Palaeozoic tectonics of the south-western Chinese Tianshan: new insights from a structural study of the high-pressure/low-temperature metamorphic belt

The south-western Chinese Tianshan orogenic belt is famous for its omphacite-bearing blueschists and associated eclogite-facies metavolcanic rocks. Although numerous petrologic, geochemical and geochronological studies are available, structural data and interpretations are still rare. This paper provides new structural data, including bulk geometry of structures and kinematic analyses, based on field and laboratory studies along the Akyazhi, Keburt and Muzaert Rivers. The study area is divided into three tectonic units, namely (1) a Southern Unit composed of weakly metamorphosed sedimentary rocks of Silurian age; (2) a Central HP/LT Unit composed of blueschist-eclogite-facies metamorphic rocks derived from basalts, pelites and volcaniclastic rocks; (3) a Northern Unit, which consists of a Carboniferous magmatic arc developed upon an amphibolite-facies metamorphic continental basement. Our structural analysis documents a polyphase deformation. The main event (D₁) is reflected by Devonian to Carboniferous top-to-the northwest ductile shearing, coeval with HP/LT metamorphism. This is followed by north-directed thrusting (D₂) of the Southern Unit over the Central HP/LT Unit, coeval with retrogression of the high-pressure rocks. A top-to-the-S (SE) deformation (D₃) overprints the earliest events and is observed in the Northern and Central Units. Lastly, Permian dextral ductile-brittle wrenching (D₄) overprints the older flat-lying fabrics. D₄ is conspicuous along the Nalati Fault that separates the Northern Unit from the Central HP/LT Unit. The absolute timing of these deformation events is discussed in the light of available radiometric dating. The structural, metamorphic and geochronological data are integrated into a geodynamic model of the south-western Chinese Tianshan that emphasizes south-directed subduction of microcontinents located between Tarim and Junggar.     

Influence of shear velocity on frictional characteristics of rock surface

Understanding the fundamental issues related with the effect of shear velocity on frictional characteristics at the interface of rock surfaces is an important issue. In this paper, strain-rate dependence on friction is investigated in relation to sliding behaviour under normal load. The phenomenon of stick-slip of granite and shaly sandstone with a tribometer at constant rate of strain under normal loads was observed.     

滇西昌宁─孟连带南部地层地质问题

滇西孟连以南，整合于南段组浊积岩之上的拉巴群硅质岩含晚二叠世早期放射虫化石，南段组时代不仅限于石炭纪，可能延入二叠纪。二者为晚古生代思茅地块的外陆坡沉积。其西面的南基河杂岩（新名）由层序混乱的晚古生代硅质岩、泥岩和少量砂岩、玄武岩构成。放射虫化石证据表明，硅质岩时代不仅限于晚泥盆世－早二叠世，还延入晚二叠世，而有的砂岩时代为早石炭世，它们是经过强烈构造变动的古特提斯洋的沉积记录。昌宁－孟连带向南可能延至泰国北部的清迈带，而非东北部的难河带。     

黄土高原黄土、红色粘土与古湖盆沉积物关系

本文通过磁性地层学、古生物地层学、沉积学的对比研究，讨论了中国黄土高原地区黄土，红色粘土与该区重要古湖盆之一，古三门湖堆积物之间关系，并分析气候环境对它们的影响。主要结论如下：１）红色粘土与上覆黄土可以是连续沉积，并呈相渐变关系。２）中国黄土与三门组记录了布容正极性带与松山负极性带。Ｂ／Ｍ界限位于Ｌ８，Ｊ亚带位于标志层Ｌ９与Ｌ１５之间，大约Ｓ１０－Ｓ１３之间，Ｏ亚带位于Ｓ２２－Ｓ３３，或三门组之中。Ｍ／Ｇａ界限对应于黄土与红土界限。并基本对应于三门组与游河组界限。３）红色粘土（三趾马红粘土）并非仅仅是中新世保德期沉积物。它包括上新统与中新统，上新世静乐组记录了高斯正极性带，吉尔伯特负极性带，中新世蓝田组记录了Ｅｐｏｃｈ５。４）古三门湖堆积包括早更新世早期三门组（１．２０—２．５０Ｍａ，松山负极性带），上新世晚期游河组（２．５０—３．５０Ｍａ，高斯正极性带），更早期的三门湖沉积未出露。三门组与午域黄土为同期异相沉积，记录了松山负极性带，游河组则与该区上部红色粘土（静乐组上段）为同期异相沉积，记录了高斯正极性带     

Snow Depth Inversion Using the Localized HUT Model Based on FY-3B MWRI Data in the Farmland of Heilongjiang Province,China

Snow depth parameter inversion in the farmland using passive microwave remote sensing is of great significance to the agricultural production in Northeast China. Firstly, the Helsinki University of Technology (HUT) snow emission model was validated in the farmland based on microwave radiation imager (MWRI) onboard FengYun-3B satellite (FY-3B). The results showed that there was a big difference between the brightness temperature of HUT model simulation and MWRI for 18.7 GHz horizontal polarization (18.7 H) and 36.5 GHz horizontal polarization (36.5 H). To improve HUT model, the empirical parameter in the model was localized. Then the localized HUT (LHUT) model was built, where the extinction coefficient was calculated by the new extinction coefficient formula. Next, LHUT model was validated based on MWRI data and compared with HUT model. The results showed that LHUT underestimates slightly the brightness temperature with 0.91 and 4.19 K for 18.7 and 36.5 H respectively, and LHUT is superior to HUT model. Finally, the genetic algorithm (GA) was used to invert snow depth based on LHUT. The results showed that snow depth was underestimated with 6.79 cm based on LHUT. The inverted snow depth based on LHUT model is in better agreement with the measured snow depth.     

Environmental tracers as indicators of karst conduits in groundwater in South Dakota,USA

Environmental tracers sampled from the carbonate Madison aquifer on the eastern flank of the Black Hills, South Dakota, USA indicated the approximate locations of four major karst conduits. Contamination issues are a major concern because these conduits are characterized by direct connections to sinking streams, high groundwater velocities, and proximity to public water supplies. Objectives of the study were to estimate approximate conduit locations and assess possible anthropogenic influences associated with conduits. Anomalies of young groundwater based on chlorofluorocarbons (CFCs), tritium, and electrical conductivity (EC) indicated fast moving, focused flow and thus the likely presence of conduits. δ¹⁸O was useful for determining sources of recharge for each conduit, and nitrate was a useful tracer for assessing flow paths for anthropogenic influences. Two of the four conduits terminate at or near a large spring complex. CFC apparent ages ranged from 15 years near conduits to >50 years in other areas. Nitrate-N concentrations >0.4 mg/L in groundwater were associated with each of the four conduits compared with concentrations ranging from <0.1 to 0.4 mg/L in other areas. These higher nitrate-N concentrations probably do not result from sinking streams but rather from other areas of infiltration.     

浙江杭嘉湖平原区环境地球化学研究

根据杭嘉湖平原区区域地球化学调查结果,对本区开展了区域和城市(杭州市)环境质量评价的环境地球化学研究。研究结果表明,杭嘉湖平原区区域环境质量和杭州市区环境质量良好,各环境质量区较好的反映各区内工业生产水平、人口密集程度、历史长短。通过对杭州市不同环境质量区内蔬菜的分析研究证明,杭州市区污染区内有害元素尚未对人体健康产生影响,但为防止今后出现超标现象,应当高度重视,加强土壤环境保护。     

石英SEM-CL微结构及其在岩石学中的应用

综述了国外扫描电镜一阴极发光(SEM-CL)成像技术在岩石学研究中的应用实例.采用阴极发光探测器和扫描电镜结合的方法对石英等矿物进行观察,可以在高放大倍数和高分辨率下获得其他方法所无法揭示的丰富的微结构信息,如暗条痕和斑块、愈合裂纹、环带、复杂剪切纹、面状结构等,这些不同的微结构成为不同类型岩石中所特有的特征,因此,对...     

Measurement of radon exhalation rate in various building materials and soil samples

Indoor radon is considered as one of the potential dangerous radioactive elements. Common building materials and soil are the major source of this radon gas in the indoor environment. In the present study, the measurement of radon exhalation rate in the soil and building material samples of Una and Hamirpur districts of Himachal Pradesh has been done with solid state alpha track detectors, LR-115 type-II plastic track detectors. The radon exhalation rate for the soil samples varies from 39.1 to 91.2 mBq kg^?1 h^?1 with a mean value 59.7 mBq kg^?1 h^?1. Also the radium concentration of the studied area is found and it varies from 30.6 to 51.9 Bq kg^?1 with a mean value 41.6 Bq kg^?1. The exhalation rate for the building material samples varies from 40.72 (sandstone) to 81.40 mBq kg^?1 h^?1 (granite) with a mean value of 59.94 mBq kg^?1 h^?1.     

Recycling of Organic Matter in the Sediments of Santa Monica Basin,California Borderland

Geochemical and isotopic data for the uppermost 1.2 m of the sediments of the central Santa Monica Basin plain were examined to better understand organic matter deposition and recycling at this site. Isotopic signatures (Δ¹⁴C and δ¹³C) of methane (CH₄) and dissolved inorganic carbon (DIC) indicate the occurrence of anaerobic oxidation of CH₄ that is fueled by CH₄ supplied from a relict reservoir that is decoupled from local organic carbon (C_org) degradation and methanogenesis. This finding was corroborated by a flux budget of pore-water solutes across the basal horizon of the profile. Together these results provide a plausible explanation for the anomalously low ratio between alkalinity production and sulfate consumption reported for these sediments over two decades ago. Shifts in Δ¹⁴C and δ¹³C signatures of C_org have previously been reported across the 20-cm depth horizon for this site and attributed to a transition from oxic to anoxic bottom water that occurred ~350 years BP. However, we show that this horizon also coincides with a boundary between the base of a hemipelagic mud section and the top of a turbidite interval, complicating the interpretation of organic geochemical data across this boundary. Radiocarbon signatures of DIC diffusing upward into surface sediments indicate that remineralization at depth is supported by relatively ¹⁴C-enriched C_org within the sedimentary matrix. While the exact nature of this C_org is unclear, possible sources are hemipelagic mud sections that were buried rapidly under thick turbidites, and ¹⁴C-rich moieties dispersed within C_org-poor turbidite sections.