西藏高原南部雅鲁藏布江缝合带地区地壳电性结构研究

为了探测西藏高原南部雅鲁藏布江缝合带地区地壳浅部和深部构造沿东西和南北方向的变化特征,在雅鲁藏布江缝合带地区布设了三条南北向剖面(错那—墨竹工卡、亚东—雪古拉、吉隆—措勤),采用超宽频带大地电磁测深方法进行了地壳、上地幔电性结构探测研究,发现该区主要电性结构特征为：1. 雅鲁藏布江缝合带附近表层发育大规模的高阻体,岩体延伸最深达30km以上,是冈底斯花岗岩体的反映. 2. 雅鲁藏布江缝合带的南部有小规模的良导体,在其下方和北侧发育有大规模良导体. 3. 沿剖面从南往北壳内普遍发育良导体,各良导体主体间是不连续的,规模逐渐增大,总体北倾,在缝合带附近产状较陡. 4. 在雅鲁藏布江缝合带附近良导体由西往东规模逐渐增大,导电性逐渐变好,相对雅鲁藏布江在剖面上的位置逐渐南移. 这些重要的电性特征可能是印度板块向北俯冲所形成的,深部大规模的良导体特征沿东西向的差异可能是板块碰撞引起物质沿东西向运移作用的结果.     

基于大地电磁测深的藏南雅鲁藏布江缝合带电性结构研究

为研究日喀则市活动断裂深浅部构造关系及深部孕震机制,跨雅鲁藏布江谢通门—日喀则段部署了48个宽频大地电磁测深点,剖面长度为108 km。在二维反演的基础上对壳幔200 km深度范围内的电性结构进行了探测研究。剖面自南向北依次经过喜马拉雅地块、雅鲁藏布江缝合带和拉萨—冈底斯地块。喜马拉雅地块地壳表现为高阻特性,其北侧的仲巴—郎杰学陆缘移置混杂地体发育了深达上地幔盖层的巨厚的北倾低阻体;雅鲁藏布江主缝合带表现为喇叭状低阻通道,宽约10 km,存在深浅部两处低阻体,浅部南倾深部北倾,低阻通道南部发育近似直立或南倾的高阻日喀则蛇绿岩,北部发育近直立的高阻冈底斯花岗岩体,整体表现为两个高阻异常体中间夹一个连通壳幔的带状低阻通道;拉萨—冈底斯地块以高阻为主,中下地壳普遍发育低阻体。缝合带附近因板块俯冲作用导致壳幔局部增厚或减薄,表现为电性的梯度变化,表现为低阻特性的部分则是壳幔物质的运移通道。      

贺根山镁铁-超镁铁岩与缝合带的关系——来自地球物理的证据

长期以来,对内蒙古贺根山缝合带中的镁铁-超镁铁岩,有着"蛇绿岩"、"岩浆岩"、"幔源熔-流体"等不同认识.近年来在铬铁矿中发现了金刚石等深部地幔矿物,如何认识携带这些物质的幔源熔-流体的上涌?缝合带在镁铁-超镁铁岩的形成过程中起到什么作用?解决问题的关键之一是弄清镁铁-超镁铁岩的深部产状,这需要来自地球物理观测数据的依据.本文基于航磁和重力数据的研究表明,贺根山地区的蛇绿岩块均呈现高磁异常特征,其中贺根山岩块埋深明显大于其他岩块,表现为高磁异常与低重力异常,与地表出露的蛇纹石化的镁铁-超镁铁岩带对应.对航磁化极异常与布格重力异常数据做了向上延拓处理,进行了磁源形态及底界深度的估算,并利用基于相异度算子的边缘增强方法辅助识别断裂.结果表明,贺根山岩块贯穿地壳,且附近存在超壳断裂.地表至中地壳主要由蛇纹石化的镁铁-超镁铁岩组成,下地壳主要为超镁铁质岩组成,它们充填在一组宽约30km的NEE向断裂带中,大地电磁测深剖面揭示的壳-幔电性结构进一步证实控制缝合带的是岩石圈断裂,贺根山缝合带具有明显的根部.由此推测,在地幔底辟上涌的背景下,幔源熔-流体沿着岩石圈断裂持续上升到达浅表,暗示该区板块的...     

西伯利亚板块与华北克拉通碰撞带地电结构及对深部缝合边界的讨论

西伯利亚板块与华北克拉通碰撞导致古亚洲洋闭合,形成了幅员辽阔的中亚造山带,该带内记录了丰富的板块碰撞信息,揭示深部缝合边界对于研究洋-陆俯冲到陆-陆碰撞的深部动力学过程具有重要的科学意义.本文对查干敖包-化德410 km大地电磁测深（MT）剖面数据进行反演,获得二维电性结构,为研究西伯利亚板块与华北克拉通碰撞带深部构造形迹、碰撞边界问题提供地电结构的依据.结合人工反射地震及地质资料获得以下认识：（1）西伯利亚板块与华北克拉通碰撞带地壳存在多组"U"型低阻异常,多对应弧型、倾斜或"鳄鱼嘴"状反射界面.莫霍面存在两处错断现象,并与深部电性梯度带对应.岩石圈地幔除白乃庙岛弧呈低阻块体外,均为高阻块体,这些电性结构特征反映了南北汇聚所形成的构造形迹.（2）碰撞带可分为二连-贺根山和索伦-西拉木伦河两个不同时期的汇聚体系,晚泥盆世-晚石炭世早期形成的二连-贺根山汇聚体系由二连-贺根山增生杂岩带、宝力岛弧地体及断裂带组成,深部缝合边界位于二连浩特.而晚二叠-早三叠的索伦-西拉木伦河汇聚体系由二道井子增生杂岩带和温都尔庙增生杂岩带及断裂带组成,深部缝合边界位于苏尼特右旗.（3）在锡林浩特地区软流圈内部存在高阻异常,可能为俯冲消失的洋壳或碰撞造山后拆离的岩石圈残片.     

新疆北天山推覆带大地电磁测深应用研究

利用远参考与Robust技术手段对新疆北天山地区大地电磁原始资料进行去噪处理,以及静态校正、逐级反演、梯度法、残差法等处理与综合地质解释,取得了较好成效。将该区划分为四棵树凹陷、山前断褶带、北天山推覆带、中天山隆起带四大构造单元,其中北天山推覆带地表裸露石炭系基岩。在推覆断层之下,显示中浅部存在层状低阻异常带,推测为侏罗与白垩系地层,为油气远景区。     

大地电磁数据揭示中国东北地区牡丹江缝合带俯冲极性及活化特征

佳木斯地块和松嫩地块位于中亚造山带最东端,两者的汇聚受控于二叠纪至侏罗纪期间牡丹江洋的俯冲及闭合作用.牡丹江缝合带后期又受到古太平洋板块和太平洋板块俯冲作用的直接影响,因此是研究古缝合带俯冲极性和后期改造作用的理想地区.本文对跨越牡丹江缝合带的160km长大地电磁剖面数据进行三维反演,建立了缝合带及邻区的电阻率模型.结果揭示了牡丹江洋的俯冲极性和俯冲痕迹,并提供了(古)太平洋板块俯冲作用导致牡丹江缝合带活化的地电学证据.缝合带表现为复杂的高导结构,位于松嫩地块-佳木斯地块碰撞带下方的地壳尺度西倾高导体,代表牡丹江洋闭合的古俯冲带,表征了牡丹江洋西向俯冲的极性.同时,由地表地质定义的牡丹江断裂不能完全代表牡丹江缝合带的深部结构,对于该缝合带的定义应扩展至横向延伸约70km的整个高导区域.俯冲前缘弧下的固体导电矿物由深部被抬升至上地壳,其下与地幔连通的“烟囱”状高导结构代表了幔源物质的上侵通道,表明牡丹江缝合带受古太平洋板块和太平洋板块的俯冲作用影响发生活化,导致通道内原本冷却、结晶的物质发生重熔.因此,(古)太平洋板块的俯冲作用破坏了中亚造山带东段古碰撞带的岩石圈结构,其下方大尺度地壳高...     

郯城-涟水综合地球物理剖面

在穿过苏鲁地体的郯城-涟水剖面上进行了深反射地震和大地电磁调查,剖面全长１３９．５ｋｍ,取得了高质量记录,一级品记录高达８５％。结果表明：（１）苏鲁超高压－高压变质岩片向北西倾斜,表现为高速高阻岩片,并受到强烈的变形,反映了超高压岩片的俯冲与折返;（２）杨子克拉通向北俯冲在苏鲁地体之下,表现为常速、中低阻的挠曲板状体,内部有大量反映碰撞的反射楔形体;（３）嘉山-响水断裂带向南陡倾,低阻带直通浅地幔,具有燕山期裂谷的特征,估计有可能是与沂沭断裂带同期的中生代裂谷;（４）印支期俯冲扬子地壳的古Ｍｏｈｏ面与期后形成的新Ｍｏｈｏ面都有强反射,表明中新生代在地壳底部有强烈的岩浆活动与壳幔相互作用,促使新Ｍｏｈｏ面的形成;（５）超高压变质带下方有一组南倾的逆断层,与折返有关,在此处进行科学钻探对了解超高压变质带形成和折返机制很有利。     

徐闻地区综合地球物理勘探方法应用研究

徐闻地区位于北部湾盆地向雷州半岛的延伸部分,具有较好的油气勘探前景.2003年至今,江苏油田在徐闻地区先后开展了重力、大地电磁测深、二维地震和三维地震,以及钻探、VSP和试油测试等油气勘探工作.徐闻地区存在比较特殊的地表与地下地质条件.工区跨越半岛陆上和浅海水域,浅表层多套火成岩覆盖(出露),深层构造破碎、地震反射成像困难.因此,开展了具有针对性的综合地球物理方法(重力、大地电磁测深和地震)研究与勘探实践,克服了单一地球物理方法的局限性,获得了较好的数据资料,减少了多解性并为该地区的油气发现奠定基础.     

郯城-涟水综合地球物理剖面

在穿过苏鲁地体的郯城-涟水剖面上进行了深反射地震和大地电磁调查,剖面全长１３９．５ｋｍ,取得了高质量记录,一级品记录高达８５％。结果表明：（１）苏鲁超高压－高压变质岩片向北西倾斜,表现为高速高阻岩片,并受到强烈的变形,反映了超高压岩片的俯冲与折返;（２）杨子克拉通向北俯冲在苏鲁地体之下,表现为常速、中低阻的挠曲板状体,内部有大量反映碰撞的反射楔形体;（３）嘉山-响水断裂带向南陡倾,低阻带直通浅地幔,具有燕山期裂谷的特征,估计有可能是与沂沭断裂带同期的中生代裂谷;（４）印支期俯冲扬子地壳的古Ｍｏｈｏ面与期后形成的新Ｍｏｈｏ面都有强反射,表明中新生代在地壳底部有强烈的岩浆活动与壳幔相互作用,促使新Ｍｏｈｏ面的形成;（５）超高压变质带下方有一组南倾的逆断层,与折返有关,在此处进行科学钻探对了解超高压变质带形成和折返机制很有利。     

索伦-西拉木伦缝合带中段及周边区域面波层析成像

索伦-西拉木伦缝合带中段及周边区域先后经历了古生代古亚洲洋闭合、中生代蒙古鄂霍茨克洋闭合和中新生代太平洋俯冲等构造复合叠加,导致该区深部构造异常复杂。本研究从该区近年来累积的宽频地震探测资料的地震面波和环境噪音互相关格林函数中提取瑞雷波群速度频散,并据此反演区域尺度的三维横波速度。结果发现：区域地壳厚度横向变化不大,松辽盆地和下辽河盆地地壳比大兴安岭薄,地壳厚度与地形吻合表明这些地区基本达到重力均衡状态;而辽东隆起和渤海湾盆地地壳厚度与地形高度呈反相关,表明这些地区可能仍处于构造改造过程中。在80 km深度之下,波速分布则呈现与索伦-西拉木伦缝合带走向近似平行的东西向展布。以索伦-西拉木伦缝合带为界,南北两侧横波速分布复杂程度明显不同且南侧的东西两部分复杂程度也不同。这些结果表明区域受太平洋俯冲体系冲破坏程度存在明显差异,同时索伦-西拉木伦缝合带以南可能仍有古亚洲洋板片残留。     

红河断裂带研究区深部结构特点的地球物理研究

红河断裂带是认识板块相互运动、深部过程和地质演化的窗口，一直受到重视与关注，关于红河断裂带入海后的去向问题特一直是讨论和研究的热点.本文对15°N~25°N，102°E~112°E地区的重力、磁力数据进行了相关研究，结合哀牢山—红河断裂带地区的地震层析成像结果，对该断裂带入海之后的去向进行了讨论.并依据重力数据对莺歌海中的两条剖面重建了密度结构，认为该区浅部与深部构造存在明显的不协调性.同时认为莺歌海地区的中地壳中有一低密度层存在，推测红河断裂带在莺歌海地区的走滑，很有可能就是沿着这一层发生的.     

Denitrification in a hyporheic riparian zone controlled by river regulation in the Seine river basin (France)

The purpose of this paper is to study denitrification and the conditions for its development in a hyporheic zone. The study site is the riparian zone of a former branch of the Seine River, where the river stage is kept almost constant during the year by hydraulic regulation. Hydrological and geochemical surveys were performed by monitoring four wells, ten shorter piezometers and the river over a 15‐month period. The water fluxes originating from the chalky hillsides and the river converge in a zone parallel to the river that acts as a drainage flow path through the floodplain. The riparian zone between this flow path and the river shows an important depletion of nitrate during the summer and autumn period, which cannot be explained by a simple mixing of waters coming from the river and the chalky hillsides. It can be attributed to denitrification as it occurs when oxygen concentration is below 2 mg l^?1, and goes along with a consumption of dissolved organic carbon and a decrease of redox potential. The river completely controls these hydro‐geochemical conditions. It also keeps the wetness of the riparian zone almost constant, which allowed us to isolate the high temperatures in summer and autumn as an important triggering factor for denitrification through its influence on the reaction rate and oxygen deficits. We also found a small isotopic enrichment of nitrate, suggesting that denitrification occurs after diffusion of nitrate through the sediment and riparian zone matrix, which is consistent with the hyporheic functioning of the study site. Copyright © 2008 John Wiley & Sons, Ltd.     

太湖水系结构特点及其功能的变化

太源水系上游为树状排列的河流,下游为扇形排水系统,全区江河湖海相贯通,受海潮和江流的作用,下游水系多变,防洪抗灾能力脆弱。近年来,虽经治理,该水系仍出现了“中雨大灾”,水资源不足及水质污染突出等一系列功能性的变化。     

Control of river stage on the reactive chemistry of the hyporheic zone

We examined the influence of river stage on subsurface hydrology and pore water chemistry within the hyporheic zone of a groundwater‐fed river during the summer baseflow period of 2011. We found river stage and geomorphologic environment to control chemical patterns in the hyporheic zone. At a high river stage, the flux of upwelling water in the shallow sediments (>20 cm) decreased at sample sites in the upper section of our study reach and increased substantially at sites in the lower section. This differential response is attributed to the contrasting geomorphology of these subreaches that affects the rate of the rise and fall of a river stage relative to the subsurface head. At sites where streamward vertical flux decreased, concentration profiles of a conservative environmental tracer suggest surface water infiltration into the riverbed below depths recorded at a low river stage. An increase in vertical flux at sites in the lower subreach is attributed to the movement of lateral subsurface waters originating from the adjacent floodplain. This lateral‐moving water preserved or decreased the vertical extent of the hyporheic mixing zone observed at a low river stage. Downwelling surface water appeared to be responsible for elevated dissolved organic carbon (DOC) and manganese (Mn) concentrations in shallow sediments (0–20 cm); however, lateral subsurface flows were probably important for elevated concentrations of these solutes at deeper levels. Results suggest that DOC delivered to hyporheic sediments during a high river stage from surface water and lateral subsurface sources could enhance heterotrophic microbial activities. Copyright © 2013 John Wiley & Sons, Ltd.     

Mesozoic radiolarian chert from the middle sector of the Yarlung Zangbo suture zone,Tibet and its tectonic implications

The middle sector of the Yarlung Zangbo suture zone stretches over 200 km long from Ngamring through Geding to Rinbung, roughly along Yarlung Zangbo River valley (Fig. 1). This belt resulted from the closure of the Tethyan ocean and the collision be- tween Indian plate and Lhasa block[1―8]. Lots of works demonstrated that rifting of the Tethyan basin in southern Tibet started from Triassic time. Initial oce- anic crust appeared in the Late Jurassic, and then ex- perienced a rapid sprea…     

中国东部大兴安岭重力梯级带域地球物理场特征及其成因

综合利用7条地学断面（GGT）资料研究了大兴安岭重力梯级带附近的壳幔地球物理特征模式.分析了形成上述地球物理特征的3种因素:东亚大陆边缘周边三大板块运动、地幔流运动和地幔热柱。对大兴安岭重力梯级带的重力异常的正演拟合结果表明,壳幔物质密度不均匀和莫霍界面超伏造成该带的重力异常,地应力场的综合作用产生了该重力梯级系列地球物理特征。最后,探讨了大兴安岭重力梯级带成因机制,提出了以“挤”、“涌”为动力的“三结点模型”。     

The neotectonic deformation and earthquake activity in Zhuanglang river active fault zone of Lanzhou

Introduction Zhuanglang river active fault zone, which located in the western of Zhuanglang river valley, north of Hekou, the Xigu district of Lanzhou city, is composed of several echelon small faults, these faults display not very clear on surface. Predecessors thought that this fault from Yongdeng to Hekou was active in Late Pleistocene and even in Holocene through limited research works, they also believed that these earthquakes with magnitude 641 happened at Yongdeng and magnitude 521 …     

阿尼玛卿缝合带及两侧上地壳泊松比分布

本文通过对马尔康－古浪宽角反射和折射剖面高精度观测段（200～400 km）的Pg、Sg资料的分析解释,给出了该区段上地壳速度结构和泊松比分布.并利用震相识别误差分析、分辨率计算及不同初始模型筛选等方法,使走时反演结果的可靠性进一步提高.研究表明：对应于阿尼玛卿缝合带的275km～355 km桩号段内平均泊松比高达0.297,P波和S波速度呈横向高低速条带变化,库赛湖－玛沁断裂和舟曲－两当断裂基本上均位于高泊松比和低速带内,并分别处在缝合带与若尔盖盆地和西秦岭褶皱带的分界上.阿尼玛卿缝合带南侧的若尔盖盆地平均泊松比较低,约为0.257,北侧西秦岭褶皱带的平均泊松比为0.264.     

Spectral responses of water level in tidal river and groundwater

The water level of five river stages and seven groundwater wells in the Taipei Basin were analysed by spectral analysis in the frequency domain. The diurnal, semi‐diurnal and quarter‐diurnal tidal components of the Tanshui River appear to relate closely to astronomical tides as K₁, M₂ and M₄, respectively. It is also found that the diurnal component reveals a reversed phase angle in the middle section of the Tanshui River; the phase of the quarter‐diurnal component is also found to be reversed at stations upstream in the Tanshui River and Hsintien Stream. It is believed that these phenomena could be caused by local variation in the river channel topography. The autospectrum and cross‐spectrum between groundwater elevation and nearby river stage were observed to correlate highly with the frequency of the astronomical tides K₁, M₂ and M₄. From the study of the phase shift and time lag of water level fluctuations at river stages and groundwater wells, it was found that the tidal effects of diurnal, semi‐diurnal, and quarter‐diurnal components were significantly different. The relationships between phase and the fluctuated range of atmospheric pressure and water level imply that change in atmospheric pressure does not affect water level fluctuation in the river stage and groundwater well. Copyright © 1999 John Wiley & Sons, Ltd.     

Fate of pioneering vegetation patches in a dynamic meandering river

Fluvial biomorphodynamics in actively meandering rivers entail interactions between hydromorphodynamics and pioneering tree species that have eco-engineering effects. Here we study spatiotemporal patterns of vegetation patches smaller than 150 m² in a 4 km reach of the river Allier in France in order to unravel causes for tree persistence and mortality and identify spatial trends across the river valley. To this end we analysed aerial photographs by object-based image analysis over a period of 56 years and tracked individual patches through time. Furthermore the cover and surface age of the study reach were classified. The large-scale shifts of channels, bars and vegetation are consistent with the meandering process and chute cutoffs. However, the spatiotemporal patterns of the vegetation patches are surprising in that they are ubiquitous and have ages up to decades on the highly dynamic meander belt, but hardly expand into larger vegetation patches. Patches disappear exponentially as a function of their age, and faster so in the last decades. Causes are amalgamation into the riparian forest flanking the meander belt and mortality likely due to desiccation or erosion. Patches have a higher probability of survival when further away from the active channel and closer to high vegetation patches and valley boundary. The window of opportunity of vegetation settlement widens towards the valley boundaries and in floodplain lows of former channels and chutes. These results imply a gradual cross-valley gradient of riparian vegetation settling, survival and succession. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.