Shape, size, spatial distribution and composition of garnet crystals in highly deformed gneiss of the Otter Lake area, Québec, and a model for garnet crystallization

Garnet–biotite–(sillimanite) gneiss (～700 °C, 7 kbar) of the Otter Lake area in the Western Grenville Province (Canadian Shield) occurs as granitic gneiss (group 4) that forms a large part of the Otter Complex, and as widely distributed, more heterogenous metasedimentary gneiss (group 2). In one sample of group 4 gneiss (Qtz₂₅ Pl₃₄ Kfs₂₈ Bt₁₀ Grt_2.5 Sil₁) the true diameter (determined by serial grinding) of subhedral garnet crystals ranges from 0.2 to 3.0 mm, with a mode at 1.0 mm. Nearest‐neighbour measurements in this sample, and in surfaces of nine additional samples (all <5% garnet) confirm that garnet crystals are distributed mainly at random; slight clustering was detected in two samples. In one sample of group 4 gneiss, microprobe analyses on sections through crystal centres (obtained by serial slicing), reveal that small crystals and margins to large crystals contain more Fe and Mn and less Mg than the broad central regions of large crystals. Based on these and previous results, together with theoretical considerations, a crystallization model is proposed, in which, (i) garnet was produced by the continuous reaction, Ms + Bt + Qtz → Grt + Kfs + H₂O, (ii) nucleation occurred by the random selection of randomly distributed Ms–Bt–Qtz triple junctions, (iii) the rate of linear growth remained constant, and (iv) as temperature increased, the rate of nucleation first increased slowly, then remained nearly constant, and finally declined. Within‐population compositional homogenization was followed, on cooling, by local Fe–Mg–Mn exchange with biotite.     

安宁河断层地震成核条件研究——来自天然花岗岩断层泥摩擦实验的启示

安宁河断层历史上发生过多次强震,现存的地震空区反映了其断层中部近30年来的断层闭锁和应变积累情况,是潜在的大地震危险区.本研究采用断层带内的新鲜花岗岩断层泥样品,在水热条件下开展了摩擦滑动实验,以研究安宁河断层摩擦特性和地震成核条件.实验有效正应力200 MPa,孔隙水压30 MPa,温度25~600℃,剪切滑移速率在1 μm·s^-1,0.2 μm·s^-1,0.04 μm·s^-1之间切换.实验结果显示,在100~400℃,摩擦系数随着温度的增加而增大（约0.663~0.704）,温度高于400℃时略有降低.从200℃开始,花岗岩断层泥的摩擦滑动表现出由速度强化向速度弱化转变,并随温度升高速度弱化程度增强,在600℃时仍然具有显著的速度弱化,具备地震成核条件.本研究获得的花岗岩断层发生不稳定滑动的温度范围为200~600℃,远大于已有研究中给出的350~400℃这一不稳定滑动的温度上限.本实验首次发现,在相同温度条件下花岗岩断层滑动稳定性与加载速率转变方向有关,向慢速切换或低速下（0.04 μm·s^-1）可以促进花岗岩断层由稳定滑动向不稳定滑动转变.基于本实验结果,结合川滇地区的地温梯度,推测得出安宁河断层中北段的地震成核深度为10~30 km,该断层的地震空区是断层闭锁的具体表现.

     

Numerical simulation of diffusion‐controlled nucleation and growth of porphyroblasts

This article presents the conceptual basis for a new numerical model of diffusion‐controlled nucleation and growth of porphyroblasts, describes its implementation, and illustrates the range of crystallization behaviours encompassed by it. The model differs from previous efforts principally in its ability to track explicitly the evolution in time and space of the chemical affinity for reaction in the intergranular medium, which provides a more accurate characterization of nucleation suppression in the vicinity of pre‐existing crystals and of growth suppression due to competition for nutrients among neighbouring crystals. Critical new features of these numerical simulations include: maintenance of local equilibrium for fluid in contact with reactants or products; persistence of reactants until they are eliminated by dissolution due to reaction progress and local diffusive flux; nucleation rates that vary as the local reaction affinity evolves; complex initial distributions of reactants if desired; and the flexibility to encompass any porphyroblast‐forming reaction for which changes in free energy as a function of time and temperature are specified. Model results reveal that radial growth rates remain proportional to the square‐root of time in diffusion systems buffered by persistent reactants; they document the interchangeable effects of diffusivity, porosity, and solubility on material fluxes and thus growth rates; and they illustrate the offsetting textural effects of rates of diffusion, nucleation, and heating. The initial distribution of reactants is found to exert a first‐order effect on crystal size distributions, confirming their limited utility for diagnosing crystallization mechanisms. These numerical simulations yield novel and rigorous confirmation of the textural effects of nucleation‐site saturation and variation in interconnected porosity, and reproduce with high fidelity much of the textural and chemical information gathered from natural specimens.     

A dynamic model for fault nucleation and propagation in a mechanically layered section

When a mechanically layered section of rock is subject to a horizontal strain, faults often nucleate preferentially in one or more layers before propagating through the rest of the section. The result is a high density of small, low-throw faults within these layers, and a much smaller number of large, through-cutting faults which nevertheless accommodate most of the strain due to their much larger displacement. A dynamic model of fault nucleation and propagation has been created by combining analytical and finite element techniques to calculate the energy balance of these propagating faults. This model shows that: 1) faults may nucleate in either mechanically weak layers, or in stiff layers with a high differential stress; 2) fault propagation may be halted either by strong layers (in which the sliding friction coefficient is high), or by layers which deform by flow and thus have low differential stress. This model can predict quantitatively the horizontal strain required for faults to nucleate, and to propagate across mechanical layer boundaries. The model is able to explain the complex pattern of fault nucleation and propagation observed in a mechanically layered outcrop in Sinai, Egypt.     

二水硫酸钙结晶动力学研究

主要研究了过饱和溶液中CaSO4 ·2H2 O晶体成核及生长现象 ,同时对垢的形成机理进行了探讨。实验表明 ,成核延迟时间随溶液过饱和度增大而减小 ;CaSO4 ·2H2 O晶体生长属于表面反应控制 ,且与粒径相关 ,当温度为 3 0℃ ,粒径为2 8～ 67μm ,Ca2 + 浓度为 0 .0 3 5mol/L时 ,晶体生长速度在 0 .5× 10 - 8～ 5 .8× 10 - 8m/s之间     

Ice Nucleation of Cirrus Clouds Related to the Transported Dust Layer Observed by Ground-Based Lidars over Wuhan,China

Cirrus clouds related to transported dust layers were identified on 22 occasions with ground-based polarization lidar from December 2012 to February 2018 over Wuhan (30.5°N, 114.4°E), China. All the events occurred in spring and winter. Cirrus clouds were mostly located above 7.6 km on top of the aloft dust layers. In-cloud relative humidity with respect to ice (RH_i) derived from water vapor Raman lidar as well as from ERA5 reanalysis data were used as criteria to determine the possible ice nucleation regimes. Corresponding to the two typical cases shown, the observed events can be classified into two categories: (1) category A (3 cases), in-cloud peak RH_i ≥ 150%, indicating competition between heterogeneous nucleation and homogeneous nucleation; and (2) category B (19 cases), in-cloud peak RH_i < 150%, revealing that only heterogeneous nucleation was involved. Heterogeneous nucleation generally took place during instances of cirrus cloud formation in the upper troposphere when advected dust particles were present. Although accompanying cloud-top temperatures ranged from –51.9°C to –30.4°C, dust-related heterogeneous nucleation contributed to primary ice nucleation in cirrus clouds by providing ice nucleating particle concentrations on the order of 10^?3 L^?1 to 10² L^?1. Heterogeneous nucleation and subsequent crystal growth reduced the ambient RH_i to be less than 150% by consuming water vapor and thus completely inhibited homogeneous nucleation.     

2014年春季华北两次降水过程的人工增雨催化数值模拟研究

在WRF中尺度模式中耦合了中国气象科学研究院发展的CAMS（Chinese Academy of Meteorological Sciences）云微物理方案,并在CAMS方案中增加了直接播撒冰晶（S1方案）和播撒碘化银催化剂（S2方案）两种云催化方案。利用此模式,对2014年我国华北干旱期间开展飞机增雨作业的两次降水过程（个例1:5月9～10日;个例2:5月10～11日）进行了云催化数值模拟研究,分析了催化对降水和云物理量场影响,对比了S1和S2方案催化效果的异同。结果表明,在云层适当部位播撒催化剂,两种催化方案均会达到增雨效果,催化会引起云中各水凝物的明显变化,并导致催化区域温度、垂直速度的变化。个例1中,S2方案的催化影响范围要大于S1方案,在播撒区下游地区,S2方案催化效果要强于S1方案;而个例2中两方案催化效果没有表现出显著差异。S1和S2方案的催化效果在不同个例中表现不同,其重要原因在于两种催化方案的催化机制差异以及云系动力条件、水汽条件的不同。通过采用适当的催化剂量,在其他催化设置条件相同的情况下,S1和S2方案可以取得相似的催化效果,但需注意由于二者催化机制的差异,在一些具体云系条件下,二者的催化效果会有一定差异。当实际人工增雨作业采用碘化银催化剂时,相应的催化模拟研究使用S2方案更为适合。     

The experimental investigation of micro-cracks nucleation in typical tectonics

IntroductionTheexistenceandmeasurabilityofearthquakenucleationinvariousgeologicalbackgroundareimportantbasicproblems.Generally,crowdingtogetherandzonationdistributionofmoderateandsmaIlearthquakes(orsourceofAE)arenormalphenomenon(Mei,etal,l993).However,itisnotreliabIetoidentifythecrowdingofmoderateandsmallearthquakesasforeshockofstrongearthquake.Someauthors(Yu,Li,l998,Wang,l999)studiedthemethodstofindtheprecursorinformationastojudgetheriskofstrongearthquakesfromthefiguresofspace-timeevoluti…     

新型AgI末端燃烧器及其在增雨作业中的应用

文章对我国新型AgI末端燃烧器的研制情况、结构和改造及其使用作了介绍,简述了这种新催化工具的特点,结合2002年12月至2004年9月,新型AgI末端燃烧器在河北、河南、青海、山东和北京飞机人工增雨探测作业试验,介绍了新型AgI末端燃烧器在3种增雨探测作业机型中的使用情况,并就其中遇到的问题进行了讨论,对如何结合探测作业飞机上所加载的GPS导航数据记录系统及其它辅助记录数据进行催化作业情况记录进行了说明。