Speleothems, such as stalagmites and flowstones, are invaluable archives of past environmental and climatic conditions due to their layered growth and suitability for precise 230
Advances in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) have largely focused on improving spatial resolution through progressively smaller laser spot sizes. Here, we explore the opposite end of the analytical limits by investigating the lower concentration limits of in-situ U–Pb geochronology in garnet. Using a Neptune Plus multi-collector ICP-MS equipped with seven ion counters, we developed an analytical workflow specifically designed for metamorphic garnet with ultra-low U concentrations (< 10 ng g−1). The method was used to date garnet from a wide range of ages and geological settings, including granulites, eclogites and hydrothermal demantoids. Uranium concentrations were exceptionally low, even below 1 ng g−1UUPb concentrations, but we have obtained precisions of ca. 5 %–6 % for garnet containing less than 1 ng g−1  U. In garnet with higher U concentrations or ages as old as the Archean, internal precision of ca. 1 % may be achieved. These results expand the applicability of in-situ garnet U-Pb geochronology to the vast majority of metamorphic garnet, providing a powerful new tool for constraining garnet growth, prograde metamorphism, and deep crustal evolution.
Thermochronology provides a unique perspective on the timing and magnitude of erosion during the generation of unconformities. Recently, thermochronology has been used to reinvigorate a long-standing debate about the origin of the Great Unconformity, a geological feature representing a period of missing time of almost a billion years from the stratigraphic record at the end of the Precambrian. Our ability to resolve thermal histories is fundamentally limited by how well we know parameters describing the temperature sensitivity of a thermochronometric system. The (U-Th)/He< 200–250 °C). Here we determine uncertainties in the Zircon Radiation Damage and Annealing Model (ZRDAAM, Guenthner et al. 2013) that describes changes in 4He diffusion kinetics as a function of radiation damage accumulation and annealing. We show that the dispersion in predicted zircon (U-Th)/HeMa
Interpreting thermochronological data of a partially reset detrital sample is challenging because its age distribution reflects a mixture of each grain's individual pre-depositional and the shared post-depositional thermal history. A promising approach to meet this challenge is combined geo- and thermochronological dating on the same grains. We present an algorithm for disentangling the pre- and post-depositional thermal histories using data from zircon
A noble-gas analysis line capable of accurate and precise measurements of small absolute amounts of 4He
Many geological processes influence or perturb the thermal state of the lithosphere. This presents a challenge for relating thermal history data modeled from thermochronometers such as apatite and zircon fission-track and (U–Th)
The use of in situ Rb–Sr geochronology has boomed in recent years following its implementation using LA-ICP-MS/MS technology, which enables fast, in situ analyses at the micron scale on selected minerals. The Rb–Sr geochronometer applied to micas is now commonly used to date the crystallization or cooling of metamorphic and magmatic rocks, based on the assumptions of a closed isotope system after passing the closure temperature and of a homogeneous Sr isotopic composition at the time of crystallization. In situ Rb–Sr geochronology applied to micas and related alteration products in geological contexts involving hydrothermal fluid circulation affecting micas after crystallization could provide a new way to decipher the timing and duration of fluid circulation in various settings such as mountain belts or sedimentary basins. The behavior and applicability of the Rb–Sr system in such contexts are, however, poorly understood, as the system may be partially reopened with differential redistribution of Rb and Sr at the grain scale. To test this hypothesis, we selected a case study related to unconformity-related U deposits from the Athabasca Basin (Canada), which formed through intense hydrothermal fluid circulation at the interface between crystalline basement and siliciclastic sedimentary rocks and represent archetypes of unconformity-related metal deposits. Muscovite grains from metamorphic and magmatic rocks were targeted across a range of alteration states, from hydrothermally unaltered to strongly altered domains. We focused on a specific hydrothermal alteration linked to the formation of hydrothermal illite and sudoite at the expense of metamorphic or magmatic minerals. In unaltered zones, muscovite displays variable but high Rb 
It is generally accepted that the commonly used fission track age equation accurately calculates the cooling age for apatite minerals when the cooling rate is fast. Nevertheless, it is used when the cooling rate is gradual, for example when the age of transition through the partial annealing window is to be estimated. Added age information is here obtained by inclusion of the length distribution of fully included near horizontal tracks. The tendency that the shortest tracks are the oldest ones, and the longest ones are the youngest enables the age dating of a given track by counting the number of shorter tracks, adding one, and dividing by the volumetric track generation rate. The difficulty is that the track length–age relation is blurred by the spread in lengths due to the inherent spread in fission decay energies, crystallographic anisotropy and observational uncertainties. The blurring can be reduced by mathematical deconvolution in which the blurring of tracks in annealing experiments is used. A previously given equation for the oldest track in each histogram column is mathematically further reduced. This paper presents a method where deblurring is first performed by projecting the observed track lengths on the mineral c-axis and then by deblurring using probabilistic least squares inversion. This leads to the extraction of several track ages with deviations for each deconvolved track length histogram. This information may be used to constrain the timing of tectonic events and provide the basis for calculation of past temperature.
We present high-resolution 10Be10Be10Be192.0±1.4) ka BP and (185.6±1.4) ka BP. A clear asymmetric structure is observed, with a rapid decline of the geomagnetic dipole, followed by a three-step recovery. Two dipole decreases of lower amplitude are also resolved in relation with the Pringle Falls Excursion (PFE), lasting from (218.5±1.90) to (206.0±0.8) ka BP, and the Mamaku Excursion (ME), identified at (242.0±0.3) ka BP, both showing an increase of the 10Be10Be
Cosmogenic nuclide surface-exposure dating (SED) is a rapidly growing tool in geoscience owing to its unrivalled potential for directly dating rock surfaces and thus the geomorphic and climatic events they represent. Fundamental to the efficacy of the SED method is reliable constraint of the in situ production rate, which is typically calculated via calibration experiments: cosmogenic nuclide concentrations are measured in surfaces for which the true exposure age is known independently, allowing the production rate to be derived (in atoms g−1 yr−1) for the specific calibration site. This value can then be extrapolated to distal field sites using numerical scaling methods designed to account for spatial and elevational differences in geomagnetic and atmospheric shielding. Thanks to successive and increasingly co-ordinated calibration efforts, production rate estimates for the most widely used cosmogenic nuclide, beryllium-10 (10Be), have improved in recent decades, with the majority converging on sea-level high-latitude (SLHL) values of ∼ 3.8–4.1 atoms g−1 yr−110Be concentrations from deglacial surfaces on the Redpoint Peninsula in north-west Scotland that were exposed during retreat of the last British ice sheet. By comparing the surface-exposure results from eight current 10Be production rates to local radiocarbon constraint for deglaciation, we (1) evaluate the viability of each production rate for this site and (2) report a maximum SLHL value of 3.925 ± 0.07 atoms g−1 yr−110Be production rate, calibrated against independently dated glacial landforms in the central Scottish Highlands, gives the best match with the 14C control and thus is appropriate for Late Pleistocene applications at these geomagnetic latitudes.
High-temperature contact metamorphism in the aureole of the 1322 Ma Makhavinekh Lake Pluton, Labrador, led to progressive consumption of 1850 Ma garnet formed during upper-amphibolite facies regional metamorphism that produced migmatitic paragneiss (Tasiyuak Gneiss). Biotite Rb–Sr isotope measurements were carried out in situ by laser ablation ICP-MS/MS allowing biotite in a variety of textural settings to be characterized. This natural laboratory provides important information about the nature of Rb–Sr closure temperature (Tc) as a function of textural setting in high-grade metamorphic rocks. Intact biotite inclusions armoured in garnet preserved in the outer aureole (>4 km from the contact) display a range of Rb–Sr isochron ages between ∼1850∼1322 Ma consistent with a zone of partial retention of Sr in biotite. Isotopic resetting in the outer aureole was controlled by microfractures in garnet that provided short-circuit diffusion pathways for redistribution of radiogenic Sr into plagioclase-bearing contact metamorphic assemblages; biotite inclusions isolated from microfractures retain 1850 Ma Rb–Sr isochron ages. Biotite grains falling along a ∼1322 Ma isochron attest to efficient intra- and intercrystalline Sr diffusion at T≥500 °C≥5 Myr. Samples in the central part of the contact aureole (3.7 to 1.1 km from the contact) contain partly resorbed biotite surrounded by contact metamorphic Opx + Crd coronal assemblages in addition to armoured inclusions in relict garnet. These display similar Rb–Sr behaviour to outer aureole samples with the exception that ∼1322 Ma biotite domains display higher
Post-infrared infrared stimulated luminescence (post-IR IRSL) signals from potassium feldspars are gaining prominence in both luminescence dating and luminescence-based sediment tracing techniques. To enhance the accuracy and reliability of these applications, it is essential to develop a comprehensive understanding of how post-IR IRSL signals undergo bleaching. While previous studies have explored post-IR IRSL bleachability using multi-grain approaches, a systematic single-grain investigation on modern analogues has not been conducted. In this study, we examined the bleaching behaviour of the post-infrared infrared stimulated luminescence signal measured at 200 °C (post-IR IRSL200) at the single-grain level in eleven modern floodplain samples from the tectonically active Southern Central Andes. Our study demonstrated considerable variation in the residual doses following 2 d of laboratory solar simulator bleaching across the sample set. This variability was evident not only between different samples but also among individual grains within the same sample. Thus, we evaluated the influence of bleaching duration, grain-specific geochemical composition, catchment-scale lithological variability, and the size of the natural dose on the laboratory-measured residual doses.Our laboratory bleaching experiments in which single grains were given a fixed regenerated dose of 30 Gy prior to solar simulator exposure showed similar post-IR IRSL200R2= 0.89) between residual dose and natural remnant dose, revealing dose-dependent bleaching efficiency and the presence of a negligible unbleachable component at the time of deposition. This relationship between residual dose and natural remnant dose also suggests that while the youngest samples (with low natural remnant dose) could reach zero residual dose, the relatively older samples (with more than 10 Gy of natural remnant dose) could show a significant amount of residual dose. By integrating insights on bleachability with the information on the unbleachable component and remnant doses derived from modern analogues, we highlight the limitations of correcting palaeodoses by directly using either residual or remnant doses and evaluate three context-sensitive correction strategies. Finally,
The Christiana Islands group consists of three at present uninhabited islands 20 km SW of Santorini, Aegean Sea, Greece, that are the subaerial remnants of the Christiana volcano. The age of the Christiana Islands has been unclear and has been previously assumed to have started around the same time as the emergence of Santorini (600 ka). Other studies, based on seismic reflection, have correlated volcanic deposits of the Christiana archipelago to Pliocene sedimentary layers. Five subaerial Christiana volcanic rocks of the Upper Lava formation cluster tightly between 2.57–2.69 Ma with relatively small uncertainties (0.02–0.03 Ma). One sample dated much younger: 133 ka; this obsidian from a pyroclastic deposit is most likely derived from the Middle Pumice Plinian eruption of Santorini. The 2.5–2.7 Ma age for Christiana volcano shows that all volcanic fields of the South Aegean Volcanic Arc (SAVA) were active around 3 Ma ago and started when oceanic crust arrived at 100 km depth below the SAVA volcanic fields after a long period of continental lithosphere subduction. The Christiana volcano was constructed when the local stress field showed NNE-SSW extension. During the transition from NNE-SSW to NW-SE extension the Christiana volcano became extinct and a period of >1.0 Ma with volcanic quiescence and/or low volcanic output followed until the start of submarine volcano Poseidon and present-day volcanic centres Santorini and Kolumbo.
Cosmogenic-nuclide surface exposure ages provide empirical data for validating models simulating the timing and pace of ice-sheet response to a warming climate. Increasing emphasis is being placed on obtaining exposure ages that both accurately constrain Holocene deglaciation and are precise enough to capture ice sheet change at the sub-millennial scale. However, longer-lived nuclides such as 10Be14C14C) is largely insensitive to nuclide inheritance pre-dating the last glacial maximum (LGM), and when combined with longer-lived nuclides can be used to constrain complex ice sheet histories over Holocene timescales. Here, we present new in situ 14C10Be14C–10Behttps://version2.ice-d.org/, last access: 29 March 2024). Our analysis reveals that neither variations in geologic setting nor modelled scenarios of subsurface nuclide production can explain the conflicting Mt Murphy ages. However, replicate in situ 14C14C2σ14C2σ14C
This study examines the feasibility of dating pluvial lake beach ridges using rock surface luminescence dating techniques. Dating pluvial lake highstands in the internally drained Great Basin of the United States helps us understand the timing of changes in precipitation and temperature patterns in western North America during the Late Pleistocene. The majority of highstand ages have relied on few radiocarbon ages of shell and/or charcoal sometimes coupled with luminescence dating of sand. Within our study area in the south-central Great Basin, luminescence ages of sand-size particles have successfully dated aeolian influxes of sand during arid intervals, but have not successfully dated the highstand beach ridges, the best preserved of which are largely gravel.Directly dating when these gravel clasts were last exposed to sunlight via luminescence is ideal but their limestone and volcanic lithologies prove challenging. Initial measurements from these lithologies show that feldspar luminescence signals are suited to single-aliquot regenerative (SAR) dose measurement protocols and show evidence for heterogeneous bleaching of rock surfaces. Polymineral extracts from dissolved limestone clast surfaces from Coal Valley that contain sufficient detrital sediment exhibit infrared signals measured at 50 °C (IR50) with low to moderate fading rates. Single-grain ages from detrital sediment from three clasts, calculated using the central dose model, are statistically consistent with the radiocarbon age estimate of the Pluvial Lake Coal highstand.Crushed slices from volcanic clasts from Cave Valley could be dated using a high-temperature (290 °C) post-infrared infrared stimulated luminescence (pIRIR) signal with a correction for fading. Many ages obtained from volcanic clast surfaces are observed to be several thousand years younger than the expected age of the ∼ 18–20 ka beach ridge. This suggests that the volcanic rocks have been exposed to light long after the pluvial lake highstand, likely because of bioturbation, and that their most recent burial occurred in response to climatically driven soil formation processes. Comparisons between age-depth profile plateau ages from inside volcanic rocks and independent age control suggest that gravel-sized volcanic rocks were small enough to have been bleached throughout their entire thickness in the pluvial lake beach environment and that pIRIR signals that record the time of beach ridge formation and subsequent soil formation during the Pleistocene-Holocene transition may be preserved within the rock sub-surface.This study develops novel dating approaches for challenging rock lithologies. Rock surface dating techniques for pluvial lake beach ridges in the Great Basin should be further developed with consideration of local bedrock type(s), clast size, sample collection and preparation methods, gravel bleaching processes in pluvial lake environments and the impact of soil development and bioturbation on study sites.
Low-temperature thermochronology provides a powerful means of extracting quantitative information on the thermal evolution of different tectonic settings from rocks exposed at the surface of the Earth. Geodynamic numerical models enable tracking the entire thermal structure of simulated tectonic settings throughout their evolution. Despite the highly complementary nature of these two approaches, few geodynamic modeling studies have used the thermal information in models to predict thermochronometric ages as a means of comparing model results with observational data. Here, we present Geodynamic Thermochronology (GDTchron): an open-source Python package designed to forward model large numbers of low-temperature thermochronometric ages from time–temperature paths output by geodynamic numerical models. This package uses existing techniques to estimate apatite
Bayesian modelling is often implemented in geochronology and its applications to geomorphology, archaeology, etc. The rationale behind such practices is the aim to improve robustness, precision and accuracy thanks to the use of prior knowledge regarding the studied sites, and in particular the order of samples constrained by stratigraphy. All chronological models tested in this study (OxCal, Chronomodel and BayLum) use the same mathematical model to handle stratigraphic constraints. However, this model has been shown to lead to estimation biases. First, this bias is illustrated with BayLum modelling on a high-resolution OSL dataset. Then, this paper compares statistical inferences obtained with the three above-mentioned modelling software on the Neolithic East mound of Çatalhöyük (Turkey). For this site, 49 radiocarbon ages were obtained with the aim to determine the start of occupations at this locality. Interestingly, age uncertainties are rather large, because of calibration curve plateaus. Therefore, the conditions for estimation biases are met. We discuss the behaviour of the different models and show that caution must be taken when modelling results are at odds with measurements. While OxCal, Chronomodel and BayLum are all affected by a spread in ages resulting from their common model of stratigraphic errors, Chronomodel suffers from a great loss of precision and OxCal, through the phase model, concentrates ages undesirably. We also conclude that the onset of occupations at Çatalhöyük was probably earlier than previously thought based on the OxCal model.
(U-Th-Sm) 
The dating of supergene copper minerals has been widely used as a proxy to investigate the evolution and onset of hyperaridity in the Atacama Desert. However, investigation of supergene copper mineralisation in the Atacama Desert has been restricted to two physiographic units favourable for the industrial extraction of copper: the Central Depression and the Precordillera. Furthermore, these studies dated the timing of supergene mineralisation by secondary non-copper minerals like alunite. In this study, we present new results of LA-ICP-MS U-Pb dating of chrysocolla from supergene deposits hosted in the western part of the Coastal Cordillera of northern Chile. The obtained U-Pb ages range from 8.0±1.20.045±0.027 Ma. Supergene mineralisation ages point to significantly reduced precipitation, necessary for leaching and mineral precipitation process, since the Late Miocene to Pleistocene in the Coastal Cordillera, later than the secondary supergene mineralisation ages from the Precordillera. The data point to repeated phases of sufficient moisture along the Coastal Cordillera that promoted chrysocolla mineralisation during the Pliocene and Pleistocene. We propose that due to the position of the study areas near the coastal escarpment, and the predominant hyperarid environment in this part of the Coastal Cordillera since at least the Mid-Miocene, pluvial periods and/or intensification of coastal fog events caused alternating phases of supergene activity.
The rate at which ice sheets erode rock and produce sediment is poorly known. Here, we use paired cosmogenic nuclides in both deglacial and modern sediment to understand better the efficacy with which the Quebec-Labrador Ice Dome (QLID) of the Laurentide Ice Sheet eroded bedrock and generated sand and boulders across the landscape of eastern Canada. We sampled deglacial sediment (esker and delta sand, n= 10), sediment from modern streams (n= 11), one bedrock outcrop, and a bedrock depth profile (n= 7), measuring concentrations of 10Be and 26Al in quartz isolated from all samples. We also collated published cosmogenic nuclide measurements of boulders and bedrock from eastern Canada (n= 237 samples), and using independent estimates of deglaciation timing, calculated initial nuclide concentrations when the material was exposed by the most recent deglaciation, between 6.3 to 15.2 ka.At the time of deposition, all 10 deglacial sand samples contained 10Be and 26Al, on average equivalent to several thousand years of surface exposure. The ubiquitous presence of 10Be and 26Al in eastern Quebec deglacial sediment is consistent with older-than-expected exposure ages for bedrock outcrops (n= 26 of 46 samples) and boulders (n= 65 of 192 samples) once covered by the QLID. Error-weighted averages of 26Al