城市轨道交通车站基坑事故统计分析

本文从工程风险的角度对所搜集的52例城市轨道交通车站基坑事故进行分析,归纳了6种事故类型,并明确指出"渗流破坏、支撑失稳、坑内滑坡"为最常见的三类事故。通过对各事故类型进行事故原因的统计分析,得知地下水的防治是关乎基坑工程安全的首要因素,不规范作业是基坑事故发生的第二诱因。     

Geological and geochemical characteristics of the Baogudi Carlin-type gold district (Southwest Guizhou,China) and their geological implications

The newly discovered Baogudi gold district is located in the southwestern Guizhou Province, China, where there are numerous Carlin-type gold deposits. To better understand the geological and geochemical characteristics of the Baogudi gold district, we carried out petrographic observations, elemental analyses, and fluid inclusion and isotopic composition studies. We also compared the results with those of typical Carlin-type gold deposits in southwestern Guizhou. Three mineralization stages, namely, the sedimentation diagenesis, hydrothermal (main-ore and late-ore substages), and supergene stages, were identified based on field and petrographic observations. The main-ore and late-ore stages correspond to Au and Sb mineralization, respectively, which are similar to typical Carlin-type mineralization. The mass transfer associated with alteration and mineralization shows that a significant amount of Au, As, Sb, Hg, Tl, Mo, and S were added to mineralized rocks during the main-ore stage. Remarkably, arsenic, Sb, and S were added to the mineralized rocks during the late-ore stage. Element migration indicates that the sulfidation process was responsible for ore formation. Four types of fluid inclusions were identified in ore-related quartz and fluorite. The main-ore stage fluids are characterized by an H₂O–NaCl–CO₂–CH₄ ± N₂ system, with medium to low temperatures (180–260 °C) and low salinity (0–9.08% NaCl equivalent). The late-ore stage fluids featured H₂O–NaCl ± CO₂ ± CH₄, with low temperature (120–200 °C) and low salinity (0–7.48% NaCl equivalent). The temperature, salinity, and CO₂ and CH₄ concentrations of ore-forming fluids decreased from the main-ore stage to the late-ore stage. The calculated δ¹³C, δD, and δ¹⁸O values of the ore-forming fluids range from − 14.3 to − 7.0‰, −76 to −55.7‰, and 4.5–15.0‰, respectively. Late-ore-stage stibnite had δ³⁴S values ranging from − 0.6 to 1.9‰. These stable isotopic compositions indicate that the ore-forming fluids originated mainly from deep magmatic hydrothermal fluids, with minor contributions from strata. Collectively, the Baogudi metallogenic district has geological and geochemical characteristics that are typical of Carlin-type gold deposits in southwest Guizhou. It is likely that the Baogudi gold district, together with other Carlin-type gold deposits in southwestern Guizhou, was formed in response to a single widespread metallogenic event.

     

Thermal and rheological structures of the Xisha Trough, South China Sea

The Xisha Trough, located in the northwest of the South China Sea (SCS) mainly rifted 30 Ma ago, has been a failed rift since the cessation of the seafloor spreading of the NW subbasin. Based on the velocity–depth model along Profile OBH-4 across the Xisha Trough, a seven-layer density–depth model is used to estimate density structure for the profile. The relationship between seismic velocity and radiogenic heat production is used to estimate the vertical distribution of heat sources in the lower crust. The 2-D temperature field is calculated by applying a 2-D numerical solution of the heat conduction equation and the thermal lithosphere thickness is obtained from the basalt dry solidus (BDS). The rheology of the profile is estimated on the basis of frictional failure in the brittle regime and power-law steady-state creep in the ductile regime. Rheological model is constructed for a three-layer model involving a granitic upper crust, a quartz diorite lower crust and an olivine upper mantle. Gravity modeling supports basically the velocity–depth model. The Moho along Profile OBH-4 is of relatively high heat flow ranging from 46 to 60 mW/m² and the Moho heat flow is higher in the trough than on the flanks. The depth of the “thermal” lithospheric lower boundary is about 54 km in the center, deepens toward two sides, and is about 75 km at the northern slope area and about 70 km at the southern Xisha–Zhongsha Block. Rheological calculation indicates that the two thinnest ductile layers in the crust and the thickest brittle layer in the uppermost mantle lie in the central region, showing that the Xisha Trough has been rheologically strengthened, which are mainly due to later thermal relaxation. In addition, the strengthening in rheology during rifting was not the main factor in hampering the breakup of the Xisha Trough.     

五台山西部狐狸山含金韧性剪切带的地球化学研究

狐狸山金矿区，在无蚀变作用参与的韧性变形过程中，岩石化学成分发生了明显的变化。但大多数微量元素含量变化不大，稀土元素配分模式基本不变，它们可以反映原岩的特点。蚀变糜棱岩型矿体与围岩相比，稀土配分模式、亲硫元素Ａｕ、Ａｇ、Ｃｕ和两性元素Ａｓ、Ｓｂ含量差别显著，尤其是Ａｕ含量，前者是后者的百倍～几万倍，金的成矿作用主要与韧性变形后期富金流体的蚀变作用关系密切。     

辽宁榴辉岩包体的石榴石中金云母出溶片晶的发现

在辽宁复县50号金伯利岩岩筒中,发现了罕见的榴辉岩包体,在该包体的主要组成矿物石榴石中发现了金云母出溶片晶。通过显微镜、透射电镜及其能谱观察分析测定与研究,确认该片晶为金云母。金云母无色,断面呈针状,一般宽0.5—5μm,长10—100μm;但宽0.05—0.1μm,长1—2μm的细小片晶也较发育。金云母片晶沿石榴石[111]晶带大致呈夹角为60°—70°的三组定向排列,表明它是由于榴辉岩从地幔深处上升到较浅部时释压作用从石榴石中出溶的产物。世界各地金伯利岩中榴辉岩包体的石榴石、辉石中微小针状出溶矿物(或包裹体)普遍存在,据文献报道,已经鉴定的出溶物有辉石和金红石。迄今为止,金云母出溶片晶的发现尚属首次。     

Landslide susceptibility mapping based on GIS and information value model for the Chencang District of Baoji,China

The main objective of this study was to apply a statistical (information value) model using geographic information system (GIS) to the Chencang District of Baoji, China. Landslide locations within the study area were identified using reports and aerial photographs, and a field survey. A total of 120 landslides were mapped, of which 84 (70 %) were randomly selected for building the landslide susceptibility model. The remaining 36 (30 %) were used for model validation. We considered a total of 10 potential factors that predispose an area to a landslide for the landslide susceptibility mapping. These included slope degree, altitude, slope aspect, plan curvature, geomorphology, distance from faults, lithology, land use, mean annual rainfall, and peak ground acceleration. Following an analysis of these factors, a landslide susceptibility map was produced using the information value model with GIS. The resulting landslide susceptibility index was divided into five classes (very high, high, moderate, low, and very low) using the natural breaks method. The corresponding distribution area percentages were 29.22, 25.14, 15.66, 15.60, and 14.38 %, respectively. Finally, landslide locations were used to validate the results of the landslide susceptibility map using areas under the curve (AUC). The AUC plot showed that the susceptibility map had a success rate of 81.79 % and a prediction accuracy of 82.95 %. Based on the results of the AUC evaluation, the landslide susceptibility map produced using the information value model exhibited good performance.     

Dating of multi-period earthquake-triggered rockfalls: a method for revealing paleo-seismic events that occurred along the Yushu fault in the eastern Tibetan Plateau

Landslides - The quantitative study of earthquake-triggered rockfall debris along seismogenic fault zones has proven to be a valid approach for use in identifying paleo-earthquakes and faulting...