松辽盆地早白垩世火山岩地球化学特征及其构造意义

松辽盆地早白垩世发育基性岩类的橄榄玄武岩、玄武岩,中性岩类的玄武安山岩、安山岩、粗安岩,酸性岩类的粗面岩、粗面英安岩、英安岩和流纹岩。早白垩世火山岩都具有大离子亲石元素(LILE)、轻稀土元素(LREE)相对富集的特征,并具有较低的(~(87)Sr/~(86)Sr)_i值和较高的(~(143)Nd/~(144)Nd)_i值。基性岩类Ce/Nb=1.92～8.31,Th/Nb=0.08～0.44,(~(87)Sr/~(86)Sr)_i=0.7031～0.7047,ε_(Nd)(t)=+1.7～+5.2;中性岩类Ce/Nb=3.70～15.80,Th/Nb=0.34～2.58,(~(87)Sr/~(86)Sr)_i=0.7040～0.7054,ε_(Nd)(t)=0～+3.0;酸性岩类Ce/Nb=4.29～15.80,Th/Nb=0.11～1.02,(~(87)Sr/~(86)Sr)_i=0.7038～0.7066,ε_(Nd)(t)=+1.0～+3.3。基性岩类岩浆主要来自被富集了的亏损地幔源的部分熔融,受混染程度很小;中性岩类岩浆源于年轻地壳组分被来自亏损地幔岩浆的再次部分熔融;酸性岩类浆岩可能主要来自源于亏损地幔的初生地壳部分熔融,并受到了上地壳的混染。晚侏罗世-早白垩世,由于蒙古-鄂霍次克洋关闭引发强烈的挤压造山后,发生的岩石圈拆沉作用致使来自亏损地幔的岩浆熔融上涌导致岩石圈主动伸展拉张,地表则表现出大规模的裂谷断陷作用和大范围的火山活动。这个阶段的伸展拉张以主动拉张为主。     

Rapid topographic change measured by high-resolution satellite radar at Soufriere Hills Volcano,Montserrat, 2008–2010

High-resolution satellite radar observations of erupting volcanoes can yield valuable information on rapidly changing deposits and geomorphology. Using the TerraSAR-X (TSX) radar with a spatial resolution of about 2 m and a repeat interval of 11 days, we show how a variety of techniques were used to record some of the eruptive history of the Soufriere Hills Volcano, Montserrat between July 2008 and February 2010. After a 15-month pause in lava dome growth, a vulcanian explosion occurred on 28 July 2008 from a vent that was hidden by dense cloud. We were able to show the civil authorities using TSX difference images of surface roughness change that this explosion had not disrupted the dome sufficiently to warrant continuation of a previous, precautionary evacuation. Change difference images also proved to be valuable in mapping new pyroclastic flow deposits: the valley-occupying block-and-ash component tended to increase backscatter and the marginal surge deposits to reduce it, with the pattern reversing after the event due to erosion and deposition. By comparing east- and west-looking images acquired 12 h apart, the deposition of some individual pyroclastic flows can be inferred from change differences. Some of the narrow upper sections of valleys draining the volcano received many tens of metres of rockfall and pyroclastic flow deposits over periods of a few weeks. By measuring the changing radar shadows cast by these valleys in TSX images the changing depth of infill by deposits could be estimated. In addition to using the amplitude data from the radar images we also used their phase information within the InSAR technique to calculate the topography during a period of no surface activity. This enabled areas of transient topography, crucial for directing future flows, to be captured.     

Short-term variation in thermal stratification complicates estimation of lake metabolism

Previous studies have used sondes to measure diel changes in dissolved oxygen and thereby estimate gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP). Most of these studies estimate rates for the surface layer and require knowing the depth of the mixed layer (Z_mix), which is usually determined from discrete daily or weekly temperature profiles. However, Z_mix is dynamic, as the thermal structure of lakes may change at scales of minutes rather than days or weeks. We studied two thermally stratified lakes that exhibited intermittent microstratification in the mixed layer. We combined sonde-based estimates of metabolism with high-frequency measurements of stratification using thermistor chains to determine how the short-term dynamics of stratification affect metabolic rates. We calculated estimates of metabolism using time series of Z_mix measured at seasonal, weekly, daily, and 5-min intervals. Areal rates of GPP and R were up to 24 and 29% less, respectively, using the 5-min measurements of Z_mix rather than weekly Z_mix, while NEP was not significantly different. These reduced areal rates are mostly the consequence of the reduction in the depth of the mixed layer. Microstratification occurred frequently in both lakes and affected volumetric rates in one lake where R was significantly lower, NEP was significantly higher, and GPP was marginally lower compared to days without microstratification. Hence, microstratification not only affects the depth of the mixed layer, but also alters the processes that influence photosynthesis and respiration. Future studies should consider microstratification and possibly employ multiple sondes with thermistor chains that enable integrating metabolic rates to a specific depth, rather than assuming a stable upper mixed layer as the basis for calculations.     

Micron‐scale hypervelocity impact craters: Dependence of crater ellipticity and rim morphology on impact trajectory,projectile size,velocity, and shape

The interstellar collector on NASA's Stardust mission captured many particles from sources other than the interstellar dust stream. Impact trajectory may provide a means of discriminating between these different sources, and thus identifying/eliminating candidate interstellar particles. The collector's aerogel preserved a clear record of particle impact trajectory from the inclination and direction of the resultant tracks. However, the collector also contained aluminum foils and, although impact crater studies to date suggest only the most inclined impacts (>45° from normal) produce crater morphologies that indicate trajectory (i.e., distinctly elliptical), these studies have been restricted to much larger (mm and above) scales than are relevant for Stardust (μm). It is unknown how oblique impact crater morphology varies as a function of length scale, and therefore how well Stardust craters preserve details of impactor trajectory. Here, we present data from a series of impact experiments, together with complementary hydrocode modeling, that examine how crater morphology changes with impact angles for different‐sized projectiles. We find that, for our smallest spherical projectiles (2 μm diameter), the ellipticity and rim morphology provide evidence of their inclined trajectory from as little as 15° from normal incidence. This is most likely a result of strain rate hardening in the target metal. Further experiments and models find that variation in velocity and impactor shape complicate these trends, but that rim morphology remains useful in determining impact direction (where the angle of impact is >20° from normal) and may help identify candidate interstellar particle craters on the Stardust collector.     

The effects of photoionization on galaxy formation – II. Satellite galaxies in the Local Group

We use a self-consistent model of galaxy formation and the evolution of the intergalactic medium to study the effects of the reionization of the Universe at high redshift on the properties of satellite galaxies like those seen around the Milky Way. Photoionization suppresses the formation of small galaxies, so that surviving satellites are preferentially those that formed before the Universe reionized. As a result, the number of satellites expected today is about an order of magnitude smaller than the number inferred by identifying satellites with subhaloes of the same circular velocity in high-resolution simulations of the dark matter. The resulting satellite population has an abundance similar to that observed in the Local Group, although the distribution of circular velocities differs somewhat from the available data. We explore many other properties of satellite galaxies, including their gas content, metallicity and star formation rate, and find generally good agreement with available data. Our model predicts the existence of many as yet undetected satellites in the Local Group. We quantify their observability in terms of their apparent magnitude and surface brightness, and also in terms of their constituent stars. A near-complete census of the Milky Way's satellites would require imaging to   V ≈20  and to a surface brightness fainter than 26 V -band magnitudes per square arcsecond. Satellites with integrated luminosity   V =15  should contain of order 100 stars brighter than   B =26  , with central stellar densities of a few tens per square arcminute. Discovery of a large population of faint satellites would provide a strong test of current models of galaxy formation.     

The 2dF Galaxy Redshift Survey: a targeted study of catalogued clusters of galaxies

We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information is used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10 per cent, whereas the APM catalogue suffers only 5 per cent contamination. If we use the original catalogue centroids, the level of contamination rises to approximately 15 per cent for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at     that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive a space density of     clusters of     This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum.     

The 2dF Galaxy Redshift Survey: luminosity functions by density environment and galaxy type

We use the 2dF Galaxy Redshift Survey to measure the dependence of the b _J-band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius  8  h ⁻¹ Mpc  , and on spectral type, determined from principal component analysis. We find that the galaxy populations at both extremes of density differ significantly from that at the mean density. The population in voids is dominated by late types and shows, relative to the mean, a deficit of galaxies that becomes increasingly pronounced at magnitudes brighter than   M _{b J}−5log₁₀ h ≲−18.5  . In contrast, cluster regions have a relative excess of very bright early-type galaxies with   M _{b J}−5log₁₀ h ≲−21  . Differences in the mid- to faint-end population between environments are significant: at   M _{b J}−5log₁₀ h =−18  early- and late-type cluster galaxies show comparable abundances, whereas in voids the late types dominate by almost an order of magnitude. We find that the luminosity functions measured in all density environments, from voids to clusters, can be approximated by Schechter functions with parameters that vary smoothly with local density, but in a fashion that differs strikingly for early- and late-type galaxies. These observed variations, combined with our finding that the faint-end slope of the overall luminosity function depends at most weakly on density environment, may prove to be a significant challenge for models of galaxy formation.