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81.
华北板块北缘活动带元古宙构造岩片 总被引:15,自引:3,他引:15
新的研究证实 ,华北板块北缘残存一条元古宙构造岩片堆集带 ,包括古元古代、中元古代、新元古代等多期构造岩片。并相伴有 180 0Ma±、140 0Ma±、10 0 0Ma±、6 5 0Ma±的花岗岩类的侵入活动和构造变质成矿等热事件的年代记录 ,并在华北板块北部金镶边带中保存了相一致的信息 ,揭示了它们是陆缘多期拼贴造山的产物。这为超大陆旋回 ,特别是元古宙两次超大陆的聚合与裂解及其构造演化过程的研究提供了良好的野外实验园地 ,并为元古宙、特别是古元古代大陆的增生及Rodinia超大陆在北半球的存在或构造响应提出新的课题。 相似文献
82.
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84.
地壳由半无限大的基岩上一层厚度为H^-的表土层组成,入射地震波为垂直的SH波,产生水平地面运动。当浅源大地震发生时,在极震区以外行波传播产生地面运动将使地壳介质有非线性的有限弹性变形。用小参数摄动法使非线性控制方程为线性化的小参数各阶控制方程,得出头两阶线性控制方程的解析解。 相似文献
85.
86.
Based on remote sensing information sources including B/W aerial photos of 1983, pseudo-color aerial photos of 1992 and JERS-1/OPS VNIR image of 1996, vegetation types of Yingbazha, in the middle reaches of the Tarim River Basin in Xinjiang, China are mapped using ARC/INFO and related software. The changes in vegetation areas and distribution conditions are analyzed. As a result of natural and human influences, vegetation changes have temporal and spatial characteristics. According to the principles of landscape ecology and geographical information science, the landscape changes are indicated. Moreover, the remote sensing and GIS techniques are integrated to study vegetation and its landscape. 相似文献
87.
Zili Fan Xuncheng Xia Yuling Shen Kurban Alishir Ranghui Wang Shengyu Li Yingjun Ma 《中国科学D辑(英文版)》2002,45(1):102-108
Because of the human exploitation and utilization of water resources in the Tarim Basin, the water resources consumption has changed from mainly natural ecosystem to artificial oasis ecosystem, and the environment has changed correspondingly. The basic changes are: desertification and oasis development coexist, both “the human being advance and the desert retreat” and “the desert advance and the human being retreat” coexist, but the latter is dominant. In the upper reaches, water volume drawing to irrigated agricultural areas has increased, artificial oases have been enlarging and moving from the deltas in the lower reaches of many rivers to the piedmont plains. In the middle and lower reaches of the Tarim River, the stream flow has decreased, old oases have declined, natural vegetations have been degenerating, desertification has been enlarging, and the environment has deteriorated. The transition regions, which consist of forestlands, grasslands and waters between the desert and the oases, have been decreasing continuously, their shelter function to the oases has been weakened, and the desert is threatening the oases seriously. 相似文献
88.
Che Yong-tai Yu Jin-zi Zhang Shu-liang Fan Xue-fang Guo Jun-jie Zhang Tian-yuan Yang Jin-lan 《地震学报(英文版)》2002,15(2):226-233
A lot of slow fluctuations of water level have been observed in the original recording maps of subsurface fluid in Well Shuozhou,
Shanxi Province. Some typical recording maps of the “precursors” are introduced in the paper and the features of the “precursors”
recorded by the well are analyzed. The results show that 38% strong earthquakes possess this kind of record, which has a fluctuation
period arranging from several to tens of minutes and appear mostly two days before the earthquakes. Moreover, the mechanism,
transmission and responding conditions of well water level are discussed, as well as the scientific meaning and practical
value of the “precursor” of the well water level in earthquake predictions.
Foundation item: State Natural Science Foundation of China (19973011). 相似文献
89.
Early Yanshanian post-orogenic granitoids in the Nanling region
Petrological constraints and geodynamic settings 总被引:1,自引:0,他引:1
Petrological constraints and geodynamic settings 总被引:1,自引:0,他引:1
Early Yanshanian magmatic suites predominate absolutely in the Nanling granite belt. They consist mainly of monzogranite and K-feldspar granite. There occur associations of early Yanshanian A-type granitoids (176 Ma-178 Ma) and bimodal volcanic rocks (158 Ma-179 Ma) in southern Jiangxi and southwestern Fujian in the eastern sector of the granite belt and early Yanshanian basalts (177 Ma-178 Ma) in southern Hunan in the central sector of the belt. Both the acid end-member rhyolite in the bimodal volcanic rock association and A-type granitoids in southern Jiangxi have the geochemical characteristics of intraplate granitic rocks and the basic end-member basalt of the association is intraplate tholeiite, while the basaltic rocks in southern Hunan include not only intraplate tholeiite but also intraplate alkali basalt. Therefore the early Yanshanian magmatic suites in the Nanling region are undoubtedly typical post-orogenic rock associations. Post-orogenic suites mark the end of a post-collision or late orogenic event and the initiation of Pangaea break-up, indicating that a new orogenic Wilson cycle is about to start. Therefore it may be considered that the early Yanshanian geodynamic settings in the Nanling region should be related to post-orogenic continental break-up after the Indosinian orogeny and the break-up did not begin in the Cretaceous. 相似文献
90.
The null distribution of the lag-k sample serial correlation coefficient (r
k
, k=1,2,3) was investigated by Monte Carlo simulation. For a time series with normal, exponential, Pearson 3, EV1 (Gumbel), or
generalized Pareto (GP) distribution type, the null distribution of its r
k
can be approximated by the normal distribution with mean −1/(n−k) and variance 1/(n−1). But for a time series with the lognormal, EV2 or EV3 (Weibull) distribution type, the null distribution of r
k
is skewed distributed. In such cases, a simulation technique is suggested to construct percentile confidence intervals at
a given significance level. 相似文献