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911.
天山造山带自新元古代以来,经历了漫长而复杂的俯冲增生造山作用和陆内构造活化过程,属于典型的复合型造山带。基于近年研究进展,本文对伊犁、境内外中天山和南天山构造带前寒武纪基底、古生代沉积序列、多期陆缘弧岩浆岩和构造缝合带的变形变质特征、形成环境和年代学等进行了总结分析,梳理了天山古生代增生造山作用中的三次重要构造转换事件及其地质记录。① 伊犁南北两缘、中天山、南天山和塔里木北缘,均发育中奥陶世—志留纪的大陆弧岩浆作用,伊犁北缘、南天山 塔里木北部早古生代沉积环境发生显著变化,表明天山 塔里木北缘在中—晚奥陶世发生了从被动陆缘向活动陆缘的转换。② 伊犁南、北两缘和中天山的早古生代岩层在晚志留世—早泥盆世普遍发生了强烈的韧性变形和角闪岩相变质作用,其上不整合覆盖有弱变形未变质的晚泥盆世—石炭纪火山 沉积地层;该区域不整合是哈萨克斯坦微大陆拼合事件在研究区的构造响应,也标志着准噶尔洋和南天山洋的俯冲方式在泥盆纪发生了由前进式(东太平洋型)向后撤式(西太平洋型)的构造转换,导致伊犁和中天山在晚泥盆世—石炭纪经历了伸展背景下的大陆弧岩浆作用,在南天山 塔里木北缘则形成了一系列弧后有限洋盆。③ 天山各构造单元及其边界缝合带中普遍发育晚石炭世逆冲推覆构造和二叠纪走滑韧性剪切带、晚石炭世—早二叠世滑塌堆积和二叠纪后造山岩浆岩,指示晚石炭世—早二叠世发生了由汇聚造山向陆内构造的转换。这些构造转换事件是认识古亚洲洋各分支洋盆从初始俯冲、俯冲方式转换到俯冲终结过程的基础,也是探讨增生造山动力学的关键。 相似文献
912.
The changing patterns of cropland conversion to built-up land in China from 1987 to 2010 总被引:2,自引:0,他引:2
Hongrun Ju Xiaoli Zhao Xiao Wang Wenbin Wu Ling Yi Qingke Wen Fang Liu Jinyong Xu Shunguang Hu Lijun Zuo 《地理学报(英文版)》2018,28(11):1595-1610
Over the past few decades, built-up land in China has increasingly expanded with rapid urbanization, industrialization and rural settlements construction. The expansions encroached upon a large amount of cropland, placing great challenges on national food security. Although the impacts of urban expansion on cropland have been intensively illustrated, few attentions have been paid to differentiating the effects of growing urban areas, rural settlements, and industrial/transportation land. To fill this gap and offer comprehensive implications on framing policies for cropland protection, this study investigates and compares the spatio- temporal patterns of cropland conversion to urban areas, rural settlements, and industrial/ transportation land from 1987 to 2010, based on land use maps interpreted from remote sensing imagery. Five indicators were developed to analyze the impacts of built-up land expansion on cropland in China. We find that 42,822 km2 of cropland were converted into built-up land in China, accounting for 43.8% of total cropland loss during 1987–2010. Urban growth showed a greater impact on cropland loss than the expansion of rural settlements and the expansion of industrial/transportation land after 2000. The contribution of rural settlement expansion decreased; however, rural settlement saw the highest percentage of traditional cropland loss which is generally in high quality. The contribution of industrial/transportation land expansion increased dramatically and was mainly distributed in major food production regions. These changes were closely related to the economic restructuring, urban-rural transformation and government policies in China. Future cropland conservation should focus on not only finding a reasonable urbanization mode, but also solving the “hollowing village” problem and balancing the industrial transformations. 相似文献
913.
Theoretical and Applied Climatology - Climate change is widely accepted to be one of the most critical problems faced by the Huang-Huai-Hai Plain (3H Plain), which is a region in which there is an... 相似文献
914.
Wave ray theory is employed to study features of propagation pathways(rays) of vortex Rossby waves in typhoons with asymmetric basic flow, where the tangential asymmetric basic flow is constructed by superimposing the wavenumber-1 perturbation flow on the symmetric basic flow, and the radial basic flow is derived from the non-divergence equation. Results show that, in a certain distance, the influences of the asymmetry in the basic flow on group velocities and slopes of rays of vortex Rossby waves are mainly concentrated near the radius of maximum wind(RMW), whereas it decreases outside the RMW. The distributions of radial and tangential group velocities of the vortex Rossby waves in the asymmetric basic flow are closely related to the azimuth location of the maximum speed of the asymmetric basic flow, and the importance of radial and tangential basic flow on the group velocities would change with radius. In addition, the stronger asymmetry in the basic flow always corresponds to faster outward energy propagation of vortex Rossby waves. In short, the group velocities, and thereby the wave energy propagation and vortex Rossby wave ray slope in typhoons, would be changed by the asymmetry of the basic flow. 相似文献
915.
Laboratory Generation of Solitary Waves: An Inversion Technique to Improve Available Methods简 总被引:1,自引:1,他引:0
Solitary waves are often used in laboratory experiments to study tsunamis propagation and interaction with coasts. However, the experimental shape of the waves may differ from the theoretical one. In this paper, a correction technique aiming at minimizing the discrepancies between the two profiles is presented. Laboratory experiments reveal their effectiveness in correcting the experimental shape of solitary waves, mainly for low nonlinearities. 相似文献
916.
利用南极大陆12个累积观测数据超过3年的GNSS跟踪站的监测序列,比较分析了其径向的形变趋势与GIA(Glacial Isostatic Adjustment)模型预测形变,并且与GRACE(Gravity Recovery and Climate Experiment)估计的径向位移结果进行相关性分析。GNSS结果显示跟踪站的径向形变多呈现上升趋势,少量出现下降的跟踪站多分布在东南极沿海区域,下降速度较小。与GRACE计算结果相比,两者的相关系数在0.241—0.663之间,表明两种观测手段得到的结果总体呈现较强的相关性。GNSS形变趋势与最新的GIA模型(W12a)预测形变趋势有一定的偏差,但总体吻合。 相似文献
917.
918.
We observed Mrk 421 in V and R band using the 1.0 m telescope at Weihai Observatory of Shandong University since 2009 April to 2012 May. The available historical data in B and V band were also assembled for constructing light curves. The brightness of Mrk 421 ranges from 11.40 to 16.14 in the B band light curve, and from 11.38 to 14.56 in the V band. Analyses with the Jurkevich method and the structure function method showed a possible period of about 1.36 years for its long periodic variability. This period could be explained by a close binary black hole system (BBHS) model with a primary black hole mass of 1.70×108 M ⊙ and a secondary ~(0.49–2.9)×107 M ⊙. We showed the color variability of Mrk 421, a bluer when brighter behavior during its lower state. Analyses of spectral index variations show that only a host galaxy contribution is not sufficient to explain the spectral index variations in Mrk 421, and some intrinsic mechanism is needed. 相似文献
919.
在阿拉善和华北陆块南缘结合部位的牛首山地区,出露一套连续的中—上泥盆统陆相沉积组合。该套沉积组合的沉积相和沉积物源区的变化特征,可帮助理解阿拉善和华北陆块及相邻地区晚古生代构造演化。根据野外研究结果,该套沉积组合在牛首山南麓石峡沟地区呈现河流相、湖泊相和小型冲积扇相共同发育的沉积面貌,可分为河道、堤岸、河漫平原、滨湖、浅湖、扇根、扇中和扇端共8个沉积亚相。其中,中泥盆统石峡沟组总体呈现由河流沉积向湖泊沉积过渡,而上泥盆统老君山组则呈现下部为扇根、扇中、扇端亚相与河道亚相的粗碎屑沉积,上部由滨湖沉积向浅湖沉积过渡的沉积组合变化特征。牛首山地区老君山组砾岩层数、厚度及砾石砾径分别呈现向南逐渐减少、减薄和减小的特征。古水流分析结果显示,石峡沟组下部碎屑沉积物来自于北东东—东向物源区,上部沉积物主要来自于南东向物源区,而老君山组沉积物主要来自于北东向物源区。结合前人对老君山组古水流的系统测量、石峡沟组和老君山组砂岩碎屑锆石研究结果以及区域地质资料综合分析,认为中—晚泥盆世时期阿拉善地块东南缘总体具有北高南低的古地理格局,且该时期的沉积物为一套具有向南水体逐渐加深的陆相沉积组合,沉积物源区主要位... 相似文献
920.
多源数据是当前信息时代下进行城市研究的重要基础和支撑,也是地理学和城市规划学重点研究方向。城市体检作为城市高质量发展背景下的新命题,多源数据在城市体检中的有机融合与科学应用对城市问题的深入剖析及其影响机制的探究中至关重要。从梳理主观和客观两类数据在现有城市研究中的应用出发,结合了2019年、2020年全国城市体检和2018年、2019年、2020年北京城市体检实践工作,探讨了多源数据在城市体检不同空间尺度、不同时间尺度和不同体检维度的应用,辨析了不同数据间的优劣势,提出了多源数据有机融合的方式,并以“城市停车问题”进行案例分析。以期为城市体检中数据应用方式的改进方向提出建议,为城市体检的研究发展提供思路。 相似文献