The Apuseni‐Banat‐Timok‐Srednogorie Late Cretaceous magmatic arc in the Carpathian‐Balkan orogen formed on the European margin during closure of the Neotethys Ocean. It was subsequently deformed into a complex orocline by continental collisions. The Cu‐Au mineralized arc consists of geologically distinct segments: the Apuseni, Banat, Timok, Panagyurishte, and Eastern Srednogorie segments. New U‐Pb zircon ages and geochemical whole rock data for the Banat and Apuseni segments are combined with previously published data to reconstruct the original arc geometry and better constrain its tectonic evolution. Trace element and isotopic signatures of the arc magmas indicate a subduction‐enriched source in all segments and variable contamination by continental crust. The magmatic arc was active for 25 Myr (~92–67 Ma). Across‐arc age trends of progressively younger ages toward the inferred paleo‐trench indicate gradual steepening of the subducting slab away from the upper plate European margin. This leads to asthenospheric corner flow in the overriding plate, which is recorded by decreasing ⁸⁷Sr/⁸⁶Sr (0.70577 to 0.70373) and increasing ¹⁴³Nd/¹⁴⁴Nd (0.51234 to 0.51264) ratios over time in some segments. The close spatial relationship between arc magmatism, large‐scale shear zones, and related strike‐slip sedimentary basins in the Timok and Pangyurishte segments indicates mild transtension in these central segments of the restored arc. In contrast, the Eastern Srednogorie segment underwent strong orthogonal intraarc extension. Segmental distribution of tectonic stress may account for the concentration of rich porphyry Cu deposits in the transtensional segments, where lower crustal magma storage and fractionation favored the evolution of volatile‐rich magmas.

Field portable X-ray fluorescence (pXRF) spectrometers are routinely used in mineral resources studies. To date, mineral resources studies have largely focussed on the application of pXRF to the exploration for deposits of base and precious metals. By contrast, studies using pXRF for the quantification of critical elements in geological materials are scarce since these elements are difficult to determine with energy-dispersive pXRF technology. This study explores the capability of pXRF spectrometers to detect and quantify critical elements (Ba, P, Nb, V, Co, REE, W, Bi, Hf, and Ta) in certified reference materials (CRMs). While precision of many critical elements is acceptable (50% difference) when using pre-installed factory calibration software. Spectra collected during the pXRF measurements show that poor accuracy and false positives tend to be associated with spectral interferences. Distinct combinations of spectral interferences (line overlaps, Compton scattered peaks, and Si escape peaks) were observed in the different matrix types. Our results show that critical elements may be determined in common geological materials when pronounced peaks occur in the spectra and that matrix-match of standards and samples is essential. Hence, XRF spectra should be routinely reviewed to identify erroneous quantification due to spectral interferences.

The Jurassic ophiolites in the South Apuseni Mountains represent remnants of the Neotethys Ocean and belong to the East Vardar ophiolites that contain ophiolite fragments as well as granitoids and volcanics with island-arc affinity. New U–Pb zircon ages, and Sr and Nd isotope ratios give insights into their tectono-magmatic history. The ophiolite lithologies show tholeiitic MOR-type affinities, but are occasionally slightly enriched in Th and U, and depleted in Nb, which indicates that they probably formed in a marginal or back-arc basin. These ophiolites are associated with calc-alkaline granitoids and volcanics, which show trace element signatures characteristic for subduction-enrichment (high LILE, low HFSE). Low ⁸⁷Sr/⁸⁶Sr ratios (0.703836–0.704550) and high ¹⁴³Nd/¹⁴⁴Nd ratios (0.512599–0.512616) of the calc-alkaline series overlap with the ratios measured in the ophiolitic rocks (0.703863–0.704303 and 0.512496–0.512673), and hence show no contamination with continental crust. This excludes a collisional to post-collisional origin of the granitoids and is consistent with the previously proposed intra-oceanic island arc setting. The new U–Pb ages of the ophiolite lithologies (158.9–155.9 Ma, Oxfordian to Early Kimmeridgian) and granitoids (158.6–152.9 Ma, latest Oxfordian to Late Kimmeridgian) indicate that the two distinct magmatic series evolved within a narrow time range. It is proposed that the ophiolites and island arc granitoids formed above a long-lived NE-dipping subduction zone. A sudden flip in subduction polarity led to collision between island arc and continental margin, immediately followed by obduction of the ophiolites and granitoids on top of the continental margin of the Dacia Mega-Unit. Since the granitoids lack crustal input, they must have intruded the Apuseni ophiolites before both magmatic sequences were obducted onto the continental margin. The age of the youngest granitoid (~153 Ma, Late Kimmeridgian) yields an estimate for the maximum age of emplacement of the South Apuseni ophiolites and associated granitoids onto the Dacia Mega-Unit.

The scarcity of well-preserved and directly dateable sedimentary sequences is a major impediment to inferring the Earth’s paleo-environmental evolution. The authigenic mineral glauconite can potentially provide absolute stratigraphic ages for sedimentary sequences and constraints on paleo-depositional conditions. This requires improved approaches for measuring and interpreting glauconite formation ages. Here, glauconite from a Cretaceous shelfal sequence (Langenstein, northern Germany) was characterized using petrographical, geochemical (EMP), andmineralogical (XRD) screening methods before in situ Rb-Sr dating via LA-ICP-MS/MS. The obtained glauconite ages (~101 to 97 Ma) partly overlap with the depositional age of the Langenstein sequence (±3 Ma), but without the expected stratigraphic age progression, which we attribute to detrital and diagenetic illitic phase impurities inside the glauconites. Using a novel age deconvolution approach, which combines the new Rb-Sr dataset with published K-Ar ages, we recalculate the glauconite bulk ages to obtain stratigraphically significant ‘pure’ glauconite ages (~100 to 96 Ma). Thus, our results show that pristine ages can be preserved in mineralogically complex glauconite grains even under burial diagenetic conditions (T < 65 °C; <1500 m depth), confirming that glauconite could be a suitable archive for paleo-environmental reconstructions and direct sediment dating.

We characterise zircon megacrysts from the Kawisigamuwa carbonatite as a new potential reference material for laser ablation‐inductively coupled plasma‐mass spectrometry U‐Pb and Hf isotope measurement. We studied ten 0.5–4 cm long, brown megacrysts that consist of oscillatory zoned (OZ) and nearly featureless cathodoluminescence‐bright recrystallised (RX) zircon domains. The zircons have low to moderate radiation damage (total α‐dose < 0.5 x 10¹⁸ events g^‐1), tested by the measured FWHM of the ν₃ (SiO₄) Raman band < 5 cm^‐1. An ID‐TIMS weighted mean ²⁰⁶Pb/²³⁸U age of 532.39 ± 0.66 Ma (2s uncertainty) was determined for OZ zircon domains of three grains. While hafnium content varies within and between crystals (6630–9960 μg g^‐1) the in situ mean ¹⁷⁶Hf/¹⁷⁷Hf ratios of ten crystals overlap within uncertainty. We recommend a mean ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282003 ± 0.000020 (2s) as preliminary working value for OZ domains. Two OZ megacrysts yield indistinguishable δ¹⁸O_VSMOW of 12.1 ± 0.4‰ and 12.2 ± 0.4‰ (2s). Elevated Th/U (> 1.5), Zr/Hf (59–75) and low hafnium contents in OZ domains are similar to those of zircons from carbonatites of mantle origin, while high δ¹⁸O and low εHf_i (‐15.8 to ‐17.1) indicate a crustal contribution. The zircons probably grew from crustal‐derived carbonate melts under high grade metamorphic conditions.

Heavy mineral sands (HMS) are a resource of Ti minerals, zircon, monazite and critical elements such as Hf and the rare earth elements (REE). Portable field techniques capable of measuring the geochemical composition, such as portable XRF (pXRF), may assist in identifying and quantifying the multiple minerals present in HMS. In this study, we assess the application of pXRF to the characterization of garnet–magnetite mineral sands from the Namibian coastline. Forty-six HMS samples from the northern Namibian coast were analysed by pXRF for SiO ₂ , Ti, Mn, Fe, Zr, Th, Y, V and Hf. The HMS were analysed as powdered and unground samples to test whether minimal sample preparation yields reliable results. Our tests show that the pXRF results of unground sands scatter widely due to sample heterogeneity. Powdered samples, however, can be measured precisely and can be corrected with conventional laboratory analyses. Some spectral interference specific to this material occurs, e.g. Th on Pb and Bi and Hf on Cu. Selectively corrected pXRF data for powdered HMS were compared to XRD Rietveld data to determine proportions of heavy minerals (Ti minerals, Fe oxides, zircon, garnet). Geochemical and mineralogical data correlated well for garnet and moderately for Fe oxides and Ti minerals. The presence of zircon and monazite is also indicated by Zr, Hf and Th concentrations, which demonstrates that pXRF is a useful tool for HMS characterization. Supplementary material: Tables of raw data (Supplementary Table S1), statistical parameters (Supplementary Table S2) and corrected pXRF values (Supplementary Table S3) are available at https://doi.org/10.6084/m9.figshare.c.4536992