Alkalic parental magmas for chassignites?     

Hanna NEKVASIL  Justin FILIBERTO  Francis M. McCUBBIN  Donald H. LINDSLEY 《Meteoritics & planetary science》2007,42(6):979-992

Abstract Detailed analysis of cumulate and melt inclusion assemblages in the chassignites provide important constraints on the nature of the melt trapped as inclusions in cumulus olivine (and, by extension, parental magma compositions), the pressures of crystallization, and magmatic volatile contents. These mineral assemblages show strong similarities to the experimental fractionation assemblages that produce the sodic silica‐saturated alkalic lavas on Earth (e.g., Ascension Island, Azores, the Nandewar volcano of Australia). The experimental assemblages were produced from silica‐saturated hawaiite at pressures above 4.3 kbar with dissolved water contents above 0.5 wt%. Such pressures are consistent with Ti:Al ratios of the melt‐inclusion pyroxenes in the Chassigny meteorite. Pyroxene compositions suggest early high crystallization temperatures and thus relatively low initial water and F contents. Feldspars indicate that melt evolution proceeded to rhyolite compositions both within the interstices of the cumulate olivine and within the melt inclusions, even though rhyolitic glass is only found within olivine‐hosted polyphase melt inclusions. The observed rhyolite glass is compositionally similar to the alkali‐rich rhyolite of Ascension Island which is produced experimentally by crystallization of hawaiite. It is proposed that the melt trapped in cumulus olivine of the Chassigny dunite was similar to a terrestrial silica‐saturated hawaiite, while that trapped in olivine of the Northwest Africa (NWA) 2727 dunite was less evolved, perhaps mildly alkalic basalt. Melts similar to terrestrial intra‐plate tholeiite could be parental to the cumulus minerals and evolve upon crystallization at pressures above 4.3 kbar and water contents above ?0.4 wt% to mildly alkalic basalt, silica‐saturated hawaiite, and alkali‐rich rhyolite. The melt inclusion assemblages are inconsistent with either crystallization of a low‐Al, high‐Fe basalt, or low‐pressure crystallization of a terrestrial‐like tholeiite.  相似文献   

Palaeo‐ice streams,trough mouth fans and high‐latitude continental slope sedimentation     

Colm Cofaigh  Justin Taylor  Julian A. Dowdeswell  Carol J. Pudsey 《Boreas: An International Journal of Quaternary Research》2003,32(1):37-55

The classical model of trough mouth fan (TMF) formation was developed in the Polar North Atlantic to explain large submarine fans situated in front of bathymetric troughs that extend across continental shelves to the shelf break. This model emphasizes the delivery of large volumes of subglacial sediment to the termini of ice streams flowing along troughs, and subsequent re‐deposition of this glacigenic sediment down the continental slope via debris‐flow processes. However, there is considerable variation in terms of the morphology and large‐scale sediment architecture of continental slopes in front of palaeo‐ice streams. This variability reflects differences in slope gradient, the relative contributions of meltwater sedimentation compared with debris‐flow deposition, and sediment supply/geology of the adjacent continental shelf. TMF development is favoured under conditions of a low (<1°) slope gradient; a passive‐margin tectonic setting; abundant, readily erodible sediments on the continental shelf ‐ and thus associated high rates of sediment delivery to the shelf edge; and a wide continental shelf. The absence of large sediment fans on continental slopes in front of cross‐shelf troughs should not, however, be taken to indicate the former absence of palaeo‐ice streams in the geological record.  相似文献   

Igneous and shock processes affecting chassignite amphibole evaluated using chlorine/water partitioning and hydrogen isotopes          下载免费PDF全文

Paul A. Giesting  Susanne P. Schwenzer  Justin Filiberto  Natalie A. Starkey  Ian A. Franchi  Allan H. Treiman  Andy G. Tindle  Monica M. Grady 《Meteoritics & planetary science》2015,50(3):433-460

Amphibole in chassignite melt inclusions provides valuable information about the volatile content of the original interstitial magma, but also shock and postshock processes. We have analyzed amphibole and other phases from NWA 2737 melt inclusions, and we evaluate these data along with published values to constrain the crystallization Cl and H₂O content of phases in chassignite melt inclusions and the effects of shock on these amphibole grains. Using a model for the Cl/OH exchange between amphibole and melt, we estimate primary crystallization OH contents of chassignite amphiboles. SIMS analysis shows that amphibole from NWA 2737 currently has 0.15 wt% H₂O. It has lost ~0.6 wt% H₂O from an initial 0.7–0.8 wt% H₂O due to intense shock. Chassigny amphibole had on average 0.3–0.4 wt% H₂O and suffered little net loss of H₂O due to shock. NWA 2737 amphibole has δD ≈ +3700‰; it absorbed Martian atmosphere‐derived heavy H in the aftermath of shock. Chassigny amphibole, with δD ≤ +1900‰, incorporated less heavy H. Low H₂O/Cl ratios are inferred for the primitive chassignite magma, which had significant effects on melting and crystallization. Volatiles released by the degassing of Martian magma were more Cl‐rich than on Earth, resulting in the high Cl content of Martian surface materials.  相似文献   

Fundamental differences between SPH and grid methods   总被引：1，自引：0，他引：1  

Oscar Agertz  Ben Moore  Joachim Stadel  Doug Potter  Francesco Miniati  Justin Read  Lucio Mayer  Artur Gawryszczak  rey Kravtsov  Åke Nordlund  Frazer Pearce  Vicent Quilis  Douglas Rudd  Volker Springel  James Stone  Elizabeth Tasker  Romain Teyssier  James Wadsley  Rolf Walder 《Monthly notices of the Royal Astronomical Society》2007,380(3):963-978

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X-ray absorption via Kα resonance complexes in oxygen ions     

Anil K. Pradhan  Guo Xin Chen  Franck Delahaye  Sultana N. Nahar  Justin Oelgoetz 《Monthly notices of the Royal Astronomical Society》2003,341(4):1268-1271

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The Kwakshua Watersheds Observatory,central coast of British Columbia,Canada     

Ian J. W. Giesbrecht  William C. Floyd  Suzanne E. Tank  Ken P. Lertzman  Brian P. V. Hunt  Maartje C. Korver  Allison A. Oliver  Ray Brunsting  Paul Sanborn  Santiago G. Gonzalez Arriola  Gordon W. Frazer  Kyra A. St. Pierre  Shawn Hateley  James McPhail  Colby Owen  Stewart Butler  Bryn Fedje  Emma Myers  Lucy Quayle  Emily Haughton  Isabelle Desmarais  Rob White  David J. Levy-Booth  Colleen T. E. Kellogg  Jennifer M. Jackson  William W. Mohn  Steven J. Hallam  Justin Del Bel Belluz 《水文研究》2021,35(6):e14198

The Kwakshua Watersheds Observatory (KWO) is an integrative watersheds observatory on the coastal margin of a rain-dominated bog-forest landscape in British Columbia (BC), Canada. Established in 2013, the goal of the KWO is to understand and model the flux of terrestrial materials from land to sea – the origins, pathways, processes and ecosystem consequences – in the context of long-term environmental change. The KWO consists of seven gauged watersheds and a network of observation sites spanning from land to sea and along drainage gradients within catchments. Time-series datasets include year-round measurements of weather, soil hydrology, streamflow, aquatic biogeochemistry, microbial ecology and nearshore oceanographic conditions. Sensor measurements are recorded every 5 min and water samples are collected approximately monthly. Additional observations are made during high-flow conditions. We used remote sensing to map watershed terrain, drainage networks, soils and terrestrial ecosystems. The watersheds range in size from 3.2 to 12.8 km², with varying catchment characteristics that influence hydrological and biogeochemical responses. Despite local variation, the overall study area is a global hotspot for yields of dissolved organic carbon, dissolved organic nitrogen and dissolved iron at the coastal margin. This observatory helps fill an important gap in the global network of observatories, in terms of spatial location (central coast of BC), climate (temperate oceanic), hydrology (very high runoff, pluvial regime), geology (igneous intrusive, glacially scoured), vegetation (bog rainforest) and soils (large stores of organic carbon).  相似文献   

A multi-sensor evaluation of precipitation uncertainty for landslide-triggering storm events     

Elsa S. Culler  Andrew M. Badger  Justin Toby Minear  Kristy F. Tiampo  Spencer D. Zeigler  Ben Livneh 《水文研究》2021,35(7):e14260

Extreme precipitation can have profound consequences for communities, resulting in natural hazards such as rainfall-triggered landslides that cause casualties and extensive property damage. A key challenge to understanding and predicting rainfall-triggered landslides comes from observational uncertainties in the depth and intensity of precipitation preceding the event. Practitioners and researchers must select from a wide range of precipitation products, often with little guidance. Here we evaluate the degree of precipitation uncertainty across multiple precipitation products for a large set of landslide-triggering storm events and investigate the impact of these uncertainties on predicted landslide probability using published intensity–duration thresholds. The average intensity, peak intensity, duration, and NOAA-Atlas return periods are compared ahead of 177 reported landslides across the continental United States and Canada. Precipitation data are taken from four products that cover disparate measurement methods: near real-time and post-processed satellite (IMERG), radar (MRMS), and gauge-based (NLDAS-2). Landslide-triggering precipitation was found to vary widely across precipitation products with the depth of individual storm events diverging by as much as 296 mm with an average range of 51 mm. Peak intensity measurements, which are typically influential in triggering landslides, were also highly variable with an average range of 7.8 mm/h and as much as 57 mm/h. The two products more reliant upon ground-based observations (MRMS and NLDAS-2) performed better at identifying landslides according to published intensity–duration storm thresholds, but all products exhibited hit ratios of greater than 0.56. A greater proportion of landslides were predicted when including only manually verified landslide locations. We recommend practitioners consider low-latency products like MRMS for investigating landslides, given their near-real time data availability and good performance in detecting landslides. Practitioners would be well-served considering more than one product as a way to confirm intense storm signals and minimize the influence of noise and false alarms.  相似文献   

The Wave Glider: enabling a new approach to persistent ocean observation and research     

Tom Daniel  Justin Manley  Neil Trenaman 《Ocean Dynamics》2011,61(10):1509-1520

The Wave Glider^TM wave-powered unmanned maritime vehicle represents a novel and unique approach to persistent ocean presence. Wave Glider is a hybrid sea-surface and underwater vehicle in that it is comprised of a submerged “glider” attached via a tether to a surface float. The Wave Glider vehicle is propelled by the purely mechanical conversion of ocean wave energy into forward thrust, independent of wave direction. In this paper, we provide an overview of the design of this new platform and present results from the engineering sea trials conducted with several prototype and production versions of the vehicle. In addition to the Wave Glider technology, we present results from ongoing scientific demonstration programs. Results from test deployments of a conductivity–temperature–depth sensor and its applicability to oceanography are discussed. An evaluation of horizontal current profiles and current velocity estimation from a Wave Glider operating in Monterey Bay (California, USA) are presented.  相似文献   

A physicochemical framework for interpreting the biological calcification response to CO₂-induced ocean acidification   总被引：2，自引：0，他引：2  

Justin B. Ries 《Geochimica et cosmochimica acta》2011,75(14):4053-4064

A generalized physicochemical model of the response of marine organisms’ calcifying fluids to CO₂-induced ocean acidification is proposed. The model is based upon the hypothesis that some marine calcifiers induce calcification by elevating pH, and thus Ω_A, of their calcifying fluid by removing protons (H⁺). The model is explored through two end-member scenarios: one in which a fixed number of H⁺ is removed from the calcifying fluid, regardless of atmospheric pCO₂, and another in which a fixed external-internal H⁺ ratio ([H⁺]_E/[H⁺]_I) is maintained. The model is able to generate the full range of calcification response patterns observed in prior ocean acidification experiments and is consistent with the assertion that organisms’ calcification response to ocean acidification is more negative for marine calcifiers that exert weaker control over their calcifying fluid pH. The model is empirically evaluated for the temperate scleractinian coral Astrangia poculata with in situ pH microelectrode measurements of the coral’s calcifying fluid under control and acidified conditions. These measurements reveal that (1) the pH of the coral’s calcifying fluid is substantially elevated relative to its external seawater under both control and acidified conditions, (2) the coral’s [H⁺]_E/[H⁺]_I is approximately the same under control and acidified conditions, and (3) the coral removes fewer H⁺ from its calcifying fluid under acidified conditions than under control conditions. Thus, the carbonate system dynamics of A. poculata’s calcifying fluid appear to be most consistent with the fixed [H⁺]_E/[H⁺]_I end-member scenario. Similar microelectrode experiments performed on additional taxa are required to assess the model’s general applicability.  相似文献   

Effect of chlorine on near‐liquidus crystallization of olivine‐phyric shergottite NWA 6234 at 1 GPa: Implication for volatile‐induced melting of the Martian mantle          下载免费PDF全文

Benjamin J. Farcy  Juliane Gross  Paul Carpenter  Jacob Hicks  Justin Filiberto 《Meteoritics & planetary science》2016,51(11):2011-2022

Martian magmas are thought to be rich in chlorine compared with their terrestrial counterparts. Here, we experimentally investigate the effect of chlorine on liquidus depression and near‐liquidus crystallization of olivine‐phyric shergottite NWA 6234 and compare these results with previous experimental results on the effect of chlorine on near‐liquidus crystallization of the surface basalts Humphrey and Fastball. Previous experimental results showed that the change in liquidus temperature is dependent on the bulk composition of the basalt. The effect of chlorine on liquidus depression is greater for lower SiO₂ and higher Al₂O₃ magmas than for higher SiO₂ and lower Al₂O₃ magmas. The bulk composition for this study has lower Al₂O₃ and higher FeO contents than previous work; therefore, we provide additional constraints on the effect of the bulk composition on the influence of chlorine on near‐liquidus crystallization. High pressure and temperature crystallization experiments were performed at 1 GPa on a synthetic basalt, of the bulk composition of NWA 6234, with 0–4 wt% Cl added to the sample as AgCl. The results are consistent with previous notions that with increasing wt% Cl in the melt, the crystallization temperature decreases. Importantly, our results have a liquidus depression ?T (°C) from added chlorine that is consistent with the difference in bulk composition and suggest a dependence on both the bulk Al₂O₃ and FeO content. Our results suggest that the addition of chlorine to the Martian mantle may lower magma genesis temperatures and potentially aid in the petrogenesis of Martian magmas.  相似文献