首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The South East Sayan area, W of the Lake Baikal is subjected to a very complex tectonic setting where the extensional stress field of the Baikal Rift System meets the compressional stress field generated by the India–Asia collision further south. Using satellite images, aerial photographs, SRTM DEM, field mapping of geomorphological structures, and published neotectonics and geological data we show that most of the relief in the SE Sayan initiated during Late Pliocene–Pleistocene through compressive reactivation of inherited structures. By Late Quaternary, clockwise rotation of the compressive field generated strike–slip faulting and local, secondary extension still within a general compressional stress field. We demonstrate that the formation of the small-scale extensional basins within the East Sayan range is not linked to general the extension in the Baikal Rift System nor to a possible asthenospheric plume acting at the base of the crust but rather to the rotation of small rigid tectonic blocks driven by the compression.  相似文献   

2.
Based on multiyear measurements of present-day motions in the central area of the Baikal rift system, new data on the kinematics of horizontal motions, relative horizontal deformation rates, and rotation velocities in the area of junction of the South Baikal, North Baikal, and Barguzin rift basins have been obtained. This area is an intricate structure with two transfer zones: Ol’khon–Svyatoi Nos and Ust’-Barguzin.It is shown that crustal blocks are moving southeastward, normally to the structures of transfer zones and at an acute angle to the Baikal Rift strike, which corresponds to the right-lateral strike-slip extensional faulting along the major structure. The average horizontal velocities increase from 3.0 mm yr–1 in the northern South Baikal basin to 6.5 mm yr–1 in the Barguzin basin. The elongation axes prevailing in the study region are mainly of NW–SE direction. The areas of intense deformations are confined to structures with high seismic activity in the South Baikal and, partly, Barguzin basins. This confirms the existence of a present-day zone of the Earth’s crust destruction in the Baikal rift system, which is the most likely source of strong earthquakes in the future. Two zones with rotations in opposite directions are recognized in the rotation velocity field. Clockwise rotation is typical of structures of N–NE strike (Maloe More basin, southern North Baikal basin, Barguzin Ridge rise). Counterclockwise rotation is determined for NE-striking structures (northern South Baikal basin, southern Barguzin basin). In general, the obtained data show an intricate pattern of present-day horizontal dislocations and deformations in the area of junction of NE- and N–NE-striking rift structures. This suggests left- and right-lateral strike-slip faults, respectively, within them.  相似文献   

3.
The results of geological, structural, tectonic, and geoelectric studies of the dry basins in the Baikal Rift Zone and western Transbaikalia, combined under the term Baikal region, are integrated. Deformations of the Cenozoic sediments related to pulsing and creeping tectonic processes are classified. The efficiency of mapping of the fault-block structure of the territories overlapped by loose and poorly cemented sediments is shown. The faults mapped at the ground surface within the basins are correlated with the deep structure of the sedimentary fill and the surface of the crystalline basement, where they are expressed in warping and zones of low electric resistance. It is established that the kinematics of the faults actively developing in the Late Cenozoic testifies to the relatively stable regional stress field during the Late Pliocene and Quaternary over the entire Baikal region, where the NW-SE-trending extension was predominant. At the local level, the stress field of the uppermost Earth’s crust is mosaic and controlled by variable orientation of the principal stress axes with the prevalence of extension. The integrated tectonophysical model of the Mesozoic and Cenozoic rift basin is primarily characterized by the occurrence of mountain thresholds, asymmetric morphostructure, and block-fault structure of the sedimentary beds and upper part of the crystalline basement. The geological evolution of the Baikal region from the Jurassic to Recent is determined by alternation of long (20–115 Ma) epochs of extension and relatively short (5.3–3.0 Ma) stages of compression. The basins of the Baikal Rift System and western Transbaikalia are derivatives of the same geodynamic processes.  相似文献   

4.
Results of investigations of Baikal bottom sediments from a long core (BDP-97) and several short (0–1 m) cores are presented. It has been shown that the Holocene sediments in the Baikal basins consist of biogenic-terrigenous muds, accumulated under calm sedimentation conditions, and of turbidites, formed during catastrophic events. The turbidites can be distinguished from the host sediments by their enrichment in heavy minerals and thus their high magnetic susceptibility. Often, Pliocene and Pleistocene diatom species observed in the Holocene sediments (mainly in the turbidites) point to redeposition of ancient offshore sediments. Our results indicate that deltas, littoral zones, and continental slopes are the source areas of turbidites. The fact that the turbidites occur far from their sources confirms the existence of high-energy turbidity currents responsible for long-distance lateral-sediment transport to the deep basin planes of the lake.  相似文献   

5.
The data obtained from long-term field studies in the Baikal Rift area are summarized. A new stratigraphic scheme is developed on the basis of previous stratigraphic research of N.A. Logachev. The new elements of the scheme are (1) the use of regional correlation horizons; (2) recognition of pre-Tankhoi (pre-Late Oligocene) sediments correlated with the Maastrichtian-Early Oligocene deposits of the Baikal Fore-deep; (3) elimination from the scheme of the Khalagai and Anosovka formations and distinction on their basis of the Tagai, Sasa, Osinovka, and Shankhaikha formations; (4) recognition of several weathering crust beds and Neogene paleosols. The “lower Eopleistocene (Upper Pliocene)” red-rock formation of Logachev is subdivided into the following stratigraphic units: the Cretaceous-Paleogene unit characterized by a few finds of Early Oligocene fossils, the Upper Miocene-Lower Pliocene red clay bearing numerous fossil remains, and the Upper Pliocene reddish clay with abundant localities of fossils. The sections examined in the land portion of the Baikal Rift are correlated with bottom sediments of the Baikal depression and are subdivided into three instead of the two commonly accepted large tectonic-lithological-stratigraphic complexes. Stratigraphic studies provide a new insight into the history of the Baikal Rift and into some general questions of the continental rift formation.  相似文献   

6.
贝加尔裂陷新构造特征   总被引：2，自引：0，他引：2  
贝加尔裂谷系的断裂发育阶段和沉积作用过程基本一致,除沉积作用前的前裂谷断裂已经活化外,整个裂谷系的发育及演化过程大体可划分为两个阶段,即始新世中晚期-上新世早期(E22-3-N21)的开始阶段和上新世中晚期-第四纪(N22-3-Q)的主要阶段。前者属塑性形变,地形反差小,断裂活动弱;后者属脆性形变,地形反差大,断裂活动强。
贝加尔裂谷拗陷是贝加尔裂谷系中发育最早、规模最大的水下拗陷,新构造运动表现明显,升降幅度自西南向东北增大。区内及其四周断块山体及盆地多显示了自西向东翘起的特点。夷平面及冲、洪积扇发生大量拱曲和拗曲。各方向断裂力学属性组合特征,反映了NE-SW向的挤压构造应力场。   相似文献   

7.
A new composite BDP-96 biogenic silica record over the entire Pleistocene was generated by splicing BDP-96-1 and BDP-96-2 drill cores from Lake Baikal, crosschecked against a similar record from a nearby BDP-98 drill core. A new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of September perihelia. This target is derived from analysis of regional climate proxy responses during the Holocene, the last interglacial and around paleomagnetic reversals. By resolving virtually every precessional cycle during the Pleistocene, the new age model represents a major improvement compared with previously reported Lake Baikal timescales. The astronomically tuned ages of the Pleistocene paleomagnetic reversals are consistent with published dates. The minimal tuning approach we used (precession only) has also aligned high signal power in a narrow obliquity band, confirming the strong presence of orbital forcing. There are also strong ca 100-ka scale cycles, but these are not aligned with the orbital eccentricity.Despite the location of Lake Baikal in a continental interior that is highly sensitive to insolation forcing, the tuned biogenic silica record reveals a consistent phase difference of −32° (ca 4 ka) relative to insolation in the obliquity band. An inherent lag embedded in a continental proxy record, not driven by global ice volume, is an intriguing finding. Another new observation is that long-term changes in sedimentation rates in Lake Baikal appear to be related to the amplitude of orbital forcing; both amplitudes and sedimentation rates undergo significant changes during MIS 24-MIS 19 interval corresponding to the Middle Pleistocene Transition. With potential for linking continental and marine climato-stratigraphies, the new Baikal record serves a new benchmark correlation target in continental Eurasia, as an alternative to June 65°N insolation and ODP-correlated timescales.  相似文献   

8.
利用1961 - 2017年青海省43站逐日最低气温观测资料, 依据区域持续性低温事件判识标准, 提取历史上61次典型事件, 对影响该类事件的环流演变和前兆信号进行分析。结果表明： 事件发展中北半球极涡经历分裂 - 收缩增强的变化过程, 中高纬自西向东逐渐发展为“正 - 负 - 正”异常波列状分布; 事件发生当日, 大西洋地区、 乌拉尔山及西伯利亚地区高度场异常偏高, 东亚大槽偏深, 利于自极地南下的冷空气在西欧上空堆积并沿纬向西风急流路径向东传播影响东亚地区。进一步分析表明, 当出现该类事件时, 中高纬地区存在三个关键影响区, 其中乌拉尔山关键区高度场正异常同此类事件的联系最紧密。  相似文献   

9.
New data are reported on the stratigraphy of the Oligocene deposits of Lake Baikal (the Tankhoi field, the outcrops near the mouths of the Osinovka, Polovinka, and Klyuevka Rivers). Detailed paleontological analysis of the key sections on the continental part of the Baikal eastern coast revealed four floristic horizons that could be used as indicator horizons and showed that the Tankhoi Formation formed throughout the Oligocene and at the early Early Miocene. Lithologically, blue vivianite clays and coal beds could be used as the most important indicator horizons. Formation of the deposits began after a long stratigraphic break from the Early Cretaceous to the Early Oligocene. The deposits were formed by erosion and denudation of weathering crust and accumulation of redeposited weathering residues in the Tankhoi paleobasin with a lacustrine-marsh landscape. Coarse-clastic foehn deposits of the Osinovka Formation, containing rich Miocene palynological assemblages, were eroded and overlie concordantly the Upper Tankhoi Subformation and redeposited weathering residues of the weathering crust, and underlie the Anosovka Formation. The study suggests that the Baikal rift valley began to form at 38 Ma.  相似文献   

10.
Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and alongshore winds and are traced along the coast to a distance of up to 60–100 km and up to 250 km in North Baikal. Analogous to the way it occurs in seas, water rises from the depths of 100–200 m (350 m as a maximum) at the velocity of 0.1 × 10−2−6.5 × 10−2 cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80–300 m in August and up to 400–800 m in early-mid November. The area of upwellings occupies up to 20–60% of the separate basins of the lake. Vertical circulation of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at that.  相似文献   

11.
俄罗斯贝加尔湖区伸展构造及与中国东部伸展构造对比   总被引：4，自引：0，他引：4  
在晚白垩世-始新世夷平面基础上,由于断裂作用形成了贝加尔裂谷系。断裂作用最大幅度超过10 km。在裂谷系中心部位发育的断层长度最大、最深、最早,并以准对称形式向四周扩展。贝加尔裂谷系是在地幔隆起和印度-欧亚大陆碰撞双重作用下形成。贝加尔裂谷系与中国东部新生代断陷盆地和汾渭裂谷系同时形成,并有密切的成因联系。它们的形成不仅受太平洋板块的俯冲和印度-欧亚大陆碰撞的制约和影响,而且位于中国西南部的地幔流发散中心,呈扇状向太平洋区流动,可能是它们在更深层次上的共同场源基础。  相似文献   

12.
The first tectonophysical model of the Baikal seismic zone represents a separate complex region of the lithosphere. It has a pinnate structure with a backbone belt of current deformation, which is a concentrator of largest earthquakes, and branching, repeatedly reactivated large and small faults. In its vertical section, the seismic zone is tree-like, the stem and the branches being faults of different size ranks which can generate earthquakes when reactivated. The real-time short-period fault motions and the respective seismicity occurring at a certain time and in certain places are triggered by strain waves, which disturb the metastable state of the faulted lithosphere subject to regional stress. The modeling work includes developing general requirements for tectonophysical models of continental rifts and special methods for identifying the faults that become active within short historic time spans, as well as techniques for locating potential events in space and time in specific active faults. The methods and model testing for medium-term earthquake prediction are described by the example of the well-documented Baikal seismic zone, which is the most active part of the Baikal rift system. The tectonophysical model for the Baikal zone is statistically supported by field data, and this allows estimating the velocities and periods of strain waves for different zone segments and faults, with implications for nearest-future earthquake prediction.  相似文献   

13.
Petit 《地学学报》1998,10(3):160-169
To better understand how active deformation localizes within a continental plate in response to extensional and transtensional tectonics, a combined analysis of high-quality gravity (Bouguer anomaly) and seismicity data is presented consisting of about 35000 earthquakes recorded in the Baikal Rift Zone. This approach allows imaging of deformation patterns from the surface down to the Moho. A comparison is made with heat flow variations in order to assess the importance of lithospheric rheology in the style of extensional deformation. Three different rift sectors can be identified. The southwestern rift sector is characterized by strong gravity and topography contrasts marked by two major crustal faults and diffuse seismicity. Heat flow shows locally elevated values, correlated with recent volcanism and negative seismic P-velocity anomalies. Based on earthquake fault plane solutions and on previous stress field inversions, it is proposed that strain decoupling may occur in this area in response to wrench-compressional stress regime imposed by the India–Asia collision. The central sector is characterized by two major seismic belts; the southernmost one corresponds to a single, steeply dipping fault accommodating oblique extension; in the centre of lake Baikal, a second seismic belt is associated with several dip-slip faults and subcrustal thinning at the rift axis in response to orthogonal extension. The northern rift sector is characterized by a wide, low Bouguer anomaly which corresponds to a broad, high topographic dome and seismic belts and swarms. This topography can be explained by lithospheric buoyancy forces possibly linked to anomalous upper mantle. At a more detailed scale, no clear correlation appears between the surficial fault pattern and the gravity signal. As in other continental rifts, it appears that the lithospheric rheology influences extensional basins morphology. However, in the Baikal rift, the inherited structural fabric combined with stress field variations results in oblique rifting tectonics which seem to control the geometry of southern and northeastern rift basins.  相似文献   

14.
《Gondwana Research》2014,25(3-4):918-935
The Baikal Rift System in southern Siberia is one of the main intracontinental extensional features on Earth. The rift system represents the northwestern boundary of the Amuria plate and in that respect can be considered as an evolving plate boundary. The Baikal Rift System has been widely studied both in terms of geology and geophysics and many models have been proposed for its formation and evolution. However, the age of the initiation of deformation and the mechanism driving this deformation are still largely debated. While major extension has occurred since the Late Miocene–Pliocene, the onset of extension seems older than the India–Asia collision, implying that several driving mechanisms may have acted together or in relay through time. In this work, we review the available data and models for deformation in an area encompassing the Baikal Rift System, the Sayan ranges to the west and the Transbaikal to the east. Using a synthesis of this data and our own field and mapping observations, we show that the Baikal Rift System, along with transpressional deformation in the Sayan ranges and transtension in the Transbaikal area, can be explained through major left-lateral strike–slip systems. The deformation is strongly controlled by inherited crustal and lithospheric structures, and is distributed over a wide area within the western Amuria plate that consequently cannot be considered as a rigid block. Such distributed deformation is likely to have a strong effect on the structure of the future continental margin if extension evolves towards the formation of oceanic crust.  相似文献   

15.
在某些浅水区域中, 常有大量工程障碍, 如磁性柱状体。依据磁性柱状体的特点, 从顺轴磁化无限延深柱状磁性体这一简化数学模型的磁场分析入手, 进而对更近实际的顺轴磁化有限延深柱状磁性体的磁场及其梯度场的分布规律进行讨论, 并据此提出了采用水平磁梯度测量法对磁性柱状体磁特性实施探测的可取途径。  相似文献   

16.
At the present time, the induction of several microgauss in large-scale fields of the Galaxy has been repeatedly confirmed. There are numerous arguments in favor of the fact that the magnetic field exhibits so-called reversals associated with a direction change from one region to another. Such configurations are allowed in the nonlinear equations context of the dynamo theory, which describes the large-scale magnetic-field evolution. In the present study, reversals are modeled using the so-called no-z approximation based on the fact that the galactic disk is sufficiently thin. The magnetic field generation that exhibit both single and double sign changes with distance from the center is observed. From an observational point of view, one of the main methods for studying magnetic fields is to gauge the Faraday rotation measure of radio waves coming from pulsars. Its value can characterize the integral magnitude of the magnetic field, and the sign indicates its direction. A study of the pulsar distribution with large Faraday rotation measures ($$\left| {RM} \right| > 200$$ rad/m2) is presented. The results indicate that there is a region of $$4.8\;{\text{kpc}} < r < 7.3\;{\text{kpc}}$$ in the Galaxy in which the magnetic field is oriented counterclockwise. At the ring edges, the magnetic field reverses its direction. These results are in close agreement both with theoretical concepts and other studies dedicated to the structure observations of the magnetic field in the Galaxy.  相似文献   

17.
为了深入认识与理解南北地震带北段和蒙古中部大陆强震孕育与发生的深部构造环境,在南北纵贯蒙古国全境的苏赫巴托尔—乌兰巴托—达兰扎达嘎德剖面上开展了大规模重磁测量及岩石样品采集。笔者系统地分析与总结了剖面上585块岩石样品的密度、磁化率和天然剩余磁化强度等物性参数。结果表明,整个剖面以火成岩为主,沉积岩为辅,仅有少量变质岩出露,且各岩石大类、类和亚类以及各年代地层之间,均存在着不同程度的密度与磁性差异。火成岩磁化率和天然剩余磁化强度分别具有3~5个数量级差异,密度变化范围较大;而沉积岩磁化率和天然剩余磁化强度相对较弱。一方面,物性差异为利用重磁测量开展剖面地壳结构的反演与研究奠定了基础;另一方面,这些物性参数为相关地球物理测量数据的反演与解释提供了重要约束。  相似文献   

18.
The seismicity of the Baikal rift zone is considered on the basis of instrumental and field observations. The spatial pattern of epicentres, the frequency of earthquakes and the relations between seismicity and the elements of fault tectonics are analyzed. The regional and local stress states in the crust of the Pribaikalye region, obtained from studying earthquake focal mechanisms for various energies are summarized.  相似文献   

19.
Anhydrous and amphibole-bearing peridotite xenoliths occur in roughly equal quantitites in the Bartoy volcanic field about 100 km south of the southern tip of Lake Baikal in Siberia (Russia). Whole-rock samples and pure mineral separates from nine xenoliths have been analyzed for Sr and Nd isotopes in order to characterize the upper mantle beneath the southern Baikal rift zone. In an Sr-Nd isotope diagram both dry and hydrous xenoliths from Bartoy plot at the junction between the fields of MORB and ocean island basalts. This contrasts with data available on two other localities around Lake Baikal (Tariat and Vitim) where peridotites typically have Sr–Nd isotope compositions indicative of strong long-term depletion in incompatible elements. Our data indicate significant chemical and isotopic heterogeneity in the mantle beneath Bartoy that may be attributed to its position close to an ancient suture zone separating the Siberian Platform from the Mongol-Okhotsk mobile belt and occupied now by the Baikal rift. Two peridotites have clinopyroxenes depleted in light rare earth elements (LREE) with Sr and Nd model ages of about 2 Ga and seem to retain the trace element and isotopic signatures of old depleted lithospheric mantle, while all other xenoliths show different degrees of LREE-enrichment. Amphiboles and clinopyroxenes in the hydrous peridotites are in Sr–Nd isotopic disequilibrium. If this reflects in situ decay of 147Sm and 87Rb rather than heterogeneities produced by recent metasomatic formation of amphiboles then 300–400 Ma have passed since the minerals were last in equilibrium. This age range then indicates an old enrichment episode or repeated events during the Paleozoic in the lithospheric mantle initially depleted maybe 2 Ga ago. The Bartoy hydrous and enriched dry peridotites, therefore, are unlikely to represent fragments of a young asthenospheric bulge which, according to seismic reflection studies, reached the Moho at the axis of the Baikal rift zone a few Ma ago. By contrast, hydrous veins in peridotites may be associated with rift formation processes.  相似文献   

20.
On relationships between the Baikal rift and ancient structures   总被引：1，自引：0，他引：1  
The formation of young geological structures in Pribaikalye has frequently been controlled by structural anisotropy of the basement. Orientation of the stress field associated with rifting favoured a parallelism of rift structures with ancient dislocations, primarily of northeastern trend, but sometimes submeridional or sublatitudinal. The initiation of the Baikal rift along the boundary between the Siberian platform and the Sayan—Baikal fold belt was likely associated with recurrent renewal of activity of a deep-seated energy source under East Siberia.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号