迈入新千年的大地测量学——第22届IUGG大会有关大地测量部分的技术总结

本文较系统地介绍了１９９９年７月在英国伯明翰举行的第２２届ＩＵＧＧ大会反映出来的大地测量的最新进展情况。全文共分４个部分：卫星定位技术的新进展,地球重力场的研究进展,地球动力学的新进展及大地测量理论与方法新进展。对其中若干领域,还提出我国今后发展的建议。     

Selection of the wavenumbers k using an optimization method for the inverse Fourier transform in 2.5D electrical modelling

An optimization method is used to select the wavenumbers k for the inverse Fourier transform in 2.5D electrical modelling. The model tests show that with the wavenumbers k selected in this way the inverse Fourier transform performs with satisfactory accuracy.     

Galaxy destruction and diffuse light in clusters

Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of diffuse light that stretch for over 100 kpc, yet are just a few kiloparsecs wide. At a surface brightness of m _b ∼27–28 mag arcsec⁻² , the Centaurus arc is the most striking example known of structure in the diffuse light component of a rich galaxy cluster. We use numerical simulations to show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709. The surface brightness and narrow dimensions of the diffuse light suggest that the disc was corotating with its orbital path past pericentre. Features this prominent in clusters will be relatively rare, although at fainter surface brightness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveys may be able to trace this feature for several times its presently observed extent, and somewhere along the tidal debris, a fraction of the original stellar component of the disc will remain bound, but transformed into a faint spheroidal galaxy. It should be possible to confirm the galactic origin of the Centaurus arc by observing planetary nebulae along its length with redshifts close to that of NGC 4709.     

高海拔宇宙线观测站LHAASO概况

宇宙线发现百年以来,宇宙线起源仍然是一个谜.研究宇宙线起源主要在甚高能(VHE)伽马射线天文学和宇宙线物理学两个领域交叉展开.新一代高海拔宇宙线观测站(LHAASO)拥有高海拔、全天候和大规模优势,利用多种探测手段对宇宙线开展联合观测,大幅提升对伽马射线和宇宙线的鉴别能力.LHAASO将开展全天区伽马源扫描搜索以大量发现新伽马源,将获得30TeV以上伽马射线探测的最高灵敏度,将在宽达5个数量级的能量范围内精确测量宇宙线分成份能谱,为揭开宇宙线起源谜团给出重要判据.系统介绍了LHAASO的探测器结构、性能优势和科学目标.     

湖泊水体叶绿素a含量估算的波段宽度变化影响分析——以太湖为例

为研究不同波段宽度遥感数据对监测水体叶绿素a含量的影响,以太湖水体实测高光谱遥感反射率数据为基础,分析计算不同波段宽度下遥感反射率的归一化值与叶绿素a浓度之间的相关系数。随着波段宽度在75.93nm范围内不断递增,最大相关系数逐渐减小,最大正相关波段向长波方向移动,最大负相关波段向短波方向移动。而波段宽度在31.6nm范围内变化时,最大正相关波段和最大负相关波段都会保持相对稳定。通过对不同波段处相关系数平均值和标准差的对比分析认为,718.77^~34.58nm为叶绿素a遥感监测的最佳波段范围。这将对遥感传感器的波段设置,以及实际水体叶绿素a遥感监测时的波段选择,具有重要的参考价值。     

青海冷湖盐场北山黑云母二长花岗岩年代学、地球化学及其地质意义

柴北缘西端青海冷湖盐场北山地区发育黑云母二长花岗岩,岩体高硅(Si O2=73.92%~75.98%)、富钾(K2O=3.71%~4.78%)、贫镁钙,铝饱和指数A/CNK介于1.03~1.11,属强过铝质花岗岩。稀土元素球粒陨石标准化曲线呈右倾型,Eu异常不明显;岩体含有富铝矿物石榴子石,刚玉标准分子约为1%,Th、Y含量低,且与Rb呈负相关性,源岩为沉积岩,具S型花岗岩特征,是幔源岩浆底侵作用引发地壳物质部分熔融的产物。LA-ICP-MS锆石U-Pb测年结果表明岩体形成于254±4 Ma。结合区域地质背景及岩石地球化学特征认为盐场北山黑云母二长花岗岩形成与俯冲作用有关,类似于岛弧环境产物,从而揭示柴北缘晚二叠世具有活动大陆边缘性质。     

大别造山带毛屋岩体的解体及古地幔性质的厘定

根据详细的地球化学 (特别是稀土元素地球化学 )的研究资料 ,提出大别造山带毛屋岩体应该解体。毛屋岩体不是由多幕式镁铁 超镁铁质层状堆晶作用形成的一套岩石系列 ,而是由橄榄岩类、含石榴石方辉岩类、榴辉岩类和绿辉石岩类组成的一个混杂岩体。其中含石榴石方辉岩类与绿辉石岩类之间存在成因上的联系 ,含石榴石方辉岩类的原岩是本区原始地幔经约36 %的部分熔融后剩下的残余 ,而绿辉石岩的原岩是由该熔融体结晶的产物。根据含石榴石方辉岩与绿辉石岩之间的成分制约关系 ,对该区古地幔的稀土元素组成和地幔性质进行了反演 ,结果表明 ,该区原始地幔稀土元素成分与球粒陨石中的相似 ,为轻稀土略亏损的平坦型组成模式 ;该区原始地幔矿物成分为橄榄石 (72 8% )、单斜辉石 (12 4% )和石榴石 (14 8% ) ,属含单辉石榴橄榄岩的地幔。     

南秦岭佛坪隆起的成因探讨——构造解析的证据

通过对佛坪隆起基底及其周围地区构造面理和线理的系统测量和统计,恢复其古应力场,揭示区域构造应力场的分布规律,进而探讨佛坪隆起的成因机制。研究结果表明,佛坪隆起主体及其北部龙草坪隆起区外围地层中的构造片理呈外倾的封闭环状展布,结合古构造应力场分析,证明佛坪基底抬升主要生成于穹状隆起,这种穹状隆升与该区岩浆侵入活动密切相关。综合区域构造解析与古应力场分析表明,佛坪穹隆是在早期近垂向的穹状隆升的基础上,叠加了后期南北向挤压构造才奠定了其基本构造面貌。     

Diffusion gradients in an eclogite xenolith from the Roberts Victor kimberlite pipe: (2) kinetics and implications for petrogenesis

In a bimineralic eclogite xenolith (sample JJG41) from the Roberts Victor kimberlite, compositional gradients in clinopyroxene are related to garnet exsolution. Two principal reactions involving clinopyroxene and garnet occur: (i) The net-transfer Al₂Si^-1Mg^-1 which is responsible for garnet growth according to the equation 2Di+Al₂Si^-1Mg^-1=Grossular+MgCa^-1 (reaction 1). This has created substantial compositional gradients in Al, Si and Mg within clinopyroxene. (ii) The exchange of Fe–Mg between garnet and clinopyroxene (reaction 2). During the stage of garnet growth (reaction 1) the lamellae crystallized sequentially as a result of a temperature decrease from around 1400 to 1200° C. This exsolution growth-stage was under the control of Al diffusion in clinopyroxene and at around 1200° C further growth of garnet lamellae became impeded by the sluggishness of Al diffusion in the clinopyroxene host. However, reaction 2 continued during further cooling down to about 1000° C; this temperature being inferred from the constant Fe–Mg partitioning at clinopyroxene-garnet interfaces for the whole set of lamellae. The initial clinopyroxene in JJG41 was probably formed by crystallization from a melt in Archaean time. The cessation of Fe–Mg exchange between garnet and clinopyroxene at about 1000° C may well predate the eruption of the eclogite in kimberlite at around 100 Ma. Kinetic models of reaction are examined for both reactions. Modelling of reaction 1, involving both diffusion and interface migration, allows several means of estimating the diffusion coefficient of Al in clinopyroxene; the estimates are in the range 10^-16-10^-20 cm²/s at 1200° C. These estimates bracket the experimentally determined data for Al diffusion in clinopyroxene, and from these experimental data a preferred cooling rate of about 300° C/Ma is obtained for the period of growth of garnet exsolution lamellae. A geospeedometry approach (Lasaga 1983) suitable for a pure-exchange process (reaction 2) is used to estimate the cooling rate in the later stages of the thermal history (after garnet growth); values 4–40° C/Ma are consistent with the shape of the Fe-diffusion gradients in the clinopyroxene. The extensive thermal history recorded by JJG41, including probable melt involvement at ca. 1400° C, demonstrates the complex evolution of rocks within the mantle. Whilst the notion of formation of mantle eclogites from subducted oceanic crust has become fashionable, it is clear that tracing eclogite geochemical and P-T characteristics backwards from their nature at the time of xenolith eruption, through high-temperature mantle events to the characteristics of the original subducted oceanic crust, will be very complex.     

实验研究不同盐离子对水分子拉曼效应的影响

对流体包裹体中常见的几种盐水溶液进行了拉曼光谱分析.采用了频移参数描述水分子拉曼峰的形变强度,并讨论了频移参数与盐度之间的关系.实验分析结果表明,盐度越大,频移参数越大,水分子拉曼峰形变越大.对频移参数曲线斜率分析显示,盐类对水分子拉曼峰偏移程度影响的强弱顺序为NaCl＞Na2SO4＞NaHCO3＞Na2CO3.讨论了不同阳离子和阴离子对水伸缩振动拉曼峰的影响,结果表明,高价阳离子的影响明显高于低价阳离子;而阴离子对水拉曼峰影响的强弱顺序初步确定为Cl-≈SO2-4-＞HCO-3＞CO2-3≈NO-3.