Observation of centimetre-scale argon diffusion in alkali feldspars: implications for ⁴⁰Ar/³⁹Ar thermochronology

New data from a gem-quality feldspar from Itrongay, Madagascar, record naturally occurring 40Ar/39Ar age profiles which can be numerically modelled by invoking a single diffusion mechanism and show that microtexturally simple crystals are capable of recording complex thermal histories. We present the longest directly measured, naturally produced 40Ar*-closure profiles from a single, homogeneous orthoclase feldspar. These data appear to confirm the assumption that laboratory derived diffusion parameters are valid in nature and over geological timescales. Diffusion domains are defined by crystal faces and ancient cracks, thus in gem-quality feldspars the diffusion domain size equates to the physical grain size. The data also illustrate the potential of large, gem-quality feldspars to record detailed thermal histories over tens of millions of years and such samples should be considered for future studies on the slow cooling of continental crust

The ⁴⁰Ar–³⁹Ar dating and geochemistry of the Carpathian C1 obsidians (Zemplín, Slovakia)

In situ 40Ar–39Ar UV laser ablation dating of the Carpathian C1 obsidians from the Slovakian part of the Zemplín –Tokaj area yielded new 40Ar–39Ar obsidian glass ages that fall in a narrow time interval of 12.07 ± 0.37 to 11.44 ± 0.39 Ma. This indicates that most of the Zemplín obsidian findings come from one short-time monogenic volcano, forming part of a long-lasting volcanism over the 15–10 Ma period. Chemical compositions of the Carpathian C1 obsidians clearly indicate common similarities between all examined localities (Brehov, Cejkov, Hraň, and Viničky). Geochemically, these obsidians belong to the silica-rich, peraluminous, high-potassium, calc-alkaline rhyolite series volcanic rocks of ferroan character. They were derived by multi-stage magmatic processes, from mixed mantle and crustal sources, and generated during subduction in a volcanic arc tectonic setting. The primary basaltic magma formed from the melting of the lower crustal source at the mantle/crust boundary. Subsequent formation of melt reservoirs in the middle and upper crust, accompanied by secondary melting of the surrounding rocks with continual addition of ascending melt, and repeated processes of assimilation and fractionation produced rhyolitic rocks with obsidians in the Zemplínske vrchy Mts

Widespread tephra dispersal and ignimbrite emplacement from a subglacial volcano (Torfajökull, Iceland)

The tephra dispersal mechanisms of rhyolitic glaciovolcanic eruptions are little known, but can be investigated through the correlation of eruptive products across multiple depositional settings. Using geochemistry and geochronology, we correlate a regionally important Pleistocene tephra horizon—the rhyolitic component of North Atlantic Ash Zone II (II-RHY-1)—and the Thórsmörk Ignimbrite with rhyolitic tuyas at Torfajökull volcano, Iceland. The eruption breached an ice mass >400 m thick, leading to the widespread dispersal of II-RHY-1 across the North Atlantic and the Greenland ice sheet. Locally, pyroclastic density currents traveled across the ice surface, depositing the variably welded Thórsmörk Ignimbrite beyond the ice margin and ~30 km from source. The widely dispersed products of this eruption represent a valuable isochronous tie line between terrestrial, marine, and ice-core paleoenvironmental records. Using the tephra horizon, estimates of ice thickness and extent derived from the eruption deposits can be directly linked to the regional climate archive, which records the eruption at the onset of Greenland Stadial 15.2

Evidence for southward subduction of the Mongol-Okhotsk oceanic plate: Implications from Mesozoic adakitic lavas from Mongolia

A combination of new 40Ar/39Ar dating results, major- and trace-element data, plus Sr-Nd-Pb-Hf isotope data, are used to investigate the petrogenesis of Triassic high-Si adakite (HSA), Cretaceous low-Si adakite-like (LSA) lavas, and Cretaceous high-K and shoshonitic trachyandesite lavas, from eastern and south-central Mongolia. All samples are light rare-earth element and large-ion lithophile element enriched but depleted in some high-field strength elements (notably Nb, Ta and Ti). Two alternative models are proposed to explain the petrogenesis of the HSA samples. (1) A southward-subducting Mongol-Okhotsk slab underwent partial melting in the Triassic during the closure of the Mongol-Okhotsk Ocean, with the resultant melts assimilating mantle and crustal material. Alternatively (2), a basaltic underplate of thickened (>50 km; >1.5 GPa), eclogitic lower crust foundered into the underlying mantle, and underwent partial melting with minor contamination from mantle material and some shallow-level crustal contamination. The LSA samples are interpreted as melts derived from a lithospheric mantle wedge that was previously metasomatised by slab melts. Similarly, the trachyandesite lavas are interpreted as melts deriving from a subduction-enriched subcontinental lithospheric mantle. The spatial distribution of these samples implies that metasomatism likely occurred due to a southward-subducting Mongol-Okhotsk slab associated with the closure of the Mongol-Okhotsk Ocean. When this interpretation is combined with previous evidence for a northward-subducting Mongol-Okhotsk slab it advocates that the Mongol-Okhotsk Ocean closed with double-sided subduction

Effectiveness of a structured, framework-based approach to implementation: the Researching Effective Approaches to Cleaning in Hospitals (REACH) Trial

BACKGROUND: Implementing sustainable practice change in hospital cleaning has proven to be an ongoing challenge in reducing healthcare associated infections. The purpose of this study was to develop a reliable framework-based approach to implement and quantitatively evaluate the implementation of evidence-based practice change in hospital cleaning. DESIGN/METHODS: The Researching Effective Approaches to Cleaning in Hospitals (REACH) trial was a pragmatic, stepped-wedge randomised trial of an environmental cleaning bundle implemented in 11 Australian hospitals from 2016 to 2017. Using a structured multi-step approach, we adapted the integrated Promoting Action on Research Implementation in Health Services (i-PARIHS) framework to support rigorous and tailored implementation of the cleaning bundle intervention in eleven diverse and complex settings. To evaluate the effectiveness of this strategy we examined post-intervention cleaning bundle alignment calculated as a score (an implementation measure) and cleaning performance audit data collected using ultraviolet (UV) gel markers (an outcome measure). RESULTS: We successfully implemented the bundle and observed improvements in cleaning practice and performance, regardless of hospital size, intervention duration and contextual issues such as staff and organisational readiness at baseline. There was a positive association between bundle alignment scores and cleaning performance at baseline. This diminished over the duration of the intervention, as hospitals with lower baseline scores were able to implement practice change successfully. CONCLUSION: Using a structured framework-based approach allows for pragmatic and successful implementation of clinical trials across diverse settings, and assists with quantitative evaluation of practice change. TRIAL REGISTRATION: Australia New Zealand Clinical Trial Registry ACTRN12615000325505, registered on 4 September 2015

New ⁴⁰Ar/³⁹Ar dating of the Antrim Plateau Volcanics, Australia: clarifying an age for the eruptive phase of the Kalkarindji continental flood basalt province

The Kalkarindji flood basalt province of northern Australia erupted in the mid-Cambrian. Today the province consists of scattered volcanic and intrusive suites, the largest being the Antrim Plateau Volcanics (APV) in Northern Territory. Accurate dating of Kalkarindji has proved challenging with previous studies focused on minor volcanics and intrusive dykes in Northern Territory and Western Australia. These previously published data, corrected to the same decay constants, range from 512.8 to 509.6 ± 2.5 Ma [2σ], placing Kalkarindji in apparent synchronicity with the Cambrian Stage 4–5 biotic crisis at 510 ± 1 Ma. This study utilises 40Ar/39Ar dating of basalts from the APV to accurately date the major volcanic eruptions in this province. Results yield an age of 508.0–498.3 ± 5.5 Ma [2σ], indicating the APV is younger than the intrusives. These dates allude to a relative timing discrepancy, where intrusive activity in the North Australian Craton preceded the eruption of the APV as the last magmatic activity in the region. The determination of these largest eruptions to be later than 510 Ma, effectively disassociates Kalkarindji lavas from being a major cause of the 510 Ma biotic crisis, but cannot definitively discount any deleterious effects on the fragile Cambrian ecosystem

Oligocene deformation of the Chuandian terrane in the SE margin of the Tibetan Plateau related to the extrusion of Indochina

Mechanisms driving the tectonic evolution of the southeast (SE) margin of Tibet include the Paleogene extrusion of the coherent Indochina lithospheric block, and the continuous deformation caused by lower crustal flow since the middle Miocene. The timing and style of regional deformations are key to determining the role of each mechanism. Fault-bounded and -controlled Cenozoic basins within the SE margin of Tibet record regional deformation, surface uplift and variations in paleoclimate, but often are poorly dated. New magnetostratigraphy and 40Ar/39Ar dating of volcanic ashes constrain precisely the timing of sedimentation within the Lühe Basin to between ~35 and 26.5 Ma. The basin is located in the Chuandian terrane along the Chuxiong fault, which lies ~70 km north of, and parallel to, the Ailao Shan-Red River fault. The asymmetric syncline of the Lühe Basin suggests syn-contractional sedimentation and the basal age of the basin represents the initiation of the Chuxiong fault and crustal shortening at ~35 Ma. This is coincident with the onset of the Ailao Shan-Red River fault, and supports a kinematic link between them. Our study suggests that, like the Ailao Shan-Red River fault, the Chuxiong fault is a Paleogene transpressional structure that developed during the extrusion and clockwise rotation of Indochina around the Eastern Himalayan Syntaxis, which caused the late Paleogene deformation and surface uplift of the Chuandian terrane and Indochina. Our revised chronostratigraphy of the Lühe Basin provides further evidence that many of the “Neogene” sedimentary basins in the SE margin of Tibet may be much older than previously thought

Argon behaviour in an inverted Barrovian sequence, Sikkim Himalaya: the consequences of temperature and timescale on ⁴⁰Ar/³⁹Ar mica geochronology

40Ar/39Ar dating of metamorphic rocks sometimes yields complicated datasets which are difficult to interpret in terms of timescales of the metamorphic cycle. Single-grain fusion and step-heating data were obtained for rocks sampled through a major thrust-sense shear zone (the Main Central Thrust) and the associated inverted metamorphic zone in the Sikkim region of the eastern Himalaya. This transect provides a natural laboratory to explore factors influencing apparent 40Ar/39Ar ages in similar lithologies at a variety of metamorphic pressure and temperature (P–T) conditions. The 40Ar/39Ar dataset records progressively younger apparent age populations and a decrease in within-sample dispersion with increasing temperature through the sequence. The white mica populations span ~ 2–9 Ma within each sample in the structurally lower levels (garnet grade) but only ~ 0–3 Ma at structurally higher levels (kyanite-sillimanite grade). Mean white mica single-grain fusion population ages vary from 16.2 ± 3.9 Ma (2σ) to 13.2 ± 1.3 Ma (2σ) from lowest to highest levels. White mica step-heating data from the same samples yields plateau ages from 14.27 ± 0.13 Ma to 12.96 ± 0.05 Ma. Biotite yield older apparent age populations with mean single-grain fusion dates varying from 74.7 ± 11.8 Ma (2σ) at the lowest structural levels to 18.6 ± 4.7 Ma (2σ) at the highest structural levels; the step-heating plateaux are commonly disturbed. Temperatures > 600 °C at pressures of 0.4–0.8 GPa sustained over > 5 Ma, appear to be required for white mica and biotite ages to be consistent with diffusive, open-system cooling. At lower temperatures, and/or over shorter metamorphic timescales, more 40Ar is retained than results from simple diffusion models suggest. Diffusion modelling of Ar in white mica from the highest structural levels suggests that the high-temperature rocks cooled at a rate of ~ 50–80 °C Ma− 1, consistent with rapid thrusting, extrusion and exhumation along the Main Central Thrust during the mid-Miocene

Corruption and the Composition of Public Expenditures: Evidence from OECD Countries

This paper analyzes how corruption affects the composition of public expenditures. First, a two-stage rent-seeking model with endogenous rent-setting is derived that captures both "political corruption" and "bureaucratic corruption". The model illustrates how asymmetries between industries in the degree of competition and in the difficulty of concealing bribery may influence the allocation of public spending. The theoretical implications are tested with a panel dataset for 26 OECD countries over the 1996 - 2008 period. The results suggest that the shares of spending on health and environmental protection increase, while the shares of spending on social protection and recreation, culture and religion decline with higher levels of corruption. The significance of these distortions is robust to a variety of specifications such as fixed effects, random effects, seemingly unrelated regressions, the inclusion of additional controls, and the use of alternative corruption indicators

Argon redistribution during a metamorphic cycle: Consequences for determining cooling rates

40Ar/39Ar thermochronology is commonly used to constrain the rates and times of cooling in exhumed metamorphic terranes, with ages usually linked to temperature via Dodson's closure temperature (TC) formulation. Whilst many metamorphic 40Ar/39Ar data are consistent with the timing of crystallisation or cooling within a chronological framework defined by other, higher temperature, chronometers, other 40Ar/39Ar data are more difficult to interpret. We report white mica and biotite single grain fusion and laser ablation 40Ar/39Ar ages from felsic gneisses from the Western Gneiss Region, Norway. The rocks record isothermal decompression from peak eclogite-facies conditions (white mica stable) to amphibolite-facies conditions (biotite stable) at c. 700 °C. White mica and biotite yield dispersed single grain fusion dates from 416 to 373 Ma and 437 to 360 Ma respectively. In-situ laser ablation analyses provide a similar range, with white mica spot ages ranging from 424 to 370 Ma and biotite spot ages ranging from 437 to 370 Ma. The dates span the duration of the metamorphic cycle suggested by previous studies, and cannot be reconciled with the results of simple models of Ar loss by diffusion during cooling. Samples that show evidence for different physical processes, such as the chemical breakdown of white mica, partial melting, and fluid ingress, generated different age populations to samples that did not experience or record obvious petrological evidence for these processes. Samples that record significant recrystallization and deformation yielded younger white mica (but older biotite) single grain fusion ages than more pristine samples. Amphibolite-facies gneisses that preserve evidence for significant partial melting generated younger biotite ages than samples that recorded evidence for significant hydration. Our data support other reported observations that high-temperature metamorphic mica 40Ar/39Ar dates cannot be assumed to record the timing of cooling through a specific temperature window. Careful assessment of the petrographic context of the dated minerals and consideration of their post-crystallisation history may provide a more robust insight into whether ‘age’ links to ‘stage’ in a temporally meaningful way