腾格里沙漠地区砂质管状物的发现及其地质意义

砂质管状物,浅褐色,管状,致密,硬脆,中空,内孔贯通。长度3.4～18.1cm,外径1.55～3.5cm,内径0.6～1.9 cm,壁厚1～11mm。随着长度由长到短,外径、内径及壁厚均逐渐变小。管内孔壁上时有白色微晶方解石薄膜,或有管孔被白色微晶方解石半堵塞。有的管子上有与主孔相通的小孔,小孔与管壁垂直、呈30°交角或近于相切。按砂粒粒度,管子分为粗砂型和细砂型两种,其中粗砂型管子暗色砂粒含量略多。砂粒成分主要为硅质,胶结物主要为微晶方解石,孔隙式胶结。说明在地表砂层之下存在弱承压碳酸盐型咸水,这种水的上涌、渗透作用及沙漠特有干旱、风力等条件,是其主要成因。显示古腾格里湖在干涸过程中,湖水经历了"碳酸盐型→硫酸盐型→氯化物型"的浓缩过程。如果在古代砂岩中发现相同或类似的管状物,可进一步推断,该砂岩形成环境为古沙漠、有在同一套地层中存在蒸发盐矿产的可能。     

湘西北宁乡式铁矿的成因与质量

宁乡式铁矿在湘西北主要分布在三个层位,存在两类矿石结构,这两类矿石结构的铁矿是由不同的成矿方式形成,因而矿石质量也是不同的,具体表现在两类矿石中P、SiO2的含量存在明显差异。通过分析对比,Fe0、Fe22层砾状、豆状类赤铁矿的质量优于鲕状赤铁矿,其中位于二户溪至西界地区的FeO层砾状、豆状赤铁矿矿石质量全区最佳,应为该区的赤铁矿下一步工作的主要方向。     

Geochemistry of the Jinduicheng Mo-bearing porphyry and deposit,and its implications for the geodynamic setting in East Qinling,P.R. China

Simultaneous determinations of U–Pb dating and Hf isotopes on single zircon grains by excimer laser-ablation quadrupole and multiple-collector ICP-MS and petrologic and ore geochemical studies have been applied to the ore-bearing porphyry of the Jinduicheng porphyritic molybdenum deposit in East Qinling. Lithogeochemical data show that the porphyry is characteristic of high K₂O, K-feldspar porphyritic calc-alkaline granitoids with ¹⁷⁶Hf/¹⁷⁷Hf=0.282020–0.282436 and ε_Hf(t)=?23.7 to ?8.9, which indicates its mixed origin involving a crustal and a mantle component. The weighted average U–Pb age from single zircon grains of the porphyry is 141.5±1.5 Ma. This age coincides with the oldest molybdenite Re-Os model age as dated by others, suggesting that the period of mineralization was almost simultaneous with the porphyry emplacement, or slightly later. The porphyry intrusion and the molybdenum mineralization occurred during the transition from compression to extension in the Jurassic – Cretaceous periods. The corresponding tectonic setting was the intracontinental orogenic and extension stage after collision and orogenesis between the Southern China plate and the Northern China plate. The Jinduicheng porphyry and the deposit's geochemical data indicate that the ore-forming material originated from a mixing of lower crust and upper mantle. When the molybdenum-enriched magma intruded into the upper crust along zones of structural weakness, ore-forming fluid generated by magma crystallization of the porphyry interacted with wall rock or mingled with meteoric water to form the deposit.     

Historical contamination and sources of organochlorine pesticides in sediment cores from Quanzhou Bay, Southeast China

Three sediment cores were collected from the top to the mouth of Quanzhou Bay, Southeast China, in order to establish sources and historical trends of organochlorine pesticides (OCPs) in the region. The spatial distribution of OCPs in surface sediments implies that Quanzhou Bay received the contamination inputs not only from rivers near the shore, but also from outside the bay. The variation profiles of concentrations clearly showed that OCPs were widely used between 1960s and 1980s in China. A recent increasing trend was found in all cores despite their ban in China in 1983. Different ratios of (DDD+DDE)/DDTs indicated that DDTs at the top of the bay were mainly derived from long-term weather soils, while DDTs near the mouth of the bay were mainly derived from fresh inputs from outside the bay. Higher percentage of gamma-HCH in HCHs deposited after 1990 implies that lindane may have been used recently around Quanzhou Bay.     

Pyritization of trace metals in estuarine sediments and the controlling factors: a case in Jiaojiang Estuary of Zhejiang Province,China

Three undisturbed sediment samples were collected from the intertidal zone of the Jiaojiang Estuary of Zhejiang Province, China. The sediments were found to contain remarkably low concentrations of organic carbon (<0.6%) and acid volatile sulfide (AVS) (<30 μmol g⁻¹). The availability of these two substrates likely constrained sulfate reduction and pyritization of several trace metals, respectively. This was especially true at one station where AVS concentrations in the upper 20 cm averaged less than 0.05 μmol g⁻¹. Although the depth dependence of the degree of trace metal pyritization was generally consistent with expectations based on redox conditions, depth profiles of reactive-metal and pyrite-metal concentrations in several cases revealed more complex behavior and a positive correlation between reactive-metal concentrations and pore water metal concentrations.     

Detecting water yield variability due to the small proportional land use and land cover changes in a watershed on the Loess Plateau,China

Soil conservation practices have been widely implemented on the Loess Plateau to reduce severe soil erosion in north‐central China over the past three decades. However, the hydrologic impacts of these practices are not well documented and understood. The objective of this study was to examine how water yield has changed after implementing soil conservation practices that resulted in changes in land use and land cover in a small agriculture‐dominated watershed, the LuErGou Watershed in Tianshui City, Gansu Province, China. We collected 23 years of hydro‐meteorological data along with three land use surveys of 1982, 1989, and 2000. The land use survey in 2000 suggested that the soil conservation efforts resulted in a 16·6%, 4%, and 16% increase in area of grassland, forested land, and terraces respectively over the two periods from 1982 to 1988 (baseline) and 1989 to 2003 (soil conservation measures implemented). Rainfall–runoff regression models developed for both time periods at the annual and monthly time steps were used to examine the significance of change in water yield in the second time period. The averaged annual run‐off coefficient over 1989–2003 did not change significantly (at the α = 0·05 level) as compared to that in the period 1982–1988. However, we found that soil conservation practices that included re‐vegetation and terracing reduced water yield during wet periods. This study highlights the importance of the precipitation regime in regulating hydrologic effects of soil conservation measures in a semi‐arid environment. We concluded that adequately evaluating the effects of land use change and soil conservation measures on water yield must consider the climatic variability under an arid environment. Copyright © 2009 John Wiley & Sons, Ltd.     

利用非差资料的精密点定位方案

单站精密定位 (PrecisePointPositioning ,以下简称PPP)是在同时固定GPS精密星历和卫星钟的前提下 ,利用载波相位和伪距资料进行单台站的精密点定位 .采用该方法时不同台站之间不存在共同的待估参数 ,即各台站互不相关 ,这一特点大大降低了计算量 .采用美国喷气推进实验室JPL发展的数据处理软件GIPSY处理APSG联测资料 ,计算表明PPP的重复率相当于目前国内普遍采用的双差解算结果 .采用较好保持地面网构型的无基准算法 ,计算表明通过Helmert参考系转换后 ,PPP的解算结果与双差算法的外符精度大致相当 .解算表明 ,采用PPP处理 1 0 0个台站约需 3 .5小时 ,而处理同样的资料采用双差算法则需 1 8～2 0小时 .对于我国即将建成的大科学工程或地震监测的多达 2 0 0 0个接收机的GPS网而言 ,在保持精度前提下的节省计算资源和计算时间的PPP解算方案值得广泛的应用     

雷达发射机灯丝电源故障维修

灯丝电源是一个交流稳压电源,通过灯丝中间变压器和位于油箱中的脉冲变压器及灯丝变压器,为速调管灯丝供电.2011年7月18日,内蒙古气象局通辽天气雷达站的CINRAD/CB雷达发射机反复出现灯丝电源故障,且无法加高压导致雷达停机,经分析和排查故障原因,最终排除了雷达故障.就此次故障的出现,分析其原因,举一反三,对雷达台站在今后的工作中加强备件的管理和测试数据的管理有一定的启示.