大别超高压变质岩折返过程中的部分熔融作用   总被引：16，自引：3，他引：13  

钟增球  张宏飞  索书田  游振东 《地球科学》1999,24(4):393-399

研究表明,在大别超高压变质岩的折返过程中,超高压变质岩一方面要经受中下地壳所特有的角闪岩相退变质作用,另一方面要在合适环境下发生部分熔融作用,超高压变质岩在中下地壳的减爱变和部分熔融作用,是一个重要的物理化学过程,它可以降低岩石的强度,提高岩石的可变性,促进挤压（碰撞）体制向伸展体制的转变。超高压变质岩折返过程减压退变和部分熔融作用的确定,进一步支持了“原地”观点。它不仅说明了超高压榴辉岩石和围岩  相似文献   

五台山及邻近地区强对流天气分析   总被引：1，自引：0，他引：1  

李云川  田利庆  赵亚民 《气象》1999,25(9):45-48

讨论了五台山和邻近平原地区雷暴和冰雹的时空分布。指出五台山是强对流天气的多发区。提出了对流风暴越过山脉的４种情况：（１）在太行山脉的西侧停滞,减弱或消失。（２）对流云 的中上部越过山脉演变为中高云。（３）原有的对流云图越山后冲击出新对流云图。（４）对流云图正面越过山脉,形成下坡风暴 。  相似文献   

陆内碰撞体制的流体作用模式及与成矿的关系—理论推导和东秦岭金矿床的研究结果   总被引：15，自引：0，他引：15  

陈衍景 《地学前缘》1996,3(4):0-0

陆内碰撞和流体作用都是当前地球科学的前沿领域,但陆内碰撞体制流体作用以及有关成矿作用的研究仍很薄弱。文章以陆内碰撞成岩成矿模式为基础,通过理论分析,建立了陆内碰撞体制流体作用的模式,即在陆内俯冲体制中,随板片俯冲深度的增加,依次产生改造流体、变质流体和岩浆流体,所产生的流体在空间上具有分带性,并造成岩石、元素、矿化蚀变的成带规律分布;陆内俯冲的早期挤压阶段的流体作用以深部物质分泌的上升流体（改造、变质和部分熔融）为主,晚期伸展阶段以浅层下渗流体（来自大气降水）循环为主,中期由挤压向伸展的转变阶段为深分泌上升流体与浅层下渗流体的混合作用。为检验模式的科学性,选择典型的陆内碰撞带——东秦岭作为实例解剖,发现该区的陆内碰撞作用与金矿床等的成矿作用在时间、空间、地质地球化学特征等方面都十分吻合,且与理论推导的陆内俯冲体制的流体作用规律一致。对若干典型矿床成矿流体的氢同位素研究表明,成矿流体的性质、来源和演变特征等与理论推导的陆内碰撞体制流体作用规律完全符合。  相似文献   

大兴安岭南段巴彦高勒银多金属矿地质地球化学特征及找矿标志          下载免费PDF全文

朵兴芳  屠立鹏  李志丹  王丽瑛  魏子鑫  王俊  高洪生 《地质找矿论丛》2020,35(4):390-398

巴彦高勒银多金属矿是大兴安岭南段新发现的一例小型银多金属矿床,矿体多呈脉状、透镜状产于古元古界锡林郭勒杂岩中,受NE向断裂控制。矿石矿物主要有方铅矿、闪锌矿、黄铁矿、辉银矿、黝锑银矿等,脉石矿物主要有萤石、毒砂、石英、绿帘石、绿泥石等。围岩蚀变主要为褐铁矿化、硅化、高岭土化、黄铁矿化、绿泥石化、绿帘石化等。通过在该矿区开展1∶1万土壤地球化学测量,共圈定出编号为Ht-1至Ht-4的4个矿致组合异常区,并发现了对应的矿脉和蚀变带。根据矿体发育部位和围岩蚀变分带特征,推测成矿与热液活动有关,矿床成因为中低温热液型。通过分析成矿地质特征,得出该矿床浅表以褐铁矿化,深部以硅化、高岭土化为重要的找矿标志,北东向构造破碎带是重要的控矿构造,而1∶1万土壤地球化学测量成果圈出的Ag、Pb、Zn单元素地球化学异常及Ag-Sb-Sn-Cu-Pb-Zn组合异常是十分有效的化探标志。  相似文献   

Rayleigh波入射下相邻山体地震响应边界元法模拟          下载免费PDF全文

张雪  刘中宪    何颖 《世界地震工程》2018,34(4):008-15

采用间接边界元法（IBEM）,对Rayleigh波入射下两邻近山体的地震响应进行了定量分析。结果表明:与单个山体在Rayleigh波入射下的地震响应相比,两山地形的地震反应规律更为复杂,反应特征受控于入射波频率和山体间距等因素。总体上看:入射Rayleigh波频率较低时,两山间距对双山地形地震反应影响较大。低频波入射,受邻近山体影响,迎波面山体水平位移峰值约为入射波水平位移的6.3倍,放大效应可达单山作用的1.5倍。且山体山脚处竖向位移的频谱振荡更为剧烈,特定频率下山脚的竖向位移反应可达单山放大效应的1.6倍。较高频波入射时,迎波面一侧山体受邻近山体影响较小,且对波表现出明显的屏障效应,背波面山体地震反应强度被削弱。  相似文献   

Radiocarbon and optically stimulated luminescence dating of sediments from Lake Karakul,Tajikistan     

《Quaternary Geochronology》2017

Lake Karakul in the eastern Pamirs is a large and closed-basin lake in a partly glaciated catchment. Two parallel sediment cores were collected from 12 m water depth. The cores were correlated using XRF analysis and dated using radiocarbon and OSL techniques. The age results of the two dating methods are generally in agreement. The correlated composite core of 12.26 m length represents continuous accumulation of sediments in the lake basin since 31 ka. The lake reservoir effect (LRE) remained relatively constant over this period. High sediment accumulation rates (SedARs) were recorded before 23 ka and after 6.5 ka. The relatively close position of the coring location near the eastern shore of the lake implies that high SedARs resulted from low lake levels. Thus, high SedARs and lower lake levels before 23 ka probably reflect cold and dry climate conditions that inhibited the arrival of moist air at high elevation in the eastern Pamirs. Low lake levels after 6.5 ka were probably caused by declining temperatures after the warmer early Holocene, which had caused a reduction in water resources stored as snow, ice and frozen ground in the catchment. Low SedARs during 23–6.5 ka suggest increased lake levels in Lake Karakul. A short-lived increase of SedARs at 15 ka probably corresponds to the rapid melting of glaciers in the Karakul catchment during the Greenland Interstadial 1e, shortly after glaciers in the catchment had reached their maximum extents. The sediment cores from Lake Karakul represent an important climate archive with robust chronology for the last glacial–interglacial cycle from Central Asia.  相似文献   

The role of fault reactivation in the development of tropical montane lakes     

Pedro Walfir M. Souza-Filho  Roberto Vizeu L. Pinheiro  Francisco R. Costa  José Tasso F. Guimarães  Prafulla K. Sahoo  Marcio S. Silva  Cleverson G. Silva 《地球表面变化过程与地形》2020,45(14):3732-3746

This work details the role of fault reactivation in the development of tropical montane lakes by using basin morpho-structural analysis and seismostratigraphic studies. The upland lakes are severely faulted sinkholes, whose faults penetrate the Quaternary sedimentary units. Four main stages are related to the lake formation: (i) an Early Proterozoic tectonic deformation of the rocks along the southern border of the Carajás Structure, where the lake is placed; (ii) differential erosion by – and building of – the formation of the South Carajás Hill; (iii) Fe-rich crust formation by weathering and gravitational collapse faults following the E–W plateau border and the start of Violão Lake formation during the Pliocene–Pleistocene; and (iv) episodic fault-fracture reactivation by gravitational collapse causing pulses of subsidence in the lake and outlining its faulted borders. Dissolution of the lateritic crust and erosion by runoff drainage under wet climate conditions were coeval with fault activities, which allowed the deposition of relatively thick clastic deposits organized in three main seismostratigraphic units associated with major lake-level fluctuations. Initial fault reactivation under low-level water started lacustrine basin development with deposition of prograding fan deltas related to the main drainage. A second fault reactivation by gravitational collapse increased the lake accommodation space and resulted in the deposition of fine-grained sediments from dilute interflows or overflows until 36 000 cal year BP. At about 31 000 cal year BP, rapid decreases in the lake water level under redox conditions at the sediment/water interface allowed widespread siderite formation. A third gravitational collapse episode was responsible for the increase in the lake area and depth and the returning of clastic/organic deposition up to the present. This tropical montane lake can be seen as a representative example for understanding the formation of other upland lakes controlled by fault reactivation. © 2020 John Wiley & Sons, Ltd.  相似文献   

甘肃主动源建设发展与展望          下载免费PDF全文

郭晓  张元生  刘旭宙  秦满忠  魏从信  邹锐  王亚红  孙点峰  刘志国 《地震工程学报》2020,42(5):1146-1150

利用大容量气枪震源探测已成为探索地震预报新途径的一个重要发展方向,将推进经验性地震预测与物理预测的结合。祁连山、刘家峡气枪发射台的选址与建设经历曲折过程,在多方努力和帮助下,克服重重困难,最终高质量完成。祁连山气枪发射台的稳定运行,已积累了丰富的主动源气枪激发数据,并取得了多项创新性成果。新建的刘家峡气枪发射台将实现对海原断裂和西秦岭北缘深大断裂的连续监测,通过多点监测,分析强震孕育与区域应力场和介质变化的关系,开展地震危险性的分析研究。位于青藏高原东北缘强震活动强烈地区的甘肃未来计划再建设3个气枪主动源,联合祁连山、刘家峡气枪主动源,实现对青藏高原东北缘断裂带系进行主动源四维探测,对于甘肃的防震减灾和地震预测具有重要意义。  相似文献   

Drainage Density and Relative Relief in Humid Steep Mountains with Frequent Slope Failure     

Takashi Oguchi 《地球表面变化过程与地形》1997,22(2):107-120

Previous studies in Japanese mountains have shown that drainage density (D) correlates negatively with relief (R) and the erosion rate (E), whereas elsewhere both R and E correlate positively with D. To investigate the inconsistency, this paper compares two types of D–R relations for eight mountain river basins in central Japan. R is computed from a digital elevation model for 1109 morphometric samples of area 0·5 km × 0·5 km. Drainage networks in these cells were first constructed by map criteria applied previously in Japan — deeply notched V-shaped contours with an angle <53°. The resulting D correlates negatively with R, confirming preceding studies. When drainage lines along shallower hollows were added, however, the calculated D essentially constant. These relations arise from active landsliding in high-relief terrains, which has eroded steep channel banks into gentle ones. The decline of channel banks with increasing R is accelerated in terrains underlain by soft rocks, because of rapid erosion. The constant D for all the drainage lines indicates a uniform frequency or spacing of ridges and hollows on hillslopes in rugged humid mountains. Because the D–R and D–E relations for Japan reflect a uniquely Japanese physiographic setting characterized by frequent landsliding, they differ from those relations for other regions where channelization by gullying predominates. © 1997 by John Wiley & Sons, Ltd.  相似文献   

长白山地区遥感生态指数时空变化及其气候响应          下载免费PDF全文

马云飞  李建平  陈长胜  吴玉洁  袁福香  刘星辰 《沙漠与绿洲气象(新疆气象)》2023,17(2):91-97

利用Google Earth Engine(GEE)云平台，在原有遥感生态指数（RSEI）基础上，选用增强型植被指数（EVI）代替原绿度指标中的NDVI，构建并计算2001—2020年长白山地区植被生长季RSEI，采用回归分析、波动分析、Hurst指数等方法，分析长白山地区RSEI时空变化特征并探讨其气候影响因素。研究表明：（1）2001—2020年长白山地区RSEI波动缓慢上升，生态环境质量整体呈上升趋势。RSEI多年均值空间分布具有明显的分异性，长白山保护开发区生态环境质量较好，通化市、白山市大部较差。（2）近20年长白山地区RSEI稳定性较差，生态环境质量较脆弱。未来生态环境趋势总体向好，但局部地区仍存在持续恶化态势。（3）长白山地区RSEI主要受降水影响较大，与降水呈显著正相关，与气温相关性不强。  相似文献