Structure,mechanical properties and evolution of the lithosphere below the northwest continental margin of India

International Journal of Earth Sciences - The continental breakup history at the northwest continental margin of India remained conjectural due to lack of clearly discernable magnetic anomaly...     

Delineation of groundwater prospective zones from a delta region of India,using geoelectrical and water quality approach

Geoelectrical survey was carried out in the western delta region of River Vasista Godavari, Andhra Pradesh, India, for delineation of groundwater prospective zones due to acute shortage of water supply for various purposes. Forty-six vertical electrical soundings (VES) were done, employing the Schlumberger configuration with a maximum AB/2 of 160 m. The interpreted results of VES show four to five layers with variable thicknesses, such as topsoil zone (1.5–3 m), clay zone (0.84–32 m), finer sand zone (2–72 m), medium to coarse sand zone (4 to 28.8 m) and clay zone (1.2–∞ m), indicating a multi-aquifer system. These results are corroborated with the known lithologs of the study area. Further, the resistivity is also compared with electrical conductivity (EC) of groundwater observed nearby shallow wells representing buried channel (BC), flood plain (FP) and coastal (C) zones, which indicate slightly brackish to brackish water (EC: 1470–6010 µS/cm), whereas the groundwater observed from deep wells shows the fresh (EC: 726–1380 µS/cm), fresh to brackish (EC: 1010 to 3250 µS/cm), and brackish water (EC: 3020 to 4170 µS/cm) located in BC, FP and C zones, respectively. This survey reveals the prospective aquifer zones with potable water at VES locations of 4–6, 8, 10, 11, 14, 16–28, 33–36, 39 and 42–44, where the resistivity values vary from 10 to 40 Ω m. The slightly brackish and brackish water zones are also observed from the resistivity of less than 10 Ω m at shallow depth in BC (VES-22, 37, 38 and 46), FP (VES-1, 2, 7, 29, 30 and 40) and C (VES-3, 4, 9, 12, 13, 15, 31, 32, 41 and 45) zones. As a result, the present investigation has delineated the freshwater zones at shallow (<?12 m) and also at deeper depths (30–45 m) as prospective areas, where BC zone occurs. Freshwater pockets also identified in FP (VES-8 and 39) and C (VES-11, 14 and 15) zones. Thus, this study helps to solve the drinking and irrigation water problems.     

Petrography and geochemistry of the Proterozoic sandstones of Somanpalli Group from Pomburna area,Eastern Belt of Pranhita–Godavari Valley,central India: Implications for provenance,weathering and tectonic setting

In this paper, we, for the first time, report geochemistry of sandstone from Somanpalli Group from Pomburna area in the Eastern Belt of Pranhita–Godavari (PG) Valley, central India and studied to infer their provenance, intensity of paleo-weathering and depositional tectonic setting. Petrographic study of sandstones show QFL modal composition of arenite. Chemical results show high \(\hbox {SiO}_{2}\) and CIA but lower \(\hbox {Al}_{2}\hbox {O}_{3}, \hbox {TiO}_{2}\), Rb, Sr, \(\hbox {K}_{2}\hbox {O}\) indicating mixed sources. Major elements chemistry parameters such as, \(\hbox {K}_{2}\hbox {O/Al}_{2}\hbox {O}_{3}\) ratio and positive correlation of Rb with \(\hbox {K}_{2}\hbox {O}\), reflects a warm and humid climate for study area. The tectonic discrimination plots (\(\hbox {SiO}_{2}/20\)–\(\hbox {K}_{2}\hbox {O} + \hbox {Na}_{2}\hbox {O}\)–\(\hbox {TiO}_{2} + \hbox {Fe}_{2}\hbox {O}_{3} + \hbox {MgO};\,\hbox {K}_{2}\hbox {O}/\hbox {Na}_{2}\hbox {O}\) vs. \(\hbox {SiO}_{2}\); Th–Sc–Zr/20) indicate dominantly passive margin and slight active tectonic setting. Concentrations of Zr, Nb, Y, and Th are higher compared to the UCC values and the trends in Th/Cr, Th/Co, La/Sc and Cr/Zr ratios support a felsic and mafic source for these sandstones and deposition in passive margin basin. Chondrite normalized REE pattern reflects LREE depletion, negative Eu anomaly and flat HREE similar to UCC, felsic components. ICV value (0.95) also supports tectonically quiescent passive margin settings. CIA values (74) indicate high degree of chemical weathering and warm and humid paleoclimatic condition.     

Geochemical characteristics of Proterozoic granite magmatism from Southern Granulite Terrain,India: Implications for Gondwana

Granitoid intrusions occur widely in the Southern Granulite Terrain (SGT) of India, particularly within the Cauvery Suture Zone (CSZ), which is considered as the trace of the Neoproterozoic Mozambique ocean closure. Here we present the petrological and geochemical features of 19 granite plutons across the three major tectonic blocks of the terrain. Our data show a wide variation in the compositions of these intrusions from alkali feldspathic syenite to granite. The whole rock geochemistry of these intrusions displays higher concentrations of \(\hbox {SiO}_{2}\), FeO*, \(\hbox {K}_{2}\hbox {O}\), Ba, Zr, Th, LREE and low MgO, \(\hbox {Na}_{2}\hbox {O}\), Ti, P, Nb, Y and HREE’s. The granitoids are metaluminous to slightly peraluminous in nature revealing both I-type and A-type origin. In tectonic discrimination plots, the plutons dominantly show volcanic arc and syn-collisional as well as post-collisional affinity. Based on the available age data together with geochemical constrains, we demonstrate that the granitic magmatism in the centre and south of the terrain is mostly associated with the Neoproterozoic subduction–collision–accretion–orogeny, followed by extensional mechanism of Gondwana tectonics events. Similar widespread granitic activity has also been documented in the Arabian Nubian shield, Madagascar, Sri Lanka and Antarctica, providing similarities for the reconstruction of the crustal fragments of Gondwana supercontinent followed by Pan-African orogeny.     

沁水盆地原始水动力场类型及其对煤层气排采的影响

水动力场研究在煤层气勘探开发中具有重要作用。本文首先讨论了基于煤层气井排采资料的水动力场研究方法,在分析沁水盆地柿庄区块原始水动力场特点的基础上,结合前人在盆地其他区块水动力场的研究成果,分析了沁水盆地原始水动力场的类型,进而探讨了水动力场类型对煤层气排采的控制作用。研究表明:沁水盆地自边缘向腹部依次存在重力驱动型、滞流型和压实驱动型三种类型的区域原始水动力场;重力驱动型和滞流型水动力场具备煤层气保存条件,含气量高,煤层气排采效果相对较好,而压实驱动型水动力场虽具备一定的保存条件,但因地层压力较高,煤层气井排水降压困难,产气效果较差;无论是在重力驱动型还是滞流型的区域水动力场中,局部的低势汇聚区具备煤层气保存和排采的有利条件,煤层气开发效果一般较好。在未来煤层气勘探开发过程中,应将重力流驱型或滞流型水动力场所在区域中的局部低势汇聚区作为煤层气开发的甜点区。     

东昆仑志留纪辉长岩地球化学特征及与铜镍成矿关系探讨

东昆仑造山带新发现的夏日哈木超大型岩浆铜镍矿床、石头坑德大型岩浆铜镍矿床及冰沟南小型岩浆铜镍矿床,其矿体均赋存于橄榄辉石岩内,而辉长岩又是该含矿橄榄辉石岩的直接围岩,并且辉长岩的形成时代相近(夏日哈木辉长岩431Ma、石头坑德辉长岩425Ma、冰沟南辉长岩427Ma),产出位置属于同一大的构造单元,均邻近昆北及昆中断裂。通过对辉长岩的地球化学特征研究,发现明显富集轻稀土元素和明显的Nb-Ta负异常,亏损高场强元素。Sr-Nd同位素研究,表明东昆仑夏日哈木和石头坑德辉长岩岩体的母岩浆来自一个曾经被交代富集的地幔源区,可能揭示了由于从洋壳释放出的流体交代地幔楔的岩石成因。结合区域构造演化和辉长岩形成时代,认为东昆仑夏日哈木和石头坑德辉长岩形成于碰撞后伸展环境。辉长岩岩浆源区性质与赋矿辉石岩存在明显不同,并非同一岩浆活动的产物。辉长岩在东昆仑造山带地区直接充当了含矿辉石岩的直接围岩,与岩浆铜镍硫化物矿体的形成没有关系,富含橄榄石的超镁铁质岩石更有利于形成具有较大经济价值的铜镍矿体。这为指导东昆仑找矿实践和岩浆铜镍矿床成矿理论研究提供了基础。     

The Derivation and Validation of TBM Disc Cutter Wear Prediction Model

The problem of disc cutter wear is inevitable when shield or TBM excavating hard rock for a long distance, thus, the study of disc cutter wear model has an important project value on predicting its service life and replacement opportunity. It is put forward by analyzing disc cutter wear mechanism that the main wear form is abrasive wear, which is based on plastic removal mechanism. Then, disc cutter wear rate and linear wear rate prediction models are obtained by approximate calculation and mathematical deduction, which are based on Rabinowicz equation and CSM model. At last, the two models are verified through field test data from three projects, and the results show that the prediction model can accurately reflect the real wear situation of disc cutter.     

基于人工鱼群算法和SCA等效理论的井中横波速度预测方法

在建立页岩岩石物理模型的基础上,根据等效自相容近似(SCA)岩石物理模型,构建出岩石的纵波速度、横波速度与岩石密度、组分和孔隙度等的定量关系,得出使理论纵波速度和实际纵波速度最接近的孔隙纵横比,进而将该孔隙纵横比作为约束条件来实现横波速度预测。反演算法利用人工鱼群算法来计算最佳孔隙纵横比,并将预测的横波速度与实际测得的横波速度对比,证明了人工鱼群算法的有效性。     

桂林毛村岩溶区与碎屑岩区檵木和马尾松凋落叶分解研究

为探究岩溶生态环境对凋落叶分解的影响,选用碎屑岩区相同树种作为对比,运用凋落物分解网袋法研究其凋落物分解初期动态,研究结果表明:（1）岩溶区檵木和马尾松凋落叶分解速率总体上均小于碎屑岩区相同树种凋落叶分解速率;（2）凋落叶分解速率k与凋落叶初始养分碳含量呈显著负相关（P<0.05）,与木质素含量呈极显著负相关（P<0.01）;（3）在凋落叶分解过程中,各养分释放规律具有一定的差异,凋落叶养分元素碳在分解过程中呈现出净释放;（4）岩溶区树种的碳释放速率比碎屑岩区慢,说明岩溶区两树种的凋落在一定程度上延长了C的循环周期      

轨道误差对InSAR相位影响的BP神经网络去除法

针对用二次多项式法去除轨道误差对InSAR相位影响时,须对干涉相位其他项分布性质作假设,且自身存在一定的模型缺陷的问题,该文提出用BP神经网络去除轨道误差对InSAR相位影响的方法。研究表明:BP神经网络法在使用时无须对干涉相位其他项分布性质作假设,模型更优。模拟实验中,轨道误差相位拟合残差更小;真实数据实验中,纠正后非形变区相位集中在零值附近,且波动趋势更为平稳。该方法一定程度上降低了传统二次多项式法的应用局限性。