High-pressure eclogites in northern Jiangsu – southern Shandong province, eastern China

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.     

嵩县螃蟹沟隐爆角砾岩体与钼金矿化成因探讨

螃蟹沟隐爆角砾岩体是河南省嵩县西北部众多含钼、金角砾岩体之一,这些角砾岩体具有成群、成带分布的特点.螃蟹沟角砾岩体的定位与分布受北西向背形、北西向和北东向断裂构造的复合控制,由燕山期钙碱性岩体与岩脉的侵入,以及随后发生的隐蔽爆发-坍塌作用而生成了角砾岩体.其中包括了震碎角砾岩、隐爆角砾岩、侵入角砾岩及坍塌角砾岩.岩体被后期断裂构造作用所复合叠加,致使钼、金富集成矿,形成"多型一体"的钼金矿床.     

城市景观三维重建中的三角剖分算法

在构建城市景观时,为了快速精确地重建建筑物、绿地、河流等三维模型,提高自动化程度,缩短建设周期,需对用户采集的矢量地物数据进行三角剖分,再以OpenGL重绘三维模型。本文提出了一种对多边形进行三角剖分的递归分割算法,并以VisualC++实现,以实际的4万多个建筑物进行三角剖分实验,充分证明其是有效的。     

元胞自动机城市增长模型的空间尺度特征分析

基于元胞自动机模拟城市系统的复杂行为时,空间尺度是一个非常重要的概念,模型的模拟结果往往会随着输入数据的空间尺度变化而发生变化。然而,目前的元胞自动机城市增长模型大多没考虑数据的空间尺度特征,本文拟通过改变模型中输入数据的空间尺度来验证元胞自动机城市增长模型对尺度的敏感性及其空间尺度特征,并以长沙市为例进行实证研究。研究结果表明:元胞自动机城市增长模型只有在一定的尺度范围内才具有较高的模拟精度,并且模型对尺度具有一定的敏感性,因此为了使模型能够具有较高的模拟精度,并较好地反映城市形态特征,应认真选择模型中输入数据的空间尺度。     

高斯投影公式的机助推导

随着GPS应用的普及,高斯投影在测量中出现的机会越来越多。许多文献上都给出了推导过程,这个推导过程的运算量是非常大的,而且计算精度难于提高。经过研究,一种易于编程的递推公式被发现,虽然这个公式在计算量上没有减少,但是可以较好地解决精度问题。     

濮阳市地下水开采引起的环境地质问题及防治措施

濮阳市是新兴的石油化工基地,国家级卫生城市和园林城市,由于人口的增长、工农业的迅猛发展,地下水超量开采而引起的地面沉降、地裂缝等一系列环境地质问题,针对所出现的环境地质问题提出相应的防治措施.     

燕山水库坝基防渗墙优化设计

因现场资料不足或分析手段落后等原因,当前进行水库坝基防渗墙设计,往往存在过于保守的倾向。以河南省燕山水库为例,基于优化设计的思路,采用目前较为成熟的二维有限单元法,对不同防渗条件下的坝基渗流场分别进行了模拟,并将计算所得比降、流量与允许比降、允许流量做了对比,从定量的角度提出了既安全、又经济的防渗方案:防渗墙厚度取0.8m,深度取打入破碎带5m。     

遗传算法在边坡数值计算中的应用

改进了进化方向的遗传算法与有限元数值法，结合并研制了相应的软件。应用该软件对多类型岩土边坡进行弹性模量、内聚力、内摩擦角等参数反演分析，显示误差很小，收敛速度也很快，这说明改进进化方向遗传算法这种新型的优化算法在多类型岩土参数优化估计中具有独特的优势。     

疏勒河流域昌马灌区泉水量预测分析

疏勒河流域农业灌溉主要采用地表水灌溉 ,泉水为该区农业灌溉的主要水源之一 ,该文利用 2 0世纪 90年代的测流资料 ,采用有限差分方法对疏勒河中游泉水量的变化趋势进行预测分析 ,结果显示 ,随着时间的延长 ,泉流量呈逐渐减小的趋势 ,但下降梯度逐渐变小 ,最终趋于稳定     

正电子断层扫描仪与PET图像重建概述

概述了PET（Positron emission tomography，正电子断层扫描仪）及其图像重建的基本原理、方法与临床使用，介绍了常用的图像重建FBP（滤波反投影，Filtered Back-Projection)算法和OSEM（有序子集最大似然法，Ordered Subset Expectation Maximization)算法，描述了如何通过PET的临床协议中的参数选择以得到满意的重建效果。此外，对PET的准三维重建也做了一些简介。