平面应变下原状黄土的剪切带研究

针对黄土地区工程建设中的平面应变问题,使用改进的西安理工大学真三轴仪进行了不同侧向固结压力、不同含水率下原状黄土的平面应变剪切试验,得出了剪切破坏时剪切带倾角试验值,根据应力-应变关系曲线求出了剪切带倾角的Mohr-Coulomb、Roscoe理论解,分析了相应控制因素下原状黄土强度、剪切带破坏模式与倾角的变化。结果表明：应力-应变曲线随含水率、侧向固结压力的增大从原生软化型向次生硬化型转变;剪切带破坏模式随侧向固结压力的增大依次呈现单一剪切带、锥型剪切带和X型剪切带;随着含水率的增大,黏聚力、内摩擦角减小导致Mohr-Coulomb剪切带倾角减小,剪胀作用增强导致Roscoe剪切带倾角增大;随侧向固结压力增大,动内摩擦角增大及剪胀作用增强,导致Mohr-Coulomb、Roscoe剪切带倾角增大。     

Electron Probe Microanalysis of Variable Oxidation State Oxides: Protocol and Pitfalls

Electron probe microanalysis of geological oxide materials relies on stoichiometric considerations to estimate the content of undetermined oxygen and thus calculate ZAF (atomic number, absorption, fluorescence) matrix correction factors, requiring the valences of cations in the corresponding software to be unambiguously defined. However, stoichiometric ZAF corrections may be problematic in the presence of other undetermined elements or variable valence state cations. Herein, we analyse several oxides containing such cations, that is magnetite (Fe₃O₄), haematite (Fe₂O₃), hausmannite (Mn₃O₄) and cuprite (Cu₂O). We compare data re‐calculated for incorrect valence states ( Method 1 ) with reference values, revealing incorrect results, due to an incorrect amount of oxygen used in the matrix correction. Some solid‐solution series of haematite and magnetite were also modelled in CalcZAF program to prove the relative errors when the incorrect oxygen is used. To resolve these issues, we describe two accurate methods. Method 2 uses the true valence states of analysed elements. In Method 3, all cations are analysed as metals, with the content of undetermined oxygen determined by difference. As EPMA software does not allow the use of non‐integer valences, Method 3 is applicable to cations with non‐integer or dubious valences in cases where these non‐integer valences cannot be defined.     

The Clock gene clone and its circadian rhythms in Pelteobagrus vachelli

The Clock gene,a key molecule in circadian systems,is widely distributed in the animal kingdom. We isolated a 936-bp partial c DNA sequence of the C lock gene( Pva- clock) from the darkbarbel catfish P elteobagrus vachelli that exhibited high identity with C lock genes of other species of fish and animals(65%–88%). The putative domains included a basic helix-loop-helix(b HLH) domain and two period-ARNT-single-minded(PAS) domains,which were also similar to those in other species of fish and animals. P va- Clock was primarily expressed in the brain,and was detected in all of the peripheral tissues sampled. Additionally,the pattern of P va- Clock expression over a 24-h period exhibited a circadian rhythm in the brain,liver and intestine,with the acrophase at zeitgeber time 21:35,23:00,and 23:23,respectively. Our results provide insight into the function of the molecular C lock of P. vachelli.     

湘西大脑坡铅锌矿床地质特征及成因分析

总结大脑坡铅锌矿床地质特征,对矿床微量元素、稀土元素地球化学特征进行了分析。从矿化产出形式、矿物共生组合和矿石组构、围岩蚀变、成矿方式及成矿物质来源等方面探讨矿床成因,综合分析认为矿床形成晚于围岩,属于层控型浅成低温热液型矿床,与MVT矿床相似。     

Monitoring the Grassland Change in the Qinghai-Tibetan Plateau: A Case Study on Aba County

Located on the southeast edge of the Qinghai-Tibetan plateau, Aba County is the core area of the Returning Grazing Land to Grassland Project (RGLGP) on the plateau. For the purpose of monitoring the grassland change before and after the grassland protection project in Aba County, Landsat images acquired in 1996, 2003 and 2009 were analyzed. Using Spectral Mixture Analysis (SMA) model, sub-pixel fractions of land cover components were obtained: bright vegetation (BV), dark vegetation (DV), bright soil (BS), dark soil (DS) and water. Fraction images present the distribution and proportions of typical land cover components in this study. Fractions BV and BS were chosen as two indicators for grassland degradation. Thereafter, Change Vector Analysis (CVA) model was applied on the two indicators. After the performance of the CVA model, change results which consisted of both grassland degradation and vegetation re-growth were obtained, showing the change patterns of grassland degradation and vegetation re-growing in Aba County between two gaps: from 1996 to 2003 (before the RGLGP) and from 2003 to 2009 (after the RGLGP). The change patterns of grassland degradation and vegetation re-growing can effectively assist in the development of environmental restoration measures and in the RGLGP plans for the Qinghai-Tibetan plateau.     

Contributions of trans-magmatic fluid in the formation of porphyry copper deposits: A case study from the Baoshan deposit,South China

The classical mechanism “source-transport-storage” of the formation of porphyry copper deposit has been advanced in recent studies, as the “source” is not the main factor for the mineralization in some Cu deposits, and the metallogeny may be affected by other variables factors during the magma-fluid transportation or storage. We recommend the essential role of trans-magmatic fluid in the ore-forming process, this fluid is released from the melting of the sedimentary overlying the subducted plate with high water and volatiles concentrations and high oxygen fugacity. The Baoshan granodioritic cryptoexplosion breccia representing the influence of hydrothermal events as well as the unaltered Baoshan granodiorite porphyry are conducted by LA-MC-ICP-MS analysis, to identify the contribution of trans-magmatic fluid. In case of the ε_Nd(t) of whole rock do not increase with the MgO increasing and SiO₂ decreasing, the large variations of zircons ε_Hf(t) values in Baoshan granodiorite porphyry (BGP, ?14.24 to ?6.38) and Baoshan granodioritic crypto-explosion breccia (BGCB, ?25.24 to ?6.62) were considered to be the interaction of partial melting of ancient mafic lower crust and Neoproterozoic juvenile crust. However, the copper mineralization requires high oxygen fugacity and a large amount of water, according to the tectonic settings of Baoshan, we recommend that it is the trans-magmatic fluid trapping and concentrating Cu from the whole pluton during the upwelling driven by magma convection. The initial magma was stalled by the ductile-brittle transition at shallow depths of upper-crust. The trans-magmatic fluid leads to the pressure increases at the top of the initial magma, then the overlying rock is ruptured and cryptoexplosion produced. Moreover, after the cryptoexplosion, the sudden reduction of circumference temperature and pressure leads to the decrease in the oxygen fugacity of the ore-forming system, which will change the valence state of sulfur from S⁶⁺ to S^2?. Finally, sulfur precipitates with chalcophile elements like copper in the metallogenic system and forms porphyry copper deposits with the low Sr/Y ratio. This study highlights the use of trans-magmatic fluid and ductile-brittle transition in the formation of the Baoshan porphyry copper deposits.     

南海北部白垩纪—渐新世早期沉积环境演变及构造控制*

南海北部珠江口—琼东南盆地白垩系—下渐新统记录了华南大陆边缘从主动陆缘向被动陆缘的转换过程。基于盆地构造-地层、单井相、地震相等特征的综合分析,结合南海中南部的沉积环境和区域构造演化,探讨南海北部白垩纪—渐新世早期的沉积环境演变及构造控制背景。研究发现: (1)南海北部白垩系广泛分布,古新统分布极为有限; 始新世早-中期,琼东南盆地只在部分凹陷深部发育了小规模的滨浅湖相和扇三角洲相沉积,珠江口盆地白云凹陷以大规模发育的湖泊相为特征; 始新世晚期—渐新世早期,琼东南盆地和珠江口盆地白云凹陷都受到海侵作用的影响,以海岸平原相和滨浅海相为主。 (2)构造演变包括5期:包括白垩纪安第斯型大陆边缘的“弧—盆”体系发育期,古新世区域隆升剥蚀山间盆地发育期,始新世早-中期裂陷发育,始新世晚期—渐新世早期陆缘破裂期,渐新世晚期东部海盆稳定扩张期。最后,探讨了南海盆地中生代末/新生代初的动力学转换过程及特征。     

Numerical study on the dynamic behavior of rock avalanche: influence of cluster shape,size and gradation

Acta Geotechnica - In this paper, we present a numerical study of dynamic behavior of rock avalanche by using three-dimensional particle flow simulation. The emphasis is put on the influence of...