Zeitschriftenartikel: „Datation au carbonate U-Pb“

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Jahn, Bor-ming, und Henri Cuvellier. „PbPb and UPb geochronology of carbonate rocks: an assessment“. Chemical Geology 115, Nr. 1-2 (Juli 1994): 125–51. http://dx.doi.org/10.1016/0009-2541(94)90149-x.

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Cocherie, Alain, Jean Chantraine, C. Mark Fanning, Marie-Pierre Dabard, Florentin Paris, Alain Le Hérissé und Emmanuel Égal. „Datation U/Pb : âge Briovérien de la série d'Erquy (Massif armoricain, France)“. Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science 333, Nr. 8 (Oktober 2001): 427–34. http://dx.doi.org/10.1016/s1251-8050(01)01669-x.

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Tartèse, Romain, und Ian C. Lyon. „In situ U–Pb dating of 4 billion-year-old carbonates in the martian meteorite Allan Hills 84001“. Geochronology 4, Nr. 2 (06.12.2022): 683–90. http://dx.doi.org/10.5194/gchron-4-683-2022.

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Abstract. In situ carbonate U–Pb dating studies have proliferated dramatically in recent years. Almost all these studies have targeted relatively young terrestrial calcite up to Carboniferous in age. To assess the robustness of the carbonate U–Pb chronometer in deep time, we carried out in situ U–Pb analyses in magnesite–ankerite–calcite carbonates in the martian meteorite Allan Hills (ALH) 84001. Carbonates in ALH 84001 formed at ca. 3.94 Ga, and there is little evidence that much happened to this rock since then, making it an ideal sample to test the robustness of the U–Pb system in old carbonates. We obtained a concordant date of 3941 ± 49/110 Ma (n=14, MSWD = 2.0), which is identical to the step-leaching Rb/Sr date determined previously. These results thus confirm that old carbonates are amenable to U–Pb dating in samples that have had a relatively simple history post-carbonate formation.

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Gorokhov, I. M., I. M. Vasil'eva, A. B. Kuznetsov, N. G. Rizvanova und G. V. Konstantinova. „A Stepwise Dissolution Method Applied to Isotopic Chemostratigraphic and Geochronological Studies of Riphean Carbonate Rocks of the Baykit Uplift“. Геохимия 68, Nr. 7 (01.07.2023): 669–86. http://dx.doi.org/10.31857/s0016752523070038.

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The potential of the stepwise dissolution analytical procedure to obtain chemostratigraphic and geochronological information is demonstrated by a case study of Riphean carbonate rocks of the Kamovskaya Group of the Baykit Uplift (Eastern Siberia). The procedures suggested for studying Rb–Sr and U–Pb systems in carbonate rocks included (1) selection of samples with the lowest 87Sr/86Sr ratio on the basis of preliminary Rb–Sr analysis of the collection using the routine procedure of bulk leaching in 0.1N CH3COOH; (2) detailed study of the Rb–Sr system in selected samples using two-step dissolution in 0.2N CH3COOH and derivation of L(Rb–Sr)1 and L(Rb–Sr)2 fractions; (3) analysis of Pb isotope composition of the selected samples to derive the preliminary value of their age; (4) detailed study of U–Pb system of carbonate rocks using the stepwise dissolution in 0.5N HBr, resulting in six dissolved fractions L(U–Pb)1–L(U–Pb)6 for each of the selected samples; and (5) a final calculation of the Pb–Pb age of the studied rocks, based on the results from the obtained fractions, with the exclusion from the calculation of the initial fractions of this dissolution containing epigenetically altered carbonate material. The values of the primary 87Sr/86Sr ratio in L(Rb–Sr)2 fractions of carbonate rocks of the Kamovskaya Group are as follows: limestone of the Madrinskaya Formation, 0.70490; dolomites of the Yurubchenskaya Formation, 0.70495–0.70503; and dolomites of the Kuyumbinskaya and Vingoldinskaya formations, 0.70580 and 0.70521, respectively. These values characterizing the least altered carbonate material correspond to 87Sr/86Sr ratios in the Early Archean and can be used for chemostratigraphic calculations. Taking into account the Rb–Sr data, the U–Pb age of the Yurubchenskaya Formation carbonate rocks dissolved in six steps was calculated, starting from L(U–Pb)3. The slope of the resulting isochron in the coordinates 206Pb/204Pb–207Pb/204Pb corresponds to 1501 ± 23 Ma, which supports the conclusion that the carbonate rocks of the lower part of the Kamovskaya Group of the Baykit Uplift were formed in the Early Riphean.

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Stifeeva, M. V., N. V. Vladykin, A. B. Kotov, E. B. Salnikova, I. A. Sotnikova, E. V. Adamskaya, V. P. Kovach, Y. V. Plotkina, E. V. Tolmacheva und N. V. Alymova. „AGE OF THE FORMATION OF EARLY PRECAMBRIAN CARBONATITES IN THE SOUTH-EASTERN PART OF THE CHARO-OLEKMINSKY GEOBLOCK, ALDAN SHIELD“. Доклады Российской академии наук. Науки о Земле 508, Nr. 1 (01.01.2023): 32–36. http://dx.doi.org/10.31857/s2686739722601880.

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Presents the results of U–Pb geochronological (ID–TIMS) studies of garnet and U–Th–Pb (LA–ICP–MS) “screening” geochronological studies of zircon from pyroxene-carbonate rocks of the Ukduska massif. The U–Pb age of garnets (1881 ± 8 million years) and age of zircon rim (1865 ± 16 million years) indicate the early Proterozoic age of these rocks. The results of geochronological studies allow to identify a new stage of carbonate magmatism within the southeastern part of the Charo-Olekminsky geoblock.

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Cocherie, Alain, Catherine Guerrot, C. Mark Fanning und Albert Genter. „Datation U–Pb des deux faciès du granite de Soultz (Fossé rhénan, France)“. Comptes Rendus Geoscience 336, Nr. 9 (Juli 2004): 775–87. http://dx.doi.org/10.1016/j.crte.2004.01.009.

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Winter, Bryce L., und Clark M. Johnson. „UPb dating of a carbonate subaerial exposure event“. Earth and Planetary Science Letters 131, Nr. 3-4 (April 1995): 177–87. http://dx.doi.org/10.1016/0012-821x(95)00026-9.

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Beranoaguirre, Aratz, Iuliana Vasiliev und Axel Gerdes. „In situ LA-ICPMS U–Pb dating of sulfates: applicability of carbonate reference materials as matrix-matched standards“. Geochronology 4, Nr. 2 (06.09.2022): 601–16. http://dx.doi.org/10.5194/gchron-4-601-2022.

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Abstract. Recent developments in analytical capabilities in the field of in situ laser ablation mass spectrometry (LA-ICPMS) have expanded the applications of U–Pb geochronometers in low-U minerals such as carbonates or garnets. The rapid evolution of the technique relies on well-characterized matrix-matched reference materials. In this article, we explore the suitability of using carbonate as an “almost-matrix-matched reference material” for in situ U–Pb dating of sulfates. For such purpose, we have used the astrochronologically dated gypsum and anhydrite samples deposited during the Messinian Salinity Crisis (5.97–5.33 Ma) and compared these dates with the U–Pb ages obtained by LA-ICPMS. Although the majority of the samples failed due to the elevated common Pb content and low 238U/204Pb ratios, five of the samples showed a higher dispersion on U/Pb ratios. The obtained dates in four of these samples are comparable with the expected ages, while another gave an unexpected younger age, each of them with 6 %–11 % of uncertainty. The pit depth of the spots showed that the sulfates ablate similar to carbonates, so the offset due to the crater geometry mismatch or downhole fractionation can be assumed to be negligible. To sum up, the bias between the U–Pb and expected cyclostratigraphic ages, if any, is included in the uncertainty, and thus the results obtained here suggest that carbonate reference material is currently the best option for standardization of in situ U–Pb sulfate analyses.

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Rasbury, E. Troy, Theodore M. Present, Paul Northrup, Ryan V. Tappero, Antonio Lanzirotti, Jennifer M. Cole, Kathleen M. Wooton und Kevin Hatton. „Tools for uranium characterization in carbonate samples: case studies of natural U–Pb geochronology reference materials“. Geochronology 3, Nr. 1 (16.02.2021): 103–22. http://dx.doi.org/10.5194/gchron-3-103-2021.

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Abstract. Laser ablation U–Pb analyses of carbonate (LAcarb) samples has greatly expanded the potential for U–Pb dating to a variety of carbonate-producing settings. Carbonates that were previously considered impossible to date using isotope dilution methods may preserve radiogenic domains that can be dated using spatially resolved laser ablation geochronology techniques. Work is ongoing to identify reference materials and to consider best practices for LAcarb. In this study we apply standard and emerging characterization tool sets on three natural samples with the dual goal of enhancing the study of carbonates and establishing a new set of well-characterized natural reference materials for LAcarb studies. We start with the existing carbonate reference material WC-1 from the Permian Reef Complex of Texas, building on the published description to offer a deeper look at U and associated trace elements. We consider a tufa sample from the Miocene Barstow Formation of the Mojave Block, California, as a possible secondary calcite reference material due to its well-behaved U–Pb systematics. There are currently no natural dolomite standards. We present an unusual dolomite sample with very well-behaved U–Pb systematics from the Miocene of the Turkana Basin of Kenya as a possible dolomite reference material for LAcarb dating. In addition to using X-ray fluorescence (XRF) mapping and spectroscopy to better understand U in these natural samples, we have analyzed multiple aliquots of each of them for 87Sr/86Sr by thermal ionization mass spectrometry (TIMS). The Sr isotope compositions are analytically homogeneous within petrographically homogeneous regions of all three samples, and thus these materials could be used as Sr isotope standards as well. While not part of the current contribution, this combination could streamline simultaneous LA analyses of 87Sr/86Sr and U–Pb geochronology.

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Vetrova, N. I., E. V. Vetrov und E. F. Letnikova. „СHEMOSTRATIGRAPHY OF THE CARBONATE DEPOSITS OF THE KINTEREP FORMATION IN NORTHWESTERN SALAIR: FIRST DATA“. Geology and mineral resources of Siberia, Nr. 2 (Juni 2022): 10–23. http://dx.doi.org/10.20403/2078-0575-2022-2-10-23.

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The results of geochemical, isotope-geochemical (Sr, C, O) surveys of the Kinterep Formation carbonate deposits of Northwestern Salair and U-Pb dating (LA-ICP-MS) of zircons were given. Carbonate rocks represented by pure limestones are characterized by normal values of δ18OSMOW from 19.8 to 23.8 ‰ and δ13 CPDB from –0.7 to +0.9, the isotopic composition of Sr (87Sr/86Sr ratio) varies in a narrow range from 0.708486 to 0.708582.Using Sr and C isotope chemostratigraphy and U-Pb dating of zircons, age limits (525-510 Ma) were determined for the formation time of carbonate deposits of the Kinterep Formation. The first data of isotope chemostratigraphy in combination with the results of geochronological studies made it possible to compare the limestones of the Kinterep Formation of Northwestern Salair with carbonate sections of Siberia and Central Asia.

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Mangenot, Xavier, Marta Gasparrini, Axel Gerdes, Magali Bonifacie und Virgile Rouchon. „An emerging thermochronometer for carbonate-bearing rocks: ∆47 /(U-Pb)“. Geology 46, Nr. 12 (09.11.2018): 1067–70. http://dx.doi.org/10.1130/g45196.1.

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Roberts, Nick M. W., Kerstin Drost, Matthew S. A. Horstwood, Daniel J. Condon, David Chew, Henrik Drake, Antoni E. Milodowski et al. „Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb carbonate geochronology: strategies, progress, and limitations“. Geochronology 2, Nr. 1 (09.04.2020): 33–61. http://dx.doi.org/10.5194/gchron-2-33-2020.

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Abstract. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb geochronology of carbonate minerals, calcite in particular, is rapidly gaining popularity as an absolute dating method. The high spatial resolution of LA-ICP-MS U–Pb carbonate geochronology has benefits over traditional isotope dilution methods, particularly for diagenetic and hydrothermal calcite, because uranium and lead are heterogeneously distributed on the sub-millimetre scale. At the same time, this can provide limitations to the method, as locating zones of radiogenic lead can be time-consuming and “hit or miss”. Here, we present strategies for dating carbonates with in situ techniques, through imaging and petrographic techniques to data interpretation; our examples are drawn from the dating of fracture-filling calcite, but our discussion is relevant to all carbonate applications. We review several limitations to the method, including open-system behaviour, variable initial-lead compositions, and U–daughter disequilibrium. We also discuss two approaches to data collection: traditional spot analyses guided by petrographic and elemental imaging and image-based dating that utilises LA-ICP-MS elemental and isotopic map data.

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Woodhead, Jon, und Joseph Petrus. „Exploring the advantages and limitations of in situ U–Pb carbonate geochronology using speleothems“. Geochronology 1, Nr. 1 (05.12.2019): 69–84. http://dx.doi.org/10.5194/gchron-1-69-2019.

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Abstract. The recent development of methods for in situ U–Pb age determination in carbonates has found widespread application, but the benefits and limitations of the method over bulk analysis (isotope dilution – ID) approaches have yet to be fully explored. Here we use speleothems – cave carbonates such as stalagmites and flowstones – to investigate the utility of in situ dating methodologies for “challenging” matrices with typically low U and Pb contents and predominantly late Cenozoic ages. Using samples for which ID data have already been published, we show that accurate ages can be obtained for many speleothem types by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Consideration of our own and literature data suggest that most carbonates with >1 ppm uranium and a few hundred parts per billion of Pb should be good targets for in situ methodologies, regardless of age. In situ analysis often provides a larger spread in U∕Pb ratios, which can be advantageous for isochron construction, but isochron ages rarely achieve the ultimate precision of ID analyses conducted on the same samples simply because signal sizes are dramatically reduced. LA analysis is faster than ID and thus will play a significant role in reconnaissance studies. The major advantage of the in situ methodology appears to be the potential for successful dating outcomes in sample types requiring high spatial-resolution analysis or those with a high common-Pb component where LA approaches may facilitate identification of the most radiogenic regions for analysis.

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Vermeesch, Pieter. „Unifying the U–Pb and Th–Pb methods: joint isochron regression and common Pb correction“. Geochronology 2, Nr. 1 (11.05.2020): 119–31. http://dx.doi.org/10.5194/gchron-2-119-2020.

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Abstract. The actinide elements U and Th undergo radioactive decay to three isotopes of Pb, forming the basis of three coupled geochronometers. The 206Pb ∕238U and 207Pb ∕235U decay systems are routinely combined to improve accuracy. Joint consideration with the 208Pb ∕232Th decay system is less common. This paper aims to change this. Co-measured 208Pb ∕232Th is particularly useful for discordant samples containing variable amounts of non-radiogenic (“common”) Pb. The paper presents a maximum likelihood algorithm for joint isochron regression of the 206Pb ∕238Pb, 207Pb ∕235Pb and 208Pb ∕232Th chronometers. Given a set of cogenetic samples, this total-Pb/U-Th algorithm estimates the common Pb composition and concordia intercept age. U–Th–Pb data can be visualised on a conventional Wetherill or Tera–Wasserburg concordia diagram, or on a 208Pb ∕232Th vs. 206Pb ∕238U plot. Alternatively, the results of the new discordia regression algorithm can also be visualised as a 208Pbc ∕206Pb vs. 238U ∕206Pb or 208Pbc ∕207Pb vs. 235U ∕206Pb isochron, where 208Pbc represents the common 208Pb component. In its most general form, the total-Pb/U-Th algorithm accounts for the uncertainties of all isotopic ratios involved, including the 232Th ∕238U ratio, as well as the systematic uncertainties associated with the decay constants and the 238U ∕235U ratio. However, numerical stability is greatly improved when the dependency on the 232Th ∕238U-ratio uncertainty is dropped. For detrital minerals, it is generally not safe to assume a shared common Pb composition and concordia intercept age. In this case, the total-Pb/U-Th regression method must be modified by tying it to a terrestrial Pb evolution model. Thus, also detrital common Pb correction can be formulated in a maximum likelihood sense. The new method was applied to three published datasets, including low Th∕U carbonates, high Th∕U allanites and overdispersed monazites. The carbonate example illustrates how the total-Pb/U-Th method achieves a more precise common Pb correction than a conventional 207Pb-based approach does. The allanite sample shows the significant gain in both precision and accuracy that is made when the Th–Pb decay system is jointly considered with the U–Pb system. Finally, the monazite example is used to illustrate how the total-Pb/U-Th regression algorithm can be modified to include an overdispersion parameter. All the parameters in the discordia regression method (including the age and the overdispersion parameter) are strictly positive quantities that exhibit skewed error distributions near zero. This skewness can be accounted for using the profile log-likelihood method or by recasting the regression algorithm in terms of logarithmic quantities. Both approaches yield realistic asymmetric confidence intervals for the model parameters. The new algorithm is flexible enough that it can accommodate disequilibrium corrections and intersample error correlations when these are provided by the user. All the methods presented in this paper have been added to the IsoplotR software package. This will hopefully encourage geochronologists to take full advantage of the entire U–Th–Pb decay system.

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Davis, D. W., C. N. Sutcliffe, A. M. Thibodeau, J. Spalding, D. Schneider, A. Cruden, J. Adams, A. Parmenter, M. Jensen und Z. Zajacz. „Hydrochronology of a proposed deep geological repository for low- and intermediate-level nuclear waste in southern Ontario from U–Pb dating of secondary minerals: response to Silurian and Cretaceous events“. Canadian Journal of Earth Sciences 57, Nr. 4 (April 2020): 464–76. http://dx.doi.org/10.1139/cjes-2019-0004.

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A record of fluid flow has been documented within a Paleozoic carbonate platform sequence by U–Pb dating of calcite in veins and vugs from rock core sampled through a shallowly dipping sequence of sedimentary rocks beneath the Bruce nuclear site, Ontario, Canada. Secondary calcite from >650 m deep Ordovician carbonate rocks yields a Silurian age of 434 ± 5 Ma possibly related to infiltration of seawater from overlying evaporitic basins as well as hydrothermal solutions that infiltrated from below. In contrast, near-surface Devonian rocks mostly give vein infill ages over the range of 80–100 Ma with evidence for younger infill down to 50 Ma. Vein calcite samples previously dated from surface outcrops of Ordovician carbonate exposed up to 500 km to the east yielded similar U–Pb ages. Coincidence of near-surface vein calcite ages indicates widespread vein emplacement synchronous with a change in direction of motion of the North American plate as well as possible erosional unroofing following passage of the region over the Great Meteor hotspot approximately 125 Myr ago. Deeper carbonate formations have remained apparently impermeable to post-Paleozoic disturbance despite these perturbations.

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Gulbranson, Erik L., E. Troy Rasbury, Greg A. Ludvigson, Andreas Möller, Gregory A. Henkes, Marina B. Suarez, Paul Northrup et al. „U–Pb Geochronology and Stable Isotope Geochemistry of Terrestrial Carbonates, Lower Cretaceous Cedar Mountain Formation, Utah: Implications for Synchronicity of Terrestrial and Marine Carbon Isotope Excursions“. Geosciences 12, Nr. 9 (17.09.2022): 346. http://dx.doi.org/10.3390/geosciences12090346.

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The terrestrial Lower Cretaceous Cedar Mountain Formation, Utah, is a critical archive of paleoclimate, tectonics, and vertebrate ecology and evolution. Early Cretaceous carbon cycle perturbations associated with ocean anoxia have been interpreted from this succession, as expressed in stable carbon isotopes. However, refining the timing of the observed stable isotope excursions remains a key challenge in understanding how marine anoxia affects the Earth system, and is ultimately recorded in the terrestrial realm. The geochronology and geochemistry of a terrestrial carbonate near the base of this succession, which potentially records the Ap7 global carbon isotope excursion, is studied here. Petrographic and geochemical analyses are used to test plausible mechanisms for U incorporation into the calcite lattice in this sample. Using these methods, the hypothesis that the incorporation of U was at or close to the timing of carbonate precipitation is evaluated. U–Pb geochronology of calcite indicates a plausible Early Cretaceous age. However, comparison of the new U–Pb ages of calcite with detrital zircon maximum depositional ages immediately beneath the studied sample indicates a disparity in the apparent sedimentation rates if both types of geochronologic information are interpreted as reflecting the timing of sediment deposition. The totality of data supports an early, and high-temperature, diagenetic timing of U incorporation, with potential for minor leaching of U in subsequent fluid–rock interaction. The most likely mechanism for U transport and immobilization in these samples is hydrothermal fluid–rock interaction. Therefore, the radiometric ages, and corresponding stable isotope composition of U-bearing carbonate domains in this sample, indicate early subsurface fluid–rock interactions and not a record of atmosphere–soil geochemical reactions.

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Nuriel, Perach, Jörn-Frederik Wotzlaw, Maria Ovtcharova, Anton Vaks, Ciprian Stremtan, Martin Šala, Nick M. W. Roberts und Andrew R. C. Kylander-Clark. „The use of ASH-15 flowstone as a matrix-matched reference material for laser-ablation U − Pb geochronology of calcite“. Geochronology 3, Nr. 1 (14.01.2021): 35–47. http://dx.doi.org/10.5194/gchron-3-35-2021.

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Abstract. Latest advances in laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) allow for accurate in situ U−Pb dating of carbonate material, with final age uncertainties usually >3 % 2σ. Cross-laboratory reference materials (RMs) used for sample-bracketing are currently limited to WC1 calcite with an age of 254.4±6.5 (2σ). The minimum uncertainty on any age determination with the LA-ICPMS method is therefore ≥2.5 %, and validation by secondary RMs is usually performed on in-house standards. This contribution presents a new reference material, ASH-15, a flowstone that is dated here by isotope dilution (ID) thermal ionization mass spectrometry (TIMS) analysis using 37 sub-samples, 1–7 mg each. Age results presented here are slightly younger compared to previous ID isotope ratio mass spectrometry (IRMS) U−Pb dates of ASH-15 but within uncertainties and in agreement with in situ analyses using WC1 as the primary RM. We provide new correction parameters to be used as primary or secondary standardization. The suggested 238U∕206Pb apparent age, not corrected for disequilibrium and without common-lead anchoring, is 2.965±0.011 Ma (uncertainties are 95 % confidence intervals). The new results could improve the propagated uncertainties on the final age with a minimal value of 0.4 %, which is approaching the uncertainty of typical ID analysis on higher-U materials such as zircon. We show that although LA-ICPMS spot analyses of ASH-15 exhibit significant scatter in their isotopic ratios, the down-hole fractionation of ASH-15 is similar to that of other reference materials. This high-U (≈1 ppm) and low-Pb (<0.01 ppm) calcite is most appropriate as a reference material for other speleothem-type carbonates but requires more-sensitive ICP-MS instruments such as the new generation of single-collector and multi-collector ICP-MS. Reference materials with high-Pb and low-U or both low-U and low-Pb compositions are still needed to fully cover the compositional range of carbonate material but may introduce analytical challenges.

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Kaurova, O. K., G. V. Ovchinnikova und I. M. Gorokhov. „U-Th-Pb systematics of precambrian carbonate rocks: Dating of the formation and transformation of carbonate sediments“. Stratigraphy and Geological Correlation 18, Nr. 3 (Juni 2010): 252–68. http://dx.doi.org/10.1134/s0869593810030032.

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Sitkina, D. R., A. B. Kuznetsov, G. V. Konstantinova und T. L. Turchenko. „The Isotopic Age and Correlation of Carbonate Rocks of the Ara-Oshei Formation (Tunka Ridge, East Sayan)“. Russian Geology and Geophysics 63, Nr. 8 (01.08.2022): 901–14. http://dx.doi.org/10.2113/rgg20214378.

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Abstract —We present results of Pb–Pb geochronology and Sr- and C- chemostratigraphic study of limestones and dolomites of the Ara-Oshei Formation of the Tunka ridge in East Sayan. The δ13C value of the limestones varies from –0.6 to 2.3‰ PDB, the 87Sr/86Sr ratio is within 0.70851–0.70864, and the Pb–Pb age is 521 ± 21 Ma (MSWD = 0.9). The δ13C value of the dolomites varies from –3.9 to 0.5‰ PDB, the 87Sr/86Sr ratio is 0.70844–0.70882, and the Pb–Pb age is 417 ± 8 Ma (MSWD = 2.5). The U–Pb isotope system of the dolomites was disturbed during the geologic evolution of the region, which led to the rejuvenation of their Pb–Pb age in the Early Devonian. The obtained Sr-chemostratigraphic and Pb–Pb data show that the limestones of the Ara-Oshei Formation accumulated in the early Cambrian. This provides a reliable proof that the limestones are part of the Vendian–Cambrian sedimentary cover of the Tuva–Mongolian massif.

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Scott, David J. „Geology, U – Pb, and Pb – Pb geochronology of the Lake Harbour area, southern Baffin Island: implications for the Paleoproterozoic tectonic evolution of northeastern Laurentia“. Canadian Journal of Earth Sciences 34, Nr. 2 (01.02.1997): 140–55. http://dx.doi.org/10.1139/e17-012.

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Geological and geochronological results of an investigation of the Paleoproterozoic siliciclastic and carbonate supracrustal rocks of the Lake Harbour Group (LHG) and surrounding tonalitic gneisses on southern Baffin Island are presented. Conventional U – Pb geochronology of monazite from rocks of the LHG suggest that penetrative deformation of these rocks occurred prior to, or during, peak metamorphic conditions at ca. 1845 –1840 Ma. Conventional U – Pb zircon results indicate that much of the tonalitic gneiss ranges in age from [Formula: see text] to 1827[Formula: see text]. The tonalitic gneisses and Lake Harbour Group units were tectonically imbricated by ca. 1805 Ma, and are part of a southwest-verging thrust belt interpreted from regional considerations to represent the northern continuation of the Ungava Orogen. The present results indicate that current tectonic models for the evolution of northeastern Laurentia that involve a dominantly Archean southeastern Rae province require revision. It is proposed that much of the metaigneous material that lies between the Archean Superior and Nain cratons represents a composite subduction-related domain.

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Essaifi, Abderrahim, Alain Potrel, Ramon Capdevila und Jean-Louis Lagarde. „Datation UPb : âge de mise en place du magmatisme bimodal des Jebilet centrales (chaı̂ne Varisque, Maroc). Implications géodynamiques“. Comptes Rendus Geoscience 335, Nr. 2 (Januar 2003): 193–203. http://dx.doi.org/10.1016/s1631-0713(03)00030-0.

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Cawood, Peter A., Jeroen A. M. van Gool und Greg R. Dunning. „Geological development of eastern Humber and western Dunnage zones: Corner Brook–Glover Island region, Newfoundland“. Canadian Journal of Earth Sciences 33, Nr. 2 (01.02.1996): 182–98. http://dx.doi.org/10.1139/e96-017.

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The Corner Brook–Glover Island region records the development of the internal domain of the Humber Zone and its relationship to the adjoining external domain and Dunnage Zone. The region preserves both the Laurentian margin basement–cover contact and the siliciclastic–carbonate transition within the cover sequence. Precambrian Grenville basement of the Corner Brook Lake Complex is the oldest lithostratigraphic unit and yielded a U/Pb zircon age of 1510 ± 6 Ma. Three main lithostratigraphic assemblages overlie basement: silicic and mafic igneous rocks of the Lady Slipper Pluton which yielded a U/Pb zircon age of [Formula: see text] Ma; siliciclastic lithologies which include the South Brook and Summerside formations; and carbonate-dominated sequences with clastic incursions which include the Port au Port, St. George, and Table Head groups, and the Breeches Pond, Irishtown, and Pinchgut formations. Dunnage Zone units include plutonic ultramafic to mafic rocks of the Grand Lake Complex, dated by U/Pb zircon from trondhjemite at 490 ± 4 Ma, volcanic and epiclastic rocks of the Glover Island Formation, and the Matthews Brook Serpentinite, the latter restricted to fault slivers within the Humber Zone sequence. The deformed Glover Island Granodiorite intrudes the Dunnage Zone rocks on Glover Island and is dated by U/Pb zircon and titanite at 440 ± 2 Ma. Little deformed Carboniferous sedimentary rocks unconformably overlie both Humber Zone and Dunnage Zone rock units. Timing of regional deformation and peak amphibolite-facies metamorphism in the eastern Humber Zone is constrained by isotopic data to the Early Silurian. In the Dunnage Zone, shear zones and foliation development both pre- and postdate the age of the Glover Island Granodiorite, with the later possibly temporally equivalent to deformation in the Humber Zone. Final juxtaposition of the two zones occurred during Carboniferous movement of the Cabot Fault.

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Ghobadi, Mahdi, Gerhard P. Brey, Axel Gerdes, Heidi E. Höfer und Jörg Keller. „Accessories in Kaiserstuhl carbonatites and related rocks as accurate and faithful recorders of whole rock age and isotopic composition“. International Journal of Earth Sciences 111, Nr. 2 (09.12.2021): 573–88. http://dx.doi.org/10.1007/s00531-021-02130-9.

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AbstractThe accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites and carbonate-rich foidites from the Kaiserstuhl are variously suited for the in situ determination of their U–Pb ages and Sr, Nd- and Hf-isotope ratios by LA-ICP-MS. The 143Nd/144Nd ratios may be determined precisely in all five phases, the 176Hf/177Hf ratios only in calzirtite and the 87Sr/86Sr ratios in perovskites and pyrochlores. The carbonatites and carbonate-rich foidites belong to one of the three magmatic groups that Schleicher et al. (1990) distinguished in the Kaiserstuhl on the basis of their Sr, Nd and Pb isotope ratios. Tephrites, phonolites and essexites (nepheline monzogabbros) form the second and limburgites (nepheline basanites) and olivine nephelinites the third. Our 87Sr/86Sr isotope data from the accessories overlap with the carbonatite and olivine nephelinite fields defined by Schleicher et al. (1990) but exhibit a much narrower range. These and the εNd and εHf values plot along the mantle array in the field of oceanic island basalts relatively close to mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar and fission track ages for the Kaiserstuhl lie between 16.2 and 17.8 Ma. They stem entirely from the geologically older tephrites, phonolites and essexites. No ages existed so far for the geologically younger carbonatites and carbonate-rich foidites except for one apatite fission track age (15.8 Ma). We obtained precise U–Pb ages for zirconolites and calzirtites of 15.66, respectively 15.5 Ma (± 0.1 2σ) and for pyrochlores of 15.35 ± 0.24 Ma. Only the perovskites from the Badberg soevite yielded a U–P concordia age of 14.56 ± 0.86 Ma while the perovskites from bergalites (haüyne melilitites) only gave 206Pb/238U and 208Pb/232Th ages of 15.26 ± 0.21, respectively, 15.28 ± 0.48 Ma. The main Kaiserstuhl rock types were emplaced over a time span of 1.6 Ma almost 1 million years before the carbonatites and carbonate-rich foidites. These were emplaced within only 0.32 Ma.

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Engel, John, Roland Maas, Jon Woodhead, Jan Tympel und Alan Greig. „A single-column extraction chemistry for isotope dilution U-Pb dating of carbonate“. Chemical Geology 531 (Januar 2020): 119311. http://dx.doi.org/10.1016/j.chemgeo.2019.119311.

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Smith, P. E., R. M. Farquhar und R. G. Hancock. „Direct radiometric age determination of carbonate diagenesis using U-Pb in secondary calcite“. Earth and Planetary Science Letters 105, Nr. 4 (August 1991): 474–91. http://dx.doi.org/10.1016/0012-821x(91)90186-l.

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Montano, Damaris, Marta Gasparrini, Sébastien Rohais und Ramon De Luca. „A Lacustrine Record for the Cretaceous–Paleogene Boundary—Yacoraite Fm., (Northwest Argentina)“. Geosciences 13, Nr. 8 (27.07.2023): 227. http://dx.doi.org/10.3390/geosciences13080227.

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The Yacoraite Fm. (Salta rift basin, Argentina) consists of a mixed carbonate–siliciclastic lacustrine succession, interbedded with volcanic ash layers and organised in four third-order stratigraphic sequences. It is one of the few sites in South America that encompass the Cretaceous–Paleogene (K–Pg) transition, the position of which remains debated. Here, samples were collected along a depocentral stratigraphic section that was previously dated by zircon and carbonate U-Pb geochronology. The consistency between zircon and carbonate U-Pb ages, together with an accurate petrographic analysis, allowed the selection of carbonates potentially preserving the original geochemical signature. Accordingly, C-O stable isotopes were analysed from microbialites, oncoids, ooids and lacustrine cements. The available depositional age model from zircon geochronology defined the stratigraphic interval, potentially including the K–Pg transition. Within this interval, carbonates provided negative δ13C values consistent with the negative C anomaly recorded in various K–Pg sites elsewhere. Additionally, spherical particles resembling spherulites related to meteorite impacts were found in two samples. Accordingly, the K–Pg transition could be placed at the top of the second stratigraphic sequence. These findings encourage further investigation of the Yacoraite Fm. to gain insights into the response of South American terrestrial settings to the K–Pg palaeoenvironmental crisis.

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Plášil, J., J. Čejka, J. Sejkora, P. Škácha, V. Goliáš, P. Jarka, F. Laufek, J. Jehlička, I. Němec und L. Strnad. „Widenmannite, a rare uranyl lead carbonate: occurrence, formation and characterization“. Mineralogical Magazine 74, Nr. 1 (Februar 2010): 97–110. http://dx.doi.org/10.1180/minmag.2010.074.1.97.

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AbstractThe rare uranyl lead carbonate widenmannite, Pb2(UO2)(CO3)3, was found at the Jánská vein, Příbram, Czech Republic, where two generations occur in several morphological types and mineral associations in hydrothermal veins. Alpha spectroscopy shows that these two generations have different ages, >220,000 and 118±12 y. ICP-MS analysis indicates that both widenmannites have a dominance of non-radiogenic Pb which originates from weathered galena. The older widenmannite I forms fine-grained, grey to beige aggregates in the highly altered supergene part of the hydrothermal ore vein in association with pyromorphite, cerussite and goethite. The younger widenmannite II occurs as white, yellow or greenish-yellow thin tabular crystals upto 0.5 mm long in association with cerussite, anglesite, limonite, kasolite and an unnamed Pb-U-O phase. Thermal analysis suggests that widenmannite decomposes in several steps, with Pb uranate as the final product. Infrared and Raman spectroscopy confirm the presence of non-equivalent (CO3)2– groups, bidentately coordinated in uranyl hexagonal polyhedra, forming the well known uranyl tricarbonate complex. Infrared spectroscopy shows conclusively that widenmannite does not contain molecular H2O.

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Alexandrov, Pavel, Jean-Pierre Floc'h, Michel Cuney und Alain Cheilletz. „Datation U–Pb à la microsonde ionique des zircons de l'unité supérieure de gneiss dans le Sud Limousin, Massif central“. Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science 332, Nr. 10 (Mai 2001): 625–32. http://dx.doi.org/10.1016/s1251-8050(01)01586-5.

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Letnikova, E. F., A. A. Zhdanov, A. V. Ivanov, A. V. Maslov, A. E. Izokh, A. F. Letnikova und N. G. Soloshenko. „Sr-ISOTOPIC COMPOSITION OF PALEOOCEAN WATER ON THE BORDER OF 960 Ma (DATA FOR NIZHNY TUNGUSKA FORMATION OF TURUKHAN UPLIFT OF SIBERIAN PLATFORM)“. Доклады Российской академии наук. Науки о Земле 513, Nr. 1 (01.11.2023): 66–76. http://dx.doi.org/10.31857/s2686739723600960.

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At the boundary of the Meso- and Neoproterozoic, Grenville collision events were widely manifested on the margins of ancient continental blocks. Most of the sedimentary sequences that had accumulated by that time had undergone significant thermal–metamorphic changes. In many ways, this is the main reason for the lack of isotopic data for carbonate deposits in the interval of 1200–900 Ma in world practice. Sr–isotopic composition in carbonate rocks with an age of 980–920 Ma was determined in the only section of the World – the Huainan Formation of the North China Platform with accumulation time determined by U–Pb dating of detrital zircon grains. In the upper part of the Nizhny Tunguska suite of the Turukhansk uplift, among carbonate deposits, we established the presence of altered volcanic rocks, as well as weathering crust products along them – poor bauxite and chamosite ores. Based on U–Pb zircon isotope dating, the age of the volcanic rocks is 964 Ma. For the least altered limestones of the upper part of the Nizhny Tungusska Formation, received 87Sr/86Sr values are 0.70532–0.70578, which are close enough to those found in the rocks of the Huainan Formation. Geochronological age of the studied limestones gives us more correct data. These data can be used to refine the previously proposed configuration of the Sr–isotopic composition variation curve in the Early Neoproterozoic. The Nizhny Tunguska Formation is the only carbonate section of the Early Neoproterozoic in the world with correctly geochronologically substantiated dating (based on zircon from subsynchronous volcanic rocks). This compares favorably with the Huainan formation.

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Bonev, Nikolay, Petyo Filipov, Raya Raicheva, Massimo Chiaradia und Robert Moritz. „Detrital zircon age and Sr isotopic constraints for a Late Palaeozoic carbonate platform in the lower Rhodope thrust system, Pirin, SW Bulgaria“. Geological Magazine 156, Nr. 12 (29.10.2019): 2117–24. http://dx.doi.org/10.1017/s0016756819001183.

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AbstractWe focused on the Pirin–Pangeon–Thasos carbonate sequence of the Rhodope thrust system, combining Sr isotopes from marble with U–Pb dating of detrital zircons from interlayered schists with outcrop near the villages of Ilindentsi and Petrovo in Bulgaria. The youngest zircon age at Ilindentsi is 266 Ma, i.e. Middle Permian, while the youngest zircon at Petrovo yielded an age of 290 Ma, i.e. Early Permian. Strontium isotopes range from 0.707420 to 0.707653, and are consistent with a Middle Permian maximum depositional age. Middle Permian sedimentation of this carbonate platform most likely occurred along the Eurasian margin rather than the Gondwana margin.

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Wei, Zhenquan, Jinfeng Ma, Gaowen He, Lifeng Zhong, Limin Zhang und Bin Zhao. „Laser In Situ U–Pb Isotope Dating of Carbonate Rocks in Weijia Guyot in the Western Pacific Ocean and Its Geological Significance“. Journal of Marine Science and Engineering 12, Nr. 5 (28.04.2024): 737. http://dx.doi.org/10.3390/jmse12050737.

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Shallow-water carbonate rocks constitute a crucial component of large guyots, arising in distinct environments and harboring valuable insights into the evolutionary stages of seamount islands as well as the tectonic conditions of the underlying oceanic plate. Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) was used to conduct in situ U–Pb isotope dating of carbonate minerals with low uranium content collected from Weijia Guyot. This dating approach yielded crucial evidence for the vertical development of the seamount. Our study indicates that shallow-water carbonate rocks in Weijia Guyot had a temporal range between 91 My and 137 My. The carbonate rocks underwent two growth phases, Hauterivian to Barremian and Cenomanian to Turonian, with a hiatus of approximately 20 My. Since the Hauterivian age, the shield volcano of Weijia Guyot is essentially complete, with its seamount top exposed at or near sea level and receiving its first stage of shallow-water carbonate sedimentation. Based on the dating of both shallow-water carbonate rocks and hawaiite within the Weijia Guyot, it is inferred that approximately 10 My elapsed from shield-building volcanism to late alkalic volcanism. During the Turonian age, the main reason for the second phase of shallow-water carbonate rocks in the seamounts was the regional tectonic uplift triggered by the drift of the Weijia Guyot along with the Pacific Plate toward the Society hotspot.

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Lenoir, Louise, Thomas Blaise, Andréa Somogyi, Benjamin Brigaud, Jocelyn Barbarand, Claire Boukari, Julius Nouet, Aurore Brézard-Oudot und Maurice Pagel. „Uranium incorporation in fluorite and exploration of U–Pb dating“. Geochronology 3, Nr. 1 (19.04.2021): 199–227. http://dx.doi.org/10.5194/gchron-3-199-2021.

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Abstract. The age of ore deposits constitutes a decisive element in understanding their formation. Deciphering their precise chronology may be a challenge in the absence of mineral phases that can be dated by conventional geochronometers. Fluorite is very common either as the major or accessory mineral in a wide variety of ores and may provide information regarding the origin and timing of mineralizing fluid flows. In this contribution, we explore U–Pb dating on fluorite crystals from the world-class carbonate strata-bound fluorite ore of Pierre-Perthuis in Burgundy (Morvan massif, France). The uranium distribution within fluorite is mapped using induced fission-track and synchrotron radiation X-ray fluorescence nano-imaging, showing that higher U content is measured in an overgrowth of fluorite (Flog) as a discrete band. Preservation of a micrometer-thick zonation in U, associated with other substituted elements such as Sr, Y, Fe and Zr, implies that neither solid-state diffusion nor dissolution–recrystallization occurred. These U-bearing external fluorite overgrowths contain solid inclusions of about 30 µm globular pyrite crystals with a mean δ34S of −23.6 ± 0.4 ‰V-CDT. We propose that the U incorporation in the fluorite lattice results from the development of a redox front during bacterial sulfate reduction. Flog generation sampled and analyzed by laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS) on four different crystals provides identical U–Pb ages within the limits of analytical uncertainty. Considered altogether, these four crystals yield an age estimate of 40.0 ± 1.7 Ma, not corrected for matrix-related elemental fractionation. Our results show that fluorite LA-ICP-MS U–Pb geochronology has potential for dating distinct crystal growth stages, although further research should be conducted to evaluate its accuracy.

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Shabaga, Brandi M., Mostafa Fayek, David Quirt, Charlie W. Jefferson und Alfredo Camacho. „Mineralogy, geochronology, and genesis of the Andrew Lake uranium deposit, Thelon Basin, Nunavut, Canada“. Canadian Journal of Earth Sciences 54, Nr. 8 (August 2017): 850–68. http://dx.doi.org/10.1139/cjes-2017-0024.

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The Thelon Basin located in Nunavut, Canada, shares many similarities with the U-producing Athabasca Basin in Saskatchewan. The Kiggavik project area, located near the northeastern edge of the Thelon Basin, contains U deposits and showings along the ∼30 km long NE–SW Kiggavik – Andrew Lake structural trend. The Andrew Lake deposit is near the southern end of this trend. Pre-mineralization is characterized by quartz ± carbonate veins that occupy fault systems later reactivated as conduits for U-mineralizing fluids. A four-phase genetic model is proposed for the Andrew Lake deposit. Phase 1 comprises vein-style uraninite (U1; 1031 ± 23 Ma) that is associated with illite and hematite, and contains variable PbO contents (0.2–9.5 wt.%). Phase 2 is characterized by altered uraninite (U2; ∼530 Ma) that is associated with coffinite. Altered uraninite (U3; <1 Ma) characterizes phase 3 and occurs as centimetre-scale “roll-fronts”. In phase 4, all three uraninite stages, and coffinite, are altered to boltwoodite. Although the oldest uraninite U–Pb age is ∼1030 Ma, illite associated with the U mineralization gives 40Ar/39Ar ages of 941 ± 31 and 1330 ± 36 Ma. The younger age is similar to the age for U1, suggesting that there was a fluid event that either precipitated U1 or reset the U–Pb isotopic system at ∼1000 Ma. While the older age for illite (1330 Ma) does not correlate with Andrew Lake U–Pb uraninite ages, it does correlate with ages previously reported for uraninite and clay alteration minerals in the Kiggavik area.

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Jin, Xiao-Ye, Jian-Xin Zhao, Yue-Xing Feng, Albert H. Hofstra, Xiao-Dong Deng, Xin-Fu Zhao und Jian-Wei Li. „CALCITE U-Pb DATING UNRAVELS THE AGE AND HYDROTHERMAL HISTORY OF THE GIANT SHUIYINDONG CARLIN-TYPE GOLD DEPOSIT IN THE GOLDEN TRIANGLE, SOUTH CHINA“. Economic Geology 116, Nr. 6 (01.09.2021): 1253–65. http://dx.doi.org/10.5382/econgeo.4870.

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Abstract The ages of Carlin-type gold deposits in the Golden Triangle of South China have long been questioned due to the general lack of minerals unequivocally linked to gold deposition that can be precisely dated using conventional radiogenic isotope techniques. Recent advances in U-Pb methods show that calcite can be used to constrain the ages of hydrothermal processes, but few studies have been applied to ore deposits. Herein, we show that this approach can be used to constrain the timing of hydrothermal activity that generated and overprinted the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle. Three stages of calcite (Cal-1, Cal-2, and Cal-3) have been recognized in this deposit based on crosscutting relationships, cathodoluminescence colors, and chemical (U, Pb, and rare earth element [REE]) and isotope (C, O, Sr) compositions. Cal-1 is texturally associated with ore-stage jasperoid and disseminated Au-bearing arsenian pyrite in hydrothermally altered carbonate rocks, which suggests it is synmineralization. Cal-2 fills open spaces and has a distinct orange cathodoluminescence, suggesting that it precipitated during a second fluid pulse. Cal-1 and Cal-2 have similar carbonate rock-buffered chemical and isotopic compositions. Cal-3 occurs in veins that often contain realgar and/or orpiment and are chemically (low U, Pb, and REE) and isotopically (higher δ13C, lower δ18O and Sri values) distinct from Cal-1 and Cal-2, suggesting that it formed from a third fluid. U-Pb isotope analyses, by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for U-rich Cal-1 and Cal-2 and by LA-multicollector (MC)-ICP-MS for U-poor Cal-3, yield well-defined age constraints of 204.3 to 202.6, 191.9, and 139.3 to 137.1 Ma for Cal-1, Cal-2, and Cal-3, respectively. These new ages suggest that the Shuiyindong gold deposit formed in the late Triassic and was overprinted by hydrothermal events in the early Jurassic and early Cretaceous. Given the association of Cal-3 with orpiment and realgar, and previous geochronologic studies of several other major gold deposits in the Golden Triangle, we infer that the latest stage of calcite may be associated with an early Cretaceous regional gold metallogenic event. Combined with existing isotopic ages in the region, these new ages lead us to propose that Carlin-type gold deposits in the Golden Triangle formed during two metallogenic episodes in extensional settings, associated with the late Triassic Indochina orogeny and early Cretaceous paleo-Pacific plate subduction. This study shows that the calcite U-Pb method can be used to constrain the timing of Carlin-type gold deposits and successive hydrothermal events.

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Park, Yuem, Nicholas L. Swanson-Hysell, Scott A. MacLennan, Adam C. Maloof, Mulubrhan Gebreslassie, Marissa M. Tremblay, Blair Schoene et al. „The lead-up to the Sturtian Snowball Earth: Neoproterozoic chemostratigraphy time-calibrated by the Tambien Group of Ethiopia“. GSA Bulletin 132, Nr. 5-6 (17.10.2019): 1119–49. http://dx.doi.org/10.1130/b35178.1.

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Abstract The Tonian-Cryogenian Tambien Group of northern Ethiopia is a mixed carbonate-siliciclastic sequence that culminates in glacial deposits associated with the first of the Cryogenian glaciations—the Sturtian “Snowball Earth.” Tambien Group deposition occurred atop arc volcanics and volcaniclastics of the Tsaliet Group. New U-Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates demonstrate that the transition between the Tsaliet and Tambien Groups occurred at ca. 820 Ma in western exposures and ca. 795 Ma in eastern exposures, which is consistent with west to east arc migration and deposition in an evolving back-arc basin. The presence of intercalated tuffs suitable for high-precision geochronology within the Tambien Group enable temporal constraints on stratigraphic data sets of the interval preceding, and leading into, the Sturtian glaciation. Recently discovered exposures of Sturtian glacial deposits and underlying Tambien Group strata in the Samre Fold-Thrust Belt present the opportunity to further utilize this unique association of tuffs and carbonate lithofacies. U-Pb ID-TIMS ages from zircons indicate that Tambien Group carbonates were deposited from ca. 820 Ma until 0–2 m.y. before the onset of the Sturtian glaciation, making the group host to a relatively complete carbonate stratigraphy leading into this glaciation. New δ13C and 87Sr/86Sr data and U-Pb ID-TIMS ages from the Tambien Group are used in conjunction with previously published isotopic and geochronologic data to construct newly time-calibrated composite Tonian carbon and strontium isotope curves. Tambien Group δ13C data and U-Pb ID-TIMS ages reveal that a pre-Sturtian sharp negative δ13C excursion (referred to as the Islay anomaly in the literature) precedes the Sturtian glaciation by ∼18 m.y., is synchronous in at least two separate basins, and is followed by a prolonged interval of positive δ13C values. The composite Tonian 87Sr/86Sr curve shows that, following an extended interval of low and relatively invariant values, inferred seawater 87Sr/86Sr rose ca. 880–770 Ma, then subsequently decreased leading up to the ca. 717 Ma initiation of the Sturtian glaciation. These data, when combined with a simple global weathering model and analyses of the timing and paleolatitude of large igneous province eruptions and arc accretion events, suggest that the 87Sr/86Sr increase was influenced by increased subaerial weathering of radiogenic lithologies as Rodinia rifted apart at low latitudes. The following 87Sr/86Sr decrease is consistent with enhanced subaerial weathering of arc lithologies accreting in the tropics over tens of millions of years, lowering pCO2 and contributing to the initiation of the Sturtian glaciation.

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Drost, Kerstin, David Chew, Joseph A. Petrus, Frank Scholze, Jon D. Woodhead, Joerg W. Schneider und David A. T. Harper. „An Image Mapping Approach to U-Pb LA-ICP-MS Carbonate Dating and Applications to Direct Dating of Carbonate Sedimentation“. Geochemistry, Geophysics, Geosystems 19, Nr. 12 (Dezember 2018): 4631–48. http://dx.doi.org/10.1029/2018gc007850.

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Lan, Zhongwu, Nick M. W. Roberts, Ying Zhou, Shujing Zhang, Zhensheng Li und Taiping Zhao. „Application of in situ U-Pb carbonate geochronology to Stenian-Tonian successions of North China“. Precambrian Research 370 (März 2022): 106551. http://dx.doi.org/10.1016/j.precamres.2021.106551.

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Parrish, Judith Totman, E. Troy Rasbury, Marjorie A. Chan und Stephen T. Hasiotis. „Earliest Jurassic U-Pb ages from carbonate deposits in the Navajo Sandstone, southeastern Utah, USA“. Geology 47, Nr. 11 (04.09.2019): 1015–19. http://dx.doi.org/10.1130/g46338.1.

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Abstract New uranium-lead (U-Pb) analyses of carbonate deposits in the Navajo Sandstone in southeastern Utah (USA) yielded dates of 200.5 ± 1.5 Ma (earliest Jurassic, Hettangian Age) and 195.0 ± 7.7 Ma (Early Jurassic, Sinemurian Age). These radioisotopic ages—the first reported from the Navajo erg and the oldest ages reported for this formation—are critical for understanding Colorado Plateau stratigraphy because they demonstrate that initial Navajo Sandstone deposition began just after the Triassic and that the base of the unit is strongly time-transgressive by at least 5.5 m.y.

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Kim, Ha, Seongsik Hong, Chaewon Park, Jihye Oh, Jonguk Kim und Yungoo Song. „Principle and Application of 'Image-mapping' in-situ U-Pb Carbonate Age-dating“. Economic and Environmental Geology 56, Nr. 2 (30.04.2023): 115–23. http://dx.doi.org/10.9719/eeg.2023.56.2.115.

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Georgieva, Sylvina, Rossitsa Vassileva und Georgi Milenkov. „Mineral association in pegmatites from the Djurkovo Pb-Zn deposit, Central Rhodopes: preliminary results“. Review of the Bulgarian Geological Society 83, Nr. 3 (Dezember 2022): 19–22. http://dx.doi.org/10.52215/rev.bgs.2022.83.3.19.

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Deformed pegmatites of varying thickness and position are a significant constituent intruded in the metamorphic complex, hosting the Djurkovo Pb-Zn deposit in Central Rhodopes. The mineral composition of the pegmatites consists of plagioclase, K-feldspar, quartz, and minor micas. The main accessory minerals are allanite, titanite, apatite and zircon. Late hydrothermal alteration of pegmatites led to the formation of epidote, adularia, sericite, chlorite, carbonate, quartz and leucoxene. Rare earth carbonate-phosphate assemblage (REE+Y, Th, U), manifested as ˂ 20 µm anhedral grains, is observed along fractures and dissolved zones in allanite and titanite. Because of the limited mobility of REE in fluids, these elements are barely transported during the hydrothermal activity and are incorporated in new phases, precipitated in the frames of the altered accessory minerals. The studied pegmatites contain a significant amount of accessory minerals rich in incompatible elements and therefore could be considered as their potential source.

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Lancelot, J., und V. Vella. „Datation U-Pb liasique de la pechblende de Rabejac; mise en evidence d'une preconcentration uranifere permienne dans le Bassin de Lodeve (Herault)“. Bulletin de la Société Géologique de France V, Nr. 2 (01.03.1989): 309–15. http://dx.doi.org/10.2113/gssgfbull.v.2.309.

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Dawson, J. B., und R. W. Hinton. „Trace-element content and partitioning in calcite, dolomite and apatite in carbonatite, Phalaborwa, South Africa“. Mineralogical Magazine 67, Nr. 5 (Oktober 2003): 921–30. http://dx.doi.org/10.1180/0026461036750151.

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AbstractA carbonatite sample from Phalaborwa, South Africa, consists of apatite, magnetite and a calcitedolomite ‘perthite’ which is interpreted as being due to exsolution of dolomite from a high-Mg calcite precursor. Carbon and oxygen isotope data indicate that the carbonates are equilibrated. In situ ionmicroprobe analyses for Fe, Mn, Na, Si, Y, the REEs, Pb, Th and U give the following average concentrations (in ppm) in the sequence apatite, calcite, dolomite: Fe 98, 1680, 8190; Mn 61, 510, 615; Na 1171, 627, 125; Si 368; 1.6, 0.2; Sr 4447, 5418, 2393; Ba 37, 2189, 75; La 1245, 300, 67; Y 121, 50, 5.8; Pb 16, 5.4, 1.4; Th 20, 0.02, 0; U 2.4, 0, 0.01. The concentrations are reasonably uniform in both apatite and dolomite, but in calcite are more variable. Na, Si, Y, the REEs, Pb, Th and U partition into apatite relative to both carbonates (and, hence, the precursor carbonate); KD ap/cc for REE decreases from ∽4 for La to ∽2 for Tm. There is almost equal partitioning of Sr between apatite and calcite. During separation of dolomite from calcite, Sr and Ba partition strongly into calcite and all the other analysed elements, except Fe and Mn, also preferentially enter calcite. The REEs prefer calcite relative to dolomite, and the KD dol/cc is reasonably constant, only varying from 0.23 to 0.17. Sr, Ba and Pb in the carbonates, and their partitioning between the calcite and dolomite, differ from other carbonatite carbonates reported in the literature.

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Guillong, Marcel, Jörn-Frederik Wotzlaw, Nathan Looser und Oscar Laurent. „Evaluating the reliability of U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) carbonate geochronology: matrix issues and a potential calcite validation reference material“. Geochronology 2, Nr. 1 (30.06.2020): 155–67. http://dx.doi.org/10.5194/gchron-2-155-2020.

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Abstract. We document that the reliability of carbonate U–Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is improved by matching the aspect ratio of the LA single-hole drilling craters and propagating long-term excess variance and systematic uncertainties. We investigated the impact of different matrices and ablation crater geometries using U–Pb isotope analyses of one primary (WC-1) and two secondary reference materials (RMs). Validation RMs (VRMs) include a previously characterised one (ASH-15D) and a new candidate (JT), characterised by ID-TIMS (intercept age: 13.797±0.031 Ma) with excellent agreement to pooled LA-ICP-MS measurements (13.75±0.11 | 0.36 Ma), a U concentration of approx. 1 µg g−1 and 238U∕206Pb ratios from 5 to 460, defining the isochron well. Differences in ablation crater depth to diameter ratios (aspect ratio) introduce an offset due to downhole fractionation and/or matrix effects. This effect can be observed either when the crater size between U–Pb RM and the sample changes or when the ablation rate for the sample is different than for the RM. Observed deviations are up to 20 % of the final intercept age depending on the degree of crater geometry mismatch. The long-term excess uncertainty was calculated to be in the range of 2 % (ASH-15D) to 2.5 % (JT), and we recommend propagating this uncertainty into the uncertainty of the final results. Additionally, a systematic offset to the ID-TIMS age of 2 %–3 % was observed for ASH-15D but not for JT. This offset might be due to different ablation rates of ASH-15D compared to the primary RM or remaining matrix effects, even when the aspect ratios chosen are similar.

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Khotylev, A. O., N. B. Devisheva, Al V. Tevelev und V. M. Moseichuk. „The first data on possible Mezozoic magmatism within the Western slope of the Southern Urals“. Moscow University Bulletin. Series 4. Geology, Nr. 5 (28.10.2018): 24–34. http://dx.doi.org/10.33623/0579-9406-2018-5-24-34.

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Within the Western slope of the Southern Urals, there are plenty of basite dyke complexes of Riphean to Vendian among Precambrian terrigenous-carbonate formations. In metamorphic formations of the Taratash complex (Archean to Early Proterozoic, the northern closure of the Bashkirian meganticlinorium) there was observed the andesitic dyke with isotopic age of 71±1 Ma (U-Pb SHRIMP II on zircons) and near Bakal two bodies of gabbroids with zircons of similar ages were found. These are the first evidence of possible Mezozoic magmatism in this region.

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Kuzyura, A. V., F. Wall, T. Jeffries und Yu A. Litvin. „Partitioning of trace elements between garnet, clinopyroxene and diamond-forming carbonate-silicate melt at 7 GPa“. Mineralogical Magazine 74, Nr. 2 (April 2010): 227–39. http://dx.doi.org/10.1180/minmag.2010.074.2.227.

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AbstractConcentrations of trace elements in coexisting garnet, clinopyroxene and completely miscible carbonate-silicate melt (formed at 7 GPa from the Chagatai silicocarbonatite rock known to be diamondiferous) were determined using LA-ICP-MS. The partition coefficients for Li, Rb, Cs, Ba, Th, U, Ta, Nb, La, Ce, Pb, Pr, Sr, Nd, Zr, Hf, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, Lu, Sc and Zn were determined. The new experimental data for trace-element partitioning between garnet, clinopyroxene and carbonate-silicate melt have been compared with published data for partitioning between garnet, clinopyroxene and carbonatite melt, and garnet, clinopyroxene and silicate melt. The results show that the trace-element partitioning is not significantly altered by changes in melt composition, with HREE always concentrated in the garnet. Carbonate-silicate melt, as a diamond-forming medium, and carbonatite or silicate melt equilibrated with mantle silicate minerals, behave similarly in respect of trace-element distribution.

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Georgieva, Hristiana, Rossen Nedialkov, Elitsa Stefanova, Georgi Milenkov, Ivan Krumov und Neven Georgiev. „Preliminary data on the mineral chemistry of garnet from the skarn alteration associated with the Elatsite porphyry-copper gold deposit, Bulgaria“. Review of the Bulgarian Geological Society 84, Nr. 3 (Dezember 2023): 31–34. http://dx.doi.org/10.52215/rev.bgs.2023.84.3.31.

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The skarn alteration is poorly preserved at the Elatsite, restricted to the hornfelses from the East, Southeast and Southern part of the deposit. The rocks are defined as exoskarns, with a mineral composition including garnets, epidote, pyroxene, amphiboles, carbonates, prehnite, quartz, sulphides. The newly formed minerals occur in poorly preserved layers. The garnet grains are subhedral with inclusions of epidote and quartz, while some of them are corrode with carbonate and zeolites formed in the fractures. The garnets are grossular-andradite type, with higher values for HREE over LREE, and low values for Rb, Sr, Ba, Pb and U. The skarn formation is related with the intrusion of the magma which causes the heating of the metamorphic rocks (rich in carbonate material – chlorite-sericite-carbonite, sericite-carbonate schists, etc.) from the low-grade metamorphic rocks. The Fe+3–Al+3 exchanges in the cores of the garnets indicate their formation from fluids with high oxygen fugacity.

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Zou, Yu, Donghua You, Bo Chen, Huamin Yang, Zhixing Tian, Dongna Liu und Liyu Zhang. „Carbonate U-Pb Geochronology and Clumped Isotope Constraints on the Origin of Hydrothermal Dolomites: A Case Study in the Middle Permian Qixia Formation, Sichuan Basin, South China“. Minerals 13, Nr. 2 (03.02.2023): 223. http://dx.doi.org/10.3390/min13020223.

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Reservoirs in the dolomites of the Middle Permian Qixia Formation in the Sichuan Basin are currently important oil and gas exploration objects in China. However, the questions concerning the sources of the dolomitized fluids and the control factors of the Qixia hydrothermal dolomites remain unclear. In this study, the original hydrothermal dolomites (the replacement dolomites (RDs) and saddle dolomites (SDs)) from the Qixia Formation in the southwestern Sichuan Basin (the PR1 well and Baoxing section) were mainly examined using novel in situ carbonate U-Pb dating with clumped isotopes (∆47). Our results show that the U-Pb ages of the latest SDs from the PR1 well (located in the middle zone of the Emeishan large igneous province (ELIP) and distanced from the Orogenic Belt of Longmenshan) are 257.9–251.0 Ma, coincident with the period of main activity of the ELIP. Combined with the previous U-Pb dating, we propose that the high-temperature T∆47 (82.2–108.4 °C and 127.5–205.9 °C) recorded for SDs from the PR1 well and Baoxing section may have responded to ELIP activity and Longmenshan orogeny activity, respectively. In addition, in the entire southwestern Sichuan Basin, the RDs and SDs yield similar δ13C and δ18O values, indicating that the dolomites were formed by hydrothermal fluids of similar sources, with marine hydrothermal fluids being a highly possible source. Finally, this study proposes a new hydrothermal dolomite genesis model for the Qixia Formation, emphasizing that the formation of hydrothermal dolomites mainly depends on the proximity to tectonic thermal events in space and time.

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Duff, Martine C., Caroline F. V. Mason und Douglas B. Hunter. „Comparison of acid and base leach for the removal of uranium from contaminated soil and catch-box media“. Canadian Journal of Soil Science 78, Nr. 4 (01.11.1998): 675–83. http://dx.doi.org/10.4141/s97-059.

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Several leach solutions have been developed for the removal of uranium (U) from contaminated media such as soil and military catch-box sand used for the ballistics testing of U-containing projectiles. Leach solutions of concentrated sulfuric acid and of carbonate (with and without oxidants such as peroxides) have also been used in the mining of U from high-grade ore deposits. Many of these solutions have been used at U-contaminated environmental sites with varying degrees of success. Batch leaches with six characterized U-contaminated media and seven leach solutions were conducted. After the leach solutions were reacted with the media (five soils and a catch-box sand), the solutions were analyzed for dissolved U, Ca, Si, Fe, Mn, Pb and Cr. We study the ability of acidic, basic, acidic-oxidizing and basic-oxidizing solutions to leach U from contaminated media. The results suggest the removal efficiency of soil U for each leach solution varies with the nature of the U-contamination in the media and the media composition. It is likely the forms of U in the contaminated media such as reduced, absorbed, complexed and solid species influence the solubilization of U by the leaching agents. Key words: Uranium, synchrotron X-ray fluorescence (SXRF), remediation, chromium, lead, leaching, catch-boxes

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Mottram, C. M., D. A. Kellett, T. Barresi, H. Zwingmann, M. Friend, A. Todd und J. B. Percival. „Syncing fault rock clocks: Direct comparison of U-Pb carbonate and K-Ar illite fault dating methods“. Geology 48, Nr. 12 (19.08.2020): 1179–83. http://dx.doi.org/10.1130/g47778.1.

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Abstract The timing of slip on brittle faults in Earth’s upper crust is difficult to constrain, and direct radiometric dating of fault-generated materials is the most explicit approach. Here we make a direct comparison between K-Ar dating of fault gouge clay (authigenic illite) and U-Pb dating of carbonate slickenfibers and veins from the same fault. We have dated fault generated materials from the Big Creek fault, a northwest-striking, dextral strike-slip fault system in Yukon Territory, Canadian Cordillera. Both methods yielded dates at ca. 73 Ma and ca. 60–57 Ma, representing at least two periods of fault slip that form part of a complex fault and fluid-flow history. The Cretaceous result lies within previous indirect estimates for major slip on the fault. The Paleocene–Eocene result coincides with the estimated timing of slip of the nearby Tintina and Denali faults, which are crustal-scale, northwest-striking dextral faults, indicating Big Creek fault reactivation during regional faulting. The coincidence of periods of carbonate-crystallizing fracturing and fluid flow with intervals of seismic, gouge-generating slip supports the fault valve model, where fault strength is mediated by fluid pressures, and fluid emplacement requires seismic pumping in otherwise impermeable aseismic fault zones. The reproducibility of slip periods for distinct fault-generated materials using different decay systems indicates that these methods provide complimentary results and can be reliably applied to date brittle fault slip, opening new opportunities for investigating fault conditions with associated mineralizing fluid events.

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Munksgaard, Niels C., Yasmin Antwertinger und David L. Parry. „Laser Ablation ICP-MS Analysis of Faviidae Corals for Environmental Monitoring of a Tropical Estuary“. Environmental Chemistry 1, Nr. 3 (2004): 188. http://dx.doi.org/10.1071/en04058.

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Environmental Context: The composition of calcium carbonate in annual skeletal growth bands reflects the environmental conditions in which coral grows, enabling their use as long-term bio-monitors and archives of environmental conditions. Such archives will provide a baseline against which recent and future pollutant levels can be compared. Abstract: An LA-ICP-MS linescan procedure has been developed for the determination of sub-millimetre scale elemental compositions of Al, Ba, Cu, La, Mg, Mn, Pb, Rb, Sr, U, and Zn in corallite walls of Faviidae corals, with the aim of establishing coral-based pollution monitoring in a tropical estuary. By selectively analyzing corallite walls, analytical signals from voids, organic, and detrital phases were minimized. Although the relative ablation yields of coral aragonite and NIST glass calibration standards differed and was dependent on pulse energy, accurate internal-standard normalized results could be verified for Ba, Cu, La, Mn, Pb, Sr, U, and Zn through the use of a secondary carbonate standard (MACS-1) and comparison with solution ICP-MS analysis. Signal smoothing and pre-acquisition surface cleaning procedures were applied. Corallite wall compositions varied by factors of up to five over distances of a few hundred micrometres. Significantly, the compositional variations along and perpendicular to the coral growth axis were of similar magnitude on a sub-millimetre scale. Consequently, compositional variations along the growth axis could not be interpreted chronologically on a sub-annual time scale. However, compositional records based on multi-annual integrated line scans should still reflect long-term environmental influences.

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