Technical note: In situ U–Th–He dating by 4He ∕ 3He laser microprobe analysis

In situ U-Th-He geochronology is a potentially disruptive technique that combines laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with laser microprobe noble gas mass spectrometry. Despite its potential to revolutionize (detrital) thermochronology, in situ U-Th-He dating is not widely used due to persistent analytical challenges. A major issue is that current in situ U-Th-He dating approaches require that the U, Th, and He measurements are expressed in units of molar concentration, in contrast with conventional methods, which use units of molar abundance. Whereas molar abundances can be reliably determined by isotope dilution, accurate concentration measurements are not so easy to obtain. In the absence of matrix-matched U-Th concentration standards and accurate He ablation pit measurements, the required molar concentration calculations introduce an uncertainty that is higher than the conventional method, an uncertainty that is itself difficult to accurately quantify. We present a solution to this problem by using proton-induced 3He as a proxy for ablation pit volume and by pairing samples with a standard of known U-Th-He age. Thus, the U-Th-He age equation can be solved using relative rather than absolute concentration measurements. Pilot experiments show that the new method produces accurate results. However, it is prone to overdispersion, which is attributed to gradients in the proton fluence. These gradients can be measured, and their effect can be removed by fixing the geometry of the sample and the standard during the proton irradiation

Improved methods for high-precision Pb-Pb dating of extra-terrestrial materials

Dating meteoritic materials by the Pb–Pb isochron method depends on constructing linear arrays typically defined by mixtures of initial and radiogenic Pb after the removal of terrestrial contaminant Pb. The method also depends on minimizing the amount of laboratory Pb blank added to the sample during processing and analyses. With the aim to analyze smaller sample sizes and decrease processing times, we have devised a new method for the construction of isochrons using the stepwise dissolution of meteoritic materials that better defines reduced amounts of Pb blank, reduces the risk of random anomalous Pb contamination, and increases sample throughput. Samples are processed in a PFA Teflon™ pipette tip fitted with a frit inside a heated, sealed chamber that can be manually over-pressured to expel reagents directly into a PFA Teflon™ vial below. With four independent chambers, three samples can be processed simultaneously with a fourth position to assess the Pb contribution of the combined blank and spike for each step. The matched blank-spike Pb for each step provides a specific blank estimate for each step that ensures a more accurate correction for non-sample Pb and, therefore, reduces the uncertainty on each analysis. We assess the performance of this new method by reporting the results of dating a fragment of a chondrule from the well-characterized CBa chondrite Gujba and compare these results with previously published data for this meteorite. The improvements reduce the minimum sample sizes that can be successfully dated by the Pb–Pb method, an important development for size-limited materials such as small chondrules and samples returned from space missions

Oligocene-Early Miocene river incision near the first bend of the Yangze River: Insights from apatite (U-Th-Sm)/He thermochronology

The southeastern Tibetan Plateau is deeply incised by three parallel rivers, the Salween, the Mekong and the Yangtze. The river incision and surface uplift histories of this landscape are hotly debated. This study presents bedrock apatite (U-Th-Sm)/He data from a ~ 1800 m vertical profile, located near the first bend of the Yangtze River. Ages range from 20 to 30 Ma, indicating an Oligocene-Early Miocene phase of moderate river incision at a rate of ~ 0.10–0.18 mm/yr. This is considerably older than elsewhere in the region, but consistent with a previously proposed phase of Eocene surface uplift inferred from stable isotope geochemistry. We consider the implications of the new data under two different tectonic models. If the surface uplift and river incision resulted from lower crustal flow, the new results require such flow to have commenced at Oligocene-Early Miocene time rather than during the previously proposed Late Miocene. Alternatively, Oligocene to Early Miocene plateau growth might have resulted from transpressional deformation in the southeastern Tibetan Plateau

Climatic zonation and weathering control on sediment composition (Angola)

Complementary mineralogical and geochemical datasets on fluvial, beach and dune samples collected along the Atlantic margin of subequatorial southwestern Africa are used to investigate the relationships between provenance and climatic controls on sediment composition and to test the reliability of different geochemical and mineralogical weathering proxies as climatic indicators. The studied N/S-trending coastal region is characterized by strong latitudinal and inland climatic gradients, and thus represents an excellent natural laboratory in which to study the effects of climatic-induced weathering on sediment composition. Although the mineralogy and geochemistry of suspended-load muds closely reflects the different weathering intensities over both latitudinal and inland climatic gradients, the composition of mud and sand samples are strongly affected by sediment provenance. Consequently, weathering parameters such as the α Al E values (estimating the degree of depletion in element E relative to the UCC standard), display complex patterns of variation especially for sand samples. By assuming a typical order of bulk-sediment mobility Na > Ca > Sr > Mg > K > Ba≈Rb, anomalously high or low α Al values placing a specific element off the expected mobility order are considered as an indicator of source-rock control on sediment composition. The composition of detritus recycled from Meso-Cenozoic strata reflects the cumulative effect of successive sediment cycles, with recycling processes affecting to a different extent the diverse weathering proxies. In particular, α Al Na appears to be more strongly affected by recycling in muds than in sands. Among all mineralogical and chemical parameters, those that correlate best with rainfall in the drainage areas are α Al Na for sands, α Al Mg for muds and smectite content (only in areas of low rainfall). In the geological and geomorphological setting of SW Africa these proxies turn out to be better climate estimators than the classical weathering indices CIA or WIP. This case study reminds us to carefully consider source-rock control and mixing with recycled detritus when drawing inferences on climatic conditions based on weathering indices

Molecular cytogenetic characterisation of a mosaic add(12)(p13.3) with an inv dup(3)(q26.31 --> qter) detected in an autistic boy

BACKGROUND: Inverted duplications (inv dup) of a terminal chromosome region are a particular subset of rearrangements that often results in partial tetrasomy or partial trisomy when accompanied by a deleted chromosome. Associated mosaicism could be the consequence of a post-zygotic event or could result from the correction of a trisomic conception. Tetrasomies of distal segments of the chromosome 3q are rare genetic events and their phenotypic manifestations are diverse. To our knowledge, there are only 12 cases reported with partial 3q tetrasomy. Generally, individuals with this genomic imbalance present mild to severe developmental delay, facial dysmorphisms and skin pigmentary disorders. RESULTS: We present the results of the molecular cytogenetic characterization of an unbalanced mosaic karyotype consisting of mos 46,XY,add(12)(p13.3) [56]/46,XY [44] in a previously described 11 years old autistic boy, re-evaluated at adult age. The employment of fluorescence in situ hybridization (FISH) and multicolor banding (MCB) techniques identified the extra material on 12p to be derived from chromosome 3, defining the additional material on 12p as an inv dup(3)(qter --> q26.3::q26.3 --> qter). Subsequently, array-based comparative genomic hybridization (aCGH) confirmed the breakpoint at 3q26.31, defining the extra material with a length of 24.92 Mb to be between 174.37 and 199.29 Mb. CONCLUSION: This is the thirteenth reported case of inversion-duplication 3q, being the first one described as an inv dup translocated onto a non-homologous chromosome. The mosaic terminal inv dup(3q) observed could be the result of two proposed alternative mechanisms. The most striking feature of this case is the autistic behavior of the proband, a characteristic not shared by any other patient with tetrasomy for 3q26.31 --> 3qter. The present work further illustrates the advantages of the use of an integrative cytogenetic strategy, composed both by conventional and molecular techniques, on providing powerful information for an accurate diagnosis. This report also highlights a chromosome region potentially involved in autistic disorders

The source of Dalradian detritus in the Buchan Block, NE Scotland: Application of new tools to detrital datasets

Detrital zircons from four samples of upper Dalradian metasedimentary rocks from the Buchan Block in the NE Grampian Highlands of Scotland were analysed by laser ablation inductively coupled plasma mass spectrometry to establish their U–Pb age and trace element composition. The analysed grains (magmatic cores) mainly yield concordant ages ranging from Neoproterozoic to Eoarchaean. Kernel density plots of the data show pronounced peaks in the late Mesoproterozoic, Palaeoproterozoic and Neoarchaean eras. The data are indistinguishable from detrital zircon age spectra from Dalradian rocks elsewhere, an interpretation supported by application of a non-parametric multidimensional scaling algorithm, and are consistent with a Laurentian source. Similar to existing studies from other Dalradian rocks, the age spectra from the Buchan Block reveal an increase in the relative proportion of older detritus with time, suggesting derivation from late Mesoproterozoic (Grenville) then Palaeoproterozoic orogens before widespread exposure and denudation of their Archaean basement rocks. Application of a novel approach to estimate the most likely time of radiogenic-Pb loss indicates that some detrital zircon grains were affected by element mobility around 470–450 Ma as a result of Grampian orogenesis

The response to the COVID-19 pandemic: With hindsight what lessons can we learn?

The purpose of this paper is to put forward some evidence-based lessons that can be learned from how to respond to a Pandemic that relate to healthy living behaviours (HLB). A 4-step methodology was followed to conduct a narrative review of the literature and to present a professional practice vignette. The narrative review identified 8 lessons: 1) peer review; 2) historical perspectives; 3) investing in resilience and protection; 4) unintended consequences; 5) protecting physical activity; 6) school closures; 7) mental health; and 8) obesity. As in all probability there will be another Pandemic, it is important that the lessons learned over the last three years in relation to HLB are acted upon. Whilst there will not always be a consensus on what to emphasise, it is important that many evidence-based positions are presented. The authors of this paper recognise that this work is a starting point and that the lessons presented here will need to be revisited as new evidence becomes available

High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS

The first step in most geochronological studies is to extract dateable minerals from the host rock, which is time consuming, removes textural context, and increases the chance for sample cross contamination. We here present a new method to rapidly perform in situ analyses by coupling a fast scanning electron microscope (SEM) with Energy Dispersive X-ray Spectrometer (EDS) to a Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LAICPMS) instrument. Given a polished hand specimen, a petrographic thin section, or a grain mount, Automated Phase Mapping (APM) by SEM/EDS produces chemical and mineralogical maps from which the X-Y coordinates of the datable minerals are extracted. These coordinates are subsequently passed on to the laser ablation system for isotopic analysis. We apply the APM1LAICPMS method to three igneous, metamorphic, and sedimentary case studies. In the first case study, a polished slab of granite from Guernsey was scanned for zircon, producing a 60968 Ma weighted mean age. The second case study investigates a paragneiss from an ultra high pressure terrane in the north Qaidam terrane (Qinghai, China). One hundred seven small (25 mm) metamorphic zircons were analyzed by LAICPMS to confirm a 41964 Ma age of peak metamorphism. The third and final case study uses APM1LAICPMS to generate a large provenance data set and trace the provenance of 25 modern sediments from Angola, documenting longshore drift of Orange River sediments over a distance of 1,500 km. These examples demonstrate that APM1LAICPMS is an efficient and cost effective way to improve the quantity and quality of geochronological data