Thermal controls on flexure of underthrust continental lithosphere     

C. David Brown 《Geophysical Journal International》2001,146(3):813-826

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单片机控制的步进电机定频脉宽调制可变细分驱动系统     

王菁蕙  梅安华 《武汉大学学报(信息科学版)》1994,(1)

本文介绍所研制的由ＭＣＳ－５１单片机控制的步进电机定频脉宽调制可变细分驱动系统。该系统采用单电压驱动。配有软件。在不改变硬件电路的前提下．通过键盘操作，可以改变细分数。系统采用数字式定频脉宽调制技术，直接对细分电流进行反馈控制。最后提出了用实验确定均匀细分电流状态字的新方法，并验证了其可行性。  相似文献   

Identification of an underfilled foreland basin system in the Upper Devonian of the Central Pyrenees: implications for the Hercynian orogeny     

Pierre?Souquet  Jean-Jacques?Delvolvé  Stéphane?BrussetEmail author 《International Journal of Earth Sciences》2003,92(3):316-337

A foreland basin succession has been identified in the Frasnian of the Central Pyrenees. This succession comprises a carbonate-dominated transgressive system which recorded the cratonward migration of the foreland basin subsidence, and siliciclastic depocenters which recorded the progression of the thrust-fold deformation. The foreland basin system has always been maintained in deep-marine environments, i.e., at an underfilled depositional state. It was associated with a thrust wedge which descended toward a deep-marine hinterland, i.e., with a type of orogenic wedge usually related to subduction zones. The Frasnian foreland basin system differs from the one known in the Carboniferous which evolved to overfilled depositional state and was associated with a thrust wedge rising toward a mountainous hinterland. Consequently, the Hercynian orogeny in the Pyrenees seems to result first, from a Frasnian thrusting controlled by a subduction zone located north of the Pyrenees, and second, from a Carboniferous thrusting controlled by the surrection of a frontal thrust belt in the Pyrenees. The association of underfilled foreland basin systems and hinterland-dipping thrust wedges, as exemplified in the Frasnian of the Pyrenees, can be interpreted as illustrative of the initial stages of thrust-wedge growth in deep-marine settings.  相似文献   

月球探测摄影测量数据处理系统方案分析     

尹明  王新义 《测绘科学与工程》2005,25(3):31-34

本文提出了月球摄影测量数据处理系统的设计原则，探讨了月球摄影测量数据处理系统的组成和研究的内容，分析了在月球探测摄影测量数据处理中，首先应该解决的关键技术问题。结论：对月球探测摄影测量数据处理系统的研究，可以保障月球探测卫星工程测绘月球表面三维影像图及地形图任务的完成，同时，也可以为后续的月球探测计划提供摄影测量的基础理论、技术、方法和实践经验。  相似文献   

Flexural uplift of a lithospheric slab near the Vema transform (Central Atlantic): Timing and mechanisms     

Enrico Bonatti  Daniele Brunelli  W. Roger Buck  Anna Cipriani  Paola Fabretti  Valentina Ferrante  Luca Gasperini  Marco Ligi   《Earth and Planetary Science Letters》2005,240(3-4):642-655

The Vema Transverse Ridge (VTR) is a prominent, long and narrow topographic anomaly that runs for over 300 km along a sea floor spreading flow line south of the Vema transform at 11° N in the Atlantic. It rises abruptly about 140 km from the axis of the Mid-Atlantic Ridge (MAR) in 10 Myr old crust and runs continuously up to 25 Myr old crust. It reaches over 3 km above the predicted lithospheric thermal contraction level. It is absent in crust younger than 10 Myr; thus, the uplift of the VTR must have ended roughly 10 Ma. The VTR is interpreted as the exposed edge of a flexured and uplifted slab of oceanic lithosphere that was generated at an 80 km long MAR segment. Based on satellite gravimetry imagery this MAR segment was born roughly 50 Ma and increased its length at an average rate of 1.6 mm/yr. Multibeam data show that the MAR-parallel sea floor fabric south of the VTR shifts its orientation by 5° to 10° clockwise in 11–12 Myr old crust, indicating a change at that time of the orientation of the MAR axis and of the position of the Euler rotation pole. This change caused extension normal to the transform, followed between 12 and 10 Ma by flexure of the edge of the lithospheric slab, uplift of the VTR at a rate of 2 to 4 mm/yr, and exposure of a lithospheric section (Vema Lithospheric Section or VLS) at the northern edge of the slab, parallel to the Vema transform. Ages of pelagic carbonates encrusting ultramafic rocks sampled at the base of the VLS at different distances from the MAR axis suggest that the entire VTR rose vertically as a single block within the active transform offset. A 50 km long portion of the crest of the VTR rose above sea level, subsided, was truncated at sea level and covered by a carbonate platform. Subaerial and submarine erosion has gradually removed material from the top of the VTR and has modified its slopes. Spreading half rate of the crust south of the transform decreased from 17.2 mm/yr between 26 and 19 Ma to 16.9 mm/yr between 19 and 10 Ma, to 13.6 mm/yr from 10 Ma to present. The slowing down of spreading occurred close in time to the change in ridge/transform geometry, suggesting that the two events are related. A numerical model relates lithospheric flexure to extension normal to the transform, suggesting that the extent of the uplift depends on the thickness of the brittle layer, consistent with the observed greater uplift of the older lithosphere along the VTR.  相似文献   

Gravity anomalies and segmentation at the East Coast, USA continental margin     

P. Wyer  A. B. Watts 《Geophysical Journal International》2006,166(3):1015-1038

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豫西上宫构造蚀变岩型金矿成矿过程中的流体—岩石反应   总被引：31，自引：8，他引：23  

范宏瑞  谢奕汉 《岩石学报》1998,14(4):529-541

上宫金矿赋存在中元古界熊耳群安山岩和玄武岩中,矿体受断裂破碎带控制。含矿热液在迁移过程中,与围岩发生了强烈的流体－岩石反应,造成Ａｕ、Ａｇ、Ａｓ、Ｓｂ等成矿及其相关微量元素和Ａｌ２Ｏ３、ＴｉＯ２、Ｎａ２Ｏ等常量元素含量增加,稀土元素及其总量急剧减少。流体－岩石反应第一阶段发生的温度和压力条件为３６５℃～３００℃和２８５～２００ＭＰａ,而大量金沉淀成矿时的温度和压力范围则分别为３２５℃～２４０℃和１６０～１００ＭＰａ。成矿热液类型及其演化比较简单,从初始的低盐度（９．５％～６．３％ＮａＣｌ）、ＸＣＯ２为０．１８～０．２４的含ＣＯ２流体演化为低盐度（５．９％～１．６％ＮａＣｌ）的水溶液流体。流体－岩石反应是造成上宫金矿金沉淀成矿最主要的原因  相似文献   

The influence of a stratified rheology on the flexural response of the lithosphere to (un)loading by extensional faulting   总被引：2，自引：0，他引：2  

M. ter Voorde  R. T. van Balen  G. Bertotti  & S. A. P. L. Cloetingh 《Geophysical Journal International》1998,134(3):721-735

We present a two-layered finite difference model for the flexural response of the lithosphere to extensional faulting. The model allows for three modes of flexure: (1) fully coupled, with the upper crust and mantle welded together by the lower crust; (2) fully decoupled, with the upper crust and mantle behaving as independent layers; and (3) partly decoupled, signifying that the response of the upper crust to small-wavelength loads is superimposed on the response of the entire lithosphere to long-wavelength loads. Which of these modes of flexure is to be expected depends on the rheology and especially the thermal state of the lithosphere. Coupled behaviour is related to a cold and strong lithosphere. The Baikal Rift Zone provides a typical example for this mode of flexure. A fully decoupled lithosphere is an exceptional case, related to anomalous high temperatures in the lower crust, and is observed in the Basin and Range province. The most common case is a partly decoupled lithosphere, with the degree of decoupling depending on the thickness and viscosity of the lower crust. This is inferred, for example, for the Bay of Biscay margin.  相似文献   

顺层边坡溃层问题的计算方法   总被引：9，自引：0，他引：9  

刘钧 《水文地质工程地质》1997,24(6):37-41

本文根据压杆稳定计算的基本理论，结合顺层以溃层破坏的具体情况，提出来考虑向力作用下的边坡失稳计算理论和方法，并分析了一个实例。  相似文献   

排水条件下化肥流失的研究——现状与展望   总被引：14，自引：0，他引：14       下载免费PDF全文

张蔚榛  张瑜芳 《水科学进展》1997,8(2):197-204

探讨排水对化肥流失的影响;减少排水条件下化肥流失的合理施肥措施及排水方式。根据现有研究成果,从排水条件下化肥流失的野外试验研究和数值模拟研究两方面进行了论述,在此基础上提出该项研究需进一步探讨和解决的问题,为该课题的深入研究提供了有利条件。  相似文献