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Abstract: 40Ar/39Ar dating of metamorphic white mica is commonly used to elucidate the timing of cooling and/or exhumation of metamorphic terranes. In theory, so long as the dated mineral originally crystallised above its closure temperature, the yielded 40Ar/39Ar ages should not vary significantly within or between samples, and should vary only due to grain size (~3Ma variation depending on the estimated cooling rate). Infra-red laser single grain fusion and ultra-violet laser spot muscovite and/or phengite data from mafic eclogite bodies and their host gneisses in the Nordfjord region of the Western Gneiss Complex (WGC), Norway, show that the ages yielded both within and between white micas from the same mafic eclogite sample vary by up to 284Ma. Ages yielded within the same pelitic gneiss sample vary by up to 28Ma. Overall the 40Ar/39Ar phengite dates from mafic eclogites range from ~750 to 440Ma and are significantly older than the previously reported 405–400Ma U–Pb zircon age constraining peak metamorphism in the Nordfjord WGC. The felsic host gneiss samples, which recrystalised during a post-peak, exhumation-related, amphibolite-facies overprint, yield single grain fusion and laser spot 40Ar/39Ar white mica dates spanning ~420 to 385Ma, encompassing previous estimates of the timing of the entire metamorphic cycle. These data suggest that Ar is heterogeneously distributed both within grains and between grains on the cm to sub-mm scale in all samples, and imply restricted Ar transport and inefficient removal during the metamorphic cycle. Open system (zero grain boundary Ar concentration) behaviour is an inherent assumption in the commonly applied closure temperature formulation, but unless this can be demonstrated, linking 40Ar/39Ar ages to temperature is no longer trivial. The high spatial and chronological precision afforded by UV laser ablation mean that intra-grain Ar concentration distributions may be used to assess open vs. closed system behaviour. The data presented here suggest that open system behaviour cannot be assumed in metamorphic systems, even those in which the pressure, temperature and time conditions in theory allow for efficient diffusion during the metamorphic cycle. High spatial resolution 40Ar/39Ar data and robust comparison with numerical models of open system behaviour provide the greatest future potential for unravelling the complexities of metamorphic exhumation timescales. [Copyright &y& Elsevier]

Feed-in Tariffs (FiT) for residential photovoltaic solar technologies are available in most Australian jurisdictions. Financial incentives under FiT are in addition to those provided by the Small-Scale Renewable Energy Scheme which forms part of the national 20% Renewable Energy Target. Little attention has been paid to the welfare impacts of FiT on retail electricity prices and social policy objectives. Our analysis indicates that current FiT are a regressive form of taxation. By providing estimates of household impact by income groupings, we conclude that wealthier households are beneficiaries and the effective taxation rate for low income households is three times higher than that paid by the wealthiest households. [ABSTRACT FROM AUTHOR]

Abstract: The lunar meteorites Northwest Africa (NWA) 3163, 4881, and 4483 are paired stones classified as granulitic breccias. At 2.4kg, these three stones constitute one of the largest known lunar meteorite masses. Here we describe the petrography, mineralogy, and chemistry of NWA 3163, 4881, and 4483, and present 40Ar–39Ar data for two of the meteorites. Two-pyroxene thermometry indicates that the rocks equilibrated at 1050±50°C, which represents the high-temperature, low-pressure event that generated their characteristic recrystallization textures and reset their Ar systematics. Stepped-heating, in situ infrared laser microprobe 40Ar–39Ar geochronology yields a mean age of 3327±29Ma for NWA 3163, and a more disturbed release spectrum for NWA 4881. NWA 4881 shows an upward-trending pattern, suggesting that it may have had a 40Ar–39Ar age of >3.0Ga, but that it was partially reset at ∼2.6Ga. NWA 3163 et al. exhibit shock effects, including maskelynitized plagioclase, shock veins, and melt pockets, which are absent in the Apollo granulitic breccias. Although the Apollo and meteorite samples are texturally similar and have comparable bulk compositions and equilibration temperatures, their trace and siderophile element contents point to distinct parental lithologies derived from different regions of the Moon. Based on mineralogical and geochemical differences between the Apollo and meteorite samples, we conclude that the parent rock(s) of the paired NWA meteorites came from an area outside the Imbrium region and that they underwent high-temperature (granulite event) metamorphism long after the Late Heavy Bombardment. [Copyright &y& Elsevier]

The Foca volcanic centre (FVC) occupies a NNE-SSW-oriented highland between two EW-trending structural grabens in western Anatolia, and includes early-middle Miocene mafic and felsic extrusive suites. Its evolutionary history consists of an older volcano stage (16.6-16.1 Ma) and a younger volcano stage (15.2-14.1 Ma), which are characterized by different eruption styles and compositional and geochemical features. The older units include high-K calc-alkaline basalt, andesite, trachyandesite, rhyolite, and associated pyroclastic rocks, which formed during ignimbrite eruptions and plinian-subplinian air-fall episodes. The younger sequences are composed of shoshonitic-alkaline basalt lavas and dikes, trachytes, phonolites, and phonolitic ignimbrites that formed strombolian cones. The Foca volcanic rocks display high initial 87Sr/86Sr ratios (0.7075-0.7082 for the calc-alkaline mafic lavas, 0.7073-0.7064 for calc-alkaline felsic lavas, and 0.7063-0.7075 for the alkaline series) and low 143Nd/144Nd (0.5123-0.5125 in both series with εNd values varying from - 1.3 to - 6.0). These FVC geochemical features are consistent with those of other volcanic centres in western Anatolia (i.e. Bodrum, Urla-Cumaovası) and on the Aegean islands (i.e. Samos, Patmos, Chios). The geochemical and Sr-Nd isotopic compositions of the Foca volcanic units suggest that both lithospheric and asthenospheric mantle melts were involved in their evolution; however, the mantle lithosphere fingerprint was diminished by the middle Miocene, as the asthenospheric mantle melt input became dominant. These findings, combined with the bimodal character of post-collisional volcanism in the study area, suggest that geochemical variations in the nature of volcanism from calc-alkaline to alkaline and the changes in tectonic regimes through time may have been caused by successive thermal relaxations associated with possible 'piecemeal' removal of the base of subcontinental lithospheric mantle beneath western Anatolia. This interpretation is more plausible than a catastrophic collapse or wholesale delamination of the entire lithospheric mantle. Asthenospheric upwelling caused by this inferred convective thinning provided underplating of mantle-derived magmas, which interacted with the previously metasomatized lithospheric mantle and the overlying crust, resulting in their partial melting and in production of high-K calc-alkaline to mildly alkaline, incompatible element enriched magmas in separate magma chambers in which fractional crystallization occurred. [ABSTRACT FROM AUTHOR]

Abstract: Spatially resolved argon isotope measurements have been performed on neutron-irradiated samples of two Martian basalts (Los Angeles and Zagami) and two Martian olivine-phyric basalts (Dar al Gani (DaG) 476 and North West Africa (NWA) 1068). With a ∼50μm diameter focused infrared laser beam, it has been possible to distinguish between argon isotopic signatures from host rock (matrix) minerals and localized shock melt products (pockets and veins). The concentrations of argon in analyzed phases from all four meteorites have been quantified using the measured J values, 40Ar/39Ar ratios and K2O wt% in each phase. Melt pockets contain, on average, 10 times more gas (7–24ppb 40Ar) than shock veins and matrix minerals (0.3–3ppb 40Ar). The 40Ar/36Ar ratio of the Martian atmosphere, estimated from melt pocket argon extractions corrected for cosmogenic 36Ar, is: Los Angeles (∼1852), Zagami (∼1744) and NWA 1068 (∼1403). In addition, Los Angeles shows evidence for variable mixing of two distinct trapped noble gas reservoirs: (1) Martian atmosphere in melt pockets, and (2) a trapped component, possibly Martian interior (40Ar/36Ar: 480–490) in matrix minerals. Average apparent 40Ar/39Ar ages determined for matrix minerals in the four analyzed meteorites are 1290Ma (Los Angeles), 692Ma (Zagami), 515Ma (NWA 1068) and 1427Ma (DaG 476). These 40Ar/39Ar apparent ages are substantially older than the ∼170–474Ma radiometric ages given by other isotope dating techniques and reveal the presence of trapped 40Ar. Cosmic ray exposure (CRE) ages were measured using spallogenic 36Ar and 38Ar production. Los Angeles (3.1±0.2Ma), Zagami (2.9±0.4Ma) and NWA 1068 (2.0±0.5Ma) yielded ages within the range of previous determinations. DaG 476, however, yielded a young CRE age (0.7±0.25Ma), attributed to terrestrial alteration. The high spatial variation of argon indicates that the incorporation of Martian atmospheric argon into near-surface rocks is controlled by localized glass-bearing melts produced by shock processes. In particular, the larger (mm-size) melt pockets contain near end-member Martian atmospheric argon. Based on petrography, composition and argon isotopic data we conclude that the investigated melt pockets formed by localized in situ shock melting associated with ejection. Three processes may have led to atmosphere incorporation: (1) argon implantation due to atmospheric shock front collision with the Martian surface, (2) transformation of an atmosphere-filled cavity into a localized melt zone, and (3) shock implantation of atmosphere trapped in cracks, pores and fissures. [Copyright &y& Elsevier]

Pyritized graptolites from the Welsh Basin (United Kingdom) slate belt acted as rigid bodies during cleavage formation, and epizonal white micas formed within the resulting strain shadows, orthogonal to the principal stress orientation. Although the quantities of mica are small, they are a pure synkinematic mineral and have been dated by [sup 40]Ar-[sup 39]Ar infrared laser microprobe as a means to dating cleavage. Four samples of strain-fringe mica from different hand samples yielded ages ranging from 394.4 ± 3.1 to 397.8 ± 1.8 Ma (2σ), with a mean age of 396.1 ± 1.4 Ma (2σ). By focusing on minerals that are unequivocally synkinematic, this technique provides a novel solution to the problems of isotopically dating slaty cleavage. Previous studies have predominantly relied on dating whole-rock slate samples or separated illite grains by [sup 40]Ar-[sup 39]Ar techniques; problems encountered included (1) separating the effects of isotopic contamination by detrital phases, (2) [sup 39]At loss during the irradiation of illite mineral separates, and (3) thermally induced [sup 40]Ar loss in nature from fine-grained minerals. By circumventing these problems, this new method provides the first unequivocal and high-precision age data for Acadian deformation in the well-characterized Welsh Basin slate belt. With such precision, the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent-continent collision. [ABSTRACT FROM AUTHOR]

Three different geochronological techniques (stepwise-heating, laser-ablation [sup 40]Ar/[sup 39]Ar, Rb-Sr microsampling) have been evaluated for dating fault-generated pseudotachylytes sampled along the Periadriatic Fault System (PAF) of the Alps. Because pseudotachylytes are whole-rock systems composed of melt, clast and alteration phases, chemical control from both Ar isotopes (C1/K, Ca/K ratios) and EMPA analyses is crucial for their discrimination. When applied to stepwiseheating [sup 40]Ar/[sup 39]Ar analyses, this approach yields accurate melt-related ages, even for complex age spectra. The spatial resolution of laser-ablation [sup 40]Ar/[sup 39]Ar analyses is capable of contrasting melt, clast and alteration phases in situ, provided the clasts are not too fine grained, the latter of which results in integrated "mixed" ages without geological information. Elevated C1/K and Ca/K ratios were found to be an invaluable indicator for the presence of clast admixture or inherited [sup 40]Ar. Due to incomplete isotopic resetting during frictional melting, Rb-Sr microsampling dating did not furnish geologically meaningful ages. On the basis of isotopic disequilibria among pseudotachylyte matrix phases, and independent Rb-Sr microsampling dating of cogenetic (ultra)mylonites, the concordant [sup 40]Ar/[sup 39]Ar pseudotachylyte ages are interpreted as formation ages. The investigated pseudotachylytes altogether reveal a Cretaceous to Miocene history for the entire PAF, consistent with independent geological evidence. Individual faults, however, consistently reveal narrower intervals of enhanced activity lasting a few million years. Electronic supplementary material to this paper can be obtained by using the Springer LINK server at http://dx.doi.org/ 10. [ABSTRACT FROM AUTHOR]

Background: In March 2020, Ontario instituted a lockdown to reduce spread of the SARS-CoV-2 virus. Schools, recreational facilities, and nonessential businesses were closed. Restrictions were eased through 3 distinct stages over a 6-month period (March to September 2020). We aimed to determine the impact of each stage of the COVID-19 public health lockdown on the epidemiology of operative pediatric orthopedic trauma. Methods: A retrospective cohort study was performed comparing emergency department (ED) visits for orthopedic injuries and operatively treated orthopedic injuries at a level 1 pediatric trauma centre during each lockdown stage of the pandemic with caseloads during the same date ranges in 2019 (prepandemic). Further analyses were based on patients' demographic characteristics, injury severity, mechanism of injury, and anatomic location of injury. Results: Compared with the prepandemic period, ED visits decreased by 20% (1356 v. 1698, p < 0.001) and operative cases by 29% (262 v. 371, p < 0.001). There was a significant decrease in the number of operative cases per day in stage 1 of the lockdown (1.3 v. 2.0, p < 0.001) and in stage 2 (1.7 v. 3.0; p < 0.001), but there was no significant difference in stage 3 (2.4 v. 2.2, p = 0.35). A significant reduction in the number of playground injuries was seen in stage 1 (1 v. 62, p < 0.001) and stage 2 (6 v. 35, p < 0.001), and there was an increase in the number of self-propelled transit injuries (31 v. 10, p = 0.002) during stage 1. In stage 3, all patient demographic characteristics and all characteristics of operatively treated injuries resumed their prepandemic distributions. Conclusion: Provincial lockdown measures designed to limit the spread of SARS-CoV-2 significantly altered the volume and demographic characteristics of pediatric orthopedic injuries that required operative management. The findings from this study will serve to inform health system planning for future emergency lockdowns. [ABSTRACT FROM AUTHOR]

The article offers information on the 2014 British Earth Science Teachers' Association (ESTA) Annual Course and Conference, held in Milton Keynes, England from September 26-28, 2014.

Background: Pelvic osteotomies are frequently used as part of the surgical management of bladder exstrophy. The outcomes are often measured on the basis of the residual symphyseal diastasis. The aims of this study were to evaluate and validate a more reliable radiographic measure of ischiopubic rotation, to utilize this measure in analyzing pelves from patients with exstrophy and controls, and to propose a model for rediastasis in a pelvis with exstrophy.Methods: Pelvic radiographs of 164 normal children two months to eighteen years of age were used to determine the changes in interpubic and interischial distances and in the interischial/interpubic (IS/IP) ratio with age. Twenty-one pelvic CT (computed tomography) studies of normal children, two to sixteen years of age, were also used to study the change in the ischiopubic divergence angle. The same parameters were measured on radiographs or CT or magnetic resonance imaging studies of seventy-three patients with classic bladder exstrophy who were followed for two to nineteen years after exstrophy closure with or without pelvic osteotomies.Results: In normal children, the interpubic distance and the ischiopubic divergence angle had a narrow range and were constant with age, whereas the interischial distance and the IS/IP ratio increased progressively and were strongly correlated with age. In the patients with exstrophy, the interpubic distance was positively correlated with the interischial distance, whereas the IS/IP ratio was lower than that in normal controls and was not correlated with age.Conclusions: The IS/IP ratio is a useful measure of ischiopubic rotation and can be used to characterize pelvic growth, including the phenomenon of rediastasis in patients with exstrophy. Pelvic rediastasis is a progressive increase in interpubic distance resulting from growth without loss of rotational correction, as shown by the constancy of the IS/IP ratio with age in these patients. A better rotational position at the time of osteotomy may lead to a better pelvic shape at maturity.Clinical Relevance: Symphyseal rediastasis following neonatal pelvic osteotomies in patients with exstrophy is not due to loss of correction and progressive derotation of the hemipelves but is a consequence of the normal three-dimensional growth of the pelvis. The best correction of the pelvic deformity should always be the aim even in neonatal pelvic osteotomies because this will permanently change the pelvic shape. [ABSTRACT FROM AUTHOR]

Abstract: Metamorphic cooling rates determined using muscovite 40Ar/39Ar ages underpin many tectonic models, but are based on several simplifying approximations. We demonstrate that a number of these approximations, especially those relating to the assignment of a single “closure temperature”, might not hold for certain metamorphic scenarios, and particularly for metamorphism during rapid orogenic cycles. Using numerical diffusion models that include a recently reported significant pressure dependence of Ar diffusion in muscovite, we systematically interrogate the approximations associated with linking 40Ar/39Ar dates to pressure–temperature histories. The results of the simulations are presented in a simple graphic form allowing evaluation of the pressure–temperature (PT) regions in which Ar diffusion is efficient, and hence those in which the muscovite may yield true 40Ar/39Ar cooling ages. We suggest that a robust method for determining whether metamorphic muscovite 40Ar/39Ar ages relate to the timing of cooling involves: (1) the determination of the PT conditions and relative timing of muscovite crystallisation during the metamorphic cycle, (2) the collection of high precision and high spatial resolution 40Ar/39Ar data from muscovite grains and (3) the comparison between analytical data and numerical diffusion models which test different post-crystallisation pressure–temperature histories. [Copyright &y& Elsevier]

Oil-bearing fluid inclusions trapped within authigenic K-feldspar in Late Jurassic reservoirs throughout the UK Atlantic margin are evidence for an early oil migration event from Late Jurassic source rocks in the Faeroe-Shetland Basin. Previous compound-specific isotope studies confirm the hydrocarbon provenance. Temperaturecomposition- time data show that the Late Jurassic source rocks were oil mature 113 ± 3.5 Ma (2σ). This new 40Ar/39Ar authigenic K-feldspar age shows that the Late Jurassic source rocks were oil mature 30-40 m.y. prior to current estimates. [ABSTRACT FROM AUTHOR]

Abstract: Syn-kinematic pure muscovite strain-fringes grew around pyritized graptolites in response to the early Devonian (Acadian) closure and uplift of the Peri-Gondwanan Welsh Basin. They record Ar-isotope information on the timing of low-temperature deformation and the mudrock to slate transition. Here we have applied three different 40Ar/39Ar laserprobe dating methods to strain-fringes from the central Welsh Basin to test for variations in age and to explore the technical limitations of the method. Infrared laserprobe step-heating analyses yielded only occasional plateau ages (varying between ca. 403 Ma and 422 Ma) and strong evidence for discordance in the Ar-system. Likewise, ages from infrared laserprobe total fusion analysis are scattered, and range from ca. 390 Ma to 651 Ma. By contrast, ultraviolet laserprobe intra-fringe age profiles revealed a complex pattern of ages across individual strain-fringes. This is the highest spatial resolution technique available, and the resulting age profiles consistently showed an oscillatory pattern comprising troughs, or ‘baseline’ ages that are all within error of ca. 397 Ma, and peaks, or ‘apparent’ ages, ranging up to ca. 550 Ma. These ‘apparent’ ages we interpret as the results of repeated, periodic assimilation of excess 40Ar (40ArE) during deformation and the mudrock to slate transition. Here, basinal fluids carrying 40ArE are driven through bulk mudrock during contractional phases of the Acadian orogen, and 40ArE is taken up by muscovite strain-fringes. The concentration of 40ArE varies with metamorphic grade, and is inversely proportional to the temperature of metamorphism, and we suggest is controlled by the solubility of Ar in water, which has potentially quite severe implications for 40Ar/39Ar dating of K-bearing minerals in any mudrock. These results provide a first record of Ar-isotope information in strain-fringes, and a first record of orogenically-driven fluid-flow through bulk deforming mudrock. They also demonstrate how the high spatial resolution ultraviolet laserprobe 40Ar/39Ar method can access Ar-isotope information that is obscured by lower spatial resolution laser analysis, or bulk sampling methods. [Copyright &y& Elsevier]

Abstract: Infrared laser probe 40Ar/39Ar geochronology, instrumental neutron activation analysis (INAA) and analytical electron microscopy have been performed on four 0.5×1.0×0.3cm polished rock tiles of Apollo 16 and 17 granulitic breccias (60035, 77017, 78155, and 79215). Pyroxene thermometry indicates that these samples were re-equilibrated and underwent peak metamorphic sub-solidus recrystallization at 1000–1100°C, which resulted in homogeneous mineral compositions and granoblastic textures. 40Ar/39Ar data from this study reveal that three samples (60035, 77017, and 78155) have peak metamorphic ages of ∼4.1Ga. Sample 79215 has a peak metamorphic age of 3.9Ga, which may be related to Serenitatis basin formation. All four samples contain moderately high concentrations of meteoritic siderophiles. Enhanced siderophile contents in three of the samples provide evidence for projectile contamination of their target lithologies occurring prior to peak metamorphism. Post-peak metamorphism, low-temperature (<300°C) events caused the partial resetting of argon in the two finer-grained granulites (60035 and 77017). These later events did not alter the mineralogy or texture of the rocks, but caused minor brecciation and the partial release of argon from plagioclase. Interpretation of the low-temperature data indicates partial resetting of the argon systematics to as young as 3.2Ga for 60035 and 2.3Ga for 77017. Cosmic ray exposure ages range from 6.4 to ∼339Ma. Our results increase the amount of high-precision data available for the granulitic breccias and lunar highlands crustal samples. The results demonstrate the survival of pre-Nectarian material on the lunar surface and document the effects of contact metamorphic and impact processes during the pre-Nectarian Epoch, as well as the low-temperature partial resetting of ages by smaller impact events after 3.9Ga. The mineralogy and chemical composition of these rocks, as well as exhumation constraints, indicate that the source of heat for metamorphism was within kilometers of the surface via burial beneath impact-melt sheets or hot ejecta blankets. [Copyright &y& Elsevier]

Abstract: Mineral–melt partition coefficients of all noble gases (min/melt D i ) have been obtained for olivine (ol) and clinopyroxene (cpx) by UV laser ablation (213nm) of individual crystals grown from melts at 0.1GPa mixed noble gas pressure. Experimental techniques were developed to grow crystals virtually free of melt and fluid inclusions since both have been found to cause profound problems in previous work. This is a particularly important issue for the analysis of noble gases in crystals that have very low partition coefficients relative to coexisting melt and fluid phases. The preferred partitioning values obtained for the ol–melt system for He, Ne, Ar, Kr, and Xe are 0.00017(13), 0.00007(7), 0.0011(6), 0.00026(16), and , respectively. The respective cpx–melt partition coefficients are 0.0002(2), 0.00041(35), 0.0011(7), 0.0002(2), and . The data confirm the incompatible behaviour of noble gases for both olivine and clinopyroxene but unlike other trace elements these values show little variation for a wide range of atomic radius. The lack of dependence of partitioning on atomic radius is, however, consistent with the partitioning behaviour of other trace elements which have been found to exhibit progressively lower dependence of min/melt D i on radius as the charge decreases. As all noble gases appear to exhibit similar min/melt D i values we deduce that noble gases are not significantly fractionated from each other by olivine and clinopyroxene during melting and fractional crystallisation. Although incompatible, the partitioning values for noble gases also suggest that significant amounts of primordial noble gases may well have been retained in the mantle despite intensive melting processes. The implication of our data is that high primordial/radiogenic noble gas ratios (3He/4He, 22Ne/21Ne, and 36Ar/40Ar) characteristic of plume basalt sources can be achieved by recycling a previously melted (depleted) mantle source rather than reflecting an isolated, non-degassed primordial mantle region. [Copyright &y& Elsevier]

Through ultraviolet laser argon-argon dating of potassium feldspar cements containing fluid inclusions, we determined temperature-composition-time data for paleofluids in a sedimentary basin, including data for an evolving episode of fluid flow recorded in distinct phases of cement. The fluid evolved from mixed aqueous oil 83 million years ago to purely aqueous by 76 million years ago, thus dating the time of oil charge in this reservoir. [ABSTRACT FROM AUTHOR]

Detrital zircon ages are commonly used to investigate sediment provenance and supply routes. Here, we explore the advantages of employing multiple, complimentary techniques via a case study of the Neoproterozoic and Cambrian of the Adelaide Rift Complex, South Australia. Detrital muscovite Ar–Ar ages are presented from stratigraphic units, or equivalents, that have previously been the subject of U–Pb detrital zircon dating, and, in some cases, whole-rock Sm–Nd isotope studies. The zircon age ranges and whole-rock Sm–Nd isotope data suggest that early Neoproterozoic sediments from near the base of the Adelaide Rift Complex comprise a mixture of detritus derived from the adjacent Gawler Craton (Palaeoproterozoic to earliest Mesoproterozoic) and overlying Gairdner flood basalts. In contrast, detrital muscovites from this level have a broad scatter of Mesoproterozoic infrared (IR) laser total fusion Ar–Ar ages, while UV laser traverses indicate that the age spread reflects partial resetting by multiple heating events, rather than a mixture of sources. Younger Neoproterozoic sediments document replacement of the Gawler Craton by the more distant Musgrave and/or Albany–Fraser Orogens as the main provenance. The Cambrian Kanmantoo Group marks an abrupt change in depositional style and a new sediment source. The Kanmantoo Group have older Nd model ages than underlying strata, yet are dominated by near to deposition-aged (∼500–650 Ma) detrital zircons and muscovites, suggesting rapid cooling and exhumation of a tectonically active provenance region. Although this source remains uncertain, evidence points towards the distant Pan-African orogenic belts. Deposition in the Adelaide Rift Complex was terminated in the late Early Cambrian by the Delamerian Orogeny, and the results of previous detrital mineral dating studies from the Lachlan Fold Belt to the east are consistent with at least partial derivation of these sediments from reworked upper Adelaide Rift Complex (Kanmantoo Group), rather than a continuation of sediment supply from the Kanmantoo Group sediment source. More broadly, the data suggest a close link between basin formation and orogen exhumation, and we also speculate that mantle plumes have played a significant role in crustal evolution at this Palaeo-Pacific margin of Gondwanaland, challenging the notion that subduction zones are the principle sites of crustal growth and sediment provenance. [Copyright &y& Elsevier]

Investigates the utilization of [sup 40]Ar/[sup 39]Ar ultraviolet laser microprobes (UVLAMP) in the analysis of detrital white micas. Characteristic of detrital micas evolution; Efficiency of UVLAMP in the analysis of now-eroded mountain belts; Implication of [sup 40]Ar/[sup 39]Ar geochronology for orogenic uplift.

The 40Ar/39Ar dating method is among the most versatile of geochronometers, having the potential to date a broad variety of K-bearing materials spanning from the time of Earth's formation into the historical realm. Measurements using modern noble-gas mass spectrometers are now producing 40Ar/39Ar dates with analytical uncertainties of ~0.1%, thereby providing precise time constraints for a wide range of geologic and extraterrestrial processes. Analyses of increasingly smaller subsamples have revealed age dispersion in many materials, including some minerals used as neutron fluence monitors. Accordingly, interpretive strategies are evolving to address observed dispersion in dates from a single sample. Moreover, inferring a geologically meaningful "age" from a measured "date" or set of dates is dependent on the geological problem being addressed and the salient assumptions associated with each set of data. We highlight requirements for collateral information that will better constrain the interpretation of 40Ar/39Ar data sets, including those associated with single-crystal fusion analyses, incremental heating experiments, and in situ analyses of microsampled domains. To ensure the utility and viability of published results, we emphasize previous recommendations for reporting 40Ar/39Ar data and the related essential metadata, with the amendment that data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR) by both humans and computers. Our examples provide guidance for the presentation and interpretation of 40Ar/39Ar dates to maximize their interdisciplinary usage, reproducibility, and longevity. [ABSTRACT FROM AUTHOR]