贺兰山中段米钵山组沉积特征及其意义

贺兰山中段中、上奥陶统米钵山组,在整个区域地层中占有重要地位,它是贺兰山南北向构造形成的重要标志。其地层明显区别于相邻地台区的沉积,对探讨贺兰山早古生代的构造格局及岩相古地理尤为重要。但对米钵山组沉积环境多有争论,观点各不相同。本文对该区米钵山组沉积特征、沉积层序、沉积岩相和古地理环境进行了分析研究,并划分为碎屑流、浊流和正常深水沉积三种类型,推断贺兰山南北向构造在加里东中期开始形成,并延续到白垩纪的新认识。     

Characteristics,origins, and significance of pyrites in deep-water shales

As important metal sulfides in the geochemical cycle of sulfur, the characteristics and formation processes of pyrites can provide useful clues regarding their environment. Based on previous findings, shale pyrites were divided into three major classes(euhedral pyrites, framboidal pyrites(framboids) and metasomatic pyrites) and six sub-classes in this study. At the microscopic scale, each type of pyrite is associated with a different formation process. Framboids are formed by burst nucleation in...     

Distribution characteristics of lipids from salt sediments in Qaidam Basin and their astrobiological significance

On Earth,salt environments are the most relevant analogues to Martian salt deposits with regard to the search for preserved biomolecules.In this study,we analyzed the distribution of lipids in salt samples from Dalangtan and Qarhan in the Qaidam Basin,which is the most important area to carry out analog research of Mars in China.Furthermore,we compared the lipids distribution results with that from other typical Martian analog sites such as the Atacama Desert.Salt samples in the Qaidam Basin are enriched with fatty acid compounds,including normal fatty acids,unsaturated fatty acids,branched fatty acids,and acyclic isoprene acids.In addtion,glycerol dialkyl glycerol tetraethers(GDGTs)and archaeol compounds were also detected in these salt samples.Compared with the hypersaline samples,the clay samples not only have higher abuandance of fatty acids,GDGTs and archaeol compounds,but also a more diversed lipids composition.Only a few lipids were detected in the pure-saline samples,such as archaeol compounds.These clues suggest that content of salt minerals is the major factor affecting the distribution of lipids.This study provides an analogy for detecting and evaluating the traces of life that may exist on Mars.     

辽宁地区震群序列统计特征及预测意义研究

系统研究了1970年以来辽宁及邻区发生的25次震群活动,总结了辽宁地区震群活动的参数特征,探讨了该地区震群活动与未来中强震的关系。结果表明:1研究区的25次震群中,最大地震优势发生时段在震群出现后3天内的占68%,84%的震群中最大地震与次大地震的震级差≤0.5级,平均为0.35。80%的震群持续活动时间约2个月;2震群中最大地震的震级越大,相应地2、3级地震频次也越多,通常1个4级左右的震群,2级地震频次平均约为28,3级地震平均约为6;3当震群中3、4级地震频次分别≥10和4,同时序列的b值为0.6~0.9,此时可判定震群为前兆震群。未来中强震3要素的判定依据为:发震时间为震群开始后1年内,平均6个月;震中距离震群所在地约0~400km,平均为180km;最大强度为G-R预测的最大地震震级加2.0级。当b0.5时,震群有可能为前震序列,即震群开始后1~20天内原地有发生M≥5地震的危险;425次震群中的80%在震群出现1年后对应了M≥4.6地震,空间上辽宁内陆的震群对辽南和唐山地区的M≥4.6地震有较好的指示,长岛和黑山岛附近海域的震群对渤海海峡及其附近地区的M≥4.6地震有较好的指示。     

Spongy pahoehoe in Hawaii: A study of vesicle-distribution patterns in basalt and their significance

A well-defined pahoehoe lava type that is very common medially and distally in Hawaii is characterized by a high concentration and fairly uniform distribution of spherical or near-spherical vesicles. Measurements of vesicle sizes and concentrations have been made on ten of these spongy pahoehoe lava flow-units. The vesicles increase in size toward the middle, accompanied by a moderate increase in lava porosity. The close approach to bilateral symmetry on either side of the horizontal median plane and the common occurrence of a median gas blister shows that no significant upward movement of vesicles occurred, suggesting that the lava possessed a yield strength and was more or less static. Olivine phenocrysts when present are, however, concentrated in the lower half of the same flow units, showing that the lava previously lacked a significant yield strength. The vesicles are regarded as early, inherited from the vent, but the size characteristics of the vesicle population are a late-formed feature. Vesicles grew in static lava mostly by coalescence, and it is postulated that coalescence was promoted by the presence of abundant diktytaxitic voids which punctured the walls of contiguous vesicles. Zones in which the vesicle concentration is lower and the vesicles are larger and strongly deformed interrupt the symmetry of some spongy pahoehoe units, and gas blisters higher than the median plane occur in many examples. These zones are interpreted to result from late-stage shearing, and point to a mechanism by which vesicles may be eliminated from a lava.     

Mining seismicity, gas outburst and the significance of their relationship in the study of physics of earthquake source

This paper presents an overview of mining seismicity, gas outburst and their origin. The internal relation of mining seismicity and gas outburst in the dynamic process is studied on the basis of the fact that these disasters sometimes occur simultaneously. The examples show a close relationship between mining seismicity and gas outburst in high gassy coal mines. It is proposed that strong mine shocks plus the response of low value and delay time are early warning signals. The mechanism of the relationship between mining seismicity and gas outburst is analyzed by using the location of mining shocks, focus mechanism, cause of mining shocks and conditions of gas outburst. The trigger action of gas fluid on mining shocks, especially the effect of the anomalous property of supercritical fluid on the preparation and occurrence of mining shocks is discussed. According to the similarity between min-ing-induced earthquakes and tectonic earthquakes in terms of mechanism, the significance of the above results in the study of physics of earthquake source is also discussed.     

A note on the characteristics and possible origins of desert varnishes from southeast Morocco

Two substrate-controlled varnish types were identified from arid southeast Morocco: (1) patchy varnish interspersed with ‘silica glaze’ on silicified limestone and (2) a complete varnish cover on partially-silicified limestone. Electron probe microanalysis was used in conjunction with scanning electron microscopy to investigate their chemical composition. In both instances, varnishes are predominantly silica and iron-rich with localized concentrations of manganese. Inorganic fixation of iron and manganese is the preferred explanation, with manganese and iron derived predominantly from external sources—possibly wind-blown dust. Some iron and silica may also be derived by outward migration from within the substrate, particularly on partially silicified limestone.     

Exsolution microstructures in titanomagnetites and their magnetic significance

A survey, carried out using transmission electron microscopy, of exsolution-derived microstructures developed in titanomagnetites is presented. Microstructures, probably produced by spinodal decomposition, consist of a three-dimensional lamellar framework of ulvospinel, separating magnetite-enriched blocks. In coarser textures the magnetite-enriched regions have a plate morphology, and the ulvospinel-enriched lamellae develop secondary exsolution textures. The implications of exsolution for the magnetic properties of titanomagnetites are discussed. The coarsening of exsolution textures will cause the blocking temperature of the magnetite-enriched regions to increase with time. The development of magnetite-enriched plates may alter the magnetic properties of the titanomagnetite, as may the stress associated with some of the small scale, coherent microstructures.     

苏州澄湖SC7孔沉积物粒度特征及其古环境意义

苏州澄湖湖底主要由硬粘土组成,同时残留有湖沼洼地和古河道,古河道大致呈NNW-SSE延伸,与历史文献所载"古三江"之一的东江基本一致.保存着硬粘土平原形成后从河流到湖泊环境演化的良好沉积记录,通过对湖心区古河道SC7孔2cm间隔取样和AMS14C测年、粒度、磁化率等测试分析,初步探讨了该孔的沉积粒度特征及古环境意义,研究结果表明,沉积物粗粉砂含量极少或不含,中-细粉砂和粘土分别占53%-65.8%和19.7%-40.1%;与河床硬粘土相比,粉砂含量较低,粘土含量较高,平均粒径较小,为正偏(硬粘土为极正偏),磁化率也明显较高,多种粒度指标和磁化率指标均表明,澄湖的形成具有河流、河流-湖泊过渡到湖泊的阶段性演化特点,为太湖平原湖荡区湖泊的河泛成因提供了新的证据,现代澄湖则明显受到人类活动的扰动影响.     

Multiple calcrete profiles in the Tabernas Basin,southeast Spain: their origins and geomorphic implications

The paper describes a sequence of Pliocene(? ) to Quaternary age calcretes developed within alluvial fan and fluvial gravels in the Tabernas Basin, Almería Province, southeast Spain. Calcrete profiles are described from sites adjacent to major tributaries of the Rambla de Tabernas. Six distinct calcrete units are identified within the basin. These have variable distributions but have developed in an identifiable evolutionary sequence. Two pairs of calcrete units are widely present across the basin preserving two former land surfaces. Each of the former land surfaces has been planated and subsequently buried by alluvial fan or fluvial gravels. A massive calcrete unit is present at the base of each gravel sequence, immediately in contact with the underlying bedrock, with a less well developed calcrete unit situated at the top of the gravel sequence. The lowest two calcrete units within the basin are more spatially restricted and are confined to the floors and flanks of incised drainage lines. The geochemistry, macro- and micromorphological properties and geomorphological positions of the calcrete units are outlined and, on the basis of this information, their mode of origin identified. Two main modes of calcrete genesis appear to be present: massive calcretes situated in direct contact with bedrock are suggested to have formed by groundwater processes, whilst calcretes situated at the top of gravel sequences are likely to have developed by pedogenic processes. Calcrete genesis is subsequently considered in the context of the reconstruction of the early phases of landscape development, and is suggested to have been controlled by phases of uplift and stability within the Tabernas Basin. © 1998 John Wiley & Sons, Ltd.     

A comparative study of sea surface wind datasets and their induced circulation characteristics in the North Pacific Ocean

Ocean Dynamics - Mainly driven by wind stress, the upper ocean dynamic processes in the North Pacific Ocean serve as important pathways for mass and energy exchanges of the global ocean and thus...     

The characteristics,origins, and geodynamic settings of supergiant gold metallogenic provinces

An investigation of the rock magnetic properties using stepwise isothermal remanence (IRM) acquisition, thermomagnetic analysis and temperature-dependent susceptibility history, identifies magnetite as the carrier of the main fraction of the remanence, associated with maghemite and hematite in Malan loess (L1), Holocene soil (S0) and last-glacial paleosol (S1). The presence of short-lived direction fluctuations indicates that no significant smoothing occurs in L1 when its remanence is locked, and thus L1 is capable of recording the geomagnetic secular variation (PSV), while the PSV has been severely smoothed or wiped out by pedogenic processes during S1 formation. It has been suggested that the Mono Lake and Laschamp excursions are two independent geomagnetic events based on this study.     

The characteristics,origins, and geodynamic settings of supergiant gold metallogenic provinces

There are six distinct classes of gold deposits, each represented by metallogenic provinces, having 100's to >1000 tonne gold production. The deposit classes are: (1) orogenic gold; (2) Carlin and Carlin-like gold deposits; (3) epithermal gold-silver deposits; (4) copper-gold porphyry deposits; (5) iron-oxide copper-gold deposits; and (6) gold-rich volcanic hosted massive sulfide (VMS) to sedimentary exhalative (SEDEX) deposits. This classification is based on ore and alteration mineral assemblages; ore and alteration metal budgets; ore fluid pressure(s) and compositions; crustal depth or depth ranges of formation; relationship to structures and/or magmatic intrusions at a variety of scales; and relationship to the P-T-t evolution of the host terrane. These classes reflect distinct geodynamic settings. Orogenic gold deposits are generated at mid-crustal (4–16 km) levels proximal to terrane boundaries, in transpressional subduction-accretion complexes of Cordilleran style orogenic belts; other orogenic gold provinces form inboard, by delamination of mantle lithosphere, or plume impingement. Carlin and Carlin-like gold deposits develop at shallow crustal levels (<4 km) in extensional convergent margin continental arcs or back arcs; some provinces may involve asthenosphere plume impingement on the base of the lithosphere. Epithermal gold and copper-gold porphyry deposits are sited at shallow crustal levels in continental margin or intraoceanic arcs. Iron oxide copper-gold deposits form at mid to shallow crustal levels; they are associated with extensional intracratonic anorogenic magmatism. Proterozoic examples are sited at the transition from thick refractory Archean mantle lithosphere to thinner Proterozoic mantle lithosphere. Gold-rich VMS deposits are hydrothermal accumulations on or near the seafloor in continental or intraoceanic back arcs.

The compressional tectonics of orogenic gold deposits is generated by terrane accretion; high heat flow stems from crustal thickening, delamination of overthickened mantle lithosphere inducing advection of hot asthenosphere, or asthenosphere plume impingement. Ore fluids advect at lithostatic pressures. The extensional settings of Carlin, epithermal, and copper-gold porphyry deposits result from slab rollback driven by negative buoyancy of the subducting plate, and associated induced convection in asthenosphere below the over-riding lithospheric plate. Extension thins the lithosphere, advecting asthenosphere heat, promotes advection of mantle lithosphere and crustal magmas to shallow crustal levels, and enhances hydraulic conductivity. Siting of some copper-gold porphyry deposits is controlled by arc parallel or orthogonal structures that in turn reflect deflections or windows in the slab. Ore fluids in Carlin and epithermal deposits were at near hydrostatic pressures, with unconstrained magmatic fluid input, whereas ore fluids generating porphyry copper-gold deposits were initially magmatic and lithostatic, evolving to hydrostatic pressures. Fertilization of previously depleted sub-arc mantle lithosphere by fluids or melts from the subducting plate, or incompatible element enriched asthenosphere plumes, is likely a factor in generation of these gold deposits. Iron oxide copper-gold deposits involve prior fertilization of Archean mantle lithosphere by incompatible element enriched asthenospheric plume liquids, and subsequent intracontinental anorogenic magmatism driven by decompressional extension from far-field plate forces. Halogen rich mantle lithosphere and crustal magmas likely are the causative intrusions for the deposits, with a deep crustal proximal to shallow crustal distal association. Gold-rich VMS deposits develop in extensional geodynamic settings, where thinned lithosphere extension drives high heat flow and enhanced hydraulic conductivity, as for epithermal deposits. Ore fluids induced hydrostatic convection of modified seawater, with unconstrained magmatic input. Some gold-rich VMS deposits with an epithermal metal budget may be submarine counterparts of terrestrial epithermal gold deposits. Real time analogs for all of these gold deposit classes are known in the geodynamic settings described, excepting iron oxide copper-gold deposits.

     

Dust storms in northern China and their significance for the concept of the Anthropocene

Science China Earth Sciences - A key scientific issue in the study of the Anthropocene is the determination of the corresponding stratigraphic marker in geological archives. The arid and semi-arid...     

Geochemical and Sm–Nd isotopic characteristics of metabasites from central Hainan Island, South China and their tectonic significance

Abstract   Major and trace elements and Sm–Nd isotopic data are presented for metabasites that are present as lenses within Paleozoic metasediments in the Chenxing and Bangxi regions, central Hainan Island, Southeast (SE) China. Most metabasites are metamorphosed cumulated gabbroic rocks tholeiitic in nature, and characterized by varying degrees of depletion in Th, Nb, Ta and light rare earth elements (LREE). Moreover, they show high positive ∈Nd(T) values of approximately +7, similar to those of mid-ocean ridge basalts (MORB). A Sm–Nd isochron age of 333 ± 12 Ma obtained for the metabasites is interpreted as their crystallization age. The combined geochemical and Sm–Nd isotopic data suggest that the metabasites were generated by dynamic partial melting from a MORB-like mantle source in an oceanic regime. These rocks probably represent remnants of fragmented oceanic crust of the eastern part of Paleo-Tethys. They were obducted onto the continental crust as part of the 'Shilu Mélange' in earliest Mesozoic time when southern Hainan (part of the Indochina block) collided with northern Hainan (part of South China). Alternatively, they could be formed in a volcanic rifted passive margin at the sea-floor spreading stage as part of MORB-like seaward-dipping reflector break-up packages.     

Isotopic variations in precipitation at Bangkok and their climatological significance

The stable isotopic composition of precipitation from low to mid latitudes contains information about changes of some climatic factors, such as temperature, precipitation and atmospheric circulation patterns. However, the isotopic variations in the area are very complicated because of the combined influences of these factors. Proper interpretation of the patterns of isotopic variations for palaeoclimate reconstructions in this area requires a detailed understanding of these complex stable isotope controls. The isotopic data (δ¹⁸O and δ²D) in precipitation at the International Atomic Energy Agency–World Meteorological Organization Bangkok station were collected and analysed because of the relatively long and unbroken isotopic records and the particular geographical location. The isotopic variations at Bangkok have strong seasonal patterns owing to distinct source regions in different seasons. In summer, the remote sources of water there can influence the δ¹⁸O values significantly, which is verified by the simple Rayleigh model. In winter, the mixing of isotopically distinct air masses with different origins, i.e. the continental and oceanic air masses, accounts for the isotopic variations. In the transition periods of the Asia–Australia monsoon, namely in May and October, the local vapour contribution may play a role in the isotopic ratios. On the interannual time‐scale, the influences of El Niño–southern oscillation (ENSO) and the Indian Ocean dipole (IOD) on isotopic composition are examined. The indications are that both the ENSO and IOD indices have a significant correlation with the δ¹⁸O ratios, and that the δ¹⁸O ratio in summer rains is significantly more enriched (depleted) during the warm (cold) phase of ENSO/IOD events. All the results suggest that it is useful for us in understanding the water cycling process and may be helpful in palaeoclimate reconstruction in this monsoon region. Copyright © 2006 John Wiley & Sons, Ltd.     

廊固凹陷冶炼厂孔孢粉组合及其地层意义

冶炼厂LFK1孔位于河西务断裂上盘,孔深249m,自下而上依次为更新统中部杨柳青组、更新统上部欧庄组及全新统等.对LFK1的孢粉资料进行详细分析,自下而上划分出六个孢粉组合带,反映廊固凹陷地区植被演替及相应的气候演变,并结合测年和钻井资料,确定孢粉带Ⅰ为中更新世,孢粉带Ⅱ、Ⅲ、Ⅳ和Ⅴ为上更新世,孢粉带Ⅵ为全新世.