Aseismic negative dislocation model and deformation analysis of crustal horizontal movement during 1999——2001 in the northeast margin of Qinghai-Xizang block

Through numerical simulation for GPS data, aseism/c negative dislocation model for crustal horizontal movement during 1999-2001 in the northeast margin of Qinghai-Xizang block is presented, combined with the spatial distri-bution of apparent strain field in this area, the characteristics of motion and deformation of active blocks and their boundary faults, together with the place and intensity of strain accumulation are analyzed. It is shown that: a) 9 active blocks appeared totally clockwise motion from eastward by north to eastward by south. Obvious sinistral strike-slip and NE-NEE relative compressive motion between the blocks separated by Qilianshan-Haiyuan fault zone was discovered; b) 20 fault segments (most of them showed compression) locked the relative motion between blocks to varying degrees, among the total, the mid-east segment of Qilianshan fault (containing the place where it meets Riyueshan-Lajishan fault) and the place where it meets Haiyuan fault and Zhuanglanghe fault, more favored accumulation of strain. Moreover, the region where Riyueshan-Lajishan fault meets north boundary of Qaidam block may have strain accumulation to some degree, c) Obtained magnitude of block velocities and locking of their boundaries were less than relevant results for observation in the period of 1993-1999.     

Gravity variation before Kunlun mountain pass western Ms=8.1 earthquake

The relation between the gravity variation features and Ms=8.1 earthquake in Qinghai-Xizang monitoring area is analyzed preliminarily,by using spatial dynamic variation results of regional gravity field from absolute gravity and relative gravity observation in 1998 and 2000.The results show that:1)Ms\8.1 earthquake in Kulun mountain pass westem occurred in the gravity variation high gradient near gravity‘s high negative variation;2)The Main tectonic deformation and emnergy accumulation before MS=8.1 earthquake are distributed at south side of the epicenter;3)The range of gravity‘s high negative variation at east of the MS=8.1 earthquake epicenter relatively coincides with that rupture region according to field geology investigation;4)Gravity variation distribution in high negative value region is just consistent with the second shear strain‘s high value region of strain field obtained from GPS observation.     

CDP mapping in tilted transversely isotropic (TTI) media. Part I: Method and effectiveness

Transverse isotropy with a tilted axis of symmetry (TTI) causes image distortion if isotropic models are assumed during data processing. A simple anisotropic migration approach needs long computational times and is sensitive to the signal-to-noise ratio. This paper presents an efficient, general approach to common-depth-point (CDP) mapping to image the subsurface in TTI media from qP-wave seismic data by adding anisotropic and dip parameters to the velocity model. The method consists of three steps: (i) calculating traveltimes and positions of the CDP points; (ii) determining CDP trajectories; (iii) CDP imaging. A crucial step is the rapid computation of traveltimes and raypaths in the TTI media, which is achieved by the Fermat method, specially adapted for anisotropic layered media. The algorithm can image the subsurface of a given model quickly and accurately, and is suitable for application to a bending reflector. The effectiveness of the method is demonstrated by comparing the raypaths, the traveltimes and the results of CDP mapping, when assuming isotropic media, transversely isotropic media with a vertical axis of symmetry (TIV), and TTI media.     

Relationship between light rare earth deposits and mantle processes in Panxi rift,China

Many light rare earth deposits, such as Maoniuping, Dalucao, Panzhihua deposits, are collectively distributed in Panxi rift of Sichuan Province, China, and closely associated with the aegirine quartz syenite-carbonatite complex. Carbon and oxygen isotope studies demonstrate that the carbonatites in the complex are of typical igneous origin related to mantle processes. Electronic microprobe studies show that the fluid-melt inclusions found in the complex are enriched in light rare earth elements (LREE), which suggests that the magma was rich in LREE and could serve as the ore source for the regional LREE mineralization. Both the aegirine quartz syenite-carbonatite complex and the LREE mineralization found therein were derived from the mantle. The rare gas isotope analyses also support that there is a genetic association between the LREE mineralization and mantle processes.

     

路基施工沉降观测精度要求及数据处理

本文通过对路基施工沉降观测的精度分析,提出了路基施工沉降观测的精度要求；根据路基施工沉降观测的特点，提出了相应的观测措施及数据处理方法。     

基于关系数据库的邻接域处理

本文就跨图幅的地物(邻接域)的管理问题作了一些有益的探讨，为了达到有效管理这个目的，本文采用Oracle公司提供的空间数据插件Spatial将空间数据和属性数据存入Oracle数据库中，这样不仅可以通过标准SQL语句可下裁任意区域的数据，而且数据库还会自动维护数据的完整性。因此，用空间数据库的管理方式使邻接域问题就不存在了。     

高职GIS专业实践教学及实践基地建设

高职教育是GIS人才培养的重要组成部分。本文通过介绍职教GIS专业的建设，探索GIS实践教学与实践基地建设模式、方法及对人才培养的影响。     

Caledonian Low-Temperature Granulite-Facies Metamorphism in the West Kunlun Orogenic Belt—SHRIMP Chronological Evidence from Zircon

The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system. Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz. The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun Early Paleozoic. Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program “ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National Geological Surveying Bureau.     

Geology and Genesis of the Ta'ergou Skarn - Quartz Vein Tungsten Deposit in the North Qilian Caledonian Orogenic Belt, Northwest China

Abstract. The Ta'ergou tungsten deposit in Gansu province, northwestern China, is located in the western part of the North Qilian Caledonian orogen, and consists of scheelite skarn bodies and wolframite quartz veins. The tungsten‐bearing skarn developed by the replacement of carbonate layers intercalated in the Precambrian schist and amphibolite whereas wolframite‐quartz ore veins developed along a group of fractures that cut through horizontal skarns. The Ta'ergou tungsten deposit is genetically related to the Caledonian Yeniutan granodiorite intrusion and occurs ca. 500 m wide in the exo‐contact zone 300 ～ 500 m apart from the intrusion. The granodiorite displays a lower grade of differentiation, low content of SiO₂ and high contents of mafic components. There are three types of fluid inclusions in the wolframite‐quartz vein systems, i. e. aqueous, CO₂‐H₂O and CO₂‐rich. The homogenization temperature of aqueous inclusion ranges from 140 to 380d?C and their salinities from 6.4 to 17.4 equivalent wt% NaCl. Laser Raman spectroscopy shows that the inclusions contain a relatively high content of CO₂. The δ³⁴S values of skarn type sulfides range from +8.1 to +12.7 per mil and those of quartz vein sulfides from +9.3 to +14.9 per mil, similar to sulfides of the granodiorite with from +6.0 to +11.7 per mil. The δ¹⁸O values of quartz are between +10.5 and +13.3 per mil and those of wolframite between +3.4 and +5.1 per mil. The δ¹⁸O water values of ore forming fluids range from +0.6 to +6.4 per mil and suggest the mixture of magmatic fluids with meteoric water formed the ore‐forming fluids. It has been proved that Precambrian strata in the west sector of North Qilian region are enriched in tungsten. We propose the strata were remelted to be tungsten‐granitoid during subduction. The polymetallic tungsten was gradually accumulated into the roof pendants of the granite intrusion by fractional crystallization and then was deposited by hydrothermal fluids during metasomatism and infilling along fractures. On the other hand, the granite intrusion also acted as “heating machine” to make hydrothermal fluids leach out the metals from Precambrian strata and these metals joined the ore‐forming hydrothermal system.     

Cretaceous deformation history of the middle Tan-Lu fault zone in Shandong Province, eastern China

Based on field analysis of fault-slip data from different rock units of the Cretaceous basins along the middle part of the Tan-Lu fault zone (Shandong Province, eastern China), we document polyphase tectonic stress fields and address the changes in sense of motion of the Tan-Lu fault zone during the Cretaceous. The Cretaceous deformation history of the Tan-Lu fault zone can be divided into four main stages. The first stage, during the earliest Cretaceous, was dominated by N-S extension responsible for the formation of the Jiaolai basin. We interpret this extension to be related to dextral strike-slip pull-apart opening guided by the Tan-Lu fault zone. The second stage, during the middle Early Cretaceous, was overwhelmingly rift-dominated and characterized by widespread silicic to intermediate volcanism, normal faulting and basin subsidence. It was at this stage that the Tan-Lu-parallel Yi-Shu Rift was initiated by E-W to WNW-ESE extension. The tectonic regime then changed during the late Early Cretaceous to NW-SE-oriented transpression, causing inversion of the Early Cretaceous rift basin and sinistral slip along the Tan-Lu fault zone. During the Late Cretaceous, dextral activation of the Tan-Lu fault zone resulted in pull-apart opening of the Zhucheng basin, which was subsequently deformed by NE-SW compression. This deformation chronology of the Tan-Lu fault zone and the associated Cretaceous basins allow us to constrain the regional kinematic models as related to subduction along the eastern margin of Asia, or related to collision in the Tibet region.