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Zircon fissiona??track and Ua??Pb double dating using femtosecond laser ablationa??inductively coupled plasmaa??mass spectrometry: A technical note
摘要： We present a new LA–ICP–MS system for zircon fission-track (FT) and U–Pb double dating, whereby a femtosecond laser combined with galvanometric optics simultaneously ablates multiple spots to measure average surface U contents. The U contents of zircon measured by LA–ICP–MS and standardized with the NIST SRM610 glass are comparable to those measured by the induced fission track method, and have smaller analytical errors. LA–ICP–MS FT dating of seven zircon samples including three IUGS age standards is as accurate as the external detector method, but can give a higher-precision age depending on the counting statistics of the U content measurement. Double dating of the IUGS age standards gives FT and U–Pb ages that are in agreement. A chip of the Nancy 91500 zircon has a homogeneous U content of 84 ppm, suggesting the possibility of using this zircon as a matrix-matched U standard for FT dating. When using the Nancy 91500 zircon as a U standard, a zeta calibration value of 42–43 yr cm?2 for LA–ICP–MS FT dating is obtained. While this value is strictly only valid for the particular session, it can serve as a reference for other studies.
关键词： dating,femtosecond laser,U–Pb,fission track,zircon,LA–ICP–MS
更新于2025-09-23 15:21:01
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An Image Mapping Approach to U-Pb LA-ICP-MS Carbonate Dating, and Applications to Direct Dating of Carbonate Sedimentation
摘要： We present a new approach to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of carbonates based on selection and pooling of pixels from 2D elemental and isotopic ratio maps. This image mapping technique is particularly useful for targeting sub-domains in samples with complex geological histories. Key major and trace elements that are sensitive to detrital components, post-formational fluid ingress, mineralogical changes or diagenetic overprinting are measured along with the Pb and U isotopic data. Laser sampling is undertaken along successive linear rasters that are compiled into maps using the Monocle add-on for Iolite, with one pixel in the map corresponding to one time-slice of the time-resolved signal. These element, element-ratio and isotope ratio maps can be overlain over photomicrographs or SEM images to spatially link compositional data to textural and structural features. The pixels corresponding to likely homogeneous age domains can be isolated by applying appropriate selection criteria (e.g., Th<0.3 ppm, Mg/Ca<0.004) and pooled into pseudo-analyses using a proxy for the parent/daughter ratio (e.g., 207Pb/235U, 238U/208Pb) to retrieve the largest possible spread of the data points on isochron diagrams. The approach is best suited for analytical setups capable of rapidly or simultaneously scanning over a large mass range, and can yield a precision of ±1 % or better on quadrupole instruments depending on U concentration, 238U/204Pb and age of the sample. The sample-specific filtering criteria for selection and rejection of data and their rationale can be reported, resulting in more transparency with regards to data processing.
关键词： image mapping,carbonates,Monocle,Iolite,LA-ICP-MS,U-Pb dating
更新于2025-09-23 15:21:01
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Generating long chronologies for lacustrine sediments using luminescence dating: a 250,000 year record from Lake Tana, Ethiopia
摘要： The lakes of the eastern Africa Rift often contain great thicknesses of sediment that may provide continuous records of environmental change over decadal to million-year timescales. However interpretation of these changes is greatly compromised without a reliable chronology. Luminescence dating has not been used extensively in lacustrine settings; instead previous studies have often relied upon radiocarbon dating, using extrapolation beyond the upper limit of that technique, and employing opportunistic sampling of tephra and palaeomagnetic signatures where possible. This study from Lake Tana, Ethiopia, demonstrates that recent advances in luminescence methodology can provide long chronologies for lake sediments that are not dependent on the intermittent presence of dateable material, as is the case for radiocarbon and tephra-based methods. Specifically, this study generates luminescence ages that agree with independent chronology based on radiocarbon dating in the upper part of the core, and extends significantly beyond the range of radiocarbon dating to provide one of the longest independently dated lacustrine sediment records in eastern Africa, thus demonstrating the tremendous potential of luminescence for constructing lacustrine sediment chronologies over 100,000 year timescales.
关键词： OSL,Lacustrine sediments,Luminescence dating,Post-IR IRSL signal,Direct dating,Polymineral fine-grains,Palaeolimnology,Radiocarbon
更新于2025-09-09 09:28:46
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Roman traces in Germania magna: New thermoluminescence and pIRIR <sub/>290</sub> data from a lime kiln at Bergisch Gladbach, Germany
摘要： The applicability of a post-infrared infrared stimulated luminescence (pIRIR290) protocol and two different thermoluminescence (TL) protocols—a single aliquot regeneration (SAR) and a multiple aliquot additive dose (MAAD)—was tested on six polymineral fine-grain (4–11 μm) samples extracted from the wall remains of a Roman lime kiln and a Roman roof tile. These remains had been excavated close to Bergisch Gladbach, which was at that time part of Germania magna. For the pIRIR290 measurements, no dependence of De on first-stimulation temperature was detectable, and the standard first stimulation temperature at 50°C was adopted. Fading tests and dose-recovery tests were made for all samples. Background subtracted glow curves were recorded up to 480°C for TL after a preheat of 220°C for 120 s. A-values were determined for all TL and pIRIR measurements. The results for all three protocols were fairly consistent, and TL and pIRIR290 protocols are shown to be suitable to estimate reliable equivalent doses for the fired kiln walls. The resulting ages are in agreement with the expected time range—Roman Iron Age—and with independent age control provided by radiocarbon ages of animal bones and charcoal from the firing chamber.
关键词： pIRIR290,GERMANIA MAGNA,THERMOLUMINESCENCE,POLYMINERAL,ROMAN LIME KILN,FINE GRAIN,LUMINESCENCE DATING
更新于2025-09-09 09:28:46