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Peter A Cawood - One of the best experts on this subject based on the ideXlab platform.
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detrital Zircon record and tectonic setting
Geology, 2012Co-Authors: Bruno Dhuime, C. J. Hawkesworth, Peter A CawoodAbstract:ABSTRACTDetrital Zircon spectra refl ect the tectonic setting of the basin in which they are deposited. Convergent plate margins are charac-terized by a large proportion of Zircon ages close to the depositional age of the sediment, whereas sediments in collisional, extensional and intracratonic settings contain greater proportions with older ages that refl ect the history of the underlying basement. These differences can be resolved by plotting the distribution of the difference between the measured crystallization ages (CA) of individual Zircon grains present in the sediment and the depositional age (DA) of the sedi-ment. Application of this approach to successions where the original nature of the basin and/or the link to source are no longer preserved constrains the tectonic setting in which the sediment was deposited.INTRODUCTION Detrital Zircons are a minor constituent of clastic sedimentary rocks, yet their physiochemical resilience and high concentrations of certain key trace elements means that they have become an important phase in sedimentary provenance analysis and in crustal evolution studies (e.g., Cawood et al., 2007b; Hawkesworth et al., 2010). Large numbers of in situ, high precision analyses of both igneous and detrital Zircons are now available, and a striking feature of the Zircon record is that it clusters into peaks of crystallization ages (Condie et al., 2009). Compilations of crys-tallization ages for detrital and igneous Zircons show remarkably similar patterns of peaks and troughs, although with some variation in the rela-tive amplitude of the peaks (Condie et al., 2009). This coincidence sug-gests that the sedimentary record is a valid representation of the magmatic record (Hawkesworth et al., 2010).We establish that detrital Zircon spectra have distinctive age distribu-tion patterns that refl ect the tectonic setting of the basin in which they are deposited. These patterns are principally controlled by (i) the volumes of magma generated in each tectonic setting and their preservation poten-tial, (ii) the ease with which magmatic and detrital Zircons of various ages and origins become incorporated into the sedimentary record, and (iii) the record of old Zircons incorporated into the sediment. These in turn provide a framework that can be used to constrain the tectonic setting of sedimen-tary packages. This approach distinguishes between three tectonic settings (i.e., convergent, collisional, and extensional), and it is most sensitive when the depositional age of the sediment investigated is well constrained. Basin setting will evolve with tectonic regime; for example, arc-continent or continent-continent collision will result in the evolution of convergent and extensional basins into collisional foreland basins. Hence the three settings distinguished herein are end-members, and the Zircon age patterns associ-ated with each show a spectrum of distributions that merge and overlap rather than defi ne discrete fi elds. Discriminant plots developed for igneous rock geochemistry (e.g., Pearce and Cann, 1973) or sediment framework modes (e.g., Dickinson and Suczek, 1979) often have diffuse boundaries or overlap between fi elds, but remain important approaches in understanding and constraining tectonic setting. Equally important, exceptions to simple end-member classifi cations can provide insight into subtleties of tectonic process, such as outlined below for Avalonia in eastern North America.
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large igneous province and magmatic arc sourced permian triassic volcanogenic sediments in china
Sedimentary Geology, 2012Co-Authors: Jianghai Yang, Peter A Cawood, Yuansheng Du, Hu Huang, Hongwei HuangAbstract:Abstract Whole-rock geochemistry and Zircon trace element and U-Pb age data for Late Permian–early Middle Triassic volcanogenic sedimentary rocks in SW China show a change from Large Igneous Province to subduction-related sources immediately before the Permian–Triassic boundary. Zircons from Late Permian samples give identical within-error ages to the adjoining Emeishan Large Igneous Province (LIP). The bulk-rock geochemistry of these Late Permian units shows no depletion in high field strength elements and is similar to the high-titanium basalts of the Emeishan. Six samples of latest Permian–earliest Triassic tuff and two earliest Middle Triassic tuffs samples yield U-Pb Zircon ages at of ~ 252 Ma and ~ 247 Ma, respectively. These tuffs and interstratified volcanogenic sedimentary rocks show significant depletion in high field strength elements, akin to magmatic arc-related rocks. Zircons from the tuffs have Nb/Hf, Th/Nb and Hf/Th ratios similar to those from arc/orogenic-related settings and distinct from the Zircons from the Late Permian samples which display within-plate/anorogenic characteristics. Our data demonstrate that there is a compositional change of the volcanogenic sediments across the Permian–Triassic boundary in South China.
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Large Igneous Province and magmatic arc sourced Permian–Triassic volcanogenic sediments in China
Sedimentary Geology, 2012Co-Authors: Jianghai Yang, Peter A Cawood, Yuansheng Du, Hu Huang, Hongwei HuangAbstract:Abstract Whole-rock geochemistry and Zircon trace element and U-Pb age data for Late Permian–early Middle Triassic volcanogenic sedimentary rocks in SW China show a change from Large Igneous Province to subduction-related sources immediately before the Permian–Triassic boundary. Zircons from Late Permian samples give identical within-error ages to the adjoining Emeishan Large Igneous Province (LIP). The bulk-rock geochemistry of these Late Permian units shows no depletion in high field strength elements and is similar to the high-titanium basalts of the Emeishan. Six samples of latest Permian–earliest Triassic tuff and two earliest Middle Triassic tuffs samples yield U-Pb Zircon ages at of ~ 252 Ma and ~ 247 Ma, respectively. These tuffs and interstratified volcanogenic sedimentary rocks show significant depletion in high field strength elements, akin to magmatic arc-related rocks. Zircons from the tuffs have Nb/Hf, Th/Nb and Hf/Th ratios similar to those from arc/orogenic-related settings and distinct from the Zircons from the Late Permian samples which display within-plate/anorogenic characteristics. Our data demonstrate that there is a compositional change of the volcanogenic sediments across the Permian–Triassic boundary in South China.
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shrimp u pb Zircon ages of the fuping complex implications for late archean to paleoproterozoic accretion and assembly of the north china craton
American Journal of Science, 2002Co-Authors: Guochun Zhao, Simon A Wilde, Peter A CawoodAbstract:The Fuping Complex is situated in the central part of the North China Craton and consists of four major lithological assemblages: Fuping tonalitic-trondhjemitic-granodioritic gneisses, Longquanguan augen gneisses, Wanzi supracrustal assemblage and Nanying granitic gneisses. SHRIMP U-Pb geochronology combined with U-Th and cathodoluminescence (CL) imaging of Zircon enables resolution of magmatic and metamorphic events that can be directed towards understanding the late Archean to Paleoproterozoic history of the Fuping Complex. CL images reveal the coexistence of magmatic and metamorphic Zircons in nearly all rock types of the Fuping Complex. The metamorphic Zircons occur as either single grains or overgrowth (or recrystallization) rims surrounding and truncating oscillatory-zoned magmatic Zircon cores, and are all characterized by nebulous zoning or being structureless, with extremely high luminescence and very low Th contents. These features make them distinct from magmatic Zircons that are characterized by concentric oscillatory zoning, comparatively low luminescence and high Th and U contents. SHRIMP U-Pb analyses on magmatic Zircons reveal that the tonalitic, trondhjemitic and granodioritic plutons of the Fuping gneisses were emplaced at 2523 ′ 14 Ma, 2499 ′ 10 Ma and 2486 ′ 8 Ma, respectively; whereas the monzogranitic and granitic plutons of the Longquanguan augen gneisses were intruded, respectively, at 2510 ′ 22 Ma and 2507 ′ 11 Ma. Prismatic and oscillatory-zoned Zircons dominate in the pelitic rocks of the Wanzi supracrustal assemblage and are interpreted as detritus from igneous source rocks. The concordant and discordant U-Pb ages of 2502 ′ 5 Ma and 2507 ′ 14 Ma obtained from two pelitic rock samples indicate these rocks must have been deposited no earlier than ∼2507 Ma ago. In addition, a zoned Zircon grain in one pelitic rock sample has a near concordant age of 2109 ′ 5 (1σ) Ma, which may provide a maximum depositional age for the Wanzi supracrustal rocks. SHRIMP results also reveal that granitic magmatism assigned to the Nanying granitic gneisses occurred over a protracted interval from ∼2077 ′ 13 Ma to ∼2024 ′ 21 Ma. The nebulously-zoned Zircon grains and overgrowth/recrystallization Zircon rims from different rocks yielded similar concordant 2 0 7 Pb/ 2 0 6 Pb ages in the range 1875 to 1802 Ma, interpreted as approximating the age of regional metamorphism of the Fuping Complex. Timing of primary Zircon crystallization and regional metamorphism of the Fuping Complex is in general agreement with recent U-Pb Zircon ion probe results for the Wutai and Hengshan Complexes that bound the Fuping Complex to the northwest. These areas are characterized by the emplacement of major granitoid bodies at around 2.50 Ga to 2.48 Ga ago, deposition of supracrustal rocks in the Paleoproterozoic, intrusion of Paleoproterozoic granitic bodies at 2.1 to 2.0 Ga, and regional metamorphism at 1.875 to 1.802 Ga. These data indicate that the Fuping and Hengshan Complexes do not represent an older crystalline basement to the Wutai Complex, as suggested in previous tectonic models but, together with the Wutai Complex, represent elements of a single late Archean to Paleoproterozoic magmatic arc system that has been subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western North China blocks at ∼1.85 Ga, which resulted in the final assembly of the North China Craton.
Takafumi Hirata - One of the best experts on this subject based on the ideXlab platform.
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Geochemical characteristics of Zircons in the Ashizuri A‐type granitoids: An additional granite topology tool for detrital Zircon studies
Island Arc, 2017Co-Authors: Yusuke Sawaki, Kazue Suzuki, Hisashi Asanuma, Satoki Okabayashi, Kentaro Hattori, Takuya Saito, Takafumi HirataAbstract:Zircon is resistant to alteration over a wide range of geological environments, and isotopic ratios within the mineral provide constraints on ages and their parental magmas. Trace element compositions in Zircon are also expected to reflect those of their parent magmas, and have a potential as essential indicators for their host rocks. Because most detrital Zircons that accumulate at river mouths are derived primarily from granitoids, the classification of Zircon within granitoids is potentially meaningful. This study employs the conventional classification scheme of granites (I-, S-, M-, and A-types). To clarify geochemical characteristics of Zircons in A-type granites, trace element compositions of Zircons extracted from the A-type Ashizuri granitoids were examined. Zircons from the Ashizuri granitoids commonly show enrichments of heavy rare earth elements and positive Ce anomalies, indicating that these Zircons were igneous in origin. In addition, Zircons in these A-type granites are characterized by enrichments of Nb, Y, Ta, Th, and U and strong negative Eu anomalies, which exhibit good positive correlations with those in their whole rocks. This fact indicates that these signatures in Zircons reflect well those in their parental bodies and are useful in identifying Zircons derived from A-type granite. Based on compilations of available data, Zircons from A-type granites can be clearly discriminated from other-types of granites within Nb/Sr–Eu anomaly, U/Sr–Eu anomaly, Nb/Sr–U/Sr, and Nb/Sr–Ta/Sr cross-plots. All indices used in these diagrams were selected based on the geochemical features of both Zircon and whole rock of A-type granites. Application of these discrimination diagrams to detrital Zircons will likely provide further insights. For example, some Hadean detrital Zircons plot in similar fields to A-type granites, implying the existence of A-type magmatism in the Earth's earliest history.
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behavior of Zircon in the upper amphibolite to granulite facies schist migmatite transition ryoke metamorphic belt sw japan constraints from the melt inclusions in Zircon
Contributions to Mineralogy and Petrology, 2013Co-Authors: Tetsuo Kawakami, Isao Yamaguchi, Akira Miyake, Tomoyuki Shibata, Kenshi Maki, Takaomi D Yokoyama, Takafumi HirataAbstract:Behavior of Zircon at the schist/migmatite transition is investigated. Syn-metamorphic overgrowth is rare in Zircon in schists, whereas Zircon in migmatites has rims with low Th/U that give 90.3 ± 2.2 Ma U–Pb concordia age. Between inherited core and the metamorphic rim, a thin, dark-CL annulus containing melt inclusion is commonly developed, suggesting that it formed contemporaneous with the rim in the presence of melt. In diatexites, the annulus is further truncated by the brighter-CL overgrowth, suggesting the resorption and regrowth of the Zircon after near-peak metamorphism. Part of the Zircon rim crystallized during the solidification of the melt in migmatites. Preservation of angular-shaped inherited core of 5–10 μm in Zircon included in garnet suggests that Zircon of this size did not experience resorption but developed overgrowths during near-peak metamorphism. The Ostwald ripening process consuming Zircon less than 5–10 μm is required to form new overgrowths. Curved crystal size distribution pattern for fine-grained Zircons in a diatexite sample may indicate the contribution of this process. Zircon less than 20 μm is confirmed to be an important sink of Zr in metatexites, and ca. 35-μm Zircon without detrital core are common in diatexites, supporting new nucleation of Zircon in migmatites. In the Ryoke metamorphic belt at the Aoyama area, monazite from migmatites records the prograde growth age of 96.5 ± 1.9 Ma. Using the difference of growth timing of monazite and Zircon, the duration of metamorphism higher than the amphibolite facies grade is estimated to be ca. 6 Myr.
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Detrital Zircon evidence for Hf isotopic evolution of granitoid crust and continental growth
Geochimica et Cosmochimica Acta, 2010Co-Authors: Tsuyoshi Iizuka, Shuji Rino, Tsuyoshi Komiya, Shigenori Maruyama, Takafumi HirataAbstract:We have determined U-Pb ages, trace element abundances and Hf isotopic compositions of approximately 1000 detrital Zircon grains from the Mississippi, Congo, Yangtze and Amazon Rivers. The U-Pb isotopic data reveal the lack of >3.3 Ga Zircons in the river sands, and distinct peaks at 2.7-2.5, 2.2-1.9, 1.7-1.6, 1.2-1.0, 0.9-0.4, and
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U-Pb age determination for seven standard Zircons using inductively coupled plasma-mass spectrometry coupled with frequency quintupled Nd-YAG (?? = 213 nm) laser ablation system: Comparison with LA-ICP-MS Zircon analyses with a NIST glass reference m
Resource Geology, 2008Co-Authors: Yuji Orihashi, Shun'ichi Nakai, Takafumi HirataAbstract:This paper evaluates the analytical precision, accuracy and long-term reliability of the U-Pb age data obtained using inductively coupled plasma2013mass spectrometry (ICP-MS) with a frequency quintupled Nd-YAG (03BB†=†213nm) laser ablation system. The U-Pb age data for seven standard Zircons of various ages, from 28†Ma to 2400†Ma (FCT, SL13, 91500, AS3, FC1, QGNG and PMA7) were obtained with an ablation pit size of 30†03BCm diameter. For 207Pb/206Pb ratio measurement, the mean isotopic ratio obtained on National Institute of Standards and Technology (NIST) SRM610 over 4†months was 0.9105†±†0.0014 (n†=†280, 95% confidence), which agrees well with the published value of 0.9096. The time-profile of Pb/U ratios during single spot ablation showed no significant difference in shape from NIST SRM610 and 91500 Zircon standards. These results encouraged the use of the glass standard as a calibration standard for the Pb/U ratio determination for Zircons with shorter wavelength (03BB†=†213†nm) laser ablation. But 206Pb/238U and 207Pb/235U ages obtained by this method for seven Zircon standards are systematically younger than the published U-Pb ages obtained by both isotope dilution2013thermal ionization mass spectrometry (ID-TIMS) and sensitive high-resolution ion-microprobe (SHRIMP). Greater discrepancies (320134% younger ages) were found for the 206Pb/238U ages for SL13, AS3 and 91500 Zircons. The origin of the differences could be heterogeneity in Pb/U ratio on SRM610 between the different disks, but a matrix effect accuracy either in the ICP ion source or in the ablation-transport processes of the sample aerosols cannot be neglected. When the 206Pb/238U (= 0.2302) newly defined in the present study is used, the measured 206Pb/238U and 207Pb/235U ages for the seven Zircon standards are in good agreement with those from ID-TIMS and SHRIMP within ±2%. This suggests that SRM610 glass standard is suitable for ICP-MS with laser ablation sampling (LA-ICP-MS) Zircon analysis, but it is necessary to determine the correction factor for 206Pb/238U by measuring several Zircon standards in individual laboratories.
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improvements of precision and accuracy in in situ hf isotope microanalysis of Zircon using the laser ablation mc icpms technique
Chemical Geology, 2005Co-Authors: Tsuyoshi Iizuka, Takafumi HirataAbstract:Abstract We have developed a new analytical technique for precise and accurate in situ Hf isotope ratio measurements for Zircons by means of laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS). Newly designed sample cell and N2 mixing technique provided higher elemental sensitivity with smoother signal intensity profiles. In order to improve the accuracy of the Hf isotope ratio analysis, previously reported correction methods for isobaric interferences on 176Hf by 176Yb and 176Lu were rigorously evaluated, and we found that the use of independent mass bias factors for Hf and Yb in the isobaric interference correction resulted in more reliable Hf isotopic data. In order to test the reliability of the Hf isotopic data from ∼35 μm diameter ablation pits that are smaller than the typical size of most Zircon grains, Lu–Hf isotopes for three Zircons (Harvard 91500, Antarctic Zircon PMA7 and Acasta Zircon AY199) were measured. The present 176Hf / 177Hf isotope ratio of 0.282321 ± 46 (2 S.D.) and initial 176Hf / 177Hf isotope ratio of 0.282315 ± 47 (2 S.D.) were obtained for Zircon standard 91500. The resulting present 176Hf / 177Hf isotope ratio shows an excellent agreement with the previously reported data. Our in situ isotopic data revealed that the Lu / Hf ratio varied significantly within the 91500 grain (176Lu / 177Hf = 0.000130–0.000345), suggesting the existence of slight isotopic heterogeneity in present 176Hf / 177Hf (approximately 15 ppm). For Antarctic Zircon PMA7, despite the smaller size of the single grain (50–100 μm wide, 80–300 μm long) and the presence of various mineral inclusions, resulting analytical precision for the initial 176Hf / 177Hf ratio was 128 ppm [0.281208 ± 36 (2 S.D.)]. For Acasta Zircon AY199, despite the high Yb / Hf (∼0.05) and Lu / Hf (∼0.01) isotope ratios with the early Archean crystallization age (3.74 Ga), resulting analytical precision for the initial 176Hf / 177Hf ratio was 187 ppm [0.280160 ± 52 (2 S.D.)]. These results demonstrate clearly that in situ Hf isotope ratio microanalysis developed here has the potential to become a significant tool for Zircon Lu–Hf isotopic study.
W L Griffin - One of the best experts on this subject based on the ideXlab platform.
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extreme lithium isotopic fractionation in three Zircon standards plesovice qinghu and temora
Scientific Reports, 2015Co-Authors: Xianhua Li, Yanjie Tang, Norman J Pearson, Qiuli Li, Guo Qiang Tang, W L Griffin, Suzanne Y OreillyAbstract:To understand the behavior of Li in Zircon, we have analyzed the abundance and isotopic composition of Li in three Zircon standards (Plesovice, Qinghu and Temora) widely used for microbeam analysis of U-Pb ages and O-Hf isotopes. We have mapped Li concentration ([Li]) on large grains, using a Cameca 1280HR Secondary Ion Mass Spectrometer (SIMS). All Zircons have a rim 5–20 μm wide in which [Li] is 5 to 20 times higher than in the core. Up to ~20‰ isotopic fractionation is observed on a small scale in the rims of a single Zircon grain. The measured δ7Li values range from –14.3 to 3.7‰ for Plesovice, –22.8 to 1.4‰ for Qinghu and –4.7 to 16.1‰ for Temora Zircon. The [Li] and δ7Li are highly variable at the rims, but relatively homogenous in the cores of the grains. From Zircon rim to core, [Li] decreases rapidly, while δ7Li increases, suggesting that the large isotopic variation of Li in Zircons could be caused by diffusion. Our data demonstrate that homogeneous δ7Li in the cores of Zircon can retain the original isotopic signatures of the magmas, while the bulk analysis of Li isotopes in mineral separates and in bulk-rock samples may produce misleading data.
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the application of laser ablation inductively coupled plasma mass spectrometry to in situ u pb Zircon geochronology
Chemical Geology, 2004Co-Authors: Simon E Jackson, Norman J Pearson, W L Griffin, E A BelousovaAbstract:This paper reports new developments in in situ U–Pb Zircon geochronology using 266 and 213 nm laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Standard spot ablation (spot diameters 40–80 μm) was employed, with no sampling strategies employed specifically to minimise elemental fractionation. Instead, He ablation gas and carefully replicated ablation conditions were employed to maintain constant ablation-related elemental fractionation of Pb and U between analyses. Combining these strategies with calibration on a new Zircon standard (GJ-1) allows elemental fractionation and instrumental mass bias to be corrected efficiently, and accurate 206Pb/238U and 207Pb/235U ratios to be measured with short-term precision (2 r.s.d.) of 1.9% and 3.0%, respectively. Long-term precision (2 r.s.d.) of the technique (266 nm ablation), based on 355 analyses of the 91500 Zircon (1065 Ma) standard over more than a year, was 3.8%, 4.0% and 1.4% for the 206Pb/238U, 207Pb/235U and 207Pb/206Pb ratios, respectively. Long-term precision (2 r.s.d.) for the 206Pb/238U, 207Pb/235U and 207Pb/206Pb ratios of the Mud Tank Zircon (732 Ma) was 3.9%, 4.1% and 1.7%, respectively (359 analyses). Selective integration of time-resolved signals was used to minimise the effect of Pb loss and common Pb enrichments on the measured ages. The precision and accuracy of our data compare very favourably with those obtained using more involved procedures to correct or minimise ablation- and ICP-MS-induced biases. 213 nm laser ablation produced comparable precision to 266 nm ablation using generally smaller spot sizes (40–50 vs. 60–80 μm), and offered significant advantages in terms of ablation duration and stability, particularly for small Zircons (<60 μm). For the 91500 Zircon, but not the Mud Tank Zircon, 213 nm ablation also produced significantly older and more accurate Pb/U ages. This suggests that shorter wavelength ablation may have reduced a matrix-dependent elemental fractionation difference between sample and standard. The accuracy and precision of the technique for young Zircons are demonstrated by analysis of three Zircon populations ranging in age from 417 to 7 Ma. In each case, the Zircons have yielded concordant ages or common Pb discordia which give concordia intercept ages that are in agreement with independently determined ages for the same samples. Application of Tera–Wasserburg diagrams [Earth Planet. Sci. Lett. 14 (1972) 281] was found to be the most useful approach to handling common Pb contributions that were not removed by selective integration of signals.
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igneous Zircon trace element composition as an indicator of source rock type
Contributions to Mineralogy and Petrology, 2002Co-Authors: E A Belousova, Suzanne Y Oreilly, W L Griffin, N I FisherAbstract:Trace element abundances in igneous Zircons, as determined by electron microprobe and laser-ablation microprobe ICPMS analysis, are shown to be sensitive to source rock type and crystallisation environment. The concentrations of 26 trace elements have been determined for Zircons from a wide range of different rock types and reveal distinctive elemental abundances and chondrite-normalised trace element patterns for specific rock types. There is a general trend of increasing trace element abundance in Zircons from ultramafic through mafic to granitic rocks. The average content of REE is typically less than 50 ppm in kimberlitic Zircons, up to 600–700 ppm in carbonatitic and lamproitic Zircons and 2,000 ppm in Zircons from mafic rocks, and can reach per cent levels in Zircons from granitoids and pegmatites. Relatively flat chondrite-normalised REE patterns with chondrite-normalised Yb/Sm ratios from 3 to 30 characterise Zircons from kimberlites and carbonatites, but Yb/Sm is commonly over 100 in Zircons from pegmatites. Th/U ratios typically range from 0.1 to 1, but can be 100–1000 in Zircons from some carbonatites and nepheline syenite pegmatites. The geochemical signatures characteristic of Zircon from some rock types can be recognised in bivariate discriminant diagrams, but multivariate statistical analysis is essential for the discrimination of Zircons from most rock types. Classification trees based on recursive partitioning techniques provide a rapid means of relating parent rock type to Zircon trace element analysis; Zircons from many rock types can be discriminated at confidence levels of 75% or more. These trees allow recognition of the provenance of detrital Zircons from heavy mineral concentrates, and significantly enhance the usefulness of Zircon in regional crustal studies and as an indicator mineral in mineral exploration.
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the hf isotope composition of cratonic mantle lam mc icpms analysis of Zircon megacrysts in kimberlites
Geochimica et Cosmochimica Acta, 2000Co-Authors: Norman J Pearson, Suzanne Y Oreilly, W L Griffin, E A Belousova, Simon E Jackson, E Van Achterbergh, S R SheeAbstract:Zircon megacrysts represent a late stage in the crystallisation of the magmas that produced the low-Cr megacryst suite (Ol1Opx1Cpx1Gnt1Ilm1Phl1Zir) found in many kimberlites, and may carry information on the sources of the parent magmas and the interaction of these magmas with the cratonic lithosphere. The isotopic composition of Hf has been measured in 124 mantle-derived Zircon megacrysts from African, Siberian and Australian kimberlites, using a laser-ablation microprobe (LAM) and a multi-collector (MC) ICPMS. The Zircons range in age from 90 Ma to ca 2500 Ma, allowing indirect analysis of mantle-derived Hf over a long time span. Most values of «Hf fall between 0 and 110, but Zircon suites from several kimberlites range down to «Hf 52 16. Combined with published Nd data on the silicate members of the low-Cr megacryst suite, these data indicate crystallisation of Zircon from magmas lying well below the terrestrial «Hf-«Nd array. LAM-ICPMS analyses of garnets and clinopyroxenes from mantle-derived peridotite xenoliths suggest that cratonic lithospheric mantle has Hf/Nd (0.3- 0.5) greater than estimated Bulk Silicate Earth. The depleted and metasomatised lherzolites and harzburgites that make up much of the Archean lithospheric mantle have Lu/Hf ratios (#0.15) low enough to account for the lowest «Hf observed in the Zircons, over time spans of 1-3.5 Ga. We therefore suggest that the magmas from which the kimberlitic Zircons crystallised were derived from Depleted Mantle or OIB-type sources, and developed negative «Hf through reaction with the subcontinental lithospheric mantle. Copyright © 2000 Elsevier Science Ltd
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three natural Zircon standards for u th pb lu hf trace element and ree analyses
Geostandards and Geoanalytical Research, 1995Co-Authors: M Wiedenbeck, W L Griffin, P Alle, Fernando Corfu, M Meier, F Oberli, A Von Quadt, J C Roddick, W SpiegelAbstract:We report here the results of a study to develop natural Zircon geochemical standards for calibrating the U-(Th)-Pb geochronometer and Hf isotopic analyses. Additional data were also collected for the major, minor and trace element contents of the three selected sample sets. A total of five large Zircon grains (masses between 0.5 and 238 g) were selected for this study, representing three different suites of Zircons with ages of 1065 Ma, 2.5 Ma and 0.9 Ma. Geochemical laboratories can obtain these materials by contacting Geostandards Newsletter.
Norman J Pearson - One of the best experts on this subject based on the ideXlab platform.
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extreme lithium isotopic fractionation in three Zircon standards plesovice qinghu and temora
Scientific Reports, 2015Co-Authors: Xianhua Li, Yanjie Tang, Norman J Pearson, Qiuli Li, Guo Qiang Tang, W L Griffin, Suzanne Y OreillyAbstract:To understand the behavior of Li in Zircon, we have analyzed the abundance and isotopic composition of Li in three Zircon standards (Plesovice, Qinghu and Temora) widely used for microbeam analysis of U-Pb ages and O-Hf isotopes. We have mapped Li concentration ([Li]) on large grains, using a Cameca 1280HR Secondary Ion Mass Spectrometer (SIMS). All Zircons have a rim 5–20 μm wide in which [Li] is 5 to 20 times higher than in the core. Up to ~20‰ isotopic fractionation is observed on a small scale in the rims of a single Zircon grain. The measured δ7Li values range from –14.3 to 3.7‰ for Plesovice, –22.8 to 1.4‰ for Qinghu and –4.7 to 16.1‰ for Temora Zircon. The [Li] and δ7Li are highly variable at the rims, but relatively homogenous in the cores of the grains. From Zircon rim to core, [Li] decreases rapidly, while δ7Li increases, suggesting that the large isotopic variation of Li in Zircons could be caused by diffusion. Our data demonstrate that homogeneous δ7Li in the cores of Zircon can retain the original isotopic signatures of the magmas, while the bulk analysis of Li isotopes in mineral separates and in bulk-rock samples may produce misleading data.
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Magmatic evolution of the ultramafic–mafic Kharaelakh intrusion (Siberian Craton, Russia): insights from trace-element, U–Pb and Hf-isotope data on Zircon
Contributions to Mineralogy and Petrology, 2010Co-Authors: Kreshimir Nenadovitch Malitch, Norman J Pearson, Elena A. Belousova, William L. Griffin, Inna Yu Badanina, Sergey L. Presnyakov, Evgeniya V. TuganovaAbstract:The ultramafic–mafic Kharaelakh intrusion in the northwestern part of the Siberian Craton (Russia) hosts major economic platinum-group-element (PGE)–Cu–Ni sulphide deposits. In situ U–Pb, REE and Hf-isotope analyses of Zircon from these rocks, combined with detailed study of crystal morphology and internal structure, identify four Zircon populations. U–Pb ages of these populations cover a significant time span (from 347 ± 16 to 235.7 ± 6.1 Ma) suggesting multiple magmatic events that cluster around 350 and 250 Ma, being consistent with two recognised stages of active tectonism in the development of the Siberian Craton. The oldest Zircon population, however, represents previously unknown stage of magmatic activity in the Noril’sk area. Epsilon-Hf values of +2.3 to +16.3 in the analysed Zircons reflect a dominant role of mantle-derived magmas and suggest that juvenile mantle material was the main source for the ultramafic–mafic Kharaelakh intrusion. A significant range in initial ^176Hf/^177Hf values, found in Zircons that cluster around 250 Ma, indicate mixing between mantle and crustal magma sources. Our findings imply that economic intrusions hosting PGE–Cu–Ni deposits of the Noril’sk area have a far more complex geological history than is commonly assumed.
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Zircon u pb and hf isotope constraints on the mesozoic tectonics and crustal evolution of southern tibet
Geology, 2006Co-Authors: Sunlin Chung, Norman J Pearson, Suzanne Y Oreilly, Biao Song, Jianqing JiAbstract:The first in situ Hf and U-Pb isotope analyses of Zircon separates from Mesozoic granites in southern Tibet identify a significant, previously unknown stage of magmatism. Igneous Zircons (n = 34) from a granite within the Gangdese batholith show a weighted mean 206 Pb/ 238 U age of 188.1 ± 1.4 Ma and e Hf (T) (the parts in 10 4 deviation of initial Hf isotope ratios between the Zircon sample and the chondritic reservoir) values between +10.4 and +16.8, suggesting predominantly Early Jurassic intrusive activity with a juvenile mantle contribution. Of 40 inherited Zircons from two Cretaceous S-type granites in the northern magmatic belt, 23 delineate a slightly older 206 Pb/ 238 U age cluster between 188 and 210 Ma. These Zircons have e Hf (T) values from −3.9 to −13.7, yielding crustal Hf model ages from ca. 1.4 to 2.1 Ga, suggesting a major episode of crustal growth in Proterozoic time and remelting of this crust in Early Jurassic time. Combining these with literature data, we interpret the Jurassic Gangdese magmatism as an early product of the Neo-Tethyan subduction that played a long-lasting role in the tectonic evolution of southern Tibet prior to the India-Asia collision.
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the application of laser ablation inductively coupled plasma mass spectrometry to in situ u pb Zircon geochronology
Chemical Geology, 2004Co-Authors: Simon E Jackson, Norman J Pearson, W L Griffin, E A BelousovaAbstract:This paper reports new developments in in situ U–Pb Zircon geochronology using 266 and 213 nm laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Standard spot ablation (spot diameters 40–80 μm) was employed, with no sampling strategies employed specifically to minimise elemental fractionation. Instead, He ablation gas and carefully replicated ablation conditions were employed to maintain constant ablation-related elemental fractionation of Pb and U between analyses. Combining these strategies with calibration on a new Zircon standard (GJ-1) allows elemental fractionation and instrumental mass bias to be corrected efficiently, and accurate 206Pb/238U and 207Pb/235U ratios to be measured with short-term precision (2 r.s.d.) of 1.9% and 3.0%, respectively. Long-term precision (2 r.s.d.) of the technique (266 nm ablation), based on 355 analyses of the 91500 Zircon (1065 Ma) standard over more than a year, was 3.8%, 4.0% and 1.4% for the 206Pb/238U, 207Pb/235U and 207Pb/206Pb ratios, respectively. Long-term precision (2 r.s.d.) for the 206Pb/238U, 207Pb/235U and 207Pb/206Pb ratios of the Mud Tank Zircon (732 Ma) was 3.9%, 4.1% and 1.7%, respectively (359 analyses). Selective integration of time-resolved signals was used to minimise the effect of Pb loss and common Pb enrichments on the measured ages. The precision and accuracy of our data compare very favourably with those obtained using more involved procedures to correct or minimise ablation- and ICP-MS-induced biases. 213 nm laser ablation produced comparable precision to 266 nm ablation using generally smaller spot sizes (40–50 vs. 60–80 μm), and offered significant advantages in terms of ablation duration and stability, particularly for small Zircons (<60 μm). For the 91500 Zircon, but not the Mud Tank Zircon, 213 nm ablation also produced significantly older and more accurate Pb/U ages. This suggests that shorter wavelength ablation may have reduced a matrix-dependent elemental fractionation difference between sample and standard. The accuracy and precision of the technique for young Zircons are demonstrated by analysis of three Zircon populations ranging in age from 417 to 7 Ma. In each case, the Zircons have yielded concordant ages or common Pb discordia which give concordia intercept ages that are in agreement with independently determined ages for the same samples. Application of Tera–Wasserburg diagrams [Earth Planet. Sci. Lett. 14 (1972) 281] was found to be the most useful approach to handling common Pb contributions that were not removed by selective integration of signals.
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the hf isotope composition of cratonic mantle lam mc icpms analysis of Zircon megacrysts in kimberlites
Geochimica et Cosmochimica Acta, 2000Co-Authors: Norman J Pearson, Suzanne Y Oreilly, W L Griffin, E A Belousova, Simon E Jackson, E Van Achterbergh, S R SheeAbstract:Zircon megacrysts represent a late stage in the crystallisation of the magmas that produced the low-Cr megacryst suite (Ol1Opx1Cpx1Gnt1Ilm1Phl1Zir) found in many kimberlites, and may carry information on the sources of the parent magmas and the interaction of these magmas with the cratonic lithosphere. The isotopic composition of Hf has been measured in 124 mantle-derived Zircon megacrysts from African, Siberian and Australian kimberlites, using a laser-ablation microprobe (LAM) and a multi-collector (MC) ICPMS. The Zircons range in age from 90 Ma to ca 2500 Ma, allowing indirect analysis of mantle-derived Hf over a long time span. Most values of «Hf fall between 0 and 110, but Zircon suites from several kimberlites range down to «Hf 52 16. Combined with published Nd data on the silicate members of the low-Cr megacryst suite, these data indicate crystallisation of Zircon from magmas lying well below the terrestrial «Hf-«Nd array. LAM-ICPMS analyses of garnets and clinopyroxenes from mantle-derived peridotite xenoliths suggest that cratonic lithospheric mantle has Hf/Nd (0.3- 0.5) greater than estimated Bulk Silicate Earth. The depleted and metasomatised lherzolites and harzburgites that make up much of the Archean lithospheric mantle have Lu/Hf ratios (#0.15) low enough to account for the lowest «Hf observed in the Zircons, over time spans of 1-3.5 Ga. We therefore suggest that the magmas from which the kimberlitic Zircons crystallised were derived from Depleted Mantle or OIB-type sources, and developed negative «Hf through reaction with the subcontinental lithospheric mantle. Copyright © 2000 Elsevier Science Ltd
E A Belousova - One of the best experts on this subject based on the ideXlab platform.
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the application of laser ablation inductively coupled plasma mass spectrometry to in situ u pb Zircon geochronology
Chemical Geology, 2004Co-Authors: Simon E Jackson, Norman J Pearson, W L Griffin, E A BelousovaAbstract:This paper reports new developments in in situ U–Pb Zircon geochronology using 266 and 213 nm laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Standard spot ablation (spot diameters 40–80 μm) was employed, with no sampling strategies employed specifically to minimise elemental fractionation. Instead, He ablation gas and carefully replicated ablation conditions were employed to maintain constant ablation-related elemental fractionation of Pb and U between analyses. Combining these strategies with calibration on a new Zircon standard (GJ-1) allows elemental fractionation and instrumental mass bias to be corrected efficiently, and accurate 206Pb/238U and 207Pb/235U ratios to be measured with short-term precision (2 r.s.d.) of 1.9% and 3.0%, respectively. Long-term precision (2 r.s.d.) of the technique (266 nm ablation), based on 355 analyses of the 91500 Zircon (1065 Ma) standard over more than a year, was 3.8%, 4.0% and 1.4% for the 206Pb/238U, 207Pb/235U and 207Pb/206Pb ratios, respectively. Long-term precision (2 r.s.d.) for the 206Pb/238U, 207Pb/235U and 207Pb/206Pb ratios of the Mud Tank Zircon (732 Ma) was 3.9%, 4.1% and 1.7%, respectively (359 analyses). Selective integration of time-resolved signals was used to minimise the effect of Pb loss and common Pb enrichments on the measured ages. The precision and accuracy of our data compare very favourably with those obtained using more involved procedures to correct or minimise ablation- and ICP-MS-induced biases. 213 nm laser ablation produced comparable precision to 266 nm ablation using generally smaller spot sizes (40–50 vs. 60–80 μm), and offered significant advantages in terms of ablation duration and stability, particularly for small Zircons (<60 μm). For the 91500 Zircon, but not the Mud Tank Zircon, 213 nm ablation also produced significantly older and more accurate Pb/U ages. This suggests that shorter wavelength ablation may have reduced a matrix-dependent elemental fractionation difference between sample and standard. The accuracy and precision of the technique for young Zircons are demonstrated by analysis of three Zircon populations ranging in age from 417 to 7 Ma. In each case, the Zircons have yielded concordant ages or common Pb discordia which give concordia intercept ages that are in agreement with independently determined ages for the same samples. Application of Tera–Wasserburg diagrams [Earth Planet. Sci. Lett. 14 (1972) 281] was found to be the most useful approach to handling common Pb contributions that were not removed by selective integration of signals.
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igneous Zircon trace element composition as an indicator of source rock type
Contributions to Mineralogy and Petrology, 2002Co-Authors: E A Belousova, Suzanne Y Oreilly, W L Griffin, N I FisherAbstract:Trace element abundances in igneous Zircons, as determined by electron microprobe and laser-ablation microprobe ICPMS analysis, are shown to be sensitive to source rock type and crystallisation environment. The concentrations of 26 trace elements have been determined for Zircons from a wide range of different rock types and reveal distinctive elemental abundances and chondrite-normalised trace element patterns for specific rock types. There is a general trend of increasing trace element abundance in Zircons from ultramafic through mafic to granitic rocks. The average content of REE is typically less than 50 ppm in kimberlitic Zircons, up to 600–700 ppm in carbonatitic and lamproitic Zircons and 2,000 ppm in Zircons from mafic rocks, and can reach per cent levels in Zircons from granitoids and pegmatites. Relatively flat chondrite-normalised REE patterns with chondrite-normalised Yb/Sm ratios from 3 to 30 characterise Zircons from kimberlites and carbonatites, but Yb/Sm is commonly over 100 in Zircons from pegmatites. Th/U ratios typically range from 0.1 to 1, but can be 100–1000 in Zircons from some carbonatites and nepheline syenite pegmatites. The geochemical signatures characteristic of Zircon from some rock types can be recognised in bivariate discriminant diagrams, but multivariate statistical analysis is essential for the discrimination of Zircons from most rock types. Classification trees based on recursive partitioning techniques provide a rapid means of relating parent rock type to Zircon trace element analysis; Zircons from many rock types can be discriminated at confidence levels of 75% or more. These trees allow recognition of the provenance of detrital Zircons from heavy mineral concentrates, and significantly enhance the usefulness of Zircon in regional crustal studies and as an indicator mineral in mineral exploration.
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the hf isotope composition of cratonic mantle lam mc icpms analysis of Zircon megacrysts in kimberlites
Geochimica et Cosmochimica Acta, 2000Co-Authors: Norman J Pearson, Suzanne Y Oreilly, W L Griffin, E A Belousova, Simon E Jackson, E Van Achterbergh, S R SheeAbstract:Zircon megacrysts represent a late stage in the crystallisation of the magmas that produced the low-Cr megacryst suite (Ol1Opx1Cpx1Gnt1Ilm1Phl1Zir) found in many kimberlites, and may carry information on the sources of the parent magmas and the interaction of these magmas with the cratonic lithosphere. The isotopic composition of Hf has been measured in 124 mantle-derived Zircon megacrysts from African, Siberian and Australian kimberlites, using a laser-ablation microprobe (LAM) and a multi-collector (MC) ICPMS. The Zircons range in age from 90 Ma to ca 2500 Ma, allowing indirect analysis of mantle-derived Hf over a long time span. Most values of «Hf fall between 0 and 110, but Zircon suites from several kimberlites range down to «Hf 52 16. Combined with published Nd data on the silicate members of the low-Cr megacryst suite, these data indicate crystallisation of Zircon from magmas lying well below the terrestrial «Hf-«Nd array. LAM-ICPMS analyses of garnets and clinopyroxenes from mantle-derived peridotite xenoliths suggest that cratonic lithospheric mantle has Hf/Nd (0.3- 0.5) greater than estimated Bulk Silicate Earth. The depleted and metasomatised lherzolites and harzburgites that make up much of the Archean lithospheric mantle have Lu/Hf ratios (#0.15) low enough to account for the lowest «Hf observed in the Zircons, over time spans of 1-3.5 Ga. We therefore suggest that the magmas from which the kimberlitic Zircons crystallised were derived from Depleted Mantle or OIB-type sources, and developed negative «Hf through reaction with the subcontinental lithospheric mantle. Copyright © 2000 Elsevier Science Ltd
