (organic-walled microfossils), evidencing the diversification of complex life (early eukaryotes) for the first time in mid-Proterozoic redox stratified oceans of Central Africa (Baludikay et al., in review). This Supergroup is composed of two distinct lithostratigraphic successions (i) BI Group: a lower siliciclastic sequence (ca. 1175 Myr to ca. 882 Myr or ca. 1050 Myr (Cahen, 1954; Holmes & Cahen, 1955; Delpomdor et al., 2013) unconformably overlying the ca. 2.82-2.56 Gyr granitoid Dibaya Complex to the North (Cahen & Snelling; recent notice on DRC geological map); and (ii) BII Group: a poorly age-constrained upper carbonate sequence with sparse shales . Basaltic lavas (including pillow lavas) overlying the Mbuji-Mayi Supergroup were dated around 950 Myr (Cahen et al., 1974; Cahen et al., 1984). To better constraint the age of this Supergroup in the Meso-Neoproterozoic limit, we combine different geochronological methods, in particular on diagenetic minerals such as monazite (Montel et al., 1996; Rasmussen & Muhling, 2007) and xenotime (McNaughton et al., 1999) but also on detrital zircons. For the BI Group, results of in situ U-Pb dating with LA-ICP-MS on monazite, xenotime and zircon (Laboratoire Magmas et Volcans, Clermont-Ferrand) provide ages between 2.9 and 1.2 Gyr for zircons and between 1.4 and 1.03 Gyr for monazites and xenotimes. New results of in situ U-Th-Pb dating of well-crystallized monazites and xenotimes with Electron MicroProbe (Camparis, UPMC, Paris), highlight that some crystals display zonations with an inherited core older than 1125 Myr and diagenetic rims around 1050-1075 Myr. This suggests that the diagenesis of BI Group is younger than 1175 Myr (Delpomdor et al., 2013) and probably around 1030-1075 Myr, coherent with an age on 2 syngenetic galenas around 1055 Myr for the top of BI Group (Cahen, 1954; Holmes & Cahen, 1955). Sm-Nd datings on basaltic pillow lavas overlying the Mbuji-Mayi Supergroup (previously dated around 950 Myr (Cahen et al., 1974; Cahen et al., 1984) are in progress (Laboratoire G-Time, ULB, Bruxelles) to precisely limit in time the end of deposition of this Supergroup.

U-Pb detrital zircon geochronology from the basement of the Central Qilian Terrane: implications for tectonic evolution of northeastern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Liu, Changfeng; Wu, Chen; Zhou, Zhiguang; Yan, Zhu; Jiang, Tian; Song, Zhijie; Liu, Wencan; Yang, Xin; Zhang, Hongyuan

2018-03-01

The Tuolai Group dominates the Central Qilian Terrane, and there are different opinions on the age and tectonic attribute of the Tuolai Group. Based on large-scale geologic mapping and zircon dating, the Tuolai Group is divided into four parts: metamorphic supracrustal rocks, Neoproterozoic acid intrusive rocks, early-middle Ordovician acid intrusive rocks and middle Ordovician basic intrusive rocks. The metamorphic supracrustal rocks are the redefined Tuolai complex-group and include gneiss and schist assemblage by faulting contact. Zircon U-Pb LA-MC-ICP-MS dating was conducted on these samples of gneiss and migmatite from the gneiss assemblage, quartzite, two-mica schist and slate from the schist assemblage. The five detrital samples possess similar age spectra; have detrital zircon U-Pb main peak ages of 1.7 Ga with youngest U-Pb ages of 1150 Ma. They are intruded by Neoproterozoic acid intrusive rocks. Therefore, the Tuolai Group belonging to late Mesoproterozoic and early Neoproterozoic. With this caveat in mind, we believe that U-Pb detrital zircon dating, together with the geologic constraints obtained from this study and early work in the neighboring regions. We suggest that the formation age of the entire crystalline basement rocks of metasedimentary sequence from the Central Qilian Terrane should be constrained between the Late Mesoproterozoic and the Late Neoproterozoic, but not the previous Paleoproterozoic. The basement of the Central Qilian Terrane contains the typical Grenville ages, which indicates the Centre Qilian Terrane have been experienced the Grenville orogeny event.

Age of the moon: An isotopic study of uranium-thorium-lead systematics of lunar samples

USGS Publications Warehouse

Tatsumoto, M.; Rosholt, J.N.

1970-01-01

Concentrations of U, Th, and Pb in Apollo 11 samples studied are low (U. 0.16 to 0.87; Th, 0.53 to 3.4; Pb, 0.29 to 1.7, in ppm) but the extremely radiogenic lead in samples allows radiometric dating. The fine dust and the breccia have a concordant age of 4.66 billion years on the basis of 207Pb/206Pb, 206Pb/238U, 207Pb/235U, and 208Pb/232Th ratios. This age is comparable with the age of meteorites and with the age generally accepted for the earth. Six crystalline and vesicular samples are distinctly younger than the dust and breccia. The 238U/235U ratio is the same as that in earth rocks, and 234U is in radioactive equilibrium with parent 238U.

Enhanced piezoelectricity and high temperature poling effect in (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 ceramics via an ethylene glycol route

NASA Astrophysics Data System (ADS)

Tailor, H. N.; Ye, Z.-G.

2010-05-01

A solution chemical method utilizing ethylene glycol as solvent has been developed to prepare the ceramics of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3[(1-x)PMN-xPT] from a precursor powder that can be pressed and fired in one step to produce high quality ceramics with excellent piezoelectric properties. The ceramics reach a relative density of up to 97% of the theoretical value after direct calcinations. This high density is achieved without the need of additional sintering after calcination which is usually required in conventional solid state syntheses to produce ceramics. The ceramics exhibit a unipolar piezoelectric coefficient d33 of 848 pC/N, which is one of the highest values for any unmodified/untextured binary systems reported to date. Since the piezoelectric properties depend on composition and electric field, the effect of poling conditions was investigated. A critical temperature limit has been found, above which poling can dramatically impair the piezoelectric properties due to a field-induced increase in the monoclinic phase component around the morphotropic phase boundary.

In-Situ U-Pb Dating of Apatite by Hiroshima-SHRIMP: Contributions to Earth and Planetary Science.

PubMed

Terada, Kentaro; Sano, Yuji

2012-01-01

The Sensitive High Resolution Ion MicroProbe (SHRIMP) is the first ion microprobe dedicated to geological isotopic analyses, especially in-situ analyses related to the geochronology of zircon. Such a sophisticated ion probe, which can attain a high sensitivity at a high mass resolution, based on a double focusing high mass-resolution spectrometer, designed by Matsuda (1974), was constructed at the Australian National University. In 1996, such an instrument was installed at Hiroshima University and was the first SHRIMP to be installed in Japan. Since its installation, our focus has been on the in-situ U-Pb dating of the mineral apatite, as well as zircon, which is a more common U-bearing mineral. This provides the possibility for extending the use of in-situ U-Pb dating from determining the age of formation of volcanic, granitic, sedimentary and metamorphic minerals to the direct determination of the diagenetic age of fossils and/or the crystallization age of various meteorites, which can provide new insights into the thermal history on the Earth and/or the Solar System. In this paper, we review the methodology associated with in-situ apatite dating and our contribution to Earth and Planetary Science over the past 16 years.

In-Situ U–Pb Dating of Apatite by Hiroshima-SHRIMP: Contributions to Earth and Planetary Science

PubMed Central

Terada, Kentaro; Sano, Yuji

2012-01-01

The Sensitive High Resolution Ion MicroProbe (SHRIMP) is the first ion microprobe dedicated to geological isotopic analyses, especially in-situ analyses related to the geochronology of zircon. Such a sophisticated ion probe, which can attain a high sensitivity at a high mass resolution, based on a double focusing high mass-resolution spectrometer, designed by Matsuda (1974), was constructed at the Australian National University. In 1996, such an instrument was installed at Hiroshima University and was the first SHRIMP to be installed in Japan. Since its installation, our focus has been on the in-situ U–Pb dating of the mineral apatite, as well as zircon, which is a more common U-bearing mineral. This provides the possibility for extending the use of in-situ U–Pb dating from determining the age of formation of volcanic, granitic, sedimentary and metamorphic minerals to the direct determination of the diagenetic age of fossils and/or the crystallization age of various meteorites, which can provide new insights into the thermal history on the Earth and/or the Solar System. In this paper, we review the methodology associated with in-situ apatite dating and our contribution to Earth and Planetary Science over the past 16 years. PMID:24349912

A Search for Charged Massive Stable Particles at D0

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eads, Michael Terry

2005-08-01

A search for charged massive stable particles has been performed with the D0 detector at the Fermilab Tevatron. The signature is two particles reconstructed as muons, but with speed and invariant mass inconsistent with beam-produced muons. No excess of events is observed and limits are set on the production cross-section for pair-produced stable stau sleptons based on 390 pb -1 of data. Limits vary from 0.06 pb to 0.62 pb, depending on the stau mass, and are the strictest Tevatron limits to date. Mass limits are also set for stable charginos. The limits are 140 GeV/c 2 for a higgsino-likemore » chargino and 174 GeV/c 2 for a gaugino-like chargino. These are currently the best limits to date for stable charginos.« less

Lead contamination of subarctic lakes and its response to reduced atmospheric fallout: can the recovery process be counteracted by the ongoing climate change?

PubMed

Klaminder, Jonatan; Hammarlund, Dan; Kokfelt, Ulla; Vonk, Jorien E; Bigler, Christian

2010-04-01

Can a climate-triggered export of old contaminants from the soil alter the lead (Pb) contaminant burden of subarctic lakes? To address this question, we reconstructed the pollution history of three high latitude lakes situated in a region where a recent climatic shift has occurred. Dated sediment records were used as archives of past Pb inputs to the lakes, where the difference in the (206)Pb/(207)Pb ratio between atmospheric contaminants ((206)Pb/(207)Pb ratio <1.16) and geogenic Pb in the catchment soil ((206)Pb/(207)Pb ratio >1.22) were used to trace fluxes of Pb contaminants. Lead contaminants were found in sediments deposited since Roman times. A significant export of Pb from the soil contaminant pool is indicated in two of the lakes surrounded by near-shore permafrost soils. Here, levels of Pb contaminants and (206)Pb/(207)Pb ratios of sediments deposited after the 1970s appear not to have been strongly affected by the >or=90% reduction in atmospheric deposition rates and increasing (206)Pb/(207)Pb ratios of atmospheric Pb since the 1990s. We concluded that soil processes stimulated by the ongoing climate change at high latitudes might work counteractive to efforts to reduce contaminant levels in subarctic lakes.

Reply to Comment on "Zircon U-Th-Pb dating using LA-ICP-MS: Simultaneous U-Pb and U-Th dating on the 0.1 Ma Toya Tephra, Japan"

NASA Astrophysics Data System (ADS)

Ito, Hisatoshi

2015-04-01

Guillong et al. (2015) mentioned that corrections for abundance sensitivity for 232Th and molecular zirconium sesquioxide ions (Zr2O3+) are critical for reliable determination of 230Th abundances in zircon for LA-ICP-MS analyses. There is no denying that more rigorous treatments are necessary to obtain more reliable ages than those in Ito (2014). However, as shown in Fig. 2 in Guillong et al. (2015), the uncorrected (230Th)/(238U) for reference zircons except for Mud Tank are only 5-20% higher than unity. Since U abundance of Toya Tephra zircons that have U-Pb ages < 1 Ma is in-between that of FCT and Plesovice, the overestimation of 230Th by both abundance sensitivity and molecular interferences is expected to be 5-20% for the Toya Tephra. Moreover Ito (2014) obtained U-Th ages of the Toya Tephra by comparison with Fish Canyon Tuff (FCT) data. Because both the FCT and the Toya Tephra have similar trends of overestimation of 230Th, the effect of overestimation of 230Th to cause overestimation of U-Th age should be cancelled out or negligible. Therefore the pivotal conclusion in Ito (2014) that simultaneous U-Pb and U-Th dating using LA-ICP-MS is possible and useful for Quaternary zircons holds true.

Anomalous Lead Isotopic Composition of Galena and Age of Altered Uranium Minerals: a Case study of Chauli Deposits, Chatkal-Qurama District, Uzbekistan

NASA Astrophysics Data System (ADS)

Chernyshev, I. V.; Golubev, V. N.; Chugaev, A. V.

2017-11-01

The enrichment of lead isotopic composition of nonuranium minerals, in the first place galena in 206Pb and 207Pb, as compared to common lead is a remarkable feature of uranium deposits. The study of such lead isotopic composition anomalous in 206Pb and 207Pb in uranium minerals provides an opportunity for not only identification of superimposed processes resulting in transformation of uranium ores during deposit history but also calculation of age of these processes under certain model assumptions. Galena from the Chauli deposit in the Chatkal-Qurama district, Uzbekistan, a typical representative of hydrothermal uranium deposits associated with domains of Phanerozoic continental volcanism, has been examined with the highprecision (±0.02%) MC-ICP-MS method. Twenty microsamples of galena were taken from polished sections. Six of them are galena hosted in carbonate adjacent to pitchblende spherulites or filling thin veinlets (approximately 60 μm) cutting pitchblende. Isotopically anomalous lead with 206Pb/204Pb and 207Pb/204Pb values reaching 20.462 and 15.743, respectively, has been found in these six microsamples in contrast to another fourteen in which the Pb-Pb characteristics are consistent with common lead. On the basis of these data and with account for the 292 ± 2 Ma age for the Chauli deposit, the age of epigenetic transformation of uranium ores of this deposit has been estimated. During this process, radiogenic lead partly lost from pitchblende was captured into galena. The obtained date is 170 Ma. In the Chatkal-Qurama district, these epigenetic processes are apparently caused by the interaction of uranium minerals with activated underground water under tectonic activity and relief transformation, which took place from the post-Permian (i.e., after the Chauli formation) to the Jurassic period.

Approaches for the accurate definition of geological time boundaries

NASA Astrophysics Data System (ADS)

Schaltegger, Urs; Baresel, Björn; Ovtcharova, Maria; Goudemand, Nicolas; Bucher, Hugo

2015-04-01

Which strategies lead to the most precise and accurate date of a given geological boundary? Geological units are usually defined by the occurrence of characteristic taxa and hence boundaries between these geological units correspond to dramatic faunal and/or floral turnovers and they are primarily defined using first or last occurrences of index species, or ideally by the separation interval between two consecutive, characteristic associations of fossil taxa. These boundaries need to be defined in a way that enables their worldwide recognition and correlation across different stratigraphic successions, using tools as different as bio-, magneto-, and chemo-stratigraphy, and astrochronology. Sedimentary sequences can be dated in numerical terms by applying high-precision chemical-abrasion, isotope-dilution, thermal-ionization mass spectrometry (CA-ID-TIMS) U-Pb age determination to zircon (ZrSiO4) in intercalated volcanic ashes. But, though volcanic activity is common in geological history, ashes are not necessarily close to the boundary we would like to date precisely and accurately. In addition, U-Pb zircon data sets may be very complex and difficult to interpret in terms of the age of ash deposition. To overcome these difficulties we use a multi-proxy approach we applied to the precise and accurate dating of the Permo-Triassic and Early-Middle Triassic boundaries in South China. a) Dense sampling of ashes across the critical time interval and a sufficiently large number of analysed zircons per ash sample can guarantee the recognition of all system complexities. Geochronological datasets from U-Pb dating of volcanic zircon may indeed combine effects of i) post-crystallization Pb loss from percolation of hydrothermal fluids (even using chemical abrasion), with ii) age dispersion from prolonged residence of earlier crystallized zircon in the magmatic system. As a result, U-Pb dates of individual zircons are both apparently younger and older than the depositional age of the ash, therefore masking the true age of deposition. Trace element ratios such as Th/U, Yb/Gd, as well as Hf isotope analysis of dated zircon can be used to decipher the temporal evolution of the magmatic system before the eruption and deposition of the studied ashes, and resolve the complex system behaviour of the zircons. b) Changes in the source of the magma may happen between the deposition of two stratigraphically consecutive ash beds. They result in the modification of the trace element signature of zircon, but also of apatite (Ca5 (F, Cl, OH) (PO4)3). Trace element characteristics in apatite (e.g. Mg, Mn, Fe, F, Cl, Ce, and Y) are a reliable tool for distinguishing chemically similar groups of apatite crystals to unravel the geochemical fingerprint of one single ash bed. By establishing this fingerprint, ash beds of geographically separated geologic sections can be correlated even if they have not all been dated by U-Pb techniques. c) The ultimate goal of quantitative stratigraphy is to establish an age model that predicts the age of a synchronous time line with an associated 95% confidence interval for any such line within a stratigraphic sequence. We show how a Bayesian, non-parametric interpolation approach can be applied to very complex data sets and leads to a well-defined age solution, possibly identifying changes in sedimentation rate. The age of a geological time boundary bracketed by dated samples in such an age model can be defined with an associated uncertainty.

Chemical-abrasion SIMS dating of zircon from the Eocene Caetano caldera, Nevada

NASA Astrophysics Data System (ADS)

Colgan, J.; Watts, K. E.; John, D. A.; Henry, C. D.; Coble, M. A.; Vazquez, J. A.

2012-12-01

The Eocene Caetano caldera in northern Nevada formed during eruption of ~1100 km3 of crystal-rich rhyolite. Miocene extension cut the caldera into a set of fault blocks that expose minor pre-caldera volcanic rocks, two units of intracaldera Caetano Tuff up to 4 km thick, ash-flow tuff feeder dikes and ring-fracture intrusions, caldera collapse breccias, and post-collapse resurgent intrusions. Single-crystal 40Ar/39Ar sanidine dates on all parts of the caldera system overlap, yielding a 34.01 ± 0.05 Ma (n=17, Fish Canyon sanidine = 28.201 Ma) age for the eruption. 40Ar/39Ar dating also documents several preceding episodes of magmatism: 35.69 ± 0.06 Ma (sanidine, n =13) rhyolite dikes in the nearby Cortez gold district, 35.21 ± 0.18 Ma (plagioclase, n=1) andesite lava underlying Caetano Tuff, and a 38.90 ± 0.11 Ma (biotite, n=1), dacite dike in the northeastern caldera wall. Extensive U-Pb SHRIMP dating of zircon from both the Cortez dikes and all phases of the Caetano system suggests continuous magmatism from 40-34 Ma. However, all samples contain at least some—sometimes many—zircons with U-Pb ages younger than the 34.0 Ma argon age. To determine if anomalously young zircon ages are due to Pb-loss, we analyzed representative samples of the upper Caetano Tuff and the Redrock Canyon resurgent pluton with and without chemical abrasion to mitigate Pb-loss. Bulk zircon separates were annealed at 850°C for 48 hours, then chemically abraded with 10:1 HF/HNO3 vapor in a Parr bomb at 225°C for 8 hours, based on protocols outlined by Mattinson (2005). Both treated and untreated zircons from the same sample were mounted in epoxy and polished to their midsections, then imaged on the SEM using BSE and CL. The SHRIMP-RG at Stanford University was used to determine U-Pb ages and trace element concentrations in single spots for ~25 to 30 individual zircons per sample, using a round-robin procedure and two zircon age standards (R33 and 080) to monitor external precision. Analyses revealed distinctly different age populations for the abraded and untreated zircons. The chemically abraded populations yielded unimodal zircon age distributions with mean ages that overlap with the 40Ar/39Ar age. Untreated zircon populations yielded mean ages 0.9-1.5 Ma younger than the 40Ar/39Ar. In the untreated populations, 50-60% of zircon ages are younger than 34.0 Ma at 1σ, versus 15-20% in the chemically abraded populations. Comparison of trace element data from treated and untreated populations indicates that trace element concentrations are apparently unaffected by the chemical abrasion procedure. Further experiments are underway, but we tentatively conclude that chemical abrasion is effective for removing damaged Pb-loss portions of zircons while still enabling high spatial resolution U-Pb dating and trace element analysis. It appears to be a relatively fast and low-cost way to improve the accuracy of SIMS dating of large populations of zircon from Tertiary and older plutonic and volcanic rocks where Pb-loss is frequently an issue.

U-Pb-Th geochronology of monazite and zircon in albitite metasomatites of the Rožňava-Nadabula ore field (Western Carpathians, Slovakia): implications for the origin of hydrothermal polymetallic siderite veins

NASA Astrophysics Data System (ADS)

Hurai, V.; Paquette, J.-L.; Lexa, O.; Konečný, P.; Dianiška, I.

2015-10-01

Sodic metasomatites (albitites) occur around and within siderite veins in the southern part of the Gemeric tectonic unit of the Western Carpathians. Accessory minerals of the metasomatites represented by monazite, zircon, apatite, rutile, tourmaline and siderite are basically identical with the quartz-tourmaline stage of other siderite and stibnite veins of the tectonic unit. Statistical analysis of chemical Th-U(total)-Pb isochron method (CHIME) of monazite dating yielded Jurassic-Cretaceous ages subdivided into 3-4 modes, spreading over time interval between 78 and 185 Ma. In contrast, LA-ICPMS 206Pb/238U dating carried out on the same monazite grains revealed a narrow crystallization interval, showing ages of Th-poor cores with phengite inclusions identical within the error limit with Th-rich rims with cauliflower-like structure. The determined lower intercept at 139 ± 1 Ma overlapped the Vallanginian-Berriasian boundary, thus corroborating the model of formation of hydrothermal vein structures within an arcuate deformation front built up in the Variscan basement as a response to Early Cretaceous compression, folding and thrusting. In contrast, associated zircons are considerably older than the surrounding Early-Palaeozoic volcano-sedimentary rocks, showing Neoproterozoic ages. The zircon grains in albitite metasomatites are thus interpreted as fragments of Pan-African magmatic detritus incorporated in the vein structures by buoyant hydrothermal fluids.

77 FR 12524 - Approval and Promulgation of Air Quality Implementation Plans; Indiana; Lead Ambient Air Quality...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-03-01

... Promulgation of Air Quality Implementation Plans; Indiana; Lead Ambient Air Quality Standards AGENCY... Indiana State Implementation Plan (SIP) for lead (Pb) under the Clean Air Act (CAA). This submittal incorporates the National Ambient Air Quality Standards (NAAQS) for Pb promulgated by EPA in 2008. DATES...

Elemental and Molecular Segregation in Oil Paintings due to Lead Soap Degradation

DOE PAGES

Chen-Wiegart, Yu-chen Karen; Catalano, Jaclyn; Williams, Garth J.; ...

2017-09-14

The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques. X-ray fluorescence (XRF) microscopy, quantified with elemental correlation density distribution,more » showed Pb and Sn segregation in the soap-affected areas. X-ray absorption near edge structure (XANES) around the Pb-L3 absorption edge showed that Pb pigments and Pb soaps can be distinguished while micro-XANES gave further information on the chemical heterogeneity in the paint film. The advantages and limitations of these synchrotron-based techniques are discussed and compared to those of methods routinely used to analyze paint samples. The results presented set the stage for improving the information extracted from samples removed from works of art and for correlating observations in model paint samples to those in the naturally aged samples, to shed light onto the mechanism of soap formation.« less

Elemental and Molecular Segregation in Oil Paintings due to Lead Soap Degradation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen-Wiegart, Yu-chen Karen; Catalano, Jaclyn; Williams, Garth J.

The formation of Pb, Zn, and Cu carboxylates (soaps) has caused visible deterioration in hundreds of oil paintings dating from the 15th century to the present. Through transport phenomena not yet understood, free fatty acids in the oil binding medium migrate through the paint and react with pigments containing heavy metals to form soaps. To investigate the complex correlation among the elemental segregation, types of chemical compounds formed, and possible mechanisms of the reactions, a paint sample cross-section from a 15th century oil painting was examined by synchrotron X-ray techniques. X-ray fluorescence (XRF) microscopy, quantified with elemental correlation density distribution,more » showed Pb and Sn segregation in the soap-affected areas. X-ray absorption near edge structure (XANES) around the Pb-L3 absorption edge showed that Pb pigments and Pb soaps can be distinguished while micro-XANES gave further information on the chemical heterogeneity in the paint film. The advantages and limitations of these synchrotron-based techniques are discussed and compared to those of methods routinely used to analyze paint samples. The results presented set the stage for improving the information extracted from samples removed from works of art and for correlating observations in model paint samples to those in the naturally aged samples, to shed light onto the mechanism of soap formation.« less

Magma evolution as seen through zircon geochemistry: an example from the Southern Adamello Batholith, N. Italy

NASA Astrophysics Data System (ADS)

Broderick, C.; Schaltegger, U.; Gerdes, A.; Frick, D.; Guenther, D.; Brack, P.

2012-04-01

Zircon is an ubiquitous accessory mineral often used for U-Pb geochronology but is also an important recorder of geochemical information. The trace element and isotopic characteristics of zircon yield potential for tracking changes in an evolving magma through time. With recent advances in U-Pb zircon geochronology, 10-100 ka to Ma timescales are observed for incremental pluton construction (Michel et al., 2008, Schaltegger et al., 2009). In observed 100 ka timescales of zircon crystallization, can zircon record the processes that produce trace element variations in a magma? This study focuses on the Val Fredda Complex (VFC) in the southern tip of the 43 to 33 Ma Adamello batholith, N. Italy. The VFC displays complex relationships among mafic melts that were injected into solidifying felsic magmas. Single zircon crystals were dated using CA-ID-TIMS. With permil uncertainties on 206Pb/238U zircon dates, zircons reveal complexities within single populations. The mafic units crystallized potential autocrystic zircons over a duration of 100 - 150ka, whereas the felsic units record up to 200ka of zircon crystallization. In order to understand these complex zircon populations, we analyzed Hf isotopes and trace elements, on the same volume of zircon used for U-Pb dating, following the TIMS-TEA method (Schoene et al., 2010). This detailed zircon study will allow us to look at how magmas are evolving with time. Hf isotopes of VFC mafic zircons reveal distinct ɛHf values between the three mafic units and their ɛHf values remain consistent through time, whereas the VFC felsic units record more complexity in their ɛHf values. We observe changes such as increasing and slight decreases in ɛHf with time which suggest different processes are occurring to produce the different felsic units. Trace element ratios in zircon reveal differences which allow us to make distinctions between felsic and mafic units (e.g. Th/U, (Lu/Gd)N, REEs). The VFC records 200 ka of zircon crystallization and our data suggests that zircons do in fact reflect changes in isotopic and in trace element signatures on 100 ka timescales. Although we observe changes in our trace elements, the TIMS-TEA method provides an average of trace element concentrations from a zircon volume, dominated by more marginal growth zones. Therefore we will compare our data with in situ methods to determine how our trace element data compares with trace elements across zircon profiles. We acknowledge funding of FNS in the frame of ProDoc Adamello 4-D. Michel et al., 2008, Geol. 36 : 459-462 ; Schaltegger et al., 2009, Earth Planet. Sci.Lett. 286: 208-218; Schoene et al., 2010, Geochim. Cosmochim. Acta 74, 7144-7159.

The mesoproterozoic Beaverhead impact structure and its tectonic setting, Montana-Idaho: 40Ar/39 and U-Pb isotopic constraints

USGS Publications Warehouse

Kellogg, K.S.; Snee, L.W.; Unruh, D.M.

2003-01-01

New 40Ar/39Ar and uranium-lead (U-Pb) zircon data from the Beaverhead impact structure, first identified by extensive shatter coning of Proterozoic quartzite and gneiss from the Beaverhead Mountains near the Montana-Idaho border, indicate that the structure formed at or after 900 Ma. The 40Ar/39Ar age spectra from fine-grained muscovite and biotite from a breccia zone in high-grade gneiss show significant argon loss but yield dates for highest-temperature steps that cluster between 899 and 908 Ma. The dated minerals probably formed by recrystallization of impact glass, so on both geologic and isotopic grounds, the dates probably represent the minimum age of impact. U-Pb data for zircons from the same breccia are strongly discordant and yield an upper intercept apparent age of 2464 ?? 56 Ma and a lower intercept apparent age of 779 ?? 69 Ma. Another brecciated gneiss about 7 km to the northeast that does not contain secondary mica does contain zircons that yield a concordant apparent age of 2455 ?? 9 Ma. Nearby gneiss that neither is brecciated nor contains shatter cones yields an apparent age of 2451 ?? 46 Ma. The 40Ar/39Ar results constrain the age of the shatter-coned quartzite and indicate that it is >900 Ma and possibly correlative with the Gunsight Formation of the Mesoproterozoic Lemhi Group. The upper intercept U-Pb age of ???2450 Ma from all three dated samples also shows that the Paleoproterozoic basement rocks of the area are among the youngest in the mostly Archean Wyoming province of North America. The impact site lies near the margin of the province, along the northeast-trending Great Falls tectonic zone, and the relatively young crustal age may reflect Early Proterozoic marginal accretion.

Geochronology and sources of heavy metal pollution in sediments of Istanbul Strait (Bosporus) outlet area, SW Black Sea, Turkey.

PubMed

Sarı, Erol; Çağatay, M Namık; Acar, Dursun; Belivermiş, Murat; Kılıç, Önder; Arslan, Tuğçe Nagihan; Tutay, Ali; Kurt, Mehmet Ali; Sezer, Narin

2018-08-01

Geochemical and sedimentological analyses and radionuclide ( 210 Pb and 137 Cs) dating of three cores from the Bosporus outlet area of the Black Sea, north of Istanbul, were conducted to assess the sources and history of heavy metal pollution. The sedimentary succession in the shelf core KD12-01 consists mainly of clay (49-80%) and silt (15-41%). Radionuclide dating of the core indicates that it consists of old sediments that are uncontaminated with heavy metals. In contrast, cores KD12-04 and KD12-07 recovered from -350 m and -304 mm in the upper slope area represent sediments consisting of silt and clay that were deposited since at least the last 120 years and 60 years, respectively. The latter core contains two mass-flow units represented by relatively old sedimentary material according to the low 210 Pb activity and relatively low heavy metal contents. The upper 40 and 48 cm of cores KD 12-04 and KD 12-07 represent sediments deposited since 1970s and 1980s that are significantly polluted with Cu, Ni, Zn, Mo, Pb and Cr, Cu, Co, Ni, Mo, Pb, Zn, respectively. However, high Pb and Cr concentrations with high TOC contents date back to early part of the 20th century in core KD 12-04. The geochemical data, together with the high 137 Cs concentrations of the contaminated sediments, strongly suggest that the pollution is mainly delivered to the western and north western Black Sea by the large European rivers, from there transported to the study area by the rim current, and deposited in the sediments under anoxic conditions. Copyright © 2018 Elsevier Ltd. All rights reserved.

(210)Pb and compositional data of sediments from Rondonian lakes, Madeira River basin, Brazil.

PubMed

Bonotto, Daniel Marcos; Vergotti, Marcelo

2015-05-01

Gold exploration has been intensive in Brazilian Amazon over the last 40 years, where the use of mercury as an amalgam has caused abnormal Hg concentrations in water bodies. Special attention has been directed to Madeira River due to fact it is a major tributary of Amazon River and that since 1986, gold exploration has been officially permitted along a 350km sector of the river. The (21)(0)Pb method has been used to date sediments taken from nine lakes situated in Madeira River basin, Rondônia State, and to verify where anthropogenic Hg might exist due to gold exploitation in Madeira River. Activity profiles of excess (21)(0)Pb determined in the sediment cores provided a means to evaluate the sedimentation rates using a Constant Flux: Constant Sedimentation (CF:CS) and Constant Rate of Supply (CRS) of unsupported/excess (21)(0)Pb models. A significant relationship was found between the CF:CS sedimentation rates and the mean values of the CRS sedimentation rates (Pearson correlation coefficient r=0.59). Chemical data were also determined in the sediments for identifying possible relationships with Hg occurring in the area. Significant values were found in statistical correlation tests realized among the Hg, major oxides and Total Organic Carbon (TOC) content in the sediments. The TOC increased in the sediment cores accompanied by a loss on ignition (LOI) increment, whereas silica decreased following a specific surface area raising associated to the TOC increase. The CRS model always provided ages within the permitted range of the (21)(0)Pb-method in the studied lakes, whereas the CF:CS model predicted two values above 140 years. Copyright © 2015 Elsevier Ltd. All rights reserved.

The link between volcanism and plutonism in epizonal magma systems; high-precision U–Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico

USGS Publications Warehouse

Rioux, Matthew; Farmer, Lang; Bowring, Samuel; Wooton, Kathleen M.; Amato, Jeffrey M.; Coleman, Drew S.; Verplanck, Philip L.

2016-01-01

The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes associated with caldera volcanism. Here we present high-precision thermal ionization mass spectrometry U–Pb zircon dates from throughout the caldera and batholith, and use these dates to test and improve existing petrogenetic models. The new dates indicate that Eocene volcanic and plutonic rocks in the Organ Mountains formed from ~44 to 34 Ma. The three largest caldera-related tuff units yielded weighted mean 206Pb/238U dates of 36.441 ± 0.020 Ma (Cueva Tuff), 36.259 ± 0.016 Ma (Achenback Park tuff), and 36.215 ± 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean 206Pb/238U date of 36.259 ± 0.021 Ma. Weighted mean 206Pb/238U dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 ± 0.031 to 36.071 ± 0.012 Ma, and the youngest sample is 144 ± 20 to 188 ± 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 ± 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a high-silica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 ± 20 ka after the final eruption. Calculated magmatic fluxes for the Organ Needle pluton range from 0.0006 to 0.0030 km3/year, in agreement with estimates from other well-studied plutons. The petrogenetic evolution proposed here may be common to many small-volume silicic volcanic systems.

Did the Kiruna iron ores form as a result of a metasomatic or igneous process? New U-Pb and Nd data for the iron oxide apatite ores and their host rocks in the Norrbotten region of northern Sweden

NASA Astrophysics Data System (ADS)

Westhues, A.; Hanchar, J. M.; Whitehouse, M. J.; Fisher, C. M.

2012-12-01

A number of iron deposits near Kiruna in the Norrbotten region of northern Sweden are of the iron oxide apatite (IOA) type of deposits; also referred to as Kiruna-type deposits. They are commonly considered a subgroup or end-member of iron oxide copper gold (IOCG) deposits, containing no economic grades of copper or gold. Both IOCG and IOA deposits are characterized by abundant low-Ti Fe oxides, an enrichment in REE, and intense sodium and potassium wall-rock alteration adjacent to the ores. Deposits of these types are of a great economic importance, not only for iron, but also for other elements such as rare earth elements (REE) or uranium. Kiruna, the type locality of the IOA type of mineral deposits, is the focus of this study. Despite a century-long mining history and 2500 Mt of iron ore produced in the region to date (with grades of 30 to 70 wt.% Fe), the genesis of these deposits is poorly understood: theories of a magmatic vs. a hydrothermal or metasomatic origin have been debated, and the timing of mineralization of the ores in the Norbotten region has never been directly dated. The results anticipated from this study will provide a better understanding of the nature of the IOA type of mineral deposits and their relation to IOCG deposits such as Olympic Dam in Australia. An array of geochemical methods is used in order to gain insights on the emplacement history of the host rocks, their subsequent alteration, and the ore genesis of these deposits. This includes in situ U/Pb geochronology of zircon, monazite, and titanite to constrain the timing between host rock emplacement, alteration and mineralization. Isotopic data from whole rocks and in situ at mineral scale will provide constraints on the involvement of hydrothermal fluids and their possible sources, as well as on the sources of Fe, U, and the REE. Newly obtained Sm-Nd isotopic data points to distinct source differences between host rocks, ore and alteration related samples. Preliminary in situ U-Pb dating of zircon from both host rock and ore samples confirms a previously documented event around 1880 - 1900 Ma in the Norrbotten region. However, U-Pb in monazite from an ore sample suggests a further event at ca. 1650 Ma, a period of known activity in Fennoscandia. Further investigation and more U-Pb data are needed to confirm those dates and how the iron mineralization is related to those two events. The combination of U-Th-Pb ages, tracer isotopes and trace element abundances at mineral scale (e.g., Lu-Hf in zircon, and Sm-Nd in monazite, apatite, titanite), along with the O isotopic composition of zircon, will be used to decipher whether the Kiruna iron ore deposits are of metasomatic or igneous origin. Overall, the study also intends to develop a predictive model for exploration of similar iron oxide apatite deposits worldwide.

Atmospheric residence time of (210)Pb determined from the activity ratios with its daughter radionuclides (210)Bi and (210)Po.

PubMed

Semertzidou, P; Piliposian, G T; Appleby, P G

2016-08-01

The residence time of (210)Pb created in the atmosphere by the decay of gaseous (222)Rn is a key parameter controlling its distribution and fallout onto the landscape. These in turn are key parameters governing the use of this natural radionuclide for dating and interpreting environmental records stored in natural archives such as lake sediments. One of the principal methods for estimating the atmospheric residence time is through measurements of the activities of the daughter radionuclides (210)Bi and (210)Po, and in particular the (210)Bi/(210)Pb and (210)Po/(210)Pb activity ratios. Calculations used in early empirical studies assumed that these were governed by a simple series of equilibrium equations. This approach does however have two failings; it takes no account of the effect of global circulation on spatial variations in the activity ratios, and no allowance is made for the impact of transport processes across the tropopause. This paper presents a simple model for calculating the distributions of (210)Pb, (210)Bi and (210)Po at northern mid-latitudes (30°-65°N), a region containing almost all the available empirical data. By comparing modelled (210)Bi/(210)Pb activity ratios with empirical data a best estimate for the tropospheric residence time of around 10 days is obtained. This is significantly longer than earlier estimates of between 4 and 7 days. The process whereby (210)Pb is transported into the stratosphere when tropospheric concentrations are high and returned from it when they are low, significantly increases the effective residence time in the atmosphere as a whole. The effect of this is to significantly enhance the long range transport of (210)Pb from its source locations. The impact is illustrated by calculations showing the distribution of (210)Pb fallout versus longitude at northern mid-latitudes. Copyright © 2016 Elsevier Ltd. All rights reserved.

SHRIMP U-Pb detrital zircon dating to check subdivisions in metamorphic complexes: a case of study in the Nevado-Filábride complex (Betic Cordillera, Spain)

NASA Astrophysics Data System (ADS)

Santamaría-López, Ángel; Sanz de Galdeano, Carlos

2018-04-01

U-Pb dating on inherited detrital zircons has been applied to obtain the probable maximum age of deposition of the detrital protolith of the Nevado-Filábride complex (Betic Cordillera, Spain). Five of eight samples correspond to the lower part of the lithologic sequence of this complex, where radiometric dating of metasediments has not been presented till the present. The youngest age populations in the majority of samples are Carboniferous. The estimation of the maximum age of deposition in the lower and upper units is 349.1 ± 1.6 and 334.6 ± 2.9 Ma, respectively. In addition, samples show common age populations at ca. 490-630 and ca. 910-1010 Ma. Observations agree with the Carboniferous to early Permian U-Pb ages previously obtained in orthogneisses levels which are situated in the upper part of the complex. Combination of the minimum age of deposition deducible from the orthogneisses studies and the maximum ages of deposition obtained from the detrital zircons of this work, allow establishing the deposition of de studied lithological succession comprised between ca. 282 and 349 Ma or a shorter period.

An algorithm for U-Pb isotope dilution data reduction and uncertainty propagation

NASA Astrophysics Data System (ADS)

McLean, N. M.; Bowring, J. F.; Bowring, S. A.

2011-06-01

High-precision U-Pb geochronology by isotope dilution-thermal ionization mass spectrometry is integral to a variety of Earth science disciplines, but its ultimate resolving power is quantified by the uncertainties of calculated U-Pb dates. As analytical techniques have advanced, formerly small sources of uncertainty are increasingly important, and thus previous simplifications for data reduction and uncertainty propagation are no longer valid. Although notable previous efforts have treated propagation of correlated uncertainties for the U-Pb system, the equations, uncertainties, and correlations have been limited in number and subject to simplification during propagation through intermediary calculations. We derive and present a transparent U-Pb data reduction algorithm that transforms raw isotopic data and measured or assumed laboratory parameters into the isotopic ratios and dates geochronologists interpret without making assumptions about the relative size of sample components. To propagate uncertainties and their correlations, we describe, in detail, a linear algebraic algorithm that incorporates all input uncertainties and correlations without limiting or simplifying covariance terms to propagate them though intermediate calculations. Finally, a weighted mean algorithm is presented that utilizes matrix elements from the uncertainty propagation algorithm to propagate random and systematic uncertainties for data comparison between other U-Pb labs and other geochronometers. The linear uncertainty propagation algorithms are verified with Monte Carlo simulations of several typical analyses. We propose that our algorithms be considered by the community for implementation to improve the collaborative science envisioned by the EARTHTIME initiative.

Application of the Weibull extrapolation to 137Cs geochronology in Tokyo Bay and Ise Bay, Japan.

PubMed

Lu, Xueqiang

2004-01-01

Considerable doubt surrounds the nature of processes by which 137Cs is deposited in marine sediments, leading to a situation where 137Cs geochronology cannot be always applied suitably. Based on extrapolation with Weibull distribution, the maximum concentration of 137Cs derived from asymptotic values for cumulative specific inventory was used to re-establish 137Cs geochronology, instead of original 137Cs profiles. Corresponding dating results for cores in Tokyo Bay and Ise Bay, Japan, by means of this new method, are in much closer agreement with those calculated from 210Pb method than the previous method.

Trace- and rare-earth element geochemistry and Pb-Pb dating of black shales and intercalated Ni-Mo-PGE-Au sulfide ores in Lower Cambrian strata, Yangtze Platform, South China

NASA Astrophysics Data System (ADS)

Jiang, Shao-Yong; Chen, Yong-Quan; Ling, Hong-Fei; Yang, Jing-Hong; Feng, Hong-Zhen; Ni, Pei

2006-08-01

The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb-Pb isotope dating for the Ni-Mo-PGE-Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni-Mo-PGE-Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb-Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni-Mo-PGE-Au sulfide ores, and two Pb-Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni-Mo-PGE-Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.

Mercerized mesoporous date pit activated carbon—A novel adsorbent to sequester potentially toxic divalent heavy metals from water

PubMed Central

Aldawsari, Abdullah; Hameed, B. H.; Alqadami, Ayoub Abdullah; Siddiqui, Masoom Raza; Alothman, Zeid Abdullah; Ahmed, A. Yacine Badjah Hadj

2017-01-01

A substantive approach converting waste date pits to mercerized mesoporous date pit activated carbon (DPAC) and utilizing it in the removal of Cd(II), Cu(II), Pb(II), and Zn(II) was reported. In general, rapid heavy metals adsorption kinetics for Co range: 25–100 mg/L was observed, accomplishing 77–97% adsorption within 15 min, finally, attaining equilibrium in 360 min. Linear and non-linear isotherm studies revealed Langmuir model applicability for Cd(II) and Pb(II) adsorption, while Freundlich model was fitted to Zn(II) and Cu(II) adsorption. Maximum monolayer adsorption capacities (qm) for Cd(II), Pb(II), Cu(II), and Zn(II) obtained by non-linear isotherm model at 298 K were 212.1, 133.5, 194.4, and 111 mg/g, respectively. Kinetics modeling parameters showed the applicability of pseudo-second-order model. The activation energy (Ea) magnitude revealed physical nature of adsorption. Maximum elution of Cu(II) (81.6%), Zn(II) (70.1%), Pb(II) (96%), and Cd(II) (78.2%) were observed with 0.1 M HCl. Thermogravimetric analysis of DPAC showed a total weight loss (in two-stages) of 28.3%. Infra-red spectral analysis showed the presence of carboxyl and hydroxyl groups over DPAC surface. The peaks at 820, 825, 845 and 885 cm-1 attributed to Zn–O, Pb–O, Cd–O, and Cu–O appeared on heavy metals saturated DPAC, confirmed their binding on DPAC during the adsorption. PMID:28910368

Characterization of a new candidate isotopic reference material for natural Pb using primary measurement method.

PubMed

Nonose, Naoko; Suzuki, Toshihiro; Shin, Ki-Cheol; Miura, Tsutomu; Hioki, Akiharu

2017-06-29

A lead isotopic standard solution with natural abundance has been developed by applying a mixture of a solution of enriched 208 Pb and a solution of enriched 204 Pb ( 208 Pb- 204 Pb double spike solution) as bracketing method. The amount-of-substance ratio of 208 Pb: 204 Pb in this solution is accurately measured by applying EDTA titrimetry, which is one of the primary measurement methods, to each enriched Pb isotope solution. Also metal impurities affecting EDTA titration and minor lead isotopes contained in each enriched Pb isotope solution are quantified by ICP-SF-MS. The amount-of-substance ratio of 208 Pb: 204 Pb in the 208 Pb- 204 Pb double spike solution is 0.961959 ± 0.000056 (combined standard uncertainty; k = 1). Both the measurement of lead isotope ratios in a candidate isotopic standard solution and the correction of mass discrimination in MC-ICP-MS are carried out by coupling of a bracketing method with the 208 Pb- 204 Pb double spike solution and a thallium internal addition method, where thallium solution is added to the standard and the sample. The measured lead isotope ratios and their expanded uncertainties (k = 2) in the candidate isotopic standard solution are 18.0900 ± 0.0046 for 206 Pb: 204 Pb, 15.6278 ± 0.0036 for 207 Pb: 204 Pb, 38.0626 ± 0.0089 for 208 Pb: 204 Pb, 2.104406 ± 0.00013 for 208 Pb: 206 Pb, and 0.863888 ± 0.000036 for 207 Pb: 206 Pb. The expanded uncertainties are about one half of the stated uncertainty for NIST SRM 981, for 208 Pb: 204 Pb, 207 Pb: 204 Pb and 206 Pb: 204 Pb, or one eighth, for 208 Pb: 206 Pb and 207 Pb: 206 Pb, The combined uncertainty consists of the uncertainties due to lead isotope ratio measurements and the remaining time-drift effect of mass discrimination in MC-ICP-MS, which is not removed by the coupled correction method. In the measurement of 208 Pb: 204 Pb, 207 Pb: 204 Pb and 206 Pb: 204 Pb, the latter contribution is two or three times larger than the former. When the coupling of a bracketing method with the 208 Pb- 204 Pb double spike solution and a thallium internal addition method is applied to the analysis of NIST SRM 981, the measured lead isotope ratios are in good agreement with its certified values. This proves that the developed method is not only consistent with the conventional one by NIST SRM 981 but also enables measurement of the lead isotope ratios with higher precision. Copyright © 2017 Elsevier B.V. All rights reserved.

Pb-Pb dating of individual chondrules from the CBa chondrite Gujba: Assessment of the impact plume formation model

PubMed Central

Bollard, Jean; Connelly, James N.; Bizzarro, Martin

2016-01-01

The CB chondrites are metal-rich meteorites with characteristics that sharply distinguish them from other chondrite groups. Their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the CBa chondrite Gujba are interpreted to reflect a single-stage impact origin. Here, we report high-precision internal isochrons for four individual chondrules of the Gujba chondrite to probe the formation history of CB chondrites and evaluate the concordancy of relevant short-lived radionuclide chronometers. All four chondrules define a brief formation interval with a weighted mean age of 4562.49 ± 0.21 Myr, consistent with its origin from the vapor-melt impact plume generated by colliding planetesimals. Formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4.8 ± 0.3 Myr. Finally, given the well-behaved Pb-Pb systematics of all four chondrules, a precise formation age and the concordancy of the Mn-Cr, Hf-W, and I-Xe short-lived radionuclide relative chronometers, we propose that Gujba may serve as a suitable time anchor for these systems. PMID:27429545

U-Pb dating of large zircons in low-temperature jadeitite from the Osayama serpentinite melange, southwest Japan: insights into the timing of serpentinization

USGS Publications Warehouse

Tsujimori, T.; Liou, J.G.; Wooden, J.; Miyamoto, T.

2005-01-01

Crystals of zircon up to 3 mm in length occur in jadeitite veins in the Osayama serpentinite mélange, Southwest Japan. The zircon porphyroblasts show pronounced zoning, and are characterized by both low Th/U ratios (0.2-0.8) and low Th and U abundances (Th = 1-81 ppm; U = 6-149 ppm). They contain inclusions of high-pressure minerals, including jadeite and rutile; such an occurrence indicates that the zircon crystallized during subduction-zone metamorphism. Phase equilibria and the existing fluid-inclusion data constrain P-T conditions to P > 1.2 GPa at T > 350°C for formation of the jadeitite. Most U/Pb ages obtained by SHRIMP-RG are concordant, with a weighted mean 206Pb/238U age of 472 ± 8.5 Ma (MSWD = 2.7, n = 25). Because zircon porphyroblasts contain inclusions of high-pressure minerals, the SHRIMP U-Pb age represents the timing of jadeitite formation, i.e., the timing of interaction between alkaline fluid and ultramafic rocks in a subduction zone. Although this dating does not provide a direct time constraint for serpentinization, U-Pb ages of zircon in jadeitite associated with serpentinite result in new insights into the timing of fluid-rock interaction of ultramafic rocks at a subduction zone and the minimum age for serpentinization.

High-precision U-Pb geochronologic constraints on the Late Cretaceous terrestrial cyclostratigraphy and geomagnetic polarity from the Songliao Basin, Northeast China

NASA Astrophysics Data System (ADS)

Wang, Tiantian; Ramezani, Jahandar; Wang, Chengshan; Wu, Huaichun; He, Huaiyu; Bowring, Samuel A.

2016-07-01

The Cretaceous continental sedimentary records are essential to our understanding of how the terrestrial geologic and ecologic systems responded to past climate fluctuations under greenhouse conditions and our ability to forecast climate change in the future. The Songliao Basin of Northeast China preserves a near-complete, predominantly lacustrine, Cretaceous succession, with sedimentary cyclicity that has been tied to Milankocitch forcing of the climate. Over 900 meters of drill-core recovered from the Upper Cretaceous (Turonian to Campanian) of the Songliao Basin has provided a unique opportunity for detailed analyses of its depositional and paleoenvironmental records through integrated and high-resolution cyclostratigraphic, magnetostratigraphic and geochronologic investigations. Here we report high-precision U-Pb zircon dates (CA-ID-TIMS method) from four interbedded bentonites from the drill-core that offer substantial improvements in accuracy, and a ten-fold enhancement in precision, compared to the previous U-Pb SIMS geochronology, and allow a critical evaluation of the Songliao astrochronological time scale. The results indicate appreciable deviations of the astrochronologic model from the absolute radioisotope geochronology, which more likely reflect cyclostratigraphic tuning inaccuracies and omitted cycles due to depositional hiatuses, rather than suspected limitations of astronomical models applied to distant geologic time. Age interpolation based on our new high-resolution geochronologic framework and the calibrated cyclostratigraphy places the end of the Cretaceous Normal Superchon (C34n-C33r chron boundary) in the Songliao Basin at 83.07 ± 0.15 Ma. This date also serves as a new and improved estimate for the global Santonian-Campanian stage boundary.

Hydrothermal titanite from the Chengchao iron skarn deposit: temporal constraints on iron mineralization, and its potential as a reference material for titanite U-Pb dating

NASA Astrophysics Data System (ADS)

Hu, Hao; Li, Jian-Wei; McFarlane, Christopher R. M.

2017-09-01

Uranium-lead isotopes and trace elements of titanite from the Chengchao iron skarn deposit (Daye district, Eastern China), located along the contact zones between Triassic marine carbonates and an early Cretaceous intrusive complex consisting of granite and quartz diorite, were analyzed using laser ablation inductively coupled plasma mass spectrometry to provide temporal constraints on iron mineralization and to evaluate its potential as a reference material for titanite U-Pb geochronology. Titanite grains from mineralized endoskarn have simple growth zoning patterns, exhibit intergrowth with magnetite, diopside, K-feldspar, albite and actinolite, and typically contain abundant primary two-phase fluid inclusions. These paragenetic and textural features suggest that these titanite grains are of hydrothermal origin. Hydrothermal titanite is distinct from the magmatic variety from the ore-related granitic intrusion in that it contains unusually high concentrations of U (up to 2995 ppm), low levels of Th (12.5-453 ppm), and virtually no common Pb. The REE concentrations are much lower, as are the Th/U and Lu/Hf ratios. The hydrothermal titanite grains yield reproducible uncorrected U-Pb ages ranging from 129.7 ± 0.7 to 132.1 ± 2.7 Ma (2σ), with a weighted mean of 131.2 ± 0.2 Ma [mean standard weighted deviation (MSWD) = 1.7] that is interpreted as the timing of iron skarn mineralization. This age closely corresponds to the zircon U-Pb age of 130.9 ± 0.7 Ma (MSWD = 0.7) determined for the quartz diorite, and the U-Pb ages for zircon and titanite (130.1 ± 1.0 Ma and 131.3 ± 0.3 Ma) in the granite, confirming a close temporal and likely genetic relationship between granitic magmatism and iron mineralization. Different hydrothermal titanite grains have virtually identical uncorrected U-Pb ratios suggestive of negligible common Pb in the mineral. The homogeneous textures and U-Pb characteristics of Chengchao hydrothermal titanite suggest that the mineral might be a suitable internal reference material for U-Pb dating.

Heavy metals in Antarctic ice from Law Dome: Initial results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, S.; Boutron, C.F.; Edwards, R.

1998-08-01

Pb, Cd, Cu, and Zn have been measured using ultraclean procedures in eight sections taken from two well-dated ice cores from Law Dome, an independent small size ice cap with high accumulation rate situated in the coastal area of East Antarctica. Seven sections were dated from the 1830s to 1940s and one was dated from three millennia ago. The data show that there are strong seasonal variations in the concentrations of Pb and Cd, with values {approximately} two- to four-fold higher in winter than in spring-summer. Evaluation of the contributions from the different sources suggests that contribution from sea saltmore » spray is relatively important, especially for Cd. Contribution from marine biogenic emissions could also be very significant. The importance of marine contributions is consistent with strong intrusions of marine air masses at this coastal site, especially during wintertime.« less

U, Th, Pb and REE abundances and Pb 207/Pb 206 ages of individual minerals in returned lunar material by ion microprobe mass analysis.

NASA Technical Reports Server (NTRS)

Andersen, C. A.; Hinthorne, J. R.

1972-01-01

Results of ion microprobe analyses of Apollo 11, 12 and 14 material, showing that U, Th, Pb and REE are concentrated in accessory minerals such as apatite, whitlockite, zircon, baddeleyite, zirkelite, and tranquillityite. Th/U ratios are found to vary by over a factor of 40 in these minerals. K, Ba, Rb and Sr have been localized in a K rich, U and Th poor glass phase that is commonly associated with the U and Th bearing accessory minerals. Li is observed to be fairly evenly distributed between the various accessory phases. The phosphates have been found to have REE abundance patterns (normalized to the chondrite abundances) that are fairly flat, while the Zr bearing minerals have patterns that rise steeply, by factors of ten or more, from La to Gd. All the accessory minerals have large negative Eu anomalies. Radiometric age dates (Pb 207/Pb 206) of the individual U and Th bearing minerals compare favorably with the Pb 207/Pb 206 age of the bulk rocks.

Apollo 12 breccia 12013: Impact-induced partial Pb loss in zircon and its implications for lunar geochronology

NASA Astrophysics Data System (ADS)

Thiessen, F.; Nemchin, A. A.; Snape, J. F.; Bellucci, J. J.; Whitehouse, M. J.

2018-06-01

Apollo 12 breccia 12013 is composed of two portions, one grey in colour, the other black. The grey portion of the breccia consists mainly of felsite thought to have formed during a single crystallisation event, while the black part is characterized by presence of lithic fragments of noritic rocks and individual plagioclase crystals. In this study, U-Pb analyses of Ca-phosphate and zircon grains were conducted in both portions of the breccia. The zircon grains within the grey portion yielded a large range of ages (4154 ± 7 to 4308 ± 6 Ma, 2σ) and show decreasing U and Th concentrations within the younger grains. Moreover, some grains exhibit recrystallisation features and potentially formation of neoblasts. The latter process requires high temperatures above 1600-1700 °C leading to the decomposition of the primary zircon grain and subsequent formation of new zircon occurring as neoblasts. As a result of the high temperatures, the U-Pb system of the remaining original zircon grains was most likely open for Pb diffusion causing partial resetting and the observed range of 207Pb/206Pb ages. The event that led to the Pb loss in zircon could potentially be dated by the U-Pb system in Ca-phosphates, which have a weighted average 207Pb/206Pb age across both lithologies of 3924 ± 3 Ma (95% conf.). This age is identical within error to the combined average 207Pb/206Pb age of 3926 ± 2 Ma that was previously obtained from Ca-phosphates within Apollo 14 breccias, zircon grains in Apollo 12 impact melt breccias, and the lunar meteorite SaU 169. This age was interpreted to date the Imbrium impact. The zircon grains located within the black portion of the breccia yielded a similar range of ages (4123 ± 13 to 4328 ± 14 Ma, 2σ) to those in the grey portion. Given the brecciated nature of this part of the sample, the interpretation of these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no direct link to their source rocks via textural relationships or crystal chemistry. Similarly, the currently available zircon data set for all lunar samples may be distorted by partial Pb loss, resulting in meaningless and misleading age distribution patterns. Therefore, it is crucial to fully understand and recognize the processes and conditions that may lead to partial resetting of the U-Pb system in zircon in order to better constrain the magmatic and impact history of the Moon.

Using zircon (U-Th)/He damage-diffusivity patterns to quantify detachment-related basement exhumation in the Mecca Hills, CA

NASA Astrophysics Data System (ADS)

Moser, A. C.; Ault, A. K.; Evans, J. P.; Reiners, P. W.; Stearns, M.; Guenthner, W.

2017-12-01

Exposures of gneiss and Orocopia Schist (OS) in the Mecca Hills, California, adjacent to the southernmost San Andreas Fault system, preserve the exhumation history of Oligocene detachment faulting. We investigate the duration, magnitude, and mechanisms of exhumation of these units at regional and local scales using in situ U-Pb zircon dating (n = 248), (U-Th)/He (He) thermochronometry (n = 39), and He date-effective U (eU) patterns. Zircons with variable preserved visual metamictization were targeted for He analyses to purposefully build a dataset with a range in eU concentration and zircon He closure temperatures, as well as induce a He date-eU correlation. Analyzed zircon crystals range from clear and transparent to purple-brown and translucent in each sample. Zircon cathodoluminescence images reveal oscillatory and sector chemical zoning. Each sample contains a population of largely Proterozoic U-Pb dates implying some grains accumulated radiation damage since 1.9-1.1 Ga. Zircon (U-Th)/He dates from seven samples of OS and gneiss yield a mean date of 24 ± 3.5 Ma (n = 32) and uniform dates over an 90-2950 ppm eU range. One gneiss sample yields a mean date of 65 ± 5.6 Ma (n = 7) over a limited eU spread ( 500-950 ppm). Mean zircon He dates from these two units overlap, but dates are broadly younger in northeastern exposures dominated by OS. Preliminary thermal history simulations integrating zircon U-Pb data, He date-eU patterns, and independent geologic constraints require at least 200 °C of cooling through the zircon He partial retention zone 30-21 Ma and show that the pre-70 Ma thermal history does not affect the predicted date-eU correlation. This shared rapid cooling history documented in the OS and gneiss imply these units were juxtaposed prior to 30 Ma and exhumed as a coherent structural block within the footwall of the Orocopia Mountains Detachment Fault in the Mecca Hills. Spatio-temporal variation in mean zircon He dates may delineate time-transgressive cooling of these units as they exhumed. Zircon textures and overall invariant He dates regardless of eU imply that visual metamictization persists in zircons at temperatures >200 °C and indicates these grains experienced a thermal history characterized by temperatures that preserved visual damage but fully induced He loss in the crystals prior to exhumation.

Radiometric age dating of peat cores from ombrotrophic bogs: challenges and opportunities presented by the Industrial Period

NASA Astrophysics Data System (ADS)

Shotyk, W.; Appleby, P.; Davies, L. J.; Froese, D. G.; Magnan, G.; Mullan-Boudreau, G.; Noernberg, T.; Bob, S.; van Bellen, S.; Zaccone, C.

2016-12-01

The upper layers of ombrotrophic (rain-fed) bogs are hydrologically isolated from surface waters and groundwaters and, in consequence, contaminants are supplied exclusively from the atmosphere. Peat cores from bogs have been used to reconstruct the history of heavy metal pollution since mining and metallurgy began, but the greatest changes have taken place since the start of the Industrial Revolution which was well underway by the middle of the 19th century. Dating peat, accumulated since this time has been made possible using 210Pb (t1/2 = 22.3 yr), but the validity of the age-depth relationship obtained must always be assessed using one or more chronostratigraphic markers. The post-industrial period provides an enormous range of possible time markers including various fallout radionuclides, numerous trace metals and their isotopes, and countless organic contaminants. Most of these have not yet been explored, and will be helpful only if they are immobile in the peat column; often, their fate during chemical diagenesis in anoxic, acidic bog waters is either unknown or at least poorly understood. The atmospheric bomb pulse curve of 14C for the period since AD 1950 has proved to be particularly valuable for validating 210Pb chronologies by providing accurate dates for individual plant macrofossils. Peat cores collected in northern Alberta, surrounding open pit mines and upgraders of Athabsca Bituminous Sands, were carefully dated using 210Pb and the age-depth relationship evaluated using both 241Am and 14C. The cores nearest industry (MIL, JPH4) show that atmospheric deposition of trace metals has been declining ever since industrial-scale mining and refining began in 1967. This includes all of the potentially toxic trace elements (Ag, Cd, Pb, Sb, Tl), but also the metals known for their enrichment in bitumen (V, Ni, Mo). In fact, the surface layers of these bogs today are comparable in composition to the "cleanest" peat samples ever found in the northern hemisphere. Our findings are completely opposed to recent claims about environmental pollution by metals from mining and upgrading in this region, illustrating the importance of reliable age dates and the value of robust age-depth models.

Zircon U-Pb dating of eclogite from the Qiangtang terrane, north-central Tibet: a case of metamorphic zircon with magmatic geochemical features

NASA Astrophysics Data System (ADS)

Zhai, Qing-guo; Jahn, Bor-ming; Li, Xian-hua; Zhang, Ru-yuan; Li, Qiu-li; Yang, Ya-nan; Wang, Jun; Liu, Tong; Hu, Pei-yuan; Tang, Suo-han

2017-06-01

Zircon is probably the most important mineral used in the dating formation of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks. The origin of zircon, i.e., magmatic or metamorphic, is commonly assessed by its external morphology, internal structure, mineral inclusions, Th/U ratios and trace element composition. In this study, we present an unusual case of metamorphic zircon from the Qiangtang eclogite, north-central Tibet. The zircon grains contain numerous eclogite-facies mineral inclusions, including omphacite, phengite, garnet and rutile; hence, they are clearly of metamorphic origin. However, they display features similar to common magmatic zircon, including euhedral crystal habit, high Th/U ratios and enriched heavy rare earth elements pattern. We suggest that these zircon grains formed from a different reservoir from that for garnet where no trace elements was present and trace element equilibrium between zircon and garnet was achieved. U-Pb dating of zircon gave an age of 232-237 Ma for the eclogite, and that of rutile yielded a slightly younger age of ca. 217 Ma. These ages are consistent with the reported Lu-Hf mineral isochron and phengite Ar-Ar ages. The zircon U-Pb and mineral Lu-Hf isochron ages are interpreted as the time of the peak eclogite-facies metamorphism, whereas the rutile U-Pb and phengite Ar-Ar ages represent the time of exhumation to the middle crust. Thus, the distinction between metamorphic and magmatic zircons cannot be made using only Th/U ratios and heavy REE compositions for HP-UHP metamorphic rocks of oceanic derivation.

Textural and U-Pb systematics (CA-TIMS) of stepwise leaching in zircon from granophyres in the Archean Stillwater Complex

NASA Astrophysics Data System (ADS)

Wall, C. J.; Scoates, J. S.; Friedman, R. M.; Meurer, W. P.

2011-12-01

The chemical abrasion-TIMS method or CA-TIMS uses a high-temperature annealing treatment to remove the effects of Pb-loss from radiation damaged parts of the zircon lattice and allows for highly precise and accurate U-Pb dating [1]. Zircon with high U-Th concentrations can be strongly metamict and it is not yet clear how effective the chemical abrasion treatment is when applied to these types of grains. In this study, we evaluate the link between the textural response and U-Pb systematics of zircon during chemical leaching for a granophyric rock from the Archean Stillwater Complex in Montana. The sample was selected based on the high abundance of zircon and the high degree of metamictization of the grains. Untreated and leached zircon grains were analyzed by scanning electron microscopy (SEM) and isotope dilution thermal ionization mass spectrometry (ID-TIMS). In thin section, zircon grains are euhedral in morphology and tend to be associated with amphibole-rich zones. Under the SEM, zircon grains typically have two distinct zones, a Ca-rich amorphous zone in the core and a more intact outer shell. Five acid-leaching steps were carried out on grains with each step increasing in temperature and acid strength until the zircon residue completely dissolved (starting at a 50% strength HF/HNO3 mixture at 100°C for 4 hours and finishing at full strength acid at 170°C for 4 hours). SEM imaging was conducted on grains after each step with a noticeable change in the morphology of the grains. As the leaching progressed, the acid leach created large pathways through the crystal lattice until only grain fragments remained, in some cases even boring large holes into the centre of the zircon grain. The acid preferentially dissolved the more soluble Ca-rich zones leaving behind fragile zircon "shells". U-Pb results of untreated grains are highly discordant (37-80%) and yield a chord with an upper intercept age of 1981 ± 140 Ma, whereas leached grains are slightly less discordant (12-69%) and define a much different chord with an upper intercept age of 2618 ± 4 Ma. Both ages are too young in comparison to the crystallization age of the Stillwater Complex (ca. 2709 Ma) and are considered to represent two discrete Pb-loss events that have reset the U-Pb systematics of these zircon grains. These Pb-loss events may be due to hydrothermal events associated with the emplacement of mafic dikes or the crystallization of regionally extensive monzonite plutons that intruded the Stillwater Complex. Dating different geological events using the U-Pb isotopic compositions of untreated metamict zircon and leached zircon by systematic acid leaching could prove to be a useful application of CA-TIMS. [1] Mattinson (2005) Chemical Geology 220, 47-66.

Lead in Chinese villager house dust: Geographical variation and influencing factors.

PubMed

Bi, Xiangyang; Liu, Jinling; Han, Zhixuan; Yang, Wenlin

2015-12-01

House dust has been recognized as an important contributor to Pb exposure of children. Here we conducted a comprehensive study to investigate geographical variation of Pb in Chinese villager house dust. The influences of outdoor soil Pb concentrations, dates of construction, house decoration materials, heating types, and site specific pollution on Pb concentrations in house dust were evaluated. The concentrations of Pb in 477 house dust samples collected from twenty eight areas throughout China varied from 12 to 2510 mg/kg, with a median concentration of 42 mg/kg. The median Pb concentrations in different geographical areas ranged from 16 (Zhangjiakou, Hebei) to 195 mg/kg (Loudi, Hunan). No correlations were found between the house dust Pb concentrations and the age of houses, as well as house decoration materials. Whereas outdoor soil, coal combustion, and site specific pollution may be potential Pb sources. Principal component analysis (PCA) confirmed that elemental compositions of the house dust were controlled by both anthropogenic and geogenic sources. Using scanning electron microscopy (SEM), the Pb bearing particles in the house dust were also studied. Copyright © 2015 Elsevier Ltd. All rights reserved.

Geochronology, petrogenesis and tectonic settings of pre- and syn-ore granites from the W-Mo deposits (East Kounrad, Zhanet and Akshatau), Central Kazakhstan

NASA Astrophysics Data System (ADS)

Li, GuangMing; Cao, MingJian; Qin, KeZhang; Evans, Noreen J.; Hollings, Pete; Seitmuratova, Eleonora Yusupovha

2016-05-01

There is significant debate regarding the mineralization ages of the East Kounrad, Zhanet and Akshatau W-Mo deposits of Central Kazakhstan, and the petrogenesis and tectono-magmatic evolution of the granites associated with these deposits. To address these issues, we present molybdenite Re-Os dating, zircon U-Pb dating, whole rock geochemistry as well as Sr-Nd-Pb and zircon O-Hf isotopic analyses on the pre-mineralization and ore-forming granites. U-Pb dating of zircons from pre-mineralization granitic rocks yield Late Carboniferous ages of 320-309 Ma, whereas ore-forming granites have Early Permian ages of 298-285 Ma. Molybdenite Re-Os isotopic data indicate a mineralization age of 296 Ma at East Kounrad, 294 Ma at Akshatau and 285 Ma at Zhanet. The pre-ore and ore-forming granites are high-K calc-alkaline, metaluminous to slightly peraluminous I-type granites. The pre-mineralization granites are relatively unfractionated, whereas the ore-forming granites are highly fractionated. The fractionating mineral phases are probably K-feldspar, apatite, Ti-bearing phases and minor plagioclase. The pre-mineralization and ore-forming rocks are characterized by similar Sr-Nd-Pb-Hf-O isotopic compositions ((87Sr/86Sr)i = 0.70308-0.70501, εNd (t) = - 0.5 to + 2.8, 207Pb/204Pb = 15.60-15.82, zircon εHf (t) = + 1.2 to + 15.6 and δ18O = + 4.6 to + 10.3‰), whole rock TDMC (Nd) (840-1120 Ma) and zircon TDMC (Hf) (320-1240 Ma). The isotopic characteristics are consistent with a hybrid magma source caused by 10-30% assimilation of ancient crust by juvenile lower crust. The geochronology and geochemistry of these granites show that the Late Carboniferous pre-mineralization granitic rocks formed during subduction, whereas the Early Permian ore-forming, highly fractionated granite probably underwent significant fractionation with a restite assemblage of K-feldspar, apatite, Ti-bearing phases and minor plagioclase and developed during collision between the Yili and Kazakhstan terranes commenced at the latest Late Carboniferous.

The double-edged sword of high-precision U-Pb geochronology or be careful what you wish for. (Invited)

NASA Astrophysics Data System (ADS)

Bowring, S. A.

2010-12-01

Over the past two decades, U-Pb geochronology by ID-TIMS has been refined to achieve internal (analytical) uncertainties on a single grain analysis of ± ~ 0.1-0.2%, and 0.05% or better on weighted mean dates. This level of precision enables unprecedented evaluation of the rates and durations of geological processes, from magma chamber evolution to mass extinctions and recoveries. The increased precision, however, exposes complexity in magmatic/volcanic systems and highlights the importance of corrections related to disequilibrium partitioning of intermediate daughter products, and raises questions as to how best to interpret the complex spectrum of dates characteristic of many volcanic rocks. In addition, the increased precision requires renewed emphasis on the accuracy of U decay constants, the isotopic composition of U, the calibration of isotopic tracers, and the accurate propagation of uncertainties It is now commonplace in the high precision dating of volcanic ash-beds to analyze 5-20 single grains of zircon in an attempt to resolve the eruption/depositional age. Data sets with dispersion far in excess of analytical uncertainties are interpreted to reflect Pb-loss, inheritance, and protracted crystallization, often supported with zircon chemistry. In most cases, a weighted mean of the youngest reproducible dates is interpreted as the time of eruption/deposition. Crystallization histories of silicic magmatic systems recovered from plutonic rocks may also be protracted, though may not be directly applicable to silicic eruptions; each sample must be evaluated independently. A key to robust interpretations is the integration high-spatial resolution zircon trace element geochemistry with high-precision ID-TIMS analyses. The EARTHTIME initiative has focused on many of these issues, and the larger subject of constructing a timeline for earth history using both U-Pb and Ar-Ar chronometers. Despite continuing improvements in both, comparing dates for the same rock with both chronometers is not straightforward. Compelling issues range from pre-eruptive magma chamber residence, recognizing open system behavior, accurately correcting for disequilibrium amounts of 230Th and 231Pa, precise and accurate dates of fluence monitors for 40Ar/39Ar, and inter-laboratory biases. At present, despite the level of internal precision achievable by each technique, obstacles remain to combining both chronometers.

Ancient Pb and Ti mobilization revealed by Scanning Ion Imaging

NASA Astrophysics Data System (ADS)

Kusiak, Monika A.; Whitehouse, Martin J.; Wilde, Simon A.

2014-05-01

Zircons from strongly layered early Archean ortho- and paragneisses in ultra-high temperature (UHT) metamorphic rocks of the Napier Complex, Enderby Land, East Antarctica are characterized by complex U-Th-Pb systematics [1,2,3]. A large number of zircons from three samples, Gage Ridge, Mount Sones and Dallwitz Nunatak, are reversely discordant (U/Pb ages older than 207Pb/206Pb ages) with the oldest date of 3.9 Ga [4] (for the grain from Gage Ridge orthogneiss). To further investigate this process, we utilized a novel high spatial resolution Scanning Ion Imaging technique on the CAMECA IMS 1280 at the Natural History Museum in Stockholm. Areas of 70 μm x 70 μm were selected for imaging in mono- and multicollection modes using a ~2 μm rastered primary beam to map out the distribution of 48Ti, 89Y, 180Hf, 232Th, 238U, 204Pb, 206Pb and 207Pb. The ion maps reveal variable distribution of certain elements within analysed grains that can be compared to their CL response. Yttrium, together with U and Th, exhibits zonation visible on the CL images, Hf shows expected minimal variation. Unusual patchiness is visible in the map for Ti and Pb distribution. The bright patches with enhanced signal do not correspond to any zones or to crystal imperfections (e.g. cracks). The presence of patchy titanium is likely to affect Ti-in-zircon thermometry, and patchy Pb affecting 207Pb/206Pb ages, usually considered as more robust for Archean zircons. Using the WinImage program, we produced 207Pb/206Pb ratio maps that allow calculation of 207Pb/206Pb ages for spots of any size within the frame of the picture and at any time after data collection. This provides a new and unique method for obtaining age information from zircon. These maps show areas of enhanced brightness where the 207Pb/206Pb ratio is higher and demonstrate that within these small areas (μm scale) the apparent 207Pb/206Pb age is older, in some of these patches even > 4 Ga. These data are a result of ancient Pb mobilization, which is independent of the degree of metamictisation, oxygen isotope and REE content of the zircons [5]. The Antarctic zircons experienced ancient Ti and Pb mobilization and redistribution, most likely caused by polyphase metamorphism at ~2.8 Ga and ~2.5 Ga, the latter documented as reaching temperatures of >1100ºC [5]. References: [1] Williams et al., 1984, Contr. Min. Petrol. 88, 322-327. [2] Black et al., (1986), Contr. Min. Petrol. 94, 427-437. [3] Harley & Kelly, 2007, Earth's Oldest Rocks: Developments in Precambrian Geology 15, 149-186. [4] Kusiak et al., 2013, Geology 41, 291-294. [5] Kusiak et al., 2013, American J. of Sci. 313, 933-967. [5] Hokada et al., 2004, Contr. Min. Petrol. 147, 1-20.

40 CFR Table C-3 to Subpart C of... - Test Specifications for Pb in TSP and Pb in PM10 Methods

Code of Federal Regulations, 2011 CFR

2011-07-01

... Pb in PM10 Methods C Table C-3 to Subpart C of Part 53 Protection of Environment ENVIRONMENTAL..., Subpt. C, Table C-3 Table C-3 to Subpart C of Part 53—Test Specifications for Pb in TSP and Pb in PM10 Methods Table C-3 to Subpart C of Part 53—Test Specifications for Pb in TSP and Pb in PM10 Methods...

40 CFR Table C-3 to Subpart C of... - Test Specifications for Pb in TSP and Pb in PM10 Methods

Code of Federal Regulations, 2010 CFR

2010-07-01

... Pb in PM10 Methods C Table C-3 to Subpart C of Part 53 Protection of Environment ENVIRONMENTAL..., Subpt. C, Table C-3 Table C-3 to Subpart C of Part 53—Test Specifications for Pb in TSP and Pb in PM10 Methods Table C-3 to Subpart C of Part 53—Test Specifications for Pb in TSP and Pb in PM10 Methods...

A century long sedimentary record of anthropogenic lead (Pb), Pb isotopes and other trace metals in Singapore.

PubMed

Chen, Mengli; Boyle, Edward A; Switzer, Adam D; Gouramanis, Chris

2016-06-01

Reconstructing the history of metal deposition in Singapore lake sediments contributes to understanding the anthropogenic and natural metal deposition in the data-sparse Southeast Asia. To this end, we present a sedimentary record of Pb, Pb isotopes and eleven other metals (Ag, As, Ba, Cd, Co, Cr, Cu, Ni, Tl, U and Zn) from a well-dated sediment core collected near the depocenter of MacRitchie Reservoir in central Singapore. Before the 1900s, the sedimentary Pb concentration was less than 2 mg/kg for both soil and sediment, with a corresponding (206)Pb/(207)Pb of ∼1.20. The Pb concentration increased to 55 mg/kg in the 1990s, and correspondingly the (206)Pb/(207)Pb decreased to less than 1.14. The (206)Pb/(207)Pb in the core top sediment is concordant with the (206)Pb/(207)Pb signal of aerosols in Singapore and other Southeast Asian cities, suggesting that Pb in the reservoir sediment was mainly from atmospheric deposition. Using the Pb concentration in the topmost layer of sediment, the estimated atmospheric Pb flux in Singapore today is ∼1.6 × 10(-2) g/m(2) yr. The concentrations of eleven other metals preserved in the sediment were also determined. A principal component analysis showed that most of the metals exhibit an increasing trend towards 1990s with a local concentration peak in the mid-20(th) century. Copyright © 2016. Published by Elsevier Ltd.

Accumulation rates and predominant atmospheric sources of natural and anthropogenic Hg and Pb on the Faroe Islands

NASA Astrophysics Data System (ADS)

Shotyk, W.; Goodsite, M. E.; Roos-Barraclough, F.; Givelet, N.; Le Roux, G.; Weiss, D.; Cheburkin, A. K.; Knudsen, K.; Heinemeier, J.; van Der Knaap, W. O.; Norton, S. A.; Lohse, C.

2005-01-01

A monolith representing 5420 14C yr of peat accumulation was collected from a blanket bog at Myrarnar, Faroe Islands. The maximum Hg concentration (498 ng/g at a depth of 4.5 cm) coincides with the maximum concentration of anthropogenic Pb (111 μg/g). Age dating of recent peat accumulation using 210Pb (CRS model) shows that the maxima in Hg and Pb concentrations occur at AD 1954 ± 2. These results, combined with the isotopic composition of Pb in that sample ( 206Pb/ 207Pb = 1.1720 ± 0.0017), suggest that coal burning was the dominant source of both elements. From the onset of peat accumulation (ca. 4286 BC) until AD 1385, the ratios Hg/Br and Hg/Se were constant (2.2 ± 0.5 × 10 -4 and 8.5 ± 1.8 × 10 -3, respectively). Since then, Hg/Br and Hg/Se values have increased, also reaching their maxima in AD 1954. The age date of the maximum concentrations of anthropogenic Hg and Pb in the Faroe Islands is consistent with a previous study of peat cores from Greenland and Denmark (dated using the atmospheric bomb pulse curve of 14C), which showed maximum concentrations in AD 1953. The average rate of atmospheric Hg accumulation from 1520 BC to AD 1385 was 1.27 ± 0.38 μg/m 2/yr. The Br and Se concentrations and the background Hg/Br and Hg/Se ratios were used to calculate the average rate of natural Hg accumulation for the same period, 1.32 ± 0.36 μg/m 2/yr and 1.34 ± 0.29 μg/m 2/yr, respectively. These fluxes are similar to the preanthropogenic rates obtained using peat cores from Switzerland, southern Greenland, southern Ontario, Canada, and the northeastern United States. Episodic volcanic emissions and the continual supply of marine aerosols to the Faroe Islands, therefore, have not contributed significantly to the Hg inventory or the Hg accumulation rates, relative to these other areas. The maximum rate of Hg accumulation was 34 μg/m 2/yr. The greatest fluxes of anthropogenic Hg accumulation calculated using Br and Se, respectively, were 26 and 31 μg/m 2/yr. The rate of atmospheric Hg accumulation in 1998 (16 μg/m 2/yr) is comparable to the values recently obtained by atmospheric transport modeling for Denmark, the Faroe Islands, and Greenland.

Dating sub-20 micron zircons in granulite-facies mafic dikes from SW Montana: a new approach using automated mineralogy and SIMS U-Pb geochronology

NASA Astrophysics Data System (ADS)

Ault, A. K.; Mahan, K. H.; Flowers, R. M.; Chamberlain, K.; Appleby, S. K.; Schmitt, A. K.

2010-12-01

Geochronological data is fundamental to all tectonic studies, but a major limitation for many lithologies is a paucity of sizeable zircons suitable for conventional U-Pb techniques. In particular, mafic dike swarms provide important time markers for tectonometamorphic activity in Precambrian terranes, but commonly yield little or no zircon or baddeleyite sufficient for TIMS or standard ion-probe analysis of crystal separates. We apply a new approach involving in-situ automated mineralogy and high spatial resolution Secondary Ion Mass Spectrometry (SIMS) geochronology to a mafic dike swarm exposed in the Northern Madison Range of SW Montana. The dikes cross-cut early fabrics but are also variably deformed and metamorphosed to P-T conditions as high as 1.2 GPa and 850 C. The swarm emplacement age is inferred to be ca. 2.1 Ga based on similarities to dated dikes in the adjacent Tobacco Root Mountains. Resolving the timing of dike emplacement and high-grade metamorphism in the study area is important for understanding the extent of post-Archean modification to the northwest margin of the Wyoming craton. Identification and textural characterization of zircons were facilitated by in-situ automated mineralogical analysis, in contrast to a standard elemental X-ray mapping approach. Our technique uses an SEM-based platform coupling calibrated BSE data with X-ray data collected by multiple energy dispersive spectrometers to rapidly identify target accessory phases at high spatial resolution. Whole thin section search maps were generated in ~30 minutes at 4 µm pixel resolution. Our dike thin sections commonly contained >300 zircons in a variety of textural settings, with 80% having a short dimension <10 µm. Zircons were dated in-situ by adjusting the field aperture of the CAMECA ims1270 to preferentially collect secondary ions emitted from within the inner few microns of the ~15 µm diameter analysis pit. This allows us to analyze zircon grains with a minimum dimension as small as 8 μm at radiogenic yields typically >95% for 206Pb. SIMS data for 22 zircons from a granulite-facies mafic dike thin section define a chord with upper and lower intercepts of 1753.1 ± 9.5 Ma and 63.2 ± 7.9 Ma, respectively (2 sigma error, MSWD = 1.6). A positive correlation between U concentration and degree of discordance indicates that the more radiation-damaged zircons underwent greater Pb loss. We infer Pb loss to reflect re-heating linked to emplacement of the nearby Tobacco Roots Batholith (ca. 74-71 Ma). Metamorphic zircon growth ca. 1750 Ma indicates that the high-grade metamorphic core of the Big Sky orogeny extends into the Northern Madison Range, farther inboard into the Wyoming craton than previously recognized. Coupling automated mineralogy searching with refined SIMS methods enables acquisition and interpretation of in-situ U-Pb data from zircons of a size that would not be feasible with most other techniques.

Time-scale calibration by U-Pb geochronology: Examples from the Triassic Period

NASA Astrophysics Data System (ADS)

Mundil, R.

2009-05-01

U-Pb zircon geochronology, pioneered by Tom Krogh, is a cornerstone for the calibration of the time scale. Before Krogh's innovations, U-Pb geochronology was essentially limited by laboratory blank Pb (typically hundreds of nanograms) inherent in the then existing zircon dissolution and purification methods. The introduction of high pressure HF dissolution combined with miniature ion exchange columns (1) reduced the blank by orders of magnitude and allowed mass-spectrometric analyses of minute amounts of material (picograms of Pb and U). Krogh also recognized the need for minimizing the effects of Pb loss, and the introduction of the air-abrasion technique was the method of choice for two decades (2), until the development of the combined annealing and chemical abrasion technique resulted in essentially closed system zircons (3). These are the prerequisite for obtaining precise (permil-level) and accurate radio-isotopic ages of individual zircons contained in primary volcanic ash deposits, which are primary targets for the calibration of the time scale if they occur within fossil bearing sediments. A prime example is the calibration of the Triassic time scale which improved significantly using these techniques. The ages for the base and the top of the Triassic are constrained by U-Pb ages to 252.3 (4) and 201.5 Ma (5), respectively. These dates also constrain the ages of major extinction events at the Permian-Triassic and Triassic-Jurassic boundaries, and are statistically indistinguishable from ages obtained for the Siberian Traps and volcanic products from the Central Atlantic Magmatic Province, respectively, suggesting a causal link. Ages for these continental volcanics, however, are mostly from the K-Ar (40Ar/39Ar) system which requires accounting and correcting for a systematic bias of ca 1 % between U-Pb and 40Ar/39Ar isotopic ages (the 40Ar/39Ar ages being younger) (6). Robust U-Pb age constraints also exist for the Induan- Olenekian boundary (251.2 Ma, (7)) and the Early-Middle Triassic (Olenekian-Anisian) boundary (247.2 Ma, (8, 9)), resulting in a surprisingly short duration of the Early Triassic which has implications for the timing of biotic recovery and major changes in ocean chemistry during this time. Furthermore, the Anisian-Ladinian boundary is constrained to 242.0 Ma by new U-Pb and 40Ar/39Ar ages. Radio-isotopic ages for the Late Triassic are scarce and the only reliable and biostratigraphically controlled age is from an upper Carnian tuff dated to 230.9 Ma (10), yielding a duration of more than 35 Ma for the Late Triassic. The resulting time-scale is at odds with the most recent compilation (11) but arguably more accurate because it is entirely based on U-Pb analyses applied to closed-system zircons with uncertainties at the permil level or better. 1. T. E. Krogh, Geochimica et Cosmochimica Acta 37, 485 (1973); 2. T. E. Krogh, Geochimica et Cosmochimica Acta 46, 637 (1982); 3. J. M. Mattinson, Chemical Geology 220, 47 (2005); 4. R. Mundil, K. R. Ludwig, I. Metcalfe, P. R. Renne, Science 305, 1760 (2004); 5. U. Schaltegger, J. Guex, A. Bartolini, B. Schoene, M. Ovtcharova, Earth and Planetary Science Letters 267, 266 (2008); 6. R. Mundil, P. R. Renne, K. K. Min, K. R. Ludwig, in Eos Trans. AGU, Fall Meet. Suppl. (2006), vol. 87(52), pp. V21A-0543; 7. T. Galfetti et al., Earth and Planetary Science Letters 258, 593 (2007). 8. M. Ovtcharova et al., Earth and Planetary Science Letters 243, 463 (2006). 9. J. Ramezani et al., Earth and Planetary Science Letters 256, 244 (2007). 10. S. Furin et al., Geology 34, 1009 (2006); 11. J. G. Ogg, in A Geologic Time Scale 2004 F. M. Gradstein, J. G. Ogg, A. G. Smith, Eds. (University Press, Cambridge, 2004) pp. 271-306.

Timing of global regression and microbial bloom linked with the Permian-Triassic boundary mass extinction: implications for driving mechanisms

NASA Astrophysics Data System (ADS)

Baresel, Bjoern; Bucher, Hugo; Bagherpour, Borhan; Brosse, Morgane; Guodun, Kuang; Schaltegger, Urs

2017-04-01

High-precision U-Pb dating of single-zircon crystals by chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) is applied to volcanic beds that are intercalated in sedimentary sequences across the Permian-Triassic boundary (PTB). By assuming that the zircon crystallization age closely approximate that of the volcanic eruption and subsequent deposition, U-Pb zircon geochronology is the preferred approach for dating abiotic and biotic events, such as the formational PTB and the Permian-Triassic boundary mass extinction (PTBME). We will present new U-Pb zircon dates for a series of volcanic ash beds in shallow-marine Permian-Triassic sections in the Nanpanjiang Basin, South China. These high-resolution U-Pb dates indicate a duration of 90 ± 38 kyr for the Permian sedimentary hiatus and a duration of 13 ± 57 kyr for the overlying Triassic microbial limestone in the shallow water settings of the Nanpanjiang pull apart Basin. The age and duration of the hiatus coincides with the formational PTB and the extinction interval in the Meishan Global Stratotype Section and Point, thus strongly supporting a glacio-eustatic regression, which best explains the genesis of the worldwide hiatus straddling the PTB in shallow water records. In adjacent deep marine troughs, rates of sediment accumulation display a six-fold decrease across the PTB compatible with a dryer and cooler climate during the Griesbachian as indicated by terrestrial plants. Our model of the PTBME hinges on the synchronicity of the hiatus with the onset of the Siberian Traps volcanism. This early eruptive phase likely released sulfur-rich volatiles into the stratosphere, thus simultaneously eliciting a short-lived ice age responsible for the global regression and a brief but intense acidification. Abrupt cooling, shrunk habitats on shelves and acidification may all have synergistically triggered the PTBME. Subsequently, the build-up of volcanic CO2 induced this transient cool climate whose early phase saw the deposition of the microbial limestone.

National geochronological and natural radioelement data bases

USGS Publications Warehouse

Zartman, Robert E.; Bush, Charles A.; Abston, C.C.

1995-01-01

This CD-ROM contains both the National Geochronological Data Base [NGDB] and the Natural Radioelement Data Base [NRDB]. Supporting location, geologic, and reference information is provided for both data bases. The NGDB is a compilation of more than 30,000 individual published Pb-alpha, fission-track, K-Ar, Rb-Sr, U-Th-Pb, and Sm-Nd rock and mineral ages reported on approximately 18,000 dated samples from the United States. A program is provided to search the data files by latitude and longitude, state, analytical method, and age range. The NGDB is provided as quote-comma delimited files that can be entered into most commercial spreadsheet programs. The NRDB gives gamma-ray spectrometric analyses of the natural radioelements (U, Th, and K) for more than 8500 whole-rock samples obtained under the USGS Natural Radioelement Distribution Project. A program is provided to search the data files by state, keyword, U content, Th content, and K content.

The presence of lead decreases the availability of meso-2, 3-dimercaptosuccinic acid for analysis in the monobromobimane assay.

PubMed

Lever, S Z; Parsons, T L

1999-11-01

meso-2,3-Dimercaptosuccinic acid is a suitable chelating agent for routine pharmacotherapy of lead poisoning in children. Administration of meso-2,3-dimercaptosuccinic acid presumably permits complexation of lead in vivo, allowing excretion through urine or feces. Quantification of the lead is achieved independently from the analysis of meso-2,3-dimercaptosuccinic acid and metabolites from the monobromobimane assay. To date, no direct chemical characterization of the Pb species excreted in urine has been successful. Pharmacokinetic correlation of lead excretion with excretion of meso-2,3-dimercaptosuccinic acid and metabolites has been utilized as an indirect method to draw conclusions regarding the identity of the active chelating agent. In this study, we hypothesized that the Pb-coordinated thiols are not reactive with respect to monobromobimane, and thus, the active chelator contained in the lead complex escapes detection. We performed variations of the assay and found that (1) the fluorescence detector response for the meso-2,3-dimercaptosuccinic acid-monobromobimane adduct was clearly attenuated as a function of added Pb, (2) when meso-2, 3-dimercaptosuccinic acid and monobromobimane were mixed prior to the addition of lead, the lead had no effect on detector response, (3) the addition of dithiothreitol does not affect the ability of Pb to react with meso-2,3-dimercaptosuccinic acid and verifies that oxidation of meso-DMSA had not occurred, and (4) the addition of ethylenediaminetetraacetic acid to the assay reverses the result found in point 1, presumably through trans chelation of the Pb-DMSA complex. Indirect quantification of the Pb-DMSA complexes found in urine might be accomplished through modification of the standard monobromobimane assay for analysis of meso-2,3-dimercaptosuccinic acid.

U-Pb geochronology and Hf-Nd isotope compositions of the oldest Neoproterozoic crust within the Cadomian orogen: new evidence for a unique juvenile terrane

NASA Astrophysics Data System (ADS)

Samson, S. D.; D'Lemos, R. S.; Blichert-Toft, J.; Vervoort, J.

2003-03-01

New U-Pb dates, combined with Nd and Hf isotopic data, from rocks within the Port Morvan area of the Baie de St Brieuc region of Brittany identify a unique portion of the Neoproterozoic Cadomia terrane. Two gneisses near Port Morvan yielded U-Pb dates of 754.6±0.8 Ma and 746.0±0.9 Ma, ages that are more than 130 Myr older than the oldest units formed during the main phase of early Cadomian magmatism. Two trondhjemite boulders from the monogenetic facies of the Cesson conglomerate yielded identical ages of 665.2±0.5 Ma and 665.5±0.7 Ma, and a cobble from the polygenetic facies yields a 207Pb- 206Pb date of 637±2 Ma. Individual detrital zircons from a sandstone associated with the Cesson conglomerates yield concordant U-Pb dates ranging from 650±3 Ma to 624.1±0.6 Ma. Initial ɛNd values for the rocks in this region range from +5.0 to +6.6, indicative of a substantial input from depleted mantle. Initial ɛHf values determined on zircons from these Neoproterozoic rocks, including the detrital zircons, range from +6.7 to +14.5, consistent with the Nd isotopic results. Maximum initial ɛHf values for two 2 Ga Icartian gneisses, considered basement to Cadomia, average +8.4 and +8.7. In contrast to the results of the Port Morvan rocks, 616-608 Ma syn-tectonic intrusions from Normandy and the British Channel Islands all have negative initial ɛNd values (-10.4 to -8.3) consistent with significant contamination by ancient crust such as the 2 Ga gneisses. The oldest arc-related magmas should have interacted most extensively with Cadomian basement, buffering younger mantle-derived magmas that were generated in subsequent magmatic episodes. The rocks within the Port Morvan region are thus inconsistent as examples of the earliest Cadomian intrusions as they show no evidence of interaction with 2 Ga basement. Instead, the older ages and mantle-like isotopic composition of these rocks suggest they are part of an independent terrane that formed prior to, and independently from, the Cadomian arc. Possible terrane-scale structural boundaries have recently been identified, including the newly recognized Port Morvan thrust fault and the NW-dipping Main Cadomian thrust.

Estimation of a Historic Mercury Load Function for Lake Michigan using Dated Sediment Cores

EPA Science Inventory

Box cores collected between 1994 and 1996 were used to estimate historic mercury loads to Lake Michigan. Based on a kriging spatial interpolation of 54 Pb-210 dated cores, 228 metric tons of mercury are stored in the lake’s sediments (excluding Green Bay). To estimate the time ...

The basement of the Mount Athos peninsula, northern Greece: insights from geochemistry and zircon ages

NASA Astrophysics Data System (ADS)

Himmerkus, F.; Zachariadis, P.; Reischmann, T.; Kostopoulos, D.

2012-09-01

The Mount Athos Peninsula is situated in the south-easternmost part of the Chalkidiki Peninsula in northern Greece. It belongs to the Serbo-Macedonian Massif (SMM), a large basement massif within the Internal Hellenides. The south-eastern part of the Mount Athos peninsula is built by fine-grained banded biotite gneisses and migmatites forming a domal structure. The southern tip of the peninsula, which also comprises Mount Athos itself, is built by limestone, marble and low-grade metamorphic rocks of the Chortiatis Unit. The northern part and the majority of the western shore of the Mount Athos peninsula are composed of highly deformed rocks belonging to a tectonic mélange termed the Athos-Volvi-Suture Zone (AVZ), which separates two major basement units: the Vertiskos Terrane in the west and the Kerdillion Unit in the east. The rock-types in this mélange range from metasediments, marbles and gneisses to amphibolites, eclogites and peridotites. The gneisses are tectonic slivers of the adjacent basement complexes. The mélange zone and the gneisses were intruded by granites (Ierissos, Ouranoupolis and Gregoriou). The Ouranoupolis intrusion obscures the contact between the mélange and the gneisses. The granites are only slightly deformed and therefore postdate the accretionary event that assembled the units and created the mélange. Pb-Pb- and U-Pb-SHRIMP-dating of igneous zircons of the gneisses and granites of the eastern Athos peninsula in conjunction with geochemical and isotopic analyses are used to put Athos into the context of a regional tectonic model. The ages form three clusters: The basement age is indicated by two samples that yielded Permo-Carboniferous U-Pb-ages of 292.6 ± 2.9 Ma and 299.4 ± 3.5 Ma. The main magmatic event of the granitoids now forming the gneiss dome is dated by Pb-Pb-ages between 140.0 ± 2.6 Ma and 155.7 ± 5.1 Ma with a mean of 144.7 ± 2.4 Ma. A within-error identical age of 146.6 ± 2.3 Ma was obtained by the U-Pb-SHRIMP method. This Late Jurassic age is also known from the Kerdillion Unit and the Rhodope Terrane. The rather undeformed granites are interpreted as piercing plutons. The small granite stocks sampled have Late Cretaceous to Early Tertiary ages of 66.8 ± 0.8 Ma and 68.0 ± 1.0 Ma (U-Pb-SHRIMP)/62.8 ± 3.9 Ma (Pb-Pb). The main accretionary event was according to these data in the Late Jurassic since all younger rocks show little or no deformation. The age distribution together with the geochemical and isotopic signature and the lithology indicates that the eastern part of the Mount Athos peninsula is part of a large-scale gneiss dome also building the Kerdillion Unit of the eastern SMM and the Rhodope Massif. This finding extends the area of this dome significantly to the south and indicates that the tectonic boundary between the SMM and the Rhodope Massif lies within the AVZ.

Large-scale sill emplacement in Brazil as a trigger for the end-Triassic crisis.

PubMed

Heimdal, Thea H; Svensen, Henrik H; Ramezani, Jahandar; Iyer, Karthik; Pereira, Egberto; Rodrigues, René; Jones, Morgan T; Callegaro, Sara

2018-01-09

The end-Triassic is characterized by one of the largest mass extinctions in the Phanerozoic, coinciding with major carbon cycle perturbations and global warming. It has been suggested that the environmental crisis is linked to widespread sill intrusions during magmatism associated with the Central Atlantic Magmatic Province (CAMP). Sub-volcanic sills are abundant in two of the largest onshore sedimentary basins in Brazil, the Amazonas and Solimões basins, where they comprise up to 20% of the stratigraphy. These basins contain extensive deposits of carbonate and evaporite, in addition to organic-rich shales and major hydrocarbon reservoirs. Here we show that large scale volatile generation followed sill emplacement in these lithologies. Thermal modeling demonstrates that contact metamorphism in the two basins could have generated 88,000 Gt CO 2 . In order to constrain the timing of gas generation, zircon from two sills has been dated by the U-Pb CA-ID-TIMS method, resulting in 206 Pb/ 238 U dates of 201.477 ± 0.062 Ma and 201.470 ± 0.089 Ma. Our findings demonstrate synchronicity between the intrusive phase and the end-Triassic mass extinction, and provide a quantified degassing scenario for one of the most dramatic time periods in the history of Earth.

Simultaneous in situ determination of both U-Th-Pb and Sm-Nd isotopes in monazite by laser ablation using a magnetic sector ICP-MS and a multicollector ICP-MS

NASA Astrophysics Data System (ADS)

Goudie, D. J.; Fisher, C. M.; Hanchar, J. M.; Davis, W. J.; Crowley, J. L.; Ayers, J. C.

2012-12-01

We present a method for the simultaneous in situ determination of U-Th-Pb and Sm-Nd isotopes in monazite, using a laser ablation (LA) system coupled to both a magnetic sector inductively coupled plasma mass spectrometer (HR) ICP-MS and a multicollector (MC) ICP-MS. The ablated material is split using a glass Y-connector and transported simultaneously to both mass spectrometers via helium carrier gas. The MC-ICP-MS is configured to provide relative Ce, Gd, and Eu contents, in addition to Sm and Nd. This approach obtains both age (U-Pb), tracer isotope (Sm-Nd), and REE element data (Ce, Gd, and Eu), in the same ablation volume, thus reducing sampling problems associated with fine-scale zoning and other internal structures. The accuracy and precision of the U-Pb data are demonstrated using six well characterized monazite reference materials from the Geological Survey of Canada (three of which are currently used as SHRIMP standards) and agree well with previously determined ID-TIMS ages. The accuracy of the Sm-Nd isotopic data was assessed by comparison to TIMS measurements on a well-characterized in-house monazite standard. The dual LA-ICP-MS method was applied to the Birch Creek Pluton (BCP) in the White Mountains, California in a case study to test the utility of U-Th-Pb dating coupled with Sm-Nd (and Ce, Gd, Eu) isotopic data for solving geologic problems. Previous work on the Cretaceous BCP [1] used Th-Pb ages coupled with O isotopic data to constrain hydrothermal fluid events, as recorded in monazite. The original study suggested that the high delta 18O monazite in Paleozoic country rocks adjacent to the BCP grew in response to fluid alternation associated with the intrusion of the BCP, based on overlapping age with the BCP. New monazite split-stream U-Pb and Sm-Nd data show that monazite from the BCP pluton and monazite from altered country rock have homogenous and overlapping initial Nd isotopic composition, further strengthening the proposal that monazite in altered country rock can be a tracer of fluid alternation events. The split-stream U-Pb ages agrees with new high precision ID-TIMS U-Pb ages from the same monazite grains. These results demonstrate how monazite age and Sm-Nd isotopic data, coupled with delta 18O, can identify hydrothermal monazite and constrain the timing and potential sources of fluid events. [1] Ayers et al., Geology 34 (2006) 653-656.

Combined oxygen-isotope and U-Pb zoning studies of titanite: New criteria for age preservation

DOE PAGES

Bonamici, Chloe E.; Fanning, C. Mark; Kozdon, Reinhard; ...

2015-02-11

Here, titanite is an important U-Pb chronometer for dating geologic events, but its high-temperature applicability depends upon its retention of radiogenic lead (Pb). Experimental data predict similar rates of diffusion for lead (Pb) and oxygen (O) in titanite at granulite-facies metamorphic conditions (T = 650-800°C). This study therefore investigates the utility of O-isotope zoning as an indicator for U-Pb zoning in natural titanite samples from the Carthage-Colton Mylonite Zone of the Adirondack Mountains, New York. Based on previous field, textural, and microanalytical work, there are four generations (types) of titanite in the study area, at least two of which preservemore » diffusion-related δ 18O zoning. U-Th-Pb was analyzed by SIMS along traverses across three grains of type-2 titanite, which show well-developed diffusional δ 18O zoning, and one representative grain from each of the other titanite generations.« less

Volatile Element Geochemistry in the Lower Atmosphere of Venus

NASA Technical Reports Server (NTRS)

Schaefer, L.; Fegley, B., Jr.

2004-01-01

We computed equilibrium abundances of volatile element compounds as a function of altitude in Venus lower atmosphere. The elements included are generally found in volcanic gases and sublimates on Earth and may be emitted in volcanic gases on Venus or volatilized from its hot surface. We predict: 1) PbS, Bi2S3, or possibly a Pb-Bi sulfosalt are the radar bright heavy metal frost in the Venusian highlands; 2) It should be possible to determine Venus' age by Pb-Pb dating of PbS condensed in the Venusian highlands, which should be a representative sample of Venusian lead; 3) The gases HBr, PbCl2, PbBr2, As4O6, As4S4, Sb4O6, BiSe, InBr, InCl, Hg, TlCl, TlBr, SeS, Se2-7, HI, I, I2, ZnCl2, and S2O have abundances greater than 0.1 ppbv in our nominal model and may be spectroscopically observable; 4) Cu, Ag, Au, Zn, Cd, Ge, and Sn are approx. 100 % condensed at the 740 K (0 km) level on Venus.

Concordant Rb-Sr and Sm-Nd Ages for NWA 1460: A 340 Ma Old Basaltic Shergottite Related to Lherzolitic Shergottites

NASA Technical Reports Server (NTRS)

Nyquist, L. E.; Shih, C-Y; Reese, Y. D.; Irving, A. J.

2006-01-01

Preliminary Rb-Sr and Sm-Nd ages reported by [1] for the NWA 1460 basaltic shergottite are refined to 336+/-14 Ma and 345+/-21 Ma, respectively. These concordant ages are interpreted as dating a lava flow on the Martian surface. The initial Sr and Nd isotopic compositions of NWA 1460 suggest it is an earlier melting product of a Martian mantle source region similar to those of the lherzolitic shergottites and basaltic shergottite EETA79001, lithology B. We also examine the suggestion that generally "young" ages for other Martian meteorites should be reinterpreted in light of Pb-207/Pb-206 - Pb-204/Pb-206 isotopic systematics [2]. Published U-Pb isotopic data for nakhlites are consistent with ages of approx.1.36 Ga. The UPb isotopic systematics of some Martian shergottites and lherzolites that have been suggested to be approx.4 Ga old [2] are complex. We nevertheless suggest the data are consistent with crystallization ages of approx.173 Ma when variations in the composition of in situ initial Pb as well as extraneous Pb components are considered.

Upper Mississippi Pb as a mid-1800s chronostratigraphic marker in sediments from seasonally anoxic lakes in Eastern Canada

NASA Astrophysics Data System (ADS)

Gobeil, Charles; Tessier, André; Couture, Raoul-Marie

2013-07-01

Sediment cores from eight headwater lakes located in Southern Québec, Eastern Canada, were analyzed for Pb, stable Pb isotopes, and the radioelements 210Pb, 137Cs, 241Am and 226Ra. The depth profiles of stable Pb isotope ratios show, for the post-19th century period, the influence of several isotopically distinct anthropogenic lead sources, mainly including emissions from two Canadian smelters and from leaded gasoline combustion in Canada and in the United States. A most interesting feature of the profiles, however, is the presence of sharp stable Pb isotope ratio peaks near the depth horizon, where excess 210Pb becomes undetectable. Using a binary mixing model and assuming that natural Pb concentrations and isotopic compositions from the catchment are given by the pre-industrial sediments at the bottom of the cores, we find that a significant part of the anthropogenic Pb supplied to the sediments at this horizon originated from smelting activities in the Upper Mississippi Valley. We assess that the Pb isotope ratio peaks, also observed in the laminated sediments of the Pettaquamscutt Estuary, Rhode Island, USA, are an accurate chronostratigraphic marker for the validation of mid-19th century 210Pb-derived dates. Given that the study lakes are located up to 2000 km from the Mississippi Valley, we conclude that this isotopic Pb signal provides a widely distributed time-marker that is key to validate 210Pb chronologies in environmental archives from Eastern North America.

40Ar/39Ar dating of oceanic plagiogranite: Constraints on the initiation of seafloor spreading in the South China Sea

NASA Astrophysics Data System (ADS)

Zhong, Li-Feng; Cai, Guan-Qiang; Koppers, Anthony A. P.; Xu, Yi-Gang; Xu, He-Hua; Gao, Hong-Fang; Xia, Bin

2018-03-01

The Cenozoic opening of the South China Sea was one of the most significant tectonic events in SE Asia, coinciding with complex regional rifting, subduction, terrane collision, and large-scale continental strike-slip faulting. The timing of the initiation of seafloor spreading in the South China Sea remains controversial due to a scarcity of incontrovertible age data. This work provides the first report of an oceanic plagiogranite from the Penglai Seamount, located on the 17°N fossil spreading center of the East Sub-basin of the South China Sea, near the Manila Trench. Pyroxene and whole-rock 40Ar/39Ar dating yields ages of 32.3 ± 0.5 Ma and 28.9 ± 1.9 Ma, respectively. The plagiogranite show trace element and isotopic composition similar to those of mid-oceanic ridge basalts (MORB), with 87Sr/86Sr(t) = 0.70394; εNd(t) = 8.21; 206Pb/204Pb = 17.9930, 207Pb/204Pb = 15.4839, 208Pb/204Pb = 37.8852; εHf(t) = 20.95; and γOs(t) = 15.89. It suggested that the rock formed due to differential cooling between adjacent layers of oceanic crust and asthenospheric shearing at the oceanic spreading ridge, resulting in the development of detachment faults. This triggered the subsequent ingress of seawater along the faults, which transformed into a hydrothermal fluid under the influence of shear and geothermal heating, altering the parent gabbro, and leading to the generation of the daughter plagiogranite by anatexis during the early Oligocene. This new geochronology also demonstrates that the initial opening of the South China Sea occurred before 32 Ma, thereby constraining the Cenozoic tectonic evolution of Southeast Asia.

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

NASA Astrophysics Data System (ADS)

Kunz, Barbara E.; Regis, Daniele; Engi, Martin

2018-03-01

Granulite facies rocks frequently show a large spread in their zircon ages, the interpretation of which raises questions: Has the isotopic system been disturbed? By what process(es) and conditions did the alteration occur? Can the dates be regarded as real ages, reflecting several growth episodes? Furthermore, under some circumstances of (ultra-)high-temperature metamorphism, decoupling of zircon U-Pb dates from their trace element geochemistry has been reported. Understanding these processes is crucial to help interpret such dates in the context of the P-T history. Our study presents evidence for decoupling in zircon from the highest grade metapelites (> 850 °C) taken along a continuous high-temperature metamorphic field gradient in the Ivrea Zone (NW Italy). These rocks represent a well-characterised segment of Permian lower continental crust with a protracted high-temperature history. Cathodoluminescence images reveal that zircons in the mid-amphibolite facies preserve mainly detrital cores with narrow overgrowths. In the upper amphibolite and granulite facies, preserved detrital cores decrease and metamorphic zircon increases in quantity. Across all samples we document a sequence of four rim generations based on textures. U-Pb dates, Th/U ratios and Ti-in-zircon concentrations show an essentially continuous evolution with increasing metamorphic grade, except in the samples from the granulite facies, which display significant scatter in age and chemistry. We associate the observed decoupling of zircon systematics in high-grade non-metamict zircon with disturbance processes related to differences in behaviour of non-formula elements (i.e. Pb, Th, U, Ti) at high-temperature conditions, notably differences in compatibility within the crystal structure.

Internal structures and dating of non-sulphide Zn deposits using rock magnetism: insights from the Moroccan High Atlas

NASA Astrophysics Data System (ADS)

Charles, Nicolas; Choulet, Flavien; Sizaret, Stanislas; Chen, Yan; Barbanson, Luc; Ennaciri, Aomar; Badra, Lakhlifi; Branquet, Yannick

2016-01-01

The renewal of interest in Zn-Pb non-sulphide ores has been induced by mineral processing improvement and leads to new exploration and mining projects in the world. Although the mineralogy is often precisely known, and despite several studies linking ore deposition to regional tectonics, absolute dating of non-sulphide stages is rare and structure of ore bodies was largely disregarded. Geochronological data from non-sulphide ores are essential to timely constrain alteration episodes and to insert supergene ore genesis in the climate and tectonic evolution of the metallogenic province. The access to internal organization of ore could reveal post-mineralization episodes related to supergene evolution. Thus, a rock magnetism study combining anisotropy of magnetic susceptibility (AMS) and palaeomagnetism was performed on four non-sulphide deposits from the Moroccan High Atlas. AMS generally shows similar horizontal magnetic fabrics for ores and the clayey and carbonaceous internal sediments filling karstic cavities. The palaeomagnetic directions of ores and internal sediments are compatible, and the calculated poles are consistent with the last 30 Ma of the Africa apparent polar wander path, with an upper age at 0.78 Ma. The proposed three-step scenario is placed within the evolution of the Moroccan High Atlas belt. Deposition of primary sulphides is contemporaneous with opening of the Tethyan and Atlantic oceans. During the Tertiary, intracontinental deformation gave rise to the High Atlas fold-and-thrust belt and to regional uplift. Finally, Zn-Pb sulphides hosted in carbonates experienced oxidation under an arid climate to form karst-related Zn-Pb non-sulphide ores. These promising results pave the way for an efficient method to constrain the internal fabrics and age of Zn supergene deposits.

A new insight into Pan-African tectonics in the East-West Gondwana collision zone by U-Pb zircon dating of granites from central Madagascar

NASA Astrophysics Data System (ADS)

Nédélec, A.; Paquette, J.-L.

1998-02-01

The assembly of Gondwana was the result of a major collision orogen, the East African Orogen, between East and West Gondwana during Neoproterozoic times. Madagascar, which represents a fragment of East Gondwana, is located in a key area of this Pan-African orogen. Granites of unambiguous tectonic setting have been dated using the U-Pb zircon method in order to constrain the timing of orogenic events. The central part of Madagascar is characterized by syntectonic alkaline granitic sheets, referred to as ``stratoid'' granites. These are of both mantle and crustal derivation. Their U-Pb zircon ages are well defined between 627 and 633 Ma for both plutonic suites, regardless of either mainly mantle or crustally origin. It is not surprising that the crustally-derived suite contains inherited zircons in the 2.2-2.4 Ga range attesting to the existence of Lower Proterozoic crust in northern central Madagascar. The generation of huge amounts of granitic magma is regarded as the result of post-collision extension under a high heat flow regime. Therefore, an age between 700 and 650 Ma is inferred for the beginning of Gondwana assembly along the collision zone between central Madagascar and Kenya, i.e., in the central part of the East African Orogen. Following this, brittle fracturing of the stratoid granite series permitted the emplacement of the Ambatomiranty granitic dyke swarm at a minimum age of 560 Ma, in possible connection with a nearby shear belt. The strike-slip tectonic regime at ~570-560 Ma is well known in southern Madagascar and in its Gondwana connections. This stage corresponds to intracontinental reworking and the final suturing of Gondwana.

A new insight into Pan-African tectonics in the East-West Gondwana collision zone by U-Pb zircon dating of granites from central Madagascar

NASA Astrophysics Data System (ADS)

Paquette, Jean-Louis; Nédélec, Anne

1998-02-01

The assembly of Gondwana was the result of a major collision orogen, the East African Orogen, between East and West Gondwana during Neoproterozoic times. Madagascar, which represents a fragment of East Gondwana, is located in a key area of this Pan-African orogen. Granites of unambiguous tectonic setting have been dated using the U-Pb zircon method in order to constrain the timing of orogenic events. The central part of Madagascar is characterized by syntectonic alkaline granitic sheets, referred to as "stratoid" granites. These are of both mantle and crustal derivation. Their U-Pb zircon ages are well defined between 627 and 633 Ma for both plutonic suites, regardless of either mainly mantle or crustally origin. It is not surprising that the crustally-derived suite contains inherited zircons in the 2.2-2.4 Ga range attesting to the existence of Lower Proterozoic crust in northern central Madagascar. The generation of huge amounts of granitic magma is regarded as the result of post-collision extension under a high heat flow regime. Therefore, an age between 700 and 650 Ma is inferred for the beginning of Gondwana assembly along the collision zone between central Madagascar and Kenya, i.e., in the central part of the East African Orogen. Following this, brittle fracturing of the stratoid granite series permitted the emplacement of the Ambatomiranty granitic dyke swarm at a minimum age of 560 Ma, in possible connection with a nearby shear belt. The strike-slip tectonic regime at ˜570-560 Ma is well known in southern Madagascar and in its Gondwana connections. This stage corresponds to intracontinental reworking and the final suturing of Gondwana.

Mineralogy and geochemistry of triassic carbonatites in the Matcha alkaline intrusive complex (Turkestan-Alai Ridge, Kyrgyz Southern Tien Shan), SW Central Asian orogenic belt

NASA Astrophysics Data System (ADS)

Vrublevskii, V. V.; Morova, A. A.; Bukharova, O. V.; Konovalenko, S. I.

2018-03-01

Postorogenic intrusions of essexites and alkaline and nepheline syenites in the Turkestan-Alai segment of the Kyrgyz Southern Tien Shan coexist with dikes and veins of carbonatites dated at ∼220 Ma by the Ar-Ar and Rb-Sr age methods. They are mainly composed of calcite and dolomite (60-85%), as well as sodic amphibole, phlogopite, clinopyroxene, microcline, albite, apatite, and magnetite, with accessory niobate, ilmenite, Nb-rutile, titanite, zircon, baddeleyite, monazite-(Ce), barite, and sulfides. The rocks share mineralogical and geochemical similarity with carbonatites that originated by liquid immiscibility at high temperatures above 500 °C. Alkaline silicate and salt-carbonate melts are derived from sources with mainly negative bulk εNd(t) ∼ from -11 to 0 and high initial 87Sr/86Sr ratios (∼0.7061-0.7095) which may be due to mixing of PREMA and EM-type mantle material. Pb isotopic ratios in accessory pyrrhotite (206Pb/204Pb = 18.38; 207Pb/204Pb = 15.64; 208Pb/204Pb = 38.41) exhibit an EM2 trend. The intrusions bear signatures of significant crustal contamination as a result of magma genesis by syntexis and hybridism. Concordant isotope composition changes of δ13C (-6.5 to -1.9‰), δ18O (9.2-23‰), δD (-58 to -41‰), and δ34S (12.6-12.8‰) in minerals and rocks indicate inputs of crustal material at the stage of melting and effect of hot fluids released during dehydration of metamorphosed oceanic basalts or sediments. The observed HFSE patterns of the oldest alkaline gabbro may be due to interaction of the primary mafic magma with IAB-type material. The isotope similarity of alkaline rocks with spatially proximal basalts of the Tarim large igneous province does not contradict the evolution of the Turkestan-Alai Triassic magmatism as the "last echo" of the Tarim mantle plume.

A Uranium-Lead Chronology of Speleothem Deposition in the Canadian Arctic

NASA Astrophysics Data System (ADS)

Gambino, C.; Shakun, J. D.; McGee, D.; Ramezani, J.; Khadivi, S.; Wong, C. I.

2017-12-01

The Artic is one of the fastest warming regions on the planet. Currently much of the Arctic is covered by permafrost, which contains approximately 1,700 gigatons of organic carbon. Permafrost thaw could release a substantial amount of this carbon as greenhouse gases into the atmosphere through microbial decomposition, potentially dramatically amplifying anthropogenic warming. However, the risk of permafrost thaw is uncertain, with models exhibiting a wide range of possibilities. Assessing the stability of permafrost during past interglacial periods enables evaluation of the sensitivity of permafrost to warming. Cave mineral deposits (speleothems) in areas currently covered with permafrost can act as a proxy for past permafrost thaw, as liquid water is one criteria of speleothem growth and thus implies thawed ground conditions. Previous uranium-thorium (U-Th) dating of speleothems (n=67) from a wide range of latitudes and permafrost zones across the southern Canadian Rockies, Northwest Territories, and the northern Yukon suggest deposition during Marine Isotope Stage (MIS) 11 and 13. The majority of U-Th dates of these speleothems, however, exceed the U-Th dating limit of 600 ka. In this study, we apply uranium-lead (U-Pb) geochronology to several of these speleothems to extend the records of speleothem growth further back in time. Initial results include a U-Pb age of 428 ± 14 ka that replicates a previous U-Th age of 416.8 ± 7.9 ka, and U-Pb ages on two other speleothems of 870 ± 100 ka and 1502 ± 30 ka. The results of currently in progress U-Pb analyses and a comparison of results with paleo-temperature and ice volume reconstructions will also be presented.

A Triassic to Cretaceous Sundaland-Pacific subduction margin in West Sarawak, Borneo

NASA Astrophysics Data System (ADS)

Breitfeld, H. Tim; Hall, Robert; Galin, Thomson; Forster, Margaret A.; BouDagher-Fadel, Marcelle K.

2017-01-01

Metamorphic rocks in West Sarawak are poorly exposed and studied. They were previously assumed to be pre-Carboniferous basement but had never been dated. New 40Ar/39Ar ages from white mica in quartz-mica schists reveal metamorphism between c. 216 to 220 Ma. The metamorphic rocks are associated with Triassic acid and basic igneous rocks, which indicate widespread magmatism. New U-Pb dating of zircons from the Jagoi Granodiorite indicates Triassic magmatism at c. 208 Ma and c. 240 Ma. U-Pb dating of zircons from volcaniclastic sediments of the Sadong and Kuching Formations confirms contemporaneous volcanism. The magmatic activity is interpreted to represent a Triassic subduction margin in westernmost West Sarawak with sediments deposited in a forearc basin derived from the magmatic arc at the Sundaland-Pacific margin. West Sarawak and NW Kalimantan are underlain by continental crust that was already part of Sundaland or accreted to Sundaland in the Triassic. One metabasite sample, also previously assumed to be pre-Carboniferous basement, yielded Early Cretaceous 40Ar/39Ar ages. They are interpreted to indicate resumption of subduction which led to deposition of volcaniclastic sediments and widespread magmatism. U-Pb ages from detrital zircons in the Cretaceous Pedawan Formation are similar to those from the Schwaner granites of NW Kalimantan, and the Pedawan Formation is interpreted as part of a Cretaceous forearc basin containing material eroded from a magmatic arc that extended from Vietnam to west Borneo. The youngest U-Pb ages from zircons in a tuff layer from the uppermost part of the Pedawan Formation indicate that volcanic activity continued until c. 86 to 88 Ma when subduction terminated.

Exploring the Photovoltaic Performance of All-Inorganic Ag2PbI4/PbI2 Blends.

PubMed

Frolova, Lyubov A; Anokhin, Denis V; Piryazev, Alexey A; Luchkin, Sergey Yu; Dremova, Nadezhda N; Troshin, Pavel A

2017-04-06

We present an all-inorganic photoactive material composed of Ag 2 PbI 4 and PbI 2 , which shows unexpectedly good photovoltaic performance in planar junction solar cells delivering external quantum efficiencies of ∼60% and light power conversion efficiencies of ∼3.9%. The revealed characteristics are among the best reported to date for metal halides with nonperovskite crystal structure. Most importantly, the obtained results suggest a possibility of reaching high photovoltaic efficiencies for binary and, probably, also ternary blends of different inorganic semiconductor materials. This approach, resembling the bulk heterojunction concept guiding the development of organic photovoltaics for two decades, opens wide opportunities for rational design of novel inorganic and hybrid materials for efficient and sustainable photovoltaic technologies.

The 238U/235U isotope ratio of the Earth and the solar system: Constrains from a gravimetrically calibrated U double spike and implications for absolute Pb-Pb ages

NASA Astrophysics Data System (ADS)

Weyer, Stefan; Noordmann, Janine; Brennecka, Greg; Richter, Stephan

2010-05-01

The ratio of 238U and 235U, the two primordial U isotopes, has been assumed to be constant on Earth and in the solar system. The commonly accepted value for the 238U/235U ratio, which has been used in Pb-Pb dating for the last ~ 30 years, was 137.88. Within the last few years, it has been shown that 1) there are considerable U isotope variations (~1.3‰) within terrestrial material produced by isotope fractionation during chemical reactions [1-3] and 2) there are even larger isotope variations (at least 3.5‰) in calcium-aluminum-rich inclusions (CAIs) in meoteorites that define the currently accepted age of the solar system [4]. These findings are dramatic for geochronology, as a known 238U/235U is a requirement for Pb-Pb dating, the most precise dating technique for absolute ages. As 238U/235U variations can greatly affect the reported absolute Pb-Pb age, understanding and accurately measuring variation of the 238U/235U ratio in various materials is critical, With these new findings, the questions also arises of "How well do we know the average U isotope composition of the Earth and the solar system?" and "How accurate can absolute Pb-Pb ages be?" Our results using a gravimetrically calibrated 233U/236U double spike IRMM 3636 [5] indicate that the U standard NBL 950a, which was commonly used to define the excepted "natural" 238U/235U isotope ratio, has a slightly lower 238U/235U of 137.836 ± 0.024. This value is indistinguishable from the U isotope compositions for NBL 960 and NBL112A, which have been determined by several laboratories, also using the newly calibrated U double spike IRMM 3636 [6]. These findings provide new implications about the average U isotope composition of the Earth and the solar system. Basalts display a very tight range of U isotope variations (~0.25-0.32‰ relative to SRM 950a). Their U isotope composition is also very similar to that of chondrites [4], which however appear to show a slightly larger spread. Accepting terrestrial basalts to be the best representation of the U isotope composition of the Earth and the solar system, and the new 238U/235U for SRM 950a of 137.836, this would result in an average 238U/235U for the Earth and the solar system of ~ 137.80. The effect of a revised 238U/235U ratio on Pb-Pb ages is age dependent. It results in an age overestimation of ~0.8 Ma for the age of the solar system and up to 1.5 Ma for very young material (with bulk Earth U isotope composition). [1] Stirling, C.H., Andersen, M.B., Potter, E.-K., et al. (2007) EPSL 264, 208-225; [2] Weyer, S., Anbar, A. D., Gerdes, A., et al. (2008) GCA 72, 345-359. [3] Bopp, C.H., Lundstrom, C.C., Johnsons, T.M., Glessner, J.G. (2009) Geology 37, 611-614. [4] Brennecka, G.A., Weyer, S., Wadhwa, et al. (2010) Science, 327, p. 449. [5] Richter, S., Alonzo-Munoz, A., Eykens, R., et al. (2008) IJMS 269, 145-148. [6] Richter, S., et al. EGU meeting 2010.

High-resolution 14C dating of a 25,000-year lake-sediment record from equatorial East Africa

NASA Astrophysics Data System (ADS)

Blaauw, Maarten; van Geel, Bas; Kristen, Iris; Plessen, Birgit; Lyaruu, Anna; Engstrom, Daniel R.; van der Plicht, Johannes; Verschuren, Dirk

2011-10-01

We dated a continuous, ˜22-m long sediment sequence from Lake Challa (Mt. Kilimanjaro area, Kenya/Tanzania) to produce a solid chronological framework for multi-proxy reconstructions of climate and environmental change in equatorial East Africa over the past 25,000 years. The age model is based on a total of 168 AMS 14C dates on bulk-organic matter, combined with a 210Pb chronology for recent sediments and corrected for a variable old-carbon age offset. This offset was estimated by i) pairing bulk-organic 14C dates with either 210Pb-derived time markers or 14C dates on grass charcoal, and ii) wiggle-matching high-density series of bulk-organic 14C dates. Variation in the old-carbon age offset through time is relatively modest, ranging from ˜450 yr during glacial and late glacial time to ˜200 yr during the early and mid-Holocene, and increasing again to ˜250 yr today. The screened and corrected 14C dates were calibrated sequentially, statistically constrained by their stratigraphical order. As a result their constrained calendar-age distributions are much narrower, and the calibrated dates more precise, than if each 14C date had been calibrated on its own. The smooth-spline age-depth model has 95% age uncertainty ranges of ˜50-230 yr during the Holocene and ˜250-550 yr in the glacial section of the record. The δ 13C values of paired bulk-organic and grass-charcoal samples, and additional 14C dating on selected turbidite horizons, indicates that the old-carbon age offset in Lake Challa is caused by a variable contribution of old terrestrial organic matter eroded from soils, and controlled mainly by changes in vegetation cover within the crater basin.

Intercomparison of radiocarbon bomb pulse and 210Pb age models. A study in a peat bog core from North Poland

NASA Astrophysics Data System (ADS)

Piotrowska, Natalia; De Vleeschouwer, François; Sikorski, Jarosław; Pawlyta, Jacek; Fagel, Nathalie; Le Roux, Gaël; Pazdur, Anna

2010-04-01

Radiocarbon and 210Pb were measured on the uppermost 40 cm of a Wardenaar peat core retrieved from a Baltic raised bog at Słowińskie Błota (Pomerania, North Poland). This site is the subject of ongoing multiproxy studies covering the last 1300 years. Radiocarbon age model was constructed on the basis of 14 AMS dates obtained on selected Sphagnum spp. fragments, with use of P_Sequence tool. We present here a comparison of this model with the age model obtained using CRS model classically applied to 210Pb measurements.

Zircon Zoning, Trace Elements and U-Pb Dates Reveal Crustal Foundering Beneath the Pamir

NASA Astrophysics Data System (ADS)

Hacker, B. R.; Shaffer, M. E. F.; Ratschbacher, L.; Kylander-Clark, A. R.

2017-12-01

Xenoliths that erupted in the SE Pamir of Tajikistan at 11.2 Ma from 1000-1050°C and 90 km depth illuminate what happens when crust founders into the mantle. The xenoliths are a broad range of crustal rock types and contain abundant xenoliths whose U-Pb isotopic ratios and trace-element contents were examined by laser-ablation split stream inductively coupled plasma mass spectrometry. Cathodoluminescence imaging of the grains shows igneous cores with oscillatory zoning overprinted by substantial recrystallization. The bulk of the U-Pb dates are concordant and range from 160 Ma to 11 Ma. The range of dates suggest that the xenoliths were likely derived from the Jurassic-Cretaceous Andean-style magmatic arc and its Proterozoic-Mesozoic host rocks along the southern margin of Asia. The zircons show distinct changes in Eu anomaly, Lu/Gd ratio, and Ti concentrations that are interpreted to indicate garnet growth and minimal heating at 22-20 Ma, and then 200-300°C of heating, 25 km of burial, and alkali-carbonate melt injection at 14-11 Ma. These changes are interpreted to coincide with: i) heat input due to Indian slab breakoff at 22‒20 Ma; ii) rapid thickening and foundering of the Pamir lithosphere at 14‒11 Ma, prior to and synchronous with collision between deep Indian and Asian lithospheres beneath the Pamir.

In situ rutile petrochronology: texture-related T, Paleoproterozoic inheritance and a Pan-African overprint in the oldest subduction-related eclogites, Usagaran Orogen, Tanzania

NASA Astrophysics Data System (ADS)

Moeller, A.; Kraus, K.; Herms, P.; Appel, P.; Raase, P.

2014-12-01

Rutile U-Pb thermochronology is applied successfully by both TIMS and beam methods to date cooling events in mafic and metapelitic rocks, as well as in detrital studies. The Zr-in-rutile thermometer is very robust to thermal diffusion, and generally requires complete recrystallization to change recorded crystallization temperatures. Evidence for diffusion of HFSE elements in rutile is sparse; whereas U-Pb chronology generally records diffusion controlled cooling from the last event. This study follows conventional thermobarometry and U-Pb TIMS results on monazite, sphene and rutile of Möller et al. (1995) establishing a 2 Ga eclogite facies event from MORB-like metabasic, and metapelitic rocks in the Usagaran Orogen of Tanzania, interpreted to be the oldest outcrops of subduction-related eclogites. Rutile from both rock types were discordant near a ca. 500 Ma lower intercept, confirming a thermal overprint postulated on the basis of K-Ar and Rb-Sr mica ages by e.g. Wendt et al. (1972). The age of the eclogite-facies event was confirmed by U-Pb zircon dating of a 1991±2 Ma crosscutting pegmatite (Collins et al., 1999). We present in situ LA-ICP-MS rutile petrochronology on five metabasic and metapelitic eclogite facies samples with variable retrograde amphibolite-facies recrystallization. Thermometry confirms conventional Fe-Mg results, including higher peak temperatures in metabasites. Traverses on rutile inclusions in large garnet prophyroblasts in metapelites show increasing temperatures from cores outwards and a slight decrease towards outermost rims, with peak T coinciding with highest Mg# and highest grossular content, hence consistent with preservation of prograde zoning in the garnets and a brief eclogite facies event. Large rutiles (800μm) in recrystallized samples record temperature zoning profiles. U-Pb results show inheritance of near concordant 2 Ga domains, but dominantly confirm the ca. 490 Ma amphibolite facies overprint. The study is an excellent example of the potential of in-situ rutile petrochronology in complex, polymetamorphic rocks when meticulous attention is given to textural context. Möller et al., 1995, Geology, v. 23, p. 1067-1070. Collins et al., 2004, Earth Planet. Sci. Lett., v. 224, p. 175-192. Wendt et al., 1972, 24th Internat. Geol. Congr., Proc., p. 295-314.

Real-time subsecond voltammetric analysis of Pb in aqueous environmental samples.

PubMed

Yang, Yuanyuan; Pathirathna, Pavithra; Siriwardhane, Thushani; McElmurry, Shawn P; Hashemi, Parastoo

2013-08-06

Lead (Pb) pollution is an important environmental and public health concern. Rapid Pb transport during stormwater runoff significantly impairs surface water quality. The ability to characterize and model Pb transport during these events is critical to mitigating its impact on the environment. However, Pb analysis is limited by the lack of analytical methods that can afford rapid, sensitive measurements in situ. While electrochemical methods have previously shown promise for rapid Pb analysis, they are currently limited in two ways. First, because of Pb's limited solubility, test solutions that are representative of environmental systems are not typically employed in laboratory characterizations. Second, concerns about traditional Hg electrode toxicity, stability, and low temporal resolution have dampened opportunities for in situ analyses with traditional electrochemical methods. In this paper, we describe two novel methodological advances that bypass these limitations. Using geochemical models, we first create an environmentally relevant test solution that can be used for electrochemical method development and characterization. Second, we develop a fast-scan cyclic voltammetry (FSCV) method for Pb detection on Hg-free carbon fiber microelectrodes. We assess the method's sensitivity and stability, taking into account Pb speciation, and utilize it to characterize rapid Pb fluctuations in real environmental samples. We thus present a novel real-time electrochemical tool for Pb analysis in both model and authentic environmental solutions.

Superfund record of decision amendment (EPA Region 5): Ninth Avenue Dump, Gary, IN, September 13, 1994

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

The decision document, together with Records of Decision dated June 30, 1989 (PB90-114810) and September 20, 1988 (PB89-153837) and an Explanation of Significant Differences dated October 1991, present the selected remedial action for the Ninth Avenue Dump site. The remedial action for the site consists of two operable units. The first operable unit addressed an oil layer floating on the groundwater by means of oil and groundwater extraction, oil storage, reintroduction of the groundwater, containment with a slurry wall, and management of excess surface water. The extracted groundwater was treated prior to reintroduction. The second operable unit, which is beingmore » amended by this decision document, addresses the remaining threats at the site.« less

Calculation of the Coulomb Fission Cross Sections for Pb-Pb and Bi-Pb Interactions at 158 A GeV

NASA Technical Reports Server (NTRS)

Poyser, William J.; Ahern, Sean C.; Norbury, John W.; Tripathi, R. K.

2002-01-01

The Weizsacker-Williams (WW) method of virtual quanta is used to make approximate cross section calculations for peripheral relativistic heavy-ion collisions. We calculated the Coulomb fission cross sections for projectile ions of Pb-208 and Bi-209 with energies of 158 A GeV interacting with a Pb-208 target. We also calculated the electromagnetic absorption cross section for Pb-208 ion interacting as described. For comparison we use both the full WW method and a standard approximate WW method. The approximate WW method in larger cross sections compared to the more accurate full WW method.

Ore genesis of the Wusihe carbonate-hosted Zn-Pb deposit in the Dadu River Valley district, Yangtze Block, SW China: evidence from ore geology, S-Pb isotopes, and sphalerite Rb-Sr dating

NASA Astrophysics Data System (ADS)

Xiong, Suo-Fei; Gong, Yong-Jun; Jiang, Shao-Yong; Zhang, Xiao-Jing; Li, Qian; Zeng, Guo-Ping

2018-01-01

The Wusihe carbonate-hosted Zn-Pb deposit (3.7 Mt. Zn + Pb at a grade of 8.6% Zn and 2.0% Pb) is the largest deposit in the Dadu River Valley district of the Sichuan-Yunnan-Guizhou metallogenic province of southwest China. Three types of orebodies occur: (1) stratiform, banded and lamellar, within dolomite of the Neoproterozoic Dengying Formation; (2) vein type; and (3) breccia type. Four stages of mineralization are distinguished: (i) pyrite stage, (ii) pyrite-pyrrhotite-galena-sphalerite-bitumen stage, (iii) sphalerite-galena stage, and (iv) bitumen-calcite stage. Sphalerite and galena from stages II and III show δ34S ranges from +7.1 to +9.7‰ and +9.1 to +13.1‰, respectively. High-precision in situ lead isotope analyses of sulfides show 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb ratios of 37.938 to 38.336, 15.579 to 15.682, and 17.951 to 18.195, respectively, which suggest a mixing of lead from the basement and the host rocks. Rb-Sr isotope analyses for six sphalerite samples of stage II yielded an isochron age of 411 ± 10 Ma (MSWD = 1.4). Combining all available ore geology and geochemical data, together with fluid inclusion data reported previously, we suggest that the Wusihe deposit is a Mississippi Valley-type (MVT) deposit.

Contemporaneous alkaline and tholeiitic magmatism in the Ponta Grossa Arch, Paraná-Etendeka Magmatic Province: Constraints from U-Pb zircon/baddeleyite and 40Ar/39Ar phlogopite dating of the José Fernandes Gabbro and mafic dykes

NASA Astrophysics Data System (ADS)

Almeida, Vidyã V.; Janasi, Valdecir A.; Heaman, Larry M.; Shaulis, Barry J.; Hollanda, Maria Helena B. M.; Renne, Paul R.

2018-04-01

We report the first high-precision ID-TIMS U-Pb baddeleyite/zircon and 40Ar/39Ar step-heating phlogopite age data for diabase and lamprophyre dykes and a mafic intrusion (José Fernandes Gabbro) located within the Ponta Grossa Arch, Brazil, in order to constrain the temporal evolution between Early Cretaceous tholeiitic and alkaline magmatism of the Paraná-Etendeka Magmatic Province. U-Pb dates from chemically abraded zircon data yielded the best estimate for the emplacement ages of a high Ti-P-Sr basaltic dyke (133.9 ± 0.2 Ma), a dyke with basaltic andesite composition (133.4 ± 0.2 Ma) and the José Fernandes Gabbro (134.5 ± 0.1 Ma). A 40Ar/39Ar phlogopite step-heating age of 133.7 ± 0.1 Ma from a lamprophyre dyke is identical within error to the U-Pb age of the diabase dykes, indicating that tholeiitic and alkaline magmatism were coeval in the Ponta Grossa Arch. Although nearly all analysed fractions are concordant and show low analytical uncertainties (± 0.3-0.9 Ma for baddeleyite; 0.1-0.4 Ma for zircon; 2σ), Pb loss is observed in all baddeleyite fractions and in some initial zircon fractions not submitted to the most extreme chemical abrasion treatment. The resulting age spread may reflect intense and continued magmatic activity in the Ponta Grossa Arch.

Geochemical Cruise Report SO226/2 RV Sonne Chatham Rise Expedition

DTIC Science & Technology

2013-05-28

selection of samples for radiocarbon, stable carbon and radioisotopes ( 230 Th, 210 Pb, and 231 Pa) to date (~20,000 years back) vertical CH4 fluxes and...i REPORT DOCUMENTATION PAGE Form ApprovedOMB No. 0704-0188 3. DATES COVERED (From - To) Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18...TYPE1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 6. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND

Ediacaran ( 620 Ma) high grade regional metamorphism in the northern Arabian Nubian Shield: U/Th-Pb monazite ages of the Elat schist

NASA Astrophysics Data System (ADS)

Elisha, Bar; Katzir, Yaron; Kylander-Clark, Andrew

2017-04-01

Ediacaran times witnessed a hemisphere-scale orogenesis forming the extensive Pan-African mountain ranges and resulting in the final assembly of Gondwana supercontinent. The Elat metamorphic basement (S Israel) located at the northernmost tip of a major Pan-African orogenic suture, the Arabian Nubian Shield (ANS), comprises amphibolite facies schists and gneisses and was most likely shaped by this major continental collision. However the timing, number and duration of metamorphic events in Elat and elsewhere in the ANS are non-conclusive and a major emphasis was given to pre-Ediacaran island-arc related tectonics. This is mostly because U-Pb dating of zircon, widely used in Elat and elsewhere, is very successful in constraining the ages of the igneous and sedimentary protoliths, but is 'blind' to metamorphism at grades lower than granulite. Here U/Th-Pb dating of monazite, a precise chronometer of metamorphic mineral growth, is systematically applied to the Elat schist and unveils the tectono-metamorphic evolution of the Elat basement. Previous U-Pb dating of detrital zircon has shown that the sedimentary protoliths of the Elat schist are the oldest basement components (≥800 Ma), and detailed structural observations of the schists portrayed a complex deformation history including four successive phases (Shimron, 1972). The earliest three phases were defined as ductile and penetrative, but some of the available geochronological data apparently contradict field relations. In-situ analysis of metamorphic monazites by LASS (Laser Ablation Split Stream) involves simultaneous measurement of U/Th-Pb isotope ratios and REE contents in a single 10 μm sized grain or domain, thus allowing determining the age of specific texture and metamorphic assemblage. Monazite dating of the Elat schist yielded two concordant age clusters at 712±6 and 613±5 Ma. The corresponding REE patterns of the dated monazite grains indicate that porphyroblast growth, either garnet or staurolite, took place only during the younger event (M2). Likewise the regional south dipping penetrative foliation, common to the Elat schist and to all of the rocks of the Elat association, formed during the Ediacaran event (M2). This profound event started at 630 Ma and reached peak conditions of mid amphibolite facies at 620 Ma. Retrogression and stress relaxation shortly followed, involving overprint of staurolite schists by a cordierite-bearing assemblage at 613 Ma (M3), and was contemporaneous with the intrusion of andesitic dykes that were immediately metamorphosed to low-amphibolite. This metamorphic P-T-t path corresponds to the collision of East- and West-Gondwana as constrained by large goechronological database of post collision batholiths from all around the Arabian-Nubian Shield.

Pharmacologic study of C-terminal fragments of frog skin calcitonin gene-related peptide.

PubMed

Ladram, Ali; Besné, Isabelle; Breton, Lionel; de Lacharrière, Olivier; Nicolas, Pierre; Amiche, Mohamed

2008-07-01

The calcitonin gene-related peptide from the skin of the frog Phyllomedusa bicolor (pbCGRP) is a 37-residue neuropeptide that differs from human alpha CGRP (halphaCGRP) at 16 positions. The affinities of the C-terminal fragments of pbCGRP and halphaCGRP were evaluated in SK-N-MC cells: pbCGRP(8-37) (K(i)=0.2nM) and pbCGRP(27-37) (K(i)=95nM) were, respectively, 3 times and 20 times more potent than the human fragments halphaCGRP(8-37) and halphaCGRP(27-37). Their antagonistic potencies were measured in SK-N-MC and Col 29 cells, and the rat vas deferens. pbCGRP(8-37) inhibited the halphaCGRP-stimulated production of cAMP by SK-N-MC and Col 29 cells 3 to 4 times more strongly than halphaCGRP(8-37). Thus pbCGRP(8-37) is the most potent CGRP-1 competitive antagonist of all the natural sequences reported to date. pbCGRP(27-37) was also as potent as [D(31), A(34), F(35)] halphaCGRP(27-37), a prototypic antagonist analog derived from structure-activity relationship studies of halphaCGRP(8-37).

Historical records of atmospheric Pb deposition in four Scottish ombrotrophic peat bogs: An isotopic comparison with other records from western Europe and Greenland - article no. GB2016

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cloy, J.M.; Farmer, J.G.; Graham, M.C.

2008-05-15

Cores collected from ombrotrophic peat bogs in west central, east central, northeast and southwest Scotland were dated (C-14, Pb-210) and analyzed (ICP-OES, ICP-MS) to derive and compare their historical records of atmospheric anthropogenic Pb deposition over the past 2500 years. On the basis of Pb isotopic composition (e. g., Pb-206/Pb-207), clear indications of Pb contamination during the pre-Roman/Roman, post-Roman and medieval periods were attributed to the mining and smelting of Pb ores from Britain and elsewhere in Europe. Between the 17th and early 20th centuries, during the industrial period, the mining and smelting of indigenous Scottish Pb ores were themore » most important sources of anthropogenic Pb deposition at three of the sites. In contrast, at the most southerly site, influences from the use of both British Pb ores and imported Australian Pb ores (in more southern parts of Britain) since the late 19th century were evident. At each of the sites, Australian-Pb-influenced car exhaust emissions (from the 1930s to late 1990s), along with significant contributions from coal combustion (until the late 1960s and onset of the post industrial period), were evident. Atmospheric anthropogenic Pb deposition across Scotland was greatest (similar to 10 to 40 mg m{sup -2} a{sup -1}) between the late 1880s and late 1960s, increasing southward, declining to 0.44 to 5.7 mg m{sup 2} a{sup -1} by the early 2000s.« less

Developing an Age Model for the Cryogenian: the South China perspective

NASA Astrophysics Data System (ADS)

Condon, D. J.; Zhu, M.; Macdonald, F. A.; Tapster, S.

2014-12-01

The Neoproterozoic stratigraphic record of South China contains distributed volcanic ash beds, which can be dated and used to provide a backbone for Cryogenian and Ediacaran 'age models'. When integrated with geochemical and paleontological data, both locally and from other regions, these successions inform our understanding of environmental and biological change from these intervals. At present the South China stratigraphy provides the dates that best approximate the termination of the Marinoan glaciation (ca. 635 Ma, U-Pb single zircon isotope dilution1) from a dated volcanic ash bed that occurs in the cap carbonate sequence (Doushantuo Formation) which directly overlies the Nantuo Tillite (Marinoan glaciation equivalent). A number of other ash beds have been documented in both the Nantuo Tillite and throughout the Datangpo Formation (pre-Marinoan non-glacial succession) and have been variably dated using U-Pb microbeam and multi-grain isotope dilution studies2-4. These published data sets have produced dates that have uncertainties on the order of 4 Myr but are built upon single-analyses data points, which have uncertainties on the order of 10 Myr or greater thereby limiting their utility for assessing temporal relationship with other dated section. We present new U-Pb single zircon isotope dilution geochronology data from a suite of samples from the Datangpo, Nantuo and Doushantuo Formations. New dates from the base of the Datangpo Formation confirm a ca. 660 Ma end to the Sturtian glacial epoch, which is represented by underlying glacial deposits. Additional dates from ash beds from the Datangpo Formation and the lower Nantuo Tillite will refine the duration of the Cryogenian non-glacial interlude and Marinoan glaciation as recorded in South China. Combined with published data from Namibia, Australia and Canada, these new data will permit the development of a more highly resolved age model for the Cryogenian, enabling estimation of duration and synchronicity of proxy records. They will also provide further tests and input data for numerical models that seek to simulate Cryogenian climate drivers and responses. 1. D. Condon et al., (2005) Science308, 95; 2. C. M. Zhou et al., (2004) Geology32, 437; 3. S. Zhang, et al., (2008) Terra Nova20, 289; 4. S. Zhang et al., (2005) Geology 33, 473

Transboundary atmospheric lead pollution.

PubMed

Erel, Yigal; Axelrod, Tamar; Veron, Alain; Mahrer, Yitzak; Katsafados, Petros; Dayan, Uri

2002-08-01

A high-temporal resolution collection technique was applied to refine aerosol sampling in Jerusalem, Israel. Using stable lead isotopes, lead concentrations, synoptic data, and atmospheric modeling, we demonstrate that lead detected in the atmosphere of Jerusalem is not only anthropogenic lead of local origin but also lead emitted in other countries. Fifty-seven percent of the collected samples contained a nontrivial fraction of foreign atmospheric lead and had 206Pb/207Pb values which deviated from the local petrol-lead value (206Pb/207Pb = 1.113) by more than two standard deviations (0.016). Foreign 206Pb/207Pb values were recorded in Jerusalem on several occasions. The synoptic conditions on these dates and reported values of the isotopic composition of lead emitted in various countries around Israel suggest that the foreign lead was transported to Jerusalem from Egypt, Turkey, and East Europe. The average concentration of foreign atmospheric lead in Jerusalem was 23 +/- 17 ng/m3, similar to the average concentration of local atmospheric lead, 21 +/- 18 ng/ m3. Hence, the load of foreign atmospheric lead is similar to the load of local atmospheric lead in Jerusalem.

U-Pb Ages of Lunar Apatites

NASA Technical Reports Server (NTRS)

Vaughan, J.; Nemchin, A. A.; Pidgeon, R. T.; Meyer, Charles

2006-01-01

Apatite is one of the minerals that is rarely utilized in U-Pb geochronology, compared to some other U-rich accessory phases. Relatively low U concentration, commonly high proportion of common Pb and low closure temperature of U-Pb system of apatite inhibit its application as geochronological tool when other minerals such as zircon are widely available. However, zircon appear to be restricted to certain type of lunar rocks, carrying so called KREEP signature, whereas apatite (and whitlockite) is a common accessory mineral in the lunar samples. Therefore, utilizing apatite for lunar chronology may increase the pool of rocks that are available for U-Pb dating. The low stability of U-Pb systematics of apatite may also result in the resetting of the system during meteoritic bombardment, in which case apatite may provide an additional tool for the study of the impact history of the Moon. In order to investigate these possibilities, we have analysed apatites and zircons from two breccia samples collected during the Apollo 14 mission. Both samples were collected within the Fra Mauro formation, which is interpreted as a material ejected during the impact that formed the Imbrium Basin.

Structural characterization of recombinant IAV polymerase reveals a stable complex between viral PA-PB1 heterodimer and host RanBP5.

PubMed

Swale, Christopher; Monod, Alexandre; Tengo, Laura; Labaronne, Alice; Garzoni, Frédéric; Bourhis, Jean-Marie; Cusack, Stephen; Schoehn, Guy; Berger, Imre; Ruigrok, Rob W H; Crépin, Thibaut

2016-04-20

The genome of influenza A virus (IAV) comprises eight RNA segments (vRNA) which are transcribed and replicated by the heterotrimeric IAV RNA-dependent RNA-polymerase (RdRp). RdRp consists of three subunits (PA, PB1 and PB2) and binds both the highly conserved 3'- and 5'-ends of the vRNA segment. The IAV RdRp is an important antiviral target, but its structural mechanism has remained largely elusive to date. By applying a polyprotein strategy, we produced RdRp complexes and define a minimal human IAV RdRp core complex. We show that PA-PB1 forms a stable heterodimeric submodule that can strongly interact with 5'-vRNA. In contrast, 3'-vRNA recognition critically depends on the PB2 N-terminal domain. Moreover, we demonstrate that PA-PB1 forms a stable and stoichiometric complex with host nuclear import factor RanBP5 that can be modelled using SAXS and we show that the PA-PB1-RanPB5 complex is no longer capable of 5'-vRNA binding. Our results provide further evidence for a step-wise assembly of IAV structural components, regulated by nuclear transport mechanisms and host factor binding.

Cross-sectional and temporal association between non-suicidal self-injury and suicidal ideation in young adults: The explanatory roles of thwarted belongingness and perceived burdensomeness.

PubMed

Chu, Carol; Rogers, Megan L; Joiner, Thomas E

2016-12-30

Non-suicidal self-injury (NSSI) is a strong predictor of suicidal ideation and attempts. Consistent with the interpersonal theory of suicide, preliminary evidence suggests that NSSI is associated with higher levels of perceived burdensomeness (PB) and thwarted belongingness (TB). However, no study to date has examined the cross-sectional and prospective relationships between NSSI, TB, PB, and suicidal ideation (SI). To fill this gap, this study examined the mediating role of TB and PB in the relationship between NSSI and SI at baseline and follow-up. Young adults (N=49) with and without histories of NSSI completed self-report measures of TB, PB, and SI at three time points over two months. NSSI history was associated with higher levels of PB, TB, and SI at all time points. TB and PB significantly accounted for the relationship between NSSI history and SI at baseline. However, the relationship between NSSI history and SI at follow-up was mediated by PB, not TB. Findings provide evidence for the roles of TB and PB in the relationship between NSSI and SI, and partial support for the interpersonal theory of suicide. Future research and clinical implications are discussed. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Cross-sectional and temporal association between non-suicidal self-injury and suicidal ideation in young adults: The explanatory roles of thwarted belongingness and perceived burdensomeness

PubMed Central

Chu, Carol; Rogers, Megan L.; Joiner, Thomas E.

2016-01-01

Non-suicidal self-injury (NSSI) is a strong predictor of suicidal ideation and attempts. Consistent with the interpersonal theory of suicide, preliminary evidence suggests that NSSI is associated with higher levels of perceived burdensomeness (PB) and thwarted belongingness (TB). However, no study to date has examined the cross-sectional and prospective relationships between NSSI, TB, PB, and suicidal ideation (SI). To fill this gap, this study examined the mediating role of TB and PB in the relationship between NSSI and SI at baseline and follow-up. Young adults (N=49) with and without histories of NSSI completed self-report measures of TB, PB, and SI at three time points over two months. NSSI history was associated with higher levels of PB, TB, and SI at all time points. TB and PB significantly accounted for the relationship between NSSI history and SI at baseline. However, the relationship between NSSI history and SI at follow-up was mediated by PB, not TB. Findings provide evidence for the roles of TB and PB in the relationship between NSSI and SI, and partial support for the interpersonal theory of suicide. Future research and clinical implications are discussed. PMID:27835855

Measurement of nuclear modification factors of $$\\Upsilon$$(1S), $$\\Upsilon$$(2S), and $$\\Upsilon$$(3S) mesons in PbPb collisions at $$\\sqrt{s_{_\\mathrm{NN}}} =$$ 5.02 TeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sirunyan, Albert M; et al.

The cross sections formore » $$\\Upsilon$$(1S), $$\\Upsilon$$(2S), and $$\\Upsilon$$(3S) production in lead-lead (PbPb) and proton-proton (pp) collisions at $$\\sqrt{s_{_\\mathrm{NN}}} =$$ 5.02 TeV have been measured using the CMS detector at the LHC. The nuclear modification factors, R$$_\\mathrm{AA}$$, derived from the PbPb-to-pp ratio of yields for each state, are studied as functions of meson rapidity and transverse momentum, as well as PbPb collision centrality. The yields of all three states are found to be significantly suppressed, and compatible with a sequential ordering of the suppression, R$$_\\mathrm{AA}$$($$\\Upsilon$$(1S)) $>$ R$$_\\mathrm{AA}$$($$\\Upsilon$$(2S)) $>$ R$$_\\mathrm{AA}$$($$\\Upsilon$$(3S)) . The suppression of $$\\Upsilon$$(1S) is larger than that seen at $$\\sqrt{s_{_\\mathrm{NN}}} =$$ 2.76 TeV, although the two are compatible within uncertainties. The upper limit on the R$$_\\mathrm{AA}$$ of $$\\Upsilon$$(3S) integrated over $$p_\\mathrm{T}$$ and rapidity is 0.094 at 95% confidence level, which is the strongest suppression observed for any hadron species in heavy ion collisions to date.« less

Reconstruction of historical lead contamination and sources in Lake Hailing, Eastern China: a Pb isotope study.

PubMed

Zhang, Rui; Guan, Minglei; Shu, Yujie; Shen, Liya; Chen, Xixi; Zhang, Fan; Li, Tiegang; Jiang, Tingchen

2016-05-01

The history records of lead and its stable isotopic ratios were determined in a sediment core to receive anthropogenic impacts on the Lake Hailing in eastern China. The sediment core was dated based on (210)Pb, (137)Cs, and (239+240)Pu. The historical changes of Pb/Al and Pb isotope ratios showed increasing trend upward throughout the core, suggesting changes in energy usage and correlating closely with the experience of a rapid economic and industrial development of the catchment, Linyi City, in eastern China. Based on the mixing end member model of Pb isotope ratios, coal combustion emission dominated anthropogenic Pb sources in the half part of the century contributing 13 to 43 % of total Pb in sediment. Moreover, contributions of chemical and organic fertilizer were 1-13 and 5-14 %, respectively. In contrast, the contribution of leaded gasoline was low than 8 %. The results indicated that historical records of Pb contamination predominantly sourced from coal combustion and chemical and organic fertilizer in the catchment. In addition, an increase of coal combustion source and fertilizers was found throughout the sediment core, whereas the contribution of leaded gasoline had declined after 2000s, which is attributed to the phaseout of leaded gasoline in China.

Bacteria mediated dissolution of pyromorphite Pb5(PO4)3Cl in presence of Pseudomonas putida bacteria - an effect on Pb remobilization in the environment

NASA Astrophysics Data System (ADS)

Flis, Justyna; Manecki, Maciej; Merkel, Broder J.; Latowski, Dariusz

2010-05-01

The objective of the study was to determine the mechanisms of microbially enhanced dissolution of lead phosphate-pyromorphite Pb5(PO4)3Cl). Contrary to the current literature, the results of our experiments indicate a great potential for Pb remobilization in the environment by an aerobic microorganism acquiring phosphates. Broad knowledge exists about the role of Pb-apatites in regulating the behavior and the bioavailability of Pb in soils and wastewater. In situ Pb immobilization is one of the methods now routinely applied for the reclamation of Pb-contaminated soils, including shallow unconfined aquifers (Magalhaes & Silva, 2003; Magalhaes, 2002; Ma et al. 1993). This method is based on the principle that aqueous phosphates added to soil pore solutions form a very stable (insoluble) mineral pyromorphite (Pb-apatite) Pb5(PO4)3Cl. Bioavailability of aqueous Pb is thus minimized due to the very low solubility and the high thermodynamic stability of pyromorphite (Flis, 2007; Nriagu, 1974). Several reports have examined the ability of different bacterial species including Pseudomonas to solubilise insoluble inorganic phosphate compounds for example apatites (Welch et al., 2002; Maurice et al., 1999; Rodriguez and Fraga, 1999 ). Various species of Pseudomonas genera are encountered as common inhabitants of soils and wastes in the industrial areas under strong pollution influence. To date, there has not been any published evidence of microbial dissolution of pyromorphite. The major objective of the project was to study Pseudomonas putida growth in the presence of Pb-apatite (Pb5(PO4)3Cl) as the sole source of phosphate. It was to test the hypothesis that in the phosphate deficient environment bacteria are able to actively scavenge for P from the Pb-apatite which results in remobilization of Pb in the environment. The bacteria growth was investigated at 22oC. Commercially available Pseudomonas putida strain was used throughout. The experiment and its controls were run in standard growth medium for the period of 10 days, at starting pH=6.5. Samples were periodically analysed for pH, bacterial density, Pb and P (UV-vis, ICP). Our results indicate that Pb may be mobilized from pyromorphite by microbial activity, both in phosphorous-rich and phosphorous-deficient environment. At the experimental conditions the presence of bacteria enhances the dissolution of pyromorphite, resulting in up to 20 times increase of Pbaq. The observed effects of microorganisms on Pb remobilization need to be considered in Pb remediation strategies that rely on pyromorphite formation. References: FLIS J.M., (2007). "Thermodynamic properties of minerals from pyromorphite-mimetite series"- Master Thesis, AGH-University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, Department of Mineralogy, Petrography and Geochemistry, Cracow, Poland. MA Q.Y., TRAINA S.J., LOGAN T.J., RYAN J.A. (1993). "In-situ lead immobilization by apatite". Environ. Sci. Technol., 27: 1803-1810. MAURICE P.A, LEE Y.J., HERSMAN L.E. (1999). "Dissolution of Al-substituted goethites by an aerobic Pseudomonas mendocina var. Bacteria." Gechim. Cosmochim. Acta. 64: 1363-1374. MAGALHÃES M.C.F. (2002). "Arsenic. An environmental problem limited by solubility". Pure Appl. Chem., 74(10): 1843-1850. MAGALHÃES M.C.F., SLIVA, M.C.M.(2003). "Stability of lead(II) arsenates". Monat. fur Chem. 134: 735-743 NRIAGU J.O., (1974). "Lead orthophosphates IV. Formation and stability in the environment." Geochim. Cosmochim. Acta, 37: 367-377. RODRIGUEZ H. & FRAGA R. (1999). "Phosphate solubilizing bacteria and their role in plant growth promotion". Biotechn. Advan. 17: 319-339. WELCH S.A., TAUNTON A.E., BANFIELD J.F. (2002). "Effect of Microorganisms and Microbial Metabolites on Apatite Dissolution". Geomicrobil. J. 19: 343-367.

Lead contamination of the Seine River, France: geochemical implications of a historical perspective.

PubMed

Ayrault, Sophie; Roy-Barman, Matthieu; Le Cloarec, Marie-Françoise; Priadi, Cindy Rianti; Bonté, Philippe; Göpel, Christa

2012-05-01

Four sediment cores collected in the Seine River basin and dated between 1916 and 2003 were analyzed for lead concentrations and isotopic composition. In all four cores, the measured Pb concentration (up to 460 mg kg(-1)) lies significantly above the natural background (27-40 mg kg(-1)), although a significant decrease (down to 75 mg kg(-1)) was observed during the second half of the 20th century which can be explained by the reduction of lead emissions. The (206)Pb/(207)Pb ratio measured in these samples indicates that the main source of Pb used in the Paris conurbation is characterized by a "Rio Tinto" signature (defined as (206)Pb/(207)Pb=1.1634 ± 0.0001). A high contribution, up to 25%, from the leaded gasoline (characterized by (206)Pb/(207)Pb=1.08 ± 0.02) is revealed in the Seine River downstream Paris, indicating that lead from the leaded gasoline is preferentially released to the river. The dominating Pb signature in the Paris conurbation that is currently sampled through incinerators fumes ((206)Pb/(207)Pb=1.1550 ± 0.0005) and waste water treatment plant ((206)Pb/(207)Pb=1.154 ± 0.002), represents a mixture of highly recycled lead from the Rio Tinto mine and lead from leaded gasoline (imprinted by the low (206)Pb/(207)Pb of the Broken Hill mine). This signature is called "urban" rather than "industrial", because it is clearly distinct from the Pb that is found in areas contaminated by heavy industry, i.e. the heavy industries located on the Oise River which used lead from European ores characterized by high (206)Pb/(207)Pb ratios (~1.18-1.19) and possibly a minor amount of North American lead ((206)Pb/(207)Pb ratios>1.20). The "urban" signature is also found in a rural area upstream of Paris in the 1970's. At the Seine River mouth in 2003, Pb with an urban signature represents 70% of the total Pb sediment content, with the 30% remaining corresponding to natural Pb. Copyright © 2012 Elsevier Ltd. All rights reserved.

Iodide-assisted total lead measurement and determination of different lead fractions in drinking water samples.

PubMed

Zhang, Yuanyuan; Ng, Ding-Quan; Lin, Yi-Pin

2012-07-01

Lead and its compounds are toxic and can harm human health, especially the intelligence development in children. Accurate measurement of total lead present in drinking water is crucial in determining the extent of lead contamination and human exposure due to drinking water consumption. The USEPA method for total lead measurement (no. 200.8) is often used to analyze lead levels in drinking water. However, in the presence of high concentration of the tetravalent lead corrosion product PbO(2), the USEPA method was not able to fully recover particulate lead due to incomplete dissolution of PbO(2) particles during strong acid digestion. In this study, a new procedure that integrates membrane separation, iodometric PbO(2) measurement, strong acid digestion and ICP-MS measurement was proposed and evaluated for accurate total lead measurement and quantification of different lead fractions including soluble Pb(2+), particulate Pb(II) carbonate and PbO(2) in drinking water samples. The proposed procedure was evaluated using drinking water reconstituted with spiked Pb(2+), spiked particulate Pb(II) carbonate and in situ formed or spiked PbO(2). Recovery tests showed that the proposed procedure and the USEPA method can achieve 93-112% and 86-103% recoveries respectively for samples containing low PbO(2) concentrations (0.018-0.076 mg Pb per L). For samples containing higher concentrations of PbO(2) (0.089-1.316 mg Pb per L), the USEPA method failed to meet the recovery requirement for total lead (85-115%) while the proposed method can achieve satisfactory recoveries (91-111%) and differentiate the soluble Pb(2+), particulate Pb(II) carbonate and PbO(2).

Solving the Martian meteorite age conundrum using micro-baddeleyite and launch-generated zircon.

PubMed

Moser, D E; Chamberlain, K R; Tait, K T; Schmitt, A K; Darling, J R; Barker, I R; Hyde, B C

2013-07-25

Invaluable records of planetary dynamics and evolution can be recovered from the geochemical systematics of single meteorites. However, the interpreted ages of the ejected igneous crust of Mars differ by up to four billion years, a conundrum due in part to the difficulty of using geochemistry alone to distinguish between the ages of formation and the ages of the impact events that launched debris towards Earth. Here we solve the conundrum by combining in situ electron-beam nanostructural analyses and U-Pb (uranium-lead) isotopic measurements of the resistant micromineral baddeleyite (ZrO2) and host igneous minerals in the highly shock-metamorphosed shergottite Northwest Africa 5298 (ref. 8), which is a basaltic Martian meteorite. We establish that the micro-baddeleyite grains pre-date the launch event because they are shocked, cogenetic with host igneous minerals, and preserve primary igneous growth zoning. The grains least affected by shock disturbance, and which are rich in radiogenic Pb, date the basalt crystallization near the Martian surface to 187 ± 33 million years before present. Primitive, non-radiogenic Pb isotope compositions of the host minerals, common to most shergottites, do not help us to date the meteorite, instead indicating a magma source region that was fractionated more than four billion years ago to form a persistent reservoir so far unique to Mars. Local impact melting during ejection from Mars less than 22 ± 2 million years ago caused the growth of unshocked, launch-generated zircon and the partial disturbance of baddeleyite dates. We can thus confirm the presence of ancient, non-convecting mantle beneath young volcanic Mars, place an upper bound on the interplanetary travel time of the ejected Martian crust, and validate a new approach to the geochronology of the inner Solar System.

Palaeo-pollution from mining activities in the Vosges Mountains: 1000 years and still bioavailable.

PubMed

Mariet, Anne-Lise; de Vaufleury, Annette; Bégeot, Carole; Walter-Simonnet, Anne-Véronique; Gimbert, Frédéric

2016-07-01

Mining and smelting activities have contaminated the environment with trace metals (TMs) at a worldwide scale for at least two millennia. A combination of chemical approaches and active biomonitoring was performed to analyse the environmental availability and bioavailability of TM palaeo-pollution in a former PbAg mining district in the Vosges Mountains, France. Along a soil TM contamination gradient that covered eight stations, including two archaeological mining sites, the toxicokinetics of six TMs (Pb, Cd, As, Ag, Co, Sb) in the snail Cantareus aspersus revealed that palaeo-pollution from the studied sites remains bioavailable. This study provides the first data on the accumulation kinetics of Ag and Co for C. aspersus. The environmental availability of the TMs was estimated with three chemical extraction methods (aqua regia, EDTA 50 mM, CaCl2 10 mM). Univariate regression analyses showed that EDTA extraction is the best method for estimating the bioavailability of Pb, As, Ag, Co and Sb to snails. None of the three extractants was efficient for Cd. A multivariate analysis of bioaccumulation data revealed that TM bioavailability and transfer were modulated by exposure sources (soil, humus and vegetation) rather than by soil physico-chemical characteristics. Hence, although the deposition of mining wastes dates back several centuries, these wastes still represent a source of contamination that must be considered to develop relevant site management and environmental risk assessment. Copyright © 2016 Elsevier Ltd. All rights reserved.

A Complication in Determining the Precise Age of the Solar System

NASA Astrophysics Data System (ADS)

Brennecka, G. A.

2010-01-01

Primitive components in meteorites contain a detailed record of the conditions and processes in the solar nebula, the cloud of dust and gas surrounding the infant Sun. Determining accurately when the first materials formed requires the lead-lead (Pb-Pb) dating method, a method based on the decay of uranium (U) isotopes to Pb isotopes. The initial ratio of U-238 to U-235 is critical to determining the ages correctly, and many studies have concluded that the ratio is constant for any given age. However, my colleagues at Arizona State University, Institut fur Geowissenschaften, Goethe-Universitat (Frankfurt, Germany), and the Senckenberg Forschungsinstitut und Naturmuseum (also in Frankfurt) and I have found that some calcium-aluminum-rich inclusions (CAIs) in chondritic meteorites deviate from the conventional value for the U-238/U-235 ratio. This could lead to inaccuracies of up to 5 million years in the age of these objects, if no correction is made. Variations in the concentrations of thorium and neodymium with the U-238/U-235 ratio suggest that the ratio may have been lowered by the decay of curium-247, which decays to U-235 with a half-life of 15.6 million years. Curium-247 is created in certain types of energetic supernovae, so its presence suggests that a supernova added material to the pre-solar interstellar cloud between 110 and 140 million years before the Solar System began to form.

Evolution of Palaeoproterozoic mafic intrusions located within the thermal aureole of the Sudbury Igneous Complex, Canada: Isotopic, geochronological and geochemical evidence

NASA Astrophysics Data System (ADS)

Prevec, Stephen A.; Baadsgaard, Halfdan

2005-07-01

Impact cratering and their resultant geological phenomena are recognised as significant factors in the lithological and biologic evolution of the earth. Age-dating of impact events is critical in correlating cause and effects for these catastrophic processes. The Falconbridge and Drury Township (Twp) intrusions were emplaced at the contact between Neoarchaean basement and Palaeoproterozoic volcanosedimentary rocks, and also lie at the southeast and southwest edges of the Sudbury Igneous Complex (SIC), within its thermal contact aureole. The Falconbridge Twp intrusion is dated at 2441 ± 3 Ma by U-Pb zircon, with evidence of Archaean inheritance from its host granitoids. Granitoids from the southernmost Abitibi Subprovince are dated here between 2670 ± 11 Ma for an undeformed Algoman granite, and 2696 ± 18 Ma for a foliated granitoid, consistent with existing data from the Abitibi Greenstone Belt and from the Wawa Subprovince. Major and trace element geochemical evidence, common-Pb isotopic compositions, and ɛNd2440 values between 0 and -1 are all consistent with a Palaeoproterozoic origin for the Falconbridge Twp intrusion, and support inclusion in the East Bull Lake-type suite of leucogabbroic plutons and sills. In contrast, the Drury Twp intrusion gives a U-Pb zircon age of 1859 ± 13 Ma, coincident with the date of SIC-emplacement. While the major and trace element compositions are comparable to the Falconbridge data, the Drury displays significant heterogeneity in ɛNd2440, with values ranging from +3.7 to -0.1, and contains more radiogenic Pb isotopic compositions. Field, geochemical and isotopic evidence clearly distinguishes this intrusion from constituents of the SIC itself, and indicates that the Drury too is a Palaeoproterozoic intrusion. This requires that apparently unshocked, undeformed magmatic-looking zircon has been grown or reset in a postmagmatic setting. This has significant implications for the identification of mantle-derived magmas and crustal remelts associated with large impact craters. A resetting mechanism involving aggressive hydrothermal alteration of zircon facilitated by halogen-complexing is proposed, inducing rapid, postshock lead loss and subsequent annealing.

The Onset of the Sturtian Snowball Earth: New Geochronology and Chemostratigraphy from the Tambien Group of Ethiopia

NASA Astrophysics Data System (ADS)

Park, Y.; MacLennan, S. A.; Swanson-Hysell, N.; Maloof, A. C.; Schoene, B.; Alene, M.; Tremblay, M. M.; Anttila, E.; Haileab, B.

2016-12-01

The Snowball Earth hypothesis proposes that the onset of global glaciation was a rapid event, particularly at low-latitudes, due to a runaway ice-albedo instability in the climate system. Currently, the Neoproterozoic Sturtian Snowball Earth Glaciation is constrained to have been ongoing at low-latitudes in present day NW Canada at 716.47 ± 0.24 Ma based on a U-Pb date from a tuff within glacial diamictite (Macdonald et al., 2010). A date from a rhyolite underlying this diamicitite of 717.43 ± 0.14 Ma has been inferred to precede the glaciation, although this age is not a strict maximum for the initiation of the snowball Earth since evidence of glaciation may have been obscured in volcanic units. The Tonian-Cryogenian Tambien Group of northern Ethiopia is a mixed carbonate-siliciclastic sequence deposited in an arc proximal basin that conformably culminates in diamictite associated with the Sturtian Glaciation. This study exploits the presence of tuffs suitable for high precision U-Pb zircon geochronology interbedded with recently discovered exposures of the transition into the snowball Earth. Dates from tuffs stratigraphically <100 m below massive diamictite enable a test of synchronicity for the initiation of the Sturtian Glaciation when compared with data from NW Canada and S China. Furthermore, tuffs in the proximity of the chemostratigraphically defined Islay negative δ13C anomaly give the opportunity to develop new U-Pb dates to test the prediction from Re-Os dating of black shales in NW Canada that the Islay significantly predates the Sturtian ice age, decoupling the sharpest negative downturns in inorganic δ13C values from glacial initiation. These data also augment and temporally constrain the pre-glacial 87Sr/86Sr curve, informing ongoing modeling efforts of global weathering and seawater chemistry as they relate to hypotheses of the role of large igneous province emplacement and paleogeography in the initiation of Snowball Earth glaciation.

Zircon U-Pb dating, Hf analysis from the Horoman perdiotite -age constraint for lithospheric process, and tectonic juxtaposition of collision root zone-

NASA Astrophysics Data System (ADS)

Okamoto, K.; Yi, K.; Wang, K. L.; Chung, S. L.

2017-12-01

Hidaka metamorphic belt, Hokkaido, Japan is known as youngest arc-arc collision in the world. It ncludes the youngest granulite and the Horoman peridotite complex in the highest grade zone. Age of these rocks have been determined by various methods (K-Ar, U-Pb, Rb-Sr). However, the age of Horoman peridotite complex has not been determined yet. Only Yoshikawa et al 1993) reported the cooling age of the complex as 23 Ma according to whole rock Rb-Sr isochron. This study has performed U-Pb dating of zircons from the Horoman peridotite, and from the paragneiss surrounding the peridotite complex in order to determine the intrusive age of the Horoman peridotite complex into the lower crustal conditions. Several zircon grains were separated from the peridotite. All zircons are homogeneous exhibiting different age group; 267-278 Ma, 33-40 Ma and 18-20 Ma. Hf isotope analysis indicates that the 267-278 Ma is juvenile age and other two are recycled. As a result of this measurement, rims of the zircons from the gneisses show that 238U-206Pb ages are 20 Ma and detrital cores are ranging from 580-510 Ma, 60-50 Ma, 46-40 Ma and 27 Ma. The rim ages are from the gneiss suffered amphibolite facies and granulite faices, and there is a consistancy with zircon rim ages (19 Ma) from the granulite (Kemp et al 2007, Usuki et al 2006 and so on). That is, granulite faices metamorphism was coeval to regional metamorphism in the lower crust at 20 Ma. The zircon ages from the peridotite was probably related to local hydration related to precipitation of phlogopite at 20 Ma, I type magma infiltration at 40 Ma and lithosphere formation at 270 Ma. It is considered that the Horoman peridotite complex was part of the lithosphere at 270 Ma, and the joined as subarc mantle prior to I type magma activity at 40 Ma, aud suffered local hydration and regional metamorphism at 20 Ma. Ref. Kemp, A.I.S., et al., 2007, Geology, 35, 807-810; Usuki, T. et al, 2006, Island Arc, 14, 503-516.

Historical record of lead accumulation and source in the tidal flat of Haizhou Bay, Yellow Sea: Insights from lead isotopes.

PubMed

Zhang, Rui; Guan, Minglei; Shu, Yujie; Shen, Liya; Chen, Xixi; Zhang, Fan; Li, Tiegang

2016-05-15

In order to investigate the historical records of lead contamination and source in coastal region of Haizhou Bay, Yellow Sea, a sediment core was collected from tidal flat, dated by (210)Pb and (137)Cs. Lead and its stable isotopic ratios were determined. The profiles of enrichment factor (EF) and Pb isotope ratios showed increasing trend upward throughout the core, correlating closely with the experience of a rapid economic and industrial development of the catchment. According to Pb isotopic ratios, coal combustion emission mainly contributed to the Pb burden in sediments. Based on end-member model, coal combustion emission dominated anthropogenic Pb sources in recent decades contributing from 48% to 67% in sediment. And the contribution of leaded gasoline was lower than 20%. A stable increase of coal combustion source was found in sediment core, while the contribution of leaded gasoline had declined recently, with the phase-out of leaded gasoline in China. Copyright © 2016 Elsevier Ltd. All rights reserved.

Lifetime of an ocean island volcano feeder zone: constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40/39Ar age determinations, Fuerteventura, Canary Islands

USGS Publications Warehouse

Allibon, James; Ovtcharova, Maria; Bussy, Francois; Cosca, Michael; Schaltegger, Urs; Bussien, Denise; Lewin, Eric

2011-01-01

High-precision isotope dilution - thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 ± 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. 40Ar/39Ar amphibole dating yielded ages from 21.9 ± 0.6 to 21.8 ± 0.3, identical within errors to the U-Pb ages, despite the expected 1% theoretical bias between 40Ar/39Ar and U-Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (Tc) of zircon (699-988 °C) to amphibole (500-600 °C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the 40Ar/39Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole Tc is 0.8 Ma, suggesting PX1 lifetime of 520,000 to 800,000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 ± 0.07/0.08/0.15 Ma and 21.58 ± 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope δ18O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.

Zircon U-Pb geochronology and Sr-Nd-Pb-Hf isotopic constraints on the timing and origin of Mesozoic granitoids hosting the Mo deposits in northern Xilamulun district, NE China

NASA Astrophysics Data System (ADS)

Shu, Qihai; Lai, Yong; Zhou, Yitao; Xu, Jiajia; Wu, Huaying

2015-12-01

Located in the east section of the Central Asian orogen in northeastern China, the Xilamulun district comprises several newly discovered molybdenum deposits, primarily of porphyry type and Mesozoic ages. This district is divided by the Xilamulun fault into the southern and the northern parts. In this paper, we present new zircon U-Pb dating, trace elements and Hf isotope, and/or whole rock Sr-Nd-Pb isotopic results for the host granitoids from three Mo deposits (Yangchang, Haisugou and Shabutai) in northern Xilamulun. Our aim is to constrain the age and petrogenesis of these intrusions and their implications for Mo mineralization. Zircon U-Pb LA-ICP-MS dating shows that the monzogranites from the Shabutai and Yangchang deposits formed at 138.4 ± 1.5 and 137.4 ± 2.1 Ma, respectively, which is identical to the molybdenite Re-Os ages and coeval well with the other Mo deposits in this region, thereby indicating an Early Cretaceous magmatism and Mo mineralization event. Zircon Ce/Nd ratios from the mineralized intrusions are significantly higher than the barren granites, implying that the mineralization-related magmas are characterized by higher oxygen fugacity. These mineralized intrusions share similar zircon in-situ Hf and whole rock Sr-Nd isotopic compositions, with slightly negative to positive εHf(t) ranging from - 0.8 to + 10.0, restricted εNd(t) values from - 3.7 to + 1.6 but a little variable (87Sr/86Sr)i ratios between 0.7021 and 0.7074, indicative of formation from primary magmas generated from a dominantly juvenile lower crust source derived from depleted mantle, despite diverse consequent processes (e.g., magma mixing, fractional crystallization and crustal contamination) during their evolution. The Pb isotopes (whole rock) also show a narrow range of initial compositions, with (206Pb/204Pb)i = 18.03-18.88, (207Pb/204Pb)i = 15.48-15.58 and (208Pb/204Pb)i = 37.72-38.28, in agreement with Sr-Nd-Hf isotopes reflecting the dominance of a mantle component. An integration of geochronological and isotopic data points to three stages of Mo mineralization events (i.e., Triassic, Late Jurassic, and Early Cretaceous) associated with magmas generated from three different source regions in the Xilamulun district, NE China. The variation in the origin of the magmas from which the porphyry Mo systems were generated suggests that the formation of Mo deposit lies not in the composition of magma sources. Other factors, including high magma oxygen fugacity, may have taken a fundamental role in Mo enrichment and subsequent mineralization.

A two century record of lead isotopes in high altitude Alpine snow and ice

NASA Astrophysics Data System (ADS)

Rosman, K. J. R.; Ly, C.; Van de Velde, K.; Boutron, C. F.

2000-03-01

A 140 m snow/ice core drilled at Mont Blanc, France, has been analysed for Pb isotopes, Pb and Ba concentrations. The 206Pb/ 207Pb ratio, which was measured by thermal ionisation mass spectrometry, decreased steadily from ˜1.18 about two centuries ago to ˜1.17 in 1960, then fell rapidly to ˜1.15 by 1968. Evidence of the Italian (Turin) isotopic lead experiment (IILE) was found in samples dated ˜1977 where the ratio dipped to 1.117. By the early 1990s it had returned to mid 1960s values. Large seasonal variations were found in Pb and Ba concentrations. Summer samples were associated with smooth changes in the 206Pb/ 207Pb ratio while larger fluctuations were encountered in winter which is consistent with a low altitude inversion near Mont Blanc in the winter and free transfer of pollutants from lower to higher altitudes at other times. A plot of 208Pb/ 207Pb versus 206Pb/ 207Pb ratios reveals three isotopic groupings, associated with the periods pre-1923, 1923-1968 and 1969-1991. In the first group, the isotopic composition is consistent with local mining, smelting and coal burning, while in the second, motor vehicle exhaust emissions dominate. In the third group, motor vehicle emissions also dominate but the Pb is even less radiogenic. During this period the IILE occurred and there was a reduction in the use of leaded gasoline in Europe. A comparison of the Mont Blanc and Summit (central Greenland) records shows they contain similar 206Pb/ 207Pb ratios between 1960 and 1968, although small differences in isotopic composition can be detected by also considering the 208Pb/ 207Pb ratio. However, after 1969 the two records diverge markedly, with the Greenland ratios being dominated by the highly radiogenic Mississippi valley-type Pb from the USA and with the Mont Blanc ratios moving to lower values particularly about the time of the IILE.

Ar-39 - Ar-40 Dating of Two Angrites and Two Brachnites

NASA Technical Reports Server (NTRS)

Garrison, Daniel; Bogard, Donald

2003-01-01

Angrites are a rare group (approx.7 known) of igneous meteorites with basalt-like composition, which probably derive from a relatively small parent body that differs from those of other igneous meteorites. Angrites show evidence for extinct Mn-53, Sm-146, and Pu-244, and precise U-Pb, and Pb-Pb ages of 4.558 Gyr for two angrites define the time of early parent body differentiation. The S-147 - Nd-143 ages of two angrites range between 4.53+/-0.04 and 4.56+/-0.04 Gyr, but no Ar-39 - Ar-40 or Rb-Sr ages have been reported. Most angrites show no evidence for either shock brecciation or metamorphism.

[High-precision in situ analysis of the lead isotopic composition in copper using femtosecond laser ablation MC-ICP-MS and the application in ancient coins].

PubMed

Chen, Kai-Yun; Fan, Chao; Yuan, Hong-Lin; Bao, Zhi-An; Zong, Chun-Lei; Dai, Meng-Ning; Ling, Xue; Yang, Ying

2013-05-01

In the present study we set up a femtosecond laser ablation MC-ICP-MS method for lead isotopic analysis. Pb isotopic composition of fifteen copper (brass, bronze) standard samples from the National Institute of Standards Material were analyzed using the solution method (MC-ICP-MS) and laser method (fLA-MC-ICPMS) respectively, the results showed that the Pb isotopic composition in CuPb12 (GBW02137) is very homogeneous, and can be used as external reference material for Pb isotopic in situ analysis. On CuPb12 112 fLA-MC-ICPMS Pb isotope analysis, the weighted average values of the Pb isotopic ratio are in good agreement with the results analyzed by bulk solution method within 2sigma error, the internal precision RSEs of the 208 Pb/204 Pb ratio and 207 Pb/206 Pb ratio are less than 90 and 40 ppm respectively, and the external precision RSDs of them are less than 60 and 30 ppm respectively. Pb isotope of thirteen ancient bronze coins was analyzed via fLA-MC-ICPMS, the results showed that the Pb isotopic composition of ancient coins of different dynasties is significantly different, and not all the Pb isotopic compositions in the coins even from the same dynasty are in agreement with each other.

200 Years of Pb deposition throughout the Czech Republic: Patterns and sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vile, M.A.; Wieder, R.K.; Novak, M.

2000-01-01

Historical rates of Pb deposition were determined over the past 150--200 years for eight sites throughout the Czech Republic using {sup 210}Pb-dated, Sphagnum-derived peat cores. Maximum historical Pb deposition was greater at sites in the northern and western parts of the Czech Republic than at sites in the southern part of the Czech Republic. Lead deposition patterns generally reflect increasing industrialization over the past 100--200 years, especially in the post-World War II era. For seven of the eight sites, maximum Pb deposition occurred between 1965 and 1992, corresponding to a period of peak production and burning of lignite coal. Amore » decrease in Pb deposition rates since 1975--1980 was evident in seven of the sites. The most recent Pb deposition rates (1992), estimated from the uppermost peat core sections, averaged 32, 11, and 7 mg m{sup {minus}2} yr{sup {minus}1} for the northern, western, and southern sites, respectively, are higher than current Pb deposition in the eastern United States of 4 mg m{sup {minus}2} yr{sup {minus}1}. Lead deposition rates prior to Czech industrialization, estimated from the deepest dateable peat core sections, averaged 8, 5, and 1 mg m{sup {minus}2} yr{sup {minus}1} for the northern, western, and southern sites, respectively. Using acid-insoluble ash concentrations in peat and peat magnetic susceptibility determinations, the authors were able to identify past periods of elevated Pb deposition related to local mining of Pb-containing ore deposits at three of the sites and periods of elevated Pb deposition from fossil fuel combustion at five of the sites. Without stable Pb isotopic determinations, the importance of leaded gasoline-derived Pb could not be determined.« less

Establishing geochemical background levels of selected trace elements in areas having geochemical anomalies: The case study of the Orbetello lagoon (Tuscany, Italy).

PubMed

Romano, Elena; Bergamin, Luisa; Croudace, Ian W; Ausili, Antonella; Maggi, Chiara; Gabellini, Massimo

2015-07-01

The determination of background concentration values (BGVs) in areas, characterised by the presence of natural geochemical anomalies and anthropogenic impact, appears essential for a correct pollution assessment. For this purpose, it is necessary to establish a reliable method for determination of local BGVs. The case of the Orbetello lagoon, a geologically complex area characterized by Tertiary volcanism, is illustrated. The vertical concentration profiles of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were studied in four sediment cores. Local BGVs were determined considering exclusively samples not affected by anthropogenic influence, recognized by means of multivariate statistics and radiochronological dating ((137)Cs and (210)Pb). Results showed BGVs well-comparable with mean crustal or shale values for most of the considered elements except for Hg (0.87 mg/kg d.w.) and As (16.87 mg/kg d.w.), due to mineralization present in the catchment basin draining into the lagoon. Copyright © 2015 Elsevier Ltd. All rights reserved.

Evidence for large-scale submarine mass wasting associated with growth of oceanic core complexes, 16°N, Mid-Atlantic Ridge.

NASA Astrophysics Data System (ADS)

Urann, B.; Cheadle, M. J.; John, B. E.; Dick, H. J.

2016-12-01

Slow spreading ridges display distinct geomorphologic features, often interpreted as long-lived detachment faults, where mafic and ultramafic rocks are exposed at the seafloor. Many bathymetric features in these regions are viewed as the result of tectonic processes (long lived detachment faults), however other features are clearly the result of mass wasting. Here we report zircon U-Pb dates from four gabbro and Fe-Ti oxide gabbro dredge samples recovered from the North Segment on the western flank of the mid-Atlantic ridge (MAR) at 16°N. Initial SIMS U-Pb zircon dating using the Stanford-USGS SHRIMP-RG ion-microprobe yield 230 Th-corrected zircon 206Pb/238U dates within error of one another. The two westernmost samples are separated by 14km along strike, and come from dredges on the footwall of a high-angle normal fault. They have dates of 1.112 +/-0.083 Ma and 1.181 +/- 0.074Ma, and both lie 12-13km west of the present day axial volcanic ridge, These samples therefore yield a spreading rate of 12km/Ma, as expected for this part of the MAR. The two eastern samples lie up to 4.5 km east of the western samples and yield dates of 1.14_/-0.55Ma and 1,221+/-0.027Ma, indistinguishable from those of the samples to the west. Given the predicted spreading rate of 12 km/Ma, these samples should be 0.375Ma younger than those to the west, and should yield dates of 0.74Ma. To account for the similarity in age, we suggest that mass wasting and large landslides from the high angle fault scarps displaced as much as 40km3 of material into the axial valley, dispersing gabbro of similar age over a wide area. This interpretation is consistent with the available multi-beam bathymetry that can be explained in terms of large landslides flowing from the bounding fault scarps into the axial valley towards the present day axial volcanic ridge. If correct, this interpretation has significant implications for evaluating potential tsunami hazards at mid-ocean ridges.

Source, evolution and emplacement of Permian Tarim Basalts: Evidence from U-Pb dating, Sr-Nd-Pb-Hf isotope systematics and whole rock geochemistry of basalts from the Keping area, Xinjiang Uygur Autonomous region, northwest China

NASA Astrophysics Data System (ADS)

Zhang, Dayu; Zhou, Taofa; Yuan, Feng; Jowitt, Simon M.; Fan, Yu; Liu, Shuai

2012-04-01

Permian basalts distribute at least 250,000 km2, and underlie the southwest Tarim Basin in Xinjiang Uygur Autonomous region, northwest China. This vast accumulation of basalt is the main part of the Tarim Large Igneous Province (LIP). The basaltic units in the Lower Permian Kupukuziman and Kaipaizileike Formations in the Keping area, Tarim Basin; were the best exposure of the Permian basalt sequence in the basin. LA-ICP-MS U-Pb dating of zircon from the basal basaltic unit in the section gives an age of 291.9 ± 2.2 Ma (MSWD = 0.30, n = 17); this age, combined with previously published geochronological data, indicates that the basalts in the Tarim Basin were emplaced between 292 Ma and 272 Ma, with about 90% of the basalts being emplaced between 292 and 287 Ma. Basalts from the Keping area have high FeOT (10.8-18.6 wt.%), low Mg#s (0.26-0.60), and exhibit primitive mantle normalized patterns with positive Pb, P and Ti but negative Zr, Y and Ta anomalies. The basalts from both formations have similar 206Pb/204Pb (18.192-18.934), 207Pb/204Pb (15.555-15.598) and 208Pb/204Pb (38.643-38.793) ratios. The basalts also have high ɛSr(t) (45.7-62.1), low ɛNd(t) (-3.6 to -2.2) and low zircon ɛHf(t) (-4.84 to -0.65) values. These characteristics are typical of alkali basalts and suggest that the basalts within the Tarim Basin were derived from an OIB-type mantle source and interacted with enriched mantle (EMI-type) before emplacement. Rare earth element systematics indicate that the parental melts for the basalts were high-degree partial melts derived from garnet lherzolite mantle at the base of the lithosphere. Prior to emplacement, the Tarim Permian Basalts (TPB) underwent fractional crystallization and assimilated crustal material; the basalts were finally emplaced during crustal extension in an intra-plate setting. The wide distribution, deep source and high degree partial melting of the TPB was consistent with a mantle plume origin. The TPB and other coeval igneous rocks in the Tarim Basin constitute a Permian LIP formed by a mantle plume in a similar fashion to the plume-related Emeishan LIP in southwest China.

U-Pb, Re-Os and Ar-Ar dating of the Linghou polymetallic deposit, Southeastern China: Implications for metallogenesis of the Qingzhou-Hangzhou metallogenic belt

NASA Astrophysics Data System (ADS)

Tang, Yanwen; Xie, Yuling; Liu, Liang; Lan, Tingguan; Yang, Jianling; Sebastien, Meffre; Yin, Rongchao; Liang, Songsong; Zhou, Limin

2017-04-01

The Qingzhou-Hangzhou metallogenic belt (QHMB) in Southeastern China has gained increasingly attention in recent years. However, due to the lack of reliable ages on intrusions and associated deposits in this belt, the tectonic setting and metallogenesis of the QHMB have not been well understood. The Linghou polymetallic deposit in northwestern Zhejiang Province is one of the typical deposits of the QHMB. According to the field relationships, this deposit consists of the early Cu-Au-Ag and the late Pb-Zn-Cu mineralization stages. Molybdenite samples with a mineral assemblage of molybdenite-chalcopyrite-pyrite ± quartz are collected from the copper mining tunnel near the Cu-Au-Ag ore bodies. Six molybdenite samples give the Re-Os model ages varying from 160.3 to 164.1 Ma and yield a mean age of 162.2 ± 1.4 Ma for the Cu-Au-Ag mineralization. Hydrothermal muscovite gives a well-defined Ar-Ar isochron age of 160.2 ± 1.1 Ma for the Pb-Zn-Cu mineralization. Three phases of granodioritic porphyry have been distinguished in this deposit, and LA-ICP-MS zircon U-Pb dating shows that they have formed at 158.8 ± 2.4 Ma, 158.3 ± 1.9 Ma and 160.6 ± 2.1 Ma, comparable to the obtained ages of the Cu-Au-Ag and Pb-Zn-Cu mineralization. Therefore, these intrusive rocks have a close temporal and spatial relationship with the Cu-Au-Ag and Pb-Zn-Cu ore bodies. The presences of skarn minerals (e.g., garnet) and vein-type ores, together with the previous fluid inclusion and H-O-C-S-Pb isotopic data, clearly indicate that the Cu-Au-Ag and Pb-Zn-Cu mineralization are genetically related to these granodiorite porphyries. This conclusion excludes the possibility that this deposit is of ;SEDEX; type and formed in a sag basin of continental rifts setting as previously proposed. Instead, it is proposed that the Linghou polymetallic and other similar deposits in the QHMB, such as the 150-160 Ma Yongping porphyry-skarn Cu-Mo, Dongxiang porphyry? Cu, Shuikoushan/Kangjiawang skarn Pb-Zn, Fozichong skarn Pb-Zn and Dabaoshan porphyry-skarn deposits are of magmatic-hydrothermal origin and likely formed in a subduction-related setting. This work provides new insight that these intrusion-related deposits (e.g., porphyry and skarn types) of middle to late Jurassic age can be the most important targets for exploration in the QHMB.

Mercury anomalies as a proxy for large igneous province volicanism and effects on the carbon cycle in a U-Pb age-constrained section spanning the end-Triassic mass extinction, Levanto, Peru

NASA Astrophysics Data System (ADS)

Yager, J. A.; West, A. J.; Bergquist, B. A.; Thibodeau, A. M.; Corsetti, F. A.; Berelson, W.; Rosas, S.; Bottjer, D. J.

2017-12-01

Understanding the causes of the end-Triassic extinction and their potential relationship to Central Atlantic Magmatic Province (CAMP) volcanism necessitates careful correlation of carbon cycle records (largely from marine sections) and volcanism (largely from terrestrial successions) in a robust chronological framework. Here, we report stable carbon isotopes and mercury concentrations and isotopes from the Levanto section in Northern Peru as a putative proxy for CAMP (a large igneous province) in a marine section. Levanto represents deposition well below storm wave base and is lithologically homogenous before, during, and after the end-Triassic extinction interval, making it ideal for detailed chemostratigraphy. Furthermore, abundant intercalated ash beds allow us to correlate mercury concentrations in the marine record directly with CAMP basalt ages, providing a test of the correspondence of mercury anomalies with the eruption of CAMP volcanics. Age dating and C isotope analyses provide an opportunity to explore orbital tuning of the carbon isotope record and ground truth it with existing U-Pb ages from the section, a feature not available in any other marine sections examined to date. The abundance of U-Pb dated ashes in the Levanto section allows us to correlate orbital tuning with other basins, which lack absolute age control, providing a better understanding for the C cycle changes associated with the Triassic-Jurassic boundary.

A millennial-scale record of Pb and Hg contamination in peatlands of the Sacramento-San Joaquin Delta of California, USA.

PubMed

Drexler, Judith Z; Alpers, Charles N; Neymark, Leonid A; Paces, James B; Taylor, Howard E; Fuller, Christopher C

2016-05-01

In this paper, we provide the first record of millennial patterns of Pb and Hg concentrations on the west coast of the United States. Peat cores were collected from two micro-tidal marshes in the Sacramento-San Joaquin Delta of California. Core samples were analyzed for Pb, Hg, and Ti concentrations and dated using radiocarbon and (210)Pb. Pre-anthropogenic concentrations of Pb and Hg in peat ranged from 0.60 to 13.0μgg(-1)and from 6.9 to 71ngg(-1), respectively. For much of the past 6000+ years, the Delta was free from anthropogenic pollution, however, beginning in ~1425CE, Hg and Pb concentrations, Pb/Ti ratios, Pb enrichment factors (EFs), and HgEFs all increased. Pb isotope compositions of the peat suggest that this uptick was likely caused by smelting activities originating in Asia. The next increases in Pb and Hg contamination occurred during the California Gold Rush (beginning ~1850CE), when concentrations reached their highest levels (74μgg(-1) Pb, 990ngg(-1) Hg; PbEF=12 and HgEF=28). Lead concentrations increased again beginning in the ~1920s with the incorporation of Pb additives in gasoline. The phase-out of lead additives in the late 1980s was reflected in changes in Pb isotope ratios and reductions in Pb concentrations in the surface layers of the peat. The rise and subsequent fall of Hg contamination was also tracked by the peat archive, with the highest Hg concentrations occurring just before 1963CE and then decreasing during the post-1963 period. Overall, the results show that the Delta was a pristine region for most of its ~6700-year existence; however, since ~1425CE, it has received Pb and Hg contamination from both global and regional sources. Published by Elsevier B.V.

A millennial-scale record of Pb and Hg contamination in peatlands of the Sacramento-San Joaquin Delta of California, USA

USGS Publications Warehouse

Drexler, Judith; Alpers, Charles N.; Neymark, Leonid; Paces, James B.; Taylor, Howard E.; Fuller, Christopher C.

2016-01-01

In this paper, we provide the first record of millennial patterns of Pb and Hg concentrations on the west coast of the United States. Peat cores were collected from two micro-tidal marshes in the Sacramento-San Joaquin Delta of California. Core samples were analyzed for Pb, Hg, and Ti concentrations and dated using radiocarbon, 210Pb, and 137Cs. Pre-anthropogenic concentrations of Pb and Hg in peat ranged from 0.60 to 13.0 µg g-1and from 6.9 to 71 ng g-1, respectively. For much of the past 6000+ years, the Delta was free from anthropogenic pollution, however, beginning in ~1425 CE, Hg and Pb concentrations, Pb/Ti ratios, Pb enrichment factors (EFs), and HgEFs all increased. Pb isotope compositions of the peat suggest that this uptick was likely caused by smelting activities originating in Asia. The next increases in Pb and Hg contamination occurred during the California Gold Rush (beginning ~1850 CE), when concentrations reached their highest levels (74 µg g-1 Pb, 990 ng g-1 Hg; PbEF = 12 and HgEF = 28). Lead concentrations increased again beginning in the ~1920s with the incorporation of Pb additives in gasoline. The phase-out of lead additives in the late 1980s was reflected in Pb isotope ratios and reductions in Pb concentrations in the surface layers of the peat. The rise and fall of Hg contamination was also tracked by the peat archive, with the highest Hg concentrations occurring just before 1963 CE and then decreasing during the post-1963 period. Overall, the results show that the Delta was a pristine region for most of its ~6700-year existence; however, since ~1425 CE, it has received Pb and Hg contamination from both global and regional sources.

Radioisotopes in sedimentary study of the Black Sea and Caspian Sea

NASA Astrophysics Data System (ADS)

Laptev, Gennady; Voitsekhovych, Oleg V.

2013-04-01

Natural archives, such as lake or marine sediment, are widely used in erosion/sedimentation, water quality, climate change and eutrophication study alongside with the retrospective reanalysis of contaminants fluxes (trace metals, organic pollutants or radionuclides). In order to "read" information stored in sediment sequences a chronostatigraphic method have been developed and used since 1950s which is based upon variation of activity of 210Pb over the sediment profile, natural radioisotope of Uranium decay series with half-life 22 years, and hence valid for the last 100-150 years of recent sedimentation history. The 210Pb chronology is prone to be validated by other time-markers, such as artificial radionuclides globally dispersed after the nuclear weapons tests of 1960s or major accidents on NPP (the Chernobyl accident of 1986 or latest on the Fukushima Daiichi in 2011). In the last decade an intensive study using sediment cores collected from shelf and deep-sea areas in the Black Sea and the Caspian Sea have been undertaken within the framework of a number of international research projects organized by IAEA and UNOPS-GEF and devoted to environmental problems of this enclosed, and therefore sensitive to environmental impact, marine systems. Elaborative analysis of the experimental data and sediment age calculation have been done by application of CRS and CIC dating models to unsupported 210Pb activity over the sediment profile. Measured in sediment 137Cs and 241Am clearly showed well resolved Bomb test and Chernobyl fallout peaks and were used as markers in order to corroborate radiometrically determined age of sediment. Geochronological reconstruction of the fallout radionuclides inventory, fluxes and accumulation rate in the sediment of the Black Sea and Caspian Sea by application of combined radiometric dating technique proved to be very consistent with the historical data of atmospheric fallout observations of that artificial radionuclides recorded worldwide since nuclear era onset in early 1950s. Another finding of the initially radioactivity related to project was suitability of unmixed sediment cores recovered from the deep anoxic floor and continental slope of the Black Sea to be used for proxy reconstruction of the late Holocene climate variability in the region. This well preserved sediment are characteristic in finely laminated coccolith ooze (Unit I - approximate age 2000 years) overlaying above rich in organic matter sapropels of Unit II. Variations in accumulation rates of biogenic carbonate sediment fraction of Unit I were found to be satisfactory correlate with changes in winter SST anomaly calibrated in recent radiometricaly dated topmost sediment. Further development and rectification of the proposed interdisciplinary method is in progress.

Magmatic tempo of Earth's youngest exposed plutons as revealed by detrital zircon U-Pb geochronology.

PubMed

Ito, Hisatoshi; Spencer, Christopher J; Danišík, Martin; Hoiland, Carl W

2017-09-29

Plutons are formed by protracted crystallization of magma bodies several kilometers deep within the crust. The temporal frequency (i.e. episodicity or 'tempo') of pluton formation is often poorly constrained as timescales of pluton formation are largely variable and may be difficult to resolve by traditional dating methods. The Hida Mountain Range of central Japan hosts the youngest exposed plutons on Earth and provides a unique opportunity to assess the temporal and spatial characteristics of pluton emplacement at high temporal resolution. Here we apply U-Pb geochronology to zircon from the Quaternary Kurobegawa Granite and Takidani Granodiorite in the Hida Mountain Range, and from modern river sediments whose fluvial catchments include these plutons in order to reconstruct their formation. The U-Pb data demonstrate that the Kurobegawa pluton experienced two magmatic pulses at ~2.3 Ma and ~0.9 Ma; whereas, to the south, the Takidani pluton experienced only one magmatic pulse at ~1.6 Ma. These data imply that each of these magmatic systems were both spatially and temporally distinct. The apparent ~0.7 Myr age gap between each of the three magmatic pulses potentially constrains the recharge duration of a single pluton within a larger arc plutonic complex.

Isotopic chemical weathering behaviour of Pb derived from a high-Alpine Holocene lake-sediment record

NASA Astrophysics Data System (ADS)

Gutjahr, Marcus; Süfke, Finn; Gilli, Adrian; Anselmetti, Flavio; Glur, Lukas; Eisenhauer, Anton

2017-04-01

Several studies assessing the chemical weathering systematics of Pb isotopes provided evidence for the incongruent release of Pb from source rocks during early stages of chemical weathering, resulting in runoff compositions more radiogenic (higher) than the bulk source-rock composition [e.g. 1]. Deep NW Atlantic seawater Pb isotope records covering the last glacial-interglacial transition further support these findings. Clear excursions towards highly radiogenic Pb isotopic input in the deep NW Atlantic seen during the early Holocene, hence after the large-scale retreat of the Laurentide Ice Sheet in North America, are interpreted to be controlled by preferential release of radiogenic Pb from U- and Th-rich mineral phases during early stages of chemical weathering that are less resistant to chemical dissolution than other rock-forming mineral phases [2-4]. To date, however, no terrestrial Pb isotope record exists that could corroborate the evidence from deep marine sites for efficient late deglacial weathering and washout of radiogenic Pb. We present a high-resolution adsorbed Pb isotope record from a sediment core retrieved from Alpine Lake Grimsel (1908 m.a.s.l.) in Switzerland, consisting of 117 Pb compositions over the past 10 kyr. This high-Alpine study area is ideally located for incipient and prolonged chemical weathering studies. The method used to extract the adsorbed lake Pb isotope signal is identical to previous marine approaches targeting the authigenic Fe-Mn oxyhydroxides fraction within the lake sediments [5, 6]. The Pb isotope compositions are further accompanied by various elemental ratios derived from the same samples that equally trace climatic boundary conditions in the Grimsel Lake area. The Pb isotopic composition recorded in Lake Grimsel is remarkably constant throughout the majority of the Holocene until ˜2.5 ka BP, despite variable sediment composition and -age, and isotopically relatively close to the signature of the granitic source rock. In contrast, adsorbed Th and U concentrations (given in concentrations of ng/g of sediment) are indeed significantly elevated during the earliest part of the record, while other adsorbed metals such as Al and Ti display highest adsorbed concentrations during the mid-Holocene. Elements such as Nd display fairly constant normalised concentrations throughout the record. Hence, while our Pb isotopic record appears remarkably insensitive towards climatic perturbations seen during the Holocene, the various elemental records display a striking sensititivity towards the overall climate evolution of the Holocene. Finally, the rise and fall of the Roman Empire as well as the onset of the industrial revolution are clearly resolvable in our Pb isotopic records. References [1] Harlavan, Y. Y. et al. (1998), GCA 62, 33-46; [2] Gutjahr, M. et al. (2009), EPSL 286, 546-555; [3] Kurweil, F. et al. (2010), EPSL 299, 458-465; [4] Crocket, K.C. et al. (2012) QSR 38, 89-99; [5] Gutjahr et al. (2007) Chem. Geol. 242, 351-370; [6] Blaser, P. et al. (2016) Chem. Geol. 439, 189-204.

Paleomagnetism and geochronological studies on a 450 km long 2216 Ma dyke from the Dharwar craton, southern India

NASA Astrophysics Data System (ADS)

Nagaraju, E.; Parashuramulu, V.; Kumar, Anil; Srinivas Sarma, D.

2018-01-01

Paleomagnetic and geochronological studies were carried out on a ∼ 450 km long (from 17 sites) N-S striking Paleoproterozoic dyke swarm exposed along a natural crustal cross section of about 10 km (increasing from North to South) in the Dharwar Craton, to study the characteristics of paleomagnetism and geochronology in vertical dimension. U-Pb/Pb-Pb dating on baddeleyite gives a crystallisation age of 2216.0 ± 0.9 Ma for long dyke AKLD. Paleomagnetic data from this well dated ∼ 2216 Ma dyke swarm in Dharwar Craton are of excellent quality. High coercivity and high blocking temperature components are carried by single domain magnetite and show dual polarity remanence directions. Combined normal and reverse polarity remanences on AKLD and other N-S dykes define the most reliable paleomagnetic pole for ∼ 2216 Ma at latitude 36°S and longitude 312°E (A95 = 7°). Though paleomagnetic data is unavailable on other N-S dykes below the Cuddapah basin, high precision geochronology suggest that they are of similar age within errors. Though there is a variation in the crustal depth of Dharwar craton from north to south, consistent Pb-Pb/U-Pb baddeleyite geochronology and paleomagnetic studies along the AKLD established its continuity and preservation along its entire strike length. The virtual geomagnetic poles of these sites confirm a stable remanence and are almost identical to the previously reported paleomagnetic pole and also supported by positive reversal test. Positive paleomagnetic reversal test on these dykes signify that the remanent magnetization is primary and formed during initial cooling of the intrusions. Updated apparent polar wander path of Dharwar craton indicates relatively low drift rate during 2.21-2.08 Ga interval. Magnetogranulometry and SEM studies show that remanent magnetization in this dyke was carried by single domain magnetite residing within silicate minerals.

Ar-40/Ar-39 and U-Th-Pb dating of separated clasts from the Abee E4 chondrite

NASA Technical Reports Server (NTRS)

Bogard, D. D.; Unruh, D. M.; Tatsumoto, M.

1983-01-01

Ar-40/Ar-39 and U-Th-Pb are investigated for three clasts from the Abee (E4) enstatite chondrite, yielding Ar-40/Ar-39 plateau ages (and/or maximum ages) of 4.5 Gy, while two of the clasts give average ages of 4.4 Gy. The 4.4-4.5 Gy range does not resolve possible age differences among the clasts. The U-Th-Pb data are consistent with the interpretation that initial clast formation occurred 4.58 Gy ago, and that the clasts have since remained closed systems which have been contaminated with terrestrial Pb. The thermal history of Abee deduced from Ar data seems consistent with that deduced from magnetic data, suggesting that various Abee components experienced separate histories until brecciation no later than 4.4 Gy ago, experiencing no significant subsequent heating.

Escherichia coli yjjPB genes encode a succinate transporter important for succinate production.

PubMed

Fukui, Keita; Nanatani, Kei; Hara, Yoshihiko; Yamakami, Suguru; Yahagi, Daiki; Chinen, Akito; Tokura, Mitsunori; Abe, Keietsu

2017-09-01

Under anaerobic conditions, Escherichia coli produces succinate from glucose via the reductive tricarboxylic acid cycle. To date, however, no genes encoding succinate exporters have been established in E. coli. Therefore, we attempted to identify genes encoding succinate exporters by screening an E. coli MG1655 genome library. We identified the yjjPB genes as candidates encoding a succinate transporter, which enhanced succinate production in Pantoea ananatis under aerobic conditions. A complementation assay conducted in Corynebacterium glutamicum strain AJ110655ΔsucE1 demonstrated that both YjjP and YjjB are required for the restoration of succinate production. Furthermore, deletion of yjjPB decreased succinate production in E. coli by 70% under anaerobic conditions. Taken together, these results suggest that YjjPB constitutes a succinate transporter in E. coli and that the products of both genes are required for succinate export.

The timing of high-temperature retrogression in the Reynolds Range, central Australia: constraints from garnet and epidote Pb-Pb dating

NASA Astrophysics Data System (ADS)

Buick, Ian S.; Frei, Robert; Cartwright, Ian

Lower Calcsilicate Unit metasediments and underlying migmatitic Napperby Gneiss metagranite at Conical Hill in the Reynolds Range, central Australia, underwent regional high-grade ( 680 to 720°C), low-pressure/high-temperature metamorphism at 1594+/- 6Ma. The Lower Calcsilicate Unit is extensively quartz veined and epidotised, and discordant grandite garnet+epidote quartz veins may be traced over tens of metres depth into pegmatites that pooled at the Lower Calcsilicate Unit-Napperby Gneiss contact. The quartz veins were probably precipitated by water-rich fluids that exsolved from partial melts derived from the Napperby Gneiss during cooling from the peak of regional metamorphism to the wet granite solidus. Pb stepwise leaching (PbSL) on garnet from three discordant quartz veins yielded comparable single mineral isochrons of 1566+/-32Ma, 1576+/-3Ma and 1577+/-5Ma, which are interpreted as the age of garnet growth in the veins. These dates are in good agreement with previous Sensitive High Resolution Ion Microprobe (SHRIMP) ages of zircon and monazite formed during high-temperature retrogression (1586+/-5 to 1568+/-4Ma) elsewhere in the Reynolds Range. The relatively small age difference between peak metamorphism and retrograde veining suggests that partial melting and melt crystallisation controlled fluid recycling in the high-grade rocks. However, PbSL experiments on epidote intergrown with, and partially replacing, garnet in two of the veins yielded isochrons of 1454+/-34 and 1469+/- 26Ma. The 100-120Ma age difference between intergrown garnet and late epidote from the same vein suggests that the vein systems may have experienced multiple episodes of fluid flow.

The Mesozoic metamorphic-magmatic events in the Medog area, the Eastern Himalayan Syntaxis: constraints from zircon U-Pb geochronology, trace elements and Hf isotope compositions in granitoids

NASA Astrophysics Data System (ADS)

Dong, Hanwen; Xu, Zhiqin; Li, Yuan; Liu, Zhao; Li, Huaqi

2015-01-01

Based on the regional geological mapping, several granitoid intrusions had been discovered in the Eastern Himalayan Syntaxis (EHS). In order to constrain their petrogenesis and discuss their relations with the regional tectonics, we carried out U-Pb dating, trace elements and Hf isotope geochemistry studies on zircons separated from the granitoid rocks, in the area of the EHS. In this contribution, the granitoid rocks are mainly composed of diorites (X20-1-6) and granitic gneissic rocks (X2-15-1). The U-Pb zircon dating of diorites yields a crystallization age of 193.8 ± 2.0 Ma. These zircon have ɛ Hf( t) values ranging from -6.48 to -0.05, indicating an involvement of ancient crustal materials in the generation of these igneous rocks. The zircons from the Medog granitic gneissic rock commonly show zoning structures. The REE patterns and abundances of the inherited cores are different from those of the oscillatory rims. The LA-ICP-MS U-Pb zircon in situ analyses indicate that: (1) the zircon cores give multi-stage magmatic event ages ranging from 516 to 1,826 Ma, of which six ages are converged on 1,330-911 Ma, it is considered that the migmatitic gneiss has been formed in this time, and (2) while the zircon rims yield 206Pb/238U weighted mean ages of 217.4 ± 3.0 Ma (MSWD = 3.2), which was interpreted to represent the ages of the Triassic anatexis. Their ɛ Hf( t) values range from -18.98 to -8.36 and -14.22 to 8.72, respectively. The timing of the anatexis in the Medog area is coeval with the widespread metamorphism in Lhasa terrane.

U-Pb dating of uranium deposits in collapse breccia pipes of the Grand Canyon region

USGS Publications Warehouse

Ludwig, K. R.; Simmons, K.R.

1992-01-01

Two major periods of uranium mineralization are indicated by U-Pb isotope dating of uranium ores from collapse breccia pipes in the Grand Canyon region, northern Arizona. The Hack 2 and 3, Kanab North, and EZ 1 and 2 orebodies apparently formed in the interval of 200 ?? 20 Ma, similar to ages inferred for strata-bound, Late Triassic-hosted uranium deposits in southern Utah and northern Arizona. Samples from the Grand Canyon and Pine Nut pipes, however, indicate a distinctly older age of about 260 Ma. The clustering in ages for a variety of uranium deposits at about the age of the lower part of the Chinle Formation (Late Triassic) suggests that uranium in these deposits may have been derived by leaching from volcanic ash in the Chinle and mobilized by ground-water movement. Pb isotope ratios of galenas in mineralized pipes are more radiogenic than those of sulfides from either uranium-poor pipes or occurrences away from pipes. Fluids which passed through the pipes had interacted with the Proterozoic basement, possibly through the vertical fractures which influenced the location and evolution of the pipes themselves. -from Authors

A (210)Pb-based chronological model for recent sediments with random entries of mass and activities: Model development.

PubMed

Abril Hernández, José-María

2016-01-01

Unsupported (210)Pb ((210)Pbexc) vs. mass depth profiles do not contain enough information as to extract a unique chronology when both, (210)Pbexc fluxes and mass sediment accumulation rates (SAR) independently vary with time. Restrictive assumptions are needed to develop a suitable dating tool. A statistical correlation between fluxes and SAR seems to be a quite general rule. This paper builds up a new (210)Pb-based dating tool by using such a statistical correlation. It operates with SAR and initial activities that closely follow normal distributions, what leads to the expected correlation between fluxes and SAR. An intelligent algorithm solves their best arrangement downcore to fit the experimental (210)Pbexc vs. mass depth profile, generating then solutions for the chronological line, and for the histories of SAR and fluxes. Parametric maps of a χ-function serve to find out the solution and to support error estimates. Optionally, the model's answers can be better constrained through the use of time markers. The performance of the model is illustrated with a synthetic core, and with real cases using published data for varved sediment cores. Copyright © 2015 Elsevier Ltd. All rights reserved.

Marine and Lacustrine Organic-rich Sedimentary Unit Time Markers: Implications from Rhenium-Osmium Geochronology

NASA Astrophysics Data System (ADS)

Selby, D.

2011-12-01

Geochronology is fundamental to understand the age, rates and durations of Earth processes. This concerned Arthur Holmes who, for much of his career, attempted to define a geological time scale. This is a topic still important to Earth Scientists today, specifically the chronostratigraphy of sedimentary rocks. Here I explore the Re-Os geochronology of marine and lacustrine sedimentary rocks and its application to yield absolute time constraints for stratigraphy. The past decade has seen the pioneering research of Re-Os organic-rich sedimentary rock geochronology blossom into a tool that can now to be used to accurately and precisely determine depositional ages of organic-rich rock units that have experienced up to low grade greenschist metamorphism. This direct dating of sedimentary rocks is critical where volcanic horizons are absent. As a result, this tool has been applied to timescale calibration, basin correlation, formation duration and the timing of key Earth events (e.g., Neoproterozoic glaciations). The application of Re-Os chronometer to the Devonian-Mississippian boundary contained within the Exshaw Formation, Canada, determined an age of 361.3 ± 2.4 Ma. This age is in accord with U-Pb dates of interbedded tuff horizons and also U-Pb zircon date for the type Devonian-Mississippian Hasselbachtal section, Germany. The agreement of the biostratigraphic and U-Pb constraints of the Exshaw Formation with the Re-Os date illustrated the potential of the Re-Os chronometer to yield age determinations for sedimentary packages, especially in the absence of interbedd tuff horizons and biozones. A Re-Os date for the proposed type section of the Oxfordian-Kimmeridgian boundary, Staffin Bay, Isle of Skye, U.K., gave an age of 154.1 ± 2.2 Ma. This Re-Os age presents a 45 % (1.8 Ma) improvement in precision for the basal Kimmeridgian. It also demonstrated that the duration of the Kimmeridgian is nominally 3.3 Ma and thus is 1.6 Ma shorter than previously indicated. In addition to these examples, several studies have presented precise dates for Phanerozoic marine organic-rich units that are in excellent agreement with biostratigraphic determinations. A recent Re-Os study of the Woodford Shale (that was deposited throughout the Frasnian and Famennian) has provided important time markers as well as suggesting that the sedimentation rate of the Formation was relatively constant for ~20 Ma. To date only marine organic-rich sedimentary rocks have been utilized for Re-Os geochronology. However, lacustrine sedimentary rocks provide an invaluable archive of continental geological processes responding to tectonic, climatic and magmatic influences. Correlating these rocks to global geological phenomena requires accurate geochronological frameworks. The organic-rich lacustrine sedimentary units of the Eocene Green River Formation are enriched is Re and Os comparable to that of marine units. The Re-Os dates for the Green River Formation from the Uinta basin are 48.5 ± 0.6 Ma and 49.2 ± 1.0 Ma. These dates are in excellent agreement with Ar/Ar and U/Pb dates of interbedded tuffs in the GRF, therefore demonstrating that lacustrine units can be used for Re-Os geochronology in addition to marine organic-rich units.

Community-based Approaches to Improving Accuracy, Precision, and Reproducibility in U-Pb and U-Th Geochronology

NASA Astrophysics Data System (ADS)

McLean, N. M.; Condon, D. J.; Bowring, S. A.; Schoene, B.; Dutton, A.; Rubin, K. H.

2015-12-01

The last two decades have seen a grassroots effort by the international geochronology community to "calibrate Earth history through teamwork and cooperation," both as part of the EARTHTIME initiative and though several daughter projects with similar goals. Its mission originally challenged laboratories "to produce temporal constraints with uncertainties approaching 0.1% of the radioisotopic ages," but EARTHTIME has since exceeded its charge in many ways. Both the U-Pb and Ar-Ar chronometers first considered for high-precision timescale calibration now regularly produce dates at the sub-per mil level thanks to instrumentation, laboratory, and software advances. At the same time new isotope systems, including U-Th dating of carbonates, have developed comparable precision. But the larger, inter-related scientific challenges envisioned at EARTHTIME's inception remain - for instance, precisely calibrating the global geologic timescale, estimating rates of change around major climatic perturbations, and understanding evolutionary rates through time - and increasingly require that data from multiple geochronometers be combined. To solve these problems, the next two decades of uranium-daughter geochronology will require further advances in accuracy, precision, and reproducibility. The U-Th system has much in common with U-Pb, in that both parent and daughter isotopes are solids that can easily be weighed and dissolved in acid, and have well-characterized reference materials certified for isotopic composition and/or purity. For U-Pb, improving lab-to-lab reproducibility has entailed dissolving precisely weighed U and Pb metals of known purity and isotopic composition together to make gravimetric solutions, then using these to calibrate widely distributed tracers composed of artificial U and Pb isotopes. To mimic laboratory measurements, naturally occurring U and Pb isotopes were also mixed in proportions to mimic samples of three different ages, to be run as internal standards and as measures of inter-laboratory reproducibility. The U-Th community is undertaking many of the same protocols, and has recently created publicly available gravimetric solutions, and large volumes of three age solutions for widespread distribution and inter-laboratory comparison.

U-Pb systematics of zircon and titanite from the Gardnos impact structure, Norway: Evidence for impact at 546 Ma?

NASA Astrophysics Data System (ADS)

Kalleson, E.; Corfu, F.; Dypvik, H.

2009-05-01

Zircon and titanite were investigated in impactites of the Gardnos structure, a crater formed in Sveconorwegian (ca. 1 Ga) crust, which was then overridden in the Devonian by Caledonian nappes. Observed deformation features in zircons are granular texture, planar microstructures, and likely the incorporation of organic carbon during impact causing black staining of the zircon grains. The grains were studied by scanning electron microscopy (SEM) and cathode luminescence (CL) and dated by U-Pb isotope dilution - thermo-ionization mass spectrometry (ID-TIMS). Zircon grains without impact related features have U-Pb data showing moderate discordance (5-13%) and indicating formation ages mostly in the range of 1600-1000 Ma, except detrital zircon ages as old as >2481 Ma, reflecting the diversity of target rocks in the area. Titanite with concordant ages of 995-999 Ma dates metamorphism during final juxtaposition of the Telemarkia on the Idefjorden terrane to the east. Zircon grains with demonstrated or presumed shock features yield highly discordant (14-40%) U-Pb data, with a majority of them plotting along an array with a lower intercept of about 340 Ma reflecting the influence of the Caledonian orogeny and recent Pb-loss. One zircon grain was totally reset at 379 Ma during late Caledonian metamorphism, which also caused local growth of new titanite. A specific group of zircon grains yields data with relatively high discordance for moderate U contents, and five of these analyses, including that of a grain with proven granular or aggregate texture, fit a discordia line with an upper intercept of 546 ± 5 Ma. These features are interpreted as indicating zircon break-down to an amorphous state during impact, with subsequent recrystallization into microcrystalline aggregates causing extensive to complete Pb loss. We further suggest that their crystallinity prevented Pb loss during the Caledonian orogeny, while the small subgrain size and increasing metamictisation allowed more recent disturbances. We thus interpret the 546 Ma age as the approximate time of impact.

Timescales of Crustal Cooling of the Superior Craton near Attawapiskat, Ontario, Canada, and Implications for Extent of Keweenawan Plume Heating.

NASA Astrophysics Data System (ADS)

Edwards, G. H.; Blackburn, T.; Smit, K.

2017-12-01

The thermal history of the Superior Craton was punctuated by a period of mantle plume heating at 1.1 Ga associated with the Keweenawan Rift, though the plume's spatial extent, temperature, and duration of heating remain unresolved. Kimberlites of Mesoproterozoic and Jurassic age in the Attawapiskat area, Northern Ontario contain lithospheric mantle and lower crustal xenoliths that record the thermal history 600km to the north of exposed 1.1 Ga Keweenawan volcanics and the topographically and gravimetrically defined plume center. Previous work on Attawapiskat kimberlites identified two populations of diamonds with differing thermal histories, suggesting two distinct phases of diamond growth. Corresponding geothermobarometric data indicate geotherm relaxation and broadening of the diamond stability field between the Mesoproterozoic and Jurassic. These data, however, do not uniquely resolve whether the region experienced significant heating coincident with Keweenawan rifting ( 1.1 Ga) or prolonged, unperturbed cooling since amalgamation of the Superior Craton ( 2.6 Ga). To discern between these two possible histories, we use accessory phase U-Pb thermochronology to construct a continuous thermal record of the lower crust. Here we present a dataset of U-Pb ID-TIMS measurements of rutile and apatite from xenoliths (n=8) sourced from the Jurassic age Victor Kimberlite. The U/Pb and Pb isotopic compositions of rutile and apatite from shallow-residing amphibolite xenoliths exhibit Proterozoic dates with a high degree of U-Pb discordance, reflecting slow cooling of the middle crust prior to 1.1 Ga. Granulite and eclogite xenoliths record younger dates consistent with their deeper sample residence, but with a high degree of U-Pb concordance that is inconsistent with continuous cooling through the Proterozoic. Reproducing the measured trend with numerical models requires a reheating event at 1.1 Ga. Imposing a 60-70mW/m2 geotherm at 1.1 Ga is high enough to replicate the observed U-Pb data but low enough to permit cooling that satisfies diamond thermal data. This indicates that the Keweenawan plume head extended to at least the Attawapiskat area, where plume heating abutted, and likely extended beyond, the associated topographic and gravity anomalies of the Superior Region.

Earth's youngest exposed granite and its tectonic implications: the 10-0.8 Ma Kurobegawa Granite.

PubMed

Ito, Hisatoshi; Yamada, Ryuji; Tamura, Akihiro; Arai, Shoji; Horie, Kenji; Hokada, Tomokazu

2013-01-01

Although the quest for Earth's oldest rock is of great importance, identifying the youngest exposed pluton on Earth is also of interest. A pluton is a body of intrusive igneous rock that crystallized from slowly cooling magma at depths of several kilometers beneath the surface of the Earth. Therefore, the youngest exposed pluton represents the most recent tectonic uplift and highest exhumation. The youngest exposed pluton reported to date is the Takidani Granodiorite (~ 1.4 Ma) in the Hida Mountain Range of central Japan. Using LA-ICP-MS and SHRIMP U-Pb zircon dating methods, this study demonstrates that the Kurobegawa Granite, also situated in the Hida Mountain Range, is as young as ~ 0.8 Ma. In addition, data indicate multiple intrusion episodes in this pluton since 10 Ma with a ~ 2-million-year period of quiescence; hence, a future intrusion event is likely within 1 million years.

Earth's youngest exposed granite and its tectonic implications: the 10–0.8 Ma Kurobegawa Granite

PubMed Central

Ito, Hisatoshi; Yamada, Ryuji; Tamura, Akihiro; Arai, Shoji; Horie, Kenji; Hokada, Tomokazu

2013-01-01

Although the quest for Earth's oldest rock is of great importance, identifying the youngest exposed pluton on Earth is also of interest. A pluton is a body of intrusive igneous rock that crystallized from slowly cooling magma at depths of several kilometers beneath the surface of the Earth. Therefore, the youngest exposed pluton represents the most recent tectonic uplift and highest exhumation. The youngest exposed pluton reported to date is the Takidani Granodiorite (~ 1.4 Ma) in the Hida Mountain Range of central Japan. Using LA-ICP-MS and SHRIMP U-Pb zircon dating methods, this study demonstrates that the Kurobegawa Granite, also situated in the Hida Mountain Range, is as young as ~ 0.8 Ma. In addition, data indicate multiple intrusion episodes in this pluton since 10 Ma with a ~ 2-million-year period of quiescence; hence, a future intrusion event is likely within 1 million years. PMID:23419636

Dating of Submarine Landslides and Their Tsunami Deposits Using Hawaii as an Example

NASA Astrophysics Data System (ADS)

McMurtry, G. M.; Herrero-Bervera, E.

2003-12-01

There have been several approaches to dating the initiation of submarine landslides and the tsunamis they inevitably produce. In Hawaii, the timing of flank failures of major volcanoes has been estimated by radiometric and paleomagnetic dating of the youngest shield-building flows and dikes, the apex ages of the volcanoes, which can also be constrained by the oldest flows of post-collapse volcanism. More precise age estimates can be obtained by direct dating of the landslide. These approaches include paleomagnetic and U-series stratigraphic dating of the overlying pelagic sediment cover upon and in front of the landslide, the latter method producing minimum ages of last landslide turbidite emplacement, e.g., the ca. 120 ka Alika phase 2 event. Elevated, detached landslide blocks make the best targets for such dating because it is assumed that smaller post-emplacement turbidites will not reach their summits. Catastrophic events such as the 1.0 Ma Wailau giant landslide have, however, been dated by turbidite deposition upon large, elevated blocks of the nearby 1.8 Ma Nuuanu giant landslide. Other direct methods for older events include use of thickness of ferromanganese crusts collected from steep, exposed rock scarps and cosmogenic Be-10 or U-series radiometric determination of the few mm/Ma rate of accumulation. In subtropical areas such as Hawaii, coral clast-bearing, elevated marine deposits on the southeastern islands have been identified as deposits from giant tsunamis. Among the key evidence are the great age and paleo-elevations of the coral clasts found in situ. Since modern coral clasts are relatively young, a few thousand years old or less, older analogs swept from the presently submerged reefs offshore can reliably date tsunamigenic depositional events within the late Quaternary using U-series methods. The age of the tsunami will date within these limits (and the analytical precisions) to the youngest in situ coral clast that was entrained by the waves. U-series dates approximately coeval with the Alika 2 giant landslide suggest a youngest 100 ka tsunami emplacement age from 100-137 ka corals collected on Lanai and Hawaii; likewise, older deposits on Molokai and Lanai suggest a 200 ka tsunami emplacement age from corals that range 200-258 ka in age, but interpretative care must be taken as open-system behavior upon weathering may produce apparently younger dates. Other promising methods for dating these deposits include cosmogenic Cl-36 exposure ages of cements and Cl-36 and He-3 exposure ages of the entrained volcanic rocks. Younger events can be dated by the above methods using C-14 or unsupported Pb-210.

CH3NH3PbI3 and CsPbI3 Supramolecular Clusters in 1D: Do They Evolve with the Same Principle of Cooperative Binding?

NASA Astrophysics Data System (ADS)

Varadwaj, Arpita; Varadwaj, Pradeep R.; Yamashita, Koichi

Development of novel semiconductor-based photo-catalytic and -voltaic systems is a major area of research in nanoscience and technologies, and engineering. The process can be either direct or indirect in converting the light energy into electricity. Some of the photovoltaics include the organic, dye-sensitized, and halide perovskite solar cells, among others. Methylammonium lead iodide (CH3NH3PbI3) inorganic-organic hybrid perovskite is one among the many highly valued semiconductors reported till date, comparable with the inorganic cesium lead iodide (CsPbI3) perovskite. These are competitive candidates in the solar energy race. Nevertheless, this study was concentrated on the fundamental understanding of the rational designs of the CH3NH3PbI3 and CsPbI3 supramolecular materials using first-principles calculations, emerged though the self-assembly of the respective building blocks. It therefore addresses the question whether the (CH3NH3PbI3)n and (CsPbI3)n (n =1-10) supramolecular clusters are the consequences of additivity, or non-additive cooperative binding? For addressing this question, the supramolecular properties such as the polarizability, the intermolecular charge transfer, and the binding energy, etc., all w.r.t the cluster size n, are exploited. CREST-JST, 7 Gobancho, Chiyoda-ku, Tokyo, Japan 102-0076.

Evolution Of An Upper Crustal Plutonic-Volcanic Plumbing System:Insights From High Precision U-Pb Zircon Geochronology Of Intracaldera Tuff And Intrusions In Silver Creek Caldera, Arizona, USA

NASA Astrophysics Data System (ADS)

Zhang, T.; Mundil, R.; Miller, C. F.; Miller, J. S.; Paterson, S. R.

2010-12-01

Study of both plutonic and volcanic regimes in one single magmatic system is a powerful approach towards obtaining a more complete view of the long-term evolution of magma systems. The recently discovered Silver Creek caldera is the source of the voluminous Peach Spring Tuff (PST) (Ferguson, 2008) and presents a unique opportunity to study a field laboratory of a linked plutonic-volcanic system. This relict west-facing half caldera is predominantly filled with trachytic intracaldera tuff with the caldera margin intruded by several petrologically distinct hypabyssal intrusions. These include porphyritic granite with granophyric texture, felsic leucogranite, porphyritic monzonite exposed on NE side of the caldera that is zoned from more felsic to more mafic, and quartz-phyric dikes that intrude the caldera fill. We present preliminary single zircon ages from 4 samples that have been analyzed using the CA-TIMS method after thermal annealing and chemical leaching (Mattinson 2005), including 1 sample from intracaldera tuff and 3 samples from caldera-related intrusions. 3-D total U/Pb isochron ages from all four samples fall within a range of 18.32-18.90 Ma with uncertainties between 0.09 and 0.39 Ma, although some of them lack precision and are compromised by elevated common Pb. For example, zircon from the dated porphyritic monzonite yields an age of 18.32±0.42 Ma (MSWD=2.7) where the excess scatter may result from real age dispersion and/or different compositions of the common Pb contribution. The PST had been dated to ~18.5 Ma by 40Ar/39Ar techniques (Nielson et al., 1990). In order to be compared to U/Pb ages the 40Ar/39Ar age must be adjusted for a revised age for the then used flux monitor (MMbh-1) and corrected for the now quantified systematic bias between 40Ar/39Ar and U/Pb ages (Renne et al., 2010), which results in a corrected age of 18.8 Ma. Thus, the ages for our samples match that of the PST within error. Based on current results, the age difference between the different phases of the intrusion is very small and the ages of the intrusion match within errors the age of the PST. This tight time range indicates that the super-eruption and the subsequent reactivation of the caldera by hypabyssal intrusions happened on a much shorter timescale than the evolution of large magma systems that have been described with durations of up to 10 m.y. Additional geochronology in combination with geochemical and AMS analyses are aimed at a more detailed reconstruction of the emplacement and eruption history of this plutonic-volcanic system.

40 CFR Table C-3 to Subpart C of... - Test Specifications for Pb in TSP and Pb in PM 10 Methods

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 6 2014-07-01 2014-07-01 false Test Specifications for Pb in TSP and Pb in PM 10 Methods C Table C-3 to Subpart C of Part 53 Protection of Environment ENVIRONMENTAL..., Subpt. C, Table C-3 Table C-3 to Subpart C of Part 53—Test Specifications for Pb in TSP and Pb in PM 10...

40 CFR Table C-3 to Subpart C of... - Test Specifications for Pb in TSP and Pb in PM 10 Methods

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 6 2013-07-01 2013-07-01 false Test Specifications for Pb in TSP and Pb in PM 10 Methods C Table C-3 to Subpart C of Part 53 Protection of Environment ENVIRONMENTAL..., Subpt. C, Table C-3 Table C-3 to Subpart C of Part 53—Test Specifications for Pb in TSP and Pb in PM 10...

40 CFR Table C-3 to Subpart C of... - Test Specifications for Pb in TSP and Pb in PM10 Methods

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 6 2012-07-01 2012-07-01 false Test Specifications for Pb in TSP and Pb in PM10 Methods C Table C-3 to Subpart C of Part 53 Protection of Environment ENVIRONMENTAL..., Subpt. C, Table C-3 Table C-3 to Subpart C of Part 53—Test Specifications for Pb in TSP and Pb in PM10...

Identification of human-to-human transmissibility factors in PB2 proteins of influenza A by large-scale mutual information analysis

PubMed Central

Miotto, Olivo; Heiny, AT; Tan, Tin Wee; August, J Thomas; Brusic, Vladimir

2008-01-01

Background The identification of mutations that confer unique properties to a pathogen, such as host range, is of fundamental importance in the fight against disease. This paper describes a novel method for identifying amino acid sites that distinguish specific sets of protein sequences, by comparative analysis of matched alignments. The use of mutual information to identify distinctive residues responsible for functional variants makes this approach highly suitable for analyzing large sets of sequences. To support mutual information analysis, we developed the AVANA software, which utilizes sequence annotations to select sets for comparison, according to user-specified criteria. The method presented was applied to an analysis of influenza A PB2 protein sequences, with the objective of identifying the components of adaptation to human-to-human transmission, and reconstructing the mutation history of these components. Results We compared over 3,000 PB2 protein sequences of human-transmissible and avian isolates, to produce a catalogue of sites involved in adaptation to human-to-human transmission. This analysis identified 17 characteristic sites, five of which have been present in human-transmissible strains since the 1918 Spanish flu pandemic. Sixteen of these sites are located in functional domains, suggesting they may play functional roles in host-range specificity. The catalogue of characteristic sites was used to derive sequence signatures from historical isolates. These signatures, arranged in chronological order, reveal an evolutionary timeline for the adaptation of the PB2 protein to human hosts. Conclusion By providing the most complete elucidation to date of the functional components participating in PB2 protein adaptation to humans, this study demonstrates that mutual information is a powerful tool for comparative characterization of sequence sets. In addition to confirming previously reported findings, several novel characteristic sites within PB2 are reported. Sequence signatures generated using the characteristic sites catalogue characterize concisely the adaptation characteristics of individual isolates. Evolutionary timelines derived from signatures of early human influenza isolates suggest that characteristic variants emerged rapidly, and remained remarkably stable through subsequent pandemics. In addition, the signatures of human-infecting H5N1 isolates suggest that this avian subtype has low pandemic potential at present, although it presents more human adaptation components than most avian subtypes. PMID:18315849

Re-appraisal of the stratigraphy and determination of new U-Pb dates for the Sterkfontein hominin site, South Africa.

PubMed

Pickering, Robyn; Kramers, Jan D

2010-07-01

Sterkfontein Caves is the single richest early hominin site in the world with deposits yielding one or more species of Australopithecus and possible early Homo, as well as an extensive faunal collection. The inability to date the southern African cave sites accurately or precisely has hindered attempts to integrate the hominin fossil evidence into pan-African scenarios about human evolutionary history, and especially hominin biogeography. We have used U-Pb and U-Th techniques to date sheets of calcium carbonate flowstone inter-bedded between the fossiliferous sediments. For the first time, absolute age ranges can be assigned to the fossil-bearing deposits: Member 2 is between 2.8 +/- 0.28 and 2.6 +/- 0.30 Ma and Member 4 between 2.65 +/- 0.30 and 2.01 +/- 0.05 Ma. The age of 2.01 +/- 0.05 Ma for the top of Member 4 constrains the last appearance of Australopithecus africanus to 2 Ma. In the Silberberg Grotto we have reproduced the U-Pb age of approximately 2.2 Ma of for the flowstones associated with StW573. We believe that these deposits, including the fossil and the flowstones, accumulated rapidly around 2.2 Ma. The stratigraphy of the site is complex as sediments are exposed both in the underground chambers and at surface. We present a new interpretation of the stratigraphy based on surface mapping, boreholes logs and U-Pb ages. Every effort was made to retain the Member system, however, only Members 2 and 4 are recognized in the boreholes. We propose that the deposits formally known as Member 3 are in fact the distal equivalents of Member 4. The sediments of Members 2 and 4 consisted of cone-like deposits and probably never filled up the cave. The U-Th ages show that there are substantial deposits younger than 400 ka in the underground cave, underlying the older deposits, highlighting again that these cave fills are not simple layer-cakes.

Ligand-mediated synthesis of compositionally related cesium lead halide CsPb2X5 nanowires with improved stability.

PubMed

Ruan, Longfei; Lin, Jin; Shen, Wei; Deng, Zhengtao

2018-04-26

Compositionally related cesium lead halide materials, such as CsPb2X5, have attracted great interest due to their considerable optoelectronic/optical properties as well as improved stability. Currently, CsPb2Br5 nanocrystals can be well-designed by tuning the ligands or precursor ratio, whereas, CsPb2X5 (with Cl- or I-) nanocrystals can only be obtained by the anion exchange method. Herein, we report a method to directly synthesize CsPb2X5 facilitated by thiol ligands. The morphology of CsPb2X5 can be designed as a nanowire. Importantly, the stability of directly synthesized CsPb2X5 nanowires is much improved when compared with the stabilities of the materials obtained by the anion-exchange method. We believe that this method will promote the application of 1D tetragonal CsPb2X5 in optoelectronics, optics and other fields.

Neodymium Isotopic Compositions of the Titanite Reference Materials Used in U-Pb Geochronology

NASA Astrophysics Data System (ADS)

Ma, Q.; Yang, Y.; Zhao, Z.

2017-12-01

Titanite (CaTiSiO5) is a widespread mineral and preferentially incorporates considerable uranium and significant light rare earth elements (LREEs) in its structure. Geochronology based upon U-Pb and Pb-Pb analyses of titanite has proven to be useful for understanding the P-T-t evolution of many igneous, metamorphic and hydrothermally altered rock samples (Scott and St-Onge, 1995). In the meantime, Sm-Nd isotopic composition in single titanite can be used to obtain initial Nd isotope composition at the time of titanite crystallization when combined with its U-Pb age, making titanite the most versatile mineral for dating metamorphism and tracing hydrothermal source (Amelin et al., 2009). The widely utilized in situ analyses by SIMS and LA-(MC)-ICP-MS have emphasized the significance for uniform and homogeneous reference materials for external correction (Liu et al., 2012, Sun et al., 2012, Yang et al., 2014). Here, we present U-Pb ages and Sm-Nd isotope analyses of twelve natural titanite crystals (12YQ82, T004, Ontario, BLR-1, OLT1, Khan, Qinghu, TLS-36, NW-IOA, C253, Pakistan and MKED1) acquired by Agilent 7500a Q-ICP-MS and Neptune MC-ICP-MS, respectively, combined a 193 nm ArF excimer laser ablation system. For U-Pb dating, elemental fractionation and instrumental drift were externally corrected using MKED1 titanite standard, showing results of U-Pb analyses all within error of those recommended values. With respect to Sm-Nd isotopes, we employed the interference-free 147Sm/149Sm to deduct 144Sm isobaric interference on 144Nd, and the fractionation between 147Sm and 144Nd was calibrated using BLR-1 titanite, which is proved homogenous in Sm-Nd isotopic system. The obtained Sm-Nd isotopic compositions for natural titanite samples are all consistent with those values determined by isotope dilution (ID) MC-ICP-MS, demonstrating the precision and accuracy currently available for in situ Sm-Nd analyses. Our results demonstrate that BLR-1, OLT1 and Ontario titanites are relatively uniform and homogeneous in Sm-Nd isotopic system and thus can serve as ideal reference materials for external calibration during in situ Sm-Nd analysis.

Resistivity behavior of optimized PbTiO3 thin films prepared by spin coating method

NASA Astrophysics Data System (ADS)

Nurbaya, Z.; Wahid, M. H.; Rozana, M. D.; Alrokayan, S. A. H.; Khan, H. A.; Rusop, M.

2018-05-01

Th is study presents the resistivity behavior of PbTiO3 thin films which were prepared towards metal-insulator-metal capacitor device fabrication. The PbTiO3 thin films were prepared through sol-gel spin coating method that involved various deposition parameters that is (1) different molar concentration of PbTiO3 solutions, (2) various additional PbAc-content in PbTiO3 solutions, and (3) various annealing temperature on PbTiO3 thin films. Hence, an electrical measurement of current versus voltage was done to determine the resistivity behavior of PbTiO3 thin films.

Sulfide minerals as new Sm-Nd geochronometers for ore genesis dating of mafic-ultramafic layered intrusions

NASA Astrophysics Data System (ADS)

Serov, Pavel; Ekimova, Nadezhda; Bayanova, Tamara

2014-05-01

The main method of dating the ore process was the Re-Os method of sulfides (Luck, Allegre, 1983; Walker et. al., 1991). However, studies of Re-Os systematics of sulfide minerals do not always give the correct ages and showing the disturbances of the Re-Os systematics. At the same time, Sm-Nd age of sulfides in good agreement with the U-Pb dating on zircon and baddeleyite and suggests that the Sm-Nd system of sulfides is more resistant to secondary alteration processes. Our studies have shown that along with rock-forming, ore minerals (sulfides) can be used to determine the ore genesis time of industrially important geological sites, since exactly with the sulfides the industry Pt-Pd mineralization is closely connected. The Sm-Nd investigations steadily employ new minerals-geochronometers. Of these, sulfides of PGE-bearing layered intrusions are quite important in terms of dating the process of ore origin. Studying the REE distribution in the sulfides of MOR hydrothermal sources has shown possible REE presence in the sulfide lattice (Rimskaya-Korsakova et. al., 2003). These are difficult to carry out because the concentrations of Sm and Nd isotopes in sulfides are much lower than chondrites (Rimskaya-Korsakova et. al., 2003). For the first time in Russia with sulfide and rock-forming minerals and WR in Sm-Nd method have been dated impregnated and brecciform ores of the following objects: Pilguyarvi Cu-Ni deposits, Pechenga (1965±87 Ma); impregnated (2433±83 Ma) and redeposited (1903±24 Ma) ores of Ahmavaara intrusion (Finland); ore gabbronorites of Penikat PGE-bearing layered intrusion (2426±38 Ma (Ekimova et.al., 2011); Pt-Pd gabbro-pegmatite ores (2476± 41 Ma, which agrees with the U-Pb zircon age - 2470±9 Ma (Bayanova, 2004) and gabbronorites (2483±86 Ma) of PGE Kievei deposit and Fedorova Tundra metagabbroids (2494±54 Ma); Monchetundra gabbronorites - 2489±49 Ma. In (Kong et. al., 2000) sulfides from two metamorphosed chondrites studied by instrumental neutron activation analysis (INAA) and ion probe. As shown, the level of REE in the sulfide phase determined by the ion probe is quite similar to that obtained by INAA. Although the concentrations of REE in the enstatite and the Fe, Si, Cr-rich inclusions are comparable to those in sulfide, estimates based on mass balance calculations show that the silicate inclusions would not noticeably contribute to the REE budget in sulfides (Kong et. al., 2000). These studies were supported by the RFBR 13-05-00493, OFI-M 13-05-12055, State Earth Division Program #4 and IGCP-599.

Enhanced Performance of Perovskite CH3NH3PbI3 Solar Cell by Using CH3NH3I as Additive in Sequential Deposition.

PubMed

Xie, Yian; Shao, Feng; Wang, Yaoming; Xu, Tao; Wang, Deliang; Huang, Fuqiang

2015-06-17

Sequential deposition is a widely adopted method to prepare CH3NH3PbI3 on mesostructured TiO2 electrode for organic lead halide perovskite solar cells. However, this method often suffers from the uncontrollable crystal size, surface morphology, and residual PbI2 in the resulting CH3NH3PbI3, which are all detrimental to the device performance. We herein present an optimized sequential solution deposition method by introducing different amount of CH3NH3I in PbI2 precursor solution in the first step to prepare CH3NH3PbI3 absorber on mesoporous TiO2 substrates. The addition of CH3NH3I in PbI2 precursor solution can affect the crystallization and composition of PbI2 raw films, resulting in the variation of UV-vis absorption and surface morphology. Proper addition of CH3NH3I not only enhances the absorption but also improves the efficiency of CH3NH3PbI3 solar cells from 11.13% to 13.37%. Photoluminescence spectra suggest that the improvement of device performance is attributed to the decrease of recombination rate of carriers in CH3NH3PbI3 absorber. This current method provides a highly repeatable route for enhancing the efficiency of CH3NH3PbI3 solar cell in the sequential solution deposition method.

Two-step extraction method for lead isotope fractionation to reveal anthropogenic lead pollution.

PubMed

Katahira, Kenshi; Moriwaki, Hiroshi; Kamura, Kazuo; Yamazaki, Hideo

2018-05-28

This study developed the 2-step extraction method which eluted the Pb adsorbing on the surface of sediments in the first solution by aqua regia and extracted the Pb absorbed inside particles into the second solution by mixed acid of nitric acid, hydrofluoric acid and hydrogen peroxide solution. We applied the method to sediments in the enclosed water area and found out that the isotope ratios of Pb in the second solution represented those of natural origin. This advantage of the method makes it possible to distinguish the Pb between natural origin and anthropogenic source on the basis of the isotope ratios. The results showed that the method was useful to discuss the Pb sources and that anthropogenic Pb in the sediment samples analysed was mainly derived from China because of transboundary air pollution.

GHR1 - A new Eocene natural reference material for U-Pb and Hf isotopic measurements in zircon

NASA Astrophysics Data System (ADS)

Ibanez-Mejia, M.; Eddy, M. P.

2017-12-01

We present chemical abrasion-isotope dilution-thermal ionization (CA-ID-TIMS) U-Pb zircon geochronology and solution multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) Hf isotopic data from a proposed natural zircon reference material for use during in situ analyses of U-Pb and Hf isotopic ratios. The sample, GHR1, was collected from the rapakivi intrusive phase of the Eocene Golden Horn batholith in Washington, USA. Zircons separated from this sample range up to 250-300 μm in length and have moderate aspect ratios. A weighted mean of 15 Th-corrected 206Pb/238U zircon dates from GHR1 produced at the Massachusetts Institute of Technology is 48.132 ± 0.023 Ma (2σ analytical and tracer uncertainties only, MSWD=1.70) confirming that there is little or no inter-crystal age heterogeneity at the scale of a few 10 kyr. Solution MC-ICP-MS measurements of chemically purified aliquots give a 176Hf/177Hf weighted mean of 0.283050 ± 17 (2σ, n=10), corresponding to a ɛHf0 of ca. +9.3. The 2σ variability of these measurements is comparable to our reproducibility of the JMC-475 Hf isotopic standard 0.282160 ± 14 (n= 13), suggesting that GHR1 zircons are homogenous with respect to 176Hf/177Hf. In situ 206Pb/238U dates from collaborating secondary ion mass spectrometry (SIMS), sensitive high-resolution ion microprobe (SHRIMP), and laser ablation ICP-MS (LA-ICP-MS) laboratories are in excellent agreement with the CA-ID-TIMS date and illustrate the reproducibility and potential value of this reference zircon. The mean values of 176Hf/177Hf measurements from two LA-ICP-MS laboratories are in agreement with the solution MC-ICP-MS value, but show slightly greater dispersion and higher (Lu+Yb)/Hf values. We attribute this discrepancy to apatite inclusions that are high in REE and may lead to greater isobaric interferences on 176Hf. These inclusions and potential isobaric interferences from REE were removed during the chemical abrasion step prior to bulk dissolution and ion-exchange purification in the solution data. Nevertheless, the apparent isotopic homogeneity and reproducibility of 206Pb/238U and 176Hf/177Hf ratios and the potentially unlimited reserves of GHR1 suggest that it is a promising reference material. We plan to distribute GHR1 at the meeting to interested laboratories.

A new method for stable lead isotope extraction from seawater.

PubMed

Zurbrick, Cheryl M; Gallon, Céline; Flegal, A Russell

2013-10-24

A new technique for stable lead (Pb) isotope extraction from seawater is established using Toyopearl AF-Chelate 650M(®) resin (Tosoh Bioscience LLC). This new method is advantageous because it is semi-automated and relatively fast; in addition it introduces a relatively low blank by minimizing the volume of chemicals used in the extraction. Subsequent analyses by HR ICP-MS have a good relative external precision (2σ) of 3.5‰ for (206)Pb/(207)Pb, while analyses by MC-ICP-MS have a better relative external precision of 0.6‰. However, Pb sample concentrations limit MC-ICP-MS analyses to (206)Pb, (207)Pb, and (208)Pb. The method was validated by processing the common Pb isotope reference material NIST SRM-981 and several GEOTRACES intercalibration samples, followed by analyses by HR ICP-MS, all of which showed good agreement with previously reported values. Copyright © 2013 Elsevier B.V. All rights reserved.

Exposure to Pb, Cd, and As mixtures potentiates the production of oxidative stress precursors: 30-day, 90-day, and 180-day drinking water studies in rats.

PubMed

Whittaker, Margaret H; Wang, Gensheng; Chen, Xue-Qing; Lipsky, Michael; Smith, Donald; Gwiazda, Roberto; Fowler, Bruce A

2011-07-15

Exposure to chemical mixtures is a common and important determinant of toxicity and is of particular concern due to their appearance in sources of drinking water. Despite this, few in vivo mixture studies have been conducted to date to understand the health impact of chemical mixtures compared to single chemicals. Interactive effects of lead (Pb), cadmium (Cd) and arsenic (As) were evaluated in 30-, 90-, and 180-day factorial design drinking water studies in rats designed to test the hypothesis that ingestion of such mixtures at individual component Lowest-Observed-Effect-Levels (LOELs) results in increased levels of the pro-oxidant delta aminolevulinic acid (ALA), iron, and copper. LOEL levels of Pb, Cd, and As mixtures resulted in the increased presence of mediators of oxidative stress such as ALA, copper, and iron. ALA increases were followed by statistically significant increases in kidney copper in the 90- and 180-day studies. Statistical evidence of interaction was identified for six biologically relevant variables: blood delta aminolevulinic acid dehydratase (ALAD), kidney ALAD, urinary ALA, urinary iron, kidney iron, and kidney copper. The current investigations underscore the importance of considering interactive effects that common toxic agents such as Pb, Cd, and As may have upon one another at low-dose levels. The interactions between known toxic trace elements at biologically relevant concentrations shown here demonstrate a clear need to rigorously review methods by which national/international agencies assess health risks of chemicals, since exposures may commonly occur as complex mixtures. Copyright © 2011. Published by Elsevier Inc.

Pb-Pb systematics of lunar rocks: differentiation, magmatic and impact history of the Moon

NASA Astrophysics Data System (ADS)

Nemchin, A.; Martin, W.; Norman, M. D.; Snape, J.; Bellucci, J. J.; Grange, M.

2016-12-01

Two independent decay chains in U-Pb system allow the determination of both ages and initial isotope compositions by analyzing only Pb in the samples. A typical Pb analysis represents a mixture of radiogenic Pb produced from the in situ U decay, initial Pb and laboratory contamination. Utilizing the ability of ion probes to analyse 10-30 micrometer-sized spots in the samples while avoiding fractures and other imperfections that commonly host contamination, permits extraction of pure lunar Pb compositions from the three component mixtures. This results in both accurate and precise ages of the rocks and their initial compositions. Lunar Mare and KREEP basalts postdating the major lunar bombardment are likely to represent such three component mixtures and are therefore appropriate for this approach, also giving an opportunity to investigate Pb evolution in their sources. A source evolution model constrained using available data indicates a major differentiation on the Moon at 4376±18 Ma and very radiogenic lunar mantle at this time. This age is likely to reflect the mean time of KREEP formation during the last stage of Magma Ocean differentiation. Rocks older than about 3.9 Ga are more complex than basalts and may include an extra Pb component, if modified by impacts. An example of this is presented by Pb-Pb data obtained for the anorthosite sample 62236, where the age of the rock is determined as 4367±29 Ma from analyses of CPx lamellae inside the large Opx grains: however large plagioclase crystals do not contain Pb in quantities sufficient for ion probe analysis, precluding determination of the initial Pb composition of the sample. Most of Pb is found in the brecciated parts of the anorthosite between the large grains. The composition of this Pb is similar to the initial Pb of 3909±17 Ma Apollo 16 breccia 66095, suggesting that is was injected into the anorthosite during a 3.9 Ga impact. Similar ca 3.9 Ga ages were determined for 1-2 millimeter size feldspathic clasts from several Apollo 14 breccias, where they are likely to date Pb homogenization during the Imbrium impact. Combined with U-Pb data obtained previously using U-bearing minerals such as zircon and phosphates, the new Pb-Pb data sets open an opportunity for a detailed chronological and isotopic investigation of lunar differentiation, magmatic evolution and impact history.

High-temperature metamorphism and its relation with magmatism (Svecofennian Belt, the Ladoga region, Russia)

NASA Astrophysics Data System (ADS)

Baltybaev, Shauket

2010-05-01

The Ladoga region, situated in the south-eastern part of the Fennoscandian shield, is subdivided into the Archean (ARD) and the Proterozoic (PRD) domains. The boundary between them is a wide shear-zone. The ARD consists mostly of AR-PR middle-low temperature gneisses and the PRD consists of turbidites, pelites, volcanics metamorphosed under HT-conditions (granulite facies). Metamorphism within the PRD is culminated at T= 800-900C and P=5-6 kbar. The peak of metamorphism of granulite facies is dated at 1881 Ma by Pb-Pb stepwise leaching method of rock-forming minerals of the granulites. Pb-Pb results are within error limits coeval with the U-Pb ages of metamorphic monazites. The same (1881Ma) age has gabbro-enderbites. Next stage of metamorphism lasts from 1881 to 1860 Ma under conditions of amphibolite facies. It was restricted with U-Pb, Pb-Pb, Sm-Nd data based on the closure temperature of zircon, monazite, garnet, sillimanite from gneisses, leucosomes of migmatites and synmetamorphic diorites and tonalites. The lowermost point of the trend shows P-T: ~3-4 kbar, 600C. By the time 1860 Ma K-rich granites were emplaced and the uppermost limit for granulite metamorphism comes from the ages of the aplitic/pegmatitic veins (1860-1850 Ma), which cut the K-rich granites. Thermal and tectonic settings can be described based on spatial and temporal changes during magma emplacement. The granulites of the PRD were produced by the emplacement of the extensive basic intrusion (gabbro-enderbites) into the lower-middle crust. A prolonged thermal flux over all area was supported by new generated dioritic and tonalitic melts, which were intruded into the middle crust. The final stage of tectono-metamorphic evolution was marked by emplacement of the K-rich granites. Numerical simulation of the process of magma emplacement (sequences: gabbro-enderbites, diorites and tonalites) and related heat production shows good correlation between intrusive activity and metamorphism of the surrounding rocks. Baltybaev Sh. K., Levchenkov O. A., Levsky L. K., Eklund O., Kilpeläinen T. 2006. Two metamorphic stages in the Svecofennian Domain: evidence from the isotopic geochronological study of the Ladoga and Sulkava metamorphic complexes. Petrology, 14(3), 247-261.

Environmental geochemistry and sediment quality in Lake Pontchartrain: database development and review

USGS Publications Warehouse

Manheim, Frank T.; Flowers, George C.; McIntire, Andrew G.; Marot, Marcie; Holmes, Charles

1997-01-01

This paper reports on preliminary results of a project to develop a comprehensive data base of chemical and environmental information on sediments from Lake Pontchartrain, Louisiana, and surrounding water bodies. The goal is to evaluate all data for reliability and comparability, and to make it widely accessible and useful to all users. Methods for processing heterogeneous, historical data follow previous methods employed in the Boston Harbor and Massachusetts Bay area. Data from 11 different data sets, encompassing about 900 total samples, have been entered to date. Questionable or anomalous data were noted in a minority of cases. Problems tend to follow distinct patterns and are relatively easy to identify. Hence, comparability of data has not proven to be the major obstacle to synthesis efforts that was anticipated in earlier years (NRC, 1989). Quality-controlled data sets show that the bulk of sediment samples in the more central parts of Lake Pontchartrain have values within normal background for heavy metals like Cu, Pb, and Zn. The same or lower concentrations were found in the vicinity of the Bonnet Carre Spillway, representing influx from the Mississippi River. Mean concentrations for Cu, Pb, and Zn were 17, 21, and 74 µg/g (total dissolution analyses), respectively. However, values as high as 267 µg/g Pb and comparable increases for other metal and organic contaminants are found in sediments within 2 km of the coastal strip of New Orleans. Additional sampling in such areas and in other inland coastal waterways is needed, since such levels are above the threshold for potential toxic effects on benthic organisms, according to effects-based screening criteria. The most contaminated sites, Bayou Trepagnier and Bayou Bonfouca, involve industrial areas where waste discharge has now been controlled or remediated, but where sediments may retain large concentrations of contaminants, e.g. tenths of a percent of Pb, Cr, and Zn or more for Bayou Trepagnier.

A combined Sm-Nd, Rb-Sr, and U-Pb isotopic study of Mg-suite norite 78238: Further evidence for early differentiation of the Moon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Edmunson, J; E.Borg, L; Nyquist, L E

2008-11-17

Lunar Mg-suite norite 78238 was dated using the Sm-Nd, Rb-Sr, and U-Pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of Mg-suite magmatism, as well as to provide a direct comparison between the three isotopic systems. The Sm-Nd isotopic system yields a crystallization age for 78238 of 4334 {+-} 37 Ma and an initial {var_epsilon}{sub Nd}{sup 143} value of -0.27 {+-} 0.74. The age-initial {var_epsilon}{sub Nd}{sup 143} (T-I) systematics of a variety of KREEP-rich samples, including 78238 and other Mg-suite rocks, KREEP basalts, and olivine cumulate NWA 773, suggest that lunar differentiationmore » was completed by 4492 {+-} 61 Ma assuming a Chondritic Uniform Reservoir bulk composition for the Moon. The Rb-Sr isotopic systematics of 78238 were disturbed by post-crystallization processes. Nevertheless, selected data points yield two Rb-Sr isochrons. One is concordant with the Sm-Nd crystallization age, 4366 {+-} 53 Ma. The other is 4003 {+-} 95 Ma and is concordant with an Ar-Ar age for 78236. The {sup 207}Pb-{sup 206}Pb age of 4333 {+-} 59 Ma is concordant with the Sm-Nd age. The U-Pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the Pb-Pb system, and may reflect fractionation of U and Pb during sample handling. Despite the disturbed nature of the U-Pb systems, a time-averaged {mu} ({sup 238}U/{sup 204}Pb) value of the source can be estimated at 27 {+-} 30 from the Pb-Pb isotopic systematics. Because KREEP-rich samples are likely to be derived from source regions with the highest U/Pb ratios, the relatively low {mu} value calculated for the 78238 source suggests the bulk Moon does not have an exceedingly high {mu} value.« less

A new insight to adsorption and accumulation of high lead concentration by exopolymer and whole cells of lead-resistant bacterium Acinetobacter junii L. Pb1 isolated from coal mine dump.

PubMed

Kushwaha, Anamika; Rani, Radha; Kumar, Sanjay; Thomas, Tarence; David, Arun Alfred; Ahmed, Meraz

2017-04-01

A lead-resistant bacterial strain was isolated from coal mine dump and identified as Acinetobacter junii Pb1 on basis of 16S rRNA (ribosomal ribonucleic acid) gene sequencing. The minimum inhibitory concentration of lead for the strain was 16,000 mg l -1 and it showed antibiotic and multi metal resistance. In aqueous culture, at an initial lead (Pb(II)) concentration of 100 and 500 mg l -1 , lead adsorption and accumulation by the isolate was 100 and 60%, at pH 7 at 30 °C after 48 and 120 h, respectively. The two fractions of exopolysaccharide (EPS), loosely associated EPS (laEPS) and bound EPS (bEPS), and whole cells (devoid of EPS) showed high binding affinity towards Pb(II). The binding affinity of laEPS towards Pb(II) (1071 mg Pb g -1 ) was three times higher than that of bEPS (321.5 mg Pb g -1 ) and 6.5 times higher than that of whole cells (165 mg Pb g -1 ). The binding affinity of EPS and whole cells with Pb(II), reported in the current study, is considerably higher as compared to that reported in the literature, till date. SEM analysis, showed an increase in thickness of cells on exposure to Pb(II) and TEM analysis, revealed its accumulation (interior of cell) and its adsorption (with the external cell surface). The isolate was also found to be positive for indole acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase production which helps in promoting plant growth. Thus, this study provides a new understanding towards Pb(II) uptake by A. junii Pb1, highlighting its potential on the restoration of Pb(II) contaminated repositories.

2010 Lead (Pb) Air Monitoring Requirements & 2013 Method for Determination of Lead (Pb) in Total Suspended Particulate Matter Fact Sheets

EPA Pesticide Factsheets

This page contains a variety of fact sheets and other documents that are supplementary to the 2010 final revisions to lead (Pb) ambient air monitoring requirements and the 2013 final method for determination of Pb in total suspended particulate matter.

Early atmospheric metal pollution provides evidence for Chalcolithic/Bronze Age mining and metallurgy in Southwestern Europe.

PubMed

Martínez Cortizas, Antonio; López-Merino, Lourdes; Bindler, Richard; Mighall, Tim; Kylander, Malin E

2016-03-01

Although archaeological research suggests that mining/metallurgy already started in the Chalcolithic (3rd millennium BC), the earliest atmospheric metal pollution in SW Europe has thus far been dated to ~3500-3200 cal.yr. BP in paleo-environmental archives. A low intensity, non-extensive mining/metallurgy and the lack of appropriately located archives may be responsible for this mismatch. We have analysed the older section (>2100 cal.yr. BP) of a peat record from La Molina (Asturias, Spain), a mire located in the proximity (35-100 km) of mines which were exploited in the Chalcolithic/Bronze Age, with the aim of assessing evidence of this early mining/metallurgy. Analyses included the determination of C as a proxy for organic matter content, lithogenic elements (Si, Al, Ti) as markers of mineral matter, and trace metals (Cr, Cu, Zn, Pb) and stable Pb isotopes as tracers of atmospheric metal pollution. From ~8000 to ~4980 cal.yr. BP the Pb composition is similar to that of the underlying sediments (Pb 15 ± 4 μg g(-1); (206)Pb/(207)Pb 1.204 ± 0.002). A sustained period of low (206)Pb/(207)Pb ratios occurred from ~4980 to ~2470 cal.yr. BP, which can be divided into four phases: Chalcolithic (~4980-3700 cal.yr. BP), (206)Pb/(207)Pb ratios decline to 1.175 and Pb/Al ratios increase; Early Bronze Age (~3700-3500 cal.yr. BP), (206)Pb/(207)Pb increase to 1.192 and metal/Al ratios remain stable; Late Bronze Age (~3500-2800 cal.yr. BP), (206)Pb/(207)Pb decline to their lowest values (1.167) while Pb/Al and Zn/Al increase; and Early Iron Age (~2800-2470 cal.yr. BP), (206)Pb/(207)Pb increase to 1.186, most metal/Al ratios decrease but Zn/Al shows a peak. At the beginning of the Late Iron Age, (206)Pb/(207)Pb ratios and metal enrichments show a rapid return to pre-anthropogenic values. These results provide evidence of regional/local atmospheric metal pollution triggered by the earliest phases of mining/metallurgy in the area, and reconcile paleo-environmental and archaeological records. Copyright © 2016. Published by Elsevier B.V.

Geochronology and geochemistry of lavas from the 1996 North Gorda Ridge eruption

NASA Astrophysics Data System (ADS)

Rubin, K. H.; Smith, M. C.; Perfit, M. R.; Christie, D. M.; Sacks, L. F.

1998-12-01

Radiometric dating of three North Gorda Ridge lavas by the 210Po- 210Pb method confirms that an eruption occurred during a period of increased seismic activity along the ridge during late February/early March 1996. These lavas were collected following detection of enhanced T-phase seismicity and subsequent ocean bottom photographs documented the existence of a large pillow mound of fresh-appearing lavas. 210Po- 210Pb dating of these lavas indicates that an eruption coinciding with this seismicity did occur (within analytical error) and that followup efforts to sample the recent lava flows were successful. Compositions of the three confirmed young lavas and eleven other samples of this contiguous "new flow" sequence are distinct from older lavas from this area but are variable at a level outside analytical uncertainty. These intraflow variations can not easily be related to a single, common parent magma. Compositional variability within the new flow is compared to that of other recently documented individual flow sequences, and this comparison reveals a strong positive correlation of compositional variance with flow volumes spanning a range of >2 orders of magnitude. The geochemical heterogeneity in the North Gorda new flow probably reflects incomplete mixing of magmas generated from a heterogeneous mantle source or from slightly different melting conditions of a single source. The compositional variability, range in sample ages (up to 6 weeks) and range in active seismicity (4 weeks) imply that this relatively large flow was erupted over an interval of several weeks.

A Millennial-Scale Record of Mercury and Lead Contamination in Peatlands of the Sacramento-San Joaquin Delta of California

NASA Astrophysics Data System (ADS)

Drexler, J. Z.; Alpers, C. N.; Neymark, L. A.; Paces, J. B.; Fuller, C.

2015-12-01

Peat cores from two micro-tidal marshes in the Sacramento-San Joaquin Delta of California (the landward end of the San Francisco Estuary) were used to track the onset of anthropogenic pollution on the west coast of the United States. Cores were sectioned into 2-cm depth intervals and analyzed for lead (Pb), mercury (Hg), and titanium (Ti) concentrations and Pb isotope compositions. Peat profiles were dated using radiocarbon, 210Pb, and 137Cs. Pre-anthropogenic concentrations of Pb and Hg in peat ranged from 0.60 to 13.0 μg g-1and from 6.9 to 71 ng g-1, respectively. For much of the past 6,000+ years, the Delta was free from anthropogenic pollution; however, beginning in ~1425 CE, Hg and Pb concentrations, Pb/Ti ratios, Pb enrichment factors (EFs), and HgEFs all increased. Pb isotope compositions of the peat suggest that this uptick was likely caused by mining and smelting activities originating in Asia. The next increases in Pb and Hg contamination occurred during the California Gold Rush (beginning ~1850 CE), when concentrations reached their highest levels (74 μg g-1 Pb, 990 ng g-1 Hg; PbEF = 12 and HgEF = 28). Pb concentrations increased again beginning in the ~1920s with the incorporation of Pb additives in gasoline. The phase-out of lead additives in the late 1980s was reflected in Pb isotope ratios and reductions in Pb concentrations in the surface layers of the peat. The rise and fall of Hg contamination was also tracked by the peat archive, with the highest Hg concentrations occurring just before 1963 CE and then decreasing during the post-1963 period. Overall the results show that the Delta was a pristine region for most of its ~6,700-year existence; however, since ~1425 CE, it has received Pb and Hg contamination from both global and regional sources. This study demonstrates that micro-tidal peatlands can be a highly useful archive for establishing the onset of anthropogenic contamination and chronicling the transition from a pristine to a polluted landscape.

Environmental impact of coal ash on tributary streams and nearshore waters of Lake Erie. Quarterly reports, August 31 and November 30, 1975, combined. [Cd, Zn, Cu, Fe, Mn, Cr, Ca, K, Mg, Na, Pb, As, Se

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

The study of coal wastes in Chautauga County, New York was begun on June 1, 1975. The major effort to date has been made on the fly ash dump west of Dunkirk, N.Y. The following topics are covered: description of the site; invertebrate biology; selection of trace elements for study and methods of analysis; water analyses; analyses of invertebrates; literature search; physical chemistry of coal ash and the leaching process; and study of lake sediments.

Identification of EayjjPB encoding a dicarboxylate transporter important for succinate production under aerobic and anaerobic conditions in Enterobacter aerogenes.

PubMed

Fukui, Keita; Nanatani, Kei; Hara, Yoshihiko; Tokura, Mitsunori; Abe, Keietsu

2018-05-01

Enterobacter aerogenes, a gram-negative, rod-shaped bacterium, is an effective producer of succinate from glucose via the reductive tricarboxylic acid cycle under anaerobic conditions. However, to date, succinate-exporter genes have not been identified in E. aerogenes, although succinate exporters have a large impact on fermentative succinate production. Recently, we genetically identified yjjP and yjjB, as genes encoding a succinate transporter in Escherichia coli. Evaluation of the yjjPB homologs in E. aerogenes (EayjjPB genes) showed that succinate accumulation increased from 4.1 g L -1 to 9.1 g L -1 when the EayjjPB genes were expressed under aerobic conditions. Under anaerobic conditions, succinate yield increased from 53% to 60% by EayjjPB expression and decreased to 48% by deletion of EayjjPB. Furthermore, the production levels of fumarate and malate, which are intermediates of the succinate-biosynthesis pathway, were also increased by EayjjPB expression. A complementation assay conducted in Corynebacterium glutamicum strain AJ110655ΔsucE1 demonstrated that both EaYjjP and EaYjjB are required for the restoration of succinate production. Taken together, these results suggest that EaYjjPB function as a dicarboxylate transporter in E. aerogenes and that the products of both genes are required for dicarboxylate transport. Copyright © 2017 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Dating of coastal marine sediments: 210Pb versus 137Cs signal on the Danube-influenced Black Sea shelf

NASA Astrophysics Data System (ADS)

Friedrich, Jana; Laptev, Gennady

2010-05-01

Coastal marine sediments represent a natural archive of pelagic processes, coastal erosion and river discharge of suspended matter. Correct dating of those sediments is a prerequisite for chronological reconstruction of the flux of pollutants and organic matter from the water column to the sediments and hence, the reconstruction of the pollution and eutrophication events. In the reconstruction of the sedimentation history during the pre-industrial and industrial periods, which usually spans the past 100 years, the natural occurring radionuclide 210Pb and the artificial radionuclides 137Cs and 241Am are widely applied tracers. 137Cs is used as an independent time marker for end the atmospheric bomb test fallout in 1963 and the Chernobyl accident in 1986. As the 137Cs signal is often weakened due to its mobility in sediments, 241Am, less mobile than 137Cs and derived from decay the bomb fallout of 241Pu, is used as a second time marker of the 1963 event. The northwestern shelf of the Black Sea has been seriously affected by eutrophication and pollution from the late 1960's to the mid-1990's, largely triggered by Danube River input of nutrients and pollutants. The aim of our study is ultimately to reconstruct the eutrophication history and recycling of nutrients following the deposition of organic matter. The ‘memory effect' of sediment recycling plays a critical role in maintaining eutrophic conditions in enclosed seas such as the Black Sea. Here we present results from sediment cores taken within the Danube River plume on the shallow northwestern shelf of the Black Sea. The cores have been dated in two laboratories to rule out artifacts. The sediment record is repeatedly interrupted by so-called turbidites that consist of stiff clay. The clay horizons display a drop in unsupported 210Pb and 137Cs and a higher signal of supported 210Pb than the non-clay horizons. Below the turbidite, the unsupported 210Pb and 137Cs increase again to values above the turbidite. This points to a non-marine origin of the turbidite. In such sediment sequence, the classical application of the CRS model would provide false ages and sedimentation rates. We hypothesize that the turbidite represents terrestrial clay eroded from the Danube Delta that had been transported in pulse-like events during flash floods of the Danube River.

The disruption of H and L ordinary chondrite parent bodies at 60 Ma

NASA Astrophysics Data System (ADS)

Blackburn, T.; Alexander, C.; Carlson, R.; Elkins-Tanton, L. T.

2016-12-01

A working timeline for the history of ordinary chondrites (OCs) includes chondrule formation as early as 1-2 Ma after our Solar System's earliest forming solids (CAIs), followed by rapid accretion into undifferentiated planetesimals that were heated internally by 26Al decay and cooled over a period of tens of millions of years. There remains conflict, however, between metallographic cooling rates and radioisotopic thermochronometric data over the sizes and lifetimes of the chondrite parent bodies, as well as the timing of impact related disruption. The importance of establishing the timing of parent body disruption is heightened by the use of meteorites as recorders of asteroid belt wide disruption events as suggested by various dynamical models. Here we attempt to resolve these records with new Pb-phosphate dates for 9 previously unstudied OCs. These new results, along with previously published Pb-phosphate and metallographic data, are interpreted with a series of numerical models designed to simulate the thermal evolution for a chondrite parent body that is disrupted by impact prior to forming smaller unsorted "rubble piles". One model that could satisfy both the available thermochronologic and Ni-metal data takes into account subtle differences in closure temperatures for each system. It requires that disruption occur early enough such that the Ni-metal system can record the cooling rate associated with a rubble pile (<70 Ma), yet late enough that the Pb-phosphate system can record an onion shell structure (>30 Ma). For this 30-70 Ma timeline, reaccretion into smaller rubble piles will ensure that the originally deeply buried and hot Type 6 samples will always cool faster as a result of disruption, yielding nearly uniform ages that date parent body disruption. This is consistent with the available Pb-phosphate data, where all but one Type 6 chondrite (H, n=3; L, n=4) records a uniform cooling age (4508 ± 5 Ma). Our model results suggest that a disruption at this time is: 1) late enough so that shallow chondrite layers will have cooled and H5/L5s will always have older Pb-phosphate dates than deeper H6/L6s; 2) early enough to precede Ni-metal closure, replicating the lack of correlation between Ni-metal cooling rates and petrologic Type suggestive of cooling through Ni-metal closure in a reaccreted rubble pile.

Controlling factors of spatial and temporal preservation of the geochronological signal in sediments during an orogenic cycle

NASA Astrophysics Data System (ADS)

Rat, Juliette; Mouthereau, Frédéric; Bernet, Matthias; Brichau, Stéphanie; Balvay, Mélanie; Garzanti, Eduardo; Ando, Sergio

2017-04-01

Detrital content of sediments preserved in basins provide constraints on the nature of source rocks, dynamics of sediment transport, and potentially on tectonics and climate changes. U-Pb dating method on detrital zircon is ideally suited for provenance studies due to the ability of U-Pb age data to resist several orogenic cycles. However, with the aim to track sediment source evolution over a single orogenic cycle and determine characteristic time and parameters controlling the geochronological signal preservation throughout the cycle from rifting, mountain building to post-collision evolution, low-temperature thermochronology combined with sediment petrography are more appropriate than the U-Pb dating approach taken alone. To better understanding processes at play in the long-term geochronological signal preservation we focus on the sediment record associated with the Iberia plate tectonic evolution, which is part of the OROGEN research project, co-financed by BRGM, TOTAL & CNRS. The Iberian plate recorded a period of extension in the Late Jurassic, followed during the Early Cretaceous (Aptian-Albian) by a major thinning event documented by thick syn-rift sediments in intraplate basins and plate-scale heating/cooling of the Iberia crust, as argued by published fission track ages. Paleogeographic reconstructions that are based on stratigraphic and lithofacies analyses in northern Iberia (Iberian Range, Pyrenees and Basque-Cantabrians Range), describe a large domain of continental/fluvial and shallow-marine siliciclastic deposition. The related detrital content was then recycled during the subsequent Pyrenean orogenic phase in the Ebro foreland basin, and eventually transfer to the Mediterranean realm during post-orogenic re-excavation of the Ebro basin. In this study, we complete the published time-temperature paths in the mesozoic syn-rift basins by providing new thermo-chronological analyses of well-dated syn-collision and post-collision stratigraphic sections of the Ebro basin to determine thermal control on preservation through burial and geothermal evolution. We combined this study with sediments petrography analyses to identify relative control of source petrography, hydraulic sorting, alteration and diagenesis processes on the signal preservation during sediment transfer. All these observations will ultimately be incorporated in a geodynamic reconstruction of Iberia, and compared with age predictions from a model coupling surface processes and thermal evolution.

Carnivoran Remains from the Malapa Hominin Site, South Africa

PubMed Central

Kuhn, Brian F.; Werdelin, Lars; Hartstone-Rose, Adam; Lacruz, Rodrigo S.; Berger, Lee R.

2011-01-01

Recent discoveries at the new hominin-bearing deposits of Malapa, South Africa, have yielded a rich faunal assemblage associated with the newly described hominin taxon Australopithecus sediba. Dating of this deposit using U-Pb and palaeomagnetic methods has provided an age of 1.977 Ma, being one of the most accurately dated, time constrained deposits in the Plio-Pleistocene of southern Africa. To date, 81 carnivoran specimens have been identified at this site including members of the families Canidae, Viverridae, Herpestidae, Hyaenidae and Felidae. Of note is the presence of the extinct taxon Dinofelis cf. D. barlowi that may represent the last appearance date for this species. Extant large carnivores are represented by specimens of leopard (Panthera pardus) and brown hyaena (Parahyaena brunnea). Smaller carnivores are also represented, and include the genera Atilax and Genetta, as well as Vulpes cf. V. chama. Malapa may also represent the first appearance date for Felis nigripes (Black-footed cat). The geochronological age of Malapa and the associated hominin taxa and carnivoran remains provide a window of research into mammalian evolution during a relatively unknown period in South Africa and elsewhere. In particular, the fauna represented at Malapa has the potential to elucidate aspects of the evolution of Dinofelis and may help resolve competing hypotheses about faunal exchange between East and Southern Africa during the late Pliocene or early Pleistocene. PMID:22073222

Carnivoran remains from the Malapa hominin site, South Africa.

PubMed

Kuhn, Brian F; Werdelin, Lars; Hartstone-Rose, Adam; Lacruz, Rodrigo S; Berger, Lee R

2011-01-01

Recent discoveries at the new hominin-bearing deposits of Malapa, South Africa, have yielded a rich faunal assemblage associated with the newly described hominin taxon Australopithecus sediba. Dating of this deposit using U-Pb and palaeomagnetic methods has provided an age of 1.977 Ma, being one of the most accurately dated, time constrained deposits in the Plio-Pleistocene of southern Africa. To date, 81 carnivoran specimens have been identified at this site including members of the families Canidae, Viverridae, Herpestidae, Hyaenidae and Felidae. Of note is the presence of the extinct taxon Dinofelis cf. D. barlowi that may represent the last appearance date for this species. Extant large carnivores are represented by specimens of leopard (Panthera pardus) and brown hyaena (Parahyaena brunnea). Smaller carnivores are also represented, and include the genera Atilax and Genetta, as well as Vulpes cf. V. chama. Malapa may also represent the first appearance date for Felis nigripes (Black-footed cat). The geochronological age of Malapa and the associated hominin taxa and carnivoran remains provide a window of research into mammalian evolution during a relatively unknown period in South Africa and elsewhere. In particular, the fauna represented at Malapa has the potential to elucidate aspects of the evolution of Dinofelis and may help resolve competing hypotheses about faunal exchange between East and Southern Africa during the late Pliocene or early Pleistocene.

Age mapping and dating of monazite on the electron microprobe: Deconvoluting multistage tectonic histories

NASA Astrophysics Data System (ADS)

Williams, Michael L.; Jercinovic, Michael J.; Terry, Michael P.

1999-11-01

High-resolution X-ray mapping and dating of monazite on the electron microprobe are powerful geochronological tools for structural, metamorphic, and tectonic analysis. X-ray maps commonly show complex Th, U, and Pb zoning that reflects monazite growth and overgrowth events. Age maps constructed from the X-ray maps simplify the zoning and highlight age domains. Microprobe dating offers a rapid, in situ method for estimating ages of mapped domains. Application of these techniques has placed new constraints on the tectonic history of three areas. In western Canada, age mapping has revealed multiphase monazite, with older cores and younger rims, included in syntectonic garnet. Microprobe ages show that tectonism occurred ca. 1.9 Ga, 700 m.y. later than mylonitization in the adjacent Snowbird tectonic zone. In New Mexico, age mapping and dating show that the dominant fabric and triple-point metamorphism occurred during a 1.4 Ga reactivation, not during the 1.7 Ga Yavapai-Mazatzal orogeny. In Norway, monazite inclusions in garnet constrain high-pressure metamorphism to ca. 405 Ma, and older cores indicate a previously unrecognized component of ca. 1.0 Ga monazite. In all three areas, microprobe dating and age mapping have provided a critical textural context for geochronologic data and a better understanding of the complex age spectra of these multistage orogenic belts.

Perceived Family Cohesion Moderates Environmental Influences on Prosocial Behavior in Nigerian Adolescent Twins.

PubMed

Hur, Yoon-Mi; Taylor, Jeanette; Jeong, Hoe-Uk; Park, Min-Seo; Haberstick, Brett C

2017-06-01

Research shows that perceived family cohesion is positively related to prosocial behavior in adolescents. In this study, we investigated heritability of prosocial behavior (PB) and perceived family cohesion (FC) among Nigerian twins attending public schools in Lagos State, Nigeria (mean age = 14.7 years, SD = 1.7 years), and explored the issue of whether children's perception of cohesive family environment moderated genetic and environmental influences on (PB). The PB scale of the Strengths and Difficulties Questionnaire and the FC scale of the Family Adaptability and Cohesion Evaluation Scale III were completed by 2,376 twins (241 monozygotic (MZ) male, 354 MZ female, 440 dizygotic (DZ) male, 553 DZ female, and 788 opposite-sex DZ twins). A general sex-limitation and the bivariate genotype by environment interaction (G×E) models were applied to the data. The general sex-limitation model showed no significant sex differences, indicating that additive genetic and non-shared environmental influences were, 38% (95% CI = 31, 46) and 62% (95% CI = 54, 69) for PB and 33% (95% CI = 24, 40) and 67% (95% CI = 60, 76) for FC in both sexes. These estimates were similar to those found in Western and Asian twin studies to date. The correlation between PB and FC was 0.36. The best-fitting bivariate G×E model indicated that FC significantly moderated non-shared environmental influence unique to PB (E×E interaction). Specifically, non-shared environmental contributions to PB were highest when FC was lowest, and decreased as the levels of FC increased. However, genetic variances in PB were stable across all levels of FC. These findings suggest that FC reduces individual differences in PB by changing non-shared environmental experiences rather than genetic factors in PB.

U-Th-Pb zircon ages of some Keweenawan Supergroup rocks from the south shore of Lake Superior

USGS Publications Warehouse

Zartman, R.E.; Nicholson, S.W.; Cannon, W.F.; Morey, G.B.

1997-01-01

New single-crystal zircon U-Th-Pb ages for plutonic and rhyolitic Keweenawan Supergroup rocks from the south shore of Lake Superior provide geochronological constraints on magmatic evolution associated with the 1.1 Ga Midcontinent rift. Analyses of a granophyric phase of the Mineral Lake intrusion and the Meilen granite, both parts of the Meilen Intrusive Complex, and a laterally extensive rhyolite from the top of the Kallander Creek Volcanics have weighted average 207Pb/206Pb ages of 1102.0 ?? 2.8 Ma (N = 2), 1100.9 ?? 1.4 Ma (N = 5), and 1098.8 ?? 1.9 Ma (N = 4), respectively. Analyses of a pyroclastic rhyolite flow at the top of the Porcupine Volcanics result in variable 207Pb/206Pb ages that range from 1080 to 1137 Ma. This rhyolite exhibits a continuum between morphologically complex and simpler prismatic zircon crystals, the latter yielding concordant analyses having a weighted average 207Pb/206Pb age of 1093.6 ?? 1.8 Ma (N = 2). Four prismatic zircons from an aphyric rhyolite of the Chengwatana Volcanics in the Ashland syncline form a linear array intersecting concordia at 1094.6 ?? 2.1 Ma (MSWD = 1.3). Another presumed Chengwatana rhyolite recovered from drill core intersecting the Hudson-Afton horst in southeast Minnesota yielded only ???20 morphologically indistinguishable zircons. Six analyses give 207Pb/206Pb ages ranging from 1112 to 1136 Ma, including one analysis with a virtually concordant age of 1130 Ma. This age, however, is considerably older than that obtained for the Chengwatana Volcanics in the Ashland syncline or any other precisely dated rock from the Midcontinent rift.

ESR dating of submarine hydrothermal activities using barite in sulfide deposition

NASA Astrophysics Data System (ADS)

Toyoda, S.; Fujiwara, T.; Ishibashi, J.; Isono, Y.; Uchida, A.; Takamasa, A.; Nakai, S.

2012-12-01

The temporal change of submarine hydrothermal activities has been an important issue in the aspect of the evolution of hydrothermal systems which is related with ore formation (Urabe, 1995) and biological systems sustained by the chemical species arising from hydrothermal activities (Macdonald et al., 1980). Determining the ages of the hydrothermal deposit will provide essential information on such studies. Dating methods using disequilibrium between radioisotopes such as U-Th method (e.g. You and Bickle, 1998), 226}Ra-{210Pb and 228}Ra-{228Th method (e.g. Noguchi et al., 2011) have been applied to date submarine hydrothermal deposits. ESR (electron spin resonance) dating method is commonly applied to fossil teeth, shells, and quartz of Quaternay period where the natural accumulated dose is obtained from the intensities of the ESR signals which are created by natural radiation. The natural dose is divided by the dose rate to the mineral/sample to deduce the age. Okumura et al., (2010) made the first practical application of ESR (electron spin resonance) dating technique to a sample of submarine hydrothermal barite (BaSO4) to obtain preliminary ages, where Kasuya et al. (1991) first pointed out that barite can be used for ESR dating. Knowing that ESR dating of barite is promising, in this paper, we will present how we have investigated each factor that contributes ESR dating of barite in submarine hydrothermal sulfide deposition. (1) The best ESR condition for measuring the SO3- signal in barite is with the microwave power of 1mW and modulation amplitude of 0.1mT. (2) As results of heating experiments, the signal was found to be stable for the dating age range of several thousands. (3) 226Ra replacing Ba in barite is the source of the radiation. The amount of radioactive elements in sulfide mineral surrounding barite is negligible. (4) The external radiation from the sea water is negligible even in the submarine hydrothermal area where the radiation level is much higher than usual sea water. (5) The decay of 226Ra has to be considered. (6) Major terms of dose rate are the internal alpha dose rate and the external beta and gamma dose rates. (7) The alpha effectiveness, the ratio of forming the radical by internal alpha particles to by beta and gamma rays, was obtained to be 0.043±0.018. (8) The shape of the chimney sample should be considered for gamma ray dose. Examples of dating results for submarine hydrothermal deposits from South Mariana and Okinawa Trough will be presented.

Detection of Operator Performance Breakdown as an Automation Triggering Mechanism

NASA Technical Reports Server (NTRS)

Yoo, Hyo-Sang; Lee, Paul U.; Landry, Steven J.

2015-01-01

Performance breakdown (PB) has been anecdotally described as a state where the human operator "loses control of context" and "cannot maintain required task performance." Preventing such a decline in performance is critical to assure the safety and reliability of human-integrated systems, and therefore PB could be useful as a point at which automation can be applied to support human performance. However, PB has never been scientifically defined or empirically demonstrated. Moreover, there is no validated objective way of detecting such a state or the transition to that state. The purpose of this work is: 1) to empirically demonstrate a PB state, and 2) to develop an objective way of detecting such a state. This paper defines PB and proposes an objective method for its detection. A human-in-the-loop study was conducted: 1) to demonstrate PB by increasing workload until the subject reported being in a state of PB, and 2) to identify possible parameters of a detection method for objectively identifying the subjectively-reported PB point, and 3) to determine if the parameters are idiosyncratic to an individual/context or are more generally applicable. In the experiment, fifteen participants were asked to manage three concurrent tasks (one primary and two secondary) for 18 minutes. The difficulty of the primary task was manipulated over time to induce PB while the difficulty of the secondary tasks remained static. The participants' task performance data was collected. Three hypotheses were constructed: 1) increasing workload will induce subjectively-identified PB, 2) there exists criteria that identifies the threshold parameters that best matches the subjectively-identified PB point, and 3) the criteria for choosing the threshold parameters is consistent across individuals. The results show that increasing workload can induce subjectively-identified PB, although it might not be generalizable-only 12 out of 15 participants declared PB. The PB detection method based on signal detection analysis was applied to the performance data and the results showed that PB can be identified using the method, particularly when the values of the parameters for the detection method were calibrated individually.

Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules

PubMed Central

Bollard, Jean; Connelly, James N.; Whitehouse, Martin J.; Pringle, Emily A.; Bonal, Lydie; Jørgensen, Jes K.; Nordlund, Åke; Moynier, Frédéric; Bizzarro, Martin

2017-01-01

The most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. Using Pb-Pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after the formation of the Sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. This finding is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. An abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion. PMID:28808680

Developing Zircon as a Probe of Planetary Impact History

NASA Astrophysics Data System (ADS)

Wielicki, Matthew

2014-12-01

The identification of Meteor Crater in Arizona as an extraterrestrial impact by Eugene Shoemaker provided the first evidence of this geologic phenomenon and opened the door to a new field of research that has eventually lead to the identification of over ~150 terrestrial impact structures. Subsequently impacts have been evoked in the formation of the moon, delivery of volatiles and bio-precursors to early Earth, creation of habitats for the earliest life and, in more recent times, major mass extinction events. However, understanding the impact flux to the Earth-Moon system has been complicated by the constant weathering and erosion at Earth's surface and the complex nature of impactite samples such that only a hand full of terrestrial craters have been accurately and precisely dated. Currently 40Ar/39Ar step-heating analysis of impactite samples is commonly used to infer impact ages but can be problematic due to the presence of relic clasts, incomplete 40Ar outgassing or excess 40Ar, and recoil and shock effects. The work presented here attempts to develop zircon geochronology to probe planetary impact histories as an alternative to current methods and provides another tool by which to constrain the bolide flux to the Earth-Moon system. Zircon has become the premier geo-chronometer in earth science and geochemical investigation of Hadean zircon from Western Australia has challenged the long-standing, popular conception that the near-surface Hadean Earth was an uninhabitable and hellish world; Zircons may preserve environmental information regarding their formation and thus provide a rare window into conditions on early Earth. Isotopic and petrologic analyses of these ancient grains have been interpreted to suggest that early Earth was more habitable than previously envisioned, with water oceans, continental crust, and possibly even plate tectonics. The Hadean is also suspected to be a time of major planetary bombardment however identifying impact signatures within the Hadean population remains difficult and this study hopes to develop criteria to recognize impact zircon and possibly provide constraints on the early impactor flux. Five large terrestrial craters, Vredefort and Morokweng, South Africa, Sudbury and Manicouagan, Canada, and Popigai, Russia, are the focus of this study as smaller craters do not have the energy to produce thick melt sheets, which persist over time-scales sufficient for crystallization of zircon, permitting geochemical and geochronological analysis. Geochemical analysis of these impact-produced zircons yields similar chemical signatures to endogenic igneous zircon from crustal melts and highlights the need for well-developed criteria for discriminating impact and endogenic grains for impact geochronology. One such criterion is modeling of impact zircon crystallization temperature spectra for simulated impact events on targets of varying composition. Provided some assumptions the zircon crystallization spectra can be estimated from well established Zr systematics in crustal melts. Results for impacts into an Archean terrestrial surface (used as a proxy for the Hadean as little to no rock record exists >4.0 Ga) yields a crystallization spectra significantly higher than that reported for the Hadean zircon population and appears to rule out impacts as a dominant source for these ancient grains. When no dateable impact melt sheet exists, either due to the lack of energy of the impact itself or from subsequent erosion at Earth's surface, loss of radiogenic lead, Pb*, has been suggested as an alternative method to date the event. Pb*-loss was investigated from target rocks from Vredefort and Morokweng and suggests that Pb* diffusion, even in zircon isolated from shocked and brecciated target rocks, is remarkably slow. This may explain the seeming lack of 'reset' zircon in terrestrial impactites. Little is known about Pb* diffusion pathways associated with shock microstructures introduced during impact cratering and future diffusion studies may provide better constraints on this problem. Although little disturbance was identified in Pb* of target zircon, other low temperature geochronometers, zircon (U-Th)/He dating in this case, have been shown to be completely 'reset' and accurately date impacts. Zircon (U-Th)/He ages isolated from the target rock below ~850 m of well-dated impact melt at Morokweng yield ages consistent with the impact melt sheet and provide an alternative tool to dating events where such melts no longer exists. This geochronometer was also applied to impactites from Popigai, Russia and results in an age that is significantly younger than that reported in the literature and coincident with the Eocene-Oligocene boundary mass extinction event however the lack of any impact signatures at this boundary is puzzling. Constraining the impact flux to the Earth-Moon system not only allows for a better understanding into early Earth evolution and the formation of a habitable planet but also provides constraints on the modern impactor flux, important criteria for estimating the likelihood of future impact events. Zircon geochronology offers an exciting new tool by which to date impact events and has the potential to assist understanding of complex impactite samples from terrestrial craters and future sample return missions.

ESR dating of barite in sulphide deposits formed by the sea-floor hydrothermal activities.

PubMed

Toyoda, Shin; Fujiwara, Taisei; Uchida, Ai; Ishibashi, Jun-ichiro; Nakai, Shun'ichi; Takamasa, Asako

2014-06-01

Barite is a mineral newly found to be practically useful for electron spin resonance (ESR) dating of sulphide deposits formed by the sea-floor hydrothermal activities. The recent studies for the properties of the ESR dating signal in barite are summarised in the present paper as well as the formulas for corrections for accurate dose-rate estimation are developed including the dose-rate conversion factors, shape correction for gamma-ray dose and decay of (226)Ra. Although development of the techniques for ESR dating of barite has been completed, further comparative studies with other dating techniques such as U-Th and (226)Ra-(210)Pb dating are necessary for the technique to be widely used. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Gunbarrel mafic magmatic event: A key 780 Ma time marker for Rodinia plate reconstructions

USGS Publications Warehouse

Harlan, S.S.; Heaman, L.; LeCheminant, A.N.; Premo, W.R.

2003-01-01

Precise U-Pb baddeleyite dating of mafic igneous rocks provides evidence for a widespread and synchronous magmatic event that extended for >2400 km along the western margin of the Neoproterozoic Laurentian craton. U-Pb baddeleyite analyses for eight intrusions from seven localities ranging from the northern Canadian Shield to northwestern Wyoming-southwestern Montana are statistically indistinguishable and yield a composite U-Pb concordia age for this event of 780.3 ?? 1.4 Ma (95% confidence level). This 780 Ma event is herein termed the Gunbarrel magmatic event. The mafic magmatism of the Gunbarrel event represents the largest mafic dike swarm yet identified along the Neoproterozoic margin of Laurentia. The origin of the mafic magmatism is not clear, but may be related to mantle-plume activity or upwelling asthenosphere leading to crustal extension accompanying initial breakup of the supercontinent Rodinia and development of the proto-Pacific Ocean. The mafic magmatism of the Gunbarrel magmatic event at 780 Ma predates the voluminous magmatism of the 723 Ma Franklin igneous event of the northwestern Canadian Shield by ???60 m.y. The precise dating of the extensive Neoproterozoic Gunbarrel and Franklin magmatic events provides unique time markers that can ultimately be used for robust testing of Neoproterozoic continental reconstructions.

Preparing ultrafine PbS powders from the scrap lead-acid battery by sulfurization and inert gas condensation

NASA Astrophysics Data System (ADS)

Xia, Huipeng; Zhan, Lu; Xie, Bing

2017-02-01

A novel method for preparing ultrafine PbS powders involving sulfurization combined with inert gas condensation is developed in this paper, which is applicable to recycle Pb from lead paste of spent lead-acid batteries. Initially, the effects of the evaporation and condensation temperature, the inert gas pressure, the condensation distance and substrate on the morphology of as-obtained PbS ultrafine particles are intensively investigated using sulfur powders and lead particles as reagents. Highly dispersed and homogeneous PbS nanoparticles can be prepared under the optimized conditions which are 1223 K heating temperature, 573 K condensation temperature, 100 Pa inert gas pressure and 60 cm condensation distance. Furthermore, this method is successfully applied to recycle Pb from the lead paste of spent lead acid battery to prepare PbS ultrafine powders. This work does not only provide the theoretical fundamental for PbS preparation, but also provides a novel and efficient method for recycling spent lead-acid battery with high added-value products.

Zircon age-temperature-compositional spectra in plutonic rocks

DOE PAGES

Samperton, Kyle M.; Bell, Elizabeth A.; Barboni, Mélanie; ...

2017-08-23

We present that geochronology can resolve dispersed zircon dates in plutonic rocks when magma cooling time scales exceed the temporal precision of individual U-Pb analyses; such age heterogeneity may indicate protracted crystallization between the temperatures of zircon saturation (T sat) and rock solidification (T solid). Diffusive growth models predict asymmetric distributions of zircon dates and crystallization temperatures in a cooling magma, with volumetrically abundant old, hot crystallization at T sat decreasing continuously to volumetrically minor young, cold crystallization at T solid. We present integrated geochronological and geochemical data from Bergell Intrusion tonalites (Central Alps, Europe) that document zircon compositional changemore » over hundreds of thousands of years at the hand-sample scale, indicating melt compositional evolution during solidification. Ti-in-zircon thermometry, crystallization simulation using MELTS software, and U-Pb dates produce zircon mass-temperature-time distributions that are in excellent agreement with zircon growth models. In conclusion, these findings provide the first quantitative validation of longstanding expectations from zircon saturation theory by direct geochronological investigation, underscoring zircon’s capacity to quantify supersolidus cooling rates in magmas and resolve dynamic differentiation histories in the plutonic rock record.« less

Zircon age-temperature-compositional spectra in plutonic rocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samperton, Kyle M.; Bell, Elizabeth A.; Barboni, Mélanie

We present that geochronology can resolve dispersed zircon dates in plutonic rocks when magma cooling time scales exceed the temporal precision of individual U-Pb analyses; such age heterogeneity may indicate protracted crystallization between the temperatures of zircon saturation (T sat) and rock solidification (T solid). Diffusive growth models predict asymmetric distributions of zircon dates and crystallization temperatures in a cooling magma, with volumetrically abundant old, hot crystallization at T sat decreasing continuously to volumetrically minor young, cold crystallization at T solid. We present integrated geochronological and geochemical data from Bergell Intrusion tonalites (Central Alps, Europe) that document zircon compositional changemore » over hundreds of thousands of years at the hand-sample scale, indicating melt compositional evolution during solidification. Ti-in-zircon thermometry, crystallization simulation using MELTS software, and U-Pb dates produce zircon mass-temperature-time distributions that are in excellent agreement with zircon growth models. In conclusion, these findings provide the first quantitative validation of longstanding expectations from zircon saturation theory by direct geochronological investigation, underscoring zircon’s capacity to quantify supersolidus cooling rates in magmas and resolve dynamic differentiation histories in the plutonic rock record.« less

Contamination of arctic Fjord sediments by Pb-Zn mining at Maarmorilik in central West Greenland.

PubMed

Perner, K; Leipe, Th; Dellwig, O; Kuijpers, A; Mikkelsen, N; Andersen, T J; Harff, J

2010-07-01

This study focuses on heavy metal contamination of arctic sediments from a small Fjord system adjacent to the Pb-Zn "Black Angel" mine (West Greenland) to investigate the temporal and spatial development of contamination and to provide baseline levels before the mines re-opening in January 2009. For this purpose we collected multi-cores along a transect from Affarlikassaa Fjord, which received high amounts of tailings from 1973 to 1990, to the mouth of Qaumarujuk Fjord. Along with radiochemical dating by (210)Pb and (137)Cs, geochemical analyses of heavy metals (e.g. As, Cd, Hg, Pb, and Zn) were carried out. Maximum contents were found at 12 cm depth in Affarlikassaa. After 17 years the mine last closed, specific local hydrographic conditions continue to disperse heavy metal enriched material derived from the Affarlikassaa into Qaumarujuk. Total Hg profiles from multi-cores along the transect clearly illustrate this transport and spatial distribution pattern of the contaminated material. Copyright 2010 Elsevier Ltd. All rights reserved.

Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe2.

PubMed

Guan, Syu-You; Chen, Peng-Jen; Chu, Ming-Wen; Sankar, Raman; Chou, Fangcheng; Jeng, Horng-Tay; Chang, Chia-Seng; Chuang, Tien-Ming

2016-11-01

The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level ( E F ) combined with fully gapped bulk superconductivity. We report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe 2 . Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point at E ≅ 1.0 eV, of which the inner TSS and the partial outer TSS cross E F , on the Pb-terminated surface of this fully gapped superconductor. This discovery reveals PbTaSe 2 as a promising candidate for TSC.

Search for diphoton events with large missing transverse energy with 36 pb-1 of 7 TeV proton-proton collision data with the ATLAS detector

NASA Astrophysics Data System (ADS)

Aad, G.; Abbott, B.; Abdallah, J.; Abdelalim, A. A.; Abdesselam, A.; Abdinov, O.; Abi, B.; Abolins, M.; Abramowicz, H.; Abreu, H.; Acerbi, E.; Acharya, B. S.; Adams, D. L.; Addy, T. N.; Adelman, J.; Aderholz, M.; Adomeit, S.; Adragna, P.; Adye, T.; Aefsky, S.; Aguilar-Saavedra, J. A.; Aharrouche, M.; Ahlen, S. P.; Ahles, F.; Ahmad, A.; Ahsan, M.; Aielli, G.; Akdogan, T.; Åkesson, T. P. A.; Akimoto, G.; Akimov, A. V.; Akiyama, A.; Alam, M. S.; Alam, M. A.; Albert, J.; Albrand, S.; Aleksa, M.; Aleksandrov, I. N.; Alessandria, F.; Alexa, C.; Alexander, G.; Alexandre, G.; Alexopoulos, T.; Alhroob, M.; Aliev, M.; Alimonti, G.; Alison, J.; Aliyev, M.; Allport, P. P.; Allwood-Spiers, S. E.; Almond, J.; Aloisio, A.; Alon, R.; Alonso, A.; Alviggi, M. G.; Amako, K.; Amaral, P.; Amelung, C.; Ammosov, V. V.; Amorim, A.; Amorós, G.; Amram, N.; Anastopoulos, C.; Andari, N.; Andeen, T.; Anders, C. F.; Anderson, K. J.; Andreazza, A.; Andrei, V.; Andrieux, M.-L.; Anduaga, X. S.; Angerami, A.; Anghinolfi, F.; Anjos, N.; Annovi, A.; Antonaki, A.; Antonelli, M.; Antonov, A.; Antos, J.; Anulli, F.; Aoun, S.; Aperio Bella, L.; Apolle, R.; Arabidze, G.; Aracena, I.; Arai, Y.; Arce, A. T. H.; Archambault, J. P.; Arfaoui, S.; Arguin, J.-F.; Arik, E.; Arik, M.; Armbruster, A. J.; Arnaez, O.; Arnault, C.; Artamonov, A.; Artoni, G.; Arutinov, D.; Asai, S.; Asfandiyarov, R.; Ask, S.; Åsman, B.; Asquith, L.; Assamagan, K.; Astbury, A.; Astvatsatourov, A.; Atoian, G.; Aubert, B.; Auerbach, B.; Auge, E.; Augsten, K.; Aurousseau, M.; Austin, N.; Avramidou, R.; Axen, D.; Ay, C.; Azuelos, G.; Azuma, Y.; Baak, M. A.; Baccaglioni, G.; Bacci, C.; Bach, A. M.; Bachacou, H.; Bachas, K.; Bachy, G.; Backes, M.; Backhaus, M.; Badescu, E.; Bagnaia, P.; Bahinipati, S.; Bai, Y.; Bailey, D. C.; Bain, T.; Baines, J. T.; Baker, O. K.; Baker, M. D.; Baker, S.; Dos Santos Pedrosa, F. Baltasar; Banas, E.; Banerjee, P.; Banerjee, Sw.; Banfi, D.; Bangert, A.; Bansal, V.; Bansil, H. S.; Barak, L.; Baranov, S. P.; Barashkou, A.; Barbaro Galtieri, A.; Barber, T.; Barberio, E. L.; Barberis, D.; Barbero, M.; Bardin, D. Y.; Barillari, T.; Barisonzi, M.; Barklow, T.; Barlow, N.; Barnett, B. M.; Barnett, R. M.; Baroncelli, A.; Barone, G.; Barr, A. J.; Barreiro, F.; Barreiro Guimarães da Costa, J.; Barrillon, P.; Bartoldus, R.; Barton, A. E.; Bartsch, D.; Bartsch, V.; Bates, R. L.; Batkova, L.; Batley, J. R.; Battaglia, A.; Battistin, M.; Battistoni, G.; Bauer, F.; Bawa, H. S.; Beare, B.; Beau, T.; Beauchemin, P. H.; Beccherle, R.; Bechtle, P.; Beck, H. P.; Beckingham, M.; Becks, K. H.; Beddall, A. J.; Beddall, A.; Bedikian, S.; Bednyakov, V. A.; Bee, C. P.; Begel, M.; Harpaz, S. Behar; Behera, P. K.; Beimforde, M.; Belanger-Champagne, C.; Bell, P. J.; Bell, W. H.; Bella, G.; Bellagamba, L.; Bellina, F.; Bellomo, M.; Belloni, A.; Beloborodova, O.; Belotskiy, K.; Beltramello, O.; Ami, S. Ben; Benary, O.; Benchekroun, D.; Benchouk, C.; Bendel, M.; Benedict, B. 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A.; Schune, Ph.; Schwanenberger, C.; Schwartzman, A.; Schwemling, Ph.; Schwienhorst, R.; Schwierz, R.; Schwindling, J.; Schwindt, T.; Scott, W. G.; Searcy, J.; Sedykh, E.; Segura, E.; Seidel, S. C.; Seiden, A.; Seifert, F.; Seixas, J. M.; Sekhniaidze, G.; Seliverstov, D. M.; Sellden, B.; Sellers, G.; Seman, M.; Semprini-Cesari, N.; Serfon, C.; Serin, L.; Seuster, R.; Severini, H.; Sevior, M. E.; Sfyrla, A.; Shabalina, E.; Shamim, M.; Shan, L. Y.; Shank, J. T.; Shao, Q. T.; Shapiro, M.; Shatalov, P. B.; Shaver, L.; Shaw, C.; Shaw, K.; Sherman, D.; Sherwood, P.; Shibata, A.; Shichi, H.; Shimizu, S.; Shimojima, M.; Shin, T.; Shmeleva, A.; Shochet, M. J.; Short, D.; Shupe, M. A.; Sicho, P.; Sidoti, A.; Siebel, A.; Siegert, F.; Siegrist, J.; Sijacki, Dj.; Silbert, O.; Silva, J.; Silver, Y.; Silverstein, D.; Silverstein, S. B.; Simak, V.; Simard, O.; Simic, Lj.; Simion, S.; Simmons, B.; Simonyan, M.; Sinervo, P.; Sinev, N. B.; Sipica, V.; Siragusa, G.; Sisakyan, A. N.; Sivoklokov, S. Yu.; Sjölin, J.; Sjursen, T. B.; Skinnari, L. A.; Skovpen, K.; Skubic, P.; Skvorodnev, N.; Slater, M.; Slavicek, T.; Sliwa, K.; Sloan, T. J.; Sloper, J.; Smakhtin, V.; Smirnov, S. Yu.; Smirnova, L. N.; Smirnova, O.; Smith, B. C.; Smith, D.; Smith, K. M.; Smizanska, M.; Smolek, K.; Snesarev, A. A.; Snow, S. W.; Snow, J.; Snuverink, J.; Snyder, S.; Soares, M.; Sobie, R.; Sodomka, J.; Soffer, A.; Solans, C. A.; Solar, M.; Solc, J.; Soldatov, E.; Soldevila, U.; Solfaroli Camillocci, E.; Solodkov, A. A.; Solovyanov, O. V.; Sondericker, J.; Soni, N.; Sopko, V.; Sopko, B.; Sorbi, M.; Sosebee, M.; Soukharev, A.; Spagnolo, S.; Spanò, F.; Spighi, R.; Spigo, G.; Spila, F.; Spiriti, E.; Spiwoks, R.; Spousta, M.; Spreitzer, T.; Spurlock, B.; Denis, R. D. St.; Stahl, T.; Stahlman, J.; Stamen, R.; Stanecka, E.; Stanek, R. W.; Stanescu, C.; Stapnes, S.; Starchenko, E. A.; Stark, J.; Staroba, P.; Starovoitov, P.; Staude, A.; Stavina, P.; Stavropoulos, G.; Steele, G.; Steinbach, P.; Steinberg, P.; Stekl, I.; Stelzer, B.; Stelzer, H. J.; Stelzer-Chilton, O.; Stenzel, H.; Stevenson, K.; Stewart, G. A.; Stillings, J. A.; Stockmanns, T.; Stockton, M. C.; Stoerig, K.; Stoicea, G.; Stonjek, S.; Strachota, P.; Stradling, A. R.; Straessner, A.; Strandberg, J.; Strandberg, S.; Strandlie, A.; Strang, M.; Strauss, E.; Strauss, M.; Strizenec, P.; Ströhmer, R.; Strom, D. M.; Strong, J. A.; Stroynowski, R.; Strube, J.; Stugu, B.; Stumer, I.; Stupak, J.; Sturm, P.; Soh, D. A.; Su, D.; Subramania, H. S.; Succurro, A.; Sugaya, Y.; Sugimoto, T.; Suhr, C.; Suita, K.; Suk, M.; Sulin, V. V.; Sultansoy, S.; Sumida, T.; Sun, X.; Sundermann, J. E.; Suruliz, K.; Sushkov, S.; Susinno, G.; Sutton, M. R.; Suzuki, Y.; Svatos, M.; Sviridov, Yu. M.; Swedish, S.; Sykora, I.; Sykora, T.; Szeless, B.; Sánchez, J.; Ta, D.; Tackmann, K.; Taffard, A.; Tafirout, R.; Taga, A.; Taiblum, N.; Takahashi, Y.; Takai, H.; Takashima, R.; Takeda, H.; Takeshita, T.; Talby, M.; Talyshev, A.; Tamsett, M. C.; Tanaka, J.; Tanaka, R.; Tanaka, S.; Tanaka, S.; Tanaka, Y.; Tani, K.; Tannoury, N.; Tappern, G. P.; Tapprogge, S.; Tardif, D.; Tarem, S.; Tarrade, F.; Tartarelli, G. F.; Tas, P.; Tasevsky, M.; Tassi, E.; Tatarkhanov, M.; Taylor, C.; Taylor, F. E.; Taylor, G. N.; Taylor, W.; Castanheira, M. Teixeira Dias; Teixeira-Dias, P.; Temming, K. K.; Ten Kate, H.; Teng, P. K.; Terada, S.; Terashi, K.; Terron, J.; Terwort, M.; Testa, M.; Teuscher, R. J.; Thadome, J.; Therhaag, J.; Theveneaux-Pelzer, T.; Thioye, M.; Thoma, S.; Thomas, J. P.; Thompson, E. N.; Thompson, P. D.; Thompson, P. D.; Thompson, A. S.; Thomson, E.; Thomson, M.; Thun, R. P.; Tic, T.; Tikhomirov, V. O.; Tikhonov, Y. A.; Timmermans, C. J. W. P.; Tipton, P.; Tique Aires Viegas, F. J.; Tisserant, S.; Tobias, J.; Toczek, B.; Todorov, T.; Todorova-Nova, S.; Toggerson, B.; Tojo, J.; Tokár, S.; Tokunaga, K.; Tokushuku, K.; Tollefson, K.; Tomoto, M.; Tompkins, L.; Toms, K.; Tong, G.; Tonoyan, A.; Topfel, C.; Topilin, N. D.; Torchiani, I.; Torrence, E.; Torres, H.; Torró Pastor, E.; Toth, J.; Touchard, F.; Tovey, D. R.; Traynor, D.; Trefzger, T.; Tremblet, L.; Tricoli, A.; Trigger, I. M.; Trincaz-Duvoid, S.; Trinh, T. N.; Tripiana, M. F.; Trischuk, W.; Trivedi, A.; Trocmé, B.; Troncon, C.; Trottier-McDonald, M.; Trzupek, A.; Tsarouchas, C.; Tseng, J. C.-L.; Tsiakiris, M.; Tsiareshka, P. V.; Tsionou, D.; Tsipolitis, G.; Tsiskaridze, V.; Tskhadadze, E. G.; Tsukerman, I. I.; Tsulaia, V.; Tsung, J.-W.; Tsuno, S.; Tsybychev, D.; Tua, A.; Tuggle, J. M.; Turala, M.; Turecek, D.; Turk Cakir, I.; Turlay, E.; Turra, R.; Tuts, P. M.; Tykhonov, A.; Tylmad, M.; Tyndel, M.; Tyrvainen, H.; Tzanakos, G.; Uchida, K.; Ueda, I.; Ueno, R.; Ugland, M.; Uhlenbrock, M.; Uhrmacher, M.; Ukegawa, F.; Unal, G.; Underwood, D. G.; Undrus, A.; Unel, G.; Unno, Y.; Urbaniec, D.; Urkovsky, E.; Urrejola, P.; Usai, G.; Uslenghi, M.; Vacavant, L.; Vacek, V.; Vachon, B.; Vahsen, S.; Valenta, J.; Valente, P.; Valentinetti, S.; Valkar, S.; Valladolid Gallego, E.; Vallecorsa, S.; Valls Ferrer, J. A.; van der Graaf, H.; van der Kraaij, E.; Van Der Leeuw, R.; van der Poel, E.; van der Ster, D.; Van Eijk, B.; van Eldik, N.; van Gemmeren, P.; van Kesteren, Z.; van Vulpen, I.; Vandelli, W.; Vandoni, G.; Vaniachine, A.; Vankov, P.; Vannucci, F.; Varela Rodriguez, F.; Vari, R.; Varnes, E. W.; Varouchas, D.; Vartapetian, A.; Varvell, K. E.; Vassilakopoulos, V. I.; Vazeille, F.; Vegni, G.; Veillet, J. J.; Vellidis, C.; Veloso, F.; Veness, R.; Veneziano, S.; Ventura, A.; Ventura, D.; Venturi, M.; Venturi, N.; Vercesi, V.; Verducci, M.; Verkerke, W.; Vermeulen, J. C.; Vest, A.; Vetterli, M. C.; Vichou, I.; Vickey, T.; Viehhauser, G. H. A.; Viel, S.; Villa, M.; Villaplana Perez, M.; Vilucchi, E.; Vincter, M. G.; Vinek, E.; Vinogradov, V. B.; Virchaux, M.; Virzi, J.; Vitells, O.; Viti, M.; Vivarelli, I.; Vives Vaque, F.; Vlachos, S.; Vlasak, M.; Vlasov, N.; Vogel, A.; Vokac, P.; Volpi, G.; Volpi, M.; Volpini, G.; von der Schmitt, H.; von Loeben, J.; von Radziewski, H.; von Toerne, E.; Vorobel, V.; Vorobiev, A. P.; Vorwerk, V.; Vos, M.; Voss, R.; Voss, T. T.; Vossebeld, J. H.; Vranjes, N.; Vranjes Milosavljevic, M.; Vrba, V.; Vreeswijk, M.; Anh, T. Vu; Vuillermet, R.; Vukotic, I.; Wagner, W.; Wagner, P.; Wahlen, H.; Wakabayashi, J.; Walbersloh, J.; Walch, S.; Walder, J.; Walker, R.; Walkowiak, W.; Wall, R.; Waller, P.; Wang, C.; Wang, H.; Wang, H.; Wang, J.; Wang, J.; Wang, J. C.; Wang, R.; Wang, S. M.; Warburton, A.; Ward, C. P.; Warsinsky, M.; Watkins, P. M.; Watson, A. T.; Watson, M. F.; Watts, G.; Watts, S.; Waugh, A. T.; Waugh, B. M.; Weber, J.; Weber, M.; Weber, M. S.; Weber, P.; Weidberg, A. R.; Weigell, P.; Weingarten, J.; Weiser, C.; Wellenstein, H.; Wells, P. S.; Wen, M.; Wenaus, T.; Wendler, S.; Weng, Z.; Wengler, T.; Wenig, S.; Wermes, N.; Werner, M.; Werner, P.; Werth, M.; Wessels, M.; Weydert, C.; Whalen, K.; Wheeler-Ellis, S. J.; Whitaker, S. P.; White, A.; White, M. J.; White, S.; Whitehead, S. R.; Whiteson, D.; Whittington, D.; Wicek, F.; Wicke, D.; Wickens, F. J.; Wiedenmann, W.; Wielers, M.; Wienemann, P.; Wiglesworth, C.; Wiik, L. A. M.; Wijeratne, P. A.; Wildauer, A.; Wildt, M. A.; Wilhelm, I.; Wilkens, H. G.; Will, J. Z.; Williams, E.; Williams, H. H.; Willis, W.; Willocq, S.; Wilson, J. A.; Wilson, M. G.; Wilson, A.; Wingerter-Seez, I.; Winkelmann, S.; Winklmeier, F.; Wittgen, M.; Wolter, M. W.; Wolters, H.; Wooden, G.; Wosiek, B. K.; Wotschack, J.; Woudstra, M. J.; Wraight, K.; Wright, C.; Wrona, B.; Wu, S. L.; Wu, X.; Wu, Y.; Wulf, E.; Wunstorf, R.; Wynne, B. M.; Xaplanteris, L.; Xella, S.; Xie, S.; Xie, Y.; Xu, C.; Xu, D.; Xu, G.; Yabsley, B.; Yamada, M.; Yamamoto, A.; Yamamoto, K.; Yamamoto, S.; Yamamura, T.; Yamaoka, J.; Yamazaki, T.; Yamazaki, Y.; Yan, Z.; Yang, H.; Yang, U. K.; Yang, Y.; Yang, Y.; Yang, Z.; Yanush, S.; Yao, W.-M.; Yao, Y.; Yasu, Y.; Ybeles Smit, G. V.; Ye, J.; Ye, S.; Yilmaz, M.; Yoosoofmiya, R.; Yorita, K.; Yoshida, R.; Young, C.; Youssef, S.; Yu, D.; Yu, J.; Yu, J.; Yuan, L.; Yurkewicz, A.; Zaets, V. G.; Zaidan, R.; Zaitsev, A. M.; Zajacova, Z.; Zalite, Yo. K.; Zanello, L.; Zarzhitsky, P.; Zaytsev, A.; Zeitnitz, C.; Zeller, M.; Zemla, A.; Zendler, C.; Zenin, A. V.; Zenin, O.; Ženiš, T.; Zenonos, Z.; Zenz, S.; Zerwas, D.; della Porta, G. Zevi; Zhan, Z.; Zhang, D.; Zhang, H.; Zhang, J.; Zhang, X.; Zhang, Z.; Zhao, L.; Zhao, T.; Zhao, Z.; Zhemchugov, A.; Zheng, S.; Zhong, J.; Zhou, B.; Zhou, N.; Zhou, Y.; Zhu, C. G.; Zhu, H.; Zhu, J.; Zhu, Y.; Zhuang, X.; Zhuravlov, V.; Zieminska, D.; Zimmermann, R.; Zimmermann, S.; Zimmermann, S.; Ziolkowski, M.; Zitoun, R.; Živković, L.; Zmouchko, V. V.; Zobernig, G.; Zoccoli, A.; Zolnierowski, Y.; Zsenei, A.; zur Nedden, M.; Zutshi, V.; Zwalinski, L.

2011-10-01

Making use of 36 pb-1 of proton-proton collision data at sqrt{s} =7 TeV, the ATLAS Collaboration has performed a search for diphoton events with large missing transverse energy. Observing no excess of events above the Standard Model prediction, a 95% Confidence Level (CL) upper limit is set on the cross section for new physics of σ<0.38-0.65 pb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, and of σ<0.18-0.23 pb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 560 GeV, for bino masses above 50 GeV, is set on the GGM gluino mass, while a lower limit of 1/ R>961 GeV is set on the UED compactification radius R. These limits provide the most stringent tests of these models to date.

Radioecological assessment and radiometric dating of sediment cores from dynamic sedimentary systems of Pra and Volta estuaries (Ghana) along the Equatorial Atlantic.

PubMed

Klubi, E; Abril, J M; Nyarko, E; Laissaoui, A; Benmansour, M

2017-11-01

The Volta and Pra estuaries (Ghana, West Africa) are dynamical sedimentary systems whose natural equilibrium is being affected by anthropogenic activities. This paper reports depth-distributions of 210 Pb, 226 Ra, 234 Th, 40 K, 228 Ra and 137 Cs for two sediment cores from these estuaries. Bulk densities were not steady-state and well correlated with 40 K (p < 0.00005). Unsupported 210 Pb profiles were incomplete, non-monotonic and showed large fluctuations. The assumptions involved in the common 210 Pb-based dating models were not meet in these dynamical scenarios, and the use of 137 Cs as a time-marker is difficult in Equatorial and South-Hemisphere countries due to its low fallout rates. Chronologies have been solved with the new 210 Pb-based TERESA model, which operates with varying but statistically correlated fluxes and sediment accumulation rates (SAR). The core from the Volta reflects the conditions prevailing after the construction of the Akosombo Dam, with a mean SAR of 1.05 ± 0.03 g cm -2 ·y -1 , while a higher value of 2.73 ± 0.06 g cm -2 ·y -1 was found in the Pra, affected by intense gold mining activities along its course. Radiological and radioecological assessments have been conducted by applying the UNSCEAR protocols and the ERICA model, respectively. The measured radionuclide concentrations do not pose any significant risk for the environment and human health. Copyright © 2017 Elsevier Ltd. All rights reserved.

Lead contamination in sediments in the past 20 years: A challenge for China.

PubMed

Han, Lanfang; Gao, Bo; Hao, Hong; Zhou, Huaidong; Lu, Jin; Sun, Ke

2018-06-04

Lead (Pb) contamination was recognized in China early in the 1920s. However, the response of Pb contamination in sediments to China's rapid economic and social development remains uncertain to date. We conducted a literature review of over 1000 articles from 1990 to 2016 and the first national-scale survey of Pb contamination in China. A literature review showed that available research in China focused on the economically highly developed river basins, including the Pearl River Basin (PRB), Yellow River Basin (YRB), and Yangtze River Basin (YtRB), whereas those in the less developed southeastern, southwestern, and northwestern river basins received limited attention. The YtRB and YRB had higher Pb contamination levels than other basins, corresponding with the rapid economic development in those regions. However, the less economically developed river basins in the southeastern and northwestern regions of China were also contaminated by Pb. Analysis of 146 studies in the PRB, YRB, and YtRB revealed that Pb contamination in PRB sediments showed a tendency to improve over time, whereas that from the YtRB exhibited a tendency to worsen. For the YRB, there was a slight increase from 1990 to 2006 and a decreasing trend from 2007 to 2014. The overall temporal trend in Pb levels in PRB and YRB sediments corresponded with that of the Pb discharged in wastewater in the surrounding cities, indicating that industrial wastewater discharge was possibly one of the main anthropogenic sources of Pb in those sediments. For the YtRB, the increasing trend in Pb concentrations was related to the considerably high atmospheric Pb emissions in the surrounding cities and its geographical characteristics. These findings suggested that China should develop systematic and consistent approaches for monitoring Pb contents in sediments and adopt a regional economic development policy focusing on pollution prevention. Copyright © 2018 Elsevier B.V. All rights reserved.

The Chronology of Asteroid Accretion, Differentiation, and Secondary Mineralization

NASA Technical Reports Server (NTRS)

Nyquist, L. E.; Kleine, T.; Shih, C.-Y.; Reese, Y. D.

2008-01-01

We evaluate initial (Al-26/Al-27)(sub I), (Mn-53/Mn-55)(sub I), (Hf-182/Hf-180)(sub I), and Pb-207/Pb-206 ages for igneous differentiated meteorites and chondrules from ordinary chondrites for consistency with radioactive decay of the parent nuclides within a common, closed isotopic system, i.e., the early solar nebula. We find that the relative abundances of Al-26, Mn-53, and Hf-182, here denoted by I(Al)(sub CAI, I(Mn)(sub CAI) and I(Hf)(sub CAI), are consistent with decay from common initial values for the bulk solar system. I(Mn)(sub CAI) and I(Hf)(sub CAI) = 9.1+/-1.7 x 10(exp -6) and 1.06+/-0.09 x 10(exp -6) respectively, correspond to the canonical value of I(Al)(sub CAI) = 5.1 x 10(exp -5). I(Hf)(sub CAI) thus determined is consistent with I(Hf)(sub CAI) = 1.003+/-0.045 x 10(exp -6) directly determined in separate work. I(Mn)(sub CAI) is within error of the lowest value directly determined for CAI. We suggest that erratically higher values directly determined for CAI in carbonaceous chondrites reflect proton irradiation of unaccreted CAIs by the early Sun after other asteroids destined for melting by Al-26 decay had already accreted. The Mn-53 incorporated within such asteroids would have been shielded from further "local" spallogenic contributions. The relative abundances of the short-lived nuclides are less consistent with the Pb-207/Pb-206 ages of the corresponding materials with the best consistency being obtained between (Hf-182/Hf-180)(sub I) and Pb-207/Pb-206 ages of angrites. (Hf-182/Hf-180)(sub I) decreases with decreasing Pb-207/Pb-206 ages at the rate expected from the 8.90+/-0.09 Ma half-life of Hf-182. However, the model "CAI age" thus determined, T(sub CAI,Mn-W) = 4568.6+/-0.7 Ma, is older than the commonly accepted directly measured value T(sub CAI) = 4567.l+/-0.2 Ma. I(Al)(sub I), and (Mn-53/Mn-55)(sub I) are less consistent with Pb-207/Pb-206 ages, but determine T(sub CAI, Mn-Cr) = 4568.3+/-0.5 Ma relative to I(AI)(sub CAI)= 5.1 x 10(exp -5) and a Pb-207/Pb-206 age of 4558.6 Ma for the LEW86010 angrite. However. the (Mn-53/Mn-55)(sub I) and Pb-207/Pb-206 ages of "intermediate" age D'Orbigny-clan angrites and Asuka 881394 are inconsistent with radioactive decay from CAI values with a Mn-55 half-life of 3.7+/-0.4 Ma. in spite of consistency between (Mn-53/Mn-55)(sub I) and (Al-26/Al-27)(sub I). Nevertheless, it appears that the Mn-Cr method with I(Mn)(sub CAI) = 9.1+/-1.7 x 10(exp -6) can be used to date primary igneous events and also secondary mineralization on asteroid parent bodies. We summarize ages thus determined for igneous events on differentiated asteroids and for carbonate and fayalite formation on carbonaceous asteroids.

Growing large columnar grains of CH3NH3PbI3 using the solid-state reaction method enhanced by less-crystallized nanoporous PbI2 films

NASA Astrophysics Data System (ADS)

Zheng, Huifeng; Wang, Weiqi; Liu, Yangqiao; Sun, Jing

2017-03-01

Compact, pinhole-free and PbI2-free perovskite films, are desirable for high-performance perovskite solar cells (PSCs), especially if large columnar grains are obtained in which the adverse effects of grain boundaries will be minimized. However, the conventional solid-state reaction methods, originated from the two-step method, failed to grow columnar grains of CH3NH3PbI3 in a facile way. Here, we demonstrate a strategy for growing large columnar grains of CH3NH3PbI3, by less-crystallized nanoporous PbI2 (ln-PbI2) film enhanced solid-state reaction method. We demonstrated columnar grains were obtainable only when ln-PbI2 films were applied. Therefore, the replacement of compact PbI2 by ln-PbI2 in the solid-sate reaction, leads to higher power conversion efficiency, better reproducibility, better stability and less hysteresis. Furthermore, by systematically investigating the effects of annealing temperature and duration, we found that an annealing temperature ≥120 °C was also critical for growing columnar grains. With the optimal process, a champion efficiency of 16.4% was obtained and the average efficiency reached 14.2%. Finally, the mechanism of growing columnar grains was investigated, in which a VPb″ -assisted hooping model was proposed. This work reveals the origins of grain growth in the solid-state reaction method, which will contribute to preparing high quality perovskite films with much larger columnar grains.

Late Vendian Complexes in the Structure of Metamorphic Basement of the Fore Range Zone, Greater Caucasus

NASA Astrophysics Data System (ADS)

Kamzolkin, V. A.; Latyshev, A. V.; Vidyapin, Yu. P.; Somin, M. L.; Smul'skaya, A. I.; Ivanov, S. D.

2018-05-01

The paper presents new data on the composition, age, and relationships (with host and overlying deposits) of intrusive rocks in the basement of the Fore Range zone (Greater Caucasus), in the Malaya Laba River Basin. The evolutionary features of intrusive units located within the Blyb metamorphic complex are described. It is shown for the first time that the lower levels of this complex are, in a structural sense, outcrops of the Late Vendian basement. The basement is composed of the Balkan Formation and a massif of quartz metadiorites that intrudes it; for the rocks of this massif, ages ranging from 549 ± 7.4 to 574.1 ± 6.7 Ma are obtained for three U-Pb datings by the SHRIMP-II method. The Herzyinan magmatic event is represented by a group of granodiorite intrusions penetrating the Blyb complex on a series of faults extending along its boundary with the Main Range zone. The obtained estimate for the U-Pb age of one of the intrusions (319 ± 3.8 Ma) corresponds to the end of the Serpukhovian stage of the Early Carboniferous.

A simple method to fabricate an NIR detector by PbTe nanowires in a large scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baghchesara, Mohammad Amin; Yousefi, Ramin, E-mail: Yousefi.ramin@gmail.com; Cheraghizade, Mohsen

2016-05-15

Highlights: • PbTe nanowires were grown by tellurization of the Pb sheets for the first time. • It was observed a band gap value for the PbTe nanostructures in the NIR region. • NIR detector was fabricated in a large scale using a simple method. • Effect of Te concentration on morphology of PbTe nanostructures was investigated. - Abstract: A simple method was used to fabricate a near-infrared (NIR) detector using PbTe nanostructures. Samples were synthesized by tellurization of lead sheets in a tube furnace. PbTe nanostructures with wires and flakes shapes were grown on the lead sheets that weremore » placed at 300 and 330 °C, respectively, while, PbTe nanoporous were grown at 360 and 390 °C. X-ray diffraction patterns and X-ray photoelectron spectra results indicated that, the PbTe phase was formed in all samples. UV–vis diffuse reflectance spectra measurements showed a band gap for the PbTe nanostructures in the near-infrared region of the electromagnetic spectrum. Actually, the results indicated that, the band gap values of the PbTe nanowires and nanoporous were 1.54 eV and 1.61 eV, respectively. Finally, the PbTe nanostructures were used as a simple photoresponse device under a red light source. The photoresponse results revealed, PbTe nanowires are promising for photoelectrical applications in the NIR region.« less

Age of metamorphic events : petrochronology and hygrochronology

NASA Astrophysics Data System (ADS)

Bosse, Valerie; Villa, Igor M.

2017-04-01

Geodynamic models of the lithosphere require quantitative data from natural samples. Time is a key parameter: it allows to calculate rates and duration of geological processes and provides informations about the involved physical processes (Vance et al. 2003). Large-scale orogenic models require linking geochronological data with other parameters: structures, kinematics, magmatic and metamorphic petrology (P-T-A-X conditions), thermobarometric evolution of the lithosphere, chemical dynamics (Muller, 2003). This requires geochronometers that are both powerful chemical and petrological tracers. In-situ techniques allow dating a mineral in its petrological-microstructural environment. Getting a "date" has become quite easy... But what do we date in the end ? What is the link between the numbers obtained from the mass spectrometer and the age of the metamorphic event we are trying to date ? How can we transform the date into a geological meaningful age ? What do we learn about the behavior of the geochronometer minerals? Now that we can perform precise dating on very small samples directly in the studied rock, it is important to improve the way we interpret the ages to give them more pertinence in the geodynamic context. We propose to discuss the Th/U/Pb system isotopic closure in various metamorphic contexts using our published examples of in situ dating on monazite and zircon (Bosse et al. 2009; Didier et al. 2014, 2015). The studied examples show that (i) fluid assisted dissolution-precipitation processes rather than temperature-dependent solid diffusion predominantly govern the closure of the Th/U/Pb system (ii) monazite and zircon are sensitive to the interaction with fluids of specific composition (F, CO2, K ...), even at low temperature (iii) in the absence of fluids, monazite is able to record HT events and to retain this information in poly-orogenic contexts or during partial melting events (iv) complex chemical and isotopic zonations, well known in monazite, reflect the interaction with the surrounding mineral assemblages. An often neglected observation is that the K-Ar chronometer minerals show similar patterns of isotopic inheritance closely tied to relict patches and heterochemical retrogression phases (Villa and Williams 2013). Isotopic closure in the U-Pb and K-Ar systems follows the same principle: thermal diffusion is very slow, dissolution and reprecipitation are several orders of magnitude faster. This means that both U-Pb and K-Ar mineral chronometers are hygrochronometers. The interpretation of the ages of the different domains cannot be decoupled from the geochemical and petrological context. The focus on petrology also requires, following Villa (1998, 2016), that the ages measured in metamorphic rocks no longer can be used in geodynamic models according to the "closure temperature" concept as originally defined by Dodson (1973). Bosse et al. (2009) Chem Geol 261: 286 Didier et al. (2014) Chem Geol 381: 206 Didier et al. (2015) Contrib Mineral Petrol 170: 45 Dodson (1973) Contrib Mineral Petrol 40: 259 Muller (2003) EPSL, 206: 237 Villa (1998) Terra Nova 10: 42 Villa (2016) Chem Geol 420: 1 Villa & Williams (2013) In: Harlov & Austrheim (eds.), Metasomatism and the Chemical Transformation of Rock. Springer, p171

Bleogens: Cactus-Derived Anti-Candida Cysteine-Rich Peptides with Three Different Precursor Arrangements

PubMed Central

Loo, Shining; Kam, Antony; Xiao, Tianshu; Tam, James P.

2017-01-01

Cysteine-rich peptides (CRPs) play important host-defense roles in plants. However, information concerning CRPs in the Cactaceae (cactus) family is limited, with only a single cactus-derived CRP described to date. Here, we report the identification of 15 novel CRPs with three different precursor architectures, bleogens pB1-15 from Pereskia bleo of the Cactaceae family. By combining proteomic and transcriptomic methods, we showed that the prototype, bleogen pB1, contained 36 amino acid residues, a six-cysteine motif typical of the six-cysteine-hevein-like peptide (6C-HLP) family, and a type I two-domain precursor consisting of an endoplasmic reticulum (ER) and a mature domain. In contrast, the precursors of the other 14 bleogens contained a type II three-domain architecture with a propeptide domain inserted between the ER and the mature bleogen domain. Four of these 14 bleogens display a third type of architecture with a tandemly repeating bleogen domain. A search of the Onekp database revealed that <1% plant species possess three different precursor architectures for the biosynthesis of 6C-HLPs, including Lophophora williamsii, Pereskia aculeate, Portulaca cryptopetala, Portulaca oleracea, Portulaca suffruticosa, and Talinum sp. NMR analysis confirmed that bleogen pB1 has cystine-knot disulfide connectivity as well as a two-beta-sheet and a four-loop structural fold that is similar to other 6C-HLPs. Sequence analysis, structural studies, and in silico modeling revealed that bleogen pB1 has a cation-polar-cation motif, a signature heparin-binding motif that was confirmed by heparin affinity chromatography. Cell-based assays showed that bleogen pB1 is non-toxic to mammalian cells but functions as an anti-Candida peptide. Taken together, our findings provide insight into the occurrence, functions and precursor architectures of CRPs in the cactus family. PMID:29312404

Blood Erythrocyte Concentrations of Cadmium and Lead and the Risk of B-Cell Non-Hodgkin’s Lymphoma and Multiple Myeloma: A Nested Case-Control Study

PubMed Central

Porta, Miquel; Bergdahl, Ingvar A.; Palli, Domenico; Johansson, Ann-Sofie; Botsivali, Maria; Vineis, Paolo; Vermeulen, Roel; Kyrtopoulos, Soterios A.; Chadeau-Hyam, Marc

2013-01-01

Background Cadmium (Cd) and lead (Pb) are hypothesised to be risk factors for non-Hodgkin’s lymphoma (NHL), a group of haematological malignancies with a suspected environmental aetiology. Within the EnviroGenoMarkers study we utilised pre-diagnostic erythrocyte concentrations of Cd and Pb to determine whether exposure was associated with risk of B-cell NHL and multiple myeloma. Methods 194 incident cases of B-cell NHL and 76 cases of multiple myeloma diagnosed between 1990 and 2006 were identified from two existing cohorts; EPIC-Italy and the Northern Sweden Health and Disease Study. Cases were matched to healthy controls by centre, age, gender and date of blood collection. Cd and Pb were measured in blood samples provided at recruitment using inductively coupled plasma-mass spectrometry. Logistic regression was applied to assess the association with risk. Analyses were stratified by cohort and gender and by subtype where possible. Results There was little evidence of an increased risk of B-cell NHL or multiple myeloma with exposure to Cd (B-cell NHL: OR 1.09 95%CI 0.61, 1.93, MM: OR 1.16 95% CI: 0.40, 3.40 ) or Pb (B-cell NHL: 0.93 95% CI 0.43, 2.02, multiple myeloma: OR 1.63 95%CI 0.45, 5.94) in the total population when comparing the highest to the lowest quartile of exposure. However, gender and cohort specific differences in results were observed. In females the risk of B-cell NHL was more than doubled in those with a body burden of Cd >1µg/L (OR 2.20 95%CI; 1.04, 4.65). Conclusions This nested case-control study does not support a consistent positive association between Cd or Pb and NHL, but there is some indication of a gender specific effect suggesting further research is warranted. PMID:24312375

A 2000-yr High-resolution Stalagmite Record From Zhenzhu Cave in Hebei, North China: Interpretations of AMS 14C, 230Th/U, 210Pb Dating, and δ18O, δ13C Results

NASA Astrophysics Data System (ADS)

Li, H. C.; Yin, J.; Rao, Z.; Mii, H. S.; Shen, C. C.; Pillutla, R. K.; Li, Y. X.

2016-12-01

An 11.1-cm long stalagmite (ZZ12) collected from Zhenzhu cave (38°15'N, 113°42'E, 975m a.s.l.) located at Tiangui mountain of Hebei province, North China. The 230Th/U dates on 12 horizons exhibit large uncertainties with many reversed age sequences due to low U contents and low 230Th/232Th ratios. While the 230Th/U dating is not able to provide the chronology of this stalagmite, AMS 14C dating on 27 samples from various depths of the stalagmite yields a reliable age-depth relationship. Three AMS 14C dates from the top 5 mm appear nuclear bomb carbon indicating that this part was deposited after AD 1950. Seven samples for 210Pb dating were taken from the upper 14 mm with 2 mm intervals, showing exponential decay of excess 210Pb and supporting the AMS 14C dating results. At the base of the stalagmite, charcoal grains were included in the carbonate stalagmite. This charcoal sample has a Calibrated 14C age of 1865±20 a BP. The carbonates at adjacent depths show Calibrated 14C ages of 1900±15 and 2215±75 a BP respectively. The bomb carbon and similar ages between the charcoal and carbonates indicate that dead carbon influence on the 14C dates in some horizons may not be serious. From the 27 AMS 14C dates, we select 17 AMS 14C dates which have minimal influence of dead carbon fraction to construct the chronology. The established chronology shows that slow growth rates occurred prior to 1100 a BP and after 600 a BP. This time interval involves the Medieval Warm Period, while the fast growth rate during this interval may reflect warm and wet climatic conditions. A total of 835 samples were drilled from the stalagmite for δ18O and δ13C analyses. The current 900-year δ18O and δ13C records reveal climate and vegetation changes in the study area. Strong decadal oscillations in the δ18O record reflect variations of monsoonal rain, with relatively dry between AD 1350 and AD 1550 and after AD 1960. The δ13C record appears mainly multi-centennial variations with a 4‰ fluctuation range and an average value of -8‰ (VPDB). The δ13C values were lighter than the average during AD 1150 1480 and AD 1700 1920, whereas the δ13C values were heavier than the average during AD 1480 1700 and AD 1820 the present. The δ13C record mainly reflects the vegetation change above the cave, with lighter value indicating better vegetation coverage and vice versa.

Effects of Simple Leaching of Crushed and Powdered Materials on High-precision Pb Isotope Analyses

NASA Astrophysics Data System (ADS)

Todd, E.; Stracke, A.

2013-12-01

We present new results of simple leaching experiments on the Pb isotope composition of USGS standard reference material powders and on ocean island basalt whole rock splits and powders. Rock samples were leached with 6N HCl in two steps, first hot and then in an ultrasonic bath, and washed with ultrapure H2O before conventional sample digestion and chromatographic purification of Pb. Pb isotope analyses were determined with Tl-doped MC-ICP-MS. Intra- and inter-session analytical reproducibility of repeated analyses of both synthetic Pb solutions and Pb from single digests of chemically processed natural samples were generally < 100 ppm (2 S.D.). The comparison of leached and unleached samples shows that leaching reliably removes variable amounts of different contaminants for different starting materials. For repeated digests of a single sample, the leached samples reproduce better than the unleached ones, showing that leaching effectively removes heterogeneously distributed extraneous Pb. However, the reproducibility of repeated digests of variably contaminated natural samples is up to an order of magnitude worse than the analytical reproducibility of ca. 100 ppm. More complex leaching methods (e.g., Nobre Silva et al., 2009) yield Pb isotope ratios within error of and with similar reproducibility to our method, showing that the simple leaching method is reliable. The remaining Pb isotope heterogeneity of natural samples, which typically exceeds 100 ppm, is thus attributed to inherent isotopic sample heterogeneity. Tl-doped MC-ICP-MS Pb ratio determination is therefore a sufficiently precise method for Pb isotope analyses in natural rocks. More precise Pb double- or triple-spike methods (e.g., Galer, 1999; Thirlwall, 2000), may exploit their full potential only in cases where natural isotopic sample heterogeneity is demonstrably negligible. References: Galer, S., 1999, Chem. Geol. 157, 255-274. Nobre Silva, et al. 2009, Geochemistry Geophysics Geosystems 10, Q08012. Thirlwall, M.F., 2000, Chem. Geol. 163, 299-322.

Fluorescent Lead(IV) Sulfide Nanoparticles Synthesized by Idiomarina sp. Strain PR58-8 for Bioimaging Applications.

PubMed

Srivastava, Pallavee; Kowshik, Meenal

2017-04-01

The fabrication of nanoparticles by microorganisms presents a "green" method for generating biocompatible nanomaterials. We discovered the intracellular biosynthesis of fluorescent lead(IV) sulfide nanoparticles by the moderate halophile, Idiomarina sp. strain PR58-8. The bacterium tolerated up to 8 mM Pb(NO 3 ) 2 during growth. Non-protein thiols dose-dependently increased in response to metal exposure, which suggests they are involved in the growth of PbS 2 crystals and lead detoxification. Using X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, and energy dispersive analysis of X-rays, the nanoparticles were characterized as spherical β-PbS 2 nanoparticles (PbS 2 NPs) with a tetragonal crystal lattice, a crystallite domain size of 2.38 nm, and an interplanar distance of 0.318 nm. A narrow symmetric emission spectrum with a Gaussian distribution and an emission maximum at 386 nm was obtained when the particles were excited at 570 nm. The PbS 2 NPs exhibited a large Stokes' shift (8,362 cm -1 ) and a relatively high quantum yield (67%). These properties, along with fluorescence that was maintained in various microenvironments and their biocompatibility, make these nanoparticles excellent candidates for bioimaging. The particles were internalized by HeLa cells and evenly distributed within the cytoplasm, exhibiting their potential for in situ bioimaging applications. The "as-synthesized" lead(IV) sulfide nanoparticles may provide expanded opportunities for targeted bioimaging via modifying the surface of the particles. IMPORTANCE This article reports the intracellular synthesis of fluorescent lead(IV) sulfide nanoparticles (PbS 2 NPs) by a microorganism. All previous reports on the microbial synthesis of lead-based nanoparticles are on lead(II) sulfide that exhibits near-infrared fluorescence, requiring expensive instrumentation for bioimaging. Bioimaging using PbS 2 NPs can be achieved using routine epifluorescence microscopes, as it fluoresces in the visible range. The research on PbS 2 nanoparticles to date is on their chemical synthesis employing toxic precursors, extreme pH, pressure, and temperature, resulting in cytotoxic products. In this context, the synthesis of PbS 2 nanoparticles by Idiomarina sp. strain PR58-8, described in this work, occurs at ambient temperature and pressure and results in the generation of biocompatible nanoparticles with no hazardous by-products. The excellent fluorescence properties that these particles exhibit, as well as their abilities to easily penetrate the cells and evenly distribute within the cytoplasm, make them exceptional candidates for bioimaging applications. This study demonstrated the synthesis and fluorescence bioimaging application of microbially synthesized PbS 2 nanoparticles. Copyright © 2017 American Society for Microbiology.

Phosphorus Amendment Efficacy for In Situ Remediation of ...

EPA Pesticide Factsheets

A validated method is needed to measure reductions of in vitro bioaccessible (IVBA) Pb in urban soil remediated with amendments. This study evaluated the effect of in vitro extraction solution pH and glycine buffer on bioaccesible Pb in P-treated soils. Two Pb-contaminated soils (790-1300 mg Pb kg-1), one from a garden and one from a city lot in Cleveland, OH, were incubated in a bench scale experiment for 1 yr. Six phosphate amendments, including bone meal, fish bone, poultry litter, monoammonium phosphate, diammonium phosphate, and triple superphosphate, were added to containers at two application rates. Lead IVBA was assessed using USEPA Method 1340 and three modified versions of this method. Modifications included using solutions with pH 1.5 and 2.5 as well as using solutions with and without 0.4 mol L-1 glycine. Soil amendments were effective in reducing IVBA Pb in these soils as measured by pH 1.5 with glycine buffer. The greatest reductions in IVBA Pb, from 5 to 26%, were found using pH 2.5 extractions. Lead mineral results showed several soil amendments promoted Pb phosphate formation, an indicator of remediation success. A significant negative linear relationship between reduction in IVBA Pb and Pb-phosphate formation was found only for pH 2.5 without glycine extraction solution. A modified USEPA Method 1340 without glycine and using pH 2.5 has the potential to predict P soil treatment efficacy and reductions in bioavailable Pb. Developing mana

Population-based survey of the prevalence of type 1 and type 2 diabetes in school children in Philadelphia.

PubMed

Lipman, Terri H; Ratcliffe, Sarah J; Cooper, Rhona; Levitt Katz, Lorraine E

2013-12-01

Population-based (PB) registries of type 1 diabetes mellitus (T1DM) in children have been essential in determining the geographic, racial, and temporal patterns of the disease. There is a paucity of PB data on the prevalence of type 1 and type 2 diabetes (T2DM) in youth. The prevalence of diabetes in children was determined using a PB survey of the 628 schools in Philadelphia. Data obtained included type of diabetes, date of birth, race, gender, date of diagnosis, diabetes treatment, and most recent height and weight. The survey was completed by nurses at 510 schools (81% of schools) representing 252,896 children (70% of children in Philadelphia). Prevalence (per 1000) was computed. The survey identified 492 cases (355 T1DM, 88 T2DM, 49 type unknown). The overall prevalence of T1DM was 1.58 (0.73 White, 0.56 African American, 0.50 Hispanic); of T2DM was 0.35 (0.03 White, 0.28 African American, 0.05 Hispanic). Mean age at diagnosis was 8.6 and 11.9 years for T1DM and T2DM, respectively. The prevalence of T1DM was higher in boys--T2DM was higher in girls. Of children with T2DM, 25% were treated with insulin. BMI was ≥95th percentile in 20% of children weighed (10% of T1DM, 57% of T2DM). Although the Philadelphia Pediatric Diabetes Registry is the longest ongoing US registry of its kind, these are the first PB diabetes prevalence data of children in Philadelphia. PB studies in schools are able to capture children with diabetes who are diagnosed and treated in a variety of settings. © 2013 Wiley Publishing Asia Pty Ltd and Ruijin Hospital, Shanghai Jiaotong University School of Medicine.

Assessing element-specific patterns of bioaccumulation across New England lakes

PubMed Central

Ward, Darren M.; Mayes, Brandon; Sturup, Stefan; Folt, Carol L.; Chen, Celia Y.

2012-01-01

Little is known about differences among trace elements in patterns of bioaccumulation in freshwater food webs. Our goal was to identify patterns in bioaccumulation of different elements that are large and consistent enough to discern despite variation across lakes. We measured methylmercury (MeHg) and trace element (As, Cd, Hg, Pb, and Zn) concentrations in food web components of seven New England lakes on 3–5 dates per lake, and contrasted patterns of bioaccumulation across lakes, metals and seasons. In each lake, trace element concentrations were compared across trophic levels, including three size fractions of zooplankton, planktivorous fish, and piscivorous fish. The trophic position of each food web component was estimated from N isotope analysis. Trace element concentrations varied widely among taxa, lakes and sampling dates. Yet, we identified four consistent patterns of bioaccumulation that were consistent across lakes: (1) MeHg concentration increased (i.e., was biomagnified) and Pb concentration decreased (i.e., was biodiminished) with increased trophic position. (2) Zinc concentration (as with MeHg) was higher in fish than in zooplankton, but overall variation in Zn concentration (unlike MeHg) was low. (3) Arsenic and Cd concentrations (as with Pb) were lower in fish than in zooplankton, but (unlike Pb) were not significantly correlated with trophic position within zooplankton or fish groups. (4) Average summer concentrations of As, Pb, Hg, and MeHg in zooplankton significantly predicted their concentrations in either planktivorous or piscivorous fish. Our secondary goal was to review sampling approaches in forty-five published studies to determine the extent to which current sampling programs facilitate cross-lake and cross-study comparisons of bioaccumulation. We found that studies include different components of the food web and sample too infrequently to enable strong cross-lake and cross-study comparisons. We discuss sampling strategies that would improve our capacity to identify consistent patterns of bioaccumulation and drivers of elevated trace element concentrations under naturally high levels of variability. PMID:22356871

Exploring As-Cast PbCaSn-Mg Anodes for Improved Performance in Copper Electrowinning

NASA Astrophysics Data System (ADS)

Yuwono, Jodie A.; Clancy, Marie; Chen, Xiaobo; Birbilis, Nick

2018-06-01

Lead calcium tin (PbCaSn) alloys are the common anodes used in copper electrowinning (Cu EW). Given a large amount of energy consumed in Cu EW process, anodes with controlled oxygen evolution reaction (OER) kinetics and a lower OER overpotential are advantageous for reducing the energy consumption. To date, magnesium (Mg) has never been studied as an alloying element for EW anodes. As-cast PbCaSn anodes with the addition of Mg were examined herein, revealing an improved performance compared to that of the industrial standard PbCaSn anode. The alloy performances in the early stages of anode life and passivation were established from electrochemical studies which were designed to simulate industrial Cu EW process. The 24-hour polarization testing revealed that the Mg alloying depolarizes the anode potential up to 80 mV; thus, resulting in a higher Cu EW efficiency. In addition, scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the alteration of the alloy microstructure and the corresponding interfacial reactions contribute to the changes of the anode electrochemical performances. The present study reveals for the first time the potency of Mg alloying in reducing the overpotential of PbCaSn anode.

A green preparation method of battery grade α-PbO based on Pb-O2 fuel cell

NASA Astrophysics Data System (ADS)

Wang, Pingyuan; Pan, Junqing; Gong, Shumin; Sun, Yanzhi

2017-08-01

In order to solve the problem of high pollution and high energy consumption of the current lead oxide (PbO) preparation processes, a new clean and energy saving preparation method for high purity α-PbO via discharge of a Pb-O2 fuel cell is reported. The fuel cell with metallic lead anode, oxygen cathode, and 30% NaOH electrolyte can provide a discharge voltage of 0.66-0.38 V corresponding to discharge current range of 5-50 mA cm-2. PbO is precipitated from the NaHPbO2-containing electrolyte through a cooling crystallization process after discharge process, and the XRD patterns indicate the structure is pure α-PbO. The mother liquid after crystallization can be recycled for the next batch. The obtained PbO mixed with 60% Shimadzu PbO is superior to the pure Shimadzu PbO in discharge capacity and cycle ability.

Improved 206Pb/238U microprobe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, ID-TIMS, ELA-ICP-MS and oxygen isotope documentation for a series of zircon standards

USGS Publications Warehouse

Black, L.P.; Kamo, S.L.; Allen, C.M.; Davis, D.W.; Aleinikoff, J.N.; Valley, J.W.; Mundil, R.; Campbell, I.H.; Korsch, R.J.; Williams, I.S.; Foudoulis, C.

2004-01-01

Precise isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) documentation is given for two new Palaeozoic zircon standards (TEMORA 2 and R33). These data, in combination with results for previously documented standards (AS3, SL13, QGNG and TEMORA 1), provide the basis for a detailed investigation of inconsistencies in 206Pb/238U ages measured by microprobe. Although these ages are normally consistent between any two standards, their relative age offsets are often different from those established by ID-TIMS. This is true for both sensitive high-resolution ion-microprobe (SHRIMP) and excimer laser ablation-inductively coupled plasma-mass spectrometry (ELA-ICP-MS) dating, although the age offsets are in the opposite sense for the two techniques. Various factors have been investigated for possible correlations with age bias, in an attempt to resolve why the accuracy of the method is worse than the indicated precision. Crystallographic orientation, position on the grain-mount and oxygen isotopic composition are unrelated to the bias. There are, however, striking correlations between the 206Pb/238U age offsets and P, Sm and, most particularly, Nd abundances in the zircons. Although these are not believed to be the primary cause of this apparent matrix effect, they indicate that ionisation of 206Pb/238U is influenced, at least in part, by a combination of trace elements. Nd is sufficiently representative of the controlling trace elements that it provides a quantitative means of correcting for the microprobe age bias. This approach has the potential to reduce age biases associated with different techniques, different instrumentation and different standards within and between laboratories. Crown Copyright ?? 2004 Published by Elsevier B.V. All rights reserved.

U-Pb thermochronology of the lower crust: producing a long-term record of craton thermal evolution

NASA Astrophysics Data System (ADS)

Blackburn, T.; Bowring, S. A.; Mahan, K. H.; Perron, T.; Schoene, B.; Dudas, F. O.

2010-12-01

The EarthScope initiative is focused on providing an enhanced view of the North American lithosphere and the present day stress field of the North American continent. Of key interest is the interaction between convecting asthenosphere and the conducting lithospheric mantle that underlie the continents, especially the cold ‘keels’ that underlie Archean domains. Cratonic regions are in general characterized by minimal erosion and or sediment accumulation. The Integration of seismic tomography, and mantle xenolith studies reveal a keel of seismically fast and relatively buoyant and viscous mantle; physical properties that are intimately linked with the long-term stability and topographic expression of the region. Missing from this model of the continental lithosphere is the 4th dimension--time--and along with it our understanding of the long-term evolution of these stable continental interiors. Here we present a thermal record from the North American craton using U-Pb thermochronology of lower crustal xenoliths. The use of temperature sensitive dates on lower crustal samples can produce a unique time-temperature record for a well-insulated and slowly cooling lithosphere. The base of the crust is insulated enough to remain unperturbed by any plausible changes to surface topography, yet unlike the subadjacent lithospheric mantle, contains accessory phases amenable to U-Pb dating (rutile, apatite, titanite). With near steady state temperatures in the lower crust between 400-600 °C, U-Pb thermochronometers with similar average closure temperatures for Pb are perfectly suited to record the long-term cooling of the lithosphere. Xenoliths from multiple depths, and across the craton yield time-temperature paths produced from U-Pb thermochronometers that record extremely slow cooling (<0.25 °C/Ma) over time scales of billions of years. Combining these data with numerical thermal modeling allow constraints to be placed on the dominant heat transfer mechanisms operating within the lithosphere including exhumation, conduction, decay of heat producing elements and thickness of crustal layers/lithospheric mantle. The thermal histories produced from this numerical model can in turn be used to calculate model U-Pb thermochronometric data using a numerical solution to the diffusion/production equation. Integration of thermal and volume diffusion models for the U-Pb system suggests that the extreme slow cooling recorded by U-Pb thermochronology is consistent with low integrated exhumation rates (<0.005 km/Ma). This exhumation rate is integrated over time-scales of hundreds of million to a billion years and does not preclude the possibility for rapid or short-wave length uplift/subsidence. This long-term record of continental lithosphere stability and apparent neutral buoyancy of the craton within a cooling mantle may be further used to refine our estimates of secular cooling within the mantle.

Fingerprinting the K/T impact site and determining the time of impact by U-Pb dating of single shocked zircons from distal ejecta

NASA Technical Reports Server (NTRS)

Krogh, T. E.; Kamo, S. L.; Bohor, B. F.

1993-01-01

U-Pb isotopic dating of single 1 - 3 micrograms zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 +/- 5 Ma primary age for a component of the target site, while those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 +/- 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With U-Pb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age.

U-Pb detrital zircon dates and provenance data from the Beaufort Group (Karoo Supergroup) reflect sedimentary recycling and air-fall tuff deposition in the Permo-Triassic Karoo foreland basin

NASA Astrophysics Data System (ADS)

Viglietti, Pia A.; Frei, Dirk; Rubidge, Bruce S.; Smith, Roger M. H.

2018-07-01

Detrital zircon U-Pb age dating was used for provenance determination and maximum age of deposition for the Upper Permian (upper Teekloof and Balfour formations) and Lower Triassic (Katberg Formation) lithostratigraphic subdivisions of the Beaufort Group of South Africa's Karoo Basin. Ten samples were analysed using laser ablation - single collector - magnetic sectorfield - inductively coupled plasma - mass spectrometry (LA-SF-ICP-MS). The results reveal a dominant Late Carboniferous-Late Permian population (250 ± 5 Ma - 339 ± 5 Ma), a secondary Cambrian-Neoproterozoic (489 ± 5 Ma to 878 ± 24 Ma) population, a minor Mesoproterozoic (908 ± 24 Ma to 1308 ± 23) population, and minor occurrences of Devonian, Ordovician, Proterozoic and Archean zircon grains. Multiple lines of evidence (e.g. roundness and fragmentary nature of zircons, palaeo-current directions, and previous work), suggest the older zircon populations are related to sedimentary recycling in the Gondwanide Orogeny. The youngest and dominant population contain elongate euhedral grains interpreted to be directly derived from their protolith. Since zircons form in felsic igneous rocks, and no igneous rocks of Late Permian age occur in the Karoo Basin, these findings suggest significant input of volcanic material by ash falls. These results support sedimentological and palaeontological data for a Lopingian (Late Permian) age for the upper Beaufort Group, but contradict previous workers who retrieved Early Triassic dates from zircons in ashes for the Beaufort and Ecca Groups. Pb-loss not revealed by resolvable discordance on the concordia diagram, and metamictization of natural zircons are not factored into the conclusions of earlier workers.

U-Pb baddeleyite ages and geochemistry of dolerite dykes in the Bas Drâa Inlier of the Anti-Atlas of Morocco: Newly identified 1380 Ma event in the West African Craton

NASA Astrophysics Data System (ADS)

El Bahat, Abdelhakim; Ikenne, Moha; Söderlund, Ulf; Cousens, Brian; Youbi, Nasrrddine; Ernst, Richard; Soulaimani, Abderrahmane; El Janati, M'hamed; Hafid, Ahmid

2013-08-01

In the Bas-Drâa Inlier (Anti-Atlas, Morocco), the Paleoproterozoic basement which is cut by the Ediacaran Taourgha granite is also crosscut by numerous dykes of a variety of trends, mostly of uncertain age. Two doleritic dykes are dated by the ID-TIMS U-Pb method on baddeleyite and yield emplacement ages of 1381 ± 8 Ma (MSWD = 0.84) and 1384 ± 6 Ma (MSWD = 1.4) determined for a N135°E and a N40°E trending dyke, respectively. These dates represent the first geochronological evidence of a Mesoproterozoic magmatic event in the Anti-Atlas. This magmatic event falls in the previously considered ca 1.7-1.0 Ga (Mesoproterozoic) gap in geological activity in the Anti-Atlas. The poorly dated Taghdout and Taarotihate sequences could represent remnants of the ca. 1380 Ma magmatism and rift-related sedimentation. The Mesoproterozoic sedimentary succession of the Atar Group in the Taoudeni basin (Mauritania) could also represent a good candidate for rift-related sedimentation but it postdates the 1380 Ma magmatic event by 270 Ma. The dated 1380 Ma dykes are transitional to mildly alkaline basalts, not unlike some Hawaiian lavas. However, these dykes have a distinct negative Nb anomaly (a common features in many Large Igneous Provinces, LIPs), and this requires interaction with the lithosphere. This interaction may have occurred at the level of the lithospheric mantle or the crust. These newly dated 1380 Ma dykes may converge to the north, speculatively suggesting a magmatic center (associated with a 1380 Ma mantle plume?) along the northern margin, and possibly linked to rifting and possible breakup on that margin, and also to a regional uplift that largely removed the evidence of a 1380 Ma cover sequence. Contemporaneous 1380-1390 Ma magmatism is reported elsewhere on other crustal blocks, and that in northeastern Laurentia (northern Greenland), northern Siberia (Anabar shield), and Baltica (southern Urals) can be reconstructed with that of the Bas Drâa Inlier (Anti Atlas region of the West African Craton, WAC) into a single Large Igneous Province (LIP) extending over an area of > 1 million km2, and associated with the final fragmentation of the Columbia (Nuna) supercontinent.

EDTA-assisted leaching of Pb and Cd from contaminated soil.

PubMed

Qiao, Jiangbo; Sun, Huimin; Luo, Xiuhua; Zhang, Wang; Mathews, Shiny; Yin, Xianqiang

2017-01-01

Lead (Pb) and cadmium (Cd) contamination of soil and its harmful effects on human and environmental health have been one concern. In this study, batch and column leaching experiments were conducted to investigate the effects of two EDTA-assisted leaching methods, continuous and intermittent (dry-wet alternate), on the removal of Pb and Cd from contaminated soil. Total content and fractions of Pb and Cd at every 1 cm soil column depth were analyzed before and after the leaching. The results indicated that continuous leaching removed 75.43% of Pb (19.370 mg) and 53.21% of Cd (6.168 mg) and intermittent leaching removed 78.08% of Pb (20.051 mg) and 57.37% of Cd (6.650 mg), which showed intermittent leaching removed more Pb and Cd, but didn't differ significantly (P > 0.05) compared to the continuous leaching. In both leaching methods, total Pb and Cd content in all soil depths reduced after leaching. The two leaching methods made no significant differences in Pb and Cd distributions at different depths of the soil column. Copyright © 2016 Elsevier Ltd. All rights reserved.

Reducing Error Bars through the Intercalibration of Radioisotopic and Astrochronologic Time Scales for the Cenomanian/Turonian Boundary Interval, Western Interior Basin, USA

NASA Astrophysics Data System (ADS)

Meyers, S. R.; Siewert, S. E.; Singer, B. S.; Sageman, B. B.; Condon, D. J.; Obradovich, J. D.; Jicha, B.; Sawyer, D. A.

2010-12-01

We develop a new intercalibrated astrochronologic and radioisotopic time scale for the Cenomanian/Turonian (C/T) boundary interval near the GSSP in Colorado, where orbitally-influenced rhythmic strata host bentonites that contain sanidine and zircon suitable for 40Ar/39Ar and U-Pb dating. This provides a rare opportunity to directly intercalibrate two independent radioisotopic chronometers against an astrochronologic age model. We present paired 40Ar/39Ar and U-Pb ages from four bentonites spanning the Vascoceras diartianum to Pseudaspidoceras flexuosum biozones, utilizing both newly collected material and legacy sanidine samples of Obradovich (1993). Full 2σ uncertainties (decay constant, standard age, analytical sources) for the 40Ar/39Ar ages, using a weighted mean of 33-103 concordant age determinations and an age of 28.201 Ma for Fish Canyon sanidine (FCs), range from ±0.15 to 0.19 Ma, with ages from 93.67 to 94.43 Ma. The traditional FCs age of 28.02 Ma yields ages from 93.04 to 93.78 Ma with full uncertainties of ±1.58 Ma. Using the ET535 tracer, single zircon CA-TIMS 206Pb/238U ages determined from each bentonite record a range of ages (up to 2.1 Ma), however, in three of the four bentonites the youngest single crystal ages are statistically indistinguishable from the 40Ar/39Ar ages calculated relative to 28.201 Ma FCs, supporting this calibration. Using the new radioisotopic data and published astrochronology (Sageman et al., 2006) we develop an integrated C/T boundary time scale using a Bayesian statistical approach that builds upon the strength of each geochronologic method. Whereas the radioisotopic data provide an age with a well-defined uncertainty for each bentonite, the orbital time scale yields a more highly resolved estimate of the duration between stratigraphic horizons, including the radioisotopically dated beds. The Bayesian algorithm yields a C/T time scale that is statistically compatible with the astrochronologic and radioisotopic data, but with smaller uncertainty than either method could achieve alone. The results firmly anchor the floating orbital time scale and yield astronomically-recalibrated radioisotopic ages with full uncertainties that approach the EARTHTIME goal of permil resolution.

Chronology of magmatism and mineralization in the Kassandra mining area, Greece: The potentials and limitations of dating hydrothermal illites

NASA Astrophysics Data System (ADS)

Gilg, H. Albert; Frei, Robert

1994-05-01

Various geochronological methods ( U/Pb, Rb/Sr, and K/Ar) have been applied to constrain the timing of magmatism and polymetallic mineralization in the Kassandra mining district, northern Greece. These data provide the first geochronological evidence that porphyry copper mineralization, proximal copper skarns, and distal high-temperature carbonate-hosted Pb-Zn-Ag-Au replacement ores formed contemporaneously and probably within less than 2 million years. Polymetallic mineralization is temporally related to the emplacement of granodioritic to quartz dioritic porphyries (24-25 Ma) that postdate the largest post-tectonic intrusion of the area, the Stratoni granodiorite (27.9 ± 1.2 Ma). Andesite porphyry dikes, which crosscut the Pb-Zn-Ag-Au ores and associated alterations, represent the last magmatic phase in the area (19.1 ± 0.6 Ma) and did not contribute to metal concentration. The combination of K/Ar, Rb/Sr, and oxygen isotope studies of hydrothermal illite-rich clays and careful granulometric analysis constrains the reliability of these geochronological methods and emphasizes the importance of characterizing the post-formational history of the sample. We identify various processes which partly disturbed the K/Ar and Rb/Sr system of some clays, such as retrograde alteration by heated meteoric waters, superimposed supergene illitization, and resetting of both isotopic systems due to a hydrothermal overprint related to the intrusion of the andesite porphyry. Our data, however, suggest that diffusive Ar loss from the finest clay fractions (< 0.6 μm) during cooling of the hydrothermal system probably played the most important role in the disturbance of the K/Ar system. Conventional K/Ar ages of < 2 μm fractions from high-temperature illites (> 200°C), therefore, do not give reliable formation ages. The loss of Ar may be used to model the cooling history of the hydrothermal system applying the concept of closure temperatures ( DODSON, 1973). 40K- 40Ar rad isochrons of natural, coarser grained (> 0.6 μm) size fractions of illites from single samples, even when slightly contaminated with feldspars, may yield meaningful ages either of the formation or of a reheating event. The Rb/Sr dating of hydrothermal clays is sensitive to contamination by adsorbed strontium, which may not be cogenetic with the clay, as well as feldspars, which may not have been homogenized isotopically by the illitization process.

Diabetic Ephrin-B2-Stimulated Peripheral Blood Mononuclear Cells Enhance Poststroke Recovery in Mice.

PubMed

Hilal, Rose; Poittevin, Marine; Pasteur-Rousseau, Adrien; Cogo, Adrien; Mangin, Gabrielle; Chevauché, Marie; Ziat, Yasmine; Vilar, José; Launay, Jean-Marie; Gautier, Jean-François; Broquères-You, Dong; Levy, Bernard I; Merkulova-Rainon, Tatyana; Kubis, Nathalie

2018-01-01

Clinical trials of cell therapy in stroke favor autologous cell transplantation. To date, feasibility studies have used bone marrow-derived mononuclear cells, but harvesting bone marrow cells is invasive thus complicating bedside treatment. We investigated the therapeutic potential of peripheral blood-derived mononuclear cells (PB-MNC) harvested from diabetic patients and stimulated by ephrin-B2 (PB-MNC+) (500,000 cells), injected intravenously 18-24 hours after induced cerebral ischemia in mice. Infarct volume, neurological deficit, neurogenesis, angiogenesis, and inflammation were investigated as were the potential mechanisms of PB-MNC+ cells in poststroke neurorepair. At D3, infarct volume was reduced by 60% and 49% compared to unstimulated PB-MNC and PBS-treated mice, respectively. Compared to PBS, injection of PB-MNC+ increased cell proliferation in the peri-infarct area and the subventricular zone, decreased microglia/macrophage cell density, and upregulated TGF- β expression. At D14, microvessel density was decreased and functional recovery was enhanced compared to PBS-treated mice, whereas plasma levels of BDNF, a major regulator of neuroplasticity, were increased in mice treated with PB-MNC+ compared to the other two groups. Cell transcriptional analysis showed that ephrin-B2 induced phenotype switching of PB-MNC by upregulating genes controlling cell proliferation, inflammation, and angiogenesis, as confirmed by adhesion and Matrigel assays. Conclusions . This feasibility study suggests that PB-MNC+ transplantation poststroke could be a promising approach but warrants further investigation. If confirmed, this rapid, noninvasive bedside cell therapy strategy could be applied to stroke patients at the acute phase.

Diabetic Ephrin-B2-Stimulated Peripheral Blood Mononuclear Cells Enhance Poststroke Recovery in Mice

PubMed Central

Hilal, Rose; Poittevin, Marine; Pasteur-Rousseau, Adrien; Cogo, Adrien; Mangin, Gabrielle; Chevauché, Marie; Ziat, Yasmine; Vilar, José; Launay, Jean-Marie; Gautier, Jean-François; Broquères-You, Dong; Levy, Bernard I.; Merkulova-Rainon, Tatyana

2018-01-01

Clinical trials of cell therapy in stroke favor autologous cell transplantation. To date, feasibility studies have used bone marrow-derived mononuclear cells, but harvesting bone marrow cells is invasive thus complicating bedside treatment. We investigated the therapeutic potential of peripheral blood-derived mononuclear cells (PB-MNC) harvested from diabetic patients and stimulated by ephrin-B2 (PB-MNC+) (500,000 cells), injected intravenously 18–24 hours after induced cerebral ischemia in mice. Infarct volume, neurological deficit, neurogenesis, angiogenesis, and inflammation were investigated as were the potential mechanisms of PB-MNC+ cells in poststroke neurorepair. At D3, infarct volume was reduced by 60% and 49% compared to unstimulated PB-MNC and PBS-treated mice, respectively. Compared to PBS, injection of PB-MNC+ increased cell proliferation in the peri-infarct area and the subventricular zone, decreased microglia/macrophage cell density, and upregulated TGF-β expression. At D14, microvessel density was decreased and functional recovery was enhanced compared to PBS-treated mice, whereas plasma levels of BDNF, a major regulator of neuroplasticity, were increased in mice treated with PB-MNC+ compared to the other two groups. Cell transcriptional analysis showed that ephrin-B2 induced phenotype switching of PB-MNC by upregulating genes controlling cell proliferation, inflammation, and angiogenesis, as confirmed by adhesion and Matrigel assays. Conclusions. This feasibility study suggests that PB-MNC+ transplantation poststroke could be a promising approach but warrants further investigation. If confirmed, this rapid, noninvasive bedside cell therapy strategy could be applied to stroke patients at the acute phase. PMID:29736174

Phosphorus Amendment Efficacy for In Situ Remediation of Soil Lead Depends on the Bioaccessible Method.

PubMed

Obrycki, John F; Basta, Nicholas T; Scheckel, Kirk; Stevens, Brooke N; Minca, Kristen K

2016-01-01

A validated method is needed to measure reductions of in vitro bioaccessible (IVBA) Pb in urban soil remediated with amendments. This study evaluated the effect of in vitro extraction solution pH and glycine buffer on bioaccessible Pb in P-treated soils. Two Pb-contaminated soils (790-1300 mg Pb kg), one from a garden and one from a city lot in Cleveland, OH, were incubated in a bench scale experiment for 1 yr. Six phosphate amendments, including bone meal, fish bone, poultry litter, monoammonium phosphate, diammonium phosphate, and triple superphosphate, were added to containers at two application rates. Lead IVBA was assessed using USEPA Method 1340 and three modified versions of this method. Modifications included using solutions with pH 1.5 and 2.5 as well as using solutions with and without 0.4 mol L glycine. Soil amendments were ineffective in reducing IVBA Pb in these soils as measured by pH 1.5 with glycine buffer. The greatest reductions in IVBA Pb, from 5 to 26%, were found using pH 2.5 extractions. Lead mineral results showed several soil amendments promoted Pb phosphate formation, an indicator of remediation success. A significant negative linear relationship between reduction in IVBA Pb and Pb-phosphate formation was found only for pH 2.5 without glycine extraction solution. A modified USEPA Method 1340 without glycine and using pH 2.5 has the potential to predict P soil treatment efficacy and reductions in bioavailable Pb. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Isotopic and geothermometric constraints on the structural and metamorphic evolution of Homestake gold deposit, Black Hills, South Dakota (USA)

NASA Astrophysics Data System (ADS)

Terry, M.; Dahl, P.; Frei, R.

2003-04-01

The Homestake Deposit, located in the northern Black Hills and host for 40 million ounces of gold, shows evidence for extensive remobilization of gold related to regional metamorphism deformation associated with the Early Proterozoic assembly of supercontinent Laurentia. Field and petrographic evidence for gold remobilization includes the occurrence of abundant quartz veins associated with selvages of chlorite-siderite-ankerite-pyrrhotite-arsenopyrite-gold in the Homestake Fm. The deposit is located on the western limb of a major anticlinorium that coincides with a vertical N-S-striking garnet isograd, and garnet-biotite geothermometry of metapelites sampled across the anticlinorium indicates a steep metamorphic field gradient of 150^oC/km (east side warmer). This gradient is mirrored by a pronounced fractionation of oxygen isotopes observed in the vein quartz, with δ18O ranging from 10 to 18 ppm. The isograd is parallel with a major N-S-striking shear zone, and kinematic indicators predominantly indicate oblique sinistral motion with east-side up. Garnet was separated from a subsurface sample of the Homestake Fm. collected from the nose of the so-called "main ledge" synform and subjected to Pb stepwise leaching (PbSL) to determine the age of garnet growth and thus metamorphism. PbSL analysis revealed a 207Pb/206Pb age of 1746 ± 10 Ma (± 2σ). Recent work in the southern Black Hills indicates that almandine does not contain sufficient Pb to be dated directly by this method; instead, the PbSL result represents the bulk age of abundant allanite inclusions observed in the garnet. Thus, 1746 Ma is interpreted as a maximum age of prograde garnet growth during regional thermotectonism. Mineral assemblages from selvages in Main Ledge indicate that mineralization occurred at or after peak metamorph, which indicates that 1746 Ma also represents a maximum age for gold remobilization. A minimum 1715 Ma age of these events is indicated by published ages of post-tectonic leucogranite in the Black Hills. Regionally, the N-S orientation, 1746--1715 Ma timing, and sinistral-transpressive motion combine to suggest that this major shear zone in the northern Black Hills represents a northerly extension of the Hartville fault, which is exposed in SE Wyoming, ˜200 km SSW. Correlation of these shear zones would have important implications for Proterozoic terrane assembly in this part of Laurentia.

Monzonitoid magmatism of the copper-porphyritic Lazurnoe deposit (South Primor'e): U-Pb and K-Ar geochronology and peculiarities of ore-bearing magma genesis by the data of isotopic-geochemical studies

NASA Astrophysics Data System (ADS)

Sakhno, V. G.; Kovalenko, S. V.; Alenicheva, A. A.

2011-05-01

Magmatic rocks from the copper-porphyritic Lazurnoe deposit (Central Primor'e) have been studied. It has been found that rocks from the Lazurnyi massif are referred to gabbro-monzodiorites, monzodiorites, and monzo-granodiorites formed during two magmatic phases of different ages. The earlier phase is represented by gabbro-monzodiorites and diorites of the North Stock, and the later one, by gabbro-monzodiorites and monzo-grano-diorites of the South Stock. On the basis of isotopic dating by the U-Pb (SHRIMP) method for zircon and by the K-Ar method for hornblendes and biotites, the age of magmatic rocks is determined at 110 ± 4 for the earlier phase and at 103.5 ± 1.5 for the later one. Examination of the isotopic composition for Nd, Sr, Pb, Hf, δ18O, and REE spectra has shown that melts of the first phase are contaminated with crustal rocks and they are typical for a high degree of secondary alterations. Potassiumfeldspar, biotite, propylitic alterations, and sulfidization are manifested in these rocks. The rocks of the later stage of magmatism are characteristic for a primitive composition of isotopes and the absence of secondary alterations. They carry the features of adakite specifics that allows us to consider them derivatives of mantle generation under high fluid pressure. The intrusion of fluid-saturated melts of the second phase into the magmatic source of the first phase caused both an alteration pattern of rocks and copper-porphyritic mineralization. Isotopes of sulfur and oxygen allow us to consider the ore component to be of magmatic origin.

Improved performance of CdSe/CdS co-sensitized solar cells adopting efficient CuS counter electrode modified by PbS film using SILAR method

NASA Astrophysics Data System (ADS)

Zhang, Xiaolong; Lin, Yu; Wu, Jihuai; Fang, Biaopeng; Zeng, Jiali

2018-04-01

In this paper, CuS film was deposited onto fluorine-doped tin oxide (FTO) substrate using a facile chemical bath deposition method, and then modified by PbS using simple successive ionic layer absorption and reaction (SILAR) method with different cycles. These CuS/PbS films were utilized as counter electrodes (CEs) for CdSe/CdS co-sensitized solar cells. Field-emission scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer was used to characterize the CuS/PbS films. The results show that CuS/PbS (10 cycles) CE exhibits an improved power conversion efficiency of 5.54% under the illumination of one sun (100 mW cm-2), which is higher than the CuS/PbS (0 cycles), CuS/PbS (5 cycles), and CuS/PbS (15 cycles) CEs. This enhancement is mainly attributed to good catalytic activity and lower charge-transfer and series resistances, which have been proved by electrochemical impedance spectroscopy, and Tafel polarization measurements.

Lead isotopes in North Pacific deep water - Implications for past changes in input sources and circulation patterns

USGS Publications Warehouse

van de Flierdt, T.; Frank, M.; Halliday, A.N.; Hein, J.R.; Hattendorf, B.; Gunther, D.; Kubik, P.W.

2003-01-01

The sources of non-anthropogenic Pb in seawater have been the subject of debate. Here we present Pb isotope time-series that indicate that the non-anthropogenic Pb budget of the northernmost Pacific Ocean has been governed by ocean circulation and riverine inputs, which in turn have ultimately been controlled by tectonic processes. Despite the fact that the investigated locations are situated within the Asian dust plume, and proximal to extensive arc volcanism, eolian contributions have had little impact. We have obtained the first high-resolution and high-precision Pb isotope time-series of North Pacific deep water from two ferromanganese crusts from the Gulf of Alaska in the NE Pacific Ocean, and from the Detroit Seamount in the NW Pacific Ocean. Both crusts were dated applying 10 Be/9Be ratios and yield continuous time-series for the past 13.5 and 9.6 Myr, respectively. Lead isotopes show a monotonic evolution in 206Pb/204Pb from low values in the Miocene (??? 18.57) to high values at present day (??? 18.84) in both crusts, even though they are separated by more than 3000 km along the Aleutian Arc. The variation exceeds the amplitude found in Equatorial Pacific deep water records by about three-fold. There also is a striking similarity in 207Pb/204Pb and 208Pb/ 204Pb ratios of the two crusts, indicating the existence of a local circulation cell in the sub-polar North Pacific, where efficient lateral mixing has taken place but only limited exchange (in terms of Pb) with deep water from the Equatorial Pacific has occurred. Both crusts display well-defined trends with age in Pb-Pb isotope mixing plots, which require the involvement of at least four distinct Pb sources for North Pacific deep water. The Pb isotope time-series reveal that eolian supplies (volcanic ash and continent-derived loess) have only been of minor importance for the dissolved Pb budget of marginal sites in the deep North Pacific over the past 6 Myr. The two predominant sources have been young volcanic arcs, one located in the northeastern part and one located in the northwestern part of the Pacific margin, from where material has been eroded and delivered to the ocean, most likely via riverine pathways. ?? 2003 Elsevier Science B.V. All rights reserved.

Removal of lead and cadmium from aqueous solutions by using 4-amino-3-hydroxynaphthalene sulfonic acid-doped polypyrrole films.

PubMed

Sall, Mohamed Lamine; Diaw, Abdou Karim Diagne; Gningue-Sall, Diariatou; Chevillot-Biraud, Alexandre; Oturan, Nihal; Oturan, Mehmet Ali; Fourdrin, Chloé; Huguenot, David; Aaron, Jean-Jacques

2018-03-01

Water pollution by heavy metals is a great health concern worldwide. Lead and cadmium are among the most toxic heavy metals because they are dangerous for the human and aquatic lives. In this work, the removal of lead and cadmium from aqueous solutions has been studied using electrosynthesized 4-amino-3-hydroxynaphthalene-1-sulfonic acid-doped polypyrrole (AHNSA-PPy) films as a new adsorbent. Two distinct methods, including the immersion method, based on the Pb 2+ and Cd 2+ spontaneous removal by impregnation of the polymer in the solution, and the electro-elimination method, consisting of removal of Pb 2+ and Cd 2+ ions from the solution by applying a small electrical current (5 mA) to the polymer film, were developed: the evolution of Pb 2+ and Cd 2+ concentrations with time was monitored by inductively coupled plasma optical emission spectrometry (ICP-OES). The effect of pH on the adsorption and electro-elimination of Pb 2+ and Cd 2+ using the AHNSA-PPy film was investigated and optimized, showing that the ionic adsorption and electro-elimination processes were highly pH-dependent. The kinetics of Pb 2+ and Cd 2+ adsorption and electro-elimination were found to follow second-order curves. The maximum adsorption capacity values of the AHNSA-PPy film were 64.0 and 50.4 mg/g, respectively, for Pb 2+ and Cd 2+ . The removal efficiency values were, respectively, for Pb 2+ and Cd 2+ , 80 and 63% by the immersion method, and 93 and 85% by the electro-elimination method. Application of both methods to Senegal natural waters, fortified with Pb 2+ and Cd 2+ , led to removal efficiency values of, respectively for Pb 2+ and Cd 2+ , 76-77 and 58-59% by the immersion method, and of 82-90 and 80-83%, by the electro-elimination method.

The Age of Rift-Related Basalts in East Antarctica

NASA Astrophysics Data System (ADS)

Leitchenkov, G. L.; Belyatsky, B. V.; Kaminsky, V. D.

2018-01-01

The Lambert Rift, which is a large intracontinental rift zone in East Antarctica, developed over a long period of geological time, beginning from the Late Paleozoic, and its evolution was accompanied by magmatic activity. The latest manifestation of magmatism is eruption of alkaline olivine-leucite basalts on the western side of the Lambert Rift; Rb-Sr dating referred its time to the Middle Eocene, although its genesis remained vague. In order to solve this problem, we found geochronometer minerals in basaltic samples and 68 apatite grains appeared to be suitable for analysis. Their ages and ages of host basalts, determined by the U-Pb local method on the SIMS SHRIMP-II, were significantly different (323 ± 31 Ma) from those assumed earlier. This age corresponds to the earliest stage of crustal extension in East Antarctica and to most of Gondwana. The new data crucially change the ideas about the evolution of Lambert Rift and demonstrate the ambiguity of K-Ar dates of the alkali effusive formed under long-term rifting.

ECOLOGICAL RISKS OF DIOXINS IN LAKE ONTARIO: A TALE OF TWO SEDIMENT CORES

EPA Science Inventory

Sediment box cores have frequently been used to determine organochlorine chemical loading histories of lakes and reservoirs. 137Cs and 210Pb radionuclide dating techniques are employed synchronously with chemical analyses of the contaminants for thin sections extruded from adjace...

Permian A-type rhyolites of the Muráň Nappe, Inner Western Carpathians, Slovakia: in-situ zircon U-Pb SIMS ages and tectonic setting

NASA Astrophysics Data System (ADS)

Ondrejka, Martin; Li, Xian-Hua; Vojtko, Rastislav; Putis, Marian; Uher, Pavel; Sobocký, Tomas

2018-04-01

Three representative A-type rhyolitic rock samples from the Muráň Nappe of the inferred Silicic Unit of the Inner Western Carpathians (Slovakia) were dated using the high-precision SIMS U-Pb isotope technique on zircons. The geochronological data presented in this paper is the first in-situ isotopic dating of these volcanic rocks. Oscillatory zoned zircon crystals mostly revealed concordant Permian (Guadalupian) ages: 266.6 ± 2.4 Ma in Tisovec-Rejkovo (TIS-1), 263.3 ± 1.9 Ma in Telgárt-Gregová Hill (TEL-1) and 269.5 ± 1.8 Ma in Veľká Stožka-Dudlavka (SD-2) rhyolites. The results indicate that the formation of A-type rhyolites and their plutonic equivalents are connected to magmatic activity during the Permian extensional tectonics and most likely related to the Pangea supercontinent break-up.

Historical records of mercury, lead, and polycyclic aromatic hydrocarbons depositions in a dated sediment core from the Eastern Mediterranean.

PubMed

Azoury, S; Tronczyński, J; Chiffoleau, J-F; Cossa, D; Nakhlé, K; Schmidt, S; Khalaf, G

2013-07-02

Depth profiles of mercury, lead and its stable isotopes, and polycyclic aromatic hydrocarbons were determined in a dated sediment core from the Levantine basin. Sedimentary records show that preindustrial fluxes and levels of Hg, Pb, and PAHs remained generally constant in the region before 1850. An almost concurrent uniform increase of both metals and PAHs deposition occurring at the beginning of the Industrial Revolution suggests coal combustion as a main source of these contaminants in the Levantine basin after the 1850s. However, none of the contaminant profiles indicates a decline after 1950-60, the characteristic period of coal use reduction. The modern fluxes of Hg and Pb reveal a 3- to 5-fold increase over preindustrial loads, while the contemporaneous flux of PAHs rises by 4-7 times. On the whole, records in the Eastern Mediterranean suggest atmospheric inputs from relatively distant sources, likely from Central and Eastern Europe.

Green synthesis, spectroscopic investigation and photocatalytic activity of lead nanoparticles.

PubMed

Elango, Ganesh; Roopan, Selvaraj Mohana

2015-03-15

Most of researcher focused their research towards synthesize of nanoparticles by the method of applied chemical method which was one of the costliest method. We have focused cheapest and simplest method for the synthesizing of lead nanoparticles (Pb-NPs) using cocos nucifera L extract. The methanolic extract of cocos nucifera L was efficiently used as a reducing agent for synthesizing Pb-NPs. On treatment of lead acetate with cocos nucifera coir extracts, stable Pb-NPs were formed. The synthesized Pb-NPs were further confirmed by UV-visible spectroscopy, X-ray diffraction (XRD), Transmission electron microscope (TEM) and Energy Dispersive (EDAX) analysis. The secondary metabolites present in methanolic extract which can mainly act as a reducing and capping agents for the formation of Pb-NPs were identified by GC-MS. Anti-microbial activity for Pb-NPs against four pathogenic strain's such as Staphylococcus aureus, Escheria coli, Staphylococcus epidermis and Bacillus subtilis. Result states that Pb-NPs size was 47 nm and also shows good activity against S. aureus. Further we report on photocatalytic absorption of malachite green dye processed in short UV wavelength at 254 nm. UV spectral analysis showed peak absorbance at 613 nm with special reference to the excitation of surfaces plasmon vibration by Pb-NPs. Copyright © 2014 Elsevier B.V. All rights reserved.

Green synthesis, spectroscopic investigation and photocatalytic activity of lead nanoparticles

NASA Astrophysics Data System (ADS)

Elango, Ganesh; Roopan, Selvaraj Mohana

2015-03-01

Most of researcher focused their research towards synthesize of nanoparticles by the method of applied chemical method which was one of the costliest method. We have focused cheapest and simplest method for the synthesizing of lead nanoparticles (Pb-NPs) using cocos nucifera L extract. The methanolic extract of cocos nucifera L was efficiently used as a reducing agent for synthesizing Pb-NPs. On treatment of lead acetate with cocos nucifera coir extracts, stable Pb-NPs were formed. The synthesized Pb-NPs were further confirmed by UV-visible spectroscopy, X-ray diffraction (XRD), Transmission electron microscope (TEM) and Energy Dispersive (EDAX) analysis. The secondary metabolites present in methanolic extract which can mainly act as a reducing and capping agents for the formation of Pb-NPs were identified by GC-MS. Anti-microbial activity for Pb-NPs against four pathogenic strain's such as Staphylococcus aureus, Escheria coli, Staphylococcus epidermis and Bacillus subtilis. Result states that Pb-NPs size was 47 nm and also shows good activity against S. aureus. Further we report on photocatalytic absorption of malachite green dye processed in short UV wavelength at 254 nm. UV spectral analysis showed peak absorbance at 613 nm with special reference to the excitation of surfaces plasmon vibration by Pb-NPs.

A rapid and reliable method for Pb isotopic analysis of peat and lichens by laser ablation-quadrupole-inductively coupled plasma-mass spectrometry for biomonitoring and sample screening.

PubMed

Kylander, M E; Weiss, D J; Jeffries, T E; Kober, B; Dolgopolova, A; Garcia-Sanchez, R; Coles, B J

2007-01-16

An analytical protocol for rapid and reliable laser ablation-quadrupole (LA-Q)- and multi-collector (MC-) inductively coupled plasma-mass spectrometry (ICP-MS) analysis of Pb isotope ratios ((207)Pb/(206)Pb and (208)Pb/(206)Pb) in peats and lichens is developed. This technique is applicable to source tracing atmospheric Pb deposition in biomonitoring studies and sample screening. Reference materials and environmental samples were dry ashed and pressed into pellets for introduction by laser ablation. No binder was used to reduce contamination. LA-MC-ICP-MS internal and external precisions were <1.1% and <0.3%, respectively, on both (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios. LA-Q-ICP-MS internal precisions on (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios were lower with values for the different sample sets <14.3% while external precisions were <2.9%. The level of external precision acquired in this study is high enough to distinguish between most modern Pb sources. LA-MC-ICP-MS measurements differed from thermal ionisation mass spectrometry (TIMS) values by 1% or less while the accuracy obtained using LA-Q-ICP-MS compared to solution MC-ICP-MS was 3.1% or better using a run bracketing (RB) mass bias correction method. Sample heterogeneity and detector switching when measuring (208)Pb by Q-ICP-MS are identified as sources of reduced analytical performance.

Determination of total lead in lipstick: development and validation of a microwave-assisted digestion, inductively coupled plasma-mass spectrometric method.

PubMed

Hepp, Nancy M; Mindak, William R; Cheng, John

2009-01-01

Recent reports describing the presence of lead (Pb) in lipsticks have suggested that, under ordinary use, the potential amount of Pb exposure is harmful. To permit independent assessment of the Pb contamination, a method for determining total Pb in lipstick using microwave-assisted digestion and analysis employing inductively coupled plasma-mass spectrometry (ICP-MS) was developed and validated. Since lipsticks may contain fats, oils, pigments, dyes, and minerals, several reference materials (RM) were analyzed, including coal, wear metals in oil, organic Pb in oil, milk powder, and estuarine sediment. With the exception of the RM with mineral content (estuarine sediment), complete recovery of Pb from the RMs was obtained by simple nitric acid (HNO(3)) digestion. Complete recovery of Pb from estuarine sediment was achieved only when hydrofluoric acid (HF) was added to the digestion mix, followed by treatment with excess boric acid (H(3)BO(3)) to neutralize the HF and to dissolve insoluble fluorides. Commercial lipsticks were tested for total Pb by the validated method. The detection limit was estimated to be 0.04 microg Pb/g. The average value obtained for the lipsticks was 1.07 microg/g. Undigested material was present in some lipstick digests when only HNO(3) was used, and generally lower Pb values were obtained. All of the Pb levels found by the U.S. Food and Drug Administration (FDA) were within the range the agency would expect to find in lipsticks formulated with permitted color additives and other ingredients prepared under good manufacturing practice (GMP) conditions. This method will be useful for the FDA and industry in helping to ensure the safety of cosmetic products.

Tsunami Evidence in South Coast Java, Case Study: Tsunami Deposit along South Coast of Cilacap

NASA Astrophysics Data System (ADS)

Rizal, Yan; Aswan; Zaim, Yahdi; Dwijo Santoso, Wahyu; Rochim, Nur; Daryono; Dewi Anugrah, Suci; Wijayanto; Gunawan, Indra; Yatimantoro, Tatok; Hidayanti; Herdiyani Rahayu, Resti; Priyobudi

2017-06-01

Cilacap Area is situated in coastal area of Southern Java and directly affected by tsunami hazard in 2006. This event was triggered by active subduction in Java Trench which active since long time ago. To detect tsunami and active tectonic in Southern Java, paleo-tsunami study is performed which is targeted paleo-tsunami deposit older than fifty years ago. During 2011 - 2016, 16 locations which suspected as paleo-tsunami location were visited and the test-pits were performed to obtain characteristic and stratigraphy of paleo-tsunami layers. Paleo-tsunami layer was identified by the presence of light-sand in the upper part of paleo-soil, liquefaction fine grain sandstone, and many rip-up clast of mudstone. The systematic samples were taken and analysis (micro-fauna, grainsize and dating analysis). Micro-fauna result shows that paleo-tsunami layer consist of benthonic foraminifera assemblages from different bathymetry and mixing in one layer. Moreover, grainsize shows random grain distribution which characterized as turbulence and strong wave deposit. Paleo-tsunami layers in Cilacap area are correlated using paleo-soil as marker. There are three paleo-tsunami layers and the distribution can be identified as PS-A, PS-B and PS-C. The samples which were taken in Glempang Pasir layer are being dated using Pb - Zn (Lead-Zinc) method. The result of Pb - Zn (Lead-Zinc) dating shows that PS-A was deposited in 139 years ago, PS-B in 21 years ago, and PS C in 10 years ago. This result indicates that PS -1 occurred in 1883 earthquake activity while PS B formed in 1982 earthquake and PS-C was formed by 2006 earthquake. For ongoing research, the older paleo-tsunami layers were determined in the Gua Nagaraja, close to Selok location and 6 layers of Paleo-tsunami suspect found which shown a similar characteristic with the layers from another location. The three layers deeper approximately have an older age than another location in Cilacap.

The sequential use of washing and an electrochemical reduction process for the remediation of lead-contaminated soils.

PubMed

Demir, Aydeniz; Köleli, Nurcan

2013-01-01

A two-step method for the remediation of three different types of lead (Pb)-contaminated soil was evaluated. The first step included soil washing with ethylenediaminetetraacetic acid (EDTA) to remove Pb from soils. The washing experiments were performed with 0.05 M Na2EDTA at 1:10 soil to liquid ratio. Following the washing, Pb removal efficiency from soils ranged within 50-70%. After the soil washing process, Pb2+ ions in the washing solution were reduced electrochemically in a fixed-bed reactor. Lead removal efficiency with the electrochemical reduction at -2.0 V potential ranged within 57-76%. The overall results indicate that this two-step method is an environmentally-friendly and effective technology to remediate Pb-contaminated soils, as well as Pb-contaminated wastewater treatment due to the transformation of toxic Pb2+ ions into a non-hazardous metallic form (Pb(0)).

Ore genesis dating: implication of Sm-Nd method using sulfide minerals for mafic-ultramafic layered intrusions of Fennoscandian Shield

NASA Astrophysics Data System (ADS)

Serov, Pavel; Bayanova, Tamara; Steshenko, Ekaterina; Ekimova, Nadezhda

2015-04-01

The main method of dating the ore process was the Re-Os method of sulfides (Luck, Allegre, 1983; Walker et. al., 1991). However, studies of Re-Os systematics of sulfide minerals do not always give the correct ages and showing the disturbances of the Re-Os systematics. At the same time, Sm-Nd age of sulfides in good agreement with the U-Pb dating on zircon and baddeleyite and suggests that the Sm-Nd system of sulfides is more resistant to secondary alteration processes. Our studies have shown that along with rock-forming, ore minerals (sulfides) can be used to determine the ore genesis time of industrially important geological sites, since exactly with the sulfides the industry Pt-Pd mineralization is closely connected. In to Sm-Nd measurements steadily introduce new minerals-geochronometers (i.e. titanite, burbancite, eudialite etc.). Of these, sulfides of PGE-bearing layered intrusions are quite important in terms of dating the process of ore origin. Studying the REE distribution in the sulfides of MOR hydrothermal sources has shown possible REE presence in the sulfide lattice (Rimskaya-Korsakova et. al., 2003). These are difficult to carry out because the concentrations of Sm and Nd isotopes in sulfides are much lower than those in chondrites (Rimskaya-Korsakova et. al., 2003). In (Kong et. al., 2000) sulfides from two metamorphosed chondrites were studied by instrumental neutron activation analysis (INAA) and ion probe. As shown, the level of REE in the sulfide phase determined by the ion probe is quite similar to that obtained by INAA. Although the concentrations of REE in the enstatite and the Fe, Si, Cr-rich inclusions are comparable to those in sulfide, estimates based on mass balance calculations show that the silicate inclusions would not noticeably contribute to the REE budget in sulfides (Kong et. al., 2000). For the first time in Russian geochemistry laboratories using sulfide and rock-forming minerals and WR in Sm-Nd method have been dated impregnated and brecciform ores of the following objects - Pilguyarvi Cu-Ni deposits, Pechenga (1965±87 Ma); impregnated (2433±83 Ma) and redeposited (1903±24 Ma) ores of Ahmavaara intrusion (Finland); Kolvitsa massif metagabbro (1990±92 Ma, which reflect the age of Sm-Nd system closure in sulfide minerals); olivine orthopyroxenites of Sopcha 'Ore bed' (2442±59 Ma); ore gabbronorites of Penikat PGE-bearing layered intrusion (2426±38 Ma (Ekimova et.al., 2011); Pt-Pd gabbro-pegmatite ores (2476± 41 Ma, which agrees well with the U-Pb zircon age - 2470±9 Ma (Bayanova, 2004) and gabbronorites (2483±86 Ma) of PGE Kievey deposit and Fedorova Tundra metagabbroids (2494±54 Ma); Monchetundra gabbronorites - 2489±49 Ma. All investigations are devoted to memory of academician RAS, professor F. Mitrofanov (Russia), he was a leader of scientific school for geology, geochemistry and metallogenesis of ore deposits. The studies were supported by the RFBR 13-05-00493, OFI-M 13-05-12055, Department of Earth Sciences RAS (programs 2 and 4), IGCP-599.

U-Pb Geochronology and Hf-isotope constrains on Formation of Archaean Crust From the Lewisian of NW Scotland, Great Britain

NASA Astrophysics Data System (ADS)

Crowley, Q. G.; Noble, S. R.; Key, R.

2006-12-01

The Lewisian complex of NW Scotland is dominantly composed of Archaean tonalitic to granodioritic gneisses, ultramafic bodies and minor metasedimentary components. Although the area is internationally well known and has been much studied for over a century, the precise timing of crustal forming events has proven difficult to ascertain. We present data from both in-situ laser ablation (LA) ICP-MS and an adaptation of a new U-Pb chemical abrasion ID-TIMS technique (Mattinson 2006) applied to multi-age component zircons from the Assynt block of this region. The new data reveal a previously unrecognised complexity and provide the first unequivocal proof of an Archean metamorphic event in the area. In a wider context the data also elucidate some of the processes involved in early global crust formation and plate tectonic events. In-situ LA-ICPMS U-Pb dating has indicated a ca 2.8Ga protolith age for a tonalite gneiss with evidence for a ca. 3.6Ga xenocrystic component (the oldest discovered in the UK). Non-conventional U-Pb ID-TIMS utilising a combination of high-temperature annealing followed by multi-step incremental dissolution on single grains has dated zircon growth at ca 2.7Ga (Badcallian) and 2.5Ga (Inverian) with later Pb-loss occurring at ca 1.9Ga and ca 1.7Ga (early and late Laxfordian respectively). This latter method combines a pseudo-spatial resolution normally associated with an in-situ technique but benefits from the high-precision analysis of ID-TIMS. Zircon Hf isotopes indicate that some rocks from the Assynt area are typical of Archaean continental crust (epsilon Hf ca -1. The tonalite gneisses however have strongly negative epsilon Hf values of -7 to -10 indicating a more complex history of derivation through partial melting of ancient crust with residual garnet as a long- lived control on Hf. Archaean events at ca. 3.6Ga, ca 2.8Ga and ca 2.7Ga have also been recorded in west Greenland (e.g. Mojzsis & Harrison 1999, Richards and Appel, 1987, Whitehouse et al 1999). This points towards widespread and important crustal forming events. Locally in Assynt in the Lewisian of NW Scotland these events are recorded with zircon crystallisation from a magma at ca 3.6Ga, partial melting and crustal recycling producing the tonalite gneiss protoliths at ca 2.8Ga, a prolonged lower crustal residence in granulite P-T conditions by ca 2.7Ga, further metamorphism in amphibolite conditions at ca 2.5Ga and later deformation associated with punctuated terrane amalgamation events between ca 1.9Ga and ca 1.7Ga.

CONSTRAINTS ON EXHUMATION AND SEDIMENTS PROVENANCE DURING PALEOGENE IN THE NORTHERN PYRENEES (FRANCE) USING DETRITAL AFT, ZHe AND Z(U/Pb) THERMOCHRONOLOGY

NASA Astrophysics Data System (ADS)

Filleaudeau, P.; Mouthereau, F.; Fellin, M.; Pik, R.; Lacombe, O.

2009-12-01

The Pyrenees are a doubly vergent orogenic wedge built by the convergence between the subducting Iberian microplate and the European plate lasting from late Cretaceous to early Miocene. The backbone of the Pyrenean belt (Axial Zone) consists in a stack of thrusts units composed of Paleozoic series intruded by late-Variscan granitoids. Both pro- and retro-wedge sides of the Pyrenees are fold-and-thrust belts made of Meso-Cenozoic sediments thrusted onto the Ebro and Aquitaine foreland basins. The deep structure, highlighted by the ECORS profile, shows a strong asymmetry caused by the southward migration of deformation associated with the development of a Paleogene antiformal stack emplaced during wedge growth in the Iberian plate. The present study focuses on the synorogenic deposits of the retro-foreland basin in the northern part of the belt. To examine the source rocks and quantify the exhumation rates, we combine fission track thermochronometry on detrital apatites with Helium diffusion and U/Pb thermochronometry on zircons. Due to the very high closure temperature of the U/Pb system and the wide range of age distribution, the U/Pb method, that provides zircon crystallisation ages, is a powerful tool to distinguish the various eroded sources feeding the North Pyrenean basin. Thus, we can separate grains coming from Variscan intrusive basement with ages around 310 Ma from younger grains coming from Permian or Triassic to lower Jurassic volcanics. Zircon ages of 220 Ma found in the Paleocene sandstones point to the Triassic volcanic rocks (the so-called “ophites”) as the main source of detrital grains. We infer that Paleozoic units of the Axial Zone were not outcropping in the Paleocene catchments. Exhumation rates are estimated through apatite fission track grain-age distributions and (U-Th)/He dating for two Lutetian and Bartonian synorogenic sandstone samples of the North Pyenean foreland basin. The first results obtained with AFT dating show two main grain populations, with ages ranging from Albian (around 100 Ma) to Paleocene-Eocene (50-60 Ma). These cooling ages are interpreted as related to the Albian post-rift exhumation and the syn-collisional exhumation, respectively. We finally estimate constant exhumation rates of 0.3-0.4km/Ma of the Paleozoic granitoides of the Axial Zone during the Lutetian. Since Paleocene Z(U/Pb) in the sandstones are essentially younger than in situ basement ages, we conclude that the Paleozoic basement of the Axial Zone was not exhumed at the surface before the Lutetian. This brings us new constraints on the timing of Pyrenean wedge growth along ECORS profile.

Pseudorapidity and transverse momentum dependence of flow harmonics in pPb and PbPb collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sirunyan, Albert M; et al.

2017-10-21

Measurements of azimuthal angular correlations are presented for high-multiplicity pPb collisions atmore » $$\\sqrt{s_\\mathrm{NN}}=$$ 5.02 TeV and peripheral PbPb collisions at $$\\sqrt{s_\\mathrm{NN}}=$$ 2.76 TeV. The data used in this work were collected with the CMS detector at the CERN LHC. Fourier coefficients as functions of transverse momentum and pseudorapidity are studied using the scalar product method, 4-, 6-, and 8-particle cumulants, and the Lee-Yang zeros technique. The influence of event plane decorrelation is evaluated using the scalar product method and found to account for most of the observed pseudorapidity dependence.« less

Metabolic profiling of root exudates from two ecotypes of Sedum alfredii treated with Pb based on GC-MS

NASA Astrophysics Data System (ADS)

Luo, Qing; Wang, Shiyu; Sun, Li-Na; Wang, Hui

2017-01-01

Phytoremediation is an effective method to remediate Pb-contaminated soils and root exudates play an important role in this process. Based on gas chromatography-mass spectrometry (GC-MS) and metabolomics method, this study focuses on the comparative metabolic profiling analysis of root exudates from the Pb-accumulating and non-accumulating ecotypes of Sedum alfredii treated with 0 and 50 μmol/L Pb. The results obtained show that plant type and Pb stress can significantly change the concentrations and species of root exudates, and fifteen compounds were identified and assumed to be potential biomarkers. Leaching experiments showed that l-alanine, l-proline and oxalic acid have a good effect to activate Pb in soil, glyceric acid and 2-hydroxyacetic acid have a general effect to activate Pb in soil. 4-Methylphenol and 2-methoxyphenol might be able to activate Pb in soil, glycerol and diethyleneglycol might be able to stabilize Pb in soil, but these activation effect and stabilization effect were all not obvious.

A simple fabrication of CH3NH3PbI3 perovskite for solar cells using low-purity PbI2

NASA Astrophysics Data System (ADS)

Guo, Nanjie; Zhang, Taiyang; Li, Ge; Xu, Feng; Qian, Xufang; Zhao, Yixin

2017-01-01

The CH3NH3PbI3 (MAPbI3) perovskite was usually prepared by high-purity PbI2 with high cost. The low cost and low-purity PbI2 was seldom reported for fabrication of MAPbI3 because it cannot even dissolve well in widely adopted solvent of DMF. We developed an easy method to adapt low-purity PbI2 for fabrication of high quality MAPbI3 just by the simple addition of some hydrochloric acid into the mixture of low-purity PbI2, MAI and DMF. This straightforward method can not only help dissolve the low quality PbI2 by reacting with some impurities in DMF, but also lead to a successful fabrication of high-quality perovskite solar cells with up to 14.80% efficiency comparable to the high quality PbI2 precursors. Project supported by the National Natural Science Foundation of China (Nos. 51372151, 21303103) and Houyingdong Grant (No. 151046).

Post-collisional alkaline magmatism as gateway for metal and sulfur enrichment of the continental lower crust

NASA Astrophysics Data System (ADS)

Fiorentini, Marco L.; LaFlamme, Crystal; Denyszyn, Steven; Mole, David; Maas, Roland; Locmelis, Marek; Caruso, Stefano; Bui, Thi-Hao

2018-02-01

Mafic and ultramafic magmas that intrude into the lower crust can preserve evidence for metal and sulfur transfer from the lithospheric mantle into the lower continental crust. Here we focus on a series of ultramafic, alkaline pipes in the Ivrea Zone (NW Italy), which exposes deeply buried (6-11 kbar), migmatitic metasedimentary rocks intruded by voluminous basaltic magmas of the Mafic Complex, a major crustal underplating event precisely dated via U/Pb CA-IDTIMS on zircon at 286.8 ± 0.4 Ma. The ultramafic pipes postdate the Mafic Complex and from 100 to 300 m wide cumulate-rich conduits. They are hydrated and carbonated, have unusually high incompatible element concentrations and contain blebby and semi-massive Ni-Cu-PGE sulfide mineralisation. The sulfides occur as coarse intergranular nodules (>10 mm) and as small intragranular blebs (<1 mm) hosted in olivine, and have homogeneous, mantle-like δ34S (+1.35 ± 0.25‰). This homogeneity suggests that the pipes reached sulfide supersaturation without addition of crustal sulfur, and that the δ34S signature is representative of the continental lithospheric mantle. One of the pipes, the 249 Ma Valmaggia pipe, carries a very distinctive Sr-Nd-Hf-Pb isotopic composition in its core (87Sr/86Sr 0.70250, εNd-18, εHf-18, 206Pb/204Pb 16.0, 207Pb/204Pb 15.16, 208Pb/204Pb 35.87), very different from the margin of this pipe and from other pipes that have higher 87Sr/86Sr, εNd and 206Pb/204Pb. The unusual isotopic composition of the Valmaggia pipe requires a source with long-term (2500-1500 million years) U-, Th- and Rb-depletion and LREE enrichment. Such compositions are found in Late Archean/Early Proterozoic granulites and lower crustal xenoliths. We suggest that the unusual isotopic composition of the Valmaggia pipe reflects contamination of the mantle source of the pipe with a crustal component that is neither represented in the local Paleozoic crust nor in the isotopically anomalous hydrated mantle inferred as the source of the large-volume mafic underplate that formed the Mafic Complex. During post-collisional gravitational collapse of the Variscan Orogen, this source produced the alkaline, metal (Ni, Cu, PGE)- and volatile (H2O, CO2, S)-rich mafic-ultramafic magma that formed the deep-crustal intrusion at Valmaggia. U/Pb dating of other chemically and geologically comparable pipes in the area shows that this process was active over at least 40 Ma. The Ivrea pipes illustrate how the lower continental crust can be fertilised with mantle-derived metals and volatiles, which are available for later remobilisation into upper-crustal ore systems. World-class mineral deposits along the margins of lithospheric blocks may thus be the result of both favourable crustal architecture (focussing of magmas and fluids) and localised volatile and metal enrichment of the lower crust related to mantle-derived hydrous metasomatism.

Interpreting U-Pb data from primary and secondary features in lunar zircon

NASA Astrophysics Data System (ADS)

Grange, M. L.; Pidgeon, R. T.; Nemchin, A. A.; Timms, N. E.; Meyer, C.

2013-01-01

In this paper, we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon U-Pb isotopic systems and the significance of these features for understanding lunar processes. Lunar zircons can be classified according to: (i) textural relationships between zircon and surrounding minerals in the host breccias, (ii) the internal microstructures of the zircon grains as identified by optical microscopy, cathodoluminescence (CL) imaging and electron backscattered diffraction (EBSD) mapping and (iii) results of in situ ion microprobe analyses of the Th-U-Pb isotopic systems. Primary zircon can occur as part of a cogenetic mineral assemblage (lithic clast) or as an individual mineral clast and is unzoned, or has sector and/or oscillatory zoning. The age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data. A secondary set of microstructures, superimposed on primary zircon, include localised recrystallised domains, localised amorphous domains, crystal-plastic deformation, planar deformation features and fractures, and are associated with impact processes. The first two secondary microstructures often yield internally consistent and close to concordant U-Pb ages that we interpret as dating impact events. Others secondary microstructures such as planar deformation features, crystal-plastic deformation and micro-fractures can provide channels for Pb diffusion and result in partial resetting of the U-Pb isotopic systems.

40 Ma of hydrothermal W mineralization during the Variscan orogenic evolution of the French Massif Central revealed by U-Pb dating of wolframite

NASA Astrophysics Data System (ADS)

Harlaux, Matthieu; Romer, Rolf L.; Mercadier, Julien; Morlot, Christophe; Marignac, Christian; Cuney, Michel

2018-01-01

We present U-Pb thermal ionization mass spectrometer (TIMS) ages of wolframite from several granite-related hydrothermal W±Sn deposits in the French Massif Central (FMC) located in the internal zone of the Variscan belt. The studied wolframite samples are characterized by variable U and Pb contents (typically <10 ppm) and show significant variations in their radiogenic Pb isotopic compositions. The obtained U-Pb ages define three distinct geochronological groups related to three contrasting geodynamic settings: (i) Visean to Namurian mineralization (333-327 Ma) coeval with syn-orogenic compression and emplacement of large peraluminous leucogranites (ca. 335-325 Ma), (ii) Namurian to Westphalian mineralization (317-315 Ma) synchronous with the onset of late-orogenic extension and emplacement of syn-tectonic granites (ca. 315-310 Ma) and (iii) Stephanian to Permian mineralization (298-274 Ma) formed during post-orogenic extension contemporaneous with the Permian volcanism in the entire Variscan belt. The youngest ages (276-274 Ma) likely reflect the reopening of the U-Pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration (e.g. ferberitization). Our results demonstrate that W(±Sn) mineralization in the FMC formed during at least three distinct hydrothermal events in different tectono-metamorphic settings over a time range of 40 Ma.

High precision time calibration of the Permian-Triassic boundary mass extinction event in a deep marine context

NASA Astrophysics Data System (ADS)

Baresel, Björn; Bucher, Hugo; Brosse, Morgane; Bagherpour, Borhan; Schaltegger, Urs

2015-04-01

To construct a revised and high resolution calibrated time scale for the Permian-Triassic boundary (PTB) we use (1) high-precision U-Pb zircon age determinations of a unique succession of volcanic ash layers interbedded with deep water fossiliferous sediments in the Nanpanjiang Basin (South China) combined with (2) accurate quantitative biochronology based on ammonoids, conodonts, radiolarians, and foraminifera and (3) tracers of marine bioproductivity (carbon isotopes) across the PTB. The unprecedented precision of the single grain chemical abrasion isotope-dilution thermal ionization mass spectrometry (CA-ID-TIMS) dating technique at sub-per mil level (radio-isotopic calibration of the PTB at the <100 ka level) now allows calibrating magmatic and biological timescales at resolution adequate for both groups of processes. Using these alignments allows (1) positioning the PTB in different depositional setting and (2) solving the age contradictions generated by the misleading use of the first occurrence (FO) of the conodont Hindeodus parvus, whose diachronous first occurrences are arbitrarily used for placing the base of the Triassic. This new age framework provides the basis for a combined calibration of chemostratigraphic records with high-resolution biochronozones of the Late Permian and Early Triassic. Here, we present new single grain U-Pb zircon data of volcanic ash layers from two deep marine sections (Dongpan and Penglaitan) revealing stratigraphic consistent dates over several volcanic ash layers bracketing the PTB. These analyses define weighted mean 206Pb/238U ages of 251.956±0.033 Ma (Dongpan) and 252.062±0.043 Ma (Penglaitan) for the last Permian ash bed. By calibration with detailed litho- and biostratigraphy new U-Pb ages of 251.953±0.038 Ma (Dongpan) and 251.907±0.033 Ma (Penglaitan) are established for the onset of the Triassic.

Neoproterozoic transpression and granite magmatism in the Gavilgarh-Tan Shear Zone, central India: Tectonic significance of U-Pb zircon and U-Th-total Pb monazite ages

NASA Astrophysics Data System (ADS)

Chattopadhyay, Anupam; Chatterjee, Amitava; Das, Kaushik; Sarkar, Arindam

2017-10-01

The Gavilgarh-Tan Shear Zone (GTSZ) is a crustal-scale shear/fault zone that dissects the unclassified basement gneisses separating two major supracrustal belts, viz. the Paleo- to Mesoproterozoic (≥1.5 Ga) Betul Belt and the Neoproterozoic (∼1.0 Ga) Sausar Belt, of the Central Indian Tectonic Zone (CITZ). The GTSZ extends for more than 300 km strike length, partly covered by the Deccan Trap flows. Granitoid rocks ranging from syenogranite to granodiorite in composition, sheared at temperatures corresponding to the amphibolite facies metamorphic condition, define the GTSZ in the Kanhan River Valley. Earlier geological studies have suggested that the GTSZ underwent a sinistral-sense partitioned transpression in response to an oblique collision between two continental fragments, possibly related to crustal thickening and high-pressure granulite metamorphism (the Ramakona-Katangi granulite: RKG) in the northern part of the Sausar Belt. LA-ICP-MS U-Pb dating of zircon and EPMA U-Th-total Pb dating of monazite grains from four different types of syn-tectonic granitoids of the GTSZ carried out in the present study show that granitoids intruded the basement gneisses between 1.2 Ga and 0.95 Ga, given the error limit of the calculated ages. The age of transpression and mylonitization is more definitely bracketed between 1.0 Ga and 0.95 Ga, which correlates well with the published ages of deformation and metamorphism in the Sausar Belt. This age data strongly supports the suggested collisional tectonic model involving the GTSZ and the RKG granulites of the Sausar Belt and underlines a Grenvillian-age tectonic history for the southern part of the Central Indian Tectonic Zone (CITZ), which possibly culminated in the crustal assembly of the Neoproterozoic supercontinent Rodinia.

New igneous zircon Pb/Pb and metamorphic Rb/Sr ages in the Yaounde Group (Cameroon, Central Africa): implications for the Central African fold belt evolution close to the Congo Craton

NASA Astrophysics Data System (ADS)

Owona, Sébastien; Tichomirowa, Marion; Ratschbacher, Lothar; Ondoa, Joseph Mvondo; Youmen, Dieudonné; Pfänder, Jörg; Tchoua, Félix M.; Affaton, Pascal; Ekodeck, Georges Emmanuel

2012-10-01

Three meta-igneous bodies from the Yaounde Group have been analyzed for their petrography, geochemistry, and 207Pb/206Pb zircon ages. According to their geochemical patterns, they represent meta-diorites. The meta-plutonites yielded identical zircon ages with a mean of 624 ± 2 Ma interpreted as their intrusion age. This age is in agreement with previously published zircon ages of meta-diorites from the Yaounde Group. The meta-diorites derived mainly from crustal rocks with minor contribution from mantle material. The 87Rb/86Sr isochron ages of one meta-diorite sample and three meta-sedimentary host rocks are significantly younger than the obtained intrusion age. Therefore, they are not related to igneous processes. 87Rb/86Sr isochron ages differ from sample to sample (599 ± 3, 572 ± 4, 554 ± 5, 540 ± 5 Ma) yielding the oldest Neoproterozoic age (~600 Ma) for a paragneiss sample at a more northern location. The youngest Rb/Sr isochron age (~540 Ma) was obtained for a mica schist sample at a more southern location closer to the border of the Congo Craton. The 87Rb/86Sr whole rock-biotite ages are interpreted as cooling ages related to transpressional processes during exhumation. Therefore, several discrete metamorphic events related to the exhumation of the Yaounde Group were dated. It could be shown by Rb/Sr dating for the first time that these late tectonic processes occurred earlier at more distant northern locations of the Yaounde Group and lasted at least until early Cambrian (~540 Ma) more closely to the border of the Congo Craton.

Ore genesis and geodynamic setting of the Lianhuashan porphyry tungsten deposit, eastern Guangdong Province, SE China: constraints from muscovite 40Ar-39Ar and zircon U-Pb dating and Hf isotopes

NASA Astrophysics Data System (ADS)

Liu, Peng; Mao, Jingwen; Pirajno, Franco; Jia, Lihui; Zhang, Feng; Li, Yang

2017-12-01

The Lianhuashan deposit has long been regarded as a typical tungsten porphyry deposit, located in the eastern Guangdong Province, in the Southeastern Coastal Metallogenic Belt (SCMB). LA-MC-ICP-MS zircon U-Pb dating of the quartz porphyry yielded a weighted mean 206Pb/238U age of 137.3 ± 2.0 Ma, which is interpreted as the emplacement age of the quartz porphyry. Hydrothermal muscovite yielded a plateau 40Ar/39Ar age of 133.2 ± 0.9 Ma, which is consistent with the zircon U-Pb age, suggesting that the tungsten mineralization is genetically related to the quartz porphyry. Combined with previous studies, we suggest that there is a 145-135 Ma episode linking the granitic magmas with W-Sn ore systems in the SCMB. Zircon ɛHf (t) values of the quartz porphyry are in range of - 3.8 to 0.9, and the two-stage Hf model ages (TDM2) are 1.1-1.4 Ga, which is younger than the basement rocks in the Cathaysia Block (1.8-2.2 Ga), signifying that the quartz porphyry was predominantly derived from melting of Mesoproterozoic crust containing variable amounts of mantle components. In combination with the newly recognized coeval alkaline/bimodal magmatism and A-type granites in eastern Guangdong, we suggest that the 145-135 Ma W-Sn metallogenic event of the SCMB is related to a geodynamic setting of large-scale lithospheric extension and thinning, which can be ascribed to melting of the crust caused by mantle upwelling, triggered by the oblique subduction of the Izanagi plate.

Use of natural radionuclides to determine the time range of the accidental melting of an orphan radioactive source in a steel recycling plant.

PubMed

Cantaluppi, Chiara; Ceccotto, Federica; Cianchi, Aldo

2012-02-01

In the rare event that an orphan radioactive source is melted in an Electric Arc Furnace steel recycling plant, the radionuclides present are partitioned in the different products, by-products and waste. As a consequence of an unforeseen melting of a radiocesium source, cesium radioisotopes can be found in the dust, together with many natural radionuclides from the decay of radon and thoron, which are present in the atmosphere, picked up from the off-gas evacuation system and associated with the dust of the air filtration system ("baghouse"). In this work we verified that the activity concentration of ²¹²Pb in this dust is essentially constant in a specific factory so that it is possible to use it to date back to the time of the accidental melting of the orphan radioactive source. The main features of this method are described below, together with the application to a particular case in which this method was used for dating the moment in which the dust was contaminated with ¹³⁷Cs. Copyright © 2011 Elsevier Ltd. All rights reserved.

U-Pb zircon geochronology of the Paleoproterozoic Tagragra de Tata inlier and its Neoproterozoic cover, western Anti-Atlas, Morocco

USGS Publications Warehouse

Walsh, G.J.; Aleinikoff, J.N.; Benziane, F.; Yazidi, A.; Armstrong, T.R.

2002-01-01

New U-Pb zircon data obtained by sensitive high resolution ion microprobe (SHRIMP) from the Tagragra de Tata inlier in the western Anti-Atlas, Morocco establish Paleoproterozoic ages for the basement schists, granites, and metadolerites, and a Neoproterozoic age for an ignimbrite of the Ouarzazate Series in the cover sequence. The age of interbedded felsic metatuff in the metasedimentary and metavolcanic sequence of the basement schists is 2072 ?? 8 Ma. This date represents: (1) the first reliable age from the metasedimentary and metavolcanic sequence; (2) the oldest reliable age for the basement of the Anti-Atlas; (3) the first date on the timing of deposition of the sediments on the northern edge of the Paleoproterozoic West African craton; (4) a lower age limit on deformation during the Eburnean orogeny; and (5) the first date obtained from the non-granitic Paleoproterozoic basement of Morocco. Ages of 2046 ?? 7 Ma (Targant granite) and 2041 ?? 6 Ma (Oudad granite) support earlier interpretations of a Paleoproterozoic Eburnean igneous event in the Anti-Atlas. The granites post-date the Eburnean D1 deformation event in the Paleoproterozoic schist sequence, and place a ???2046 Ma limit on short-lived Eburnean deformation in the area. Cross-cutting metadolerite is 2040 ?? 6 Ma; this is the first date from a metadolerite in the western Anti-Atlas. All of the dolerites in the area post-date emplacement of the two granites and the new age constrains the onset of late- or post-Eburnean extension. Ignimbrite of the Ouarzazate Series, immediately above the Paleoproterozoic basement is 565 ?? 7 Ma. This Neoproterozoic age agrees with ages of similar volcanic rocks elsewhere from the Ouarzazate Series. The date also agrees with the ages of associated hypabyssal intrusions, and marks the second and final stage of Pan-African orogenic activity in the western Anti-Atlas. ?? 2002 Elsevier Science B.V. All rights reserved.

Incremental heating of Bishop Tuff sanidine reveals preeruptive radiogenic Ar and rapid remobilization from cold storage

NASA Astrophysics Data System (ADS)

Andersen, Nathan L.; Jicha, Brian R.; Singer, Brad S.; Hildreth, Wes

2017-11-01

Accurate and precise ages of large silicic eruptions are critical to calibrating the geologic timescale and gauging the tempo of changes in climate, biologic evolution, and magmatic processes throughout Earth history. The conventional approach to dating these eruptive products using the 40Ar/39Ar method is to fuse dozens of individual feldspar crystals. However, dispersion of fusion dates is common and interpretation is complicated by increasingly precise data obtained via multicollector mass spectrometry. Incremental heating of 49 individual Bishop Tuff (BT) sanidine crystals produces 40Ar/39Ar dates with reduced dispersion, yet we find a 16-ky range of plateau dates that is not attributable to excess Ar. We interpret this dispersion to reflect cooling of the magma reservoir margins below ˜475 °C, accumulation of radiogenic Ar, and rapid preeruption remobilization. Accordingly, these data elucidate the recycling of subsolidus material into voluminous rhyolite magma reservoirs and the effect of preeruptive magmatic processes on the 40Ar/39Ar system. The youngest sanidine dates, likely the most representative of the BT eruption age, yield a weighted mean of 764.8 ± 0.3/0.6 ka (2σ analytical/full uncertainty) indicating eruption only ˜7 ky following the Matuyama‑Brunhes magnetic polarity reversal. Single-crystal incremental heating provides leverage with which to interpret complex populations of 40Ar/39Ar sanidine and U-Pb zircon dates and a substantially improved capability to resolve the timing and causal relationship of events in the geologic record.

Incremental heating of Bishop Tuff sanidine reveals preeruptive radiogenic Ar and rapid remobilization from cold storage.

PubMed

Andersen, Nathan L; Jicha, Brian R; Singer, Brad S; Hildreth, Wes

2017-11-21

Accurate and precise ages of large silicic eruptions are critical to calibrating the geologic timescale and gauging the tempo of changes in climate, biologic evolution, and magmatic processes throughout Earth history. The conventional approach to dating these eruptive products using the 40 Ar/ 39 Ar method is to fuse dozens of individual feldspar crystals. However, dispersion of fusion dates is common and interpretation is complicated by increasingly precise data obtained via multicollector mass spectrometry. Incremental heating of 49 individual Bishop Tuff (BT) sanidine crystals produces 40 Ar/ 39 Ar dates with reduced dispersion, yet we find a 16-ky range of plateau dates that is not attributable to excess Ar. We interpret this dispersion to reflect cooling of the magma reservoir margins below ∼475 °C, accumulation of radiogenic Ar, and rapid preeruption remobilization. Accordingly, these data elucidate the recycling of subsolidus material into voluminous rhyolite magma reservoirs and the effect of preeruptive magmatic processes on the 40 Ar/ 39 Ar system. The youngest sanidine dates, likely the most representative of the BT eruption age, yield a weighted mean of 764.8 ± 0.3/0.6 ka (2σ analytical/full uncertainty) indicating eruption only ∼7 ky following the Matuyama-Brunhes magnetic polarity reversal. Single-crystal incremental heating provides leverage with which to interpret complex populations of 40 Ar/ 39 Ar sanidine and U-Pb zircon dates and a substantially improved capability to resolve the timing and causal relationship of events in the geologic record.

Phytoremediation of wastewater containing lead (Pb) in pilot reed bed using Scirpus grossus.

PubMed

Tangahu, Bieby Voijant; Abdullah, Siti Rozaimah Sheikh; Basri, Hassan; Idris, Mushrifah; Anuar, Nurina; Mukhlisin, Muhammad

2013-01-01

Phytoremediation is a technology to clean the environment from heavy metals contamination. The objectives of this study are to threat Pb contaminated wastewater by using phytoremediation technology and to determine if the plant can be mention as hyperaccumulator. Fifty plants of Scirpus grossus were grown in sand medium and 600 L spiked water in various Pb concentration (10, 30 and 50 mg/L) was exposed. The experiment was conducted with single exposure method, sampling time on day-1, day-14, day-28, day-42, day-70, and day-98. The analysis of Pb concentration in water, sand medium and inside the plant tissue was conducted by ICP-OES. Water samples were filtered and Pb concentration were directly analyzed, Pb in sand samples were extracted by EDTA method before analyzed, and Pb in plant tissues were extracted by wet digestion method and analyzed. The results showed that on day-28, Pb concentration in water decreased 100%, 99.9%, 99.7%, and the highest Pb uptake by plant were 1343, 4909, 3236 mg/kg for the treatment of 10, 30, and 50 mg/L respectively. The highest BC and TF were 485,261 on day-42 and 2.5295 on day-70 of treatment 30 mg/L, it can be mentioned that Scirpus grossus is a hyperaccumulator.

EVALUATION OF EXTRACTION AND SPECTROSCOPIC METHODS FOR PB SPECIATION IN AN AMENDED SOIL

EPA Science Inventory

Immobilization of pyromorphite (Pbs(PO4hCI) via P amendments to Pb contaminated soils is proving to be a viable method of remediation. However, the issue of ascertaining the amount of soil Pb converted to pyromorphite is difficult in heterogeneous soil systems. Previous attempts ...

Geochronology, geochemistry and Sr-Nd-Pb-Hf isotopes of the Early Jurassic granodiorite from the Sankuanggou intrusion, Heilongjiang Province, Northeastern China: Petrogenesis and geodynamic implications

NASA Astrophysics Data System (ADS)

Deng, Ke; Li, Qiugen; Chen, Yanjing; Zhang, Cheng; Zhu, Xuefeng; Xu, Qiangwei

2018-01-01

Mesozoic granitoid rocks represent a volumetrically component of the Northeastern (NE) China and preserve useful information about the tectonomagmatic history of this region. The Sankuanggou intrusion associated with skarn Fe-Cu deposit in the Duobaoshan ore field within NE China primarily consists of granodiorite with minor alkali-feldspar granite and diorite, which intrudes the Ordovician Duobaoshan Formation in the region. Zircon LA-ICP-MS U-Pb geochronology and whole-rock geochemistry, and Sr-Nd-Pb-Hf isotope analysis were performed on the Sankuanggou intrusion to investigate the petrogenesis and geodynamic implications. Zircon U-Pb dating of magmatic zircons from the granodiorite rock suggests that the intrusion was emplaced in the Early Jurassic (177 ± 1 Ma). Geochemically, it belongs to the metaluminous to slightly peraluminous high-K calc-alkaline I-type granitoids with a narrow range of SiO2 concentration (65.73-67.33 wt.%), high Ba, Sr, LREE and LILE contents and low abundance of Rb, Y, HREE and HFSE. All of these studied samples have homogeneous initial isotope traits with (87Sr/86Sr)i ranging from 0.70415 to 0.70423, εNd(t) of + 3.6 to + 4.0, (206Pb/204Pb)i = 17.933-18.458, (207Pb/204Pb)i = 15.520-15.587 and (208Pb/204Pb)i = 37.523-38.087, and zircon εHf(t) values varying from + 4.8 to + 9.9. These results, combined with the previous data, demonstrate that the Sankuanggou granitoids were formed by partial melting of the pre-existing juvenile crust in an extensional regime related to the post-collisional setting following the closure of the CAOB rather than previously proposed continental arc setting related to Paleo-Pacific or the Mongol-Okhotsk subduction, although their potential influence should not be dismissed.

Geochemical and geochronological constraints on the genesis of Au-Te deposits at Cripple Creek, Colorado

USGS Publications Warehouse

Kelley, K.D.; Romberger, S.B.; Beaty, D.W.; Pontius, J.A.; Snee, L.W.; Stein, H.J.; Thompson, T.B.

1998-01-01

The Cripple Creek district (653 metric tons (t) of Au) consists of Au-Te veins and disseminated gold deposits that are spatially related to alkaline igneous rocks in an Oligocene intrusive complex. Vein paragenesis includes quartz-biotite-K feldspar-fluorite-pyrite followed by base metal sulfides and telluride minerals. Disseminated deposits consist of microcrystalline native gold with pyrite that are associated with zones of pervasive adularia. New 40Ar/39Ar dates indicate that there was a complex magmatic and hydrothermal history. Relatively felsic rocks (tephriphonolite, trachyandesite, and phonolite) were emplaced into the complex over about 1 m.y., from 32.5 ?? 0.1 (1??) to 31.5 ?? 0.1 Ma. A younger episode of phonolite emplacement outside of the complex is indicated by an age of 30.9 ?? 0.1 Ma. Field relationships suggest that at least one episode of mafic and ultramafic dike emplacement occurred after relatively more felsic rocks and prior to the main gold mineralizing event. Only a single whole-rock date for mafic phonolite (which indicated a maximum age of 28.7 Ma) was obtained. However, constraints on the timing of mineralization are provided by paragenetically early vein minerals and K feldspar from the disseminated gold pyrite deposits. Early vein minerals (31.3 ?? 0.1-29.6 ?? 0.1 Ma) and K feldspar (29.8 ?? 0.1 Ma) from the Cresson disseminated deposit, together with potassically altered phonolite adjacent to the Pharmacist vein (28.8 and 28.2 ?? 0.1 Ma), suggest there was a protracted history of hydrothermal activity that began during the waning stages of phonolite and early mafic-ultramafic activity and continued, perhaps intermittently, for at least 2 m.y. Estimated whole-rock ??18O values of the alkaline igneous rocks range from 6.4 to 8.2 per mil. K feldspar and albite separates from igneous rocks have lead isotope compositions of 206Pb/204Pb = 17.90 to 18.10, 207Pb/204Pb = 15.51 to 15.53, and 208Pb/204Pb = 38.35 to 38.56. These isotopic compositions, together with major and trace element data, indicate that the phonolitic magmas probably evolved by fractional crystallization of an alkali basalt that assimilated lower crustal material. Upper crustal contamination of the magmas was not significant. The 206Pb/204Pb compositions of vein galenas almost entirely overlap those of phonolites, suggesting a genetic relationship between alkaline magmatism and mineralization. However, a trend toward higher 207Pb/204Pb (15.57-15.60) and 208Pb/204Pb ratios (38.94-39.48) of some galenas suggests a contribution to the ore fluid from surrounding Early Proterozoic rocks, probably through leaching by mineralizing fluids. Limited stable isotope compositions of quartz, K feldspar, and biotite from this and previous studies support a largely magmatic origin for the early vein fluids. It is suggested that three features were collectively responsible for generating alkaline magmas and associated mineral deposits: (1) the timing of magmatism and mineralization, which coincided with the transition between subduction-related compression and extension related to continental rifting; (2) the location of Cripple Creek at the junction of four major Precambrian units and at the intersection of major northeast-trending regional structures with northwest-trending faults, which served as conduits for magmas and subsequent hydrothermal fluids; and (3) the complex magmatic history which included emplacement of relatively felsic magmas followed by successively more mafic magmas with time.

CHRONOLOGICAL CONSTRAINTS ON FLUID CIRCULATION IN MESOZOIC FORMATIONS OF THE EASTERN PART OF THE PARIS BASIN INFERRED FROM U-Pb DATING OF SECONDARY INFILLING CARBONATES

NASA Astrophysics Data System (ADS)

Pisapia, C.; Deschamps, P.; Hamelin, B.; Buschaert, S.

2009-12-01

The French agency for nuclear waste management (ANDRA) developed an Underground Research Laboratory in the Mesozoic formations of Eastern part of the Paris Basin (France) to assess the feasibility of a high-level radioactive wastes repository in sedimentary formations. The target host formation is a low-porosity detrital argillite (Callovo-Oxfordian) embedded between two shelf limestones formations (of Bajocian-Bathonian and Oxfordian-Kimmeridgian ages). These formations are affected by fracture networks, likely inherited mainly from the Eocene-Oligocene extension tectonics, also responsible of the Rhine graben formation in the same region. The limestones have very low permeability, the primary and secondary porosity being infilled by secondary carbonated minerals. The inter-particle porosity is filled with euhedral calcite spar cements. Similarly, macro-cavities and connected micro-fractures are almost sealed by euhedral calcite. Geochemical evidences (δ18O) suggest that the secondary carbonates likely derived from a common parent fluid (Buschaert et al., 2004, Appl. Geochem. (19) 1201-1215p). This late carbonated precipitation phase is responsible for the intense cementation of the limestone formations and bears witness of a major phase of fluids circulation that marked the late diagenetic evolution of the system. Knowledge of the chronology of the different precipitation phases of secondary minerals is thus of critical importance in order to determine the past hydrological conditions of the geological site. The aim of this study is to provide chronological constraints on the secondary carbonate mineral precipitation using U/Th and U/Pb methods. Analyses are performed on millimeter to centimeter scale secondary calcites collected within fractures outcropping in the regional fault zone of Gondrecourt and in cores from the ANDRA exploration-drilling program. Preliminary U-Th analyses obtained on secondary carbonates from surface fractures infillings yield secular equilibrium composition, indicating that the precipitation phase was older than 650 ky. U-Pb measurements were performed on a VG sector Thermal Ionization Mass Spectrometer (TIMS) using a 205Pb-236U-233U-229Th spike. Pb contents are generally very low, between 3 and 20 ppb, while U contents are more variable, leading to μ = 238U/204Pb up to ~600. Sub-samples with high μ show radiogenic 206Pb/204Pb ratio, but at this stage isochrons generally show high scatter. These U-Pb data however are consistent with an Eocene-Oligocene period for the late carbonates precipitation phase. We will discuss the different processes that may be responsible for these errorchrons (i.e. heterogeneities in the initial isotopic composition; multi-stage growth) as well as the chronological constraints that can be drawn from these data.

TEMORA 1: A new zircon standard for Phanerozoic U-Pb geochronology

USGS Publications Warehouse

Black, L.P.; Kamo, S.L.; Allen, C.M.; Aleinikoff, J.N.; Davis, D.W.; Korsch, R.J.; Foudoulis, C.

2003-01-01

The role of the standard is critical to the derivation of reliable U-Pb zircon ages by micro-beam analysis. For maximum reliability, it is critically important that the utilised standard be homogeneous at all scales of analysis. It is equally important that the standard has been precisely and accurately dated by an independent technique. This study reports the emergence of a new zircon standard that meets those criteria, as demonstrated by Sensitive High Resolution Ion MicroProbe (SHRIMP), isotope dilution thermal ionisation mass-spectrometry (IDTIMS) and excimer laser ablation- inductively coupled plasma-mass-spectrometry (ELA-ICP-MS) documentation. The TEMORA 1 zircon standard derives from the Middledale Gabbroic Diorite, a high-level mafic stock within the Palaeozoic Lachlan Orogen of eastern Australia. Its 206Pb/238U IDTIMS age has been determined to be 416.75??0.24 Ma (95% confidence limits), based on measurement errors alone. Spike-calibration uncertainty limits the accuracy to 416.8??1.1 Ma for U-Pb intercomparisons between different laboratories that do not use a common spike. ?? 2003 Published by Elsevier Science B.V. All rights reserved.

Search for diphoton events with large missing transverse energy with 36 pb –1 of 7 TeV proton–proton collision data with the ATLAS detector

DOE PAGES

Aad, G.; Abbott, B.; Abdallah, J.; ...

2011-10-05

Making use of 36 pb –1 of proton–proton collision data at √s = 7 TeV, the ATLAS Collaboration has performed a search for diphoton events with large missing transverse energy. Observing no excess of events above the Standard Model prediction, a 95% Confidence Level (CL) upper limit is set on the cross section for new physics of σ<0.38–0.65 pb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, and of σ<0.18–0.23 pb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 560more » GeV, for bino masses above 50 GeV, is set on the GGM gluino mass, while a lower limit of 1/ R>961 GeV is set on the UED compactification radius R. In conclusion, these limits provide the most stringent tests of these models to date.« less

Detrital zircon ages from southern Norway - implications for the Proterozoic evolution of the southwestern Baltic Shield

NASA Astrophysics Data System (ADS)

Knudsen, T.-L.; Andersen, T.; Whitehouse, M. J.; Vestin, J.

An ion-microprobe (SIMS) U-Pb zircon dating study on four samples of Precambrian metasediments from the high-grade Bamble Sector, southern Norway, gives the first information on the timing of discrete crust-forming events in the SW part of the Baltic Shield. Recent Nd and Pb studies have indicated that the sources of the clastic metasediments in this area have crustal histories extending back to 1.7 to 2.1Ga, although there is no record of rocks older than 1.6Ga in southern Norway. The analysed metasediments are from a sequence of intercalated, centimetre to 10-metre wide units of quartzites, semi-metapelites, metapelites and mafic granulites. The zircons can be grouped in two morphological populations: (1) long prismatic; (2) rounded, often flattened. The BSE images reveal that both populations consist of oscillatory zoned, rounded and corroded cores (detrital grains of magmatic origin), surrounded by homogeneous rims (metamorphic overgrowths). The detrital zircons have 207Pb/206Pb ages between 1367 and 1939Ma, with frequency maxima in the range 1.85 to 1.70Ga and 1.60 to 1.50Ga. There is no correlation between crystal habit and age of the zircon. One resorbed, inner zircon core in a detrital grain is strongly discordant and gives a composite inner core-magmatic outer core 207Pb/206Pb age of 2383 Ma. Two discrete, unzoned zircons have 207Pb/206Pb ages of 1122 and 1133Ma, representing zircon growth during the Sveconorwegian high-grade metamorphism. Also the μm wide overgrowths, embayments in the detrital cores and apparent ``inner cores'' which represent secondary metamorphic zircon growth in deep embayments in detrital grains, are of Sveconorwegian age. The composite-detrital-metamorphic zircon analyses give generally discordant 206Pb/238U versus 207Pb/235U ratios and maximum 207Pb/206Pb ages of 1438Ma. These data demonstrate the existence of a protocrust of 1.7 to 2.0Ga in the southwestern part of the Baltic Shield, implying a break in the overall westward younging trend of the Precambrian crust, inferred from the southeastern part of the Baltic Shield.

Identification of 210Pb and 210Po in the bulk of copper samples with a low-background alpha particle counter

NASA Astrophysics Data System (ADS)

Abe, K.; Hiraide, K.; Ichimura, K.; Kishimoto, Y.; Kobayashi, K.; Kobayashi, M.; Moriyama, S.; Nakahata, M.; Norita, T.; Ogawa, H.; Sato, K.; Sekiya, H.; Takachio, O.; Takeda, A.; Tasaka, S.; Yamashita, M.; Yang, B. S.; Kim, N. Y.; Kim, Y. D.; Itow, Y.; Kanzawa, K.; Kegasa, R.; Masuda, K.; Takiya, H.; Fushimi, K.; Kanzaki, G.; Martens, K.; Suzuki, Y.; Xu, B. D.; Fujita, R.; Hosokawa, K.; Miuchi, K.; Oka, N.; Takeuchi, Y.; Kim, Y. H.; Lee, K. B.; Lee, M. K.; Fukuda, Y.; Miyasaka, M.; Nishijima, K.; Nakamura, S.

2018-03-01

We established a method to assay 210Pb and 210Po contaminations in the bulk of copper samples using a low-background alpha particle counter. The achieved sensitivity for the 210Pb and 210Po contaminations reaches a few mBq/kg. Due to this high sensitivity, the 210Pb and 210Po contaminations in oxygen free copper bulk were identified and measured for the first time. The 210Pb contaminations of our oxygen free copper samples were 17-40 mBq/kg. Based on our investigation of copper samples in each production step, the 210Pb in oxygen free copper was understood to be a small residual of an electrolysis process. This method to measure bulk contaminations of 210Pb and 210Po could be applied to other materials.

Identification of 210Pb and 210Po in the bulk of copper samples with a low-background alpha particle counter

NASA Astrophysics Data System (ADS)

Kobayashi, Kazuyoshi

2018-01-01

We established a method to assay 210Pb and 210Po contaminations in the bulk of copper samples using a low-background alpha particle counter. The achieved sensitivity for the 210Pb and 210Po contaminations reaches a few mBq/kg. Due to this high sensitivity, the 210Pb and 210Po contaminations in oxygen free copper bulk were identified and measured for the first time. The 210Pb contaminations of our oxygen free copper samples were 17-40 mBq/kg. Based on our investigation of copper samples in each production step, the 210Pb in oxygen free copper was understood to be a small residual of an electrolysis process. This method to measure bulk contaminations of 210Pb and 210Po could be applied to other materials.

Paleomagnetic and mineral magnetic constraints on Zn-Pb ore genesis in the Pend Oreille Mine, Metaline district, Washington, USA

USGS Publications Warehouse

Pannalal, S.J.; Symons, David T. A.; Leach, D.L.

2007-01-01

Zinc-lead mineralization in the Metaline mining district of northeastern Washington, USA, is hosted by the Cambrian Metaline Formation and is classified into Yellowhead-type (YO) and Josephine-type (JO) ore based on texture and mineralogy. Paleomagnetic results are reported for four Cambrian Metaline Formation sites, one Ordovician Ledbetter slate site, 12 YO and 13 JO (including two breccia sites) mineralization sites in the Pend Oreille Mine, and eight sites from the nearby Cretaceous Kaniksu granite batholith. Thermal and alternating field step demagnetization, saturation isothermal remanence analysis, and synthetic specimen tests show that the remanence in the host carbonates and Zn-Pb mineralization is carried mostly by pseudosingle (PSD) to single domain (SD) pyrrhotite and mostly by PSD to SD magnetite in the Kaniksu granite. Based on thermomagnetic measurements, sphalerite and galena concentrates and tailings from the mine's mill contain hexagonal and monoclimc pyrrhotite. The postfolding characteristic remanent magnetization (ChRM), known thermal data, and paleoarc method of dating suggest that the Zn-Pb mineralization carries a primary chemical remanent magnetization (CRM), and Metaline Formation carbonates a secondary CRM that were acquired during the Middle Jurassic (166 ??6 Ma) during the waning stages of the Nevadan orogeny. A paleomagnetic breccia test favours a solution-collapse origin for the Josephine breccia. Finally, the Kaniksu paleopole is concordant with the North American Cretaceous reference paleopole, suggesting the Kootenay terrane has not been rotated since emplacement of the batholith at ???94 Ma. ?? 2007 NRC Canada.

Timing of porphyry (Cu-Mo) and base metal (Zn-Pb-Ag-Cu) mineralisation in a magmatic-hydrothermal system—Morococha district, Peru

NASA Astrophysics Data System (ADS)

Catchpole, Honza; Kouzmanov, Kalin; Bendezú, Aldo; Ovtcharova, Maria; Spikings, Richard; Stein, Holly; Fontboté, Lluís

2015-12-01

The Morococha district in central Peru is characterised by economically important Cordilleran polymetallic (Zn-Pb-Ag-Cu) vein and replacement bodies and the large Toromocho porphyry Cu-Mo deposit in its centre. U-Pb, Re-Os, and 40Ar/39Ar geochronology data for various porphyry-related hydrothermal mineralisation styles record a 3.5-Ma multi-stage history of magmatic-hydrothermal activity in the district. In the late Miocene, three individual magmatic-hydrothermal centres were active: the Codiciada, Toromocho, and Ticlio centres, each separated in time and space. The Codiciada centre is the oldest magmatic-hydrothermal system in the district and consists of a composite porphyry stock associated with anhydrous skarn and quartz-molybdenite veins. The hydrothermal events are recorded by a titanite U-Pb age at 9.3 ± 0.2 Ma and a molybdenite Re-Os age at 9.26 ± 0.03 Ma. These ages are indistinguishable from zircon U-Pb ages for porphyry intrusions of the composite stock and indicate a time span of 0.2 Ma for magmatic-hydrothermal activity. The small Ticlio magmatic-hydrothermal centre in the west of the district has a maximum duration of 0.3 Ma, ranging from porphyry emplacement to porphyry mineralisation at 8.04 ± 0.14 Ma (40Ar/39Ar muscovite cooling age). The Toromocho magmatic-hydrothermal centre has a minimum of five recorded porphyry intrusions that span a total of 1.3 Ma and is responsible for the formation of the giant Toromocho Cu-Mo deposit. At least two hydrothermal pulses are identified. Post-dating a first pulse of molybdenite mineralisation, wide-spread hydrous skarn covers an area of over 6 km2 and is recorded by five 40Ar/39Ar cooling ages at 7.2-6.8 Ma. These ages mark the end of the slowly cooling and long-lived Toromocho magmatic-hydrothermal centre soon after last magmatic activity at 7.26 ± 0.02 Ma. District-wide (50 km2) Cordilleran base metal vein and replacement bodies post-date the youngest recorded porphyry mineralisation event at Toromocho by more than 0.5 Ma. Polymetallic veins (5.78 ± 0.10 and 5.72 ± 0.18 Ma; 40Ar/39Ar ages) and the Manto Italia polymetallic replacement bodies (6.23 ± 0.12 and 6.0 ± 0.2 Ma; 40Ar/39Ar ages) are interpreted to have been formed by a single hydrothermal pulse. Hydrothermal activity ceased after the formation of the base metal vein and replacement bodies. Overlapping monazite U-Pb (8.26 ± 0.18 Ma) and muscovite 40Ar/39Ar ages (8.1 ± 0.5 Ma) from the early base metal stage of one Cordilleran vein sample in the Sulfurosa area provide evidence that a discrete hydrothermal pulse was responsible for polymetallic vein formation 2.6 Ma prior to the district-wide polymetallic veins. These ages pre-date those of Toromocho porphyry Cu-Mo formation and show that Zn-Pb-Ag-Cu mineralisation formed during several discrete magmatic-hydrothermal pulses in the same district.

Quantitation of lead-210 (210Pb) using lead-203 (203Pb) as a "Massless" yield tracer.

PubMed

May, D; Nelson, A N; Schultz, M K

2017-05-01

Determination of Pb-210 ( 210 Pb) in aqueous solution is a common radioanalytical challenge in environmental science. Widely used methods for undertaking these analyses (e.g., ASTM D7535) rely on the use of stable lead (Pb) as a yield tracer that takes into account losses of 210 Pb that inevitably occur during elemental/radiochemical separations of the procedures. Although effective, these methods introduce technical challenges that can be difficult to track and potentially introduce uncertainty that can be difficult to quantify. Examples of these challenges include interference from endogenous stable Pb in complex sample matrices; contamination of stable Pb carrier with 210 Pb; and high detection limits due to counting efficiency limitations. We hypothesized that many of these challenges could be avoided by the use of the electron-capture, gamma-emitting isotope, 203 Pb as a chemical yield tracer in the analysis of 210 Pb. A series of experiments were performed to evaluate the efficacy of 203 Pb as a tracer. Four different matrices were analyzed, including a complex matrix (hydraulic-fracturing produced fluids); and samples comprising less complicated matrices (i.e., river water, deionized water, and tap water). Separation techniques and counting methodologies were also compared and optimized. Due to a relatively short-half life (52 h), 203 Pb tracer is effectively massless for the purposes of chemical separations, allowing for reduced chromatography column resin bed volumes. Because 203 Pb is a gamma emitter (279 keV; 81% intensity), recovery can be determined non-destructively in a variety of matrices, including liquid scintillation cocktail. The use of liquid scintillation as a counting methodology allowed for determination of 210 Pb activities via 210 Pb or 210 Po; and recoveries of greater than 90% are routinely achievable using this approach. The improved method for the analysis of 210 Pb in aqueous matrices allows for the analysis of complex matrices, at reduced cost, while providing greater counting flexibility in achieving acceptable detections limits. Copyright © 2017 Elsevier Ltd. All rights reserved.

Newly Described Tephra Provide Middle Pleistocene Age Constraints to Stegodon Fossils in West (Indonesian) Timor

NASA Astrophysics Data System (ADS)

Jensen, B. J. L.; Dufrane, A.; Mark, D.; Zaim, Y.; Rizal, Y.; Aswan, A.; Hascaryo, A.; Ciochon, R.; Gunnell, G.; Larick, R.; Zonnveld, J. P.

2017-12-01

As the Asian proboscidian Stegodon dispersed across Island Southeast Asia during the Pleistocene, multiple forms developed. On Timor, a southerly island east of Wallace's Line, the Ainaro gravels have yielded a highly dwarfed S. timorensis and a larger S. `trigonocephalus.' During a half-century of exploration, the age of the fossil bearing gravels remains in question, with only one age determination of >130 ka derived from six 230Th- 238U dates on a tusk fragment found in the Raebia area (Louys et al. 2016). Here we present radiometric ages for two tephra deposits bracketing Ainaro gravels at Raebia, a S. timorensis fossil locality 8 km northeast of Atambua city. The Raebia ravine exposes 2-10 meters of coarse-grained gravels incised into silt and clay deposits, bracketed by two indurated and largely devitrified tephras. Some intact glass was present to geochemically characterize each unit, which are both high-silica rhyolites. Biotite and zircons for 40Ar/39Ar and laser ablation U-Pb dating were extracted from the upper unit (Raebia Tuff 1; RT1), and zircons from the lower unit (Raebia Tuff 2; RT2). RT1 had zircons with two distinct age populations, but the youngest yield a 230Th deficiency corrected 206Pb/238U age of 665 ± 19 ka, (2s, n = 23, MSWD = 0.81), consistent with the 40Ar/39Ar age 614.9 ± 16.4 ka (2s, full external precision). Preliminary zircon dates on RT2 are more problematic, providing a large range that suggests inheritance by xenoliths and/or locally-sourced detrital zircons. However, a single zircon yielded 230Th deficiency corrected 206Pb/238U age of 708 ± 66 ka (2s, n=17, MSWD = 0.41), which is stratigraphically consistent. These are the first reliable age constraints on a higher elevation Ainaro gravel terrace and fossils they contain. The only other direct ages on the gravels are 230Th- 238U dates on lower terraces interbedded with coral, ranging from 130 ka to Holocene in age (Roosmawati and Harris 2009). These two newly described and dated tephra are likely regionally distributed and may represent important stratigraphic horizons for this portion of Southern Wallacea. They also provide useful data for calculating uplift rates for the region from the middle Pleistocene.

Cretaceous crust beneath SW Borneo: U-Pb dating of zircons from metamorphic and granitic rocks

NASA Astrophysics Data System (ADS)

Davies, L.; Hall, R.; Armstrong, R.

2012-12-01

Metamorphic basement rocks from SW Borneo are undated but have been suggested to be Palaeozoic. This study shows they record low pressure 'Buchan-type' metamorphism and U-Pb SHRIMP dating of zircons indicates a mid-Cretaceous (volcaniclastic) protolith. SW Borneo is the southeast promontory of Sundaland, the continental core of SE Asia. It has no sedimentary cover and the exposed basement has been widely assumed to be a crustal fragment from the Indochina-China margin. Metamorphic rocks of the Pinoh Group in Kalimantan (Indonesian Borneo) are intruded by granitoid rocks of Jurassic-Cretaceous age, based on K-Ar dating, suggesting emplacement mainly between 130 and 80 Ma. The Pinoh metamorphic rocks have been described as a suite of pelitic schists, slates, phyllites, and hornfelses, and have not been dated, although they have been correlated with rocks elsewhere in Borneo of supposed Palaeozoic age. Pelitic schists contain biotite, chlorite, cordierite, andalusite, quartz, plagioclase and in some cases high-Mn almandine-rich garnet. Many have a shear fabric associated with biotite and fibrolite intergrowth. Contact metamorphism due to intrusion of the granitoid rocks produced hornfelses with abundant andalusite and cordierite porphyroblasts. Granitoids range from alkali-granite to tonalite and contain abundant hornblende and biotite, with rare white mica. Zircons from granitoid rocks exhibit sector- and concentric- zoning; some have xenocrystic cores mantled by magmatic zircon. There are four important age populations at c. 112, 98, 84 and 84 Ma broadly confirming earlier dating studies. There is a single granite body with a Jurassic age (186 ± 2.3 Ma). Zircons from pelitic metamorphic rocks are typically euhedral, with no evidence of rounding or resorbing of grains; a few preserve volcanic textures. They record older ages than those from igneous rocks; U-Pb ages are Cretaceous with a major population between 134 and 110 Ma. A single sample contains Proterozoic and Phanerozoic zircons. The metamorphic rocks from SW Borneo are not an ancient core to the island as previously assumed. We propose that extensive arc volcanism produced fine grained volcanogenic sediments during the Early Cretaceous deposited on, or reworking, older crust. These sediments were subjected to low pressure 'Buchan-type' metamorphism soon after deposition. Magmatism continued into the Late Cretaceous, resulting in contact metamorphism.

U-Pb geochronologic constraints on the origin of a unique monazite- xenotime gneiss, Hudson Highlands, New York

USGS Publications Warehouse

Aleinikoff, J.N.; Grauch, R.I.

1990-01-01

A unique rock composed almost entirely of equal proportions of monazite and xenotime occurs as a small, lenticular body (2 ?? 0.5 ?? 0.3 m) in association with paragneiss, migmatite, and Canada Hill Granite in an outcrop in the Hudson Highlands of southeastern New York. The paragneiss contains detrital zircon (207Pb/206Pb ages of 1150-1460 Ma), monazite, and xenotime (both dated at about 1000 Ma). Zircons from the monazite-xenotime gneiss contain dark, rounded cores and clear rims, a morphology suggestive of derivation from the paragneiss, with subsequent metamorphic overgrowth. We conclude, based on results from xenotime and zircon rims, that the monazite-xenotime gneiss formed at about 985 Ma. Based on zircon morphology and age relations within the outcrop, we prefer a metasomatic origin over other possibilities such as a paleo-placer or anatectic restite. -from Authors

Possible Mesozoic age of Ellenville Zn-Pb-Cu(Ag) deposit, Shawangunk Mountains, New York

USGS Publications Warehouse

Friedman, J.D.; Conrad, J.E.; McKee, E.H.; Mutschler, F.E.; Zartman, R.E.

1994-01-01

Ore textures, epithermal open-space filling of Permian structures of the Alleghanian orogeny, and largely postorogenic mineralization of the Ellenville, New York, composite Zn-Pb-Cu(Ag) vein system, provide permissive evidence for post-Permian mineralization. Isochron ages determined by 40Ar/39Ar laser-fusion techniques for K-bearing liquid inclusions in main-stage quartz from the Ellenville deposit additionally suggest a Mesozoic time of mineralization, associated with extensional formation of the Newark basin. The best 40Ar/39Ar total-fusion age range is 165 ?? 30 to 193 ?? 35 Ma. The Mesozoic 40Ar/39Ar age agrees with that of many other dated northern Appalachian Zn-Pb-Cu(Ag) deposits with near-matching lead isotope ratios, and adds new evidence of Jurassic tectonism and mineralization as an overprint to Late Paleozoic tectonism at least as far north as Ellenville (lat. 41??43???N). ?? 1994 Springer-Verlag.

Discrimination of the Cigarettes Geographical Origin by DRC-ICP-MS Measurements of Pb Isotope Compositions

NASA Astrophysics Data System (ADS)

Guo, W.; Hu, S.; Jin, L.

2014-12-01

Trace Pb are taken up with the same isotopic ratios as is present in the source soil, and the isotopic composition of Pb could used to reflect these sources and provide powerful indicators of the geographic origin of agriculture products derived from vegetative matter. We developed a simple and high throughput method, which based on DRC-ICP-MS for determination of Pb isotope ratios for discriminating the geographic origin of cigarettes. After acid digestion procedure, the cigarette digested solutions were directly analyzed by ICP-QMS with a DRC pressurized by the non-reactive gas Ne. In the DRC, Ne molecules collision with Pb ions and improves Pb isotope ratios precision 3-fold, which may be due to the collisional dampling smoothes out the ion beam fluctuations. Under the optimum DRC rejection parameter Q (RPq = 0.45), the main matrix components (K, Na, Ca, Mg, Al, Fe etc.) originating from cigarettes were filtered out. Mass discrimination of 208Pb/206Pb ratio in Ne DRC mode increased 0.3% compared to the standard mode, the mass bias due to the in-cell Ne gas collision can be accurately corrected by NIST 981 Pb isotope standard. This method was verified by a tobacco reference material CTV-OTL-2. Results of 208Pb/206Pb and 207Pb/206Pb were 2.0848 ± 0.0028 (2δ) and 0.8452 ± 0.0011 (2δ) for CTA-VTL-2, which were agreed with the literature values (208Pb/206Pb = 2.0884 ± 0.0090 and 207Pb/206Pb = 0.8442 ± 0.0032). The precision of Pb isotope ratios (208Pb/206Pb and 207Pb/206Pb) for the cigarette samples are ranged from 0.01 to 0.08% (N = 5). It has sufficient precision to discriminate 91 different brand cigarettes originated from four different geographic regions (Shown in Fig).

Dating sediment in a fast sedimentation reservoir using 137Cs and 210Pb

USDA-ARS?s Scientific Manuscript database

Over 10,000 reservoirs have been constructed in agricultural watersheds in the United States since the 1940s to control floods and sediments. Reservoir sedimentation records provide a unique opportunity to retrospectively study the effects of land use changes and climate variations on sediment produ...

Métamorphisme miocène de granites panafricains dans le massif de l'Edough (Nord-Est de l'Algérie)

NASA Astrophysics Data System (ADS)

Hammor, Dalila; Lancelot, Joël

1998-09-01

The Edough Massif is the easternmost crystalline core of the Maghrebides that represents the African segment of the west Mediterranean Alpine belt. U-Pb zircon dating provides upper intercept ages of 595 ± 51 My and 606 ± 55 My for an orthogneiss of the lower unit and a deformed leucogranite of the upper pelitic unit, respectively. These ages suggest emplacement of the two granitoids during the Pan-African orogeny. Monazites from a paragneiss sample gave a 18 ± 5 My U-Pb age that points to a Miocene age of the high-temperature metamorphism.

Phosphorus Amendment Efficacy for In Situ Remediation of Soil Lead Depends on the Bioaccessible Method

EPA Science Inventory

A validated method is needed to measure reductions of in vitro bioaccessible (IVBA) Pb in urban soil remediated with amendments. This study evaluated the effect of in vitro extraction solution pH and glycine buffer on bioaccesible Pb in P-treated soils. Two Pb-contaminated soils...

A millennium of metallurgy recorded by lake sediments from Morococha, Peruvian Andes.

PubMed

Cooke, Colin A; Abbott, Mark B; Wolfe, Alexander P; Kittleson, John L

2007-05-15

To date, information concerning pre-Colonial metallurgy in South America has largely been limited to the archaeological record of artifacts. Here, we reconstruct a millennium of smelting activity in the Peruvian Andes using the lake-sediment stratigraphy of atmospherically derived metals (Pb, Zn, Cu, Ag, Sb, Bi, and Ti) and lead isotopic ratios (206Pb/ 207Pb) associated with smelting from the Morococha mining region in the central Peruvian Andes. The earliest evidence for metallurgy occurs ca. 1000 A.D., coinciding with the fall of the Wari Empire and decentralization of local populations. Smelting during this interval appears to have been aimed at copper and copper alloys, because of large increases in Zn and Cu relative to Pb. A subsequent switch to silver metallurgy under Inca control (ca. 1450 to conquest, 1533 A.D.) is indicated by increases in Pb, Sb, and Bi, a conclusion supported by further increases of these metals during Colonial mining, which targeted silver extraction. Rapid development of the central Andes during the 20th century raised metal burdens by an order of magnitude above previous levels. Our results represent the first evidence for pre-Colonial smelting in the central Peruvian Andes, and corroborate the sensitivity of lake sediments to pre-Colonial metallurgical activity suggested by earlier findings from Bolivia.

Unraveling the Decomposition Process of Lead(II) Acetate: Anhydrous Polymorphs, Hydrates, and Byproducts and Room Temperature Phosphorescence.

PubMed

Martínez-Casado, Francisco J; Ramos-Riesco, Miguel; Rodríguez-Cheda, José A; Cucinotta, Fabio; Matesanz, Emilio; Miletto, Ivana; Gianotti, Enrica; Marchese, Leonardo; Matěj, Zdeněk

2016-09-06

Lead(II) acetate [Pb(Ac)2, where Ac = acetate group (CH3-COO(-))2] is a very common salt with many and varied uses throughout history. However, only lead(II) acetate trihydrate [Pb(Ac)2·3H2O] has been characterized to date. In this paper, two enantiotropic polymorphs of the anhydrous salt, a novel hydrate [lead(II) acetate hemihydrate: Pb(Ac)2·(1)/2H2O], and two decomposition products [corresponding to two different basic lead(II) acetates: Pb4O(Ac)6 and Pb2O(Ac)2] are reported, with their structures being solved for the first time. The compounds present a variety of molecular arrangements, being 2D or 1D coordination polymers. A thorough thermal analysis, by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), was also carried out to study the behavior and thermal data of the salt and its decomposition process, in inert and oxygenated atmospheres, identifying the phases and byproducts that appear. The complex thermal behavior of lead(II) acetate is now solved, finding the existence of another hydrate, two anhydrous enantiotropic polymorphs, and some byproducts. Moreover, some of them are phosphorescent at room temperature. The compounds were studied by TGA, DSC, X-ray diffraction, and UV-vis spectroscopy.

Monazite paragenesis and U-Pb systematics in rocks of the eastern Mojave Desert, California, U.S.A.: implications for thermochronometry

USGS Publications Warehouse

Kingsbury, J.A.; Miller, C.F.; Wooden, J.L.; Harrison, T.M.

1993-01-01

Studies of the paragenesis and U-Pb systematics of monazite in rocks from the eastern Mojave Desert, California, corroborate its potential usefulness as a prograde thermochronometer and in dating granite inheritance. Unmetamorphosed Latham Shale and its equivalents at grades ranging from greenschist to upper amphibolite facies are virtually identical in composition. Monazite is absent in the shale and low-grade schists, but it is abundant in schists at staurolite and higher grades. Lower-grade schists instead include minute Th- and Ce-oxides and unidentified Ce-poor LREE-phosphates that apparently are lower-temperature precursors to monazite. Thus monazite originates when the pelite passes through lower-amphibolite-facies conditions. Monazites from three Upper Cretaceous granites yield ages that are strongly discordant. Upper intercepts of 1.6-1.7 Ga are similar to those defined by U-Pb data for coexisting zircons and coincide with a period of copious magmatism in the Mojave crust. As the host Upper Cretaceous granitic magmas were all above 700??C, effective closure of the restitic monazites to Pb loss must be well in excess of this temperature. U-Pb compositions of monazite from Proterozoic granitoids and schist also indicate high Pb retentivity. Taken together, these studies support the suggestion that monazite can be an effective prograde thermochronometer. At least in pelites, it is not usually retained as a detrital mineral, but rather forms during moderate-temperature metamorphism. Its U-Pb system should not be reset by subsequent higher-grade metamorphism. ?? 1993.

Metal Halide Solid-State Surface Treatment for High Efficiency PbS and PbSe QD Solar Cells

PubMed Central

Crisp, Ryan W.; Kroupa, Daniel M.; Marshall, Ashley R.; Miller, Elisa M.; Zhang, Jianbing; Beard, Matthew C.; Luther, Joseph M.

2015-01-01

We developed a layer-by-layer method of preparing PbE (E = S or Se) quantum dot (QD) solar cells using metal halide (PbI2, PbCl2, CdI2, or CdCl2) salts dissolved in dimethylformamide to displace oleate surface ligands and form conductive QD solids. The resulting QD solids have a significant reduction in the carbon content compared to films treated with thiols and organic halides. We find that the PbI2 treatment is the most successful in removing alkyl surface ligands and also replaces most surface bound Cl- with I-. The treatment protocol results in PbS QD films exhibiting a deeper work function and band positions than other ligand exchanges reported previously. The method developed here produces solar cells that perform well even at film thicknesses approaching a micron, indicating improved carrier transport in the QD films. We demonstrate QD solar cells based on PbI2 with power conversion efficiencies above 7%. PMID:25910183

Metal halide solid-state surface treatment for high efficiency PbS and PbSe QD solar cells.

PubMed

Crisp, Ryan W; Kroupa, Daniel M; Marshall, Ashley R; Miller, Elisa M; Zhang, Jianbing; Beard, Matthew C; Luther, Joseph M

2015-04-24

We developed a layer-by-layer method of preparing PbE (E = S or Se) quantum dot (QD) solar cells using metal halide (PbI2, PbCl2, CdI2, or CdCl2) salts dissolved in dimethylformamide to displace oleate surface ligands and form conductive QD solids. The resulting QD solids have a significant reduction in the carbon content compared to films treated with thiols and organic halides. We find that the PbI2 treatment is the most successful in removing alkyl surface ligands and also replaces most surface bound Cl(-) with I(-). The treatment protocol results in PbS QD films exhibiting a deeper work function and band positions than other ligand exchanges reported previously. The method developed here produces solar cells that perform well even at film thicknesses approaching a micron, indicating improved carrier transport in the QD films. We demonstrate QD solar cells based on PbI2 with power conversion efficiencies above 7%.

Metal Halide Solid-State Surface Treatment for High Efficiency PbS and PbSe QD Solar Cells

DOE PAGES

Crisp, R. W.; Kroupa, D. M.; Marshall, A. R.; ...

2015-04-24

We developed a layer-by-layer method of preparing PbE (E = S or Se) quantum dot (QD) solar cells using metal halide (PbI 2, PbCl 2, CdI 2, or CdCl 2) salts dissolved in dimethylformamide to displace oleate surface ligands and form conductive QD solids. The resulting QD solids have a significant reduction in the carbon content compared to films treated with thiols and organic halides. We find that the PbI 2 treatment is the most successful in removing alkyl surface ligands and also replaces most surface bound Cl- with I-. The treatment protocol results in PbS QD films exhibiting amore » deeper work function and band positions than other ligand exchanges reported previously. The method developed here produces solar cells that perform well even at film thicknesses approaching a micron, indicating improved carrier transport in the QD films. We demonstrate QD solar cells based on PbI 2 with power conversion efficiencies above 7%.« less

Colorimetric Assay for Determination of Lead (II) Based on Its Incorporation into Gold Nanoparticles during Their Synthesis

PubMed Central

Ding, Nan; Cao, Qian; Zhao, Hong; Yang, Yimin; Zeng, Lixi; He, Yujian; Xiang, Kaixiang; Wang, Guangwei

2010-01-01

In this report, we present a new method for visual detection of Pb2+. Gold nanoparticles (Au-NPs) were synthesized in one step at room temperature, using gallic acid (GA) as reducer and stabilizer. Pb2+ is added during the gold nanoparticle formation. Analysis of Pb2+ is conducted by a dual strategy, namely, colorimetry and spectrometry. During Au-NPs synthesis, addition of Pb2+ would lead to formation of Pb-GA complex, which can induce the aggregation of newly-formed small unstable gold nanoclusters. Consequently, colorimetric detection of trace Pb2+ can be realized. As the Pb2+ concentration increases, the color turns from red-wine to purple, and finally blue. This method offers a sensitive linear correlation between the shift of the absorption band (Δλ) and logarithm of Pb2+ concentration ranging from 5.0 × 10−8 to 1.0 × 10−6 M with a linear fit coefficient of 0.998, and a high selectivity for Pb2+ detection with a low detection limit down to 2.5 × 10−8 M. PMID:22163517

Nanocomposite bulk of mechanically milled Al-Pb samples consolidated pore-free by the high-energy rate forming technique.

PubMed

Csanády, Agnes; Sajó, István; Lábár, János L; Szalay, András; Papp, Katalin; Balaton, Géza; Kálmán, Erika

2005-06-01

It is shown that pore-free bulk samples were produced by the high-energy rate forming axis-symmetrical powder compaction method for different application purposes in case of the very different, immiscible Al and Pb metal pair. The starting Al-Pb nanocomposites were made by mechanical milling of atomized Al and Pb powders either in a SPEX 9000 or a Fritsch Pulverisette 4 mill. Due to the conditions that milling was carried out in air, the PbO layer, originally existing at the surface of the atomized Pb powder, ruptured and was also dispersed in the composite. The presence of the nano PbO particles was proven by XRD and TEM (BF, DF, SAED). When the energy of milling was high, the PbO crystallites became so small that they could hardly be seen by XRD technique. Local distribution of the PbO nanoparticles was still visible in a TEM, using the process diffraction method. Both XRD and SAED proved to be useful for the evaluation of the results of the milling process and compaction.

Single-Shot Laser Ablation Split-Stream (SS-LASS) Analysis Depth Profiling

NASA Astrophysics Data System (ADS)

Kylander-Clark, A. R.; Stearns, M. A.; Viete, D. R.; Cottle, J. M.; Hacker, B. R.

2014-12-01

Laser ablation depth profiling of geochronometers—such as zircon, monazite, titanite and rutile—has become popular in recent years as a tool to both determine date vs. depth or trace-element (TE) composition vs. depth; the former allows the dating of thin rims and, potentially, inversion of Pb-loss profiles for thermal histories, whereas the latter can yield insight into changes in PTX or mineral parageneses and inversion of trace-element profiles for thermal histories. In this study, we combine both techniques, enabling simultaneous acquisition of U-Th/Pb isotopic ratios and trace-element compositions, by joining a 193 nm excimer laser to a multi-collector ICP-MS and single-collector ICP-MS. The simultaneous acquisition allows direct shot-by-shot linkage between time and petrology, expanding our ability to understand the evolution of complex geologic systems. We construct each depth profile by capturing the analyte with a succession of individual laser pulses (each ~100 nm deep) . This has two main advantages over a typical time-dependent analysis of a multi-shot routine composed of tens to hundreds of shots and a several μm deep hole. 1) The reference material is analyzed between each shot for a more-accurate standardization of each aliquot of ablated material. 2) There is no mixing of material ablated from successive laser pulses during transmission to the ICP. The method is limited by count rate, which depends on spot size, excavation rate, instrument sensitivity, etc., and, for single-collector ICP, the switching time, which limits the number of elements that can be analyzed and their total counts. We explore the latter theoretically and experimentally to provide insight on both the ideal number of elements to measure and the dwell time in any given sample. Examples of the utility of SS-LASS include the comparison of apparent Pb loss to diffusion profiles of trace elements in rims of metamorphic rutile and titanite, as well as the determination of the timing and petrologic conditions of thin zircon rims in metamorphic rocks.

U-Th-Pb systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks.

NASA Technical Reports Server (NTRS)

Tera, F.; Wasserburg, G. J.

1972-01-01

The isotopic composition of Pb and the elemental concentration of U, Th and Pb were measured on 'total' rock samples 14053, 14073 and 14310 and on mineral separates of 14310 and 14053. These are the first Pb-U isochrons obtained for lunar basalts and indicate a reasonable solution to the previous discrepancy between the different methods of 'absolute' age determination. The resulting U-Pb isochron ages are compatible with the Rb-Sr and K-Ar ages on the same rocks. However, it is not possible to establish a precise time of 'crystallization' from the Pb-U data because of the small angle of intersection between the linear arrays and the concordia curve. These data show that total rock model ages do not in general yield crystallization ages. The data on 14310 and 14053 show that these rocks were formed containing a highly radiogenic initial lead which accounts for the excessively high total rock model ages by the U-Th-Pb method. The data prove that at the time of extrusion of some basalts, unsupported lead with extremely high Pb-207/Pb-206 ratios was added to the lunar surface.

Sediment deposition rates on the continental margins of the eastern Arabian Sea using 210Pb, 137Cs and 14C.

PubMed

Somayajulu, B L; Bhushan, R; Sarkar, A; Burr, G S; Jull, A J

1999-09-30

Eight gravity cores from the active eastern continental margins of the Arabian Sea were dated using 210Pbxs, 137Cs and 14C. The short-term (< or = 100 years) sedimentation rates range from 0.06 to 0.66 cm/year where as the long-term (> or = 1000 years) ones using AMS 14C on planktonic foraminifera varied from 0.004 to 0.13 cm/year. For long-term chronology (< or = 50,000 years) AMS dating of well-cleaned planktonic foraminifera is most suited.

Evaluation of purity with its uncertainty value in high purity lead stick by conventional and electro-gravimetric methods

PubMed Central

2013-01-01

Background A conventional gravimetry and electro-gravimetry study has been carried out for the precise and accurate purity determination of lead (Pb) in high purity lead stick and for preparation of reference standard. Reference materials are standards containing a known amount of an analyte and provide a reference value to determine unknown concentrations or to calibrate analytical instruments. A stock solution of approximate 2 kg has been prepared after dissolving approximate 2 g of Pb stick in 5% ultra pure nitric acid. From the stock solution five replicates of approximate 50 g have been taken for determination of purity by each method. The Pb has been determined as PbSO4 by conventional gravimetry, as PbO2 by electro gravimetry. The percentage purity of the metallic Pb was calculated accordingly from PbSO4 and PbO2. Results On the basis of experimental observations it has been concluded that by conventional gravimetry and electro-gravimetry the purity of Pb was found to be 99.98 ± 0.24 and 99.97 ± 0.27 g/100 g and on the basis of Pb purity the concentration of reference standard solutions were found to be 1000.88 ± 2.44 and 1000.81 ± 2.68 mg kg-1 respectively with 95% confidence level (k = 2). The uncertainty evaluation has also been carried out in Pb determination following EURACHEM/GUM guidelines. The final analytical results quantifying uncertainty fulfills this requirement and gives a measure of the confidence level of the concerned laboratory. Conclusions Gravimetry is the most reliable technique in comparison to titremetry and instrumental method and the results of gravimetry are directly traceable to SI unit. Gravimetric analysis, if methods are followed carefully, provides for exceedingly precise analysis. In classical gravimetry the major uncertainties are due to repeatability but in electro-gravimetry several other factors also affect the final results. PMID:23800080

Evaluation of purity with its uncertainty value in high purity lead stick by conventional and electro-gravimetric methods.

PubMed

Singh, Nahar; Singh, Niranjan; Tripathy, S Swarupa; Soni, Daya; Singh, Khem; Gupta, Prabhat K

2013-06-26

A conventional gravimetry and electro-gravimetry study has been carried out for the precise and accurate purity determination of lead (Pb) in high purity lead stick and for preparation of reference standard. Reference materials are standards containing a known amount of an analyte and provide a reference value to determine unknown concentrations or to calibrate analytical instruments. A stock solution of approximate 2 kg has been prepared after dissolving approximate 2 g of Pb stick in 5% ultra pure nitric acid. From the stock solution five replicates of approximate 50 g have been taken for determination of purity by each method. The Pb has been determined as PbSO4 by conventional gravimetry, as PbO2 by electro gravimetry. The percentage purity of the metallic Pb was calculated accordingly from PbSO4 and PbO2. On the basis of experimental observations it has been concluded that by conventional gravimetry and electro-gravimetry the purity of Pb was found to be 99.98 ± 0.24 and 99.97 ± 0.27 g/100 g and on the basis of Pb purity the concentration of reference standard solutions were found to be 1000.88 ± 2.44 and 1000.81 ± 2.68 mg kg-1 respectively with 95% confidence level (k = 2). The uncertainty evaluation has also been carried out in Pb determination following EURACHEM/GUM guidelines. The final analytical results quantifying uncertainty fulfills this requirement and gives a measure of the confidence level of the concerned laboratory. Gravimetry is the most reliable technique in comparison to titremetry and instrumental method and the results of gravimetry are directly traceable to SI unit. Gravimetric analysis, if methods are followed carefully, provides for exceedingly precise analysis. In classical gravimetry the major uncertainties are due to repeatability but in electro-gravimetry several other factors also affect the final results.

Mass-spectrometric mining of Hadean zircons by automated SHRIMP multi-collector and single-collector U/Pb zircon age dating: The first 100,000 grains

NASA Astrophysics Data System (ADS)

Holden, Peter; Lanc, Peter; Ireland, Trevor R.; Harrison, T. Mark; Foster, John J.; Bruce, Zane

2009-09-01

The identification and retrieval of a large population of ancient zircons (>4 Ga; Hadean) is of utmost priority if models of the early evolution of Earth are to be rigorously tested. We have developed a rapid and accurate U-Pb zircon age determination protocol utilizing a fully automated multi-collector ion microprobe, the ANU SHRIMP II, to screen and date these zircons. Unattended data acquisition relies on the calibration of a digitized sample map to the Sensitive High Resolution Ion MicroProbe (SHRIMP) sample-stage co-ordinate system. High precision positioning of individual grains can be produced through optical image processing of a specified mount location. The focal position of the mount can be optimized through a correlation between secondary-ion steering and the spot position on the target. For the Hadean zircon project, sample mounts are photographed and sample locations (normally grain centers) are determined off-line. The sample is loaded, reference points calibrated, and the target positions are then visited sequentially. In SHRIMP II multiple-collector mode, zircons are initially screened (ca. 5 s data acquisition) through their 204Pb corrected 207Pb/206Pb ratio; suitable candidates are then analyzed in a longer routine to obtain better measurement statistics, U/Pb, and concentration data. In SHRIMP I and SHRIMP RG, we have incorporated the automated analysis protocol to single-collector measurements. These routines have been used to analyze over 100,000 zircons from the Jack Hills quartzite. Of these, ca. 7%, have an age greater than 3.8 Ga, the oldest grain being 4372 +/- 6 Ma (2[sigma]), and this age is part of a group of analyses around 4350 Ma which we interpret as the age when continental crust first began to coalesce in this region. In multi-collector mode, the analytical time taken for a single mount with 400 zircons is approximately 6 h; whereas in single-collector mode, the analytical time is ca. 17 h. With this productivity, we can produce significant numbers of zircons for statistically limited studies including correlations between age and morphology, mineral-inclusion paragenesis, as well as isotopic studies including Hf and O isotopic compositions, Pu-Xe, and Sm-Nd isotopes.

Determination of pyridostigmine bromide and its metabolites in biological samples.

PubMed

Zhao, Bin; Moochhala, Shabbir M; Lu, Jia; Tan, Donna; Lai, Mui Hoon

2006-01-01

Pyridostigmine bromide (PB) is a quartenary ammonium compound that inhibits the hydrolysis of acetylcholine by competitive reversible binding to acetylcholinesterase. PB is used for the symptomatic treatment of myasthenia gravis and has been applied as a prophylaxis against nerve agents. Many studies on PB have involved the reliance on techniques that extract and quantify PB in biological samples. This article presents an overview of the currently applied methodologies for the determination of PB and its metabolites in various biological samples. Articles published from January 1975 to the July 2005 were taken into consideration for the discussion of the metabolism and analytical method of PB. HPLC and GC methods have been used and discussed in most of the references cited in this review. Other methods such as RIA and CE that have been recently reported are also mentioned in this article. Basic information about the type of sample used for analysis, sample preparation, chromatographic column, mobile phase, detection mode and validation data are summarized in a table.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Despotopulos, John D.; Kmak, Kelly N.; Gharibyan, Narek

Eichrom’s Pb resin, a crown-ether-based extraction chromatography resin, was characterized for separation of the flerovium (Fl) homologs, Pb and Sn. Batch uptake of Pb(II) and Sn(IV) radionuclides was determined from an HNO 3 matrix. Pb(II) was strongly retained on the resin at all HNO 3 concentrations, while Sn(IV) showed no uptake. Extraction kinetics for Pb(II) were examined and show suitable uptake on the second time scale. Here, separation methods for the isolation of individual homologs, Pb(II) and Sn(IV), have been established using 2 mL pre-packed vacuum flow Pb resin columns.

Cretaceous joints in southeastern Canada: dating calcite-filled fractures

NASA Astrophysics Data System (ADS)

Schneider, David; Spalding, Jennifer; Gautheron, Cécile; Sarda, Philippe; Davis, Donald; Petts, Duane

2017-04-01

To resolve the timing of brittle tectonism is a challenge since the classical chronometers required for analyses are not often in equilibrium with the surrounding material or simply absent. In this study, we propose to couple LA-ICP-MS U-Pb and (U-Th)/He dating with geochemical proxies in vein calcite to tackle this dilemma. We examined intracratonic Middle Ordovician limestone bedrock that overlies Mesoproterozoic crystalline basement, which are cut by NE-trending fault zones that have historic M4-5 earthquakes along their trace. E-W to NE-SW vertical joint sets, the relatively youngest stress recorded in the bedrock, possess 1-7 mm thick calcite veins that seal fractures or coat fracture surfaces. The veins possess intragranular calcite that are lined with fine-grained calcite along the vein margin and can exhibit µm- to mm-scale offset (e.g. displaced fossil fragments in host rock). Calcite d18O and d13C values are analogous to the bulk composition of Middle to Late Ordovician limestones, and suggest vein formation from a source dominated by connate fluids. The calcite contain trails of fluid inclusions commonly along fractures, and 3He/4He analyses indicate a primitive, deep fluid signature (R/Ra: 0.5-2.7). Trace element geochemistry of the calcite is highly variable, generally following the elevated HREE and lower LREE of continental crust trends but individual crystals from a single vein may vary by three orders of magnitude. LA-ICP-MS geochemical traverse across veins show elevated concentrations along (sub)grain boundaries and the vein-host rock contact. Despite abundant helium concentrations, (U-Th)/He dating was unsuccessful yielding highly dispersed dates likely from excess helium derived from the fluid inclusions. However, LA-ICP-MS U-Pb dating on calcite separated from the veins yielded model ages of 110.7 ± 6.8 Ma (MSWD: 0.53; n: 16) to 81.4 ± 8.3 Ma (MSWD: 2.6; n: 17). Since all veins are from the same ENE-trend, we regressed all the calcite dates together, yielding an age of 101 ± 6 Ma (MSWD: 2.3). These veins are 200 km to the west and slightly younger than the c. 140-120 Ma alkaline igneous rocks which mark the surface trace of the Great Meteor Hotspot. The period of 110-90 Ma has been identified as a time of major plate reorganization that involved tectonic and magmatic events, which may be reflected in our new calcite dates. Nonetheless, LA-ICP-MS U-Pb dating of vein calcite was successful, and coupled with other geochemical information, can yield primary information about the timing and source of fluid flow through joints and fractures, which has direct applications to reducing risk associated with characterizing hydrocarbon reservoirs and deep geological repositories for nuclear waste.

Petrogenesis of the Yaochong granite and Mo deposit, Western Dabie orogen, eastern-central China: Constraints from zircon U-Pb and molybdenite Re-Os ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes

NASA Astrophysics Data System (ADS)

Chen, Wei; Xu, Zhaowen; Qiu, Wenhong; Li, Chao; Yu, Yang; Wang, Hao; Su, Yang

2015-05-01

The Dabie orogen is among the most famous continent-continent collisional orogenic belts in the world, and is characterized by intensive post-collisional extension, magmatism and Mo mineralization. However, the genetic links between the mineralization and the geodynamic evolution of the orogen remain unresolved. In this paper, the Yaochong Mo deposit and its associated granitic stocks were investigated to elucidate this issue. Our new zircon U-Pb ages yielded an Early Cretaceous age (133.3 ± 1.3 Ma) for the Yaochong granite, and our molybdenite Re-Os dating gave a similar age (135 ± 1 Ma) for the Mo deposit. The Yaochong stock is characterized by high silica and alkali but low Mg, Fe and Ca. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta, Ti and Y). The Yaochong granite has initial 87Sr/86Sr ratios of 0.7087-0.7096, and Pb isotopic ratios of (206Pb/204Pb)i = 16.599-16.704, (207Pb/204Pb)i = 15.170-15.618 and (208Pb/204Pb)i = 36.376-38.248. The granite has εNd(t) of -18.0 to -16.3 and εHf(t) values of -26.5 to -20.0. All these data indicate that the Yaochong granite is a high-K calc-alkaline fractionated I-type granite, and may have originated from partial melting of the thickened Yangtze continental crust. The Mo ores also show low radiogenic Pb isotopes similar to the Yaochong stock. Medium Re content in molybdenite (21.8-74.8 ppm) also suggests that the ore-forming materials were derived from the thickened lower crust with possibly minor mixing with the mantle. Similar to the Eastern Dabie orogen, the thickened crust beneath the Western Dabie orogen may also have experienced tectonic collapse, which may have exerted fundamental geodynamic controls on the two-stage Mo mineralization in the region.

Unraveling the Switch from Subduction to Exhumation within a Collisional Orogen: Split-stream U-Pb and Trace-element Results from the Western Gneiss Region, Norway (Invited)

NASA Astrophysics Data System (ADS)

Gordon, S. M.; Whitney, D. L.; Teyssier, C. P.; Fossen, H.; Desormeau, J. W.; Jessen, B.

2013-12-01

During continental collision, crustal material may be subducted to great depths and subsequently exhumed. Ultrahigh-pressure (UHP) terranes preserve a record of the subduction of crustal material during suturing of colliding continents and the exhumation of this material during extension and, in some cases, collapse of the orogen. The UHP rocks of the Western Gneiss Region (WGR), Norway, resulted from the collision of Baltica with Laurentia during the final stages of the Caledonian orogeny. The WGR represents one of the two largest UHP terranes on Earth and consists of a UHP eclogite-bearing domain south of the Møre-Trøndelag strike-slip fault and a HP mafic granulite-bearing domain north of the fault. At least some of the HP granulite is overprinted eclogite. To evaluate the metamorphic and structural relationship of mafic rocks and associated migmatite in both regions, we obtained LA-ICP-MS U-Pb dates and trace-element analyses for zircon from a variety of textural types of leucosome associated with mafic layers and lenses. Five leucosomes within highly deformed migmatite in the HP granulite complex on the Roan Peninsula reveal U-Pb lower-intercept ages from ca. 405 to 409 Ma and upper-intercept Proterozoic dates. These zircons have distinct trace-elements patterns: all of the zircons that yield Proterozoic dates have overall much higher REE concentrations, a more significant negative Eu anomaly (-0.3 to -0.7) and steeper HREE patterns (Lu/Dy = 5-12). In comparison, the Caledonian zircons reveal flatter Eu anomalies (-0.3 to 0.2) and less steep HREE patterns (Lu/Dy = 2-7), although the individual patterns do not seem to correlate with age. The Caledonian zircon patterns suggest crystallization at high-pressures and are distinct from the inherited Proterozoic grains. Similar results were obtained from zircon rims extracted from layer-parallel to crosscutting leucosomes from the UHP domain. Trace elements in zircon in these samples record the transition from high-pressure (garnet-present, plagioclase-absent) crystallization to lower-pressure (plagioclase-present) crystallization with garnet-present × plagioclase-absent REE patterns. Moreover, dates from the layer-parallel leucosomes are as old as 410-406 Ma. The new U-Pb dates suggest a similar melt crystallization history that was coeval with previously determined ages of (U)HP metamorphism of WGR eclogite. The More-Trondelag fault acted as a transform fault and accommodated coeval extension that exhumed both the (U)HP and granulite domains. Results are consistent with the presence of partially molten crust in a large part of the WGR at HP or UHP conditions during the latest stages of the Caledonian orogeny. The decreased viscosity and increased buoyancy and strain weakening induced by partial melting may have triggered or at least contributed to the switch from subduction to exhumation in the WGR, marking the end of collisional orogeny.

Two high resolution terrestrial records of atmospheric Pb deposition from New Brunswick, Canada, and Loch Laxford, Scotland.

PubMed

Kylander, Malin E; Weiss, Domink J; Kober, Bernd

2009-02-15

Environmental archives like peat deposits allow for the reconstruction of both naturally and anthropogenically forced changes in the biogeochemical cycle of Pb as well as the quantification of past and present atmospheric Pb pollution. However, records of atmospheric Pb deposition from pre-industrial times are lacking. In a publication by Weiss et al. [Weiss, D., Shotyk, W., Boyle, E.A., Kramers, J.D., Appleby, P.G., Cheburkin, A.K., Comparative study of the temporal evolution of atmospheric lead deposition in Scotland and eastern Canada using blanket peat bogs. Sci Total Environ 2002;292:7-18]. Pb isotopes data measured by Q-ICP-MS and TIMS, concentration and enrichment data was presented for sites in eastern Canada (PeW1) and northwestern Scotland (LL7c), dating to 1586 A.D and 715 A.D., respectively. Here these same cores are re-analysed for Pb isotopes by MC-ICP-MS thereby acquiring 204Pb data and improving on the original data in terms of resolution and temporal coverage. Significant differences were found between the Q-ICP-MS/TIMS and MC-ICP-MS measurements, particularly at PeW1. These discrepancies are attributed to the problematic presence of organic matter during sample preparation and analysis complicated by the heterogeneity of the organic compounds that survived sample preparation steps. The precision and accuracy of Pb isotopes in complex matrices like peat is not always well estimated by industrial standards like NIST-SRM 981 Pb. Lead pollution histories at each site were constructed using the MC-ICP-MS data. The entire LL7c record is likely subject to anthropogenic additions. Contributions from local mining were detected in Medieval times. Later, coal use and mining in Scotland, Wales and England became important. After industrialization (ca. 1885 A.D.) contributions from Broken Hill type ores and hence, leaded petrol, dominate atmospheric Pb signatures right up to modern times. At PeW1 anthropogenic impacts are first distinguishable in the late 17th century with the mining and use of local coal. After industrialization (ca. 1810 A.D.), coal and petrol are the main Pb sources. A comprehensive estimate of the natural atmospheric background 206Pb/207Pb signature in eastern Canadian aerosols is made with a value of approximately 1.19.

Metallogeny of precious and base metal mineralization in the Murchison Greenstone Belt, South Africa: indications from U-Pb and Pb-Pb geochronology

NASA Astrophysics Data System (ADS)

Jaguin, J.; Poujol, M.; Boulvais, P.; Robb, L. J.; Paquette, J. L.

2012-10-01

The 3.09 to 2.97 Ga Murchison Greenstone Belt is an important metallotect in the northern Kaapvaal Craton (South Africa), hosting several precious and base metal deposits. Central to the metallotect is the Antimony Line, striking ENE for over 35 km, which hosts a series of structurally controlled Sb-Au deposits. To the north of the Antimony Line, hosted within felsic volcanic rocks, is the Copper-Zinc Line where a series of small, ca. 2.97 Ga Cu-Zn volcanogenic massive sulfide (VMS)-type deposits occur. New data are provided for the Malati Pump gold mine, located at the eastern end of the Antimony Line. Crystallizations of a granodiorite in the Malati Pump Mine and of the Baderoukwe granodiorite are dated at 2,964 ± 7 and 2,970 ± 7 Ma, respectively (zircon U-Pb), while pyrite associated with gold mineralization yielded a Pb-Pb age of 2,967 ± 48 Ma. Therefore, granodiorite emplacement, sulfide mineral deposition and gold mineralization all happened at ca. 2.97 Ga. It is, thus, suggested that the major styles of orogenic Au-Sb and the Cu-Zn VMS mineralization in the Murchison Greenstone Belt are contemporaneous and that the formation of meso- to epithermal Au-Sb mineralization at fairly shallow levels was accompanied by submarine extrusion of felsic volcanic rocks to form associated Cu-Zn VMS mineralization.

Shocked monazite chronometry: integrating microstructural and in situ isotopic age data for determining precise impact ages

NASA Astrophysics Data System (ADS)

Erickson, Timmons M.; Timms, Nicholas E.; Kirkland, Christopher L.; Tohver, Eric; Cavosie, Aaron J.; Pearce, Mark A.; Reddy, Steven M.

2017-03-01

Monazite is a robust geochronometer and occurs in a wide range of rock types. Monazite also records shock deformation from meteorite impact but the effects of impact-related microstructures on the U-Th-Pb systematics remain poorly constrained. We have, therefore, analyzed shock-deformed monazite grains from the central uplift of the Vredefort impact structure, South Africa, and impact melt from the Araguainha impact structure, Brazil, using electron backscatter diffraction, electron microprobe elemental mapping, and secondary ion mass spectrometry (SIMS). Crystallographic orientation mapping of monazite grains from both impact structures reveals a similar combination of crystal-plastic deformation features, including shock twins, planar deformation bands and neoblasts. Shock twins were documented in up to four different orientations within individual monazite grains, occurring as compound and/or type one twins in (001), (100), ( 10bar{1} ), {110}, { 212 }, and type two (irrational) twin planes with rational shear directions in [0bar{1}bar{1}] and [bar{1}bar{1}0]. SIMS U-Th-Pb analyses of the plastically deformed parent domains reveal discordant age arrays, where discordance scales with increasing plastic strain. The correlation between discordance and strain is likely a result of the formation of fast diffusion pathways during the shock event. Neoblasts in granular monazite domains are strain-free, having grown during the impact events via consumption of strained parent grains. Neoblastic monazite from the Inlandsee leucogranofels at Vredefort records a 207Pb/206Pb age of 2010 ± 15 Ma (2 σ, n = 9), consistent with previous impact age estimates of 2020 Ma. Neoblastic monazite from Araguainha impact melt yield a Concordia age of 259 ± 5 Ma (2 σ, n = 7), which is consistent with previous impact age estimates of 255 ± 3 Ma. Our results demonstrate that targeting discrete microstructural domains in shocked monazite, as identified through orientation mapping, for in situ U-Th-Pb analysis can date impact-related deformation. Monazite is, therefore, one of the few high-temperature geochronometers that can be used for accurate and precise dating of meteorite impacts.

The self-absorption correction factors for 210Pb concentration in mining waste and influence on environmental radiation risk assessment.

PubMed

Bonczyk, Michal; Michalik, Boguslaw; Chmielewska, Izabela

2017-03-01

The radioactive lead isotope 210 Pb occurs in waste originating from metal smelting and refining industry, gas and oil extraction and sometimes from underground coal mines, which are deposited in natural environment very often. Radiation risk assessment requires accurate knowledge about the concentration of 210 Pb in such materials. Laboratory measurements seem to be the only reliable method applicable in environmental 210 Pb monitoring. One of the methods is gamma-ray spectrometry, which is a very fast and cost-effective method to determine 210 Pb concentration. On the other hand, the self-attenuation of gamma ray from 210 Pb (46.5 keV) in a sample is significant as it does not depend only on sample density but also on sample chemical composition (sample matrix). This phenomenon is responsible for the under-estimation of the 210 Pb activity concentration level often when gamma spectrometry is applied with no regard to relevant corrections. Finally, the corresponding radiation risk can be also improperly evaluated. Sixty samples of coal mining solid tailings (sediments created from underground mining water) were analysed. Slightly modified and adapted to the existing laboratory condition, a transmission method has been applied for the accurate measurement of 210 Pb concentration . The observed concentrations of 210 Pb range between 42.2 ÷ 11,700 Bq·kg -1 of dry mass. Experimentally obtained correction factors related to a sample density and elemental composition range between 1.11 and 6.97. Neglecting this factor can cause a significant error or underestimations in radiological risk assessment. The obtained results have been used for environmental radiation risk assessment performed by use of the ERICA tool assuming exposure conditions typical for the final destination of such kind of waste.

Isotopic and trace element compositions of upper mantle and lower crustal xenoliths, Cima volcanic field, California: Implications for evolution of the subcontinental lithospheric mantle

USGS Publications Warehouse

Mukasa, S.B.; Wilshire, H.G.

1997-01-01

Ultramafic and mafic xenoliths from the Cima volcanic field, southern California, provide evidence of episodic modification of the upper mantle and underplating of the crust beneath a portion of the southern Basin and Range province. The upper mantle xenoliths include spinel peridotite and anhydrous and hydrous pyroxenite, some cut by igneous-textured pyroxenite-gabbro veins and dikes and some by veins of amphibole ?? plagioclase. Igneous-textured pyroxenites and gabbros like the dike rocks also occur abundantly as isolated xenoliths inferred to represent underplated crust. Mineral and whole rock trace element compositions among and within the different groups of xenoliths are highly variable, reflecting multiple processes that include magma-mantle wall rock reactions, episodic intrusion and it filtration of basaltic melts of varied sources into the mantle wall rock, and fractionation. Nd, Sr, and Pb isotopic compositions mostly of clinopyroxene and plagioclase mineral separates show distinct differences between mantle xenoliths (??Nd = -5.7 to +3.4; 87Sr/86Sr = 0.7051 - 0.7073; 206Pb/204Pb = 19.045 - 19.195) and the igneous-textured xenoliths (??Nd = +7.7 to +11.7; 87Sr/86Sr = 0.7027 - 0.7036 with one carbonate-affected outlier at 0.7054; and 206Pb/204Pb = 18.751 - 19.068), so that they cannot be related. The igneous-textured pyroxenites and gabbros are similar in their isotopic compositions to the host basaltic rocks, which have ??Nd of+5.1 to +9.3; 87Sr/86Sr of 0.7028 - 0.7050, and 206Pb/204Pb of 18.685 - 21.050. The igneous-textured pyroxenites and gabbros are therefore inferred to be related to the host rocks as earlier cogenetic intrusions in the mantle and in the lower crust. Two samples of peridotite, one modally metasomatized by amphibole and the other by plagioclase, have isotopic compositions intermediate between the igneous-textured xenoliths and the mantle rock, suggesting mixing, but also derivation of the metasomatizing magmas from two separate and distinct sources. Sm-Nd two-mineral "isochrons" yield apparent ages for petrographically identical rocks believed to be coeval ranging from -0 to 113 ?? 26 Ma, indicating the unreliability of dating these rocks with this method. Amphibole and plagioclase megacrysts are isotopically like the host basalts and probably originate by mechanical breakup of veins comagmatic with the host basaltic rocks. Unlike other Basin and Range localities, Cima Cr-diopside group isotopic compositions do not overlap with those of the host basalts. Copyright 1997 by the American Geophysical Union.

77 FR 12482 - Approval and Promulgation of Air Quality Implementation Plans; Indiana; Lead Ambient Air Quality...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-03-01

... Promulgation of Air Quality Implementation Plans; Indiana; Lead Ambient Air Quality Standards AGENCY... incorporates the National Ambient Air Quality Standards (NAAQS) for Pb promulgated by EPA in 2008. DATES: This... FR 66964) and codified at 40 CFR 50.16, ``National primary and secondary ambient air quality...

Protocol to Reconstruct Historical Contaminant Loading to Large Lakes: The Lake Michigan Sediment Record of Mercury

EPA Science Inventory

Samples of opportunity from Pb-210 dated sediment cores collected from Lake Michigan between 1994 and 1996 were analyzed for mercury. The storage of both anthropogenic and total (post-1850) mercury in the lake was calculated to be 186 and 228 metric tons, respectively. By setti...

Early Pan-African evolution of the basement around Elat, Israel, and the Sinai Peninsula revealed by single-zircon evaporation dating, and implications for crustal accretion rates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kroener, A.; Eyal, M.; Eyal, Y.

1990-06-01

The authors report {sup 207}Pb/{sup 206}Pb single-zircon evaporation ages for early Pan-African rocks from southern Israel and the northeastern Sinai Peninsula, the northernmost extension of the Arabian-Nubian shield. The oldest rocks are metamorphic schists of presumed island-arc derivation; detrital zircons date the source terrain at ca. 800-820 Ma. A major phase of tonalite-trondhjemite plutonism occurred at ca. 760-780 Ma; more evolved granitic rocks were emplaced at about 745 Ma. A metagabbro-metadiorite complex reflects the youngest igneous phase at ca. 640 Ma. We find no evidence for pre-Pan-African crust, and our data document important crust-forming events that correlate with similar episodesmore » elsewhere in the shield. The widespread presence of early Pan-African juvenile rocks (i.e., ca. 760-850 Ma) in many parts of the Arabian-Nubian shield makes this period the most important in the magmatic history of the shield and supports earlier suggestions for unusually high crust-production rates.« less

Comment on "Zircon U-Th-Pb dating using LA-ICP-MS: Simultaneous U-Pb and U-Th dating on 0.1 Ma Toya Tephra, Japan" by Hisatoshi Ito

NASA Astrophysics Data System (ADS)

Guillong, M.; Schmitt, A. K.; Bachmann, O.

2015-04-01

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of eight zircon reference materials and synthetic zircon-hafnon end-members indicate that corrections for abundance sensitivity and molecular zirconium sesquioxide ions (Zr2O3+) are critical for reliable determination of 230Th abundances in zircon. Other polyatomic interferences in the mass range 223-233 amu are insignificant. When corrected for abundance sensitivity and interferences, activity ratios of (230Th)/(238U) for the zircon reference materials we used average 1.001 ± 0.010 (1σ error; mean square of weighted deviates MSWD = 1.45; n = 8). This includes the 91500 and Plešovice zircons, which were deemed unsuitable for calibration of (230Th)/(238U) by Ito (2014). Uranium series zircon ages generated by LA-ICP-MS without mitigating (e.g., by high mass resolution) or correcting for abundance sensitivity and molecular interferences on 230Th such as those presented by Ito (2014) are potentially unreliable.

Refined depositional history and dating of the Tongaporutuan reference section, north Taranaki, New Zealand: new volcanic ash U-Pb zircon ages, biostratigraphy and sedimentation rates

USGS Publications Warehouse

Maier, K.L.; Crundwell, Martin P.; Coble, Matthew A.; Kingsley-Smith, Peter R.; Graham, Stephan A.

2016-01-01

This study presents new radiometric ages from volcanic ash beds within a c. 1900 m thick, progradational, deep-water clastic slope succession of late Miocene age exposed along the north Taranaki coast of the North Island, New Zealand. The ash beds yield U–Pb zircon ages ranging from 10.63 ± 0.65 Ma to 8.97 ± 0.22 Ma. The new ages are compatible with and provide corroboration of New Zealand Tongaporutuan Stage planktic foraminiferal and bolboformid biostratigraphic events identified in the same section. The close accord between these two age datasets provides a stratigraphically consistent and coherent basis for examining margin evolution. The arrival of a prograding clastic wedge and ensuing upward shoaling is recorded by sedimentation rates c. 2000 m/Ma–1 that are an order of magnitude higher than sedimentation rates on the precursor deep basin floor. This outcrop study provides new constraints for interpreting analogous subsurface deposits in Taranaki Basin and complements the regional late Miocene biostratigraphic dating framework.

Late Pleistocene granodiorite beneath Crater Lake caldera, Oregon, dated by ion microprobe

USGS Publications Warehouse

Bacon, C.R.; Persing, H.M.; Wooden, J.L.; Ireland, T.R.

2000-01-01

Variably melted granodiorite blocks ejected during the Holocene caldera-forming eruption of Mount Mazama were plucked from the walls of the climactic magma chamber ~15 km depth. Ion-microprobe U-Pb dating of zircons from two unmelted granodiorite blocks with SHRIMP RG (sensitive high-resolution ion microprobe-reverse geometry) gives a nominal 238U/206Pb age of 101+78-80 ka, or 174+89-115 ka when adjusted for an initial 230Th deficit. SHRIMP RG U-Th measurements on a subset of the zircons yield a 230Th/238U isochron age of 112 ?? 24 ka, considered to be the best estimate of the time of solidification of the pluton. These results suggest that the granodiorite is related to andesite and dacite of Mount Mazama and not to magmas of the climactic eruption. The unexposed granodiorite has an area of at least 28 km2. This young, shallow pluton was emplaced in virtually the same location where a similarly large magma body accumulated and powered violent explosive eruptions ~7700 yr ago, resulting in collapse of Crater Lake caldera.

Zircon U-Pb and molybdenite Re-Os geochronology and geological significance of the Baoshan porphyry Cu polymetallic deposit in Jiangxi province

NASA Astrophysics Data System (ADS)

Jia, Liqiong; Wang, Liang

2017-10-01

Baoshan porphyry Cu polymetallic deposit belongs to Jiujiang-Ruichang Cu-Au ore field, which is a component part of the Middle-Lower Yangtze River Cu-Au metallogenic belt. The U-Pb LA-MC-TCP MS dating of the zircons from Baoshan granodiorite porphyry yields an age of 147.81±0.48Ma (MSWD=1.07). Six molybdenite samples separated from Baoshan deposit are used for Re-Os dating and obtained the weighted average age of 147.42±0.84Ma and an isochron age of 147.7±1.2Ma. These ages suggest that the mineralization in the Baoshan deposit is genetically associated to the granodiorite porphyry, and the process of rock-and ore-forming is continuous. These data indicate that ages of intrusion and ore-body from Baoshan deposit are almost identical to other typical magmatic intrusion and deposits in Jiujiang-Ruichang metallogenic district. Tt is inferred that the Baoshan deposit was formed in the transition from EW-striking Tndosinian tectonic domain to NE-striking Paleo-Pacific tectonic domain.

Post-17th-century changes of European lead emissions recorded in high-altitude alpine snow and ice.

PubMed

Schwikowski, Margit; Barbante, Carlo; Doering, Thomas; Gaeggeler, Heinz W; Boutron, Claude; Schotterer, Ulrich; Tobler, Leo; van de Velde, Katja; Ferrari, Christophe; Cozzi, Giulio; Rosman, Kevin; Cescon, Paolo

2004-02-15

Lead concentrations and lead isotope ratios were analyzed in two firn/ice cores covering the period from 1650 to 1994, which were obtained from the 4450 m high glacier saddle Colle Gnifetti located in the Monte Rosa massif at the Swiss-Italian border. This study presents the first glaciochemical time series with annual resolution, spanning several centuries of lead concentrations and lead isotopic compositions in precipitation in Europe. Lead concentrations in firn dated from the 1970s are approximately 25 times higher than in ice dated from the 17th century, confirming the massive rise in lead pollution in Europe during the last few centuries. A decline of the lead concentration is then observed during the last two decades, i.e., from 1975 to 1994. The lead isotope ratio 206Pb/207Pb decreased from about 1.18 in the 17th and 18th centuries to about 1.12 in the 1970s. These variations are in good agreement with available information on variations in anthropogenic lead emissions from West European countries, especially from the use of lead additives in gasoline.

Assay Methods for 238U, 232Th, and 210Pb in Lead and Calibration of 210Bi Bremsstrahlung Emission from Lead

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orrell, John L.; Aalseth, Craig E.; Arnquist, Isaac J.

2016-02-13

Assay methods for measuring 238U, 232Th, and 210Pb concentrations in refined lead are presented. The 238U and 232Th concentrations are assayed via inductively coupled plasma mass spectrometry (ICP-MS) after anion exchange column separation on dissolved lead samples. The 210Pb concentration is inferred through α-spectroscopy of a daughter isotope, 210Po, after chemical precipitation separation on dissolved lead samples. Subsequent to the 210Po α-spectroscopy assay, a method for evaluating 210Pb concentrations in solid lead samples was developed via measurement of bremsstrahlung radiation from β-decay of a daughter isotope, 210Bi, by employing a 14-crystal array of high purity germanium (HPGe) detectors. Ten sourcesmore » of refined lead were assayed. The 238U concentrations were <34 microBq/kg and the 232Th concentrations ranged <0.6 – 15 microBq/kg, as determined by the ICP-MS assay method. The 210Pb concentrations ranged from ~0.1 – 75 Bq/kg, as inferred by the 210Po α-spectroscopy assay method.« less

Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia

USGS Publications Warehouse

Aleinikoff, J.N.; Horton, J. Wright; Walter, M.

1996-01-01

Uranium-lead dating of zircons from the Montpelier Anorthosite confirms previous interpretations, based on equivocal evidence, that the Goochland terrane in the eastern Piedmont of Virginia contains Grenvillian basement rocks of Middle Proterozoic age. A very few prismatic, elongate, euhedral zircons, which contain 12-29 ppm uranium, are interpreted to be igneous in origin. The vast majority of zircons are more equant, subangular to anhedral, contain 38-52 ppm uranium, and are interpreted to be metamorphic in origin. One fraction of elongate zircon, and four fragments of a very large zircon (occurring in a nelsonite segregation) yield an upper intercept age of 1045 ?? 10 Ma, interpreted as the time of anorthosite crystallization. Irregularly shaped metamorphic zircons are dated at 1011 ?? 2 Ma (weighted average of the 207Pb/206Pb ages). The U-Pb isotopic systematics of metamorphic titanite were reset during the Alleghanian orogeny at 297 ?? 5 Ma. These data provide a minimum age for gneisses of the Goochland terrane that are intruded by the anorthosite. Middle Proterozoic basement rocks of the Goochland terrane may be correlative with those in the Shenandoah massif of the Blue Ridge tectonic province, as suggested by similarities between the Montpelier Anorthosite and the Roseland anorthosite. Although the areal extent of Middle Proterozoic basement and basement-cover relations in the eastern Piedmont remain unresolved, results of this investigation indicate that the Goochland terrane is an internal massif of Laurentian crust rather than an exotic accreted terrane.

Pre-Variscan evolution of the Western Tatra Mountains: new insights from U-Pb zircon dating.

PubMed

Burda, Jolanta; Klötzli, Urs

In situ LA-MC-ICP-MS U-Pb zircon geochronology combined with cathodoluminescence imaging were carried out to determine protolith and metamorphic ages of orthogneisses from the Western Tatra Mountains (Central Western Carpathians). The metamorphic complex is subdivided into two units (the Lower Unit and the Upper Unit). Orthogneisses of the Lower Unit are mostly banded, fine- to medium-grained rocks while in the Upper Unit varieties with augen structures predominate. Orthogneisses show a dynamically recrystallised mineral assemblage of Qz + Pl + Bt ± Grt with accessory zircon and apatite. They are peraluminous (ASI = 1.20-1.27) and interpreted to belong to a high-K calc-alkaline suite of a VAG-type tectonic setting. LA-MC-ICP-MS U-Pb zircon data from samples from both units, from crystals with oscillatory zoning and Th/U > 0.1, yield similar concordia ages of ca. 534 Ma. This is interpreted to reflect the magmatic crystallization age of igneous precursors. These oldest meta-magmatics so far dated in the Western Tatra Mountains could be linked to the fragmentation of the northern margin of Gondwana. In zircons from a gneiss from the Upper Unit, cores with well-developed oscillatory zoning are surrounded by weakly luminescent, low contrast rims (Th/U < 0.1). These yield a concordia age of ca. 387 Ma corresponding to a subsequent, Eo-Variscan, high-grade metamorphic event, connected with the formation of crustal-scale nappe structures and collision-related magmatism.

Determination of (210)Pb and (210)Po in water using the extractive scintillation cocktail Polex™.

PubMed

Landstetter, Claudia; Hiegesberger, Bernd; Sinojmeri, Merita; Katzlberger, Christian

2014-11-01

Method validation was performed to achieve the accreditation for our determination method of (210)Pb and (210)Po in water. A Pb(NO3)2 carrier is added to the sample and lead is precipitated with Na2SxH2O. (210)Po is co-precipitated and the extractive scintillation cocktail Polex(™) is used to determine (210)Po and (210)Pb. Uranium is also extracted by Polex(™). It can be removed by washing the precipitate with 1% HNO3. The ingrowth of (210)Pb from (222)Rn during transportation time must be calculated. It has to be subtracted from the original (210)Pb in the sample and taken into account for the calculation of the lower limit of detection. Copyright © 2014 Elsevier Ltd. All rights reserved.

Why would we use the Sediment Isotope Tomography (SIT) model to establish a 210Pb-based chronology in recent-sediment cores?

PubMed

Abril Hernández, José-María

2015-05-01

After half a century, the use of unsupported (210)Pb ((210)Pbexc) is still far off from being a well established dating tool for recent sediments with widespread applicability. Recent results from the statistical analysis of time series of fluxes, mass sediment accumulation rates (SAR), and initial activities, derived from varved sediments, place serious constraints to the assumption of constant fluxes, which is widely used in dating models. The Sediment Isotope Tomography (SIT) model, under the assumption of non post-depositional redistribution, is used for dating recent sediments in scenarios in that fluxes and SAR are uncorrelated and both vary with time. By using a simple graphical analysis, this paper shows that under the above assumptions, any given (210)Pbexc profile, even with the restriction of a discrete set of reference points, is compatible with an infinite number of chronological lines, and thus generating an infinite number of mathematically exact solutions for histories of initial activity concentrations, SAR and fluxes onto the SWI, with these two last ranging from zero up to infinity. Particularly, SIT results, without additional assumptions, cannot contain any statistically significant difference with respect to the exact solutions consisting in intervals of constant SAR or constant fluxes (both being consistent with the reference points). Therefore, there is not any benefit in its use as a dating tool without the explicit introduction of additional restrictive assumptions about fluxes, SAR and/or their interrelationship. Copyright © 2015 Elsevier Ltd. All rights reserved.

Natural and Human Impacts on the Coastal Environment of Taiwan Recorded in Marine Sediments During the last century

NASA Astrophysics Data System (ADS)

Li, H.; Chen, Z.; Huh, C.; Chen, K.; Lin, Y.; Hsu, F.

2012-12-01

Located at tropical-to-subtropical region on the Pacific rim, Taiwan has very high erosion rate due to steep topography and heavy rainfall especially typhoons. The high sedimentation rates in Taiwan Strait allow us to retrieve high-resolution marine records which reveal natural changes and human impacts on the coastal environment of Taiwan over the past 100 years. Five gravity and box cores well dated by 210Pb and 137Cs methods were analyzed for elemental concentrations in the acid-leachable phase, total organic carbon (TOC), δ13CTOC, δ13C and δ18O of carbonates. The results show that: (1) Positive correlation between TOC and typhoon rainfall since 1940 indicate that decline of vegetation coverage resulted in intensification of soil erosion. The δ13CTOC values illustrate that the organic carbon in the sediments was originated mainly from land input. (2) The δ18O difference between foraminiferal shells and carbonate grains can be used for rainfall reconstruction. (3) The Ca concentrations mainly from carbonates in the sediments were decreased since AD 1940, reflecting changes in sedimentary source and ocean acidfication. As development of the land use, more and more soil erosion caused depletion of authigenic marine sediments in the coast region. Ocean acidification led to less carbonate formation in seawater. (4) Since 1920, Pb concentration rapidly increased and peaked at ~1970 as Pb input from gasoline usage. Pb concentration dropped from 1970 to 1975 perhaps due to unleaded gasoline replacement. (5) In the nearshore environment, heavy metals such as Mn, Cu and Pb in the acid-leachable phase of the sediments strongly increased from 1950 to 1965 then kept relatively high level, reflecting heavy metal contamination from industrial source. The human impact on the coastal region of Taiwan not only caused changes in marine sediments and ocean water, but also disturbed the marine ecosystem. This study has been funded by NSC-100-3113-E-002-009: Study of CO2 capture, conversion, storage and reuse through the coastal ocean of Taiwan: The biological pump.

Method for preparing Pb-. beta. ''-alumina ceramic

DOEpatents

Hellstrom, E.E.

1984-08-30

A process is disclosed for preparing impermeable, polycrystalline samples of Pb-..beta..''-alumina ceramic from Na-..beta..''-alumina ceramic by ion exchange. The process comprises two steps. The first step is a high-temperature vapor phase exchange of Na by K, followed by substitution of Pb for K by immersing the sample in a molten Pb salt bath. The result is a polycrystalline Pb-..beta..''-alumina ceramic that is substantially crack-free.

Method for preparing Pb-.beta."-alumina ceramic

DOEpatents

Hellstrom, Eric E.

1986-01-01

A process is disclosed for preparing impermeable, polycrystalline samples of Pb-.beta."-alumina ceramic from Na-.beta."-alumina ceramic by ion exchange. The process comprises two steps. The first step is a high-temperature vapor phase exchange of Na by K, followed by substitution of Pb for K by immersing the sample in a molten Pb salt bath. The result is a polycrystalline Pb-.beta."-alumina ceramic that is substantially crack-free.

Zircon U-Pb geochronology, Sr-Nd isotope analyses, and petrogenetic study of the Dehnow diorite and Kuhsangi granodiorite (Paleo-Tethys), NE Iran

NASA Astrophysics Data System (ADS)

Karimpour, M. H.; Stern, C. R.; Farmer, G. L.

2010-03-01

The Paleo-Tethys ocean opened in Silurian time, and its subduction under the Turan plate started in the Late Devonian. By Late Triassic time (225 Ma), no Paleo-Tethys crust remained on the surface of the Iranian plate. Subsequently, however, obduction of the Turan plate over the Iranian plate emplaced allochthonous sheets in what is now northeastern Iran. The sheets contain meta-ophiolites, which have been dated at 281.4 and 277.4 Ma by the 40Ar- 39Ar method. These remnant Paleo-Tethys meta-ophiolites and associated metaflysch sequences were intruded by the Dehnow diorite and Kuhsangi granodiorite. Zircon U-Pb dating indicates that the age of the Kuhsangi granodiorite is 217 ± 4 Ma and that of the Dehnow diorite is 215 ± 4 Ma (Late Triassic, Norian). The granodiorite and diorite have magnetic susceptibilities of between 5 × 10 -5 and 20 × 10 -5 (SI units) and therefore are classified as belonging to the ilmenite series of reduced-type granitoids. Chemically, the Dehnow diorite and Kuhsangi granodiorite are moderately peraluminous S-type plutons with (La/Yb) N = 7-22 and no, or only small, negative Eu anomalies (Eu/Eu* = 0.55-1.1). Their initial 87Sr/ 86Sr ratios range from 0.707949 to 0.708589, and their initial ɛNd values range from -6.63 to -5.90 when recalculated to an age of 216 Ma. These values could be considered to represent continental crust-derived magmas, and metagreywacke to metapelite with initial ɛNd values of -15.01 may have been involved in their genesis, but these were not the sole parent material.

In Vitro And In Vivo Approaches For The Measurement Of Oral Bioavailability Of Lead (Pb) In Contaminated Soils: A Review

EPA Science Inventory

We reviewed the published evidence of lead (Pb) contamination of urban soils, soil Pb risk to children through hand-to-mouth activity, reduction of soil Pb bioavailability due to soil amendments, and methods to assess bioaccessibility which correlate with bioavailability of soil ...

Ultrasensitive detection of lead (II) based on fluorescent aptamer-functionalized carbon nanotubes.

PubMed

Taghdisi, Seyed Mohammad; Emrani, Somayeh Sarreshtehdar; Tabrizian, Kaveh; Ramezani, Mohammad; Abnous, Khalil; Emrani, Ahmad Sarreshtehdar

2014-05-01

Lead contamination is a serious environmental problem with toxic effects in human. Here, we developed a simple and sensitive sensing method employing ATTO 647N/aptamer-SWNT ensemble for detection of Pb(2+). This method is based on the super quenching capability of single-walled carbon nanotubes (SWNTs), high affinity of the aptamer toward Pb(2+) and different propensities of ATTO 647N-aptamer and ATTO 647N-aptamer/Pb(2+) complex for adsorption on SWNTs. In the absence of Pb(2+), the fluorescence of ATTO 647N-aptamer is efficiently quenched by SWNTs. Upon addition of Pb(2+), the aptamer binds to its target, leading to the formation of a G-quadruplex/Pb(2+) complex and does not interact with SWNTs and ATTO 647N-aptamer starts fluorescing. This sensor exhibited a high selectivity toward Pb(2+) and a limit of detection (LOD) as low as 0.42 nM was obtained. Also this sensor could be applied for detection of Pb(2+) ions in tap water and biological sample like serum with high sensitivity. Copyright © 2014 Elsevier B.V. All rights reserved.

U-Pb Dating of Calcite to Constrain Basinal Brine Flux Events: An Example from the Upper Midwest USA

NASA Astrophysics Data System (ADS)

Rasbury, T.; Luczaj, J.

2017-12-01

Calcite forms in a variety of settings and can be the product of surface to deep basinal fluids. As such, this mineral can uniquely record details of the fluids responsible for its formation. The forms of calcium carbonates and their stratigraphic relationships from the thin section to the regional scale give important insights on pulses of fluids. A fundamental question is the age of such fluid pulses. While calcite excludes uranium (U) from its crystal structure, some is incorporated and depending on the U/Pb ratio, this provides an opportunity for radiometric dating. Calcite crystals of various sizes and crystal habits are found in Paleozoic carbonate rocks throughout the region from the western Michigan basin to the upper Mississippi valley. These are typically associated with Mississippi Valley-type (MVT) mineralization, including galena, sphalerite, and iron sulfides, but typically post-date the main MVT event. We have analyzed a variety of these calcites and find multiple generations of calcite, separated by tens of millions of years. The initial Pb isotope ratios are similar to the isotope ratios of nearby galena, strongly suggesting a genetic relationship. Our oldest ages are 200 Ma, and we find ages ranging into the Cenozoic. Based on the Paleozoic-hosted galena Pb-isotope isoscapes from the region, the fluids may have been sourced from both the Michigan and Illinois basins. An important and unanswered question is what would cause significant fluid movement out of the basins substantially after Appalachian orogenesis. Noble gas data from brines in the Michigan Basin have a mantle component and have been suggested to be responsible for recognized elevated temperatures across the basin (Ma et al., 2009). Multiple thermal events during the Paleozoic and Mesozoic eras may have an internal heat source related to reactivation of faults of the Keweenawan Rift system below the Michigan Basin. Perhaps a mantle heat source from below episodically fluxes into the basins and displaces brines with important ore metals out of the basin. More work on the calcites will help to establish the geographic extent of the various fluid pulses in the region, which will lead to an improved understanding of the sources and paths of these fluids.

New high precision U-Pb calibration of the late Early-Triassic (Smithian-Spathian Boundary, South China)

NASA Astrophysics Data System (ADS)

Widmann, Philipp; Leu, Marc; Goudemand, Nicolas; Schaltegger, Urs; Bucher, Hugo

2017-04-01

Following the Permian-Triassic mass extinction (PTME), the Early Triassic is characterized by large short-lived perturbations of the global carbon cycle associated with radiation and extinction pulses of the biota. More stable conditions resumed in the Middle Triassic (Anisian). The exact ages and duration of these short-lived but intense radiation-extinction events as well as carbon cycle perturbations are poorly constrained and a robust intercalibration of U-Pb dates, biochronozones and carbon isotope fluctuations is still lacking. An accurate and precise time frame is essential in order to quantify the dynamics of the underlying mechanistic processes and to assess the validity of the various explanatory scenarios. The most drastic Early Triassic extinction occurred at the Smithian-Spathian boundary (SSB) and is associated with a globally recognized sharp positive excursion of the marine d13C signal. Based on the most recently published ages for the Permian-Triassic boundary (251.938 ± 0.029 Ma, Baresel et al., 2016) and for the Early-Middle Triassic boundary (247.05 ± 0.16 Ma, Ovtcharova et al., 2015), we know the Early Triassic lasted 4.9 myr. However, neither the position of the SSB nor the durations of the major biotic and abiotic events around the SSB are constrained by radiometric dates. Here, we will present new high precision, chemical abrasion, isotope dilution, thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb ages from single zircon crystals, sampled from closely spaced volcanic ash layers that bracket the SSB in the Nanpanjiang Basin (Guizhou province, South China). These ash layers are found in a mixed carbonate-siliciclastic, conodont-rich sedimentary succession (Luolou Formation) that is well calibrated biochronologically. We obtained best estimates of the ages of the SSB and associated events by applying Bayesian age modelling. References: Baresel, B., Bucher, H., Brosse, M., Cordey, F., Guodun, K., and Schaltegger, U., 2016. Precise age for the Permian-Triassic boundary in South China from high precision U-Pb geochronology and Bayesian age-depth modelling: Solid Earth Discussions, doi: 10 .5194 /se -2016 -145. Ovtcharova, M., Goudemand, N., Hammer, O., Guodun, K., Cordey, F., Galfetti, T., Schaltegger, U. and Bucher, H. 2015. Developing a strategy for accurate definition of a geological boundary through radio-isotopic and biochronological dating: the Early-Middle Triassic boundary (South China). Earth-Science Reviews, 146, 65-76.

Long wavelength PbSnTe lasers with CW operation above 77 K

NASA Technical Reports Server (NTRS)

Shinohara, K.; Yoshikawa, M.; Ito, M.; Ueda, R.

1980-01-01

Lead tin telluride diode lasers with emission wavelengths of 6 to 9 micrometers easily operate continuously at temperatures above 77K. These lasers have the Pb(1-y) Sn(y) TE/Pb(1-y) Te/Pb(1-y) Sn(y) Te/PbTe (substrate), (x y) double heterostructure. To prepare this structure by LPE, the growth temperature must be below 600 C to suppress diffusion of the tin during the epitaxial growth. When the heterojunctions are formed by the usual LPE method, the junction boundaries become irregular in the case for the lasers with wavelengths of over 10 micrometers at 77K. The mechanism by which the heterojunction boundaries become irregular is cleared and a new LPE method which prevents the irregularity is explained. The lasers prepared from the wafers grown by the new method have demonstrated CW operation at wavelengths longer than 10 micrometers above liquid nitrogen temperature.

GePb Alloy Growth Using Layer Inversion Method

NASA Astrophysics Data System (ADS)

Alahmad, Hakimah; Mosleh, Aboozar; Alher, Murtadha; Banihashemian, Seyedeh Fahimeh; Ghetmiri, Seyed Amir; Al-Kabi, Sattar; Du, Wei; Li, Bauhoa; Yu, Shui-Qing; Naseem, Hameed A.

2018-04-01

Germanium-lead films have been investigated as a new direct-bandgap group IV alloy. GePb films were deposited on Si via thermal evaporation of Ge and Pb solid sources using the layer inversion metal-induced crystallization method for comparison with the current laser-induced recrystallization method. Material characterization of the films using x-ray diffraction analysis revealed highly oriented crystallinity and Pb incorporation as high as 13.5% before and 5.2% after annealing. Transmission electron microscopy, scanning electron microscopy, and energy-dispersive x-ray mapping of the samples revealed uniform incorporation of elements and complete layer inversion. Optical characterization of the GePb films by Raman spectroscopy and photoluminescence techniques showed that annealing the samples resulted in higher crystalline quality as well as bandgap reduction. The bandgap reduction from 0.67 eV to 0.547 eV observed for the highest-quality material confirms the achievement of a direct-bandgap material.

GePb Alloy Growth Using Layer Inversion Method

NASA Astrophysics Data System (ADS)

Alahmad, Hakimah; Mosleh, Aboozar; Alher, Murtadha; Banihashemian, Seyedeh Fahimeh; Ghetmiri, Seyed Amir; Al-Kabi, Sattar; Du, Wei; Li, Bauhoa; Yu, Shui-Qing; Naseem, Hameed A.

2018-07-01

Germanium-lead films have been investigated as a new direct-bandgap group IV alloy. GePb films were deposited on Si via thermal evaporation of Ge and Pb solid sources using the layer inversion metal-induced crystallization method for comparison with the current laser-induced recrystallization method. Material characterization of the films using x-ray diffraction analysis revealed highly oriented crystallinity and Pb incorporation as high as 13.5% before and 5.2% after annealing. Transmission electron microscopy, scanning electron microscopy, and energy-dispersive x-ray mapping of the samples revealed uniform incorporation of elements and complete layer inversion. Optical characterization of the GePb films by Raman spectroscopy and photoluminescence techniques showed that annealing the samples resulted in higher crystalline quality as well as bandgap reduction. The bandgap reduction from 0.67 eV to 0.547 eV observed for the highest-quality material confirms the achievement of a direct-bandgap material.

Multi-proxy dating of Holocene maar lakes and Pleistocene dry maar sediments in the Eifel, Germany

NASA Astrophysics Data System (ADS)

Sirocko, Frank; Dietrich, Stephan; Veres, Daniel; Grootes, Pieter M.; Schaber-Mohr, Katja; Seelos, Klemens; Nadeau, Marie-Josée; Kromer, Bernd; Rothacker, Leo; Röhner, Marieke; Krbetschek, Matthias; Appleby, Peter; Hambach, Ulrich; Rolf, Christian; Sudo, Masafumi; Grim, Stephanie

2013-02-01

During the last twelve years the ELSA Project (Eifel Laminated Sediment Archive) at Mainz University has drilled a total of about 52 cores from 27 maar lakes and filled-in maar basins in the Eifel/Germany. Dating has been completed for the Holocene cores using 6 different methods (210Pb and 137Cs activities, palynostratigraphy, event markers, varve counting, 14C). In general, the different methods consistently complement one another within error margins. Event correlation was used for relating typical lithological changes with historically known events such as the two major Holocene flood events at 1342 AD and ca 800 BC. Dating of MIS2-MIS3 core sections is based on greyscale tuning, radiocarbon and OSL dating, magnetostratigraphy and tephrochronology. The lithological changes in the sediment cores demonstrate a sequence of events similar to the North Atlantic rapid climate variability of the Last Glacial Cycle. The warmest of the MIS3 interstadials was GI14, when a forest with abundant spruce covered the Eifel area from 55 to 48 ka BP, i.e. during a time when also other climate archives in Europe suggested very warm conditions. The forest of this "Early Stage 3 warm phase" developed subsequently into a steppe with scattered birch and pine, and finally into a glacial desert at around 25 ka BP. Evidence for Mono Lake and Laschamp geomagnetic excursions is found in two long cores. Several large eruptions during Middle and Late Pleistocene (Ulmener Maar - 11,000 varve years BP, Laacher See - 12,900 varve years BP, Mosenberg volcanoes/Meerfelder Maar 41-45 cal ka BP, Dümpel Maar 116 ka BP, Glees Maar - 151 ka BP) produced distinct ash-layers crucial for inter-core and inter-site correlations. The oldest investigated maar of the Eifel is 40Ar/39Ar dated to the time older than 520 ka BP.

{sup 210}Pb chronology of sequences affected by burrow excavation and infilling: Examples from shallow marine carbonate sediment sequences, Holocene South Florida and Caicos Platform, British West Indies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tedesco, L.P.; Aller, R.C.

A variety of sedimentological criteria and direct field observations indicate that deposits of shallow carbonate platforms and mud banks are extensively transformed during megafaunal bioturbation by deep-burrowing crustaceans. {sup 210}Pb dating of surficial sediment and burrow fills dissected from the upper 1--3 m of sediments at four sites on the Caicos Platform and in South Florida corroborates sedimentologic descriptions of rapid biogenic alteration of entire facies. {sup 210}Pb distributions from the study sites show that at least some infill is predominantly surficial sediment. Assuming that all identifiable deep burrow fills containing excess {sup 210}Pb derive from the uppermost 0--5 cmmore » interval, an estimate of facies replacement by nonlocal transport can be made based on measured excess {sup 210}Pb values of fill and the corresponding total discernible fill volume in cores. Calculations indicate that at the sites studied, burrow excavation and infilling can completely transform the upper 1--2 m, and possibly 3.5 m, of deposits in 100--600 yr. More rapid transformation of deposits is required if fill is derived from below 5 cm. Biogenic transformation rates are sufficiently fast compared to net sedimentation that burrow infills, not primarily physical deposition, determine the composition, porosity, fabric, and texture of the preserved facies. The {sup 210}Pb profiles in the deepest regions of deposits in the present cases are further complicated by basal enrichments of {sup 226}Ra, which apparently diffuses upwards from Pleistocene calcrete surfaces into overlying Holocene sediment. This diffusion requires careful documentation of supported {sup 210}Pb near this contact, but also offers the potential for an additional transport tracer internal to the deposits.« less

Mobility and phytoavailability of As and Pb in a contaminated soil using pine sawdust biochar under systematic change of redox conditions.

PubMed

Beiyuan, Jingzi; Awad, Yasser M; Beckers, Felix; Tsang, Daniel C W; Ok, Yong Sik; Rinklebe, Jörg

2017-07-01

Biochar has been adopted to control the mobility and phytoavailability of trace elements (TEs) in soils. To date, no attempt has been made to determine the mobility and phytoavailability of arsenic (As) and lead (Pb) in a contaminated soil with biochars as amendments under predefined redox potentials (E H ). Thus, in this study, a soil contaminated with As and Pb (2047 and 1677 mg kg -1 , respectively) was pre-incubated for 105 days with three amendments (pine sawdust biomass (BM) and two biochars produced from the same feedstock at 300 °C (BC300) and 550 °C (BC550)). The aged samples were then exposed to dynamic E H conditions to evaluate the mobility and phytoavailability of As and Pb after immobilization. The BM amendment significantly decreased and the BC300 slightly reduced the mobility and phytoavailability of As and Pb, which may be related to the oxygen-containing functional groups on the surface of BM and BC300. In contrast, BC550 increased the mobility of As at -300 to -100 mV and 100 mV, enhanced the phytoavailability of As under oxidizing condition (>100 mV), but reduced the phytoavailability of Pb, which might be caused by the properties of amendments and redox chemistry of the TEs. The effectiveness of BM and biochars for the stabilization of As and Pb varied under dynamic E H conditions, which indicates that detailed investigations should be conducted before the applications of biochar as soil amendment under variable environmental conditions, especially for contaminated paddy soils. Copyright © 2017 Elsevier Ltd. All rights reserved.

Primary Data on U/Pb-Isotope Ages and Lu/Hf-Isotope Geochemical Systematization of Detrital Zircons from the Lopatinskii Formation (Vendian-Cambrian Transition Levels) and the Tectonic Nature of Teya-Chapa Depression (Northeastern Yenisei Ridge)

NASA Astrophysics Data System (ADS)

Kuznetsov, N. B.; Priyatkina, N. S.; Rud'ko, S. V.; Shatsillo, A. V.; Collins, W. J.; Romanyuk, T. V.

2018-03-01

The main results are presented on U/Pb-isotope dating of 100 detrital zircons and, selectively, on the Lu/Hf-isotope system of 43 grains from sandstones of the Lopatinskii formation (the lower stratigraphic level of the Chingasan group). Ages from 896 ± 51 to 2925 ± 38 Ma were obtained with a pronounced maximum of 1890 Ma in the curve of probability density, along with ɛHf estimates from +8.4 to-15.1, which allow one to throw doubt upon the molasse nature of the Lopatinskii formation.

The Age of the Moon

NASA Astrophysics Data System (ADS)

Barboni, M.; Boehnke, P.; Keller, C. B.; Kohl, I. E.; McKeegan, K. D.; Schoene, B.; Young, E. D.

2016-12-01

Knowledge of the age of the Moon is important for understanding the early evolution of the solar system, including the timing of the hypothesized Giant Impact (GI). There have been many attempts to determine the Moon's age, but significant disagreement remains with some authors favoring an early formation and others arguing for a relatively young Moon formed at 4.4 Ga. Attempts to date the GI indirectly through its effects on the asteroid belt are problematic as there is no way to uniquely ascertain the cause of the observed disturbances (e.g., GI or meteorite parent body breakup). Determining the timing of the Lunar Magma Ocean (LMO) crystallization provides a more direct constraint on the age of the Moon, but interpreting the chronologic significance of LMO products is complicated by the fact that the only rock samples available are breccias. A better approach is to construct a model age for the fractional crystallization of the LMO since this should provide a global signature. Zircons from the Apollo samples are ancient, robust against later disturbances, and amenable to precise U-Pb geochronology and Hf isotope analyses that can be used to construct Lu-Hf model ages for the silicate differentiation of the Moon. Previous isotopic studies of Apollo zircons yielded artificially young Hf model ages because of the (then unknown) effect of neutron capture on Hf isotopic ratios generated by long exposure to cosmic radiation, and were unable to determine whether or not the U-Pb dates were concordant due to insufficient precision of in situ dating techniques. We have addressed these issues by carrying out CA-ID-TIMS U-Pb geochronology on Apollo 14 zircon fragments, followed by Hf isotope determination by solution MC-ICP-MS on the same volume of zircon. By constructing Hf model ages from zircons that are concordant to the sub-permil level, we show that the minimum age for the end of differentiation of the LMO, and by extension, the formation of the Moon, is 4.52 ± 0.01 Ga.

Antiquarian books as source of environment historical water data.

PubMed

Schram, Jürgen; Schneider, Mario; Horst, Rasmus; Thieme, Hagen

2009-05-01

Historical environment considerations are inevitable also for modern environmental analysis. They alone allow evaluation of anthropogenic impact into the environment. To receive information about the historical environment situation in inhabited regions, we approached this task by examining historical well dated and locatable products of the Homo faber. The work introduced here uses books as a source of environment historical data specially for the environmental compartment of water. The paper of historical books, dated by their printing and allocated by their watermark(1) (Wasserzeichensammlung Piccard, Piccard online, Hauptstaatsarchiv Stuttgart, ) is a trap for traces of heavy metals contaminating their production water in historical times. Great amounts of water were brought into contact with the paper pulp in the historical paper mill process. The cellulose of the pulp acts as an ion exchange material for heavy metals, forming a dynamic equilibrium. A well defined pulp production process, starting with used clothes, allows estimation of the concentration of historical heavy metals (Cu(2+), Pb(2+), Zn(2+), Cd(2+)) in the production water (river water). Ancient papers from well dated books are eluted without destruction of their paper and the resulting solution is analysed by ETAAS and inverse stripping voltammetry to determine the historical impact of metals. Afterwards in a flow system the eluted paper spot is equilibrated with different concentrations of heavy metals (Cu(2+), Pb(2+), Zn(2+), Cd(2+)) to plot the adsorption isotherm of that very spot. Both data together allows a calculation of the heavy metal content of the historical river. For different waters of Germany and the Netherlands of the 16th-18th Century the heavy metal load could be estimated. The resulting concentrations were mostly similar to the level of modern surface waters, but in the case of the Dutch waters of the 17th Century, they were e.g. for Pb(2+) significantly higher than modern values.

Magnesium Alleviates Adverse Effects of Lead on Growth, Photosynthesis, and Ultrastructural Alterations of Torreya grandis Seedlings.

PubMed

Shen, Jie; Song, Lili; Müller, Karin; Hu, Yuanyuan; Song, Yang; Yu, Weiwu; Wang, Hailong; Wu, Jiasheng

2016-01-01

Magnesium (Mg 2+ ) has been shown to reduce the physiological and biochemical stress in plants caused by heavy metals. To date our understanding of how Mg 2+ ameliorates the adverse effects of heavy metals in plants is scarce. The potential effect of Mg 2+ on lead (Pb 2+ ) toxicity in plants has not yet been studied. This study was designed to clarify the mechanism of Mg 2+ -induced alleviation of lead (Pb 2+ ) toxicity. Torreya grandis ( T. grandis ) seedlings were grown in substrate contaminated with 0, 700 and 1400 mg Pb 2+ per kg -1 and with or without the addition of 1040 mg kg -1 Mg 2+ . Growth parameters, concentrations of Pb 2+ and Mg 2+ in the plants' shoots and roots, photosynthetic pigment, gas exchange parameters, the maximum quantum efficiency (Fv/Fm), root oxidative activity, ultrastructure of chloroplasts and root growth were determined to analyze the effect of different Pb 2+ concentrations on the seedlings as well as the potential ameliorating effect of Mg 2+ on the Pb 2+ induced toxicity. All measurements were tested by a one-way ANOVA for the effects of treatments. The growth of T. grandis seedlings cultivated in soils treated with 1400 mg kg -1 Pb 2+ was significantly reduced compared with that of plants cultivated in soils treated with 0 or 700 mg kg -1 Pb 2+ . The addition of 1040 mg kg -1 Mg 2+ improved the growth of the Pb 2+ -stressed seedlings, which was accompanied by increased chlorophyll content, the net photosynthetic rate and Fv/Fm, and enhanced chloroplasts development. In addition, the application of Mg 2+ induced plants to accumulate five times higher concentrations of Pb 2+ in the roots and to absorb and translocate four times higher concentrations of Mg 2+ to the shoots than those without Mg 2+ application. Furthermore, Mg 2+ addition increased root growth and oxidative activity, and protected the root ultrastructure. To the best of our knowledge, our study is the first report on the mechanism of Mg 2+ -induced alleviation of Pb 2+ toxicity. The generated results may have important implications for understanding the physiological interactions between heavy metals and plants, and for successful management of T. grandis plantations grown on soils contaminated with Pb 2+ .

Concentration and Particle Size of Airborne Toxic Algae (Brevetoxin) Derived from Ocean Red Tide Events

PubMed Central

Cheng, Yung Sung; Mcdonald, Jacob D.; Kracko, Dean; Irvin, C. Mitch; Zhou, Yue; Pierce, Richard H.; Henry, Michael S.; Bourdelaisa, Andrea; Naar, Jerome; Baden, Daniel G.

2009-01-01

Red tides in the Gulf of Mexico are formed by blooms of the dinoflagellate Karenia brevis, which produces brevetoxins (PbTx). Brevetoxins can be transferred from water to air in the wind-powered whitecapped waves during red tide episodes. Inhalation exposure to marine aerosol containing PbTx causes respiratory problems. A liquid chromatograph/ tandem mass spectrometric method was developed for the detection and quantitation of several PbTxs in ambient samples collected during red tide events. This method was complemented by a previously developed antibody assay that analyzes the entire class of PbTx compounds. The method showed good linearity, accuracy, and reproducibility, allowing quantitation of PbTx compounds in the 10 pg/m3 range. Air concentrations of PbTxs and brevenal for individual samples ranged from 0.01 to 80 ng/m3. The particle size showed a single mode with a mass median diameter between 6 and 10 μm, which was consistent for all of the PbTx species that were measured. Our results imply that individual PbTxs were from the same marine aerosol or from marine aerosol that was produced from the same process. The particle size indicated the likelihood of high deposition efficiency in the respiratory tract with the majority of aerosol deposited in the upper airways and small but not insignificant deposition in the lower airways. PMID:15954221

Synthesis and Microstructure of Highly Oriented PbTiO3 Thin Films Prepared by a Sol-Gel Method

DTIC Science & Technology

1989-06-01

lead acetate with titanium isopropoxide * in 2-methoxyethanol,* in a method similar to that reported by Gurkovitch and Blum." The resulting yellow-gold...orientation by a sol-gel processing method. EXPERIMENTAL Precursor Solution Preparation Stock solutions of complex Pb-Ti alkoxide were prepared by reacting... solution had an equivalent PbTiO 3 concentration of approximately 66 wt%. The alkoxide solutions were handled as moisture-sensitive reagents and, as

Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%.

PubMed

Kim, Hui-Seon; Lee, Chang-Ryul; Im, Jeong-Hyeok; Lee, Ki-Beom; Moehl, Thomas; Marchioro, Arianna; Moon, Soo-Jin; Humphry-Baker, Robin; Yum, Jun-Ho; Moser, Jacques E; Grätzel, Michael; Park, Nam-Gyu

2012-01-01

We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH(3)NH(3))PbI(3) as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI(2) and deposited onto a submicron-thick mesoscopic TiO(2) film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (J(SC)) exceeding 17 mA/cm(2), an open circuit photovoltage (V(OC)) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH(3)NH(3))PbI(3) NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO(2) film. The use of a solid hole conductor dramatically improved the device stability compared to (CH(3)NH(3))PbI(3) -sensitized liquid junction cells.

U-Pb isotopic systematics of zircons from prograde and retrograde transition zones in high-grade orthogneisses, Sri Lanka

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baur, N.; Liew, T.C.; Todt, W.

1991-07-01

The authors present U-Pb zircon isotopic data from locally restricted prograde (arrested in situ charnockitization) and retrograde metamorphic transition zones, which are well exposed in Proterozoic orthogneisses tectonically interbanded with granulite facies supracrustal rocks of the Highland Group in Sri Lanka. These granitoid rocks yield apparent ages of 1942 {plus minus} 22 Ma, {approximately} 770 Ma, {approximately} 660 Ma, and {approximately} 560 Ma. All samples show severe Pb-loss some 550-560 Ma ago. The main phase of granulite-formation could not be dated unambiguously but is bracketed between {approximately} 660 Ma and {approximately} 550 Ma. The pervasive Pb-loss event around 550-560 Mamore » reflects the end of this period of high-grade metamorphism and was associated with widespread igneous activity and retrogression. This is constrained by the 550 {plus minus} 3 Ma intrusion age for a post-tectonic granite. They relate this late phase of thermal activity to crustal uplift of the Sri Lankan granulites. This data unambiguously prove the high-grade history of the Sri Lanka gneisses to be a late Precambrian event that may be related to the Pan-African evolution along the eastern part of Africa.« less

Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%

PubMed Central

Kim, Hui-Seon; Lee, Chang-Ryul; Im, Jeong-Hyeok; Lee, Ki-Beom; Moehl, Thomas; Marchioro, Arianna; Moon, Soo-Jin; Humphry-Baker, Robin; Yum, Jun-Ho; Moser, Jacques E.; Grätzel, Michael; Park, Nam-Gyu

2012-01-01

We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH3NH3)PbI3 as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI2 and deposited onto a submicron-thick mesoscopic TiO2 film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (JSC) exceeding 17 mA/cm2, an open circuit photovoltage (VOC) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH3NH3)PbI3 NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO2 film. The use of a solid hole conductor dramatically improved the device stability compared to (CH3NH3)PbI3 -sensitized liquid junction cells. PMID:22912919

Radionuclide activities and metal concentrations in sediments of the Sebou Estuary, NW Morocco, following a flooding event.

PubMed

Laissaoui, A; Mas, J L; Hurtado, S; Ziad, N; Villa, M; Benmansour, M

2013-06-01

This study presents metal concentrations (Fe, Mg, Mn, Co, Cu, Zn, Pb, As, Sr and V) and radionuclide activities ((40)K, (137)Cs, (210)Pb, (226)Ra, (228)Ac, (234)Th and (212)Pb) in surface deposits and a sediment core from the Sebou Estuary, Northwest Morocco. Samples were collected in April 2009, about 2 months after a flooding event, and analysed using a well-type coaxial gamma-ray detector and inductively coupled plasma-quadrupole mass spectrometry. Activities of radionuclides and concentrations of almost all elements in surface samples displayed only moderate spatial variation, suggesting homogenous deposition of eroded local soil in response to intense precipitation. Excess (210)Pb displayed relatively constant activity throughout the sediment core, preventing dating and precluding determination of the historical accumulation rates of pollutants at the core site. Some elements showed non-systematic trends with depth and displayed local maxima and minima. Other elements presented relatively systematic concentration trends or relatively constant levels with discrete maxima and/or minima. Except for Mn, Sr and Cr, all metal concentrations in sediment were below levels typical of polluted systems, suggesting little human impact or losses of metals from sediment particles.

Rapid determination of N,N-diethyl-m-toluamide and permethrin in human plasma by gas chromatography-mass spectrometry and pyridostigmine bromide by high-performance liquid chromatography.

PubMed

Cherstniakova, Svetlana A; Garcia, Gregory E; Strong, John; Bi, Daoqin; Weitz, Julie; Roy, Michael J; Cantilena, Louis R

2006-01-01

A rapid and highly sensitive gas chromatography-mass spectrometry (GC-MS) method for simultaneous determination of N,N-diethyl-m-toluamide (DEET) and permethrin with (2)H(10)-phenanthrene (98 atom %) as an internal standard and a separate external standard high-performance liquid chromatography (HPLC) method for pyridostigmine bromide (PB) determination in human plasma were developed and validated. The GC-MS method for DEET and permethrin quantification utilizes a one-step extraction with tert-butylmethylether. The HPLC method for PB quantification involves a solid-phase extraction and UV detection. The range of the analytical method for DEET and permethrin was 1 ng/mL to 100 ng/mL and for PB was 5 ng/mL to 100 ng/mL. Recovery from plasma proved to be more than 80%. The intraday precision ranged from 1.3% to 8% for DEET, from 2.1% to 11.4% for permethrin, and from 3.0% to 4.8% for PB. The interday precision was 3% for DEET, ranged from 5% to 9% for permethrin, and from 5% to 9% for PB. The accuracy for the limit of quantification was 92% +/- 8% relative standard deviation (RSD) for DEET, 112% +/- 11% RSD for permethrin, and 109% +/- 5% RSD for PB. All 3 compounds were stable in human plasma at -80 degrees C for at least 12 months and after 2 freeze-thaw cycles with RSD values ranging from 7.1% (DEET, 80 ng/mL) to 8.1% (DEET, 8 ng/mL), from 2.3% (permethrin, 80 ng/mL) to 11.6 % (permethrin, 8 ng/mL), and from 0.2% (PB, 80 ng/mL) to 3.6% (PB, 8 ng/mL). Both methods were successfully applied to pharmacokinetic/ pharmacodynamic studies of combined exposure of DEET (skin application), permethrin (treated uniforms), and PB (30 mg orally three times/day for four doses) in healthy volunteers (n = 81).

Small Volume Isotopic Analysis of Zircon Using LA-MC-ICP-MS U-Pb and Lu-Hf and Sub-ng Amounts of Hf in Solution

NASA Astrophysics Data System (ADS)

Bauer, A.; Horstwood, M. S.

2016-12-01

Crust-mantle evolution studies are greatly informed by zircon U-Pb and Lu-Hf isotopic datasets and the ease with which these data can now be acquired has seen their application become commonplace. In order to deconvolute geochemical change and interpret geologic variation in complexly zoned zircons, this information is most ideally obtained on the smallest volume of zircon by successive SIMS U-Pb and LA-MC-ICP-MS Lu-Hf isotopic analyses. However, due to variations in zircon growth zone geometry at depth, the Lu-Hf analysis may not relate to the lower volume U-Pb analysis, potentially causing inaccuracy of the resultant age-corrected Hf isotope signature. Laser ablation split-stream methods are applied to be certain that U-Pb and Lu-Hf data represent the same volume of zircon, however, the sampling volume remains relatively large at 40x30µm1. Coupled ID-TIMS U-Pb and solution MC-ICP-MS Lu-Hf work traditionally utilize whole-zircon dissolution ( 10-50ng Hf), which has the potential to homogenize different zones of geologic significance within an analysis. Conversely, modern ID-TIMS U-Pb methods utilize microsampling of zircon grains, often providing < 5ng Hf, thereby challenging conventional Lu-Hf acquisition protocols to achieve the required precision. In order to obtain usable precision on minimal zircon volumes, we developed laser ablation methods using successive 25um spot U-Pb and Lu-Hf ablation pits with a combined depth of 18um, and low-volume solution introduction methods without Hf-REE separation utilizing Hf amounts as low as 0.4ng, while retaining an uncertainty level of ca. 1 ɛHf for both methods. We investigated methods of Yb interference correction and the potential for matrix effects, with a particular focus on the accurate quantification of 176Lu/177Hf. These improvements reduce the minimum amount of material required for U-Pb and Hf isotopic analysis of zircon by about an order of magnitude. 1Ibanez-Mejia et al (2015). PreRes, 267, 285-310.

The Late Paleozoic magmatic evolution of the Aqishan-Yamansu belt, Eastern Tianshan: Constraints from geochronology, geochemistry and Sr-Nd-Pb-Hf isotopes of igneous rocks

NASA Astrophysics Data System (ADS)

Zhao, Liandang; Chen, Huayong; Zhang, Li; Zhang, Weifeng; Yang, Juntao; Yan, Xuelu

2018-03-01

The Aqishan-Yamansu belt in the Eastern Tianshan (Xinjiang, NW China) is an important mineralization belt. The belt mainly comprises Carboniferous volcanic, volcaniclastic and clastic rocks, and hosts many intermediate-felsic intrusions and Fe (-Cu) deposits. The biotite diorite, felsic brecciated tuff, granodiorite and syenite from the western Aqishan-Yamansu belt are newly zircon U-Pb dated to be 316.7 ± 1.4 Ma, 315.6 ± 2.6 Ma, 305.8 ± 1.9 Ma and 252.5 ± 1.4 Ma, respectively. The mafic rocks (mafic brecciated tuff and diabase porphyry) are tholeiitic to calc-alkaline series, LILE-rich (e.g., Rb, Ba and Pb), HFSE-depleted (e.g., Nb and Ta), and have high Mg#(44-60), Nb/Ta (15.0-20.0), Ba/La (>30) and Ba/Nb (>57) values/ratios, and low Th/Yb ratios (<1), probably originating from mantle wedge metasomatized by slab-derived fluids. The intermediate-felsic igneous rocks are LILE-rich, HFSE-depleted, with high Sr and Y contents showing typical of normal arc magma affinity. Moreover, the depleted εHf(t) (>2.10) and positive εNd(t) (>5.7), combined with variable Nb/Ta ratios (9.52-21.4), Y/Nb ratios (1.47-39.7) and Pb isotopes (206Pb/204Pb = 16.225-17.640, 207Pb/204Pb = 15.454-15.520, 208Pb/204Pb = 37.097-38.025) suggest that these rocks were magma mixing products between juvenile crustal-derived magmas and minor mantle-derived magmas. Combined published works with our new ages, geochemical and isotopic data, we propose that the Aqishan-Yamansu belt was an Early Carboniferous fore-arc basin during the southward subduction of the Kangguer oceanic slab beneath the Yili-Central Tianshan block. With the continuing southward subduction, the Aqishan-Yamansu fore-arc basin initiated to close, which generated the mafic and intensive intermediate-felsic magmatism associated with regional Fe (-Cu) mineralization.

A 300 year history of lead contamination in northern French Alps reconstructed from distant lake sediment records.

PubMed

Arnaud, F; Revel-Rolland, M; Bosch, D; Winiarski, T; Desmet, M; Tribovillard, N; Givelet, N

2004-05-01

Lead concentrations and isotopic ratios were measured along two well-dated sediment cores from two distant lakes: Anterne (2100 m a.s.l.) and Le Bourget (270 m a.s.l.), submitted to low and high direct human impact and covering the last 250 and 600 years, respectively. The measurement of lead in old sediment samples (>3000 BP) permits, in using mixing-models, the determination of lead concentration, flux and isotopic composition of purely anthropogenic origin. We thus show that since ca. 1800 AD the regional increase in lead contamination was mostly driven by coal consumption ((206)Pb/(207)Pb approximately 1.17-1.19; (206)Pb/(204)Pb approximately 18.3-18.6), which peaks around 1915 AD. The increasing usage of leaded gasoline, introduced in the 1920s, was recorded in both lakes by increasing Pb concentrations and decreasing Pb isotope ratios. A peak around 1970 ((206)Pb/(207)Pb approximately 1.13-1.16; (206)Pb/(204)Pb approximately 17.6-18.0) corresponds to the worldwide recorded leaded gasoline maximum of consumption. The 1973 oil crisis is characterised by a drastic drop of lead fluxes in both lakes (from approximately 35 to <20 mg cm(-2) yr(-1)). In the late 1980s, environmental policies made the Lake Anterne flux drop to pre-1900 values (<10 mg cm(-2) yr(-1)) while Lake Le Bourget is always submitted to an important flux (approximately 25 mg cm(-2) yr(-1)). The good match of our distant records, together and with a previously established series in an ice core from Mont Blanc, provides confidence in the use of sediments as archives of lead contamination. The integration of the Mont Blanc ice core results from Rosman et al. with our data highlights, from 1990 onward, a decoupling in lead sources between the high elevation sites (Lake Anterne and Mont Blanc ice core), submitted to a mixture of long-distance and regional contamination and the low elevation site (Lake Le Bourget), where regional contamination is predominant.

Ultrasonic-energy enhance the ionic liquid-based dual microextraction to preconcentrate the lead in ground and stored rain water samples as compared to conventional shaking method.

PubMed

Nizamani, Sooraj; Kazi, Tasneem G; Afridi, Hassan I

2018-01-01

An efficient preconcentration technique based on ultrasonic-assisted ionic liquid-based dual microextraction (UA-ILDµE) method has been developed to preconcentrate the lead (Pb +2 ) in ground and stored rain water. In the current proposed method, Pb +2 was complexed with a chelating agent (dithizone), whereas an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) was used for extraction purpose. The ultrasonic irradiation and electrical shaking system were applied to enhance the dispersion and extraction of Pb +2 complex in aqueous samples. For second phase, dual microextraction (DµE phase), the enriched Pb +2 complex in ionic liquid, extracted back into the acidic aqueous solution and finally determined by flame atomic absorption spectrometry. Some major analytical parameters that influenced the extraction efficiency of developed method, such as pH, concentration of ligand, volume of ionic liquid and samples, time of shaking in thermostatic electrical shaker and ultrasonic bath, effect of back extracting HNO 3 volume, matrix effect, centrifugation time and rate were optimized. At the sample volume of 25mL, the calculated preconcentration factor was 62.2. The limit of detection of proposed procedure for Pb +2 ions was found to be 0.54μgL -1 . The validation of developed method was performed by the analysis of certified sample of water SRM 1643e and standard addition method in a real water sample. The extraction recovery of Pb +2 was enhanced≥2% with shaking time of 80s in ultrasonic bath as compared to used thermostatic electrical shaker, where for optimum recovery up to 10min was required. The developed procedure was successfully used for the enrichment of Pb +2 in ground and stored rain water (surface water) samples of an endemic region of Pakistan. The resulted data indicated that the ground water samples were highly contaminated with Pb +2 , while some of the surface water samples were also have higher values of Pb +2 than permissible limit of WHO. The concentration of Pb +2 in surface and ground water samples was found in the range of 17.5-24.5 and 25.6-99.1μgL - 1 respectively. Copyright © 2017 Elsevier B.V. All rights reserved.

Polarization Bremsstrahlung: what is it and why haven't we seen it?

NASA Astrophysics Data System (ADS)

Quarles, C. A.

1997-10-01

Normal bremsstrahlung (NB) is the radiation by a charged particle when deflected in the Coulomb field of a target atom. This process has been studied in some detail since identification of the continuous x-ray spectrum early in this century. Since the early 1980's it has been possible, mainly due to the work of R. H. Pratt and co-workers, to obtain good theoretical predictions for NB for a wide range of incident electron energies and target atomic numbers. In the early 1980's, a second, distinct and competing process which has come to be called polarization bremsstrahlung (PB) was proposed by M. Ya. Amusia and others. PB is the radiation by a polarizable target due to the changing dipole moment induced by the passing charged projectile. It was argued that in some cases, especially for photon energies near the target atom absorption edges, PB would dominate over NB. Only recently, however, with the calculations of A. Korol and his co-workers has it been possible to consider what PB may look like over the whole range of the photon spectrum observed in a typical bremsstrahlung experiment. This paper will discuss, from the point of view of an experimentalist, what is involved in looking for the PB effect, why perhaps it has not been convincingly detected in bremsstrahlung experiments to date, and what the prospects are for its future observation.

Analysis and Tendencies of Metals and POPs in a Sediment Core from the Alvarado Lagoon System (ALS), Veracruz, Mexico.

PubMed

Botello, A V; Villanueva, F S; Rivera, R F; Velandia, A L; de la Lanza, G E

2018-07-01

This study focused on dating of a sediment core from the Alvarado Lagoon System, Veracruz, Mexico, calculating the sedimentation rate by using 210 Pb to determine the tendency towards pollution by polycyclic aromatic hydrocarbons, organochlorides, the metals Cd, Cr, Cu, Hg, Ni, Pb, and V, and organic matter content. The activity of total Pb and supported Pb in the samples was 83.1 and 29.5 Bq kg -1 , respectively, whereas the average estimated sedimentation rate was 0.48 ± 0.09 cm per year -1 . The organic matter values exhibited linear behavior throughout the historical profile, with values under 2.5%. Metal concentrations followed the order V > Cr > Ni > Cu > Pb > Hg > Cd. Variations found in Cr, Ni, Pb, and V concentrations are basically due to three meteorological phenomena that hit the region: hurricanes Gladys, Hilda, and Janet in September of 1955. V, Ni, and Hg input comes from anthropogenic and lithogenic sources. The presence of individual polycyclic aromatic hydrocarbons showed no ascending accumulation pattern over time, nor did it show any significant statistical correlation to OM. As for the organochlorine pesticides, 63.61% of the total sum of these compounds were from the ciclodienics family. Concentration of p,p'-DDT was observed only in the earliest profile, from 1929.

U-Pb geochronology of zircon and monazite from Mesoproterozoic granitic gneisses of the northern Blue Ridge, Virginia and Maryland, USA

USGS Publications Warehouse

Aleinikoff, J.N.; Burton, W.C.; Lyttle, P.T.; Nelson, A.E.; Southworth, C.S.

2000-01-01

Mesoproterozoic granitic gneisses comprise most of the basement of the northern Blue Ridge geologic province in Virginia and Maryland. Lithology, structure, and U-Pb geochronology have been used to subdivide the gneisses into three groups. The oldest rocks, Group 1, are layered granitic gneiss (1153 ?? 6 Ma), hornblende monzonite gneiss (1149 ?? 19 Ma), porphyroblastic granite gneiss (1144 ?? 2 Ma), coarse-grained metagranite (about 1140 Ma), and charnockite (>1145 Ma?). These gneisses contain three Proterozoic deformational fabrics. Because of complex U-Pb systematics due to extensive overgrowths on magmatic cores, zircons from hornblende monzonite gneiss were dated using the sensitive high-resolution ion microprobe (SHRIMP), whereas all other ages are based on conventional U-Pb geochronology. Group 2 rocks are leucocratic and biotic varieties of Marshall Metagranite, dated at 1112??3 Ma and 1111 ?? 2 Ma respectively. Group 3 rocks are subdivided into two age groups: (1) garnetiferous metagranite (1077 ?? 4 Ma) and quartz-plagioclase gneiss (1077 ?? 4 Ma); (2) white leucocratic metagranite (1060 ?? 2 Ma), pink leucocratic metagranite (1059 ?? 2), biotite granite gneiss (1055 ?? 4 Ma), and megacrystic metagranite (1055 ?? 2 Ma). Groups 2 and 3 gneisses contain only the two younger Proterozoic deformational fabrics. Ages of monazite, seprated from seven samples, indicate growth during both igneous and metamorphic (thermal) events. However, ages obtained from individual grains may be mixtures of different age components, as suggested by backscatter electron (BSE) imaging of complexly zoned grains. Analyses of unzoned monazite (imaged by BSE and thought to contain only one age component) from porphyroblastic granite gneiss yield ages of 1070, 1060, and 1050 Ma. The range of ages of monazite (not reset to a uniform date) indicates that the Grenville granulite event at about 1035 Ma did not exceed about 750??C. Lack of evidence for 1110 Ma growth of monazite in porphyroblastic granite gneiss suggests that the Short Hill fault might be a Grenvillian structure that was reactivated in the Paleozoic. The timing of Proterozoic deformations is constrained by crystallization ages of the gneissic rocks. D1 occurred between about 1145 and 1075 Ma (or possibly between about 1145 and 1128 Ma). D2 and D3 must be younger than about 1050 Ma. Ages of Mesoproterozoic granitic rocks of the northern Blue Ridge are similar to rocks in other Grenville terranes of the eastern USA, including the Adirondacks and Hudson Highlands. However, comparisons with conventional U-Pb ages of granulite-grade rocks from the central and southern Appalachians may be specious because these ages may actually be mixtures of ages of cores and overgrowths.

Anthropic influences on the sedimentation rates of lakes situated in different geographic areas.

PubMed

Simon, Hedvig; Kelemen, Szabolcs; Begy, Róbert-Csaba

2017-07-01

The aim of this study is to determine the effects of natural and anthropic events occurring in the last 30 years in the catchment areas of four Romanian lakes (St. Anna Lake, Red Lake, Vârşolţ Lake and Matiţa Lake) originating from four different geomorphologic areas. A total of eleven sediment cores have been processed for age and sedimentation rate determination using the 210 Pb dating method. Total 210 Pb was measured via alpha spectrometry by 210 Po using PIPS detectors, while supported 210 Pb was measured by 226 Ra using HPGe detectors. Ages and sedimentation rates were calculated using the CRS model. The values of the sedimentation rates have grown multiply in the last three decades: 2.66 times in case of the St. Anna Lake (from 0.06 ± 0.01 g/cm 2 y to 0.16 ± 0.02 g/cm 2 y), up to 6.72 times in case of Red Lake (0.36 ± 0.04 g/cm 2 y to 2.42 ± 0.36 g/cm 2 y), 4.02 times in case of Vârşolţ Lake (04 g/cm 2 y to 1.53 ± 0.18 g/cm 2 y) and up to 16.18 times in case of Matiţa Lake (0.27 ± 0.03 g/cm 2 y to 4.37 ± 0.32). Copyright © 2016 Elsevier Ltd. All rights reserved.

Th-U-total Pb Geochronology of Authigenic Monazite Near the top of the Sturtian-Marinoan Interglacial, Adelaide Rift Complex, South Australia

NASA Astrophysics Data System (ADS)

Mahan, K. H.; Wernicke, B. P.; Jercinovic, M. J.

2007-12-01

The Adelaide Rift Complex in South Australia contains the type sections for Sturtian and Marinoan glacial deposits. The litho- and chemostratigraphy of these deposits play a central role in evaluating global Neoproterozoic ice age hypotheses ("snowball Earth") and Rodinia supercontinent reconstructions, but precise ages on igneous units do not yet exist. We report preliminary results of in situ Th-U-total Pb electron microprobe dating of monazite in sandstones within the Holowilena Ironstone ("older" Sturtian glacial at Enorama Creek) and at the top of the Enorama Shale (youngest pre-Marinoan, interglacial clastics at Elatina Creek). Several distinct populations are recognized. First, rounded cores with high Th, U, and Y + HREE abundances are interpreted as igneous or metamorphic detrital grains and yield ca. 1590 Ma, ca. 1280-1300 Ma, and ca. 1040 Ma dates related to well-known orogenic events in surrounding cratonic regions. A second group also occurs as "cores" but contains significantly lower U and Y + HREE, characteristics that may be indicative of an authigenic origin. Some rounded domains may represent "recycled" authigenic grains and yield dates of ca. 880 Ma and ca. 760 Ma. However, a subset observed in the Enorama sample occurs as very small (~2 x 10 microns), euhedral lathes that are unlikely to have survived a detrital history and yield a date of 680 +/-23 Ma. The youngest population forms very low Th and U, inclusion-rich overgrowths with ca. 500 Ma dates (Delamerian Orogeny) that probably grew hydrothermally. The recognition of "recycled" authigenic monazite further emphasizes the detail in textural and petrological documentation that is required for accurate geochronological interpretations. The date of 680 +/-23 Ma (1) provides an estimate for the age of the base of the Trezona carbon isotopic anomaly just beneath the Marinoan glacial deposits, (2) provides an absolute minimum age constraint on the underlying Sturtian glacial deposits, and (3) is confirming of proposed correlations between type Marinoan deposits and precisely dated glacial deposits in Namibia and China.

Evaluating the utility of detrital thermochronometric studies: detrital laser ablation (U-Th)/He dating and conventional bedrock zircon (U-Th)/He analyses from the eastern Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Horne, A.; Hodges, K. V.; Van Soest, M. C.

2016-12-01

Recent applications of the newly developed `laser ablation double dating' (LADD) technique, an integrated laser microprobe U/Pb and (U-Th)/He dating method, have showcased the potential utility of LADD for detrital thermochronologic studies. However, detrital thermochronologic techniques rely on confidence that detrital data adequately represent the full range of bedrock cooling ages within a catchment. To test this primary assumption, we compare (U-Th)/He zircon ages from age-elevation transects to LADD (U-Th)/He zircon ages from modern fluvial detritus collected at the range front in the eastern Sierra Nevada, California. Terminated by a normal fault escarpment, the small, steep catchments along the eastern side of the Sierra Nevada batholith are apropos locations for comparing the ability of detrital data to deduce the exhumation history of a source terrain with standard age-elevation transects. Additionally, the exhumation of the Sierra Nevada batholith is also intriguing, as past evaluations of the post-emplacement exhumation history of the range have yielded discrepant results. Thus far, analyses from the southern extent of the eastern Sierra Nevada show narrow ranges of cooling ages consistent with simple, relatively rapid exhumation. Ongoing analyses will expand the dataset such that we can fully compare bedrock and detrital age ranges as well as characterize the exhumation history of the range with a thermochronometer that has not been used to date the batholith.

Determinations of rare earth element abundance and U-Pb age of zircons using multispot laser ablation-inductively coupled plasma mass spectrometry.

PubMed

Yokoyama, Takaomi D; Suzuki, Toshihiro; Kon, Yoshiaki; Hirata, Takafumi

2011-12-01

We have developed a new calibration technique for multielement determination and U-Pb dating of zircon samples using laser ablation-inductively coupled plasma mass spectrometry (ICPMS) coupled with galvanometric optics. With the galvanometric optics, laser ablation of two or more sample materials could be achieved in very short time intervals (~10 ms). The resulting sample aerosols released from different ablation pits or different solid samples were mixed and homogenized within the sample cell and then transported into the ICP ion source. Multiple spot laser ablation enables spiking of analytes or internal standard elements directly into the solid samples, and therefore the standard addition calibration method can be applied for the determination of trace elements in solid samples. In this study, we have measured the rare earth element (REE) abundances of two zircon samples (Nancy 91500 and Prešovice) based on the standard addition technique, using a direct spiking of analytes through a multispot laser ablation of the glass standard material (NIST SRM612). The resulting REE abundance data show good agreement with previously reported values within analytical uncertainties achieved in this study (10% for most elements). Our experiments demonstrated that nonspectroscopic interferences on 14 REEs could be significantly reduced by the standard addition technique employed here. Another advantage of galvanometric devices is the accumulation of sample aerosol released from multiple spots. In this study we have measured the U-Pb age of a zircon sample (LMR) using an accumulation of sample aerosols released from 10 separate ablation pits of low diameters (~8 μm). The resulting (238)U-(206)Pb age data for the LMR zircons was 369 ± 64 Ma, which is in good agreement with previously reported age data (367.6 ± 1.5 Ma). (1) The data obtained here clearly demonstrate that the multiple spot laser ablation-ICPMS technique can become a powerful approach for elemental and isotopic ratio measurements in solid materials.

Advances in superconductivity and Co3O4 nanoparticles as flux pinning center in (Bi, Pb)-2223/Ag superconductor tapes

NASA Astrophysics Data System (ADS)

Abd-Shukor, R.; Jannah, A. N.

2017-09-01

Many new superconducting materials have been discovered in recent years. This includes hydrogen sulfide which superconducts at 203 K under high pressure and Fe-As based materials. To this date the copper oxide-based materials remain as the highest transition temperature superconductor under normal pressure. In this paper we discuss the use of nano-sized particle as pinning center in the Ag-sheathed high temperature superconductor tapes to enhance the transport properties. When the size d of the pinning center is between the coherence length ξ and the penetration depth λ (ξ < d < λ), a stronger interaction between the pinning center and flux lines leading to higher transport critical current density, Jc can be expected. The effect of nanoparticle with size between the coherence length and the penetration depth i.e. ξ < d < λ, Co3O4 on superconductor tapes is discussed in this paper. Three types of Bi(Pb)-Sr-Ca-Cu-O starting materials namely from co-precipitation method without Co3O4 and with 30 nm and 50 nm Co3O4 addition have been prepared. The composition of the 30 nm and 50 nm Co3O4 added samples is (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(Co3O4)0.02 and (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(Co3O4)0.01, respectively. The tapes (˜2-3 cm long) were heated at 845°C for 100 and 150 h. All nanoparticles added tapes showed higher Jc compared to the non-added tapes. By comparing the current results with our previously reported results, the tapes with 30 nm Co3O4 sintered for 50 h showed the highest Jc at all temperatures. This work also showed that smaller magnetic nanoparticles enhanced Jc better than larger particles, A longer sintering time (> 50 h) degraded Jc.

Constraining the 40K decay constant with 87Rb-87Sr - 40K-40Ca chronometer intercomparison

NASA Astrophysics Data System (ADS)

Naumenko-Dèzes, Maria O.; Nägler, Thomas F.; Mezger, Klaus; Villa, Igor M.

2018-01-01

A literature survey reveals that the K-Ar chronometer gives ages that are ca. 1% younger than U-Pb ages. This offset is generally attributed to an inaccurate 40K decay constant. Three geological samples selected from a shortlist of eight with known U-Pb ages were investigated using detailed petrological methods and subsequently the Rb-Sr and K-Ca chronometers in order (a) to evaluate if they meet the requirement of a geological history reflecting a ;point-like; event (i.e. isochronous formation and subsequent ideal closure of chronometers) and (b) to narrow down the systematic uncertainty on the 40K decay constant by investigating the metrologically traceable K-Ca decay branch. Lepidolite of the Rubikon pegmatite, Namibia, was dated with Rb-Sr at 504.7 ± 4.2 Ma and the phlogopite and apatite from the Phalaborwa carbonatite complex, South Africa, yielded a Rb-Sr age of 2058.9 ± 5.2 Ma. Both Rb-Sr ages agree with published U-Pb ages. The Rb-Sr age of the late Archean Siilinjärvi carbonatite, Finland, records a later regional metamorphic event at 1869 ± 10 Ma. Only the samples from the Phalaborwa complex represent a ;point-like; magmatic event and meet all the criteria to make them suitable for the 40K decay constant intercalibration. The Phalaborwa K-Ca isochron has a slope of 1.878 ± 0.012. Forcing the K-Ca isochron to coincide with the U-Pb and Rb-Sr ages gives one equation with two unknowns. Assuming that the branching ratio of the K-Ca branch, BCa, lies in the interval (k = 2) of all published references, 0.8925 < BCa < 0.8963, then the most reliable uncertainty interval (k = 2) for the total 40K decay constant, λtot, is calculated as 5.484 × 10-10 a-1 < λtot < 5.498 × 10-10 a-1. This confirms that the currently used IUGS recommendation is inaccurate.

Archaean and Palaeoproterozoic gneisses reworked during a Neoproterozoic (Pan-African) high-grade event in the Mozambique belt of East Africa: Structural relationships and zircon ages from the Kidatu area, central Tanzania

NASA Astrophysics Data System (ADS)

Vogt, M.; Kröner, A.; Poller, U.; Sommer, H.; Muhongo, S.; Wingate, M. T. D.

2006-06-01

This study presents new zircon ages and Sm-Nd whole-rock isotopic compositions for high-grade gneisses from the Udzungwa Mountain area in the central part of the Mozambique belt, Tanzania. The study area comprises a succession of layered granulite-facies para- and orthogneisses, mostly retrograded to amphibolite-facies. The original intrusive contacts became obscured or severely modified during non-coaxial ductile deformation, and extensive shearing occurred during retrogression. Structures reflecting the early deformational history were mostly obscured when the rocks were transported into the lower crust as documented by severe flattening. Only the fragmented gneisses in the eastern part of the area testify to a brittle regime. Structures in narrow low strain zones that predate the currently observed layering are preserved in rootless isoclinal folds and boudins. Magmatic and detrital zircons from tonalitic to felsic orthogneisses and a metapelite sample were dated using the U-Pb and Pb-Pb evaporation methods and SHRIMP II. Cathodoluminiscence images reveal ubiquitous xenocrystic cores, rimmed by clear, unzoned overgrowth due to high-grade metamorphism. Discordant U-Pb data therefore reflect core-rim relationships, and it was not always possible to obtain precise crystallisation ages. The analyses reveal Neoarchaean, Palaeoproterozoic and Neoproterozoic protolith ages. Nd isotopic systematics yielded strongly negative ɛNd( t) -values and Neoarchaean to Palaeoproterozoic model ages, even for gneisses emplaced in the Neoproterozoic. The trace element distribution suggests upper crustal derivation of the gneisses. Therefore, our study provides evidence that recycling of older crust played a major role during the evolution of the Kidatu area. Neoarchaean rocks are interpreted to represent fragments of the Tanzania craton. Our results, together with those of earlier workers, lead to the conclusion that the central part of the Mozambique belt mainly consists of ancient crustal remnants that were reworked during the Neoproterozoic Pan-African orogeny.

Isotopes and Trace Elements as Natal Origin Markers of Helicoverpa armigera – An Experimental Model for Biosecurity Pests

PubMed Central

Holder, Peter W.; Armstrong, Karen; Van Hale, Robert; Millet, Marc-Alban; Frew, Russell; Clough, Timothy J.; Baker, Joel A.

2014-01-01

Protecting a nation's primary production sector and natural estate is heavily dependent on the ability to determine the risk presented by incursions of exotic insect species. Identifying the geographic origin of such biosecurity breaches can be crucial in determining this risk and directing the appropriate operational responses and eradication campaigns, as well as ascertaining incursion pathways. Reading natural abundance biogeochemical markers using mass spectrometry is a powerful tool for tracing ecological pathways as well as provenance determination of commercial products and items of forensic interest. However, application of these methods to trace insects has been underutilised to date and our understanding in this field is still in a phase of basic development. In addition, biogeochemical markers have never been considered in the atypical situation of a biosecurity incursion, where sample sizes are often small, and of unknown geographic origin and plant host. These constraints effectively confound the interpretation of the one or two isotope geo-location markers systems that are currently used, which are therefore unlikely to achieve the level of provenance resolution required in biosecurity interceptions. Here, a novel approach is taken to evaluate the potential for provenance resolution of insect samples through multiple biogeochemical markers. The international pest, Helicoverpa armigera, has been used as a model species to assess the validity of using naturally occurring δ2H, 87Sr/86Sr, 207Pb/206Pb and 208Pb/206Pb isotope ratios and trace element concentration signatures from single moth specimens for regional assignment to natal origin. None of the biogeochemical markers selected were individually able to separate moths from the different experimental regions (150–3000 km apart). Conversely, using multivariate analysis, the region of origin was correctly identified for approximately 75% of individual H. armigera samples. The geographic resolution demonstrated with this approach has considerable potential for biosecurity as well as other disciplines including forensics, ecology and pest management. PMID:24664236

Influence of accretion on lead in the Earth

NASA Astrophysics Data System (ADS)

Galer, Stephen J. G.; Goldstein, Steven L.

The Pb abundance and isotope composition of the Earth is fundamentally altered from bulk solar system values by the processes occurring during accretion. The most important of the possible processes are volatile element loss and core formation, or some form of inhomogeneous accretion/condensation. The final result is an Earth highly impoverished in 204Pb and other Pb isotopes in primordial abundance. Depending on the exact timing, some radiogenic Pb is also lost either to space or to the core; the degree of loss occurs in the same order as the parent decay constants, namely 207Pb > 206Pb > 208Pb. In this contribution, we explore the likely effects accretion had on the Pb isotope composition of the present day bulk silicate Earth and its secular isotope evolution. This is used to address a number of questions: (1) What can be learned about accretion from the Pb isotope composition of the bulk silicate Earth? (2) Can effects of accretion reconcile the classical "Pb paradox" of a 206Pb-rich bulk silicate Earth? (3) What exactly is the meaning of the "age of the Earth" within the context of Pb isotopes? By consideration of a number of accretion scenarios it is demonstrated that Pb isotopes yield information only on the following two coupled quantities: Firstly, the accretion interval Δ T, the time between initial condensation of the solar nebula (at 4.566Ga) and when accretion-produced U/Pb fractionation (whether loss of Pb to the core or to space) in the silicate Earth ceased. Secondly, the mean 238U/204 Pb ratio μ during accretion—no details of changes in μ during the accretion interval can be resolved. The effects of accretion are thus adequately considered in terms of a simple two-stage model described by μ over ΔT followed by a postaccretion μ. The systematics of μ and ΔT are then examined for the cases of present day terrestrial reservoirs and Archean leads. These estimates of μ and ΔT for the present and past silicate Earth are not compatible with ΔT = 0; rather, they require ΔT ≥ 50Ma and μ ≥ 0 in all instances, with our best estimate of ΔT being 80±40Ma. From a number of lines of argument it can be demonstrated that the U-Pb "age of the Earth" records an endogenous process actively taking place during accretion. Further, this process cannot be volatile loss of Pb, but rather it actually records the termination of Pb partitioning into the core. This does not necessarily date the endpoint of growth of the Earth for two reasons: Firstly, this core formation "age" may itself in part reflect that occurring on bodies later contributing to the Earth; secondly, later infall of bodies may alter μ but leave the U-Pb "age" of the silicate Earth effectively unaltered. Overall, the Earth can be considerably `younger' than previous single-stage model U-Pb ages for the silicate Earth have suggested. In addition, the "lead paradox" is seen to be a natural consequence of the finite time taken for accretion and core formation on the Earth.

Characterization of the homologs of flerovium with crown ether based extraction chromatography resins: studies in nitric acid

DOE PAGES

Despotopulos, John D.; Kmak, Kelly N.; Gharibyan, Narek; ...

2016-09-17

Eichrom’s Pb resin, a crown-ether-based extraction chromatography resin, was characterized for separation of the flerovium (Fl) homologs, Pb and Sn. Batch uptake of Pb(II) and Sn(IV) radionuclides was determined from an HNO 3 matrix. Pb(II) was strongly retained on the resin at all HNO 3 concentrations, while Sn(IV) showed no uptake. Extraction kinetics for Pb(II) were examined and show suitable uptake on the second time scale. Here, separation methods for the isolation of individual homologs, Pb(II) and Sn(IV), have been established using 2 mL pre-packed vacuum flow Pb resin columns.