粒度统计分析方法在青藏高原隆升研究中的运用及效果--以昌马洪积扇为例   总被引：2，自引：0，他引：2  

李增  王云斌  梁明宏  徐景明  刘土改  王启航 《西北地质》2005,38(3):16-20

通过运用粒度统计方法对昌马洪积扇沉积物进行研究，结果显现自早更新世晚期以来存在7次沉积物粒度变粗事件，说明青藏高原东北缘自早更新世晚期以来发生了7次隆升，其间为稳定期.该结论与通过青藏高原东北缘盆地沉积分析、活动断裂及河流阶地活动时代对比而厘定的青藏高原东北缘构造活动时段基本一致，同时与整个青藏高原自早更新世晚期以来的隆升具有很好的耦合.由此为山前洪积扇研究提供了新的方法和线索。  相似文献   

Joint inversion of travel times and waveforms by means of annealing algorithms. Application to a seismic refraction experiment     

X. Lana  M. D. Martinez 《Pure and Applied Geophysics》1990,134(1):117-133

An algorithm of annealing is applied to a joint inversion of travel times and waveforms belonging to a synthetically generated seismic refraction experiment. The medium (crust and upper mantle) is modelled by a set of plane stratified layers and a halfspace. The obtained structure (elastic parameters and depth of layers) shows that, in spite of contaminating seismic noise and poor knowledge of the seismic source, annealing methods are a good tool in these kinds of inversion problems. We think that many characteristics of the annealing process described here could be used with real data and more sophisticated media for the crust and upper mantle of the earth than the present example.  相似文献   

Interpretation of porphyroblast inclusion trails: limitations imposed by growth kinetics and strain rates   总被引：3，自引：0，他引：3  

A. J. BARKER 《Journal of Metamorphic Geology》1994,12(5):681-694

Porphyroblast inclusion trails provide important information about the tectonometamorphic evolution of a metamorphic rock. However, there remains considerable controversy over whether porphyroblasts rotate during bulk non-coaxial deformation.
With reference to an area of the Scandinavian Caledonides and utilizing existing data from theoretical and experimental modelling, this study demonstrates that both 'straight' and 'S-shaped' inclusion trails are consistent with an interpretation in terms of syndeformational porphyroblast growth in a regime approximating to Newtonian simple shear. At crustal strain rates of 10^-14 s^-1 and porphyroblast growth times of 0.1–1.0 Ma, it is shown that a maximum of 5-9 angular rotation would occur during growth. At faster strain rates of 10^-12 s^-1 (e.g. those in a shear zone) porphyroblast angular rotations of 90 are shown to occur in 0.1–0.25 Ma (i.e. times comparable with or faster than porphyroblastesis). In view of this, 'S-shaped' inclusion trails are to be expected in porphyroblasts growing in active shear zones or other situations of high shear strain, whereas 'straight' inclusion trails can be interpreted as static overgrowth of an existing fabric or as syndeformational porphyroblastesis at low strain rates.  相似文献   

长江第一弯成因及形成时代探讨   总被引：1，自引：0，他引：1  

明庆忠  史正涛  董铭 《地理科学进展》2007,26(3):119-126

长江第一弯成因及形成时代关系到金沙江—长江水系的形成演化、西南纵向岭谷地理环 境演化、青藏高原隆升对周边环境的影响等重大科学问题, 故近百年来一直为学术界所关注。本 文通过综合考察、地貌和沉积物等的综合分析认为: 长江第一弯是在金沙江水系未曾溯源连通至 三江口段之前的古金沙江与古冲江河、水洛河的汇流口。长江在三江口袭夺了水洛河, 导致水洛 河倒流, 古金沙江与三江口下的长江贯通, 才形成真正的金沙江—长江水系。根据玉龙山强烈隆 起时间、周边层状地貌发育年代、中国水系大局形成等进行推断, 长江第一弯形成时代为中更新 世以来, 说明昆黄运动为本区构造地貌—水系发育的重大转型事件。  相似文献   

西藏冈底斯带石炭纪陆缘裂陷作用：火山岩和地层学证据   总被引：12，自引：1，他引：12       下载免费PDF全文

耿全如王立全  潘桂棠金振民朱弟成  廖忠礼李光明 李奋其 《地质学报》2007,81(9):1259-1276

冈底斯作为重要的中、新生代岛弧岩浆岩带,历来是青藏高原最热门的地质研究领域,但是对晚古生代火山岩的性质及其形成的构造背景仍缺乏研究。本文在区域地质调查资料的基础上,对冈底斯带石炭纪火山-沉积岩系进行了系统的地层学和岩石地球化学研究,测量了重点剖面,对火山岩进行了常量、微量元素和Sr、Nd、Pb同位素地球化学测试。研究表明,石炭系与下伏泥盆系或前寒武系之间普遍存在不整合或岩性、沉积相的突变面,代表重要的构造转换面。石炭纪的沉积环境大致有两次滨海-深海或深水斜坡-滨海沉积演化旋回,深海-深水斜坡沉积或冰海相含砾板岩与两次火山活动伴生。石炭纪火山岩主要为安山玄武岩和英安岩、流纹岩类,略具双峰式火山岩特点。安山玄武岩类的成分与典型MORB和岛弧玄武岩相比,具有MgO含量低,TiO2、Al2O3、P2O5含量高等特点,稀土和微量元素为LREE和LILE富集型分配模式,与大陆拉斑玄武岩相似。石炭纪酸性火山岩的稀土和微量元素地球化学特征与陆内流纹岩相似。岩石地球化学示踪和地层学研究表明,冈底斯带石炭纪为伸展背景下的冈瓦纳陆缘裂陷环境。火山岩的源区地幔具有典型的Dupal异常,发生过复杂的混合作用,涉及到原始地幔、富集地幔EMII和地壳成分等,说明发生过冈瓦纳古陆壳俯冲、再循环进入古老地幔等过程。玄武岩类成分的某些特殊性,可能与源区混合作用有关。  相似文献   

利用中国地震台网（CSN）记录到的PKP波研究中太平洋下地幔底部的小尺度P波速度变化   总被引：3，自引：0，他引：3       下载免费PDF全文

郑斯华  孙新蕾  宋晓东 《地球物理学报》2007,50(1):184-192

PKP震相包含了下地幔底部P波速度结构的重要信息.中国地震台网（CSN）台站记录到的南美洲地震的PKP波的射线，对中太平洋下的D″层有很好的采样.本研究采用这些PKP波的AB和DF两个分支的走时差，研究了中太平洋下地幔底部P波速度的小尺度变化.AB DF的走时差减小了上地幔横向不均匀性的影响，而对下地幔底部P波速度的横向变化十分敏感.与此同时，AB DF的走时差也减小了地震定位误差的影响，消除地震发震时间测定误差的影响.本研究的结果表明，在中太平洋的地幔底部存在着大范围的AB DF走时正残差，也即低速异常区，这可能是太平洋下超大地幔热柱的源处.观测到的P波速度异常的空间分布总体上与Grand通过层析成像得到的CMB的S波的速度异常相一致，并在变化的幅度上很好地相关，P波速度的扰动值（在D″层大约为2%）是Grand 速度模型中的S波异常的36%.这一结果有助于太平洋下超大地幔热柱的结构和性质的进一步研究.  相似文献   

某通讯基站对炸药库雷击风险的影响分析   总被引：1，自引：0，他引：1  

葛意活  杨经科 《广西气象》2007,28(2):66-68,87

以移动通讯基站为例，从基站“引雷”作用的角度，通过理论和计算分析，认为基站能使周边环境雷击频率和雷电强度增加，但基站周边建筑物自身受直击雷危害的影响远大于受基站雷击感应的影响，所以基站周边建筑物自身要有完善的防雷装置才能保证其安全。  相似文献   

THE IDENTIFICATION OF REGIONAL BOUNDARIES ON COGNITIVE MAPS*     

Robert Lloyd  Theodore Steinke 《The Professional geographer》1986,38(2):149-159

This study investigates regions on cognitive maps and methods used to identify their boundaries. Subjects either drew regional boundaries on a map or decided in which region sample points were located. These methods produced similar results with differences associated more with regional boundaries than cores. The amount of time needed to make point decisions demonstrated the subjects' cognitive process and corroborated boundaries and cores for the cognitive regions. Differences among subjects' maps were greater when boundaries were drawn.  相似文献   

Transient oceanic and tidal contributions to water exchange and residence times in a coastal upwelling system in the NE Atlantic: the Pontevedra Ria, Galicia     

Dale AW  Prego R  Millward GE  Gómez-Gesteira M 《Marine pollution bulletin》2004,49(3):235-248

An analysis of the intra-annual variability of hydrographic residence times, tau, is presented for the Pontevedra Ria--a large coastal system in NW Spain with a deep, unobstructed connection with the Atlantic Ocean. Ria-offshore water exchange and tau were quantified with an iterative approach to the fraction of freshwater method using 23 quasi-steady state water-salt budgets. Excluding prolonged flushing due to downwelling events at the end of the upwelling season, mean was 6 +/- 2 day in the central ria and 2 +/- 1 day in the internal ria. The tidal contribution, equal to 10-25% of total water renewal, was quantified for the first time for a Galician ria with the hydrodynamic model estuarine contaminant simulator (ECoS). The relationship between tau and residual freshwater input, Qz, was atypical, since Qz played a minor role in water exchange in comparison to periodic upwelling of East North Atlantic Central Water (ENACW) from the continental shelf mainly during spring and summer. During positive upwelling stress, the intrusion of ENACW into the ria produced enhanced flushing and tau < 4 day in the central ria and < 2 days in the internal ria. Under downwelling favourable conditions, water was retained and tau prolonged to >8 and >5 days, respectively. A quantitative parameterisation of tau with upwelling and Qz was weakly significant, due to the short-term variability in ria salinity. This paper elucidates problems associated with the use of water budgets to transient coastal systems such as the Pontevedra Ria.  相似文献   

基于DEM和SCS模型的重庆岩溶槽谷区塘堰复蓄次数的计算   总被引：1，自引：1，他引：0  

左烽林  魏朝富 《中国岩溶》2016,35(1):87-97

文章以重庆市九龙坡区中梁村和云峰村两个典型岩溶槽谷区为研究区,通过利用数字高程模型(DEM)划分集水区,依据径流曲线数模型(SCS)模拟降雨径流,CROPWAT8.0计算作物需水量,对该区塘堰灌溉系统进行水量平衡分析,计算得到了塘堰复蓄次数。结果表明:(1)SCS模型推算出研究区的径流系数范围为0.16~0.27,该模型模拟产流合理可靠;(2)在岩溶槽谷区以集水区为单位进行塘堰工程来水计算较以行政区划为单位更为准确;(3)岩溶槽谷地区在枯水年时塘堰对雨水利用效率最高,弃水率最小为50.98%;(4)当降雨频率分别为P=50%、75%和95%时,重庆岩溶槽谷地区相应的塘堰复蓄次数为2.51、2.60和2.12。  相似文献