新疆吐尔库班套蛇绿混杂岩的发现及其地质意义

蛇绿岩作为残留洋壳的良好记录,对于研究古板块构造及其演化具有重要意义。新发现的吐尔库班套蛇绿混杂岩位于新疆阿尔泰布尔津南部,主要由超镁铁岩、辉长岩、辉绿岩、玄武岩、复理石建造等构成。其中辉长岩和片麻状花岗岩的锆石U Pb年龄在363～355 Ma,指示蛇绿岩的形成、洋壳俯冲时代在晚泥盆世晚期。岩石地球化学特征表明,该蛇绿岩套的镁铁超镁铁岩和玄武岩属低碱、低钛、富镁的拉斑玄武岩系列,具有较典型的幔源岩石特征,玄武岩形成于类似洋中脊的构造环境。混杂岩带中的片麻状花岗岩属于钠质的低钾岩石系列,形成于火山弧或同碰撞构造环境,亦为洋壳俯冲的结果。吐尔库班套蛇绿岩与科克森套、乔夏哈拉、布尔根蛇绿岩一起构成了沿额尔齐斯分布的蛇绿混杂岩带,构成了分割西伯利亚板块和哈萨克斯坦-准噶尔板块的斋桑-科克森套-南蒙古缝合带。     

兰州庄浪河阶地差分GPS测量与构造变形分析

在综合分析兰州庄浪河河流阶地发育和分布特征的基础上,采用高精度差分GPS对Ⅰ～Ⅲ级阶地进行了详细的测量,获得了庄浪河阶地纵横剖面图.结合不同级别阶地年代学资料研究了其构造变形特征,获得了穿越断裂带地区的阶地变形特点、变形带宽度、变形幅度和速率等定量参数.研究表明:兰州庄浪河阶地构造变形主要表现为断裂扩展褶皱模式,阶地变形速率在晚第四纪以来有逐渐加速的特点.     

长江三峡地区仙女山断裂北端延伸问题探讨

The Xiannvshan fault zone, lying along the western margin of the Huangling anticline, is one of the most important fault zones in the Three Gorges reservoir area. The fault experienced strong activity during the Cenozoic Era. The question of whether the fault zone goes through the Yangtze River has been one of the key problems faced in previous studies as it has a significant influence upon the assessment of geological hazards and earthquake stability in the reservoir area. Based on tectonic and geomorphic observations along the fault zone between the Baixianchi village in Changyang county and Huangkou village in Zigui town, together with the comparisons between the geology in Guizhou and Quyuan town in the north bank of the Yangtze River and the Xiannvshan fault zone, it is suggested that the north end of this fault zone is located around Huangkou village and does not go through the Yangtze rivers northward. The evidence is as follows: ① On the basis of field data collection, it is found that the Xiannvshan Fault zone, which stretches 80km, underwent thrust movement in the Cenozoic period, resulting in ravines and fault scarps, topographically. Whereas, on the northern bank of the Yangtze River, faults are rarely found, and most of the faults are developed in the Jurassic strata,without topographical effects. Therefore, the Xiannvshan Fault zone has not stretched to the north bank of the Yangtze River. ② The fault gouge and tectonite zone were found developed on the Xiannvshan Fault zone at Baixianchi village, but only a tectonite zone was found at Zhouping village. There are also some branch faults close to the northern end of the fault zone. So, the activity of the fault zone weakened from south to north in Cenozoic. The fault zone extends northward and dies out at Huangkou. It doesn’t stretch forward any longer as indicated by continuous strata, sparse joints, and small folds, etc.     

中国东北古亚洲与古太平洋构造域演化与转换

现今分布于中朝、塔里木古陆与西伯利亚古陆之间的古亚洲构造域,既存在于前中生代,也存在于中新生代.古亚洲构造域不能等同于古亚洲洋及其构造域.作为古亚洲构造域一部分的古亚洲洋开始于晚寒武世-奥陶纪,结束于中三叠世.古太平洋及其构造域形成于晚古生代,印支期后,成为滨太平洋构造域.在晚三叠世-侏罗纪时期与古亚洲构造域并存,形成两个构造域的板内造山带、局部盆山构造和东北高原.早白垩世形成以滨太平洋构造域为主体的北北东向盆山体系.     

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山东地区近期重力场动态变化特征

利用2009年以来的山东流动重力网复测数据,给出了区域重力场差分和累积动态变化图像及GPS站的重力值时间序列分析。结果表明:重力场动态变化图像大体反映出近期山东地壳物质运动状态,累积动态变化更能反映区域构造块体之间的运动与断裂构造作用。     

The Pinjaur dun (intermontane longitudinal valley) and associated active mountain fronts, NW Himalaya: Tectonic geomorphology and morphotectonic evolution

The Himalayan orogenic belt, formed as a result of collision tectonic processes, shows abundant evidence of neotectonic activity, active tectonics, and the occurrence of historical earthquakes. Its frontal deformation zone is characterized, in some segments, by intermontane longitudinal valleys (duns). Such frontal segments of the Himalaya are marked by the occurrence of multiple mountain fronts.In one such segment of the foothills of the NW Himalaya, the Pinjaur dun is developed and marked by three mountain fronts: MF1A and MF1B associated with the southernmost Himalayan Frontal Thrust (HFT), MF2 associated with the Sirsa fault, and MF3 associated with the Barsar thrust along the southern margin of the relatively higher main part of the sub-Himalaya. Geomorphic responses to the tectonic activity of these and related structural features have been analyzed through the use of geomorphic indices, drainage density, stream longitudinal profiles, drainage anomalies, and hypsometric analysis. Also, fault and fold growth and their expression on landform development was studied using a combination of surface profiles and field observations.The values of valley floor width to height ratio (V_f) for valleys associated with MF1 ranged between 0.07 and 0.74, and for valleys associated with MF2 ranged from 1.02–5.12. V_f for the four major valleys associated with MF1B ranged from 1.1–1.7. The asymmetry factor for 26 drainage basins related to MF1A indicate these have developed under the influence of a transverse structure. These results taken together with those obtained from the Hack profiles and SL index values, hypsometry, drainage density, and drainage anomalies suggest that the faults associated with the mountain fronts and related structures are active.Active tectonics and neotectonic activity have led to the formation of four surfaces in the Pinjaur dun. In addition, an important drainage divide separating the Sirsa and Jhajara drainage networks also developed in the intermontane valley. Surface profile analysis helped in deciphering the growth history of the fault bend fold structures of the outermost Siwalik hills. The effects of tectonic activity on the proximal part of the Indo-Gangetic plains are interpreted from the remarkable river deflections that are aligned linearly over tens of kilometers in a zone about 10 km south of the HFT.Based on these integrated structural and tectonic geomorphological approaches, a morphotectonic evolutionary model of the dun has been proposed. This model highlights the role of uplift and growth history of the fault bend fold structures of the outermost Siwalik hills on (i) the depositional landforms and drainage development of the Pinjaur dun, and (ii) valley development of the outermost Siwalik hills.Importantly, this study postulates the formation of an incipient mountain front that is evolving ahead of the HFT and the outermost Siwalik hills in the Indo-Gangetic plains.     

基于地壳介质各向异性分析青藏高原东北缘构造应力特征

青藏高原东北缘由于受到多个构造块体的共同约束,表现出复杂的地球物理特性和地质特性,本文利用甘肃数字地震台网(2001-2008年)的观测资料,采用系统分析方法(SAM),进行地壳剪切波分裂分析,获得研究区内18个台站共1005条记录的剪切波分裂参数.研究结果表明,青藏高原东北缘介质各向异性在空间上存在差异,慢剪切波延迟时间表明了地壳介质各向异性的强弱变化特征,快剪切波平均偏振方向则反映了本区区域构造应力的空间变化特征.分析认为,祁连山-河西走廊活动构造区直接受青藏地块与阿拉善地块间相互作用,与青藏地块构造应力一致;甘东南活动构造区的应力环境主要受到内部活动断裂的共同作用,具有局部构造应力的特征.     

基于汶川地震序列震源机制解对龙门山地区构造变形模式的初步探讨

本文采用理论震源机制解的分析方法,以汶川地震序列震源机制解为约束,探讨龙门山地区构造变形模式及其与汶川地震序列的关系.通过有限元模拟,计算了龙门山地区不同构造变形模式下的构造应力场,得到了理论震源机制解,并与汶川地震序列实际震源机制解进行对比分析,初步探讨了该区构造变形模式对汶川地震序列的影响.结果显示,在龙门山地区,青藏高原内深部构造变形快于地表的构造变形模式下,区域构造应力场对应的理论震源机制解与汶川地震序列震源机制解的相符程度较高.这种一致性可能表明:(1)青藏高原内部深部构造变形快于地表,是龙门山地区比较合理的构造模式;(2)构造应力场是影响汶川地震序列震源机制的重要力学因素.     

吉南太古宙岩群中的大型构造置换及其对BIF矿体的控制

以吉林省白山市板石沟铁矿区为典型实例,系统地论述了太古宙岩群中广泛发育的大型和区域性构造置换的几何特征和对BIF矿体的控制规律。本区构造置换主要表现为:在紧闭同斜褶皱发育的持续变形过程中形成S₁≈S₀,并伴有钩状褶皱、石香肠构造和各类型线理的生成。按照主构造面均匀性法则,划分了构造均匀区段,并对其中8个区段(Ⅰ～Ⅷ)进行了详细的SFLπ组构分析。基于构造置换规律研究,提出本区褶皱轴与包络线双向找矿的理论与方法,经工程验证,取得显著的经济效益。