浅谈山区构造物地基基础不均匀沉降问题

针对山区构造物地基基础不均匀沉降问题的重要性,通过比较山区和平原地区建造地基的区别,提出了山区建造地基的特点,详细地介绍了山区构造物地基基础不均匀沉降的处理问题,从而保障山区构造物的安全。

高精度三维地震勘探在八宝矿区的应用

以八宝矿区为例,针对山区存在的复杂浅表层地震地质条件,进行了高精度三维地震勘探,取得了准确率较高的成果。以往山区三维地震勘探漏掉解释小型构造和构造偏移较大的现象有了很大的改善,所以在山区地形高差大、浅表层地震条件复杂、深层地震条件一般、南部地层反转等特点下,开展高精度三维地震勘探具有重要的意义。

THE THRUST AND NAPPE TECTONIC ZONE ALONG THE SOUTHERN MARGIN OF THE COAL-FORMING REGION OF NORTH CHINA

A thrust and nappe tectonic zone with imbricate branch thrusts is developed along the southern margin of the coal-forming region of North China. This tectonic zone is tightly related to the Qinling-Dabie collision orogen in genesis and belongs to the frontal zone of a huge thrust system developed during Yanshanian episode at the northern foot of the orogen. It is pointed out that thrusting had distorted the original depositional margin of the coal-forming region and some new coal-bearing blocks would be found out in the frontal sheets and under the undulate sole thrust.

Study on deep structure in Ailaoshan region based on aeromagnetic interpretations

Linear and circular interpretation structure maps of different relative depths are obtained by processing 1:200000 aeromagnetic data to the pole in Ailaoshan region,interpreting upward extension of 4 heights,extracting a vertical second derivative line of 0 value and a series of calculations. Concealed boundary of deep magnetic rocks can be delineated according to the maps. On the basis of the conclusions above,a set of economical and practical methods to graph the deep structure are summarized. In addition,the relationship between deep structure and mineralization positions is discussed.

FORMATION AND EVOLUTION OF THE CENOZOIC THRUST FOLD BELT IN JINPING, SICHUAN

The Jinping orogenic belt in Sichuan, China consists mainly of the Jinpingshan intracontinental thrust-nappe belt, foreland thrust-nappe belt and foreland uplift belt. Based on analyses about the characteristics of the structural units in this area, the authors propose in this paper that Chapuzi-Bazhe revival fault belt is the regional boundary fault, and points out that after the formation of the Pre-Sinian basement, the western edge of the Yangtze paraplatform was turned into the passive continental margin in Sinian to Triassic, then into the Mesozoic collision orogenic belt, and finally into the Cenozoic orogenic belt through intracontinental orogeny.

Research on the Seismotectonic Zones and Seismicity State in the Southern Xinjiang Region

Based on the studies of earthquake activity, tectonic movement, crustal shortening rate, fault activity, local stress field and historical characteristics of strong earthquake activities in Xinjiang, we divide the south part of Xinjiang into 4 seismotectonic zones, namely, the eastern segment of south Tianshan seismic belt, the Kalpin block, the Kashi-Wuqia junction zone, and the west Kunlun Mountains seismic belt. Using earthquake catalogues from Xinjiang since 1900, and on the basis of integrity analysis of earthquake records in different magnitude ranges, the seismicity state of different seismotectonic zones is analyzed quantificationaUy by calculating the mean value of annual strain energy release, annual rate of earthquakes with different lower limits of magnitude, b-value, and the parameter m of accelerating strain release model. The characteristic indexes of seismicity state for each of the seismic tectonic zones are then determined, which provide a quantitative basis for earthquake tendency analysis and judgment.

Geological division of gas in the Pingdingshan mine area based on its tectonic dynamics characteristics

In this paper,we used tectonic dynamics theories to study the tectonic evolution characteristics of the Pingdingshan mine area,and analyzed the impact of tectonic progressive control on gas occurrence.The study results are as follows:the Pingdingshan mine area has been mainly controlled by multiple squeezing and shearing actions of the Qinling orogenic belt since early and middle Yanshan,forming the tectonic control characteristics of master control in two directions,namely NWW trending and NNE trending;the NWW trending structure is dominated by squeezing and shearing,while the NNE trending structure is dominated by tension.Progressively controlled by the structure,the gas occurrence presents partition and zonation,i.e.compared with the western structure,the eastern NWW-NW trending structure of the mine area is more highly developed,resulting in the mine area gas occurrence distribution characteristics are distinct in the east while indistinct in the west.Based on this,the mine area can be divided into the following two geological dynamic areas:the western half of mine area,namely the Guodishan fault control area,where the NW-SE trending synchronous tension action suffered by the northeast side(footwall) is relatively strong,and compared with the southwest side(hanging wall),its coal and gas outburst seriousness is weak;and the eastern half of mine area,namely the NWW-NW thrust nappe fracture fold control area,which is a serious area of coal and gas outburst,in particular the axial area of the Likou syncline is the intersection compound and combination position of the NW and NE trending structures,a tectonic concentrated area,and the gas pressure and content here are the largest.

The Focal Mechanism Solutions of the M_S 8.0 Wenchuan Earthquake in Sichuan on May 12,2008 and Some of Its Aftershocks

The focal mechanism solutions of the Wenchuan earthquake （Ms8.0） of May 12, 2008 and some of its aftershocks occurring up to December I0, 2008 are determined with lower semisphere of equal-projection and first motion sign data of P waves from regional and distant stations. The focal mechanism solutions of the Ms8.0 Wenchuan earthquake are： Nodal plane I：strike 5°, dip angle 48°, slip angle 39°; Nodal plane II： strike 247°, dip angle 62°, slip angle 131°; P axis azimuth 309°, plunge 8°, T axis azimuth 208°, plunge 54°, B axis azimuth 44°, plunge 35% Combining geological tectonics and spatial distribution of aftershocks, nodal plane II can be identified as a seismogenic fault. According to focal mechanism solutions, the fault activity that triggered the huge earthquake is reverse thrusting. The main rupture surface is S67°W, basically identical to the fault strike on which the earthquake occurred. The main compression stress P axis is N51°W, which is basically the same as the direction of the regional tectonic stress field. According to the results of focal mechanism solutions of aftershocks, the aftershocks occurring in the southern and northern sections of the Longmenshan fault zone have predominant orientations and are obviously different. For the main shock and the early aftershocks occurring on the southern section of the Longmenshan fault, the rupturing is mainly characterized by reverse-dip slip with some strike-slip, and over time, the aftershocks migrated towards the northern section. The rupturing in the source is mainly characterized by strike-slip with some reverse-dip slips. The stress field is controlled by the main shock stress field in the southern section of the Longmenshan tectonic zone, while it is controlled by the main shock stress field and regional stress field in the northern section of the Longmenshan tectonic zone.

Anatomy of composition and nature of plate convergence： Insights for alternative thoughts for terminal India-Eurasia collision

The pattern and timing of collision between India and Eurasia have long been a major concern of the international community. However, no consensus has been reached hitherto. To explore and resolve the disagreements in the Himalayan study,in this paper we begin with the methodology and basic principles for the anatomy of composition and nature of convergent margins,then followed by an effort to conduct a similar anatomy for the India-Eurasia collision. One of the most common patterns of plate convergence involves a passive continental margin, an active continental margin and intra-oceanic basins together with accreted terranes in between. The ultimate configuration and location of the terminal suture zone are controlled by the basal surface of the accretionary wedge, which may show fairly complex morphology with Z-shape and fluctuant geometry. One plausible method to determine the terminal suture zone is to dissect the compositions and structures of active continental margins. It requires a focus on various tectonic elements belonging to the upper plate, such as accretionary wedges, high-pressure(HP)-ultra-high-pressure(UHP) metamorphic rocks, Barrovian-type metamorphic rocks and basement nappes, together with superimposed forearc basins.Such geological records can define the extreme limits and the intervening surface separating active margin from the passive one,thus offering a general sketch for the surface trace of the terminal suture zone often with a cryptic feature. Furthermore, the occurrence of the cryptic suture zone in depth may be constrained by geophysical data, which, in combination with outcrop studies of HP-UHP metamorphic rocks, enables us to outline the terminal suture zone. The southern part of the Himalayan orogen records complicated temporal and spatial features, which are hard to be fully explained by the classic "two-plate-one-ocean" template,therefore re-anatomy of the compositions and nature for this region is necessitated. Taking advantage of the methodology and basic principles of plate convergence anatomy and synthesizing previous studies together with our recent research, we may gain new insights into the evolution of the Himalayan orogeny.(1) The Yarlung-Zangbo ophiolite is composed of multiple tectonic units rather than a single terminal suture zone, and a group of different tectonic units were juxtaposed against each other in the backstop of the Gangdese forearc.(2) The Tethyan Himalayan Sequence(THS) contains mélanges with typical block-in-matrix structures, uniform southwards paleocurrents and age spectra of detrital zircons typical of Eurasia continent. All of these facts indicate that the THS belonged to Eurasia plate before the terminal collision, emplaced in the forearc of the Gangdese arc.(3) The Greater Himalayan Crystalline Complex(GHC) and Lesser Himalayan Sequence(LHS) comprise complex components including eclogites emplaced into the GHC and the upper part of the LHS. Judging from the fact that HP-UHP metamorphic rocks are exhumed and emplaced in the upper plate, the GHC and the upper part of the LHS where eclogite occur should be assigned to the upper plate, lying above the terminal subduction zone surface. It is the very surface along which the continuous subduction of the India subcontinent occurred, therefore acting as the terminal, cryptic suture. From the suture further southward, the bulk rock associations of the LHS and Sub-Himalayan Sequence(Siwalik) show little affinity of mélange, probably belonging to the foreland system of the India plate. By the anatomy of tectonic features of all the tectonic units in the Himalayan orogen as well as the ages of the subduction-accretion related deformation, we conclude that the terminal India-Eurasia collision occurred after 14 Ma, the timing of the metamorphism of the eclogites emplaced into the upper plate. The development of rifts stretching in N-S direction in Tibet and tectonic events with the transition from sinistral to dextral movements in shear zones, such as the Ailaoshan fault in East Tibet, can coordinately reflect the scale and geodynamic influence of the India-Eurasia convergence zone.By conducting a detailed anatomy of the southern Himalayas, we propose a new model for the final collision-accretion of the Himalayan orogeny. Our study indicates that the anatomy of structures, composition, and tectonic nature is the key to a better understanding of orogenic belts, which may apply to all the orogenic belts around the world. We also point out that several important issues regarding the detailed anatomy of the structures, compositions and tectonic nature of the Himalayan orogeny in future.

Spatio-temporal framework of tectonic uplift stages of the Tibetan Plateau in Cenozoic

Four intensive uplift periods, i.e., 60–35, 25–17 and 12–8 Ma (but 18–13 Ma in the Himalayas of the southern Tibet), and since about 5 Ma, can be determined on the Tibetan Plateau by synthetical analysis of low-temperature thermo-chronology data, sedimentary deposit records, and structural deformation records of different areas. The strong tectonic uplift periods in different areas on the Tibetan Plateau are penecontemporaneous, except for the Himalayan area of the southern Tibet, where a rapid uplift and exhumation period, controlled by the activity of the South Tibetan Detachment System faults, occurred during 18–13 Ma. These strong uplift and exhumation periods correspond well to intensive deformation activity periods, suggesting tectonically-controlled uplift and exhumation. The deposit records, such as the distribution of coarse clastic sediments, the distribution of tectonically-controlled basins, stratigraphic discontinuousness or unconformity, and fault-controlled geomorphologic evolution, also match well with the strong uplift and exhumation periods. Expanding processes of the plateau are also discussed.