Mantle Branch Structure in the South-Central Segment of the Da Hinggan Mts.,Inner Mongolia and Its Ore-controlling Role   总被引：1，自引：0，他引：1  

NIU Shuyin  SUN Aiqun  WANG Baode  NIE Fengjun  JIANG Sihong  SHAO Ji’an  GUO Lijun  LIU Jianming 《《地质学报》英文版》2009,83(6):1148-1162

Abstract: Mantle branch structure is the third tectonic unit of multiple evolution of a mantle branch. It is not only the main mechanism of intercontinental orogeny, but also an important ore-forming and ore-control structure. Studies on geotectonic evolution, regional geological characteristics and ore-forming and ore-control structures have shown that since the Mesozoic the Da Hinggan Mts. region has entered a typical intercontinental orogenic stage, and it is closely related to mantle branch activities. The south-central segment of the Da Hinggan Mts. is a typical mantle branch structure and possesses obvious magmatic-metamorphic complexes in the core, detachment slip beds in the periphery and overlapped fault depression basins. Moreover, all of these are the principal factors leading to ore formation and ore control in the region. This paper also further explores the mechanism of mineralization in the south-central segment of the Da Hinggan, summaries the rules of mineralization, puts forward the models of mineralization and points out future ore-exploring orientation.  相似文献   

龙门山前山断裂大地震原地重复发生的地质地貌证据   总被引：9，自引：7，他引：2       下载免费PDF全文

陈立春  冉勇康  陈杰  王虎  史翔  刘进峰  董少鹏 《第四纪研究》2009,29(3):472-483

龙门山前山断裂大地震是原地重复发生的吗？针对这一问题,对前山断裂的同震地表形变带进行了追踪,并选择5.12汶川地震区九龙、白鹿以及汉旺等3个地点开展了古地震探槽研究工作。调查结果是： 前山断裂5.12地震地表形变带基本沿1 ∶200000地质图上先存基岩断裂发育,但仅限于通济－安昌以南段; 白鹿－八角一带同震地表形变带继承先存断层陡坎或断层沟谷发育; 偏离先存断裂而被一些学者视为断裂全新世活动重要证据的永安附近T1阶地上线性陡坎实为废弃河岸; 白鹿、汉旺探槽剖面揭示这两个地点5.12汶川地震之前至少有过一次古地震事件。这些研究结果表明前山断裂大地震是沿晚第四纪活动断裂原地重复发生的,此次地震是沿先存活动断裂又一次发生的大地震事件,为大地震原地复发模型提供了一个新的震例支持。在沿该断裂周边进行规划建设时应当合理避让。  相似文献   

龙门山小鱼洞断裂在汶川地震中的地表破裂及地质意义   总被引：8，自引：5，他引：3       下载免费PDF全文

李勇  黄润秋  A.L.Densmore  周荣军  闫亮  张毅  N.Richardson  董顺利  乔宝成  M.A.Ellis  何玉林  陈浩  马博琳 《第四纪研究》2009,29(3):502-512

在龙门山中段小鱼洞地区映秀－北川断裂和彭县－灌县断裂发生了同震位移,同时在该地区新出现了一条北西向的同震破裂带——小鱼洞断裂的破裂带,并分割了两条近于平行的北东向逆冲－走滑型的主断裂。汶川特大地震发生后重点对小鱼洞断裂的地表破裂开展了详细的野外地质填图,利用全站仪和GPS对地表破裂进行了精确的测量。初步调查的结果表明,小鱼洞断裂位于映秀－北川断裂与彭县－灌县断裂之间,走向近于北西向,延伸约15km,以脆性破裂为特征,穿过小鱼洞大桥,并切割了多种类型的地貌单元,使道路发生拱曲、破坏和桥梁垮塌或移位。单个破裂长度在几米到300m不等,其南西盘为上升盘,北东盘为下降盘,平均垂直位错为1.0m,平均水平位错为2.3m,垂直与水平位错量之比1 ∶1～1 ∶2,显示为逆冲分量小于或等于左旋走滑分量,并以左旋走滑作用为主。同时,研究表明小鱼洞断裂属于映秀－北川断裂与彭县－灌县断裂之间的捩断层,其主要特征包括： 1)是在汶川地震中由于龙门山逆冲体之间的差异逆冲运动过程中而形成的断裂; 2)其走向近于北西向,垂直于龙门山北东向的主干断裂,而平行于逆冲体的逆冲运动方向; 3)具有高角度断面的断层,以左旋走滑作用为主。  相似文献   

地震断层摩擦残余热异常测量方法探讨———以WFSD- 1钻孔温度测量为例     

李振  彭华  马秀敏  姜景捷 《地质力学学报》2011,17(1):15-26

以汶川地震断裂带科学钻探工程WFSD-1钻孔高精度相对温度梯度测量确定汶川地震断层为例,探讨了地震断裂带断层摩擦残余热温度测量方法。利用WFSD-1钻孔相对温度梯度温度测量取得的科学数据进行分析,发现在400~500 m、580~610 m及620~750 m三个测量段内存在温度正异常。结合地质资料综合分析,判定400~500 m、620~750 m段温度异常可能由地层热导率差异引起,并非断层摩擦残余热异常,判定位于不透水断层泥中温度异常深度580~610 m范围为断层主滑移带位置。   相似文献   

Focal Mechanism Solutions of the 2008 Wenchuan earthquake sequence from P-wave polarities and SH/P amplitude ratios: new results and implications     

Yuan Tian  Jieyuan Ning  Chunquan Yu  Chen Cai  Kai Tao 《地震科学（英文版）》2013,26(6):357-372

The 2008 Wenchuan earthquake, a major intraplate earthquake with M _w 7.9, occurred on the slowly deforming Longmenshan fault. To better understand the causes of this devastating earthquake, we need knowledge of the regional stress field and the underlying geodynamic processes. Here, we determine focal mechanism solutions (FMSs) of the 2008 Wenchuan earthquake sequence (WES) using both P-wave first-motion polarity data and SH/P amplitude ratio (AR) data. As P-wave polarities are more reliable information, they are given priority over SH/P AR, the latter of which are used only when the former has loose constraint on the FMSs. We collect data from three categories: (1) permanent stations deployed by the China Earthquake Administration (CEA); (2) the Western Sichuan Passive Seismic Array (WSPSA) deployed by Institute of Geology, CEA; (3) global stations from Incorporated Research Institutions for Seismology. Finally, 129 events with magnitude over M _s 4.0 in the 2008 WES are identified to have well-constrained FMSs. Among them, 83 are well constrained by P-wave polarities only as shown by Cai et al. (Earthq Sci 24(1):115–125, 2011), and the rest of which are newly constrained by incorporating SH/P AR. Based on the spatial distribution and FMSs of the WES, we draw following conclusions: (1) the principle compressional directions of most FMSs of the WES are subhorizontal, generally in agreement with the conclusion given by Cai et al. (2011) but with a few modifications that the compressional directions are WNW–ESE around Wenchuan and ENE–WSW around Qingchuan, respectively. The subhorizontal compressional direction along the Longmenshan fault from SW to NE seems to have a left-lateral rotation, which agrees well with regional stress field inverted by former researchers (e.g., Xu et al., Acta Seismol Sin 30(5), 1987; Acta Geophys Sin 32(6), 1989; Cui et al., Seismol Geol 27(2):234–242, 2005); (2) the FMSs of the events not only reflected the regional stress state of the Longmenshan region, but also were obviously controlled by the faults to some extent, which was pointed out by Cai et al. (2011) and Yi et al. (Chin J Geophys 55(4):1213–1227, 2012); (3) while the 2008 Wenchuan earthquake and some of its strong aftershocks released most of the elastic energy accumulated on the Longmenshan fault, some other aftershocks seem to occur just for releasing the elastic energy promptly created by the 2008 Wenchuan earthquake and some of its strong aftershocks. (4) Our results further suggest that the Longmenshan fault from Wenchuan to Beichuan was nearly fully destroyed by the 2008 Wenchuan earthquake and accordingly propose that there is less probability for great earthquakes in the middle part of the Longmenshan fault in the near future, although there might be a barrier to the southwest of Wenchuan and it is needed to pay some attention on it in the near future.  相似文献   

2008年5月12日汶川M_S8.0地震动力学背景的数值模拟实验          下载免费PDF全文

廖力  张东宁  杨建思 《地球物理学报》2012,55(1):126-136

2008年5月12日汶川M_S8.0地震发生在龙门山断裂带.本文基于龙门山断裂带的地质与地球物理研究结果,以及高精度的地形数据、大地热流测量数据,建立了以龙门山断裂带为主要研究对象的有限元模型;以GPS观测数据、构造应力场和震源破裂过程研究结果为约束,研究了此次强烈地震的动力学背景.模拟实验结果显示:在考虑青藏高原物质向东挤压流动的同时,青藏高原与四川盆地的地形差异和流变强度差异、断层摩擦强度差异和断层产状形式均对地震起始破裂的发生位置和断层错动形式有着重要影响.本文利用地球动力学的有限元软件模拟了汶川地震地表破裂在龙门山断裂带上传播的过程.  相似文献   

青藏高原东缘变形机制的讨论: 来自数值模拟结果的限定   总被引：5，自引：3，他引：2       下载免费PDF全文

姚琪  徐锡伟  邢会林  张微  高翔 《地球物理学报》2012,55(3):863-874

青藏高原东缘的地壳结构是两种主流青藏高原隆升模式争辩的焦点之一.中下地壳流曾经被认为是高原东缘隆升的主要构造驱动力,但是中上地壳之间低阻低速层的发现及其与2008 M_S8.0汶川地震良好的对应关系表明,高原东缘具有向东刚性挤出的可能性.然而大部分关于龙门山断裂的数值模拟仍建立在下地壳流的基础上,仅将低阻低速层作为断裂的延续或是弱化地壳物性参数的软弱层,而非能够控制块体滑动的"解耦层",也没有考虑到刚性块体变形中的断裂相互作用.本文建立了包含相互平行的龙门山断裂与龙日坝断裂的刚性上地壳模型,用极薄的低阻低速层作为块体滑动的解耦带,采用速率相关的非线性摩擦接触有限元方法,基于R最小策略控制时间步长,计算了在仅有侧向挤压力作用下,低阻低速层对青藏高原东缘的刚性块体变形和断裂活动的作用.计算结果显示,低阻低速层控制了刚性块体的垂直变形和水平变形分布特征.在侧向挤压力的持续作用下,在低阻低速层控制下的巴颜喀拉块体能够快速隆升,而缺乏低阻低速层的四川盆地隆升速度和隆升量均极小,隆升差异集中在龙门山断裂附近,使其发生应力积累乃至破裂.龙日坝断裂被两侧的刚性次级块体挟持着一起向南东方向运动,但该断裂的走滑运动分解了绝大部分施加在块体边界上的走滑量,使得相邻的龙门山次级块体的走滑分量遽然减少,也使得龙门山断裂表现出以逆冲为主,兼有少量走滑的运动性质.本文所得的这些计算结果显示了在缺乏中下地壳流,仅在低阻低速层解耦下刚性块体隆升过程及相关断裂活动,提供了青藏高原东缘刚性块体挤出的可行性,为青藏高原东缘隆升机制的研究讨论提供了重要依据.  相似文献   

2008年汶川8．0级地震前川青块体及邻区地震活动性分析     

张永久 《四川地震》2012,(1):17-23

本文简要分析了2008年5月12日汶川8．0级地震前川青块体及邻区的地震活动性特征。结果表明,汶川地震发生的龙门山断裂本身历史地震活动水平不高,其周边的鲜水河断裂、岷江断裂、虎牙断裂等历史上强震多发;汶川8．0级地震前龙门山断裂带3级以上中小地震活动增强或平静异常现象不明显,地震活动参数值均在正常变化区间内;4级以上地震异常平静,形成了地震空区;2007年底到2008年初位于龙门山断裂带及其附近台站的0．1级以上小震月频度增强明显。  相似文献   

气候变暖背景下祁连山区秋季层状云变化特征     

石光普  石圆圆  郭玉珍  陈少勇  林纾  郭俊庭 《地理科学进展》2012,31(5):609-616

利用祁连山区及周边29 个气象观测站近41 年秋季云形状和气温观测资料, 分析了祁连山区秋季层状云出现频率的空间分布与时间变化特征, 探讨了秋季层状云出现频率与气候变暖的关系, 并选用同期NCEP/NCAR全球再分析资料, 对祁连山区秋季层状云的环流特征和水汽输送进行了分析。结果表明:①祁连山区秋季层状云出现频率为8%～26%, 呈西少东多的空间分布。②近41 年来, 祁连山区秋季增温1.2℃, 气温变化的倾向率为0.29℃/10a, 80 年代中期以后发生了增温的突变。③祁连山区秋季层状云的出现频率呈明显的减少趋势, 近41 年来减少约11%, 倾向率为-2.7%/10a, 尤其在20 世纪80 年代中期以后与同期祁连山区显著增温相对应, 层状云出现频率减少更为明显, 层状云出现频率与气温呈明显的反相变化趋势。④在气候变暖的背景下, 祁连山区的层状云出现频率减少, 减少的幅度从西北向东南递增。当祁连山区秋季平均气温在升高1℃ 时, 祁连山区层状云出现频率减少2%～10%, 祁连山西段、中段减少2%～4%, 祁连山东段减少4%～10%。⑤祁连山区秋季层状云偏多与偏少年在欧亚500 hPa 环流场上存在明显的差异, 层状云偏多年, 极涡向亚洲北部伸展, 东亚大槽较偏弱, 乌拉尔山高压脊偏强, 脊前偏北气流引导极地冷空气沿偏西北路径向中国西北地区输送, 中亚地区到高原上不断有低值系统发展东移, 同时南支槽加强, 来自阿拉伯海、南海、东海的暖湿气流向内陆地区的输送明显加强, 与进入高原北部的冷空气交绥, 从而使祁连山区层状云出现频次增多;层状云偏少年, 中亚-中国西北地区暖性高压异常加强, 东亚大槽偏强, 冷空气活动路径偏东, 亚洲大陆至西太平洋冬季风特征明显, 偏北风加强, 不利于东南暖湿气流向西北内陆地区的输送, 冷暖气流在祁连山区交绥次数减少, 从而使祁连山区层状云出现频次减少。⑥印度洋沿孟加拉湾的向北的水汽输送, 副热带西太平洋的偏东气流在南海和中南半岛附近转为向北的水汽输送, 地中海、里海的西风带纬向水汽输送是3支影响祁连山区秋季层状云多寡的水汽输送通道, 进而对祁连山区秋季降水产生影响。  相似文献   

Heterogeneous strain regime in the eastern margin of Tibetan Plateau and its tectonic implications     

Guojie Meng  Xiaoning Su  Weiwei Wu  Jinwei Ren  Yonglin Yang  Jicang Wu  Chieh-Hung Chen  Nikolay V. Shestakov 《地震科学（英文版）》2015,28(1):1-10

The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode global position system(GPS) stations throughout the northwest of Longmenshan fault. A new GPS field over 1999–2011 is derived from measurements of the newly built and pre-existing stations in this region. Sequentially,two strain rate fields, one preceding and the other following the 2008 MW7.9 Wenchuan earthquake, are obtained using the Gausian weighting approach. Strain field over1999–2007 shows distinct strain partitioning prior to the2008 MW7.9 Wenchuan earthquake, with compression spreading over around Longmenshan area. Strain field derived from the two measurements in 2009 and 2011 shows that the area around Longmenshan continues to be under striking compression, as the pattern preceding the Wenchuan earthquake, implying a causative factor of the sequent of 2013 MW6.7 Lushan earthquake. Our GPSderived dilatation shows that both the Wenchuan and Lushan earthquakes occurred within the domain of pronounced contraction. The GPS velocities demonstrate that the Longriba fault underwent slight motion with the faultnormal and-parallel rates at 1.0 ± 2.5 mm and 0.3 ± 2.2 mm/a; the Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 ± 1.7 mm/a. Longriba fault is on a par with Longmenshan fault in strain partitioning to accommodate the southeastward motion of eastern margin of the Tibetan Plateau. Integrated analysis of principal strain tensors, mean principal stress, and fast directions of mantle anisotropy shows that west of Sichuan is characterized as mechanically strong crust-mantle coupling.  相似文献