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141.
越南西北部Pu Sam Cap高钾碱性杂岩位于哀牢山剪切带南段西侧,由粗面岩、煌斑岩、碱性正长岩与碱性花岗岩组成。其中粗面岩不整合于晚白垩世陆相沉积岩之上,碱性侵入岩侵入到三叠纪陆源沉积岩、侏罗纪流纹岩及40~35Ma含角闪石二长岩-花岗岩中。该杂岩的岩石具有低TiO2(0.8%)、P2O5(0.64%)和FeO*(7.74%),高Na2O(1.41%~4.5%)和K2O(5.22%~9.4%)的地球化学属性,属于高钾碱性玄武质到高钾碱性长英质岩浆岩类型与钾质至超钾质岩浆系列。这套岩石富集大离子亲石元素LILE、轻稀土元素LREE和一组相容元素,具有明显的Ta、Nb和Ti异常,表明Pu Sam Cap高钾碱性杂岩形成于与俯冲带有关的大陆弧和后碰撞弧构造环境。锆石LA-ICPMS U-Pb年代学研究表明碱性正长岩与碱性花岗岩分别形成于32.70±0.24Ma、35.1±0.06Ma,上述年龄代表了Pu Sam Cap高钾碱性杂岩的侵入岩结晶年龄。两个样品中锆石的εHf(t)变化范围分别为-2.8~2.5和-4.9~0.1,在t-εHf(t)相关图上分析点落在下地壳和亏损地幔演化线之间,两阶段模式年龄变化范围为950~1286Ma和1107~1421Ma。该杂岩的εNd(t)变化范围-5.63~-3.26,具有低143Nd/144Nd比值(0.512336~0.512447)和高87Sr/86Sr比值(0.706254~0.707273),Sr-Nd同位素相关图上接近于EM2地幔端元趋势线,与大理地区新生代高钾岩浆岩十分相似,表明PuSamCap高钾碱性杂岩的岩浆是幔源岩浆和壳源岩浆的混合结果,同时可与大理地区新生代高钾岩浆岩对比,它们形成于哀牢山-红河左行走滑活动之前,墨江古特提斯洋盆的消减与印度-欧亚陆陆碰撞活动提供了宏观区域性构造背景。 相似文献
142.
Tuan Nguyen-Sy Quy-Dong To Minh-Ngoc Vu The-Duong Nguyen Thoi-Trung Nguyen 《Geophysical Prospecting》2020,68(8):2557-2578
This paper aims to demonstrate that the elastic stiffnesses and the anisotropic parameters of rocks can be accurately predicted from geophysical features such as the porosity, the density, the compression stress, the pore pressure and the burial depth using relevant machine learning methods. It also suggests that the extreme gradient boosting method is the best method for this purpose. It is more accurate, extremely faster to train and more robust than the artificial neural networks and the support vector machine methods. Very high R-squared scores was obtained for the predicted elastic stiffnesses of a relevant dataset that is available in the literature. This dataset contains different types of rocks, and the values of the features are in large ranges. An optimal set of parameters was obtained by considering an appropriate sensitivity analysis. The optimized model is very easy to implement in Python for practical applications. 相似文献
143.
144.
Thai Anh Tuan N. Purnachandra Rao Kalpna Gahalaut Cao Dinh Trong Le Van Dung Cao Chien K. Mallika 《Journal of Seismology》2017,21(5):1131-1143
In the Song Tranh 2 (ST2) hydropower reservoir located in the Quang Nam province, Central Vietnam, earthquakes started occurring soon after impoundment of the reservoir in late 2010. Earthquakes continue to occur in the region, and two earthquakes of M 4.6 and 4.7 on October 22, 2012 and November 15, 2012, respectively, have been reported (Trieu et al. 2014; Giang et al. 2015) in the vicinity of the reservoir. In the present study, b-value has been estimated, and focal mechanism solutions have been computed for the first time using moment tensor inversion approach. Also, the influence of impoundment of reservoir on the occurrence of earthquakes has been computed for the ST2 region based on Coulomb stress. A quality data set of 595 earthquakes recorded for the period of October 2012 to April 2014 at ten stations of the seismic network operated by the Institute of Geophysics (IGP) has been used to calculate b-values for the northern and southern seismicity clusters of the region. In general, the b-values associated with reservoir-triggered seismicity (RTS) are found to be higher than the regional b-values in the frequency-magnitude relation of earthquakes. For the ST2 region, it is found that the b-values for the northern and southern clusters are 0.94 ± 0.04 and 0.90 ± 0.04, respectively. Focal mechanism solutions obtained for the two earthquakes close to the reservoir have a right-lateral strike-slip mechanism, with the preferred planes trending NW-SE. These results are concurrent with the orientation of the nearby local surface faults, which we confirm as the active faults in this region. Influence of the stresses due to reservoir water load on the local seismicity is computed based on the obtained focal mechanism by using the concept of fault stability. It is found that most of the earthquakes occur in the positive Coulomb stress region, which shows the influence of reservoir impoundment on earthquake occurrence in the vicinity. Our results suggest that the local earthquakes are triggered by the impoundment of the ST2 reservoir. 相似文献