Magmatic Differentiation at an Island-arc Caldera: Okmok Volcano, Aleutian Islands, Alaska

Okmok volcano is situated on oceanic crust in the central Aleutianarc and experienced large (15 km³) caldera-forming eruptionsat 12 000 years BP and 2050 years BP. Each caldera-forming eruptionbegan with a small Plinian rhyodacite event followed by theemplacement of a dominantly andesitic ash-flow unit, whereaseffusive inter- and post-caldera lavas have been more basaltic.Phenocryst assemblages are composed of olivine + pyroxene +plagioclase ± Fe–Ti oxides and indicate crystallizationat 1000–1100°C at 0·1–0·2 GPain the presence of 0–4% H₂O. The erupted products followa tholeiitic evolutionary trend and calculated liquid compositionsrange from 52 to 68 wt % SiO₂ with 0·8–3·3wt % K₂O. Major and trace element models suggest that the moreevolved magmas were produced by 50–60% in situ fractionalcrystallization around the margins of the shallow magma chamber.Oxygen and strontium isotope data (¹⁸O 4·4–4·9,⁸⁷Sr/ ⁸⁶Sr 0·7032–0·7034) indicate interactionwith a hydrothermally altered crustal component, which led toelevated thorium isotope ratios in some caldera-forming magmas.This compromises the use of uranium–thorium disequilibria[(²³⁰Th/ ²³⁸U) = 0·849–0·964] to constrainthe time scales of magma differentiation but instead suggeststhat the age of the hydrothermal system is 100 ka. Modellingof the diffusion of strontium in plagioclase indicates thatmany evolved crystal rims formed less than 200 years prior toeruption. This addition of rim material probably reflects theremobilization of crystals from the chamber margins followingreplenishment. Basaltic recharge led to the expansion of themagma chamber, which was responsible for the most recent caldera-formingevent. KEY WORDS: Okmok; caldera; U-series isotopes; Sr-diffusion; time scales; Aleutian arc     

森林景观模型研究新进展及其应用

森林景观模型(forest landscape models)是基于森林动态机制和干扰作用在景观尺度上模拟和预测森林时空变化特征的计算机模型。该类模型越来越多地用于森林规划、经营管理、生态资源保护与恢复及全球气候变化研究。本文通过对大量文献资料的整理,对森林景观模型的概念、尺度、类型、方法、应用和最新研究进展进行了综述。随着计算机、地理信息系统、遥感等技术的迅猛发展,森林景观模型将会越来越多地与地理信息系统、规划经营管理决策等紧密结合,未来将向服务性决策模型方向发展。     

测度链上微分方程的进展

综述测度链上微分方程理论的基本概念及其最新进展，包括作者的研究集体所做的工作，也提出一些值得进一步研究的课题。     

Microstructure measurements in natural waters: Methodology and applications

Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate ε and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding.A new analytical approximation for the 1D Panchev–Kesich spectrum is deduced and the results of ε computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute ε from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations.Statistical analysis of eddy K_b and thermal K_θ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between K_b and K_θ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged K_b and K_θ differ significantly, which may point to the inapplicability of isotropic formulae used for ε and temperature dissipation χ_θ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence.     

Inertial oscillations and frontogenesis driven by a quadratic horizontal density variation

We consider inviscid rotating flow driven by a horizontally quadratic density variation in a horizontally unbounded slab. This configuration permits a similarity solution, removing the dependence on the horizontal coordinate from the vorticity and temperature equations, which are then solved by numerical integration along characteristics. At large values of Rossby number, the flow proceeds to a singularity in a similar manner to the non-rotating flow with the same initial conditions. At small values of Rossby number there are inertial oscillations of growing amplitude, which have been analysed using the method of multiple scales. The oscillations become desynchronised between the upper and lower parts of the domain, and static instability appears for a small fraction of each oscillation period. Eventually the oscillations give way to the rapid formation of a singularity, in contrast to geostrophic adjustment theory which predicts that a singularity will form only if the Rossby number is sufficiently large.     

Two possible mechanisms for vortex self-organization

Since the 21st century, the self-organization phe-nomenon has drawn a wide attention of Chinese sci-ence and technology researchers, and the study fields involve silicate chemistry[1, 2], the classification of re-mote sensing data[3], nanometer material[4―6], medium resistance to discharges[7], forest fires[8], mud-rock flow[9], sandpile formation[10, 11], urban geography[12], economic geography[13], intense storms over the Loess Plateau[14] and vortices over the Tibetan Plateau[15], etc. Re…     

基于小波变换的大安地区年降水量变化特征

基于小波分析的方法,对吉林省大安地区1959—2007年的年降水量序列的变化特征进行了分析。经分析表明,大安地区年降水量在其计算时域内各时间尺度分布不均匀,具有明显的局部化特征;其中4～6 a尺度主要发生在1959—1969年和1984年之后,10～12 a尺度主要发生在1965—1999年,20～25a尺度在整个计算时域内均有发生。不同时间尺度下,降水量偏多、偏少交替变化也不相同。此外,分析结果显示该地区年降水量具有4 a、10 a和21 a左右的主周期,其中4 a周期为第一主周期。     

毫秒(ms)脉冲星计时观

简介了国际上脉冲星计时研究的成果。主要评述中国在脉冲星计时研究方面的进展和观点:某些ms脉冲星可以用作天然的高精度的频率标准源。ms脉冲星时(PTens)的长期稳定度随观测时间的加长而提高,同时,它具有寿命长,稳定、可靠、不需要维修等优点。尽早适时地建立专门用于测量ms脉冲星时(PTens)的脉冲星钟系统网络是有益的。我国正在建设用于脉冲星脉冲到达时间(TOA)测量的50m射电望远镜,和正在研究(FAST)500m射电望远镜。论述了脉冲星时间尺度的建立是可行的,脉冲星时和原子时可以"交叉比对,相互检验,并肩发展"。研究表明综合脉冲星时的长期稳定度明显优于原子时。阐述了把小波分析方法应用于时间尺度,研究结果比较传统方法有明显的优势。对国际间的合作提出建议。并展望了中国的脉冲星计时规划。     

Empirical Global Relations Converting M S and m b to Moment Magnitude

The existence of several magnitude scales used by seismological centers all over the world and the compilation of earthquake catalogs by many authors have rendered globally valid relations connecting magnitude scales a necessity. This would allow the creation of a homogeneous global earthquake catalog, a useful tool for earthquake research. Of special interest is the definition of global relations converting different magnitude scales to the most reliable and useful scale of magnitude, the moment magnitude, M _W. In order to accomplish this, a very large sample of data from international seismological sources (ISC, NEIC, HRVD, etc.) has been collected and processed. The magnitude scales tested against M _W are the surface wave magnitude, M _S, the body wave magnitude, m _b, and the local magnitude, M _L. The moment magnitudes adopted have been taken from the CMT solutions of HRVD and USGS. The data set used in this study contains 20,407 earthquakes, which occurred all over the world during the time period 1.1.1976–31.5.2003, for which moment magnitudes are available. It is shown that well-defined relations hold between M _W and m _b and M _S and that these relations can be reliably used for compiling homogeneous, with respect to magnitude, earthquake catalogs.