Chhotanagpur granite gneiss in relation to the schistose rocks around Murhu,Ranchi district,Bihar: a structural approach

Structural analysis of the Chhotanagpur gneiss and the adjoining schistose rocks of the Singhbhum Group indicates perfect conformity in their structures on macroscopic, mesoscopic and microscopic scales. This precludes the possibility of the gneissic rocks having intruded into the deformed and metamorphozed schistose rocks. The observed features can be best explained by considering the gneissic rocks as the basement and the schistose rocks as the cover, both deformed and metamorphozed together. However, this does not exclude the possibility of the gneissic rocks being reactivated and intruding elsewhere.     

北天山山前乌鲁木齐—乌苏地区的构造变形特征

北天山山前乌鲁木齐—乌苏地区的构造变形,是在挤压兼左行剪切作用下形成的.根据皱皱构造的排列组合、地层组成、变形强度及构造线等特征,将本区划分为五个构造带,分属于两个构造系.其中小渠子构造带的成因与博格达山活动相关,属于另一个构造系.其四余个构造带组成独立的玛纳斯构造系,叠加在燕山期构造之上.     

RECENT UNDERTHRUSTS OF TIANSHAN AND POSSIBLE MECHANISM OF THEIR ORIGIN

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Measurement of terrace deformation and crustal shortening of some renascent fold zones within Kalpin nappe structure

The Kalpin nappe structure is a strongest thrust and fold deformation belt in front of the Tianshan Mountains since the Cenozoic time. The tectonic deformation occurred in 5―6 striking Meso-zoic-Cenozoic fold zones, and some renascent folds formed on the recent alluvial-proluvial fans in front of the folded mountains. We used the total station to measure gully terraces along the longitudinal to-pographic profile in the renascent fold zones and collected samples from terrace deposits for age de-termination. Using the obtained formation time and shortening amount of the deformed terraces, we calculated the shortening rate of 4 renascent folds to be 0.1±0.03 mm/a, 0.12±0.04 mm/a, 0.59±0.18 mm/a, and 0.26±0.08 mm/a, respectively. The formation time of the renascent folds is some later than the major tectonic uplift event of the Qinghai-Tibet Plateau 0.14 Ma ago. It may be the long-distance effect of this tectonic event on the Tianshan piedmont fold belt.     

A mathematical model for orientation data from macroscopic cylindrical folds

An asymptotic form of Bingham's distribution on the sphere is applied to orientation data from cylindrical folds. Data from cylindrical folds typically form two clusters, one cluster for each fold limb. A bimodal distribution is obtained by fitting a unimodal distribution to each cluster. One parameter of the distribution gives the fold axis, another parameter is directly related to the curvature of the fold limb. Certain tests of hypotheses based on this distribution are the same as tests based on the Dimroth—Watson (symmetric girdle)distribution. One such is the test of whether two folds have the same fold axis.     

Strain and vorticity analysis using small-scale faults and associated drag folds

Small-scale faults with associated drag folds in brittle-ductile rocks can retain detailed information on the kinematics and amount of deformation the host rock experienced. Measured fault orientation (α), drag angle (β) and the ratio of the thickness of deflected layers at the fault (L) and further away (T) can be compared with α, β and L/T values that are calculated with a simple analytical model. Using graphs or a numerical best-fit routine, one can then determine the kinematic vorticity number and initial fault orientation that best fits the data. The proposed method was successfully tested on both analogue experiments and numerical simulations with BASIL. Using this method, a kinematic vorticity number of one (dextral simple shear) and a minimum finite strain of 2.5–3.8 was obtained for a population of antithetic faults with associated drag folds in a case study area at Mas Rabassers de Dalt on Cap de Creus in the Variscan of the easternmost Pyrenees, Spain.     

Fry and Rf/ϕ strain methods constraints and fold transection mechanisms in the NW Iberian Variscides

Apúlia is a small Portuguese sector in NW of Central-Iberian Zone, that have been deformed in a non-coaxial sinistral transpressive regime during the first and main Variscan tectonic event (D₁). This deformation give rise to a major NW–SE anticline, where the S₁ N–S cleavage transect the inverted short NE limb; two and three-dimensional strains analysis have been done in the low metamorphic grade Ordovician quartzites of this limb using Fry and Rf/ϕ methods. The data show that most deformation was due to intergranular deformation mechanisms. The intragranular deformation leading to the distortion of strain markers and to cleavage was very incipient and a latter event in the D₁ phase. The apparent plane strain ellipsoids (if no volume change is assumed) related to the intragranular mechanisms contrast with the more prolate strain ellipsoids related to the bulk deformation of Apúlia Quartzites. This constrictional bulk strain fabrics are characteristic of the sinistral transpressive regimes dominant in the northern sectors of the Central-Iberian Zone.     

环肋圆柱壳体在水下冲击波作用下的动力弹塑性屈曲

本文以加肋圆柱壳体为对象建立力学模型，在水下爆炸产生的冲击波作用下，考虑流体与结构的耦合效应，研究加肋圆柱壳体的弹塑性失稳变形量及动力响应特性。数值分析显示出的最终变形形状和压力变化过程与实验资料一致的     

Tectonic constraints on watershed development on frontal ridges: Mohand Ridge, NW Himalaya, India

Uplifting frontal ridges are one of the most conspicuous geomorphic features that mark the frontal parts of actively converging mountain belts. Growth of these ridges can lead to the simultaneous development of a drainage system that is defined by watersheds, stream network and long profiles of channels. In the present study, shape parameters of watersheds, stream network characteristics and pattern of network growth, shape of long profiles, and the SL index have been investigated in a part of NW Himalaya to understand the relationship between endogenic tectonic processes and exogenic fluvial processes. This explains the tectonic control on drainage systems in the uplifting frontal ridge. This watershed analysis was carried out using a Digital Elevation Model (DEM) and a number of anomalies have been identified and analysed. The most striking is the asymmetric development of watersheds on either side of an almost straight ridge crest. Watershed asymmetry along the ridge crest is characterized by larger area and less elongated watersheds in the southern flank (forelimb) in comparison to the northern flank (backlimb). Drainage network and long profile analysis establishes that the larger watershed area in the forelimb is due to dominance of headward erosion and its impact on drainage network growth. Dominance of headward erosion is due to slope variation in response to forelimb development along a fault-related fold. Even through, headward erosion has shifted the ridge crest; it is parallel with the trace of the Himalayan Frontal Thrust (HFT). The parallel ridge crest with reference to the HFT is indicative of the tectonic control of the HFT on the development of the watersheds. Hence, a well developed linkage between tectonic processes (fold development) and surface processes (headward erosion) is responsible for variation in watershed and drainage network pattern across the ridge crest. The study also investigates the role of planform ridge curvature on watershed development. The effect is more pronounced on an asymmetric ridge, such as the Mohand ridge, than on a symmetric ridge.     

利用2.5维数值模式匹配算法高效高精度建立垂直井眼中多分量阵列感应井眼校正库

本文将应用2.5维数值模式匹配算法研究建立柱状横向同性地层中偏心条件下磁流源并矢Green函数的高效算法,并利用该算法高效计算多分量阵列感应井眼校正库.首先,通过Fourier展开技术将偏心条件下磁流源并矢Green函数的数值模拟转化为一系列的轴对称问题;然后利用模式匹配算法求解轴对称问题,得到柱状介质中偏心条件下磁流源并矢Green函数的半解析解;最后,结合中国石油集团测井有限公司开发的三维感应测井仪器(TDIT)的结构参数,推导出复合线圈系视电导率张量的计算公式.在此基础上,根据井场实际地层资料归纳出理论地层模型相应参数的变化范围,高效高精度建立一套直接应用于工业生产的多分量阵列感应井眼校正库,并利用井眼校正库详细地分析考察各模型参数对TDIT响应的影响.