Orals: Thu, 7 May, 08:30–12:30 | Room K1
Constraining the depths, temperatures and rates of Archean metamorphism may provide a window into possible tectonic styles at this time. However, several Archean metamorphic terranes record polymetamorphism, and unravelling the pressure-temperature-time (P-T-t) histories of such terranes has proven difficult, with complexity inherent in both chronologic and petrologic data.
Here we synthesize results of a multi-analytical study in which (Sm-Nd) garnet and (U-Pb) monazite petrochronology, thermodynamic, diffusion, and thermal modeling were applied to Archean granulites from the Beartooth Mountains in the northern Wyoming Province. The data reveal two phases of garnet growth and high-temperature metamorphism likely driven by magmatic heat advection. Garnet cores grew coeval with emplacement of a granitoid batholith at ~2.78-2.76 Ga. This was followed by a distinct, second phase of peritectic garnet rim growth at ~2.71 Ga, during biotite breakdown melting at peak temperatures of ~750˚C. Diffusion modeling of chemical zoning in garnet rims shows that this second event was brief: near-peak temperatures were maintained for < 1 Myrs. In contrast, core and rim dates of garnet from a meta-granitoid from the same outcrop record only the initial phase of growth, most likely because a lack of grain boundary fluids inhibited further crystallization in these rocks. Evidence for this second event is cryptic in other granitoid samples, such that this period of heating to at least 750˚C, ~50-100 Myrs after initial batholith emplacement, is poorly recorded in the broader rock record of the Beartooths.
We propose that emplacement of the Stillwater Complex was responsible for high-grade metamorphism at ~2.71 Ga. 1-D thermal models suggest that the P-T-t path determined from our pelitic samples can be reproduced by emplacement of a large mafic sheet with the geometry of the Stillwater ~10 km above the current exposure of the Beartooth mountains. Our work serves as a case study in which: 1) field and petrologic evidence for polymetamorphism is cryptic, but can be revealed through detailed petrochronology, and 2) rapid granulite-facies metamorphism of mid-crustal rocks was coeval with, and likely driven by, high magmatic flux during upper crustal emplacement of a potential large igneous province. Lastly, we highlight the potential challenges associated with the dating of high metamorphic grade, Archean lithologies, which include the effects of deleterious mineral inclusions, polymetamorphism and multi-stage melting episodes.
How to cite: Dragovic, B., Guevara, V., Caddick, M., Inglis, J., Kylander-Clark, A., and Raimondo, T.: Neoarchean polymetamorphism and crustal melting due to magmatic heat advection in the northern Wyoming Province, U.S.A: insights from petrochronology and thermal modeling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13988, https://doi.org/10.5194/egusphere-egu26-13988, 2026.
Zircon is a key accessory mineral because it can retain geochronological and geochemical information. In mafic and ultramafic rocks, zircon is scarce and restricted to localised microstructural domains, making its detection difficult and largely dependent on sampling strategy. We present a reproducible workflow for locating zircon directly within mafic and ultramafic rocks, designed to improve detection efficiency while preserving textural context. The approach is based on preparing multiple small rock slabs with carefully controlled polishing quality, allowing systematic inspection of large surface areas. This slab-scale screening strategy departs from conventional thin-section-based searches and is essential for accessing zircon in zircon-poor systems. Large-area elemental mapping is performed using SEM, EPMA, and micro-XRF, all of which can identify Zr-enriched domains. Comparative testing shows that micro-XRF provides the most favourable balance between acquisition time, analysed surface area and sensitivity to zirconium, making it suitable for first-pass screening of large sample sets. Across the different analytical methodologies used, the Zr signal can be affected by spectral interferences from other elements. For this reason, zircon detection in this study relies on the combined behaviour of multiple elements and on their statistical consistency across the mapped area. Zircon candidates are retained only when they meet several independent criteria, thereby reducing misidentification due to background noise or overlapping mineral phases. This approach enables the recovery of zircon grains down to ~50 µm and can be readily adapted for the in-situ detection of other scarce accessory minerals. More generally, it provides a practical framework for accessing mineral-scale records in systems where key phases are sparse, heterogeneous and difficult to locate using conventional approaches.
Work supported by the Spanish Ministerio de Ciencia e Innovación, Fondos Feder, PID2023-149105NA-I00. M.S.F. benefits from the FPI-PRE2023-002262.
How to cite: Salguero Fuentes, M., Barcos, L., Cambeses, A., Garcia Casco, A., Molina, J. F., Montero, P., Novo Fernández, I., Pujol Solà, N., Repczyńska, M. M., and Bea, F.: How to find rare zircon in mafic and ultramafic rocks: an integrated in-situ detection workflow, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6729, https://doi.org/10.5194/egusphere-egu26-6729, 2026.
In-situ U-Pb carbonate geochronology is a well-established technique that directly constrains the timing and rates of important geological processes including fluid flow, diagenesis, and tectonic events. However, the fundamental controls on U behaviour in carbonate minerals remain unclear, limiting geological interpretations. Knowledge gaps include the controls on U incorporation, the highly heterogeneous distribution of U at a crystal scale, and the incorporation of U with respect to other (redox-sensitive) elements. The application of synchrotron X-ray microspectroscopy (µXAS) is ideal for investigating these topics, as it can map chemical changes and measure the valance state of key elements at the micron-scale.
Here we combine µXAS, in-situ laser ablation U-Pb carbonate geochronology, and EPMA analyses to temporally track U distribution, redox state, and dolomite-ankerite composition in a porphyry-epithermal system. Multiple generations of carbonate minerals record fluid conditions and processes which control the solubility and deposition of metals, including U. Results show that temporally distinct generations of carbonate record both oxidized UO22+ and reduced U4+ species within a single sample section. Mapping of individual carbonate crystals reveals that UO22+ and U4+ also occur within individual growth bands at a sub-millimetre scale, and in rare samples, may coexist. µXAS data from the sample suite demonstrate that local fluid conditions in the case-study mineralized system changed from more oxidized to more reduced over a period of ca. 16 Ma and corresponds with an increase in U levels in crystallizing carbonate.
The preservation of two U oxidation states during discrete precipitation events requires U retentivity within older domains, indicating that the U-Pb carbonate geochronometer is robust under hydrothermal conditions (e.g., ~200–350ºC) and through rapid local redox state changes. Furthermore, crystal zones with abundant fluid/vapour inclusions linked to boiling processes coincide with higher levels of U in the carbonate and favourable U/Pb. Our results suggest redox changes and boiling conditions may be critical for both the deposition of ore minerals, as well as increased U uptake in carbonate minerals. Targeting carbonate domains with these features may therefore increase success for U-Pb geochronology. U-Pb carbonate dating combined with µXAS can track the temporal evolution of processes critical for metal deposition in long-lived and multistage hydrothermal-magmatic ore deposit settings.
How to cite: Bowie, S., Mottram, C., Rasbury, E. T., Northrup, P., Tappero, R., and Kellett, D.: With or without U: uranium distribution and redox state in carbonate tracks protracted porphyry-epithermal mineralization through time, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20163, https://doi.org/10.5194/egusphere-egu26-20163, 2026.
Highly fractionated granites are important hosts for rare metals (Li, Be, Nb, Ta, Rb, Cs, Zr, Hf, etc.). Dating the mica minerals abundant within them can more accurately constrain the timing of rare metal mineralization. To investigate the episodes and chronology of rare metal mineralization in the Koktokay region, we conducted precise Rb-Sr dating by Isotope Dilution Mass Spectrometry (ID-MS) on muscovite separates, along with apatite and whole-rock powder, from six samples collected from this highly fractionated granite. The obtained age for this highly fractionated granite is 200.86 ± 0.29 Ma(2σ, n = 21), with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.805598 ± 0.000069. This age is younger than the main Triassic magmatic phase (ca. 210 Ma) but falls within the mineralization window of the No. 3 pegmatite vein (220-175 Ma). Meanwhile, the initial Sr ratio is significantly higher than that of typical crust-derived granites (~0.720), indicating derivation from a highly evolved source.
In recent years, laser ablation (multi-collector) inductively coupled plasma tandem mass spectrometry (LA-(MC)-ICP-MS/MS) techniques for in-situ Rb-Sr analysis have developed rapidly and become indispensable tools in geological research. However, the accuracy of LA-ICP-MS/MS Rb-Sr dating relies on matrix-matched reference materials to correct for instrumental drift (e.g., sensitivity changes) and elemental fractionation effects during analysis. For high Rb/Sr systems, there is still a lack of reference materials with high ⁸⁷Rb/⁸⁶Sr and high ⁸⁷Sr/⁸⁶Sr ratios.
The six muscovite samples analyzed in this study exhibit exceptionally high ⁸⁷Rb/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr ratios. Electron Probe Microanalysis (EPMA) shows that these micas have high and stable Al and K contents of 10.755 ± 0.0373% and 33.39 ± 0.16%, respectively. Backscattered Electron (BSE) imaging confirms their homogeneous major element composition, devoid of impurities.
Given their exceptionally high ⁸⁷Rb/⁸⁶Sr ratios, we further analyzed these six muscovite samples using LA-ICP-MS/MS. The measured ages range from 190 Ma to 200 Ma. Rb concentrations vary from 2300 to 3700 µg/g, while Sr concentrations are low, at 2.5 and 3.5 µg g⁻¹. Among these samples, four exhibit extremely high ⁸⁷Rb/⁸⁶Sr ratios (28000-35000) and ⁸⁷Sr/⁸⁶Sr values (80-100). In contrast, the remaining two samples show moderately high ⁸⁷Rb/⁸⁶Sr ratios (11000-12000) and ⁸⁷Sr/⁸⁶Sr values (30-35). Based on the ID–MS isochron results and detailed LA-ICP-MS/MS data, all six muscovite samples show potential as candidate reference materials for LA-ICP-MS/MS Rb-Sr dating. Further detailed and systematic work is required to rigorously evaluate and validate their suitability.
How to cite: Cui, T., Chu, Z., Shen, P., Feng, H., Zhang, M., and Yang, Y.: High Rb/Sr Muscovite from the Koktokay Highly Fractionated Granites: Implications for Rb–Sr Chronology and LA-ICP-MS/MS In Situ Reference Material Development, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11115, https://doi.org/10.5194/egusphere-egu26-11115, 2026.
Molybdenite is the principal host mineral for rare metals such as molybdenum and rhenium and is widely distributed in various hydrothermal deposits. Owing to its high rhenium content and negligible common osmium, molybdenite is an ideal target for Re–Os isotopic dating. Re–Os ages of molybdenite can directly constrain the timing of metal sulfide mineralization.
In recent years, the development of inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) has provided a new analytical approach for in situ β-decay isotopic dating, including Rb–Sr, Lu–Hf, K–Ca, and Re–Os. In this study, an i CAP ICP-MS/MS coupled with a 193 nm G2 laser and N2O as the reaction gas was employed (Fig. 1). Based on systematic characterization of the reaction products between N₂O and Re and Os, the reaction gas flow rates were optimized, and in situ Re–Os dating of molybdenite was established.
This present protocol was applied to Re–Os age determinations of various molybdenite with ages ranging from 2.7 Ga to 0.15 Ga. The obtained results are consistent with those from ID-NTIMS or ID-ICP-MS. The study demonstrates that reliable in situ Re–Os ages can be achieved when the Re content of molybdenite more than 5 ppm. When combined with trace-element geochemical characteristics, in situ Re–Os dating of molybdenite provides important constraints on the timing of mineralization and genetic processes, offering valuable insights into the detailed geological evolution of metal sulfide deposits.
Figure 1. Schematic illustration of the basic principles of plasma tandem mass spectrometry. In the Re–Os system, reactions between rhenium (Re) and osmium (Os) with nitrous oxide (N2O) produce oxide species exhibiting a mass shift of 64 amu. However, a small proportion of Re also reacts with N2O to form 187ReO4, which interferes with the target ion 187OsO4, requiring appropriate interference correction.
How to cite: Wang, Y., Yang, Y., Wu, S., Chu, Z., Xie, L., and Xu, J.: In situ Re-Os dating of molybdenite by LA-ICP-MS/MS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7759, https://doi.org/10.5194/egusphere-egu26-7759, 2026.
The transformation of medieval castles in Italy, especially between the 11th and 12th centuries during the process of incastellamento, represents a crucial yet complex phase in European history. The transition from early wooden fortifications to durable stone structures is often poorly documented and broadly dated. PRIN 2020 CASTLES Project integrates archaeology, history, geology, conservation science, and physics in a multidisciplinary framework aimed at building a new and more precise chronology of medieval castle construction in northern and central Italy. The project focuses on 25 castles in Piedmont, Liguria, and Tuscany, combining historical and archaeological evidence with archaeometric analysis of masonry to refine the dating of construction phases and improve understanding of building practices. For this purpose, radiocarbon dating (14C) is used as an absolute dating technique. In this study, the 14C method was applied for dating ancient mortars of masonry castles, targeting both inorganic material (binder and lump calcite) and organic inclusions (charcoal). However, selection of the inorganic datable fraction and elimination of potential contamination proves to be a challenge for the international radiocarbon community. To select the most suitable mortar binder for 14C dating, a key step in the research is mortar sampling and the characterisation of the raw materials used in mortars. To minimise mortar contamination, samples were carefully taken with consideration for the archaeological structure and the preservation of the masonry. Once the mortar samples were selected, penetrometric and carbonation tests were carried out on site. Subsequently, mineralogical, petrographic, and chemical analyses were performed using XRPD, OM, SEM–EDS, OM-CL, and ATR-FTIR. These analyses enabled the identification of binder types, aggregate composition, and hydraulic properties. Air-hardening lime mortars proved to be the most reliable, whereas natural hydraulic and magnesium-rich limes often introduced complications. Further analyses were performed on powders of binder-rich portions or lumps, using non-destructive techniques, such as XRPD, OM-CL, ATR-FTIR [1]. More than 120 mortar samples were analysed, from which 63 powder samples were selected and prepared for ¹⁴C dating. Mortar radiocarbon results were cross-checked with charcoal dating and archaeological data, confirming the reliability of the methodological procedure. Several case studies from Tuscan castles demonstrate strong coherence between mortar characterization and radiocarbon ages, validating the approach. On a larger scale, the project is defining chronological trends that reflect different phases of castle development, from early fortifications to fully developed lordly residences and village centers. Overall, the project offers a reproducible and multidisciplinary framework that significantly improves the chronological reconstruction of medieval castles in Italy and provides a model applicable to similar contexts elsewhere.
[1] Calandra S., et al. 2024, A new multi-analytical procedure for radiocarbon dating of historical mortars, Sci Rep, 14(1), 19979.
How to cite: Calandra, S., Pecchioni, E., Garzonio, C. A., Salvatici, T., Intrieri, E., Lubritto, C., Mantile, N., Giacometti, V., Di Cicco, M. R., Bellato, G., Provero, L., Fiore, A., Arrighetti, A., Buonincontri, M. P., Bardi, A., and Bianchi, G.: The Time of Castles Project: Characterization of Mortar Raw Materials for ¹⁴C Dating in Medieval Castles of Northern and Central Italy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12387, https://doi.org/10.5194/egusphere-egu26-12387, 2026.
Understanding rare-gas release requires interdisciplinarity. Hydrous minerals degas 39Ar and 40Ar in vacuo during structural collapse due to dehydroxylation [1,2], never by Fick's Law in an inert, homogeneous matrix. Therefore monomineralic micas always give "plateaus" [3,4] despite age-zoning. Discordant age-spectra instead proceed from polymineralic, heterochemical, diachronous mixtures, unambiguously revealed by common-denominator three-isotope correlations [5,2]. The "Bruderheim staircase archetype" [6] wasn't a "lognormal distribution of monomineralic whole-rock crystals" but a more mundane polyphase maskelynite-pyroxene-anorthite assemblage [7,8]. For micas and Bruderheim, downslope extrapolations are arbitrary.
The inertness of the Itrongay sanidine crystal structure during laboratory heating was assessed by Raman microspectroscopy from 300 to 1000 °C [9]. Raman modes define robust trends at increasing temperature and over time at constant temperature, mirroring progressive excitation of phonon modes associated with structure modifications: interatomic bond stretching/deformation; Si,Al disordering; deformation/rotation of SiO2 tetrahedra. Differential activation of phonon modes is reversible, but disordering is are irreversible. The K-feldspar structure is not inert during laboratory heating, explaining the observed break in Arrhenian slope of Ar release rate [10]. This forbids downslope extrapolation of laboratory data to geological conditions.
The in vacuo releases between 500-1460 °C of 4He*, 20NeF, 37ArCa, 38ArCl, 80KrBr, 128XeI, 131XeBa, 134XeU from irradiated fluorapatite are linear, parallel Arrhenius trajectories. E=62±5 kJ/mol is independent of atomic radius, D0 values decrease from He to Xe by ~4 orders of magnitude [11]. Differential release diagrams show bimodal degassing patterns for Ne and Ar and a single burst above 1360 °C for Kr and Xe. The crystallographic site of Ba and I had no control on Xe release. All degassing rates steepen by 500 times at 1360 °C, and merge. The extreme Arrhenian break-in-slope and the merger of trajectories widely separated below 1360 °C reflect sudden, major, energetically very costly structural reordering at 1360 °C, which was documented by Raman spectroscopy, XRD, TEM and microchemical analysis by LIBS. Complete outgassing of Ne, Ar, Kr and Xe requires complete defluorination reaction modifying the apatite structure. Discrete phase transitions at high T make downslope extrapolations to low T incorrect.
[1] Zimmermann 1970, https://doi.org/10.1016/0016-7037(70)90045-1
[2] Villa 2021, https://doi.org/10.1016/j.chemgeo.2021.1.120076
[3] Foland 1983, https://doi.org/10.1016/S0009-2541(83)80002-3
[4] Hodges &al 1994, https://doi.org/10.1130/0091-7613(1994)022<0055:AAAGIM>2.3.CO;2
[5] Villa & Hanchar 2017, https://doi.org/10.1016/0012-821X(66)90061-6
[6] Turner &al 1966, https://doi.org/10.1016/0012-821X(71)90051-3
[7] Duke &al 1961, https://doi.org/10.1029/JZ066i010p03557
[8] Baadsgaard &al 1961, https://doi.org/10.1029/JZ066i010p03574
[9] Kung & Villa 2021, https://doi.org/10.1016/j.chemgeo.2021.120382
[10] Wartho &al 1999, https://doi.org/10.1016/S0012-821X(99)00088-6
[11] Villa &al 2024, https://doi.org/10.1016/j.chemgeo.2023.121860
How to cite: Villa, I. M.: Ar data extrapolation from the lab to rocks: systematics of noble gas release in vacuo from micas, feldspars, etc., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3984, https://doi.org/10.5194/egusphere-egu26-3984, 2026.
Dating submarine volcanic rocks is essential for understanding the relationship between tectonics and volcanism, as well as for characterizing the evolution of volcanic systems, for instance. The K-Ar chronometer is generally used but dating young rocks (<50 ka) remains a significant challenge, particularly because their amount of radiogenic 40Ar is low. Here, we present a comparison of K-Ar and the 40Ar/39Ar ages obtained from submarine samples from the Eastern Mayotte Volcanic Chain (EMVC; Comoros Archipelago). This volcanic chain consists of monogenetic pyroclastic cones, lava domes and lava flow fields with basanitic to phonolitic compositions. It includes the Fani Maoré, a new submarine volcano that formed a few years ago, and the Horseshoe, a potentially active U-shaped morphological structure, located only 10 km offshore Mayotte. A total of 19 samples were collected in the Horseshoe and Fani Maoré regions, by dredging and/or using the Victor6000 remotely operated vehicle (ROV), during 6 oceanographic campaigns. These samples were dated using both the K-Ar and the 40Ar/39Ar methods, on a carefully selected groundmass fraction obtained within a narrow density range with heavy liquids. Both methods used here allow dating of very young samples with ages as young as 3 ± 1 ka for phonolitic samples, with radiogenic content as low as 0.1%. The 40Ar /39Ar inverse isochrons confirm the atmospheric initial trapped 40Ar/36Ar component, suggesting that no argon fractionation affected the ages from either method, and flat 40Ar/39Ar age spectra indicate that the K-Ar system remained closed. In order to further check both methods with zero-age basanitic lavas, we have analysed samples from the 2018 and 2020 eruptions of the Fani Maoré volcano. The relatively precise ages obtained by both methods confirmed that, following a carefully sample selection and preparation, both K-Ar and 40Ar /39Ar methods are well suited for dating submarine Holocene volcanics such as the phonolitic lavas and pyroclasts. Finally, the comparison between K-Ar and 40Ar/39Ar shows coherent results in most cases, enabling a precise temporal framework to be established for the Horseshoe region.
How to cite: Frey, M., Quidelleur, X., Ricci, J., Feuillet, N., Médard, É., Berthod, C., Komorowski, J.-C., Puzenat, V., Thinon, I., Rinnert, E., Cathalot, C., Jorry, S., Paquet, F., and Lebas, É.: Dating of submarine volcanism based on combined K-Ar and 40Ar/39Ar methods: example from the Eastern Mayotte Volcanic Chain (Comoros Archipelago)., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20451, https://doi.org/10.5194/egusphere-egu26-20451, 2026.
Low-temperature geochronology using multiple isotopic systems is a powerful approach for reconstructing the tectono-thermal evolution of sedimentary basins. As individual dating techniques have distinct strengths and limitations, integrating complementary geochronological methods provides a more robust framework for constraining shallow-crustal thermal events. In this study, we examine the thermal and tectonic evolution of east-central Australia, from the eastern coast to the continental interior, through isotopic dating of authigenic illitic clay minerals. We integrate new and published Rb–Sr, K–Ar, and 40Ar/39Ar illite geochronology and critically assess the applicability of these methods when applied to low-temperature mineral systems.
Our results identify multiple episodes of thermal and fluid-flow activity during the Early Jurassic (~200–190 Ma), Middle Jurassic (~165 Ma), Early Cretaceous (~120–115 Ma), and Late Cretaceous (~100–95 Ma, ~85–80 Ma, and ~70 Ma). These events broadly coincide with periods of subduction-related orogenesis and rifting along eastern Australia. Jurassic illite ages from the Permo-Carboniferous Galilee Basin are nearly synchronous with the development of the Eromanga, Surat, and Clarence–Moreton basins, and reflect contemporaneous intraplate tectonism linked to subduction processes.Early Cretaceous ages correspond with magmatic activity in eastern Queensland, including the Whitsunday Volcanic Province, and associated arc- or rift-related tectonism. Late Cretaceous ages are consistent with apatite fission-track (AFT) data and indicate a regional extensional regime that culminated in sea-floor spreading east of the Australian continent.
Although these thermal events occurred far from the active Mesozoic plate margin, they are best explained by the dynamic effects of shallow subduction and/or the transmission of far-field stresses into a mechanically and thermally weakened continental interior, resulting in widespread subsidence, extension, and enhanced heat and fluid flow. These findings have important implications for energy and resource exploration, as Cretaceous tectonic reactivation defines fault zones that currently facilitate geothermal fluid upwelling in east-central Australia. Interaction of these fluids with Precambrian granitic basement rocks enriched in incompatible and radioactive elements highlights the potential of low-temperature geochronology to constrain the timing of fluid–rock interaction and to inform exploration strategies for critical metals and carbon-free gas resources in sedimentary basins.
How to cite: Uysal, I. T., Babaahmadi, A., Zhao, J., Aykut, T., and Todd, A.: Tectono–thermal evolution of the east-central Australian intraplate: Rb–Sr, K–Ar and 40Ar/39Ar geochronology of authigenic illite., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8468, https://doi.org/10.5194/egusphere-egu26-8468, 2026.
Low-temperature thermochronology has traditionally relied on apatite and zircon minerals that are commonly absent from carbonate platforms, leaving large regions effectively blind to shallow crustal thermal reconstructions. Recent methodological advances now permit the application of (U-Th)/He dating to iron oxides, but so far this approach has only been tested in crystallization contexts and has rarely been used to quantify burial-exhumation trajectories.
Here we explore karst-hosted bauxite deposits as a new natural laboratory for oxide thermochronology. These lateritic bodies, developed on the Durancian structural high in southeastern France, contain abundant hematite and goethite that formed during intense Lower Cretaceous weathering and were subsequently buried beneath Upper Cretaceous to Cenozoic sedimentary sequences. Such conditions provide the requirement for oxide thermochronology: iron oxides that experienced post-crystallization heating.
We report a large dataset of (U-Th)/He ages obtained from more than one hundred individual hematite and goethite grains sampled across south of France. All ages postdate bauxite formation and independent depositional constraints, demonstrating that these minerals systematically record post-depositional thermal overprints.
Coexisting hematite and goethite systematically yield distinct age populations, with goethite consistently recording younger apparent ages. This reproducible offset demonstrates that these two iron oxides behave as independent low-temperature chronometers.
Because diffusion parameters for goethite remain poorly constrained, thermal history modelling was performed using hematite only. Thermal inversion modelling, is supported by regional stratigraphic and tectonic frameworks. It identifies two successive heating phases linked to Pyrenean compression and to Oligocene–Miocene rifting. Reheating during this latter event temporally correspond to goethite ages. This age comparisons between both phases provide empirical constraints on reset temperatures of goethite about 60-40°C.
Our results demonstrate that karst-hosted bauxites constitute a robust archive for oxide-based thermochronology, and provide the first natural framework for empirically constraining reset temperature in goethite. This approach opens new perspectives for reconstructing shallow thermal histories in carbonate-dominated regions where conventional chronometers are absent.
How to cite: Boschetti, L., Schwartz, S., Gautheron, C., Rolland, Y., Mouthereau, F., Balvay, M., Cogné, N., and Campillo, S.: Karst-hosted bauxites as a new archive for oxi-hydroxide (U-Th)/He thermochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12699, https://doi.org/10.5194/egusphere-egu26-12699, 2026.
Mafic and ultramafic rocks provide critical insights into ophiolite formation and obduction, orogenic suturing, and rock magnetism, yet they are difficult to date due to the absence of conventional radioisotopic chronometers. Magnetite and chromite are common primary or secondary mineral phases that often preserve growth zoning and complex overprinting, but extremely low eU concentrations and intragrain heterogeneity have limited the application of (U–Th)/He dating. Here we report recent progress at the University of Texas at Austin (UTChron) toward establishing protocols of routine laser ablation (LA) (U–Th)/He in-situ dating of magnetite and chromium spinel (chromite) with eU <10 ppb and ultra-low He concentrations. Our analytical procedures couple in-vacuo laser ablation and ultra-low-blank magnetic-sector noble gas mass spectrometry (Thermo Fisher SFT) for He with U–Th quantification by laser-ablation ICP-MS (Thermo Element2) and ablation pit volume measurements using white-light interferometry. This integrated workflow supports targeted analyses of discrete textural growth zones and complex intragrain textures at ~100 μm spatial resolution, with typical analytical precision of ~5–10%.
We present three applications for in-situ He dating of magnetite and chromite from mafic and ultramafic rocks: (1) magnetite and chromite from kimberlitic diatremes that yield LA-(U–Th)/He ages consistent with independent emplacement constraints, providing a practical alternative where conventional datable minerals are absent; (2) He ages from primary chromite from obducted orogenic ophiolitic units that record thermal resetting and subsequent cooling, offering new leverage on the tectonic histories of ultramafic sequences that are traditionally challenging to date; and (3) He dates from secondary magnetite growth in sheared serpentinites that provide direct constraints on fluid-rock interaction during deformation in ultramafic shear zones. Collectively, these results establish magnetite and chromite as viable targets for in situ (U–Th)/He thermochronometry and broaden the range of geological problems accessible to in-situ dating.
How to cite: Ehrenfels, M., Stockli, D., Prior, M., Patterson, D., Stockli, L., and Martin, C.: Extending Laser-Ablation (U-Th)/He to Ultra-Low-eU Magnetite and Chromite: A New Tool for Mafic and Ultramafic Rocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19596, https://doi.org/10.5194/egusphere-egu26-19596, 2026.
Pyromorphite [Pb5(PO4)3Cl] is an end-member phase of the apatite-group minerals. It commonly forms during supergene weathering of Pb-rich ore deposits. Owing to its chemical stability and low solubility under natural environmental conditions, pyromorphite preserves a record of supergene weathering events. The U concentration of pyromorphite is typically high (up to several thousand ppm) making it a potential as a (U-Th)/He and/or (U-Th)/Ne chronometer of paleoenvironmental change. (U-Th)/He ages of nine pyromorphite specimens from around the globe are less than 5 Ma. The near complete absence of fission tracks in all samples, despite the relatively high U concentration (1-30 ppm), is consistent with the young He ages. Complete helium extraction requires considerably shorter heating at lower temperature than similar sized Durango apatite fragments implying that He closure temperature in pyromorphite is lower than apatite.
A detailed study of an inclusion-free pyromorphite crystal from Daoping mine, Guangxi (China) has been undertaken to determine its suitability as a chronometer of supergene mineralisation. Incremental extraction of He from 250-500 mm fragments display good linearity on an Arrhenius diagram for temperature steps less than 220°C. The kinetic parameters (E and ln(D0/a2)) display a range of values that we use to determine a helium closure temperature in the range -30°C to -84°C for a nominal cooling rate of 10°C/Myr. This range may reflect the presence of varying size sub-grains that are evident from EBSD. Density functional theory modelling shows that the substitution of Ca2+ (0.99 Å) by Pb2+ (1.19 Å) expands the interstitial sites in the pyromorphite lattice compared to apatite, likely lowering the energy barrier for helium diffusion and changing the global minimum location, thus changing the diffusion pathway of He in pyromorphite. EBSD shows that lattice distortion is ubiquitous, perhaps due to the off-centre position of the electron pair of Pb2+ within its coordination environment or the substitution of V. The dislocations may function as sinks for He and impede helium diffusion. This leads us to conclude that pyromorphite is unlikely to find use as He thermo/geochronometer but further study may aid understanding He diffusion in apatite group minerals.
How to cite: Stuart, F., Yan, M., Wang, Y., Pang, J., and Spruženiece, L.: Is (U-Th)/He dating of pyromorphite a new chronometer of weathering?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21743, https://doi.org/10.5194/egusphere-egu26-21743, 2026.
Thermochronology has advanced through the development of new methods and applicable mineral systems, with multi-method approaches proving essential for bridging temperature–time gaps and improving the resolution of thermal history reconstructions. Here, we apply a zircon-based multi-method approach to investigate the thermotectonic evolution of the Araçuaí Orogen, along the São Francisco Craton in Brazil. While the Mesozoic–Cenozoic evolution of the orogen is relatively well constrained, its earlier thermal history remains poorly understood. To address this gap, we expand an existing apatite fission-track (AFT) dataset of 20 samples by adding new zircon (U–Th–Sm)/He (ZHe) ages, extending thermal constraints from the apatite partial fission-track annealing zone (APAZ; ~60–120 °C) to higher-temperature conditions (~140–220 °C). In addition, four representative samples were selected along a north–south transect across the craton–orogen interaction zone for zircon Raman multi-band thermochronology and zircon U–Pb analyses. Zircon Raman multi-band thermochronology, a recently developed approach, further extends thermal constraints to mid- and high-temperature conditions (~260–370 °C).
The ZHe dataset reveals a systematic relationship between effective uranium (eU) concentration and single-grain ages. Zircons with low eU contents (<500 ppm) yield predominantly Paleozoic ZHe ages, ranging from the Cambrian to Carboniferous (ca. 500–350 Ma), whereas grains with progressively higher eU concentrations record younger ages spanning the Late Paleozoic to Early Cretaceous (ca. 350–100 Ma). This inverse age–eU relationship is consistent with radiation-damage–controlled helium diffusion in zircon, as predicted by established diffusion models.
Raman ages derived from multiple zircon bands (ν1, ν2, ν3, and external bands) indicate distinct thermal responses across the transect. Two samples record Raman ages overlapping with or being older than the Araçuaí orogeny, suggesting preservation of pre- to syn-orogenic thermal signatures. In contrast, Raman ages from the other two samples correspond to the late stages of the orogeny or post-date it.
Comparison of Raman-derived ages with ZHe and AFT data provides constraints on cooling rates through successive temperature windows. Samples showing convergence of Raman, ZHe, and AFT ages indicate relatively rapid cooling through mid- and low-temperature regimes, whereas increasing separation between these chronometric results reflects more prolonged cooling histories. Variations in the thermal sensitivity of individual Raman bands, reflected in their accumulated radiation damage, constrain the rate of cooling across mid-temperature ranges: synchronous band resetting indicates faster cooling whereas differential band behavior suggest slower, stepwise cooling.
These results reinforce evidence that the craton–orogen interaction zone of the São Francisco Craton experienced significant thermal overprinting associated with the development of the Araçuaí orogenic front (ca. 500 Ma), even though the underlying crust is of Rhyacian (~2.1 Ga) and Archean (~3.2 Ga), as indicated by zircon U–Pb data. Thermal history modelling indicates that following orogenesis, the region underwent substantial cooling, allowing samples to pass through progressively lower-temperatures and reach shallow crustal levels by the end of the Paleozoic. Subsequent opening of the South Atlantic Ocean preferentially affected structurally weakened domains, particularly areas associated with deep-seated faults and shear zones.
How to cite: Fonseca, A., De Grave, J., Novo, T., J. Sieber, M., Wilke, M., Hartel, B., van Schijndel, V., Stammeier, J., Wapenhans, I., van der Beek, P., and Sobel, E.: Zircon triple dating (U–Pb, Raman, and U–Th–Sm/He) constraints on the thermotectonic evolution of the Araçuaí Orogen at the craton–orogen interface (Brazil), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7226, https://doi.org/10.5194/egusphere-egu26-7226, 2026.
The accumulation of alpha radiation damage and its annealing in apatite are critical to thermochronological studies but remain difficult to characterize. We conducted annealing experiments on four slices from a single Durango apatite crystal and used high-resolution Raman spectroscopy mapping to analyse peak positions and full width at half maximum (FWHM) of the ν₁(PO₄) and ν₃(PO₄) bands. Track densities were measured in different regions of the crystal, and a normalized track-density reduction model was applied to estimate the original alpha radiation damage. In addition, heavy-ion irradiation was used to simulate the fission process and enhance the visibility of confined tracks.
Our results show that the FWHM of the ν₁(PO₄) band is a robust indicator of alpha radiation damage accumulation in apatite and does not correlate with fission-track damage in Durango apatite. The spatial zoning pattern of FWHM closely matches that of effective uranium (eU), and among samples with similar eU contents, those subjected to higher annealing temperatures exhibit lower FWHM values. Furthermore, alpha radiation damage does not significantly influence the annealing behaviour of fission tracks in Durango apatite. Although the behaviour of Raman peak positions remains enigmatic, our results suggest that it is influenced by both apatite chemical composition and radiation damage accumulation. This study demonstrates that high-resolution Raman spectroscopy provides a novel and quantitative approach to directly link radiation damage with thermal history in apatite. This methodology could potentially improve thermochronological apatite models and interpretation enabling detailed, spatially resolved insights into damage accumulation and annealing processes in geological studies.
How to cite: Pastore, G., Zeng, X., Shen, C., Resentini, A., Fu, H., Yang, C., Vermeesch, P., Fox, M., Buret, Y., and Malusà, M. G.: Raman mapping reveals alpha radiation damage zonation and its annealing in Durango apatite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14548, https://doi.org/10.5194/egusphere-egu26-14548, 2026.
The Cenozoic India-Eurasia collision drove widespread intracontinental deformation across Central Asia, culminating in northward indentation of the Pamir and its eventual contact with the South Tianshan. However, the timing and kinematic development of the Pamir-Tianshan convergence, as well as its influence on shaping regional topography and climate, remain debated. Here we report more than 200 new apatite (U-Th-Sm)/He (AHe), apatite fission-track (AFT), and zircon (U-Th-Sm)/He (ZHe) dates from 49 samples collected from the North Pamir-South Tianshan convergence zone in the westernmost Tarim Basin, NW China. These data, integrated with inverse thermal history modeling and probabilistic estimates of cooling onset, reveal a protracted, stepwise convergence history since the late Eocene. Initial convergence occurred from the late Eocene to the middle Miocene (~35-15 Ma), marking the onset of cooling and deformation in the hinterlands. During the middle Miocene (~15-10 Ma), deformation propagated basinward into the foreland, accompanied by the activation of frontal thrust systems in both orogens. Continued convergence during the late Miocene (~10-5 Ma) led to initial interaction between the North Pamir and South Tianshan thrust systems, followed by propagation of deformation along frontal thrusts during the Pliocene to Quaternary (~5-0 Ma), producing the present-day superimposed and imbricated thrust architecture in the convergence zone. This progressive convergence and surface uplift gradually narrowed and closed topographic corridors between the Pamir and Tianshan, restricting westerly moisture transport into the Tarim Basin and promoting the development of the Taklimakan Desert. Together with existing paleoclimate records, our results demonstrate that regional tectonic processes, acting in concert with global climatic forcing, played a dominant role in the long-term aridification of Central Asia.
How to cite: Wang, F., R. Sobel, E., van der Beek, P., L. Colleps, C., Stammeier, J., Glodny, J., and Zhu, W.: Late Cenozoic Pamir-Tianshan convergence and its tectonic-climatic implications revealed by low-temperature thermochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8250, https://doi.org/10.5194/egusphere-egu26-8250, 2026.
Cratons are ancient parts of the lithosphere, often characterised by long-term stability. Geological observations indicate that the Fennoscandian Shield in the East European craton has likely experienced some of the slowest erosion rates on Earth over the past approximately 1.5 billion years1. However, a contrasting perspective has emerged based on apatite fission-track thermochronology, suggesting multiple episodes of kilometre-scale burial and exhumation during the past 1.1 Ga2. This raises the question: How stable has the Fennoscandian Shield been since the Mesoproterozoic?
Since a Phanerozoic sedimentary record is not preserved in Finnish Fennoscandia, we investigate this question using new data from (U-Th)/He thermochronology and integrated modelling of multiple thermochronometer systems.
We have collected 20 samples from Finnish Fennoscandia, from which we obtained 64 single-grain zircon (U-Th)/He dates (1553 to 1.8 Ma) and 55 single-grain apatite (U-Th)/He dates (1178 to 99 Ma). In addition, we analysed 25 zircons from the Kola peninsula in Russia and obtained (U-Th)/He dates ranging from 1929 to 215 Ma. Samples from southern Finland and the Kola peninsula show a strong decrease in zircon (U-Th)/He dates with increasing U-Th concentrations, due to the effects of radiation damage. We leverage this date dispersion to determine plausible thermal histories using different inverse modelling software (QTQt3, Thermochron.jl4 and Tc1D5) and explore the complex (U-Th)/He date patterns through separate and joint inversion of the zircon and apatite data.
Preliminary inverse modelling results using QTQt and Thermochron.jl suggest that regions in southern Finland and the Kola peninsula may have experienced protracted residence at shallow upper crustal levels for at least 1 Ga. In contrast, areas in northern Finland, near the Caledonian front, show evidence of heating and cooling likely linked to burial and exhumation following Caledonian orogenesis.
Ongoing work focuses on refining the preliminary thermal history models by integrating published apatite fission track and 40Ar/39Ar data with our (U-Th)/He dataset to more effectively constrain the magnitude, timing and rates of burial and exhumation in Fennoscandia and its possible drivers (e.g. extreme glaciation, orogenies). This will not only provide insight into the exhumation history of Fennoscandia, but also the resolving power of low-temperature thermochronology for reconstructing thermal histories in cratonic areas where timescales are immense and the geological record is limited.
1 Hall, A.M., Putkinen, N., Hietala, S., Lindsberg, E. and Holma, M., 2021. Ultra-slow cratonic denudation in Finland since 1.5 Ga indicated by tiered unconformities and impact structures. Precambrian Research, 352, p.106000.
2 Green, P.F., Japsen, P., Bonow, J.M., Chalmers, J.A., Duddy, I.R. and Kukkonen, I.T., 2022. The post-Caledonian thermo-tectonic evolution of Fennoscandia. Gondwana Research, 107, pp.201-234.
3 Gallagher, K. (2012), Transdimensional inverse thermal history modeling for quantitative thermochronology, J. Geophys. Res., 117, B02408, doi:10.1029/2011JB008825.
4 Keller, C.B., McDannell, K.T., Guenthner, W.R., and Shuster, D.L. (2022). Thermochron.jl: Open-source time-Temperature inversion of thermochronometric data. 10.17605/osf.io/wq2U5
5 Whipp et al. (2025). HUGG/Tc1D: v0.3.2 (v0.3.2). Zenodo. https://doi.org/10.5281/zenodo.17590819
How to cite: Maier, A.-K., Gérard, B., Whipp, D., Laaksonen, S., and McDannell, K.: How stable is the Fennoscandian Shield? Insights from low-temperature thermochronology and numerical models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17806, https://doi.org/10.5194/egusphere-egu26-17806, 2026.
Thermochronological data can provide robust constraints on crustal exhumation, erosion, and burial, yet their interpretation often requires forward and/or inverse models to account for thermal evolution and the effects of surface processes. Here we present recent developments in Tc1D, a one-dimensional thermal and thermochronometer age prediction package designed to explore exhumation, burial, and other thermal processes and their effects on low-temperature thermochronometers.
Tc1D generates thermal histories by solving the transient one-dimensional heat transfer equation to predict apatite and zircon (U-Th)/He and fission-track ages using established thermochronological models, including RDAAM and ZRDAAM. The thermal model is controlled by user-defined thermal boundary conditions and prescribed vertical crustal dynamics, including erosion and burial. These histories can be parameterized through multiple erosion model options (e.g., stepwise or linearly varying rates) as well as simplified 1-D representations of tectonically driven vertical motions (e.g., thrust-sheet emplacement/removal and extensional/thrust faulting). This physics-based yet computationally efficient setup enables rapid exploration of how various thermal and crustal scenarios translate into predicted age patterns.
Tc1D adopts a complementary approach, compared to commonly used thermal history modeling tools such as HeFTy, QTQt, or Thermochron.jl, enabling direct connection between different vertical-motion scenarios, measured ages, and physical parameters (e.g., erosion rates or eroded thicknesses), while retaining fast execution times suitable for large sensitivity and ensemble analyses. Furthermore, by remaining one-dimensional, Tc1D avoids the computational cost of full 3D thermo-kinematic models such as PECUBE, while still capturing the first-order effects of vertical lithospheric processes. Tc1D is also fully open source and Python based, facilitating transparency, extensibility, and integration into reproducible research workflows.
Recent developments in Tc1D (from version 0.3) expand its scope beyond earlier releases, which were primarily limited to forward modeling and simple erosion scenarios. Recent versions introduce support for data-driven inverse modeling, flexible definitions of exhumation and burial histories, and the inclusion of additional thermal perturbations such as magmatic intrusions. Tc1D now supports parameter inversion using either the Neighborhood Algorithmor a Markov Chain Monte Carloapproach, enabling systematic exploration of exhumation and burial histories. These histories can be defined through an external input file, allowing complex, multi-stage scenarios combining piecewise constant, linear, or exponential phases of erosion/burial.
Ongoing developments focus on improving usability and physical realism. A new unified YAML-based input file is currently being developed to provide an alternative to command-line–driven usage, improving reproducibility while simplifying model design. This structure facilitates the definition and modification of complex model configurations, including multi-stage erosion and burial histories, thermal boundary conditions, and is designed to support future inversion of stage durations and erosion parameters. In parallel, software developments aim to incorporate more realistic representations of crustal structure and rock properties, including depth-dependent density variations based on mineral phase transitions, to better account for crustal composition, thermal properties, and their influence on thermal evolution and erodibility.
These developments are being applied to investigate the long-term thermal evolution of the crust in the Fennoscandian Shield, where low relief, limited sedimentary archives, episodic burial, and subtle post-orogenic exhumation pose major challenges for thermochronological data interpretation.
How to cite: Gérard, B., Whipp, D., Laaksonen, S., and Maier, A.-K.: Tc1D: a fast and flexible 1-D thermal and thermochronology modeling package for complex exhumation, burial, and transient thermal histories, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17436, https://doi.org/10.5194/egusphere-egu26-17436, 2026.
Thermal-kinematic modeling of thermochronometric datasets is widely used to reconstruct exhumation histories. Yet, the sensitivity of model outputs to input parameters is rarely evaluated, even within a given modeling framework. Comparative sensitivity analysis across multiple tools is even less common, even though these models differ substantially in their treatment of heat transport, inversion structure, and kinetic behavior. In this study, we apply the Taguchi method, a statistical design of experiments, to assess parameter sensitivity in four thermal-kinematic modeling packages. We systematically vary thermal, kinetic, and optimization parameters across each tool and quantify their influence on predicted exhumation rates. Our results reveal substantial model-specific differences in sensitivity patterns. Two modeling platforms that use the same formulation, namely, Gaussian linear inversion of an age-elevation relationship, are most responsive to different things, with one most sensitive to thermal field parameters such as heat production and thermal diffusivity, and the other strongly influenced by inversion settings, including time step and prior exhumation rate. In age2exhume, activation energy (Ea) dominates, underscoring the role of kinetic parameters in diffusion-based models. These findings demonstrate that parameter sensitivity is not intrinsic to the thermochronometric system but is shaped by modeling assumptions. As tool selection influences both interpretation and uncertainty, there is a risk that model structure may overwhelm geological signals if not explicitly tested. We advocate for broader model intercomparisons and increased flexibility in parameter configuration to support more robust and transparent thermochronologic analysis.
How to cite: Sparks, S. and Hodges, K.: Comparison of thermal-kinematic modeling approaches based on Taguchi method sensitivity analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22116, https://doi.org/10.5194/egusphere-egu26-22116, 2026.
Posters on site: Thu, 7 May, 16:15–18:00 | Hall X2
Molybdenite is an ideal mineral for Re-Os isotopic dating, and its Re-Os isotopic systematics are widely employed to constrain the timing of hydrothermal metal mineralization. However, high-precision Re-Os isotopic dating (precision <1‰) remains a global challenge, as most published molybdenite Re-Os isotopic ages exhibit dating precisions far above 3‰, with only scarce data falling between 1‰ and 3‰, and very few cases achieving <1‰, which severely hinders the understanding of metallogenic regularity and the optimization of mineral exploration targets. In this study, the chemical separation and instrumental analysis methods for molybdenite Re-Os isotopic dating have been optimized. Using this improved isotopic dilution method, we analyzed the Huanglongpu molybdenite (a widely utilized molybdenite reference material) and molybdenite samples from four representative metal deposits. Each individual analysis achieved a dating precision of <1‰, with the best dating precision reaching 0.13‰. In addition, the weighted mean age precision of molybdenite from the Baishiding polymetallic deposit also reached 1‰. This study reveals that the molybdenite Re-Os isotopic dating can indeed serve as another reliable high-precision dating tool, complementing the well-established U-Pb dating method for deciphering Earth's geological timescale.
How to cite: Fan, X., Xu, J., Li, J., Wang, G., and Zeng, Y.: High precision Re-Os isotopic dating of molybdenites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7785, https://doi.org/10.5194/egusphere-egu26-7785, 2026.
Establishing the age of mineral deposits and their host rock sequences is fundamental to mineral exploration, as it constrains the temporal evolution of prospective geological environments and the geodynamic processes responsible for ore formation. This is particularly critical for syn-genetic stratiform systems such as volcanogenic massive sulfide (VMS) deposits, which are typically localized along favorable stratigraphic horizons within volcanic belts and linked to episodes of regional extension and magmatism. In Archean cratons, however, VMS deposits commonly experience multiple post-ore deformation, metamorphic, and hydrothermal events that may obscure primary isotopic signatures and result in metal remobilization, complicating efforts to constrain the timing of syn-genetic mineralization.
In this study, we apply an integrated geochronological approach including U–Pb zircon and titanite, Lu–Hf garnet, Re–Os sulfide and molybdenite, and Pb–Pb galena dating to constrain the age of syn-genetic mineralization in an Archean VMS deposit metamorphosed to amphibolite facies. Our results demonstrate that the Re–Os isotopic system in syn-genetic pyrite can be preserved through high-grade metamorphism and yields ages consistent with U–Pb zircon ages of the felsic host rocks, providing a robust means to directly date VMS mineralization in highly metamorphosed Archean terranes. In contrast, Re–Os ages obtained from pyrrhotite record prograde metamorphism and align with Lu–Hf garnet ages, indicating their utility for constraining metamorphic overprinting and metal remobilization events.
We further show that Re–Os dating of bulk massive sulfide ore dominated by both pyrite and pyrrhotite produces mixed, geologically meaningless ages, rendering this approach unreliable where extensive pyrrhotite formation has occurred via pyrite desulfidation. Although molybdenite within the footwall stratigraphy yields robust Re–Os ages despite amphibolite-facies metamorphism, these ages reflect late granitoid emplacement and regional metamorphism rather than syn-genetic VMS mineralization. Collectively, our findings provide new constraints on the timing of metamorphosed VMS deposits and have significant implications for regional exploration strategies, particularly within the Yilgarn Craton.
How to cite: Dana, C., Hollis, S., Tavazzani, L., Chelle-Michou, C., Glorie, S., Kuwahara, Y., Mimura, K., Yano, M., Ohta, J., Selby, D., Kato, Y., Pashley, V., James, M., and Podmore, D.: What do Re-Os ages of sulfide minerals at amphibolite facies mean: resolving syngenetic vs metamorphic ages in an Archean VMS deposit, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9932, https://doi.org/10.5194/egusphere-egu26-9932, 2026.
LA-ICP-MS/MS single-spot Rb–Sr analysis has become a powerful tool for in situ dating of ultra-radiogenic minerals such as muscovite. However, this technique relies critically on matrix-matched, highly radiogenic reference materials (RMs) for external calibration. Accurate characterization of such RMs, in turn, requires high-precision isotope dilution mass spectrometry (ID-MS).
Nevertheless, ID-MS analysis of highly radiogenic materials remains technically challenging. First, extremely high Rb/Sr ratios hinder complete separation of Sr from Rb, resulting in potential 87Rb interference on 87Sr during TIMS Sr isotope measurements. Second, very high 87Sr/86Sr ratios combined with low absolute 86Sr abundances render analyses highly sensitive to Sr procedural blanks. Consequently, robust data quality control for ID-MS itself is essential, necessitating the availability of highly radiogenic RMs suitable for ID-MS validation. At present, however, such reference materials remain scarce.
In this study, we developed an improved Sr-specific resin separation protocol aimed at maximizing Sr recovery during ID-MS Rb–Sr analysis of highly radiogenic samples. The key modification involves dissolving HF-digested sample residues in a mixed acid of 7.5 M HNO₃ and 2.5 M HCl, rather than the conventionally used 3 M or 7 M HNO₃ alone, prior to loading onto the Sr-specific resin column. The mixed HCl–HNO₃ acid significantly enhances dissolution of fluoride-bearing residues following HF digestion. In contrast, when pure HNO₃ is used, more than 95% of Sr is coprecipitated with fluorides for muscovite samples, leading to substantial Sr loss. The improved protocol results in markedly increased Sr recovery and more reliable ID-MS measurements.
Using this optimized separation procedure, we conducted comprehensive ID-MS Rb–Sr analyses of two candidate reference materials: the pegmatite RM OU-9 (IAGeo Limited) and the muscovite Ar–Ar age RM ZMT04. OU-9 yields Rb and Sr mass fractions of 1227 ± 17 μg g⁻¹ and 13.07 ± 0.18 μg g⁻¹, respectively, with 87Rb/86Sr = 843.1 ± 3.8 and 87Sr/86Sr = 22.217 ± 0.089, corresponding to an Rb–Sr age of ~2650 Ma with an initial 87Sr/86Sr of ~1.2. ZMT04 contains 2494 ± 22 μg g⁻¹ Rb and 36.05 ± 0.25 μg g⁻¹ Sr, with 87Rb/86Sr = 832.4 ± 5.2 and 87Sr/86Sr = 32.60 ± 0.19, corresponding to an Rb–Sr age of ~1800 Ma with an initial 87Sr/86Sr of ~0.705. These results demonstrate that both materials have strong potential as highly radiogenic reference materials for ID-MS Rb–Sr geochronology.
How to cite: Chu, Z., Cui, T., Shi, W., Zhang, W., Li, Y., Yang, Y., Xu, L., and Peng, P.: Improved Sr-Specific Resin Separation Protocol and Development of High-Radiogenic Reference Materials for ID-MS Rb–Sr Geochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8484, https://doi.org/10.5194/egusphere-egu26-8484, 2026.
Carbonite forms in a wide variety of geological environments as both a primary and secondary mineral phase and may contain sufficient U for U-Pb geochronology. The limited availability of well-characterized calcite reference materials, however, has impeded its broader application in microanalysis, in particular for the low-U (<0.1 mg g-1) calcite and dolomite. In this study, four potential carbonite reference materials (JCL03, THMT, TL-2, TL10-7) were primary characterized for in situ U-Pb geochronology. JCL03 and THMT are low-Mg calcite with Mg concentrations of ~0.35 wt.%, ~0.39 wt.%, respectively. TL-2, TL10-7 are the dolomite with Mg concentrations of ~21.5 wt.%, ~17.4 wt.%, respectively. JCL03 and THMT were characterized as low-U calcite with U concentrations of ~0.036 mg·g-1, ~0.021 mg·g-1, respectively. TL-2 and TL10-7 have U concentrations of ~2.3 mg·g-1, ~1.5 mg·g-1, respectively. JCL03 and THMT have homogeneity ages, while TL-2 and TL10-7 shows multiple dolomitization process. Multiple LA-ICP-MS analytical sessions yielded ages of 428.7 ± 5.2 Ma, 286.3 ± 7.1 Ma, 233.8 ± 4.4 Ma and 180.0 ± 6.3 Ma for JCL03, THMT, TL-2 and TL10-7, respectively. These four carbonaite are the useful additions to the widely distributed WC-1 reference material for LA-ICP-MS U-Pb geochronology.
How to cite: Xiao, F., Li, T., Wu, S., and Yang, Y.: Four potential carbonite reference materials for in situ U-Pb geochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10876, https://doi.org/10.5194/egusphere-egu26-10876, 2026.
Ti-bearing andradite [Ca3Fe2+Ti4+Si3O12] is generally widespread, a diagnostic accessory phase of silica undersaturated alkalic plutonic and volcanic rocks but also occurs in skarn and hydrothermal alteration assemblages, which is associated with the major economic critical metals (Nb, LREE) mineral in deposits related to carbonatite and alkaline intrusions, although it never occurs in large quantities. Because of their enrichment in incompatible elements, carbonatites and alkaline rocks have also been increasingly used by isotope geochemists to study mantle evolution processes leading to continental magmatism and to track the pathways of lithospheric recycling. For both practical and academic applications, it is important to understand the timing of carbonatite and alkaline magmatism relative to such geodynamic processes as plate collisions, rifting, crustal upcoming.
Considering its potential U-Pb dating and perseverance later alteration as well LREE-enrichment, in situ laser ablation is considered as the most suitable method to measure their U-Pb and Sm-Nd isotopic compositions. Twenty-seven Ti-bearing andradite samples from thirteen typical carbonatite and/or alkaline intrusions in Prairie Lake and Ice River, Canada, Magnet Cove, USA, Alnö, Sweden, Fen, Norway, Ozernaya and Ural, Russia, Zijinshan and Fanshan, China, Tamazert, Morocco, San Ieo, Italy, Kaiserstuhl, Germany, Schaffhausen, Switzerland, were conducted for major, trace, U-Pb and Sm-Nd measurement using Electron microprobe (EPMA) and laser ablation (multicollector) inductively coupled plasma mass spectrometer (LA-(MC)-ICP-MS). Based on development of several in-house Ti-bearing andradite reference materials (PL34, IR18, MC15) demonstrates that precise and accurate U-Pb ages can be obtained after common Pb correction. Moreover, we obtained a reliable in situ Sm-Nd isotopic data because of the relatively moderate LREE content in our samples. These results will have significant implications for understanding the genesis of carbonatite or alkaline intrusion related to metallogenic geochronology and ore deposits research.
How to cite: Yang, Y.-H., Wu, F.-Y., Zhao, H., Xu, L., Huang, C., Wu, S.-T., Xie, L.-W., and Yang, J.-H.: U–Pb dating and Sm–Nd isotopic measurement of Ti–bearing andradite: Reference material development and in situ applications by LA-(MC)-ICP-MS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6557, https://doi.org/10.5194/egusphere-egu26-6557, 2026.
Monazite U–Th–Pb ages are commonly coupled with Y and heavy rare earth element (HREE) contents to link reactions, particularly those involving the formation and breakdown of garnet, with pressure–temperature (P–T) paths to constrain and uncover orogenic processes. This link assumes that changes in garnet modal abundances reflect changes in P–T and no other processes. Here we show that protracted and cryptic fluid-driven dissolution-reprecipitation of garnet and monazite disturbed the P–T–time(t) relationship between these two minerals.
We collected samples of metapelitic schists from the Yardoi gneiss dome, southern Tibet. The central portion of the Yardoi dome comprises orthogneiss and metapelites intruded by Eocene (43–35 Ma) to Miocene (17 Ma) granitoids, providing a critical window investigate fluid–rock interaction in mid-crustal metamorphic rocks. Our data constrain prograde to peak metamorphism from 5.7 kbar and 550°C to 7.5–8.5 kbar and 650–750 °C, followed by retrograde metamorphism at 5.5–6.5 kbar and 650–700°C. Low Y+HREE monazite domains dated to 41–46 Ma indicate peak metamorphism in the presence of garnet at this time, whereas high Y+HREE contents between 23 and 15 Ma indicate the timing of garnet breakdown during isothermal decompression. These data indicate 20–30 Myr at 650–700°C, consistent with near complete resetting of garnet major element zoning in most samples.
One sample near the core of the dome displays atoll garnets along with biotite, muscovite, plagioclase, quartz, and rutile. Annuli of plagioclase, quartz, and biotite grains separate the garnet core from the rim. Monazite from this sample show a quasi-continuous age spread from 50 Ma to 19 Ma, with an increase in Y + HREE between 45 and 38 Ma, followed by a decrease after ~38 Ma. These data suggest a period of garnet breakdown followed by (re-)growth between 45 and 20 Ma. Phase diagram models show very limited variation in garnet modal abundance at >7 kbar and 600–700 °C, indicating that changes in P–T are unlikely to influence garnet modes. Additionally, there are no other phases like staurolite, which may have reacted with garnet.
We propose instead cryptic dissolution-reprecipitation of garnet. Maps of grossular content (XGrs) shows a pebbly texture with interconnected moats of low XGrs garnet surrounding islands of high XGrs garnet, whereas other endmember fractions show flat garnet cores and mantles with slight increases in spessartine at the rim. We suggest that garnet recrystallization was driven by the release of magmatic-hydrothermal fluids from nearby 43–35 Ma granite intrusions. We suggest that fluid-assisted recrystallization can generate age-composition trends that mimic monazite zoning patterns of P–T path controlled garnet breakdown or growth. Misinterpretations of such data would propagating significant errors into tectono-metamorphic reconstructions, emphasizing the necessity of microstructurally constrained petrochronology when interpreting monazite U–Th–Pb ages.
How to cite: Wang, D., Walters, J., Ding, H., and Kohn, M.: Decoupling of monazite petrochronology from P–T evolution during garnet hydrothermal dissolution–reprecipitation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9890, https://doi.org/10.5194/egusphere-egu26-9890, 2026.
In situ garnet U-Pb geochronology by laser ablation-inductively coupled mass spectrometry (LA-ICPMS) is a powerful tool for rapid and high-spatial resolution dating of metamorphic pressure-temperature–time histories. Yet, the substitution of U and Pb into the structure of common pyralspite garnet and its influence on diffusion and potential age-resetting is poorly constrained. Studies by Mezger et al. (1989), Burton et al. (1995), and Dahl (1997) estimate U-Pb system closure temperatures in garnet of >800 °C. Similarly, Shu et al. (2024) proposed a closure temperature of >1100 °C but suggested that recrystallization may have reset some garnet U-Pb ages. However, there is little information on how dynamic processes, such as recrystallization, may impact the closure of the U-Pb system in garnet.
Here we examine the impacts of garnet recrystallization on U-Pb ages by examining ultrahigh-temperature (UHT) crustal xenoliths from the southwestern USA and northern Mexico. These metapelitic granulites experienced isobaric heating at >900 °C between 36 and 30 Ma and UHT conditions were maintained until eruption at <1 Ma (Droubi et al., 2024; Cipar et al., 2020; 2024). Garnet trace element zoning shows diffusively reset growth zoning overprinted by island-moat structures, which formed via melt-driven loss of REE and HFSE along now-healed fractures (Droubi et al., 2024). Zircon HREE depletions and ages suggest garnet initially formed at ca. 30 Ma, whereas diffusion modeling indicates that garnet island-moat structures formed rapidly <1 Myr before eruption (Droubi et al., 2024; Cipar et al., 2020; 2024). Our in situ U-Pb garnet ages, as measured by split-stream LA-MC-ICPMS, range from 4.6 ± 2.3 Ma (2s) to 1.77 ± 0.32 Ma (2s). The corresponding trace element data show decreasing U contents with decreasing LREE and HFSE, consistent with significant (but partial) resetting of U contents during the formation of the island-moat structures. In contrast, Pb contents show no trends with REE and HFSE. These data, combined with the overlap of our U-Pb ages with the eruption age of the magmas that entrained the xenoliths, are consistent with complete resetting of Pb contents during melt-garnet interaction. Overall, we demonstrate that garnet ages are susceptible to (near-)complete resetting via dynamic open-system processes.
Burton et al. (1995). Earth Plan. Sci. Lett. 133, 199–211.
Cipar et al. (2020). Nat. Geosci. 13(11), 758–763.
Cipar et al. (2024). Geochem. Geophys. Geosys. 25(7), e2023GC011177.
Dahl (1997). Earth Plan. Sci. Lett. 150, 277–290.
Droubi et al. (2024). JGR Solid Earth 129, e2024JB029138.
Mezger et al. (1989). Contrib. Min. Pet. 101, 136–248.
Shu et al. (2024). Contrib. Min. Pet. 179 (49).
How to cite: Walters, J. B., Millonig, L. J., Beranoaguirre, A., Smye, A. J., Garber, J. M., Gerdes, A., and Marschall, H. R.: Garnet U-Pb ages reset during ultrahigh temperature melt-rock interaction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10272, https://doi.org/10.5194/egusphere-egu26-10272, 2026.
One of the principles of Geochronology states that below a certain temperature (i.e. closure temperature), a system has cooled so that daughter isotopes no longer diffuse out of the mineral, and the geochronometer starts recording the time. However, there are multiple examples in the literature in which these geochronometers have been totally or partially reopened by subsequent geological events.
Accepting that transport in the host magma is too short-lived to thermally affect its xenolith cargo, in this contribution, we have studied the effect on the Lu-Hf and U-Pb systems of pre-entrainment percolation of high-temperature kimberlite melts, which is known to result in heating and precursory metasomatism of cratonic lithospheric mantle [e.g. 1]). We do so by analysing garnet from kimberlite‐borne eclogite xenoliths from the Namaqua‐Natal Fold Belt, at the southwestern Kaapvaal craton margin, which was affected by the 1.2-1.0 Ga Namaqua-Natal orogeny, whereas the kimberlites were emplaced in the Cretaceous ([2,3] and references therein). The xenoliths yielded emplacement pressures and temperatures of 1.7±0.4 GPa and 815-1000 oC, respectively ([2]). The analyses were done by LA-ICPMS for both Lu-Hf and U-Pb systems.
The results obtained for each of the geochronometers are different and not comparable. On the one hand, the U-Pb analyses result in a relatively precise Cretaceous age, similar in all samples within the uncertainty, consistent with a complete reset during interaction with kimberlite melts and/or the eruption. On the other hand, the Lu-Hf ages show a wide range of ages, from the Mesoproterozoic to the Cenozoic, in many cases with a large uncertainty. This I) may imply a partial reset of Hf during secular cooling and/or the heating produced by kimberlite melts, II) it may be associated with the higher closure temperature for the Lu-Hf system.
References:
[1] Fitzpayne et al. (2020) Lithos 370-371: 105595; [2] Le Roex et al. (2020) J. Petrol. 61: egaa040; [3] Aulbach S et al. (2024) J. Geophys. Res. Solid Earth 129: e2023JB027894.
How to cite: Beranoaguirre, A., Aulbach, S., Millonig, L. J., Kutzschbach, M., Le Roex, A., Tinguely, C., and Gerdes, A.: Effect of kimberlite melts on garnet U-Pb and Lu-Hf geochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22769, https://doi.org/10.5194/egusphere-egu26-22769, 2026.
The Orlica-Śnieżnik Dome is located in the NE part of the Bohemian Massif within the Sudetes, forming part of the European Variscan Belt. It comprises mostly orthogneisses, that host lenses of ultrahigh-pressure (UHP) eclogites and granulites. Peak-pressure metamorphic conditions recorded by these rocks have previously been estimated at 2.9–3.2 GPa and 750°C–830°C, based on thermodynamic modelling, conventional geothermobarometry, and Zr-in-rutile thermometry.
In this contribution, we present preliminary U-Pb zircon ages and trace element characteristics from two localities, Bielice and Nowa Wieś. The analysed zircons are mostly isometric or slightly elongated. Their internal structure was documented using back-scattered electron (BSE) and cathodoluminescence (CL) imaging prior to analysis. Zircons from Nowa Wieś predominantly display fir-tree and sector zoning patterns, whereas those from Bielice are mainly characterized by irregular and diffuse (aurora-light) zoning. Some grains from both localities contain possible inherited cores. Zircons from both localities show flat HREE patterns, a slight positive Ce anomaly, and no Eu anomaly. These features support the interpretation that zircon growth occurred under HP condition, contemporaneous with the eclogite-facies assemblage. Metamorphic zircon ages from Bielice cluster at 338.3 ± 3.4 Ma, whereas those from Nowa Wieś yield an age of 341.5 ± 3.4 Ma.
This project was supported by the Polish National Science Centre (UMO-2024/53/N/ST10/03586).
How to cite: Nowak, M., Szczepanski, J., and Anczkiewicz, R.: U-Pb zircon geochronology of coesite-bearing eclogites from the Orlica-Snieznik Dome (SW Poland) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19270, https://doi.org/10.5194/egusphere-egu26-19270, 2026.
Understanding the emplacement timescales of the Cornubian Batholith is important due to the association of widespread mineralisation that is spatially and temporally linked to the magmatism. Historically, dating has been focussed on xenotime and monazite which established the magmatism to have occurred from ~295-275 Ma (Chen et al., 1993, Chesley et al., 1993). However, these minerals are less precise for dating due to issues with low U/Pb ratios and inability to perform chemical abrasion. Our project aims to build a temporal framework for the formation of nested plutons by utilising high precision zircon U-Pb dating on the Variscan S-type Cornubian Batholith of southwest England.
To minimise issues of inheritance, cathodoluminescence scanning electron microscope imaging (CL-SEM) was used to identify inherited cores and fractures/inclusions within zircon. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was then completed on cores and rims of zircon, with the aim of selecting the best zircon crystals for further chemical-abrasion isotope-dilution thermal-ionisation mass spectrometry (CA-ID-TIMS) analysis. The LA-ICP-MS data confirmed the complicated geochronological history, with issues of inheritance and Pb-loss ubiquitous across all sampled plutons. Whilst an accurate and precise emplacement age could not be identified based on the spread of data, most sampled plutons did show promising trends that could be related to peaks in magmatism within the currently established period of activity. Zircon rims were isolated in preparation for CA-ID-TIMS to minimise issues with inheritance.
Applying CA-ID-TIMS, 204Pb and 230Th corrections, and Bayesian modelling will improve precision with the aim of filtering out complicating effects to produce reliable emplacement ages for the main phases of Cornubian magmatism. Achieving accurate zircon U-Pb ages from S-type granites is both challenging and significant as it would open avenues for reinterpreting ages from difficult-to-date plutonic bodies, a potential milestone for U-Pb geochronology.
Bibliography
Chen, Y., Clark, A.H., Farrar, E., Wasteneys, H.A.H.P., Hodgson, M.J., Bromley, A.V., 1993. Diachronous and independent histories of plutonism and mineralization in the Cornubian Batholith, southwest England, Journal of the Geological Society.
Chesley, I., J.T., Halliday, A.N., Snee, L.W., Mezger, K., Shepherd, T.J., Scrivener, R.C., 1993. Thermochronoloy of the Cornubian batholith in southwest England: Implications for pluton emplacement and protracted hydrothermal mineralization, Geochimica et Cosmochimica Acta.
How to cite: Day, L., Mark, D., and Barfod, D.: Redefining the emplacement age of the Cornubian Batholith: applying Bayesian statistics to zircon U-Pb LA-ICP-MS data , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13084, https://doi.org/10.5194/egusphere-egu26-13084, 2026.
This project set out to temporally constrain Carboniferous (ca. 359-299 Ma) volcanic, magmatic, and interbedded sedimentary basins which host the important Midland Valley coal seams. We are interrogating rates of eruption and temporal variations in the magma source geochemistry to link these to palaeoclimate variability as recorded by these classic sedimentary successions.
Rifting of the Midland Valley, Scotland and synchronous short-lived volcanism (ca. 30 Myr) [7] is associated with the eruption of mildly alkaline olivine basalts and associated intrusive rocks (e.g. micro-gabbro, phonolite). Remnants of this volcanism are exposed across the Midland Valley, including the world-famous geological site, Arthur’s Seat, Edinburgh. Arthur’s Seat is a classic example of a volcanic cross section with approximately nineteen lava layers and numerous vents exposed and characterised [1, 6]. Previous mapping efforts established a stratigraphy for this Site of Special Scientific Interest (SSSI) landmark, constrained by interbedded palynological zones. This has since been succeeded by direct radio-isotopic dating including K-Ar and 40Ar/39Ar geochronological techniques [2, 3, 4]. The most recent published ages constrained the eruption and emplacement of the Arthur’s Seat volcano with a precision ranging between 0.18-1.40% [5, 6].
New high precision (<0.1%) ⁴⁰Ar/³⁹Ar geochronology on lavas and CA-ID-TIMS U-Pb zircon geochronology on intrusive rocks and explosive eruptions, has been completed in addition to a suite of geochemical and isotopic data (e.g. Nd, Sr and Pb isotopes; major and trace elements). New developments in sample preparation, mass spectrometry, standard mineral characterisation, and data reduction software have enabled significant refinement of the 40Ar/39Ar technique. For example, our re-examination of the Arthur’s Seat Volcanic Formation has obtained an improved precision, achieving eruption and emplacement ages ranging 0.018-0.052%.
Our integrated geochronologic, geochemical and isotopic data underpin a robust temporal framework that tracks the evolution of the magmatic system, places the volcano-sedimentary sequences within the global Geologic Time Scale, and constrains the ages of key fossil-bearing horizons. By directly linking the magmatism to sedimentary basin development through dating of intercalated tephras, we aim to deliver a high precision chronology for Carboniferous climate change and the evolution of flora and fauna within the Midland Valley. Our preliminary results represent an order of magnitude improvement in precision and, in some cases, are sufficient to allow Carboniferous climate variability to be examined at orbital timescales (<100 kyr).
References
[1] Clarkson, E. and Upton, B. (2007) Geological Magazine, 144(3), pp. 603–603.
[2] De Souza, H.A,. (1979) Geochronology of Scottish Carboniferous volcanism. Ph.D. University of Edinburgh.
[3] De Souza, H.A,. (1982) ‘Age data from Scotland and the Carboniferous Time Scale’.
[4] Fitch et al, (1970) Isotopic ages of British Carboniferous rock. Sheffield, 1967, (2), pp. 771–790.
[5] Monaghan, A.A. and Browne, M.A.E. (2010) British Geological Survey, pp. 41.
[6] Monaghan, A.A., Browne, M.A.E. and Barfod, D.N. (2014) Scottish Journal of Geology, 50(2), pp. 165–172.
[7] Upton et al, (2020) Scottish Journal of Geology, 56(1), pp. 63–79.
How to cite: Pegge, E., Mark, D., and Barfod, D.: Geochronology and geochemical evolution of Carboniferous volcanism in Scotland’s Midland Valley: Insights from Arthur’s Seat, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13082, https://doi.org/10.5194/egusphere-egu26-13082, 2026.
The PRIN 2020 CASTLES Project focuses on studying mediaeval castles in Italy, particularly their chronology and dating through archaeometric analysis of castles walls mortars. The project is based on a multidisciplinary approach and aims at establishing a new chronology for the construction sites of incastellamento (11th-12th centuries).
A multidisciplinary team integrated their expertise into exploring the subject from multiple perspectives. The team consists of archaeologists and historians (respectively the Universities of Siena and Turin), geologists and conservation scientists (University of Florence), and physicists and archaeologists (University of Campania "Luigi Vanvitelli"). The group selected several sites across three regions of Italy (Piedmont, Liguria and Tuscany). The criteria for selecting the castles were: chronology, state of conservation, historical context, available historical and archaeological data, significant historical relevance. Before starting the sampling of the walls structures mortars, and proceeding to the characterization and dating, it was of fundamental importance to geolocate the castles. This is basilar to understand the geology of the areas where the castles were located and be able to identify the supply sources of the raw materials used by workers to build them. The study was carried out by researching geological maps, aerial photographs, drone images, and scientific publications concerning each castle’s area of the Piedmont, Liguria, and Tuscany regions, as well as sampling rocks of outcropping and constituting the walls. Minero-petrographic and chemical characterization of rock and mortar samples were performed, using X-Ray Diffraction Powder (XRPD), Polarized Light Microscopy (PLM) and Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS). The mineralogical and petrographical analyses of the rocks from each castle area were then compared with the components constituting the mortars (aggregate and binder) from the same castles, to identify correlations. It is essential to establish whether the materials used by the workers were sourced locally or from elsewhere. The results of this first step of the research showed that the raw material used in the realization of Ligurian and Tuscany castles was local. The origin of the rocks used to produce lime in Piedmont's castles is uncertain. In fact, limestone outcrops are very rare in the north of the region. Beyond dating, the analysis of raw materials provides important insights into medieval building organization, showing that most of studied castles relied on local geological resources, while changes in supply areas may reflect settlement expansion and/or a different and more complete organization of the sites of incastellamento.
How to cite: Intrieri, E., Pecchioni, E., Calandra, S., Garzonio, C. A., Salvatici, T., Lubritto, C., Mantile, N., Giacometti, V., di Cicco, M. R., Bellato, G., Provero, L., Fiore, A., Arrighetti, A., Buonincontri, M. P., Bardi, A., and Bianchi, G.: The Times of Castles Project: A Combined Study of Rocks and Mortars for Geological Provenance, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12199, https://doi.org/10.5194/egusphere-egu26-12199, 2026.
The Ag-Au (Cu,Pb,Zn) San Pedro epithermal system at Andacollo, Argentina, has been dated using 39Ar-40Ar together with Sr and Pb stepwise leaching. A precondition for multi-isotope analysis was a very detailed petrographic study of 12 hydrothermal pulses. Element maps were obtained by SEM-EDS on three thin sections from two drillcores, DHA-30 and -35. Twelve samples for isotope analyses, weighing ca. 2-10 mg, were cut with a steel blade from the analyzed thin sections, intentionally collecting "fresh" paragenetic adularia mantled by secondary alteration products to different degrees, in order to constrain the alteration trends in the Ar, Sr and Pb isotopic systems. Nine were analyzed by 39Ar-40Ar step-heating and three were step-leached [1] measuring both Sr and Pb isotopic compositions.
The Ar results demonstrate a plurality of alteration phases. A broad correlation trend between Cl/K (which should be zero in fresh feldspars) and step ages confirms the variable mass balance between primary adularia and secondary sericite, smectite, chlorite, kaolinite, and apatite. The end-members of the alteration trends observed in the scattered Ca/K-age correlation are different from those of the Cl/K-age correlation, requiring ≥ 4 compositionally different alteration phases. A regression to zero Cl/K in the three DHA-30 aliquots indicates that the primary adularia is 77±6 Ma old (2 sigma), consistent with cutting relations with dacitic dykes. The saline fluid inclusions, observed in different thick sections of the same cores, were decrepitated at low furnace temperature giving a very high 38Ar/39Ar ratio and an 40Ar*/Cl ratio of 7.7×10-5, the same order of magnitude as the 40Ar*/Cl ratio measured by Turner in fluid inclusions from Cornwall [2], whereby primary and secondary fluid inclusion in Andacollo have different 40Ar*/Cl ratios.
The six DHA-35 aliquots also show a broad Cl/K-age correlation; Cl/K ratios are higher, indicating a higher overall contamination. The extrapolated adularia age, 85±13 Ma, is statistically indistinguishabe from DHA-30.
The three Sr-Pb leach fractions gave alteration signatures very distinct from the adularia proper, both in Sr and Pb. The signature of the DHA-30 alteration is different from DHA-35. The Sr, and especially Pb, signature of both alteration fluids is very radiogenic, i.e. compatible with circulation through old country rocks. The host rocks are Carboniferous; however, significant inherited and detrital zircon contributions of Eo- to Mesoproterozoic age have been reported in both volcaniclastic and sedimentary rocks respectively [3,4]. This suggests the reworking of a Proterozoic basement, and hence a contribution to the isotopic signature of the analysed hydrothermal minerals.
The compositional and isotopic differences between the two drillcores are compatible with, but not proof of, a long-lasting alteration history as documented in other large ore deposits [5,6].
[1] Villa & Hanchar (2013) Geochim. Cosmochim. Acta 101, 24-33
[2] Turner (1988) Geochim. Cosmochim. Acta 52, 1443-1448
[3] Dicaro et al (2024) J. South American Earth Sci 148, 105158
[4] Pons et al, in preparation
[5] Kang et al (2020) Ore Geol. Rev. 122, 103527, 1-23
[6] Virmond et al (2024) Contrib. Min. Petrol. 179, 88
How to cite: Dicaro, S., Villa, I. M., and Pons, M. J.: Multi-isotopic chronology of the polygenetic San Pedro epithermal vein system, Andacollo Mining District, Argentina, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8286, https://doi.org/10.5194/egusphere-egu26-8286, 2026.
Large-scale strike-slip structures in the northeastern Tibetan Plateau, such as the West Qinling Fault, have accommodated the northeastward extrusion of the plateau crust, thereby recording its outward growth. However, the Cenozoic tectonic evolution of the West Qinling Fault remains incompletely understood. In this study, we integrate new and published apatite (U-Th)/He thermochronology with exiting sedimentary and geomorphological records to refine the exhumation history of the West Qinling in response to the kinematic evolution of the West Qinling Fault. The combined apatite (U-Th)/He dataset and thermal history modeling reveal two significant episodes of accelerated exhumation in the West Qining during the Eocene (~44–36 Ma) and the Miocene (~17–10 Ma). We attribute the Eocene exhumation to enhanced thrusting along the West Qinling Fault, representing a direct far-field response to the India-Asia collision. In contrast, the Miocene exhumation is linked to oblique-slip motion along the West Qinling Fault, marking a kinematic transition of the fault from thrust- to strike-slip-dominated deformation since the middle Miocene. Integration of our findings with geophysical, sedimentary, and petrological evidence suggests that this kinematic change was caused by a rheological weakening of the lower crust due to localized asthenospheric upwelling. The synchronous kinematic shift along the East Kunlun Fault, along with its similar deep lithospheric structure beneath the Hoh Xil region, implies a genetic link between the West Qinling and East Kunlun faults. We propose that localized asthenospheric upwelling thermally weakened the lower crust beneath both fault systems, thereby driving the kinematic shift during the middle Miocene. This analogy underscores the potential major role of small-scale asthenospheric upwelling-induced thermal weakening of the lower crust in affecting surface deformation during the late stage of orogenic plateau formation.
How to cite: Guo, C., Zhang, Z., Xiao, W., Malusà, M., von Hagke, C., Wu, L., Heberer, B., Friedrichs, B., Wang, N., Xiang, D., and Grasemann, B.: Eocene thrust vs. Miocene strike-slip: Kinematic transition of the West Qinling Fault driven by localized asthenospheric upwelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5908, https://doi.org/10.5194/egusphere-egu26-5908, 2026.
The West Kunlun (WKL) orogen, a pivotal boundary on the western Tibetan Plateau, records the dynamic interplay between northward underthrusting Indian lithosphere and the Tarim craton. Despite its significance, the exhumation history and mechanisms of plateau growth in this region remain contentious. Here, apatite fission-track (AFT) and (U-Th)/He (AHe) thermochronology data from three bedrock elevation transects across the WKL were used to refine the Miocene exhumation processes in the region. Our results reveal a regionally consistent two-phase acceleration in late Miocene exhumation at ca. 11–10 and ca. 7–6 Ma. Integration with regional thermochronologic, magmatic, and seismic data shows a systematic younging of cooling ages and (ultra)potassic magmatism toward the WKL, alongside increasing exhumation rates. These trends reflect outward plateau expansion driven by progressive indentation of the Indian plate into Asia. This culminated at ca. 11–10 Ma, when the cratonic Indian slab directly impinged the Tarim craton, as evidenced by rapid surface uplift and the formation of ca. 10 Ma and younger (ultra)potassic magmas in the WKL orogen. Our findings highlight the coupling between deep lithospheric processes and surface deformation, providing critical constraints on the timing of the India-Tarim collision and the mechanisms driving plateau growth along the northwestern margin of the Tibetan Plateau.
How to cite: Xiang, D.: Late Miocene rapid exhumation in the West Kunlun range: Insights into Tibetan Plateau growth and India-Asia lithosphericcollision, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9727, https://doi.org/10.5194/egusphere-egu26-9727, 2026.
Over the past 30 years, the number of low-temperature thermochronological data has grown, driven by advances in analytical techniques and the proliferation of studies. While generating and sharing these data with the scientific community presents the initial challenge, a second appears during their interpretation through inverse modelling. While performing joint data inversion on few samples is common, scaling this process to larger datasets (>50 samples) remains rare.
In recent years, several research teams have addressed the data sharing challenge by standardizing data-sharing formats (Flowers et al., 2023b, 2023a) and developing dedicated platforms for low-temperature thermochronological data (lithodat.com). Here, we test a "large data-set inversion" approach using a large dataset from Madagascar.
Madagascar has been the focus of over 10 studies since the 1990s, producing a dataset of ~250 samples analysed using two methods ((U-Th)/He and fission track) across various minerals, including apatite and zircon. In this study, we exploited available data (201 AFT and 87 AHe) in a large-scale inversion using a preliminary spatial clustering version of the Bayesian thermal history modelling software, QTQt. The clustering approach follows that presented in Stephenson et al. (2006) but allows for trans-dimensional thermal history models. The approach tries to determine both the number of clusters (i.e. sample groupings) and the thermal histories in each cluster that can reproduce the observed data.
We present (very) preliminary results of this approach applied to the Madagascar dataset, that divide the data in 3 clusters. Although run for 6 weeks, we managed to do just a small number of iterations (<100), and the algorithm was not converged. The inferred 3 clusters are compared to Madagascar’s known tectono-morphological blocks, and the inferred time-temperature paths can then be tentatively assigned to these blocks, potentially offering new insights into the associated vertical dynamics of the island.
Flowers, R.M., Ketcham, R.A., Enkelmann, E., Gautheron, C., Reiners, P.W., Metcalf, J.R., Danišík, M., Stockli, D.F., Brown, R.W., 2023a. (U-Th)/He chronology: Part 2. Considerations for evaluating, integrating, and interpreting conventional individual aliquot data. GSA Bulletin 135, 137–161. https://doi.org/10.1130/B36268.1
Flowers, R.M., Zeitler, P.K., Danišík, M., Reiners, P.W., Gautheron, C., Ketcham, R.A., Metcalf, J.R., Stockli, D.F., Enkelmann, E., Brown, R.W., 2023b. (U-Th)/He chronology: Part 1. Data, uncertainty, and reporting. GSA Bulletin 135, 104–136. https://doi.org/10.1130/B36266.1
Stephenson, J., Gallagher, K., & Holmes, C. (2006). A Bayesian approach to calibrating apatite fission track annealing models for laboratory and geological timescales. Geochimica et Cosmochimica Acta, 70(20), 5183-5200.
How to cite: Derycke, A., Large, E., and Gallagher, K.: Towards large-scale low-temperature thermochronological data inversion: an assessment using a dataset from Madagascar , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18783, https://doi.org/10.5194/egusphere-egu26-18783, 2026.
Thermochronology provides powerful tools for reconstructing Earth’s thermal and tectonic history. Among low-temperature thermochronometers, zircon (U–Th)/He (ZHe) dating has gained particular importance due to its sensitivity to deep-time thermal events, enabling tight temperature constraints even for thermal histories that span billions of years.
Helium diffusivity in zircon is strongly controlled by radiation-damage accumulation. This causes complex diffusion behaviour and a wide range of effective closure temperatures especially in (meta-)sedimentary rocks, where detrital zircons share their post-depositional thermal history but differ in provenance age and uranium content, leading to variable radiation-damage and annealing histories.
The widely used zircon radiation damage accumulation and annealing model (ZRDAAM; Guenthner et al., 2013) predicts complete resetting of ZHe ages for samples heated above ~200 °C during burial. Consequently, highly dispersed ZHe datasets in sedimentary rocks are commonly interpreted as reflecting mixed detrital populations and limited heating below this threshold. However, this interpretation remains largely untested against natural field laboratories.
In this study, ZHe closure and annealing is re-investigated based on two field areas with independently constrained thermal histories: (1) the Austroalpine Drau Range and adjacent Southalpine units and (2) the Helvetic Glarus Alps. Peak temperatures in these regions are well defined by vitrinite reflectance, Raman spectroscopy of carbonaceous material, Kübler-Index and fluid inclusion data as well as by metamorphic assemblages. In both areas, ZHe data systematically conflict with model predictions. The Austroalpine and Southalpine (meta-)sedimentary units targeted within this study experienced upper-diagenetic to low-grade metamorphic conditions (T>200 °C), but ZHe ages are largely not reset and show strong dispersion, contrary to ZRDAAM expectations. Combined ZHe–U–Pb double dating confirms substantial differences in pre-depositional provenance ages, but this age variation cannot explain the obvious difference to modelled age predictions.
A similar pattern is observed in the Glarus Alps, where peak metamorphic temperatures range from diagenesis to greenschist facies. ZHe ages show a systematic younging trend but retain large single-grain age dispersion and partially inherited ages even under very low-grade metamorphic conditions.
Results demonstrate significant helium retention in zircons at temperatures above 200 °C and reveal limitations of our understanding of the ZHe system. Interpreting dispersed ZHe datasets solely in terms of detrital inheritance fails to explain field constraints. Ongoing work combining U-Pb-He double dating with cathodoluminescence imaging, Raman spectroscopy, and spatially resolved U-Pb and isotopic mapping aims to identify the mechanisms responsible for this behavior and to improve the interpretation of ZHe data in sedimentary and remain-grade metamorphic rocks.
Reference:
Guenthner, W. R., Reiners, P. W., Ketcham, R. A., Nasdala, L., & Giester, G. (2013). Helium diffusion in natural zircon: radiation damage, anisotropy, and the interpretation of zircon (U-Th)/He thermochronology. American Journal of Science, 313(3), 145-198. ://WOS:000319306100001
How to cite: Heberer, B., Rahn, M., Dunkl, I., Lünsdorf, K., Neubauer, F., and Rantitsch, G.: Field constraints on zircon (U-Th)/He closure from the European Alps, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14110, https://doi.org/10.5194/egusphere-egu26-14110, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 3
EGU26-2274 | Posters virtual | VPS25
Geochemical and Geochronological approaches of Baskil Dikes (Elazığ, Eastern Turkey): Discrimination between the Late Cretaceous Continental and Oceanic Arc-related Magmatism in the Southern NeotethysThu, 07 May, 14:21–14:24 (CEST) vPoster spot 3
The Southeast Anatolian Suture Belt hosts the oceanic and continental remnants of the southern Neotethyan realm. During the Late Cretaceous, the southern Neotethyan domain experienced an Andean-type magmatism on its northern continental margin (the Tauride-Anatolide Platform), characterized by the Baskil Magmatics. The plutonic part of this unit is intruded by numerous dikes, which are the primary focus of this study. The U-Pb zircon dating of the dikes and their granodioritic host rocks indicates that their emplacement occurred within a narrow interval, between 81-79 Ma. The dikes vary chemically from basalt to dacite, while the host rocks range from andesitic to dacitic. On the normal mid-ocean ridge (N-MORB)-normalized plots, all samples exhibit negative Nb anomalies. Trace element systematics reveals that this dike system is chemically heterogeneous, consisting of five distinct chemical types. The elemental and isotope ratios indicate varying contributions from depleted and enriched components. All chemical types, with relative Nb depletion, suggest incorporation of slab-derived and/or crustal additions. This interpretation is further supported by the EM-2-like Pb isotopic ratios. Based on the variability in elemental and isotopic composition, this intrusive system appears highly heterogeneous, likely due to the combined effects of mantle source, crustal contamination, and fractional crystallization. The bulk geochemical characteristics of the studied dikes and their host rocks suggest that these intrusives formed at a continental arc. Considering the available paleontological and geochronological age data, it appears that the intraoceanic subduction and continental arc magmatism in the Southern Neotethys occurred simultaneously; the former created the Yüksekova arc-basin system, whereas the latter formed the Baskil Arc.
Note: This study was supported by project Fübap-MF.15.12.
How to cite: Ural, M., Sayit, K., Koralay, E., and Göncüoglu, M. C.: Geochemical and Geochronological approaches of Baskil Dikes (Elazığ, Eastern Turkey): Discrimination between the Late Cretaceous Continental and Oceanic Arc-related Magmatism in the Southern Neotethys, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2274, https://doi.org/10.5194/egusphere-egu26-2274, 2026.
EGU26-2243 | ECS | Posters virtual | VPS25
Post-mineralization exhumation of gold deposits on the northern margin of the North China Craton: constraints from low-temperature thermochronologyThu, 07 May, 14:27–14:30 (CEST) vPoster spot 3
Low-temperature thermochronology provides key constraints on the post-mineralization exhumation and preservation of orogenic gold deposits. In this study, we investigate the exhumation histories of the Anjiayingzi and Jinchanggouliang gold deposits, located respectively in the Kalaqin metamorphic core complex (MCC) and the Nuluerhu magmatic dome within the Chifeng–Chaoyang metallogenic belt on the northern margin of the North China Craton.
Both deposits formed in the Early Cretaceous (~130 Ma), but at significantly different depths (5.6–7.1 km for Anjiayingzi and 1.0–2.6 km for Jinchanggouliang), and are currently exposed at the surface, implying differential post-mineralization exhumation. Zircon and apatite (U–Th)/He and fission-track analyses were conducted on ore-hosting rocks to reconstruct cooling and exhumation histories. Combined age–elevation relationships and thermal history modeling reveal that the Anjiayingzi deposit experienced multi-stage, rapid exhumation totaling ~6.75 km since mineralization, with the most intense exhumation occurring between 130 and 80 Ma. In contrast, the Jinchanggouliang deposit underwent slower and more limited exhumation, with a total exhumation of ~2.50 km over the same period.
The contrasting exhumation histories coincide with an Early Cretaceous regional extensional regime affecting the northern margin of the North China Craton. We suggest that tectonic setting plays a first-order role in controlling post-mineralization exhumation. Deposits hosted within MCCs are characterized by rapid extensional denudation related to detachment faulting, whereas deposits hosted in magmatic domes are mainly exhumed through regional uplift and surface erosion. These results emphasize the importance of structural architecture in governing the exhumation, preservation, and exposure of gold deposits in extensional orogenic systems.
How to cite: Li, A. and Fu, L.: Post-mineralization exhumation of gold deposits on the northern margin of the North China Craton: constraints from low-temperature thermochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2243, https://doi.org/10.5194/egusphere-egu26-2243, 2026.
