A visage of early Paleozoic Japan: Geotectonic and paleobiogeographical significance of Greater South China     

Yukio Isozaki 《Island Arc》2019,28(3)

The current state of knowledge on the early Paleozoic evolution of Japan is reviewed. Although early Paleozoic Japan marked the foundation of long‐lasting subduction‐related orogenic growth throughout the Phanerozoic, details of this have not been fully revealed. Nevertheless, U‐Pb dating of zircons both in Paleozoic granitoids and sandstones is revealing several new aspects of early Paleozoic Japan. The timing of the major tectonic change, from a passive continental margin setting (Stage I) to an active one (Stage II), was constrained to the Cambrian by identifying the oldest arc granitoid, high‐P/T blueschist, and terrigenous clastics of arc‐related basins. Ages of recycled zircons in granitoids and sandstones provided critical information on the homeland of Japan, i.e. the continental margin along which proto‐Japan began to grow. The early Paleozoic continental margin that hosted the development of an arc‐trench system in proto‐Japan had cratonic basement composed mostly of Proterozoic crust with a minor Archean component. The predominant occurrence of Neoproterozoic zircons in Paleozoic rocks, as xenocrysts in arc granitoids and also as detrital grains in terrigenous clastics, indicates that the relevant continental block was a part of South China, probably forming a northeastern segment of Greater South China (GSC) together with the Khanka/Jiamsi/Bureya mega‐block in Far East Asia. GSC was probably twice as large as the present conterminous South China on mainland Asia. Paleozoic Japan formed a segment of a mature arc‐trench system along the Pacific side of GSC, where the N–S‐trending Pacific‐rim orogenic belt (Nipponides) developed with an almost perpendicular relationship with the E–W‐trending Central Asian orogenic belt. The faunal characteristics of the Permian marine fauna in Japan, both with the Tethyan and Boreal elements, can be better explained than before in good accordance with the relative position of GSC with respect to the North China block during the late Paleozoic.  相似文献   

大兴安岭造山带及两侧邻区莫霍面深度与泊松比分布特征     

杨彦明  张建中  黄瑞滨 《中国地震》2019,35(2):211-225

利用2009～2016年内蒙古自治区数字地震台网宽频带固定地震台站的远震波形数据,采用接收函数H-k算法获得23个基岩台站下方的莫霍面深度和泊松比,同时,收集并筛选出277个已有探测台阵和流动台站的接收函数研究结果,综合分析给出大兴安岭造山带及两侧邻区莫霍面深度、泊松比的分布特征。研究表明,研究区域的莫霍面在整体上呈现自东向西逐渐加深的特征,莫霍面深度为25.0～42.3km,平均约为33.5km。莫霍面最浅的区域为松辽盆地(深度为27.0～35.0km),最深的区域为大兴安岭重力梯级带以西地区(深度为41.0～42.3km)。研究区域泊松比为0.19～0.33,平均值为0.26,大于全球大陆地壳的平均值。泊松比高值异常区集中在火山岩区及具有较厚沉积层的盆地。台站所处位置的海拔与莫霍面深度之间具有较强的正相关性,艾里补偿模式在研究区成立,莫霍面起伏与区域地形地貌特征间具有显著的镜像关系。大兴安岭地区的莫霍面深度与泊松比间存在显著的反相关关系,而在松辽盆地及周缘地区未发现明显的规律性,这也意味着松辽盆地在构造演化过程中经历了更为复杂的地壳改造过程。  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   

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   

西天山温泉地区奥陶纪侵入岩地球化学特征及成因探讨          下载免费PDF全文

孟令华 《山东国土资源》2022,38(2):1-9

西天山温泉地区是以温泉岩群为基底的古老地块,岩浆活动强烈,发育大量不同期次花岗岩类,奥陶纪侵入岩为一套准铝质过铝质钙碱性岩石,(La/Yb)N值为6.22～13.02,轻稀土元素富集,δEu为0.77～0.96,具轻微负Eu异常,微量元素中富集Sr、Ba等大离子亲石元素,亏损Th、Nb、P、Ti等高场强元素,属于中等分...  相似文献   

WRF/CALMET/BP预报系统对内陆山区风电场的一次滚动预报检验北大核心          下载免费PDF全文

刘伟  李艳  杜钦 《气象科学》2022,42(1):79-88

利用以中尺度数值模式WRF/CALMET作为风电场预报系统的动力模块,及BP神经网络法(BP-ANN)作为风电场预报系统的统计订正方法,对重庆市齐跃山风电场进行了一次时间分辨率为5 min的24 h风速、风功率的滚动预报试验,探讨了适用于中国典型内陆山区的风电场预报系统。结果显示:以WRF/CALMET/BP组成的动力—统计预报系统能够较好地模拟出内陆山区的风场特征,系统对正午至傍晚时段的风速预报准确率较高。WRF/CALMET动力模式对于风速中心振幅的模拟能力较好,经过BP神经网络订正后,模拟结果会趋于均值。不同风速段中,模式对低风速段(3~8 m·s^(-1))的预报效果较好,BP神经网络对中风速段(8~14 m·s^(-1))预报结果的订正效果最明显。  相似文献