The Lower Zone-Critical Zone Transition of the Bushveld Complex: a Quantitative Textural Study   总被引：7，自引：0，他引：7  

BOORMAN  SONJA; BOUDREAU  ALAN; KRUGER  F. J. 《Journal of Petrology》2004,45(6):1209-1235

The Lower Zone–Critical Zone boundary of the BushveldComplex is an intrusion-wide, major stratigraphic transitionfrom ultramafic harzburgite and pyroxenite in the Lower Zoneto increasingly plagioclase-rich pyroxenites and norites inthe Critical Zone. Quantitative textural and compositional datafor 29 samples through this transition show the following: LowerZone orthopyroxene grains are larger, have higher aspect ratios,are better foliated and have a lower trapped liquid componentthan those of the Critical Zone. The larger grain size of theLower Zone results in crystal size distribution plots that arerotated to lower slopes and intercepts relative to those inthe Critical Zone. Although all rocks show differing amountsof foliation, mineral lineations are weak to absent. These dataare consistent with significant compaction-driven recrystallizationin the study section. Numerical modeling of concurrent compactionand crystallization provides a quantitative model of how theLower Zone–Critical Zone transition may have formed: plagioclaseis rare in the Lower Zone because compaction removes interstitialliquid before it reaches plagioclase saturation. However, asthe crystal pile grows, plagioclase saturation is reached inthe interstitial liquid before compaction is complete in moreevolved pyroxenites, producing more abundant but still modestamounts of plagioclase characteristic of the Lower CriticalZone. It is concluded that both the textures and the modal mineralogyare largely controlled by compaction and compaction-driven recrystallization;primary magmatic textures are not preserved. KEY WORDS: Bushveld Complex; compaction; crystal size distributions; crystal aging; igneous textures  相似文献   

World patterns and amounts of detrital soil carbon     

Vernon Meentemeyer  John Gardner  Elgene O. Box 《地球表面变化过程与地形》1985,10(6):557-567

Soil carbon data were collected from published sources for 50 measurement sites spanning the globe's major climate and vegetation types. For each site, climate, vegetation, and land-use variables were determined and entered into a multiple curvilinear regression program to predict soil carbon. The best model incorporates an estimate of site disturbance, annual actual evapotranspiration, and annual soil moisture deficit, and yields an R = 0-803. The curvilinear regression equation was coupled with a large climatic database and computer cartography programs to produce first-generation maps of estimated soil carbon. These maps correctly portray soil carbon as high in boreal and cool temperate zones and low in deserts and tropical zones. Computer planimetry of maps of soil carbon for an ‘undisturbed’ world and for a ‘disturbed’ world resulted in estimates of 1457 × 10⁹ mtC and 504 × 10⁹ mtC respectively. These estimates compare favourably with recent estimates using other approaches. Clearly, the disturbance factor is critical to future refinements in estimates, suggesting the need for detailed studies of the relationship between land-use history and the creation and destruction of this important carbon pool.  相似文献   

华东登陆热带气旋降水不同分布的对比分析     

卜松  李英 《大气科学》2020,44(1):27-38

利用CMORPH降水资料，将热带气旋（TC）登陆后的降水分为路径左侧降水（L型）和右侧降水（R型）两类，并针对登陆华东地区TC的 L型和R型降水的大气环流场、环境水平风垂直切变以及台风环流内的动热力条件进行对比分析，结果表明:2005～2014年间登陆华东地区的20例TC中包括12例L型和8例R型。总体来看，大气环流因子对于登陆华东TC降水分布起主要作用。L型降水TC高层南亚高压主要呈纬向带状分布，在登陆过程中路径左侧维持偏东风高空辐散气流，中层西风槽偏东，西太平洋副热带高压（简称副高）偏南，环境水平风垂直切变指向西南。R型降水TC高层南亚高压断裂，呈经向分布。TC路径左侧风场较均匀，右侧东南风高空辐散气流明显。副高的位置偏北呈块状，同时环境水平风垂直切变指向东北，有利于路径右侧降水。台风环流内，低层冷暖平流输送以及水汽辐合与降水落区也有较好对应关系。L型TC低层暖平流的输送使TC西南象限低层增暖，大气稳定度降低。同时水汽辐合区也主要位于西南象限，有利于TC路径左侧降水。而R型TC副高位置偏北可将南侧的东南暖湿气流向台风环流更西部输送，东北象限维持暖平流，有利于路径右侧降水发生。  相似文献   

同步辐射X射线荧光微探针测定岩石中的元素分布   总被引：10，自引：1，他引：10  

安庆骧  巢志瑜 《岩矿测试》1991,10(2):84-88

同步辐射X射线(白光)荧光微探针在大气环境下,光斑尺寸为(50×50)μm~2,位移为1mm/步,计数时间30s,扫描测量了含石榴石紫苏花岗岩中多元素(K、Ca、Ti、Cr、Mn、Fe、Cu、Zn、Rb和Sr)的分布并绘制成图。检测限达x×10ppm,绝对量为10~(-10)—10~(-11)g范围。  相似文献   

Stochastic overland flows     

R. S. govindaraju  M. L. Kavvas 《Stochastic Environmental Research and Risk Assessment (SERRA)》1991,5(2):89-104

A theoretical solution framework to the nonlinear stochastic partial differential equations (SPDE) of the kinematic wave and diffusion wave models of overland flows under stochastic inflows/outflows, stochastic surface roughness field and stochastic state of flows was obtained. This development was realized by means of an eigenfunction representation of the time-space overland flow depths, and by transforming the problem into the phase space. By using Van Kampen's lemma and the cumulant expansion theory of Kubo-Van Kampen-Fox, the deterministic partial differential equation (PDE) for the evolutionary probability density function (pdf) of overland flow depths was finally obtained. Once this deterministic PDE is solved for the time-varying pdf of overland flow depths, then the time-space varying pdf of overland flow depths can be obtained by a transformation given in the text. In this solution framework it is possible to incorporate the stochastic dynamic behavior of the parameters and of the forcing functions of the overland flow process. For example, not only the individual rainfall duration and fluctuating rain intensity characteristics but also the sequential behavior of rainfall patterns is incorporated into the evolutionary probability density function of overland flow depths.  相似文献   

Vertical distribution of dimethylsulfide,sulfur dioxide,aerosol ions,and radon over the Northeast Pacific Ocean     

M. O. Andreae  H. Berresheim  T. W. Andreae  M. A. Kritz  T. S. Bates  J. T. Merrill 《Journal of Atmospheric Chemistry》1988,6(1-2):149-173

Dimethylsulfide (DMS), sulfur dioxide (SO₂), methanesulfonate (MSA), nonsea-salt sulfate (nss-SO₄ ^2–), sodium (Na⁺), ammonium (NH₄ ⁺), and nitrate (NO₃ ^–) were determined in samples collected by aircraft over the open ocean in postfrontal maritime air masses off the northwest coast of the United States (3–12 May 1985). Measurements of radon daughter concentrations and isentropic trajectory calculations suggested that these air masses had been over the Pacific for 4–8 days since leaving the Asian continent. The DMS and MSA profiles showed very similar structures, with typical concentrations of 0.3–1.2 and 0.25–0.31 nmol m^–3 (STP) respectively in the mixed layer, decreasing to 0.01–0.12 and 0.03–0.13 nmol m^–3 (STP) at 3.6 km. These low atmospheric DMS concentrations are consistent with low levels of DMS measured in the surface waters of the northeastern Pacific during the study period.The atmospheric SO₂ concentrations always increased with altitude from <0.16–0.25 to 0.44–1.31 nmol m^–3 (STP). The nonsea-salt sulfate (ns-SO₄ ^2–) concentrations decreased with altitude in the boundary layer and increased again in the free troposphere. These data suggest that, at least under the conditions prevailing during our flights, the production of SO₂ and nss-SO₄ ^2– from DMS oxidation was significant only within the boundary layer and that transport from Asia dominated the sulfur cycle in the free troposphere. The existence of a sea-salt inversion layer was reflected in the profiles of those aerosol components, e.g., Na⁺ and NO₃ ^–, which were predominantly present as coarse particles. Our results show that long-range transport at mid-tropospheric levels plays an important role in determining the chemical composition of the atmosphere even in apparently remote northern hemispheric regions.  相似文献   

Grain-size distribution patterns of suspended sediment in response to hydrodynamics on the Dafeng intertidal flat, Jiangsu, China     

LI Zhanhai  GAO Shu  CHEN Shenliang  WANG Yaping 《海洋学报(英文版)》2006,25(6):63-77

1Introduction The sediment dynamics of intertidal flats in-volves erosion, transport, and settling processes. A-mong these, the mechanisms of sediment transportare a key question. Progress has been made in awide range of associated areas, including sedime…  相似文献   

海洋底边界层中实测海流的垂直分布Ⅱ·潮流边界层     

乐肯堂  庄国文  宋金宝  侯一筠  朱兰部 《海洋与湖沼》2003,34(2):187-193

为了满足海洋工程设计的需要,作者从理论上研究了海底以上1－2m处潮流边界层的结构。把传统上用于稳定海流的底Ekman层理论发展成为用于潮流运动的振荡Ekman边界层,给出了潮流Ekman方程的解析解[式（32）－（35）],提出了对数边界层中潮流运动的方程组（式4－8）及其约束条件（式48）,并给出了潮流Ekman层与潮流对数边界层的匹配条件（式43）,还给出了计算浅海潮流垂直分布的解析表达式（36）－（39）。  相似文献   

Spatial Distributions of Phyllosoma Larvae (Crustacea: Decapoda: Palinuridae and Scyllaridae) in Taiwanese Waters     

Nariaki Inoue  Hideo Sekiguchi  Shinn-Pyng Yeh 《Journal of Oceanography》2001,57(5):535-548

Distributions and taxonomy of phyllosoma larvae were examined in Taiwanese waters, based on ichthyoplankton samples collected from May 1990 to July 1995. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae representing 6 genera and 13 species. Of the collected phyllosoma larvae, those of Scyllarus and Panulirus species were most abundant, forming 90% of total numbers. Early stage Scyllarus and Panulirus phyllosoma larvae were abundant in Taiwanese waters. Middle to late stages (except the final stage) of Panulirus phyllosoma larvae were absent from the waters throughout the year, while those of Scyllarus phyllosoma larvae were collected in the waters. This suggests that all stages of Scyllarus phyllosoma larvae may be retained in the northern part of the waters around northern Taiwan while middle to late stages of Panulirus phyllosoma larvae may be flushed out from the waters, the sub-final and final stages then possibly returning to the waters. An anticlockwise eddy existed in the waters off northeastern Taiwan, which may be closely related to flushing out and returning of Panulirus phyllosoma larvae through a much longer planktonic period. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

我国东北地区夏季暴雨的气候学特征   总被引：5，自引：0，他引：5  

孙力  隋波  王晓明  刘实 《气候与环境研究》2010,15(6):778-786

利用东北三省和内蒙古东部200个测站1961～2005年的逐日降水资料,分析了东北地区夏季暴雨的空间分布特征和时间演变规律,以及各类暴雨与各种影响天气系统之间的气候统计关系。结果表明,在空间分布上,暴雨由东北地区的东南部向西北部递减的地域特征十分明显,绝大多数大范围和区域性暴雨一般都集中出现在东北地区的南部和中部,而局地暴雨的分布范围相对较广,地域差别也较小。在时间分布上,几十年来东北地区暴雨的阶段性变化特征十分明显,多暴雨和少暴雨的出现具有11～12年左右的低频变化周期。20世纪80年代初以来,暴雨日出现的年际变率有明显增加的趋势,特别是20世纪90年代中期以后,东北地区暴雨发生的次数虽然明显减少,但平均每个暴雨日的暴雨量却有所增加。在东北地区出现的局地暴雨中,以北方天气系统的影响贡献最大,而在区域性暴雨和大范围暴雨中,南方天气系统影响的比例明显增加。  相似文献