攀西地区晚新生代沉积研究回顾与问题讨论

攀西地区晚新生代沉积是研究青藏高原东南缘隆升演化历史及其周缘环境响应、中国第一第二阶梯地貌格局演变和高原东南缘水系变迁的天然地质记录,具有重要科学意义。对该区晚新生代河湖相沉积,尤其是昔格达组和大箐梁子组的研究历史、岩性内涵、形成时代、古地理与古气候意义等进行了较全面的回顾。在此基础上对晚新生代冰碛物记录的冰川发育过程、青藏高原东南缘新构造运动和隆升历史、水系格局变迁等过程进行了评述。针对该区晚新生代沉积研究中存在的问题和分歧,提出了今后研究的方向,认为在详细的地层学和地貌学等综合研究基础上开展高精度的年代学研究是当前攀西地区晚新生代沉积研究的重点。     

Response of groundwater chemistry to water deliveries in the lower reaches of Tarim River,Northwest China

In this paper, we analysed the monitored data from nine groundwater-monitoring transects in the lower reaches of Tarim River during the five times of stream water deliveries to the river transect where the stream flow ceased. The results showed that the groundwater depth in the lower reaches of Tarim River rose from −9.30 m before the conveyances to −8.17 and −6.50 m after the first and second conveyances, −5.81 and −6.00 m after the third and fourth the conveyance, and −4.73 m after the fifth. The horizontal extent of groundwater recharge was gradually enlarged along both sides of the channel of conveyance, i.e., from 250 m in width after the first conveyance to 1,050 m away from the channel after the fourth delivery. With the rising groundwater level, the concentrations of major anions Cl⁻, SO₄²⁻ and cations Ca²⁺, Mg²⁺, Na⁺, as well as total dissolved solids (TDS) in groundwater underwent a significant change. The spatial variations in groundwater chemistry indicated that the groundwater chemistry at the transect near Daxihaizi Reservoir changed earlier than that farther from it. In the same transect, the chemical variations were earlier in the monitoring well close to watercourse than that farther away from the stream. In general, the concentration of the major ions and TDS at each monitoring well increased remarkably when the water delivery started, and decreased with the continued water delivery, and then increased once again at the end of the study period. Hence, the whole study period may be divided into three stages: the initial stage, the intermediate stage and the later stage. According to the three stages of groundwater chemistry reaction to water delivery and the relationships between groundwater chemical properties and groundwater depths, we educe that under the situation of water delivery, the optimum groundwater depth in the lower reaches of the Tarim River should be −5 m.     

中国锂矿的多旋回深循环内外生一体化成矿理论及其找矿应用

中国锂资源的分布具有卤水型与硬岩型相伴相随、若即若离的特点。“多旋回深循环内外生一体化”成锂理论,在多年三稀金属矿产找矿实践和理论研究的基础上不断丰富完善。中国锂矿的形成与“多旋回”构造运动密切相关,从前寒武纪到新生代均有成矿潜力,可构成一个完整的多旋回成矿谱系。锂的“深循环”,一是锂深度参与成岩成矿的物质循环;二是需要一个“圈闭”的构造背景将锂“捕获”以避免其过度分散,锂从开始加入到岩浆与最终定位的深度之差,是硬岩型锂矿成矿的关键之一,压差越大越有利于伟晶岩型锂矿的形成。大量锂矿实例显示锂的物质循环是“内外生一体化”的统一过程,高海拔地区(山上)的含锂地质体(花岗岩类甚至直接就是含锂矿床)经风化剥蚀之后,可能成为沉积型锂矿的物质来源之一;而富含锂的沉积岩经过埋藏、变质、深熔也可以形成含锂的岩浆岩、伟晶岩。我国西部塔里木盆地、四川盆地、扎布耶盆地及东部的江汉盆地、吉泰盆地、周田盆地等大小不一的盆地均含锂,而其周边造山带中也不同程度发育硬岩型锂矿,这就为区域找矿指明了方向。“多旋回深循环内外生一体化”成锂理论是三稀矿产成矿理论的重要组成部分,为我国锂矿找矿工作提供了指导和借鉴,在甲基卡、可尔因、阿尔金、幕阜山等锂矿矿集区的找矿实践中发挥了积极作用。     

Analysis of buried pipelines subjected to reverse fault motion

Presently available simplified analytical methods and semi-empirical methods for the analysis of buried pipelines subjected to fault motion are suitable only for the strike-slip and the normal-slip type fault motions, and cannot be used for the reverse fault crossing case. A simple finite element model, which uses beam elements for the pipeline and discrete nonlinear springs for the soil, has been proposed to analyse buried pipeline subjected to reverse fault motion. The material nonlinearities associated with pipe-material and soil, and geometric nonlinearity associated with large deformations were incorporated in the analysis. Complex reverse fault motion was simulated using suitable constraints between pipe-nodes and ground ends of the soil spring. Results of the parametric study suggest that the pipeline's capacity to accommodate reverse fault offset can be increased significantly by choosing a near-parallel orientation in plan with respect to the fault line. Further improvement in the response of the pipeline is possible by adopting loose backfill, smooth and hard surface coating, and shallow burial depth in the fault crossing region. For normal or near normal orientations, pipeline is expected to fail due to beam buckling at very small fault offsets.     

New and little‐known arietellidae (Copepoda: Calanoida) mainly from the south‐west pacific

Three species of Arietellidae are described from the south‐west Pacific: a new species of Paraugaptilus, a species which can not be separated from P. buchani, and Arietellus aculeatus. The identity of A. aculeatus is clarified by comparison of type material and material from the U.S. National Museum of Natural History, and an unidentified Atlantic species of Arietellus, evident from the comparison, is described.     

地震作用下非贯通节理岩体斜坡破坏的物理模型试验研究

地震作用下高斜坡破坏的发生发展过程比较短暂、剧烈,破坏机理相对复杂。本文采用模型试验的方法来研究地震作用下非贯通节理岩体斜坡的反应。试验结果表明:节理上的应变最大,模型上部应变大于下部应变;节理贯通机理复杂,多为拉剪复合型破坏;节理的贯通并不意味着斜坡的破坏,而是破坏了斜坡的整体性,使其处于临界状态。试验揭示了此类斜坡在地震作用下的动力响应及破坏机理,可为理论和工程实践应用提供有益的参考和指导。     

High-harmonic geoid signatures related to glacial isostatic adjustment and their detectability by GOCE

The Earth’s asthenosphere and lower continental crust can regionally have viscosities that are one to several orders of magnitude smaller than typical mantle viscosities. As a consequence, such shallow low-viscosity layers could induce high-harmonic (spherical harmonics 50–200) gravity and geoid anomalies due to remaining isostasy deviations following Late-Pleistocene glacial isostatic adjustment (GIA). Such high-harmonic geoid and gravity signatures would depend also on the detailed ice and meltwater loading distribution and history.ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission, planned for launch in Summer 2008, is designed to map the quasi-static geoid with centimeter accuracy and gravity anomalies with milligal accuracy at a resolution of 100 km or better. This might offer the possibility of detecting gravity and geoid effects of low-viscosity shallow earth layers and differences of the effects of various Pleistocene ice decay scenarios. For example, our predictions show that for a typical low-viscosity crustal zone GOCE should be able to discern differences between ice-load histories down to length scales of about 150 km.One of the major challenges in interpreting such high-harmonic, regional-scale, geoid signatures in GOCE solutions will be to discriminate GIA-signatures from various other solid-earth contributions. It might be of help here that the high-harmonic geoid and gravity signatures form quite characteristic 2D patterns, depending on both ice load and low-viscosity zone model parameters.     

Palaeosurfaces in central West Greenland as reference for identification of tectonic movements and estimation of erosion

Landform analysis of basement rocks has been undertaken with the aid of digital elevation data, aerial photographs and field observations in central West Greenland (69°15′N–66°00′N). Palaeosurfaces have been identified, dated relatively to each other, used to quantify uplift and fault movements and also used to estimate differential erosion. Two types of palaeosurfaces were mapped across the Precambrian basement: a surface at low elevation with distinct hills (hilly relief), and two planation surfaces formed across different types of basement rocks. The hilly relief surface emerges as an inclined surface from Cretaceous cover rocks in Disko Bugt and is interpreted as a stripped late Mesozoic etch surface. This surface is cut off towards the south by a less inclined planation surface, which is younger and thus of Cenozoic age. It is similar to the post-Eocene (Miocene?) planation surfaces identified on Disko and Nuussuaq in other studies. The planation surface splits in two southwards towards high areas around Nordre Isortoq and Sukkertoppen Ice Cap. The upper planation surface forms near-summit areas of tectonic blocks dipping in different directions and with different tilts. The uplift centres define the crests of two mega blocks, separated by the ‘Sisimiut Line’ which coincides with the Precambrian Ikertôq thrust zone. A partially developed lower planation surface indicates a first uplift of maximum 500 m followed by a second uplift of maximum 1000 m. We infer that these uplift events occurred during the late Neogene based on correlation with similar surfaces on Nuussuaq and the timing of exhumational events estimated from apatite fission track analyses of samples from a deep borehole on Nuussuaq (reported elsewhere). The difference between a reconstruction of the upper planation surface across the entire area and the present topography was used as an estimate of erosion of basement rock since the formation of the upper planation surface. The erosion is unevenly distributed and varies from almost none on the well-preserved planation surfaces to 800–1300 m along valleys, and even more in the fjords. Erosion is less within areas of gneiss in granulite facies, than in areas of gneiss in amphibolite facies.     

Implications of geomorphological research for recent and prehistoric avalanches and related hazards at Huascaran,Peru

Detailed research of superficial deposits below the northern peak of Huascaran (Cordillera Blanca) provides new information on the limits of a paleo-avalanche originating from this mountain. Geomorphological mapping of the sediments identified glacial deposits, deposits from historical rock-debris avalanches and huge boulders from a paleo-avalanche. Schmidt Hammer rock-hardness tests were used to distinguish between the several generations of rock-debris avalanches, but largely failed to distinguish between the much older moraine and the paleo-avalanche sediments. Thus, only the field geomorphological mapping proved to be reliable for identifying the limits of the paleo-avalanche. The limits identified as granite boulders deposited over volcanic rocks were found to extend 30 m further up the opposite valley slope than previously had been mapped. This larger extent implies a greater volume and/or greater mobility for the prehistoric event.     

扰动方式对水华微囊藻(Microcystis flos-aquae)群体大小的影响

风浪扰动是影响湖泊生态系统的重要环境因素之一.为了解扰动方式对微囊藻群体大小的影响,在实验室可控条件下,模拟不同扰动方式（持续扰动和间歇扰动）对太湖水华微囊藻（Microcystis flos-aquae）群体大小的影响.结果显示,间歇扰动组水华微囊藻群体从35.09 μm迅速增大至43.73 μm,实验第17天时为59.00 μm;而持续扰动组水华微囊藻群体大小先从35.07 μm增大到43.51 μm,实验第17天时减小至13.95 μm;不扰动组整个实验期间群体大小相对稳定,实验初为35.38 μm,实验第17天时为33.67 μm.方差分析显示,间歇扰动组群体大小显著大于持续扰动组和不扰动组,持续扰动组显著小于不扰动组.实验第17天时间歇扰动组藻细胞密度（1.675×10⁶ cells/ml）显著高于持续扰动组（0.344×10⁶ cells/ml）和不扰动组（1.461×10⁶ cells/ml）.研究结果表明,适当强度下的间歇扰动能促使水华微囊藻群体显著增大和生长,而长时间的持续扰动则会抑制水华微囊藻群体的聚集和生长,该结果有助于人们对太湖微囊藻水华暴发机理的认识.