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11.
长江口海域新生代地层与断裂活动性初探   总被引:7,自引:1,他引:7  
长江口海域通过浅层人工地震勘察查明,新生代地层可分为5个地震层。分别为第四系、上新统、中新统上段、中新统下段及始新统。第三纪地层自东北向西南依次超覆、减薄尖灭,上部被第四纪地层不整合覆盖。沉积基底主要由晚侏罗世火山岩系及燕山晚期酸性小岩体构成,未发现早第三纪及晚白垩世断陷盆地。断裂构造很发育,按展布方向大体可归为北东、北西及近东西向3组,皆为正断层。前两者数量多、延伸长、断距大,与同区的航磁异常构架吻合。北东向断裂分段明显,西南段为第四纪断裂,中段为晚第三纪断裂,东北段为早第三纪断裂;而北西向断裂分段不很清晰。两者的垂直位移速率平均在0.015mm/a。本文对该海域有关的几个地质问题进行了讨论。  相似文献   
12.
房毅卓 《盐湖研究》1997,5(1):55-58
采用调速稳速集成电路通过电位调节买现自反馈电子稳速,克服了实验过程中溶液阻尼变化对电机转速的影响,并利用高精度时钟信号与十进制记数器完成光电测速过程。  相似文献   
13.
This paper presents the attenuation relations of peak ground acceleration and spectral accelerations for rock and soil sites in the central and eastern United States (CEUS). For the bedrock site condition, 56 pairs of moment magnitude M and epicentral distance R are used to simulate ground motion, and for each pair of M and R, 550 samples of ground motion parameters are generated using a seismological model together with random vibration theory and distribution of extreme values. From the regression analyses of these data, the attenuation relations of ground motion parameters for the bedrock site are established. With the aid of appropriate site coefficients, these attenuation relations are modified for the site categories specified in the 1994 NEHRP Provisions. These attenuation relations are appropriate for the assessment of seismic hazards at far-field rock and soil sites in the CEUS.  相似文献   
14.
Introduction As far as the frequency and magnitude are concerned, the earthquakes in the sea area to the east of Shanghai are far more strong than in land area with the largest one in the sea area near the Yangtze River mouth being MS=436, while in land, only MS=434 occurred on Sept. 1, 1624. As a moderately strong earthquake active area, the sea area near the Yangtze River mouth, may cause a potential risk to Shanghai. In 1971 and 1996, earthquakes with MS=5~6 occurred in this area. Geo…  相似文献   
15.
By shallow seismic prospecting, the Cenozoic Group in the sea area near the Yangtze Rver Mouth can be divided into five seismic sequences. They correspond to the Quaternary,Pliocene, Upper Miocene, Lower Miocene and Eocene respectively. The Quaternary System covers all the detecting area. The Tertiary System overlaps and thins out from NE to SW. The sedimentary basement mainly consists of volcanic rock (J3) and acidic rock (r35). Paleogene or Late Cretaceous basins are not found there. The faults that have been detected are all normal faults. They can be divided into three groups (NE, NW, near EW) by their trend. The NE and NW-trending faults are predominant, and agree with aeromagnetic anomaly. Their length and displacement are larger than that of the EW-trending faults. The activity of the NEtrending faults is different in different segments. The SW segment is a Quaternary fault, the middle segment is a Neogene fault, The NE is Paleogene. But the segment of the NW-trending fault is not obvious. The average vertical displacement rate is about 0.015mm/a.  相似文献   
16.
重点介绍大顶金矿区的地质特征及区内主要矿脉体(36号矿脉群)特征,同时,对控矿因素作了一定的分析,初步总结了36号矿脉群在双顶矿段北东缘的成矿规律,指明了本矿区的找矿标志及下一步的找矿方向。  相似文献   
17.
The effects of climate change and population growth in recent decades are leading us to consider their combined and potentially extreme consequences, particularly regarding hydrological processes, which can be modeled using a generalized extreme value (GEV) distribution. Most of the GEV models were based on a stationary assumption for hydrological processes, in contrast to the nonstationary reality due to climate change and human activities. In this paper, we present the nonstationary generalized extreme value (NSGEV) distribution and use it to investigate the risk of Niangziguan Springs discharge decreasing to zero. Rather than assuming the location, scale, and shape parameters to be constant as one might do for a stationary GEV distribution analysis, the NSGEV approach can reflect the dynamic processes by defining the GEV parameters as functions of time. Because most of the GEV model is designed to evaluate maxima (e.g. flooding, represented by positive numbers), and spring discharge cessation is a ?minima’, we deduced an NSGEV model for minima by applying opposite numbers, i.e. negative instead of positive numbers. The results of the model application to Niangziguan Springs showed that the probability of zero discharge at Niangziguan Springs will be 1/80 in 2025, and 1/10 in 2030. After 2025, the rate of decrease in spring discharge will accelerate, and the probability that Niangziguan Springs will cease flowing will dramatically increase. The NSGEV model is a robust method for analysing karst spring discharge. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
18.
为研究松辽盆地西缘大兴安岭早白垩世火山岩的构造属性,对研究区内流纹岩开展锆石U-Pb测年和地球化学测定。锆石U-Pb定年结果显示,流纹岩形成于131.6±0.6~123.9±1.7Ma,属早白垩世。主量元素分析表明,流纹岩具高硅(SiO_2=69.08%~79.58%)、富碱(K_2O+Na_2O=5.93%~9.76%,平均为8.14),富钾(K_2O/Na_2O大于1.0,平均为2.14)、贫钙镁(平均CaO为0.60、MgO为0.27)和高FeOT/MgO(平均为6.77)比值的特征,属过铝质(A/CNK=1.35~1.78)高钾钙碱性—钾玄武岩系列岩石。据微量元素地球化学特征将其划分为两组:Ⅰ组流纹岩稀土元素总量较高(∑REE介于149.04×10~(-6)~213.18×10~(-6)之间,平均为172.35×10~(-6)),轻稀土元素(LREE)富集、轻重稀土元素分馏较强[(La/Yb)_N=4.89~11.87,平均为7.75)],中等—弱负铕异常(δEu=0.54~0.88,平均为0.70),配分曲线右倾模式,强烈富集大离子亲石元素(LILE)Rb,Ba,Th,K和亏损高场强元素(HFSE)_Nb,Ta,P和Ti;Ⅱ组流纹岩以稀土总量(∑REE平均为142.60×10~(-6))相对较低,具相对较强的负铕异常(δEu=0.05~0.46,平均为0.27),配分曲线相对较平缓以及Ba,Sr,P,Ti元素的强烈亏损与Ⅰ组流纹岩相区别,两组流纹岩地球化学成分相关性较好,二者均有低的Sr(206×10~(-6))和高Yb(大于2)含量,具壳源和造山后花岗岩的特征。结合最新资料及本文研究成果,初步认为研究区流纹岩为地壳部分熔融的产物,之后经历强烈的矿物分离结晶作用,与蒙古—鄂霍次克造山后伸展作用有关。  相似文献   
19.
内蒙古东乌旗早二叠世超镁铁岩的发现及其构造意义   总被引:1,自引:0,他引:1  
为研究东乌旗晚古生代地幔性质和造山演化特征,对在东乌旗西部首次发现的超镁铁岩—辉闪橄榄岩进行系统的岩相学和元素地球化学研究。东乌旗辉闪橄榄岩主要由橄榄石、角闪石、斜方辉石及少量斜长石、单斜辉石组成,SiO_2含量介于42.84%~43.96%、MgO(24.10%~26.10%)、Na_2O+K_2O(1.52%~2.32%,小于3.5%),低m/f(3.03~3.54)比值和高FeO~T(12.67%~14.33%)的含量、高Mg~#(76.42~79.20),属铁质超镁铁岩和拉斑玄武岩系列。岩石稀土总量较高(∑REE=39.57×10~(-6)~83.32×10~(-6)),轻稀土(LREE)相对于重稀土(HREE)明显富集[(La/Yb)_N=4.04~7.66],Eu异常不明显(δEu=0.90~0.95),稀土元素球粒陨石标准化配分模式表现为轻稀土相对富集的右倾型。岩石富集大离子亲石元素(LILE)Cs、Rb、Ba、Sr、K等,相对亏损高场强元素(HFSE)Nb、Ta,具明显的Nb、Ta、Ti负异常,而又有别于强烈Nb、Ta亏损的岛弧岩浆岩;相容元素Cr(769×10~(-6)~2480×10~(-6))、Ni(454×10~(-6)~901×10~(-6))含量较高;低Th/U(2.54~3.03)、Nb/U(3.40~12.85)比值和高La/Nb(2.60~3.63)、Ba/Nb(43.11~72.52)、Zr/Y(5.45~7.83)比值。综上,结合区域最新研究成果,我们认为辉闪橄榄岩来源于受俯冲流体交代的尖晶石相地幔橄榄岩部分熔融,上升过程中受地壳物质不同程度的混染,形成于早二叠世板内伸展构造体制,与古亚洲洋闭合之后板内非造山作用有关。这一认识填补了早二叠世幔源岩浆事件和非造山阶段超镁铁质岩石记录的空白。  相似文献   
20.
In this study, the method of divergent selection was employed to test the larval and juvenile growth performance within a full-sib family of Manila clam Ruditapes philippinarum. The 10% largest and 10% smallest clam individuals (on the basis of shell length) of a full-sib family were selected as parents for the fast and slow growing lines, respectively. The difference in shell length was significant among the three lines (fast, control, and slow) tested. The sequence of shell length were fast line > control line > slow line. The responses to selection, realized heritability, and genetic gain were 0.06%–0.81%, 0.04%–0.47% and 0.58%–18.89% in the fast direction, respectively; and were 0.14%–1.27%, 0.08%–0.73%, and 0.31%–49.03% in the slow direction, respectively. The results suggested that there was a large portion of additive genetic variance affecting the growth in the full-sib family. Selection in the fast direction within the full-sib family would greatly improve the growth of R. philippinarum.  相似文献   
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