Earthquakes and strength in the laminated lower crust —Can they be explained by the “corset model”?     

Rolf Meissner  Hartmut Kern 《Tectonophysics》2008,448(1-4):49-59

We present a model that may explain deep crustal earthquakes observed, in particular, in several areas of highly reflective (laminated) lower continental crust. We combine observations from earthquake seismology, crustal reflection seismics and tectonic-rheological concepts. The study concentrates on parts of the northern Alpine foreland where many earthquakes occur inside the laminated lower crust, which is generally considered to be warm and weak. Thin mafic/ultramafic, sill-like intrusions and invisible dykes are assumed to form a corset-like network with high strength. This model can explain the observed strong and multiple reflections and the occurrence of rupture inside a stable structure within a weak lower crust. Tectonic stress transfer (from the Alpine collision zone or/and the Upper Rhine Graben) and its release may follow classical friction concepts. In addition, the heterogeneity of the laminated lower crust may also favour various viscous instabilities.  相似文献   

大别造山带早白垩世基性岩的同位素特征及下地壳物质对岩浆源区的贡献   总被引：3，自引：2，他引：1  

李全忠  谢智  徐夕生  陈江峰  高天山 《岩石学报》2008,24(8)

大别造山带中生代岩浆岩的物质来源和成因机制,是大陆碰撞造山带研究的热点和前沿问题之一.本文通过对北大别椒子岩和沙村岩体的早白垩世基性岩进行全岩的主量、微量元素特别是Pb-Sr-Nd同位素研究,探讨了北大别基性岩的岩浆源区性质及下地壳的贡献.椒子岩基性岩的(87Sr/86Sr);的范围为0.7072～0.7075,εNd(t)范围为-10.4～11.9;椒子岩和沙村基性岩的(206Pb/204Pb)i为16.464～17.394,(207Pb/204Pb)i为15.349～15.453,(208Pb/204Pb)i为37.338～37.976.这样的同位素组成显示岩浆源区中下地壳物质的贡献显著;尤其Pb同位素特征表明下地壳贡献来自大别造山带自身的下地壳.下地壳物质的参与可能与拆沉有关.  相似文献   

Biological soil crust development and its topsoil properties in the process of dune stabilization, Inner Mongolia, China   总被引：4，自引：0，他引：4  

Yirui Guo  Halin Zhao  Xiaoan Zuo  Sam Drake  Xueyong Zhao 《Environmental Geology》2008,54(3):653-662

This study was undertaken at Horqin Sand Land, Inner Mongolia, Northern China. Field samples of biological soil crusts (BSCs) and underlying topsoil (0–5 cm under BSC) were taken in areas of different dune stabilization stages, and their physicochemical properties were analyzed, including particle size distribution, bulk density, organic matter, nitrogen, phosphorus, electrical conductivity (EC), pH, and CaCO₃ content. The results revealed that semi-mobile dunes, semi-fixed dunes and fixed dunes had developed a physical crust, algae crust and moss crust, respectively. The thickness, hardness, water content, fine fraction and nutrient contents of BSCs were gradually increasing along the dune stabilization gradient. Meanwhile, BSC establishment and development enhanced the bulk density, silt and clay content, and nutrients of the topsoil under it, in an increasing tend from semi-mobile dune to fixed dune. Organic matter concentrations and other nutrients in the 0–5 cm topsoil layer under BSCs were significantly higher compared to unconsolidated soil (control). Moreover, there were strong significant positive correlations between topsoil and BSCs’ organic matter, total nitrogen, available nitrogen, available phosphorus, CaCO₃, and <0.05 mm particle content, suggesting that BSCs have an influence on some of the properties of the underlying topsoil.  相似文献   

Neoproterozoic crustal growth: The solid Earth system during a critical episode of Earth history   总被引：5，自引：3，他引：2  

Robert J. Stern   《Gondwana Research》2008,14(1-2):33

The behavior of the solid Earth system is often overlooked when the causes of major Neoproteozoic (1000–542 Ma) climate and biosphere events are discussed although  20% of the present continental crust formed or was remobilized during this time. Processes responsible for forming and deforming the continental crust during Neoproterozoic time were similar to those of the modern Earth and took place mostly but not entirely at convergent margin settings. Crustal growth and reworking occurred within the context of a supercontinent cycle, from breakup of Rodinia beginning  830 Ma to formation of a new supercontinent Greater Gondwana or Pannotia,  600 Ma. Neoproterozoic crust formation and deformation was heterogeneous in space and time, and was concentrated in Africa, Eurasia, and South America during the last 300 million years of Neoproterozoic time. In contrast, the solid Earth system was relatively quiescent during the Tonian period (1000–850 Ma). The vigor of Cryogenian and Ediacaran tectonic and magmatic processes and the similar timing of these events and development of Neoproterozoic glaciations and metazoa suggest that climate change and perhaps increasing biological complexity was strongly affected by the solid Earth system.  相似文献   

冈瓦纳大陆北缘早期的洋壳信息──来自青藏高原羌塘中部早古生代蛇绿岩的依据   总被引：2，自引：0，他引：2  

李才  翟庆国  董永胜  蒋光武  王明  解超明  吴彦旺 《地质通报》2008,27(10)

普遍认为冈瓦纳大陆北缘裂解发生在泥盆纪,形成了古特提斯洋并持续演化到晚三叠世.最近在羌塘中部的桃形湖一果干加年山-带发现了完整的蛇绿岩组合,蛇绿岩中的堆晶辉长岩具有洋中脊玄武岩的地球化学特征,在堆晶辉长岩中获得467-431Ma的锆石SHRIMP U-pb年龄,这是龙木错-双湖缝合带首次发现早古生代蛇绿岩,应记录了冈瓦纳北缘早期的洋壳演化信息,冈瓦纳大陆北缘的裂解可能发生于早古生代.  相似文献   

Geology of the Hubert Miller seamount,Marie Byrd seamounts province,Amundsen Sea,West Antarctic     

N. A. Kurentsova  G. V. Udintsev  D. E. Teterin  I. A. Roshchina 《Russian Journal of Pacific Geology》2008,2(5):377-384

This work is dedicated to the results of joint Russian-German geodynamic studies carried out in the West Antarctic (areas of the Amundsen Sea, the Southern Ocean, the Marie Byrd seamounts, and the foot of the continental slope of Marie Byrd Land) during cruises 18/5a and 23/4 of the “R/V Polarstern” in 2001 and 2006, respectively. The material collected on the Hubert Miller seamount (Marie Byrd seamount) attests to the relict continental appearance of the rocks. This suggests the heterogeneity of the Amundsen seafloor and its formation through a spatiotemporal combination of the destruction of continental crust, progressive thalassogenesis (oceanization-taphrogenesis), and rifting, as opposed to a spreading origin. The high postconsolidation mobility during the destruction stage led to the areal dismembering and high permeability of the continental crust, as well as tectonomagmatic activation. The main process during the reworking of the continental crust is its magmatic substitution by mantle-derived basic-ultrabasic material with subsequent formation of a secondary oceanic crust and preservation of relics of the continental crust. The endogenic activity of the Earth was driven by transmagmatic fluids, which were supplied from the liquid core and caused transformation of the Earth’s crust and mantle.  相似文献   

赣南花岗岩风化壳型稀土矿床中纳米级稀土矿物的研究   总被引：1，自引：0，他引：1  

刘容  王汝成  陆现彩  李娟 《岩石矿物学杂志》2016,35(4):617-626

为揭示次生风化成因稀土矿物的赋存形态和分布特征,对赣南安远岗下稀土矿区花岗岩风化壳剖面进行了研究。采集风化壳不同层位的样品进行分选、提纯,场发射扫描电镜和透射电镜研究结果表明,与稀土矿物紧密相关的粘土矿物是高岭石和埃洛石等,风化壳中发现的纳米级稀土矿物既有附着于其他矿物表面的微细颗粒,也有呈集合体存在的稀土矿物(可能为方铈石),这一现象有助于进一步认识风化壳稀土矿床的形成过程。  相似文献   

Velocity structure and active fault of Yanyuan-Mabian seismic zone—The result of high-resolution seismic refraction experiment   总被引：3，自引：0，他引：3  

FuYun Wang  YongHong Duan  ZhuoXin Yang  ChengKe Zhang  JinRen Zhao  JianShi Zhang  XianKang Zhang  QiYuan Liu  AiLan Zhu  XiWei Xu  BaoFeng Liu 《中国科学D辑(英文版)》2008,51(9):1284-1296

The authors processed the seismic refraction Pg-wave travel time data with finite difference tomography method and revealed velocity structure of the upper crust on active block boundaries and deep features of the active faults in western Sichuan Province. The following are the results of our investigation. The upper crust of Yanyuan basin and the Houlong Mountains consists of the superficial low-velocity layer and the deep uniform high-velocity layer, and between the two layers, there is a distinct, and gently west-dipping structural plane. Between model coordinates 180–240 km, P-wave velocity distribution features steeply inclined strip-like structure with strongly non-uniform high and low velocities alternately. Xichang Mesozoic basin between 240 and 300 km consists of a thick low-velocity upper layer and a high-velocity lower layer, where lateral and vertical velocity variations are very strong and the interface between the two layers fluctuates a lot. The Daliang Mountains to the east of the 300 km coordinate is a non-uniform high-velocity zone, with a superficial velocity of approximately 5 km/s. From 130 to 150 km and from 280 to 310 km, there are extremely distinct deep anomalous high-velocity bodies, which are supposed to be related with Permian magmatic activity. The Yanyuan nappe structure is composed of the superficial low-velocity nappe, the gently west-dipping detachment surface and the deep high-velocity basement, with Jinhe-Qinghe fault zone as the nappe front. Mopanshan fault is a west-dipping low-velocity zone, which extends to the top surface of the basement. Anninghe fault and Zemuhe fault are east-dipping, tabular-like, and low-velocity zones, which extend deep into the basement. At a great depth, Daliangshan fault separates into two segments, which are represented by drastic variation of velocity structures in a narrow strip: the west segment dips westward and the east segment dips eastward, both stretching into the basement. The east margin fault of Xichang Mesozoic basin features a strong velocity gradient zone, dipping southwestward and stretching to the top surface of the basement. The west-dipping, tabular-like, and low-velocity zone at the easternmost segment of the profile is a branch of Mabian fault, but the reliability of the supposition still needs to be confirmed by further study. Anninghe, Zemuhe and Daliangshan faults are large active faults stretching deep into the basement, which dominate strong seismic activities of the area. Supported by the National Basic Research Program of China (Grant No. 2004CB428400)  相似文献   

钴结壳矿区圈定和资源评价的参数指标   总被引：4，自引：0，他引：4  

张富元  章伟艳  朱克超  胡光道  殷汝广  程永寿 《地球科学》2008,33(2):251-258

大洋海山钴结壳集海洋资源和环境双重信息, 各国对它的调查研究方兴未艾.钴结壳资源勘查的最终目的是圈定钴结壳矿区和开发钴结壳资源.迄今为止, 国内外尚未就钴结壳矿区圈定和资源评价给出具体的参数指标, 基于我国近十年对西太平洋26座海山钴结壳资源调查, 结合太平洋环境资料, 在深入分析钴结壳厚度、丰度、品位、覆盖率、资源量、面积, 海山坡度和水深资料的基础上, 对13座重点海山进行了钴结壳矿区圈定、资源评价和钴结壳分布规律的系统研究, 进而提出圈定钴结壳矿区的八项重要参数指标: 钴结壳矿区的结壳厚度为≥3cm或≥4cm, 取决于海山具体地理位置; 水深为≤2500m或≤3000m;Co含量为≥0.50%或≥0.60%;丰度为≥60kg/m2或≥70kg/m2; 坡度为≤15°; 结壳覆盖率为≥30%;钴结壳矿区的申请面积为17000~20000km2, 矿区最终保留面积为5000~6000km2.钴结壳矿区8项参数指标的提出, 将有力地促进大洋钴结壳矿区圈定、资源量计算和资源评价工作, 为我国积极参与联合国海底管理局制定钴结壳资源开发利用规章制度提供量化参考指标.   相似文献   

沙坡头植被固沙区生物结皮对土壤水文过程的调控作用   总被引：37，自引：18，他引：19  

李守中  肖洪浪  罗芳  宋耀选  刘立超  李守丽 《中国沙漠》2005,25(2):228-233

生物结皮的土壤水文过程一直是学术界比较关注的争议性问题。通过对生物结皮的生态调查和水文物理实验分析、野外人工模拟降雨条件下的土壤水动力学试验、以及天然降雨后土壤水分的动态监测,分析了生物结皮对降雨渗透、土壤水分再分配和土面蒸发等土壤水文过程的调控作用,认为:(1)生物结皮层不仅降低了水分渗透速度和深度,还引起了土壤水分渗透的不稳定性,即指状流的出现;(2)生物结皮的逐年发育使土壤水分的分配格局和分配过程发生了很大变化,土壤水分再分配过程有明显的浅层化趋势,即生物结皮的降雨拦截作用;(3)生物结皮通过降低反射率和提高毛管作用,大大提高了土面蒸发。生物结皮对土壤水文过程的调控作用正在深刻地改变着固沙区的土壤水环境。  相似文献