南极威尔克斯地SGR钻孔处雪冰转化过程中的密度变化特征

本文着重描述了SGR钻孔处冰盖上的积雪在密实化过程中的特征变化,并对该过程进行了分段的和全面的回归分析.结果表明,冰盖密度随深度增大,但增长幅度随深度减小.作者提出密度变化减小度的概念.计算得出的所研究冰芯钻取点的密度变化减小度为-0.15kg/m~3·m~2,粒雪成冰前的密实速率平均值为4.08kg/m~3·a.本文得到的冰盖密度变化“临界点”与以往报道的有所不同.分析这一现象时,作者强调当积雪还在活动层时冰盖温度的影响,并以此解释密度剖面的异常变化以及离差的回升.特别指出,积雪的密度变化具有气候学意义,它在一定程度上能够反映出积雪形成及变化过程中气候变化的某些信息.本文由密度变化确定的钻孔点雪冰转化深度为50米.     

Alluvial architecture of the Holocene Rhine–Meuse delta (the Netherlands)

Ancient fluvial successions often act as hydrocarbon reservoirs. Sub‐surface data on the alluvial architecture of fluvial successions are often incomplete and modelling is performed to reconstruct the stratigraphy. However, all alluvial architecture models suffer from the scarcity of field data to test and calibrate them. The purposes of this study were to quantify the alluvial architecture of the Holocene Rhine–Meuse delta (the Netherlands) and to determine spatio‐temporal trends in the architecture. Five north–south orientated cross‐sections, perpendicular to the general flow direction, were compiled for the fluvial‐dominated part of the delta. These sections were used to calculate the width/thickness ratios of fluvial sandbodies (SBW/SBT) and the proportions of channel‐belt deposits (CDP), clastic overbank deposits (ODP) and organic material (OP) in the succession. Furthermore, the connectedness ratio (CR) between channel belts was calculated for each cross‐section. Distinct spatial and temporal trends in the alluvial architecture were found. SBW/SBT ratios decrease by a factor of ca 4 in a downstream direction. CDP decreases from ca 0·7 (upstream) to ca 0·3 (downstream). OP increases from less than 0·05 in the upstream part of the delta to more than 0·25 in the downstream delta. ODP is approximately constant (0·4). CR is ca 0·25 upstream, which is approximately two times larger than in the downstream part of the delta. Furthermore, CDP in the downstream Rhine–Meuse delta increases after 3000 cal yr BP. These trends are attributed to variations in available accommodation space, floodplain geometry and channel‐belt size. For instance, channel belts tend to narrow in a downstream direction, which reduces SBW/SBT, CDP and CR. Tectonics cause local deviations in the general architectural trends. In addition, the positive correlation between avulsion frequency and the ratio of local to regional aggradation rate probably influenced alluvial architecture in the Rhine–Meuse delta. The Rhine–Meuse data set can be a great resource when developing more sophisticated models for alluvial architecture simulation, which eventually could lead to better characterizations of hydrocarbon reservoirs. To aid such usage of the Rhine–Meuse data set, constraints for relevant parameters are provided at the end of the paper.     

Detailed <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of geologic events associated with the Mantos Blancos copper deposit,northern Chile

The ⁴⁰Ar/³⁹Ar geochronological method was applied to date magmatic and hydrothermal alteration events in the Mantos Blancos mining district in the Coastal Cordillera of northern Chile, allowing the distinction of two separate mineralization events. The Late Jurassic Mantos Blancos orebody, hosted in Jurassic volcanic rocks, is a magmatic-hydrothermal breccia-style Cu deposit. Two superimposed mineralization events have been recently proposed. The first event is accompanied by a phyllic hydrothermal alteration affecting a rhyolitic dome. The second mineralization event is related to the intrusion of bimodal stocks and sills inside the deposit. Because of the superposition of several magmatic and hydrothermal events, the obtained ⁴⁰Ar/³⁹Ar age data are complex; however, with a careful interpretation of the age spectra, it is possible to detect complex histories of successive emplacement, alteration, mineralization, and thermal resetting. The extrusion of Jurassic basic to intermediate volcanic rocks of the La Negra Formation is dated at 156.3 ± 1.4 Ma (2σ) using plagioclase from an andesitic lava flow. The first mineralization event and associated phyllic alteration affecting the rhyolitic dome occurred around 155–156 Ma. A younger bimodal intrusive event, supposed to be equivalent to the bimodal stock and sill system inside the deposit, is probably responsible for the second mineralization event dated at ca. 142 Ma. Other low-temperature alteration events have been dated on sericitized plagioclase at ca. 145–146, 125, and 101 Ma. This is the first time that two distinct mineralization events have been documented from radiometric data for a copper deposit in the metallogenic belt of the Coastal Cordillera of northern Chile. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Statistical analysis of sand grain/bed collision process recorded by high-speed digital camera

A high‐speed digital camera was employed to record the sand grain/bed collision process. With image processing and a statistical method, a series of parameters of the collision process were obtained. The results show that the collision process of a grain with rebounding can be represented by two parameters: the kinetic energy restitution coefficient and the collision angle. Both parameters satisfy a normal distribution, and they are dependent on one another. With an increase of the collision angle, the distribution of the kinetic energy restitution gradually reduces from a broad to a narrow range with low values. The percentage of vertical velocity restitution coefficients greater than 1 can reach 70% or more, which ensures that the settling time of the sand grains in the air increases and that they receive more energy from the air to progress the saltation movement.     

Possible chemical structures and biological precursors of different vitrinites in coal measure in Northwest China

Chemical structure of Jurassic vitrinites isolated from the coals in basins in NW China have been checked using solid state ¹³C NMR and flash pyrolysis-GC/MS. Study shows some Jurassic collodetrinites are rich in aliphatic products in pyrolysates, consisting with the high amount of methylene carbon in ¹³C NMR spectra. In contrast, pyrolysates of Jurassic collotelinites are rich in phenols and alkylbenzenes. Also one Pennsylvanian and one Permian vitrinite selected from the Ordos basin, NW China have been checked for comparison. The proportion of aliphatics is low in pyrolysates, and aliphatic carbon peak in ¹³C NMR spectrum of Permian vitrinite is mostly composed of gas-prone carbons compared with collodetrinites in those Jurassic basins. But both pyrolysis and ¹³C NMR data shows the Pennsylvanian vitrinite is not only gas-prone but also oil-prone. Relatively high proportion of long chain aliphatic structure of some Jurassic vitrinite in Junggar, Turpan-Hami basins may be due to the contribution of liptodetrinites, which may be included during the formation of vitrinites. And it seems that suberinite is the most possible precursor of long chain aliphatics in the structure of Jurassic collodetrinite.     

赣南淘锡坑钨多金属矿床花岗岩和云英岩岩石特征及云英岩中白云母40Ar/39Ar定年

赣南崇义县淘锡坑钨矿位于南岭东西向构造带东段,属于以黑钨矿石英脉型为主的钨多金属矿床。矿床形成与燕山期中酸性岩浆作用有密切关系,石英矿脉受一组北西向断裂控制,穿切新元古界。本文在淘锡坑钨矿区3个揭露到花岗岩体顶部的中段（206、106、56中段）采集到岩体顶部云英岩样品,利用40Ar/39Ar同位素定年测得云英岩中的白云母的坪年龄分别为152.7 ± 1.5 Ma（206中段）,153.4 ± 1.3 Ma（106中段）,155.0 ± 1.4 Ma（56中段）。与前人用其他方法测定的花岗岩成岩和成矿年龄几乎一致。花岗岩和云英岩全岩稀土元素均具有M型四分组效应和强烈的Eu亏损特征,反映出花岗质岩浆经历了高度分异演化及其岩体结晶晚期流体/熔体相互作用。综合前人在南岭地区同类矿床的研究资料,可知南岭地区160～150Ma成岩成矿作用主要分布于南岭中-东段,可能为大陆边缘弧后岩石圈伸展的构造动力学背景的产物。     

History of crustal growth and recycling at the Pacific convergent margin of South America at latitudes 29°–36° S revealed by a U–Pb and Lu–Hf isotope study of detrital zircon from late Paleozoic accretionary systems

Detrital zircon provides a powerful archive of continental growth and recycling processes. We have tested this by a combined laser ablation ICP-MS U–Pb and Lu–Hf analysis of homogeneous growth domains in detrital zircon from late Paleozoic coastal accretionary systems in central Chile and the collisional Guarguaráz Complex in W Argentina. Because detritus from a large part of W Gondwana is present here, the data delineate the crustal evolution of southern South America at its Paleopacific margin, consistent with known data in the source regions.Zircon in the Guarguaráz Complex mainly displays an U–Pb age cluster at 0.93–1.46 Ga, similar to zircon in sediments of the adjacent allochthonous Cuyania Terrane. By contrast, zircon from the coastal accretionary systems shows a mixed provenance: Age clusters at 363–722 Ma are typical for zircon grown during the Braziliano, Pampean, Famatinian and post-Famatinian orogenic episodes east of Cuyania. An age spectrum at 1.00–1.39 Ga is interpreted as a mixture of zircon from Cuyania and several sources further east. Minor age clusters between 1.46 and 3.20 Ga suggest recycling of material from cratons within W Gondwana.The youngest age cluster (294–346 Ma) in the coastal accretionary prisms reflects a so far unknown local magmatic event, also represented by rhyolite and leucogranite pebbles. It sets time marks for the accretion history: Maximum depositional ages of most accreted metasediments are Middle to Upper Carboniferous. A change of the accretion mode occurred before 308 Ma, when also a concomitant retrowedge basin formed.Initial Hf-isotope compositions reveal at least three juvenile crust-forming periods in southern South America characterised by three major periods of juvenile magma production at 2.7–3.4 Ga, 1.9–2.3 Ga and 0.8–1.5 Ga. The ¹⁷⁶Hf/¹⁷⁷Hf of Mesoproterozoic zircon from the coastal accretionary systems is consistent with extensive crustal recycling and addition of some juvenile, mantle-derived magma, while that of zircon from the Guarguaráz Complex has a largely juvenile crustal signature. Zircon with Pampean, Famatinian and Braziliano ages (< 660 Ma) originated from recycled crust of variable age, which is, however, mainly Mesoproterozoic. By contrast, the Carboniferous magmatic event shows less variable and more radiogenic ¹⁷⁶Hf/¹⁷⁷Hf, pointing to a mean early Neoproterozoic crustal residence. This zircon is unlikely to have crystallized from melts of metasediments of the accretionary systems, but probably derived from a more juvenile crust in their backstop system.     

Landslide susceptibility mapping for a landslide-prone area (Findikli,NE of Turkey) by likelihood-frequency ratio and weighted linear combination models

Landslides are very common natural problems in the Black Sea Region of Turkey due to the steep topography, improper use of land cover and adverse climatic conditions for landslides. In the western part of region, many studies have been carried out especially in the last decade for landslide susceptibility mapping using different evaluation methods such as deterministic approach, landslide distribution, qualitative, statistical and distribution-free analyses. The purpose of this study is to produce landslide susceptibility maps of a landslide-prone area (Findikli district, Rize) located at the eastern part of the Black Sea Region of Turkey by likelihood frequency ratio (LRM) model and weighted linear combination (WLC) model and to compare the results obtained. For this purpose, landslide inventory map of the area were prepared for the years of 1983 and 1995 by detailed field surveys and aerial-photography studies. Slope angle, slope aspect, lithology, distance from drainage lines, distance from roads and the land-cover of the study area are considered as the landslide-conditioning parameters. The differences between the susceptibility maps derived by the LRM and the WLC models are relatively minor when broad-based classifications are taken into account. However, the WLC map showed more details but the other map produced by LRM model produced weak results. The reason for this result is considered to be the fact that the majority of pixels in the LRM map have high values than the WLC-derived susceptibility map. In order to validate the two susceptibility maps, both of them were compared with the landslide inventory map. Although the landslides do not exist in the very high susceptibility class of the both maps, 79% of the landslides fall into the high and very high susceptibility zones of the WLC map while this is 49% for the LRM map. This shows that the WLC model exhibited higher performance than the LRM model.     

Estimating potential landslide sites of an upland sub-watershed in Western Ghat’s of Kerala (India) through frequency ratio and GIS

The purpose of this study is to assess the susceptibility of landslides in parts of Western Ghats, Kerala, India, using a geographical information system (GIS). Landslide inventory of the area was made by detailed field surveys and the analysis of the topographical maps. The landslide triggering factors are considered to be slope angle, slope aspect, slope curvature, slope length, distance from drainage, distance from lineaments, lithology, land use and geomorphology. ArcGIS version 8.3 was used to manipulate and analyse all the collected data. Probabilistic-likelihood ratio was used to create a landslide susceptibility map for the study area. The result was validated using the Area under Curve (AUC) method and temporal data of landslide occurrences. The validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide locations. As the result, the success rate of the model was (84.46%) and the prediction rate of the model was (82.38%) shows high prediction accuracy. In the reclassified final landslide susceptibility zone map, 5.68% of the total area is classified as critical in nature. The landslide susceptibility map thus produced can be used to reduce hazards associated with landslides and to land cover planning.     

The double solid reactant method: II. An application to the shallow groundwaters of the Porto Plain,Vulcano Island (Italy)

This paper presents an example of application of the double solid reactant method (DSRM) of Accornero and Marini (Environmental Geology, 2007a), an effective way for modeling the fate of several dissolved trace elements during water–rock interaction. The EQ3/6 software package was used for simulating the irreversible water–rock mass transfer accompanying the generation of the groundwaters of the Porto Plain shallow aquifer, starting from a degassed diluted crateric steam condensate. Reaction path modeling was performed in reaction progress mode and under closed-system conditions. The simulations assumed: (1) bulk dissolution (i.e., without any constraint on the kinetics of dissolution/precipitation reactions) of a single solid phase, a leucite-latitic glass, and (2) precipitation of amorphous silica, barite, alunite, jarosite, anhydrite, kaolinite, a solid mixture of smectites, fluorite, a solid mixture of hydroxides, illite-K, a solid mixture of saponites, a solid mixture of trigonal carbonates and a solid mixture of orthorhombic carbonates. Analytical concentrations of major chemical elements and several trace elements (Cr, Mn, Fe, Ni, Cu, Zn, As, Sr and Ba) in groundwaters were satisfactorily reproduced. In addition to these simulations, similar runs for a rhyolite, a latite and a trachyte permitted to calculate major oxide contents for the authigenic paragenesis which are comparable, to a first approximation, with the corresponding data measured for local altered rocks belonging to the silicic, advanced argillic and intermediate argillic alteration facies. The important role played by both the solid mixture of trigonal carbonates as sequestrator of Mn, Zn, Cu and Ni and the solid mixture of orthorhombic carbonates as scavenger of Sr and Ba is emphasized.