Production of 21 Ne in depth-profiled olivine from a 54 Ma basalt sequence, Eastern Highlands (37° S), Australia

In this study we investigate the cosmogenic neon component in olivine samples from a vertical profile in order to quantify muogenic 21Ne production in this mineral. Samples were collected from an 11 m thick Eocene basalt profile in the Eastern Highlands of southeastern Australia. An eruption age of 54.15 ± 0.36 Ma (2σ) was determined from 40Ar/39Ar step-heating experiments (n = 6) on three whole-rock samples. A 36Cl profile on the section indicated an apparent steady state erosion rate of 4.7 ± 0.5 m Ma−1. The eruption age was used to calculate in situ produced radiogenic 4He and nucleogenic 3He and 21Ne concentrations in olivine. Olivine mineral separates (n = 4), extracted from the upper two metres of the studied profile, reveal cosmogenic 21Ne concentrations that attenuate exponentially with depth. However, olivine (Fo68) extracted from below 2 m does not contain discernible 21Ne aside from magmatic and nucleogenic components, with the exception of one sample that apparently contained equal proportions of nucleogenic and muogenic neon. Modelling results suggest a muogenic neon sea-level high-latitude production rate of 0.02 ± 0.04 to 0.9 ± 1.3 atoms g−1 a−1 (1σ), or <2.5% of spallogenic cosmogenic 21Ne production at Earth’s surface. These data support a key implicit assumption in the literature that accumulation of muogenic 21Ne in olivine in surface samples is likely to be negligible/minimal compared to spallogenic 21Ne

Provenance history of detrital diamond deposits, West Coast of Namaqualand, South Africa

The West Coast of Namaqualand in South Africa hosts extensive detrital diamond deposits, but considerable debate exists as to the provenance of these diamonds. Some researchers have suggested derivation of the diamonds from Cretaceous-Jurassic kimberlites (also termed Group I kimberlites) and orangeites (also termed Group II kimberlites) located on the Kaapvaal Craton. However, others favour erosion of diamonds from the ca.300 Ma Dwyka Group sediments, with older, pre-Karoo kimberlites being the original source(s). Previous work has demonstrated that 40Ar/39Ar analyses of clinopyroxene inclusions, extracted from diamonds, yield ages approaching the time(s) of source kimberlite emplacement, which can be used to constrain the provenance of placer diamond deposits. In the current study, 40Ar/39Ar analyses were conducted on clinopyroxene inclusions from two similar batches of Namaqualand detrital diamonds, yielding (maximum) ages ranging from 117.5 ± 43.6 Ma to 3684 ± 191 Ma (2σ) and 120.6 ± 15.4 Ma to 688.8 ± 4.9 Ma (2σ), respectively. The vast majority of inclusions (88%) produced ages younger than 500 Ma, indicating that most Namaqualand diamonds originated from Cretaceous-Jurassic kimberlites/orangeites, with few, if any, derived from the Dwyka tillites. The provenance of the Namaqualand diamonds from ca.115–200 Ma orangeites is consistent with Late Cretaceous paleo-drainage reconstructions, as these localities could have been sampled by the ‘paleo-Karoo’ River and transported to the West Coast via an outlet close to the current Olifants River mouth. At ca.90 Ma, this drainage system appears to have been captured by the ‘paleo-Kalahari’ River, a precursor to the modern Orange River system. This latter drainage is considered to have transported diamonds eroded from both ca.80–90 Ma kimberlites and ca.115–200 Ma orangeites to the West Coast, which were subsequently reworked along the Namibian coast, forming additional placer deposits

The Hera orebody: a complex distal (Au–Zn–Pb–Ag–Cu) skarn in the Cobar Basin of central New South Wales, Australia

The Hera Au–Pb–Zn–Ag deposit in the southeastern Cobar Basin of central New South Wales preserves calc-silicate veins and remnant sandstone/carbonate-hosted skarn within a reduced anchizonal Siluro-Devonian turbidite sequence. The skarn orebody distribution is controlled by a long-lived, basin margin fault system, that has intersected a sedimentary horizon dominated by siliciclastic turbidite, with lesser gritstone and thick sandstone intervals, and rare carbonate-bearing stratigraphy. Foliation (S1) envelopes the orebody and is crosscut by a series of late-stage east–west and north–south trending faults. Skarn at Hera displays mineralogical zonation along strike, from southern spessartine–grossular–biotite–actinolite-rich associations, to central diopside-rich–zoisite–actinolite/tremolite–grossular-bearing associations, through to the northern most tremolite–anorthite-rich (garnet-absent) association in remnant carbonate-bearing lithologies and sandstone horizons; the northern lodes also display zonation down dip to garnet present associations. High-T, prograde skarn assemblages rich in pyroxene and garnet are pervasively replaced by actinolite/tremolite–biotite-rich retrograde skarn which coincides with the main pulse of sulfide mineralization. The dominant sulfides are high-Fe–Mn sphalerite–galena–non-magnetic high-Fe pyrrhotite–chalcopyrite; pyrite, arsenopyrite; scheelite (low Mo) is locally abundant. The distribution of metals in part mimics the changing gangue mineralogy, with Au concentrated in the southern and lower northern lode systems and broadly inverse concentrations for Ag–Pb–Zn. Stable isotope data (O–H–S) from skarn amphiboles and associated sulfides are consistent with magmatic (or metamorphic) water and sulfur input during the retrograde skarn phase, while hydrosilicates and sulfides from the wall rocks display comparatively elevated δD and mixed δ34S consistent with progressive mixing or dilution of original magmatic (or metamorphic) waters within the Hera deposit by unexchanged waters typical of low latitude (tropical) meteoritic waters. High precision titanite (U–Pb) and biotite (Ar–Ar) geochronology reveals a manifold orebody commencing with high-T skarn and retrograde Pb–Zn-rich skarn formation at ≥403 Ma, Au–low-Fe sphalerite mineralization at 403.4 ± 1.1 Ma, foliation development remobilization or new mineralization at 390 ± 0.2 Ma followed by thrusting, orebody dismemberment at 384.8 ± 1.1 Ma and remobilization or new mineralization at 381.0 ± 2.2 Ma. The polymetallic nature of the Hera orebody is a result of multiple mineralization events during extension and compression and involving both magmatic and likely formational metal sources

Формирование эмоциональной культуры как компонента инновационной культуры студентов

Homozygosity has long been associated with rare, often devastating, Mendelian disorders1 and Darwin was one of the first to recognise that inbreeding reduces evolutionary fitness2. However, the effect of the more distant parental relatedness common in modern human populations is less well understood. Genomic data now allow us to investigate the effects of homozygosity on traits of public health importance by observing contiguous homozygous segments (runs of homozygosity, ROH), which are inferred to be homozygous along their complete length. Given the low levels of genome-wide homozygosity prevalent in most human populations, information is required on very large numbers of people to provide sufficient power3,4. Here we use ROH to study 16 health-related quantitative traits in 354,224 individuals from 102 cohorts and find statistically significant associations between summed runs of homozygosity (SROH) and four complex traits: height, forced expiratory lung volume in 1 second (FEV1), general cognitive ability (g) and educational attainment (nominal p<1 × 10−300, 2.1 × 10−6, 2.5 × 10−10, 1.8 × 10−10). In each case increased homozygosity was associated with decreased trait value, equivalent to the offspring of first cousins being 1.2 cm shorter and having 10 months less education. Similar effect sizes were found across four continental groups and populations with different degrees of genome-wide homozygosity, providing convincing evidence for the first time that homozygosity, rather than confounding, directly contributes to phenotypic variance. Contrary to earlier reports in substantially smaller samples5,6, no evidence was seen of an influence of genome-wide homozygosity on blood pressure and low density lipoprotein (LDL) cholesterol, or ten other cardio-metabolic traits. Since directional dominance is predicted for traits under directional evolutionary selection7, this study provides evidence that increased stature and cognitive function have been positively selected in human evolution, whereas many important risk factors for late-onset complex diseases may not have been

Calibration of the cosmogenic 21Ne exposure dating technique for application to Quaternary volcanic chronology

© 2012 Dr. Erin Lesley MatchanThe use of terrestrial cosmogenic nuclides to investigate surface exposure histories continues to gain popularity due to the applicability of the technique to many different minerals and rock types. However, errors associated with cosmogenic exposure ages are typically either poorly specified or relatively high compared to other more established dating methods. This is dominantly due to large systematic uncertainties. This study focused on the stable cosmogenic nuclides 21Ne and 3He, and investigated their production in olivine and clinopyroxene from young (<150 ka) basalt flows. The primary aims of this study were to (i) improve the cosmogenic 21Ne dating technique for application to these minerals, (ii) develop in-house methods for dating young basalt flows by the 40Ar/39Ar step-heating technique, and (iii) inter-calibrate cosmogenic 21Ne surface exposure ages with corresponding 40Ar/39Ar eruption ages, in order to test available cosmogenic nuclide production rate scaling models. Alkali basalt flows (~30 – 130 ka) from three mid-latitude localities were studied: Mount Porndon (Victoria, Australia), Amboy Crater (Mojave Desert, California, USA), and the Nave flow, Mount Etna (Sicily, Italy). Helium and neon isotopic compositions of olivine (n = 13) and clinopyroxene (n = 7) separates from the above localities were determined from two-step heating experiments (900 ̊C and 1600 ̊C) using a VG5400 mass spectrometer. All samples showed evidence of variable degrees of helium loss and isotope mass fractionation, which compromised the calculation of cosmogenic 3He (3Hec) ages. Although minor neon loss was also apparent in most samples, it did not affect calculation of cosmogenic 21Ne (21Nec) ages. Overall, olivine separates yielded more consistent cosmogenic 21Ne ages than corresponding clinopyoxene separates extracted from the same samples. Crushing experiments on selected samples demonstrated an atmospheric composition for the 21Ne/20Ne ratio of the trapped neon component. Apparent weighted mean 21Nec exposure ages were calculated at: 64 ± 10 (2σ, Mount Porndon), 105 ± 23 ka (2σ, Amboy Crater), 29.0 ± 7.6 ka (2σ, Nave flow), respectively. Prior to analysing the very young (<150 ka) basalts from the selected calibration sites by the 40Ar/39Ar technique, studies of slightly older samples (300-600 ka) collected from the Newer Volcanic Province of southeastern Australia (Mount Rouse basalt (n = 4) and Mount Warrnambool basalt (n = 2)) were carried out on a VG3600 mass spectrometer in order to establish appropriate sample preparation procedures and analytical protocols. Multi-aliquot 40Ar/39Ar furnace step-heating analyses of whole-rock samples from several (n = 4) Mount Rouse basalt flows yielded weighted mean ages of: 309 ± 20 ka (2σ, NVP19), 382 ± 24 ka (2σ, NVP06); 301 ± 27 ka (2σ, NVP20) and 280 ± 19 ka (2σ, NVP21). Samples from Mount Warrnambool (n = 2) yielded weighted mean ages of: 547 ± 23 ka (2σ, NVP03) and 535 ± 27 ka (95% CI. NVP04). The internal concordance of results and agreement with previous K-Ar ages enabled validation of the experimental protocols adopted. Basalt samples younger than 150 ka from Mount Porndon, Amboy Crater and Mount Eccles were analysed on a new generation multi-collector ARGUSVI mass spectrometer via laser step-heating. This system yielded significantly more precise isotopic measurements than was possible using the older VG3600 system. Two to four groundmass aliquots were analysed per sample (n = 4), giving weighted mean 40Ar/39Ar ages of: 105 ± 22 ka (2σ; Mount Porndon, NVP14), 121 ± 8 ka (2σ; Amboy Crater, 08010), 92 ± 8 (2σ; Mount Eccles, NVP18)), 84 ± 13 (2σ; Mount Eccles, NVP12) and 293 ± 7 ka (95% CI; Mount Rouse, NVP21). Although lava surfaces showing apparent primary flow textures were sampled for cosmogenic dating, comparison of the cosmogenic 21Ne and 40Ar/39Ar ages indicates that significant erosion has occurred at the outcrops sampled for exposure dating from the Mount Porndon lava flows. Erosion modelling assuming an eruption age of 105 ± 22 ka (2σ, 40Ar/39Ar) suggests an erosion rate ranging from 2 - 7 mm/ka, depending on the value assumed for the scaled 21Nec production rate. As estimated 21Nec production rates for Mount Porndon are at the lower end of the range predicted by latitudinal production rate scaling models, it is possible that available scaling models may require further refinement for application to Southern Hemisphere localities. For the Amboy Crater flow, an erosion rate of 1 mm/ka is estimated, consistent with previous studies. In the case of the Nave flow, the agreement of the 21Nec exposure age for sample 08025 with the weighted mean K-Ar age (32 ± 8 ka (2σ)) of Blard et al. (2005) is interpreted as evidence for minimal erosion at this outcrop. However, the other two samples collected from adjacent outcrops on the Nave flow yielded slightly younger results, suggesting that erosion cannot be excluded for this flow. In order to refine estimates for 21Nec production rates in olivine and clinopyroxene, studies involving step-heating of large (several grams) mineral separates from young (ca. < 30 ka) basalt flow surfaces that have undergone negligible erosion and have independently constrained eruption ages are recommended. For the purposes of investigating muon-induced production of cosmogenic neon in olivine, 21Nec concentrations were studied in samples spanning an 11 m vertical profile through an Eocene basalt flow located in the Monaro Volcanic Province, NSW, Australia. A 40Ar/39Ar age of 55.52 ± 0.02 Ma (2σ) is calculated for this flow from step-heating (n = 4) experiments on whole-rock samples. It is demonstrated that excess 21Ne in the deepest samples can be accommodated solely by nucleogenic neon production, meaning that muogenic neon production in olivine is insignificant, even over million year time-scales. This justifies the assumption implicit in previous studies that 21Nec production in olivine (and likely clinoproxene) is purely the result of spallation reactions. Preliminary modelling based on 21Nec concentrations in the studied profile suggests an appreciably low average Cainozoic erosion rate of ca. 1 m/Ma

Geochronological, morphometric and geochemical constraints on the Pampas Onduladas long basaltic flow (Payún Matrú Volcanic Field, Mendoza, Argentina)

The Pampas Onduladas flow in southern Mendoza, Argentina, is one of the four longest Quaternary basaltic flows on Earth. Such flows (\u3e 100 km) are relatively rare on Earth as they require special conditions in order to travel long distances and there are no recent analogues. Favourable conditions include: a gentle topographic slope, an insulation process to preserve the melt at high temperature, and a large volume of lava with relatively low viscosity. This study investigates the rheological and geochemical characteristics of the ~ 170 km long Pampas Onduladas flow, assessing conditions that facilitated its exceptional length. The study also reports the first geochronological results for the Pampas Onduladas flow. 40Ar/39Ar step-heating analyses of groundmass reveal an eruption age of 373 ± 10 ka (2σ), making the Pampas Onduladas flow the oldest Quaternary long flow. The methods used to assess the rheological properties include the application of several GIS tools to a digital elevation model (DEM) to determine the length, width, thickness, volume and topographic slope of the flow as well as algorithms to determine its density, viscosity and temperature. The slope of the Pampas Onduladas flow determined from the initial part of the flow on the eastern side of La Carbonilla Fracture to its end point in the province of La Pampa is 0.84% (0.29°), the steepest substrate amongst long Quaternary flows. The rheological properties, such as density viscosity and temperature from the Pampas Onduladas flow are similar to values reported for other long Quaternary flows. However, the minimum volume calculated is relatively low for its length compared with other long Quaternary flows. Therefore, the extension of the Pampas Onduladas flow was probably controlled by a steep slope, combined with an insulating mechanism, which helped in providing optimal conditions for a travel length of almost 170 km

Astronomical calibration of Ar-40/Ar-39 reference minerals using high-precision, multi-collector (ARGUSVI) mass spectrometry

The new generation of multi-collector mass spectrometers (e.g. ARGUSVI) permit ultra-high precision (1%) in K-40 decay constants and the ages of natural reference minerals that form the basis of the technique. For example, reported ages for widely used Ar-40/Ar-39 reference materials, such as the ca. 28 Ma Fish Canyon Tuff sanidine (FCTs) and the ca. 1.2 Ma Alder Creek Rhyolite sanidine (ACRs), vary by >1%. Recent attempts to independently calibrate these reference minerals have focused on K-Ar analyses of the same minerals and inter-comparisons with astronomically tuned tephras in sedimentary sequences and U-Pb zircon ages from volcanic rocks. Most of these studies used older generation (effectively single-collector) mass spectrometers that employed peak-jumping analytical methods to acquire Ar-40/Ar-39 data. In this study, we reassess the inter-calibration and ages of commonly used Ar-40/Ar-39 reference minerals Fish Canyon Tuff sanidine (FCTs), Alder Creek Rhyolite sanidine (ACRs) and Mount Dromedary biotite (MD2b; equivalent to GA-1550 biotite), relative to the astronomically tuned age of A1 Tephra sanidine (A1Ts), Faneromeni section, Crete (Rivera et al., 2011), using a multi-collector ARGUSVI mass spectrometer. These analyses confirm the exceptional precision capability (0.1% in the Ar-40/Ar-39 ages of reference minerals without consideration of recoil artefacts, thus limiting the benefits of high precision multi-collector analyses.This study is supported by Australian Research Council Discovery grant DP130100517 to D. Phillips

Quaternary volcanic evolution in the continental back-arc of southern Mendoza, Argentina

The Payenia Basaltic Province (PBP) is the largest and the northernmost of the Quaternary back-arc Patagonian basaltic provinces in South America. In the last 10 years, several studies have investigated either, the geochemistry or the geochronology of this basaltic province. However, only a few investigations have focused on the two aspects simultaneously in order to reconstruct its Quaternary volcanic history. Consequently, this study aims to provide new Quaternary ages and to contribute in understanding how its geochemistry evolved though time. In the current study nine basaltic flows from the PBP in central west Argentina were dated using a combination of cosmogenic surface exposure, 40 Ar/ 39 Ar, and thermoluminescence dating methods. Seven flows have Middle to Late Pleistocene ages and two erupted in the Holocene. Using the new ages here inferred and the previously published Quaternary geochronology, together with the available geochemical data, maps of Pleistocene geochemical evolution have been generated. These maps indicate that two geochemically distinct magma types erupted over the same time interval (ca. 1.5 Ma) within the PBP: In the north-eastern part (Nevado volcanic field) of the province, an arc-like signature is distinguishable, whereas the southern part of the PBP (Río Colorado volcanic field) exhibits an intraplate, Ocean Island Basalt (OIB)-like signature. The arc-like signature decreases in the Early to Middle Pleistocene as indicated by a reduction in Ba/La and La/Ta values in the Nevado volcanic field. At ca. 0.25 Ma a similar disparity has been inferred between two volcanic fields on the western part of the PBP, one erupting lavas with arc-like characteristics and the other with OIB-like signatures, despite being only tens of kilometres apart. Holocene volcanism is restricted to the western side of the Payún Matrú volcanic field and is dominated by OIB-like signatures, notably high Ta/Hf and low Ba/La and La/Ta values

Production of \u3csup\u3e21\u3c/sup\u3eNe in depth-profiled olivine from a 54 Ma basalt sequence, Eastern Highlands (37° S), Australia

In this study we investigate the cosmogenic neon component in olivine samples from a vertical profile in order to quantify muogenic 21 Ne production in this mineral. Samples were collected from an 11 m thick Eocene basalt profile in the Eastern Highlands of southeastern Australia. An eruption age of 54.15 ± 0.36 Ma (2σ) was determined from 40 Ar/ 39 Ar step-heating experiments (n = 6) on three whole-rock samples. A 36 Cl profile on the section indicated an apparent steady state erosion rate of 4.7 ± 0.5 m Ma −1 . The eruption age was used to calculate in situ produced radiogenic 4 He and nucleogenic 3 He and 21 Ne concentrations in olivine. Olivine mineral separates (n = 4), extracted from the upper two metres of the studied profile, reveal cosmogenic 21 Ne concentrations that attenuate exponentially with depth. However, olivine (Fo 68 ) extracted from below 2 m does not contain discernible 21 Ne aside from magmatic and nucleogenic components, with the exception of one sample that apparently contained equal proportions of nucleogenic and muogenic neon. Modelling results suggest a muogenic neon sea-level high-latitude production rate of 0.02 ± 0.04 to 0.9 ± 1.3 atoms g −1 a −1 (1σ), or \u3c 2.5% of spallogenic cosmogenic 21 Ne production at Earth\u27s surface. These data support a key implicit assumption in the literature that accumulation of muogenic 21 Ne in olivine in surface samples is likely to be negligible/minimal compared to spallogenic 21 Ne