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81.
郯庐断裂带内岩浆岩及糜棱岩的年龄及野外研究表明以中-酸性为主的岩浆活动主要发生在早白垩世走滑运动的晚期,岩石化学以富钾、富碱为特征;稀土元素以轻稀土富集、重稀土亏损为特征;微量元素表现出富集大离子亲石元素,尤其是强不相容元素;同位素组成显示岩浆来源于壳幔过渡带.带内岩浆活动明显受断裂带控制,走滑晚期的岩浆活动起源于地幔底侵、壳幔相互作用下的壳幔过渡带,在伊泽奈崎板块斜向俯冲、中国东部遭受区域性剪切-挤压的背景下出现.在此背景下中国东部发生了岩石圈减薄,同时出现了一系列北东-北北东向已深切至壳幔边界的左行平移断裂系,从而诱发了大规模的岩浆活动. 相似文献
82.
下蜀土边坡地震稳定性的大型振动台试验研究(Ⅰ)——模型试验设计 总被引:1,自引:0,他引:1
为研究下蜀土边坡的地震稳定性,选用天然下蜀土,按照Meymand的相似法则,对一坡高为0.5m、宽度为1.05m、坡角为45°的模型边坡进行了几何相似常数为20的1g大型振动台模型试验详细设计。首先,运用数值模拟的方法确定了模型边坡尺寸适当的边界范围,模型边坡地基厚度、坡脚前缘和坡肩后缘长度均取为0.5m;其次,按照确定的模型几何尺寸设计了符合试验要求的模型箱,其内壁净尺寸(长×宽×高)为1500mm×1050mm×1100mm,属刚性模型箱,且不会与模型边坡发生共振;最后,制定了包括加速度和位移在内的数据量测策略,运用拟静力法求得下蜀土边坡平均屈服加速度为0.561g,综合确定了地震动峰值(PGA)按0.1g、0.3g、0.6g和0.9g的顺序逐级加载的原则,并制定了详细的试验步骤,从而可保障试验得到可靠的结果。 相似文献
83.
From water to tillage erosion dominated landform evolution 总被引:3,自引:1,他引:3
While water and wind erosion are still considered to be the dominant soil erosion processes on agricultural land, there is growing recognition that tillage erosion plays an important role in the redistribution of soil on agricultural land. In this study, we examined soil redistribution rates and patterns for an agricultural field in the Belgian loess belt. 137Cs derived soil erosion rates have been confronted with historical patterns of soil erosion based on soil profile truncation. This allowed an assessment of historical and contemporary landform evolution on agricultural land and its interpretation in relation to the dominant geomorphic process. The results clearly show that an important shift in the relative contribution of tillage and water erosion to total soil redistribution on agricultural land has occurred during recent decades. Historical soil redistribution is dominated by high losses on steep midslope positions and concavities as a result of water erosion, leading to landscape incision and steepening of the topography. In contrast, contemporary soil redistribution is dominated by high losses on convex upperslopes and infilling of slope and valley concavities as a result of tillage, resulting in topographic flattening. This shift must be attributed to the increased mechanization of agriculture during recent decades. This study shows that the typical topographical dependency of soil redistribution processes and their spatial interactions must be accounted for when assessing landform and soil profile evolution. 相似文献
84.
Ryder Allen Burton Ashley & Storey 《Monthly notices of the Royal Astronomical Society》1998,294(2):338-346
The newly commissioned University of New South Wales Infrared Fabry–Perot (UNSWIRF) has been used to image molecular hydrogen emission at 2.12 and 2.25 μm in the reflection nebula Parsamyan 18. P 18 is known to exhibit low values of the (1–0)/(2–1) S(1) ratio, suggestive of UV-pumped fluorescence rather than thermal excitation by shocks. Our line ratio mapping reveals the full extent of this fluorescent emission from extended arc-like features, as well as a more concentrated thermal component in regions closer to the central exciting star. We show that the emission morphology, line fluxes and gas density are consistent with the predictions of photodissociation region (PDR) theory. Those regions with the highest intrinsic 1–0 S(1) intensities also tend to show the highest (1–0)/(2–1) S(1) line ratios. Furthermore, variations in the line ratio can be attributed to intrinsic fluctuations in the incident radiation field and/or the gas density, through the self-shielding action of H2 . An isolated knot of emission discovered just outside P 18, and having both an unusually high (1–0)/(2–1) S(1) ratio and relative velocity, provides additional evidence for an outflow source associated with P 18. 相似文献
85.
Angelo Paone 《International Journal of Earth Sciences》2008,97(3):635-650
A compilation of B–Be–Li data on rocks that cover the entire eruptive history of Somma-Vesuvius is presented and interpreted
in the light of evolution models for the Somma-Vesuvius rocks. Using major and trace element data, fractional crystalllization
models are presented for different geochemical units. These data were used to constrain the source mineralogy of the Somma-Vesuvius
rocks (ol-opx-cpx-gar-amp of 0.4-0.3-0.1-0.1-0.1), the amount of sediment added (5–10%) and the melt fraction from batch partial
melting computations (0.05–0.1). From the B–Li data it is inferred that the main process responsible for the B isotopic signature
is sediment recycling. However, the B–Li data show a major variation in Li abundances respect to B which is explained with
Li dehydration before the fluid enriched the mantle wedge that produced the arc magmas. The Somma-Vesuvius B isotope composition
is intermediate between that of the Campi Flegrei and the broad field of the Eolian Island arc. A low Be isotopes in the recent
volcanic rocks can be explained as: (a) the top 1–22 m of the incoming sediment is accreted, (b) large amounts of sediment
erosion, (c) a slow rate of subduction which have provoked a long magmatic history for the Vesuvius magma, (d) the sediment
component takes several Myr longer than the subducting plate to reach the magma source region beneath Italy. 相似文献
86.
87.
云南老王寨金矿的深部地质过程——来自显微岩相学和元素地球化学的证据 总被引:4,自引:0,他引:4
通过老王寨金矿围岩、蚀变岩石、矿石的显微岩相学和元素地球化学的系统研究发现:伴随硅化、碳酸盐化等蚀变和硫化物矿化,岩(矿)石中发育沿粒间、裂隙或角闪石解理纹贯入或穿插的黑色不透明超显微隐晶,经电子探针、扫描电镜和能谱分析鉴定,该固体物质主要由超显微晶石英、硅酸盐、碳酸盐、硫化物以及呈熔离交生关系的金红石、白钨矿和镜铁矿(磁铁矿)组成;熔离交生结构与沉淀共晶结构共存的特有岩相学特征指示成矿流体具备由熔体性质向热液性质转化的特性。结合岩(矿)石稀土微量元素研究,认为这种在透射光显微镜下呈黑色不透明的超显微隐晶固体物质,是具熔浆流体特点和超临界流体性质的地幔流体引发交代蚀变的直接微观表现之一;在交代蚀变过程中其性质由熔浆向地壳热液过渡,同时与地壳物质发生混染而有利于成矿作用的进行。 相似文献
88.
89.
人工影响天气的学科基础是中小尺度天气动力学与云降水物理学,需要将天气-动力-云降水物理耦合为一体。考虑到目前将天气动力学性质的基础数值模式用于人工影响天气中的问题,从数值模式动力方程、模式分辨率、云物理过程、数值求解方案、初边值条件等方面系统地探索了发展人工影响天气数值模式中一些需要重点解决、且不可忽视的特色问题,并举例对相关问题提出了解决思路和方法。期望提出的问题有助于构思更适合于人工影响天气数值模式,使数值模式功能真正向满足人工影响天气的要求靠近一步。 相似文献
90.