LA‐ICP‐MS Pb isotope test of meteorite provenance: A terrestrial origin for Lovina

Lovina, classified as an ungrouped ataxite, is controversial and its identity as a meteorite has been questioned. In this work, we use Pb isotopes on targeted troilite nodules in Lovina as a test of its antiquity and provenance. Although precise ages cannot be obtained, LA‐ICP‐MS offers a rapid, straightforward procedure to establish the source of lead, whether ancient (meteoritic) or modern (terrestrial). For nine pristine, unweathered nodules in Lovina, we find a lead isotopic composition of: ²⁰⁶Pb/²⁰⁸Pb = 0.492 ± 0.003 (2σ, MSWD 0.79; 95%) and ²⁰⁷Pb/²⁰⁶Pb = 0.852 ± 0.003 (2σ, MSWD 1.09; 95%) with no detectable uranium. All lead compositions of the troilite fall in the range expected for modern environmental and mantle lead and are distinctly different from the primordial Canyon Diablo Troilite (CDT) composition of ancient meteoritic troilite. Although the origin of Lovina remains unknown, we conclude that lead in the Lovina troilite is unsupported by U decay and originated from a terrestrial source.     

A unique type B inclusion from Allende with evidence for multiple stages of melting

Abstract— A large (7 mm in diameter) Allende type B inclusion has a typical bulk composition and a unique structure: a fassaite‐rich mantle enclosing a melilite‐rich core. The core and mantle have sharply contrasting textures. In the mantle, coarse (?1 mm across), subhedral fassaite crystals enclose radially oriented melilite laths about 500 μm long that occur at the inclusion rim. The core consists of blocky melilite grains 20–50 μm across and poikilitically enclosed in anhedral fassaite grains that are optically continuous over ?1 mm. Another unique feature of this inclusion is that melilite laths also extend from the core into the mantle. Fassaite in both the core and mantle is very rich in fine‐grained (1–10 μm) spinel. The rim laths are normally zoned (Åk_30–70) inward from the rim of the inclusion with reverse zoning over the last ?200 μm to crystallize. A very wide range of melilite compositions is found in the core of the inclusion, where gehlenitic grains (Åk_5–12) occur. These grains are enclosed in strongly zoned (Åk_15–70) overgrowths. The gehlenitic cores and innermost parts of the overgrowths are Na₂O‐free, but the outer parts of the overgrowths are not. In the laths at the rim, Na₂O decreases inward from the rim, then increases. Fassaite in the core has the same range of Ti contents as that in the mantle: 2–9 wt% TiO₂ + Ti₂O₃. Two melting events are required to account for the features of this inclusion. In the first event, the precursor assemblage is heated to ?1400 °C and melts except for gehlenitic (Åk_5–12) melilite and some spinel. These grains become concentrated in the core. During cooling, Na₂O‐free melilite nucleates at the rim of the inclusion and on the relict grains in the core. After open system secondary alteration, the inclusion is heated again, but only to ?1260 °C. Melilite more gehlenitic than Åk₄₀ does not melt. During cooling, Na₂O‐bearing melilite crystallizes as small, blocky grains and laths in the core and as overgrowths on relict grains in the core and at the rim. Eventually melilite co‐crystallizes with fassaite, leading to the reverse zoning observed in the laths. The coexistence in this inclusion of Na‐free and Na‐bearing melilite, plus a positive correlation between Na₂O and åkermanite contents in melilite in an inclusion with a bulk Mg isotopic composition that is mass‐fractionated in favor of the heavy isotopes, are both consistent with at least two melting events. Several other recently described coarse‐grained inclusions also have features consistent with a sequence of early, high‐temperature melting, secondary alteration, and remelting at a lower temperature, suggesting that remelting of refractory inclusions was a common occurrence in the solar nebula.     

The NOAA Goes-12 Solar X-Ray Imager (SXI) 2. Performance

The Solar X-ray Imager (SXI) was launched on 23 July 2001 on NOAAs GOES-12 satellite and completed post-launch testing on 20 December 2001. It was brought into operations on 21 January 2003. This paper documents SXI performance and calibrations prior to an instrument degradation that occurred on 5 November 2003 and thus covers more than 420000 soft X-ray images of the Sun. This paper details component-level as well as full-system calibrations characterizing the spatial and spectral performance of the instrument, including the grazing-incidence mirror, filters, and the properties of the MCP-intensified CCD detector system. Routine image corrections are also described. These include background (dark current) subtraction, flat-fielding, off-band light-leak correction, and image pointing and timing considerations. In addition, a signal-to-noise analysis is presented. The information contained in this study is intended to enable researchers to conduct quantitative analysis of GOES-12 SXI images.     

Discrete Alfvén waves in planar flux tubes

Properties of discrete Alfvén wave modes are derived, at frequencies up to the ion-cyclotron frequency, for current-carrying plasma slabs with non-uniform densities. It is shown that the essential features of the dispersion relations can be derived by examining the dominant terms in the potential function, when the wave equation is cast in the Schrödinger equation form. Analytical predictions for a class of mass and current density profiles are compared with numerically calculated dispersion relations and wavefields for particular profiles.     

Planetary brightness temperature measurements at 8.6 mm and 3.1 mm wavelengths

New measurements of the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn at 3.1 and 8.6 mm wavelengths are given. The temperatures reported for the planets at 3.1 mm wavelength are higher than previous measurements in this wavelength range and change the interpretation of some planetary spectra. For Mercury, it is found that the mean brightness temperature is independent of wavelength and that a temperature dependent thermal conductivity is not required to match the observations. In the case of Mars, the spectrum is shown to rise in the millimeter region as simple models predict. For Jupiter, the need to recalculate the spectrum with recent models is demonstrated. The flux density scale proposed by Dent (1972) has been revised according to a more accurate determination of the millimeter brightness temperature of Jupiter.     

The importance of radiative transfer in stellar pulsation models

With the advent of new astrophysical opacities it seems appropriate to discuss the need for a full radiative transfer (RT) theory instead of the usual equilibrium diffusion theory used in most nonlinear pulsation codes. Early studies on the importance of RT in the calculation of light curves for Cepheid models showed little effect over diffusion theory. The new opacities though may help to explain the bump mass discrepancy problem. For RR Lyrae models the use of RT theory causes some effects both in the color differences (U-B) as well as in the light curves. New opacities help to explain the period ratios for double mode RR Lyrae and beat Cepheids. A new area of research is in the modeling of stars with high luminosity to mass ratios that show tendencies for doubling and transitions to chaos, such as W Virginis and RV Tauri stars. For these stars it has been shown that RT is necessary in calculating their light curves and that the understanding of the shock dynamics depends on the transfer of lines in the pulsating RT dependent atmospheres (Fokin 1991).     

华北燕山带东部三叠纪和侏罗纪大地构造演化：来自备受争议的邓杖子组及相邻地层的线索

位于辽西凌源市南部的牛营子-邓杖子地区侏罗系地质问题多年来困扰着地质学家。争论最多的构造形迹是一套平面上呈狭长矩形,以断层为界的近直立中元古界常州沟组石英岩,及局部长城系顶部地层。这套地层绵延35 km,呈北北东展布。其西界为近直立的大齐子断层（新命名断层）和大部分向东倒转的陡倾下侏罗统邓杖子组;东界为近直立的朱杖子断层（新命名断层）和西倾的中侏罗统郭家店组。前人的构造解释倾向于大齐子断层为邓杖子组一侧下降的陡倾正断层,朱杖子断层为郭家店组一侧下降的陡倾逆断层。文中不同意这样的解释,并发现有证据表明上述两个断层都形成于之前尚未识别出的侏罗纪构造事件时期。将大齐子断层解释为早侏罗世晚期-中侏罗世早期形成的一条向西逆冲的断层,沿着它使长城系推覆于邓杖子组之上,然后,该逆冲断层上、下盘地层共同卷入后期褶皱变形当中。朱杖子断层原本为正断层,形成于原来未识别出的中侏罗世伸展变形阶段,并构成了郭家店半地堑边界断层。朱杖子断层沿着向东倾斜的常州沟组石英岩与串岭沟组页岩的界面发育。随着断层的发育,位于常州沟组石英岩之上的串岭沟组及长城系上部地层发生拆离沉降并被埋藏在半地堑之下。随后,发生在中侏罗世晚期或晚侏罗世早期收缩构造变形,改造了邓杖子-常州沟-郭家店组构造组合的几何形态。本期改造导致以下结果：（1）朱杖子正断层发生反转成为逆断层;（2）蓟县系沿着杨杖子-瓦房店逆冲断层向东掩覆于断层围限的长城系地层及相邻侏罗系之上。同时,邓杖子组倾角加大并向东倒转。研究表明,辽西地区的侏罗纪构造演化过程远比原先所认为的要复杂。     

Small-scale auroral arc distortions

Small-scale spatially periodic distortions of auroral forms have been studied utilizing low-light level television observations made at various locations in the Northern and Southern Hemispheres. The most commonly observed features were folds and vortex-like curl formations. The curls, identified here with the Kelvin-Helmholtz instability due to fluid shear, invariably had a counterclockwise rotational shape and motion when viewed in a direction anti-parallel to the Earth's magnetic field. The typical measured wavelength (5 km) and measured growth rate (4.2 sec⁻¹) were used to evaluate the Kelvin-Helmholtz dispersion relation for the apparent shear ω_s = ∂ ν_x/ ∂y (28 sec⁻¹). The apparent horizontal velocities of both folds (0–5 km/sec) and curls (0–22 km/sec) were invariably observed to be counterclockwise with respect to the multiple arc centre when viewed antiparallel to B. Consistent agreement between rotational shape and rotational motion suggests that the apparent growth rate and the apparent horizontal velocities closely approximate the actual values. If the shear results from E×B drifts in a space charge field, the calculated value for ω_s, implies an unneutralized electron density 0–1 cm⁻³ and a ΔE across the arc element 500mV/m. The velocity measurements indicate that the ΔE values for individual elements can combine to produce transient electric fields at the edges of multiple arcs as high as 1000 mV/m.     

A fluid inclusion study of the porphyry-greisen,tungsten-molybdenum deposit at Mount Pleasant,New Brunswick,Canada

Homogenization temperatures and salinity data are presented for fluid inclusions from hydrothermal gangue minerals (quartz and fluorite) associated with porphyry wolframite-molybdenite-arsenopyrite-sphaleritebismuth-chalcopyrite-cassiterite mineralization within the Fire Tower ore zone, Mt Pleasant, New Brunswick. The data indicate that ore mineral precipitation occurred within a temperature range of 260° to 490°C from moderate to high salinity (10–42 wt% NaCl equivalent) aqueous fluids. Two stages of hydrothermal activity characterized by high (>30 wt% NaCl equivalent) salinity fluids are recognized; one which occurred at relatively high temperature (350°–490°C); and one which took place at lower temperature (180°–250°C). The high salinity, high temperature stage is interpreted to be the result of resurgent boiling. Dilution of these early fluids by convecting meteoric water resulted in low to moderate salinity fluids, which dominate the inclusion population. The low temperature, high salinity fluid inclusions are interpreted to represent late residual fluids derived from boiling which occurred as a result of a change in the pressure regime from dominantly lithostatic to hydrostatic conditions.     

Lamprothamnium prosperity in permannetly hypersaline water

The leuco-halophytic charophyte,Lamprothamnium papulosum, readily germinates, grows and reproduces in C1 Pond of ICI's solar saltworks near Port Alma, a permanently hypersaline waterbody in Queensland, Australia. Its morphology very much resembles that ofChara corallina, although the two central cells of the axial node are subdivided, a feature found inLamprothamnium but not inChara. Some of the characteristics of the Port Alma population, like the occurrence of a considerable proportion of pedicellate gametangia among the normal sessile ones, or the deviation in the sizes of some plant parts from the ranges that have been reported previously, are unusual, even for this highly variable species. Florida Agricultural Experiment Station Journal Series No. 6876