Early Cretaceous exhumation of the Qiangtang Terrane during collision with the Lhasa Terrane,Central Tibet   总被引：1，自引：0，他引：1       下载免费PDF全文

Zhongbao Zhao  Paul D. Bons  Konstanze Stübner  Gen‐Hou Wang  Todd A. Ehlers 《地学学报》2017,29(6):382-391

The timing of the closure of the Bangong Ocean between the Lhasa and South Qiangtang Terranes in central Tibet and the resulting crustal thickening are still under debate. We integrate published apatite fission track and (U–Th)/He thermochronometer data with new zircon (U–Th)/He ages from eight samples and with structural profiles to document that the South Qiangtang Terrane experienced slow exhumation between 200 and 150 Ma, associated with the opening of the Bangong Ocean. Accelerated exhumation (around 0.2–0.3 mm/a) of the South Qiangtang Terrane was initiated at around 150 Ma. This exhumation event is interpreted to reflect collision between the Lhasa and South Qiangtang Terranes after closure of the Bangong Ocean, associated with crustal thickening via thick‐skinned folding and thrusting within the South Qiangtang Terrane. The amalgamation of the Lhasa and South Qiangtang Terranes recorded here may represent the first stage of crustal thickening in the central Tibetan Plateau.  相似文献   

Research Progress of Quality Control for AIRS Data     

Wang Gen  Zhang Hua  Yang Yin 《地球科学进展》2017,32(2):139-150

Satellite data assimilation can provide accurate initial field for Numerical Weather Prediction (NWP) models. So far, data variational assimilation is based on the theory where error obeys Gaussian distribution, so as to apply the least square method. During classical variational assimilation, if the data contain outliers, the results of optimal parameter estimation is meaningless. Therefore, quality control is quite necessary for Atmospheric Infrared Sounder (AIRS) data before data assimilation. This paper made a comment of the advances in the quality control using AIRS data, which analyzed and discussed the research status from five aspects: channel selection, outliers elimination, bias correction, cloud detection and data sparseness. Three methods for channel selection were summarized, which are stepwise iterative method based on information entropy, the cumulative effect coefficient of principal component and principal components—Stepwise regression, respectively. Comparatively, stepwise iterative method based on information entropy is more widely used, but the selected channels are weak related; Channel combination with large amount of information can be obtained through the method of principal components—stepwise regression, but the implementation process is time-consuming due to the algorithm. Both the lane of law and the double weight method were used in outliers elimination, and the result shows that the latter one is better. Two kinds of bias correction method including off-line and on-line, were introduced, which contain static, adaptive, regression method, variational, method based on the radiative transfer model, bias correction with Kalman filter and dynamic update of bias correction technique. It is found that the timeliness of static method is better; while variational method could solve the problems of data drift and so on. The result is better when using bias correction based on the model and Kalman methods, but it is more time-consuming and not suitable for business application. Generally, the effect and timeliness of dynamic update one is the best among them. In this paper four kinds of cloud detection method are discussed here, including the sky field-of-view, sky channel, cloud radiation correction and different instrument cloud products matching. The first two methods are more feasible from the perspective of timeliness for numerical prediction, but the data quantity using could detection method of sky field-of-view is less than sky channel, leading to discarding of lots of channel data in climate sensitive area such as upper channel, and thus affecting the quality of analysis field. Further on, the methods of hops jumper, box and principal component applied to AIRS data sparseness were analyzed. From assimilation timeliness and operability, box method is feasible; although there is high complexity with algorithm of principal component analysis, which has a certain application prospect. After reviewing the quality control section, some further research directions in these fields were given respectively.  相似文献   

近50a来黑河流域水文及生态环境的变化   总被引：82，自引：17，他引：65  

王根绪  程国栋 《中国沙漠》1998,18(3):233-238

利用详实资料,对比分析了40年代以来不同时期黑河流域水文及生态环境的变化特征,并对不同时期流域水土资源开发利用规模及出山径流的变化进行对比分析,结果说明:本世纪40年代以来,流域中游地区地表水利用量增加了19倍,灌溉绿洲扩大了89.5%,使流域33条支流相继断流,干流下游水量减少了51%,终端湖泊干涸,水质恶化,土地盐碱化和沙漠化在全流域发展,沙漠化土地面积自1949年以来增加了4%~11%。人类对流域水土资源的大规模开发利用是产生这些变化的主要因素。  相似文献   

Research on the Seismic Wave Characteristics of Low Frequency Signals before the Alxa Left Banner MS5.8 Earthquake in Inner Mongolia, China     

Liang Shash  Gao Lixin  Dai Yong  Ge Gen  Wang Lei 《中国地震研究》2018,32(3):367-376

In order to search for the seismic wave characteristics of low frequency signals in the Alxa Left Banner region,Inner Mongolia,the low frequency signals of seismic wave data are extracted from the earthquakes of MS5. 8 in 2015 and MS5. 0 in 2016 in this area. The results show that:① Before the MS5. 8 earthquake,the seismic stations located near the epicenter in Wuhai,Dongshengmiao,and Shizuishan recorded seismic waves that showed the phenomenon of spectrum shift from high to low frequency.② The low frequency signals recorded by different stations have obvious difference.③ According to the data recorded by the station closest to the epicenter,low-frequency signals were recorded about120 hours before the earthquake and had obvious anomalies. This may reflect slow slip before the earthquake.  相似文献   

海滩养护修复过程中拦沙堤的应用     

朱君  蔡锋  刘建辉  刘根  戚洪帅  雷刚  郑吉祥  曹慧美 《海洋工程》2021,39(6):152-165

拦沙堤作为海滩养护最常用的辅助工程之一,在全球范围内得到广泛应用。在总结我国海滩养护过程中拦沙堤应用现状的基础上,将拦沙堤的功能分为3类（防泥沙扩散、防沿岸输沙、防浪+防输沙）,并详细分析这3类拦沙堤在我国海滩养护的应用现状和发展规律。基于国内外工程实践,进一步探讨海滩养护中拦沙堤的多项应用创新：组合式拦沙堤设计、拦沙堤平面形态优化、拦沙堤堤群设计、拦沙堤+潜堤组合优化、拦沙堤+旁通输沙/循环养护。最后,展望未来海滩养护中拦沙堤的发展应用趋势（拦沙量的精准调控、丰富多样的形态设计、基于“自然工法”的生态化建设）,并给出了相关建议。  相似文献   

Different Configurations of Interannual Variability of the Western North Pacific Subtropical High and East Asian Westerly Jet in Summer     

Xinyu LI  Riyu LU  Gen LI 《大气科学进展》2021,38(6):931-942

This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH) and the East Asian westerly jet(EAJ) in summer on interannual timescales. The in-phase configuration of the WNPSH and EAJ is characterized by the westward(eastward) extension of the WNPSH and the southward(northward) shift of the EAJ, which is consistent with the general correspondence between their variations. The out-of-phase configuration includes the residual cases. We find that the in-phase configuration manifests itself as a typical meridional teleconnection. For instance, there is an anticyclonic(cyclonic) anomaly over the tropical western North Pacific and a cyclonic(anticyclonic) anomaly over the mid-latitudes of East Asia in the lower troposphere. These circulation anomalies are more conducive to rainfall anomalies over the Yangtze River basin and south Japan than are the individual WNPSH or EAJ. By contrast, for the out-of-phase configuration, the mid-latitude cyclonic(anticyclonic) anomaly is absent, and the lower-tropospheric circulation anomalies feature an anticyclonic(cyclonic)anomaly with a large meridional extension. Correspondingly, significant rainfall anomalies move northward to North China and the northern Korean Peninsula. Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO, with strong and significant sea surface temperature(SST) anomalies in the tropical central and eastern Pacific which occur simultaneously during summer and persist into the following winter. This is sharply different from the in-phase configuration, for which the tropical SSTs are not a necessity.  相似文献   

Surface Temperature Changes Projected by FGOALS Models under Low Warming Scenarios in CMIP5 and CMIP6     

Shang-Min LONG  Kai-Ming HU  Gen LI  Gang HUANG  Xia QU 《大气科学进展》2021,38(2):203-220

To meet the low warming targets proposed in the 2015 Paris Agreement,substantial reduction in carbon emissions is needed in the future.It is important to know how surface climates respond under low warming targets.The present study investigates the surface temperature changes under the low-forcing scenario of Representative Concentration Pathways(RCP2.6)and its updated version(Shared Socioeconomic Pathways,SSP1-2.6)by the Flexible Global Ocean-Atmosphere-Land System(FGOALS)models participating in phases 5 and 6 of the Coupled Model Intercomparison Project(CMIP5 and CMIP6,respectively).In both scenarios,radiative forcing(RF)first increases to a peak of 3 W m^?2 around 2045 and then decreases to 2.6 W m^?2 by 2100.Global mean surface air temperature rises in all FGOALS models when RF increases(RF increasing stage)and declines or holds nearly constant when RF decreases(RF decreasing stage).The surface temperature change is distinct in its sign and magnitude between the RF increasing and decreasing stages over the land,Arctic,North Atlantic subpolar region,and Southern Ocean.Besides,the regional surface temperature change pattern displays pronounced model-to-model spread during both the RF increasing and decreasing stages,mainly due to large intermodel differences in climatological surface temperature,ice-albedo feedback,natural variability,and Atlantic Meridional Overturning Circulation change.The pattern of tropical precipitation change is generally anchored by the spatial variations of relative surface temperature change(deviations from the tropical mean value)in the FGOALS models.Moreover,the projected changes in the updated FGOALS models are closer to the multi-model ensemble mean results than their predecessors,suggesting that there are noticeable improvements in the future projections of FGOALS models from CMIP5 to CMIP6.  相似文献   

A four‐node plane parametric element based on quadrilateral area coordinate and its application to coupled solid‐deformation/fluid‐flow simulation for porous geomaterials          下载免费PDF全文

Gen Li 《国际地质力学数值与分析法杂志》2015,39(3):251-276

A four‐node plane parametric element AQGβ6‐I is constructed on the basis of the quadrilateral area coordinate, the generalized conforming principle and the projection technique with a penalty factor β within an interval of 0–1. When β = 0, the element has excellent bending performance. When β = 1, the element can pass patch test strictly; its performance is as good as many famous elements. When β value is between 0 and 1, such as β = 0.5, the element can arrive at a compromise between (relatively) low sensitivity to mesh distortion and perfect convergence. The work provides an illuminating method to alleviate a difficult problem in finite element modelling using the four‐node quadrilateral element, which can pass the strict patch test, but has poor performance in bending dominated problem; on the contrary, it has excellent performance in bending dominated problem but cannot pass the strong patch test. The AQGβ6‐I with the convergence formulation (β = 1) is then applied to coupled solid‐deformation/fluid‐flow simulation for porous geomaterials. The computational examples are carried out to demonstrate that the AQGβ6‐I (β = 1) element is not only stable, reliable and efficient but also of high accuracy. The present study provides a good applicable element for finite element simulations of solid‐deformation/fluid‐flow for porous geomaterials. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Evidence from the Rb‐Sr system for 4.4 Ga alteration of chondrules in the Allende (CV3) parent body     

Gen SHIMODA  Noboru NAKAMURA  Makoto KIMURA  Tomomi KANI  Susumu NOHDA  Koshi YAMAMOTO 《Meteoritics & planetary science》2005,40(7):1059-1072

Abstract— The timing and processes of alteration in the CV parent body are investigated by the analysis of Sr isotopes, major and trace elements, and petrographic type and distribution of the secondary minerals (nepheline and sodalite) in 22 chondrules from the Allende (CV3) chondrite. The Sr isotopic compositions of the chondrules are scattered around the 4.0 Ga reference line on the ⁸⁷Sr/⁸⁶Sr evolution diagram, indicating that the chondrules have been affected by late thermal alteration event(s) in the parent body. The degree of alteration, determined for individual chondrules based on the distribution of nepheline and sodalite, is unrelated to the disturbance of the Rb‐Sr system, suggesting that the alteration process that produced nepheline and sodalite is different from the thermal process that disturbed the Rb‐Sr system of the chondrules. Considering the geochemical behavior of Rb and Sr, the main host phase of Sr in chondrules is likely to be mesostasis, which could be most susceptible to late thermal alteration. As there is a poor connection between the alteration degree determined from abundances of nepheline and sodalite and the disturbance of Rb‐Sr isotopic system, we consider the mesostasis to provide a constraint on the late parent body alteration process. From this point of view, 23 mesostasis‐rich chondrules, including those from literature data, were selected. The selected chondrules are closely correlated on the ⁸⁷Sr/⁸⁶Sr evolution diagram, with an inferred age of 4.36 ± 0.08 Ga. This correlation would represent an age of the final major Sr isotopic redistribution of the chondrules in the parent body.  相似文献   

新疆库马苏-小土尔根一带化探异常特征及找矿前景     

王晓刚  陈根  严云峰  范小军 《四川地质学报》2011,(3):353-358

诺尔特地区下石炭统红山嘴组火山岩为Pb、Zn、Ag、Au矿源层,燕山期岩浆活动对矿源层中的成矿元素进一步富集,并在构造有利部位成矿。该区1∶20万、1∶5万水系沉积物测量和l∶2.5万土壤化探测量资料显示,区内下石炭统中-酸性火山岩出露区以P b、Zn、Ag、Au元素组合为特色的化探综合异常带具有规模大,强度高,浓集中心明显的特点,在异常周边已先后发现了多个铅锌、金、多金属矿床、矿点和矿化点,显示了库马苏-小土尔根地区具有非常好的找矿前景。  相似文献