中国东南部丹霞地貌的区域构造控制

中国东南部是＂中国丹霞＂地貌的典型代表地区,位于中新生代滨太平洋构造域的大陆边缘活动带。中生代内陆断陷盆地沉积了一套巨厚的紫红色类磨拉石建造,奠定了丹霞地貌造形成景的岩石地层基础;新近纪以来的新构造运动,使地壳差异性抬升,形成了南岭和武夷山脉等构造山地。紫红色砂砾岩建造在强烈的流水切割及重力崩塌作用下,发育了一大批极具观赏价值的丹霞地貌,构成了武夷山丹霞地貌密集带等区域性的重要旅游景观资源。从燕山期岩石地层建造到喜山期改造成景,区域构造作用始终是主导性的地球动力学因素。     

滇西维西-德钦-带花岗岩年代学、地球化学和岩石成因

金沙江弧盆体系消减与碰撞的确切时间存在较大的争议.运用LA-ICP-MS地质年代学、地球化学及Sr-Nd同位素方法研究金沙江缝合带周边的花岗岩体.贡卡花岗闪长岩(232Ma)和羊拉花岗闪长岩(229.6Ma)形成于印支期,羊拉二长花岗岩(261Ma)形成于海西-印支期.羊拉二长花岗岩地球化学特征类似O型埃达克岩,由大洋板片熔融与地幔楔交代(Mg#=55～61.8>40),且上升过程与岩浆房酸性岩浆混合,形成于俯冲消减环境;贡卡花岗闪长岩和羊拉花岗闪长岩可能由类似扬子地块的崇山群玄武质岩石和变质表壳岩部分熔融形成,产于碰撞后环境.金沙江缝合带从中二叠世末期-晚二叠世早期持续俯冲;碰撞阶段可能于晚二叠世末期开始,在中三叠世早期结束.     

深井填砾工艺关键技术探讨

在河北平原新近系地热井施工时采用填砾工艺具有防砂、稳定孔壁的优点,但具有一定的施工难度。通过实践应用提出了管孔径级配方案,总结了终孔替浆工艺,分析并论证了填砾数量计算方法、填砾速度的确定原则及静水填砾方法的可行性。     

长江北支口门圆陀角附近潮滩沉积物粒度记录及其对环境变化的响应

江苏圆陀角位于长江口北支与江苏海岸交汇处,海岸沉积动力环境复杂,潮滩沉积物粒度变化记录了潮滩环境变化的信息.根据2007年4月采集的表层样和钻孔岩芯粒度分析,圆陀角附近Yyb断面表层沉积物粒度在互花米草滩前缘较粗,大堤前岸滩最粗,光滩和互花米草滩粒度较细.YY孔岩芯沉积物粒度组成以砂质粉砂为主,粒度变化自下向上呈先由粗变细再变粗的特点,表层样和钻孔岩芯粒度变化反映了潮滩沉积物对风暴潮、潮汐海洋动力、大米草和互花米草种植以及大规模围垦的综合响应.173Cs测年结果推算出YY孔岩芯1954年以来、1963年以来、1975年以来和1986年以来的平均沉积速率分别为2.38cm/a,2.23cm/a,2.44cm/a和1.24cm/a.岩芯沉积物的沉积速率总体随潮滩淤积增高而下降,1975～1986年间沉积速率的快速增加,主要与圆陀角附近互花米草的快速淤积有关.     

甘肃省岷县马坞金矿地质特征及找矿方向

马坞金矿分布于岷-礼成矿带的东部,矿体产于中泥盆统浅变质碎屑岩中,受断裂破碎蚀变带的控制。围岩蚀变以中-低温热液蚀变为主,蚀变强度与金矿化强度呈正相关;矿区共圈定6条矿脉,沿走向及倾向具有尖灭再现、局部膨大缩小的特点,沿裂隙发育的矿脉金品位较高。     

煤储层各向异性地震波场模拟

对中国煤层的裂隙系统进行了系统分类;阐述了各类裂隙的主要成因。基于二维二分量各向异性弹性波方程交错网格高阶有限差分法数值模拟,对各向同性介质模型和高裂隙密度(含干裂隙和饱和水裂隙)煤层的二维层状模型进行了弹性波场数值模拟。结果表明:煤层含裂隙后与不含裂隙时相比,反射时差的变化已不足以识别,但由于波速的改变会使煤层顶底、界面的波阻抗发生变化,从而引起波的动力学特征的改变,AVO现象尤其明显。含气和含水裂隙煤层中在x分量和z分量表现为极性相反,而且含水裂隙煤层中的波速比含气裂隙煤层的波速要快。因此,应用各向异性理论研究煤层裂隙的特征是可能的。     

Long-Term Variability of Nutrients and Chlorophyll in the Chesapeake Bay: A Retrospective Analysis, 1985–2008

A retrospective analysis of freshwater discharge, riverine dissolved nutrient loads, dissolved nutrients, and chlorophyll in the Chesapeake Bay from 1985 to 2008 is presented. It is evident that each field displays an interannual variability averaged over the Bay. The N and P loads peaked in 1997 and have fluctuated with a decreasing trend since early 2004. Dissolved nutrient concentrations in the Bay appear to be largely controlled by riverine nutrient loads. The temporal variability of chlorophyll is positively correlated with nutrient loads and concentrations. Over the study period, N:P (DIN:DIP) molar ratios were consistently higher than the Redfield ratio (N:P?=?16:1) and strongly correlated with river discharge (R ²?=?0.68, p??16:1), and N is the limiting nutrient in summer and early autumn (N:P?4 from anoxic sediments. Long-term climate indices, such as El Niño Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), appear to exert only a moderate control over the riverine discharge to the Bay or over the ecosystem response in terms of chlorophyll in the Bay. While not all related mechanisms can be inferred from available data, this analysis should help in determining future data needs for monitoring water quality and human and climate influence on the health of the Bay.     

分布式光纤在桩基静载试验中的应用

分布式光纤在桩基静载试验中的应用,是近年来才兴起的一种新技术。介绍了该技术的应用原理、方法及质量控制参数等。通过工程实践,表明该方法具有测试精度高、质量可靠、抗干扰能力强等优点。     

Magnetic susceptibility as a proxy for rainfall: Worldwide data from tropical and temperate climate

The magnetic susceptibility of soils has been linked with climate, mainly through rainfall, by numerous investigators. For this study we assembled a worldwide dataset of 272 samples, both published and new, to determine the nature of the relationship between MS and rainfall. On a worldwide basis there is a crude relationship (r² = 0.265) between MS and rainfall. MS increases with increasing rainfall from about 200 mm/yr to 1000–1200 mm/yr. Above 1200 mm/yr, MS decreases as rainfall increases up to about 2000 mm/yr. Under arid and semi-arid conditions, below about 200 mm/yr of rainfall, MS and rainfall exhibit no relationship, likely the result of limited pedogenic activity.When tropical and temperate localities are analyzed separately, the correlation between MS and rainfall exhibits a dramatic improvement, r² = 0.568 and 0.520, respectively. For similar amounts of rainfall tropical localities generally exhibit lower MS values which may be related to differences in the seasonal variation of rainfall. Because the soil environment is highly variable, it is unlikely that a global or even regional equation could accurately estimate rainfall from MS. Using data from Morocco and Mali we demonstrate that local equations using only MS to estimate rainfall produce reasonable results, r² = 0.700 for Morocco and 0.611 for Mali. However, a single independent variable is unlikely to capture the variability of the complex soil system. To the local equations described above we experimented with adding several independent variables in addition to MS including diffuse reflectance spectral data (DRS), x-ray diffraction (XRD), and x-ray fluorescence (XRF). For DRS data, % reflectance and red, yellow, and near-infrared wavelengths appear important; for XRD illite and kaolinite counts are important whereas for XRF Fe₂O₃ is important. The addition of these other independent variables dramatically improves prediction quality. In the case of the Mali transect, estimating rainfall from these variables produces an r² that exceeds 0.9. Based on these data we conclude that MS has the potential to be a reasonable proxy of rainfall for mean annual precipitation values from 200 to 2000 mm/yr, especially if local equations are used. Predictions can be improved by including other independent variables that show sensitivity to climate and are related to MS through the chemistry of the weathering process; we included DRS, XRD, and XRF data with good results.     

Seismic stratigraphy records the deglacial history of Jakobshavn Isbræ, West Greenland

Jakobshavn Isbræ is one of the largest ice streams in the Greenland Ice Sheet, presently draining c. 6.5% of the Inland Ice. Here we present high‐resolution Chirp and Sparker sub‐bottom profiles from a seismic survey conducted just outside of the Jakobshavn Isfjord, which provides detailed insight into the glacimarine sedimentary history of the Jakobshavn ice stream during the Holocene. We observe acoustically stratified and homogeneous sediments that drape an irregular substratum and were deposited between ～10 and c. 7.6k cal a BP. The stratified lower units are interpreted as the product of ice‐proximal glacimarine sedimentation deposited rapidly when the grounded ice margin was located close to depositional basins on topographic highs. The upper acoustically homogenous units reflect suspension settling of fine‐grained material and gravitational flows that were extruded from an increasingly unstable ice margin as the ice retreated into the fjord. Proximity to the ice margin and bedrock topography were the dominant controls on sediment accumulation during deglaciation although the 8.2‐ka cooling event probably influenced the position of the ice margin at the fjord mouth. The post‐glacial sedimentary record is characterized by glacimarine and hemipelagic rainout with an increased ice‐rafted detritus fraction that records sedimentation following ice stream retreat into Jakobshavn Isfjord sometime after c. 7.8k cal a BP. Copyright © 2011 John Wiley & Sons, Ltd.