A new ideal zircon microanalytical reference material (Tanz) is presented for in situ U–Pb, O and Zr isotope measurements.

The oxygen (O) and neodymium (Nd) isotopic composition of monazite provides an ideal tracer of metamorphism and hydrothermal activity. Calibration of the matrix effect and monitoring of the external precision of monazite O–Nd isotopes with microbeam techniques, such as secondary ion mass spectrometry (SIMS) and laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICPMS), require well-characterized natural monazite standards for precise microbeam measurements. However, the limited number of standards available is impeding the application of monazite O–Nd isotopes. Here, we report on the RW-1 monazite as a potential new working reference material for microbeam analysis of O–Nd isotopes. Microbeam measurements by electron probe microanalysis (EPMA), SIMS, and LA-MC-ICPMS at 10–24 µm scales have confirmed that it is homogeneous in both elemental and O–Nd isotopic compositions. SIMS measurements yield δ¹⁸O values consistent, within errors, with those obtained by laser fluorination techniques. Precise analyses of Nd isotope by thermal ionization mass spectrometry (TIMS) are consistent with mean results of LA-MC-ICPMS analyses. We recommend δ¹⁸O = 6.30‰ ± 0.16‰ (2SD) and ¹⁴³Nd/¹⁴⁴Nd = 0.512282 ± 0.000011 (2SD) as being the reference values for the RW-1 monazite.

Zircon U–Pb geochronology and Hf–O isotope composition provide important information on geological events. This matrix-matched reference material is routinely used to yield accurate and precise zircon U–Pb ages and Hf–O isotope ratios with in situ techniques. In this study, a new potential zircon reference material (Jilin) separated from gabbro diorite was introduced for microbeam U–Pb age and Hf–O isotope analysis. The obtained average U, Th, Pb, Lu and Hf concentrations were 439 ± 26 ppm (1 s), 378 ± 39 ppm (1 s), 67.6 ± 1.6 ppm (1 s), 54.6 ± 6.5 ppm (1 s), and 9135 ± 510 ppm (1 s) respectively. The chemical abrasion isotope dilution thermal ionization mass-spectrometry (CA-ID-TIMS) method yielded a Th-corrected weighted mean ²⁰⁶Pb/²³⁸U age of 117.63 ± 0.04 Ma (2 s, MSWD = 1.9). The homogeneity of U–Pb ages in Jilin zircon was also investigated in two independent secondary ion mass spectrometry (SIMS) laboratories and four different laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) laboratories. The obtained mean ²⁰⁶Pb/²³⁸U ages with SIMS and LA-ICP-MS were 116.8 ± 2.9 Ma and 117.8 ± 2.7 Ma, respectively, which are consistent with the CA-ID-TIMS value within the analytical uncertainties. The distribution of Hf isotopic composition was evaluated with LA-multicollector-ICP-MS (LA-MC-ICP-MS) and solution MC-ICP-MS. The results acquired in two LA-MC-ICP-MS laboratories were identical to the solution value with a mean ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282926 ± 0.000014 (2SD, n = 17). The O isotope obtained with the laser fluorination method is also in agreement with the SIMS analysis with the recommended mean δ¹⁸O value of 6.05 ± 0.25‰ (2SD, n = 8). The results obtained with multianalytical techniques clearly indicate that the U–Pb age and Hf–O isotopic composition are homogenous in Jilin zircon grains. We propose the Jilin zircon as a potential reference material for the primary external calibration or monitoring of analytical validation for Mesozoic U–Pb geochronology and Hf–O isotopic measurements.

This study reports the Neotethyan Meliata Basin ophiolite fragments in the Late Jurassic–Early Cretaceous accretionary wedge mélange in the southern part of the Inner Western Carpathians (IWC). Here we present new lithostratigraphical, petrographical, geochemical, and geochronological data obtained from the mélange blocks used to reconstruct the Meliaticum paleotectonic zones in a tentative evolutionary model of this accretionary wedge. The Dobšiná mélange block continental margin carbonatic and siliciclastic sediments have calc-alkaline basalt intercalations. The basalt Concordia age dated to 245.5 ± 3.3 Ma by U–Pb SIMS on zircon most likely indicates the pre-oceanic advanced early Middle Triassic continental rifting stage. The evolving marginal oceanic crust is composed of Middle to Upper Triassic cherty shales to radiolarites. The detrital zircon U–Pb SIMS Concordia ages of 247 ± 4 Ma and 243 ± 4 Ma from a cherty shale, and the xenocryst zircon population Concordia age of 266 ± 3 Ma from a 0.5 m thick “normal” mid-ocean ridge (N-MOR) basalt layer in this cherty shale reveal the connection of the oceanic basin to the adjacent rifting continental margin. The chertified reddish limestone transition to radiolarite indicates syn-rift basin deepening. Upwards, regular alternating N-MOR basalts and radiolarites are often disturbed by peperite breccia horizons. The Nd isotope values of these basalts (εNd₂₄₀ = 7–8) are consistent with their chondrite normalized rare earth element (REE) patterns and indicate a depleted mantle source. The Triassic ophiolitic suite also comprises rare ocean island (OI) basalts (εNd₂₄₀ = 5) and serpentinized subduction unrelated peridotites. The Middle to Late Jurassic shortening and southward intra-oceanic and continental margin subduction at approximately 170–150 Ma enhanced the formation of the trench-like Jurassic flysch succession which preceded the closure of the Meliata Basin. The flysch sediments form a mélange matrix of olistolithic unsubducted, obducted, and MP–HP/LT metamorphosed exhumed blocks of the Triassic to Lower Jurassic successions. Blocks of peridotites, rodingites, blueschists, greenschists, rare amphibolites, deep-water shaly sediments and shallow- to deep-water carbonates are typical members of the mélange. The Meliatic accretionary wedge mélange nappe outliers were incorporated in the IWC orogenic wedge in the late Early Cretaceous according to metamorphic rutile U–Pb SIMS ages of 100 ± 10 Ma determined from a Jaklovce metabasalt.

Monazite ((Ce, La, Nd, Th)PO₄) is one of the widely used minerals for U–Th–Pb dating in geochronology. To better understand the possible effects of radiogenic Pb on the in situ dating method, a natural monazite U–Th–Pb standard sample (RW-1) was chemically and structurally characterized down to atomic scales by using the combination of Raman spectrum (RM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The experimental results revealed that radiogenic Pb exists as Pb²⁺ and substitutes for the Ce site in the monazite crystal lattice. Moreover, TEM imaging demonstrated that monazite is well crystalline revealed by an atomic structure in most areas except for a few tiny defects, which are likely attributed to alpha self-healing from an electronic energy loss of α particles. The characterization of the chemical state and occupancy of radiogenic Pb, and the distribution of Pb and Th in monazite at the nanoscale and atomic scale could provide insight for us to understand the mechanisms of the nanogeochronology.