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191.
Hossein Ghadiri 《地球表面变化过程与地形》2004,29(1):77-89
The process of crater formation by the impact of water drops on soil, sand and various other target material was studied. Craters of various shapes and sizes were observed on different target materials or conditions, ranging from circumferential depression to completely hemispherical shape. Crater shape was dependent upon target material, its ?ow stress or shear strength and the presence and thickness of water on the surface. Between 5 and 22 per cent of impact energy was spent on cratering, but the relationship between crater volume and kinetic energy of a raindrop was curvilinear, indicating a lower ef?ciency of impact energy in removing target material as the energy increases. Impact impulse, on the other hand, showed a more linear relationship with crater volume, and the ratio of impulse over crater volume (I/V) remained constant for the entire range of drop sizes, impact velocities, and surface conditions used in this study. Surface shear strength, represented by the penetration depth of fall‐cone penetrometer, appeared to be a key factor involved in this process. An equation was developed which related crater volume to cone penetration depth and impact impulse. Crater volume, which appeared to be a better indicator of the total amount of material dislodged by a raindrop than splash amount, can thus be predicted using this equation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
192.
大气季节内振荡对印度洋—西太平洋地区热带低压/气旋生成的影响 总被引:24,自引:4,他引:24
文中利用EOF分析大气季节内振荡 (MJO)的时空变化的方法 ,研究了 1996年 9月~ 1997年 6月间的MJO活动对生成在印度洋—西太平洋海域的热带低压 /气旋的影响。结果发现 ,除西北太平洋之外 ,发生在其他区域的热带低压 /气旋有半数以上生成在向东移动的MJO的湿位相中。伴随MJO的向东传播 ,热带低压 /气旋平均生成位置也随之向东移动 ,而生成在西北太平洋的热带低压 /气旋分别受到向东和向西传播的MJO影响 相似文献
193.
依据英吉沙县卡拉巴西塔克山新发现的牙形石化石,结合所发现的腕足、珊瑚等化石,认为库山河组的时代为晚泥盆世法门阶中晚期.其生物群面貌与中国南部同期陆架相(珊瑚一腕足相)地层生物面貌相似.塔里木盆地西南缘泥盆一石炭系界线位于库山河组和克里塔克组之间. 相似文献
194.
议京西大台地区的燕山运动 总被引:3,自引:1,他引:3
作者研究了京西大台地区的燕山运动,初步研究表明:这里不存在强烈的挤压变形迹象和显著的角度不整合.缺乏磨拉石建造。龙门组是厚度有限的河流相沉积,九龙山组是具有弱火山活动的湖相一滨湖相沉积。在隆起带和沉降带之间侏罗系地层显著的厚度变化率、大安山一斋堂滑覆构造及其派生的髫髻山断陷盆和大量高角度滑动面理,都显示了伸展构造背景下基底断块的差异升降。髫髻山组与壳幔相互作用有关的一套火山岩显示了上述运动的深部背景。 相似文献
195.
江苏西南部晚侏罗世西横山组为一套粗碎屑岩—细碎屑岩及泥灰岩组成的陆相沉积岩,普遍含有火山物质。从地层分布、岩性特征、碎屑岩粒度统计分析表明,天生桥盆地和西横山盆地基本上是连续、贯通的,自东向西,由冲积扇相—河流相—湖泊相逐渐过渡,属于同一水中盆地中不同沉积相的产物。沉积物主要来自盆地东部,可能与“古茅山”隆起带有关。 相似文献
196.
大渡河次级支流斯合沟泥石流特征研究 总被引:1,自引:1,他引:1
泥石流作为地质环境较差、的山区的主要自然灾害之一,对它的研究尤其是泥石流规律方面的研究已取得了较大的成绩。但是对于泥石流的研究思路却有待进一步发展和完善,这在很大程度上将对山区的工程建设有很重要的指导意义。论文从工程地质研究思路的角度出发,对位于大渡河支流官料河上某水电站下闸址区的斯合沟泥石流进行了研究。文中采用工程地质分析的方法对大渡河次级支流斯台沟泥石流的形成环境(地层岩性条件、构造条件、地貌条件、气象条件、植被发育及人类活动)、基本特征(泥石流沟的基本特征、泥石流的堆积特征)进行了系统的研究,提出了该泥石流的形成演化过程及其机制模型(初期是堰塞式沟谷型泥石流,后期逐渐转向汇聚式沟谷型泥石流)。并在此基础上对泥石流沟沿岸的岸坡稳定性(可能泥石流的物源)等进行了评价分析。将定性分析和定量分析相结合,对泥石流的活动趋势以及可能泥石流的体积(未来泥石流形成将主要是在面蚀和沟蚀作用下的坡面泥石流。泥石流规模较小,且由于沟谷中下游坡降的进一步减缓,形成的泥石流物质一般将沿途停积.实际进入官料河内的体积很小)做出了较为科学的评价预测。经过这样的系统分析对工程建设中的泥石流防治有着积极的指导意义。 相似文献
197.
Roberto Torra 《中国地球化学学报》2004,23(3):220-237
Littoral siliciclastic shallow marine horizontal conformable beds (a heterolithic succession), Middle to Late Miocene, outcropping
in northeastern Argentina (Ituzaingó Formation) and overlying transitional conformable horizontal regolithic mantle-rock bed
derived from them (the Pampean and Post-Pampean Formations), were geochemically analyzed. The focus of this study is placed
on the application of geochemical parameter and signature analyses related with the aforementioned geological units, which
are of subcontinental extension into South America. The encountered results show an outstandingly similar geochemical behaviour
between them. The main conclusion is that regolithic mantle-rock beds were derived from the littoral shallow marine mudstone
(silty-argillaceous) beds. This is in oposition to previous aeolian processes proposed early in the 50’s and later. These
mudstone beds constitute important sections of the littoral shallow marine sequence beds (outcropping HST parasequence). Such
regolitization proposed for the Pampean and Post-Pampean Formations predominantly developed in-situ during the Late Pleistocene
and Holocene. The main erosional and mobilized agents were the surface free water (pluvial, fluvial and laminar water sheets)
and vadose water. So, the wind flows and/or the immense air flow hurricanes are of insignificant sedimentological influence.
Otherwise, there is not a proved appropiate sandy-silty reservoir for a reasonable support of the “aeolian hypothesis”, as
well as clear aeolian structures settled in the regolithic mantle-rock bed. In spite of these lines of equality textural-structural
evidence, the geochemical values for both major elements and trace elements, demonstrate that the Miocene heterolithic marine
succession was the mother rock of the overlying regolithic mantle-rock bed, which was formed as an in-situ mantle-rock bed. 相似文献
198.
Formation of arcs and backarc basins inferred from the tectonic evolution of Southeast Asia since the Late Cretaceous 总被引:6,自引:0,他引:6
Results of the geological and geophysical surveys in the Daito ridges and basin in the northern West Philippine Basin suggest that the Daito Ridge was an arc facing toward the south from the Late Cretaceous to the Early Tertiary. The Late Cretaceous and Tertiary history of Southeast Asia is evaluated based on these data in the Daito ridges and basins and reconstructed based on overall plate kinematics that have operated in this area. During the Late Cretaceous, the Daito Ridge and the East Philippine Islands were positioned along the boundary between the Indian and Pacific Plates. The western half of the Philippines setting on the Indian Plate approached from the south and collided with the East Philippine–Daito Arc either during the latest Paleocene or the earliest Eocene. It is inferred that the bulk of the Philippine archipelago rotated clockwise and Borneo spun counterclockwise during the Tertiary.From the reconstruction, the formation of backarc basins and their spreading direction are assessed. As a result, some primary causes and significant characteristics are suggested for the opening of backarc basins in Southeast Asia. First, opening of some backarc basins commenced with or was triggered by collisions. Second, backarc basins opened approximately parallel to oceanic plate motion. Third, the formation of some backarc basins was triggered by the approach of a hot spreading center. Fourth, the spreading mode or direction of backarc basins was greatly affected by the configuration of the surrounding continent and was also rearranged to spread approximately parallel to oceanic plate motion.The formation of backarc basins and their spreading direction can be reasonably explained by plate kinematics. However, the generative force responsible for their formation is possibly within the subduction system, particularly to form horizontal tensional force in backarc side. 相似文献
199.
Mechanism of arrested charnockite formation at Nemmara, Palghat region, southern India 总被引:3,自引:0,他引:3
The formation of arrested charnockite is an excellent example of structurally controlled channellised fluid flow along specific sites accompanied by selective elemental mobility and mineralogical changes. The present paper recognises and focuses study on three types of arrested charnockite formation from Palghat region, namely, shear-controlled, foliation parallel and boudin-neck types, and address their spatio-temporal relations to regional-scale charnoenderbite. The shear-controlled and foliation parallel types post-date deformation and migmatisation. The boudin-neck type, on the contrary, is coeval with partial melting and followed the path of cooling and decreasing water activity in the gneiss. K-feldspar veining around plagioclase and quartz, symplectitic intergrowth of biotite+quartz after orthopyroxene and K-feldspar, and fluid inclusion data suggests the presence of alkalic supercritical brine and low-density CO2-rich fluid during charnockite formation. Charnockite domains developed following the breakdown of hornblende, biotite and quartz are characterised by a more or less pronounced depletion of Fe, Ca, Mg and Ti and trace elements Y and Zr, compared to their counterpart gneiss. REE spectra indicate a subtle depletion in the HREE near the centre of the charnockite domain. Although close-pair samples of gneiss–charnockite are isochemical, on a scale of a few millimetres, bi-directional element movement, related to the formation of new mineral was noted. It is postulated that arrested charnockite formation developed in situ on local scale within the granitic domains of the hornblende-biotite gneiss, in the presence of CO2-rich fluids and alkalic supercritical saline brine. This process post-dated the time of regional granulite (charnoenderbite) and large regional scale retrogression and migmatisation. 相似文献
200.