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1.
The Feiran–Solaf metamorphic belt consists of low-P high-T amphibolite facies, partly migmatized gneisses, schists, amphibolites and minor calc-silicate rocks of metasedimentary origin. There are also thick concordant synkinematic sheets of diorite, tonalite and granodiorite orthogneiss and foliated granite and pegmatite dykelets. The gneissosity (or schistosity) is referred to as S1, and is almost everywhere parallel to lithological layering, S0. This parallelism is not due to transposition. The gneissosity formed during an extensional tectonic event (termed D1), before folding of S0. S1 formed by coaxial pure shear flattening strain (Z normal to S0, i.e. vertical; with X and Y both extensional and lying in S1). This strain also produced chocolate tablet boudinage of some layers and S1-concordant sills and veins. S1 has a strong stretching lineation L1 with rodding characteristics. Within-plane plastic anisotropy (lower ductility along Y compared to along X) resulted in L1-parallel extensional ductile shears and melt filled cracks. Continued shortening of these veins, and back-rotation of foliations on the shears produced intrafolial F1 folds with hinges parallel to the stretching lineation. F1 fold asymmetry variations do not support previous models involving macroscopic F1 folds or syn-gneissosity compressional tectonics. The sedimentary protoliths of the Feiran–Solaf gneisses were probably deposited in a pre-800 Ma actively extending intracratonic rift characterizing an early stage of the break-up of Rodinia. 相似文献
2.
In this paper, we analyse the ability of the nonlinear shallow-water (NSW) equations to predict wave distortion and energy dissipation of periodic broken waves in the inner surf zone. This analysis is based on the weak-solution theory for conservative equations. We derive a new one-way model, which applies to the transformation of non-reflective periodic broken waves on gently sloping beaches. This model can be useful to develop breaking-wave parameterizations (in particular broken-wave celerity expression) in both time-averaged wave models and time-dependent Boussinesq-type models. We also derive a new wave set-up equation which provides a simple and explicit relation between wave set-up and energy dissipation. Finally, we compare numerical simulations of both, the NSW model and the simplified one-way model, with spilling wave breaking experiments and we find a good agreement. 相似文献
3.
安徽巢湖大型平卧褶皱研究 总被引:3,自引:0,他引:3
巢湖平卧褶皱由一个背斜和一个向斜组成,枢纽呈NNE向,轴面微向NWW平卧背斜根部倾斜。卷入褶皱的地层为上震旦统至上三叠统,厚达3.1km。褶皱分布面积约380km~2,波长9km,波幅18km。后期直立褶皱叠加于平卧褶皱之上,褶皱缩短量达19.17km,缩短率约53.7%,褶皱受控于大玵台阶状滑脱断层。褶皱地层由NWW往SEE运动,是一种变动滑脱褶皱。 相似文献
4.
E. Schill C. CrouzetP. Gautam V.K. SinghE. Appel 《Earth and Planetary Science Letters》2002,203(1):45-57
In metacarbonates of the Lesser (LH) and Tethyan (TH) Himalayas of Kumaon/Garhwal (N-India) characteristic remanent magnetisations carried by pyrrhotite (unblocking temperatures: 250-330°C) and magnetite (demagnetising spectra: 15-50 mT) have been identified. Negative fold tests indicate remanence acquisition after the main folding phase, which is of short-wavelength character and occurs during the early orogenese of the Himalayas. A thermal or thermochemical origin of magnetisation is likely and the age of remanence acquisition is indicated to be about 40 Ma by 40K/39Ar cooling and 40Ar/39Ar crystallisation ages. In the Kumaon LH a long-wavelength tilting is indicated by a distribution of the remanence directions along a small-circle in N-S direction. Steepening of the remanence directions in the TH related to ramping on the Main Central Thrust (MCT) was not observed, in contrast to other related studies. In the Alaknanda valley of LH a 38±8 Ma age of remanence acquisition is supported by comparison of observed inclinations to the apparent polar wander path of India. Clockwise rotation of 20.3±11.7° (LH/Alaknanda valley) and 11.3±8.5° (TH) with respect to the Indian plate is observed, indicating that there is no significant evidence for rotational shortening along the MCT since about 40 Ma. Our results suggest that most of rotational underthrusting and oroclinal bending has not been accommodated by the MCT, but by the main thrusts south of it. The latest Miocene/Pliocene age of the Main Boundary Thrust indicates that oroclinal bending is a late-orogenic process. 相似文献
5.
属于帕米尔弧山前带的乌帕尔剖面和属于南天山山前带的巴对布拉克剖面,现今的纬度差为0.56°,但是下第三系古地磁测定结果表明其古纬度差很大.乌帕尔剖面齐姆根组上部的古纬度为8°N,而巴什布拉克剖面巴什布拉克组第5段的古纬度为36.1°N。若考虑到当时板块的相对运移速度,估计始新世早期巴什布拉克地区的古纬度大致为31°N,与当时乌帕尔所处位置的纬差达23°。又根据Klootwijk测得的帕米尔西北缘利什坦层的古纬度值,在始新世末期.包括乌帕尔在内的帕米尔前缘与以巴什布拉区为代表的南天山山前带之间还有至少10°的纬度差。古地磁资料表明,始新世早期,塔里木海宽达2000km,此时印度板块西北端已与欧亚板块局部碰撞,至始新世末,印度板块向北推进20°,帕米尔弧前缘与南天山山前的距离缩短到约1000km,原塔里木海的两侧上升为山前平原。 相似文献
6.
7.
利用两步变分反演方法,研究2006年第4号台风“碧利斯”,对照单部雷达资料和两部雷达资料的反演结果。结果表明:利用单部雷达资料不能很好的反演出台风的风场结构特征,而两部雷达资料在第一步反演背景场时,可以看出台风的涡旋特征。通过检验发现,此次台风过程的水平切向风在最大风速半径内部与Rankine模型相近,外部与Chen 3模型接近。为了更有效地利用单部雷达的观测信息准确定位台风的移动路径,故在单部雷达资料第一步反演背景场时加入模型弱约束。反演结果表明,加入模型弱约束后,反演的背景风场就能看出台风的涡旋特征,通过第二步反演后与两部雷达资料结果相近;加模型弱约束的单部雷达反演结果与两部雷达反演结果间u、v分量的相关系数均在0.8或以上,2-7 km高度层u、v分量的均方根误差明显减小。 相似文献
8.
It seems to be progressively recognized that the stress of the India-Asia convergent front can be transferred rapidly through the southern and central Tibetan lithosphere to the northern Tibet, hence leading to the crustal thickening deformation there during or immediately after the onset of the India-Asia collision(ca.55 Ma).This study focuses on the late Cenozoic deformation and tectonic uplift of the northern Tibet and Tian Shan area.Detailed compilations of a variety of proxy data from sediments and bedrocks suggest that the northern Tibet and Tian Shan area underwent one stage of approximately synchronous widespread contractile deformation since 25–20 Ma, which seemed to decrease at circa 18 Ma as revealed by low-temperature thermochronological data.The latest Oligocene-early Miocene was also significant basin-forming episodes when many intermontane subbasins began to receive syntectonic sedimentation in the northeastern Tibet.Subsequently, the other phase of compressional deformation began to encroach more widely into the northern Tibet and Tian Shan area in episodic steps or continuously from 16–12 Ma to present. 相似文献
9.
10.
将区域重力场多尺度刻痕分析用于提取青藏高原地壳变形带的信息,可了解高原内地壳变形带从浅到深的变化和平面分布特征,并对青藏高原主要地体的空间分布定位,为岩石圈研究提供地表地质难以取得的新信息.多尺度脊形化系数的图像刻划不同深度平面上的地壳变形带.青藏高原地壳变形带从上到下由细密逐渐变为粗稀型,而且细密型变形区分布的范围逐渐缩小,到下地壳完全消失.从这种情况可以推测,以垂直地面方向上看,地壳变形带应该是树形的,下地壳粗稀型的变形带为树的主干,而中地壳粗稀型的变形带为树的分枝,上地壳的变形带为树枝的小枝杈.上地壳细密型变形分布区反映了与中新生代地壳缩短变形区的范围,下地壳清晰连续的变形带反映了青藏高原的构造骨架.多尺度边界刻痕系数的图像刻画不同深度平面上的地体边界,下地壳的刻痕边界系数与密度剧烈变化带位置吻合;因此,由多尺度刻痕分析划分地体时同时取得地体密度信息.青藏高原内密度较高的地体包括喜马拉雅地体、克什米亚地体、察隅河地体、柴达木地体、巴颜喀拉地体和羌塘地体.柴达木地体、巴颜喀拉地体和羌塘地体是青藏高原中有壳根的核,而密度最高的克什米亚和察隅河地体在大陆碰撞时不易碎裂,对东西两个构造结的形成起了关键作用. 相似文献