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LKZ-1: A New Zircon Working Standard for the In Situ Determination of U–Pb Age, O–Hf Isotopes, and Trace Element Composition

Korea Basic Science Institute, Cheongju 28119, Korea
Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea
Core Research Facilities, Pusan National University, Busan 46241, Korea
Korea Polar Research Institute, Incheon 21990, Korea
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100027, China
Jack Satterly Geochronology Laboratory, University of Toronto, Toronto, ON M5S 3B1, Canada
Author to whom correspondence should be addressed.
Minerals 2019, 9(5), 325;
Received: 3 April 2019 / Revised: 23 May 2019 / Accepted: 24 May 2019 / Published: 27 May 2019
(This article belongs to the Section Mineral Geochemistry and Geochronology)


This study introduces a new zircon reference material, LKZ-1, for the in situ U–Pb dating and O–Hf isotopic and trace element analyses. The secondary ion mass spectrometric analyses for this gem-quality single-crystal zircon yielded a weighted mean 206Pb/238U age of 572.6 ± 2.0 Ma (2σ, n = 22, MSWD = 0.90), with moderately high U concentrations (619 ± 21 ppm, 1 SD), restricted Th/U ratios (0.146 ± 0.002, 1 SD), and negligible common Pb content (206Pbc < 0.2%). A comparable 206Pb/238U age (570.0 ± 2.5 Ma, 2σ) was produced by the isotope dilution-thermal ionization mass spectrometry. The secondary ion mass spectrometric and laser ablation-assisted multiple collector inductively coupled plasma mass spectrometer analyses respectively showed that LKZ-1 had little variation in O (δ18OV-SMOW = 10.65 ± 0.14‰; laser fluorination value = 10.72 ± 0.02‰; 1 SD) and Hf (176Hf/177Hf = 0.281794 ± 0.000016, 1 SD) isotopic compositions. LKZ-1 was also fairly homogeneous in its chemical composition (RSD of laser ablation ICPMS data ≤ 10%), displaying a relatively uniform chondrite-normalized rare earth element pattern ((Lu/Gd)N = 31 ± 3, Eu/Eu* = 0.43 ± 0.17, Ce/Ce* = 44 ± 32; 1 SD). These consistencies suggest that the LKZ-1 zircon is a suitable working standard for geochronological and geochemical analyses.

1. Introduction

Geochemical and geochronological data for rocks and minerals have long been obtained by wet chemical and isotopic analyses [1,2]. Despite the constraints of time-consuming and labor-intensive sample preparation, wet analysis is still widely used, particularly when a high level of precision is demanded. However, if the sample is composed of chemically or isotopically heterogeneous domains that have their own petrogenetic significance, microsampling strategies are inevitably required.
Technical advances during the past several decades have facilitated the routine analysis of tiny single crystals at the subgrain scale. The high spatial resolution of microbeam techniques, typically of the micrometer- or submicrometer-scale [3,4], provides an excellent opportunity to integrate the chemical and isotopic data from individual subgrain domains with textural observations (e.g., [5]). Zircon (ZrSiO4) has been a prime target of in situ analysis using secondary ion mass spectrometry (SIMS) [6,7] or laser ablation (LA)-assisted inductively coupled plasma mass spectrometry (ICPMS) [8,9], mainly for its ability to retain the original isotopic signature due to its strong resistance to physicochemical breakdown and slow intracrystalline diffusion of constituent ions [10]. Zircon can provide U–Pb age constraints, as well as trace element and O–Hf isotope data for given microdomains. The integration of such multifaceted zircon data has proven to be a powerful tool for addressing the diverse issues related to crustal evolution [11,12,13,14].
Microbeam analysis can be performed rapidly and requires minimal sample preparation; however, the measured data should be carefully corrected and calibrated for spectral and isobaric interference and instrumental fractionation. This process is generally achieved using matrix-matched standards, which are used as a reference material to check the data accuracy and, more importantly, as a primary standard to calculate the inter-elemental isotope ratios or instrumental mass fractionation (IMF) factors. In the latter case, the relative isotopic composition of the standard should be uniform and accurately known, because it directly affects the results calculated for unknown samples. Many zircon standards have been suggested for U–Th–Pb dating and chemical/isotopic analyses. Among these, 91500 [15], FC1 [16], Temora [17,18], and Plešovice [19] are widely used; however, their supply is quite limited. For example, the International Association of Geoanalysts provides only a limited amount of zircon 91500 per laboratory, with the recommendation that it be used initially to establish an in-house reference material. It is also noted that some zircon standards are chemically inhomogeneous [19,20]. Thus, there is still demand for high-quality zircon standards.
This study introduces a new zircon reference material LKZ-1. We measured its U–Pb age and Hf isotopic composition using a high-resolution (HR)-SIMS, isotope dilution thermal ionization mass spectrometry (ID-TIMS), and LA-multiple collector (MC)-ICPMS. The oxygen isotopic composition of LKZ-1 was measured using a laser fluorination system and HR-SIMS. The chemical composition of LKZ-1 was measured using a quadrupole ICPMS connected to a femtosecond LA system.

2. Materials and Methods

2.1. LKZ-1

LKZ-1 is a single transparent pale yellow megacryst of gem-quality zircon with no visible inclusions or cracks (Figure 1). The total mass was 0.83 g. The LKZ-1 was imported from Sri Lanka by an online gem dealer and purchased by the Korea Basic Science Institute (KBSI) in 2014. No information about the nature of its host rock is available.
Our previous LA-MC-ICPMS analyses confirmed that this zircon is in a 238U–230Th radioactive equilibrium [21]. It is noted that the preliminary ion microprobe U–Pb data for LKZ-1, presented by Kim et al. (2015) [22], are revised in this study.

2.2. HR-SIMS U–Pb Analysis

Fragments of the LKZ-1 zircon were mounted in epoxy with reference zircons for in situ isotopic and chemical analyses. The U–Th–Pb isotopic analyses were conducted using a sensitive high-resolution ion microprobe (SHRIMP IIe/MC) at the KBSI Ochang Center. Before the SHRIMP analyses, cathodoluminescence (CL) and backscattered electron (BSE) images of the fragments were examined using a scanning electron microscope (SEM) (JEOL JSM-6610LV). The primary O2 beam was focused into a ~25-μm-diameter spot at an accelerating voltage of 10 kV. The collector slit width was fixed at 100 μm, achieving a mass resolution of about 5000 at 1% peak height. We used the 91500 (206Pb/238U age = 1062.4 Ma, [15]) and SL13 (U = 238 ppm) standard zircons for Pb/U calibration and to determine the U abundance, respectively. The Pb/U ratios were calibrated against the 91500 zircon according to the power law relationship between Pb+/U+ and UO+/U+. The Th/U ratios were estimated using a fractionation factor derived from the measured 232Th16O+/238U16O+ versus 208Pb/206Pb of the SL13 standard. The common Pb was corrected using the 207Pb method [23]. Data processing was conducted using the SQUID 2.50 and Isoplot 3.75 software [24,25]. The weighted mean ages were calculated after excluding the outliers using the Student’s t-test and reported at the 95% confidence level.

2.3. ID-TIMS U–Pb Analysis

ID-TIMS U–Pb isotopic analyses were performed at the Jack Satterly Geochronology Laboratory in the Department of Earth Sciences, University of Toronto (Toronto, ON, Canada). Four fragments were selected for analyses. The fragments were chemically abraded prior to dissolution [26]. This process involved thermal annealing in a muffle furnace at 900 °C for 48 h followed by a chemical etch for 9 h in ~0.10 mL concentrated hydrofluoric acid and ~10 µL 8N nitric acid in Teflon dissolution vessels at 200 °C. The fragments were rinsed with distilled water, and washed in 8N HNO3. A mixed 205Pb–235U spike was added to the Teflon dissolution capsules during sample loading. The zircon-spike mixture was dissolved using ~0.10 mL concentrated hydrofluoric acid and ~0.02 mL 8N nitric acid at 200 °C [27] for 5 days, dried to a precipitate, and re-dissolved in ~0.15 mL 3N hydrochloric acid. The U and Pb were isolated from the zircon solutions using anion exchange chromatography, dried in dilute phosphoric acid, and deposited onto outgassed rhenium filaments with silica gel [28]. The U and Pb were analyzed using a VG M354 mass spectrometer with multiple Faraday collectors in static mode for Pb and a single Daly pulse-counting system in dynamic mode for U measurements. The dead time of the Daly measuring system for U was 14.5 ns. The mass discrimination correction for the Daly detector was constant at 0.03%/atomic mass unit. The amplifier gains and Daly characteristics were monitored using the SRM 982 Pb standard. A thermal mass fractionation correction of 0.1(±0.05)% per atomic mass unit for Pb and U was applied. The total common Pb in each zircon analysis was assumed to have the isotopic composition of laboratory blank (206Pb/204Pb = 18.49 ± 0.4%; 207Pb/204Pb = 15.59 ± 0.4%; 208Pb/204Pb = 39.36 ± 0.4%). The total amount of common Pb in the present analyses ranged from 0.5 to 4.7 picograms. The Pb/U and Pb/Pb isotopic ratios were corrected for IMF, common Pb in the spike, and blank. The Th/U ratios were calculated from the radiogenic 208Pb/206Pb ratio and 207Pb/206Pb age assuming concordance. Corrections for 230Th disequilibrium in 206Pb/238U and 207Pb/206Pb were made assuming Th/U of 4.2 in the magma. We used the decay constants of Jaffey et al. (1971) [29] (238U and 235U are 1.55125 × 10−10 and 9.8485 × 10−10 per year, respectively). The 238U/235U ratio of 137.88 was used for the 207Pb/206Pb model age calculations. All the age errors quoted in the text and table, and error ellipses in the concordia diagram are given at 2σ. Plotting and age calculations were obtained using the Isoplot/Ex 3.00 software [30].

2.4. Oxygen Isotope Analysis

Zircon oxygen isotopes were measured using a laser fluorination system at the Korea Polar Research Institute (KOPRI), and the Cameca IMS 1280 ion probe at the SIMS laboratory of the Institute of Geology and Geophysics, Chinese Academy of Sciences (CAS) in Beijing, China.
The laser fluorination system at the KOPRI for oxygen isotopic analysis is well described elsewhere [31]. About 3 mg of the LKZ-1 zircon was loaded in the nickel sample holder, and then the sample holder was placed in the reaction chamber. The chamber that was assembled with a purification line was evacuated to 10−3 mbar or better, and heated for over 10 h by an external heater to eliminate the absorbed moisture inside the chamber. Before the sample was analysed, the chamber was pre-fluorinated by a small amount of BrF5 for 1 h at room temperature to completely remove the moisture absorbed on the sample surfaces and inside the chamber. Any remaining gases in the reaction chamber were thoroughly evacuated by a diffusion pump (<10−4 mbar), and then sufficient BrF5 was introduced into the chamber for laser fluorination of the sample. The sample was gradually heated using a defocused CO2 infrared laser beam by automatically increasing the lasing power up to 60%. All the gaseous species derived from the samples were introduced into the purification line consisting of two cryogenic traps (liquid nitrogen, −196 °C) and a heated KBr getter. A molecular sieve (MS13X) pellet on the final cryogenic trap collected the pure O2 for 10 min at liquid nitrogen temperature. The oxygen yield of the sample was calculated by the pressure value of the recovered O2 gas from MS13X. The oxygen isotopic composition of the sample gas was analyzed using a dual-inlet isotope ratio mass spectrometer (MAT 253 Plus, Thermo Fisher Scientific, Waltham, MA, USA) connected on-line to the laser fluorination system. The measured 18O/16O ratios were normalized to the Vienna standard mean oceanic water (V-SMOW) (18O/16O = 0.0020052, [32]) and presented as δ18O notation. The long-term reproducibility of the laser fluorination system based on the repeated analyses (n = 28) of in-house obsidian standard is ±0.08‰ (1σ) for δ18O [31].
For the SIMS analyses at the CAS, the Gaussian focused Cs+ primary ion beam was accelerated at 10 kV, with an intensity of ~1.6 nA. The spot size was approximately 20 μm in diameter (10 μm beam + 10 μm raster). A normal incidence electron flood gun was used to compensate for sample charging. The magnetic field was stabilized using a nuclear magnetic resonance controller. Negative secondary ions were extracted with a potential of −10 kV. The field aperture was 6000 × 6000 μm2. A ~120 μm entrance slit, 40 eV energy slit, ~133 transfer magnification, and 500 μm exit slit provided a mass resolution of ~2500 at 1% peak height. Under these conditions, the count rate of 16O was typically ~1 × 109 cps/nA. The 16O and 18O ions were detected simultaneously using two Faraday cups with 1010 and 1011 Ω resistors, respectively. The in-run precision was typically better than 0.2 ‰ (2 standard errors). The IMF was corrected based on the 91500 zircon value suggested by Valley (2003) [7] (δ18OV-SMOW = 10.07 ± 0.03‰).

2.5. LA-MC-ICPMS U–Pb and Lu–Yb–Hf Isotope Analysis

Zircon U–Pb and Lu–Yb–Hf isotopes were measured using a Plasma II MC-ICPMS (Nu Instruments) equipped with an NWR193-nm ArF Excimer laser ablation system at the KBSI Ochang Center. The instrumental parameters for the U–Pb and Lu–Yb–Hf isotopic analyses are summarized in Table 1. The raw data were processed using Iolite 2.5 within the Igor Pro software [33], and corrected for the background. The instrumental mass discrimination and laser-induced elemental fractionation during the U–Pb analysis were corrected by calibration against the 91500 zircon. No common Pb correction was performed. The ages were calculated using the Isoplot 3.75 software [25]. All the ratios were calculated with 2σ errors.
The 176Lu and 176Yb interferences on the 176Hf signal were corrected using the isotopic values suggested by Chu et al. (2002) [34] and Vervoort et al. (2004) [35], respectively, on the basis of previous MC-ICPMS results for mixed standard solutions [36]. The mass bias of the measured Hf isotopic ratios was corrected to 179Hf/177Hf = 0.7325 using an exponential correction law. The 176Lu/177Hf and 176Yb/177Hf ratios were calculated following the method of Iizuka and Hirata (2005) [37]. The εHf values were calculated using a 176Lu decay constant of 1.865 × 10−11 per year [38] and the chondritic values suggested by Blichert-Toft and Albarède (1997) [39].

2.6. LA-Quadrupole ICPMS Analysis

The minor and trace elements were analyzed using a 343 nm femtosecond laser ablation microprobe (J200 LA model, Applied Spectra Inc., Fremont, CA, USA) coupled to an iCapQ model (Thermo Fisher Scientific, Bremen, Germany) quadrupole ICPMS at the Core Research Facilities, Pusan National University, Korea. The zircon surfaces were ablated at a pulse repetition rate of 10 Hz and a pulse energy of 250 μJ, producing a ~30-μm-diameter crater pit. Helium (700 mL/min) was flushed into the sample cell to increase the sample transport efficiency and reduce aerosol deposition around the ablation pit [40]. The instrumental parameters of ICPMS were optimized to provide the highest sensitivity, whilst maintaining the ratio of ThO+/Th+ below 0.005. The zircon data were externally calibrated using NIST 610 standard glass, and internally normalized using 29Si and 91Zr. The reference values for the NIST 610 were taken from Jochum et al. (2011) [41], and the stoichiometric values of zircon (Si = 15.3%, Zr = 47.6%) were used for normalization.

3. Results and Discussion

3.1. U–Pb Age

As shown in Figure 1, the LKZ-1 fragments were relatively dark under CL. The CL and BSE images showed no clear zonation patterns. The HR-SIMS (SHRIMP) U–Th–Pb isotope data are presented in Table 2. The common Pb proportion in 206Pb, calculated using the 204Pb counts and an assumed Pb isotopic composition after the model of Stacey and Kramers (1975) [42], was mostly less than 0.1%. The SHRIMP analyses produced consistently concordant data (Figure 2). The 207Pb-corrected data generated a weighted mean 206Pb/238U age of 572.6 ± 2.0 Ma (n = 22, MSWD = 0.90), which was consistent with the 204Pb-corrected 207Pb/206Pb age (weighted mean = 573 ± 12 Ma, n = 21, MSWD = 1.4). The relatively uniform concentrations of U (619 ± 21 ppm, 1 standard deviation, same hereafter unless otherwise stated) and Th (90.2 ± 4.2 ppm) yielded highly consistent Th/U ratios of 0.146 ± 0.002. The Plešovice zircon (ID-TIMS 206Pb/238U age = 337.13 ± 0.37 Ma; [19]), analyzed together with LKZ-1, yielded a weighted mean 206Pb/238U age of 338.7 ± 1.4 Ma (n = 15, MSWD = 0.81) (Table S1).
The LA-MC-ICPMS U–Pb results for the LKZ-1 zircon are listed in Table 3, and shown graphically in Figure 3. The LA-MC-ICPMS analyses produced concordant age data, with a weighted mean 206Pb/238U age of 574.8 ± 1.3 Ma (n = 28, MSWD = 1.13).
Four U-Pb ID-TIMS zircon analyses produced two overlapping, concordant results and two that were slightly discordant (1.2%), but within error of the concordant results (Table 4, Figure 4). Four U-Pb data together yielded a weighted mean 207Pb/206Pb age of 575.22 ± 0.98 Ma (MSWD = 0.16, probability = 0.92). The weighted mean 206Pb/238U age of the four data was 570.0 ± 2.5 Ma (MSWD = 5.4, probability = 0.001), but if only the two concordant results are considered, a more precise 206Pb-238U age of 571.7 ± 1.1 Ma is obtained. The Th/U ratios (0.148 ± 0.001) were consistent with those from the SHRIMP analyses (0.146 ± 0.002). The ID-TIMS results may indicate that discordant parts remained in the analyzed fragments in spite of thermal annealing and chemical etching. The discordance of U–Pb age is not attributable to metamictization because the U contents and 206Pb/238U dates of the SHRIMP spots did not show any particular trend (Figure S1). If the discordance of our ID-TIMS ages reflects the thermal disturbance experienced by LKZ-1, then the concordance of SHRIMP U–Pb dates may have been caused by the selective analysis of inner, unaffected parts of the crystal. The SEM observation was not helpful to identify the discordant parts because the fragments appeared homogeneous in CL and BSE (Figure 1).
In fact, zircon megacrysts commonly show U–Pb age discordance [6]. The discordancy is typically small. For example, the ID-TIMS results for the 91500 zircon reported by Wiedenbeck et al. (1995) [15] were ~0.3% discordant (207Pb/206Pb age = 1065.4 ± 0.3 Ma, 206Pb/238U age = 1062.4 ± 0.4 Ma). The ID-TIMS results for SL13, listed by Claoué-Long et al. (1995) [43], were also discordant. The weighted mean 207Pb/206Pb and 206Pb/238U ages were 576.3 ± 0.8 Ma and 572.1 ± 0.4 Ma, respectively. The discordance of SL13 data was attributed to the extraneous addition of 231Pa into the crystal or uncertainties of the U decay constants [44,45]. The identical U–Pb ages of the SL13 and LKZ-1 zircons may represent an important geologic event in Sri Lanka.
We conclude that the best 206Pb/238U ratio of LKZ-1 is equivalent to the SHRIMP age (572.6 ± 2.0 Ma), considering that discordant parts in the zircon fragments may have been included in the ID-TIMS analyses. As stated earlier, this age is consistent with the ID-TIMS 206Pb/238U age constrained by concordant results (571.7 ± 1.1 Ma).

3.2. O and Lu–Y–Hf Isotopic Compositions

The O and Lu–Yb–Hf isotopic compositions of LKZ-1 are presented in Table 5 and Table 6, respectively. The δ18OV-SMOW value of LKZ-1 measured by the laser fluorination system was 10.72 ± 0.02 ‰. The oxygen yield of LKZ-1 was 97.8%, meaning that almost all the oxygen was released from the sample. Thus, any kinetic isotopic fractionation effect caused by incomplete fluorination of sample can be ignored.
During the analytical session at the CAS, the 91500 and Penglai [46] zircons yielded an average measured δ18OV-SMOW value of 15.16 ± 0.17 ‰ and 10.40 ± 0.21‰, respectively. Detailed data, including 16O intensities, 18O/16O ratios, and spot locations on the mount, are given in Table S2. The interlaboratory calibration work of Wiedenbeck et al. (2004) for the 91500 zircon [47] reported laser fluorination δ18OV-SMOW values between 10.07‰ and 9.74‰. Although the simple mean was 9.86 ± 0.11‰ (n = 13), the high-end value (10.07‰) was preferred in this study to correct the IMF because the simple mean yielded a slightly underestimated δ18OV-SMOW average (5.08‰) for the Penglai zircon (laser fluorination δ18OV-SMOW = 5.31 ± 0.12‰; [46]). An IMF value of –5.09‰, with reference to the 91500 zircon value of 10.07‰, generated an average δ18OV-SMOW value of 10.65 ± 0.14‰ for the LKZ-1 zircon (Figure 5). This value was indistinguishable from that obtained by the laser fluorination method (10.72 ± 0.02‰). The Penglai zircon measured during several analytical sessions yielded an IMF-corrected δ18OV-SMOW of 5.29 ± 0.34 ‰ (n = 23) (Table S2).
The LA-MC-ICPMS analyses produced an average 176Hf/177Hf of 0.282294 ± 0.000021 (n = 41) for the 91500 zircon (Table S3), which was consistent with the MC-ICPMS result obtained by solution chemistry (0.282308 ± 0.000006; [48]). The 176Lu/177Hf results (0.00028 ± 0.00010) for the 91500 zircon (Table S3) were also consistent with the solution chemistry-based data (0.00031 ± 0.00007; [48]). The LKZ-1 zircon showed little intra- and inter-grain variation in 176Hf/177Hf (0.281794 ± 0.000016; Figure 6), 176Lu/177Hf (0.000104 ± 0.000001), and 176Yb/177Hf (0.00358 ± 0.00035) (n = 45). The 178Hf/177Hf ratios were indistinguishable between 91500 (1.467289 ± 0.000059) and LKZ-1 (1.467286 ± 0.000057), with their 176Lu/177Hf and 176Yb/177Hf ratios showing a good positive correlation (R2 = 0.97). The initial εHf values calculated from the 176Hf/177Hf and 176Lu/177Hf ratios and SHRIMP 206Pb/238U age (572.6 Ma) varied narrowly and gave an average value of –22.0 ± 0.6. The 176Hf/177Hf and 176Lu/177Hf ratios did not show a clear trend (Figure S2).

3.3. Chemical Composition

The LA-quadrupole ICPMS results for the 91500 and LKZ-1 zircons are summarized in Table 7 with literature data [15,47,49,50,51]. The individual spot data analysed in this study are listed in Table S4.
For the 91500 zircon, the internal normalization by 91Zr generated concentration results close to the literature data, except for U and Th. We employed 29Si-normalization for the calculation of U and Th concentrations because the 91Zr-normalization for these elements yielded results consistently ~15% lower than the recommended values. The 29Si-normalized results for U (83 ± 14 ppm) and Th (30 ± 6 ppm), and the 91Zr-normalized result for Hf (5780 ± 340 ppm) agreed well with the ID-TIMS data ([U] = 81.2 ppm, [Th] = 28.61 ppm, [Hf] = 5895 ppm; [15]). The 91Zr-normalized results for P (14 ± 7 ppm) and Y (148 ± 36 ppm) were marginally or closely similar to the literature data [[P] = 35 ± 17 ppm, [Y] = 153 ± 14 ppm; [47]). As shown in Figure 7a, the chondrite-normalized pattern of our 91Zr-normalized rare earth element (REE) data generally matched the recommended values. The slightly negative Eu anomalies in our data (Eu/Eu* = 0.72 ± 0.17) are consistent with the data previously obtained by inter-laboratory SIMS analyses [47].
For most elements >1 ppm, the relative standard deviation values for the concentration data for the LKZ-1 zircon were <10%. The chondrite-normalized REE pattern of LKZ-1 (Figure 7b) was highly consistent, with prominently positive Ce (Ce/Ce* = 44 ± 32) and negative Eu (Eu/Eu* = 0.43 ± 0.17) anomalies. The ratios between the heavy and middle REEs were also consistent ((Lu/Gd)N = 31 ± 3). The U (654 ± 31 ppm) and Th (94 ± 6 ppm) concentrations, and their ratios (Th/U = 0.144 ± 0.004), were comparable to the SHRIMP results. The positive correlations observed between U and Th concentrations and Yb and Y concentrations (Figure 7c–f) indicate that our data reflect inter- and intra-grain chemical variation, rather than random analytical errors.

4. Conclusions

The results of our ID-TIMS, HR-SIMS, and LA-MC-ICPMS analyses demonstrate that the LKZ-1 zircon is nearly concordant in U–Pb age, with negligible common Pb content and a consistent Th/U ratio. LKZ-1 is fairly homogeneous in O–Hf isotopic and chemical composition. These consistencies suggest that LKZ-1 can be used as a suitable working standard for geochronological and isotopic/geochemical analyses. Fragments of the LKZ-1 zircon are available upon request from the lead author of this paper.

Supplementary Materials

The following are available online at, Figure S1: Plot of 206Pb/238U dates and U concentrations for the SHRIMP spots of the LKZ-1 zircon. Figure S2: 176Hf/177Hf vs. 176Lu/177Hf plot for the LKZ-1 zircon. Table S1: SHRIMP U–Th–Pb results for the Plešovice zircon. Table S2: HR-SIMS (Cameca 1280) oxygen isotope data for the analyzed zircons. Table S3: LA-MC-ICPMS Lu–Yb–Hf isotopic results for the 91500 zircon. Table S4: LA-ICPMS results for the 91500 and LKZ-1 zircons.

Author Contributions

Conceptualization, A.C.-s.C.; methodology, Y.-J.J., S.L., K.Y., H.J.J., H.-S.L., C.P., N.K.K., X.-H.L. and S.L.K.; compiling and writing of the manuscript, A.C.-s.C.


This research was supported by a Korea Basic Science Institute grant (C39709) and a National Research Foundation of Korea grant funded by the government of Korea’s Ministry of Science and ICT (2016R1A2B4007283), awarded to A.C.C.


We are grateful for the assistance of Sook Ju Kim, Seon Gyu Kim, and Guo-Qiang Tang in the laboratory work. Insightful reviews by the editor and three anonymous journal reviewers improved the manuscript substantially.

Conflicts of Interest

The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.


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Figure 1. A photograph of the LKZ-1 zircon (inset) and representative backscattered electron (upper) and cathodoluminescence (lower) images. The grain and spot numbers are the same as in Table 2.
Figure 1. A photograph of the LKZ-1 zircon (inset) and representative backscattered electron (upper) and cathodoluminescence (lower) images. The grain and spot numbers are the same as in Table 2.
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Figure 2. 206Pb/238U-207Pb/235U concordia diagram showing the SHRIMP results for the LKZ-1 zircon with ±1σ error ellipses. The plotted data are uncorrected for common Pb.
Figure 2. 206Pb/238U-207Pb/235U concordia diagram showing the SHRIMP results for the LKZ-1 zircon with ±1σ error ellipses. The plotted data are uncorrected for common Pb.
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Figure 3. 206Pb/238U–207Pb/235U concordia diagram showing LA-MC-ICPMS results for the LKZ-1 zircon with ±2σ error ellipses.
Figure 3. 206Pb/238U–207Pb/235U concordia diagram showing LA-MC-ICPMS results for the LKZ-1 zircon with ±2σ error ellipses.
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Figure 4. Concordia diagram showing U–Pb data obtained by ID-TIMS analysis of LKZ-1 zircon with ±2σ error ellipses. The concordia curve is depicted as a band, which incorporates the uncertainty of the U decay constants.
Figure 4. Concordia diagram showing U–Pb data obtained by ID-TIMS analysis of LKZ-1 zircon with ±2σ error ellipses. The concordia curve is depicted as a band, which incorporates the uncertainty of the U decay constants.
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Figure 5. O isotopic variation in the LKZ-1 zircon based on HR-SIMS analyses. Vertical error bars denote 2 standard errors. Solid and dashed lines represent the average (10.65‰) and standard deviation (±0.14‰), respectively.
Figure 5. O isotopic variation in the LKZ-1 zircon based on HR-SIMS analyses. Vertical error bars denote 2 standard errors. Solid and dashed lines represent the average (10.65‰) and standard deviation (±0.14‰), respectively.
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Figure 6. Hafnium isotopic variation in the LKZ-1 zircon. Vertical error bars denote 2 standard errors. Solid and dashed lines represent the average (0.281794) and standard deviation (±0.000016), respectively.
Figure 6. Hafnium isotopic variation in the LKZ-1 zircon. Vertical error bars denote 2 standard errors. Solid and dashed lines represent the average (0.281794) and standard deviation (±0.000016), respectively.
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Figure 7. Chondrite-normalized REE patterns of 91500 (a) and LKZ-1 (b) zircons. Chondrite values were taken from McDonough and Sun (1995) [52]. Vertical error bars denote 1 standard deviation of our data, or uncertainties reported in previous works. (cf) U vs. Th and Yb vs. Y variations for 91500 and LKZ-1 zircons.
Figure 7. Chondrite-normalized REE patterns of 91500 (a) and LKZ-1 (b) zircons. Chondrite values were taken from McDonough and Sun (1995) [52]. Vertical error bars denote 1 standard deviation of our data, or uncertainties reported in previous works. (cf) U vs. Th and Yb vs. Y variations for 91500 and LKZ-1 zircons.
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Table 1. LA-MC-ICPMS instrument and operational parameters for U–Pb dating and Lu–Yb–Hf isotope analysis.
Table 1. LA-MC-ICPMS instrument and operational parameters for U–Pb dating and Lu–Yb–Hf isotope analysis.
InstrumentNu Plasma II
RF power1300 W1300 W
Reflected power<1 W<1 W
Mixed gas & flow rateAr, ~0.9 L/minAr, ~0.7 L/min
Auxiliary gas & flow rateAr, 0.9 L/minAr, 0.9 L/min
Cool gas & flow rateAr, 13 L/minAr, 13 L/min
Sampler coneNi (1 mm orifice)Ni (1 mm orifice)
Skimmer coneNi (0.7 mm orifice)Ni (0.7 mm orifice)
Data acquisition modeTime resolved analysisTime resolved analysis
Integration time0.2 s0.2 s
Collectors2 Faraday cups and 5 ion counters10 Faraday cups
Measured isotopes238U, 232Th, 208Pb, 207Pb, 206Pb, 204Pb, 202Hg172Yb, 173Yb, 174(Hf + Yb), 175Lu, 176(Hf + Yb + Lu), 177Hf, 178Hf, 179Hf, 180Hf, 183W
Laser ablation system
LaserESI machines 193nm ArF excimer laser
Ablation modeSingle hole drilling
CellTwo volume 2 cell (10 × 10 cm)
Sample transport tubing0.5 m length0.5m length
Pulse repetition rate & width5Hz, <4 ns10Hz, <4 ns
Pulse energy density~3 J/cm2~ 8 J/cm2
Ablation duration30 s60 s
Carrier gas & flow rateHe, 0.65 L/minHe, 0.65 L/min; N2, 0.002 L/min
Crater size~15 µm~50 µm
Drill depth~4 µm~20 µm
Table 2. SHRIMP U–Th–Pb results for the LKZ-1 zircon.
Table 2. SHRIMP U–Th–Pb results for the LKZ-1 zircon.
Spot No.206Pbc1 (%)206Pb/238U2±%207Pb/206Pb2±%Th (ppm)U (ppm)Disc.%Date3 (Ma)
LKZ_5.1 0.22481.420.05870.8990.3621−3.8580.8±4.7
LKZ_5.2 0.21891.760.05840.8990.3627−5.9577.8±4.6
LKZ_6.1 0.22242.140.06000.8889.16198.3568.0±4.5
LKZ_6.2 0.21850.450.05910.8996.36561.1580.1±4.6
LKZ_9.2 0.22452.200.05871.5786.8607−3.6578.7±4.7
LKZ_10.1 0.22752.000.05980.8596.86496.2571.1±4.6
LKZ_11.1 0.23131.840.05930.8887.76023.8564.7±4.6
1204Pb-based common 206Pb proportion; 2 Uncorrected data; 3 207Pb-corrected 206Pb/238U date.
Table 3. LA-MC-ICPMS U–Pb results for the LKZ-1 zircon.
Table 3. LA-MC-ICPMS U–Pb results for the LKZ-1 zircon.
Spot No.206Pb/238U2SEDate (Ma)2SE207Pb/206Pb2SEDate (Ma)2SE
Table 4. U–Pb isotopic data for the LKZ-1 zircon obtained by ID-TIMS.
Table 4. U–Pb isotopic data for the LKZ-1 zircon obtained by ID-TIMS.
No.Weight (mg)U (ppm)Th/UPbc (pg)206Pb/204Pb207Pb/235U206Pb/238UError Corr.
No.207Pb/206Pb206Pb/238U Age (Ma)207Pb/235U Age (Ma)207Pb/206Pb Age (Ma)Disc. %
Pbc is total common Pb, and assumes all has laboratory blank isotopic composition; Error Corr. is correlation coefficients of X-Y errors on the concordia plot; Disc. is percent discordance for the given 207Pb/206Pb age.
Table 5. HR-SIMS O isotopic results for the LKZ-1 zircon.
Table 5. HR-SIMS O isotopic results for the LKZ-1 zircon.
Spot No.δ18OV-SMOW (‰)2SESpot No.δ18OV-SMOW (‰)2SE
[email protected]10.580.18[email protected]10.770.19
[email protected]10.790.28[email protected]10.880.22
[email protected]10.520.25[email protected]10.480.21
[email protected]10.370.34[email protected]10.680.12
[email protected]10.590.43[email protected]10.630.29
[email protected]10.600.33[email protected]10.620.28
[email protected]10.960.28[email protected]10.540.23
[email protected]10.600.45[email protected]10.810.31
[email protected]10.560.32[email protected]10.740.17
[email protected]10.690.23[email protected]10.560.31
Laser fluorination value = 10.72 ± 0.02‰ (1SD).
Table 6. LA-MC-ICPMS Lu–Yb–Hf results for the LKZ-1 zircon.
Table 6. LA-MC-ICPMS Lu–Yb–Hf results for the LKZ-1 zircon.
Spot No.176Hf/177Hf2SE (ppm)178Hf/177Hf2SE (ppm)176Lu/177Hf2SE (%)176Yb/177Hf2SE (%)εHf(0)εHf(t)
Average0.281794 1.467286 0.000104 0.00358 −34.6−22.0
SD0.000016 0.000057 0.000001 0.00035 0.60.6
Table 7. Summary of chemical data for the 91500 and LKZ-1 zircons (unit: ppm).
Table 7. Summary of chemical data for the 91500 and LKZ-1 zircons (unit: ppm).
91500 LKZ-1
[15,47] [49] [50] [51] This StudySD (n = 37)This StudySD (n = 28)
P35±17 147178
Ca 102666850
Y153±14147±22 14836866
Tb0.78±0.12 0.75±0.201.11±0.250.940.310.610.06
Tm5.95±0.71 7.5±1.88.44±1.276.811.633.440.32
Hf5895 6400±900 57803407740310
Th28.61±0.0731±4.9 306946
U81.2 88±15 831465431
For LKZ-1, U and Th concentrations were normalized by 29Si. All the other elements were normalized by 91Zr. [15]; ID-TIMS results (Hf, Th, U), [47]; P, EPMA result. Y and REE concentrations are working values from inter-laboratory SIMS analyses. [49,51]; LA-ICPMS results, [50]; HR-SIMS results.

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Cheong, A.C.-s.; Jeong, Y.-J.; Lee, S.; Yi, K.; Jo, H.J.; Lee, H.-S.; Park, C.; Kim, N.K.; Li, X.-H.; Kamo, S.L. LKZ-1: A New Zircon Working Standard for the In Situ Determination of U–Pb Age, O–Hf Isotopes, and Trace Element Composition. Minerals 2019, 9, 325.

AMA Style

Cheong AC-s, Jeong Y-J, Lee S, Yi K, Jo HJ, Lee H-S, Park C, Kim NK, Li X-H, Kamo SL. LKZ-1: A New Zircon Working Standard for the In Situ Determination of U–Pb Age, O–Hf Isotopes, and Trace Element Composition. Minerals. 2019; 9(5):325.

Chicago/Turabian Style

Cheong, Albert Chang-sik, Youn-Joong Jeong, Shinae Lee, Keewook Yi, Hui Je Jo, Ho-Sun Lee, Changkun Park, Nak Kyu Kim, Xian-Hua Li, and Sandra L. Kamo. 2019. "LKZ-1: A New Zircon Working Standard for the In Situ Determination of U–Pb Age, O–Hf Isotopes, and Trace Element Composition" Minerals 9, no. 5: 325.

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