北京昌平高崖口-南口隐伏岩溶水系统地质构造新认识

高崖口-南口岩溶水系统是北京七大岩溶水系统之一,其东北部位于昌平南口,是隐伏岩溶地下水排泄区。查明该区地质构造发育情况,可以为评价岩溶水资源及北京优选战略后备水源地提供依据。本文在分析前人区域性重磁资料基础上,完成了5条总长30 km、总测点数626个的可控源音频大地电磁测深(CSAMT)剖面,采用SCS2D程序对CSAMT数据进行了二维反演解释,并实施了4眼勘探孔。物探和钻探研究结果表明:南口-孙河断裂是该系统的北东边界,走向北西,倾向南西,在雪山村附近断层落差达1017.5 m,是目前发现的断距最大的地区;断裂上盘蓟县系碳酸盐岩与侏罗系火山岩的地层界线,向西移动了2.4 km;南口山前断裂是山区裸露岩溶与平原隐伏岩溶的分界断裂,断裂走向北东,倾向南东,断距大于700 m,断裂上盘曹庄至南口一带有燕山期二长岩侵入,流村-葛村一带有燕山期闪长岩侵入。广泛发育的断层、岩体和火山岩,使这一区域岩溶含水层空间受到较大制约。     

春季欧亚-北太平洋上空大气质量迁移规律及其对中国同期气候异常的可能影响

利用1979～2013年NCEP/NCAR月平均再分析资料及NOAA研究中心的CMAP（CPC Merged Analysis of Precipitation）月平均降水资料,通过定义欧亚—北太平洋间大气质量迁移指数I_MAMEP,分析了春季欧亚—北太平洋上空大气质量迁移（MAMEP,Migration of Atmospheric Mass over Regions between Eurasia and North Pacific）的年际变化规律及其与同期中国气候异常的联系。结果表明:在北半球中高纬度存在一个纬向分布的欧亚—北太平洋遥相关型,且其可能对中国同期气候异常的形成具有重要影响。春季MAMEP指数具有显著的长期趋势,同时还具有2～4年及5～7年的振荡周期及明显的年代际变化特征。垂直环流和波动运动对欧亚—北太平洋间大气质量迁移具有重要作用。大气质量在欧亚西部低层异常辐合,高层异常辐散,在中、西太平洋地区低层异常辐散,高层异常辐合,在纬向上构成了顺时针的垂直环流圈,将西北太平洋地区的大气质量变动与欧亚大陆上空的变动联系了起来。另外,来自西欧大陆的波扰能量可传播至北太平洋,有利于这些区域上空位势高度异常扰动的维持。I_MAMEP与春季同期降水及地表气温异常关系密切。I_MAMEP为正时,东亚以北地区、鄂霍次克海西岸以及西欧沿岸降水显著减少,欧亚西部及我国华北地区降水显著增加。850 hPa上西伯利亚受反气旋式环流控制,太平洋上空受气旋式环流控制,引起欧亚大陆北部地表显著增温,西伯利亚以东、我国东北、华北—江淮地区及韩国、日本南部地表显著降温。西欧—我国西北部分地区大面积显著降温现象与这两个地区受异常反气旋东侧的偏北气流影响有关。这些结果有利于人们更深刻认识区域春季气候异常形成机理。     

Effects of pre-existing discontinuities on the residual strength of rock mass – Insight from a discrete element method simulation

When rock failure is unavoidable, the designer of engineering structures must know and account for the residual strength of the rock mass. This is particularly relevant in underground coal mine openings. Pre-existing discontinuities play an important role in the mechanical behavior of rock masses and thus it is important to understand the effects of such pre-existing discontinuities on the residual strength. For this purpose, the present study demonstrates a numerical analysis using a discrete element method simulation. The numerical results indicate that fracture intensity has no significant influence on the residual strength of jointed rock masses, independent of confining conditions. As confining pressures increase, both peak and residual strengths increase, with residual strength increasing at a faster rate. The finding was further demonstrated by analyzing documented laboratory compressive test data from a variety of rocks along with field data from coal pillars. A comprehensive interpretation of the finding was conducted using a cohesion-weakening-friction-strengthening (CWFS) model. The effect of rock bolts on rock mass strength was also evaluated by using a discrete element method model which suggested that rock bolts can significantly increases residual strength but have limited effect on increasing the peak strength of rock masses.     

Dinosaur eggshell assemblage from Japan reveals unknown diversity of small theropods

The Lower Cretaceous (Albian) Sasayama Group in the Hyogo Prefecture of southwestern Japan has yielded various vertebrate fossils, including skeletal remains of dinosaurs, anurans, lizards, and mammals, and recently eggshell fragments. Here we report on numerous fossil eggshells from the bone-bearing Kamitaki locality in Tamba City, which represents a diverse dinosaur eggshell assemblage. Of the more than 90 eggshell fragments recovered, five different types were identified, including eggshells that likely belong to a variety of theropods (Nipponoolithus ramosus oogen. et oosp. nov., Elongatoolithus sp., Prismatoolithus sp., and Prismatoolithidae indet.) and at least one ornithopod (Spheroolithus sp.). All eggshells are relatively thin, and a new derived estimation method correlating egg mass with eggshell thickness indicates that they are among the smallest (28–135 g) theropod eggs known, likely laid by small bodied forms. The eggshell assemblage from this locality suggests that a diverse small dinosaur fauna, consisting primarily of theropods, nested in the region, a diversity yet to be evidenced from skeletal remains in Japan.     

Calcium Isotopic Fractionation during Ion‐Exchange Column Chemistry and Thermal Ionisation Mass Spectrometry (TIMS) Determination

Significant isotopic fractionation can occur during column chemistry and determination by mass spectrometry. Improper correction may produce uncertainties in the isotopic composition of geological samples. We investigated calcium isotopic fractionation during these two processes and set up a model to check data quality. The δ^44/40Ca_915a value of IAPSO seawater in different Ca cuts (e.g., 0–20, 20–40, 40–60, 60–80 and 80–100%) on column chemistry ranged from ~ 4‰ to 0‰. The more Ca was eluted, the lower the δ^44/40Ca_915a value of the elution was found. The isotopic fractionation of calcium on the column appeared to follow the exponential law. However, TIMS instrumental fractionation during Ca runs did not always follow the exponential law due to mixing effects from sample reservoirs on the filament. Our results show that errors could be caused if the instrumental fractionation deviates from the exponential law, especially when the fractionation degree is large. To improve the measurement uncertainty, a model is proposed to check the behaviour and degree of instrumental fractionation, which will provide a quick and reasonable verdict on the data quality of TIMS runs.     

Elimination of Interferences in the Determination of Palladium,Platinum and Rhodium Mass Fractions in Moss Samples using ICP‐MS/MS

Moss samples (Pleurozium schreberi) exposed to traffic‐related emission of Pd, Pt and Rh were analysed in this study. Successful elimination of interferences was achieved in the determination of Pd, Pt and Rh mass fractions in these samples using inductively coupled plasma‐tandem mass spectrometry (ICP‐MS/MS). Based on the results, a reliable determination of Pd, Pt and Rh mass fractions in microwave‐digested moss samples was obtained using ammonia (10% NH₃ in He) in the collision/reaction cell when ¹⁰³Rh was measured either on‐mass (103→103) or with mass‐shift (103→171) and mass‐shifts for ¹⁰⁸Pd (108→159) and ¹⁹⁵Pt (195→229) were used. The ICP‐MS/MS procedure was validated using BCR‐723 (road dust) as a reference material. In addition, a good agreement between the ICP‐MS/MS results and the results obtained with cloud point extraction and quadrupole ICP‐MS was observed for the moss samples.     

Research Progress of Leaf-wax Hydrogen Isotope Paleoaltimetry

Leaf waxes/lipids which are derived from terrestrial higher plants are ubiquitous in fluvial, lake, and marine sediments. N-alkanes are an important component of leaf waxes. Modern leaf wax n-alkanes from terrestrial higher plants are characterized with long chains with 27 to 33 carbon atoms (nC₂₇-nC₃₁) and high carbon preference index (CPI) values (>5). The hydrogen isotopes in n-alkanes are determined by meteoric water compositions, which makes them a potential proxy in paleoaltimetry studies. The lapse rates at which n-alkane hydrogen isotopes in modern soils change with altitude vary in different areas, implying that local calibration has to be conducted. The enrichment due to evapotranspiration and difference in fractionation during biosynthesis also influence n-alkane hydrogen isotopes values. When using long-chain n-alkanes to reconstruct paleoaltitude, many factors such as paleoclimate, paleolatitude and paleobotany should be considered.     

湖南产铀花岗岩体的某些特征

湖南产铀花岗岩体主要分布在湘南和湘东南地区,属扬子板块南缘至华夏板块湘东南加里东褶皱区,主要有诸广山、九嶷山、苗儿山等产铀岩体,岩体是由志留、三叠纪、侏罗―白垩纪岩浆侵入体构成的大型复式花岗岩体,花岗岩具有富碱、富钾和铁镁成分较高的特征,原始铀含量高,铀钍分异明显,铀趋向侏罗纪补体富集,在较晚期次侵入体的内外接触带是铀成矿有利空间。     

滇西象达地区蚌渺岩体地球化学特征及其构造意义

蚌渺花岗岩体出露于保山微地块与腾冲微地块之间的泸水―潞西海槽内;该海槽是古生代地史时期保山微地块西侧的一个半深水沉积盆地,随着中三叠世时期古特提斯主洋盆的关闭及弧-陆碰撞作用,该海槽内的岩层普遍发生褶皱、断裂及不同程度的变质作用;在三台山一带还发育有蛇绿混杂岩。蚌渺岩体的主量元素显示了堇青石过铝花岗岩(CPG)的特点,稀土及微量元素资料表明其属典型的高Sr低Yb花岗岩类,具有类似于埃达克岩的地球化学特征。蚌渺岩体形成于中侏罗世,是三叠纪碰撞造山作用结束之后陆内应力松弛阶段的岩浆活动,属后碰撞花岗岩。可能涉及俯冲板片或造山带山根在榴辉岩相温-压条件下的部分熔融作用,是造山运动加厚的地壳向正常地壳恢复的重要机制;也是滇西地区晚中生代大规模中酸性岩浆活动及相关成矿作用的前奏。     

岩石矿物中锆的测定方法研究

测定岩石类样品中的Zr含量,酸溶经常结果偏低,碱溶通常较难获得较低的检出限。本文选取了不同岩性的岩石类国家标准物质GBW07104、GBW07106、GBW07107、GBW07114、GBW07835、GBW07836、GBW07837作为实验样品,分别采用酸溶后复溶、Na2O2碱熔、赶硅后Na2CO3和Na2B4O7三种前处理方法,对电感耦合等离子体质谱仪进行参数优化后上机测定,结果表明:对样品赶硅后加入少量Na2CO3和Na2B4O7混合试剂高温熔融处理岩石样品后,锆的测量值准确度高,而且获得了最低的检出限,同时缩短了方法流程,操作快捷。该方法更适用于各类岩石样品锆的测定。