Crystal-melt partitioning of noble gases (helium, neon, argon, krypton, and xenon) for olivine and clinopyroxene     

Veronika S. Heber  Richard A. Brooker  Simon P. Kelley 《Geochimica et cosmochimica acta》2007,71(4):1041-1061

Mineral-melt partition coefficients of all noble gases (^min/meltD_i) have been obtained for olivine (ol) and clinopyroxene (cpx) by UV laser ablation (213 nm) of individual crystals grown from melts at 0.1 GPa 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/meltD_i on radius as the charge decreases. As all noble gases appear to exhibit similar ^min/meltD_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.  相似文献   

The M 4 Core Project with HST: I. Overview and first epoch     

L.R. Bedin  J. Anderson  D.C. Heggie  G. Piotto  A.P. Milone  M. Giersz  V. Nascimbeni  A. Bellini  R.M. Rich  M. van den Berg  D. Pooley  K. Brogaard  S. Ortolani  L. Malavolta  L. Ubeda  A.F. Marino 《Astronomische Nachrichten》2013,334(10):1062-1085

We present an overview of the ongoing Hubble Space Telescope large program GO‐12911. The program is focused on the core of M 4, the nearest Galactic globular cluster, and the observations are designed to constrain the number of binaries with massive companions (black holes, neutron stars, or white dwarfs) by measuring the “wobble” of the luminous (mainsequence) companion around the center of mass of the pair, with an astrometric precision of ∼50 µas. The high spatial resolution and stable medium‐band PSFs of WFC3/UVIS will make these measurements possible. In this work we describe (i) the motivation behind this study, (ii) our observing strategy, (iii) the many other investigations enabled by this unique data set, and which of those our team is conducting, and (iv) a preliminary reduction of the first‐epoch dataset collected on 2012 October 10. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Solar Rotational Periodicities and the Semiannual Variation in the Solar Wind, Radiation Belt, and Aurora     

Barbara A. Emery  Ian G. Richardson  David S. Evans  Frederick J. Rich  Gordon R. Wilson 《Solar physics》2011,274(1-2):399-425

The behavior of a number of solar wind, radiation belt, auroral and geomagnetic parameters is examined during the recent extended solar minimum and previous solar cycles, covering the period from January 1972 to July 2010. This period includes most of the solar minimum between Cycles 23 and 24, which was more extended than recent solar minima, with historically low values of most of these parameters in 2009. Solar rotational periodicities from 5 to 27 days were found from daily averages over 81 days for the parameters. There were very strong 9-day periodicities in many variables in 2005?–?2008, triggered by recurring corotating high-speed streams (HSS). All rotational amplitudes were relatively large in the descending and early minimum phases of the solar cycle, when HSS are the predominant solar wind structures. There were minima in the amplitudes of all solar rotational periodicities near the end of each solar minimum, as well as at the start of the reversal of the solar magnetic field polarity at solar maximum (～?1980, ～?1990, and ～?2001) when the occurrence frequency of HSS is relatively low. Semiannual equinoctial periodicities, which were relatively strong in the 1995?–?1997 solar minimum, were found to be primarily the result of the changing amplitudes of the 13.5- and 27-day periodicities, where 13.5-day amplitudes were better correlated with heliospheric daily observations and 27-day amplitudes correlated better with Earth-based daily observations. The equinoctial rotational amplitudes of the Earth-based parameters were probably enhanced by a combination of the Russell-McPherron effect and a reduction in the solar wind-magnetosphere coupling efficiency during solstices. The rotational amplitudes were cross-correlated with each other, where the 27-day amplitudes showed some of the weakest cross-correlations. The rotational amplitudes of the >?2 MeV radiation belt electron number fluxes were progressively weaker from 27- to 5-day periods, showing that processes in the magnetosphere act as a low-pass filter between the solar wind and the radiation belt. The A _p/K _p magnetic currents observed at subauroral latitudes are sensitive to proton auroral precipitation, especially for 9-day and shorter periods, while the A _p/K _p currents are governed by electron auroral precipitation for 13.5- and 27-day periodicities.  相似文献   

Asteroids (65) Cybele, (107) Camilla and (121) Hermione: Infrared spectral diversity among the Cybeles     

Kelsey D. Hargrove  Michael S. Kelley  Humberto Campins  Javier Licandro  Josh Emery 《Icarus》2012,221(1):453-455

We find a clear diversity in the 3 μm and 10 μm features of three Cybele asteroids: (107) Camilla, (121) Hermione, and (65) Cybele. (121) Hermione exhibits a “check-like” 3 μm feature, which may be attributed to OH-dominated minerals and (107) Camilla shows a rounded “bowl” like feature closer to that of (65) Cybele, which may be attributed to H₂O-dominated minerals. The 10 μm features of these three asteroids are also different from each other.  相似文献   

Estimating fractional land cover in semi-arid central Kalahari: the impact of mapping method (spectral unmixing vs. object-based image analysis) and vegetation morphology     

Niti B. Mishra  Kelley A. Crews 《国际地球制图》2013,28(8):860-877

Focusing on the central Kalahari, this study utilized fractional cover of photosynthetic vegetation (f_PV), non-photosynthetic vegetation (f_NPV) and bare soil (f_BS), derived in situ and estimated from GeoEye-1 imagery using Multiple Endmember Spectral Mixture Analysis (MESMA) and object-based image analysis (OBIA) to determine superior method for fractional cover estimation and the impact of vegetation morphology on the estimation accuracy. MESMA mapped fractional cover by testing endmember models of varying complexity. Based on OBIA, image was segmented at five segmentation scales followed by classification. MESMA provided more accurate fractional cover estimates than OBIA. The increasing segmentation scale in OBIA resulted in a consistent increase in error. Different vegetation morphology types showed varied responses to the changing segmentation scale, reflecting their unique ecology and physiognomy. While areas under woody cover produced lower error even at coarse segmentation scales, those with herbaceous cover provided low error only at the fine segmentation scale.  相似文献   

Long-term electromagnetic core–mantle coupling and the Earth’s rotation acceleration in the Mesozoic Era     

Weijia Zhang  Yuanlin Sun  Neil Kelley  Yang Lei  Hangjie Yu 《Russian Geology and Geophysics》2012,53(5):491-499

Growth lines in the mineralized tissues of living and fossil organisms often exhibit regular patterns that record daily, monthly, or annual cycles. Growth laminations in fossil corals and other marine invertebrates indicate long-term deceleration of the Earth’s rotation, probably largely due to tidal friction, resulting in a decline in the number of days per year over the Earth’s history. Fossils suggest the rate of decline has not been uniform, with the trend between the late Carboniferous and Cretaceous in particular departing from preceding and subsequent periods. However, insufficient data have obscured the nature and cause of the apparent halt in despinning within this time interval. Here we present new fossil geochronometer data that reveal a sustained acceleration in the Earth’s rotation in the early Mesozoic Era, lasting about 90 million years and producing a decrease in the length of day (LOD) at an average rate of about 3 ms/cy. The coincidence of this acceleration with certain geophysical events including the final assembly of Pangaea and a change in the intensity and stability of the geomagnetic field strongly suggests that its cause is rooted in the deep interior of the Earth. A similar explanation has been proposed for observed decadal variations in the Earth’s rotation. Our results suggest large-scale linkage of rotational variation, tectonics, and the geomagnetic field to core–mantle boundary (CMB) dynamics. Furthermore the newly identified acceleration in the Earth’s rotation which began at the end of the Paleozoic, and the geophysical factors that are associated with it, can ultimately bear on the causal mechanisms behind the Permo-Triassic mass extinction.  相似文献   

The emergent urban imaginaries of geosocial media     

Matthew James Kelley 《GeoJournal》2013,78(1):181-203

A class of geosocial software applications has begun to emerge that integrates location and social networking. These applications enable public participation in the production of datasets that reveal patterns of individual perception, interaction, and experience in space. Geosocial data consist of point locations that have been created and tagged by participants with short statements about their perceptions and/or experiences. Increasingly, these data are streamed via map interface by ‘meta-geosocial’ aggregation services and are freely available to the public. In this article I suggest that as geosocial applications become more popular, the composite sketches of place that result from them will constitute increasingly accurate representations of the local collective socio-spatial imaginary. Using data collected from one of the more popular geosocial media services, I explore the proposition that collective digital imaginaries have the potential to emerge from geosocial data. And drawing on the literature of the imaginary, I argue that geosocial-based imaginaries do not simply reflect socio-spatial practice, but also inform and influence the ways that we perceive, experience and interact in space.  相似文献   

Fumarolic pipes in the Tshirege Member of the Bandelier Tuff on the Pajarito Plateau, Jemez Mountains, New Mexico     

Florie A. Caporuscio  Jamie N. Gardner  Emily S. Schultz-Fellenz  Richard E. Kelley 《Bulletin of Volcanology》2012,74(5):1023-1037

The objective of this study is to demonstrate the relationships among devitrification, vapor phase alteration, localization of gas emanations into fumarolic pipes, and initial deformation of the ash flow sheet during cooling and lithification. Utilizing a unique and temporary exposure of the Tshirege Member of the Bandelier Tuff near Los Alamos, New Mexico, we identify several zones of distinctly preserved fossil fumarolic activity. The fumarolic zones vary in width from a few centimeters to more than a meter. Almost ubiquitously, these zones demonstrate fines-depletion, induration of the margins, upward-flaring geometries, and intense fracturing of overlying geologic units. The fumaroles were preferentially located on post welding, early formed cooling joints that vented to the surface after the vapor phase alteration stage. The pipes were regularly spaced at distances of approximately 4.5?m (N–S) to 7?m (E–W). In turn the pipes were covered by a surge deposit and overlying tuff which rapidly lithified. The overlying tuff was then brecciated during continued fumarolic pipe emissions. Geochemical evaluations confirm the presence of high-temperature mineral (scapolite) indicative of transport of hot volcanic gases through these zones. The pipe centers and walls are depleted in SiO₂, and enriched in Al₂O₃ and FeO. The overlying tuff breccia zones are enriched in Al₂O₃, FeO and MgO, and depleted in SiO₂, NaO, and K₂O. From comparison to other ignimbrite cooling histories, the fissures, fumaroles, and structures observed all likely formed in the first few decades after the deposition of the upper Tshirege subunits. This may have significant implications as to timing of initial cooling fractures and subsequent consolidation of gas emission pathways.  相似文献   

Observations of polar mesospheric summer echoes using PFISR during the summer of 2007     

Roger H. Varney  Michael J. Nicolls  Craig J. Heinselman  Michael C. Kelley 《Journal of Atmospheric and Solar》2009,71(3-4):470-476

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Spectacular low- and mid-latitude electrical fields and neutral winds during a superstorm     

Michael C. Kelley  Ronald R. Ilma  Michael Nicolls  Philip Erickson  Larisa Goncharenko  Jorge L. Chau  Nestor Aponte  Janet U. Kozyra 《Journal of Atmospheric and Solar》2010,72(4):285-291

In November 2004, a major magnetic storm occurred, a lengthy portion of which was recorded by the Upper Atmospheric Radar Chain. On the 9th and 10th, the Jicamarca Radar detected the highest magnitude penetrating electric fields (±3 mV/m) and vertical drifts (±120 m/s) ever seen at this premiere facility. These large and variable drifts were highly correlated with the interplanetary magnetic and electric fields and created a double F layer on the dayside and unusual TEC behavior throughout the low-latitude zone. These solar wind-induced drifts both suppressed and generated irregularities at the magnetic equator at different times. Large-scale thermospheric disturbances were generated by high-latitude heating and tracked through the middle- to low-latitude zones where both parallel and perpendicular plasma drifts created major ionospheric changes. The auroral oval was located at a magnetic L shell of about three for many hours.  相似文献