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1.
Abstract Eclogites are distributed for more than 500 km along a major tectonic boundary between the Sino-Korean and Yangtze cratons in central and eastern China. These eclogites usually have high-P assemblages including omphacite + kyanite and/or coesite (or its pseudomorph), and form a high-P eclogite terrane. They occur as isolated lenses or blocks 10 cm to 300 m long in gneisses (Type I), serpentinized garnet peridotites (Type II) and marbles (Type III). Type I eclogites were formed by prograde metamorphism, and their primary metamorphic mineral assemblage consists mainly of garnet [pyrope (Prp) = 15–40 mol%], omphacite [jadeite (Jd) = 34–64 mol%], pargasitic amphibole, kyanite, phengitic muscovite, zoisite, an SiO2 phase, apatite, rutile and zircon. Type II eclogites characteristically contain no SiO2 phase, and are divided into prograde eclogites and mantle-derived eclogites. The prograde eclogites of Type II are petrographically similar to Type I eclogites. The mantle-derived eclogites have high MgO/(FeO + Fe2O3) and Cr2O3 compositions in bulk rock and minerals, and consist mainly of pyrope-rich garnet (Prp = 48–60 mol%), sodic augite (Jd = 10–27 mol%) and rutile. Type III eclogites have an unusual mineral assemblage of grossular-rich (Grs = 57 mol%) garnet + omphacite (Jd = 30–34 mol%) + pargasite + rutile. Pargasitic and taramitic amphiboles, calcic plagioclase (An68), epidote, zoisite, K-feldspar and paragonite occur as inclusions in garnet and omphacite in the prograde eclogites. This suggests that the prograde eclogites were formed by recrystallization of epidote amphibolite and/or amphibolite facies rocks with near-isothermal compression reflecting crustal thickening during continent–continent collision of late Proterozoic age. Equilibrium conditions of the prograde eclogites range from P > 26 kbar and T= 500–750°C in the western part to P > 28 kbar and T= 810–880°C in the eastern part of the high-P eclogite terrane. The prograde eclogites in the eastern part are considered to have been derived from a deeper position than those in the western part. Subsequent reactions, manifested by (1) narrow rims of sodic plagioclase or paragonite on kyanite and (2) symplectites between omphacite and quartz are interpreted as an effect of near-isothermal decompression during the retrograde stage. The conditions at which symplectites re-equilibrated tend to increase from west (P < 10 kbar and T < 580°C) to east (P > 9 kbar and T > 680°C). Equilibrium temperatures of Type II mantle-derived eclogites and Type III eclogite are 730–750°C and 680°C, respectively. 相似文献
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基于拉格朗日余流及其输运过程的一种三维空间弱非线性理论,进一步假定Si在河口的无因次化学转移项量级为k^2,给出了Si的长期输运方程。对于一种二维模型河口,数值求解了零阶天文潮,欧拉余流、斯托克斯漂移、拉格朗日余流和盐度的分布;分别计算了平均逼留时间为13,30,60,180d等所对应的Si浓度分布;给出了Si-s相关图,讨论了河口中Si的保守性问题。 相似文献
4.
本文分析了雷达观测结果,发现近海海面上的水汽向上输送随季节而变化,由于季节的变化和不同的天气情况,海表面大气现象在雷达中有不同的显示,根据这些显示得到了不同的信息,由此而得出春秋两季海表面水汽向上输送量的不同。 相似文献
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Pavel Spurný 《Earth, Moon, and Planets》1995,68(1-3):529-537
Many Perseid meteors were photographed in the Czech part of the European Fireball Network during the activity of the new strong and sharp maximum on August 12, 1993. Basic data on many of them were evaluated and radiants, atmospheric trajectories and some orbital elements are presented here and compared with atmospheric and orbital data of regular Perseids, which were photographed outside the new activity in 1993 and preceding years. No substantial difference between these two groups of Perseid meteors was found. 相似文献
7.
Study of geothermal water intrusion due to groundwater exploitation in the Puebla Valley aquifer system, Mexico 总被引:1,自引:1,他引:1
E. Leticia Flores-Márquez Gabriel Jiménez-Suárez Raymundo G. Martínez-Serrano René E. Chávez Daniel Silva Pérez 《Hydrogeology Journal》2006,14(7):1216-1230
Significant intrusion of geothermal water into fresh groundwater takes place in the Puebla Valley aquifer system, Mexico. The decline in the potentiometric surface due to the overexploitation of the groundwater induces this intrusion. This hydrological system comprises three aquifers located in Plio-Quaternary volcanic sediments and Mesozoic calcareous rocks. The hydraulic balance of the aquifer shows that the annual output exceeds the natural inputs by 12 million m3. Between 1973 and 2002, a drop in the potentiometric surface, with an 80 m cone of depression, was identified in a 5-km-wide area located southwest of the city of Puebla. Chemical analyses performed on water samples since 1990 have shown an increase in total dissolved solids (TDS) of more than 500 mg/L, coinciding with the region showing a cone of depression in the potentiometric surface. A three-dimensional flow and transport model, based on the hydrogeological and geophysical studies, was computed by using the MODFLOW and MT3D software. This model reproduces the evolution of the aquifer system during the last 30 years and predicts for 2010 an additional drawdown in the potentiometric surface of 15 m, and an increase in the geothermal water intrusion. 相似文献
8.
Abstract Physical stratigraphy within shoreface‐shelf parasequences contains a detailed, but virtually unstudied, record of shallow‐marine processes over a range of historical and geological timescales. Using high‐quality outcrop data sets, it is possible to reconstruct ancient shoreface‐shelf morphology from clinoform surfaces, and to track the evolving morphology of the ancient shoreface‐shelf. Our results suggest that shoreface‐shelf morphology varied considerably in response to processes that operate over a range of timescales. (1) Individual clinoform surfaces form as a result of enhanced wave scour and/or sediment starvation, which may be driven by minor fluctuations in relative sea level, sediment supply and/or wave climate over short timescales (101?103 years). These external controls cannot be distinguished in vertical facies successions, but may potentially be differentiated by the resulting clinoform geometries. (2) Clinoform geometry and distribution changes systematically within a single parasequence, reflecting the cycle in sea level and/or sediment supply that produced the parasequence (102?105 years). These changes record steepening of the shoreface‐shelf profile during early progradation and maintenance of a relatively uniform profile during late progradation. Modern shorefaces are not representative of this stratigraphic variability. (3) Clinoform geometries vary greatly between different parasequences as a result of variations in parasequence stacking pattern and relict shelf morphology during shoreface progradation (105?108 years). These controls determine the external dimensions of the parasequence. 相似文献
9.
Ü. Rannik T. Markkanen J. Raittila P. Hari T. Vesala 《Boundary-Layer Meteorology》2003,109(2):163-189
Observations of wind statistics within and above a Scots pine forest are comparedwith those predicted from an analytical second-order closure model. The roughnesssublayer (RSL) effects, and the influence of stability on similarity functions, arestudied using observations. The commonly accepted forms of similarity functionsdescribe the influence of diabatic effects above the RSL well. According to earlierstudies they are expected also to apply within the RSL. As an exception, the averagewind speed normalised with friction velocity was found to be invariant with stabilityclose to the canopy top under unstable conditions. Lagrangian stochastic trajectorysimulations were used to evaluate the influence of canopy turbulence profiles onfootprint prediction. The main uncertainty was found to arise from parameterisationof the random forcing term in the Lagrangian velocity equation. The influence ofdiabatic conditions was studied, and it was found that thermal stability affectssignificantly the footprint function above the forest canopy, but significantuncertainty exists because of uncertainties in the formulation of stability functions. 相似文献
10.
在使用2.5维混合模拟方法研究了Petschek模型稳态驱动磁场 重联演化的基础上, 本文考察了计算域内各典型区域中粒子分布函数的变化,描绘了重联区不同位置几种类型的 非Maxwell分布函数. 结果表明,磁场重联会将重联区少部分粒子加速到很高的能量,不同 加速程度的粒子将形成球壳状的速度分布. 粒子的轨道特征表明,在重联区中出流的粒子, 有一部分被磁镜捕获,其回旋半径大于重联区宽度,并构成整个流体速度的低速部分. 另外 ,在X中性点附近进入重联区的粒子沿磁力线向出流区以三种形式漂移,分别为:沿磁力线 逃逸、捕获在磁镜中随流体运动、横越磁力线漂移,其比例分别约为70%,20%和10%。 相似文献